Elemental composition of lime mud recovered from coral reef Lagoonal basins, the Yaeyama Islands, Okinawa, Japan

Abstract

Surface unconsolidated carbonates were sampled from lagoonal basins in the Shiraho and Sekisei Coral Reef areas, the Yaeyama Islands. Lime mud fractions were isolated from these carbonates by sieving and sedimentation methods to collect particles between 62.5 and 2 ,u. The isolated lime mud fractions were analyzed for carbonate-bound trace elements, C03 contents, mineralogical compositions by the X-ray diffraction analysis (XRD) , and petrographic observations including scanning electron microscope (SEM) observations. The carbonatebound trace element concentrations were determined by subtracting the 0.75 N LiCI-0.25 N CsCI in 60% ethanol leachable fraction from the 1 N ammonium acetate-acetic acid (pH adjusted to 5.2) leachable fraction. Lime mud is composed mineralogically by HMC (high-Mg calcite), HSA (high-Sr aragonite), LSA (low-Sr aragonite), and LMC (low-Mg calcite). However, the carbonate-bound Mg/Ca and Sr/Ca ratios are considerably lower in lime mud than the carbonate sand and gravels which contain the same amount of carbonate minerals with the lime mud. This suggests that Mg and Sr were leached without changing mineralogy during the formation of lime mud from coarse carbonate grains. Diagenetic changes in lime mud might have already started before its lithification processes to limestone.

Sealevel history recorded in the Pleistocene carbonate sequence in IODP Hole 310‐M0005D, off Tahiti

“…Fifty‐three thin‐sections were examined for microfacies analysis of carbonate deposits. The content of terrigenous material in deposits (wt%) was measured following the method of Yamamoto and Ishihara (1998).…”

Geochemical study of lime-mud borings and associated coral-reef limestones in the intertidal flat of Kondoi Beach, Taketomi Island, Okinawa, Japan

“…Lime mud is constituted by silt-and clay-size carbonates of both detrital and authigenic origins. Genesis of clay fraction of lime mud in particular has been much investigated by workers (Hoskin 1968;Stieglitz 1972;Yamamoto and Ishihara 1998;Yamamoto and Oshima 2000). Two types ofclay fractions are recognized for lime mud in the various coral-reef environments of the world.…”