A catastrophic meltwater flood event and the formation of the Hudson Shelf Valley

This paper is not subject to U.S. copyright. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 246 (2007): 120-136, doi:10.1016/j.palaeo.2006.10.030.The Hudson Shelf Valley (HSV) is the largest physiographic feature on the U.S. mid-Atlantic continental shelf. The 150-km long valley is the submerged extension of the ancestral Hudson River Valley that connects to the Hudson Canyon. Unlike other incised valleys on the mid-Atlantic shelf, it has not been infilled with sediment during the Holocene. Analyses of multibeam bathymetry, acoustic backscatter intensity, and high-resolution seismic reflection profiles reveal morphologic and stratigraphic evidence for a catastrophic meltwater flood event that formed the modern HSV. The valley and its distal deposits record a discrete flood event that carved 15-m high banks, formed a 120-km2 field of 3- to 6-m high bedforms, and deposited a subaqueous delta on the outer shelf. The HSV is inferred to have been carved initially by precipitation and meltwater runoff during the advance of the Laurentide Ice Sheet, and later by the drainage of early proglacial lakes through stable spillways. A flood resulting from the failure of the terminal moraine dam at the Narrows between Staten Island and Long Island, New York, allowed glacial lakes in the Hudson and Ontario basins to drain across the continental shelf. Water level changes in the Hudson River basin associated with the catastrophic drainage of glacial lakes Iroquois, Vermont, and Albany around 11,450 14C year BP (~ 13,350 cal BP) may have precipitated dam failure at the Narrows. This 3200 km3 discharge of freshwater entered the North Atlantic proximal to the Gulf Stream and may have affected thermohaline circulation at the onset of the Intra-Allerød Cold Period. Based on bedform characteristics and fluvial morphology in the HSV, the maximum freshwater flux during the flood event is estimated to be ~ 0.46 Sv for a duration of ~ 80 days.Support for N. Driscoll was provided by the Office of Naval Research and the National Science Foundatio

Use of a reciprocal transplant study to measure the rate of plant community change in a tidal marsh along a salinity gradient

The relationship between environmental factors and the spatial distribution of maintained and actively used burrows of the grapsid crab Helograpsus haswellianus was studied at three saltmarsh sites in southeast Queensland, Australia. The sites had been modified by runnelling for mosquito-control, a method that transports low-amplitude tides to areas of saltmarsh. The study investigated the relationship between burrow density, burrow aperture size, and runnelling, as well as the effect of flooding or non-flooding tides and distance from a tidal source. Responses differed at the three sites. The most consistent pattern across all sites was that active burrows were most numerous between 30 and 50 m from the saltmarsh / mangrove interface at the landward side of the tidal source. At particular sites, there were significant relationships between burrow aperture size, tidal period, and the presence of runnels. Generally, few small burrows occurred low on the shore, while larger burrows were distributed across the shore to 50 m. At naturally dry sites, more burrows occurred within 5 m of the runnel, whereas at naturally wet sites, fewer burrows were found close to the runnel. As runnels transport low-amplitude tides, moisture conditions required for burrowing may very between flooding and non-flooding tides. Overall, the influence of tides on the density of crab burrows and their aperture sizes was of more importance than the presence of runnels alone

Texas A & M University Radiocarbon Dates III

This material was digitized as part of a cooperative project between Radiocarbon and the University of Arizona Libraries.The Radiocarbon archives are made available by Radiocarbon and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform February 202

29. DATA REPORT: DEPTH AND DENSITY CORRECTIONS FOR LEG 150 SHIPBOARD GRAPE DATA 1

ABSTRACT Shipboard gamma-ray attenuation porosity evaluator (GRAPE) records from Ocean Drilling Program (ODP) Leg 150 contain inaccuracies in both depth and density caused by pervasive gas expansion voids and other coring disturbances. This paper describes the sequential procedure used to correct Leg 150 GRAPE data and presents corrected GRAPE data for Holes 902D, 903A, 904A, and 906A. Corrections to shipboard GRAPE depth records were made for voids and for measurements taken from beyond the end of a section. Corrections to shipboard GRAPE densities were made for (1) narrow core diameters, (2) saline pore fluids, and (3) drill slurry. Records of voids and partially filled voids are identified by implementation of a minimum wet bulk density cutoff obtained from Leg 150 gravimetric density measurements. Records failing to meet the minimum density criterion are identified, tallied, and subtracted from the shipboard GRAPE data on a core-by-core basis. Density corrections for undersized core and for the Compton mass attenuation coefficient of pore-filling fluid are taken from earlier works; a new deterministic method of correcting for drill slurry is derived. Corrected data are shown to closely match gravimetric and downhole log bulk density records and visual estimates of depth corrections. Results will be useful to sedimentologists, biostratigraphers, and geophysicists using Leg 150 data. Future physical properties specialists working in gassy sediments should find this work of particular interest