Click on image to view larger version.
Fig. 18. Natural 
, density, density porosity, epithermal-neutron porosity, and resistivity logs for borehole CdV-16-2(i) located in the western part of the plateau. The borehole is filled drilling fluid below 289.6-m (950-ft) depth. Because of higher concentrations of U, Th, and K, the rhyolitic Tshirege and Otowi Members of the Bandelier Tuff have elevated natural signatures relative to the dacitic sedimentary deposits of the Puye Formation. The density porosity was calculated from the density log using a sandstone grain density of 2.65 gm cm–3. While appropriate for the Puye Formation and crystalline tuffs, this value is about 6 to 8% too high for tuff units containing large amounts of volcanic glass (Qbo and Qbt 1 g). The large density and porosity variations in the Tshirege Member reflect vertical compaction and welding variations in this compound cooling unit. The Otowi Member shows less variability, but density and porosity shifts suggest a small increase in compaction below 190.5-m (625-ft) depth. The epithermal neutron porosity log is sensitive to water content in the unsaturated rocks, and it shows a general trend toward higher moisture with depth through the Bandelier Tuff. The relatively high density and low porosity of the Puye Formation reflects the high percentage of dense, crystalline dacite gravels, cobbles, and boulders embedded in a silty matrix.
