Page 34 - Carbonate Facies in Geologic History

Definitions for Configurations of Local Carbonate Features 21

CARBONATE MASS

CAIlBo ..... n IUllDUPS
Fig. II -1. Definition of carbonate masses and carbonate buildups

Carbonate mass: A carbonate localization developed with only slight relief
caused by facies change from compactible argillaceous strata to noncompactible
pure limestone (Fig. II -1).
Geologic reef (Dunham, 1969, p. 190) or stratigraphic reef (Dunham, 1970),
(Heckel, 1974 p. 93): A general term for a carbonate body which encompasses
both the above concepts and includes both local mound-like and regional curvili-
near trends. No inference as to origin or internal composition is included.

Definitions Based on Configuration of Regional Features

Carbonate ramps: Huge carbonate bodies built away from positive areas and
down gentle regional paleoslopes. No striking break in slope exists, and facies
patterns are apt to be wide and irregular belts with the highest energy zone
relatively close to the shore (Fig. II-2).

Carbonate platform: Huge carbonate bodies built up with a more or less
horizontal top and abrupt shelf margins where "high energy" sediments occur.
The normal processes of carbonate sedimentation effectively and rapidly turn
ramps into platforms and create narrow, steep shelf margin ridges. Slopes on
some ramps may be so gentle as to make them commonly indistinguishable from
platforms. Thus, these terms are often used interchangeably (Fig. 11-2).
Major offshore banks: Complex carbonate buildups of great size and thickness
well offshore from the coastal ramps or platforms (Fig.II-3).
Shelf: An area on top of a ramp or platform.
Shelf margin: The edge of the shelf on a platform.
Shelf lagoon: Often used for the shallow neritic shelf seas on a platform.

Definitions for Configurations of Local Carbonate Features
(Mostly implying organic accumulation rather than purely mechanical accumula-
tion.)
Mound: Equidimensional or ellipsoidal buildup.