Geological Field Trip 11-The Cameros Basin: From Late Jurassic-Early Cretaceous Extension to...

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AAPG International

Conference and Exhibition BARCELONA, SPAIN

September 21 - 24, 2003

GEOLOGICAL FIELD TRIP 11

Cameros Basin

d~b -;-nstitut Cartográfic de Catalunya

Barcelona, Spain ""' Formated and Published by

INSTITUT (AKTOG RÁflC Of CATALUNYA

TOTAL

AAPG International Conference and Exhibition

BARCELONA, SPAIN 21 - 24 September 2003

GEOLOGICAL FIELD TRIP 11

The Cameros Basin: From Late Jurassic-Early Cretaceous Extension to Tertiary

Contractional Inversion-Implications of Hydrocarbon Exploration

Northwest Iberian Chain, North Spain Ramón Mas, M8 Isabel Benito (Department of Estratigrafía, University Complutense of Madrid - CSIC),

José Arribas (Department of Petrología y Geoquímica, University Complutense of Madrid - CSIC), Ana

Serrano (REPSOL-YPF; Madrid, Spain), Joan Guimera (Department of Geodinamica i Geofísica,

University of Barcelona), Ángela Alonso (Department of Ciencias da Navegación e da Terra, University of

A Coruña), Jacinto Alonso-Azcárate (Department of Química-Física, University of Castilla-La Mancha)

Formated and Published by

TOTAL

AAPG GEOLOGICAL FIELD TRIP 11

BARCELONA GENERALITAT DE CATALUNYA (SPAIN). 21 ·24 September 2003 ?

Table of contents

INTRODUCTION TO THE FIELD TRIP 4

INTRODUCTION TO THE BASIN 4

Geological Setting 4

The Mesozoic Substrate of the Cameros Basin 9

The Cameros Basin fill (Rift cycle 2): The Latest Jurassic - Early Cretaceous Megacycle 3 16

Metamorphism affecting the Cameros Basin 24

Structural features of the basin 25

Evolution of the Cameros basin: Basin Model 27

Potential Petroleum Systems of the Cameros Basin. Discussion 32

1 . BIGORNIA TROUGH 33

2. CAMEROS TROUGH 33

3 . RIOJA TROUGH 34

FIELD TRIP ITINERARY 35

Day 1 Thursday, September 25,2003 37

Day2 Friday, September 26, 2003 39

Day3 Saturday, September 27,2003 42

Day4 Sunday, September 28, 2003 44

REFERENCES 45

FIGURE CAPTIONS 50


BARCELONA GENERALlTAT DE CATALUNYA (SPAIN), 21 - 24 September 2003 3

INTRODUCTION TO THE FIELD TRIP

Aim of the field trip The main objectives ofthe excursion are:

To visit seismic scale outcrops, stratigraphy and sedimentology of outer marine, reefal, coastal, lacustrine, fluvial and alluvial deposits and different tectonic structures by means of several transects to the Cameros Basin. To exchange ideas about the evolutionary geological model proposed for the Cameros Basin.

To discuss the hydrocarbon geology of this area. With special attention to a review of Potential Petroleum Systems in the Cameros area: reservoirs, source rocks, oil seeps, thermal events, etc.

INTRODUCTION TO THE BASIN

Geological Setting

The Cameros Basin in tlle Iberian Chain. The Cameros Basin is located in the Northwest of the Iberian Chain (Fig. 1). This is one of the basins forming part of the Mesozoic Iberian Rift System (Mas et al., 1993; Guimera et al., 1995; Salas et al. , 2001). These basins are located in the north-eastern part oflberia and in the adjacent Mediterranean offshore (Fig. 1), containing thick sequences oflate Permian and Mesozoic continental and shallow marine cIastics, carbonates and minor evaporites . These sediments rest on the regional Late Variscan unconformity which truncates folded Palaeozoic sediments, metamorphic and intrusive rocks. The Mesozoic sedimentary sequences of the Iberian basins show dramatic lateral changes of thickness from less than 1000 m to almost 6000 mover distances of a few kilometers, indicating considerable tectonic influence on their development. The Iberian Rift System was inverted during the Paleo gene generating the Iberian and Catalan Coastal Chains (Salas et al. , 1992; Salas et al., 2001). These chains are complex intraplate compressional features that strike NW -SE and NE-SW respectively (Fig.l) . Simultaneously with the inversion of the Iberian Rift System, the basement block ofthe NE-SW trending Central System was upthrusted, leading to isolation ofthe Duero Basin and subsidence ofthe flexural Tajo Basin.


BARCELONA GENERALlTAT DE CATALUNYA (SPAIN), 21 · 24 September 2003 4

3°

. . :

Lote Cretoceovs

Late Jurossic & eorly Cre1aceous Triossic ond eorly ond mlddle Jurassic

bosement ...... __ TeniolY Ihrvst

Mesozoic 1--- normol loull

Fig. 1. The Cameros Basin in the overall structure ofthe Iberian Range (modified from Guimera et al.,

in press)

This Paleogene phase of compressional intraplate deformation was directly related to the collision of the Iberian craton with Europe during the Pyrenean Orogeny (Guimera, 1984 and Guimera and Álvaro, 1990) and to the contemporaneous early phases of the Betic Orogeny (Vera et al. , 2001). The Ebro Basin represents the southern flexural foreland basin of the Pyrenees. The Iberian Chain is a fold-and-thrust belt whose overall structure is defined by two NW-SE trending arches with a wave-length ranging from 70 to 120 km (Fig. 1) where the basement was involved during the Tertiary contractional deformation. The cores of both arches are located in thickened crust which mimics their shapes (Fig. 1). The arches are neatly separated by the Almazán basin and merge towards the Southeast, in an area where a wide gravimetric minimum (-110 mGal) can be observed (Mezcua et al., 1996). This gravimetic minimum corresponds to the area ofthicker crust (Salas et al. , 2001). Hence, both arches are crustal-scale structures (Guimerá et al. , 1999; Salas et al., 2001 ; Gumerá et al., in press).


BARCELONA GENERALlTAT DE CATALUNYA (SPAIN), 21 ·24 September 2003 5

The north eastern arch contains the Cameros Unit, the Aragonese Branch and the northern part of the Almazán Basin, while the southwestern arch includes most of the Castilian-Valencian Branch and the southern part of the Almazán Basin (Fig. 1). In the area located at the southwest of the latter arch contraction only involved the Mesozoic and Tertiary cover. In the Iberian Chain, NW-SE trending thrusts and folds verge in two directions: most ofthe structures ofthe NE arch to the NE and most ofthe structures of the SW arch to the SW. In contrast, the Catalan Coastal Chain is dominated by northwestverging structures with a NE-SW trend. Many of the structures of the Iberian Chain are interpreted as being associated with major extensional faults which bounded Mesozoic rift basins and which were compressionally reactivated during the Palaeogene and early Miocene. The kinematics of reactivation of such faults depend largely on their orientation with regard to the regional compression direction (approximately N-S, perpendicular to the Pyrenees, Guimera, 1984; Guimera & Álvaro, 1990; Salas el al. , 2001). Two types of structural sty1es are recognized depending on the composition of the deformed rock succession. Jurassic and younger strata are decoupled from Variscan basement and its Permian to Lower Triassic sedimentary cover in areas where middle Muschelkalk and Keuper shales and evaporites provide a detachment horizon. However, in areas where Triassic shales and evaporites are thin 01'

missing, no such strain partitioning is evident. The Iberian Chain is in thrust contact with the flanking Paleogene basins. For instan ce, the northern margin of the Cameros unit is thrusted over the margin of the Ebro Basin; the respective thrust-fault is sealed by Late Miocene post-tectonic sediments. Beneath such sediments, this thrust (Fig. 1) can be traced south-eastward along the Aragonese Branch.

Tite Cameros Unit (NW Iberian Cltain)

The Cameros tectonic Unit ineludes the Cameros basin fill , its Mesozoic substratum and the Variscan basement (which crops to the northwest and southeast). It is located in the northern part of the IberÍan Chain between the Tertiary Ebro and Almazán basins (Fig. 1). This unit was the result of inversion of the late Jurassic-early Cretaceous Cameros Basin which had a sedimentary fill up to 5 km thick. These deposits overlie up to 1.5 km of the Triassic and Jurassic series (Mas el al., 1993 ; Guimera el al. , 1995). The structure of the Cameros Unit is characterized by (1) a major newly formed north-verging thrust sheet, which has a horizontal displacement ofup to 28 km and overrides the Tertiary Ebro Basin; and (2) a conjugate, south-verging imbricate fan fold-and-thrust system that encroaches on the Almazán Basin (Fig. 2 A, B-B ' ; Mas el al., 1993; Guimera el al. , 1995).



A SSW NNE ls N

e - Om

SSE

c:::J Jurassic

c:::J Triassic

D Mesozoic

..., Hercynian L.....J Basement

CJ Tertiary

[r::JJ Upper Cretaceous

11 Upper Albian L-I (Utrillas Fm)

Uppermost Jurassic - Lower Cretaceous (Cameros Basin Depositional Sequences)

DS 8

DS 7 NNW i~ SSW NNE

B'~~~íIOiiii;¡¡¡ij~.~~~BA~1 A "~ ... , __ ....... l,o_:S_::_~:_+6....J:;O km

B BURGOS

•

Syncline

Anticl ine

Normal fault

---r--v- Thrust BURGO DE OSMA .,. ~

~ Cameros thrust -_ Triassic and Jurassic

Carboniferous

Variscan Basement

LOGROÑO-

Late Albian and Late Cretaceous

Depositional Sequences of Cameros Basin fill

20 km

Post-tectonic rocks

Pre and Syntectonic Tertiary

Fig. 2. A. A-A', B-B ', and C-C': geological cross-sections through the Cameros basin. D-D': partial restoration of cross sections A-A' and B-B ' at the previous state of basin inversion. See fig. 2B for location .. B. Geological map ofthe Cameros Basin. A-A', B-B' and C-C' Location of cross-sections from fig. 2A. (modified from Guimera et al., 1995).



Cameros Basin in the Mesozoic Iberian Rift System realm

In the Iberían Chain two riftíng cycles can be distinguished during the late Permian to late Cretaceous extensional stage (Alvaro el al., 1979; Vilas el al. , 1983; Salas & Casas, 1993 ; Roca el al. , 1994; Salas el al. , 2001): 1) a Triassic Rift, Late Permian to Hettangian; and 2) a Latest Jurassic-Early Cretaceous Rift, Kimmeridgian (southeastward) or Tithonian (northwestward) to Early Albian (Fig. 3 A). During the Latest Jurassic-Early Cretaceous Rift cycle four more subsident basins up to 3-5 km thick developed in the Iberian Rifting (Fig. 3 B): the Cameros Basin in the northern part of the Iberian Chain (Mas et al. , 1993); the Maestrat Basin (or Maestrazgo Basin) in the eastern part (Salas, 1987, 1989); the Columbrets Basin (or Columbretes Basin) in the "Valencia trough" (Roca & Guimera, 1992) and the South Iberian Basin in the southern part of the Chain (Vilas el al. , 1982, 1983). Outside of these more subsiding areas, rocks ofthis age are absent or only a few hundred meters thick.

A R1FT 1 I RtFT2 B

IBERIAN RIFT SYSTEM TECTONIC SUBSIDENCE COMPARISON

R. Salas & R. Mas. 1998

Fig. 3. A. Backstripped tectoníc subsidence for the Cameros, south Iberían and Maestrat basins. Triassic and Late Jurassic-Early Cretaceous rifting phases have been colored. B. Simplified geological map of part of the Iberian Peninsula showing the four most subsident basins of the Iberian Rifting.

The Cameros Basin is atypical of the different basins of the Chain. It is a synclinal basin with no maj or fault bounding during its development (Fig. 2 A). The genesis of this kind of basin is frequently explained by thermal subsidence. These basins are generally very extensive and display slow subsidence. However, the Cameros Basin (1) is not too extensive (30 to 80 km wide and about 150 km long: Fig. 2 B), and (2) during its development subsidence and sedimentation rates were very high, with vertical thickness of sediments (which represent up to 9 km of stratigraphic record in the direction of the northward migration of the successive depositional sequences which filled the basin) reaching up to 5 km (Fig. 2 A).



This assemblage of peculiar features can be explained by assuming that this is a hanging wall basin formed over a roughly south-dipping ramp in a horizontal extensional fault. Thus, the Cameros Basin is interpreted as an extensional-ramp basin (Mas et al. , 1993 ; Guimera et al. , 1995).

This basin is also the only one of the Mesozoic basins in the Chain in which deposits have been partialIy affected by low-grade and very low-grade metamorphism (Fig. 4).

Syncllne

Antlcllne

Normal fault

~ Thrust

"TTT Cameros thrust

[;i}Md Triassic and Jurassic

~~~fim Carboniferous

O Variscan Basement

~ Late Albian and ~ Late Cretaceous

~~ Cameros basin fill ., Depositional ~ Sequences ° t ·

1\ {fj)

20km

D Post-tectonic rocks

¡:t/~i:3 Pre and Syntectonic Tertiary {

Fig. 4. Geological map ofthe Cameros Basin showing the areas affected by low and very low grade metamorphism. A. Yanguas - San Pedro Manrique area. B. El Pégado antic1ine area.

Tbe Mesozoic Substrate of tbe Cameros Basin

During Late Variscan movements (Stephanian and part of the Permian) a system of wrench faults developed in Iberia with a predominant NE-SW and NW -SE trend. This tectonic activity generated transtensional basins associated with intrusive and extrusive magmatism, and dismantlement of the Variscan Oro gen (Capote, 1983 ; Virgili et al. , 1983 ; Arche y López-Gómez, 1996; Salas et al. , 2001). The Late Permian and Mesozoic evolution of the Iberian Rift System have been divided into four major rift cyc1es and post-rift stages (Salas el al. , 2001) (Fig. 5 A). In the NW sector ofthe Iberian Chain four megacyc1es or depositionaI supersequences which are bounded by regional unconformities have been distinguished in the stratigraphic record ofthis Late Permian to Mesozoic extensionaI stage (Guimera et al. , in press): the Late Permian to Triassic Megacyc1e 1; the EarIy to Late Jurassic Megacyc1e 2; the Latest Jurassic to EarIy Cretaceous Megacyc1e 3; and the Late Cretaceous Megacyc1e 4 (Fig. 5 B). The two first megacycles correspond to the "Mesozoic" substrate of the Cameros Basin.



A

--.J

~~ --.J

1\1 nin ~

--.J

í m\H r~

B

POSTRIFT -2 -

RIFT-2 ----..o.

POSTRIFT-1~

PALEOZOIC

GROUPS I FORMATIONS

~ W -1 U >U oC(

<.!> w :!:

..-W -1 U >U oC( <.!> w :!:

Fig. 5. A. Rift cycles and Post-rift stages on the evolution of the Iberian Basin (modified from Salas et al., 2001). B. Idealized and synthetic sketch/stratigraphic section showing the latest Paleozoic and Mesozoic stratigrphic record in the Cameros are a (North Iberian Range).

THE LATE PERMIAN TO TRIASSIC MEGACYCLE 1

During this megacycle, development of the Iberian Basin began with the reactivation of late-Variscan faults (Vegas y Banda, 1982). As a consequence, Late Permian and Triassic deposits unconformably overlaid the Variscan basement. In most of the Iberian Basin these deposits correspond to continental environments (Buntsandstein Facies) that evolved progressively to shallow marine and coastal carbonate environments (Muschelkalk Facies) and coastal evaporitic environments (Keuper Facies). In the Cameros area these deposits outcrop on the edges of the Demanda Massif to the north of Cameros Range, and to the southeast in the Moncayo area where local volcanoclastic deposits of Autunian age are founded.

THE EARLY TO LATE JURASSIC MEGACYCLE 2

In the Iberian basin this megacycle was mainly dominated by thermal subsidence and very extensive development of carbonate platforms (Salas et al. , 2001). Several depositional sequences have been identified in the northwestern sector of the Iberian Chain:



Early and Middle Jurassic sequences

Hettangian-Earliest Pliensbachian Sequence. This last still syn-rift sequen ce (end ofRift cycle 1; Fig. 5 A) is constituted by dolomitic breccias and dolomites deposited in an environment of coastal sabhkas evolving upwards to well stratified limestones (mudstone and wackestone) with some intervening marls deposited in a shallow inter- and sub-tidal marine environment.

Pliensbachian Sequence. This fust post-rift sequence (beginning of Post-rift stage 1; Fig. 5 A) consists of a first marly unit and a second unit formed by bioclastic limestone. These two units were deposited in shallow marine ramps, the first low energy and the second high energy.

Toarcian Sequence. This sequence consists of a rhythmic alternation of limestones and marls deposited in an outer ramp environment.

Aalenian-Bajocian and Late Bajocian Sequences. These sequences are represented by lime mudstone and wackestone, generally bioturbated; sorne levels contain abundant reworked fossils and some contain abundant sponges. These deposits were sedimented in a mid-outer ramp environment. During the first sequence, accommodation was very small and non-depositional gaps were frequent.

Bathonian Sequence. This sequence is typically formed by oolitic and bioclastic limestone (generally grainstone) corresponding to calcarenitic bars deposited in a shallow ramp environment.

Callovian Sequence. The Callovian Sequence is represented in most of the Cameros sector by a wellstratified alternation of banks of limestone and dark-colored marls which were deposited in a mid-outer ramp environment. During this sequence, black-shales corresponding to sorne anoxic episodes were recorded in the depocentral areas of the basin. However, towards the south and the northeast of the basin, this sequence generally consists of sandstones and sandy limestones deposited in coastal environments.

Late Jurassic Sequences

The Late Jurassic marine record in the Cameros area is described in more detail below, since it generally constitutes the substratum of the Latest Jurassic-Early Cretaceous sin-rift deposits of Cameros Basin. Four depositional sequences have been identified:

Earlv Oxfordian and Early-Middle OxfOrdian Sequences. In the northwestern part of the Cameros area these two sequences are represented by a level offerruginous oolites that appears on top ofthe Callovian deposits. However, towards the South, in the Soria sector, this level is not present; in its place on top of the Callovian record there is a bio-perforated and bio-incrusted ferruginous surface (Alonso & Mas, 1990).

Middle-Late OxfOrdian Sequence: The Aldealpozo Formation (Alonso & Mas, 1990). In the southem part of the area, this depositional sequence is formed by muddy and grainy shallowing-upwards carbonate sequen ces deposited in an inner shallow ramp environment with carbonate to mixed tidal flats and lagoons (Alonso & Mas, 1990). Its thickness declines northwestwards, where it consists of a rhythmic succession of intervening silty limestones and black marls deposited in a mid-outer ramp environment with a low rate of sedimentation (Alonso & Mas, 1990).

Early Kimmeridgian Sequence: The Torrecilla en Cameros Formation (Alonso & Mas, 1990). The last episode of sedimentation ofthe Post-rift stage 2 (prior to the Late Jurassic-Early Cretaceous rifting; Fig. 5) in the northern fberian Ranges corresponds to the early Kimmeridgian, a period of globally rising sea level (Vail et al., 1977; 1984; Haq et al. , 1988; Hallan, 1988) apparent throughout the IberÍan and North Tethys domain. Sedimentation in the Iberian Basin mainly occurred in a shallow carbonate stormdominated ramp which was opened southeastwards to the Tethys and northwards to the boreal realm (Alonso & Mas, 1990; Bádenas & Aurell; 2001). The connection between both domains was located in an epicontinental seaway (the Soria Seaway, Bulard, 1972), generated between the Iberian and the Ebro massifs (Fig. 6).



A BOREAL

~ BILBAO. I , ~~~ASTIAN

I \ I I

VITORlfj. / / • PAMPLONA

:LO~~ÑO <"~~ BU~GOS I \ O

1 1* ' ~ , __ ** '\ I.S'~-<, \

..--=-_""-"\.Q~I~ _* * ~~ 2- -~ '\ '\

1- I

~~ I \l}..(\,'

MADRID I • Infered~

coastline r ., CUENCA'

/LARAGOZA . l':

() ~)-It 041. r.s-

TERU EL "1/1' . CASTELLÓ

• LÉRIDA

100 Km I

B

BURGOS

(.l

~_/ ------

Fig. 6. A. Palaeogeographic map of northeastern Iberia during Kimmeridgian times. The location of the two main reefal complexes is shown by asterisks: 1. Soria and South ofMoncayo area; 2. Torrecilla area (modified from Alonso and Mas, 1990). B. Location map of the marine Jurassic outcrops in northern Iberian ranges (in black). A, B and C corresponds to the three studied sectors where the Torrecilla en Cameros Fm. is best developed: A. South of Moncayo sector; B. Soria sector; C. Torrecilla sector (modified from Alonso & Mas, 1990).

Sedimentation in this seaway was characterized by the development of coral reefs (Torrecilla en Cameros Formation). Reefal units were restricted to the western margin of the seaway (Alonso & Mas, 1990; Mas el al. , 1997) and are best developed in two areas of the basin: (1) to the southeast in the eastern part of Soria (inc1uding the southern Moncayo sector), and (2) to the north, near Torrecilla en Cameros (Fig. 6). The growth geometry of these reef complexes was controlled by the prevailing positive eustatic conditions during Kimmeridgian times, and by the basin tectonics. At this time, the North Iberian Basin was tilted with subsidence to the east and uplifted to the west (Alonso and Mas 1990). In the southern part of the basin (in the Soria and southern Moncayo areas) reef geometry was dominated by vertical and seaward accretion (Mas el al. , 1997; Benito el al. , 2001; Benito & Mas, 2002), suggesting that despite the combination of positive eustatism and subsidence, the high rates of carbonate production controlled overall reef growth. In contrast, in the Torrecilla area to the north, an off-lapping complex ofreefs developed in response to local tectonism (Alonso el al., 1986-1987; Mas el

al. 1997; Benito & Mas, in press) (Fig. 7).



W PRE-KIMMERIDGIAN JURASSIC

Gl REEF-FRAMEWORK FACI ES

~CORALS

o REEF-SLOPE FACIES

O LAGOONAL FACIES

...... ALGAE ONCOL ITES

El LONG,SHORE SAND BARS

~ CROSS-BEDDED STRATIFICATION

_ MATRIX,SUPPORTED REEFAL BRECCIA

_ BOUNDARY BEn"/EEN ACCRETIONARY UNITS -- INFERRED BOUNDARY BETWEEN ACCRETIONARY UNITS

. _,~,,~~f¡l'jrj~~ =" " ,., ORTIGOSA ~/.J'~::: .: :: .: : •. :;'.::: .. -;:.::: .:~FLATS

:::::::<1.. LAGOON-¡Q\/~i;. ~~~pR ~~~,: : : ::>:}~~~~?~ ..... /' /1 MONI EN OGRO ~~~~ .•. ;;::-. ~.:-..,-.., •.. : -.., .. • : •.• : • . :-"':..

a:¡""" TIDAL FL~T~<i~~~)§~. ,/j// '. <¿q~~l/.~

",/'.: .:::. -:: .-:."'\... ? -~<~?" , ~.{: .: >: >: >: . . 1 N>-< N>\ /' «-

.BIGORNIA

i.-__ ......;2 .. 0 Km ,'..... ,1" •• ".' ./. ./ -,o' o," • -BIJUESCA

2

D Mlddle-inner ramp facies D Inner ramp facies

Fig. 7. Idealized sketches illustrating the palaeogeograhic map of the Cameros area at the Kimmeridgian times, and the sedimentary evolution of the reefal complexes of the Torrecilla en Cameros Fm. in the three studied sectors: A. South ofMoncayo; B. Soria; C. Torrecilla (from Benito, 2001),

Diagenetic evolution oftlte Torrecilla en Cameros Formation

Diagenetic sequences of the Torrecilla Fm. were determined by (1) the sedimentary evolution and facies distribution, (2) the earlier diagenetic processes associated with late Kimmeridgian subaerial exposure of reefs, and (3) the subsequent burial history in the different areas of the basin.

During the Late Kimmeridgian, synsedimentary diagenetic pro ces ses of micritization and precipitation of peloidal micrite and fibrous calcite occurred throughout reefal unit. However, in northern Torrecilla sector, where off-lapping reefs developed, the combination of rising sea-level and tectonism led to alternating reef exposure and submergence. Consequently, coral s underwent neomorphism and dissolution, and both primary and secondary porosity were filled by early marine and meteoric cements prior to extensive exposure during the Late Kimmeridgian,



During the Late Kimmeridgian the Torrecilla en Cameros Formation was extensively exposed and there were widespread diagenetic processes of neomorphism, dissolution of aragonite and HMC and precipitation of meteoric calcite cements. During this stage, specific meteoric diagenetic evolution, as for instance the generation and occlusion of porosity in the different sectors of the basin, was considerably influenced by the length of time during which that reefal unit was exposed (Benito, 2001 ; Benito el al., 2001 ; Benito & Mas, 2002) (Figs. 8; 9 A-H). From the Tithonian to the Early Albian, deposition of marine sediments within Soria Seaway was replaced by a continental sedimentary regime in response to the episode of rifting that led to the formation of the Cameros Basin. At this time, diagenetic evolution in Soria and Torrecilla areas was characterized by burial of the reefal unit and ferroan calcite cementation. In the South of Moncayo sector, on the other hand, the Torrecilla en Cameros Formation was only slight1y buried as sedimentation started later and the thickness of sediment was lower. Here, diagenesis was still controlled by meteoric waters and most of the remaining porosity was almost completely closed by meteoric cements (Figs. 8; 9 A, B, D, E, G, H) (Benito, 2001 , Benito el al. , 2001; Benito & Mas, 2002).

BURtAL (LESS THAN

2000 m I

BURtAL (2000 TO saoo m )

? ?

AG E EAfl:LY LATE KIMME I TIlHONII'.NI 8ERRI"'S'ANf 8ARftEMIAt4 LATE TERTIAR'f1 D IAGE . KIMMERIOC. T~6~Y~ DERRIASIAN BARREIo"AN APTlAN CREYACfOUS PRESENl

N N .

BURIAL ( 2000TO 5000 mi

I ? ?

4

AGE EARlY LATEKIMME. nTHONIANI BERRIASIAw l aARREMIAU LATE TERHARY¡ OIA GE • I'(II.IM.ERIOG. T~~~Y;H BERRtASIAN BARREMIAH APTI,t\N CRETACEOUS PRESENT

BURIAL (2000 TO 5000 mi

Fig. 8. Idealized sketches of paragenetic sequence and their respective environment of precipitation (to the right) of the main diagenetic phases and events affecting the reefal complexes of the Torrecilla en Cameros Fm. in the three studied sectors: A. South of Moncayo; B. Soria; C. Torrecilla (modified from Benito, 2001).



Fig. 9. Photographs A, B and e are from the reefal complex ofthe Southem Moncayo sector. Photographs D to F are from the Soria sector; and photographs G to 1 are from the Torrecilla sector (from Benito, 2001).



Saddle ankerite precipitated in the remaining porosity postdating ferroan calcite cement, in the Soria and Torrecilla sectors and following meteoric non-ferroan calcite in the southern Moncayo area (Figs. 8; 9 C, E, H, I). Precipitation of ankerite was probably associated with the hydrothermal metamorphism that affected Cameros Basin during mid-Iate Cretaceous (Benito, 2001 , Benito et al. , 2001 ; Benito and & dolomite, followed by kaolin and pyrite, precipitated after corrosion of ankerite. Most of the remaining porosity after saddle ankerite was later occ1uded by a non ferroan sparry calcite cement in the Soria and Torrecil1a sectors, and by ferroan calcite in southern Moncayo area (Figs. 8; 9 F, I) . Possibly these cements precipitated during Alpine contraction. Subsequently, and only in the Torrecilla area, fluorite, celestite and sphalerite al so precipitated. These minerals are associated with the presence of solid hydrocarbons (Fig. 8; 9 I) (Benito, 2001). In response to tectonic uplift, renewed erosion and subaerial exposure, the reefal unit was again modified by meteoric diagenetic processes. Under such conditions, ankerite and ferroan calcite were surely unstable and were replaced by non-ferroan c10udy calcite containing abundant inc1usions of iron oxides and hydroxides (Figs. 8; 9 A, B, E, G, H).

Tbe Cameros Basin fill (Rift cycle 2): Tbe Latest Jurassic - Early Cretaceous Megacycle 3

The basin fill (Rift 2; Fig. 5 A), which extended from the Titbonian to tbe Early Albian, corresponds to a large cyc1e or megasequence bounded by two main unconformities at the base and the top (Figs.5 B and 10). The stratigraphic gap which corresponds to the unconformity ofthe lower limit is more important in the northern part of the basin than in the central and southern areas (Fig. 2 A); in the North of the basin it extends mainly from the Late Kimmeridgian to part of the Barremian. To the center and south, on the other hand, it generaIly extends only from the Late Kimmeridgian to the Early Tithonian (Mas el al., 1993; Benito & Mas 2001 ; Arribas elaI..2003). The upper limit is the intra-Albian unconformity bounding the base ofthe Late Cretaceous Megacyc1e 4 of the lberian Ranges (Fig. 5 B), which begins with the Utrillas Formation. From this unconformity at the base of the Late Albian to Maastrichtian post-rift megacyc1e (Post-Rift Stage 2; Fig 5 A), the Cameros Basin lost its identity like other Latest Jurassic-Early Cretaceous basins of the Iberian rifting, and large carbonate platforms occupied the Iberian realm (Alonso el al. , 1989; Alonso el al. , 1993).

Depositional Sequences

The Latest Jurassic-Early Cretaceous megacyc1e supersequence tbat filled the basin can be divided into eight depositional sequences bounded by unconformities (Mas el al. , 1993 ; Mas el al. , 1997; Martín i Closas & Alonso Millán, 1998; Arribas et al. , 2003) (Fig. 10). This sedimentary record consists mainly of continental sediments corresponding to aIluvial and lacustrine systems, with very rare marine incursions (Gómez Fernández, 1992; Alonso and Mas, 1993) ("M" in Figs. 10 and 11). These sequences are usuaIly organized in sedimentary cyc1es starting with alluvial clastic deposits at the base changing to lacustrine limestones towards the top (Figs. 10 and 11). Chronostratigraphic data are not yet complete because of a generally pOOl' fossil record and local metamorphism. The main stratigraphic data are based on charophites, ostracods, palynological associations for the continental record, and a few marine calcareous algae (mainly Dasycladacean) from the rare marine incursions (Brenner, 1976; Guiraud and Seguret, 1985; Schudack, 1987; Martín i Closas, 1989; Clemente el al. , 1991 ; Alonso & Mas, 1993; Martín i Closas & Alonso Millán, 1998). Ages for the different sequences are shown in Figure 10. These depositional sequences are generalIy very thick. The second and third sequences (DS 2 and DS 3) are especially thick, each containing 1500 m of stratigraphic record, as are the last two sequences (DS 7 and DS 8), with respective thicknesses of 1900 m and 1500m (Fig. 11).



s N

Utrillas Fm Late Albian

Oliván Gr OS 8 Late Aptian-Early Albia n

OS 7 Late Barrem.-Early Apti an

Pantano Fm / OS 6 Barremian

" IGOlmayo Fml remo OS 5 Late Hauteriv.-Early Bar

OS 4 Latest Berrias.-Valangin

+----------- LJ -------------+

MARINE JURASSIC

TRIASSIC

c=J Alluvial fans

c=J Fluvial - lacustrine

c=J Fluvial - alluvial fans

Lacustrine

J = Jubera Fm L = Leza Fm

OS 3

OS2

OS 1

LJ= Late Jurassic -MJ- Mlddle Jurasslc

EJ= Early Jurassic

c=J Fluvial

I

~ ~

~ o

.t::. -i=

@ Marine incursions

Fig. 10. Simplified stratigraphy ofthe Depositional Sequences (DS) which fill the Cameros basin. (modified from Guimera et al., 1995) .



~

.!:S! 1/) ~ .¡: ~

Q)

ce I

ian

'/ ,

BU • '/

BU

, , ,

LO •

" ,

SO 1&2 (Tithonian-Berriasian)

LO • . '/ ,,' , '/ A2 ,

'/ t!fff A1

, , '/ , ,

, A2+A3 '/

, , " ........ ",-- "

, '" SO "

SO 4 (Latest Berriasian-Valanginian)

BU • '/

LO •

,,' '/ ,

'/ '/

'/ ~

@ .... ", "" '/ ~O'

C1 C1 ~'

'/ .... , ..... ~oo 2+C3 '/' , ca '/

, ..... " .... -- ",-- " '/ '", SO" '/

SO 6 (Barremian)

BU . '/

'/ '/

'/ '/ "

'/ //

, -- ? ..... ......... ..... --

..... --..... ', ? / ...... ... ~ ....... / ,/ ......

'"

LO •

~

/.~

.... /. ~~~ "" ~OL 1 50 " ... '

OL1+0L2 '/

--.... "'SO""

SO 8 (Late Aptian-Early Albian)

50 km

N

BU . '/

'/ON2+0N5 ....

LO •

,,' ,

,/'/~ ON5'

.... "

, , , , ,

'" SO 3 (Berriasian)

BU . '/

'/

J2:x B1

'/~ B1

'/

LO •

,,' ,

, .... ,..... B1 +~

" " .... ~--" , " SO " '/

'/

SO 5 (Late Hauterivian-Early Barremian)

BU . '/

LO •

SO 7 (Late Barremian-Early Aptian) M

r - - 1

+ SEDlMENTATION AREA

M

-c=J D

OEPOCENTRALAREAS

MARINE INFLUENCE

CARBONATE FACIES (LACUSTRINE)

EVAPORITIC FACIES (LACUSTRINE)

SILlCICLASTIC FACIES (ALLUVIAL)

, '/

~ MAIN PALEOCURRENT TRENO T, ON, A, B, C, D. E Y Ol + number = facies assoeia!ion of ea eh uni!

Fig. 11. Schematic palaeogeographic evolution ofthe Cameros Basin. BU: Burgos, LO: Logroño; SO: Soria.(from Mas et al. , 1997).



Paleocurrent data on the different sequences (Fig. 11) show that the main source of siliciclastic input to the basin was the Iberian Massif in the Southwestern margin (Mas et al. , 1997). With regard to sandstone sources, two major megasequences can be distinguished in the Western sector ofthe basin: (1) Tithonian - Berriassian including depositionaI sequences DS 1, 2 and 3; and (2) Valanginian-Lower Albian including depositional sequences DS 4, 5, 6 and 7. Both megasequences start with a quartzolithic petrofacies (A and C in Fig. 12) generated by the erosion of Mesozoic pre-rift sedimentary cover and evolve to quartzofeldspathic petrofacies (B and D in Fig. 12) originated by the erosion of the Variscan basement (Iberian 01' Hesperian Massif). The petrographic characteristics of this megasequences are related to the paleogeographic configuration of the Cameros Basin. Thus, the first megasequence (Tithonian - Berriassian) developed in NW-SE trending troughs generated in the West Asturian Leonese zone. Propagation of normal faults to the SW originated similarly trending troughs, but on crystalline terrains from the Central Iberian zone (Arribas et al., 2003) .

Qm

"

Rg

Rs

Iberian Massif (Hesperian) ez -Cdll lalmau Zone

IseClmeoIS.& met3seCII~ls)

WALZ - Wesl AslulI,m leorlt":-.e Zone (cuarUllc :.lales. !!ctllstS I

Cll - Cenlral lbe:nan ZOfIC'

Qm

K Petrofacies A

DS-1 Petrofacies B

DS-2 DS-3

Petrofacies e DS-4

Petrofacies D DS-5 DS-6 DS-7

Rm

sw

Petrofacies B

2 Petrofacies e

2

Petrofacies D

NE

TithonianBerriasian

ValangillianHauterivian

BarremianEarly Albian

Fig. 12. Evolution of sandstone petrofacies during Late Jurassic - Middle Albian clastic deposition in the western Cameros Basin and their genetic and tectonic relationships with the Iberian Massif zones. Arrows in ternary diagrams show the evolution of petrofacies through time. Note that marine Jurassic deposits are poorly represented in the Central Iberian Zone. Qm: Monocrystalline quartz. F: Feldspar. K: K-feldspar. P: Plagioclase. Lt: Totallithics. Rg: Plutonic/gneissic rock fragment. Rm: Metamorphic rock fragment. Rs: Sedimentary rock fragment (from Arribas et al. , 2003).



Facies and Sedimentar y Environments

Proximal facies are commonly concentrated towards the southwest margin (Fig. 11). These deposits are essentiaIly formed by aIluvial facies associations of sandstones and conglomerates corresponding to braided systems. (Fig. 13: TI and Fig. 14: eo, DI). However, the more distal deposits, lacustrine carbonates and shales, are gene rally displaced towards the northeastem margin (Fig. 11). One of the more characteristic facies associations correspond to lacustrine-palustrine cycIes of relatively permanent shaIlow carbonate lakes (Fig. 11: ON5, El , E2; Fig. 13 : T4 and Fig. 15: El , E2) that occasionaIly accumulated major quantities of organic matter. Other distal facies associations correspond to ephemeral lakes with frequent cyanobacterial colonies and evaporite pseudomorphs (Fig. 11: T5, ON4, E3 ; Fig. 13 : T5; Fig. 16: ON4 and Fig. 15: E3). LocaIly, a laminated micritic facies also appears associated to black-shales (Fig 16: ON6). This facies presumably correspond to relatively deep lacustrine environments where conditions became anoxic.

MAIN FACIES ASSOCIATIONS OF DEPOSITIONAL SEQUEN CES DS1 and DS2 (Tera Gr.)

BRAIOEO FLUVIAL SYSTEM

¡_ l' Braided channels . deposits and .::s.>:: overbank deposits ~. JI ; .: tJ;o/'

MEANOERING FLUVIAL SYSTEM (PROXIMAL)

Channel l ill deposits (sandy and gravelly poit-bars ) and f100d plain overbank deposits (vertical accretion and crevasse splays)

MEANOERING FLUVIAL SYSTEM (DISTAL)

20m

l I

O :

Channel fill deposits (mainly point-bars) and Ilood plain overbank deposits (vertical accretion , crevasse splays and carbonate lacustrine deposits)

T1

T2

T3

CARBONATE ANO MIXEO SILlCLAST.-CARB. SHALLOW LAKES

i' ~ Lacustrine-palustrine -- ... - ®e '" cycles with ..... ' -2)0

A\ "Y'r coco predom inance 01 10m

l >~ (/) (6'>: ) carbonate (W/M) and

A\ y-y-y-.- coco clastic muds. Very ':'.- ®e> 08 occasional marine

O . ; W influence.

CARBONATE SHALLOW LAKES (L1TTORAL AREAS)

10m

l I~~· Shallow zones --- :' periodically wave = "Y'r - ' e influenced with

, e • development 01 li toral O = -e stromatolites


T4

T5


Between the areas dominated by proximal aIluvial systems and those dominated by distal carbonate lakes, meandering fluvial systems were dominant. (Fig. 11: T2, T3, ON2, Al , A2, B1 , el , e2, D2, D3, OLl ,OL2; Fig. 13: T2, T3; Fig. 14: Al , A2, B1 , el , e2, D2, D3 ; Fig. 17: OL1 , OL2). In these fluvial systems, two basic types of successions are identified: (1) those displaying a high ratio between channeled facies and flood plain facies with coalescent point bars (which are cIose to the proximal areas), and (2) those displaying a low ratio between channeled and flood plain facies with isolated point bars. The marine incursions from the Tethian realm to the basin, which are coincident with the stages of greater development of the lacustrine facies (Mas et al. , 1993), occurred during the Tithonian-Berriasian and Late Barremian-Aptian (Fig. 11). These incursions produced the sporadic development of lagoonal environments with micrite facies of wackestones having benthic forams and ca1careous green algae, mainly DasycIadacean (Fig. 13 : TI; Fig. 15: El; Fig 16: ON5).

Fig. 13. Main facies associations of the

depositional sequen ces DS 1 and DS 2

(Tera Gr.).

MAIN FACIES ASSOCIATIONS FOR OEPOSITIONAL SEQUENCES: 054 = A ; OS5 = B ; OS6 = C and OS7 (Iower part) = O

(Urbión Gr. in the Eastern sector of the Basin)

BRAIDED FLUVIAL SYSTEM

I~ Braided channel fill

~ deposlts and variable overbank

.::;s:: JI deposits (high in ca . . !lb/' and low in 01 ) o

CO 0 1

MEANDERING FLUVIAL SYSTEM (PROXIMAL-MIDDLE)

20 ml e;Al _ Al ~

O . . .-#

20 m

l I I

O'

Channel fill deposits (mainly point-bars) and overbank deposits (flood plain)

Channel fill deposits (mainly point-bars) and low record of overbank deposits

MEANDERING FLUVIAL SYSTEM (DISTAL)

a

Flood plain overbank deposits (vertical accretion. crevasse splays and carbonate lacustrine deposits) and channel fill deposits (mainly poin! bars)

MARGINAL LACUSTRINE AREAS

Major crevassesplays lobes rela ted wi!h marginal lacustrine areas on flood plains .

SHALLOW LAKES

Carbonate and mixed si liciclasticcarbonate shallow lacustrine

A1 C1 02

A2 B1 C2 0 3

A3 B2 C3 04

B3

Fig. 14. Main facies associations for depositional sequences: DS4=A; DS 5 = B; DS 6=C DS 7 (lower part) = D (Urbión Gr. in the Eastem sector ofthe Basin)_

AAPG GEOLOGICAL FIELO TRIP 11

BARCELONA GENERAlITAT DE CATALUNYA (SPAIN), 21 - 24 September 2003 21

10 mi

O

lo m

l o ·

ENCISO GROUP : MAIN FACIES ASSOCIATIONS (E = upper part of OS7)

CARBONATE SHALLOW LAKES Lacustrine-palustrine

~'~ . cycles wi!h -- ee~ a-.:) carbonate muds

-yy- <D<D predominance ee " (<2>3:) Al -y-y-yy- <D<D (W/M). Very -- 0 occasional marine . ee 0'" W

influence.

MIXED CARBONATE-SILlCICLASTIC SHALLOW LAKES

1'-~.- ®e~ (;} Lacustrine-palustrine 0(:) cycles with í A\ .,..... <D<D

. -, e W predominance of

A\ -v-v-v-r <DCD carbonate (W/M) and

-- 0 clastic muds. So me .~. ee> 0"

. J W organic-rich layers.

EPHEMERAL CARBONATE SHALLOW LAKES

O

Playa-Iakes deposits with important development of litoral stromatolites

LlTTORAL LACUSTRINE ZONES

Oeltaic lobes in litoral areas of carbonate perennial lakes

MEANDERING FLUVIAL SYSTEM (DISTAL)

Flood plains with carbonate lacus!rine areas and channel fill deposits (pointbars)

E1

E2

E3

E4

E5

Fig. 15. Main facies associations for the

upper part ofDS 7 = E (Enciso Gr.)

o

MAIN FACIES ASSOCIATIONS OF DEPOSITIONAL SEQUENCE DS3 (Oncala Gr)

MUDFlATS CONECTED TO PlAYA-lAKES

Mudflats with sheet fiood deposits and ephemeral lakes conected to playalakes

ON1

1 '~ Etape: Huérte les Fm

MEANDERING FLUVIAL SYSTEM

o

o

Channel fil l deposits (mainly point-bars) and flood plain overbank deposits (vert ical accretion , crevasse-splays and carbonate lacustrine deposits)

lACUSTRINE MARGINAL DELTAS

Discrete deltas in lacustrine litloral areas with so me organic-rich layers

CARBONATE-SALINE SHALlOW lAKES

ON2

2'· Elape: Valdeprado Fm

ON3

2"~ Etape: Valde prado Fm

10 mi i-yy-e -yy- Carbonate and " _ -yy- Ii evaporitic playa-Iakes

I .:;::;- , deposits. Leached

O ' .. e - w colapse breccias .

ON4

1" Eta pe: Huerteles Fm

CARBONATE SHALLOW lAKES

Lacustrine filling cycles with moderate rough episodes (oolithic and bioclastic grainstones). Very occasional marine

ON5

influence. 2~ Elape: Valdeprado Fm

RELATIVElY DEEP CARBONATE lAKES

Relatively deep lakes with laminated carbonate muds deposits (mudstones) and some organicrich layers

ON6

2nM Etape: Valdeprado Fm

Fig. 16. Main facies associations of depositional

Sequence DS 3 (Oncala Gr)



MAIN FACIES ASSOCIATIONS OF DEPOSITIONAL SEQUENCE DS8 (Oliván Gr)

MEANDRING FLUVIAL SYSTEM (MIDDLE)

, -;

_ A\ '<: . /'

OL1

O· 1·."",·7

A\ 'R

. /'

Channel fill deposits (mainly point-bars) and overbank deposits (fl ood pla in )

MEANDRING FLUVIAL SYSTEM (DISTAL)

Flood plain overbank ~ deposits (verti cal

accretion, crevasse-splays and OL2

/' carbonate lacustrine

20 ml deposits) and ~ channel ti ll deposits -n-

(mainly point-bars).

O

El> A\ .E' ~

Fig. 17_ Main facies associations of

depositionaI Sequence DS6 (Oliván Gr)

LEGEND:

~ Ccnglomtr.lte5. Icl;¡sl-1Uppo11

l' ' . .1 SIlOd~ & undj;tonll~

P.Ie<>I<.¡¡,stlbr.chlr,itd~ Pln1lm1ll0r(l1

fl.O 1'11.:11\.: .. 1,, 0,; \.I",IM~~ @: OSlracoocs

~ Trough cr~" be<jj ng e Ch~rofI IC$

Planarcronboddll'lg

", tpsHo'1 eran beddng CUlTenl ll llPles

,Q..=- L.:U ltl..'u ol r IJuULl"q

GaSlrop<XlS

LJme$tont'~ mtJdslOl'1e.w.,ke, lc·1l';' -rr M ... ctcrO\cks

., T ... clO~r l o;;lresI1lill_l.brllllii!O}

./' Dor"'~ U"II,,\oIIl¡¡1 \\'l1cbl';ol~1 ... '! Oncolllltli

BIacIo;¡;c:bblcli CiIl lllOll¡¡¡!en:>d1l1t!i. BlOllnOO! 1Ot'I

.,. .... T'<lc~

W G)·p¡:.'IfTl O$;ltudOr>\orphs

.t\ Roo!>

crl Bf!ntncfor;¡mnlfflr;'t

Fig. 18_ Legend for Figures 13, 14,

15, 16 and 17.

Geometry oftlte basinflll

The geometry of the basin fill has been reconstructed using the following tools (Mas el al., 1993; Guimera el al. , 1995): (1) geological mapping of the basin and its surrounding geological setting (Fig. 2 B); (2) stratigraphic analysis based on both outcrop data and wells; and (3) balanced structural cross sections through the basin, based on seismic profiles and field data (Fig. 2 A). The cross-sections allow two-dimensional reconstructions ofthe basin geometry. These data show that the different depositional sequences that filled the basin onlap northwards on the Mesozoic substratum (Fig. 2: A and B). The result is a northward migration of the depocentres of the depositional sequences and their areal distribution. The maximum vertical thickness is up to 5 km, but thanks to this migration, the stratigraphic record can be measured down to 9 km in the field (Fig. 2 A) . On the other hand, no major fauIts have been found in the north margin ofthe basin to explain so great a thickness. Indeed, the boundary between the basin fill and the bounding previous rocks is generally a sedimentary contact. In the southern part of the basin the first sequences (DS 1 to DS 3, TithonianBen'iasian) onlap an unconformity over the Kimmeridgian reefal complexes ofthe Torrecilla en Cameros Fm. In the northern are a, however, the DS 7 (Late Barremian-Early Aptian) sequence lies ul1conformably on the Kimmeridgian Torrecilla Fm. (Fig. 2 B). The Cameros basin is atypical among the basins of the Mesozoic Iberian Rifting, but analysis of the sedimentation rate based on field data (Mas el al., 1993: Fig. 7) clearly reveals two stages of rifting acceleration, a Tithonian-Berriasian stage and a Barremian-Early Albian stage, which clearly parallel other contemporaneous Iberian basins. Subsidence analysis on the basis of three virtual wells (Fig. 19) reveals that the two stages of rifting acceleration are present in the depocentral area. However, in the northern part, only the second stage is recorded. Tectonic subsidence in the depocentral area is more than twice that in the northern area.

~ ~~. + ~~~~. ~., . ~2~?~_ ?i2~~7~~ 121~. _.'==~"~~. :., ~~. "=". '--,.,-'-,.,-.". -=. .• •. •• • •

Cameros 1

lao 135 130 125 120 11~ 110 105- 1:xI My

o~ . . ---. TS 10~JO

--------Is

:;:000

3000 Cameros 2

I.U 135 IJO 125 120 115 110 lO!: 100 "v

:~" 3000 \

4UOU - ~ ~ IS

6000

Cameros 3

I .lO 13:' 130 125 120 115 110 105 100 M-,

o------------------~~--------~

1000 TS

2000 -~

Is

Fig. 19. Subsidence analysis performed on the basis ofthree virtual wells (1 , 2 and 3) in the

Cameros Basin.


BARCELONA GENERALlTAT DE CATALUNYA (SPAIN) , 21 · 24 September 2003 23

Metamorphism affecting the Cameros Basin

A large proportion of the deposits in the eastern sector of the Cameros Basin have been affected by lowgrade and very low-grade metamorphism (Fig. 4). This metamorphism is recognizable macroscopically by intense recrystallization that transformed the layers of sandstones to metaquarzites; at a microscopic level, we would stress the appearance of chloritoid, which is typical of low-grade metamorphism. This was once treated as an example of regional dynamo-thermal metamorphism coinciding with the filling of the basin (Guiraud & Seguret, 1985 ; Golberg el al. , 1988). The same idea is al so maintained today by other authors (Casas Sáinz & Simón Gómez, 1992; Mata el al. 2001), who view it as isochemical low grade metamorphism associated with the burial conditions at the depocentral area of the basin. However, recent findings, based on a detailed study of the basin combining mineralogical, petrological, geochemical and structural approaches, have defined the metamorphism as hydrothermal and alochemical (Casquet el al. , 1992; Barrenechea et al. , 1995 ; Alonso-Azcárate el al. , 1995 ; Mantilla et al. , 1998; Alonso-Azcárate et al. , 1999; Mantilla., 1999; Barrenechea et al., 2000; Alonso-Azcárate el al. , 2001). A number of different analytical methods have been applied in these studies: microthermometry of fluid inc1usions, radiometric dating, mineral assemblages ("chloritoi~chlorite at the metamorphic peak), crystallochemical parameters of phyllosilicates, chlorite microthermometry, isotopic thermometry and the geochemical study of sulphide deposits. The most important conc1usions to be drawn from these studies are: (1) metamorphism displays very c1ear thermal inversions in the depocentral areas, and the grade reached is influenced by the changes in permeability and composition of the sediments rather than by the burial depth; (2) metamorphism was later than the basin fill, with a post-rift age of -1 06 to -86 Ma, that is to say from Late Albian to Coniacian; (3) the metamorphic conditions range from low-grade or epizone to very low-grade or anchizone, with a maximum temperature of 350-370°C at the metamorphic peak and a maximum pressure of 1 kbar. AIso, Mantilla (1999) has more precisely identified the metamorphic areas in the basin (Fig. 4) and their thermal and geochronological characteristics. Two main metamorphic areas have been defined: Yanguas-San Pedro Manrique, with a low grade Upper Cretaceous metamorphic event and a very low grade Lower-Mid Eocene metamorphic event (A in Fig. 4); and the Pégado antic1ine, where only a very low grade Lower-Mid Eocene metamorphic event has been recognized (B in Fig. 4). Slaty c1eavage occurring in fine-grained incompetent layers is a common feature of the Yanguas-San Pedro Manrique metamorphic area (A in Fig. 4). This type of penetrative foliation is oblique to bedding; however, the bedding-oblique foliation in the Pégado antic1ine metamorphic area (B in Fig. 4) is different, consisting exc1usively of an axial plane c1eavage type tectonically related with the Pégado alpine fold . Another distinctive feature genetically related to hydrothermal metamorphism is the frequency of pyrite ore deposits in the eastern sector of the Cameros Basin (Alonso-Azcárate 1999; Alonso-Azcárate el al. , 1999). Sulphur isotope studies of pyrite crystals (Alonso-Azcárate, 1997; Alonso-Azcárate el al. , 1999) show that the sulphur source is a combination of thermal breakdown of sedimentary sulphide and evaporite-derived, thermochemically reduced sulfate. Pyrite crystals are renowned world-wide for their size, lustre and perfect crystal shape. Recent findings show that fonner sedimentary facies in the basin have considerably influenced the different crystalline habits of the pyrite crystals (Alonso-Azcárate el al. , 2001).



Structural features of the basin

The Cameros Basin was completely inverted and is part of an Alpine thrust-sheet (Fig. 2 A) larger than the Cameros Basin (Guimera et al. , 1995). The Cameros thrust-sheet includes the Latest Jurassic-Early Cretaceous basin fill , its Mesozoic substratum, and the Variscan basement which crops to the northwest and southeast (Fig. 2 B). It also includes the Tertiary Almazan Basin, which is in fact a piggy-back basin. The inverted Cameros Basin has overthrust the Almazan basin along its southern boundary (Fig. 2 A: cross-sectíon B-B '). The thrust-sheet lies in a roughly east-west orientatíon and is at least 150 km in length and 80 km wide. The northern border ofthis thrust-sheet is the Cameros sole thrust, whích crops out for 120 km roughly in a WNW-ESE dírection. Its actuallength is greater, as deduced from bore hole data (Guimenl et al., 1995). This thrust was synchronous with the sedimentation of the Paleo gene to Middle Miocene rocks of the Ebro basin, which were likewise folded synchronously (Mas el al. , 1993 ;

Guimenl et al., 1995). The basal thrust fault of the north-verging Cameros thrust sheet displays a typical ramp-flat-ramp geometry. Beneath the internal pa11s of the Cameros Unit, this fault ramps up from the basement, flattens out at the base of the Keuper for about 20 km and ramps up through Jurassic carbonates and Tithonian-Lower Albian clastics at the 1eading edge ofthis thrust sheet. The axial parts of the Cameros Unit are underlain by a basement involving ramp anticline and were uplifted by 2-3 km

(Fig. 2 A). Moreover, beneath the deeper parts of the early Cretaceous basin, bore-hole and reflectionseismic data indicate the presence of a basement short cut (Ramírez Merino el al., 1990; Casas, 1992). The total shortening across the Cameros Basin is estimated at 33 km (Guimera el al. , 1995).

To the west and southeast, the basin fill rapidly loses thickness, and folds and faults appear involving Variscan Basement, the Mesozoic Cover, and the Pre- and Syntectonic Tertiary deposits (Fig. 2 B). The southern border of the inverted Cameros basin is a roughly east-west system of south-oriented imbricate thrust and thrust-propagation folds, stretching for about 150 km. Thrust and folds were syncronous with the sedimentation of the Tertiary rocks of the Almazan Basin, which was its local foreland basin (Fig. 2 A: B-B ' and Fig. 2 B). The southern imbricate fold-and-thrust fan is associated with the faulted southern margin of the Latest Jurassic-Early Cretaceous Cameros Basin, as indicated by the results oftwo wells and surface geological data (Meléndez & Vilas, 1980; Clemente & Alonso, 1990, Guimera et al. , 1995). This early Cretaceous normal fault was pat1ially inverted. However, a short-cut involving the late Triassic rocks, preventing inversion of its upper parts, resulted in thrusting and folding of the Pre-Cretaceous and late Cretaceous. Moreover, this external deformation zone was uplifted in conjunction with the development of a basement short-cut (Fig. 2 A: B-B '). The total shortening along the southern margin of the Cameros unit amounts to about 5.4 km (Guimera et al., 1995).

The transport direction ofthe thrust-sheet is NNE-SSW (Fig. 20 A) and the cumulative strain during the Paleogene inversion of the Cameros Unit is estimated to be in the range of 38.4 km (Guimenl el al.,

1995). The direction of regional extension during formation of the basin was also NNE-SSW (Fig. 20 B). This direction has been estimated from tension gashes essentially filled by quartz in the case of sandstones and by calcite and occasionally quartz in the case of carbonates (Guiraud and Seguret, 1985; Guimera el al. ,

1995). The total extension ca1culated by a computer model is 33.3 km (Guimera el al. , 1995). Jurassic marine carbonates (max thickness approx 0.5 to 1 km) are present throughout the Cameros unit as a substrate of the Cameros Basin fill. (Mas et al. , 1993; Guimera el al. , 1995). These strata provide only minor evidence for syn-depositional extensional faulting (Guiraud, 1983; Díaz Martínez, 1988; Mas el

al. , 1993); also, as noted earlier, the Cameros Basin fill shows progressive northward migration of depocenters and onlaps the northern basin margin (Fig. 2 A).The Cameros Basin is therefore interpreted as an inverted extensional ramp basin (Mas et al. , 1993; Guimera el al. , 1995).



A

B o .::- "

~..;;. el ( . :;.. ('.;;.J V V ~

;. (" n e- -" u ~ I ... .... .::! ~ l :. J r: :I .J {' (; ~. '" ::J :1 ':' . '

~) " ' ." ~ \. , /-, ,

¡ \ _- >

\ 1." I 1, -- '1' .. , . .... '.

o

N

A

}

20 km

Fig. 20. A. Simplified map of the Cameros basin and the sole thrust cropping out north of it. The application of the bow and arrow rule (Elliot, 1976) is shown, to estímate the displacement direction of the Cameros thrust-sheet (from Guimera et al. , 1995). B. Geological map of the north-eastern part of the Cameros basin, showíng the dírectíons of extensíon at outcrop scale deduced from quartz dykes or calcite veins by Guiraud & Séguret (1985).



Evolution of the Cameros basin: Basin Model

Following is a summary of the conclusions regarding the formation of the basin, its later metamorphism and the subsequent basin inversion. These conclusions constitute the core of the proposed evolutionary model that explain this basin. As regards formation, we conclude that the Cameros basin is a synclinal basin with no major fault bounding it during its development (Fig. 2 A). The idea of a major extensional fault that surfaced at the northem boundary of the basin (Fig. 21 A), controlling its geometry and the northward migration of the successive sequences, was rejected early on in view of the practically total continuity of the Jurassic substratum of the basin (Fig. 21 B). In fact, the northward migration of the basin fill depositional sequences and its lapping on the pre-basin Mesozoic substratum (Fig. 2 A), which in almost all cases is Malm, may be explained by assuming that the basin formed over a roughly south dipping ramp in a horizontal extensional fault. This means that it would be an extensional-ramp basin. Indeed, in scale models (McClay, 1990; Roure et al. , 1992), the same pattems in the units filling a synclinal basin have been obtained on horizontal-extensional faults containing ramp segments over which the basin was developed (Fig. 22) . In these models, the extension in the hanging wall rocks previous to the basin takes place outside the synclinal basin around the area where the extensional faults surface, so that the extension of the basin substratum is very small and its rock units remain continuous.

A s N

10 20 30 40 S O 6 0 70 8 0 90 km ! ! ! ! ! ! ! ! !

B s N

3 0 40 SO 60 9 0 ! ! ! ! !

c h ar l a2 km

Fig. 21. Two sketch es explaining the geometry of the basin fil!. Both hypothesis (A and B) explain the north migration of the basin fill depositional sequences, but only hypothesis B explains how the basin fill depositional sequen ces lap on the pre-basin Jurassic substratum which displays practically total continuity.



A

B

al

b l

1 r"n s lat lon r----.,lId ~:~~ I~~:r u..i: ano r--- RO h"ltlOn 1 r;:, rlSlation slJb",idence .,~ c sub!' idenct'

~ Upoer roll -over anc -+- Ramp 70m:: -----.1 LO 'Ner roll - over ancl ¡ ("'''' e ~ t ",, 1 CO lli'lDSe lone ~ uc-Sot,;, i ("(\IJilp'i('> - 1 0 n('

, Uoper crest.l Lowi: " ,....ol l-ov~r and IUPPt'r rOd - over l coll floc¡ e Tr;Jn s! ;'1 Ion ¡RrZ¡ RSZ¡ c r es ta ! cOllapse I

t!rt l l t ltnf> graben ' 9ril~n

reve-rse faull s due lo benolnQ a ' t'1e ' 0

0 1 'he l amp t:' raoen Oue

!O ou~er a"e Strelc~IOQ I .

(OUl er are 01 )

reverse lault , / norma l fau lt s ro ll -ovcr I > . I

~':.'( " jo -\" _ 1, .r • - • .lo x 0,., ' _ • • ,. •

~- . - w

\ I

norma l Icults Induced by shea r illong tho ramo o ___ ~~

no~:nal faulis ';

~.~I==·~lo vi

Fig. 23. 2D sketches illustrating the hypothetical location of the main extensional fault plane (red line) during the extension of the basin. A. The extensional fault is located in the Upper Triassic Keuper beds and coincides with the thrust that inverted the basin (after Guiraud & Seguret, 1985 and Casas & Simón, 1992 hypothesis). B. The extensional fault is located inside the Hercynian Basement at an approximate depth of seven to eleven kilometres (after Mas et al. , 1993 and Guimera et al, 1995 hypothesis). Both cases: 1. Pre- extension situation and 2. Post-extension situation.



One important question is the depth at which the extensional fault was located. Other authors (Guiraud & Seguret, 1985; Casas & Simón, 1992; Casas, 1993; Mata et al. 2001) have suggested that the fault is located in the Upper Triassic Keuper beds and so should coincide with the thrust that inverted the basin (Fig. 23 A). This hypothesis has a mechanical flaw which in our opinion makes it unlikely. To produce the basin, a slab of Jurassic rocks only 500-800 m thick, more than 30 km wide and more than 100 km long would have to have been pulled from the south without any break in its continuity and without the formation of a fault over the ramp at the north basin boundary. Moreover, this would have had to occur under sub-aerial conditions, as can be deduced from the continental nature of the rocks which filled the basin. To get round the problem, it has been suggested that the extensional fault is located deep inside the Variscan Basement (Fig. 23 B and Fig. 24) at a depth of 7 to 11 km (Guimenl et al. , 1995), coincident with the position of the sole thrust of the Iberian Chain proposed by Gimera & Álvaro (1990). The hanging wall would then be several kilometers thick and susceptible of southward displacement without significant internal deformation. The extension in the hanging wall block took place outside the basin, around the area where the extensional fault surfaced towards the north. This zone would correspond to the area of the Vasco-Cantabrian Basin, where an important system of half-grabens was contemporaneously very active. Moreover, small half graben basins developed in the Ebro block (Fig. 23 B), as deduced from seismic and well data (Guimera et al. , 1995). Briefly, then, the Cameros basin could have been produced by the motion of a deep extensional fault containing two nearly horizontal sections (flats) separated by an intermediate section dipping to the south (ramp). The direction of displacement for the hanging wall was S-SW, parallel to the direction of the basin extension mentioned.

el Cameros trough

81 Bigornia trough

Fig. 24. 3D sketch iIlustrating the general geometry ofthe Cameros Basin and the location of the main extensional fault plane (yellow line) during the extension, and the thrust-sheet plane position prior to contraction (red line). Afier hypothesis ofMas et al. (1993) and Guimera et al. (1995) .



To illustrate this hypothesis, a computer model was constructed (Mas el al. , 1993 ; Guimera el al. ,1995) using the Fault! program (Wilkerson and Usdansky, 1989). Despite sorne limitations of the program, in our opinion the resulting computer model is a good representation of the evolution proposed for the Cameros Basin (Fig. 25). Figure 25 shows the evolution deduced by the program for the cross section A-A' and B-B' in Figure 2 A. The first stage (A) shows the geometry of the extensional fault before formation of the basin. Stages (B) to (F) show the Tithonian to EarIy Albian evolution of the basin as an extensional-ramp sync1ine resulting from the hanging wall displacement to the South.

The width of the basin increases progressively until it reaches its final state. At every stage the corresponding depocentre is always located aboye the ramp and the former sedimentary units are displaced southwards as a consequence ofthe progressive hanging wall movement. The result is an onlap of every unit northwards over the Mesozoic substratum. To explain the secondary depocentres at the southern border of the Cameros basin, an antithetic fault is introduced during stages (D) and (E) (Fig. 25). This represents the major fault in cross-section B-B ' (Fig. 2 A). Similar faults have also been deduced in the scale models ofMc Clay (1990) and Roure e l al. (1992), as a result of the extension in the hanging wall where it passes from the ramp to the lower flat of the foot wall (Fig.22). Thus, the Cameros Basin is a hanging-wall basin (Gibbs, 1987) which constitutes a good real example of the extensional-ramp basin scale model ofMc Clay (1990). The low- and very low-grade Late Cretaceous hydrothermal metamorphism affecting the basin could be related to the post-rift thermal evolution caused by crustal thinning generated during the prior Latest Jurassic-EarIy Cretaceous basin formation. On the other hand, the very low grade Lower-Mid Eocene metamorphic event would be related to the Alpine contraction of the basin. Basin inversion took place during the Paleo gene to the Early-Middle Miocene due to Pyrenean compression (Guimera el al. , 1995). To illustrate the process of inversion, Figure 25 (stage H) shows the location ofthe Tertiary thrust in relation to the previous Mesozoic structure. The main northern thrust is a newly formed fault. Its formation would have been facilitated by: (1) sealing ofthe Mesozoic extensional fault beneath the basin as a result of Late Cretaceous metamorphism, and (2) the presence on the northern flank of the basin of a potential weakness zone located in the Keuper beds. This zone exhibits a uniform dip of about 100 to the south for about 30 km as shown in cross-section D-D' (Fig. 2 A) and in Fig. 25 (H). From this weak zone, the new

ssw NNE

--- ] A

t E

e

o

E

r-- --.':..'..::::::::.:-___ - __


ssw NNE Fig. 25. Computer modelling of the Cameros Basin formation and

'--__ --=-_~ __ _'_____"_'__''____'_''·"'''_L" inversion, using the program Fault! G

." .. H

By Wilkerson & Usdansky (1989). A. Pre-rift situation; B. DS 1 and 2; C. DS 3; D. DS 4, 5 and 6; E.DS 7; F. DS 8; G. Late Cretaceous (metamorphism);

, H. Location of the faults which ~'. -=~~"--~~. -=~~~~~~"~~~~~~

!!!Tithonian-Early Albian n·· Cretaceous (Cameros bas,n f,II'ng) - metamorphism

•Triassic and Jurassic

D Hercynían basement

U Tertiary

• Late Abian-Late Cretaceous

Evolution of the Cameros basin

inverted the basin (before the basin inversion); 1. Situation after the basin inversion (which took place during the Paleo gene and EarIy-Middle Miocene) (from Mas el al. , 1993).


A s End of the marine Jurassic (Kimmeridgian) N

1

Starting of the rifting. s Deposition of the Tithonian and Berriasian N

2 /V

Depositon of the Barremian and Early Aptian s PICOFRENTES _____ Cameros Trough------- Luezas Rioja N

Trough Trough ZONE CENTRALZONE

3a /V

s Depositon of the Late Aptian-Early Albian. End of the rifting. Maturation and migration of hydrocarbons N

3b

Deposition of the Late Crataceous post-rift. s Metamorphism of the basin (Late Cenomanian) N

/V

Preserved hydrocarbons? S ..

Destroyed hydrocarbons Preserved hydrocarbons? .. .. .. N

4b

Tectonic inversion of the basin (Eocene-Early Miocene).

S Local metamorphism (Early-Mid. Eocene; Miocene?) #

• New migration of hydrocarbons? R~5

o 10 .... 11' __ .' __ .'

[[]] Triassic and pre-rift Jurassic

~ Variscan basement L.....J and Lower Triassic

DTertiary

D

Late Albian and . Late Cretaceous

(post-rift)

OS 8

OS 7 Tithonian to Early Albian

OS 4+5+6 (Cameros Basin syn-rift depositional sequen ces)

OS3

OS 1+2

Fig. 26. A. Evolutionary Model for the Cameros Basin.



N R·3

• Oil , condensates, oil seeps

# Gas

B BURGOS

@

LOGROÑO @

_ ·DA-

• Arnedo

(- - - - - - - CENTRA.L ............................

"CAMERO ZONE ", ~ ........ ........ ........ SI- !JROUG "- ''\:Tarazona - - - . DA__ H" --- '" --- "-~ ~ ........ PICOFRENTES SORIA ........ ........ \

~ --- ZONE@--__ ........ "-\

s • Burgo de Osma • Almazán

"-./

-<f~ 20 Km

Fig. 26. B. The Cameros Basin (Cameros Trough) and their related satellite basins (Bigomia, Luezas

and Rioja troughs).

thrust could have nucleated and spread to the north and to the south during deformation, then branched southwards to the lower flat of the "Iberian sol e thrust" proposed by Guimera and Alvaro (1990). The thrust system to the south of the basin (Fig. 25, H) developed from the inversion of the minor normal faults which bounded the Mesozoic basin towards the south (Fig. 2 A). The Cameros Basin therefore appears at present as a pop-up structure bounded by the Cameros thrust to the north and a minor back-thrust system to the south (Fig. 2 A). In the proposed model, the Almazan Tertiary Basin is a piggy-back basin (Guimera et al. 1995; Casas Sainz et al. , 2000) resting on the Cameros thrust-sheet which is located inside the Iberian Chain (Fig. 2 A and B).

Figure 26 is a schematic representation of the genesis and evolution of the Cameros Basin and sorne related sub-basins.

Potential Petroleum Systems of the Cameros Basin. Discussion

This section reviews the potential Petroleum Systems based on an analysis of the main depocentral Cameros Extensional Ramp Basin and two surrounding half-graben sub-basins. This analysis follows the S-N distribution of troughs in the Cameros area: Bigomia Trough, Cameros Trough (Central part and South-edge) and Rioja Trough (Fig. 26 A and B).



1. BIGORNIA TROUGH (Southeast of Cameros Trough, inverted half-graben outcropping) Status: Oil seeps in the Escucha Fm. (Syn-Rift Early Cretaceous, DS 8 = Escucha I 01iván Fms) Source rocks:

Callovian organic marls and black shales (type Ir) Early Cretaceous lacustrine organic marls (type 1111)

Reservoir: Fluvial channels ofEscucha Fm. (Syn-Rift Early Cretaceous, DS 8) Seal: lntervening mudstone Kitchen: Cameros Trough (Moncayo zone) Timing of hydrocarbon generation: Early to Late generation

Early generation: Late Cretaceous (maturation of organic matter: abnormal heat flow - 1 sI

hydrothermal event) and/or burial? Late generation: Tertiary (maturation of organic matter abnormal heat flow - 2nd hydrothermal event)

Trap: Mixed structural and stratigraphic trap associated to early features carried out during Early Cretaceous rifting stage and/or to Alpine structure.

Comments: Trap lost its integrity during the last phases of Alpine compression and subsequent exhumation;

2. CAMEROS TROUGH (Main Depocentral Extensional Ramp Basin, in the hanging-wall of the North Cameros Thrust, Cameros structural Unit)

2a CENTRAL PART OF CAMEROS AREA. (Outcropping) Status: metamorphic area Source rocks: Callovian organic marls and black shales (type II) (today over-mature) Early Cretaceous lacustrine organic marls (type II/I) (today over-mature) Syn-Rift Early Cretaceous lignites and organic rich shales (type III) (today over-mature) Reservoirs (today lacking porosity):

Bathonian oolitic bars Jurassic reefs Syn-Rift Early Cretaceous fluvial sandstone channels (DS 4, 5, 6, 7 and 8?)

Seal: lntervening mudstone Kitchen: Cameros Trough Timing of hydrocarbon generation: Early generation

Albian (maturation of organic matter: burial) Late Cret. (maturation of organic matter: abnormal heat flow - 1 sI hydrothermal event)

Trap: Mixed structural and stratigraphic trap associated with early features carried out during Early Cretaceous rifting stage

Comments: In this central part ofthe Cameros Trough there was undoubtedly early oil generation from the sources (today over-matureJ towards the reservoirs (today, tight "paleo-reservoirs "J. The different hydrothermal phases have affected the Cameros Trough, destroying hydrocarbons and porosity of early reservoirs. Nevertheless, those hydrocarbons which migrated early from the Cameros kitchen toward the margins of the basin could still be preserved as they were no! affected by hydrothermalism.



2b SOUTH-EDGE PART OF CAMEROS AREA. PICOFRENTES ZONE (Outcropping, South Cameros structural Unit). Status: Oil seeps in the Utrillas Fm. (Post-Rift EarIy Cretaceous) Source rocks: Callovian organic marIs and black shales (type II) (today oil window) Early Cretaceous lacustrine organic marls (type IlII) Syn-Rift Early Cretaceous lignite and organic rich shales (type 111) Reservoir: Utrillas Fm. (Post-Rift Early Cretaceous)

Commenfs: The sfafe of biodegradation made it impossible fo draw definitive conclusions as to the origin ofthe hydrocarbon. There were no correlations between the oil seepsfound in the Pico frentes area and the bitumen extractedfrom Syn-Rift Early Cretaceous lignite samples (Escucha Fm. DS 8) (early mature samples corresponding to the northern edge of the Cameros area, today overthrust by the Cameros structural unit)

Seal: intervening mudstone Kitchen: Cameros Trough Timing of hydrocarbon generation: Early to Late generation

Early generation : Late Cretaceous (maturation of organic matter: abnormal heat flow - 1 st

hydrothermal event and/or burial?). Late generation: Tertiary (maturation of organic matter abnormal heat flow - 2nd hydrothermal event)

Trap: Mixed structural and stratigraphic trap associated to early features carried out during Early Cretaceous rifting stage

Comments: The trap lost its integrity during late phases of Alpine compression and subsequent exhumation

3. RIOJA TROUGH (North of Cameros Trough, semigraben below Tertiary cover, in the foot-wall of the Cameros Thrust, Ebro Foreland Block)

Status: Light oil and gas in Rioja 4 well, gas and condensates in Rioja 5 well in the Escucha I Olivan Fms. (Syn-Rift) . Non-commercial due to mixture of oil with water and very low permeability. Source rocks : Callovian organic marls and black shales (type II) if present

Early Cretaceous lacustrine organic marls (type IlII) if present Syn-Rift Early Cret. lignites and organic rich shales (Escucha/Olivan Fms, DS8) (type III)

Reservoir: Syn-Rift Early Cretaceous fluvial sandstone channels (DS 8 and 77) Seal: Intervening flood plain mudstones Kitchen: Rioja Trough Timing of hydrocarbon generation: Early to Late generation

Early generation: Late Cretaceous (maturation of organic matter: abnormal heat flow - 1 st

hydrothermal event) Late generation: Tertiary (maturation of organic matter by lower to middle Eocene abnormal heat flow - 2nd hydrothermal event )

Trap: Mixed structural and stratigraphic trap associated with early features carried out during Early Cretaceous rifting stage and/or to Alpine structure (ramp anticline related to Tertiary compressional stage).

Comments: The load of the Tertiary overburden was the same for both Rioja 4 and Rioja 5 wells. However, geochemical data show that today, Syn-Rift Cretaceous materials of the Rioja 4 well are in the early oil window, while in the Rioja 5 well they are today in the gas window. Thus, the Tertiary overburden did not irifluence the maturation of the source rocks, hydrothermalism being the most acceptable originfor organic maUer maturation. Low porosity values ofthe Lower Cretaceous sandstone in Rioja 5 (3%) and Rioja 4 (8%) wells, drilled in the Rioja Trough. Although almost unknown, Westphalian cannot be discounted as another possible so urce rock.



FIELD TRIP ITINERARY

CAMEROS BASIN FIELD TRIP La Rioja - Soria, 25th-28th September, 2003

FRANCE

SPAIN

CAMEROS BASIN FIELD TRIP ITINERARY

BURGOS ~

2"

®~1,2 & 3 LOGROÑO

Fig. 27. Field trip itinerary and stops.


BARCELONA GENERALlTAT DE CATALUNYA (SPAIN), 21·24 September 2003 35

El Villar de Arnedo

Arnedo

N

t 10 km

to Calatayud

BURGOS •

Syncline

Anticline

Normal fault BURGO DE OSMA ~ Thrust

......-rT" Cameros thrust -_ Triassic and Jurassic

Carboniferous

Variscan Basement

Late Albian and Late Cretaceous

Depositional Sequen ces of Cameros Basin fill

20 km

,------- Post-tectonic rocks

Pre and Syntectonic Tertiary

Fig. 28. Location ofthe field trip stops on the schematic geological map ofthe Cameros Basin (modified from Guimera et al. , 1995).



Day 1: Thursday, September 25, 2003

Departure 8:30 a.m. from Barcelona (Pala u de Congressos de Catalunya).

TOPIC 1: THE SOUTHERN BORDER OF THE CAMEROS BASIN: SOUTHERN SECTOR OF THE MONCAYO PEAK - SORIA (ZARAGOZA - SORIA). FIRST GENERAL VIEW OF THE BASIN.

OBJECTlVES OF TOPIC 1: ·EXTENSIONAL MESOZOIC EPISODES STRATIGRAPHIC RECORD OF THE BASIN FILL. ·DIAGENETIC EVOLUTlON OF THE LATE JURASSIC MARINE CARBONATES 'OIL SEEPS DISCUSSION ABOUT THE ORIGIN OF HYDROCARBONS

Stop 1.1. Bigornia Pass (limít 01 Soria and Zaragoza provínces). Introduction to tbe Cameros Basin.

The first deposits (Titbonian-Berriasian, DS 1-2) of the Syn-rift Stage 2 (Fig. 5) unconformably overlies both the Oxfordian and the Early Kimmeridgian marine sequences, and postdates faults that affect these two marine units ofthe Post-Rift Stage I(Fig. 29).

Fig. 29. Bigomia Pass: The first syn-rift sequence (Tera Gr) unconformably overlies the Kimmeridgian sequence (Torrecilla en Cameros Fm.), post-dating sorne faults that affect Late Jurassic marine units.



Stop 1.2. Bigornia Pass - Torrelapaja (Zaragoza province).

The first syn-rift deposits (DS 1-2) fills a half-grabens system (fig. 30). An angular unconformity is developed between this Titbonian-Berriasian sequence and the DS 7 (Early Aptian). The Depositional Sequence 8 (Late Aptian-Early Albian) contains bituminous sandstones.

Torrecilla Frn (Kirnrneridgian)

Bijuesca Frn (Tera Gr.)

Ciria Fm (Tera Gr.)

Fig. 30. Bigomia Pass-Torrelapaja: Tera Gr, filling a half-graben basin and unconformably overlaying the Kimmeridgian Torrecilla Fm.

Stop 1.3. Renieblas (Soria province).

The southem border ofthe Cameros Basin. Tbe first syn-rift depositional sequence (DS 1) overlies the Early Kimmeridgian marine pre-rift sequence.

Stop 1.4. Piqueras Pass (limit of Soria and La Rioja provinces).

Panoramic view of tbe Cameros Basin from the alluvial conglomerates at the base of DS 7 (Late Barremian - Early Aptian) .

Accommodation in Logroño (La Rioja).



Day 2: Friday, September 26,2003

TOPIC 11: FEATURES OF THE CAMEROS BASIN SUBSTRATE IN THE IREGUA RIVER VALLEY (LA RIOJA)

OBJECTIVES OF TOPIC II:

'SEDIMENTARY AND DIAGENETIC EVOLUTION OF THE LAST MARINE REEFAL UNIT. MISSISSIPPI VALLEY TYPE MINERAL ASSOCIATIONS RELATED TO THE CAMEROS NORTHERN THRUST. 'POSSIBLE SOURCE ROCKS AND RESERVOIRS. POTENTIAL GENERATION OF TYPE 11 HYDROCARBONS. 'ONLAP OF THE SUCCESSIVE SYN-RIFT SEQUENCES OVER THE LAST MARINE JURASSIC UNIT (EARLY KJMMERIDGIAN).

Stop 2.1. Torrecilla en Cameros (La Rioja). Tómalos hermitage:

General view of contact between marine late Jurassic and syn-rift units. The late Jurassic coral reef complex (early Kimmeridgian) (Fig. 31). Geometry and diagenesis ofthe coral reefs.

Fig. 31. Prograding reefs ofthe Torrecilla en Cameros Fm. from Tómalos hermitage.

Stop 2.2. Torrecilla en Cameros. Old Soria-Logroño road.

Stratigraphic section of the upper part of the middle to late Jurassic marine units. Bathonian: oolitic bars; Callovian: calcareous rhythmite with bituminous marls and black shales. Malm: calcareous rhythmite and coral reefs.

Stop 2.3. Torrecilla en Cameros (La Rioja). Ribavellosa road (optional) :

The first and syn-rift sequences (DS 1, 2 and 3) onlap the last marine deposits of early Kimmeridgian age.


BARCELONA GENERALlTAT DE CATALUNYA (SPAIN), 21 "24 September 2003 39

TOPIC IlL THE NORTHERN BORDER OF THE CAMEROS BASIN: THE CAMEROS NORTHERN THRUST (LA RIOJA).

OBJECTIVES OF TOPIC IIl: 'STRUCTURAL ANALYSIS. DISCUSSION ABOUT THE EXTENSIONAL FAULTING OF THE MESOZOIC SUBSTRATE AND THE ORIGIN OF SMALL EXTENSIONAL BASINS IN THE FOOT-WALL OF THE CAMEROS THRUST ·THE ONLAP OF THE SUCCESSIVE DEPOSITIONAL SEQUENCES TOWARD THE NORTH OF THE BASIN. IMPLICATIONS ON HYDROCARBONS EXPLORATION. ·ROLE OF THE TERTIARY BURDEN AND HYDROTHERMAL EVENTS IN THE SOURCE ROCK MATURATION. DISCUSSION ABOUT THE AGE OF THE SOURCE ROCK GENERATION.

Stop 2.4. Viguera. (Valley of Iregua river, La Rioja).

The front of tbe Cameros nortbern tbrust. Tertiary alluvial fans associated witb tbe tbrust (Fig. 32).

Fig. 32. Panoramic view ofTertiary alluvial fans from Viguera.



Stop 2.5. Valley of Leza river (Clavijo-Leza-Soto en Cameros, La Rioja).

Snake's Head geometry in the Cameros northern thrust. Active faulting during sedimentation of the alluvial fans and carbonate lacustrine systems of the DS 7 (Late Barremian-Early Aptian) (Fig. 33). Lateral facies cbange between siliciclastic-poor and silicic1astic-rich shallow carbonate lakes (DS 7).

Fig. 33. Synsedimentary faults in the Leza Fm (SD 7).

Stop 2.6. Valley ofthe Jubera river (Jubera-Robres-San Vicente, La Rioja).

Syn-rift active faulting controls the depositional architecture ofthe alluvial sediments and the carbonate lacustrine systems ofDS 7 (Late Barremian-Early Aptian). Onlap relation ofthe syn-rift sequences over the Late Jurassic marine units (Fig. 34).

Visit to a famous old Rioja wine cellar (it wine is available for purchase). Accommodation in Logroño (La Rioja).

Leza Fm / Jubera Fm

/

Fig. 34. San Vicente: Faulting in the Jurassic substrate.



Day 3: Saturday, September 27, 2003

TOPIC IV. GENERAL N-S CROSS SECTION TO THE CAMEROS BASIN ACROSS THE DEPOCENTRAL AREA (VALLEY OF THE CIDACOS RIVER - ONCALA PASS). THE METAMORPHISM OF THE BASIN.

OBJECTIVES OF THE TOPIC IV:

·ALPINE COMPRESSIONAL TECTONICS. THE CAMEROS THRUST SHEET STRUCTURE IN THISAREA.

·THE DECREASE IN THICKNESS FROM THE SOUTH TO THE NORTH OF THE DEPOSITIONAL SEQUENCES. POSSIBLE RESERVOIRS AND SOURCE ROCKS. THERMAL MATURATION.

·LACUSTRINE CARBONATES AS POSSIBLE TYPE 11 AND TYPE 111 SO URCE ROCKS.

·HYDROTHERMAL EVEN TS. AGES OF THE METAMORPHISM

·AGE OF THE HYDROCARBON GENERATION. PALAEO-RESERVOIRS. STRATIGRAPHIC TRAPS. SEALS.

Stop 3.1. Peña/monte (near Préjano, La Rioja).

Structure ofthe Cameros Northern Thrust (Fig. 35). The Early Albian syn-rift unit with interbedded coal layers, and the Paleogene in the foot-wall of the thrust. General view ofthe Late Aptian-Early Albian sequence (DS 8) in the hanging-wall ofthe thrust.

Fig. 35. Peñalmonte: The Cameros northem thrust.



Stop 3.2. Arnedillo (La Rioja).

Reduced thickness ofthe DS 7 (Late Barremian-EarIy Aptian) towards the north. This sequence overlies the marine pre-rift Kimmeridgian unit. The Callovian and Malm are mainly composed of nearshore siliciclastic facies.

Stop 3.3. Enciso (La Rioja).

Siliciclastic-rich shallow carbonate lakes in the upper part ofDS 7. Visit to sorne of the best dinosaur footprints sites of the Cameros Basin.

Stop 3.4. Yanguas (Soria) (Fig. 36).

Fluvial systems in DS 4, DS 5, DS6 and lower part ofDS 7 (Latest Berriasian to Late Barremian). Hydrothermal metamorphism ofthe basin.

Fig. 36. Yanguas : Urbión Gr (DS 4, metaquartcites and shales) unconformably overlies the Oncala Gr (DS 3, rhythmic limestone and black-shales) .

Stop 3.5. Villar del Río - Oncala Pass (Soria).

Inter-bedded black shales with carbonate lacustrine facies . DS 3 (Berriasian).

Stop 3.6. Lumbreras (La Rioja).

Proximal alluvial systems at the base ofDS 7 (Late Barremian-EarIy Aptian) .

Accommodation in Logroño (La Rioja).



Day 4: Sunday, September 28,2003

TOPIC v. GENERAL CROSS SECTION TO THE BASIN IN THE WESTERN SECTOR (VALLEY OF MAYOR RIVER - STA. INÉS PASS - CIDONES - PICOFRENTES). OBJECTIVES OF THE TOPIC V:

·FILLING OF THE WESTERN CAMEROS EASIN. ·ORGANIC MATTER-RICH LAYERS. POSSIELE SOURCE ROCKS AND RESERVOIRS IN THE CONTINENTAL LOWER CRETA CEO US AND MARINE JURASSIC UNITS. ·OIL SEEPS IN THE LATE ALElAN POST-RIFT SANDSTONES.

Stop 4.1. Villoslada (La Rioja)-Montenegro (Soria). Stratigraphic section (from top to base) of the first syn-rift sequen ces DS 3, DS 2 and DS 1 (general view). Organic matter-rich layers towards the upper part of the Berriasian lacustrine facies and Tithonian fluvial facies .

Stop 4.2. Montenegro - Sta. Inés Pass (Soria). Marine Jurassic units. Bathonian oolitic bars and very thick Callovian carbonate rhythmite with bituminous marls and black shales.

Stop 4.3. Cuerda del Pozo water reservoir (Soria). General panoramic view of the syn-rift units in the southwest of the Cameros basin: DS 2 (TithonianBerriasian), DS 6 (Barremian), DS 7 (Late Barremian-Aptian). The Late Cretaceous Megacycle (post-rift) unconformably overlies the Latest Jurassic-Early Cretaceous Megacycle (syn-rift). Sandstone composition from the Cameros Basin sedimentary fill and source areas during the main rifting events. Diagenetic paths and quality as potential reservoirs.

Stop 4.4. Fuentetoba (Soria). The base of the Late Cretaceous Megacycle (Post-rift Stage 2) containing bituminous sandstones (tar sands) (Fig. 37). Retum to Barcelona (Palau de Congressos de Catalunya): 9:30 p.m. (approximately).

Fig. 37. Bituminous sandstones (tar sands) at the base ofthe Late Cretaceous

Megacyc1e (Utrillas Fm.).

Acknowledgements Most of this work summarizes the contributions from an interdisciplinary scientific team (sedimentologists, mineralogists, petrologists, structural geologists, palaeontologists, petroleum geologists) from different research departments which have participated in several projects funded by Spanish public institutions (CICYT, DGICYT, DGESEIC-SGPICYT, .. . ).



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WILKERSON, M.S. and USDANSKY, S.l. (1989): Fault! A Cross Section Modeling Programfor the IBM, memo 22 p.



FIGURE CAPTIONS

Fig. 1. The Cameros Basin in the overall structure ofthe Iberian Range (modified from Guimera et al. , in press)

Fig. 2. A. A-A ', B-B ', and C-C' : geological cross-sections through the Cameros basin. D-D': partial restoration of cross sections A-A' and B-B' at the previous state of basin inversion. See fig. 2B for location .. B. Geological map of the Cameros Basin. A-A', B-B' and C-C' Location of cross-sections from fig. 2A. (modified from Guimera et al. , 1995).

Fig. 3. A. Backstripped tectonic subsidence for the Cameros, south Iberian and Maestrat basins. Triassic and Late JurassicEarly Cretaceous rifting phases have been colored. B. Simplified geological map of part of the Iberian Peninsula showing the four most subsident basins ofthe Iberian Rifting.

Fig. 4. Geological map of the Cameros Basin showing the areas affected by low and very low grade metamorphism. A. Yanguas - San Pedro Manrique area. B. El Pégado anticline area.

Fig. 5. A. Rift cycles and Post-rift stages on the evolution ofthe Iberian Basin (modified from Salas et al. , 2001). B. Idealized and synthetic sketch/stratigraphic section showing the latest Paleozoic and Mesozoic stratigrphic record in the Cameros area (North Iberian Range).

Fig. 6. A. Palaeogeographic map of northeastern Iberia during Kimmeridgian times . The location of the two main reefal complexes is shown by asterisks: l . Soria and South of Moncayo area; 2. Torrecilla area (modified from Alonso and Mas, 1990). B. Location map of the marine Jurassic outcrops in northern Iberian ranges (in black). A, B and C corresponds to the three studied sectors where the Torrecilla en Cameros Fm. is best developed: A. South of Moncayo sector; B. Soria sector; C. Torrecilla sector (modified from Alonso and Mas, 1990).

Fig. 7. Idealized sketch es illustrating the palaeogeograhic map of the Cameros area at the Kimmeridgian times, and the sedimentary evolution of the reefal complexes of the Torrecilla en Cameros Fm. in the three studied sectors: A. South of Moncayo; B. Soria; C. Torrecilla (from Benito, 2001).

Fig. 8. Idealized sketch es of paragenetic sequence and their respective environment of precipitation (to the right) of the main diagenetic phases and events affecting the reefal complexes of the Torrecilla en Cameros Fm. in the three studied sectors: A. South ofMoncayo; B. Soria; C. Torrecilla (modified from Benito, 2001).

Fig. 9. Photographs A, B and C are from the reefal complex ofthe Southern Moncayo sector. Photographs D to F are from the Soria sector; and photographs G to I are from the Ton'ecilla sector (from Benito, 2001). A. Cathodoluminescence (CL) photomicrograph of zoned, nonferroan meteoric calcite developed in the reefal unit. The cement sequence is as follows: (C 1) Non luminescent (NL) with a thin bright-Iuminescent (BL) subzone, corresponding to Cement 1 generation of cal cite. (C 11) Cement Ir and (C I1I) Cement lIT are fOlmed by an initial NL zone and terminate with a BL zone. Porosity is completely occluded by a generation of BL c10udy calcite (CC), which replaces ankerite and ferroan calcite. B. CL photomicrograph illustrating the timing of brecciation relative to emplacement of Cements 1, 11, and 1Il. Breccia fragments of reefal carbonate (BC) and Cement I NL cement (C 1) serve as the substrate for subsequent precipitation of Cements 11 and IlI . Fragments are first overgrown by Cement II (C Il), which is formed by a thin dullluminescent (DL) zone, followed by NL ca1cite and finally by BL zones. In this example, Cement II is then overlain by Cement III (C I1I) along a noncorrosive contact. Cement 1II begins with a NL zone and terminates with thin BL zones. This generation completely occludes the remaining porosity. C. CL photomicrograph reveals relicts of NL ankerite (A) enclosed within a matrix of replacive CC, BL to light DL, nonferroan cal cite and iron oxides. Here, ankerite is nucleated on Cement III (C 1Il) and is followed by a dark-DL ferroan calcite (FC). D. CL photomicrograph showing the intergranular and moldic porosity first cemented by an early, thin generation of nonferroan NL-BL meteoric calcite (MC). Porosity is much later occluded by a generation of cloudy cal cite (CC) which replaces ankerite and ferroan ca1cite. E. CL photomicrograph showing a dissolution cavity frrst cemented by a thin generation ofnonferroan NLBL meteoric cal cite (MC). This generation is followed by a DL ferroan cal cite (FC). Porosity is completely occluded by cloudy calcite (CC). In this case, CC replaces ankerite. F. CL photograph showing a moldic cavity of a branching coral cemented by a frrst thin generation of nonferroan NL-BL meteoric ca1cite (MC). This generation is followed by a euhedral ferroan cal cite cement (FC) partially replaced by cloudy calcite (CC). Remaining pores are later completely filled by a nonferroan DL mosaic of calcite cement (MgC). G. CL photograph showing primary porosity first cemented by a generation ofNL marine columnar cal cite (BC) which is followed by a nonferroan NL-BL meteoric calcite (MC). Porosity is later filled by a Iight DL slightly ferroan cal cite (fC) and lastly by a dark DL ferroan calcite (FC). H. Dissolution cavity of a massive coral first cemented by a generation of NL marine columnar calcite (BC) which is followed by a light DL slightly fen'oan (fC) and later a dark DL ferroan cal cite (FC). Porosity occluded by ankerite (A), which is NL. 1. Transmitted Iight photograph showing a partial view of a dissolution cavity filled by cloudy saddle ankerite (A) followed by c1ear syntaxial dolomite (SD). This cement is followed by precipitation of a nonferroan mosaic of calcite (MgC), purple fluorite (F) and black solid hydrocarbons (SH).



Fig. 10. Simplified stratigraphy ofthe Depositional Sequences (DS) which fill the Cameros basin. (modified from Guimera et al. , 1995).

Fig. 11. Schematic palaeogeographic evolution ofthe Cameros Basin. BU : Burgos, LO: Logroño; SO: Soria.(from Mas et al. , 1997).

Fig. 12. Evolution of sandstone petrofacies during Late Jurassic - Middle Albian clastic deposition in the westem Cameros Basin and their genetic and tectonic relationships with the Iberian Massif zones . Arrows in temary diagrams show the evolution of petrofacies through time. Note that marine Jurassic deposits are poorly represented in the Central Iberian Zone. Qm: Monocrystalline quartz. F: Feldspar. K: K-feldspar. P: Plagioclase. Lt: Total lithics. Rg: Plutonic/gneissic rock fragment. Rm: Metamorphic rock fragment. Rs: Sedimentary rock fragment (from Arribas el al. , 2003).

Fig. 13 . Main facies associations ofthe depositional sequences DS 1 and DS 2 (Tera Gr.) .

Fig. 14. Main facies associations for depositional sequences: DS 4 = A; DS 5 = B; DS 6 = C and DS 7 (lower part) = D (Urbión Gr. in the Eastem sector ofthe Basin).

Fig. 15 . Main facies associations for the upper part ofDS 7 = E (Enciso Gr.)

Fig. 16. Main facies associations of depositional Sequence DS 3 (Oncala Gr)

Fig. 17. Main facies associations of depositional Sequence DS6 (Oliván Gr)

Fig. 18. Legend for figures 13 , 14, 15, 16 and 17.

Fig. 19. Subsidence analysis perforrned on the basis ofthree virtual wells (1 ,2 and 3) in the Cameros Basin.

Fig. 20. Á . Simplified map of the Cameros basin and the sol e thrust cropping out north of it. The application of the bow and arrow rule (ElIiot, 1976) is shown, to estimate the displacement direction of the Cameros thrust-sheet (from Guimera et al. , 1995). B. Geological map of the north-eastem part of tbe Cameros basin, showing the directions of extension at outcrop scale deduced from quartz dykes or calcite veins by Guiraud and Séguret (1985).

Fig. 2l. Two sketch es explaining the geometry ofthe basin fill. Both bypothesis (A and B) explain the north migration ofthe basin fill depositional sequences, but only hypothesis B explains how the basin fill depositional sequences lap on the pre-basin Jurassic substratum which displays practically total continuity.

Fig. 22. Scale models (A : McClay, 1990; B: Roure el al. , 1992) displaying the same patlems in the units filling synclinal basins in an arrangement similar to the Cameros Basin.

Fig. 23 . 2D sketches illustrating the hypotheticallocation ofthe main extensional fault plane (red line) during the extension of the basin . A. The extensional fault is located in the Upper Triassic Keuper beds and coincides with the thrust that inverted the basin (afier Guiraud and Seguret, 1985 and Casas and Simón, 1992 hypothesis). B. The extensional fault is located inside the Hercynian Basement at an approximate depth of seven to eleven kilometres (afier Mas et al. , 1993 and Guimera et al , 1995 hypothesis). Both cases: l. Pre- extension situation and 2. Post-extension situation.

Fig. 24. 3D sketch illustrating the general geometry of the Cameros Basin and the location of the main extensional fault plane (yellow line) during the extension, and the thrust-sbeet plan e position prior to contraction (red line). Afier hypothesis of Mas el

al. (1993) and Guimera el al. (1995).

Fig. 25 . Computer modelling ofthe Cameros Basin formation and inversion, using the program Fault! by Wilkerson and Usdansky (1989) . Á . Pre-rifi situation; B. DS 1 and 2; C. DS 3; D. DS 4, 5 and 6; E. DS 7; F. DS 8; G . Late Cretaceous (metamorphism); H. Location ofthe faults which inverted the basin (before the basin inversion); l. Situation afier the basin inversion (which took place during the Paleogene and Early-Middle Miocene). (from Mas el al. , 1993).



Fig. 26. A. Evolutionary Model for the Cameros Basin: (1) End ofthe Post-Rift Stage 1 (Marine Jurassic) just befo re the begilming of Syn-Rift Stage 2 (Tithonian to Early Albian continental record); (2) From Tithonian to Berriasian times, the Cameros trough began to forrn as an extensional ramp basin with a maximum depocenter at the Central zone over the rampo At the same time, towards the south secondary depocentres (Picofrentes zone) and half-graben satellite sub-basins (Bigomia trough, not at the figure) began to develop in connection with antithetic faults related to the ramp; (3) From Barremian to Early Albian times, maximum extension took place in the area and subsidence was strongly accelerated at the Cameros trough; at the same time, towards the north sorne satellite half-graben sub-basins were formed in connection with synthetic faults (Luezas and Rioja troughs). Maximum thickness was reached at the Central zone ofthe Cameros trough provoking O.M. maturation in the basin and hydrocarbons migration towards permeable units (3b); (4) During Late Cretaceous ages (Post-Rift Stage 2) marine environments reoccupied the Cameros area and extensive carbonate platforms developed at the Iberian Seaway (Alonso et al, 1993) in response to slower and more extensive post-rift thermal subsidence. At the beginning ofthis stage (mainly during Cenomanian times) hydrothermal metamorphism affected to an important volume ofthe basin fill in the Central zone ofthe Cameros trough and possible hydrocarbons reservoirs were destroyed; (5) Finally, Tertiary contractional inversion ofthe Cameros Basin too k place. During this episode new hydrotherrnal events (Early-Mid Eocene and Miocene) provoked local metamorphism, but possibly they also generated new migrations ofhydrocarbons related to local O.M. maturation in satellite basins (Rioja and Bigomia troughs) and peripheral areas (Picofrentes zone) . B. The Cameros Basin (Cameros Trough) and their related satellite basins (Bigomia, Luezas and Rioja troughs) .

Fig. 27. Field trip itinerary and stops.

Fig. 28 Location of the field trip stops on the schematic geological map of the Cameros Basin (modified from Guimera et al. , 1995).

Fig. 29. Bigomia Pass: The first syn-rift sequence (Tera Gr) unconforrnably overlies the Kirnmeridgian sequen ce (Torrecilla en Cameros Fm.), post-dating sorne faults that affect Late Jurassic marine units.

Fig. 30. Bigomia Pass-Torrelapaja: Tera Gr, filling a half-graben basin and unconformably overlaying the Kimmeridgian Torrecilla Fm.

Fig. 31. Prograding reefs ofthe Torrecilla en Cameros Fm. from Tómalos hermitage.

Fig. 32. Panoramic view ofTertiary alluvial fans from Viguera.

Fig. 33. Synsedimentary faults in the Leza Fm (SD 7).

Fig. 34. San Vicente: Faulting in the Jurassic substrate.

Fig. 35. Peñalmonte: The Cameros northem thrust.

Fig. 36. Yanguas: Urbión Gr (DS 4, metaquartcites and shales) unconformably overlies the Oncala Gr (DS 3, rhythmic limestone and black-shales).

Fig. 37. Bituminous sandstones (tar sands) at the base ofthe Late Cretaceous MegacycIe (Utrillas Fm.) .



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Geological Field Trip 11-The Cameros Basin: From Late Jurassic-Early Cretaceous Extension to...

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