A Geochemical Proxy for Recognizing Sequence Stratigraphic Surfaces in Late Cretaceous Sediments of Ariyalur Area, Cauvery Basin, South India

The geochemical tool is employed to recognize the sequence stratigraphic surfaces of the Campanian-Maastrichtian sediments of the Ariyalur area in the Cauvery Basin. The Sillakkudi Formation (Campanian) underlies the Kallankurichchi Formation of Maastrichtian age. The sequence stratigraphic surfaces are recognised by employing the major and trace elements. The high ratio of Mn/Al concentrations confirms the relative rise of sea-level and the Mn Maxima coincides with biostromal limestone, which marks the MFS in the outcrop section. The TST and MFS in both Sillakkudi and Kallankurichchi Formations are recognized by the positive digressions in Ti/Al. The sequence boundaries are identified based on the low trends Ti/Al and Zr/Al chemical contents. The high Ti/Al ratios in the Sillakkudi sandstone are derived from the increased siliciclastic supply, and the low values of Ti/Al in the Maastrichtian limestones are derived from the non-siliciclastic supply

Depositional and post-depositional setting of Maastrichtian limestone, Ariyalur Group, Cauvery Basin, South India:a geochemical appraisal

Major, trace, REE, and stable isotopic composition of Maastrichtian limestones of Cauvery Basin were studied to decipher their depositional and post-depositional environment. The major oxides and trace elements concentration of these limestones were normalized using Post-Archean Australian Shale (PAAS) values. The concentration of CaO is having a significant enrichment, and MgO, K2O, Co, Ni, Cu, Zn, Pb, Ba, U, and Th are moderately depleted, whereas Sr and Na2O contents are relatively similar to the PAAS values. The PAAS-normalized REE + Y pattern of Maastrichtian limestones display relatively uniform pattern among the compositionally different limestones: (1) enriched LREE (average NdSN/YbSN = 5.03 ± 0.92); (2) positive Ce anomaly (average 1.79 ± 0.16); (3) negative GdSN/Gd* anomaly (average 0.52 ± 0.02); (4) low Y/Ho ratio (average Y/Ho = 0.14 ± 0.01). The average ΣREE contents in ferruginous, arenaceous, and biostromal limestones are 65, 64, and 52 ppm, respectively, which indicate that the mineralogical variation plays a major role in incorporation of ΣREE. The Kallankurichchi limestones have δ13C values range from −3.2 to −1.1‰PDB, and the δ18O values range between −7.8 and −5.5‰PDB. The negative δ13C and δ18O values and a moderate co-variation between δ13C and δ18O (r 2 = 0.35) indicate that the alteration of original isotopic composition is due to diagenesis.The positive Ce/Ce* confirms the clastic input into the system, and negative Mn* values and Th/U ratios (~0.29–1.4) in these limestones indicate their association with precipitation of carbonates in reducing (anoxic–dysoxic: Th/U ≤ 2) conditions

Sediment geochemistry of coastal environments, southern Kerala, India: implication for provenance

Late Quaternary sediments representing the floodplain, estuary and offshore environments of southern Kerala were investigated to infer provenance. The grain size reveals the dominance of sand to silty clay, clay to clayey silt and clayey silt in the floodplain, estuary and offshore sediments, respectively. The chemical index of alteration (CIA) values and A-CN-K plot attributes to high, moderate and low weathering in floodplain, estuary and offshore regions, respectively. The SiO 2 /Al 2 O 3 values lesser than Post-Archean Australian Shale indicate low to moderate maturity for the estuarine and offshore sediments. The geochemical immaturity indicates its derivation from low to moderately weathered source rocks. The major and trace elemental ratios and discriminant function diagrams attribute that the sediments were derived from intermediate to felsic source rocks. The enrichment of Cr and Ni concentration in the sediments compared to the upper continental crust, related to the contribution of orthopyroxenes, weathered from charnockite and garnets from the granulite terrain, respectively

Geochemistry of Sandstones from the Upper Cretaceous Sillakkudi Formation, Cauvery Basin, Southern India: Implication for Provenance

Major, trace and rare earth elements (REE) composition of sandstones from the Upper Cretaceous Sillakkudi Formation, Ariyalur Group, Cauvery Basin were studied to decipher their weathering and provenance history. Texturally, these sandstones are immature, poorly sorted and grain supported. Abundance of feldspars especially, plagioclase indicates rapid deposition of sediments from a nearby source rocks. Using the geochemical classification diagram the Sillakkudi sandstones are classified as fe-sand, quartz arenite, litharenite, sub-litharenite, sub-arkose, arkose, and wacke types,which is also supported by the petrography study. The transition trace elements like Co, Ni, and V are higher in theSillakkudi sandstones than upper continental crust (UCC) values. However, the Sillakkudi sandstones are lower in Cr (mean ~21) content than average UCC value (~ 35). The poor correlation between Cr and Ni (r = 0.08, number of samples n = 20) imply that these sandstones were derived from felsic source rocks. Similarly, the Eu/Eu* (0.35-1.73), La/Sc (1.93-9.36), Th/Sc (0.41-6.57), Th/Co (0.14-5.01), Th/Cr (0.23-2.94), and Cr/Th (0.34-4.28) ratios support a felsic source for the Sillakkudi sandstones.The significant enrichment of Zr, Hf, and Th in fe-sand, sub-arkose and litharenite could be related to the presence of heavy minerals, especially zircon. However, the zircon geochemistry did not affectthe REE distribution and its patterns in the Sillakkudi sandstones. The Chondrite normalized REE patterns of Sillakkudi sandstones are characterized by relatively flat HREE (Gd/YbCN = ~ 0.73-2.41; subscript CN refers to chondrite normalized value), enriched LREE (La/SmCN = ~ 3.39-5.82) and negative Eu anomaly (mean value Eu/Eu* = 0.80). The Gd/YbCN ratios (~0.73-2.50) are less than 2.5, which suggest that these Sillakkudi sandstones were derived from the less HREE depleted source rocks. The comparison of REE patterns and its Eu anomalies to the source rocks reveals that the Sillakkudi sandstones received a major contribution of sediments from Dharwar craton

Provenance and tectonic setting of Miocene siliciclastic sediments, Sibuti formation, northwestern Borneo

Provenance and tectonic setting of sandstone and mudstone units of the Miocene Sibuti Formation from northwest Borneo have been studied based on the mineralogy, major and trace element geochemistry data. The X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) data revealed that the sandstones and mudstones were abundant in quartz, pyrite, clay, and heavy minerals such as zircon, rutile, and some detrital cassiterite. Geochemically, the sandstones and mudstones are classified into quartz arenite, litharenite, sublitharenite, arkose, and wacke. Quartz arenites are enriched with SiO2, Zr, and Th and depleted in Al2O3, CaO, and other elements compared to other sandstone types, indicating high maturity and intensive weathering. Chemical index of alteration (CIA: 77–90), plagioclase index of alteration (PIA: 86–100), and A-CN-K diagram suggest intense weathering in the source area. Elemental ratios such as La/Sc, Th/Sc, Cr/Th, La/Co, and Th/Co are similar to sediments derived from the felsic rocks. Also, the provenance discrimination diagrams suggest recycled continental nature of these clastic sediments which are mostly derived from metasedimentary source (Rajang Formation). Discriminant-function diagram for the tectonic discrimination of siliciclastic sediments revealed that the sediments of Sibuti Formation were derived from a collision zone, which is consistent with the geology of the study area