In situ velocities in pelagic carbonates; new insights from Ocean Drilling Program Leg 130, Ontong Java Plateau

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doi: 10.1029/93JB00013
Author(s): Urmos, Jozsef; Wilkens, Roy A.
Author Affiliation(s): Primary:
University of Hawaii, School of Ocean and Earth Science and Technology, Honolulu, HI, United States
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 98(B5), p.7903-7920. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. Univ. Hawaii, Sch. Ocean and Earth Sci. and Technol., Contrib. No. 3050. 36 refs.; illus. incl. 3 tables
Summary: Ocean Drilling Program Leg 130 returned an extensive suite of in situ borehole logging and closely spaced shipboard physical properties measurements from four sites drilled in carbonate-rich pelagic oozes and chalks on the Ontong Java Plateau. Using these data, we evaluated factors responsible for observed differences between laboratory data and in situ values. Laboratory and log differences for bulk density/porosity are small and nearly constant and can be accounted for by hydraulic rebound of pore fluid following sediment recovery. Evidence for mechanical rebound of sediments was not observed. Velocity-porosity relationships cannot be used to indirectly correct laboratory velocities to in situ because fundamental assumptions required for rebound corrections are not satisfied. Velocity-porosity systematics are also complicated by foraminiferal intraparticle porosity variations. We derived empirical laboratory velocity corrections using log and laboratory velocity differences expressed as functions of depth and effective pressure. We tested the velocity corrections using data for carbonates recovered from Ocean Drilling Program Sites 704, 722, and 762; comparisons with logs show that corrected velocities accurately estimate in situ values for oozes and chalks (CaCO3 >60%). For applications to unlogged Deep Sea Drilling Project Leg 85 sites, igneous basement travel times calculated using corrected velocities agree with acoustic basement travel times from seismic records, implying that corrected velocities are realistic in situ estimates. At Site 574, we used our corrected velocities to reevaluate previous lithostratigraphic and seismostratigraphic correlations based on mechanical rebound-corrected velocities. The new velocities correlate reflectors to progressively greater core depths. Although changes are minor above 200 m below seafloor, the lowest assigned reflector is shifted 36 m deeper to more closely coincide with a diagenetic boundary and acoustic basement correlates with igneous basement instead of with postulated high-impedance reflectors within the sediments. Copyright 1993 by the American Geophysical Union.
Year of Publication: 1993
Research Program: ODP Ocean Drilling Program
Key Words: 07 Marine Geology and Oceanography; Carbonate sediments; Clastic sediments; Elastic properties; Experimental studies; In situ; Leg 130; Marine sediments; Ocean Drilling Program; Ontong Java Plateau; Ooze; Pacific Ocean; Pelagic sedimentation; Physical properties; Porosity; Sedimentation; Sediments; Velocity; Well-logging; West Pacific
Coordinates: N001906 N033626 E1613538 E1563728
Record ID: 1993019282
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