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

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

Článek WoS

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 lavaflows 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 SiO2, Al2O3 and FeOtot, as well as in trace elements such as Ni and Cr. In contrast, these samples are depleted in Hg (<10 ppb).

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 lavaflows 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 SiO2, Al2O3 and FeOtot, as well as in trace elements such as Ni and Cr. In contrast, these samples are depleted in Hg (<10 ppb).

Faroe Islands; coal composition; alteration; depositional environment

Faroe Islands; coal composition; alteration; depositional environment

KUBOUŠKOVÁ, S.; KRMÍČEK, L.; COUFALÍK, P.; POKORNÝ, R.

2017

10.08.2016

Elsevier

Amsterdam

0166-5162

INTERNATIONAL JOURNAL OF COAL GEOLOGY

165

8

Nizozemsko

157

172

16

http://www.sciencedirect.com/science/article/pii/S0166516216304517