The Wunstorf Drilling Project : Coring a Global Stratigraphic Reference Section of the Oceanic Anoxic Event 2

The mid-Cretaceous greenhouse world (Albian–Turonian) was characterized by high atmospheric carbon dioxide levels, much higher global temperatures than at present, and  a lack of permanent ice caps at the poles (Bice et al., 2006; Huber et al., 2002; Wilson et al., 2002). A characteristic feature of this greenhouse world was the deposition of black shales during the Cenomanian / Turonian boundary interval (CTBI; Schlanger and Jenkyns, 1976; Arthur et al., 1990). These carbon-rich sediments reflect a major perturbation of  the global carbon cycle, with an associated global Ocean Anoxic Event (OAE 2). Despite twenty years of research, the  OAE 2 still remains critical for the understanding of some of the mechanisms driving the climate and ocean systems during this period of extreme warmth. Numerous Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites and many on-shore sections throughout the world have recovered sediments of CTBI age. However, many of these  CTBI records and OAE 2 suffer from relatively poor stratigraphic control, which greatly reduces the options to  correlate paleotemperatures and carbon isotope records to microand macropaleontological findings on a high-resolution scale.


Introduction and Goals
The mid-Cretaceous greenhouse world (Albian-Turonian) was characterized by high atmospheric carbon dioxide levels, much higher global temperatures than at present, and , and and a lack of permanent ice caps at the poles (Bice et al., 2006;Huber et al., 2002;Wilson et al., 2002). A characteristic feature of this greenhouse world was the deposition of black shales during the Cenomanian / Turonian boundary interval (CTBI; Schlanger and Jenkyns, 1976;Arthur et al., 1990). These carbon-rich sediments reflect a major perturbation of -rich sediments reflect a major perturbation of rich sediments reflect a major perturbation of the global carbon cycle, with an associated global Ocean Anoxic Event (OAE 2). Despite twenty years of research, the twenty years of research, the years of research, the OAE 2 still remains critical for the understanding of some of the mechanisms driving the climate and ocean systems during this period of extreme warmth. Numerous Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) sites and many on-shore sections throughout the world have recovered sediments of CTBI age. However, many of these However, many of these any of these CTBI records and OAE 2 suffer from relatively poor stratigraphic control, which greatly reduces the options to , which greatly reduces the options to which greatly reduces the options to which greatly reduces the options to greatly reduces the options to es the options to the options to correlate paleotemperatures and carbon isotope records to micro-and macropaleontological findings on a high-resolution scale.
In order to fill this gap, an onshore drilling project, funded by the Deutsche Forschungsgemeinschaft (DFG), has been initiated. In March 2006, an 80-m-long -m-long m-long -long long core, covering the CTBI, has been successfully recovered near Wunstorf (20 km east of Hannover, Germany, Fig. 1). The easily accessible Wunstorf section is a highly expanded, middle Cenomanian to Cenomanian to Cenomanian to early Turonian succession exposing a thick Turonian succession exposing a thick Turonian succession exposing a thick black shale sequence. The Wunstorf drilling site was placed next to a former quarry which supplied abundant and well preserved macro-and microfossils.
The Wunstorf drilling project aims at establishing a high resolution stable isotope record for the black shale succession (OAE 2) of the CTBI and developing ing this into a globally applicable high resolution bio-and chemostratigraphic reference section. Disciplines involved include micropaleontology (calcareous nannofossils, planktonic foraminifera), macropaleontology (ammonites, inoceramids), stable isotopes and cyclostratigraphy mainly based on borehole logging, multi sensor core logging, and x-ray fluorescence (XRF) scanning , and x-ray fluorescence (XRF) scanning and x-ray fluorescence (XRF) scanning data. The combination of geochemical, paleontological, and , and and logging data will allow high resolution chemo-and biostratigraphy for the CTBI which may in the future serve as an I which may in the future serve as an which may in the future serve as an the future serve as an future serve as an international standard.

The Wunstorf Core
In northwest Germany, the sediments of the CTBI are northwest Germany, the sediments of the CTBI are orthwest Germany, the sediments of the CTBI are partly represented by finely laminated, total organic carbon (TOC) rich black shales deposited under dysoxic to anoxic conditions (at Wunstorf, Misburg, and Hesseltal) in shallow at Wunstorf, Misburg, and Hesseltal) in shallow Wunstorf, Misburg, and Hesseltal) in shallow and Hesseltal) in shallow Hesseltal) in shallow basins on a wide shelf at a paleolatitude of approximately 40°N (e.g., Ernst et al., 1984;Wilmsen, 2003). Out of these , Ernst et al., 1984;Wilmsen, 2003). Out of these Ernst et al., 1984;Wilmsen, 2003). Out of these , 2003). Out of these 2003). Out of these ). Out of these . Out of these localities Wunstorf (Fig. 1) offers the most expanded black shale sequence and, micropaleontologically, the best suited , micropaleontologically, the best suited micropaleontologically, the best suited , the best suited the best suited best suited st suited lithology. Based on field studies and archive data, the drill , the drill the drill site was chosen about 500 m west of the former quarry m west of the former quarry m west of the former quarry (Fig. 1). Tertiary TOC-rich beds up to 110 cm thick interbedded with pale and green marls (Fig. 3). .
After the core was split into an archive and a working half, was split into an archive and a working half, into an archive and a working half, , a detailed description of the whole core was made (Fig. 4).
core was made (Fig. 4). was made (Fig. 4). was made (Fig. 4). made (Fig. 4). made (Fig. 4). (Fig. 4). Subsequently, the core has been logged with the Multisensor , the core has been logged with the Multisensor the core has been logged with the Multisensor Core Logger available at the BCR. After an initial sampling party in April 2006, the first studies of this core are currently , the first studies of this core are currently the first studies of this core are currently underway, including stratigraphy and sedimentology , including stratigraphy and sedimentology including stratigraphy and sedimentology (Würzburg, Berlin), stable isotope stratigraphy (Federal Institute for Geosciences and Natural Resources, BGR, Hannover; Bochum, Germany), inorganic geochemistry (University Oldenburg, Germany), organic geochemistry, x-ray fluorescence (XRF) spectroscopy scans, benthic and planktonic foraminifera (BGR Hannover, Germany), tetraether index (TEX86, Netherlands Institute for Sea Research, NIOZ, Texel, The Netherlands), dinoflagellates (Kingston, Frankfurt, Germany), and cyclicity (IfM and cyclicity (IfM cyclicity (IfM GEOMAR, Leibniz Institute for Marine Geosciences, Kiel, Germany).
The analytical phase of the multi-disciplinary project is scheduled for the next two years. Samples will be prepared s will be prepared will be prepared prepared according to the disciplines involved. Following compilation of data by each group/discipline, a synthesis study is planned , a synthesis study is planned a synthesis study is planned for the final phase of the project.

First Data
The core description and the gamma-ray data from gamma-ray data from -ray data from downhole logging revealed eight to nine short-termed, potential eccentricity cycles (100 ky) for the 26.5-m-thick OAE 2 black shale succession, giving a duration of 850 ky for this interval with a mean sedimentation rate of ~31 m My -1 . Stedten did a great job by drilling the Wunstorf core in such a high quality. Thanks also to Ferdinand Hölscher and The Wunstorf core was successfully drilled in early March 2006 by a truck-mounted mobile drilling system in a five-day -mounted mobile drilling system in a five-day mounted mobile drilling system in a five-day -day day campaign (Fig. 2). The 80-m-long core, which had excellent -m-long core, which had excellent m-long core, which had excellent -long core, which had excellent long core, which had excellent d excellent excellent recovery (>98�), is now stored in the Bremen Core Repository (BCR). Subsequently downhole logging has been conducted has been conducted with a broad variety of logging tools-including spectral gamma ray, density, neutron porosity, geochemical logging, sonic, borehole televiewer, resistivity, induced polarization, zation, ation, dipmeter, susceptibility, temperature, and salinity-and will , and salinity-and will and salinity-and will be integrated with the core logging data.  Thomas Grelle for spending a very cold day logging the borehole. The coring of the Wunstorf Core was funded by the Deutsche Forschungsgemeinschaft project number DFG Er 226/5-1.