Geological settings of the protected Selisoo mire (northeastern Estonia) threatened by oil shale mining

Abstract

The protected Selisoo mire in northeastern Estonia is located above valuable oil shale resources, partly in the permitted mining area. We describe in detail the geomorphology and geological setting of the mire to understand the natural preconditions for its formation, development and preservation. We used the LiDAR-based digital elevation model for relief analysis, mapped the peat thickness with ground-penetrating radar and described the Quaternary cover through corings. Ridges, oriented perpendicular to the generally southward-sloping terrain, and shallow depressions at the surface of mineral soil have influenced mire formation and its spatio-temporal dynamics. The Quaternary cover under the mire is thin and highly variable. Therefore the mire is hydrogeologically insufficiently isolated from the limestone bedrock that is drained by the nearby oil shale mine and consequently the mining activities approaching the mire may have a negative influence on the wetland and proposed Natura 2000 site. Natura 2000 type wetlands, both protected or currently outside the nature reserves, cover a significant portion of the prospective oil shale mining areas. The distribution and resilience of those sites may significantly influence further utilization of oil shale resources.

Saturated hydraulic conductivity of boreal peat and its relationships with peat properties and sampling depth

“…As mires are groundwater‐dependent ecosystems, drainage of the regional aquifers can cause damage to these natural habitats (Regan et al, 2019). This problem is more severe in areas where peat is underlain by geological formations that are more permeable or have a non‐continuous extent over the whole mire area (Auterives et al, 2011; Hiiemaa et al, 2014; Regan et al, 2019; Whittington & Price, 2013). To assess how the mire responds to regional groundwater drainage and if it could sustain itself in such conditions, the hydrological structure of peatlands must be researched.…”

Underground mining magnifies drought impacts in an adjacent protected raised bog

“…The Selisoo peatland complex has been extensively studied previously by Hiiemaa et al (2014), providing a more detailed description of the site's geology. The complex consists of two merged bog domes, with peat thicknesses reaching up to 7.2 m at the centre of the southern dome (Figure 1).…”

“…Plado et al, 2011). The GPR studies in Selisoo (Hiiemaa et al, 2014) show that the underlying topography consists of different sandy landforms, some of which cut though the thin, less conductive peat layers. Such buried landforms may act as 'windows' through which water can flow more quickly from the bog surface to the underlying mineral sediments.…”

Determining the age and possibility for an extraterrestrial impact formation mechanism of the Ilumetsa structures (Estonia)

“…Data were processed and interpreted with Prism2 software. The sub-peat reflection two-way time was converted to depth using a relative permittivity value 70 that commonly holds for boreal bogs (Plado et al 2011;Hiiemaa et al 2014;Habicht et al 2017;Sibul et al 2017). The thickness of peat and peat/sub-peat sediment types determined by the GPR was checked at five locations using a hand drill.…”