From widespread Mississippian to localized Pennsylvanian extension in central Spitsbergen, Svalbard

Jean-Baptiste P Koehl,Jhon M Muñoz-Barrera

doi:10.5194/se-9-1535-2018

Abstract

Abstract. In the Devonian–Carboniferous, a rapid succession of clustered extensional and contractional tectonic events is thought to have affected sedimentary rocks in central Spitsbergen, Svalbard. These events include Caledonian post-orogenic extensional collapse associated with the formation of thick Early–Middle Devonian basins, Late Devonian–Mississippian Ellesmerian contraction, and Early–Middle Pennsylvanian rifting, which resulted in the deposition of thick sedimentary units in Carboniferous basins like the Billefjorden Trough. The clustering of these varied tectonic settings sometimes makes it difficult to resolve the tectono-sedimentary history of individual stratigraphic units. Notably, the context of deposition of Mississippian clastic and coal-bearing sedimentary rocks of the Billefjorden Group is still debated, especially in central Spitsbergen. We present field evidence (e.g., growth strata and slickensides) from the northern part of the Billefjorden Trough, in Odellfjellet, suggesting that tilted Mississippian sedimentary strata of the Billefjorden Group deposited during active (Late/latest?) Mississippian extension. WNW–ESE-striking basin-oblique faults showing Mississippian growth strata systematically die out upwards within Mississippian to lowermost Pennsylvanian strata, thus suggesting a period of widespread WNW–ESE-directed extension in the Mississippian and an episode of localized extension in Early–Middle Pennsylvanian times. In addition, the presence of abundant basin-oblique faults in basement rocks adjacent to the Billefjorden Trough suggests that the formation of Mississippian normal faults was partly controlled by reactivation of preexisting Neoproterozoic (Timanian?) basement-seated fault zones. We propose that these preexisting faults reactivated as transverse or accommodation cross faults in or near the crest of transverse folds reflecting differential displacement along the Billefjorden Fault Zone. In Cenozoic times, a few margin-oblique faults (e.g., the Overgangshytta fault) may have mildly reactivated as oblique thrusts during transpression–contraction, but shallow-dipping, bedding-parallel, duplex-shaped décollements in shales of the Billefjorden Group possibly prevented substantial movement along these faults.

Highlights

Knowing that the study area (Odellfjellet; Figs. 1 and 4) and, conceivably, most areas in central Spitsbergen were subjected to tectonic extension in the (Late/latest?) Mississippian (Figs. 8b–c and 10d), we propose that N–S- and NE–SW-striking faults formed and acted simultaneously with WNW–ESEstriking faults during Mississippian extension, the only difference being that faults of the former two trends (N–S and NE–SW) experienced further normal movement, possibly during (Early–Middle?) Pennsylvanian extension (Braathen et al, 2011), crosscutting rocks of the Hultberget Formation (Figs. 8a and 9b–d)
WNW–ESE- to NW–SE-striking faults systematically die out upwards within sedimentary strata of the Billefjorden Group and, occasionally, of the Hultberget Formation. This suggests a switch from widespread extension in the Mississippian, involving faults of as many as three trends (WNW– ESE, N–S, and possibly NE–SW) during the rift initiation phase, to more localized extension in (Early–Middle?) Pennsylvanian times when normal displacement progressively localized along fewer fault trends (N–S and NE–SW) during the interaction and linkage phase and, eventually, along a few major basin-parallel faults (e.g., Billefjorden Fault Zone) during the through-going fault phase before extension ceased in the Middle–Late Pennsylvanian
In the Carboniferous, central Spitsbergen was probably subjected to WNW–ESE- to NW–SE-directed extension, potentially explaining why unsuitably oriented margin-oblique WNW–ESE-striking faults die out within Mississippian–lowermost Pennsylvanian strata of the Billefjorden Group and Hultberget Formation, while N–S- and NE–SW-striking faults experienced further normal faulting in the Pennsylvanian

Summary

Introduction

At the end of the Caledonian Orogeny in late Paleozoic times, Norway (Séranne et al, 1989; Osmundsen and Andersen, 2001; Gudlaugsson et al, 1998; Koehl et al, 2018a), Greenland (Hartz and Torsvik, 1997; Sartini-Rideout et al, 2006; Hallett et al, 2014; McClelland et al, 2016), and Svalbard (Manby and Lyberis, 1992; Braathen et al, 2018) were part of a large E–W trending intra-cratonic basin (Ziegler et al, 2002) that was subjected to a major episode of gravitational collapse, resulting in the formation of thick, Early to Middle Devonian sedimentary basins that evolved into rift basins in Late Devonian (?) to Carboniferous times (Fig. 1). M. Muñoz-Barrera: Widespread Mississippian extension in Spitsbergen lated to the opening of the northeast Atlantic Ocean and the formation of a major fold-and-thrust belt in Cenozoic times complicates the study of Mississippian sedimentary rocks, making it difficult to identify and resolve Mississippian fault movements

Methods

Results

Discussion

Conclusion