Simplified Geologic Map and Cross Sections of Central and East Anchorage, Alaska

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What does this data set describe?

Title:
Simplified Geologic Map and Cross Sections of Central and East Anchorage, Alaska
Abstract:
This geologic map and preliminary cross sections of central and east Anchorage, Alaska, are based on previous mapping, limited new photointerpretation, and available subsurface data. Using PC-based Geographic Information System (GIS) software, the existing geologic map has been updated and simplified by adding recent fill deposits and combining units of similar genesis, composition, and age that are also recognizable in the subsurface. The GIS database consists of a USGS geologic map and over 4,000 geotechnical boreholes and water-well logs provided by numerous public and private sources. Geologic cross sections were developed by using GIS to project graphic lithologic logs into scaled vertical layouts along selected lines. Stratigraphic units were manually correlated using the log sections as guides. Identification and correlation of subsurface units are somewhat hampered by complex glacial geology, sparseness of deep boreholes, and significant variation in lithologic descriptions among many drillers. Although these limitations result in some generalized, undifferentiated geologic units, the differences among interpreted units are of the level desired by the geotechnical user community for highlighting engineering and seismic behavior.
Supplemental_Information:
The layers listed below are present as ArcGIS shape files. Attribute information for the following layers (entities) is included in this metadata file under the "Entity_and_Attribute_Information" section. Each layer is listed and described in detail under its own heading starting "Entity_Type_Label." Basic unit information is also included in the geologic unit code set file "PIR1999-1_codeset.pdf". Layers include:
anch_boreholes_font_point     borehole and well log locations
bcc_elmendorf_region     approximate surface extent of Elmendorf-age outwash deposits
bcclimit_polyline     approximate subsurface limit of thick, fine-grained facies of Bootlegger Cove Formation (BCF)
geology_region     geologic unit polygons
  1. How should this data set be cited?

    Combellick, R.A., 1999, Simplified Geologic Map and Cross Sections of Central and East Anchorage, Alaska: Preliminary Interpretive Report PIR 1999-1, State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys, Fairbanks, Alaska - USA.

    Online Links:

    Other_Citation_Details: 13 p., 2 sheets, scale 1 inch = 0.5 miles

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -149.941055
    East_Bounding_Coordinate: -149.642279
    North_Bounding_Coordinate: 61.252123
    South_Bounding_Coordinate: 61.067689

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Calendar_Date: 1999
    Currentness_Reference: publication date

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: tabular digital data, map, vector digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

    2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator
      Universal_Transverse_Mercator:
      UTM_Zone_Number: 6
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -147.00000
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.0
      False_Northing: 0

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.000032
      Ordinates (y-coordinates) are specified to the nearest 0.000032
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1927.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378206.4.
      The flattening of the ellipsoid used is 1/294.978698.

      Vertical_Coordinate_System_Definition:
      Depth_System_Definition:
      Depth_Datum_Name: Local surface
      Depth_Resolution: 0.5
      Depth_Distance_Units: feet
      Depth_Encoding_Method: Explicit depth coordinate included with horizontal coordinates

  7. How does the data set describe geographic features?

    geology_region.shp
    Object type is vector, there are 771 rows associated with this entity, and the entity values refer to the unit name abbreviations for each specific polygon represented on the map. (Source: Alaska Division of Geological & Geophysical Surveys)

    UNIT
    A unique one to two letter abbreviation given to each map unit represented on the map. (Source: Alaska Division of Geological and Geophysical Surveys)

    Formal codeset
    Codeset Name:PIR1999-1_codeset.pdf
    Codeset Source:Alaska Division of Geological & Geophysical Surveys <http://www.dggs.dnr.state.ak.us/metadata/PIR1999-1_codeset.pdf>

    bcclimit_polyline.shp
    Object type is vector, there is 1 row associated with this entity, and the entity value refers to the approximate 30-ft isopach of the Bootlegger Cove Formation. Question marks on the printed map indicate areas of poor data control. Note: This feature wasn't assigned any user defined attribute. (Source: Alaska Division of Geological & Geophysical Surveys)

    bcc_elmendorf_region.shp
    Object type is vector, there are 25 rows associated with this entity, and the entity values refer to polygons showing the approximate surface extent of Elmendorf age outwash deposits. Note: This feature wasn't assigned any user defined attribute. This feature shown on map as polygon outline filled with stippled pattern. (Source: Alaska Division of Geological & Geophysical Surveys)

    anch_boreholes_font_point.shp
    Object type is point, there are 3206 rows associated with this entity, and the entity values refer to symbols for various types of boreholes, well logs, or geologic sections. (Source: Alaska Division of Geological & Geophysical Surveys)

    NUMBER
    Number assigned to identify borehole. (Source: Alaska Division of Geological & Geophysical Surveys)

    Unique alphanumeric code assigned to each borehole.

    MOA_GRID
    Municipality of Anchorage grid square within which borehole, well log, or geologic section is located. (Source: Alaska Division of Geological and Geophysical Surveys)

    Unique alphanumeric code assigned to each grid square.

    HOLE_TYPE
    Type of borehole. (Source: Alaska Division of Geological and Geophysical Surveys)

    ValueDefinition
    1Hollow-stem borehole without standard penetration test
    2Hollow-stem borehole with standard penetration test (SPT)
    3Cone penetration test (CPT)
    4Solid stem auger (no cores or SPT)
    5Water well
    6Pit or trench
    7Natural exposure

    DRILLED
    Date on which borehole or well was drilled. (Source: Alaska Division of Geological and Geophysical Surveys)

    Range of values
    Minimum:9/17/1953
    Maximum:8/21/2000

    METHOD
    Method by which the borehole or well log locations were determined (Source: Alaska Division of Geological and Geophysical Surveys)

    ValueDefinition
    1Digitized from 1:24,000-scale topographic map
    2Digitized from 1:10,000 or larger scale map with UTM or lat/long coordinates
    4Determined by differentially corrected GPS
    5Coordinates provided by driller
    6Center of 4th quarter section (2-1/2 acre square) within which hole was drilled; actual location unknown
    7Center of 3rd quarter section (10 acre square) within which hole was drilled; actual location unknown
    9Location within land parcel or project site is unknown

    FT
    Depth of borehole. (Source: Alaska Division of Geological and Geophysical Surveys)

    Range of values
    Minimum:0
    Maximum:902
    Units:feet

    INDEX
    Unique index number assigned to borehole or well log (Source: Alaska Division of Geological and Geophysical Surveys)

    Unique index number assigned to each borehole.


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?

    This research was partially supported by the U.S. Geological Survey (USGS), Department of the Interior, under USGS award number 1434-HQ-96-GR-02713. Additional Acknowledgments: Geology modified from Schmoll and Dobrovolny (1972). Digital cartography by R.A. Combellick and S.M. Weems, with suggestions by A.L. Schell. R.D. Reger and P.J. Haeussler provided helpful comments on the draft map and cross sections.

  3. To whom should users address questions about the data?

    State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
    GIS Data Manager/Cartographer
    3354 College Road
    Fairbanks, AK 99709-3707

    (907) 451-5020 (voice)
    (907) 451-5050 (FAX)
    dggspubs@alaska.gov

    Contact_Instructions:
    You may view our web site at <http://www.dggs.dnr.state.ak.us> for the latest information on available data. Please e-mail your questions and data requests when possible since our web site and e-mail address will remain current even if our phone number and mailing address change.


Why was the data set created?

The purpose of this project was to acquire existing surficial geologic and subsurface data, both borehole and well-log, and incorporate it into an updated and simplified geologic map and cross sections of central and east Anchorage.


How was the data set created?

  1. From what previous works were the data drawn?

    Schmoll and Dobrovolny, 1972 (source 1 of 1)
    Schmoll, H.R., and Dobrovolny, E., 1972, Generalized Geologic Map of Anchorage and Vicinity, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-787-A.

    Other_Citation_Details: 1 sheet, scale 1:24,000
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 24000
    Source_Contribution:
    This publication is the original geologic map from which the simplified geologic map of the area was derived.

  2. How were the data generated, processed, and modified?

    Date: 1999 (process 1 of 2)
    Geologic map compilation - Map data compiled for the GIS database include five 1:25,000-scale U.S. Geological Survey (USGS) topographic quadrangles and a carefully digitized version of the most recent geologic map of Anchorage (Schmoll and Dobrovolny, 1972). The topographic maps were digitally trimmed and spliced seamlessly together, then geographically registered to provide an accurate base map for the geology and for digitizing borehole locations. All geotechnical borehole data and some water-well data were obtained in paper form from public agencies and private companies that have drilled significant boreholes in the Anchorage area since the late 1950s. The U.S. Geological Survey provided most of the water-well data in digital format from its Groundwater Site Inventory System.

    Data sources used in this process:

    • Schmoll and Dobrovolny, 1972

    Date: 1999 (process 2 of 2)
    Revision of geologic map: The geologic map on sheet 1 is based on an existing map (Schmoll and Dobrovolny, 1972), with four features that distinguish my simplified map from their original: (1) Grouping of units to create a simpler map with fewer geologic units highlighting differences in materials content and gross physical properties that are of engineering significance and can be recognized in the subsurface in borehole and water-well logs. (2) Updating of geology using interpretation of 1993 color vertical aerial photographs, primarily by adding significant artificial-fill deposits that have been emplaced since 1972. (3) Updating of topographic base map to those revised in 1993 and 1994. (4) 30-ft isopach of Bootlegger Cove clay through inspection of ~300 borehole logs to identify those in which soft, fine-grained deposits of Bootlegger Cove Formation (BCF) have a continuous or nearly continuous thickness of 30 ft (10 m) or more.

  3. What similar or related data should the user be aware of?


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

  1. How well have the observations been checked?

    Geologic point, line, and polygon data were derived by digitizing the geologic map by Schmoll and Dobrovolny (1972), then combining selected units. The location of the 30-ft isopach of Bootlegger Cove clay depicted in the layer pir1999-1_bcclimit_polyline was estimated by identifying boreholes in which soft, fine-grained deposits of the Bootlegger Cove formation have a continuous or nearly continuous thickness of 30 ft (10 m) or more. Hence this isopach is interpreted and its horizontal accuracy is unknown. With the exception of digital water-well logs, for which geographic positions were provided by the supplying agency, all borehole locations in the layer pir1999-1_anch_boreholes_font_point were digitized in GIS from project site maps provided with the drilling reports. The scale and detail of these site maps are highly variable, resulting in variation in accuracy of the digitized locations. See the Horizontal_Positional_Accuracy_Report below.

  2. How accurate are the geographic locations?

    The accuracy of geologic unit boundaries in the layers pir1999-1_geology_region and and pir1999-1_bcc_elmendorf_region depend on the accuracy of the original geologic map by Schmoll and Dobrovolny (1972) and the accuracy of digitizing. In the layer pir1999-1_anch_boreholes_font_point, the attribute "location_method" is a code indicating the method by which the borehole or well log locations were determined (see Entity_and_Attribute_Information).

  3. How accurate are the heights or depths?

    Measurements of boreholes and wells for the attribute "FT" in the layer pir1999-1_anch_boreholes_font_point were taken from the original driller's reports, which do not contain information about measurement accuracy. Depth is generally reported as the total length of drill string below ground surface, including the auger and all drill rods.

  4. Where are the gaps in the data? What is missing?

    This dataset includes geospatial information related to geologic map units and borehole localities.

  5. How consistent are the relationships among the observations, including topology?

    Polygon topology present and clean on appropriate data. Other data are line, point, or annotation data and do not require topologic relationships.


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 are 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. 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.

  1. Who distributes the data set? (Distributor 1 of 1)

    State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
    Natural Resource Technician
    3354 College Road
    Fairbanks, AK 99709-3707
    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 web site (<http://www.dggs.dnr.state.ak.us>) 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?

    Preliminary Interpretive Report 1999-1

  3. What legal disclaimers am I supposed to read?

    The State of Alaska makes no express or implied warranties (including warranties of merchantability and fitness) with respect to the character, function, or capabilities of the electronic services 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, any failure thereof, or otherwise, and in no event will the State of Alaska's liability to the requester or anyone else exceed the fee paid for the electronic service or product.

  4. How can I download or order the data?

  5. What hardware or software do I need in order to use the data set?

    Please check the MapInfo web site (<http://www.mapinfo.com/>) for the latest documentation on importing ESRI shape files.


Who wrote the metadata?

Dates:
Last modified: 06-May-2008
Last Reviewed: 06-May-2008
To be reviewed: 15-Mar-2009
Metadata author:
State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
Metadata Manager
3354 College Road
Fairbanks, AK 99709-3707
USA

907-451-5039 (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 contact us through the e-mail address above whenever possible.
Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)


Generated by mp version 2.9.6 on Tue May 06 14:29:35 2008