Deposition and Stratification
Published:January 01, 1982
As every sedimentologist knows, there is a great variety of primary sedimentary structures—some restricted to bedding planes, other involving a definite thickness of sediment. Terminology and classification are necessarily somewhat intricate and confusing, and are far from having reached an ultimate state of perfection. We do not intend to review classification of primary sedimentary structures here; for those interested, the following references offer a fairly compete spectrum of views: McKee and Weir (1953), Allen, (1963), Campbell (1967), Conybeare and Crook (1968), Pettijohn, Potter and Siever (1973, p. 102-127), and Blatt, Middleton, and Murray (1980, p. 123-132).
The most common primary sedimentary structures are formed by currents. In the belief that utility rather than completeness should be the goal in a course of this kind, we emphasize stratification features produced by migrating bed forms in sediment from coarse silt to finest gravel size as being among those most useful in interpreting deposition of coarse clastic sediments. Of course, this by no means exhausts the list of common current-generated sedimentary structures that are valuable in interpretation; current-generated sole markings are an obvious example of others.
At first sight there is a bewildering variety of stratification types produced by bed-form migration. If we look at a certain point in some depositional environment, direction and magnitude of flow and thus also of rates of sediment transport and deposition vary substantially with time in response to changing flow and sediment supply. And deposition
Figures & Tables
Structures and Sequences in Clastic Rocks
These notes are for a course on the use of primary structures and stratification sequence as tools for interpretation of depositional environments. The emphasis is to provide a concise review of the factors that had led to the renaissance in clastic sedimentology during the decade leading up to 1975. The attempt is to provide an organized summary of both experimental studies and ideas on bed forms and primary sedimentary structures that was then relatively new and to show how this information could be applied to solving geologic problems. A second broad objective of the course is more philosophical, in that there is an attempt to outline some general approaches to interpretation and convey the goals of interpretation. The authors believe that there are a fairly small number of general depositional settings but that numerous environmental and process variables within each general setting lend considerable variation to the deposits themselves. The emphasis is at the scale of features and sequence that can commonly be observed in individual outcrops or cores. Interpretation begins with data collected at this level.