Extended grab sampling

This extended grab sampling survey was undertaken to add to results already obtained in the grab sampling survey conducted in 2003-2004 in order to understand the relationship between struck flint and palaeogeographic features identified during the Round One project.

The fieldwork took place during May and June 2005. 400 ten litre benthic grab samples were collected from a survey area consisting of four 1km² blocks. 100 samples were taken at regular intervals of 100m. The samples were collected using a Hamon grab.

Proposed grab sampling locations illustrated on bathymetric dataThe samples were sieved on board through a 1mm mesh sieve and then transferred to a sample container. The samples were then transferred to the environmental department at Wessex Archaeology where they were wet sieved through 10mm, 4mm and 1mm sieves. The residues were scanned for archaeological material.

Results

668 flints were recovered. The assemblage is dominated by small chips and flakes with no definitely recognisable tool types. The flints were enigmatic due to the ambiguous nature of their means of production. In no instance was it absolutely certain that any piece was of human or anthropogenic manufacture.

Many of the samples contained large amounts of peat. In one sample a lump of mature oak charcoal was recovered. It is likely that this material is the product of deliberate burning or from fuel within a hearth. The peat itself contained large amounts of Phragmites sp. (common reed) stems. The deposit and the charcoal are currently being radiocarbon dated.

Other environmental remains were encountered including bone (amphibian, bird) molluscs (terrestrial, freshwater and marine taxa) moss, twigs all pointing towards wetland and terrestrial environments in the area.

Modern finds including slag and clinker were common within the samples. These are most likely the result of modern and industrial shipping activities.

Processing the grab samples

 

 

 

 

 

 

 

Conclusions

The finds from the grab sampling have provided possible evidence of human occupation of the palaeo-Arun area. The charcoal recovered from a lump of peat is unlikely to have been produced by natural causes. Flints recovered from both this survey and the earlier Round One grab sampling surveys are also arguably of anthropogenic origin, although in many cases it is difficult to distinguish from flint produced by mechanical or natural processes.

These results will enable industry to adopt systematic archaeological procedures for the treatment of benthic grab samples obtained during the environmental impact assessment stage of marine aggregate licence applications.

East English Channel

MV Ocean SeekerThe Eastern English Channel was chosen as a study area due to its abundance of marine aggregates and lack of research with regard to prehistoric seabed deposits. A palaeovalley feature was chosen as a study area, situated between the licensed aggregate extraction areas 464 West and 464 East, both of which are operated by United Marine Aggregates. Palaeovalleys relating to offshore continuations of French and English rivers during periods of lowered sea level are known from the English Channel. Some of these palaeogeographic features are up to 50m in depth and several kilometres wide. Sediments within these channels, particularly those at depth can often be overlooked as they do not contain deposits economically exploited by the aggregate extraction industry. The survey was conducted aboard the MV Ocean Seeker between the 14th and 24th September 2005. The survey area was targeted for survey using geophysical (seismic and sidescan survey) and geotechnical (vibrocore and grab samples) methods.

Geophysical survey

Sidescan survey

The review of the sidescan sonar data showed a seabed comprising sandy gravel with trawl scars caused by fishing activity. During the data interpretation, the presence of irregular objects with shadows that could possibly be anthropogenic debris was noted.

Seismic survey

Palaeochannel seen on sub-bottom profiler dataThe seismic data was acquired using a boomer sub-bottom profiler. A palaeovalley feature was identified in the seismic data. It extended throughout the study area, a distance of approximately four kilometres. The valley ranged in width from between 1.5 and 2 kilometres, with a depth of 40 – 45 metres. Evidence of several phases of cut and fill events were identified in the palaeovalley feature, some of which could not be traced in all the seismic profiles. This suggests that certain phases in the development of the valley are not fully represented. It is therefore difficult to postulate on the continuous development of the valley. An example of the boomer seismic data and a modelled surface are shown.

 

Geotechnical survey

Vibrocore survey

16 vibrocores were collected from eight sites identified from the geophysical data. Two cores were collected at each site. One core was taken for Optically Stimulated Luminescence (OSL) dating which was kept in a blackened sleeve. The other core was taken for geoarchaeological description and for retrieval of environmental and radiocarbon dating samples.

Grab sampling survey

Grab SamplingThe grab samples were acquired using a Hamon grab. Each sample was approximately 8-10 litres in volume and retrieved from the upper 0.15 metres of the seabed. The samples were transferred to the environmental department at Wessex Archaeology and wet sieved through a nest of sieves in accordance with standard artefactual recovery procedures. None of the finds recovered were of prehistoric date.

Geoarchaeological analysis

The geoarchaeological analysis showed sediments relating to fluvial estuarine and marine processes. One important alluvial sequence featuring silts and clayey silts with interbedded fine sands was targeted for environmental sampling. One of the vibrocores featured gravels which had been oxidised. This is clear evidence that this deposit had been exposed to the air at some stage. This deposit was stratigraphically the oldest sediment (above bedrock) identified in this area and it is possible that it has been exposed on more than one occasion.The types of sediment units identified in the lower stratigraphy reflect high and low energy environments possibly relating to fluvial/estuarine sedimentation. Sub-units identified within these major sedimentary units revealed repeated layers of fine sands and silty clays which could indicate repeated, possibly seasonal, flooding. A brown sandy gravel with occasional mussel shell occurring in one of the vibrocores was considered to be indicative of a high energy environment with a possible marine contact inferred from the molluscs. It is possible that this may reflect rising sea levels represented by a transition between fluvial/estuarine conditions and marine conditions.

Vibrocore VC-3Vibrocore VC-7

 

 

 

 

 

 

Environmental analysis

The pollen spectrum from the silts and clays in the analysed sample is dominated by pine and birch pollen. Although both of these species are often over represented in pollen spectra, the substantial numbers recorded here do suggest local growth and dominance on drier ground. The absence of any other tree and shrub reflects and environment likely to have existed either in the very early Holocene, Flandrian Chronozone I (c. 10,000 BP) or possibly the Windermere/Allerød late glacial interstadial (c. 13,500 BP). Foraminifera and ostracods were retrieved proving sub-littoral, estuarine and freshwater environments during the early Holocene period. The general trend shows estuarine and freshwater environments replaced by sub-littoral and shallow marine deposits. The most interesting ostracod assemblage shows silts and clays which appear to have been deposited in slow moving and still freshwater environments as demonstrated by the dominance of the taxa Ilyocypris monstrifica. This is the same deposit identified from the pollen data as being a freshwater fen possibly of very early Holocene or Windemere/Allerod date.

Dating

No stasis horizons (soils) were encountered in the vibrocores suitable for radiocarbon dating. Shells were abundant in some of the deposits. Due to the well preserved nature and probable rapid deposition of some of these deposits molluscan material from suitable deposits were chosen for radiocarbon dating. The latest episode of deposition is sub-littoral gravels and sands which have been dated to 8442±35 BP. This is a clear indication that the study area was being submerged at this time. Beneath this deposit samples from series of channel features thought to form part of a braided channel system are dated to 9811±35BP and 9663±35 BP. Five samples have been chosen for OSL dating and these have been sent to OSL Laboratory, Royal Holloway where they are currently being processed.

Conclusions

The area revealed a complex sedimentary sequence relating to fluvial activity during the Pleistocene period. Terrestrial, fluvial, freshwater, estuarine and shallow marine sediments were identified proving both the preservation of non-marine sediments and that landscapes with environments favourable for occupation existed in this area. The original formation of the main valley feature is difficult to date although they are probably pre-Anglian (c. 478,000 BP). OSL dating is currently being undertaken on some of the sediments in order to test this hypothesis. By counting back the major cut and fill events observed within the seismic data it is possible to generate nine possible rises and falls of sea level in the study area. This suggests that the earliest deposit might be of Cromerian date (c. 700,000BP). This is well beyond the range of radiocarbon and OSL dating. OSL dating of some of the sediments is hoped to generate a terminus ante quem (earlier than) date for some of the earlier deposits.

Happisburgh and Pakefield

The inspiration for the Happisburgh and Pakefield exposures project came from the unique opportunity to trace very early sediments of known archaeological potential offshore into the marine environment. The fine-grained sediments onshore are unique and have changed our understanding of the earliest occupation of Britain. Finds within these sediments have demonstrated that human occupation of northwest Europe may date to c. 700,000 BP rather than c. 500,000 BP as previously thought.

The survival of these deposits at the base of the cliffs at Happisburgh and Pakefield is unexpected considering their character and nature, and the series of geomorphological processes that have affected them. As these deposits reside at the base of the cliff line and on the foreshore there is a possibility for their survival offshore.

Cliff exposures at PakefieldDemonstrating the survival of pre-Devensian fine-grained sediments offshore will radically alter the interpretations for very early prehistoric material in the seas around the UK, and therefore change the advice given to aggregate companies in the course of licence applications.

The method for this stage has involved geophysical survey, comprising bathymetric, seismic and sidescan surveys of areas off the coast of Happisburgh and Pakefield. Based on preliminary interpretations of the geophysical data, a further variation to the project was developed. This involved a geotechnical (vibrocore) survey at three locations identified from the geophysical data at the Pakefield site.

Geophysical survey

At Pakefield, the cliff exposure sediments comprise units of Cromer Forest-bed Formation overlying Wroxham Crag Formation sediments. The Cromer Forest-bed Formation cannot be traced offshore based on the data from the geophysical survey, though sediments interpreted as being part of the Wroxham Crag Formation were identified. It is possible that the Cromer Forest-bed Formation is preserved between the foreshore and the western limit of the study area. Offshore, it is considered that any sediments of the Cromer Forest-bed Formation that were deposited have been removed during either the Anglian glaciation or subsequent marine transgressions and regressions.

At Happisburgh, the survey was carried out further from the coast in deeper water to that of Pakefield due to the presence of beach groynes that posed a risk to the equipment. Only sediments interpreted as older than those identified in the cliff exposures and on the foreshore were identified on the geophysical data. However, it is possible that younger sediments relating to the Cromer Forest-bed Formation observed on the foreshore and related early Middle Pleistocene sediments may be preserved closer to the shoreline.

Geotechnical survey

Deploying the vibrocorerA total of five vibrocores were acquired from three locations identified from the geophysical data at the Pakefield site. The purpose of these cores was to confirm and add detailed information on the stratigraphy observed from seismic survey and to provide environmental samples. At two of the three site locations, cores were specifically taken for Optically Stimulated Luminescence (OSL) dating.

Geoarchaeological analysis

Vibrocore VC-P2Vibrocore analyses enhanced the geophysical data interpretation and enabled a better understanding of the sediments and sediment deposition environments. This enabled correlation between onshore and offshore sediments. Although sediments of the Cromer Forest-bed Formation no longer exist offshore, older sediments interpreted as the Wroxham Crag Formation were identified. It was within the upper part of the Wroxham Crag Formation that worked flint was found onshore. The survey at Pakefield successfully demonstrated that sediment units identified onshore can be traced offshore and that not all of these very early terrestrial sediments that are now in submerged areas have been removed by glacial processes and/or marine erosion.

Environmental analysis

Pollen, diatom, foraminifera and ostracod subsamples have been taken from two vibrocores. These samples are currently being assessed in order to provide environmental information, biostratigraphic correlation and possible dating evidence from the described sedimentary sequence.

Great Yarmouth

The Great Yarmouth study area was selected as one of the new areas in which to trial the Seabed Prehistory project methodologies as it represents an aggregate dredging area with a different geological setting, and as such different archaeological potential, to areas previously surveyed during the course of the project.

Previous work in this area has highlighted peat and clay deposits close to the seabed occurring as part of a fine-grained sediment unit closely associated with the aggregate deposits within dredging area 254. These sediments are considered to be infill deposits within the Yare Palaeovalley. The River Yare was cut prior to the most recent marine transgression and is known to have extended offshore during periods of lowered sea level. Gravel deposits within area 254 could possibly contain reworked archaeological material including flint tools. Five flint implements of Palaeolithic date are known to have been found along the coast near Great Yarmouth. These records (based on a SMR data search) relate to finds of single stone tools, none of which are specifically dated to the Lower or Middle Palaeolithic.

A geophysical survey was conducted in the south-western corner of dredging area 254 (currently licensed to United Marine Aggregates Limited), approximately 10km to the east of Great Yarmouth. Survey work was carried out between August and October 2005. Based on the geophysical data, a geotechnical (vibrocore) survey was conducted in July 2006.

Geophysical survey

Bathymetric dataThe geophysical survey involved the acquisition of bathymetry, sidescan sonar and sub-bottom profiler seismic data.

The results of the geophysical survey indicated the presence of a mound feature, predominantly composed of coarse sediments with areas of onlapping fine-grained sediments. At present it is unknown whether this feature is a landform which existed prior to the area being submerged by rising sea levels or if it is a product of erosion caused by rising sea levels.

The deepest sediment unit observed in the seismic data has been interpreted as the Yarmouth Roads Formation; a sediment formation which dates from the Cromerian period (478,000 to 787,000 BP). Throughout the study area the Yarmouth Roads Formation is overlain by a unit distinguished on the seismic data as high acoustic amplitude with irregular and chaotic reflections which have been interpreted as coarse sands and gravels. This structure reflects a high energy depositional environment as a large amount of energy would be required to transport particles of this size.

Geotechnical survey

Deploying the vibrocorerThe vibrocores were targeted at specific deposits so that detailed geoarchaeological interpretation and environmental sampling could be carried out. Geoarchaeological and environmental analysis of those deposits is currently being conducted at Wessex Archaeology’s headquarters in Salisbury. This will enable firmer conclusions to be drawn on the chronological, environmental and archaeological importance of Marine Aggregate Deposits in the Southern North Sea.

Humber

The Humber area has been chosen as one of the new study areas in which to trial the Seabed Prehistory project methodologies in the 2004 – 2007 season. A survey area has been chosen adjacent to licensed dredging areas.

The survey methodology from the Round One survey will be applied including seismic survey, vibrocoring and grab sampling. Geophysical survey data has been collected and is currently being processed. This part of the project is due to be completed in March 2007 which will include an interpreted suite of geophysical and geotechnical data.