Changes in Palaeoenvironmental Conditions in Late Devonian Reef Systems from the Canning Basin, WA: A Biomarker and Stable Isotope Approach

Svenja Tulipani¹, Kliti Grice¹, Paul F. Greenwood^1,2, Peter Haines³, Roger E. Summons⁴, Michael E. Böttcher⁵, Clinton Foster⁶, Ted Playton⁷, Lorenz Schwark⁸, Peter Sauer⁹, and Arndt Schimmelmann^9
1WA Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University, Perth, Western Australia
²Centres for Exploration Targeting and Biogeochemistry Centre, The University of Western Australia, Perth, Western Australia
³Geological Survey of Western Australia, Perth, Western Australia
⁴Department of Earth, Atmospheric and Planetary Sciences, MIT, Boston, Massachusetts, USA
⁵Leibniz-Institute for Baltic Sea Research, Warnemünde, Germany
⁶Geoscience Australia, Canberra, Australia
⁷Chevron Energy Technology Company, Houston, Texas, USA
⁸Institute of Geoscience, Kiel University, Kiel, Germany
⁹Department of Geological Sciences, Indiana University, Bloomington, Indiana, USA

During the Late Devonian one of the biggest mass extinctions in Earth’s history wiped out the extensive reef systems prominent in that era. The most severe loss of species occurred at the Frasnian – Famennian (F-F) boundary; however also the Givetian and Famennian time periods were closed by major extinctions. Cause and nature (distinct events or several smaller pulses) of the extinctions continue to be debated. Hypotheses range from bolide impacts to climate change and anoxia/eutrophication in the oceans linked to the rise of terrestrial vegetation.

The current study includes RockEval, elemental (C,S,N), stable isotope (δ¹³C; δ³⁴S; δD; CCSIA) and biomarker analyses combined with palynology in two sample sets (Frasnian and potentially Givetian) from the Canning Basin (Western Australia) to investigate palaeoenvironmental conditions in marine settings associated with reef systems prior to the FF boundary. Both sample sets exhibited an extraordinarily low maturity evident in both, Rock Eval and biomarker data and are probably the oldest samples in which the original N content has been preserved. Furthermore, we found evidence of photic zone euxinia (PZE) in combination with a stratified water column (freshwater incursions over saline bottom waters) in an interval of the Gogo formation, the source rock yielding the high quality oils of the Canning Basin. In contrast, the other sediment set was deposited under oxic conditions with no signs of hypersalinity or stratification indicating that extensive biotic crises only occurred periodically throughout the Frasnian.

5,7,8,-trimethyl-2-methyl-2-trimethyltridecylchromans (triMeMTTCs) and mono- and dimethylated homologues, which are established salinity indicators albeit with an unknown origin, were abundant in all samples. Abundance profiles of chromans and δ¹³C of the triMeMTTC and its pyrolysis products, which correlated with δ¹³C and abundances of pristane and phytane (mainly originating from phytoplankton), are in accordance with the formation of MTTCs from condensation reactions of phytol with higher plant derived methylated phenols in the water column during early diagenesis.

AAPG Search and Discovery Article #90175©2013 AAPG Hedberg Conference, Beijing, China, April 21-24, 2013