Rock-eval pyrolysis, vitrinite reflectance, and kerogen microscopy results from Miocene carbonaceous mudstones and coals in outcrop, McGrath Quadrangle, southwestern Alaska

The Cenozoic Holitna basin is a gravity-defined feature that sits astride the Denali-Farewell fault zone in southwestern Alaska. The basin corresponds to a gravity low in excess of -40 milligals (mGals). No outcrops exist within the footprint of the gravity low and no subsurface data are available; consequently, the stratigraphy and age of its fill are unknown. The Alaska Division of Geological & Geophysical Surveys (DGGS) investigated the shallow gas potential of the basin during the summers of 2000 and 2002 by studying Tertiary coal-bearing rocks exposed along the Denali-Farewell fault zone to the northeast of the basin in the southern McGrath Quadrangle as an outcrop analog to the subsurface stratigraphy of the basin. We visited exposures along Windy Fork Middle Fork River to collect samples for source-rock characterization, including Rock-Eval pyrolysis, vitrinite reflectance measurements, and visual kerogen analysis. Rock-Eval pyrolysis results from carbonaceous mudstone and coal samples along Windy Fork indicate the presence of Type II and Type III kerogen, which are expected to be excellent sources of oil and gas under favorable subsurface conditions. Available thermal maturity data for the samples indicate they are immature for oil and gas, but are in the late pre-oil phase of maturity. If a coal- and carbonaceous-mudstone-bearing succession similar to the rocks discussed in this report from the McGrath Quadrangle are present in the subsurface of the gravity-defined Holitna basin at favorable depths, they can be expected to have significant thermogenic oil and gas generative potential.

Data and Resources

Field Value
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bbox-east-long -154.13548
bbox-north-lat 62.4190
bbox-south-lat 62.40706
bbox-west-long -154.1718
contact-email dggsgis@alaska.gov
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dataset-reference-date [{"type": "publication", "value": "2015-01-01"}]
frequency-of-update notPlanned
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licence ["The State of Alaska makes no expressed or implied warranties (including warranties for merchantability and fitness) with respect to the character, functions, or capabilities of the electronic data or products or their appropriateness for any user's purposes. In no event will the State of Alaska be liable for any incidental, indirect, special, consequential, or other damages suffered by the user or any other person or entity whether from the use of the electronic services or products or any failure thereof or otherwise. In no event will the State of Alaska's liability to the Requestor or anyone else exceed the fee paid for the electronic service or product."]
lineage This lineage was generated by the FGDC CSDGM to 19139 transformation
metadata-date 2015-04-28
metadata-language eng; USA
metadata_type geospatial
old-spatial {"type": "Polygon", "coordinates": [[[-154.1718, 62.40706], [-154.13548, 62.40706], [-154.13548, 62.419], [-154.1718, 62.419], [-154.1718, 62.40706]]]}
progress completed
resource-type dataset
responsible-party [{"name": "Alaska Division of Geological & Geophysical Surveys", "roles": ["pointOfContact"]}]
spatial {"type": "Polygon", "coordinates": [[[-154.1718, 62.40706], [-154.13548, 62.40706], [-154.13548, 62.419], [-154.1718, 62.419], [-154.1718, 62.40706]]]}
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temporal-extent-begin 2002-01-01
temporal-extent-end 2015-01-01
Groups
  • AmeriGEOSS
  • National Provider
  • North America
Tags
  • AmeriGEO
  • AmeriGEOSS
  • CKAN
  • GEO
  • GEOSS
  • National
  • North America
  • United States
  • carboniferous
  • coal
  • energy
  • mcgrath quadrangle
  • miocene
  • pyrolysis
  • resources
  • rock-eval pyrolysis
  • vitrinite
isopen False
metadata_created 2025-09-24T04:51:56.263357
metadata_modified 2025-09-24T04:51:56.263366
notes The Cenozoic Holitna basin is a gravity-defined feature that sits astride the Denali-Farewell fault zone in southwestern Alaska. The basin corresponds to a gravity low in excess of -40 milligals (mGals). No outcrops exist within the footprint of the gravity low and no subsurface data are available; consequently, the stratigraphy and age of its fill are unknown. The Alaska Division of Geological & Geophysical Surveys (DGGS) investigated the shallow gas potential of the basin during the summers of 2000 and 2002 by studying Tertiary coal-bearing rocks exposed along the Denali-Farewell fault zone to the northeast of the basin in the southern McGrath Quadrangle as an outcrop analog to the subsurface stratigraphy of the basin. We visited exposures along Windy Fork Middle Fork River to collect samples for source-rock characterization, including Rock-Eval pyrolysis, vitrinite reflectance measurements, and visual kerogen analysis. Rock-Eval pyrolysis results from carbonaceous mudstone and coal samples along Windy Fork indicate the presence of Type II and Type III kerogen, which are expected to be excellent sources of oil and gas under favorable subsurface conditions. Available thermal maturity data for the samples indicate they are immature for oil and gas, but are in the late pre-oil phase of maturity. If a coal- and carbonaceous-mudstone-bearing succession similar to the rocks discussed in this report from the McGrath Quadrangle are present in the subsurface of the gravity-defined Holitna basin at favorable depths, they can be expected to have significant thermogenic oil and gas generative potential.
num_resources 11
num_tags 17
title Rock-eval pyrolysis, vitrinite reflectance, and kerogen microscopy results from Miocene carbonaceous mudstones and coals in outcrop, McGrath Quadrangle, southwestern Alaska