| Title: | Orbitally forced black shale accumulation during Coniacian-Santonian times in the Ivory Coast Basin |
| Author: | Peter M. Hofmann |
| Date Submitted: | 04/24/2002 |
| Address: | Zulpicher Str. 49a
Cologne
Germany
50674
|
| Phone: | +49-221-470-4008 |
| Email: | adg03@Uni-Koeln.de |
| Co-Authors: | Wagner, Thomas, University of Bremen, twagner@uni-bremen.de; Beckmann, Britta, Universtiy of Bremen, bbeckman@uni-bremen.de |
| Affiliation: | University of Cologne |
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| Abstract URL: | http://cis.whoi.edu/science/GG/ccod/viewAbstracts.cfm?RefNumber=19725482 |
| Keywords: | black shales, orbital forcing, African climate, Ivory Coast Basin |
| Abstract: | The accumulation of black shales in the Ivory Coast Basin (ICB) during Coniacian to Santonian times displays characteristic cycle patterns, which can be recognized based on the fluctuation of organic carbon content (TOC) and selected geochemical ratios (e.g. K/Al, Si/Al and Ti/Al). We constructed a floating orbital time scale for nanno-fossil zone CC 15 on the assumption that the cycle pattern is controlled by orbital forcing. The time scale allows to address accumulation rates for selected chemical elements which can be related to specific mineral phases. The timing of peak accumulation for these minerals within the orbital cycles indicates detrital sediment input from at least two distinct source areas, i.e. kaolinite and smectite input from tropical regions, which coincides with peak TOC accumulation, and quartz and illite input from arid source regions. A comparison of our results with climate reconstructions for the Upper Cretaceous suggest that the detrital sediment supply and the related black shale accumulation at the ICB is controlled by the precession forced migration of the inner tropic convergence zone (ITC) across western Africa. A northern paleo-position of the ITC allowed the transport of quartz and illite from a proto-Namib desert to the ICB via the SE-trade wind system and resulted in low accumulation rates for TOC. A southern position of the ITC kept the ICB under the influence of tropical condition, which resulted in extensive continental run-off, and locally developed an estuarine circulation pattern. The supply of nutrients to the ICB related to the later climate situation fostered the accumulation of black shales. |
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