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Forcing mechanisms for mid-Cretaceous black shale formation: evidence from the Upper Aptian and Lower Albian of the Vocontian Basin (SE France)

Forcing mechanisms for mid-Cretaceous black shale formation: evidence from the Upper Aptian and Lower Albian of the Vocontian Basin (SE France)
Forcing mechanisms for mid-Cretaceous black shale formation: evidence from the Upper Aptian and Lower Albian of the Vocontian Basin (SE France)
Calcareous nannoplankton, palynomorph, benthic foraminifera, and oxygen isotope records from the supraregionally distributed Niveau Paquier (Early Albian age, Oceanic Anoxic Event 1b) and regionally distributed Niveau Kilian (Late Aptian age) black shales in the Vocontian Basin (SE France) exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid-Cretaceous low latitudes. To quantify surface water productivity and temperature changes, nutrient and temperature indices based on calcareous nannofossils were developed. The nutrient index strongly varies in the precessional band, whereas variations of the temperature index reflect eccentricity. Since polar ice caps were not present during the mid-Cretaceous, these variations probably result from feedback mechanisms within a monsoonal climate system of the mid-Cretaceous low latitudes involving warm/humid and cool/dry cycles. A model is proposed that explains the formation of mid-Cretaceous black shales through monsoonally driven changes in temperature and evaporation/precipitation patterns. The Lower Albian Niveau Paquier, which has a supraregional distribution, formed under extremely warm and humid conditions when monsoonal intensity was strongest. Bottom water ventilation in the Vocontian Basin was diminished, probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes. Surface water productivity in the Vocontian Basin was controlled by the strength of monsoonal winds. The Upper Aptian Niveau Kilian, which has a regional distribution only, formed under a less warm and humid climate than the Niveau Paquier. Low-latitude deep water formation was reduced to a lesser extent and/or on regional scale only. The threshold for the formation of a supraregional black shale was not reached. The intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale. At least in the Vocontian Basin, the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity.
black shale, Cretaceous, benthic foraminifera, calcareous nannofossils, palynomorphs, monsoon
0031-0182
399-426
Herrle, J.O.
666d87e9-0e21-4d4f-bb8e-51f7b0a15a87
Pross, J.
e6953dba-20e4-4abd-8b01-4e1ac8d1e14a
Friedrich, O.
219eb084-560e-4c36-b2f5-b33a8b582c33
Kößler, P.
47022f04-c051-4928-b5e6-4a73282d7a32
Hemleben, C.
0f45ede4-dfec-457e-8a64-b96a5b8c71f0
Herrle, J.O.
666d87e9-0e21-4d4f-bb8e-51f7b0a15a87
Pross, J.
e6953dba-20e4-4abd-8b01-4e1ac8d1e14a
Friedrich, O.
219eb084-560e-4c36-b2f5-b33a8b582c33
Kößler, P.
47022f04-c051-4928-b5e6-4a73282d7a32
Hemleben, C.
0f45ede4-dfec-457e-8a64-b96a5b8c71f0

Herrle, J.O., Pross, J., Friedrich, O., Kößler, P. and Hemleben, C. (2003) Forcing mechanisms for mid-Cretaceous black shale formation: evidence from the Upper Aptian and Lower Albian of the Vocontian Basin (SE France). Palaeogeography, Palaeoclimatology, Palaeoecology, 190, 399-426. (doi:10.1016/S0031-0182(02)00616-8).

Record type: Article

Abstract

Calcareous nannoplankton, palynomorph, benthic foraminifera, and oxygen isotope records from the supraregionally distributed Niveau Paquier (Early Albian age, Oceanic Anoxic Event 1b) and regionally distributed Niveau Kilian (Late Aptian age) black shales in the Vocontian Basin (SE France) exhibit variations that reflect paleoclimatic and paleoceanographic changes in the mid-Cretaceous low latitudes. To quantify surface water productivity and temperature changes, nutrient and temperature indices based on calcareous nannofossils were developed. The nutrient index strongly varies in the precessional band, whereas variations of the temperature index reflect eccentricity. Since polar ice caps were not present during the mid-Cretaceous, these variations probably result from feedback mechanisms within a monsoonal climate system of the mid-Cretaceous low latitudes involving warm/humid and cool/dry cycles. A model is proposed that explains the formation of mid-Cretaceous black shales through monsoonally driven changes in temperature and evaporation/precipitation patterns. The Lower Albian Niveau Paquier, which has a supraregional distribution, formed under extremely warm and humid conditions when monsoonal intensity was strongest. Bottom water ventilation in the Vocontian Basin was diminished, probably due to increased precipitation and reduced evaporation in regions of deep water formation at low latitudes. Surface water productivity in the Vocontian Basin was controlled by the strength of monsoonal winds. The Upper Aptian Niveau Kilian, which has a regional distribution only, formed under a less warm and humid climate than the Niveau Paquier. Low-latitude deep water formation was reduced to a lesser extent and/or on regional scale only. The threshold for the formation of a supraregional black shale was not reached. The intensity of increases in temperature and humidity controlled whether black shales developed on a regional or supraregional scale. At least in the Vocontian Basin, the increased preservation of organic matter at the sea floor was more significant in black shale formation than the role of enhanced productivity.

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More information

Published date: 3 January 2003
Keywords: black shale, Cretaceous, benthic foraminifera, calcareous nannofossils, palynomorphs, monsoon

Identifiers

Local EPrints ID: 49995
URI: https://eprints.soton.ac.uk/id/eprint/49995
ISSN: 0031-0182
PURE UUID: d951c3d1-b02c-46e6-80f9-5a5d2619b735

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Date deposited: 08 Jan 2008
Last modified: 13 Mar 2019 20:52

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Contributors

Author: J.O. Herrle
Author: J. Pross
Author: O. Friedrich
Author: P. Kößler
Author: C. Hemleben

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