The Afon Ystwyth Experiment Archaeology Project
Contents
Introduction
The
Afon Ystwyth Experimental Archaeology Project (2000-2003) was undertaken by Dr Robert Hosfield and Ms
Jenni Chambers, with assistance from Professor Mark Macklin and Dr Paul Brewer
(
1.
Processes of stone tool transportation, modification and deposition within a
fluvial system, with respect to core tools (bifaces) and flake material.
2.
Process of stone tool modification and burial within fine-grained sedimentary
systems (aeolian silt), with respect to core tools (bifaces) and flake
material.
3.
Processes of short-term change in river system morphology.
The
project was carried out on the Afon Ystwyth in mid-Wales, at two study sites:
Llanilar and Llanafan (Figure 1).
The sites were selected due to:
Figure 1: The Llanafan experimental site
i. The
absence of indigenous Palaeolithic material – there are no records of
Palaeolithic stone tool artefacts having been recovered from the Afon Ystwyth
valley, although later prehistoric lithics have been recovered.
ii.
The suitability of the sites for tracer recovery, as illustrated by previous
experimental archaeological research during the 1980s (Harding et al. 1987; Macklin 1995).
iii.
The rapid shifting of the Afon Ystwyth channel at Llanafan, associated with
developing bars and active transport of bed materials.
iv.
The contrast between the sites, which assisted in the investigation of a range
of different processes. The Llanafan site boasts a dynamic floodplain
environment, with regular changes in river channel morphology, sediment
distribution, and floodplain vegetation coverage. In comparison, the Llanilar
site is subject to relatively little morphological change, partially due to
engineering works undertaken since the 1960s.
v.
Existing topographic surveys of the Llanafan site’s floodplain and channels,
undertaken by the
vi.
A river bed-load dominated by Palaeozoic shales and gritstones, which aided the
recovery of tracers produced in ‘exotic’ raw materials (flint and chert).
A summary of the experiments
undertaken and the main conclusions from the 1st phase of the project
(2000-2003) are included below.
The Experiments
21
individual experiments were undertaken between September 2000 and July 2003.
These can be summarised as follows:
1.
Biface tracer experiments (Llanilar). Replica bifaces were emplaced across the
Afon Ystwyth channel and recovered (where possible) after transportation.
2.
Biface tracer experiments (Llanafan, Grogwynian Reach). Replica bifaces were
emplaced on the vegetated floodplain, point bars and midstream bars and
recovered (where possible) after transportation and/or modification by aerial
and sub-aerial processes.
3.
Flake tracer experiments (Llanafan). Replica flake scatters (knapped in situ and pre-knapped) were emplaced
on the vegetated floodplain and point bars and recovered (where possible) after
transportation and/or by modification by aerial and sub-aerial processes.
1. Biface Experiments (Llanilar)
The
positions of all the emplaced bifaces were 3-dimensionally surveyed. The
orientation and dip of the bifaces was also recorded. The key conclusions from
the Llanilar biface experiments are as follows:
1.1
Bifaces have a tendency for both in situ
burial and transportation.
1.2
The tendency of an individual biface for burial or transportation relates not
only to flow velocity (i.e. flood magnitude) but also to the local river bed
morphology.
1.3
Bifaces may be subject to abrasion development while in phases of partial
burial (Figure 2), as well
as during periods of active transportation.
1.4
The development of diagnostic transport features (e.g. edge micro-flaking and
incipient percussion cones) may be hindered in fluvial environments with a
significant vegetation (algae) component.
Figure 2: A 'buried' biface during
excavation, at the Llanilar study site
2. Biface Experiments (Llanafan)
The
positions of all the emplaced bifaces were 3-dimensionally surveyed. The
orientation and dip of the bifaces was also recorded. The key conclusions from
the Llanilar biface experiments are as follows:
2.1
Bifaces have a tendency for both in situ burial (Figure 3) and transportation.
2.2
Bifaces demonstrated potential for burial within fine-grained floodplain and
bar form sediments.
2.3
Transportation distances (and therefore step lengths) tend to be relatively
short (this assumes that the majority of un-recovered bifaces were buried
rather than transported downstream of the study area).
2.4
Bifaces may be subject to abrasion development and related damage while in
phases of partial burial, as well as during periods of active transportation.
2.5
The development of incipient percussion cones may occur over short distances.
Figure 3: A partially 'buried' biface, at the
Llanafan study site
3. Flake Experiments (Llanafan)
Flake
scatters were emplaced at the Llanafan site (Figure 4), to explore the
transformation of flake materials as a consequence of fluvial disturbance and
other aerial and sub-aerial processes. A total of 13 scatters were emplaced, of
which 4 were knapped in situ, and 9
were pre-knapped and emplaced to mimic the spatial density of a scatter knapped
in situ. Scatters were pre-knapped as
it enabled the recording of flake weight and the a, b and c-axes. It also
facilitated material identification and recovery (pre-knapped scatters were
individually numbered). As the main focus of the experiments was flake
movement, it was considered to be more important to record accurate size data
than to create ‘authentic’ knapping scatters. Two flake dimensions (a and
b-axis) were recorded for the in situ
knapped scatters. The orientation and dip of all flakes were recorded after the
scatters were emplaced.
Figure 4: An experimental flake scatter,
emplaced on a gravel bar at the Llanafan study site
In
general, the key conclusions from the Llanafan flake experiments are as
follows:
3.1
Flake scatters demonstrate a degree of structural integrity, with flakes being
transported short distances (generally sub-10m) in the initial phases of
fluvial dispersal.
3.2
However, flakes are transported significant distances during subsequent
dispersal phases (demonstrated minimum of 80m).
3.3
Flakes are damaged during transport episodes, but while this damage may modify
the specific morphology of individual flakes (see below), it does not modify
them beyond the point of recognition as anthropogenic flakes.
3.4
High percentages of the transported flakes display varying degrees of edge micro-flaking
(Figure 5). As
transportation distances and the quantities of micro-flaking increase, it is
suggested that the micro-flaking increasingly resembles intentional retouch.
3.5
Flake material from separate scatters (knapped in relatively close spatial
proximity) tends to become spatially indistinguishable during fluvial
dispersal.
Figure 5: Micro-flaking (along the distal
edge) on a transported flake
Floodplain Monitoring
A
photographic archive was recorded between May 2000 and July 2003, documenting
the evolution of the Afon Ystwyth floodplain at the Llanafan site:
i.
Variations in gravel bar type. In response to changes in water levels, the
barforms varied between point bar complexes and complexes of midstream barforms
intersected by minor channels. The midstream barforms displayed varying levels
of fragmentation in response to specific water levels.
ii.
Variations in bar presence, due to fluctuations in channel width and depth,
water levels and (possibly) sediment transport.
iii.
Vegetation development. Patterns in the locations of semi-stable vegetation
provided a ‘negative’ image of the position of the ‘overflow’ channels that
fragmented the barforms during periods of high water levels. The presence of
vegetation also indicated relatively highly elevated sections of the barforms,
which were clearly rarely inundated by flooding. The presence of this
semi-stable vegetation therefore indicated that, over relatively short periods
(e.g. the 3 years of this study), the location of ‘overflow’ channels and the
fragmentation of barforms follows repetitive patterns in response to high level
flows and flooding events. Over slightly longer time-spans, the distribution of
vegetation on the floodplain to the south of the main channel indicates
shifting patterns in the distribution of the main channel. From east to west,
the transition from vegetation (grasses and shrubs) to bare gravel and silt, to
partial vegetation (shrubs and some grasses) suggests the relatively recent
existence of a major palaeochannel flowing from north to south across the
floodplain.
iv.
Variations in channel types and locations. The major channel of the Afon
Ystwyth showed considerable variation in width between periods of low and high
flow. There was also an extensive development of multiple channels associated
with the barform complex at the upstream end of the study site. Finally, during
periods of extremely high flows there was evidence of ‘overflow’ channels
fragmenting the floodplain to the north of the main channel.
v.
Erosion. There was extensive evidence of bank erosion at the downstream end of
the study site. It has not been possible to accurately measure the quantities
of bank erosion that have occurred (due to difficulties of access), although
the undercutting of fence lines has provided a subjective measure of erosion
rates in this part of the Llanafan site (Figure 6).
Figure 6: Bank erosion at the Llanafan site
Summary
Overall,
the first phase of the project has provided valuable information with respect
to the processes of stone tool transport and modification, which are important
for the interpretation of secondary context stone tools assemblages from the
Lower and Middle Palaeolithic archaeological record.
References
Harding, P., Gibbard,
P.L., Lewin J., Macklin, M.G. & Moss, E.H. 1987. The transport and abrasion
of flint handaxes in a gravel-bed river. In G. de G. Sieveking & M.H.
Newcomer (ed’s) The Human Uses of Flint
and Chert: Proceedings of the Fourth International Flint Symposium Held at
Brighton Polytechnic, Oct 15th April 1983: 115–126.
Macklin, M.G. 1995.
Archaeology and the river environment of
Further details of
the project can also be found in the following:
Hosfield, R.T. & Chambers, J.C. 2004.
Experimental Archaeology on the Afon Ystwyth,
Hosfield, R.T. &
Chambers, J.C. 2004. The Archaeological
Potential of Secondary Contexts. English Heritage Project Report (Project
No. 3361). English Heritage Archive Report,
Hosfield, R.T. & Chambers, J.C.
Submitted. River gravels and flakes: new experiments in site formation, stone
tool transportation and transformation. In M. Fansa (ed.) Experimentelle Archäologie in Europa.
Hosfield, R.T. & Chambers, J.C.
In press. Flake modifications during fluvial transportation: three cautionary
tales. Lithics: The Newsletter of the
Lithic Studies Society.
Contacts
Dr Robert Hosfield
E-mail: r.hosfield@rdg.ac.uk
Dept. of Archaeology
Whiteknights
Reading RG6 6AB
Tel: (0118) 378 7632
Fax: (0118) 931 6718
WWW: http://www.personal.rdg.ac.uk/~sgs04rh/
Jenni Chambers
E-mail: j.c.chambers@soton.ac.uk