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Abstract

Carbonate sequences and parasequences that formed under known or inferred 1 to 40 m.y. tectono-eustatic and 20 to 400 k.y. Milankovitch low to high amplitude sea level changes are shown to leave distinctive diagenetic records.

On carbonate platforms, low amplitude, high frequency sea level fluctuations typical of global green-house times form thick accumulations of meter-scale cycles with regional tidal flat caps, and there is only limited erosion of cycle tops. Humid climate cycles have early cemented, typically undolomitized intertidal fenestral caps and some supratidal laminites; aragonite fossils commonly are leached. If the climate is sufficiently arid, the cycles are dolomitized and aragonite is leached during falling sea level. Primary intergranular and moldic porosity is preserved in lower parts of cycles, and intercrystal and vuggy porosity is present in dolomitized subtidal facies and laminite caps beneath cycle top anhydrites and fine dolomite.

Moderate amplitude, high frequency fluctuations in sea level occur during times of intermediate continental glaciation. Cycles commonly have muddy facies grading up into grain-rich facies; they lack tidal flat facies and instead have small scale karstic surfaces or caliche directly over shallow subtidal facies. In humid climates, cementation plugs porosity in the upper phreatic zone, typically in grainstones just below the karstic surface. Zoned cement overgrowths in the deeper phreatic zone, although volumetrically minor, show a partial to complete record of high frequency sea level fluctuations that affected the sequence.

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