Filters: Tags: Chalcedony (X)
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Temporal and spatial sources of silica for chert remain poorly constrained. Modern sources to the worlds oceans include silica in rivers > aeolian (dust) deposition > sea floor vents and submarine weathering. However, changes in aridity and dust flux during the Phanerozoic may explain variations in the ocean silica cycle and times and places of chert formation. The chemistry of fine quartz dust (FQD) provides a chemical mechanism for the transformation of FQD to polymorphs of silica in chert; FQD is readily dissolved, then reprecipitated as Opal-A by either biotic or abiotic processes. An unequivocal relation between increases in dust flux and biogenic opal-A in the western Pacific Ocean during the past 200 kyr...
The Tyonek area in the northwestern Cook Inlet trough is rich in petroleum, coal, geothermal, aggregate, and timber resources, but the detailed geologic mapping necessary for planning future resource development exists only in part of the area. This report and geologic map provide basic surficial-geologic information useful for exploiting those resources and planning future utility corridor developments. In addition to mapping of surficial geologic units, we provide discussion of strategraphic evidence pertaining to physiographic relations and geologic history of volcaniclastic deposits derived from ancestral Mount Spurr, multiple phases of Quaternary glacial activity, Chakachatna River valley landslide complexes...
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