Folks, This is a reminder about the Brown Bag Lunch today. I have been contacted by a few folks that can't attend this presentation. I'm sorry but we're not set up to record the Brown Bags but Bruce has offered to talk with people that are interested. He can be reached at bdarl...@geosyntec.com<mailto:bdarl...@geosyntec.com>
Hope to see you there. Geary Edwards Aquifer Philosophical Society - aka brown bag luncheon Wednesday, February 15, 2017 at 11:55 AM. Carbon-14 (14C) and Abundances of Deuterium (D) and Oxygen-18 (18O) along Groundwater Flow Paths of West Texas Bolson Aquifers as Indicators of Post-Pleistocene Warming By Bruce K. Darling, Ph.D., P.G. At Edwards Aquifer Authority Training Room 900 E Quincy Street, San Antonio, TX 78215 Dr. Bruce K. Darling will make a presentation titled: Carbon-14 (14C) and Abundances of Deuterium (D) and Oxygen-18 (18O) along Groundwater Flow Paths of West Texas Bolson Aquifers as Indicators of Post-Pleistocene Warming." Wednesday, February 15, 2016 at 11:55 AM. The presentation will be held in the Training Room at the Edwards Aquifer Authority, 900 E. Quincy Street, San Antonio, Texas. These are informal presentations so please feel free to bring your lunch. You may also contact the EAA at 210.222.2204 or www.edwardsaquifer.org<http://www.edwardsaquifer.org/> for additional directions. If you are traveling a long distance for the talk, I would recommend that you call our receptionist at 210.222.2204 that morning to make sure that the talk is still scheduled. On very rare occasions, we have had to cancel or move the talk. I apologize for any inconvenience this may cause. Abstract Carbon-14 (14C) data from hydrogeologic studies in western Texas and southeastern New Mexico indicate that groundwaters of the region range in age from modern to late Pleistocene, with oldest apparent (uncorrected) residence times of 15,000 to as much as 30,000 years. The use of 14C in groundwater age-dating studies, however, is complicated by geochemical processes which render the isotope unreliable as an estimator of absolute age. These include dilution of 14C by interaction with Cretaceous and Permian carbonate rocks, and mixing of old and young groundwaters in dual-porosity systems. We present an indirect approach to the problem of estimating residence time based on the integration of 14C with deuterium (D) and oxygen-18 (18O) - water-cycle stable isotopes with known temperature-fractionation gradients. Confined groundwaters of southeastern New Mexico and the Southern High Plains have been documented to be more depleted in D and 18O than unconfined waters. The lower δD-δ18O ratios of the confined waters have been attributed to the effects of depletion from heavier precipitation and/or lower temperatures of the late Wisconsinan glacial period. In the Eagle Flat and Red Light basins (Hudspeth County) of the West Texas system of bolson aquifers, we have found groundwaters to be increasingly depleted in D and 18O along flow paths between basin margins and basin centers. The depletion corresponds well with decreasing 14C measurements reported as percent of modern carbon (PMC), with increased depletion of D and 18O occurring at 15 PMC and lower. We postulate that the association between δD-δ180 and 14C may constitute a semi-quantitative basis for differentiation of late Pleistocene and Holocene recharge dates, and that the trend toward younger waters more enriched in D and 18O is a reflection of a warming and increasingly arid regional climate over the last 10,000 to 11,000 years. Furthermore, based on the range of lightest to heaviest δ180 ratios in groundwater, we estimate temperature differences of 5.5 to 7.5°C between the late Pleistocene and modern climates. Biography Bruce K. Darling, Ph.D., P.G., has 35 years of experience as a geologist and geochemist in the energy and environmental industries. He is a Senior Consultant with Geosyntec Consultants, Austin, Texas. Thank you. Geary [https://ucarecdn.com/cfe99bfa-9ee9-4330-862f-aee807af1b4c/-/resize/132x68/img.png]<http://www.edwardsaquifer.org/> Geary Schindel Director/CTO, Aquifer Science www.edwardsaquifer.org<http://www.edwardsaquifer.org/> 210.222.2204 ext 346 900 E Quincy San Antonio, TX 78215 [https://app.zippysig.com/social-icons/24/000055/03facebook.gif]<https://www.facebook.com/TheEdwardsAquifer/?sk=wall> [https://app.zippysig.com/social-icons/24/000055/03twitter.gif] <https://twitter.com/EdwardsAquifer> [https://app.zippysig.com/social-icons/24/000055/03youtube.gif] <https://www.youtube.com/edwardsaquiferauthorityeaa>
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