Reference Section and Type Localities
Ulrich (1911) first used the term “Bromide” for a unit that lay unconformably below the “Viola Limestone” (Fig. 2), but did not propose any type locality or section. Edson (1927) later designated the McLish Ranch, near the town of Bromide, Coal County, Oklahoma as the type locality for the formation. This locality was not accessible for this study (see Fay et al. 1982b, section 5, p. 343). Cooper (1956) divided the Bromide into the Mountain Lake and overlying Pooleville members, with type sections at the Johnston Ranch (DRa here). He defined the Mountain Lake as including the basal fine-grained quartz arenite sandstone, overlying interbeddedillitic-chloritic shale and sandstone, and an uppermost limestone and shale sequence at the top (Fay and Graffham 1982). The Pooleville comprised limestones (occasionally interbedded with calcareous shales and marls) that overlie the Mountain Lake at the type locality. Unfortunately, Cooper's definition of these members was vague and our new analysis shows that they have been miscorrelated away from the type section in subsequent work (e.g., Longman 1976; Fay et al. 1982). What has been called "Pooleville" up-ramp is not the same stratigraphic interval down-ramp. To stabilize nomenclature, we designate a complete, readily accessible section along I35 (I35N) as a reference section, which is a composite of excellent exposures at the east and west sides of the road cut and in the median. At this section, Mountain Lake and Pooleville have been identified consistently in previous work (e.g., Bauer 1994; Williams and Siveter 1996.) as units of sandstone, shale and carbonate and entirely carbonate, respectively. Revising the members at the reference section necessitates restriction of the type Pooleville to massive and nodular limestone without shale near the top of the succession; the remainder of the type Poolville is lithologically similar to, and correlative with, the upper Mountain Lake Member of the reference section. The reference section is near the hinge of the SOA, and provides an excellent framework for correlation of both up-ramp and down-ramp sections. Furthermore, the completeness and preservation is such that it serves as an ideal “model” to characterize both meter-scale and higher rank sequences.
Pontotoc Member Designation
In his original definition of the Mountain Lake, Cooper (1956) did not place the lower sandstones in the member, though Fay and Graffham (1982) suggested they should be included in the unit. Our new designation is necessary to separate the primarily sandstone and siltstone unit from the largely limestone and marl succession in the Mountain Lake. Moreover, the discovery of a significant mineralized transgressive surface (RC) at the top of the sandstone sequence suggests they are temporal units, and indeed are traceable from the Arbuckle Platform into the deepest part of the SOA. In the absence of the transgressive surface, the rather abrupt transition from predominantly sandstone to limestone lithofacies is the criterion for recognition of the Pontotoc Member. This change is evident across most of the study area, though the extremely upramp successions (HWY99) still deposit sandstone and siltone into the lower Mountain Lake. Two facies (F3 and F5) are present in the new formal unit.