An updated radiocarbon-based ice margin chronology for the last deglaciation of the North American Ice Sheet Complex

The North American Ice Sheet Complex (NAISC; consisting of the Laurentide, Cordilleran and Innuitian ice sheets) was the largest ice mass to repeatedly grow and decay in the Northern Hemisphere during the Quaternary. Understanding its pattern of retreat following the Last Glacial Maximum is critical for studying many facets of the Late Quaternary, including ice sheet behaviour, the evolution of Holocene landscapes, sea level, atmospheric circulation, and the peopling of the Americas. Currently, the most up-to-date and authoritative margin chronology for the entire ice sheet complex is featured in two publications (Geological Survey of Canada Open File 1574 [Dyke et al., 2003]; ‘Quaternary Glaciations – Extent and Chronology, Part II’ [Dyke, 2004]). These often-cited datasets track ice margin recession in 36 time slices spanning 18 ka to 1 ka (all ages in uncalibrated radiocarbon years) using a combination of geomorphology, stratigraphy and radiocarbon dating. However, by virtue of being over 15 years old, the ice margin chronology requires updating to reflect new work and important revisions. This paper updates the aforementioned 36 ice margin maps to reflect new data from regional studies. We also update the original radiocarbon dataset from the 2003/2004 papers with 1541 new ages to reflect work up to and including 2018. A major revision is made to the 18 ka ice margin, where Banks and Eglinton islands (once considered to be glacial refugia) are now shown to be fully glaciated. Our updated 18 ka ice sheet increased in areal extent from 17.81 to 18.37 million km2, which is an increase of 3.1% in spatial coverage of the NAISC at that time. Elsewhere, we also summarize, region-by-region, significant changes to the deglaciation sequence. This paper integrates new information provided by regional experts and radiocarbon data into the deglaciation sequence while maintaining consistency with the original ice margin positions of Dyke et al. (2003) and Dyke (2004) where new information is lacking; this is a pragmatic solution to satisfy the needs of a Quaternary research community that requires up-to-date knowledge of the pattern of ice margin recession of what was once the world’s largest ice mass. The 36 updated isochrones are available in PDF and shapefile format, together with a spreadsheet of the expanded radiocarbon dataset (n = 5195 ages) and estimates of uncertainty for each interval

OFR19-1, Geologic Mapping Forum 2019 Abstracts

Abstracts for the Geologic Mapping Forum conference in Minneapolis from April 10 to 12, 2019At the Geologic Mapping Forum in Minneapolis from April 10th to 12th, 2019, ~100 geological map authors, program managers and allied professionals from geological surveys and associated agencies met to discuss the status and future of geologic mapping in the USA and neighboring countries. The meeting was hosted by the Minnesota Geological Survey on the University of Minnesota campus. The meeting was held at the Humphrey School of Public Affairs on the West Bank campus, in the Humphrey School Conference Center at 301 19th Avenue South, Minneapolis, MN 55455. Participants were invited to present a 30-minute plenary or 15-minute talk, or a poster, and submitted a 1 to 2-page abstract published in this Open File. The meeting opened with registration and a reception on Tuesday evening followed by conference sessions beginning at 8:30 AM Wednesday and ending 2:30 PM Friday. Regional organization business meetings followed on Friday afternoon and Saturday

OFR20-01, Minnesota Data Preservation Report for 2019/2020: Updated Data Inventory, Preservation of Pillsbury Hall Rock Collections and Documentation, Assembly of Mineral Potential Related Information

UPDATED DATA INVENTORY, PRESERVATION OF PILLSBURY HALL ROCK COLLECTIONS AND DOCUMENTATION, ASSEMBLY OF MINERAL POTENTIAL RELATED INFORMATIONMinnesota Geological Survey (MGS) activity is focused primarily on recommendations of Legislative panels that indicate that statewide coverage of layered County Geologic Atlases will be needed to support management of water resources, while concurrently being needed for applications such as mineral resources, engineering, hazards, and research. All MGS activity is reliant on geological specimens, as well as geological, geophysical, and geochemical data. The MGS long-term data preservation plan prepared in 2009 identified the highest priorities in relation to applications such as groundwater management and mineral resource assessment. Included were: 1) reprocessing of the aeromagnetic database; 2) enhancement of location precision for gravity stations; 3) vertical georeferencing of the rock property database; 4) cataloging and georeferencing of rocks and thin sections stored at the building MGS occupied from 1983 to 2015; 5) standardized formats for existing databases; and 6) scan and web enable all publications. More recently, a need was recognized for: 7) scanning, digitizing, and enhanced cataloging of borehole geophysical records, 8) comprehensive regional geophysical survey rescue, 9) enhancements to the cuttings collection and database. Objectives 1, 2, and 3 were completed with State of Minnesota support. Objective 4 was completed with multiple years of NGGDPP support. Objective 5 is ongoing. Objective 6 was completed with University of Minnesota Library support. Objective 7 was completed for gamma logs with our 2015 NGGDPP grant, and was completed for all borehole geophysical logs due to 2017 NGGDPP support. Geophysical survey rescue will remain unfulfilled due to staff availability constraints. Work on cuttings will be carried out due to NGGDPP support during 2020/2021.A report prepared in fulfillment of National Geological and Geophysical Data Preservation Program Award Number G19AP00064; 1 July 2019 – 30 June 202

Re-Os isotope characteristics of postorogenic lavas: Implications for the nature of young lithospheric mantle and its contribution to basaltic magmas

Re-Os isotopes have been measured on postorogenic potassic lavas from the Tibetan Plateau, the Betic domain of southeastern Spain, and the Colorado Plateau of the southwestern United States. Previous work has established that these lavas were all derived from parts of the subcontinental lithospheric mantle that had undergone metasomatic enrichment in incompatible elements, following various degrees of melt depletion. Cratonic depleted subcontinental lithospheric mantle peridotites typically have subchondritic 187Os/188Os; however, the postorogenic lavas are characterized by radiogenic 187Os/188Os ratios (0.139-0.559). Simple modeling shows that only very large degrees of melt depletion (>25-30) can lower source Re/Os ratios sufficiently to permit time-integrated development of subchondritic 187Os/188Os ratios. Such processes may have been largely restricted to the older Precambrian, and the peridotite component of the postorogenic lavas source was probably depleted by <25. The more radiogenic values may reflect increasing contributions from metasomatic components or possibly crustal contamination. Our findings imply the need for caution in the use of Os isotopes as a diagnostic tracer of subcontinental lithospheric mantle contributions to lavas erupted through younger Proterozoic and Phanerozoic lithosphere