CORAL TAXONOMIC RICHNESS AND CHEMICAL ANALYSIS OF BASALTS IN BIOCLASTIC ROCKS, MOLOKAI, HI

Bioclastic sedimentary rocks of marine origin are exposed between 8.2 and 80 m above present sea level on the southwest flank of East Molokai, HI. These deposits may provide information regarding the depositional environment based on taxonomic richness and basalt clast origin. Coral genus richness, matrix composition and basalt clast origin were used to determine differences at low and high elevations. Outcrops were assessed for coral identification and sample collection. Assessed sites suggest that the geologic unit, QCBC, is broader than previous mapping.The matrix of these outcrops at high elevations (70-80 m) were composed mostly of basalts with some sand, shell and coral fragments. The basalts ranged in size from 8-200 mm. The matrix at low elevations (8.2-34.8 m) consisted mostly of sand with coral and shell fragments. Smaller basalt pieces were found, ranging in size from 0.064-200 mm. Genus richness increased from 3 at high elevations to 7 at low elevations. Coral taxonomic richness and difference in the matrix at low elevations indicates variability in depositional environments. Basalt samples were chemically analyzed by EDXRF and EDS, based on relative abundance of Na₂O, SiO₂ and K₂O, the basalts were a mixture of East and West Molokai volcanics.