Diagenesis of skeletal and nonskeletal components of Mid-Cretaceous limestones

Journal Article · Fri Jan 01 00:00:00 EST 1993 · Journal of Sedimentary Petrology; (United States)

OSTI ID:6373053

Woo, Kyungsik; Anderson, T F; Sandberg, P A ^[1]

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1. Univ. of Illinois, Urbana (United States)

Skeletal and nonskeletal components from Mid-Cretaceous limestones have been investigated using coordinated textural, isotopic, and chemical methods to delineate the conditions under which they formed or were altered. The degree of alteration was determined by means of cathodoluminescence, light microscopy, and scanning electron microscopy, along with inferences from isotopic and chemical compositions. Oxygen isotopic values of non-luminescent parts of most bivalves of radiaxial fibrous calcite appear to reflect isotopic equilibrium with contemporaneous Mid-Cretaceous surface seawater. In contrast, oxygen isotopic compositions of non-luminescent, texturally unaltered calcite outer layers of rudists and the calcitic shells of some oysters are significantly lower than luminescent, altered portions of the same specimens of equant calcite cements within skeletal molds. This apparent isotopic reversal suggests that vital effects are involved in the secretion of skeletal calcite in rudists and some oysters. All the radiaxial fibrous calcite (RFC) cements analyzed contain less than 1 mole % MgCO[sub 3]. Retention of a primary marine [delta][sup 18]O signature and the absence of microdolomite inclusions within well-preserved RFC suggest that this cement precipitated as primary low-Mg calcite cements. Isotopic and chemical contents of calcitized skeletons, together with coexisting equant calcite cements indicate that the sediments were mostly stabilized during meteoric-phreatic diagenesis and that effects of deep-burial diagenesis were negligible. The similarity of isotopic and chemical trends in those calcitized skeletons and the equant cements suggests that the skeletons were altered by fluids in a diagenetic system which was open with respect to [sup 18]O, Sr, and Mg, but closed with respect to [sup 13]C, Fe, and Mn.

• OSTI ID: 6373053
• Journal Information: Journal of Sedimentary Petrology; (United States), Vol. 63:1; ISSN 0022-4472
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
LIMESTONE
DIAGENESIS
GEOCHEMISTRY
CALCITE
CATHODOLUMINESCENCE
CHEMICAL COMPOSITION
COMPARATIVE EVALUATIONS
CRETACEOUS PERIOD
DEPOSITION
GEOLOGIC HISTORY
ISOTOPE RATIO
MOLLUSCS
OXYGEN ISOTOPES
SCANNING ELECTRON MICROSCOPY
SEAWATER
ANIMALS
AQUATIC ORGANISMS
CARBONATE MINERALS
CARBONATE ROCKS
CHEMISTRY
ELECTRON MICROSCOPY
EVALUATION
GEOLOGIC AGES
HYDROGEN COMPOUNDS
INVERTEBRATES
ISOTOPES
LUMINESCENCE
MESOZOIC ERA
MICROSCOPY
MINERALS
OXYGEN COMPOUNDS
ROCKS
SEDIMENTARY ROCKS
WATER
580000* - Geosciences