Publikationsdatum:
2022-05-25
Beschreibung:
Author Posting. © The Author(s), 2011. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Geochimica et Cosmochimica Acta 84 (2012): 104-125, doi:10.1016/j.gca.2012.01.004.
Beschreibung:
Many biogeochemical anomalies coincide with the Late 1 Permian Extinction
(LPE; 252.28 Ma). Several mechanisms have been proposed to explain the
moretane/hopane anomaly that has been identified in samples from Meishan GSSP
section in southeastern China. Here, we report homohopane, 2α- and 3β-
methylhomohopane and lithological data for a drill core from the Meishan section in
southeastern China. Three intervals of elevated C30 moretane/hopane ratios are recorded
in the Lungtan, Yinkeng and Helongshan Formations. Moretane/hopane ratios of C31-34
homohopanes and the 2α- and 3β-methylhomohopanes display the same stratigraphic
patterns as the C30 moretane/hopane record. In light of the multiple and parallel moretane
anomalies for the homohopane and 2α- and 3β-methylhomohopane series, enhanced input
from higher plant organic matter, such as coal and peat, does not adequately explain the
observed isomer patterns. Correlation of high moretane/hopane ratios with low C35 HHI
and high hopane/sterane values suggest increased input of hopanoids from oxic soils.
Additionally, moretane/hopane ratios show excellent correlations with total clay
percentages and specific clay types, particularly chlorite, illite, and mixed layer
illite/smectite. We conclude that a combination of episodic hopanoid input from soil
bacteria and diagenetic effects related to redox and detrital clays generated the unique
moretane/hopane patterns at Meishan. Similar relationships of Ts/(Ts+Tm) with redox and source indicators and
lithology indicate that Ts/(Ts+Tm) is affected by the same factors controlling the moretane/hopane ratios. Berthierine, a clay that requires reducing conditions for
formation, was detected in samples from the Lungtan Formation. We are unable to
determine from our results whether the berthierine is authigenic or detrital, but future
determination of the origin of berthierine at Meishan may offer additional environmental
insight. No link between diasteranes and lithology was observed in this study suggesting
that diasteranes are relatively unaffected by the detrital clay component of the Meishan
sediments. In total, the results point toward the complex role of source input, lithology,
and depositional redox conditions in the transformation of organic matter during
maturation. Future work is required to elucidate the lithological effects on diagenetic
processes, including biomarker genesis isomerization, and thermal degradation.
Beschreibung:
KLF is supported by a National Science Foundation Graduate Fellowship. Research at
MIT was supported by an award (NNX09AM88G) from the NASA Exobiology Program
to RES. Research at Nanjing was supported by the 973 Project of the MST of China
(2011CB808905) and NSF of China. NJT acknowledges support from Churchill College
and the Royal Society (RG 2009/R2).
Schlagwort(e):
Late Permian extinction
;
Meishan Section
;
Hydrocarbon biomarkers
;
Hopanes
;
Moretanes
;
Clay composition
;
Diagenesis
;
Berthierine
Repository-Name:
Woods Hole Open Access Server
Materialart:
Preprint
Format:
application/pdf
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