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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 54 (1970)

Issue: 5. (May)

First Page: 864

Last Page: 864

Title: Reefs and Previous HitWaveNext Hit Action: ABSTRACT

Author(s): Michael E. Philcox

Article Type: Meeting abstract


Previous HitWaveNext Hit resistance is used in many definitions as a criterion for "reef." It is therefore important to clarify what Previous HitwaveNext Hit resistance means, whether it can be recognized in ancient reefs, and what effect the use of this criterion has on our thinking. For present purposes the noun "buildup" is used for all organically constructed mounds, including reefs, mudbanks, and algal stromatolites, irrespective of Previous HitwaveNext Hit activity.

Previous HitWaveNext Hit resistance has several legitimate meanings, but none can be used as a reef criterion unless a definite degree of Previous HitwaveNext Hit action is specified. Reefs would then be arbitrarily and undesirably separated from other buildups, whatever their biologic relations. Previous HitWaveNext Hit resistance as a criterion is therefore rejected, but as a variable characteristic, differing from one buildup to the next, it allows each to be placed in a unified Previous HitwaveNext Hit-resistance hierarchy.

The degree of Previous HitwaveNext Hit resistance required in a buildup depends on the Previous HitwaveNext Hit environment, defined by the depth of water over the buildup, Previous HitwaveNext Hit dimensions, and the relative frequency of waves of various dimensions. Previous HitWaveNext Hit energy increases rapidly upward, so that small depth changes involve large energy differences. Previous HitWaveNext Hit action (water-particle velocity) diminishes downward through the Previous HitwaveNext Hit zone to 4% of its surface value at a depth equal to half the wavelength. Turbulence in the lower part of the Previous HitwaveNext Hit zone requires no special adaptation by organisms; other forms of current may have more influence. Increase in Previous HitwaveNext Hit size lowers the depth to which Previous HitwaveNext Hit action is effective and increases turbulence at all depths in the Previous HitwaveNext Hit zone. If large waves damage the buildup, their relative frequency becomes i portant, because Previous HitwaveNext Hit resistance depends on a balance between Previous HitwaveNext Hit damage and repair by organisms. The critical size of damaging waves depends on the "Previous HitwaveNext Hit-resistance efficiency" of the constructing organisms, a function of growth form and strength. Organism growth rate contributes indirectly to the Previous HitwaveNext Hit-resistant capacity of a buildup through its role in repairing damage.

Diagnosis of the Previous HitwaveNext Hit-resistant capacity of ancient buildups is difficult. The geologic history of modern turbulence-indicative species (such as Acropora palmata) is short. Growth forms, distinctive in strong surf, become less diagnostic with decreasing Previous HitwaveNext Hit action. Current action must be distinguished from Previous HitwaveNext Hit action. Erosional debris, such as detached blocks, may be the product of slumping or boring organisms rather than turbulence. Storm damage may leave a record which gives a false impression of prevailing Previous HitwaveNext Hit conditions.

Previous HitWaveNext Hit-resistance as a variable characteristic must, despite difficulties, become increasingly important in the study of buildups through geologic time. Organic evolution made possible the development of increasingly Previous HitwaveNext Hit-resistant buildups and culminated in modern coral-algal reefs.

As a wider variety of constructing organisms became available and a correspondingly greater range of Previous HitwaveNext Hit environments was colonized, the range of buildups that could exist at any one time increased. Thus, if one considers Previous HitwaveTop-resistance as a variable characteristic instead of an absolute value, arbitrary definitions are less important than environments and evolutionary relations.

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