Biogenic Sedimentary Structures (Trace Fossils) in Leg 15 Cores

Abstract

Sediment cores from the deep sea rarely show biogenic sedimentary structures so well preserved, in such variety, and so readily comparable with land-based occurrences as those in Deep Sea Drilling Project Leg 15 cores from the Caribbean Sea. These markings, or fossils, were formed by sediment-dwelling benthonic animals that structured the sediment into distinctive patterns. Most trace fossils exhibited in the cores are records of the feeding behavior of marine invertebrates that exploited the sediment for food. The well-indurated Upper Cretaceous sediments from Sites 146, 152 and 153 best show the suite of traces. The majority of our examples are from Site 146, which was continuously cored and offers the greatest number and variety of specimens. In the overlying relatively unconsolidated Cenozoic sediments, the activity of benthonic animals is usually expressed as indistinct mottles or homogeneous beds. It is likely that the degree of induration of the Cretaceous rocks served to accentuate and better reveal the trace fossils described herein. Our purposes are to document the trace fossils in the Caribbean cores, to compare them with traces described elsewhere, and to discuss the implications of these occurrences for paleogeographical and paleoecological studies. We thank DSDP personnel for the opportunity to study the cores and for numerous courtesies, and C. Kent Chamberlain for thoughtful review of the manuscript.