Regional Seismic Architecture Tied to Cores: Results from IODP Exp313
Abstract
Siliciclastic sediments at passive margins contain stratal discontinuities at many scales; most can be imaged in seismic profiles. Regional unconformities associated with lowering of baselevel (‘sequence boundaries’) are of special importance because they provide the means to objectively divide the stratigraphic record, and intervening sequences provide the basis for evaluating controls on facies successions and overall sedimentary architecture. Furthermore, sequences of similar age and shape at margins of contrasting tectonic and sedimentary histories suggest eustatic control, though this needs to be tested. IODP Exp313 was designed to contribute to such a test by determining the age and facies of sediments cored at several locations within mid-Tertiary sequences ~45-65 km offshore New Jersey. The reliability of seismic-core correlations essential to this effort required high core recovery, high resolution seismic data, and techniques for matching the two; here we report progress in this effort. Three holes were drilled and logged in ~35 m of water in May-July 2009. Roughly 9500 km of profiles were examined and correlated to these and 6 additional sites drilled previously on the outer shelf and upper slope. 13 additional holes drilled into correlative sediments on the adjacent coastal plain provided up-dip facies and age control, though onshore seismic data are lacking. Prior studies identified seismic sequence boundaries at the NJ margin on the basis of seismic onlap/offlap and ties to drill cores on the continental slope. 15 regionally mapped reflectors intersect the Exp313 sites, and as a first step in tying each to a feature in a core, stacking velocities from the processing of seismic data passing through Exp313 sites were used to derive an acoustic travel time to depth-below-seafloor conversion. This relationship provided expectations of depths at which surfaces and/or facies changes would be found. Typically these occur within 5-10 m of a probable match to features in the cores or to various properties measured by wireline logs and/or the Multi-Sensor Core Logger. Within clinoform top-set beds these reflectors often match transgressive or regressive facies and an accompanying change in density over a depth of 10 cm or less. Finer toe-set strata seaward of clinoform slopes contain beds of gravity-transported sediment where again abrupt changes in bulk density is a typical cause of acoustic reflections. A previously mapped 500 km2 seismic surface ties to the deeply eroded core of a clinoform buildup that failed locally and was redeposited in mass-flow deposits 10's of km seaward of its original location; that it can be traced elsewhere to an intact deposit underscores the importance of along-strike mapping that guards against hasty conclusions of eustatic influence. Facies changes separated by less than 5 m are difficult to link to one in a group of closely-spaced reflectors. Physical properties measured in core material or derived from wireline logs will be used in the future to develop synthetic seismograms and refine core-log-seismic correlations further.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP11E1463M
- Keywords:
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- 1641 GLOBAL CHANGE / Sea level change;
- 3025 MARINE GEOLOGY AND GEOPHYSICS / Marine seismics;
- 8169 TECTONOPHYSICS / Sedimentary basin processes