OR/18/016 Conclusions

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Palamakumbura, R. 2018. A new palaeogeographic model for the post-glacial marine and estuarine sediments of the Firth of the Forth, Scotland. Nottingham, UK, British geological Survey. (OR/18/016).

This report aims to provide an overview of the post-glacial evolution of the Firth of the Forth since the Last Glacial Maximum to Recent, and assess this understanding using geotechnical borehole records. The borehole records enable a new insight into the composition and thickness of the superficial sediments associated infilling the Firth of the Forth.

The post-LGM sediments of the Firth of the Forth reflect a deglaciated estuarine environment that was strongly influenced by allocyclic controls, such as isostatic rebound and eustatic sea-level change. The impact of these larger scale controls is reflected in the superficial sedimentary infill of the estuary. The post-LGM deglaciation resulted in a prolonged marine incursion, represented by relatively thin marine deposits preserved on an uplifted shoreline uplifted to 30–40 m A.O.D. The falling sea-level resulted in the partial infilling of the Forth Fjord region, with sub-tidal sediments. These sediments were sub-aerially exposed, represented by discontinuous peat deposit in the upper parts of the estuary. Following this was the Holocene marine transgression, which resulted in marine sediments deposited on the flanks of the estuary and further sub-tidal to intertidal sediments being deposited across the Firth of the Forth.

This work presents the first overview of the post-LGM depositional history of the Firth of the Forth, which is combined with new interpretations from geotechnical borehole records. The data provided in geotechnical borehole records provides is an important stepping stones toward further work, such more detailed sedimentary interpretations from field work and geotechnical classifications of the various superficial sediments observed in the Firth of the Forth.