Geochemical characterisation, provenance, source and depositional environment of ‘Roches Argilo-Talqueuses’ (RAT) and Mines Subgroups sedimentary rocks in the Neoproterozoic Katangan Belt (Congo): Lithostratigraphic implications
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Bayana Basin, sited along the eastern margin of the north Delhi fold belt of the Aravalli Craton, contains an ∼3000 m-thick sequence comprising one volcanic and seven sedimentary formations of the Delhi Supergroup. The sedimentary units are the Nithar, Jogipura, Badalgarh, Bayana, Damdama, Kushalgarh, and Weir formations in order of decreasing age. Petrographic study of the sandstones as well as major and trace elements (including rare earth elements) and bulk-rock analyses of the shales and sandstones allow the determination of their provenance, source-rock weathering, and basinal tectonic setting. The sandstones are quartz rich and were derived mainly from exhumed granitoids typical of a craton interior. Geochemical patterns of the sandstones and shales are similar. However, trace element abundances are low in sandstones, probably due to quartz dilution. The coarser clastic Damdama and Weir sandstones, which occur at higher stratigraphic levels, have strikingly low trace element concentrations compared with the underlying Bayana and Badalgarh sandstones. All samples show uniform LREE-enriched patterns with negative Eu-anomalies (Eu/Eu* = 0.16–0.23) and are similar to those of post-Archaean Australian shales (PAAS). However, the (La/Yb) n ratios (averages 11–18) of all the sedimentary units are higher than those of PAAS, except for the Bayana Sandstone, which has low values (average 6.77). The chemical index of alteration (70–78) and the plagioclase index of alteration (87–97) values and the A–CN–K diagram suggest moderate to intense weathering of the source area. The provenance analyses indicate that basin sedimentation was discontinuous. It received input from a terrain comprising granitoids, mafic rocks, sedimentary sequences, and tonalite-trondhjemite-granodiorite (TTG) suites. The Nithar and Badalgarh sandstones received input from a source consisting predominantly of granitoids. The succeeding Damdama and Weir sandstones received debris from granitoids and TTG in different proportions. The Kushalgarh shale was possibly derived from a source consisting granites and mafic rocks with a TTG component. The pre-existing sedimentary formations also contributed intermittently during the different phases of sedimentation. Bulk-rock geochemical data suggest Mesoarchaean gneisses and late Archaean granites of BGC/BGGC (Banded Gneissic Complex/Bundelkhand Granitic Gneiss Complex) basement as possible source terrains. These data indicate deposition in a continental rift setting. The coeval formation of many rift-related Proterozoic sedimentary basins in the BGC/BGGC terrain suggests that the North Indian Craton underwent major intracratonic extension during Proterozoic time, probably triggering the break up of Earth's first supercontinent.
Trace element
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Continental Margin
Felsic
Large igneous province
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The Mesoproterozoic clastic sedimentary rocks, comprising pelites and quartzites from the Rautgara Formation, Kumaun Lesser Himalaya, have been analysed for major and trace elements, including Rare Earth Elements (REEs) to evaluate their provenance and weathering history. The pelitic rocks are characterized by moderate SiO 2 and Al 2 O 3 contents and show consistent REE patterns with LREE (light REE)-enriched and HREE (heavy REE)-depleted patterns (La N /Yb N = 7.4-10.3). The total REE abundances of Rautgara pelites are high (up to 266 ppm) with large negative Eu-anomalies (Eu/ Eu* = 0.57-0.64). Except high SiO 2 contents, the other major and trace element concentrations are significantly low in the associated quartzites. Although the quartzites contain low REE abundances (up to 41 ppm), their patterns, including negative Eu anomalies, are akin to pelites, suggesting that both the rock types be derived from similar source. The Chemical Index of Alteration and A-CN-K parameters indicate that moderate chemical weathering has taken place in the source region of the Rautgara rocks. The linear correlation coefficients between Al 2 O 3 , K 2 O, TiO 2 and total REE reveal that the accessory minerals (mainly Ti-bearing phases) have hosted the REEs. The striking similarities between the REE patterns of Rautgara pelites and BGC of Aravalli and Bundelkhand granitoids, which are consistent with the palaeocurrent studies of the area, indicate that the granitoid rocks from these regions have supplied detritus to the Lesser Himalayan Rautgara sedimentary basin.
Pelite
Detritus
Siliciclastic
Parent rock
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Breccia
Terrigenous sediment
Lithology
Pelagic sediment
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Progradation
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Turbidity current
Banded iron formation
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Lithology
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ABSTRACT The Moose Channel Formation of the Fish River area, Northwest Territories, comprises over 8200 ft of clastic rocks. The strata, of Maestrichtian-Paleocene age, are genetically equivalent to much of the thick clastic section underlying the Mackenzie Delta. The sandstones in the Moose Channel Formation are mineralogically and texturally immature. An abundance of feldspars, chert grains, and sedimentary and volcanic rock fragments indicates granitic, sedimentary and volcanic source terranes. The Old Crow granites and the volcanic rocks of the British Mountains are possible sources of the igneous clasts. Many of the sedimentary rock fragments are assumed to have been derived from the Richardson Mountains south of the study area. Paleocurrent measurements show that northerly and easterly transport directions prevailed during deposition of the Moose Channel clastics. Grain-size analyses of 125 sandstone samples indicate that unidirectional current energy and gravitational energy were the two basic kinds of energy responsible for deposition of most of the sandstones. These two energy types are compatible with fluvial depositional processes. The Moose Channel Formation has been divided into five units after Young (1971, 1972). The depositional environment of each unit has been interpreted as follows: Unit 1, the oldest, is a regressive sequence containing prodelta and braided-stream deposits. Unit 2, a transgressive sequence, contains prodelta deposits grading upwards into nearshore marine silty shale and fine-grained sandstone. Unit 3, dominantly sandstone, is interpreted as fluvial deposits. Unit 4 is interpreted as a transitional marine-nonmarine delta-plain complex. The youngest strata, in Unit 5, are interpreted as nearsource channel and overbank deposits. An analogy is drawn between the depositional settings of these units and those of the Wilcox Group of Texas (Fisher and McGowen, 1969).
Paleocurrent
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Understanding how the sedimentary responses adapt to the structural styles of fault basins in the strike-slip fault systems is one of the key goals of basin analysis. Variability of volcanic and epiclastic provenance-depositional systems and tectonic controls of the Lower Cretaceous Hengtongshan Formation in the Tonghua Basin are crucial to determine the evolution of the fault basins and wrench tectonics in southern Jilin and eastern Liaoning provinces (SJELP), NE China. Study of volcanism-induced sedimentation, composition plot, and depositional systems elucidates the sequence stratigraphy and volcano-sedimentary responses to wrench tectonics based on cores, outcrop sections, and seismic profiles of the Tonghua Basin. Two types of provenance-depositional systems (volcanic and epiclastic) were reconstituted using eight lithofacies and seven lithofacies associations. Of the lithofacies, six pyroclastic lithofacies and two epiclastic lithofacies were identified based on compositions, textures, and sedimentary structures. The presence of these lithofacies in different vertical successions was described as different lithofacies associations to interpret depositional processes and sedimentary environments. Depositional-system maps of the three sequences in the Hengtongshan Formation and analysis of structural framework indicate that volcanism and sedimentation were controlled by wrench faulting. Statistical analysis of rock compositions reveals that the deposition of the Hengtongshan Formation shows mixed contribution from both the volcanic and granitic fragments. Triangular compositional plots of detrital composition suggest a diverse provenance by straddling the litho-feldspatho-quartzose (lFQ), feldspatho-litho-quartzose (fLQ), feldspatho-quartzo-lithic (fQL), and quartzo-feldspatho-lithic (qFL) fields, indicating that the sources were derived from uplifted basement blocks and volcanic eruptions in a rift basin related to strike-slip faulting. The Tonghua Basin developed as a wrench-fault basin on the east side of Dunhua–Mishan Fault systems (DMF). This model for the Tonghua Basin can be used to understand the Liuhe Basin in the DMF and other Early Cretaceous basins in adjacent areas.
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Provenance study of the clastic deposits of the asymmetric half
graben basin can bring important data of the tectonic evolution
of the oposite margins. Tectonic processes influenced the basin
morphology, the gradient of the basin bottom. distribution of
depositional environments and cyclicity of deposits. Different
role of the axial and transverse transport within the basin can
be assumed.
Arenite
Back-stripping
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