Postglacial tectonic structures and mass wasting in Lake Vättern, southern Sweden

O’Regan, Matt; Greenwood, Sarah L.; Flodén, Tom; Swärd, Henrik; Björck, Svante; Skelton, Alasdair

doi:10.1144/m46.58

Cited by 3 publications

(12 citation statements)

References 10 publications

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“…These boreholes were drilled in an attempt to obtain a near complete late Pleistocene -Holocene sedimentary sequence. Detailed sedimentological, geochemical and geotechnical analyses of these sediments were used to reconstruct deglacial and Holocene environmental changes in Lake Vättern (Swärd et al 2016(Swärd et al , 2018, and to further constrain ice dynamics in the Vättern region during deglaciation (Greenwood et al 2015;O'Regan et al 2016).…”

Section: Coring Of Unconsolidated Sedimentsmentioning

confidence: 99%

“…No sediment was retained from the upper 155 m of the borehole, but the drilling logs indicate that at 86.5 mblf, sandy-sediments were encountered, and that between 111 and 155 mblf, pebble and cobble-sized clasts of sandstone and ultramafic/mafic rocks exist. The near continuous composite stratigraphy from the five shallow boreholes extends to 74 mblf (Swärd et al 2016). Three primary sedimentary units were described in the composite sequence from these boreholes (Swärd et al 2016(Swärd et al , 2018.…”

Section: Lithology and Stratigraphymentioning

confidence: 99%

“…The near continuous composite stratigraphy from the five shallow boreholes extends to 74 mblf (Swärd et al 2016). Three primary sedimentary units were described in the composite sequence from these boreholes (Swärd et al 2016(Swärd et al , 2018. These include 1) An organic-rich, silty-clay interpreted as a lacustrine clay; 2) sulphide laminated, silty clay deposited in a post-glacial environment and; 3) laminated silty-clays with low organic carbon content, deposited in a glacial/pro-glacial lake environment (Swärd et al 2016).…”

Section: Lithology and Stratigraphymentioning

confidence: 99%

“…Three primary sedimentary units were described in the composite sequence from these boreholes (Swärd et al 2016(Swärd et al , 2018. These include 1) An organic-rich, silty-clay interpreted as a lacustrine clay; 2) sulphide laminated, silty clay deposited in a post-glacial environment and; 3) laminated silty-clays with low organic carbon content, deposited in a glacial/pro-glacial lake environment (Swärd et al 2016). A sharp unconformity above visibly deformed, highly overconsolidated sediments exist at 55 mblf.…”

Section: Lithology and Stratigraphymentioning

confidence: 99%

“…This is interpreted as the last time that glacial ice was in contact with the lake floor (O'Regan et al 2016; Swärd et al 2016; Greenwood et al 2015). The silty-clays above this glacial unconformity (55-25 mblf) contain cyclic changes in sediment texture and composition, interpreted as varves deposited in a pro-glacial lake setting (Swärd et al 2016). The sulphide laminated post-glacial clays (25-15 mblf) were deposited in a brackish water environment following the final drainage of the Baltic Ice Lake (Swärd et al 2016(Swärd et al , 2018.…”

Section: Lithology and Stratigraphymentioning

confidence: 99%

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Geothermal evidence for groundwater flow through Quaternary sediments overlying bedrock aquifers below Lake Vättern, Sweden

Preto

Stranne

Greenwood

et al. 2019

GFF

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Groundwater discharge into lakes is an important component of the fluid and nutrient budgets, and a possible route for contaminant transport. However, groundwater flow beneath lakes is difficult to investigate due to the need for drilling deep boreholes. In 2012, a 2,000 m deep borehole was drilled in Lake Vättern, the second largest lake in Sweden. A continuous temperature profile was collected from the borehole. The geothermal gradient in the upper 180 m is highly non-linear, and not controlled by variability in the measured thermal properties of the sediments and rocks. The anomalous temperature profile is best explained by fluid flow into the borehole and subsequent vertical flow of warm waters towards the lake floor. Combining the temperature profile with stratigraphic information from drilling logs and seismic data, we find that fluid flow into the borehole occurs in glacial and glaciofluvial sediments deposited on top of a large sandstone aquifer (the Visingsö Group). The warm waters flowing through the glacial and glaciofluvial sediments are likely sourced from the underlying Visingsö Group sandstones. There is no evidence for substantial vertical migration of these waters through the overlying glacial and postglacial sediments. We speculate that they escape either along lake margins where overlying sediments become thinner, or along faults that are known to exist in the deeper basin.These results highlight an important hydraulic transport pathway between recognised regional aquifers and Lake Vättern. Further work is needed to evaluate the significance of groundwater discharge on the water and nutrient budget of the lake.

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Section: Coring Of Unconsolidated Sedimentsmentioning

confidence: 99%

Section: Lithology and Stratigraphymentioning

confidence: 99%