An evaluation of inoceramid single-prism sclerochronology

摘要: Abstract Inoceramid prisms are among the most common microfossils that can be found in Late Cretaceous strata. Since these biomineral units were formed by sequential accretion outer shell layer of bivalves, they potentially serve as archives short-term (circa-annual) paleowater temperature fluctuations. In present study, we tested to what extent intra-prismatic stable isotope variations individual inoceramid reflect sub-annual δ13C and δ18O patterns. We obtained multiple carbonate samples from recovered sediment a cross-sectioned fragment compared data classical sclerochronological sampling (i.e., drilling). The analyzed material belonged species Platyceramus platinus Smoky Hill Chalk Member (Niobrara Formation, Kansas, USA). Scanning electron microscopy (SEM) was used evaluate diagenetic alteration studied allowed identify suitable for analyses. values drilled (δ18ODrill) (δ18OIP) compare very well each other when temporally aligned (R2 = 0.98). carbon (δ13CDrill; δ13CIP), however, show less agreement (R2 = 0.28), which is likely attributable different time-averaging samples. discuss how paleotemperature reconstructions disarticulated using microgrowth patterns geometrical features proxies changing growth rates. Finally, apply novel strategy naturally occurring their (δ13CIPS δ18OIPS) those bulk-analyzed prism fragments (δ13CBPS δ18OBPS). Sclerochronological analysis yields δ18OIPS fluctuations 1.89‰, virtually identical δ18OIP chronologies extracted cross-section (1.90‰). overall ranges (2.60‰) capture expected seasonal oxygen oscillation derived δ18ODrill (2.61‰). range two-fold larger than δ18OBPS (1.19‰), suggesting strong effect on fragments. According our statistical model, resolution increased preferentially analyzing short (ca. 300 μm) (at least n = 20).