The Upper Devonian Fenstermaker Limestone is a thickening-upward sequence
of interbedded sandy intrapelsparite and subordinate calcareous siltstone and mudstone
which averages 190 ft (58 m) thick in the northern Antelope Range. The Fenstermaker
Limestone is revised and restricted herein to include only those rocks above a basinal
shale sequence of the upper Denay Limestone and below the Mississippian Davis Spring
Formation, and replaces the names "Devonian sandstone" of Trojan (1978) and the
"Fenstermaker Wash Formation" of Hose and others (1982).
Sandy limestone of the Fenstermaker Limestone was deposited rapidly, above
upper Denay basinal shales, as resedimented beds in Frasnian Montagne Noir conodont
zone 13 and the Lower Famennian Middle triangularis Zone. Reworked conodonts are
present at numerous stratigraphic levels in the Fenstermaker, indicating erosion on the
inner or middle carbonate platform during two Upper Devonian eustatic regressions (in
lower and upper T-R cycle Ild; western U. S. events 7 and 8). Deposition of the
Fenstermaker Limestone was by allodapic sediment gravity flows on an outer-shelf-basin
ramp or at the toe of a low-angle (<4°) carbonate slope during incipient outer-shelf-
basin filling, i.e. as reciprocal sedimentation.
Detrital quartz sand averages 11% but ranges much higher in sand-rich laminae
preserved in strata along the western range front. Sorting characteristics of the sand
were attained in a siliciclastic beach environment prior to deposition in the carbonate
lithotope. Pitting and frosting of grain surfaces are at least partially diagenetic in origin
and not necessarily a product of eolian transport.
Two allochthonous limestone blocks in the southern Fish Creek Range, northern
Nye County (blocks A and C of Sans, 1986), are assigned to the Fenstermaker
Limestone and are considered to have been derived from the west.
Beds the age of the Fenstermaker Limestone are absent at an unconformity in the
Cortez Mountains, west-central Eureka County.
Detrital quartz sand concentrated along stylolites in the Upper Devonian part of
the Popovich Formation, southern Tuscarora Mountains, northern Eureka County, were
point-counted as an aid in determining formational thickness loss due to pressure-solution.
Thickness reductions are estimated at 12-13%.
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