Kongsfjorden‐Krossfjorden and the adjacent West Spitsbergen Shelf meet at the common mouth of the two fjord arms. This paper presents our most up‐to‐date information about the physical environment of this fjord system and identifies important gaps in knowledge. Particular attention is given to the steep physical gradients along the main fjord axis, as well as to seasonal environmental changes. Physical processes on different scales control the large‐scale circulation and small‐scale (irreversible) mixing of water and its constituents. It is shown that, in addition to the tide, run‐off (glacier ablation, snowmelt, summer rainfall and ice calving) and local winds are the main driving forces acting on the upper water masses in the fjord system. The tide is dominated by the semi‐diurnal component and the freshwater supply shows a marked seasonal variation pattern and also varies interannually. The wind conditions are characterized by prevailing katabatic winds, which at times are strengthened by the geostrophic wind field over Svalbard. Rotational dynamics have a considerable influence on the circulation patterns within the fjord system and give rise to a strong interaction between the fjord arms. Such dynamics are also the main reason why variations in the shelf water density field, caused by remote forces (tide and coastal winds), propagate as a Kelvin wave into the fjord system. This exchange affects mainly the intermediate and deep water, which is also affected by vertical convection processes driven by cooling of the surface and brine release during ice formation in the inner reaches of the fjord arms. Further aspects covered by this paper include the geological and geomorphological characteristics of the Kongsfjorden area, climate and meteorology, the influence of glaciers, freshwater supply, sea ice conditions, sedimentation processes as well as underwater radiation conditions. The fjord system is assumed to be vulnerable to possible climate changes, and thus is very suitable as a site for the demonstration and investigation of phenomena related to climate change.

New geological mapping has revealed further details of the tectonic and stratigraphic effects of Devonian and later reactivations of the Billefjorden Fault Zone, one of a number of important north-south trending lineaments in Svalbard. Analysis of offsets along the many steeply-dipping faults within the zone, and effects on the subsidence and deformation of the adjacent crustal blocks, is presented as a series of tectonic maps from the Late Devonian through to the Tertiary. Late Devonian sinistral transpression, suggested previously, cannot be ruled out, and Carboniferous reactivation was dominated by extension, with possibly a slight dextral strike-slip component. After Late Carboniferous to Early Cretaceous platform subsidence, during which the fault zone had little effect on sedimentation, development of the Tertiary West Spitsbergen Fold Belt (related to the opening of the Arctic Ocean) involved compressive (and transpressive?) reactivation of basement-seated structures further east, including the Billefjorden Fault Zone. In the Billefjorden-Austfjorden area this produced a large monoclinal fold across the fault zone, which was later cross-cut by extensional structures to produce the present day Billefjorden syncline. This localized late extension is related to a slight variation in the trend of the Billefjorden Fault Zone through this area.

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The tectonic map presented here shows the distribution of the major post-Ellesmerian and pre-Eurekan sedimentary basins, parts of the Caledonian orogen, the

Several publications propose that main-phase fold-thrust development on Spitsbergen was Late Cretaceous and not Tertiary as previously thought. The question of timing is crucial to models for crustal response to transpressive plate motions. Involvement of Tertiary strata in fold-thrust structures, the sedimentology of the Tertiary basin strata, and studies of paleo-stress field evolution all indicate Paleocene to Eocene fold-thrust development during opening of the Norwegian-Greenland oceanic basin. A regional angular unconformity of < 1 ø between Paleocene and Early Cretaceous strata is consistently disconformable to the eye and precludes any signifxcant older deformation in the immediate area. Preunconformity deformation was likely strike slip in character and concentrated in the west. The proposal for Late Cretaceous fold-thrust belt formation is inconsistent with the geology. Introduction A fold-thrust belt exposed on Spitsbergen, Norway has generally been considered Tertiary in age [e.g. Orvin, 1940; Harland, 1969; Birkenmajer, 1981; Steel et al., 1986; Dallmann et al., 1993] and to be coeval with Tertiary strata deposited in a central basin (Figure 1). Several recent papers argue that the main phase of fold-thrust belt development that affects platform cover rocks (Carboniferous to Middle Cretaceous in age) is Late Cretaceous in age [Hanisch, 1984; Lyberis and Manby, 1993a b, 1994]. Specifically, Lyberis and Manby [1993a, p. 134] state that "We suggest that the WSFB (West Spitsbergen Fold Belt) and Eurekan Fold Belt of North Greenland formed as a result of the Late Cretaceous to Palaeocene convergence between the Greenland and Svalbard blocks, and not by dextral transpression as previously suggested .... Plate kinematic considerations also lead us to the conclusion that the bulk of shortening across the two fold belts could have taken place before the Late Paleocene." Tertiary fold-thrust development synchronous with the dextral intracontinental transform plate motion [Talwani and Eldholm, 1977; Myhre et al., 1982] led to the use of