Geological Survey Professional Paper Volume 871 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. Excerpt: ...formed an important but varying part of the CO2 reservoir, in addition to the normal atmospherederived ocean water bicarbonate. Keith and Parker (1965) found that the 5C13 of mollusk shells growing in marginal marine environments was dependent upon the accessibility of continental (land plant-derived) carbon, and that the 5C13 values of the samples approached the marine values as the sampling sites progressed from estuarine to marginal bays. The samples from marginal bays also show a variable 5C13, which Keith and Parker (1965, p. 127) attribute to "variable effects due to locally-produced CO2 from decompositon of organic detritus, both continental and marine (Landegren, 1954) and from respiration of aquatic plants. Development of a local C13 deficiency by aquatic plants in waters with restricted circulation is consistent with observations by Wickman (1952)." That the covering beds contained organic matter is shown by the rich fauna (trilobites and particularly brachiopods). The decomposition of the soft parts probably contributed light CO2 to the pore water. Restricted circulation resulted in some of this CO2 being incorporated into the shells of organisms living in this environment. In the mudmound the similarity of 5C13 between the calcilutite and the coarse calcite indicates either that both formed from the same well-mixed, large carbon reservoir, or that one formed from this reservoir and the other formed by recrystallization of the first-formed material without a significant admixture of carbon from decomposing organic matter. The cause of this recrystallization can be found in the greater solubility of the fine particles as compared to the coarse spar crystals. The large surface area of the calcilutite particles results in greater surface energy...