Geochemical Record of the Cenomanian-Turonian Anoxic Event in Tunisia:Is it Correlative and Isochronous to the Biotic Signal?  

作　　者：Mohamed SOUA Dalila ZAGHBIB-TURKI Hela BEN JEMIA Jalel SMAOUI Amel BOUKADI 

机构地区：[1]Exploration and Studies Department Entreprise Tunisienne d'Activités Pétrolières(ETAP),Charguia Ⅱ,2035 Tunisia [2]Département of Geology Faculty of sciences of Tunis,University of Tunis El Manar,1068 Tunisia [3]Petroleum Research and Development Center(CRDP-ETAP) Charguia Ⅱ,2035 Tunisia

出　　处：《Acta Geologica Sinica(English Edition)》2011年第6期1310-1335,共26页地质学报（英文版）

摘　　要：In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy （foraminifera and radiolarians） and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian-Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Ai and K/ Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni （organic matter related trace elements） suggests that the Bahloul, deposited during a relatively short period （0.5 Ma）, was of relatively elevated primary productivity and minimal detrital input. While higher D＊ values concurrent with lower Ti/AI ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/（V＋Ni）, U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo- environmental relevant indicators. High Ba~ values and Uauth may indicate anoxic conditions at least at the water-sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate-reduction reactions.In Tunisia, five Bahloul spaced sections, Bargou, Jerisa, Guern Halfaya, Kherij and Gafsa were analyzed for biostratigraphy （foraminifera and radiolarians） and major and trace elements. This high-resolution biostratigraphic and chemostratigraphic integrated analyses for the Late Cenomanian-Early Turonian Bahloul Formation provide new insight into the palaeoceanographic evolution of the southern Tethyan margin. Relative low abundance of related terrigenous Ti/Ai and K/ Al ratios and enrichment of some productivity proxies such as Ba, Cu, and Ni （organic matter related trace elements） suggests that the Bahloul, deposited during a relatively short period （0.5 Ma）, was of relatively elevated primary productivity and minimal detrital input. While higher D＊ values concurrent with lower Ti/AI ratios are interpreted as caused by enhanced fluvial material contribution, due to more humid climate during the OAE-2. Enhanced humidity triggered probably fluvial influxes, resulted in a sluggish water circulation and consequent anoxic/euxinic conditions favoring the preservation of organic matter at the bottom. Enrichments in redox-sensitive trace metals U, V, and Mo in the Bahloul Formation deposits and redox indices, such as V/（V＋Ni）, U/Th, V/Cr, and Ni/Co, indicate that oxygen-restricted conditions prevailed during the Late Cenomanian to earliest Turonian times and correlate well with relative abundances of some foraminiferal and radiolarian paleo- environmental relevant indicators. High Ba~ values and Uauth may indicate anoxic conditions at least at the water-sediment interface during the Bahloul Formation deposition and provide information about low to moderate sulfate-reduction reactions.

关 键 词：Bahloul Formation FORAMINIFERA CHEMOSTRATIGRAPHY OAE-2 

分 类 号：P593[天文地球—地球化学]