Distribution of Foraminifera in the Arabian Gulf

Ninety-eight foraminiferal species identified in forty sediment samples collected from different parts of the Arabian Gulf (Persian Gulf) are illustrated and their distribution investigated. The identified foraminiferal fauna of the Gulf consists of 15% Textulariina (agglutinated forms), 37% Miliolina (porcellaneous forms), 0. 1% Lagenina, 1% Globigerinina (planktic forms) and 47% Rotaliina (the last mentioned three suborders constituting the hyaline forms). Cluster analysis of quantitative data on the distribution of tests of foraminiferal species in the samples allow us to determine four assemblages, generally corresponding to the major geomorphic provinces of the Gulf: a western Iranian Shallow Shelf assemblage, an assemblage distributed all over the Axial Zone of the Arabian Gulf, a deep water assemblage of the Central Basin of the Gulf extending up to the Strait of Hormuz and an Arabian Shallow Shelf assemblage. The study of the geographical distribution of these assemblages and their relation to major geographical characteristics of the surrounding lands suggests that the nature of the foraminiferal assemblages depends mainly on biotic factors. The fauna of the Iranian Shelf displays a high diversity (average Yule-Simpson diversity index for the assemblage 39.2) as it receives an appreciable amount of nutrients from drainages in the topographically high Iranian hinterland. The fauna of the Arabian Shelf displays relatively low diversities (average Yule-Simpson diversity index for the assemblage 16.1) as the arid Arabian hinterland is practically deprived of active drainage. The foraminiferal fauna of the deepest parts of the investigated localities display low diversities and include appreciable proportions of agglutinated forms. Lowest diversities are observed near the Strait of Hormuz (Yule-Simpson diversity index of 14.9), highest diversities near the mouth of Shatt Al-Arab (Yule-Simpson diversity index of 62.9). This suggests that the amounts of nutrients provided by drainages debouching in a landlocked basin is an important factor determining the constitution of the foraminifera of bottom sediments. INTRODUCTION Publications concerning the foraminifera of the Arabian Gulf include the works of Murray (1965a,b, 1966a,b,c, 1970a,b), Haake (1970, 1975), Lutze et al. (1971), Hughes-Clarke and Keij (1973), Evans et al. (1973), Lutze (1974), Anber (1974), Lutze and Wolf (1976), Shublak (1977), Al-Abdul-Razzaq and Shublak (1983), Al-Abdul-Razzaq and Bhalla (1987a,b) and El-Deeb (1990). Most of these works did not aim at extensive taxonomic treatment of the considered fauna. The use of the latest advances in foraminiferal classification compiled and discussed by Loeblich and Tappan in 1988, and also the consultation of some recent works on the subject as those of Cimerman and Langer (1991) and Levi et al. (1989, 1991, 1992), enables to present in this work an up-to-date illustrated account of the taxonomy, distribution and ecology of 98 species of foraminifera recognized in 40 sediment samples collected all over the Arabian Gulf in the winter of 1992 by the US oceanographic research vessel "Mount Mitchell." Text-figure 1 shows the study area and the location of sampled stations. The aim of this paper is to investigate the areal distribution of the foraminiferal species in this landlocked sea, situated under arid climatic conditions, and to relate this distribution to prevailing sedimentational processes. The distribution of sedimentary facies and the sedimentary processes prevailing in this sea have been the object of a series of important publications presented in a book edited by Pursuer (1973). Before dealing with the investigated foraminiferal fauna, a brief account of the general geographic (climatic) setting of the Arabian Gulf and characteristics of its sedimemts will be presented to better illustrate the discussion of the factors affecting the distribution of foraminiferal assemblages in the study area. GEOGRAPHIC SElTTING AND GEOMORPHOLOGY The Arabian Gulf is a marginal sea measuring some 1,000km in length and 200-300km in width. It has an average depth of 35m and a maximum depth of about 100m, near its connection to the Indian ocean, in the strait of Hormuz. It covers an area of 226,000km2. Its elongate bathymetric axis subdivides it into two geomorphic provinces: a stable Arabian foreland and an unstable Iranian fold belt. The individuality of each one of these provinces is expressed by the contrasting coastal and bathymetric morphologies of Arabia and Iran (text-fig. 2). Excessive evaporation and partial isolation from the Indian Ocean induces abnormally high salinities throughout most of the basin. Salinities reaching 70% have been recorded in remote Arabian lagoons (Pursuer and Seibold 1973). Because the prevailing NW "Shamal" wind blows down the axis of the gulf, most coastal environments are affected by wave and surface currents favoring the formation and dispersal of carbonate sand on the Arabian side and terrigenous material on the Iranian. Tidal currents affect the texture of sediments, even in the deepest parts of the gulf. Holocene sediments in the gulf are mixed significantly with relict older sediments, especially in the deepest parts of the basin. Seibold and Volbrecht (1969) subdivided the Arabian Gulf into several bathymetric provinces (text-fig. 2). micropaleontology, vol. 43, no. 3, pp. 253-280, text-figures 1-7, plates 1-10, tables 1-2, 1997 253 This content downloaded from 207.46.13.163 on Fri, 08 Jul 2016 06:07:19 UTC All use subject to http://about.jstor.org/terms Omar H. Cherifet al.: Distribution offoraminifera in the Arabian Gulf TEXT-FIGURE 1 Location map showing the study area and sample sites. TEXT-FIGURE 2 Map showing the principal bathymetric provinces of the Arabian Gulf (after Seibold and Vo'lbrecht 1969). 254 This content downloaded from 207.46.13.163 on Fri, 08 Jul 2016 06:07:19 UTC All use subject to http://about.jstor.org/terms Micropaleontology, vol. 43, no. 3, 1997 TEXT-FIGURE 3 Areal distribution of frequencies of foraminiferal tests in sediment samples of the Arabian Gulf. TEXT-FIGURE 4 "Facies" distribution map of foraminiferal assemblages in the Arabian Gulf. The map is based on the relative proportions of agglutinated, porcellaneous and hyaline forms in the investigated samples. 255 This content downloaded from 207.46.13.163 on Fri, 08 Jul 2016 06:07:19 UTC All use subject to http://about.jstor.org/terms Omar H. Cherifet al.: Distribution offoraminifera in the Arabian Gulf Group 2 Axial Zone Assemblage