Andrew G. Whitham

Mid-Tertiary rifting and magmatism in the Traill Ø region, East Greenland

A number of planar normal faults displace Tertiary basaltic intrusions in the Traill Ø region of East Greenland. This post-magmatic extension occurs over an along-strike length of >350 km and over an across-strike width of >100 km with fault displacements and fault-block rotations indicating that (3 increases in magnitude eastwards from near unity to β ≈ 1.1. The stretching direction was approximately E-W, orthogonal to the strike of major faults in the region, most of which are reactivated Mesozoic structures. Two periods of Tertiary basaltic magmatism are recognized in the area. 40Ar–39Ar step heating suggests that the first event, which gave rise to tholeiitic sills with a composite exposed thickness of c. 1 km, occurred at c. 54 Ma, and the second, which formed smaller volumes of alkaline dykes and two large syenite complexes, occurred at c. 36 Ma. Field observations indicate that post-magmatic extension occurred after 54 Ma and possibly continued after 36 Ma. The tholeiitic intrusions are probably related to a stretching event (β ≤ 1.1) prior to the onset of sea-floor spreading in the Norway Basin, whilst the alkaline basalts and post-magmatic rifting are associated with the separation of the Jan Mayen continental block from the East Greenland margin during the Eocene-Oligocene. Both tholeiitic and alkaline basalts formed by the partial melting of garnet-spinel peridotite with greater degrees of partial melting (8–16%) for the earlier tholeiitic group. Rifting in East Greenland ceased with the development of an oceanic ridge between Jan Mayen and East Greenland in late Oligocene time. Subsequent minor compression, probably the result of ridge-push, is suggested by the development of broad wavelength, low amplitude folds in the Traill Ø region.

Early Cretaceous giant bivalves from seep-related limestone mounds, Wollaston Forland, Northeast Greenland

Abstract Anomalous mound-forming limestones, here termed the Kuhnpasset Beds, occur within Late Barremian (Early Cretaceous) mudstones on Wollaston Forland, Northeast Greenland. The normal mudstones contain a sparse fauna of small nuculoids, arcoids and inoceramids; by contrast, the mounds contain an unusual faunal assembage, dominated by large bivalves. These include an abundant lucinid, Cryptolucina kuhnpassetensis sp. nov., and, less commonly, Solemya, both known seep-associated genera. Locally, a large modiomorphid, Caspiconcha whithami gen. et sp. nov., is common and reaches > 300 mm in length and has a shell up to 28 mm thick. Also, the wood-boring bivalve Turnus is abundant in driftwood. Gastropods are rare, but the associated cephalopod fauna includes ammonites, belemnites, nautiloids and a remarkable large orthoconic phragmocone. The form of the mounds with calcite-cemented tube systems, associated laminated calcite crusts and void fills, together with the fauna, is analogous to those of methane-based cold-seep complexes. However, preliminary studies indicate that much of the original aragonitic shell is now replaced by silica. This precluded conclusive geochemical studies based on the shells themselves. It is believed that the mounds formed on the seafloor in a mid- to outer shelf situation at the end of a period of extensional rifting on the eastern Greenland passive Atlantic margin. The vents occur near the footwall crest of a tilted fault block. The underlying faults may have provided routes or influenced direction of movement for nutrient migration. Source rocks were probably the Late Jurassic black shales from depths of < 600–1200 m. If methane was being generated, it was probably forming by shallow-depth organic breakdown rather than by thermogenic processes, which require greater burial.

New constraints on the thermal history of North-East Greenland from apatite fission-track analysis

Apatite fission-track analyses from the area north of Jameson Land, East Greenland, indicate that the region has undergone at least three phases of cooling during the Mesozoic and Cenozoic. Two major periods of cooling during the Tertiary have been identified: a middle Tertiary episode, in which cooling began between 40 and 30 Ma, and a late Tertiary episode, in which cooling began between 10 and 5 Ma. The middle Tertiary event is synchronous with emplacement of major intrusive bodies associated with continental rifting and may be due either to uplift and erosion or hydrothermal effects. The late Tertiary event appears to be related to erosion associated with uplift resulting from changes in the North Atlantic spreading direction and associated events. No paleothermal effects have been identified related to the onset of rifting in the early Tertiary. Results from samples farthest from the continental margin reveal an earlier event in which cooling began between 225 and 165 Ma. The origin of this event is not clear, but it may reflect uplift and erosion associated with recognized unconformities within the Jurassic section.

Exhumed hydrocarbon traps in East Greenland; analogs for the Lower-Middle Jurassic play of Northwest Europe

Four exhumed hydrocarbon traps crop out in the Traill O region of East Greenland, each at the footwall crest of a fault-block formed during Early Cretaceous rifting. Former oil accumulations are indicated by a pore fill or pore lining of solid bitumen within the Jurassic sandstone-dominated Vardekloft and Olympen formations. The Vardekloft Formation is divided into an undated fluvial-dominated lower unit (0-520 m) and a Bajocian-Callovian upper unit (65-1020 m) deposited in a shallow-marine environment. The Oxfordian Olympen Formation (0-250 m) contains shallow-marine and fluviodeltaic deposits. The sandstones are dominantly quartzarenites, and petrographic fabrics, such as dissolved feldspar, late quartz cement, and stylolites, are consistent with burial depths in excess of 2.5 km. Porosities ranged from 7 to 27% (generally about 20%, about one-half of which was primary), and permeabilities ranged from 1 to 622 md, prior to the formation of solid bitumen. The distribution of solid bitumen in each trap can be mapped out, allowing sealing elements and original oil-water contacts to be defined. Three of the four exhumed traps (Mols Bjerge, Laplace Bjerg, and Bjornedal) were simple one-seal structural traps. Conformable Upper Jurassic mudstone, unconformable Albian-Cenomanian mudstone, and normal faults are the three top-sealing elements. The fourth (Svinhufvuds Bjerge) was a poly-seal trap with a combined top-seal and a low-side fault closure. Preliminary estimates of the volume of original oil in place within these structures range from 0.2-1.1 billion bbl for the Mols Bjerge trap to 5.3-11.9 billion bbl for the Bjornedal trap. These estimates are prone to large errors, due to uncertainties in estimating original trap geometry, hydrocarbon saturation, and net/gross ratio, and in the understanding of volume changes of hydrocarbon in each trap during thermal degradation of the oil. The Upper Jurassic Bernbjerg Formation is the only known potential source rock in the region, which would require a drainage distance of less than the fault-block spacing to fill the largest of the traps. Secondary hydrocarbon migration into these traps occurred between the Cenomanian (age of the youngest sealing element) and early Eocene to late Oligocene (when widespread volcanism and sill intrusion resulted in thermal degradation of the oil). Each of these structures is relatively well exposed and accessible; we believe that they will provide excellent analogs for studies of enhanced recovery from the mature Lower-Middle Jurassic oil fields of Northwest Europe.

The World’s biggest relay ramp: Hold With Hope, NE Greenland

Abstract Fault interaction in the Hold With Hope region of NE Greenland occurs between basin-margin faults that have a separation of about 100 km, with the relay ramp covering an area of about 25u2008000 km 2 . This structure is therefore much larger than previously described relay ramps, showing that interaction between normal faults can occur over large areas and can control deformation across a region. The Western Fault Zone links north and eastwards with the Hochstetters Forland Fault via the Gauss Halvo Fault. These faults that control the relay ramp have kilometre-scale throws, juxtaposing Pre-Caledonian basement against Upper Palaeozoic and Mesozoic cover. The relay ramp initiated during the Devonian, but was at least partially breached at the end of the Devonian or beginning of the Carboniferous. Beds in the relay ramp are tilted towards the footwall, this tilt being similar to the results of recent numerical models of interacting normal faults. The relay ramp is affected by faults that are synthetic to, and that link, the basin-margin faults. These breaching faults suggest that stresses can interact over distances of at least 100 km. This model explains variations in the depth of the Moho across Kong Oscar Fjord. The basin-margin faults may be linked at depth, passing down into a relatively shallow detachment, or into a lower-crustal shear zone. Alternatively, the faults may not be directly connected at depth, but pass down into a zone of distributed ductile deformation.

Rift-related Devonian sedimentation and basin development in South China

Abstract During Devonian times South China lay to the north of the Palaeo-Tethyan ocean, the boundary being a passive continental margin. A shallow sea covered the southern parts of the continent while northern areas, forming the Huanan Landmass, were emergent. At the beginning of the Devonian most of South China was above sea level. Subsequent transgression from the south gave rise to an irregular coastline with the development of many fault-controlled gulfs. Further transgression led to the development of an epicontinental sea with reefs forming along the margins of the submerged gulfs and black shales deposited within them. By Emsian time a widespread carbonate platform was established, while anoxic deposition continued in the troughs. The marine transgression peaked in the Frasnian Stage. During Famennian time widespread regression occurred and much of South China became once more emergent. Peneplanation of the Huanan Landmass led to the partial infilling of many of the older fault-bounded depressions. Throughout the Devonian the local distribution of sediments was strongly controlled by NE-SW trending transtensional faults that bounded NW-SE trending normal faults. These structures continued to influence sedimentation in the Late Palaeozoic, the Mesozoic and possibly the Tertiary in the offshore Beibu Gulf Basin.

Lithostratigraphy of the Cretaceous (Barremian–Santonian) Hold with Hope Group, NE Greenland

The finest exposures of Barremian to Santonian sedimentary rocks in the northern North Atlantic region are exposed in Hold with Hope, NE Greenland. These rocks comprise the Hold with Hope Group which, together with its constituent formations and members are defined here as new lithostratigraphic units. The strata are dated as Cretaceous by use of molluscan macrofaunas and dinoflagellate cysts. The marine mudstone-dominated Hold with Hope Group is over 1300 m thick and is divided into the Steensby Bjerg and Home Forland formations. The sandstone-dominated Steensby Bjerg Formation (Barremian–Albian) is 300 m thick. It rests with angular unconformity on sandstones attributed to the Vardekløft Formation (Middle Jurassic) and is subdivided into the Diener Bjerg, Gulelv, Stribedal, Blåelv, Stensiö Plateau and Rødelv members. The mudstone-dominated Home Forland Formation (Albian–Santonian) is over 1000 m thick. It rests unconformably on the Steensby Bjerg, Vardekløft and Wordie Creek (Triassic) formations. It is subdivided into the Fosdalen, Nanok, Østersletten, and Knudshoved members. The Hold with Hope Group is overlain unconformably by Tertiary basalts and sedimentary rocks. The original proximity of Hold with Hope to the Vøring Basin is significant for possible Cretaceous hydrocarbon plays on the formerly adjacent NW European margin.

Insights into Cretaceous–Palaeogene sediment transport paths and basin evolution in the North Atlantic from a heavy mineral study of sandstones from southern East Greenland

Major changes in sandstone provenance occurred during the deposition of the Cretaceous–Eocene succession in Kangerlussuaq, southern East Greenland. These changes can be recognized on the basis of provenance sensitive heavy mineral parameters (apatite:tourmaline and rutile:zircon ratios and garnet geochemistry) and the SHRIMP U–Pb dating of detrital zircons. The results support the subdivision of the succession into three units separated by major unconformities spanning the Late Coniacian to Late Campanian and Late Maastrichtian to Early Eocene. Rifting during the deposition of the first unit (Aptian–Late Coniacian) led to rift flank uplift and resulted in the local sourcing of sediment. Thermal subsidence during the deposition of the second unit (Late Campanian–Late Maastrichtian) led to rift flank subsidence and sediment sourcing from outside the immediate region. Renewed rifting immediately preceding the third unit (Early Eocene) resulted in a return to local sediment sourcing. The basin morphology during the deposition of the second unit would have been more conducive for the long-distance transport of sediment into the adjacent Faroe–Shetland Basin than during deposition of the first and third units. The results provide a framework for the identification of Greenland-sourced material in the Faroe–Shetland Basin.

The role of East Greenland as a source of sediment to the Vøring Basin during the Late Cretaceous

Provenance-sensitive heavy mineral criteria, mineral chemistry and detrital zircon age data show that there are strong links between Cretaceous sandstones in the Voring Basin and East Greenland areas. There are marked differences in the age spectra of detrital zircons from wells along the eastern margin of the Voring Basin (sandstone type K1) and those in the centre and west of the basin (sandstone type K2). The K1 sandstones have relatively simple zircon age spectra with largely Mid-Late Proterozoic zircons and a number of Caledonian age zircons. By contrast, the K2 sandstones have complex zircon age spectra, with Archaean, Early Proterozoic, Permo-Triassic and mid-Cretaceous zircons that are absent in the k1 sandstones. Some sandstones of Cenomanian and younger are from East Greenland share mineralogical features with the K2 sandstone type, having overlapping ranges of critical provenance sensitive parameters, such as RuZi, MZi and CZi, and similar types of detrital tourmalines and garnets. Detrital zircon age spectra from East Greenland samples include critical Archaean, Early Proterozoic and Permo-Triassic populations found in K2 sandstones. The zircon age data, therefore, provide support for sourcing of K2 sandstones from East Greenland. However, a source for the K2 sandstones to the cast of the Caledonian front in Scandinavia cannot be ruled out, neither can the recycling of older sediment previously transferred across the rift.