“…Several rift-related igneous units exposed east of the Transcontinental Arch also provide important depositional constraints on the Sauk Sequence, such as those in the Wichita Mountains (534 ± 2 Ma; Gilbert and Hogan, 2010), the Shenandoah felsic dikes (555 ± 4 Ma and 567 ± 4 Ma; revised from Aleinkoff et al, 1995, by Burton and, and the Catoctin Rhyolite (571 ± 1 Ma; Southworth et al, 2009). It is noteworthy that the timing of deposition based upon biostratigraphic studies substantiates the maximum depositional age as constrained by the youngest most concordant single zircon grain from this and other detrital zircon studies (e.g., Wood Canyon Formation: Hunt, 1990;Hagadorn et al, 2000;Bolsa Formation: Jones and Bacheller, 1953;Gilluly et al, 1956;Coronado Formation: Ethington and Clark, 1964;Bliss Formation: LeMone, 1969; La Paz and El Desecho formations: Naipauer et al, 2010). However, we note that the youngest zircon age likely represents an underestimation of the maximum depositional age given the assumed normal age distribution of the youngest contributing source of detrital zircons.…”