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

Abstract

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.