Hambrey update – E. Finnmark – 2008_10_14 1

Glacigenic rocks of the Neoproterozoic Smalfjord and Mortensnes Formations, Vestertana Group, E.

Finnmark, Norway

1A. Hugh N. Rice,

2Marc B. Edwards,

3Tor A. Hansen,

4Emmanuelle Arnaud &

5Galen P. Halverson

1 Vienna University, Structural Processes Group, Department of Geodynamics and Sedimentology,

Althanstrasse 14, 1090 Vienna, Austria, Europe.

25430 Dumfries Drive, Houston, Texas, USA.

3Talisman Energy Norge AS, Verven 4, PO Box 649, Stavanger, Norway.

4 Department of Land Resource Science, University of Guelph, Guelph, Ontario, N1G 2W1, Canada.

5Department of Geology & Geophysics, School of Earth & Environmental Sciences, University of Adelaide, North

Terrace, Adelaide, SA 5005, Australia.

* corresponding author alexander.hugh.rice@univie.ac.at

Chapter Summary

The Vestertana Group in E Finnmark, N Norway, contains two Neoproterozoic glacigenic sequences, the Smalfjord

and Mortensnes Formations, preserved on the northern edge of Baltica. The former comprises up to 420 m of aeolian,

fluvioglacial and glaciomarine sediments and terrestrial diamictite. The latter consists of up to 50 m of predominantly

diamictite. The Smalfjord Formation is underlain by dolostones (Grasdalen Formation, Tanafjorden Group), only

locally preserved due to the sub-Smalfjord Formation unconformity, which cuts down-section through a ca. 2.5 km

dominantly clastic sequence to rest on Baltic Shield gneisses. The two glacigenic successions are separated by ca. 350

m of mostly clastic sediments (Nyborg Formation), with thin dolostones at the base and towards the top. The latter are

generally absent due to the sub-Mortensnes Formation unconformity, which also cuts down southwards through the

Nyborg and Smalfjord Formations to the Baltic Shield. No robust isotopic age constraints are available for the

succession. δ13

C data, together with cap dolostone characteristics, offer paradigmic correlations with other areas

(SmalfjordMarinoan; MortensnesGaskiers). A limited Ediacaran fauna, including Aspidella, give only broad age

constraints. Palaeomagnetic data are ambiguous; some suggest Baltica lay at equatorial (15° S) to mid-latitudes (50° S)

for the period 750-550 Ma, respectively, whilst other interpretations place it at either 30° N or S at ca. 550 Ma.

Introduction

This article is concerned with the glacigenic sediments of the Smalfjord and Mortensnes Formations (Lower and

Upper Tillites, respectively, in older literature), lying at the base of the Vestertana Group, within a ca. 5 km thick,

predominantly clastic sequence of Tonian/Cryogenian to Tremadocian age. The former glacigenic unit only occurs in

three areas, all in E Finnmark; Laksefjordvidda, Tanafjord and Varangerfjord (Fig 1). In contrast, the latter unit has

tentatively been correlated with many other diamictite bearing units in the Scandinavian Caledonides (see

Kumpulainen 2011, Kumpulianen & Greiling 2011, Nystuen & Lamminen 2011, Stodt et al. 2011). Due to significant

facies variations, no single outcrop/area can be taken as a type locality/region.

The rocks have been studied by many authors (see references in Føyn 1937, Bjørlykke 1967, Føyn & Siedlecki 1980,

Laajoki 2002) but detailed sedimentological studies remain few (Reading & Walker 1966, Edwards 1972, 1975, 1979,

Hambrey update – E. Finnmark – 2008_10_14 2

1984, Hansen 1992, Arnaud & Eyles 2002, Arnaud 2007, Baarli et al. 2006). An overview of δ13

C data from

associated dolostones was given by Halverson et al. (2005).

The Smalfjord Formation is significant in having provided some of the first evidence for a glacial event specifically

attributed to a pre-Pleistocene age, at Oaibaččanjar’ga (formerly Bigganjar’ga, Reusch 1891). Interpretation of this

outcrop has remained a bone of contention ever since its discovery; recent results indicate that intense high-

temperature brittle deformation occurred during rapid glacial movement (Bestmann et al. 2006).

The two glacigenic sequences became an informal ‘type sequence’ for late Precambrian glaciations in the North

Atlantic region (e.g. Hambrey 1983), known as the Varang(er)ian glaciation (Varangeristiden; Kulling 1951), later

developed into the Varanger Epoch (cf Harland et al. 1989). Use of the term Varang(er)ian is here discouraged for

reasons given below.

Structural Framework

During the Neoproterozoic in northern Scandinavia, the NNE-SSW trending western Baltica continental shelf, now

preserved in the Scandinavian Caledonides, was joined to the WNW-ESE trending Timan Basin in northeast Baltica

(Siedlecka 1985, Gayer & Rice 1989, Siedlecka et al. 2004). Both of these margins are thought to have experienced

extensional rift tectonics from c. 1000-c. 630 Ma, associated with the break up of Rodinia, followed by relatively

quiescent passive margin conditions during the deposition of the two glacigenic units (Røe 2003, Siedlecka et al.

2004). The Timan Basin has been divided into northerly basinal and southerly shelf regions (Siedlecka et al. 1995),

with the WNW-ESE trending dextral strike-slip Trollfjorden-Komagelva Fault (cf Rice et al. 1989) forming the

boundary between these two regions (Fig 1). The Smalfjord Formation was deposited (or has only been preserved in;

but see Kumpulainen 2011) the eastern part of the Gaissa Basin, which palaeogeographically formed a linking area

between the Timanian shelf region and the western Baltica continental shelf. In contrast, the Mortensnes Formation

and its presumed correlatives were deposited and preserved over much of western Baltica.

The rocks were shortened predominantly during Silurian-Devonian Caledonian orogenesis (Scandian event).

Deformation was essentially in-sequence, with ca. 50% shortening in the external imbricate zone (Gaissa Thrust Belt;

imbricated Gaissa Basin sediments) west of Laksefjordvidda (Townsend et al. 1986). East of Laksefjordvidda,

shortening decreased to ca. 15% (Chapman et al. 1985) and dies out very gradually across Varangerhalvøya. In the

Digermul-Tanafjord region, large-scale folds developed, sometimes with a back-thrusting vergence (Reading 1965,

Chapman et al. 1985, Siedlecka 1987). These likely formed by buttressing, as the sole thrust attempted to footwall-

shortcut through NNE-SSW trending extensional structures.

Although the strain decreases to the east, most pelitic rocks have a cleavage, locally with crenulations of sedimentary

laminae in flexural-slip fold hinges, whilst diamictites may carry a spaced (~ cm scale) anastamosing cleavage.

Pressure-solution was common in carbonate rocks, including dolomite-rich diamictites. However, in sandier

lithologies, finite strains are generally low, with sedimentary structures well preserved.

Stratigraphy

Hambrey update – E. Finnmark – 2008_10_14 3

The glacigenic sequences in E. Finnmark lie at the base of the Vestertana Group, within the ca. 4.7 km thick,

predominantly shallow marine and siliciclastic, Tonian (inferred) to Tremadocian East Finnmark Supergroup (Fig 2;

Føyn 1937, Johnson et al. 1978, Siedlecka et al. 2004). The sub-Smalfjord Formation unconformity at the base of the

Vestertana Group cuts down-section to the south until it lies on the Baltic Shield around Varangerfjord (Fig 1).

Between the Tana River west of Varangerfjord and Andabakoaivi (Fig 1), the Vestertana Group forms the most

southerly Caledonian Neoproterozoic rocks, although the basement-cover contact is not exposed.

The Smalfjord Formation has been preserved in two major palaeovalleys (Varanger and Krokvatn palaeovalleys;

Bjørlykke 1967, Føyn & Siedlecki 1980) and in the intervening Tanafjord area. The maximum preserved thickness

occurs in the Krokvatn palaeovalley (ca. 420 m), but facies variations preclude formation-wide member names. The

Mortensnes Formation (and equivalents; see Kumpulainen 2011, Kumpulainen & Greiling 2011, Nystuen &

Lamminen 2011, Stodt et al. 2011), which is more widespread across the orogen, often lying unconformably on

autochthonous or allochthonous basement, is < 50 m thick. The two glacigenic units are separated by ca. 350 m of

clastic and minor carbonate sediments of the Nyborg Formation (Edwards 1984). The uppermost sediments of the

Tanafjorden Group that underlie the Smalfjord Formation are the mixed carbonate and clastic sediments of the

Grasdalen and Fadnuvag’gi formations. The Mortensnes Formation is overlain by mudstones and sandstones of the

Stappogiedde Formation (Lillevannet Member).

The Precambrian-Cambrian boundary lies near the base of the overlying Breidvika Formation (Føyn & Glaessner

1979, Farmer et al. 1992, Crimes & McIlroy 1999).

Glacigenic deposits and associated strata

Grasdalen Formation, Tanafjord. The Grasdalen Formation (230 m), which only outcrops in the Grasdal-Gulgofjord

area, very close to the top of the Tanafjorden Group, was divided into three major parts by Siedlecka & Siedlecki

(1971) and Johnson et al. (1978); a lower mixed sand/silt-marl-dolostone unit (111 m), a massive dolostone (58 m) and

an interbedded dolostone-clastic sequence (61 m). In detail, however, the stratigraphy is considerably more complex

(Rice, unpubl. data.; Fig. 2).

Fadnuvag’gi formation, Tanafjord. Although the Grasdalen Formation is usually taken to continue up to the base of

the Smalfjord Formation (Siedlecka & Siedlecki 1971), the interbedded dolostone-clastic sequence is overlain by c. 20

m of a distinctly more fissile, darker, pyritiferous and finely interbanded shale silt/sandstone without carbonate

interlayers, informally termed the Fadnuvaggi formation (Halverson et al. 2005).

Smalfjord Formation, Krokvatn Palaeovalley, Laksefjordvidda. Føyn & Siedlecki (1980) documented three diamictite

units with intervening sandstones (Lower, Middle and Upper Krokvatn Diamictites, Lower and Upper Krokvatn

Sandstones; Fig. 2) deposited within an essentially N-S oriented palaeovalley cut into the Tanafjorden Group on

Laksefjordvidda (Fig 1). Fig. 3A shows a semi-schematic profile across the northern part of the palaeovalley

(Uccaskai’di-Vaððasbak’te); further south (Čikkojokka; Fig 1), the sequence comprises only the middle diamictite and

upper sandstone (Føyn & Siedlecki 1980). The Tanafjorden Group dips to the northwest compared to the 420 m thick

palaeovalley infill, with 600 m of tilted stratigraphy eroded.

Hambrey update – E. Finnmark – 2008_10_14 4

The Lower and Middle Krovatn Diamictites are both < 25m thick, with a grey to reddish colour and a sandy matrix.

The former includes a two-metre thick sandstone whilst the latter has interlayered sandstones in the basal part and has

faint banding and rare dropstones (Føyn & Siedlecki 1980). Clasts, sometimes faceted, are predominantly from the

Tanafjorden Group, with rare kilometre-sized dolostone blocks at the base (Edwards et al. 1973) and some basement

material. The upper diamictite (< 100 m thick) is more variable, with dolomitic and sandy matrices and a buff or grey

colour. These are interbedded with sandstones and siltstones with a few lonestones. On Uccaskai’di, the Upper

Krokvatn Diamictite has abundant dolostone clasts, possibly reflecting the nearby presence of Tanafjorden Group

dolostones (Fig. 1; Føyn & Siedlecki 1980). In contrast, in the northeastern part of the valley, the Nyborg Formation

rests unconformably on the Lower Krokvatn Diamictite and Lower Sandstone, the higher units having been removed

either during deposition of the third diamictite elsewhere, or afterwards.

The massive, homogenous very fine-grained sandstones and very coarse-grained siltstones are essentially devoid of

sedimentary structures throughout the succession; ripples occur at only one locality. Beds are from one to several

metres thick, without sorting of the angular grains, although larger grains (> 0.2 mm) are rounded. Hand-sized

basement lonestones occur at two localities. Directly above the Middle Krokvatn Diamictite, the sediments are red

(Føyn & Siedlecki 1980).

Smalfjord Formation, Varanger Palaeovalley, Varangerfjord. The Smalfjord Formation in the Varangerfjord area

(Bjørlykke 1967, Edwards 1975, 1984, Arnaud & Eyles 2002, Arnaud 2007, Laajoki 2001, 2002, Baarli et al. 2006)

has been correlated with the lower to middle part of the Krokvatn succession (Føyn & Siedlecki 1980). The following

descriptions are based on outcrops at Vieranjar’ga, Nesseby, Handelsneset, Skjåholm and Oaibaččanjar’ga (Edwards

1975, 1984, Arnaud & Eyles 2002, Arnaud 2007, Baarli et al. 2006).

Two diamictite and four sandstone and conglomerate (S1-S4) facies have been identified in this area. The first type of

diamictite is a massive, matrix supported, pink diamictite with a medium- to coarse-grained matrix with only a few

granitic and sandstone clasts. These are up to 20 cm across, sub-rounded to sub-angular and without striae or faceting.

This unit, in beds up to 1 m thick, can be traced over several hundred metres. The second diamictite, which is also

mostly matrix supported and massive, with a distinctly grey colour in outcrop, consists of a muddy, medium grained

sandstone matrix and abundant granite and sandstone clasts, < 50 cm across, some with faceting. Bjørlykke (1967)

also noted striated clasts in grey diamictite.

The S1 facies comprises well-stratified pebble conglomerates, occasionally imbricated, sandstones showing cross-

bedding and parallel lamination, with fining-upwards trends between these lithologies and rare mud-drapes. S2 is

typified by large-scale inclined bedding, 5-10 m thick and continuous for up to several kilometres. These include

steeply dipping poorly sorted pebble conglomerates to well-sorted gently dipping parallel-laminated sandstones. S3

comprises medium-bedded parallel-sided to slightly lenticular sandstones, usually internally massive, but at times

parallel-laminated or rippled. Mudstone partings are thin or absent but soft-sediment deformation, with convolute

bedding, recumbent folds and faulting occur. Steep-sided isolated channels filled with poorly sorted conglomerate are

also present. S4 comprises interbeddded sandstones and mudstones; the former in thin to medium, laterally continuous

beds. These display many turbiditic features (erosive surfaces, sole marks, grading, convolute bedding). A three metre

Hambrey update – E. Finnmark – 2008_10_14 5

thick, crudely stratified breccia contains angular sandstone clasts < 40 cm across, sometimes graded, in a coarse-

grained sandstone matrix.

The stratigraphic and lateral distribution of these facies varies from place to place. Laterally, lithofacies can often be

traced for several tens of metres, although abrupt facies changes are common (cf Edwards 1984). Complex soft

sediment deformation in sandstone and conglomerate facies is particularly notable at the base of the Smalfjord

Formation at Handelsneset (Arnaud 2007). Overall, the diamictite, breccia and S4 facies tend to occur near the base of

the sequence, whereas the S1 facies occurs near or at the top.

Smalfjord Formation, Tanafjord area. The Smalfjord Formation in this region (Reading & Walker 1966, Edwards

1984, Hansen 1992, Arnaud & Eyles 2002) has been correlated with the Upper Krokvatn Diamictite (Laksefjordvidda

region; Føyn & Siedlecki 1980, Edwards 1984). The best outcrops in this area are those exposed at Gæssenjar’ga and

Luovtat.

Based on outcrops in the Vestertana to Smalfjord area, with additional important outcrops between Njukčagai’sa and

east of the Tana River, Edwards (1984) recognised a five-fold (a-e) repetitive cycle of erosion surface, diamictite and

laminated mudstone, occasionally with intervening sandstones. Some units can be traced over hundreds of square

kilometres. Diamictite units are from 2–40 m thick, structureless or stratified, and have erosive bases, at both outcrop

and regional scales. Diamictites are all matrix-supported, with clasts up to 1m in diameter (most are < 35 cm) in a

siltstone to sandstone matrix. Material from underlying beds was often incorporated into the overlying diamictite,

forming inclusions of diamictite, conglomerate, sandstone or mudstone, folds and faults, load-casts, boudinage, shear

bands and flame structures. Some diamictite units have gradational contacts (Hansen 1992; Arnaud & Eyles 2002).

Stratified sandstone/conglomerate bodies are present within the diamictite; these deposits resemble the facies in the

Varangerfjord area (see above). In some cases, the basal diamictite represents mixing of far-travelled and locally

derived material. The dominant clast and matrix source areas determine the diamictite lithology; buff and brown-

colours indicate a dolostone source (cycles B, C and E). Cycle A is purple, with a haematitic matrix, and was derived

from ferruginous sandstones of the Dakkovarre Formation (Fig 2). Diamictites are also often distinguished by variable

clast abundance. Some diamictite units exhibit normal grading with a sandier matrix at the base and muddier matrix at

the top (Hansen 1992, Arnaud & Eyles 2002).

The Smalfjord Formation in the Tanafjord area has a much higher proportion of diamictite and is laterally much more

consistent compared to outcrops and lithofacies distributions in the Varangerfjord area; in the Gæssenjar’ ga area, over

85% of the sections consist of diamictite units and these tend to be traceable over several kilometres (Edwards 1984,

Arnaud & Eyles 2002). One exception is that of a 1-5 m thick purple diamictite that grades into a laminated mudstone

with outsized clasts within several hundred metres of lateral exposure at Gæssenjar’ga (Arnaud & Eyles 2002).

Sandstone beds are massive, graded (normal or reverse), rippled and cross-bedded (trough and planar). Laminated

mudstones, 0.3 to 10 m thick, vary in colour, lamination prominence, whether this is random or rhythmic, and size,

abundance and composition of lonestones. The latter are predominantly dolostones, <1 to 30 cm in size and are either

dispersed throughout the lithology or lie in discrete layers. Some laminated mudstone units are interbedded with

sandstone or diamictite.

Hambrey update – E. Finnmark – 2008_10_14 6

In the Gæssenjar’ga area, Hansen (1992) and Arnaud & Eyles (2002) recognised essentially the same lithologies and

units as Edwards (1984), but ordered them differently, without any depositional cyclicity.

In the Grasdal area, Edwards (1979) described a 3-6 m thick dark grey siltstone with an unusually high silt and low

clay content; this may also occur on the southern side of Leirpollen (Fig 1). Clasts consist of angular quartz and

feldspar grains of very-fine sand to coarse silt size, forming ca. 77% of the rock, with a statistically non-random

preferred N-S to NE-SW orientation. This unit has sharp contacts with the over- and underlying units (the latter is a

very dark diamictite with abundant dolomitic clasts) and an internal stratification defined by isolated, typically

dolomitic, clasts (< 7.5 mm sized) in discrete layers about 30 cm apart, together with very faint grey colour variations.

Nyborg Formation, E. Finnmark (0-350 m). The Smalfjord and Mortensnes Formations are separated by the Nyborg

Formation. The lowest part of this unit (Member A) comprises lateral and vertical gradations between massive buff-

weathering dolomicrites with sheet cracks and pseudo-tepees, through massive to thinly bedded dolomicrites to

interbeddded red sandstones/shales and dolomicrites, locally reworked as edgewise breccias, to dolomite-cemented

orange-red sandstones, as well as white-weathering green-grey sandstones and red and dark grey shales (Edwards

1984, Reading & Walker 1966, Rice & Hofmann 2001). Such sequences are usually only few tens of metres thick

(Reading & Walker 1966, Edwards 1984) although the succession is ca. 160 m thick at Alduskaidi (Fig 1; Føyn &

Siedlecki 1980). Generally, successions become more clastic upwards. On Ruos’soai’vi, west of Varangerfjord, 10

mm barite crystal fans grew on the basement, preserved within a 12 mm thick biotite extraclastic recrystallized

dolostone overlain by white-weathering sandstones. Similar white-weathering sandstones, likely cannibalised from the

Smalfjord Formation, also directly overlie very irregular basement surfaces on Ruos’soai’vi. White-weathering green-

grey sandstones (18.5 cm thick) also unconformably overlie ca 20. m of massive sheet-cracked dolomicrite in the

Miel’kejåkka area, SW of Tanafjord (Fig 1). Members B-D of the Nyborg Formation comprise, respectively,

interbedded reddish-purple shales/sandstones (ca. 200m), interbedded grey-green shales/sandstones (ca. 150-200 m)

and purple sandstone/grey-green shales (ca. 70 m; Edwards 1984). Member E (ca. 25 m thick), exposed only in the

Gulgofjord-Grasdal area (Fig 1), consists of white to grey sandstones with two thin (~1 m thick) buff-weathering

extraclast dolomicrites at the base (Edwards 1984).

Mortensnes Formation, E. Finnmark (<50 m). Edwards (1984) recognised three members, the lowest (<30 m) being a

northwards-thinning wedge of predominantly grey-green to purple massive diamictite (depending on the substrate

colour) of highly variable clast/matrix composition, with basement clasts and minor intrabasinal clasts from the

underlying substrate. This dies out around the southern end of Vestertana. Brecciation of the substrate has been found

below some diamictites, with substrate blocks up to 20 m long and 1 m thick incorporated into the overlying

diamictite. Lenses and bands of extra-basinal dark diamictite occur within more mixed lithologies. Basic clasts may

show facets and striations (Banks et al. 1971), whilst clast sizes decrease overall to the north (Edwards 1984). The

middle member has a gradational contact to the underlying rocks and is distinguished from it by its buff-brown

weathering, dolomitic composition of matrix and clasts with subordinate chert. This member rapidly increases in

thickness from < 4 m in the south to >10 m, approximately coincident with the southern end of Vestertana, giving two

sub-members. The thin sub-member comprises 2-4 m of stratified diamictite with primary and soft-sediment

deformation structures. The thick sub-member comprises five lithofacies; a blanket of massive purple to grey-green

Hambrey update – E. Finnmark – 2008_10_14 7

deformation diamictite, a zone of large tabular blocks (of Nyborg Formation, diamictite and white sandstone), a

relatively rare stratified dolomitic diamictite, a prominent buff-brown diamictite with a sandy matrix, which thins from

20 to 8 m from south to north, and, at the top, a bedded buff brown diamictite. The unconformably overlying upper

member (<40 m) consists of dark grey massive diamictite overlain north of Stappugied’di and Leirpollen by a 40 cm

thick dolomitic matrix diamictite with small dolostone and occasional large basement clasts. A 20-30 cm thick

polymict conglomerate overlies the formation over a large area (Edwards 1984).

Lillevannet Member, Stappogiedde Formation (40-110 m). The Mortensnes Formation is overlain by the Lillevannet

Member of the Stappogiedde Formation (Reading & Walker 1966), which thins from south to north, approximately

coincident with the southern end of Vestertana (Edwards 1984). The lower sub-member (3-55 m) comprises grey,

parallel laminated mudstones, silty to sandy in the north, grading upwards into a siltstone with some ripple cross-

lamination and with fine to medium grain lenticular sandstones (Edwards 1984). The upper sub-member is a complex

assemblage of sandstone and shale facies, including coarse arkosic sandstones, poorly cross-bedded and granule

conglomerates, medium grained sub-arkosic sandstone, relatively well sorted and rounded sandstones, thin to medium

bedded fine to very fine lenticular, erosive based sandstones, dark grey, brown weathering rippled and finely laminated

micaceous silty-sandy mudstone, sometimes in coarsening-upwards cycles and finely parallel laminated grey

mudstones (Edwards 1984).

Boundary relations with overlying and underlying non-glacial units

Southwards, the Smalfjord Formation cuts down through up to 2.5 km of the Tanafjorden, Ekkerøya and Vadsø

Groups, to lie on the basement around Varangerfjord. Minor outliers of Neoproterozoic sediments overlie the

basement, preserving an irregular unconformity, locally palaeo-frost-shattered (Bjørlykke 1967, Siedlecka 1990, Rice

& Hofmann 2000, Rice et al. 2001, Laajokki 2001, 2002, Edwards 1984, 1975). The base of the Smalfjord Formation

is characterised by rare E-W to WNW-ESE oriented sub-glacial striations; the best developed occur at Oaibaččanjar’ga

(Bigganjar’ga) in Varangerfjord (Reusch 1891, Strahan 1897), although others have been reported (Bjørlykke 1967,

Rice & Hoffman 2000, Laajoki 2002). Rice & Hofmann (2000) and Bestmann et al. (2006) documented a thin breccia

within and as ridges beside the striations at Oaibaččanjar’ga.

Regionally, the upper contact of the Smalfjord Formation with the overlying Nyborg Formation is also an

unconformity, since the latter rests on different parts of the former in different areas; specifically, the upper part of the

Smalfjord Formation in the Vaððasbak’te area of the Krokvatn Palaeovalley and in the Varanger palaeovalley are

absent (Fig. 1; Føyn & Siedlecki 1980, Edwards 1984). In the Ruos’soai’vi-Lap’paluokoai’vi area (Fig. 1), the Nyborg

Formation rests directly on the basement (Siedlecka 1990, Rice unpubl. data).

The base of the Mortensnes Formation is an invariably planar surface at outcrop-scale that cuts down-section towards

the south at a very low angle. The contact often exhibits brecciation or homogenisation of the underlying sediments

(deformation diamictite; Edwards 1984). At its upper contact, the Mortensnes Formation is overlain with a sharp or

rapid transition by the Lillevannet Member (Fig 2; Reading & Walker 1966, Edwards 1984).

Hambrey update – E. Finnmark – 2008_10_14 8

Chemostratigraphy

13

C data from E. Finnmark were briefly reviewed by Halverson et al. (2005); although more data are now available

the results are essentially the same as those previously reported. All data are standardised to VPDB; see Halverson et

al. (2005) for analytical methods.

The Grasdalen Formation has variable values, passing from -2 to -3 ‰ at the base, gradually rising to + 6 ‰ and then

falling very rapidly to -3 ‰; the two stratigraphically highest samples record values of +3 to +4 ‰.

Ten profiles through the dolostone (or interlayered dolostones-shales/siltstones/sandstones) sequences lying directly

above the Smalfjord Formation have been analysed over a wide geographic area and include the ca. 160 m thick

dolostone at Alduskaidi (Fig 1; Føyn & Siedlecki 1980). Although few profiles expose both the bottom and top of the

dolomite unaffected by either tectonic or penecontemporaneous erosional processes, all samples show 13

C values

between –1.0 and –5.9 ‰ (VPDB). Most have essentially constant 13

C values or show either a slight increase or

decrease in concentration. Only the 14 m thick profile at Miel’kejåkka (Fig. 1) shows a major variation, passing from –

2.55 ‰ at the base to –5.92 ‰ at the erosive upper contact. These data are comparable to the upper, ‘concave-down’,

part of the slope-bank (shelf) 13

C profile documented by Hoffman et al. (2007).

Thin dolostones in Member E of the Nyborg Formation, lying ca. 20 m below the sub-Mortensnes unconformity in the

Gulgofjord area (Edwards, 1984; Figs 1 & 2), gave δ13

C values between -7.6 and -9.9 ‰ (VPDB). Significantly, the

thin carbonate-matrix diamictite forming the uppermost part of the Mortensnes Formation on the NW side of

Tanafjord (Edwards 1984) also gave extreme negative values (down to –10.44 ‰ VPDB), taken to reflect erosion of

the underlying dolostones of Member E in the Nyborg Formation (Rice & Halverson unpubl. data).

Palaeolatitude and palaeogeography

Palaeomagnetic analyses on the Nyborg Formation have yielded palaeolatitudes for this area of 33°S to 41°S (Torsvik

et al. 1995), though no robust geochronological constraint is associated with this palaeolatitude. Samples were

subjected to thermal demagnetization and some also to alternating field demagnetization. High-temperature

components from 2 field areas (55 samples) were identified with a positive fold test at 95% significance level (κ = 4.9

in situ and 14.6 100% unfolded; α95=33.8 in situ and 18.1 100% unfolded, Torsvik et al. 1995).

The palaeogeography of Baltica as a whole has been constrained from other sites in Baltica, though well-dated

palaeopoles remain few (see reviews in Bingen et al. 2005, Cocks & Torsvik 2005). At ca. 750 Ma, a southwards

facing Finnmark-Kola region at ca. 15° S formed the southern margin of Baltica (Hartz & Torsvik 2002). This region

lay adjacent to a roughly E-W trending rift (Timanian margin) that to the west linked with the N-S trending

rift/spreading axis developing between Baltica and Laurentia (Greenland). At 616 Ma, Baltica is thought to have been

at polar latitudes (75°S) based on the well-dated Egersund dolerite dykes in southern Norway (Bingen et al. 2005). By

ca. 550 Ma, E. Finnmark was lying at ca. 50°S (Cocks & Torsvik 2005). In contrast, Cawood & Pisarevsky (2006) and

Pisarevsky et al. (2008) place Baltica in a more equatorial position (ca. 30°) although whether it lay in the northern or

southern hemisphere is unclear.

Hambrey update – E. Finnmark – 2008_10_14 9

Other Characteristics

No economic deposits have been reported in these rocks. Acritarchs have been documented from the Vadsø, Ekkerøya,

Tanafjorden and Vestertana Groups, though only reworked acritarchs and vase shaped fossils have so far been found

in the Smalfjord and Mortensnes Formations (Vidal 1981, Vidal and Siedlecka 1983). A limited Ediacaran fauna

(Farmer et al. 1992, Crimes & McIlroy 1999), dominated by discoidal forms (cf Gehling et al. 2000) and including

Aspidella (Narbonne, pers.comm 2008), has been documented, the oldest forms occurring in the Innerelv Member (Fig

2).

Geochronological constraints

No robust and high-resolution geochronological constraints are available. Rb-Sr dating of shales associated with the

glacigenic strata provides broad constraints for the deposition of the Smalfjord and Mortensnes formations (630-560

Ma; Pringle 1973, Gorohkov et al. 2001).

Discussion

Føyn & Siedlecki (1980) interpreted the Lower Krokvatn Diamictite as a massive indurated ground moraine and the

Middle and Upper Krokvatn diamictites as partly ground moraine and partly deposited under water. Aeolian or fluvial

processes deposited the intervening sandstones into quiet lakes or marine basins in the palaeovalley, whilst the red

sediments above the middle diamictite are likely loessites. Essentially, Føyn & Siedlecki (1980) interpreted the

sequence as alternating glacial stadial and interstadial events. However, Eyles (1983) noted that this argument was

presumptive; the interpretation that the rocks are glacial in origin was based on their stratigraphic position rather than

any diagnostic glacial criteria and thus the alternations were simply presumed to represent cyclical glacial advances

and retreats, without substantive proof.

Bjørlykke (1967) and Edwards (1984) interpreted the Varangerfjord succession as an infill of a glacially scoured

valley, the ice moving towards the northwest (see also Laajoki 2003, Baarli et al. 2006). Irregular glacier retreat left

ice-cored moraines that were submerged by rising water levels. Bathymetric lows were filled first by sediment gravity

flows and overlain subsequently by rapidly prograding deltas and sandur plains. Later diamictites may represent

glacial advances and/or sediment slumping.

At Oaibaččanjar’ga, Edwards (1975) suggested that the diamictite overlying the striations formed as a melt-out

diamictite from sediment-laden dead-ice, with the margins slumping and being eroded as the ice-entrained sediment

lost cohesion. In contrast, Schermerhorn (1974), Jensen & Wulff-Pedersen (1996), Crowell (1999) and Arnaud &

Eyles (2002) argued that the diamictite formed during slumping, possibly of glacigenic deposits, with some

suggestions that the striations also formed during slumping as the overriding diamictite was deposited; some of these

authors did not realise that the pavement is part of a major, deep regional angular unconformity. The very thin breccia

preserved in a number of striations and as ridges beside striations on the pavement has been ascribed to glacio-tectonic

brittle deformation processes, preserved by the instantaneous recrystallization of the highly strained comminuted

material, associated with flash-heating of the substrate, possibly up to ca. 1,700°C, during rapid glacial movement.

This was likely associated with glacial earthquakes (Rice & Hofmann 2000, Bestmann et al. 2006). The comminuted

material represents proto-rock-flour.

Hambrey update – E. Finnmark – 2008_10_14 10

In the Tanafjord area, Edwards (1984) interpreted the Smalfjord Formation (equivalent to the Upper Krokvatn

Diamictite of Føyn & Siedlecki 1980; Fig. 2) as a cyclic deposit of glacial advances and retreats, with the former

yielding a basal massive lodgement tillite, locally with sandstones deposited in situ by sub-glacial meltwater at the ice

margin. At the base of cycles, ice movement resulted in the formation of deformation tillites, comprised solely of

deformed substrate sediments, whilst mixing of local and far-travelled material formed banded tillites. Erosional bases

of the cycles are recorded at the outcrop-scale by deformation structures and mixing with subjacent material and on a

regional scale by the absence of stratigraphy below diamictites. During retreat, poorly sorted sand and silt with pebbles

were deposited at the ice margin by tractional underflows and gravity flows. In interglacial periods, finer grained

sediments accumulated, occasionally with dropstones, attesting to a glaciomarine environment. The dark silt-

dominated deposit at Grasdal was interpreted to be a loessite (Edwards 1979).

Hansen (1992), whilst agreeing that most of the diamictites were of glacial origin, argued for a shelf depositional

environment dominated by undermelt- and flow-tillites, some heavily deformed by an advancing glacier. Rapid

vertical and lateral thickness variations and terminations of both tillites and associated facies were interpreted to have

been mostly associated with changes in glacial movement directions and local bathymetrical conditions rather than

glacial erosion and lodgement. Glacigenic mass-movement tillites (flow-tillite) laterally grading into

sandstones, and at other stratigraphic levels grading into rhythmites, indicates transport directions and the relative

location of the basin/continent.

In contrast, Arnaud & Eyles (2002) suggested that the diamictites in both the Gæssenjar’ga and the southern and

western shores of Varangerfjord accumulated from subaqueous gravity flows from the basin margin, with the latter

forming part of a debris apron (see also Crowell 1999, Schermerhorn 1974, Jensen & Wulff-Pedersen 1996). Thus,

although the slumped material may have been of glacial origin, seen in rare faceted and striated clasts and lonestones,

the diamictites were not directly deposited by ice and so cannot be considered to be tillites. Instead, Arnaud & Eyles

(2002) suggested that they record deposition of unstable sediments on the edge of an active extensional basin (but see

Edwards 2004, Arnaud & Eyles 2004), in which icebergs or sea-ice contributed dropstones. Ice proximal settings were

inferred only for the eastern shore of Skjåholmen, where sediment gravity flow diamictite is closely associated with

well stratified glaciofluvial sandstones and conglomerates and at Handelsneset, where complex deformation observed

in conglomerates and sandstones suggests active deformation by overriding ice (Arnaud 2007).

The proposed source areas, and thus sediment transport (ice or otherwise) directions for the Smalfjord Formation, also

vary. Føyn & Siedlecki (1980) argue that the Middle and probably also the Lower Krokvatn Diamictite were derived

from the south. Arnaud & Eyles (2002) also proposed a southerly source area for the probable equivalent rocks at

Vieranjarg’a in the Varangerfjord area. Edwards (1984) inferred a westward ice flow along the Varanger palaeovalley,

with two dominant striation directions documented: NW-SE and E-W (Bjørlykke 1967, Edwards 1975, Jensen and

Pedersen 1996, Rice & Hofmann 2000, Laajoki 2002). Edwards (1984) also proposed that of the five advance/retreat

cycles identified in the Tanafjord area, the first was southerly derived, the subsequent three northerly derived and the

last of unknown origin. Hansen (1992), in contrast, suggested that the lower part of the succession was NE-derived

whilst the latter part was SE-derived. These differences are not simply due to the different order of the units proposed

by the two authors.

Hambrey update – E. Finnmark – 2008_10_14 11

Member A of the Nyborg Formation represents post-glacial transgression. Although Edwards (1984) suggested that

the dolostones formed around topographically high areas, correlation of the carbonates with Marinoan cap dolostones

(see below) suggests that deposition was not directly related to palaeodepth (cf Hoffman et al. 2007). Variations in the

clastic input certainly controlled which lithology formed. Subsequently, Members B-D reflect a rapid deepening of the

basin (Fig. 3) followed by a more gradual shallowing, with Member E representing a barrier lagoon facies, with

intermittent carbonate deposition (Edwards 1984).

The Mortensnes Formation represents two advances and retreats of ice (Edwards 1984); the first was initially derived

both from the south (lower member) and later from the north (middle member). The source area of the second advance

(upper member), which had a major change in provenance, is not known, although the extreme negative 13

C values of

the dolomitic diamictite at the top of the formation are thought to indicate derivation from the underlying Member E of

the Nyborg Formation. For both cycles, lodgement tillite was followed by floating ice, giving finer-grained

sedimentation and dropstones. The polymict conglomerate draping the formation has been interpreted as a lag-

conglomerate, formed during local isostatic uplift, after glacial retreat (Edwards 1984). The succession passed

essentially conformably upwards into the postglacial Lillevannet Member, representing fluvio-deltaic and subsequent

marine deposition.

Halverson et al. (2005) gave probable correlations of the glacigenic units in E. Finnmark with those documented

elsewhere, based on chemostratigraphy and carbonate lithologies. Dolostones at the base of the Nyborg Formation

have negative δ13

C values (-1 to -5.9 ‰), and, where massive, have sheet cracks, pseudo-tepees and, at one locality,

barite crystal fans. This, in combination with their buff-weathering colour strongly suggests that this is a Marinoan-

type cap dolostone (cf Kennedy et al. 1998). δ13

C data from the 230 m thick Grasdalen Formation in the Gulgofjord

area (Fig. 1) show positive values (6 ‰), falling rapidly to negative values and then recovering to positive values

below the c. 20 m thick Fadnuvag’gi formation, which lies directly under the Smalfjord Formation in the Grasdal area

(Fig. 1). Halverson et al. (2005) equated this δ13

C pattern with the Trezona anomaly, but since a broadly similar

anomaly occurs under the Port Askaig Formation, which is no longer considered to be a Marinoan equivalent (McCay

et al. 2006), this is not a robust constraint. Nevertheless, the characteristics of the cap dolostone secure the Smalfjord

Formation as an equivalent of the 635 Ma (Hoffmann et al. 2004) Marinoan glacigenic succession.

Thin dolostones in the upper part of the Nyborg Formation (Member E), with δ13

C values of -7.6 to -9.9 ‰, are likely

correlatives of the Wonoka anomaly, which elsewhere has δ13

C values as low as -12.81 ‰ (VPDB: Le Guerroué

2006); this implies that the almost immediately overlying Mortensnes Formation is broadly a correlative of the 580 Ma

Gaskiers diamictite (cf Halverson et al. 2005).

Kulling (1951) introduced the term Varangeristiden in a discussion of diamictites in northern Sweden. Although those

diamictites are now correlated solely with the Mortensnes Formation (cf Stodt et al. 2009), the term originally included

all the Neoproterozoic glacigenic rocks in E. Finnmark and implied one glacial period. However, as the Smalfjord and

Mortensnes Formations are now correlated with two distinct glacial events (Halverson et al. 2005), one of which was

world-wide and the other only a localised event, the concept of a Varangeristiden (Varangian/Varangerian ice age) is

no longer valid. Further, taking a 12 Ma duration for the Marinoan glaciation (Bodiselitsch et al. 2005) and 1 Ma for

the Gaskiers (Bowring et al. 2003) implies a total time span of 647-579 Ma for the two glacial events, of which only

Hambrey update – E. Finnmark – 2008_10_14 12

13 Ma (18 %) were actually spent under ice; scarcely enough to justify the term ‘ice-age’. For these reasons, use of the

term Varang(er)ian ice age is here discouraged.

No evidence of an older, Sturtian equivalent, glaciation has been recorded in this area. The Lille Molvika Formation

(Ekkerøya Group; Fig. 2) is bounded by two regional unconformities (Rice 1994, Siedlecka 1995), either of which

may ‘hide’ a pre-Marinoan glacial event. These unconformities are of post-800 Ma age, based on correlations in the

Manjunnas area (Fig. 1), where the Ekkerøya Group overlies the Båtsfjord Formation of the Barents Sea Group (Rice

1994). δ13

C data from the 1,400-1,600 m thick Båtsfjord Formation in the North Varanger Region (Fig. 1) are

consistently negative (Rice & Halverson, unpubl. data), suggesting a correlation with the ca. 800 Ma old Bitter Springs

anomaly (cf Halverson et al. 2005).

In the North Varanger Region (Fig 1), the Barents Sea (max. 9 km thick) and overlying Løkvikfjell (ca. 5.7 km)

Groups are separated by a major angular unconformity (Johnson et al. 1978, Siedlecki & Levell 1978); no glacial

deposits occur in these sequences. Biostratigraphic data (Vidal & Siedlecka 1983) are too imprecise to estimate the age

of the youngest rocks in the Barents Sea Group (Moczydlowska-Vidal, pers. comm. 2007), although it is younger than

800 Ma (see above). Mafic dykes cutting the unconformity and basal part of the Løkvikfjell Group were intruded at ca.

577 ±14 Ma (Rice et al. 2004). Thus the glacial conditions recorded by the Smalfjord and Mortensnes Formations may

not have been preserved in this basin.

Acknowledgements

AHNR thanks Arild & Jorun Pettersen, Gisle Stensvold, Per Sørflaten, Øystein Hauge and the extended Larsen family

(Vestertana) for hospitality and boating assistance during fieldwork in E. Finnmark; Christa & Rhian Hofmann and

Marcus Ebner for assistance in the field. MBE thanks Arild & Jorunn Pettersen for their hospitality; Harold Reading,

Sven Føyn, Stan Siedlecki, Anna Siedlecka, Signe-Line Røe, Tony Spencer, Knut Bjørlykke and Geoffrey Boulton for

scientific assistance in the field and/or discussions; the New York State Higher Education Assistance Program and

family for financial and moral support. Other acknowledgements are given in Edwards (1984). EA thanks the Natural

Sciences and Engineering Research Council of Canada for funding; Christina Trotter and Steven Aspden for assistance

in the field.

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Hambrey update – E. Finnmark – 2008_10_14 17

Figure Captions

Fig 1 Map of NE. Scandinavian Caledonides showing the main localities and distribution of glacigenic lithologies. A-

Alduskai’di; An-Andabakoai’vi; C-Čikkojåkka; D-Digermul; G-Gæssenjar’ga; Gr-Grasdal; Gu-Gulgofjord; H-

Handelsneset; L-Lappaluokoai’vi; Lp-Leirpollen; Lv-Laksefjordvidda; M-Mortensnes; Mi-Miel’kejåkka; Mn-

Manjunnas; N-Nyborg; Ne-Nesseby; Nj-Njukčagai’sa; O-Oaibaččannjar’ga; R-Ruos’soai’vi; S-Skjåholm; Sm-

Smalfjord; St-Stappugied’di; U-Uccaskai’di; V-Vestertana; Vb-Vaððasbak’te; Vr-Vieranjar’ga.

Fig 2 Regional stratigraphic profiles showing position of glacigenic units (modified from Johnson et al. 1978, Føyn &

Siedlecki 1980, Edwards 1984, Rice & Townsend 1997, Halverson et al. 2005). The Lille Molvika formation

and Ekkerøya group (formerly known as the Ekkerøya Formation, within the Vadsø Group) were informally

defined based on regional correlations by Rice & Townsend (1996). UE, LE – position of uppermost and

lowermost Ediacaran fauna. Pl – position of Platysolenites antiquissimus (Eichw.). Note different vertical scales

for columns A, C compared to B.

Fig 3 A. Schematic profile from Uccaskai’di to Vaððasbak’te through the glacial successions in the Krokvatn

Palaeovalley (modified from Føyn & Siedlecki 1980). LKD, MKD, UKD – Lower, Middle and Upper Krokvatn

Diamictites; B. Schematic profile from Varangerfjord to Gulgofjord (modified from Edwards & Føyn 1981;

Nyborg facies are N2 - fan channel; N3, N4 - fine and coarse submarine fan, respectively; N5 - tidal

distributary; N6 - bay/lagoon; N7 - offshore barrier. lsm, usm – lower and upper sub-member of the Lillevannet

Member).

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