Larry G. Marshall

Geochronology and Land-Mammal Biochronology of the Transamerican Faunal Interchange

In recent years a combination of biostratigraphic, magnetostratigraphic, and radioisotopic data has been employed to calibrate aspects of the Great American Faunal Interchange (sensu Webb, 1976) that occurred in the late Cenozoic between North and South America. Many of these studies have focused on documenting the time of first appearance of immigrant taxa that participated in the interchange. These multidisciplinary studies were first applied to North American rocks and faunas (e.g., Johnson et al., 1975; Lindsay et al., 1976, 1980, 1984; Opdyke et al., 1977; Tedford, 1981; Galusha et al., 1984) and, subsequently (or concurrently) to those in South America (e.g., Marshall et al., 1977, 1979, 1982,a,b,c, 1983c; Marshall, 1982; MacFadden et al., 1983; Butler et al., 1984).

Magnetic Polarity Stratigraphy and 40 K- 40 AR Dating of Late Miocene and Early Pliocene Continental Deposits, Catamarca Province, NW Argentina

Magnetostratigraphic and

Late Cretaceous vertebrates, including mammals,from Tiupampa, Southcentral Bolivia

^{40}K -^{40}Ar

Geology of the deseadan (early oligocene) age estratos salla in the salla-luribay basin, Bolivia, with description of new marsupialia

data on a 2300 m thick sequence of continental sediments at Puerta de Corral Quemado in Catamarca Province, NW Argentina permit calibration of land mammal faunas of late Tertiary (Huayquerian and Montehermosan) age. The sequence represents (from oldest to youngest) the Chiquimil A, Araucanense, and Corral Quemado Formations. Paleomagnetic samples were collected from 99 stratigraphic levels. Strong-field thermomagnetic and isothermal remanent magnetization experiments indicate that the dominant ferrimagnetic mineral is magnetite. Progressive alternating-field (AF) and themal demagnetization of the natural remanent magnetism (NRM) demonstrates that AF demagnetization to 20 mT peak field is sufficient to isolate the primary NRM which is of depositional origin. The resulting paleomagnetic data provide a well-defined magnetic polarity zonation, although sampling is less dense in the upper half of the section.

Calibration of the age of mammals in South America

^{40}K-^{40}Ar

The Mesozoic and Paleocene vertebrates of Bolivia and their stratigraphic context : a review

data obtained from mineral separates of four tuffs within the section allow reliable age determinations for those levels. The combined magnetostratigraphic and