Journal of Geological Society of India (Online archive from Vol 1 to Vol 78)

B. S. Kotlia ¹, M. S. Bhalla ², Nalin Shah ¹, G. Rajagopalan ³

Affiliations
1 Department of Geology, Kumaun University, Nainital-263 002, IN
2 National Geophysical Research Institute, Hyderabad-500 007, IN
3 Birbal Salmi Institute of Palaeobotany, Lucknow-226 007, IN

Abstract

Palaeomagnetic studies were carried out in the fluvio-Iacustrine sediments of Bhimtal and Bhowali basins (Kumaun Himalaya) and of Lamayuru basin (Ladakh Himalaya). The results were supplemented by radiocarbon dating. For the first time in the terrestrial sediments of the Quaternary-Holocene age in the Indian subcontinent, three minor reversal polarity events have been recorded at Lamayuru (ca. 35.5 ± 0.6 ka BP), Bhimtal (29.8-25.6 ka BP), and Bhowali (ca. 7.7 ± 0.13 ka BP). Since the upper most portion of the Lamayuru section indicated a reversal event, it may be significant to correlate it with the Indian Ocean event estimated as 40 ka BP. It is suggested that the Bhimtal event may be correlated with the widely known Mono Lake excursion which is fixed at 28-26 ka BP. Among the Holocene events, only a few are known, e.g., an event in the Solberga sediments (Sweden) estimated at ca. 10 ka BP; an event from Central Asia, dated at about 9 ka BP; the Erieau excursion, upper part of which has been estimated at about 7.6 ka BP; and the youngest event known as the Starno event (2.8 ka BP). The initial reports of the palaeomagnetic events, described in this paper, may be highly significant for examining several more sections as the events should he found repeatedly in sediments of same age in a given sedimentary environment.

Keywords

Magnetostratigraphy, Quaternary-Holocene, Reversal events, Fluvio-Iacustrine Deposits, Kumaun, Ladakh Himalaya.

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A. Ranga Rao ¹, R. P. Agarwal ¹, U. N. Sharma ¹, M. S. Bhalla ², A. C. Nanda ³

Affiliations
1 Oil and Natural Gas Commission, Dehradun, IN
2 National Geophysical Research Institute, Hyderabad, IN
3 Wadia Institute of Himalayan Geology, Dehradun, IN

Abstract

Magnetic polarity stratigraphy of Upper Siwalik Subgroup, Jammu Hills was worked out based on partially demagnetized data from 208 sites in three sections: Parmandal-Utterbeni, Nagrota-Jammu and Balli. One/two bentonitized tuff horizons occur close to the base of a long reversed polarity zone associated with Pinjor age fossils. Fisson track dates of 2.8±0.56 m.y. and 2.31±0.54 m.y. have been obtained on the zircon phenocrysts from these tuffs. These data permit correlation of our magnetic stratigraphy with the standard magnetic polarity time scale. The longest sampled section spans the interval from 4.92 to 0.22 m.y. This dating places the lower part of Upper Siwalik in the early Pliocene.

In the sampled parts of the sections, the magnetic polarity zonation establishes 16 magnetozones in Parmandal-Utterbeni, 13 in Nagrota and one in Balli. Individual magnetic transitions can be correlated over a lateral distance of 62 km and these provide time lines for correlation of lithology from one section to the other.

Estimated rates of sedimentation indicate rates varying from 0-45 m to 0.71 m/l000 years for Gilbert and Gauss epochs, while a decreased rate varying from 0.21 m to 0.37 m/l000 years is indicated during the Matuyama epoch.

The ]ast folding event of Suruin-Mastgarh anticline is not older than 0.22 m.y. However, the decrease in the rate of sedimentation during post Gauss time could possibly be due to an earlier period of deformation.

A significant change in fauna near the Gauss-Matuyama boundary is observed by the appearance of Equus and cervids with antlers and by the absence of Hipparion. We correlate this boundary with the Tatrot-Pinjor faunal boundary, No change either in lithology or in the vertebrate fauna is observed at the Pliocene-Pleistocene boundary if it is to be placed at the top of the Olduvai Normal Subchron.

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G. V. S. Poornachandra Rao ¹, M. S. Bhalla ¹

Affiliations
1 Palaeomagnetism Division, National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

In the absence of conventional radiometric dating and fossil evidence, magnetostratigraphy is considered to be a very powerful tool to correlate rock formations. Often the magnetozones are used as bench marks in correlation of rocks as the geomagnetic field reversals are ubiquitously synchronous. The Vindhyan sedimentation in the Indian stratigraphy represents a very important time period between 1400-400Ma with lithounits quite suitable for recovering the geomagnetic field signatures. With the recently obtained results from the Senui Group, palaeomagnetic field during the main Vindhyan Groups namely the Semri, Kaimur, Rewa and Bhander periods is available. It is quite interesting to note that all the formations investigated from these groups reveal both normal and reversed polarities of the palaeomagnetic field. Using this information a magnetic polarity time scale (GPTS) is constructed for the Vindhyan Supergroup during the late Proterozoic. When correlated with the Russian magnetostratigraphic scale for the Riphean period, it is noticed that the geomagnetic field during the late Proterozoic is similar to that of the Phanerozoic with superchrons at some periods and frequent reversals at others throughout the Precambrian.

Keywords

Magnetostratigraphy, Palaeomagnetism, Vindhyan Basin.

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K. Subrahmanyam ¹, M. S. Bhalla ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad - 500 007, IN

Abstract

Prominent resistivity lows in the profiles correlate with fault zones. Resistivity values of the formations are in the range 6 ohm-m to 186 ohm-m.

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M. S. Bhalla ¹, B. S. Kotlia ², K. Subrahmanyam ¹

Affiliations
1 National Geophysical Research Institute, Hyderabad, IN
2 Kumaon University, Nainital, IN

Abstract

Magnetostratigraphy of fluviolacustrine sediments from a 10 m thick section of a palaeolake near Wadda, Pithoragarh district, Uttar Pradesh bas been studied. The results indicate a prominent change in inclination of the remanent field in the age span 24 to 25 Ka, correlating with the widely known Mono lake excursion. Higher susceptibility values for the sediments of a part of the section are inferred to be due to rapid erosion rate associated with the transport of magnetite-rich sediments from the catchment area.

Keywords

Magnetostratigraphy, Fluviolacustrine, Uttar Pradesh.

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B. S. Kotlia ¹, K. Nakayama ², M. S. Bhalla ³, B. Phartiyal ¹, T. Kosaka ⁴, Moulishree Joshi ¹, Jaishri Sanwal ¹, R. N. Pande ¹

Affiliations
1 Department of Geology, Kumaun University, Nainital - 263002, IN
2 Department of Geosciences, Shimane University, Matsue - 690-8504, JP
3 National Geophysical Research Institute, Hyderabad - 500007, IN
4 Department of Geology, Shinshu University, Matsurnoto - 390-8621, JP

Abstract

A 2600 m thick succession, exposed between Kathgodam and Ranibagh in the Kumaun Himalaya and belonging to the Lower and Middle Siwalik, was subjected to lithological and palaeomagnetic studies. Lithologically, four units are recognized in the sequence. Units 1-2 are correlated with the upper part of the Lower Siwalik, whereas the Units 3-4 are correlated with the Middle Siwalik. In the absence of the vertebrate fossils and absolute chronology, the lithological boundaries are used to explain the magnetic polarity stratigraphy. We suggest that the lithological boundary between the Lower and Middle Siwalik (e.g., Chinji-Nagri) in the Kathgodam-Ranibagh section lies at ca. 850 m level and is palaeomagnetically estimated as ca. 9.8 Ma. If such a correlation is correct, the section ranges in age from Chron 5 An to Chron 2 Ar (ca. 12.0 to 4.0 Ma).

Keywords

Siwalik, Lithology, Palaeomagnetic Chronology, Kumaun Himalaya.

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