Leah E. Morgan 20250314 Version 1.0 (if applicable) tabular digital data Denver, CO U.S. Geological Survey Additional information about Originator: Morgan, L.E., https://orcid.org/0000-0001-9930-524X Suggested Citation: Morgan, L.E., 2024, Argon data for East African samples, U.S. Geological Survey data release, https://doi.org/10.5066/P148SEGR. https://doi.org/10.5066/P148SEGR Ar/Ar data are for 12 samples that record the eruption age of tephra. The geochronology provides time constraints for the ages of tephra and interbedded sediments and fossils from Kenya and Ethiopia. Samples were collected by Erin Dimaggio (Pennsylvania State University), who brought them to the USGS Denver Argon Geochronology Laboratory for Ar/Ar analysis. Samples were analyzed in January 2024. Data were obtained in order to determine the timing of tephra eruption. Data were shared to meet open data requirements. References: Kuiper, K.F., Deino, A., Hilgen, F.J., Krijgsman, W., Renne, P.R. and Wijbrans, J.R., 2008, Synchronizing rock clocks of Earth history: Science 25 April 2008, v. 320, issue 5875, pp. 500-504, available at https://doi.org/10.1126/science.1154339. Lee, J.-Y., Marti, K., Severinghaus, J., Kawamura, K., Yoo, H. and Kim, J., 2006, A redetermination of the isotopic abundances of atmospheric Ar: Geochimica et Cosmochimica Acta v. 70, pp. 4507-4512, available at https://doi.org/10.1016/j.gca.2006.06.1563. Min, K.W., Mundil, R., Renne, P.R. and Ludwig, K.R., 2000, A test for systematic errors in 40Ar/39Ar geochronology through comparison with U/Pb analysis of a 1.1-Ga rhyolite: Geochimica et Cosmochimica Acta v. 64, pp. 73-98, available at https://doi.org/10.1016/S0016-7037(99)00204-5. Niespolo, E.M., Rutte, D., Deino, A.L., Renne, P.R., 2016, Intercalibration and age of the Alder Creek sanidine 40Ar/39Ar standard: Quaternary Geochronology , available at http://dx.doi.org/10.1016/j.quageo.2016.09.004. Renne, P.R., Knight, K.B., Nomade, S., Leung, K.-N. and Lou, T.-P., 2005, Application of deuteron–deuteron (D–D) fusion neutrons to 40Ar/39Ar geochronology: Applied Radiation and Isotopes v. 62, pp. 25-32, available at https://doi.org/10.1016/j.apradiso.2004.06.004. Ross, J., 2015. Pychron Software Suite. https://pychron.readthedocs.io/en/latest/intro.html. Stoenner, R.W., Schaeffer, O.A. and Katcoff, S., 1965, Half-Lives of Argon-37, Argon-39, and Argon-42: Science v. 148, pp. 1325-1328, available at https://www.jstor.org/stable/1716001. 20240105 20240223 ground condition Complete None planned 35.9367 40.8661 11.4010 -1.3101 ISO 19115 Topic Category geoscientificInformation none U.S. Geological Survey USGS Mineral Resource Program MRP Geology, Geophysics, and Geochemistry Science Center GGGSC Geochronology Tephra Denver Argon Geochronology Laboratory USGS Metadata Identifier USGS:66f7012cd34e98f05fb37f5d NGA GEOnet Names Server (GNS) Kenya Ethiopia None. Please see 'Distribution Info' for details. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although these data have been processed successfully on a computer system at 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. The USGS or the U.S. Government shall not be held liable for improper or incorrect use of the data described and/or contained herein. Leah E. Morgan U.S. Geological Survey mailing

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Denver CO 80225 USA 303-236-4729 lemorgan@usgs.gov This release of the dataset was funded by the U.S. Geological Survey Mineral Resources Program (MRP). Windows 10, Pychron v.20.1.1 These data have been peer reviewed and compared with related ancillary data. Data were reviewed for consistency and analyses results were checked for validity and fidelity of relationships. Data set is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. All data as part of this collection were included in this data release for the region and time period specified in this metadata. (Include information about omissions, generalizations, selection criteria here - see guidance) Spatial locations were determined from hand-held global positioning system (GPS) devices. No formal positional accuracy tests were conducted. Samples, together with neutron flux monitor FCs-EK (Morgan and others, 2014), were loaded into specific positions of an aluminum irradiation disc, wrapped in Al foil, then vacuum encapsulated in quartz glass. The quartz glass tube was irradiated in the CLICIT facility of the Oregon State University TRIGA Reactor. Following irradiation, samples and neutron fluence monitors were placed in Cu laser discs for analysis. 202312 Mass spectrometry was performed at the U.S. Geological Survey Argon Geochronology Laboratory in Denver, Colorado. Laser disks with samples were placed into a stainless-steel laser chamber and covered by an externally pumped flange with a ZnSe viewport. Each sample was degassed using a Photon Machines 50 W CO2 laser with a homogenizing lens to ensure even heating across each 3mm diameter pit. Gas released by laser heating was purified using a cryotrap held at ca. -130 degrees C; gas was then exposed to two SAES GP50 getters (one held at 2 A, the other at room temperature) for further purification. Purified noble gases were then expanded into a Thermo Scientific ARGUS VI mass spectrometer and analyzed in static mode, in multi-collection mode with four Faraday collectors (for masses 40, 39, 38 and 37) and one ion-counting compact discrete dynode (CDD) collector (for mass 36). Argon isotope data were collected and reduced using the Pychron software package (Ross, 2015). Full-system backgrounds (with the same procedures as sample runs, except the laser is not turned on) were measured between every 5 samples or air pipettes. Background corrections were made using a long-term mean and standard deviation; this method incorporates a larger uncertainty than individual background measurements, as it also encompasses the variability in background values throughout the run. Faraday detectors were intercalibrated by peak-hopping an 40Ar beam from an air pipette between detectors, and an intercalibration factor is determined from the resulting data. The CDD was intercalibrated with Faraday collectors via air pipette measurements of 40Ar on the H1 detector and 36Ar on the CDD; this detector intercalibration thus accounts for both discrimination and variations in detector sensitivity. Air pipettes were analyzed in groups of three, approximately twice per day; detector intercalibration corrections were made using a long-term mean and standard deviation of air pipette analyses based on the atmospheric argon composition (Lee et al. 2006). Interference corrections were made using a combination of coirradiated salts and values from Renne et al. (2005). Decay corrections were made using values from Stoenner et al 1965 (39Ar) and Renne and Norman (2001) for 37Ar. Neutron fluence monitors and decay constants used are provided and cited in Parameters table (e.g. Kuiper et al. 2008, Min et al. 2000, Niespolo et al. 2016). 202401 0.001 0.001 Decimal degrees World Geodetic System 1984 (WGS 84) WGS_84 6378137.0 298.257223563 A data dictionary, EA_Data_Dictionary_Master.csv, was used to define the attributes of the data files. https://doi.org/10.5066/P148SEGR ScienceBase U.S. Geological Survey mailing and physical

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Denver CO 80225 USA 1-888-275-8747 sciencebase@usgs.gov https://www.sciencebase.gov/catalog/item/66f7012cd34e98f05fb37f5d 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. Describe any technical prerequisites required for reading the data 20250314 Leah E. Morgan U.S. Geological Survey mailing

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Denver CO 80225 USA 303-236-4729 gs_gggsc_dm_team@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998