Examples of post-mortality alteration in Recent brachiopod shells and (paleo)ecological consequences

Autor: C. C. Emig
Rok vydání: 1990
Předmět:
Zdroj: Marine Biology. 104:233-238
ISSN: 1432-1793
0025-3162
DOI: 10.1007/bf01313263
Popis: Post-mortality alteration of brachiopod shells under normal environmental conditions leads to high taphonomic loss, and to a poor contribution to the biodetrital soft sediment. The successive stages of alteration which shells undergo are: (bio)degradation of the organic matrix → shell softening → structural disaggregation or/and mechanical fragmentation; these processes depend on the shell structure (number of layers) and composition (organic and inorganic components), but very little on environmental conditions, except for the dissolution of inorganic shell constituents. Among the Brachiopoda, three types of alteration occur to different types of shells — Type I: two-layered chitino-phosphatic shell (species ofLingula andGlottidia) displays a rapid degradation of the organic matrix and mechanical abrasion, leading to total disappearance of the shell in 2 to 3 wk; Type II: two-layered carbonate shell, e.g.Terebratulina spp. [but notNotosaria nigricans (Sowerby) which may constitute a fourth shell type], exhibits degradation of the organic matrix of the secondary layer, shell softening, and structural disaggregation leading to shell disintegration in 6 to 7 mo with a concomitant contribution of calcitic microfibres to the sediment; Type III: three-layered carbonate shell, e.g.Gryphus vitreus (Born), undergoes organic degradation of the secondary layer, fragmentation of the anterior two-thirds of the shell, and slow degradation (because of the thick tertiary layer) of the posterior portion of the shell, with dissolution of the inorganic components (mainly in the tertiary layer) which make a relatively minor contribution to the sediment.
Databáze: OpenAIRE
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