Attachment_-_Statement_of_work_1.pdf

STATEMENT OF WORK

Detrital Zircon Geochronology using LA-MC-ICPMS

Section 1. General Information

A. Introduction

Scientists from the U.S. Geological Survey (USGS) Geology, Energy, and Minerals

Science Center (GEMSC), and Florence Bascom Geoscience Center (FBGC) in Reston, VA requires detrital zircon U/Pb, Hf, and T/REE analyses for rock and modern sediment samples.

Samples will support scientific work across multiple projects, including, but not limited to, the

Gulf of Mexico Petroleum Systems Project and the Alaska Petroleum Systems Project. U/Pb geochronology is increasingly a routine element of basin analysis, and ongoing USGS Energy

Resources research campaigns have been designed, in part, on the basis of being able to generate and utilize this type of data. Data analyses have been conducted over the past 5 FY via a BPA with the Arizona LaserChron Center, and this PR seeks to continue that effort, which concluded in March of 2026.

B. Background

Detrital zircon U/Pb geochronology is a powerful provenance tool for fingerprinting sediment sources and defining maximum depositional ages. Furthermore, detrital zircon U/Pb ages can provide precise ages for deposits that otherwise have poor or no biostratigraphic age control. In addition, U/Pb provenance is particularly useful in study locations where multiple sediment source areas have similar lithologic composition but have distinguishable U/Pb age signatures. In areas with both similar lithologies and ages, additional zircon chemical information (Hf and T/REE) can be used together to elucidate provenance.

In sedimentary basins, examining U/Pb age spectra from sediments allows one to characterize the relative contributions of different sediment source areas during basin filling.

Furthermore, age spectra from several levels within a stratigraphic succession that spans several million years can define chronostratigraphy and track the evolving sediment source regions.

Section II. Work Requirements

Task 1: PWS: Given samples of sand and sandstone, the contractor shall conduct U-Pb geochronologic analysis for 100–300 zircons per sample. Upon request, the contractor may be asked to determine 600 or more analyses per sample in order to statistically characterize the entire detrital age population and/or screen for grains (zircons) that constrain the maximum depositional age of a sample.

Task 1 Standards:

Quality Standards: The contractor shall perform all U-Pb geochronologic analysis following the protocols outlined in Gehrels et al. (2006, 2008) and Sundell et al. (2020), and Hf isotope geochemistry following the protocols reported in Cecil et al. (2011) and Gehrels and

Pecha (2014).

To ensure data continuity with existing USGS data, the contractor shall combine single shot laser ablation methods with inductively coupled plasma mass spectrometer measurements of isotopic abundances. These requirements mean that the contractor shall also employ data reduction methods that integrate isotope signal intensities over the duration of a single laser pulse to calculate isotope ratios for unknowns, in order to avoid systematic errors that may arise from tau (decay) and/or response time offset effects for different types of ion counters/detectors.

Importantly, the geochronologic method must be nondestructive and consume a diameter of ≤30 microns and depth of ~15 microns of material per zircon, such that additional geochemical measurements may be made on grains as necessary, including Hf isotopic abundances. In order to discriminate between provenance areas with similar geochronologic ages, the contractor may be asked to first analyze a large number of grains for U-Pb, and then subsequently perform laser ablation analysis on optimal grains of known U-Pb ages to measure T/REE and Hf isotopic concentrations (SC-ICPMS) on a specific population of zircon grains.

The contractor shall be able to demonstrate reproducibility of 238U/206Pb and 206Pb/207Pb ratios for geochronologic reference materials of better than 3%, using the analytical protocols described above. The precision and accuracy of geochronologic measurements should be demonstrated by bracketing measurements of unknowns with measurements of geochronologic standards.

In order to provide USGS researchers with the ability to constrain maximum depositional ages for samples lacking sufficient independent age control, the contractor shall, upon request, measure 600 U-Pb zircon ages per sample at a rate of 600 analyses per hour following the method of Sundell et al (2020). For these samples, reproducibility of 238U/206Pb and 206Pb/207Pb ratios for geochronologic reference materials of better than 5% is sufficient. Similar to the requirement described above, the data reduction methods must integrate isotope signal intensities over the duration of a single laser pulse in order to calculate isotope ratios for unknowns.

Time Standard(s): The total performance period for analysis of all samples included in the purchase request shall not exceed one year. The contractor and the USGS will agree upon a timeframe for the work to be completed once samples are shipped, depending on whether mineral separation is required. The contractor may complete the work at any time during this agreed upon timeframe. The USGS will provide samples in advance with sufficient time for the contractor to perform mineral separation (usually ~8 weeks), if needed, and in advance for mounting and BSE imaging (usually ~2 weeks), unless otherwise expedited.

Deliverable: The contractor shall deliver U-Pb and Pb-Pb ages for each single grain, as well as the corresponding U and/or Pb isotope ratios, analytical uncertainties, error correlations, and mass spectrometer signal intensity data. The contractor shall also deliver Uranium and

Thorium concentration measurements for each grain, in a formatted Excel spreadsheet. The locations of each analysis will be provided either as an annotated image of the back-scatter electrons (BSE) map of the mount or as a data file.

Quality Assurance: Geochronologic reports that are less than the quality standard shall be redone by the contractor at no additional cost to the government.

Acceptance: The U.S. Geological Survey’s Technical Liaison (TL) will accept the work if the 100% complete U-Pb geochronologic measurements are presented for >100 zircons from each sample, and for 600 zircons per sample as requested by USGS scientists.

Section III. Supporting Information

A. Place of performance

To be determined.

B. The contractor and the USGS will mutually agree upon a timeframe for the work to be completed within 1–3 months of the order, depending on whether mineral separation is required.

The contractor shall provide analytical services from, at minimum, a M.S. with expertise in analytical geochemistry and continental tectonics.

C. References

Cecil, R., Gehrels, G., Patchett, J., and Ducea, M., 2011, U-Pb-Hf characterization of the central

Coast Mountains batholith: Implications for petrogenesis and crustal architecture: Lithosphere, v.

3, no. 4, p. 247–260, doi:10.1130/L134.1.

Gehrels, G.E., and Pecha, M.E., 2014, Detrital zircon U-Pb geochronology and Hf isotope geochemistry of Paleozoic and Triassic passive margin strata of western North America:

Geosphere , v. 10, no. 1, p. 49–65, doi:10.1130/GES00889.1.

Gehrels, G.E., Valencia, V., Ruiz, J., 2008, Enhanced precision, accuracy, efficiency, and spatial resolution of U-Pb ages by laser ablation–multicollector–inductively coupled plasma–mass spectrometry: Geochemistry, Geophysics, Geosystems, v. 9, Q03017, doi:10.1029/2007GC001805.

Gehrels, G.E., Valencia, V., Pullen, A., 2006, Detrital zircon geochronology by Laser-Ablation

Multicollector ICPMS at the Arizona LaserChron Center, in Loszewski, T., and Huff, W., eds., Geochronology: Emerging Opportunities, Paleontology Society Short Course: Paleontology

Society Papers, v. 11, 10 p.

Sundell, K.E., Gehrels, G.E., and Pecha, M.E., 2020, Rapid U-Pb Geochronology by Laser

Ablation Multi-collector ICP-MS: Geostandards and Geoanalytical Research doi:10.1111/ggr.12355

Quality Assurance Surveillance Plan (QASP)

Sample Analyses. The Technical Liaison (TL) will inspect every sample report to assure that the quality of the report meets 100% of the standards required by this work statement. If the work fails to meet the standards required, then the contractor shall redo the work at no additional cost to the government.

LA-MC-ICPMS Usage. The TL will conduct U-Pb geochronologic analysis on geochronologic standards, as described in Gehrels et al. (2006, 2008) and Sundell et al. 2020, to verify that the geochronologic data meets the standards described by Gehrels et al. (2006, 2008).