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