The Bengal Fan
The Bengal fan, also known as the Ganges fan, is the world's largest undersea fan. It is situated near the countries of India and Bangladesh. This fan formed as a result of Himalayan uplift and Tibetan plateau erosion processes that occurred along collision plates in India and Bangladesh. Many geologists consider the Bengal fan to be one of the most amazing land shapes ever created.
Formation of the Bengal Fan
The Bengal fan structure was formed by the collision of the Eurasian and Indian plates. This collision of the two plates led to an uplift as well as an erosion process of the Himalayas along the Tibetan plateau. The sediments found in these regions are supplied by the Brahmaputra River as well as the Ganges. These two rivers contribute almost the significant amount of the deposits along the fan. These two streams result in sedimentation in the ongoing process of supplying lower Meghan delta located in Bangladesh and estuary referred to as the Hoolgly which, unlike the former, is found in India specifically in West Bengal.
Sediment Supply and Deposition
Other larger, minor rivers and streams also play a great role in the provision of sediments. Due to turbidity currents, these sediments are slowly yet consistently carried down along a series of submarine canyons that within a period eventually depositing the sediments in the Bay of Bengal at the latitude of approximately thirty degrees where the whole process began. Some of these deposits are dated way back with some even dated to the Early Miocene age (Frisch, Wolfgang, Meschede, Ronald and Blakey, 154). These sediments furthermore, have characteristics that relate them to the Himalayan origin because of their mineral composition plus their geochemical composition as well. This Himalayan origin sediments date back to approximately 20 million years back. The Bengal fan wholly takes a cover of the floor Bay of Bengal.
Size of the Bengal Fan
Also known as the Ganges fan is the largest Submarine fan on the planet. The Bengal fan is approximated to be roughly three thousand kilometers long, a thousand kilometers wide, with a thickness ranging up to sixteen kilometers wide.
Location of the Bengal Fan
The Bengal fan is bordered on the western side by the continental slope of Eastern India and the North by Bangladesh and specifically by the continental slope while to the East it is bordered by the northern side of Sunda trench which is away from the Islands Andaman and Myanmar. These two islands are mostly associated with the accretionary wedge which experiences a lot of subduction from the Indo-Australian plate which is beneath the Sunda plate and progresses along the west part of Ninety East Ridge (Frisch, Wolfgang, Meschede, Ronald and Blakey, 335). This fan is also close to the Nicobar fan which is east of Ninety East Bridge. A deep-sea canyon referred to as "Swatch of no Ground" is located in the South part of Sundarbans National Park close to the Island of Dubler Char.
Sediment Stratigraphy of the Bengal Fan
Currently, the Bengal Fan (Ganges fan) is mainly fed by extensive volumes of sediment loads of the Ganges and Brahmaputra rivers, which drain from the Himalayas at its southern and northern slopes, respectively. Furthermore, delivering their load to the edge of the delta in the Bengal Basin, to the Bengal Shelf plus the deep-sea fan. Thus, as a result, the Bengal Fan is a suitable recorder to help in the study of interactions among the growth and expansion of the Himalaya and Tibet, the extensive development of the Asian monsoon, and activities affecting the carbon cycle and global climate. Since sedimentation in the Bengal Fan responds to them in total, climate and tectonic processes, its terrigenous sediment records the later stages of evolution of the Himalaya and regional climate (Niklas, 432). This growth process is also expressed in the stratigraphy of the fan regarding unconformities and primary critical horizons, average processes of sedimentation rates as a function of given the distance from the basement ridges at approximately 85°E to an estimated 90°E and the presence or rather the absence of channel-levee systems.
IODP Expedition and Drilling
The histories behind the Himalaya/Tibetan system and the Asian monsoon require consistent sampling with different periods of time again with various high-quality levels of precision. Thus, IODP Expedition, which was drilled in the months of February to March 2015, a seven-site, 320 km-long transect across the Bengal Fan measured at 8°N. This particular strategy has been settled on because sediment transport most certainly took place by turbidity currents following transport routes leading to deposition on and between levees. As a consequence, depocenters were laterally drifting over hundreds of kilometers on millennial time spans. Three deep penetration and an additional four shallow holes are continuously drilled to enable the archive of the spatial and temporal overview of this particular primarily turbidity depositional system. By that Expedition, the initial record of early fan deposition has been extended back by 10 million years into the Late Oligocene. As a result of this drilling, various stratigraphic marker horizons across the transect could be easily identified, cored, and furthermore, even dated. In combination with the existing seismic data collected during the RV Sonne cruises SO125 and SO188, a detailed reconstruction of reoccupation, overall uniform growth of the fan, channel-levee growing, migration, and abandonment can be carried out.
Impact on the Surrounding Environment
The Bengal Fan greatly affects the regions surrounding the area in one way or another. The impacts on the surrounding environment may be negative or positive, basing on the ways they are affected. The Bengal Basin, located in the northeastern part of the Indian subcontinent, in the middle of the Indian Shield and Ranges located in Indo-Burman, comprises three provinces that are geo-tectonic: that is the Stable Shelf, the Central Deep Basin (which extends from the Sylhet Trough found in the northeast towards Hatia Trough positioned in the south), and the Chittagong-Tripura Fold Belt. The location of the basin right at the juncture of these three interacting plates, i.e., viz, the Tibetan (Eurasian) Plates, Indian and Burma, and, the basin-fill history of these given geotectonic provinces alternated considerably. Precambrian metasediments and Permian-Carboniferous rocks have mainly been experienced in drill holes in the region of a stable shelf (Schwenk and Tilmann, 123).
Basin Formation and Sedimentation
After penne planation (specifically Precambrian) of the Indian Shield, sedimentation in the Bengal Basin occurred in selected graven-controlled basins around the basement. With the breakup of Gondwanaland in the Jurassic and Cretaceous, and northward movement of the Indian Plate, the basin started down warping in the Early Cretaceous and sedimentation began along the stable shelf and in the deep basin; hence since then, sedimentation has been a continuous process for most of the region occupied by the basin. Subsidence taking place in the basin is greatly attributed to differential adjustments in the crust. Collision experienced in these parts, within the various elements of South Asia and uplift movement of the eastern Himalayas as well as the Indo-Burman Ranges (Niklas, 194). Continuous movements along several faults that are perfectly and well established were initiated due to the breakup of Gondwanaland and during the process of down warping in the Cretaceous. By Eocene, As a result of significant marine transgression, the stable shelf experienced a carbonate regime; while on the contrary, the deep basined area was by a great margin dominated by deep volumes of water sedimentation. A huge change in the pattern of deposition over the Bengal Basin occurred during the Middle Eocene to Early Miocene influenced greatly by a collision of Tibetan Blocks and India with Burma (Thomas, 2002). The influx of elastic sediment that results into the basin from the Himalayas to the north part and the Indo-Burman Ranges located to the east rapidly rose at such a time, and this was closely followed by an increase in the volume of subsidence close by the basin.
Changes in Depositional Setting
At this juncture, deep-marine sedimentation is in the deep part of the basin, while slightly deep to shallow marine conditions continued to prevail in the east of the pool. By Middle Miocene, with continuous collision events between the plates and the uplift in the Himalayas and Indo-Burman Ranges, a massive influx of elastic sediments came into the basin traveling from the northeast and east (Schwenk and Tilmann, 142). Throughout the Miocene, the depositional settings that are prevalent all along continued to vary from the deep marine in the basin to the shallow and coastal marine in most of the marginal parts of the basin. From Pliocene onwards, large volumes of sediment were continuously filling the Bengal Basin from the west and northwest; and significant delta-building processes were still developing the current-day delta morphology. Since the Cretaceous, the architecture of the Bengal Basin has been deforming due to the collision pattern and movements of some major plates in the surrounding region. In contrast, though, three easily notable changes in the configuration of the basin can be recognized as occurring during Early Eocene, Middle Miocene, and Plio-Pleistocene time-span, during which time both the paleogeographic settings and source areas were different compared to their more initial states. The current time basin configuration with the Ganges - Brahmaputra delta standard system on the North and Bengal Deep Sea Fan to the South was developed during the later part of Pliocene and Pleistocene, and delta progradation since that time has been strongly influenced in both ways by orogeny in the Eastern Himalayas. Pleistocene glacial activities in the Northern part are accompanied by changes in the sea level in the Bay of Bengal.
Conclusion
It is evident that the world is filled with many geological features, which are very important study sites. Additionally, an in-depth analysis of the formation and positioning of the feature, many hypotheses can be evolved to describe its current situation. Overall, the Bengal Fan plays a major role in the study of Geology.
Works cited
Frisch, Wolfgang, Martin Meschede, and Ronald C. Blakey. Plate Tectonics: Continental Drift and Mountain Building. Berlin, Heidelberg: Springer Berlin Heidelberg, 2011. Internet resource.
Mutti, Emiliano, Daniel Bernoulli, Franco R. I. C. C. I. Lucchi, and Roberto Tinterri. "Turbidities and Turbidity Currents from Alpine ‘flysch’ to the Exploration of Continental Margins." Sedimentology. 56.1 (2009): 267-318. Print.
Pisias, Niklas G. Conference on Multiple Platform Exploration of the Ocean: May 1999, Vancouver, British Columbia. Washington, DC: Joint Oceanographic Institutions, 1999. Print.
Schwenk, Tilmann. The Bengal Fan: Architecture, Morphology and Depositional Processes at Different Scales Revealed from High-Resolution Seismic and Hydro acoustic Data. Bremen: Stats- und Universitätsbibliothek [Host, 2003. Internet resource.
Thomas, Stefan The Tectonic and Climatic Evolution of the Arabian Sea Region. London: Geological Society, 2002. Print.
