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Blum, Mike1
(1) Louisiana State University, Baton Rouge, LA

ABSTRACT: Signatures of Climate vs. Sea-Level Change in Quaternary Incised Valley-Fill Successions: Examples from the Texas Gulf Coast

Recognizing the signatures of climate vs. sea-level change within incised valley fills has become increasingly important. For Quaternary analog systems, reconstructions of changes through time in long profiles, as geometric representations of former floodplain surfaces, play key roles in understanding the relative importance of climatic vs. sea-level controls.
Based on data from river systems of the passive margin Texas Coast, the fundamental signature of climatically-modulated changes in discharge and sediment load is illustrated by downstream continuity of long profiles, stratigraphic units, and component facies. This continuity extends from upstream, where sea level is not an issue, downstream to where sea-level change becomes increasingly important. Conversely, the influence of sea-level change is shown by downstream crossovers in long profiles and systematic changes in stacking patterns for stratigraphic units that represent different periods within a eustatic cycle.
Sea-level change is a necessary condition for large-scale incision and partitioning of incised valleys as channels extend basinward, or large-scale valley filling as channels shorten during sea-level rise, but climate changes in the hinterland trigger such events. Interactions between climate and sea-level change therefore control changes in accumulation space and resultant valley-fill stratigraphic architecture. However, preservation in the stratigraphic record reflects controls that operate over different time scales. Upstream from a passive margin flexural hinge, preservation space is zero, and the record will be eroded away. Preservation space increases downstream and preservation of the signatures of climate vs. sea-level change depends on how rapidly the record subsides below the maximum lowstand depth of incision.


AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.