Bathymetry and productivity of the southern Great Basin seaway, Nevada, USA: An evaluation of isotope and trace element chemistry in mid-Carboniferous and modern brachiopods

Abstract

The stable isotope and trace element chemistry of brachiopods from stratigraphically, paleontologically, and geochemically three coeval intervals about the mid-Carboniferous boundary in the Bird Spring Formation were evaluated for their potential of serving as proxies of bathymetry and productivity of the southern Great Basin seaway, an eastern arm of the Panthalassa Ocean. Oxygen isotopes delineate both spatial and temporal differences in values of brachiopods from the three coeval mid-Carboniferous sections. Based on pristine brachiopod δ 18 O values and supported by paleoecological information, water depth increased from Apex to Kane Springs Wash East to Arrow Canyon. In addition, there is also an increase in values from the latest Mississippian to the earliest Pennsylvanian suggesting a water temperature (cooling), a water depth (increase), and/or change in both of the habitat of the penecontemporaneous brachiopods.Analogous to values and trends observed in modern brachiopods, the Fe/Mn ratio of fossil counterparts may be a potential proxy of seawater productivity related to the micronutrient iron. Overall, the high ratios of Fe/Mn suggest highly productive waters for the southern Great Basin seaway, with somewhat reduced productivity during the earliest Pennsylvanian. In contrast, the carbon isotope values of the coeval material are relatively invariant with respect to productivity; trends similar to observations on modern carbonate allochems. Based on habitat and paleogeography, the Antler Orogenic Highlands west of the foreland basin are considered a potential source for the micronutrient iron enrichment of the carbonate platform shelf-edge environment. It is further postulated that upwelling currents, in part, which weakened from the latest Mississippian through to the earliest Pennsylvanian, may have transported the micronutrient iron onto the shelf/basin environments of the Bird Spring Formation of the southern Great Basin.

Strontium isotope geochemistry of modern and ancient archives: tracer of secular change in ocean chemistry

“…Horizons marked in bold font have conodont archives that carry presumed primary 87 Sr/ 86 Sr values. Lane et al, 1999) at Arrow Canyon (AC; Brand et al, 2012a), Apex (Apex; Brand et al, 2007) in Nevada, Snake Canyon Formation at Arco in east-central Idaho (Arco; this study), lower Ely Limestone of the Granite Mountain section in west-central Utah (GM; this study), Kane Springs Wash (KSW; Brand et al, 2007) and D r a f t Fig. 13.…”

“…The Sr isotopic trend of the Carboniferous (Fig. 10) Bruckschen et al, 1999;Mii et al, 1999;Brand and Bruckschen, 2002;Azmy et al, 2009;Brand et al, 2007;2012a;Woodard et al, 2013). The Early Carboniferous depletions were attributed to the waning of the Acadian orogeny and the subsequent decrease in continental weathering rates, whereas the Mid-Mississippian shift (Fig.…”

“…Formation (Lane et al, 1999) exposed at Arrow Canyon (Brand et al, 2012a), Apex and Kane Springs Wash East (Brand et al, 2007) (Fig. 12).…”

Diagenetic alteration in low-Mg calcite from macrofossils: a review

“…lead ing to the use of Dy namic El e men tal Lim its (Brand et al, 2007). Here, the sed i men tary suc ces sion is sub di vided into mul ti ple zones for which the el e men tal trends are eval u ated sep a rately.…”

Assessing kinetic fractionation in brachiopod calcite using clumped isotopes

“…Their high abundance in Palaeozoic sediments makes them particularly valuable for deep-time seawater temperature reconstructions based on shell oxygen isotope compositions 2 . Unlike many other biogenic archives fossil and modern brachiopods can be found from tropical to polar environments and from a great range of water depths 1 , 3 .…”