Browsing by Author "Seetharamaiah, J."

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    9 - Holocene environmental magnetic records of Indian monsoon fluctuations
    (Elsevier, 2022) Basavaiah, N.; Seetharamaiah, J.; Appel, Erwin; Juyal, Navin; Prasad, Sushma; Rao, Nageswara K.; Khadkikar, A.S.; Nowaczyk, N.; Brauer, A.
    Holocene history of the Indian monsoon reconstruction using environmental magnetism has emerged as an effective paleoclimate proxy with its fast, efficient, and repeatable measuring procedures. In this chapter, we have made an attempt to provide a broad synthesis of the available sediment magnetic records obtained from the loess-paleosols (central Himalaya), lake (western India), delta and lagoon sequences (eastern coast Godavari and Iskapalli). Variations in magnetomineralogical S-ratio values of sediment archives were combined and stacked as a surrogate for Holocene paleomonsoon change. High S-ratio results from low weathering rates were attributed to more wet conditions, while low S-ratios were related to dry conditions from intense low temperature oxidation. Combining the S-ratio data from diverse environments collectively revealed three broad climate phases with minor oscillations during the past 20 ka. These are (i) a step-wise intensification of the SW monsoon since the Last Glacial Maximum with its peak level at ∼9.0 ka, (ii) the prevalence of a prolonged dry spell along the eastern coast and western India at ∼3.5 ka that led to the collapse of the Harappan civilization, and (iii) reduction of monsoon rainfall during the period of global cooling events such as Last Glacial Maximum, Younger Dryas, and Little Ice Age. We observed that instead of the concentration-specific magnetic susceptibility (χ), the combined remanence S-ratio seems to be a more sensitive proxy responding to the monsoon variability both at centennial and millennial time scales.
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    Distribution of organic matter and calcium carbonate in the shelf sediments off Penner River, east coast of India
    (Elsevier, 1997) Seetharamaiah, J.; Swamy, A.S.R.
    Organic matter and calcium carbonate in the shelf sediments off penner river are mainly controlled by the texture of the sediments. The outer shelf (30-50 m depth) sediments of the southern and northern parts have a higher content of organic matter (1.2 to 2.22%). The sharp differences in organic matter content (varies from 0.8-1.6%) and fine nature of the sediments at the river mouth reveals detrital contribution. A calcium carbonate rich zone (30-40%) associated with coarse sands occurs opposite to penner river mouth (20-50 m depth). The source for high concentration of calcium carbonate in the coarse sands (relict) are molluscan shells, shell fragments and foraminifera indicative of the in situ origin . It is inferred that the calcium carbonate supports that the coarse sands are stillstand deposits admixtured with present conditions.
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    Geochemical and well logs evaluation of the Triassic source rocks of the Mandawa basin, SE Tanzania: implication on richness and hydrocarbon generation potential
    (Elsevier, 2019) Godfray, G.; Seetharamaiah, J.
    Selected core and cutting samples from the Triassic succession of the Mbuo claystone and the Nondwa shale were collected from the Mandawa-7, Mbuo-1 and Mbate-1 wells, onshore Mandawa basin, to understand the hydrocarbon generation potential. Earlier studies show that Mbuo claystone and Nondwa shale source rocks have fair to good generation potential based on percent total organic carbon (TOC) with kerogen type II/III, but no detailed studies include the potential for hydrocarbon generation from Triassic source rocks in the Mandawa basin. Detailed parameters like TOC, level of organic maturity (LOM), net to gross (NTG) ratio and integrated geochemical and well log analysis approaches are applied to understand the generation potential of the Triassic source rocks. The results show that TOC derived from well log analysis ranges from 0.01 to 11 wt percent (wt%), clearly including fair to good average TOC values with less than 0.5 NTG for both the Mbuo claystone and the Nondwa shales using a marginal cut-off value of 0.5 wt% TOC. The S1 and S2 values range from 0.1 to 1.7mgHC/g Rock and 1.2–17.2mgHC/g Rock respectively. The cross plot between TOC and S1 and S2 values from Rock Eval shows that these source rocks have low potential for hydrocarbon generation, and that S1 and S2 are independent to the thermal maturity. Integrating results obtained from various studies shows that both Mbuo claystone and Nondwa shales in the Mbate-1 and Mandawa-7 wells have poor hydrocarbon generation potential in their respective organic-rich intervals.