Dating of late Pleistocene interglacial and interstadial periods in the United Kingdom from...

QUATERNARY RESEARCH 31, 1426 (1989)

Dating of Late Pleistocene Interglacial and lnterstadial Periods in the United Kingdom from Speleothem Growth Frequency

DAVID GORDON AND PETER L. SMART

Department of Geography, University of Bristol, Bristol BS8 ISS, England

D. C. FORD

Department of Geography, McMaster Universiv, Hamilton LBS 4K1, Canada

J. N. ANDREWS

Department of Chemistry, University of Bath, Bath BA2 7A Y, England

T. C. ATKINSON AND P. J. ROWE

School of Environmental Sciences, University of East Anglia, Norwich NR4 7JT, England

AND

N. S. J. CHRISTOPHER

Housman (Burnham) Ltd., The Priory, Burnham, SLI 7LS, England

Received April 22, 1987

The growth of speleothems is indicative of interglacial and interstadial conditions in the United Kingdom, since their growth is dependent on two factors. First, the occurrence of significant diffuse groundwater recharge and, second, the biogenic production of carbon dioxide in the soil, both are dependent on temperature and water availability. The growth frequency of speleothems is examined using a cumulative distributed error frequency method applied to 341 uncontaminated uranium-series age determinations. The curves derived are shown to be statistically stable, and the ages of the peaks are interpreted as the best estimates of the ages of interglacial and interstadial periods. Ten such periods are recognized during the interval 220,000 to 20,008 yr B.P., consider- ably more than are currently recognized in the UK pollen- and coleoptera-based Quatemary stratigraphy. Correlations between the speleothem growth frequency peaks and last interglacial (Ipswichian) sites can be made, but correlations with last glacial (Devensian) interstadial sites are limited because of the paucity of dates. The speleothem growth frequency record provides a well-dated terrestrial chronology for the past 140,000 yr B.P., which directly reflects regional palaeoclimatic conditions in Britain, and should prove very useful in unravelling the complex stratigraphy of the Devensian and Ipswichian stages. 0 1989 University of Washington.

PALAEOCLIMATIC SIGNIFICANCE OF SPELEOTHEM GROWTH

Speleothems are secondary deposits of calcium carbonate, such as stalagmites, which accumulate in limestone caverns. They are of importance in Quaternary studies both because they may be dated by uranium-series methods (Schwartz, 1980) and because they yield useful palaeoclimatic information (Atkinson et al., 1978; Harmon

et al., 1977,1978; Gascoyne et al., 1983). In this paper we consider the palaeoclimatic implications of speleothem growth frequency in the British Isles during the last 220,000 yr, and interpret the results with respect to the recognized stages and substages of the British Quaternary.

While other processes driving speleothem deposition are known, including evaporation (Harmon et al., 1983), temperature changes (Dreybrodt, 1982), and the

14 0033-5894189 $3.00 Copyright 0 1989 by tbe University of Washington. All rights of reproduction in any form reserved.

BRITISH SPELEOTHEM AGES 15

common ion effect (Atkinson, 1983), in deep caves of limestone terrains these are unimportant compared to the degassing of percolating groundwaters with elevated dis- solved carbon dioxide concentrations (White, 1976). The carbon dioxide is derived from the soil atmosphere, where it is generated by microbial processes and root respiration. Drake and Wigley (1975) have demonstrated that the observed relation between the Pco, of carbonate groundwaters and mean annual temperature (Drake, 1980) is due to the control of temperature on these biological processes. More recently, Brook et al. (1983) argued that moisture availability is also important and modeled world soil Pco, using actual evapotranspi- ration. Soil Pco2 is also dependent on the type of vegetation cover, with higher values under woodland than adjacent grassland (Gunn and Trudgill, 1982). Thus, groundwaters collected below the tree line in alpine carbonate terrains have a higher Pco2 than groundwaters from above the tree line (Ford, 1971).

The theory outlined above provides the basis for the palaeoclimatic interpretation of speleothem growth frequency. During cold climatic phases, the generation of bio- genie carbon dioxide in the soil is limited because of sparser vegetation, low temper- atures, and reduced water availability (Van Cleve and Sprague, 1971; Poole and Miller, 1982), and in the case of glacierization may stop completely. Furthermore, where permafrost develops, diffuse groundwater recharge will be greatly reduced (Kane and Stein, 1984), although concentrated recharge may still continue (Tolstikhin et al., 1963). Consequently, under cold conditions, speleothem deposition will be very slow or cease entirely. This is supported by observations in alpine areas and those of northerly latitude which at present have cold climates (Harmon et al., 1977; Lau- ritzen and Gascoyne, 1980). In contrast, during warm periods increased biological activity yields high soil Pco2 and recharge

can occur freely, resulting in the deposition of speleothem.

Initial studies of the timing of periods of speleothem growth were limited by the small number of uranium-series analyses available (Harmon et al., 1975; Atkinson et al., 1978), but developments in instrumen- tation and the establishment of new analytical facilities permitted a gradual increase in the data base. An encouraging degree of agreement between the speleothem record based on global or supraregional compila- tions, and that derived from the oxygen- isotope curves from ocean cores was reported by Harmon et al. (1977) and Hennig et al. (1983). However, paleoclimatic changes over such large areas were neither synchronous nor of similar magnitude, and degradation of the resultant composite record may therefore be a problem. A second major constraint was the simple histogram- based data presentation, which neccessi- tates a broad fixed time-class interval and assumes all dates have similar uncertainties. Hennig et al. (1983) were the first to suggest an alternative scheme of analysis, but their technique was crude and also in- troduced a weighting on each date propor- tional to its age.

Here we employ the more rigorous cumulative distributed error frequency curve technique of Gordon and Smart (1984) to analyze the now considerable number of uranium-series analyses of speleothems from sites in the British Isles. This area is sufficiently small that climatic change has been essentially synchronous, and while there are climatic differences between Scotland and the Channel Islands, these are relatively small compared to the magnitude of Quaternary climatic changes.

DATA AND METHODS

Of the 521 uranium-series analyses used in this study, 329 are from published sources, while 192 are drawn from unpublished data. Three analyses of tufa are also

16 GORDON ET AL.

included. Only finite dates with finite uncertainties have been included; all dates less than 1500 yr old (the effective lower limit of the method) are excluded. All analyses have also been screened to ensure that the calculated ages are reliable. Thus, analyses for which the chemical yields are known to be less than 10% are excluded, although this information is not always included in published results. A more significant problem occurs for analyses in which leaching of 23”Th, and probably also uranium isotopes, has occurred from insoluble detritus (quartz grains and clays) present in the speleothem. This is indicated by the presence of significant 232Th, which should be absent in pure calcite containing no thorium on deposition. We have therefore excluded all analyses for which the 23”Th/ 232Th ratio is less than 20. While this signif- icantly reduces the available data, it will enhance the clarity with which periods of active growth can be defined, and is therefore desirable. Just over 34% of the available analyses have been discarded, leaving 341 in the final compilation (Table 1).

The geographical distribution of the areas sampled is shown in Figure 1, and can be seen to cover all of the significant cavern-

ous karst areas in Britain. Northwest York- shire is particularly well represented, due primarily to the extensive and exemplary work of Gascoyne et al. (1983). The remaining analyses are spread evenly between the southern and central sample areas, with 35% of the sample drawn from beyond the southern limit of the Devensian ice sheet, as defined by Bowen et al. (1986). In some areas the samples are from a single site, for instance, Pontnewydd Cave in North Wales (Green et al., 1981), and may therefore reflect the particular conditions at the site. However, for the main areas, a relatively large number of caves have been sampled, although there remains some bias due to particularly intense sampling.

The cumulative distributed error frequency curve technique employed provides a rigorous treatment of the counting uncertainties associated with each age estimate, by modeling the probable distribution of the true age about the quoted value (Fig. 2). Thus, analyses with low counting uncertainties are represented by peak distribu- tions with low dispersion (A, Fig. 2), while poor analyses with high uncertainty are much broader (C, Fig. 2). These distribu- tions are discretized at a preselected time

TABLE 1. GEOGRAPHICAL DISTRIBUTION AND SOURCES OF URANIUM SERIES ANALYSES (UNPUBLISHED ANALYSES ARE FROM THE AUTHORS LABORATORIES)

Area No. Analyses sites used

Analyses rejected Source

Jersey S. Devon Mendip Hills Cower Tawe Valley Marsworth Pontnewydd

Peak District 15 19 16 Creswell Craggs 4 26 11 N.W. Yorkshire 12 157 63

Sutherland 5 9 2 Total 57 341 179

0 1 4 0

59 44 11 20 16 13

1 2 39 7

Keen et al. (1981) Unpublished (4) Atkinson et al. (1978, 1984); Unpublished (89) Stringer et al. (1986); Sutcliffe and Currant (1984) Unpublished (29) Green et al. (1984) Schwartz, Ivanovich et al., and Debenham et al. in

Green (1984) Ford et al. (1983); Unpublished (6) Unpublished (37) Atkinson et al. (1978); Latham et al. (1979); Gascoyne et al. (1983); Sutcliffe ef al. (1985); Unpublished (2) Atkinson et al. (1986)


FIG. 1. Map of areas in the United Kingdom from which uranium series ages on speleothems and tufa were compiled, and glacial limits after Bowen et al. (1986).

interval and the cumulative frequencies for successive intervals calculated by summing the respective fractional probabilities for all analyses. All analyses are equally weighted by normalization, so the results can be expressed in terms of frequency (probability) of dates per time interval. This technique allows much smaller time intervals to be used in the cumulative compilation than in the histogram method, reduces problems at class boundaries, and permits much better temporal discrimination. We have employed an interval of 500 yr, allowing the potential recognition of events of twice this frequency and generating a smooth curve

over the time interval considered (O- 300,000 yr B.P.).

The distribution of the true age about the quoted value is asymmetric because age is related to the 23@I’h/234U ratio in a nonlinear manner, the upper error bound always being the larger. However, the errors in the isotopic ratios can be approximated by the normal distribution (Gascoyne , 1977)) and the probability density for each date can therefore be estimated in terms of the 23”Th/ 234U ratio. The ages and their upper and lower limits are therefore converted into 23aTh/234U ratios (which requires that the 234U/238U ratio is also known), and the probability distribution is calculated using the normal probability function. A check is made that the upper and lower limits of the ratio are equidistant from the mean; reported dates for which this is not the case are discarded. The boundaries between successive time intervals are also expressed in terms of the 230Th/234U ratio using the 234U/238U ratio for each date, and the respective cumulative probabilities calculated. The results of the compilation can be displayed in the form of a smooth curve describing the variation in the probability of true ages, or frequency of dates with time.

RELIABILITY OF THE SPELEOTHEM GROWTH RECORD

The cumulative age frequency curve for the compiled UK speleothem data is shown in Figure 3. Before discussing the paleoclimatic implications of this curve, it is necessary to consider other factors which may affect it. Of particular significance is the stability of the curve and the extent to which it may be biased by the inclusion and exclusion of particular analyses. This was tested in five runs for which 100 analyses (approximately 30% of the data) were removed at random from the screened data set. The results are shown in Figure 4 for the interval between 20,000 and 140,000 yr B.P. (only four of the five runs are shown

18 GORDON ET AL.

zp2-3 = 4.2-3 + p&2-3 + ‘C.2-3

Cumulative distributed error frequency curve

..,...... ZP=Po-,+p,+ PA+Ps+Pc=3

Age A 3tlx103years

Age 6 6’lxlO’years

Interval i = 1 x 103years

Age (lO$ears)

FIG. 2. Construction of the cumulative distributed error frequency curve (top graph). Three analyses are included in the compilation; two analyses (A and B) with identical counting uncertainties (expressed as rl SD), and one with a similar age to B but double the counting uncertainty (C). The time interval used for the frequency distribution is 1000 yr.

for clarity). It can be seen that the temporal suggest that smaller data sets than that used stability of the main peaks is very high. Mi- in this study are capable of generating rea- nor peaks such as A and C are more vari- sonably unbiassed curves. able (Table 2), as is the peak magnitude, Because of the exclusion of dates particularly when the peak forms a shoul- younger than 1500 yr B.P. and those with der on a broader peak (G and D for infinite error bars, there is a significant cut- instance). The results are encouraging and off at both the upper and lower limits of the


FIG. 3. Cumulative distributed error frequency curve for UK speleothem growth 0 to 300,000 yr B.P.

age range. This explains the general decline collected. Furthermore, many workers de- in frequency for ages in excess of 200,000 yr liberately select the geologically more im- B.P. In the case of the lower limits, the portant older material. The frequency dis- effect of the exclusion is augmented by tribution for ages less than 5000 yr B.P. is sampling bias. For conservation reasons, probably severely curtailed by these ef- fresh actively growing speleothems are not fects. Sampling bias may also be of signifi-

~ Rl ---_.-___.--- R2

------- R3

R‘f

0.1-l 20 40 60 60 100 120 1

Age (103years)

0

FIG. 4. Comparison of four UK speleothem growth frequency curves derived from the screened data set, but from which approximately 30% of the analyses have been removed by random sampling. Note the temporal stability of the peaks.

20 GORDON ET AL.

TABLE 2. VARIATION OF PEAK AGE AND PEAK HEIGHT FOR FIVE RUNS FROM WHICH 100 ANALYSES HAVE BEEN ABSTRACTED AT

RANDOM FROM THE MAIN DATA SET

Peak age Peak height (lo3 yr B.P.) (dates per 500 yr)

Peak x Range x SD

Ab 29.5 0.5 25.1 1.9 B 36.5 2.5 56.9 6.5 C” 44.5 0.5 42.4 8.9 D 49.5 2.0 49.3 4.0 E 57.0 1.5 54.3 7.6 F 76.0 1.0 37.9 3.3 H 105.5 1.5 85.9 3.2 I 119.5 1.5 72.8 3.2

Note. Peaks are lettered on Figure 3. a Peak absent in 1 run. b Peak absent in 2 runs.

cance in controlling the trend to lower frequencies with increasing age. Older deposits are often buried by more recent speleothem or sediments in caves, or may have been removed by erosion. The speleothems most readily available for sampling therefore tend to be young. Despite efforts to sample the geologically older material, this bias still remains. Thus, for the period 5000 to 15,000 yr BP., 55 analyses are included in the compilation, while only 24 are included for the period 100,000 to 110,000 yr B.P. Attempts to correct for this sampling bias by applying weightings based on the observed frequencies in climatically broadly comparable periods are unsuccess- ful because of the lack of structure in the frequency curve beyond 150,000 yr B.P.

The reduction in peak size with increasing age is not solely explained by the effects of sampling bias. There is a decrease in the absolute precision of the dates with increasing age, although the percentage error typ- ically remains about 10%. For a date of 10,000 yr BP. with 10% errors, the +l standard deviation zone (within which there is a 68% chance that the true age ac- tually lies) occupies four 500-yr class intervals. However, for a date of 100,000 yr B.P. the probability distribution is very much

broader, occupying forty SOO-yr class intervals. As a result, the cumulative frequency curve becomes smoother and the peak heights are reduced with increasing age, giving poorer discrimination of individual peaks. To overcome this effect, it will be necessary either to obtain much higher precision analyses of older samples or to employ a transformation of the time axis, the approach currently being developed.

An associated problem, recently also considered by Kaufman (1986), is the degree of temporal discrimination which can be achieved by ages having a particular uncertainty. It is clear from the form of the growth frequency curve that some relatively small peaks are almost obscured by the much larger adjacent peaks (Fig. 3). This may cause a shift in the temporal position of the lesser peak toward the larger peak, a factor of some significance if the speleothem growth frequency curve is to be employed as a terrestrially based timescale for Quaternary events. We have investi- gated this problem by recalculation of the growth frquency curve after the progressive removal of dates with standard deviations greater than a series of specified values (Fig. 5). There is, of course, some mi- nor distortion caused by clusters of particularly high precision dates, most no- ticeably for peak B. More significant, however, is the very high degree of peak per- sistence displayed, confirming the findings of the random sampling discussed above. The group of peaks G, H, I (and C, D, E) do display the shift hypothesized above, peak G being slightly displaced to a greater age by the larger peak H, and peak I being af- fected in the opposite direction. The shift in both cases is less than 2500 yr. Note that the shift is most apparent between ~10% and ~7.5% analytical uncertainty, when the individual peaks cease to be represented as shoulders.

RESULTS AND INTERPRETATION

Figure 6 provides a composite represen- tation of speleothem growth frequency in


1.0 i t

o-l-” ‘. c

20 40 60 80 100 120 140 160

Age(103years)

FIG. 5. Speleothem growth frequency curves derived from the screened data set after progressive removal of analyses with standard deviations in excess of 15, 12.5, 10, and 7.5% of the quoted age.

the United Kingdom for the period 220,000 terglaciations and interstades. Although to 20,000 yr B.P. The periods of active spe- there are clear differences in the peak leothem growth defined by the frequency heights, as would be expected if the spele- peaks correspond to times of increased veg- othem record is responding to climatically etation growth and climatic warming in in- controlled variations in biological activity

Dev.4

b a 2 0.6- 5 0

:

_

$0.4-

; - Dev.

0.2- counting uncerteinty

67.6% n=21 (vertical scale x2.4)

01 I I I 1 I I 1 1 20 40 60 80 100 120 140 160 180 200 220

Age (lb3 years)

FIG. 6. Composite UK speleothem growth frequency curve, giving the best resolution of the peaks.

22 GORDON ET AL.

TABLE 3. BEST ESTIMATE AGES FOR UK

SPELEOTHEM GROWTH FREQUENCY PEAKS

Peak Age (yr B.P.)

Dev. 1 29,000 Dev. 2 36,000 Dev. 3 45,ooo Dev. 4 50,000 Dev. 5 57,ooo Dev. 6 76,000

Ip. 1 90,500

Ip. 2 105,000 Ip. 3 124,000

Pre-Ip. 1 180,000

and groundwater recharge (as described above), we do not here consider the significance of peak magnitude for the definition of interglacial and interstadial conditions. Ten peaks can be identified between 220,000 and 20,000 yr B.P., and their ages (derived from peak centers) are shown in Table 3. Before 140,000 yr B.P. only one broad peak is present (at 180,000 yr B.P.), but we are not satisfied that the resolution of this part of the record is adequate, due to the large uncertainties associated with the uranium-series ages, and therefore concen- trate here on the record since 140,000 yr B.P. The small peak at 23,000 yr B.P. is related to a single analysis and is not considered reliable (note that unlike other peaks in Fig. 4, it does not persist).

We have prefixed the peaks Devensian (Dev.) and Ipswichian (Ip.) in accordance with the stage names of Mitchell et al. (1973), and numbered them from young to old following the recommendations of the International Stratigraphic Guide. There is now considerable doubt about the status of the Wolstonian stage (Cox, 1981; Perrin et al., 1979; Sumbler, 1983); we have therefore labeled the peak at 180,000 yr B.P. the pre-Ipswichian (pre-Ip.). There has been general agreement that the last interglaciation ended between 82,000 to 73,000 yr B.P., this age range being accounted for by the different evidence used in deep-sea cores to define the last interglacial/glacial

boundary, the different methods of dating employed, and their uncertainties. In the speleothem record (Fig. 6), there is a marked reduction in growth frequency after the peak at 90,500 yr B.P. marking the on- set of much colder conditions. While the position of growth minima defined by our method is somewhat dependent on the rel- ative size of the adjacent peaks, that at 20,000 yr B.P. corresponds well with the generally accepted timing of the last glacial maximum. The minimum at 80,000 yr B.P. is therefore taken to be the last interglacial/ glacial boundary (the subsequent minimum at 66,000 yr being well outside the range of other estimates). Peaks prior to 80,000 yr are therefore representative of warm episodes within the Ipswichian and are labeled Ip. 1, Ip. 2, and Ip. 3.

Considerable confusion exists as to the duration and continuity of the last interglacial (Ipswichian) stage in Britain. Mitchell et al. (1973) defined the base of the Ips- wichian at Bobbitshole, but no site which spans the entire Ipswichian stage is known (Hall, 1980), and the Devensian/Ipswichian boundary has not been fixed stratigraph- ically. On the basis of their contained pollen, a large number of Ipswichian sites have been grouped into a single temperate forest stage (Phillips, 1974). However, the fauna1 evidence does not support the agglomera- tion of all these sites, and suggests that at least two and possibly three separate interglacial periods occurred (Stringer and Cur- rant, 1981; Stringer et al., 1986; Sutcliffe, 1985; Sutclitfe and Kowalski, 1976). Three such stages are recognized from the pollen contained in continuous cores spanning the last interglaciation from Grande Pile in northern France (Woillard, 1978) and from Tenagai Phillipon in Greece (Wijmstra and van der Hammen, 1974). These correspond to peaks in stage 5 of the oxygen isotope record from deep-sea cores (substages 5a, 5c, and 5e; Mangerud et al., 1979; Turon, 1984). These three periods of climatic ame- lioration are clearly recorded in the UK speleothem growth frequency record


(peaks Ip. 1, Ip. 2, and Ip. 3; Fig. 6), the first time that they have been unambiguously recognized from terrestrial deposits in Britain.

There is no general agreement on the number and timing of interstadial periods in the last glaciation of Northern Europe. Un- til recently, only three last-glacial (Deven- Sian) interstades were recognized in the United Kingdom prior to the glacial maximum (Wretton, Chelford, and Upton War- ren; Mitchell et al., 1973). However, there is considerable debate on the status of the proposed Wretton Interstade as the pollen and coleoptera evidence of the palaeoclimatic conditions is contradictory (West et al., 1974). Two further interstadial periods have also been proposed: the Brimpton, between the Chelford and Upton Warren (Bryant et al., 1983), and an as-yet un- named post-Upton Warren interstade (Gib- bard et al., 1986). There are six speleothem growth peaks prior to the glacial maximum (Dev. 1-6, Fig. 6), supporting the more complex view of this period only now emerging from conventional studies.

CORRELATION OF THE CONVENTIONAL STRATIGRAPHIC AND

SPELEOTHEM GROWTH FREQUENCY RECORD

Problems arise in attempting to make correlations between the speleothem growth frequency peaks and the conventional stratigraphic record, because the cave sites may only rarely be directly related to the surface sites by normal stratigraphic techniques. Whereas the speleothem record is intrinsically well-dated, this is not necessarily the case with the conventional stratigraphic record, particularly beyond the 45,000-yr effective limit of 14C dating. Furthermore, despite the high precision of the 14C method, its accuracy beyond 8000 yr B.P. is unknown due to fluc- tuations in the rate of production of 14C in the atmosphere. Comparative studies using the 14C and uranium-series techniques are therefore needed before exact correlations can be attempted. Much of the late Pleisto-

cene British stratigraphy is based on pollen or coleoptera, but little progress has been made in the study of pollen in caves. Reli- able records are only availabe for Kirkhead Cave (Gale et al., 1984) and Gough’s Cave (Leroi-Gourhan, 1985), both late-glacial sites. Correlations must therefore rely on the examination of sites where mammalian fauna1 material is unambiguously associated with speleothems which have been dated by uranium series. Unfortunately for the Devensian, no such sites have yet been reported that range between 70,000 and 20,000 yr B.P.

In the case of the Ipswichian (135,000 to 80,000 yr B.P.), four such sites are known. Deposits correlated with the Ipswichian (sensu strictu) have been dated at Victoria Cave, northwest Yorkshire by Gascoyne et al. (1981, 1983). Speleothem was found in association with a typical “hippopotamus fauna” similar to those described by Sut- clilfe and Kowalski (1976) as highly charac- teristic of Ipswichian deposits. Seven samples of speleothem that contained faunal remains have been analyzed and they yielded eight reliable ages ranging from 135,000 +9000/-8000 to 114,000 + 5000 yr B.P., with a mean age of 125,000 yr B.P. The classic interglacial Ipswichian hippopotamus fauna is thus clearly correlated with the 124,000-yr-old Ip. 3 peak of the speleothem record, and with isotope stage 5e, as recognized by Gascoyne et al. (1983). The “8-m” raised beach at Belle Hougue, Jer- sey, which contains a molluscan fauna interpreted as Ipswichian, has also been correlated with isotope stage 5e (Keen et al., 1981). A single uranium-series analysis from travertine cementing the top of the deposits yielded a date of 121,000 +14,000/-12,000 yr B.P., although the 23@Th/232Th ratio of 16 indicates some con- tamination by detrital thorium.

An interglacial molluscan and vertebrate fauna associated with speleothem has also been reported at Bacon Hole, Gower (Stringer et al., 1986) where two vertebrate faunas of interglacial character are sepa- rated by deposits that contain a cold-

24 GORDON ET AL.

climate fauna. The interglacial faunas are generally similar to that at Victoria Cave, but hippoptamus is absent. The lower interglacial fauna is associated with broken blocks of stalagmite that predate the deposits. Five age determinations have been made on two samples. Three of these analyses were heavily contaminated by detrital thorium, while the two remaining dates are 124,000 f 16,000 and 122,000 + 11,000 yr B.P. The fauna, therefore, is again correlated with Ip. 3 (or if a hiatus is present, with Ip. 2). The upper interglacial fauna is capped by a speleothem dated at 81,000 + 18,000 yr B.P. The fauna may therefore be associated with the Dev. 6 peak or, more probably, the Ip. 1 peak. At the adjacent Minchin Hole (Sutcliffe and Currant, 1984), cave earth containing an interglacial mammalian fauna, that lacks hippopotamus overlies the “Patella Beach,” correlated with isotope stage 5e. It is associated with derived blocks of flowstone dated at 107,000 k 10,000 yr B.P. The cave earth therefore probably correlates with peak Ip. 2 or Ip. 3. Further work is needed at these important sites to match their stratigraphy and faunas, and to improve the precision of the dating.

A single fauna indicative of cold climatic conditions has been found associated with speleothem at Stump Cross Cavern, northwest Yorkshire (Sutcliffe et al., 1985). Thirty-two age determinations have been made on 19 samples. The youngest speleothems predating the main bone deposit range in age from 108,000 + 18,000 to 118,000 + 12,000 yr B.P., while four dates on flowstone encrusting bone yielded a mean age of 83,000 f 6000 yr B.P. This fauna clearly represents the colder period separating the Dev. 6 and Ip. 1 peaks. In- deed, at one section (their site II), the cold fauna is immediately overlain by speleothem dated at 72,000 ? 6000 yr B.P., which is clearly representative of Dev. 6.

CONCLUSIONS

The speleothem growth frequency curve presented here records nine periods of en-

hanced speleothem growth between 140,008 and 20,000 yr B.P. which correspond to warmer periods with increased growth of vegetation. There is a further broad peak at 180,000 yr B.P., but the resolution of this part of the record is poor and the peak may therefore be composite. Some progress has been made in interrelat- ing the speleothem and other stratigraphic records during the Ipswichian interglaciation, with the charactertistic hippopotamus fauna and highest sea levels being correlated with peak Ip. 3. However, further work is needed on the dating of Devensian interstadial deposits. At present none of these can be reliably correlated with the speleothem peaks because they are dated using the i4C method. Clearer correlations between the pollen and speleothem record will require examination of the pollen pre- served in cave sediments (Hunt and Gale, 1986), and particularly in speleothems (Bas- tin, 1979). Meanwhile, we believe that the speleothem growth frequency curve provides the most useful and complete record of interstadial and interglacial periods in the late Pleistocene of the United Kingdom. Not only is it based on a sensitive terrestrial palaeoclimatic indicator, but it has the major advantage of being calibrated by a reliable radiometric time scale. It thus provides a useful complement to the record derived from deep-sea cores.

ACKNOWLEDGMENTS

We thank Sally Howes and Ed Thomas for assis- tance with computing, and Keith Crabtree, Keith Clayton, and Jim Rose for comments on the manu- script. The Natural Sciences and Engineering Council of Canada are acknowledged for continuing support of the McMaster uranium-series dating laboratory via grants to D. C. Ford and H. P. Schwartz. The Natural Environment Research Council funded some of the dating work through grants to T. C. Atkinson, J. N. Andrews, and P. L. Smart, and supported D. Gordon by a Studentship. Additional dating facilities were pro- vided by our respective universities. Simon Godden drew the diagrams.

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Dating of late Pleistocene interglacial and interstadial periods in the United Kingdom from...

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