GEOCHRONOLOGY AND STRATIGRAPHY OF THE UPPER FURNACE CREEK FORMATION, DEATH VALLEY, INYO COUNTY, CALIFORNIA

The mid-Miocene to Pleistocene Furnace Creek Basin consists of clastic sediments and volcanic tuffs of the Furnace Creek Formation and overlying Funeral Formation. In order to resolve the timing of the formational boundary, we measured a 115 m thick continuous stratigraphic section along Zabriskie Wash across the upper Furnace Creek and lower Funeral Formations and collected samples for tephrochronologic and paleomagnetic analyses. Four tuff beds in the upper Furnace Creek have been correlated on the basis of their major element composition; they are the: Curry Canyon tuff, lower Mesquite Springs tuff, (pumiceous) Mesquite Springs tuff (informally named here), and the Nomlaki Tuff (3.28 Ma). Paleomagnetic data indicate that the Curry Canyon and lower Mesquite Springs tuffs are magnetically normal, whereas the overlying pumiceous Mesquite Springs and Nomlaki tuffs have reversed polarity. By pinning the normally magnetized section to the 3.28 Ma Nomlaki Tuff, we correlate the N to R polarity change below the pumiceous Mesquite Springs tuff with the 3.330 Ma base of the Mammoth subchron. This is consistent with the 3.35 Ma age for the lower Mesquite Springs tuff (Snow and Lux, 1999) and shows that the Curry Canyon tuff must be >3.35 Ma and <3.58 Ma. Lithologically, the section changes from conglomerates to sandstones to mudstones, just above the Curry Canyon tuff, and back to sandstones above the Nomlaki Tuff. We interpret these changes to signify a rising lake in the basin in response to the onset of glacial climates in mid Pliocene time.