Petrography and diagenesis of deep-sea cherts from the central Atlantic

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doi: 10.1002/9781444304855.ch14
Author(s): von Rad, Ulrich; Rosch, Heinrich
Author Affiliation(s): Primary:
Bundesanstalt fuer Bodenforschung, Hanover, Federal Republic of Germany
Volume Title: Special Publication of the International Association of Sedimentologists
Source: Special Publication of the International Association of Sedimentologists, 1, p.327-347. Publisher: Blackwell, Oxford, International. ISSN: 0141-3600. ISBN: 978-1-444-30485-5 CODEN: SPISDS
Note: In English; illus. incl. tables
Summary: Chert layers of Cenomanian to Early Miocene age and covered by 100-700 m of sediments were recovered by Leg 14 of the Deep Sea Drilling Project. Four types of silicified sediments can be distinguished by optical, X-ray, infrared absorption, scanning and transmission electron microscope analysis. (I) Clay-rich lussatite porcelanite (Maastrichtian-Lower Miocene). (II) Bedded, carbonaceous, more or less zeolitic lussatite-chalcedony-quartz porcelanite (Upper Cretaceous-Palaeocene). (III) Faintly bedded, dolomitic and pyritic palygorskite-lussatite (-quartz) porcelanite (mostly Palaeocene). (IV) Homogenized, ferruginous quartz (-lussatite) chert (Middle-Upper Cretaceous). Remobilization of dissolved, mainly biogenous opal-A and precipitation of lussatite blades, randomly crystallizing in microspherules, are the first steps of chertification. The following diagenetic sequence is suggested. (1) Biogenous opal-A in siliceous oozes and ± zeolitic (marl) muds → (2) 'precursor stage' (semi-consolidated porcelaneous mudstone with well-preserved, tangentially welded siliceous organisms, incipient mass polarization and precipitation of lussatite spherules, palygorskite and/or clinoptilolite) → (3) 'immature' lussatite porcelanite (type I) → (4) type II or (the palygorskite-rich) type III porcelanite → (5) 'mature' quartz chert (type IV) with almost all siliceous fossils obliterated. This maturation involves a gradual decrease of the lussatite: quartz ratio from 28 (type I) via 5-14 (II-III) to about zero (IV). In the sites investigated, the maximum age of well-preserved skeletal opal-A ranges from 20 to 40 million years. Starting from the deposition of suitable sediments, it takes at least 20-50 million years to produce the porcelanites of types I-III and at least 70-90 million years to produce quartz cherts (type IV). Abstract Copyright (1974), The International Association of Sedimentologists.
Year of Publication: 1974
Research Program: DSDP Deep Sea Drilling Project
Key Words: 07 Marine Geology and Oceanography; Atlantic Ocean; Biogenic; Cenomanian; Cenozoic; Central; Chemically precipitated rocks; Chert; Chertification; Clastic rocks; Clastic sediments; Cretaceous; Deep Sea Drilling Project; Diagenesis; Framework silicates; Leg 14; Lower Miocene; Lussatite; Maturation; Mesozoic; Microspherules; Miocene; Mud; Neogene; Ooze; Opal; Petrography; Porcellanite; Sedimentary petrology; Sedimentary rocks; Sediments; Silica minerals; Silicates; Siliceous; Tertiary; Upper Cretaceous; Zeolitic
Record ID: 1975026001
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute.

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