GULF OF NUNA: ASTROCHRONOLOGIC CORRELATION OF A MESOPROTEROZOIC OCEANIC EUXINIC EVENT

The ca. 1.4 Ga Velkerri and Xiamaling formations from Australia and North China, respectively, are both carbonaceous shale deposits that record a prominent euxinic interval and were intruded by ca. 1.3 Ga dolerite sills. These similarities raise the possibility that these two units correlate, which would suggest the occurrence of widespread euxinia, organic carbon burial, and source rock deposition. Paleomagnetic data are consistent with Australia and North China being neighbors in supercontinent Nuna and thus permit deposition in a single large basin, and the putative stratigraphic correlation. However, lack of geochronological data has precluded definitive testing. The Xiamaling Formation has been shown to exhibit depositional control by orbital cycles. Here we test the putative correlation with the Velkerri Formation by cyclostratigraphic analysis. The Velkerri Formation exhibits sedimentological cycles that can be interpreted to represent, according to a sedimentation rate that is consistent with Re-Os ages, the entire hierarchy of orbital cycles. Comparison of the inferred durations of the euxinic intervals preserved in both the Xiamaling and Velkerri formations reveals a nearly identical ~10-m.y.-long oceanic euxinic event. This permits the two hydrocarbon-rich units to have been deposited and matured in the same basin of Nuna, similar to the Gulf of Mexico during the breakup of Pangea.