| Summary: | This dataset consists of a polygon coverage and associated attribute data derived from the onshore portion of the 1996 "Generalized Thermal Maturity Map of Alaska" compiled by M.J. Johnsson and D.G. Howell, which was published as Plate 1 in US Geological Survey Bulletin 2142: "Thermal Evolution of Sedimentary Basins in Alaska". The published map summarizes vitrinite reflectance and conodont alteration index data (both measure the thermal maturity of rocks) into generalized units that can be shown cartographically at 1:2,500,000. This digital dataset includes the 8 map units indicated on the original map. (5 thermal maturity levels; 2 rock or sediment type; 1 "no data"). The data quality of the generalized information is retained, with an attribute value for "certainty" whose value choices are "questioned" or "certain". Additional data retained in a look-up table are the maximum and minimum vitrinite reflectance and conodont alteration index values assigned to each thermal maturity level. This coverage is not intended to be a complete representation of the printed map. It does NOT include the following features: locations of individual vitrinite or conodont sample data points (these data are available in: Johnsson and others, 1992, USGS Open File Report 409, 3 diskettes); faults; offshore maturity data (from dredge and well samples); cities, glaciers, wells; inset maps and subsurface contours for the Colville basin and Cook Inlet; the correlation chart, text or references printed on the map.
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