28 Thomas G. Thompson and Tsaihwa J. Chow ' 



mixture in their shells. The strontium-calcium atom ratios of this group were 1-94 x 

 10-3 and 1-49 X 10-^ respectively. 



Aragonite was reported only in the calcareous portions of Coelenterata (Hydrozoa 

 and Madreporaria) and Mollusca (Amphineura, Scaphopoda, Cephalopoda and 

 Nudibranchia). The strontium-calcium atom ratios of the aragonite group ranged 

 from 2-35 to 10 X 10-^. Scaphopoda and Cephalopoda which contain aragonite had 

 atom ratios of 2-35 X 10-^ and 3-74 x 10 -^ respectively. When comparisons are 

 made mineralogically among molluscs, there is demonstrated a very definite trend for 

 the occurrence of strontium, that is, aragonite Mollusca (10, 8-06, 3-74 and 2-35 X 

 10-3), aragonite-calcite mixture Mollusca (1-94 and 1-68 x 10-^) and calcite Mollusca 

 (1 -31 and 1 •2^''x lO-^). It appears logical to conclude, therefore, that marine skeletons 

 consisting of aragonite contain more strontium than those of calcite. 



The mineralogical structure of calcium carbonate in Polychaeta (Annelida) is not 

 certain. It was reported (Chave, 1954) that species of Serpula contained calcium 

 carbonate that varies from pure calcite in one specimen to pure aragonite in another. 

 The Polychaeta shown in Table I (E) had an average strontium-calcium atom ratio 

 of 5-86 X 10-3, 2^_nd thus it may be concluded that for most specimens examined, the 

 calcium carbonate is predominantly aragonite. 



The Decapoda (Arthropoda), which were found to contain an appreciable amount 

 of phosphorite as well as calcite, showed an average strontium-calcium atom ratio of 

 6-17 X 10-3. jj^jg jg jjj agreement with Odum's findings (1951 b) on the phosphate in 

 Brachiopoda, and with the statement of Kulp, et al. (1952) that the presence of 

 phosphate in the shells tends to yield a high strontium-calcium atom ratio. 



Analyses (Table II) on Globigerina ooze of the Pacific Ocean which consists mainly 

 of calcium carbonate, showed a strontium-calcium atom ratio of 1-49 X 10-3. jj^g 

 calcareous deep-sea sediments from the Indian Ocean showed an atom ratio of 

 1-94 X 10-3. xhese values are in marked contrast to those obtained by Kulp, et al. 

 (1952) but are in excellent agreement with an average value of 1-86 x 10-3 given by 

 Odum(1951 b). 



The matrix of Permian limestone deposits from Roche Harbour, Washington, 

 showed the lowest strontium-calcium atom ratio, 0-63 X 10-3, Qf ^jj materials 

 examined. This finding is comparable to the average atom ratio of 0-71 X 10-3 q^ 

 a number of limestone samples obtained by Kulp, et al. (1952) and to the value cited 

 by Rankama and Sahama (1949). The matrix of strontionite deposits from Anacortes, 

 Washington, contained 3-56% of calcium and 52-5% of strontium respectively, 

 equivalent to an atom ratio of 6,750 X 10-3. 



Most of the analyses of calcareous portions of living marine organisms showed 

 strontium-calcium atom ratios greater than those obtained on marine sediments. 

 The strontium-calcium atom ratio for these marine sediments in turn was greater 

 than those for the matrix of geologically older limestone deposits of marine origin. 

 Furthermore, calcium carbonate deposited originally as aragonite should contain 

 more strontium than that of calcite, as evidenced by analyses given above. Aragonite 

 limestones are metastable and, in geological time, eventually change into calcite 

 limestones which have a strontium-calcium atom ratio much less than that of marine 

 organisms. Thus it seems logical to conclude that the strontium content of calcareous 

 deposits decreases as the result of geological aging. 



To explain the elimination of strontium from calcareous deposits, the following is 



