Citation:

dsdp.proc.69.116.1983

Name: Petrology and geochemistry of silicified upper Miocene chalk at DSDP Site 69-504
Published: 1983
License: https://creativecommons.org/licenses/by/3.0/

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Abstract:

Chert, Porcellanite, and other silicified rocks formed in response to high heat flow in the lower 50 meters of 275 meters of sediments at Deep Sea Drilling Project Site 504, Costa Rica Rift. Chert and Porcellanite partly or completely replaced upper Miocene chalk and limestone. Silicified rock occurs as nodules, laminae, stringers, and casts of burrows, and consists of quartz and opal-CT in varying amounts, associated with secondary calcite. The secondary silica was derived from dissolution of opal-A (biogenic silica), mostly diatom frustules and radiolarian tests.

Temperature data obtained at the site indicate that transformation of opal-A to opal-CT began at about 50°C, and transformation from opal-CT to quartz at about 55°C. Quartz is most abundant close to basement basalts. These silica transformations occurred over the past 1 m.y., and took place so rapidly that there was incomplete ordering of opal-CT before transformation to quartz; opal-CT formed initially with an uncommonly wide d spacing. Quartz shows poor crystallinity.

Chemical data show that the extensively silicified rocks consist of over 96% SiO2; in these rocks, minor and trace elements decreased greatly, except for boron, which increased. Low Al2O3 and TiO2 contents in all studied rocks preclude the presence of significant volcanic or terrigenous detritus. Mn content increases with depth, perhaps reflecting contributions from basalts or hydrothermal solutions. Comparisons with cherts from oceanic plateaus in the central Pacific point to a more purely biogenic host sediment for the Costa Rica Rift cherts, more rapid precipitation of quartz, and formation nearer a spreading center. Despite being closer to continental sources of ash and terrigenous detritus, Costa Rica Rift cherts have lower Al2O3, Fe2O3, and Mn concentrations.

Project(s):

Deep Sea Drilling Project (DSDP)

Coverage:

Median Latitude: 1.226836 * Median Longitude: -83.731731 * South-bound Latitude: 1.226300 * West-bound Longitude: -83.732500 * North-bound Latitude: 1.227200 * East-bound Longitude: -83.730200

Date/Time Start: 1979-09-20T00:00:00 * Date/Time End: 1979-10-07T00:00:00

Event(s):

69-504 * Latitude: 1.226300 * Longitude: -83.732200 * Date/Time: 1979-09-20T00:00:00 * Elevation: -3460.0 m * Penetration: 237 m * Recovery: 10 m * Campaign: * Basis: Glomar Challenger * Method/Device: Drilling/drill rig (DRILL)

69-504A * Latitude: 1.226800 * Longitude: -83.732500 * Date/Time: 1979-09-24T00:00:00 * Elevation: -3458.0 m * Penetration: 277 m * Recovery: 207 m * Campaign: * Basis: Glomar Challenger * Method/Device: Drilling/drill rig (DRILL)

69-504B * Latitude: 1.227200 * Longitude: -83.730200 * Date/Time: 1979-10-07T00:00:00 * Elevation: -3460.0 m * Penetration: 489 m * Recovery: 262 m * Campaign: * Basis: Glomar Challenger * Method/Device: Drilling/drill rig (DRILL)

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

3 datasets

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Datasets listed in this publication series

Hein, JR; Sancetta, CA; Morgenson, LA (1983): (Table 1) Characteristics of DSDP Site 69-504 late Miocene siliceous rocks and associated rocks. https://doi.org/10.1594/PANGAEA.816319
Hein, JR; Sancetta, CA; Morgenson, LA (1983): (Table 3) Geochemistry at DSDP Site 69-504. https://doi.org/10.1594/PANGAEA.816321
Hein, JR; Sancetta, CA; Morgenson, LA (1983): (Table 2) Quartz/(Opal-CT x 8) ratios, quartz crystallinity, opal-CT d-spacings, and opal-CT crystallite sizes across a single calcareous porcellanite chert bed at DSDP Hole 69-504A. https://doi.org/10.1594/PANGAEA.816320