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Carboniferous reef's massif of the Berkha Island as a model of the potential collector of hydrocarbon resources on the Novaya Zemlya Archipelago
Published in Vladimir Litvinenko, Innovation-Based Development of the Mineral Resources Sector: Challenges and Prospects, 2018
Pinnacles - are prepared carbonate cliffs. Formation of the reef was completed in the Vosnesenskoe time (Bashkirian stage). Clay sedimentation began to dominate over the carbonate sedimentation. Only carbonate pinnacles remained. These are separate bioherms, which located on clay-carbonate shoal, along the periphery of the reef in the direction from South-East to the North-West. They stacked by foraminiferal-crinoidal sparry limestones - grainstones and rudstones with carbonate intraclasts and crystals of dolomite (10 lithotype). At the base of some pinnacles there are colonies of corals (the first meters in size). Rare ammonoids are found.
Sedimentary rocks
Published in W.S. MacKenzie, A.E. Adams, K.H. Brodie, Rocks and Minerals in Thin Section, 2017
W.S. MacKenzie, A.E. Adams, K.H. Brodie
176 is a very porous limestone from the Arab D Formation in Saudi Arabia. This unit forms the world’s biggest oil reservoir. The limestone is a grainstone with a mixture of bioclasts, intraclasts and peloids. There is a high intergranular porosity between the grains and some intragranular porosity within Foraminifera (chambered microfossils seen, for example, on left hand side of photograph). Some of the pore-spaces between grains look quite large and it is possible that a component of the rock has dissolved out to increase overall porosity.
Sedimentary Petrology
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
Two types of dolomites are recognised: (i) primary dolomite and (ii) secondary dolomite. The primary are extremely fine-grained (maximum size 0.020 mm, generally much smaller) dolomite (‘dolomicrite’ of Folk). These contain unmistakable signs of primary deposition, such as lamination, ripple marks and mud cracks. Dolostones laterally passing into calcitic limestones, microbeddings of dolomite and limestone and limestone intraclasts within dolostones also indicate the primary nature of dolostone. The secondary dolomites are the coarsely crystalline, saccharoidal rocks bearing evidence of replacement. The evidence of replacement includes faint outlines (‘ghosts’) of former grains in rocks composed wholly of dolomite, preservation of original shapes of dolomitised fossils, presence of grains of detrital particles within dolomites and other similar features. Dolomite veins cutting into calcitic limestones, dolomite rhombs crossing the boundary of CaCO3 fossils, also indicate the secondary nature of the rock.
Marine depositional signatures of the Aptian Oceanic Anoxic Events in the Eastern Tethys, Lower Indus Basin, Pakistan
Published in Australian Journal of Earth Sciences, 2022
S. Khan, D. Kroon, B. Wadood, S. Ahmad, X. Zhou
The skeletal components of this microfacies comprise planktonic foraminifers, radiolarians, peloids, echinoderms, benthic foraminifers, molluscs, and carbonate intraclasts (Table 1). These components are uniformly distributed in lime-mud. Hedbergella dominates the planktonic foraminifers. Well-sorted siliciclastic quartz grains and rare calcareous algae were also observed (Figure 6a–d). The textural features and concomitant presence of radiolarians and planktonic foraminifers indicate deposition on an outer ramp (Flügel, 2004; Heldt et al.,2008). The abundance of radiolarians among the plankton indicates ocean eutrophication, while the presence of fine siliciclasts suggests that continental dust aerosols have possibly caused ocean fertility. The organic enrichment indicates dysoxic–anoxic bottom-water conditions (e.g. Leckie et al.,2002).
Glaciations at high-latitude Southern Australia during the Early Cretaceous
Published in Australian Journal of Earth Sciences, 2020
N. F. Alley, S. B. Hore, L. A. Frakes
A fairly continuous section of Cadna-owie Formation can be traced from the bedrock unconformity to the unconformity with the Bulldog Shale at the Chimney Springs–Petermorra Creek site, the lower 6 m of which we include in the Livingston Tillite Member (Figure 16). At the base is gritty, bouldery, calcareous cross-bedded sandstone in which the boulder and pebble fraction exhibits a great range in clast size and shape, with many very angular, and with common quartzite (dominant), granite, volcanics (a dark variety), gneiss and milky quartz. At 1.0–6.0 m pebbly, partly bioturbated trough cross-bedded medium to coarse sandstone contains lenses of gravel and boulders, which become more common near the top of this part of the unit. The boulder/gravel lenses may consist of gritty tillite with intraclasts of pebbly fine sandy silt and blocks of gritty sand. Some boulders are greater than a metre in diameter and polished, facetted and striated. The lithologies of the boulders include quartzite (dominant), sandstone, gneiss, granite (including Mt Neill Granite type), dark volcanics (including porphyry) chert, milky quartz, conglomerate, tillite (probably Neoproterozoic Bolla Bollana Tillite) and limestone.
Stromatolite framework builders: ecosystems in a Cryogenian interglacial reef
Published in Australian Journal of Earth Sciences, 2020
Facies 1 Interbedded micritic mudstone and intraclastic packstone comprises thin to medium, laterally discontinuous, interbeds of micritic mudstone and intraclastic packstone. Laminae show low-angle cross-stratification, poorly developed hummocky cross-stratification, convolutions, overturned beds, scour and infill, edgewise breccia, ripples and draping fabric (Figure 5a, b). Locally, packstone is dedolomitised to sparry limestone, which weathers recessively compared with dolomitic mudstone interbeds. Packstone comprises coarse sand-to-gravel-sized micrite intraclasts, ooids and aggregates in a micritic matrix with cement-filled vughs. The lime mudstone is homogenous with very subtle layer-parallel lamination. Discontinuous amorphous dark wrinkly stringers encrust and bind small angular intraclasts and minor quartz silt (Figure 5c).