Late Pleistocene glacial-deglacial facies success1ons and geologic history at Vuolgamasjåkka, Finnmarksvidda, Norway ASTRID LYSÅ & GEOFFREY D. CORNER Lyså, A. & Corner, G. D.: Late Pleistocene glacial-deglacial facies successions and geologic history at Vuolgamasjåkka, Finnmarksvidda, Norway. Norsk Geologisk Tidsskrift, Vol. 74, pp. 9-23. Oslo 1994. ISSN 0029-196X. A 50 m high river section at Vuolgamasjåkka, Finnmarksvidda, Norway, has heen studied with regard to lithofacies, glaciotectonics and geologic history. Six formations reveal a history of four glacial events and two deglacial events spanoing the Weichselian back to the Saalian. Ice-free conditions are represented by deglacial sediments consisting of proximal to distal outwash facies and, at one horizon, delta foreset beds deposited in an ice-dammed lake. These sediments occur together with tills in stacked glacial-deglacial successions. Four kinetostratigraphic uoits are recogoized on the basis of glaciotectonic structures, till fabrics and palaeocurrent directions. Glaciotectonic structures were formed in both frozen and unfrozen sediments during successive glacier advances. Astrid Lyså & Geoffrey D. Corner, Department of Geo/ogy, /BG, University of Tromsø, N-9037 Tromsø, Norway. Thick til! sheets and subtil! and intertill sorted sediments on the inner Finnmark plateau (Finnmarksvidda) of northem Norway (Fig. l) record a history of multiple glacial phases and intervening ice-free periods extending back through the Weichselian and earlier (Olsen & Ham­ borg 1983, 1984; Olsen 1988, 1989). One of the longest and most complete succession of till-intertill sediments occurs in a 50 m high river section at Vuolgamasjåkka Fig. 2. The Vuolgamasjåkka section before excavations started, viewed from the north. (Figs. l, 2). Four major till formations and two intertill formations comprising sandy glacioftuvial sediments are exposed. Previous work on the exposure focused on lithostratigraphy, till fabrics and regional stratigraphic correlation (Olsen & Hamborg 1983, 1984; Olsen 1988, 1989). The present article presents the results of a detailed study of the sedimentary succession at Vuolgamasjåkka, with emphasis on lithofacies, interpretation of deposi­ tional environment, glaciotectonic structures and till fab­ rics. The results show that the lithostratigraphic units can be grouped into two major glacial-deglacial successions, capped by a multiple till succession (Figs. 3, 4). Map showing the location of (A) Vuolgamasjåkka area on Finn­ Location and setting Fig. I. marksvidda, 18 km northeast of Kautokeino, northem Norway, (8) the section at Vuolgamasjåkka river. The Kautokeino river drains towards the northeast. Vuolgamasjåkka is a tributary stream of the Kautokeino Elevations in meters. river (Fig. 1). The topography consists of a low-relief 10 NORSK GEOLOGISK TJDSSKRIFf A. Lyså & G. D. Corner 74 (1994) m a.s.l. ---+N Vuolgamasjåkka River Om 25m som 75m 100m 125m 150m 175m Fig. Sketch of the Vuolgamasjåkka section showing formation boundaries. Black areas represent investigated protiles. The main protiles (A-D) are indicated. The 3. profile line (X) studied by Olsen & Hamborg (1983, 1984) is shown dotted. The shaded area is covered with colluvium, the remainder vegetated. undulating moraine plateau, 300-400 m a.s.l. Bedrock, Table l. Lithofacies codes for sorted sediments at Vuolgamasjåkka based on exposed only on promontories and in incised valleys texture (adapted from Washburn et al. 1963 and Corner 1977). (Fig. 2), consists of Archaean and Early Proterozoic Constituent fractions Occurrence basement (mainly metamorphic and sedimentary rocks Facies ( > 5% in total) in (no. of beds in and granites) (Siedlecka et al. 1985). code Description order of amount section) The partly exposed, partly vegetated 50 m high, 225 m bG bouldery grave! cbsG long exposure was studied at 4 main sections (profiles eG cobbly grave! seG 7 A-D, Fig. 3). The sections are located close to sections sG sand y gra vel sG, csG 3 1-4 of Olsen (1989) and include a continuous vertical eS cobbly sand gcS 3 profile (A) situated 25m south of a comparable profile gS gravelly sand gS 23 1983). s sand s 50 studied by Olsen and Hamborg ( In addition, pS pelitic sand pS 15 numerous small sections were studied in order to trace qS gravelly pelitic sand gpS 7 major lithological boundaries laterally. 1973) and a facies code to denote all main fractions Stratigraphic fr amework 5% comprising > (Ta ble l). Grain-size analysis was car­ The sedimentary succession at Vuolgamasjåkka is di­ ried out in the laboratory using pipette analysis for the 63 63 vided into six informally named formations (Olsen 1988). < J.l.ID fraction, and wet or dry sieving for the > J.l.m These are, from bottoni to top (Figs. 3, 4): Mieron till, fraction. In the field, sieving was carried out on some Vuolgamasjåkka sand, Gardejåkka till, Eiravarri sand, samples for fractions 16 mm to 128 mm using sample Vuoddasjavri till and Kautokeino till. Based on local weights of 25-100 kg. TL-dates and regional lithostratigraphic and till fabric Orientation measurements are given uncorrected for correlations of younger tills, the Mieron till and Vuolga­ the local declination deviation (2° in 1992). Fabric analy­ masjåkka sand are thought to be of pre-Eernian and sis was carried out on clasts having an a/b axis ratio 1.5. Eemian age, respectively, while the overlying Gardejåkka > The results are plotted and contoured on a till and Eiravarri sand are thought to be of Early Weich­ Schmidt net (lower hemisphere) and statistical eigenval­ selian age (Olsen 1988, 1989). An interstadial of possible ues S1 , S3, and eigenvector V1 calculated. Till fabrics Middle Weichselian age (Sargejåk interstadial) is thought generally show a strong orientation and all are statisti­ to separate deposition of the two uppermost formations, cally significant at the 99% confidence level (Woodcock 1983). the Vuoddasjavri till and the Kautokeino till (Olsen & Naylor 1988, 1989). Sediment type and texture Methods Sorted sediments and diarnictons are subdivided into Sediment texture was recorded in the field using a lithofacies types based on grain size and sedimentary modified Udden-Wentworth-Krumbein scale (Shea structures (Tables 1-3). NORSK GEOLOGISK TIDSSKRIFT 74 (I994) Late Pleistocene g/acial-deg/acial facies successions, Finnmarksvidda Il Q) t C. «i E·o:l til ::!:C» • 370 ""-=.!.-.........,.." NE wedges w � � z ·(ij tilu ' c;,Q) u t \ ·(ij tilu a N f t 340 r Poles to w ·(ij reverse ( ·) and tilu normal ( +) faults w z c;,Q) u (ij ·util la Fig. 4. Composite litho- and kinetostratigraphy at Vuolgamasjåkka. For details on lithofacies, palaeocurrent and till fabrics, see Figs. 7, 8, 10, 12 and 14. The four kinetostratigraphic units are num bered 1-4. Kinetostratigraphic directions in parentheses are after Olsen ( 1988). Sorted sediments show considerable diversity in grain the glacier or reworked by glacial processes (Table 3). .size, sorting and type of bedding structure (Fig. 5). They show a relatively uniform composition, having a Facies are subdivided primarily on the basis of texture matrix mode in the very coarse silt to medium sand 5%) (component main fractions > and secondarily on fraction, and a subordinate clast mode in the very the basis of structure (Tables l, 2). coarse gravel fraction (Fig. 6). A minor but signifi­ The diamictons are essentially non-sorted sediments cant difference is shown between silty sandy tills of comprising tills that have been deposited directly by the Mieron Till (Fig. 6A) and tills from overlying 12 A. Lyså & G. Corner NORSK GEOLOGISK TIDSSKRIFT (1994) D. 74 Table 2. Lithofacies codes for bedding types among sorted sediments at Vuolgamasjåkka, and their interpretation (based partly on Miall 1977 and Eyles et al. 1983). Facies Occurrence code Description (facies types) lnterpretation Horizontal/subhorizontal stratification: m massive to crudely bedded cGm, sGm, gSm, longitudinal bars, debris Sm, qSm, pSm flow, waning flood deposits h horizontal/subhorizontal bGh, cGh, sGh, cSh, longitudinal bars, lag ( parallel bedding) gSh, Sh, pSh deposits, planar bed ftow (lower and upper ftow regime) low-angle cross-bedding gSI, Sl, qSI, pSI scour fills, waning ftood deposits c scour-and-fill, crude gSc, pSc scour fills, minor channel Se, trough cross-bedding fills p planar cross-bedding Sp transverse bars, magaripples ripple cross-bedding pSr, Sr ripples d deformed bedding pSd, Sd slump, liquefied ftow Inclined (large-scale foreset) stratification: f parallel laminated cSf, gSf, Sf, qSf grain ftow, turbidity current, suspension settling fm massive gSfm, qSfm turbidity current, debris ftow fl low-angle cross-bedding Sti turbidity current fr ripple cross-bedding Sfr, pSfr ripples, turbidity current fd deformed beds Sfd, qSfd, pSfd slump, liquefied flow CLAY SLT SAND GRAVEL COBBLE CLAY SILT SAND GRAVEL COBBLE A 8 40 40 Gravels Gravelly sand (bG, eG, sG) (gS) 30 30 20 20 10 10 � � >- >- o o c: c: Q) Q) 60 :::J :::J c D 60 CT CT Q) Q) Sand (S) Pelitic sand ot ot (pS, qS) 50 50 40 40 30 30 20 20 10 10 phi 9 4 -1 -6 -8 9 4 ·1 ·6 -8 mm 0.002 0.063 2 64 128 0.002 0.063 2 64 128 Grain size Fig. 5. Grain-size frequency curves showing sorted sediments at Vuolgamasjåkka grouped according to grain-size distribution: (A) grave!, (B) gravelly sand, (C) sand, (D) pelitic sand. Continuous lines represent grain-size distribution for samples < 16 mm. Dashed lines represent grain-size distributions for samples < 128 mm. Dotted lines indicate the total amount of fines (clay) in the unanalysed part of the sample. NORSK GEOLOGISK TIDSSKRIFT 74 (1994) Late Pleistocene glacial-deg/acial facies successions, Finnmarksvidda 13 Table 3. Lithofacies codes and inferred genesis of glacial diamictons at Vuolga­ formations which have a slight coarser, sandier compo­ masjåkka. sition. Facies code Description Interpretation Lithostratigraphy, facies interpretation and Dm Massive diamicton, normal Lodgement and basal melt-out silty-sandy composition till directional elements Dms Massive diamicton with thin Lodgement and basal melt-out sand lenses and linings till Mieron til/ around clasts The base of the Mieron till (Fig.