PALYNOLOGICAL ANALYSIS OF THE LATEST FAMENNIAN MIDDLE BAKKEN FORMATION IN NORTHEASTERN MONTANA, USA: AN AGE AND PALEOENVIRONMENTAL FACIES CORRELATIVE OF THE SAPPINGTON FORMATION IN WESTERN MONTANA

DI PASQUO, M.; RICE, B.J.,; P.T. DOUGHTY; G.W. GRADER

Paraná

Simposio; 17 Simposio Argentino de Paleobotanica y Palinologia; 2018

ALPP y UADER

di Pasquo M., B.J. Rice, P.T. Doughty, G.W. Grader, 2018. Palynological analysis of the Latest Famennian Middle Bakken Formation in Northeast Montana, USA: An age and paleoenvironmental facies correlative of the Sappington Formation in western Montana. XVII Simposio Argentino de Paleobotánica y Palinología, Paraná (Entre Ríos, Argentina, 30 de julio al 05 de agosto).New palynology from three straVgraphic intervals from the Middle Bakken FormaVon in the WillistonBasin of northeastern Montana (Enterprise Archer well core) is presented: two samples from the topof the lower Middle Bakken siltstone (Archer 1=7,625.0-7,626.7 feet); six samples from silty shalefacies above the Middle Bakken sandstone (A2=7,600.4-7602.7 {) and two samples from the siltyshales above a bioclasVc lag, below a limestone bed of the upper Middle Bakken (A3=7,599.0-7599.8{). Re0spora lepidophyta is recorded throughout A1-A3 assemblages (A1: 28 spores, 13phytoplankton, 1 scolecodont; A2: 65 spores, 14 phytoplankton; A3: 30 spores, 4 phytoplankton). Theassemblages share 22 spores species (e.g. Crista0sporites mapheusii, Diaphanospora perplexa,Grandispora echinata, Grandispora sen0cosa, Pustula0sporites dolbii, Spelaeotriletes crustatus,Tumulispora rarituberculata, Velamisporites perinatus) and few acritarchs/prasinophytes(Gorgonisphaeridium winslowiae, G. absitum), which most of them are also recorded in MiddleBakken FormaVon of the Montague Lake core (C-69809-21/26) of southern Canada. Even though Verrucosisporites ni0dus is absent in Archer, this work proves that the Middle Bakken and MiddleSappington are coeval (latest Devonian R. lepidophyta-Verrucosisporites ni0dus Zone) based on theoccurrence of Claytonisporites rarisetosa, Convolu0spora major, Cyma0osphaera sp., Dictyotriletesflavus, Endoculeospora setaceae, Grandispora praecipua, Knoxisporites literatus, Navifusa bacilla,Retusotriletes crassus, Valla0sporites drybrookensis, V. splendens, Verrucosisporites mesogrumosus, V.papulosus between others. The Marine Index (A1=150, A2=121.5 and A3=113.3) confirms that A1 wasdeposited in a shallow marine se`ng whilst A2 and A3 in brackish embayments, as suggestedpreviously from ichnologic and sedimentologic analyses.*Project supported by CONICET PIP 0812-2015; NGS (9808-15); University of Idaho; PRISEM GeoconsulVng.