Correlations along a 140 km transect in the westernmost Peach Spring Tuff, and tracing changing facies through depositional environments

Tephrochronology is the correlation of tephra beds and tuffs by various means, and it is an important tool in refining stratigraphic and structural interpretations. The 18.78 Ma Peach Spring Tuff (PST) is a large-volume ignimbrite that was deposited across a ~200 km x 360 km area of southeastern California, northwestern Arizona, and southern Nevada. The PST is a valuable stratigraphic marker in several stratigraphic sequences in this area. In this study, the field characteristics, mineral abundance, and feldspar composition of eight ignimbrite locations are examined along a 140 km swath across the northwestern extent of the PST in the Mojave Desert. Based on geochronologic or paleomagnetic data, five of the ignimbrites are PST, and three are possible PST ignimbrites do not have supporting geochronologic or paleomagnetic data. In 53 regionally dispersed locations of the PST, including the three possible PST ignimbrites in this study, the overlying and underlying sedimentary deposits are described in order to determine the depositional changes, if any, resulting from the geologically instantaneous deposition of the ignimbrite. Of the 53 locations, 37 locations allow interpretation of the pre- and post-PST depositional environments. Of the 37, 25 have an upward fining-thinning trend indicating that the deposition of the ignimbrite resulted in (1) disruption and change in local stream gradients and sediment supply, (2) a long period of time for depositional systems to propagate to and regenerate at a location, or (3) a lack of re-establishment of the pre-PST environments. However, 12 have no significant change, so there was minimal disruption to the depositional system.