To Split or to Lump? The Importance of Facies Analysis for Interpreting Stable Isotope Paleoclimate Proxies from Lacustrine and Palustrine Carbonates
Conference Proceeding
; Stable isotope geochemistry of terrestrial carbonates provides important; opportunities to answer questions about climates, environments, and; ecosystems both in the present day and the geologic past. Here we; present a case study from the Cretaceous Newark Canyon Formation (NCF); type section (~98–113 Ma), where we explore how climate; and depositional settings influence the stable isotope record in highly; variable lacustrine and palustrine carbonates. The NCF was deposited; within the hinterland of the Sevier orogenic belt and allows us to; examine how North American terrestrial climate changed during the; mid-Cretaceous, a time of potentially significant regional surface; uplift and increasing global temperatures related to the Cretaceous; Thermal Maximum (Di Fiori et al., 2020; Huber et al., 2018). In this; study, we find substantial inter- and intra-facies heterogeneity,; despite having formed in the same overall climate setting, highlighting; the differences between lacustrine and palustrine environments. Stable; carbon, oxygen, and clumped isotopes (δ; 13; C,; δ; 18; O; carbonate; , and; Δ; 47; ) paired with optical and cathodoluminescence; petrography from along-strike lateral and vertical stratigraphic; sections show significant isotopic variability between and within seven; carbonate facies (Fetrow et al., 2020). Palustrine deposition is; interpreted to have occurred along a spectrum of shallow water depths; preserved in two key palustrine sub-facies endmembers – shallower; mottled micrite and deeper pebbly, peloid-rich micrite. These record; mean Δ; 47; temperatures of 51ºC and 44°C, respectively.; The mottled micrite has heavier calculated δ; 18; O of; formation water (δ; 18; O; water; ) values; indicating increased evaporative enrichment, which suggests more intense; desiccation during deposition. Lacustrine sediments preserved in; laminated biomicrite to massive micrite have mean Δ; 47; temperatures of 50ºC and 37°C, respectively. Elevated temperatures and; δ; 13; C, δ; 18; O; carb; , and; δ; 18; O; water; values more similar to; values from NCF secondary spar veins indicate that the biomicrite; sub-facies underwent diagenetic alteration. We will discuss the; implications of these results for the NCF and the Cretaceous western USA; paleoclimate record, as well as general lessons learned for interpreting; mixed terrestrial carbonate facies records.;
