Mica in the Indus river : an indicator of changes in the depositional environment

الملخص EN

The abundance of mica has been used to determine the energy levels of the depositional environments of the Indus River/ Estuary in terms of the interactions between the river currents and tidal, wind and wave induced currents.

Three distinct zones have been identified on the basis of sediment texture and mica content.

Based on textural class, the Indus River/Estuary along the 40 km stretch upstream is subdivided into three distinct classes: sandy silt, silty clay and sand silt clay.

The textural data demonstrate the hydraulic association of mica with finer sediments.

The excess presence of mica in areas of fine sediment and its relative abundance in coarser sediments have been used to identify the boundaries between the three zones which are classified into environments of high-medium-low energy.

Marine processes in the lower reaches (mouth) of the Indus River are responsible for winnowing of finer sediments, leaving coarser materials as lag deposits.

However, the presence of coarser sediments in the upper limits shows the incompetency of the river flow to transport material and the waning effects of wave and wind generated currents on the depositional regime.

The presence of abundant mica within mud is attributed to flocculation induced by the mixing of fresh and saline waters and the limit of tidal intrusion.

Mica dominates in the mud and mimics the depositional characteristics of clay.

The distribution of mica and sediment texture suggest that sedimentation is controlled primarily by different energy levels, flocculation, and by provenance (metamorphic rocks in the Himalayan range).