Petrography, geochemistry, and origin of burial diagenetic facies, Siluro-Devonian Helderberg Group (carbonate rocks), central Appalachians

Journal Article · Fri May 01 04:00:00 EDT 1987 · AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States)

OSTI ID:6455626

Dorobek, S L

Petrographic and geochemical studies of pore-filling cements and replacement products in the Helderberg Group (Upper Silurian-Lower Devonian, central Appalachians) document the diagenetic history of these rocks. Shallow-ramp skeletal limestones and buildups were partially lithified by marine cements. However, most porefilling cement formed under shallow (< 300 m) to deep burial (300-4000 m) conditions. Regional cathodoluminescent zonation patterns in early, calcite cements indicate meteoric ground waters were involved in shallow burial cementatoin. Early zoned calcite cements consist of updip nonluminescent cements with thin luminescent laminae in limestone or sandstone, that pass downdip into subzoned dull cements (interlayered bright and dull laminae), and then into nonzoned dull cement in basinward limestone. The regional distribution, stable isotopic compositions, and timing of early zoned cements relative to other diagenetic events suggest that all of the early cements formed synchronously from meteoric ground waters that became progressively more reducing as they flowed downdip (at least 150 km). Helderberg sandstone tongues probably were preferential conduits for meteoric ground waters because early calcite cements formed only on scattered skeletal grains in sandstones. Late, void-filling dull cement formed from deep burial pore fluids at burial depths of 300 to 4000 m. Deep burial pore fluids were dilute to saline Na-Ca-Cl brines (from primary fluid inclusion data) with stable isotopic compositions that probably were similar to isotopic compositions of formation waters from modern oil fields. Void-filling dull calcite cements occluded nearly all remaining porosity before late Paleozoic fracturing and deformation. Latest diagenetic phases include dolomite, fluorite, silica, and fracture-filling dull calcite. 19 figures, 2 tables.

• Research Organization: Virginia Polytechnic Institute and State Univ., Blacksburg
• OSTI ID: 6455626
• Journal Information: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States), Journal Name: AAPG (Am. Assoc. Pet. Geol.) Bull.; (United States) Vol. 71:5; ISSN AABUD
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
020200* -- Petroleum-- Reserves
Geology
&amp; Exploration
ALKALINE EARTH METAL COMPOUNDS
APPALACHIAN MOUNTAINS
BRINES
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATE ROCKS
CARBONATES
CHEMISTRY
DEVONIAN PERIOD
DIAGENESIS
DOLOMITE
GEOCHEMISTRY
GEOLOGIC AGES
MAGNESIUM CARBONATES
MAGNESIUM COMPOUNDS
MINERALS
MOUNTAINS
OXYGEN COMPOUNDS
PALEOZOIC ERA
PETROGRAPHY
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SILURIAN PERIOD