Geology and Geochemistry of Shale and Quartzite of the Cumbum Formation: Implications for Provenance, Source Area Weathering, Climatic Conditions and Tectonic Settings

Raghunath Mishra, Snigdha Dash

Abstract: The Mesoproterozoic Cumbum Formation, composed of shales and quartzite, combines geochemical, mineralogical, and sedimentological analyses to unravel the region?s ancient climate and tectonic history. High weathering indices and clay mineralogy point to a warm, humid to semi-arid climate during deposition, while provenance and structural aspects reveal a tectonic history dominated by passive margin development. The shales have high Al2O3, Fe2O3, K2O, TiO2, Ga, La, Nb, Rb, Sc, Sr, Th and Y content more than the quartzites, whereas, quartzites are higher in SiO2, Cu, Hf and Zr than the shales. The shale samples plot on the two triangular diagrams in the relatively more weathered region and in the A-CN-K diagram above the granodiorite and shale suggesting a source which had suffered relatively a high degree of chemical weathering. For the quarzitic samples, La/Sc, Th/Sc, La/Co and Th/Co values are more similar to values for sediments derived from felsic source rocks than to those for mafic source rocks, thus suggesting felsic source rock. Th/U ratios in the quartzites range from 0.83 to 1.45 indicating the quartzites neither suffered intense weathering nor intense recycling. When Th/Sc is plotted on the diagram of Zr/Sc-Th/Sc, the recycled source rocks for the all-quartzite samples from the study area are further supported by their high Zr/Sc ratio. Out of four samples two samples are enriched in zircon due to sedimentary sorting and recycling and the rest two samples fall in between andesitic to felsic magmatism field. On a chondrite-normalised diagram, the studied shales display slightly enriched LREE patterns (average LaN/SmN = 5.27), small negative Eu (average Eu/ Eu* = 0.69) and fairly flat HREE patterns (average GdN /YbN = 0.13) except for Yb which are characteristic of sediments derived from upper continental crust. The chondrite-normalized REE patterns for the studied quartzites are characterized by high light REE/heavy REE (LREE/HREE) ratio (6.79 - 15.52), flat HREE pattern except Yb and pronounced negative Eu anomaly. LREEs are fractionated, (La/Sm)n = 4.98 and the HREE patterns are almost flat, (Gd/ Yb) n= 0.15. This chondrite-normalized pattern is typical of sediments and sedimentary rocks enriched in light REE (LREE), flat heavy REE (HREE) and negative Eu anomaly. The quartzites and shales are mostly of quartzose sedimentary provenance, derived from a cratonic interior or recycled orogen with felsic sources input. The shales and quartzites were deposited in a passive margin setting. Th/U versus Th systematics suggests a high degree of chemical weathering for the Cumbum shales suggesting them to be derived from an older crustal material and a depleted mantle source for the quartzites. The geochemistry of the studied shales suggests their origin to be a combination of felsic volcanic rocks (predominantly) and granitic rocks (to a lesser extent).

Keywords: Cumbum Formation, Geochemistry, provenance, weathering, tectonic setting

How to Cite?: Raghunath Mishra, Snigdha Dash, "Geology and Geochemistry of Shale and Quartzite of the Cumbum Formation: Implications for Provenance, Source Area Weathering, Climatic Conditions and Tectonic Settings", Volume 15 Issue 6, June 2026, International Journal of Science and Research (IJSR), Pages: 1174-1196, https://www.ijsr.net/getabstract.php?paperid=SR26619103119, DOI: https://dx.doi.org/10.21275/SR26619103119

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