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AAPG Bulletin

Abstract


Volume: 60 (1976)

Issue: 11. (November)

First Page: 2048

Last Page: 2057

Title: Vadose Pisolite and Caliche: GEOLOGIC NOTES

Author(s): Mateo Esteban (2)

Abstract:

The "vadose pisolite"(FOOTNOTE 3) facies of the Capitan reef complex of New Mexico, the Italian Calcare Massiccio, and the Saskatchewan Winnipegosis generally is interpreted as fossil caliche. This interpretation appears incompatible for four reasons. (1) "Vadose pisolite" is associated closely with fenestral grain-supported carbonate rocks within a facies belt between a marine shelf edge of oolitic carbonate rocks and more shelfward evaporites. This is in contrast with the substrate independence of modern caliche. "Vadose pisolite" has not been associated directly with erosional surfaces, stratigraphic discontinuities, or terrestrial deposits. (2) Described "vadose pisolite" lacks lithologic sequences comparable to caliche profiles. (3) "Vadose pisoliths" have many more egular laminae than the caliche pisoliths, which are present in micritic rather than grain-supported rocks and display characteristic fabrics not present in "vadose pisolite." (4) Evidence of alteration and replacement of original textures has not been presented for "vadose pisolite." The currently accepted evidence of polygonal fitting, downward elongations, and perched inclusions for the caliche origin of the "vadose pisolite" only indicates in-place, nonalgal, accretionary growth of pisoliths; it does not require soil processes. The "vadose pisolites" can be interpreted better as a depositional facies close to an intertidal setting in hypersaline environments where pisoliths can grow in place in protected localities as reverse-graded, bedded cycles. Although inadequate as a model, thi hypothetical environment has some similarities with the Persian Gulf coniatolite belt. Modern caliche involves very specific rock types created by soil processes in semiarid environments; this term should not be applied to the "vadose pisolite" facies.

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