Tectonic controls on deposition: delineating geodynamic constrains of western Gondwanaland (Cambrian-Ordovician; Argentina)

VACCARI, N. EMILIO; WAISFELD, BEATRIZ G.; BALSEIRO, DIEGO; BUATOIS, LUIS A.; VAUCHER, ROMAIN; MUÑOZ, DIEGO F.

Roma

Congreso; 34th IAS International Meeting of Sedimentology; 2019

At least since the early Paleozoic, the western Gondwanaland have been an active margin.Although several studies have tried to tackle its complex geodynamics, there are still majoruncertainties regarding the role of tectonism in sedimentary dynamics. This study providesnew data to delineate a tectonic pulse recorded in the southern area of the Central AndeanBasin during the Cambrian-Ordovician transition. Sedimentary rocks of this time intervalcrop out extensively in northwest Argentina. However, these fluvio-marine sedimentarysuccessions lack detailed reconstructions that are crucial to constrain the evolution of thebasin. This study focuses on upper Cambrian ? Lower Ordovician strata containing thelowermost fossil-bearing levels of the basin (Santa Rosita Formation and Guayoc ChicoGroup). Bounded by two major regional unconformities, this stratigraphic interval waspreviously considered as a retro-arc foreland basin displaying evidence of westwardprogradation without tectonic activity during its deposition. Throughout the sedimentarysuccessions, four main facies zones are described, namely fluvial-estuarine, shorefaceforeshore,delta-front, and offshore-shelf environments. Biostratigraphic constrain isprovided by trilobite biozones (Neoparabolina frequens argentina, Jujuyaspis keideli,Kainella andina, Kainella meridionalis and Kainella teiichii). Integrating sedimentary faciesanalysis, biostratigraphy, and sequence stratigraphy information from four selected areasacross the Cordillera Oriental (Sierra de Cajas, Angosto del Moreno, Quebrada de Trancasand Quebrada de Moya; Jujuy Province), a more complex evolution of the basin is proposed.Newly acquired data attest for a northward progradation of the system associated with apartially diachronic basin closure related to a first tectonic pulse induced by the Oclóyicphase. This southernmost tectonic pulse is recorded in various areas at the Cambrian-Ordovician boundary. It is highlighted by large highly erosive wave ravinement surfaces anddepositional geometries suggesting a major change in the basin physiography during theCambrian-Ordovician transition. This study provides new results helping to constrain theevolution of the western Gondwana margin during the early Palaeozoic.