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

Abstract

Clarey's (2012) model for South Fork (SF) thrusting contains major errors as regards timing of emplacement, number of emplacement events, magnitude of displacement, and geometry of the SF allochthon. A model better supported by data: (1) has SF thrusting taking place before local emplacement of the Heart Mountain (HM) allochthon, rather than after; (2) has emplacement of the SF allochthon by multiple events rather than by a single catastrophic event; (3) envisions only gradual changes in the magnitude of displacement along strike of the SF thrust system, rather than abrupt doubling of displacement across tear faults; (4) regards the SF allochthon as segmented by tear faults only where it has moved across footwall lateral ramps, not in its hinterland; and (5) recognizes that the fault viewed by Clarey (2012) as a break-away to the SF system is instead a fault within the HM allochthon. Clarey's (2012) claim that SF thrusting postdated emplacement of the HM allochthon is based on his assertion that the HM detachment and overlying allochthon are folded above the SF frontal ramp, both on his section A–A′ and near the Castle fault. This argument is disproven by the geologic map of Pierce and Nelson (1969), which presents a much more complete picture of relevant relationships than is shown in Clarey (2012). Pierce and Nelson's (1969) cross section A–A′ is drawn where the preserved HM allochthon and the SF frontal ramp are in …