Clast rind analysis using multi-high resolution instrumentation.

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.

Localized grounding, excavation, and dissection using in-situ probe techniques for focused ion beam and scanning electron microscopy: experiments with rock varnish.

While investigating rock varnish, we explored novel uses for an in-situ micromanipulator, including charge collection, sample manipulation, as well as digging and dissection at the micron level. Dual-beam focused ion beam microscopes (DB-FIB or FIBSEM) equipped with micromanipulators have proven to be valuable tools for material science, semiconductor research, and product failure analysis. Researchers in many other disciplines utilize the DB-FIB and micromanipulator for site-specific transmission electron microscope (TEM) foil preparation.

Investigation of Tibetian Plateau varnish: new findings at the nanoscale using focused ion beam and transmission electron microscopy techniques.

Dual-beam focused ion beam microscopy (FIB/SEM) preparation of rock varnish for high-resolution transmission electron microscopy (HR-TEM) has enabled us to characterize unreported nanostructures. Fossils, unreported textures, and compositional variability were observed at the nanoscale. These techniques could provide a method for studying ancient terrestrial and extra-terrestrial environments to better understand geological processes at the nanoscale.

Astrobiological implications of rock varnish in Tibet.

The study of terrestrial geomicrobiology and its relationship to rock weathering processes is an essential tool in developing analogues for similar processes that may have occurred on Mars. Most studies of manganese-enhanced rock varnish have focused on samples taken from warm arid desert regions. Here, we examine samples obtained from eolian-abraded lava flows of the 4700-4800 m high Ashikule Basin in Tibet.

Diagenetic origin of quartz silt in mudstones and implications for silica cycling.

Mudstone--the most abundant sedimentary rock type, composed primarily of clay- or silt-sized particles--contains most of the quartz found in sedimentary rocks. These quartz grains, which are chemically and mechanically resistant and therefore preserve their characteristics well, have long been considered to be derived from the continental crust. Here we analyse quartz silt from black shales in the eastern USA, dating back to the Late Devonian period (about 370 million years ago), using backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe.

Diagenesis of US Gulf Coast shales.

The burial diagenesis of mudstones is of major interest in petroleum geology. Key questions which remain incompletely answered include the relative importance of temperature, time, changes in pore-water chemistry and organic maturation as driving mechanisms, and the relationship between diagenesis in mudstones and neighbouring sandstones. We reconsider here the nature and timing of diagenesis in Gulf Coast Tertiary mudstones using data obtained by backscattered electron microscopy (BSEM) and energy-dispersive X-ray analysis (EDS) of cuttings from two Texas wells.

Uranium-bearing stratiform organic matter in paleoplacers of the lower Huronian Supergroup, Elliot Lake--Blind River region, Canada.

The Elliot Lake-Blind River, Ontario, paleoplacer deposits in the basal Matineda Formation, lowermost member of the 2.25-2.45 Ga old Huronian Supergroup, contain organic matter chemically consistent with kerogen.

Shape and nature of small sedimentary quartz particles.

Quartz particles in sediments become flatter with decreasing size; a cleavage mechanism may operate below the critical size of about 100 microns. Flat particles would tend to form a more open packing than spherical particles, and this may contribute to the collapse of loess and similar soils and the sudden loss of strength observed in "sensitive" clay soils.

Micromorphology and surface characteristics of lunar dust and breccia.

Although nothing of direct biologic interest was observed in the sample studied, small shaped glass particles and glazed pits resemble objects which elsewhere have been described as fossils. These features, although nonbiological, do bear on processes of lunar weathering and outgassing. The glazed pits are impact features.

Pleistocene Glaciation: A Criterion for Recognition of Its Onset.

The various biostratigraphic boundaries proposed for the base of the Pleistocene are not necessarily synchronous with the onset of continental glaciation. Electron-microscopic examination of surface textures of sand grains suggests a widely applicable rock-stratigraphic and geologic-climate boundary that may mark the point at which glaciers of continental proportions began to launch debris-carrying icebergs into the world's oceans.

Surface Textures of Sand Grains--an Application of Electron Microscopy: Glaciation.

To simulate glacial conditions, a mixture of ice and quartz grains was subjected to grinding under hydrostatic pressure of 500 bars. Electron microphotographs of these "synthetic" glaciated surfaces were then compared with electron microphotographs of grain surfaces which had been abraded and crushed by glacial action, and the correspondence was found to be good. Thus it appears possible to distinguish glacial sands from beach and eolian sands byexamining the surface textures of these grains with the electron microscope.

Surface Textures of Sand Grains: An Application of Electron Microscopy.

Crushed quartz was subjected to wind, ball mill, and shaking-table action to simulate eolian and beach conditions. Electron microphotographs of these surfaces were then compared with those of grain surfaces which had been frosted naturally, and the correspondence between them was good. Thus, the transportation history of many sand deposits may be identified by this technique.