Determination of Mean Sediment Thickness in the Crust: A Sedimentologic Method

19From a Quaternary science perspective, sand-sized quartz as well as silt-sized quartz is often 20 acknowledged as final products of glacial abrasion through different evolution mechanisms. This view 21 challenges the existence of any universal comminution process, which may relate the formation of detrital 22 quartz sand and silt. The contribution of grain size, energy input, and crystalline integrity in the scale of 23 quartz crushability has long been matter of much debate. The present empirical work examines the 24 micromechanics of sand-to-silt size reduction in the quartz material. A series of grinding experiments was 25 performed on Leighton Buzzard Lower Greensand using a high-energy disc mill. Analogous conditions to 26 glacial abrasion are provided due to the combined abrasion between grains' asperity tips, and also 27 between grains and rotating smooth tungsten carbide pestle. Discontinuous breakage approach allowed 28 a control on grains' crystalline defects. To enable an objective assessment of micromechanics of size 29 reduction, measurements of particle and mode size distribution, fractal indexes and micro-morphological 30 signatures were made. The crushing approach was probed through varied grinding time at a constant 31 energy input, as well as varied energy input at constant grinding time. Breakage pathway was inspected 32 via laser diffraction spectroscopy and transmission light microscopy. Results suggested that the grain 33 breakdown is not necessarily an energy-dependent process. Non-crystallographically pure quartz sand 34 and silt are inherently breakable materials through a fractal breakdown process. Results also revealed 35 that the internal defects in quartz are independent from size and energy input. 36

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“…9 -in agreement with Blatt (1970)). Breakdown in larger grains was 307 more pronounced than in finer grains (Fig.…”

Section: Fractal Dimension On Breakdown Timeline 295supporting

confidence: 76%

Micromechanics of quartz sand breakage in a fractal context

et al. 2014

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“…Moreover, the smaller the grains become the more easily, in general, can they escape the further action of fragmentation processes (Moss, 1966. If the presently studied plutonic quartz is typical and the conclusions of Blatt (1970) are approximately correct, then the natural breakage processes, although they release individual crack-bounded volume elements, do not normally reach a stage wherein all quartz is broken down to such elements, The breakage appears to asymptote to a somewhat larger size (mode about 60 pm). From this hypothesis loess, the quartz of which is approximately 10-60 pm in diameter, should span the range from single units to a thousand or so per grain.…”

Section: Discussionmentioning

confidence: 85%

“…Copious production of fine quartz by breakage alone obviates the need to cite attrition as a cause of the large quantities of this material stored in the earth's crust. The processes described could readily move the bulk size analyses of nascent quartz to to that of quartz stored in sediments (Blatt, 1970). Blatt's computations, it will be recalled, gave the mode of the former at about 1 mm and that of the latter at about 0.06 mm.…”

Section: Discussionmentioning

confidence: 99%

Fragmentation of granitic quartz in water

Moss¹,

Walker²,

Hutka³

1973

Sedimentology

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Studies of grain fragmentation in natural streams have the limitation that the full size range of the debris produced is virtually unobtainable. Experiments described here for grain fragmentation in a rotating drum permitted the study of all of the debris, and a fragmentation load technique was used to relate experimentally and naturally fragmented material. The present investigation has been focused on granitic quartz.Relatively gentle collective movement in water can cause significant fragmentation of coarse, nascent, granitic quartz grains. The debris produced by rotating in a drum a range of single sieve fractions, taken from gravel in the headwaters of a stream draining granite, had continuous size distributions down to (and probably beyond) 0.06 wm. Quartz was the dominant fragmentation product in all fractions down to 2 pm and present in finer fractions. When pebbles moved with sand in these experiments, breakage of the latter was greatly increased. In comparison with that of breakage, the effect of attrition on granitic quartz was negligible. At least a proportion of granitic quartz grains are subject to a fatigue effect as a result of impacts in water. Evidently they are thus progressively weakened prior to being broken. Size analysis of debris showed a significant break at 20 pm, suggesting some special production of quartz particles just below this size.Granitic quartz is criss-crossed with partially healed cracks acquired before the zone of weathering is reached. The wholesale breakage that affects it, particularly in pebbly streams, is largely due to the reopening of these cracks. Progressive fragmentation of this material must eventually reach a stage wherein grains comprising single original crack-bounded volume elements are produced. Such grains, lacking significant internal weaknesses, must strongly resist further breakage. Possibly the preferential production of quartz grains just below 20 pm in size may represent an accumulation of these single, crack-bounded volume elements.

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“…Quartz sand grains, apparently broken in situ, can often be seen in thin sections of soil. Blatt (1967Blatt ( , 1970 showed that, whereas the size mode of plutonic quartz was about 1.0 mm, that of quartz stored in sediments had fallen to about 0.06 mm, and ascribed this difference to breakage. His assessment suggests that only some 3 percent of quartz is broken down to clay size (< 0.002 mm), and general observation tends to confirm its scarcity in clay fractions (Berry, 1974).…”

Section: Sand and Silt Grains: Predetermination Of Their Formation Anmentioning

confidence: 96%