Reverse weathering, the carbonate-feldspar system, and porosity evolution during burial of sandstones

Conference · Fri Mar 01 00:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:7013177

Milliken, K L; Land, L S ^[1]

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1. Univ. of Texas, Austin (United States)

Acid generated by reverse weathering in mudrocks drives linked reactions involving carbonates and feldspars that in turn have a profound impact on the evolution of porosity during burial diagenesis of sandstones. In the Oligocene Frio Formation along the Texas Gulf Coast, petrographic evidence at various scales in both sandstones and shales, and modern pore fluid compositions are all consistent with this idea. Acid released during illitization of smectite dissolves marine skeletal and detrital carbonate in shales. Shales export excess H+, dissolved CA++, and CO{sub 2} to the sandstones. Resultant interaction of sandstones with these shale-derived fluids is primarily controlled by the feldspar content of the sandstones. If the sandstones contain reactive feldspar content of the sandstones. If the sandstones contain reactive feldspar, acid from the shales is effectively buffered, thus allowing precipitation of calcite as cements and grain replacements in the sandstones and maintenance of fluids with low pCO{sub 2}. Once the supply of reactive detrital feldspar is exhausted through dissolution and albitization, shale-derived H+ remobilizes carbonate in sandstones, generating secondary porosity and fluids with high pCO{sub 2}. Acid generated through thermal maturation of organic matter plays only a trivial role in this system of reactions because the quantity of acid required for dissolution of carbonate and feldspar far exceeds the amount of kerogen in the system. The balance between the local acid generation capacity of shales, the local buffering capacity of feldspars in sandstones, and the availability of externally derived acids and ions is the primary control on the sequence of reactions occurring during burial metamorphism of sandstones.

• OSTI ID: 7013177
• Report Number(s): CONF-910403-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
INTERSTITIAL WATER
ROCK-FLUID INTERACTIONS
WATER CHEMISTRY
SANDSTONES
DIAGENESIS
WEATHERING
ACID NEUTRALIZING CAPACITY
CARBONATE MINERALS
CEMENTS
CHEMICAL REACTION KINETICS
DISSOLUTION
DISSOLVED GASES
FELDSPARS
GEOLOGIC FORMATIONS
PARTIAL PRESSURE
PETROGRAPHY
PH VALUE
POROSITY
TERTIARY PERIOD
TEXAS
BUILDING MATERIALS
CENOZOIC ERA
CHEMISTRY
DEVELOPED COUNTRIES
FEDERAL REGION VI
FLUIDS
GASES
GEOLOGIC AGES
GROUND WATER
HYDROGEN COMPOUNDS
KINETICS
MATERIALS
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
REACTION KINETICS
ROCKS
SEDIMENTARY ROCKS
SILICATE MINERALS
SOLUTES
USA
WATER
580000* - Geosciences