South Fork Fault as a gravity slide: its break-away, timing, and emplacement, northwestern Wyoming, U.S.A.

Abstract

Hauge (2013) claims to present a better model for the South Fork Fault System (SFFS) involving multiple movement events, yet he offers minimal evidence to support his fault timing and interpretation of non-catastrophic emplacement. In addition, he provides little data in terms of an emplacement mechanism for the SFFS. Likewise, his model (Beutner and Hauge, 2009) requires an unusual, concealed, linking fault between the Heart Mountain Fault System (HMFS) and SFFS that cuts downward approximately 1,500 m into underlying rocks. Hauge points out that Pierce and Nelson's (1969) cross section A–A' (east of Castle Tear Fault and south of Sheep Mountain) shows no evidence of folding of the HMFS by the underlying SFFS. However, Pierce and Nelson (1969) drew their cross section where they placed no orientation data on the south edge of Sheep Mountain, a carbonate block emplaced by the HMFS. Therefore, they assumed no folding or displacement had occurred within the allochthonous block. In contrast, limited published orientation data were collected by Stevens (1938) and shown on the southeast edge of his map of Sheep Mountain. Stevens placed northwesterly and westerly dips along the southeast edge of the allochthon consistent with his orientation data in the underlying Mesozoic rocks. He interpreted (in cross section A–A') that subsequent movement of the SFFS folded the Sheep Mountain allochthon (as part of the HMFS). Clarey (2012) also interpreted that the observed folding of the …