Hydrology of South Bonaire, N.A.--A Rock Selective Dolomitization Model

Abstract

ABSTRACT Study of the hydrology of the south end of the island of Bonaire indicates that flow of fresh sea water onto the land takes place through permeability conduits in the underlying rock and emerges as numerous springs. Reflux of some heavy brine is probably continuously taking place because of gravitational instability. In addition, evidence suggest a major annual reflux event in early summer that causes a significant loss of heavy brine. This annual event is controlled by the total pressure of the brine exerted at the level of an impermeable clay layer within the Recent sediments being greater than the pressure exerted by the sea water at equivalent level. This annual return flow of brine moves through some of the same permeability conduits that supply fresh water through most of the ye r. Dolomite formed by such a hydrology should be confined to the permeability paths underneath an evaporitic sediment in older rocks. This pattern of rock-selective or permeability-controlled dolomitization may be common in ancient rocks.