Palaeoenvironment and provenance of the Early Eocene arenaceous sequence of Neyshaboor, Binalud region, Iran

Abstract

The Early Eocene sequence of Neyshaboor, Binalud region of Iran is predominantly composed of arenaceous deposits. Two stratigraphically important sections from the Damanjan and Taghan areas have been investigated based on field work, petrographic and geochemical analyses. Eight lithofacies were identified and have been grouped in to conglomerate, sandstone, and mudstone facies association. Petrographic and geochemical data show that the Early Eocene sandstones are mainly composed of arkoses and litharenites classes. Provenance analysis indicates that sediments were supplied from a nearby andesitic-granitic source with minor contribution of metamorphic and sedimentary sources. The presence of predominance of monocrystalline over polycrystalline quartz and abundance of K-feldspars; Cu and Pb contents also support this interpretation. However, subordinate representation of polycrystalline quartz grains, chert, volcanic rock fragments, biotite, zircon, as well as higher percentage of MgO and Fe2O3, suggest some contribution from high-grade metamorphic gneissic rocks and, to a lesser degree, from intermediate to basic volcanics. Climate varied from humid in the beginning of the sedimentation to sub-humid and arid during the later phases. Sedimentation was also influenced by prominent tectonic activity in the source when coarser clastic sediments were deposited as multistoried conglomerates. Lithofacies characters of the rock succession suggest sedimentation took place in a piedmont fan environment, adjacent to a rising orogeny in an active foreland basin setting. Clay to sand and gravel-sized sediments were laid down by meandering and braided rivers and by debris flows under changing conditions of climate and tectonics.