Frank Wiese

The Cenomanian - Turonian of the Wunstorf section - (North Germany): global stratigraphic reference section and new orbital time scale for Oceanic Anoxic Event 2

The Cenomanian–Turonian Boundary Event (CTBE) is reflected by one of the most extreme carbon cycle perturbations in Earths history and is characterized by the widespread occurrence of sediments indicating oxygen deficiency in oceanic waters (Oceanic Anoxic Event 2 = OAE 2). At Wunstorf (northern Germany) the CTBE is represented by a 26.5 m thick sedimentary succession consisting of rhythmically bedded laminated black shales, dark organic-rich marls and marly limestones yielding abundant micro- and macrofossils, making the locality particularly well suited to serve as an international standard reference section for the CTBE. In 2006 a newly drilled continuous core recovered 76 m of middle Cenomanian to middle Turonian sediments. A high-resolution carbonate δ13C curve derived from core samples resolves all known features of the positive δ13C anomaly of OAE 2 with high accuracy. Throughout the middle Cenomanian – middle Turonian succession, the δ13C curve shows numerous small-scaled positive excursions, which appear to be cyclic. High-resolution borehole geophysics and XRF core scanning were performed to generate two time series of gamma-ray data and Ti concentrations for the CTBE black shale succession. Hierarchical bundling of sedimentary cycles as well as spectral analysis and Gaussian filtering of dominant frequencies reveal cycle frequency ratios characteristic for short eccentricity modulated precession (100 kyr, 21 kyr). This new orbital time scale provides a time estimate of 430–445 kyr for the duration of OAE 2 and refines the existing orbital age models developed at localities in the English Chalk, the Western Interior Basin and the Tarfaya Basin. Based on the new age model and high-resolution carbon isotope correlation, our data allow for the first time a precise basin-wide reconstruction of the palaeoceanographic modifications within the European shelf sea during OAE 2.

Evidence for Late Cretaceous (Late Turonian) climate cooling from oxygen-isotope variations and palaeobiogeographic changes in Western and Central Europe

Trends of stable oxygen-isotope data through four European sections of Middle–Upper Turonian sediments show three phases of synchronous variations, each phase having a duration of about 250 ka. The isotopic variations are independent of local facies, sedimentary thickness and diagenetic history. Two positive δ18O shifts are associated with a southward spread of northern macrofaunas. This coincidence of geochemical and palaeontological data implies that the δ18O trends reflect a southward shift of cooler water masses. This southward extension of cooler waters was caused by changes in ocean circulation and was associated with a major regression in the early Late Turonian.

Late Turonian (Cretaceous) climate cooling in Europe: faunal response and possible causes

Abstract Isochronous variations of δ18O curves within several European basins indicate a period of Late Turonian climate cooling, which is characterized by two distinct cooling phases, separated by a period of climate stability. Literature data for macrofauna (ammonites, echinoids, and belemnites) indicate that the cooling phases are associated with a southward shift of taxa. Concomitant Late Turonian events (volcanism and relative sea-level changes) suggest the migration to be triggered mainly by relative sea-level falls. The inferred cooling phases are seen in context with a general cooling trend due to the decrease in Mid-Cretaceous volcanogenic CO2 emission. Short-term stagnation of cooling in the Late Turonian has been probably triggered by renewed volcanism. Due to the general high temperatures during Mid-Cretaceous times, a glacio-eustatic explanation for the coincidence of cooling and sea-level fall is considered unlikely.

Shallow-water methane-seep faunas in the Cenomanian Western Interior Seaway: No evidence for onshore-offshore adaptations to deep-sea vents

Sulfi de-rich environments in shallow water were considered as sites where animals acquired preadaptations enabling them to colonize deep-sea hydrothermal vents and seeps or where they survived extinction events in their deep-sea habitats. Here we document late Cenomanian shallow-water seep communities from the Tropic Shale in the Western Interior Seaway, United States, as a possible refutation of these hypotheses. The late Cenomanian was a time of extremely warm deep-water temperatures, which supposedly facilitated adaptations to the deep sea, and of widespread oceanic anoxia (oceanic anoxic event 2) that supposedly extinguished deep-water vent and seep faunas. Contrary to the expectations, the taxa of the Tropic Shale seeps were not found at coeval or younger deep-water seep or vent deposits. Furthermore, a cluster analysis of faunal similarity among Cretaceous vent and seep faunas revealed no distinction between pre- and post-Cenomanian seep faunas, but instead strong similarities among Aptian to Late Cretaceous seep faunas. This suggests that a low temperature gradient from shallow to deep water did not facilitate invasions of deep-sea vents and seeps from shallow water and that preadaptation for living at deep-sea vents and seeps did not evolve at shallow-water methane seeps. The vast majority of adaptations to successfully colonize deepsea vents and seeps were most likely acquired below the photic zone.

Lower Turonian record of belemnite Praeactinocamax from NW Siberia and its palaeogeographic significance

Specimens of the belemnitellid Praeactinocamax Naidin, 1964 are described from the Upper Cretaceous of NW Siberia (Taimyr Region, Lower Agapa River, Russia). The rostra determined as Praeactinocamax aff. plenus consist of an aragonitic anterior part and a calcitic posterior part with a sharp boundary in between. This boundary surface is referred to as the “alveolar fracture”, and it is a typical morphological feature of early belemnitellids and not a result of diagenetic processes. The occurrence of Praeactinocamax in Arctic areas shows a wider palaeobiogeographical distribution of the genus in the Late Cenomanian—Early Turonian interval than previously known. This finding suggests that migration of the late Cenomanian—early Turonian fauna occurred across Turgai channel. The geographic position of these new records may also explain the occurrence of Praeactinocamax in the Turonian of the US Western Interior Seaway, the origin of which has been hitherto unclear.

Extremely Rare Turonian Belemnites from the Bohemian Cretaceous Basin and Their Palaeogeographical Importance

New records of extremely rare late Turonian belemnites are described from the Úpohlavy working quarry in the Bohemian Cretaceous Basin. These specimens are referred to Praeactinocamax bohemicus (Stolley, 1916). An alveolar fragment possibly represents Praeactinocamax strehlensis (Fritsch, 1872) and would be the third find of this species ever recorded. All finds derive from a thin horizon in the uppermost part of the Hudcov limestone (Teplice Formation, uppermost Subprionocyclus neptuni Ammonite Zone). The small faunule most likely had its origin in a taxon from the Praeactinocamax manitobensis/walkeri/sternbergi group of the North American Province, and its occurrence in Europe can be seen in the context of a southward shift of Boreal taxa in the course of a late Turonian cooling event.

Inoceramids and biozonation across the Turonian – Coniacian boundary (Upper Cretaceous) at El Rosario, Coahuila, northeastern Mexico

The Rosario section in northern Coahuila, northeastern Mexico, contains a complete record of sediment across the Turonian–Coniacian boundary. Here we describe the inoceramids and the biozonation based on these bivalves. Inoceramus longealatus, Mytiloides herbichi, M. incertus, M. scupini, Didymotis costatus, Cremnoceramus waltersdorfensis waltersdorfensis, C. waltersdorfensis hannovrensis, C. deformis erectus, and C. crassus inconstans, were identified at El Rosario. The uppermost Turonian Mytiloides scupini and C. waltersdorfensis w. zones and the lower Coniacian C. crassus inconstans zones are well represented and are much more expanded than in sections of the US Western Interior and Europe. The index for the base of the Coniacian, C. deformis erectus, is also present, although few data exist to date from the critical Turon ian–Coniacian boundary level. Ammonites are rare, mostly endemic and provide a much lower resolution across the Turonian–Coniacian boundary than inoceramids. We suggest that various acmes observed across the Turonian–Coniacian boundary are driven by local or regional rather than by global causes. The Rosario section provides an expanded sediment and complete inoceramid record across the Turonian–Coniacian boundary.