16-Jan-2023: Studies indicate tectonically driven changes in the ocean gateways had a dramatic impact on the global overturning circulations

Deep-Water Circulation

• Movement of water in the deep ocean
• Driven by density differences caused by variations in temperature and salinity
• Creates a circulation pattern known as the thermohaline circulation
• Helps distribute heat around the globe
• Controls atmospheric carbon dioxide levels
• Shapes ocean currents and circulation patterns
• Influences marine ecosystem, weather patterns, and coastal regions
• Affects sea level by redistributing heat and thermal expansion

Impact of Tectonic Changes

• Central American Seaway closing created two distinct water bodies
  1. Northern component water in North Atlantic Ocean
  2. Antarctic Bottom Water (AABW) in Southern Ocean
• Large-scale changes in Deep-Water Circulation (DWC) across the world
• Impacted global climate and heat exchanges

Deep-Water Circulations of Indian Ocean

• Indian Ocean does not produce its own deep water. It receives it from other sources such as North Atlantic and Antarctic.
• Northern part of Indian Ocean is good place to study ocean circulation changes as it is located far away from the areas where deep water is formed and ocean routes.
• Studies done using records from iron-manganese crusts and authigenic neodymium isotope composition of sediment cores.

Limitations of records

• Iron-manganese crusts are found at deeper depths and are only bathed by Antarctic Bottom Water (AABW), so they can only provide information about the history of AABW.
• Authigenic neodymium isotope records are only available from the Bay of Bengal region, but they are also not accurate as the Himalayan rivers that flow into the Bay bring in a lot of neodymium particulates which can interfere with the results.
• Despite all this, Scientists have generated an authigenic neodymium isotope record from the Arabian Sea and reconstructed the DWC record of the Indian Ocean for the period from 11.3 million years ago (Miocene era) to 1.98 million years ago (Pleistocene era).

11-Jan-2023: Decoding depositional environment of subsurface sediments in Dibrugarh field of Upper Assam basin: An aided tool for exploration of Hydrocarbons

Using 3D seismic data, scientists have traced how the depositional history of sediments in a basin can be deciphered, which in turn, can pave the way for the exploration of hydrocarbons and provide insights to geo- or seismo-tectonics of the area.

The Upper Assam basin in NE India is surrounded by the Himalayan Mountain belt in the north, Naga Hills in the south, and Mishmi Hills in the east. Most of the sediments belong to the Tertiary period (66 - 2.5 million years ago ) and recent alluvium cover. Seismic data can play an important role in unraveling the depositional environment of these sediments in basin.

Scientists at Wadia Institute of Himalayan Geology (WIHG) explored the textural responses from high-resolution 3D seismic data within the Dibrugarh field in Upper Assam basin to untangle the depositional environment of the sedimentary succession.

The study shows that the textural characteristics of the Oligocene Barail coal-shale unit (deposited between 33.9 to 20.4 million years ago) is associated with the deformed, wavy, chaotic, and heterogeneous texture indicating a deeper basinal condition prevailing during its deposition. Whereas the overlying Miocene Tipam sandstone unit (deposited between 20.4 to 11.6 million years ago) is associated with less chaotic and high homogeneity textures (molassic type), indicating a fluvial environment during its deposition.

This research was carried out by Seismic Interpretation Laboratory (SIL), established at WIHG, Dehradun, and is published in the journal of Geological Society of India. Such study is useful not only for the exploration of hydrocarbons in the thrust-fold belt but can also provide insightful implications to the geo- or seismo-tectonics of an area on a finer scale.

11-Jun-2021: 3-D seismic data can help apprehend precursors of marine geohazards from interactions between seabed & marine sediments

Deep down in the ocean, marine sediments move over the base of the ocean, shaping the probability of geohazards. Scientists have now used 3D seismic data to understand the interaction between bottom surface of marine sediments and the seafloor in the northern Taranaki basin offshore New Zealand. This can help apprehend the precursors of marine geohazards.

Marine geohazards take place when the seafloor is unstable and is not able to withstand the transport processes of marine sediments from landwards deep into the ocean bottom. In such a situation, placement of drilling rigs becomes hazardous due to instability of the seabed.

While understanding marine sediments' interaction during their flow over the seabed is crucial to detect triggers of marine hazards like landslides, associated morphological investigation is a very challenging task, and geophysical/seismic prospecting methods are essential for it.

Scientists from Wadia Institute of Himalayan Geology (WIHG), an autonomous institute under the Department of Science and Technology, Govt. of India, and scientists from Norway and Switzerland used high-resolution 3D seismic data to unravel geomorphology of recurrent cases of movement of soil, sand, regolith, and rock downslope like a solid in Taranaki basin off New Zealand.  This is technically called mass wasting of sediments.  The study led by Prof. Kalachand Sain was published in the journal ‘Basin Research’.

With the help of 3D seismic data, the study offers a unique approach to comprehend the recurrent mass wasting processes and also understand how the seabed interacts with the bottom surface of marine sediments. The geological period between 23.03 and 2.5 Million years ago called Neogene succession preserves vertical stacks of mass transport deposits (MTDs) from the Miocene to Pliocene --- different epochs that fall within the Neogene geological period. The Miocene (23.03 to 5.33 Mn years ago) is the first geological epoch of the Neogene period and towards the end of this epoch starts the Pliocene epoch (5.33 to 2.5 Mn years ago. The study shows that the mass transport deposits are characterized into blocky-MTDs consisting of moderate to high amplitude, variably deformed rafted blocks, and chaotic masses composed of slides and debris flow deposits indicating a disturbed marine environment.

The study will help understand different flow mechanisms associated with sediment movement over the seafloor. It will also shed light on several flow indicators that define the dynamics of the sediment mass movement or the dominant transport directions and mechanism of the mass flow. Understanding of these phenomena can help apprehend precursors of marine geohazards or the nature and physiography of the seafloor over which sediments can move.  According to WIHG team, similar geomorphological exercises can be extended to Indian and global marine sedimentary basins.