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Abstract

This chapter is an account of the contemporary system in the evaporite basin. It is organized around components of the basinal water balance—storage, inflow, and outflow—with attention to control factors, dynamics, and hydrochemistry. There also is focus on the precipitates and those chemical, physical, and biological processes that shape them into a variety of evaporite sediments and rocks. The chapter concludes with analysis of the salt budget.

The prevailing basin system is based on seepage. Seawater flows in via permeable rocks in the barrier, and brine flows out into receptor formations that underlie the basin and crop out in the surrounds. The contemporary basin floor lies between sea level and −4.3 m, therefore, Indian Ocean water is driven by hydrostatic pressure through permeable barrier materials. Permanent brine ponds and brine sheets occur in the northern basin where there is high inflow and consequent local seawater discharge. However, seepage inflow is puny against avast evaporative outflow, and the basinal brine surface mostly is suppressed below the floor so that the basin is dominated by a phreatic majanna (Chapter 1). Brine (and salts) outflows by seepage, mostly through brine sinks along the hinterland margin of the basin.

Brackish inflow from river and/or from direct rainfall occasionally disturbs the prevailing marine brine system. Vast shallow flood sheets then cover the basin floor, engulfing marine ponds and majanna. Brackish inflow is highly irregular, and inflow volumes are less than 20% of annual evaporative outflow, so that flood sheets have short-lived impact on the prevailing

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