Distinguishing environmental signals in a syn-orogenic, volcaniclastic to erosional engine sediment routing system: a case study from the Patagonian Foreland, Argentina

D'ELIA, LEANDRO; BILMES, ANDRÉS; VARELA, AUGUSTO; BUCHER, JOAQUÍN; LÓPEZ, MANUEL; GARCÍA, MICAELA; FUNES, DANIELA; FRANZESE, JUAN

Congreso; International Meeting of Sedimentology 2017; 2017

International Association of Sedimentologists

The analysis of the controls in the sedimentation and surface processes into integrated, cause-effectmodels are in the spotlight during last years. The sedimentary record has been long used to analyze thedeformation and determining climate proxies at different temporal-spatial scales, motivating works focusedon to detect the tectonics and climate impact in non-marine basins infill. From the perspective of sedimentarysystem analysis, signals were defined as changes in sediment production, transport, or deposition that originatefrom perturbations of environmental variables for several timescales. However, relatively few studies haveconsidered the volcanism into all these schemes. This work examines the syn-orogenic Miocene succession inthe Southern Patagonian Broken-Foreland, Argentina, in an attempt to understand the coupling effects ofvolcanism, tectonic and climate controls to set signals in a complex sediment routing system (SRS). Based ona multidisciplinary approach, which includes structural analysis, facies model, palaeosol analysis, sequencestratigraphy, together with Digital Outcrop Modeling (DOM) and geochronology techniques, the main goalsof this study are to analyze: (1) how in a syn-orogenic context the volcaniclastic supply affects theclimatecontrolled erosion, and (2) how it affects environmental signals.The Miocene (21?9 My) foreland infill megasequence (FIMS) of the Southern PatagonianBrokenForeland shows four major regional extended discontinuity surfaces. Facies analysis determined thatthe main sediment transfer systems to the FIMS correspond to alluvial?fluvial/alluvial?palustrineenvironments. The recognizing of local unconformities allowed to divide the FIMS in 6 depositional sequences(DS). Structural and DOM analyses determined inter-tectonic and syn-tectonic DS in which progressivediscordances were recorded. The palaeosol study established a humid?dry climate changes out of phase withDS. The major truncation/incision surfaces, sedimentary environment changes, and the stratigraphicarchitecture of DS, made it possible to determine 4 orders of variations in the FIMS, caused by the couplingeffects of tectonics, volcanim and climate at four different orders of magnitude. The very high order ofvariation is marked by the upper incision surface of the FIMS, that separate the positive accommodation (21-9 My) from the bypassing since 9 My. This order is mainly attributed to tectonic subsidence and regional upliftof the orogen. A high order (~5 My) is limited by internal regional erosional unconformities that separate 3retrogradational cycles of different SRS, alternating volcaniclastic (nov. nom.) and erosional engine SRS. Thesignals are chiefly in response to subsidence and regional uplift cycles at the foreland system, combining withvolcanism that caused changes in the type of the SRS. The low order (~5 My) is defined by inter/syn-tectonicDS, under a climate changecorrelated with Mid Miocene Climate Optimun-, that controls the transference ofsediments and pedogenesis. The very low order (~1My) is determined by the internal arrangements of DS inresponse to tilting pulses, episodic volcanic supply, climate, and palaeoenvironment autocyclic variations.This multidisciplinary work allows to distinguish different environmental signals and their magnitudeorder that, depending on the resolution scale of the approach, could be not detected or overlooked in aframework of a basin analysis.