Sediment grain size does matter: implications of spatiotemporal variations in detrital zircon provenance for early Paleozoic peri-Gondwana reconstructions

초록

A comprehensive understanding of the relationship between the Sino-Korean Craton (SKC) and the Gondwana supercontinent is crucial for accurate reconstruction of the tectonic evolution and early Paleozoic paleogeography of East Asia. To explore the link between the SKC and peri-Gondwana, we provide new detrital zircon U-Pb age data from litho- and bio-stratigraphically constrained lower Cambrian to Lower Ordovician sandstone deposits from the eastern margin of the SKC (Taebaeksan Basin). Results indicate that the two distinct age spectra of detrital zircon resulted from provenance change combined with a strong function of sediment grain size within host siliciclastic rocks of the Taebaek Group. The age spectra from coarse-grained sandstones display Paleoproterozoic (1.9Ga) and Neoarchean (2.5Ga) peaks, indicating that the sediments were supplied from the basement rocks of the SKC. Conversely, age spectra from fine-grained siliciclastics contain late Mesoproterozoic (1.0Ga) and Neoproterozoic (0.6Ga) peaks, with or without a Paleoproterozoic signal, consistent with a Gondwanan sediment origin. These different age populations have been documented in multiple Cambrian and Ordovician sequences of the SKC and are consistently well correlated with sediment grain size. Coarse-grained sediments, sourced primarily from local basement rocks, were deposited in coastal, nearshore, and shelf environments, whereas fine-grained sediments were derived from more distal sources (i.e., the Gondwana mainland and/or the Gyeonggi Marginal Belt) and deposited in inner to outer shelf settings. Therefore, the repeated occurrence of sediment with two distinct provenances in the Cambrian-Ordovician siliciclastics of the SKC is likely a result of provenance shift integrated with changing depositional environments in an epeiric platform. This yielded variations in sediment grain size and source rock provenance, with and/or without a tectonic activity. Consequently, our results indicate that the SKC was adjacent to Gondwana during the early Paleozoic.

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