Selective microbial-induced biomineralization of a siliciclastic zoned coastline in a constricted modern tidal flat, Kuw
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ORIGINAL PAPER
Selective microbial-induced biomineralization of a siliciclastic zoned coastline in a constricted modern tidal flat, Kuwait (Northern Arabian Gulf) Eissa A. Ahmad 1
&
Michael J. Duane 1
Received: 24 December 2019 / Accepted: 2 September 2020 # Saudi Society for Geosciences 2020
Abstract At Ras Kadhma embayment (north Kuwait), fabrics such as micrite envelopes, calcified microbial filaments, and micritic grain-to-grain bridges are observed in this modern sabkha environment in Kuwait Bay, associated with a tripartite facies classification. Three tidal zones were delineated by 8 vertical core samples, each marked by laterally diachronous units with different lithofacies and biofacies. Microbial populations (Lyngbya and Schizothrix), living within a distinct differentiated intertidal flat zone, were identified and their effects on sediments recorded. The extreme salinity, temperature, and chemical gradients in the shoreline environment have contributed to a microbial ecosystem that is trapping, binding, and biologically inducing CaCO3 precipitation, producing a variety of sedimentary structures now conventionally regarded as MISS (microbially induced sedimentary structures). The microbial fabrics are preserved in aggregates within the intertidal to the continental vadose zone. Core samples and outcrops were collected and analyzed mineralogically, chemically, and microbiologically. Field mapping on a meter scale reveals a concentric zonation, subtidal, intertidal, and supratidal zones, distinguished by textural and biological differences. Distinct lithofacies reveal varying stages of biomineralization with optimum conditions developed in the intertidal and lagoon sediments enhanced by microbial populations. The results of the study contribute to the understanding of the complex interaction between microorganism forming mats, the tidal flat sediments, and the physical parameters that control this setting in Kadhma Bay. Recurring colonization of these siliciclastic sediments in the intertidal zone will be permanently terminated in the coming decades by advancing intertidal sand bars resulting from the destruction of the Tigris-Euphrates delta. Keywords Microbial mats . MISS . Intertidal . Arabian Gulf . Kuwait Bay
Introduction Ras Kadhma embayment is a small 2-km2 area in the northwest Arabian Gulf within Kuwait Bay (Fig. 1). The region is recognized for its prolific microbial sedimentary structures in both carbonate-rich and siliciclastic-dominant environments (Picha and Saleh 1977; Al-Yamani et al. 2004). Kuwait Bay is a shallow basin (approximately 8 m deep) with high salinity (36.5 to 43.5‰) (Jacob 1980; Al-Bader et al. 2011), fed by sediments Responsibile Editor: Haroun Chenchouni * Eissa A. Ahmad [email protected] 1
Department of Earth and Environmental Sciences, College of Science, Kuwait University, P.O. Box 5969, 13060 Safat, Kuwait
from the Tigris-Euphrates delta (Al-Yamani et al. 2007). The area is influenced by anticlockwise currents in the gulf and the dominant shamal NW winds,
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