8th International Nannoplankton Association Conference


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Muhammad Z. Iqbal:
Calcareous nannofossils from Ghazij Formation in Sulaiman Fold-belt, Pakistan and their application in biostratigraphy

The main sedimentary basin of Pakistan is the Indus Basin, which is subdivided into three parts, the Upper, Middle and Lower Indus Subbasins. The Indus Basin as a whole belongs to the western part of the Indo-Pakistan Plate. Triassic to Tertiary sediments of the eastern fold-belt of the Indus Basin were deposited on a broad shelf area of the passive continental margin of the Indo-Pakistan Plate. The fold-belt developed as a result of the main collision of the Indo-Pakistan Plate with the Eurasian Plate.

A well section from the Middle Indus Basin was selected for calcareous nannoplankton study. The samples were taken only from the Early Eocene part (Ghazij Formation) of the well section. The Ghazij Formation consists of pale, greenish-grey or brown shale and white or pale grey limestone that increases in proportion upwards. The shale is calcareous, hard, flaky and, in places, grades into marl and limestone. The limestone is thinly- to thickly-bedded and weathers yellowish-white or chalky white. The formation is divided into four lithological units: the Upper Rakhi Gaj Shales, Green and Nodular Shales, Rubly Limestone, and Shales with Alabaster.

Spot-samples have been previously studied for calcareous nannoplankton, the authors reporting some reworked species from the Late Cretaceous and rarely occurring specimens of Late Paleocene (NP9) and Early Eocene (NP11) ages. Previous workers did not define any biozones but assigned an Early Eocene age to this formation. On the basis of larger foraminifera, previous workers have dated this formation as Early Eocene, and planktonic foraminifera have been used to define four local biozones, based on open nomenclature, and which cannot be correlated with standard planktonic foraminiferal biozonations. The upper part of the Ghazij Formation has been reported as barren of planktonic foraminifera. Further work has reported planktonic and benthic (smaller and larger) foraminifera from the formation, assigning the lower half to Biozone P8 and the upper half to P9.

In the present study, 52 samples were analysed for calcareous nannoplankton. The samples were taken from Well Miriwah-1, between 30-1280m, through the Early Eocene sequence of the Ghazij Formation. The calcareous nannoplankton record is interpreted to provide a precise age and to establish the nannoplankton biozones. The interval yielded typical Eocene calcareous nannoplankton. However, age-diagnostic index-fossils were absent. Therefore, some secondary marker-species, such as Coccolithus crassus, Chiasmolithus grandis, Sphenolithus radians, Toweius gammation, Sphenolithus conspicuus, Neococcolithes protenus and Campylosphaera dela, were used. Based on these species, three calcareous nannofossil biozones were assigned for the Early Eocene: mid-NP14-13 (30-310m), NP12-11 (310-1000m) and NP10 (1015-1280m). The poster shows the stratigraphic sequence of the Sulaiman Fold-belt, distribution chart of the calcareous nannoplankton, suggested biozones with additional markers, and photomicrographs of the important species.


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 [Division of Micropalaeontology] [Department of Geosciences] [Bremen University]

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