Cenomanian Turonian Transition Research Articles

The Cenomanian–Turonian boundary in the Gafsa-Chott area (southern part of central Tunisia): biostratigraphy, palaeoenvironments

This study is based on biostratigraphical and palaeoenvironmental analyses of four columnar sections exposed in the Gafsa-Chott area of central Tunisia. The Cenomanian-Turonian deposits in this area are divisible into Zebbag s.s. (at base), Bahloul and Gattar Formations or their equivalents. The Cenomanian-Turonian boundary is placed within the Bahloul Formation s.s.on the basis of the occurrence of several index ammonite faunas including Choffaticerasaff. massipianum(Pervinqui ère). The Gattar Formation and its equivalents are assigned to a part of the late Early Turonian (Thomasites rollandiand Choffaticeras luciaeIntervals). The occurrence of Spathites (Jeanrogiceras)aff. revelieranus (Courtiller) encrusting the top of the Gattar equivalent probably indicates the top of the Lower Turonian. The meaning of the association C. luciaePervinquière, Thomasites rollandiforma jordaniPervinquière and S. (J.)aff. revelieranuswith respect to the M. nodosoidesZone needs to be clarified. A wide lateral variation in facies is the characteristic feature of the sequence, caused by a rapid change in the depositional setting. It has been concluded that the Cenomanian-Turonian transition of the area under consideration was deposited in a dysaerobic environment, as evidenced by the occurrence in a basin setting of a micritic limestone unit rich in organic matter with planktonic and nektonic organisms and certain stunted neritic fossils. Oxygen impoverishment was less drastic on the carbonate platforms, as indicated by the occurrence of pelagic white limestones devoid of organic matter and containing cephalopods as well as planktonic foraminifers and minute bivalves.

Stratigraphy, microfossils and depositional environments of the lowermost part of the Welton Chalk Formation (late Cenomanian to early Turonian, Cretaceous) in eastern England

SUMMARY The lowermost part of the Welton Chalk Formation in eastern England conforms to a succession of eight beds, lettered here A to H in ascending order. Beds A and B are equated with the Plenus Marls ( Metoicoceras geslinianum Zone) of southern England. The Black Band (beds C to E) has yielded palynological assemblages containing the dinoflagellate cysts Adnatosphaeridium tutulosum and Carpodinium obliquicostatum. Their presence, along with the absence of Litosphaeridium siphonophorum, indicates a late Cenomanian age ( Neocardioceras juddii Zone) for the Black Band. Bed H contains the planktonic foraminiferan Praeglobotruncana praehelvetica, an early morphotype of a Turonian marker fossil. The dark, organic-rich marls of beds C to G are probably contiguous with those of the lowermost part of the Herring Formation in the North Sea Basin and together comprise the regional sedimentary record of a much more widespread ‘black shale’ depositional episode. Alternative hypotheses concerning the origin and timing of this episode are reviewed with reference to new microfossil evidence from eastern England. The late Cenomanian to early Turonian dinoflagellate cyst stratigraphy discussed here appears to be compatible with stratigraphies based on planktonic foraminifera, ammonites and geochemistry (δ 13 C) in north-west Europe and the western interior of the USA, possibly indicating connected basin water masses over much of the area during the Cenomanian–Turonian transition.

The Cenomanian-Turonian transition on the Peruvian margin

In Peru, various deposittonal sequences can be recognized during the late middle Cenomanian to early Coniacian timespan, most of which seem to have an eustatic origin. For instance, the early late Cenomanian, late early Turonian and early Coniacian maximum floodings identified in Peru coincide with well-known global eustatic events. The Mammites nodosoides-bearing marls probably correspond to the major Cretaceous marine transgression on the Peruvian margin. However, tectonic movements may have occurred during late Cenomanian times. The widespread hiatus of lalest Cenomanian to earliest Turonian age, probably owing to a significant lowering of sea level, may have been amplified by tectonically-induced erosion. Restricted to disaerobic conditions reach a maximum close to the Cenomanian-Turonian boundary and coincide with the well-known oceanic anoxic event. However, anoxia seems to have been less important than elsewhere, probably because of better oceanic circulation. Large benthonic foraminifera are represented by Perouvianella peruviana, Archaecyclus sp. and species of Sellialveolina. The remarkable persistence of P. peruviana through the Cenomanian-Turonian boundary crisis could be related to the less drastic anoxic conditions, responsible for continuous carbonate shelf sedimentation.

Stratigraphy and interregional correlation of the Cenomanian-Turonian transition in the Western Interior of the United States near Pueblo, Colorado, a potential boundary stratotype for the base of the Turonian stage

Stratigraphy and interregional correlation of the Cenomanian-Turonian transition in the Western Interior of the United States near Pueblo, Colorado, a potential boundary stratotype for the base of the Turonian stage

Geochemical and palaeontological studies of the δ 13C anomaly in boreal and North Tethyan cenomanian-turonian sediments in Germany and adjacent areas

In two sections of the Upper Cenomanian and Lower Turonian of Northwest Germany (boreal realm, North Sea Basin) and southeast Germany (North Tethys, Regensburg area) stable isotopes ( 13C, 18O), acid-soluble manganese, carbonate contents and foraminifera were investigated. In addition, other sections across Norttwest- and Middle Europe are reviewed with respect to the detailed stratigraphy of a positive δ 13C anomaly which was found earlier to be of global importance in the archaeocretacea foraminiferal zone (Cenomanian-Turonian transition). The δ 13C excursion was found to be isochronous, with the lower limit marked by the extinction of the foraminiferal genus Rotalipora. The upper limit is found immediately above the entry of the foraminiferal Praeglobotruncana helvetica Bolli. In the macrofossil zonation, the base is marked by the occurrence of the belemnite Actinocamax plenus (Blainville) in the upper part the Metoicoceras geslinianum ammonite zone. The upper limit falls in the Watinoceras coloradoense ammonite zone just above the entry of the inoceramid genus Mytiloides. In some cases the “δ 13C excursion” refers to a maximum of a more or less well expressed oscillation of the δ 13C values with minima in the lowermost Cenomanian and the Upper Turonian. In other cases δ 13C is constant with a marked “spike” at the position of the anomaly. The locally different structures of the δ 13C trends point to incomplete mixing of water masses between basins in Northwest Europe. A manganese anomaly associated with the δ 13C excursion in the Anglo-Paris Basin was found at a higher position in northwest Germany and is apparently absent from the German North Tethys. In both cases high Mn-contents appear to be associated with a markedly increased terrigenous input expressed by an increase in grainsize of the acid-insoluble residue. The stratigraphical value of the Mn anomaly is therefore limited. The palaeoecological conditions are discussed in terms of foraminiferal diversity and the occurrences of macrofossils. A shift to higher δ 18O values coincident with the δ 13C excursion is possibly a response to cooling of ocean water for which evidence is provided by a low diversity globular planktonic assemblage. The correlation of δ 18O and foraminiferal diversity is suggested to provide a tool for bathymetric interpretations of sections, but needs further investigations.

Some remarks on the maintenance of the salinity distribution in estuaries

An upper Albian–lower Turonian shallow-water carbonate succession cropping out near the village of Monteforte Cilento (Campania Apennines, southern Italy) was analyzed in detail within the framework of studies showing contrasting climatic evidence from the “middle” Cretaceous peri-Mediterranean carbonate successions. The full succession covers a time span in which there was a major global transgression, superimposed by fluctuating sea levels, coupled with a significant increase in temperature. There is also evidence of repeated climatic shifts from humid to dry with seasonal contrasting conditions. Restricted peritidal facies dominate the section and demonstrate the general characteristics associated with restricted brackish/schizohaline up to hypersaline depositional settings in which mesotrophic to mildly eutrophic conditions largely prevail. However, an opening and/or deepening trend of the depositional areas is recorded upward in the succession by deeply bioturbated plankton-rich strata at the Cenomanian–Turonian transition. This trend stopped with the inception of new shallow-water depositional settings which radiolitid rudists repopulated or from which shallow-water skeletal remains were supplied. This transient drowning event was anticipated and then marked by the occurrence of sediments bearing low-oxygen tolerant planktonic assemblages adapted to mesotrophic conditions. This suggests ecological conditions that were unfavourable to the main carbonate-producing shallow-water assemblages at the Cenomanian/Turonian boundary. Conditions of stress in the reconstructed shallow-water settings correlate with the deterioration of the water mass that culminated in deep-water domains with the well-known OAE2 anoxic crisis. The uppermost Albian–lower Cenomanian interval is characterized by intertidal to supratidal, partially dolomitized limestone with abundant silica pseudomorphs after evaporites. The silicified evaporite nodules and layers are evidence of episodes of highly evaporitic conditions in very shallow subtidal to supratidal settings in which salty to hypersaline ponds and areas of sabkha occurred. The occurrence of xerophytic megafloral remains also suggests that an arid, evaporite-promoting climate obtained in the depositional areas of the Albian–Cenomanian succession studied. Within the framework of the climatic evolution of “middle” Cretaceous time, the evaporite cycles of the Monteforte Cilento section are of particular interest. The different peri-Mediterranean carbonate successions record widespread karst phenomena and bauxite, which are expressions of hot/humid climates. Accurate biostratigraphic analyses and published geochemical data constrain the evaporitic episodes recorded in the Monteforte Cilento section. The related arid/semiarid climatic conditions fall within a time interval in which different coeval Apennine successions show shallow-water deposits (from stromatolitic/loferitic peritidal cycles of restricted inner shelf areas to more open, subtidal deposits of an open shelf) sandwiched between two tectonically uplifted surfaces marked by humid climate-related mature soils (bauxite) and/or karst phenomena. This suggests that dry climatic episodes post-dated the hot/wet intervals in which the bauxite and karst systems developed but, in turn, predated more recent hot/wet climatic conditions that resulted in the karst systems which occur at the top of the upper Cenomanian limestone.