The role of siliciclastics in carbonate fabric diversity and preservation: A case study from the Neoproterozoic carbonate − siliciclastic Horse Thief Springs Formation, Death Valley

The sedimentary record of the Pahrump Group in Death Valley comprises well-exposed successions of mixed carbonate and siliciclastic deposits. Despite the abundance of studies focussing on the depositional dynamics of mixed carbonate – siliciclastic deposition in the Phanerozoic, the record of similar Proterozoic examples is comparatively sparse. Using high-resolution stratigraphy and microfacies analyses, this study investigates the Tonian Horse Thief Springs Formation within the Pahrump Group of Death Valley, California, in order to propose first-order constraints on the interplay between carbonate and siliciclastic deposition in the early Neoproterozoic. The mixed successions are unlike many previously studied examples interpreted as being caused by glacio-eustatic sea-level changes, thus arguing for a more relevant tectonic influence on siliciclastic deposition. This interpretation is supported by detailed microfacies analyses of siliciclastic-rich dolostones, which show abundant soft-sediment deformation features suggesting sudden pulses of sandstone deposition onto a shallow marine carbonate shelf. The Tonian carbonate factory recovered quickly after being smothered by siliciclastics, particularly due to abundant stromatolite growth. A new relationship between siliciclastic input, carbonate fabric diversity, and carbonate preservation is established based on microfacies analyses, putting forward that siliciclastic deposition had a significant impact on the formation and preservation of later-stage diagenetic dolomite cements, as well as on stromatolite morphology and carbonate fabric diversity within the microbialites. This study shows how repeated siliciclastic incursions had a significant impact on the Proterozoic carbonate factory of the Horse Thief Springs Formation, as well as on diagenetic modification and preservation of shallow marine carbonates, and establishes previously unexplored relationships between carbonate and siliciclastic strata in the Proterozoic.