Types Of Paleosols Research Articles

Paleosol Stratigraphy of the Eskridge Formation; Early Permian Pedogenesis and Climate in Southeastern Nebraska

ABSTRACT At least five Aridisol- and Vertisol-like paleosols are developed within the Eskridge Formation (Lower Permian) in Richardson County, Nebraska; these soils are recognized by their prominent soil structure (peds, nodules and filled cracks), micromorphology (oriented clay fabrics, and iron cutans), and well-developed carbonate-enriched horizons. Eskridge paleosols represent significant decreases or cessations in terrestrial sedimentation during long-term subaerial exposure; direct evidence for drowning of three out of the five paleosols (by subsequent marine transgressions) indicates strong marine influence on the duration of pedogenesis. Stratigraphic fluctuations in the 13C and 18O values of Eskridge pedogenic micrites are potentially compatible with climatic fluctuations between wetter and drier conditions during the Permian, based on comparisons with isotope values from Cenozoic paleosols. Occurrence of fossil plants and coals, along with evaporites, as well as the different paleosol types, tends to support an interpretation of varying climate. Recognition of paleosols within the Eskridge improves the understanding of cyclic sedimentation and sea level change by recording several episodes of low terrestrial sedimentation and geomorphic stability; these episodes probably correspond to peak marine regressions.

Paleosols Capping Regressive Carbonate Cycles in the Pennsylvanian Black Prince Limestone, Arizona

ABSTRACT The lower Pennsylvanian (Morrowan to early Derryan) Black Prince Limestone, exposed in southeastern Arizona, consists of shallowing-upward (regressive) carbonate cycles that accumulated on a shallow-shelf platform. A typical complete cycle from the base upward consists of the following fades: mixed skeletal mudstones to grainstones(subtidal shelf, open circulation), mixed skeletal to nonskeletal packstones and grainstones (restricted shelf-lagoon), nonskeletal fenestral mudstones to grainstones (intertidal), nonskeletal cryptalgally laminated, brecciated mudstones to wackestones (supratidal), and paleosol horizons (terrestrial). Two paleosol types occur, calcrete and terra rossa. Calcrete occurs as thin (< 5-10 cm) profiles consisting of laminar micrite, coated grains, aggregate grains, and vadose diagenetic features. Terra rossa paleosols consist of subspherical nodules derived from pedogenic alteration of parent limestones, separated by a reddish, insoluble accumulation ofclays, iron oxides, calcite skeletal debris, and quartz silt. The terra rossa paleosols occur as in situ preserved C horizons and as reworked soil residuum. The first occurrence is marked by parent limestone in completely brecciated into nodules, whereas reworked paleosols consist of nodules enveloped in red matrix. Both calcrete and terra rossa paleosols record subaerial exposure, although the terra rossa paleosols suggest that signi icant amounts of limestone were removed during pedogenesis. The terra rossa paleosols also favor an extrinsic versus anintrinsic mechanism for the origin of the cycles.

Ichnofossils of the alluvial Willwood Formation (lower Eocene), Bighorn Basin, northwest Wyoming, U.S.A

The ichnofossil assemblage of the lower Eocene Willwood Formation consists of at least nine distinct endichnia that are preserved in full relief. Four forms (three ichnogenera and four ichnospecies) are new and represent fodinichnia and domichnia of oligochaete worms, an insect or spider, an unknown vertebrate (probably a mammal), and domichnia of an unidentified organism. Other potential trace makers of the ichnofauna include insects, mollusks, and decapods. In contrast to an Egyptian Oligocene fluvial ichnofauna produced largely by animals that burrowed in stream channel deposits, the Willwood assemblage is principally of flood-plain origin. Though the ichnofauna occurs in a variety of paleosol types, most of the fossils are restricted in distribution to specific sediment and soil types and, within paleosols, to specific identifiable horizons. This attribute will make them valuable indiced of paleoenvironment once they are better known in other ancient alluvial sequences. The environment suggested by the Willwood trace fossils (damp, but not wet soils with fluctuating water tables) is consistent with the warm temperate to subtropical (possibly monsoonal) conditions that are interpreted for the Willwood Formation by independent evidence of body fossils and paleopedology.