Jens Wendler

Rapid resurgence of marine productivity after the Cretaceous-Paleogene mass extinction.

Algal Rebound The extinction at the Cretaceous-Paleogene boundary 65.5 million years ago represented a sudden and dramatic disruption of global ecosystems. Sepúlveda et al. (p. 129) now show, however, that algae recovered rapidly and that photosynthesis and primary production thus also recovered. The authors tracked algal productivity in the thick boundary layer in Denmark through a series of diagnostic biomarkers and isotopes. Algal productivity dropped abruptly during the extinction event but then recovered within the boundary layer, perhaps as quickly as within 50 years of the impact. Preserved lipids imply that primary production recovered perhaps within 50 years of the end-Cretaceous extinction. The course of the biotic recovery after the impact-related disruption of photosynthesis and mass extinction event at the Cretaceous-Paleogene boundary has been intensely debated. The resurgence of marine primary production in the aftermath remains poorly constrained because of the paucity of fossil records tracing primary producers that lack skeletons. Here we present a high-resolution record of geochemical variation in the remarkably thick Fiskeler (also known as the Fish Clay) boundary layer at Kulstirenden, Denmark. Converging evidence from the stable isotopes of carbon and nitrogen and abundances of algal steranes and bacterial hopanes indicates that algal primary productivity was strongly reduced for only a brief period of possibly less than a century after the impact, followed by a rapid resurgence of carbon fixation and ecological reorganization.

Reconstruction of mid-Cenomanian orbitally forced palaeoenvironmental changes based on calcareous dinoflagellate cysts

Abstract Mid-Cenomanian, precession-controlled (21 ka) chalk–marl couplets of the Cap Blanc Nez section (Anglo–Paris Basin) have been studied with focus on the effects which Milankovitch cycles have had on the palaeoenvironment. In this paper, we present micropalaeontological and lithological proxies that enable the reconstruction of both the cycle architecture and the transformation of the orbitally forced signal into the sediment. A palaeoecological reconstruction based on changes in calcareous dinoflagellate cysts (c-dinocysts) assemblages was carried out, in which two characteristic ecological assemblages of c-dinocysts were identified. Gradual changes in absolute and relative abundance of the cyst species in these assemblages over several couplets depict a bundling pattern which is interpreted to reflect the modulation of the intensity of the precession cycle by the eccentricity cycle (100 ka). The stacking pattern in the natural gamma ray signal and the carbonate and TOC content has the same period and provides lithological support of the bundling. A shelf basin circulation model is proposed to explain the relation between orbitally forced climate change, its palaeoenvironmental consequences and the resulting sedimentary cyclicity. Variations in surface water circulation are reflected in the sediment by the chalk–marl couplets, the most distinctive couplets ocurring at the base and top of the bundles. While the chalks reflect well-mixed surface water conditions, the marls, particularly those at the bundle boundaries, can be interpreted as the sedimentary expression of stratified water masses. During deposition of these marls, reduced oceanic mixing due to low seasonality during strong precession maxima at the eccentricity maxima caused periods of water column stratification that in turn led to nutrient depletion and decreased productivity in the surface water masses.

Orbital time scale, intra-platform basin correlation, carbon isotope stratigraphy and sea-level history of the Cenomanian–Turonian Eastern Levant platform, Jordan

Abstract Two Cenomanian–Turonian boundary (CTBE) sections (KB3 and GM3) of the Karak–Silla intra-platform basin of the Eastern Levant carbonate platform, Jordan, are correlated based on high-resolution calcimetry. KB3 contains black shales with over 7 wt% total organic carbon (TOC). GM3 was deposited at shallower water depth and reveals four conspicuous gypsum beds used for sea-level reconstruction. Spectral analysis of carbonate content and TOC reveals forcing, mainly by the 100 ka cycle of Earths orbit eccentricity. Whole rock stable carbon isotope data show a conspicuous positive δ13C excursion representing the Oceanic Anoxic Event 2 (OAE2). The carbon isotope records of KB3 and GM3 correspond well with the cycles in the δ13C record of the global stratotype (GSSP) at Pueblo (USA). The GSSP orbital timescale, thus, can be applied to the Jordan record. Furthermore, all stable isotope events defined in the English chalk reference record are recognized in Jordan. Our orbital model for the Jordan sequence-stratigraphical framework reveals approximately 1.2 (+0.2) Ma duration of a third-order sequence, proposed to represent one cycle of the long obliquity (1.2 Ma). This long-term period is superimposed on three fourth-order fluctuations of 400 ka length (long eccentricity; fourth-order sea-level fluctuations), each of which comprises four carbonate cycles (100 ka eccentricity; fifth-order sea-level fluctuations). Demise of the Levant platform occurred during the phase of decreasing δ13C values after OAE2 in the interval between the Cenomanian–Turonian (C–T) boundary and the end of the Early Turonian.

Biostratigraphy, palaeoecology and palaeogeography of the Middle Cenomanian-Early Turonian Levant Platform in Central Jordan based on ostracods

Abstract Study of a Cenomanian–Turonian sequence, including the oceanic anoxic event 2 (OAE2) in Central Jordan, yielded 22 ostracod species from the Middle–Late Cenomanian interval; no ostracods were found in the Early Turonian. The majority of the taxa have a wide geographical distribution along the southern shores of the Tethys; from Morocco in the west to the Arabian Gulf region in the east. Biogeographical homogeneity of the ostracod associations in North Africa and the Middle East reflects facilitated communication along the whole expanse of the southern Tethys margin during the Cenomanian, and suggests similar living conditions and absence of important geographical barriers that could hinder marine faunal exchange. Biostratigraphically, the investigated fauna revealed five informal ostracod biozones (I to V from older to younger). The recorded assemblages are characterized by ostracod faunas of typical marine shelf setting in biozone I, shelf lagoonal setting with fresh-water influence in biozone II, marine shelf setting with intervals of fresh-water supply in biozones III and IV, and reduced oxygen levels in the interval of biozone V. This sequence of biozones provides palaeontological evidence for the occurrence of an interval of enhanced fresh-water influence in Levant platform lagoons preceeding OAE2. A combined biostratigraphic and chemostratigraphic time scale based on stable carbon isotopes reveals the first appearance of Reticulicosta kenaanensis, previously described as an Early Turonian indicator species already in the Late Cenomanian. Absence of ostracods throughout the Early Turonian indicates environmental conditions adverse to ostracods during most of OAE2 and its aftermath interpreted to reflect strong water column stratification.

Orthopithonella collaris sp. nov., a new calcareous dinoflagellate cyst from the K/T boundary (Fish Clay, Stevns Klint/Denmark).

A new calcareous dinoflagellate cyst species, Orthopithonella collaris sp. nov., is described from the Cretaceous/Tertiary (K/T) boundary clay (Fish Clay) of Stevns Klint, Denmark, on the basis of SEM studies and light-microscopic analyses of thin sections of single specimens. The species has been found exclusively in the Fish Clay and as such may be a potential marker for the K/T boundary. Its pulse-like occurrence is thought to be due to the abrupt, relatively short-term ecological catastrophe associated with the K/T boundary event.

Tetratropis terrina sp. nov., a new calcareous dinoflagellate cyst from the Upper Campanian polyplocum zone of Lägerdorf (NW Germany)

A new calcareous dinoflagellate cyst species, Tetratropis terrina sp. nov., with an apparent stratigraphically narrow range is described from the Upper Campanian Bostrychoceras polyplocum zone of the Lägerdorf chalk sequence (NW Germany). The electron microscopic and light microscopic analyses show that T. terrina has both a pithonelloid wall type with uniformly inclined wall crystallites and a reduced peridiniacean paratabulation pattern. The prominent morphological similarities of T. terrina to the other two Tetratropis species (T. patina and T. corbula) justify the affiliation of the new species to the genus. As a result of the extension of the morphological spectrum by the new species, the genus Tetratropis Willems, 1990 has been emended.