The Miocene phosphogenic episode on the Florida platform: Implications for the positive. delta. sup 13 C excursion

Conference · Tue May 01 00:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6720493

Compton, J S ^[1]; Snyder, S W ^[2]

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1. Univ. of South Florida, St. Petersburg (USA)
2. North Carolina State Univ., Raleigh (USA)

The authors propose that deposition and later alteration of the enormous phosphorite deposits of the southeastern US best explain the Miocene {delta}{sup 13}C excursion. The positive {delta}{sup 13}C shift in the early to early middle Miocene resulted from increased organic carbon burial rates when transgressive seas flooded the Florida platform and forced the Gulf Stream to migrate landward. Gulf Stream flow around topographic highs produced upwelling of P-rich water capable of sustaining high surface productivity. Organic carbon burial lowered P{sub CO{sub 2}} and eventually resulted in global cooling (reverse greenhouse effect). Cooling intensified oceanic circulation (coastal and equatorial upwelling), increased ice volume, and lowered eustatic sea level. The overall decrease in sea level exposed shallow-water shelf sediments to subaerial and supergene weathering. Most of the buried early Miocene organic matter was oxidized and caused {delta}{sup 13}C to shift back to its preexcursion level by the middle Miocene. Meteoric alteration removed organic matter and oxidized pyrite, but much of the diagenetic phosphorite, dolomite, and silica remained. The greenhouse effect from increased P{sub CO{sub 2}} eventually led to a marked slowdown in cooling and ice buildup as reflected in the slope of the global {delta}{sup 18}O curve. Available age dates for the organic-rich phosphatic member of the Monterey Formation suggest it was deposited after the maximum {delta}{sup 13}C positive shift. Oxidation of large amounts of organic carbon on the Florida platform may have lowered atmospheric O{sub 2} and enhanced organic matter preservation in deep-water basins of the circum Pacific during the middle Miocene.

• OSTI ID: 6720493
• Report Number(s): CONF-900605-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
FLORIDA
PHOSPHORITES
DEPOSITION
CARBON 13
CARBON DIOXIDE
GEOLOGIC HISTORY
OXYGEN 18
SEA LEVEL
SEDIMENTARY BASINS
TERTIARY PERIOD
CARBON COMPOUNDS
CARBON ISOTOPES
CARBON OXIDES
CENOZOIC ERA
CHALCOGENIDES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
FEDERAL REGION IV
GEOLOGIC AGES
GEOLOGIC STRUCTURES
ISOTOPES
LEVELS
LIGHT NUCLEI
NORTH AMERICA
NUCLEI
OXIDES
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PHOSPHATE ROCKS
ROCKS
SEDIMENTARY ROCKS
STABLE ISOTOPES
USA
580000* - Geosciences