Petrological and geochemical characteristics of Palaeogene low-rank coal on the Faroe Islands: Restricted effects of alteration by basaltic lava flows

Abstract

The first combined petrographic and geochemical investigation of coal from the Faroe Islands was performed as a case study to understand thermal effects from basaltic lava flows on immature coal. The samples were divided into two distinct groups: "normal" coal (xylite and detroxylite) and "altered organic matter" (charcoal and organic particles dispersed in samples rich in altered clastic mineral components or enriched via hydrothermal fluids). The "normal" coal consists primarily of huminite-group material dominated by ulminite. The proportions of material from inertinite and liptinite groups vary from sample to sample. The studied macerals are anisotropic with no observed reaction rims or vacuoles. According to the mean ulminite reflectance in combination with ultimate and proximate analyses, the coal reached the lignite and subbituminous stages. The maceral compositions together with coal palynology indicate a predominance of gelified wood-derived tissues and demonstrate that the coal evolved in wet forest swamps under limno-telmatic to telmatic conditions. Alteration effects on immature coals from overlying basalt flows were relatively limited. Due to relatively rapid heat loss from the basaltic lava, as verified by the presence of volcanic glass (tachylyte), its imposed thermal effects resulted only in development of a thin "anthracite-like" crust on samples with no elevated coal rank. Associated hydrothermal fluids induced coal hydrofracturing with subsequent mineral precipitation and decomposition of the ambient feldspar-rich volcaniclastic sediments. Altered organic matter is enriched in SiO 2 , Al 2 O 3 and FeO tot , as well as in trace elements such as Ni and Cr. In contrast, these samples are depleted in Hg (b10 ppb).

Basaltic Dyke with Specific Volcanogenic Structures and Its Geomorphic Evolution: Unique Geoheritage of the Faroe Islands (North Atlantic Ocean)

“…Relatively uniform distribution of interstitial tachylyte is indicative of rapid cooling during the dyke emplacement without dramatic changing of P-T-X conditions (e.g. Kuboušková et al 2016;Ulrych et al 2017). Petrographic thin sections made from marginal pseudo-hieroglyphs revealed that they do not texturally or compositionally deviate from the host basaltic rock (Fig.…”

“…and Enni Fm (Passey and Jolley, 2009). The individual basaltic flows are often separated by volcaniclastic sediments (occasionally coal-bearing tuffitic claystone, sandstone or conglomerate of terrestrial origin) deposited between individual volcanic eruptions (Andersen et al 2002;Waagstein et al 2002;Passey and Jolley 2009;Pokorný et al 2015;Kuboušková et al 2016).…”

Driftwood in the Eemian interglacial lacustrine unit from the Faroe Islands and its possible source areas: palaeobotanical and ichnological analysis

“…1A, B) consists of Palaeocene basaltic lava flows of the North Atlantic Igneous Province, often interbedded with volcaniclastic layers, mostly tuffitic sandstones, while less common are siltstones and locally coal-bearing claystones (Storey et al 2007;Pokorn y et al 2015;Kubou skov a et al 2016). 1A, B) consists of Palaeocene basaltic lava flows of the North Atlantic Igneous Province, often interbedded with volcaniclastic layers, mostly tuffitic sandstones, while less common are siltstones and locally coal-bearing claystones (Storey et al 2007;Pokorn y et al 2015;Kubou skov a et al 2016).…”

“…The geological basement of the Faroe Islands (61°20 0 N-62°24 0 N and 6°15 0 W-7°41 0 W; Fig. 1A, B) consists of Palaeocene basaltic lava flows of the North Atlantic Igneous Province, often interbedded with volcaniclastic layers, mostly tuffitic sandstones, while less common are siltstones and locally coal-bearing claystones (Storey et al 2007;Pokorn y et al 2015;Kubou skov a et al 2016). The Quaternary sedimentary cover is represented by unconsolidated or weakly consolidated glacial deposits, such as tills, glaciofluvial and glaciolacustrine deposits, Pleistocene blockfields and aeolian sands, and abundant Holocene peat deposits.…”

Chemical Composition Variations of Altered and Unaffected Coals from the Huaibei Coalfield, China: Implications for Maturity

“…This stage enriches some harmful elements [2], but the impact on rare earths is not pronounced [4,5]. Vanadium (V) and chromium (Cr) from magmatic hydrothermal fluids are thus enriched in coal seams [6][7][8][9]. In addition, the relative proportion of carbon (C) increases as the magma intrusion distance increases, whereas the residual elements, such as hydrogen (H), oxygen (O), nitrogen (N) and sulfur (S), showing an opposite tendency [10][11][12][13][14].…”