Atanikerluk Formation Depositional Environment

Pedersen 1978). The beds are usually structureless, but Boundaries. A sharp lithological boundary occurs between cross-bedding has been recognised locally. Volcaniclastic the sandstones of the Agatdal Formation and the interbed- sandstones also occur as thin streaks in the mudstones ded mudstones and volcaniclastic sandstones of the and may include spherules of volcanic glass or tuff with Abraham Member (Figs 114, 115). At Qilakitsoq and in a distinct chemical composition known only from the the northern part of Agatdalen, the Abraham Member Asuk Member erupted from the Ilugissoq graphite andesite is succeeded by hyaloclastites of the Naujánguit Member, volcano (A.K. Pedersen 1985; A.K. Pedersen & Larsen whereas in the eastern part of Agatdalen the Abraham 2006). In the lower part of the member, the mudstones Member is succeeded by hyaloclastites of the Tunoqqu are very dark, fossiliferous and rich in concretions. At one Member (A.K. Pedersen 1978; Piasecki et al. 1992; A.K. horizon, in situ corals are present in small bioherms, Pedersen, personal communication 1999). 10–20 cm high and less than 1 m wide (Plate 3, section 4). This horizon can be followed for more than a kilo- Geological age. As for the Eqalulik Formation, i.e. latest metre on the eastern bank of Qaersutjægerdal. The con- Danian to early Selandian. tent of volcaniclastic sandstones increases upwards in the section. Correlation. The geochemical correlation of the Abraham Member with the hyaloclastites of the Asuk Member of Fossils. A sparse but diverse marine fauna and flora has the Vaigat Formation (A.K. Pedersen 1978, 1985; A.K. been recorded from the Abraham Member, comprising Pedersen & Larsen 2006) ties these isolated outcrops to scleractinian corals, echinoids, bivalves, gastropods, crus- the mapped volcanic succession on the south coast of taceans, fish remains and palynomorphs (Bendix- Nuussuaq (A.K. Pedersen et al. 1993). Almgreen 1969; Rosenkrantz 1970; Floris 1972; Koll - mann & Peel 1983; Piasecki et al. 1992; Petersen & Vedelsby 2000). Atanikerluk Formation Depositional environment. The macrofossil content in the new formation lower part of the member indicates a marine depositional environment. However, an increase up-section in History. The Atanikerluk Formation comprises the syn- terrestrially derived palynomorphs indicates that the volcanic non-marine sediments in the Nuussuaq Basin; environment became increasingly brackish with time. in the eastern part of the basin, it includes almost all the Sedimentary structures in the volcaniclastic sandstones sediments overlying the Atane Formation (Fig. 16). It is indicate deposition from turbidity currents. The corals divided into five members (Fig. 123), which are corre- suggest a shallow water (50?–80 m) marine environment lated to members in the volcanic Vaigat and Maligât in a warm temperate climate (Floris 1972), but where Formations (Fig. 131). The intra- and post-volcanic sed- the corals were redeposited the water depth may well iments of the Nuussuaq Basin are not included in the have exceeded 80 m. Nuussuaq Group and are therefore not discussed here. Koch 1959 This paper NuussuaqNuussuaq Disko Point 976 Member Assoq Member Assoq Member Aussivik Member Upper Umiussat Member Umiussat Member Umiussat Member Atanikerluk Atanikerdluk Formation Formation Pingu Member Akunneq Member Naujât Member Naujât Member Fig. 123. Lithostratigraphical subdivisions Naujât Mb Quikavsak of the synvolcanic, non-marine deposits of Quikavsak Member Not present the Nuussuaq Basin. Formation 139 Illukunnguaq Ujarasussuk Sullorsuaq Nuugaarsuk Vaigat nneq u Ak Inngigissoq Q E Q E R T A R S U A Q Pingu D I S K O 69°45’ Sul lorsua q Kvandalen Aqajaruata Qaqqaa Frederik Lange Dal Aqajarua n Mudderbugten Sorte Hak e æ r b r o t S B lå bæ r da g le n Ku uk q Laksedalen Q Gule Ry a a am u a s so r q e m r Flakkerhuk Daugaard-Jensen Dal e S Akuliarutsip Qaqqaa Killussaatsut KuuatSkorstensfjeldet t 69°30’ Killussaatsut Quaternary cover Maligât Formation k Qaama uu soq K Aamaruutissat Illunnguaq Intrusion Tuapaat ansen Qaqqaat Sk Innaarsuit Atanikerluk Formation Tuapaat Skansen Sandstone Atanikerluk Formation Mudstone Marraat Nuuk Atane Formation Skansen Member Killuusat Innanguit Ice Siniffik Sea/lake Niuluut 500 Contour in metres Assoq 5 km 53° 52°30’ 52° Fig. 124. Geological map showing the distribution of the Atane and Atanikerluk Formations on eastern Disko, simplified from A.K. Pedersen et al. (2001). Note that the outcrops of the Atanikerluk Formation are discontinuous. Contour interval is 200 m. For location, see Fig. 2. 140 In detail, however, the boundary between the Atanikerluk Distribution. The Atanikerluk Formation is known on Formation and the volcanic formations can be complex, south-east Nuussuaq (Saqqaqdalen, Atanikerluk, Kingit - hyaloclastite breccias and invasive lavas interdigitating with toq, Paatuut, and Ataata Kuua), on central Nuussuaq the sedimentary succession. These sediments, inter- (Nassaat and locally in Aaffarsuaq), on eastern Disko stratified locally with the lowermost volcanic layers, are (Assoq, Tuapaat Qaqqaat, Gule Ryg, Pingu, Nuugaarsuk, intimately associated with the uppermost Nuussuaq Frederik Lange Dal) and central Disko (Daugaard Jensen Group strata and are thus referred to the Atanikerluk Dal and Sorte Hak; Figs 2, 40, 124). In the Atanikerluk Formation where demonstrably related to an interdigi- area, the formation was mapped in great detail by Koch tating volcanic–sediment facies front (Figs 17, 131). & Pedersen (1960). Paleocene siliciclastic sediments are Two new formations, the Quikavsak Formation and also present on Svartenhuk Halvø, where they are over- the Atanikerluk Formation, replace the ‘Upper Atani kerd - lain by the volcanic Vaigat and Svartenhuk Formations luk Formation’ of Nordenskiöld (1871), Troelsen (1956) (J.G. Larsen, personal communication 2008). These sed- and Koch (1959). The term ‘Upper Atanikerdluk For - iments remain unstudied in detail and the distribution mation’ dates back to Nordenskiöld (1871), who used of marine pre-volcanic, marine synvolcanic and non- this name for the beds (Öfre Atanekerdluklagren) con- marine synvolcanic deposits is not known at present. In taining the upper flora in the Atanikerluk area. The plant the future, Paleocene non-marine, synvolcanic sediments fossils occur in concretions that are dark grey on fresh on Svartenhuk Halvø may be established as one or more surfaces but weather to a dark red colour (Nordenskiöld members within the Atanikerluk Formation. 1871 pp. 1051–52). Koch (1959) reported that these concretions contain the Upper Atanikerdluk A flora of Type section. The section in the south-facing slope between Heer (1883a, b) and that they occur in his Quikavsak Atanikerluk and Tartunaq on south-east Nuussuaq is Member, i.e. the Quikavsak Formation of the present retained as the type section (Figs 125, 126) for the paper. The name Atanikerluk Formation is proposed Atanikerluk Formation. This was described in detail by because it does not imply the existence of a ‘Lower Koch (1959), who defined type sections for several mem- Atanikerd luk Formation’. Although a Lower Atanikerdluk bers of the formation in this area. The type section is Flora was mentioned by Heer (1868), this originated located at 70° 03.63´N, 52°13.53´W. from the Atane Formation as recognised as early as 1871 by Nordenskiöld. Reference sections. Reference sections of the Atanikerluk Koch (1959) subdivided the Upper Atanikerdluk Formation are found at Kingittoq, at Pingu and in the Formation into five members on Nuussuaq (Fig. 123) Tuapaat area (Figs 7, 132, 140). The stratigraphic suc- but attempted no subdivision of the formation on Disko. cession in north-east Disko has been compiled from the His Quikavsak Member is here established as the Qui - (mainly sedimentary) sections on both sides of Akunneq kavsak Formation. Two of Koch’s members on Nuus - and the volcanic succession at Aqajaruata Qaqqaa, south suaq are retained (the Naujât and Umiussat Members), of Akunneq (A.K. Pedersen et al. 2005) (Figs 124, 131). whereas the Aussivik and Point 976 Members are aban- doned and the sediments are referred to the new Assoq Thickness. The Atanikerluk Formation is up to 500 m Member. The reason for this is that the Aussivik and thick in a composite section, but individual outcrops Point 976 Members are only found in a very small area reach thicknesses of c. 400 m (Pingu), c. 300 m (Kingittoq, of south-eastern Nuussuaq (A.K. Pedersen et al. 2007b). Atanikerluk) and 200–250 m (Saqqaqdalen) (Figs 126, On Disko, a subdivision into five members is proposed 128). At Tuapaat Qaqqaat, the thickness is difficult to (the Naujât, Akunneq, Pingu, Umiussat, and Assoq Mem - measure due to landslides and interbedding of sediments bers; Fig. 123). The subdivision of the Atanikerluk and invasive lava flows (Fig. 140). Invasive lava flows are Formation into five members reflects the dramatic palaeo- discussed below under ‘Lithology’. geographic changes that accompanied the intense volcanic activity. Lithology. The Atanikerluk Formation comprises mudstones, heterolithic sandstones, and fine-grained, loosely Name. The formation is named after the Atanikerluk cemented sandstones. Mudstones are dominant in the peninsula formed by a sill on the south coast of Nuussuaq Naujât and Pingu Members (Fig. 127) and in the lower (Fig. 40). The name was formerly spelled Atanekerdluk part of the Assoq Member, whereas very friable sand- or Atanikerdluk. stones characterise the Akunneq and

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