Geochemistry of metastable carbonate minerals from the Brush Creek marine interval (Missourian), Indiana County, Pennsylvania

Conference · Thu Aug 01 00:00:00 EDT 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5695970

Cercone, K R; Kime, A; Mutchler, S; Rittle, K ^[1]

---

1. Indiana Univ., PA (United States)

Many marine fossils from the Missourian Brush Creek interval of western Pennsylvania display partial preservation of metastable aragonite and high-magnesium calcite shell material. Bivalve mollusks have been shown by x-ray diffraction to contain as much as 96% aragonite, with lesser amounts of both high-magnesium and low-magnesium calcite. Stable carbon and oxygen isotopic ratios from these bivalves suggest they precipitated in equilibrium with Pennsylvanian ocean water. The bellerophontid Pharkidonotus, which exhibits partial recrystallization textures under scanning electron microscopy, consists of 45% aragonite and 55% low-magnesium calcite, and has slightly more depleted isotopic values than bivalves. Crinoids also appear to have been partially recrystallized, resulting in a mixture of primary high-magnesium calcite and secondary low-magnesium calcite and microdolomite, with much of the original shell structure still preserved. The degree of preservation of metastable carbonate minerals varies both stratigraphically and spatially within the Brush Creek interval. Maximum preservation occurs in organic-rich shales deposited in low-lying areas of the Brush Creek sea floor. The preservation of aragonite and high-magnesium calcite in such units may have resulted from a lack of circulating porewater during early diagenesis.

• OSTI ID: 5695970
• Report Number(s): CONF-9109238-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:8; Conference: American Association of Petroleum Geologists (AAPG) eastern section meeting, Pittsburgh, PA (United States), 8-10 Sep 1991; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ARAGONITE
GEOCHEMISTRY
CALCITE
DOLOMITE
DIAGENESIS
EQUILIBRIUM
FOSSILS
GEOLOGIC FORMATIONS
ISOTOPE RATIO
MOLLUSCS
PENNSYLVANIA
RECRYSTALLIZATION
STABILITY
ANIMALS
AQUATIC ORGANISMS
CARBONATE MINERALS
CHEMISTRY
DEVELOPED COUNTRIES
INVERTEBRATES
MINERALS
NORTH AMERICA
USA
580000* - Geosciences