Carboniferous-Rotliegend Total Petroleum 

System Description and Assessment 

Results Summary 

By Donald L. Gautier 

U.S. Geological Survey Bulletin 2211

U.S. Department of the Interior

U.S. Geological Survey
Carboniferous-Rotliegend Total Petroleum 

System Description and Assessment 

Results Summary 

By Donald L. Gautier 

U.S. Geological Survey Bulletin 2211

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary 

U.S. Geological Survey

Charles G. Groat, Director 

U.S. Geological Survey, Reston, Virginia: 2003 

For sale by U.S. Geological Survey, Information Services


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iii 

Contents 

Foreword ........................................................................................................................................................ 1


Abstract .......................................................................................................................................................... 2


Introduction ................................................................................................................................................... 2


Province Geology and Petroleum Occurrence ........................................................................................ 2


Province Boundaries........................................................................................................................... 2


Structural-Tectonic Controls on Sedimentary Sequences ........................................................... 2


Petroleum System Summary............................................................................................................ 12


History of Hydrocarbon Exploration and Production ................................................................... 12


Total Petroleum System: Carboniferous-Rotliegend (403601) ............................................................. 14


Source Rocks ..................................................................................................................................... 14


Organic Geochemistry of Kerogen and Hydrocarbons ...................................................... 14


Burial History, Gas Generation, and Migration.................................................................... 14


Reservoirs ........................................................................................................................................... 16


Seals ................................................................................................................................................. 17


Traps and Timing ................................................................................................................................ 17


Assessment Units .............................................................................................................................. 17


Assessment Unit: Southern Permian Basin-Offshore (40360103) ....................................................... 17


Description.......................................................................................................................................... 17


Offshore Exploration Plays and Their Resource Potential.......................................................... 17


The Rotliegend Sandstone Play ............................................................................................. 17


Play Description ............................................................................................................... 17


Exploration Potential of the Rotliegend Play ............................................................... 18


Carboniferous Play ................................................................................................................... 18


Play Description ............................................................................................................... 18


Exploration Potential ....................................................................................................... 18


Zechstein Play ........................................................................................................................... 18


Play Description ............................................................................................................... 18


Exploration Potential ....................................................................................................... 18


Mesozoic Plays ......................................................................................................................... 18


Play Description ............................................................................................................... 18


Exploration Potential ....................................................................................................... 18


Assessment Unit: Southern Permian Basin-Europe Onshore (40360102) ......................................... 19


Description.......................................................................................................................................... 19


Exploration Plays and their Resource Potential ........................................................................... 19


The Rotliegend Sandstone Play ............................................................................................. 19


Play Description ............................................................................................................... 19


Exploration Potential of the Rotliegend Play ............................................................... 19


Carboniferous Play ................................................................................................................... 19


Play Description ............................................................................................................... 19


Exploration Potential ...................................................................................................... 19


Zechstein Play ........................................................................................................................... 19


Play Description ............................................................................................................... 19

iv 

Exploration Potential ....................................................................................................... 19


Mesozoic Plays ......................................................................................................................... 20


Play Description ............................................................................................................... 20


Exploration Potential ....................................................................................................... 20


Assessment Unit: Southern Permian Basin-U.K. Onshore (40360101) ............................................... 20


Description.......................................................................................................................................... 20


Carboniferous Play ............................................................................................................................ 20


Play Description ........................................................................................................................ 20


Resource Potential ................................................................................................................... 20


Undiscovered Gas Resources of the Carboniferous-Rotliegend Total Petroleum System ............ 20


References Cited ........................................................................................................................................ 22


Figures 

1. 	 Provinces, coastlines, and national boundaries associated with the Carboniferous-


Rotliegend Total Petroleum System.......................................................................................... 3 


2. 	 Prominent oil and gas fields of the southern North Sea and adjacent onshore


areas .............................................................................................................................................. 4


3. 	 Carboniferous-Rotliegend Total Petroleum System boundary, locations of oil


and gas fields, and U.S. Geological Survey World Energy Project province


boundaries .................................................................................................................................... 5


4. 	 Southern Permian Basin-Offshore Assessment Unit boundary .......................................... 6


5. 	 Southern Permian Basin-Europe Onshore Assessment Unit boundary............................. 7


6. 	 Southern Permian Basin-U.K. Onshore Assessment Unit boundary .................................. 8


7. 	 Some structural features of the southern North Sea and adjacent areas ........................ 9


8. 	 Events chart for the Carboniferous-Rotliegend Total Petroleum System ........................ 10


9. 	 Late Carboniferous Variscan orogenic front, and the distribution of Permian


Rotliegend sedimentary facies and Zechstein halite deposits .......................................... 11


10. 	 Stratigraphic column of the southern Permian Basin ......................................................... 13


11. 	 Comparison of published burial curves for Carboniferous-age rocks in and


around the southern North Sea............................................................................................... 15


Table 

1. 	 Carboniferous-Rotliegend Total Petroleum System (403601), Assessment Results


Summary—Allocated Resources ................................................................................................... 21

Carboniferous-Rotliegend Total Petroleum System 

Description and Assessment Results Summary 

By Donald L. Gautier 

Foreword 

This report was prepared as part of the World Energy 

Project of the U.S. Geological Survey. In the project, the world 

was divided into 8 regions and 937 geologic provinces, and 

the provinces were then ranked according to the discovered 

oil and gas volumes within each (Klett and others, 1997). Of 

these, 76 priority provinces (exclusive of the U.S. and chosen 

for their high ranking) and 26 emerging (boutique) provinces 

(exclusive of the U.S. and chosen for their anticipated petroleum richness or special regional economic importance) were 

selected for appraisal of oil and gas resources. The petroleum 

geology of these priority and boutique provinces is described 

in this series of reports. A detailed report containing the 

assessment results is available separately (U.S. Geological 

Survey Assessment Team, 2000). 

The purpose of the World Energy Project is to aid in 

assessing the quantities of oil, gas, and natural gas liquids that 

have the potential to be added to reserves within the next 30 

years. These potential resources reside either in undiscovered 

fields whose sizes exceed the stated minimum field-size (in 

this case one million barrels of oil equivalent) or they occur as 

potential reserve growth of fields already discovered. 

The total petroleum system (TPS) is the basic geologic 

unit of the World Energy Project. The TPS includes all genetically related shows and accumulations of petroleum (discovered and undiscovered) that (1) have been generated by a pod 

or by closely related pods of mature source rock, and (2) exist 

within a limited mappable geologic space. The petroleum system concept is modified from Magoon and Dow (1994). The 

minimum petroleum system is defined as that part of a total 

petroleum system encompassing discovered shows and accumulations together with the geologic space in which the various essential elements of the system (source, reservoir, seal, 

and overburden rocks) have been proved by these discoveries. 

An assessment unit (AU) is a mappable part of a total 

petroleum system in which discovered and undiscovered fields 

constitute a single relatively homogenous population such 

that the chosen methodology of resource assessment based on 

estimation of the number and sizes of undiscovered fields is 

applicable. A TPS might equate to a single AU or, if necessary, 

a TPS may be subdivided into two or more AUs such that each 

is sufficiently homogeneous in terms of geology, exploration 

history, and risk to be assessed individually. Assessment units 

are considered to be: (1) established units if they contain more 

than 13 fields, (2) frontier units if they contain 1 – 13 fields, or 

(3) hypothetical units if there are no discovered fields. 

A graphical depiction of the elements of a total petroleum 

system is provided in the form of an events chart, which shows 

the time of deposition of essential rock units and the timing of 

processes, such as trap formation, necessary for the accumulation of hydrocarbons. 

A unique eight-digit numeric code identifies each AU 

with respect to the region, province, and TPS. For example, 

the Southern Permian Basin-Offshore AU was assigned number 40360103. The first digit is the region number, indicating 

the AU is in Europe (Region 4). The next three digits uniquely 

identify the province; in this case the Anglo-Dutch Basin is 

number 036. The following two digits, 01, refer to the TPS, 

and the final two digits are the unique AU number (03 in this 

example). 

The codes for the regions and provinces were established 

and listed by Klett and others (1997); provinces for Europe 

(Region 4) are shown and listed in greater detail in USGS 

Digital Data Series DDS-60, the principal publication of the 

World Petroleum Assessment 2000 (U.S. Geological Survey 

Assessment Team, 2000). Oil and gas reserves quoted in this 

report are derived from Petroleum Exploration and Production 

database (Petroconsultants, 1996) and other area reports from 

Petroconsultants, Inc., unless otherwise noted. 

Figures in this report that show boundaries of the total 

petroleum systems, assessment units, and pods of active 

source rocks were compiled using geographic information 

system (GIS) software. Political boundaries and cartographic 

representations were taken, with permission, from Environmental Systems Research Institute’s ArcWorld 1:3 million 

digital coverage (1992), have no political significance, and are 

displayed for general reference only. Oil and gas field center 

points, shown on these figures, are reproduced, with permission, from Petroconsultants (1996). 
2 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary 

Abstract 

The Anglo-Dutch Basin and the Northwest German 

Basin are two of the 76 priority basins assessed by the U.S. 

Geological Survey World Energy Project. The basins were 

assessed together because most of the resources occur within a 

single petroleum system (the Carboniferous-Rotliegend Total 

Petroleum System) that transcends the combined Anglo-Dutch 

Basin and Northwest German Basin boundary. The juxtaposition of thermally mature coals and carbonaceous shales of 

the Carboniferous Coal Measures (source rock), sandstones 

of the Rotliegend sedimentary systems (reservoir rock), and 

the Zechstein evaporites (seal) define the total petroleum 

system (TPS). Three assessment units were defined, based 

upon technological and geographic (rather than geological) 

criteria, that subdivide the Carboniferous-Rotliegend Total 

Petroleum System. These assessment units are (1) the Southern Permian Basin-Offshore Europe Assessment Unit, (2) the 

Southern Permian Basin Onshore Europe Assessment Unit, 

and (3) the Southern Permian Basin Onshore United Kingdom 

Assessment Unit. Although the Carboniferous-Rotliegend 

Total Petroleum System is one of the most intensely explored 

volumes of rock in the world, potential remains for undiscovered resources. Undiscovered conventional resources associated with the TPS range from 22 to 184 million barrels of 

oil, and from 3.6 to 14.9 trillion cubic feet of natural gas. Of 

these amounts, approximately 62 million barrels of oil and 13 

trillion cubic feet of gas are expected in offshore areas, and 

26 million barrels of oil and 1.9 trillion cubic feet of gas are 

predicted in onshore areas. 

Introduction 

The Northwest German Basin and the Anglo-Dutch Basin 

of northern Europe (U.S. Geological Survey World Energy 

Project provinces 4036 and 4035, respectively) are two of the 

76 World Energy Project priority provinces. The Northwest 

German Basin is number 21 and the Anglo-Dutch Basin is 

number 39 in the World Energy Project global ranking (Klett 

and others, 1997). These basins share common boundaries 

with the North Sea Graben Province (number 4025), which 

ranks number 8 in the world. Taken together, these three provinces account for the vast majority of oil and gas resources 

known in Western Europe. The location and boundaries of 

these provinces are shown in figure 1. 

In contrast to the oil-prone North Sea Graben, the 

Anglo-Dutch and Northwest German Basins are gas-prone. 

The Groningen gas field, located just onshore in the Netherlands (fig. 2), is the largest hydrocarbon accumulation in the 

Northwest German Basin and one of the largest gas fields in 

the world. Groningen contains approximately 100 trillion 

cubic feet (TCF) of produced or proved reserves of natural 

gas. The largest field in the Anglo-Dutch Basin is the Leman 

field, in the United Kingdom continental shelf (fig. 2), which 

accounts for approximately 12 TCF of produced and proven 

gas reserves. 

The Northwest German Basin and the Anglo-Dutch Basin 

were combined for the purposes of the petroleum resource 

assessment. This lumping was considered justifiable because 

the basins are contiguous and because most of the natural gas 

in these provinces has been generated and entrapped within a 

single total petroleum system (TPS), referred to as the Carboniferous-Rotliegend TPS. Geographically, it occupies most of 

the Anglo-Dutch Basin and the Northwest German Basin as 

well as parts of the adjacent North Sea Graben and Polish-German Basin provinces (fig. 3). The Carboniferous-Rotliegend 

was the only TPS assessed in the Anglo-Dutch and Northwest 

German Basins, even though other geologically interesting but 

less economically important petroleum systems are present 

(Kockel, Wehner and Gerling, 1994; Fraser and others, 1990). 

The Carboniferous-Rotliegend TPS was subdivided into three 

assessment units, based largely on economics, accessibility, 

and exploration history; these are Southern North Sea Offshore (AU40360103, fig. 4), Europe Onshore (AU40360102, 

fig. 5), and United Kingdom Onshore (AU40360101, fig. 6). 

Province Geology and Petroleum 

Occurrence 

Province Boundaries 

The Anglo-Dutch Basin and the Northwest German Basin 

geologic provinces are contiguous regions (fig. 1) that include 

onshore and offshore areas of Belgium, Denmark, France, 

Germany, United Kingdom, and the Netherlands. The AngloDutch Basin contains a number of smaller sub-basins, including the Sole Pit Basin (also referred to as the Sole Pit High, as 

the basin was the site of a tectonic inversion), East Midlands 

Shelf, West Netherlands, Broad Fourteens, and Central Netherlands sub-basins (fig. 7). The Northwest German Basin is also 

a compound basin, including the Lower Saxony Basin (fig. 7). 

The two provinces are bounded on the southwest and south by 

the London-Brabant Platform and the Rhenish Massif, on the 

north and northwest by the Mid-North Sea High, the Central 

Graben, the Ringkobing-Fyn High, and the Horn Graben (fig. 

7). The provinces are bounded on the east by a structurally 

positive saddle near the Polish-German border, on trend with 

the northeast-striking Hesse Depression (Ziegler, 1990), which 

is not shown on figure 7. 

Structural-Tectonic Controls on Sedimentary 

Sequences 

The elements giving rise to petroleum generation and 

accumulation in the Carboniferous-Rotliegend TPS are largely 

the result of structural and sedimentary events that took place 
Province Geology and Petroleum Occurrence 3

4025

4036 4035

4033

4039

4035

4036

Index Map

North 

Sea

0 250 KILOMETERS

UNITED KINGDOM NETHERLANDS

BELGIUM

GERMANY

DENMARK

Copenhagen

Hamburg

Bremen

Amsterdam

Dortmund

Bonn Brussels

Paris

London

Antwerpen

Northwest German Basin geologic province 4035 

Anglo-Dutch Basin geologic province 4036

Other geologic province boundary

National boundary

Oil field centerpoint

Gas field centerpoint

EXPLANATION

50°N

55°N

0° 5°E 10°E

Figure 1. Provinces, coastlines, and national boundaries associated with the Carboniferous-Rotliegend 

Total Petroleum System (403601).
0° 5°E 

55°N 

50°N 

Leman 

Clipper 

Lille 

London 

Antwerpen 

Amsterdam 

Sheffield 

Oil field 

Gas field 

West Sole D

EXPLANATION 

0 135 KILOMETERS 

Figure 2. Prominent oil and gas fields of the southern North Sea and adjacent onshore areas. 
4028

4035

4036

4037

4038

4025

EXPLANATION

Geologic province code and boundary

Total petroleum system National border

Oil field centerpointGas field centerpoint

4037

UNITED KINGDOM

DENMARK

GERMANY

NETHERLANDS

BELGIUM

Leeds

H

Sheffield

Bremen

Birmingham

Amsterdam

Rotterdam

Dortmund London Duisburg

Essen

Antwerpen

Gent

Koln

Bruxelles Bonn

Lille Liege

North

Sea

NORTHWEST GERMAN

BASIN

ANGLO-DUTCH BASIN

NORTH SEA 

GRABEN

The Hague

403601

0 150 KILOMETERS

52°N

54°N

2°W 0° 2°E 4°E 6°E 8°E 10

Figure 3. Carboniferous-Rotliegend Total Petroleum System with center point locations of oil and gas fields and U.S. Geological Survey Wor

boundaries.
40360103 UNITED KINGDOM DENMARKGERMAN

NETHERLANDS North Sea 4028 4035 4036 4037 4038 

Leeds Ham

Sheffield Bremen Birmingham Amsterdam The Hague Rotterdam 

0 150 KILOMETERS 

4037 EXPLANATION Geologic province code and boundary Assessment unit boundary National border Oil field centerpoint Gas field centerpoint 2°W 0° 2°E 4°E 6°E 8°E 10°

52°N 54°N Figure 4. Southern Permian Basin-Offshore Assessment Unit (40360103) boundary.
during Carboniferous and Permian time (fig. 8). Particularly important is the juxtaposition of the western part of the 

Southern Rotliegend sedimentary basin and related Zechstein 

evaporite deposits on the Late Carboniferous Variscan foreland 

basin (fig. 9). 

The Variscan foreland is a downward flexure, caused by 

tectonic loading north of the active Variscan orogenic belt that 

formed as African Gondwana collided with European Laurasia 

during the final stages (Visean to Westphalian) of the assembly 

of the Pangaea supercontinent. The earliest Variscan deformation probably occurred to the south of the foreland in the 

Late Devonian. Deformation progressed northward during the 

Early Carboniferous as a back-arc seaway (the Rheno-Hercynian Basin) was first closed and then deformed into a series 

of complex thrust/nappe pairs. The northernmost (and latest) 

Variscan deformation occurred during the Late Carboniferous 

and was soon followed by eruption of the Lower Rotliegend 

Volcanics (Ziegler, 1990). Tectonic relaxation of the foreland 

and Late Carboniferous tectonic inversion are represented in 

the stratigraphic record by a major unconformity at the base of 

the Upper Rotliegend (Glennie, 1998; Gast, 1993) (fig. 10). 

The rapidly subsiding Variscan foreland accommodated 

as much as 9,000 m of nonmarine sedimentary rocks of 

Westphalian age, collectively called the Coal Measures 

(Collinson and others, 1993), that accumulated at tropical 

40360102 4033

Odense

Hamburg

Bremen

4036

4037

4046

4038

Amsterdam

The Hague

Rotterdam

Duisburg Dortmund

Essen Antwerpen

Gent

Koln

Bruxelles Bonn

Liege

4035

4036 LOWER SAXONY BASIN

LONDON-BRABAN

PLATFORM

North

Sea

DENMARK

GERMANY

NETHERLANDS

BELGIUM

Robertson projection, Central meridian 0

EXPLANATION

Geologic province code and boundary

Assessment unit 40360102

National border

Oil field centerpoint

Gas field centerpoint

4037

0 100 KILOMETERS

4°E 6°E 8°E 10°E 12°E

52°N

54°N

Figure 5. Southern Permian Basin-Europe Onshore Assessment Unit (40360102) boundary.

Province Geology and Petroleum Occurrence 7
8 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary

latitudes with luxuriant vegetation in a variety of depositional 

settings within extensive fluvial systems. In northwestern 

continental Europe and the southern North Sea, these 

fluvial systems generally flowed northward, whereas in the 

British Isles and the central North Sea, fluvial systems were 

southward flowing (Ramsbottom and others, 1978; Ziegler, 

Figure 6. Southern Permian Basin-U.K. Onshore Assessment Unit (40360101) boundary.

40360101

4036

1°W 0°

53°N

54°N

55°N

4037

North

Sea

UNITED

KINGDOM

Leeds

Sheffield

EXPLANATION

Geologic province code and boundary

Assessment unit boundary

Oil field centerpoint

Gas field centerpoint

4037

0 50 KILOMETERS
M I D N O R T H S E A H I G H 

CENTRAL 

GRABEN 

L O NDON - BRABANT PLATFORM 

Shallow Paleozoic basement 

Basin/graben boundary Fault 

SOLE PIT HIGH 

FOURTEENS BROAD NETHERLAND

CENTRAL 

NETHERLAND

WEST

EAST MIDLANDS SHELF 

RING K O 

5°W 0° 5°E 

55°N 

50°N 

Figure 7. Some structural features of the southern North Sea and adjacent areas. 

EXPLANATION 
Figure 8. 0

600

500

400

300

200

100

50

550 

450

350

250

150

PERMIAN

TRIASSIC

JURASSIC

570

510

439

408

363

248

206

144

65

PRECAMBRIAN

CAMBRIAN

ORDOVICIAN

SILURIAN

DEVONIAN

323 

290

EMLEEE

E 

EMMEEEE

M 

LLLLLLMLML

L 

MISSISSIPPIAN

NEOGENE

24 

EOC. 

OLIGOCENE 

MIO. 

PLIOCENE 

PRCR

GENE

TR

OV

RE

SESO

RO

S

GETI

SC

Events chart for the Carboniferous-Rotliegend Total Petroleum System. 

CRETACEOUS 

PALEOGENE 

PENNSYLVANIAN

PAL.
0° 4°E 8°E 

54°N 

52°N 

DENMARK 

GERMANY BELGIUM 

UNITED KINGDOM 

NETHERLANDS 

ANGLO-DUTCH BASIN 

NORTHWEST GERMAN BASIN 

50 0 50 100 150 200 250 MILES 

50 0 50 100 150 200 250 300 350 KILOMETERS 

EXPLANATION 

National b

Sand Sand and conglomerate Halite and shale 

Front of V

Sand and shale Sulphate and shale Zechstein halite 

Geologic p

Figure 9. Late Carboniferous Variscan orogenic front, and the distribution of Permian Rotliegend sedimentary facies and Zechstein Ziegler, 1990). 
12 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary 

1990). Coals and carbonaceous shales in the fluvial sequences 

are thought to be the source rocks for natural gas in the 

Carboniferous-Rotliegend TPS (Cornford, 1998). 

Permian sedimentary rocks record profound changes in 

climate, vegetation, and sedimentary processes in the Variscan 

foreland. A decrease in the rate of erosion of the adjacent 

highlands and northward drift of Pangaea into arid latitudes 

resulted in declining sediment supply and continuous desertification (Ziegler, 1990). In the Southern Permian Basin, which 

trends east-west between the northeast coast of England across 

the southern North Sea and into northernmost Germany and 

southern Denmark, continental desert sedimentary sequences, 

collectively constituting the Rotliegend, were deposited at the 

site of the old foreland basin (Glennie, 1998). Alluvial fans 

and braid-plain deposits that accumulated near the Variscan 

front grade northward into eolian and fluvial (wadi) facies, 

and, farther north, to sabkha and desert-lake evaporites and 

shales such as the Silverpit Claystone Formation (fig. 10) 

(George and Berry, 1997). 

The end of Permian glaciation caused global sea level rise 

and marine transgression across the Rotliegend desert. The 

Zechstein sea expanded into the Southern Permian Basin from 

the north, probably flowing along pre-existing Proto-Atlantic 

and Proto-North Sea fracture systems. The basin is believed 

to have lain below sea level prior to the Permian Zechstein 

transgression, and the scouring, reworking, and soft-sediment 

deformation seen in the uppermost Rotliegend is consistent 

with speedy filling of the basin (Glennie, 1990; 1998). Organic 

carbon-rich mud of the Kupferschiefer (Copper Shale) draped 

desert sediments and basal Zechstein lag deposits. High evapotranspiration rates in conjunction with restricted flow caused 

persistent evaporite accumulation. The resulting Zechstein 

Group consists of thick carbonate and evaporite rocks that are 

largely of Late Permian age (Taylor, 1998). The Zechstein is 

present throughout the southern North Sea and onshore areas 

of northwestern Europe, especially in England, Denmark, 

the Netherlands, Germany, Poland, and Lithuania. Zechstein 

evaporites occupy two sub-basins, the southern one of which 

coincides with the boundaries of the Carboniferous-Rotliegend 

TPS, wherein the Zechstein is more than 2,000 m thick. 

In the southern North Sea and on the continent, the 

Zechstein is characterized by four major (Z1, Z2, Z3, Z4) and 

one or more minor cycles of evaporite deposition. The ideal 

cycle, reflecting increasing evaporation and salinity through 

time, consists of (1) a thin basal clastic deposit, (2) a middle 

limestone, dolomite, anhydrite, and halite sequence, and (3) an 

upper unit of bittern salts of magnesium and potassium. Each 

successive cycle is more evaporitic than the previous one, and 

there is an inverse correspondence between areal distribution 

of evaporite facies and intensity of evaporation (Tucker, 1991); 

for example, carbonate rocks are much more extensive than 

halite or bittern salts. 

A deep basin model has been popular among geologists 

studying the German Zechstein for many years, but lithologic 

and stratigraphic relations in the southern North Sea Basin 

seem to require additional constraints. In particular, the large 

volumes of evaporites indicate continual or episodic influx of 

marine water, as might result from the presence of a sill that 

separated the evaporite basin from its water source. Close 

examination of various Zechstein cores and outcrops seems 

to indicate episodes of partial to complete desiccation of the 

Zechstein basin (Tucker, 1991; Kiersnowski and others, 1995). 

Carbonate rocks form platform and slope facies that 

bound the margins of the first three evaporite cycles (Z1–Z3). 

Such carbonates can locally form reservoir rocks, but they do 

not serve as seals to gas accumulations in underlying Rotliegend reservoirs. Some basin-center carbonate rocks, however, 

have low porosities and permeabilities and are effective parts 

of the seal-rock system. Thick halite beds are prominent in 

the second Zechstein cycle (the Z2 beds), which, in addition to 

providing tight seals, are the main salts involved in the diapiric 

movements that have influenced oil entrapment in the southern 

and central North Sea (Schultz-Ela and Jackson, 1996). 

Petroleum System Summary 

Over a wide area of the southern North Sea, and adjacent onshore areas of Europe and England, hydrocarbons are 

predominantly found associated with the same source rocks 

(Carboniferous Coal Measures), reservoir rocks (Permian Rotliegend sandstones), and evaporite seals (Zechstein) that combine to form the Carboniferous-Rotliegend TPS. The southern 

boundary of the TPS is determined by the northern edge of the 

old Variscan deformed zone. The northern, eastern, and western boundaries are near the approximate limit of the evaporite 

facies of the Zechstein (fig. 9). This single petroleum system 

accounts for most hydrocarbon accumulations in this area and 

forms the basis for resource assessment. 

History of Hydrocarbon Exploration and 

Production 

The geographic area encompassed by the Carboniferous-Rotliegend TPS became the site of one of the world’s first 

oil developments when production began in Lower Saxony in 

1858 (Kockel and others, 1994). Although this development 

established hydrocarbon production in the area, the Lower 

Saxony oil is not geologically part of the Carboniferous-Rotliegend TPS but instead was generated from Mesozoic source 

rocks such as the Posidonia Shale (not shown in figure 10). 

The defining event in the development of the Carboniferous-Rotliegend TPS occurred in 1959, when a wildcat well 

(the Slochtern-1) discovered a gas-bearing Rotliegend sandstone 180 m thick. Seismic exploration and additional drilling 

identified a large, gas-bearing structure (Stauble and Milius, 

1970) that became known as the Groningen field (figs. 2, 7). 

It was initially estimated to contain about 58 trillion cubic feet 

(TCF) of natural gas, but subsequent work has increased the 

estimated recoverable resources to about 100 TCF (Glennie, 

1997a). The discovery of this prolific gas field changed the 

energy landscape of Europe; in a region where every town 
Province Geology and Petroleum Occurrence 13 

SW NE

Ma 

CENOZOIC JURASSIC TRIASSIC PERMIAN CARBONIFEROUS 

MIDDLE 

MIDDLE 

INVERSION 

INVERSION 

BANK HIGH 

(Extensional thermal uplift) 

CHALK 

GROUP 

LIAS 

GROUP 

AGE Midland Shelf Sole Pit 

High 

Mid-North Sea 

High 

Central Graben 

(Dutch Sector) ROCK UNIT 

SEA 

GROUP 

COAL 

MEASURES 

BARREN RED 

MEASURES 

CARBONIFEROUS 

LIMESTONE 

HOLLAND 

VLIELAND 

DELFLAND 

SCRUFF 

WERKENDAM 

KEUPER 

BUNTER 

ZECHSTEIN 

Sole 

Group 

MUSCHELKALK 

U. ROTLIEGEND 

SAALIAN UNCONFORMITY 

Dinantian 

INVERSION 

INVERSION 

Red 

Chalk 

Speeton 

Clay 

Humber 

Group 

Haisborough 

Group 

Bactron 

Group 

Winterton 

Namurian 

Leman Sandstone 

Graben - Flank fault 

EUSTATIC FALL IN SEA LEVEL 

CRETACEOUS

EARLY 

LATE 

EARLY 

EARLY 

EARLY 

LATE 

LATE 

LATE 

MID TERTIARY 

LATE 

CRETACEOUS 

LATE CIMMERIAN TECTONISM 

INDE-CLEAVER 

NORTH 

West 

NOT PENETRATED 

POST-VARISCAN 

LATE 

CRETACEOUS 

Silverpit Clst./Ten Boer Fms. 

50 

100 

150 

200 

250 

300 

350 

EXPLANATION 

Sandstone Dolomitic Volcanics 

Chalk Evaporites Unconformity

Limestone Shale 

Figure 10. Stratigraphic column of the southern Permian Basin (modified from Glennie, 1997a). 
14 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary 

previously relied on coal, or had its local town-gas facility, gas 

was delivered via pipeline from the Groningen field. 

Original work by K.W. Glennie and others at Royal 

Dutch Shell (Glennie, 1970, 1972) led to the interpretation of 

the Rotliegend reservoirs as eolian deposits and identified the 

source rock as Carboniferous Coal Measures. The investigations also indicated the possible existence of gas accumulations offshore, with the result that exploratory drilling in the 

United Kingdom sector of the North Sea was undertaken in 

1964. After a few unsuccessful wells, the West Sole gas field 

(fig. 2) was discovered in late 1965, confirming the facies 

model and exploration concept. This initial discovery was 

followed closely by a string of successes that pursued the 

Carboniferous-Rotliegend play model through large structural 

closures in the southern North Sea (Brennand and others, 

1998). 

By 1969, the large discoveries saturated the United Kingdom gas market, which at that time was managed as a monopoly by the British Gas Council (later British Gas), and led to a 

dramatic downturn in drilling during the 1970s. Exploration 

companies then turned north to explore for oil in the central 

and northern North Sea. However, in 1981, fearing a national 

gas shortage, British Gas raised the price for new gas, starting 

a renewed pattern of discovery and development that continues 

to the present. As of 1997, 290 gas fields had been discovered 

offshore in the southern North Sea, accounting for approximately 75 TCF of recoverable natural gas and more than 400 

million barrels of oil (MMBO). Onshore in the Netherlands 

and Germany, more than 229 gas fields had been discovered 

accounting for about 150 TCF of gas, as well as some oil and 

natural gas liquids. 

Total Petroleum System: 

Carboniferous-Rotliegend (403601) 

Source Rocks 

Coals and carbonaceous shales of the Westphalian-age 

(Carboniferous) Coal Measures (fig. 10) are believed to be the 

principal source rocks for gas accumulations in the southern 

North Sea and adjacent areas (fig. 2) (Cornford, 1998). By 

even conservative estimates, the generative capacity of the 

Coal Measures is considered to far exceed the amount of gas 

presently discovered (Barnard and Cooper, 1983; Cornford, 

1998). 

Although complex in detail, the Coal Measures in general 

consist of upward-coarsening deltaic rocks that are overlain by 

fluvial deposits and associated coals. The fluvial rocks include 

conglomeratic, complexly stacked sandstones attributed to 

deposition in major braided stream systems. Within the bounds 

of the Carboniferous-Rotliegend TPS, the Coal Measures are 

probably 1,000 to 3,000 m thick (Leeder and Hardman, 1990), 

although reliable estimates are difficult to make. Elsewhere 

the Carboniferous can be much thicker. Coal seams account 

for about 3 percent of the total stratigraphic sequences (Lutz 

and others, 1975), and carbonaceous shales account for a 

much larger percentage (Cornford, 1998). 

Organic Geochemistry of Kerogen and 

Hydrocarbons 

Westphalian coals and carbonaceous shales are dominated by type III kerogen, which is rich in vitrinite derived 

from terrestrial plant tissues, and in charcoal (inertinite) 

(Cornford, 1998). Such humic kerogen displays hydrogen/ 

carbon ratios of 1.0 to 0.5 and oxygen/carbon ratios of 0.4 

to 0.02, both of which decline as time-temperature exposure 

increases (Hunt, 1995). 

According to Cornford (1998) and Bernard and Cooper 

(1983), relatively little information concerning gas composition in the southern North Sea has been publicly released. In 

any case, correlation of natural gases to particular source rocks 

is difficult. Generally, gases of the Carboniferous-Rotliegend 

TPS are reported to be sweet, dry gas with carbon isotopic 

compositions consistent with derivation from strata of the Coal 

Measures (-22 to -28o/oo, PDB for gases, compared with -22 

to -25o/oo, PDB for kerogen). Regional trends in carbon dioxide and nitrogen content have been reported (Boigk and Stahl, 

1970; Boigk, 1981; Kettel, 1982, 1989; Krooss and others, 

1995); the most significant trend being an increase in nitrogen 

content eastward from the northern Netherlands and Groningen, where nitrogen content is about 4 percent and about 15 

percent, respectively, into Germany and Poland where nitrogen 

is so abundant that the gas is considered uneconomic. Kettel 

(1982, 1989) and Krooss and others (1993, 1995) have argued 

that such a trend reflects the increasing contribution of latestage gas generation from the most thermally mature terrigenous source rocks. 

Burial History, Gas Generation, and Migration

 Carboniferous strata in the undeformed foreland basin 

north of the Variscan highlands emerged from the Paleozoic 

without having been buried sufficiently for maximum gas 

generation (fig. 11). Within the deformed zone, south of the 

Variscan front (fig. 9), most Carboniferous rocks have been 

metamorphosed to at least greenschist facies, and kerogen 

has been overly mature with respect to maximum gas generation since the Late Carboniferous. Onshore in northwestern 

Europe, rank of Westphalian coal ranges from subbituminous 

to meta-anthracite, corresponding to vitrinite reflectance values of 1 to 3 percent (Cornford, 1998). 

North of the Variscan front (fig. 9), post-Paleozoic burial 

of Coal Measures strata has occurred to various degrees 

from the Triassic to the present day. However, the burial 

history has differed considerably from place to place (fig. 

11). Several areas of post-Carboniferous gas generation have 
Total Petroleum System: Carboniferous-Rotliegend (403601) 15 

DEPTH (Km) 

0 

2 

4 

6 

8 

CARBONIFEROUS 

TIME (MILLIONS OF YEARS BEFORE PRESENT) 

300 200 100 0 

Horn 

Graben 

Broad Fourteens 

Basin 

TYPE lll 

KEROGEN 

Sole Pit 

High 

Central 

Graben 

NE SW 

North 

German 

Basin { 

PERMIAN

TRIASSIC

JURASSIC CRETACEOUS TERTIARY 

Figure 11. Comparison of published burial curves for Carboniferous-age rocks in and around 

the southern North Sea (after Cornford, 1998). 

been identified based upon lithology, kerogen content, and In the Sole Pit High, the Coal Measures were rapidly 

reconstructed burial and time-temperature history. In the buried from the time of deposition until the end of the 

southern North Sea these areas include the Sole Pit High, the Cretaceous, when they had reached depths as great as 4,000 

West Netherlands and Broad Fourteens Basins, and northern m (Cornford, 1998). The burial depths are indicated by 

Germany-southern Denmark (Fig. 7). stratigraphic reconstruction, sonic velocity, fission track 
16 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary 

analysis, and measured vitrinite reflectance values ranging 

from about 1 percent near the basin margin to nearly 3 percent 

near the basin axis (Cornford, 1998; Glennie and Boegner, 

1981). These data have been interpreted to indicate that at least 

one and possibly two episodes of gas generation and migration 

from the basin center to basin-flanking traps occurred between 

Early Jurassic and Late Cretaceous time. Thinning and onlap 

of the Chalk Group onto the Sole Pit High (fig. 7) indicate a 

Late Cretaceous inversion from a structural low to a structural 

high. This inversion is believed to have caused remigration 

of gas, making structural interpretation of gas accumulations 

and thermal maturity difficult (Green and others, 1995). 

Another inversion of the Sole Pit Basin during the Tertiary 

evidently resulted in erosion or non-deposition of pre-Miocene 

rocks (Glennie, 1997a; Alberts and Underhill, 1991). Similar 

two-stage inversions also occurred in the West Netherlands 

Basin and in the Broad Fourteens Basin, although the Late 

Cretaceous inversion was relatively stronger in those basins 

than in the Sole Pit High, where the Tertiary inversion seems 

to have had greater effect (Cornford, 1998). 

Areas of deep burial and subsequent inversion, such 

as the Sole Pit High and the West Netherlands Basin, are 

probably the sites of gas generation for the gas fields in the 

southern North Sea. In the Coal Measures, most gas generation occurred at vitrinite reflectance values of 1 to 3 percent, 

corresponding to the Middle Jurassic in the Sole Pit High 

and Broad Fourteens Basin (fig. 11) and only slightly later in 

the Central Netherlands Basin (Cornford, 1998). The timing 

of generation is estimated from burial history modeling and 

from K/Ar ages of diagenetic illite in gas-bearing sandstone 

reservoirs of the Rotliegend (Hamilton and others, 1989). In 

the vicinity of the Sole Pit, gas migration is believed to have 

occurred after 158±18.6 Ma (Robinson and others, 1993). In 

the Broad Fourteens, gas entered the reservoirs after 140 Ma. 

Most of the natural gas entrapped onshore, especially 

that of the Groningen field, is believed to have been generated in northern Germany and southern Denmark, but possibly also just offshore in the West Netherlands Basin (fig. 

7). Additional onshore gas generation may have taken place 

as a result of contact metamorphism (Glennie, 1986). K/Ar 

studies of authigenic illite in the Rotliegend reservoirs of the 

Groningen field indicate the structure was progressively filled 

over a period of about 30 million years. Natural gas entrapped 

onshore in the southern United Kingdom was probably also 

generated from Carboniferous strata, although specific source 

rocks and generation sites are not well known. 

In the Carboniferous strata of northeastern England, 

the coals and shales constitute two distinct source rock 

components, with the coals containing approximately 60 

percent total organic carbon (TOC) and type III kerogen, 

whereas the shales have approximately 1 percent TOC and 

mixed type II and type III kerogen. Marine shales range 

from less than one percent to several percent TOC, mostly 

in type II kerogen. Oil accumulations are directly related to 

the presence of prodelta marine shales with type II kerogen. 

Source rocks became mature for oil and other liquids as early 

as the Late Carboniferous in some areas. Although these 

diverse Carboniferous source rocks were included in the World 

Energy Assessment (U.S. Geological Survey Assessment 

Team, 2000) of this area, at least the oil-prone shales are 

considered to constitute a separate petroleum system. 

Reservoirs

 Sandstones of the Rotliegend are the predominant reservoirs of the Carboniferous-Rotliegend TPS, accounting for 

more than 85 percent of the discovered gas accumulations in 

the offshore and virtually all of the gas in the giant Groningen 

field onshore in the Netherlands. In addition, these sandstones 

have significant potential for undiscovered small accumulations offshore and for further growth of reserves in existing 

fields. However, much of the undiscovered natural gas in 

the southern North Sea may occur in sandstones of the Coal 

Measures, adjacent to the carbonaceous source rocks, and in 

the overlying Bunter Sandstone (fig. 10). 

Based upon the work of Glennie (1970, 1972) and 

many others, the Rotliegend sandstones have been attributed 

to deposition in a variety of arid, terrestrial environments. 

Dominant among these are ephemeral fluvial (wadi) systems, 

various types of eolian deposits, desert-lake environments, 

and adjacent sabkhas. According to Glennie (1998), in the 

southern North Sea and adjacent onshore areas of the Netherlands, Rotliegend facies representing these depositional 

environments are systematically arranged areally from south to 

north and stratigraphically from bottom to top. The lowest and 

southernmost sandstones and gravels of wadi and eolian origin 

give way northward and upward to successive accumulations 

of eolian sandstone, sabkha deposits, and desert-lake sedimentary sequences. 

Reservoir quality is strongly influenced by the depositional environments of the Rotliegend. Most commercial gas 

accumulations are found in eolian dune deposits, with some 

production coming from fluvial facies. Those sandstones 

with the cleanest, best porosity at the time of deposition, and 

those sandstones deposited away from the water table tend 

to display the best preservation of porosity and permeability. 

Eolian facies of all types generally make better reservoirs than 

do interdune deposits, laterally adjacent wadi and sheet flood 

deposits, or any other fluvial, alluvial, or sabkha rocks. The 

best reservoirs are thus commonly found in the middle of the 

Rotliegend, within which eolian facies predominate (George 

and Berry, 1993; 1997). However, considerable variation in 

reservoir quality exists within the eolian facies. Compared 

to horizontally stratified, finely laminated ripple strata of the 

dune bases and tops, the more steeply dipping foreset beds, 

consisting of avalanche and grainfall strata, tend to be initially 

less compacted and to be less affected by burial diagenesis 

(Glennie and others, 1978). 

Diagenesis is a problem for reservoir quality in 

the Rotliegend. Fluvial sandstones are commonly so 

extensively altered by diagenetic processes as to render them 
Assessment Unit: Southern Permian Basin-Offshore (40360103) 17 

noncommercial for hydrocarbon production (Glennie and 

others, 1978). Effects of compaction, pressure solution, and 

precipitation of chlorite all negatively impact the porosity and 

permeability of Rotliegend reservoirs. However, the most 

damaging diagenetic effect is the precipitation of fibrous 

illite in sandstones that had already undergone significant 

porosity reduction (Ziegler, 1992). Successful gas production 

of illitized reservoirs is only possible where there has been 

natural fracturing, such as the inversion fractures observed 

at Clipper or West Sole fields (fig. 2), or where directional 

drilling and expensive reservoir engineering is employed 

(Glennie, 1998). 

Seals 

Evaporite deposits of the sabkha and desert-lake 

sequences of the Rotliegend may seal gas accumulations in 

underlying Carboniferous reservoirs, but the Zechstein salt 

is the seal for virtually all gas accumulations in Rotliegend 

reservoirs themselves. The near-perfect seal of the Zechstein is 

the main reason for the existence of the large gas fields of the 

Carboniferous-Rotliegend TPS. Radiometric ages of diagenetic illite in the reservoirs show that the Zechstein evaporites 

have effectively sealed gas in structural and stratigraphic traps 

for approximately 150 million years (Lee and others, 1985; 

Hamilton and others, 1989; Robinson and others, 1993). These 

observations are consistent with Klemme’s (1983) assertion 

that giant gas fields are in large structures that have highly 

effective seals. 

Traps and Timing 

Gas accumulations in Carboniferous reservoirs depend 

upon traps developed (1) wholly within the Carboniferous, (2) 

by lateral facies changes from sandstone or gravel to mudstone 

which occurs within the thick sequences of fluvially dominated rocks, and (3) by being sealed beneath the desert-lake 

evaporites of the Rotliegend (for example, Silverpit Claystone 

Formation). Gas-bearing structures found to date consist of 

Variscan-age folds and various Late Jurassic – Early Cretaceous and Late Cretaceous – early Tertiary uplifts. However, 

intraformational stratigraphic traps could also have developed 

where thermally mature coals or carbonaceous shales are in 

contact with the reservoirs. 

Gas accumulations in Upper Permian Rotliegend strata 

depend upon the juxtaposition of mature Carboniferous source 

rocks, the Rotliegend sandstone or conglomeratic reservoir 

rocks, and the Zechstein evaporite seals. Effective gas 

trapping structures formed after deposition of the evaporite, 

but were of insufficient magnitude to breach the seal. These 

gas-filled structures date from the Late Jurassic to Early 

Cretaceous and from the Late Cretaceous to early Tertiary. In 

addition, transpression in the Tertiary caused localized basin 

inversions that also resulted in the development of gas-bearing 

structures. Diapiric movements of the Zechstein salt at various 

times in the burial history have also been responsible for 

primary gas-bearing structures and traps for remigrated gas. 

Assessment Units 

The close relations and similar distribution patterns of 

Carboniferous source rocks, Rotliegend sandstone reservoirs, 

and Zechstein evaporites in gas fields led to the decision to 

consider the voluminous gas accumulations of the southern 

North Sea and adjacent onshore areas of Europe as forming 

a single petroleum system—the Carboniferous-Rotliegend 

TPS (AU403601, fig. 3). Division into assessment units was, 

however, based upon technological and geographic criteria 

rather than upon geological distinction. Three AUs were 

identified: (1) the Southern Permian Basin-Offshore Europe 

(AU40360103, fig. 4), (2) the Southern Permian BasinOnshore Europe (AU40360102, fig. 5), and (3) Southern 

Permian Basin Onshore United Kingdom (AU40360101, fig. 

6). Within the AUs, various geologic settings of hydrocarbon 

accumulation, informally referred to here as exploration plays, 

were considered for resource assessment purposes. 

Assessment Unit: Southern Permian 

Basin-Offshore (40360103) 

Description 

The Southern Permian Basin-Offshore AU coincides with 

the extent of the Carboniferous-Rotliegend TPS in the offshore area of the southern North Sea between England and the 

European continent (fig. 4). It is bounded on the south by the 

London Brabant Platform and on the north by the mid-North 

Sea high (fig. 7). Northwestern and southeastern boundaries, 

respectively, are the coastlines of England and the European 

continent (figs. 1, 7). 

Offshore Exploration Plays and Their Resource 

Potential 

The Rotliegend Sandstone Play 

Play Description 

All of AU40360103 is predominantly the Rotliegend 

sandstone play, which has been the objective of intensive 

exploration since the beginning of offshore drilling. Over most 

of the area, the Coal Measures have provided abundant hydrocarbon charge in all settings and retain generative capacity 

even today. Likewise, Zechstein seal exists in almost all areas 

and seal integrity has been preserved, even in areas of intense 
18 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary 

deformation. Failures of charge are most commonly related 

to timing of structural inversion relative to gas generation or 

due to leakage in those few areas where the seals are thin. Seal 

quality also is locally inadequate where carbonate rocks supplant evaporite beds as a result of facies variation. Exploration 

uncertainties arise from poor reservoir quality where either 

the best eolian reservoir facies is absent, or where depth and 

facies-related diagenetic effects have reduced reservoir porosity and permeability. Identification of structural closures can 

be difficult, as Rotliegend closures are small compared to the 

thick and lithologically heterogeneous overburden. 

Exploration Potential of the Rotliegend Play 

The Rotliegend play is presently highly mature. Years of 

intense and expensive exploration drilling and a dense seismic 

grid appear to have identified most of the significant footwall 

closures. Nevertheless, discovery of progressively smaller 

fields continues and potential remains in limited hanging-wall 

traps, in known closures previously judged too small to warrant development, and in subtle stratigraphic traps that have 

thus far avoided detection. 

Carboniferous Play 

Play Description 

Comparatively few wells have been drilled and few fields 

have been found in the Carboniferous, but the stratigraphic 

interval remains prospective because of its substantial gas 

generative capacity and complex lithologic variations. Various 

sandstones in valley fill sequences should be of acceptable reservoir quality, but the stratigraphic complexities that characterize this thick section of fluvio-deltaic rocks make for problems 

in the location of exploration targets. Compared to the quartzose Rotliegend reservoirs, the sandstones of the Carboniferous 

are mineralogically immature. Consequently, loss of reservoir 

quality from burial-related compaction and diagenesis may 

be the limiting factor in successful development of reservoir 

targets within the Carboniferous. So far, all Carboniferous 

discoveries have been in two structural settings—the Variscan 

folds and the post-Paleozoic structures reactivated during tectonic inversion. Traps are expected to result from lateral and 

vertical permeability barriers at the margins of discontinuous 

sandstones. The best seals are probably the Permian desertlake evaporites such as the overlying Rotliegend Silverpit 

Claystone Formation (fig. 10). 

Exploration Potential 

The Carboniferous strata have considerable exploration 

potential in offshore settings, but technical problems involved 

with exploration have so far discouraged extensive drilling. 

The lateral and vertical variability of sedimentary facies, 

the difficulties in discerning gas-saturated rocks within the 

complex lithologies, and the paucity of reliable stratigraphic 

markers offshore combine to make fields in the Carboniferous 

difficult to exploit given current exploration technology and 

economics. Nevertheless, the Carboniferous is probably the 

most prospective stratigraphic interval remaining in the southern North Sea. Success will require the ability to overcome 

seismic imaging problems in order to identify thick channel 

sandstones that are gas-charged. 

Zechstein Play 

Play Description 

Shelf-edge and slope carbonate facies of the Zechstein 

are potential exploration targets. Oil-prone source rocks, such 

as the Kupferschiefer Shale, could provide a local charge, but 

the most likely potential would be realized where Zechstein 

carbonates are charged from the Carboniferous Coal Measures 

underlying the Rotliegend. Except for Z-1 carbonates, which 

are not separated from the Rotliegend by salt, this scenario 

requires that the near-perfect Zechstein seal be breached. 

Exploration Potential 

Although oil, gas, and condensate are produced from the 

Zechstein in Germany, Poland, and the Netherlands, where the 

source rock is the Stinkschiefer Shale, the Zechstein has never 

yielded much gas in offshore areas. Nevertheless, moderate to 

small stratigraphic traps for gas and possibly for Zechstein oil 

may be expected. Loss of reservoir quality in the carbonate 

facies adjacent to the evaporites, however, may substantially 

reduce the economic potential of these small traps. 

Mesozoic Plays 

Play Description 

Gas accumulations sourced from the Coal Measures have 

been discovered within the Triassic Bunter and Hewett Sandstones (fig. 10) in fault-bounded anticlines. Other possibilities for undiscovered accumulations include stratigraphically 

entrapped gas within the Bunter, as well as within the overlying Lower Cretaceous sandstones. 

Exploration Potential 

Obvious structures including Bunter and younger reservoirs have been tested, which leaves relatively subtle stratigraphic or structural traps as remaining exploration targets. 

An obvious negative aspect of this play is the Zechstein and 

Rotliegend seals, which are as effective in shielding these 

sandstones from a gas charge as they are at preventing leakage 

from Rotliegend and Carboniferous reservoirs. Potential exists 

for discovery of additional small accumulations, possibly in 

association with other traps. 
Assessment Unit: Southern Permian Basin-Europe Onshore (40360102) 19 

Assessment Unit: Southern Permian 

Basin-Europe Onshore (40360102) 

Description 

The Carboniferous-Rotliegend TPS and the Southern 

Permian Basin-Europe Onshore AU coincide with the extent 

of thermally mature Westphalian (Coal Measures) source 

rocks and related gas and liquid accumulations in the onshore 

area on the European continent adjacent to the southern North 

Sea (fig. 5). Assessment Unit 40360102 is located mainly 

in the Netherlands and Germany, but also includes parts 

of Belgium and Denmark. It contains several sub-basins, 

including onshore areas of the West Netherlands Basin and the 

Lower Saxony sub-basins (fig. 7). The AU is bounded on the 

southwest and south by the London-Brabant Platform and by 

the Rhenish Massif, on the north and northwest by the North 

Sea and the Trans-European fault, and on the east, near the 

German border, by a structurally positive saddle on trend with 

the northeast-striking Hesse Depression (Ziegler, 1990). The 

boundary separating AU 4060103 and AU 4030102 is placed 

at the coastline because of the distinct differences in technology, economics, and regulations encountered in onshore 

versus offshore settings. Because the two assessment units 

share most formation boundaries, structural properties, and 

geologic history, the following description of exploration plays 

in the onshore assessment unit is necessarily abbreviated and 

somewhat redundant with play descriptions from the offshore 

assessment unit. 

Exploration Plays and their Resource Potential 

The Rotliegend Sandstone Play 

Play Description 

The prolific source rock capacity of the Carboniferous 

Coal Measures is present throughout the AU and can be relied 

upon to provide adequate hydrocarbon charge to fill structures, 

including fields as large as the giant Groningen gas field, to 

their spill-point (Lutz and others, 1975). Similarly, the effective seal of the overlying Zechstein carbonate-evaporite complex is present throughout the AU. All discovered Rotliegend 

fields are underlain by coals and carbonaceous shales of the 

Coal Measures and overlain by Zechstein evaporites. 

Exploration Potential of the Rotliegend Play 

The Rotliegend sandstone play has been extensively 

developed and is in a mature state of exploration. Potential for 

new discoveries is mainly in small structural traps, some of 

which have already been identified during exploratory studies 

but not drilled, and in subtle stratigraphic traps. 

Carboniferous Play 

Play Description 

The prolific gas-prone source rocks of the Carboniferous 

Coal Measures, the abundance of closely associated channel 

sandstones and related valley-fill complexes, and the presence 

of shales and evaporitic rocks of the overlying Rotliegend, 

indicate that the Carboniferous should be an important exploration target. Traps are to be expected where the Carboniferous 

is overlain by fine-grained, desert-lake facies of the Rotliegend. In this setting, accumulations could exist in structural 

closures. Accumulations may also occur as stratigraphically 

entrapped gas where lithologic boundaries within the Carboniferous provide the trapping mechanism. Possible examples 

include intraformational traps formed where Carboniferous sandstones are enclosed by fine-grained rocks or where 

unconformable contacts exist, such as at the overlying Saalian 

unconformity (fig. 10). 

Exploration Potential 

Although most of the obvious larger structures have been 

tested, the Carboniferous remains comparatively unexplored. 

Successful exploration will probably require both significantly 

improved seismic resolution and more reliable sedimentologic 

and stratigraphic models. This play and its offshore counterpart probably hold the greatest potential for new gas discoveries in the Southern Permian Basin, some of which could be 

large fields. However, burial-related diagenetic loss of reservoir quality in the highly feldspathic, lithic-rich Carboniferous 

sandstones is commonly severe, and lack of adequate porosity 

and permeability may ultimately limit resource potential. 

Zechstein Play 

Play Description 

Although the Zechstein is mainly valued as a seal, shelf 

and slope carbonate facies might represent an exploration 

target. Traps would be provided by Zechstein evaporites or 

by permeability barriers caused by lithologic discontinuities 

within the carbonate sequences. The play requires reservoirquality carbonate rocks, which have generally been limited 

to oncolitic and oolitic shelf margin facies of the Zechstein. 

Fractured reservoirs may also provide attractive targets 

(Cooke-Yarborough, 1994). 

Exploration Potential 

According to Glennie (1997a), the Zechstein was the 

original exploration target when Groningen was discovered. 
20 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary 

Oil-prone shales are present in the Zechstein, but the most 

likely potential would be where Zechstein carbonates have 

been charged by the Coal Measures underlying the Rotliegend. 

This model is risky for all but Z-1 carbonates because effective 

charge requires the Zechstein seal to have been breached. 

Mesozoic Plays 

Play Description 

Gas accumulations, sourced from the Coal Measures, 

have been discovered within the Triassic Bunter and Hewett 

Sandstones in fault-bounded anticlines in the southern North 

Sea. Other possibilities include stratigraphically entrapped gas 

within the Bunter and within the overlying Lower Cretaceous 

sandstones. 

Exploration Potential 

Most structures with Bunter and younger reservoirs have 

been tested. This leaves subtle stratigraphic traps and small 

structures within which Triassic reservoirs are in direct contact 

with pre-salt Carboniferous strata. 

Assessment Unit: Southern Permian 

Basin-U.K. Onshore (40360101) 

Description 

The total petroleum system (403601) and corresponding 

assessment unit (40360101) coincide with the extent of thermally mature Carboniferous source rocks and related gas and 

oil accumulations in the onshore area of the Southern Permian 

Basin in the East Midlands of England (fig. 6). Within this 

assessment unit only a single exploration play is defined. 

Carboniferous Play 

Play Description 

For purposes of the World Energy Project, the resource 

potential in the U.K. onshore part of the Carboniferous-Rotliegend TPS is considered to consist mainly of reserve growth 

and undiscovered accumulations within and in close association with the Carboniferous strata of part of northeast England. 

Source rocks include calcareous marine shales of Dinantian 

age and deltaic shales and carbonaceous shales and coals, 

mainly of Namurian and Westphalian (Carboniferous) age. 

Organic matter in these diverse source rocks ranges from small 

volumes of hydrogen-rich type II kerogen related to marine 

deposition, to carbonaceous shales and coals of the deltaic 

sequences. Distribution of fields in this well-explored province 

depends critically on the burial depth of good quality type II 

organic matter. 

Correlation of depth to thermal maturity of organic 

matter indicates relatively short distances of migration along 

pathways provided mainly by porous and permeable sandstones, as well as along fractures in fine-grained sedimentary 

rocks. Most reservoir rocks are of Carboniferous age, but 

also include the Old Red Sandstone, Waulsortian mounds and 

other carbonates of Dinantian age, deltaic and fluvial sandstones associated with the Coal Measures, and Permian red 

beds. Local lithologic variations provide a variety of complex 

seals, including calcareous marine shales resting above deltaic 

sandstones and lithologic variations within the sandstone-shale 

sequences of the Carboniferous. 

Resource Potential 

Hydrocarbon accumulations have been known from 

England’s Carboniferous strata since before the Second World 

War. In spite of relatively mature exploration and small 

sizes of discovered fields, the area continues to be the target 

of a rather low but persistent level of exploration interest, 

largely because of the inexpensive exploration and development programs needed to bring discoveries to market. Future 

discoveries will probably continue to consist of small, shallow 

accumulations. 

Undiscovered Gas Resources of 

the Carboniferous-Rotliegend Total 

Petroleum System 

The recent USGS World Petroleum Assessment (U.S. 

Geological Survey Assessment Team, 2000) included an evaluation of undiscovered resources in the three assessment units 

of the Carboniferous-Rotliegend TPS in and adjacent to the 

southern North Sea. The results of this assessment are summarized in table 1 and reported in USGS Digital Data Series 

DDS-60 (U.S. Geological Survey Assessment Team, 2000). 

Undiscovered resources associated with the CarboniferousRotliegend TPS in the European and United Kingdom onshore 

areas are estimated to range from 23 to 148 MMBO and 

from 5.0 to 21.6 TCF of natural gas, plus gas associated with 

undiscovered oil and quantities of natural gas liquids. Undiscovered resources in the onshore part of the United Kingdom 

are considered to be relatively minor. Offshore undiscovered 

oil resources are estimated to range from a minimum of 13 

MMBO to about 133 MMBO. Undiscovered natural gas 

resources are estimated to range from 2.8 TCF to more than 

27.6 TCF, not including additional resources of natural gas 
Table 1. Carboniferous-Rotliegend Total Petroleum System (403601), Assessment Results Summary—Allocated Resources. 

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids; MFS, minimum field size assessed (MMBO or BCFGleast one field equal to or greater than the MFS. Results shown are fully risked estimates. For gas fields, all liquids are included under the NGL (natural gas liquids) catepercent chance of at least the amount tabulated. Other fractiles are defined similarly. Fractiles are additive under the assumption of perfect positive correlation. Shading 
22 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary 

liquids and associated and dissolved gas. Thus, estimated 

mean values of undiscovered resources in the onshore and offshore areas of the Anglo-Dutch Basin and adjacent parts of the 

Northwest German Basin provinces are about 144 MMBO and 

more than 26 TCF of natural gas. These estimates are comparable to those reported by the USGS in 1997 (mean = 24 TCF) 

(Masters and others, 1997). In addition to the undiscovered 

resources, significant volumes of gas will probably be added 

to reserves as a result of growth of existing fields. 

References Cited 

Alberts, M.A., and Underhill, J.R., 1991, The effect of Tertiary 

structuration on Permian gas prospectivity, Cleaver bank 

area, southern North Sea, UK, in Spencer, A.M., ed., Generation, accumulation, and production of Europe’s hydrocarbons: European Association of Geoscientists and Engineers 

Special Publication, Oxford, Oxford University Press, p. 

161–173. 

Barnard, P.C., and Cooper, B.S., 1983, A review of geochemical data related to the north-west European gas province, in 

Brooks, J., ed., Petroleum geochemistry and exploration of 

Europe: Geological Society of London Special Publication 

12, p. 19–33. 

Boigk, H., 1981, Erdol und Erdgas in der Bundesrepublik 

Deutschland: Stuttgart, Ferdinand Enke Verlag, 330 p. 

Boigk, H., and Stahl, W., 1970, Zum Problem der Entstehun 

Nordwestdeutcher Erdgaslagerstratten: Erdol Kohle, Erdgas, and Petrochemiie, v. 23, p. 104–111. 

Brennand, T.P., Van Hoorn, B., James, K.H., and Glennie, 

K.W., 1998, Historical review of North Sea exploration, 

in Glennie, K.W., ed., Petroleum geology of the North 

Sea—Basic concepts and recent advances: London, Blackwell Science Publishers, p. 1–41. 

Collinson, J.D., Jones, C.M., Blackbourn, G.A., Besly, B.M., 

Archard, G.M., and McMahon, A.H., 1993, Carboniferous 

depositional systems of the southern North Sea, in Parker, 

J.R., ed., Petroleum geology of northwest Europe: Proceedings of 4th Conference, Geological Society, London, p. 

677–687. 

Cooke-Yarborough, P., 1994, Analysis of fractures yields 

improved gas production from Zechstein carbonates, Hewett 

field, U.K. Continental Shelf: First Break, v. 12, p. 243–252. 

Cornford, C., 1998, Source rocks and hydrocarbons of the 

North Sea, in Glennie, K.W., ed., Petroleum geology of the 

North Sea—Basic concepts and recent advances: London, 

Blackwell Scientific Publishers, p. 376–462. 

Fraser, A.J., Nash, D.F., Steele, R.P., and Ebdon, C.C., 1990, 

A regional assessment of the intra-Carboniferous play of 

northern England, in Brooks, Jim, ed., Classic petroleum 

provinces: Geological Society of London Special Publication 50, p. 417–440. 

Gast, R.E., 1993, Sequenzanalyse von aoelischen Abfolgen 

im Rotliegenden underen Verzahnung mit Kukstgensedimenten: Geologische Jahrbuch A 131, p. 117–139. 

George, G.T., and Berry, J.K., 1993, A new palaeogeographic 

and depositional model for the Upper Rotliegend, offshore 

The Netherlands: First Break, v. 12, p. 147–158. 

George, G.T., and Berry, J.K., 1997, Permian Upper Rotliegend synsedimentary tectonics, basin development and 

palaeogeography of the southern North Sea, in Ziegler, P., 

Turner, P., and Daines, S.R., eds., Petroleum geology of the 

southern North Sea: Geological Society of London Special 

Publication 123, p. 31–61. 

Glennie, K.W., 1970, Desert sedimentary environments: 

Developments in Sedimentology 14, Amsterdam, Elsevier, 

222 p. 

———1972, Permian Rotliegendes of north-west Europe 

interpreted in light of modern desert sedimentation studies: 

American Association of Petroleum Geologists Bulletin, v. 

56, p. 1048–1071. 

———1986, Development of NW Europe’s Southern Permian 

gas basin, in Brooks, J., Goff, J., and van Hoorn, B., eds., 

Habitat of Palaeozoic gas in northwest Europe: Geological 

Society of London Special Publication 23, p. 3–22. 

———1990, Lower Permian-Rotliegend, in Glennie, K.W., 

ed., Introduction to the petroleum geology of the North Sea: 

Oxford, Blackwell Scientific Publications, p. 120–149. 

———1997a, History of exploration in the southern North 

Sea, in Ziegler, Karen, Turner, Peter, and Daines, Stephen 

R., eds., Petroleum geology of the southern North Sea— 

Future potential: Geological Society of London Special 

Publication 123, p. 5–16. 

———1997b, Recent advances in understanding the southern 

North Sea Basin—A summary, in Ziegler, Karen, Turner, 

Peter, and Daines, S. R., eds., Petroleum geology of the 

southern North Sea—Future potential: Geological Society 

of London Special Publication 123, p. 17–29. 

———1998, Lower Permian-Rotliegend, in Glennie, K.W., 

ed., Petroleum geology of the North Sea—Basic concepts 

and recent advances: London, Blackwell Scientific Publishers, p. 137–173. 

Glennie, K.W., and Boegner, P., 1981, Sole Pit inversion 

tectonics, in Illing, L.V., and Hobson, G.P., eds., Petroleum 

geology of the Continental Shelf of north-west Europe: 

London, Institute of Petroleum, p. 110–120. 
23 

Glennie, K.W., Mudd, G.C., and Nagtegaal, P.J.C., 1978, 

Depositional environment and diagenesis of Permian Rotliegendes sandstones in Leman Bank and Sole Pit areas of the 

UK southern North Sea: Journal of the Geological Society 

of London, v. 135, p. 25–34. 

Green, P.F., Duddy, I.R., and Bray, R.J., 1995, Applications 

of thermal history reconstructions in inverted basins, in 

Buchanan, J.G. and Buchanan, P.G., eds., Basin inversion: 

Geological Society of London Special Publication 88, p. 

149–166. 

Hamilton, P.J., Kelly, S., and Fallick, A.E., 1989, K-Ar dating 

of illite in hydrocarbon reservoirs: Clay Minerals, v. 24, p. 

215–232. 

Hunt, J.M., 1995, Petroleum geochemistry and geology, (2d 

ed.): New York, W.H. Freeman and Company, 743 p. 

Kettel, D., 1982, Norddeutsche Erdgase—Stickstoff Gehald 

und Isotopenvariationen als Reife-und Faziesindkatoren: 

Erdol und Kohle, Erdgas, Petrochemie mit Brenstoff-Chemie, v. 35, p. 557–559. 

———1989, Upper Carboniferous source rocks north and 

south of the Variscan front, northwest and central Europe: 

Marine and Petroleum Geology, v. 6, p. 170–181. 

Kiersnowski, H., Paul, J., Peryt, T., and Smith, D.B., 1995, 

Facies, paleogeography and sedimentary history of the 

southern Permian Basin in Europe, in Scholle, P.A., Peryt, 

T.M., and Ulmer-Scholle, D.S., eds., The Permian of 

Northern Pangaea, vol. 1, paleogeography, paleoclimates, 

stratigraphy: Berlin, Springer-Verlag, p. 119–136. 

Klemme, H.D., 1983, The geologic setting of giant gas fields, 

in Delahaye C., and Grenon M., eds., Conventional and 

unconventional world natural gas resources: Laxenburg, 

International Institute for Applied Systems Analysis, p. 

133–160. 

Klett, T.R., Ahlbrandt, T.S.J., and Schmoker, J.W., 1997, 

Ranking of the world’s oil and gas provinces by known 

petroleum volumes: U.S. Geological Survey Open-File 

Report 97-463, one CD-ROM. 

Kockel, Franz, Wehner, Hermann, and Gerling, Peter, 1994, 

Petroleum systems of the Lower Saxony Basin, Germany, in 

Magoon, L. B., and Dow, W. G., eds., 1994, The petroleum 

system—From source to trap: American Association of 

Petroleum Geologists Memoir 60, p. 573–586. 

Krooss, B.M., Leythaeuser, D., and Lillack, H., 1993, 

Nitrogen-rich natural gases—Qualitative and quantitative 

aspects of natural gas accumulation in reservoirs: Erdol 

Kohle-Erdgas-Petrochem, v. 46, p. 271–276. 

Krooss, B., Littke, R., Muller, B., Frielingsdorf, J., 

Schwochau, K., and Idiz, R. F., 1995, Generation of 

nitrogen and methane from sedimentary organic matter— 

References Cited 

Implications on the dynamics of natural gas accumulations: 

Chemical Geology, v. 126, p. 291–318. 

Lee, M., Aronson, J.L., and Savin, S.M., 1985, K/Ar dating 

of time of gas emplacement in Rotliegendes Sandstone, 

Netherlands: American Association of Petroleum Geologists 

Bulletin, v. 9, p. 1381–1385. 

Leeder, M.R., and Hardman, M., 1990, Carboniferous geology 

of the southern North Sea Basin and controls on hydrocarbon prospectivity, in Hardman, R.F.P., and Brooks, J., 

eds., Tectonic events responsible for Britain’s oil and gas 

reserves: Geological Society of London Special Publication 

55, p. 87–105. 

Lutz, M., Kaaschister, J.P.H., and Van Wijhe, D.H., 1975, Geological factors controlling Rotliegend gas accumulations in 

the Mid-European Basin: Proceedings, 9th World Petroleum 

Congress, v. 22, p. 93–97. 

Masters, C.D., Root, D.H., and Turner, R.M., 1997, World 

resource statistics geared for electronic access: Oil and Gas 

Journal, v. 95, no. 41, p. 98–104. 

Magoon, L. B., and Dow, W. G., 1994, The petroleum system, 

in Magoon, Leslie B., and Dow, Wallace G., The petroleum 

system—From source to trap: American Association of 

Petroleum Geologists Memoir 60, p. 3–24. 

Petroconsultants, 1996, Petroleum exploration and production 

database: Houston, Texas, Petroconsultants, Inc. [Database 

currently available from IHS Energy Group, 5 Inverness 

Way East, D205, Englewood, CO 80112] 

Ramsbottom, W.H.C., Claver, M.A., Eagar, R.M.C., Hodson, 

F., Holliday, D.W., Stubblefield, C.J., and Wilson, R.B., 

1978, Silesian (Upper Carboniferous): Geological Society 

of London Special Publication 10, 82 p. 

Robinson, A.G., Coleman, M.L., and Gluyas, J.G., 1993, The 

age of illite cement growth, Village Fields area, southern 

North Sea—Evidence from K-Ar ages and 18O/16O ratios: 

American Association of Petroleum Geologists Bulletin, v. 

77, p. 68–81. 

Schultz-Ela, D.D., and Jackson, M.P.A., 1996, Relation of 

subsalt structures to suprasalt structures during extension: 

American Association of Petroleum Geologists Bulletin v. 

80, p. 1896–1924. 

Stauble, A.J., and Milius, G., 1970, Geology of Groningen gas 

field, Netherlands, in Michael T. Halbouty, ed., Geology of 

giant petroleum fields: American Association of Petroleum 

Geologists Memoir 14, Tulsa, p. 359–369. 

Taylor, J.C.M., 1998, Upper Permian-Zechstein, in Glennie, 

K.W., ed., 1998, Petroleum geology of the North Sea— 

Basic concepts and recent advances: London, Blackwell 

Scientific Publishers, p. 174–211. 
24 Carboniferous-Rotliegend Total Petroleum System Description and Assessment Results Summary 

Tucker, M.E., 1991, Sequence stratigraphy of carbonate-evaporite basins—Models and application to the Upper Permian 

(Zechstein) of northeast England and adjoining North Sea: 

Journal of the Geological Society of London, v. 148, p. 

1019–1036. 

U.S. Geological Survey Assessment Team, 2000, U.S. Geological Survey World Petroleum Assessment 2000—Description and results: U.S. Geological Survey Digital Data Series 

DDS-60, four CD-ROMs. 

Ziegler, Karen, 1992, Authigenic illites in the Rotliegend 

Leman Sandstone, southern North Sea—K/Ar dating, 

oxygen and hydrogen isotopes [abs.]: BSRG, 31st Annual 

Meeting, Southampton, U.K., p. 23. 

Ziegler, P.A., 1990, Geological atlas of Western and 

Central Europe (2d ed.): Shell International Petroleum 

Maatschappij, 238 p., 52 enclosures.