A Source-to-Sink Perspective of Rift Basins: From the Half Graben to the Rift Scale

Gawthorpe, Robert ¹; Leeder, Mike ²; Finch, Emma ^1
1 SEAES, University of Manchester, Manchester, United Kingdom.
² Environmental Sciences, University of East Anglia, Norwich, United Kingdom.

Research on landscape evolution around normal fault arrays has improved our knowledge of the spatial and temporal evolution of sediment supply from evolving footwall uplands. Similarly, detailed analysis of the sedimentology and sequence stratigraphy of depositional systems within hangingwall depocentres has yielded constraints on the roles of relative sea-level change, sediment supply and tectonics. However, there is still a need to fully couple knowledge and research of the controls on footwall catchment evolution with analysis of hangingwall depositional systems, in order to deconvolve signals of climate, tectonics and sea-level change from the preserved stratigraphic record. Attempts at source-to-sink analysis tend to focus on catchment-depositional system pairs across individual fault zones where knowledge of the controls and feedbacks at the larger half-graben to rift-scale is generally lacking. This larger scale coupling of sediment supply, routing and depositional systems is not only of academic interest but is of fundamental importance in developing new play concepts for subtle syn-rift reservoirs in many mature petroleum provinces.

In this presentation we investigate the coupled response of the catchment-sedimentary system in rift basins by taking examples from active and ancient basins and investigating the controls and feedbacks on coupled landscape-depositional system evolution around growing normal faults using simple numerical models. At the scale of a linked, border fault zone, we will illustrate how variations in uplift and subsidence around growing and linking fault segments impacts on catchment growth and the resulting stratigraphic evolution. Despite a clear tectonic drive on catchment evolution, sediment supply and stratigraphic architecture, other factors such as bedrock lithology and fault array geometry have a major impact on the volume and routing of sediment to half-graben depocentres. For example, basin margins comprising a series of fault terraces have complex sediment transport pathways involving fault-parallel reaches and internal sediment sinks compared to simple basin margins comprising a single border fault. At the rift scale, the evolution of major sediment entry points from hinterland drainage catchments have a dominating effect on gross depositional environments and stratigraphic evolution in both rift margin and rift axis locations. Understanding these major depositional systems is critical to assess syn-rift plays.

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009