Sedimentary provenance analysis of the ordovician to devonian siliciclastic units of the Subandean Ranges and Santa Barbara System, northwestern Argentina

摘要

This paper explores the sedimentary provenance of the Ordovician to Devonian siliciclastic sequences of the Subandean Ranges and Santa Barbara System in the northwest (NW) of Argentina. We performed a comprehensive sediment provenance analysis of the Zapla Formation (upper Ordovician), Lipeon Formation (Ordovician-Silurian) and Arroyo Colorado Formation (Devonian) from the Zapla, Puesto Viejo and Unchime ranges, using sedimentological descriptions and U-Pb age dating of detrital zircons.The Zapla Formation represents the glacial Hirnantian period; it encompasses mostly sandstones composed of quartz that were mainly derived from Cambrian granitic rocks and a minor proportion of metamorphic grains (slates and gneisses). The main mode of detrital zircon ages for the Zapla Formation is early Cambrian ( approximate to 530 Ma, Pampean). The younger detrital zircon ages cluster around 475 Ma, an age that is older than the depositional age given by the fossil content.The Lipeon Formation is a transgressive deposit, represented mostly by shales composed of quartz, feldspar, illite and chlorite. The youngest concordia zircon age cluster is Ediacaran, 621 +/- 3 Ma, suggesting that the main contributions came from the recycled Puncoviscana Complex. In turn, The Arroyo Colorado Formation is a regressive deposit that comprises mostly sandstones made up of quartz and scarce lithic clasts. The rocks are mostly altered to kaolinite, indicating a change in climate towards more warm and humid. The youngest concordant zircon age cluster is 635 +/- 6 Ma (Ediacaran). Our results indicate that the U-Pb zircon maximum depositional ages are not only much older than its stratigraphic age, but also progressively older upwards in the sedimentary column, suggesting that the units recorded the unroofing history of the basin in a probable foreland basin setting.