Physical properties of a porcellanite layer (Southwest Indian Ridge) constrained by geophysical logging.

Gerland, Sebastian, Kuhn, Gerhard and Bohrmann, Gerhard (1997) Physical properties of a porcellanite layer (Southwest Indian Ridge) constrained by geophysical logging. Marine Geology, 140 (3-4). pp. 415-426. DOI 10.1016/S0025-3227(97)00046-7.

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Abstract

A distinct porcellanite layer from the Southwest Indian Ridge intercalated in Pleistocene diatom ooze was studied using nondestructive physical property measurements and sedimentological data. This bed was sampled by two piston cores at a water depth of 2615 m. The 3–5 cm thick porcellanite layer appears in the cores at a depth of 6.03 m (Core PS2089-2) and 7.73 m (Core PS2089-1) below the seafloor. Due to its characteristic physical properties the porcellanite bed can be detected with core measurements, and its distribution and lateral extent mapped with echosounding. The physical index properties, wet bulk density and electrical resistivity, increase significantly across this bed. Magnetic susceptibility is used to compare the lithological units of both cores and to distinguish whether resistivity anomalies are caused by a higher amount of terrigenous components or by the presence of porcellanite. The porcellanite has the special characteristic to affect a positive anomaly in resistivity but not in susceptibility. Most marine sediments, in contrast, show a positive correlation of magnetic susceptibility versus electrical resistivity; therefore a combination of electrical resistivity and magnetic susceptibility logs yields a definite detection of the porcellanite bed. Images from the X-ray CT survey indicate that the porcellanite is lithified and brittle and fragmented when the piston corer penetrated the bed.

Document Type: Article
Keywords: physical properties; porcellanite; marine sediments; nondestructive methods; high-resolution methods; cores
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
AWI
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/S0025-3227(97)00046-7
ISSN: 0025-3227
Expeditions/Models/Experiments:
Date Deposited: 01 Jul 2019 13:02
Last Modified: 01 Jul 2019 13:02
URI: http://oceanrep.geomar.de/id/eprint/47059

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