Diagenesis of Middle to Upper Devonian Catskill Facies Sandstones in Southeastern New York
Peter E. Gale, Raymond Siever
Middle to Upper Devonian Catskill facies sandstones exposed in southeastern New York form part of a regressive alluvial plain sequence, 1.5 km thick, deposited in a foreland basin as a result of the Middle Devonian Acadian orogeny. Petrologically, most Catskill sandstones are litharenites whose detrital composition was important in determining the course of diagenesis. Foliated metamorphic rock fragments, sedimentary rock fragments, monocrystalline quartz, and polycrystalline quartz volumetrically comprise 80% or more of the Catskill sandstones. Metamorphic rock fragments are by far the most important rock fragment type. Both sandstone grain size and the modal percentages of monocrystalline and polycrystalline quartz increased stratigraphically upsection in the facies. These two trends reflect progradation and a possible change in sandstone provenance during Catskill facies deposition.
Point counting using cathodoluminescence petrography demonstrated that these sandstones are characterized by abundant pseudomatrix. Ductile-grain deformation and alteration of metamorphic and sedimentary rock fragments contributed heavily to the formation of pseudomatrix. Compaction and chemical diagenesis have effectively reduced Catskill sandstone porosity to irreducible levels. Porosity ranges from 7.1 to 0.9%, whereas permeability ranges from 0.06 to less than 0.001 md (unstressed measurements). Much of the porosity is present as microporosity. Chemical diagenetic events recognized in the Catskill sandstones include (listed in general paragenetic order): (1) authigenic quartz overgrowths; (2) chlorite and illite clay recrystallization, replacement, and pore filling; (3) calcite re lacement; (4) dolomite pore filling/replacement; and (5) secondary porosity formation and kaolinite replacement/pore filling. Compactional diagenetic processes recognized include (listed in general paragenetic order): (1) brittle-grain deformation (fracturing); (2) intergranular pressure solution; and (3) ductile-grain deformation.
Textural evidence suggests that much of the authigenic quartz precipitation preceded extensive sandstone compaction. The timing of the paragenetic sequence appears to be related to the early diagenetic infiltration of meteoric waters, continued subsidence and deep burial during the late Paleozoic, and uplift and erosion after the Allegheny orogeny.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.