Abstract

Biostratigraphy in combination with magnetostratigraphy yields a stratigraphic-chronologic foundation in which biological and environmental changes can be correlated with an independent time frame. This combination promises greater resolution of chronostratigraphic units than those based on faunal change and superposition. The occurrences of early and middle Paleocene land mammals in the San Juan Basin are bracketed relative to the magnetic polarity time scale: mammals of Puercan (early Paleocene) age occur in rocks deposited during magnetic anomaly 28, and mammals of Torrejonian (middle Paleocene) age occur in rocks deposited during magnetic anomaly 26 and during the reversed polarity interval preceding anomaly 26.

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