The Steptoean Positive Carbon Isotope Excursion (SPICE), inorganic aragonite precipitation and sea water chemistry: Insights from the Middle–Late Cambrian Port au Port Group, Newfoundland

Abstract

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Environmental and temporal patterns in bioturbation in the Cambrian–Ordovician of Western Newfoundland

“…Formation-and member-level units were broadly binned into "nearshore" (i.e., peritidal, beach and upper shoreface), "shallow subtidal" (lower shoreface, shelf, subtidal platform), and "deep marine" (slope and below) inferred depositional paleoenvironments based both on our field observations (e.g., Figure 4, Table 1, both previous studies and our own field observations suggest that the Petit Jardin, on the whole, records more subtidally dominated settings whereas the Boat Harbor is more peritidally influenced, including intertidal to supratidal as well as shallow subtidal settings (Table 1; e.g., Knight et al, 2008;Neilson et al, 2022;Pratt & James, 1986;Pruss & Knoll, 2017;Pruss et al, 2010). Following paleoenvironmental binning, we observed marked disparities in average ii and BPBI values.…”

“…Carbon isotope data, notably the occurrence of a pronounced positive carbon isotope excursion correlative to the SPICE in the upper Petit Jardin Formation of the Port au Port Group, provide additional chemostratigraphic support for these age assignments (Hagen et al, 2022;Hurtgen et al, 2009;Neilson et al, 2022;Saltzman et al, 2004). Conodont and gastropod assemblages (e.g., the Glyptoconus and Macerodus-Striatodontus Conodont Communities and Lecanospira gastropod assemblages in the middle Boat Harbor Formation) provide biostratigraphic constraints on the Lower Ordovician St. George Group (Boyce et al, 2011;Ji & Barnes, 1994;Knight et al, 2008;Rohr et al, 2001Rohr et al, , 2003.…”

“…(Hawke Bay and Boat Harbor formations; Boyce et al, 2011;Knight & Boyce, 2014;Knight & James, 1987;Knight et al, 2008;Pratt & James, 1986;Pruss & Knoll, 2017;Pruss et al, 2010) Cowan & James, 1993;Neilson et al, 2022;Pruss et al, 2010) are characterized by intermediate ii values (mean ii = 1.7; median ii = 2; n = 90.9 m), whereas "deep-marine" strata (Green Point Formation; Cooper et al, 2001;James & Stevens, 1986) are characterized by the lowest ii values (mean ii = 1.2; median ii = 1; n = 63.7 m). These These paleoenvironmental disparities were found to be statistically significant for both the ii and BPBI datasets (Mann-Whitney U test p < .05; Table S4).…”

“…The lower Cambrian–Lower Ordovician Labrador, Port au Port and St. George groups of western Newfoundland (Figure 1) comprise part of an autochthonous mixed carbonate–siliciclastic succession interpreted to have been deposited in a passive margin, platform, or shelfal setting (Chow & James, 1987; James & Stevens, 1982, 1986; Knight & James, 1987; Neilson et al, 2022; Pruss et al, 2010). In the Port au Port region, part of the Laurentian tectonostratigraphic Humber Zone, these units occur along both limbs of a broad, shallowly dipping anticline, exposed in a series of sea cliffs and coastal outcrops along the south‐facing shore of the peninsula (Figure 1; James & Stevens, 1982; Pratt & James, 1982; Knight & James, 1987; Boyce et al, 2011).…”

Calcium Isotopic Constraints on the Transition From Aragonite Seas to Calcite Seas in the Cambrian

“…Petrographic data, including skeletal macrofossils, ooids and marine cements, suggest that the Neoproterozoic Era may have been characterized by “aragonite‐dolomite seas”, during which primary shallow‐marine carbonates were dominated by aragonite, high‐Mg calcite and dolomite (Hood & Wallace, 2012, 2018; Hood et al., 2011; Tucker, 1989, 1992; Wood et al., 2017). Several studies have highlighted that the minerology of the carbonate factory in the Cambrian may have been more variable and aragonite deposition may have been more common than traditional envisioned (e.g., Hood & Wallace, 2018; Wood et al., 2017; Zhuravlev & Wood, 2008; Neilson et al., 2021). Well‐preserved shallow‐marine cements and ooids can be useful petrographic indicators of marine carbonate mineralogy (e.g., Hood & Wallace, 2018), but successions in which these archives are sufficiently stratigraphically abundant to provide extensive and relatively continuous records of depositional mineralogy in the Neoproterozoic and Cambrian have not been systemically investigated.…”