The Relic Palaeo-landscapes of the Thames Estuary

Abstract

A geological and heritage assessment of the Outer Thames Estuary as part of an MALSF-MEPF Regional Environmental Characterisation project revealed c.15,000 km2 of palaeo-landscapes hypothesised as dating from 600,000 to 720,000 years ago. These deposits lie immediately offshore from the region that has produced the earliest archaeological evidence for the occupation of the British Isles (c. 600,000 to 700,000 years ago). The exceptional level of preservation of this landscape holds great potential for: understanding our earliest archaeological heritage; understanding the broader geological changes which have occurred during several episodes of sea level change; and providing an enhanced context for a number of aggregate licensing areas and other commercial seabed projects.

To resolve the true importance of this landscape this, one year, follow-on project aimed to improve the chronology of this very important submerged landscape. In order to establish the chronology of this area the project aimed to collect 30 (<6 m) long vibrocores from carefully chosen locations distributed across this landscape. These sites were identified from the interpretation of new and legacy seismic data collected during the project and provided by the aggregate industry (Resource Management Association). The retrieved sediments would be logged and appropriate materials selected for analysis by a combination of dating techniques (palaeo-secular variation (PSV), amino acid racemization (AAR), electron spin resonance (ESR), optically stimulated luminescence (OSL) and radiocarbon dating.

Over the twelve months of the project: fifty-five square kilometres of swath bathymetry data and co-registered backscatter have been acquired; a further thirty square kilometres of swath bathymetry has been provided by the Harwich Harbour Authority; twenty-five line kilometres of boomer data from the main palaeo-river channel in the area has been acquired; and finally several hundred line kilometres of extant boomer data and a total of 133 borehole logs and photo imagery have been provided by the Resource Management Association. These datasets were fully processed and integrated with data acquired during the initial REC project to provide a three phase model of landscape evolution.

The proposed thirty vibrocores were successfully acquired giving a total of 140 m of sedimentary core, an intact archive of which now resides in the BOSCOR facility at the NOCS. These cores have been fully logged, photographed and analysed for grain size. In turn, these lithological data sets have been correlated with the appropriate seismic sections to further enhance a geological model of the area. In addition, we have undertaken extensive sampling and analysis of the cores, for PSV, AAR, ESR, OSL and radiocarbon dating to build up a chronological picture of the development of the submerged landscapes of the Outer Thames Estuary.

The sampled sedimentary sequences are dominated by Late Glacial to mid- Holocene sediments deposited since the Last Glacial Maximum c. 20,000 years ago. However, the project has provided significant evidence to support the original hypothesis of a much longer term evolution of this river system, which can be split into two distinct phases. Firstly, there is a record of river channel activity across the area in the Middle to Late Pleistocene (c. 160,000 – 70,000 years ago) and secondly, from a more restricted number of sites we have identified both morphological and dating evidence to support our original hypothesis of a landscape that potentially dates back to the early Middle Pleistocene (significantly older than 420,000 years ago).

This intensive project has successfully accomplished all that it set out to do in the tight time frame and in addition to the immediate results will provide a platform for more intense study over the next year, where additional dating will be undertaken; more detailed analysis of the environmental information in the cores will be done; and integration with the extensive but sparsely distributed onshore record can be made.

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Identifiers

ORCID for Justin Dix: orcid.org/0000-0003-2905-5403

ORCID for Fraser Sturt: orcid.org/0000-0002-3010-990X

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