Distinguishing base-level change and climate signals in a Cretaceous alluvial sequence
Geology
By: T. White, B. Witzke, G.A. Ludvigson, and R. Brenner
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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.
Suggested Citation
White, T., Witzke, B., Ludvigson, G., Brenner, R., 2005, Distinguishing base-level change and climate signals in a Cretaceous alluvial sequence: Geology, v. 33, no. 1, p. 13-16, https://doi.org/10.1130/G20995.1.
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Distinguishing base-level change and climate signals in a Cretaceous alluvial sequence |
| Series title | Geology |
| DOI | 10.1130/G20995.1 |
| Volume | 33 |
| Issue | 1 |
| Year Published | 2005 |
| Language | English |
| Larger Work Type | Article |
| Larger Work Subtype | Journal Article |
| Larger Work Title | Geology |
| First page | 13 |
| Last page | 16 |