J.K.A. U.: Mar" Sci., Vol. 3, pp. 25-38"(1412 A.H./1992 A.D.)

Foraminiferal Distriqution in Recent Sediments of JizanShelf, Red Sea, Saudi Arabia

M. ABOU aUFFaculty of Marine Science, King Abdulaziz University,

Jeddah, Saudi Arabia

ABSTRACT. Thirty-four bottom sediments samples from Jizan shelf havebeen analysed for benthic foraminifera where hyaline, porcelaneous andagglutinated foraminifera have been recorded. In contrast with the north-eastern parts of the Red Sea, hyaline foraminifera dominate over por-celaneous foraminifera in about 68% of the samples. The relative abun-dance of hyaline foraminifera over porcelaneous ones is attributed to theperiodic influx of fresh water and mixing of terrigenous sediments with thein situ carbonates.

The total number of foraminifera is highly variable and the sedimentsgenerally poor in foraminifera compared to those of the central and north-ern part of the Red Sea. Such a depletion is due to the mixed nature of thesediments and is independent on their mean-grain size. However, hyalineforaminifera shows a general negative relationship with the mean grain sizeof the sediments; agglutinated foraminifera shows preference to sandy orsilty sediments.

The faunal assemblage identified do not show a clear relationship withdepth. However, hyaline foraminifera reveals a positive correlation withorganic carbon, while porcelaneous foraminifera shows a positive correla-tion with carbonate contents. This may explain the maximum distributionof both the hyaline and porcelaneous foraminifera in the northern and cent-ral part of the study area, respectively. Also, it confirms the opinion that thehyaline foraminifera uses an organic nucleating surface for calcite growth,and dominates environment with somewhat lower concentration of calciumcarbonate than those required by porcelaneous foraminifera.

Introduction

Numerous studies on the distribution of Recent bentlj1onic foraminifera have beencarried out at various places. Their results indicate that the distributions aTe ~ontrol-

25

Foraminiferal Distribution in Recent. 27

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Foraminifera! Distribution in Recent 29

FIG Bathymetric map of the study area.

Faunal Composition

Figures 6 and 7 shows th~ faunal distribution of these sediments. Generally, theirassemblage is dominated by hyaline calcareous foraminifera ranging between 44.0%and 64.0%, with an average of 55 .5% and porcelaneous calcareous foraminifera withbetween 25.0% to 69.9%. Agglutinants are present with only 2.1 % to 15.7%.

Discussion

Foraminifera in the studied sediments include hyaline, porcelaneous, and aggluti-nated species. Hyaline foraminifera dominate over porcelaneous ones (Fig. 5,6 &7). This distribution trend is in contrast with that noticed in the Jeddah Bay (Bahaf-zallah 1979), in beaches of Farasan Islands (Bahafzallah 1984), and in the beachsands of Jeddah, central Red Sea coast (Bahafzallah and EI Askary 1981) where por-celaneous foraminifera overwhelm the hyaline ones. It is also in contrast with thefaunal assemblage in the Arabian Gulf (Wagner and Togt 1973; Murray 1973 andAbou Ouf 1982). However the present results agree with the study of Abou Ouf et al.(1988) on the littoral sediments of Al Lith-AI Qunfidah coast, Red Sea.

This anomalous distribution is considered to be due to the oscillations in theecological parameters caused by the influx of fresh water and mixing in various prop-ortions of the terrigenous material with the in situ carbonates. In places, where theclastic sediment dilution is minimal, the miliolids dominate indicating the typicalcharacter of shallow water tropical or subtropical carbonate sediments (Murray1973).

Foraminiferal Distribution in Rec

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33Foraminiferal Distribution in Recent.

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Foraminiferal Distribution in Recent. 35

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PI 8a. Variation of the identified fauna contents in the Jizan shelf with the phi mean size of the sedi-ments.

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8b. Variation of the identified fauna contents in the Jizan shelf sediments with depth

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Foraminiferal Distribution in Recent. 37

Durgaprasada, Rao, N.V.N, and Behairy, A.K.A. (1.986) Nature and composition of shore-zone sedi-ments between leddah and Yanbu, eastern Red Sea, Mar. Geol., 70: 287-305.

EI Wakeel, S.K. and Riley, J.P. (1957) The determination of organic carbon in marine muds, JournalCons. Int. Expl. Mer., 22: 180-183.

Greiner, G. (1974) Environmental factors controlling the distribution of recent benthic Foraminifera,Brevoria, Museum. of Comparative Zoology, 420: 1-35.

Murray, J. W. (1973) Distribution and ecology of living benthic Foraminiferids. Heineman, London, 274.Wagner, C. W. and TOgt, C. V. (1973) Holocene sediment types and their distribution in the southern Per-

sian Gulf. in: The Persian Gulf, Holocene carbonate sedimentation and diagenesis in a shallowepicontinental sea, New York, Springer-Verlag, pp. 123-155.