The tectonic environment of the early Earth is a key issue in Precambrian geology (e.g. Palin and Santosh, 2021). One proposed setting to exist before modern plate tectonics is partial convective overturn (PCO) driven by a density instability between light felsic plutonic rock emplaced beneath dense mafic and ultramafic volcanic deposits (Van Kranendonk et al., 2007). However, what the basinal record would look like is not understood due to the lack of a modern analogue. A potential, if imperfect, model exists in modern salt basins. They form through similar gravitational instabilities, causing diapirism of underlying salt and accommodation developed through sagging of the overlying sediments. In this project we study the sedimentology and provenance of the Parriott salt minibasin of the Paradox Basin, United States, as a potential analogue for PCO settings. Results highlight the impact of salt diapirism on the basin infill, sedimentology, and structure. Clast counts of conglomerates deposited during diapirism show an unroofing sequence: initial reworking of immediately underlying siliciclastics, followed by older fossiliferous limestone, and lastly erosion into the salt diapirs. The basin evolution shows a shift from a braided channel complex into a lacustrine environment as accommodation increases with diapirism. Paleoflow indicates an initial shedding of sediment off the rising diapirs followed by a more mixed signal, including longitudinal transport and breaching of the salt walls during slower rates of salt diapir growth (Trudgill, 2011). The basin is symmetric, with uplift occurring on both sides of the sinking crust, despite a potentially different rate and height of uplift of each diapir (Trudgill, 2011). Angular unconformities during times of an increased rate of diapirism are present adjacent to the salt diapirs, but diminish to conformable surfaces towards the center of the basin. Based on these results, an unroofing sequence and symmetric geometry may be key indicators of a PCO basin. Sedimentology would be dictated by the rate of diapirism and thus accommodation, and paleoflow should come from the uplifted domes formed by diapirism during times of rapid uplift. Additionally, an angular unconformity close to the basin margins would be consistent with PCO. Thus, identifying these features in an Archean basin would suggest it formed under non-uniformitarian tectonics and provide support for the existence of PCO in the early Earth.

Reference(s)

Palin, R. M., & Santosh, M. (2021). Plate tectonics: What, where, why, and when? Gondwana Research, 100, 3–24. Trudgill, B. D. (2011). Evolution of salt structures in the northern Paradox Basin: Controls on evaporite deposition, salt wall growth and supra-salt stratigraphic architecture. Basin Research, 23(2), 208–238.

Van Kranendonk, M.J., Smithies, H.R., Hickman, A.H., Champion, D.C. (2007). Review: Secular tectonic evolution of Archean continental crust: interplay between horizontal and vertical processes in the formation of the Pilbara Craton, Australia. Terra Nova, 19(1), 1–38.