Cécile Robin

Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints

Abstract 3D stratigraphic geometries of the intracratonic Meso-Cenozoic Paris Basin were obtained by sequence stratigraphic correlations of around 1 100 wells (well-logs). The basin records the major tectonic events of the western part of the Eurasian Plate, i.e. opening and closure of the Tethys and opening of the Atlantic. From earlier Triassic to Late Jurassic, the Paris Basin was a broad subsiding area in an extensional framework, with a larger size than the present-day basin. During the Aalenian time, the subsidence pattern changes drastically (early stage of the central Atlantic opening). Further steps of the opening of the Ligurian Tethys (base Hettangian, late Pliensbachian;...) and its evolution into an oceanic domain (passive margin, Callovian) are equally recorded in the tectono-sedimentary history. The Lower Cretaceous was characterized by NE–SW compressive medium wavelength unconformities (late Cimmerian–Jurassic/Cretaceous boundary and intra-Berriasian and late Aptian unconformities) coeval with opening of the Bay of Biscay. These unconformities are contemporaneous with a major decrease of the subsidence rate. After an extensional period of subsidence (Albian to Turonian), NE–SW compression started in late Turonian time with major folding during the Late Cretaceous. The Tertiary was a period of very low subsidence in a compressional framework. The second folding stage occurred from the Lutetian to the Lower Oligocene (N–S compression) partly coeval with the E–W extension of the Oligocene rifts. Further compression occurred in the early Burdigalian and the Late Miocene in response to NE–SW shortening. Overall uplift occurred, with erosion, around the Lower/Middle Pleistocene boundary.

Tectonic and stratigraphic evolution of Zagros and Makran during the Mesozoic-Cenozoic

The Zagros fold-thrust belt (ZFTB) extends from Turkey to the Hormuz Strait, resulting from the collision of the Arabian and Eurasian plates during Cenozoic times, and separates the Arabian platform from the large plateaux of central Iran. To the east a pronounced syntaxis marks the transition between the Zagros collision belt and the Makran accretionary wedge. In the ZFTB, the Proterozoic to Recent stratigraphic succession pile is involved in huge folds, and offers the opportunity to study the stratigraphic and tectonic evolution of the Palaeo-Tethyan margin.nnFew recent data were widely available on the southern Tethys margin preserved in the Zagros Mountains. The Middle East Basins Evolution (MEBE) program was an excellent opportunity to go back to the field and to collect new data to better constrain the evolution of this margin. In this volume the structure of the Zagros Mountains is explored through different scales and using different methodologies.

Three-dimensional accommodation analysis of the Keuper of the Paris Basin: discrimination between tectonics, eustasy and sediment supply in the stratigraphic record

Abstract During the Keuper, the Paris Basin was an intracratonic sedimentary basin filled by continental deposits. Using paleo-environmental, isopach and paleo-altitude maps, we estimate the variations of accommodation rate at the scale of stratigraphic minor hemi-cycle (1–3xa0Ma). An analysis of the short- and long-wavelength accommodation variations allows us to assess the relative influence of tectonics, eustasy and sediment supply on the stratigraphic record. Our data suggest a pattern of subsidence along three trends: E–W in the Carnian, E–W to NNE–SSW in the Norian and NE–SW in the Norian–Rhaetian. During the Keuper, the Paris Basin accurately records the different phases of the opening of the Tethys Ocean associated with a rotation of the extension direction. The Norian cycle could thus reflect the intraplate stresses in a transitional period between the Triassic and the Liassic.

Echelles de temps et d'espace du controle tectonique d'un bassin flexural intracratonique; le bassin de Paris

The Meso-Cenozoic intracratonic flexural Paris Basin is a good tool to determinate the time/space-scales of the tectonic control on the sedimentary record. This study is based on basin-scale 2D sedimentary geometries of the different orders of stratigraphic cycles and on 1D/3D accommodation space measurements (space available for sediments created by subsidence and/or eustatism). Tectonic controls occur at least at three different time-scales: 230 m.y. (basin evolution), 10-40 m.y. (major stratigraphic cycles) and 1-5 m.y. (minor stratigraphic cycles). The evolution of the flexural intracratonic Paris basin can be described as the result of a long term thermal subsidence component with superimpositions of short-term tectonic components, due to intraplate deformations of 10-40 Ma and 1-5 Ma frequencies.

Mesozoic deep-water carbonate deposits from the southern Tethyan passive margin in Iran (Pichakun nappes, Neyriz area): biostratigraphy, facies sedimentology and sequence stratigraphy

Abstract The objective of this work is to study the Mesozoic turbiditic sediments from the southern Tethys margin in Iran. These sediments are exposed as nappes in the Pichakun Mountains (i.e. the Zagros Mountains in the Neyriz area), which inverted during latest Cretaceous time. Radiolarians are used to both define and date four main lithostratigraphic formations: (1) the Bar Er Formation (undated, probably Late Triassic to Early Jurassic); (2) the Darreh Juve Formation (Aalenian–early Bajocian to middle Callovian–early Oxfordian); (3) the Imamzadeh Formation (middle Callovian–early Oxfordian to Aptian); (4) the Neghareh Khaneh Formation (late Aptian to Turonian–Coniacian). Most of the sediments are deep-sea gravity-flow lobe deposits. Channel deposits occurred during the Bajocian (i.e. the Darreh Juve Fm) and deeply incised channels (canyons?) occurred during the Albian (i.e. the Neghareh Khaneh Fm). Twenty-seven facies, grouped into eight facies associations, are defined. Based on a sequence stratigraphic study (i.e. the stacking pattern), five second-order cycles (10–30 Ma duration), defined between two successive distal facies time-intervals, are characterized: (1) the J2 (Toarcian?–middle Oxfordian, unconformity: Late Toarcian–Aalenian); (2) the J3 (middle Oxfordian–Berriasian, unconformity: middle? Tithonian); (3) the K1.1 (Berriasian–undated top); (4) the K1.2 (undated base–early Aptian, unconformity: late Hauterivian); (5) the K1.3 (early Aptian–at least Turonian–Coniacian, unconformity: Aptian–Albian boundary). The most important tectonic event recorded occurred at the Aptian–Albian boundary (a deposition of olistoliths, from a few metres to 100 m thick, in debris flows; related to Austrian deformations). The Arabian-scale late Toarcian and early Tithonian deformations have been recorded as unconformities. It is expected that another tectonic event occurred during the late Hauterivian. The unconformity of cycle K1.1 could be a late Valanginian eustatic fall of climatic origin.

Tectonic and stratigraphic evolution of Zagros and Makran during the Mesozoic-Cenozoic: introduction

The Zagros fold–thrust belt (ZFTB) extends for c. 2000 km from Turkey in the NW to the Hormuz Strait in the SE. This belt results from the collision of the Arabian and Eurasian plates during Cenozoic times and constitutes a morphological barrier (with some peaks exceeding 4000 m) separating the Arabian platform from the large plateaux of central Iran. To the east a pronounced syntaxis marks the transition between the Zagros collision belt and the Makran accretionary wedge. In the ZFTB, the Proterozoic to Recent stratigraphic succession pile of the southern Tethys margin is involved in huge folds detached from the Pan-African basement and offers the opportunity to study the stratigraphic and tectonic evolution of the Palaeo-Tethyan margin over large time periods. Few recent data are widely available on the southern Tethys margin as preserved in the Zagros Mountains. Since the classical works of James & Wynd (1965) and Murris (1980), the most recent synthesis is the palaeogeographical reconstruction of the Arabian platform published by Ziegler (2001). Many petroleum data have been acquired during the last 10 years, but few of these have been published. The Middle East Basins Evolution (MEBE) Programme, coordinated by P. Barrier and M. F. Brunet, in close relationship with colleagues of the Geological Survey of Iran, was an excellent opportunity to go back to the field and to collect new data to better constrain the evolution of this margin. In this volume, the structure of the Zagros Mountains is explored through different scales and using different approaches.

Vertical movements of the Paris Basin (Triassic-Pleistocene): from 3D stratigraphic database to numerical models

Abstract A 3D stratigraphic database has been constructed from the inspection of 1100 wells and outcrops in the Paris basin. The database contains 88 surfaces correlated at high temporal resolution using sequence stratigraphy. For each well and each surface, the present-day depth, the depositional environment and the lithology between two layers are available. This database provides a key to quantify the tectonics associated with this intracratonic basin and to model the thermal and mechanical processes at the origin of the tectonics. Three types of numerical modelling have been carried out in order (1) to better constrain the long-term thermal subsidence and its cause, (2) to characterize the spatial and temporal evolution of the crustal tectonics during the ‘extensional’ period and (3) to test a lithospheric folding origin during the end-Cretaceous to present-day compressional period. The philosophy of these three models are different. The Chablis model for the lithospheric thermal evolution is used to predict the long-term subsidence of the Paris Basin. The thermal evolution of the lithosphere is computed, taking account of a constant temperature or heat flow at the base of the lithosphere, temperature- and pressure-dependent thermal characteristics, metamorphism in the crust, top-crustal erosion and phase transition in the mantle. The long-term subsidence of the Paris basin results from the decay of a thermal anomaly initiated during late Variscan times. The subsidence data can be explained by short- (Stephano-Autunian) as well as long- (Stephano-Triassic) lasting extension. These hypotheses both implicitly refer to extensional collapse of the Variscan belt. The characterization of the spatial and temporal evolution of the crustal tectonics during the thermal relaxation period has been need to quantify the local effect of the sediment load on vertical crust movements. From sedimentary thickness and bathymetric data, maps of relative tectonics have been drawn at a time scale around 500 ka. These maps show two different tectonic behaviours: (1) narrow regions with a high horizontal gradient of tectonics (faults), and (2) domains with a diffuse subsidence correlated with topographic domes and high rates of sedimentation. The geometrical and temporal characteristics of the regions of diffuse subsidence are compatible with a model of flow of the lower crust if the thickness of the flowing channel is at least 20 km with a viscosity of 1020 Pas. The Tertiary characteristics of the Paris Basin could be the record of large-scale lithospheric folding. The numerical experiments demonstrate that extremely low (0.2 mm a−1) shortening rates are largely sufficient to induce large-scale low-amplitude folding under low maximum values of tectonic stresses (c. ∼50 MPa). These values suggest that alpine compression is largely sufficient to activate this deformation. From the data collected in this database and from the models described here, the evolution of the Paris Basin is better understood. The Paris Basin Meso-Cenozoic evolution can be described as a long-term thermal subsidence, inherited from the Permian extension and perturbed by intraplate deformations in reaction to the geodynamic events occurring in western Europe, i.e. the Ligurian Tethys opening and closure, and the Atlantic opening. Those tectonic events modify in space and time both subsidence and facies distributions. The Paris Basin was initially an ‘extensional’ basin which progressively evolved into a compressional one, temporarily (lower Berriasian and late Aptian) and then permanently (late Turonian to present day). The present-day geometry of the Paris Basin is the consequence of lithospheric folding occurring mainly during the Tertiary. In consequence, (1) the Paris Basin is not still a subsiding basin but an uplifted area, and (2) during the Jurassic and part of the Cretaceous, the surrounding present-day outcropping basement massifs were subsiding areas flooded by the sea.

The influence of syndepositional basin floor deformation on the geometry of turbiditic sandstones: a reinterpretation of the Côte de L’Âne area (Sanguinière-Restefonds sub-Basin, Grès d’Annot, Late Eocene, France)

Abstract The Côte de l’Âne section has been previously interpreted as shallow marine deposits (deltaic system with delta-front to bay head and back-barrier environments). The purpose of this article is (1) to suggest a reinterpretation of these facies of the Grès d’Annot in this area as deep marine deposits and (2) to discuss the effect of an evolving seafloor topography during sedimentation on the stacking pattern of turbiditic deposits. The facies analysis of the sedimentary succession is based on eight measured sedimentological logs and on the visual correlation of identified surfaces. Detailed sedimentological observations permitted the identification of a turbidite facies spectrum, schematized in nine facies associations. Outcrop-scale analysis highlights a downstream thickening of the sedimentary sequence resulting from a strong control by tectonic deformation. This deformation is mainly a flexure with a half-wavelength longer than 500m. Associated normal faults may be related to a gravity slide of unconsolidated sediments accommodated within the flexure. Finally, detailed correlations based on the genetic unit model in the Restefonds-Sanguinière system establish the effect of an evolving seafloor topography during sedimentation on the stacking pattern of turbiditic deposits.

Genetic units/parasequences of the Annot turbidite system, SE France

Abstract High-frequency cycles (genetic units or parasequences), with a mean duration of 20000 years, have been identified in the Grè d’Annot turbidite system of the southern Alpine foreland basin (Late Eocene/Early Oligocene). They filled a narrow (2–8 km wide) synsedimentary syncline that formed a confined basin fed upward by a fan-delta located on a narrow shelf. These cycles are 10m thick, and each consists of a basal heterolithic component and an upper sandy homolithic unit, traceable over at least 10 km. They result from the superposition of (1) a progradational phase with an accretionary system (low-angle accretionary bedsets) and a feeder system (by-pass to high preservation oblique laminasets) and (2) an aggradational phase with a ‘spread’ system overlain by a condensed interval. The progradational phase shows very low-angle clinoforms (low-angle accretionary sets, 1–2 m high, a few tens to a few hundreds of metres long) fed by erosional structures (channels or large scours, 0.2–2 m deep, a few metres to a few tens of metres wide). The aggradational phase (subplanar laminasets, ‘scour and fill’ structures) forms a ramp, and drapes the underlying sediments. These progradational geometries may be explained by the narrow sub-basin morphology and by the transition from channelled flow (updip narrow part) to unconfined flow (downdip wider part). These genetic units directly record the variations in sedimentation rate of the feeding fan-delta on the shelf, which are controlled by the 20 000 year cycles of sea-level change.

Deux siècles de stratigraphie dans le bassin de Paris

Abstract Stratigraphy is the book of Earth history. This book has been read for a long time, and each reader tries to improve its general understanding. Since the introduction of the concept of stratotypes by d’Orbigny, nearly two centuries ago, the point of view has evolved and shifted from a one-dimension perception, the vertical one, the time one, to a four-dimension comprehension, the time–space one. The Paris Basin illustrates the evolution of the main concepts that prevailed in stratigraphy.