Tectonic framework, stratigraphy, sedimentation and volcanism of the Late Precambrian Group, Østerdalen, south Norway

TORMOD SÆTHER & JOHAN PETTER NYSTUEN

Sæther. T. & Nystuen, J. P. 1981: Tectonic framework, stratigraphy, sedimentation and volcanism of the Late Precambrian Hedmark Group, Østerdalen, south Norway. Norsk Geologisk Tidsskrift, Vol. 61, pp. 193-211. Oslo 1981. ISSN 0029-196X. The Hedmark Group in the Imsdalen - BjØrånes - Atna - Øvre Rendal area belongs to the Osen-Røa Nappe Complex, and crops out northwest of the late-Caledonian central Østerdalen structural depression. The Brøttum Formation and the Imsdalen Conglomerate occur on the southwestern side of the Imsdalen fault (IMF), which is a synthrust high angle reverse fault. The pre-Varanger Brøttum Formation (turbidites, deltaic, fluvial) is correlated with the fluvial Formation NE of IMF. Basin evolution prior to the Varanger glaciation also includes carbonate sedimentation, black mud deposition in stagnant secondary basins, and block faulting accompanied by basalt volcanism and coarse-clastic, subaqueous resedimentation. The glacial Moelv Tillite rests unconformably on various units and was succeeded by post-glacial deltaic and fluvial sedimentation and earl y Cambrian deposition of shallow-marine quartz sands. New formations are defined: the Imsdalen Conglomerate and the Svartt}Ørnkampen Basalt. The Atna Quartzite is given the rank of formation, and the B}Ørånes Shale Member is referred to the Biri Formation. Parts of the Sollia Formation are correlated with well-established formations in the Hedmark Group.

T. Sæther, Saga Petroleum, Maries vei 20, P. O. Box 9, 1322 Høvik, Norway. J. P. Nystuen, Institutt for geologi, Norges landbrukshØgskole, 1432 As-NLH, Norway.

The Late Precambrian (Upper Proterozoic) Hed­ note arkoses and feldspathic sandstones which mark Group consists of sandstones, conglomer­ we can now refer to formations in the Hedmark ates, tillite, shales, carbonate rocks as well as a Group and the Kvitvola Nappe. The magnitude basalt in an area extending from the river Imsa of horizontal displacements during the Caledo­ and northwards to Bjørånes, Atna and Øvre nian orogeny has been another main problem of Rendal (Figs. l & 2). The stratigraphical rela­ controversy. tions within the sequence are of importance for The purpose of the present study has been to the interpretation of facies variations within the elucidate the stratigraphical relations within the Hedmark Group and for the Late Precambrian to Hedmark Group and to define the tectonic struc­ Early Cambrian palaeogeography in southern tures in which the sequence occurs. The main Scandinavia. Acritarchs sampled from the type part of the field work was carried out in the years area at Mjøsa indicate Vendian to Early Cam­ 1977-1979, with supplementary investigations in brian age for the Hedmark Group; the lowermost 1980 by J. P. Nystuen in the Imsdalen area part may be of Late Riphean age (Vida! 1980, p. (valley district along the river Imsa and the !akes 41). northern and southern Imssjøen). Stratigraphical and structural problems in the central part of the Østerdalen area have been dealt with by Tornebohm (1986), Bjørlykke Tectonostratigraphy (1905), Werenskiold (1911), Oftedahl (1943, 1954, in Oftedahl & G. Holmsen 1952, in P. Oftedahl (1943, in Oftedahl & G. Holmsen 1952) Holmsen & Oftedahl 1956), BjØrlykke (1965, considered the Hedmark Group in the area to be 1969), Prost (1975), KjØlberg (1980) and Nystuen allochthonous, thrust from northwest of the & Hebekk (1981). The discussions have particu­ AtnsjØen window (Fig. 1). Later, Oftedahl (1954) larly concerned the litho- and tectonostrati­ and P. Holmsen and Oftedahl (1956) suggested graphical positions of the area's 'light and dark that the Hedmark Group rocks occurred in two sparagmites'. These old lithological terms de- tectonostratigraphical units. The sequence in the

13 - Geologisk Tidskr. 3/81 194 T. Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFf 3-4 (1981)

Sparagmite Region

southern Norway

J.P Nystuen 1980

20 p 19 s 18 1',,1

17

16

15

14

13

12

11

10

9

8

7 + + + + + +

6 + + + + + + + 5 + + + + + + + + +++ +++++ 4 ++++ +++-+ ++++ + +++++ +++++++ +++++++++++ 3 + + + + + ... ..+ + + 2 . + + . km + + moA NORSK GEOLOGISK TIDSSKRIFf 3-4 (1981) Late Precambrian Hedmark Group 195

Bjørånes area was considered parautochthonous rocks can be followed into the Osen Nappe at the and belonging to the upper part of the Hedmark southern nappe front of the Sparagmite Region Group (Ring Formation and younger). These in southern Norway; the complete thrust unit strata were interpreted to outcrop within a was called the Osen-Røa Nappe Complex. 'Bjørånes window', overthrust by older forma­ The Røa Nappe consists of three thrust sheets tions within a 'Sparagmite nappe'. This latter in the area between the Atnsjøen window and tectonic unit was thought to comprise a giant the Rendalen fault (Nystuen & Hebekk 1981). fold nappe within the central, southern part of The basal thrust of the upper thrust sheet is very the Sparagmite Region (P. Holmsen & Oftedahl prominent in the area at Langtjørna, northwest 1956, p. 18). The hypothesis of a 'Bjørånes of Øvre Rendal (KjØlberg 1980). The thrust has window' was further evolved by BjØrlykke been mapped westwards to Hanestad, but its (1965, 1969), who interpreted the Bjørånes shale, further continuation is uncertain; it probably Moelv Tillite and Ekre Shale in the Bjørånes joins the sole thrust of the Røa Nappe along the area as parautochthonous, being exposed within southem boundary of the Atnsjøen window. The an antiform. This sequence was suggested to be upper thrust sheet comprises the Hedmark overlain by an imbricated thrust unit consisting Group sequence which can be followed from mainly of the Vangsås Formation, which, in Øvre Rendal in the northeast through the turn, was overthrust by the Kvitvola Nappe. Bjørånes area to the mountains Famphøgdene Prost (1975, p. 545) interpreted the lower part of and Piggvola in the southwest (Fig. 2). The the sequence in the Imsdalen - Atna - Sollia area sequence is here cut by the Imsdalen fault as autochthonous and a higher part (his 'Atna (IMF); the structural significance of the fault is Unit' and 'Sollia Formation") as an allochtho­ discussed below. nous equivalent to the Osen Nappe at the The Kvitvola Nappe, which is thrust upon the southern front of the Sparagmite Region. Røa Nappe, consists of Upper Proterozoic An allochthonous position for the Hedmark metasediments (the Engerdalen Group, Nystuen Group is . demonstrated by its thrust contact 1980) and sheets of Precambrian crystalline along the boundary of the Atnsjøen and basement rocks. Spekedalen windows. Older units of the group Iie here tectonically above a thin and discon­ tinuous sequence of younger strata which also The Øvre Rendal- Piggvola fo/ds include Cambrian phyllites. The lower sequence has sedimentary contact to the Precambrian The Osen-Røa Nappe Complex forms a duplex crystalline basement within the windows (Ofte­ (Elliott & Johnson 1980, McClay 1981) between dahl 1943, Oftedahl in Oftedahl & G. Holmsen its gently dipping sole thrust and the weakly 1952, Nystuen 1978, Siedlecka 1979, Nystuen & undulating basal thrust of the Kvitvola Nappe; Hebekk 1981). folds and steeply dipping secondary thrusts in The 3000-4000 m thick allochthonous sed­ the Osen-Røa Nappe unit are cut by the over­ imentary sequence in the northern part of the lying Kvitvola thrust (Nystuen 1981). The inter­ Sparagmite Region belongs to the Røa Nappe face between these two nappe units is deformed which extends eastwards into Harjedalen in into a structural depression in the central Øster­ Sweden (Tomebohm 18%, Nystuen 1975a). In dalen - Storsjøen area (Fig. l). This central Sweden, this tectonostratigraphical unit was Østerdalen depression (CØD, Fig. l) is formed named the Hede Nappe by Roshoff (1978). by the interference between two major syn­ According to Nystuen (1981), the Røa Nappe forms. The Storsjøen - Øvre Rendal synform

Fig. l. Geological map of the Sparagmite Region. Position of map area in Fig. 2 is shown by frame. l Precambrian crystalline basement, 2 crystalline basement rocks in the Røa Nappe, 3 Brøttum Fm, 4 Rendalen Fm with overlying Atna Quartzite (tight dots), 5 Biskopås, Osdalen, Imsdalen & Håkenstad Cgls, 6 Biri Fm, 7 Ring Fm, 8 SvarttjØmkampen Basalt, 9 Moelv Tillite & Ekre Shale, 10 Vangsås Fm, Il Sollia Fm, 12 Cambro-Silurian, 13 Kvitvola Nappe, 14 Rondane Nappe, 15 Trondheim Nappe Complex, 16 Thrust plane beneath the Osen - Røa Nappe Complex, 17 thrust plime in general, 18 normal fault, 19 S =Storskarven Sandstone, 20 P= Permian, CØD =central Østerdalen depression. Compiled from: A. Bjørlykke (1973a, 1973b). A. Bjør1ykke & Skå1voll (1979), K. Bjørlykke (1976), E1vsborg & Nystuen (1978), Englund (1972, 1973, 1978), Englund & Seip (1973), Løberg (1970), Nystuen (1974, 1975b, 1975c, 1975d, 1976b, 1978, 1979a, 1979b), Nystuen & Hebekk (1981), Prost (1975), Sæther (1979), Sæther & Bjørlykke (1979), Schiøtz (1902), Siedlecka (1979), Skjeseth (1%3) and unpublished data from J.-0. Englund, L. A. Kirkhusmo and J. P. Nystuen. 196 T. Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFf 3-4 (1981)

Geological map of the lmsdalen-Bjørånes-Atna­ Øvre Rendal area Sparagmite Region, southern Norway T. Sæther & J.P. Nystuen 1980

� Kvitvola Nappe

� Sollia Fm.

[\ l Vangsås Fm.  Ekre Shale � Moelv Tillite � Limestone & t2=I5J dolomite E Hedmark Group �,::-- Black shale "- Turbidite sst. :� l Ill lmsdalen Cgl. Håkenstad cgl. l • Svarttjørnkampen Basalt � AtnaOuartzite � -:-:-: Brøttum Fm. D Rendalen F m. §j;HStorskarven Sst. l D Gran i te NE of IMF SW of IMF ( lmsdalen fault) � Thrust plane in general

...... _._ Røa Nappe thrust plane -50- Fault )! Bedding

W, T.Sæther 1976, 11111111111 H.Dypvik 1976 � J.P.Nystuen & S.llebekk J.P.Nystuen 1980

Surveyed by: J.P.Nystuen & T.Sæther 1977

Fig. 2. Geological map of the Imsdalen-Bjørånes-Atna-Øvre Rendal area. A-A', B-B', C-C', D-D' and E-E' are section lines of profiles shown in Fig. 3. Abbreviations: Atna st. =Atna railway station, Gr. h. =Gråhammaren, s.Kj.b. = søndre Kjølsjøberget, Sv.k. = Svarttjømkampen, Gardb. = Gardbekken, Langtj. = Langtjøma. runs NNW-SSE in the area between Glomma south west to the mountain K vitåsen in the east and Storsjøen - Rendalen, and the Imsa-Kvit­ (Fig. 1). The axis of the latter synform is arcuate, åsen synform can be traced from Imsdalen in the being orientated WNW-ESE .in the west and NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981) Late Precambrian Hedmark Group 191

NE-SW in the east. The central Østerdalen railway station. The NNW-SSE running Kiva depression is cut by the post-Caledonian Ren­ fault is characterized by a red-coloured fault dalen fault, with subsidence on the western side. breccia which is very similar to rupture breccias The structural depression has probably been along Permian faults in the Oslo Region. formed contemporaneously with the late­ Caledonian antiform farther north, along which Imsdalenfault windows are preserved, exposing the Precam­ brian basement. The Imsdalen fault (IMF, Fig. 2) cuts the Øvre The Hedmark Group crops out in a series of Rendal-Piggvola folds in the area southwest of subordinate anticlines and synclines along the FamphØgdene and Piggvola. The Imsdalen fault north western boundary of the central Østerdalen forms the northeastern limit of the extensive depression, from Øvre Rendal in the northeast to Brøttum Formation area, within the Sparagmite Piggvola in the southwest (Fig. 2). These folds Region (Fig. l). predate the formation of the central Østerdalen The fault does not appear to cut the Kvitvola depression, but their orientation is affected by Nappe in the southeast. It dips nearly vertically the late-Caledonian large-scale deformation. in the area southeast of FamphØgdene, but the The thick Rendalen Formation, consisting of dip decreases towards the northwest and is sandstones, is folded into broad, open folds in about 50° to the SW in the area north of northern the area north of Atna, but farther south this unit Imssjøen. The fault has not been investigated in is broken up in imbricated sheets which dip to detail outside the map area of Fig. 2. Recon­ the north-west and north (Fig. 2). The formation naissance studies indicate that it continues for at occurs in a major anticline which is overturned least ten kilometres farther to the NNW, follow­ to the south and southeast in the FamphØgdene­ ing the eastern side of Imsdalen (Fig. l). Gardbekken-BjØrånes area and at Øvre Rendal The axial planes of the folds on the northeast­ (Figs. 2 & 3). This anticline is cut by high angle ern side of the fault are cut by the fault at an thrusts along which the Rendalen Formation has acute angle, but bedding planes in the Brøttum been locally displaced above younger units, as Formation on the southwestem side strike paral­ recorded in the area from Harrsjøen to Kivfjell lel with the fault line. The Imsdalen Conglomer­ and also in the area between FamphØgdene and ate forms a marker horizon in the sequence Gråhammaren (Figs. 2 & 3). The units which Iie southwest of the fault. The folds here include an above the Rendalen Formation are in part tightly anticline which is slightly overturned to the folded and cut by thrusts, as seen in southern northeast and cut by the Imsdalen fault (profile side of FamphØgdene and Piggvola and in south­ B-B', Fig. 3). The Brøttum Formation and the em Kjølsjøberget and Svarttjømk�mpen. Imsdalen Conglomerate dip 30°-60° to the SW in Sediments younger than the Rendalen Forma­ the area north west of northern Imssjøen, and the tion also occur in the Hira- Granåsen- Løvåsen strata here are probably stacked into imbricated area (Fig. 2). This is the eastern limb of a sheets. synclinorium which extends westwards to the The Brøttum sandstones in the hanging wall northernmost part of Imsdalen (Fig. l). are strongly sheared along the fault, being The Øvre Rendal - Piggvola folds display an altered to quartz-sericite phyllonites in a 10-20m arcuate trend in the Bjørånes - Piggvola area thick zone. The rocks in the footwall, on the (Fig. 2). Steeply inclined thrusts within the im­ other hand, are much lesser deformed along the bricated Rendalen Formation are also curved in fault. In general, there is no difference in degree the horizontal section; the convex sides face of tectonic deformation and metamorphism be­ southeastwards, in the direction of the nappe's tween the rocks southwest and northeast of the movement. A similar structural style has been fault. In both areas severe tectonic deformation formed also in other parts of the Osen-Røa with growth of light mica and quartz is mostly Nappe Complex. Nystuen (1981) explained this limited to zones which have suffered high strain. arcuate fold and imbrication pattern as the result As pointed out in a later chapter, the Brøttum of one single phase of deformation, produced and Rendalen Formations are interpreted as within a decollement nappe driven by gravity lithostratigraphical equivalents; the Rendalen forces. Formation consists offluvial sandstones, where­ Post-Caledonian normal faults cut the folds as the Brøttum Formation in the Imsdalen area along the river Kiva and in the area east of Atna includes turbidites, shallow-marine sediments as 198 T. Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981)

E (NNW) Øvre Rendal (SSE) E' -- - ......

/ V/• / ... o �-�;-:-;�_:;-:��-;:--;" o •••• o o. o. o •••• km L------�

D (WSW) (EN E) D'

Glomma C (NW) Månsæterkletten (SE) C'

, ..., - 1...... t,.-' .,� 1 , '. . o )l�" ," ,.., l..'-�--:::::_ :-...... ,...._.._...... ,-.� ...._-....,..._ •·· ·· ...._,.._ o l',,_,:;/_ ,•'_ ·_ ,··" y>'."'. ·_ ,'··· t _ . \,.._ \.:'-'-'"'- ...... · ������� kmL_···�··:�/�·_ -�·-· . ·_·�·/___ ,_�_,. _._·_'_,_�_-� -·__ ·_·______· ______

B ( NNE) (SSW) B'

o km L------� Famphøgdene A (N) (S) A' ____ ...------'i� • .-:.:�, ------; lmsa 1 ...- · · · . · · � ____:- _--_ -�--�--·_ _-:-_..._ _.: -_ -:-_ -�_-.:�__·:_· �_·:::__ ��_:� _·:_\,:_ .:�_::_;_,[_ t;_ \_ t·_ ·_.: _:_�:_>':_;::,_:t_t_ �_I_�:__,_;;,;_·_>_;,�_�,_:-:�-_-�-::�-.:,__:-:��_-�-�-:��-�::_ _:·______------::_. k L _ · · ""

Fig. 3. Geological profiles from the Imsdalen-Bjørånes-Atna-Øvre Rendal area. Positions of profiles are shown on map of Fig. 2. Symbols as in the legend of Fig. 2.

well as fluvial sandstones similar to those in the this interpretation. On the other hand, the thick Rendalen Formation. phyllonite zone at the base of the hauging wall is The Imsdalen fault is of syn-Caledonian origin very similar to the strongly deformed arkosic and predates the emplacement of the K vitvola sandstones which occur at the sole of several Nappe. It is a high angle reverse fault, and it may major thrust sheets in the Sparagmite Region. have been formed contemporaneously with the The northeastern tectonic boundary of the Brøt­ folding along the axial plane of a tightly com­ tum Formation can be explained by an inclined pressed syncline (Fig. 3). A high degree of sole thrust of a separate nappe unit, lying above concordance in fold axis orientations, deforma­ the Røa Nappe. The Imsdalen fault could thus be tional style and metamorphism between the interpreted as a folded ramp structure, i.e. a sequences separated by the fault is in favour of thrust which cuts up stratigraphically from a NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981) Late Precambrian Hedmark Group 199 bedding plane thrust (McClay 1981). This the Brøttum Formation at Mjøsa (BjØrlykke et hypothesis has to be tested by detail studies of al. 1976) and in (Englund 1972). the Imsdalen fault farther to the north. The turbidites here in the easternmost part of At the present stage of our investigations in Imsdalen are probably located within an anti­ this area, we prefer to consider the Imsdalen form and probably represent a deep, strati­ fault as a high angle reverse fault which was graphical level of the formation. The facies asso­ formed in consequence of folding within the ciation probably represents channels (sand­ upper thrust sheet of the Røa Nappe. The fault's stones), levees (sandstone and shale) and inter­ particular location between the Brøttum and channel areas (shale) in a mid fan position of a Rendalen Formations could be due to synse­ turbidite fan (see Rupke 1978, p. 408). dimentary faults or flexures in the transitional In the area south of southern Imssjøen, and zone between a fluvial basin in the northeast stratigraphically below the Imsdalen Conglomer­ (Rendalen Formation) and a turbidite basin in ate, there are very thick (5-30 m) sedimentary the southwest (Brøttum Formation). units of coarse-grained and conglomeratic arkoses. The units have erosional lower contacts with 1-2 m deep channels. Remnants of shale beds are preserved at the base of some sand­ Lithostratigraphy and depositional stones. Scattered, irregular shale flakes occur in environment the lower part of the units. Individual units are composite, consisting of massive, graded and BrØttum Formation ungraded sequences with transitional lower and The Brøttum Formation crops out in a large area upper contacts. This facies is associated with in the central and southern part of the Sparag­ dark grey feldspathic sandstones which occur in mite Region. Our investigations have revealed 50 cm to 4 m thick graded beds. The facies that the formation extends far to the north in the association is considered to be of turbiditic ori­ area west of the Imsdalen fault (Fig. l). The gin, deposited within the channels of an upper stratigraphical and structural features of the turbidite fan in front of a steep, submarine slope. · formation are still uncertain in the area south of A third facies association occurs west of Sollia (Fig. l) (see the section below on the Sollia northern lmssjøen and stratigraphically above Formation). the Imsdalen Conglomerate. It comprises a Neither base nor top of the formation is known series of 50 cm to 3. 5 m thick beds of well­ from the studied area (Fig. 2). However, correla­ sorted, coarse- to medium-grained light grey tion between the Imsdalen Conglomerate (see feldspathic sandstones. The beds reveal parallel below) and the Biskopås Conglomerate at Mjøsa and undulatory stratification and tabular cross­ (Fig. 4) suggests that the Brøttum Formation in bedding. They are usually ungraded. The sand­ the area (Fig. 2) represents the upper part of the stone units are separated by thin, grey mudstone unit. The minimum thickness in the area is at beds, and together these facies comprise a c. 200 least 1500 m. m thick fining- to coarsening-upward sequence. The sediments are dominated by medium- to This sequence is terminated by a multistorey 15 coarse-grained, grey to light-grey and red feld­ m thick conglomeratic red arkose which occurs spathic sandstones and arkoses. Four major within a channel, at least 50 m broad. The facies facies associations have been distinguished. association is suggested to represent shallow­ In the southeasternmost part of Imsdalen (Fig. marine or deltaic sediments overlain by a fluvial, 1), grey, feldsphathic sandstones occur in l-5 m distributary channel sandstone. thick beds, alternating with black shale (slate) The fourth facies association has been re­ beds up to 5 m thick. The sandstone beds corded from the hillside east of southern Ims­ commence with a conglomeratic basal part sjøen. The sediments here are dominated by 1-4 above an erosional contact, succeeded by a m thick graded units of red, coarse-grained massive and graded part and an upper division to medium-grained arkoses. The lower contacts with parallel lamination. The graded and lami­ are erosional, and in the lower part the sand­ nated units correspond to the A and B divisions stones display large-scale (20-70 cm) through of the Bouma sequence (Bouma 1%2, p. 48- cross-bedding, succeeded by small-scale (5-20 54), respectively. The facies association is simi­ cm) trough cross-bedding and parallel stratifica­ lar to the typical turbidite facies which occurs in tion at the top. The arkoses are interpreted to be 200 T. Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFT� (1�81) of fluvial origin, deposited by low-sinuosity dalen (Fig. l). In our opinion the name 'Biskop­ streams on a delta plain. This facies is very ås' should not be applied to these conglomer­ similar to the fluvial arkoses which occur in the ates mere ly on the basis of lithological similarity Rendalen Formation northeast of the Imsdalen and a rough correspondence in stratigraphical fault. The fluvial Brøttum sandstones occur position with the Biskopås Conglomerate. within the core of a tight syncline which is over­ tumed to the NE; this indicates a stratigraphical Geographical extent. - The Imsdalen Con­ position above the lmsdalen Conglomerate glomerate crops out along the fold limbs of a (Fig. 3.) large anticline in the Imsdalen area (Figs. 2 & 3). Bjørlykke et al. (1976, p. 239) suggested that The formation is best exposed along the south­ the conglomeratic arkose facies of the Brøttum em fold limb and is here followed as a mappable Formation in Østerdalen south of Imsa was unit for 10 km. From the western side of north­ deposited as turbidites on the submarine slope of em Imssjøen, the conglomerate continues as a large fan delta. The results of the present study several lenticles in the strike direction for 15 km fit well into this interpretation, suggesting that to the NNW (Fig. l). The total extent of the the facies associations in the Imsdalen area formation to the west, east and south is unknown comprise environments including middle to up­ due to the cover of the Kvitvola Nappe in these per turbidite fan, shallow-marine to deltaic and areas (Figs. l & 2). jluvial delta plain. Similar facies transitions from Type locality. - The river section at Imsa (map turbidites to continental facies have been de­ sheet Stor-Elvdal 1918 Ill, NP 928 227) is scribed from the Tertiary in California by Kamp selected as the type locality. et al. (1974, pp. 562-563). Thickness. - The conglomerate unit is about 200 Imsdalen Conglomerate m thick in the northeast (Fig. 2). The thickness varies westwards, but is generally decreasing; it This conglomerate occurs as a marker horizon is about 50 mat the type locality, 5-10 m SSE of and a mappable unit in the Imsdalen area (Fig. 2) southem Imssjøen, 15-50 m SW of the same lake and is below defined as a formation in the and 30-100 m west of northem Imssjøen. Hedmark Group. Lower boundary. - This is either gradational or Name. - The name is taken from lmsdalen, the erosional. Gradational contacts have been valley of the river Imsa, in which the conglomer­ ate crops out at several places (Fig. 2). observed in two localities, one in the eastern part of the area (Stor-Elvdal 1918 Ill, NP 921 239) Historical background. - The conglomerate was and the other in the southwest (map sheet !ms­ called the 'Biri Conglomerate' by Oftedahl (in dalen 1818 Il, NP 859 236). In these localities the P. Holmsen & Oftedahll956, p. 70), because of Brøttum sandstones pass upwards into the mat­ correlation with the Biskopås Conglomerate (pre­ rix of the conglomerate. The boundary of the viously referred to as the Biri Conglomerate, see formation is here defined to the base of the Bjørlykke et al. 1967) at Mjøsa. Prost (1975, p. lowermost conglomerate bed. Erosional con­ 198) presented a section through the conglomerate tacts with 1-2 m deep channels cut into the from the southem side of Imsdalen. However, underlying sandstones are present north of Imsa he did not recognize the K vitvola thrust above (Stor-Elvdal 1918 Ill, NP 937 237) and SSE of the conglomerate and thus misinterpreted the southem Imssjøen (lmsdalen 1818 Il, NP 897 carbonate rocks at the base. of the K vitvola 238). Nappe as the Biri Formation in the Hedmark Up per boundary. - The conglomerate grades Group (see Fig. 4). The Imsdalen Conglomerate upwards into overlying sandstones of the Brøt­ occurs as a wedge-shaped or lenticular body tum Formation. This type of contact is exposed within the Brøttum Formation. Similar con­ north of Imsa (Stor-Elvdal 1918 Ill, NP 933 232) glomerates are present also at lower strati­ and SSE of southem Imssjøen (lmsdalen 1818 Il, graphical levels in the Brøttum sandstones in NP 897 238). Østerdalen (Oftedahl in P. Holmsen & Oftedahl 1956, p. 68). None of these conglomerate units Description. - The formation is in the type are laterally continuous with the Biskopås Con­ section at the river Imsa developed as a massive, glomerate, either at Mjøsa or at Rena in Øster- unstratified and disorganized conglomerate in NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981) Late Precambrian Hedmark Group 201 the lower part. In the upper part there are Conglomerate has been formed by the mixing of inversely graded, clast-supported beds about l m long-transported, rounded extrabasinal stones in thickness. A matrix-supported texture domi­ and angular short-transported clasts derived nates in the lower part of the conglomerate from intrabasinal sources. The association of which here contains several irregular slabs of graded feldspathic sandstones, black shale, peb­ black shale. The !argest shale clast measures, in bly mudstone, graded and massive conglomerate the vertical section, 4 m x 30 cm. The clasts are beds with ruptured shale layers suggests a sub­ confined to one particular leve! in the con­ aqueous origin by gravity flow processes. The glomerate and are obviously the remains of a types of internal structures in the Imsdalen Con­ ruptured shale bed. Several of the rounded ex­ glomerate have all been described from deep­ trabasinal stones are part! y covered by thin shale water conglomerates associated with turbidites envelopes. This feature demonstrates that the (Walker 1975, 1979). The depositional site has black shale beds have been only weakly consoli­ probably been braided, distributary channels on dated when they were torn up and mixed with the upper part of a coarse-clastic subaqueous fan the extrabasinal material. Impure limestone in front of the steep slopes of a grave! delta. (maximum clast diameter of 80 cm) is another intrabasinal clast type at the Imsa locality. Rendalen Formation In other localities the conglomerate consists of either one single massive, disorganized unit, or The Rendalen Formation is the dominating bed­ of several beds, 70 cm to 5 m thick, which are rock in the Sparagmite Region in the area north­ either graded or ungraded. In the southwestern­ east of the Imsdalen fault (Fig. 1). It rests with most locality (Fig. 2), the graded units display sedimentary contact on the Storskarven Sand­ lower erosional contacts and commence with stone in the area just east of the Atnsjøen conglomerates which grade upwards into dark­ window (Figs. l & 2). The Storskarven Sand­ grey feldspathic sandstones, eventually with stone was defined as a formation by Nystuen & black shale on the top. In this locality there are Hebekk (1981, p. 21), and this unit is dominated also thin beds (30 cm) of black, pebbly mudstone. by well-sorted, fine- to medium-grained feld­ The clast size varies considerably within one spathic sandstones and has a thickness of at !east single outcrop and from the east towards the 2000 m. In all other areas in the eastern and west. In the east the maximum diameter of northeastern part of the Sparagmite Region, the extrabasinal clasts is 80 cm and in the west 15 Rendalen Formation has been recorded as the cm. lowermost unit in the Hedmark Group. The The clast assemblage is composed of grey formation is preserved with sedimentary con­ quartzite (25-70 %), red quartzite (8-20 %), tacts on Precambrian granite within thrust sheets granite (3-12%), aplite and felsite (5-50%), in the Røa Nappe at Femunden (Nystuen 1978, porphyry (1-6%), vein quartz (2- 10 %) and 1979 a), but is elsewhere cut by the Røa Nappe gneiss, basalt, black and grey shale and lime­ sole thrust (Fig. 1). stone, each of the last four types in amounts of The Rendalen Formation consists of coarse­ less than about 5 %. Quartzite, granite, aplite, grained to conglomeratic red and light arkoses felsite, porphyry and quartz clasts are usually and feldspathic sandstones. 1-8 m thick units rounded, whereas those of intrabasinal origin, are usually graded, and reveal structures such shale, limestone and also basalt are angular to as trough, tabular and low-angle cross-bedding, subangular. parallel stratification and scour-and-fills. Thin In general, the conglomerate is only slightly beds or laminae of red mudstone are locally deformed tectonically. Imbrications along high . preserved between the sandstone units. The angle thrusts have taken place in the conglomer­ sandstones are obviously of fluvial origin and ate beneath the K vitvola thrust in the south­ have probably been deposited by braided flood westernmost area. In parts of the conglomerate streams on a wide alluvial plain. west of northern Imssjøen, the quartz and quart­ The stratigraphical position of the Rendalen zite clasts have been elongated in the NNW -SSE Formation within the map area of Fig. 2 has been direction. The deformation of the conglomerate a matter of some controversy. The unit, pre­ increases towards the NNW. viously called 'red' or 'light sparagmite', was correlated with pre - Moelv Tillite sandstones at Depositional environment. - The Imsdalen Mjøsa by Oftedahl (1943, in Oftedahl & G. 202 T. Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981)

Holmsen 1952, in P. Holmsen & Oftedahl 1956), named the 'Hira Quartzite Formation', and the but was later correlated with the Vangsås name 'Atna' was applied to a supposed nappe Formation by Bjørlykke (1965, 1969), Prost unit (Prost 1975, 1977). Nystuen & Hebekk (1975) and partly also Kjølberg (1980). Within (1981, p. 23) defined the Atna Quartzite Member the map area of Fig. 2 the stratigraphical position as the uppermost member of the Rendalen For­ of the formation beneath the Atna Quartzite (s�e mation. The quartzite is an important mappable below), the Moelv Tillite and the Biri Formation unit in the area south of the Atnsjøen window is shown at FamphØgdene, northern Bjøråa, (Fig. l) and attains here a thickness of c. 200 m southern KjØlsjØb�rget, SvarttjØrnkampen, Øvre (Siedlecka 1979). The fluvial arkoses of the Ren­ Rendal and LangtjØrna (Figs. 2-4), and at some dalen Formation thin out towards the west in this other localities farther to the north (Nystuen & area, and the Atna Quartzite comprises the basal Hebekk 1981). The boundary relations at the unit in the Røa Nappe (Fig. 1). We have consider­ northern BjØråa and Øvre Rendal are of particu­ ed these features of the Atna unit and found them lar significance. to be substantial reasons (see Hedberg 1976, p. 32) In the river section and road cuts (highway to change its stratigraphical rank to formation. No. 3, previously No. 30) at northern BjØråa The Atna Quartzite has a gradational lower (Stor-Elvdal 1918 Ill, NP 997387), the red, contact to the Rendalen Formation (Nystuen & coarse-grained arkose of the Rendalen Forma­ Hebekk 1981). Within the map area (Fig. 2), it is tion is overturned; it passes stratigraphically overlain by the Svarttjørnkampen Basalt, the upwards into a 5-8 m thick dark grey arkose Biri Formation and the Moelv Tillite (Fig. 4). which is, in turn, conformably overlain by dark The thickness varies considerably within the mudstone of the BjØrånes Shale Member in the area (Fig. 2): absent at Øvre Rendal, 30 m at Biri Formation. The inverted relationships are southern KjØlsjØberget, lO m at FamphØgdene shown by trough cross-bedding in the arkoses and 100-150 mat Granåsen. and by ripple-lamination and load casts in sand­ The Atna Quartzite is a light gre y, fine- to stone lenticles in the mudstone. medium-grained feldspathic quartzite. It is well­ A similar inverted contact between the Ren­ sorted and occurs in 10--80 cm thick beds. The dalen Formation and the stratigraphically over­ beds are parallel-stratified, and wave-ripples are lying Biri Formation is exposed at Øvre Rendal observed on bedding planes. In the northern part (map sheet Hanestad 1918 IV, PP 087 644), see of the lmsdalen area, there are greyish-green Fig. 5. The basal beds of the Biri Formation are shale beds within the quartzite. A 10-- 15 m thick here represented by grey siltstone, black shale clast-supported conglomerate occurs locally at and the Håkenstad conglomerate (see below). the base of the Atna Quartzite at Gråhammaren On recently compiled maps of the Sparagmite and at Kivfjell. The clasts are up to 10--15 cm in Region (Prost 1975, Prost et al. 1977, Bjørlykke diameter, are rounded and dominated by quart­ et al. 1976, BjØrlykke 1978), the Rendalen zite. Formation (named Ring Formation) has been The Atna Quartzite is suggested to be of considered to exist only on the eastern side of fluvial to shallow-marine origin (Nystuen & the Rendalen fault line. In most earlier Hebekk 1981). palaeogeographical reconstructions of the sedimentary basin of the Hedmark Group, it has SvarttjØrnkampen Basalt been suggested that the area east of the Rendalen fault line was a separate 'eastern basin' which The unit is here definedas aformation within the evolved later than the 'western basin' (Englund Hedmark Group. 1972, 1973, Nystuen 1976a, Bjørlykke 1978). The Name.- The name is taken from the mountain identification of the Rendalen Formation in the SvarttjØrnkampen, which is located east of area west of the Rendalen fault line is important G�omma between the Atna and Hanestad railway to discussions about the sedimentary evolution stations (Hanestad 1918 IV, NP 980 492). of the Hedmark Group. Historical background. - Werenskiold's (1911, p. 64) 'diabase dyke' in the southern side of Atna Quartzite FamphØgdene must have been the basalt here. The name of this formation was originally intro­ Oftedahl (in P. Holmsen & Oftedahl 1956, p. duced by Prost (1970). Later the unit was re- 116-117) interpreted the basalt in northern and NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981) Late Precambrian Hedmark Group 203

Ri

Va

Ek

Br Mo

Bi

At lms 0- 300

Br Re Re

Mjøsa Rendalen lmsdalen Famp­ n. Bjøråa Gråham- s.Kjølsjøbg. Øvre Langtj. Tysta høgdene Bjørånes maren Svarttj. kp. Rendal

At: Atna Quartzite Mo• Moelv TiHite etf-4;;;1] Feldspathic Quartzite � Basalt Bi:Biri Fm. Os-Osdalen Cgl. � Cross-bedded E'.i:2i'l Limestone & Bis•Biskopås Cgl. R·Ring Fm. � fluvial sandstone l:i:55:5l dolomite � Massive or graded Bi•Bjørånes Shale Mb. Re- Rendalen Fm. • Black shale sandstone c::::::::J Br· Brøttum Fm. Ri· Quartzite Mb. ToHote � �. .. Shale Ek• Ekre Shale Sv· Svarttjørnkampen Basalt Hå· Håkenstad cgl. Va: Vardal Sandstone Mb. ��$'1Conglomerate � OrthoQuartzite lms -lmsdalen Cgl. Va+Ri-Vangsås Fm.

Fig. 4. Stratigraphical sections through the Hedmark Group from the lmsdalen-BjØrånes-Atna-Øvre Rendal area together with the type profile from Mjøsa (Bjørlykke 1978) and a compositesection from the area east of the Rendalen fault line and a section from the eastern side of Tysla, north of the map area of Fig. 2.

southern Kjølsjøberget as a sediment with lava Svarttjømkampen and at Kivfjell. The unit is fragments and the basalt at Kivfjell as gabbro continuous for about 5 kilometres in the area belonging to the 'Lower Jotun Nappe'. Bjørlyk­ northeast of the Atna railway station and for ke (1969, p. 316) was the first to identify the about 2 kilometres at Famphøgdene (Fig. 2). 'basalt and greenstone' in FamphØgdene and KjølsjØberget as a volcanic rock on which the Type locality - The mountain Svarttjørnkampen Moelv Tillite was resting with depositional con­ is chosen as type locality. The basalt is well tact. However, he interpreted the basalt as a exposed at all sides of the top (870 m a.s.l.). sheet of the Precambrian crystalline basement, Thickness.- The basalt has a lenticular geometry separated from the sequence beneath by a thrust in all outcrops, and the maximum thickness plane. Prost (1975, p. 206-207) considered the varies between 5m and 30 m. The thickness is dark crystalline rock in FamphØgdene to be an greatest in the SvarttjØrnkampen area and !east altered dolerite and part of an autochthonous at FamphØgdene. Precambrian basement which had been folded together with its sedimentary cover. Lower boundary. - The formation rests on the Atna Quartzite. There is a distinct, lithological Geographical extent. - The Svartjørnkampen contact between the two rock types. Within the Basalt occurs in the southern side of FamphØg­ folded sequence at SvarttjØmkampen the con­ dene, at Gråhammaren, southem Kjølsjøberget- tact is slightly disturbed due to differential tecto- 204 T. Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981) nic movements along the boundary. The strata The rock is a greenstone which is strongly are also folded and cut by minor thrusts at deformed and is associated with a limestone of FamphØgdene, but the primary features of the the Biri Formation. contact are preserved locally (lmsdalen 1818 Il, Clasts of greenstone, lithologically very simi­ NP 902 294). The interface here between quart­ lar to the SvarttjØrnkampen Basalt, occur in the zite and basalt is uneven and irregular, suggest­ Biskopås Conglomerate at MjØsa (Bjørlykke et ing that the quartzite was unlithified when the al. 1976) and are present in the Imsdalen Con­ lava flowed over it. glomerate and the Håkenstad conglomerate (see below) in the area of the present study. These Upper boundary. - The basalt is overlain by the fragments have been derived from pre-Moelv Moelv Tillite. The contact appears undisturbed Tillite basalts which could have been lateral at SvarttjØrnkampen. The tillite is in its basal equivalents to the SvarttjØrnkampen Basalt, or part enriched in fine-clastic detritus and larger separate, local lava flows of approximately same clasts derived from the basalt. Thus the contact age (for further discussion, see the last section). is of erosional origin.

Description. - Tectonic deformation and altera­ tion of the basalt vary. In shear zones, it is Biri Formation penetrated by a fracture cleavage and all primary textures are destroyed. A porphyritic texture The Biri Formation rests with sedimentary con­ and undeformed calcite-filled amygdules are well tact on the Rendalen Formation and the Atna preserved in some exposures at SvarttjØrnkam­ Quartzite and is unconformably overlain by the pen, southern Kjølsjøberget and FamphØgdene. Moelv Tillite (Figs. 2-5). The maximum thick­ ness (at Øvre Rendal and Bjørånes) can be The plagioclase phenocrysts are thin (up to l estimated to 150--200 m. mm) plates up to l cm long. They have numerous inclusions of sericite, and the very finely crystal­ The formation is dominated by (l ) black and line groundmass consists of chlorite, epidote, grey shale and mudstone and (2) carbonate sericite and iron ore minerals. Pyroxene is pre­ rocks. Within the former facies there occur at served at FamphØgdene. The alteration is prob­ Øvre Rendal the (3) Håkenstad conglomerate ably in part of synvolcanic origin. Preliminary and (4) a sandstone unit. analyses on the major elements show the rock to Bjørlykke (1965) introduced the 'Bjørånes be an alkali basalt; further studies on its geoche­ shale' as a formation name for the black and dark mistry are in progress. grey, alumina-rich shale which occurs in the area east of FamphØgdene and continues northwards - The SvarttjØrnkampen Basalt is the Origin. to Gråhammaren (Fig. 2). It is proposed here to first volcanic rock encountered from the Upper change the rank of the unit to the BjØrånes Shale Proterozoic Hedmark Group. It is probably the Member of the Biri Formation and to include the result of fissure eruptions along intrabasinal fault black and grey shale at Øvre Rendal in this zones. A diabase dyke in the Storskarven Sand­ member (Fig. 4). stone north of Hanestad (Nystuen & Ilebekk The Bjørånes Member at Øvre Rendal is a 1981, p. 22) may have been one of several black, organic-rich and pyritic shale in its lower feeders. part but grades upwards into a more silty, gre y Correlations. - Basaltic rocks which may be shale. This, in turn, passes gradually into an stratigraphically equivalent to the SvarttjØrn­ overlying grey and pink dolomitic limestone. kampen Basalt have been recorded from two The limestone is rich in shaly laminae. It thins other areas. In 1970, a 8 m thick basalt was out towards the southwest at Harrsjøen and also identified in two drill cores from the area be­ towards the southeast, as shown in the tunnel to tween the river Rena and the lake Ossjøen (J. P. the Rendalen hydroelectric power plant (Kjøl­ Nystuen, unpublished technical report). The berg 1980). The dolomite at Langtjørna displays basalt here occurs within a quartzite unit similar a transitional contact to the underlying Atna to the Atna Quartzite and displays primary lower Quartzite. A similar dolomite rests on the Atna and upper contacts towards its host. The quart­ Quartzite in the area west of Glomma (Fig. 1). zite is overlain by black shales and limestones of However, in the area between the river Atna and the Biri Formation. The other occurrence is LØvåsen (Fig. 2), there are also dolomitic lime­ located east of the lake Storsjøen (Sæther 1979). stones associated with black and green shale and NORSK GEOLOGISK TIDSSKRIFf 3-4 (1981) Late Precambrian Hedmark Group 205

s N Håkenstad conglomerate Rendalen Formation Conglomerate beds, graded , matrix- supported

Fig. 5. A simplified drawing of the section at Øvre Rendal (Hanestad 1918 IV , PP 087 644) showing the Light feldsp. sst., inverted boundary between the Ren­ Cross bedded dalen Formation (to the right) and the laminated l Grey feldsp. sst., overlying grey massive sandstone, graded and massive shale and the 'Håkenstad con­ glomerate' of the Biri Formation (to the left). Biri Formation

black pebbly mudstones. The primar:y contacts wards, and the conglomerate is clast-supported are here tectonically disturbed. in the westernmost exposure. The Håkenstad conglomerate is the informal The Håkenstad conglomerate reveals structu­ name of a conglomerate which occurs at the base ral and petrographical similarities with the !ms­ of the Biri Formation west of the farm Råken­ dalen Conglomerate , and a corresponding mode stad at Øvre Rendal (Hanestad 1918 IV, PP 087 of deposition is suggested. The conglomerate 644). The conglomerate is interstratified with probably represents a small subaqueous grave! dark grey shales and siltstones which belong to fan in the black shale basin of the Bj ørånes the Bjørånes Shale Member (Fig. 5). The gre y, Member. It has been formed by resedimentation graded and massive feldspathic sandstones, of rounded, fluvial extrabasinal debris mixed which occur stratigraphically beneath the conglo­ with short-transported intrabasinal clasts. The merate-shale sequence and above the Rendalen geometry of the conglomerate body and the Formation, have also been referred to the Biri decrease of clast diameters towards the west Formation. The conglomerate is about 50 m favour a sediment transport· in this direction. thick at the easternmost locality and thins out Another body of coarse-clastic sediments westwards over a distance of c. 2 km and is here occurs higher up in the black shale member at laterally replaced by the BjØrånes Shale Mem­ Øvre Rendal (Fig. 4). The up to 15 m thick unit is ber. This shale unit also Iies stratigraphically composed of coarse-grained, grey feldspathic above the conglomerate. sandstone. The unit comprises � beds which The Håkenstad conglomerate consists of 1-2 are massive and partly graded, partly ungraded. m thick graded units which have erosional lower The lithofacies of this sandstone unit is similar to contacts. The units commence with matrix-sup­ the coarse-grained turbidites in the Brøttum ported conglomerate in which clast size and clast Formation. It marks an isolated event with frequency decrease upwards; the conglomerate coarse-clastic influx by turbidity currents in the facies passes in to dark grey, massive and black shale basin. medium- to fine-grained feldspathic sandstone The Biri Formation is absent from the area (Fig. '5). Rounded clasts of grey quartzite, por­ between the mountains southern Kjølsjøberget phyry and granite (few) are the extrabasinal and Kivfjell, and it thins out towards FamphØg­ stones, whereas irregular fragments of shale, dene (Fig. 2). The present outcrop pattern along mudstone, calcareous sandstone, limestone and the Øvre Rendal-Piggvola folds may reflect ori­ basalt (up to 25 cm) are considered to be of ginal topographic highs and depressions within intrabasinal origin. Shale fragments are very the major sedimentary basin. The sedimentation abundant in the upper part of the Håkenstad has taken place between emerged areas on shal­ conglomerate. The clast size decreases west- low marine carbonate flats and in deeper, secon- 206 T.Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981) dary stagnant basins where organic-rich mud The Moelv Tillite at FamphØgdene was the settled. These basins received intermittently westernmost locality in the Imsdalen area where coarse-clastic detritus, deposited by turbidity Prost (1975) identified this formation. We have currents and other sediment gravity flows. mapped the tillite with 'classical' diamictite facies, normal thickness (10-15 m) and with overlying Ekre Shale and Vangsås Formation to Moelv Ti/lite a stream (Kvernbekken) northwest of Piggvola The Moelv Tillite was fo rmed during the Varan­ (Fig. 2). The sequence obviously continues from ger lee Age about 650 Ma ago (Bjørlykke & here farther to the north along the eastern side of Nystuen 1981). The fo rmation forms the most the Imsdalen fault. In September 1980 we identi­ significant unit within the area, for stratigraphic­ fied the Moelv Tillite at Skjerdingfjell, 13 km al correlations (Figs. 2-4). It rests with erosional NNW of Piggvola. The diamictite includes clasts unconformity on the Sv�rttjØrnkampen Basalt of porphyries, granite, quartzite, carbonate and the Biri Formation; farther north it also rests rocks and greenstone. It is associated with on the Rendalen Formation and the Atna Quart­ greenish-grey shale and phyllite, quartz pebble zite (Nystuen & Hebekk 1981). conglomerates and feldspathic sandstones. The Bjørlykke (1965, 1969) thought the Moelv Til­ sequence is complicatedly folded and rests at lite was present along the western boundary of this locality with thrust contact on the light the Bj ørånes Shale Member, in the streams north­ dolomite of the Biri Formation. Prost (1975) em BjØråa and Gardbekken (Fig. 2). The small included all rock types at these outcrops in his scattered clasts, reported by Bj ørlykke (1965), in Sollia Formation (see below). the mudstone here are probably irregularly out­ lined secondary aggregates of calcite and quartz. Ekre Shale The Moelv Tillite is a 2-20 m thick diamictite, which normally is massive but locally reveals a The Ekre Shale is a laminated grey, green and faint, discontinuous stratification. Angular to red silt-rich shale with thin sandstone beds and rounded clasts consist of red and grey quartzite, laminae. The sand content increases towards the granite, porphyry, felsite, gneiss, greenstone top of the unit. In the area east of Gråhammaren (basalt), shale and carbonate rocks. The !argest a fine-grained sandstone with calcareous matrix observed block is l min diameter (granite). The occurs in the border zone to the overlying poorly sorted matrix is dominated by the silt and Vangsås Formation. sand fractions. The Ekre Shale is about 5-50 m thick. The The diamictite has been fo rmed as a basal till lower part of the unit may have been formed in from grounded glacier ice (Bjørlykke et al. 1976, response to a post-glacial rise of sea leve! as Nystuen 1976a, Bj Ørlykke & Nystuen 1981). The pro-delta sediments (Nystuen 1976a). A general glacier ice moved across a basin floor which low boron content of the Ekre Shale has been consisted of sandstones, shales, carbonate rocks interpreted to indicate low water-salinity in the and basalt. Debris deri ved from these intrabasin­ depositional basin (Bjørlykke & Englund 1979). al source rocks were incorporated in the sole of the basal till. This intrabasinal glacial erosion Vangsås Formation accounts for the present local variations in com­ position of matrix and abundance of various This fo rmation consists of the lower Vardal intrabasinal clasts in the tillite of the area. The se Sandstone Member and the upper Ringsaker relationships have also been found for the Moelv Quartzite Member, as in the Mj øsa area (Bjør­ Tillite in the area east of the Rendalen fault lykke et al. 1967). (Nystuen & Sæther 1979) . The Vardal Sandstone Member has a tran­ The boundary with the Ekre Shale is exposed sitional lower contact to the Ekre Shale. The at Øvre Rendal. It is transitional through an contact is seen at Øvre Rendal and northwest of uppermost laminated zone (20-100 cm thick) in Piggvola. which the clast frequency decreases. This tran­ At Øvre Rendal the member is a greyish­ sitional zone has been interpreted as a gla­ green, fine-grained sandstone with silty inter­ ciomarine facies with ice-dropped clasts (Bjør­ beds in the lower part. The grain size increases lykke et al. 1976, Nystuen 1976a, Bj Ørlykke & upwards, and this part of the unit is a medium- to Nystuen 1981). coarse-grained, dark grey feldspathic sandstone. NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981) Late Precambrian Hedmark Group 207

The facies is characterized by 50--200 cm thick pond to feldspathic sandstones, rich in phyllosili­ beds which are massive and graded and locally cates (Prost 1975, p. 379). interbedded with thin, dark shales. The facies The first facies assemblage (l) has been corre­ here is probably of turbiditic origin. lated with the Biri Formation in this paper (see In the area south west of Harrsjøen and south­ above). Our investigations have proved that the wards to Bjørånes, the Vardal Member includes second facies assemblage (2) consists of the lithologies such as grey, greenish-grey or red Moelv Tillite, Ekre Shale and the Vangsås feldspathic sandstones with interbeds of green­ Formation (Vardal Sandstone Member) in the ish-grey siltstone and shale. This facies associa­ area east of the Imsdalen fault, northwest of tion reflects fluvial to deltaic sediments. Piggvola. The sediments here were also included In the FamphØgdene - Piggvola area, the in the Sollia Formation (Prost 1975, Fig. 90, p. Vardal Sandstone Member is developed as a 531). The identification of the Moelv Tillite coarse-grained feldspathic sandstone with within this second facies assemblage at Skjer­ trough cross-bedding and horizontal stratifica­ dingfjell (see above) suggests that the Moelv, tion. This facies is suggested to be of fluvial Ekre and Vangsås Formations are present also in origin. that northem area of the Sollia Formation. The Ringsaker Quartzite Member is a dark, The third facies assemblage (3), in the area bluish-grey to light and nearly white orthoquart­ west of the Imsdalen fault, has been found to zite which appears to be massive. The thickness consist of the Brøttum Formation and the Ims­ is up to 50 m, but the unit is absent or very thin at dalen Conglomerate (see chapters above on Øvre Rendal. In the area east of Glomma, prim­ these formations). Prost (1975, Fig. 90, p. 531) ary features are disturbed by imbrications be­ suggested that the Sollia and Brøttum Forma­ neath the Kvitvola Nappe. tions were separated by a regional, post-Caledo­ The Ringsaker Quartzite Member has a wide nian fault in the area NW of northem Imssjøen. regional development within the Hedmark The mapping in this area (J.P.N.) has not given Group and also occurs autochthonously, depo­ any evidence for the inferred fault. sited on the Precambrian crystalline basement The 'Sollia Formation' has been applied on beneath the Osen-Røa Nappe Complex (Nystuen our maps (Figs. l & 2) for sequences of unknown 1981). The quartzite has generally been consi­ stratigraphical position which occur in the tecto­ dered as a shallow-marine deposit; its high nostratigraphical interval between the Atna mineralogical maturity is a response to a reduced Quartzite and the Kvitvola Nappe. relief on the Baltoscandian craton (see Bjørlykke et al. 1976).

Sollia Formation Tectonic framework and basin Prost (1970, p. 761) introduced this formation evolution; summary and name for fo1ded, imbricated and in part strongly conclusions deformed rocks beneath the Kvitvo1a Nappe in the area south of the Atnsjøen window. The Hedmark Group rocks in the Imsdalen - Prost (1975) included into the Sollia Formation Bjørånes - Atna - Øvre Rendal area belongs to a number of different sedimentary rocktypes, the Røa Nappe and were deposited in a basin comprising the following facies assemblages northwest of the Atnsjøen window. The tectonic above the Atna Quartzite: (l) dolomite, 1ime­ framework of the sequence consists of a series of stone and associated black and green shales, and syn- and anticlines which in part are cut by phyllites and pebbly mudstone and (2) diamic­ northward dipping high angle thrusts. From tite, greenish-grey sha1e and phyllites, quartz­ Øvre Rendal to Piggvola in Imsdalen the trend of pebble conglomerates, greenish-grey and red, folds and associated thrusts changes from NE­ medium- to coarse-grained fe1dspathic sand­ SW to SE-NW. This arcuate pattem was pro­ stones and 'greywackes'. In the Imsdalen area, duced during the phase of deformation when the west of the Imsdalen fault, the Sollia Formation decollement nappe moved towards the SE. comprised (3) thick-bedded, grey feldspathic The se Øvre Rendal - Piggvola folds are cut by sandstones, 'greywackes', shales (and phyllites) the Imsdalen fault in the SW; the fault is a high and conglomerates. The 'greywackes' corres- angle reverse fault, dipping to the SW and form- 208 T. Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981)

ing the northeastern boundary of the Brøttum As the results of tectonic movements (faults, Formation. The fault is suggested to have been flexures), secondary stagnant basins with de­ formed at a late stage during the origin of the position of organic-rich, black mud were form ed; Øvre Rendal - Piggvola fold structure. However, the Bjørånes Shale Member characterizes the we leave the possibility open to interpret the 'Øvre Rendal sub-basin' and the 'Bjørånes sub­ fault as an inclined major thrust beneath a sepa­ basin'. Other parts of the basinal area arose rate nappe, lying above the Røa tectonic unit. tectonically and suffered erosion. Clasts of intra­ The Røa Nappe structures are discordantly basinal origin became intermingled with long­ cut by the Kvitvola Nappe sole thrust. The Røa transported, fluvial grave! derived from extraba­ and Kvitvola Nappe were folded during a late­ sinal source rocks. The detritus of mixed origin Caledonian deformation phase which produced was ultimately lain down by gravity sediment the wide and open central Østerdalen structural flows as subaqueous fans (lmsdalen and Råken­ depression, in which the Kvitvola Nappe has stad conglomerate beds). During a single event, been preserved as the highest tectonic unit. the mud sedimentation in the 'Øvre Rendal The stratigraphical columns from the studied sub-basin' was interrupted by the influx of area iue correlated with the type stratigraphy coarse-grained sands, deposited from turbidity from Mjøsa and with the stratigraphy in the currents. A shallowing of the 'Øvre Rendal district east of the Rendalen fault line (Fig. 4). sub-basin' gave rise to carbonate sedimentation The Brøttum and Rendalen Formations occur at the top of the Bjørånes Shale Member. The in corresponding stratigraphical levels beneath grey, silt-rich shale, in to which the limestone the Moelv Tillite and the Biri Formation. The passes laterally, has probably been deposited in presence of deltaic to shallow-marine and fluvia! lagoonal areas at the flanks of a carbonate sediments, besides turbidites, in the Brøttum mound. Formation in the Imsdalen area suggests that The Imsdalen Conglomerate and the upper there has been a transition from fluvial plains in part of the Brøttum Formation can be correlated the east (Rendalen Formation) to a large turbi­ with the Biskopås Conglomerate in the MjØsa dite basin in the west (Brøttum Formation). type sections. Like the lmsdalen Conglomerate, Arkoses and feldspathic sandstones are domi­ the Biskopås Conglomerate also contains clasts nant lithologies in both units in Østerdalen, and derived from the early transgressive carbonate lithoclasts (porphyries, felsite, granite, quart­ rocks of the Biri Formation. The latter con­ zite) in associated conglomerates indicate a glomerate wedges into the Biri shales (Bjørlykke source area lying to the east (Nystuen & Sæther et al. 1976, Bjørlykke 1978) in a way similar to 1979). that of the Håkenstad conglomerate. A phase of submergence commenced with The Biskopås Conglomerate, occurring in deposition of well-sorted sands on distal fluvial several bodies in the central Sparagmite Region plains and adjacent shallow marine areas; the (Fig. l), has been ascribed to various physical event is marked by the Atna Quartzite. In shal­ factors: tectonic subsidence and rise along mar­ low seas and embayments, where the ter­ ginal faults (Skjeseth 1963, p. 29, Løberg 1970, p. rigenous influx became restricted, carbonate 181, Englund 1973, p. 9), regression due to sedimentation succeeded the 'Atna sands', and epeirogenic lowering of sea leve! (Bjørlykke the early dolomite, limestone and calcareous 1966, p. 13, Spjeldnæs 1967, p. 56) and glacioflu­ sandstones of the Biri Formation were formed. vial transport (Oftedahl 1945, p. 291, Bjørlykke The early submergence (the 'Biri transgres­ et al. 1976, p. 243). In our opinion, the 'con­ sion') was probably initiated by a regional, mod­ glomerate phase' in the evolutionary history of erate downwarping of the basin floor. The pre­ the Hedmark Group's basin is associated with sence of the Svarttjørnkampen Basalt above the faulting, local basaltic fissure eruptions, forma­ Atna Quartzite probably reflects the onset of a tion of secondary basins and erosion within phase with high tectonic activity. The basalt emerged intrabasinal areas as well as in areas eruptions must have been of the fissure type, adjacent to the basin. restricted to fault zones. The presence of similar A hiatus is represented by the erosional un­ basalt in other parts of the Sparagmite Region, conformity beneath the Moelv Tillite. The unit and as fragments in the Imsdalen, Håkenstad was deposited during the Varanger lee Age when and Biskopås conglomerate beds, suggests that glacier ice moved from the east towards the there must have been several local lava flows. west, crossing the basin floor. Nystuen (1976, p. NORSK GEOLOGISK TIDSSKRIFT 3--4 (1981) Late Precambrian Hedmark Group 209

38) and Nystuen & Sæther (1979, p. 250) sug­ maximum crustal attenuation along the failed gested that there was an open bay during glacial arm. maximum in that part of the basin which is Acknowled ements The field work of the present study was represented by the sequence in the studied area. g financed by Norges geologiske undersøkelse and Norges However, the diamictite of basal till facies here almenvitenskapelige forskningsråd. We thank Jens-Olaf Eng­ proves that also this part of the basin was lund, David G. Gee and Anna Siedlecka for critical comments covered by grounded glacier ice. The Varanger and proposals for improvements of an earlier draft of the manuscript, Åslaug Borgan for drawing the figures, and Anne glaciation in southern Norway has been re­ Evensen and Marie-Louise Falch for typewriting. viewed recently by Bjørlykke & Nystuen (1981). The Ekre Shale and Vangsås Formation have Manuscript received June 1980, revised August 1981 great lateral extent in the Spargmite Region (Fig. l); their general depositional history has been described by Bjørlykke et al. (1976). In the International Geological Correlation Programme present area, both units display their maximum Norwegian Contribution No. 46 thickness at Øvre Rendal. This may imply a IU S to Project Caledonide Orogen recurrent subsidence of the 'Øvre Rendal sub­ UNES O basin'; the turbidite facies here in the Vardal l Sandstone Member was probably formed in front of a steep delta slope. Delta progradation and fluvial sedimentation (Ekre Shale and Var­ dal Member) were succeeded by the early Cam­ brian transgression and deposition of quartz References sands, forming the shallow-marine Ringsaker Bjørlykke, A. 1973a: Dokka, berggrunnsgeologisk kart 1816 Quartzite Member at the top of the Hedmark IV. M. 1:50000. Nor.Geol.Unders. Group. Bjørlykke, A. 1973b: Gjøvik, berggrunnsgeologisk kart 18161. The evolution of the Hedmark Group's basin M. 1:50000. Nor.Geol.Unders. is characterized by a late Riphean (?) to Vendian BjØrlykke, A. & Skålvoll, H. 1979: Bruflat, berggrunnsgeolog­ isk kart 17161. M. 1:50000. Nor.Geo/.Unders. phase with block faulting, coarse-clastic sedi­ Bjørlykke, K. 1965: The Eocambrian stratigraphy of the mentation and episodic basalt volcanism, re­ Bjørånes window and the thrusting of the Kvitvola nappe. placed by a late Vendian to early Cambrian Nor.Geol.Unders. 234, 5-14. phase with slow submergence and deposition of Bjørlykke, K. 1966: Sedimentary petrology of the sparagmites of the Rena district, S. Norway. Nor.Geol.Unders. 238, mature sands. This latter phase introduced the 5-53. Lower Palaeozoic epicontinental sedimentation Bjørlykke, K. 1969: Geologien i sentrale deler av Østerdalen. on the Baltoscandian craton. Nor.Geo/.Tidsskr. 49, 31:>-318. A similar evolution is revealed by the alloch­ Bjørlykke, K. 1976; Rena, berggrunnsgeologisk kart 1917 Il. M. 1: 50000. Nor.Geol.Unders. thonous sequences in Valdres (Nickelsen 1974) Bjørlykke, K. 1978: The eastern marginal zone of the Caledo­ and northern Jamtland (Gee et al. 1974). Howev­ nide orogen in Norway. In IGCP Project 27, Caledonian­ er, none of these sequences contain volcanic Appalachian Orogen of the North Atlantic Region. Geo/. units. The presence of basalt in the Hedmark Surv. Canada, Paper 78-13,49-55. Bjørlykke, K., Elvsborg, A. & Høy, T. 1976: Late Precam­ Group indicates that the original position of its brian sedimentation in the central sparagmite basin of South basin was rather far west on the Baltoscandian Norway. Nor.Geol.Tidsskr. 56, 233-290. craton. The rifting phase of the lapetus Ocean is Bjørlykke, K. & Englund, J-0. 1979: Geochemical response to considered to be reflected by dolerite dyke upper Precambrian rift basin sedimentation and lower Palaeozoic epicontinental sedimentation in South Norway. swarms in the Sarv Nappe and equivalent nappe Chemical Geo/. 2 7, 271-295. units in the Central Scandinavian Caledonides Bjørlykke, K., Englund, J.-0. & Kirkhusmo, L.A. 1967: (Gee 1975, 1977, 1978, Claesson 1976, Krill 1980, Studies on the Latest Precambrian and Eocambrian stra­ Kumpulainen 1980). The eastward displacement tigraphy of Norway. Nor.Geol.Unders. 251, 5-17. Bjørlykke, K. & Nystuen, J. P. 1981: Late Precambrian tillites of the Sarv Nappe exceeds 250 km (Kumpu­ of south Norway. In Hambrey, M. J. & Harland, W. B. lainen 1980). The Hedmark Group's basin has (eds.) Earth' s pre-Pleistocene glacial record. Cambridge been located east of the 'Sarv basin' (Nystuen & Univ.Press, Cambridge, 1024 pp. Kumpulainen 1981) and may have been formed Bjørlykke, K. O. 1905: Det centrale Norges fjeldbygning. Nor.Geol.Unders. 39, 595 pp. as an aulacogen relative to the central rift axis Bouma, A. H. 1962: Sedimentology of same flysch deposits: A farther west (see Dickinson 1974, p. 16). The graphic approach to facies interpretation. Elsevier, Amster­ basalt eruptions probably denote the stage of dam, 168 pp.

14- Geologisk Tidskr. 3/81 210 T. Sæther & J. P. Nystuen NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981)

Claesson, S. 1976: The age of the Ottfjallet dolerites of Sarv Nystuen, J. P. 1975c: Jordet, berggrunnsgeologisk kart 2017 1. Nappe, Swedish Caledonides. Geo/. Foren.Stockho/m Forh. M. 1:50 000. Nor.Geol.Unders. 98, 37(}..374. Nystuen, J. P. 1975d: Elvdal, berggrunnsgeologisk kart 2018 Dickinson, W. R. 1974: Plate tectonics and sedimentation. In Ill. M. 1:50 000. Nor.Geol.Unders. Dickinson, W. R. (ed.) Tectonics and sedimentation, 1-27. Nystuen, J. P. 1976a: Facies and sedimentation of the Late Soc.Econ.Pa/.Min.Spec.Pub/.22, 204 pp. Precambrian Moelv Tillite in the eastern part of the sparag­ Elliott, D. & Johnson, M. R. W. 1980: Structural evolution in mite region, Southern Norway. Nor.Geol.Unders. 329, 70 the Northern part of the Moine Thrust Belt. Trans.­ pp. Roy.Soc.Edinburgh: Earth Sciences 71 (2), 69-96. Nystuen, J. P. 1976b: Engeren, berggrunnsgeologisk kart 2018 Elvsborg, A. & Nystuen, J. P. 1978: Evenstad, berggrunns­ Il. M. 1:50000. Nor.Geol.Unders. geologisk kart 1917 l. M. 1:50 000. Nor.Geoi.Unders. Nystuen, J. P. 1978: Holøydal, berggrunnsgeologisk kart 1719 Englund, J.-0. 1972: Sedimentological and structural inves­ Ill. M. 1:50 000. Nor.Geol.Unders. tigations of the Hedmark Group in the Tretten-Øyer-Fåberg Nystuen, J. P. 1979a: Elgå, berggrunnsgeologisk kart 1719 Il. district, Gudbrandsdalen. Nor.Geoi.Unders. 276, 59 pp. M. 1:50000. Nor.Geol.Unders. Englund, J.-0. 1973: Stratigraphy and structure of the Ringe­ Nystuen, J. P. 1979b: Grøthogna, berggrunnsgeologisk kart bu-Vinstra district, Gudbrandsdalen; with a short analysis of 1819 Ill. M. 1:50 000. Nor.Geol.Unders. the western part of the Sparagmite Region in southern Nystuen, J. P. 1980: Stratigraphy of the Upper Proterozoic Norway. Nor.Geo/.Unders. 293,58 pp. Engerdalen Group, Kvitvola Nappe, southeastern Scandina­ Englund, J.-0. 1978: , berggrunnsgeologisk kart vian Caledonides. Geol.Foren.Stockholm Forh. 102, 551- 1817 Il. M. 1:50 000. Nor.Geoi.Unders. 560. Englund, J.-0. & Seip, H.C. 1973: Fåvang, berggrunnsgeolog­ Nystuen, J. P. 1981: The Late Precambrian 'Sparagmites' of isk kart 1817 IV. M. 1:50000. Nor.Geo/.Unders. southern Norway: a major Caledonian allochthon - the Gee, D. G. 1975: A tectonic model for the central part of the Osen-Røa Nappe complex. Am.J.Sci. 281, 69-94. Scandinavian Caledonides. Am.J.Sci. 275-A, 468-515: Nystuen, J. P. & Hebekk, S. 1981: Stratigraphy and Caledo­ Gee, D. G. 1977: Extension of the Offerdal and Sarv Nappes nian structures in the area between the Atnsjøen and and Seve Supergroup into northern Trøndelag. Nor.Geoi.­ Spekedalen windows, Sparagmite Region, southern Nor­ Tidsskr. 57, 163-170. way. Nor.Geo/.Tidsskr.61, 17-24. Gee, D. G. 1978: Nappe displacements in the Scandinavian Nystuen, J. P. & Sæther, T. 1979: Clast studies in the Late Caledonides. Tectonophysics 47, 393-419. Precambrian Moelv Tillite and Osdal Conglomerate, Sparag­ Gee, D. G., Karis, L., Kumpulainen, R. & Thelander, T. 1974: mite Region, south Norway. Nor.Geol.Tidsskr.59, 239-251. A summary of Caledonian front stratigraphy, northern Jamt­ Nystuen, J. P. & Kumpulainen, R. 1981: Upper Proterozoic landlsouthern Vasterbotten, central Swedish Caledonides. basin evolution and sedimentation on the western margin of Geo/.Foren.Stockholm Forh. 96, 389-397. the Baltoscandian craton, southern and central Scandinavia. Hedberg, H. 1976: International Stratigraphic Guide, XVI & Terra cognita l (I), 62 (Abstract). 200 pp. Wiley-Intersci.Publ., New York. Oftedahl, C. 1943: Om sparagmiten og dens skyvning innen Holmsen, P. & Oftedahl, C. 1956: Ytre Rendal og Stor-Elvdal. kartbladet Øvre Rendal. Nor.Geol.Unders. /6/, 65 pp. Beskrivelse til de geologiske rektangelkart. Nor.Geol.Un­ Oftedahl, C, 1945: Om tillitene i det central-norske sparagmit­ ders. /94, 173 pp. område. Nor.Geol.Tidsskr. 25, 285-294. Kamp, P. C. Van De, Harper, J. D., Coniff, J. J. & Morris, D. Oftedahl, C. 1954: Dekketektonikken i den nordlige del av det A. 1974: Facies relations in the Eocene-Oligocene in the Østlandske sparagmittområde. Nor.Geo/.Unders. 188,5-20. Santa Ynez Mountains, California. J.Geol.Soc.London 130, Oftedahl, C. & Holmsen, G. 1952: Øvre Rendal. Beskrivelse til 545-565. det geologiske rektangelkart. Nor.Geol.Unders. 177, 47 pp. Kjølberg, R. S. 1980: Tektonikk og senprekambrisk stratigrafi i Prost, A. 1970: Sur la nature et la delimitation des nappes de Øvre Rendal. Geologiske undersøkelser i forbindelse med charriage dans la partie nord de la 'region sparagmitique' de Rendalen Kraftverk. Rep. 13, Geoi.Insl., NTH, Trondheim, Norvege meridionale (Caledonides externes). Bull.Soc.­ 29 pp. Geol.de France (7), 12, 755-764. Krill, A. G. 1980: Tectonics of the Oppdal area, central Prost, A. 1975: Etude geologique des Caledonides externes Norway. Geo/.Foren.Stockholm Forh. /02, 523-530. dans la region du fjell de . (Provinces de Hedmark et Kumpulainen, R., 1980: Upper Proterozoic stratigraphy and d'Oppland, Norvege centrale). These de doetoral d' etat es depositional environments of the Tossåsfjiillet Group, Sarv sciences naturel/es. L'Universite Pierre et Marie Curie. 606 Nappe, southern Swedish Caledonides. Geol.Foren.Stock­ pp. holm Forh. /02, 531-550. Prost, A. 1977: Repartition et evolution geodynamique des LØberg, B. E. 1970: Investigations at the south-western border externides Caledoniennes Scandinaves. Revue de geog­ of the sp!lfl1811lite basin ( Vestfjell and Fåberg Vest, raphie physique et de geo/ogie dynamique (2) 19, 421-432. fjell). Southern Norway. Nor.Geol.Unders. 266, 166-205. Prost, A. E., Guezou, J.-C. Point, R., Quenardel, J.-M., McClay, K. R. 1981: What is a thrust? What is a nappe? In Santarelli, N., Henry, A. & Ellenberger, F. 1977: Une McClay, K. R. & Price, N. J. (eds.) Thrust and Nappe transversale dans les Caledonides Scandinaves centrales: du Tectonics, 7-9. Geo/.Soc.Lond.Spec.Publ. 9, VI & 539 pp. socle Baltique a la cote Atlantique. Revue de geographie Nickelsen, R. P. 1974: Geology of the Røssjøkollan - Dokk­ physique et de geologie dynamique (2) /9, 481-502. vatn area, Oppland. Nor.Geol.Unders. 314, 53-100. Roshoff, K. 1978: Structures of the Tannas augen gneiss nappe Nystuen, J. P. 1974: , berggrunnsgeologisk kart 2018 and its relation to under- and overlying units in the central l. M. 1:50000. Nor.Geol.Unders. Scandinavian Caledonides. Sver.Geol.Unders.Ser.C. 739, Nystuen, J. P. 1975a: Hovedtrekk av den tektoniske utvikling­ 35 pp. en i østre del av sparagmittområdet i Sør-Norge. Inst.Geo/.­ Rupke, N. A. 1978: Deep clastic seas. In Reading, H.G. (ed.) Nor.LandbrukshØgskole Rep. 2, 22 pp. Sedimentary Environments and Facies, pp. 372-415. Black­ Nystuen, J. P. 1975b: Nordre Osen, berggrunnsgeologisk kart well Sei. Publ., London, 577 pp. 2017 IV. M. 1:50000. Nor.Geol.Unders. NORSK GEOLOGISK TIDSSKRIFT 3-4 (1981) Late Precambrian Hedmark Group 211

Sæther, T. 1979: Storsjøen, berggrunnsgeologisk kart 1918 Tiirnebohm, A. E. 1896: Grunddragen af det centrala Skan­ 11-M. 1:50 000. Nor.Geol.Unders. dinaviens bergbyggnad. Kgl.Sv. Vet.Akad.Handl. 28 (5), 210 Sæther, T. & Bjørlykke, K. 1979: Stor-Elvdal, berggrunns­ pp. geologisk kart 1918 Ill, M. 1:50 000. ForelØpig utgave. Vida!, G. 1980: Micropalaeontology and biostratigraphy of the Nor.Geol.Unders. Upper Proterozoic and Lower Cambrian sequence in East SchiØtz, O. E. 1902: Den sydøstlige del av Sparagmit-Kvarts­ Finnmark, northern Norway. Nor.Geol.Unders. 59, 53 pp. Fjeldet i Norge. Nor.Geol.Unders. 35, 135 pp. Walker, R. G. 1975: Generalized facies models for re­ Siedlecka, A. 1979: Atnsjøen, berggrunnskart 1818 IV, M. sedimented conglomerates of turbidite association. 1:50000. Foreløpig utgave. Nor.Geo/.Unders. Geol.Soc.Am.Bull. 86, 737-748. Skjeseth, S. 1963: Contributions to the geology of the Mjøsa Walker, R. G. 1979: Turbidites and associated coarse clastic districts and the classical sparagmite area in southern Nor­ deposits. In Walker, R. G. (ed.) Facies Mode/s, 91-103. way. Nor.Geol.Unders. 220, 126 pp. Geoscience Canada, Reprint Series l, 211 pp. Spjeldnæs, N. 1967: Fossils from pebbles in the Biskopåsen Werenskiold, W. 1911: Søndre Fron. Fjeldbygningen inden Formation in southern Norway. Nor.Geo/.Unders. 251, rektangelkartet Søndre Frons omraade. Nor.Geol.Unders. 534!2. 60, 107 pp.