Facies Characterization and Stratigraphic Prediction of Proximal Fluvial Systems in Endorheic Basins — The View from the Margins
Tectonically active continental basins feature large volumes of deposits from short-range, high-energy alluvial systems developed at basin margins, such as alluvial fans and high-gradient ephemeral rivers. The latter are widely distributed in present-day environments, but underrepresented in the mainstream literature and poorly recognized in the rock record. Given their great relative volume in topographically complex basins, they can form important reservoirs for hydrocarbon and water resources. The ‘marginalization' of such systems in fluvial research is probably due to their unconventional facies and architectures, which differ significantly from those of larger rivers fed by regional-scale catchments.
Endorheic basins are ideal settings to analyze proximal fluvial systems, due to the virtually complete preservation of their stratigraphic record and the possibility to relate sedimentological and architectural traits to independently constrained allogenic forcing. The Teruel Basin (Spain) developed during the Neogene as an association of half-grabens under semiarid climate. Ephemeral fluvial systems at basin margins terminated in lower-energy distal environments. Distinct overbank and channel-fill elements characterize these proximal successions as the products of channelized drainage pathways; however, dominant facies consist of coarse, poorly organized deposits from hyperconcentrated flows and possible in-channel debris flows.
Active tectonics at basin margin and a semiarid climate favored high-gradients, proximity to sediment sources and flash-flood events, which commonly led to poor sediment organization. Triassic claystones in catchment areas produced high concentrations of suspended fines, which damped turbulence and enhanced flow viscosity; this inhibited the development of sorting, bedforms and common architectural elements. This hypothesis is tested by comparing two distinct fluvial systems from the Miocene of the central basin sector and the Quaternary of the northern sector: striking facies differences reveal a prevalence of hyperconcentrated and debris flows in the older system, sourced by the Triassic basement.
The brief lifespans, short range, and direct proximity to catchment areas of ephemeral rivers in the Teruel Basin translated into consistent links with catchment geology and with the progressive evolution of internal base-level. This provides an excellent potential for stratigraphic prediction both at regional and local scales.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013