Vejle Fjord Formation: Mineralogy and geochemistry

Abstract

The Vejle Fjord Formation comprises three members; the Brejning Clay, the Vejle Fjord Clay, and the Vejle Fjord Sand (Late Oligocene-Early Miocene). The lower part of the Brejning Clay was laid down in a shelf environment with a reduced influx of siliciclastic detritus. This resulted in deposition of clay minerals enriched in iron. The early diagenesis was characterized by pyrite and siderite formation within an anoxic sedimentary environment which was established due to degradation of organic matter just below the water/ sediment surface. The clay mineral assemblages of the upper part of the Brejning Clay, Vejle Fjord Clay and Vejle Fjord Sand, which were deposited in a lagoonal environment, reflect different stages in the development of the lagoon. When the lagoon was protected from marine influence, the clay mineral assemblage was dominated by kaolinite. During periods with open marine influence the smectite and illite content increased markedly. Authigenic mineral assemblages are characterized by pyrite and siderite in the lagoonal deposits and pyrite in the tidal flats deposits. The absence of siderite from the latter is due to insufficient reactive iron to form siderite