Geochemical indicators of a biogenic component in source materials of moldavites

ABSTRACT Formation of the Central European tektites, known as moldavites, has been associated with a large meteorite impact in southern Germany 14.8 m.y. ago. The geochemical link between moldavites and their source materials, and the processes of their possible chemical differentiation still remain uncertain. Some differences in chemical composition between moldavites and sediments of corresponding age from the surroundings of the Ries crater could be explained by a hypothesis according to which biomass covering the pre-impact area contributed to the source materials. In a comparison of the geochemical compositions of a large representative set of moldavites and suitable Ries sediments, enrichment in elements K, Ca, Mg, and Mn and depletion of Na in moldavites, similar to redistribution of these elements during their transfer from soil to plants, could indicate the unconventional biogenic component in moldavite source materials. Simple mixing calculations of the most suitable Ries sediments and a model biogenic component represented by burned biomass residue are presented. The plausibility of the estimated biomass contribution considering reconstructions of the middle Miocene paleoenvironment in the pre-impact Ries area is discussed. No significant vapor fractionation is required to explain the observed variability of moldavite chemical composition.

Premature rejection in science: The case of the Younger Dryas Impact Hypothesis

The progress of science has sometimes been unjustifiably delayed by the premature rejection of a hypothesis for which substantial evidence existed and which later achieved consensus. Continental drift, meteorite impact cratering, and anthropogenic global warming are examples from the first half of the twentieth century. This article presents evidence that the Younger Dryas Impact Hypothesis (YDIH) is a twenty-first century case. The hypothesis proposes that the airburst or impact of a comet ∼12,850 years ago caused the ensuing ∼1200-year-long Younger Dryas (YD) cool period and contributed to the extinction of the Pleistocene megafauna in the Western Hemisphere and the disappearance of the Clovis Paleo-Indian culture. Soon after publication, a few scientists reported that they were unable to replicate the critical evidence and the scientific community at large came to reject the hypothesis. By today, however, many independent studies have reproduced that evidence at dozens of YD sites. This article examines why scientists so readily accepted the early false claims of irreproducibility and what lessons the premature rejection of the YDIH holds for science.

Изменение сукцессионных систем палеофитоценозов на границе межледниковья и ледниковья позднего эоплейстоцена в пыльцевой записи оз. Эльгыгытгын (Центральная Чукотка)

Lake El'gygytgyn is located beyond the Arctic Circle in Chukotka at 67°30' N, 172°05' E and formed following a meteorite impact that occurred 3.6 million years ago (core interval 45.79-43.65 m). In its sediments, 5 palinologic zones are distinguished; they reflect changes in paleosuccessional systems and are consistent with MIS 33, 32, and 31 (1.114-1.062 mya). During warmings, thickets of birch trees and alder were widely spread. Cliseries, caused by macroclimate changes in cold substages, are characterized by a significant reduction in tree and shrub vegetation as well as by expansion of the arctic and subarctic tundras. Grass tundras dominated and were replaced by forest tundra communities in the valleys of the Anadyr Plateau surrounding the lake. The most abrupt change of phytocenosis succession systems is observed at the border of 32 and 31 isotopic stages. The succession processes are primarily expressed in a sharp increase of birch-shrub communities in the vegetation cover and in the appearance of late succession edificators (Carpinus, Corylus, Myrica, Quercus) forming forest climax associations.

Late Ediacaran organic microfossils from Finland

Here we present a detailed accounting of organic microfossils from late Ediacaran sediments of Finland, from the island of Hailuoto (northwest Finnish coast), and the Saarijärvi meteorite impact structure (~170 km northeast of Hailuoto, mainland Finland). Fossils were recovered from fine-grained thermally immature mudstones and siltstones and are preserved in exquisite detail. The majority of recovered forms are sourced from filamentous prokaryotic and protistan-grade organisms forming interwoven microbial mats. Flattened Nostoc-ball-like masses of bundled Siphonophycus filaments are abundant, alongside Rugosoopsis and Palaeolyngbya of probable cyanobacterial origin. Acritarchs include Chuaria, Leiosphaeridia, Symplassosphaeridium and Synsphaeridium. Significantly, rare spine-shaped sclerites of bilaterian origin were recovered, providing new evidence for a nascent bilaterian fauna in the terminal Ediacaran. These findings offer a direct body-fossil insight into Ediacaran mat-forming microbial communities, and demonstrate that alongside trace fossils, detection of a bilaterian fauna prior to the Cambrian might also be sought among the emerging record of small carbonaceous fossils (SCFs).

Ejecta Discovered Near Site of Ancient Meteorite Impact

South Africa’s Vredefort impact structure is the largest on the planet, and researchers have now discovered the first proximal ejecta possibly deriving from the cataclysmic impact.

Glassy Nodules Pinpoint a Meteorite Impact

Researchers working in Chile’s Atacama Desert have collected thousands of “atacamaites” that suggest a meteorite struck the region roughly 8 million years ago.