Paleochannels in lower Delaware Bay and the Delaware inner continental shelf

Childers, Daniel P.
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University of Delaware
A method is developed for taking older analog seismic profiles and building a database of depths to significant reflection events that can be entered into GIS software to create models of subsurface features. Subsequent maps and three-dimensional (3-D) images of the subsurface can then be visualized allowing for more accurate analysis and interpretation. This methodology is applied to paleochannel networks present in the subsurface beneath the lower portion of Delaware Bay and the bordering Mid-Atlantic inner continental shelf. The project uses older analog seismic profiles to model these paleochannels in ArcGI(TM) and as a 3-D model in ArcScene(TM). To constrain optimal parameters to be used in the subsurface modeling, seafloor depths were determined from the seismic profiles, input into the Geostatistical Analyst routines, and then correlated to existing NOAA DEM bathymetry. Simple kriging for extended areas and Universal Kriging using anisotropy, for paleochannels channels gave the best statistical and visual results. The models of the paleochannels were then entered into ArcScen(TM) to create 3-D views allowing the subsurface geology to be analyzed and interpreted. The modeling results provide better constraints on the geometry of the paleochannels and can be used to better understand the recent geologic evolution of the region in response to sea-level fluctuations. Located under the lower Delaware Bay are three buried drainage systems of the Delaware River the Northern, Central and Southern as suggested by Knebel and Circé (1988). On the inner continental shelf four major subsurface paleochannels of the Delaware River were identified in several seismic profiles collected by Belknap and Kraft (1985), and McGeary et al., 1991; Krantz et al., 1993; 1994). This study improves the understanding of the stratigraphy underlying Delaware Bay and the inner shelf and examines the correlation to the paleochannels within bay and determines the relative ages. The Central paleochannel is the youngest and continues on the shelf as the Blue paleochannel, heading southeast 50 km, where it turns to the east and extends toward Baltimore Canyon. The Southern paleochannel extends as the Orange and appears also to extends toward Baltimore Canyon, is the next oldest. The oldest paleochannel is the Northern which is suggested to connect to the Green on the inner shelf. During the analysis of the seismic profiles along the inner continental shelf, a deeper reflection (40 m to 60 m below sea level) was observed in many of the profiles. This reflection was modeled in the same manner with ArcGIS(TM) Geostatistical Analysis and correlated with onshore strata. Two models were produced: the first used the seismic data above to model a surface, and the second used onshore well data to model surfaces of two likely candidates. Then each of the onshore surface models is projected to connect with the offshore surface model. The best match was the Beaverdam Formation with the overlying Omar Formation. This was then confirmed by using near shore seismic profiles and associated core data. The Beaverdam Formation underlies much of the state of Delaware and Atlantic inner continental.