Search This Blog

Tuesday, 5 December 2017

Holocene landscape dynamics in the Ghaggar-Hakra palaeochannel region at the northern edge of the Thar Desert, northwest India

Here is another important research on Sarasvati (Ghaggar-Hakra) . It seems to suggest that flow continued in post urban phases after major dry ups   , which is quite likely  as per the accounts of Indian tradition . Harsha  in 7th Century said to have  performed for example funeral rites of his father near the Sarasvati . Even today it exists , especially in monsoon season , Ghaggar in upper course (also in other periods) , using google maps you can see it stops only near Suratgarh.
Also the Sarsuti river, which is identified as the original upper course of Sarasvati, is still an ephemeral river.

Holocene landscape dynamics in the Ghaggar-Hakra palaeochannel region at the northern edge of the Thar Desert, northwest India
Julie A.Durcan a David S.G.Thomas a Sanjeev Gupta b Vikas Pawar c Ravindra N.Singh d Cameron A.Petrie e
Precession-forced change in insolation has driven de-intensification of the Asian Monsoon systems during the Holocene. Set against this backdrop of a weakening monsoon, Indus Civilisation populations occupied a number of urban settlements on the Ghaggar-Hakra plains during the mid-Holocene from 4.5 ka until they were abandoned by around 3.9 ka. Regional climatic variability has long been cited as a potential factor in the transformation of Indus society, however there remain substantial gaps in the chronological framework for regional climatic and environmental change at the northern margin of the Thar Desert. This makes establishing a link between climate, environment and society challenging. This paper presents 24 optically stimulated luminescence ages from a mixture of 11 fluvial and aeolian sedimentological sites on the Ghaggar-Hakra floodplain/interfluve, an area which was apparently densely populated during the Indus urban phase and subsequently. These ages identify fluvial deposition which mostly pre-dates 5 ka, although fluvial deposits are detected in the Ghaggar palaeochannel at 3.8 ka and 3.0 ka, post-dating the decline of urbanism. Aeolian accumulation phases occur around 9 ka, 6.5 ka, 2.8 ka and 1.7 ka. There is no clear link to a 4.2 ka abrupt climate event, nor is there a simple switch between dominant fluvial deposition and aeolian accumulation, and instead the OSL ages reported present a view of a highly dynamic geomorphic system during the Holocene. The decline of Indus urbanism was not spatially or temporally instantaneous, and this paper suggests that the same can be said for the geomorphic response of the northern Thar to regional climate change.
Indus Civilisation Fluvial Aeolian OSL dating Palaeo environment Drylands Northern Thar Desert

From the paper :

 6. Conclusion 
This study presents OSL ages for Holocene fluvial and aeolian activity in the Ghaggar-Hakra inter fluve on the northern margin of the Thar Desert. This chronology shows fluvial deposition in the currently visible palaeochannel during the early Holocene from 8.5ka until ~3 ka. More intensive fluvial processes are inferred prior to 5 ka, when thicker fluvial units are deposited. After 3 ka, sediments in the Ghaggar-Hakra channel adjacent to the Indus Civilisation urban site of Kalibangan fine significantly, and slightly further to the west, sediment dated to 3 ka are capped by a silty unit of 0.75 m.This may suggest a weakening of fluvial activity post 3 ka and possibly ephemeral overbank flooding in this area at least. These findings complement other studies in the Ghaggar-Hakra system(e.g. Saini et al., 2009; Saini and Mujtaba, 2010) and are consistentwith regional palaeo hydrological records (e.g. Dixit et al., 2014a,2014b). Like the fluvial sedimentation, aeolian accumulation is recorded across the Holocene, with a period of enhanced accumulation at around 9 ka identified, as well as two ranges of ages at around ~7.1-5.7 ka and later between ~2-1.7 ka. These ages are consistent with regional records of aeolian accumulation in Ghaggar-Hakra region (e.g. Shitaoka et al., 2012) and more broad lyin the Thar Desert (e.g. Kar et al., 1998; Thomas et al., 1999; Singhviand Kar, 2004). In this study we demonstrate phases of fluvial ac-tivity and aeolian accumulation coincide, which should be considered as normal behaviour in a dry land context (Thomas,2013).This evidence adds to the emerging picture of the Holocene Ghaggar-Hakra as a low energy fluvial system broadly driven by regional changes in the monsoon, however, this response appearsto be neither simple nor linear. Thicker units of fluvial sediment are deposited in the early Holocene, although in the sediments sampled, there is no statistically significant change in particle size which can be used to infer a weakening of fluvial transport energies with time. Thinner fluvial units accumulated during the mid-Holocene and the presence of fine sediments, predominantly silts,in the channel close to the Indus Civilisation urban site Kalibangan after 3 ka may represent a phase of weakened fluvial activity.Coeval fluvial and aeolian accumulation provides a view of oscil-lating phases of relative humidity and aridity throughout the Holocene, resulting in the accumulation of dune sediments on the Ghaggar-Hakra inter fluve. Further research considering the geomorphic and environmental response to climatic fluctuation across the full extent of the Ghaggar-Hakra interfluve, which will further improve our understanding of changing environmental conditions under fluctuating monsoon regimes, as well as in form the response of past civilisations to climatic and environmental variability. 

Yog (Science Direct) .

See also :
Counter-intuitive influence of Himalayan river morphodynamics on Indus Civilisation urban settlements

The Chronology of Puranic Kings and Rigvedic Rishis in Comparison with the Phases of the Sindhu–Sarasvati Civilization

No comments: