Mollusc shells

Spencer DW, Bacon MP, Brewer PG (1981) Models of the distribution of " b in a section across the North Equatorial Atlantic Ocean. J Mar Res 39(1) 119-137 Staubwasser M, Henderson GM, Berkman PA, Hall BL (in press) Ba, Ra, Th and U in marine mollusc shells and the potential of Ra/Ba dating of Holocene marine carbonate shells. Geochim Cosmochim... 

Ca-binding systems have not only been identified in egg shells and mollusc shells but also in mucosal cells of shell glands as well an in uterine fluid of hens. Ca-binding systems from mucosal cells and uterine fluid resemble each other, but differ in some respects from those of egg shells. 

The organic matrix of mollusc shells consists of soluble and insoluble fractions. The insoluble material is primarily hydrophobic. This is best demonstrated by the affinity of the matrix for lipoidal stains such as Sudan Black, even after thorough lipid extraction. The preponderance of aliphatic amino acids may explain this property413. ... 

Fossil glycoproteins of the soluble organic matrix are present in an 80-million year old mollusc shell from the Late Cretaceous Period. Discrete molecular weight components, as determined by gel electrophoresis, are preserved. A particular repeating amino acid sequence (—Asp—Y—) found in contemporary mollusc shell proteins was identified in fossil glycoproteins425. ... 

Krampitz, G., Engels, J., Hamm, M., Samata, T., Cazaux, C. Biochemical studies on the components of mollusc shells. In The 3rd Internat. Symp. Mechanisms of Biomineralization in the Invertebrates and Plants, Kashikojima, Japan, 8-11 Oct. 1977 Abstr. No. 16... 

Watabe, N. Crystal matrix relationship in the inner layers of mollusc shells. J. Ultrastrucrt. Res. 12, 351 (1965)... 

Weiner, S., Hood, L. Soluble protein of the organic matrix of mollusc shells A potential template for shell formation. Science 190, 987 (1975)... 

Weiner, S., Lowenstam, H. A., Hood, L. Characterization of 80-million-year old mollusc shell proteins. Proc. Nat, Acad. Sci. (Wash.) 73, 2541 (1976)... 

The amount of organic matter in skeletal material can be as low as 0.01 percent in some mollusc shells, and as high as 20 to 30 percent in vertebrate bones or teeth in a few isolated instances concentrations may go up to 90 percent. The origin, nature and function of mineralized tissues in calcification is only tentatively known. 

Keith, M. L., Anderson, G. M., and Eichler, R. Carbon and oxygen isotopic composition of mollusc shells from marine and fresh-water environments. Geochim. Cosmochim. Acta 28, 1757-1786 (1964). 

Keith, M. L., and Parker, R. H. Local variation of 13C and 180 content of mollusc shells and the relatively minor temperature effect in marginal marine environments. Mar. Geol. 3, 115-129 (1965). 

Figure 5.18. Relationship between the Sr/Ca ratio of aragonitic freshwater mollusc shells and the Sr2+/Ca2+ ratio of the water in which they grew. The distribution coefficient fitting these data has a value of 0.24. (After Speer, 1983.)...

Racemization rates (Table I) clearly differ among these seven amino acids. To compare results from the four proteins, rate constants were calculated from these data. For casein, D/L ratios were measured at 0, 1, 3, 8 and 24 hours. These results are plotted in Figure 2. The curves have two regions of different racemization rates. Rapid initial rates observable up to about 3 hours are followed by slower rates up to 24 hours. The amino acids apparently have not reached equilibrium by 24 hours of incubation. Theoretically for amino acids having one asymmetric center, the equilibrium D/L ratio is 1.0. This value has been observed in fossil bone protein (see 13) and in dry roasted proteins (10), but not in calcareous marine sediments (17) nor in fossil mollusc shell (18). 

Although the first demonstration that amino acid racemization took place in fossils used mollusc shells (23), the application of this reaction in dating these materials has been extensively investigated only recently (19,20). Work on Mercenaria (19), Chione (20), and other species (24) has tested the application of racemization dating to fossil mollusc shells from geological contexts and Indian shell middens. These and other studies have shown that there are problems with amino acid racemization dating of carbonaceous fossils which are not encountered with bone. Reversible first-order racemization kinetics which are observed in bone... 

Amino Acid Racemization Dating of Fossil Mollusc Shell... 

Amino acid racemization dating of mollusc shell has not been investigated as extensively as that of fossil bone. Recently several studies have used d/l enantiomeric ratios to resolve stratigraphic relationships (24) and to date geological deposits by the calibration procedure (19,20). Racemization dating has also been applied to midden shell from archaeological sites with limited success (20). 

Species Effects. Another problem with racemization analyses of mollusc shell is that different mollusc species taken from the same deposit can vary considerably in the extent of racemization (20, 21). The variation in alleu/iso ratios again may be attributed to different types of stmctural proteins and to differing rates of diagenetic hydrolysis of these proteins, resulting in variable proportions of free amino acids, small peptides, and protein-bound amino acids (20). 

Racemization Dating of Chione from Indian Middens. The prehistoric inhabitants of coastal southern California left abundant kitchen midden deposits marking their living sites. Mollusc shells are the major constituents found in these middens. We attempted to deduce racemization dates for shell from six archaeological sites along the coast of southern California (20). All of these sites had carbon-14 dates on shell carbonate available for comparison. 

Radiocarbon Dating of Amino Acids Extracted from Chione Shell. We attempted to resolve the question of which dating method produced more accurate shell dates by submitting amino acids extracted from Chione shell for a radiocarbon analysis (20). Because of the possibility of exchange with groundwater carbonates, the inorganic carbon in mollusc shell can be contaminated easily. We reasoned that the carbon in the amino acids would provide a more reliable age estimate than the carbon-... 

Samdal, I.A., Olseng, c.D., Sandvik, M., Miles, C.O., Briggs, L.R., Torgersen, T, and Jensen, D.J. 2006. Profile of yessotoxin analogues in a Norwegian strain of Protoceratium reticulatum. Pp. 242-247 in Proc. 5th, Inti. Conf Mollusc. Shell/. Safety, June 14—18, 2004, Galway, Ireland. Published hy Marine Institute. 

Pp. 495—501 in Proc. 5th. Inti. Conf. Mollusc. Shell/. Safety, June 14-18, 2004, Galway, Ireland. Published by Marine Institute. 

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