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Synsedimentary Faulting Controls on Sandstone Distribution in an Incipient Slope System, Tres Pasos Formation, Southern Chile


The influence of synsedimentary deformation and slope failure on submarine slope topography is well documented in many modern systems. Growth fault development and related mass wasting processes are commonly associated with localized sites of accommodation in fault-bounded minibasins, where sand-laden turbidity currents tend to accumulate. Though these processes have been characterized extensively in modern seafloor environments, their impact on the distribution and architecture of turbiditic sandstone is poorly understood, especially at sub-seismic scales.

We examine 3 contiguous outcrops along a 2000 m long by 450 m thick transect located 75 km north of Puerto Natales, Chile. This succession is interpreted to record the transition from mudstone-rich levee deposits of the upper Cerro Toro Formation to the basal siltstone-rich deposits of the early Tres Pasos Formation slope system. The outcrop features >300 m of mudstone-dominated strata with cm-scale turbidite sandstone beds, and two ~50 m-thick sandstone-prone packages that crop out near the base and the top of the succession. All of these units are cut by a series of syndepositionally active normal faults and a network of 5 to 80 cm-thick sandstone injectites, which can disrupt several 10s of meters of stratigraphy. Overlying the entire succession is a widespread package (100s m thick) of siltstone-prone mass wasting deposits with restricted lenticular to channelized sandstone-dominated deposits.

Previous workers have interpreted the upper sandstone package to record deposition in an intraslope mini-basin setting, where partially ponded turbiditic sands were influenced by syndepositional faulting. However, the orientation of growth normal faults and injectites to the regional paleoslope was not documented. Moreover, the relationship of turbidite bed and bedset architecture (e.g., lateral thinning and pinch-outs) to syndepositional deformation features was not well constrained. Here, we present results of an analysis of more than 200 individual structural measurements integrated with ~1200 m of bed scale stratigraphic logging enhanced with structure-from-motion (SfM) 3D photogrammetry. The results provide insights into the development of slope systems where accommodation generated by incremental growth faulting produces reservoir-scale sandstone accumulations and where connectivity can be enhanced by cross-cutting sandstone-injectites.