Top Mesozoic unconformity depth map of the Cook Inlet Basin, Alaska

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Frequently-anticipated questions:


What does this data set describe?

Title:
Top Mesozoic unconformity depth map of the Cook Inlet Basin, Alaska
Abstract:
Alaska Division of Oil and Gas personnel collected and interpreted various data sources related to the interpretation of the Base Tertiary unconformity surface in the Cook Inlet Basin, Alaska.Data sources included public literature, public well data information (from the AOGCC-Alaska Oil and Gas Conservation Commission), a palynology database (Greater Cook Inlet Stratigraphic Palynology Control Database and Stud,Zippi, P.A., 2006) and over 2000 miles of 2D marine seismic data (CI-88 and CI-89 licensed from, and complements of, CGGVeritas.) Interpreted formation tops of the Base Tertiary unconformity are tabulated on the map.
Supplemental_Information:
This dataset includes three shapefiles and an CSV spreadsheet.The files are organized into four entities as described in this metadata file under the "Entity_and_Attribute_Information" section. The files are as follows:
control-points	Well locations and interpreted depth to top Mesozoic unconformity in oil and gas wells. This table is provided as Table 1 on the printed map and in the csv file "control-points.csv"
contours	Lines of equal elevation (shapefile)
faults		Polyline representing the location of a displacement of rocks along a planar surface (shapefile)
folds		Polyline indicating the location of an anticlinal or synclinal fold axis (shapefile)
  1. How should this data set be cited?

    Shellenbaum, D.P., Gregersen, L.J., and Delaney, P.R., 2010, Top Mesozoic unconformity depth map of the Cook Inlet Basin, Alaska: Report of Investigations RI 2010-2, Alaska Division of Geological & Geophysical Surveys, Fairbanks, Alaska.

    Online Links:

    Other_Citation_Details: 1 sheet, scale 1:500,000

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -155.00
    East_Bounding_Coordinate: -149.00
    North_Bounding_Coordinate: 62.00
    South_Bounding_Coordinate: 59.00

  3. What does it look like?

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

    Calendar_Date: 2010
    Currentness_Reference: publication date

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

    Geospatial_Data_Presentation_Form: vector digital data

  6. How does the data set represent geographic features?

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

      Indirect_Spatial_Reference:
      Well locations were extracted from the Alaska Oil and Gas Conservation Commission (AOGCC) online catalog, accessed in 2010. Each well is indexed in the AOGCC catalog by well name and and API number. Well locations are displayed in the printed map and well names and API numbers are provided in table 1.
      This is a Vector 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: 5
      Transverse_Mercator:
      Scale_Factor_at_Central_Meridian: 0.999600
      Longitude_of_Central_Meridian: -153.000000
      Latitude_of_Projection_Origin: 0
      False_Easting: 500000.000000
      False_Northing: 0

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.000001
      Ordinates (y-coordinates) are specified to the nearest 0.000001
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Clarke 1866.
      The semi-major axis of the ellipsoid used is 6378137.
      The flattening of the ellipsoid used is 1/298.25722210088.

  7. How does the data set describe geographic features?

    contours.shp
    Lines of equal elevation (Source: Alaska Division of Geological & Geophysical Surveys)

    Elevation
    vertical depth in feet (Source: Alaska Division of Oil & Gas)

    Range of values
    Minimum:0
    Maximum:-25000
    Units:feet

    contour_type
    differentiates contours as index or intermediate and the associated level of certainty for the purpose of symbolizing (Source: Alaska Division of Oil & Gas)

    ValueDefinition
    int_dashintermediate_dashed; refers to approximately located intermediate contour
    intintermediate contour
    index_dashapproximately located index contour
    indexindex contour

    faults.shp
    Polyline representing the location of a displacement of rocks along a planar surface. (Source: Alaska Division of Geological & Geophysical Surveys)

    Fault_ID
    defines the type of fault (Source: Alaska Division of Oil & Gas)

    ValueDefinition
    normal_seisnormal fault derived from seismic interpretation
    strike_slipstrike-slip fault
    strike_slip_dashapproximately located strike-slip fault
    thrustthrust fault
    thrust_dashapproximately located thrust fault
    thrust_seisthrust fault derived from seismic interpretation

    folds.shp
    Polyline indicating the location of an anticlinal or synclinal fold axis. (Source: Alaska Division of Geological & Geophysical Surveys)

    Fold_ID
    refers to the type of fold (Source: Alaska Division of Oil & Gas)

    ValueDefinition
    aclanticline
    acl_dashapproximately located anticline
    sclsyncline
    scl_dashapproximately located syncline

    control-points.csv
    Depth to top Mesozoic unconformity in oil and gas wells (Source: this report)

    Well Number
    provides a cross reference between the well location displayed on the printed map and the interpreted depth values provided in table 1. (Source: this report)

    Range of values
    Minimum:1
    Maximum:101

    API No.
    API number - AOGCC catalog index number for each well (Source: Alaska Oil and Gas Conservation Commission (AOGCC))

    Alaska Oil and Gas Conservation Commission (AOGCC) catalog index number

    Measured Depth (ft)
    measured distance along the path of a wellbore from the kelly bushing to the interpreted top Mesozoic unconformity. (Source: this report)

    Range of values
    Minimum:670
    Maximum:16650
    Units:feet

    True Vertical Depth, Subsea (ft)
    vertical distance from sea level to the interpreted top Mesozoic unconformity (Source: this report)

    Range of values
    Minimum:-591
    Maximum:-16221
    Units:feet


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?

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


Why was the data set created?

The purpose of the map is to provide an interpretation of the Cook Inlet basin Base Tertiary depth structure to the public. While most oil and gas exploration companies active in the Cook Inlet Basin have proprietary databases of seismic and well data with which they have created proprietary depth surface maps, a detailed map incorporating a significant amount of seismic data has not been available in the public domain, and to new companies who may be interested in exploring in the basin.This map incorporates seismic data over most of the marine portion overlying the basin.Additionally, this map will be used in a subsequent map of the Mesozoic subcrop surfaces, where Cretaceous and Jurassic subcrops will be displayed on the Base Tertiary depth surface.


How was the data set created?

  1. From what previous works were the data drawn?

    Zippi, 2006 (source 1 of 8)
    Zippi, P.A., 2006, Greater Cook Inlet stratigraphic palynology control database and study.

    Online Links:

    • www.biostratigraphy.com

    Other_Citation_Details: unpublished proprietary report, 187 p.
    Type_of_Source_Media: online
    Source_Contribution: stratigraphic palynology control

    AOGCC, 2010 (source 2 of 8)
    Alaska Oil & Gas Conservation Commission (AOGCC), 2010, Annual Report and public well databases: Annual Report and public well databases 2010.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution: well data

    AKDOG, 2010 (source 3 of 8)
    Alaska Division of Oil & Gas, 2010, Alaska Oil and Gas Report 2009: Alaska Division of Oil & Gas, Anchorage, Alaska.

    Online Links:

    Type_of_Source_Media: online
    Source_Contribution: structure contour data

    Canstrat, 2010 (source 4 of 8)
    Canadian Stratigraphic Services Lithologic Logs, 2010, USA Well Log Index.

    Online Links:

    • www.canstrat.com

    Other_Citation_Details: choose "log index" for details
    Type_of_Source_Media: online
    Source_Contribution: well logs

    Magoon and others, 1976 (source 5 of 8)
    Magoon, L.B, Adkison, W.L, and Egbert, R.M., 1976, Map showing geology, wildcat wells, Tertiary plant-fossil localities, K-Ar age dates and petroleum operations, Cook Inletarea, Alaska: USGS Miscellaneous Investigation Map I-1019.

    Other_Citation_Details: 3 sheets, scale 1:250,000
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 250000
    Source_Contribution: geology

    Wilson and others, 2009 (source 6 of 8)
    Wilson, F.H., Hults, C.P., Schmoll, H.R., Haeussler, P.J., Schmidt, J.M., Yahle, L.A., and Labay, K.A., 2009, Preliminary Geologic Map of the Cook Inlet Region, Alaska: USGS Open File Report OF 2009-1108.

    Other_Citation_Details: 2 sheets, scale 1:250,000
    Type_of_Source_Media: paper
    Source_Scale_Denominator: 250000
    Source_Contribution: geologic map

    CGGVeritas, 2010 (source 7 of 8)
    CGGVeritas, 2010, 2010, CGGVeritas CI88 and CI89 marine 2D seismic speculative data.

    Online Links:

    • www.cggveritas.com

    Other_Citation_Details: website under Products & Services / Data Library for details
    Type_of_Source_Media: online
    Source_Contribution: seismic data

    DNR, 2010 (source 8 of 8)
    Staff, DNR, Unpublished material, State of Alaska, Department of Natural Resources, Alaska Statewide Core GIS database.

    Type_of_Source_Media: digital file
    Source_Contribution: base map

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

    Date: 2010 (process 1 of 6)
    Well Interpretation - Public well logs were obtained from the Alaska Oil and Gas Conservation Commission (AOGCC). The depth to the top Mesozoic unconformity was interpreted using borehole geophysical log character, lithologic logs, and palynology data (Zippi, 2006). Where available, sonic and density logs were edited and combined to create synthetic seismograms used in calibrating to the seismic data.

    Data sources used in this process:

    • AOGCC, 2010
    • Zippi, 2006

    Date: 2010 (process 2 of 6)
    Seismic Interpretation - The seismic dataset used for interpretation consists of proprietary, speculative two-dimensional marine data (CI88 and CI89 prefix lines, owned and marketed by CGGVeritas and used by the Alaska Department of Natural Resources with permission from CGGVeritas). To tie the seismic data to the well data, calibrations were attempted for all synthetic seismograms of wells on or near seismic lines. Well ties to seismic were analyzed both visually and statistically. Two wells yielded synthetic seismogram to seismic ties of good quality to the top Mesozoic unconformity. Additional synthetic seismograms were useful in predicting the seismic character of the West Foreland Formation. Check shot velocity surveys were publicly available from two wells, OCS 0243 (Falcon) #1 and OCS 0086 (Guppy) #1. Depth-variant velocities were calculated from the synthetic seismogram ties and from the measured check shots to generate a depth and spatially variant velocity field. The following data and observations were integrated to generate the top Mesozoic unconformity seismic interpretation: 1) Time-to-depth relationships based on synthetic seismograms and checkshot velocity surveys 2) Top Mesozoic unconformity well picks displayed in time 3) Top West Foreland Formation seismic interpretation. This prominent seismic horizon is a short distance above, and generally conformable with, the top Mesozoic unconformity. Synthetic seismograms at this horizon generally showed a significant decrease in acoustic impedance, which should translate to a consistent strong reflector on the seismic.Interpretation of this horizon helped guide the underlying top Mesozoic unconformity pick. 4) The top Mesozoic is sometimes an angular unconformity, and seismic reflectors below it can have steeper dips, and be truncated by the unconformity surface.

    Data sources used in this process:

    • CGGVeritas, 2010

    Date: 2010 (process 3 of 6)
    Seismic time-to-depth conversion - Two-way time seismic picks on the top Mesozoic unconformity were gridded to form a surface.Time values were extracted at well penetrations by piercing the time surface with the well paths. The top Mesozoic unconformity depths at the well penetrations were divided by one-way time values to create ‘pseudo-velocities’, or average velocities from the horizon to the surface. An implicit assumption in this depth conversion methodology is that the structural dip varies smoothly between control points. However, wells are mostly drilled on major structural highs in Cook Inlet, resulting in additional velocity control points being needed in areas of inadequate sampling, predominantly in the deeper parts of the basin. The additional control point values were estimated from cross plots of time versus pseudo-velocity, extrapolating an interpreted time-velocity slope to the deeper times observed on the seismic. The velocities from well penetrations and added control were then gridded to form a horizon velocity surface, which was multiplied with the seismic one-way time surface to create a depth surface. The depth surface contours were hand edited to remove computer-generated artifacts, which were especially apparent on the edges of seismic control and near faults and other areas of strong structural variability.

    Date: 2010 (process 4 of 6)
    Interpretation Outside Seismic Control - The following data were used to interpret the top Mesozoic unconformity depth surface where seismic was not available: 1) Well penetrations 2) Bounding faults and fold axes 3) Contacts between Mesozoic and Tertiary geologic units from surface geologic mapping 4) Structural contour maps from AOGCC annual reports.

    Data sources used in this process:

    • Magoon and others, 1976
    • Wilson and others, 2009

    Date: 2010 (process 5 of 6)
    Digital Cartography - Contours, fold axes, and faults were initially constructed using GeoGraphix software.Due to software issues, the data was not exported directly from GeoGraphix in shapefile format.Rather, the data was saved as a .pdf document and sent to Design Presentation Associates for georeferencing and vectorization of all line work.The line work was then checked for positional accuracy and completeness and was attributed in ESRI ArcGIS.All final annotation, editing, and layout was done in CorelDraw.

    Date: 2010 (process 6 of 6)
    Base layer was extracted from State of Alaska, Department of Natural Resources, Alaska Statewide Core GIS database.

    Data sources used in this process:

    • DNR, 2010

  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?

    Contours outside of the CI88 and CI89 two-dimensional seismic coverage are dashed to indicate uncertainty. Contours outside seismic coverage with little well control have even higher uncertainties, and are designated with question marks.The absolute depth error at any given point on the map is difficult to quantify and results from uncertainties in a) the depth pick in wells, b) interpolation between and extrapolation away from wells, c) time picks on seismic, d)variations in the seismic velocity field, and e) gridding, contouring, and smoothing artifacts, particularly in areas of sparse seismic and well control. There is also a certain amount of spatial uncertainty regarding the intersection of the top Mesozoic unconformity horizon with the Bruin Bay and Castle Mountain - Lake Clark fault systems that bound the basin to the west. The fault traces (Magoon and others, 1976) indicate surface expression, whereas the Base Tertiary surface lies at varying depths. The unconformity depth surface has been contoured as if the faults are single vertical entities, but the reality is certain to be more structurally complex.The magnitude of this spatial uncertainty depends on the dips and complexity of the faults as well as the depth of the Base Tertiary surface.The deeper the surface and the shallower the actual fault dips, the larger the potential error. This report has received two technical reviews by scientists familiar with the subject matter as well as technical editing.

  2. How accurate are the geographic locations?

    Horizontal positional accuracy of entities outside of the two-dimensional seismic coverage area and where there is little well control is difficult to quantify.Error at any given point results from uncertainties in a) the depth pick in wells, b) interpolation between and extrapolation away from wells, c) time picks on seismic, d)variations in the seismic velocity field, and e) gridding, contouring, and smoothing artifacts, particularly in areas of sparse seismic and well control.

  3. How accurate are the heights or depths?

    The location accuracy of interpreted depths displayed by the depth contours and presented in the "contours file" is discussed in Horizontal Positional Accuracy Report. The depth to the top Mesozoic unconformity for each well is presented in table 1 (Depth to top Mesozoic unconformity in oil and gas wells) and was interpreted using borehole geophysical log character, lithologic logs, and palynology data. The accuracy of our interpreted depths varies according the quality and density of the available data. Additional detail regarding the accuracy of our interpretations at each specific hole is not available.

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

    The map was constructed primarily from marine seismic reflection data and oil and gas wells that penetrated the top Mesozoic unconformity.Where the well control is too dense to differentiate at the 1:500,000 scale, an inset map is provided. Previous mapping and well penetrations were used to interpret the top Mesozoic unconformity depth surface where seismic was not available.The data set displays contours as well as fault and fold traces.This dataset does not include locations of oil and gas wells or seismic lines used to interpret the top Mesozoic unconformity.

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

    The digitized lines representing faults, folds, and contours in this dataset were checked visually for duplication using ESRI ArcMap software.


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
    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.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?

  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. Is there some other way to get the data?

    DGGS publications are available as free online downloads or you may purchase paper hard-copies or digital files on CD/DVD or other digital storage media over the counter by mail, phone, fax, or email from the DGGS Fairbanks office.Turn around time is 1-2 weeks unless special arrangements are made and an express fee is paid. Shipping charge will be the actual cost of postage and will be added to the total amount due. Contact us for a exact shipping amount.


Who wrote the metadata?

Dates:
Last modified: 04-Dec-2010
Metadata author:
Metadata manager
State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys
Fairbanks, AK 99709-3707
USA

907-451-5020 (voice)

Metadata standard:
FGDC Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)
Metadata extensions used:


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