Calcareous thrombolitic crust on Late Quaternary beachrocks in Kuwait, Arabian Gulf
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ORIGINAL PAPER
Calcareous thrombolitic crust on Late Quaternary beachrocks in Kuwait, Arabian Gulf A. A. AlShuaibi & F. I. Khalaf & A. Al-Zamel
Received: 14 October 2014 / Accepted: 26 February 2015 # Saudi Society for Geosciences 2015
Abstract Thinly bedded beachrocks exposed within the intertidal zone on the northern coast of Kuwait are coated with a calcareous microbialite crust that varies in thickness from a few millimetres to several centimetres. A macromorphological investigation revealed the occurrence of two primary crust types: a thick fenestral crust and a thin massive crust. The latter includes compound laminite/columnar crusts and planar laminite crusts. The thick fenestral crust is restricted to the lower part of the intertidal zone, whereas the compound laminite/columnar and the planar laminite crusts dominate the middle and upper parts of the intertidal zone, respectively. Micro- and nanoscopic examinations have revealed that these crusts are composed of thrombolitic microbialite, in which the thrombolite clots consist of aragonitic nanoglobules that nucleate in association with extracellular polymeric substances (EPS) and microbial fossils. It is suggested that these crusts have been constructed during two phases. The first phase involved the prevalence of organomineralisation processes, which formed the thrombolitic microbialite, while the second phase was dominated by physiochemical processes, which led to the precipitation of fibrous aragonite. The interlamination of dark microbialitic laminae with light-coloured isopachous fibrous aragonite results in the development of stromatolite-like structure. These results may provide support for the importance of the combination of biogenic and abiogenic processes in the formation of Precambrian stromatolites.
A. A. AlShuaibi : F. I. Khalaf (*) : A. Al-Zamel Department of Earth and Environmental Sciences, Faculty of Science, Kuwait University, P.O.Box 5969, 13060 Safat, Kuwait e-mail: [email protected] A. A. AlShuaibi e-mail: [email protected] A. Al-Zamel e-mail: [email protected]
Keyword Microbialite . Thrombolite . Stromatolite-like . Kuwait Bay . Arabian Gulf
Introduction Calcareous microbialites are made of carbonate organominerals (Burne and Moore 1987; Riding 1991; Perry et al. 2007) that are characterized by distinctive sedimentary structures. These microbialites are formed as a result of interaction of physical sedimentary dynamics with benthic microbial mats that consist of the individual cells of highly organized communities of microorganisms and their extracellular polymeric substances (EPS) (Noffke and Awramik 2013). Microbialites include stromatolites, thrombolites, dendrolites and leiolites, and similar structures that occur as domes and columns in the shallow waters of lakes and seas. The term can also apply to many additional authigenic accumulations in which microbes are locally conspicuous, such as certain tufas, travertines, speleothems and spring, seep, and vent deposits (Riding 2011). The study of modern microbialites
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