Outcrop 13. Tres Pasos Formation Slope Minibasin Fill, El Chingue Bluff

Abstract

Abstract Outcrop accessibility: moderate Outcrop Coordinates: 51.1537°S, 72.4725°W Refer to outcrop 13 on location map Limited exposures of sandstone are present in the Tres Pasos Formation between Sierra Contreras and Laguna Figueroa; an important exception is a 60 m thick succession dominated by coarse-grained turbiditic units at El Chingue Bluff. The stratigraphic section is characterized by an upward coarsening of grain size, and the vertical progression of facies indicating increasing energy. The top of the bluff is defined by the thick sandstone package; beds at the base of this sandstone package are truncated by a normal fault at the southern end of the outcrop, and lap out towards the north onto the tilted hanging wall. Stratal thickening and thinning across the fault, and unfaulted overlying deposits, have led to the interpretation that the fault was active during sand deposition (a growth fault), and that it created accommodation space for the partially ponded sand body (Shultz and Hubbard, 2005). This, and other growth faults in the underlying strata, have contributed to the development of an intraslope minibasin model for deposition. The sandstone package is overlain by a thick succession of mass transport deposits, recording the progradation of the slope across the area. Sandstone dikes are extensive, paralleling growth fault planes. Shultz (2004) has speculated that these dikes were injected downwards, sourced from the coarse sandstone present in the top of the measured section.