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The AAPG/Datapages Combined Publications Database
Journal of Sedimentary Research (SEPM)
Abstract
Sedimentation of Middle Devonian Carbonates, Southeastern Indiana
Brian J. Bluck
ABSTRACT
A quantitative study is made of the organic and inorganic constituents of a sequence of Devonian limestones and dolomites occurring between the base of the New Albany shale and the top of the Jeffersonville 'coralline zone' of Indiana. On the basis of composition and texture the rocks are grouped into seven microfacies, which represent lacustrine, mudflat, lagoonal and off-shore environments.
Rocks which formed under lacustrine conditions are algal. They are typified by fine grained limestones and dolomites which are often irregularly laminated; the laminae frequently occurring as cabbage shaped masses. Cavities, present in these beds, are sub-divided into three groups:--(i) being irregular in shape, and representing the original pores in the spongy algae, (ii) later in age than (i), formed in collapse breccias, and (iii) cavities formed by the leaching away of a known mineral. Most of the cavities are filled with large, often single crystals of calcite.
Mat type algae, found on the mud flats, are recognized by growth structures, associated sedimentary structures and their paleogeographical position in relation to other environments.
Rocks characterized, almost exclusively, by a fauna of thin shelled brachiopods, are enclosed in lime mud and are assigned to a lagoonal type of environment. Calcarenites, with an abundant and diverse fauna, belong to the shallow water regime of an off-shore environment, being well sorted rocks with granular cement. Poorly sorted calcarenites, with evidence of extensive scavenging, are the product of somewhat deeper, quieter parts of the off-shore environment.
Using distinctive quartz bands, the limestones can be correlated over a considerable part of the area, while from a study of the changes in quartz particle size, a northerly land area is demonstrated.
The history of the rocks begins with the regression of the sea off this northerly land area and the extensive development of algal limestones in the so formed lakes and mudflats. The bodies of water, left beyond by the receding seas, probably became sites of penecontemporaneous dolomitization. This dolomite, being continually eroded, was fed to areas farther south. The regression was followed by a transgression of the sea into the northerly areas, and well washed calcarenites were deposited on top of the algal limestones. Before the deposition of the succeeding New Albany shale there was a general shallowing of the water throughout most of the area.
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