Age of Middle Pleistocene fauna and Lower Palaeolithic industries from Kent's Cavern, Devon

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Quaternary Science Reviews 24 (2005) 1243–1252

Age of Middle Pleistocene fauna and Lower Palaeolithic industries from Kent’s Cavern, Devon C.J. Proctora,, P.J. Berridgeb, M.J. Bishopc, D.A. Richardsd, P.L. Smartd a

37 Grenville Avenue, Torquay, Devon TQ2 6DS, UK Colchester Museums, Museum Resource Centre, 14 Ryegate Road, Colchester CO1 1YG c Museum Service, Isle of Wight Council, The Guildhall, High Street, Newport, Isle of Wight PO30 1TY d Department of Geography, University of Bristol, University Road, Bristol BS8 1SS b

Received 16 April 2004; accepted 14 July 2004

Abstract Kent’s Cavern has long been known as potentially among the oldest Palaeolithic sites in the country, with the basal Breccia deposit containing a sparse Lower Palaeolithic industry. The sediment consists of a chaotic clayey conglomerate emplaced as a series of debris flows, which entered the cave via blocked entrances at its southwest end. The Breccia contains a fauna dominated by the bear Ursus deningeri, with lion Felis leo and the voles Arvicola cantiana and Microtus oeconomus, establishing a late Cromerian age for the deposit. The artefacts comprise an industry of crudely manufactured handaxes and flakes, and show damage suggesting that they were brought into the cave by the debris flows, and may thus predate the sediment and fauna. We demonstrate an age of 4340 ka for the Breccia using two independant dating methods, consistent with existing models of the age of the British Middle Pleistocene sequence. r 2004 Elsevier Ltd. All rights reserved.

1. Introduction Kent’s Cavern, in Torquay, Southwest England (NGR SX 934 642), occupies an important position in the British Pleistocene for two reasons. Firstly, the cave is of historical significance as one of the sites at which the antiquity of man was first demonstrated. Secondly, it is a major Palaeolithic site in its own right, having a long Devensian sequence with copious evidence of human occupation, and a much earlier Middle Pleistocene deposit, also with a Palaeolithic industry (Campbell and Sampson, 1971). The cave comprises an extensive network of roughly horizontal passages with a total passage length of 934 m (Fig. 1), lying on the flanks of the dry Ilsham valley and underlying a terrace on the flank of Lincombe Hill, which is a fragment of a much Corresponding author.

E-mail address: [email protected] (C.J. Proctor). 0277-3791/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.quascirev.2004.07.022

more extensive surface (Proctor and Smart, 1989). The site has a long history of at least 15 excavations (Pengelly, 1884; Campbell and Sampson, 1971; Proctor, 1994) but interpretation has been hampered by lack of good stratigraphic data. However, large areas of unexcavated sediment remain, and here we report on recent sampling and dating work which has provided a much firmer sedimentological, biostratigraphic and chronostratigraphic context for the basal deposit, the Breccia, and its associated Lower Palaeolithic industry.

2. The sediments Pengelly (1884) established a basic stratigraphic scheme comprising a sequence (from the base) of Breccia, Crystalline Stalagmite, Cave Earth, Granular Stalagmite and Black Mould. These units have traditionally been portrayed as a simple vertical sequence, but Pengelly’s descriptions show that the sediments were

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Fig. 1. Plan of Kent’s Cavern showing distribution of the Breccia.

very unevenly distributed, with significant differences between the outer (northeast) and inner (southwest) ends of the cave. The presence of further units predating the Breccia has also been proposed (Pengelly, 1884; Campbell and Sampson, 1971) but most are no longer exposed, and in general these have not been sufficiently well mapped and characterised to demonstrate that they are older than the Breccia. A possible exception is a small exposure of sandstone gravel in the Little Oven, which is poorly exposed but by virtue of its position high in the roof might be a remnant of a stream gravel dating from the formation of the cave (Proctor, 1994). Previous workers have not described the sediments in detail; so the cave was resurveyed (Proctor and Smart, 1989) and the surviving sediments were mapped and sampled to determine their distribution, structure and lithology. Standard geological techniques were used to examine field sections and this was supplemented by a series of small (1–2 kg) samples taken from the Long Arcade and Bear’s Den to further characterise the lithology, clast orientation and clast size distribution of the sediment. Detailed results are presented in Proctor (1994). The Breccia is widely distributed in Kent’s Cavern, forming thick sediment bodies sloping gently downward

from the High Level Chamber and the Bear’s Den at the southwest end of the cave (Fig. 1). Numerous sections of the Breccia up to around 2.5 m in thickness survive, although some are preserved only as thin skins of sediment left on the walls after Pengelly’s excavations. The deposit comprises a chaotic, very poorly sorted, matrix supported conglomerate of angular to rounded sandstone, slate and quartz cobbles in a dense clayey matrix. Thick bedding on a 30 cm scale is evident, and is partially defined by discontinuous lenses of laminated clay. Individual beds are generally quite homogeneous, with little or no fabric visible and chaotic or weakly subhorizontal clast orientation. There is significant compositional variation between beds, some of which contain large quantities of angular slate debris. The presence of rounded sandstone, quartz and slate cobbles and the almost total lack of limestone in the sediment shows that the Breccia is an allochthonous deposit derived from an earlier sediment body. In all probability this was alluvium and head from the level terrace overlying the cave, which may represent the former valley floor. The very poor sorting, dense chaotic matrix and form of the sediment body suggests that the Breccia was emplaced as a series of subaerial debris flows. Individual flows were separated by periods of quiescence

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when dewatering and reworking of the matrix by runoff and percolation water led to local ponding and the deposition of the fine grained clay lenses (Proctor, 1994). The Breccia slopes down from three point sources at the southwest end of the cave, with major deposits being derived from the Bear’s Den, the High Level Chamber and a much smaller deposit from the Great Oven (Fig. 1), suggesting that it entered the cave via blocked entrances at these points. This is supported by evidence of significant roof collapse in both the Bear’s Den and High Level Chamber at the locations where the main Breccia flows appear to have entered the cave (Fig. 1). The Breccia is overlain by a thick speleothem floor, the Crystalline Stalagmite, which shows a complex stratigraphy unrecognised by previous workers. Careful mapping of surviving sediment sections around the Bear’s Den (Figs 2–4) shows that the lowest growth layer of Crystalline Stalagmite has been broken up, accompanied by localised reworking of the Breccia to form a lens of sediment overlying the Breccia and broken speleothem close to the blocked entrance in the Bear’s Den. A further growth layer of Crystalline Stalagmite caps this sediment lens (Figs. 3 and 4). Later erosion of the Crystalline Stalagmite and the Breccia

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beneath has occurred in the High Level Chamber, the Long Arcade and the Southwest Chamber (Fig. 1; Proctor, 1994). This erosion probably dates from the start of deposition of the Devensian Cave Earth, which in some areas of the cave has a basal bed of gravel reworked from the Breccia (Proctor, 1994). The Breccia and Crystalline Stalagmite is in turn overlain by a thin deposit of Cave Earth and Granular Stalagmite of Devensian to Holocene age. At the modern North and South Entrances at the northeast end of the cave, the Cave Earth forms thick sediment wedges several metres thick, topped by the Holocene Granular Stalagmite and Black Mould (Campbell and Sampson, 1971; Proctor, 1994).

3. Fauna The Breccia contains a sparse mammal fauna which occurs as poorly preserved bone scattered throughout the sediment, and rich concentrations of much better preserved material near the top of the deposit. Previous work on the fauna has been reviewed by Cook and Jacobi (1998). However, none of these materials had

Fig. 2. Location plan of the Bear’s Den, showing sediment sections and speleothem sample sites.

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Fig. 3. Stratigraphic section of the Bear’s Den area, showing speleothem sample sites.

been examined in recent decades (some not for over a century) and there are problems with the derivation of some of the materials (notably microfauna, which were not systematically collected during the 19th century excavations). Therefore, we searched the museum collections of Breccia fauna to locate as much of the surviving materials as possible, and new collections of microfauna were made from in situ remnants of Breccia in the cave, as well as from sediment samples preserved in museums. All the materials so located was examined and identified to provide a new faunal list and form a more reliable basis for biostratigraphic correlation of the site. The fauna of the Breccia is dominated by the early Middle Pleistocene cave bear Ursus deningeri. Biometric analysis of the Kent’s Cavern U. deningeri shows that it is a late type; the available sample is small, but measurements of the teeth (in particular the M2, M1 and M2) suggest that it is a late form larger than those from sites early in the Cromerian complex, but comparing well with U. deningeri from Westbury–subMendip (Table 1). Similarly, biometric analysis of the cheek teeth excludes the later U. spelaeus; the M1, M2 and M3 teeth in particular are all significantly smaller in the Kent’s Cavern bears than in U spelaeus (Table 1). The only near-complete bear skull recovered from the Breccia (on display at Kent’s Cavern), exhibits classic morphological features associated with U.deningeri,

being relatively shorter in length, and wider across the zygomata than U.spelaeus. This specimen (belonging to a female) is very closely comparable with the classic U. deningeri cranial material from Hundsheim, Austria (Zapfe, 1946). All ages are present including very young animals, demonstrating that the cave was used as a hibernaculum and breeding site. The poor preservation of the bone scattered through the sediment can be attributed to damage during transport by the Breccia debris flows. The rich concentrations of much better preserved bones found near the top of the Breccia represent latest use of the site by the bears after major debris flow activity ceased. The sparse associated fauna includes a very large form of lion Panthera leo, probably referrable to the early Middle Pleistocene P. leo fossilis found at Westbury and other European sites (Table 2). The microfauna comprises the voles Arvicola cantiana and Microtus oeconomus, both of which were recovered from the Breccia during this investigation. Another Middle Pleistocene vole Pitymis gregaloides was also recorded from Kent’s Cavern by Hinton (1926), and another specimen by J.W.Jackson at Bristol City Museum (sp. no. CA 6342) prior to the destruction of the Museum in 1940 by bombing (Jackson, unpub. MS notes in Buxton Museum); the precise context in both cases is not known, but they are likely to have come from the Breccia. A record of scimitar cat, Homotherium latidens

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(Campbell and Sampson, 1971) from the Breccia is erroneous: teeth of this species were found in the overlying Devensian Cave Earth (Pengelly, 1884). Although this species has traditionally been regarded as characteristic of the Early Middle Pleistocene, recent work suggests that Homotherium survived in Northwest Europe until well into the Devensian (Reumer et al., 2003); thus, its presence as an element of the Cave Earth fauna is reasonable. In this context the interesting suggestion by Cook and Jacobi (1998), that the Homotherium teeth were introduced by humans during the Devensian should also be noted. Pengelly (1884) also reported fox and deer from the Breccia. However, we have been unable to locate this material despite extensive searches of the museum collections. They were restricted to areas where the Crystalline Stalagmite had been eroded away from the top of the Breccia and they may represent late intrusions of Devensian or Holocene age.

4. Artefacts

Fig. 4. Sediment section between point A and KC-90-5 in the Bear’s Den, showing Breccia overlain by Crystalline Stalagmite. The location of sample KC-90-5 in a broken slab of the lowest growth layer of Crystalline Stalagmite is arrowed: for further explanation see text and Fig. 3.

Lower Palaeolithic flint and Greensand chert implements are found scattered through the Breccia at Kent’s Cavern. The majority occur in the deposit sloping down from the High Level Chamber, with much smaller numbers in the Bear’s Den and associated passages. Cook and Jacobi (1998) have most recently described the assemblage in a preliminary report related to a more extensive study. Little needs to be added to their interim comments but there is one additional observation and one area of disagreement to consider. Firstly, the assemblage is most commonly referred to in relation to a series of crudely manufactured handaxes but as

Table 1 Comparative lengths of cheek teeth from Pleistocene bears (mm).

P4 M1 M2 P4 M1 M2 M3

Kent’s Cavern Breccia

U. deningeri a Bacton, Cromer forest bed

U. deningeri Mosbach

19.30 ðn ¼ 1Þ 25.1571.22 ðn ¼ 8Þ 43.4973.36 ðn ¼ 8Þ 15.3771.18 ðn ¼ 3Þ 28.8471.92 ðn ¼ 7Þ 28.2171.37 ðn ¼ 12Þ 24.470.83 ðn ¼ 7Þ

17.95 ðn ¼ 2Þ 25.2470.74 ðn ¼ 5Þ 37.471.71 ðn ¼ 6Þ 14.6671.01 ðn ¼ 15Þ 26.0371.01 ðn ¼ 13Þ 26.471.44 ðn ¼ 13Þ 23.673.3 ðn ¼ 9Þ

18.4671.17 ðn ¼ 26Þ 25.8571.63 ðn ¼ 46Þ 41.272.89 ðn ¼ 52Þ 15.1571.36 ðn ¼ 51Þ 27.0471.56 ðn ¼ 36Þ 27.7471.72 ðn ¼ 67Þ 24.1271.96 ðn ¼ 49Þ

Measurements are given as mean and standard deviation. a Data from Kurten and Poulianos (1981). b Data from Bishop (1982). c Data from Prat and Thibault (1976).

b

U. deningeri b Westbury-sub-Mendip

U. spelaeus

19.0071.18 ðn ¼ 51Þ 26.2271.5 ðn ¼ 52Þ 42.473.95 ðn ¼ 56Þ 15.271.12 ðn ¼ 54Þ 27.8571.52 ðn ¼ 46Þ 28.2471.92 ðn ¼ 95Þ 24.7772.35 ðn ¼ 129Þ

20.5771.65 ðn ¼ 89Þ 29.1371.68 ðn ¼ 90Þ 44.9572.81 ðn ¼ 75Þ 15.3871.36 ðn ¼ 101Þ 30.7971.69 ðn ¼ 83Þ 30.6971.85 ðn ¼ 116Þ 27.2871.95 ðn ¼ 66Þ

c

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Table 2 Comparative lengths of P3 and P4 teeth in Pleistocene lions (mm)

Length P

4

Length P3 a

Kent’s Cavern Breccia

Panthera leo fossilis

43.1 ðn ¼ 1Þ 30.0 ðn ¼ 1Þ

36.4–45.1 mean 39.9 ðn ¼ 6Þ 23.8–29.3 mean 26.7 ðn ¼ 3Þ

a

Early Middle Pleistocene

Panthera leo spelaea

a

Upper Pleistocene

35.5–41.4 mean 39.3 ðn ¼ 9Þ 25.4–28.6 mean 26.5 ðn ¼ 8Þ

Data from Schutt (1969).

of the artefacts shows that this is not the case. While it is true that the majority fit within a middle range, there are artefacts that clearly fall either side of this with several that are in relatively fresh condition with only limited signs of abrasion (such as a flint core, Pengelly number 6137). It is also true that the handaxes are generally much more poorly preserved than the flakes; many of them show evidence of rolling in a fluvial environment and extensive rotting of the flint and some are also heavily stained with Fe–Mn oxides. There is no evidence of occupation sites within the cave, which together with the scattered distribution of the artefacts throughout the Breccia suggests that all the implements were introduced into the cave by the debris flows and must therefore predate the Breccia and the overlying Crystalline Stalagmite. The condition of the handaxes implies that they may have lain on the surface for some time before their emplacement into the cave (Cook and Jacobi, 1998).

5. Age of the deposits

Fig. 5. Artefacts from the Breccia, 6022, 7323; handaxes, 7040, 7059; flaked flakes.

noted particularly by Cook and Jacobi it is more extensive than this with the largest component consisting of a range of flakes. The additional observation to make about these is the presence of a small number of ‘flaked flakes’, an artefact type now recognised among a number of Lower Palaeolithic assemblages in Southern Britain (e.g. Ashton et al., 1991). Two such flakes are illustrated in Fig. 5. Cook and Jacobi also state that the artefacts are fairly uniformly abraded but examination

Speleothem samples from the Crystalline Stalagmite floor were collected from several sites within the cave (Figs. 2–4) and dated using the 230Th/234U uranium series and electron spin resonance (ESR) methods (Schwarcz, 1980; Edwards et al., 1987; Smith et al., 1986). Alpha spectrometric uranium series (ASU) analysis was carried out on 12 samples. Most show 232 Th/230Th ratios 420 indicating that detrital contamination was not significant. Three samples showed minor detrital contamination, corrected for using method 1 (Equation 8) of Schwarcz (1980): in all cases the correction was well under the 1 standard deviation counting error (Table 3). As an independant check on the ages obtained, ESR dating was also undertaken. Standard techniques were used (Smith et al., 1986; Smart et al., 1988): due to sampling constraints, dosimetry could not be carried out at the exact sample sites; so CaSO4:Dy thermoluminescence dosimeters were instead placed nearby in equivalent stratigraphic positions. The outer layers of the speleothem were removed to eliminate external alpha

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Table 3 Alpha spectrometric uranium series analyses from the Crystalline Stalagmite in Kent’s Cavern. U (mg g1)

Sample (a) Basal growth KC3-83B1 KC3-83B2 KC-90-2AB KC-90-2D1 KC-90-3A KC-90-3B KC-90-5B1 KC-90-5B2 KC2-83B1

(234U/238U)act

layer of Crystalline Stalagmite 0.039 1.10170.020 0.036 1.09970.014 0.044 1.07470.015 0.043 1.07570.015 0.017 1.14270.018 0.017 1.14670.019 0.092 1.19970.037 0.064 1.13570.012 0.042 1.07070.022

(b) Higher growth layers of Crystalline Stalagmite KC-90-4A2 0.031 1.15870.025 KC4-83B 0.045 1.29670.033 KC4-83C 0.047 1.34170.018

(230Th/234U)act

(230Th/232Th)act

Age, uncorrected (ka)

Age, corrected (ka)

0.99270.038 0.99170.017 1.02170.028 1.00270.021 0.98470.026 1.06270.020 0.94470.035 1.00070.027 0.94770.037

27.675.3 39.772.4 28.673.0 23.771.3 12.170.9 21.171.0 17.070.4 25.872.0 36.077.9

355 355 550 410 318 N 253 354 286

— — — — 311 (267384) — 247 (214297) — —

0.88870.040 0.88270.016 0.67770.012

56.6720.0 61.678.0 25.071.4

213 (186249) 198 (175228) 115 (111119)

— — —

(280698) (312427) (368N)* (337723)* (275391) (484N)* (219303) (299468) (240373)

Analytical errors and age ranges are 1 standard deviation of the mean. * Marks analyses considered to be unreliable due to recrystallisation of the speleothem.

Table 4 Mass-spectrometric uranium-series analyses from Kent’s Cavern. Sample

238

(234U/238U)act

(230Th/238U)act

(230Th/232Th)act

Age, uncorrected (ka)

Age, corrected (ka)

KC2-83 KC3-83 KC-98-1

31.9 39.4 51.6

1.07770.002 1.11570.002 1.15070.003

1.04770.009 1.10570.006 1.22070.011

6.0 20.2 1300

326 (310–344) 345 (334–358) 4495

310 (293–329) 341 (329–354) 4495

U (ng g1)

Analytical errors are 2 standard deviations of the mean, ages are quoted at 95% confidence intervals. [230Th/238U]activity ¼ 1el230T+(d234Umeasured/ 1000)[l230/(l230l234)](1e(l230 l234) T), where T is the age. Decay constants are 9.195  106 yr1 for 230Th, 2.835  106 yr1 for 234U, and 1.55125  1010 yr1 for 238U (Cheng et al., 2000). The degree of detrital 230Th contamination is indicated by the measured [230Th/232Th] activity ratio. Age corrections were calculated using an average crustal Th/U ¼ 3.8.

and beta radiation, and the measurements of Debenham and Aitken (1984) used to correct for attenuation of the external gamma dose by the speleothem calcite. The internal alpha, beta and gamma doses were calculated from measurements of the uranium concentration and the 234U/238U and 230Th /234U activity ratios provided by the uranium series analyses, with a correction for the speleothem size applied to the gamma dose (Table 4). To correct for changes in the internal dose due to ingrowth of daughter isotopes with time, an iterative procedure was used to calculate the internal dose and the ESR age. Two speleothems (KC-90-2 and KC-90-3b) showed considerable differences between the ESR and ASU ages obtained. In each case anomalously low ESR ages and high ASU ages suggested that they had recrystallised, a conclusion supported by the position of both samples below weathered growth hiatuses in the speleothems. This is supported by a negative calculated internal dose for one of the KC-90-2 ESR analyses (Table 5) showing that the iterative method used to calculate the internal dose has failed (the method works on the assumption that the sample starts with an equivalent dose of 0 and 230Th/234U activity ratio of 0

simultaneously, which is not the case for a recrystallised speleothem). Thus, the ages obtained from these samples are likely to be unreliable and they are rejected. The remaining samples gave very good agreement between the ESR and ASU ages (Tables 3 and 5). The basal growth layer of the Crystalline Stalagmite yielded ASU ages ranging from 247 to 355 ka. Because the ages lie near the limit of ASU dating and the relation between age and isotope ratios is exponential in form, we calculate a log mean age of 315+16/19 ka (1 standard error of mean) for the speleothem. ESR analyses on the same samples show a range of 225–363 ka, yielding a mean age of 306724 ka (1 standard error of mean), in excellent agreement with the ASU result. ASU analyses from higher in the Crystalline Stalagmite, above the break up and Breccia remobilisation event, yield ages of 213–110 ka. Two samples from the basal growth layer of the Crystalline Stalagmite floor were also dated using thermal ionisation mass-spectrometric uranium series (TIMS) analysis, the higher analytical precision of which may more reliably constrain the determined ages. This yielded age estimates of 341+13/12 and 310+19/17 ka (Table 4,

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Table 5 ESR analyses from the basal growth layer of the Crystalline Stalagmite Kent’s Cavern. Sample

U (mg g1)

Accumulated dose (Gy)

External dose rate (mGy a1)

Internal dose (Gy)

Age (ka)

KC3-83B2 KC-90-2AB KC-90-2AB KC-90-3A KC-90-3A KC-90-3B KC-90-5B1 KC-90-5B2

0.036 0.044 0.044 0.017 0.017 0.017 0.092 0.064

81.972.9 90.0713.6 87.576.8 181718 229728 192717 229722 184716

0.50870.099 1.13070.09 0.96470.080 0.43270.075 0.50870.088 0.70170.121 0.59770.103 0.43270.075

2.37 0.27 0.15 5.53 6.19 3.08 25.6 19.1

157 80 91 405 439 270 340 382

(1.42–3.76) (.91–0.48) (.35–0.74) (3.84–8.09) (4.15–9.36) (2.03–4.62) (18.1–36.1) (13.8–26.5)

(128–198) (63–99)* (78–106)* (313–533) (330–591) (211–354) (270–434) (305–485)

Analytical errors and age ranges are 1 standard deviation of the mean. * Marks analyses considered unreliable due to recrystallisation of speleothem.

errors are 2 standard deviation), confirming the validity of the ASU and ESR results. All these ages provide a minimum age for the bulk of the Breccia and its associated fauna. A detrital speleothem block from near the top of the Breccia, KC-98-1, was also TIMS dated yielding an age of 4495 ka. Such detrital blocks have the potential to provide a maximum age for the deposit; unfortunately, as only a minimum age was obtained this was not possible here.

6. Discussion The presence of U. deningeri and perhaps Pitymys gregaloides implies a pre-Anglian Early Middle Pleistocene age for the fauna as U. deningeri was replaced by U.spelaeus following the Anglian Glaciation in Britain (Schreve, 2001a) and P. gregaloides became extinct at this time. The late Early Middle Pleistocene age suggested for the Kent’s Cavern U. deningeri by the biometric analysis is confirmed by the presence of A. cantiana, which replaces the extinct water vole Mimomys savini late in the Early Middle Pleistocene (Stuart and Lister, 2001). Similar late Early Middle Pleistocene A. cantiana faunas are now known from several British sites including Westbury–sub-Mendip, Ostend and Boxgrove (Bishop, 1982; Currant, 1989; Roberts, 1986; Roberts et al., 1994; Roberts and Parfitt, 1999; Stringer et al., 1996; Stuart and West, 1976; Stuart and Lister, 2001). At Ostend, the deposit underlies Anglian till demonstrating that these A. cantiana faunas predate the Anglian Glaciation (Stuart and West, 1976). Comparison with the more complete Netherlands sequence suggests a correlation late in the Netherlands ‘‘Cromerian Complex’’ (Meijer and Preece, 1996; Zagwijn, 1996; Stuart and Lister, 2001). The implements from Kent’s Cavern are notably cruder than Lower Palaeolithic artefacts elsewhere in Britain and these typological differences have been used to suggest that they represent an extremely early industry (Roe, 1981). However, the faunal correlation

now established suggests that while the Breccia is indeed early, the site fits into a pattern of pre-Anglian human presence in Britain mostly notably represented by Boxgrove (Roberts, 1986; Roberts et al., 1994; Roberts and Parfitt, 1999), where a much more sophisticated industry is present. As the implements in the Breccia are clearly derived they could conceivably substantially predate the deposit; however, a more prosaic explanation for their crudity may lie in the low quality of the locally available raw material. At Boxgrove, highquality fresh flint was readily available from the Chalk cliff backing the site (Roberts, 1986). At Kent’s Cavern by contrast, the nearest Chalk exposures lie over 30 km away and locally available beach flint and Greensand chert were used instead, both low-quality raw materials when compared to fresh flint. Thus, the crudity of the industry may be the result of poor-quality raw material, rather than a lack of sophistication in the people who made them. Nonetheless, given that the industry is in a derived context it might substantially predate the emplacement into the cave and the associated fauna, implying that it might also predate sites such as Boxgrove (Cook and Jacobi, 1998). All the dating techniques yield similar ages for the basal growth layer of the Crystalline Stalagmite: TIMS ages of 341+13/12 ka and 310+19/17 ka, a mean ASU age of 315+16/19 ka and mean ESR age of 306724 ka. This suggests that its growth commenced during marine oxygen isotope stage (OIS) 9 (Bassinot et al., 1994), with ASU ages from higher in the floor suggesting that growth continued through OIS 7 and 5. The best constraint on the age of the speleothem is provided by the TIMS ages. The mass spectrometric uranium series age of 341+13/12 ka, from the base of the floor immediately overlying bear bones, suggests growth began at the start of OIS 9: this is supported by the second age of 310+19/17 ka which was obtained some distance above the base of the floor (Fig. 3). These provide a minimum age for the underlying Breccia, which must therefore date from OIS 10 or earlier. The third mass spectrometric uranium series age, of

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4495 ka, from a detrital stalagmite fragment recovered from near the top of the Breccia, unfortunately does not further constrain the age of the deposit. However, it does provide a minimum age for formation and drainage of the cave prior to emplacement of the Breccia and is thus a useful addition to our understanding of the site as a whole. The age of 4341+13/12 ka provided by the older of the TIMS analyses provides a robust minimum age for the Kent’s Cavern Breccia and its fauna as the Crystalline Stalagmite dated can be securely demonstrated to overlie the Breccia fauna, and because two independent dating techniques have yielded similar results on a material (clean, crystalline speleothem) which generally shows the closed-system behaviour necessary for accurate dates to be obtained (Smart, 1991). This result is consistent with the widely suggested correlation of the Anglian Glaciation with OIS 12 (e.g. Bowen, 1999; Bridgland, 1994; Schreve, 2001a, b). However, it should be noted that Zagwijn (1996) suggests a correlation of Anglian’s continental European correlative the Elsterian with OIS 10 which may have been a glaciation of comparable severity to OIS 12 (Bassinot et al., 1994; Shackleton et al., 1990), and this would also be in line with the Kent’s Cavern Breccia dates. The Anglian Glaciation represents the most widely recognised stratigraphic event in the British Middle Pleistocene, but its age and correlation with the marine oxygen isotope record has yet to be conclusively resolved. Both before and after the Anglian, disagreement about the correlation of individual sites and the nature and timing of climatic events is widespread (e.g. Bridgland, 1994; Gibbard, 1999; Lewis, 1999; Schreve, 2001a, b). The complex lithostratigraphy and biostratigraphy reported for long river terrace sequences in the Thames by Bridgland (1994) and Schreve (2001a, b) certainly hint at an early (OIS 12) date for the Anglian, although even here the stratigraphy is disputed (Gibbard, 1999) and in any case correlation with the marine oxygen isotope record remains highly problematic due to the presence of complex climatic fluctuations within each single isotope stage. Likewise, aminostratigraphy provides a relative dating tool but cannot be used to correlate terrestrial sites with the marine oxygen isotope record; indeed its use to differentiate Middle Pleistocene interglacials remains controversial (McCarroll, 2002). Thus, it is necessary to seek further numerical ages for Middle Pleistocene sites to resolve this issue. Radiometric and radiogenic dating of open Middle Pleistocene sites in Britain has had mixed success with conflicting results attributable largely to the scarcity of suitable dateable materials and due to persistent problems with major detrital contamination and open system behaviour which make it difficult to obtain accurate ages. Attempts to date interglacial sites immediately overlying Anglian tills have produced mixed results. Some are

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consistent with an OIS 10 Anglian model (Gladfelter et al., 1993; Rink et al.,1996; Rowe et al., 1997; Schwarcz and Grun, 1993). However, recalculation of ESR ages for the interglacial site at Hoxne previously reported by Schwarcz and Grun (1993) has yielded results suggesting an OIS 11 age more consistent with an OIS 12 Anglian (Grun and Schwarcz, 2000). Other recent work has also yielded ages supporting the OIS 12 Anglian model (Preece et al., 2000; Rowe et al., 1999). Clearly, further work is still needed to test these competing correlations of the terrestrial Middle Pleistocene sequence with the marine oxygen isotope record. Given the reliability of mass spectrometric uranium series dating of speleothem, further work in Kent’s Cavern and similar Cave sites has great potential for further progress in this field.

Acknowledgements The authors wish to thank Kent’s Cavern Ltd. for permission to work at the site and for their tolerance of our sometimes disruptive activities. We also thank Chuck Borton for help with MSU analyses, Martyn Symons, Nick Debenham and Ian Podmore for help with ESR analyses, Simon Godden for drawing some of the diagrams and Andy Currant and Allan Straw for discussion. Thanks also to Allan Straw and Chris Caseldine for permitting us to process sediment samples at Exeter University Geography Department. Chris Proctor was in receipt of NERC training award no. GT4/88/GS/122 during the period of this research.

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