Late Cretaceous incident light reduction: evidence from benthic algae

Abstract

The Cretaceous-Palaeogene record of benthic marine algae is dominated by two calcified groups: red Corallinales and green Dasycladales. Non-geniculate corallines range to depths of -268 m from tropics to poles. In contrast, dasycladaleans are restricted to shallow, warm waters. During the Maastrichtian, both groups suffered extinction of two-thirds of their species. Extinction among deeper-water species (61–70%) was only slightly less than for shallow-water species (67–79%). This small amount of selectivity between species with very different depth-temperature distributions implicates a factor capable of affecting most of the photic zone. Large-scale reduction in incident light is more likely to have this effect than changes in factors such as temperature or sea level, which would affect shallow water species more intensely than those in deep water. Significant incident light reduction features in both the bolide impact and extensive volcanism hypotheses of Cretaceous-Palaeogene extinction. Dating of this major Late Cretaceous benthic algal extinction event requires further stratigraphic resolution. Available evidence suggests that it occurred in the latter part of the Maastrichtian. Its precise timing could clarify debate concerning the nature and cause of end-Cretaceous mass extinction. Both corallines and dasycladaleans recovered their diversity in Early Palaeocene species radiations.