Terminology

The inner crater (Fig. 4) is a just over 7 km wide, almost circular depression floored by crushed, crystalline basement rocks at depths mostly over 100 m below the surface, and filled with sediments laid down either as resurge deposits within minutes after the impact or as secular deposits during the following epoch. The inner crater appears in the landscape as a relatively smooth, low terrain, much of which is surrounded by hills that are several tens of meters higher. The rim of this inner crater is a narrow (not over tens of meters wide) zone in which crushed crystalline basement comes to the surface and meets the filling referred to above. In most cases this happens in the lower slope of the surrounding hills. Thus defined, the rim is not appreciably raised.

The brim is an essentially flat and as much as 2.5 km wide zone of more or less crushed basement rocks. It surrounds the inner crater, from which is delimited by the rim. The term brim alludes to the resemblance to the brim

Fig. 3. Geological sections through the Lockne crater. The sections are located as shown in Fig. 1. The orientation of the sections is with west to the left. B is at the centre of the inner crater. Symbols are the same as in Fig. 1.

of a conventional-style plate, the deeper, inner part of which corresponds to the inner crater. For a comparison with the brim of a hat, one must think of the hat as turned upside down.

Resurge gullies cut radially through the brim. They are tens of meters deep, and can be filled with resurge deposits and post-impact secular deposits.

The twelve-figure references given for different localities identify their positions on the Swedish National Grid (=modified UTM) coordinates that are used on Swedish ordnance survey maps, such as the 1:50,000 topographic maps in common use in the country. They give the position to the nearest ten meters.

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