- The Paleontological Society
Unfossiliferous marine sedimentary rocks of Phanerozoic age are known to all field-oriented paleontologists. These troublesome units are often encountered in the field, perhaps cursed roundly for a moment or two, and usually shrugged off in pursuit of the next fossiliferous interval. Paleontologists tend not to discuss barren units, and they rarely publish on the absence of a fauna from what appears to be unaltered marine rock. But aren't barren marine sediments revealing something important about their paleoenvironment and possibly about the paleoenvironments of conformably adjacent fossil-bearing units? Shouldn't paleontologists be just as interested in knowing the locations and ages of unfossiliferous sediments as they are fossiliferous strata?
In this essay, I discuss the possible environmental significance of barren marine sediment and present preliminary data to suggest that its frequency may have varied considerably during the Phanerozoic. I also present evidence to suggest that this variation is associated with shifts in the prevailing location of preserved marine sediment accumulation from expansive epicontinental seas to comparatively narrow continental shelves. Finally, I propose that such shifts in the physiographic contexts of marine shelf habitats and their preserved sediments are associated with oceanographic effects that have greatly influenced environmental and biological evolution, the character of the fossil record, and our perception of marine biodiversity and macroevolution at many different temporal and spatial scales.
Nobody Home: Causes
In the short time that I knew Jack Sepkoski, he told me at least twice about all of his favorite Cambrian formations. He was particularly fond of puzzling over those unaltered marine sedimentary rocks that contained no, or exceedingly few, body fossils. The absence of skeletal material might, he reasoned, be the result of taphonomic or diagenetic loss. After all, it is widely appreciated that dissolution can substantially modify the diversity and composition of fossil assemblages (e.g., Cherns and Wright 2000 …