Provenance analysis of Early Jurassic Datta Formation, Western Salt Range, Upper Indus Basin, Pakistan

Abstract

Rocks of the Jurassic sequence are excellently exposed in the
Western Salt Range. Early Jurassic Datta Formation has been
selected for detailed study. The formation is well exposed at the
Nammal Gorge section. It predominately consists of sandstone with
a minor amount of carbonaceous shale and marl units. The
petrographic analysis has been carried out to decipher the
provenance of extrabasinal sediments, tectonic setting and
paleoclimate conditions present at the time of deposition of the
Jurassic Datta Formation. The aforementioned analysis of twenty
representative fresh samples displays the dominance of quartz,
feldspar, and lithic fragments making the framework grains of the
lithostratigraphic unit. The study highlights that the lithological
units are mature both mineralogically and texturally, and have been
classified as quartz arenite, subarkose, sublithic arenite, lithic
arkose, and feldspathic lithic arenite on the basis of the QFL
diagram. Quartz grains are both monocrystalline and
polycrystalline while feldspars are mainly composed of plagioclase
and microcline. The majority of lithic fragments like granite, chert,
siltstone, shale and schist with subordinate quartzite, phyllite and
volcanic fragments are present in these sandstones beds. The main
cementing materials are silica, quartz while minor substitutes are
clay, mud and calcite. Quartz (total)-Feldspar-Lithic fragments
(QtFL) and Quartz (monocrystalline)-Feldspar-Lithic fragments
(total) (QmFLt) plots mostly indicate recycled orogen field and
some samples fall in mixed, while others in recycled quartzose,
transitional continental and basement uplift fields of provenance.
The bi-variant log-log Qt/F+R and Qp/F+R plots of sandstone
samples from the Datta Formation show deposition in cold arid and
semi humid climate conditions. Petrographic analysis indicates that
the transitional continental region representing the sandstone may
have been sourced from acidic igneous (Plutonic), sedimentary,
metasediments and/or metamorphic rocks. These outcrop analogues
of the mature sandstone units of the Datta Formation help delineate
the exact reservoir during the exploration and exploitation of
Jurassic plays of the Upper Indus Basin.