Provenance of lower Cambrian quartz arenite on southwestern Baltica: Weathering versus recycling
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ABSTRACT Lower Cambrian quartz arenite deposits have a world-wide occurrence and are also present on Baltica. However, the processes influencing the deposits from source to sink have not been accordingly investigated. The provenance of these deposits is crucial for the understanding of the extent of chemical weathering in the cratonic drainage area and reworking at the broad shallow shelves of Baltica during early Cambrian time. Provenance analysis and study of weathering effects was done for lower Cambrian sandstone from southern Scandinavia, including southern Norway, southern Sweden, and Bornholm (Denmark). For the quartz-arenite sandstone of the Ringsaker Member and the Hardeberga Formation, predominantly moderately weathered felsic–intermediate plutonic and meta-igneous source terranes are suggested from negative Eu anomalies, high LaN/YbN, and low to moderate Ti/Nb ratios, as well as trace amounts of plutonic lithoclasts. Similarly, a felsic–intermediate igneous and metamorphic signature is indicated in the heavy-mineral assemblage and a dominance of dark cathodoluminescence of quartz in a special study of samples from Bornholm, thus suggesting a mixed provenance of local granitoid–orthogneissic Mesoproterozoic basement and distant sources from the Transscandinavian Igneous Belt for the Hardeberga Formation on Bornholm. High percentages of mostly rounded ultra-stable heavy-mineral grains, quartz, and extremely high SiO2/Al2O3 ratios indicate a compositionally and texturally mature sand that was subjected to extensive to moderate weathering following removal of detritus from the source area. The main controls on the alteration of framework composition and the heavy-mineral assemblage are interpreted as surface weathering, based on moderate Chemical Index of Alteration values and meteoric flushing, and reworking by waves, based on an estimated low amount of feldspar before burial. Thus, the maturation of lower Cambrian quartz arenite on southwestern Baltica can be ascribed to a combination of processes including weathering in the source-rock area, extensive reworking, and early diagenesis. This study also highlights the importance of understanding alteration processes affecting the deposits from source to sink, and to be careful to describe quartz-rich rocks as simply recycled deposits.Keywords:
Felsic
Arenite
Baltica
Detritus
Heavy mineral
Petrographic and heavy mineral compositions of the Oligocene Barail sandstones exposed in and around Longsa village of Wokha District, Nagaland, have been utilized for provenance interpretation. Grey and yellow coloured sandstones of the study area are comprised of angular to sub-rounded monocrystalline, non-undulatory quartz and the various lithic fragments. The overall composition of sandstones (Q-90.10%, F-1.70 %, RF-8.18%) matches with those of sublith-arenites category. The heavy mineral assemblage of the studied Barail sandstones is represented by euhedral/rounded to sub-rounded grains of zircon, tourmaline, rutile, kyanite, sillimanite, andalusite, titanite, staurolite and iron oxide. The studied sandstone composition suggests that the Barail sediments were derived from mixed provenance. Heavy mineral analysis also corroborates the above. Keywords: Petrography, Heavy Minerals, Provenance, Barail Group, Nagaland
Heavy mineral
Andalusite
Staurolite
Arenite
Sillimanite
Tourmaline
Lithic fragment
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ABSTRACT Lower Cambrian quartz arenite deposits have a world-wide occurrence and are also present on Baltica. However, the processes influencing the deposits from source to sink have not been accordingly investigated. The provenance of these deposits is crucial for the understanding of the extent of chemical weathering in the cratonic drainage area and reworking at the broad shallow shelves of Baltica during early Cambrian time. Provenance analysis and study of weathering effects was done for lower Cambrian sandstone from southern Scandinavia, including southern Norway, southern Sweden, and Bornholm (Denmark). For the quartz-arenite sandstone of the Ringsaker Member and the Hardeberga Formation, predominantly moderately weathered felsic–intermediate plutonic and meta-igneous source terranes are suggested from negative Eu anomalies, high LaN/YbN, and low to moderate Ti/Nb ratios, as well as trace amounts of plutonic lithoclasts. Similarly, a felsic–intermediate igneous and metamorphic signature is indicated in the heavy-mineral assemblage and a dominance of dark cathodoluminescence of quartz in a special study of samples from Bornholm, thus suggesting a mixed provenance of local granitoid–orthogneissic Mesoproterozoic basement and distant sources from the Transscandinavian Igneous Belt for the Hardeberga Formation on Bornholm. High percentages of mostly rounded ultra-stable heavy-mineral grains, quartz, and extremely high SiO2/Al2O3 ratios indicate a compositionally and texturally mature sand that was subjected to extensive to moderate weathering following removal of detritus from the source area. The main controls on the alteration of framework composition and the heavy-mineral assemblage are interpreted as surface weathering, based on moderate Chemical Index of Alteration values and meteoric flushing, and reworking by waves, based on an estimated low amount of feldspar before burial. Thus, the maturation of lower Cambrian quartz arenite on southwestern Baltica can be ascribed to a combination of processes including weathering in the source-rock area, extensive reworking, and early diagenesis. This study also highlights the importance of understanding alteration processes affecting the deposits from source to sink, and to be careful to describe quartz-rich rocks as simply recycled deposits.
Felsic
Arenite
Baltica
Detritus
Heavy mineral
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Staurolite
Heavy mineral
Arenite
Sillimanite
Lithic fragment
Andalusite
Tourmaline
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Felsic
Arenite
Rare-earth element
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Viviparus deposits are clastic sediments that were deposited in the southwestern part of the Pannonian Basin system during the Pliocene and the beginning of the Pleistocene, in the regional floor Cernikij. The aim of this study was to determine the structural characteristics, mineral composition and origin of clastic detritus Viviparus deposits of Banovina by analysis of granulometric composition of sediments, X-ray diffraction analysis of pelitic sediments and analysis of the community of heavy sand minerals. The obtained results show that it is a poorly sorted, structurally immature detritus. The heavy minerals community is dominated by opaque minerals, and among the transparent heavy minerals, garnets and resistant minerals such as zircon, rutile and tourmaline are the most common. The structural features of detritus indicate its local origin, and its composition indicates the origin of detritus from older sedimentary and acidic igneous rocks. The source areas were most likely local uplifted areas within the SW part of the PBS and the marginal areas of the Dinarides.
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Tourmaline
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Abstract Rare late Neoproterozoic (Cryogenian and Ediacaran) detrital zircons are detected in sedimentary sequences of Ediacaran to Carboniferous age in SW Scandinavia. New data on five samples of clastic metasediment corroborate their presence. Three distinct sources are proposed for late Neoproterozoic zircons based on new and literature data: (1) rift‐related magmatism along the W margin of Baltica connected with the opening of Iapetus in the Neoproterozoic, (2) the Neoproterozoic to Cambrian Timanian orogeny at the NE margin of Baltica and (3) Cadomian terranes incorporated into the Variscan orogen accreted from the south to Laurussia during the Devonian and Carboniferous. The appearance of late Neoproterozoic detritus, which is otherwise exotic to Baltica, is therefore bound to tectonic processes active at the margins of the palaeocontinent. In a broader perspective, rare detrital zircon populations, when confirmed as genuine, are extremely valuable provenance indicators.
Baltica
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Devonian
Orogeny
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Detritus
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Abstract Petrographic analysis and chemical analysis of major and trace elements including rare earth elements of the Neoproterozoic sandstones from the Chandarpur Group and the Tiratgarh Formation have been carried out to determine their provenance, tectonic setting and weathering conditions. All sandstone samples are highly enriched in quartz but very poor in feldspar and lithic fragments. Petrographically and geochemically these sandstones are classified as subarkose, sublitharenite and arenite. The Chemical Index of Alteration (CIA mean 68) and Th/U ratios (mean 4.2) for these sandstones suggest their moderate weathering nature. Generally, all sandstone samples are strongly depleted in major elements (except SiO 2 ), trace elements (except Zr) and REE in comparison with Post Archean Australian Shale (PAAS) and Upper Continental Crust (UCC). Their mineralogy and mean of elemental ratios suitable for determination of provenance and tectonic setting, e.g. Al 2 O 3 /SiO 2 (0.02), K 2 O/Na 2 O (10), Eu/Eu* (0.67), (La/Lu)n (10.4), La/Sc (3), Th/Sc (1.2), La/Co (0.22), Th/Co (0.08), and Cr/Th (7.2), support a felsic source and a passive margin tectonic setting for these sandstones. Also these key elemental ratios do not show much variation over a range of SiO 2 . Thus we attest their significance in determining source rock characteristics of quartz rich sandstones. Chondrite‐normalized REE patterns with LREE enrichment and a strong negative Eu anomaly are also attributed to felsic source rock characteristics for these sandstones. The source rocks identified are granite and gneiss of the Bastar craton. Minor amounts may have been derived from older supracrustals of the Bastar craton. However, the major element data of the Paleoproterozoic Sakoli schists when compared with those of the Neoproterozoic sandstones indicate that the schists were derived from a mafic source and deposited in an active continental margin tectonic setting. There is, however, little difference in CIA values between the Paleoproterozoic Sakoli schists and Neoproterozoic sandstones, indicating prevailing of similar (moderate‐intense) weathering conditions throughout the Proterozoic in the Bastar craton. Our study also suggests a change in the provenance and tectonic setting of deposition of sediments from dominantly a mafic source and an active continental margin in the Paleoproterozoic to dominantly granite and gneiss (felsic source) and a passive continental margin in the Neoproterozoic in the Bastar craton.
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More than 27 mineral species have been identified in Cenozoic sediments of varying lithology within the Safford Valley of Arizona. The mineral assemblages suggest the following possible sources for the basin-filling detritus: (1) acid igneous rocks, (2) basic igneous rocks, (3) high-rank metamorphic rocks, (4) reworked sediments, and (5) ex plosive volcanic activity. The high angularity and low stability of most of the heavy min erals suggests that the crystalline rocks of the mountains that flank the valley were the source of most of the detritus. The presence of glass and fresh euhedral volcanic minerals suggests that explosive volcanic activity has also contributed greatly to the detritus that fills the valley. The use of heavy minerals as a means of differentiation and correlation of strata must be based upon frequency of occurrence of mineral species, rather than on any major mineralogical changes.
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