Radiocarbon Users Conference

RADIOCARBON USERS CONFERENCE

WELLINGTON 17th & 18th August 1971

RÄBIOCABBON USERS' CONíERENCE held at INSTITUTE OP NUCLEAR SCIENCES LOWER HUTT NEW ZEALAND 17TH to 18TH AUGUST 1971

Department of Scientific & Industrial Research New Zealand

Government Printer 1 Aug 1971 Wellington

2a INDEX continued

The Selection of Archaeological Samples for 196-205 Radiocarbon Dating L. Lockerbie Possible Use of Natural ffax Extracted from 206-209 Peat? as a Radiocarbon Sating Material T.L.Grant-Taylor The Reporting of Very Old Radiocarbon Dates 210-213 K. J. Gougfa

FOREWORD

This Radiocarbon Users conference was first suggested by Dr David Kear, Director of New Zealand Geological Survey and enthusiastically taken up by Dr Rafter, Director of the Institute of Nuclear Sciences. It was organised with a view to providing a single forum for many of the aspects that affect radiocarbon dates, hoping to avoid the pitfalls of tco great specialisation in any field.

There are continuous developments as might be expectedt and quite a number of these developments have been made here at the New Zealand Laboratory, not only in the actual mechanical process of dating but also in the background philosophy, and understanding of lene natural processes affecting the carbon component of fossils. The New Zealand Laboratory was one of the first two or three to be established, and is now the oldest contin- uously operating radiocarbon laboratory in the world. The laboratory has been in existence now for about 20 years» our first date list being published in 1953» I wish to thank all who have helped me in the preparation for this conference, particularly those people who are presenting papers and especially Mrs E.M. Tiller of my office. '

T.L. Grknt-Taylor INDEX History and Concepts of Radiocarbon Dating 3-21 T. A. Rafter An Evaluation of Some Methods of Radiocarbon 22-28 Counting K. J. Gough Gas Counters and Counting 29-36 D.R. Currie Practionation of Carbon Isotopes by Higher Plante 37-46 J. H. Troughton Tree Rings and Radiocarbon Dates 4-7-51 H. S. Jansen The Presence of Humic Acias in Radiocarbon-Dated 52-58 Charcoal J.M.Bailey and K. S.Birrell Contamination of Radiocarbon Samples 59-64- T.L.Grant-Taylor Selection of Samples for Radiocarbon Dating for 65-70 Geological Purposes T. L. Grant-Taylor Radiocarbon Dating of Soil Organic Matter: 71-85 Its Scope and Limitations K. M. Goh The Use of Radiocarbon in Measuring the Turnover 86-98 of Soil Organic Blatter J.D.Stout Radiocarbon Dating in Botany 99-111 N. T. Moar Radiocarbon Chronology of Late Quaternary Rhyolite 112-116 Tephra Deposits C.G.Vucetich and ff.A. Pu"> lar Ages, inferred from 11+C Da tes,of some Tephra and 117-138 other deposits from Rotorua, Taupo, Bay of Plenty, Gisborne, and Hawke'a Bay Districts W.A.Pullar and Janice £. Heine 1UC Dates in the Quaternarj^Geology of t^e "Golden Coast".Wellington C. A. Fleming Identification of ffood from Tree Stumps and Drift 14.9-I56 flood associated witb Tephra Layers in Alluvium ani of Charcoal from Tephra Layers ff.A. Pullar and R.N.Patel The Use of Radiocarbon Dating in Marine Geology 137-164 J.V.Eade Radiocarbon Dating of Bone Organic and Inorganic 163-181 Matter H.Polach Degradative Methods as Aids in Soil Humic Acid 182-191 Characterisation K.R.Tate Low Temperature Ashing 192-195 P.C.Rankin 3.

HISTORY ANO CONCEPTS OF RADIOCARBON DAi.%

An address to the Radiocarbon Users Conference

Wellington - August 17-18, 1971

by O T.A. Rafter

SUMMARY

The paper discusses some of the main controversial issues reported to the "Radiocarbon Variations and Absolute Chronology" symposium held at Uppsala from 11 to 15 August 1969. 14 The ccnst&ncy of the C production rate is one of the main. uncertainties in the reliability of the carbon-14 dating Method.

How this is being estimated, and preliminary suggested corrections for carbon-14 against dendrochronological ages, are given. 4.

In 1969 I was invited to attend the XII Nobel Symposium at Uppsala, where I presented four papers on the work of the Institute. The proceedings of the symposium were published recently in this rather elegant volume and I have reprints here of the four papers we presented. After the Uppsala Conference, I was invited to the ANZAAS Conference at Adelaide on my way home. I said that I would review the papers presented at Uppsala on Radiocarbon Variations and Absolute Chronology. I spent a wet Sunday in Zurich working on this review and a day before the lecture, preparing notes. Since then I have had little opportunity to go over these notes again, but I felt they would 09 worth revising for. this Radiocarbon Users Conference. Thirty-two papers were presented that could be loosely grouped into sessions devoted to: (1) Historical Chronology (£) l/arved Clay Chronology (3) Dendrochronology (4) Radiocarbon Reservoir Problems (5) Astro - and Geophysical Phenomena and their Effect on Radiocarbon Variations (6) Dating Methods and Related Analyses Dr W.F. Libby, in an open session at the conclusion of the Conference, gave an excellent review of the carbon-14 method. I think it would be appropriate here to briefly¿go over the principles of the method so that we can see more clearly the problems involved as far as our own interests are concerned. Carbon>14 is produced by cosmic rays coming from outer space that, bombarding the atmospheric gases, produce neutrons that,

fortunately for us, are rapidly absorbed by nitrogen atoms, forming

C-14 as illustrated by the equation

14 * n • 14W

14 • The excitad C atom, by a process we are still not sure about,

oxidises to CO..

14 • 14 * CO C • IL

Carbon-14 is a radioactive species of carbon, disintegrating back to 14

N by the emission of a beta particle. Carbon-14 has a half-life

of 55B0 years or a mean life of 8033 years and its decay follows what

mathematicians call an exponential curve.

5600 11,200 Time

This curve relates activity to time by an equation

A. = A e that we need not worry about any further, t o 6.

14 The C0? molecules rapidly mix with the normal CCL molecules of the atmosphere and through the sun's energy and the photosynthetic process in the green leaves of plants is assimilated intu plants and so into animals and human beings such as you and me. We therefore have the relationship

sunlight • 'CO--*- HO + plants —> complex organic compounds

* The indicates that the organic compounds are tagged by a v/ery símil number of C-14 atoms present (actually only about one C-14 atom per 1012 D-12 atoms). If uie are to use the radioactive decay of carbon-14 as a method of dating, we must not only be confident that the decay rate is constant but also that the concentration of C-14 per unit weight initially was also constant. By this I moan that the number of C-14 atomg per gram of carbon synthesised by trees at the beginning of this

Í¡ century is the same as that synthesised by trees 10, 20, 30 or 40,000 •t years agoc

The concentration of C-14 is therefore controlled by the relationship

¿C-14/ = Cosmic ray production rate Pool of carbon

2n per cm /sec 8g carbon/cm the pool is made up approximately as follows: 2 living matter = 0.3 g per cm atmosphere oceans humus 7. Note that most of the carbon is in the oceans so that the circulation patterns of the norId*s oceans is of great importanos in what follows. WB have assumed that the C-14 production rate has remained constant over the last 40,000 years and that the C-14 produced was uniformly mixed in a few hundred years within the "pool" and finally, that after death on removal from its natural environment, the specimen be it human, plant, animal, shell or soil, is isolated from C-14 contamination with the anvironment, so that decay of C-14 is the only process that can vary 'che C-14 concentration. When the C-14 dating method was first developed, it was accurate to only _• 250 years and its reliability was checked against historically dated materials. Subsequently, the accuracy was improved to _• 50 years. Troubles were then experienced with historical specimens because in many cases the C-14 method dated only the time of removal of the carbon specimen from its natural environment, not the historicel event. These two events could be separated by hundreds of years, e.g., a coffin to date the death of an Egyptian king. This difficulty could at first be overcome by using short-lived materials, e.g., seeds, leaves, sandals, etc., bu*- the question that remained unanswered was the constancy of the C-14 production rate. An attempt to arrive at this was attempted by comparing the C-14 activity in trees, that had been accurately dated by the science of dendrochronology. In 1958 a Dutch scientist, ds vries showed for the first time that a secular effect existed, i.e., a set 14 of long-term changos in the contemporary concentration of CO. in 8,

the atmosphere at a particular location, as well as differences that

may exist between different locations. This work was extended by

Suess of the University of California, San Diego, using the giant

sequoia that had a tree-ring age over 2,000 years.

The possibility of studying in more detail the C-14 variations

in the atmosphere was greatly extended by Dr C.W. Farquason of the

Laboratory of Tree-ring Research at the University of Arizona. He

presented a paper at the conference on the dendrochronology of the

Bristlecone pine, Pinus aristata, and has established a 7,104 year

tree-ring chronology using Bristlecone pine from the White

mountains area of east-central California. i

In 1965 Curney reported the existence of a 4,900 year old

Bristlecone pine in the Snake Range of east-central Nevada and this

find provided a considerable impetus to dendrochronology and its

relationship to C-14 secular variations.

Beyond the range of the sequoia and Egyptian material, samples

of Bcistlacone pine constitute the sole source of dated wood for the

calibration of the radiocarbon time scale.

In Way 1969, 471 ring-dated samples, mostly in 10-year units,

of Bristlecone pine mere sent to the radiocarbon laboratories of

Arizona, San Diego and Pennsylvania. The results will form the

basis of a good part of this lecture and, toward the and, I will

show you slides of our New Zealand work as far as we have been able

to follow it with Australian and New Zealand trees.

By 1965. Damon. Lona and Gray had shown that secular effects

could amount to BOO years for specimens that grew 5,000 years B.P., but at that time not sufficient work had been done to allow for corrections, to be made for this effect, by international agreement. 9.

Known age B.C. 4800 y C-14 age B.C. 4000 y

800

AD. 1600 t I » O Q 8 ° 8 8 O O 8 00 VHO CU 3- KNOWN AGE ¿

Suess (1969). u/tio up to 1965 had made 130 radiocarbon measurements on dendrochronologically dated wood samples, has now completed a further 315 measurements on dated Bristiecone pine. The results showed a continuous sequence of deviations from ths calculated radiocarbon content. Many ways of plotting these results were given at the conference, but I think we will understand the point if I draw a simple graph, taken from a paper by Michael and Ralph of the Pennsylvanian Carbon-14 Laboratory. Suess suggested that his results can be used to derive a calibration curve from 5,200 B.C. to the present. From 2,000 B.C. to the present, the curve he says can be taken to be accurate within less than 100 years. 10.

Becauee of the peculiar windings in Suess' calibration curve, one particular radiocarbon content may indicate several dates of origin and it may only be possible to «»¿polish a time interval during which the sample had originated. For certain periods of time this interval will ba quite large. Suess quotes the ease of a radiocarbon date of 4,400 ± 100 years 8.P., indicates a true date between 2,950 and 2,500 ELC« In other cases it is possible to assign to one particular radiocarbon date a well-defined true age. For example, 3,600 ± 100 B.P. correspond» to 2,100 ¿ 100 B.C. There was a considerable amount of discussion regarding this calibration curve and whether or not it could be used to calibrate over the entire earth. Should the results be made available in tables or calibration curve form? Should the results from the three laboratories be published separately, or all the results given to a computer to give us a curve of best fit for present available data? It was decided to report carbon-14 results as at present in y ear8 B.P., but to ultimately endeavour to make known the most likely error involved with respect to the tree-ring carbon-14 chronology. Rsason3 for the Carban-14 Variations Seven papers discussed possible reasons for the carbon-14 variations observed. Or Buena of the Geophysical Institute of Czechoslovakia discussed the influence of the earth's magnetic field on the radiocarbon dating method. From a study of 300 samples he has been able to construct a curve characterising the earth's magnetic field intensity over the last 8,500 years. Around 400 B.C. the field intensity reached 1*6 times its present value and around 4,000 B.C. the field dropped to around 0.5 times preaent intensity. 11.

The reasons far these changes can be found in the source of the

earth's magnetic fieldf i.e., hydro-magnetic procesase in the boundary layers of tha earth's core and mantla. If tha magnetic moment decreases» the cosmic-ray flux reaching the earth is increased; if we increase the magnetic field, the reverse happens. Buche*3 Fig. 6 shouts a most interesting comparison between radiocarbon deviations and changes in the earth's geomagnetic moment.

M 14 A Geomagnetic Variations C-14 Variations - -* 12.

- -2 Adi /\ \ #\ J 0- / r V -0 A// AT A A, S\/ \/\ % ,' V —^Nv 8* — . v -4

6- • I 1 1000 A.

Lingenfelter and Ramaty (UCLA and NASA) then gave an excellent 14 analysis of astro-physical and geophysical variations in C production. Geomagnetic and solar variations, solar flare variations, 12.

supernova variations were discussed and in summary stated that they have re-normalised the absolute C production rate based on new atmospheric neutron measurements and from cosmic-ray neutron and icniaation monitor records to give the averags neutron production 2 rate of 2.2 ±0,4 carbon-14 atoms per cm per sec. for the last three solar cycles (1937 to 1967). This geophysical and geomagnetic data was taken by Damon of Arizona, Suess. San Diego, and Lai. India» in attempts to present simple reasons how such measurements can be related to carbon-14 variations. Lai introduced two naw concepts. One, the importance of biological transport, and direct input into the deep layers of the ocean via the surface outcrop south of the Antarctic Convergence. The biological transport mechanism was suggested to him by experiments in which he was using sponges to collect silicate from sea water. Checking for carbonate, he found sufficient to do a u estimation and found bomb C-14 at depth. Lai considere that the input into the deep Antarctic oceans has a considerable effect upon the å1 4C value of the atmosphere. During glacial and colder periods, when the ssa-lrvel was lower, the effect would be to increase A 14C valúas in the atmosphere beesuae of a reduction in the exchange parameter faa a result of covering the Southern ocean surface by pack-ice and drift-ice. He calculated A 14C values could be higher by up to 10-14jg. Climatic changes are important and seems to explain the broad features in secular variations in A C. Demon, University of Arizona, in a highly mathematical analysis of present data, conciudad that fluctuations in A C during the "Little Ice Age" of the 15th-17th century could largely be explained by good 14 correlation between sunspots end A' C velues during that time and that there now seemed to be little doubt that the long-tarm trend of the radiocarbon content of the atmosphere during the last 8,000 years is dominated by geomagnetic effects, ¡sftareas short-tern fluctuations are dominated by heliomagnetic modulations. Damon also claimed that the affect of changes in climate on the radiocarbon content of the atmospheric reservoir appears to be of minor importance during the last 8,000 years. However, larger climatic variations during and immediately following the last major glaciation may have had a much greater effect.

5000 BC AD

Suess, San Diego, who considers himself the father of the greater part of the secular variation story, took exception to everyone taking his data and trying to interpret it even before he had a chanca. 14. His paper on the three causes of the secular carbon-14 variations went over much the same ground, i.e., changes due to the geomagnetic field, modulation of cosmic rays by sun spots (i.e., solar winds blow back the cosmic rays) and changas in the geochemical radiocarbon reservoirs. He brought out again how the Bristlecone pine wood measurements show a long-term C-14 level change on a time-scale of 10,000 years of 10JÉ. This would require a 5ü% change in the C-14 production rate, equivalent to a change by a factor of 2 in the intensity of the geomagnetic field.

He presented his data, through which he claimed to be able to fit a sine-wave curve for Å1 4C variations with time and that this agreed almost quantitatively with the expected change in the production rate J that would result from changes in the geomagnetic dipole moment. The period of his sine-wave curve was 8,000 years, but this could be improved to agree with the geomagnetic curve of period 10,000 years by assuming a steady dsorease of the total carbon-14 inventory since the last Ice Age.

+30 i \\ o H "i '•: 10 i 1 I i 0 i i -10 1 \ H »i» 11 V tí ' / > V- -30 i i * i 1 5~ 4000 BC AD 1000 Sueas Fig.2

He also presented his data as deviation» from the eine-wave curve that looks something like the above, Fig. 2. In his data he can see changes in C-14 during the "Little Ice

Age" when Central Europe had a sequence of exceptionally severe winters

and glaciers were advancing everywhere. During the sam9 time the sun

was quiet, and sun-spot numbers were low.

A most conspicuous and so far unparalleled irregularity in tha 14 A C as a function of time is the rapiti C-14 increase at the

.-^ of the 8th century B.C. and the sharp maximum between

780T770 B.C. At this time a general climatic change took place on the

North American Continent that marked the beginning of a completely new climatic epoch.

CHRONOLOGY

For those of you more interested in chronology than in tha difficulties associated with giving you dates, papers were read on

Carbon-14 dating and Egyptian Chronology,

Problems in dating the late Paleolithic in Egypt, t Chronology, Pre-hiatory and history of the Near-East, Reconciliation of Radiocarbon and Sidereal Years in Meao- American Chronology, and Thrse papers on Scandinavian l/arve Chronology.

Dr SaVe-SOderberoh, Uppsala, quoted Professor Brew's attitude among archaeologists towards C-14 datings:

"If a C-14 date supports our theories, we put it in the main text. If it does not entirely contradict them, we put it in a foot-note. If it is completely 'out of dste1, we just drop it".

It would seem that when C-14 dating as applied to Egyptian material was investigated to check the exactitude of the C-14 method with the aid of the so-called absolute dates of Egyptian history, 46. the results were rather disappointing. It was obvious that one isolated sample or laboratory dating is«of little value. Houaver, when the radiocarbon ages were compared with the dendrochronoilogical checks of the C-14 variations, the; apparent agreament between the two independent checking methods was rather satisfactory. Michael and Ralph. Pennsylvania, whose work I have mentioned earlier on the correction factor applied to Egyptian radiocarbon dates of the B.C. era, showed an increasing unilateral divergence of precisely dated woods and radiocarbon dates beginning about 800 B.C. and continuing to the present limit of tree-ring dated samples which is 5,150 B.C. Fergusson, at the conference, said that this time-scale could now be pushed back to 5,400 B.C.

They also suggested that climatic changes, such as an "Ice Age" occurring several millennia before the limit of available dated wood samples, sssme to be the most probable ultimate cause of the deviations between dendro-dates and radiocarbon dates. They presented a correction table for¿ C-14 dates based on the 5,730 year half-life, as follows: TABLE I * Suggested method of adjustment of radiocarbon dates to calendric dates based on the determination of average deviations for 500-year periods in the A.D. and B.C. eras as calculated with the 5,730 half-life

Time Period Repre- Average deviation Caiendric Period Number sented by of C-14 Dates Represented by of Radiocarbon Dates (+ = younger, Precisely Dated Samples - = older) Tree-ring Samples

A.D. 1525-2000 + 50 fc.D. 1500 to 1950 13 A.D. 975-1524 0 A.D. 1000 to 1499 10 A.D. 450- 974 - 50 A.D. 500 to 999 13 A.D. 1- 449 - 50 A.D. 1 to 499 13 449- 1 B.C» + 50 499 to 1 B.C. 8 924- 450 B.C. • + 50 999 to 500 B.C 9 1324- 925 8.C. +100 1499 to 1000 B.C. 14 ' 1699-1325 B.C. +250 1999 to 1500 B.C. 13 2099-1700 B.C. +350 2499 to 2000 B.C 13 2499-2100 B.C. +450 2999 to 2500 B.c. 7 2949-2500 B.C. +550 3499 to 3000 B.c. 12

(3999-2950 B.C.) +600 4395 to 4135 B4 c. i 9 'l! (260 years) ii (4499-4000 B.C.) +750 5110 to 4810 B.c. í 8 (300 years) Total Í143

From a careful axaminacion of fifty-five Egyptian samples, they were able to conclude that the short-lived samples served well as' a check on the correction factors derived from C-14 dates of tree-ring dated Bristlecone pine and sequoia samples. 18.

Johnson and milis attempted a raooncilation of radiocarbon and sidereal years in Maso-American chronology for, as they pointed out, the newly established variation» in the radiocarbon chronology mada a significant difference to the interpretation of pre-historic events, It is important to know whether there was really more time for a culture to develop than was first thought. For example, the early appearance of the Neolithic in N.W. Europe hitherto pieced at around 3,300 B.C. must now be thought of as 4,100 B.C. There is thus 700 more years available for the development of agriculture, forest clearance and the development of metals prior to the advent of the Iron Age in 500 B.C. They discussed the culture sequence in the Tehucan Valley of Mexico.

The major effect of the C-14 correction in their study ie the pushing back in time of numerous significant factors in culture development which took place between about 150 B.C. and 7,400 B.C. and perhaps somewhat before.

: VARVE CHRONOLOGY

As the conference was held in Sweden, papers were presented on 'Varve Chronology*. This is based upon regular seasonal changes in the discharge of sedimente, e.g., in the drainage of ice-damnecrlakes. Ta Liber of Copenhagen was able to conclude that during the period 8,000 to 12,500 B.P. there is a close agreement between varve datee and C-14 dates, This conformity precludes significant oscillations in the atmospheric C-14 activity within this period and suggests that both s C-14 datee and varve dates ai*e close to true ages during the late glacial and early post-glacial. 19.

From 3,000 to 8,000 B. P. when varva dates are compared to C-14 dates, the C-14 ages show deviations of the same magnitude as found in comparisons between C-14 dates and tree-ring chronology. To obtain data on C-14 variations beyond the last 7,000 years, Stuivar. Yale University, discussed lake sedimentation rates and lake varve chronology of a core from Laka of Clouds, Minnesota. The Swedish verves used by de Geer for his chronology of the retreat of the wurm ice sheet from Sweden, contained insufficient organic material for direct C-14 measurements.

An essential aspect of Stuiv/er's approach is the recognition that variations ir* atmospheric C-14 content causes apparent changes in sedimentation rates expressed in C-14 years.

VOQOI'B (South Africa) paper on C-14 trends before 6,000 B.P. is important, because it was an attempt at evaluation of the C-14 inventory back to tha Late Glacial period that would indicate whether any direct or indirect correlation with climate exists and thus helps clarify the causes of the C-14 variations of the past. Some indications of the trend in C-14 level before 6,000 8.P, can be gained by measuring samples from fossil trees with several hundred year-rings even though their actual date be unknown. • Results on stumps of about 6,000 B.C. and about 5,000 B.C. indicate that the C-14 level was not decreasing at the rate observed between 3,500 B.C. and 1,500 B.C., but that it was nearly constant.

Now finally, it may be of interest to you to say briefly what Rafter of New Zealand talked about. - Our labcratory presented four papers that meant a considerable amount of work, but we are not far from the right track in helping to understand some of the problema I 20. have mentioned.

CONCLUSIÓN

I have attempted to bring myself, and I hope you also, up-to-date in the art» or is it ¿he science, of radiocarbon dating. It is no longer a straight-forward chemical preparation and lew- background counting project as it appeared to be some fifteen years ago when I was first invited to ANZAAS in Melbourne to discuss the development of our work in New Zealand. Now it i3 the welding together of every type of scientific discipline - the historian, the archaeologist, the geologist, the geophysicist, the dendrochronologist, chemist, physicist and mathe- matician. No man can be all these; he must co-operate. It is somewhat difficult to see where we are going or what are the most important measurements to be made in our attempts to unravel, past times and temperatures.

Keys exist for pur understanding from the polar ice caps to the pines of ths high Sierra Nevada. But what is important, is that we are all custodians of past heritages, nothing must be destroyed without reason or needlessly thrown away. What I would like to emphasise is the great function of the Museum in our understanding of past events. The sophistication of modern scientific measurements, the intricacy of the computer and our outstanding technology in efforts to reach to planets, seem to over- shadow the painstaking work of those who gather, preserve and correlate the artefacts of the past. All too frequently we find our modern scientific sophistication hindered by inadequate reference samples from ths past. 21. In shell, in pottery, in human and animal remains, in water, ice, meteorites and minerals, in bricks and mortar, we will find a history of the past in our attempt to understand the implications that lie ahead for future generations in the catastrophic climatic events that must surely follow as has appeared in the past. Men will be able to meat these challenges because of his great intellect, for he has the power to control or to destroy, not only himself, but the very tools given by a Creator for his own complete development and fulfilment of the reasons of his own creation, though the actual date is still unknown.

0 22.

AN EVALUATION OF SOME METHODS OF RADIOCARBON COUNTING

K.J. Gough Institute of Nuclear Sciences, D.S.I.R., Lower Hatt

ABSTRACT

A brief review of the relationship between the parameters of a counting system and the maximum age is given, and the values for the INS systems are given.

The chief advantages and disadvantages of the two m>v}n methods of counting are- reviewed and the future development of the INS dating equipment is discussed. ;

0 INS Contribution No. 23. I. GENERAL

In evaluating different methods of counting radiocarbon there are two obvious criteria to consider: the ease of sample preparation, and the "efficiency" of the counting scheme. Clearly, no matter how efficient the actual counting may be,a method involving a difficult, low yield synthesis is not feasible. Conversely a simple preparation is of little advantage if the counting procedure is difficult.

In addition to the above obvious criteria, there are more disguised factors which may tip the final balance in favour of one or other method. These hidden factors include the effects of contaminants, the ease with which these may be removed, the effect of instrumental drifts, nucleonic and electrical interference. Finally ea3e of operation and maintenance of equipment must be considered.

II ACCURACY AND MAXIMUM AGE

If a very old sample is to be dated the calculated age determined from the recorded count loses all significance if the count is within two standard deviations of the mean background. One may thus calculate the age of a sample which will have an expected count of background plus two standard deviations. If it is optimistically asserted that the standard deviation is due to the Poisson statistics alone, then

max where for x C TA = 5570 years

Mn is the nett modern count B is the background t is the counting interval. Just for the record, table I gives the maximum ages with the

INS equipment. However in any conceivable counting equipment there

will exist other disturbing factors which will increase the variance

of the background.

Table I.

Counter Count Time Gross Modern Background Lmax mins. Duplication, Large 1000 fe.o 18.5 42000 Duplication, Snail 1000 38.0 11.5 38OOO Original 1 Atm. 1000 54.0 14.5 41000 Original 2 Atm. 1000 96.5 16.5 46000 Original 2 Atm. 2000 96.5 I6.5 49000 Original k = 1.5 1000 96.5 16.5 43OOO Original k = 2.0 1000 96.5 I6.5 40000

Original 2 Atm/ (I961) 1000 101 13.0 48000

This is more so in the case of liquid scintillation equipment, according to some reports, but even in the case of gas counting there are significant deviations. Some of the deviations are deterministic in the sense that the expectation of the background is a known function of a measurable parameter. A classic example of this is the correction for thenucleonic component of cosmic radiation which is applied at the

Institute on the basis of the measured neutron flux.

If the actual standard deviation exceeds the Poisson-based value, but is still the result of an approximately «ncorrelated

Gaussian process, then the formula (l) becomes

(2) 'max loge2 25.

-where k is the factor by which the deviation exceeds the Poisson

value. The effect an Taax at aasumtnír £>.i is shown in the final

rows of Table I. unfortunately the L-J.6 _.J.3C€ F~S are usually correlated with quite long time const. and thus the 2V values must be treated with some caution.

There are at least two ways of decreasing the variance of the background: assuming long period exponential correlation, one may measure the background at time intervals comparable with the correlation time and thus find a mean background 'trajectory' or one may accumulate a total count in short intervals spread over a total time long compared to the correlation time.

Finally it should be noted that the above considerations apply to more modern samples since the uncertainty in count for such samples depends on the Poisson statistics, the uncertainty in the current background and the drift in the counting efficiency. This last factor although small, is also a long term correlated effect.

Ill DIFFERENT SYSTEMS OF COUNTING

Almost all radiocarbon counting is done either by liquid scintillation counting or proportional gas counting.

There have been a number of different gases used for proportional gas counting, including carbon dioxide, methane, acetylene and ethane. Carbon dioxide has the advantage of theoretically simple preparation with 100# yield but is a difficult gas to count compared to the others. Acetylene has the advantage of having twice the amount of carbon per mole of gas but has a pressure limitation and 26.

is more hazardous to handle than the other gases. Methane and ethane will count in a given counter at lower voltages than either of the above two gases and are less susceptible to poisoning by electronegative impurities; of the two, methane has the simpler preparation and purification. In most circumstances the choice would be between CO2 and City, with no obvious determining factor between the two when both are operated under optimum conditions. It may be that starting from scratch a methane system would be easier to get operational than

CC^>f but the advantages do not seem to warrant switching gases with an operating CO2 system.

A number of different liquid scintillation systems have been investigated since the 1950's, but the vast majority of present systems use benzene samples mixed with a toluene/PPO (2,5-diphenylcxazole) scintillator. The CC^-to-benzene synthesis can be carried out with yields exceeding 90^ an* without detectable isotopic fractiönation. The possible efficiency of counting radiocarbon by this method falls below 100$. This is due in part to the disintegrations which do not produce sufficient photons to generate a pulse in each photomultiplier of the coincidence arrangement; and also to the normal requirement that only the middle energy channel of the three channel system be used, to cancel out the effect of scintillation impurity quenching.

The main advantages of liquid scintillation counting are the comparative freedom from nudeonic interference, the ease with which the system may be automated and the electronic simplicity (the system requires no anti-coincidence umbrella). To some extent these offset the added sample preparation steps and the less favourable signal to noise ratio. 2?.

IV. IffiVELOFMENTS IN l4C COÜHTIKJ AT INS.

The Institute has recently undertaken the setting up of a pilot liquid scintillation counting system. With this system it is hoped to evaluate the comparative merits of gas and liquid scintillation counting in seme detail, in particular the relative ease of operation and susceptibility to contamination and interference.

Unlike most liquid scintillation dating laboratories we are initially planning to not use a comnercial liquid scintillation spectrometer, but to build a simple but specialised shield and sample changer. The reasons for this are partly economic and partly the special requirements of long period counting of very low activity samples. It is intended to count a «mall group of samples and standards in ro- tation over a period of many days. This eliminates some of the effects of correlated noise mentioned above, reduces the error due to short term nudeonic background fluctuations, particularly those of the man- made variety, and makes ouch of the sophistication and expense of a modern sample changer unnecessary. A preliminary investigation will determine whether a single photomultiplier will allow a low enough background to count satisfactorily, the advantages of added simplicity and more efficient optics being balanced by higher photomultiplier dark noise. It is not expected that the normal problem of fluores- cence with single photomultiplier systems will cause problems, because of the extremely long tines the samples will be in the dark during counting.

In addition to the above, some consideration has been given tc the streamlining of the present gas counting system. This involves 28.

the integration of the pulse sorting and data storing function of the electronics of all three present counters, using common electronic units. It is believed that such a change will relieve the maintenance problems of the present ageing equipment. It will go some «ay toward Increasing reliability, but it will not markedly improve on the best accuracy available with the present equipment: no radiocarbon counting system can hope to do more than count all the disintegrations and show a standard deviation due to the Poisson statistics of counting, and the present equipment approaches this ideal remarkably closely. 29.

GAS COUNTERS AND COUNTING

by D,R. Currie

Abstract

Some explanations about gas counting are provided for the initiated together with elucidation of counting statistics so that the user can understand exactly what a quoted radiocarbon age and associated error means. The concept of limit age is explained and means of raising limit ages are investigated showing that in practice ultimate low background laboratories would do better to measure normal range ages from small samples than endeavouring to extend the range using large samples. 30.

GAS COPHTERS AND COUNTING by D.R. Currie

Given a specimen to undergo radioactive dating the problem ia to estimate the concentration of radiocarbon in the carbon content of the sample. Once this is done the age of the sample is given by equation 1.

T -TMIogeAo (1#)

Ao « a standard concentration AS - concentration of radiocarbon in the sample Tj, » mean life of carbon 14- T - Radiocarbon age of sample In practice the carbonaceous fraction of the sample is concentrated into a standard counting material such as methane gas or carbon dioxide for a gas counter or benzene for a liquid scintillation counter. The P - particles given off by the radiocarbon are then counted by the detector for some time after which an estimate can be made of Ao and AS and the radiocarbon age of the sample can be deduced» When radiocarbon dating was initiated by the D.S.I.R. the sample was put into the form of a cylinder of solid carbon which was inserted in a goiger counter and about 5% of the total carbon 14- disintegrations in the sample during the measuring time were recorded. \ This procedure was abandoned in 1955 when the proportional gas counting of carbon dioxide was adopted. Gas counting is superior tú the solid carbon technique in that nearly 100% of the radioactive disintegrations occurring in the counting gas are recorded. This same method is still being used today at the D.S.I.E. although some thought has been given recently to using the scintillation method of counting carbon-14-. The chemical purification of carbon dioxide for gas counting is relatively uncomplicated one main necessity being to rid the chemically pure gas of electronegative impurities by a lime furnace as even small amounts of these substances will make the counting gas uncountable. 51.

Because the ground and all laboratory materials contain radioactive nuclei and because of cosmic rays any laboratory always has background radiation which will affect measurements of weak radioactivity. Por a carbon 14 counter a background radiation count in the absence of shielding would exceed Ao by a factor of about 70. This would be highly undesirable for carbon dating leading to reduced maximum measurable ages and large errors in smaller ages. In practice steps are always taken to exclude or eliminate as much of the background as is practical so as to increase the accuracy of the measurement. There are four main components in the background of a carbon 14 gas counter namelyo 1. Very penetrating rays which defy normal shielding but would require several hundred metres of rock to eliminate. These are the cosmic ray mesons. 2. Gamma rays coming from radio isotopes such as radium, thorium and potassium 40 in the surroundings and shield. 3. Cosmic ray gammas electrons and neutrons formed when energetic cosmic rays interact with nuclei in the heavy shielding surrounding the counter» 4. Corpuscular radiation ^€* s and P's) emitted by the internal surface of the proportional counter wall. The penetrating mesons fortunately form dens© ion'' tracks and to reduce them an anticoincident ring of geiger counters or better, proportional counters are placed surrounding the ^ carbon 14 counter to detect and eliminate the mesons jj electronically„ ¿ The gamma rays are readily stopped with several inches "'! of iron shieldingo It is interesting to note that an iron % shield more than 14 cms» thick ceases to be more effective \ with additional thickness because gamma emittens in the i iron shield itself keep the gamma level constant after :1j this critical -thickness. Further improvement can b@ made :¡ by having an extra layer consisting of 118 of mercury which being much less radioactive than iron will reduce the remanent gamma radiation coming from the iron shield by a j? factor of sis. It is unfortunate that a Kajor component j' of the background namely the cosmic ray shouer particles || 32.

including electrons gammas and neutrons are formed when energetic cosmic rays interact with nuclei in the iron shield. The neutrons can be absorbed by a layer of several inches of paraffin wax impregnated with boric and acid. Some workers have favoured making part of the rati gamma shield from boron wax of low radioactive content the thus reducing residual gamma radiation and neutrons in and one step. Of course if the counting laboratory is located several hundred meters underground all the cosmic ray components of background will completely disappear., Corpuscular radiation emitted by the wall of the counter can be reduced in one way namely by having the wall made of material which does not contain much radioactivity. Quartz is one such material and De Vries describes a quartz counter constructed at Groningen» The The quartz tube was surrounded by a copper tube to hold the COH gas and was coated with tin oxide on its inside surface of which being conducting acted as the counter cathode» san Other counters which have been successful in having reduced surface corpuscular radiation include counters with a multianode ring in the same gas volume as the main counter, the separating partition between the two counting systems being a thin metallized plastic film. Even though such a design of counter has considerable wasted volume of counting gas in the proportional ring nevertheless because of the extremely low background obtained it can still prove to be the best way of measuring limit ages with a given gas volume. The conducting foil can be replaced by a ring of earthed wires, then the counter becomes wall-less but this wall-less counter would be more satisfactory for counting tritium than ra carbon-14 since some of the B's escaping frosa the central mo counter to the ring will register as coincidences thus es causing loss of counter efficiency., du no Counting Statistics On ax If the number of disintegrations coming from a c-3 radioactive source is Ei then according to Poisson cc statistics the standard deviation of the recorded count will be simply the square root of the number of counts i.e. ()^ One standard deviation means that it is 68„3% probable that the true result lies within this range» Two standard deviations places a 95»5% confidence level on the result lying within the quoted limits« 33.

Let S be the gross counting rate of a C-14 sample and let Ts be the counting time. Let B be the background rate and let Tb be the background counting time. Then by the laws of statistics the net counting rate will be S-B and the standard deviation of the result is +(S B S* TV i.e. STS BTB (BTB)^ W

S-B (S (TS = A3 Í dås (2) The standard deviation of a quoted radiocarbon age is compounded of the Standard deviations in the mean life of carbon 14-, the standard counting rate and the net sample counting rate according to the following formula.

dt = T dTM)2 dAo (dASy M TOT • =(3)

TM - mean life of carbon 14 t = radiocarbon age AO = standard counting rate AS = net sample counting rate It is important to note that the standard counting rate AO which is supposed to represent the 'eternal modern count' throughout the ages has undoubtedly varied especially so at present when it has been raised by 50% due to nuclear bombs. Also the standard deviation takes no account of modern carbon 14 contaminating a sampleo One can never be sure whether traces of radoa or thoron are not in fact given off by the counters aad storage cylinders o In addition the statistical error does not cover undetected spurious pulses which may arise from faulty electronics dirty insulators and etc»

Limit Ages When, the sample is very old S = B -s- A S = gross counting rate B - background Å = a very small count rate less than two standard o deviations o then a convention is adopted, that the smallest couat- rate detectable is equal to two standard deviations o 34.

The standard deviation of S-B when S T B will be

Hence the smallest detectable count-rate

2 { B(|S+TB) ) Hence the maximum age that t, lüia ) one can measure on this premise is: 8033 log. Ao o(B(q?S ( (4) Ideally when S Ä B TS should equal TB.

Then the limit age becomes 8033 lose AO

For the DoSoIoR. 4.1 litre carbon-14 counter TS = 1000 minutes Tb » 4000 minutes Á0 = 26 CPM B = 10.5 CPM Heace the maximum measurable age

» 8033 loge 26

5000 ^ 389000 years

To show how important backgroizad is in measuring limit ages the massimum age for the 4,1 litre counter is re- calculated on the asgsuaption that by various measures the background was reduced to 1 cpmo Then the maximum age becomes 8033 log0 26 { mm] - It is easily seen that by raising AO or in effect the amount of gas being measured in the counter the limit age can be raised still further» For Ínstame© by billing the DoS.IoRo 401 litre conanter to tuo atmospheres with acetylene aad assuming the background to remain at 1 CPM the limit age then becomes

8033 log@ 104 2 C 5 - 599000 years ( 4-000 It is easily seen that when measuring limit ages even a email proportion of modern material or radioactive contamination will lead to erroneous results. For instance in the above case where the sample was genuinely 59j000 years or more had there been but \% of modern material there would be measured an age of 4-2855>O years rather than the limit age. Ultimately the maximum age measurable even with perfect non~contaminated material, assuming it exists, may be limited more than the formula by variable counter contamination. Possibly gases such as radium and thorium are present in counters and storage cylinders to a variable extent leading to a greater standard deviation than that due to statistics only»

As a matter of interest and even accepting that such an aim is impractical a counter capable of measuring 100,000 years id 11 be designed in principle. It is assumed that the cosmic ray components of background are eliminated by operating the counter under a few hundred meters of rock and the corpuscular radiation from the counter wall' is zero. Presumably the only count rate wil be from ever present gammas f om the surroundings» If this is reduced as far as possible with 8" of iron shielding and 1" of mercury from an analysis by Fergusson the residual gamma component can be taken to be 0d6 V CPM V = counter vol. in litres. The modern or standard count AO can be taken to be 6.25V CPM.

? Then 10 years = 8053 6.25V o o o o o o o (5) —-— i II 16V (4000 4-000)^ 16000,000 Assuming that both sample and background are counted for 4O00 minutes each. Solving for V we find V = 530,000 litres requiring nearly quarter of a ton of elemental carbon. However gamma shielding can be improved and it has been suggested that an underground counter be surrounded with ten feet of refined sugar as shielding. Aether this amount of sugar would reduce the gamma rays enough to enable say a 4- litre counter to measure 100,000 years is debatable and more would be needed to toe kaoun concerning the absorption coefficient of sugar for gammas. To raise the limit age to this figure for the D.S.I.R. 4-o1 litre counter filled with 1 at, of GOp would require the background to be reduced to 0.00006 CPM. The seduction factor for the shielding would have to be 22 x 10 or about 9M of mercury equivalent, 36.

It would seem that similar problems exist for scintillation counters and it can be guessed without making any real investigation that ^scintillation counters would provide no improvement on gas counters in measuring ages of 100,, 000 years. A more ready application of very low background counters is the carbon dating of very small samples» For instance to date polar ice, om© would seed many tons of ice to yield enough COp to fill a normal sisod counter (e.ge 4 litres). One 'eon of ice yields 50 mg to 150 mg of elemental carbon representing 90 to 27Oee of C02°

100CC of C02 would not be Measurable in a four litre counter but woula be quite measurable in a 100cc ultimate background counter. Even without extra special shielding sueh as 10° of refined sugar one could expect in an underground laboratory with normal iron and mercury shielding to attain backgrounds as low as 0o01 to 0o02 CM. This background range when insertad into the limit foriaula provides limit ages of some 37«000 to 289000 years on a 4000 minute counto 37.

FRACTIONATION OF CAH30N ISOTOPES BY HIGHER PLANTS

John H. Troughton Physics and Engineering Laboratory^ D.S.I.R. Private Bag, Lower Hutt

ABSTRACT

There is a pronouaged bimodal distribution of § C\'alues among a wide range of genera in both monocotyledenous and dicotyledonous plants. One group of plants has a mean £^3^ value of »I^ácand the other a mean value of about ~27#o The cause of the difference in S13c values between the two groups can be directly related to processes involving C0¿ exchange; plants with the C^ pathway of photosynthesis occur in the group with the less negative ¿13c value while C-z type plants occur in the other group. Differences between tne two groups may be due to the particular enzyme involved in the photosynthetic carboxylation reaction although the carboxylating species, photorespiration and diffusion will also affect the «S13Q value.

Within each of the two major groups of plants there are considerable variations in the & 13(j values which are likely to be due to genetic differences in the processes involved in carbon dioxide exchange by these plants. Although the processes likely to cause fractionation of carbon by plants can be identified, the relative magnitude and importance of these steps in different plants has yet to be established» '/• Furthermore, other factors such as the environment in which the plants are grown and metabolic reactions after carboxylation will also cause some variation in the S ?C values of plants,.

Variation in the fractionation of the stable isotopes of carbon by plants is useful in investigating intercellular processes involving C@g exchange and has important consequences to radiocarbon studies dependent on carbon derived from plants» 38.

1. INTRODUCTION

A feature of all higher plants is that they distinguish between the two naturally occurring stable isotopes of carbon and preferentially take up 12C with respect to 13c by small, but measurable, amounts. Therefore the ratio of 1^C to 13c is higher in plants than in air and this ratio is normally expressed as a £ 13c value in parts per thousand {%% where

$ ) - 1 ) X 1,000 -,

The standard is that for CO2 obtained from a belemnite (Peedee Formation, Upper-Cretaceous, South Carolina; PDB standard). Values of £ 13c which are negative with respect to the standard implies that the sample is depleted in 13 Higher plants have S^3c values more negative than the standard and also more negative than air (-

Procedures for the determination of $^C values have been outlined by McKinney et al (1950) who discuss the refinement of the Nier-type mass spectrometer and Craig (1953; 1957) with a discussion of the combustion system for organic matter. Degens (1967) has recently summarised several aspects of carbon isotope studies in relation to geochemistry»

2. VARIATION IN THE g13C VALUE AMONG PLANTS

VJickman (1952) and Craig (195^) surveyed a wide range of higher plants but did not find a systematic variation in the g» 13c value between plant species. Wickman (1952) did find that the Gymnospermáe values were slightly less negative than for other higher plants where the £ 13c value of about -26?íciwas similar to results from Craig (195*0 «>

In the results of both 0ickman (1952) and Craig there were anomalous plants, i.so plants where the S value was less negative than the majority of plants that were sampled„ Although several explanations were advanced by Craig (195*0 to account fcr the anomalies it is now apparent that these plants had different photosynthetic carbon pathways from the other plants. Recently several investigators have ehovm that plants which are known to be Cz^ type plants (plants with the enzyme phosphoenolpyruvate carboxylasej PEP carboxylase) have J13c values which are about 135ásless negative than C-z type plants (plants with the enzyme ribulose-1;5=diphosphate carboxylase9 RuDP carboxylase) (Bender 1968; Vogel and Lerman 1969; Smith 1970; Oeschgen et al 1970; Troughton, Hendy and Card 1971)° Extensive 59.

measurements of the S'^C value for over 100 species have shown 1 a pronounced bimodal distribution with a mean £ ^C vaiue of -27%oíor the C3 group of plants and about -1**&>for the Ci+ type type of plants, As yet there have been no exception to the general rule that the £ 13c value for Gj type higher plants is more negative than that for Ci* type plants. Low £ 13c values have been reported for some plants which would indicate the Cif type carbon metabolism but confirmatory biochemical tests have yet to be carried out (Troughton et al 1971; Smith and Epstein 1970),

The bimodal distribution of S^^G values occurs in mono- cotyledons, dicotyledons and in succulents from both these orders while there has been a noticeable lack of any gymnosperms with % 13Q values less than -19&4 The variation ini1^C values between plants has not been correlated with any particular plant family and it has been shown that two plant species within the same genus can have differing pathways of carbón metabolism and the associated difference in S ^3c value. Thus Atriplex spongiosa has a J^c value of about -15«9/¿eand is known to have the Cif pathway whereas Atriplex hastata has a £ 13C value of -30»3%*> and has the C-^ pathway (Osmond et al 1969; Troughton et al 197D» In spite of the large variation in £^C values between plants it has not yet been possible to adequately describe the mechanisms responsible for the fractionation of the stable isotope of carbon by plantsB

3. MECHANISMS OF CARBON ISOTOPE FRACTIONATION IN PLANTS

There are several chemical and physical reactions occurring in the process of photosynthesis and the subsequent metabolic steps that,may be the cause of fractionation. These processes include diffusion of CO2 in the gaseous phase, diffusion in the liquid phase, the carbosylation step9 subsequent transformations of the photosynthetically produced carbon compounds and photorespiration. The cause of the fractioaation of carbon will, as a first approximation, be determined by the magnitude of kinetic fractionations in bimolecular reactions, or diffusion which in turn depend on the square root of the ratio of the masses of the molecules involved in the rate-limiting step° If the rate-limiting step involves diffusion of small molecules such as C0¿ (molecular weight kk) the kinetic fractions will be large (•^11^5 whereas if it involves large molecules (simple sugars etc), molecular weight'^ 200) the kinetic fractionations will be small (*

The rate-limiting step involving CO2 in plants can be variable both between plant species and with time» The rate of CO2 uptake by plants can be formulated (Monteith 19&3) aB 40.

= (r rm)

where P rate of photosynthesis g cm~ C concentration of CO2 in the bulk air g cm-3

ra boundary layer resistance secern leaf resistance secern"^

mesophyll resistance sec.cm"' e photosynthetic efficiency ? —1 i light level cal.era sec carboxylation resistance sec.cm"1

(a) Gaseous Diffusion of COj Into Plants

The initial process in photosynthesis ie the transfer of carbon dioxide from the atmosphere to the cell surface-air interface. The maximum fractionation due to diffusion of gaseous CO2 will be -11?a©and the actual fractionation will depend on the site of the rate-limiting process in the chain of reactions. Eapid and sometimes large variations are known to occur in stomatal aperture which may cause the diffusion step to be rate limiting even if the mesophyll and carboxylation step is large. It is of interest that some succulent plants that possess Crassulacean Acid Metabolism, and therefore take up CO2 at night, have $ 13c values comparable to the plants with the Ci). pathway of photosynthesis.

(b) Liquid Phase Transport of CO2 within Cells

The second phase of transport of CO2 into plants is in the step from the cell wall where CO2 goes into solution to the surface of the carboxylating enzymes which are associated with the chloroplasts. There will be a email fractionation of ~0.5?a»due to the step involving CO2 going into solution at the cell wallo In C3 type plants the pathway within the cell includes 41.

the transport of C04 in solution across the cell wall, plasmalemma, within the cytoplasm, across the chloroplast outer envelope and within the chloroplast to HuDP carboxylase. Some transport of CO2 may occur as bicarbonate ions at high pH and carbonic anhydrase may be involved in the transport mechanism. In C($ type plants the exact location of PEP carboxylase has yet to be determined but it has been suggested that th© ensyme is outside of the chloroplast and probably closely associated vriV-i the outer membrane. With the enzyme in this positioct an*, in the presence of carbonic anhydrase, th© shorter pathlength for diffusion of CO2 may lead to differences in fractionation of carbon due to these stepa in Cj¿ compared with C 3 plants.

The species used in carboxylation will have a large effect upon the extent of fractionation. For example, if bicarbonate rathsr than CO2 is involved in carboxylation then the S^C values will be less negative by about 9&* It has now been firmly established that for aost higher terrestrial plants of the C^ type that free, unhydrated carbon dioxide is the form of carbon used in carboxylation (Cooper et al 1969)» There is some doubt about the form of carbon used in C4 type plants, although CO2 is favoured (Cooper et al 19685 Waygood et al 1969).

å second posaible source of fractionation of carbon isotopes associated with carboxylation would be due to the particular enzyme involved. A comparison of the Kin's of the two enzymes in vitro are suggestive that the values for PEP carboxylase are lower than for RuDP carboxylase (Maruyama et al 1966; Cooper et al 1969) which may suggest that fractionation of carbon isotopes would be less for PEP carboxylaseo Fractionation due to the enzymes in vitro has not been measured for PEP carboxylase but for PuDP carboxylase estimates were made by Park and Epstein (19OO). Using bicarbonate as a source of CO2 they suggested that RuDP carboxylase would cause a maximum fractionation of -17$©but as CO2 is involved in the reaction, the maximum S1^C fractionation effect may be about =8?¿a

Cd) Fractionation Due to Biochemical Reactions Within the Plant

There have been numerous reports of variation in % Z values between biochemical components within higher plants (Abelson and Hoering 1961; Whelan et al 197O5 Park and Epstein 196O; Degens et al 1968). In general, pectin and protein tends to be less negative than the total carbohydrate or cellulose compounds whereas the lipide tend to be more negative than the bulk of the plant by up to -10?!» These variations in the £ 13c value between compounds within the plant are important in understanding the biosynthetic pathways and may contribute to some of the observed variation in the % 13(J value between species. ( In general, however, variations in components such as lipids in higher plants will only have a small effect on the mean S1^C value of the plant because the bulk of the organic material will be cellulose. In some tree species however the proportion of lignin can also be high and therefore cause the£i3c value to be more negative than that which would be expected from the fractionation due to photosynthesis.

It has been shown by Whelan et al 1970 that in sorghum (Cif type plant), malic acid, aspartic acid and glucose all have similar £ 13c values. In these plants it has been suggested that CO2 is fixed initially by PEP carboxylase but that subsequently a decarboxylation occurs and the CO2 released is refixed by RuDP carboxyl.ase in a different cell (Hatch and Slack 1970). The similarity in ¿'13C vaiue between malic acid and glucose in the results of Whelan et al 1970 suggest that there is no fractionation associated with the decarboxylation and second carboxylation step» This may be due to the fact that the decarboxylation process takes place within the bundle sheath cell and if this is a closed system all the CO2 will be refixed by RuDP carboxylase and, as no new CO2 from outside the system is introduced, there will be no further fractionation»

(e) Effect of Respiration on the&^c Value of Plants

It has been shown by Park and Epstein (1960) that the CO2 released by the plant in the dark has a £ 13c value which ia close to the mean value for the plant» CO2 released at night is not immediately refixed and is therefore unlikely to influence the S^^C value of the plant. In the light CO2 released by the non- photosynthetic organs or by the soil and soil organisms may be recycled but the transfer of CO? in the atmosphere is so rapid that it will tend to equalise the $ 13c value of the air in the vicinity of plants and in the bulk atmosphere c In the light carbon dioxide is released by photorespiration in the photosynthetically active cells» Photorespiration is associated with the glycollate metabolism of plants and results in the release of COp by mitochondria which are in the close vicinity of the chloroplasts. C(>2 released by this process may therefore be reassimilated by the plant before the CO2 can reach the air outside the plant. The £13r; value of the respired CO2 being taken up in photosynthesis will be more negative than the air surrounding the plant but the effect of this CO2 on the g13c value of the plant will depend on the magnitude of photTespiration and the site at which this CO2 re-enters the photosynthetic pathway» With high rates of photorespiration and if all the CO2 respired reached the outside air before entering the photosynthetic pathway then the £1^C value of the.plant could be reduced by up to -8?á> Under normal conditions the extra fractionation would be much less than this, and could even be absent if the C02 was recycled without reaching the rate-limiting step or the step with the maximum fractionation.

Differences in the rate of photorespiration between species could, however, be a significant cause of variations in the £1*C values between plants. Genetic variation in photorespiration within species may occur but the most pronounced difference is between the C3 and Ci^ type plants * There is a low rate of loss of C0¿ in the light in C¿* type plants and this loss is not necessarily associated with low photorespiraticn but it may be influenced by the site of photorespiration. In C/j. plants photorespiration ie most likely to occur in the bundle sheath cells and it is therefore in a different cell from that in which the initial reactions of photosynthesis are occurring. Only if CO2 released by photorespiration in these plants can diffuse through the cell wall separating the raesophyll and bundle sheath cells will it have any influence on the %'X^>Z value of the CO2 taken up in photosynthesis.

In some grasses it has been shown that there is an electron opaque layer between these two ceils and this may prevent exchange of gases between these cells8 except through the plasmodesmata» Consequently in some Cif plants the bundle sheath may consist of a closed system and without any further fractionation of carbon» In other Cif plants, and Atriplex spongiosa may be an example, some C02 Kiay be respired or come from the de car boxy lat i on process in the bundle sheath cell and leak into the 44,

mesophyll cell or into the intercellular air and therefore be recycled. However this CO2 would have to enter the CO2 uptake pathway before the rate-limiting step for it to affect the $^C value of the plant.

6. PROBLEMS IN INTERPRETING THE MEAN g13C VALUE OF PLANTS

The basic problem in interpreting the J* C value of whole plants is that these values represent a mean value for all the carbon which has been accumulated over long periods of time,, It is likely that the process causing the bulk of the fractionation will vary with time and even within the course of a day photosynthesis may be regulated by different components at different times. For example, light is likely to be the limiting factor in photosynthesis during the initial and last periods of the day, whereas under normal conditions carbon dioxide supply will limit photosynthesis at high light in the middle of the day. Even under these conditions a closure of stomata due to water stress may change the location of the rate-limiting step in the CO2 uptake pathway»

The bulk of the carbon in the plant will have been accumulated during periods of high photosynthesis and it is therefore likely that the £^C value for the nlant will normally reflect a rate-limiting step up associated with (X>2 transfer. However, under conditions of long periods of low light or prolonged water stress suffic;ent carbon may accumulate to significantly affect the $^^c value of the planto

Plants growing naturally in different ecological sites are subjected to numerous environmental features which may also alter the£'^c values. However: neither temperature nor the localised reduction in C02 concentration round plants appear to be important. It has been suggested that soil conditions 1 may alter the£ 3c values (Kfickman 1952; Craig 1953) but this is unlikely to be significant for higher plants and Bender (1968) has shown that corn, wheat, barley, tomothy and oats growing together on a limestone soil had $ '3c values consistent with their different photosynthetic pathway0 Results of Smith and Epstein (1970) suggest that some plants groning under mareh conditions have lowJp-^C, but it will be necessary to establish the pathnay of carbon metabolism in these plants before the significance of their ecological site on the fc^C value can be evaluated,. ?. CONCLUSIONS

The lack of critical experimental data prevents the interpretation of the cause of variation in ¿> 13c values between plants and especially between C^ and C/+ type plants, although some inferences about the likely sites of fractionation can be made from C02 exchange data. In high light it has been shown in Cif type plants that the intra- cellular resistance (r¿ where r^o r + r ) is about 1 sec- cm whereas the minimum leaf resistance is >» 1 and close to 2 sec.cm"1 (Osmond et al 1969; Raven 1970). Hence it is likely that the fractionation of carbon in these plants will be associated with diffusion of CO2 in the gaseous phase and may be as great as 11$e> In contrast to this the C3 type plants have values of r± of about 3 sec.ca-1 which is very much greater than the minimum gaseous phase resistances of about 1<,5 seo.cm-1 (Troughton and Slatyer 1969)» Consequently, in these plants the cellular processes may be a more important source of fractionation and this would include diffusion of CO2 in the liquid phase within the cell and the carboxylation events» Furthermore there will be an effect of photorespiration which would cause the S ^C value to be even more negativeo

The processes associated with the fractionalion of the naturally occurring stable isotopes of carbon by photosynthesis has important consequences to many aspects of carbon isotope work» Our interest in understanding the processes involved "»J vä in fractionation have been directed at investigating CO2 uptake by plants and the biosynthetic processes within plants. Investigations of systems denendent on carbon from plants k fea may be able to utilise the information about the variation 1 i ° in the £I^c value by plants and, for example, the particular plant material utilised by animals will be reflected in the S ^C value of their tisaues. Some examples would be in ground water studies, exudation of compounds from roots, oil, coal and gas interrelationships„ and the evolution and geographical distribution of plants during geological timeo tö • * 4t 46.

ACKNOWLEDGEMENTS

The author acknowledges the encouragement of Dr T.A, Rafter, Institute of Nuclear Sciences, D0S.I.R., to investigate fractionation of carbon isotogs© ia photosynthesis and with the provision of experimental facilities. Dr C.I. Hendy and Mrs K.A. Card have assisted by discussion and with technical aspects»

REFERENCES

Abelson, P.H. and T.C. Hoering. 1961. Proco NatnoAcad.Sci6 47,623» Bender, H.M. 1968. Radiocarbon» 10, 468O Cooper, T.G., T.T. Tchen, H.G. Wood and CR. Benedicto 1968O J. biol. Cheo. 243, 3857. Cooper, T.G., D. Filmer, Mo Wisanik and D.M. Lase* 1969o J. biol. Chem. 244, 1082. Craig, H. 1953» Geochim. Cosmochim<, Acta., 53* Craig, H. 1954 « J» of Geolc, 62, 115. Craig, H. 1957. Geochim. Cosmochim» Actao, 12, 133 Degens, E.T. Hatch, M.D. and C.R. Slack. 19700 Ann. Revo Plo Physiolc 21, Maruyama, H., R.L. Sasterday, HOCO Chang and MoDo Laneo 1966 Jo Biolo Chem. 241, 2405. McKinney, CRO9 J.M. McCrea, So Epstein9 HOA9 alien and 1950. Rev. Scio Instro, 219 724. M Monteith,, JOLO 19^3 In "Emrironmental Coatrol ©f Plant Grouth o Ed. LoT. Evans. Academic Presso po95o Oeschgsr9H., T. Riesen and J,C. Lerman 1970» Radioearboa (In Press) Oemond, C.BO, J.H6 Troughtoa and D.JO Goodchild 1969° Z. fur Pflana», 61, 218. Park9 R. ana S. Epstein 196O« GeochiiBo Cosmochimo åctaO0 21,110, Raven, J.A. 1970. Biel. Rev., 459 167O Smith, B.Wc and S. Epstein. 1970. Plast Physiol=0 469 738» Troughton, J.H.9 C.H. Hendy amd K.A. Ca£"d3 1971 o %<, 3 (In Press)„ J.EO and R.0o Slatyer 1969o åust. J=. Biolc 22, 815O Vogel9 J0C0 and JOCO Leraan» 1969» Radieearbon, 11, 351 o Waygood, E0Ro, R. Mache and C.K0 Tano 1969o Cano Jo Bots 47, 1455» Whelan, T., 17.M. Sackett and CoRo Benedicto 1970O Bi©chesit Biophytäo Bes. Coma., 41, 1205» DickEian, F.E0 1952O Geochiao CosiaochiQo ActaOs 2,

té--/1 3$ * THEE HINGS AND RADIOCARBON DATES

by H.S. Jansen

ABSTRACT

The significance of growth patterns for the C-14 age determination of wood or charcoal is discussed. Knowledge of C 02 concentration in the atmosphere is important» It cas foe derived from wood of known ring' age. C-14!- dates in. the Southern Hemisphere have been related to those in the Northern Hemisphere and the position uith respect to corrections for secular variations is clarified. Sher® are problems in selecting wood components representative of contemporary atmospheric COp° Solutions depend on circumstances.

•tí" 48,

RADIOCABBOH USERS COHEEREHCE 1971

THEE KDKJS AMD RADIOCARBON TtåTES

by H. S. Jansen

Among samples supplied for carbon dating,, wood and charcoal rank prominently. Less prominent in all-too-aiany instances is the submitter's understanding of what a carbon date will teU him^ even now.

Clean wood dates the time of its formation, by«=and<=largefi so that wood from the outside of a tree dates the time of its death,,, usually the time of the tree's falling. The inside of the wood dates an earlier event and, if growth rings are available, seme idea may be olrfcained of the period by x&ich the wood age exceeds the age of the tree's death. It is helpful all round if the wood or charcoal can be identified botanically and Dr Wardle and Dr MoUoy of Botany Division have made this possible in many cases. If a species is knowi

Ob* to be short-lived, it might not matter greatly in particular case \ihether the wood is from inside or outside.

For all carbon dating it is essential to know how the C=14 level in atmospheric carbon dioxide has varied over the years. After all, it is this C0_ that becomes plaat by photosynthesis and plants become animals via the eating process. Tree rings are playing a star° role in checking the past atmospheric C =14 levels „ Trees are logs ia more ways than one. Roughly each ring has a C=14 ]Lsvel that cosrespcada 49.

to the atmosphere of the time. If we can trust tree rings to be annual,

we have a record of the C-14 level in air for the time the tree grew.

We must know the year it died and we must have a number of trees to

compare and eliminate idiosyncrasies.

Much of this work has been done in the Northern Hemisphere,

some of it by people who get their tree rings from the University of

Arizona, where a special laboratory for tree ring research takes care of

that aspect. Our data and those of Lerman and others hint at slightly

f\Lder C-14 ages in the Southern Hemisphere. It has been suggested a

number of times that we correct for this "secular" effect. Most

people feel that it is too early to standardise such corrections., espe°

cially for the Southern Hemisphere. There is nothing to prevent indi=

viduals from making these corrections^ just as there is nothing to stop

them from converting reported ages for the improvement in knowledge

of the C~l4 half°lifej, a matter of three percent. What is necessary iSj,

that authors explicitly point out what adjustments they have made.

A list of suggested corrections £>r the secular effect was

1 published by Ralph and Michael in 'Radiocarbon vol, 11, Noo2 (1969).

Where it has been possible to check ring data with historical 4 records the two logs agreed remarkably well.

The whole U.S. tree ring chronology now goes back some 8000 years. It is a little alarming that C-14 ages of 4500~70Q%ears are too young by 400-1000 years. It is unsatisfactory in a way because i-re cannot check the remaining 405000 years of C=l4 dating. 50. Six thousand years B.P. corresponds to a climactic optimum. Fortuna» tely errors of 1000 years or so are less serious for ages of tens of thousands of years. Also the error appears to flatten out as one goes back further. :

In work of this kind it is important that the components of '. wood which are studied for C-14 are representative for the sir in which it grew, and mobile components must be removed AS much as possible. „ i Such components are mineral grease, introduced during felling and sub» • sequent cutting of the wood, resins, oils, fats and waxes. :

The former in particular should be born in mind by everyone. A small piece of wood has been found and a C-14 date is deemed desirable. The wood weighs 8 grams, but in a shake is a one gram blob of grease from a chainsaw. If the wood itself has an age of 300 years and if the grease remains unnoticed under some sawdust or charcoal, the greasy wood will give an age of 2500 years and nobody may ever know why the result was way out. Of course 0.1 gram of grease would make the result only 730 years, but that is still 230 years too many at an age when the statistical error is 40 years on the same machine.

To remove both mobile wood components and matter such as grease, the wood used for tree ring C-14 work has to be chemically treated.

There are three schools of thought. The first ignores the problem, the second treats the splintered or ground sample with a.3 frail and acid somehow. This removes resin acids, but not reseñes. Other components are removed under vigorous conditions and it is not difficult to dissolve the whole sample. A third approach is to extract the 51.

grcund wood with organic solvents. This satisfactorily removes all

one wishes to remove but may ¡introduce some undesired carbon of its

own. For many years this remained a fear and inorganic treatment was

favoured by most people but facts on which to base a judgement were

lacking and this was highlighted in the discussion that followed my

paper for the Nobel Symposium in 1969. I then used seme C-14-labelled

solvents and got carbon from this solvent into the wood residue as

well as in the resin, etc., after drying. This carbon transfer proved

to be large in some instances and quite small in others. If manufac-

turing specifications are correct, the C-transfer amounted to 3/4$ for

ethanol extraction of rimu and 5~1Q# for benzene extraction of this

. It was interesting that an ethanol-benzene mixture gave the

same C-transfer as ethanol alone. Resin extracts were many times

worse off. Since then I have searched for methods to remove solvents

and to use the most favourable solvent. It is very unlikely that each

species of tree will behave in the same way. Unfortunately some common

solvents such as ether are not commercially available in C-l4-labelled

form. They will have to be» made on the spot where and when facilities

are available.

At present I am using alkali when a sample is large and a

carefully balanced mixture of an inert solvent and one of known activi-

ty when it is not. The solvent is then driven off as well as possible

with water. If the sample is very small and only an order of magni-

tude is desired for its age,, the whole wood is counted.

Reference Suggested correction for Northern Hemisphere: E.K. Ralph ajxd H.N. Michael. University of Pennsylvania Radiocarbon Dates HI, Radiocarbon, vol. U, No. 2, 1969, pp. 469-481.

53. THE PRESENCE OF HUMIC ACIDS TN RADIOCARBON-DATED CHARCOAL

By J.M. Bailey and K.S. Birrell Soil Bureau, Department of Scientific and Industrial Research, Lower Hutt.

' • Summary

° Some radiocarbon dated "charcoal" samples were examined to test the assumption that they were composed of elementary carbon together , ' with a little inorganic material. All samplet were shown to contain ~¿ humic acids some being almost entirely composed of it. The presence s" oí' humic acids, in the guise of charcoal or in the soil associated : with charcoal, could produce dates which are younger or older than ; the event investigated,

; Introduction

Carbonised wood or charcoal is generallv considered to be a • suitable material for radiocarbon dating. The assumption is usually made that samples presented for radiocarbon dating, which look like charcoal, are composed of elementary carbon together with j some inorganic matter. During studies of loess stratigraphy Mr E. Griffiths, Soil Bureau, Christchurch, (pers.comm) discovered "charcoal" in the loess

deposit at Barrys Bay, Banks Peninsu3.ao This "charcoal" (radiocarbon date 17,^5OÍ2,O7O yr BP) was shown to be composed mainly of humic acids by Bailey (1971). Following this discovery a number of "charcoal" samples which had been radiocarbon dated were selected for analysis. This paper describes the results of the analyses and their implications.

Results and Discussion

Some "charcoal" samples with radiocarbon dates placing them in the Holocene or Pleistocene periods were analysed. Carbon, and exchangeable calcium and magnesium were determined. Three ':' fractions of organic matter »ere also determined or examined. . [ First, the humic fraction which dissolves in dilute sodium ; hydroxide and is precipitated by acid (H.), second, the fulvie i fraction which does not precipitate with acid, and third, the J humic fraction which dissolves in dilute sodium hydroxide after '\

dilute acid treatment (H?). Certain samples were analysed by ; infrared absorption. The results are given in Tables 1 and 2, and J some infr-red spectra are shown in Figure 1* '; Table 1 shows that all the samples had carbon contents well below that of laboratory activated charcoal and similar to that of soil organic matter extracted from a paleosol (BP171). Humic acids were present in all samples examined* Soft lumps fr n sample N77/556 closely resembled charcoal in appearance but were found to ; be composed entirely of huSic acids* The ash of some samples -• contained high, amounts of magnesium and calcium, probably combined with humic acids as humates. ; Infrared spectra data given in Table 2 also indicate the { presence of functional groups associated with huinic acids (Goh, ] 1970), Figure 1 also shows the infrared spectra for sample N77/5^8 (NZ 106? age 36,200Í2,100 yr BP) after sodium hydroxide \ and hydrofluoric/hydrochloric acid treatments compared with a : sample of barbecue charcoal which had received similar treatments. ' It has been suggested that Hp humic acids would resist decomposition in nature so that older materials would tend to contain relatively ; more. Samples BP171 and N77/556 are however, similar in their H_ ' content but greatly differ •'n age. A significant difference between I the "charcoal" samples and modern soil organic matter is that j fulvic acids are absent from the former. (Birrell, Pullar, and ! Heine, 1971). j

j Implications 'Aj The presence of humic acids in the guise of charcoal or in ! the soil could produce radiocarbon dates which ar- younger or | older than the event being investigated* Humic acids carried i down from above might normally be expected to be younger but since 55. the dates of origin of humic acids cannot be known, datings from charcoal containing them, could, in some instances, be unreliable.

References

BAILEY, J M. 1971: The Extraction and Radiocarbon Dating of Dispersed Organic Material From Loess in the South Island of New Zealand. Hew Zealand Journal of Science (in press). BIRRELL, K.S.; PULLAR, W.A.; HEINE, Janr.ce, 1971: Pedological, Chemical, and Physical Properties of Organic Horizons of Paleosols Underlying the Tarawera Formation. Mew Zealand Journal of Science 1*t; 187-218. uOH., K.M. 1970: Organic Matter in New Zealand Soils. Part 1. Improved Methods for Obtaining Humic and Fulvic Acids with Low Ash Content. New Zealand Journal of Science 15? 669-86.

» Acknowledgements

The help of Dr R.J. Furkert and Miss G. Mather with some ¡of the infrared analyses is gratefully acknowledged. > 56.

3000 MOO OSO MMVCNUMN* KM'1) Figure 1. Infrared spectra for "charcoal" sample N77/548 (NZ 1067, age 36|200-2,10Q yr BP), after various treatments compared with a sample of barbecue charcoal» - 1 Curve A represents the original "charcoal" NZ 1O67 (1.0 mg/300 m« """""""""""*** *l 1 K B r) Note presence of peaks at 1720 cm"" t 1380 cm" and 16OO -1 cm . Curve B represents the residue from NZ 1067 after removal of the 0.1N sodium hydroxide soluble fraction. Note lack of peak at 1720 cm". Curve C represents the residue after sodium hydroxide followed by hydrofluoric and hydrochloric acid treatments (1 N HF/0.1N HCl), Note significant return of peak at 1?20 cm and l~ck of peak at 1390 cm"1.

Curves Dt E and F represent the effect of sodium hydroxide and then hydrofluoric and hydrochloric acids, on a sample of barbecue charcoal. Note the complete absence of peaks at 1720 cm" and 1380 cm but the presence of peaks at 1600 cm • Table 1. Analytical data on charcoals and soil organic matter

Fossil Age,' Material Remarks C$ C$ Percent total C Ca + Hg or yr B.P actual ash-free as humle acids me.$ Lab. of O.N, number BP 64 Soil organic matter H F treatment 56*6 66.5 11.3 24.1 260 SB2O73 thought to Charcoal lumps from Taupo be 1820 Ash 59.2 63.8 nd nd nd T 683 Charcoal lumos middle of (£. 8000) more than 2.5 cm Rotoma Ash 58.4 70.2 nd nd 86 N77/555 Charcoal lumps (c. 8000) more than 0*6 cm re-samples 58.4 68.3 11.0 nd 55.6 »77/555 Residue re-s»mpled (c. 8000) less than 0.6 cm 12.8 nd 36 nd nd Ss B77/556 Soft charcoal (c. 20,000) more than 7 mesh re-sampled 57.1 64.5 53.5 45.4 H77/548 Charcoal (NZ 1067) 36,200±2,100 more than 0.6 cm re-sampled 59.1 67.7 nd nd 166 N277/548 Residue (NZ 1067) less than 0.6 cm re-eampled 19.95 nd 91 nä nd B.D.H. Hedern Charcoal, de- colourising Lab. reagent 88.8 91.7 nd nd nd

Note nd = not determined * Brackets indicate samples that have not been individually litC dated.

' ' "' i\ ' , 58. Table 2. Data from infrared spectra of charcoals, soil organic matter, and humic acid.

Sample Age Carboxylic acid Peak height Aromatic or yrs B.P.* (1720 cm-1) Or (1720 cm-1) ketonic peak carboxylate ion £. 1600 cm-1 (£. 1380 cm-1)

BP 171 64 N13V594 1.76OÍ8O (=NZ 158) 0.43 N85/5O1 1.84OÍ5O («NZ 163) 0.25 N85/5O2 (=NZ 164) 0.22 SB 2073 (thought to be 1,820) 0.27 N77/555 £. 8000 T 683 £. 8000 N77/556 (soft) (£. 20,000) 0.38 N77/556 (hard) (£. 20,000) 0.31 N77/5V8 (=NZ 1067) 36,200^2,100 Hi humic (36.200Í2.100) acid from 0.31 "Barbecue" Modern charcoal Activated Modern charcoal

Brackets indicate samples that have not been individually % dated. 59.

OONTAIIIIULTIOH OF BADIOCABBON SAMPLES

T.L.* Grant-Taylor N.Z. Geological Survey Lower Hutt

ABSTRACT

Contamination is the most serious of dating problemsc This paper deals only with contamination after sample formation. Woods and peats may be contaminated by soluble organic substances which may not be removed by caustic soda treatment} there are several objections to this treatment. Contaminating influences on charcoal, bone, shell, horn and other substances are described, with safe- guards against them outlined. Mention is made of routine testing methods and affects of contamination on ages.

í I

J 60.

CONTAMINATION OP RADIOCARBON SAMPLES by T.L. Grant-Taylor N.Z. Geological Survey

Contamination of samples for radioactive dating is one of the most serious problems facing any dating technique . Although one might consider any process that causes a date to depart from true age as contamination. IpShall discuss only those processes whicl* alter the C /C ratios after the sample was formed. There are a number of different materials which contain carbon deposited by organic processes that would be suitable for carbon dating. Wood and peat Charcoal Bone Shell Skin and flesh Contamination of all of these is possible, contamination of some is almost certain, of others quite probable. My later discussion touches on certain aspects of this in selection of samples. Wood and Peat Although it might appear that wood enclosed in peat would be likely to be a more reliable dating medium than the peat itself, in practice this does not appear to be the case, and wood is usually found to give an age similar to the peat enclosing it. A detailed examination of peat and wood of late last interglacial to early last glaciation age, showed apparently irregular variations in age of both wood and peat. Drs Stout, Birrell and Goh have discussed certain aspects of soluble organic substances produced during the breakdown of plant matter in the soil which substances are probably the contaminating agents. The soluble substances appear to permeate both wood and peat. J Presumably this "stewing" continues from the time of initial deposition, and there can be no confidence that J material introduced as soluble compounds will remain j soluble or extractable by simple routine methods. j \

'' i \. 61.

In many laboratories overseas it has become standard practice to extract with caustic soda. This practice is based on the assumption that the contaminating substances are acids and can form salts with sodium. It can only work if the assumption that the soluble acids remain soluble and are not altered to insoluble substances by the process of fossilisation. I have several objections to the use of this extraction process as a routine procedure. (1) Humic acids are not the only water soluble substances likely to be present. (2) Some of these substances are not soluble in alkali. (3) The routine processes used can only give a partial positive answer to the question "is this sample contaminated" they cannot give a negative answer nor can they be relied on to give an uncontaminated sample. (4) Because of the uncertainty of the consequences of the extraction process, a treated sample is in no better relative condition than before! It is likely to be still contaminated, and a "date" determined on it is still wrong. (5) The fact that treatment has been given will lead to an unjustified confidence in the result. (6) Processing would require at least two date type determinations per sample with no certainly improved result. Charcoal Dr Birrell has already discussed his discovery of the presence of massive quantities of humic acid occurring with charcoal in the tephra of the volcanic district. This discovery, precipitated by very large discrepancies in the ages of some of the oldest tephra, shows that at least under certain conditions the effect of contamination of charcoal can be extreme. Bis attempts.to remove the carboxyl and aromatic double bond infrared peaks from charcoal samples have been unsuccessful. 62.

The examination of Taupo sub group charcoals showed the presence of humic acids, with,.the strength of infrared peaks increasing with higher C count (younger apparent age). There is therefore a tentative inference that the older dates are more reliable and that the true age is probably nearer 1890 years before 1950 than Mr Healy's 1964 estimate of 1824 years obtained by statistical analysis of dates weighted towards those produced from twigs rather than logs. Bone For a number of years bone was acidified to release COp from so called "bone carbonate". This process produced results that often departed very largely from those obtained from shells, wood and charcoal buried with the bone. After 1954 when the Redwing Hydrogen Bomb wag exploded there was a dramatic rise in atmospheric G. A bone sample collected in 1962 gave an impossible date as post 19^4 indicating substantial exchange of COp since the first explosion of thermo-nuclear devices. This result immediately precipitated an intensified examination of bone as a dating material, (Rafter 1965) and experiments showed that the organic component in bone was usually present in sufficient quantity to form a dating material not subject to the dangers of exchange type contamination. Solution carried addition type contamination is a remaining possibility, but because most suitable bones dated have so far been geologically very young, such contamination is unlikely to have a very large effect. Older bones contain a diminished amount of organic carbon and therefore with increasing age are less likely to provide dateable material. Shell Shell is composed of calcium carbonate with varying amounts of an organic horny substance. Because there have been numerous instances of exchange type contamination of shell it is widely considered to be an undesirable material for dating. Although we initially held the common view, X-ray examination of a range of marine organisms in the early sixties showed that many marine organisms deposited aragonite as the main carbonate bearing crystal form. Aragonite is metastable under ordinary surface and near surface conditions and any interference with the crystal structure causes formation of calcite the stable 63. y form. This then permitted a simple and rapid test for possible contamination of a wide range of carbonata depositing organisms. Since 1963 samples have been routinely tested for the presence of calcite bj diffraction X-ray (Grant-Taylor & Rafter 1971). Presence of calcite is regarded as demonstrating unsuitabiDity of the sample, When a group of carbonate producing organisms is ; first dated a fresh skeleton is examined under X-ray for presence of calcite. Unfortunately some groups do deposit calcite e.g. oysters, pectens, barnacles, calcareous algae etc. Nonetheless some of these produce organic layers in sufficient volume to provide a dating material e.g. some oysters and pectens, and these are then dated by use of this horny material. Intertidal marine aragonite depositing organisms produce the only material that can be considered to give a date of tested reliability. Skin, Flesh, Hair and Horn Skin and flesh will very seldom be preserved. Samples from Antarctica have been dated but the ages obtained suggested that they were modern. Burial and pre- _;> servat i on in a peat bog introduces the possibility of i solution borne contamination. No pragmatic answers can be given on this possibility. Prom the nature of hair and horn it might be expected that they could be better dating material, but no testing has been carried out and it is not very likely that large enough samples from a wide range of conditions of preservation will be obtained tc properly test them. Carbonate Contamination of Carbonaceous Sample In many carbonaceous samples some carbonate is present. This will often have been derived from surrounding rocks and is very likely to have an apparent age greatly different from the organic sample. Organic samples are routinely acidified to remove carbonate. Routine Testing For some time now X-ray diffraction has been used to ! examine carbonate samples. Mass spectroscope examination has been used for a long i time to examine bone and shell samples and randomly selected wood and peat samples. Now all samples are examined by mass spectroscope land the results used to calculate dates. Affect on Age of Contamination Although most contamination causes a reduction of apparent age. There are some ways by which old contamination can occur. (1) Exchange of dissolved CO, from limestone (2) Included charcoal (3) Included coa?. Young contamination can occur in the following ways: (1) Root penetration (2) Solution transported products (3) Exchange with air in dry state (4) Exchange in solution

References Grant-Taylor, T.L. & Rafter T.A. 1964: New Zealand Radiocarbon Age Measurements -6. N.Z. Journal of Geology & Geophysics V14:364-402. Olson, E.A. & Broecker, W,A. 1959: Sample Contamin- ation & Reliability of Radiocarbon Dates : New York Academy of Sciences Transactions Ser.II v.20:593-604. AU Rafter, T.A. 1965: C Variations in Nature Part V. The Age of the New Zealand Moa from Carbon 14 Measurements. Institute of Nuclear Sciences Report 37 16 pp. 65. SELECTION OP SAMPLES FOR RADIOCARBON DATING FOR GEOLOGICAL PURPOSES

T.L. Grant-Taylor N.Z. Geological Survey Lower Hutt

ABSTRACT

Por correct inferences to be drawn from the age of a sample submitted for dating, the relationships of the sample to geological and biological agents must be carefully considered, along with possible isotopic renewal and other chemical processes. If samples are to have scientific value they must have information presented with them. Supplying adequate information assists the dating laboratory in guarding against possible sources of contamination and in choosing the correct counting standard; these measures result in a more reliable date for the collector. 66.

SELECTION OP SAMPLES TOR RADIOCARBON DATING FOR GEOLOGICAL PURPOSES

by T.L. Grant-Taylor N.Z. Geological Survey

Introduction The carbon dating process is based on two assumptions (1) That the concentration of radiocarbon in the environ- ments has been constant with time. (2) That in aay given sample the radiocarbon has entered the sample in a predict- able manner. For the purpose of this discussion all studies that refer to natural phenomena as distinct from man made processes, are regarded as geologic. These are almost always concerned with the establishment of a sequence of events, and fitting this sequence into a framework usually erected elsewhere, but sometimes established locally. A number of questions have to be answered before the suitability of the sample can be assessed. The collector almost invariably hopes to date a geological event by its inferred relationship with a carbon bearing sample, e.g. a fragment of wood buried in terrace gravels. The inference is that the fragment is a piece of drift wood from a tree that was alive immediately prior to its transportation and deposition. It is assumed that it is not re-excavated fossil and that it is not a fragment of root intruded into its present position by growth of a "modern" tree. Sometimes the state of preservation of the sample can suggest the validity of these assumptions. If the fragment includes bark it is unlikely that it is re-excavated fossil. If the fragment had conchoidal fracture planes with sediment on them then it was probably of substantial age at the time of burial, and might have been a re-excavated fossil. If the timber has been identified then it can be determined also whether it is root or stem. If the broken ends of the fragment as buried are jagged then it was probably broken when the timbfex- was fresh. If on the other hand the sample is from a peat lens then the problem of the relationship to the enclosing beds is much more straight forward, but the presence of a peat lens inside an aggrading gravel terrace implies a halt in deposition at least at that point and therefore a special significance within the sequence, and this special aspect should be considered. It is obvious that if an event to be dated is thought to be very young the relationship of the sample to the event to be dated must be much more carefully ¿judged. 67.

A fragment of the trunk of a large tree cannot give any more than a younger or older limit of an event only a few hundred years old even if the number of ringa inside or outside the sample were known. Some estimate will have to tie made of time elapsed between formation of the sample and the event to be dated. Events such as development of a moraine, only, say 300 years old, are very difficult to date with an accuracy say of - 50 years because of the coincidental relationship between the carbonaceous sample used to give the age. As an example two samples are obtained one of wood from a 3" branch buried by the moraine the other from the base of a small bog formed in o hollow on the moraine. Por the bog to develop» the permeability of the moraine surface has to be locally much reduced or the water table to be*locally high. This first process would be likely to require a very long time, and therefore the date of establishment of the bog would only very loosely fix the date of formation of the moraine. It does however permit a definite statement that the moraine is substantially older than the first formed peat in the overlying bog. The wood buried in the moraine could be re-excavated fossil in which case it would place a distant older limit. If it could be shown either because of intact trunk, branches and roots and the nature of breaks of limbs that it was alive immediately before burial then the date would be as close to the time of involvement as the nature of the sample would permit say +10 yrs. In the example then, the peat cannot date the deposition of the moraine and wood could, so one sample of the wood would be accepted, the other would not. It has recently been found that at least under certain kinds of plant cover the organic part of the soil takes on a renewed carbon isotopic composition so that an actively forming soil will give a moderate date. Burial is assumed to freeze the isotopic composition therefore a soil can be used to date quite precisely a burial event. Unfortunately if the soil contains charcoal or wood this relationship no longer holds, as unseparable fragments of greater age could be present, and the total soil would no longer give a relevant "age*. Marine Samples When dealing with marine samples the same kind of reasoning is used. It has been found that the carbon dioxide in water in the ocean can vary greatly in apparent age sometimes having an isotopic ratio equivalent to 3000 years. Organisms living in this water will have an apparent "age" during life of 3000 years. Therefore unless the apparent age of the environment is known, no 66.

ages in the true sense are possible from the deop ocean. Nonetheless if an estimate of age within about 3000 years is permissible then such a sample could be worth analysis* Around Antarctica the sea has an apparent age of about 1200 years as determined from Antarctic organismst and therefore a local secondary standard can be used to give Antarctic dates, but the remaining uncertainty in initial C/ C ratios prevents a high precision of the determined age, even though this age is reported in the same way as other ages. In surface ocean waters and along most sea shores the atmosphere and ocean approach equilibrium and appropriate animals can be dated against littoral marine standards, and dates from them have the same validity as dates determined on remains of terrestrial organisms. Presentation of Data Because radiocarbon samples are usually used for stratigraphic purposes, a standard geological Fossil Record Form is expected to be completed, but a modified form specifically for radiocarbon is beiiig designe!. This form has the advantage that it provides space for the essential data, making it easier for this to bo supplied. The standard numbering system used by the ordinary fossil record system is retained to make recording and retrieval much simpler, and the filing of a duplicate record in the masterfile permits location of records in the event of loss or destruction elsewhere. Any sample collected for any purpose whatsoever ia required to have several kinds of data with it. The nature of this data is determined by general requirements of all samples if they are to have scientific value. LOCATION They must be located in space by the kind of description that would Thermit another person to collect a further sample identical with the first, or to re- examine the stratigraphic or any other kind of setting. A sample without this kind of fixing is of no value. It is not enough to say oh but I have a recordI This record must accompany the sample, and without it the sample must be rejected.

Vi 69.

Nature of Sample It is usually desirable, although not always essential, to identify the organisms present in a sample. This identification may sometimes add valuable information concerning vegetation cover or climate. From time to time I have made suggestions to collectors, and whea the identifications were made it was realised that the sample had a much wider significance than originally thought. shell samples identification is of vital importance, If the shell is of intertidal origin the assumed standard will give a valid age. If, however, it is from deeper^ water there is an uncertainty about the initial G /C ratio that may be solvable 'by reference to an ocean water profile. The true age is likely to be 300-3000 years younger than the apparent ago and in absence of a local reference sea water profile the study for which the dating is being carried out must be able to absorb such uncertainties. Lacustrine, fluviatile and terrestrial shells use dissolved carbon dioxide, and in an area where there is appreciable calcium carbonate there is often a disturbance of C /C z ratios. Por some places in N.Z. we already have determinations that provide local standards, but for others the possibility of such disturbances needs to be considered When assessing the best method of dating an event. SIGNIFICANCE A statement of significance of the sample is essential. This statement is required not only for publication in the date list but also in assessing. (1) The suitability of the sample to determine what the collector wishes to demonstrate. (2) The possibility of certain kinds of contamination that might determine the nature of certain kinds of routine pretreatment. A full discussion is much more helpful than bare details.

U 70.

Estimate of Age Host new collectors do not appreciate the significance of this requirement. In order to obtain the most reliable possible date the sample is counted as closely as possible in time to the counting of one c-? other of the two primary standards used by our lab. These standards are counted on alternating weekends so that a "young" sample would be counted immediately before or after the counting of the young standard, while an old sample would be counted close to the old standard. Packaging We have neither time nor facilities to dry samples, so samples sent in wet condition are returned to the collector to dry. Samples should be thoroughly air dried before being stored. Although some collectors pack samples in aluminium foil«leakage from one foil wrapped sample to another in the same parcel often occurs. The best packaging is heavyweight plastic bags folded and stapled at the top. It is most undesirable to include paper identifying labels in the bag with most kinds of samples. The sample bag should be marked with the sheet fossil number in the same way as the sample sheet. This is best done with indelible spirit ink. Two copies of the sample form should be included in the parcel with the sample.

Date Lists Date lists published by other Laboratories are nc$ necessarily a good guide of the kind of information required. In the New Zealand date lists a broad project method of grouping is used, and samples collected by many people will be included to make as coherent an overall story as possible without concealing the significance of an individual sample. This "project" method of presentation ie becoming much more widely used in Date Lists, as I believe its superiority was so clearly demonstrated in Hew Zealand Date List No.5. You have with you copies of Date VI in which I believe this presentation is even more strongly developed. 71.

RADIOCARBON DATING OF SOIL ORGANIC MATTES s

ITS SCOPE AND LIMITATIONS

K. M. GOH

Department of Soil Science, Lincoln College, Canterbury 72.

ABSTRACT

Few published data are available on the radiocarbon dating of soil organic matter* Data reported to-date indicated that fractionation of organic matter occurred in surface soils and the ages obtained for soil organic carbon represented average ages or mean residence times* However, for buried soils, differences between the ages of the various organic carbon fractions might be lower than the inherent deviations expected from radiocarbon dating measurements* Considerably more research is needed if the method is to be useful for dating paleosols. Improvement should be sought in the selection of sites, sampling, and isolation of the most inert fraction of soil humus for dating purposes. 73

INTRODUCTION

Paleosols are of widespread occurrence in New Zealand. Radiocarbon dating of their organic matter components may provide valuable information as to the age, climate, vegetation, and other associated environmental conditions of their geologic past. However, the usefulness of the radiocarbon dating technique as applied to soil organic matter is very often limited by the lack of knowledge of the chemical nature of organic matter constituents present in the soil.

Few published data are available on the variability of radiocarbon dates shown by soil organic matter. For this reason, the major discussion in this paper will be on results obtained by two groups of workers, one in Canada and the other in Australia. Radior carbon dating of organic matter in New Zealand soils is now in progress at Lincoln College and the results will be reported when available. Components of Soil Organic Matter

An understanding of the chemical nature and types of major organic matter components in soils is necessary for the interpretations of radiocarbon dates obtained for these materials. Uncritical dating of soil organic matter might give an under- estimate of the true age (Campbell e£ al. 1967 a) and lead to erroneous conclusions.

Generally speaking, soil organic matter is a diverse mixture consisting of soil biomass, partially degraded plant, ajiimal, and microbial components and soil humic constituents. The latter constitutes the bulk of soil organic matter while the recognizable plant and microbial components seldom exceed more than 25 per cent of the total soil organic carbon.

Humic substances are a series of acidic, yellow - to black - coloured moderately high-molecular-weight polymers containing nitrogen. They bear little or no resemblance to the organic compounds present in living organisms and generally represent a heterogeneous mixture of molecules. Their molecular weights may range from 2,000 to as much as 300,000.

In recent years, a number of mild reagents and caustic alkalis had been used to recover humic substances from soil. The fractions normally obtained, based on their solubility characteristics are: humic acid, soluble in alkali, insoluble in acid; hymatomelanic acid, alcohol-soluble part of humic acid; fulvic acid, soluble in both alkali and acid. German organic chemists further subdivide humic acid into grey humic acid, precipitated by electrolyte at alkaline pH; brown humic acid, not affected by the above treatment (Scharpenseel et al. 1968). The organic matter not solubilized by alkali is generally referred to as hutnin, which may represent an intimate mixture of humic and fulvic acids strongly bound to the mineral matter in soils. A typical fractionation scheme is shown in Figure 1.

The undesirability of regarding each individual component as chemically homogeneous has been stressed by several workers (Scheffer and Ulrich, 1960; Swain, 1963; Felbeck, 1965; Kononova, 1966). According to present-day concepts, the various groups are part of a system of polymers and the differences between the fractions are due to systematic variations in elemental composition, acidity, degree of polymerization and molecular weight. No sharp demarcation exists between the humic and fulvic acids although Kononova (1966) regards the latter as simple representatives of the former. She considers humin as the 75. most inert humus fraction. However, it has been reported that humin turned over relatively rapidly - within 50 to 1,000 years - although not as rapidly as humic and fuXvic acids (Campbell et al. 19&7 b)

On the whole humic substances differ from kerogen and brown coals in having higher carboxyl and hydroxyl functional group contents, lower carbon, but higher oxygen contents and are soluble in alkali. The broad inter-relationships according to Stevenson and Butler (19&9) *s as follows:

Lignin - > Primary structural units

•v Humic acids "^ Fulvic acids Í Metabolites of Coal micro-organisms

The conversion of humic to fulvic acids has recently been shown to occur in both synthetic and natural humic substances (Goh and Stevenson, 1971). ;-, 76.

SOIL

extract with alkali

(insoluble) (soluble) hum in

treat with acid

(precipitated) (not precipitated) I I humic acid fulvie acid

extract with alcohol redissolve in base and add electrolyte

hymatomelanic acid

(precipitated) (not precipitated) grey humic acid brown humic acid

Figure 1. Fractionation of humic substances (Stevenson and Butler, 1969) 77.

Data from Dating Experiments

As discussed above, soil organic matter represents a mixture of substances. Hence, the age obtained for soil organic carbon will be an average age rather than a specific one. In dating surface soils, Paul e_t al. (1964) used the term "mean residence time" (M.R.T.) for the age of the soiJ organic car'ion.

Later works by Paul and his associates (Campbell e_t al. 1967 a; 1967 b; Paul, 1969) indicated that the mein residence times differed not only fron soil to soil in several Canadian surface soils but also in the various soil organic matter fractions from the same surface soil. For example, in one of their studies of surface soils in Saskatchewan, Canada, in one soil, where the M.R.T. of the unfractionated carbon was 870 ¿ 50 years, the M.R.T."s of the various organic matter fractions ranged from 25 to 1,41C years. In another soil, the M.R.T. of the un ractionated carbon was 250 - 60 years while the fractions showed a range of M.R.T.'s from 0 to 485 years (see Table 1). From the above data, these workers were able to estimate the relative turnover rates of the various soil humus fractions (Paul, 1969) and also to characterize the so-called "stable" and "relatively mobile and -unstable" fractions.

Very little published data is available on the radiocarbon dating of organic matter in buried soils. Costin and Polach (1969) recently reported the results for two Australian paleosols. These workers found that in one buried soil, the humic acid fraction showed an age similar to that of the carbonised wood while in another soil, the humic acid was considerably younger (see Table 2). The latter result was attributed to shallow burial and contamination by translocation of younger humus from the soil above.

Discussion

It would appear from the above discussions of the experimental data obtained by the various workers on the radiocarbon dating of soil organic matter that the method is only useful for determining the turnover rates of organic mattor in surface soils and has limited value for dating paleosols. However, as the data are limited and inconclusive, considerably more research is needed before a definite conclusion can be reached. For example, little, if any, of the work has been done on the effects of various extraction techniques on the radiocarbon detes obtained for organic matter fractions.

L - 78.

Table 1 A summary of mean residence times as obtained by Campbell et al. O967 t>) for soil organic matter fractions in two Canadian soils.

Mean residence timeCyrT Fraction Melfort Soil Waitvill- Soil

Ünfractionated soil 870 i 50 250 í 60 + Fulvic acids I 555 - h5 50 Humic acids I ("mobile") 785 - 50 85 Humin I 1135 i 5° 335 - 50 Humic acids II ("total") 1235 * 60 195 - 50 Non-hydrolysable 1400 í 60 Hydrolysable 25 - 50 Fulvijc acids II 495 - 60 Acid extract 325 ¿ 60 Fulvic acids II + Acid Extract 470 i 60 0

Humin II 50 i 70 Non-hydrolysable 1230 - 60 - Hydrolysable 50 79.

Table 2 Radiocarbon dates of soil organic natter fractions in two buried Australian soils (Costin and Polach, 1969)

Age of Buried Soil at Component Munyang Geehi

2200 Carbonised wood „ <. + 2030 30,920 - 162O

Í- 1500 1650 32,050 - 24,960 Í 580 Hunic acid 1370

Humin t 890 25,360 * 580

Soil (after removal of wood) 19.730 - 600 19,980 I 370

bl 60.

Data reported by Paul and his associates suggested that the most representative fraction of soil humus for the age of a surface soil «as the humin fraction (see Table 1). This is in agreement with the view of other workers on soil organic matter (Kononova, 1966). However, results from Costin and Polach (1969) for buried soils indicated that the oldest organic matter carbon was in humic acid (see Table 2). This discrepancy could have arisen from differences in the organic matter extraction techniques used by these two groups.of workers. Although the same alkali was used for organic matter extraction by these workers, differences in the extraction time and soil: extraction ratio can significantly affect the extent of recovery of the various soil organic matter fractions. The yields of soil humus fractions have been found to be dependent on a number of extraction conditions (Gascho, 1965; Goh, 1970). Any incomplete removal of the relatively acre mobile and hence younger humic and fulvic acid fractions froa the mineral part of the soil may lead to a lowering in the age of the humin fraction since this fraction is the one remaining after the removal.of humic and fulvic acids. In addition, the presence of any fibrous plant tissues will be included in the humin fraction in the conventional organic matter fractionation scheme as these residues are insoluble in alkali. They might cause a lowering in the age of humin. This was found to be the case by Scharpenseel ejt al. (1968); who reported that for peedogley-chernozem and low moor, instead of tha age increasing in the order, fulvic acid £ hymatomelanic acid —> grey humic acid —> brown humic acid • •> humin — -> humus coal,as expected froa the increasing molecular weight and decreasing functional group contents, it followed the order only to the grey humic acid. Humin and humus coal were found to be younger than grey liumic acid and the other hv.auB fractions preceding grey buraic acid in the order as shown above. For buried soils, differences in the ages of the various organic matter fractions due to fractionation may not be as important as in present-day surface soils* According to Libby (1965), the half-life of radiocarbon of 5,568 ¿ 30 years is probably accurate to within 50 years or almost certainly within 100 years, thus representing an error of 1 to 2 per cent. For a 10,000 - years - old sample the limit will be 100 to 2CO years while for a 20,000 - year- - old sample, it is from 200 to 400 years» Therefore the precision of radiocarbon measurement decreases with the increasing age of a sample.

u 81.

Bangos of deviations in the ages of Iowa soils as found by Sube (19¿5) are summarized in Table 3. This worker contended that for buried soils the deviation inherent in the radiocarbon measurement far exceeded the deviations of M.R.T.'a of the various soil organic matter fractions from that of the unfractionated carbon. Whether this is the case in true situations, will need to be examined in greater details by more extensive dating of a wider range of buried soils.

85.

Conclusions

It is apparent from the discussions above that considerably more research is needed in the dating of soil organic matter. Greater attention should be devoted to improvement in the method oí extracting organic natter and more efficient separation of the various fractions extracted. The final objective will be the isolation of the most inert fraction of the organic matter that has the age very siailar to the true age of the soil. As under New Zealand conditions, nost of the buried soils might have a grassland rather than a forest vegetation before burial, the difficulty of finding suitable carbonised wood for dating purposes leaves much to be lesired from the dating of soil organic matter. References

CAMPBELL, C.A., PAUL, E.A., RENNIE, D.A. and McCALLUM, K.J. 1967 a. Factors affecting the accuracy of carbon dating in soil humus studies. Soil Sci. 10^ (2) : 81-85.

CAMPBELL, C.A., PAUL, E.A., RENNIE, D.A. aad McCALLUM K.J. 1967 b. Applicability of the ciirbon dating method of analysis to soil humus studies. Ibid 10*f (3) : 217-224. : • 1 ! -1 COSTIN, A.B. and POLACH, H.A. 1969. Dating soil organic matter. i ! Applicability to buried soils in the Kosciusko area, N.S,W. » ; • ( Atomic Energy in Australia. 12 : 13-17» •> ] I- ¡ FELBECK,G.T. Jr. 1965. Structural chemistry of soil humic ' | substances. Advan. Agron. 1? : 327-368. ! j ('' I GASCHO, G.J. 1965. Extraction of soil organic matter. M.Sc. I > Thesis, University of Illinois, Illinois, U.S.A. | j

'• i GOH, K.h. 1970. Organic matter in New Zealand soils. 1, N Improvep d methods for obtaining humic and fulvic acids í j with low ash content. N.Z. J. Sci. 13 : 699-686. n GOH, K.H. and STEVENSON, F.J. 1971• Comparison of infrared 1 spectra of synthetic and natural humic and fulvic acids. j Soil Sci. (In Press). !

KONONOVA, M.M. 1966. "Soil Organic Hatter" 2nd ed. j j •v Pergamon Press, New York. US

LIBBÍ, W.F. 1965. "Radiocarbon Dating" 2nd ed. Univ. Chicago [J Press, Chicago, U.S.A. |

PAUL, E.Ao 1969o Characterization and turnover rate of soil ' | humic constituents. In "Pedology and Quaternary Research" ¡D | ed. 3. Pavluk, Univ. Alberta Printing Dept. Canada. i J

ft 85.

PAUL, E.A., CAMPBELL, G.A., RENNIE, D.A. andMcCALLUM, K.J. 196^. Investigations of the dynamics of soil humus utilizing carbon dating techniques. Trans. 8th Int. Congr. Soil Sci., ?! 201-208.

RUHE, R.V. 1965 "Quaternary Landscapes In Iowa" Iowa State Univ. Press, Iowa, U.S.A.

SCHARPENSEEL, H.W., RONZANI, C and PIETIG, F. 1968. Comparative age determination of different humic - matter fractions, ¿n "Isotopes and Radiation in Soil Organic Matter Studies." Proc. Symp. I. A. E. A. Vienna. Pp. 67-73.

SCHEFFER, F. and ULRICH, 8. i960. Humus and Humusdungung. Bd. I. Stuttgart, Germany.

STEVENSON, F.J. and BUTLER, J.H.A. 1969. Chemistry of humic acids and related pigments. In "Organic Geochemistry" ed. G. Eglinton and M.T.J. Murphy, Springer - Verlag, Berlin.

SWAIN, F.M. 1963. Geochemistry of Humus. In "Organic Geochemistry" ed. I.A. Berger. Pergamon Press, New York, THE USE OF RADIOCARBON

IN MEASURING THE TURNOVER OF

SOIL ORGANIC HATTER

By J. D. Stout

Soil Bureau, Department of Scientific and Industrial Research, Lower Butt

Paper presented to RADIOCARBON USERS CONFERENCE Lover Hutt 17th & 18th August 1971

1 ¡i i;: ií 87.

THE USB OF BiDIOCAHBON IN MEASURING SHE TURNOVER OF SOIL ORGANIC MATTER

J.D. Stout Soil Bureau, New Zealand Department of Scientific and Industrial Research, Lower Hutt

Abstract

The increase in atmospheric radiocarbon following thermonuclear testing has made possible the study of turnover rates of soil organic 14- matter. From measurements to date the patterns of C enrichment in soils under pasture and under beech forest are quite different. Under pasture enrichment tends to be limited principally to the topsoil but under forest there is enrichment all down the profile. The implication of these measurements are discussed in relation to differences in the organic cycle.

Introduction

The rate of turnover of soil organic matter is important since it affects the availability OJ" plant nutrients. In general these become available only when organic matter is mineralized, that is when nitrogen, phosphorus, and sulphur are released from organic compounds, usually by microbial activity. This prooess is commonly associated '< with the mineralization of organic carbon to carbon dioxide. Since, ,| apart from water, carbon is the principal constituent of living tissue the release of carbon dioxide is a good measure of mineralization. The rate of turnover of soil organic matter io also important as soil ' organic matter confers many important physical, chemical, and pedological properties on soil, in particular those affecting structure and water-holding capacity. Finally, as part of the general cycling of oarbon, mineralization determines the balance ; between levels of carbon dioxide in the atmosphere, in the biosphere, and in the accumulated reserves of incompletely decomposed organic i. matter. In this respect, soil contains very large reserves of ¡;

i-- H; 86.

organic carbon, figures of 100,000 kg / ha being typical of modal New Zealand soils. The measurement of organic matter turnover in soils presents many practical problems. It is necessary to know the amount of organic matter in the soil; the rate of accretion from plant debris and other jouroes; and the rate of mineralization. Only very approximate measurements can be made of these three parameters. Any soil type shows considerable variation in depth and therefore in organic matter on an area basis. Die measurement of leaf and litter fall may be attempted with some confidence in a forest, it is less easy in a grassland, and measurement of accretions from roots presents very real difficulties. Bie release of carbon dioxide may be measured in the field by measuring fluctuations in the rate of flow tvlth an infrared gas analyser or by sampling carbon dioxide from a given area of so: 1 over a given period of time by absorption in alkali, or other methods. Alternatively respiratory measurements may be made on samples in the laboratory. All these methods impose artificial conditions and few have given reliable quantitative results. Bie main problem is to discriminate between release of carbon dioxide due to plant, particularly root, respiration and that due to the mineralization of soil organic matter. For these reasons, where annual losses balance annual gains the addition of labelled substrate to the soil can give information on the rate of turnover of organic matter obtainable in no other way.

Die use of radiocarbon in soil studies has expanded greatly in reoent years (Jenkinson, 1971) but there have so far been only limited attempts at measuring rates of turnover. Experimentally, two techniques have been used. The addition of labelled material, either plant material or a substrate such as glucose, or the subjection of soils and growing plants to an atmosphere of known radiocarbon composition. The increase in atmospheric radiocarbon following thermonuclear testing has made it possible to do turnover studies anywhere in the world. Only the quantitative determinations of the magnitude of the organic oycle need to be known and the distribution and concentration of radiocarbon enrichment. 89.

Enrichment of soil organic carbon by C is due primarily to the addition of residues from plants growing in the enriched atmosphere. Such residues includes leaves, litter, soluble fractions carried to the soil in leaf drip and stem flow, root exudates, the carbon dioxide respired by the roots, and the residues of dead root material. Enrichment may also take place through the direct incorporation of atmospheric carbon dioxide into the soil biomass. Finally, enrichment can take place by physical absorption of atmospheric carbon dioxide or by chemical substitution. Mineralization, including the release of carbon dioxide, is commonly associated with decomposition by animals or microorganisms, but of the material decomposed only part is mineralized. Part is converted to animal or microbial tissue and part is excreted or left incompletely decomposed. Obviously substrates which are readily metabolized by soil organisms do not remain long in the soil. They are either mineralized, converted to animal or microbial tissue, or transformed into substances not readily metabolized. There are two principal barriers to metabolism, physical and chemical. Substrates may not be physically accessible to soil organisms or they may be chemically too complex for the available enzymes to metabolize. Physical barriers may be due to plant structure and may be removed by comminution of plant remains by soil animals or they may be due to the physical relationships of the organic and mineral soil fractions, particularly the association with clays and colloids in the soil. Because of these barriers rates of decomposition and mineralization of soil organic matter may vary greatly and some soil organic material may be thousands of years old, while other fractions may have been incox^ »rated into the soil only a few days or even a few hours previously. For this reason dating the soil organic matter by C may be misleading as it is likely to relate to only a fraction of the total soil organic carbon. Similarly, measurement of rates of turnover from natural or artificial enrichment relate only to one fraction of soil organic matter but this is the most active fraction.

J 90.

Bate of Turnover in Soil trader Pasture

Top-dressed pastures on fertile soils consist predominantly of rye-grass (Lolium perenne) and clover (Trifolium repens) and may produce up to 20,000 kg/ha of dry matter of herbage a year and up to 5,000 kg/ha of roots. About 8O?5 of the herbage is eaten by grazing stock, the residue being returned to the soil as plant debris or animal faeces. The dead leaves, and root material are eaten by exotic earthworms, which are present in very large numbers, about three to four million/ha. Their numbers increase in the autumn and winter, when the plant roots die, and diminish in the spring and summer. There is a ! relatively stable ratio between the productivity of the pasture, the mass of the grazing animal, and the mass of earthworms. For every 1,000 kg of dry matter of herbage produced, there is 150 kg (live weight) of grazing animal, and 170 kg (live weight) of earthworms. Because of the earthworm activity, there is very rapid comminution of plant and animal debris and a rapid rate of decomposition. An example of a moderately producing pasture (ca. 7,500 kg/ha/yr) is a site near Wellington on Judgeford silt loam. Measurements of 1¿f C enrichment since 1963 have been made on samples of topsoil from 14- i this site, and measurements have also been made of the C activity of the herbage, the earthworms, and the subsoil (Rafter and Stout, ! 1970). The results are plotted in Figure 1. These showi 14 1 ; 1. The C of the pasture is the same as that of the atmosphere; 14 2. There is a steady enrichment in C in the topsoil; 3> The earthworm population, sampled in November, 1968, had an activity approximately 87$ of the herbage collected at the i -( same time. ¡ ¡; The results imply t 1. No significant fractionation in photosynthesis; ' 2. No significant enrichment in the soil due to physical or I 1 •' chemical causes, since these would be reflected in the sub- : I ; soil as well as the topsoil; 91.

3. No significant accumulation of fresh organic matter in the subsoil; k. That the earthworms (a) are feeding on the plant material, and (b) must either be relatively young or have a very high rate of tissue turnover. If the exchange of C between the air and the soil is assumed to be a single rate process it is possible to relate soil activity to atmospheric activity and determine the exchange rate and the mean turnover time. This has been done for the Judgeford soil (Rafter and Stout, 1970) and the calculated values are shown in Figure 1. These imply a turnover time of 21 years. Other pastures measured give values of 10 and 15 years, but the calculations do not fit the Hfemont soil, which is rich in allophane» and this suggests a different pattern of decomposition in such soils. There are two possible checks on these measurements; firstly the pattern of decomposition and mineralization of pasture grass in experimental situations, and secondly, the calculated rate of turnover from annual increment and total mass of soil organic matter, assuming the system to be in balance. Experiments adding labelled rye-grass to soil have shown that one third of the added carbon remains in the soil after one year and about 15 - 21$ after five years (Jenkinson, 1971). It is also estimated that about 10$ of the added carbon is in the biomass after one year and about Uffc after 4- years. In other words there is a fairly high rate of mineralization in the first year, but the rate falls later after the residual oarbon has been incorporated into the biomass. The distribution of oarbon from readily decomposable substances, such as glucose, hemicellulose, and cellulose, added to the soil is similar to that of soil organic nitrogen which suggests that it is closely associated with, if not actually part of, the biomass. Much residual material is probably contained in dead microbial oell wall material since amino-acide extracted from soil are generally identical with those constituting oell wall material. 92.

If we assume that the total dry matter added to the topsoil each year is about 3 - 4,000 kg/ha, representing about 1,500 - 2,000 kg/ha of oarbon, and that the topsoil may contain about 100,000 kg/ha of oarbon then the turnover rate estimated from these figures is lower 14 than that estimated from the C enrichment but this may be explained by the decreasing rate of mineralization with increasing age. Hate of Turnover in Soil under Beech Forest '• In a beeoh forest the C enrichment of the leaves falling to the ground is less than that of the atmosphere when the C levels of the atmosphere are rising (Figure 2). This is because the leaf takes longer to develop than grass leaves, and remains longer on the tree. Compared with a soil profile under pasture, however, a profile under beeoh is more enriched in C in all horizons (Figure 3). By extra- 14 polating to the curve of Figure 2, the soil C figures would suggest that the oldest organic matter in the deepest horizons is only 8 years old. However if it is assumed that only 2 to 3,000 kg/ha of oarbon are added each year and that the total soil organio oarbon is about 100,000 • kg/ha the turnover rate oannot be less than 40 years if the system is f in equilibrium. This anomaly might be explained if there was fraction- •$ 14 i ation during decomposition. Figure 4 shows the loss of weight, C, * 13 and C, of leaves kept on the forest floor in nylon net bags. This shows that there is no fraotionation of oarbon, at least in the early w 14 stages of decomposition, nor is there further C enriohment. There is a steady decrease of weight over four years but after this period only 65% of the leaves has disappeared. This is much less than might be expected from the annual increment to the organio horizons which is equal to about 25 - 30$ of the total weight. The decomposition of the fresh leaves takes plaoe by three prooesses - by oomminution, by leaehix!&, esså fey oxidation. The loss by comminution is reflected in the loss of ash, principally silica» which is very small. Only about éflí of the ash is lost over the four year f period. This is also oonfirmed by the well preserved leaf structure. Only about jf> of the unground freshly failed leaf is water soluble, 93. although the proportion rises to 155^ in the ground leaves. Much of tikis probably consista of amino-aoids and sugars whioh are accessible to miorobial attack and are therefore either oxidised or oonverted to miorobial tissue rather than lost be leaching. There is no marked difference in thec!j( oarbon of tbe freshly fallen leaf and the four year old leaf. Consequently the proportion of oarbon lost is proportional to the total loss of weight which is 16JJ& per year, or about ¿tOO kg/ha. This suggests that the greater part of the estimated annual loss of carbon takes place in the lower horizons. This is supported by a uniformly high rate of respiration per unit weight of oarbon down tiie profile (Dutoh and Stout, 1?68). If the basic moleoule in the leaf is assumed to be oellulose, then for every gram of oarbon completely oxidised, about 1 Ag of oxygen plus hydrogen would be released) with incomplete oxidation less oarbon dioxide will be evolved. With complete oxidation the % of oarbon would tend to increase but the actual change in $> carbon over the four year period is from k$ to kjfi and oonsequently the total loss of weight attributable to the completa oxidation of the leaf must be very small. The loss of carbon must be chiefly attributable to incomplete oxidation. There is also no significant change in the total amount of nitrogen in the leaves after four years. If we assume a mean C/H ratio of animal and microbial tissue of about 8, then this tissue would oomprise about tifao f the four year old leaves. An inspection of the leaves with the scanning electron microscope confirms the accumulation of animal and microbial debris with the passäjfe of time. Apart from the leaves, organic material is added to the soil in leaf drip and trunk flow. This material includes a high proportion of polyphenols. These pbenolio materials inolude substanoes which are fairly readily attacked by microorganisms and substanoes resistant to miorob'ial attack. The resistant substanoes will tend to accumulate and move down the profile and may help to explain the distribution of enriched material. 9*. References BUTCH, Nary E. and STOUT;, J.D. 1968* The carbon cycle in a beech forest eooeystem in relation to miorobial and animal populations. of tirut Qtíi IntafnjitianAl Catumma at Skill Adelaide» vol. II, pp. 37-46* JEKKHSOH, S.S. 1971» Studies on the decomposition of C labelled organic natter in soil. Sbil Soianca. vol. Ill, pp. 64-70. RAFTER, T.A. and STOUT, J.D. 1970s Radiocarbon measurements as an index of the rate of turnover of organic matter in forest and grassland ecosystems in Hew Zealand. Hobel Symposium 12, pp. 95.

FIG. 1

400

• ATMOSPHERE O • GRASS 400 O EARTHWORMS

JUDGEFORD SILT LOAM UNDER PASTURE

200 CALCULATED TURNOVER RATE 21 years

o TOPSOIL (0-10 cms)

x CALCUUTED VALUES

100

SUtSOIL (25-40 cm)

é 6t «*

A (609-3) . 600- K NUCLEAR BOMB TESTING 500- U 400- ATMOSPHERE-

300- ECH A14C LEAVES

200

100-

-too- f i i r i i i i i i i T i i i i 1951 52 53 54 55 56 57 58 591960 61 62 63 64 65 66 FIG 2 ORGANIC C THICKNESS kgs/ha 600- •/• 000

500-

400-

300-

200-

100-

SAMPLED -100 NOVEMBER 1986 1951 52 53 54 55 56 57 58 59 1960 61 62 63 64 65 66 FI&3 98.

LOSS OF WEIGHT OF LEWES IN NYLON NET 8AGS CHANGES IN %C, ¿14c AND &C

350

300 -27 513c

25O 25

100 LOSS BY 90- COMMINUTION ! LEACHING. ' 80 AND • OXIDATION

40 30- ••ASH 2O- i

0 1004 1905 1966 1967 »68 FIG. 4

.•! i

¡i .', i 99.

RADIOCARBON DATING IN BOTANY N.T. Moar

Botany Division, Department of Scientific and Industrial Research, Christchurch

SUMMARY

Radiocarbon dating has allowed a clearer insight into the history of the flora and vegetation over the last 40,000 years* Application of the technique in pollen analysis has focussed attention upon problems inherent in the interpretation of pollen diagrams. The identification, and dating, of charcoal remainf in eastern South Island soils has added much to our understanding of the more recent history of the vegetation. The technique is also successfully applied to studies of plant succession on moraine of different ages and at different altitudes, and is important in establishing correlation with a time scale based on dendrochronology. 100.

INTRODUCTION The technique of radiocarbon dating is as important to botany as it is to any other discipline. It has provided a reliable time scale to which the history of the flora and vegetation can be securely tied at a local or regional level. This has focussed attention more sharply upon the botanical problems of migration, succession, and regional variations in patterns of vegetation. The nature of the samples, peat, wood, lake muds, charcoal, etc., is the same as those submitted by I' í , I ! t workers in other' disciplines,and the dates ii !' t obtained are doubtless of use to others, but the main purpose for dating is to solve some problem in botany* The problems associated with dating these various materials have been reviewed by Godwin (1969) and need no further emphasis.

HISTORY OF FLORA AND VEGETATION Pollen Analysis: I !' Radiocarbon dating provides an absolute time scale for the last 40,000 years and has thus replaced pollen analysis, during that time, as a

of bio-stratigraphic, litho-stratigraphic and time- stratigraphic data when constructing zoning systems for pollen diagrams. This has led to testing, by radiocarbon assay, various pollen zone boundaries hitherto considered synchronous over wide areas, such as north-west Europe. The rising Picea (spruce) pollen curve considered to mark the Sub- boreal/Sub-atlantic boundary in Finland at about 2,500 years ago is an interesting example. There were doubts about this timing and they were confirmed when Aario (1965) demonstrated, with radiocarbon dates, that a westward spread of Picaa began about 5000 years ago and that it took more than 2,000 years to complete. Similarly, :; Kubitzki (1961) has shown that the spread of Fagüa (beech) in north-west Europe is highly diachronotis, the result of control largely by anthropogenic factors (Godwin, 1966). Harris (1963) concluded that palynological data indicated a slow eastward migration of Nothofagus (southern beech) in Southland, implying that the pollen zone boundary II/III of Cranwell and von Post (1936) is diachronous. More recently radiocarbon dates relating to pollen diagrams from central South Island

i s' 102.

(Moar, 1971) provide data on the migration rate of Nothofagus and indicate clearly that pollen zone boundaries based on the rising Nothofagus curve, i.e. bio-stratigraphic criteria, are diachronous. Radiocarbon dates therefore, not only add precision to our knowledge of post-glacial patterns of vegetation, but they also focus attention more clearly upon stratigraphical problems. There is a great need to extend this work in New "Zealand. There are only a few dates relating to the beginning of the post-glacial spread of forest, and none which can be directly related to the earlier grassland and shrubland phases as they are revealed in long pollen diagrams. We have enough information to conclude that post-glacial patterns of vegetation were complex and that they varied over fairly short distances. To produce a detailed history of vegetation therefore, many more pollen diagrams are required together with A series of radiocarbon dates relating to at least one selected diagram from each region» This is especially urgent since present problems can only be understood in terms of past events.

. 103. That interpretation of pollen diagrams in terms of vegetation is vital before any inferences can be drawn about climate, is obvious. The usual method of presenting the data is to express the abundance of each pollen type as a percentage of the total pollen counted in each sample and to draw a pollen diagram from these. Although the pitfalls are recognised, errors of interpretation are possible since percentage values are interdependent and a change in abundance of one pollen type must affect the value of all other types recorded. Von Post (I9l6) recognised this difficulty more than fifty years ago and suggested the use of absolute pollen frequencies (APF) per unit weight of sediment, but since absolute numbers are dependent upon rates of peat accumulation the idea was not generally taken up. Radiocarbon assay has altered this, and recently a number of papers discussing the problem have appeared (Davis and Deevey, 1964; Davis, 1967; 1969» Tsukada, 1967). Davis and Deevey have presented the concept of pollen accumulation rate,the annual input of pollen grains per square centimetre, calculated by dividing APF by sediment accumulation rate (x yrs. per cm.)* This permits presentation of the

1 1 104. data in an absolute pollen diagram in which the fluctuation of the various pollen types recorded more truly reflect the history of the parent plants.

: However, it is expensive in terms of radiocarbon dates. The most studied site, Rogers Lake, ' Connecticut, has more than 2k radiocarbon dates | ; spread more or less evenly through some 11 m. of [ '* sediment. Available New Zealand data suggests that rates of sediment accumulation vary so much at • any one site that close sampling for radiocarbon t assay would be needed to be certain of reliable

i results» One may question such expense especially Í when studies of current pollen rain may provide an jj alternative for interpreting pollen frequencies. ; However, we cannot be sure that the plant communities in the early post-glacial for example, have modern counterparts, and it is this sector which could justify the expense of radiocarbon dates at close intervals from the one site. The frequencies j; ofbeech pollen vary considerably in many early

| post-glacial South Island sediments, and the -i 'i !| !j meaning of this in terms of vegetation certainly

'i Í • needs more detailed study. •i í

' • Í ! Í • I' • S. 105. Soil Charcoal and Plant History; Charcoal in soils provides evidence of fire resulting from human activity or other causes. In many instances it can also be used as evidence of former vegetation, and Molloy (1964) has demonstrated that wood charcoal can be identified to the species level. This has led to an increased knowledge of forest and shrubland vegetation growing on different soil types in c Canterbury (Cox and Mead, 19<>3) before its widespread destruction by fire. Radiocarbon assay provides the dimension of time and it is now well established that there were catastrophic fires in eastern- South Island about 600 years ago (Molloy et al., 1963). There is also increasing evidence, based on charcoal finds, that fire has been a factor in vegetation history for thousands of years. Whether these have been local events, or of regional significance, remains to be tested by dating as more charcoal is unearthed.

Glaciers and Plant Succession; Radiocarbon assay has contributed a great deal

to our understanding of the history of recent

glacial advances. Mercer C1965; 1968; 1970) has

1 106. investigated the fluctuations of ice- margins on both sides of* the Andes in southern South America and has correlated a series of advances by dating saaples taken in close proximity to moraine, or outwash associated wdroh moraine. Similar work has been attempted in New Zealand (e.g. McGregor, 1967) although dating by radiocarbon assay has been minimala These investigations have been aimed at resolving geological problems, but the ecologist concerned with the course of plant succession is also interested in studies of this sort. Thus, Dr P. Wardie, Botany Division, D.S.I.R., has been investigating plant succession on a series of moraines from lowland to upland situations in South Westland. In most cases, radiocarbon dates are a necessary aid in establishing the age of the moraine and consequently the time available for any particular plant community to develop. At higher altitudes there is an absence of trees and shrubs to provide ring dates. It is pertinent to note here that some of the; youngest dates depend upon tree ring analysis, and although Dr Jansen has already discussed this matter, it is worth emphasising that correlation between a time scale based on tree rings, and one based on radiocarbon 107. assay, is a valid application of the technique for a botanist (Jansen and Wardle, 1971).

CONCLUSION

To further the q-¿est for a better understanding

of our vegetation and the environment in which it

has developed, we need more data from every region within the country. As has already been indicated

this requires much more work by botanists who must make use of radiocarbon dating techniques. How soon this objective can. be obtained depends upon a number of factors, mot the least of which is the strength of palynology in the country, for pollen diagrams provide a continuous story, through a particular period of time, of the development of regional vegetation. Probably the greatest need is to relate radiocarbon dates to critical phases of vegetation history in every region throughout

New Zealand.

REFERENCES

AARIO, E. 1965: ¡Die Fichtenverhaufigung im Lichte von C i4 bestinmuxigeji und die Altersverhält-

uisse der Finnischen pollenzonen. Comptes Rendns Société geóloyique de Finlande

No. 37: 215-231. 108.

C0Xt J.E. and MEAD, C.3. 1963: Soil evidence relating to post-glacial climate on the

Canterbury Plains.

Proceedings of the New Zealand Ecological

Society, No. 10; 28-37'

CRANWELL, L.M. and VON POST, L. 1936: Post-

pleistocene pollen diagrams from the

Southern Hemisphere. I. New Zealand.

Geografiska Annaler 5-ff: 308-47.

DAVIS, Margaret Ba 1967: Pollen accumulation rates at Rogers Lake, Connecticut, during Late-

and Post-glacial tine. Review of Palaeobotany

and Palynology 2: 219-30.

: Palynology and Environmental history during the Quaternary period.

American Scientist 57: 317-33.

DAVIS, Margaret B. and DEEVEY Jr., E.S. 1964: Pollen

accumulation rates: estimates from Late-

glacial sediment of Rogers Lake.

Science 145(3638}: 1293-95.

•GODWIN, H* 1966: Introductory address "World Climate

fron 8,000 to 0 B.C."

Proceedings, International Symposium, Royal

Meteorological Soci-ety, London, pp 3-l4. 109. 1969: The value of plant materials for radiocarbon dating.

American Journal of_Botany 56; 723-31.

HARRIS, W.F. 1963: Paleo-ecological evidence from pollen and' spores. e Proceedings New Zealand Ecological Society No. 10; 38-44. JANSEN, U.S. and WAHDLE, P. 1971: Comparisons between l4 ring age and C age in rimu trees from

Westland and Auckland.

New Zealand Journal of Botany 9: 2l5-l6.

KUBITZKI, K. 19Ó1:- Zur Sync ironis i erumg der

nordwesteuropSischen Pollendiagramrae (mit

Beitrá"gen) zur Waldgeschichte Nordwestdeutschlands. Flora 150: 43-72. McGREGOR, V.R. 1967: Holocene moraines and rock glaciers in the centra. Ben Ohau Range, South Canterbury^ New Zealand.

Journal of Glaciology 6; 737-48.

MERCER, J.H. 1965í Glacier variations in southern Patagonia.

The Geographical Review 55: 390-413. 110. _1968: Variations of some Patagonian glaciers since the Late-glacial.

American Journal of Science 266: 91-109. ^1970: Variations of some Patagonian glaciers since the Late-glacial.

American Journal of Science 269; 1-25.

MOAR, N.T. 1971: Contributions to the Quaternary o history of the New Zealand flora. 6. Aranuian pollen diagrams from Canterbury, Nelson and north Westland, South Island. New Zealand Journal of Botany 9: 80-1%5 • MQL-OY, B.P.Jc 196%: Soil genesis and plant succession in the sub-alpine and alpine zones of Torlesse Range, Canterbury, New Zealand. 2. Distribution, characteristics, and genesis of soils. New Zealand Journal of Botany 2: 143-76.

MOLLOY, B.P.J., BURROWS, C.J., COXt J.E., JOHNSTON, J.A., and VARÓLE, P. 1963: Distribution of subfossil forest remains, eastern South Island, New Zealand. New Zealand Journal of Botany 1: 68-77• TSUKADA, Matsuo 1967: Pollen succession, absolute pollen frequency and recurrence surfaces in 111. central Japan. American Journal of Botany 5**: 821-31. VON POST, L. I9l6: On skogstrSdpollen: sydsvenska torfmoss elagerf81jder. Geol. FCren. Stockholm FSrnandl. 38: 38*4-90.

I 112.

RADIOCARBON CHRONOLOGY OF LATE QUATERNARY RHYQLITE 1EPHRA DEPOSITS

C.G. vucetich, Geology Department, Victoria University of Wellington W.A, Pullar, Soil Bureau, Department of Scientific and Industrial Research, Whakataoe

ABSTRACT

Rhyolite tephra formations erupted from the Okataina Vol- canic Centre and the Taupo Volcanic Centre, Central Volcanic Region, North Island, have been dated using a range of materials: charcoal, wood, peat, mineralised peat and organic mud. For the younger tephras bracket sampling within peat or sediments has given dates of high reliability and within the range of dates for charcoals sampled from the tephra columns in the Central Volcanic Region. For the older tephras these sampling techniques have not been tested so thoroughly but results are in reasonable agreement.

In all, eighteen tephra formations covering a complete time span of 900 to 44,000 yrs. B.P. have been dated with reliabilities ranging from high to low.

INTRODUCTION

Radiocarbon chronology of rhyolitic tephra deposits has tended to follow rather than aecoapany the stratigraphic mapping of these deposits. On mapping alona it has been difficult to demonstrate convincingly the validity of the stratigraphy.

Tephra formation mapping (Vucetich and Pullar, 1964; 1969) has been largely dependent on recognising weathering breaks in the fom of paleosols which mark tha contact between the deposits of two successive eruptive episodes. Each episode is assumed to be a relatively brief event whereas the time interval between successive eruptions is relatively long, commonly 1,000 to 2,000 years with a miniEun of 200 years. During the hiatus between each major eruptive 'episode,soil formation proceeds accompanied by minimal erosion and generally minimal accretion of further tephra.

Most tephra deposits (air fall origin) contain negligible wood and only a little charcoal. Charcoal is better preserved in appreciably thick tephra deposits near an eruptive source and in particular within localised ash-flow units (nuée ardente origin). The dating of Taupo Pumice has in large measure depended on the good preservation in particularly widespread ash-flow members (ash-lapilli breccia). In most cases, tha choice of material for 14C dating is 113.

restricted to small discrete charcoal fragments occurring directly upon or within paleaseis. The reliability of such material to date the event of its burial(by a tephra eruption) is limited because the charring process may substantially predate this event.

Paleosols are recognised from their colour - greyish-brown (rarely black) ranging to bright yellowish-brown, and from their appreciable content of colloid. They form a distinctive layer lacking both the well-defined aggregates and rhyzomorphs and the high organic content so characteristic of modem soils. Occasional very dark, almost black, coloured tongues of organic rich material (highly stable polypnenolic compounds) and rare fragments of carbonised wood survive in addition to the more stable charcoals.

Paleosols are themselves commonly unlayered over appreciable areas and serve as additional diagnostics. Each paleosol (and Formation) inevitably thins laterally so as to lose its identity within the somewhat thicker paleosol of a lower more persistent formation. The "over thick" paleosols declare themselves in tephra mapping where stratigraphic control of the complete tephra column is essential.

Charcoal occurs sparingly within some formations and choice of sampling at times is "Hobson's Choice". Alternative materials such as wood, peat, mineralised peat, and organic mud, have been sampled to date tephras from swamps and flood plains in the Bay of Plenty, Gisborne and Hawkes Bay districts. At these sites the usual practice is to sample above and below the tephra layer so as to bracket it with a minimum and a maximum age.

Of the sixteen named tephra formations or members erupted from the Oltataina Volcanic Centre, seven are dated with high reliability, five with low to moderate reliability, and four remain undated. Of the ten deposits (defined as formations; in prep.) erupted from the Taupo Volcanic Centre, four are dated with high reliability, two have unreliable dates, and five remain undated.

PROBLEMS ASSOCIATED WITH SAMPLING

Ao CHARCOAL

1. In the Rerewfoakaaitu District a lens of charcoal within a paleosol (assumed Waiahou Fornation) and 3 ins below the unweathered basal ash of the Rotoma Ash Formation was sampled to date the latter formation. This sample was dated 10,700 + 120 yrs "B.P.

Waiahou Ash with an optimum age of 11,250 + 250 yrs carries a well developed paleosol indicating an appreciable period of soil formation. The paleosol has subsequently been found to contain weathered andesitic ash (Mt. To'igariro source) and its age status is uncertain.

TT5. é ' Z high ay and another sampled by MT. J.A. Berry within the same ash at Napier gave dates of 19,850 + 310 yrs B.P. (N.Z.1056) and 20,600 + 300 yrs B.P. (N.Z.12) respectively. No comparison is yst available for charcoal.

\ C. PEAT

In the swampy fringe of Lake Repongaere, near Gisborne, samples of peat above and below an air fall Taupo Pumice layer gave ; dates of 1,770 + 70 yrs B.P. (N.Z. 502) and 1,920 + 70 yrs B.P. (N.Z. ;i 503) respectively. At tha sama site, samples of peat abova and below an air fall Wairaihia Lapilli layer gave dates of 3,170 + 80 ,rs B.P. (N.Z.504) and 3,440 + 80 yrs B.P. (N.Z. 505} respectively. The dates obtained for Taupo Punice bracket the statistical average of 1,810 + 17 yrs B.P. for charcoal in the Taupo district and those obtained för Kainihia Lapilli bracket the dates obtained by Healy and BauEgart JLn Healy, 1964 (pp. 40-41) for charcoal in tha same district.

D. MINERALISED PEAT (Peaty Loan)

1. For the tsg 9-10 bed in the Taupo locality, Healy (1964, p. 40) has reported dates of 2,270 + 100 yrs B.P. (N.Z.157) and 2,500 + 200 yrs B.P. (Ii.Z.177) from separate saoples of carbonised twigs and stems and fron charcoal. For a thin tephra correlated with tsg 9-10 on Rangitaiki Plains, Pullar obtained dates of 2,010 + 60 yrs B.P. (N.Z.1068) and 2,150 • 48 yrs B.P. (K.Z.1069) from mineralised peat immediately above and below the bed respectively.

2. For the tsg 11 - 13 bed in the Taupo locality Healy (1964, :• p. 40) obtained a date of 2,800 + 100 yrs B.P. (N.Z. 182) fron carbon- ; ised twigs. For a thin ash correlated with tsg 11 - 13 on Rangitaiki Plains Pullar obtained dates of 2,670 + 50 yrs Ii.P. (.N.Z.1070), and f fron mineralised paat imasdiately above and below uhe bed 2,730 + 60 !__ yrs B.P. (N.Z. 1071) respectively, In each case the dates obtained by I ' Pullar for bracketed samples are in close agreement and have a high ¿ reliability. The mean of these dates makes boch events (eruptio.i of f, tsg 9-10 and 11 - 13) appreciably younger than indicated fron the | dates obtained by Healy.

B. OEGANIC MUD

At Gisbome samples of organic mud from above and below an unknown ash bed were sampled for dating. The dates obtained are 27,000 + 1,200 yxs B.P. (N.Z.1147) and 29,700 + 1,500 yrs B.P. (N.Z. 1136) respectively.

The dates indicate that the ash bed is one of the several 116.

oenbers of Mangaoai Lapilli Formation which because of limited exposure have not been correlated in this area. Mangaoni (c) has been dated as 30,100 + 1,300 yrs B.P. (N.Z.868) from charcoal sampled within an ash-flow unit near Kawerau and the date is considered optimum for this member*

The "unknown" Gistoome ash has a probable age within the range 26,700 and 31,200 years, and may reasonably be identified as Mangaoni Member (c). However the unknown ash may also be Mangaoni (d), at present not dated but known from the paleosol separating the two members (c) and Cd) to ba appreciably older.

CONCLUSIONS

The dates obtained for samples of different material in > widely different localities for dating one formation are in reasonable 1 agreement. Reliable dates are consistently obtained for samples of peat, organic mud or wood collected so as to bracket the ash bed.

For future tephra dating the emphasis should be on sampling ! charcoal from near the eruptive source where it is likely to represent 1 _in situ charring of trees, or sampling in peripheral areas where the tephra layers are enclosed in peat and are little contaminatedc j Because the least confidence may be placed in charcoal sampled from i, paleosols, such sampling should be confined to special projects aimad at interpreting both eruptive and other events. Such projects could well be extended to dating fractionations of fulvic acid and humic acid Wcause of their believed differential shift (Dr. K.S. Birrell, pers cocoa.). This technique may also be considered for dating non • tephra soils providing that sampling is controlled by general time planes, viz. the loess soils of Manawatu and Hawkes Bay.

REFERENCES

Healy, J. 1964» Stratigraphy and Chronology of Late Quaternary 1 Volcanic Ash in Taupo, Hotorua, and Gisborne districts. Part 1. Bull. N.2. Geol. Surv. n.s.73» 7-42.

Vucetich, C.G., Pullar, W.A. 1964» Stratigraphy and Chronology of ,! Late Quaternary Volcanic Ash in Taupo, Rotorua and Gisborne Districts. Part 2. Bull. N.Z. Geol. Surv. n.s.73: 43-83.

Vucetich, C.G., fullar, H.A. 19691 Stratigraphy and Chronology of Late Pleistocene Voleaaic Ash Beds in Central North Island, New Zealand. N.Z. Jl. Ceol. Geophys. 12(4)t 784-837. 1¿fr AGES, iMh-MHHWii FHCM c DATES, OF SOME TEPHEA AND GIBER DEPOSITS FBDM HOTOEUA, TláUPO, BAY OP PLMTY, GISBOHHE, AHL HaWKE'S BAY DISOÍEICTS

By W.A. Pallar, Batorua, and Janice C. Heine, Lower Hutt, Soil Bureau, Department of Scientific and Industrial Research, Few Zealand

Paper presented to RADIOCARBON Ü3ERS GO1IPEHESCE Lower Satt 17th and 18th August 1971

H.Z. Soil Bureau Publication 118.

ABSTRåCT

The G dating »cults of ¿2 saaples of carbonaceous aaterials, taken to date taphra depoait» that ooour In the Botorua, ftupc, Bay of Plenty, Giaborne, and BsMka's Bay district», ax* tabulated. The results are arranged to show the obxonologloal sequence of tephra deposits fro» the tise of the Taupo Btaiioe eruptions (e.. 1817 years

B.P.) to that of the Botoiti Breooia eruptions (o.. í»0t000 to W,000 years B.P.). Ik C dates are usually used to date a know identifiable tephra deposit. Hoverar, C dates aay also be used, in conjunction with stratigrapbio position, to identify a thin tephra deposit that has fev readily Identifiable lithologio properties. 119. ib 1GES, IKS'EEHED FECM C HATES, OF SOME TEPHRA AHL OTHER DEPOSITS

PBDM ROTOHQå, TADPO, BAY OP PLJSÍTY, GISBOHNE, AND

HAVKE'S MY DISTBICTS

By W.A. Pallar, Rötorna, and Janice C. Heine, Lower Hut t, Soil Bureau, Department of Scientific and Industrial Research, New Zealand

INTHODUCEION

1^f 62 samples of carbonaceous material have been collected for C dating, from tepbra foznations and members, and from other deposits.

The saaples have been collected in the Rotorua, Taupo, Bay of Plenty, Gisbome, and Hawke's Bay districts. About JO of these samples have been collected by the senior author between 1957 and 1971. lite remainder, collected by other workers, I.L. Baungart, J.A. Berry, R.A. Berry, J.W. Cole, J.E. Cox, D. Cross, J. Healy, I.A. Mairn, B.N. Thompson, C.G. Tucetich, and H.W. Wellnan, are included to provide a continuous chronological record of ^C dates for these tephra deposits.

Each sanple and its C date is listed against the Formation it dates in Table 1 in order of increasing age. Locations of samples are shown in Figure 1.

la Taupo, Rotorua, and Bay of Plenty districts where sampling sites are close to the eruption sources, identification of tephra deposits by their distinctive lithologic properties is usually possible and saaples of carbonaceous materials are taken to determine the ages of the deposits and stratigraphic sequence.

In the Gisborne district, identification of thin ash beds by lithologic properties alone has always been difficult and most samples collected for C dating are in effect 'grab' saaples taken to deternine correlation, and therefore identification, of a sample with an ash hså of known age.

She Taupo Subgroup meabera (Tsg) axe rather similar in their lithologic properties and therefore they are difficult to identify using only lithologic criteria. Howevez; when the stratigraphy of Tag Daubers is better understood (Vusetich and Pallar, in prep.) the dates obtained fron carbonaceous caterials that occur between the beds in the Gisborne district will be used, in conjunction with stratigraphic positions, to date and therefore to identify ths Tag beds elsewhere. 120. lit- TÜBL2 1 i IQBS, JSFESEEB IBGR C MISS, OF SONE TBPHRA AHD OTHER DEPOSITS, FROM

Sample Fossil Becord Ho. Description; Tephxa Fbzoation H.Z. ^C. Ho. Years B.P. Stratig. aphic (1950) Position

Taupo Puaico 1,819-17 Charcoal

Taupo Pumice H98/515 1,770-70 Peat; above ash H.Z. 502 bad

H98/516 1,900-56 Feat; below H.Z. 503 ash bed

Taupo Posies 1,870-60 Mood: twigs and H.Z. 1059 rootaj above ash bed

2,090-60 Wood1 twigs and H.Z. 10é0 roots; belov ash bed

Water-boras ash, H69/531 1,775-75 Bark, from log .Hatepe tapilli msaber H.Z. 52k overlying Hatepe water- borne ash

H69/517 2,010-75 Outer (1 in.) H.Z. 525 wood from stumps ¿¡ buried by Hatepe water- borne ash

¥ater-boros ash, 1,995-60 Bark, from Hatepe Lapilli nearer H.Z. 869 stusro in situ: Eatepe water- borne ash rests on root flange and on paleosol

Puaica (being Charcoal, from processed) loga occurring with Taupo Pumice cobbles 121.

EOTOHTA, WJPO, BAY OF PLEHTY, GISBOMB AND BAWKE'S BAY DISTRICTS, EEW ZEåLAHD

Collector (Date); Sampling Locality; Notes

Healy 33, 3^, W-2); Taupo; statistical mean of many dates.

W.A. Pullar (1^/12/57); L. Repongaere, Gisborne (N3-IS (19W-), N98/258^58); ash bed at 7 ft 3 in. to 7 ft 7 in. below surface; unidentified at time of collection; as samples bracket Taupo Pumice ash bed, dates are good.

W.A. Pallar, B.P. Kohn (12/10/68); L. Poukawa (NM33 (1952), N1ÍH/14105<0; drained swamp fringing lake; as samples bracket Taupo Pumice ash bed, dates are goodj (Pullar, 1970).

W.A. Pullar (28/8/63); Whakatane Borough (1IZMS3 (1950), K69A29238); ash .bed of pale grey ash speckled with dark grains not identified at time of sanplingj dates obtained above and below the bed suggest that it was associated with Taupo Punice eruptions; it is not the Taupo Pumice tephra deposit seen in awaaps near the sampling site that comprise mainly Taupo Paaice Lapilli member; lithology of the beds is similar to that of Hatepe Lapilii member seen on High Level load, Kaingaroa Forest; bed is considered to be water-borna ash derived from Hatepe Lapilli, the first of the Taupo Pusice eruptions; samples give maximum and minimum dates for the Tsupo Punice eruptions; distribution of Hatepe water-borne ash delineates the flood plain of Whakatane River at the time of the Taupo Punice eruptions.

¥.å. Fallar (27/IO/66); right bank Eangitaiki River, Te Mahoe (HZMS 1 U952)t N77/255Í07/; caxLnua date for deposition of water-borne ash derived from Hatepe Lapilli; ash is coarser than fag 9-^0 and Tsg 11-12; important laarker bed in flangitaiki Plains alluvium; extent of Hatepe water-borne ash delineates flood plain of ¿langitaiki Rivor at time of Taupo Puaice eruptions.

W.A. Pallar (19/3/7T); Hangitaiki Plains (NZM31 (1967), H68/315283); charcoaj fron Pod'oearpua spicatus and P. Hallii: collected to date pumice alluviuzi occuring 8 ft below codern sea level; infoiaaation required for sea level curves. 122.

Sample Foasil Beooxd No. Description; Teplira Poxisation H.Z. ™C. Ho. Years B.P. Stratigraphio (1950) Position

Tsg 9-10 N9V506 2,270-100 Carbonised N.Z. 157 twigs, steins; paleosol on Tsg 11

N9V513 2,500-200 Carbonised F.Z. 177 wood and root fragments; paleosol on Tsg 11

Tsg 9-10 N68/511 2,010^60 Peat; above F.Z. 1068 ash bed Tsg 9-10 K68/512 Peat; below ÍI.Z. 1069 ash bed (Fot related to m 05/521 2,200^60 Wood, from eruptive event) N.Z. 100 standing tree F105/522 2,190-60 Wood, from H.Z. 101 standing tree

Tag 11-13 H94/509 2,800-100 Carbonised H.Z. 182 twigs end stems; from paleosol on Tsg Ik

11-13 ÍJ68/5I3 2,670^50 Peat; above B.Z. 1070 ash bed

Tsg 11-13 2,730-60 Peat; below F.Z. 1071 ash bed Wainihia Lapilli Carbonised F.Z. 179 twigs and stems; from paleosol on Tsg 16

Vairaihia 3,270-200 carbon- F.Z. 2 aceous fragments; from paleosol on H.Z. 2 Tsg 16 123.

Collector (Date); Sampling Locality; Notes

Healy (196^1 16-17, 3^-5, 40); Kaimanawa (N9V695523);

Healy (I96if: 12, 34-5, 40); Taupo (N94/589347);

W.Á. Pullar (27/IO/67); Awakeri, flangitaiki Plains (N24S1 (1944), N68/333230); as samples bracket ash bed,dates are good; eruption event suggested to be at 2,100 yr B.P.; Healy (1964: 35) obtained weighed nean of 2,304±90 yr B.P.

H.W. Wellman (28/11/56); eastern shore L. Waikaremoana (NZMS 1 (1967), c,. H105/568287); samples from stumps, in situ, of standing trees that grew in valley and later were inundated by water when L. Waikaremoana was formad by landslide; Taupo Pumice mantles landslide; no Waimihia Lapilli present; dates indicate time of landslide; ^» 3).

Healy (1964: 17, 18, 35, ^0); Kaimanawa (^9^/695523); (2> 3^.

W.A. Pullar (27/10/67); Awakeri, fiangitaiM Plains (NZMS1 (9), IÍ68/333230); as samples bracket ash bed, dates are good; eruption event suggested to fee at 2,700 yr B.P.; in a section nearby both Rotokawau Ash and Wainihia Lapilli are seen below Tag 11-13.

Hsaly (196^: 19, 20, 36, kO); Wairakei (I9V5ÓO^39);

I.L. Baufflgart (in Healy, \96ki 41); Taupo (N9V589347); gives maximum age for'Waimihia Lapilli; 0» 3). 124.

Sample Fossil Record Ho. 0 Age Description; Tephra Formation N.Z. V*C. Bo. Years B.P. Stratigraphic (1950) Position.

Waioihia Lapilli K98/517 3,170-80 Peat; above N.Z. ash bed N98/518 3,^0-80 Peat; below H.Z. 505 ash bed

Wainihia Lajilli / 3,130-65 Woodt tree H.Z. 1062 roots; above ash bed 3,270^65 Woodt tree H.Z. 1061 roots; belov ash bed Whakatane ¿ah. HOS/515 3,200^65 Peat; above H.Z. 1072 Wimkatane Ash Whakataae N86/509 5,180-80 Charcoal; N.Z. 1066 in paleosol of Botona Ash

Tsg 17- H106/- (being Organic mud; processed) with 1 in. thick bed of scattered pale yellow ash; 32 in. below Waimihia Lapilli

Wnakatane Ash B106/575 6,39?-120 Organic mud; N.Z. 1137 above 1 in. thick ash bed ÍT106/576 (being Organic mud; processed) below ash bed Whakatane Ash. H106/521 6,3^5-130 Wood from N.Z. ^27 totara stumps; at base of peat deposit, 37 in. belov Vhakatane ash bed ;

125-

Collector (Date); Sampling Locality; Notes

W.Å. Pallar (14/12/57)i L. Repongaere, Giaborne (K2MS1 (1944), N98/258458); aah bed at 11 ft 7 in. to 12 ft 3 in. from surface; unidentified at time of sampling; as samples bracket aah bed, dates are good.

W.A. Pullar, B.P. Kohn (12/1O/6S); L. Poukawa (NZMS3 (1952), N141/141054); drained swamp fringing lake; as samples bracket ash bed, dates are good; (Pullar, 1970).

W.A. Pullax (27/10/67); Awakeri, Rangitaiki Plains (I2ÍS1 (19, H68/333230); gives minicum age for eruption of Whakatans Aah; Whakatane Ash rests on dunes at Awakeri.

tf.A. Pullar, C.P. Pain (3O/ii/6?); Galatea (IJZMS1 (19^8), N86/214734); charcoal collected froa uppsr 1 in. of paleosol on Rotoma ash immediately below Whakatane Ash; gives a maximum age to Whakatans Ash? date may also -represent an event such as a fire on Rotoma surface.

tf.A. Pullar, B.P. Kbhn (15/12/69); R.J. Berry's fazm, üniroto, Giaborne district (17ZMS1 (1953), KIO6/935255); in peat deposit; napped as Whakatane Ash (in Healy, 1964: 12-3); at tine of sampling (15/12/69) thought to be fiotokawau Aah which has since been found aa a black ash on Rangitaiki Plains could be Tag 17-18 bed,

tf.A. Pullar, B.P. Kohn (15/12/69); H.J. Berry's farm, Ilniroto, Gisborne district (H3S1 (1953), K106/935255); in peat deposit; mapped aa Kotorna Ash in Healy, et al.(1964t 72-3^ ash bed now thought to be Whakatane Ash; contains green hornblende (B.P. Koim, pers.cozcm.).

R.J. Berry; Tiniroto, Gisbome district (EJZMS1 (1953), N106/935255); (Healy ét al.. t96kt 73). 126.

Sample Fossil fiecord Ho. Description; Tepkra Formation H.Z. ^C. Ho. Years B.P. Stratigraphic (1950) Position

Macaku Ash 8,050-105 Charcoal; from H.Z. 719 paleosol in Botoma Ash, below contact with Mamaku Ash

(experimental} N77/555 (being Charcoal; from processed) upper 3 in. of paleosol on Eotoca Ash, below contact with Maraaku Ash

Botona Aeh H86/510 7,050-77 Charcoal; in upper F.Z. 1152 6 in. of paleoeol in Botoma Ash, below contact with Whakatane Ash

Botona Ash (being Charcoal; in basal processed) 6 in. of Botoma Ash and over Waiohau Ash

Tag 18 E9V52O 8,850-1000 Pine carbon- 1T.Z. 185 aceous fragments; from paleosol in Tsg ^9

1-Bg 19 F85/511 10,700-120 Charcoal; from (aaåesitic ash) F.Z. 1133 andesitie ash bed between Botoma Ash and Waiohau Ash; collected 3 in. below base of Botoma Ash 127.

Collector (Date); Sampling Locality; Notes

W.A. Pallar (16/6/65); Kawerau-Rotorua higbwa», Kawerau (HZMS1 (1952), H77/123129); abundant charcoal (Podocarpua spp.; Dacrydiuq spp.; Metroaideroa app.); position of charcoal is close to contact with base of Mamaku Ash; date is good.

K.S. Birrell, W.A. Pullar (26/3/?i); Kawerau (N77/123129); re-collected; charcoal in pockets.

W.A. Pallar, K.S. Birrell (15/5/68); liortharn Boundary Boad, Rerewhakaaitu (H31S1 (1968), N86/933779); ¥hakatane Ash rests on Rotoma Ash with Mamaku Ash ajiparently nissing at this site; date is older than that obtained for Whskatane Ash at Galatea (5»18Q±80; N.Z. 1066); date may represent Tiring of vegetation on Rotoaa surface and not an eruptive event; Rotoma Ash noted for irregul«u. pockets of fine charcoal. ;.

W.A. Pullar (29/3/70); farawera Forest, Upper Tarawera Valley (NZMS1 (1965), N77/167060); to date eruption of Hotonaa Ash.

C.G. Tuceticii in. Healy (I96ifrs 36, Terraces pumice pit, Taupo (/) ( )

W.A. Pallar, K.S. Birrell (19/12/69); Gavin load, Rerewhakaaitu (NZMS1 (1968)» 1186/99582^); at time of collection thought to date Eotoma Ash; more recent work established presence of andesitic ash between Rotoma Ash ana Waioaau Ash; dates eruption of Tsg 19 bed. 528.

C Age Sample Fossil Record No. Description; Tephra Pora:" tion H.Z. 1*C. No. Years B.P. Stratigrapuic (1950) Position

Tag 23-25 N9V5I6 c..9»000 Carbonaceous (not allocated) (estimate) material; from paleosol on Tsg 26

Vaiohau Ash 577/5*2 11,250-200 Charcoal; near H.Z. 568 base of Waiohau Ash

Waiohsu ash H76/505 11,100-210 Charcoal; N.Z. 878 upper 3 in. of paleosol in Berewfaakaaitu Ash, below Waiohau Ash Vaiohaa Ash (?) S86/512 11,800-150 Charcoal; or Tsg 2>25 bed N.Z. 1135 from upper 3-6 in. of paleosol in Kerewhakaaitu Ash, and below

• Waiohau Ash Barewhakaaita Ash 077/5^1 1 if-, 700-200 Charcoal; 11.z. 716 from upper 3 in. of paleosol in Okareka Ash, and below Herewhakaaitu Ash Okareka Ash H76/502 20,700-^50 Subfoasil wood; 1T.Z. 523 in unweathered basal part of ash bed below Berewhakaaztu Ash and above Oruanui Ash

Qruanoi 20,670-300 Wood; within II.Z. 12 weathered ash 129.

Collector(Date); Sampling Locality; Notes

I.L. Bauogart in Healy (1964: 36-7, ^1); Terraces pumice pit, Taupo (119^1/5893^7)1 dating inaccurate because insufficient sample available.

J.W. Cole (28/5/&0; gully, south side Mt Tarawera (NZMS1 (1952), H77/9Ä908).

W.A. Pullar (17/^/6?); entrance lioose Lodge, Rotorua-Whakatane highway, L. Botoiti (NZMS1 (1952), N76/875151); paleosol in Waiohau Ash above the sample has a B horizon which was mistaken for Rotorua Ash; dates Waiohau eruption; agrees with N.Z. 568(11,250-200 yr B.P.).

W.A. Pullar, K.S. Birrell (19/"l2/69); Northern Boundary and Rerewhakaaitu (NZHS1 (1968), 1186/'933779); sample may date Waiohau eruption or that of a Tsg 23-25(?) bed between Waiohau Ash and Rerewhakaaitu Ash; may also date an event such as a fire on Rerewhakaaitu surface; date seems rather old for Waiohau Ash (11,100-210; N.Z. 878); Rotorua Ash which occurs stratigraphically between Waiohau Ash and Rerewhakaaitu Ash is apparently missing at this site but present 2 miles to east.

W.A. Pullar (8/6/65); refuse dump, Kawerau (NZMS1 (1952), N77/I60090); dates eruption of Rerewhakaaitu Ash; no intercalation with Tsg beds at this site as too far from Taupo and Tongariro sources.

C.G. Vucetich, W.A. Pullar (19/10/62); deep benched cutting, entrance to Moo3e Lodge, L. Hotoiti (NHISI (1952), N76/875151); may date eruption or nay date wood swept in with eruption products; similar date to Oruanui Ash (c_. 20,000 yr B.P.) (Vucetich and Pullar, 1969' 812).

J.A. Berry (1928); Hapier; excavation, Napier (N134/317397)i for other results sse Vucetich and Pullar (1969s 812); C1» 3). 130.

Hp Sample Fossil Record So. „ ^% Description; Tephra íbzmation s N.Z. ^C. No. (íLo) Stratigraphitratigraphi(c Position

Oruanui Ash N112/527 19,850-310 Wood; N.Z. IO56 immediately below 3 ft thick ash bed

Mangaoni Lapilli N98/562 27,900-1200 Organic mud: Member (d) ? N.Z. 114-7 above ash bed

+ N98/561 29,700-1500 Organic mud; N.Z. 1136 immediately below ash bed

Mangaoai Lapilli N76/5O3 27,900-850 Charcoal; Member (d) ? N.Z. 876 from log on Hotoiti Breccia

Mangaoni Lapilli 26,300-700 Charcoal; Ifeaber (c) N.Z. 867 from log; in upper 12 in. of ash bed and at base of j paleosol i + li 21,900-400 Charcoal; N.Z. 866 from log at ; base of bed I

(experimental) U77/556 (being Cha.7?coal; from I processed) twigs and I stems, within j ash bed | Mangaoni Lapilli 177/5^6 30,100--t300 Charcoal; 1 Meaber (o) IT.Z. 868 from twigs and 1 stems, within 1 lower part of 1 ash bed 1 131.

Collector (Date); Sampling Locality; Notes

I .A. Nairn (14/4/68); Taurewa, -g- mile south V.U.W. Field Station, National P&ric-Taupo highway (NZMS1 (1968), ill 12/050896); dates eruption of Oruanui Ash; wood in peat buried by ash; only dated sample from Central Volcanic Region; Oruanui Ash is good marker bed in Tongariro andesitic ash and lahar deposits; 6 ft below Mangatawai Ash that is dated c..^500 yr B.P.

W.A. Pullax, Å.P. Holoes f28/6/69); Stout Street, Gisborne (NZMS1 (1957), N98/394392); organic mid (peaty loam, 5 in. thick) underlies dunes and over- liea grey silt ^12 in. thick) and ash bed (18 in. thick); date gives a minimum age for Mangaoni Lapilli Member (d); also gives a maximum age for dune fornation at Gisbome; Pullar and Warren (1968) assumed ash bed to be Waionau Ash (c.. 11,000 yr B.P.), therefore maximum age for dune formation is erroneous.

W.A. Pullar, B.P. Kohn (II/10/68); Stout Street, Gisborne (NZMS1 (1957), £198/394392); date gives Eaximum age of Mangaoni Lapilli Member (d) eruption.

J.E. Coz (l0/i/6^); Tikitere hill, Rotorua-Whakatans highway (NZMS1(1956), N76/828133/; TOO t correlated; log on top of Rotoiti Breccia, overlain by a thin layer of Mangaomi Lapilli(?) and aah drift; capped by Rotorua Ash and other Holocene ash beds; nay date Mangaoni Lapilli Member (d) eruption or an event during th= erosion interval between eruptions of Rotoiti Breccia and those of Ifangaoni Lapilli.

W.A. Pallar (7/3/6?); Bowdioh's quarry, V/hakatana-Rotorua highway, Onepu, HangitaiM Plains (TÜMSI (1952), N77/173172); in a3h-flow bed; sample found to be contaninated with fresh roots; result discarded as chronology is reversed with sanple 1777/544 (I7.Z. 866).

W.A. Pullar; R.H. King (?/3/67); Bowdich's quarry, Whakatane-Rotorua highway, Qnepu, Bangitaiki Plain3 (N77/I73172); in ash-flow bed; contaminated with fresh root3; result discarded as chronology is reversed with sample M (K.Z. 867).

W.A. Pullar (7/3/6?)y Bowdich's quarry, Whsk&tsxis-Rötorna highway, Onepu, Hangitaild. Plains 1177/i73t?2); duplicate saaple to N77/544, including fresh roots to be processed for oxidising organic matter, sent to Cheai'stry Division, D.S.I.R. (29/3/71).

W.A. Pullar (7/3/67); River Road, Onspu, Hangitaiki Plains (IÍ2ÍS2 (, IT77/19OI83); charcoal free branches swept in with ash-flow material (similar to- logs seen in upper Esapo Punice); slow carbonisation with fornation of high quality charcoal, te-perature was high enough to fuse ash to charcoal; dates eruption of Mangaoni Lapilli Member (c). 132.

1^- Sample 1 Fossil Record No• v xf^s Description; I Tepara Fornation 1 Years B.P. „. ,. . . 1 N.Z. MJ. NO. (1Q «in ^ Stratigraphic • U95OJ Position I + I1I (not an eruptive event) N66/501 33,800-1000 Charcoal; 1 N.Z. 156 from logs, in 1 sands derived 11 from 1 ignimbrite I + 1 Mangaoni Lapilli 1177/5^ 36,200-2100 Soft charcoal; ¡1 """ Meaber (c) ? N.Z. 1067 from twigs ¡ lying flat at : contact between \ Mangaoni I Lapilli and j Rotoiti Breccia j

+ ! Mangaoni Lapilli K93/553 >4-9,300-10 Organic mud; Menber (a) ? N.Z. 834- compact; below 18 in. thick Mangaoni Lapilli ! Member (a) ash ¡ bed and over 26 in. thick Rotoehu Ash bed

Botoehu Ash casber (?) >^6,300 Organic mud; K.Z. 635 compact; below 26 in. thick ! Rotoehu ash , bed

Rotoiti Breccia IS67/506 ¿*1,000 Wood; from i 11.Z. &±'j (675& paleosol below prob.) base of 200 ft thick, Rotoiti Breccia

Eotoiti Breccia H77/553 (being Charcoal; from processed) carbonaceous ! logs in lower 20 ft of Eotoiti Breccia L 133.

Collector (Bate); Sampling Locality; Ho tes

CG. Yucetich, D. Cross; Putaruru-Rotorua Road, Jk mile ÍSE Putaruru (1766/308204); sands with pseudo-current bedding; possibly representing rapid physical erosion with insufficient rainfall to remove the debris, and .... wind action"; (Healy, 19#f: 37); C2' 3).

W.A. Pallar, I. McLean (10/10/67); refuse dump (now abandoned), Kawerau (ua9S1 (1952), N77/160089); significance not understood; may date eruption of Mangaoni Lapilli Member (b), eruption of Rotoiti Breccia, or may indicate an erosion interval between times of eruptions; Mangaoni Lapilli Member (a) missing at this site.

W.A. Pallar (12/3/67); Stout St, Gisborae (N2MS1 (1957), N98/393392)} 6 in. organic mud between Mangaoni Lapilli Meuber (a) and Rotoehu Ash; gives naxLnua date for upper bed(Mangaoni Lapilli Member (a)) and ninicraa for lower (Rotoehu Ash, N98/55*0» reversed chronology with 1198/55^» tephroatratigraphy uncertain at this site; no correlation; no restätenent of significance.

V.A. Pullar (12/3/67); Stout St, Gisbome (ITZMS1, (1957), N98/393392); najrinuE date for Rotoehu Ash; three thin peaty diastema; ash bed rests on 32 in. layered organic mid on green clay; reversed chronology with N98/553; tephrostratigraphy uncertain at this site; no correlation; no restatement of significance.

B.I7. !Eaoap3on; Zaituna Siver hydro-electric schene (N67/825235); dates eruption of Rotoiti Breccia.} collected 18/9/57»

W.A. Pt-'llar, (2k/6/70); Tarawera Forest, Upper Tarawera Valley (H22ÍS1 (1965), IT77/059033); charcoal fros 6 in. dian.-carbonised log swept in with braccia during eruption; sinilar to logs seen in Upper Taupo Pumice; brecci-'A fired and fus.ed around logs suggests intense heat leading to carbonisation by slo«r coabiastion; nay date Rotoiti Breccia eruption, or date cf burning of logs before eruptionx core likely the former. 134.

Sample Fossil Eecord No. Description; Tephra Formation Years B.P. F.Z. ^C. No. Stratigraphic 0950) Position

Hotoití. Breccia 29,400-800 Organic matter; N.Z. 1132 from paleosol on ignimbrite, and below Rotoiti Breccia

Hotoshu. Äsh inenber H76/50Í)- ¿&, 200-4-300 Peat, similar K.Z. 877 (675S prob.) to lignite; > ^3,700 compact; from (# prob.) base of peat below Botoehu Ash bed

Eotoélsi ásh nenber (being Organic mud (Botoiti Breccia) processed) and wood; below Rotoehu Åsh bed

Rotoehu Äsh member N85/523 ¿fl,700-3500 Wood and peat; (Eotoiti Breccia) íí.Z. 1126 from paleosol below Rotoehu Äsh 135.

Collector (Sate); Sampling Looality; Hötes

W.A. Follar, R.F. Jeune (I6/II/67); eaat shore of L. Rotoma at present lake level (HZHS1 (1952), H77/052152)» Baximum date for Rotoiti Breccia (Botoehu Ash member) eruptions) date unacceptable as is much younger than other dates for Rotoehu Ashj contamination by fresh roots suspected.

J.E. Coz (1O/1/64)| Otaxaaarae, Onepoto Bay, L. Rotoiti (NZMS1 (1956), H76/840165)} site re-exanined by V.A. Billar and C.G. Vuoetioh who consider the sample was collected froo paleosol of ündifferentiated Brown Ash (Vucetich and Pallar, 19691 814) which conformably underlies Rotoehu Ash member and confomably overlies weathered Haoaku Ignimbrite; gives aazinuo date for Rotoehu Ash member of Rotoiti Breccia eruption.

V.A. Pullar, B.P. Kohn (19/3/71); Qhope-Eutarere Road, Valnui (NZMS1 (19¿2), H78/535174-); to date a sanple of Rotoehu Ash member that is further away froa source than other samples dated.

I.A. Nairn (18/12/68); foot of cliff in Haumai Stream, at intersection of tributary froo L. Okaro (B2MS1 (1967), H85/868855)j paleosol overlain by "Haunai Stream Breccia", soy correlated with Rotoiti Breccia (and Rotoehu Ash member at its base); Rotoiti Breccia overlain conformably, with no weathering break (paleosol), by Earthquake Flat Brecoia; dates eruptions of Rotoiti Breccia (and Rotoehu Ash) and Earthquake Flat Breccia.

Sate recorded in Fergusson and Rafter (1955) Bate recorded in Fergusson ana Rafter (1959) Bate recorded in Grant-Taylor and Rafter (1963) 136.

174° 176° 178° i

Locality Map Snowing Sampling N8 Sites & NZ Numbers With Each S te.

36e

1068 K>69 1O7O 0

NJ3

137 ÍÍN138 ! NI29 137»

CONCLUSIONS

Bie 14C dates that have been obtained from the samples listed in Table 1, can be used to give approximate ages to the following tephra formations and their members«

Formation or Member Approximate Age in Years B.P.

Taupo Pumice Formation (c. Hatepe Lapilli Heober (c.. 1,900) Tsg 9-10 members (c.. 2,100) Tag 11-13 members (c. 2,700) Waioihia Lapilli Formation (c. 3,^00) Vhakatane Ash Formation (c.. 5,200-6,300) Mam-c^ini kaft Formation (c.. 8,000) Botosa Ash Formation No date Tsg 18 member (c.. 8,800) Tsg 19 member (c.10,700) Vaiohau Aah Formation (£..11,000) Rerewnakaaitu Ash Formation Ckareka Ash Fornation (c.. 20,000) Oruanui Ash Formation (¿.20,000) Mangaoni Lapilli Formations member (d) (c.28,000) member (c) (c_.26,000-30,000) member (b) Bo daté member (a) (c.. 36,000) Botoiti Breccia Fornation / (c.ifO, 000-46,000) Botcetu Aah nenber > 139.

Dates in the Quaternary Geology of the "Golden Coast", Wellington

by C* A. Fleming

Abstract

1. Use of ikC dates In a continuing study has contributed to the geochronology of the last 35,000 years, when climate, vegetation, and sea-level fluctuated dramatically in response to the last 2 diacernable cold stadials of the Last Glaciation (0tiran) and to post-glacial warming. Several points may tie emphasized.

2. The time-span covered by i4c is small compared with the total spectrum of geological history, but disproportion- ately significant because of the importance of late events to the understanding of present geography and vegetation.

3* What can be dated depends more on the limited occurrence of datable material (lignite, peat, wood fragment.) than on the sediments one wants to date; many sequences spanning parts of the 14C range remain undatable because they contain no carbon.

h» The early temptation to submit samples on the chance of them being datable resulted in dates beyond the limit of the method. With more knowledge of the geochronology, later samples have all produced positive dates. In an unknown area, it is most profitable to work back in stratigraphic framework, from known post-glacial samples towards the Late Glacial, awaiting results from younger samples before asking for older ones, but this assumes a leisurely timetable for the project.

5. Palynological examination provides so much more significant history to date than a mere lithological sequence that it is perhaps unjustified to submit i4C samples from a carbonaceous sequence unless pollen analysis has already determined its vegetational and climatic history.

6'» The geological interest in testing the contemporaneity of coolings in different parts of New Zealand and the biological interest in vegetation history during the Otiran ("Glacial"} Stage give dates in the range 20 to 40 thousand years a particular importance so that improvement of the reliability of the method in this range is Justified. i 140.

DATES IN THE QUATERNARY GEOLOGY OF THE "GOLDEN COAST", WELLINGTON

by C.A. Fleming

The area called the Golden Coast by land-agents is the coastal lowland between Paekakariki and Otalci, a triangle with Its apex in the south, lying between the west coast and the mountains. The object of this paper is not to advance knowledge of the geology of the coastal lowland, but to demonstrate to non-geologists the contribution made by tkC dates to this knowledge, its limitations, and the kinds of problems the geologist tries to solve by this special tool.

The total span of time represented by the deposits ("rocks") of tfc-j district covers about 200 million years, back to the Triasslc greywacke suite forming the Tararua Range and ita foothills: t4C dating covers at most 40,000 years. But because we look back to the past through "perspective spectacles", the period to which ihC can contribute is far more important to the geologist than fyOiOOO » i.e. the last 40,000 years has much more auu,uuu,uuu interest than any 40,000 year period in the first 199 «a. years. We can skip over the deposition of the Triassic grey- wackes (Fig. A, I), their deformation and elevation in the Rangitata Orogeny (L. Cretaceous) , subsequent peneplanatlon and transgression by Oligocene seas (kO m. years), and the deformation that resulted in a narrow infaulted strip of Oligocene greens arid behind Otaihanga (Fig. A, II). Later isi the Tertiary, about 10 m. years ago, the deformation of the Kalkoura Orogeny began to raise the Tararua R. as a complex of high blocks (and probably Kapiti is a smaller one); these anticlinals were progressively elevated in relation to the synclinal or relatively subsiding area of Cook Strait and the narrower synclinal between Kapiti and the Mainland»

Older Pleistocene (Fangantii Series): The Quaternary Era (the Pleistocene Ice Ages, intarglacials, and postglacial tfaef embracing approximately the last 2 m. years) is first represented by a formation of ancient coarse gravels (Keikorangi Gravels, III in Fig. A) that are strongly deformad and weathered. They probably represent the early Pleistocene Wanganui Series and are in part equivalent to 141.

the Kaitoke Gravels of Hut t, the Moutere Gravels of Nelson, and tlie marine Wanganui Series of" the Palmerston-Wanganui Basin to the N.W. At some later Quaternary date the land surface was deeply weathered to a bright rosy red colour, probably in an interglacial age when climate was unlike any modern New Zealand climate. From experience, we know that deposits older than the period or periods of red weathering are well outside the period of 1*10 dating, but 20 years ago geologists were less experienced and wood or lignite from such beds could still be submitted in error (but would probably not get past the screening process).

Younger Pleistocene (Hawera Series): Before the later ice-ages, the land gained more or less its present outline, although tilting and faulting movements have continued. Interpretation of younger Pleistocen deposits is within the framework of several theoretical generalizations, some of which are still being tested:

(a) climatic fluctuations (and the deposits they controlled) were contemporaneous, in a general way through New Zealand if not throughout the world. (b) During each glacial period, when glaciers advanced in the South Island ¡mountains, the Tararua Range suffered a periglacial climate even if it did not support glaciers. Mountain vegetation was reduced to sub- alpine grassland and herb fields, solifluction was widespread, and streams and rivers, overloaded with waste, aggraded their beds to a steep gradient with coarse ill-sorted gravels derived by even steeper fans from tributary streams. Small glaciers (VIII in Fig* A) were certainly present in the Tararuas in the L&st Ice Age (Adkin). (c) World wide withdrawal of ocean water to form ice sheets and glaciers lowered ocean leval to depths of some 120 to 200 m below ita present level. Because deep water is quite close to the Golden Coast (S. of Kapiti), ice age gravel plains plunged steeply to coastlines at no great distance front the present shores. (d) During interglacial periods, .elting of ice raised sea levels generally to heights above present sea-level. The land was fully forested; rivers cut down in their inland courses. Gravels in rivers and on coasts tended to be better sorted. (e) Tectonic movements, continuing through the Pleistocene, have caused irregularities in the levels of glacial 142.

and interglacial shorelines but were not sufficiently strong to obliterate completely the cycle of relatively low levels for glacial and high levels for interglacial ages. Therefore marine deposits on land are almost certainly interglacial, coarse ill-sorted gravels probably glacial.

(f) Sand dunes characterise stable or prograding coasts (not advancing seas), so that most dune-sand deposits, especially those containing mica derived by long- shore drift from Tertiary beds further north, probably date from a period of sea retreat from a high inter- I glacial level. (There are, in fact, some dune sands | (Koputaroa and Te Whaka Dunesand) of glacial age, derived not from beaches but from glacial river-beds, but they can be distinguished from beach-derived interglacial dune-sands by absence of mica).

In the valleys of ths Waikanae and other rivers terrace remnants of the penultimate and probably anti-penultimate glacial gravels (Fig. A, IV) can be recognised as such by their altitude, dissection and strongly weathered loess soils that are developed on them. Remnants of the deposit of the antipenultímate Interglacial are also suspected in several places. These have to be recognised and classified by geomorphological, pedológica!, and lithologic criteria; they are all beyond the range of íkC. In practice, so little carbonaceous material jccurs in gravels formed by cold-climate aggradation that there has been little temptation to submit material from such deposits.

Last Interglacial (Oturian Stage): The most conspicuous formation of the coastal lowland has long been known as the Otaki Sandstone or Otaki Formation (Fig. A, V) and was studied by Adkin, Oliver, and Cotton before the development of 1^C techniques. Te Punga (1962) described a well- expos ed section near Te Horo and collected a sample (NZ 65) dated as greater than 451000 years from a lignite band. By the criteria listed above, the Otaki Formation is Interglacial, consisting of the marine beach gravels and sands of a transgressive high-level sea, the beach-derived micaceous dune sands that advanced as the sea retreated, and lignite deposited in swamps ponded by the dunes. It is backed by an old cliff-line (Fig. B, Line A-A). As it is, the latest Iraterglacial deposit recognised on the coast, the Ote.ki is attributed to the Last Interglacial Age, which from isotope datings overseas is thought to be about , 80,000 to 120,000 years old and thus beyond the range of i iftc. 145.

Last Glacial (Otiran Stage): Overlying the Otaki Formati>n are a variety of deposits attributed to the last glacial stage: coarse illsorted river gravels in terraces, sometimes with erect pebbles indicating frost climate near the surface (Parata Gravels, VI in Fig. A); mantling loess deposits with fossil soils; gravel fans of angular Matenga Fanglomerate sloping from the hills to the lowland (VII in Fig. A; see also Fig. B); their stratigraphic relations have to be pieced together, partly from their geomorphic relations, as exposures showing them in sequence are rare. The gravels, like most cold climate gravels, lack wood or carbonaceous deposits, probably because vegetation was sparse and not woody. The loesses were mainly deposited under oxidising conditions that burnt out their carbon content. i4C dates would be very valuable for correlation with other N.Z. sequences.

The fan gravels occasionally preserve thin lenses of carbonaceous silt, representing swampy deposits later buried by the growing fan (Fleming, 1970). One such deposit yielded a sequence of pollen samples indicating cold wet grasslands - shrubland vegetation with a temporary silver beech phase, dated (NZ 573) as 19,200 years BP (¿ 56O years), and thus falling in the period of the Later Kmnara-2 glacial advance of Westland (Suggate, 1965)eun ^L (less precisely) of the Takapau Stadial of Wellington Peninsula {Brodie, 1957). The fans appear to slope con- cordantly to the main terrace of the Parata Gravels, which is thus correlated on indirect evidence. This 14C date has been extremely valuable.

In two exposures near the crossing of Waikanae River by Main Highway No. 1, Parata Gravels overlie a sequence of older rocks. In the railway underpass, Parata Gravel overlies a silt deposit with most of the characteristics of a buried loess but with carbon preserved by burial in reducing conditions, overlying a weathered gravel. The buried loess (Tini Loess) contains pollen of grassland- shrubland vegetation (cold climate) and branchlets near its top have given a i4c age (NZ 700) of 35,400 + 900 years. This result, the cold climate vegetation and the stratigraphic relations with the overlying Parata Gravals (correlated with Later Kumara-2, say 22 to 18 thousand years HP) suggest that the Tini Loess and underlying gravel date from an early Otiran glacial, probably the undated Earlier Kumara-2 of Westland, and the Opunake glacial cooling of Taranaki (Grant-Taylor, 1964), dated as 30,000- 38,000 BP.

In the second exposure, -J m. downstream, a relatively complete section of the Otiran Stage overlies Otaki Formation (Oturian Stage):

(7m) Parata Gravel (correlated with Later Kumara-2, 18,000-20,000 BP) 0») Tin! Loess (35,^00 BP at top) (1m) Unnamed gravel, weathered Earlier Kumara-2 /Pollen Zones; Grassland (cold). Silver beech (cooling) Beech (cooling) Beech-Podocarpus (cooling) (i.5m) Waimahoe Lignite Podocarpus (cooling) Rimu (warm) Podocarpus (warming) Beech-Podocarpus (warming) Beech (cool)

(0.5m) Strong soil, with rhizomorphs of clay- mineral, developed on (2-5m) Otaki Ihinesand - Last Interglacial (Oturian).

The Waimahoe Lignite records a cool-warm fluctuation before the cooling that presumably led to the "Earlier Kumara-2 = Opunake" glacial. The only tUC sample, collected by Te Punga from an uncertain horizon is NZ 22 (more than 351000 BP) . If confident dating In the range 35,000-40,000 becomes possible the section is worth re- sampling for lhC.

27 miles N. of Walkanae on broad surfaces above the aggrading river beds, Eoputaroa Dunesand (a cold climate dtamesand) accumulated over a span of time that included a climatic cooling indicated by pollen in peat (McJntyre, in Cowie, 1963) since dated as. 35,000 ± 1?00 years BP (NZ 522) (i.e. equivalent to Early Kumara-2) and also the Akaotore Ash (dated as about 20,000 BP by correlation and thus Later Kumara-2). A similar but younger cold climate dunesand (Te Whaka Dunesand) overlies the Parata Gravels at Otaki but carbon for dating it has not yet been found. Such glacial-stage dunesands seem to have accumulated when streams began to incise below an aggraded terrace, lowering the water-table, i.e. after the peak of a cooling Jiad passed.

Post-glacial (Aranuian Stage): During the 0tIran, the sea is assumed to have been at low levels (c. 120-200 m) and 145.

the coast to have been somewhere south of the Kapiti Strait synclinal, which was a deep depression receiving the gravels from Waikanae district.

As sea level rose it flooded the Kapiti Strait depression which later was partly filled by long-shore drift an1 prograding deposits. At Foxton, sea level had risen to -50 o by 9,900 (+ 150) years HP (NZ 8i). Thick beach sands with shells (e.g. at -6j m at Paraparaumu Aero- drome) presumably represent this period of rising sea level, but have not been dated. They are represented by IX on Pig. A, and "have been named Kenakena Formation. Post- glacial aea level rose to its maximum at ^kO +_ 90 years BP, a date (NZ 519) from the beach deposits (Paripari Formation) near Centennial inn, Paekakariki (Fleming, 1966). At about tbis date, the sea cut a prominent low cliff (Te Punga, 1962) truncatijig the older formation of the coastal lowland (Fig. A, X; Fig. B, line B-B) . Sea-level may have been higher than now by a few metres, but part of this elevation is due to subsequent tectonic uplift. From this time onward, the coast prograded and fed a succession of dunes which now form a coastal belt of variable width, separated by peaty lowlands. The oldest dune group (Foxton Dunesand, see Cowie, 1963) laps on the poat-glacial cliff and probably began to accumulate soon after the sea retreated from it as pro- gradation began (say 4,500 BP). A ikC date for peat iraterfingeriuLg with the oldest Foxton dunes is at present awaited. The next formation, Taupo Dunesand, formed largely from pumice granules derived from drift pumice piled on the beaciies after the Taupo Pumice eruption (c. 1800 BP) is a prominent marker from Paekakariki to Te Horo; its date has not been independently tested, Cowie attributes the next younger Motuiti Dunesand to early human disturbance, citing a date of 855 + 50 BP (NZ 293) from a forest tree overwhelmed by Motuiti dunesand at Taikorea, Manawatu. Finally, Cowie's Waitarere Dunesand is attributed to the European period when fire and grazing animals reactivated the dunes.

Toe table of formations (Table 1) summarises the s t ra ti gr apiiy. 146.

References

Adkin, G.L. 1951s Trana. R. Soc. N.Z. 79: 157; 1910: Trana. N.Z. Inat. 43: »96; 1919: Trans. N.Z. Inat. 51s 108. Brodie, J.W. 1957: N.Z. Jl Sci. Tech. B38: 623. Cotton, C.A. 1918: Trana. N.Z» Bist. 50: 212. Cowie, J.D. 1963: N.Z. Jl Geol. Geopnys. 6s 268. Fleaing, C.A. 1966: N.Z. Jl Geol. Geophva. 8: 1222; 1970: Trana. R. Soc. N.Z. {Earth Sci.f 7 (11) s 197. Grant-Taylor, T.L. 1964: Geology, in Egmont National Park (Egmont Nat. Park Board). Oliver, R.L. 1948: N.Z. D.S.I.R. Geol. Mem. 7. Suggate, R.P. 1965: N.Z. Geol. Surv. Bull, n.a. 77. Te Punga, M.T. 1962: N.Z. Jl Geol. Geophys. 5: 51?. 147.

Younger Quaternary Deposits near Waikanae

Stratigraphic Table

Waitarere Dunesand European Period, 0-150 BP Motuiti Dunesand Polynesian Period í50-1000 BP (includes NZ 293: 855 ± 50 BP) 0 a +> Taupo Dunesand c. 1800 BP to Foxton Dunesand 1800-c. 4500 BP

Ppraparavumi Peat 0-4500 BP (ini erfinge r ing with above) Paripari Formation 5140 BP + 90 (NZ 519)

Kenakena Formation 5140-710,000 BP

Te Vaka Dunesand ? c. 16,000 BP i "Judgeford Loess" (contemp. with next two) H a +» Parata Gravels c. 18-23,000 BP (0 3 Ma tenga Fanglomerate 19.200 + 560 BP (NZ 573) Q H Tini Loess 35,400 + 900 BP (NZ 700) -P O (older gravels) ? c. 38,000 BP

Waimahoe Lignite "Early Otiran" >35.OOQ BP (NZ 22)

to Otaki Dunesand as +> CO Awatea Lignite Otaki Formation (> 45,000 BP § NZ 65) c. 80,000-120,000 BP) h 2 P Otaki Beach Sand

Penultimate Glacial Stage Deposits not detailed Penultimate Zhterglacial Stage I 148.

Fig. A. Diagram showing topographic expression of the main formations of the Paekakariki-Otaki district. I Greywacke suite. II Oligocene. Ill Reikorangi Gravels. IV Penult, glacial stage terraces. V Otaki Formation. VI Parata Gravels. VII Matenga Fanglomerate. VIII Glacial Valley in Tararua R. IX Kenakena Formation. X Post- glacial cliff. XI Foxton Dunesand. XII Taupo Dunesand. XIII Motuiti and Waitarere Dunesand.

inefcuzosxhip of äjatecga- Fanglanaerate (&4) laid down án during the Otñan glacial to th dit f th di íUdl (Old Sd O) d t th F D ), p togladal te pcit- gtariil «a cliff. Fig. B. (From Fleming, 1970) 149. JDEOTIFICATION OP 1OOD FHOM TREE STUMPS AHD DRIFT WOOD ASSOCIATED WITH TEPHBA LAYERS IN ALLUVIUM AND OP CHARCOAL FHOM TEPHRA LAYERS

by W.A. Pullar. Soil Bureau, D.S.I.R., Rotorua and B.N. Fatal» Wood and Fibre Structure, Forest Research Institute, Sotorua

SUMMARY

Specimens from drift wood and stumps buried in dunes and alluvium within the last 3000 years were identified largely as species of podocarp.

INTRODUCTION

Thirteen specimens of wood were collected in the Gisborme and Whakatane localities (Table 1). Host specimens were obtained from drift wood in the walls of trenches excavated for sewer and storm water pipes and from stumps in river diversion channels. The trenches and channels provided a long line of section and so the stratigraphic relationship of drift wood and stumps to the associated tephra layers was easily seen. One sample of charcoal was obtained from the paleosol of a taphra layer near Kawerau.

LABORATORY EXAMINATION

Most samples of geological and archaeological importance sent to the Forest Research Institute belong to the indigenous softwoods. Methods for the identification of these conifer woods have been described by Patel (1967a, 196?b, 1968a, 1968b). Geological and archaeological wood specimens may be in the form of sound wood, decayed wood or charcoal. The identity of a wood specimen may be determined macroscopically or microscopically. The former method which usually depends on general appearance of wood is quite useful when relatively few familiar woods are being dealt with. Accurate identification of wood on the 150. basis of its microscopic structure is more reliable and has a wider application. Thin sections of sound wood for microscopic examination can be cut free-haad with, a razor blade. The wood should be kept wet with water while it is cut. Decayed xiooú. and charcoal require some treatment before being sectioned. Wood in such forms is impregnated with paraffin wax or celloidin to support the fragile cellular structure. This is a time consuming process which does not always give satisfactory results. Trans- verse» tangential, longitudinal and radial longitudinal sections ¡oust be cut in order to study the structure and arrangement of cells.

DISCUSSION

(a) Drift wood: mainly Podocarpus app. and preserved. vSKev conditions of high water table. Drift wood on old shore lines is a useful marker in separating the «rave-cast component from the wind-blown component in a dune. Large logs, however, have been noted on the incipient beru at + 11 ft at Whakatane. (b) Stumps in situ; mainly Podocarpus spp. Stumps exposed in the Whakatane River antit waipaoa Biver diversion channels represent trees that once grew in bacl&swamp lowlands. These lowlands are now being infilled with alluvium from flooding. At Gisborne, infilling commenced after the Tsg 9-10 eruption c.2100 years ago and has proceeded in stages until 1950 when the Waipaoa Biver was stopbanked. A marked hiatus in infilling occurred c. A.D. 1450. Catastrophic infilling recommenced e. A.D. 1630. Åt fhakatane, infilling commenced after the Taupo Pumice eruptions c. A.D. 1J0. Most infilling seems to have occurred during the intTval c, A.D. 130 and £. A.D. 900 (Kftharoa eruption). The Leptospermum app. found in a swamp at Awakerl near WJiaJfcatane suggest that the swamp was better drained during periods c. 130 B.C. to c. A.D. 130* at c. A.D. 130, and* between c. A.DT ISO and c. A.DT 900. "" 151.

(c) Charcoal: in paleoeol of Rotoaa Åsh. Bepresents trees growing on Botoma surface. The date obtained from this charcoal, c. 9000 yr B.P. suggests either a fire on~the Botona surface before the Mamaku eruption or a fire at the time of the eruption.

HEFEHENGES

Patel, H.H. (1967a) Wood anatomy of Podocarpaceae indigenous to lew Zealand. 1. Dacrydium. N.Z. Jl. Bot. 5(2}: 171-&*-. (1967b) Wood anatomy of Podocarpaceae indigenous to New Zealand. 2. Podocarpua. N.Z. Jl. Bot.. 5(5): 507-21. (1968a) Wood anatomy of Podocarpaceae indigenous to New Zealand. 3. Fhyllocladus. N.Z. Jl. Bot. h{i): 3^H7 (1968b) Wood anatomy of C apres sac eae and Iraucaruaceae indigenous to New Zealand. N.Z. Jl. Bot. 6(1): 9-18. 150. basis of its microscopic structure is more reliable and lias a wider application. Thin sections of sound wood for microscopic examination can be cut free-hand with a razor blade. The wood should be kept wet with water while it is cut. Decayed wood and charcoal require some treatment before being sectioned. Wood in such forms is impregnated with paraffin wax or celloidin to support the fragile cellular structure. TMs is a fcijse-consuaingproces s which does not always give satisfactory results. Trans- verse, tangential, longitudinal and radial longitudinal sections must be cut in order to study the structure and arrangeaent of cells.

DISCUSSION

(a) Brift wood; mainly Podocarpus app. and preserved VSEBT conditions of high water table. Brift wood on old shore lines is a useful marker in separating the wave-cast component from the wind-blown component in a dune. Large logs, however, have been noted on the incipient bera at + 11 ft at Whakatane. (b) Stuapa in situ: aainly Podocarpus sop. Stumps exposed in the Whakatane Hi ver and weipaoa liver diversion channels represent trees that once grew is bacf*-swaaip lowlands. These lowlands are now being infilled with alluvium fro» flooding. At Gisborne, infilling commenced after tfre Tsg 9-10 eruption c.2100 years ago and has proceeded in stage's until 1930 when the Waipaoa Sirer was stopbanked. A marked hiatus in infilling occurred c. A.D. 14^0. Catastrophic infilling recommenced c. A.B. 1630. At Whakatane, infilling commenced after the Taupo Pumice eruptions c_. A.B. 130. Most infilling seems to have occurred during the interval c. A.D. 130 aad c. A.D. 900 (Kaaaroa enupfion). "" The Leytoapermum app» found in a swamp at Awakeri near WJiakacane suggest that the swamp was bitter drained during periods c. 150 B.C. to c. A.B. 130, at c. A.D. 130, and* between c. A.DT 130 end c. A.BT 900. 151.

(e) Charcoal: in paleoaol of Rotosa Ash. Bepreaents trees growing on Botona anar face. The date obtained from this charcoal, £. 8000 yr B.P. auggeata either a fire on""the Botona surface before the Mamaku eruption or a fire at the tine of the eruption.

2EFEEENGES

Patel, 2.F. (196?a): Sood an&toay of Fodocarpaceae indigenous to Hew Zealand. 1. Bacrydium. H.Z. Jl. Bot. 5(2): "171-ä^ (1967b): Wood anatoaj of Fodocarpaceae indigenous to New Zealand. 2. PodocagpuB. M.Z. Jl. Bot. 5(3): 507-21. (1968a): Wood anatomy of Podocarpaceae indigenous to New Zealand. 3. Phyllocladue. K.Z. Jl. Bot, bjij: 5-6. (1968b): Wood anatosy of Cupresaaceae and Iraucaruaceae indigenous to New Zealand. I.Z. Jl. Bot. 6(1): t

TABTM 1 : IDENTIFICATION OP WOOD FBQM THEE 9EUMPS AND DRIFT 1OOD ASSOCIATED WITH TEPHRA LAYERS IN ALLUVIUM AND OF CHAECOAL FROM TEPHRA UYEES

Specimen Stratigraphie (Data Position Identification Locality: Notea Collected). Charred Drift wood embed- podocarpua apleatus Rangitaiki Plains; pump bay wood ded in pumice ¡silt excavated on Pederson's farm, (6/5/67) and Tftupo Pumice Podocarpua totara Thornton; NZMS1, 1967; N68/ cobbles; overlain or P 315283; collected at depth of by peat and iaha- 3ft below sea level; wood roa Ash charred during Taupo pumice eruptions in head waters of Rangitaiki River and subsequently deposited on Rangit- aiki plains. Wood In aitu. in peat, Leptpapermum sp. Rangitaiki Plains; Fermah's fid, (17/11/65) •Between Esharoa Ash probably L.eriooldes and Rotorua-Gisborne highway, (c.900 yr B.P.) and Awakeri; NZMS1, 1962; N78/ IU Täupo Pumice tephra 370198; samples collected at layers (c.1800 yr depths of 23 in., 33in., 42in., B.P.)» also in peat 4-5in., and 59i&* from surface; uútween Taupo Pumice mat of one inch diam. stems layer and Tag 9-10 lying flat; elevation +15ft; tephra layer (c.2i00 collected by J.E. Cox. yr B.P.) Specimen (Date Stratigraphlc Collected) Position Identification Locality: Notes Wood Stump in situ buried Podocarpus dacrydioi- Rangitaiki Plains; Te Mahoe, (27/10/66) by 35ft Taupo Pumice des """ downstream of Matahina Dam; alluvium; Hatepe right bank of Rangitaiki water-borne ash rests River, N3MS1, 1952; N77/ on root flange; date 255107; stump about 24in. from bark, 1995^60 yr diam. B.P. (NZ869). Wood Taupo Pumice tephra Podocarpus spicatus Rangitaiki Plains; Poroporo; (10/5/6?) layer resting on root diversion channel of flange of stumps in P.hallii or P.totara Whakatane River excavated situ; 10ft below 1967-8; NZMS1, 1969; N69/ surface. 404239; elevation -1ft. Charcoal In paleosol of Rö- Dacrydium sp« Kawerau; Kawerau-Rotorua (16/6/65) torna Ash; at contact highway, near Kawerau; with Mamaku Ash; date Podoearpue sp. NZMS1, 1952; N77/123129; 8050 ¿105 yr B.P. rtetrosideros sp. charcoal abundant; occurs (NZ719). (root) in pockets; plant species unable to determine as charcoal fragile and shows little anatomical detail. Specimen Stratigraphie (Bate Position Identification Locality: Notes Collected) Wood Drift wood; Log Baerydlmn coleasoi Gishorne City; sewer trench (17/7/57) lying horizontally in Elm St; N2MS1, 1957; in wave-cast gand; Podocarpue spicatus N98/59539O; unable to deter- 5ft from surface; mine between these species pre-Waimihia with certainty; Taupo Pumice Lapilli (3,400 yr and Waimihia Lapilli tephra B.P.) at surface. Wood Drift wood; log lying Podocarpus totara Gisborne City; sewer trench (17/7/57) horizontally in wave- in Elm St; NZMS1, 1957; cast sand; 5ft from N98/39339O; Taupo Pumice surface; pre-Waimihia and Waimihia Lapilli tephra Lapilli. at surface. Wood Drift wood; log lying Podocarpus sp. Gisborne City; storm water (17/7/57) horizontally in wave- trench; Ghilders Rd and cast sand; post-Tag Lytton Bd; N2MS1, 1957; 9-10 and pre-Taupo N98/377383; unable to place Pumice; log parallel species. to Taupo pumice shoreline. Speeimon (Date Stratigraphic Collected) Position Identification Locality; Notes Wood Sfcumpa in situ; Podoearpus Gisborne; Iflatawhero locality; (17/7/5?) buried by lOft of dacrydioides Waipaoa River diversion alluvium; Tag 9-10 channel; NZMS1, 1957; N98/ tephra layer on 302377; stumps at elevation root flange. + 5ft; Taupo Pumice tephra layer 2ft above root flange. Wood Drift wood; log in Podocarpua Gisborne; railway bridge (17/7/57) alluvium 30ft below däcrydioidea near mouth of Waipaoa River; aea level; much NZMS1, 1957; N98/509325; older than T aupo from excavation for No.4 Pumice tephra pier, 1957. layer which is at VJ1 sea level. VJ1

Charred Drift wood; log Podocarpus sp. Gisborne; Sponge Bay; NZMS1, wood lying horizontally 1957; N98/43328; aea erosion in organic mud; has exposed buried forest; (26/10/57) 30ft below surface; charcoal specimens difficult and at about mean to determine with any degree oea level; much of certainty. older than Whaka- tane Åsh tephra layer which occurs near surface. I

'Specimen (Date Stratigraphie Collected) Position Identification Locality: Notes Wood Stump in oitu; Metroaideroa sp. Gisborne; Sponge Bay; (26/10/57) from buried" forest ITT N3MS1, 1957; N98/43328; 30ft below surface; a hardwood which appears at sea level. to have been subjected to considerable crushing (earth movements); sea erosion has exposed buried forest.

Wood Drift vood; logs Podocarpua totara Gisborne; sewer trench in (1S/V57) lying horizontally Pödocartms totara Pine St; NZMS1, 1957; N98/ in organic mud; pre* taurelia novae- 393390; tephra layers and Taupo pumice. £elandiae organic mud layers tilted seaward about 3 degrees; tilting occurred pre-Taupo Pumice eruptions.

Wood Drift wood in Podocarpus totara Gisborne; left bank of (16/4/57) alluvium; 34in. Maraetaha River- near from surface; in mouth; N2MS1; 1944 (1957 grid) Maori occupation cupreséiñum N1O7/3O2229; specific site; poat-Taupo identification difficult pumice. because of poor conditions of specimen.

tfl U H- pi o IT i-r1 M if •• 157. THE USE OF RADIOCARBON DATING IN MARINE GEOLOGY

J.V. Eade N.Z. Oceanographic Institute.

ABSTRACT

In marine geology radiocarbon dating has increased our understanding of sea level changes, especially for ths period 10-20 thousand years 3.P. It has also increased o\ir understanding of Upper Quaternary stratigraphy seen in deep-sea cores. It has made possible positive correlation of such observed events as changes in fauna and flora and changes in sea surface temperature measured by oxygen isotope ratios. 14 using C dates from cores accurate sedimentation rates and frequency of special sedimentary events, such as turbidity currents have been calculated. Problems associated with dating deep-sea cores include : 1. the small size of the sample available; 2. the non-zero age of the top of the core; 3. different ages for different material from the same core level.

INTRODUCTION

14 The discovery of C dating has resulted in a detailed •understanding of the last 40,000 years as recorded in marine sedinents. Several fields of marine geological research have benefited from this discovery.

Late Quaternaxy Positions of Sea Level: 14- C dates provide a firm basis for evaluating the history of sea level changes (Shepard and Curray 1967). As well as data fron the study of land margins and shallow borings, information, on late Quaternary positions of sea level is available fron a study of continental shelf sediments (Curray 1965; Shépard 1960). Shells of animals known to live at or near sea level and not in deeper water are found on the outer continental 158.

shelf. Dates from these shells range from 20,000 years B.P. to 10,000 years B.P. with the younger dates coming from shells from shallower depths. This chronology of sea level rise has been recognised along the Texas coast and off the eastern margin of the United States (Curray 1965). These results agree with results from land based studies from other relatively stable areas of the world.

Stratigraphy of Marine Sediments: Stratigraphy of continental shelf and upper slope sediments can be interpreted from seismic reflection profiles. Reflectors, when no more than a few metres beneath the sea floor may be sampled by coring and bt dated. Shell layers forming reflectors in Hawke Bay have been dated (Pantin 1966) and can be related to the Holocene transgression.

Sedimentation Bates: Determination of sedimentation rates involves absolute dating of selected core layers (Broecker et al 1958; Emery and Bray 1962). Age determinations are made on shell material; fragmented bivalves etc. or occasionally whole shell in cores from the continental shelf and foraminiferal or coccolith ooze in deep-sea cores. Sedimentation rates on the continental shelf are extremely variable and are usually very high compared to those front the deep-sea floor. Hates of foraminiferal ooze accumulation from the deep sea for the last 11,000 years are in the order of 1-3cn/1000 years for the Pacific and 2-3cm/1000 years for the Atlantic (Emiliani and Milliman 1966). Sediment- ation rates for the last glacial period are approximately double those for the last 11,,000 years (Broecker et al 1958; Ead'e and van der Linden 1970). Cores containing alternating calcareous pelagic ooze and turbidite layers have been collected from areas adjacent to land nasses. lite frequency of turbidity currents that produced the turbidites may be calculated by dating the calcareous pelagic interval. Off the Bahamas it has been 159.

established that turbidity currents have occurred once every 500 years to once every 10,000 years (Emiliani and Hilliman 1966). 14- C dates of coarse and fine material in the turbidites are older than dates from the pelagic sediment on which they rest (Emery and Bray 19&2). This shows the turbidite material to be reworked and supports a turbidity current origin. The history of oolite formation may also be obtained using C dating. Oolites are roughly spherical bodies made up of layers of inorganically precipitated calcium carbonate. Dates from the inner and outer parts of several oolites from the continental shelf off eastern United States show that oolite formation began with the formation of the bank 5,000 years B.P. and is still continuing (Newell et al 1960).

Climates of the Past: AH C dating is used in conjunction with estimations of past temperature from both 0/ 0 ratio measurements and paleontology to establish the climate of the last 50,000 years. 1fi 1fi The 0/ 0 method of paleotemperature measurement is based on 18 16 the fact that the 0/ 0 fractionation factor between carbonate and ".rnter in the H^O-CO-j-CaCO, system is measurably temperature- dependent (Urey 19*7). Different species of planktonic foram- iziifera live at different depths in the water column. By 18 16 measuring the 0/ 0 ratio in those species which lived very near the surface of the ocean, temperatures of past oceanic surface water nay be calculated (Emiliani and Milliman 1966). When a date has been measured or an age estimated for each tenperature a time-temparature curve may be constructed. A generalised curve combining the results from many cores 1961) shows the following stages dated by C : warm stages at 30,000-50,000 years and 12,000 years - present, and a cold stage at 12,000-30,000 years. Similar results nay be obtained by studying the proportions of present day, typically warm and cold water species of planktonic foraminifera at regular intervals from deep-sea cores (Ericson et al 1964). Cold periods can be recognised by

160.

a reduction in the number of "warm" species and an increase in the number of "cold" species and the reverse for warm periods. Temperature changes can also be recognised from a study of coiling ratios of certain planktonic foramini fera. An example of this is Globigerina pachyderma (Ehrenberg) which when observed from the doisal side is seen to coil sinistrally in present day specimens from the Arctic and Antarctic and dextrally in specimens from more temperate regions (Bandy 1960). Both these paleontologic methods have shown that there is a change from cold to warm over a period of time which centres on 11,000 years B.P. Because of differing rates of sedimentation in different cores, dates are needed so that climatic events may be positively correlated between cores.

PROBLEMS ASSOCIATED WITH DATING COBES

-lit In marine geology C dates are most useful in studies c|f deep-sea cores of CaCO, ooae» Such cores usually represent periods greater than the last 50,000 years and contain abundant material for dating. However several problems exist when dating core material.

1. The Size of the Sample Because of the difficulty in getting long, large- diameter cores, the diameter of cores collected have been small, in the range of 5 to Scias. From these cores several centimetres of sediment are needed to get a date and this usually represents several thousand years. The date obtained may be accurately assigned to the middle of the sampling interval. But even wher the samples are adjacent only one date for every several thousand years is the narrowest time interval that can be dated. This will therefore be a limiting factor when trying to date events that occur at cloje intervals down a. core.

2. The Zero Age Because the top of almost all cores are disturbed 161.

during i""lie collecting process a reliable surface age can only rarely be obtained. However both, ages from undisturbed samples and extrapolated ages for the surface material from cores from many parts of the world give positive ages. Off Southern California, Emery and Bray (1962) found two measured surface ages to be 1,230 and 2,100 years B.P. and extrapolated surface ages ranging from 1,400 to 6,400 years B.P. The mean of all these ages is 2,500 years. This phenomena may be explained by combinations of the following factors although none explain this positive age on their own.

(a) The age of sea wafcer - An early explanation, was that the radiocarbon in sea water is old and that the organic matter containing it must also be old. However many measurements show that radiocarbon ages of sea-water carbon are only a few hundred years and that the mixing time of the reservoir is too short to account for the age in surface sediments (Craig 1957).

("b) The mixing of sediments - The mixing of surface sediments Tby mechanical processes and organisms with older underlying sediments may be an explanation in some areas. But the presence of layering in many cores shows this is not an universal explanation (Emery and Bray 1962).

(c) Erosion or non-deposition - If erosion was active or areas of non-deposition common on the sea floor at present, positive ages would be recorded for surface sediments. But the very '/idespread nature of the phenomenum argues against such an explaaation. Off Southern California cores with, positively dated surface layers are from areas where active sedimentation is kiiown (Emery 1960).

(&) Introduction of older material - In deep-sea areas adjacent to continental shelf regions older calcium carbonate may be transported from the shelf to the deep sea in sufficient quantity to affect the age. Such material can usually be recognised as contaminant on examination. Older material may 162.

also be introduced by upward transfer in solution followed by recrystallization.

(e) Fractionation of carbon isotopes - Fractiönation of carbon isotopes can occur during photosynthesis, respiration and the metabolic processes of animals and bacteria. Emery (1960) reports an age of 167Q+./'5O years from living benthos, mostly worms and echinoids. However, Emery and Bray (1962) conclude that fractionation does not satisfactorily account for the old surface ages.

3« Different Ages for Different Material from the Same Core Level Measurements on the finer carbonate fraction have been found to give ages significantly greater than thos? obtained from the associated coarser fraction (Ericson et al 1956). This is mostly likely caused by a reworking of a significant proportion of the finer material. Measurements based on the coarse carbonate fraction therefore probably provide more Ah reliable ^0 dates. 163.

REFERENCES

BANDY, O.L. 1960: The geologic significance of coiling ratios in the foraminifer Globigerina pachyderma (Ehrenberg). Journal of Paleontology 34(4) : 671-81. BROECKER, W.S.; TURESIAN, K,&.; HEEZEN, B.C. 1958: The relation of áeep sea sedimentation rates to variations in climate. American Journal of Science 256 : 503-1?. CRAIG, H. 1957: Tne natural distribution of radiocarbon and the exchange time of carbon dioxide between atmosphere and sea. Tellus 9 : 1-1?. CURRAY, J.R. 1965: Late Quaternary history, continental shelves of the United States. In H.E. Wright and D.G. Frey (Eds) "The Quaternary History of ühe United States". Princeton University Preps, pp 723-35. EADE, J.V.; VAN DEE LINDEN, W.J.M. 1970: Sediments and stratigraphy of deep-sea cores from the Tasman Basin. N.Z. Journal of Geology and Geophysics 13(1) : 228-68. EMERY, K.O. 1960: The sea off Southern California : a modern habitat of petroleum. 366 p. New York, John Wiley and Sons, Inc. EMERY, K.O.; BRAY, E.E. 1962: Radiocarbon dating of California Bnsin sediments. Bulletin of the American Association of Petroleum Geologists 46(10) : 1839-56. \ EKLuIANI, C. 1961: Cenozoic climatic changes as indicated by the stratigraphy and chronology of deep-sea cores of Globigerina -ooze facies. Annals New York Academy of Sciences 95 : 521-36. EMLÍANI, C; KLLLIHåli, J.D. 1966: Deep-sea sediments and their geological record. Earth-Science Reviews 1 : 105-32. ERICSON, D.B.; BEOECKER, W.S» ; KIXLP, J.L.; WOLLIN, J. 1956: Late Pleistocene climates and deep-sea sediments. ¡1 Scieora 124 : 385-89- ERICSON, B.B.; EWING, M.; WOLLIN, G. 1964: The Pleistocene epoch in deep-sea sediments. Science 146 : 723-32. 164-,

KEWELL, N.D.; PURDY, E.G.; IMBRIE, J. 1960: Bahamian oolitic sand. Journal of Geology 68(5) : 461-9?. PANTIN, H.M. 1966: Sedimentation in Hawke Bay. N.Z. Depart- ment of Scientific and Industrial Research Bulletin 171. 70 p. (Memoir N»Z. Oceanographic Institute 28). SEEPABD, P.P. 1960: Rise of sea level along northwest Gulf of Mexico. In P.P. Shepard, R.F. Phleger, Tj.H. van Andel (Eds) "Recent Sediments, Northwest Gulf of Mexico". American Association of Petroleum Geologists, Tulsa, Oklahoma. Pp 338-44. SHEPAED, P.P.; CUERAT, J.R. 1967: Carbon-14 determination of sea level changes in stable areas. Progress in Oceano- graphy 4 : 283-91. UREY, H.C. 194-7: The thermodynamic properties of isotopic substances. Journal of the Chemical Society, 1947 : 562-81. Proceedings of the Radiocarbon Users Conference,

August, 19711 Wellington, New Zealand.

165.

RADIOCARBON DATING OF BONE ORGANIC AND INORGANIC MATTER

(A progress report on the Australian Experience)

Henry Polach*

Abstract Overseas bone dating expertise and procedures are listed and a comparison is nade with those practiced at the ANU R.C. laboratory. So far none of the fractions isolated, hot water soluble collagen, acid insoluble collagen, bone carbonate (acetic acid hydrolysis), bone apnatlte (hydrochloric acid hydrolysis of ac. ac. treated sample), and total bone carbonate (hydrochloric ac. hydrolysis oí untreated sample), yielded consistently 'correct' (perhaps 'acceptable1 would be a better terra) ages. Undoubtedly each fraction in turn can yield to or be contaminated by environmental factors and the role of 6C*3 values as a tracer of CO2 pathways is discussed. Hucic acid contamination of collagen is suspected, but current collagen purification techniques as practiced at ANU do not remove fauaic acids systematically.

Introduction Froa the archaeological point of view, bones are one of the most desirable materials for radiocarbon age determinations. Not only are they often found where charcoal or wood Is absent, but their age is directly related to the event the archaeologist wishes to date.

Carbon within the bones is held in inorganic and organic forms. Rafter (1555) observed that CO2 derived fron total inorganic Carbon had a different stable isotope composition than organic carbon forms, and not altogether surprisingly had also a different C1** concentration, hence different 'age'. Where bone was charred, the acid insoluble residue, a mixture of charred organic matter and residual bone protein (collagen), was considered to give reliable ages.

Australian National University Radiocarbon Bating Laboratory, supported jointly by the Department of Prehistory and by the Department of Geophysics and Geochemistry, Canberra, Australia. Errors: Throughout text alter 'appatite' to read 'apatite". 166. In 1964 Berger et al. have suggested several alternative methods for the preparation and extraction of collagen from bone and shell. The one method adopted most commonly was the demineralisation and hydrolysis of total bone carbonate with cold (not exceeding +10°C) HC1. This treatment yields upon filtering or centrifugation and washing a residue referred to as collagen. Krueger (1965) further perfected the technique by hydrolising bone under partial vacuum, thus

achieving a faster C02 evolution. Tamers and Pearson (1965) madt careful comparisons of ages of total bone carbonate, bone collagen and charcoal where such was found, and concluded that collagen does not necessarily yield the right age, but that it often yields an age slightly younger than the control sample. Results based on total bone carbonate were invariably least acceptable» thus confirming their previously established unreliability. Tamers and Pearson therefore suggested that collagen based R.C. ages should be considered equal to or older thsn. their derived C1** ages. This terminology was also accepted by us (Folach et al. 196S). However we have additionally pointed out that generally we are not dealing with pure collagen. Indeed, under Australian conditions, the porous structure of the bones was oftec completely and irremovably infilled with soil or sediment, sometieses cenented together or encrusted with soil derived CaCOg. The acid insoluble residue therefore had a high ash content (whilst pure collages is ashless) and would contain carbon from the soil in which the bone was found.

A major break through in bone dating came when Haynes (1968) established that the inorganic carbon fraction is held in two forms. Calcium carbonate, coluble in acetic acid, which according to Haynes Would be mostly of secondary origin, and calcium carbonate bound to boae appatite, insoluble ¿sx acetic acid but soluble in hydrochloric acid. Haynes further reasoned that huoic acids would form insoluble calcium complexes within the bone porous structure and suggested the removal of H.Ac, by treating the demineralized bone residua with dilute scdiua hydroxide. 167.

Relationship of R»C. ages of various bone fractions

One series of human boae remains studied at ANU, originated from a series of graves located within a burial mound, the size of a football field, elevated some 4 metres above the surrounding terrain. The top soil, a sub-tropical brown earth is approximately 50 to 80 cm deep, cultivated now as a crop field (maize and millet). The graves were 100 to 110 cm deep and extended into the limestone bedrock. Some of the skeletons were oriented North-South, some East-West, and archaeologists believe this to be characteristic of changes of burial habits. Cultural evidence suggested to the archaeologists that the burials should be up to 3500 to 4000 years old (Helmut Loofs, pers. coma.}.

We have isolated from the samples, after careful washing and crushing and additional washing in demineralized CO2 free water:

1. Acetic add hydrolysable CO2, which we call bone carbonate.

2. Hydrochloric acid hydrolysable CO2, which we call, if it follows ac.ac. evolution, bone appatite. (Sote: direct attack of bone by HC1 without pretreatnent by ac.ac. would yield what I in this text refer to as total carbonate).

3. The acid insoluble residue, after washing, drying,, combustion and purification, yields CO2 from bone collagen. (Note: Haynes suggested NaOH treatment was not carried cut as the samples were never large enough, but otherwise our method follows Haynes1 procedures).

Our results are set out in Table 1 (p. 12). On inspection none of the fraction ages derived from the same bone sample are in systematic agreement, or disagreement.

First sample: the carbonate age, whilst oldest, is in agreement with the appetite age. The appatite result could be significantly younger than the carbonate result.

hJ, 168. Second saaple: all ages could be aaid Co be la agreement, mainly because of the large errors associated with the aollagen determination,, is based on a small sample.

Third saaple: the carbonate age whilst younger la in agreement with the appatite age. The collagen saaple was very small, and whilst its age is apparently very young, the large error does not allow us to say conclusively if there is agreement or disagreement.

Fourth saaple: only the carbonate age appears to be significantly younger than both the appatite and the collagen, as the large error of the last two determinations makes it just possible for all three to cover the same age.

He can go on like chis and we would find that there is no systematic relationship or ever* a suggestion of grouping of the relative ages of various fractions from this single site» exposed presumably not onlj to the same climate, but also to the same chemical and biological environment.

Should we ignore the deaonstrably unreliable acabañóte ages, and relate only the appatite and collagen ages of the same bone saaple, then we can express numerically* their relationship (i.e. distance apart in terms of the magnitude of their relative errors).

* 1. Taka the arithmetic difference of the two ages (i.e. appatite minus ooZtagen). 2. Take toe square root of the sum of the squares of the respective errors (i.e. ± coablncd S.B. (Standard Deviation». 3. Take the ratio of tee arithmetic difference and the combined S.D. (for further sad detailed explanation see Polacb and Golson 1966). 169.

We can thus see, that only the sixth pair yields significantly different results (the appatite is statistically older than the collagen), whilst the other ages are all in agreement. In some the appatite is younger, in sone it is older. Such a distribution would be expected if we had performed all the measurements on one single sample. Nevertheless, it is just possible that in the third sample the appatite is once more statistically older than the collagen. However, we cannot say that this is the general trend. In fact the appabite to collagen relationship is not acting in response to known factors, as we have established that both climate and chemical environment, as we see it today, is the same for all the samples.

The size of the sample released by the anthropologists for dating (hence destruction) was snail, and therefore we cannot see any difference in ages due to orientation of burials. Nor can we speculate why most results group themselves between 1900 and 2500 B.P., rather than 2900 and 3500 B»P. as expected by the excavators. This is just one of the crosses we have to bear in R.C. dating as often, and understandably, minimal quantities of naterial are reluctantly 'sacrificed' if the skeletal remains are likely to be of interest to anthropologists.

Á current attempt to include more parameters into the search for valid C1£* ages of bone is shown in Table 2 (p. 13). Where soil carbonates (nodules) when present were collected and dated, and where charcoal was present, its age served as control. •

Sample ANU-261: the collagen appears to give an acceptable age, whilst bone carbonate distinctly shows atmospheric C0o uptake (nuclear bomb effect). Note that the appatite was also affected.

Sample ÄOT-4Q3: the bone carbonate is once more the youngest in this series. The appatite which is significantly older, falls within the expected age range. However the collagen is significantly younger. 170.

Sople AMV-618 and 375: the oollagen, still present in lurable amounts at ca. 25»000 years B.P., is in excellent agreement ', with Che charcoal control. The soil carbonate and bone appatite ! have equilibrated Clt* wise, evea in this naú arid environaent. Both pairs nean ages can be said to be statistically distinguishable from : each other. i

AKB-619 is of interest only because here oollagen is significantly younger than appatite, whilst for ANG-620 the trend is reversed. '

áJTO-359 and AHU-420 are listed because for these two samples we hare tried a new approach. Collagen (bone protein) is known to be soluble in boiling water. Geyh and Guhllch (1971) use this technique for extraction of 'Hot vater sol. Collag«nT, whilst Longin, as described in Evin et at. (1971), uses it to extract 'pure' collagen : fro» the acid insoluble residue. Í Our procedure for these two experiments was to boil clean ! crushed bone in a pressure cooker for four hours (151b pressure), j thereby solubilising bone proteins (our oollagen I). This was j followed by our usual ecatic acid treatment to recover bone oarbonate, ! followed by SCI hydrolysis to obtain our bone appatite, and finally : I

dating the acid insoluble residua as oollagen II. :-• uj 1HU-359: bone oavbenate is significantly younger than both the ; appetite and collagen J, which ax* in agreement between themselves. j j Cellagen II, the acid Insoluble residue shows modem carbon uptake.

Jubilantly we reasoned: ; Our pressure cooking of crushed bone resulted in pure collagen going into solution, and humic acids which must have been present, Í reasunta held within the bone structure 8M insoluble calcium huaates, and contaminated the acid insoluble fraction only (hence the modern age for our collagen IT}.

• > Il kin 171.

AMU-420: bone earbona&e la younger, appatite and collagen II are In disagreement, and oar 'pure collagen9, collagen J, is certainly no longer pure. Back to the drawing board, but before we do this one more consolation, the Keilor sequence.

V Rafter dated total bone carbonate as NZ-675, 1780 ± 115 B.P., and the bone collagen (acid insol. residua) as NZ-676, 6460 ± 190 B.P. Anne Birmingham (pers. cosa.) dated the charcoal as V-7S and ve dated the carbonate nodules as ANU-126, 2015 ± 65 B.P., 6C13 = -2.3 ± 0.2Z

(Polach et al,3 1970). The agreeaent between the laboratories dating the sane event is excellent*, especially if we consider that the samples were collected independently frcm the sane terrace, long after the part containing the skeleton had been bulldozed away.

The pair, bone carbonate, NZ-675, and soil carbonate ANU-126, show that the acetic acid soluble bone carbonate is in isotopic equilibrium with secondary soil carbonate (nodules). In this context, it can be said as being of secondary origin (cf. Haynes, 1968),

Fractiooatlon of stable isotopes and effect on R.C. dating.

Rafter (195S) has established that total bone calcium carbonate and bone protein (early measurements were done on fixed carbon of charred bone) had a different stable isotopic ««position. Subsequent aaas spectroaetric measurements (Rafter and Lockerbie, 1965) have shown that the initial 6C13 values of total bone carbonate w.r.t. EDB marine standard is -16Z, and that of bone protein (collagen) is -25 ± 2Z. Rafter has further shown that total bone carbonate values vary according to treatment of bone. If bone was calcined (heated during cooking proceases on an open fire) values of -25Z were obtained. If the bon» was in a soil environment, and has equilibrated with soil carbonate» then values of up to + 2.2Z vere found.

* He cannot compare the charcoal and collagen ages directly, as we have , done before, (indeed, if ve do so they do not confirm each other), but .-, due to circumstances we oust take a broader view. '

t. 172. So far we have obtained only three results for 6C13 values of bone fraction (Harold Krueger, pers. conm.).

Our bone carbonate 6C13 * -4.2 i 0.2Z appabite 6C13 » -10.7 ± 0.2Z collagen 6C13 • -25.2 ± 0.2Z

Recognising the significance of 6C13 measurements as evidence of 1 pathways of C02 exchange (hence evidence of extraneous C* * contamination) we have collected CO2 sables for all bone fractions which we have dated. Awaiting these mass spectrometric determinations, we have applied corrections to all our C1** results, baaed on the above sectioned 6C13 figures, but enlarging the error to ± 2.0Z.

This in the light of Rafter's study In which he found that ÓC13 values for total bone carbonate range frota +2.2 to -25.6Z w.r.t. FDB, hardly seen» justifiable. However, we have perforated many measurements on secondary soil carbonates (Polach et al., 1970; Williams and Polach, 1970, 1971; Bowler and Polach, 1971). The secondary soil carbonate values averaged -5.7 ± 2Z w.r.t. PDB. This is also confirmed by the <5C13 values for soil and bone carbonate cited in our earlier example, Table 2, Keilor site.

Effect of chwi^fli environment and /»t<«a,te on validity of bone appatlte and bone collagen to R.C. dating. A recent study by Geyfo and Guhlich (1971) show that when ages of appatite-collagen pairs are compared to charcoal or archaeologically established *valid' dates, the agreeaent of all fractions is excellent if the samples lay buried within the vadoze zone; i.e. above the groundwater table fluctuations, but wisfe the alternate wetting and drying zone of rainfall. 173.

Surprisingly samples of bones which for the last centuries were covered by structures (churches) gave the most discordant results. This Is .->ot entirely unexpected, and as Geyh reasoned, it is logically acceptable If we postulate that here the bones often lie within ground water aoveaent zone, mid that under these extreme conditions even the bone appatite carbonate has exchanged with ground water carbonate (bicarbonate and dissolved CO2).

Before dating ANU-618 and 315 the oldest known appatite ages were not exceeding 10,000 years B.P. Our findings on this were also confined by Vance Haynes, (pers. conns.). Now however, we can see that there is no natural oldest limit to bone appatite dating (cf. Table 2, p. 13). Our own aeasureaents however, confirm what Haynes suspected, asd Geyh demonstrated. Namely that bone appatits under suitable conditions will yield concordant results, in agreement with purified collagen, but that its age can be affected by ground water carbonate regime due to ionic diffusion and other equilibration processes.

We have further shown that even in a well drained sandy environment the bone appatite and soil carbonate can isotopically equilibrate (Table 2, ANU-618).

We have also shown that collagen can be preserved under suitable conditions in quantities sufficient' for R.C. dating, and Table 3a and 3b, list Z measured residual carbon equivalent related to climate.

We could argue from the data that irrespective of climate, bone proteins undergo an early and rapid degradation and that the residual protein is core resistant or protected from further degradation, leaving apparently equal proportions of collagen in all the samples studied. However, we prefer to subscribe to previous observations that during the course of fossilization, bone slowly loses collages. The first systematic study known to me was reported by Oakley (1955), who examined bone specimens ranging in age from

¿Li ca. 500 to 12,000 B.P. Oakley found that the amount of collagen decreases with tine. Since we have only residual collagen data and not a complete age sequence within any of the climatic zones indicated in Table 3b, we cannot indicate whether collagen decay over tine in a given climate is linear, or much faster in the beginning and slower as bone protein becomes scarce. We would support the latter as not only the past climate in Australia could have varied from humid (pluvial, cold) to arid (dry and hot) but also saprophytic degradations (oxy-reduction processes) due to microorganisms such as fungi, moulds and yeasts are enhanced by high initialjtiumldity-, steaming from initially high moisture content of organic matter.

As for bone appatite and bone carbonate, the picture is even more complicated, as we do not know the inorganic carbonate forms of modern or fossilized bone. Indeed Brophy and Nash (1968) and others paint a very complicated mineralógica! picture. I have attempted to study X-ray patterns of ancient bone before treatment with any acid, after treatment with acetic acid and after treatment with HC1. In all cases we have obtained a family of curves admittedly decreasing in intensity as hydrolysis of carbonates progressed, but all corresponding to appatite (Heinrich Beckman, pers. como.). No peaks corresponding to calcite were present at all, and a weak appatite peak remained even in samples where evolution of (X>2 (hydrolysis of carbonates with HC1) had gone to completion. As a result we certainly do not know where and how the '003' is held within the inorganic bone structure.

Conclusion

Both bone collagen and bone appatite respond to microclimatic and alcroenvlronaental changes, in which the microdtemistry plays a great but as yet not fully explored role. Each bone fraction can be independently and/or variably contaminated. The criterion so often postulated that agreement between appatite and collagen results indicate that no contamination has taken place in either of them does therefore not necessarily hold. 175.

Our recently applied technique, whereby bone collagen is solubilized by hot water before demineralization of bone is carried out, cannot be said to yield pure collagen. The correct procedure night be that suggested by Haynes (ref. cited); i.e. purification of the acid insoluble residue by NaOH. Å further purification of collagen by solubilizing it in hot water, recovering the datable material, by solution evaporation, could also be applied if one could start off with enough datable material.

Other oethods also suggest themselves, and we know that the Gronigen and Uppsala R.C. dating laboratories have considerable success witti EDTA demineralization of bone, followed by a further purification of residue first by SCI treatment and then solubilizing collagen by hot water.(Ingrid Olsson, pers. comm.; Blrkeomfljer and Olsson, 1969).

Austin Long (pers. comm.) is investigating techniques of separation of amino acids by dialysis, whilst Ho et at. (1969) separated amino acids by column chromatography. Vance Haynes (pers. conm.) is continuing his investigations into inorganic

bone fractions by looking at the iaotopic composition of C02 fractions resulting from incremental heating of bone in predetermined temperature steps. From biochemistry we may further suggest selective degradation of collagen by the highly specific enzyme collagenase.

However the most promising studies will come from laboratories where research into validity of bone organic and Inorganic fractions is coupled with a complete and comprehensive inventory of Cllf ages and C13/C12 ratio measurements of the environment in which a particular sample was found buried. Sites that will yield datable anounts of soil carbonate, soil organic matter, as well as an abundant and redundant collection of bone, charcoal, shell, will be rare but well suited for direct investigations by a radiocarbon laboratory. TABLE 1; C11» AGES FOR VARIOUS BONE FRACTIONS (all from some sitas)

Bone Bone Ratio of ANU Bone appatite collagen App. - Coll. Arlth. Is diff. No. carbonate only Acid ± Comb. S.D. Diff/Comb, significant! Ac.Ac.Sol. HC1 Sol. Iosol Res. S.D.

2670 ± 85 1900 ± 300 2550 ± 210 - 650 ± 366 - 1.77 No a in 1700 ± 85 1280 ± 300 2460 ± 500 -1180 ± 582 - 2.0 No §2 1090 ± 80 1740 ± 250 200 ± 650 +1540 ± 696 + 2.21 Yes or No 920 ± 90 2050 ± 500 2300 ± 600 - 250 ± 780 - 0.32 No fg 1290 ± 80 2510 ± 70 1980 ± 380 + 530 ± 400 + 1.35 No 1330 ± 80 2990 ± 80 1250 ± 500 +1740 ± 506 + 3.44 Yes 3

See footnote p. 4 Negative sign indicates that appatite is younger than collagen

WE.

1 A •»*• _ — TABLE 2: Other bone fraction agee of interest (various sites)

Secondary soil Bone Bone Bone ANU Bone apatite carbonate carbonate aollagen II collagen I Charcoal No. only HC1 eol. (nodules) Ac. Ac. Sol. (Acid Insol. Res.) (Hot H20 Sol.)

261 +11.6% > modern* 680 ± 130 2210 ± 330 (D B 1530 ± 342; - 4.6)**

403 4900 ± 85 10,070 t 250 7030 ± 160 9b?0 ± 130*** (D = 3040 ± 396; + 7.2)

618 & 375 20,200 ± 350 19,030 t 1410 24,710 ± 1300 25,000 ± 1400 (D * 5680 ± 1920; - 3.0)

619 9300 + 230 1730 ± 300 9590 ± 130 (D = 7510 ± 370; + 20.0)

620 7480 ± 160 13,670 ± 680 (D = 6190 ± 700; - 8.8) \ 359 1490 ±100 190 +1% > modern* 2855 ± 120 3200 ± 3275 ± 260; -12.5) (D a 420 2190 ±100 4270 ± 200 ± 2600 ± 350 +38% > modern* (D = 1670 ± 403; + 4.1)

Keilor 2015 ± 65 1780 ±115 6460 t 190 5990 ± 105 ,

* *••» bomb effect C02 indicated ** Figures listed between brackets are the same as those listed in column 5 and 6, Table 1 *** Same stratigraphy as ANU-619, hence charcoal age, ANU-619, is used as control 178. TABLE 3A: % residual carbon for various bone fractions (all from same site)

AGE OF SAMPLES 2000 - 3000 y B.P. MEAN VALUE CLIMATE: WARM HUMID RAINFALL 30 inch, p.a.

Sample : Ä B C D E Bone carbonate: 8-10% 8-10% 8-10% 5% 8-10% 7%

Bone ccppabite i 0.4% 0.27% 0.47% 0 42% 0 53Z 0.42%

Bone collagen : 0.6% 0.22% 0.11% 0.62 0 14% 0.23%

TABLE 3B: % residual carbon for various bone fractions (from sites of known climatic conditions)

APPROX. AGE 10,000 B.P. 18,000 B.P. 25,000 B.P. OF SAMPLES: MEAN VALUE RAINFALL : 20" <15" <10"

Sample : A B C Bone carbonate: 7% 5-10% 5-10% 7%

Bone appatite : 0.27% 0.47% 0.74% 0.44%

Bone collagen : 0.32% 0.22% * 1.9% 0.27%

Bone was charred, hence high residual (HC1 insoluble) carbon content 179.

Acknowledgements

The author is grateful to the Winston Churchill Memorial Trust which supported this research. John Head, Technical Officer (chemistry), has prepared the samples for dating and John Gower, Senior Technical Officer, (electronics) has maintained the counting equipment in perfect order. Dr John Chappell, Department of Geography, ANU, has in the author's absence overseas supervised the operations of the R.C. dating laboratory.

References

Beckman, Heinrich, Institut fir Bodenkunde, üniversitat Bonn, Bonn, Germany.

Berger, R., Harvey, A.G., and Libfoy, W.F., 1964, Radiocarbon Dating of Bone aad Shell from their Organic Components, Science, v. 144, p. 999-1001.

Birkenmajer, Kryszoff, and Olsson, Ingrid, U., 1971, Radiocarbon dating of raised marine terraces at Hornsund Spitsbergen, and the problem of land uplift, Norsk Polarinstitut - Arbok, p. 17-43, Oslo.

Birmingham, Anne, Institute of Applied Science of Victoria, Melbourne, Australia.

Bowler, J.M. and Polach, H.A., 1971, Radiocarbon Analyses of Soil Carbonates: An Evaluation from Paleosols in South-Eastern Australia, in Age of Parent Material and Soilsj edit. Dan Yaalon, Jerusalem, (in press).

Bropfe'y» Gerald, P. and Nash, Thomas, J., 1968, Compositional, Infrared, and X-Ray Analysis of Bone, The American

Mineralogist3 vol. 53, p. 445-454.

. i-i 180.

Evin, J., Lcngin, R., Marlen, G., and Paehiandi, Ch., 1971» Lyon Hatural Radiocarbon Measurements II, Radiocarbon* v. 13, p. 52-73.

G«yb, Mcbus, A., Hiederslchsisches Landesamt fur Bodenforachung, Hannover, Germany.

Geyh, Malms, A., and Guhlich, Erika, 1971, zur Frage der ZuferlSealichheit der C^-Alterbeatimung an Inocheu. Geschiakte NiedevsaahsenSa p. 9-16.

Eayoes» Vance» Dept. of Geological Sciences, Southern Methodiat University, Dallas, USA.

Eayces, Vance, 1968, Radiocarbon: Analysis of Inorganic Carbon

of Fossil Bone and Enamel, Science3 v. 161, p. 697-688.

Ho, T.T., Marcus, Leslie, P., and Burger, Rainer, 1969, Radiocarbon Dating of Petrol'sum-Impregiiated Bone from Tar Pits at Raandio La Brea, California, Saienae, v. 164, p. 1051-1052.

Kzuegcr, Harold, Director, Geochron Laboratories, CaaLridge, DSA.

Kcueger, H.tf., 1965, The Preservation and Dating of Collagen in

Ancient Bones, in Radioaarbon and Tritium Dating3 Froc. 6th 1st. Conf. Pulaan, Washington, p. 332-337.

Long, Austin, Geocbronology Department, university of Arizona, Tuacon, USA.

Loofs, Helsut, Oepartaent of Asian Civilisation, Australian National University Canberra, Australia.

Oakley, K.F., 1955, British Muaeum Natural History Bulletin* Geology 2, p. 254-265.

Olsson, Ingrid, U., Institute of Physics, Uppsala, Sweden. 181

Polach, H.A. and Golson, J., 1966, Collection of Specimens for Radiocarbon Dating and Interpretation of Results, Australian Institute of Aboriginal Studies, Manual Ho. 2, 42 p's.

Polach, H.A., Golaon, J., Lovering, J.P. and Stipp, J.J., 1969, ANU Radiocarbon Date Lists II, Radiocarbon, v. 10, p. 179-199.

Polach, H.A., Lovering, J.F. and Bowler, J.M., 1970, ANU Radiocarbon

Date List IV, Radiocarbont v. 12, p. 1-18.

Eafter, T.A., 1955, C1(* Variations in Nature and the Effect on

Radiocarbon Dating, N.Z. J. Sai. Teah.s B¿ v. 37, p. 20-38.

Rafter, T.A. and Lockerbie^ L., 1965, CarboE-14 Variations in Nature, Part 5, The Age of the Hew Zealand Moa from Zaxbon-lh Measurements, Institute of Nuclear Sciences Reportj IKS-R-37, Lower Hutt, K.Z.

Tamers, M.A. and Pearson, P.J., 1965, Validity of Radiocarbon Dates

on Bone, Natures v. 208, p. 1053-1055.

Williams, G.E. and Polaca, H.A., 1969, The Evaluation of Clk Ages for Soil Carbonate from the Arid Zone, Earth and Planetary Sdencs LettersjV. 7, p. 240-242.

Williams, George E. and Polach, Henry A., 1971, The Radiocarbon Dating of Arid-Zone Calcareous Paleo3ols.

Bui, Am. Geol. Soo.t (in press).

Errors: Throughout text alter 'appatlte' to read 'apatite'. n

182. DEGBADATI7E METHODS AS AIDS IN SOIL HUMIC ACID CEAEACZSRISATIOK By K.R. Tate Soil Bureau Deparianent of Scientific and Industrial Research Lower Butt

Soil organic matter is a diverse mixture that includes living plant roots, the soil biomass, and partially degraded plant, animal, and microbial components. This last fraction, which comprises perhaps 20 percent of the total 3oil organic carbon includes the carbohydrate and lipid fractions; and some organic sulphur, phosphorus, and^nitrogenous constituents which have not been extensively altered in the soil. Hie soil organic matter fraction, generally referred to as "huaic substances", may comprise 50 to 85 percent of the total soil organic natter. Humie substances have been described as hetero- polycondensatea (Eononova, 1966), a term used to describe the condensation products of aromatic compounds with products of protein decomposition and with the possible participation of carbohydrates. Ths molecular weights of these complex polymers may range from 2000 to as much as 3J0,000, and their formation is dependent on such factors as the phytochemioals entering the soil, the microbial population, and soil characteristics such as pH, extent of aeration, and content of stabilising clays and cations. Humic substances always occur in intimate association with other organic components ana with the mineral soil colloids (Scheffer and Ulrich, 19^0; Kononova, 196*6; Scharpenseel, 1966)- In recent years, a number of mild extrac tanta have been used in their recovery from soil. (Stevenson, 1965; Kbnonova, 1966). The fractions normally obtained are humic aei^soluble in alkali,, insoluble in acid; hyoatcoelanic acid; aichol-soluble humic acid; fulvic acid, soluble in both alkali and acid. The organic matter not extracted ty alkali is generally referred to as the humin fraction and probably represents an intimate association of humic materials bound to the mineral soil. The various fractions are thought to represent part of a system of polymers whose chemical properties (elemental cosapoaiticn; functiöiial group content) change systematically with increasing nsolecular weight. Humic and fulvic acids constitute the active part of soil organic matter, and much attention has been focuased on these fractions by various research groups (for resent reviews, see Stevenson and Butler, 19&9; Paul, 1970). Most work has been concentrated on the humic acid fraction which can be readily extracted and purified. ERRATA

Please make following corrections in the paper

RADIOCARBON BATING OF BORE ORGANIC ARB INORGANIC HATTER by H. POLACB

g text read apatite instead of appatite

Throughout text rsad C %ot parts per mille, instead of parts per hundred p.173 line 8, read as: Before dating AHTJ-618 and 373 etc instead of 515.

183.

STRUCTURAL CONSIDERATIONS

The problem of the molecular structure of soil humic acids has attracted the attention of chemists for over one hundred years. However, there is still no single method that can provide information on the nature of more than a fraction of the humic acid "molecule". The difficulty is due primarily to the very complex nature of humic acids. The diverse nature of the contributing structural units prevents any specific fraction being regarded as representative of the overall structure. Pelbeck (1971) lias recently estimated that only about 50-55 percent of the total humic acid "molecule" is composed of anjino acids, hexosann.nes, polycyclic aroaatics, oxygen containing functional groups, and aliphatic and mononuclear aromatics. This clearly highlights the need for much additional information before we can claim a reasonable understanding of soil humic acid structure.

DEGRAMTITflS rECHUIQUiS

Various degradative methods have been employed in the past including sodium amalgam reductions (Burges, Hurst,Walkden, 196^; Méndez and Stevenson, 1966, Stevenson and Méndez, 1967? Dormaar 1969 ), microbial metabolism (Mathur and Paul, 1966), acid hydrolysis (Méndez, 1967), and nitrobenzene oxidation (Morrison, 1958; 1963; Wildung, Cheaters, Behmer,1970). Generally low yields of phenols and phenolic derivatives have been identified as degradation products. Alkali fusion has been questioned (Cheshire, Cranwell, Haworth, 19^8) as a useful degradative technique since artifacts may be produced which no longer resemble the structural units of humic acids.

A novel approach to the structural investigation of humic acids has been reported using pyrolysis gas chromatography (Nagar, 19^3; Kanber and Searle, 1969 a,b).

REDUCTIVE DEGRADATION

Oxidative degradation methods, when applied to soil humic acids, collectively support their essentially aromatic nature (Schnitzer and Desjardins, 1970)- However, the predominance of phenolic degradation products, which are generally unstable under oxidizing conditions, suggests that some secondary product formation may occur. For this reason a procedure which relie3 on degradation in a reducing environment clearly may have some advantage over these methods.

Burges et al, (196^) claimed to ha'1'? recovered up to 30 percent of a podzolic huinic acid as phenolic and phenolic acid monomers, but this was later questioned by Stevenson and Méndez (I967) who suggested that much of the degradation product was probably low •olecular weight aliphatic material. n

184.

Units atypical of lignin vere not found by these workers in a Brunizemic hmaic acid, wiiereaa Surges et al. (196^) found that units based on the parent molecule, phloroglucinol, were quite comnon in humic acids from several sources. Our results with some New Zealand soil bmnie acids have tended to confirm that phenolic reduction products such as phloroglucinol and resorcinol (i.e. atypical of lignin derivatives) do occur in soil huaic acids. While there are likely to be differences in soil humic acids formed under different conditions, the likelihood of differences arising from the particular degradation conditions should not be overlooked. An ezperinent illustrating this point is summarised in Table 1.

BEGRAIATTOIT OF STAEDåED MIXTURES OP PHMOLS AND PHENOLIC ACIDS AT 100°C ÜKDES 0 -FREE NIlSOGESf

Source Reduction Times (hours) 0 3 6 Phenols or Phenolic Acids

Possible lignin Vanillic Acid +++ +++ ++ derivatives Syringic Acid +++ ++•*• ++ 4-^rdrosybenzoio Acid +++ +++ ++ Pzotooateoiailo -Aoid +++ ++ +

Foaaibla Phloroglucinol +++ ++ ND flaronoid or Resorcinol +-H- ++ ND •iorobial aoxurce Resorcylic Acid +++ +++ +

Concentrations; +++ strong? ++ medium; + weak HD not detected

s H a 185.

The compounds used in this experiment have all been previously- reported as humic acid degradation products (Burges et el.. 1964).

Theoretical considerations predict that in alkaline solution, phloroglucinol and units based on it should generally be more reactive than those compounds which are derived from lignin.

After 6 hours under the sane conditions used for humic acid degradation, neither phloroglucinol nor resorcinol could be detected (Table 1). This highlights the need for considerable care in choosing degradation conditions which provide a reasonable yield of phenolic and phenolic acid monomers, while minimising the fonaation of secondary products.

The method in use at Soil Bureau to degrade soil humic acids is essentially that described by Burges et al. (19<&). with some modifications•

Samples of humic acid (250 mg) in 25 ml of 1 percent sodium hydroxide are reduced under oxygen-free nitrogen for four successive three-hour periods with an excess (20g) of 5 percent sodim amalgan. The products fron reductions 1+2 and 3 + k, which are reeov-red by acidification to pH 1, and ether extraction, are combined as indicated. Separation and identification of degradation products is achieved by two-dimensional silica gel thin layer chroaatography. Gas liquid chronatography (GLC) is now being used as an additional aid in the identification of the degradation products from each huaic acid.

A sumnaxy of the results obtained from the reoent reductive degradation of two New Zealand soil humic acids is included in Table 2 with some previously reported data (Burges etal.,1964) for a Bendzina (chalk grassland) humic acid, and a humic asid formed in a lignin-free enviroment beneath Antarctic peat (moss).

A description of the soils froai which the two New Zealand humic acids were extracted (Goh,1970) is included in Table 2.

Despite «oHe tentative (as yet) identifications, it is possible (Table 3) to distinguish between the humic acids extracted from the Central Yellow-brown loams by a reductive degradation method.

The nost striking differences occurs in those units of possible lignin origin. TTanillic and syringic acids are readily identified as major degradation products of Patua loam, while vanillic acid is a minor component of the Efemont black loam bxnnic acid, amri syringic acid is barely detectable by GLC. In addition, it-hydroxybenzoic acid is present in the Egnont black loara hmnic acid, but apparently absent in the Patua loam humic acid. TABLE 2: PHENOLIC COMPOUNDS IDENTIFIED IN SOME SOIL HUMIC ACIDS

Source of Humic Acid a a Compound Rendzina N.Z. Central Yellow-brown Loam Antarctic Peat t 4 Patua Egraont

Possible Vanillic Acid lignin Syringic Acid ++ ++ trace - source 4-Hydroxybenzoic Acid + Protocatechuic Acid + (+) ! I Guiacylpropionic acid "Syringylpropionic acid 00 Possible Phloroglucinol trace (+++) +++ ++ flavonoid Resorcinol + ++ trace ++ or microbial Methylphloroglucinol trace ? (+) + source 2,4-Dihydroxy toluene trace ? (+) +

Pyrogallol Unassigned 3,5-Dihydroxy trace (+++) - + benzoic acid

Burgee et al. (1964). t Identification by TLC. % Identification by TLC and GLC, ( ) tentative identification + weak ++ medium +++ strong not present TABLE 3: DESCHIPTION OF THE N.Z. CENTRAL YELLOW-BROWN LOAMS (SOILS OF NEW ZEALAND, PAKT f)

Soil Patua loam Egmont black loam

Classification Very strongly leached central Moderately leached central yellow- yellow-brown loam brown loam

Present Vegetation White clover, cocksfoot, Cocksfoot, sweet vernal, ryegrass ryegraes, Yorkshire fog

Past Vegetation Rirau-Kamahi forest Fern, tutu, scrub

Depth (in.) 0-3 3 - 6 Horizon A12 pH 5.2 6.0 C (*) 20.3 8.7 N (#) 0.77 0.71 C/N 26 12 Parent Material Andesitic ash Andesitic ash (Stratford Ash and Egmont (Egmont Ash) Ash)

Clay Minerals Hydrous feldspar, allophane Hydrous feldspar, allophane

* N.Z. Soil Bureau Staff 1968: "Soils of New Zealand, Part 3". N.Z. Soil Bureau Bulletin 26(3). J 188.

The differences between the Central Yellow-brown Loam humic acids, and the Rendzina and Antarctic peat moss humic acids are clearly seen from the data in Table 2.

Burgeti et al» (1964-) data for the Antarctic peat (moss) humic acid demonstrates how reductive degradation may be useful in providing information on the vegetational history of a soil. The lack of lignin in the moss is reflected in the absence of lignin units in the humic acid degradation products.

There is some evidence (Leo and Barghoorn, 1970) that the lignina in cell walls of vascular plants, when decomposed under mild oxidative conditions, give patterns of aromatic aldehydes (with their acid analogues) which ara typical of broad vegetational type* Generally, grass lignins produce ¿f-hydroaybenzaldehyde, vanillin and syringaldehyde, while soft wood species yield only vanillin.Hardwood lignins produce vanillin and syringaldehyde.

The summary of data in Table 2 for Patua loam humic acid may reflect (at least as far as lignin units are concerned) the influence of the former forest vegetation on the nature of the humic substances present in the organic matter of the A., horizon of this soil.

However, much further work on soils with well documented vegetational histories will be necessary before such conclusions may be drawn with confidence.

PYROLYSIS GAS CHIKMåTOGRAPHY

Pyrolysis gas chroiaatography (PGC) has been used for the comparison and identification of many organic materials including synthetic polymers (for review, see Beroza and Coad (I966))but has thus far attracted little attention among soil organic matter research workers. Since soil humic substances are essentially polymeric in nature, the technique should be applicable when making comparisons between different "types of soil organic matter, and for structural investigations.

Nagar (1963) showed that differences occur between pyrograms of humic acids from different soils, and these in turn differed from lignin. llore recently, Kimber and Searle (1969 a,b) have examined the application of PGC to comparative studies of soil organic natter in sons detail. They reported that hutnic acids having a highly condensed structure are readily distinguishable from those that are less condensed. In addition, PGC analysis of a mmlber of hwaic acids indicated differences which were attributed to eatractant used, crop history and nitrogen addition. 189. As a degradative technique in faunic acid studies, FGC appears to offer two main advantages over other destructive msthods. Firstly, the amounts of volatilised humic acids reported by Kiober and Searle (I969 a, b) were as high as 6? percent. Providing the products formed from secondary reactions are minimised, the pyrogram obtained for a specific huaio acid is probably more representative of that fraction than the degradation patterns obtained by chemical methods. Yields of degradation products obtained by chemical degradation methods are typioally of the order of t or 2 percent of the original humio acid.

The secoüd advantage over existing methods is in the rapid nature of the analysis. Once suitable operating conditions have been established, several samples could be degraded and analysed in a single day. nevertheless, there appears to be considerable scope for development of PGC as a convenient means of qualitatively and quantitatively comparing soil organic matter fraotions. ACQÍ0WLSDOEHTS

I am grateful to Dr K.M. Gob, (Soil Science Department, Lincoln College, Canterbury) for supplying the fcumio acid samples from Patua loaa and 5gmont black loam which have been used in the reductive degradation studies. 190. REFERENCES

BEROZA, M; COAD, A. 1966: Reaction gas c lärorna tography. .Tjurnal of Gas Chromatography: 199-216.

BÜRGES, N.A.; HURST, H.M.; WALKDEB, E, 196*f: The phenolic constituents of hunic acid and their relation to the lignin of plant cover. Geochimica et Cosraochimica Acta 28: 4^

CHESHIRE, H.V.; CRANWELL, P.A.; HAWORTH, R.D. 1968: Humic acid 3. Tetrahedron 2h: 5155-67.

DORMAAR, -J.F. 1969: Reductive cleavage of huiaic acids of chernozemic soils. Plant and Soil 31(1): 182.

FELBECK, George T. Jr. 1971: Structural hypotheses of soil acids. Soil Science 111: k2.

GOH, K.H. 1970: Organic matter in New Zealand soils. Part 1. laproved methods for obtaining humic and fulvic acids with low ash content. N.Z. Journal of Science 15: 669-86,

KIMBEE, R.W.L.; SEARLE, P.L. 1969a: Pyrolysis gas chromatography of soil organic natter.1. Introduction and Hethodology. Geoderma 4; ^7-55.

KIMBEB, R.W.L.; SEARLE, P.L. 1969b: Pyrolysis gas chromatography of soil organic matter. 2, The effect of extractant and soil history on the yields of products from pyrolysis of hunic acids. Geoderaa *f: 57-71.

KOKOKOVA, M.M. 1966: "Soil Organic Matter", Oxford, Pergamon Press. Inc.

LEO, R.F.5 BARGHOORK, E.S. 1970: Phenolic aldehydes: Generation froES fossil woods and carbonaceous sediments by oxidative degradation. Science I68t" 382-^.

MATHUR, S.P.; PAUL, E.A. 1966: A microbiological approach to the problem of soil hunde acid structures» Nature, London 212: 6^6-7»

MÉNDEZ, J. 1967: Organic compounds in humic acid extracts. Geoderna 1: 27-36.

MEIÍDEZ, Jj STEVENSON, F.J. 1966: Reductive cleavage of humic acids with sodiun analgan. Soil Science 102: 85-93»

MOERISON, R.I. 1958: The alkaline nitrobenzene oxidation of soil organic matter. Journal of Soil Science 9i 130-^0. H

191.

MORRISON, B.I. 1963: Products of the alkaline nitrobenzene oxidation of soil organic matter. Journal of Soil Science 1¿: 201-16. NAGAB, B.R. 19&3: Examination of the structure of soil humic acid by pyrolysis gas chroma t ography. Nature, London 199:

PAUL, Eldor A* 1970; Plant components and soil organic matter. Pp. 60-103 in "Becent Advances in Pnytoehemistry". Vol. 3* (C. Steelink and V.C. Buneckles Eds.), Meredith Corp., New York.

SCHABPEHSEEL, H.f. 1966: The formation and type of bonding in clay-humic acid complexes Part II: The hydrothermal synthesis of clay-humic acid and other organo-aineral complexes: X-ray, Infrared spectrometer and electron microscope analysis* Zeltschrift fflr PflanzenMhrung. DUngung and Bodenkunde TWi 118-202. SCIEFFEH, F.; ULRICH, B. i960: "Humus und Humus dKngung". Stuttgart, Ferdinandenke, Verlag.

SCHNITZER, M.; DESJABDINS, J.G. 1970: Alkaline permanganate oxidation of methylated and unaethylatea fulvic acid. Proceedings. Soil Science Society of America 5*+: 77-9*

STEVENSON, F.J. 1965: Gross chemical fractionation of organic matter. Pp. 1^09-21 in "Methods of Soil Analysis" Part 2.(C.A. Black et al. Eds.), American Society of Agronomy. Madison, Wisconsin.

STEVENSON, F.J.; BUTLER, J.H.A. 1969: Chemistry of humic acids and related pigmeats. In "Organic Geochemistry, Methods and Results". (G. Eglinton and H.T.J. Murphy Eds.)t Longman Springer Verlag*

STEVENSON, F.J.; MÉNDEZ, J. 1967: Reductive cleavage products of soil humic acids. Sail Seience 103: 383-8.

1ILDÜNG, R.B.; CHESTEBS, G.i BiTHMEE, B.E. 1970: Alkaline nitrobenzene oxidation of plant lignins and soil humic colloids. Plant and Soil 32: 221-37. &T']

192. ! LOW T5HPERATUHS ASHING

Peter C. Bankia

Soil Bureau, Department of Scientific and Induatrial Sesearen, Lover Butty

A plasma represents a unique chemical environment?. There are different varieties of plasma ranging froa high energy ionised plasma (e.g. the sun) to the lov temperature plasma obijRined by raising molecules to an excited state in a radio frequency ir-f) field. It is this latter, type which is receiving considerable attention as a means of oxidising organic material without requiring the use of acids or high temperature». Before elaborating on this nev lov temperature oxidation Cashing) technique, existing ashing procedures andJsome of their disadvantages are outlined. Of course, existing techniques can be quite satisfactory for sone types of analyses and before*an existing technique is condemned) a basis for comparison should be made. The framework on which any discussion vill be baaed on the relative merits of a particular ashing procedure is its application to trace metal determinations, ¿'he removal of organic matter for trace metal analysis is not only important as a concentrating procedure but alaojin using the spark; source oasa spectrometer,the presence of large quantities of organic matter make spectra interpretation difficult and, in certain masa ranges, quantitative analysing impossible.1-

Losses occurring during vet and dry ashing procedures are probably the greatest single source of error if the majority of trace setal determinations. Vet ashing has an advantage over dry ashing methods in that losses by volatilisation are small. However there is the inconvenience and hazard of usiag corrosive and odourous mineral acids. She introduction of contaminants is a serious problem especially if one is -determining trace metals in the part per million concentration range* Finally certain organic compounds vill resist oxidation by the severest of acid treatments. Muffle furnace oxidation using temperatures of 45O-70O°C (with or without an atmosphere of oxygen) can be quite rapid. Because of the simplicity of the procedure it has been widely uaeji in spite of some serious disadvantages• Firstly the destruction of organic matter and the loss of inorganic elements is not alvays reproducible. Published results have afeova that the heating of an organic matrix containing trace quantities of inorganic elements results in severe losses by volatilisation of certain elements. For example: at 700°C there is a 6# Co loss, 52JÍ Cs loss. 35JÉ 2n loss and a 9Sf Fe loas. Uren at lover temperatures* (¿*00°C) element loss can. still be quite «substantial: 81£ loss Au, 35Jf loss Ag, 7% loss Ca, 77# loss As, and 23% loss Sb. Naturally the nature 193.

of the sample matrix, the chemical fora of the element (chlorides are usually quite volatile), and the effect of the presence of other elements are factors which will determine what losses are observed due to volatilisation. It is difficult to predict which elements will be lost in a specific sample. Elements little affected by muffle furnace oxidation at ^00-500°C were Cu, Cr, Pb, Zn, Co, Sr, and Ce. Other disadvantages of muffle furnace oxidation include reaction of the sample with the hot container, contamination from air-borne particulate matter, pL/sical and chemical changes in the inorganic compounds present, and the tendency of some biological tissues to either burst into flame or froth. The oxygen flask technique has proved useful for degrading organic matter. However, because of the high pressures developed in the flask, this procedure is limited to small samples.

Low temperature ashing, using eJp^trodelessly discharged oxygea, is a new technique for the quantitative removal of organic matter from a sample without raising the sample temperature above 150°C. Electrical energy is transferred directly to a stream of low pressure oxygen gas, producing electronically excited states within the oxygen molecule. The saraple teaperature is low during the oxidation reaction so that volatility losses are substantially decreased compared with muffle furnace oxidation. Published data show a 100JÍ recovery of Sb, As, Se, Na, Zn, Cs when these elements are added to an organic matrix which is then oxidised by the low temperature ashing method. Nonvolatile mineral constituents remain in the saaple container. If any material should volatilise (e.g. Hg, I) then this can be trapped as the low temperature ashing device is a closed system. This last feature also minimises contamination from atmospheric irapurities.

When molecular oxygen is subjected to a radio-frequency or microwave discharge, some electronically excited diatomic oxygen species, as well as atomic oxygen, are formed. The electrical moment vector of the electromagnetic field takes on sufficient strength to remove an electron from a gas molecule, accelerate it and cause collision - induced transitions. When . using oxygen gas there results a complex mixture of neutral oxygen eoiecules in excited electronic states, ionised species and oxygen atoms in the ground and in the excited states. The explanation for the increased reactivity of electronically excited oxygen can be found in the arrangement of the electrons around the oxygen molecule. Molecular oxygen, in ,. singlet (or excited) electronic state ia much more reactive than molecular oxygen in the spin unpaired (or ground) electronic state since no change in spin, multiplicity is required to form spin paired (singlet) CO2 and

Å suitable apparatus for the formation of electrodelessly discharged oxygen consists of:

1. a radio-frequency transmitter (usually 13*56 MHz with 0-300 watis of power) together with a transaitting terminating 194. network designed to suppress undesired harmonics and to match the impedance of the transmitter coils surrounding the gas- filled discharge tube with the amplifier plate circuit of the transmitter*

2. a gas-handling system which permits regulation of the oxygen gas flow into the sample chamber, allows for cold trap collection of reaction products and allows a low (approximately 1 torr) pressure to be maintained. The material to be processed is placed in a glass chamber which is surrounded by the r-f transmitting coils* The sample chamber is evacuated and oxygen gas passed through the system. The plasma is initiated within the sample chamber by applying an r-f frequency to the transmitting coils. The sample reacts with the plasma for the prescribed length of time. Oxidation rates depend upon a large number of parameters but rates of 1-2g of sample oxidised/hour are readily obtainable*

Ashing (or oxidation) rates depend primarily on the surface area of the sample exposed to the stream of activated oxygen. Therefore, the size of the sample particles, the amount of sample, position of the sample, and the frequency of stirring are important factors in determining the ashing rate. The ashing rate also increases with the addition of more oxygen until a stage is reached that more oxygen is being added to the system than there is power to totally excite, at which point there is no increase in the oxidation rate. However, as further amounts of oxygen are added, the pressure rise pi cauces loss of activated oxygen because recombination collision processes increase and therefore the oxidation rate decreases. Tnus a balance between gas flow and gas pressure has to be established to obtain maximum ashing rates. Once this balance has been achieved any increase in power output of the transmitter only increases the sample temperature without increasing the oxidation rate*

Accurate measurements of temperatures within the sample during ashing are difficult. A thermocouple cannot be used in the presence of a r-f field. Fse has been made of a "mineral thermometer*1 of gypsum added to a coal sample that is ashed, after which the phase of the gypsum is determined by X-ray diffraction* The gypsum was found to have been dehydrated to J-CaSO^ which is stable to approximately 150°C« Above this temperature there is a conversion of y-CaSOüj. to anhydrite (CaSO^).

The "gentleness" of the oxidation by activated oxygen is evident from the observation.' that structural and textural relationships among inorganic constituents are retained in a sample* Biological samples can be ashed, leaving a residue consisting of undisturbed inorganic material which retains the structural integrity of the original specimen. The oxidation temperature is low enough to enable removal of contaminating organic material from a limestone matrix without decomposing the limestone. In spite of the low temperature no evidence has been produced to indicate that there is any variation in oxidation

í i 195. rate with different types of organic compounds. Thus there is little possibility of fraetionation of the organic matter caused by a portion of the sample remaining partially oxidised.

Electronically excited molecular oxygen has a wide variety of uses:

1» lo* temperature oxidation of organic compounds in geological and soil samples,

2* preparation of surfaces for electron microscopy. There is no sintering or phase changes of the mineral matter,

3» preparation of biological samples for elemental analyses by atomic absorption and mass spectrometry,

k, quantitative carbon and hydrogen analyses,

5» pollution studies: inorganic particulates can be trapped on cellulose filters which are then oxidised.

Because oxidation by this technique is primarily a surface reaction it may be possible to successively remove layers of organic matter from particles of sample. The rate of oxidation can easily be controlled by adjusting instrumental parameters. If this process was viable then there exists the possibility that surface humic acids of recent origia might be removed from samples used in carbon-i^ dating analyses. 196.

THE SELECTION OF ARCHAEOLOGICAL SAMPLES FOB RADIOCARBON DATING by L. Lockerbie

1• Criteria to be followed in selecting samples for radiocarbon analysis, particularly wood, charcoal, shell and bone, materials most commonly found and used.

2. Methods of collection of samples; sources of error an archaeologist is most likely to encounter.

3. The importance of providing material in sufficient quantity and quality to enable accurate analysis to be made* k. Precautions to be taken to prevent contamination after exposure of the sample; methods of packing for transmission or storage»

5. The Importance of providing accurate and detailed records of techniques employed; observation and interpi'etation of strat igraphlcal and other environmental factors» 197.

THE SELECTION OF ARCHAEOLOGICAL SAMPLES FOR RADIOCARBON DATING

L. Lockerbie

Hiten excavating a site for which dates are likely to be important,

the archaeologist should collect samples as the work progresses, since

it is unlikely that the most significant samples can be selected until

after completion of the section. Those collected from a horizontal

surface are more likely to be contaminated during collection than

those from a vertical section. Moreover, it is not always easy to

determine precise stratigraphic positions from a horizontal surface

alone, particularly wheia too strata impinge and there has been a

mingling of material from upper and lower layers. The vertical

section reveals disconformity more readily and has the added

advantage of reducing the time of exposure of the sample to atmospheric

and other forms of contamination. It is therefore recommended that

samples be collected if possible from the vertical section, with exact positions clearly recorded on photographs or drawings showing stratigraphy in detail. Since excavation invariably destroys stratigraphy,

as much information as poseible should be extracted and recorded at the time of excavation. Evory care should be taken to ensure that samples selected are characteristic of the feature for which they ara expected to provide a date, meticulous attention to detail is therefore essential. r

198. SUITABLE MATERIALS Í5QST COMMONLY FOUND AND USED

Wood and Charcoal Wood and charcoal are excellent dating mataríais but, if an archasologically useful date is to be obtained, the collector must exercise great care in the selection of samples. Any date secured will be tiie date of death of a particular part of a tree and this may bear no relationship whatsoever to the date of use, or of burning, aa the following examples will show. In ths Carrick mountains of Central Otago, 3,000 feet above sea level, totara logs, roots and branches in an excellent state of preservation litter the slopes. No such trees have grown thata during the pest 100 years and, in tha dry climate of Central Otago, such wood could have lain there for ssveral hundred years. One log fr| inches in diameter contained 300* growth ringa. From a nsarby valley, similar logs collected by wardie and 14C dated by Ferguson and Rafter show that their date of death was A.D. 1290 ± 60 years. If, however, our 1955 archaeological expedition had burned such logs in our camp-fire and if subsequently an unsuspecting archaeologist had collected the resultant charcoal and had it analysed, it might well be claimed that we had camped there 500* years ego, and were in fact moa-h'jntera. In such en area, the data obtained from even small sticks does not necessarily indicate the time of usa. In another area of Central Otago, a "post" was found in association with occupation material and it was claimad that this would date the . occupation. A date far beyond possibility was obtained, indicating that ; if ths wood were rsally a post, ancient timbar hnd been uaed. j Arahaeologiats are prone t

indeterminate origin from soil strata in the hope that an acceptabla

date will result. In most cases, charcoal of this kind is archaeolo-

gically worthless. Unless there ia sound reason for hat/ing such

charcoal analysed, and unless the sample is of sufficient quantity to

make useful analysis possible, it should not be submitted.

In coastal areas where dead timber decays rapidly, there can be

reasonable expectation, particularly in the case of small twig charcoal, 14 that the C date will be close to the tima of burning. For example,

small sticks of charcoal approximately one inch in diameter and with

charred bark still adhering were identified as Senecio rotundifolius,

or muttonbird scrub, a plant common in the area today. These sticks,

absolutely free of rootlet contamination provided dating rcatsrial

believed to be of exceptionally high reliability.

Wood samples (waterlogged) from pallisads post-butts, with bark

still adhering provided what are considered to be acceptable dates for

a section of the töurdsring Beach pallisade. Archaeological evidence

suggests that the posts were part of the original structure; but to determine such a point, additional dates would be necessary.

Contamination by rootlet intrusion affects much New Zealand charcoal. Modern rootlets are easily distinguished and removed.

However, decayed rootlets are not so easily recognised and inclusion of these in a sample could result in a too recant date. In old wood samples, recent dscayed rootlets become indistinguishable from the wood.

In swamp conditions, samples may be affected by organic matter.

Charcoal, dried thoroughly in an oven, should be sealed in its container immediately after drying, otherwise readsorbtion of modsrn CCL may occur. The need to observe and record meticulously all details of sample 200.

environment should ba apparent.

Sfiell Since from earliest times shellfish have fornad a major item of diet in Ham Zealand, refuse shell is an important material fcr dating occupation 1avals. From time to time the validity of shell dates has been questioned, particularly because of the possible effects of environment both during growth and after death, and possible exchange with atmospheric carbon. However, provided hard shell (aragonite) is used, results should be satisfactory. Shell conchiolin may provide a date more reliable than that from carbonate, but because of the low conchiolin content in shall, a very large sample is required. Freshwater rauasais (Hyridells) have shown considerable discordance between carbonate dates and those of keratin from the same shells. Experimental work associated with this problem is now in progress. Care should be taken to ensure that shells being collected for analysis era actually food refuse and that their stratigraphic position has remained unaltered since ths time of original deposition, i.e. - that accumulation or placement is not ths result of erosion or other activity. In sand duns areas, shall, bone and charcoal from upper strata may well baooma ra-depositsd as a heterogeneous accumulation on a stable lower deposit. Wham this occurs and higfc-cXines have re-formed above the deposit, dstection of transposition is difficult and though the material may bs excellent for dating purposes it is archaeologically worthless. Care should also be taken to ensure that recent campers have not deposited modern refuse shall so that it has become mixed with and al!to3t indistinguishable ftco much older occupational refuse shell. 2O1.

It is important that tha collector should know something of the

gsolaqy of the area being Investigated so that fossil shall, clearly

outaide all limits of human occupation, mill not be collected. Refuse

shall may lie on a bed of fossil shell, or even be mixed with it.

Such situations are usually recognisable. Thay should be thoroughly

investigated at the time of sample collection and reported fully whan

analysis is sought.

Whenever possible, each sample should consist of one species only

and should ba large enough to allow analysis by several methods should

this ba considered desirable.

Sona

Bone carbonate dates have not always agreed with dates of other

stratigraphically associated mataríais. Exchange between the carbonate

and either recent, or old C0_ in solution is considered a likely cause of

this discordance! Experiments with charred bone have shown that when

exposed to the atmosphere for a relatively short time after burning, the

bone re-carbonates. Dates from such bons will reflect atmospheric activity at the time of exposure. Should charred bone be effectively

sealed from the atmosphere at the time of charring, but exposed some 14 time later, the C date will not necessarily indicate the date of burning. If, however, exposure occurred fjon after charring, tha date should ba a reasonable indicator of th3 event being dated.

Sons protein (Collagen) ia considered more reliable dating material.

Protein, however, decomposes udth time, and consequently, as ags increases, mora and more bone is rBquired to supply eufficient protein to provids a reliable date. Beyond 9,000 years, dating from bone protein is probably impossible. 202.

Bones for 14C dating should, as soon as exposed, be wrapped securely in heavy aluminium foil to eliminate contact with the atmosphere. Together aiith sample records, they should be sealed in strong polythene bags as describee' elsewhere. On no account should the collector remove the foil from ths bones, nor should any attempt be made to dry them in an oven. All treatment should be carried out by the Institute of Nuclear Sciences aince exposure to the atmosphere after oven-drying or oven-heating could result in ra-absorption of

atmospheric C02»

AMOUNT OF MATERIAL REQUIRED

Thaoraticaliy, twelve grains of carbon will give 22.2 litres of CO^, but in actual practice it has been found that a 12 gram sample, unless of pure carbon, will not give the theoretical yield. Ths best practice is to estimate the quantity required according to the carbon concentration of tha sample (usually estimated) and then at least double that amount of material. Fron 200 - 1,000 yaars, ths accuracy increases from about 25% error at 200 years to about 956 at 1,000 years. At 2,000 years the error is about 656. The bast results are obtained at approximately 6 - B x 10 years whan error may be as loa» as l.Bjfi for a full-sized sample. Since archaeology in HBW Zealand is more or less confined to a period of about 1,000 years, errors may be minimised by submitting sasples of adaquats size. 203. Raterial Desirable Comments Dry U/eight ____ Charcoal 25 grams Clean and of good quality Wood 50 gram9 Shell 120 grams Clean hard shell (Aragonita) Sans 800 grams Enough to cover last 1,200 years» good quality bone Fish-bone 60 grams

Other carbon-bearing materials (e.g., fern, leaves, grease, etc.)

of archaeological significance may be dated.

% PACKING SAMPLES

In 1949, when the first New Zealand archaeological samples ware

collected for radiocarbon analysis, great care was taken to ensure that fchs material did not come into contact with organic «ratter during or after collection. The samples «are removed from their stratum by means of trowel, tweezers or forceps and placed either in specially made new cans the size of which ensured the collection of adequate quantities, or were wrapped in «sveral layers of tough, heavy gauge aluminium foil (not household cooking foil). Use of thsss containers not only provided suitable protection against contamination, but facilitated the drying of samples without unnecessary exposure. Throughout, the sample remained in its original container. Immediately after the sample had dried, the container «as sealed. Containers ware permanently labelled on the site and tha samples remained in their original containers until analysis in the laboratory.

Today, such (procedure is considered unnecessary, the use of heavy- grada polythan3 bags being favoured. Mylar, flelanex and Saran are particularly suitable materials. If this method is foilowad, two bags 204.

oust bs used for each sample. The mouth of the inner bag containing the sample should b« folded over at least twice end securely stapled. It should then be adequately labelled by indelibleJ'elt pen and placed within the second bag» together with a copy of the record sheet, or a card (facing outwards) containing all necessary information. The mouth of tha bag should then be folded and stapled. On no account should paper» or other organic material be enclosed with tha sample, nor should samples be placed in glass Jars, as bottles or any other container that has held organic matter. Light, household-type plastic bags are unsuitable. A sample which requires treatment, or drying "must be removed from ita bag and as it is during this process that the risk of contamination ia greatest» it is recommended that the collector should work with only one sample at a time. If this procedure is followed, risk of mislobelling or of mixing samples will be minimised.

SAMPLE RECORDS

A record shsst must be made in triplicate for each sample ' submitted. One copy is to be securely attached to the sample package or container» one copy should be sent with the covering lettsr to the laboratory and one should be retained by the collector. All sections j of the record sheet should be completad and the atratigraphic position j sf each sample should be dearly shown either on a ¡sketch, or on a i photograph together with details of sample environment. There must i i' be a clear statement of the nature of tha research project and an estimate of the importance of a carbon date. 205.

In addition to grid numbers specific points of reference to

topographical features of reasonable prominence must be noted. For

example "Bill Smith's turnip paddock" is likely to shift, year by

year.

Whan several samples associated with the same site are submitted,

full datails should accompany each sample. The meagre statement -

"Details as for sample No. 2" urill not suffice.

Ail samples collected, u/hether submitted for analysis or not, should be adequately packed to prevent deterioration.

CONCLUSION

In final summary, it must be realised that norastter how accurate laboratory analysis may be, the archaeological value of a date is dependent upon meticulous excavation and selection of the sample, its subsequent treatment nnd the intelligent observation and interpretation of its environment.

ACKNOWLEDGMENT

The co-operation of Or T.A. Rafter and Mr R.C. WcGill is gratefully acknowledged. 206.

POSSIBLE USE OF HATUBAL WAX EXTRACTED FBOM PEATS AS A BADIOCABBON DATING MATERIAL T.L. Grant-Taylor New Zealand Geological Survey

Contamination of Radiocarbon dating materials is the most difficult of all problems facing users of the method. Various aspects have been dealt with in my previous paper. Contamination of woods, peats and soils by solution carried contaminants quite certainly affects many samples to an unknown degree. The commonly used methods of pre- treating samples as I have said before do not reliably remove contamination, and the work on charcoal recently carried out by Dr Birrell and presented at this conference adds emphasis to this. Host materials in wood, peat and soil show a great degree of chemical complexity and the composition of only a few is known. Similarities in the composition of many of the organic components of soils, peats, and woods raise doubt whether powerful reactions might not incorp- orate some of the contaminating material with the residue. The fraction that is to be used must therefore have properties sufficiently dissimilar from possible contaminants that it is readily extractable, preferably by simple solution. Possibility of Extracting Flant Waxes Over the past several months we have been examining the possibility of extracting plant waxes in solvent and using them as a dating material. Two runs have so far been carried out, using benzene. The first, on a soil gave 4-J gms of wax, the second on a peat; gave 18 gms. In the first experiment inadequate heating of solute and residue did not completely remove the solvent and apparently included some dissolved atmospheric carbon see Table. A further rutL yn Chatham Is. peat however has given an apparently satisfactory result see Table. 207.

A number of further runs have to be carried out before a final decision on the suitability of the process can be made. The method using small soxhlett extraction is unwieldy, and my thanks are given to Mr C. McGill, Institute of Nuclear Sciences who carried out the laborious extractions for the investigation. Further Work The next step will consist of runs to separate wax from a contaminated sample whose "age" lies in the 20-25,000 year range. Application If all investigations are successful there are several possible ways of using this technique. (1) direct dating of extracted wax as a routine process (2) use of wax date as a standard to develop a simple routine method of removing contaminants from the bulk carbonaceous material. (1) Providing wax can be extracted in a single pass in a soxhlett or by cold solution in a reasonably small volume of benzene it should be possible to use the extract for direct dating. The disadvantages in this procedure result from the need for large initial samples, of the order of 1-2 kilo- grams see table 1 and in poorly carbonaceous materials possibly even more. It is also a possibility that debris from some kinds of vegetation may include very little wax indeed. (2) The wax should give a material uncontaminated by material carried in water solution and therefore would permit an examination of the effectiveness of a range of chemical pretreatments. Alternative Solvents Although in this series of experiments benzene was used, hexane or some similar low boiling point solvent would probably also serve. 208.

It must be stressed that this investigation is still in its very early stages; too early yet to anticipate a fully successful conclusion, but does give some idea of an approach being used to overcome the problem of contamination. 209.

TABLE RESULTS OF EXTRACTION OF WAX FROM CARBONACEOUS MATERIALS

14« 6666 w.r.t. 0.95% Oxalic Acid % wax whole sample Air dried Air dried Oven dried Carbonaceous mud dil. wax residue residue H152/505 dried 'J NZ1208 NZ1209 NZ1210 NZ1211 0.24 -983*8% »728*11% -960*9% Wax Air dried Boiled, boiled in residue dried at Chatham Is Peat water 100°C dried at 150°C NZ1212 — - - — - w— _NZ121. -mm • — • ^5 . ••NZ121- ^ • —— - 3^r —- ^ • , - B .4¿JU/% CH/109 -992.^*2.5% -994.8*2.4% -994.6*1.8% -999.6*5|Jg 210.

THE BEPORTING OF VERY OLD RADIOCARBON DATES

K.J. Gough

When an old sample is radiocarbon dated the observed count-rate becomes close to the natural background of the equipment, and this causes certain problems in the interpretation and reporting of results. Some laboratories use a "rule of thumb11 that the maximum age that may be measured is the age which results in an expected count differing from the mean background by two standard deviations. It is normal to assume a Poisson distribution of counts, and with this assumption it may easily be shown that

where: -j- = Tj/loge2, is the mean life, M is the expected nett modern count, A 8 is the expected background, t is the counting interval. Por samples approaching this "maximum" age, it is normal to quote an expected age + an error expressed in years, corresponding to some prescribed number of standard deviations. The difficulty arises immediately because of the extreme skew of the distribution when expressed in terms of age: as an example, if a sample accumulates a count corresponding to T-o- and 2cr error limits are prescribed, w the "best guess af^he age is Tmax» minus a thousand years or so (with C ), plus infrfiftyl Quoting a minimum age only in such cases is subject to misinterpretation, since one may have to decide if there is any difference between two samples quoted at »greater than 49,000 years", and "greater than 51,000 years*. In order to circumvent such difficulties, the possibility of expressing results in a statistically complete, yet readily understandable, manner was considered and the method of conditional age distribution arrived at. 211.

If a sample of a given age T is counted, a probability distribution exists that the observed count will be any value N. A conditional probability distribution P(N/T) may thus be defined, which may include the effect of counting statistics alone, or empirical information on the actual performance of the equipment in addition. If, for the moment, it is accepted that an a priori probability density function of age may be defined, then by "Bayes Rule for the Probability of Causes"

(2) J P

where /(t) is the a priori probability density function stage, and P(N/T) is the conditional probability of a count n as previously defined. Equation (2) thus provides a method of assigning a probability to all possible ages following the observation of a given count N, provided some way of choosing«f(t) may be formulated and the integrals exist. It is important to note that equation (2) is still meaningful even when the observed count is less than the expected background! At first sight it might appear tnat in cases where no a priori information is known about a sample, that a reasonable assumption for ,f (t) would be that any age was equally likely. A little thought will show, however, that such an assumption is untenable since it has the paradoxical corollary that any given sample is almost certainly older than any finite age. The question arises as to whether it is possible to replace the upper limit in both integrals by a parameter which tends to infinity after the quotient is taken. A limit does exist in such cases but it is zero everywhere. Two different assumptions have been tested: first that the a priori distribution of age is such that the distribution of expected coun-s is uniform between the modem count and the background. This does not exclude observed counts outside this range, but insists that such events are due to the counting statistics. The assumption is equivalent to saying that any nett count is equally likely. Hence, half of the samples are expected to be younger than one he If-life, and half the remainder are in the second half-life and so on. Tfeis biasses the determination somewhat against great ages and for subjective 212.

reasons I prefer the alternative assumption which is that any age is equally likely up to a "cut-off" age of k—107 years. The difference between the two methods is insig- nificant for samples which are younger than T-^» but for older samples it does not try to 'force* a maximum age limit on *he sample. With the second assumption given above, and taking the Gaussian limit of the Poisson statistics equation (2) becomes . x Sñ-M- »>

A .A *• where If * B + 11 «xp - -~ , is the expected count of a sample of age t? and * B is the mean background M is the nett modern count V is the isotopic mean life K is the observed count and certain constant factors have been divided out. Equation £3) is simplified by the change in variable x exp S , leading to exp 2 Wr ¡Ñ) r

Equation (4) does not appear- to be integrable in tersos of finite numbers of known transcendental functions. It should be noted that the integrals differ from error functions in having the variable of integration in the denoainator of the exponent. It may be readily numerically integrated with good accuracy, however, since the singularity in the exponent of the integrand is well outside the range of integration. 213.

A computer program, described in the appendix, was written to evaluate P (T/N) and to produce graphical plots of P Versus Age. A logarithmic age scale was chosen, together with cot (jf x P^ on the ordinate so as to expand the scale at both limitsT» - o and p » 1. Figure 1 shows the effect of a variation of counting time on a sample counting 1 cpm above background. Figure 2 shows a family of curvea for results close to the background with 1,000 minute counts. The extreme skew of the distribution, previously alluded to, should be noted. Conclusions The method of conditional probability distribution provides in a straightforward and readily understandable manner all of the statistical Information which may be inferred from a single counting run on a radiocarbon sample. It may be hoped that the resulta for very old samples reported in this way might be less prone to misinterpretation than current methods. It may be wise, however, to refer to the philosoph- ical problems involved in the choice of the a priori density, Clearly the choice given above is unsuitable when 'dating* a coal sample since it leads to the 'tail* on the right hand side of the background age curve in figure 2. For samples on which no prio.? information is available, however, the above assumption is reasonable. The effect of differing assumptions is discussed in the appendix.