Revisiting Austfonna, Svalbard, with potential field methods – a new characterization of the bed topography and its physical properties

Abstract

Abstract. With hundreds of metres of ice, the bedrock underlying Austfonna, the largest icecap on Svalbard, is hard to characterize in terms of topography and physical properties. Ground-penetrating radar (GPR) measurements supply ice thickness estimation, but the data quality is temperature dependent, leading to uncertainties. To remedy this, we include airborne gravity measurements. With a significant density contrast between ice and bedrock, subglacial bed topography is effectively derived from gravity modelling. While the ice thickness model relies primarily on the gravity data, integrating airborne magnetic data provides an extra insight into the basement distribution. This contributes to refining the range of density expected under the ice and improving the subice model. For this study, a prominent magmatic north–south-oriented intrusion and the presence of carbonates are assessed. The results reveal the complexity of the subsurface lithology, characterized by different basement affinities. With the geophysical parameters of the bedrock determined, a new bed topography is extracted and adjusted for the potential field interpretation, i.e. magnetic- and gravity-data analysis and modelling. When the results are compared to bed elevation maps previously produced by radio-echo sounding (RES) and GPR data, the discrepancies are pronounced where the RES and GPR data are scarce. Hence, areas with limited coverage are addressed with the potential field interpretation, increasing the accuracy of the overall bed topography. In addition, the methodology improves understanding of the geology; assigns physical properties to the basements; and reveals the presence of softer bed, carbonates and magmatic intrusions under Austfonna, which influence the basal-sliding rates and surges.

Impact of Timanian thrust systems on the late Neoproterozoic–Phanerozoic tectonic evolution of the Barents Sea and Svalbard

“…The relatively broader geometry of Caledonian folds away from the Caledonian collision zone (e.g., in the Russian Barents Sea) is inferred to be related to gentler fold geometries due to decreasing deformation intensity in this direction. This is further supported by relatively low grade Caledonian Witt-Nilsson et al, 1998;Johansson et al, 2004Johansson et al, , 2005Dumais and Brönner, 2020) is associated with much narrower (20-50 kilometers wide) gravimetric and magnetic anomalies (Figure 5a-c). Note that the Atomfjella Antiform and Rijpdalen Anticline can be directly correlated with 20-50 kilometers wide, N-S-trending high gravimetric and magnetic anomalies (Figure 5ac).…”

“…N-S-trending upright folds involve the NNE-dipping thrust systems (Figure 3b and e) and correlate (via gravimetric and magnetic anomalies) with major Caledonian folds in northeastern Spitsbergen and Nordaustlandet, like the Atomfjella Antiform (Gee et al, 1994;Witt-Nilsson et al, 1998) and Rijpdalen Anticline (Johansson et al, 2004;Dumais and Brönner, 2020), with Caledonian grain in the southern Norwegian Barents Sea (Gernigon and Brönner, 2012;Gernigon et al, 2014), and with major NE-SW-trending Caledonian folds onshore northern Norway (Sturt et al, 1978;Townsend, 1987;Roberts and Williams, 2013). In addition, the width of the NE-SWto N-S-trending gravimetric and magnetic anomalies associated with these folds increases up to 150 kilometers eastwards, i.e., away from the Caledonian collision zone (Figure 5a-c; Corfu et al, 2014;.…”

“…The overall WNW-ESE trend and the consistent north-northeastwards dip and top-SSW sense of shear along the newly evidenced deep thrust systems preclude formation during the Grenvillian, Caledonian, and Ellesmerian orogenies, and the Eurekan tectonic event. These tectonic events all involved dominantly E-W-oriented contraction and resulted in the formation of overall N-S-to NNE-SSW-trending fabrics, structures and deformation belts in Svalbard (i.e., suborthogonal to the newly identified thrust systems) such as the Atomfjella Antiform (Gee et al, 1994;Witt-Nilsson et al, 1998), the Vestfonna and Rijpdalen anticlines (Johansson et al, 2004;Dumais and Brönner, 2020), the Dickson Land and Germaniahalvøya fold-thrust zones (McCann, 2000;Piepjohn, 2000;Dallmann and Piepjohn, 2020), and the West Spitsbergen Foldand-Thrust Belt and related early Cenozoic structures in eastern Spitsbergen (Andresen et al, 1992;Haremo and Andresen, 1992;Dallmann et al, 1993), and NE-SW-to NNE-SSW-striking thrusts and folds in northern Norway (Sturt et al, 1978;Townsend, 1987;Roberts and Williams, 2013) and the southwestern Barents Sea (Gernigon et al, 2014). A possible cause for the formation of the observed NNE-dipping thrust systems is the late Neoproterozoic Timanian Orogeny, which is well known onshore northwestern Russia (e.g., Kanin Peninsula, Timan Range and central Timan; Siedlecka and Roberts, 1995;Olovyanishnikov et al, 2000;Kostyuchenko et al, 2006) and northeastern Norway (Varanger Peninsula; Siedlecka and Siedlecki, 1967;Siedlecka, 1975;Roberts and Olovyanishnikov, 2004), and traces of which were recently found in southwestern Spitsbergen (Majka et al, 2008(Majka et al, , 2012(Majka et al, , 2014 and northern Greenland (Rosa et al, 2016;Estrada et al, 2018).…”

“…faults are assumed to have extended thousands of kilometers southwards and to represent the continuation of Caledonian faults in Scotland (Norton et al, 1987;Dewey and Strachan, 2003). Caledonian contraction resulted in the formation of large fold and thrust complexes, such as the Atomfjella Antiform in northeastern Spitsbergen (Gee et al, 1994;Witt-Nilsson et al, 1998) and the Rijpdalen Anticline in Nordaustlandet (Johansson et al, 2004;Dumais and Brönner, 2020), whereas Ellesmerian tectonism is thought to have formed narrow fold and thrust belts, like the Dickson Land and Germaniahalvøya fold-thrust zones (McCann, 2000;Piepjohn, 2000;Dallmann and Piepjohn, 2020).…”

“…Figure3), N-S-to NNE-SSW-trending gravimetric and magnetic anomalies (white and black dashed lines in Figure5a-c) are typically 20-50 kilometers wide and correlate with similarly trending Caledonian folds and thrusts onshore Nordaustlandet (e.g., Rijpdalen Anticline;Johansson et al, 2004;Dumais and Brönner, 2020) and northeastern Spitsbergen (e.g., Atomfjella…”