Hull Geological Society
Humberside Geologist Online

 

Skipsea Withow Mere

Compiled by Tracy J. Marsters

 

Abstract

Coastal erosion provides the opportunity to study mere deposits at Skipsea. If this is carried out periodically, a 3D picture of the site can be built up. In 2002 and 2008 a group of geology students from the Centre for Life Long Learning at the University of Hull recorded the stratigraphy of the site and analysed some samples of the sediment. The results published in this paper can be compared with previous publications of the site and future visits.

Introduction

Holderness Meres

The Holderness area once had many meres (Sheppard, 1956 in Flenley, 1987). They developed following glacial retreat and are the product of standing water rapidly accumulating in poorly drained, low-lying areas or in kettle holes (holes formed when blocks of ice that remained after glacial retreat finally melted) (Flenley 1987; Gilbertson, 1990). Some of the earliest lacustrine (lake) deposits date from 13,045 ± 270 radiocarbon (14C) years BP (Beckett, 1981). Today, only one mere survives with open water, Hornsea Mere. The remaining meres have either silted up naturally, been lost due to coastal erosion, or undergone drainage or in-filling by human activities (Gilbertson, 1990; Ellis, 1993). Although these meres no longer exist, their former presence can be detected by the occurrence of peat and lake-mud deposits (Ellis, 1993).

The sediments deposited in meres can still provide a large amount of information about their history and that of the surrounding area, from around 13,000 (14C) years ago onwards (Flenley, 1987; Gilbertson, 1990). Pollen analyses of the mere deposits has provided evidence on how the climate has changed, plus the invasion, colonization, and decline of the flora of the area (Godwin & Godwin, 1933; Flenley, 1987; Gilbertson, 1990). Animal fossils can help build up a picture of the changing fauna, plus archaeological evidence shows human presence from the Neolithic and Mesolithic onwards (Godwin & Godwin, 1933; Clark & Godwin, 1956; Gilbertson 1984; Gilbertson, 1990).

Skipsea Withow Mere (TA 184 547)

Skipsea Withow Mere was one of three ancient meres at Skipsea, though the only one which is exposed at the coast. The two inland meres are Skipsea Low Mere and Skipsea Bail Mere (which in Norman times provided a natural moat for the keep of Skipsea Brough) (Sheppard, 1956 in Flenley, 1987; Flenley, 1987). Skipsea Withow Mere itself was drained in the seventeenth century (Ellis, 1993).

There are two exposures at Skipsea Withow Mere, a southern exposure and a northern exposure, which are separated by a stream outlet. The southern exposure contains, what will be known in this report as the ‘southern peat beds’ and to the south of them, the ‘southern gravel beds.’ The northern exposure contains the ‘northern peat beds’ and to the north of them, the ‘northern sand/silt beds’ (see Figures 1 to 6 below).

Figure 1. Simplified schematic representation of Skipsea Withow Mere stratigraphy showing the four main beds studied in this report (for dimensions see Figure 22).

According to Flenley (1987), all of the meres appear to show a similar succession of in-filling. The base is marked by inorganic deposits, usually lacustrine clays of the Late Devensian (late glacial) period, which developed on a hummocky series of glacial deposits including the Skipsea Till. This is the ‘silt’ layer shown in Figure 1 above. A birch log from within this deposit at Skipsea Withow Mere has been dated to 10,710 ± 70 (14C) years (Gilbertson et al., 1987). The Flandrian (post-glacial) period began with the deposition of an organic lake mud (gyttja), which soon changed to peat formation in smaller meres, as their basins were more rapidly in-filled. Although these were presented as two separate beds by Gilbertson et al. (1987), it was difficult to find a definitive dividing line between the two deposits and were thus logged as a single bed in these studies. This is represented as the ‘peat’ layer in Figure 1. The base of this deposit at Skipsea Withow Mere has been dated to 9,880 ± 60 (14C) years (Gilbertson, 1984). The uppermost part of the sediment returns to mineral deposition, thought to be due to soil erosion on the surrounding slopes following deforestation. This is represented by the ‘topsoil’ layer in Figure 1. Just below this deposit has been dated to 4,500 ± 50 (14C) years at Skipsea Withow Mere (Gilbertson, 1984).

Figure 2. A photograph of the southern exposure of Skipsea Withow Mere (21.9.2008).

Figure 3. A photograph of the ‘southern gravel beds’ of Skipsea Withow Mere (21.9.2008).

Figure 4. A photograph of a section of the southern peat beds at Skipsea Withow Mere (21.9.2008)

 

Figure 5. A photograph of the northern exposure of Skipsea Withow Mere (21.9.2008).

 

Figure 6. A photograph of the ‘northern sand/silt beds’ of Skipsea Withow Mere (21.9.2008).

There have been a number of studies and observations made at Skipsea Withow Mere, dealing with its vegetational history, archaeological history and its stratigraphy. In 1894 Thomas Sheppard (1903) measured a vertical section of the cliff, noting as follows (top to bottom):

  1. the surface earth – a few inches
  2. trees & branches etc – 3 feet (~0.9m)
  3. black peaty clay – four feet (~1.2m)
  4. marl – 2 feet (~0.6m)
  5. gravel – 3 feet (~0.9m)
  6. boulder clay

Similarly, Godwin & Godwin (1933) described the mere deposits as being 100 yards (91m) wide and about nine feet (2.7m) thick in the middle tapering to nothing at the margins. Their vertical section was as follows:

  1. fine brown clay (fresh water deposit) – 2 feet 6 inches (~0.8m)
  2. solid black/brown peat with a large no. of tree trunks & branches – 7 feet (~2.1m)
  3. brown sandy silt – 6 inches (~0.2m)
  4. ‘buttery blue clay’

Obviously these results are different from each other. Firstly, it was not stated where these measurements were taken. Secondly, nearly forty years of coastal erosion have occurred between the two surveys, and many more between these and this study.

The most recent and thorough study of Skipsea Withow Mere was by Gilbertson (1984), with a more detailed analysis of the data by Gilbertson et al. (1987). These studies showed how the different beds of the mere change along the cliff, what they are comprised of, and pollen analysis of several of the beds. They also tried to explain how this mere, along with the environment, has changed over time.

This report is an attempt to amalgamate studies of the mere, undertaken in 2002 and 2008 by geology students from the Centre for Life Long Learning at Hull University, led by Mike Horne, as part of a ‘geological fieldwork techniques’ course. Since the rate of coastal erosion is fairly rapid for the Holderness coast, a comparison will be made of the plan of the cliffs and the height of the cliffs for 2002 and 2008, to see what changes have occurred in the intervening six years. Vertical logs of the four different areas of the cliff shown in Figure 1 will be compared to each other and to that of previous authors. However, one of the biggest problems faced when collating data from different people is the lack of uniformity. The students were asked to develop their own methods to create a three dimensional record of the site. Each group of students had to decide on the classification of the sediments being studied. This can create problems with consistency of results, as well as difficulty in comparing them with previously published reports. However, it does give the students a valuable insight into the subjective nature of seemingly objective results.

 

 

Materials & Methods

a) 25th May 2002

Nineteen pegs were placed along the cliff face at Skipsea Withow Mere, peg 1 being the most southerly peg and peg 19 being the most northerly. A line was marked along the beach running in a north-south direction at about 346 degrees (i.e. magnetic north). The position to the west of this line was measured for each of the 19 pegs, along with its distance north. The height of the cliff was measured from a horizontal line, which was approximately 1.5m above beach level at peg 6. The type and vertical thickness of each bed was noted at each of the 19 pegs, measuring from the top of the cliff to bottom.

 

b) 18th May 2008

Vertical logging of the southern and northern exposures peat beds

A line of string was pinned into the cliff at the southern most point of logging, for both the southern and northern exposures (each exposure was measured by a different group). This was pinned at intervals around the cliff, moving in a northerly direction and making sure that the string was parallel to the ground at all times using a spirit level. The string was used as the horizontal (i.e. local datum) and was taken as 0cm. Beds above the horizontal were assigned positive numbers, those beds falling below the horizontal were assigned negative values. The starting point of logging was taken as 0m, and commenced northwards at intervals of 1m or 2m. Each bed was measured relative to the horizontal, starting with the topsoil which was the top of every vertical log taken (see Figure 7 below). This was a slightly different approach taken from the work carried out on 25th May 2002 (see above).

 

Figure 7. A vertical log.

 

The ‘zero’ end of a tape measure was placed at the horizontal and the interface between each bed read off and noted down. The tape measure was inverted and the same procedure carried out for the beds below the horizontal, making sure a negative number was noted down. Also noted was the presence of anything of interest (e.g. pine cones) or anything that could possibly identify that particular log (e.g. large pieces of wood or drainage pipes). This procedure was carried out by three groups for the whole of the southern and northern peat bed exposures. Group A surveyed the main part of the southern peat beds (logs 0m to 21m). Group B surveyed the main part of the northern peat bed exposure (logs 0m to 36m). Group A also surveyed five sites immediately south of group B, and group C surveyed four sites immediately south of Group A’s southern peat bed survey (see Figure 8 below).

Figure 8. Generalised plan of Skipsea cliffs showing the area surveyed by the three groups.

Several pieces of wood from the peat beds were taken away for possible species identification.

 

Plan of the southern and northern exposures of the cliffs

A reference line was placed, at 345 degrees (i.e. magnetic north), between two small outcrops of rocks that approximately framed the mere peat beds to be studied. The northern most point was point 0. The distance from this line to the cliff bottom gave an east/west orientation reading. The GPS location was also noted for this point. Subsequent measurements, travelling in a southerly direction, were taken from the line to the cliff at each significant change in cliff contour. The distance travelled southwards was also noted. This was continued until the southern outcrop of rock was reached. This also had a GPS reading taken, as did 6 other locations along the way (see Appendix 2g).

 

Additional analysis

Compass readings were taken of the alignment of several large pieces of wood from the peat beds of both the northern and southern exposures.

A sample of grey shelly silt was collected and processed through a 100¼m sieve. This sample was collected at approximately point 2 on Figure 15 below. Both the mineral grains and any microfossils were subsequently analysed under the microscope.

 

c) 5th June 2008

Augers were taken at two sites at the mere, one on the northern exposure and one on the southern exposure, using a custom made screw auger. The northern exposure auger was taken at TA 18381/54628, which corresponds to the 0m log of the northern peat bed vertical logs surveyed on 25th May 2008 (see above). The southern exposure auger was taken 16.5m north of the southernmost reading, i.e. the 0m log of the southern peat bed vertical logs. This corresponds approximately half way in between logs 16m and 17m. The different beds found within the augers were measured and recorded.

 

d) 19th July 2008

Vertical logs were taken for an area at either side of the southern and northern peat bed exposures surveyed on 18th May 2008 (see Figure 1 above). However, accessibility to these cliffs made putting in a line of string to act as a horizontal (i.e. the approach taken on 18.5.2008) was impossible. Several markers were placed in the cliff at locations that were both accessible and where changes in strata appeared to occur. The beds were cumulatively measured downwards from the top of the cliff. Any identifiable plant remains and/or fossils were noted whilst vertical logs were being taken.

The actual height of the cliff was determined at several locations by levelling (this could not be done at all points as the angle between adjacent points was too small to allow calculations to be made. For the southern exposure five points were chosen where there appeared to be the greatest change in height of the cliff. Six were taken for the northern exposure.

A further auger sample was taken at the same site as that taken on 5th June 2008 (the southerly auger site at TA 18379/54616). The sample was taken from 4.00m below beach level, which was the lower limit of June 2008’s auger readings, to a depth of 6.00m. Again the different beds were measured and recorded. Samples from each of the five different beds found within this auger sample were collected, processed and analysed for mineral grains and microfossils under the microscope.

 

Results & Discussion

 

Changes in cliff height

Figure 9 below shows the changes in the height of the cliffs surveyed on the 25th May 2002 (the table of measurements can be found in Appendix 1a). Pegs 5, 18 and 19 were omitted as cliff heights were unrecorded.

Figure 9. Cliff profiles at Skipsea Withow Mere (numbers represent peg numbers; peg 1 being the most southerly reading) (25.5.2002).

The overall pattern is a drop in height on the southern exposure travelling towards the stream, followed by a rise in height on the northern exposure travelling away from the stream. Although Gilbertson et al. (1987) was a more in depth analysis of Gilbertson (1984) it is difficult to compare the above graph with their work as the shape of their cross-sections of the cliffs differed between the two papers. The cross-section illustration in Gilbertson (1984) showed the northern exposure increasing in height when travelling away from the centre of the mere, with the southern exposure rising only slightly as travelling away from the centre of the mere. However, Gilbertson et al. (1987) appears to show only a slight increase for both sides. Furthermore, Gilbertson et al. (1987) shows, like Figure 9 above, that the top of the cliff adjacent to the stream on the northern exposure (point 10 on Figure 9) is lower than the corresponding side of the southern exposure (point 9 on Figure 9). This phenomenon does not appear to occur on the cross-section illustration of Gilbertson (1984). However, it must be remembered that this study is not surveying the same cliff face as Gilbertson et al. (1987), as an area of it will have been lost to coastal erosion in the intervening 18 years since their survey.

As the four areas of Skipsea Withow Mere (see Figure 1) analysed in 2008 were studied by different groups on two different occasions, they will be looked at separately. Levelling data was produced on 19th July 2008 but there were too few points to make an accurate picture (see Appendix 4c). However, five readings were obtained (logs 1,5,9,12, and 13) for the southern gravel bed exposure and four for the northern sand/silt beds (logs A, E, J & S), so these were used to construct cross-sections of those two areas. Figures 10 to 13 below show the changes in height of the cliffs for each of the four areas surveyed, as shown on Figure 1 (travelling from south to north).

Figure 10. Cliff profile at five survey points (1, 5, 9, 12 & 13) of the ‘southern gravel beds’ at Skipsea Withow Mere (south-north) (17.9.2008).

Figure 11. Cliff profile of the ‘southern peat bed’ exposure at Skipsea Withow Mere (south-north) (18.5.2008).

 

Figure 12. Cliff profiles of the ‘northern peat bed’ exposure at Skipsea Withow Mere (south-north) at Skipsea Withow Mere (18.5.2008).

Figure 13. Cliff profiles at four survey points (A, E, J & S) of the ‘northern sand/silt beds’ (south-north) (17.9.2008).

 

The survey undertaken in 2008 shows that the southern side of the mere generally shows less fluctuation in the height of the cliffs than the northern side. The southern gravel beds fluctuate by 1.3m along the length surveyed (though only 5 of the 13 logs have a height measurement), whilst the southern peat beds only fluctuate by 0.25m. The lowest part of the southern gravel beds on Figure 10 are at logs 12 and 13. These two logs (as well as log 11) contain some peat and thus are the southern most edge of the mere. This corresponds roughly to point 3 on Figure 10, as points 1 and 2 do not contain any peat.

In contrast to the relative uniformity in height of the southern peat beds, the northern peat beds fluctuate by 3m, generally rising when travelling in a northerly direction, though undulating on the way. Although the undulating nature of the northern peat beds was not seen in Figure 9, only 7 height measurements were recorded in 2002, as opposed to 21 in Figure 12 (i.e. 2008). Points 16 and 17 on Figure 9 may correspond to the steep rise for the final part of the graph on Figure 12. The silt beds fluctuate by 1.6m (though only 4 of the 19 logs have a height measurement), then this is for the final part of the graph only (also see text regarding Figure 21 below).

In general, the shape of the graph for the peat beds taken in 2008 appears similar to that of 2002. However, the southern gravel beds and northern silt beds of 2008, which were obtained by levelling do not appear to correspond with those of 2002. This will be discussed further with regards to Figures 17 to 21 below.

Plan of the cliffs

Figures 14 and 15 below shows a plan of the cliffs surveyed on 25th May 2002 and 18th May 2008 respectively. As the position of the datum lines on the beach differed in 2002 and 2008, the cliff plans were unable to be plotted on the same graph.

Figure 14. Plan of the cliffs at Skipsea Withow Mere (numbers represent peg numbers; peg 1 being the most southerly reading) (25.5.2002).

Figure 15. Plan of the cliffs at Skipsea Withow Mere (numbers represent log numbers; log 36 being the most southerly reading) (18.5.2008).

GPS readings were taken for log numbers 0, 15 (the stream), and 36 on Figure 15 above. These were TA 18379/54651, TA 18369/54625, and TA 18393/54594 respectively.

Although the general shape of the two graphs above is the same, they indicate definite signs of coastal erosion. The most striking difference is that in 2002, the most easterly points of both the northern and southern exposures were approximately equal (pegs 6 and 10 on Figure 14). However, by 2008 the southern exposure is over 6.5m further back than the most easterly part of the northern exposure (points 14 and 20 on Figure 15). This process of erosion of the southern part of the mere must have been occurring for many years, since Gilbertson (1984) shows the southern exposure to be further east than the northern exposure. However, erosion appears to be speeding up, since Gilbertson (1984) shows the southern part to be further east by only about 1.7m i.e. 1.7m of erosion in 18 years (approximately 0.1m/year), compared with 6.5m in 6 years (approximately 1.0m/year).

Also, showing definite signs of erosion is the bay area of the northern side of the mere. In 2002, the bay extends back by 7.5m (from peg 10 to 13 on Figure 14). By 2008, the same bay extends back by 13.3m (from log 5 to 14 on Figure 15). This same area extends back approximately 1.7m according to Gilbertson (1984). Again, erosion appears to be speeding up. In the 18 years from 1984 to 2002 the bay has extended back by 5.8m (approximately 0.3m/year), and by a further 5.8m between 2002 and 2008 (approximately 1.0m/year). However, this is erosion relative to the most easterly point of the northern exposure only (i.e. peg 10 on Figure 14 and log 14 on Figure 15). Presumably this part is eroding too, but apparently at a slower rate.

The data for the plan of the cliffs taken on 19th July 2008 by levelling has not been used as there were not as many markers as that produced on the 18th May 2008 (see Appendix 4c for levelling data). However, the basic shape of the plan produced from levelling was the same as those for Figure 15 above.

Vertical logs

Appendix 1b notes, in simplified form, the types of strata occurring at each of the 19 pegs. The first two logs contain mainly sands and clays, with the peat beds starting at the third log. Figure 16 below shows a cross-section of the peat beds, which includes part of the adjacent gravel and sand/silt beds, recorded in 2002.

Figure 16. Cross-section of the stratigraphy at Skipsea Withow Mere (south-north) (25.5.2002).

 

Figures 17 to 20 below show the peat beds along with the adjacent gravel beds (southern) and sand/silt beds (northern) as recorded in 2008.

 

Figure 17. A simplified cross-section of the southern gravel beds (south-north) (19.7.2008).

Figure 18. A simplified cross-section of the southern peat beds (south-north) (18.5.2008).

Figure 19. A simplified cross-section of the northern peat beds (south-north) (18.5.2008).

Figure 20. A simplified cross-section of the northern sand/silt beds (south-north) (19.7.2008).

As only 5 of the 13 logs for the southern gravel beds and 4 of the 19 logs for the northern sand/silt beds had heights recorded, the remainder of the heights had to be calculated using trigonometry (see Appendices 4b and 4e for calculations). Obviously this assumes that the heights of the unknown logs follow a smooth gradient between two known heights, which will probably not be the case. However, this does provide a rough idea of how the different beds are laid out.

A major difference that was noted between the peat beds and the gravel and sand/silt beds was that the gravel and sand/silt beds comprised many layers, especially the gravel beds. This too was noted by Gilbertson et al. (1987). Unfortunately, the number of beds was not constant at each of the survey points (see Appendix 4b), so the beds were consolidated into ‘gravel beds’ and ‘sand/silt beds’ in Figures 16, 17 and 20. Interestingly, by log 4 (2.88m from the starting point) of the gravel beds, the soils (silts), which were interspersed with the gravel beds appeared different in colour. The upper silts tended to be brown in colour and the lower ones grey in colour. Gilbertson et al. (1987) report this is due to the aquatic environment in which the grey silts were deposited as opposed to a subaerial deposition environment for the brown silts.

Generally, boulder clay was found directly underneath the gravel beds, much of which is obscured by the beach (Figure 17 above). This is different from Gilbertson (1984) and Gilbertson et al. (1987), who found a silt bed before arriving at the boulder clay. It is possible that our survey has put two beds together, though when looking at Appendices 5a and 5b it is clear that the gravel layers did actually butt up to the boulder clay. It is also possible that this bed was misinterpreted as boulder clay in this survey – only re-investigation will tell. Also, Gilbertson et al. (1987) found nearly 4.5m of gravel beds (at its thickest point), whereas in this survey it never even reached a thickness of 2m. A further confusion is that the illustrations of the cross-section of the mere and surrounding areas appear different in Gilbertson (1984) and Gilbertson et al. (1987).

When the gravel beds disappear and change to the peat beds, a bed of black/grey silt is generally found directly underneath, before arriving at the boulder clay. This is found for both peat bed exposures (Figure 18 and 19 above). The black/grey silt layer is missing for some of the locations surveyed at the northern silt beds, where the peat was underlain by the boulder clay (Figure 20 above and Appendix 4d). These black/grey silts are organic lake muds, and indicate a nutrient-rich, biologically active lake (Gilbertson et al., 1987). In the 2002 analysis, there appears to be an upward movement of the whole peat bed of the southern exposure near to the stream. This does not appear to occur in the 2008 survey, where the peat beds appeared fairly uniform along the cliff (Figure 19 above). This anomaly appears to be due to peg 8 on Figure 16 not recording the presence of topsoil. However, this is not an error, as peg 8 was recorded as having an eroded top.

There is a general upward trend in height of the northern peat bed both in 2002 and 2008 (Figures 16 and 19 above). However, the area around the sand/silt beds appear very different (Figures 16 and 20 above). In 2002 there is a general upward trend in height of the cliff, where in 2008 it was recorded as sloping downwards. It is possible it is a true change due to the cliffs being further back in 2008 due to coastal erosion. However, it is also possible that the levelling may not be totally accurate. As can be seen on Figure 20, from about 7m the bottom of the beds appear to go below beach level, and by 15m they are well below beach level. Furthermore, at about 30m on Figure 19 the topsoil is eroded away so it virtually exposes the peat. Something similar is happening by about 2 m on Figure 20. Presumably these represent the same area of cliff. As such there must be some inaccuracies with regards to the levelling data. If the height of the cliff is plotted from beach level, there is a general trend upwards (see Figure 21 below) as seen in 2002.

Figure 21. Height of the northern gravel beds as recorded from beach level (south-north) (19.7.2008).

 

This seems to tie in better with both the 2002 data and the northerly most area in Figure 19. However, it must be borne in mind that the beach level too will not be constant, so this will not be a truly accurate picture. However, the dip in cliff about 2.5m along looks very much like the dip in the peat bed graph at about 30m on Figure 19 above, which then carries on sloping upwards, as in Figure 21 above. Similarly, the southern gravel beds appear steeper in 2002 than the 2008 survey. It is not known whether this is a true phenomenon due to six years of erosion or perhaps something to do with the levelling procedures again.

Figure 22 below is an attempt to intercalate the four areas, though as it was unknown where each of the areas actually joined or overlapped each other, this is just an approximation.

 

Figure 22. An approximate cross-section of Skipsea Withow Mere (2008).

 

Topsoil – modern soils and colluvial sandy silts.

Peat – coarser peat containing numerous large pieces of timber grading into ‘silty peats’ (gyttja, vegetation within organic lake muds) further downwards. Pieces of timber identified in this bed included alder (Alnus glutinosa), English oak (Quercus robur), elm (probably Ulmus glabra), birch (Betula pendula), and hazel (Corylus avellana). Some larger timber pieces analysed showed they were randomly orientated (see Table 2 and Figure 10 below).

Northern ‘silt beds’ – layers of silty sands. This deposit contained whole and broken mollusc shell.

Southern ‘gravel beds’ – layers of coarse gravels, sands and silts.

Silt – grey/blue organic, lacustrine silt and clay deposits. These extend down to 7.97m below the top of the cliff at the southern auger site (see Table 1 below). Broken bivalve and gastropods, ostracods, rams horn snail fossils were found along with derived chalk foraminifera and an Inoceramus prism.

Boulder clay – glacial deposits (Skipsea Till). Found to contain several derived fossils including: chalk foraminifera, an Inoceramus prism, Gryphaea and ostracods.

 

For construction of the southern gravel beds and the northern silt beds the levelling data was not used. Instead the height from beach level was used, which although will not be totally accurate, does appear to look more like the shape of the cross-section obtained for 2002. When looking at Figure 22 it is clear that obviously something has happened differently at the northern and southern edges of the mere. The southern edge of the peat bed is dominated by gravel beds. It is clear that whatever process was responsible for deposition of these gravel beds was localised as they are not present at the northern end. Gilbertson et al. (1987) suggest this process was linked to climatic deterioration that was occurring around this time. The northern edge of the peat bed was occupied by sands and silts. These are the product of weathering of late Devensian lake margin deposits, exposed during a lowering of the lake level (Gilbertson et al., 1987).

 

Augering

Auger samples were taken at two sites on the 5th June 2008, one on the southern exposure and one on the northern exposure (see Appendix 4g). A second auger sample was taken at the southernmost of the two June sites on 19th July 2008 and is shown in Table 1 below, along with June’s results (the auger site was approximately between logs 16 and 17 of the southern peat beds (see Figure 15)) (see also Appendix 3).

 

Table 1. Combined augering data from 5th June 2008 and 19th July 2008 surveys (southern auger site as shown on Figure 22).

Bed

Thickness of each bed (m)

Height of bed from top of cliff (m)

Height of bed from beach level (m)

Topsoil

1.00

1.00

+2.34

Peat

1.34

2.34

+1.34

Clay (grey, sandy)

1.15

3.49

-1.15

Clay

0.10

3.59

-1.25

Clay (grey)

1.60

5.19

-2.85

Clay (dark grey)

0.87

6.06

-3.72

Clay (blue/black)

0.18

6.24

-3.90

Clay (grey)

0.10

6.34

-4.00

Clay (blue)*

0.40

6.74

-4.40

Clay (black, greasy)*

0.50

7.24

-4.90

Clay (black, stiff)*

0.60

7.84

-5.50

Boulder clay*

0.13

7.97

-5.63

Boulder clay*

0.37

8.34**

-6.00

*these samples were analysed for mineralogy and microfossils.

As can be seen, beneath the peat beds are numerous clay (silt) beds. Some of these deposits are visible above the sand, but have been found to stretch down to 5.63m below beach level before hitting the boulder clay. Thus, at this site, the mere bottom is 5.63m below beach level.

 

Orientation of pieces of wood

The orientation of several pieces of wood were surveyed insitu within the peat beds of both the southern and northern exposures. However, only the southern exposure readings were subsequently used for analysis, as compass readings for the northern exposure appeared to vary with distance from the cliff face. This was possibly due to some local magnetic interference affecting the compass readings. The magnetic readings in degrees were converted into direction readings (e.g. N (north) or SSW (south-south west etc.)) to make analysis easier. The number of pieces of wood observed for each direction was calculated and shown in Table 2 below.

 

Table 2. Number of pieces of wood occurring at each direction.

Alignment direction of wood

Number of pieces of wood

N/S

7

NNE/SSW

6

NE/SW

4

ENE/WSW

5

E/W

5

ESE/WNW

4

SE/NW

6

SSE/NNW

5

Total

42

Figure 23. Rose diagram of log orientation.

Although numbers recorded for each compass direction appear similar, a Ç2 test was performed on the data. This shows there to be no significant difference in the orientation of the pieces of wood found in the southern exposure, and thus deposition appears random. (see Appendix 2h on web or CD ROM version of this paper for calculations). A lack of alignment of the branches implies that this is perhaps still water with no significant current.

 

Sediment, microfossil and vegetation analysis

Peat deposits

a) Subfossil vegetation

Wood and vegetation were seen throughout the peat beds. In May 2002 pieces of beech and oak were identified amongst some of the decomposed vegetation. A more detailed analysis of the plant material found within the peat beds in May 2008 identified alder (Alnus glutinosa), English oak (Quercus robur), elm (probably Ulmus glabra), birch (Betula pendula), and hazel (Corylus avellana). Pollen analysis by Gilbertson et al. (1987) of the peat (and silt) beds also showed the presence of these trees, as well as pines (Pinus), willow (Salix), lime (Tilia), and ash (Fraxinus). Hazelnuts, pine cones, and berries/seeds were also identified within the peat deposits.

 

Sand, silt and clay deposits

a) Subfossil vegetation

Hazelnuts and pine cones were identified in the silt layers of the ‘southern exposure peat beds’. Microscopic analysis of a sample from the silt layer (taken on 18.5.2008 at approximately the position of point 2 on Figure 7) showed an abundance of plant material (unidentified). Plant material was also identified in the samples of augered blue clay, black greasy clay and upper boulder clay beds (19.7.2008) (see Table 1 above).

b) Fossils

Gastropods and unidentified pieces of shell were found in some of the northern exposure sand and silt beds. Broken bivalve shells were also found in the augered black greasy clay. Several Gryphaea were identified in the underlying boulder clay of the northern exposure. Shell remains were also noted by Gilbertson et al. (1987) including the valve snail Valvata piscinalis and freshwater bivalves, possibly Anodonta.

c) Sediment grains (120 um – 2 mm fraction)

Sediment analysis from the grey silt layer mentioned above in a), showed it to be comprised mainly of clear colourless quartz, with very little other mineral material. All five augered samples showed a predominance of quartz (mainly colourless). The black stiff clay also contained a variety of other minerals and rock fragments including carnelian, schist, chalk, ironstone, with the lower boulder clay layer containing chalk, schist, a black mineral, and pyrite. The augered black greasy clay also appeared more poorly sorted compared with the other augered samples.

 

d) Microfossils (120 um – 2 mm fraction)

The grey silt sediment quoted above contained several microfossils, the dominant type being the stonewort Chara. Also recovered were derived chalk foraminifera, derived calcite needles from inoceramid bivalves, ostracods (of varying sizes), broken gastropods and their opercula, rams horn snails, and possibly some insect remains. Seeds, a derived Inoceramus prism, a derived crinoid, and possible beetle remains were identified in the augered blue clay layer. The augered black greasy clay contained plant debris, a specimen of Chara, beetle remains and ostracods. The augered black stiff clay contained an array of microfossils, including plant material, seeds, Chara, shell, ostracods, a beetle carapace and claw, derived Inoceramus shell, and possibly a fish tooth. The upper boulder clay sample contained shell, derived chalk foraminifera and plant remains, with the lower boulder clay sample containing ostracods and a derived Inoceramus prism.

 

Conclusions

One of the major findings of this report is the rapid changes occurring at this site due to coastal erosion. This can be seen not only in the intervening 18 years between the work of Gilbertson (1984) and that of the 2002 study, but also between the 2002 and 2008 studies here. Furthermore, the data here suggests that coastal erosion appears to have speeded up somewhat. However, due to the nature of the 2002 and 2008 studies, it cannot be stated how much coastal erosion is occurring in general, but only how much one area of the mere is being affected compared with another area of the mere.

Although the plan of the cliffs has changed somewhat, there doesn’t appear to have been too much change in the general shape of the height of the cliffs. As noted, it is difficult to compare our results with that of Gilbertson (1984) and Gilbertson et al. (1987) as the shape of their cross sections differ widely between the two papers.

When a cross section of the logs was produced it showed the lowest deposits to be silts/clays. Near the centre of the mere these deposits were found to extend down to 7.97m below the top of the cliff, before hitting the boulder clay underneath. These are the inorganic deposits of the Late Devensian (late glacial) period mentioned by Flenley (1987). What was noticeable from the cross-section was how different the northern and southern edges of the mere are. The southern flank of the mere deposits are dominated by gravel beds. It is clear that whatever process was responsible for deposition of these gravel beds was localised, as they are not present at the northern end. Gilbertson et al. (1987) suggest this process was somehow linked to climatic deterioration that was occurring around the time of deposition. The northern edge of the mere basin was occupied by sands and silts. These are the product of weathering of late Devensian lake margin deposits, exposed during a lowering of the lake level (Gilbertson et al., 1987). The edges of the peat layer appear to overlie the southern gravel beds and northern silt beds. The top of the peat layer has been dated to 4,500 ± 50 14C years BP and the bottom to 9,880 ± 60 14C years BP (Gilbertson et al., 1987). Thus, these deposits have built up over about 5,380 14C years. By studying some of the branches found within these peat deposits, a general picture of the trees in this area around this time can be gathered. Species identified were alder (Alnus glutinosa), English oak (Quercus robur), elm (probably Ulmus glabra), birch (Betula pendula), and hazel (Corylus avellana).

Fossils identified included freshwater molluscs and ostracods, plus some unidentified beetle remains. The dominant microfossil however, was the stonewort Chara. This alga is widely distributed in freshwater, favouring still or very slowly running water. The still nature of these waters is also indicated by the random orientation of branches found within the peat layer. Fossils and plant material found within the boulder clay could indicate that this boulder clay is not insitu, and instead is reworked material that slumped into the lake early on. However, it is not possible to tell whether this is a ‘raft’ of boulder clay within the lake deposits from just an augered sample. It is also not possible to tell if the fossils and plant material found within the boulder clay actually came from the boulder clay, or whether it was due to down hole contamination from the augering process.

 

This report summarises the data obtained from Skipsea Withow Mere in 2002 and 2008. However, since the rate of erosion of the Holderness coast is estimated to be about 2m per year (Ellis, 1993), all the data recorded here provides just a fleeting glimpse of Skipsea Withow Mere in the early 21st Century.

Acknowledgements

This data was collected by many geology students of Hull University over four different surveys.

25th May 2002: Alan Evans, Colin Clark, Kate Dennett, Mike Horne, Paul Richards, Stuart Jones.

18th May 2008: David Baker, Tony Barker, Rodney Evans, Bruce Harris, Dennis Haughey, Mike Horne, Stuart Jones, Tracy Marsters, Ros Perry, James Thompson, Gareth Waudby.

Vegetation analysis undertaken by Stuart Jones.

Grey silt sample collected and processed by Dennis Haughey, and analysed by Mike Horne and Stuart Jones.

5th June 2008: Mike Horne, Stuart Jones, Ros Perry, Ian Scott, Nina Scott, Rod Towse.

19th July 2008: Tony Barker, Mike Horne, Tracy Marsters, Stuart Jones, Ros Perry, Paul Richards, Ian Scott, Nina Scott, Rod Towse, Dennis Haughey.

Augering samples collected and processed by Dennis Haughey, and analysed by Nina Scott, Mike Horne, Stuart Jones and Dennis Haughey.

Thank you to Mike Horne for comments regarding this paper. Also thanks to members of Hull Geological Society for editing this report, especially Roger Connell for his numerous comments and recommendations.

The raw data collected for this project can be found on Mike Horne's website at http://www.horne28.freeserve.co.uk/skipsea.htm and http://www.horne28.freeserve.co.uk/skip08.htm

References

Beckett, S. C. 1981. Pollen Diagrams from Holderness, North Humberside. Journal of Biogeography 8: 177-198.

Clark, J. G. D. & H. Godwin. 1956. A Maglemosian Site at Brandesburton, Holderness, Yorkshire. Proceedings of the Prehistoric Society 22: 6-22.

Ellis, S. (ed). 1993. Wetland Heritage: An Archaeological Assessment of the Humber Wetlands. Humber Wetlands Project, University of Hull. p120.

Flenley, J. R. 1987. The Meres of Holderness. In: East Yorkshire Field Guide (ed. S. Ellis). Quaternary Research Association, Cambridge, 73-81.

Gilbertson, D. D. 1984. Early Neolithic Utilisation and Management of Alder Carr at Skipsea Witthow Mere, Holderness. The Yorkshire Archaeological Journal 56: 17-22.

Gilbertson, D. D. 1990. The Holderness Meres: Stratigraphy, Archaeology and Environment. In: Humber Perspectives (eds. Ellis, S. & D. R. Crowther). Hull University Press, 89-101.

Gilbertson, D. D., Briggs, D. J., Blackham, A. M., Gale, S. J., Hall, A. R., Hunt, C. O. and N. M. Thew. 1987. The Late Quaternary Lake Margin Sequence at Skipsea Withow Mere. In: East Yorkshire Field Guide (ed. S. Ellis). Quaternary Research Association, Cambridge, 58-68.

Godwin, H. & M. E. Godwin. 1933. British Maglemose Harpoon Sites. Antiquity 7: 36-48.

Sheppard, J. A. 1956. The Draining of the Marshlands of East Yorkshire. Ph.D. thesis, University of Hull.

 

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