NEW QUANTITATIVE ANALYSES OF THE STRATIGRAPHIC RECORD: IMPLICATIONS FOR PALEOBIOLOGY

Quantifying the sedimentary record is essential for testing many paleobiological hypotheses. Here, I utilize the stratigraphic ranges of measured sections to quantify the rock record of the U.S.A. The AAPG’s Correlation of Stratigraphic Units of North America charts provided > 3400 sections from > 430 locations in the U.S. Sections were defined as gap-bound rock packages and were resolved to stages for most of the Phanerozoic.

The sedimentary record of the U.S. exhibits considerable short- and long-term variability in both the quantity and type of rock. Long-term variations in rock quantity include a Cambrian ‘explosion’ followed by a volatile Paleozoic plateau, an end-Permian decline, and a Mesozoic rebound. Other long-term patterns include a decline in the absolute and relative abundance of carbonates and a dramatic Cenozoic increase in the quantity of terrestrial rock. On shorter time-scales, there is also considerable variation in both the quantity and type of preserved rock. For example, the Famenian saw a decrease in the amount of carbonates but an increase in the amount of clastics.

Rates of stratigraphic extinction and origination exhibit significant stage-to-stage volatility but no long-term trends. Extinction is slightly more volatile than origination. Many pronounced pulses of stratigraphic extinction correspond to major biological mass extinctions and substantial pulses in rates of stratigraphic origination occur in the Cambrian and Early Triassic. Rates of extinction and origination vary among lithologies. For example, carbonates tend to have higher rates than clastics.

Although the stratigraphic data presented here lack detailed lithologic/environmental control, include subsurface rocks, and only represent the U.S., there is remarkable similarity between these data and global marine animal genus data. For example, rates of stratigraphic extinction are positively correlated with global rates of genus extinction (p < 0.0001). The correlation between rates of stratigraphic origination and global genus origination is significant but much weaker (p=0.04). These results reveal the close relationship between many biological and stratigraphic patterns. Ongoing work to quantify both the paleo and strat records will help to test alternative biological hypotheses.