NON-MARINE FACIES OF CONIACIAN TO SANTONIAN AGE - UPPER CRETACEOUS BLACK CREEK GROUP, NORTH CAROLINA COASTAL PLAIN: WHERE DO THESE FIT IN THE SEQUENCE STRATIGRAPHIC FRAMEWORK?

Establishing the sequence stratigraphic framework for non-marine facies in the Upper Cretaceous of North Carolina is difficult. Available for correlation are discontinuous outcrops along the Cape Fear River and five deep core holes drilled by the U.S. Geological Survey, with accompanying geophysical logs. Three updip cores, from south to north – the Elizabethtown, Smith Elementary and Hope Plantation sites - include thick (8 to125 m) non-marine deposits that thicken northward. The Elizabethtown site, located in the Cape Fear River Basin near the outcrops, includes the thinnest (8 m) non-marine section.

For the three updip sites, cores were described in detail using a process-based approach; graphic logs were produced and compared with gamma ray log response patterns. A facies analysis was conducted and integrated with sequence stratigraphy. Surfaces were identified, marine facies were assigned to sequences using nannofossil zones and Sr-isotope ages, and systems tracts were interpreted. Non-marine facies were differentiated into channel and flood basin deposits, with further subdivisions into paleosol, backswamp, lacustrine, levee, crevasse splay and other facies. Composition, texture, sorting and fabric assisted in establishing vertical patterns.

In the three cores, the non-marine facies are associated with the Coniacian to Santonian, Pleasant Creek I and II sequences. Non-marine facies exposed in upstream outcrops on the Cape Fear River (the former Cape Fear Formation) correlate with fluvial facies in the Elizabethtown core that are interpreted as the highstand systems tract (HST) of the Pleasant Creek II sequence. In the Smith core, the relationship between the thick non-marine interval and marine facies tentatively assigned to the Pleasant Creek I sequence is complex; at Hope Plantation, marine units are absent.

The non-marine section will be examined in the context of allocyclic controls that include both tectonic events and sea level change. Stratigraphic position with respect to lowstand systems tracts (LST), HST, falling stage systems tracts (FSST), and aggradational systems tracts will be evaluated. The chronostratigraphic slab model proposed by Pattison (2010) will be examined. Until pollen studies confirm age relationships, interpretations remain ambiguous.