A Giant Sand Injection Complex: The Upper Jurassic Hareelv Formation of East Greenland

Sandstone intrusions have always caught the attention of geologists and are in many cases highly spectacular due to the contrast between light-coloured intrusive sandstones and dark host mudstones. In recent years it has become increasingly clear, that large, irregular bodies of massive sandstone may also be of intrusive origin, but the timing and nature of remobilization of the primary deposit, and of the subsequent injection are less well understood. It is also being recognized that remobilized and injected sands, mainly of relatively deep-water origin, may form important hydrocarbon reservoirs, which are difficult to interpret. The Upper Jurassic Hareelv Formation of Jameson Land, East Greenland is probably the World’s largest intrusive sandstone complex (SURLYK, 1987; SURLYK & NOE-NYGAARD, 2001). It comprises sandy submarine density flow deposits, which have undergone post-depositional remobilisation, liquefaction and subsequent intrusion in the surrounding compacted muds and mudstones. The sediments were sourced from shelfedge wedges and deltas. Interpretation of the depositional processes is, however, hampered by destruction of the primary sedimentary structures during remobilisation and liquefaction. However, a spectrum of sedimentary density flows involving hyperconcentrated and concentrated density flows (in the sense of MULDER & ALEXANDER, 2001) can be interpreted, depending on the position on the slope, degree of confinement and travel distance (SURLYK & NOE-NYGAARD, 2001; BRUHN & SURLYK, in press). Deposition took place in steep-sided slope gullies or in a non-confined baseof-slope and basinal setting. The aim of this study is to review the main processes acting during sand intrusion, and to interpret the possible causes. The extensive intrusive complex of the Hareelv Formation serves as a key example in order to facilitate the interpretation of similar subsurface examples.