Figure 1.

Post-Paleozoic anoxic events and biologic responses. Time (in millions of years) at the base of listed stages and epochs (16) occupies the vertical axis. The event column indicates the stages containing major anoxic events: G, global events; R, regional events; and I, events supported by carbon isotope ratio excursions. A schematic representation of major anoxic events appears in the adjacent column. Lines across the column indicate global events. Events that tended to affect deeper water or basinal events are on the left of the column. The presence of frequent anoxia in the deep Atlantic from the Aptian through Cenomanian is indicated by blocking out the left-hand side of the column. Biotic events include the presence of Ophiomorpha, a deep-burrowing trace fossil form in onshore and offshore habitats, indicated by Oph. Sampled intervals lacking Ophiomorpha are indicated by N (17). Note that Ophiomorpha occurs in all but one of the sampled offshore intervals after the Cen/Tur boundary and none before this boundary. Cheilostome diversity in onshore and offshore facies is noted by a numerical value [after Bottjer and Jablonski (3)].