Conical sandstone landforms cored with clastic pipes in Glen Canyon National Recreation Area, southeastern Utah

Abstract

Clusters of conical sandstone landforms, many with summit weathering pits, have developed on barren outcrops of the Jurassic Entrada Sandstone in Glen Canyon National Recreation Area, southeastern Utah. The conical landforms have developed on cylindrical bodies of fluidized sandstone (clastic pipes) that typically have near-vertical contacts with the enclosing cross-bedded, eolian sandstone. These landforms vary in size and shape due chiefly to differential erosion of the clastic pipe relative to the enclosing sandstone. The greater resistance to weathering of the clastic pipes is due in part to their higher content of calcite cement. Conical, pipe-cored landforms develop progressively from low domes to cones as high as 70 m. Some of the clastic pipes have relatively soft cores and resistant contacts, leading to the development of conical landforms with summit weathering pits. With time, the size of these pits increases as does the relief of the conical landform. The summit pits are as deep as 16 m and have width–depth ratios as low as 1.5. The resistant rims of these pits are due in part to calcite-enriched pipe contacts. Sandy pit-floor sediment is removed principally by strong wind rotors and vortices. Intense eolian activity in and near the landforms is indicated by abrasional features and pit-floor sand dunes. Factors that promote the development of these conical landforms include (i) the presence of clastic pipes, some with relatively soft cores; (ii) porous, friable, fine-grained pipe and host sandstones; (iii) aridity; (iv) strong winds; and (v) virtually sediment-free, unvegetated bedrock outcrops.