Twenty-five piston cores were taken from Baffin Bay, Texas, and 1 piston core was taken from an adjacent blue-green algal mat lagoon. The cores ranged in length from 85 to 670 cm. X-ray diffraction analyses and scanning electron microscope examination of the carbonate-rich layers in the sediment show that aragonite, calcite, Mg-calcite, and dolomite are all present as nonskeletal carbonates. Each varies from 0 to 100% in the individual samples studied.

Aragonite is the most common carbonate constituent, and occurs as needles less than 4µ in length. However, it also occurs as clusters of radiating needles, whose delicacy seems to indicate that the aragonite formed in situ and is not of a detrital origin. Aragonite also occurs as friable, partly lithified material and in 1-mm thick flakes. Calcite and Mg-calcite are found in unlithified muds in the form of anhedral to euhedral crystals 1-10µ in size. One sample composed of 100% Mg-calcite was semilithified. Dolomite has been reported from the subsurface where it occurs as lithified,

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laterally traceable beds composed of 1-5µ anhedral and a few euhedral stacked crystals. Two newly discovered occurrences of dolomite are as a minor constituent disseminated in unlithified carbonates and in a carbonate crust in the uppermost layer of a blue-green algal mat. The mat is growing today in a hypersaline lagoon adjacent to Baffin Bay, and the dolomite seems to be penecontemporaneous. The dolomite occurs with other carbonates which are forming as lithified grains embedded in the organic mat material.

With the exception of the lithified aragonite flakes and the lithified carbonate grains in the algal mat, all the lithified carbonates are found at core depths greater than 350 cm.

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