Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi

More documents

Recommendations

Info

Geological Survey of Finland, Special Paper 46 Raimo Sutinen, Mari Jakonen, Pauliina Liwata and Eija Hyvönen Time-stratigraphic context The alignment of sheetfl ow tracks, fanning out to the southeast and south indicates drainage of large subglacial reservoir beneath the FIS after YD (Fig. 1). The former Lokka ice-lake most likely was the source for the sheetfl ow system. The sheetfl ow pattern crosses the N-S oriented esker system (Fig. 1), previously interpreted as Mid-Weichselian by Sutinen (1992). Also, maximum σ a-anisotropy of the tills exhibited a rather concurrent pattern with the N-S eskers (Fig. 2) suggesting that the N-S oriented eskers were generated, probably through time-transgressive evolution (Banerjee & McDonald 1975), prior to the sheetfl ow drainage of Lake Lokka. The preservation of Mid-Weichselian eskers and tillsequence indicates that the erosion rate of the Late Weichselian ice-fl ow had been low in the Lokka region. Morphologically this is supported by the lack of erosional streamlined features commonly found inside the YD End Moraines (YDEMs; Nordkalott Project 1987). We also argue against high velocity fl ood events during the sheetfl ow drainage because 58 RESULTS AND DISCUSSION large regions had not eroded out of unconsolidated sediments (cf. Kor & Cowell 1998). Sheetfl ows vs. arborescent eskers The anastomosing pattern of sheetfl ow tracks in the Lokka region (Figs. 1 and 3) is different from those in lower parts of northern Fennoscandia and the Canadian Shield displaying river-like drainage pattern of widely spaced tributary branches. The arborescent esker chains can often be followed tens or even hundreds of kilometres (Nordkalott Project 1987; Clark & Walder 1994). According to Clark and Walder (1994), anastomosing or braided channel systems are attributed to sedimentary terrains with fi ne-grained and low-permeability tills, not high-permeable tills underlain by crystalline bedrock as is the case in Lokka region. We found network patterns of some eskers (Fig. 4) rather similar to those described earlier by Prest (1968) and, Shaw and Kvill (1984) in Saskatschewan, Canada. However, discontinuities or even offsets in the esker tracks are diffi cult to explain without subglacial fault instability. Fig. 2. Anastomosing network of sheetfl ow tracks crosses the N-S-oriented esker ridges in the Lokka area. Note the majority of maximum σ a-anisotropy of tills oriented transversally to the sheetfl ow system, but rather than concurrently with the N-S eskers.
In Lokka, the sheetfl ow tracks were found to be less than 20 km wide and less than 60 km long, but were minor in cross-sectional channel form (cf. Wright 1973). The tracks show convex-up parts in their long profi les and cross topography regard- Geological Survey of Finland, Special Paper 46 Late Weichselian sheetfl ow drainage of subglacial Lokka ice lake less of slope. The tracks may cross the topography with 8% of slope displaying evidence of subglacial origin. The tracks contained both erosional channels and esker ridges. In some cases, the tracks exhibited 3-12 parallel or subparallel ridges 5-10 m in height Fig. 3. A compilation of DEM (data from National Land Survey) and low altitude AGR (γ K ; by Geological Survey of Finland) outlining the anastomosing network of sheetfl ow tracks within the Suoltijoki subset area. The grid size is 5 by 5 km. Fig. 4. A downfl ow outlook of the network of parallel/ subparallel esker ridges in the Suoltijoki subset area. 59
Page 1:
GEOLOGICAL SURVEY OF FINLAND Specia
Page 4 and 5:
Johansson, P. & Sarala, P. (eds.) 2
Page 6 and 7:
4 CONTENTS Preface, Peter Johansson
Page 8 and 9:
Geological Survey of Finland, Speci
Page 11 and 12: Applied Quaternary research in the
Page 13 and 14: DRUMLINS IN KUUSAMO AND RANUA In Ko
Page 15 and 16: RIBBED MORAINES IN SOUTHERN FINNISH
Page 17 and 18: ued fl owing from west to east but
Page 19: Sarala, P. 2005a. Glacial morpholog
Page 22 and 23: Geological Survey of Finland, Speci
Page 43 and 44: Pleistocene deposits in southern Li
Page 45 and 46: Heavy minerals Medininkai Upland Ei
Page 47 and 48: The South Lithuanian phase of glaci
Page 53 and 54: Fig. 4. Lateral drainage channels o
Page 55 and 56: for dating. The deglaciation of nor
Page 59: Geological Survey of Finland, Speci
Page 63 and 64: Fig. 5. A compilation of low altitu
Page 73 and 74: deposited over the fi lled channel,
Page 75 and 76: Michigan Lobe as it advanced into t
Page 77 and 78: Type IV Tunnel channels The Type IV
Page 79: Attig, J. W., Mickelson, D. M. & Cl
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
Page 116 and 117:
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
128
Page 132 and 133:
Page 134 and 135:
Page 136 and 137:
134
Page 138 and 139:
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
146
Page 150 and 151:
Page 152 and 153:
Page 154 and 155:
Page 156 and 157:
Page 158 and 159:
In summary, the northern part of th
Page 160 and 161:
Page 162 and 163:
Page 168:
www.gtk. info@gtk. e Peribaltic Gro
show all

Geological Survey of Finland, Special Paper 46 - arkisto.gsf.fi

Create successful ePaper yourself

Delete template?

Save as template?