Stratigraphy and palaeosol profiles of the Upper Triassic Isfjorden Member, Svalbard

The Isfjorden Member forms the upper part of the De Geerdalen Formation in Svalbard andThe Isfjorden Member forms the upper part of the De Geerdalen Formation in Svalbard andis well exposed throughout central and eastern Spitsbergen, including the island ofWilhelmøya. We examine palaeosol profiles identified in the Isfjorden Member and comparethese to profiles seen in the remainder of the De Geerdalen Formation. In addition, weaddress the nuances of the Isfjorden Member, its practicality as a stratigraphic interval andattempt to constrain the unit’s presence, as well as the nature of its lower boundarythroughout outcrops in Svalbard. The Isfjorden Member is easily recognised by itsconspicuous beds of alternating red and green coloured palaeosols, occasional caliche profilesand bivalve coquina beds. These beds have commonly been used to identify the unit inoutcrop and we explore their relevance to the formal stratigraphic definition. The lowerboundary is typically difficult to identify, especially when using the original definition;however, we find that placing it at the top of the last major sandstone in the De GeerdalenFormation is a practical solution. The boundary is conformable throughout Spitsbergen withno obvious erosion or break in sedimentation observed.The abundance, thickness and maturity of palaeosols increases upwards through the DeGeerdalen Formation. Mature palaeosol and occasional caliche horizons are found todominate within the Isfjorden Member. Immature palaeosols are in general constrained to thestrata below. The position of palaeosols in relation to sedimentary successions is typicallyrestricted to floodplain and interdistributary bay deposits, or atop upper shoreface deposits. The transition from immature palaeosols with common histosols to mature palaeosols andcaliche reflects the development of the delta plain from a dynamic paralic setting to a morestable proximal system.