Authors: Jakobsen F.; Lindgreen H.; Springer N.

Source: Clay Minerals, Volume 35, Number 1, 1 March 2000 , pp. 175-175(1)

Publisher: Mineralogical Society

Abstract:

In the Maastrichtian-Danian chalk in the North Sea, discrete intervals, appearing as normal white chalk, contain up to 60% -quartz <2 m in size. Atomic force microscopy (AFM) reveals that the particles are of nm size, appearing as spherical particles and aggregates. Similar particles consisting of opal-CT were found in surface exposures of chalk in Denmark. Two new abiogenic pathways of silica formation in chalk are proposed. The first model proposes that SiO₂ nano-size particles and aggregates precipitated and flocculated in the free-water phase as opal and were diagenetically transformed from opal-CT at low temperature to -quartz at elevated temperature. In the second model, the dominance of radiolarians in the deep-water environment of the North Sea resulted in low dissolution supply with subsequent precipitation and flocculation of nano-size a-quartz particles. In the shallower water of the shelf environment of the present onshore chalk, the abundance of sponges and their dissolution supplied enough Si to precipitate opal-CT in the free-water phase.

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Language: English

Document Type: Research article

Publication date: 2000-03-01

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