Dating Cremated bone

by J.N. Lanting & A.L. Brindley

The collagen in bone contains poorly crystallised inorganic material, primarily calcium phosphate ('Bio-apatite') This bio-apatite contains a certain amount of carbonate (0.5-1.0%), substituting phosphate in the crystal lattice. This structural carbonate originates in blood bicarbonate and therefore is directly related to the food the person or animal has eaten. The use of structural bicarbonate in palaeo-dietary studies has resulted in the development of methods of collecting it from the bio-apatite and separating it from 'absorbed' carbonate (from the surrounding soil ) in archaeological bones. Structural carbonate has also been used for radiocarbon dating unburnt bone on a limited scale.

Previously, all attempts to date cremated bone had failed because radiocarbon laboratories have treated cremated bone in the same way as burnt bone. Burnt bone is heated to 200-3000C, contains carbonised fats and proteins and is grey or black inside. Cremated bone has been heated at temperatures above 6000C, contains no carbonised material and is white throughout. During the process of burning at temperatures above 6000C the bio-apatite recrystallises and larger and better structured crystals are formed. This is one of the reasons why cremated bones survive, even in acid soil. At the same time however a certain amount of the structural carbonate disappears. We considered it unlikely that all of the structural carbonate would disappear and asked the Groningen laboratory to date the structural carbonate from a number of prehistoric cremations. These cremations had been previously dated using charcoal found amongst the cremated bones, so it was possible to check the results.

The cremations did indeed still contain sufficient structural carbonate for dating by AMS, although in some cases not more than 0.1%. The results of the tests are given in the table below:

 

Site

Ref

Age

(carbonate)

Age

(charcoal)

Anlo-Molenes

GrA-11256

2970+40

2945+35

Hijkeres

GrA-11259

1160+50

1720+30

Oudemolen

GrA-11263

2460+50

2345+35

Rolde

GrA-11264

3840+50

3850*(estimate)

Vledder 271

GrA-11666

2750+40

2800* " "

Vledder 296f

GrA-11667

2930+40

2900* " "

Eext 1952

GrA-11675

2760+50

(S)

2785+35

GrA-18876

2670+50

(F)

Waspe 58

GrA-11669

2540+40

(S)

2580+40

GrA-11671

2530+40

(F)

 

 No more than 1.5-2.0g of cremated bone are required for dating, and small fragments (F), including porous bone, can be used instead of larger fragments (S), of solid bone.

It may be assumed that the 'own-age' of structural carbonate is low, and of the same order of magnitude as the own-age of bone collagen, namely 15-20 years at the most.

Further tests on dating unburnt bone using structural carbonate and comparing to dates already found by dating the bone collagen were carried out with excellent results. However it is not yet certain that carbonate in unburnt bone will be a useful substitute for collagen in all cases and more work has to be done.

In theory structural carbonate has advantages over collagen. Collagen has its origin in the proteins in the food and when diets contain considerable amounts of marine or freshwater fish, the collagen dates will be too old. Structural carbonate has it's origins in the whole diet, thus also in carbohydrates and fats which in a normal diet are the principal energy sources. Structural carbonate should therefore produce more reliable dates.

 

Dating structural carbonate in cremated bone is commercially available at the Groningen radiocarbon laboratory. The cost is 700 Dutch guilders+17.5% VAT per sample.

Contact: Dr. J. Van der Plicht at the Centre for Isotope Research, Nijenborgh 4, 9747 AG Groningen, Netherlands.

Telephone (50) 3634738, Fax (50) 3634738