Pleistocene depositional history in a periglacial terrane...

For permission to copy, contact [email protected]© 2007 Geological Society of America

199

Geosphere; August 2007; v. 3; no. 4; p. 199–219; doi: 10.1130/GES00085.1; 19 fi gures; 3 tables.

ABSTRACT

The signifi cance of the stratigraphic record in Kents Cavern, Devon, United Kingdom, to the interpretation of the British Quaternary is confi rmed on the basis of a thorough reex-amination of the deposits in concert with 2 new Al-Be cosmogenic and 34 new thermal ionization mass spectrometry U-Th dates. The deposits show evidence of complex reworking in response to periglaciation, and the main fl owstone deposit is a multilayered complex spanning marine isotope stage (MIS) 11–3. The lowermost unit of fl uvial sands is Cromerian or older. The second deposit, a muddy breccia of surfi cial periglacial solifl uc-tion material containing Acheulian artifacts, entered the cave during MIS 12 from high-level openings to the west. Cave bears denned in the cave during MIS 11, the Hoxnian inter-glacial; their bones are capped by an MIS 11 calcite fl owstone layer. From MIS 11 onward, each interglacial period and the warmer interstadial periods (MIS 11, 10b, 9, 7, 6b, 5, and 3) produced calcite fl owstone deposition in the cave; MIS 9 was particularly active. Each glacial or stadial period (MIS 10c, 10a, 8, 6c, 6a, 4, and 2) caused periglacial activity in the cave, during which the thinner layers of calcite were fractured by frost heave and redistributed by solifl uction. This sequence was interrupted during MIS 3–2 with the introduction of sandy and stony clastic sedi-ments from entrances to the east, and fi nally cemented by the uppermost layer of MIS 1 fl owstone. This is the fi rst publication of well-dated and clearly documented evidence of frost heaving in interior cave passages. The Kents Cavern record of continuous, repeated sedimentation events followed by frost shat-tering and remobilization events over the

past 500 k.y. is probably unique in the karst literature and establishes Kents Cavern as a site of international scientifi c interest.

Keywords: Kents Cavern, middle Pleisto-cene, Britain, cave bear, interglacial, MIS 11, Hoxnian, speleothem, periglacial, Acheulian, cave sediment.

INTRODUCTION

Kents Cavern, Torquay, Devon, UK (NGR SX 934 642, Fig. 1), has been a focus of scien-tifi c interest for at least the past two centuries. The extraordinarily rich record of Pleistocene mammals and human artifacts has focused interest on the paleontology and archaeology of the site (e.g., MacEnery, 1859; Pengelly, 1869, 1884; Campbell and Sampson, 1971; Cook and Jacobi, 1998), while the sedimento-logical, climatological, and geomorphological

information in the deposits has largely been ignored. Here we focus on the reconstruction of the Pleistocene depositional events of the past 500 k.y. that are recorded in this inter nationally important site.

The south Devon karst is one of the few limestone areas in Britain that was not directly affected by the Pleistocene ice sheets. Deposi-tion of both clastic and crystalline material in the cave was abundant, such that much of the site was barely accessible to early explorers (MacEnery, 1859). The fi rst systematic excava-tions began in the early 1800s; since then, the deposits have mostly been removed from the cave so that the cavity now exposed is consid-erably larger than that accessible in the early nineteenth century. The major excavation was carried out in 1868–1880 by W. Pengelly (see reconstruction of Pengelly’s excavations in McFarlane and Lundberg, 2005). MacEnery (1859) and Pengelly (1884) described the basic

*[email protected]†[email protected]

Pleistocene depositional history in a periglacial terrane: A 500 k.y. record from Kents Cavern, Devon, United Kingdom

Joyce Lundberg*Department of Geography and Environmental Studies, Carleton University, Ottawa ON K1S 5B6, Canada

Donald A. McFarlane†

W.M. Keck Science Center, The Claremont Colleges, 925 North Mills Avenue, Claremont, California 91711, USA

1 km

Tor Bay

Kents Cavern

BabbacombeBay

PAIGNTON

TORQUAY Hope’sNose

N

Berry Head

B100 km

Anglian glaciallimit: MIS 12

Devensian glaciallimit: MIS 2

Kents CavernTorquay

A

Bristol Channel

S. WALES

English Channel

S. W. ENGLAND

3 W

51 N

Figure 1. (A) Location of Kents Cavern, southwest England, in relation to the glacial limits for the Devensian, MIS 2, and the Anglian, MIS 12, glaciations (glacial limits after Culling-ford, 1982; Croot and Griffi ths, 2001). (B) Location of Kents Cavern at the northern end of the town of Torquay, and outcrops of Torquay limestone in the region (shaded areas; after Scrivener, 1987).

Lundberg and McFarlane

200 Geosphere, August 2007

sedimentological sequence, from oldest to youngest, as Breccia, Crystalline Stalagmite, Loamy Cave Earth, Stony Cave Earth, Granu-lar Stalagmite, and Black Mold, and these terms have been retained by later workers. While this stratigraphy appears to be adequate for the 14C dated material, the clastic deposits, and the upper parts of the calcite (Fig. 2; Oxford Radio-carbon Accelerator Unit, 2006), it is insuffi -cient to describe the Crystalline Stalagmite and hides a wealth of complexity. Proctor (1994) expended considerable effort to date the calcites by uranium series disequilibrium alpha count-ing (alpha U-Th) and by electron spin resonance (ESR), and continued this simple designation, with some minor variations. Proctor et al. (2005) added three thermal ionization mass spectro-metric U-Th (TIMS U-Th) dates to the data set in an attempt to clarify the interpretation of the lowermost unit, the Breccia.

Improvements in the technology of both U-Th dating and the development of cosmo-genic isotope dating for cave sediments now allow a more defi nitive dating of the older calcite and clastic deposits. The aim of this study is twofold: fi rst, we clarify the deposi-tional sequence and its paleoenvironmental context based on 34 new, high-precision TIMS

U-Th dates; second, we present the fi rst direct radiometric dates on the Breccia and its ante-cedent stratum, providing a well-supported time window for the middle Pleistocene fauna and human artifacts from the cave.

Geological Background

The geological setting was described by Dur-rance and Laming (1982) and Scrivener (1987). The cave is developed in the Middle–Upper Devonian Torquay Limestone (Fig. 1B). The underlying Nordon Slate is a gray, well-cleaved, calcareous mudstone with some bands of slaty limestone. This gives way to a complex of vol-canic tuff, agglomerate, and lava interspersed with limestone, much of which is reefal in struc-ture; the whole unit is designated as the Torquay Limestone. The overlying Upper Devonian Gurrington Slate is a gray-green and purple mudstone. These rocks were severely fractured and folded by the Variscan orogeny ca. 300 Ma. New Red Sandstones of Permian age uncon-formably overlie the uplifted and eroded post-orogenic surface. The Devonian rocks generally show substantial weathering underneath the sandstone beds.

Many relatively small caves have formed in the Torquay Limestone; Kents Cavern is the third largest, with <1 km of mapped pas-sages. Kents Cavern preserves evidence of both phreatic and vadose activity, but phreatic features generally dominate. The cave prob-ably formed in the early Pleistocene, but speleo-

genesis may have involved some rejuvenation of late Carboniferous–Permian paleokarstic features (Campbell et al., 1998b). The geomor-phological and hydrologic setting must have been different during speleogenesis, because the modern catchment for Kents Cavern, set high on a small hillside, is too small to provide substan-tial volumes of water.

The Quaternary deposits in the region include raised beach deposits, river terrace gravels, and periglacial deposits (Campbell et al., 1998a). The ice sheets of the Quaternary glaciations did not reach the Torquay district, but peri glacial conditions were widespread during glacial periods (Cullingford, 1982). The two glacial ice sheets that came closest to Kents Cavern were the last, during marine isotope stage (MIS) 2, the Devensian, peaking ca. 20 ka, and MIS 12, the Anglian, ca. 430 ka (Fig. 1A). Periglaciation triggered extensive frost action and produced thick periglacial slope deposits or solifl uction deposits (locally called “head”). The slates and mudstones were particularly susceptible to frost action and resulted in thicker than average head deposits (some sections documented as >20 m thick; Cullingford, 1982).

METHODS

Sampling (Fig. 3) was undertaken with the support and cooperation of the cave owner and under permit from English Nature. Particular care and attention was paid to environmental impact, and the work was completed with mini-

0

5

10

15

20

25

30

35

40

45

C-1

4ag

e(k

a)

GranularStalagmite

Cave Earth

MIS

1M

IS2

MIS

3

Figure 2. The distribution of 14C dates on artifacts from the Cave Earth and Granular Stalagmite (Oxford Radiocarbon Accelera-tor Unit, 2006) arranged in order of age for each type of material. The dates fi t into two clearly separated populations. The Cave Earth dates are between ca. 22 and 40 ka (MIS 3), and the Granular Stalagmite dates are between ca. 4 and 16 ka (MIS 1 and late MIS 2). This second set of dates is largely on bones cemented into the base of the fl ow-stone and thus is biased toward the begin-ning of deposition of the fl owstone.

30 m

N

NorthEntrance

SouthEntrance

SouthwestChamber

Long

arca

deRockyChamber

Clinnick’s Gallery

Swallow Hole Gallery

Hedges Boss

Bear’s DenLabyrinth

InscribedBoss

In-Between Boss

High Level Chamber

Gallery

Cave of Rodentia

South Sally Port

NorthSallyPort

CharcoalCave

Vestibule

Lake

Water Gallery

Wolf’sCave

Bear’s Den Boss

Terminal Chamber

Kents Cavern,Torquay, Devon

Figure 3. Sampling sites and names of main passages in Kents Cavern. Outline survey is based on Proctor and Smart (1989), with modifi cations.

Kents Cavern Pleistocene History

Geosphere, August 2007 201

mal or no visible trace. Samples were taken of calcite that had already been damaged by historic blasting and excavations. In order to minimize the collection of undatable specimens, all poten-tial sites were examined in the fi eld for evidence of open-system behavior such as vugs, hiatuses, loose or friable or random fabric, recrystalliza-tion, or dissolution. Sample sites were recorded on site using photographs and photographic mosaics. In view of the complicated stratigraphy and in order to avoid subsequent misinterpreta-tion of photographs, sequences were logged and photographs annotated in the cave using a por-table computer.

26Al-10Be Dating

Recent advances in dating cave sediments have achieved considerable success with 26Al-10Be dating of buried quartz (Granger et al., 2001; Anthony and Granger, 2004). Cosmic ray sec-ondary neutron bombardment of exposed or superfi cially buried quartz generates 26Al from silicon atoms and 10Be from oxygen atoms in a constant ratio of ~6:1, regardless of absolute dose. After transport and burial in a cave, these nuclides decay at differing rates (half-lives: 26Al = 1.02 Ma; 10Be = 1.93 Ma), causing a shift in the nuclide ratio that can be used to date sedi-ment burial ages in the range of ca. 100 ka to 5 Ma (Granger and Muzikar, 2001). Two mate-rials were chosen as potentially amenable to this technique (Table 1): the quartz sand from the basal Red Sands of the Gallery (cf. Camp-bell and Sampson, 1971) and quartz pebbles from the exposed Breccia in the Bear’s Den and Labyrinth areas. Samples were prepared and analyzed at the Purdue Rare Isotope laboratory, Purdue University.

U-Th Dating

The calcite samples were dated by standard U-Th disequilibrium techniques (e.g., Ivano vich and Harmon, 1992). Specimens were sliced into 2-mm-thick slivers and examined under a binocular microscope with back lighting. Only the cleanest parts were used for dating. All

visible traces of detritus, vugs, or intercrystal-lite voids were removed with a dentist’s drill under the microscope. The very low U content (0.05 ± 0.02 ppm) dictated the use of relatively large sample sizes (~2 g). Samples (n = 45) were ultrasonically cleaned, ignited for 5 h at 875 °C to remove organics, dissolved in HNO

3 and

spiked with 233U-236U-229Th tracer. Apart from the samples chosen for isochron dating (see follow-ing), no sample showed visible detrital contami-nation. U and Th were coprecipitated with iron hydroxide, and purifi ed twice on anion exchange columns (Dowex AG1-X 200–400 mesh).

Measurement of U and Th isotopic ratios was mainly done with TIMS, 14 using the VG 354 TIMS at McMaster University, Hamil-ton, Ontario, and 19 using the Triton TIMS at the Isotope Geochemistry and Geochronology Research Centre, Carleton University, Ottawa, Ontario. The 8 samples for isochron dating and 4 repeats were measured using the multi-collector inductively coupled mass spectrometer (MC-ICP-MS) at Géotop, University of Quebec at Montreal, Quebec. Each suite of measure-ments was accompanied by the processing of uraninite in secular equilibrium to ensure accu-rate spike calibration and fractionation correc-tion. Precision of isotopic ratio measurement is limited by extremely low U content and by high 232Th content. The typical 2σ error of the TIMS measurement of 234U/238U is 0.12% and of 230Th/234U is 0.46% (TIMS instrumental repro-ducibility on spiked uraninite standards is 0.06% for 234U/238U and 0.11% for 230Th/234U). The pre-cision on the resultant ages varies with age; the average 2σ precision on these mid-Pleistocene dates is 2.2% (Table 2).

Three of the hand specimens were sampled twice. CDF and B20 were measured on the McMaster TIMS and CDF2 and B20R on the Géotop MC-ICP-MS. The coincidence of the numbers (within 2σ) suggests that isotopic measure ments on TIMS and ICP are com patible. Samples CEB and CEBR were not from the same section of hand specimen: CEBR was deliber-ately chosen from a different part in the hope that it would not be leached. Similarly, LOBO and LOAN were deliberately chosen from dif-

ferent parts of the hand specimen because they had visible detrital contamination.

Two of the samples with highest detrital thorium concentration, SW1-O and LB-O, were sampled 4–6 times for isochron dating (Schwarcz and Latham, 1989; Ivanovich et al., 1992); each subsample was chosen for its vis-ibly differing detrital content. The principle of isochron dating is that the subsamples are depos-ited at the same time but with differing amounts of detrital contamination. The carbonate frac-tion 230Th is presumed to be constant for all sub-samples, but the detrital fraction 230Th varies; 232Th is used as an index of detrital content. The slope of the regression line of 234U/232Th against 238U/232Th gives the 234U/238U, and the slope of 230Th/232Th against 234U/232Th gives 230Th/234U at zero detrital contamination (Fig. 4). These ratios are then used to calculate the isochron age.

A 230Th/232Th ratio of <20 is normally consid-ered to indicate detritally contaminated material (e.g., Schwarcz and Blackwell, 1992). However, isochron dating is prohibitively expensive for many samples. A simplistic way to adjust the 230Th/234U to account for detrital contamination is to estimate an initial 230Th/232Th activity ratio for the detrital fraction. For example, Kaufman and Broecker (1965) used a value of 1.7 from measure-ment of modern detritus. In our case the sample SWO had an age of 183 ka, but a 230Th /232Th ratio of 3. It was then dated by isochron on another four fractions (SW1-O) to 152 –30/+45 ka. If this is taken as the more correct age, then the 230Th/234U ratio for SWO can be adjusted to give an age of 152 ka using an initial 230Th/232Th ratio of 1.00. This estimate for initial 230Th/232Th was then used for all the samples with a 230Th/232Th ratio of <20. It is clearly only an approxima-tion, but is an improvement over the alternate practice of simply using a standard value. If the estimated initial 230Th/232Th ratio is low, and/or if the measured 230Th/232Th ratio is high, the adjust-ment does not alter the original date.

In Table 2, the age for the samples with detrital contamination is shown fi rst as the simple calculated age; beside it in parenthe-ses is the adjusted age; the age used is high-lighted in bold. In most cases, the adjusted age

TABLE 1. DATA FROM 26Al/10Be ANALYSES OF SANDS FROM GALLERY AND QUARTZ CLASTS FROM BRECCIA IN LABYRINTH AND BEAR’S DEN

Sample Mass (g)

Be(mg)

Al(mg)

10Be/9Be±1σ

26Al/27Al±1σ

10Be(at/g)±1σ

26Al (at/g) ±1σ

26Al/10Be±1σ

Burial Age (Ma)±1σ

Gallery sand 12.1 0.755 7.26 51± 4

34± 14

163,920± 14,610

386,726± 210,621

2.36± 1.30

2.32± 1.74

Breccia quartz 40.0 0.695 5.51 93± 8

14± 26

94,878± 8388

420,568± 87,379

4.43± 1.00

0.95± 0.55

Note: Ratios are shown as atomic ratios with 1σ error.


TABLE 2. DATA FROM U-Th ANALYSES OF CALCITES

SampleAge(ka) +2σ –2σ U

(ppm)Th

(ppm)

230Th/234U±2σ

234U/238U±2σ

230Th/232Th ±2σ

234U/238U initial±2σ

G2TR † 47.4 (20.0) 3.1 3.0 0.037 0.623 0.356(18) 1.192(13) 1.6(1) 1.22(1) G2BW † 79.5 2.6 2.5 0.031 0.028 0.523(11) 1.118(10) 41.1(8) 1.15(1) CAT † 80.2 0.8 0.8 0.042 0.055 0.524(3) 1.082(4) 27.5(2) 1.103(4) CBN † 93.3 1.9 1.8 0.060 0.050 0.582(7) 1.129(3) 49.9(7) 1.167(3) CCT † 94.6 (91.0) 4.0 3.9 0.030 0.070 0.588(15) 1.130(5) 17.9(5) 1.169(5) CDF † 148.2 9.5 8.7 0.044 0.097 0.757(21) 1.116(12) 24.1(6) 1.18(1) CDF2 # 150.4 5.0 4.8 0.044 0.099 0.763(12) 1.121(2) 23.9(4) 1.185(2) CEB † Leached 0.042 0.029 1.63(5) 1.084(3) 161(5) CEBR # Leached 0.038 0.230 1.21(1) 0.955(1) 16.1(2) B20 † 210 2 2 0.078 0.010 0.985(4) 2.705(8) 1274(6) 4.08(1) B20R # 197 8 8 0.067 0.027 0.960(18) 2.752(1) 531(11) 4.057(1) WUXU † 417 104 52 0.051 0.026 0.996(12) 1.053(10) 130(1) 1.17(1) WTXT † 132 6 6 0.046 0.114 0.713(16) 1.105(13) 20.3(4) 1.15(1) WTXT2 # 150 6 6 0.047 0.114 0.759(15) 1.086(2) 21.0(4) 1.131(2) LA6R † 1.2 (–2.8) 0.2 0.2 0.048 0.323 0.011(2) 1.257(4) 0.3(1) 1.258(4) BD1 § 326 7 7 0.036 0.271 0.981(3) 1.111(1) 29.9(2) 1.279(2) BD2 § 439 (432) 23 19 0.018 0.334 1.029(4) 1.144(2) 14.0(1) 1.498(2) CGTB § 193.3 1.5 1.4 0.040 0.267 0.857(2) 1.169(1) 40.3(2) 1.291(1) CICD § 131 (100) 3 3 0.027 1.400 0.716(8) 1.169(2) 2.73(4) 1.246(2) CIE2 § 239 (220) 4 3 0.050 2.648 0.909(3) 1.094(3) 5.18(3) 1.185(3) CIF § 310 6 6 0.045 0.331 0.978(3) 1.140(1) 36.4(2) 1.336(1) CIG § 312 10 9 0.042 0.362 0.985(5) 1.161(1) 34.3(2) 1.389(2) CIH § 289 (273) 20 17 0.027 1.093 0.966(14) 1.147(1) 5.9(1) 1.332(2) HB2B § 408 (400) 15 14 0.048 0.793 0.996(3) 1.060(1) 14.0(1) 1.190(1) HLC2 § 121 1 1 0.048 0.108 0.664(2) 0.942(1) 47.4(3) 0.918(1) LB3 § 296 (288) 9 8 0.037 0.687 0.960(5) 1.102(2) 12.8(1) 1.235(2) LB4 § 315 (307) 7 6 0.034 0.652 0.964(3) 1.068(1) 12.8(1) 1.165(1) LB5 § 293 6 6 0.024 0.126 0.964(4) 1.125(2) 43.4(3) 1.286(2) SW3 § 293 (281) 14 12 0.063 2.092 0.969(9) 1.150(2) 8.2(1) 1.344(2) SW5 § 254 (245) 3 2 0.056 1.415 0.935(2) 1.143(1) 10.5(1) 1.294(1) SW6 § 238 (232) 4 4 0.054 0.907 0.917(4) 1.143(2) 14.5(1) 1.281(2) SWAN § 306 4 4 0.040 0.032 0.964(2) 1.088(1) 228(1) 1.209(1) SWIM § 352 6 6 0.068 0.708 0.993(2) 1.108(1) 27.6(1) 1.292(1) WG1U § 307 5 5 0.052 0.440 0.973(3) 1.124(1) 34.0(2) 1.295(1)

LOBO † 265 (256) 26 21 0.040 0.307 0.957(20) 1.206(12) 9.6(2) 1.44(2) LOAN † 302 (296) 30 24 0.041 0.180 0.983(18) 1.184(5) 16.7(3) 1.431(6) LB-1E # 329 31 24 0.041 1.078 0.989(14) 1.139(2) 3.6(1) LB-2F # 365 57 38 0.066 2.143 0.986(16) 1.066(1) 2.97(3) LB-3G # 362 26 21 0.059 1.257 1.020(10) 1.201(2) 5.0(1) LB-4H # 317 43 31 0.044 0.518 0.987(20) 1.157(8) 7.4(2) LB-O Isochron 311 28 22 1.6(1)

SWO † 183 (152) 23 19 0.047 1.062 0.850(41) 1.258(3) 3.0(1) 1.433(3) SW1-A # ∞ 0.107 6.611 1.006(17) 1.036(3) 2.33(4) SW1-2B # 221 6 5 0.115 2.847 0.889(7) 1.108(1) 2.49(2) SW1-3C # 305 16 14 0.075 3.249 0.952(8) 1.045(1) 1.98(2) SW1-4D # 570 8 ∞ 0.102 7.234 0.975(11) 0.956(3) 1.02(1) SW1-O Isochron 152 45 30 1.6(3)

Note: The age in bold is the one used (see text for explanation). The value in parentheses beside the age is the calculated age if detrital contamination is assumed to have had an initial 230Th/232Th activity ratio of 1.0 (indicated by isochron date)—this is relevant only for 230Th/232Thactivity ratios <20. Ratios are shown as activity ratios with 2σ error in parentheses. Half lives from Cheng et al. (2000).

† VG thermal ionisation mass spectrometer (TIMS), McMaster University, Hamilton, Ontario. # Inductively coupled plasma mass spectrometer, Geotop, Uqam, Montreal, Quebec. § Triton TIMS, Isotope Geochemistry and Geochronology Research Centre, Ottawa-Carleton Geoscience Centre, Carleton University,

Ottawa, Ontario.



is within error of the original age, so there is no justifi cation for using anything other than the original age. Only three of the dates we have used are the adjusted ones.

Initial 234U/238U ratios for the in situ fl ow-stone samples are all within a narrow range

that gradually decreases over the course of the Pleistocene, a very common pattern explained by depletion of the more soluble 234U in the overburden (Fig. 5). The values for the mate-rials that are not in situ, but rather have been transported from another part of the cave, are

well above the 3σ range. The one exception is sample HLC2, fl owstone that is in situ, but has an initial 234U/238U ratio below the 3σ range. This sample is from a high part of the cave, close to the surface with only a thin overburden.

RESULTS

Al-Be Dating

An analysis of quartz sand from the basal Red Sands of the Gallery (Figs. 6A, 6B) and quartz pebbles from the exposed Breccia in the Bear’s Den–Labyrinth area (Fig. 6C) yielded fi nite 26Al-10Be dates, albeit with very broad

234

232

U/

Th

LB-O

0 5 1510238 232U/ Th

234 238U/ U =1.20 0.02

20

15

10

5

0

SW1-O

230

232

Th/

Th

1.0 3.02.0

3

2

1

234 232U/ Th

230 234Th/ U =0.79 0.08

LB-O

230

232

Th/

Th

0 5 1510

15

10

5

234 232U/ Th

230 234Th/ U =0.97 0.01

20

0

SW1-O

234

232

U/

Th

1.0 2.0 3.0

4

3

2

1

238 232U/ Th

234 238U/ U =1.37 0.16

Figure 4. Isochron plots of samples SW1-O and LB-O.

0.6

0.8

1.0

1.2

1.4

1.6

0 100 200 300 400

Age (ka)

Init

ial

U/

Uac

tivi

tyra

tio

234

238

HLC2

SW-1 LB-O

B20: 4.07In-situ flowstoneTransported in breccia

2 rangeσ3 rangeσ

Figure 5. Change in initial 234U/238U activity ratio over time. The in situ fl owstone samples are shown as solid dots and the transported material as open circles. The dashed line shows the 95% confi dence interval, and the dotted line shows the 99% confi dence interval.

C

A

Fluvial clay

Fluvial Gravel

Gravel fallen into pit from top

Current-beddedsands

B Top of exposure

10cm

Figure 6. (A) The basal Red Sands from the Gallery. (B) Cross section through the basal Red Sands showing, from the base up, fl uvial mud, current-bedded fl uvial sands, and gravel. (C) The top of the Breccia, from the Water Gallery, looking up (stand-ing in the vacuity enlarged by Pengelly’s excavation in the Breccia), showing matrix-supported angular clasts and bone arti-facts (white arrow).



error margins (Table 1). Unfortunately the Red Sands are only exposed in this one site and the relationship with Breccia is not explicit. The Gallery Red Sands yielded a date of 2.32 ± 1.74 Ma (1σ range: 0.58–4.06 Ma) and the Breccia yielded a date of 0.95 ± 0.55 Ma (1σ range: 0.4–1.5 Ma).

U-Th dating

Data are presented in Table 2. We present the results from each site. The cave stratigraphy is complex, such that no one site offers a continu-ous sequence of events; instead the sequence must be reconstructed from the partial informa-tion from many sites.

Hedges BossOf all the sites, Hedges Boss (Fig. 7A)

has the simplest stratigraphic relationships. The Breccia (>2 m thick here) is capped by ~10 cm of orange-pink, laminated cal-cite (sample HB-2B) that was dated to 408 +15/–14 ka, early MIS 11. The sequence con-tinues with a thin layer of red, detritus-rich calcite that in this cave indicates a hiatus in deposition and/or very slow deposition. This is capped by ~10 cm of white, laminated calcite with several poorly expressed hiatuses, and a thin layer that is currently active (MIS 1). Figure 7B shows the diagrammatic interpre-tation of this section. We have no other dates from this site; therefore the layers from MIS

9, 7, and 5 are presumed, based on data from other parts of the cave. Proctor et al.’s (2005) sample KC–90–2, taken from just below the hiatus (a position confi rmed by the large saw-cut remaining from their sampling), shows evidence of recrystallization. Our sample was not taken close to the hiatus and shows the clearly defi ned fi ne growth laminations of the original fabric. Thus there is no reason to sus-pect this date.

Bear’s DenThe stratigraphic relationship of the Breccia

and the calcite is not simple here (Fig. 8A). Sample BD-1 (326 ± 7 ka, MIS 9) is a clean, orange-pink, laminated calcite from immedi-

Whitecalcite

MIS 7 ?

HB-2B: 408 -14/+15 kaMIS 11

MIS 11

MIS 5 ?

MIS 1 Active flowstone

Pink calcite Hiatus

Sampling sites in Hedges Boss

Breccia

MIS 9 ?

B

Breccia

HB-2B 397– 423 ka

Active flowstoneWhite laminated calcite

Pink laminated calcite

Hiatus

A

Figure 7. (A) The remains of Hedges Boss perched on a pedestal of thick breccia. This is the only part of the Crystalline Stalagmite in this chamber that was thick enough to have not been fractured (see discussion in text). (B) Diagrammatic interpretation of depositional sequence.

BD-1319–332 ka

Breccia

MIS 1? drapery

Laminated calcite

Breccia

BrecciaRock

Flowstone shelf/slab

Proctor’s KC4-83-C107–123 ka

BD-2: 420–462 ka

Breccia

Laminated calcite

Bedrockcave wall

MIS 1?

MIS 7 ?

MIS 5c

BD-1 326±7 ka, MIS 9

Proctor’s KC4-83-C115 ±8 ka MIS 5c

BD-2: 439-19/+23, MIS 11

MIS 9

MIS 5e

MIS 11

Sampling sites in Bear’s Den

A B

Figure 8. (A) Bear’s Den and Bear’s Den Boss, where the fl owstone was thick enough to escape fracturing. The roof shows phreatic cusps with no evidence of collapse. (B) Diagrammatic interpretation of depositional sequence.



ately above the Breccia-calcite contact, ~6 m to the right of the Bear’s Den Boss (inset Fig. 8A, placed in correct stratigraphic posi-tion). Sample BD-2 (439 +23/–19 ka, MIS 11) is from a layer of white calcite coating bedrock that curves out into the Breccia. Proctor (1994) interpreted this as a calcite vein intercalating between two beds of breccia. Having cleaned the face with wire brush and water, we inter-pret this calcite as simply fi lling a narrow gap between the Breccia and the rock, probably created by dripping, and thus postdating the Breccia (Fig. 8B).

Water GalleryBecause so little material remained, only

one sample (WG1U: 307 ± 5 ka, MIS 9) was taken of the calcite layer immediately above the Breccia. All that is left of the white, laminated

calcite fl owstone is a fl ake against the rock but separated from rock by a thin fi lm of mud, which we interpret as Breccia remains.

Clinnick’s GalleryHere the stratigraphic sequence between

the two sampling locations is not continuous. Figure 9B (shown in correct position relative to the main sampling site, Fig. 9A) shows the contact with Breccia. Immediately on top of the Breccia is ~25 cm of soft, vuggy calcite. We sampled the solid, cream colored, opaque calcite above this (CG-TB:193 ± 1 ka, MIS 7). The calcite is separated from the rock face by a thin fi lm of mud, which we interpret as the remains of Breccia. No hiatuses are apparent between the contact and the sampling site; we thus assume that the entire calcite layer was deposited during MIS 7.

The focus for the main site was on the broken fl owstone in the middle (Figs. 9A, 9D). The sequence shows that the upper layers of white, laminated calcite (sample G2-BW, 79 ± 3 ka, MIS 5a) were fractured and displaced, and cemented in place by thin layers of red calcite (sample G2-TR, 47 ± 3 ka, MIS 3). These were in turn fractured and cemented in place by the topmost layer of white vuggy Granular Stalag-mite of MIS 1 age. Figure 9C shows the dia-grammatic interpretation.

High Level ChamberIn the High Level Chamber (Figs. 10A,

10B), the remains of calcite fl owstone with a natural fracture surface (rather than the typical clean and scraped surface from excavation) are plastered to one side of the passage at ~1.5 m above the present fl oor. The lowermost 10 cm

CG-TB: 192–194 ka

Vuggy calcite

Laminatedcalcite

Breccia

BedrockB

Breccia

White laminated calcite

White Granular Stalagmite

MIS 7

MIS 5c ?

Fractured blocks of red calcite

CG-TB193 ±1 kaMIS 7

MIS 5e ?

MIS 5c ?

Red laminated calcite coatingFractured blocks ofwhite laminated calcite

White laminated calciteWhite vuggy calcite

G2-TR47 ±3 kaMIS 3

G2-BW79 ±3 kaMIS 5a

C

Bedrockcave wall

30cm

Bedrock

G2-TR 44–50 ka

CG2-BW 76–82 kaBroken slabs of white,laminated calcite

Red calcite

White “Granular Stalagmite”Broken red calcite

A

DFigure 9. (A) The main sampling site in Clinnick’s Gallery. Here the fl owstone is not in contact with breccia. (B) The secondary sampling site of fl owstone in direct contact with breccia. Mallet is 30 cm long. (C) Diagrammatic interpretation of depositional sequence. (D) Detail of broken fl owstone layers.



of fl owstone is not amenable to dating (labeled as sugary calcite in Fig. 10A). Sample HLC-2 (121 ± 1 ka, MIS 5e) comes from the fi rst layer of solid, laminated calcite. No hiatuses are apparent between the contact and the sampling site; we thus assume that the entire calcite layer was deposited during MIS 5e. On close exami-nation, it is apparent that it had been fractured and cemented with overgrowth of red, muddy calcite. The site is further complicated by the remains of white, vuggy calcite both above the 5e deposit and just below it. Proctor’s (1994) alpha-counted U-Th date on this material (the lower layer) is 53 +6/–4 ka, placing it in MIS 3.

In-Between BossThis boss, between Inscribed Boss to the north

and Hedges Boss to the south, unnamed on the Proctor and Smart (1989) survey, is shown in

Figure 11A (a circumferential mosaic). Much of the most clearly exposed face to the left could not be sampled for aesthetic reasons. Of the two samples taken in direct contact with the Breccia, CEB was leached and CI-HB dated to 289 +20/–17 ka, MIS 9. All three dates from this lowermost block of clean, white calcite are not statistically separable, showing that depo-sition was rapid in MIS 9 (CI-G, 312 +10/–9 ka and CI-F, 310 ± 6 ka). The thinner parts of this layer to either side of the main boss are cracked (see following discussion). It was originally presumed that sample CI-E2 (220 +4/–3 ka, MIS 7) would be stratigraphically equivalent to CDF (150 ± 5 ka, MIS 6b), but the dates prove otherwise. The remaining samples show a clear progression through MIS 5 (CCD, at 100 ± 3 ka, CCT, at 95 ± 4 ka, CBN, at 93 ± 2 ka, and CAT, at 80 ± 1 ka). The overlying

drapery is currently active and assigned to MIS 1. Figure 11B shows our reconstruction of the sequence of deposits.

LabyrinthThis thick layer of fl owstone emerging from

the Little Oven Exit that originally spilled into the Labyrinth (Figs. 12A, 12B) was diffi cult to sample. Much of the calcite is vuggy, and appears to have been deposited in shallow stand-ing water. The dates (LB-3: 296 +9/–8 ka; LB-5: 293 ± 6 ka; LB-4: 315 +7/–6 ka) suggest rapid deposition in MIS 9. Two samples were taken from within the Breccia. The fi rst, a broken slab of fl owstone, LB-O, was isochron dated to 311 +28/–22 ka, MIS 9. The second, a piece of sta-lagmite, broken and embedded in the Breccia, sampled ~5 m to the left of this site (sample B20, shown in correct relative stratigraphic

Sampling sites in High Level ChamberBreccia

Sugary calcite

Brecc

Sug

Laminated calciteHLC-2: 121 kaMIS 5e

±1

Proctor’s KC91-153 -4/+6 ka

MIS 3

Vuggy calcite

Vuggy white calciteFalse Floor remnant

Bedrockcave wallB

HLC-2: 120–122 ka

Proctor’s KC91-1Vuggy calcite

Laminated calcite

Sugary calcite

A

Figure 10. (A) High Level Chamber sampling site. (B) Diagrammatic interpretation of deposits.

Sampling sites at In-Between Boss, Cave of Inscriptions

Palecalcite

Breccia

Hiatus

MIS 5a

MIS 5c

MIS 7

MIS 9

MIS 1

Hiatus

HiatusMIS 6b

CI-H: 289 -17/+20

CI-G: 312 -9/+10

CI-F: 310 -6/+6

CAT: 80 ±1CBN: 93 ±2CCT: 95 ±4

CICD: 100 ±3

CI-E2: 220 -3/+4CDF: 150 ±5

B

30 cm

BrecciaSlab of flowstone within breccia

Contact of flowstonewith breccia

Hiatus lined withred flowstone

CEB: Leached

CBN: 91–95 ka

CAT: 79–81 ka

CI-G: 303–322 ka

CI-F: 304–316 ka

CI-E2: 217–224 ka

CI-HB: 272–309 ka

CI CD: 97–103 ka

CDF: 145–155 ka

CCT: 91–99 ka

A

Figure 11. (A) Photomosaic around In-Between Boss showing sampling sites. (B) Diagrammatic interpretation of sequence.



position in Fig. 12B), was dated as 210 ± 2, MIS 7. These last two have initial 234U/238U ratios well outside the 3σ range for the in situ fl owstone (Fig. 5, open circles), suggesting that they originate from elsewhere in the cave.

Southwest ChamberWe sampled from both the northwest

(Figs. 13A, 13B) and southeast (Figs. 13C, 13D) sides of this passage. The northwest side shows a simple sequence: SW-3 (293 +14/–12 ka, MIS 9) in direct contact with Breccia, up through SW-5 (245 +3/–2 ka, MIS 7) and SW-6 (238 ± 4 ka, MIS 7), and red vuggy calcite on top that was not amenable to dating. On the southeast side, the calcite remains plastered high on the wall consist of the lowermost layer of rapidly depos-ited, dendritic fabric, full of intercrystallite voids and not amenable to dating; an intermediate layer of white, laminated calcite (WUXU, dated imprecisely to 417 +104/–52 ka, MIS 11); and white laminated calcite (SWAN, 306 ± 4, MIS 9). The lower part of the southeast side shows a sequence of calcite in contact with breccia (SW1M, 352 ± 6 ka, MIS 10b); a hiatus; a thin layer of redder calcite (WTXT, 132 ± 6 ka, MIS 5e); and vuggy, Granular Stalagmite (MIS 1). The sample taken from within the Breccia, of a fractured fl owstone slab, SW1-O, was isochron

dated as 152 +45/–30 ka, MIS 6b, and shows an initial 234U/238U ratio outside of the 3σ range (Fig. 5), indicating that it probably originated in another part of the cave.

DISCUSSION

In order to understand the evidence of Qua-ternary events in Kents Cavern it is important to be aware of some of the complexities of cave sedimentology in general. The age of any one deposit cannot usually be predicted from its geomorphological position because the princi-ple of superposition does not necessarily apply in caves. In some sections deposition appears to have obvious hiatuses, but dating shows that they are in reality simply shifts of the drip point (e.g., some parts of In-Between Boss). Rework-ing of nonindurated sediments may complicate temporal relationships: we believe that the clas-tic sediments in this cave have been repeatedly remobilized since initial deposition, confusing the sequential relationships.

It is also important to be aware of the prob-lems of inconsistent application in the literature of British stage names and associations with the marine oxygen isotope record. The mid-Pleistocene record from British sites is some-what hazy because so many of the sites cannot

be radiometrically dated and the assigned age depends on a combination of paleontological, archaeological, and palynological remains, on stratigraphic position, and on sedimentology.

Differentiation of the post-Anglian interglacial sites (e.g., Purfl eet and Hoxnian Interglacials) normally relies on aminostratigraphy. However, McCarroll (2002) suggested that this method is not sensitive enough to allow confi dent separa-tion of populations into different interglacials. It is now widely accepted that sites attributed to the Hoxnian on the basis of pollen spectra may represent more than one warm stage (Scourse et al., 1999; Dowling and Coxon, 2001; Thomas, 2001). Schreve and Thomas (2001) suggested that two episodes are recorded, each with a Hoxnian-type pollen signature. As new data are published, the controversy lessens. For example, Grün and Schwarcz (2000), from U-series/ESR ages of 403 +33/–42 ka on teeth, placed deposits of the type locality of the Hoxnian Interglacial in MIS 11. Rowe et al. (1999), based on careful U-series dating of lake sediments, also assigned the Hoxnian to MIS 11.

The Anglian is the most widely recognized event in the mid-Pleistocene of Britain, yet its age is not conclusively established. The MIS 11 date for Hoxnian deposits from Rowe et al. (1999) also assigns the Anglian glacial deposits that underlie the Hoxnian deposits, with no evidence of any signifi cant break in deposition, to MIS 12. The majority of publi-cations refer the Anglian to MIS 12 (Schreve and Thomas, 2001).

Cromerian sites from Britain have, in the past, been assumed to represent a single interglacial stage, whereas in the Netherlands the Cromerian Complex has incorporated four interglacials and their intervening cold stages (Preece, 2001). Recent molluscan evidence has supported sev-eral distinct stages (Preece, 2001; Schreve and Thomas, 2001). An age of MIS 13 is gener-ally agreed as the younger limit, but there is no consensus about the age of the start of the Cromerian; Parfi tt et al. (2005) proposed at least MIS 17 for the Cromer Forest bed, and by impli-cation, the Cromerian type site at West Runton.

In the following discussion we assume that the Hoxnian stage correlates with MIS 11, the Anglian stage with MIS 12, and the Cromerian is MIS 13 to at least MIS 15.

The distribution of the standard four units, i.e., the Breccia, the Crystalline Stalagmite, the Cave Earth, and the Granular Stalagmite, was described by Pengelly (1884), Keith et al. (1931), Campbell and Sampson (1971), Proctor (1994), Straw (1997), and Proctor et al. (2005), but without a reliable temporal framework for materials outside the range of 14C dating. Proc-tor (1994) provided detailed descriptions of

Sampling sites in Labyrinth, under Little Oven Exit

LB-O: 289–339 ka

LB-3: 288–305 ka

Vuggy calcitePool deposits

Breccia

Hiatus

Laminated calciteSome pool deposits

LB-5:287–299 ka

Exit ofLittle Oven Passage

LB-4: 309–322 ka

A

Small hiatus ?

Vuggy calcitePool deposits

LaminatedcalciteSomepool deposits

LB-3: 296 -8/+9 ka, MIS 9

LB-O: 311 ka -22/+28, MIS 9

Hiatus

LB-4: 315 -6/+7 ka, MIS 9

MIS 9

B2O 210 ±2, MIS 7Broken Stalagmite

Flowstone slab

LB-5: 293 ±6 ka, MIS 9

Breccia

B

Figure 12. (A) Sampling sites from the northeast side of Labyrinth. (B) Diagrammatic inter-pretation of deposits.



facies. Here we focus on the information from the new dates and present a new interpretation of the stratigraphy.

Age and Emplacement of the Red Sands

A sometimes-overlooked deposit, the Red Sands, has been variously interpreted. Keith et al. (1931) reported the Red Sands as the basal unit below the Breccia in the Water Gallery, but this exposure is now buried by a cement path-way and cannot be reexamined. Keith et al. (1931) and Campbell and Sampson (1971) cor-related these sands with the Red Sands currently exposed in the Gallery, but Proctor (1994) inter-preted the unit as a wash facies of the loamy Cave Earth (well dated by 14C as late MIS 3, Fig. 2). The Gallery exposure remains accessible, in a

pit dug into the fl oor of the Gallery, but the rela-tionship with the Breccia is ambiguous because the sands are separated from the overlying Breccia by a substantial vacuity. The Red Sands (Fig. 6A) comprise a basal unit of horizontally bedded mud; a middle unit of bedded sands that dips steeply ~30° away from South Entrance; and an upper unit of poorly bedded gravel, the clasts of which are subrounded, poorly sorted, mostly 1–2 cm but as much as 5 cm in diameter. We interpret this as a simple fl uvial sequence of low-water mud, current-bedded sands, and high-water river gravel (Fig. 6B).

We address the relationship of the Red Sands to the Cave Earth and the relationship of the Red Sands to the Breccia. Even with the very large 1σ error, the probability that the 26Al -10Be burial age of the Red Sands is younger than the earli-

est possible age on the Cave Earth (i.e., end of MIS 5a, 79 ka) is only 0.09 (Monte Carlo simu-lation, 10,000 iterations). Thus Proctor’s (1994) hypothesis that the Gallery sands are a remnant of the Cave Earth can be rejected.

The 26Al-10Be data support a signifi cantly greater age for the Gallery sands versus the Breccia, and support Campbell and Sampson’s (1971) view that the Gallery sands are basal to the Breccia and synonymous with Keith et al.’s (1931) Red Sands, making them the oldest dated deposits preserved in the cave. In addi-tion, examination of the 26Al nuclide concen-trations in Gallery quartz versus Breccia quartz reveals that they differ by more than 4 standard deviations (Table 1), demonstrating that the exposure history of these materials has been quite different.

Bedrockcave wall

Breccia SW-1 Old: 152 ka

Laminated calcite

SW1M: 346–358 ka

Pink, vuggyGranular Stalagmite

Broken flowstone slab

WUXU: 417 ka

Dendriticcalcite

SWAN: 302–310 ka

WTXT: 126–138 ka

C

Bedrockcave wall

Breccia

SW-6: 234–242 ka

SW-5: 243–248 ka

SW-3: 281–307 kaStalagmite

Pale, laminated calcite

Red calcite

Whitish calcite

Bedrockcave wall

Red vuggy calcitePool deposits

Brecc

ia

Pale laminated calcite

Sampling sites in SouthwestChamber, NW sideA

Red, laminated calciteHiatus


Breccia

SW1-O:

MIS 6b152 -30/+45 ka

WTXT: 132 ±6MIS 5e

SW1M: 352 kaMIS 10b

±6

Flowstone slab

Dendritic calcite

Laminated calciteWUXU: 417 -52/+104 ka, MIS 11

SWAN: 306 ±4 ka, MIS 9

Sampling sites in SouthwestChamber, SE side

Pink, vuggy calcite

Bedrockcave wall

MIS 1

D Vuggy red calcite

Haitus

MIS 7?

Red calcite


Breccia

SW-3: 293 -12/+14 kaMIS 9

SW-6: 238 ±4 kaMIS 7

SW-5: 245 3 kaMIS 7

-2/+

Stalagmite enclosedin flowstone

Red vuggy calcitePool deposits

Red calcite coating


Whitish calcite

Bedrockcave wall

B

Figure 13. (A) Sampling sites on the NW side of Southwest Chamber. Mallet is 30 cm long. (B) Diagrammatic interpretation of deposits. (C) Sampling sites on the SE side of Southwest Chamber. The fi gure points to the upper level samples. The stratigraphic relationship between the upper level sequence and the lower level sequence cannot be traced. (D) Diagrammatic interpretation of deposits.



We suggest that the Red Sands are simple fl uvial deposits indicating a fl ow with a high clastic load, of variable discharge, moving up South West Chamber and diverging through the Gallery toward the Long Arcade and North Entrance. While no defi nitive date can be assigned (in view of the high error margin of the cosmogenic date), it would be reasonable to assume that the Red Sands are Cromerian (MIS 13–15, a long period of predominately temper-ate conditions), and represent the fi nal stages of vadose activity after the phreatic activity that carved the primary cave passages.

Age of the Breccia

The 26Al-10Be burial date on the quartz grains within the Breccia gives an age estimate of mid-Pleistocene. The oldest of the U-Th dates on the capping fl owstone offers an upper window. How-ever, the possibility of a potential hiatus between sediment deposition and calcite deposition must be acknowledged in view of Stock et al.’s (2005) fi ndings that U-Th dates on speleothem over-lying clastic sediments are often considerably younger than cosmogenic 26Al-10Be burial dates on the sediment. In Kents Cavern, the Breccia contains additional evidence of the time of its formation in the form of sedimentological char-acteristics and paleontological remains.

We dated 11 samples of calcite fl owstone in direct contact with the Breccia: 2 of these yielded MIS 11 dates, 5 had MIS 9 dates, 2 had MIS 7 dates, and 1 had a date of MIS 5. The simplest interpretation from the capping calcite is that the Breccia formed before MIS 11 and the younger dates represent hiatuses of various lengths. Proctor et al. (2005) tried to date the Breccia using the calcite cap, but they took the average (MIS 9) as an indication of minimum age. Any averaged time series will yield a mean that is signifi cantly younger than the actual age of the initiation of the series.

Sedimentological EvidenceSedimentologically, the Breccia is a poorly

sorted diamict of angular to subangular clasts (red sandstone, siltstone, slate, quartz, and rarely limestone) in a matrix of red mud (Fig. 6C). Proctor (1994) noted that the clasts are as large as 20 cm and are matrix supported, and that little or no fabric is visible in the generally homoge-neous deposit. This material is typical of frost-shattered regolith or head deposits that abound on the hillsides of the area as a result of former periglacial activity (Cullingford, 1982; Scriv-ener, 1987; Croot and Griffi ths, 2001). This requires a long period of cold conditions. The Cromerian represents a long period of temper-ate conditions from MIS 13 to at least MIS 15

(474–620 ka; Bassinot et al., 1994), but also incorporates the full glacial at MIS 16 together with at least one preceding interglacial (Parfi tt et al., 2005). The Breccia is unlikely to date to the early Cromerian: if the cave were open and the Breccia had been produced in the MIS 16 gla-cial, the Breccia and the cave would have to have remained completely unaffected by the 146 k.y. of Cromerian temperate conditions and another 46 k.y. of Anglian glacial conditions until the initiation of calcite deposition in MIS 11. Thus we conclude that the Breccia must have been produced in a post–MIS 16 cold stage. The only stage that is cold enough between the oldest date on the calcite, MIS 11, and MIS 16 is MIS 12, the Anglian glacial period (MIS 14 was too warm). The question is not resolved by other head deposits, because so few have been reliably dated. Bates et al. (2003) indicated that most are from MIS 4 and MIS 2, some are from MIS 6 or MIS 8, but in a few places with good dat-ing control, head deposits dating to the marine oxygen isotope stage 12 can be recognized. For example, head deposits from cold stages back to MIS 12 have been found (with ages rang-ing from MIS 11, on amino acid evidence, to MIS 13, on mammalian biostratigraphy) in the Hampshire-Sussex coastal plain. Murton and Lautridou (2003) also dated periglacial deposits along the English Channel coastlands (by radio-carbon, luminescence, and mammalian biostra-tigraphy); they place most in MIS 2, some in MIS 6, and some in other cold stages.

Paleontological EvidenceAlthough their U-series ages provide only

an upper window of MIS 9, suggesting that the Breccia could represent either MIS 12 or MIS 10 deposition, Proctor et al. (2005) argued that the faunal remains in the Breccia suggest a late Cromerian age, consistent with many examples of well-established pre-Anglian faunas in UK sites and in the Netherlands. The paleonto-logical evidence comes from both the rodent remains (generally disseminated throughout the Breccia) and bear remains (generally at the top of the Breccia).

Evidence From the RodentsPengelly’s notes (1868–1880) do not address

the microvertebrate fauna of Kents Cavern, but workers have identifi ed sparse remains of the voles Pitymys gregaloides, Arvicola “greeni” (= A. cantiana; Sutcliffe and Kowalski, 1976) (Campbell and Sampson, 1971), and Microtus oeconomus (Proctor, 1994). The evolution of voles is of great importance in the middle Pleis-tocene biostratigraphy of Europe, and provides time constraints on the Kents Cavern Breccia deposits. The British extinct water vole lineage

consists of the chronospecies Mimomys plio-caenicus (early Pleistocene), M. savini (late-early through early-middle Pleistocene), and A. canti-ana (late-middle Pleistocene to early-late Pleis-tocene) (Lister et al., 1990). Neither Mimomys species is known from the Kents Cavern Brec-cia. The appearance of unrooted molar teeth characteristic of the genus Arvicola is dated to MIS 11 in continental Europe (Pevzner et al., 2001), but to the late Cromerian (Sutcliffe and Kowalski, 1976) or immediately pre-Anglian (Andrews, 1990) at the Westbury site in Britain. This sets the maximum age limit for the Kents Cavern Breccia fauna at MIS 13. The extinct Pine vole, Pitymys gregaloides, is also present at Westbury but has not been found in any Brit-ish Hoxnian (MIS 11, sensu Schreve, 2001) site (Sutcliffe and Kowalski, 1976), and is generally presumed to be indicative of pre–MIS 11 age.

Thus the rodent fauna are MIS 13 in age (we agree with Proctor et al., 2005). The deposit in which they are incorporated may also be MIS 13, but could equally be younger. If we accept that the Breccia represents a cold-climate (periglacial) deposit, and that the oldest calcite capping is MIS 11, then the only possible age of emplacement would be MIS 12.

Evidence From the BearsThe Kents Cavern Breccia is most notable for

yielding large numbers of teeth and bones attrib-uted to the cave bear, a term that is applied to ani-mals in the Ursus savini–Ursus deningeri–Ursus speleaus chronospecifi c lineage. The exact posi-tion of the Breccia bears along this lineage has been ambiguous, in part because the material has not been formally reviewed and also because the systematics of European middle Pleistocene bears has not been fully resolved. Bishop (1982) placed the Westbury (MIS 13) bears at full U. deningeri grade. Schreve (2001) considered bears of full U. speleaus grade to be Hoxnian (MIS 11) in age. A preliminary analysis of the Breccia bear teeth (McFarlane et al., 2006) indi-cates that they are of an advanced U. deningeri–early U. speleaus grade, consistent with an age of MIS 12–11, but clearly younger than MIS 15 (U. savini; Kurtén, 1968), and probably younger than the Westbury MIS 13 bears. A small pro-portion of generally less well preserved bear material is found disseminated throughout the deposit, but the majority of the bear material is found within the uppermost 25 cm, immediately below the calcite cap, indicative of a superfi cial emplacement, so much so that MacEnery (1859, p. 27; our brackets) reported “The fi rst fl ag [of overlying fl owstone] that was turned over exhib-ited, in relief, groups of skulls and bones adher-ing to the stalagmite.” The majority of the bones are from bears using Kents Cavern as a hiber-



naculum, on top of the Breccia, and the bones are incorporated into the topmost muddy layer. Thus most of the bear material postdates the MIS 12 emplacement of the Breccia.

Evidence From the ArtifactsMuch of the historic interest in Kents Cav-

ern has resulted from the recovery of very early Acheulian fl int and chert artifacts. Acheulian bi-face tools are known elsewhere in Britain from Boxgrove (MIS 13) and Pakefi eld (MIS 17; Parfi tt et al., 2005). Campbell and Sampson (1971) noted that Pengelly recovered these artifacts throughout the thickness of the Breccia, including its lowest levels. Moreover, the largest number of artifacts (31%) came from the “4 ft” level within the Breccia. Several authors (Campbell and Sampson, 1971; Cook and Jacobi, 1998) have commented on the poor condition of the artifacts, which show evidence of both rolling and rotting, consistent with long exposure on the surface and subsequent entrain-ment in the Breccia debris fl ow.

The archaeological and paleontological evi-dence suggests that the Acheulian artifacts accu-mulated on the surface in pre-Breccia time, and were subsequently carried into the cave entrained in the Breccia debris fl ows. In contrast, the bear remains are both spatially and taphonomically consistent with having been derived from a bear hibernaculum in the cave, on top of and post-dating the Breccia. Subsequent remobilization of the Breccia (see following) has incorporated some of this bone material in its upper layers. The provenance of the rodent remains is not known with certainty, and these animals may include specimens both coeval with and postdat-ing the emplacement of the Breccia.

Emplacement of the Breccia

Generally the Breccia shows very little inter-nal structure. It is clearly not fl uvially emplaced, but rather is a mass-movement deposit. Proctor (1994) and Straw (1997) suggested that it is a debris fl ow, on the basis of the thick, structure-less beds with poor sorting, chaotic to sub hori-zontal clast orientation, and matrix support. Collcutt (1986) defi ned debris fl ows as water-saturated materials moving at speeds detect-able to the observer, up to tens of kilometers per hour. He considered them to be common events in caves and the dominant mechanism for lateral displacement of deposits. Initiation of movement requires slopes of at least 20° and a sudden input of large quantities of water. Thus, Proctor (1994) suggested that the Kents Cav-ern Breccia debris fl ows would have required a high water content and that emplacement in the cave was accompanied by small streams (a view

reiterated in Proctor et al., 2005). This suggests a warm or at least warming climate. Collcutt (1986) noted that some sorting occurs during debris fl ow, the larger particles moving to the sides and base; that for high-water-content fl ows there is a tendency for orientation of particles with fl ow; and that larger clasts or artifacts and faunal remains may be signifi cantly worn and damaged by the fl ow. While there is little clear evidence of sorting, damage to the artifacts dis-seminated throughout the Breccia (Cook and Jacobi, 1998) supports this view. However, it is apparent to us that the features of this deposit could equally be interpreted as a solifl uction fl ow (see following). Croot and Griffi ths (2001) observed that the head material on the surface has been moved downslope by solifl uction, or by rapid “slushfl ows” and slides, or by torren-tial fl ash-fl ood events. We suggest that the head material could equally have moved into the cave by such processes.

Bertran et al. (1997) defi ned solifl uction as slow mass movement caused by freezing and thawing, combining small-scale downslope frost creep and viscous fl ow from rapid release of meltwater during thawing. It produces lobes and sheets, usually with a preferred clast orientation parallel to slope. Debris fl ows are rapid mass movements of poorly sorted solids and water, usually triggered by rain events but also reported as resulting from rapid melting of ground ice triggering retrogressive thaw slumps. Fabrics for both these deposits have many analogies: both show clast orientation parallel to slope, and sometimes imbrication in clast-rich deposits. Data on clast orientation show that debris fl ows and solifl uction deposits are not clearly differ-entiated, having a similar range of a-axis vec-tor magnitudes. Both may exhibit simple shear deformation. Some differences between the two deposits can be seen, in that fabric strength is often lower in debris fl ows than in solifl uc-tion deposits, and that fabric shapes for debris fl ows are usually moderately developed girdles, whereas in solifl uction deposits clusters and gir-dles occur in equal proportions. Millar (2006) observed that debris fl ows often produce imbri-cate fabric depending on the clast frequency and slope, but in solifl uction the materials behave as a viscous fl uid and may also produce imbricate fabric, depending on clast frequency and slope.

Proctor’s (1994) description of breccia fabric is not detailed enough to allow application of Bertran et al.’s (1997) criteria. While the mode of emplacement of the Breccia does not really matter to its subsequent history, we suggest that the Breccia is a standard head deposit that was moved into the cave (through suffosion dolines, such as the Swallow Hole Gallery, and/or rifts) either by solifl uction or by debris fl ow. Collcutt

(1986) stated that excavators were too ready to blame processes such as cryoturbation. While this many be true, we suggest that not all matrix-supported, relatively homogeneous deposits in caves must necessarily now be reinterpreted as water-saturated debris fl ows, and that solifl uc-tion clearly continues to produce sediments with features similar to those in the Breccia.

The time frame available for breccia emplace-ment was relatively narrow: the head deposit that is the basis of the Breccia was formed by frost action during MIS 12; the bears moved in and used the top of the Breccia for a den; the top of the Breccia was partly encrusted in cal-cite during MIS 11 while the bears continued to use the area. Thus the bulk of the Breccia had to have been emplaced at the end of MIS 12 before the bears moved in. If the Breccia is a wet debris fl ow, then the time for emplacement had to have been during termination V or very early MIS 11.

Post-Breccia Calcite Flowstone

The appellation of all the Breccia-capping calcite as the Crystalline Stalagmite implies a simple sequence of synchronous events. In fact, except for the relatively clear case of Hedges Boss, the relationship of the Breccia and the overlying fl owstone is rarely simple and rarely synchronous.

In the Bear’s Den Boss, the visible stratig-raphy suggests a lower layer of breccia, an overlying layer of fl owstone, a second layer of breccia, and a cap of fl owstone. Proctor et al. (2005) suggested that the lowest layer of fl ow-stone was broken up, accompanied by local reworking of the Breccia. An alternative view is that the lowest layer simply represents an exposed fl owstone ledge (typical of the edge of a boss) that was buried by postdepositional movement of the Breccia creating the complex pattern of breccia-rock-ledge that is outlined in Figures 8A and 8B.

While the fi rst breccia-topping calcite deposit was from MIS 11, the majority of dates indicate a signifi cant episode of calcite deposi-tion in MIS 9, e.g., almost 1 m of MIS 9 fl ow-stone in the In-Between Boss and in the Laby-rinth. There was an even longer hiatus between breccia emplacement and calcite capping in other areas. The history of the breccia-calcite contact from Clinnick’s Gallery (Fig. 9B) con-nects with that from Rocky Chamber, at its northern end. The absence of any calcite cap-ping the Breccia until MIS 7, and the presence of red mud lining the junction of the calcite and the wall, suggests that the passage was com-pletely blocked by breccia. The occurrence of previously unreported paragenetic pendants



and anastomoses in the roof of Rocky Chamber (Fig. 14A), together with the remains of a frag-ment of breccia in the roof (Fig. 14B), suggests that Rocky Chamber was also fi lled to the roof with breccia. The paragenetic erosion suggests fl uvial action after emplacement of the MIS 11 Breccia and before deposition of MIS 7 calcite. We suggest that the most likely time was the MIS 9 interglacial period. The delay in depo-sition of the calcite cap in High Level Cham-ber (Fig. 10A) until MIS 5 is also probably explained by the passage being largely blocked by breccia, although we observed no direct evi-dence of paragenesis here.

Southwest Chamber (Fig. 13) shows evi-dence of an even more complex suite of events. The high-level remnants of MIS 11 and MIS 9 fl owstone indicate that the Breccia must have been at least 2 m deep in order to provide a substrate on which the fl owstone grew. This must have been subsequently largely removed (in MIS 10) to allow deposition of the MIS 9 fl owstone at the lower level. Drips from the roof continued to deposit calcite on top of the original MIS 11 layer (now a false fl oor or ledge), but also deposited calcite on top of the newly eroded Breccia at the same time. Thus in a single passage the thin remnants of fl owstone represent two layers that were contemporary but vertically separated by several meters.

The evidence is clear that the Crystalline Stalagmite represents a complex of fl owstone layers, and that each part of the cave requires detailed study. It is also relevant to note that the appellation Granular Stalagmite is not really adequate to represent the complex of Holocene calcite deposits. The cave opened up much more in the Holocene, so that deposition in the entrance zones and main passages was thick, porous, and vuggy, as is characteristic of rapid, evaporative deposition. However, Holo-cene deposits in less open parts of the cave are crystalline in fabric and still active.

Sequence of Events

Any scenario for the sequence of events must explain the formation and emplacement of all the sedimentary units, but it must also explain two unusual observations. The fi rst is the evi-dence for widespread cracking of fl owstone lay-ers and the second is evidence for the incorpora-tion of fractured material of younger ages within the upper layers of the Breccia.

Cracking of FlowstoneMany examples can be seen where a layer of

fl owstone is cracked and shifted, and the cracks are cemented with a thin coating of younger calcite. Most of the evidence of cracking was removed during excavations, but Straw (1997) recon-structed, from Pengelly’s original reports, the dis-tribution of Crystalline Stalagmite. Pengelly dif-ferentiated between Crystalline Stalagmite that was cracked in situ and Crystalline Stalagmite that was cracked and relocated, and was found as detached fragments in the Cave Earth. The in situ cracking was centered on the Bear’s Den, Laby-rinth, Cave of Inscriptions, and Clinnick’s Gal-lery. The relocated fragments found in the Cave Earth were moved from the Vestibule southward and into North and South Sally Ports.

Only one attempt to date the time of cracking has been published. Proctor (1994) was able to delimit the date of cracking of the edge of Bear’s Den Boss to after 115 ka (±4 ka), but this exam-ple has no younger overlying intact calcite that could provide an upper age limit. We studied several examples. The best is from Clinnick’s Gallery (Figs. 9A, 9B, 9C). We dated the white fl owstone layer that was cracked and the thin red calcite that coated the broken fragments. This gave a window for cracking and recementation of 79 ±3 ka (the end of MIS 5a interglacial) to 47 ±3 ka (the MIS 3 interstadial). Observant readers will note the high detrital content of the uppermost red calcite coating and the adjusted

age of 20 ka. However, a further constraint on the time window for cracking is the subsequent deposition of Cave Earth that has been 14C dated as ca. 23–35 ka (Fig. 2). Thus the original age is the more likely, and the timing for cracking most likely to be MIS 4, the fi rst cold stage of the Devensian glaciation. We also have to fi t into this timing the cracking of the red calcite and its subsequent cementation with Granular Sta-lagmite, well dated by 14C to MIS 1, ca. 4–16 ka (Fig. 2). The second episode of cracking must have occurred between MIS 3 and MIS 1.

The evidence from High Level Chamber sug-gests that the MIS 5 fl owstone was fractured and largely removed, and the Breccia surface level lowered, before the subsequent deposition of MIS 3 calcite under and slightly overlapping the MIS 5 fl owstone. This cracking must also have occurred during MIS 4.

Another example of cracking that we dated is from the In-Between Boss, but the evidence is not so clear cut. Here the thick basal fl owstone that was dated to MIS 9 was cracked and lined with red calcite, but only in its thinnest part, where it is ~20 cm thick. At the left side of the boss the basal layer of MIS 9 calcite is cracked and overlain by MIS 7 calcite (sample CI-E2 220 +4/–3 ka). The cracking here must have occurred during MIS 8. However, at the right side of the boss, the layer above the red calcite that cements the cracks in MIS 9 material is dated as MIS 6b (sample CDF, dated twice, 150 ± 5 ka and 148 ± 9 ka), giving a wide window for cracking from MIS 9 to MIS 6b. While the evidence is not unequivocal, we argue that if the cracking on this side had occurred dur-ing MIS 8, then we would expect the crack to have fi lled with clastic material or calcite. The fact that the fi lling material dates to MIS 6b sug-gests that the cracking on this side had occurred immediately before this, perhaps during MIS 6c, the fi rst cold period of MIS 6.

The evidence is for several episodes of cracking, and each of the times indicated, MIS 8, MIS 6c, MIS 4, and MIS 2, suggests a cold period. Further evidence for cracking is dis-cussed in the following.

Incorporation of Younger MaterialThe second of the unusual events that must

be explained in any sequence of events is the incorporation of fractured material of younger ages within the upper layers of the Breccia (in addition to blocks of angular bedrock). The three we sampled yielded dates of MIS 7, MIS 6b, and MIS 9 (B20—210 ka, SWO—152 ka, and LBO—311 ka). The standard explanation for mixing of materials of different ages is reworking of the sediment. Thus the Breccia (at least the sur-face few decimeters) must have been remobilized some time after its original emplacement.

A B10 cm

Figure 14. (A) Rocky Chamber paragenetic anastomoses in roof (looking straight up). (B) Remnants of breccia adhering to paragenetic pendants. Scale shows inches to left and centimeters to right.



The evidence for postdepositional move-ment of the Breccia is clear. MacEnery (1859), describing the cave before the major archaeo-logical excavations, noted several examples of the Breccia having been higher, having pulled away from the overlying crust, leaving the roof overhead with bones sticking out of base of the calcite. The Water Gallery illustrates this. Fig-ure 15 shows our reconstruction of the cross section at the Lake–Water Gallery, based on Pengelly’s original fi eld notes (1868–1880; still detailed at this early part of his excavations; however, they became less thorough as the dig progressed to other parts of the cave). Our date of 307 ± 5 ka (sample WGIU) places the lower layer of crystalline stalagmite in MIS 9. The dimensions and positions of the blocks of Crystalline Stalagmite distributed throughout the Breccia were carefully documented in Pengelly’s notes (1868–1880). The thin horizontal slab of calcite just beneath the bone-rich layer of breccia may have been MIS 11, deposited in situ, and then fractured during the MIS 10 glacial period. The Breccia became mobilized during MIS 10,

carrying MIS 11 bear bones from the Bear’s Den toward the South Entrance, and was then covered by MIS 9 fl owstone. (This sequence is corroborated by the evidence in the Bear’s Den and Southwest Chamber, discussed next.) It is also interesting that the MIS 9 layer had not been fractured; the Breccia must have been intact when this thin layer was deposited. Some time after MIS 9 the Breccia was partly removed to create the Vacuity in the center of the passage. If the Breccia underneath it was removed before the next fracturing episode, then the MIS 9 layer would remain intact (see discussion of mechanisms of fracturing): this second episode of Breccia remobilization was thus probably in MIS 8. There is no evidence of fl uvial activity in this movement of the Breccia: the redeposition of breccia plus bones farther down-passage still bears the marks of mass movement.

The Southwest Chamber is one of the best-documented passages because it was one of the fi rst places to be excavated by Pengelly. We have reconstructed the cross section from Pengelly’s notes (1868–1880), dated many of the calcite lay-ers, and then reconstructed the most parsimonious suite of events required to explain the deposits (Fig. 16). The high-level remnants of MIS 11 and MIS 9 fl owstone indicate that the Breccia must have been at least 2 m deep in order to provide a substrate on which the fl owstone grew. Some of the Breccia must have been removed during MIS 10 in order to make space for the lower level MIS 9 calcite deposition. The Breccia must also have been quite mobile, because artifacts from the den area were transported up this passage embed-ded in the top of the Breccia. A mobile breccia is required until MIS 6a in order to incorporate the very securely dated SW1-O MIS 6b fl owstone slab in the top of the Breccia. Another cracking event, during MIS 6a, was required to break the MIS 6b slab. Pengelly’s notes (1868–1880) docu-mented a thick layer of Crystalline Stalagmite across the passage; this must have represented the complex of deposition from MIS 11–5. The Breccia became indurated after MIS 6a, and fur-ther movement stopped.

Thus the evidence supports additional cracking events, during MIS 10 and MIS 6a, and remobili-zation of the Breccia during MIS 10, MIS 8, MIS 6c, and MIS 6a. Straw (1997; Figure 1 therein) mapped “detached Breccia pieces in Cave-Earth”; this implies that the Breccia was also cracked, probably during MIS 2 just before the Cave Earth moved from the Vestibule down toward the North and South Sally Ports. Some of the breccia in the Bear’s Den appears to have been frozen, cracked, slightly faulted, and then cemented with calcite (not dated, but stratigraphically in line with the dated MIS 9 sample, suggesting another breccia-cracking event in MIS 10).

Mechanism for Fracture of the Flowstone Sheets

The fractured fl owstone has triggered much speculation: MacEnery (1859) suggested tec-tonic activity as the cause, Pengelly (1876, p.176) suggested hydraulic pressure as the cause, and Proctor (1994) reverted to the earth-quake theory. Straw (1997), based on Proc-tor’s one date, assumed that it must have been caused by a single strong earthquake between ca. 100 ka and 75 ka. In response to Straw’s (1997) article, Ford (1997) collected several references to fractures observed in other caves in Devon, and speculated that all of them are attributable to earthquake activity; however, he offered no substantive support for the fracture events. For example, Ford reassessed Sutcliffe’s (1960) frost-heave interpretation of the fractured calcite sheet in Joint Mitnor cave as earthquake damage. The evidence Ford invoked is largely negative; he argued that frost heave is unlikely 100 km from the glacial margin and in a region under maritime infl uence, and, assuming that frost heave requires the presence of permafrost, the only explanation is earthquake damage.

We present unequivocal evidence that the fracturing occurred repeatedly throughout the middle to late Pleistocene history of the cave, and that it occurred during each cold episode since the fi rst layer of calcite was deposited in MIS 11. The arguments that the region could not have been cold enough have very little empiri-cal support. Croot and Griffi ths (2001) mapped fossil polygons and stripes within ~10 km of the cave and many examples of frost-related fea-tures both on Dartmoor and at many coastal sites all around Devon and Cornwall. Some recon-structions of conditions at 20 ka in the region ( Murton and Lautridou, 2003) show the whole region, including Torquay and Dartmoor, under continuous permafrost, while others show perma-frost only on Dartmoor (and presumably sea-sonal frost elsewhere), and some show discon-tinuous perma frost just a few kilometers north of Torquay. Evidence that Devon probably under-went discontinuous permafrost, at least during the coldest periods, was provided by Ballantyne and Harris’s (1993) fi nding of a fossil pingo on West Dartmoor. Croot and Griffi ths (2001) sug-gested that during glacial periods the climate of Devon may have been similar to that of Svalbard today (which displays excellent examples of peri-glacial activity and frost-related features).

Considering that frost heave does not require the presence of permafrost, either continuous or discontinuous, and that it only required one signifi cant frost-heave event per cold interval to fracture the relatively thin calcite sheets, we argue that the evidence for frost shattering is

Crystalline Stalagmite:112-127 cm thick

The lower layer ofCrystalline Stalagmite7.5 cm thick

The “Vacuity”

The Lake

1 m

WG1U: 307 ±5 kaMIS 9

Granular Stalagmite

Thin layer of Brecciaon underside ofCrystalline Stalagmite

Slabs of Crystalline Stalagmite and bedrock in Breccia

Reconstruction of Water Gallery looking along Pengelly’sdatum to South. Series 11, Parallel 1 to 4

Breccia: coherent, rock-like, very rich in bones

Breccia: Incoherent, poor in bones

Void

Rock

Crystalline Stalagmite flowstoneCave Earth

Granular Stalagmite flowstone

Figure 15. Reconstruction of the sedimen-tary fi ll of Water Gallery looking along Pengelly’s datum, to the south. Information taken from Pengelly’s fi eld notes (1868–1880) for series 11, parallels 1–4.


Breccia: very rich in bones and rock fragmentsBreccia: Incoherent, poor in bones

Pengelly’s categories

Southwest Chamber: Presumed sequence of events. Cross section reconstructed from Pengelly’s field notes (1868-1880).

Crystalline Stalagmite flowstoneCave EarthGranular Stalagmite flowstone

VoidRock

Late MIS 12: Breccia introduced to cave.Early MIS 11: Bears move into cave; bears den on topof breccia; bones embed into muddy breccia.MIS11: Flowstone cap protects some parts.

MIS 9: Deposition of flowstone over earlier calcite andover bone-rich breccia.

MIS 10: Upper part of breccia + bones mobilized,creating vacuity;Material moved from Bears Den into SW Gallery.

MIS 8: Frost heaving of breccia; cracking of flowstone;mobilization of breccia.

MIS 7: Deposition of flowstone. MIS 6a: Cracking of flowstone.MIS 6b: Deposition of flowstone elsewhere in cave.MIS 6c: Remobilization of breccia, incorporation of rockand flowstone blocks.

MIS 5: Induration of top layer of breccia; deposition offlowstone.

MIS 4: Cracking of flowstone.MIS 3: Cementation with thin flowstone, deposition ofcave earth.MIS 2: Cracking of flowstone + breccia,remobilization of cave earth.

MIS 1: Rapid deposition of vuggy calcite, incorporation ofbroken flowstone and rock slabs.

MIS 11

MIS 12

MIS 11

MIS 12

MIS 11 MIS 11

MIS 9

MIS 9

MIS 9

MIS 11

MIS 9

MIS 9MIS 11

MIS 9

MIS 7

MIS 11

MIS 9

MIS 7

MIS 9

MIS 11

MIS 9

MIS 7

MIS 5

MIS 11

MIS 9

MIS 7

MIS 5

MIS 9 MIS 9

MIS 9 MIS 9

MIS 11

MIS 9

MIS 7

MIS 5MIS 9

MIS 1

MIS 1MIS 3

MIS 3

MIS 3

MIS 3

MIS 10

1 m

MIS 12, 11

MIS 8 MIS 7

MIS 5 MIS 4,3,2

MIS 9

MIS 6

MIS 1

1 m

Figure 16. Reconstruction of the sedimentary fi ll of Southwest Chamber, and the sequence of events required to explain the sediments.



overwhelming. The occurrence of at least seven earthquakes of suffi cient magnitude to crack the sheets, all coincidental with glacial periods, is extremely improbable. As further argument we cite Forti’s (2004) discussion of tectonic effects on speleothems: tectonic stresses can be recog-nized by the characteristic fracture, the most typical being breakage of stalagmites along sub-horizontal planes, by the consistent breakage in certain directions, and by breakages being grouped together in time. Forti (2004) was ada-mant that all other possible causes of breakage must be discounted, such as simple mechanical failure from increase in loading, from sliding of stalagmites and columns on unconsolidated materials, and from tongues of ice during glacia-tion. All Forti’s tectonic examples are of broken stalagmites or columns; none are of fl owstone sheets, and all examples come from regions of known and signifi cant tectonic activity. We suggest that the subhorizontal shear operating on a fl owstone sheet would produce low-angle greenstick fractures: the cracks we see in the cave are subvertical.

If frost heave is responsible for fl owstone fracture, then there should be an association of the relative thickness of both the potentially heaving material and the potentially fracturing material. So, a thick layer of water-saturated breccia will expand more than a thin layer, and a thin layer of fl owstone will fracture more easily than a thick layer. Figure 17A is a simple map of the Breccia thickness. Both Proctor (1994) and Straw (1997) mapped the distribution of the Breccia from Pengelly’s original reports. This is the basis for Figure 17A, but we have divided the Breccia according to thickness, recon-structed partly from sections in Proctor (1994) and partly from fi eld observations. Figure 17B shows the distribution of intact fl owstone and fractured fl owstone, a simplifi ed version of Straw’s (1997) map. The accuracy of this recon-struction is partly limited by the detail and accu-racy of Pengelly’s reports; we are aware that the level of detail deteriorated as his dig progressed, the earlier fi eld notes being considerably more detailed than the later ones (1868–1880). For example, we are aware of some areas, such as the Labyrinth, that show evidence that Pengelly blasted through intact crystalline stalagmite, yet this is not shown in Straw’s (1997) map. Figure 17C shows the distributions overlain: the two main areas of shattered fl owstone (yellow) coincide largely with thick breccia (blue), pro-ducing the pattern of green in the Bear’s Den and the Hedges Boss–Inscribed Boss region. The intact fl owstone (red) in many areas is not underlain by any breccia: otherwise it is under-lain by thin breccia (gray). The combination of thin breccia and fractured fl owstone (gray-

green) occurs only in a very thin line on the western side of Clinnick’s Gallery. The com-bination of thick breccia and intact fl owstone (purple) occurs only under the bosses, where the fl owstone is too thick to fracture. Thus Fig-ure 17C offers support for the assertion that the fracture is associated with the thickest breccia and is thus most likely to represent frost heave. Freezing of the Breccia could easily have been achieved in a single cold season, and suffi cient aeration of the cave was likely, in view of the numerous open or semi-open routes for entry of sediments and/or animals.

Mechanism for Remobilization of Breccia

Evidence for removal and remobilization of the Breccia is clear. Some removal may have been from fl uvial activity, but the only clear evidence of this is in the paragenetic activity on the roof of Rocky Chamber. The upper few decimeters of breccia has remained mobile such that artifacts and fractured pieces of calcite were moved from their source (e.g., Bear’s Den) to new locations (e.g., Southwest Chamber) and yet are still emplaced within the Breccia matrix with no evidence for fl uvial deposition. We reject the theory that water-rich debris fl ows effected this remobilization on the basis that little evidence can be found for fl uvial orientation, sorting, or lamination. Long sections of the routes taken by the Breccia (Fig. 18) show slopes of ~3°. Debris fl ows generally require slopes of >20°, but solifl uction fl ows can operate on only a few degrees. The slopes of the entrance regions are steep enough to allow for either debris fl ow or solifl uction. However, the gentle slopes of the main passages would preclude debris fl ows as a mechanism for breccia remobilization. We sug-gest that the most likely mechanism for Breccia and Cave Earth movement is solifl uction.

CONCLUSIONS

The sedimentary history of Kents Cavern is considerably more complex than has previously been recognized. The deposits record a rich, cyclic history of events that track all the major climatic cycles of the past 500 k.y. of British Pleistocene history—a situation not known for any other European cave or subaerial site. Most of the deposits show some evidence of complex reworking, and the fl owstone layer designated in the literature as Crystalline Stalagmite is shown to be a multilayered complex spanning MIS 11 to MIS 3. In summary, the fi rst deposit is of fl uvial sands. The second deposit, of muddy breccia, incorporates the famous Acheulian artifacts that were most likely fabricated during MIS 13 (latest Cromerian) and transported into

the cave by natural processes through suffosion dolines during MIS12. Subsequently, each inter-glacial period produced calcite deposition in the cave, and each glacial period caused periglacial activity in the cave, during which the calcite was fractured by frost heave, incorporated into the mud, and the mud moved by solifl uction.

The full sequence is as follows (see Fig. 19 and Table 3).

1. MIS 15–13: late Cromerian warm stage: extensive surface weathering of hillside; deep regolith forms; vadose transport into cave of fl uvial mud, sand and gravel, the Red Sands; fabrication of Acheulian artifacts.

2. MIS 12: Anglian glaciation: formation and emplacement of breccia with entrained artifacts.

3. MIS 12 (terminal phase)–early MIS 11: Bears hibernate in cave.

4. MIS 11: Deposition of calcite layers; bears hibernate in cave.

5. MIS 10: Cracking of fl owstone and of breccia; removal and mobilization of breccia.

6. MIS 9: Deposition of calcite.7. MIS 8: Cracking of calcite, remobilization

of breccia.8. MIS 7: Deposition of calcite.9. MIS 6c: Cracking of calcite.10. MIS 6b: Deposition of thin calcite fl ow-

stone.11. MIS 6a: Cracking of fl owstone, remobili-

zation of breccia.12. MIS 5 e-a: Deposition of calcite.13. MIS 4: Cracking of calcite; remobiliza-

tion of breccia.14. MIS 3: Deposition of calcite, emplace-

ment of Cave Earth.15. MIS 2: Cracking of calcite and breccia;

mobilization of Cave Earth.16. MIS 1: Deposition of Granular Stalagmite.In addition to providing the most complete

Pleistocene record yet documented from any British cave, this report is also the fi rst publica-tion of well-dated and clearly documented evi-dence of frost heaving in interior cave passages. The magnitude of the internal cave response to major global climatic shifts is of interest. This history of repeated sedimentation events fol-lowed by frost shattering and remobilization events is probably unique in the karst literature. The uniqueness of the Kents Cavern sequence is likely an artifact of the relative lack of study that cave sedimentary sequences—rather than simply isolated speleothems—have received. We hope that the Kents cavern record will serve as a demonstration of the potential of these sequences, and focus future attention on the conservation and study of other poten-tially important cave sedimentary sequences in Britain and elsewhere.


Wolf’sCave

Bear’s Den Boss

Terminal Chamber

NorthEntrance

SouthEntrance

SouthwestChamber

Long

arca

deRockyChamber



Hedges Boss


InscribedBoss

In-Between Boss

High Level Chamber

Gallery

Cave of Rodentia

South Sally Port

NorthSallyPort

CharcoalCave

Vestibule

Lake

Water Gallery

Thin breccia andintact flowstone

Thick breccia andfractured flowstone

Thin breccia andfractured flowstone

Thick breccia andintact flowstone

30 m

N

BRECCIA FLOWSTONEA B

C BRECCIA +FLOWSTONE

Thick breccia

Thin breccia Intact flowstone

Fractured flowstone

Figure 17. (A) Simplifi ed survey (after Proctor and Smart, 1989) showing the distribution of major breccia deposits in the cave. The location of the Breccia follows Proctor (1994) and Straw (1997), both of whom based their mapping on fi eld notes of Pengelly. The division into Thick (breccia exposed is >~1.5 m thick) and Thin (breccia exposed is <~1.5 m thick) is based on sketched sections in Proctor (1994) and our own observations of the remnant breccia in the cave. (B) The distribution of the main fl owstone unit, the Crystalline Stalagmite, following Straw’s (1997) reconstruction from Pengelly’s notes. The division into Intact, representing fl owstone that has not been broken, and Fractured, representing fl owstone that is largely in situ but crazed or cracked with minor displacement, also follows Straw (1997). (C) The distributions from A and B superimposed so that four categories emerge from all possible combinations of breccia and fl owstone.


Doline/Rift ?

Bear’s Den Inlet RiftLake, Water Gallery

Bear’s Den

60 m O.D.

30

3331

3435

36

Extended Long Section from Bear’s Den to SouthWest Chamber to Lecture Hall to South Entrance

SouthwesT Chamber29Maze goingdown toHedges Boss

Breccia Route C:

Swallow HoleGallery

High Level Chamber

Hedges Boss Clinnicks GalleryRocky Chamber

60 m O.D.

910

11 7 6 5 4 3

?

Extended Long Section from Swallow Hole Gallery to Rocky Chamber

Swallow HoleGallery

High Level Chamber

Hedges Boss Long ArcadeWolf’s Cave

60 m O.D.

910

11 12 13 14 15 17

?

Extended Long Section from Swallow Hole Gallery to Long Arcade and Wolf’s Cave

Cave of Rodentia

Breccia Route A:

Breccia Route B:

To small phreatic maze passages

To small phreatic maze passages

35

Great Chamber

South Entrance

19

38

Lecture Hall

The Gallery

Charcoal Cave

Cave of Rodentia

?

18 17

Entrance route of breccia from surface

Entrance route of breccia from surfact

Slope = 3.2°

Slope = 2.9°

Slope = 2.9°

Slope= 2.8°

30 m

N

NorthEntrance

SouthEntrance

SouthwestChamber

Long

arca

de

RockyChamber



Hedges Boss


InscribedBoss

High Level Chamber

Gallery

Cave of Rodentia

CharcoalCave

Lake

Water Gallery

Wolf’sCave

Breccia Route A

Breccia Route B

Breccia Route C

Bear’s DenInlet Rift

Kents Cavern:Routes forBreccia flow

Figure 18. Probable routes for the main breccia fl ows in the cave, shown in plan view and in extended long sections. The long sections are reconstructed from the numbered cross sections in the survey of Proctor and Smart (1989). At least two entrances appear to have admitted breccia, the one in Swallow Hole Gallery and the other in the Bear’s Den area, most likely the inlet rift shown in section 30 of the survey. O.D. refers to ordinance datum.


Bas

sin

ot

(199

4)N

orm

aliz

edo

xyg

enis

oto

pe

valu

esB

riti

shn

ames

for

stag

esfr

om

ww

w.n

hm

.ac.

uk/

ho

sted

_sit

es/a

ho

b/o

verv

iew

_tim

e_ch

art.

gif

etal

.

-2 -1 0 1 2 30

2040

6080

100

120

140

160

180

200

220

240

260

280

300

320

340

360

380

400

420

440

460

480

500

520

540

Depositionofcalciteflowstone

RemobilizationofBreccia

RemobilizationorerosionofBreccia

Crackingofcalciteflowstone

Ag

e(k

a)

Ipsw

ichi

anS

tage

5

Sta

ge6

Ave

ley

Sta

ge7

Sta

ge8

Pur

fleet

Sta

ge9

Ang

lian

Sta

ge12

Cro

mer

ian

com

plex

Sta

ge13

-17

Widespreadweathering,deepregolith.FormationanddepositionofRedSands.ProductionofAcheulianartifacts.

FormationanddepositionofBreccia

Occupationbycavebears


DepositionofcalciteflowstoneFluvialerosion?Paragenesis?




CrackingofcalciteflowstoneRemobilizationofBreccia




CrackingofcalciteandBreccia

DepositionofCaveEarth

DepositionofGranularStalagmite

CrackingofcalciteflowstoneRemobilizationofBreccia

U-T

hda

te,2

rang

eσ

U-T

hda

te,i

soch

ron

date

,2ra

nge

σ

Probablecrackingofcalciteflowstone

RemobilizationofBreccia

RemobilizationofCaveEarth

RemobilizationofBrecciaH

oxni

anS

tage

11

35

42

67

89

1011

1213

1

Fla

ndria

nS

tage

1

Dev

ensi

anS

tage

2S

tage

10

Isot

ope

stag

ebo

unda

ries

Fig

ure

19. T

he P

leis

toce

ne d

epos

itio

nal h

isto

ry o

f K

ents

Cav

ern

sum

mar

ized

on

the

tim

e lin

e. T

he m

arin

e ox

ygen

isot

ope

curv

e is

fro

m

Bas

sino

t et

al.

(199

4),

as a

re t

he s

tage

mar

kers

(sh

own

here

as

red

tria

ngle

s).

The

rad

iom

etri

c da

tes

are

show

n w

ith

2σ e

rror

bar

s.

Per

iods

of

clas

tic

sedi

men

tati

on a

nd r

emob

iliza

tion

of

the

Bre

ccia

are

sho

wn

in y

ello

w. P

erio

ds o

f ca

lcit

e de

posi

tion

are

sho

wn

in p

ink.

P

erio

ds o

f fr

actu

ring

are

sho

wn

in g

ray.

The

Bri

tish

nam

es f

or s

tage

s ar

e sh

own,

in r

ed f

or t

he in

terg

laci

al p

erio

ds, a

nd in

blu

e fo

r th

e gl

acia

l per

iods

. The

dis

trib

utio

n of

dat

es r

efl e

cts

sam

plin

g ef

fort

rat

her

than

thi

ckne

ss o

f ca

lcit

e gr

owth

.


TABLE 3. SUMMARY OF EVIDENCE FOR EVENTS

Age Event Site Evidence Cromerian Red Sands deposition Gallery >580 ka Al-Be MIS 12 Breccia deposition Labyrinth >400 ka Al-Be MIS 12 Breccia deposition Hedges Under MIS 11 calcite MIS 11 Calcite deposition Hedges Calcite on top of breccia MIS 11 Calcite deposition Bear’s Den Calcite on top of breccia MIS 11 Calcite deposition Southwest On upper level, former breccia surface MIS 10c Breccia movement Southwest Breccia surface lowered between MIS 11 calcite and MIS 10b

calcite MIS 10b Calcite deposition Southwest On top of breccia MIS 11-9 ? Fracture + movement Water Gallery MIS 11? slab broken and covered by breccia, covered by MIS 9

calcite MIS 11-9 Breccia fracture + remobilization Bear’s Den Breccia remobilized to cover MIS 11 calcite, but under MIS 9

calcite; Breccia frozen, cracked and shifted; older calcite (MIS 11?) cracked and moved

MIS 11-9 Breccia remobilization Water Gallery Breccia had been higher on wall, removed before MIS 9 calcite deposition

MIS 9 Calcite deposition Bear’s Den Calcite on top of reworked breccia MIS 9 Calcite deposition Water Gallery Calcite on top of thin red muddy film on wall; remnant of breccia MIS 9 Calcite deposition In-Between Rapid, thick flowstone deposition above breccia MIS 9 Calcite deposition Labyrinth Rapid, thick flowstone deposition above breccia MIS 9 Calcite deposition Labyrinth Broken slab within breccia MIS 9 Calcite deposition Southwest Calcite flowstone on top of MIS 11 calcite and on top of breccia Post–MIS 9 Fracture + movement Labyrinth MIS 9 calcite slab in breccia broken and moved

eticlac 7 SIM yb dellif ,dekcarc ssob enotswolf 9 SIM fo egde nihT neewteB-nI erutcarF 8 SIMPre–MIS 7 Breccia remobilization Clinnick’s Breccia had been higher on wall, removed before MIS 7 calcite

depositionMIS 7 Calcite deposition In-Between Calcite on MIS 9 calcite, cementing crack MIS 7 Calcite deposition Labyrinth Slab in breccia MIS 7 Calcite deposition Southwest On top of MIS 9 calcite Post–MIS 7 Fracture + movement Labyrinth MIS 7 calcite slab in breccia broken and moved

arc eticlac 9 SIM neewteB-nI erutcarF c6 SIM cked, cemented by MIS 6b calcite but no MIS 7 calcite

MIS 6c Fracture + movement Southwest MIS 7 calcite fractured and removed to make way for MIS 6b calcite

MIS 6b Calcite deposition In-Between Calcite on top of MIS 9 calcite, cementing crack MIS 6b Calcite deposition Southwest Slab within breccia MIS 6a Fracture + movement Southwest MIS 6b calcite broken and moved, cemented by MIS 5; induration

of breccia? MIS 5 Calcite deposition In-Between Sequence from 5c to 5a MIS 5e Calcite deposition High Level Calcite on top of breccia MIS 5e Calcite deposition Southwest Calcite flowstone MIS 5e–3 Fracture + movement High Level MIS 5e calcite fractured, removed, covered with thin red calcite

coatingMIS 5a Calcite deposition Clinnick’s Top of ~30 cm laminated flowstone, probably MIS 5e–a

eticlac 3 SIM yb detnemec ,eticlac a5 SIM fo erutcarF s’kcinnilC erutcarF 4 SIMMIS 4 Fracture + movement High Level MIS 5e calcite cracked, removed, cemented by MIS 5a calcite MIS 3 Calcite deposition High Level Calcite on top of fracture surface of MIS 5e calcite MIS 3 Calcite deposition Clinnick’s Red calcite cementing broken slabs of MIS 5a calcite

eticlac der 3 SIM fo erutcarF s’kcinnilC erutcarF 1–3 SIMMIS 3–2 Cave earth deposition Radiocarbon dates

eticlac 1 SIM yb detnemec dna dekcarc eticlac 3 SIM s’kcinnilC erutcarF 2 SIMMIS 2 Fracture of breccia and calcite +

movement of cave earth Breccia and calcite fragments incorporated in cave earth;

Pengelly’s notes (1868–1880) + Straw’s (1997) map MIS 1 Calcite deposition Clinnick’s Granular stalagmite cementing broken slabs of MIS 3 calcite MIS 1 Calcite deposition In-Between Active stalagmite and curtains at top of boss MIS 1 Calcite deposition Southwest Granular Stalagmite, radiocarbon dates



ACKNOWLEDGMENTS

We are indebted to Nick Powe, owner and managing director of Kents Cavern, for his encouragement of this project. We also thank Barry Chandler of the Torquay Museum for access to specimens and manuscripts in his care, and two anonymous referees for helpful com-ments on an earlier version of this manuscript. We are grateful to Darryl E. Granger and the staff of PRIME Lab, Purdue University, for cosmogenic dating sup-port and advice. Permission to collect samples from this scheduled Ancient Monument was granted by English Heritage Secretary of State for Culture, Media and Sport under permit # HSD 9/2/7663. Partial fund-ing was provided by the Andrew Mellon Foundation under a sabbatical improvement grant through Scripps College (to McFarlane), and through a research sup-port grant from Pitzer College (to McFarlane), and Natural Sciences and Engineering Research Council grant (to Lundberg). This is Ottawa-Carleton Geo-science Centre, Isotope Geochemistry and Geo-chronology Research Facility contribution 44.

REFERENCES CITED

Andrews, P., 1990, Owls, caves and fossils: London, Natural History Museum, 231 p.

Anthony, D., and Granger, D.E., 2004, A late Tertiary ori-gin for multilevel caves along the western escarpment of the Cumberland Plateau, Tennessee and Kentucky, established by cosmogenic 26Al and 10Be: Journal of Cave and Karst Studies, v. 66, p. 46–55.

Ballantyne, C.K., and Harris, C., 1993, The periglaciation of Great Britain: Cambridge, Cambridge University Press, 330 p.

Bassinot, F.C., Labeyrie, L.D., Vincent, E., Quidelleur, X., Shackleton, N.J., and Lancelot, Y., 1994, The astro-nomical theory of climate and the age of the Brunhes-Matuyama magnetic reversal: Earth and Planetary Science Letters, v. 126, p. 91–108, doi: 10.1016/0012-821X(94)90244-5.

Bates, M.R., Keen, D.H., and Lautridou, J.-P., 2003, Pleis-tocene marine and periglacial deposits of the English Channel: Journal of Quaternary Science, v. 18, p. 319–337, doi: 10.1002/jqs.747.

Bertran, P., Hétu, B., Texier, J.-P., and Van Steijn, H., 1997, Fabric characteristics of subaerial slope deposits: Sedimentology, v. 44, p. 1–16, doi: 10.1111/j.1365-3091.1997.tb00421.x.

Bishop, M.J., 1982, The mammal fauna of the early middle Pleistocene cavern infi ll site of Westbury-sub-Mendip, Somerset: Palaeontological Association Special Paper, v. 28, p. 1–108.

Campbell, J.B., and Sampson, C.G., 1971, A new analysis of Kents Cavern, Devonshire, England: University of Oregon Anthropological Papers, v. 3, p. 1–39.

Campbell, S., Hunt, C.O., Scourse, J.D., and Stephens, N., 1998a, Quaternary of south-west England: London, Chapman and Hall, 439 p.

Campbell, S., Keen, D.H., Currant, A.P., Collcutt, S.N., and Stuart, A.J., 1998b, Pleistocene cave sequences, in Campbell, S., et al., eds., Quaternary of south-west England: Geological Conservation Review Series, v. 14, p. 129–153.

Cheng, H., Edwards, R.L., Hoff, J., Gallup, C.D., Richards, D.A., and Asmerom, Y., 2000, The half-lives of uranium-234 and thorium-230: Chemical Geology, v. 169, p. 17–33, doi: 10.1016/S0009-2541(99)00157-6.

Collcutt, S.N., 1986, Contextual archaeology: The example of debris fl ow in caves, in Collcutt, S.N., ed., The Palaeo-lithic of Britain and its nearest neighbours: Recent trends: Sheffi eld, University of Sheffi eld, p. 57–58.

Cook, J., and Jacobi, R., 1998, Observations on the artefacts from the Breccia at Kents Cavern, in Ashton N., et al., eds., Stone age archaeology: Essays in honour of John Wymer: Lithic Studies Society Occasional Paper 6, p. 77–89.

Croot, D., and Griffi ths, J.S., 2001, Engineering geological signifi cance of relict periglacial activity in South and East Devon: Quarterly Journal of Engineering Geology and Hydrology, v. 34, p. 269–281.

Cullingford, R.A., 1982, The Quaternary, in Durrance, E.M., and Laming, D.J.C., eds., The geology of Devon: Exeter, University of Exeter Press, p. 249–290.

Dowling, L.A., and Coxon, P., 2001, Current understanding of Pleistocene temperate stages in Ireland: Quaternary Science Reviews, v. 20, p. 1631–1642, doi: 10.1016/S0277-3791(01)00028-2.

Durrance, E.M., and Laming, D.J.C., eds., 1982, The geology of Devon: Exeter, University of Exeter Press, 346 p.

Ford, T.D., 1997, Stalagmite sheets shattered by earthquakes: Cave and Karst Science, v. 24, p. 140–141.

Forti, P., 2004, Paleotectonics from speleothems, in Gunn, J., ed., Encyclopedia of cave and karst science: Lon-don, Fitzroy Dearborn, p. 565–566.

Granger, D.E., and Muzikar, P., 2001, Dating sediment burial with cosmogenic nuclides: Theory, techniques, and limitations: Earth and Planetary Science Letters, v. 188, p. 269–281, doi: 10.1016/S0012-821X(01)00309-0.

Granger, D.E., Fabel, D., and Palmer, A.N., 2001, Pliocene–Pleistocene incision of the Green River, Kentucky, deter-mined from radioactive decay of cosmogenic 26Al and 10Be in Mammoth Cave sediments: Geological Society of America Bulletin, v. 113, p. 825–836, doi: 10.1130/0016-7606(2001)113<0825:PPIOTG>2.0.CO;2.

Grün, R., and Schwarcz, H.P., 2000, Revised open system U-series/ESR age calculations for teeth from Stratum C at the Hoxnian Interglacial type locality, England: Quaternary Science Reviews, v. 19, p. 1151–1154, doi: 10.1016/S0277-3791(00)00085-8.

Ivanovich, M., and Harmon, R.S., eds., 1992, Uranium-series disequilibrium: Applications to Earth, marine and environmental sciences (second edition): Oxford, Clarendon Press, 910 p.

Ivanovich, M., Latham, A.G., and Ku, T.-I., 1992, Uranium-series disequilibrium applications in geochronology, in Ivanovich, M., and Harmon, R.S., eds., Uranium-series disequilibrium: Applications to Earth, marine and envi-ronmental sciences (second edition): Oxford, Clarendon Press, p. 62–89.

Kaufman, A., and Broecker, W., 1965, Comparison of 230Th and 14C ages for carbonate materials from Lakes Lahontan and Bonneville: Journal of Geophysical Research, v. 70, p. 4039–4054.

Keith, A., Myres, J.L., Burkitt, M.C., Favell, R.V., Garfi tt, G.A., Garrod, D.A.E., and Sollas, W.J., 1931, Kents Cavern, Torquay: British Association for the Advance-ment of Science, Report of the 98th Annual Meeting, p. 266–267.

Kurtén, B., 1968, Pleistocene mammals of Europe: London, Weidenfeld and Nicolson, 317 p.

Lister, A.M., McGlade, J.M., and Stuart, A.J., 1990, The early middle Pleistocene vertebrate fauna from Little Oakley, Essex: Royal Society of London Philosophi-cal. Transactions, ser. B, v. 238, p. 359–385.

MacEnery, J., 1859, Cavern researches, or Discoveries of organic remains, and of British and Roman reliques, in the caves of Kents Hole, Anstis Cove, Chudleigh, and Berry Head: London, Simpkin, Marshall, and Co., 78 p.

McCarroll, D., 2002, Amino-acid geochronology and the British Pleistocene: Secure stratigraphical framework or a case of circular reasoning?: Journal of Quaternary Science, v. 17, p. 647–651, doi: 10.1002/jqs.690.

McFarlane, D.A., and Lundberg, J., 2005, The 19th century excavation of Kents Cavern, England: Journal of Cave and Karst Studies, v. 67, p. 39–47.

McFarlane, D.A., Lundberg, J., and Sabol, M., 2006, Middle Pleistocene cave bears from Kents Cavern, England: Geological Society of America Abstracts with Pro-grams, v. 38, no. 7, p. 214.

Millar, S.W.S., 2006, Processes dominating macro-fabric generation in periglacial colluvium: Catena, v. 67, p. 79–87, doi: 10.1016/j.catena.2006.03.003.

Murton, J.B., and Lautridou, J.-P., 2003, Recent advances in the understanding of Quaternary periglacial features of the English Channel coastlands: Journal of Quaternary Science, v. 18, p. 301–307, doi: 10.1002/jqs.748.

Oxford Radiocarbon Accelerator Unit, 2006, Results data-base: http://c14.arch.ox.ac.uk/results.html.

Parfi tt, S., Barendregt, R.W., Breda, M., Candy, I, Collins, J., Coope, G., Durbridge, G., Field, M., Lee, J., Lister, A., Mutch, R., Penkman, A., Preece, R., Rose, J., Stringer, C, Symmons, R., Whittaker, J., Wymer, J., and Stuart, A., 2005, The earliest record of human activity in

northern Europe: Nature, v. 438, p. 1008–1012, doi: 10.1038/nature04227.

Pengelly, W., 1868–1880, Typed transcripts of original handwritten fi eld notes, held in Torquay Museum, Devon, UK.

Pengelly, W., 1869, The literature of Kents Cavern: Part II: Devonshire Association Transactions, v. 3, p. 191–482.

Pengelly, W., 1884, The literature of Kents Cavern: Part V: Devon shire Association Transactions, v. 14, p. 189–343.

Pevzner, M., Vangengeim, E., and Tesakov, A., 2001, Qua-ternary zonal subdivisions of Eastern Europe based on vole evolution: Bulletino dell Società Paleontologica Italiana, v. 40, p. 269–274.

Preece, R.C., 2001, Molluscan evidence for differentiation of interglacials within the “Cromerian Complex”: Qua-ternary Science Reviews, v. 20, p. 1643–1656, doi: 10.1016/S0277-3791(01)00032-4.

Proctor, C.J., 1994, A British Pleistocene chronology based on U-series and ESR dating of speleothem [Ph.D. thesis]: Bristol, University of Bristol, 353 p.

Proctor, C.J., and Smart, P.L., 1989, A new survey of Kents Cavern, Devon: University of Bristol Spelaeological Society Proceedings, v. 18, p. 422–429.

Proctor, C.J., Berridge, P.J., Bishop, M.J., Richards, D.A., and Smart, P.L., 2005, Age of middle Pleistocene fauna and lower Palaeolithic industries from Kents Cavern, Devon: Quaternary Science Reviews, v. 24, p. 1243–1252, doi: 10.1016/j.quascirev.2004.07.022.

Rowe, P.J., Atkinson, T.C., and Turner, C., 1999, U-series dating of Hoxnian interglacial deposits at Marks Tey, Essex, England: Journal of Quaternary Sci-ence, v. 14, p. 693–702, doi: 10.1002/(SICI)1099-1417(199912)14:7<693::AID-JQS477>3.0.CO;2-X.

Schwarcz, H.P., and Blackwell, B.A., 1992, Archaeological applications, in Ivanovich, M., and Harmon, R.S., eds., Uranium-series disequilibrium: Applications to Earth, marine and environmental sciences (second edition): Oxford, Clarendon Press, p. 513–552.

Schreve, D.C., 2001, Differentiation of the British late middle Pleistocene interglacials: The evidence from mammalian biostratigraphy: Quaternary Science Reviews, v. 20, p. 1693–1705, doi: 10.1016/S0277-3791(01)00033-6.

Schreve, D.C., and Thomas, G.N., 2001, Critical issues in European Quaternary biostratigraphy: Quaternary Science Reviews, v. 20, p. 1577–1582, doi: 10.1016/S0277-3791(01)00024-5.

Schwarcz, H.P., and Latham, A.G., 1989, Dirty calcites 1: Uranium series dating of contaminated calcite using leachates alone: Chemical Geology, v. 80, p. 35–43.

Scourse, J.D., Austin, W.E.N., Sejrup, H.-P., and Ansari, M.H., 1999, Foraminiferal isoleucine epimerization determinations from the Nar Valley Clay, Norfolk, UK: Implications for Quaternary correlations in the south-ern North Sea basin: Geological Magazine, v. 136, p. 543–560, doi: 10.1017/S0016756899002812.

Scrivener, M.F., 1987, An introduction to the geology of the Torquay District: Torquay, Devon, Torquay Natural History Society, 18 p.

Stock, G.M., Granger, D.E., Sasowsky, I.D., Anderson, R.S., and Finkel, R.C., 2005, Comparison of U-Th, paleo-magnetism, and cosmogenic burial methods for dating caves: Implications for landscape evolution studies: Earth and Planetary Science Letters, v. 236, p. 388–403, doi: 10.1016/j.epsl.2005.04.024.

Straw, A., 1997, Kents Cavern—Whence and whither?: Cave and Karst Science, v. 24, p. 35–40.

Sutcliffe, A.J., 1960, Joint Mitnor Cave, Buckfastleigh: Torquay Natural History Society Transactions, v. 13, p. 3–28.

Sutcliffe, A.J., and Kowalski, K., 1976, Pleistocene rodents of the British Isles: British Museum (Natural History) Bulletin, Geology, v. 27, p. 1–147.

Thomas, G.N., 2001, Late middle Pleistocene pollen bio-stratigraphy in Britain: Pitfalls and possibilities in the separation of interglacial sequences: Quaternary Science Reviews, v. 20, p. 1621–1630, doi: 10.1016/S0277-3791(01)00026-9.

MANUSCRIPT RECEIVED 5 JANUARY 2007REVISED MANUSCRIPT RECEIVED 13 APRIL 2007MANUSCRIPT ACCEPTED 25 APRIL 2007

Pleistocene depositional history in a periglacial terrane...

Documents

Transcript of Pleistocene depositional history in a periglacial terrane...