Upper cretaceous biostratigraphy of the south-central Pyrenees (Lleida,Spain)

Abstract

Biostratigraphical data using larger foraminifera and planktonic foraminifera permitted us to establish the correlation between shallow platform sediments rich in larger foraminifera (Montsec and Serres Marginals thrust sheets) and deeper ones containing planktonic foraminifera (Boixols thrust sheet).

Consequently, the Santa Fe limestones containing Ovalveolina-Praealveolinaassemblage represent the Cenomanian. Early Turonian ( ‘IT~ archaeocretacea and P. helvetica zones) exist in both, Montsec and Boixols thrust sheets and it is constituted by Pithonella limestones. Late Turonian (M. schneegansi zone) is only present in Boixols thrust sheet (Reguard Fm.), the Montsec thrust sheet having an erosive hiatus.

Late Coniacian-Early Santonian (D. Concavata zone) is represented in the Montsec thrust sheet (Cova Limestones) and in the eastern part of the Boixols thrust sheet (St. Corneli Fm.) by two differents facies giving two different microfaunal assemblages; the firts one, characterized by Ophtalmidiidae s.l indicate a restricted lagoonal environment while the second one, characterized by diverses species of complex agglutinated, Fabulariidae, Meandropsinidae and Rotaliidae, represents an open shallow platform. In the Boixols thrust sheet (Anseroles Fm.) dominate the planktonic foraminifera and small benthic.

In the late Santonian (D. asyrnetrica zone) the sea reached as far as Serres Marginales thrust sheet where sediments (Tragó de Noguera unit) are terrigenous and deposited in a very shallow platform. In the Montsec thrust sheet (Montsec marls) the larger foraminifera indicate a platform deeper than that of the Serres Marginals thrust sheet. In the Boixols thrust sheet the sediments are deposited in an outer platform (Herbasavina Fm.) or turbiditic basin (Mascarell Mb.).

During Campanian times the transgresion reaches the maximum. In the Serres Marginals sediments are deposited in a restricted shallow environment rich in Meandropsinidae (Serres Limestones). In the Montsec thrust sheet they are deposited in a platform with patch reefs and shoals (Terradets limestones) and in the Boixols one in an outer platform, talus and/or basin.

During Early Maastrichtian times (C. falsostuarti zone) terrigenous materials arrived in the basin, the rate of sedimentation increased outstripping the subsidence rate and the retreat of the sea to the north. Late Maastrichtian (C. gansseri zone) is only present in the Boixols thrust sheet.     

Tectonic, eustatic and environmental controls on mid-Cretaceous carbonate platform deposition, south-central Pyrenees, Spain

Cenomanian–Turonian strata of the south‐central Pyrenees in northern Spain contain three prograding carbonate sequences that record interactions among tectonics, sea level, environment and sediment fabric in controlling sequence development. Sequence UK‐1 (Lower to Upper Cenomanian) contains distinct lagoonal, back‐margin, margin, slope and basin facies, and was deposited on a broad, flat shelf adjacent to a deep basin. The lack of reef‐constructing organisms resulted in a gently dipping ramp morphology for the margin and slope. Sequence UK‐2 (Upper Cenomanian) contains similar shallow‐water facies belts, but syndepositional tectonic modification of the margin resulted in a steep slope and deposition of carbonate megabreccias. Sequence UK‐3 (Lower to Middle Turonian) records a shift from benthic to pelagic deposition, as the shallow platform was drowned in response to a eustatic sea‐level rise, coupled with increased organic productivity. Sequences UK‐1 to UK‐3 are subdivided into lowstand, transgressive and highstand systems tracts based on stratal geometries and facies distribution patterns. The same lithologies (e.g. megabreccias) commonly occur in more than one systems tract, indicating that: (1) the depositional system responded to more than just sea‐level fluctuations; and (2) similar processes occurred during different times throughout sequence development. These sequences illustrate the complexity of carbonate platform dynamics that influence sequence architecture. Rift tectonics and flexural subsidence played a major role in controlling the location of the platform margin, maintaining a steep slope gradient through syndepositional faulting, enhancing slope instability and erosion, and influencing depositional processes, stratal relationships and lithofacies distribution on the slope. Sea‐level variations (eustatic and relative) strongly influenced the timing of sequence and parasequence boundary formation, controlled changes in accommodation and promoted platform drowning (in conjunction with other factors). Physico‐chemical and climatic conditions were responsible for reducing carbonate production rates and inducing platform drowning. Finally, a mud‐rich sediment fabric affected platform morphology, growth geometries (aggradation vs. progradation) and facies distribution patterns.     

Cretaceous–Tertiary tectonic inversion of the Cotiella Basin (southern Pyrenees,Spain)

The Cotiella Nappe includes one of the most important Mesozoic basins of the southern Pyrenees, which was subsequently inverted during the Tertiary compression. The Late Cretaceous Cotiella Basin is here interpreted as the western sector of the Cretaceous Cotiella-Bóixols basin (100᎜ km wide), located in the central part of the southern Pyrenees. The present-day complex structure of the Cotiella Nappe is the result of the inversion process, linked to the emplacement of basement thrust sheets of the Axial zone. In its western sector, the Cotiella Nappe consists of several superimposed thrust sheets, with complex geometry, becoming simpler towards the east, with a single thrust surface and smaller displacements. The Cotiella-Bóixols basin underwent strong subsidence during the Early Cretaceous at its eastern sector, and its depocentre migrated westward during the Late Cretaceous. The reconstruction of the sedimentary basin to the pre-compressional stage shows that during the Mesozoic the Cotiella-Bóixols basin was located to the south of a basement high, which later became the Pyrenean Axial Zone. From a balanced cross section, it can be inferred that the Cotiella, north-verging extensional system was connected with the north-Pyrenean rift by means of a 10-km deep horizontal detachment. The compressional Tertiary detachment within the upper crust was shallower than the extensional detachment, and individualised four basement thrust sheets, which form the Axial Zone antiform.     

Carbon isotope stratigraphy and depositional oxia through Cenomanian/Turonian boundary sequences (Upper Cretaceous) in New Zealand

Stratigraphic sections across the Cenomanian/Turonian boundary (C/T boundary) are identified in New Zealand and were deposited in southern high latitudes of the palaeo-Pacific. Lithological evidence for Cretaceous Oceanic Anoxic Event 2 (OAE2), which preceded and spanned the C/T boundary, is lacking in these sections. The correlative interval is identified, however, from a positive 2‰ carbon isotope excursion (CIE) and from clustered highest occurrences of Cenomanian-restricted dinoflagellate taxa together with the lowest occurrence of Turonian Heterosphaeridium difficile. A zone lacking benthic macrofossils encompasses the CIE. In some sections, this interval is also characterized by distinctive red mudstone beds; the thickest such red bed (6–18 m thick) may overlap or just overlie the main part of the CIE interval. Shelly macrobenthos, notably inoceramid bivalves, disappeared >500 kyr prior to the CIE. This suggests that environmental deterioration associated with OAE2 may have preceded the inferred volcanic trigger that has been identified from other regions. Strong intermediate water depth oxia during OAE2, which contrasts with oceanic anoxic conditions that occurred elsewhere on the globe, apparently prevailed during the later phase of OAE2 in the southernmost Pacific. New data from New Zealand indicate that causal mechanism(s) of OAE2 may be complex.     

Distinctive thin-bedded turbidite facies and related depositional environments in the Eocene Hecho Group (South-central Pyrenees, Spain)

The vertical and lateral stratigraphic relations of facies and facies associations, palaeocurrent directions, and geometry and internal organization of associated thick-bedded and coarse-grained bodies of sandstone provide the framework for distinguishing five thin-bedded turbidite facies in the Eocene Hecho Group, south-central Pyrenees, Spain. Each facies is characterized by a number of primary features which are palaeoenvironmental indicators by themselves. These features and their palaeoenvironmental significance are summarized below.

• 1 The impressive regularity and lateral persistence of bedding and depositional structures, combined with the association of thin hemipelagic intercalations are typical characteristics of the basin plain thin-bedded turbidites. Lateral variations in bed thickness, internal structures, grain size, sand: shale ratio, and amounts of hemipelagic intercalations are present in these sediments, but take place so gradually that they cannot generally be recognized at the scale of even very large exposures. The basin plain facies has a remarkable character of uniformity over great distances and considerable stratigraphic thicknesses.
• 2 Thickening-upward and/or symmetric cycles with individual thicknesses ranging from a few metres to a few tens of metres are typical of lobe-fringe thin-bedded turbidites. The sediments that comprise the cycles contain small but recognizable variations in bed thickness and sand: shale ratio. The diagnostic cyclic pattern can be detected in relatively small exposures. It should be noted that in absence of coarse-grained and thick-bedded sandstone of the depositional lobes the above cyclic pattern is diagnostic of fan-fringe areas.
• 3 An extremely irregular bedding pattern with lensing, wedding, and amalgamation of individual beds over very short distances, sharp rippled tops of many beds, and internal depositional structures indicative of mainly tractional processes without substantial fallout, are typical and exclusive characteristics of channelmouth thin-bedded turbidites.
• 4 Bundles of interbedded thin-bedded sandstone and mudstone as thick as a few metres that are separated in vertical sequences by mudstone units of roughly similar or greater thickness are typical of interchannel thin-bedded turbidites. The most diagnostic feature of this depositional environment is the presence of beds of sandstone filling broad shallow channels as probable crevasse-splays.
• 5 Thin, thoroughly rippled sandstone beds with marked divergence of the bedding attitude characterize the channel-margin facies. The divergence or expansion in thickness, is consistently toward the channel axis. Small and shallow channels filled with thin-bedded deposits, interpreted here as crevasses cut into channel edges or levees during period of severe overbanking are also characteristic.

     

Hummocky cross-stratification-like structures in deep-sea turbidites: Upper Cretaceous Basque basins (Western Pyrenees, France)

Hummocky cross-stratification is a sedimentary structure which is widely interpreted as the sedimentary record of an oscillatory current generated by energetic storm waves remobilizing surface sediment on the continental shelf. Sedimentary structures named hummocky cross-stratification-like structures, similar to true hummocky cross-stratification, have been observed in the Turonian–Senonian Basque Flysch Basin (south-west France). The bathymetry (1000 to 1500 m) suggests that the observed sedimentary structures do not result from a hydrodynamic process similar to those acting on a continental shelf. The morphology of these three-dimensional structures shares similarities with the morphology of hummocky cross-stratification despite a smaller size. The lateral extent of these structures ranges from a few decimetres to many decimetres; they consist of convex-up domes (hummock) and concave-up swales with a non-erosive base. Four types of hummocky cross-stratification-like geometries are described; they occur in association with structures such as climbing current ripple lamination and synsedimentary deformations. In the Basque Flysch, hummocky cross-stratification-like structures are only found in the Tc interval of the Bouma sequence. Hummocky cross-stratification-like structures are sporadic in the stratigraphic series and observed only in few turbidite beds or bed packages. This observation suggests that hummocky cross-stratification-like structures are linked genetically to the turbidity current but form under a very restricted range of parameters. These structures sometimes show an up-current (upslope) migration trend (antidunes). In the described examples, they could result from standing waves forming at the upper flow interface because of Kelvin–Helmholtz instability.     

Carbonate ramp depositional systems from a late Jurassic epeiric platform (Iberian Basin, Spain): a combined computer modelling and outcrop analysis

No counterparts to epeiric-sea carbonate ramps are known in present-day environments. This hinders the interpretation of the factors controlling the growth and evolution of these depositional settings. In this study we analyse the facies and geometries of two Jurassic examples both from outcrop study and through computer modelling. This analysis is constrained by two important features of these Oxfordian and Kimmeridgian ramps: firstly, they are very well exposed, allowing accurate reconstruction of a 200-km section from proximal to distal ramp environments, and, secondly, a time framework for correlation, section reconstruction and modelling is provided by a well-defined ammonite biostratigraphy. The modelling results in a synthetic stratigraphy which closely matches the reconstructed cross-sections and, when integrated with the field study, constrains and provides additional quantitative data on the following aspects of carbonate ramp systems. Resedimentation by storms is an important process in maintaining the ramp profile through time. Down-ramp transport distances of between 25 and 40 km are indicated from the distribution of storm beds and shallow-water allochems and from model-matching known stratigraphic thicknesses and geometries. Modelling sediment production within the time constraints from the ammonite biozones indicates that shallow-water carbonate production was 1–2 orders of magnitude less than that predicted for present-day open-marine carbonate platforms. Deeper-water production rates were reduced by lesser amounts. These proportionally higher, outer-ramp production rates also help to maintain ramp geometries through time. The enigmatic slope crest of ramps is shown to result from a combination of higher, shallow-water production and erosion rates, together with loss of accommodation during highstands and high-stillstands in the modelled sea-level curves. The most parsimonious modelling of the two ramp sequences comes from a relative sea-level curve composed of a linear subsidence component superposed by 20- and 100-kyr cycles on a third-order cycle. The third-order cycles and their timing do not correspond to those of the Exxon curve.     

Carbonate banks and slump beds in the Upper Cretaceous (Upper Turonian-Santonian) of Haute Normandie, France

Large scale sedimentary structures present in the Upper Turonian to Santonian chalks of Haute Normandie (northern France) represent the remains of a carbonate bank complex which formerly extended over an area of at least 1500 km². Cliff exposures along the Channel coast from St Valéry-en-Caux to Cauville and along the Seine from Sandouville to Lillebonne show sections of banks up to 50 m high and 1500 m across, their internal structures picked out by hardgrounds, nodular chalks and horizons of burrow flint. Associated with banks are slump sheets up to 20 m thick, slump scars, sedimentary breccias, injection phenomena and faults contemporaneous with sedimentation. Later diagenetic features include extensive dolomitization and silicification. These structures compare closely with the Waulsortian banks of the Palaeozoic, and bryozoan bioherms known from the Upper Cretaceous and Palaeocene of Denmark. Frame-building, sediment trapping and stabilizing organisms are absent, and bank development and stabilization was probably due to a plant covering, either algal or of marine angiosperms. Banks generated much of their own sediment, whilst a pelagic constituent (calcareous nannofossils and Foraminiferida) is also present. The distribution of the bank complex is related to a basement controlled swell area, whilst the life of the complex was limited to a relatively shallow water, regressive episode in the predominantly transgressive Upper Cretaceous history of the region. Les falaises littorales du Pays de Caux comprises entre Antifer et St Valèry-enCaux, et les affleurements de la basse vallée de la Seine permettent d'observer des formations du Turonien supérieur-Sénonien inférieur qui présentent des stratifications irrégulières soulignées par de nombreux hardgrounds, des horizons de craie noduleuse et des cordons de silex. Ces structures sont identifiées à des accumulations de calcilutite et calcarénite sous forme de bancs sous-marins dont la hauteur peut atteindre 50 m et qui couvrent une surface supérieure à 1500 km²; ils apparaissent au-dessus de hardgrounds subhorizontaux qui indiquent un haut-fond régional stable. Des glissements sous-marins sont associés à ces bancs et engendrent des niveaux avec des déformations souples atteignant 20 m d'épaisseur. Des brèches apparaissent localement et contiennent des blocs basculés de hardgrounds fragmentés lors du glissement; on y observe aussi de petites failles intrasédimentaires et des phénomènes d'injection. Aucun organisme constructeur ou capable de piéger et retenir le sédiment n'a été observé. La stabilisation de ces bancs serait due à une couverture végétale (algues ou angiospermes marines) dont on sait qu'elle peut disparâitre sans laisser de trace lors de la fossilisation. La croissance de ces bancs serait réalisée par un apport de sédiment comprenant une part de nourrissage autochtone comme cela existe pour les bancs récents en eau peu profonde, associée au dépôt d'une fraction pélagique.     

Depositional processes,triggering mechanisms and sediment composition of carbonate gravity flow deposits: examples from the Late Cretaceous of the south-central Pyrenees,Spain

Cenomanian through Coniacian strata near the town of Sopeira in the south-central Pyrenees (northern Spain) are composed of a variety of autochthonous and allochthonous carbonate slope lithologies that are divided into six depositional sequences based on facies distribution patterns and stratal relationships. The sequences record three major phases of platform margin evolution: rifting, burial, and exhumation. During the first phase (sequences UK-1, UK-2, UK-3, UK-4, and lower UK-5), deposition occurred on the edge of a wrench basin, and a normal fault located beneath the platform margin strongly influenced slope evolution. Background hemipelagic sediments on the slope were commonly redeposited by submarine slumps and slides. More intense reworking resulted in matrix-supported, slope-derived megaconglomerates (debrites).During the Cenomanian and Turonian, seismically triggered debris flows originated at the platform margin, bypassed the upper slope, and were deposited on the lower slope as polymictic, clast-supported, matrix-rich megabreccias. The megabreccias form channelized and sheet-like bodies with erosional basal surfaces. Shallow carbonate environments backstepped during the Late Turonian and Coniacian, but displacement along the fault at this time resulted in the development of a steep submarine scarp and the exposure of Cenomanian and Lower Turonian strata to submarine erosion. Matrix-poor, margin-derived megabreccias form a thick talus pile at the base of the scarp. Some of the breccias were transported into the basin as debris falls, forming sheet-like beds.Marl eventually buried the Coniacian scarp in sequence UK-5, resulting in the second major phase of platform slope evolution. The slope profile at this time was relatively gentle, and redeposited material is less common. In the third phase (sequence UK-6), tectonically induced bankward erosion during the Santonian resulted in a high (greater than 800 m) erosional scarp with a regional east–west trend that was subsequently onlapped by siliciclastic turbidites. Rejuvenation of erosion in the same vicinity suggests that long-term tectonism controlled the position of the slope, rates of erosion, and sediment type on the slope.Sediment gravity flow processes are laterally and temporally related. Submarine slide and slump deposits commonly grade laterally downslope into slope-derived megaconglomerates. Debris flows that originated at the platform margin appear to have initiated slumps, slides, and other debris flows on the slope. Debris fall deposits are commonly capped by coarse, graded, lithoclastic packstones that may represent turbidites generated by the debris falls.Sediment fabric exerted a profound impact on depositional processes, distribution of facies, and morphology of the slope. Fine-grained, mud-rich, lower slope deposits were unstable at even moderate slope angles, and have been extensively redeposited. Redeposition of grain-rich, upper slope facies was triggered by syndepositional seismic activity and upslope migration of instability and erosion. In the presence of mud, the transport mechanisms are typically cohesive debris flows, which were able to carry material onto the lower slope and into the basin. When no mud was available, rock falls and debris falls were the dominant sediment gravity flows, and their deposits are restricted to a position on the hanging wall proximal to the fault.     

Carbonate platform growth influenced by contemporaneous basaltic intrusion (Albian of Larrano, Spain)

Abstract Carbonate platform growth in active tectonic settings may be strongly influenced by the structural evolution of the basin, including volcanic activity. In this paper, the sedimentary–tectonic evolution of the Duranguesado carbonate platform (Larrano) in northern Spain is described, and an evolutionary depositional model is presented. The Albian Duranguesado carbonate platform deposits are dominated by rudist and coral limestones with small intervening argillaceous limestone-filled troughs (10–30 m deep). The platform succession is divided into two parts. The lower platform deposits were intruded by volcanics and tilted before the deposition of the upper platform succession. A volcanic vent plug filling an upward-flaring pipe occurs in the lower carbonate platform succession. The timing of intrusion is well constrained to the early Albian. Tectonic extension and active deep-seated strike-slip faults induced magma ascent at a fault intersection. Sedimentological analysis of these areas indicates that, before volcanic intrusion, they acted as weakened zones of extension, and were slightly more subsident basinal areas. These sites contain anomalous accumulations of siliceous sponge spicule deposits, linked to the release of hydrothermal fluids on the sea floor. After the phase of intrusion, tilting and erosion of the platform and its associated volcanic products occurred. As the intrusion cooled, the platform downwarped, leading to the formation of an overlying perched capping basin bordered by carbonate platforms. Over the volcanic plug, carbonate mounds grew on local palaeohighs. The presence of strike-slip and magma emplacement in the Duranguesado platform is related to movements between the Iberian and European lithospheric plates, which were accommodated by rotation and lateral movement of the crust along wrench faults.     

A long-necked pterosaur (Pterodactyloidea,Azhdarchidae) from the Upper Cretaceous of Valencia,Spain

Fragmentary remains, including cervical vertebrae and limb bones, of a large pterosaur from the Upper Cretaceous of Tous, province of Valencia (Spain), are described. The material was recovered from lacustrine beds in the upper part of the Calizas y Margas de Sierra Perenchiza Formation, which is probably Maastrichtian in age. Six fragments of vertebrae allow a reconstruction of the anatomy of the mid-series cervicals of the animal. The general morphology of the cervical vertebrae is closely similar to that of the long-necked Azhdarchidae. Compared to other azhdarchids, the Valencia pterosaur shows minor differences from the genera Azhdarcho and Quetzalcoatlus, and is here provisionally referred to as Azhdarchidae indet. A wingspan of about 5.5 m is calculated by comparison with other known azhdarchids. This is the second azhdarchid pterosaur described from the Iberian peninsula. It confirms the wide distribution of this group of large pterosaurs at the end of the Cretaceous.     

Re-evaluation of coquinoid sandstone depositional model, Upper Jurassic of central Wyoming and south-central Montana

The most extensive Jurassic marine transgression in North America reached its maximum limits during the Oxfordian Age. At this time, siliciclastic sediments were being brought into the North American seaway from an uplifted zone to the west. Within this setting, complexes of sand ridges and coquinoid sands layers were deposited. Coquinoid sandstones appear to fill erosional scours and were interpreted as channel fills. Re-evaluation of these features in the light of recently discovered attributes of modern shelf sediments and processes has produced a revised model of coquinoid sand deposition in this setting. Coquinoid sandstones which fill ‘channel-like’ scours in the Oxfordian (Upper Jurassic) rocks of central Wyoming and south-central Montana, appear to have formed through the migration of sand waves across the crests of inner shelf sand ridges during periods of storm and tidal flow. Erosion in the zone of flow reattachment in the troughs between sand waves resulted in the development of shell lags. Migration of these scour zones as the sand waves advanced resulted in the deposition of sheet-like coquinoid sandstone bodies. Sand waves crossing the ridge crest tended to migrate more slowly and to be overstepped by later sand waves. Sand wave troughs thus buried have channel-like geometries with apparent epsilon bedding.     

A new titanosaur (Dinosauria,Sauropoda) from the Upper Cretaceous of Lo Hueco (Cuenca,Spain)

The upper Campanian-lower Maastrichtian site of Lo Hueco (Cuenca, Spain) has provided a set of well-preserved partial skeletons in anatomical connection or with a low dispersion of their skeletal elements. One partial skeleton is herein described and a new titanosaurian sauropod is established, Lohuecotitan pandafilandi. This titanosaur is diagnosed by eight autapomorphic features: dorsally and ventrally widened or bifurcated posterior centrodiapophyseal lamina in anterior and middle dorsal vertebrae; short postspinal lamina with a transversely expanded distal end represented by smooth scars in the dorsal vertebrae; anteriormost caudals with the medial spinoprezygapophyseal and medial spinopostzygapophyseal laminae ventrally connected with the prespinal and postspinal laminae, respectively; anterior caudal neural spines with a dorsal projection of the prespinal and postspinal laminae; anterior caudal neural spines bears a “greek-cross”-like cross-section; middle caudal centra having two round and rough structures in the dorsal edge of the posterior articulation, which extends to the dorsal surface of the centrum; the articular ends of the rami of the haemal arches are divided in two articular surfaces; and tuberosity between the anterior and the lateral trochanter of the fibula. The herein performed phylogenetic analysis considered L. pandafilandi as a member of Lithostrotia more derived than Malawisaurus. The known palaeodiversity of the Late Cretaceous Ibero-Armorican titanosaurs is increasing, and further analyses focused on this group will be necessary to better understand the evolutionary history of European titanosaurs and to clarify their relationships within Titanosauria.     

Mineralisation from Vall de Ribes area (Eastern Pyrenees,Spain)

Vein mineralisation with no preferred orientation, cutting lower Palaeozoic rocks, and local replacement deposits in dolomite show a zoning in tungsten-bismuth, arsenic and antimony minerals away from the adjacent late-Hercynian Costabona granite. A local reversed zoning is related to higher temperatures indicated by fluid inclusion study. Many of the minerals have not previously been reported from this area.     

Tecto-sedimentary cycles and depositional sequences of the Mesozoic and Tertiary from the Pyrenees

Tectonic deformation in the Pyrenees is the result of an essentially continuous process which has a discontinuous effect in the style of deformation and consequently, in the sedimentary record. Tecto-sedimentary discontinuities can be correlated on a regional scale, allowing the differentiation of tecto-sedimentary cycles and depositional sequences. The relations between tectonics and sedimentation in the Pyrenees are expressed in the Mesozoic and Tertiary cyclicity.Ten tecto-sedimentary cycles have been distinguished. They are controlled by basin-forming and basin-modifying tectonics (rifting, wrenching, convergence) and are related to different successive basin-types.A first group of cycles corresponds to the episodic rifting: post-Hercynian interior fracture basin (cycle 1), spreading of the Ligurian Ocean (cycle 2), spreading of the central North Atlantic Ocean (cycle 3) and rifting of the Bay of Biscay in the context of the rotation of Iberia (cycle 4). A second group corresponds to the opening of the North Atlantic Ocean and to the change in the trajectory of Iberia along a W-E direction (cycle 5). The third group corresponds to prevailing wrench conditions grading from strike-slip plate displacement (cycle 6) to progressive oblique convergence (cycle 7). The fourth group of cycles (8, 9 and 10) corresponds to the generalization of convergence conditions; cycle 8 is the transition from wrench to foreland basin; cycle 9 corresponds to the development of migrating foreland basins in relation to thrust sheet emplacement; cycle 10 includes the unconformable clastic wedge ahead of the last thrust.These tecto-sedimentary cycles include one or several depositional sequences in which sedimentation is controlled by the interrelations between local tectonics, subsidence, eustacy and sediment supply. The analysis and definition of these sequences is given for the Cretaceous and Tertiary cycles. The depositional sequences from the Cretaceous wrench basin are essentially related to eustacy (sea level rise) together with subsidence during cycle 6, and wrench structuring during cycle 7. The depositional sequences from the foreland basins (cycles 8, 9 and 10) are related to changes in the type of basin.     

Cretaceous rudist-bearing platform carbonates from the Lycian Nappes (SW Turkey): Rudist associations and depositional setting

Lycian Nappes (in SW Turkey) lie between the Menderes Massif and Bey Dağları carbonates and comprise thrust sheets (nappes piles) of Paleozoic-Cenozoic rocks, ophiolitic and tectonic mélanges and serpentinized peridodites. This study focuses on identification of rudists and their palaeoenvironmental features observed within the Cretaceous low grade metamorphic successions (dominated by recrystallized limestones) from the Tavas and Bodrum nappes. The study is based on fifteen stratigraphic sections measured from Tavas, Fethiye, Köyceğiz, Bodrum, Ören and Bozburun areas. The Lower Cretaceous successions with rudists are very sparse in the Lycian Nappes and a unique locality including a Berriasian epidiceratid-requieniid assemblage is reported so far. A new requieniid-radiolitid assemblage was found within the pre-Turonian (?Albian-?Cenomanian) limestones. Four different Late Cretaceous rudist assemblages were firstly identified as well: 1) Caprinid-Ichthyosarcolitid assemblage (middle-late Cenomanian); 2) Distefanellid assemblage (late Turonian); 3) Hippuritid-Radiolitid assemblage (late Coniacian-Santonian-Campanian); 4) Radiolitid-Hippuritid assemblage (‘middle’-late Maastrichtian). Microfacies data and field observations indicate that the rudists lived in the inner and outer shelves of the Cretaceous carbonate platform(s) in this critical part of the Neotethys Ocean. Rudists formed isolated patchy aggregations in very shallow palaeoenvironments and deposited as shell fragments particularly on the outer shelf environment, which is characterized by higher energy and platform slope characteristics.     

Depositional architecture of a rimmed carbonate platform (Albian, Gorbea, western Pyrenees)

A Lower Cretaceous carbonate platform depositional system with a rimmed margin and an adjacent oversteepened slope was analysed in order to determine its depositional architecture and major depositional controls. The platform is made up of coral, rudist, orbitolinid and algal limestones and, in a 12-km dip transect, there is a gradation from lagoon to platform margin, slope and basin environments, each characterized by distinctive sedimentological features and facies associations. The rimmed platform is an aggradational system developed during approximately 4·2 million years of fluctuating relative sea-level rise, and it is bounded by unconformities at its base and top. Internal cyclicity in the construction of the system is evident, mainly in platform interior and slope settings. The seven recognized sequences average 0·6 million years in duration and are related to minor relative sea-level changes. Carbonate deposition occurred in shallow- and deep-water settings during periods of high relative sea level. Reduced rates of sea-level rise led to the development of shallowing upward sequences and, eventually, to the exposure of the shallowest parts of the platform during relative sea-level falls. During low relative sea level, erosion surfaces developed on the slope, and gravitational resedimentation occurred at the toe of slope. Basinwards, resedimented units pinch out over distances of a few hundred metres. Active faults controlled sedimentation at the platform margin, promoting the development of steep slopes (up to 35°) and preventing progradation of the shallow-water platform, despite high sediment production rates. The development of sequences is interpreted to be related to tectonic activity.