91 Introduction the Southern Part of Ostrobothnia, the Suupohja Region

Home , Isojoki, Jurva, Kauhajoki, Ostrobothnia (region), South Ostrobothnia, Suupohja

Quaternary studies in the northern and Arctic regions of Finland Edited by Antti E.K. Ojala Geological Survey of Finland, Special Paper 40, 91– 95,2005.

A PROPOSAL FOR FORMAL LITHOSTRATIGRAPHICAL NAMES IN THE SUUPOHJA REGION, WESTERN FINLAND

by Reijo Pitkäranta

Department of Geology, 20014, University of Turku, FINLAND E-mail: reijo.pitkaranta@utu.ﬁ

Pitkäranta, Reijo, 2005. Aproposal for formal lithostratigraphical names in the Suu- pohja region, western Finland. Geological Survey of Finland, Special Paper 40 , 91–95, 2 figures and 1 table. The Suupohja region in southern Ostrobothnia, western Finland, has diverse Qua- ternary lithostratigraphy. Former and recent observations of the lithostratigraphical units have been compiled and formal names for them proposed. Altogether seventeen identified units (excluding the Holocene clay, peat and eolian deposits) are included to the Suupohja Group. It consists of the following formations, from bottom to top: Karhukangas Formation (nine different lithofacies observed), Kankalo Sand (two or three different lithofacies), Kariluoma Till, Harrinkangas Formation, Kauhajoki Till and Lumikangas Formation. In addition, to the Paleozoic lithified sandstone, which locally has been observed at the bottom above the crystalline Precambrian bedrock, the name “Lauhanvuori Sandstone” is proposed. Majority of the Quaternary sediments have been depositedinglacial(till)orice-marginalenvironment(glaciofluvialandglaciolacustrine/- marine sediments). In the upper parts also shore and eolian deposits can be observed. The sediments below the surficial Kauhajoki Till are older than the Middle Weichselian Substage, and the oldest sediments in the deeper parts may originate from the Middle or even Early Pleistocene Epoch.

Key words (GeoRef Thesaurus, AGI): glacial geology, sediments, lithostratigraphy, stratigraphic units, lithofacies, Quaternary, Pleistocene, South Ostrobothnia, Finland

Introduction Formerstudies havebeen concentrated almost exclusively on eskers, which usually have distinct The southern part of Ostrobothnia, the Suupohja geomorphology and where abundant open sections region, has diverseQuaternarylithostratigraphy are observable. During the inventory of sand and withseveral clearlydistinguishable sedimentary gravel resources in the Kauhajoki district (Kurkinen units. These lithostratigraphical features have been et al. 1994), also other types of accumulations with described in several papers since the 1970’s (see e.g. multiple stratigraphy were found, and which do not Niemelä & Tynni 1979, Saarnisto & Salonen 1995, havethe geomorphological form of an esker.In Donner 1995, Nenonen 1995). The Suupohja region these accumulations different types of till units and consists of the municipalities of Isojoki, Jurva, Kari- both coarse- and ﬁne-grained sorted deposits can joki,Kauhajoki,Teuva,Kaskinen,Kristiinankaupunki be observed superimposing upon each other. The and Närpiö (Fig. 1). drilling made by the Geological Survey of Finland

91 Geological Survey of Finland, Special Paper 40 Reijo Pitkäranta

Fig. 1. The Suupohja region with the thick multilayer accumulations (grey areas). The “till-covered eskers” (see Niemelä 1978) are marked as black and eskers without till cover as white. Sites described in previous papers are also indicated.

at Karhukangas penetrated 95.3 m thick Quaternary All the observed sedimentary units in the Suupo- sediment sequence and ended into sandstone (Huhta hja region have been grouped to form the Suupohja 1997). The drill core revealed twelve distinguishable Group, which consists of six Quaternary formations. lithofacies, which obviously have been deposited The sedimentary units have been described recently in different sedimentary environments. Up to five in Pitkäranta (submitted) and in previous papers (see glacial-deglacial phases can be constructed accord- e.g. Niemelä & Tynni 1979, Donner 1988, Gibbard et ing to the drilling, although it is possible that some al. 1989, Bouchard et al. 1990, Nenonen 1995, Huhta of the multiple layers have been deposited during a 1997, Kujansuu & Uutela 1997). Four new and two single glaciation due to glacier oscillation or from previousformationnameproposalsarepresentedinthe different parts of a glacier (see e.g. Brodzikowski & following. In addition, formal name for the Paleozoic Van Loon 1991). Different till layers, glaciofluvial, sandstone (see Simonen & Kouvo 1955, Lehtovaara shore and eolian sediments, permafrost structures and 1982) is proposed. paleosoils refer to two separate glacial and deglacial phases (before the Holocene) interpretable even in the Formal lithostratigraphy in glaciated areas uppermost few metres (Fig. 2). The interpretation of different lithofacies in the drillings, open sections and Utilizing formal lithostratigraphy helps in commu- test pits is based on grain-size composition, texture, nication. It is a tool when dealing with more or less color, organic content, sedimentary structures and complexlithostratigraphy,andalsoclarifiescorrelation directionalelements(whenobservable/measureable). between units in different areas.The presupposition is In addition, refraction seismic and ground-penetrat- thattheunits,whicharegoingtobenamed,willbeduly ing radar measurements were utilized (see Pitkäranta defined, characterized, described and proposed (see 1996, Pitkäranta submitted). instructions in the International Stratigraphic Guide,

92 Geological Survey of Finland, Special Paper 40 A proposal for formal lithostratigraphical names in the Suupohja region, western Finland

Hedberg 1976 [1st edition] and Salvador 1994 [2nd One problem in the procedure of formal naming is edition]). Using formal names diminishes confusing, the designation of stratotypes (type sections). Natural subjective and nonconsistent descriptive terms. sections, such as river terraces and seaside cliffs, are Assigning formal names tolithostr atigraphical rare in these areas. Observations have been made units has been rarely used in Finland and in Fenno- usually at artificially made open sections (e.g. quar- scandia as a whole (cf. Gibbard 1992). Reasons for ries, construction sites), where excavation is going this are probably lack of tradition to name units and on and the original description sites will easily be the fact that Quaternary deposits in Fennoscandia destroyed. On the other hand, where excavation has are relatively thin and heterogenous, and particular ceased, section walls will collapse or they have been lithofacies associations occur usually in only limited filled. Consequently, designated stratotypes lose their area. This may lead to a jungle of lithostratigraphic information/position as a representative observation names, because both litho- and chronostratigraphic site for particular lithostratigraphic units. Thus, in ad- correlation between different areas is difficult, and dition to the designation ofthe original primary strato- hence combining units from different areas is often type (holostratotype), also supplementary stratotypes impossible. Deposits from the same time interval and (parastratotypes) should be indicated if possible (see even the same sedimentary event may vary a lot from Salvador 1994). One possibility is also to establish one place to another.Also sediments originating from rules, how to preserve valuable geological sections. a single sedimentary event can vary a lot in a vertical section (see e.g. Eyles et al. 1983, Johnson & Hansel Proposed formal names for the Suupohja Group 1990,Brodzikowski&VanLoon1991).Furthermore, the lack of organic sediments and fossils make the Up to seven different till units, three glaciomar- correlation uncertain. If they are present, possible ine/-lacustrine units, three glaciofluvial, two wave- redeposition must be considered. Finally, detailed de- generated and three eolian sediment units (including scriptions of the deposits have concerned only limited Holocene sediments) have been interpreted in the areas,andeventhenthedescriptionsareheterogenous. Suupohjaregion.Alltheobservedlithofaciesandtheir They don’t necessarily fill the requirements, which formal names are summarized inTable 1. Generalized should be taken into account when assigning formal cross-section from Karhukangas to Lumikangas with names (see Salvador 1994). identified lithofacies is illustrated in Figure 2. Five

Table 1. Summaryof the lithostratigraphy,brief description of the depositsand tentativechronostratigraphyof the Suupohja Groupsediments. The locations of the type sections are indicated in the Finnish co-ordinatesystem, Zone 1. Elevation (Z) in meters abovepresentsea level.

Lithostratigraphic Observable unitsShortdescription of the sediments Chronostratigra- Type section names withinterpretation phy or type area

Lumikangas Stratified sand and gravel, shore depositHolocene X=6910.00 Formation Y=1559.80 Z=165

Kauhajoki Till Twodifferent Dark massivebasal till, high contentof Middle or Late X=6915.50 types (see Bou- fines (35–60 %<0.0625mm) Weichselian Y=1560.45 chard etal. 1990) Z=140

Harrinkangas Severaldifferent Glaciofluvial gravel, sand and silt,com- LateSaalian X=6915.50 Formation units(see Gib- pact,deformed, permafroststructures –Eem Y=1560.45 bard etal. 1989) Z=140

Kariluoma Till Atleasttwo Lightcompactsandylodgementtill, 10 LatePleistocene X=6909.71 differenttypes –30 %<0.0625mm (LateSaalian) Y=1549.02 Z=140*

KankaloSand Three unitsStratified, cross-bedded and ripple cross- Middle or Late X=6914.42 laminated medium-grained glacioflu- Pleistocene (Mid- Y=1547.56 vial, shore and eolian sands, compact, dle Saalian) (?) Z=125* deformed, permafroststructures

Karhukangas Nine units(see Mainlytills and glacilacustrine/-marine Earlyor Middle Type area: Formation Huhta1997) sedimentssuperimposing each other Pleistocene (?) central partof Karhukangas

Lauhanvuori (see Simonen & Lithified sandstone(minor occurences of Paleozoic Type area: Sandstone Kouvo1955, conglomerate) Lauhanvuori hill Lehtovaara 1982)

*Also supplementarytype sections designated.

93 Geological Survey of Finland, Special Paper 40 Reijo Pitkäranta

Fig. 2. Generalized cross-section with observed lithostratigraphy through Karhukangas, Kivistönkangas and Lumi- kangas.

new formation names have been proposed: Lauhan- Sand referred to inﬁnite ages (Kujansuu & Uutela vuori Sandstone, Karhukangas Formation, Kankalo 1997), although there were some uncertainties with Sand, Kariluoma Till and Lumikangas Formation. In the timing. The Kankalo Sand is probably older than addition, two formations have been described and theHarrinkangasFormation,andpre-LateSaalianage named earlier: the Harrinkangas Formation and the can be estimated for that formation. The ages of the Kauhajoki Till (Gibbard et al. 1989, Bouchard et al. different lithofacies of the Karhukangas Formation 1990). Furthermore, the Ostrobothnia Geosol (Ku- remain unknown, as no datings are available. Middle jansuu et al. 1991) has been proposed as the formal and even Early Pleistocene age can be estimated for name for the paleosoils found in the Suupohja region. the deeper layers. Microfossil and organic contents All the formations mentioned above are included to in the ﬁne-grained sediments are negligible, and they the Suupohja Group. don’t reveal the sedimentation environments. Thepaleosoils(OstrobothniaGeos ol)areinterpreted Age estimations of the Suupohja Group to originate from the prolonged ice-free period ex- sediments tending from the Eemian to the Middle Weichselian Substage, i.e. ~ 125 – 74 ka before present (see also Chronostratigraphy of the Suupohja Group sedi- Kujansuuetal.1991,Kujansuu1992,Hüttetal.1993). ments is by far unknown at present (see Table 1). Permafrost structures in the Harrinkangas Formation Severalthermo-andopticallystimulatedluminescense and the Kankalo Sand indicate fairly long and cold datings have been made on the deposits correlative ice-free period in the Early Weichselian, although it is to the Harrinkangas Formation (see Nenonen 1995 alsopossiblethatthepermafroststructuresinthesetwo with references). They refer to ages ranging from formationsoriginatefromdifferentcoldperiods.Both around 160 ka to 70 ka, i.e. from the Late Saalian to paleosoils and permafrost features are good marker the beginning of the Middle Weichselian Substages. horizons in lithostratigraphic and chronostratigraphic Consequently, it can be assumed that all the sediments correlation. below the Kauhajoki Till are older than the Middle WeichselianSubstage(Table1andFig.2). Alsolithos- Conclusions tratigraphy and particular post-depositional features suggest older than the Middle Weichselian age for the The Suupohja Group consists of six Quaternary sediments below the Kauhajoki Till (see Pitkäranta formations. This division is based on the interpreta- submitted). Two TL datings made from the Kankalo tion that the named formations have been deposited

94 Geological Survey of Finland, Special Paper 40 A proposal for formal lithostratigraphical names in the Suupohja region, western Finland in different sedimentary environments and probably nales Academiae Scientiarum Fennicae A III 150, 36 p. in different glacial-deglacial phases. The lowermost Hedberg, H.D. (ed.) 1976. International Stratigraphic Guide – A guidetostratigraphicclassificati on,terminologya ndprocedure. Karhukangas Forma tion has been observed only New York: John Wiley and Sons, 200 p. in drillings and indirectly in refraction seismic and Huhta,P. 1997. Almost100mofQuaternarydepositsonsandstone ground-penetrating radar measurements. Tills and atKarhukangas,Kauhajoki,westernFinland.In:Autio,S.(ed.), glaciolacustrineorglaciomarinedepositspredominate Geological Survey of Finland, Current Research 1995–1996. Geological Survey of Finland, Special Paper 23, 89–91. in that formation. The upper parts of the Kankalo Hütt, G., Jungner, H., Kujansuu, R. & Saarnisto, M. 1993. Sand, as also the other formations above it, can be OSL- and TL-dating of buried podzol and overlying sands in detected at open sections. They are mainly tills and Ostrobothnia, western Finland. Journal of Quaternary Science glaciofluvial deposits. Relatively thin layers of shore 8, 125–132. Johnson, W.H. & Hansel, A.K. 1990. Multiple Wisconsinan and eolian deposits have been determined in the upper glacigenicsequencesatWedron,Illinois.JournalofSedimentary parts, too. The Kankalo Sand, Kariluoma Till, Har- Petrology 60, 26–41. rinkangasFormation,KauhajokiTillandLumikangas Kujansuu, R. 1992. Paleosols as Quaternary stratigraphical key Formation are clearly distinguishable units and prob- horizons in Ostrobothnia, western Finland. Bulletin of the Geological Society of Finland 64, 161–167. ably of different origin, and hence they have been Kujansuu, R., Saarnisto, M., Räisänen, M.-L. & Hansel, A. separated into different formations. The majority of 1991. 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