Biomorphic textures in the ferruginous-siliceous rocks of massive sulfide-bearing paleohydrothermal fields in the urals

Abstract

The work is dedicated to first finds of bacteriomorphic and microfaunal textures in the ferruginous-siliceous rocks that are widespread among volcanosedimentary complexes of the massive sulfide-bearing paleohydrothermal fields in the Urals. The bacteriomorphs are represented by: (1) single filaments with a diameter of 8-10 μm across and 80-90 μm long; (2) fascicles of branched or twisted-fibrous hematitequartz filaments 1-4 μm in diameter and up to 100 μm long; (3) microtubular textures, 20-30 μm across and up to 500 μm long, closely interlaced with thin hematite-quartz filaments (3-5 μm in diameter); (4)and hematite-quartz filaments (with the axial channel 1 μm across) formed by chains of elongated-oval lumps. These textures closely associate in the ferruginous-siliceous rocks with the fossilized tubular organisms (60-120 μm in diameter), tentaculites, remains of radiolarian skeletons, foraminifers, and others. It has been established that accumulation of various elements, such as Fe, Si, Ca, P, Mn, Ba, Ti, and K that are associated with biomorphic structures, was accompanied by the formation of their own mineral forms. Biomorphic textures in the gossanites (ferruginous-siliceous rocks forming haloes around destroyed massive sulphide mounds) differ from jasperites (not associating with sulfide ores ferruginouse-siliceous rocks), in terms of abundance, diversity, and development of tubular organisms and tentaculites. Biomineralization of different degrees of preservation in the Paleozoic ferruginous-siliceous rocks can indicate the microbial influence on geochemical processes during the decomposition of initial hyaloclastic sediments, which contain an admixture of sulfides and carbonates, under low-temperature conditions accompanied by the formation of iron and silica. © 2013 Pleiades Publishing, Ltd.