David Krinsley

Environmental Interpretation of Sand Grain Surface Textures by Electron Microscopy

More than 4000 quartz sand grain surfaces have been examined by electron micro scopy, and it has been established that specific differences exist depending on the environment of transportation and deposition. Littoral, aeolian, glacial, diagenetic, and combinations of these four environments can be distinguished; river transport and turbidity current movement do not impress characteristic surface textures on quartz sand grains.

Submicroscopic Frosting on Eolian and Subaqueous Quartz Sand Grains

Investigation of surface features on quartz sand grains of eolian origin from 20 desert and coastal dune environments from around the world reveals that chemical solution and redeposition of silica by the action of desert dew along with mechanical wind abrasion causes frosting and rounding of sand grains. Wind-induced grain impacts create small-scale fractures that are related to wind velocity and moisture as well as the roundness, degree of polish, and size of the impacting grains. This fracture pattern, which has been reproduced experimentally by simulating wind abrasion, is most pronounced on projections from the surface of the grains. Examination with a scanning electron microscope shows that this pattern consists of minute upturned plates of quartz that overlap each other and appear to be dipping in a direction possibly consistent with internal crystallographic planes. The close spacing of these fracture plates is responsible for the frosted appearance of many desert sands. These irregular fractured plates have a high chemical potential and will dissolve under favorable physicochemical conditions. This dissolved silica can be precipitated elsewhere as an amorphous layer on grain surfaces when the solution evaporates, resulting in a progressive rounding of sharp edges and subduing of irregular mechanical fracture patterns by transfer of minute amounts of silica. The occurrence, morphology, and distribution of diagnostic mechanical and chemical surface features allows differentiation between tropical desert sands, coastal dune sands, and periglacial sands. Closely spaced chemical etch pits formed on sand grains by “abrasion solution,” or during diagenesis, when grains are exposed to high p H solutions, also can result in a frosted appearance. Defrosting can be accomplished by addition of a thin amorphous layer of silica to the grain9s surface, or by polishing during turbulent subaqueous transport.

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.

Eolian transport textures on the surfaces of sand grains of Early Triassic age

The surface textures of quartz sand grains from a Lower Triassic sandstone unit are almost identical to eolian sands from modern hot deserts, suggesting similar environments. This is the earliest example known of eolian surface textures unmodified by diagenesis; it shows how studies of surface textures of pre-Pleistocene sand grains may provide information about their depositional environments and subsequent diagenetic history.

Petrographic Examination of Sedimentary Rocks in the Sem Using Backscattered Electron Detectors

ABSTRACT Most of the geological work in scanning electron microscopy has been undertaken using the secondary electron (SE) mode and, to a lesser extent, the cathodoluminescence (CL) mode, but in the last few years attention has been drawn to the advantages of imaging with backscattered electrons (BSE). The coefficient of electron backscattering from polished specimens is strongly dependent on average atomic number, allowing different mineral phases to be distinguished on the basis of differences in gray level. A great deal of useful information about the size, distribution, shape, orientation, and textural relationships of minerals in situ can be gained from BSE images. These data can be processed by various image-analysis systems which are now commercially available. This paper reviews the na ure and formation of BSE electrons, discusses some of the problems which limit the quality of BSE images of sedimentary rocks, and illustrates some applications of the technique.

Upper Paleozoic Glacial Deposits of South Africa and Southern Australia

Glacial deposits of Late Carboniferous and Early Permian age have long been recognized throughout broad areas of the “Gondwana” continental masses. This paper describes some of these deposits in South Africa and southern Australia, and summarizes information from the literature on deposits of these and other regions. The following features in combination are widespread in the Paleozoic deposits and prove continental glaciation: polished and striated pavements and roches moutonnees; massive, nonsorted debris (tillite) containing abundant clay-free rock flour, abundant fresh grains of easily weathered minerals, and stones including faceted and striated blocks from both local and distant sources; and laminated, fine-grained sediments enclosing numerous drop-stones. Electron-microscopy studies have shown that surface textures of sand grains in modern sediments vary diagnostically from one environement to another. The large suite of surface textures that uniquely characterizes Quaternary glacial grains also characterizes Paleozoic ones. X-ray study shows that the clay-sized fraction of unweathered tillites and glacial shales is largely devoid of clay. Most of the well-dated Gondwana glacial deposits are of very Early Permian age. At least local glaciation occurred during the Late Carboniferous and also during the later Early Permian. Glacial stages alternated with interglacial ones. The continental glaciers of even the now-tropical Gondwana continents reached sea level for marine deposits occur with glacial drift. Ice sheets bearing continental-shield debris flowed onto each continent from the direction of present oceans. The distribution of warm-climate Early Permian deposits is as aberrant as that of glacial deposits; red beds, evaporites, thick biochemical limestones, diverse-fauna coral bioherms, and large foraminifera occur, for example, in the northernmost lands of the Atlantic sector of the Arctic. Only continental drift offers a rational solution to the problems of distribution of paleoclimatic indicators. All the glaciated lands lay in latitudes between 45° and 90° S. in the since-fragmented continent of Gondwanaland. Long-lasting sedimentary basins were produced by permanent changes in crust and mantle configuration resulting from glacial loading.

A technique for the study of surface textures of sand grains with electron microscopy

ABSTRACT A technique for examining the surface textures of sand grains with the electron microscope is described and the basic principles for interpretation of electron micrographs are explained and illustrated. This technique is shown to be a powerful tool for the determination of the origin, history and transportation of sand deposits.

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. Fusion of their surfaces released gases. Electron microscopy of the glasses, pits, and angular microfractured mineral grains indicates a prevalence of destructive weathering processes-thermal expansion and contraction, abrasion by by-passing particles, and, of course, impact. ous at room temperature.

Argentine Basin Sediment Sources as Indicated by Quartz Surface Textures

ABSTRACT Distinctive quartz surface textures, as determined by scanning electron microscopy, can be used to identify sources of sediment in the Argentine Basin. Glacial quartz from the south, fluvial-littoral quartz from the continental margin, and windblown hot-dune sand can be identified and their distributions tentatively assessed.

Age of the Mount Laurel and Navesink Formations at Marlboro, New Jersey, from K-Ar Measurement of Glauconite

K-Ar ages of 61 and 63 m.y. for the Navesink and Mount Laurel Formations, respectively, at Marlboro, New Jersey, fit in reasonably well with previous data which indicate that the base of the Paleocene is between 62 and 67 m.y. old.