Geologia Croatica (Jun 2003)
A Giant Sand Injection Complex: The Upper Jurassic Hareelv Formation of East Greenland
Abstract
A major intrusive sandstone complex of Late Jurassic age is spectacularlyexposed in Jameson land, East Greenland. It is probably thelargest in the World, and covers an area of 55x70 km with a thicknessof 200–400 m, and forms the Upper Oxfordian–Volgian Hareelv Formation.The complex consists of black basinal mudstones and highlyirregular sandstone bodies, dykes and sills. The sand was derivedfrom collapse of the front of sandy shelf-margin wedges, which triggeredhyperconcentrated to concentrated density flows, and depositedmassive sands further down the slope, at the base-of-slope and in thebasin. The sand of some flows was loaded into the slope muds whileelsewhere it flowed in steep-sided gullies formed by retrogressiveslumping of the slope muds. All sand bodies were liquefied subsequentto burial and the sand was intruded into the surrounding blackcompacted muds and mudstones. Intrusion took place repeatedly overa long time interval, in environments ranging from very shallow torelatively deep burial, and the primary sediment structures of thesands were generally lost during these processes. It is rarely possibleto determine the degree of post-burial remobilization but it rangesfrom rather small-scale modifications to wholesale liquefaction andout-of-place intrusion of the sand over many tens of metres. Sandstonedykes and sills occur ubiquitously and were emplaced by allcombinations of stoping and dilation. The intrusive sand bodies rangein dimensions from centimetres to many hundreds of metres. Depositiontook place during the most important Mesozoic rift event in EastGreenland and the pervasive remobilization and liquefaction of allsand bodies in the Hareelv Formation is interpreted as having beencaused mainly by cyclic earthquake shocks. Additional important factorswere slope shear stress, build up of pore pressure due to loading,slumping, upwards movement of pore waters expelled from the compacting muds, and also possibly of biogenic and thermogenic gas. The Hareelv Formation is an excellent field analogue for deeply buriedhydrocarbon reservoirs, which have been modified by remobilizationand injection of the sands.
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