September 12, 2022
6:00 - 7:30 pm
Note: ETGS members will receive an email with info for logging into the meeting.
The Younger Dryas Impact Hypothesis (YDIH) - An Interesting Story .....
Gareth J. Davies, TDEC (Retired)
The end of the last glacial maximum about 18 ka
began with a steady increase in temperature. However, at 12.8 +/- 58
ka there began an abrupt cooling during a short period (~100 years)
lasting for 1,000 years (the Younger Dryas [YD]) that led to the
extinction of large mammal species and civilizations (e.g., Clovis)
across the Northern Hemisphere. Although there are several YD
hypotheses, the abruptness of the cooling poses problems for many of
those. In 2007 a NASA paper proposed an asteroid or comet impact,
now called the Younger Dryas Impact (YDI). There are now many sites
across the world that support that hypothesis, but no crater has
been found. However, we have experienced shockwave blasts
(Chelyabinsk  and Tunguska ) from asteroids (or comet
fragments) in the atmosphere that left no craters on the ground
(except building and forest damage).
Sedimentary record? Caves provide one of the most useful sedimentation records available, for both clastic (fill) sediments and travertine (speleothem) deposits. During recent years improvements in dating techniques have resulted in being able to date a longer span of time, and have also shown a general increase in age - and some big jumps. For years, most karst models involved Pleistocene origins in many areas. But, some assumed to be Pleistocene karst is actually subaerial Triassic paleokarst (Wales). The Gray Fossil Site in Tennessee is, at minimum, an older than Eocene (55 Ma) paleokarst.... There may be many more like that.
During sample collection for a large U/Th dating project in the Ogof Ffynnon Ddu, Cave, South Wales, UK, a colleague and old friend and I luckily found a stalagmite that, when dated, had grown through the YD event. The problem is that during cold periods speleothem/travertine growth is typically suppressed, but clastic deposits are often deposited. However, "confirmed" YDIH sites always have at least a few of the following: trace metals, nanodiamonds, magnetic microspherules, and Pt and Ir anomalies and a black "mat" deposit - burned organic material dated at near 12.9 ka. Are those present in the stalagmite? Clastic cave deposits are mostly transported from outside, so it is challenging to identify possible YDIH horizons in caves....
Following the solidification of the YDIH, typical "horizon signatures" have been identified worldwide. Also, in the Midwest and Eastern US many strange impact structures called Carolina Bays may be related to the YDI, and sampled sites have the same data characteristics and age.
Gareth grew up in South Wales in a coal-mining community, next to a major karst area, and thus was interested in caves from the age of 15. He spent many years traveling in Asia, Europe, North America and Mexico exploring caves before marrying and moving to the US. He was awarded a BS degree from Millsaps College and an MS degree from the University of Southern Mississippi. His thesis dated speleothems from Tennessee cave using the uranium-thorium method. He moved to Oak Ridge and spent a couple of decades running his own company doing multiple tracer work from Puerto Rico to the US Rocky Mountains. After being a contractor, he later joined TDEC (now retired). He is a Fellow of the Geological Society of America.
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Page updated August 31, 2022