Could you please tell me about the evolution of Indus Shelf with
reference to its tectonic settings, and
what kind of changes are still operating
Dear Faisal Memon, Good morning and Fraternal Greetings!
The details of Indus Shelf with reference to its tectonic setting is still unexplored, but the details of its origin and present day activities are under discussion and debate. The Indus used to be one of the most important sediment-producing rivers in the world that built an extensive alluvial plain and delta as well as the world’s second largest submarine fan. The Indus River feeds the world’s largest irrigation system, which has been developed over the last 150 years. Several large dams and barrages were built on the Indus River leading to dramatic reductions in water and sediment discharge over the last few years.
The shelf of the Indus delta remains largely unstudied. Its most prominent feature is the Indus Canyon or ‘‘The Swatch’’, a relic feature of the pre Holocene relief which dissects the shelf to within 20 m water depth at 3.5 km offshore the Khobar mouth of the Indus delta.
Detailed 19th Century bathymetric surveys show that the Indus shelf exhibits a compound clinoform morphology with separate nearshore delta front and mid-shelf clinoforms. The mid-shelf clinoform has developed asymmetrically about the Indus Canyon, which dissects the shelf to within 20 m water depth and 3.5 km of the coast. The clinoform front (foreset), located between 30 and 90 m water depth is much more advanced toward the shelf edge on the eastern vs. the western side of the canyon. A distinct lobe of the mid-shelf clinoform occurs in front of the Kutch coast and mouth of the Kutch Gulf. The mid-shelf clinoform has probably developed as a prodelta clinoform of the Holocene Indus delta. This is suggested by recent active progradation of the feature west of the Indus Canyon, in a sector re-surveyed in the 1950s. The advanced position of the clinoform east of the canyon might reflect either a prolonged sediment delivery from the Indus river in that region compared to the shelf west of the canyon or the presence of a relict pre-Holocene mid-shelf delta on the shelf east of the canyon. An analytical model based on wave climate and river discharge characteristics predicts a midshelf clinoform for the Indus shelf instead of the compound clinoform identified in the bathymetric data. One potential explanation for this discrepancy is the relatively coarse sediment discharged by the Indus that promotes rapid settling of a significant part of sediment load near the coast. Assuming that the sediment load of Indus River has been dominated by non-cohesive sediments that are not suitable to generate hyperpycnal flows, the mechanisms involved in the prodelta clinoform development remain to be identified.