By Charlie Self
This is a substantial issue of Cave and Karst Science, with eight papers dominated by earth science and archaeology in England and Wales. The issue also includes abstracts from the 24th Cave Science Symposium held at the British Geological Survey headquarters at Keyworth, Nottingham in conjunction with the BGS and the East Midlands Geological Society.
Taffs Well is the only thermal water spring in Wales. A detailed study of the inorganic chemistry of the spring water shows that it is of the calcium - bicarbonate type but with low dissolved oxygen. Low levels of modern chemical pollutants prove that there has been very little mixing with modern groundwater, while carbon dating of the bicarbonate in the water suggests it may be about 5000 years old. Other trace element and isotope results indicate that the water has travelled to a depth of about 400 metres, mainly in the Carboniferous limestone but also along the contact (if not within) the overlying Marros Group (Millstone Grit) sandstones. All this suggests that the water entered the ground as rainfall on the "North Crop" limestone of the Brecon Beacons, travelled at depth within the South Wales (coalfields) syncline, then rose up to resurge in the "South Crop". Comparison with the English thermal springs of Buxton (Derbyshire) and Bath (Somerset) is appropriate.
The caves of Mulu are a vertically stacked series of passages that formed sequentially as nearby surface river valleys became deeper. Speleothem samples were collected from the caves for analysis using modern Uranium-Thorium dating methods. The results confirm an earlier (U-Th alpha spectrometry) study, which showed that in the lower passages the speleothem age increases with elevation. This present study was able to extend this to provide radiometric ages for samples from the middle level of passages, whereas some samples from the middle and upper part of the cave that are too old for U-Th dating show suitable isotopic concentrations for future study by the Uranium-Lead dating technique.
Test excavations were conducted at two small cave sites that a previous area survey (see C&KS 37(2)) had identified as having been disturbed by unauthorised digging by cavers. At Ogof Ci Coch, small pieces of charcoal, a typical Mesolithic flint point (Middle Stone Age) and late prehistoric pottery fragments were found, but only within disturbed sediments. The intact layers beneath contained bones and bone fragments consistent with the cave's earlier use as a carnivore den. At Valley Side Cave 1, only disturbed sediments were found; the archaeological material was meagre with identifiable fox, a medium-sized bird and larger bones belonging to a small cattle species. This is an ongoing research project, but eight authors for such a short paper!?
A cosmogenic nuclide is formed when an atom of one element is struck by cosmic rays (which are a part of "sunlight") and changes into a different element. Beryllium-10 is one such nuclide. In the case of rocks exposed to sunlight, new nuclides are created //in situ and build up over time in the surface layer. By counting the number of these nuclides (and with a correction factor for surface weathering), it is possible to determine how long a rock surface has been exposed.
In this study, four glacial erratic boulders were tested and their age of deposition calculated at 17,000 years ago. The boulders were of Shap granite and they had not travelled far from their source, so the local ice mass must have been wasting away at this time. Comparative studies show that the end of the last glacial period occurred slightly later in the Lake District (to the west) but slightly earlier in Lancashire and Yorkshire (to the south). The authors then give an informative summary of climate change in the local area since deglaciation.
Glaciers and the periglacial (cold-influenced) processes associated with glaciation are very effective at destroying archaeological material. In the whole of Western Europe there are only two cave sites lying north of the last glacial maximum that still contain earlier archaeological remains. Both these caves are in North Wales. This suggests that the region might be of particular archaeological importance, but the record of sites in the scientific and caving literature is dispersed and incomplete. This paper fulfils a very important task in that it identifies (a) caves with sediments of unknown but potential archaeological importance, (b) archaeological caves with intact unexcavated deposits and (c) caves known to have yielded (human) archaeological or (animal) palaeontological materials.
Lead mining archives note the presence of mineralized caverns in the study area. The current interpretation of these caverns is that they were formed in late Carboniferous times by deep-seated hydrothermal processes, and filled with metalliferous minerals soon (in a geological timescale) afterwards. For a fuller report of similar deposits in nearby parts of Derbyshire, see C&KS 37(1).
Early in 2009, a glacial erratic boulder (well-known to all of us from school Geography textbooks) toppled from its limestone plinth and broke into two pieces. There is clear evidence that this was an act of vandalism. The boulder would eventually have toppled as a result of natural weathering processes, but one act of gratuitous stupidity has now denied generations of students the chance to see in situ an iconic sandstone boulder that was put in place by a glacier at least 17,000 years ago.
This is an important and informative study made in the difficult and dangerous conditions of underwater caving. Most of the sediments within the active caves of the Yorkshire Dales are of sand or fine gravel size. They move through the cave in a similar way to which sand dunes progress, building material up and over the crest until a grain avalanche falls down the lee side. Successive avalanche layers (foresets) show the direction of movement of the dune or (in the restricted space of a cave passage) of a sand bar.
Cave divers now realise that the main flow route in an underwater passage commonly has a network of looping conduits running parallel to it. The flow in these side loops changes direction depending on the amount of water passing through the cave, so a sandbar may move both towards and away from the resurgence, with foresets pointing in either direction or even in both directions.
The caves also contain large quantities of coarser-grained relict sediments that are not significantly being moved by the present-day streams. These must date from a time of much greater flow conditions, perhaps from the melting phase of the last glaciation. This paper is full of observations that would be useful to geomorphologists studying phreatic passages that are now dry, and to cave explorers digging in sediment-filled conduits.