German and International Research on Oman 1998

The Hawasina Nappes of the Oman Mountains: geological significance for science and economy = Geologie in Wissenschaft und Wirtschaft: Bedeutung der Hawasina-Decken der Oman-Berge
by Dr. Oliver Weidlich and Dr. Michaela Bernecker [abstract]

The main interest of geologists during the investigation of the Oman Mountains has been concentrated on the Semail Ophiolite, which is interpreted as a 90 million years old oceanic crust sheet from Cretaceous times. Currently, the Hawasina Nappes, which are regarded as a relic of a sedimentary basin situated formerly north of the Arabian platform, become increasingly interesting for various geologists.

Since 1990 our studies are focused on calcareous blocks of the Hawasina Nappes, which record a timeslice of earth history during the Permian and Triassic (285-225 million years ago). The blocks represent - comparable to modern environments in the Caribbean or the Red Sea - reefs and lagoons with a variety of organisms being significant for both working in industry and university.

Scientific significance: the reefal blocks and their fossil remains are important recorders of Permian and Triassic times. One aspect of our research is conducted to the description and quantitative analysis of the fossils. In contrast to other contemporaneous localities in Austria or Italy paleontological data are rare from the Oman Mountains and an important cornerstone for comparisons. After the description of the taxonomic inventory, the next step is an interpretation of the paleoenvironment based on fossils. Significant variations in the biotic composition record regional control mechanisms as well as dramatic global changes at the Permian-Triassic boundary, which is a global extinction event. Regional control mechanisms caused unique faunas like Permian coral reefs or distinct Triassic coral communities.

Economic significance: Beyond these academic aspects, fossiliferous reef limestones are highly attractive building stones. Further economic significance as fillers, e.g. in high quality paper, plastic, paints and medicine, resulted from extraordinary high carbonate productivity due to rapid growth of reefbuilders outpassing clastic impurities. This economic importance may be limited either by terrigenious input or by alteration processes of the carbonate in the subsurface (diagenesis). Dolomite, quartz and clay minerals reduced the carbonate content of the investigated material to a varying degree. Using a combination of staining techniques of carbonates, digital image analysis, and image arithmetics we quantify the above-mentioned phenomena on different scales (km-sized blocks to mm-sized pores) and assess the economic importance of various limestones:
(1) Reefal carbonates of Permian age are commonly of limited importance due to plastic impurities, dolomitization, and silicification.
(2) Platform limestones of Permian and Triassic age are dolomitized to a varying degree and of heterogenous quality.
(3) By contrast, Triassic reef limestones are of economic interest due to high carbonate contents.
In connection with a group of students envolved in our research project, our preliminary data will be completed by detailed geological mapping of specific areas.

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Last updated on 10 June 1998.