Seismic stratigraphy and quaternary evolution of the New York Bight Inner Continental Shelf

Abstract

Approximately 5,300 km of digitally recorded high-resolution, nested, single-channel, seismic-refection data (2.46 m³ watergun, 200-500 Hz Geopulse acoustic source, and a CHIRP 2-7 kHz subbottom profiler) and coincident sidescan-sonar data collected over the New York Bight Apex on the U. S. Atlantic inner continental shelf were analyzed to develop a better understanding of the Quaternary evolution of this inner continental shelf environment. Interpretation of the subbottom data reveals several internal reflectors, all of which are unconformities. The deepest reflector termed R7, identified in this data is a regional angular unconforming truncating the underlying Cretaceous-Tertiary coastal plain sediments. Reflector R7 was formed by multiple glacio-eustatic sea-level oscillations occurring during the Pleistocene. Incised into R7 are two major channels, an ancestral Hudson Shelf Valley and a second unnamed channel 20 km east. The geometry of reflector R7 has exerted the greatest control over the Quaternary evolution of the shelf by limiting the accommodation space available for sediment accumulation. Quaternary sediment thicknesses overlying R7 range from 0 adjacent the New Jersey shoreline and over a relative bathymetric high south of Long Island to >70 meters in the Hudson Shelf Valley thalweg. Six internal reflectors above R7 have been identified within the Quaternary sediment deposit. Three of the reflectors (R6, R5 and R4) are limited to the partially unfilled channel of the Hudson Shelf Valley and are likely the result of glacio-fluvial processes during emergent periods prior to the late Wisconsin glacial maximum. Smaller paleo-channels within the Quaternary section have been preserved north and east of the Hudson Shelf Valley. Where the Quaternary unit is thicker, channels downcut into one another, resulting in only partial preservation of the individual channels. Truncating the channels is internal reflector R2, a laterally continuous reflector which has been interpreted as the Holocene marine flooding transgressive surface. The early Holocene facies above reflector R2, termed unit U2, ranges from 0-10 meters (on average <3 meters). Above unit U2 is the shallow reflector, R1, which is discernable within a meter of the sea floor and represents late Holocene ephemeral sediments being eroded from older units and continuously reworked by modern marine processes.