T176 Interactions between Life, Tectonics, Climate, and Sedimentary Systems at the Neoproterozoic-Early Cambrian Transition I

Thursday, 29 October 2020
10:00 AM - 12:00 PM
Meeting Rooms

POTENTIAL GASKIERS CONNECTION FOR TWO MID-EDIACARAN PALEOCANYONS: EVIDENCE FROM THE WONOKA CANYONS, SOUTH AUSTRALIA AND THE JOHNNIE INCISIONS, EASTERN CALIFORNIA

Paper number: T176-4
Program: Technical Sessions
Time: 10:35 AM – 10:50 AM

Authors

Abstract

Mid-Ediacaran paleocanyons in South Australia and eastern California are of interest for their broad time concordance with the emergence of the Ediacara fauna, as well as the largest negative carbon-isotope anomaly in Earth history (the Shuram anomaly). The paleocanyons differ in several ways. 1) The Wonoka canyons are substantially deeper (~ 1 km vs as much as 150 m). 2) The Johnnie incisions possess beds and blocks of giant ooid grainstone, while the Wonoka is locally associated with tongues of micritic canyon-marginal carbonate. 3) Sedimentation in the Wonoka was influenced by salt tectonics, while subtle variations in stratigraphic thickness in the Johnnie may reflect syn-depositional normal faulting. 4) The boulder-bearing basal conglomerates in the Wonoka canyons are diffusely to well stratified, while those in the Johnnie conglomerates/breccias are primarily disorganized. Both paleocanyons nonetheless possess polymictic conglomerate/breccia in their fill, and along with the presence of stratified quartz sandstone in the Johnnie incisions both suggest local and far-traveled fill components. In both examples, the conglomerate/breccia is channelized, upward fining, and associated locally with cross-stratification. The Wonoka canyons have as many as nine conglomerate-based cycles, each passing upward into rippled and laminated sandstone event layers. While deep-water mass wasting has been invoked in both examples, we alternatively suggest that the Wonoka canyons were cut by rivers and the Johnnie incisions by a combination of mass wasting and fluvial incision, with both paleocanyons being subsequently drowned. Our interpretation is based upon a total of 168 measured sections in the Wonoka canyons and 29 in the Johnnie incisions, as well as physical stratigraphic mapping supported by 3D drone imagery. Our working hypothesis is that both the Wonoka canyons and Johnnie incisions correspond in time with a drawdown of sea level related to the Gaskiers glaciation (~580 Ma). Due to the association of the paleocanyons with the Shuram anomaly, this hypothesis implies that the Shuram anomaly may bracket the Gaskiers in South Australia and either bracket or pre-date the Gaskiers in eastern California.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-354131

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