T341 Deconstructing Rodinia: Neoproterozoic-Cambrian Geologic Evolution of Laurentia’s Margins

Wednesday, 4 November 2015
1:30 PM - 5:30 PM
Room 314

CAP CARBONATE PLATFORM FACIES MODEL, NEOPROTEROZOIC NOONDAY FORMATION, SE CALIFORNIA

Paper number: T341-10
Program: Technical Sessions
Time: 3:55 PM – 4:10 PM

Authors

Abstract

The Neoproterozoic outcrop belt of the Death Valley region, CA, preserves an oblique cross-section of the Noonday Formation, a mixed carbonate–siliciclastic platform that hosts distinctive basal Ediacaran (Marinoan) cap carbonate–affiliated sedimentary structures, stromatolite textures, and δ13Ccarb values. We address the relative contributions of syndepositional tectonism and recovery from extreme deglaciation in dictating Noonday platform architecture and an intra-Noonday sequence boundary. Noonday facies record the transition from a carbonate ramp to a stromatolitic reef-rimmed shelf. Subsequent base-level fall exposed the reef crest to karstic dissolution and cut incised valleys into the seaward margin of the reef; overlying strata record the backfilling of incised valleys and re-establishment of a carbonate-dominated backstepping ramp. The Noonday encompasses two depositional sequences that reveal two cycles of relative sea-level change within strata conventionally considered to record a single, rapid glacioeustatic sea-level rise.

Noonday deposition coincided with active extension of the Laurentian margin during Rodinian supercontinent disaggregation. Within this framework, previous work suggests the intra-Noonday sequence boundary records growth faulting that reinforced differential topography, uplifting reef-rimmed horsts—exposing the reef crest to karstic dissolution—and down-dropping footwall half-grabens. However, we trace the intra-Noonday sequence boundary seaward of the reef crest and demonstrate that, for a time, wave-base was situated downdip of the reef escarpment. Thus, if the Noonday margin were undergoing extension, then the intra-Noonday sequence boundary records a decrease in accommodation due, perhaps, to post-glacial isostatic uplift at a rate more rapid than tectonism. We speculate that the Noonday sequence architecture records immediate deglacial flooding, isostatic rebound induced by a hiatus in melt-water flux or rapid ice sheet collapse against a background of global deglaciation, and resumed flooding following complete deglaciation. Rift-related tectonism could amplify or counter isostasy, thus local estimates of the amplitude of post-glacial sea-level change require robust estimates of syndepositional tectonism on the margin.