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On the uplifted Pleistocene reef tracts of Barbados the nature and distribution of subaerial diagenetic fabrics reflect changes in 3 primary controlling factors: climate, soil, and substrate facies. These factors influence the amount and rate at which meteoric water is introduced into and held within the immediate subsurface.
Annual rainfall varies areally by a factor of 2, and evaporation, locally potentially greater than precipitation, is generally at a maximum in areas coincident with minimum rainfall. Soils grade from montmorillonitic, with an exceedingly slow rate of internal drainage, to kaolinitic, where drainage is as much as an order of magnitude faster. Substrate facies plays a subordinate but definite role in that sediments with a very open framework are incapable of retaining the pore water necessary for upward capillary transfer back to the evaporative sediment-air interface.
Subaerial fabrics are best developed in areas of low rainfall, high evaporation, and montmorillonitic soil cover. These conditions favor a local solution-reprecipitation process at or near the rock-soil-air interface. Where water is introduced into the subsurface in greater quantity or more quickly (because of higher rainfall and/or more kaolinitic soils) intense dissolution predominates, commonly with the attendant destruction of earlier formed subaerial fabrics.
Subaerial diagenesis appears to be a geologically rapid process bearing a nonlinear relation to length of exposure. Fabrics are equally well developed on successive reef tracts spanning approximately 300,000 years of exposure, and are present on subsurface discontinuities which represent breaks of only a few thousand years.
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