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Thornhill, Canada

An unusual and remarkable find of fossilized Coleoptera exoskeletons, soil organics/plant roots, and microbes—recovered from an alpine-age paleosol in moraine at New Mountain near the Taylor Glacier in the Antarctic Dry Valleys—provides evidence for an ameliorative Early to middle Miocene Climatic Optimum (MMCO). Compared with the microbial analysis of other nearby and somewhat younger paleosols (sites 827-829) in nearby moraine deposits at both New Mountain and Aztec Mountain (sites that are known to contain bacteria and fungi), paleosol horizons at the alpine-age site (831) contain prolific fossil evidence of either an expanded MMCO or an earlier Early Miocene/Oligocene age. Together with fossil filamentous forms of either algae or fungi and bacteria, these Coleoptera exoskeletons make up part of a higher-altitude tundra ecosystem distantly related to a many-fold increase in terrestrial pollen and woody plants that inhabited the Dry Valley Coast ∼15 Ma or earlier. While the age of the 831 paleosol as discussed elsewhere is impossible to assess with precision, the presence of a mix of subround/subangular sands—a high percentage carrying V-shaped percussion cracks—signals significant aqueous transport, with the sediment believed to have been deposited before the transition from warm/wet to cold/dry ice. In addition, fossilized organics— including salt-encrusted earth, roots, and clay/mineral coatings on both sands and biogenic specimens—suggest at least an early cold/semihumid environment conducive to weathering, probably mediated by microbe activity. Other chemical indices reported previously are here analyzed with extractable Fe/Al, which suggests greater antiquity, possibly Early Miocene or Oligocene. © 2015 by The University of Chicago.

Mahaney W.C.,Quaternary Surveys | Keiser L.,University of Oklahoma
Geomorphology | Year: 2013

Interhemispheric evidence of a cosmic impact 12.9ka is known now from North to South America, Europe and Eurasia, all data supporting a cosmic event derived from cores and from geological sections. Most databases supporting the impact hypothesis at the Younger Dryas Boundary (YDB) rely on high-temperature microspherules, melted minerals, cracked clasts, presence of nanodiamond, high-temperature scoria, high Fe/Ni ratios, pdf's, shock melted quartz, high 10Be/9Be ratios and occasional presence of platinum metals. Controversy over the impact, the so-called Black Mat enigma, and its relation to the Younger Dryas readvance at the end of the last ice age, is fueled by arguments over whether a single extraterrestrial impact might sustain a 1kyr-long downturn in insolation engendering a substantial increase in worldwide ice volume. New evidence in the form of impact microfeatures - extreme breccia, high crack propagation, thick carbon encrustations and partial to full shock-melted/contorted grains - in weathering rinds from the Western Alps, France, as documented here, adds to the growing body of evidence that the event was truly widespread, if not worldwide in effect. Whereas evidence of cosmic impacts may be erased by glacial and fluvial erosion in high alpine areas, such events as demonstrated herein are recorded as punctuated time-stratigraphic events in microcosm, preserved in weathered clasts. © 2012 Elsevier B.V.

Mahaney W.C.,Quaternary Surveys | Krinsley D.H.,University of Oregon | Allen C.C.R.,Queens University of Belfast
Geomicrobiology Journal | Year: 2013

Rock rinds have been used for half a century to date glacial deposits and recently inroads have been developed to use nuclides to provide absolute ages of weathering rinds in pebble clasts. Although maximum and minimum rind thicknesses have helped to elucidate time since deposition and allowed stratigraphic division of deposits at glacial rank, little has been done to investigate the wealth of mineral degradation, growth of alteration products and biomineralization that occur in these weathered crusts. In some cases the mass of microbe-mineral intergrowth is nearly present on a 50%/50% basis, with the biotic mass intergrown with mineral matter to such an extent that it probably controls pH and redox phenomena that act as accelerators in the weathering process. Assuming weathering time spans of 2 × 106 years or more for a complete cycle, eventual clast decomposition is the end product. Here we present evidence of microbe-clast intergrowth from selected sites of Pleistocene age (~70 ka to 2.0 Ma) in the lower Afroalpine of Mt. Kenya and hypothesize about its role in rock decomposition and fossilization of biotic end-members. © 2013 Copyright Taylor and Francis Group, LLC.

Mahaney W.C.,Quaternary Surveys | Krinsley D.,University of Oregon | Kalm V.,University of Tartu
Sedimentary Geology | Year: 2010

Fired sediment, considered equivalent to the 'Black Mat' impact of 12.9 ka, has been located and analyzed in the Andes of northwestern Venezuela. The 'Black Mat' refers to possible fallout from the Encke Comet airburst presumed to have occurred over the Laurentide Ice Sheet, the impact spreading ejecta over large portions of North America and Europe, making it an interhemispheric event of considerable magnitude. These possible equivalent beds in the northern Andes, first considered to result from a lightning-induced conflagration adjacent to the retreating Late Wisconsinan (Mérida Glaciation) ice, are now known to have undergone intense heating upon impact to a temperature much higher than what would occur in a wet, first-stage, successional tundra. Analyses carried out by SEM and FESEM, in SE and BSE modes, show massive micro-disruption on grain surfaces, fractures diminishing with depth toward grain interiors and C welded onto quartz and plagioclase minerals. Bubbles on some grains, possibly the result of exclusion of water-of-crystallization, are seen on some samples, principally quartz. The presence of copious monazite in the carbonaceous coatings is considered part of the incoming ejecta, as it is not a common indicator mineral in the local lithology. Analysis by SEM and FESEM of quartz and plagioclase subjected experimentally to temperatures ranging from 500 to 900 °C shows that intense heating affects resident mineralogies to differing extents, with grain disruption more prevalent along cleavage planes deep into grain interiors. The intergrowth of carbonaceous "black mat" material with thermally disrupted and fragmented quartz and feldspar, a "welded" patina of 100-400 nm thickness could only occur with temperatures in excess of 900 °C, the event interpreted here to be of cosmogenic origin. © 2010 Elsevier B.V.

Mahaney W.C.,Quaternary Surveys | Kalm V.,University of Tartu
Geomorphology | Year: 2012

Retreat of the Stabre Glacier in the Norra Storfjället Mountains of northern Sweden led to the emplacement of a broad expanse of glaciofluvial sediment, a virtual blanket of debris interspersed with recessional and push moraines. Episodic mass wasting of the glaciofluvial, moraine and loessic deposits yielded a pedostratigraphic succession of 14C-dated sub-Boreal and sub-Atlantic Cryosols in soliflucted sediment that provide weathering data related to Neoglacial perturbations, whereas weathering within polygonal complexes yielded single profile, one event, Cryosolic Gleysols of similar age. Both provide a database of paleosol extremes controlled by topography and bioclimate. Together, the paleosols provide a database of weathering of mixed amphibolitic gneiss, trachytic lavas and granite weathering under two variable redox conditions, one (soliflucted sediment) fully or partially aerated and free draining under a subaerial atmosphere with high redox potential; the other (polygonal soil) partly reduced under the influence of an active layer of sporadic permafrost. Paleosols dated to the Early Neoglacial (~3600-4200cal 14CyrBP) have variable horizon development dependent upon landform associations, and provide maximum ages for the second oldest moraine stillstand of ice retreat into the highlands on the Arctic Circle of Sweden. The Cryosolic Gleysol yields surprisingly high extractable Fe and Al suggestive of considerable redox fluctuations over the time of morphogenesis. © 2012 Elsevier B.V.

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