GRIES, J. C., and W. E. FULL, Wichita State University, Wichita, KS
Big Creek is presently a relatively short river draining the flat coastal plain at the southern edge of the North American plate, south-central Belize. The recent sediments in this river consist of very fine-grained silts and clays derived from the local coastal plain. Offshore from the mouth of the Big Creek are shallow sand bars, channels, and eroding islands consisting of well-sorted, coarse sand comprised dominantly of feldspathic minerals. The location and geometry of these sands suggest that Big Creek was the fluvial source for this material. The sedimentological implication is that the nearshore and offshore parts of Big Creek represent a relatively large drowned deltaic complex, a modern analog of some lower Morrow depositional systems.
Coarse feldspathic material found in the Cockscomb basin in the Maya Mountains is transported by the Swasey branch of the Monkey River toward the Big Creek drainage to the coast. However, the Swasey branch is abruptly diverted southward to intersect the present-day Monkey River. Drainage analysis suggests that structural features subsidiary to the Chixoy-Polochic fault zone bounding the North American plate may have diverted flow southward, beheading Big Creek. Field observations have not found any major relief changes which would have blocked the flow of the river. Sedimentological evidence and drainage analysis support tectonic diversion of the head waters of Big Creek into present-day Monkey River. Similar processes are hypothesized to have occurred during Morrow deposition.
AAPG Search and Discovery Article #91008©1991 AAPG Mid-Continent Section Meeting, Kansas Geological Society, Wichita Kansas, September 22-24, 1991 (2009)