Persistent Sediment Entry Points to Deep-Marine Slope Systems: Stratigraphic Relationships and Up-Dip Pinch-Outs of a Coarse-Grained Slope System overlying Carbonates

Abstract

Deep-marine sedimentary basins typically subside through time, resulting in the potential for accumulating thick sedimentary successions. Many basin margins are characterised by relative stability and persistent topographic relief during this process resulting in the characteristic fanning of deep-marine stratigraphy often observed in seismic data. This study examines the relationship of a coarse-grained submarine slope system, the Rosario Fm., with its entry point to the slope through a carbonate platform, the Alisitos Fm. Thick slope successions of channels, levees and mass transport complexes have been documented from the Rosario slope, with an outcropping sequence up to 1 km thick preserved down depositional dip of the sediment entry point. The carbonates appear to have undergone subaerial weathering and erosion, forming a karstified surface. The carbonates were tilted basin-ward prior to being on-lapped by fluvial and potentially shallow-marine sediments (El Gallo Fm.). In turn, the El Gallo was eroded, and stripped off the carbonates apart from a few ‘pockets’ lining the complicated topography. The sequence was tilted basin-ward again, and eroded into and on-lapped by the Rosario Fm. slope channels and coastal deposits. Presently, above this hinge-point, the Rosario Fm. is represented by several tens of metres of conglomerate incised into the fluvial El-Gallo and resting on top of the carbonates. At the margins of the carbonate, large blocks have crumbled into the slope conduits; these are often found as large sub-rounded blocks within slope channels up to 25 km down dip. The resulting sequence shows a carbonate platform which had a complicated topographic expression, with fluvial and deep-marine sediments spanning a wide time interval, occurring as lenses and probably representing multiple episodes of reworking through time. The implication is that older systems are erosionally truncated and amalgamated with their younger counterparts in proximal areas, potentially leading to confusion with biostratigraphic analysis of onlapping turbidites. From a reservoir perspective, there is potential for all of the slope channel systems deeper in the basin to be tied to a common leakage point at the hinge zone.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018