High-Resolution Sequences in Upper Cretaceous Shelf, Ramp and Incised Paleovalley Deposits - Comparisons with Holocene to Pleistocene Analogs
Comparative studies used facies analysis, process sedimentology, and well-logs to interpret environments and define high-resolution sequences in core from Upper Cretaceous and Quaternary analogs. The scale and stacking arrangements of beds, bedsets, parasequences and systems tracts are compared for several upstream to shelf analog settings.
Ancient coastal systems were evaluated in a core (CR-675) from Craven County, North Carolina (NC), that penetrated 278m of Upper Cretaceous section. Above a lower (?) Santonian exposure surface, a nearly complete (185 m) middle (?) Santonian to middle Campanian section shows an upward progression of landward (upstream) to more seaward facies. These include channel belt, levee, backswamp, crevasse splay, bayfill, marginal marine, marine deltaic?/shoreface, and mid-to outer shelf parasequences.
Analogs for ancient coastal systems were derived from 28 rotosonic cores (USGS/NC Coastal Cooperative) that penetrated Quaternary deposits in an area that includes the Suffolk paleoshoreline (MIS5), the Outer Banks barrier islands, and several incised paleovalleys. Regional-scale cross sections were based on correlations established from multiple lines of evidence - process sedimentology, facies analysis, foraminiferal biofacies, amino acid racemization and carbon-14 ages, geomorphology, and offshore geophysics. Studies in other Holocene settings provide analogs for Cretaceous fluvial and bayfill deposits.
Comparisons show that middle Campanian shelf parasequences, generated in a highstand systems tract (HST), are very similar to the shoaling upward marine fill generated in the paleo-Roanoke valley during the Late Pleistocene to Holocene transgression. Middle Campanian Tar Heel Sequence II (77.2-77.8 Ma) has a thin (3m), basal, retrogradational, transgressive systems tract (TST) that fines upward into a maximum flooding surface (MFS). The overlying HST (29m) coarsens upward from an aggrading (4m) to prograding (25m) shelf with two progressively coarser and thicker (9m, 16m) parasequences.
The Late Pleistocene to Holocene TST overlies lowstand fluvial channel deposits and includes fluvial/deltaic (bayhead delta?) and estuarine facies. These are truncated by a marine transgressive surface (TS). This TS is overlain by thin retrogradational shelf deposits that fine up into a MFS. Above this MFS, is a prograding, shoaling upward shelf to shoreface sequence comparable in scale and sequence to its Campanian analog.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009