Deltaic land subsidence and sea level fluctuations along the east coast of India since 8 ka: A palynological study

Abstract

The consequences of climate change and land subsidence are often related to sea level rise/fall. Mangrove extinction and migration were assessed through palynological studies in two sedimentary cores in order to address climate, Relative Sea level (RSL) and its relation to geomorphology since 8420 cal. yr BP from Kanuru (500 cm deep) and since 5850 cal. yr BP from Machilipatnam (118 cm deep), Krishna delta, India. Four units/nine phases of sediment depositional environment were identified on the basis of marine/terrestrial palynomorphs. In Unit 1, the marine palynomorphs indicate palaeoshoreline in Kanuru from 8420 to 8300 cal. yr BP which is now ~4–5 km from the present-day shoreline, but after a short span a retreat in sea level took place between 8300 and 7040 cal. yr BP. About three to four short-term intermittent rise/fall in RSL were recorded in Unit 2 between 7040 and 3980 cal. yr BP in Kanuru and between 5225 and 3240 cal. yr BP in Machilipatnam. During this period, the diversity of mangroves was more in Machilipatnam and only salt-tolerant mangroves were present in Kanuru. Unit 3 is characterized by non-estuarine sediment deposition since 3920–240 cal. yr BP in Kanuru and since 3240–950 cal. yr BP in Machilipatnam. Unit 4 shows a rise in RSL in both the studied sites which began much earlier in Machilipatnam than in Kanuru. Loss of mangrove diversity and dominance of salt-tolerant mangroves were recorded in Unit 4. Results indicate climate-induced RSL fluctuations highlighting the cooling event of 8.2 ka BP from Kanuru site and duration of intermittent rise/fall of RSL during middle Holocene transgression. The rate of sea level rise during the period was not continuous but interrupted by three to four retreats. At present, the evidence of these are at different depths in both the sites and in other contemporary sites along the east coast of India, suggesting neo-tectonics in the vertical stack of Holocene sediment. The geomorphology of the studied sector is tectonically controlled which may increase deltaic instability in future.

A 2600-yr multiproxy record for climate and vegetation reconstruction along the Mahanadi River delta, east coast of India

“…Presence of high percentage of back mangroves such as Excoecaria agallocha , Avicennia sp. (salt tolerant mangrove) along with the foraminiferal lining indicates marine influence at the site (Farooqui and Nautiyal, 2016). Humidity and heavy precipitation can be inferred from the occurrence of fungal spores along with pollen of terrestrial vegetation (Medeanic et al, 2008).…”

“…Additionally, as the eastern margin of Indian subcontinent is tectonically stable, thus the change in its landscape and sediment delivered to the coastal basins located at this margin are the effect of long-term climatic fluctuations (Dash et al, 2020; Vaidyanadhan and Ghosh, 1993). Many multi-proxy studies have been carried out to unravel these long-term climatic fluctuations in the coastal regions of India (Farooqui and Nautiyal, 2016; Rao et al, 2015, 2020; Shah et al, 2022; Srivastava and Farooqui, 2013). Since the Neolithic period (2300–2100 BCE), the eastern part of Odisha has given shelter to early humans (Pradhan, 2005; Tripati and Vora, 2005).…”

Catastrophism and Uniformitarianism in Decision Making of Meghalayan Age in East India

“…Kumar, et al Later transgressive events recoded between 2970±100YBP and c. 3400 YBP along the eastern coast and northern South China Sea [71]. The coastal transformations were recorded due to major transgressive event, Farooqui et al, [72] have reported sea-level regression following the major transgressive event at 3150 BCE to 2370 BCE which transformed the geomorphology of the Chilika, Kolleru and even Pulicat Lagoon in AP (Andhra Pradesh) [73,74]. A drop in regional sea level points during the Little Ice Age (LIA) (300-250YBP) (Fig 7).…”

“…Palynological studies reveal that salt tolerant Mangroves resistant to saline atmosphere were extending from Kanuru, and Machlipatnam coast until Myanmar coast including Chilika coast during mid Holocene [54], Farooqui et al, [72].…”

Coastal vegetation dynamics in response to climatic and relative sea level changes in Mahanadi River delta, NE coast of India

“…temperature, precipitation, salinity), research on both local and regional scales is necessary to determine the potential impact of climate change on mangroves (Spalding et al 2010). Many studies have been conducted to understand the response of mangroves to Holocene climate and sea level changes worldwide (Ellison 1989; Parkinson et al 1994; Behling et al 2001; Li et al 2012; Limaye et al 2014; Farooqui et al 2016; Hait and Behling 2019; Rao et al 2020).…”