| Abstract: | We present the results of oxygen isotope and electron-microprobe analyses of sphaerosiderites obtained from Cretaceous paleosols in Iowa. The sphaerosiderite ??18O 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 ??18O values ranging from -3.30??? 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. ?? 2005 Geological Society of America. |
| Genre: | Article |
| ProdID: | 70029453 |
| Citation Author: | White, T.; Witzke, B.; Ludvigson, G.; Brenner, R. |
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| Citation End Page: | 16 |
| Citation Issue: | 1 |
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| Citation Language: | English |
| Citation Larger Work Title: | Geology |
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| Citation Number Of Pages: | 4 |
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| Citation Search Results Text: | Distinguishing base-level change and climate signals in a Cretaceous alluvial sequence; 2005; Article; Journal; Geology; White, T.; Witzke, B.; Ludvigson, G.; Brenner, R. |
| Citation Start Page: | 13 |
| Citation Volume: | 33 |
| Citation Year: | 2005 |
| Type: | citation/reference |
| Text: | Distinguishing base-level change and climate signals in a Cretaceous alluvial sequence; 2005; Article; Journal; Geology; White, T.; Witzke, B.; Ludvigson, G.; Brenner, R. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1130/G20995.1 |
| Date Other: | Sat, 1 Jan 2005 00:00 -0600 |
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