--> Holocene Sea Level History and Admixed Siliciclastic and Carbonate Deposition in Southern Belize, by W. F. Precht; #90986 (1994).

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Abstract: Holocene Sea Level History and Admixed Siliciclastic and Carbonate Deposition in Southern Belize

William F. Precht

A dredge-cut across the barrier sand-spit that comprises Placentia Point in southern Belize, allows for an opportunity to observe both temporally and spatially, a dynamic relationship between reefal carbonates and siliciclastics. To better understand the origin of this juxtaposition and to decipher the progressive development of these in terms of sea level history and sedimentary sequences, an additional transect of cores were taken.

The base of this section is represented by lowstand terrigenous clastics of Pleistocene age. Immediately overlying these deposits are transgressive mangrove peats. These basal peats formed at former sea level positions and have been radiocarbon dated. These dates fit well with a previously developed sea level curve for Belize and as such, provides a good datum for reconstruction of the Holocene transgression.

Continued sea level rise led to colonization of bathymetric highs by oysters and sediment tolerant corals. These bathymetric highs reflect antecedent limestone templates that are structurally controlled. As more normal marine conditions developed, backstepping reefal carbonates comprised of sediment baffling, branching corals became established. These reef corals have been dated at approximately 3.4 Ka. Coeval with and subsequent to reef development, an influx of fine-grained siliciclastics led to the smothering of these reef corals in growth position. Continued siliciclastic deposition associated with the formation of the barrier spit, locally outpaced sea level rise and developed prograding, regressive wedges that completely buried the reef.

Presently an analogous relationship between siliciclastic dominated environments and carbonate dominated sedimentation exists between Placentia Point and Placentia Cay. Based on present sediment accretion rates for Placentia Point it is interpreted that Placentia Cay will be smothered and captured in a similar fashion within the next few hundred years.

This study reveals a developmental history that can directly be attributed to decelerating sea level rise for the mid-to-late Holocene in Belize. This study also demonstrates the application for interpreting and predicting the responses of admixed siliciclastic-carbonate facies to fifth-order sea level cycles.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994