Abstract
Abstract Seismic reflection data and shallow cores from the SE Greenland margin show that rift basins formed by the mid- to Late Cretaceous in the offshore area near Ammassalik. Here termed the Ammassalik Basin, this contribution documents the area using reprocessed older shallow seismic reflection data together with a more recent, commercial deep seismic reflection profile. The data show that the basin is at least 4 km deep and may be regionally quite extensive. Interpretation of gravity anomaly data indicate that the basin potentially covers an area of nearly 100 000 km 2 . The sediments in the basins are at least of Cretaceous age, as indicated by a sample from just below the basalt cover that was dated as Albian. Dipping sediment layers in the basins indicate that older sediments are present. Comparison of the data to the conjugate Hatton margin where older basins are exposed beneath the volcanic cover shows similar stratigraphy of similar ages. Reconstructions of the position of the basin during the Permian–Triassic and Jurassic suggest that older sedimentary strata could also be possible. In contrast to the conjugate Hatton margin, possible older strata subcrop out below the seafloor along the shallow margin, providing a future opportunity to sample some of the oldest sediments to determine the onset of rifting between SE Greenland and the Hatton margin.
Highlights
In this contribution, the sedimentary basin offshore SE Greenland, here termed the Ammassalik Basin, is investigated further using older seismic reflection data in conjunction with a recent commercial, deep seismic reflection profile and regional gravity anomaly data
Margin and regional data suggest that the Ammassalik Basin was part of a well-developed Mesozoic rift system that is observed along the Hatton margin
In the early Paleocene, submarine fan sandstones were deposited along the northern basin margin, whereas mudstone deposition continued within the basin
Summary
The onshore area along SE Greenland is dominated by the Palaeoproterozoic Nagssugtoqidian Orogen (Fig. 2) (see Kolb 2014 for a recent summary). North of Ammassalik, the nearest known sedimentary outcrops are found on Kap Gustav Holm (Figs 1 & 2). These are described as Upper Cretaceous –Cenozoic sandstones (Wager 1934), but little subsequent work has been carried out on these outcrops. Cretaceous –Paleocene sedimentary rocks of the Kangerlussuaq Basin (Fig. 2) have been well studied and are described in Larsen et al (1999). Upper Cretaceous marine mudstones interbedded with thin turbiditic sandstones overlie these successions. Fluvial sheet sandstones and conglomerates of latest Paleocene age overlie unconformably the offshore marine succession (Larsen et al 1999, 2001, 2006). Renewed subsidence and extensive volcanism initiated immediately prior to and during break-up
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