Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
- 38 - 'lhe Martin Group in the Greater Beaverlodge Area by F. F. Langford* 'Ihe Martin Lake Series was first defined by (1957, 1959) in the area arm.md Martin Lake, Before that these rocks had been incltrled with the Athabasca Series lying south of Lake Athabasca (Alcock, 1936; Christie, 1953), Fahrig (1961) proposed the narre Martin Formation, and Tremblay (1972) was the first to sub:iivide the formation beyond rrerely recognizing the presence of basaltic lavas in the central part. GusS<M In relating various outlying elastic sequences to the rocks in the Martin Lake area, the author encountered a greater variety of Table l. rocks than had been anticipated, leading to the establish.Trent of the Martin Group made up of four formations. Table 1 sha,,,s the new stratigraphic sequence COT!l")ared to Tremblay's (1972) classification and Fig. l the approximate distribution. In this paper the term "arkose" will be used only to signify a elastic sedirrent with rrore than 10 percent alkali feldspar. Since the sedimmts in this area are practically all arKosic, it seens rrore useful to use the terms sandstone and siltstone which carry a size designation and are thus rrore descriptive. Stratigraphic column of the Martin Group This report Tremblay (1972) (Table XXX and Fig. 4) M2lville Lake Formation Siltstone and argillite (as described by Tremblay) Siltstone M:!mber: "Mainly thinbedded chocolate-red siltstone interbedded with thin beds of arkose ••. " Seaplane Base Formation Bright pink sandstone and conglOTIErate; includes upper 3/4 of Trerrblay' s Upper Arkose Upper Arkose Member: "Mainly orange-red to salnon-pink arkose; locally includes thick lenses of conglorrerate; ... " Gillies 01.annel Forrnation Sandstone Menber: heterogeneous, buff and red, pebbly sandstone and pebble conglOTIErate; central portion interlayered with maf ic fl CMS Basalt and Andesite M:!mber: " .••• Basalt and Andesite interbedded with arkose .•.. " :Lower Arkose !>Ember: Boulder Conglarerate M2rrber Beaverlodge Fonnation Red-bro..m Sandstone M2mber: mainly uniform fine-grained sandstone ranging to siltstone, very well indurated Basal Conglarerate !>Ember "M:iinly orange-red to salrron-pink arkose; includes locally sane thinly bedded chocolate-red siltstone and/or thick lenses of conglorrerate; ... " Basal Conglarerate: " •.. includes up to 1000 feet of siltstone." *oepart:rrent of Geological Sciences, University of Saskatchewan, Saskatoon. This study is funded by grants from NSER:. The Saskatchewan Department of Mineral Resources supported the project by the loan of field equif(l"eilt. - 39 - LEGEND § ATHABAS CA GROU • MART1N GROUP ~ THLUICHO GROUP / / FAUlT flaggy partings are present. On good exposures , graded bedding, cross-bedding and a vari ety of scour channels are evident , which suggests they are widespread a l though not easily seen. the southwest shore of Beaverlodge Lake near Hansen Bay, there is a large zone of rrediun-grained, f eldspathic, yellow and greenish grey sandstone. r-bst of the sandstone is well laminated, and as sorre beds are rather fr i able, the rock forms l edgy outcrops . Although very conspicuous along the road to Lodge Bay, this unit seems to be a l ocal facies within the reddish brc,;.m sandstone, but detailed mapping v.0uld be required to establ ish the strati graphic relationships . On Gillies Channel Fonnation: Lake Alhahosco O :5 IO lun Fig. l - Geo l ogical map of the s ubdivisions of t he Marti n Gr oup at Beaverlodge Lake Martin Lake Area Beaverlodge Fornation: 'Ihe base of the Beaverlodge Fonnation rests unconfornably an Tazin granites, orthogneisses and paragneisses. Over much of the area thi s contact is marked by a basal conglarerate well described by Trenblay (1972, see parti cularl y Plates 17 and 18). Good exposures occur near the Fay shaft at Eldor ado , and around the old I.orado mill. Trenblay (1972) dem:mstrated that the fragirents were derived fran the underl ying rocks and that transport has been l imited to a few rretres . 'Ihickness of the oonglarerate is highly variable; in parts of the area, Trerrblay (1972) sh<:Jv,ej it to be as rruch as 700 rn thick, and in pl aces it is absE11t. MJch of the variation in thickness is due to irregul arities of the surface of the unweathered baserrent. 'Ihe Gillies Channel Formation extends around the main body of M:lrtin Lake and inclu::l.es the "Basalt and Andesite" unit of Trenblay (1972) . The base of the unit consi sts of conglarerate with rounded boulders of baserrent rock up to 40 an across set in a matrix of cobbl es and sandstone. The sandstone matrix is fr iable, yellowish grey and feldspathic, and sane lenses up to 0.5 m thick of simil ar sand are present. The rest of the fornation is made up of poorly sorted sandstone , pel::bly sandstone and conglonerate, which display many kinds of textures and structures juxtaposed. Variation in oolour is conspicuous. M:IBt rocks are various shades of yello,,r-orange with red zones scat tered throughout, and rrany bedding planes are marked by hemati tic stains . Serre cross-bedded uni ts have foresets outlined by red hernati te and sare of the massive beds are hematitic with yello,,r blotches and spots . Pebbly sandstones, both massive and crossbedded, are cnrmon, with pebbles ranging downward frau 1 cm in s i ze . Conglonerate beds, rrostly l ess than 1 m thick, occur throughout . Cross-bedding is ccmron, with uni ts 20 to 40 cm thick and foresets 0. 5 to 1 cm thick. The central part of the unit contains six major ma.fie f lows and sills (Trenblay , 1972) , but these do not seem to have had any effect upon sedirrentation. Seaelane_Ba.se Formation: Seaplane Base Formation nore or l ess corresponds to the upper three-quarters of the upper arkose of Trenblay (1972, Fig . 4). The formation is easily recognized where it occurs along the Eldorado road by the bright pink col our and good sorting of the conglonerate and sandstone units . The west ern part is rrore conglareratic than the eastern, and a thick conglooarate unit extends northeastward The ~st of the Beaverlodge Formation i s a hard, reddish b:ram, and Iredium to dark greenish grey , fine-grained sandstone and sil tstone . It is ver:y arkosic with pink streaks and thin lenses dominantl y corrp:,sed of feldspar grains . The rock i s uniform over considerable thicknesses, and bedding is conspicuous only where one-pebble thick layers of conglOI1Brate or - 40 - from Martin Lake past the hill at the hospital. The basal o::mtact extends from Cinch Bay to the southern part of Martin Lake. Eastwards it lies beneath Martin Lake, but on the east side it is close to the uppemost flo.v. LEGEND MELV ILL E L AKE F ORM ATI ON S E APL ANE BA SE FO RMATI ON Besides the colour, the rrost striking feature that separates this unit and the succeeding one from the Gillies Channel Formation is the good sorting of the sandstone, siltstone and conglonerates. Although these rocks may be interbedded on a scale of a few centinetres, each type is distinct and has a restricted grain size within its unit. Except for graded beds, the sandstones are usually of unifonn grain size. The conglarrerates have a limited range of rounded pebbles in a matrix of clean sand. Pebbles are rrostly of basement gneisses with a predominance of quartz and quartz-rich gneisses. Cross-bedding occurs everywhere. The thicknesses of rrost cross-bedded units are 5 to 10 an and foresets l to 4 nm. It is difficult to find e:xposures that show the direction of transportation. GILL IES CHANN EL F OR MATI ON BEAV ERL 00G E FOR MATI ON CO NGL OMERAT IC R O CK S ~!ville Lake Fonnation: -----------------~-~- The ~lville Lake Formation is distinguished by the abundance 'o f dark red to maroon, hard, roodium- to fine-grained, arkosic siltstone and argilli te, and corresponds to Trernblay's siltstone rrerrber (1972, Fig. 4). In places, the siltstone may have buff-yellow bleached spots and zones. Bright pink sandstone and a few thin conglonerate beds like those of the Seaplane Base Formation are intercalated with the argillites, particularly towards the base. Typical rocks of this formation are exposed in the large road cut south of ~lville Lake. Cross-beds are present, but rrost of these sedinents seem to have been deposited in ephemeral lakes, for layers grading from fine sand or silt to argilli te with abundant ripple marks and nrud cracks on top are =mon. The lower contact of the formation can be seen west of the road to Fredette Lake. The change from the conglorrerates to argillite is abrupt, but thin layers of pebbly conglorrerate occur scattered in the argillite. The upper contact has been rerroved by erosion. outlying Oc=ences Rocks correlated with the Martin Group occur at several locations within 50 km of Martin Lake (Fig. 2) • These rocks have been called Martin principally because they are corrq::osed of urutEtarrorphosed red sandstone, and lie unconforrnably over a gneissic Precarrbrian baserrent. No correlation based upon specific sedinentacy features had been undertaken previously. The present study involved visits 0 ' Fi g. 2 - Geol ogical ma p of the Martin and Thluicho Groups in the greater Bea verl odge Area to all areas; sorre were limited to a few days, and sorre for a f ew weeks. The correlations proposed are shown in Table 2. Gruchy_Ba:L_Area: The Jug Bay Fm:rnation * occurs along the -west side of the Crackingstone Peninsula and, for the rrost part, lies in a graben between the Jug Bay and Black Bay Faults (Fraser, 1954; Bell, 1959). The northern end ma.y be limited by an unconfonni ty, but it has not been well mapped. The south end lies beneath Lake Athabasca. The fonnation consists of hard, silicified, reddish brown and dark greenish grey, fine-grained sandstone. Although well ~sed, unifonn induration produced srrooth rounded outcrop during glaciation, and this, canbined with a thin tenacious cover of lichen, has produced featureless outcrops. Along the wave-washed shore of Gruchy Bay, outcrops show a great many delicate sedirrentary structures, especially cross-bedding and scour channels, that are ccrcpatible with deposition by currents from the north. In fresh hand specinens, the rock ai:pears unifonn except where bedding planes are marked by a difference in grain size. M::>st of the grains are 0.1 to 0.5 ITin across, and sporadic *Tenninology proposed in this paper ' __ _______________,, ,_, __ _ ________ - 41 - Table 2. Correlation Chart of the Martin Group, Greater Beaverlod.ge Area, Saskatchewan Tazin Lake Martin Lake Gruchy Bay Gravel Islands Cam.sell Portage & Slate Island Fair Point Formation Athabasca Group Melville Island Formation Seaplane Base Formation Gillies Channel Formation Martin Group Thluicho Group erosion erosion erosion Taz Bay Fonnation Beaver lodge Formation Jug Bay Formation Gravel I slands Formation Thluicho Group Thluicho Group pink feldspar grains up to 1 rrm are cormon, along with isolated granite and quartz pebbles 1 to 2 cm across. Grain size contrast is greatest in thick beds. This rock has a very close resemblance to the fine-grained sandstone of the Bea'\lerlodge Fornation and is considered correlati'ile with it (Table 2). Gra'\lel Islands Area: ------~-------~-- The Gravel Islands Formation* occurs as a westward dipping and facing honocline exposed on the Gravel Islands. The rocks differ from the Jug Bay Formation in the Gruchy Bay area close by, and are separated from them by the Black Bay Fault. The lower unit occurs on the southeastern islet and consists of massive conglorrerate containing cobbles and pebbles of baserrent rocks. The easte:rnrrost 60 m of the main island consists of purplish grey, well-bedded, coarse-grained arkosic sandstone. Bedding is conspicous and the sandstone is interbedded with layers of coarse pebble conglorrerate. The central part of the main island is occupied by conglorrerate much like the lower unit on the southeast islet, but it *Terminology proposed in this paper Charlot Point Formation contains layers of arkosic sandstone and about 10 per cent of the cobbles are conposed of reddish brown sandstone like the Jug Bay Formation. Arkosic, purplish grey sandstone is dcroinant on the west side of the main island. The islet to the northwest is a mixture of sandstone and conglOTIErate and the peroentage of reddish brown, fine-grained sandstone pebbles and cobbles is greater here. Cross-bedding is very COITTIDn in the sandstone beds, and indicates that the tops face west and the depositing currents cane from the north. The presenoe of substantial nurrbers of pebbles and cobbles of reddish bro,,m, fine-grained sandstone identical to that of the Jug Bay and Beaverlodge Formations suggests that part of the Gravel Islands Formation was derived from their erosion. For these pre-existing sedirrents to have survived as clasts rreans they were probably well indurated shortly after deposition. Carnsell Porta~e Area: The Charlot Point Formation occurs in a small basin at Carnsell Portage. These rocks were first designated as the Martin Formation by Scott (1978) who also established an underlying Thluicho Group. The Charlot Point - 42 - Fo:rnation oonsists of a boulder oonglorrerate facies that intertongues with a sandstone facies. Red boulder conglorrerate, like that at Charlot Point, also unconformablv overlies the Thluicho Group on Slate Island. The Charlot Point Fonnation is unconformably overlain by the Fair Point Formation of the Athabasca Group. The sandstone is pale pinkish grey, in part purplish, medium- to coarse-grained, =ossbedded and arkosic. Beds are 5 to 40 an thick and there are rrany thin conglorrerate beds with a variety of clasts. Near the conglorrerate facies, coarse trough crossbedding, with sets up to 0.5 rn thick and foresets 1 to 2 an thick. dominates the unit. The cross-bedding indicates =ents frcm the northwest. The dark red boulder conglorrerates form a thick unit lying east and north-northeast of the sandstone. The cx.mglorrerates form very cx.mspicuous outcrops along the Charlot Peninsula and the lakeshore south of the Charlot River. The conglorrerates conprise clasts ranging from pebble to boulder in size, and all are corrp::>sed of hard, reddish bro..m and greenish grey, fine-grained sandstone like that forming the Jug Bay and Beaverlodge Formations. Except at the base, where sorre of the underlying basement gneiss and Thluicho rocks are incorporated, clasts of baserrent rock oc= only as small isolated pebbles widely scattered here and there. The boulders and cobbles are rrostly subrounded. The interstitial sand, and the sand in the pebbly sand lenses in the boulder conglorrerate, is dark red, arkosic, JXX)rly sorted and quite unlike that of the sandstone facies. It is envisaged that the Charlot Point Formation was deposited in a southeasterly trending valley. The axis of the valley was occupied by a substantial stream, flowing from the ll.€st-northwest, which deposited the sands and thin gravels of the sandstone facies. The boulder conglarerates famed a series of alluvial fans along the north and east sides of the valley, which received their sedirrents from the erosion of the exposed Beaverlodge Formaticm further north and east. The presence of boulder conglorrerate at Slate Island may indicate that the stream channel curved toward the southwest. It has been suggested in discussion that the clasts in the Charlot Point conglorrerate were derived from the Thluicho Formation. Although these clasts appear to reserrble fine sandstone of the underlying Thluicho Group, the majority of rock types in the Thluicho Group, including felsic volcanics, argillite and sandstone, are not represented in these clasts, suggesting therefore that the 'Ihluicho Group was not their source. The absence of ma.fie volcanic fragrrents, which might be ~ t e d to derive from basaltic horizons in the Gillies Channel Fonnation, supports the idea that the Charlot Point clasts were derived from the Beaverlodge Formation before the Gillies Channel rocks were deposited. Thus the Charlot Point rocks are equated with an erosional period after deposition of the Beaverlodge Formation, and are possibly equivalent to the conglarerate at the base of the Gillies Channel Formation. Tazin Lake Area: Red sandstones of the Taz Bay Formation were mapped at Tazin Lake by Koster (1968, 1970) . He divided the fo:rnation into three lmits. The lower one consisted of alternating sandstone and shale on Oliver Island, but this, along with sare similar rocks at the southeast comer of Tazin Lake, was renapped by Scott (1978) as Thluicho Group. 'l'he rest of the Taz Bay Formation, the basal conglorrerate and overlying sandstone, is similar to the Beaverlodge Formation. The sandstone is rrediurn reddish brown with variable grain size, ccmronly in graded beds. Trough cross-bedding is cannon and ripple marks are conspicuous in places. r-bst of the sandstone is laminated and sorre beds are separated by shaly partings. Besides the basal conglarerate, beds of conglorrerate up to 5 rn thick, with a variety of baserrent rocks forming cobbles and snall boulders, are interbedded with the lower part of the sandstone. The Taz B":l.y rocks have nore variation in texture than typical reddish brown sandstone of the Beaverlodge Fo:rnation. Ha,,,ever, much of the sedirrent indicates depositional conditions similar to the Beaverlodge Formation. Thus, these rocks are considered correlative, and the Taz Bay Formation could have supplied many of the clasts found in the Charlot Point Formation. Conclusion The closing stages of the Hudsonian orogeny were marked by uplift, faulting and formation of epherreral sedirrentary successor basins. The roots of b,,,:J of these, the Thluicho and Martin basins, have been preserved. The initial Martin sedirrentation of the Beaverlodge Formation was widespread, and was follCMed by a sharp uplift which caused rruch of it to be eroded and redeposited in other basins. Following this, a thick sequence of elastic sed:inEnts with sorre lava flows was deposited, but only the part at Martin Lake has been preserved. '!he record of even ts and - 43 - the types of rocks produced are appropriate for this tectonic envirorurent. References Alcock , F. J. ( 19 36) : The geology of the Lake Athabasca region, Saskatchewan; Geol. Surv. Can., ~ - 196 . Bell, K.C. (1959): Saskatchewan: Map 38- 1959. Milliken Lake, Sheet 1 , C?eol. Surv. Can. , Chri stie , A.M. (1953) : The Goldfiel ds- Martin Lake m3p area, Saskatchewan; Geol. Surv. Can ., t>an. 269 . Fahrig, W.F . (1961): The geol ogy of the Athabasca Formation; Ceol . Surv. Can . , Bull. 68 . Fraser, J. A. (1954) : Crackings tone , Saskatchewan: Geol. Surv. Can., Pap . 54-8 . Gussow , W.C. (1957): Correlation and age o f the Athabasca fonration; Alberta Soc. Pet . Geol. Jour . , v . 5 , p . 2-5. (1959) : Athabasca formation of western canada; Geol. Soc. Arrer. Bull., v . 70, p . 1- 18. Koster , F. (1968) : Geology of the Zin Bay ar ea; Sask . Dept . Mineral Res . , Rept. 121. (1970) : Ceol ogy of the Burchna ll Lake area, Saskatdlewan ; Sask. Dept. Mineral Res. , Rept . 131. Scott , B.P . (1978): Geology of the area east of Thluicho Lake , Saskatchewan; Sask. Dept. Mineral Res ., Rept. 167. Tr errblay, L.P. (1972) : Geology of the Beaverlooge mining area , Saskatchewan; Ceol. Surv . Can. , t,en. 367 .