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B. M. Sharma , J. P. Gupta , S. S. Rathore

Abstract

Field trials conducted at Central Arid Zone Research Institute, Jodhpur, for seven consecutive years (1988 to 1994) revealed that yields of Cenchrus ciliaris and Lasiurus sindicus grown in association with trees were lower than the yields of sole grasses. The changes in height of Acacia tortilis and Zizyphus rotundifolia were also more under the control. The height of trees decreased in association with grasses. The average soil moisture stored in the 90 cm profile under A. tortilis was lower as compared to Z. rotundifolia. Moisture storage decreased further when the grasses were grown with the trees. Organic matter increased over the initial level in all tree-grass combinations. The uptake of P by the two grasses alone or in combination with trees, was marginally different. While the uptake of Ca, Mg and K was considerably higher by L. sindicus than C. ciliaris.

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B. M. Sharma , S. S. Rathore , J. P. Gupta

Abstract

The effect of growing pearlmillet and clusterbean crops in association with Acacia tortilis and Zizyphus rotundifolia on tree growth, crop yields, soil moisture and organic matter were ascertained for four consecutive years under arid conditions. The results revealed that the grain and straw yields of pearlmillet and clusterbean grown in association with trees decreased compared to sole crops. The reductions in yields under Acacia tortilis were more than Zizyphus rotundifolia. Clusterbean suffered greater reduction as compared to pearlmillet. Growth of trees was maximum in the control (Tree alone) while in association with the crops it decreased. Height increment in A. tortilis was more in association with clusterbean than that with pearlmillet while Z. rotundifolia attained greater height when in association with pearlmillet. Profile moisture stored at the time of crop harvest was maximum in sole crop of clusterbean and higher in clusterbean.Z. rotundifolia than clusterbean.A. tortilis. The organic matter content of soil after four years increased over the initial and followed the order: Clusterbean > Pearlmillet and Z. rotundifolia > A. tortilis.

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S. S. Rathore ¹, A. R. Vijan ¹, M. P. Singh ¹, B. N. Prabhu ², K. N. Misra ¹

Affiliations
1 Geochemistry Division, KDM Institute of Petroleum Exploration, Oil and Natural Gas Corporation Ltd., Dehra Dun - 248 195, IN
2 Regional Chemical Laboratory, EKBC, ONGC, Sibsagar, Assam - 785 640, IN

Abstract

Precambrian basement from well HBM-1 in the Heera oil field of Mumbai offshore basin has been dated by Rb-Sr and K-Ar methods. Five granulitic basement samples from three conventional drill cores have yielded Rb-Sr isochron age of 502±25 Ma with an initial Sr ratio of 0.70855±0.00013. This age has been interpreted as the time of granulite facies metamorphism of the basement rocks in the region. Two whole rock samples from the basement of this well have yielded mutually concordant K-Ar ages of 505±16 Ma and 507±17 Ma. The K-Ar ages are significantly similar to Rb-Sr age obtained from this well, suggesting complete isotopic reequilibration around 500 Ma ago. The time of secondary thermal heating around 500 Ma ago in the basement of Heera field coincides with the widespread Neoproterozoic (Pan-African) thermo-tectonic event extending from the Arabian Peninsula and eastern Africa covering Madagascar, southern India, Sri Lanka and East Antarctica. This study widens the limit of the Pan-African zone, which hitherto was thought to be confined to the western part (presently southern part) of the Indian subcontinent, towards further east.

Keywords

Neoproterozoic, Pan-African Granulite Metamorphism, Rb-Sr and K-Ar Geochronology, Heera Oil Field, Mumbai Offshore Basin.

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A. R. Vijan ¹, S. S. Rathore ¹, K. C. Vig ¹, M. Bansal ¹, M. P. Singh ¹, B. N. Prabhu ²

Affiliations
1 Geochemistry Division, KDM Institute of Petroleum Exploration, Oil and Natural Gas Corporation Ltd., Dehra Dun - 248 195, IN
2 Regional Chemical Laboratory, ERBC, ONGC, Sibsagar, Assam - 785 640, IN

Abstract

The importance of dating glauconites is that they are formed under low sedimentation rates connected with marine transgression and are commonly associated with unconformities and other stratigraphic breaks. This paper presents the first quantitative age estimation of glauconite samples separated from subsurface cores of Goru and Pariwar Formations of Jaisalmer basin, Rajasthan, India. SEM studies, X-ray diffraction patterns and high K₂O content (6.8 to 7.4%) of these samples indicate that they are highly evolved and are ideal for isotopic dating.

The Rb-Sr age of 108 ± 5 Ma and average K-Ar age of 103 ± 3 Ma obtained for the gtauconites from the Goru Formation are indistinguishable within error and agree with their biostratigraphic age. Glauconites from the upper most part of the Pariwar Formation give an average K-Ar age of 106 ± 3 Ma (early Albian), which is slightly lower than their biostratigraphic age.

Keywords

Geochronology, Glauconite, Goru and Pariwar Formations, Jaisalmer Basin, Rajasthan.

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S. S. Rathore ¹, T. R. Venkatesan ², R. K. Srivastava ³

Affiliations
1 Geochemistry Division, KDMIPE, ONGC, Dehradun-248 195, IN
2 Physical Research Laboratory, Ahmedabad - 380 009, IN
3 Geology Department, M.L. Sukhadia University, Udaipur - 313 001, IN

Abstract

Six whole rock samples have been dated by ⁴⁰Ar/³⁹Ar method to ascertain the emplacement time of the Mundwara Alkali Igneous Complex, Rajasthan, India. The dated samples include four from the Musala hill and one each from Mer and Toa hills of the complex. Out of these, only two syenite samples. viz. MR 86/4 and MR 86/7 from the Musala and Mer hills, respectively, have given plateaus at 64 Ma, while the remaining samples have exhibited saddle shaped spectra owing to the presence of excess argon. However, similar isochron ages of about 70 Ma obtained from a basalt (Musala hill) and a gabbro (Toa hill) by linear regression of all the data points might suggest initiation of igneolls activity at Mundwara around 70 Ma ago.

⁸⁷Sr/⁸⁶Sr ratios of this suite range from 0.70385 to 0.70551 indicating its derivation from a mantle source.

Keywords

Geochronology, Mundwara Alkali Igneous Complex, Rajasthan.

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