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Abstract
Chapter
from: SG 40: Paleogeography, Paleoclimate, and Source Rocks
Edited By
Alain-Yves Huc
Author:
Wolfgang Kuhnt and Jost Wiedmann
Geochemistry, Generation, Migration
Published 1995 as part of Studies in Geology 40
Copyright © 1995 The American Association of Petroleum Geologists. All Rights
Reserved.
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Chapter 10
*
Cenomanian-Turonian Source
Rocks: Paleobiogeographic and
Paleoenvironmental Aspects
Wolfgang Kuhnt
Christian-Albrechts-Universität
zu Kiel
Kiel, Federal Republic of
Germany
Jost Wiedmann*
Universität Tübingen
Tübingen, Federal Republic of
Germany
*
ABSTRACT
Biological proxy indicators (molluscs, planktonic and benthic
foraminifera) are used in combination with estimates of organic-matter accumulation to
trace mid-Cretaceous paleocirculation, paleoproductivity, and water-mass oxygenation along
the eastern Atlantic margin from Nigeria to northwestern Europe. Significant changes in
the paleobiogeographic distribution of some mollusc groups roughly coeval with the
Cenomanian-Turonian boundary include an incursion of boreal elements into lower latitudes.
These biogeographic changes may be related to climatic cooling at high latitudes and
resulting upwelling of cooler deep waters at low latitudes. Changes in benthic
foraminiferal biofacies which relate to latitude and paleobathymetry also correlate to
variations in accumulation rates and geochemical characteristics of Cenomanian-Turonian
source rocks. Assemblages which are characteristic of high productivity upwelling
conditions and high organic-matter accumulation rates are dominant in paleolatitudes
between the mid-Cretaceous equator and 20°N along the eastern North Atlantic margin and
in outer shelf to upper slope paleobathymetries. Deep sea and Northern Temperate (Boreal)
environments may allow good preservation of organic matter under oxygen-deficient
conditions, but Late Cenomanian benthic foraminiferal biofacies indicate neither enhanced
surface productivity nor substantially increased organic particle fluxes to the sea floor.
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