PHANEROZOIC TEPHROSTRATIGRAPHY: ABUNDANCE AND DISTRIBUTION OF ASH-FALL BEDS

Relating sub-aerial volcanism to geochemical and biological events requires documentation of the abundance and distribution ash-fall beds in the sedimentary rock record. Temporal relationships between volcanic, geochemical, and biological phenomena should be expressed by ash-fall bed occurrences. In this study, numbers of ash-fall beds in sedimentary rocks were tallied from published literature to test whether global-scale volcanic episodes can be detected. Over 5,000 ash-fall beds have been compiled into a database that includes age, formation, location, geographic coordinates, and bed thickness. The distribution of ash-fall beds appears to be episodic at the epoch-scale during the Phanerozoic with maxima in the Late Ordovician, Pennsylvanian, and Eocene. The episodic nature of the tephrostratigraphic record persists despite preservation and outcrop exposure biases. Preliminary results suggest that abundances of ash-fall beds display temporal relationships with other Phanerozoic geochemical and biological trends; however, more age constraints are required to fully test any correlations. A tephrostratigraphic database is an important step towards exploring global-scale volcanic trends. Also, understanding the nature of the tephrostratigraphic record should be useful for refining critical intervals of the geologic timescale.