Continental weathering as a driver of Late Cretaceous cooling : new insights from clay mineralogy of Campanian sediments from the southern Tethyan margin to the Boreal realm

21 pagesInternational audienceNew clay mineralogical analyses have been performed on Campanian sediments from the Tethyan and Boreal realms along a palaeolatitudinal transect from 45° to 20°N (Danish Basin, North Sea, Paris Basin, Mons Basin, Aquitaine Basin, Umbria-Marche Basin and Tunisian Atlas). Significant terrigenous inputs are evidenced by increasing proportions of detrital clay minerals such as illite, kaolinite and chlorite at various levels in the mid- to upper Campanian, while smectitic minerals predominate and represented the background of the Late Cretaceous clay sedimentation. Our new results highlight a distinct latitudinal distribution of clay minerals, with the occurrence of kaolinite in southern sections and an almost total absence of this mineral in northern areas. This latitudinal trend points to an at least partial climatic control on clay mineral sedimentation, with a humid zone developed between 20° and 35°N. The association and co-evolution of illite, chlorite and kaolinite in most sections suggest a reworking of these minerals from basement rocks weathered by hydrolysis, which we link to the formation of relief around the Tethys due to compression associated with incipient Tethyan closure. Diachronism in the occurrence of detrital minerals between sections, with detrital input starting earlier during the Santonian in the south than in the north, highlights the northward progression of the deformation related to the anticlockwise rotation of Africa. Increasing continental weathering and erosion, evidenced by our clay mineralogical data through the Campanian, may have resulted in enhanced CO2 consumption by silicate weathering, thereby contributing to Late Cretaceous climatic cooling

Calcareous nannofossil response to Late Cretaceous climate change in the eastern Tethys (Zagros Basin, Iran)

14 pagesInternational audienceConiacian to Maastrichtian changes in calcareous nannofossil assemblages have been investigated in the eastern Tethyan Shahneshin section (central Zagros Basin, Iran). The nannofossil assemblages are mainly composed of Watznaueria spp. (avg. 54%), Retecapsa spp (avg. 7.9%), Cribrosphaerella ehrenbergii (avg. 7.7%) and Micula spp. (avg. 5.7%). Throughout the late Campanian, there is a trend to lower abundances in Watznaueria spp. together with increasing abundances of C. ehrenbergii and Arkhangelskiella cymbiformis, which are considered in this basin as the main cool-water taxa. Our results reveal that, despite a diagenetic impact on calcareous nannoflora, a number of primary paleoecological trends are preserved which depict well features of the progressive Late Cretaceous cooling. The first pronounced cooling episode occurs across the late Campanian to early Maastrichtian. The onset of pronounced cooling in the eastern Tethys appears to occur prior to the Campanian/Maastrichtian Boundary event (CMBE) δ13C negative excursion, in contrast with the Boreal realm where pronounced cooling only occurs in the early Maastrichtian, postdating the onset of the CMBE. The coincidence of this earlier cooling in the Zagros Basin with an interval characterized by a significant increase in benthic foraminifera suggests an amplified response of the assemblage due to a change to shallower environments. Hence, the late Campanian calcareous nannofossil assemblage turnover in central Zagros is either a response to an early cooling trend in the eastern Tethys or to sea-level fall or both. The mid-Maastrichtian warming and late Maastrichtian cooling episodes are also delineated in the nannofossil assemblage of Shahneshin and likely correlate with similar episodes in the Boreal Realm

Integrated bio- and carbon isotope stratigraphy of the Campanian–Danian sedimentary succession in Lurestan (Zagros Basin, Iran): Implications for syntectonic facies distribution and basin evolution

In order to investigate the depositional history and facies architecture of the Campanian-Danian interval of the Zagros Basin, the succession of the Gurpi Formation (Fm.) was examined in the Gandab section, southwestern Lurestan Province, through an integrated study of calcareous nannofossils, planktic foraminifera, and bulk carbonate carbon isotopes. Despite the persistent occurrence of reworked fine fraction carbonates as attested by microfossils across the investigated interval, the carbon isotope stratigraphy of Lurestan shows a good correlation with those in the eastern and western Tethys from the Shahneshin section in central Zargos (Fars Province) and Gubbio of northern Apennines in Italy (Gubbio). The succession can be assigned an age range from late Campanian to early Danian based on the integrated stratigraphy. The results from the Gandab section, as well as field observations in more northeasterly areas of Lurestan, point to lateral facies variation of the Campanian–Danian interval associated with tectonic activity during the Late Cretaceous-Paleogene of the Zagros Basin. According to the known distribution of facies across the SW-NE transect of Lurestan and detailed ages delineated in the Gandab section, a schematic model of syntectonic sedimentation and facies distribution is drawn. Our model illustrates how the continental convergence and closure of Neo-Tethys resulted in uplifting/subsiding of the basin floor, shifting in depocenter, significant changes in sedimentary facies, and reworking phenomena in the Lurestan region.CVU acknowledges funding from the Natural Environment Research Council (NERC) (grant no. NE/N018508/1).Peer reviewe

Integrated bio- and carbon-isotope stratigraphy of the Upper Cretaceous Gurpi Formation (Iran):A new reference for the eastern Tethys and its implications for large-scale correlation of stage boundaries

29 pagesInternational audienceA high-resolution stratigraphic analysis of the Upper Cretaceous Gurpi Formation has been undertaken in the Shahneshin section (Zagros Basin, Iran). New results on calcareous nannofossils, planktic foraminifers, dinoflagellate cysts and high-resolution carbon and oxygen stable isotopes form the basis of a reference section for the eastern Tethys that spans the upper Coniacian to the late Danian. Carbon-isotope correlation to Gubbio, Italy and the NW German chalk allows for the identification of many isotopic events as well as for the definition of new events in the Campanian and Maastrichtian. Our results allow for a review of the accurate position of the Coniacian/Santonian, Santonian/Campanian, and Campanian/Maastrichtian stage boundaries relative to carbon isotopes and plankton bioevents. The reliability of Coniacian to Maastrichtian planktic foraminifer, dinoflagellate cysts and calcareous nannofossil biohorizons is assessed