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In two separate areas on the continental shelf of British Honduras, the accumulation of Recent carbonate mud results in a series of mud shoals, herein termed mud shoal complexes. These shoal complexes range in depth from 1-5 feet and are dissected by tidal channels 6-10 feet deep. The tidal channels have slopes approximating 15° and divide each of the mud complexes into many individual mud mounds. The long axes of these mud mounds are essentially at right angles to the long axis of each mud shoal complex.
Both mud shoal complexes are represented by 7-9 feet of silt- and clay-size carbonate overlying a Pleistocene erosion surface. However, the mineralogical and biological characteristics of the two mud shoal complexes differ. With respect to mineralogy, one mud shoal complex, the Bulkhead, contains a lower percentage of aragonite and a higher percentage of low-magnesium carbonate in both the muds and adjacent sandy sediments than the Ambergris-Cangrejo mud shoal complex. With respect to biota, the Bulkhead shoal is characterized by a relative paucity of turtle grass, whereas the opposite is true for the other mud shoal complex. In the former case, mud deposition apparently results from the confluence of currents, the deposited mud being stabilized rapidly by the mucilagenous products of diatoms and other algae and less rapidly by the production of mucous-bound fecal pellets of worms. On the Ambergris-Cangrejo shoal, mud deposition and stabilization may be a product of the current-baffling and sediment-stabilizing attributes of the dense covering of turtle grass.
The mineralogical and biological differences between these two mud shoal complexes are not likely to be preserved in the geologic record. Inversion of aragonite and high-magnesium calcite to low-magnesium calcite, decay of plants, and possible dissolution of the opal tests of diatoms will undoubtedly occur during diagenesis. Thus the tendency of diagenesis may be to reduce the lithologic and biologic distinctiveness of mud mounds of dissimilar origin. Consequently, the origin of similar-appearing ancient mud mounds may not be identical, and any theory of origin of any particular mud mound should be evaluated with respect to the source of the mud, the cause of local mud accumulation and stabilization, and the possible relation of the mound to a mud shoal complex.
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