--> Abstract: Paleosols Provide Detailed Local Correlations within the Upper Supai Group, Grand Canyon, by P. Enos, A. R. Alissa, G. Buijs, W. Joyce, A. J. Fogarty, and D. H. Chaikin; #90928 (1999).

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ENOS, PAUL, A.R. ALISSA, GOVERT BUIJS, WALTER JOYCE, A.J. FOGARTY, and D.H. CHAIKIN
University of Kansas.

Abstract: Paleosols Provide Detailed Local Correlations within the Upper Supai Group, Grand Canyon

The upper Supai Group (Wescogame Formation, Virgilian, and Esplanade “slope unit,” Wolfcampian) in the eastern Grand Canyon consists of alternating cross-bedded arenites, interpreted with some confidence as eolian deposits, and fine-grained sandstone, siltstone, and mudstone, interpreted tentatively as low-gradient fluvial deposits. Irregular, white leached horizons, peds, rhizoliths, and calcareous glaebules are consistently superposed on the top of the mudstone units. These features are interpreted as paleosols, probably aridosols.

Correlations of sections measured along the Hermit and South Kaibab Trail sections, 12 km apart, were approached objectively, based largely on lithology, thickness, and paleosol horizons. Virtually every paleosol appears to correlate and details of paleosol development are consistent. The remarkable degree of correlation in these non-marine units suggests an external control rather than autocyclic development of the fluvial-eolian couplets. A likely control is climate fluctuations, which possibly correlate with sea-level oscillations in this period of wide-spread continental glaciation.

Unit descriptions and [interpretations]

A. Mudstone: blocky weathering, dark reddish brown (10R 3/4). Locally irregular white splotches. [Paleosol]

B. Siltstone/silty mudstone: reddish brown (10R 4/4), calcareous nodules abundant, calcareous tubes, horizontal to vertical. [Paleosol, BK horizon]

C. Siltstone/silty mudstone: reddish brown (10R 4/4), Ripple cross lamination, mud cracks. [Low-gradient fluvial deposits]

D. Quartz arenite: v.f. sand, well sorted, rounded, cross bedded or massive, weathers reddish brown to pale reddish brown (10R 6/4), locally vertical calcareous tubes. [Eolianite]

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas