Ostracoda genus Alocopocythere Siddiqui from the Tertiary beds of India, with a note on its biostratigraphic significance
Ostracoda genus Alocopocythere Siddiqui from the Tertiary beds of India, with a note on its biostratigraphic significance
The Ostracoda genus Alocopocythere Siddiqui occurs abundantly in the Tertiary beds of India and ranges in age from Early Eocene to Middle Miocene. This genus evolve rapidly and in consequence its species have relatively short stratigraphic range which make them invaluable biostratigraphic markers. In all twenty-two species of genus Alocopocythere have been recorded from India. Of these, thirteen species are recorded from western part of India. A. abstracta Siddiqui, A. rajasthanensis Bhandari, A. coarctata Siddiqui and A. longilinea Siddiqui are restricted to Early Eocene. A lunejensis Guha ranges from Early Eocene to Early Oligocene. A. transcendens Siddiqui ranges from Early to Middle Eocene. A. transversa morph. A, is recorded from Middle Eocene and A. transversa morph. E is restricted to Late Eocene. While A. fossularis Guha. ranges from Late Oligocene to Early Miocene. A. gujaratensis Khosla, A. elongata Kholsa and Nagori are recorded from Early Miocene. A. mumbaiensis n.sp and A. depressa Kholsa are confined to Middle Miocene. There is strong provincialism in the ostracodes of Western India and North Eastern part of India. In the North-eastern part of India nine species of the genus Alocopocythere have been recorded from Middle and Late Eocene. Of these, A. bhandarii Neale and. Singh, A. borhollaensis Bhandari, A. gopinathkillaensis Bhandari, A. polygona Neale and Singh, A. talukdari Neal and Singh are confined to Middle Eocene. A. indica Bhandari, A. garoensis Bhandari, A. dattai Bhandari and A. meghalayaensis Bhandari are restricted to Late Eocene. On the basis of stratigraphic ranges the Early Eocene to Middle Miocene succession of western India can be divided into 10 Alocopocythere zones: They are: 1. Alocopocythere rajasthanensis Range Zone, 2. Alocopocythere rajastanensis Alocopocythere abstracta Interval Zone, 3 Alocopocythere abstracta - A. longilinea Interval Zone, 4. Alocopocythere longilinea - A. transcendens Interval Zone, 5. Alocopocythere transcendens - A. transversa morp. A. Interval Zone,6. Alocopocythere transversa morph. A - Alocopocythere transversa morp. E, 7. Alocopocythere transversa morph. - E. Alocopocythere lunejensis (Guha), 8. Alocopocythere lunejensis Alocopocythere fossularis Inter Biohorizon, 9. Alocopocythere fossularis -Alocopocythere gujaratensis - Alocopocythere elongata Assemblage Zone, 10. Alocopocythere mumbaiensis n.sp. Range Zone and Middle to Late Eocene succession of North-eastern India into five Alocopocythere zones: They are: Alocopocythere gopinathkillaensis Range Zone, 2. Alocopocythere gopinathkillaensis - Alocopocythere garoensis Interval Zone, 3. Alocopocythere garoensis Range Zone, 4. Alocopocythere garoensis - A. meghalayensis Interbiohorizon (Poorly fossiliferous) Zone, 5. Alocopocythere meghalayaensis Range Zone. Evolutionary trends and biostratigraphic significance of the genus have been briefly described.
