Owl Rock, Kayenta, Navajo County, Arizona, USAi

Regional Level Types
Owl Rock	- not defined -
Kayenta	City
Navajo County	County
Arizona	State
USA	Country

OWL ROCK MEMBER

The Owl Rock member of the Chinle formation is made up of cherty limestone and limestone conglomerate beds alternating with claystone, mudstone, and siltstone beds. Wherever this member crops out, the resistant limestone beds form a series of jutting ledges that serve partly to protect the underlying strata. In the Monument Valley area, Arizona, the Owl Rock member is best exposed at its type locality near the base of Owl Rock. Limestone conglomerate beds give way along the strike to massive cherty limestone beds which have subangular to angular nodules of black chert scattered irregularly throughout the beds. A light bluish-gray (5B 7/1) color predominates, although locally greater concentrations of chert tend to darken the limestone beds to gray blue. The ledges formed by these limestone beds normally range from about 2 to 20 feet in thickness and are separated one from another by siltstone and mudstone masses as much as 30 feet thick. The cherty limestone beds weather to form nodular blocky well-jointed ledges. As many as six of these limestone ledges were noted in the Monument Valley area. Of these only five were persistent and could be traced with any degree of confidence.

The Owl Rock member ranges in thickness from about 120 to 166 feet. At Owl Rock the member is 166 feet thick; farther south along Comb Ridge near Chaistla Butte it is about 134 feet thick; to the west along the east flank of Skeleton Mesa it is about 128 feet thick.

A comparable thickness for this unit is reported by Gregory (1917, p. 44-45) who cites a thickness of 152 feet for this member of the Chinle at the mouth of Segihatsosi Canyon near Boot Mesa (pl. 1). The following is presented as the type section of the Owl Rock member of the Chinle formation:

Section of 0wl Rock member of Chinle formation measured at Owl Rock about 7% miles north of Kayenta, Ariz.

Church Rock member of Chinle formation.

Owl Rock member of Chinle formation------------------------ Feet thickness

Limestone, pale-grayish-green, cherty; persistent cliff former; weathers to form blocky masses -------------------------------------- 7
Mudstone, pale-reddish-brown; some intercalated siltstone lenses; forms gentle slopes ----------------------------------------------- 11
Limestone, pale-grayish-green ; includes black angular chert nodules; persistent cliff former ---------------------------------------- 2
Mudstone, pale-reddish-brown; forms gentle slopes -------------------- 2
Limestone, grayish-green; includes black angular chert nodules; cliff former --------------------------------------------------------------- 2
Siltstone, brown, massive, very slightly fissile; locally stands as vertical face ---------------------------------------------------------- 11
Mudstone; pale-reddish-brown to mottled appearance resulting from scattered small green specks; forms gentle slopes ------------------- 26
Limestone, pale-gray ; includes black angular chert nodules; persistent
cliff former -------------------------------------------------------- 10
Mudstone, pale-reddish-brown; locally grades into siltstone; forms gentle slopes -------------------------------------------- 16
Limestone, light-gray, massive; includes black angular chert nodules; persistent cliff former --------------------------------------10
Mudstone, pale-red; locally altered to conglomeratic siltstone near top; lower part forms slopes, upper part stands as vertical face --- 33
Claystone, gray to purple, discontinuous; locally forms ledges ------- 1
Mudstone, reddish-brown; forms gentle slopes --------------------- 16
Limestone, light-gray: includes black angular chert nodules; weathers to form blocky masses--------------------------------------- 19

Total thickness: 166