Abstract

The definition and identification of fossil reefs has been a continually vexing problem for paleoecologists. One approach to this problem is a study of fossil orientation in "reef" strata. Orientation of corals in exposures of reef limestones has been mentioned in the literature, but usually in a brief, non-quantitative way. Eight study sites were used to investigate the nature of structures described as reef-related. Two sites were selected from the Pleistocene Key Largo Limestone of Florida, probably a backreef facies. The Florida sites were used as fossil reef reference sites, because of their close relationship to modern Florida reefs. The Devonian site at Ridgemount, Ontario, has bioherm and interreef facies. Silurian sites with bioherm facies were studied at Pekin, New York, and Maumee, Ohio. Silurian sites with flank facies were examined at Bluffton and Delphi, Indiana, and Rockford, Ohio. In this study, orientation and several width and height measurements were made on each fossil. Colonial corals were used at all sites. Stromatoporoids were also used at Pekin.

The Florida site shows the most pronounced upward orientation. Let W = fossil width, H = fossil height. In Montastrea, upright small heads generally have W 45° from vertical) small heads have W≥H. Small upright heads are probably juvenile heads in growth location. Sideways heads have been broken off, transported, and deposited in stable positions. All of the larger heads are upright and probably in growth location. Diploria has an even higher percentage of heads in growth location, probably because Diploria heads are less easily broken off than Montastrea heads. The Key Largo Limestone is a reef-related structure with a dominance of corals in growth location, and a few small broken heads with orientation determined by stability of position after transport.

Bioherm facies at Pekin and Maumee have prominent upward orientation. There is more disorientation of heads than at Florida however. The Florida sites have much more abundant and much larger corals, and much less mud in the rock matrix than the Silurian Pekin and Maumee sites. Since W>H for most of the fossils in the Silurian bioherms, this might indicate most upright fossils are merely in their most stable position after transport. Alternatively, most upright fossils may be in growth location, or the bioherms are detached allochthonous blocks which have come to rest in their present position without tilting.

Ridgemount interreef facies has dominant sideways orientations, with W>H for most fossils, indicating transport followed by deposition in stable position. Flank facies at Bluffton, Delphi, and Rockford have many more disoriented corals than the Silurian bioherms. Delphi has an almost random distribution, and also the best developed flank beds. Rockford has a prominent upward spike, possibly because the flank beds studied are near-core flank facies. At all flank facies sites, W>H is dominant, probably because fossils have been transported and deposited in stable positions. This situation is expected in flank facies.

The orientation data from the Silurian bioherms and flank beds does not contradict either the usual in-place reef facies interpretations for these rocks, or an allochthonous block origin for these bioherms. The results of this study illustrate the paleoecological and sedimentological value of orientation studies on various reef facies. An important feature is the quantitative nature of the results. The method can be used for nonreef strata also, where oriented fossils are found.

Keywords: Coral, Limestone, Orientation, Paleoecology, Reef, Sedimentology, Stromatoporoid, Pleistocene, Devonian, Silurian, Florida, Indiana, New York, Ohio, Ontario.

LLU Discipline

Biology

Department

Biology

School

Graduate School

First Advisor

Ariel A. Roth

Second Advisor

Arthur V. Chadwick

Third Advisor

Conrad D. Clausen

Fourth Advisor

Ivan G. Holmes

Fifth Advisor

Grenith J. Zimmerman

Degree Name

Doctor of Philosophy (PhD)

Degree Level

Ph.D.

Year Degree Awarded

1978

Date (Title Page)

9-1977

Language

English

Library of Congress/MESH Subject Headings

Fossil reefs--North America; Corals, Fossil--North America; Paleoecology--North America; Paleontology--Methodology; Stromatoporoidea--North America

Type

Dissertation

Page Count

viii; 131

Digital Format

PDF

Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.

Collection

Loma Linda University Electronic Theses and Dissertations

Collection Website

http://scholarsrepository.llu.edu/etd/

Repository

Loma Linda University. Del E. Webb Memorial Library. University Archives

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