Publication Date:
2023-09-07
Description:
Cretaceous chert and porcellanite recovered at Site 436, east of northern Honshu, Japan, are texturally and mineralogically similar to siliceous rocks of comparable age at Sites 303, 304, and 307 in the northwest Pacific. These rocks probably were formed by impregnation of the associated pelagic clay with locally derived silica from biogenic and perhaps some volcanic debris. Fine horizontal laminations are the only primary sedimentary structures, suggesting minimal reworking and transport. Collapse breccias and incipient chert nodules are diagenetic features related to silicification and compaction of the original sediment.
Disordered opal-CT (d[101] = 4.09 Å) and microgranular quartz (crystallinity index 〈 1.0) are the two common silica minerals present. Some samples show quartz replacing this poorly ordered opal- CT, supporting the notion that opal-CT does not become completely ordered (i.e., d[101] = 4.04 Å) in some cases before being converted to quartz. The present temperature calculated for the depth of the shallowest chert and porcellanite at this site is 30 °C; this may represent the temperature of conversion of opal-CT to quartz. High reflection coefficients (0.29-0.65) calculated for the boundary between chert-porcellanite and clay-claystone support the common observation that chert is a strong seismic reflector in deep-sea sedimentary sections.
Keywords:
56-436; Calculated, see reference(s); Crystallinity; Deep Sea Drilling Project; Density; Density, dry bulk; Density, grain; DEPTH, sediment/rock; DRILL; Drilling/drill rig; DSDP; DSDP/ODP/IODP sample designation; d-spacing; Glomar Challenger; Impedance, specific; Leg56; Lithology/composition/facies; North Pacific/RIDGE; Opal-CT; Porosity; Pycnometer; Quartz; Sample code/label; Sediment type; see reference(s); Velocity, compressional wave; X-ray diffraction (XRD)
Type:
Dataset
Format:
text/tab-separated-values, 86 data points
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