A Process-Based Approach That Integrates Sequence Stratigraphy, Sedimentary Facies and Landform Analysis for the Early Pleistocene Surry Paleoshoreline Complex: An Analog for Potential Reservoirs — Atlantic Continental Margin, North Carolina, USA

Abstract

Three-dimensional (3D) subsurface mapping techniques were used to characterize sedimentary facies, establish a sequence stratigraphic framework, and define surficial landforms for an Early Pleistocene relict landscape that includes the Surry Paleoshoreline Complex. The method combines comprehensive landscape analysis with targeted subsurface coring along key transects that crosscut landforms. A new, standardized method of textural classification, facies coding and graphic logging (Farrell and others, 2013) useful in interpreting process-generated stratigraphic sequences helped define facies and the hierarchy of bounding surfaces in the Quaternary section underlying landform elements in parts of four 7.5 minute quadrangles. To define stratigraphy, datasets included: Geoprobe® cores (+2300 ft >80% recovery, continuous discrete samples); wireline-mud-rotary/split-spoon cores (4085 ft - poor recovery; with gamma logs), and outcrops at a quarry. Correlation was difficult but several 87Sr/86Sr isotope dates provided a time frame and helped recognize stratigraphic patterns. To interpret landform elements and define depositional systems, high-resolution LiDAR (2006 bare earth – vertically accurate to 25 cm per 1m × 1m tile) data was acquired (www.ncfloodmap.com), converted to rasters, and processed to produce hillshade, slope and contours (0.25 and 0.5 m). This was used with 2011 orthoimagery. Results indicate that the Surry paleoshoreline marks the transition from normal to forced regression, and the position where the High-Stand Systems Tract is replaced seaward by the Falling Stage Systems Tract. The sequence boundary (SB) is regional in scale and is marked by a bioclastic gravel. Overlying lithofacies include offshore shelf, shoreface, barrier island-related, and estuarine facies; these are identified and correlated, providing a “3D” depositional characterization of the sequence. A proxy for permeability from standardized textural fields is applied to cross sections to demonstrate the aquifer/reservoir potential of the facies. Stratigraphically controlled reservoir rocks commonly occur in sedimentary successions including sand lithosomes that formed in coastal zone environments (e.g., barrier-island, shoreface sands, and tidal inlets). The integration of multi-dimensional techniques provides an analog for recognizing nearshore reservoirs, understanding heterogeneity distribution, and the context of interpreting core relative to paleo-landscape position.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016