Surface Textures Of Sand Grains Research Articles

Characteristics and provenance of the loess deposits of the Gharatikan watershed in Northeast Iran

Loess and loess-like deposits cover large areas of north and central parts of Iran. Studies of shapes, inclusions, and surface textures of sand grains plus mineralogical composition and trace elements of these loesses in the Gharatikan watershed basin, located in northeast Iran, show that they had been derived from crystalline rocks (mostly granitic or granitoidic). They had been modified in glacial environment during the last glacial stage, transported in eolian suspension mode and deposited during glacial periods, when the area was a cool, arid, and poorly vegetated steppe. The loess was evidently derived from the Qaraqum desert to the north because (1) the beds become thicker and coarser-grained in that direction, (2) the deposits mostly cover northward facing hills and plains. The major and trace elements distribution patterns of the Gharatikan loesses are similar to that of Uzbekistan and Tajikistan loesses. Therefore, Gharatikan loess is the extension of the Uzbekistan and Tajikistan loesses. Changes in the petrographical characteristics of loess deposits of the Gharatikan watershed allow the reconstruction of the paleoenvironments during the periods of their formation and the detection of the trends of Pleistocene climate changes.

A non‐glacial origin for the ordovician (middle caradocian) cosquer formation, veryarc'h, crozon peninsula, brittany, France

AbstractThe presence of a dispersed clast fraction in strata near the base of the Cosquer Formation in west Brittany, does not support a glacial origin for this unit. The upper 25 to 30 m of the underlying Kermeur Formation consists of a prograding sequence of very fine to fine sandstones deposited in a mid to distal current swept shelf setting. This sequence shows signs of slope instability, as do the supposed ‘glacial strata’ which overlie it. The upper two thirds of the Cosquer Formation contain spectacular slump‐breccias. Smaller clasts within the laminated mudrocks at the base of the formation are associated with thin graded and non‐graded sandstone laminae. They show no evidence of active penetration into underlying laminae other than can be explained by compaction. Larger clasts are confined to thicker massive beds, or disrupted units with marked internal contorted lamination. This, along with the abundance of slump features within the sequence suggests lateral emplacement by sediment gravity flows in a distal shelf‐slope setting. Surface textures of sand grains within the formation are related to rock disaggregation along fractures developed during post‐depositional deformation and are not related to glacial processes. Distinctive mineralogically immature, poorly‐sorted aggregate sediment pellets, which have been considered as positive proof of glaciation, are not present.

Surface Textures of Sand Grains from the Victoria Falls Region, Zambia: Implications for Depositional Environments and Local Archaeological Occurrences

Surface Textures of Sand Grains from the Victoria Falls Region, Zambia: Implications for Depositional Environments and Local Archaeological Occurrences

Wind velocities determined from the surface textures of sand grains

Krinsley and Smalley1 suggested that ‘upturned plates’, a surface texture that is represented on quartz sand surfaces by a series of thin parallel plates, either continuous or discontinuous parallel to r(10¯11) and z(01¯11), cause the frosting observed on desert sand grains. As these plates depend on the extent of physical abrasion2, the spacing between individual plates might be related to the velocity of the wind which last transported the grains. The technique described here attempts to relate experimental and modern aeolian sand grain surface textures to wind velocity via scanning electron microscopy (SEM)3.

Studies of Quartz Sand Grains By Cathodoluminiscence: ABSTRACT

Surfaces and cross sections of individual quartz sand grains have been examined and compared in the cathodoluminiscence (CL) mode with the scanning electron microscope. Six kinds of nontopographic CL have been found; the presence of non-CL areas commonly is due to the occurrence of a disrupted lattice layer wherever grinding has taken place. This layer is shown to be irregularly distributed, both in cross sections and on grain surfaces; its distribution, depth, and intensity can be examined in detail for the first time. Reversal of CL contrast has been accomplished experimentally by raising the temperature of grains above the alpha-beta transition in quartz (573°C); a similar reversal, found in certain natural sedimentary grains, suggests that they likewise have been heated above the transition temperature. Fractures present on natural grain surfaces in the CL mode can be observed in omissive-mode photographs and probably could be used for environmental interpretation. Detail of the same kind, observed in the CL mode but not in the emissive mode on other grains, could further extend the use of sand-grain surface textures for environmental interpretation. End_of_Article - Last_Page 789------------

Surface textures of sand-grains from the Hertfordshire Pebble Gravels

SummaryThe Pebble Gravels of Hertfordshire are among the earliest Pleistocene deposits of the London Basin. They comprise at least three successive units, and according to the most recent published views the oldest of these is marine, the youngest fluviatile, the intermediate partly marine and partly fluviatile. In the absence of fossils these views have remained open to question. Electron microscope studies of the surface textures of sand-grains suggest, however, that they may well be substantially correct.

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.

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.

Discussion

Mr B. Waugh said that for the past two years he had been examining by electron-microscopy the surface textures of sand grains, especially sand grains collected from modern desert and beach environments. The criteria used by the authors for distinguishing environments of deposition from distinctive surface textures were directly comparable with his results. In a study of the surface textures of sand grains from the Penrith Sandstone of the southern part of the Vale of Eden where the rock was poorly compacted, and from the Basal Yellow Sands of County Durham, electron micrographs showed the surface of the grains to be covered in conchoidal fractures, rounded abrasion-blocks, and percussion-marks (Waugh 1965, Proc. Yorks. geol. Soc. 35, 59–69). These were features of an aeolian abrasion process, and confirmed the accepted aeolian origin of these two deposits. Dr F unnell replied that it was gratifying to learn that Mr Waugh had found the suggested criteria applicable to his own results, and Mr Waugh’s confirmation of the mode of origin of the Permian occurrences by this means was most interesting. Mr W. B. H arland suggested that the evidence of glacial attrition of sand grains might not necessarily denote a glacial environment if a similar grinding process could also be shown to take place, for instance, in a mud-flow. On the other hand, it seemed that glacial action, in the sense of ice rafting, might well produce a till, possibly with little evidence of attrition of the sand grains in it unless most of

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.

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 from the Victoria Falls Area

ABSTRACT A technique for making dry mounts of sand grains is described. These slides can be used for the study of the surface textures of the grains. Rounded aeolian quartz grains from the Kalahari Sands are found to have frosted surfaces, but after these grains have travelled a few miles in the Zambezi River above the Victoria Falls this surface texture has been altered to a glassy polish. It is suggested that surface textures may give reliable evidence on the mode of transport and deposition in certain cases.