in Jurassic and Cretaceous Stratigraphy

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Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 beginning of the Jurassic period the climate turned into semi- dry-hot with a high thermal background intercalated with humid cycles which became shorter and shorter in time; all that marked the formation of the Ha Coi Continental Red Beds. Features of accumu- lation environment, associations of authigenic minerals, couples of indicator elements together with charac- teristics of distribution of the biological world in this time show that the climate became dryer and dryer. At the beginning of Jurassic, in the Quang Ninh Zone humid cycles were rather long, creating the conditions of development of marshes in the shore zone to form coaly shale beds and thin lenses of coal in the lower part of the Ha Coi Formation. Apart from this, in this part there are cycles of formation of grey to greenish-grey sediments interbedded with beds of reddish and red-brown colours. Basically, the biological world was developed and widespread in just this time that was showed by many fossil occurrences. Further, the climate became more and more dry and hot, leading to the development of the weathering crust upon acidic effusives largely distributed in the area. This formed favourable conditions for the formation of thick members of ferric oxide-rich sediments which are of red colour, very rare in fossil remains with the increase of carbonate content in the middle and upper part of the formation. 322 Key words: Jurassic sediments; Ha Coi formation; lacustrine deposits; Quang Ninh Province; Viet Nam References: Dovzhikov A.E. Geology of North Viet Nam. Ha Noi: Gen. Dept of Geology, 1965: 668 (in Russian); 1971 (in Vietnamese). Nguyen Cong Luong. Geology and Mineral Resources of the Ha Long Map Sheet, With the Geological Map of the Ha Long Sheet at 1: 200000 scale. Ha Noi: Dept of Geology and Min. of Viet Nam. 2001 (in Vietnamese and English). Nguyen Xuan Khien. Báo cáo Trầm tích luận và tướng đá, cổ địa lý các thành tạo trầm tích màu đỏ Jura-Creta và khoáng sản liên quan ở miền Bắc Việt Nam (Lithology and paleogeography of the Jurassic-Cretaceous red beds and related mineral resources in the North Việt Nam). Lưu trữ Địa chất, Hà Nội, 2003. Tran Van Tri. Geology of Viet Nam. Ha Noi: The north part. Sci. & Techn. Publ. House, 1977: 355 (in Vietnamese). Vu Khuc Bui Phu My. Geology of Viet Nam. Part I. Stratigraphy. Ha Noi: Gen. Dept of Geology, Ha Noi, 1988: 378 (in Vietnamese). Zhamoida A.I. On the two Mesozoi coal-bearing formations on the left side of the Red River. Journ. of Geology, 1962, 9 : 2-3 (in Vietnamese).
Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Revised Phosphate-water Fractionation Equation: Implications for Jurassic Paleotemperature Reconstructions from Biogenic Apatite E. Puceat 1 , M. Joachimski 2 , A. Bouilloux 3 , F. Monna 4 , A. Bonin 1 , G. Dera 1 , S. Motreuil 1 , D. Quesne 1 1. Université de Bourgogne, UMR CNRS 5561 Biogéosciences, 6 bd Gabriel, 21000 Dijon, France 2. GeoCenter Northern Bavaria, University of Erlangen-Nürnberg, Schloßgarten 5, 91054 Erlangen, Germany 3. Institut de Physique du Globe de Paris, UMR CNRS 7154, 4 place Jussieu 75252 Paris cedex 05, France 4. Université de Bourgogne, UMR CNRS 5594 Artehis, 6 bd Gabriel, 21000 Dijon, France The oxygen isotope composition (δ 18 O) of biogenic apatite has become increasingly used to re- assess anomalous temperatures inferred from biogenic calcite, more prone to diagenetic alteration (e.g. Pucéat et al., 2007; Trotter et al., 2008; Joachimski et al., 2009). However, recent studies have shown that significant differences arise in apatite oxygen isotope composition acquired using the different techniques in current use (Vennemann et al., 2002; Chenery et al., 2009). Yet all authors in the field use phosphate-water fractionation equations that have been acquired over 25 years with analytical techniques that are not applied any more (Longinelli and Nuti, 1973; Kolodny et al., 1983). The differences in apatite δ 18 O induced by analytical techniques question the applicability of these fractionation equations to more recently acquired data. In this work, we generated a phosphate-water fractionation equation using apatite from fish of a single species (Sparus aurata) raised in controlled environment (temperature and water δ 18 O), using the most recent techniques analyses. The new phosphate-water fractionation equation we establish presents a similar slope but an offset of about 2‰ with the earlier published fractionation equations. Our results have major repercussions on paleotemperature reconstructions from biogenic apatite oxygen isotope composition, as they demonstrate that calculated paleotemperatures from biogenic apatite δ 18 O in all studies since the work of Crowson et al. (1991) and O’Neil et al. (1994) have been underestimated and need to be con- sequently revised. For the Jurassic period, fish tooth δ 18 O data have been acquired using two different analytical techniques, and have been standardized using a value of either 21.7‰ or 22.6‰ for NBS120c (Lécuyer et al., 2003; Dera et al., 2009). As a result, differences of about 4 °C exist between the paleotemperatures inferred from the two data sets, which are due to data standardization only. Applying our new fractionation equation to the published data sets increases the reconstructed temperatures by about 8 °C for the Early Jurassic, and by about 4 °C for the Middle and Late Jurassic. Key words: Paleotemperature; Oxygen isotopes; Apatite; Jurassic References: Chenery C., Müldner G., Evans J., et al. Strontium and stable isotope evidence for diet and mobility in Roman Gloucester, UK. Journal of Archaeological Science, 2010, 37: 150-163. Crowson R.A., Showers W.J., Wright E.K., et al. Preparation of phosphate samples for oxygen isotope analysis. Analytical Chemistry, 1991, 63: 2397-2400. Dera G., Puceat E., Pellenard P., et al. Water mass exchange and variations in seawater temperature in the NW Tethys during the Early Jurassic: Evidence from neodymium and oxygen isotopes of fish teeth and belemnites. Earth and Planetary Science Letters, 2009, 286: 198-207. Joachimski M.M., Breisig S., Buggisch W., et al. Devonian climate and reef evolution: Insights from oxygen isotopes in apatite. Earth and Planetary Science Letters, 2009, 284: 596-599. Kolodny Y., Luz B., Navon O. Oxygen isotope variations in phosphate of biogenic apatites. I. Fish bone apatite: Rechecking the rules of the game. Earth and Planetary Science Letters, 1983, 64: 398-404. Lécuyer C., Picard S., Garcia J.P., et al. Thermal evolution of Tethyan surface waters during the 323
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