Outcrop-scale seismic reflection data and lithologic data from oil company platform borings and cores were used to construct paleogeographic maps that depict depositional systems formed during the last glacial-eustatic cycle (~120,000 years to the present). The maps depict depositional systems during the three systems tracts:
highstand (~125,000 to 40,000 yr BP)
lowstand (~40,000 to 16,000 yr BP)
transgressive (~15,000 yr BP to present).
The methodology used to generate these paleogeographic maps is described in the section Methodology. Constraints on timing are provided by radiocarbon dating, oxygen isotope stratigraphy, and biostratigraphy.
Correlation of strata between the different study areas is accomplished using three prominent stratigraphic surfaces. The oldest surface is the Stage 5e maximum flooding surface (marked yellow on seismic profiles). It is a downlap surface in most of the study area and is recognized in outer shelf cores by a sharp increase in abundance of planktonic foraminifera. The highstand systems tract occurs between this flooding surface and the Stage 2 sequence boundary (marked red on seismic profiles). In some areas, another maximum flooding surface associated with the Stage 3 highstand is seen and allows us to separate the highstand systems tract into the early highstand (~125,000 - 80,000 yr BP) and the late highstand (~80,000 - 40,000 yr BP). The Stage 2 sequence boundary is a prominent erosional surface (fluvial incision) and is manifested in cores and platform borings as an abrupt change in lithology, often with an exposure surface, and by a general absence of fossils. The upper surface is the transgressive surface. This surface is best imaged with very high-resolution (chirper and boomer) profiles. In sediment cores collected within valleys the transgressive surface is marked by a sharp lithologic change from fluvial or estuarine deposits to muds containing marine shells. On the inner and middle shelf (outside of incised valleys) the transgressive surface is amalgamated with the Stage 2 sequence boundary and marine muds commonly overlie an exposure surface.
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