• journal_title：Geology
• Contributor：T. White ; B. Witzke ; G. Ludvigson ; R. Brenner
• Publisher：Geological Society of America
• Date：2005-
• Format：text/html
• Language：en
• Identifier：10.1130/G20995.1
• journal_abbrev：Geology
• issn：0091-7613
• volume：33
• issue：1
• firstpage：13

We present the results of oxygen isotope and electron-microprobe analyses of sphaerosiderites obtained from Cretaceous paleosols in Iowa. The sphaerosiderite δ¹⁸O values record Cretaceous meteoric groundwater chemistry and an overall waning of brackish groundwater inundation during alluvial-plain aggradation and soil genesis. We focus on horizons that precipitated from freshwater, in which δ¹⁸O values ranging from −3.3‰ to −6.8‰ relative to the Peedee belemnite standard are interpreted to record variations in the Cretaceous atmospheric hydrologic cycle. During relative sea-level highstands, moisture was derived from the Cretaceous Western Interior Seaway, whereas during lowstands, when the seaway narrowed and occasionally withdrew from the Midcontinent, the dominance of hemispheric-scale atmospheric moisture transport initiated in the tropical Tethys Ocean led to decreased precipitation rates. These processes did not operate like a switch, but rather as a continuum of competing moisture sources and mechanisms of transport between the nearby epicontinental sea and the distant tropics. The sphaerosiderite data demonstrate (1) temporal variation in the intensity of hemispheric-scale atmospheric moisture transport and (2) long-term amplification of the global hydrologic cycle marked by extreme ¹⁸O depletion at the Albian-Cenomanian boundary.