Abstract
•The Espanola Formation was deposited within an extensional rift basin.•Major bounding faults are inferred to have been active during deposition.•Synsedimentary deformation structures were documented in the Espanola Formation.•Structures include forceful intrusion, slope failure, and soft-sediment structures.•A criteria-based approach was used to identify possible triggering mechanisms.
The Espanola Formation represents part of the lower Huronian Supergroup (2.45–2.2 Ga), which is interpreted to have been deposited in a restricted, fault-bound, intracontinental rift basin during Early Proterozoic episodes of crustal stretching and contemporaneous faulting along the southern margin of the Archean Superior Province. Field examination of Espanola Formation outcrops exposed north of Elliot Lake, Ontario, Canada, revealed widespread synsedimentary deformation structures, which can be broadly grouped into three main categories: (1) forceful-injection structures, (2) slump structures, and (3) soft-sediment deformation structures. Examples of these structures include clastic dykes, large-scale slump structures, intraformational conglomerate, load casts, ball-and-pillow structures, convolute laminae, and dish-and-pillar structures. Most of the reported deformation structures are restricted to discrete stratigraphic horizons, are laterally continuous on an outcrop scale, are abundant and widespread across the studied region and are confined between undisturbed strata of similar lithology. These characteristics strongly indicate an origin by liquefaction and fluidization mechanisms that were triggered by syndepositional rift-related seismic activity, inferred to have been induced by movement along bounding normal faults during subsidence of the lower Huronian basin. Autogenic triggers such as overloading by rapid sedimentation, slump emplacement, inverse density gradient, gravity-driven sediment transport and mobilization, and storm waves may have also locally contributed to the development of the reported soft-sediment deformation structures.