Mineralogy of the deep-sea sediments around RÊunion Island
(Western Indian Ocean)
Charakterystyka osad±w zrejony wyspy RÊunion
(Zachodni Ocean Indyjski)
1Institute of Geology, Adam Mickiewicz University, Pozna¡
2Institute of Geological Science, Kiel University, Germany
Abstract: Detailed petrographic and mineralogical analyses were performed in order to determine and classify ocean sediments in the vicinity of RÊunion Island. Surface sediments from the ocean floor and samples from cores of thickness down to 560 cm were classified as hemipelagic muds of volcanogenic origin, pelagic calcareous oozes and basaltic breccia. Heavy, light and pelitic fractions were investigated separately. Basaltic breccia consists of rock fragments and glass shards. Hemipelagic muds consist mostly of basaltic fragments, plagioclases, pyroxenes and olivines, basaltic glass shards, zeolites, and clay minerals. Moreover, various amounts of carbonate and siliceous bioclasts also occur. Pelagic oozes (nannoplankton and foraminifera) are composed mainly of carbonate bioclasts and micrite.
The mineral composition of the sediments and the relationship between pelagic and volcanogenic components were determined referring to the depth and distance from the RÊunion Island. The sediments from the southernmost profile are different than others taken at smaller distance from the island not only with respect to the fossil assemblage but also with respect to the occurrence of concretions (and quartz, staurolite and apatite) and greater degree of glass alteration. These sediments were formed under the conditions of pelagic sedimentation and slow sedimentation rate facilitated the formation of concretions.
The mineral composition of the sediments differs according to the distance from the volcanic RÊunion Island and the depth from which the sediment was sampled.
Key words: deep-sea sediments, mineralogy, RÊunion Island
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