• M Venkateshwarlu

      Articles written in Journal of Earth System Science

    • Anisotropy of magnetic susceptibility (AMS) studies of Campanian–Maastrichtian sediments of Ariyalur Group, Cauvery Basin, Tamil Nadu, India: An appraisal to Paleocurrent directions

      G Papanna M Venkateshwarlu V Periasamy R Nagendra

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      Oriented samples of sediments from Ariyalur Group, Cauvery Basin, south India, were studied for low field anisotropy of magnetic susceptibility (AMS) measurements to unravel the magnetic fabrics and paleocurrent directions. The results of AMS parameters of the sediments indicate primary depositional fabrics for Sillakkudi, Ottakovil and Kallamedu sandstone formations and secondary fabric for Kallankurichchi limestone formation. The obtained low degree of anisotropy ($P_j$), oblate shape AMS ellipsoid and distribution of maximum ($K_1$) and minimum ($K_3$) susceptibility axes on equal area projection confirm the primary sedimentary fabric for Sillakkudi, Ottakovil and Kallamedu Formations. In the case of ferruginous, lower arenaceous, Gryphaea limestone and upper arenaceous limestone beds of Kallankurichchi Formation have recorded more than one fabric. The observed AMS parameters like shape factor (𝑇) (prolate to oblate), 𝑞 value and random distribution of minimum ($K_3$) and maximum ($K_1$) susceptibility axes are supported for secondary fabrics in Kallankurichchi Formation as a result of post-depositional processes. Based on petrographic studies, it can be established that $K_1$ AMS axis of biotite mineral could represent the flow direction. The established paleocurrent direction for Sillakkudi is NW–SE direction while Ottakovil and Kallamedu Formations recorded NE–SW direction. Overall the paleoflow directions observed for Ariyalur Group is NE–SW to NW–SE.

    • Magnetic polarity stratigraphy of the Siwalik sequence in Nurpur area, NW Himalaya, India

      M Venkateshwarlu

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      Magnetic polarity stratigraphy studies were carried out on Jabbar Khad section of Nurpur area, Kangra District, Himachal Pradesh, India. Oriented block samples were collected at 202 sites with 3–5 samples per site from a 2350-m thick continuous sedimentary sequence consisting of sandstone–mudstone alternating beds. Specimens were subjected to thermal demagnetization (100–700°C) after measuring their natural remanent magnetization (NRM). Palaeolatitudes of virtual geomagnetic pole (VGP) from each site were calculated from the acquired characteristic remanent magnetization (ChRM) directions. The observed remanence carrier could be haematite. Magnetic polarity scale (MPS) was erected. This MPS is correlated with the standard geomagnetic polarity time scale (GPTS) of Lourens et al. (2004). The MPS readily matched from chron C2An.1n to chron C4n.2n, therefore assigning an age 8.20–2.60 Ma to the middle and upper Siwalik sections at Nurpur. The rate of sedimentation in middle Siwalik is 29 mm/yr and upper Siwalik is 59 mm/yr.

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