Albian Early Cenomanian Research Articles

Latest Albian–earliest Cenomanian monocotyledonous leaves from Australia

Two forms of monocotyledon macrofossil are documented from latest Albian–earliest Cenomanian sediments of the Eromanga Basin, central Queensland, Australia. One form is preserved as strap-shaped leaves with cross-linked parallel venation and epidermal features characteristic of monocots. Its affinities are suggested to be with the Areciflorae and it dominated a community lying between a coastal coal swamp and open marine conditions. A second form is found only as thin, dispersed cuticle, with poor detail, but is most likely also a monocot. It dominated a more inland community. These appear to be the currently known, oldest, organically preserved monocotyledonous macrofossils.

Latest Albian-earliest Cenomanian monocotyledonous leaves from Australia

Two forms of monocotyledon macrofossil are documented from latest Albian-earliest Cenomanian sediments of the Eromanga Basin, central Queensland, Australia. One form is preserved as strap-shaped leaves with cross-linked parallel venation and epidermal features characteristic of monocots. Its affinities are suggested to be with the Areciflorae and it dominated a community lying between a coastal coal swamp and open marine conditions. A second form is found only as thin, dispersed cuticle, with poor detail, but is most likely also a monocot. It dominated a more inland community. These appear to be the currently known, oldest, organically preserved monocotyledonous macrofossils.

Tectono-sedimentary controls on Cretaceous black shale deposition along the opening Equatorial Atlantic Gateway (ODP Leg 159)

Abstract The Cretaceous Equatorial Atlantic Gateway between the Central and South Atlantic basins is of interest not only for palaeoceanographic and palaeoclimatic studies, but also because it provided particularly favourable conditions for the accumulation and preservation of organic-rich sediments. Deposition of carbonaceous sediments along the Côte d’Ivoire-Ghana Transform Margin (Ocean Drilling Program Leg 159) was intimately linked to the plate tectonic and palaeoceanographic evolution of this gateway. Notably, the formation of a marginal basement ridge on the southeastern border of the transform margin provided an efficient shelter of the landward Deep Ivorian Basin against erosive and potentially oxidizing currents. Different subsidence histories across the transform margin were responsible for the development of distinct depositional settings on the crest and on both sides of the basement ridge. Whereas the southern, oceanward flank of the basement ridge was characterized by rapid, continuous deepening since the latest Albian-early Cenomanian, marine sedimentation on the northern, landward flank was interrupted by a period of uplift and erosion in the late Albian, and rapid subsidence started after the early Coniacian. Organic-rich sediments occur throughout almost the entire Cretaceous section, but hydrogen-rich marine black shales were exclusively recovered from core sections above an uplift-related unconformity. These black shales formed when separation of Africa and South America was sufficient to allow permanent oceanic midwater exchange after the late Albian. Four periods of black shale accumulation are recorded, some of them are correlated with the global oceanic anoxic events: in the latest Albian-earliest Cenomanian, at the Cenomanian-Turonian boundary, during the middle Coniacian-early Campanian, and in the mid-Maastrichtian. These periods were characterized by increased carbon fluxes to the seafloor, induced by enhanced palaeoproductivity and intensified supply of terrestrial organic matter. Black shale deposition appears to be intimately linked to periods of rising or maximum eustatic sea level and to the expansion of the oxygen minimum zone, as indicated by foraminiferal biofacies. Intervals between black shale units, in contrast, indicate a shrinking oxygen minimum zone and enhanced detrital flux rates, probably related to lowering sea level. Upper Cretaceous detrital limestones with high porosities may provide excellent hydrocarbon reservoirs, although their areal extent appears to be limited. Palaeogene porcellanites, capped by Neogene pelagic marls and clays, extend over a wider area and may provide another target for hydrocarbon exploration.

Comparative Ecology of Bryozoan Radiations: Origin of Novelties in Cyclostomes and Cheilostomes

Cyclostome and cheilostome bryozoans diversified at different times and consequently in different ecological contexts. Cyclostomes began their rebound from a Perm-Triassic bottleneck in the early Jurassic, prior to increases in bioturbation, durophagous predation, and other ecological changes of the Mesozoic Marine Revolution. Cheilostomes did not appear until the latest Jurassic and rapid diversification began only in the mid-Cretaceous, when the Mesozoic Revolution was well under way. We compare the radiations of these two groups to test for similarities in the within-group patterns of origin of biologically significant novelties, and for between-group differences that might be due to ecological context or group attributes. As seen for other invertebrate t a u , within-group novelties were not concentrated in onshore settings, in contrast to origination patterns at the ordinal level. Differences in environment of first occurrence and rapidity of novelty acquisition were not obviously related to the Mesozoic Revolution, or to the distinction between zooidand colony-level characters. The contrast in novelty acquisition rates may partly reflect group-specific constraints. In cyclostomes, novelties appeared rather evenly over 100 Ma, whereas in cheilostomes many of the novelties appeared in the Late Albian-Early Cenomanian during a period of rapid diversification. Despite a slow start (Late Jurassic-mid Cretaceous), the cheilostome radiation entered an explosive phase that may characterize successful establishment of groups founded late in the Phanerozoic.

Sedimentary and tectonic evolution of the arc zone of Southwestern Ecuador during Late Cretaceous and early Tertiary times

The eastern part of the “Celica basin” of southwesternmost Ecuador exhibits Late Cretaceous to Tertiary sediments which belong to the magmatic arc paleogeographic zone. Important N-S to NE-trending faults separate a western, mainly Late Cretaceous series (Río Playas) from an eastern succession (Catamayo-Gonzanamá) of (?) Late Cretaceous to early Tertiary age. The analysis of these sediments indicates a complex geologic history, which recorded the main stages of the early tectonic evolution of the Andes. In the Río Playas area, a submarine andesitic volcanic pile (Celica Fm) represents the products of a volcanic arc of probably Albian age. It is apparently overlain by a thick, early Late Cretaceous series of volcanic flows and coarse-grained volcaniclastic high-density turbiditic beds (Alamor Fm), the deposition of which might result from the Mochica phase (late Albian-early Cenomanian) Deformation, uplift and erosion (early Peruvian phase) are followed by the sedimentation of unconformable marls and greywackes of marine open shelf to deltaic environment. These comprise Santonian and/or Campanian fine- to mediumgrained deposits (Naranjo Fm), abruptly overlain (late Peruvian phase ?) by fan-delta coarse-grained marine deposits of latest Cretaceous age (Casanga Fm) They are locally capped by undated, partly volcaniclastic red beds, indicating an important regression/uplift of latest Cretaceous-early Tertiary age. In the Catamayo-Gonzanamá area, thick subaerial andesitic volcanic rocks (Sacapalca Fm) are intruded by Paleocene to early Eocene plutons and are overlain by undated fluvial red beds. They express uplift movements of latest Cretaceous-early Tertiary age. To the South, these are capped by slumped lacustrine black shales and greywackes of possible Maastrichtian-Paleocene age (Gonzanamá Fm) Farther north, the Sacapalca volcanics and red beds are overlain by variegated shales, sandstones and conglomerates, dated as latest Oligocene-early Miocene (Catamayo Fm) They are eroded by an angular unconformity and capped by early Miocene volcanics and sediments, which express an early Miocene deformation phase. The apparent sedimentary hiatus including most of Eocene-Oligocene times is interpreted as a result of the late Paleocene and late Eocene Incaic tectonic phases.

La sédimentation sur la plateforme de Tripolitza au Crétacé inférieur-Cénomanien en Crète centrale (Grèce)

The Tripolitza zone of the Hellenic orogen is closely related to the south Tethys passive margin. It represents the internal part of the Gavrovo-Tripolitza platform which crops out in the central-south Peloponnese, Crete and the south-east Aegean islands. From bottom to top, the Tripolitza sequence is composed of Triassic clastic sediments (Tyros beds), Triassic to upper Eocene platform carbonates and a clastic flysch series. In the present paper the sedimentation and stratigraphy of the Lower Cretaceous to Cenomanian carbonate succession of the Tripolitza zone in central Crete, are investigated. The basal beds consist of 100 m of laminated to brecciated dolomites with some intercalations of micritic limestones which are interpreted as peritidal deposits. They are of Early Cretaceous, probable Barremian age. They are overlain by 150 m of carbonates, which represent a shelf-lagoonal facies with sea-level fluctuations from upper subtidal to upper intertidal conditions. Influence of the open sea is observed towards the top of this series, dated as early Aptian on the basis of a fairly rich microfauna. The Aptian continues with 130 m of stromatolitic dolomites and dolomite breccia of intertidal to supratidal environments and 45 m of limestones reflecting a subtidal environment. A shallow water, subtidal limestone facies 15 m thick containing gastropods and rudists probably constitute the base of the Albian formation. It is followed by a regressive series 240 m thick. This is composed of laminated limestones and dolomites, gradually becoming stromatolic dolomites with dolomite breccia intercalations. This regressive carbonate sedimentation took place during the Aptian p.p.(?)-Albian-early Cenomanian. Sedimentation during the middle-late Cenomanian had a transgressive character. The succession is characterized by the presence of rudist-reef facies as well as of low-energy subtidal-lagoonal facies. The latter are expressed by limestones with intercalations of dolomites. Locally, the microfauna and microflora are rich and of high diversity.

Micropalaeontology and palynology of the Lower and Middle Cretaceous Thamama and Wasia groups, DK-C well, Dukhan oil field, Western Qatar. / Micropaléontologie et palynologie dans le Crétacé inférieur et moyen des groupes de Thamama et de Wasia, puits DK-C, champ pétrolifère de Dukhan, Qatar occidental

Well preserved, diverse sporomorphs, phytoplankton and foraminifers have been found in cores from the DK-C well, Dukhan Oil Field, Western Qatar, Arabian Gulf. Most samples studied contained dinocysts, acritarchs, foraminiferal test linings, spores, pollen grains and benthic and planktic forams. From the entire palynomorph assemblage mainly dinoflagellate cysts and miospores were studied to give a stratigraphie outline for the upper Lower and Middle Cretaceous Thamama and Wasia groups. The age of the Shuaiba Formation as indicated by dinocysts is possibly early Aptian. Deposition took place in a marine environment which could possibly reflect the extreme distal locus of deposition. A tentative late middle Albian age could be assigned to unit A of the Nahr Umr Formation on basis of palynology. However unit В is dated as late Albian by palynomorphs and early Albian by foraminifera. In view of the extremely low faunal recovery and unavailability of samples from unit С of the Nahr Umr Formation, no age assignment could be postulated. The clastic facies of the Nahr Umr Formation showed high recovery of fern spores which allows us to assume marshy environment with fluviatile deposits that phased out Albian sedimentation. The dating of the Mauddud shelf carbonate Formation as late Albian, based on foraminifera, is not supported palynologically. Unit A of the Ahmadi Formation did not yield any diagnostic fauna that did allow an age assignment. The presence of elater-bearing palynomorphs, diagnostic miospores and dinocysts in this interval confined the age of this unit to the late Albian-early Cenomanian. This aspect of the Albian-Cenomanian flora could possibly indicate the prevalence of marine conditions in its upper part and the elaters are suited to a presumed arid or semi-arid climate. Units В, С and D are of early and middle Cenomanian, based on the presence of Hensonina lenticularis and Asterohedbergella asterospinosa zones. The Mishrif shallow water limestone Formation which closes out the Middle Cretaceous with alternations of limestone and shale is attributed to the late Cenomanian Dictyoconella minima Zone reported from adjacent wells in the same region.

Mid-Cretaceous palynomorphs from the Bardawil-1 Borehole, North Sinai, Egypt

Five conventional core samples recovered from depths 3785-3799 m in the Bardawil-1 Borehole, North Sinai, Egypt, contain diverse dinoflagellate cyst and miospore assemblages which are comparable to those of the Albian stratotype and from neighbouring areas. The interval is dated as a late Albian-early Cenomanian, and a middle to outer shelf association is demonstrated on the basis of high numbers of dinoflagellate cysts reflecting marine deposition not far from the coast.

Palaeogeography and clay mineralogy of mid-Cretaceous flysches in the Gibraltar Arc area

A combined sedimentological and mineralogical study of several mid-Cretaceous sequences of the western Betic Cordillera and northern Rif has lead to the distinction of three main palaeogeographic areas. The basins of these areas received influxes of terrigenous sediments from different source areas. The southern Iberian margin was fed from the Iberian palaeocontinent and its clay-mineral association is characterized by a high content of well crystallized illite and kaolinite; the distal part of this margin was locally starved of continental sedimentation, but contains a considerable clayey contribution, probably oceanic in origin, made up mainly of smectites, illite and palygorskite. The sediments in the North African margin and the southern part of the North African Flysch Trough came from the African continent, the typical Aptian-Albian clay-mineral association being well crystallized illite, illite-smectite mixed layers, kaolinite, chlorite and lesser quantities of vermiculite. The terrigenous supply to the Mauritanian Realm of the North African Flysch Trough came from the Meso-Mediterranean terrane, and its usual Aptian-Albian clay association is illite, vermiculite, illite-smectite mixed layers and kaolinite. A significant change in the clay mineralogy occurred during the late Albian-early Cenomanian in the two former areas, consisting of a decrease in the detrital supply and a concomitant increase in smectites and palygorskite. The sedimentological and mineralogical evolution of this area was controlled by a combination of tectonic, eustatic and climatic changes in the westernmost Tethys during the mid-Cretaceous.

Nonmarine Cretaceous correlations in Egypt and northern Sudan: palynological and palaeobotanical evidence

In the nonmarine Cretaceous siliciclastics of Egypt and northern Sudan, terrestrially-derived micro- and macrofloras play an important role in subsurface and surface biostratigraphy respectively. Eight palynofloral zones and four subzones are proposed covering the Neocomian through Maastrichtian. The Barremian to Cenomanian increase in angiosperm pollen frequency and diversity is accompanied by a radiation of ephedroid plants as documented by the Ephedripites pollen maximum in the Aptian and the Albian-early Cenomanian occurrences of elaterate pollen including Elaterocolpites, Elateroplicites and Elaterosporites. A comparison of the Cretaceous palynofloras with the contemporary leaf assemblages shows the latter to be biased in favour of woody plants growing near to the sites of deposition. In contrast to this, the palynofloras provide a relatively differentiated picture of the whole flora with considerable fluctuations of the pteridophyte, gymnosperm and angiosperm components. The establishment of the angiosperms appears as a relatively sudden event in the Albian-Cenomanian leaf floras, whereas a gradual Barremian-Aptian increase in angiosperm frequency can be seen in the palynofloras. A revision of some Western Desert palynomorph records shows a relatively complete Cretaceous sequence in the Dakhla Basin and a reduced sequence in the Kharga Uplift where the pre-Aptian Six Hills Formation is directly overlain by the late Cenomanian Maghrabi Formation.

Evolution and drowning of the late cretaceous Venezuelan carbonate platform

A thick, oxic, rimmed carbonate platform (the Venezuelan carbonate platform, VCP) prograded in northern South America during the Aptian-Albian. Partial drowning of the VCP ( i.e., the Cogollo Group) occurred during the latest Aptian-earliest Albian along the Machiques trough. A definitive drowning of the VCP occurred during the latest Albian-earliest Cenomanian, when a rapid rise in sea level and intensive upwelling obliterated the platform and triggered the development of an oxygen minimum zone (OMZ). Pelagic, bituminous black limestone and shales (La Luna Formation) were deposited in a ramp setting, where anoxic sulfidic conditions prevailed immediately below the sediment-water interface. Changes in the ramp slopes are suggested for the Barquisimeto, Guajira, and Tachira regions. A maximum paleodepth (∼600 m) was reached during the Campanian with the deposition of glauconitic limestones of the Tres Esquinas Member of the Colón Formation (a regional condensed section). Anoxic post-oxic conditions are suggested for the sediment-water interface, whereas dysaerobia is suggested for the water column (for the Tres Esquinas Member). Shallower water conditions occurred from the latest Campanian to Maastrichtian. Hemipelagic limestones of the Socuy Member of the Colón Formation were deposited in the outer ramp, where the early (diagenetic) geochemical environment varied from anoxic post-oxic to anoxic sulfidic, while the water column was dysaerobic. Finally, increasing clastic input resulted in deposition of hemipelagic mudstones of the Colón Formation and establishment of aerobic conditions in the water column, compared to the early (diagenetic) geochemical environment, which remained anoxic post-oxic almost up to the end of the period.

Comparative ecology of bryozoan radiations: origin of novelties in cyclostomes and cheilostomes

The cyclostome and cheilostome bryozoan clades diversified at different times and consequently in different ecological contexts. Cyclostomes began their rebound from a Permo-Triassic bottleneck in the early Jurassic, prior to increases in bioturbation, durgophagous predation, and other ecological changes commonly termed the Mesozoic Marine Revolution. Cheilostomes did not appear until the latest Jurassic and rapid diversification began only in the mid-Cretaceous, when the Mesozoic Revolution was well under way. We compared the radiations of these clades to test for similarities reflecting general patterns in the origin of within-clade novelties, and for differences that might be due to ecological context or clade attributes. We examined the timing and environment of first occurrence of eight morphological novelties that evolved convergently in both clades (ovicells, cylindrical arborescent colony, multilayered encrusting growth [frontal budding s.l.], bilaminate erect colony, fenestrate colony, articulated colony, calcified operculae, avicularia), as well as novelties unique to cheilostomes (cribrimorph and ascophoran grades, and lunulitiform colonies) or to cyclostomes (apertures arranged in fascicles). First occurrences were traced from the literature, BMNH collections, and unpublished data provided by Prof. Dr. E. Voigt; environments were inferred within an onshore-offshore gradient using the protocol of Jablonski and Bottjer (1990).As seen for other invertebrate groups, within-clade novelties were not concentrated in onshore settings for either bryozoan clade, in contrast to the origination patterns at the ordinal level (including the Cheilostomata). Differences in sequence or environment of first occurrence were not obviously related to the Mesozoic Revolution, or to the distinction between zooid- and colony-level characters. Novelties showed a weak tendency to originate in similar sequence and in similar environments for both clades, but these numbers are small. Differences in sequence may partly reflect clade-specific constraints: for example, opercula are considered a prerequisite for the development of avicularia, so that cyclostomes needed to evolve that precursor before avicularia could appear, whereas opercula are primitive (though uncalcified) in cheilostomes and thus did not constitute such a constraint. If avicularia are omitted, the rank-order correlation of novelties becomes marginally significant (p = 0.05, Spearman rank test). The most striking difference is in the temporal pattern of novelty acquisition. In cyclostomes, these are rather evenly spread over 100 Ma, whereas in cheilostomes six of the novelties appeared in the Late Albian-Early Cenomanian during a period of rapid diversification. Despite a slow start, the cheilostome radiation enters an explosive phase that may characterize successful establishment of clades founded late in the Phanerozoic.

Permian to Cretaceous radiolarian biostratigraphic data from the Hawasina Complex, Oman Mountains

Abstract The analysis of foraminifera and radiolaria in 3000 carbonate and 150 siliceous rock samples from the Oman Mountains results in revision of the existing stratigraphy and supports the definition of new units. In the Hawasina allochthonous unit the main results are as follows: (i) Permian bedded chert exists near the base of the sequence and is thus the first Permian bedded chert occurrence reported from the Tethyan region); (ii) an important volcanic event is dated as Triassic; (iii) bedded chert horizons are dated as Liassic; (iv) the thick turbiditic sequence has been divided into several units of Middle and Late Jurassic age. In the Samail ophiolite: (i) the ages of four tectonic episodes were established from the beginning of oceanic spreading (Albian—Early Cenomanian), to the obduction of the ophiolitic nappe (Campanian).

Paleomagnetic study of the Cretaceous Morelos Formation, Guerrero State, southern Mexico

Paleomagnetic results are reported for a ~ 30 m thick limestone section of the Albian-Cenomanian Morelos Formation, Guerrero State, in southern Mexico (−17.75 °N, 99.50° W). Seventy-two specimens from 35 samples were subjected to detailed alternating field (AF) or thermal demagnetizations. Most specimens were stable and presented a single magnetization component remaining after removal of low-coercivity, low-blocking temperature components. End-point and vector analyses give a mean direction and pole position after structural correction (dip ~ 14°) of D = 332.7°, I = 46.8°, k = 215, α 95 = 4° and 63° N, 198° E ( dp = 3, dm = 5), respectively. The pole position agrees with mid-Cretaceous poles reported for cratonic North America, suggesting that the area was already keeping a similar latitudinal position relative to the North American craton by mid-Cretaceous time. Most samples present normal polarity, as expected within the Cretaceous normal interval, but four samples from a single bed present intermediate and reverse polarity, suggesting the occurrence of a reverse event during the late Albian-earliest Cenomanian.

Du Gondwana à l'atlantique sud: les connexions du fossé de la bénoué avec les bassins du Nord-Est brésilien jusqu'à l'ouverture du golfe de Guinée au crétacé inférieur

The Benue trough and the intracontinental basins of Northeast Brazil are located in the African-South American mobile belt deformed during the Pan-African (or Brazilian) orogeny. The chain trends in a N-S to NNE-SSW direction. During the Late Precambrian collision stages in between the cratons of West Africa, Sao Francisco and Congo, dominant NE-SW ductile shear zones acted as limits of mobile crustal blocks on both sides of the Gulf of Guinea. This gondwanian assemblage was reworked during the installation of the West and Central African rift system under the effects of a generalized distension which led to the opening of the Equatorial domain of the South Atlantic. Phanerozoic basins became oriented according to the inherited gondwanian mega-discontinuities along which brittle tectonics was most prominent. After an initial pre-rift deformation from Late Jurassic to Eo-Cretaceous, three principal tectono-sedimentary phases in the Benue Trough and the Northeast Brazilian basins have been shown— an eo-rift phase (Neocomian to Early Barremian) of extensional brittle tectonics and basin initiation— a syn-rift I phase (Barremian to Middle Albian) of crustal stretching, local block tilting and basin installation; associated synchronous basaltic magmatism with transitional affinities is characteristic of intracontinental distensive zones. This is the period of the Medio-African and NE-Brazilian Cretaceous Great Lakes; a syn-rift II phase (Late Albian-Early Cenomanian) of a probable crustal surextension related to regional tilting. The above evolutionary stages apply to the Equatorial domain of the South Atlantic (NE Brazil, Cameroon, Nigeria up to the Ivory Coast) deformed during the Late Jurassic to Early Cretaceous. This domain represented the final gondwanian link between the Central and South Atlantic. The new evidences of well dated polyphased intra-plate deformations are contrary to the earlier views of rigid plates in the context of continental reconstructions to obtain the pre-drift fit, different from the pre-rift one. Reconsidering the scenario of the South Atlantic opening through the geological record of its continental margins, it can be noted that the axial rift propagates from the South towards the North within successive domains (Austral, Tropical and Equatorial). The continental rifting-drifting processes were thus reproduced in the adjoining domain every 20 Ma. At the limit, transfer fault zones oriented NE-SW (with Africa in its present position) accomodate a differential deformation between each domain. In the Benue Trough, a strike-slip sinistral movement with a displacement of several tens of kilometres has been estimated along a similar NE-SW direction. The trough represents the abandoned arm of a RRF triple junction which acted at the time of the refraction of the Southern South Atlantic opening into the E-W domain of the Gulf of Guinea. The present features of the African and South American continents appeared as from the uppermost Albian to Lower Cenomanian times of final crustal disruption followed by a progressive separation of the land masses along the strike-slip equatorial margins.

Marine and brackish water Cretaceous Ostracoda from wells in central and southern Florida

Abstract. A small fauna represented by 17 species of ostracods, belonging to 13 genera, has been obtained from white oolitic limestones of probable Washitan (late Albian-early Cenomanian) age in 11 deep wells in Collier, Lee, Monroe, Pinellas, Palm Beach, Hendry, and Highlands Counties, central and southern Florida. Both marine and presumed brackish-water and/or fresh-water species are represented in the fauna. Five of the species are new; Clithrocytheridea? medioreticulata, C.? paucipunctata, C.? holoreticulata, Eocytheropteron highlandsensis and Cytheropteron? pinellensis.

Transgressions-régressions, variations eustatiques et influences tectoniques de l'Aptien au Maastrichtien dans le Bassin de Paris occidental et sur la bordure du Massif armoricain

Middle and Upper Cretaceous deposits studied in the western Paris Basin and on the Armorican Massif margin show seven transgressive pulses that can be detected in the geometrical arrangement of the sedimentary bodies and the vertical succession of facies. The transgressive episodes, each delimited by a regressive phase, reached their peak during: 1. (1) late Late Aptian —(Early Albian regression) 2. (2) mid Late Albian —(Late Albian-Early Cenomanian regression) 3. (3) mid Early Cenomanian —(late Early Cenomanian regression) 4. (4) late Middle Cenomanian —(Late Cenomanian regression) 5. (5) mid Early Turonian —(Coniacian regression) 6. (6) Santonian-Campanian —(Late Campanian regression) 7. (7) Maastrichtian —(Late Maastrichtian regression) The Cretaceous sediments occur as a series of sequences, separated by more or less important discontinuities and erosion surfaces. The features and distribution of these sequences have been studied in the nearshore region of terrigenous sedimentation and in the Chalk basin. An attempt is made to relate the bathymetric changes to either tectonic movements or more widespread eustatic oscillations.

Stratigraphie et paléoécologie des formations à Rudistes du Cénomanien : l'exemple de la Provence

In Provence three Rudists bearing formations may be identified, the first one dated as upper Albian-early Cenomanian, the second one as middle Cenomanian-upper Cenomanian, the third one as upper Cenomanian-early Turonian. The abundance of Rudists and Foraminiferas, the existence of index Ammonites allow one to realize a minute biostratigraphic investigation. Each one of these formations displays a regressive sedimentologic and paleoecologic evolution, "margino-littoral" populations replacing reef populations. The Caprinidae are dominating in the three formations. According to d'Orbigny's conceptions, the Rudists may be used to work out a biozonation of the Cenomanian and to settle its limits. The Cenomanian-Turonian boundary is characterized by the apparition of the Hippuritidae. The comparison of this biozonation to those of other regions belonging to the mesogean domain will enable one to make more precise the extent and the boundaries of sub-provinces. The position of the Ceno-manian-Turonian boundary within the eastern province is debated on the ground of these new observations. out a biozonation of the Cenomanian and to settle its limits. The Cenomanian-Turonian boundary is characterized by the apparition of the Hippuritidae. The comparison of this bio¬ zonation to those of other regions belonging to the mesogean domain will enable one to make more precise the extent and the boundaries of sub-provinces. The position of the Ceno-manian-Turonian boundary within the eastern province is debated on the ground of these new observations.