WHERE WAS THE HADLEY CELL BOUNDARY IN THE MID-CRETACEOUS AMERICAS?: CONSTRAINTS IMPOSED BY TERRESTRIAL CARBONATES OF THE MIDCONTINENT UNITED STATES

Some scientists have postulated a poleward migration of the mid-Cretaceous Hadley Cell boundary (HCB) in response to the greenhouse warming forced by higher atmospheric pCO₂. We evaluate this concept in light of observations on the paleolatitudinal distribution of mid-Cretacous pedogenic carbonates in the midcontinent United States. A N-S transect along the cratonic margin of the Cretaceous Western Interior Basin in the midcontinent U.S. provides unambiguous evidence for location of the HCB in a region free of orographic influences. Ufnar et al. (2002; Palaeo-3 188:51-71) outlined the distribution of Albian pedogenic siderites from 34 °N (central Kansas) to 75 °N (North Slope Alaska) paleolatitudes, all recording terrestrial paleoclimates with positive precipitation-evaporation balances that are to be expected north of the HCB. Calcic paleosols of the Aptian-Albian Antlers Formation of southeastern Oklahoma (29.5 °N paleolatitude) record terrestrial paleoclimates with negative precipitation-evaporation balances that are to be expected within the descending arm of the Hadley Cell. These observations place the HCB between 29.5 to 34 °N paleolatitude. Diagenetic investigations of meteoric phreatic calcites from the Antlers Formation yield meteoric calcite lines with d¹⁸O values ranging between –5.5 to –0.7 ‰ PDB. Micritic calcites from meteoric vadose settings have d¹⁸O values that were enriched by evaporation by 0.24 to 1.2 ‰. At a local zonally-averaged MAT of 27.7 °C, evaporative enrichments of these magnitudes require evaporative losses of 11-45% of the vadose soil water through simple Rayleigh distillation. Our work firmly places the Antlers Formation of southeast Oklahoma within the Aptian-Albian subtropical Hadley Cell.