Belize Model, A Carbonate-Clastic Shelf Buildup
Belize, a small Central American country located on the Caribbean Sea south of the Yucatan Peninsula, offers an excellent modern analog of a mixed carbonate/clastic shelf buildup. Its 175-mi long reef tract, second longest in the world, restricts a shallow shelf depobasin into which terrigenous clastics source from the Maya Mountains to the west and carbonates dominate from the east. Mixed lithologies occur along strandlines, in submarine channels, and in lagoons and river-delta fronts, which are scattered throughout the depobasin. Energy sources from both land and sea influence sedimentation. Heavy summer rains flood the basin with arkosic and quartzose clastics, and periodic sea storms and hurricanes drive carbonate particles from the reef tract landward into the basin. Modern environments include the reef tract, carbonate tidal flats, shallow shelf patch reefs, lagoons, cayes, mainland coast deltas, estuaries, lagoons, and beach/bar barriers. Modern sediments include reef metazoans, algae, coralline algae, lime mud, quartz, and feldspathic sand and clay. The setting for the model has been influenced by Tertiary tectonics and Pleistocene sea level changes. Karstification occurred during the past 10,000 years, partly controlling topography and resulting Holocene sediment patterns. Facies patterns of the Belize Holocene are compared to the Jurassic of Montana. The Middle Jurassic Piper Formation exhibits a nearly 100-mi long carbonate barrier/buildup restricting a clastic-dominated shelf. Other ancient mixed carbonate/clastic terranes may fit this model a well.
AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.