Calcareous thrombolitic crust on Late Quaternary beachrocks in Kuwait, Arabian Gulf

Autor: Fikry I. Khalaf, Arafat A. AlShuaibi, A. Al-Zamel
Rok vydání: 2015
Předmět:
Zdroj: Arabian Journal of Geosciences. 8:9721-9732
ISSN: 1866-7538
1866-7511
DOI: 10.1007/s12517-015-1869-5
Popis: 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.
Databáze: OpenAIRE
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