Procedures_Used: The linework was digitized in 1997 from a paper copy of the 1994 map at the U.S. Geological Survey's Alaska Section (Geologic Division) facilities in Anchorage, AK. The original Transverse Mercator projection of the map (Central Meridian: 100*W; Scale factor: 0.926; Reference ellipsoid: (6371204m, 63712004m)) was converted to an Albers equal-area coverage in ARC/INFO (version 7.1.2). The resulting coverage did not align exactly with an Albers equal-area coverage of the Alaskan coastline, so a rubber-sheeting operation was performed using points along the coastline and major rivers to match an Albers equal area projection. Map unit (polygon) locations and attributes were checked by the person responsible for the digitizing, and spot-checked by one reviewer, by comparing a printed copy of the coverage to the published map. Metadata were collected using document.aml v. 7.1.1, distributed by ESRI, Inc.
Revisions: None completed or planned.
Reviews_Applied_to_Data: See Procedures_Used.
Related_Spatial_and_Tabular_Data_Sets:
Other_References_Cited: Kirschner, C.E. 1994. Map Showing Sedimentary Basins in Alaska. Plate 7 in: Volume G-1, "The Geology of Alaska", Geology of North America series (GNA-G1). Geological Society of America, Inc., Boulder, CO. Scale 1:2,500,000.
Notes: The completeness and quality of the geologic data in the digital coverage is that of the published 1994 map, which summarized data collected prior to that date. No recent data have been added. The geographic accuracy of the published map has been slightly degraded by the rubber-sheet operation.
SED_BASINS.PAT COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME INDEXED? 1 AREA 4 12 F 3 - 5 PERIMETER 4 12 F 3 - 9 SED_BASINS# 4 5 B - - 13 SED_BASINS-ID 4 5 B - - 17 MAP_UNIT 30 30 C - - 47 EON 6 6 C - - 53 AGE/PERIOD 30 30 C - - 83 THICKNESS(KM) 4 4 N 1 -
The item 'MAP_UNIT' can have the following 6 possible descriptive values: sedimentary basin; older sedimentary basin; flysch basin, fold belt; flysch basin, deformed; flysch basin, metamorphosed; or volcanic rocks. Areas of Alaska without polygons are those areas underlain by older, basement, granitic, metamorphic or volcanic rocks unrelated to sedimentary basins.
The item 'EON' can have the following 4 possible values: Cz (Cenozoic); Mz (Mesozoic); Mz-Cz (Mesozoic to Cenozoic); or Pz-Cz (Paleozoic to Cenozoic).
The item 'AGE/PERIOD' can have the following 3 possible values: Late Tertiary and Quaternary; Lower Tertiary; Jurassic to Cretaceous; or no value (no period specified).
The item 'THICKNESS(KM)' can have the following 8 possible values: 0.1, 1.1, 3.1, 5.1, 7.1, 9.1, 11.1, or 13.1. These values are derived from isopachs of basin fill and/or the thicknesses interpreted from Bouger gravity lows, within given map units. Since a given map unit or basin contains varying thicknesses of fill, the user must query appropriately to find the range of interest. For example, to find areas with a fill thickness between 3 and 5 kilometers, select "thickness(km) > 3 and thickness(km) < 5".