DSpace Community: Assistant Professor, Ramhlun North, Aizawl

A Comparative Study of Ichnofossils from Upper and Middle Bhuban Unit of Bhuban Formation (Surma Group), Aizawl, Mizoram to Decipher the Depositional Environment

Fri, 09 Jun 2023 00:00:00 GMT

Title: A Comparative Study of Ichnofossils from Upper and Middle Bhuban Unit of Bhuban Formation (Surma Group), Aizawl, Mizoram to Decipher the Depositional Environment Authors: Lalremruatfela, C Abstract: Objectives: The aim of the present study is to interprete and compare depositional environment of Upper and Middle Bhuban rocks from its trace fossil content. Methods: The trace fossils collected from the Upper and Middle Bhuban Formation are studied group wise up to species level for their systematic paleontological description with the help of type material and available literature in the laboratory. Distribution pattern of trace fossils in the sediments such as orientation, diversity, mode of preservation, relationship with the host sediments are also collected in order to interprete the depositional environment. Findings: Ichnological analysis of Upper Bhuban and Middle Bhuban Unit has been attempted to decipher the palaeoenvironment. The Upper Bhuban Unit are represented by a diverse lithofacies comprises of sandstone, shale and silty-sandstone with the presence of wavy sedimentary structure and parallel lamination. A total of 12 ichnospecies found in Upper Bhuban Unit belongs to Skolithos, Cruziana and mixed Skolithos – Cruziana ichnofacies. Phycosiphon isp. is reported for the first time in North-East India. Middle Bhuban Unit exposed along Zuangtui section comprises ~40m thick sequence of sandstone, siltstone and shale.17 ichnospecies belonging to Skolithos, Cruziana, Teredolites and mixed Skolithos – Cruziana ichnofacies has been identified along this section. Diplopodichnus is reported for the first time from the Surma rocks of Mizoram as well as other Miocene successions in India. Presence of Teredolites ichnofacies indicates marine margin environment, Skolithos ichnofacies indicate sandy shifting substrate and high energy conditions in foreshore zone while Cruziana ichnofacies indicate unconsolidated, poorly sorted soft substrate and low energy condition in the shoreface/offshore zone. Novelty: Present study corroborate that Upper Bhuban rocks were deposited under shallow marine environment while Middle Bhuban rocks were deposited in a deeper, quiet water environment.

Trace fossil assemblage of Oligocene (Barail Group) from Zote Area, Champhai District, Mizoram

Wed, 15 Dec 2021 00:00:00 GMT

Title: Trace fossil assemblage of Oligocene (Barail Group) from Zote Area, Champhai District, Mizoram Authors: Lalremruatfela, C Abstract: The Barail Group (Oligocene) of Zote section, Champhai district, Mizoram has been studied, for the first time, on the basis of trace fossil. The study areas consist of different rocks like Sandstone, siltstone, shale and their admixture in various proportion. The present paper documents 14 ichnofossils such as Arenicolites isp., Gyrolithes lorcaensis, Helminthopsis abeli, H. hieroglyphica, H. tenuis, Laevicyclus mongraensis, Lanicodichna medulata, Palaeophycus sulcatus, P. heberti, Psilonichnus tubiformis, Skolithos linearis, S. verticalis, Teichichnus spiralis and Thalasinoides paradoxicus. The different ichnoassemblages present in Zote area correspond to the Psilonichnus, Skolithos and Cruziana facies. With the analysis of Ichnofacies and lithofacies, studied rock of Barail Group exposed in Zote area is interpreted as to have been deposited under fluctuating energy condition, sandy substrate to sublittoral zone of shallow marine environment.

Preliminary investigation on Cyclone Remal‑in‑ duced landslides in Aizawl, Mizoram, Northeast India, on the 28th of May 2024

Sat, 01 Feb 2025 00:00:00 GMT

Title: Preliminary investigation on Cyclone Remal‑in‑ duced landslides in Aizawl, Mizoram, Northeast India, on the 28th of May 2024 Authors: Lalremruatfela, C Abstract: On the 28th of May 2024, Cyclone Remal brought intense rainfall, triggering catastrophic landslides in Aizawl, the state capital of Mizoram, northeast India. The region is prone to landslides due to its fragile geology and steep terrain, and it has experienced severe damage, including loss of life, destruction of property, and disruptions to essential services. It had a severe impact on society, resulting in 34 fatalities with 33 bodies recovered and affecting 72 families, leading to the evacuation of 54 houses within Aizawl. It also affected the cemeteries of four localities. Among the numerous landslides observed during the field survey, fourteen sites were selected for the study. This study aims to assess the social impacts of these landslides and analyze the failure mechanism involved to guide future disaster preparedness and mitigation strategies. In addition to the information gathered from the government and social media, a field-based method of investigation was used in this study. The methods involve site visits, interviews with local communities, and an analysis of geological, geotechnical, and rainfall data. Geotechnical investigations were conducted at nine sites of the studied areas, all involving rock slides. An investigation was done into the stability of the affected rock slopes, including kinematic analysis, uniaxial compressive strength test (UCS), rock mass rating (RMR), continuous slope mass rating (CoSMR), and slake durability test. The field survey and interviews determined that the landslides caused 25 fatalities, with ten houses and twenty-two vehicles damaged in the Melthum and Hlimen areas. The total property loss was estimated to be Rs.3.4 crores. Landslides displaced more than 300 graves. Most of the probable slope failure observed using kinematic analysis show planar and wedge types of sliding. The studied rock mass of the slope falls under the poor to fair class in RMR ratings and ranges from partially stable to completely unstable in the CoSMR assessment. The rock collected from nine locations of the study landslide area shows medium to high durability and a strength of 14.8 to 22.6 MPa using slake durability and uniaxial compressive strength test (UCS), respectively. The study concludes that while intense rainfall was the primary cause, contributing factors like lack of expert consultation on slope modifications, weak rock mass characteristics, steep slopes, inadequate infrastructure planning, and fragile geological conditions increased the likelihood of slope failure. It seriously impacts society, resulting in many lives and infrastructure loss, economic hardship, and psychological stress, especially among those living in landslide areas. The findings emphasize the necessity of comprehensive land-use planning, improved infrastructure resilience, and coordinated disaster preparedness efforts to mitigate the risk of future landslides.

Provenance Shifts During Neogene Brahmaputra Delta Progradation Tied to Coupled Climate and Tectonic Change in the Eastern Himalaya

Fri, 04 Feb 2022 00:00:00 GMT

Title: Provenance Shifts During Neogene Brahmaputra Delta Progradation Tied to Coupled Climate and Tectonic Change in the Eastern Himalaya Authors: Lalremruatfela, C Abstract: The Bengal Basin preserves the erosional signals of coupled tectonic-climatic change during late Cenozoic development of the Himalayan orogen, yet regional correlation and interpretation of these signals remains incomplete. We present a new geologic map of fluvial-deltaic deposits of the Indo-Burman Ranges (IBR), five detrital zircon fission track analyses, and twelve high-n detrital zircon U-Pb age distributions (dzUPb) from the Barail (late Eocene–early Miocene), Surma (early–late Miocene), and Tipam (late Miocene–Pliocene) Groups of the ancestral Brahmaputra delta. We use dzUPb statistical tests to correlate the IBR units with equivalent age strata throughout the Bengal Basin. An influx of trans-Himalayan sediment and the first appearance of ∼50 Ma grains of the Gangdese batholith in the lower Surma Group (∼18–15 Ma) records the early Miocene arrival of the ancestral Brahmaputra delta to the Bengal Basin. Contributions from Himalayan sources systematically decrease up section through the late Miocene as the contribution of Trans-Himalayan Arc sources increases. The Miocene (∼18–8 Ma) deposition of the Surma Group records upstream expansion of the ancestral Brahmaputra River into southeastern Tibet. Late Miocene (<8 Ma) progradation of the fluvial part of the delta (Tipam Group) routed trans-Himalayan sediment over the shelf edge to the Nicobar Fan. We propose that Miocene progradation of the ancestral Brahmaputra delta reflects increasing rates of erosion and sea level fall during intensification of the South Asian Monsoon after the Miocene Climate Optimum, contemporaneous with a pulse of tectonic uplift of the Himalayan hinterland and Tibet.