University of Texas at Austin
Establishing chronologic control in early and middle Pleistocene deposits is difficult, all the more so in cave deposits. In the absence of a lucky infusion of datable volcanic ash (which Porcupine Cave so far seems to lack), dating methods typically are restricted to magnetostratigraphic associations, biostratigraphic and biochronologic correlations, amino acid racemi-zation, electron spin resonance, and uranium series dating. The latter two techniques have not been applied to samples from Porcupine Cave, although there is still opportunity for future attempts; therefore, all chronologic control comes from the former three. The chronologic information is augmented with sedimentological information that helps sort deposits into glacial and interglacial deposits.
Much of the information on dating the Porcupine Cave deposits, especially that from the Pit excavation, was presented in detail by Bell and Barnosky (2000). Other relevant information was detailed in Barnosky and Rasmussen (1988), Wood and Barnosky (1994), and Barnosky et al. (1996). Friedmann and Raynolds (chapter 6) discuss magnetostratigraphy in the DMNH Velvet Room excavation, and Shabel et al. (chapter 22) discuss age control in the Badger Room. This chapter integrates the earlier interpretations with some new information to hypothesize how key deposits in the cave (Pit, DMNH Velvet Room excavation, CM Velvet Room excavation, Badger Room) relate temporally to each other, to some other localities in the cave, and to the chronologic time scale. The conclusions are basically in accord with those of Bell and Barnosky (2000) but suggest that the age of the top of the Pit sequence is probably closer to circa 780 Ka than previously thought. (See chapter 2 for map locations and excavation information for each of the localities discussed in this chapter.)
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