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Lithostratigraphy, Biostratigraphy and Chemostratigraphy of Upper Cretaceous Sediments from Southern Tanzania: Tanzania Drilling Project Sites 21–26

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Lithostratigraphy, Biostratigraphy and Chemostratigraphy of Upper Cretaceous Sediments from Southern Tanzania: Tanzania Drilling Project Sites 21–26 Journal of African Earth Sciences 57 (2010) 47–69 Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci Lithostratigraphy, biostratigraphy and chemostratigraphy of Upper Cretaceous sediments from southern Tanzania: Tanzania drilling project sites 21–26 Álvaro Jiménez Berrocoso a,*, Kenneth G. MacLeod a, Brian T. Huber b, Jacqueline A. Lees c, Ines Wendler d, Paul R. Bown c, Amina K. Mweneinda e, Carolina Isaza Londoño a, Joyce M. Singano f a Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA b Department of Paleobiology, MRC 121, Smithsonian Museum of Natural History, Washington, DC 20013-7012, USA c Department of Earth Sciences, University College London, Gower Street, London WC1E 6BT, UK d Universität Bremen, FB 5, Postfach 330 440, D-28334 Bremen, Germany e School of Earth, Ocean and Planetary Sciences, Cardiff University, Park Place, Cardiff CF10 3YE, UK f Tanzania Petroleum Development Corporation, P.O. Box 2774, Dar-es-Salaam, Tanzania article info abstract Article history: The 2007 drilling season by the Tanzania drilling project (TDP) reveals a much more expanded Upper Cre- Received 20 March 2009 taceous sequence than was recognized previously in the Lindi region of southern Tanzania. This TDP Received in revised form 19 July 2009 expedition targeted recovery of excellently preserved microfossils (foraminifera and calcareous nanno- Accepted 23 July 2009 fossils) for Late Cretaceous paleoclimatic, paleoceanographic and biostratigraphic studies. A total of Available online 6 August 2009 501.17 m of core was drilled at six Upper Cretaceous sites (TDP Sites 21, 22, 23, 24, 24B and 26) and a thin Miocene–Pleistocene section (TDP Site 25). Microfossil preservation at all these sites is good to excel- Keywords: lent, with foraminifera often showing glassy shells and consistently good preservation of small and del- Tanzania drilling project icate nannofossil taxa. In addition to adding to our knowledge of the subsurface geology, new surface Late Cretaceous biostratigraphy Clay-rich shelfal facies exposures were mapped and the geological map of the region is revised herein. Glassy foraminifera TDP Sites 24, 24B and 26 collectively span the upper Albian to lower-middle Turonian (planktonic fora- Holococcoliths miniferal Planomalina buxtorfi–Whiteinella archaeocretacea Zones and calcareous nannofossil zones UC0a– OAE2 isotopic excursion UC8a). The bottom of TDP Site 21 is barren, but the rest of the section represents the uppermost Ceno- manian–Coniacian (W. archaeocretacea–Dicarinella concavata Zones and nannofossil zones UC5c–UC10). Bulk organic d13C data suggest recovery of part of Ocean Anoxic Event 2 (OAE2) from these four sites. In the upper part of this interval, the lower Turonian nannofossil zones UC6a–7 are characterized by a low-diversity nannoflora that may be related to OAE2 surface-water conditions. TDP Site 22 presents a 122-m-thick, lower-middle Turonian (W. archaeocretacea–Helvetoglobotruncana helvetica Zones) sequence that includes the nannofossil zones UC6a(-7?), but invariable isotopic curves. Further, a lower to upper Campanian (Globotruncana ventricosa–Radotruncana calcarata Zones and nannofossil subzones UC15bTP–UC15dTP) succession was drilled at TDP Site 23. Lithologies of the new sites include thin units of gray, medium to coarse sandstones, separating much thicker intervals of dark claystones with organic- rich laminated parts, irregular silty to fine sandstone partings, and rare inoceramid and ammonite debris. These lithofacies are interpreted to have been deposited in outer shelf and upper slope settings and indi- cate relatively stable sedimentary conditions during most of the Late Cretaceous on the Tanzanian margin. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction collaboration of researchers studying Upper Cretaceous–Neogene stratigraphy, micropaleontology and paleoclimate. TDP studies The sediments of southern coastal Tanzania have been targeted have recovered distinctly diverse assemblages of excellently pre- in recent years by the Tanzania drilling project (TDP), an informal served foraminifera (Pearson et al., 2001; Handley et al., 2008) and nannofossils (Bown, 2005; Bown and Dunkley Jones, 2006; Lees, 2007) from outcrop and core sediment samples. Also, stable * Corresponding author. Present address: School of Earth, Atmospheric and isotope measurements on these samples have yielded reliable tem- Environmental Sciences, University of Manchester, Williamson Building, Oxford perature estimates for the Miocene (Stewart et al., 2004), Eocene Road, Manchester M13 9PL, UK. (Pearson et al., 2001, 2007, 2008) and Maastrichtian (Pearson E-mail address: [email protected] (Á. Jiménez Berro- coso). et al., 2001). The excellent preservation of the microfossils seems 1464-343X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jafrearsci.2009.07.010 48 Á. Jiménez Berrocoso et al. / Journal of African Earth Sciences 57 (2010) 47–69 to be related to both the impermeable, clay-rich host lithologies ent here a synthesis of results from the 2007 season including the and their relatively shallow burial depth (Pearson et al., 2004, litho- and biostratigraphy of planktonic foraminifera and calcare- 2006). This discovery of excellently preserved and markedly di- ous nannofossils, and chemostratigraphy for TDP Sites 21–26 and verse microfossil assemblages, in otherwise typical shelfal mud- outcrop data. A total of 501.17 m of core was drilled in 2007, rang- stone facies, represents a significant advance in our knowledge of ing from the upper Albian–upper Campanian, in addition to a thin the biodiversity and biostratigraphy of Upper Cretaceous–Neogene Miocene–Pleistocene section. Also, isotopic evidence of partial microfossils. Also, the TDP material provides a unique opportunity recovery of Ocean Anoxic Event 2 (OAE2) (Schlanger and Jenkyns, to reconstruct the subtropical temperature record through the Late 1976; Jenkyns, 1980), close to the Cenomanian–Turonian (C–T) Cretaceous–Neogene. transition, has been discovered in several of the new sites. To- Previous TDP drilling seasons (2002–2005) targeted and recov- gether, these results help constrain the poorly known Upper Creta- ered Paleocene-lower Oligocene sediments from around Kilwa and ceous stratigraphy of southern Tanzania and establish a Lindi (Fig. 1a), as well as incomplete Upper Cretaceous (Albian– stratigraphic context for ongoing work that will examine Late Cre- Cenomanian, Turonian, upper Campanian–lower Maastrichtian) taceous extreme global warmth and proposed greenhouse sequences at TDP Sites 5 at Lindi and 9 and 15 at Kilwa (Pearson glaciations. et al., 2004, 2006; Nicholas et al., 2006; Lees, 2007). These results were synthesized in Nicholas et al. (2006), who formally named 2. Upper Cretaceous overview and defined formations (Fm) in the clay-dominated, Upper Creta- ceous–Paleogene Kilwa Group (Fig. 1b), and provided a preliminary The geology and depositional history of Tanzania are strongly sequence stratigraphy. New drilling around Lindi in 2007 demon- influenced by the break up of Gondwana, beginning with an initial strated the presence of more stratigraphically-extensive Upper rifting phase about 300 Ma (Salman and Abdula, 1995, and refer- Cretaceous sediments than appreciated in previous years. We pres- ences therein). A second rifting phase with active seafloor spread- ing from about 157 Ma separated Gondwana into western (South America and Africa) and eastern (Antarctica, India, Madagascar and Australia) blocks (Salman and Abdula, 1995), and the rifting of Madagascar away from East Africa led to development of a pas- sive margin along what is now the Tanzanian coastal region. A marine transgression accompanied seafloor spreading in the sec- ond phase of rifting and resulted in deposition of thick Upper Juras- sic and Lower Cretaceous sediments in a series of marginal basins that included the Mandawa and Rovuma basins in coastal areas of Tanzania and northern Mozambique (Salman and Abdula, 1995; Key et al., 2008). A major transgression during the Late Cretaceous caused widespread deposition of mudstones in offshore environ- ments of the Mandawa and Rovuma basins that persisted into the Paleogene. A modern review of the tectonic history of coastal Tanzania can be obtained from Nicholas et al. (2007), with refer- ence to deposition during the Late Cretaceous–Neogene. Also, Key et al. (2008) recently revised the lithostratigraphy of the Meso- zoic and Cenozoic successions of the Rovuma basin in northern coastal Mozambique. Cretaceous and Paleogene marine sediments crop out along most of the Tanzanian coastal region south of Dar es Salaam (Kent et al., 1971), and the most extensive exposures are along a contin- uous band between Kilwa and Lindi (Fig. 1a). Upper Cretaceous sediments in the area have been known since the first decades of the 1900s, but more detailed descriptions were not published until Moore et al. (1963), Gierlowski-Kordesch and Ernst (1987), Ernst and Schlüter (1989), and Ernst and Zander (1993). Schlüter (1997) named the Kilwa Group for the Upper Cretaceous sediments exposed around Kilwa, but neither divided them into formations nor defined their stratigraphic limits. Nicholas et al. (2006) as- cribed the Upper Cretaceous rocks between Kilwa and Lindi to the Nangurukuru Fm (Santonian–Maastrichtian), while the Paleo- gene sediments were divided between the overlying Kivinje
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