Origin of Sediment in a Holocene Carbonate Mud Mound, Cangrejo Shoals, Northern Belize

C. S. Teal

Cangrejo Shoals is an 18 km², Holocene, shallow-water, carbonate mud mound along the outer shelf-to-inner shelf (Chetumal Bay) transition in northern Belize. Sediments are 1.2-6.7 m thick, and were deposited during the Flandrian transgression in and around a depression on the underlying Pleistocene limestone. Biotic composition and mineralogy of these sediments were compared to those parameters of sediment standards from the outer shelf and inner shelf in order to interpret sediment source at Cangrejo.

Outer shelf sediments (n=10) are slightly muddy sands dominated by corals, Halimeda, coralline algae, and Homotrema rubrum; mineralogy of both mud and coarser size fractions averages 57% HMC, 42% aragonite and 1% LMC. In contrast, inner shelf sediments (n=10) are sandy muds dominated by miliolid and soritid foraminifers; mud and coarser size fractions average 90% HMC, 7% aragonite and 3% LMC. The upper 4.3 m of sediments at Cangrejo consist of 68% mud and 32% sand and gravel-size skeletal particles, the average compositions of which are 72% HMC, 25% aragonite, and 3% LMC. Soritid and miliolid foraminifers compose 80% of total biota, the remaining 20% represented by corals, Halimeda, coralline algae, and H. rubrum. Linear unmixing suggests that 60% o the mud at Cangrejo was derived from the outer shelf, and 80% of the skeletal particles was derived from the inner shelf. The amount of sediment produced in situ, calculated from the measured budget of epibionts on standing Thalassia, is less than 2% of total sediment volume. These data suggest that accumulation of the mud mound has resulted largely from sediment transport rather than in situ sediment production.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California