Search

The application of sequence stratigraphic concepts and methods augments the efficient development of North Sea hydrocarbon fields with Jurassic reservoirs. In particular, the approach provides enhancements to the development of robust reservoir zonations, more accurate assessments of the extent and continuity of reservoir zones and flow units, clearer identification and prediction of the most productive reservoir intervals, improved understanding of field-wide pressure barriers or baffles to fluid flow, and enhanced reservoir models. In addition, carbon capture and storage (CCS) projects in Jurassic rocks will benefit from the adoption of a sequence stratigraphic approach by enhancing the understanding of storage unit architecture, connectivity and top seals. In this chapter, these applications are discussed with reference to around 20 case studies from the North Sea Basin.

An updated, integrated biozonation scheme for the Jurassic (Hettangian)–lowermost Cretaceous (Upper Berriasian) of the North Sea Basin incorporates 49 palynology biozones plus subzones (based on dinocysts, spores and pollen) and 27 microfaunal zones plus subzones (based on foraminifera, radiolaria and ostracods) to provide the essential chronostratigraphic calibration of the defined sequences. The biozonation scheme is tied to standard ammonite zonal chronostratigraphy wherever possible. Parts of the biozonation scheme are also applicable to onshore UK (boreholes and outcrops), onshore Denmark (boreholes) and offshore Netherlands.

Sequence stratigraphy has become a powerful tool in the basin analysis of the North Sea Basin, and will continue to be important in the maximization of the remaining hydrocarbon resources of Jurassic reservoirs in the region, whilst also moving through the energy transition. This chapter provides background to the main theme of this memoir, which is the description of a revised sequence stratigraphy scheme for the Jurassic–lowermost Cretaceous of the region, recognizing 39 stratigraphic sequences (‘J sequences’). The sequences are illustrated by 85 reference wells (56 UK wells, 22 Norway wells and seven Denmark wells), showing chronostratigraphy, lithostratigraphy, wireline logs and key biostratigraphic markers. The reference wells illustrate sequence development, together with their lower and upper boundaries. Comparisons of the North Sea Jurassic sequences with onshore outcrop sections, from the UK, demonstrate that many of the sequences can be recognized onshore. A comparison of the well sequences with seismic sequences is made in 17 illustrated seismic lines, demonstrating the seismic expression of many of the defined sequences. The recognition of a consistent set of stratigraphic sequences across the region allows a much better understanding of the development of the whole area during the Jurassic, which is currently hindered by the existence of multiple local and semi-regional lithostratigraphic schemes, in particular the differing notations that are utilized in the various international offshore jurisdictions that exist across the area.

This chapter describes uppermost Middle Jurassic–lowermost Cretaceous second-order stratigraphic sequences J40, J50, J60 and J70, and their component third-order sequences J42–J46, J52–J56, J62–J66 and J71–J76. The latest Callovian–Berriasian was an interval of significant tectonism that led to the development of complex stratigraphy and highly variable successions, the elucidation of which is aided by the recognition of the correlation of the J sequences. Marine sedimentation dominated the Callovian–Berriasian interval, with the development of multiple sandstone members comprising reservoir units in many hydrocarbon fields, charged by marine source rocks (e.g. the Kimmeridge Clay Formation). Each of these units is subdivided and correlated by a succession of J sequences. Several sequences are renumbered (e.g. J54, J55, J65 and J66), some sequence definitions are amended or their basal boundaries recalibrated chronostratigraphically (J52, J54, J72, J73, J74 and J76) and new sequence subdivisions are recognized (J64a, J64b, J72a–J72c, J73a and J73b). Significant unconformities are recognized at the bases of the J54, J55, J62, J63, J64, J71 and J73 sequences. The top of J70 (J76) equates to the major ‘Base Cretaceous Unconformity’ seismic sequence boundary.

This chapter reviews sequence stratigraphic concepts and methodologies and presents an approach that is most applicable to the North Sea Jurassic, based on the concept of genetic sequence stratigraphy. The concept of depositional sequences, comprising rock units bounded by unconformities, has been developed from the late nineteenth century up to the present day. Many different studies have been carried out on North Sea Jurassic sequence stratigraphy, from the early 1980s to the present day and involving a range of different approaches. Many authors have adopted the J sequence approach that was first published in the early 1990s; however, a number of alternative North Sea Jurassic sequence schemes have also been described. A close relationship existed between tectonics and sequence boundary development, particularly during the Middle–Late Jurassic in the North Sea region. Several of the major unconformities that are known to be of regional extent can be directly related to significant tectonic phases. Other sequence boundaries, for which a tectonic control is not evident, for example, particularly in the Early Jurassic, were potentially driven by glacio-eustatic cycles, which may have been controlled by orbital forcing cycles.

This chapter describes Lower Jurassic second-order sequences J00 and J10, and their component third-order sequences J1–J6 and J12–J18. Two sequences (J1 and J3) are new, four sequences (J2, J4, J12 and J16) are amended and one sequence (J17) is renamed. A significant unconformity at the base of the J12 sequence (Upper Sinemurian) is present near the base of the Dunlin Group in the North Viking Graben–East Shetland Platform and in the Danish Central Graben, and correlates with an equivalent unconformity around the margins of the London Platform, onshore UK. A marked unconformity at the base of the J16 sequence is recognized in the North Viking Graben and onshore UK, where it is related to structural movements on the Market Weighton High, eastern England. Several levels of carbon enrichment (carbon isotope excursions (CIEs)) and associated geochemical changes tie to J sequences defining maximum flooding surfaces: the Upper Sinemurian CIE equates to the base J6 maximum flooding surface (MFS), the basal Pliensbachian CIE ties to the base J13 MFS, the basal Toarcian CIE relates to the base J17 MFS and the Toarcian Ocean Anoxic Event corresponds with the base J18 MFS.

This appendix provides lists and publication references for all microfossil taxa cited in the memoir. These species, subspecies and varieties are the most important taxa in the definition of biozones and in the biostratigraphic characterization of the defined J sequences.

The most important North Sea Jurassic–lowermost Cretaceous lithostratigraphic units, as developed in the UK, Norway and Danish sectors, are summarized in this chapter (55 units from the UK, 25 from Norway and 10 from Denmark). Some significant issues remain with the use and application of lithostratigraphic terminology in the Jurassic of the North Sea Basin. In particular, there are inconsistencies in unit definition and nomenclature changes across country sector boundaries that obscure the recognition of regional stratigraphic patterns that exist across the region. To aid clarity and to overcome some issues of definition, some revisions are made to the existing lithostratigraphic schemes. Several informal lithostratigraphic units are described, a number of unit definitions are revised and various formerly informal units are formalized (Buzzard Sandstone Member, Ettrick Sandstone Member and Galley Sandstone Member). It is recommended that use of the Heno Formation in offshore Denmark is discontinued. In addition, four new lithostratigraphic member terms are introduced (Home Sandstone Member, North Ettrick Sandstone Member, Gyda Sandstone Member and Tambar Sandstone Member). All described units are placed into a sequence stratigraphic context. All significant lithostratigraphic boundaries conform with key sequence stratigraphic surfaces.

This chapter reviews previously published North Sea Jurassic sequence stratigraphy schemes. Some of these works have applied the originally published J sequence schemes, while 18 have established new schemes. The most significant of these are discussed and compared to the newly defined J sequences. Most of these additional documented schemes have been defined for the Upper Jurassic interval, with a more limited number of schemes for the Lower and Middle Jurassic. Different authors have adopted a wide range of sequence notation methods while none of the publications describing the new sequence schemes has offered detailed sequence definitions. Due to the ensuing confusion, it is recommended that a more formal method of sequence definition is adopted in future sequence stratigraphic studies. In intervals in which reservoir successions are developed, such as the Fulmar Sandstone Member in the J56–J63 sequences, particularly in fields in which extensive coring has taken place, authors have usually been able to recognize additional sequences, which are probably at fourth-order scale, at a higher resolution than the defined third-order J sequences.

The application of sequence stratigraphic concepts and methods significantly enhances the evaluation of stratigraphic traps. In this chapter, five examples of, as yet undrilled, potential UK North Sea Jurassic combination stratigraphic traps, from the East Shetland Platform, South Viking Graben, Inner Moray Firth and Central Graben, are discussed and the potential application of sequence stratigraphic methods in their evaluation considered.

Many of the stratigraphic sequences recognized in North Sea Jurassic well sections correspond to mappable surfaces on seismic sections. Typically, however, sequences are only mappable seismically within individual sub-basins, and seismic correlation between sub-basins, or across highs, is generally impossible without independent control from wells. Particularly prominent seismic sequence boundaries occur at near-base J54 in the Inner Moray Firth (‘Intra-Oxfordian Event’) the Viking Graben (‘Top Heather’ in this area), base J62 (‘Top Heather’, Moray Firth), base J66 (‘Top Lower Hot Shale’, Inner and Outer Moray Firth), base J71 (East Shetland Platform), base J73 (‘Top Siltstone Member’, Moray Firth) and top J70/base K10 (‘Base Cretaceous Unconformity’ (BCU), basin-wide). The BCU is the most frequently mapped seismic horizon in the North Sea Basin in Jurassic–basal Cretaceous studies. This surface, at the base of the Cromer Knoll Group, separates synrift sediments from post-rift successions above and marks a major shift in the tectonic evolution of the North Sea Basin.

This chapter describes the methodology employed to recognize depositional sequences in well data, involving the integration of wireline logs, biostratigraphy, lithostratigraphy (and lithological interpretations), seismic and sedimentology (particularly facies analysis), with an emphasis on a pragmatic approach to sequence recognition in North Sea Jurassic–lowermost Cretaceous well successions. Wireline log profiles characterizing individual depositional sequences or parts of sequences are illustrated by reference to key North Sea well sections.

An updated sequence stratigraphic framework, comprising 39 third-order stratigraphic sequences, for the Jurassic–lowermost Cretaceous of the North Sea, is described by reference to key wells and seismic lines across the UK, Norway and Denmark sectors, and, where possible, to onshore UK outcrops. It appears evident that regional tectonics provided the main control on sequence development, particularly during the Late Jurassic. There is a close relationship between key sequence stratigraphic surfaces and many lithostratigraphic formation and member boundaries throughout the North Sea Jurassic. Four new sandstone members are defined. A biozonation scheme for the study interval is described that provides essential characterization of the defined sequences.

Of 40 recognized Jurassic–earliest Cretaceous sequence boundaries or surfaces, 21 are considered to have had a primary tectonic control on their generation, particularly during the Bathonian–Berriasian interval of synrift-dominated tectonism. These boundaries include the intra-J22 sequence boundary, the base J36, the base J54, the base J55, the intra-J56 transgressive surface, the base J62, the base J63, the base J64, the base J71, the base J73 and the top J76 (‘Base Cretaceous’). In the study area, these events all occurred within a marine setting and none can be unequivocally matched to times of subaerial exposure or coastal onlap. Ten Jurassic sequence surfaces appear to have had a primary eustatic control on their generation, some of which are also associated with the deposition of major marine source-rock facies, including the base J18 and the base J74.

This chapter describes Middle Jurassic second-order sequences J20 and J30, and their component third-order sequences, J22–J26 and J32–J36. The J22 sequence contains the major Intra-Aalenian Unconformity (‘Mid-Cimmerian’) across a wide area of the North Sea Basin and an equivalent event onshore UK. The base J24 (Lower Bajocian) is marked by the Rannoch Shale (Brent Group) and by the flooding of the Ollach Sandstone, Hebrides Basin. The base J26 (Upper Bajocian) ties to the Mid Ness Shale (Brent Group) and the base of the Upper Trigonia Grit Member, central England. The base J32 (Upper Bajocian) ties to the base of the Tarbert Formation, the base of the Great Oolite Group in central England and the base of the Great Estuarine Group, Hebrides Basin. The base J33 (Middle Bathonian) falls within the Tarbert Formation and the base of the Taynton Limestone, central England. The base J34 (uppermost Middle Bathonian) commonly falls at the top of the Brent Group. The base J36 (uppermost Bathonian) represents a major increase in marine influence, at the base of the Beatrice Formation, in the Inner Moray Firth and at the base of the Staffin Bay Formation, Hebrides Basin.

The thickest section of Early Jurassic strata known from onshore Ireland (total Jurassic thickness 566 m) is reported from the Ballinlea-1 well (Rathlin Basin) situated on the north coast of Northern Ireland. A biostratigraphical and palaeoenvironmental assessment is presented for this section largely based on calcareous benthic microfossils (foraminifera and ostracods). The Early Jurassic Waterloo Mudstone Formation (Lias Group) of Northern Ireland has previously received little micropalaeontological attention, therefore this work provides an opportunity to enhance palaeogeographic and palaeoenvironmental understanding for the Early Jurassic of the province, and this paper illustrates the key microfossil taxa of this age from Ireland for the first time. The records, based on ditch-cuttings samples, demonstrate a stratigraphical range from Hettangian to Early Pliensbachian, consistent with other wells and boreholes in this basin. The assemblage compositions are comparable to those elsewhere in the European boreal Atlantic realm. Hettangian to earliest Sinemurian microfossil assemblages are generally of low diversity and are numerically dominated by metacopid ostracods with occasional influxes of foraminifera. Gradually, foraminiferal abundance (often dominated by species of the Lagenida) come to exceed those of the ostracods in the Early Sinemurian reaching their greatest diversity in the Late Sinemurian. The sediments are considered to represent an inner to mid-shelf environment throughout while the record thickness for this region indicates ongoing syn-sedimentary fault movement along the basin margins within this period.

The Lough Foyle Basin is a half-graben that straddles the border between Northern Ireland and the Republic of Ireland and contains sediments that range in age from Lower Carboniferous to Holocene. The basin’s post-rift succession is represented by sediments of the Penarth Group and Lias Group. The lithostratigraphy and biostratigraphy of that interval are revised using new borehole material and existing outcrop. Palaeontological data provide a chronostratigraphic framework and aid palaeoenvironmental interpretations. Foraminifera, ostracods, palynomorphs indicate a nearshore, marginal marine depositional setting throughout much of the Rhaetian with a more marine, shelf and nearshore depositional setting for the Lias Group. The Penarth Group succession is similar to that elsewhere in Northern Ireland but the Lias Group (Waterloo Mudstone Formation) differs in that five distinct members can be recognised (Clooney Mudstone, Drummans Siltstone, Gortmore Mudstone, Tircreven Sandstone and Ballyleighery Mudstone), four of which are newly described. The deltaic and shelf sandstones of the Tircreven Sandstone Member are the only such examples preserved in the Jurassic strata of Northern Ireland and are some of the oldest in the Jurassic of the UK and Ireland, providing evidence of the proximity of the nearby Irish Landmass and representing a useful comparison for Early Jurassic sandstone reservoirs in offshore basins.

The latest Triassic to earliest Jurassic transition has been widely studied due the occurrence of a major global extinction associated with a global hyperthermal event in this interval. Furthermore, a number of distinct geochemical events in the global carbon cycle can be recognised in the stable-isotope record across this boundary interval at many localities. Two fully-cored boreholes from East Antrim in Northern Ireland (Carnduff-1 and Carnduff-2) have penetrated sediments of latest Triassic to Early Jurassic age (Rhaetian to Early Sinemurian). Ammonites, foraminifera, ostracods and palynomorphs provide a robust chronology as well as insights to palaeoenvironmental conditions during this period. The sedimentary and palynological evidence support a largely marginal-marine setting for the sediments of the Triassic Penarth Group while a range of palaeontological evidence shows that the Early Jurassic Waterloo Mudstone Formation represents shallow-marine, shelf conditions that represent generally well-oxygenated bottom waters, with little evidence for dysoxia. Detailed ammonite biostratigraphy (ammonites first occur about 7.5 m up from the base of the Lias Group) indicates that the cores represent largely continuous sedimentation through the Hettangian and earliest Sinemurian (to Turneri Chronozone, Birchi Subchronozone). Stable-isotope analysis of both carbonate and organic carbon show a distinct carbon isotope excursion (CIE) in both fractions through the Cotham and Langport members (Lilstock Formation, Penarth Group, latest Triassic) which are considered to correlate with the distinctive ‘Initial’ CIE witnessed in SW England and probably the GSSP and other sites across the world.

The uppermost Triassic to Lower Jurassic interval has not been extensively studied across the island of Ireland. This paper seeks to redress that situation and presents a synthesis of records of the uppermost Triassic and Lower Jurassic from both onshore and offshore basins as well as describing the sedimentological characteristics of the main lithostratigraphical units encountered. Existing data have been supplemented with a re-examination and logging of some outcrops and the integration of data from recent hydrocarbon exploration wells and boreholes. The Late Triassic Penarth Group and Early Jurassic Lias Group can be recognised across the Republic of Ireland and Northern Ireland. In some onshore basins, almost 600 m of strata are recorded, however in offshore basins thicknesses in excess of two kilometres for the Lower Jurassic have now been recognised, although little detailed information is currently available. The transition from the Triassic to the Jurassic was a period of marked global sea-level rise and climatic change (warming) and this is reflected in the lithostratigraphical record of these sediments in the basins of Northern Ireland and offshore basins of the Republic of Ireland. In general, the sediments of this interval are thicker than those in Great Britain and have potential for detailed study of climatic and sea-level fluctuation.

Here in the first part of this publication we discuss the possibilities for the selection of a GSSP for the Berriasian Stage of the Cretaceous System, based on the established methods for correlation in the Tithonian/Berriasian interval. This will be followed, in the second part, by an account of the stratigraphic evidence that justifies the locality of Tre Maroua (Hautes-Alpes, SE France) as the proposed GSSP. Here we discuss the possibilities for correlation in the historical J/K boundary interval, and the evolution of thinking on the positioning of the boundary over recent generations, and in relation to research in the last ten years. The Tithonian/Berriasian boundary level is accepted as occurring within magnetosubzone M19n.2n. The detailed distribution of calpionellids has been recorded at numerous sites, tied to magnetostratigraphy, and the base of the calpionellid Alpina Zone is taken to define the base of the Berriasian Stage. This is at a level just below the distinctive reversed magnetic subzone M19n.1r (the so-called Brodno reversal). We discuss a wide range of magneto­stratigraphic and biostratigraphic data from key localities globally, in the type Berriasian areas of France and wider regions (Le Chouet, Saint Bertrand, Puerto Escano, Rio Argos, Bosso, Brodno, Kurovice, Theodosia etc.). The characteristic datums that typify the J/K boun­dary interval in Tethys and its extensions are detailed, and the correlative viability of various fossil groups is discussed. The boundary level is correlated to well-known J/K sections globally, and a series of secondary markers and proxies are indicated which assist wider correlation. Particularly significant are the primary basal Berriasian marker, the base of the Alpina Subzone (marked by dominance of small Calpionella alpina, Crassicollaria parvula and Tintinopsella carpathica) and secondary markers bracketing the base of the Calpio­nella Zone, notably the FOs of the calcareous nannofossil species Nannoconus wintereri (just below the boundary) and the FO of Nannoconus steinmannii minor (just above). Notable proxies for the boundary are: 1) the base of the Arctoteuthis tehamaensis Zone in boreal and subboreal regions, 2) the dated base of the Alpina Subzone at 140.22 ±0.14 Ma, which also gives a precise age estimate for the system boundary; and 3) the base of radiolarian “unitary zone” 14, which is situated just above the base of the Alpina Subzone.

International audience; In part 1 of this work we discussed the possibilities for the selection of a GSSP for the Berriasian Stage of the Cretaceous System, based on prevailing practical methods for correlation in that J/K interval, traditional usage and the consensus over the best boundary markers that had developed in the last forty years. This consensus has developed further, based on the results of multidisciplinary studies on numerous sites over the last decade. Here in Part 2 we give an account of the application of those results by the Berriasian Working Group (ISCS), and present the stratigraphic evidence that justifies the selection of the locality of Tré Maroua (Hautes-Alpes, SE France) as the proposed GSSP. We describe a 45 m-thick section in the Calcaires Blancs vocontiens – that part of the formation covering the calpio­nellid Chitinoidella, Remanei. Intermedia, Colomi, Alpina, Ferasini, Elliptica and Simplex biozones. The stratigraphic data collected here has been compiled as part of a wider comparative study of complementary Vocontian Basin sites (with localities at Charens, St Bertrand, Belvedere and Le Chouet). Evidence from Tré Maroua thus sits in this substantial regional biostratigraphic and magnetostratigraphic context. For the purposes of the GSSP definition, here we particularly concentrate on the unbroken sequence and biotic markers in the interval immediately below the boundary, the Colomi Subzone (covering circa 675,000 years), and immediately above, the Alpina Subzone (covering circa 725,000 years). Particularly significant fossil datums identified in the Tré Maroua profile are the primary basal Berriasian marker, the base of the Alpina Subzone (a widespread event marked by dominance of small Calpionella alpina, with rare Crassicollaria parvula and Tintinopsella carpathica): the base of the Berriasian Stage is placed at the base of bed 14, which coincides with the base of the Alpina Subzone. Secondary markers bracketing the base of the Calpionella Zone are the FOs of the calcareous nannofossil species Nannoconus wintereri, close below the boundary, and the FO of Nannoconus steinmannii minor, close above. The Tithonian/Berriasian boundary level occurs within M19n.2n, in common with many documented sites, and is just below the distinctive reversed magnetic subzone M19n.1r (the so-called Brodno reversal). We present data which is congruent with magnetostratigraphic and biostratigraphic data from other key localities in France and in wider regions (Le Chouet, Saint Bertrand, Puerto Escaño, Rio Argos, Bosso, Brodno, Kurovice, Theodosia…), and thus the characteristics and datums identified at Tré Maroua are key for correlation and, in general, they typify the J/K boundary interval in Tethys and connected seas.

Numerous specimens of Ichthyosaurus are known, but only very few small examples (total length of

The uppermost Pliensbachian-Lower Toarcian sediments recovered from Llanbedr (Mochras Farm) Borehole (North Wales, UK) were deposited in the Cardigan Bay Basin and mainly consist of alternating marls and marly limestones. The current study analyses the foraminiferal assemblages from the cored interval (143 m) that has been assigned to the Spinatum Zone (Upper Pliensbachian) to the lower part of the Bifrons Zone (Middle Toarcian). The foraminiferal assemblages are dominated by the suborders Lagenina and Robertinina. Four main ecostratigraphic intervals have been identified, based on changes in the foraminiferal assemblages that occurred before, during and after the Toarcian Oceanic Anoxic Event (T-OAE). Ecostratigraphic interval I (upper part of the Spinatum Zone) is characterized by a diverse assemblage with specialist, opportunist and intermediate forms. This assemblage is interpreted to represent a phase that pre-dates the biotic crisis. The ecostratigraphic interval II (Tenuicostatum Zone) shows an abrupt increase in opportunist forms such as the genus Reinholdella, and a facultative opportunist such as Paralingulina tenera, which was tolerant to oxygen depleted conditions. This second interval represents the initial biotic crisis phase, in response to decreasing oxygenation. The ecostratigraphic interval III is considered the peak of the biotic crisis, coincident with the negative carbon isotopic excursion (at the base of the Serpentinum Zone) and characterized by the dominance of the opportunist Reinholdella (87–97% of the assemblage) and low diversity. The ecostratigraphic interval IV (upper part of Serpentinum Zone and lower part of Bifrons Zone) is characterized by an increase of diversity and an abrupt decrease in Reinholdella. This assemblage is interpreted to reflect the increased availability of oxygen from deep-infaunal to epifaunal microhabitats and the return to normal conditions at the sea bottom. Ecostratigraphic fluctuations in the Mochras foraminiferal assemblages across the T-OAE event are comparable with those from other parts of the UK, the Lusitanian Basin (Portugal), the Umbria Marche Basin (Italy) and the Atlassic Basin (North Africa). In addition, a foraminiferal turnover is evident across the Pliensbachian-Toarcian boundary and the T-OAE, and reflects the effects of the Early Jurassic biotic crisis on benthic foraminifera. Controlling factors of the biotic crisis are discussed, regarding that anoxic conditions do not necessarily have a lethal effect on all foraminiferal species and other oceanographic and environmental factors need consideration (fragmentation of epicontinental platforms, sea-level changes, crisis of carbonate productivity and temperature changes).

The complete, fully cored Lower Jurassic (Hettangian, Sinemurian, Pliensbachian, Toarcian) succession from the Llanbedr (Mochras Farm) Borehole, North Wales, the thickest known British section, has...

The Lower Palaeogene stratigraphy of the northern North Sea is described using wireline log and biostratigraphic data. At group and formation level a close similarity can be shown with the stratigraphy defined in the Outer Moray Firth area of the central North Sea. A two-fold subdivision into the Montrose and Moray Groups is recognized. The Montrose Group consists of the Maureen and Lista Formations while the succeeding Moray Group contains the Sele, Balder, Dornoch and Beauly Formations. The Maureen and Lista Formations are dominantly argillaceous units that contain poorly defined sandstones; the most laterally extensive of these is the Heimdal Member developed within the Lista Formation. The Dornoch and Beauly Formations are shelfal sandstone units that pass eastwards and northwards into the age equivalent, dominantly argillaceous Sele and Balder Formations. The Sele Formation contains the Hermod Member while the Balder Formation contains the Odin Member. These are massively developed sandstone units of very limited extent. The Lower Palaeogene succession contains a number of high gamma log markers that are often associated with influxes of microfossils and microflora. These are interpreted as condensed claystone horizons representing pauses in marine sedimentation during episodes of maximum transgression. They can be correlated with similar marker horizons described from the Outer Moray Firth area, giving further confidence that the stratigraphy forms a regional framework that can be applied over the whole North Sea area.

The Lower Palaeogene lithostratigraphy of the Outer Moray Firth has been revised using wireline log and biostratigraphic data. A two-fold subdivision into the Montrose and Moray Groups is recognized. The Montrose Group consists of the Maureen and Lista Formations, whereas the younger Moray Group contains the Sele, Balder, Dornoch and Beauly Formations. The Lista Formation contains the arenaceous Andrew and Balmoral Members, separated by the tuffaceous Glamis Member. The Dornoch and Beauly Formations are prograding shelfal sandstone units that pass basinwards into the age-equivalent, dominantly argillaceous Sele and Balder Formations. The Sele Formation contains the Forties and Cromarty Members, which are locally developed sand-rich units. Stratigraphic analysis has led to the identification of a number of consistently developed high gamma log markers that are interpreted as condensed mudstone horizons. These markers are believed to record clastic sediment starvation during periods of maximum marine transgression. They often have a strong biostratigraphic fingerprint coinciding with influxes of rich concentrations of microfossils and microflora. They are interpreted as the product of synchronous regional transgressive events and have been an important aid to the development of a confident lithostratigraphic framework for the Lower Palaeogene of the Outer Moray Firth.

The role of micropalaeontology in the hydrocarbon exploration of the North Sea is reviewed. The small size and abundance of microfossils in drill samples and their rapid evolution makes them valuable for correlation, age determination, unconformity identification, depositional sequence characterization, lithostratigraphic characterization and palaeoenvironmental interpretation in the subsurface.