Zircon U-Pb geochronology for bedrock samples from the West Susitna STATEMAP project, southcentral, Alaska

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Frequently anticipated questions:


What does this data set describe?

Title:
Zircon U-Pb geochronology for bedrock samples from the West Susitna STATEMAP project, southcentral, Alaska
Abstract:
Zircon U-Pb geochronology for bedrock samples from the West Susitna STATEMAP project, southcentral, Alaska, Raw Data File 2026-8, presents zircon uranium-lead (U-Pb) geochronologic data analyzed using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The Alaska Division of Geological & Geophysical Surveys (DGGS) staff collected ten samples for U-Pb dating during the 2024 field season as part of the West Susitna STATEMAP project. The project is a 1:50,000-scale geologic mapping initiative to characterize geology, assess geologic hazards, and investigate tectonic features within a region of increasing interest for resource development, alternative energy, and recreation. The study area lies in the West Susitna region of southcentral Alaska. It spans approximately 500 mi2 across the Tyonek C-3, C-4, D-4, and D-5 quadrangles, including approximately 50 miles of the proposed West Susitna Access Corridor, which connects Anchorage to the Happy River valley on the western margin of the Susitna Basin. Geochronological analyses were obtained to constrain the ages of mapped bedrock units and support tectonic interpretations in the map area. These data are provided as a Raw Data File under an open end-user license and are available on the DGGS website: http://doi.org/10.14509/31972.
Supplemental_Information:
analytical data:    Analytical lab data spreadsheets and accompanying data dictionary.	
summary data:    Summary data spreadsheet and accompanying data dictionary.
  1. How might this data set be cited?
    Gillis, R.J., Walser, S.L., Bernt, J.D., and O'Sullivan, P.B., 2026, Zircon U-Pb geochronology for bedrock samples from the West Susitna STATEMAP project, southcentral, Alaska: Raw Data File RDF 2026-8, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 9 p.
  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -151.957742
    East_Bounding_Coordinate: -151.064110
    North_Bounding_Coordinate: 61.943743
    South_Bounding_Coordinate: 61.641734
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 2024
    Ending_Date: 2026
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: spreadsheet
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a point data set.
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.0000001. Longitudes are given to the nearest 0.0000001. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is WGS84.
      The ellipsoid used is WGS 84.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.257223563.
  7. How does the data set describe geographic features?
    rdf2026-8-UPb-data.zip, rdf2026-8-UPb-data_dictionary.csv
    Analytical lab data spreadsheets and accompanying data dictionary. (Source: DGGS)
    rdf2026-8-UPb-summary.csv, rdf2026-8-UPb-summary-dictionary.csv
    Summary data spreadsheet and accompanying data dictionary. (Source: DGGS)

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
  2. Who also contributed to the data set?
    The authors thank GeoSep Services, LLC for their contributions to data collection. This work was funded by the U.S. Geological Survey National Cooperative Geologic Mapping Program under STATEMAP Award Number: G23AC00584-01, 2023, and the State of Alaska General Fund. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Geological Survey. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Geological Survey or by any branch or employee of the State of Alaska.
  3. To whom should users address questions about the data?
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.

Why was the data set created?

The purpose of this report is to present zircon U-Pb geochronologic data from ten samples collected during the 2024 West Susitna STATEMAP project to refine the ages of mapped bedrock units and strengthen tectonic interpretations within a 1:50,000-scale geologic mapping area in the West Susitna region of southcentral Alaska, providing geologic information that supports responsible resource development, infrastructure planning, hazard assessment, and long-term land use decision making for the State of Alaska.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: 2022 (process 1 of 2)
    Field data collection - Stratigraphic profiles were selected for study in the field. They consisted of natural stream bank exposures or hand-dug pits. We scraped exposure surfaces clean with shovels and trowels to better expose the tephra deposits and associated buried soils, recorded the apparent vertical thickness of each unit, and collected samples of tephra and soil-organic matter for later analysis.
    Date: 2023 (process 2 of 2)
    Sample analysis - Researchers collected buried soil samples from 26 sites beneath major tephra layers, then dried and prepared them before sending them to the University of Georgia's Center for Applied Isotope Studies for radiocarbon analysis. In the lab, humic acids were isolated from the soils through sieving, acid treatment, alkaline extraction, precipitation, and drying, while peat samples underwent a similar cleaning process before combustion. Radiocarbon measurements were obtained using accelerator mass spectrometry, with isotopic ratios corrected for natural fractionation. Results were reported as percent modern carbon and as radiocarbon years before present (BP), based on a 5,568-year half-life. These uncalibrated dates were then converted to calendar ages using the CALIB 7.1 calibration program, which relies on tree-ring and other independently dated records. Final calibrated ages are expressed as cal BC, cal AD, or cal BP, corresponding directly to actual calendar years. Additional methodological detail and full analytical results are provided in the accompanying report.
  3. What similar or related data should the user be aware of?
    Zechmann, J.M., and Salisbury, J.B., 2025, Lidar-derived surface elevation data for Dickason Highlands, southcentral Alaska, collected August 14, 2024: Raw Data File RDF 2025-12, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 10 p
    Walser, S.L., Gillis, R.J., Bernt, J.D., and Montayne, Simone, 2025, Major-oxide and trace-element analyses of rock samples from the West Susitna area STATEMAP project, southcentral, Alaska: Raw Data File RDF 2025-21, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 2 p
    Zippi, P.A., Walser, S.L., Gillis, R.J., and Montayne, Simone, 2025, Palynological and thermal maturity analysis of outcrop samples from the West Susitna area STATEMAP project, southcentral, Alaska: Raw Data File RDF 2025-27, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska, United States.

    Online Links:

    Other_Citation_Details: 3 p

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
    The accompanying report and data tables provide a comprehensive discussion of processing methods, with errors reported in the tables where applicable. This data is being released as part of the DGGS RDF series, which includes content describing approved techniques and methods for the collection, storage, visualization, analysis, and interpretation of scientific data. While the information has been reviewed by several geologists familiar with the study area, the data and report have not undergone formal review for technical content or conformity to DGGS editorial standards. For inquiries regarding analytical values or procedures, the originating lab is the best point of contact.
  2. How accurate are the geographic locations?
    Staff recorded geographic coordinates for sample stations using GPS-enabled tablets and smartphones running the ESRI Field Maps application, which typically provides positional accuracy within approximately 10 meters. All location data are reported in latitude and longitude using the WGS84 datum.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    This data release is complete.
  5. How consistent are the relationships among the observations, including topology?
    Not applicable

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints:
This report, map, and/or dataset is available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).
Use_Constraints:
Any hard copies or published datasets utilizing these datasets shall clearly indicate their source. If the user has modified the data in any way, the user is obligated to describe the types of modifications the user has made. The user specifically agrees not to misrepresent these datasets, nor to imply that changes made by the user were approved by the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys. The State of Alaska makes no express 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.
  1. Who distributes the data set? (Distributor 1 of 1)
    Alaska Division of Geological & Geophysical Surveys
    Metadata Manager
    3354 College Road
    Fairbanks, AK
    USA

    (907)451-5020 (voice)
    (907)451-5050 (FAX)
    dggspubs@alaska.gov
    Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
    Contact_Instructions:
    Please view our website (https://www.dggs.alaska.gov) for the latest information on available data. Please contact us using the e-mail address provided above when possible.
  2. What's the catalog number I need to order this data set? RDF 2026-8
  3. What legal disclaimers am I supposed to read?
    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.
  4. How can I download or order the data?

Who wrote the metadata?

Dates:
Last modified: 02-Mar-2026
Metadata author:
Alaska Division of Geological & Geophysical Surveys
Attn: Simone Montayne
Metadata Manager
3354 College Road
Fairbanks, AK
USA

(907)451-5020 (voice)
(907)451-5050 (FAX)
dggspubs@alaska.gov
Hours_of_Service: 8 am to 4:30 pm, Monday through Friday, except State holidays
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:

Generated by mp version 2.9.50 on Mon Mar 02 17:59:39 2026