The North Sea basin The North Sea amounts to less than 1 per cent of the world's oceans, so, in a very narrow sense, its demise would not undermine the stabilizing properties of the earth's biogeochemical cycles. But the states of the North Sea basin contain large populations of relatively wealthy people. The North Sea is an ancient sea with a long history. It is in a constant state of change, as the continental drift, tidal motion, circulatory currents, and human activity continue to modify its character. Around 350 million years ago, the land that was to become the North Sea was situated approximately 2 degrees south of the equator, in the location of the present-day Brazilian rain forests. Deposits of mud, covering and compressing the vegetation, gradually engulfed the existing swamp. As the sediments built up, the organic matter gradually changed its form, resulting in the formation of the rich coal seams In the Permian era some 240 million years ago, the swamp metamorphosed into a sea, in what is regarded as the true geological birth of the North Sea when the principal basins forming the North Sea came into existence (Mac Garvin 1990). The rock under the North Sea began to subside, a process still in progress. This allowed the surrounding seas to resurge, submerging all land except for mountainous and hilly regions. The land mass was still migrating northwards and by this stage was around 20 degrees north of the equator. Some 168 million years ago the land mass rose again, creating an intricate tangle of deltas. Many of the marine deposits created during this age were rich in tiny marine organisms. Compressed under the weight of sediments that began to engulf them, the hydrocarbon substances became sealed, forming the crude oil and natural gas reserves that have subsequently been lucratively exploited by the human race

The North Sea Area By the early Cretaceous period (around 100 million years ago) the region was about 40 degrees north and isolated except for an opening to the north. The water levels rose gradually until most of northwestern Europe lay under a chalk sea. For unknown reasons, and around the same time of the dinosaur extinction, the chalk stopped forming. The emergent land masses were recognizable as those now forming continental Europe (Mac Garvin 1990). Until the ice ages began 2 million years ago, the water levels rose and fell, joining Britain with Europe and then separating the island from the continent. The North Sea basin also continued its drift to its current position. The succession of ice ages that followed shaped the North Sea basin into what it is today. The most recent ice age, 20,000 years ago, covered the region northwards from the Wash to Jut land with ice over 2 km thick. It was responsible

for gorging deep valleys in the sea bed and channeling the rivers of northern Europe along what is now the English Channel. The ice retreated and the water flowed back in to the now familiar shape of the North Sea basin, leaving behind deposits of sand and gravel. Tidal erosion, dredging developments, reclamation, sea defenses, and harbor management are continually changing and modifying the finer details of the exact shape of the North Sea. For analytical purposes the North Sea may be conveniently divided into two parts, the southern and northern North Sea. The northern part is relatively deep, around 50-200 m, and is subject to strong oceanic influences. It has a relatively short turnover time and is surrounded by less populated and industrialized nations, and so receives less waste. Because it is larger in size, however, it receives a greater amount of atmospheric deposition. The southern North Sea is shallower, with depths varying between 20 m and 50 m. It has strong tidal currents and a short turnover time. The southern North Sea carries a large sediment load and includes many areas in which finer sediments are deposited. The water in this area has a notable oceanic component. It is noteworthy that the coasts that flank the southern North Sea are more industrialized than those in the northern sector, and therefore the southern sector receives more in the way of waste inputs (Eisma 1986). Land reclamation Land reclamation is a natural process. It usually takes place in sheltered areas such as estuaries, where rich alluvial deposit processes cause gradual accretion. The deposits eventually become colonized by plant species that drain the soil in a process known as soil ripening. The resulting soil can be drained further and is excellent for agricultural purposes, providing a stable, fertile soil for some years. Gradually man came to the assistance of nature in the North Sea area to speed up the process of accretion. Salt-marshes were embanked to protect them from further inundation. This was the beginning of the operations of land reclamation, started by the demand for fertile farmland and a need for coastal protection, for new space for industry and commerce, and in some cases for building other structures such as roads or railways. Land reclamation in the United Kingdom dates back as far as the eleventh and twelfth centuries. Some areas of the Thames may have been reclaimed by the Romans, with other similar early works around the rivers in Kent and within the Humber estuary. One area that has been well studied is the Wash, where reclamation has been taking place since the Middle Ages. The first significant gain of land reported in this area was in the seventeenth century when around 15,400 ha of salt-marsh were embanked. By 1979 this had reached 31,000 ha. Land-reclamation works have taken place in many areas along the North Sea coasts of Great Britain and the Continent - for example, at the Firth of Forth, on the banks of the rivers Tees and Humber, on the salt-marshes of the Wash, and in the Wadden area stretching from the city of Den Helder in the Netherlands to

Esbjerg in Denmark. The previously jagged coastline of the Wadden area has been either straightened or shortened artificially, resulting in the loss of tens of thousands of acres of land (including mudflats, salt-marshes, and summer polders) outside the dikes. Only an area of 375 km is left, representing less than 4 per cent of the Wadden area. And even these few areas are threatened by further reclamation. Mineral extraction Minerals required by construction industries originate from the ice ages of the Quaternary period. They are extracted on a national basis, as are oil and gas. (All figures are from Sibthorp 1975.) With regard to the geological environment of the North Sea, only three groups of minerals are likely to be present in quantities sufficient to allow them to be economically worked. These are superficial, unconsolidated deposits, such as sand and gravel and the so-called "heavy minerals" (notably including sources of titanium); bedded deposits such as coal and evaporites (e.g. halite [salt], potash, and anhydrite); and petroleum and natural gas. The only mineral being extracted on a large scale from sea water is magnesium. Extraction plants are located mainly at Hartlepool in the United Kingdom and in Norway. Current production figures are not available, although it is known that, earlier, 60-65 per cent of world magnesium production (1973 figures) was from sea water. Salt is also being recovered on a small scale at Maldon, Essex (UK). Difficulty in obtaining sufficient building aggregate on land has led to the increased usage of marine aggregates since the early 1960s. By 1972 this was contributing around 12 per cent of total production in Great Britain. The most suitable deposits are located in the British sector of the North Sea, 7-20 miles offshore at various sites from the Humber to the Thames. The continental side of the North Sea is mainly sandy, with exceptionally rare gravel deposits. As a result, dredged aggregate is delivered from the British areas to Rotterdam, Dordecht, Bruges, Dunkirk, and Calais. In 1972, about 6 million tonnes of sand and gravel were dredged from the North Sea. Technological developments and the building of very large dredgers now enable areas of lower-grade materials to be worked, but it is becoming clear that many reserves have become exhausted. Strata containing salt, anhydrite (calcium sulphate), and potash extend beneath the North Sea off the Yorkshire and Durham coasts. Salt is extracted near the Tees estuary by controlled pumping of a saturated brine solution through a network of boreholes. Although enormous deposits of salt have been found beneath the North Sea during the search for hydrocarbons, the existence of very large reserves of salt on land in Britain renders it unlikely that salt will ever be extracted from beneath the sea on a large commercial basis. Potash occurs in an extensive bed at a depth of around 1,000 m over a very

large area in Yorkshire, stretching from the Durham border to Scarborough and for a very considerable distance out to sea. Only a small proportion of this area is currently mined because of technical difficulties involved in extraction. Several coalmines extend beneath the North Sea off the Northumberland and Durham coasts. Usable deposits are located mainly in the southern North sea and are extracted mainly by the United Kingdom, Denmark, the Netherlands, and Belgium. Most of the extraction takes place near the coast, on land, though the United Kingdom disposes of the wastes at sea. The United Kingdom is currently the only country that does this, on the grounds that it is inert material. It is likely that this practice will have to cease by the end of the century if not before (see below on industrial waste).

Oil and gas extraction The first discovery of natural gas occurred in 1959 and production began in 1967. Since then large-scale production and exploration have been extensive. The search is continuing, with many of the main fields (e.g. the large Stratfjord field) already having been discovered. Gas is a non-renewable resource but it is a very important financial benefit to the economies of the countries (i.e. the Netherlands, the United Kingdom, and Norway) that have jurisdiction of the continental shelf. Gas fields owned by the United Kingdom are situated mainly in the southern and central North Sea basin, located to the east of Yorkshire, Lincolnshire, and Norfolk. Some of the natural gas fields situated in the northern sector of the North Sea are not extensively exploited commercially. These were formed from the carbonization of flora and fauna in the Carboniferous period, the salt seal that formed above them preventing anaerobic decomposition. They are mostly owned by the Netherlands and the United Kingdom. Oil fields are found mainly in the northern North Sea, from Jurassic shales. They are predominantly owned by the United Kingdom and Norway. North Sea crude oil is high quality, low in sulphur, and "light," and therefore suitable for the production of petrol and diesel fuel (but unsuitable for heating fuel). Considerable quantities of the mineral have been found in the northern North Sea off the Scottish coast. The oil and gas reserves are of enormous strategic importance to the North Sea states. They contribute significantly to the wealth of the Norwegian economy and account for more than 10 per cent of the real wealth of the British and Dutch economic output. With respect to oil, the best estimate for UK reserves is that North Sea oil will begin to decline in annual output around A.D. 2000-2010 and that the effective resource will be viable until around 2040 (BP 1991; UK Digest of Energy Statistics 1991-). Much depends on price and technological innovation. Certainly the scope exists for extending existing reserves, given the appropriate incentives.

For gas, the picture is similar to the UK oil reserves, with around 4050 years of availability at current rates of exploitation (BP 1991). Again, this could be expanded with suitable pricing and regulatory actions. For the Dutch and Norwegian reserves, the expected commercial lifetime is a little longer (about 5060 years), bearing in mind a growing demand over this time for exports to other North Sea basin states (Kemp 1990). The oil and gas industries are privately owned in the United Kingdom, and quasiprivate in Denmark, Norway, and the Netherlands. Regulatory offices and tax and depletion policies strictly enforce controls over economic exploration. The international price for fossil fuels and the current preference for gas over new coal and oil on the grounds of thermal efficiency, lower carbon-dioxide generation, and lower sulphur-dioxide production influence the management of these resources. Co-generation of gas with oil is likely to increase as a consequence. Calcareous nannofossil Biozonation of the Tertiary of the North Sea Basin Tertiary material (739 samples) from 12 released Shell/Esso exploration wells from the central and southern North Sea Basins (see Fig. 1) was studied to elucidate the distribution and character of calcareous nannofloras in this commercially valuable area. A biozonation comprising 23 zones was erected for the Pliocene-Palaeocene interval and comparisons are made with existing schemes and between different geographical areas Cenozoic Deposits in the North Sea Basin Sedimentation in the North Sea Basin is characterised by an overall increase in sediment supply with time but with large variations in the regional pattern. The mineralogical composition of basin-fill is studied to reveal depositional environments, uplift and subsidence history, sediment supply, rates of deposition and diagenesis. The clay mineral composition in particular is very useful since it also reveals weathering conditions, major contributions from North Atlantic Paleocene/Eocene volcanism and reworking from uplifted margins. Study of the thermal stability of reworked kaolinite seems to be a particularly promising tool in determining the back stripping of uplifted Tertiary and Mesozoic deposits from the basin margin. Important aquifers are found in Oligocene/Miocene deposits in the western part of Denmark. The aquifers are mainly fluvial and deltaic deposits but include some coastal sands. The facies pattern and distribution of large aquifers is studied in co-operation with county administrations in Jutland. Late Cenozoic marine deposits from the northern part of the Dutch sediment material available from the Neogene North Sea is very scarce. Its location between 400 and 1500 m below the seabed in the depocentre of the basin is usually to deep for conventional scientific drilling campaigns. These sediments, on the other hand, are situated far above economically interesting hydrocarbon occurrences and are thus not of primary interest for oil companies that usually focus on deeper targets. Recent shallow gas findings in the Netherlands offshore

sector, however, spurred exploration activity by Wintershall Noordzee B.V. and the Nederlandse Aardolie Maatschappij (NAM) within Neogene sediments. The generated high quality exploration data enabled the detailed analysis of the marine sediments above the Middle Miocene unconformity (MMU) in the northern Dutch offshore sector presented in this thesis. The extensive data compilation and comprehensive interpretation contribute to a better understanding of the paleoenvironmental history of the Late Neogene North Sea in relation to climate change. Because of the importance of adequate time control, the first aim of this thesis is to find appropriate dating methods and to establish a chronology for the marine sediments above the Middle Miocene unconformity in the northern Dutch offshore sector. Based on a firm chronology, this thesis further aims to contribute to a better understanding of the paleoenvironmental development of the Late Neogene North Sea in relation to climate changes. Information about the marine sediments from the Neogene North Sea Basin is mostly based on indirect, geophysical methods including well-log analyses and seismic interpretation of conventional 2D seismic data. Specific sedimentological investigations of the sediments are scarce and if available, only from locations at more coastal or onshore parts of the basin. Furthermore, it is difficult to tie these sediment logical data to geophysical data. The results of this thesis are obtained from geophysical data including conventional 2D-seismic data, 3D-seismic data and well-log data as well as from sediment logical analyses on discrete sediment samples (cores samples, side wall core samples and cutting material). The sediments have been analyzed on the faunal and floral elements (din cysts, pollen and foraminifers). In addition, measurements on grain-size, clay mineralogy and samarium-neodymium (Sm-Nd) isotopes were performed. These analyses depict the sediment characteristics directly and the imprint of the interacting environmental factors has been independently derived. The multidisciplinary approach of this thesis, combining well-dated climate proxy records and sediment logical data with geophysical data has been used to portray the geological development for the Pliocene North Sea as complete as actually possible. GIANT FLUIDIZED AND INJECTED SANDBODIES IN THE NORTH SEA BASIN- AN INDICATOR OF SHALLOW HYDROCARBON VENTING IN PALEOCENE-EOCENE TIMES Seismic-scale intruded sandbodies have been identified in association with deepwater depositional systems within Paleocene - Eocene successions in the Central & Northern North Sea Basin. A number of the intrusive sandbodies form part of important oil reservoirs in the area (e.g. Alba, Harding, Gryphon, Leadon and Balder fields). Core, log and seismic data from these oil fields reveals that (1) the sandbodies can have complex interconnected geometries on a millimeter to kilometer scale with dykes cross-cutting up to 200 m of stratigraphy and lowangle sill-like bodies with horizontal dimensions of up to 1000 m; (2) the parent source sands are pervasively fluidized and show few relic indicators of primary sedimentary depositional processes; (3) the dykes and sills emanate largely from the sides and the top of parent depositional sand bodies; (4) parts of the intrusion complexes are made up of fluidized, highly deformed sand-mud breccias and

slurries which may have been extruded at the sea bed. These clastic intrusions are the largest ever documented within sedimentary successions, and much larger than the sand dykes, sills and volcanoes that form after liquefaction associated with large magnitude earthquakes. The extensive occurrence of the sand intrusions in deepwater successions of the Central and Northern North Sea implies that large volumes of fluid were migrating in the shallow subsurface in latest Paleocene - Eocene times. We hypothesize that the source of the fluid was hydrocarbons migrating upwards from the deeper mature kitchen areas in the basin. Oil, and probably gas, migrated into isolated sand bodies, weakly sealed by muddy sediments. The muddy seals failed and the overpressured gas- and oil-bearing sands fluidized and injected laterally and upward into the surrounding sediments. Quaternary of the northern North Sea The Quaternary deposits found on the East Shetland Platform are thin (Johnson et al., 1993). The Quaternary thickens above the Viking Graben to as much as 300m and provides a long and relatively detailed record of glaciation. The sediments at the start of the Quaternary are sandy and point to a dominance of non-glacial marine environments. A later unconformity may relate to glaciation of Shetland at some stage in the Early Pleistocene but the timing of this event is unclear. The Middle Pleistocene starts at 730 ka and the sediments point to a range of glacimarine and marine interglacial environments. Stiff clay-rich units, with sand lenses, gravel and shell fragments probably relate to ice advances spanning the period between the start of the Cromerian Complex and the Elsterian on the north European record. A prominent seismic reflector attributed to erosion by Saalian glacial ice marks the top of the Middle Pleistocene sequence. The Saalian glaciation appears to have been the most significant erosional event in the northern North Sea (Johnson et al., 1993) and, by extension, Shetland. Laminated fine-grained sediments east of Shetland containing foraminifera of warmth-loving species represent the last interglacial. Another strong seismic reflector is developed across these and older units and is associated with deep channels, possibly tunnel valleys. Glaciation of Shetland and the adjacent shelf in the early Weichselian is indicated. Ice had retreated by around 30 ka, although marine fauna indicate cold water offshore, until the advance of the last ice sheet after 28 ka. This ice sheet reached a double maximum at 22 and 18 14C ka before retreat commenced around 15 ka. SUBSIDENCE The North se is located between Scotland and Norway. The North sea has a very long and complicated history of subsidence. Deposition of sediment is part curly rapid during the Permian and Mesozoic time periods creating layers many kilometers thick. The figure above shows the major features of the north sea. The Humber group is dominated by marine mudstones and clays. These have been deposited after a large amount of subsidence. The Cromer Knoll group is

dominated by calcareous mudstones and thin limestones.The chalk group dominates the Upper cretaceous and lowermost Paleocene ages. The late Paleocene is dominated by sandy turbidities which represent large deposits from a submarine fan system.The Witch Ground Graben were formed in the late Jurassic due to a large rifting event causing alot of extension. Considerable amounts of thermal subsidence occurred after this which continue to the present day. This rapid subsidence was interrupted by an uplift due to the opening of the North Atlantic. From the figure below we can see that there are two periods of rapid subsidence followed by two periods of declining subsidence rates. On the figure curve 1 represents back stripped subsidence curve with a constant water depth. Curve 2 is a water loaded subsidence curve. Curve 3 is a theoretical water loaded subsidence curve. Curve 4 represents the water depth profile while curve 5 is the net subsidence curve. There is very rapid subsidence in the first twenty years of the basins history. This is due to the fact that rifting lasted from 150 Ma to 130Ma.During the late cretaceous there is a rapid increase in the amount of chalk deposition this leads to a rapid increase in subsidence. During the Paleocene there is another rapid increase in sediment input leading to further subsidence.

Fig 5.2.3. Subsidence curves for Location C in the North Sea Oil and Gas from the Buried Rift Valley

The Britain's Offshore Oil and Gas in the northern and central areas of the North Sea is dominated by the geographical history of the buried rift valley, or graben. The rift is seen in the map on the right (F32), which shows the present-day shape of the surface of all rock that is more than 285 million years old. During this last 285 million years, since the start of Permian times, subsidence along the line of the rift valley created a changing pattern of land, lake and sea environments, and influenced the thickness and type of sediments that accumulated, the depth to which they are now buried, and the trap structures that formed. Consequently, hydrocarbon deposits have been trapped in a much greater variety of rocks and structures than in the southern North Sea. Much of the oil and gas is found in sandstones that are less than 200 million years old. The main sandstone and limestone reservoir rocks are shown, in green ornament in the column on the right in F32. Rifting movements affected this area for more than a hundred years. They were most intense during the Jurassic Period, and Jurassic rocks provide the most important oil source and reservoirs beneath the North Sea. The main source of oil and gas in the area is the 140 million year-old Kimmeridge Clay. The most prolific oil-bearing reservoirs beneath the northern North Sea are the Jurassic 'Brent Delta' sands. Brent Delta sediments also contain coal seams derived from vegetation on the swamps.

These are the sources of some of the gas now trapped in the area. The sediments that built up the delta were transported northwards by rivers draining volcanic uplands which had risen up at the junction of three 'arms' of the rift valley (F36). As large as the Nile Delta, the Brent Delta is now buried and broken into a series of tilted blocks (F33) which act as traps where overlying rocks seal down oil and gas.

The Kimmeridge Clay is particularly rich in hydrocarbons along the line of the rift valley. This is because the slow subsidence of the rift helped to set up the right environment for a rapid build-up of thick mud layers, rich in planktonic algal remains, on the deepest parts of the seabed (F34). Climate and sea conditions were ideal for the massive growth of 'blooms' of plankton. Dead plankton sank in vast numbers, and the seabed bacteria feeding on their remains made the mud stagnant, so that particles from the plankton cells were preserved in it and slowly buried. The buried mud became compressed to form the Kimmeridge Clay. The thickest mud layers were deposited over the rift and have since subsided deep within the rift heating up slowly as they became more deeply buried. The Kimmeridge Clay has been mature for millions of years, generating first oil and then gas (see F4, page 6). F35 shows the areas where it is mature and generating oil and gas right now.

Most of the sandstone reservoirs in the northern North Sea were originally parts of river deltas and 'submarine fans' - lobes and sheets of sediment which were re-deposited from slumping and flowing masses of unstable sea-bed (F38). Many important oil and gas occurrences are in Jurassic rocks of this type but some of the largest are in submarine fan sandstones which were deposited more recently, 50 million years ago or so (F37). Around 150 million years ago, in Jurassic and on into early Cretaceous times, parts of the sea floor repeatedly sank. The great rift valley system, or graben, was rapidly subsiding. Beneath the sea, the Earth's crust continued to fracture along huge faults, and large blocks dropped down and tilted to form long ridges along the sea floor. These movements continually triggered the slumping of soft sediments into the deeper troughs. Unstable areas of seabed would start to shift until rock fragments and particles were carried away across the sea floor as fast-flowing currents of watery sediment. These settled out as fans or more widespread sheet-like deposits. Coarse, sandy rubble was dropped near steeply sloping sea floors. Channels and fans of sand and silt spread our further across the sea floor, building thick layers out from the submarine ridges. Some of the sandy rocks which were laid down in this way are permeable enough for oil and gas to flow through them with ease. These rocks now hold oil and gas pools in trap structures, such as those of the Brae, Galley, Claymore and Magnus fields. The traps formed well before the oil and gas migrated in from the Kimmeridge Clay above or around them. The North Atlantic Ocean was opening rapidly around 50 million years ago and

through this time of great crustal activity the area from the Scottish Highlands to the Shetland Islands was uplifted (F37) causing rivers to erode and move huge amounts of sediment. Unstable masses of sand and silt built out across the surrounding shelves, while reactivation of older faults continually triggered great flows of sediment from the edges of the submarine shelves, out across the deeper sea floor underlain by the rift valley (F37). Submarine channel deposits and fans, built up into widespread layers of sandy sediment. These have hardened to form beds of silt and sandstone with shale layers. Where they have become parts of suitable trap structures, as in the Forties, Montrose, Frigg and Cod fields, they may hold considerable quantities of oil and gas which have migrated upwards from the deeply-buried source rock. Under some parts of the North Sea area, the oil and gas have then migrated almost horizontally some tens of kilometres along sandy layers until they have either escaped or become trapped. Natural storage of oil and gas beneath some parts of the North Sea depends upon the presence of thick layers of salt, especially those laid down in the tropical sea during the Permian Period, around 250 million years ago. In the arid climate, rapid evaporation of the continually inflowing seawater resulted in the build-up of more than 2000 metres of salt. In the central North Sea area, trap structures have been created where low-density salt layers have risen through overlying rock (F39). Some of these structures have trapped oil and gas, particularly within the Central Graben, where the chalk in the Norwegian and Danish sectors has been fractured and domed by rising salt. In southern areas of the North Sea, however, salt layers of the same age act as hydrocarbon seals. Here, the source rock and the main reservoir rock lie beneath the salt and are not affected by its movement. Fractures in the salt heal by salt-flow, so the rock makes an excellent seal. Chalk acts as an oil seal in some areas and as a reservoir rock in others. Normally, its permeability is low - oil will not flow through it. Chalk mainly consists of tiny mineral crystals formed by algae, which drifted as plankton in the seas about 100 to 65 million years ago. The crystals, made of calcite, collected on the seabed as white, limy mud which hardened to form chalk rock. Where deeply buried, its minute pore spaces become naturally cemented and the rock hardens. Deep within the Central Graben, however, some chalk is much more permeable than normal and contains oil and gas. Besides fracturing, a crucial factor was that of sediment-slumping on the seabed. Movements across the Central Graben riftedge caused the sediment to flow and re-deposit as a very porous, watery slurry. In places, the pores were filled with oil at high pressure before the crystals could become cemented into a tight mass.

Early Triassic North Sea rift basins In the North Sea Triassic basins, the coarsest deposits appear to have been derived from the Norwegian mainland, with finer-grained deposits becoming dominant towards the East Shetland Platform, Fladen Ground Spur and southwards (Steel & Ryseth 1990). Evidence of fault-block rotation and growth of strata towards the footwalls of individual sub-basins is seen on structural cross-sections across the Horda Platform (Fig. 3) (Steel & Ryseth 1990; Christiansson et al. 2000). The level at which the synrift strata in any sub-basin pass upwards into post-rift strata is reflected by the cessation of growth and the correlation of fairly uniform thicknesses of strata from sub-basin to sub-basin. Early and late synrift packages can be identified and enclose a strongly wedgeshaped rift-climax interval (Fig. 3). In the North Sea, data from cores penetrating Lower Triassic strata are scarce, but traditionally the sand-prone succession is believed to represent stacked deposits of fluvial systems. It is possible, in the light of the new Greenland and mid-Norway data, that these Lower Triassic deposits are deeper-water, marine sands. Previous fluvial interpretations have been coloured by knowledge from Upper Triassic successions, both in the North Sea subsurface and onshore in Scotland.