Cyclic sedimentation patterns in Middle Ordovician Trenton group in central Pennsylvania

Conference · Sat Dec 01 00:00:00 EST 1984 · Am. Assoc. Pet. Geol., Bull.; (United States)

OSTI ID:5851343

Gardiner, M A

The carbonate facies of the Middle Ordovician Trenton Group show repetitive sequences of micrite, bioclastic limestone, and siliciclastic shale. Five repetitive patterns based on sedimentologic and paleontologic data are present (in ascending order): 1) biosparite, 2) intrabiosparite, 3) pelsparite, 4) micrite, 5) alternating micrite and shale. The biosparite is of peritidal origin and is overlain by a stromatolitic cap. The average sequence thickness is 30-40 cm (12-16 in.). The intrabiosparite is a fining-upward sequence that grades to pelsparite with a micrite cap (total thickness averages 16 cm or 6 in.). This sequence is indicative of intershoal or shoaling conditions. Overlying the intrabiosparite sequence in pelsparite grading into a micrite cap. The pelsparite averages 8 cm (3 in.) in thickness, and is of shallow sublittoral origin. Highly burrowed micrite (2-6 cm or 0.8-2.4 in. thick), with a hardground cap, indicates periodic exposure. The upper unit is a deeper, sublittoral sequence of alternating kerogenic micrite and siliciclastic shale, ranging in thickness from 20 to 90 cm (7.9 to 35.4 in.). This pattern indicates a deepening of the carbonate shelf into a deeper, anoxic basin below wave base. These sequences are a result of storm deposition as indicated by shell and intraclast lags, by fining-upward trends, and by abrupt contacts between individual sequences. The series of sequences is a result of the decreasing effects of these storms in the deeper water facies.

• Research Organization: Univ. of Delaware, Newark
• OSTI ID: 5851343
• Report Number(s): CONF-8410269-
• Journal Information: Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 68:12; Conference: AAPG Eastern Section meeting, Pittsburgh, PA, USA, 10 Oct 1984
• Country of Publication: United States
• Language: English

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