Early Holocene regressive spit-platform and nearshore sedimentation on a glaciofluvial complex during the Yoldia Sea and the Ancylus Lake phases of the Baltic Basin, SW Finland
Introduction
The Säkylänharju glaciofluvial ridge and its extension the Virttaankangas plain in SW Finland are generally described as an exceptionally large, complex esker. It forms the most prominent part of a 200-km long esker system, running from the Third Salpausselkä end moraine (Glückert, 1995) to the coast of the Gulf of Bothnia (Fig. 1).
Due to the glacio-isostatic rebound following the last deglaciation, the Säkylänharju ridge emerged as an isolated island from the ancient Baltic Sea, at about 9900–9000 14C BP Glückert, 1976, Glückert, 1994, Ristaniemi and Glückert, 1988. At that time, wind fetches extended a few hundred kilometres to the SW, and towards the end of the period also to the W–N. The regressive shoreline, exposure to powerful storms, and the abundant availability of glaciofluvial source material led to a wide distribution of shore features on the esker Aartolahti, 1972, Mäkinen, 1993. This implies highly intense removal and redeposition of glaciofluvial material within the littoral zone.
Up to now, interpretations regarding the genesis of the complex have been based on geomorphological and hydrogeological data without detailed sedimentological work. Previous studies have focused on the widespread and prominent ancient beach ridges flanking the complex Aartolahti, 1972, Mäkinen, 1993. Groundwater investigations within the Säkylänharju–Virttaankangas complex since the 1960s provide a remarkable source of subsurface data, which, however, has not been adequately treated or summarised in order to interpret past depositional environments. In this paper, we combine available subsurface data and new sedimentological outcrop observations with the morphology of the complex to describe its depositional history.
The Säkylänharju–Virttaankangas complex is divided into three major facies assemblages (I–III); these are used to outline the occurrence of shoreline deposits and their sediment source areas. The two glaciofluvial facies assemblages are first briefly described and interpreted. The paper then focuses on the sedimentology of the Virttaankangas plain (i.e. Facies assemblage III). The results show that the Virttaankangas plain is not a glacigenic delta/fan delta, as suggested by previous authors Glückert, 1971, Aartolahti, 1972, nor was it formed during deglaciation as stated by Kukkonen et al. (1993). Rather, the Virttaankangas plain formed by the redeposition of the esker material transported by longshore drift towards the southeastern part of the esker during the glacio-isostatically forced regression of the Yoldia Sea phase (Fig. 2). This redeposition has resulted in the development of a prograding spit-platform overlain by numerous beach ridges.
The lithofacies interpretations presented in this article contribute to our understanding of erosional and depositional processes in nearshore environments, which are difficult to examine in modern systems, especially under severe storm conditions. The depositional model describing the deposition of the plain can be applied to several other emerged glaciofluvial ridges in Finland. Furthermore, the results of this study will be applied in the planning of an artificial groundwater-supply project on the Virttaankangas plain.
Section snippets
Study area
The study area is situated in SW Finland approximately 61°00′N and 22°35′E (Fig. 1). The geomorphological setting of the study area is illustrated in Fig. 2, Fig. 3.
Postglacial shore-level displacement
After the deposition of the Third Salpausselkä ice-marginal formation during the Younger Dryas, the climate warmed up considerably, leading to the rapid retreat of the ice margin. According to Sauramo, 1923, Sauramo, 1940 glacial varve chronology, the margin of the ice sheet was situated in the Virttaankangas area about 400 clay varve years after the final drainage of the Baltic Ice Lake (BIL) to Yoldia Sea level. The final drainage of the BIL, correlated here to ca. 11 565 GRIP ice core years
Material and methods
The facies zonation of the Säkylänharju–Virttaankangas complex is based on morphology, observations of sedimentary characteristics from six pit exposures (Fig. 4), and on a number of groundwater research reports, including drilling, seismic soundings, ground-penetrating radar (GPR) surveys, gravimetric surveys, aeromagnetic measurements and records of groundwater levels and flow paths. The drill holes cover the entire study area; they consist of 57 hammer-driven drill holes (not penetrating to
Facies zonation of the Säkylänharju–Virttaankangas complex
The study area can be divided into three major facies assemblages, referred to here as (I) esker, (II) Säkylänharju–Virttaankangas glaciofluvial ridge and related fine-grained deposits, and (III) spit-platform and related shore-zone deposits of the Virttaankangas plain Fig. 4, Fig. 5.
Discussion
The Säkylänharju–Virttaankangas complex is interpreted here as having been formed in four main depositional phases: (I) time-transgressive deposition of the esker (subglacial tunnel infill superimposed by repeated subaqueous retrogradational fans); (II) deposition of the Säkylänharju–Virttaankangas glaciofluvial ridge and related fine-grained deposits (interlobate ice-marginal crevasse deposits and related glaciolacustrine sediments); (III) erosion of glaciofluvial deposits during rapid
Concluding remarks
The results of this study demonstrate that the role of glaciofluvial processes in the genesis of the Virttaankangas plain has been overemphasized in previous reports. The morphology of the plain is predominantly ruled by the development of the spit-platform sequence and superimposed nearshore deposits. The findings thus indicate that the deposition of the Virttaankangas plain did not require a marked stillstand of the ice margin during the last deglaciation; this is also supported by the lack
Acknowledgements
We would like to thank our enthusiastic fieldwork assistants Jani Kivi, Anna-Liisa Rautionmaa, and Nyrki Rautionmaa, and also Seppo Toivonen for skillful use of his tractor–excavator. My warmest thanks are due to the Rautionmaa family for accommodation and care during the fieldwork seasons. The work was financially supported by Emil Aaltosen Säätiö (the Emil Aaltonen Foundation), Jenny ja Antti Wihurin Rahasto (the Jenny and Antti Wihuri Foundation), Suomen Kulttuurirahasto/Satakunnan Rahasto
References (73)
The occurrence and geologic work of rip currents off southern California
Marine Geology
(1970)- et al.
Holocene spit development on a regressive shoreline, Dornoch Firth, Scotland
Marine Geology
(1995) - et al.
Storm-generated currents and offshore sediment transport on a sandy shoreface, Tibjak Beach, Canadian Beaufort Sea
Marine Geology
(1993) - et al.
Sedimentology, seismic facies and stratigraphy of a Holocene spit-platform complex interpreted from high-resolution shallow seismics, Lysegrund, southern Kattegat, Denmark
Marine Geology
(2000) - et al.
The evolution of Buctouche Spit, New Brunswick, Canada
Marine Geology
(1995) - et al.
Barriers, barrier platforms, and spillover deposits in St. George's Bay, Newfoundland: paraglacial sedimentation on the flanks of a deep coastal basin
Marine Geology
(1992) Bedforms and depositional sedimentary structures of a barred nearshore system, eastern Long Island, New York
- et al.
Storm beach deposits in the Late Palaeozoic Ecca group of South Africa
Sedimentary Geology
(1977) On the beach ridges in the area of the Virttaankangas–Säkylänharju esker, SW Finland
Fennia
(1972)Storm sequences in shallow water
Correlation of Swedish glacial varves with the Greenland (GRIP) oxygen isotope record
Journal of Quaternary Science
Holocene history of the Baltic Sea as a background for assessing records of human impact in the sediments of the Gotland Basin
The Holocene
Event stratigraphy for the Last Glacial–Holocene transition in eastern middle Sweden
Quaternaria A
Sedimentation of beach gravels: examples from South Wales
Journal of Sedimentary Petrology
Clast assembling, bed-forms and structure in gravel beaches
Transactions of The Royal Society of Edinburgh: Earth Sciences
Gravel beaches of southern Namibia
Source of pebbles at Mann Hill Beach, Scituate, Massachusetts
Characterization of transport bottoms in the Gulf of Bothnia – a model approach
Aqua Fennica
The morphodynamics of coarse clastic beaches and barriers: a short and long-term perspective
Journal of Coastal Research, Special Issue
Depositional structures and processes in the non-barred high-energy nearshore
Journal of Sedimentary Petrology
Reconstruction of paleo-wave conditions during the Late Pleistocene from marine terrace deposits, Monteray Bay, California
Transgressive and progradational beach and nearshore facies in the Late Archaean Turffontein Subgroup of the Witwatersrand Supergroup, Vredefort area, South Africa
South African Journal of Geology
Postglacial evolution
Atlas of Finland
The main ancient shorelines
Atlas of Finland
Paraglacial coasts
Coarse-grained beach sedimentation under paraglacial conditions, Canadian Atlantic Coast
Stranddünenwälle am Längsoszug Virttaankangas–Säkylänharju in SW Finland
Bulletin of The Geological Society of Finland
Post-glacial shore-level displacement of the Baltic in SW Finland
Annales Academiae Scientiarum Fennicae Series A III
Maankohoamisen arvioiminen Itämeren jääkauden jälkeisen rannan–siirtymisen avulla Suomessa
The Salpausselkä End Moraines in southwestern Finland
The Vessö esker in southern Finland and its economic importance
Fennia
The effect of the sea on the eskers of an emerging coast in southern Finland
Baltica
An emerging esker in southern Finland
Geografiska Annaler
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2020, Journal of Applied GeophysicsCitation Excerpt :The MUKH-structures influence the groundwater flow paths, residence times, and flow velocities, and allow the usage of reverse gradients (Artimo et al., 2010). The Virttaankangas plain consists of six major sedimentological units: (1) Esker core, (2) subaqueous fans, (3) esker fan lobes, (4) MUKH-structures, (5) clayey bed with perched groundwater, and (6) beach deposits (Mäkinen and Räsänen, 2003). These units form the basis for the inferred units of the 3-D hydrogeological model of Virttaankangas: (a) impermeable bedrock, (b) till, (c) glaciofluvial coarse-grained sand, (d) glaciofluvial/glaciolacustrine fine-grained sand, (e) silt and clay, and (f) littoral sand (Artimo et al., 2003) (Fig. 2).
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2018, Sedimentary GeologyCitation Excerpt :A variant of this spit-platform model could entail the sole formation of a submerged platform, without coeval development of a subaerial spit (Nielsen et al., 1988; Novak and Pedersen, 2000). This would account for absence at Le Castella of low-energy, embayment-related deposits on the lee side of the presumed spit and lack of upper nearshore to backshore deposits above the topsets of the high-angle clinoformed wedge, deposits that are often preserved in spit successions (Nielsen et al., 1988; Novak and Pedersen, 2000; Mäkinen and Räsänen, 2003; Nielsen and Johannessen, 2009). Numerous similar infralittoral prisms of bioclastic, siliciclastic, and hybrid composition, with sigmoidal-oblique clinoforms, and forming elongated bodies detached from the shoreline have been described from Neogene and Quaternary deposits of the Mediterranean region (Chiocci and Orlando, 1996; Hernández-Molina et al., 2000; Pomar and Tropeano, 2001; Chiocci et al., 2004; Massari and Chiocci, 2006; Mateu-Vicens et al., 2008; Massari and D'Alessandro, 2012; Tomassetti and Brandano, 2013).
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