Neoproterozoic to Paleozoic Geology of Southwestern Mongolia

Abstract

The Neoproterozoic and Paleozoic evolution of global climate, tectonics, ocean geochemistry, and biological diversification are recorded in stratigraphic successions globally. The rock record of southwestern Mongolia has potential to reveal additional constraints as it is in the early stages of exploration. It has been known for several years that Cryogenian passive margin sedimentation on the Zavkhan Terrane hosts evidence for Neoproterozoic glaciation, and that overlying early Cambrian strata host rich records of small shelly fossils; however, the geological context for these critical records has been previously lacking.

Although these unknowns can be regarded as local geologic uncertainties, together they hold implications to test existing tectonic and crustal growth models of the Central Asian Orogenic Belt (CAOB), preservation potential of geochemical proxies within carbonate dominated strata, and biologic milestones as recorded in Paleozoic sediments. To understand and interpret the above implications, methods of field geology, litho- and chemo-stratigraphy, geochemistry, petrography, fluid inclusion and clumped isotope thermometries, and U-Pb zircon geochronology were used.

As a result, the tectonic origin and travels of the Zavkhan Terrane during the Neoproterozoic to early Paleozoic is refined and models of apparent crustal growth in the CAOB are re-assessed. Global Cryogenian and Ediacaran carbon and strontium isotope curves are constructed from limestonedominated successions of the Tsagaan-Olom Group of the Zavkhan Terrane and are integrated with available geochronologic and geochemical data from around the globe. Finally, dolomitization is shown to greatly alter primary geochemical signatures, including carbon isotope values of carbonate rocks.