Origin of dolomite in the phosphatic Hawthorne Group of Florida

Journal Article · Fri Jul 01 04:00:00 EDT 1994 · Journal of Sedimentary Research - Section A; (United States)

OSTI ID:6954705

Compton, J S; Hall, D L; Mallinson, D J ^[1]; Hodell, D A ^[2]

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1. Univ. of South Florida, St. Petersburg, FL (United States). Dept. of Marine Science
2. Univ. of Florida, Gainesville, FL (United States). Dept. of Geology

In addition to large amounts of phosphorite, the Miocene Hawthorn Group of Florida contains abundant dolomite. Dolomite is present as disseminated silt-size rhombs, as friable dolosilt beds, and as pore-filling cement in dolostone beds and clasts. The dolomite formed during early burial diagenesis both in the sulfate-reduction zone, overlapping and extending below sediment depths of phosphorite formation, and in adjacent, nonphosphatic, shallow-water lagoonal environments. Much of the dolomite is closely associated with the fibrous, Mg-rich clay minerals palygorskite and sepiolite. The percent carbonate in the Hawthorn Group increases from north to south; the dominant carbonate mineral in north Florida is dolomite, whereas dolomite and calcite are both abundant in south Florida. The [delta][sup 13]C values of the dolomite, from +1.82 to [minus]6.21[per thousand] PDB, suggest that metastable biogenic carbonate (aragonite and high-Mg calcite) and seawater were the predominant sources of carbonate. However, negative [delta][sup 13]C values of dolomite from northeast Florida suggest that as much as 30--40% of the carbonate was derived from degradation of organic matter. Degradation of organic matter enhanced dolomitization by removing sulfate ion and increasing the carbonate alkalinity of the pore waters. The oxygen and strontium isotopic values along with moderate Na contents indicate a marine origin. Evaporation of seawater or mixing of seawater and meteoric water were apparently not major factors in dolomite formation. The presence of dolomite, along with phosphorite, in reworked sequences can indicate deposition of organic-rich sediments from which most of the organic matter has since been removed.

• OSTI ID: 6954705
• Journal Information: Journal of Sedimentary Research - Section A; (United States), Journal Name: Journal of Sedimentary Research - Section A; (United States) Vol. 64:3; ISSN XZ288H
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
CARBONATE MINERALS
CHEMISTRY
DEVELOPED COUNTRIES
DIAGENESIS
DOLOMITE
FLORIDA
GEOCHEMISTRY
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
ISOTOPE DATING
MINERALOGY
MINERALS
NORTH AMERICA
ORIGIN
USA