Petrology, palynology, and depositional environments of coals of the Upper Carboniferous Barachois Group (Westphalian A and C), southwestern Newfoundland

Abstract

Coal samples from the Barachois Group of western Newfoudland vary in rank from high-volatile C to high-volatile A. The coals are vitrinite rich (>70%), except some from Coal Brook that contain substantial quantities of inertinite (up to 52%). Liptinite ranges up to 18% but is a relatively minor component. The most abundant constituents amongst the three maceral groups are vitrinite -vitrinite A, inertinite-semifusinite, and liptinite-sporinite. Compositional profiles in three of the seams show no clear correlation between maceral group content and stratigraphic position. The Barachois Group coals are relatively high in ash (mean = 12.8%) and sulphur (mean = 6.9%). Spore assemblages from coal samples of the Barachois Group indicate a Westphalian A age in the Barachois Brook and Coal Brook areas and a Westphalian C age along Blanche Brook.Barachaois coals are part of a mudstone-dominated facies association that developed in an assemblage of floodplain environments. Plots of tissue preservation -gelification indices (TPIJGI) and the assemblages of spores derived from vascular plants suggest that most peats were generated in wet, forested tracts that, from the high ash content, occupied low-lying interfluves. Less wooded fen environments are also indicated, particularly in the Blanche Brook seams, by TPIIGI plots and a spore assemblage suggesting incursion of flood waters and dominance of herbaceous vegetation. Inertinite-rich samples from Coal Brook show extreme variation in paleoenvironmental conditions, which include dry forested regions.Les Cchantillons de charbon du Groupe de Barachois, dans la partie occidentale de Terre-Neuve, sont classifiCs de hautement volatil C B hautement volatil A. Les charbons sont riches en vitrinite (>70%), sauf certains provenant de Coal Brook, qui contiennent des quantitks importantes d'inertinite (jusqu'i 52%). La liptinite peut atteindre des proportions de 18%, mais il s'agit d'un composant relativement peu abondant. Les constituants les plus abondants panni les trois groupes de macCraux sont : vitrinite -vitrinite A, inertinite-semifusinite et liptinite-sporinite. Les variations de composition au travers les couches de charbon ne montrent pas de corrClation tvidente entre la teneur des groupes de macCraux et la position stratigraphique. Les charbons du Groupe de Barachois produisent des proportions relativement ClevCes de cendre (moyenne = 12,8%) et de soufre (moyenne = 6,9%). Les associations de spores dans les Cchantillons de charbon du Groupe de Barachois rkvtlent un Ige westphalien A pour les rCgions de Barachois Brook et de Coal Brook, et un 2ge westphalien C le long de Blanche Brook.Les charbons de Barachois sont incorporCs dans un ensemble de facits, reprCsentC principalement par des mudstones sCdimentts dans une plaine d'inondation. Les diagrarnrnes des indices de prkservation de tissus -gklification (IPTIIG) et les associations de spores derivkes de plantes vasculaires suggbrent que la tourbe a ttC genCrCe en grande partie dans des Ctendues forestibres humides qui, d'apr...

Palynostratigraphy and lithostratigraphy of Carboniferous Upper Codroy Group and Barachois Group, southwestern Newfoundland

“…The tentative Langsettian age previously assigned to the assemblage in two productive samples from the Shears seam (Hyde et al 1991; Table 1) was based on a comparison with the assemblages and zones of the British Isles proposed by Smith and Butterworth (1967). Poorly preserved rare specimens identified by one of us (J.U.)…”

“…as Endosporites globiformis (Ibrahim) Schopf et al, 1944, which has its earliest occurrence in the Langsettian, was mistakenly thought to possess a limbus at the spore margin, a characteristic feature of this species (Smith and Butterworth 1967). The latter has its earliest occurrence in the stephanephorus Concurrent Range Zone of the Lower Codroy Group of Asbian age (Utting and Giles, 2004) and is known to occur in Langsettian rocks of Nova Scotia (personal observation, J.U., 1997).The Cleary seam contained similar taxa to the Shears seam (Table 1), but preservation of palynomorphs is poorer (Hyde et al 1991). The latter has its earliest occurrence in the stephanephorus Concurrent Range Zone of the Lower Codroy Group of Asbian age (Utting and Giles, 2004) and is known to occur in Langsettian rocks of Nova Scotia (personal observation, J.U., 1997).The Cleary seam contained similar taxa to the Shears seam (Table 1), but preservation of palynomorphs is poorer (Hyde et al 1991).…”

“…1b,6) and is comparable lithologically and sedimentologically with the Overfall Brook Member with which it has been correlated by Knight (1983). Hacquebard et al (1960) and Hyde et al (1991) dated coal measures at Blanche Brook near Stephenville as Westphalian C (Bolsovian) and like most previous workers included them in an undivided Barachois Group (Figs. Thus our reassignment of Knight's Overfall Brook Member to the base of the Barachois Group seems to similarly apply to rocks of the correlative Brow Pond Lentil, suggesting that the basal Barachois Group may lie directly (and unconformably) on pre-Carboniferous rocks in the St. George's Bay lowlands, as it does at Trainvain Brook in the Codroy lowlands.…”

“…In its upper part the (Hyde et al 1991). The basal part of the Barachois Group comprises the Overfall Brook Member, and correlative strata including the Brow Pond Lentil (each formerly assigned to the Codroy Group), and beds exposed in Trainvain Brook.…”

“…5a) Taxa recorded byHyde et al (1991): Acanthotriletes sp., Calamospora sp., Camptotriletes sp., Convolutispora sp., Cyclogranisporites sp. 5a) Taxa recorded byHyde et al (1991): Acanthotriletes sp., Calamospora sp., Camptotriletes sp., Convolutispora sp., Cyclogranisporites sp.…”