Preliminary multidisciplinary investigations were carried out in a 105 m thick late Pleistocene terrestrial sequence in the Lamayuru basin, Ladakh Himalaya. Palaeomagnetic studies reveal a reversal of polarity at about 35 ka BP. This is the only report of this reversal event in the late Pleistocene terrestrial sequences of the Indian subcontinent. The valley fill sequence is the product of an interplay of lacustrine with fluvio-deltaic to colluvial processes. Four fossiliferous horizons have yielded ostracods and gastropods indicating shallow freshwater conditions. The Lamayuru lake was created by tectonically induced instability about 35-40 ka BP, an event that may be represented widely throughout the Himalaya.
Palaeomagnetic and rock magnetic investigations were carried out on oriented rock samples collected from the inner walls of Lonar Lake, which is believed to be a meteorite crater. These studies show systematic variation in some magnetic parameters (Q,, Jn, K and declination) whereas at surrounding localities these parameters show random variation. A soft secondary shock component, acquired in the present field, of D = 9", I = + 47" (K = 47.6, ~1~~ = 6.4") has been successfully isolated by vector difference analysis, whereas the stable primary vector is similar to that of Lower Tertiary period reverse magnetization. NRM and IRM, of the upper and lower flows respond differently to AF demagnetization as a function of their Ha. It is shown that the NRM carried by the lower flows is similar to that of IRM probably reset by the meteorite impact because of their low H,, carriers. It is suggested that such magnetic property variations are characteristic of shock origin and hence we propose an impact origin for Lonar Lake.
Fifty-six orientated samples were collected from 13 sites on five dolerite dykes (between lat. 14"23'N, long. 77'43'E and lat. 14"08'N, long. 77"49'E), which adjoin the south-western margin of the Cuddapah basin in Anantapur district, Andhra Pradesh. After af demagnetization, two dykes (five sites) striking ENE possess similar magnetic directions, ( l ) D = 57", 1 = -6 9 " ( K = 5 2 , 0 1~~= 7 " ) and (2) D = 7 1 " , 1 = -7 2 " (K=26O,a9,=5"). Again dykes (3) (three sites), and (4) (two sites) have similar strike (NE) and magnetic directions, D = 64". I = -7" ( K = 142, ag5 = 8") and D = 53", I = -8" ( K = 142, ag5 = 6") and dyke (5) (two sites) striking NW shows D = 320", I = -34" (K = 68, ag5 = 13"). Remanent directions estimated from total field magnetic anomaly data agree well with these results. Synthesis of these data with 10 other published palaeomagnetic studies of Precambrian dolerite dykes on the Indian peninsula, suggest that these three systems of dykes adjoining the Cuddapah basin had been emplaced prior to the basin formation perhaps representing the initial thermal event responsible for the basin development and also that there have been at least three separate periods of dyke emplacement on this shield. The radiometric data, however, are very sparse and these periods cannot be dated with confidence.
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