Sequence stratigraphy of the mid-Atlantic coastal plain: an evaluation of eustasy, sediment supply variations, and passive-aggressive tectonism

Abstract

This study uses high resolution geochronology (from biostratigraphy and Sr-isotope age estimates), lithofacies analysis (from continuous coreholes), and geophysical log correlations to develop a detailed framework of sequence and facies distribution across the U.S. mid-Atlantic margin. This allows the evaluation, and quantification (through one-dimensional backstripping), of the influence of eustatic, tectonic, and sediment supply changes on the Late Cretaceous-Pleistocene U.S. mid-Atlantic margin and the post-impact section of the late Eocene Chesapeake Bay Impact Structure (CBIS). Studies of late Cretaceous sequences from the New Jersey Coastal Plain provide a long-term (35 myr), high resolution ([greater than] 1 myr) record of paleodeltaic evolution on the New Jersey Coastal Plain and document five primary phases of margin evolution in response to eustatic change, two long-lived fluvial axes, variations in sediment budget, and thermoflexural basement subsidence. This study demonstrates the facies variability of mixed-influence (wave- and tide- influenced) deltaic systems, but also documents the long-term stability of deltaic facies systems on the 106-107 yr scale, with cyclically repeating systems tracts controlled by eustatic change. Studies of the Cenozoic southern mid-Atlantic Coastal Plain and CBIS post-impact section reveal significant unconformities and the discontinuous preservation of sequences during the Oligocene, lower Miocene, and late-middle Miocene, when coeval deltaic sections in New Jersey are thick and widespread, implicating regional "passive-aggressive" non-thermal tectonic changes. We explain these observations by the differential movement (uplift and excess subsidence) of basement structures in response to variations in intraplate stress. Stratigraphic observations provide low-end estimates of uplift as 10-50 m/ 1-5 myr, while backstripping quantifies periods of excess subsidence of 10-75 m/5-10 myr. Comparison of CBIS and regional backstripped records shows the post-impact evolution was not only dominated by eustasy and regional tectonics, but also the time-dependent compaction of impact-generated materials responsible for excess subsidence on the scale of 285 +/- 50 m in the late Eocene that progressively decreased to 20 +/- 15 m by the late Miocene. These studies demonstrate that while eustasy provides the template for sequence deposition globally, regional tectonics (uplift and subsidence), local effects (impact processes) and sediment supply dictate the regional preservation of sequences.