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General geology |
Department of Geology and Geophysics, Yale University, New Haven, CT 06520-8109 USA (e-mail: timothy.raub{at}yale.edu)
The basal Ediacaran global boundary stratotype section and point (GSSP) horizon beneath Nuccaleena Formation cap dolostone in South Australia's central Flinders Ranges South Australia coincides with an interpreted unconformity preceding deglacial transgression. Detailed lithostratigraphy of three sections across the base of the Ediacaran System at its type area reveals contrasting character of the Elatina Formation—Nuccaleena Formation transition across c. 9 km of exposure, changing the interpretive context of the GSSP.
We suggest that a locally pervasive, incisive flaser-bedded sandstone exposed between Elatina diamictites and Nuccaleena cap dolostone lies above an unconformity that correlates with the defined base of Wilpena Group, reflecting onset of terminal Elatina ‘Snowball Earth’ deglaciation and dynamic interplay between eustatic sea level change and isostatic rebound. Nuccaleena cap dolostone is sedimentologically mixed and conformable with underlying siliciclastics at Elatina Creek; hence the recently defined Ediacaran GSSP horizon, at the base of solid cap carbonate at Enorama Creek, lies in continuous section and not at an unconformity.
Nuccaleena Formation cap dolostone contains pervasive terrigenous debris, including apparently detrital hematite. While magnetite and/or maghemite is produced in abundance upon heating of the cap carbonate above c. 400°C, and we cannot exclude secondary origin of any Nuccaleena magnetite, Nuccaleena Formation cap dolostone should preserve primary magnetization.
