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Titolo:
TAPHONOMIC AND SEDIMENTOLOGIC IMPLICATIONS OF CRINOID INTRASKELETAL POROSITY
Autore:
SAVARESE M; DODD JR; LANE NG;
Indirizzi:
INDIANA UNIV,DEPT GEOL SCI BLOOMINGTON IN 47405
Titolo Testata:
Lethaia
fascicolo: 2, volume: 29, anno: 1996,
pagine: 141 - 156
SICI:
0024-1164(1996)29:2<141:TASIOC>2.0.ZU;2-Y
Fonte:
ISI
Lingua:
ENG
Soggetto:
PLANKTONIC-FORAMINIFERA; UNIDIRECTIONAL CURRENTS; SETTLING VELOCITIES; SHAPE; ENTRAINMENT; THRESHOLD; DENSITY; SHELLS; GRAINS; MOTION;
Keywords:
TAPHONOMY; PALEOECOLOGY; HYDRODYNAMIC BEHAVIOR; CRINOID COLUMNALS;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Science Citation Index Expanded
Citazioni:
60
Recensione:
Indirizzi per estratti:
Citazione:
M. Savarese et al., "TAPHONOMIC AND SEDIMENTOLOGIC IMPLICATIONS OF CRINOID INTRASKELETAL POROSITY", Lethaia, 29(2), 1996, pp. 141-156

Abstract

The porous texture of crinoid columnals has a number of implications:(1) After soft tissue decays, the originally articulated skeleton of the crinoid falls apart. (2) The porous ossicles become part of the sediment, but they will behave hydrodynamically like much smaller solid mineral grains. (3) Because of their hydrodynamic behavior, crinoid plates should be transported away from their life habitat with relative ease. (4) The porous skeleton should act as a 'sponge' during diagenesis and serve as the site of deposition of diagenetic minerals. Porosity and specific gravity of columnals from five species of modern, deep-sea crinoids and from as many as seven form-species of Carboniferous crinoids were determined from either back-scatter images from an electron probe or from the volume and mass of individual columnals (extant species only). These approaches give porosity values of 52-72% for modern crinoids and 39-69% for fossil crinoids. This corresponds to net specific gravities of 1.47-1.83 for modern columnals and 1.54-2.10 for fossils (solid calcite has a specific gravity of 2.72). In order to compare hydrodynamic behavior of crinoid plates with more dense mineral grains, settling rates and flume entrainment thresholds were determinedfor columnals of the five modern species. Columnals have settling rates and entrainment thresholds equivalent to quartz spheres with diameters less than a tenth of the diameter of the columnal (measured as largest dimension). A columnal's unit immersed mass (UIM: effective mass,a function of specific gravity, divided by the projected area of the columnal) correlates fairly well with settling and entrainment velocities; however, columnal shape significantly influences behavior. Grain-size data from cross-bedded, crinoid-bearing grainstones and quartz arenites show this differential behavior between crinoid and other grains. If intraskeletal cementation predates burial, a columnal's specificgravity would be increased, affecting its hydrodynamic behavior. Therefore, both the timing of organic decay and diagenetic filling of porosity relative to final burial should influence the transport history of a columnal.

ASDD Area Sistemi Dipartimentali e Documentali, Università di Bologna, Catalogo delle riviste ed altri periodici
Documento generato il 03/12/20 alle ore 16:02:59