Kazerouni, Afsoon Moatari5; Friis, Henrik5; Svendsen, Johan B3; Weibel, Rikke4
1 Department of Earth Sciences, Faculty of Science, Aarhus University, Aarhus University2 Department of Geoscience, Science and Technology, Aarhus University3 DONG Energy, Exploration and Production4 Department of Geological Mapping, Geological Survey of Denmark and Greenland5 Department of Geoscience, Science and Technology, Aarhus University
The Palaeogene Siri Canyon fill consists of hemipelagic and turbidite marl and claystones interbedded with massive and blocky glauconitic sandstones deposited from sandy mass-flows and sandy turbidites. The Palaeogene sediments in the Danish area are rich in siliceous microfossils as well as late Paleocene–early Eocene volcanic ash layers. Zeolites have a hydrated alumosilicate framework with varying amounts of alkali and alkaline earth metals.Authigenic zeolites may be common in deep marine sediments, and in volcanoclastic deposits. They are generally related to dissolution of siliceous fossils or diagenetic alteration of volcanic glass. Authigenic zeolites are uncommon constituents in most sandstones. However, authigenic zeolites are common in some of the glauconitic sandstones from the Siri Canyon, where it is generally associated with thick coatings of opal/microquartz on the detrital framework grains. The remaining open porespace may be filled with berthierine, chlorite, calcite or quartz, together with minor amount of other minerals such alkalifeldspar, siderite or pyrite, but in general, a high porosity (25-32%) is seen. Most occurring zeolites have a void in their central part, most likely reflecting dissolution of an early phase with different chemical composition. In many samples, zeolites have been totally dissolved, leaving impression marks in the opal/microquartz coating. The textural relation demonstrates that zeolite was dissolved after microquartz precipitation. In most case, the dissolution of zeolite has exposed the surface of detrital grains, allowing large syntaxial quartz overgrowths to form in the impression.This paper presents the occurrence and compositional variance of the authigenic zeolites in the Siri Canyon sandstones, and discuss the physico-chemical conditions which prevailed during formation of zeolites, pore water chemistry, composition of mineralogical precursors and the host sediments.