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Geology of Urban Watersheds
Published in Daniel T. Rogers, Urban Watersheds, 2020
There are four basic types of sand deposits (Pettijohn et al. 1987; Boggs 2000): Quartz arenites consist almost entirely of quartz grains, are usually well-sorted and well-rounded. Quartz arenite deposits result from extensive weathering, so they consist of only the most resistant minerals. Figure 2.25 is an example of a quartz arenite sand that is medium grain, well-sorted, with sub- to well-rounded grains.Arkoses are sand deposits with a composition of 25% feldspar or more. The grains tend to be poorly rounded and less well sorted than quartz arenites. Arkoses originate from rapidly eroding granitic and metamorphic rock where physical weathering is dominant.Lithic sand deposits contain many fragments derived from fine-grained materials, mostly shales, volcanic rocks, and fine-grained metamorphic rocks.Greywacke is a heterogeneous mixture of rock fragments and angular grains of quartz and feldspar; the sand grains become surrounded by a fine-grained clay matrix.
Sediments and Sedimentary Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Arenites are sandstones that contain less than 15% matrix between grains, and even more specifically, quartz arenite is the name given to a variety of arenite, which is generally very well sorted, containing more than 90% quartz. Figure 8.54 shows an example of quartz arenite. There are many kinds of arenites; the most significant are listed in Table 8.4. Quartz arenites are quartz-rich, arkoses contain significant amounts of feldspar, lithic sandstones contain rock fragments, and graywackes contain more than 15% clay minerals.
Silurian and Lower Devonian
Published in W. A. Peck, J.L. Neilson, R.J. Olds, K.D. Seddon, Engineering Geology of Melbourne, 2018
The arenites consist of sand size particles predominantly of quartz and may also include grains of feldspars, micas, glauconite and rock particles (greywacke). Sandstone is the common basic rock type of this group. Bed thickness varies from a few millimetres to 2 metres. Sandstone comprises from less than 10 % to approximately 75 % of various parts of the Silurian-Lower Devonian sequence.
Triassic deposits of Chukotka, Wrangel Island and Mendeleev Rise, Arctic Sea: sedimentology and geodynamic implications
Published in GFF, 2020
M.I. Tuchkova, S.P. Shokalsky, O.V. Petrov, S.D. Sokolov, S.A. Sergeev, A.V. Moiseev
Triassic deposits are very deformed and folded, greenschist-facies is widespread (Kos’ko et al. 2003). Sandstone and siltstone are classified as lithic arenites. Sorting of grains is poor and a roundness is from angular and subangular to locally well rounded. Unfortunately, the intense cleavage obscures the primary shape of the grains. The ratio of rock-forming components is Q (20-40%), F (34-62%), L (11-23%) (Fig. 4A). Rock fragments are very diverse and are represented by granite, cherts, schists, felsic effusive, metamorphic rock fragments dominate (Fig. 4B). Sandstones with basal calcite cement are rare. Many feldspar and other grains are completely replaced by calcite. Also there are fragments and shells of Monotis densistriata (Tell.) (Personal communication of I.Polubotko, VSEGEI, St.Petersbourg). 7-14% of quartz grains contain microfractures, and they are most common in the eastern part of Wrangel Island (Fig. 5E, H).
Mapping a coastal transition in braided systems: an example from the Precipice Sandstone, Surat Basin
Published in Australian Journal of Earth Sciences, 2018
V. Bianchi, F. Zhou, D. Pistellato, M. Martin, S. Boccardo, J. Esterle
The main lithology encountered is very coarse- to medium-grained quartz arenite, fine- to very fine-grained quartz arenite with kaolinite clay matrix, granule to medium-pebble conglomerate and siltstone to mudstone beds. The conglomerates are composed of clasts of slightly metamorphosed siltstone and quartzite from the underlying Triassic strata (Fielding et al., 1996; Ziolkowski et al., 2014) with occasional coal chips. The coarse-grained sandstone is well sorted and mature, has well-rounded grains and is very porous. The finer-grained quartz arenite has a kaolinite clay matrix derived from weathered micas, which supports the development of ‘caves’ and overhangs in outcrops (Wray, 2009; Young & Wray, 2000). From west to east along the outcrop, the expression of the Precipice Sandstone changes, as does the nature of its erosive base.
Formation mechanisms of calcite cements in tight sandstones of the Jurassic Lianggaoshan Formation, northeastern Central Sichuan Basin
Published in Australian Journal of Earth Sciences, 2019
Y. H. Qing, Z. X. Lü, J. Y. Wu, J. J. Yang, S. L. Zhang, C. H. Xiong, J. F. Liu
Sandstones in the Lianggaoshan Formation are relatively uniform (Figure 4). Feldspathic litharenite is the major rock type (>52.1%), followed by litharenite (20.6%) and sublitharenite (18.6%); subarkose and lithic arkose are less than 8.7%. Grainsize is generally fine. Cements are dominated by calcite, with a mean content of 7.92%, and other cements are relatively rare (Figure 5). The sandstone is made up of an arenite with medium roundness, good sorting and linear contacts among grains and pore cementation patterns. Therefore, the sandstone of the Lianggaoshan Formation is characterised by its low compositional maturity and medium textural maturity.