Assemblages of Biogenic Structures in Non-Marine and Marginal Marine Environments
The papers in this first part of the volume cover trace fossil assemblages in a range of environments from dunes to marginal marine deltaic settings. The lead paper by A. A. Ekdale and M. Dane Picard deals with trace fossils and bioturbation textures in Jurassic eolianites from Utah. Most eolianites are thought to possess a sparse fossil record, but Ekdale and Picard report several new and distinctive trace fossil forms that presumably were produced by insects. Their Table 1 summarizes well the known distribution of animal traces, trace fossils, and body fossils in dune and interdune deposits.
Large escape burrows attributed to the activity of Devonian bivalves in a fluvial environment are analyzed by Richard Thoms and Thomas Berg They suggest a modern bivalve as a tracemaker analog for the fossil escape borrows. The study demonstrates well how knowledge of the structures produced by a modern organism under known living conditions can be used to interpret with greater clarity the significance of ancient biogenic sedimentary structures and their paleodepositional setting.
William Hakes reports on a trace fossil asscmblage from an Upper Pennsylvanian sequcnce in Kansas that is thought to be indicative of a lowered salinity environment The unique aspects of the assemblagc are the small size of the individual trace fossils along with high divcrsity moderate abundance and excellent preservation Small sized trace fossils easily can be overlooked but assemblages of such forms may be a real key to the recognition of brackish marinc paleoenvironments in the rock record.
Figures & Tables
Organisms of one sort or another today inhabit virtually every sediment environment on Earth, and the rock record tells us that this has been the case through the greater part of our planet’s history. Furthermore, organisms leave their mark in most sedimentary settings, either directly in the form of body fossils or indirectly as biogenic structures. In addition to their often profound modifying effects on substrates, ancient biogenic structures preserve a record of organism behavioral activity in response to substrate and other paleoenvironmental controls. Thus, biogenic structures can be highly useful as facies indicators and can provide valuable clues to the interpretation of paleodepositional environments. The purpose of this volume is to present a broad spectrum of case-book examples of the use of biogenic structures in the interpretation of depositional environments.