Open AccessCharacter and provenance of the opaque minerals in the Nexø sandstone, Bornholm
Author(s) -
Aage Jensen
Publication year - 1977
Publication title -
bulletin of the geological society of denmark
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.674
H-Index - 28
eISSN - 2245-7070
pISSN - 0011-6297
DOI - 10.37570/bgsd-1976-26-04
Subject(s) - hematite , geology , ilmenite , geochemistry , mineral , zircon , provenance , feldspar , mineralogy , quartz , opacity , paleontology , materials science , physics , optics , metallurgy
The Nexø sandstone is a subarkosic sandstone with subangular grains of quartz and feldspar: in a red coloured matrix. The sandstone was deposited in Eocambrian or early Cambrian directly on the Precambrian basement rocks of Bornholm, and was thought to have been derived from the breadown of these rocks. The amount of opaque minerals in the sandstone is about 1%. Most of the opaque grains belong to one of two groups: (I) ilmenite-hematite exsolution intergrowths with the hematite phase strongly dominant, and (2) martite with extremely fine lamellar structure indicating that the martite originates from titanomagnetite. The fine lamellar martite could have originated from dolerites on Bornholm as well as from Precambrian dolerites in Sweden, but ilmenite-hematite exsolution intergrowths are n9t known from any basement rock on Bornholm, the nearest exposure of rocks carrying ilmenite-hematite exsolutions lying in Sweden 150 km to the NW of Bornholm. It is suggested therefore that at least part of the material in the Nexl} sandstone originated in southern Sweden, a proposal that is consistent with palaeocurrent evidence from the sandstone. The relative amounts of ilmenite-hematite and fine lamellar martite vary strongly, and although the amount of martite is no proper measure of the proportion of material of local Bomholm origin this variation may be an indication of the relative amounts of material of local origin and material of more distant origin.