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.