GEOLOGICAL SOCIETY OF THE PHILIPPINES

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SEQUENCE STRATIGRAPHY IN HIGH ACCOMMODATION SETTINGS

 

Stephen Flint, John Howell, Duncan McIlroy and David Hodgetts
 STRAT Group, Department of Earth Sciences, University of Liverpool,
Liverpool L69 3BX, U.K. (E-mail: flint@liv.ac.uk)

 

ABSTRACT

        Sequence stratigraphic analysis in high accommodation settings is more difficult than in conventional settings where relatively slow subsidence is convolved with high frequency eustatic sea level fluctuations to produce ‘classical’ sequences, systems tracts and parasequences. Sequence boundaries are marked by subaerial erosion/exposure and tidal facies are restricted to times of early base level rise, usually within incised valleys. By contrast, in high accommodation settings such as extensional and strike-slip basins (common in SE Asia), sequence architecture may be quite different. The interplay of rapid and differential subsidence, complex structural topography and related sediment routing/supply leads to the dominance of aggradational stacking patterns, and suppression of subaerial erosional/exposure unconformities. Sequences thus become asymmetrical and dominated by the base level rise component. Parasequence boundaries may be recognisable only on subtle ichnofabric criteria. Additional effects of structural topography and fault segmentation may include the long-term maintenance of tidal deposition through complete base level cycles, thus reducing bathymetric range of facies. This makes the reliable delineation of key surfaces difficult as basinward and landward facies shifts are therefore suppressed. Syn-sedimentary growth faulting results in either thickening or addition of parasequences in the hangingwalls, resulting in correlation difficulties. Sequence stratigraphic analysis in the high accommodation context requires new rulebases of expected responses to combinations of external variables. The approach is still critically important because facies-related permeability distribution and permeability extremes are related to key surfaces and stratal geometries and can therefore be predicted.

 
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