Molecular (C1-C5 hydrocarbon, CO2, O2, and N2) and δ13C-CH4 composition of pressure core, void, and hydrate gases from the Terrebonne Basin, Gulf of America (Gulf of Mexico), Walker Ridge 313 Site

Frequently anticipated questions:

• What does this data set describe?
  1. How might this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
  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?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

What does this data set describe?

1. How might this data set be cited?
   Phillips, Stephen C., Pohlman, J.W., and Casso, M., 2025, Molecular (C1-C5 hydrocarbon, CO2, O2, and N2) and δ13C-CH4 composition of pressure core, void, and hydrate gases from the Terrebonne Basin, Gulf of America (Gulf of Mexico), Walker Ridge 313 Site: dataset DOI:10.5281/zenodo.15626975, U.S Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, Massachusetts, USA.

   Online Links:

   • https://doi.org/10.5281/zenodo.15626975

   Other_Citation_Details:

   Suggested citation: Phillips, S.C., Pohlman, J.W., and Casso, M., 2025, Molecular (C1-C5 hydrocarbon, CO2, O2, and N2) and δ13C-CH4 composition of pressure core, void, and hydrate gases from the Terrebonne Basin, Gulf of America (Gulf of Mexico), Walker Ridge 313 Site H [Dataset]: Zenodo, https://doi.org/10.5281/zenodo.15626975

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -91.67608
   East_Bounding_Coordinate: -91.67599
   North_Bounding_Coordinate: 26.66260
   South_Bounding_Coordinate: 26.66228
   

3. What does it look like?
4. Does the data set describe conditions during a particular time period?

   Beginning_Date: 04-Aug-2023

   Ending_Date: 27-Aug-2023

   Currentness_Reference:

   Ground condition. Cores were collected in August 2023 on the D/V Q4000 using conventional (advanced piston coring and extended core barrel coring) and pressure coring (Pressure Coring Tool with Ball Valve). Void gases were collected from conventional cores immediately after recovery by drilling a hole through the core liner. Pressure cores were collected from a bubbling chamber (an inverted graduated cylinder) during pressure core degassing. Hydrate gases were collected from cryo-frozen hydrate-bearing sediment samples that were dissociated inside a syringe used to collect the gas.

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

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. It contains the following vector data types (SDTS terminology):
      • Point (79)
   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 0.00001. Longitudes are given to the nearest 0.00001. Latitude and longitude values are specified in decimal degrees. The horizontal datum used is NAD 27.
      The ellipsoid used is Clark ellipsoid of 1866.
      The semi-major axis of the ellipsoid used is 6378206.400000.
      The flattening of the ellipsoid used is 1/294.9786982.
      

      Vertical_Coordinate_System_Definition:

      Depth_System_Definition:

      Depth_Datum_Name: local surface - depth below sea floor
      Depth_Resolution: 0.005
      Depth_Distance_Units: meters
      Depth_Encoding_Method: attribute values
      

7. How does the data set describe geographic features?

   "UT-GOM2-2_USGS-gas-data.xlsx"

   Microsoft Excel workbook that contains tabulated gas composition data by depth for UT-GOM2-2 cores. (Source: producer defined)

   Expedition

   Expedition name. UT-GOM2-2 for all entries (Source: U.S. Geological Survey) user defined text field

   Area

   Lease block area within the Gulf of America. All values are Walker Ridge 313 (WR313). (Source: U.S. Geological Survey) user defined text field

   Site

   Site within the WR313 area. In this case all from the H site. (Source: U.S. Geological Survey) user defined text field

   Hole

   Two holes were drilled at the WR313 H site: Holes 002 and 003. (Source: U.S. Geological Survey) user defined text field

   Core

   Core number, increasing with depth in each hole. (Source: U.S. Geological Survey) user defined

   Core type

   Core type used to recover core. H is advanced piston core, X is extended core barrel, CS is pressure coring tool with ball valve in the cutting shoe configuration, and FB is the pressure coring tool with ball valve in the face bit configuration. (Source: U.S. Geological Survey) user defined

   Section

   Section cut within the core. Increasing number within the core with the core catcher (CC) as the bottom section (Source: U.S. Geological Survey) user defined

   Piece

   Piece cut within each core section. Some sections were not cut into pieces. NaN = no data. (Source: U.S. Geological Survey) user defined

   Sample type

   Void gas was collected from voids within the core liner in conventional cores. Pressure core gas was collected from gas produced during depressurization of pressure cores. Hydrate gas was collected from cryo-frozen cores in which hydrate-bearing sediment was allowed to dissociate within a syringe. (Source: U.S. Geological Survey) user defined

   Gas bag #

   Number label on each Cali-5 bond gas bag. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	800
   Maximum:	880
   Units:	no unit

   Pressure core step (bar)

   Pressure within the pressure core storage chamber when the gas sample was collected. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	0
   Maximum:	30
   Units:	bar

   Compressed sample top depth (mbsf)

   Sample top depth in meters below seafloor (mbsf) based on linearly-compressed core depths, accounting for expansion of the core (total length of core = length of drilling advance). Equivalent to IODP CSF-B terminology. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	19.64
   Maximum:	818.69
   Units:	meters below seafloor (mbsf)

   Compressed sample bottom depth (mbsf)

   Sample bottom depth in meters below seafloor (mbsf) based on linearly-compressed core depths, accounting for expansion of the core (total length of core = length of drilling advance). Equivalent to IODP CSF-B terminology. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	19.64
   Maximum:	818.87
   Units:	meters below seafloor (mbsf)

   Methane (%)

   Concentration of methane (C1) within the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	2.04
   Maximum:	100.00
   Units:	percent (%)

   δ13C-CH4 (‰)

   δ13C of methane relative to Vienna Pee Dee Belemnite (VPDB). (Source: U.S. Geological Survey)

   Range of values
   Minimum:	-83.5
   Maximum:	-69.9
   Units:	per mil (‰)

   CO2 (ppm)

   Concentration of carbon dioxide in the sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	197
   Maximum:	11052
   Units:	parts per million (ppm)

   Ethane (ppm)

   Concentration of ethane (C2) in the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	1.8
   Maximum:	114.8
   Units:	parts per million (ppm)

   Propane (ppm)

   Concentration of propane (C3) in the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	1
   Maximum:	8
   Units:	parts per million (ppm)

   C1/(C2+C3)

   Ratio of methane (C1) to ethane (C2) plus propane (C3). (Source: U.S. Geological Survey)

   Range of values
   Minimum:	8076
   Maximum:	63201
   Units:	no unit

   C1/C2

   Ratio of methane (C1) to ethane (C2). (Source: U.S. Geological Survey)

   Range of values
   Minimum:	8076
   Maximum:	80025
   Units:	no unit

   i-Butane (ppm)

   Concentration of isobutane (i-C4) in the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	1
   Maximum:	6
   Units:	parts per million (ppm)

   n-Butane (ppm)

   Concentration of normal butane (n-C4) in the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	1
   Maximum:	3
   Units:	parts per million (ppm)

   neo-Pentane (ppm)

   Concentration of neopentane (neo-C5) in the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	2
   Maximum:	2
   Units:	parts per million (ppm)

   i-Pentane (ppm)

   Concentration of isopentane (i-C5) in the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	b.d.
   Maximum:	b.d
   Units:	parts per million (ppm)

   n-Pentane (ppm)

   Concentration of normal pentane (n-C5) in the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	b.d.
   Maximum:	b.d.
   Units:	parts per million (ppm)

   Oxygen (%)

   Concentration of oxygen within the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	0.77
   Maximum:	20.23
   Units:	percent (%)

   Nitrogen (%)

   Concentration of nitrogen within the gas sample. (Source: U.S. Geological Survey)

   Range of values
   Minimum:	b.d.
   Maximum:	80.40
   Units:	percent (%)

   Entity_and_Attribute_Overview:

   The workbook UT-GOM2-2_USGS-gas-data.xlsx contains one tab. The first row in the XLSX file is a header row. The remaining rows contain all data included in this data release, with non-measurements given by “NaN" as indicated in the attribute definitions in this xml file. Measurements that had concentrations below detection are listed as “b.d.” This file is part of a data release posted to the Zenodo UT-GOM2-2 community.

   Entity_and_Attribute_Detail_Citation:

   Phillips, S.C., Pohlman, J.W., and Casso, M (2025). Molecular (C1-C5 hydrocarbon, CO2, O2, and N2) and δ13C-CH4 composition of pressure core, void, and hydrate gases from the Terrebonne Basin, Gulf of America (Gulf of Mexico), Walker Ridge 313 Site H [Dataset]. Zenodo. https://doi.org/10.5281/zenodo.15626975.

Who produced the data set?

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • Phillips, Stephen C.
   • Pohlman, J.W.
   • Casso, M.
2. Who also contributed to the data set?
3. To whom should users address questions about the data?
   Stephen Phillips

   U.S. Geological Survey, Northeast Region, Woods Hole Coastal and Marine Science Center

   Research Geologist

   384 Woods Hole Rd.

   Woods Hole, MA
   

   508-457-8700 x2240 (voice)

   scphillips@usgs.gov

Why was the data set created?

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: 2024 (process 1 of 1)

   Sediment cores were collected via wireline coring tools (advance piston coring, extended core barrel coring, and pressure coring) and cut into sections at sea. Hole H002 is located at 26.66228° latitude and -91.67601° longitude at the seafloor. Hole H003 is located at 26.66263° latitude and -91.67599° latitude at the seafloor. Void gases were collected using a syringe and a puncture tool that penetrates the core liner. Pressure core gases were collected from an inverted graduated cylinder as part of the quantitative degassing system that collects gases produced from the core storage chamber during depressurization. Hydrate gases were collected from cryogenically frozen samples that were allowed to dissociate within a syringe. Void gas, pressure core gas, and hydrate gas were collected in Cali-5 Bond gas bags and were analyzed for gas composition and methane stable carbon isotopes at the U.S. Geological Survey Woods Hole Coastal and Marine Science Center using the Automated Sample Introduction Module (Auto-SIM) Gas Chromatography/Cavity Ring-Down Spectroscopy System (Auto-SIM GC/CRDS). Gas samples in Cali-5 Bond bags were attached to the 16-port Auto-SIM that automatically transfers a portion of each sample to a series of samples loops of the Auto-SIM GC/CRDS that includes the USGS Discrete Sample Introduction Module (DSIM) with a cavity ring-down spectrometer and a Scientific Research Instruments (SRI) MultipleGas#5 (MG5) gas chromatograph (GC) equipped with sample loops and injection valves for parallel analysis by flame ionization detection (FID) and thermal conductivity detection (TCD). The DSIM contains a fixed (low-volume) internal sample loop and a replaceable external sample loop (larger-volume) that allows the user to properly dilute gases so they’re within the ideal analytical range of a Picarro G2201-I CRDS (100-600 ppm). The CRDS measures methane and CO2 concentrations and stable carbon isotopes of each (see Pohlman and others (2021) for additional details). Isotope ratios measured by the CRDS are reported in the -notation (δ13C) relative to a Vienna Pee Dee Belemnite (VPDB) standard calibration. Measurement precision for methane isotope ratios improves from 1‰ at 10 ppm to less than 0.2‰ at 30 ppm and remains constant through the range of measurements made. The average sample precision for this project was 0.18‰ for methane carbon isotope ratios. Additional details of the gas collection and analysis procedures are described in Flemings and others, 2025.
   Reference: Flemings, P.B., Thomas, C., Phillips, S.C., Collett, T.S., Cook, A.E., Solomon, E., Colwell, F.S., Johnson, J.E., Awwiller, D., Aylward, I., Bhandari, A.R., Brooks, D., Buser-Young, J.Z., Cardona, A., Casso, M., Coyte, R., Darrah, T., Davis, M., Dugan, B., Duncan, D., Germaine, J.T., Holland, M., Houghton, J., Mills, N.T., Mimitz, M., Minarich, D., Morono, Y., Murphy, Z., O’Connell, J., Petrou, E., Pettigrew, T., Pohlman, J.W., Portnov, A., Phillips, M.P., Redd, T., Sawyer, D. E., Schultheiss, P., Shannon, K., Sullivan, C., Small, C., Tozier, K., Tsang, M.-Y., Maal, C.V.D., Waite, W.F., and Walton, T., 2025, Expedition UT-GOM2-2 Methods, in Flemings, P.B., ed., Proceedings of the Deepwater Hydrate Coring Expedition UT-GOM2-2: The University of Texas at Austin, University of Texas Institute for Geophysics, https://doi.org/10.5281/zenodo.13971228.
   Pohlman, J.W., Casso, M., Magen, C., and Bergeron, E., 2021, Discrete Sample Introduction Module for Quantitative and Isotopic Analysis of Methane and Other Gases by Cavity Ring-Down Spectroscopy: Environmental Science and Technology, v. 55, p. 12066-12074, https://doi.org/10.1021/acs.est.1c01386 Person who carried out this activity:
   

   Stephen Phillips

   U.S. Geological Survey, Northeast Region, Woods Hole Coastal and Marine Science Center

   Research Geologist

   384 Woods Hole Rd.

   Woods Hole, MA
   

   508-457-8700 x2240 (voice)

   scphillips@usgs.gov

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?
   
2. How accurate are the geographic locations?
   Horizontal position was determined by GPS satellite data, which provided guidance information for the dynamic positioning system (DPS) utilized by the D/V Q4000. The DPS also utilizes inputs from current, wind, tide, and wave data to control eight azimuthal thrusters beneath the ship’s hull. The thrusters are capable of 360-degree adjustment. Given the DPS capabilities, borehole locations for the D/V Q4000 are considered to be accurate to a radius of 15 meters. Details for a very similar DPS system us provided in: Chikyu Hakken – Earth Discovery, Volume 1, Spring 2005, published by JAMSTEC’s Center for Deep Earth Exploration: https://www.jamstec.go.jp/chikyu/e/magazine/backnum/pdf/hk_01_e.pdf North American Datum 27 (NAD27) is the horizontal datum used by the DPS on the D/V Q4000.
3. How accurate are the heights or depths?
   Coring depth measurements used on the D/V Q4000 during the UT-GOM2-2 expedition followed standard International Ocean Discovery Program (IODP) protocols using analogous coring tools. Assessment of these protocols by IODP had determined the vertical position accuracy is on the order of centimeters to meters relative to each coring point, depending on core recovery. Additional information about the depth conventions and accuracy are on pages 8 and 9 of the IODP report “IODP Depth Scales Terminology”: http://www.iodp.org/policies-and-guidelines/142-iodp-depth-scales-terminology-april-2011/file. Depth resolution ranges from 0.01 to 1 meter.
4. Where are the gaps in the data? What is missing?
   This Microsoft Excel workbook represents the complete collected and calculated data in support of dual-frequency magnetic susceptibility measurements for the UT-GOM2-2 project.
5. How consistent are the relationships among the observations, including topology?
   For each of the gas measurements described in the Process Steps below, standards relevant to the particular property were entrained in the measurement sequence to ensure fidelity within each Process Step. The standards are noted in the Process Steps as well as the citations for those references.

How can someone get a copy of the data set?

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

   European Organization for Nuclear Research: IT Department, Digital Repositories Section

   Meyrin, Geneva
   

   Switzerland

   +41 22 76 77777 (voice)

   info@zenodo.org
2. What's the catalog number I need to order this data set? Zenodo makes research results citable, and through OpenAIRE, integrates them into existing reporting lines to funding agencies. Citation information is also passed to DataCite and onto the scholarly aggregators. UT-GOM2-2_USGS-gas-data.xlsx (Excel spreadsheet of data). The Zenodo site does not have the complete XML metadata.
3. What legal disclaimers am I supposed to read?
   Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
4. How can I download or order the data?
   • Availability in digital form:

     Data format:	XLSX (version Created in Excel Office 365 version 2408) Size: 1
     Network links:	https://doi.org/10.5281/zenodo.15626975

   • Cost to order the data: None.

Who wrote the metadata?

Dates:

Last modified: 08-Dec-2025

Metadata author:

Stephen C. Phillips

U.S. Geological Survey, Northeast Region, Woods Hole Coastal and Marine Science Center

Research Geologist

U.S. Geological Survey

Woods Hole, MA

508-548-8700 x2240 (voice)

whsc_data_contact@usgs.gov

Contact_Instructions:

The metadata contact email address is a generic address in the event the person is no longer with USGS.

Metadata standard:

Content Standard for Digital Geospatial Metadata (FGDC-STD-001-1998)