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Pleistocene Terrace a benchlike structure bordering an undersea feature. These types of terraces formed during the Pleistocene epoch known as the Pleistocene Terraces. The development of Pleistocene multiple alluvial terraces in major deltaic areas has been thoroughly established in several parts of the world. During Pleistocene time, sea level fluctuated in response to quantity of glacial ice on the continent. With each glacial advance there was a corresponding drop of sea level. During each glacial period, major streams discharging into a sea had their gradients abruptly increased. This resulted in rapid headward erosion and scour of stream valleys to a new base level some 100 to 140m lower than at present. With waning of the glaciers sea level came back to a higher stand and the entrenched valleys gradually lost their estuarine character through filling with alluvial sediments.
The interglacial periods were of much greater duration
than the glacial periods. During the long interglacials, sediment-filled
trough roughly paralleling the coastline continued subsiding, and compensatory
inland uplift occurred. The combined effects of seaward subsidence
and landward uplift have caused a warping of the alluvial terraces. These
are called the "Pleistocene Terraces". The north south elongated reddish
brown islands of the Madhupur and Barind areas are considered as the Pleistocene
Terraces in Bangladesh. Topographically these Pleistocene Terraces are
slightly elevated from the adjacent active floodplains.
The sediments of these Terraces are deeply weathered and strongly oxidized.
The initial surface of the Madhupur and Barind areas had been deeply dissected
by Late Pleistocene erosional activities with amplified monsoon
water, leaving these Pleistocene Terraces. Afterward the dissected valleys
were filled up with alluvial sediments, generating a recent floodplain
surface at lower position than the initial Pleistocene Terraces.
[Md Hussain Monsur] |
