Hydrochemistry, etc. of the Caves Branch Karst, Belize

Abstract

<p>An extensive karst developed on Cretaceous limestones in Belize, Central America, was the site of a hydrochemical, hydrologic, and morphologic study. This thesis describes the results of analysis of several hundred water samples from this humid tropical environment (mean annual rainfall - 2376 mm; temperature - 24.5°C). An unusual positively correlated discharge/total hardness loading curve in a major cavern conduit is explained as due to a two-component mixing model. Hydrologic modelling, soil CO₂ sampling, and discriminant analysis were used to infer the interior structure of a karst aquifer. Minimum effective porosity was determined to be 0.7%. Mean areal hardness of 187 mg/L (as CaCO₃) was found for springs draining the aquifer, indicating a denudation rate of about 90 m³/Km²/year. Aqueous Pco₂ of these springs was 1.1%, significantly higher than the 0.7% of mean karst soil CO₂ levels. This implies open system calcite solution evolution and/or internal CO₂ production within the aquifer.</p> <p>Various morphologic analyses suggest the cockpit-type surfaces of numerous karsts in the tropics may be significant due to disaggregation of existing topographic lows originally formed by creation of a fluvial topography. These fluvial valleys acted as favorable sites for concentration of aggressive water and consequent cockpit formation.</p> <p>Over 40 km of cavern passage were explored in the Caves Branch, including one of the largest tropical cavern systems known. Cavern development appeared to have been chiefly influenced by regional fracture patterns and topographic dip. The present development was completed by at least 140,000-215,000 years B.P., according to results of speleothems dated by the uranium/thorium disequilibrium method.</p>