Wotte and Sundberg—Small shelly fossils from the Great Basin
885
Figure 2. Biostratigraphic zonation of the upper Dyeran–Delamaran interval, and associated lithostratigraphy on the outer, middle, and open shelf of Nevada and SE-California, western Laurentia (modified from Palmer and Halley, 1979; Sundberg and McCollum, 2000, 2003b; McCollum and McCollum, 2011; Sundberg, 2011; Webster, 2011a). Stratigraphic positions of the analyzed Dyeran–Delamaran sections are marked. Abbreviations: E Shale Mbr., Echo Shale Member; GA Lst. Mbr., Gold Ace Limestone Member; PH Shale Mbr., Pahrump Hills Shale Member; RP Lst. Mbr., Red Pass Limestone Member; SD Lst. Mbr., Susan Duster Limestone Member; Lst., limestone; Mbr., member. See Figure 1 for section abbreviations.
(Mexicella mexicana Zone) consisting of claystone, siltstone, and sandstone (Eddy and McCollum, 1998; McCollum and McCollum, 2011; Sundberg, 2011).
Middle shelf facies.—The Dyeran–Delamaran of the middle shelf facies is represented by the Carrara Formation in southern Nevada and southeastern California (Fig. 1). The Carrara Formation is separated into nine siliciclastic and carbonate intervals, ranging from the Arcuolenellus arcuatus Zone to the Glossopleura walcotti Zone (Palmer and Halley, 1979; Webster, 2011a; Fig. 2). The lowermost and uppermost carbonate members (Thimble Limestone and Desert Range Limestone members, respectively) are characterized by thin-bedded argillaceous (dolomitic) limestone (Palmer and Halley, 1979). In contrast, the other limestone portions are cliff-forming units, composed of oncolitic, oolitic, laminated, and fenestral limestone (Palmer and Halley, 1979). The lithostratigraphic nomenclature applied by Palmer and Halley (1979) does not fitwiththe sedimentary succession observed in the northern Groom Range and Belted Range (GR and BR in Fig. 1) of central Nevada, which resulted in several synonymous nomenclatures for the region (Fig. 2;McCollumandMcCollum, 2011; Sundberg, 2011; Webster, 2011a; Webster et al., 2011).
Outer shelf facies.—Sections of the outer shelf facies crop out in western Nevada and eastern California (Fig. 1). TheDyeranMule Spring Limestone is represented by predominately shallow sub- tidal–intertidal carbonates and is subdivided into: (1) a lower unit, composed of cliff-forming bioturbated limestone; (2) a middle unit, composed of bioclastic, oncolitic, oolitic, and peloidal lime- stones with numerous claystone intercalations; and (3) an upper cliff-forming unit composed of oncolitic and fenestral limestones with intercalated intraformational conglomerates (Fig. 2; Nelson, 1962; Stewart, 1970;Albers and Stewart, 1972; Webster, 2011a, b). The Mule Spring Limestone is overlain by the siliciclastic and carbonate, partly highly condensed Emigrant Formation (upper- most Dyeran–Sunwaptan Stage) in western Nevada and by the Monola FormationinDeath ValleyNationalParkofeastern California (e.g., Palmer, 1971; Palmer andHalley, 1979;McCollum andMcCollum, 2011; Sundberg, 2011; Sundberg et al., 2011). The Monola Formation is subdivided into a lower claystone portion with intercalated limestone and an upper limestone with minor siltstone intercalations (Sundberg and McCollum, 1997). McCollum and McCollum (2011) identified the depositional environment of the Monola Formation as located between the outer shelf position of the Emigrant Formation and the medial to inner shelf positions of the Carrara and Pioche formations.
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