James F. Read, 1974. "Calcrete Deposits and Quaternary Sediments, Edel Province, Shark Bay, Western Australia", Evolution and Diagenesis of Quaternary Carbonate Sequences, Shark Bay, Western Australia, Brian W. Logan, James F. Read, Gregory M. Hagan, Paul Hoffman, Raymond G. Brown, Peter J. Woods, Conrad D. Gebelein
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Wedge-shaped bodies of calcrete-ooid grainstone, calcrete-pisolite grainstone, and lithoclast breccia occur in the Edel province. Shark Bay, Western Australia. These deposits are soils formed on the eolianite (skeletal grainstone) country rocks (Pleistocene, Tamala Eolianite). Calcrete ooids are round sand-size grains consisting of a thin envelope of calcrete around a skeletal grain or lithoclast nucleus; calcrete pisolites are gravel-size particles (commonly 1-5 cm in diameter) consisting of an envelope of laminated calcrete around an eolianite lithoclast nucleus; lithoclasts in the breccias are angular fragments 5-15 cm or more) of calcretized eolianite which are commonly coated with a thin envelope of calcrete.
Fully developed weathering profiles contain, in descending order, (5) pisolitic soil horizon; (4) laminarcalcrete zone, composed of thinly laminated sheets of calcrete; (3) massive-calcrete zone, composed of dense, structureless “lime mudstone” in which calcrete fills voids and replaces carbonate grains to form secondary “mud-support” fabrics; (2) mottled zone, consisting of eolian skeletal grainstone containing scattered mottles of structureless calcrete; and (1) unaltered eolian skeletal grainstone.
The geometry of soil bodies and distribution of litho-facies are influenced by topography and differential rates of movement of soil particles in downslope transport. Soils are thickest on the lower flanks of ridges and thin toward crests and into interdune depressions. Lithofacies are distributed in broad concentric zones about “highs.” Breccias occur adjacent to ridges where slopes are steep; they grade outward into pisolite grainstones and then into calcrete-ooid grainstones as slopes decrease away from ridges.
Interdune depressions were flooded during three marine phases in the Quaternary, and sea level reached approximately similar positions at the limit of each transgression. During marine phases, indurated limestones at the shore were beveled by marine erosion to form tidal terraces and seacliffs; locally, these limestones were overlain by marine sediments. During regressive phases, marine units in coastal areas were covered by soils shed from nearby highs. Transported soils also buried coastal landforms cut during marine phases.
Stratigraphic relations between marine units and soils are extremely varied, having been influenced by topographic factors, energy conditions, lithification and erodability of sediments in coastal areas, and multiple transgression and regression. Contacts between soils and marine units are of several basic types: (1) surfaces of marine erosion, (2) nonerosional contacts, (3) irregular surfaces of weathering and subaerial erosion, and (4) gradational contacts formed by admixing of soils and marine shells in transitional marine-terrestrial environments, by infiltration, and by marine reworking of soils.
Figures & Tables
Following on the research presented in AAPG Memoir 13, which focused on environment and Quaternary history of Shark Bay, this publication examines the same area again, but with a strong stratigraphic emphasis running as a common thread through all 7 papers in this volume.