DISTRIBUTION AND TAXONOMY OF MODERN BENTHIC FORAMINIFERA OF THE WESTERN SUNDA SHELF (SOUTH CHINA SEA) OFF PENINSULAR MALAYSIA.

Book excerpt: This study investigates, for the first time, the distribution and taxonomy of modern benthic foraminifera from the western Sunda Shelf, southern South China Sea. The uppermost centimeter of 54 surface sediment samples ([greater than] 150 [mu]m) from nearshore (8 m) to inner shelf (60 m) water depths yielded 125 species. Five sample groups (CGT1–5) are recognized by cluster analysis of the total (live + dead) foraminiferal relative abundance data. Discriminant analysis and ANOVA both revealed that the five groups are statistically distinguishable at the 95% confidence level. The distribution of groups is related to variations in depth (as a proxy for several environmental factors) and substrate grain-size. This relationship is confirmed by canonical correspondence analysis. CGT1, located closest to shore (8–14 m water depth), has a high diversity assemblage (49 species) and is characterized by Amphistegina radiata and Amphistegina lessonii. CGT1 occurs in medium to coarse quartz sand substrates likely derived from the nearby Terengganu River with the exception of a single station (TR1-S2). This site is characterized by a mud substrate, the taxa Ammobaculites exiguus, Millettiana millettii, Planorbulina acervalis, and Rosulina globularis, and an unusually high relative abundance (3%) of planktonic foraminifera. CGT2 (21–22 m) has a lower diversity assemblage (33 species) and is strongly dominated by A. radiata and A. lessonii, often with tests infilled by the authigenic mineral berthierine. CGT2 occurs in gravelly quartz sand substrates. CGT3 (32–41 m) occurs in shelly muddy quartz sand substrates, has a high diversity assemblage (46 species), and is characterized by Assilina ammonoides, Discorbinella bertheloti, and Asterorotalia milletti. Like CGT2, berthierine-rich internal molds of Amphistegina tests are common. CGT4 (44–59 m) occurs in mud substrates and is characterized by Heterolepa dutemplei and A. milletti; the nearshore taxa A. radiata and A. lessonii do not occur in this group. CGT4 has the highest diversity assemblage (51 species) of all the sample groups and foraminiferal tests are well preserved. CGT5, located furthest from shore at 60 m water depth and in shelly sandy mud, has a high diversity assemblage (46 species) and is characterized by H. dutemplei and A. ammonoides, with rare A. milletti; live (rose Bengal-stained) specimens are rare in CGT5 compared to the other four groups. Comparison to foraminiferal assemblages in underlying Pleistocene core material suggests this assemblage occurs in a lag deposit possibly associated with modern bottom current activity. Combining the results of this study with previously published research, three generalized foraminifera-based subdivisions are recognized across the Sunda Shelf (8–200 m water depth). Nearshore areas ([less than] 40 m) are dominated by fine to coarse sand substrates and symbiont-bearing taxa (A. lessonii and A. radiata). Inner shelf areas (40–100 m) are associated with sandy mud substrates and high relative abundances of H. dutemplei. Outer shelf areas (100–200 m) are associated with muddy substrates and the presence of Uvigerina schwageri. These data can be used as the basis for paleoenviromental reconstruction of Quaternary core material from the Sunda Shelf.