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

LEANDRO D´ELIA; JOAQUÍN BUCHER; DANIELA FUNES; AUGUSTO N. VARELA; ANDRÉS BILMES; MICAELA GARCÍA; MANUEL LÓPEZ; JUAN FRANZESE

Toulouse

Congreso; 33th International Meeting of Sedimentology & 16th ASF; 2017

International Association of Sedimentologists

The analysis of the controls in the sedimentation and surface processes into integrated, cause-effect models are in the spotlight during last years. The sedimentary record has been long used to analyze the deformation and determining climate proxies at different temporal-spatial scales, motivating works focused on to detect the tectonics and climate impact in non-marine basins infill. From the perspective of sedimentary system analysis, signals were defined as changes in sediment production, transport, or deposition that originate from perturbations of environmental variables for several time scales. However, relatively few studies have considered the volcanism into all these schemes. This work examines the syn-orogenic Miocene succession in the Southern Patagonian Broken-Foreland, Argentina, in an attempt to understand the coupling effects of volcanism, tectonic and climate controls to set signals in a complex sediment routing system (SRS). Based on a multidisciplinary approach, which includes structural analysis, facies model, palaeosol analysis, sequence stratigraphy, together with Digital Outcrop Modeling (DOM) and geochronology techniques, the main goals of this study are to analyze: (1) how in a syn-orogenic context the volcaniclastic supply affects the climate controlled 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 that the main sediment transfer systems to the FIMS correspond to alluvial-fluvial/alluvial-palustrine environments. 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 progressive discordances were recorded. The palaeosol study established a humid-dry climate changes out of phase with DS. The major truncation/incision surfaces, sedimentary environment changes, and the stratigraphic architecture of DS, made it possible to determine 4 orders of variations in the FIMS, caused by the coupling effects of tectonics, volcanim and climate at four different orders of magnitude. The very high order of variation 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 uplift of the orogen. A high order (~5 My) is limited by internal regional erosional unconformities that separate 3 retrogradational cycles of different SRS, alternating volcaniclastic (nov.nom.) and erosional engine SRS. The signals are chiefly in response to subsidence and regional uplift cycles at the foreland system, combining with volcanism that caused changes in the type of the SRS. The low order(~5 My) is defined by inter/syn-tectonic DS, under a climate change -correlated with Mid Miocene Climate Optimun-, that controls the transference of sediments and pedogenesis. The very low order (~1My) is determined by the internal arrangements of DS in response to tilting pulses, episodic volcanic supply, climate, and palaeoenvironment autocyclic variations. This multidisciplinary work allows to distinguish different environmental signals and their magnitude order that, depending on the resolution scale of the approach, could be not detected or overlooked in a framework of a basin analysis.