ABSTRACT: Depositional Environments of the Cambro-Ordovician Rose Run Formation in N.E. Ohio and, Equivalent, Upper Sandy Member of the Gatesburg Formation in N.W. Pennsylvania
ENTERLINE, D. SCOTT, Shell Western Exploration and Production Inc., Houston, TX, and ANNABELLE FOOS, University of Akron, Akron, OH
An idealized sedimentary sequence has been developed for the Rose Run formation by describing three cores, consisting of the four facies in the following order starting with the basal facies: (1) cross-bedded sandstone facies, (2) oncolite dolomite facies, (3) bioturbated dolomite facies, and (4) algal laminated/stomatolite dolomite facies. The cross-bedded sandstone facies is characterized by low angle cross-bedded, fine to coarse grained sandstone. This sandstone is an average of 80% quartz, 12% orthoclase, 5% microline, and 1 to 2% glauconite. The heavy mineral fraction consists of tourmaline and zircon in 1 to 2% concentrations. The grains are rounded to well rounded with an average size range of 0.15 to 0.30 mm. Sedimentary structures include rip-up clasts, current ripples, herri gbone cross-bedding, and herringbone imbricate rip-up clasts.
The oncolite dolomite facies is a fine to medium crystalline dolomite with terrigenous constituents ranging from 2 to 5% and consisting of quartz and orthoclase. The oncolites are within a 1.1 m thick ooid bed. Sedimentary structures are rip-up clasts.
The bioturbated dolomite facies is a fine to medium crystalline dolomite with 8 to 15% terrigenous constituents such as quartz, orthoclase, and microcline. Bioturbation in this facies ranges from slight to well, with burrows 0.5 to 3.0 cm in diameter. Other structures observed are rip-up clasts and peloids.
The algal laminated/stomatolite dolomite facies is composed of fine crystalline dolomite with 2 to 4 cm thick laminations. Mudcracks are the only sedimentary structures observed. Terrigenous constituents are less than 5%, consisting mainly of quartz and orthoclase.
The depositional environment of the Rose Run formation is interpreted to be a tidal flat, with migrating tidal channels. The algal laminated/stromatolite dolomite facies represents an upper intertidal to supratidal environment. The bioturbated dolomite facies represents a lower intertidal to subtidal environment. A subtidal environment is indicated by the oncolite dolomite facies. The cross-bedded sandstone facies represents the tidal channel that migrates across the previously mentioned facies.
In the cross-bedded sandstone facies, there is secondary moldic porosity plus minor amounts of intercrystalline porosity. Orthoclase dissolution creates the secondary moldic porosity. Most of the primary porosity is destroyed as a result of quartz and feldspar overgrowths, along with dolomite cementation. Residual oil is present between the faces of these overgrowths which demonstrates the timing of the migration.
AAPG Search and Discovery Article #91013©1992 AAPG Eastern Section Meeting, Champaign, Illinois, September 20-22, 1992 (2009)