Oyster patch reefs as indicators of fossil hydrocarbon seeps induced by synsedimentary faults

Author(s)

E. Hatem, N. Tribovillard, O. Averbuch, D. Vidier, P. Sansjofre, Daniel Birgel-Rennebeck, F. Guillot

Abstract

The Late Jurassic deposits of the Boulonnais area (N-France) represent the proximal lateral-equivalent of the Kimmeridge Clay Formation; they accumulated on a clastic-dominated ramp subject to synsedimentary faulting as a result of the Atlantic Ocean rifting. In the Gris-Nez Cape area, i.e., close to the northern border fault zone of the Jurassic basin, the Late Jurassic sequence contains small-dimensioned oyster patch reefs (<1m) that are specifically observed at the base of an abrupt deepening trend in the depositional sequence induced by well-defined pulses of normal fault activity. Petrographic analysis of these patch reefs shows that they are exclusively composed of Nanogyra nana embedded in a microsparitic calcite matrix. ™

¹³C measurements, carried out within both the matrix and the shells, display significantly lower values in the matrix compared to the oyster shells which suggests that the carbonate matrix precipitation was involving a carbon source different from marine dissolved inorganic carbon, most probably related to sulfate reduction, which is evidenced by light ™

³⁴S in pyrites. Similarities but also differences with lucinid-rich bioconstructions, namely, the Late Jurassic pseudo-bioherms of Beauvoisin (SE-France) suggest that the patch reefs developed at hydrocarbon seeps are related to synsedimentary faults. The extensional block-faulting segmentation of the northern margin of the Boulonnais Basin in Late Jurassic times is thus believed to have induced a sort of small-dimension hydrocarbon seepage field, recorded by the patch reef distribution.

Organisation(s)

Department of Geology

External organisation(s)

Université Lille I - Sciences et Technologies, Université Paris VII - Paris-Diderot, Unknown External Organisation Frankreich

Journal

Marine and Petroleum Geology

Volume

55

Pages

176-185

No. of pages

10

ISSN

0264-8172

DOI

https://doi.org/10.1016/j.marpetgeo.2013.12.005

Publication date

08-2014

Peer reviewed

Yes

Austrian Fields of Science 2012

105106 Geodynamics

Keywords

ASJC Scopus subject areas

Economic Geology, Geology, Geophysics, Oceanography, Stratigraphy

Portal url

https://ucrisportal.univie.ac.at/en/publications/oyster-patch-reefs-as-indicators-of-fossil-hydrocarbon-seeps-induced-by-synsedimentary-faults(c22d81cd-49f2-477b-a585-3a4f10af1662).html