| The McKenzie Hill Formation (Ordovician), third from the base of the Arbuckle Group, was deposited during a Late Cambrian (Franconian) marine transgression across the Laurentian craton. The section examined represents part of a major shallowing upward trend associated with the infill of a linear "gulf " that formed as a phase in the tectonic evolution of the Southern Oklahoma aulacogen. Relatively rapid tectonic subsidence at this time created a depocenter in which over 600 m of carbonates were deposited. The beginning of this phase is marked by emergence and erosion that forms the Fort Sill - Signal Mountain Formation contact. The topmost Fort Sill Formation contains cyanobacterial (algal) boundstones of very shallow water origin; while, the Signal Mountain Formation consists of limestones that record deep water conditions. As the infill continued, limestones show increasingly shallow water facies as they pass upward into the McKenzie Hill Formation. The sections examined in this study show a lower unit that is dominated by thrombolites in complex beds up to two meters in thickness. They were deposited during a time when environmental conditions were conducive for bioherm production with thrombolitic morphologies. The topmost 23 m of the McKenzie Hill Formation, which do not contain thrombolites, are a series of bedded limestones that records a transition from deeper permanent water to more shallow settings characteristic of the Cool Creek Formation. The upper McKenzie Hill Formation contains a variety of chert most likely due to the remobilization of silica from either detrital quartz and/ or siliceous sponges. The entire Signal Mountain -- McKenzie Hill -- Cool Creek sequence records a shallowing upward trend representing a large-scale (2nd order) cycle, along with small-scale (5th order?) cycles that characterize the outcrops. |
