Newly Proposed Lithostratigraphy of the Quaternary Succession of Hanna- Spin Karez Area, Quetta, Pakistan

Abstract

The “Hanna and Spin-Karez area” in Quetta district lays at the “Quetta Syntaxes”, the intersection between Sulaiman and Kirthar Fold Thrust belts, near the Zarghun Knot, western Balochistan, Pakistan. The Quaternary succession in the area is more than 800 m thick. It had erroneously been mapped as Spin Karez Gravel by the Hunting Survey Corporation (HSC) (Jones, 1961). We remapped the succession on 1:25000 scale and defined the litho-stratigraphy of the succession that allowed us to divide the succession into four different units/formations. The names are proposed for constituting units such as the “Hanna Lake Conglomerate”, “Hanna Red Clays”, “Spin Karez Conglomerate” and “Holocene deposits”.

The “Hanna Lake Conglomerate”, which is the lowermost unit, is 200 meters thick unit. In lower part the boulder conglomerate is poorly sorted and crudely bedded, while in the upper part the conglomerate is cobble to pebble size, well-stratified, however, punctuated with sandstone lenses. The lower contact of the conglomerate is angular unconformity with the underlying “Early Eocene Ghazij Formation”. “The Hanna Red Clays” is more than 500 meters thick red mudstone/claystone succession of with rare interbedded fine- grained sandstone and siltstone. Its lower contact with “Hanna Lake Conglomerate” is transitional and conformable. “The Spin Karez Conglomerate” which is more than 100 meters thick is well bedded and moderately to well sorted cobble to pebble conglomerate with sporadic siltstone/sandstone wedges. The Holocene deposits are topmost 20 m thick unit. They are horizontally lying loose or semi-consolidated sediments composed of gravel interbedded with clay and siltstone. It lower contact with “Hanna Red Clays” is transitional and conformably. The Holocene deposits are limited to the valley and overlies the “Hanna Red Clays” with angular unconformity.