Upper Proterozoic stratigraphy and depositional environments of the Tossåsfjället Group, Särv Nappe, southern Swedish Caledonides

Abstract

A thick upper Proterozoic sedimentary sequence (4.5–6 km) has been identified in the Särv Nappe of the southern Swedish Caledonides. The sequence, defined as the Tossåsfjället Group, is divisible into five formations named in ascending order as the Lunndörrsfjällen Formation (alluvial), Kråkhammaren Formation (alluvial-littoral), Storån Formation (littoral), Lillfjället Formation (glacial-periglacial-aquatic), and Lövan Formation (alluvial). Palaeocurrents throughout the whole of the group suggest a general sediment transport from the Fennoscandian Shield towards the northwest. The group is cut at high angles by a tholeiitic dyke swarm. During the Caledonian Orogeny the Särv Nappe was displaced east-southeastwards over a distance exceeding 250 km. In its main outcrop area in Jämtland the nappe occurs as a major recumbent fold; its lower limb is highly attenuated, mylonitized and largely cut out by the basal thrust plane.

Key Words:

• Lithostratigraphy
• new stratigraphical units
• environmental analysis
• palaeocurrents
• periglacial environment
• glaciation
• alluvium
• carbonate sediments
• dolomitic composition
• chert
• nodules
• tillite
• sandstone wedges
• recumbent folds
• Särv Nappe
• Caledonides
• Upper Proterozoic
• Tossåsfjället Group
• Lunndörrsfjällen Formation
• Kråkhammaren Formation
• Storån Formation
• Lillfjället Formation
• Lövan Formation
• western Jämtland
• western Härjedalen
• central Sweden. N6220 N6315 E1345 E1230