In search of the ancient landscapes of Mahasthangarh (Bangladesh)

A blogpost by Yohan Chabot

Since February 2022, the Mahasthangarh mission in Bangladesh, directed by V. Lefèvre (musée Guimet) and C. Lefrancq (postdoc archaeologist, CEIAS) for the French side and Naheed Sultana for the Bangladeshi side, and funded by the Ministry of European and External Affairs (MEAE) and the DHARMA project (ERC n°809994), includes a paleoenvironmental component led by Yohan Chabot (postdoc geomorphologist, EFEO).

Context

In Bangladesh, there are few research projects on the paleoenvironment involving archaeologists and geomorphologists. For Mahasthangarh, the mission did not explore this matter much since the first work conducted by Christine Jacqueminet and Jean-Paul Bravard in the early 2000’S. This new project was motivated by a specific environment context in Mahasthangarh. Indeed, the site is located on the east margin of the Barind Tract, an elevated area, along the Karatoya River and its alluvial plain. Nowadays, the Karatoya is a small river but in the old time it was an important and active river as evidenced by its ancient meanders visible in the present landscape. Despite the elevated position and fortification of Mahasthangarh, the active river dynamic seems to have been damaged the eastern part of the site probably due to floods (Salles, 1995).


Field prospection in Mahasthangarh. View to the east from the northern rampart @YohanChabot_MAFBM.


Main issues

This environmental context, still poorly understood, raises questions about the paleoenvironmental changes implied by the mobility of the Karatoya and its interaction with the human occupation of Mahasthangarh:

(1) How has the Karatoya changed over the time and what impact has active fluvial dynamic had on the occupation of the site and surroundings?

(2) What were the paleoenvironmental changes at the Mahasthangarh and the dynamics of these changes? 

The main objective is to understand the past landscape dynamics of Mahasthangarh at the interface of human societies and natural forcings in order to reconstruct the paleogeography and environmental changes that affected it before, during and after its occupation.

The interest of this geomorphological research in the framework of the Mahasthangarh excavations is threefold:

(1) to define the environment in which the site was established, developed and abandoned;

(2) to understand the type of occupation of the site and its relation with its environment;

(3) to assess whether there is any past destruction of the site related to floodings.


Fieldwork

For the first campaign (February 11 to 27 2022), a survey was carried out in the first three days in order to take knowledge of the current environment of the site and its surroundings and to identify study sites. Five study areas in and around Mahasthangarh were studied, in relation to the issues and questions of the study and also, according to the limitations related to the field (accessibility, flooding, housing…). I conducted with my team (Hafizur Rahman, Afzal Hossain and some villagers) a geomorphological survey in order to define the nature of the deposits, their thickness and their chronology. The aim is to understand the hydro-sedimentary dynamics of the Karatoya. We performed 5 topographic cross sections along which we have conducted 15 boreholes and 6 stratigraphic sections for the sedimentary acquisition. Each sedimentary record extracted by boreholes or observed by stratigraphic sections was described (grain size, color, organic remains, etc.). Also, a sampling was carried out where relevant. In total, 261 samples were taken. This approach will support paleographic (evolution of the Karatoya, succession of paleomeanders and reconstruction of the landscapes); environmental (dynamics of aquatic and wetland environments, fluctuations in the level of water tables – seasonal, decadal, secular) and chronological interpretations.


Sediment core (borehole S14), Mahasthangarh @YohanChabot_MAFBM.

 


Stratigraphic survey and sampling (outcrop CP3), along the Karatoya river @YohanChabot_MAFBM.


Research prospects

At the end of the mission, the most objectives were achieved and we got numerous results. The sediment samples are currently analysed in sedimentology at the Laboratory of Physical Geography, in Paris and the data processing is now underway. We hope to return to the field in the autumn to continue the work we have started.


Stratigraphic survey and sampling (outcrop CP5) along the Karatoya river @YohanChabot_MAFBM.

 


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