A general account is given of the results of the thermoluminescence dating of objects and materials from sites in Oceania. These include potsherds from Mailu Island off the southcoast of Papua New Guinea, volcanic ash layers from near Mt Hagen in the Western Highlands of the same country, and fire hearths from ancient Aboriginal habitations at Lake Mungo, New South Wales. The differences between these results and corresponding radiocarbon ages are briefly discussed

Mortlock, A J

Australian Archaeology

Flinders Academic Commons

Australian Archaeology    Archived at Flinders University: dspace.flinders.edu.au  Full Citation Details: Mortlock, A.J. 1979. Thermoluminescence dating of objects and materials from the South Pacific region. 'Australian Archaeology', no.9, 12-17.  T H E R M O L U M I N E S C E N C E  D A T I N G  OF O B J E C T S  A N D  M A T E R I A L S  F R O M  T H E  S O U T H  P A C I F I C  R E G I O N  A ,  J .  Morttock A gene ra l  account  i s  g iven  of t h e  r e s u l t s  o f  t h e  thermo- luminescence d a t i n g  of  o b j e c t s  and m a t e r i a l s  from si tes  i n  Oceania.  These i nc lude  po t she rds  from Mailu I s l a n d  o f f  t h e  s o u t h  c o a s t  of  Papua New Guinea, v o l c a n i c  a sh  l a y e r s  from n e a r  M t  Hagen i n  t h e  Western Highlands of t h e  same c o u n t r y ,  and f i r e  h e a r t h s  from a n c i e n t  Abor ig ina l  h a b i t a t i o n s  a t  Lake Mungo, New South Wales. The d i f f e r e n c e s  between t h e s e  r e s u l t s  and corresponding radiocarbon ages  a r e  b r i e f l y  d i s c u s s e d .  h t r o d u c t i  on A thermoluminescence d a t i n g  f a c i l i t y  h a s  been i n  o p e r a t i o n  i n  t h e  Phys ics  Department a t  t h e  A u s t r a l i a n  N a t i o n a l  U n i v e r s i t y ,  Canberra,  s i n c e  about 1973. During t h e  t ime between t h e n  and now a  v a r i e t y  of  o b j e c t s  and m a t e r i a l s  have been  t e s t e d ,  main ly  from s i t e s  i n  Oceania and Southeas t  Asia .  Apar t  from r e l a t i v e l y  s t anda rd  ceramic p o t t e r y  i t  h a s  been p o s s i b l e  t o  ex t end  t h e  technique  wi th  apparent  succes s  t o  t h e  baked s a n d / s o i l  of  a n c i e n t  Abor ig ina l  f i r e  h e a r t h s  from Lake Mungo i n  New South Wales and a l s o  vo lcan ic  a sh  l a y e r s  from Papua New Guinea. It i s  t h e  purpose of t h i s  paper t o  r e p o r t  i n  a  g e n e r a l  way t h e  r e s u l t s  which have been ob ta ined  on the  samples  from t h e  s i t e s  i n  Oceania. These r e s u l t s  demonst ra te  t h e  r e l a t i v e l y  wide range  of  a p p l i c a b i l i t y  of t h e  thermoluminescence d a t i n g  t echn ique  and p o i n t  t h e  way f o r  f u r t h e r  r e sea rch  i n t o  t h e  s o u r c e s  of  v a r i a t i o n  between i t  and radiocarbon.  Pots herds from Mai l U I sl and Mailu I s l a n d  is o f f  t h e  coas t  of  Papua New Guinea s o u t h e a s t  of  P o r t  Moresby. It h a s  been f o r  many y e a r s  and i s  s t i l l  a c e n t r e  f o r  t h e  n a t i v e  product ion  of baked ceramic  p o t t e r y .  T h i s  m a t e r i a l  i s  s u i t a b l e  f o r  TL d a t i n g  u s i n g  s t a n d a r d  f i n e  g r a i n  techniques .  The e a r l y  t r a d e  p a t t e r n s  f o r  t h i s  p o t t e r y  a r e  under  i n v e s t i -  g a t i o n  by D r  G. I w i n ,  now of t h e  Department o f  Anthropology,  Archived at Flinders University: dspace.flinders.edu.auU n i v e r s i t y  of Auckland, New Zealand. Po t she rds  have been uncovered on t h i s  i s l a n d  a t  v a r i o u s  ho r i zons  below t h e  s u r f a c e .  These have been  a s s o c i a t e d  w i t h  nearby  cha rcoa l  which has  been da ted  by  H. Polach  o f  t h e  Radiocarbon Labora tory  a t  t h e  ANU. An example which shows the  r e l a t i o n  between t h e  two methods of d a t i n g  i s  a  po t she rd  recovered  from 0.8m below t h e  s u r f a c e .  The r e s u l t s  o b t a i n e d  a r e :  The 16% d i sc r epancy  between t h e  two r e s u l t s  i s  p a r t l y  due t o  t h e  l a c k  o f  samples  o f  b u r i a l  s o i l  i n  t h e  ca se  o f  t h i s  po t she rd .  When t h i s  s i t u a t i o n  a p p l i e s  i t  i s  neces sa ry  t o  assume i n  TL d a t i n g  t h a t  t h e  r a d i o a c t i v e  i m p u r i t i e s  i n  t h e  b u r i a l  s o i l  a r e  t h e  same i n  c o n c e n t r a t i o n  a s  i n  t h e  po t she rd  i t s e l f .  The r e s u l t s  h e r e  s u g g e s t  t h a t  a t  l e a s t  some of t h e s e  c o n c e n t r a t i o n s  i n  t h e  b u r i a l  s o i l  a r e  h i g h e r  t h a n  i n  t h e  po t she rd .  Volcanic ash layers from Papua New Guinea Approximately 14km n o r t h e a s t  of M t  Hagen township i n  t h e  Western H igh l ands  o f  Papua New Guinea is  a  280 h e c t a r e  p rope r ty  known a s  Kuk which is  p a r t l y  under c u l t i v a t i o n  f o r  t e a .  The a r e a  i s  d r a i n e d  swampland a s s o c i a t e d  w i t h  t h e  upper Wahgi River .  A e r i a l  pho tog raphs  show o l d  b a r e t  ( d r a inage )  systems over  v i r t u a l l y  t h e  whole swamp a r e a .  These were i n t roduced  by t h e  e a r l y  n a t i v e s  who l i v e d  i n  t h e  a r e a  t o  p r o t e c t  a  mo i s tu r e  s e n s i t i v e  crop.  The e a r l y  a g r i c u l t u r a l  h i s t o r y  of t h e  a r e a  i s  under i n v e s t i -  g a t i o n  by P r o f e s s o r  J .  Golson and o t h e r s  of t h e  Department o f  P r e h i s t o r y ,  Research  School  of P a c i f i c  S t u d i e s ,  ANU. This  h a s  been  h e l p e d  by t h e  C-14 d a t i n g  of  m a t e r i a l s  such a s  cha rcoa l ,  wood, p e a t  e t c .  found a t  v a r i o u s  ho r i zons  i n  t h e  swamp. There  a r e  a l s o  l a y e r e d  d e p o s i t s  of v o l c a n i c  a sh  i n  t h e  swamp a r e a ,  pe rhaps  2 0  i n  number, which a r e  spaced down through t h e  same sequence .  X-ray d i f f r a c t i o n  a n a l y s i s  of  powdered samples from one  o f  t h e s e  l a y e r s  shows i t  t o  b e  c l a y - l i k e  w i t h  t r a c e s  of q u a r t z ,  f e l d s p a r ,  c a l c i t e  and c h l o r i t e .  A t y p i c a l  glow curve  o b t a i n e d  u s i n g  such  a  sample is n o t  d i s s i m i l a r  t o  t h a t  found wi th  o r d i n a r y  dense  ceramic  p o t t e r y .  However, t h e  low-temperature l l O ° C  peak found w i t h  q u a r t z  could n o t  be  e x c i t e d  i n  t h i s  c a s e  s u g g e s t i n g  t h a t  t h a t  m i n e r a l  is n o t  t h e  main c o n t r i b u t o r .  Simple f a d i n g  t e s t s  c a r r i e d  o u t  on a r t i f i c i a l l y  i r r a d i a t e d  samples  from one  o f  t h e s e  l a y e r s  d i d  no t  show any s i g n i f i c a n t  e f f e c t  o f  t h i s  n a t u r e .  Furthermore p l o t s  of  t h e  r a t i o  of n a t u r a l  TL t o  n a t u r a l  p l u s  a r t i f i c i a l  TL a s  a  f u n c t i o n  of tempera ture  a r e  r ea sonab ly  f l a t  i n  t h e  r e g i o n  of  tempera ture  (37S°C) where read- o u t s  a r e  made. There  is a l s o  no ev idence  of s a t u r a t i o n  e f f e c t s  which might  be  expec t ed  w i t h  t he  o l d e r  samples.  Archived at Flinders University: dspace.flinders.edu.auDetermination of t h e  annual dose r a t e  was made us ing  a-counting f o r  U and Th and XRF f o r  K20, assuming i n i t i a l l y  a uniform environment. Monitoring f o r  evidence of non- uniformity is being c a r r i e d  ou t  with CaSOq:Dy dosimeters  mounted i n  small  s t a i n l e s s  s t e e l  capsules  embedded 30cm behind the exploratory t rench wa l l s .  A preliminary s e t  of TL d a t e s  have been computed and demonstrate a s teady inc rease  i n  apparent age a s  t h e  depth of the ash l aye r  below t h e  su r face  inc reases .  Samples a r e  a v a i l a b l e  corresponding t o  deeper ash l a y e r s  which e x t r a p o l a t i o n  i n d i c a t e s  should be o lde r  than 40,000 y BP. Pre l iminary C-14 r e s u l t s  due t o  H. Polach i n d i c a t e  t h a t  these  tend t o  f a l l  below t h e  TL d a t e s  i n  t h e  range so  f a r  explored.  However, t h e  o r d e r  of magnitude of t h e  discrepancy i s  not  i n c o n s i s t e n t  wi th  what one might expect  from t h e  well-known br i s t l e -cone  pine  c o r r e c t i o n s  necessary  t o  convert radiocarbon years  t o  t r u e  chronological  yea r s .  I t  is  poss ib le  t o  draw a smooth curve demonstrating t h e  t r end  of TL age with depth f o r  these  volcanic  ash l a y e r s .  A t  the  time of w r i t i n g  t h e  p i c t u r e  is  f a r  from complete. However, a s  the  present  measurements a r e  f i n a l i s e d  and a d d i t i o n a l  a v a i l a b l e  ash l a y e r s  a r e  measured a l s o ,  t h i s  s i t u a t i o n  w i l l  change. The preliminary ind ica t ion  i s  t h a t  vo lcan ic  a sh  l a y e r s  from t h i s  p a r t i c u l a r  s i t e  seem amenable t o  TL d a t i n g  by t h e  s t andard  f i n e  g ra in  method. It is hoped t o  carry  o u t  some conf i rmatory inclus ion measurements i n  due course and t o  i s o l a t e  t h e  mineral  responsible  f o r  t h e  major p a r t  of the  TL energy s t o r a g e .  F i r e  hearths a t  Lake Mungo, New South Wales Lake Mungo is  an ancient  d r i ed  up l ake  i n  southwestern  New South Wales. It is  approximately lOOkm n o r t h e a s t  of t h e  township of Mildura on the  Murray River,  and is one of a number of s i m i l a r  lakes  c o n s t i t u t i n g  t h e  Willandra Chain. The e a s t e r n  edge of Lake Mungo i s  composed of a long sand dune o r  l u n e t t e  c a l l e d  t h e  Walls of China. Ancient Aboriginal man l i v e d  here  many thousands of years  ago when the  lake  was f u l l ,  and a r t e f a c t s  a s s o c i a t e d  wi th  t h i s  hab i t a t ion  a r e  t o  be found i n  and on t h i s  dune. Some of these  a r t e f a c t s  have become exposed i n  r e c e n t  t i m e s  due t o  erosion caused by wind and r a i n .  Of p a r t i c u l a r  i n t e r e s t  a r e  a number of ancient  f i r e  p laces  used by t h e  Aboriginals  a s  the  baked sand / so i l  of these  seems a b l e  t o  be da ted  us ing  thermo- luminescence. There a r e  a l s o  o the r  f i r e  r e s idues  p r e s e n t  which a r e  ab le  to  be dated us ing t h e  C-14 technique.  Thus a d i r e c t  comparison between these  two methods of da t ing  becomes p o s s i b l e  a t  a time which tu rns  ou t  t o  be  30-40 x 103 y e a r s  BP. The f i r e  hea r ths  a r e  i n  t h e  form of smal l  hummocks. The reason t h e  sand/ s o i l  forms a hummock is  t h a t  the  cen t re  of the  f i r e  p l a c e  was protected t o  some ex ten t  from erosion by the  presence of cooking s tones  and because of the  hardened n a t u r e  of h e a r t h  i t s e l f .  A d iscuss ion of some of the  preliminary r e s u l t s  obta ined with measurements of t h i s  type has been given by G. Adams and Archived at Flinders University: dspace.flinders.edu.auA.J. Mortlock (1974) and A . J .  Mortlock (1974).  Then i t  seemed a s  though t h e  TL ages  and t h o s e  i n d i c a t e d  by C-14 were i n  agreement and t h a t  one  f i r e  p l a c e  (F7) was indeed 30,000 yea r s  o l d .  The t echn ique  used i n  t h e s e  TL measurements i s  known a s  f i n e  g r a i n  and makes u s e  of s m a l l  (<8pm) minera l  c r y s t a l s  der ived  from t h e  baked s a n d / s o i l  samples.  Th i s  technique ,  however, i s  no t  s p e c i f i c  t o  q u a r t z  which is  the  minera l  which is  p a r t i c u l a r l y  u s e f u l  i n  TL-dating because ,  among o t h e r  p r o p e r t i e s ,  i t  i s  v i r t u a l l y  f r e e  of f a d i n g .  I n  o t h e r  words o t h e r  minera ls  can be  p r e s e n t  which can produce TL s i g n a l s  which, because of f ad ing ,  could  confuse  t h e  p i c t u r e .  For t h i s  reason f u r t h e r  i n t e n s i v e  measurements were c a r r i e d  o u t  by T. B e l l  of t h i s  Labora tory  us ing  t h e  i nc lus ion  technique ,  where l a r g e  %100pm g r a i n s  o f  qua r t z  a r e  s epa ra t ed  ou t  magne t i ca l ly  and by  s i e v i n g  from t h e  i n i t i a l  sample m a t e r i a l .  These c r y s t a l s  were a l s o  t r e a t e d  w i t h  h y d r o f l u o r i c  a c i d  t o  remove t h e  r a d i a t i o n  dose due t o  s h o r t  range  a - p a r t i c l e s  which i s  r e s t r i c t e d  t o  t h e  nea r - su r f ace  r eg ion .  The TL glow cu rves  ob ta ined  us ing  t h e s e  samples were we l l -  behaved i n  t h e  s ense  t h a t  t h e  p l o t s  of t h e  r a t i o  of n a t u r a l  r a d i a t i o n  t o  n a t u r a l  p l u s  a r t i f i c i a l  r a d i a t i o n  dose were cons t an t  i n  t h e  h igh- tempera ture  r eg ion .  Also,  t h e r e  was no evidence o f  s a t u r a t i o n  e f f e c t s  i n  t h e  growth curves  of  TL with  r a d i a t i o n  dose.  Analys ing  t h e s e  and measur ing  the  annual  r a d i a t i o n  dose u s ing  t h e  s t a n d a r d  t echn iques  a l r e a d y  mentioned y i e l d e d  the  fo l lowing ages  (rounded) f o r  t h e  des igna t ed  f i r e  p l a c e s .  Also l i s t e d  a r e  t h e  co r r e spond ing  radiocarbon ages  r e f e r r e d  t o  by M. B a r b e t t i  and M. McElhinny (1972) - (T!5 = 5730 y ) :  F i r e  p l a c e  F6 F  7  F8 F9 TL age C-14 age 31,500 y  BP 27,000 y  BP 36,800 y  BP 31,700 y  BP 32,700 y  BP 29,200 y  BP 33,300 y  BP 28,400 y  BP It is  seen  t h a t  t h e r e  i s  a  sys t ema t i c  d i f f e r e n c e  between t h e  two e s t i m a t e s  of t h e  ages  of  t he  f i r e  h e a r t h s ,  t h e  C-14 age be ing  lower by ~5 x 1 0 ~ ~ .  T h i s  s i g n i f i c a n t  d iscrepancy may be  a s s o c i a t e d  w i t h  a  drop  i n  t h e  s t r e n g t h  of t h e  e a r t h ' s  magnetic f i e l d  a t  t h a t  t ime (M. B a r b e t t i  1972) which a l lows a  g r e a t e r  cosmic r a y  f l u x  t o  impinge upon t h e  upper atmosphere. This  i n  t u r n  l e a d s  t o  an enhancement i n  t h e  c o n c e n t r a t i o n  of C-14 i n  t h e  atmosphere r e s e r v o i r  and consequent ly  t o  an  underes t imate  of age based on t h i s  method. A d i s c u s s i o n  o f  t h i s  e f f e c t  i s  t o  be  found i n  M.J. Aitken (1975:67). F u r t h e r  i n v e s t i g a t i o n s  t o  t e s t  t h i s  hypo thes i s  a r e  i n  p rog res s  a t  t h e  t i m e  o f  w r i t i n g  u s i n g  Abor ig ina l  f i r e  h e a r t h s  from sites away from Lake Mungo and of  d i f f e r e n t  ages .  A f u l l e r  account of t h i s  work w i l l  be pub l i shed  by T .  B e l l  i n  due course.  F i n a l l y ,  i t  i s  wor th  n o t i n g  t h a t  t h e  magnitude of t h e  d i s -  c repancy found f o r  t h e  f i r e  h e a r t h s  is  c o n s i s t e n t  wi th  o t h e r  e a r l i e r  measurements. Thus measurements a t  t h e  30,000 year-old Czechoslovak f i g u r i n e  s i t e  a t  Dolni  Ves tonice  do no t  d i f f e r  from Archived at Flinders University: dspace.flinders.edu.auradiocarbon by more than 152, D.W. Zimmerman and J .  Huxtable (1971),  the  TL ages once again  being h igher .  The f i n e  g r a i n  method was used i n  t h i s  p a r t i c u l a r  i n v e s t i g a t i o n  and t h e r e  i s  no mention of fading checks having been made. I f  f ad ing  has  taken p lace ,  then t h i s  would inc rease  the  c a l c u l a t e d  TL ages  making t h e  discrepancy l a r g e r  i n  t h i s  p a r t i c u l a r  case.  Concl usions It can be seen from what has been s a i d  t h a t  t h e  technique of thermoluminescence d a t i n g  has  been a p p l i e d  wi th  apparent  success  t o  a v a r i e t y  of m a t e r i a l s  and o b j e c t s  from s i t e s  i n  Oceania. I n  t h e  cases  described i t  has  been p o s s i b l e  t o  d a t e  a s s o c i a t e d  carboniferous  ma te r i a l s  using the  o l d e r  C-14 technique.  I n  some c a s e s  the  d i f fe rence  between the  ages obta ined by t h e  two methods seems t o  be a b l e  t o  be c o r r e l a t e d  wi th  changes i n  t h e  e a r t h ' s  magnetic f i e l d  a t  t h e s e  e a r l i e r  times. Acknowledgements D r  R. Blong of Macquarie Univers i ty ,  New South Wales, brought t h e  ex i s t ence  of t h e  vo lan ic  ash l a y e r s  i n  Papua New Guinea t o  t h e  a t t e n t i o n  of the  author  and cooperated i n  recover ing samples from t h e  f i e l d .  M r  T. B e l l  is a research s tuden t  i n  t h e  Phys ics  Department a t  the  ANU, and kindly  allowed h i s  r e s u l t s  on t h e  Lake Mungo f i r e  p laces  t o  be used h e r e  p r i o r  t o  t h e i r  i n c l u s i o n  i n  h i s  PhD t h e s i s .  M r  D. P r i c e  c a r r i e d  ou t  t h e  l a b o r a t o r y  measurements i n  the  case  of t h e  vo lcan ic  a s h  l a y e r s  from Papua New Guinea and the  potsherd from Mailu I s l and .  Physics Department ANU, Canberra References Adams, G. and A.J .  Mortlock 1974 Thermoluminescent d a t i n g  of baked sand from f i r e  hea r ths  a t  Lake Mungo, New South Wales. Archaeology and Physical Anthropology i n  Oceania 9(3):236-7, 1 t a b l e  Aitken, M. 1975 Physics i n  ArchaeoZogy. Oxford: Clarendon, p.67, e t  seq.  Archived at Flinders University: dspace.flinders.edu.auBarbetti, M. 1972 Geomagnetic field behaviour between 25,000 and 35,000 years BP and its effect on atmospheric radiocarbon concentration. Proc. 8th In t .  Conf. on Radiocarbon Dating (eds T .A. Rafter and T. Grant-Taylor) , Royal Soc. New Zealand, pp.98-107 Barbetti, M. and M. McElhinny 1975 Evidence of a geomagnetic excursion 30,000 yr BP. Nature 239:327-330 Mortlock, A.J. 1974 Archaeometry at Lake Mungo, New South Wales. Australian Physicist 11 (11) : 213-5 Zimmerman, D.W. and J. Huxtable 1971 Thermoluminescent dating of Upper Paleolithic fired clay from Dolni Vestonice. Archeometry 13:53-8 Archived at Flinders University: dspace.flinders.edu.au

Thermoluminescence dating of objects and materials from the South Pacific region

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Thermoluminescence dating of objects and materials from the South Pacific region

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