THE CAMBRO - ORDOVICIAN SIGNAL MOUNTAIN FORMATION - AN ARBUCKLE GROUP ENIGMA

The Signal Mountain Formation (SMF), second oldest Formation in the Cambro-Ordovician Arbuckle Group of Oklahoma, rests unconformably on the Fort Sill Formation, the unconformity recording a craton-wide regression. Subsequent transgression coincided with rapid redefinition of the Southern Oklahoma aulacogen as a discrete linear deeper water “gulf” within the Laurentian carbonate platform. Lithologies include bioturbated and poorly sorted intrapelbiomicrites, poorly sorted biosparites, mudstones and intraformational conglomerates. Individual beds are from 1 - 5 cm thick, show little systematic ordering and were deposited in marine, aphotic, below wave base settings; density and turbidity flows contributed to the sediments. Some rocks were deposited in seafloor anoxia; they lack bioturbation, and are fine grained, laminated pelbiomicrites and thin (< 2”, [5 cm]) black shales that contain ~ 1% total organic carbon. The section presents evidence, in the form of tectonic veining, stylolites that partitioned the movement of cementing fluids, early small scale faulting and rotated lenticular carbonates, that suggest an early tectonic imprint. This imprint coincided with the tectonic redefinition of the Southern Oklahoma aulacogen. Later bedding-parallel stylolites are a response to deep burial, at ~ 3000 m for ~ 140 million years, while later complex vein fills record Pennsylvanian inversion and dilation.