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A syn‐depositional age for Earth’s deepest δ 13 C excursion required by isotope conglomerate tests
Author(s) -
Husson Jon M.,
Maloof Adam C.,
Schoene Blair
Publication year - 2012
Publication title -
terra nova
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.353
H-Index - 89
eISSN - 1365-3121
pISSN - 0954-4879
DOI - 10.1111/j.1365-3121.2012.01067.x
Subject(s) - geology , conglomerate , diagenesis , sedimentary depositional environment , carbonate , breccia , canyon , geochemistry , clastic rock , carbonate rock , paleontology , dolostone , dolomite , sedimentary rock , geomorphology , chemistry , structural basin , organic chemistry
Terra Nova, 24, 318–325, 2012 Abstract The most negative carbon isotope excursion in Earth history is found in carbonate rocks of the Ediacaran Period (635–542 Ma). Workers have interpreted the event as the oxidation of the Ediacaran oceans [Rothman et al. , Proc. Natl. Acad. Sci. USA 100 (2003) 8124; Fike et al. , Nature 444 (2006) 744; McFadden et al. , Proc. Natl. Acad. Sci. USA 105 (2008) 3197], or as diagenetic alteration of the δ 13 C of carbonates (δ 13 C carb ) [Knauth and Kennedy, Nature 460 (2009) 728; Derry, Earth Planet. Sci. Lett. 294 (2010) 152]. Here, we present chemo‐stratigraphic data from the Ediacaran‐aged Wonoka Formation (Fm.) of South Australia that require a syn‐depositional age for the extraordinary range of δ 13 C carb values (−12 to +4‰) observed in the formation. In some locations, the Wonoka Fm. is 700 metres (m) of mixed shelf limestones and siliclastics that record the full 16‰δ 13 C carb excursion. In other places, the Wonoka Fm. is host to deep (∼1 km) palaeocanyons, which are partly filled by tabular‐clast carbonate breccias that are sourced from eroded Wonoka canyon‐shoulders. By measuring the isotopic values of 485 carbonate clasts (an isotope conglomerate test ), we show that canyon‐shoulder carbonates acquired their δ 13 C carb –δ 18 O carb values before brecciation and redeposition in the palaeocanyons.