IMPACT-RELATED MICROSPHERULES IN LATE PLEISTOCENE ALASKAN AND YUKON “MUCK” DEPOSITS SIGNIFY RECURRENT EPISODES OF CATASTROPHIC EMPLACEMENT

Large quantities of impact-related microspherules have been found in fine-grained sediments retained within seven out of nine, radiocarbon-dated, Late Pleistocene mammoth (Mammuthus primigenius) and bison (Bison priscus) skull fragments. SEM/EDS data indicate the microspherules are not cosmic, anthropogenic, or volcanic in origin, but were most likely produced by hypervelocity impacts. The well-preserved fossils were recovered from frozen “muck” deposits (organic-rich silt) exposed within the Fairbanks and Klondike mining districts of Alaska, USA, and the Yukon Territory, Canada. In addition, elevated platinum abundances compared to primary air-fall loess were found in sediment analyzed from three out of four fossil skulls (0.8-1.3 ppb vs. 2.2-3.9 ppb). The demise of animals whose frozen remains have been found in Beringian mucks has long been attributed to “natural deaths” in a “rigorous environment”, and researchers have generally held to non-catastrophic or “uniformitarian concepts” in their interpretations of the causal events leading up to fossil preservation. In view of our new evidence, however, the mucks and their well-preserved but highly disrupted and damaged vertebrate and botanical remains are reinterpreted, in part, as blast deposits that resulted from several episodes of airbursts and/or ground/ice impacts within the northern hemisphere during Late Pleistocene time (~46–11 ka B.P.). Such a scenario might be explained by periodic encounters with cometary debris in Earth-crossing orbits (Taurid Complex) that was generated by the fragmentation of a large short-period comet within the inner Solar System.