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Regional Source-to-Sink Systems within Intra-Continental Rifts: The Importance of Fluvial Connectivity and Drainage Integration

Smith, Joss; Gawthorpe, Robert; Brocklehurst, Simon H.; Finch, Emma

Tectono-stratigraphic and drainage evolution models within intra-continental extensional settings dominantly focus upon individual sub-basins or half-graben. These models rarely acknowledge that, on a regional scale, extensional basins are compartmentalised into numerous sub-basins, which exist at different elevations, subside at different rates, and vary in their degree of fluvial connectivity. This study employs remote sensing, fieldwork and numerical modelling to investigate how the process of drainage integration and the degree of fluvial connectivity between adjacent sub-basins affect spatial and temporal patterns of erosion and deposition, and hence reservoir development in fluvio-lacustrine rifts.

Our observations of regional drainage systems within the Basin and Range Province indicate that isolated systems, confined to a single sub-basin, and integrated systems that connect a number of sub-basins, vary in terms of surficial facies, sediment transport distances, and the distribution of erosion and deposition. Drawing from remote sensing and fieldwork we analyse the geomorphology of the Tecopa Basin/Death Valley region and demonstrate how the process of drainage integration causes disequilibrium of the source-to-sink system. The downstream sub-basin is subject to changes in catchment size, discharge, sediment flux and sediment composition, while the upstream sub-basin is subject to base-level fall, reorganisation of drainage networks, fluvial incision and reworking of former basin fill deposits.

In order to elucidate the long term controls on stratigraphy we have devised a numerical model where three sub-basins of successively lower elevations are used to illustrate the effect of drainage integration and fluvial connectivity upon stratigraphy. We show that: i) isolated and integrated systems have different stratigraphic patterns; ii) stratigraphic architecture varies in respect to where on the chain of integration a sub-basin is positioned; iii) spatial and temporal patterns of aggradation and erosion are affected by when and where integration occurs and iv) significant local sequence boundaries can be formed due to the drainage integration process. The results highlight the importance of a regional perspective of drainage evolution within rifts and shows the stratigraphic implications are important for play fairway analysis.


AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013