WRINKLED SANDSTONE IN MISSOURIAN WANN FORMATION, LAKE KEYSTONE, OKLAHOMA

”Wrinkled sandstone” structures are small-scale, irregular, anastomosing ridges and grooves and pustules on bedding tops. Wrinkles form either by physical processes or growth of phototrophic cyanobacteria. These peculiar structures are in Precambrian to Holocene intertidal to offshore marine deposits. Microbially-induced sedimentary structures (MISS) vary from small-scale, curved to arcuate ridges and grooves to polygonal sets of ridges on tops of event beds.

Pennsylvanian strata have wrinkle marks on tops of sandstone beds in the Stull Shale Member of the Kanwaka Shale, Virgilian Shawnee Group, Kansas. Honeycomb-like structures occur between ripple crests in a mud-dominated heterolithic sandstone mud-flat facies. Wrinkle marks formed by bacteria during periodic exposure.

Newly discovered “wrinkle” structures are on tops of sandstone-siltstone beds in the Wann Formation cropping out on the eastern shore of Lake Keystone, Osage County. The Wann has been correlated lithostratigraphically with the Missourian Stage Wyandotte to Stanton limestone section in Kansas. The stratigraphic succession represents four major transgressive-regressive cycles beginning with the underlying Iola Formation and ending with the Stanton. The Wann Formation spans from the upper part of the Iola cyclothem to the Stanton cyclothem.

The “wrinkle” structures are on tops of yellow-brown, very fine-grained sandstone to coarse siltstone beds that have sharp erosional bases and rippled tops. An interval of multiple thin beds is ten to twelve meters below the base of the Washington Irving sandstone. Low-angle, wedge-shaped and hummocky cross strata are inclined 8° to 20°. The top surfaces of the beds generally have interference ripples with amplitudes of 1.5-2 cm and crest lengths 5-10 cm. Wrinkle structures overly ripples. The bases of the beds have subparallel flute casts, linear tool marks and trace fossils. Grain size is uniform from base to top though locally dark red-brown, coarse sand is concentrated at the base of some beds. The base of the wrinkled structures is a dark red-brown iron lamina. The beds represent short-term, depositional events within the photic zone following storms or floods.