Ladinian Palynofloras in the Norwegian–Danish Basin: a Regional Marker Reflecting a Climate Change
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ROSA_2008:ROSA-2008 01/07/09 15:48 Side 21 Ladinian palynofloras in the Norwegian–Danish Basin: a regional marker reflecting a climate change Sofie Lindström, Henrik Vosgerau, Stefan Piasecki, Lars Henrik Nielsen, Karen Dybkjær and Mikael Erlström The Triassic – lower Cretaceous sedimentary succession of the Norwegian–Danish Basin has for a long time been of Geological setting exploration interest, and numerous studies have been carried The intracratonic Permian–Cenozoic Norwegian–Danish out. However, high-resolution correlation within the basin Basin is bounded to the south by the Ringkøbing–Fyn High remains necessary, especially between the Danish and Nor - and to the north by the strongly faulted Sorgenfrei–Tornquist we gian parts of the basin. A variety of litho- and biostrati- Zone (Fig. 1). The basin was formed by Late Carboniferous graphic schemes have been applied to the succession over the – Early Permian crustal extension followed by thermal sag- years, but lack of consistency in terminology has often led to ging, local faulting and salt tectonics. The syn-rift succession confusing interpretations of the geological development. In consists of Rotliegendes volcaniclastic rocks, alluvial con- this study a sequence stratigraphic scheme has been devel- glomerates and sandstones as well as lacustrine mudstones. oped for the Danish Basin and a compiled palynological The overlying Zechstein–Cenozoic post-rift succession con- event stratigraphy is applied to a number of wells connecting sists of two major sequences separated by an early Middle the Danish and Norwegian parts of the basin and new marker Jurassic unconformity that reflects regional uplift and erosion horizons are identified. One of the aims of this study is to (Nielsen 2003). The lower sequence comprises Zechstein reach consistency in order to facilitate correlation within the salt, Triassic sandstones, mudstones, marls and carbonates and basin and we also emphasise the recognition of a potentially Lower Jurassic claystones, while the upper sequence encom- important mid-Triassic event in the basin. passes Middle Jurassic – Lower Cretaceous clastic rocks, West Norwegian wells Danish wells East 8/11-1 9/11-1 10/7-1 11/10-1 Inez-1 F-1X K-1X Felicia-1 Gr Sonic Gr Sonic Gr SonicFlyvbjerg Gr Sonic Gr Sonic Gr Sonic Gr Sonic Gr Sonic Fm Børglum Fm Flyvbjerg Fm Haldager Fm Gassum F-IV Fm F-III F-II m 100 m Fjerritslev F Fjerritslev F-I Marine mudstones Shallow marine sandstones and siltstones, offshore mudstones Paralic and non-marine sandstones, mudstones and coals Alluvial conglomerates, sandstones and lacustrine mudstones Gassum Fm Marine calcareous claystones, carbonates Sabkhas and lacustrine calcareous, evaporitic mudstones Ladinian palynofloras Vinding Fm Felicia-1 8/11-1 So rg en frei–To Fig. 1. Correlation of Middle Oddesund Fm No rwe rnqu Triassic to Upper Jurassic strata gia n–Da ist n Zo along a transect. The map shows ish B ne asi FFC-1/2 Rin n the location of the wells and the A-2 gkøbi Land ng – Fyn High Höllviken-2 Redbeds Middle Triassic palaeogeography. Sea Gr, gamma ray log; Sonic, sonic Skagerrak Fm 100 km Fault log. © GEUS, 2009. Geological Survey of Denmark and Greenland Bulletin 17, 21–24. Available at: www.geus.dk/publications/bull 21 ROSA_2008:ROSA-2008 01/07/09 15:48 Side 22 m Norwegian–Danish Basin Selected Stage key Last occurrence Danish part Norwegian part surfaces datums Syste Series Frederikshavn Glossodinium dimorphum, Marine mudstones and Volgian Formation Dichadogonyaulax pannea siltstones Sauda Fm SB 24 Oligosphaeridium patulum Gonyaulacysta jurassic Marine calcareous Børglum Endoscrinium luridum claystones, carbonates Kimme- Formation Tau Fm ridgian Unconformity Upper TS 23 Flyvbjerg SB 23 Shallow marine sand- Oxfordian stones and siltstones, Formation Egersund Fm Gleicheniidites conspiciendus offshore mudstones TS 22 Paralic and non-marine SB 22 sandstones, siltstones, Callovian Neoraistrickia gristhorpensis mudstones and coals Sandness Fm Chasmatosporites hians Quadraeculina anellaeformis Alluvial sandstones and Mendicodinium reticulatum Haldager Sand lacustrine mudstone Bathonian Formation SB 21 Bryne Fm Hiatus rassic Middle u J Nannoceratopsis gracilis SB Sequence boundary Bajocian Mancodinium semitabulatum SB 20 Kekryphalospora distincta MFS Maximum flooding Aalenian surface SB 19 Parvocysta spp. TS Transgressive surface Toarcian MFS 15 SB 15 Pliens- bachian Fjerritslev Fjerritslev Formation Fm Liasidium variabile Sinemurian Dapcodinium priscum SB 11 Hettangian Gassum Fm SB 9 Rhaetipollis germanicus Gassum MFS 7 Rhaerogonyallax rhaetica Rhaetian SB 5 Fig. 2. Stratigraphical Formation Enzonalasporites vigens scheme showing Upper Skagerrak Vallasporites ignaciii Vinding Formation MFS 1 Tri assic and Jurassic litho - Norian Formation stratigraphic units, selected Upper TS 1 Camerosporites secatus, sequence strati graphic Oddesund Duplicisporites granulatus Triassic Skagerrak Carnian Fm Triadispora verrucata boundaries and selected Formation Smith Bank Formation Illinites chitinoides last occurrence datums of Ladinian selected taxa in the Norwe - Muschelkalk Fm Middle Lower gian–Danish Basin. Upper Cretaceous Chalk and Cenozoic clastic rocks. Large graphic names normally applied to units in the Norwegian parts of the lower sequence are difficult to date accurately by Central Graben further contribute to the confusion. A robust biostratigraphy owing to the predominantly continental sequence stratigraphic scheme established in the Danish strata deposited during a hot and arid climate, whereas the Basin by Nielsen (2003) and a compiled palynostratigraphic upper sequence is dominated by marine fossiliferous de po - event scheme are applied to a number of wells (Felicia-1, K-1, sits, which are easier to date. F-1, Inez-1, 11/10-1, 10/7-1, 9/11-1 and 8/11-1) situated along an E–W trending transect from the Fjerritslev Fault NW of Jylland to the border of the Norwegian Central The investigated succession and Graben (Fig. 1). Based on characteristic well-log patterns the stratigraphic approach supported by lithological descriptions from well reports, for- The principal reservoir rocks and potential source rocks of mation tops and sequence stratigraphic surfaces were identi- the basin were formed during Late Triassic – Late Jurassic fied and integrated with palynological events identified in times (Petersen et al. 2008). Different lithostratigraphic ter- this study. The latter events are based on established minologies are used for the Norwegian and Danish areas (Fig. spore–pollen and dinoflagellate cyst stratigraphies for the 2). An inconsistent mixture of lithostratigraphic names from Triassic – Early Cretaceous of western Europe. Selected im - both Norwegian and Danish schemes is commonly used by portant palynostratigraphic events and sequence strati- the operators in well reports, and in some cases, lithostrati- graphic surfaces are shown in Fig. 2. 22 ROSA_2008:ROSA-2008 01/07/09 15:48 Side 23 The results of the correlation show that lithostratigraphic units and key sequence stratigraphic surfaces can be followed Ladinian spore–pollen floras across the Danish and Norwegian areas indicating that the Well-preserved, typical Middle Triassic palynofloras were general depositional development along the transect largely found in ditch cuttings from the lowermost part of the follows the pattern described by Nielsen (2003). Hence, the Oddesund Formation in the Felicia-1 well, and in the lower sequence stratigraphic and lithostratigraphic schemes estab- part of the Skagerrak Formation in K-1 and 11/10-1. These lished for the Danish part were successfully applied to the assemblages are distinguished from caved Rhaetian–Creta - Norwegian wells, as exemplified in Figs 1, 2. ceous material by their generally darker colour. All the assem- However, the lack of readily recognisable sequence strati- blages contain Illinites chitonoides, a pollen species that has a graphic key surfaces and biostratigraphic events within the last appearance datum at the top of the Ladinian in northern Middle – Upper Triassic succession is a major problem for Europe, and within the Carnian in the Arctic region (de reliable stratigraphic analyses. Graziansky et al. 1998). The assemblage from Felicia-1 is dom- inated by the bisaccate pollen Ovalipollis ovalis /pseudoalatus, which has its first common appearance datum at the base of the The Middle Triassic – an unsuitable climate for late Ladinian (de Graziansky et al. 1998). In addition, mem- palynomorph preservation bers of Protodiploxypinus, e.g. P. fastidioides and P. macroverru- During the Middle Triassic the Norwegian–Danish Basin was cosus, and Triadispora, mainly T. crassa, T. plicata, T. verrucata, situated around 35°N. The arid to semi-arid conditions that are common constituents of the palynofloras. The co-occur- had prevailed during the Early Triassic continued, as signified rence of Angustisulcites klausii, Kuglerina meieri, Podosporites by mainly fluvial and lacustrine, heterogeneous, siliciclastic amicus, Staurosaccites quadrifidus, Rimaesporites aquilonalis, Ara - rocks of the Skagerrak Formation (Michelsen & Clausen tri sporites spp., Camerosporites secatus, C. verrucatus, Dupli ci - 2002). Marine calcareous mudstones and carbonates of the sporites granulatus and Enzonalasporites vigens also suggests a Muschelkalk Formation in the North German Basin ex - late Ladinian age (de Graziansky et al. 1998; Schulz & Heu - panded northwards during a transgressive event in the nisch 2005). The presence in Felicia-1