The widespread, terminal Ediacaran Dengying Formation (~ 551–~ 542 Ma) of
South China hosts one of the most prominent negative carbonate carbon isotope
excursions in Earth's history and thus bears on the correlation of the
Precambrian–Cambrian boundary worldwide. The dominantly carbonate strata of
the Dengying Formation are largely studied for their unique preservation of
its terminal Ediacaran fauna but their geochemical context is poorly known.
This study presents the first high-resolution stable isotope record (δ13C,
δ18O) of calcareous siliciclastic shallow-water deposits of the Gaojiashan
section (Shaanxi Province). The section includes (in ascending order) the
Algal Dolomite Member, the Gaojiashan Member and the Beiwan Member of the
Dengying Formation. Our data record a major δ13Ccarb negative excursion to −6
‰ in the uppermost Gaojiashan Member which is comparable in shape and
magnitude to the global Precambrian–Cambrian boundary negative δ13C excursion.
Our data set is consistent with a "shallow-water anoxia" scenario which is
thought to contribute to the "Cambrian explosion". The stratigraphic
occurrence of Cloudina and a large negative δ13C excursion suggest that the
Precambrian–Cambrian boundary is located near the top of the Gaojiashan Member
and, consequently, that overlying carbonates and dolomites of the Beiwan
Member are of earliest Cambrian age. Thus the Gaojiashan section may represent
a new shallow-water section spanning the Precambrian–Cambrian boundary.
Although bio- and chemostratigraphic data support this novel interpretation,
we cannot exclude the possibility that the key excursions may represent a
local perturbation indicating a restricted-basin environment