Integration of Seismic, Log, and Core Data into a Sequence Stratigraphic Framework for the Miocene of the New Jersey Shallow Continental Shelf

Abstract:

IODP Expedition 313 (New Jersey shallow shelf) cored a 3-hole transect across Miocene seismic clinothems (prograding sigmoidal sequences) in topset, foreset, and bottomset locations, providing an opportunity to integrate seismic, log, and core data into a sequence stratigraphic framework. We recognize sequence boundaries (SB), stratal surfaces, and systems tracts on seismic profiles by reflector terminations and independently in the cores by integrating studies of core surfaces, facies successions, facies stacking patterns, benthic foraminiferal water depth changes, downhole and core logs, and chronostratigraphic ages. Sampling of the foresets, where the sequences are thickest, allows us to evaluate sequence stratigraphic models. We link seismic SB to impedance contrasts, as suggested by long-held tenants of sequence stratigraphy. Transgressive surfaces (TS) and SB are merged in the topsets, and are overlain by deepening/fining upward transgressive systems tracts (TST) and coarsening/shallowing upward highstand systems tracts (HST). Drilling through the foresets yields thin lowstand systems tracts (LST), thin TST, and thick HST, contrasting with previously published seismic stratigraphic predictions of thick LST and thin to absent TST. TS are recognized by upsection changes from coarsening to fining upward, and Maximum Flooding Surfaces by changes from fining to coarsening upward successions. Despite challenges posed by shallow-water sediments, we derive a chronology using integrated Sr-isotopic and bio- stratigraphy (calcareous nannoplankton, diatoms, and dinocysts), with typical age resolution of ±0.5 Myr. We find little evidence for correlative conformities on the paleoshelf. We do not resolve the issue of fractal versus hierarchical order, but our data are consistent with arrangement into orders based on Milankovitch forcing on scales driven by eccentricity (400, 100 kyr) and obliquity (1.2 Myr). Sequences are generally 1.2 Myr in duration, but sequence m5.4 (17.7-16.5 Ma) is a composite of three 100-400 kyr-scale sequences. Sequences on the New Jersey shallow shelf were preserved during times when benthic foraminiferal oxygen isotopic variations were dominated by 100 kyr cycles, but tend to be eroded away during 41 kyr-dominated worlds.