P Murphy

Thermal ionization mass spectrometer U-Th dates on Pleistocene speleothems from Victoria Cave, North Yorkshire, UK: Implications for paleoenvironment and stratigraphy over multiple glacial cycles

We present 23 new thermal ionization mass spectrometric U-Th dates for Victoria Cave, North Yorkshire, UK. Victoria Cave underwent repeated glaciation during the late Pleistocene and contains one of the longest Quaternary cave sequences in Britain. The dates reveal that speleothem formation began beyond the range of the dating technique (before 600 ka). Finite reproducible dates of 490 −9/+10 ka confirm speleothem deposition during marine isotope stage (MIS) 13, the oldest date we know of for this part of Britain. Further speleothem formation was dated to MIS 11, MIS 9, MIS 7, and MIS 5. The results are the basis for a new chronology of Quaternary events for the cave and greatly enhance our understanding of the factors affecting the formation of the sedimentary sequence. Cyclical climatic and environmental change throughout the late Pleistocene triggered cyclical sedimentation events in the cave. All the interglacial periods show calcite deposition but with growth phases postdating the warmest events of MIS 11 and MIS 5e. The position of the cave halfway up the side of a glacial trough resulted in very distinctive sediment during the more extreme glacial maxima: ice-dammed lakes formed inside the cave and deposited varve-like clay rhythmites. The dates inferred for these deposits suggest that this locality underwent significant glaciation during MIS 12, MIS 10, MIS 6, and MIS 2, and that the ice was warm based. The absence of rhythmites during MIS 8 suggests minimal ice cover at that time. This is the most complete record for glacial events in the region; it is the only site where successive glacial maxima can be identified and dated. The record of large faunal remains indicates that the cave was open to the surface, only for relatively short times, during MIS 13, MIS 12, MIS 5e, the Late Glacial Interstadial, and parts of the Holocene. It is inferred that at other times the cave was closed because scree formation blocked the entrance. The record of vertebrate remains is therefore controlled by geomorphological processes. The deteriorating state of this unprotected site remains a cause for concern.

The Role of Sulfate-Rich Springs and Groundwater in the Formation of Sinkholes over Gypsum in Eastern England

Heavily karstified gypsum and dolomite aquifers occur in the Permian (Zechstein Group) of Eastern England. Here rapid active gypsum dissolution causes subsidence and abundant sinkholes affect an approximately 140-km by 3-km area from Darlington, through Ripon to Doncaster. The topography and easterly dip of the strata feed artesian water through the dolomite up into the overlying gypsum sequences. The shallow-circulating groundwater emerges as sulfate-rich springs with temperatures between 9-12 oC, many emanating from sinkholes that steam and do not freeze in the winter (such as Hell Kettles, Darlington). Water also circulates from the east through the overlying Triassic sandstone aquifer. Calcareous tufa deposits and tufa-cemented gravels also attest to the passage and escape of this groundwater. The sizes of the sinkholes, their depth and that of the associated breccia pipes is controlled by the thickness of gypsum that can dissolve and by the bulking factors associated with the collapsed rocks. The presence of sulfate-rich water affects the local potability of the supply. Groundwater abstraction locally aggravates the subsidence problems, both by active dissolution and drawdown. Furthermore, the gypsum and dolomite karstification has local implications for the installation of ground-source heat pumps. The sulfate-rich springs show where active subsidence is expected; their presence along with records of subsidence can inform planning and development of areas requiring mitigation measures.

Sulphur springs of the Craven Basin, NW England: indicators of natural methane leakage?

Sulphidic springs are a common feature of the Craven Basin and have long histories, indicating that they are natural phenomena, and not a result of recent anthropogenic contamination of groundwater. This study identified several extant sulphur springs and these were sampled and analysed for hydrochemistry and isotopic composition (δ34S of sulphate and sulphide, δ18O of sulphate and δ13C of total dissolved inorganic carbon (TDIC)). The springs are associated with limestone units and are located in anticlinal crests that are sometimes faulted. Sulphide concentrations at these ‘sulphur springs’ range from <0.5 to 96 mg l−1 and light sulphide isotopic compositions indicate that sulphide originates by microbial sulphate reduction. One site, ‘Stinky Bottoms’, with high sulphide concentration (46 mg l−1) also has very low δ13C-TDIC (–25.3‰ V-PDB) characteristic of a significant component of TDIC generation via methane oxidation. Other sites have δ13C-TDIC more typical of shallow groundwaters (−14.2 to −16.3‰ V-PDB) and two sites with highest Cl concentration and elevated Sr:Ca have heavier δ13C-TDIC (−11.3 and −6.8‰ V-PDB), indicative of a more evolved, long residence-time brine component. At Stinky Bottoms a strong case can be made that generation of sulphidic groundwater is related to subsurface methane. At other sites, sulphide generation may also be related to hydrocarbon or methane seeps (in some cases associated with a brine component) but the δ13C-TDIC values are more equivocal.

Cavers and geoconservation: the history of cave exploration and its contribution to speleology in the Yorkshire Dales

Abstract Caves are important as they preserve archaeological and palaeoenvironmental data otherwise lost from the land surface. The fragile nature and limited extent of cave deposits is often not appreciated by non‐specialists and the activities of the main group of cave visitors (sporting cavers) are viewed as damaging to the cave interior deposits. Potential threats to the cave interior deposits of the Yorkshire Dales National Park including caver activity are reviewed. It is concluded that sporting cavers have added greatly to our knowledge of the archaeological record contained in the caves. They appreciate the value of the underground environment and take steps to preserve the cave interior deposits. Any geoconservation strategy that deals with caves must involve the caving community.