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Description
Early Silurian through Early Devonian rocks crop out widely in the southern Great Basin in southeastern California. A total of 1,544 feet of dolomite and argillaceous dolomite was measured and systematically sampled at a single section in the southern Funeral Mountains, Death Valley, California. The lower 120 feet correlate with the upper part of the Ely Springs Dolomite, while the remaining 1,424 feet are assigned to the Hidden Valley Dolomite. Conodonts recovered from the Ely Springs Dolomite and lower and upper members of the Hidden Valley Dolomite indicate an age spanning earliest Silurian (early or middle Llandoverian) to middle or late Early Devonian (Siegenian or Emsian). Conodonts from the Ely Springs Dolomite are tentatively assigned to the Bereich I Zone (early and middle Llandoverian). The overlying lower member of the Hidden Valley Dolomite contains diagnostic conodonts of the Spathognathodus celloni and Pterospathodus amorphognathoides Zones (late Llandoverian to early Wenlockian). Conodonts in the upper portion of the lower member are tentatively correlated with the Kockelella patula Zone (middle Wenlockian). The lower 38 feet of the upper member contains numerous specimens of Icriodus latericrescens and a few questionably identified as I. l. huddlei. These suggest a middle to late Early Devonian age (Siegenian or Emsian). Lithologic and paleontologic evidence suggests that upper Ely Springs and Hidden Valley strata were deposited in a variety of shelf environments ranging from moderately deep subtidal to very shallow intertidal or possibly supratidal. An earliest Silurian regression and minor erosional episode is recorded in the Ely Springs. Then moderately deep and restricted water conditions were established during deposition of the basal Hidden Valley Dolomite. Shallowing upward sequences characterize the remaining portion of the lower member. Upbuilding of organic mounds and basinward mound progradation characterize the middle member. Initial deposition may have occurred in water as deep as shallow subtidal but the bulk of the member was deposited in an intertidal, possibly very shallow, mound and/or "back-mound" environment. Lithologic evidence suggests a transgressive event slowly increased water depth during latest Silurian or earliest Devonian time, culminating in the deposition of the shallow subtidal lower part of the upper member. Shallowing followed and continued through the end of the Hidden Valley deposition. Lithologic, paleontologic, and temporal features of the inner and outer continental shelf couplet (Hidden Valley Dolomite-Vaughn Gulch Limestone) in southeastern California are similar to the couplet (Lone Mountain Dolomite-Roberts Mountains Formation) in central Nevada. The similarity of geologic features between the regions suggest deposition of the respective sequences in a similar depositional and paleogeographic framework.
