Clast rind analysis using multi‐high resolution instrumentation

Abstract

Clast weathering rinds, formed over varying lengths of time (10(2) -10(6) years) in terrestrial environments, are measured to provide relative ages for deposits in glacial sequences, specifically to differentiate between glaciations, occasionally within glaciations. Other studies have sought to reveal weathering rates in non-glacial environments using microscopic techniques and isotopes. Recent analyses of clast rinds from tropical, mid-latitude and polar areas reveal an astounding corpus of organic and inorganic paleoenvironmental data derived from atmospheric and biospheric elements active in weathering clasts in glacial deposits over varying lengths of time. In some cases, extreme biochemical products, observed within the rind matrix, are seen to play a role in adjusting redox potentials important in the production of oxides and hydroxides and biominerals with variable compositions. Up to recently, rind analysis has been limited to use of the light microscope and SEM/EDS, which has greatly advanced our understanding of compositional inter-linkages of minerals and biotic elements, but only along horizontal axes within the rind. A test involving rind surface composition using vertical axis nanospaced layer analysis within rinds using focused ion beam (FIB) and TEM/STEM/EDX imagery and chemistry illustrates the power of data acquisition within the three-dimensional weathered archive. SCANNING 38:202-212, 2016. © 2015 Wiley Periodicals, Inc.

Cosmic Airburst on Developing Allerød Substrates (Soils) in the Western Alps, Mt. Viso Area

“…These grains are typical of the population of minerals recovered from all mid-LG sites in the upper Po and Guil catchments. melted and highly fractured outer rind areas (~700 nm) as detailed by Mahaney and Keiser (2013) and Mahaney et al (2016b). Paleosols within the YD group carry similar depth/horizonation to the older mid-LG profiles and classify into the same soil order as the older paleosols.…”

“…All sites outlined below have been thoroughly analyzed for soil profile description, soil mineralogy and chemistry, with various details reported elsewhere (Mahaney and Keiser, 2013;Mahaney et al, 2013cMahaney et al, , 2016a. In the main, the mid-LG paleosols contain pebble size clasts in the upper Ah horizons from which samples have been collected for rind analysis (Mahaney et al, 2016b), the rinds carrying various archives of the airburst/impact, first recorded by Mahaney and Keiser (2013). These rinds contain melted quartz, glassy carbon spherules, opaque carbon clusters welded onto grains of country rock origin, Fe spherules and elevated variable concentrations of Co, Cu, Ni and REEs, mostly elevated above crustal averages (Rudnick and Gao, 2005).…”

“…Ensuing detailed laboratory evidence of the recovered samples revealed evidence suggestive of impact ejecta from local impact/airbursts producing ionizing/incandescent clouds which, in turn, twisted and melted quartz, producing possible deformation features (PFs) and planar deformation features (PDFs), glassy spherules, microspherules, and abnormally high concentrations of Fe, albeit with no elevated Ni (Mahaney et al, 2010). Further analytical work using a FIB (focused ion beam) and TEM (transmission electron microscope) showed abnormally disrupted minerals heated to temperatures well in excess of ~1500 o C, with the overall effect of producing considerable breccia and excessive clast fractures, as well as melted and contorted grains (Mahaney et al, 2011a(Mahaney et al, , b, 2013c(Mahaney et al, , 2016b. Similarities between the black mat sediment in MUM7B and experimentally-fired quartz (Mahaney et al, 2010) support a hypothesis that both intense heat and physical perturbations produced the Venezuelan grains.…”

“…When compared with mid-LG samples recovered from sections in the Alps, similar grain characteristics representative of melting, quenching and fracture patterns consistent with high-energy grain collisions support a mutually conclusive impact/airburst history for both sets of samples. Affected weathering rinds, in particular, show intense effects of particle collision (Mahaney et al, 2016b) with energy vectors forcing grains in the outer rind inward to 0.7 mm thickness, and individual minerals formed into reoriented mineral groups with a-axes plunging deep into the clast. These reformed and reoriented minerals are often located near Fe and C spherules formed in clusters where they first congealed and later cooled.…”

In Memory of Professor David Krinsley, University of Oregon

“…Add to this, Dave's contribution of SEM microtexture grain analysis of different lithologies in sedimentary rocks of marine and terrestrial origin, and extended through time to the Precambrian, showed investigators how the electron microscope could shed light on geologic processes and environmental reconstruction through the vast expanse of geologic time. One of his latest papers, published in Scanning (Mahaney et al, 2016), demonstrated how combinations of STEM and FIB methods could be applied to weathering rinds, the combined analyses allowing microstratigraphic imaging and chemical analyses with depth, all shedding light on the black mat event as it affected the Western Alps 12.8 ka. His participation in the discovery of airburst related sediment, possibly black mat equivalent minerals in Antarctic paleosols, continued unabated right up to his passing.…”