EXPLORING THE FRONTIER OF TERRESTRIAL APTIAN-ALBIAN (CRETACEOUS) C-ISOTOPE STRATIGRAPHY AND PALEOCLIMATOLOGY: A TRIBUTE TO THE SCIENTIFIC CAREER OF MICHAEL A. ARTHUR

Early-career sedimentary geologists in the 1980s were inspired by two developments that attended the beginning of a distributed stable isotope lab infrastructure in the United States. The publication of Cretaceous marine C-isotope curves by Scholle and Arthur (1980, AAPG Bull. 64:67-87), and Mike Arthur’s leadership in publishing the 1983 SEPM Short Course Notes No. 10 (Stable Isotopes in Sedimentary Geology) began a period during which relationships between Cretaceous marine C-isotope stratigraphy and Oceanic Anoxic Events were widely investigated. Appreciation for the global extent of carbon cycle perturbations, with synchronous shifts in δ¹³C values of marine, atmospheric, and terrestrial carbon pools, began a period of investigation of Cretaceous terrestrial C-isotope stratigraphy in the early 2000s, recently summarized by Ludvigson et al. (2015; Cret. Res. 56:1-24). The Aptian-Albian C7 and C10 carbon isotope features, initially associated with OAE 1a and OAE 1b, are now widely correlated in terrestrial sedimentary basins in stratigraphic successions of paleosols and lacustrine marls. One of the principal challenges to this line of investigation is the development of independent geochronologic calibration of terrestrial carbon isotope excursions (CIEs). We advocate wider use of chronostratigraphically-meaningful Maximum Depositional Ages via LA-ICP-MS U-Pb dating of large detrital zircon populations (n=300) from overbank mudstone paleosols as a means for calibrating Aptian-Albian CIEs in the western United States. The late Aptian C10 feature coincided with peak Aptian-Albian pCO₂ values derived from pedogenic carbonates and a pronounced aridification event in the Cretaceous North American foreland basin, a result seemingly at odds with other suggestions for a late Aptian cold snap.