Comparison of origin and mineralogy between clay fractions of lime muds recovered from the Arabian Gulf lagoons and from the Taketomi Island intertidal flats

Abstract

Lime muds and similar kinds of carbonate sediments obtained from the Arabian Gulf regions and from Taketomi Island were isolated into clay and silt fractions and their carbonate mineralogy was investigated by X-ray diffraction (XRD). Two types of lime muds were recognized in the Arabian Gulf lagoons. Aragonite rich lime muds were found in the lagoon near Abu Dhabi. In this mud the concentration of aragonite increases in the clay fraction than the silt fraction. On the other hand, high-Mg calcite (HMC) rich lime muds were found in the lagoon in the Mubarraz shoal. In this mud the concentration of HMC always increases in the clay fraction than the silt fraction. At offshore area of the Arabian Gulf, the lime mud supplied from the coastal lagoons is diluted by low-Mg calcite (LMC) coccolith ooze. In the Taketomi Island samples, it is already known that the underlying coral reef limestones contain numerous patches of lime clay in which HMC is enriched and the HMC lime clay may be supplied to the overlying lime mud by erosion. Similarly, in the Mubarraz shoal lagoon the HMC enriched clay fractions of the lime mud may be supplied from the lime clay enclosures contained in the surrounding coral reefs.