description of the regional Albian transgression as identified by wireline log, lithostratigraphy and biostratigraphy correlation - England, North Sea, Holland and Germany

1. THE “ALBIAN TRANSGRESSION” IN THE SOUTHERN
NORTH SEA BASIN
Stephen Crittenden*
The “Albian transgression” may be recognised lithostratigraphically in a number of boreholes in
the UK sector of the southern North Sea Basin. This event is also recognised onshore the United
Kingdom. The importance of this event for hydrocarbon exploration is discussed, and comparisons
are made with sections in West Germany. The “Albian transgression” is a regional event in NW
Europe which is important for understanding the pattern of basin evolution during Early and “Mid”
Cretaceous times. It is also important because the diachronous coarse clastics associated with the
transgression may prove to be of important reservoir potential in the southern North Sea area
(UK sector).
INTRODUCTION
The lithostratigraphical subdivision of the Early Cretaceous strata of the southern North Sea Basin
has been discussed previously by a number of authors (Rhys, compiler 1974, 1975; NAM and RGD,
1980; Crittenden, 1982). Crittenden (1982) discussed the lithostratigraphical scheme of NAM and
RGD (1980), and compared and contrasted it with the scheme of Rhys (1974, 1975), and presented a
lithostratigraphical and wireline log correlation, using both schemes, of the Early Cretaceous strata of
a number of boreholes in block 49 (UK sector) (see Fig. 1).
In a later publication, Crittenden (1984) discussed in detail the Aptian and Albian
lithostratigraphy and foraminiferal biostratigraphy of one of these boreholes, 49/24-1, and made some
comparisons with onshore NW European Early Cretaceous borehole and outcrop sections.
This paper complements the previous publications (Crittenden, 1982, 1984) by discussing and
comparing the Albian strata from a number of boreholes in the southern North Sea with other areas in
NW Europe. The widespread occurrence and recognition of the “Albian transgression” in NW Europe
is discussed.
Tectonic instability during Aptian and Albian times had a pronounced effect on sedimentation,
especially in marginal areas and around palaeohighs (local salt movement structures) of the NW
European sedimentary basins. The product is a profusion of non-sequences, discordances and erosion
levels of regional and local importance, which are all associated with phases of shallowing and
deepening of the sea. The resultant numerous sedimentary facies characteristic of the Aptian and
Albian strata in NW Europe may be mapped, and dated biostratigraphically, to provide an
approximation of palaeogeography and palaeogeographical changes through time (Gallois and
Morter, 1982).
Journal of Petroleum Geology, 10(4), pp. 395-414, 1987 395
* Gearhart Geo Consultants Ltd., Howe Moss Drive, Kirkhill Industrial Estate, Dyce, Aberdeen, AB2 0GL,
Scotland.

2. However, correlation difficulties are encountered as a result of the facies variations which, as they
are a result of palaeoenvironment, are concomitant with variations in the benthonic and planktonic
foraminiferal fauna. The dearth of planktonic foraminiferids during Early to Middle Albian times,
which precludes their use as accurate biostratigraphic tools, and the abundance of benthonic
foraminiferids—particularly arenaceous faunas—is undoubtedly facies related.
It is considered that an appreciation of the sedimentary facies variations—spatial and temporal—
during Aptian and Albian times is of paramount importance for hydrocarbon exploration in the
southern North Sea Basin.
It would not be incorrect to suggest that a major “gross” transgression phase commenced in Late
Aptian times (nutfieldensis—nolani—jacobi Biozones) and progressed through the tardefurcata
subzone, the regularis subzone and mammilatum Biozone of Early Albian through to Middle and
Late Albian times. Minor stillstands, tectonic movements and minor regressions/transgressions have
resulted in polyphase events throughout this interval, which make the precise geological history
difficult to unravel. Basinward, a number of unconformities/ hiatuses may be recognised, while across
high areas these unconformities/hiatuses coalesce into what appears to be a single major event
(Fig. 9). By Middle Albian—Late Albian times, the major high areas in the region were inundated by
the sea. In the United Kingdom, the Gault Clay is the earliest Mesozoic unit known to extend across
the Palaeozoic London-Brabant platform (Owen 1971 a,b). The recognition of this transgression and
associated coarser sedimentation at its base is/will be of paramount importance for the delineation of
possible stratigraphic hydrocarbon traps in the UK southern North Sea, the reservoir being the
coarser, clastic sediments associated with the transgression.
THE SOUTHERN NORTH SEA BASIN
Boreholes 49/24-3, 49/24-4 and 49/24-1 (all Shell/Esso) provide an excellent example of a
lithostratigraphical and biostratigraphical correlation of Albian age strata in the southern North Sea
Basin. These boreholes are located on Early Mesozoic structural highs/fault blocks, which during
latest Early Cretaceous time underwent uplift and erosion. These boreholes illustrate the onlap of
Early Cretaceous age sediments on to pre-Cretaceous structural highs (Permian-Triassic strata). The
onlap is a result of the Early Cretaceous marine transgression (Day et al., 1981), salt movement, and
local tectonic activity (Glennie and Boegner, 1981). This has resulted in the subsequent erosion, or
non-deposition, of either pre-Late Aptian/Early Albian age strata or pre-Late Albian age strata
(Glennie and Boegner, 1981) with, in general, an increasing hiatus towards the top of the highs. The
concept of the “coalescence of unconformities” across paleostructural highs is thus demonstrated. The
microfaunal evidence indicates that by comparison with other areas in NW Europe, only a relatively
thin veneer of Late Aptian and Albian sediments is present in the three boreholes.
Lithostratigraphy
The lithostratigraphic subdivision and correlation of the three boreholes has been discussed and
illustrated previously by Crittenden (1982, 1984)—Fig. 2. The gamma-ray and sonic/ interval transit-
time logs from boreholes in the UK sector of the southern North Sea Basin all display a similar
feature at the base of the Middle Holland Shale Member (Fig. 2, from Crittenden, 1982, 1984). This
siltstone/sandstone—phosphate nodule bed horizon can be correlated with the greensand
intercalations present toward the base of the Middle Holland Shale Member in the
Netherlands offshore (NAM and RGD, 1980). These greensand intercalations are thickest
along the margins of the southern North Sea Basin (and on the flanks of palaeohighs), and
rapidly shale out toward the depositional centres. In the West Netherlands Basin, thicker
developments of green, glauconitic, fine-grained, basin-margin sandstones and siltstones are
termed the Holland Greensand Member (NAM and RGD, 1980), and are of Late
The “Albian transgression”396

3. Aptian to Early Albian age in the offshore Netherlands area (C.A. Burton, pers. comm.). Boreholes
Vlieland Oost-1 and L5-1 in the Dutch sector of the southern North Sea illustrate the “basal Albian
Gault” transgression, as depicted by the sandy basal horizon of the Middle Holland Shale Member
(Crittenden, 1982; 1984; 1987) (Fig. 3).
Biostratigraphy
Careful microfauna (foraminiferal) analysis provides accurate age dating for the Early Cretaceous
strata of boreholes 49/24-1 and 49/24-4 (Figs.4 and 5), and reveals the presence of a basal Early
Cretaceous unconformity. Permo-Triassic sediments are overlain unconformably by a thin interval of
Late Aptian age strata, which in turn is overlain unconformably by an interval of Early to Middle
Albian age strata (Crittenden, 1984).
In borehole 49/24-3 (Fig. 6), Late Albian age sediments (Upper Holland Marl Member) overlie
unconformably the Bunter Sandstone. This suggests that the boundary between the Upper Holland
Marl and Middle Holland Shale Members is a disconformity/unconformity. The biostratigraphical
details (foraminifera) of the Early Cretaceous strata of borehole 49/24-1 have been discussed by
Crittenden (1984), and are not repeated here. However, boreholes 49/24-4 and 49/24-3 are discussed
briefly below.
(i) Borehole 49/24-3
There is an incomplete coverage of the Early Cretaceous interval, by ditch cuttings samples, of
borehole 49/24-3. The three samples from this borehole each contain a light red-brown coloured
foraminiferal fauna. This is a characteristic of the red-brown calcareous mudstones which comprise
the upper Holland Marl Member (Red Chalk Formation) in block 49. A subtle change in the fauna is
noted at 5,000 ft, where the foraminiferal fauna is a dark reddish-brown colour. This may be a
colouration artifact derived from the Bunter Sandstone Formation beneath.
Stephen Crittenden 397

5. Planktonic Foraminifera
The abundant planktonic foraminiferal fauna is dominated by the Hedbergella delrioensis
(Carsey) — Hedbergella infracretacea (Glaessner) — Hedbergella brittonensis (Loeblich and
Tappan) plexus. Members of this plexus become larger in size up the borehole section. This size
increase has been noted by Price (1977b) and Carter and Hart (1977) in the Albian strata of NW
Europe. Large, high-spired forms are attributable to H. brittonensis (= Whiteinella brittonensis of e.g.
Robaszynski and Caron, 1979), which is a characteristic species of the Late Albian and Early
Cenomanian (Carter and Hart, 1977). Small, high-spired forms are attributable to H. infracretacea.
Price (1977b) has discussed this plexus and its stratigraphical use in the Albian strata of NW Europe
in some detail, and it is not repeated here.
H. simplex (Morrow) is a Late Albian-Cenomanian species in NW Europe (Robaszynski and
Caron, 1979). Globigerinelloides bentonensis (Morrow) is an important index planktonic species, as
its occurrence in large numbers (flood horizons) is indicative of the Late Albian in NW Europe (Price
1977a,b). Floods of this species have been recorded from horizons in Late Albian sediments of
southern England, the Central North Sea, northern France and Germany (Hart, 1973; Carter and Hart,
1977a; Price 1977a,b; Burnhill and Ramsay, 1981; Harris, 1982). It is encountered rarely in the
Middle Albian and it ranges into the Cenomanian. The planktonic foraminiferal fauna indicates a Late
Albian age for the calcareous mudstones of the Upper Holland Marl Member (Red Chalk Formation)
of borehole 49/24-3.
Stephen Crittenden 399

8. Benthonic Foraminifera
The benthonic foraminifera are diverse and numerous. Arenobulimina chapmani Cushman,
A. frankei (Cushman), A. advena (Cushman), A. sabulosa, Eggerellina mariae (ten Dam) and
Quinqueloculina antiqua (Franke) are, according to Bartenstein (1976a,b,c; 1977; 1978a,b; 1979),
Carter and Hart (1977), Price (1977b) and Harris (1982), important members of the Late Albian
benthonic foraminiferal fauna in NW Europe. This species association suggests a Late Albian age for
the Upper Holland Marl Member (Red Chalk Formation). The diverse Arenobulimina fauna and the
absence of the Middle Albian species A. macfadyeni supports a Late Albian age. Walters
(unpublished Ph.D. thesis, 1958) recognized that Textularia chapmani Laliker is a typically Late
Albian species. This Late Albian age assignment is supported by the occurrence of a diverse
gavelinellid fauna, including Gavelinella cenomanica (Brotzen), G. baltica Brotzen, and
G. group intermedia (Berthelin) which are recorded together in the Late Albian of NW Europe by a
number of authors (e.g. Price, 1977b; Magniez-Jannin, 1975). The Lingulogavelinellid species
substantiate the Late Albian age; L. ciryi inflata Malapris-Bizouard, according to Magniez-Jannin
(1975), indicates an uppermost Late Albian (Vraconian-dispar Biozone) age in the Paris Basin.
Species of the Spiroplectinata/Gaudryina group were not present in sufficient numbers to enable a
rigorous application of the phylogenetic scheme of Grabert (1959) to be made. However,
S. complanata (Reuss) is recorded from the Late Albian strata of NW Germany. Gaudryina gradata
(Berthelin) is also considered to be a Late Albian/Cenomanian age species.
The benthonic foraminiferal fauna recorded from borehole 49/24-3 indicates a Late Albian age for
the Upper Holland Marl Member (Red Chalk Formation). The fauna shows an increase in arenaceous
species downhole. The basal sample (5,000 ft) has a marked increase in the number of specimens of
the Glomospira gaultina group. This is perhaps associated with the environment of deposition
(shallow marine: see Crittenden, 1984).
(ii) Borehole 49/24-4
There is good sample coverage of the Early Cretaceous strata of this borehole from 4,730 ft to
4,900 ft (every 10 ft). However, from 4,900 ft to the base of the Early Cretaceous at c. 4,955 ft the
sample coverage is poor (2 samples), which is unfortunate as this is the interval where
biostratigraphic control is most important for age dating.
Planktonic Foraminifera
The planktonic foraminiferal fauna is numerous and dominated by the H. delrioensis—
H. infracretacea—H. brittonensis plexus. This plexus dominates the fauna recorded from the Upper
Holland Marl Member (Red Chalk Formation) in the interval 4,720-30 ft to 4,860 ft. The other
species present are H. simplex, G. bentonensis and H. planispira (Tappan). The latter species is not
common, but is distinctive and present throughout the greater part of the late Early Cretaceous
(Bartenstein, 1965; Carter and Hart, 1977; Price, 1977a; Harris, 1982). By comparison with boreholes
49/24-3 and 49/24-1 (Crittenden, 1984) the planktonic foraminiferal fauna indicates a Late Albian age
for the Upper Holland Marl Member (to 4,830 ft). The marked decrease in the planktonic fauna from
4,830-40 ft downwards, coupled with the benthonic foraminiferal evidence, suggests a Middle to
Early Albian age to 4,900 ft. The presence of “Globigerinelloides”? gyroidinaeformis Moullade at
4,830-4,840 ft is interesting. This species has been used by various authors to denote the Middle and
Early Albian strata in the North Sea Basin. It’s presence (1 specimen) at 4,830-4,840 ft and the single
specimen recorded at 4,890-4,900 ft confirms a Middle-Early Albian age at those depths.
The “Albian transgression”402

10. Benthonic Foraminifera
The benthonic foraminiferal fauna is both numerous and diverse, and compares well with the
faunas recorded from the Upper Holland Marl in boreholes 49/24-1 and 49/24-3. The interval 4,730 to
4,830-40 ft is interpreted as Late Albian in age, and is characterised by an assemblage of
arenobuliminids and gavelinellids usually associated with sediments of a Late Albian age in NW
Europe (Carter and Hart, 1977).
Other taxa indicative of a Late Albian age are E. mariae, Marssonella ozawai, Flourensina
intermedia, Q. antiqua, T. pyramidata, Arenobulimina advena, T. chapmani, A. sabulosa and
Vaginulina mediocarinata (Carter and Hart, 1977).
The first downhole occurrence of A. macfadyeni at 4,820-4,830 ft denotes the penetration of
sediments of an earliest Late to Middle Albian age. This is associated with a dramatic increase in
abundance of G. gr. intermedia and denotes a faunal facies change. The sample 4,840-4,850 ft
contains the first downhole occurrences of Reophax minuta, Conorboides lamplughi and Osangularia
schloenbachi which are all considered index species for strata of Middle Albian age and older
(Crittenden, 1982,1984; Price, 1977a, b; Carter and Hart, 1977). An increase in abundance of
Glomospira gr. gaultina is also recorded in samples 4,840-50 ft and 4,850-60 ft (compare with
boreholes 49/24-3, 49/24-1, 49/25-1). The top downhole occurrence of G. dividens and
Spiroplectinata indicates sediments of an Early Albian age (Grabert, 1959; Bartenstein, op. cit.). The
top consistent and common occurrence of G. dividens, Patellina sp., together with the top occurrence
of Gaudryinella sherlocki and Conorotalites bartensteini aptiensis, associated with abundant
Glomospira gr. gaultina, are taken to indicate sediments of a Late Aptian age.
To conclude the discussion on the biostratigraphic subdivision of borehole 49/24-3, the following
breakdown can be made:
Sediments of a Late Albian are present from 4,720-30 ft to 4,820-30 ft. Middle Albian age
sediments are present to 4,870-80 ft. Beneath this depth, a pragmatic approach is used to arrive at an
Early Albian/?Late Aptian age, undifferentiated, for the interval from 4,870-80ft to 4,910-20 ft. A
Late Aptian age is indicated for the interval 4,910-20 ft to the last sample examined at 4,940-50 ft.
There is some degree of doubt involved in this age breakdown, for the data available does not permit
a finer resolution. For instance, the interval 4,820-30 ft to 4,84050 ft could be assigned a Late/Middle
(undifferentiated) Albian age.
(iii) Stratigraphical conclusions for Boreholes 49/24-3 and 49/24-4
The nature of the samples (ditch cuttings) and large sample interval precludes (as all
micropalaeontologists are aware) a detailed breakdown of the studied sections. The faunas recorded
from the two boreholes are not referred to the biozonations of Hecht (1938), Hart (1973), Carter and
Hart (1977) and Price (1977b). However, an age is assigned based upon comparison with faunas from
studied onshore sections adjacent to the southern North Sea Basin. Both the planktonic and benthonic
foraminiferal faunas recovered from the two boreholes indicate that the Upper Holland Marl
Members (Red Chalk Formation) is Late Albian in age, and Middle Albian in age at the base; and that
the Middle Holland Shale Member is Middle to Early Albian in age and, as suggested by Crittenden
(1984), Late Aptian in age at the base.
The planktonic foraminifera are dominant in the Upper Holland Marl Member, indicating deep
water with good open-ocean connections; while the benthonic foraminifera are dominant in the
Middle Holland Shale Member, suggesting more restricted oceanic circulation. This same relationship
has been noted by Price (1977b) and Magniez-Jannin (1975) for the Albian strata of onshore NW
Europe. An examination of Fig. 2 shows the diachroneity of the Early-Middle Albian Gault transgression and its
effect upon the thickness of the Albian sediments across “high areas”. It is apparent that there are probably a number
of non-sequences and unconformities present within the studied sequences, most of such small
magnitude that they cannot be detected with the biostratigraphical data available.
The “Albian transgression”404

11. ONSHORE THE UNITED KINGDOM
Regional outcrop data illustrate the “Albian transgression”:
(A) South of the London-Brabant Platform, it is expressed lithologically as the Lower Greensand,
Carstone and the nodule beds at the base of the Gault Clay. For example:
(i) Glauconitic sands of Early Albian age (mammilatum Biozone) at the base of the Gault Clay
in the western outcrop of Early Cretaceous strata in Wiltshire and Buckinghamshire
overlap onto the Kimmeridge Clay (Late Jurassic).
(ii) The Carstone of the Isle of Wight (mammilatum Biozone), which has a gradational
junction with the overlying Gault Clay.
To the best of the Author’s knowledge, there has been no study published which discusses the
reservoir potential of this stratigraphic interval onshore or offshore southern UK.
The Winterborne Kingston borehole (Fig. 7) is located at the western margin of the Early
Cretaceous depositional basin (Wessex Basin or Southern Basin of some other authors) in
Stephen Crittenden 405

12. southern England, where the Gault Clay and its sandy/conglomeratic base transgresses westward
over folded and eroded earlier Cretaceous and Jurassic strata. Morter (1982) regards the
basement beds of the Lower Gault Clay in this borehole as belonging to the mammilatum
Biozone (345.24m-345.55m), with earlier Albian (Kitchenii subzone) and perhaps Late Aptian
greensands beneath. This sub-Gault Clay transgressive episode may be a direct correlative of the
“ basal Albian” event seen in boreholes in the North Sea Basin and onshore NW Europe. This
transgression is marked by “coastal onlap”, the effects of which are also apparent in basinal areas
as phosphatic nodule beds—siltier/sandier horizons (see Fig. 8).
These horizons, indicative of erosive periods, are often correlative with a decrease in
planktonic foraminifera abundance (Price 1977b; Gallois and Morter, 1982).
(B) North of the London-Brabant Platform, this important transgression episode is represented:
(i) In Yorkshire, by the Greensand Streak at Speeton (regularis subzone of the tardefurcata
Biozone: Dilley, 1969; Owen et al., 1968) and elsewhere by the Carstone Grit..
(ii) In Central and Southern Lincolnshire, by the Cartone Grit or pebble base of the Red Chalk
where the Grit is absent (Owen, 1972; Owen et al., 1968; Rawson et al., 1978).
(iii) In Norfolk the Carstone is diachronous, and is Early Albian in age (tardefurcata— regularis
subzone and mammilatum Biozone). It is overlain by Gault Clay. Ammonites recorded from
the base of the Norfolk Carstone are derived Aptian forms (Casey, 1961) while in situ
brachiopods and ammonites at the top of the Carstone give a tardefurcata subzone and
mammilatum Biozone age (Casey, 1961; Casey and Gallois, 1973).
(iv) The Gault subcrop on the northern flank of the London-Brabant Platform is variously of the
loricatus, lautus or inflatum Biozone, and rests directly on Palaeozoic rocks. The Gault Clay
thins from west to east from its Cambridgeshire outcrop as it oversteps the Palaeozoic rocks
of the platform (Fig. 8).
GERMANY
There is a wealth of useful, highly-detailed and factual data on the Albian age strata of Germany
(e.g. for references and discussion:Kemper, 1973, 1979). This is a direct result of the economic
significance of the Early Cretaceous strata for hydrocarbon exploitation in Germany. From a brief
perusal of the literature, it is apparent that there has been a distinct polarisation of the foraminiferal
research effort on the Early Cretaceous strata of NW Europe. This polarisation, or separation into two
camps, is a result of geography and economics. The two camps are: (a) United Kingdom—southern
North Sea—West Netherlands Basin—London Paris Basin research; and (b) Germany—East
Netherlands research.
Only relatively recently (1950’s), has there been greater communication and transfer of thoughts
and ideas between these two camps. It has to be pointed out, though, that obviously some transfer
took place throughout the 19th and 20th centuries, as most geologists are aware of the overall
similarity of the Early Cretaceous sequence of northern England with the sequence in NW Germany
(Owen, 1979).
The data available from Germany provide a valuable insight into the development of Albian age
strata in NW Europe, and has a direct consequence (or should have) and bearing on hydrocarbon
exploration in the whole of the North Sea area. More importantly, Early Cretaceous exploration plays
and concepts developed and pursued in Germany may be applicable to the North Sea area—the
southern basin in particular.
The “basal Albian” transgression is represented in Germany as a development of sands, silts,
glauconitic sands and phosphatic pebble beds which lie at the base of the “Mid-Cretaceous” section
(usually basal Gault Clay or equivalent—Kemper, 1979, Fig. 2).
The “Albian transgression”406

14. The Scheerhorn oilfield (Fig. 3; Kemper 1979) provides an excellent example of the “base
Albian” transgression, and illustrates the onlap of strata onto structural high areas. The concept of
unconformity coalescence is also illustrated, as the magnitude of the stratigraphic hiatus increases
onto the high. Part of Kemper’s illustration is reproduced here as Fig. 9. The wireline log pattern is
remarkably similar to log patterns encountered over the same stratigraphic interval in the southern
North Sea Basin and onshore southern UK (Winterborne Kingston borehole— Fig. 7) (Crittenden,
1984).
Wireline log correlation diagrams from the Albian strata of Munsterland (Fig. 10) (Schuster and
Wolburg, 1962, 1963) illustrate very dramatically the “Albian transgression” and the sand facies
associated with the transgression (Osning Sandstone). This sandstone as a lithostratigraphic unit
according to Kemper (1979) is a basin margin deposit of Early Valanginian to Middle Albian age
which flanks the northern margin of the Rhenanian Massif (see Owen, 1979).
These sands pinch-out to the north toward the basin centre—a situation very similar to
the sandstone tongues which flank the northern margin of the London-Brabant Platform in the
The “Albian transgression”408

16. West Netherlands Basin Early Cretaceous strata (NAM and RGD, 1980). Various correlation profiles
of boreholes in the Munsterland area are shown in Figs. 11-14. The work performed by Schuster and
Wolburg illustrates very well how the careful integration of micropalaeontology, lithostratigraphy,
chronostratigraphy and palaeoenvironment analysis is an important technique to help unravel the
geological history, and to develop a basin evolution model, for an area to aid hydrocarbon
exploration.
The concepts, models and exploration plays developed in Germany for Early Cretaceous strata are
important for North Sea exploration, a fact which is emphasised by NAM and RGD (1980). Their
excellent stratigraphic compendium, particularly for the Early Cretaceous, stems from the unique
position of the Netherlands, encompassing as it does two exploration areas— the West Netherlands
Basin—North Sea Basin, and the Lower Saxony Basin, of which Munsterland is a part.
CONCLUSION
The “Albian transgression” is a regional event in NW Europe which is important for the
understanding of the pattern of basin evolution during Early and “Mid” Cretaceous times. It is
important for hydrocarbon exploration in Germany and the Netherlands and is of exploration
importance in the North Sea. Structural movement of post-Cretaceous age has meant that the
arenaceous sediments associated with the transgression are not necessarily located over the crests of
present-day “Jurassic structures” as delineated by seismic surveys. The development of the
arenaceous sediments and their reservoir/trapping potential is a result of the subtle interplay of
stratigraphy and structure. In consequence, a thorough palaeogeographic understanding of the Aptian
and Albian age strata in NW Europe is essential. A borehole drilled crestally to test a
Permo-Triassic or Jurassic structural play will in most cases penetrate an overlying
thin Early Cretaceous succession. The palaeogeographic configuration of the Early
The “Albian transgression”410

18. Cretaceous strata, plus the effects of Post-Jurassic and Post-Cretaceous structural movement, mean
that although a well may be ideally located to test the Permo-Triassic—Jurassic strata, it will not
necessarily be located in an optimum position to test Early Cretaceous strata (Hesjedal and Hamar,
1983).
The concept of exploring for purely Early Cretaceous hydrocarbon plays in the southern North
Sea has been developed in recent years. The reservoir potential is present, as is the source rock
potential (Cretaceous and Jurassic), but an important question for the majority of the southern North
Sea is whether the Early Cretaceous or Jurassic source is thermally mature enough to have generated
oil. However, encouragingly, the West Netherlands Basin is a proven “oil kitchen” where Jurassic
claystones source Early Cretaceous sands. Oil is found in Early Cretaceous strata of the Dutch sector
of the southern North Sea, and it is the present Author’s opinion that before long, if purely Early
Cretaceous plays are “worked-up” and drilled, hydrocarbons may be discovered in Early Cretaceous
reservoirs in the UK sector of the southern North Sea.
ACKNOWLEDGEMENTS
The initial research upon which this paper is based was carried out at the Plymouth Polytechnic,
UK., from 1980 to 1982 under the auspices of a CASE award funded jointly by the Natural
Environment Research Council (UK) and Shell UK Exploration and Production Ltd/ Esso
Exploration and Production (UK) Ltd. I am grateful for their support. I wish to thank my research
supervisor at Plymouth, Prof. Malcolm B. Hart, for his encouragement and support. His critical
comments, instruction, patience and direction have been invaluable. I thank Carla, my wife, for her
tolerance and understanding.
The opinions expressed in this paper do not reflect those of any mentioned organization.
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