PALYNOLOGICAL ZONATION AND CORRELATION OF THE PEACE RIVER COALFIELD NORTHEASTERN BRITISH COLUMBIA By Jane Broatch INTRODUCTION BurntRiver, however, the chzlractcr of the formationchanses enough to allow four distinct m8:mben to be identified and for the Strataofthe Peace Ri\erCoalfield formcd along the Southwestern Minnes Formation to become a targel. for coal exploration. edge of the Jurassic/Crclaceous (:learwntct Sed. The rocks were deposited during a series of m:tjar and minor transgressive- Cadomin Formation: The Ckidomin conglomerate lies uncon regressive cycles and reflect a conlplex depositional setting. Map- mably on the Minnes Formation. Although quite variable in 1hi:k- ping and correlation of economic cwal deposlts are difficult. but the ness (3 to 200 metres). a general trcnd of thinning eastward :and task is made more so by numerous thrusts and folds which occurred northward is evident(Stott. 196x1. Within the study are;, the when the region underwent comp:ession. A diverse body of geo- CadominFormation is predominantly conglomerate, but the logiral information from a variely of disciplines is required to northwest it becomes a pebbly sandstrlne containing silty, shaly, ;lad unravel the structure and stratigrallhy. coaly lenses. Where this occurs it is mapped as the Dresser Fortr a- tion, after the nomenclature of Hughes. PREVIOUS WORK Gething Formation: The G,:thzng Formation is a domin:mly terrestrial sequence of interbedded conglomerate, sandstone, silt- Stratigraphic work in the area (Flg. 49-1 i was carried out by Stott Stone, and mudstone. Coal occu.s in tne upper halfof the form:h,n (1968, 1973, 1974, 19x1) andHughes (1964, 1967).Extensive but is only of economic importance in the central regions 01 the drilling by coal companiesha!, provided core samples and coalfield. The conglomerates, which occur toward the base of the geophysicaldata for a number 0' morerecent studies aimed at formation, are thickest in the soltheas1 and are commonly cnnfu;:d locating.identifying. and interpr:ting environmentalindicators, with the Cadomin Formation. Although it has been noted that the rock-stratigraphic and time-stratigraphic horizons. and subtle dis- Cadomin conglomerate exhibit! a clcan matrix sand response con tinctions between similar lithologics contained within and between geophysical logs (Duff and Gilchrisr, 1981) and that the pebtmle formations(Duff and Ciilchrist, 19x1; Leckie, IYXI: Leckie and content is more quartzitic, the congl~~mcratcsare rarely drillcc to wdlker, 1982; McLean. 1977. 1932: Carmichael.1983). Paleon- allow comparison. Furthermore, the #differences are not consistrnt tological work has been attemptc,d by Bell (1956) with leaves. or easily recognizable in surface outcrop. In many places the Gcth- McL,ean and Wall (1981) with fo.aminifer;l, Chamney (report in ing Formationresembles both thr Minnes andcates Formations. :ut Stott. 196X) also with foraminifer;^, and Duff and Cilchrisl (19811 its overall texture is somewhal comer and average bedding is with marine macrofossils: but the usefulness of these studies has thicker. been limited by a paucit!, of specimens and generallypoor preserva- tion. Regular symposiums sponsor:d by the British Columbia Min- Moosebar Formation: The Gething Formation passes abruptly istry of Energy. Mines and Petmle~~mResources have encouraged a into black marine shales of the Nlooselm Formation. At its base t?e cooperative attitude amongst the c~mpaniesholding coal licenucs, formation is similar in appcarance to the marine Hulcross shale!, ti at and the many workers cc,nducting rssearchin the area. The resultant overlie the Gates Formation,however. the upper third of the unit :,a transitional sequence of interbed,led siltstones. mudstones, and t ?in exchange of information has led to B bcttcl- understanding of the complex structure, strat gaphy, artd depusitianal setting. sandstones. This sequence, althrtugh not recngnired everywhen in the field. is identifiable on geophysical logs and is now mapped Ihy The present palynological study was undertaken with the support most workers as a separate member of thc Mooscbar Formxion. of the Ministry in the hrpc of providing anorhcr tool for accurately Southeast of thc study area this lransilional unit has been pmpx,ed identifying rack units, particularly where faulting has displaccd or asaformal memberofthcGates iForm;nion (McLean, 1982). Unfw thickened them: for correlating units or horirons within units and tunately the gradational nature of thi:; unit and the uncertainty in ultimately the coal seams themselves; and for identifytng minor locating the sandstone bed which marks the base of the Gatis marine incursions and tracing theil extent. In addition, the palynu- Formation in the coalfield incrcace the confusion regarding hc morphs will provide information lor dating the rock units and for actual location of the Moosebar~Catcacontact. locating the JurassicICmaccous boundary In the undifferentiated Minnes Formation. Gates Formation: The FatesFormation consists of both marine and nun-marine sandstones. sil:stones, and mudstones: thin cx- STRATIGRAPHY glomeratesare present. Coal occurs throughout, but minrat'le seams are more common in the southeast whcrc the marine inllu- The btratigraphy of the Peace Rlver Coaltield is summarized on ence is less pronounced. Recognition of the marine componenl of Figure 49-2.The following bric' description of the rock units the formation has been the focu:; of st:veral recent studies (Lcckie. sampled for this study i!, intended :o provide: insight into prublcms 1981; Carmichael, 1983). particularly since it is thought top a) a specrfic to the region and into the interpretation of results. ma.ior role in truncating the coal in many areas Minnes Formation:The Mime', Formation south of Burnt River Although fdmiliarity with thc rock units locally allows fairly is a sequence of interfingering marine and non-marinc rocks com- accuratemapping of theformations. structural complexity oftkn posed of thin to thick-bedded mutlstonc. siltstone, conplomcratic confusesinterpretation. The n:gion is dominated by imbrcatc sandjtone. and coal beds. that r;mge from thin partings in the thrusting and associated folding which have greatly shortenci t?e southern extremes to medium th ck beds in thc northwcst: thc section in a wesf to cast direction. Idmtification of formations ;,Id sequencecannot be dif-crentiated intomappable units. North of thrust faults at surface does not g,ual.anteewhat will be encounlerzd ~ Elritish Columbia Miniatry of Enelgy, Mine? and Pelmieum Resource,. Cculogical Fieldwurk. 198s. Paper IYX6-I 32 I 322 - Northcast British Columhia North of Burnt Kiver South of Burnt River Boulder Creek Formation Hulcross Formation /'Mocntain Wrk Gates Formation - -Transition - - - Memhcr - - - - Mooschar Formation Moosebar Formation (Sukunkd Member) Gething Glad\tone Formation Frrrmation Cadomin Formation Mimes Formation indrill holes. Units often appear unusually thick mare faultcdaffto 49-41; identification and correlation of marine facies are in pro- be replaced by uncxpccted. and occasionally unidentifiable, units. gress. hut still subject to revision. Eleven ofthe X9 surface samplcs Complex structures and rapidly changing facies present a need for were selected for processing. based an results obtained from ap- highly specific information where correlation from onc drill hole to proxlmately equivalent drill-hole samples. Slides from the surface another is required. particularly if the decision to mine a cwal seam samples havc not yet been examincd. rests on the accuracy of that correlation. RESULTS CURRENT STUDY 01 the 204 samples examined to date X0 per cent haw yiclded In an attempt to identify and correlate horizons in the coal mea- palynomorphs. A species list containing approximately 370 spores sures, a study of fossil spores and marinedinocysts was undertaken. and I15 dinocysts was compiled. Although same of thespecies Two hundred thirty-eightcore samples were collected rrom I3 drill- identifications are subject to review, it is expected that this list will hole locations between Burnt River in the northwest and Narrawdy be slightly larger on completionbecause half the slides have not yet River in thesoutheast (Fig. 49-11, Thecores represent approx- been examined and these represent a section of the Minnes Fortna~ imately 3 600 metres of section, from the upper Minnes through tion which is expected to yield exclusively Jurassic palyntlmorphs. Gates Formations. sampled at 15-metre intervals on average. 'The Thc gcncralixd zonation shownon Fipre49-4 includes 2s of the drill holes have hecn pieced togethcr to obtain composite sections 43 dmocyst species and 30 of thc X5 pollen and spore species which from the regions shown on Figure 49-3. An additional XY samples are rsstrictcd to specific formations.The original plotuf spccics was were collected from surface sections adjacentto the drill-hole Inca- done on a formation basis, u,hich does not allow for easy rccogni- tions (Fig. 49-1) to determine theusefulness of surface 'grab' tion of zones within the formations. The exception is thc Minnes samplescompared to the unweathered, relatively fresh core Formation where distinct zonation is apparent at the JurassiclCre- samples. taccous boundary (dotted line). Thc division (~ccurs between 2x0 Processing andexamination of the core samples are nearcomple- and 294 metres from the tapofthc Minnes Formationin the Bclcourt tion. A preliminary zonation schemehas been workcd out (Fip. section, Mt Nerrick