Response of proto-North Atlantic carbonate-platform ecosystems to OAE1a-related stressors

authored by

Stefan Huck, Melody Stein, Adrian Immenhauser, Peter W. Skelton, Nicolas Christ, Karl B. Föllmi, Ulrich Heimhofer

Abstract

Integrated biostratigraphic-chemostratigraphic studies provide evidence that the proto-North Atlantic realm witnessed major changes in carbonate platform production in the run-up of the Early Aptian oceanic anoxic event (OAE) 1a. Whereas pervasive growth of Lithocodium microencrusters represents an early harbinger of OAE1a-related environmental perturbation, the subsequent replacement of oligotrophic rudist-coral-nerineid by mesotrophic orbitolinid-oyster communities was clearly associated with the event itself. In order to test the supra-regional relevance of this major community replacement, two shallow-water sections in the southern Lusitanian Basin (Portugal) are investigated by means of geochemistry (carbon and oxygen isotopes), cement petrography and detailed sedimentological analysis. The focus is on a regional, prominent discontinuity surface (S4) at the transition between oligotrophic and mesotrophic carbonate platform production, which might indicate that the major biotic change could have been associated with a phase of non-sedimentation and possibly erosion. The studied sections (São Julião, Crismina) provide evidence that the major Early Aptian biotic turnover was preceded by numerous subordinate but significant changes in platform ecology, which mirrored a series of progressive short-term environmental changes in the course of OAE1. Several transient mass occurrences of orbitolinids indicate repeated phases of ecological stress arguably due to enhanced nutrient input and deepening. Small-scale sea-level changes at parasequence level below the major discontinuity surface are revealed by alternations of rudist assemblages dominated by clinger or recumbent forms as well as intercalated hardground and subaerial exposure stages. Expanded phases of subaerial exposure, however, can be largely ruled out following the geochemical and cement-petrographic data presented here. Enhanced continent-derived siliciclastic input characterising the lower orbitolinid-oyster dominated limestones is in support of a shift to more humid conditions during the middle Early Aptian. This is in line with palaeoclimatic data, which propose a southward movement of the mid-latitude arid climate belt during this time. The documented rapid replacement of oligotrophic assemblages by various environmental-stress adapted carbonate platform communities might be seen as explanation for ongoing Early Aptian proto-North Atlantic carbonate production during a time of widespread platform demise and drowning in the northern Tethyan realm.

Organisation(s)

Institute of Geology

External Organisation(s)

University of Strasbourg
Ruhr-Universität Bochum
Open University
University of Potsdam
University of Lausanne (UNIL)

Type

Article

Journal

Sedimentary geology

Volume

313

Pages

15-31

No. of pages

17

ISSN

0037-0738

Publication date

01.11.2014

Publication status

Published

Peer reviewed

Yes

ASJC Scopus subject areas

Geology, Stratigraphy

Sustainable Development Goals

SDG 13 - Climate Action

Electronic version(s)

https://doi.org/10.1016/j.sedgeo.2014.08.003 (Access: Closed)