|Tertiary phosphorites in the southern North Sea Basin: origin, evolution and stratigraphic correlation|
Balson, P.S. (1989). Tertiary phosphorites in the southern North Sea Basin: origin, evolution and stratigraphic correlation, in: Henriet, J.-P. et al. (Ed.) The Quaternary and Tertiary geology of the Southern Bight, North Sea. pp. 51-70
In: Henriet, J.-P.; De Moor, G.; De Batist, M. (Ed.) (1989). The Quaternary and Tertiary geology of the Southern Bight, North Sea. Ministry of Economic Affairs. Belgian Geological Survey: Brussel. 241 pp., more
Sedimentary phosphate or phosphorite deposits are found at numerous horizons in the Tertiary sequences of the countries around the southern North Sea. Relatively little is known of the extent of these deposits in the offshore area. These phosphorites are of two main types: 1. Authigenic carbonate fluorapatite (francolite) concretions found dispersed at certain horizons within marine muds or muddy sands. 2. Conglomeratic lag or remanié deposits consisting of reworked and abraded phosphorite concretions and other phosphatic debris such as vertebrate teeth and bones, developed on prominent unconformity surfaces. The phosphogenic episodes represented by the occurrences of authigenic concretions may be correlated within the limited area of the southern North Sea, although the numerous stratigraphic gaps in the Tertiary sequences of the area hamper such correlation. The authigenic phosphorite occurrences correspond with periods of marine transgression. Remanié phosphorite deposits are developed by the winnowing of such authigenic phosphorite-bearing formations, although some reworking of earlier remanié deposits also occurs. These deposits thus correspond to periods of non-deposition and stratigraphic hiatus. The remanié deposits are most conspicuously developed in the immediate vicinity of the source formation, the transportation of phosphorite material probablv being restricted by the size of the concretions and the relativelv high specific gravity of francolite. The concentration of phosphatic material in some of these remanié deposits is sufficient to have attracted commercial exploitation in the past. Authigenic phosphorite is best developed in the Early-Middle Eocene and Miocene-Early Pliocene in the southern North Sea; periods of eustatic sea level rise, warm humid climates and global phosphogenesis.