Sedimentary Geology, 27 (1980) 1--81 1 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in the Netherlands

Sedimentary Geology, 27 (1980) 1--81 1 © Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

PRE-PERMIAN DEPOSITIONAL ENVIRONMENTS AROUND THE BRABANT MASSIF IN BELGIUM, THE NETHERLANDS AND GERMANY

M.J.M. BLESS I J. BOUCKAERT 2, R CONIL 3, E. GROEBSENS 2 W. KASIG 4 E. PAPROTH 5, E. POTY 6, M. VAN STEENWINKEL 7, M. STREEL 8 and R. WALTER4

I Geological Bureau, Netherlands Geological Survey, Heerlen (the Netherlands) 2Geological Survey of Belgium, Brussels (Belgium) 3Lab. Paleontology, University of Louvain, Louvain-la-Neuve (Belgium) 4RWTH Aachen, Aachen (F.R. Germany) 5Geological Survey Nerthrhine-Westphalia, Krefeld (F.R. Germany) 6Lab. Paleozoology, University of Liege, Liege (Belgium) 7Lab. Paleontology, University of Leuven, Leuvan (Belgium) 8 Lab. Paleobotany and Palynology, University of Liege, Liege (Belgium)

(Received 15 March 1980)

ABSTRACT

Bless, M.J.M., Bouckaert, J., Conil, R., Grsessens, E., Kasig, W., Paproth, E., Poty, E., Steenwinkel, M. van, Streel, M. and Walter, R., 1980. Pre-Permian depositianal environments around the Brabant Massif in Belgium, the Netherlands and Germany. Sediment. Geol.,27:1--81.

Pre-Permian sedimentation in northwestern Europe has been controlled by the structural evolution of this area. Cambro-Silurian deposition has been influenced by partly synsedimentary movements (among others Ordovician- Silurian uplift south of the Brabant/Condroz zone, such as the £tavelot-Venn Massif). Presence, respectively absence of important late Caledonian deformation has subdivided northwestern Europe into three major sedimentary environments during the Devono-~arbonifarous: the Caledonian fold belt and the Cornwall- Rhenish Basin which are separated by the Belgo-Dutch platform. Subsequently, the Hercynian or Variscan orogenies have gradually reduced the sedimentary area end produced the overall withdrawal of the marine environment. Eventually, large-scale overthrusts - such as the Dinant Nappe - masked parts of the original sedimentary basins.

INTRODUCTION

Our knowledge about the Pre-Permian deposits around the Brabant Massif in Belgium, the Netherlands and Germany (Fig. I) varies from rather good for the Paleozoic outcrops in the Ardennes and the Rhenish Massif to very incomplete for the areas to the north where only few boreholes have penetrated the rocks below the coal-bearing Upper Carboniferous. The investigations on the Pre-Psrmian in the subsurface south of the Brabant Massif during the pa~ ten to fifteen years have increased our kn~w- ledge about the southward extension of the Midi Overthrust, the allochLhonous nature of the Dinant Synclinorium (here called Dinant Nappe),as well as Lh~ sediments below this Dinant Nappe. But they have also created many new problems because the facts observed during these studies did not fit into the old concepts hitherto accepted as classic. Also, the first published results of the exploration of the Pre-Permian ~n the North Sea have in part b~en quite surprising and force the geologist ~m develop new working hypotheses about the structural and sedimantological evolution of that area. The present paper summarizes several conoepts which are based upon these new findings. It should be stressed, however, that many of

+,++ ,,,,-

• o°ale~ ° oo

-,AI O - ::. ":'::';..:-:.-y:.":: D • ::. o @ D minim, I; 'l

Fig. I. Location of the Brabant Massif and the Pre-Psrmian outcrops of the Ardennes and Rhenish Massif. these ideas do not pretend to be anything more than working models that need to be checked and revised by future exploration.

Structural complication: Oinant Nappe

The evolution of northwestern Europe during Pre-Permian times can only be understood if we restore the allochthonous deposits of the Dinant Nappe to their original position. The allochthonous nature of the sediments in the Dinant Synclinorium was already suggested by Fourmarier (1913), who believed the Namur Basin to extend south of Dinant below the Midi Overthrust. This is supported by several seismic surveys recently carried out in northern France (Clement, 1963), the Famenne area of southern Belgium (non-published reports of the Geological Survey of Belgium, 1976-1978; Bless et al., ~977a, b), and in the Stavelot-Venn Massif southeast of Aachen in the F.R.G. (Bartelsen & Meissner, 1979; M. & R. TeichmUller, 1979). These investigations prove a minimum extension of the Midi Overthrust of 175x40 km (Fig. 2). However, it seams reasonable to believe that this overthrust extends beyond the area studied thus far.

Thrust-folded IBIock-fau ted autochthonous deposits allochthonous rocks I

6 cP

Fig, 2. Cartoon showing the proven extension of the Dinant Nappe, (From Bless et al., Ig8Ob.)

The hypotheses, that the overthrust does not extend across the metamorphic Ardennan Belt (Bless et al., 1977a, b; R. & M. TeichmUller, 1979) seems alrea dy out of date since the thrust plane has been traced below the Stavelot-Venn Massif (Barteleen & Meieener, 1979). It appears more acceptable to suppose nowadays that the whole Dinant Nappa was derived from the northern flanks of the Armorican-Mid German Highs. This might imply that the Cambro-Silurian rocks of the Ardannee and Btavelot-Venn Massif and most of the Lower Devonian deposits in the Dinant Nappe once formed the western extension of, say, the Taunus-HunsrUck! This hypothesis also implies that the eastern border of the Dinant Nappe might coincide more or less with the N-S trending Eifel Zone. It is worthwhile to compare the N-S trending Eifel Zone and the N-S trenoing Ems Low, occurring farther north, which may be remnants of the same old 3inea merit. Little can be said about the western extension of the nappe structure, since this is covered by a thick sequence of Mesozoic strata. If we can only speculate about the real extension of the overthrust plane, we should say less about the possible displacement along the same. One may imagine that large parts of the Dinant Nappe rest directly upon Cambro- Silurian or even Precambrian basement. But, on the other hand, it cannot be excluded without further study that Devono-Carboniferous deposits reach fez to the south below the overthrust as might be deduced from thick - partly coal-bearing - Silesian strata in the autochthonous sequence of the Jeumont Borehole in northern France, as well as from the hypothetical extension o5 Devono-Dinantian avaporite deposits (recognized in several boreholes: Annappes-1, Leuze, Tournai and St.-Ghislain) below the Famenne and Ourbuy region (Bouckaert st al., 1977; Bless et el., 1977b, 1980a).

Stratigraphical complication: reworked microfoseils

Exact knowledge of the age of sediments is indispensable for the con- struction of reliable paleogeographic maps. Frequently, the age is deter- mined by means of microfossils. Often, microfossils are only considered as useful stratigraphic tools. From that viewpoint, the occurrence of reworked specimens (derived from stratigraphically older deposits) in a microfossil assemblage may be considered as a 'contamination' that may complicate the age determination. However, such reworked microfossils can also be regaroed as a special kind of 'accessory mineral grains' in the sediment. In that case, they may help in tracing the origin of (part of) the sediment, in ~ similar way as - for instance - heavy mineral associations. The most commonly occurring reworked microfossils are palynomorphs. The ages of sediments containing reworked palynomorphs are not distributed random~ ly on the geological time scale (Fig. 3). Distinct peaks occur in the Quater- nary, Lower Tertiary, Neoeomian, Rhaet/Dogger, Westphalian, Upper Devonian/ Dinantian and Lower Devonian. The fact that these peaks become smaller - ano therefore perhaps less convincing at first sight - is easily explained if we consider the circumstance that the number of papers dealing with palyno~ morphe is much lower for older than for younger deposits. We do not believe that this curious distribution of the reworked palyno-- morph record is due to a haphazard literature compilation. It rather suggests that there were periods in geological history during which the reworking pro- case was intensified by geological phenomena. We presume that a correlation Geological Time Table Main orogenic events Quaternary Holocene IIIIIIIIIIlUlIIIIIIIIII~ [Changes of base level) Pleistocene Illllllllllll"lllllllllll/ ( Olaciahons ) Pliocene Miocene I Tertiary Oligocene Iiiin Eocene IIIIIIIIIIII '~ Paleocene IIiiiiiiiiiiii/ Loramian/ Senonian I II / 'Subhercyn ian Turonian IIII Cenomanian Cretaceous Albian IiiiiI Aptian III Barremian III Neocomian (incI.Wealden) I Late Kimmerian Maim Jurassic Dogger Lias Rhaet Early Kirnmerian Keuper Triassic Muschelkalk Buntsandstein Thuringian Permian Saxonian Autunian Stephanian Westphalian Asturian Carboniferous Narnurian I Dinantian IIII11) Upper III / Bretonian Devonian Middle Lower I, ) Ludlovian/Pridolian Late Caledonian Silurian Wenlockian Llandoverian Ordovician Cambrian

Fig. 3. Tentative correlation between recorded ages of deposits containing reworked palynomorphs and main orogenic events, as well as glaciations and sea level changes in the Quaternary. (From Streel & Bless, Ig80.) can be made between these peaks and the main orogenic events inasmuch as Tertiary and older deposits are concerned, and with glaciations and base level changes (sea level changes) during the Ouaternary. Important reworked palynomorphs assemblages in the Pre-Permian deposits around the Brabant Massif have been described from the Silurian, Lower Devonian and Upper Weatphalian (Streel & Bless, 1980). These can be related to - respectively - Late Caledonian and Late Variscan movements in north-western Europe. The presence or absence of important amounts of reworked palynomorphs in the sediment has been used as one of the arguments for recognizing the presence or absence of areas with a high relative relief Presumably, a high relative relief points to orogenic movements in the area, 6 whereas a low relative relief suggests the absence of important orogenic movements. It is believed that further investigations on reworked micrefossil occurrences may considerably improve our knowledge of the structural- depositional history of the Pre-Permian in northwestern Europe.

CAMBRO-SILURIAN

Cambrian, Ordovician and Silurian rocks are exposed at many locations or are encountered by shallow borings - in the Brabant Maaeif an~ its southern adjoining areas (Fig. 4). Nevertheless, a comprehensive paleogeographic in~ terpretation of this area is rather difficult. This is due to the lithologic monotony of the almost purely clastic rock sequence, to unreliable dating ef some formations, and to the absence of comparable outcrops in the surroundings, Therefore, the stratigraphic and paleogeographic correlation with more distant occurrences of Lower Paleozoic rocks - for instance in the British Caledonides and in the Baltic area - is problematic. A concise interpretation of the Lower Paleozoic history of the Brabant Massif would, however, enable a better understanding of the paleogeogrephic conditions in the adjacent areas of the Netherlands, northern Germany and the North Sea. The paleogeographic history of the Brabant Massif end its southern adjoining areas is even more complicated by the subsequent shortening of the Old Paleozoic deposits during the Caledonian and, partly, the Hercynian ore- geneses. The different facies zones show considerable shortening in N-S direction. A particular problem is the original location of the Lower Paleozoic of the Stavelot-Venn Maeaif. The facies correlation of the Con~roz Anticline with the Ebbs Anticline for the Ordovician period reveals that the Salm facies of Stavelot-Venn is situated at least 10 to 20 km too far to the north. Probably, this phenomenon can be explained by local far-reaching overthrusts (M. & R. TeichmOller, 1979). In the paleogeographic maps of fig. 5-10 such a displacement has been aaeumed. Consequently, the sediments of the Stavelot-Venn have been placed on these maps some 20 km to the south.

Cambrian

Detailed paleogeographic concepts of the Cambrian in the Brabant Massif and the neighbouring Ardenne Massif have been preaented by Beugnies at al~ (1976) and Colbeau et el. (1977). They confirm the general peleogeographical pattern established for Central and Western Europe by Dor~ (1977) and for the northern parts of Central Europe by Walter (1978). The Deville Series which here belong - at least partly - to the Lower Cambrian, are initially ~\ ~ ~ --.__.____.~..~,r,,,~..~:~'e~l ~ \ ~x_s ;r~ellerwalo Y~ ~"~~ Skave/o~ MASSIF'

Givonne]V[ ~'/-J"~"~ t

~p Possibly allochthonous o 5o loo km /

Fig. 4. Outcrops and borings with Lower Paleozoic rocks in the Brabant Massif and adjoin~g areas.(From Walter, 1980.) characterized by psammitic and coarse-psammitic rocks deposited in a coastal shallow-water environment. Sedimentation started with pure sands as, for instance, the Assise de Dongelberg in the Brabant Massif, the massive light- colored Dvl-quartzites of the Stavelot-Venn Massif and the quartzites of the Aseise de la Longue Hale in the Rocroi Massif. The overlying sandy-clayey sediments still include coarse-grained, partly feldspar-rich duartzites and sandstone-series (feldspar-rich sandstones and arkoses of the Assise de Tubize, reddish and green sandstones and quartzites of the Dv2 in the Stavelot-Venn Massif, arkoees and fine-conglomeratic quartzites in the Assise de Quatre Fils Aymon in the northern Rocroi Massif). But in the Stavelot-Venn Massif and, particularly, in the Rocroi Massif pure pelites also occur (roof slates of the Veine St. Anne and the Veine Renaissance). All these layers contain Oldhamie, e trace-fossil characteristic for turbiditic sedimentation. They represent deposits of a slowly deepening, well-aerated shelf area. Despite mostly homogeneous depesitional conditions in all massifs, Beugnies et al. (1976) have established a subdivision for the upper sequence of the Deville Group (Lower Cambrian) of the Brabant and Ardenne Massifs. The arkose facies of the Assise de Tubize passes from the Brabant Massif in southeastern BRABANT MASSIF CONDROZ RIDGE STAVELOT ROCROI

DEVONIAN ~ ' "/~ PEWOI~KED O¢~OOVlClAN "~ 4 000 m '~ ~-- ~ ACI~ITAI~CHS Postludlow - ~ ? O NO DEWORKED Ot~DOVICIAN Z .-. I_" .--_'-:-_L E---:-* --" --.'-- . .~. ~'_AssdeCoUbeau'~xjt ACI~ITAI~CH~; I < LUO,OW J--.----.---~--Asp__de~uq~.~.e_=o--_=. oO--AssdeThimenssrtd.~'~r-~J j ~Z) "--=----__" ~oZ_---__" ...... ~-Ass de Jonquoi~Ip'~-- Wenlock I Ass de c'xv,.t.~.... ~ " --J ----'~ ~': = ...... "-'~-'- ~ -- "A ASS de Nennine-~--~--~ "~ !

......

AshgiIl J ~-~--"-- ~ ~..~Ass de F0sse'"~----- ~-- ~ "1 ...... I LlandeH0 ------~--T E --'=~'=~'"'--~"~- ...... --'--. ~.--. I, o--o Ass.de Gemb,oux-- -- o.= Ass ...... de V,tr,.,,t.....~ val- Br.uyere ...... "--" Sm3 .... 'I ~ LI ...... I ^------I I Z--~'T=-----As~'~Ri~ e"ae--" --__----~s]~;T-- £--- .... --" C:=' / Arenig " " " ASS de fribolll~ ...... ^ ..-7~ .... O , -Ass de Huy Sml ~ , Tremadoc ' "~ -- '_--Ass.de Laroche_-- ......

Upper .;, "~..-~" ._?L __ ~ ---'~-'"~vS--?~A~ss~eVeux M0uhnde rh

I ...... --- - ...... 1 ---~_.,~1~.,-~±--~-----_-~" A ssis e-'de'~ g ' • o~-~-~>o----- Rv 3 -- o -.... Ass d Ao~hs~ - I Middle ~------Oisqu-~" "~.~-----..------"~ ,~._o~ ~ ~ --P- .... I ------~'-~ ~-- ~ ..... ~v :" "-'::" " ~ T ASS de {e Roche - & - SePt - I '~- Cambr,an I ~=-- '.-.--~-.~---:-- &=~'-=-" "~'-""_%/_~ "'-'"'-Z.""~'_"~-H ~" <~ --~--~C~~ Rv 1 -- --Ass.de Transition C.) Lower " .. --- ? Cambrian ....~-,--As. s.de Tubize ..... E---=.'Dv¢, 2,,..=. E" - Ass de QuatreFds --Ayrnon ~% _" .... ~ ".','" -" '-" ...... _ o :~:.'" ~ "'..:.=" - '- • - • : o _'" • "~ - .'_:- --_=_--z_-:.z_ • ~ .Ass:de .uo.~ngelber~. ::- ...... o.,,,~...DDv 1 ,.... o. Ass.de L0n ug.~. Heye--- PRECAMBRIAI~ .~ A ? A ,~

Fig. 5. Stratigraphic scheme of the Lower Paleozoic in the Brabant Massif and adjoining areas. (From Walter, Ig80.)

direction into a quartzite-feldspar-facies and a quartzite-facies, respectively extending from the eastern parts of the Brabant Massif through the Stavelot- Venn Massif to the northern parts of the Rocroi Massif. Further south in the Rocroi Massif a third, predominantly sandy-clayey facies of the higher Oeviiie Group has been found.

The lateral facies changes from north to south indicate an increasing distance from the source area. Mortelmans (1955) has postulated north-south transport directions for the Deville sediments in the Brabant Massif because of cross-bedding features. Sediment-petrographical observations also indicate that the feldspar and quartz of the arkoses and quartzites of the Deville Group in the Brabant Massif and in the massifs of Stavelot-Venn and Rocroi originate from a northern source area (Beugnies et al. 1976; Colbeau st al. 1977).The exact position and extension of this northern source area, and a probably subordinate southern source, is still questionable. Thus the beginning of the Cambrian is cha~act~ized by a stable shelf sea being filled mainly from a large northern high. The successive subsidence ef the shelf area was more or less compensated by the sedimentation. With the beginning of the Ravin, the depositional environment of the Brabant Massif and of the Ardenne Massif became deeper. The greyish-green, J

..... 4

/ "'-- @n.d shales - ~-- --~--'~

LATE PRECAMBRIAN/LOWER CAMBRIAN / (DEVlLLE) ~__..~o ~ookml I

Fig. 6. Lower Cambrian - Lithology and paleogeography in the Brabant Massif and adjoining areas. (From Walter, 1980.) sandy-clayey layers (base) and the massive siltstones (top) of the Assise d'Oisquerq in the central and western parts of the Brabant Massif still represent deposits of a well-aerated outer shelf sea. The contemporary black, mostly pelitic rocks with sub-ordinate arenaceous intercalations and some lydites and black limestones are definitely sediments of a less aerated, though still shallow, pelagic basin. According to Beugnies (1963), similar pelagic conditions have to be assumed as normal for the Revin sediments in the Ardenne Massifs. The continuous roof slate horizons of several metres thickness in the Rocroi Massif and the very homogeneous argillaceous series of the highest Revin (Rv5) indicate episodes of pelitic sedimentation. Typi- cal for major parts of the Ardenne massifs, however, are Revin sediments with rhythmic intercalations of dark pyritic sandstones and quartzites which, certainly, developed under similar reducing conditions to the pelites. Contrary to the normal pelitic sedimentation, they always represent short events of reworking of still unconsolidated sediments from the rims of the Revin basin into its central parts (Beugnies et al., 1976). Indications for this type of displacement are to be seen in subaquatic slWd~ngs and turbiditic features as, for instance, slumping, graded bedding, flute marks etc. (Beugnies, 1963; 10

/ J

S~ fJ - ...... -~., ,,' ~, "? ,i~ ~ • q ! "4 r ' ;,

..~' .p..~. ? little or no deposition ~

* Vol..... m and d#rk quartzites~

MIDDLE/ UPPER CAMBRIAN ? positive area ? ~, (REVtN) o ...... 50 ,, ,ook~ I

Fig. 7. Middle and Upper Cambrian - Lithology and paleogeography in the Brabant Massif end adjoining areas. (From Walter, 1980.)

Geukens, 1963a; Love and Vanguestaine, 1973; Albrecht, 1971; Mortelmans, 1977). Additionally, in many cases the petrographic composition of the Ravin quartzites matches sub-greywackea rather than orthoquartzites. The influx of psammitic sediments in the central portion of the basin increased during two periods, the lower and higher Revin (Assise de la Roche-~-Sept- Heures and Assise de la Petite Commune of the Rocroi-Massif end the beds ~ the Rv2 and Rv4 of the Stavelot-Venn Massif~ as can be deduced from widely extended quartzite-dominated intervals. In this last quartzitic interval the quartzite layers are particularly thick and they extend to the north, probably as far as the eastern Brabant Massif (Assise de Jodoigne). Quiet depositional conditions predominated again at the end of the Upper Cambrian (pure pelitic rocks of the Rv5 beds in the Stavelot-Vsnn Massif and their lithologic equivalents in the other Ardenne Massifs. The available sedimentologic data are still insufficient to define the shape of the Revin basin end the exact position of the source areas. Obser- vations in the northern Stavelot-Venn Massif suggest transport directions for the Rv4 sands f~om southern or southwestern supply areas. The northern source area had almost lost its influence. According to Beugnies at al. (1976), the greeter part of the quartz minerals in the Ravin quartzites still 11 originated from the 'North Continent'. This would, however, not contradict a predominant filling of the deepening Ardennan basin from a southern supply area if repeated displacements of unconsolidated sediments by turbidity currents are accepted.

Ordovician

Incoherent exposures and insufficient stratigraphic data and correlations of the Lower and Middle Ordcvician obscure the paleogeographic history of the Brabant Massif. Important interruptions of sedimentation can certainly be excluded for the Tremadoc-Caradoc. The laminated shales of the Assise de Laroche in the southern Brabant Massif, and of the Assise de Huy and the Assise de Sart Bernard in the Condroz Anticline confirm the classic interpretation of both areas belonging to one basin, even with comparable sedimentation rates in the beginning (Martin, 1968; Michot, 1978). A gradual increase of the sand percentage in the shale sequence in the Condroz Anticline indicates a growing mobility of the southern part of this depression. Lower and Middle Ordovician sediments in the northwestern Brabant Massif have scarcely been investigated. Anyhow, no observations exclude the possibility that the Brabant depression extended far beyond the northern border of the actual Brabant Massif. A direct contact with the equivalent deposits in southeastern England is quite probable although the Ordovician sedimentary history in that area is as yet incompletely known. Since the bulk of the Ordcvician rocks in southeastern England have been dated as Tremadoc and Llanvirn, marine conditions can very likely be presumed there for the whole Lower and Middle Ordovician. Only because of the analogy with the Stavelot-Venn Massif, continuous marine sedimentation from the Upper Cambrian into the Lower Ordovician may be assumed for the southern Ardennan massifs of Rccroi, Serpont and Givonne. After a short period of nondeposition near the Revin/Salm limit (postulated by Geukens, Ig63b), about 1000 m of alternating clays and sands, partly of flysch habitue, were deposited from Tremadoc to Caradoc. The lower Salm in particular shows local intercalations of mica-rich fine-grained sandstones with flute casts at the base, graded bedding, ripple marks and convolute bedding structures. A distinction by Schmidt (1956) between a northern sedimentary province with increasing proportions of sandstones in eastern direction, and a southern province rich in roof slate horizons, does not necessarily pre- suppose a northern continent. An increasing palectectonic mobility of the area with development of independent sub-basins may have produced the 12

h '

-- ,(> ~ S"

~ -:dark graptolitic shalesL~_ ----~j~. . ( " ~. -~und finegrained sandstones ~ ~ , , ,.~ ..-, /,~ ~-2:C.L222--2-T=-_-T-:~ i- \ local upmt r

// ~[D)E~[~I~ ==shales and - quartzdes

- ~- turMdite sandst.ones

l? positive area ? TREMADOC- LLANDEILO 0 50 100 krn

Fig. 8. Lower Ordovician - Lithology and paleogeography in the Brabant Massif and adjoining areas. (From Walter, 1980.) observed changes of facies. Richter & Scholz (1972) postulate for the south-western Stavelot-Venn Massif a direction of sediment transport from the south to the north. The intercalated characteristic red pslites of the higher Salm - representing deposits of strongly oxidizing environment - indicate the gradual shallowing of the basin (Fransolet et al., 1977). The quartzite coticules, intercalated in the same shales, have been interpreted as turfs altered by halmyrolysis (Kramm, 1976). Probably, some of the dyke- shaped magmatitss in the Lower Paleozoic of the Stavelot-Venn Massif, may be related with these volcanic events (Scherp, 1960; Geukens, 1976). In the Rhenish Massif the oldest outcropping Ordovician rocks are of Llanvirn age. The pelagic character of the Plettenbmrger B~nderschiefer and the Unterer Tonschieferhorizont of the Ebbe Anticline, however, suggest similar depositional conditions as for the Brabant Massif and the $ambre- Meuse area. A direct conned~on between these areas is quits likely. During the Upper Ordoviclan a considerable change and differentiation of the paleoenvironment took place, at least for shorter intervals. The observed unconformity within the Caradoc of the Condroz Anticline proves a local emersion of the sea floor for the middle Caradoc. Further west, indications 13

~ ~o~ ~ ~-

p [. /. / ~ /~,

--~---dar~: g~ap[ohtlc shales "t -- /

~ ""~c~oa~p/ii~e s~"~st°£~X ? pos,t,ve area /~ ? positive area ? ~ ~

~olca s

? positive area CARADOC -ASHGILL " o ..... ~o, ,ookm, t

Fig. g. Upper Ordovician - Lithology and paleogeagraphy in the Brabant Massif and adjoining areas. (From Walter, 1980.)

of submarine ridges are the occurrence of intercalated conglomerates, sudden lithologic changes from pure pslites to carbonate shallow-water sediments and some coarse sand layers. Uniform pelitic sediments in the surroundings (and during the Ashgill in the entire Condroz zone) prove that this paleotectonic mobility represents only local and limited events. They are explained as synchronous phenomena of an 'Intra-Caradocian orogenesis', which took place further south in the southern Ardenne Massifs, although definitive evidence for a true Caradocian orogenesis could not yet be established from immediate observations in these massifs. Increased paleotectonic mobility of the central and western part of the Brabant Massif is suggested for the Upper Ashgill by the accumulation of acid volcanites. This mobility is reflected in shallow-water sediments which contrast with the normal graptolite-shale facies of the Ashgill. These facies differences have repeatedly been interpreted as local unconformities (Fourmarier, 1954; Legrand, 1968). The Upper Ordovician volcanism comprised eruption of lava, ignimbritss and tuffs and various intrusives such as the Quenast Porphyry and the Lessines Porphyry. In the Rhenish Massif (Ebbs Anticline, Soest-Erwitte borehole), the pelagic basin sedimentation of the Llanvirn continued with minor variations 14 probably throughout Caradocian and perhaps even into Ashgillian time. The open-sea connection with the Brabant Massif and the Condroz Anticline, ~]- ready suggested for the Lower Ordovician, very likely continued. The same applied for the southeastern England depression.

Silurian

During the Silurian period more or less uniform sedimentary conditions prevailed in the northwestern part of Central Europe. In the Brabant Massif and in the Condroz Anticline mainly dark, laminated clays with only a few sand and silt intercalations have been deposited. These are relatively thick. The Llandoverian and Wsnlockian deposits have a thickness of up to 1150 m in the Brabant Massif and up to 500 m in the Condroz Anticline. The similar lithology and the great thickness in both areas support the idea of a coherent depression, however, with greater rate of subsidence in the Brabant Massif. Similar to the Ordovician, the differentiated subsidence in south- north direction was associated with acidic and basic lavas and tuffs in the Southern Brabant Massif and in the Condroz Anticline. An overall pelagic environment can be postulated for the pelites in the Brabant Massif, whereas in the Condroz Anticline several indications for a southern uplift are present. In the Upper Llandoverian and Wenlockian, massive sandstone intercalations with turbiditic character appear. The same sequence contains rework~ Ordovician acritarchs of excellent preservation. Their occurrence can only be explained by the reworking of non-consolidated sediments from the south (Martin, 1968, Martin et el., 1970). Reworked acritarchs have not been found in the Brabant Massif. In addition, other sedimentary features confirm the presence of a southern source area for the bulk of the psammites in the Brabant and Condroz areas (8eugnies in: Martin et el., 1970). The northern extension of the Silurian basin cannot be defined. Until now, no characteristic facies changes or other indications for a naighbouring northern high have been observed. According to the frequency of Silurian shales in borings in southeastern England, the sedimentary province of the Brabant Massif and Sambre-Mause zone obviously reached far to the west. In the northeastern Rhenish Massif, the uppermost Ordovician and the Lower and Middle Silurian have orobably never been deposited. This would suggest an emersion of this area comparable with the local uplifts of the western Sambre-Meuse zone and of the Ardenne massifs in early Caledonian time. If a Silurian age of the laminated shale beds in the Soest-Erwitte borehole could be confirmed, this would imply that the Brabant Depression continues in eastern direction immediately north of that Sauerland High. Also for the Upper Silurian (Ludlowian, Post-Ludlowian), an open sea connection 15

I VAI#rL[

""~?----~--~----: [~ [~ [~ ~[~ ~. ~__~_~ _~_[~] ~,oca, uplift ?

? posirwe area ? ...... "b shallowwater

Velc~ s LLANIDO'VERY- LUDLOW I graptotitic shales o 5o lookm

Fig. 10. Silurian - Lithology and paleogeography in the Brabant Massif and adjc~ning areas. (From Walter, 1980.) has to be assumed from southeastern England to Central Europe, still with the highest subsidence rates north of the present Ardenne mountains and the Rhenish Massif. The northern limit towards an epicontinental complex was situated probably far in the north. To the south this NW European depression was limited by the residual Ardenne Uplift. The terrestrial supply from this direction obviously ceased during the Ludlowian and Post-Ludlowian- period. At the end of the Silurian the Ardenne Uplift was again partly covered by a shallow sea. This is suggested by the predominance of calcare- ous shallow-sea deposits with a rich shelly fauna in the Ebbe Anticline and the Remscheid-Altena Anticline. Uppermost Silurian strata appear in similar facies in the western extension of the Condroz Anticline near Li~vin. After strong Late-Caledonian dislocations of the Sambre-Meuae zone and the Brabant Massif, the southern border of a broad North-West-European Caledonian platform matched the southern rim of the present Ardenne mountains. 16

Conclusions

The available data on lithology and stratigraphy of the Lower Peleozoic rocks in the Brabant Massif and its surroundings do not permit of establis~ng a differentiated picture of the paleogeographic-paleotectonic history of this Caledonian dislocation area, which is important for NW-Central Europe. Comparison of the Lower Paleozoic sedimentary sequences of the Brabant Massif, the Condroz anticline and the Ardenne Massifs suggest deposition in a marginal trough south of a Pre-Cambrian stable high which was presumably located in the southern North Sea. The Lower Cambrian continues the Late Pre-Cambrian epicontinental development with shallow-sea sediments, being distributed on a large stable shelf area. Its rate of subsidence increases during the Middle Cambrian, particularly in the south, and the sediment transport from a northern high dimi- nishes gradually. Depositional conditions of deep-neritic to bathyal environments prevail. Maximum sedimentation rates were reached in the Ardenne massifs during the Middle end Upper Cambrian and Lower Ordovician. In the Brabant Massif maximum rates of sedimentation are observed in the higher Ordovician end, mainly, in the Silurian. The development of depressions was each time followed by important dislocations. At the verge of the Ordovician, the paleegeographic situation in the south was changed by the uplift of the Ardennan area. Immediately aftel the Silurian, new paleogeographic conditions were produced by the Late Caledonian dislocation of the Ordovician-Silurian Brabant Depression. The Caledonian sedimentary history and tectogenesis of the Brabant Massif and the Ardenne Massifs cannot be compared with the orogenic development of the British-Scandinavian Caledonides. It matches, however, the Early Paleozoic history of the Danish-Polonian marginal depression st the southwestern border of the East-European Platform. The paleotectonic development of the latter area during the Early Paleozoic is relatively well known from borings in northern Poland and from exposures in the Holy-Cross Mountains. Reliable indications for the nature and extension of a NW-European foreland north of the Brabant Massif - analogous to the East-European platform - are still miesing and there is still no information about the southern border with the Central-European Paleozoic geosyncline. The monotonous lithology and great thickness of the Lower Paleozoic and the subordinate magmatic activi- ties in the Brabant Maseif and in the Ardenne massifs suggest subsidence and uplift of Pre-Cambrian basement block-complexes rather than the development of an autonomous NW-Central-European Caledonian orthogeosyncline. This assumption is supported by the absence of an intensive metamorphosis and of a subsequent significant molasse-develepment. 17

DEVONO-CARBONIFEROUS: TECTONIC FRAMEWORK

The three main depositional environments which can be distinguished in NW Europe during the Devono-Carboniferous are: - the Caledonian fold belt running from Norway into Great Britain (with Devonian Old Red Sandstone deposits and Caledonian trends of basins and highs characterizing Carboniferous sedimentary pattern), - the Cornwall-Rhenish Basin (with epicontinental shale-dominated deposits in the Devonian and 'foredeep' facies in the Carboniferous), and - the Belgo-Dutch Platform (that may be considered as a micro-craton ori- ginally belonging to the Fenno-Scandian Shield and NE European Platform).

C~ ~ BELGO-DUTCH ~ 4/ PLATFORM /

Fig. 11. Cartoon of the tectonic framework for the Devono-Carboniferous of NW Europe, (From Bless at al., Ig8Ob).

Caledonian fold belt

The main belt runs from Ireland through northern England and Scotland to Norway. Secondary branches in NW Europe are found in between Pre-Cambrian blocks of Cornubian-Armorican-Mid German Highs, the Belgo-Dutch Platform and the Fenno-Scandian Shield. Denudation of the Caledonian fold belt since Silurian times took place in epicontinental and intramontane fault-bounded basins with active volcanism along faults. The main belt in Britain is marked by fault-bounded basins 18

fault-bounded linear basins

since Middle Devonian. .,

/ "\

.\\ i l',

/ ~ e n . ~,, s u b s ~ ~

Fig. 12. Cartoon of the tectonic framework for Devonian sedimentation in NW Europe. (From Bless et el., 1980b.) with non-marine Old Red Sandstone deposits. The gradual decrease of the relative relief during the Devonian can be deduced from comparison of, e.g., the thickness of Lower and Upper Old Red Sandstone deposits (respectively up to about 4000 m and about 400 m) in the Midland Valley. Continued subsidence of basinal areas in the Carboniferous can be deduced from Caledonian trends of the Carboniferous basins matching the position of the Devonian depositional areas.

Cornwall-Rhenish Basin

This basin was bounded to the south by the Cornubian-Armorican-Mid German Highs. The bulk of the sediments in this basin must have been derived from 19

with intermittent non-deposition

o g

e C t e ~ o e n

Fig. 13. Cartoon of the tectonic framework for Carboniferous sedimentation in NW Europe. (From Bless et al., 1980b.) these highs. The basin preumably has to be subdivided into several sub-basins (Paproth, 1976). Local shoals with a cover of shelf carbonates occur since the Middle Devonian (Gotthardt et al., 1978). Rapid subsidence is marked by extremely thick siliciclastic epicontinental deposits. Active volcanism occurred along several faults. A continuous northward shift of the main basin axes and gradual incorpora- tion of the southern border of the same within the Variscan belt, followed by eventual uplift and rapid denudation since the late Famennian is presumed.

Beige-Dutch Platform

With this term is indicated an area extending from northern France into northwestern Germany with a complex block-mosaic of horst areas separated 20 ~,~,9¢ ~itW:':;-"';¢.,~. .~ -,~/;~i".:'..!-~-"'",~ ,,,~.

FRASNIAN

......

PREDOMINANTLY CARBONATES

• -- . ~. " , ~ PREDOMINANTLY MARINE SILICtCLASTIC5

• ~ . .~_ ...... I~-~.":-.:..I PREDOMINANTLY PARAL/C SILICICLASTICS • ..... --..L--

SILICICLAST/CS ~ EVAPORITE5

Fig. 14. Idealized concept of the evolution of the sedimentary pattern during the Devono-Carboniferous in NW Europe. The Devonian period is characterized by localized deposition in valleys within the Caledonian fold belt. As the relative relief of this belt degraded at the end of the Devonian the depositional conditions of the Caledonian fold belt and the Belgo-Dutch Platform b~came more comparable because of the similar relative relief in both areas. 21 by quickly subsiding linear fault-bounded basins, marked by a relatively mild Caledonian deformation restricted to narrow zones, and by the practical absence of Variscan deformation (except for its southern border with the Cornwall-Rhenish Basin which is now incorporated in the Dinant Nappe). This means, that the Pre-Cambrian or Cambrian rocks are generally overlain by practically undeformed, mainly non-metamorphic deposits. Angular unconformities within the Paleozeic sequence - such as those suggested by Legrand (1968) for the Brabant Massif - may be explained by rotational tilting of blocks masked by anticlinal draping of overlying strata

Permian REGRESSION~ == TRANSGRESSION Silesi~-- u'~ ~SILICICLASTICS

~ ~ ~RRONATES ON SHELFAREA; ~; EVAPORITESIN EYAM,HATHERN (G.B.),ST. GHISLAIN, .,~ Dinantian ~. ORNEAU(BELGIUM) /

Famennian ...... OZ FACIES"

~S ON SHELFAREA; EVAPORITES "~ Eifelian-Frasnian IN ANNAPPES-I(N.FRANCE),TOURNAI,LEUZE, .~

Lower Devonian / NON-MARINETO MARINE SILICICLASTICS

Cambr~ MENTS

Fig. 15. Simplified sedimentary history of the Belgo-Dutch Platform and Cornwall-Rhenish Basin during Devono-Carboniferous, with special reference to evaporite occurrences. The origin of some reworked sediments (mainly based on studies an reworked palynomorphs and other microfossila) is also indicated.(From Bless et al., IgGOb.) 22

The absence of a strong Caledonian deformation in the Beige-Dutch Platform and of the corresponding high relative relief may be deduced from the apparent absence of an important denudation area north of the Brabant Massif during the Ordovician and Silurian (Walter, 1980), from the apparent absence of basins with Lower Devonian depoeits~ and from the fact that only few sediments have been derived from the same during the Devono-Carboniferous. During the Lower Devonian, the Beige-Dutch Platform separated the non- marine depositional environment of the British Caledonian fold belt (thickness of Lower Old Red Sandstone locally up to 4000 m in Midland Valley) from the epicontinental deposits of the Cornwall-Rhenish Basin (thickness of Lower Devonian deposits up to about 4000 m in Dinant Nappe). During the marine transgression of the Eifelian-Frasnian period, the p~at- form is characterized by widespread carbonate deposits, whereas the British Caledonides and the Cornwall-Rhenish Basin show a predominance of, respectively, non-marine and marine siliciclestics. Since the late Famennian/early Dinantian, denudation had lowered the relative relief of the British Caledonian fold belt so far, that this relief becomes comparable to that of the Beige-Dutch Platform. From that moment onwards, only the Caledonian and Armorican trends of depositional areas reflect the different evolution of these fault-bounded horsts and basins. The structural subdivision of both the Beige-Dutch Platform and the British Caledonian fold belt seems to have been rather persistent throughout the Deveno-Carboniferous. Thick, relatively complete sequences are found in the basins, whereas thin, often incomplete deposits characterize the positive areas (fig. 15). The boundary fault systems separating positive and negative sedimentation areas existed since at least late Caledonian times.

DEVONO-CARBONIFEROUS: DEPOSITIONAL ENVIRONMENTS

Lower Devonian

Lower Devonian sediments occur in the Cornwall-Rhenish Basin and in intramontane, non-marine troughs within the Caledonian fold belt. Presumably, they are practically absent on the Beige-Dutch Platform. Continuous deposition of marine sediments from Silurian into Lower Devonian times occurred only in some parts of the Cornwall-Rhenish Basin (e.g. Li~vin borehole in northern France; Lecompte, 1967). Normally, more or less important sedimentary gaps are observed, which can be attributed to late Caledonian movements. Along the flanks of the Beige-Dutch Platform end on local shoals within the Cornwall-Rhenish Basin, Lower Devonian basal conglomerates seem to rest discordantly on the Cambro-Silurian rocks. Several, possibly non-marine \ \VV.

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High High South - West Pennines Scottish High High Ba s i n Ba s in B a s in Punninas Stainmore Northumberland Basin Trough Trough

C D A B

Fig. 16. Variation in thickness of Upper Devonian and Carboniferous deposits in NW Europe. Note persistent pattern of areas with respectively high and low rates of relative subsidence. (from Bless et al., 1980) Kent gap

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(~ REWORKED SILURIAN ACRITARCHS PRESUMABLY DERIVED FROM THE NORTH (~) PREDOMINANCE OF REWORKED ORDOVICIAN ACRITARCHS PRESUMABLY DERIVED FROM THE SOUTH

Fig. 17. Stratigraphic scheme of the Devonian around the Brabant Massif.

intercalations (containing a.o. vertebrate fossils: Pteraspis) in the essentially shallow-marine siliciclastic Lower Devonian deposits of the Ardennes and the Rhenish Massif suggest the proximity of land. The strong increase of the thickness of the deposits from north to south in the Ardennee (from 0 to about 4000 m) and in the Rhenish Massif (from less than 500 m up to more than 3000 m in the Siegen Trough) suggests that the bulk of the sediments was derived from southern sources. This hypothesis is partly corroborated by the results of a first study on reworked Ordovician and Silurian acritarchs occurring Siegenian and Emsian deposits of Belgium by Vanguestaine (1979). Vanguestaine suggested that the Silurian acritarch assemblages (which occur in locations along the northern flank of the Dinant Nappe) might have been derived from the Brabant Massif. He argumented that an even more northern source area (Norway) - postulated by Michot (1976) - is not very likely. The same author presumed that the reworked Ordovician acritarch assemblages (which are predominant in locations further to the south within the Dinant Nappe) had been introduced in the basin from southern supply areas ('Mid German High'?). The Cornwall-Rhenish Basin should not be considered as a huge, uniform depositional area. Detailed studies in the Rhenish Massif (cf. Paproth, 1976) have shown that several short-living sub-basins can be distinguished (Fig. 18). These sub-basins have been interpreted as inversion troughs (sensu vl Dvorak, 1973) which are characterized by a high rate of sedimentation of 36

•'"" .....-.~ "VI "; ~ ~';.... ' ,,, 0 lOOkm - "..'-_~~---_ ,,,,',' , L I - .---- _:?:-:-----Z--~---2---- ! ,i I :I IIII111 H

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Fig. 18. Inversion troughs of Devonian age within the Rhenish Massif. (After Paproth, 1976.) mainly shallow-marine deposits in a quickly subsiding trough. In a second phase, an abrupt reduction of the rate of subsidence, matched by a tempo- rarely increased heat flow, produced strong coalification and even anchi- metamorphosis. At the same time, the basinal axis was shifted to neighbouring areas where the same process of quick subsidence and rapid deposition was repeated. Apparently, these inverted basins remained relatively stable shoals in younger Devono-Carboniferous times as can be deduced from the low degree of coalification of e.g. Middle Devonian spores derived from these shoals during the late Westphalian (Bless & Streel, lg76). The inverted sub-basins of Devonian age are distinghuished from more stable areas by the tremendous thickness of the mainly shallow-marine deposits and the high rank of coalification of the same. The shallow-marine environment that predominated in the Ardennes and Rhenish Massif during the Lower Devonian is characterized by the repeated occurrence of carbonatic sediments containing prolific, thick-shelled benthos (Aaselberghs, 1946). This environment has been described as the 'Rhenish facies'. More condensed, pelagic sediments which lack a prolific benthonic fauna have been attributed to the 'Hercynian facies' (Schmidt, 1962). /,,,. ~ MARIIYE C,4RLgOIYATE3 ALL OCHTHOIYOU3 MAIPI#E CARBOI)'/ITE3" •";' ;".':'~:.: .~..... "////~ III DIIIAIIIT IYAPPE ":./. BORDER3 OF PO31TIVE AREA3 ,',', ":..: ..~" Argyll ':[ .. -~ I -::L-~,:;,~.?:'.(MOM-MA#INE DfPO31T3 0# ~'RO31k'E ;o~- '.~.:.. .:." o:... ~l ,qPEA,~) ,:.;.:. ~/" "~:]~... ( IMARIIIE 3EDIME#T3 .#;.- (~ Mbk~s/erlend-/ u ~ ~, ...--..... ":F,.. ":b':. " ...... "" ...... Weldl/e~orn He/ n'/@//@ - @ou.s'- "-' 6. .:'~:.. Baoi#cho~ :-!-. .:.': :ET~ :':- • .5" .'i::" . ,~:.."

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Fig. 19. Middle Devonian - Lithology and paleogeography of northern Europe. (After Gotthardt et al., 1978.) 38

A rather peculiar environment occurred in Normandy (northwestern France) during the Middle Siegenian. Early diagenetic dolomites and stromatolites pass laterally into anhydrites (Poncet, 1967), suggesting sabkha-like depp- sits in that area along the southern flank of the Cornwall-Rhenish Basin.

Middle Devonian and Frasnian

A widespread marine transgression across the 8elgo-Dutch Platform durino the Middle Devonian and Frasnian is marked by the frequent occurrence of thin basal conglomerates or (sometime plant-bearing) arenites overlying th~:i~ Cambro-Silurian basement, which are followed by more marine, often carbonatin deposits. Non-marine environments persisted in the intramontane troughs of the Caledonian fold belt. Within the Cornwall-Rhenish Basin, fine-grained siliciclastics (mainly derived from southern sources) predominateo except for regional shoals which were covered by carbonatic sediments.

i 0 lkm I.L couwN " I IA MATAgN E ',~ i ! ......

IIIIIIIIII1111tl 11 t11I lllllllllllll ;;'; ;i;t;!;'; lllllllilllliVVWtllllll I tv r

Fig. 20. Frasnian bioherms in the Frasnes-Couvin area of southern Belgium. (After Tsien, Ig71, 1975.) A: simplified geological map. B: schematic cross- section showing the peculiar arrangement of the bioherms on top of each other 39

Bioherm facies on southern slope of Beige-Dutch Platform

On the southern slope of the Beige-Dutch Platform adjacent to the Cornwall-Rhenish Basin numerous isolated build-ups developed during the Eifelian-Frasnian period. These biohermal reef complexes grew in a shale- dominated environment. They consist of relatively pure limestones with abundant massive globular or lamellar stromatoporoids and rugose corals. On the flanks a talus of organoclastic limestones with a rich benthos including branched corals and stromatoporoids as well as brachiopods and crinoids was developed. In the southern part of the Dinant Nappe in the Frasnes-Couvin area (some 75 km south of Brussels) several Frasnian bicherm complexes can be observed which apparently grew on top of each other (Fig. 20). This phenomenon suggests that the occurrence of these bisherms was linked to repeated uplift of the same tectonic unit in the basement. In- creased influx of pelitic material into the basin from southern sources presumably killed these reefs. The southern origin of the Eifelian-Frasnian pelites in the southern part of the Beige-Dutch Platform and its slope to the Cornwall-Rhenish Basin has often been questioned. Some geologists have suggested that the pelites had been produced by the Old Red Continent in the north. They in- vented a complex mechanism of currents that should have 'filtered' the fine-grained siliciclastics through the carbonate shelf that separated the presumed northern source area from the Cornwall-Rhenish Basin. It is un- likely, however, that this suggestion is true since the main horst areas within the Beige-Dutch Platform (e.g. the Brabant Massif) were covered by marine carbonates during the acme of the Eifelian-Frasnian transgression. Therefore, a northern supply area for these pelites can be excluded.

Barrier reef facies

Further to the north on the edge of the platform, a barrier reef occurred that separated the shale-dominated pelagic environment of the basin from a more protected carbonate shelf facies with biastromes and patch reefs. The barrier reef environment was best developed during the acme of the transgression in Lower Frasnian times. During that period, the barrier reef extended over s distance of at least more than 200 km in a narrow belt sub- parallel to the southern slope of the Beige-Dutch Platform (Tsien, 1974). Usually, the carbonates of the barrier reef complex have been dolomitized. 40

Protected carbonate shelf facies

North of the barrier reef complex carbonates were deposited in more or less protected back-reef to sublageonal or lagoonal environments. Coral- stromatoporoid biostromes extended over vast areas. Frequently, a rhythmic or cyclic arrangement of the sediments can be observed. Kesig (1980a) described examples of Givetian-Frasnian carbonate cycles in the Aachen region. He distinguished an ideal cycle composed of three phases (Fig. 2!).

/ |~------~r-. ~ -,,,- __ ,,, "' • s~ruc~ureless 3 ~-... ~ ~,f-- _--I--~ calcilutites with birdseye Fabrics

2 StromaEoporoid bios~rome

1 Amphipora .~asen"

-- Ill ---- III I1:--I---- 3 __ *11 III I|1~ Phase

Fig. 21. Scheme of ideal cycle in the Upper Givetian and Frasnian carbonate of the Aachen region, Federal Republic of Germany. (From Kasig, 19BOa.)

The basal bed is dominated by dendroid stromatoporoids, like Amphipors, which trapped the lime mud. This bed is usually relatively thin. It is overlain by a much thicker sequence of massive globular etromatoporoids which must have lived in a high energy environment since most of the specimens do not occur in life-position. This bed is followed by often finely laminated, practically non-fossiliferous calcilutitae with birdseye fabrics, characteristic of lagoonal facies. These cycles could be followed over a distance of more than 25 km in the Aachen area. Within the restricted marine environment south of the Brabant Massif, a trough with a relatively high rate of subsidence matched by quick deposition of shallow marine carbonates and claetics developed since at least the Middle Devonian. This can be deduced from the increased thickness of 41

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Z 7- -'-'-"z t, Dolomite ~ ~'1- A^^^^ -r ~: ^^^^^ Anhydrite "I-T T T -900 E i r "':.:"":: iilurian

Fig. 22• Simplified sections of some Middle Devonian-Frasnian sequences on the Belgo-Dutch Platform which contain anhydrite intercalations• 42

Middle Devonian deposits (about 500 m) in the Annappes borehole in northerr~ France (Fig. 22) as compared with the thickness of sediments of the same age in the autochthonous sequence of the Jeumont borehole (presumably less thar~ 200 m). This trough is called here St.-Ghislain Trough after the St.-Ghislaif~ borehole (southwestern Belgium) where increased thicknesses of Upper Devonian, Dinantian and Namurian strata have been observed (of. Fig. 16). Remarkable is the occurrence of several anhydrite intercalations in the Givetian sequence of the Annappes borehole. Similar anhydrite intercalations have been described from the Givetian of the Tournai and Leuze boreholes of southwestern Belgium on the northern flank of this trough. Evaporitic environments are not restricted to the Givetian of the St.-Ghislain Trough. Graulich (1977) described nodular anhydrite intercal~ted in Frasnian shales and dolomites of the Soumagne borehole southeast of the Brabant Massif (Fig. 22). Anhydritea ere also interbedded in Givetian and Frasnian shales end siltstones of the Argyll borehole in the Central North Sea (Oeegan & Skull, 1977) where they suggest deposition in a sabkha-like environment (Fig. 22).

Brabant Massif

Although at least minor quantities of erosion products were derived from the Brabant Massif during the Lower Devonian (Vanguestaine, 1979), it is believed that this area was characterized by an essentially low relative relief. Also during the Middle Devonian and basal Frasnian period, the Brabant Massif was never completely flooded by the marine transgression. This is deduced from the occurrence of greenish and reddish conglomerates and arenites along both its southern and northern flanks. Frequently, these deposits contain large fragments of land-plants. A good example of this littoral facies has been described from the Booischot borehole (LegranO, 1964; Streel, 1965; Fig. 23). Only in the Middle to Upper Frasnian the transgression across the Brabant Massif may have become completed.

Campine-Brabant Massif

North of the Brabant Massif, the Campine-Brabant Basin became into existence sometime during the Middle Oavonian. Apart from the conglomeratic Givetian-Frasnian deposits of the Booischot area, we know that biostromal limestones of the same age developed along the northeastern border of the Brabant Massif in the Vis~-Puth area of northeastern Belgium and the southernmost Netherlands (Graulich, 1975; Fig. 23). It has been suggested (Bless et al., 1980a) that evaporites of Middle Devonian age might be found 43

BOOISCHOT HERMALLE MUNSTERLAND S.ARGENTEAU

=~ Fr2 T I

Z 900

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:~.",'.;rl / \ I , ,1 5900 '-'£ :.:.:..:"-.I..... , / \ ! ',,:,! .... ? ~T.D. Silurian

°...'.°." o'." ;;; Cyclopean Breccio •.v.::: Sondstone , ,,, Dolomite ,T--,C-q,...... Conglomerote , , , Limestone

Fig. 23. Simplified Middle-Devonian-Frasnian sections of some boreholes on the northern flank of the Brabant Massif as compared with that of the MBnsterland-1 borehole in northwestern Germany.

in the Campine-Brabant Basin. This hypothesis can only be checked by future exploration.

Zandvoort-Krefeld High

Presumably, the Campine-Brabant Basin was bordered to the north by a horst complex. The southern portion of this horst area has been named the Zandvoort-Krefeld High and is believed to match more or less the actual structural highs in the central part of the Netherlands such as Zandvoort, Maasbommel and Krefeld. The complete horst complex (including the Zandvoort Krefeld High) is called the Mid Netherlands High. Ouring the Givetian, the Zandvoort-Krefeld High may have been subjected 44 to erosion as can be deduced from the occurrence of coarse GiVetian conglomerates (containing pebbles with a diameter of up to 50 cm!) in the Schwarzbachtal (Fig. 19), which pass into marine carbonates to the east. south and west.

MOnsterland-1 borehole

The northernmost published occurrence of Givetian-Frasnian carbonates on the continent is in the M~nsterland-1 borehole (Figs. 19 and 23). The Middle Devonian sequence is incompletely known. The lowermost bad in this borehole is a quartzitic sandstone of possibly Givetian age. It is overlain by massive limestones of Givetian and Lower Frasnian age which are followed by Upper Frasnian to Lower Famennian dolomitic shales (Kelch, !g61~) One of the main problems that remains to be solved is the connection of the Givetian marine environmentsof M~nsterland and Argyll in the Central North Sea. Although several communications may have been possible, we presume that a contact between these two areas preferably followed through the Campine-Brabant Basin or through an as yet hypothetical graben north of the Mid Netherlands High (Fig. 19).

Famennian

The Famennian is marked by an important regression that started during the late Frasnian with the deposition of clays and siltstones (Matagne Shales and equivalents), and culminated in the Upper Fammennian. Non-marine environments persisted in the intramontane troughs of the Caledonian fold belt. Erosion products of this belt may have spread across the northwestern parts of the Belgo-Dutch Platform where red beds occur a.o. in the Argyll borehole. A marine environment characterized the Cornwall-Rhenish Basin that was filled with fine-grained, mostly turbidi~c siliciclastics. These sediments practically lack benthonic faunas, but contain pelagic fossil assemblages, such as cephalopods and sntomozoan ostracodes which serve as reliable guides for long-distance correlations. Sources for these turbidites are regional shoals on the Belgo-Dutch Platform as well as southern supply areas. Minor quantities of sediment were derived from local shoals within the basin. The sedimentary environment on the Belgo-Dutch Platform is known as the Condroz facies. This magnafacies includes a variety of alluvial to marine infretidal shelf environments (Fig, 24). Sedimentation was essentially rhythmic. Minor rhythms, frequently combined in major rhythms, have been recognized. These show both fining-upward and coarsening-upward tendencies 45 as has been described by Becker et al. (1974) and Thorez et al. (1977). Siliciclastics predominate. But early diagenetic, fine-grained dolomites (characteristic of lagoonal facies), cryptitic limestones and coarse-grained detrital limestones are intercalated locally in the sequence. Frequent occurrence of plant debris suggests the existence of land areas on the platform. Presumably, some erosion took place on the Brabant Massif and possibly on the Mid Netherlands High. Passage from the Condroz shelf facies into the more turbiditic basinal environment can be observed in the northwestern part of the Rhenish Massif and in the southern portion of the Dinant Nappe.

Fig. 24. Scheme showing the ideal relationship between alluvial to infratidal environments within the Condroz facies. ~rom Thorez et al., 1977). I) Alluvio-distal facies; 2) Alluvio-lagoonal facies; 3) Lagoonal facies with early diagenetic dolomites; 4) Tidal lagoon facies; 5) Barrier complex with massive sandstones; 6) Fore-barrier facies with tidal flats; 7) Fore-barrier facies with a predominantly intertidal environment; 8) Proximal subtidal facies; g) Distal subtidal facies with fluxo-turbidites; 10) Subtidal to infratidal facies with turbidites and limestone nodules; 11) Pelite-dominated infratidal facies.

Dinantian

Widespread transgressions started in latest Devonian time ('Strunian' or 'Etroeungt') and reached their acme during the late Dinantian period. These transgressions spread across the Caledonian fold belt from southern directions At the same time the Old Red Facies was pushed back to the north and to isolated horst areas. This transgression was completed in the Lower Tournaisian. The horst areas within the Caledonian fold belt influenced the thickness and facies of the Dinantian sediments, but they practically ceased to produce terrigeneous detritus. Only the area north of the Midland Valley in Scotland was marked by a slightly higher relative relief. That area was the main source for siliciclastic arenites and pelites which predominate in the Dinantian sequences of northern England, Scotland and the Central North Sea, 46 where a paralic environment was established during the Visean. Sedimentation in that paralic area was essentially rhythmic (Yoredale rhythms). The rhythms consist of seat-earth, coal, (marine limestone), shale and sandstone. The shales may contain thin resinous algal layers and serve as a source rock fo: hydrocarbons (oil shales). The marine Dinantian deposits in the Caledonian fold belt are predominantiy carbonatic on the shoals, whereas thick pelitic sequences - intercalated by local reef limestones - occur in the troughs.

NORTH-WEST! MID- J CAMPINE- J CORNWALL- GERMAN NETHERLANDS BRA@ANT ORABANT FRENCH RHENISH BASIN ] HIGH BASIN MASSIF BASIN BASIN •...~:~,, S STEPHANIAN @ I ------~....:;:.::--,,."...., a ~/-.-.":i:!.-:i:..~.O. . -... • . 0/.-.:~#,,_0I .... \ ,- ~*. , L UPPER •.,.... "'.'.; ,~ ~/.'.,.', . .'." . ,x /~-'...... ,.¢ E WESTPHALtAN v ~-~' ;~ ~.,,....__~.~: z-.T: ~:.-.~.-.--~b .-.-..<..-~..~: ~:..'.".~ ~ A E 6 I R M. e. --\ ~' S LOWER .'----"X'---T'---•--_'-EZ..--:-.--_'~--.----.--:-~:_.----:-:-~Z..--:.~T~ ~ ~ I WESTPHALIAN .----" .-:---~--.--:_--:'.--'I'.:_':'_L.--_:"~--.~'..T::,.'.~:~.'.~:~.'~ ..~.~'oo ~ .. A ira------S A R N S R A N K M B;..~_ ~ .. ', N NAMURIAN I--:------L-...,~,-.~ a:~ , , ",- - - - ,-~,'~ :...~-:.---_--~ I D L-."~.~._v~, ', ' , ', ', ', "i--r'--r'---~"["A_~^~ -- -- .:.. I VISEAN h-""~"- li'ii+i ~ i , i , ~ I , I, I il i i i I i I/%'~--i--p'l-,--~----",:::1 N F_------,,',',', : ',',',',' ',',',', 0,'~--:-"~1 NA TOURNAISIAN T. I-:L_."--~"~t .... 'ii ! ' , ~ ' ~ "~:Z-A--%-L~"@r [ ,' , ' - "--~------.:.: -- -:.'. [---- I. I I , ~7 - , , , I -----.'.v I STRUNIAN I------Z -- Tr-- -r-_. ~:~.:1 '~]:E. ------:::'.I

Fig. 25. Btratigraphic scheme of the Strunian and Carboniferous around the Brabant Massif. The term French Basin was proposed by Bless et al. (1977a~ for the Silesian deposits in Belgium and northern France, south of the Brabant Massif.

The Cornwall-Rhenish Basin continued to receive siliciclastics from the south. Two main environments can be distinguished: a proximal Kulm greywacke environment in the southern parts of the basin and a distal Kulm shale facies along its northern borders. The Belgo-Outch Platform shows a predominance of shallow-marine carbonates. However, it is not excluded that pelitic sediments occurred in the central portions of some troughs.

Kulm facies

Within the Cornwall-Rhenish Basin the Kulm sediments have been preserved in southwestern England and to the east and west of the Rhenish Massif. 47

"POSIDONIA SHALE5 11 WITH INTERCALATION5 OF TU__FFS

31LICEOU3 SHALE3 10 AND CHERTS WITH ITN/FERsCALATION5 OF

51LICEOU3 LIME3TONE

BLACK CHERT3

NODULAR LIME§TONE TRAHSIT]ONAL 61=05 ~ FAULT

3iLICEOU5 BLACK SHALI=S WITH MINOR INTERBED5 OF BLACK -- CHI:RT BLACK 5HALE

ALLODAPlC L1M ESTONE -,~ FAULT BLACK 5HALE UPPER PART

8REENISH 51LTY SHALES

LOWER PART

Fig. 26. Section through the Dinantian Kulm shale at Riascheid (Wuppertal) in the northwestern part of the Rhenish Massif. (From Zimmerle et al., 1980.) 48

Kulm greywackes predominate in the area east of the Rhenish Massif. They have been derived from the Mid German High in the south and southeast. The SW-NE axis of the basin in which they were deposited shifted rapidly to the northwest. This i8 suggested by the northwestward migration of the successi~Je greywscke lithoaomes (Kulick, 1960). The thickness of the deposits may be more than 2000 m.

CARBONATE SHELF STARVED BASIN

J~ ANOXIC ou, , SHALLOW M SHALLOW MARINE

t N FLUX OF DETRITAL CA~I~ONATES FROM ,SHELF

q3",~ '" "L , ~ i ~ ~3s/ "", !

t I I ""1,,.,., 1"...t,~) I , ~ ~" -- :-" -"[ .^ -- 1-- __!. t.,...""~,.'"." ~:~:z.i. I "., ..-"~ i ~ _1 _~ ~ 4.,'"..". o.4:.-. .." ..r 'k,- _-E _ -.- ~:i: I ' I~ ~'iI I v~35:THICKNESS OF D NANI"IAN (M)

Fig. 27. Upper Dinantian - kithology and paleogeography north of the Brabant. and Rhenish Massifa. (After Bless et el., 1976; Zimmerle et el,, 1980.)

A rapid change from Kulm greywackes into more pelitic deposits is observed north of the Rhenish Massif. The thickness of the Kulm shales is usually much lees than 200 m (Fig. 27). The facies of these Kulm shales is representative of an euxinic environment of the substratum in a starved basin. This doesn't indicate necessarily a deep water facies. The typical rock association con- sists of black shales, lydites or cherts, allodapic limestones, nodular limestones, siliceous limestones, tuffaceous vslcaniclastics and phosphorite nodules. Arenites are rare or absent. The ano×ic facies is indicated by the high organic carbon and pyrite content. A good example is the Rieecheid section at Wuppertal in the northwestern part of the Rhenish Massif o ~,o ~pkm J "'"* IT~ Om| ' ' ~-/ NETHERLANDS:.I~ I

I ~D T'O OD ~'~ f...:-....-.-'~..,::,~i1 kL~,~ i I

f/l ~.

..~.g =N~"

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• ~ r'- O t/ I SHOAL, .) ~ ~~ ~ ~ .....~ ,.-:, ~

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<- f* x, ,, ...... C 0I~.~ C ~." BETV~EE~ OOI~IN~TEO m ...... N O:'-.,.,S H k- L E __ 4) "'" ~,,~N ;.. L ~/I.SI N .~ L U X EBO M U R G""~:':" E~-CD CO "~'c ~ _~ ,~u~ "J ':i:) ''"".'. m ~

~ t~- r--- c~ m 50

(Zimmerle et el., 1980; Fig. 26). Local increase of the sediment thickness may be due to the occurrence ~:~ detrital (allodapic) limestones derived from the carbonate shelf (Fig. 27!. The most important of these is the Flaggy Limestone ('Kulm-Plattenkalk') with a thickness of slightly more than 100 m (Bless et el., 1976). The Kulm deposits of the Cornwall-Rhenish Basin in northern France were either eroded in late Variscan times or they may still exist below the Mesozoic cover of the Paris Basin. A transitional environment from this shale-dominated Kulm basin to the carbonate environment of the Dinant Shez~f is found in the Dinant area of southern Belgium where shales are interbedded in the otherwise carbonatic sequence of the Lower Oinantian Hasti~re Lime- stone (Fig. 28; Van Bteenwinkel, 1980).

Very finegrained calcilutites with algal mats and 5 birdseye fabrics v) 4)~J Mainly calcilutites 4) "5 partly laminated, with thin >,, bituminous horizons, very rich in ostracodes C Calcilutites and calcarenites with lenses of coated grams -- I l and oncolite - horizons. near the base intraclasts Calcarenites with coated grains c~ ® j'2 ~-~ca'Te~es end ~tc-~u~s- rich in intraclastS, with foraminifera / Sedimentary breccta. partly like olistostromes ~5 phasel

Fig. 29. Scheme of an ideal carbonate cycle in the Visean strata of the Aachen Shoal, Federal Republic of Germany. (From Kasig, 1980b.)

Carboniferous Limestone facies

Carbonatic sediments were deposited in a shallow to very shallow-marine environment (Carboniferous Limestone facies) on the Beige-Dutch Platform and in an important part of the Caledonian fold belt. The thickness of the deposits may be extremely variable and presumably depends on variations in the local rate of subsidence. Sedimentation was often rhythmic. Minor and major cycles can be distinguished. The boundaries between major cycles are often erosion levels which may be followed over hundreds of kilometres. These can be attributed to widespread sea level changes (Ramsbottom, 1973; Conil & Lys, 1977; George, 1978a). Minor cycles may be followed over tens of kilometres. They are often characterized by fining-upward seouences which start with fossiliferous calcarenites or calcirudites followed by practically non-fossiliferous calcilutites which may contain birdseye fabrics. Representative examples of these have been described by Pirlet (1964) from the autochthonous Namur Basin along the southern flank of the Brabant Massif, and by Kasig (1980b) from the allochthonous Aachen Shoal (Fig. 29). These minor cycles characterize deposition in an intertidal to supratidal environment. Widespread carbonate mudmounds developed in deeper water on the outer shelf. These have been called 'Waulsortian bryozoan reefs' because of the frequent occurrence of fenestellid bryozoans in these deposits. They are characterized by - often dolomitized - micritic limestones with cavity- fillings of calcite spar. Whether the fenestellid bryozoans have trapped the carbonate mud and acted as reef-constructing organisms is still problematic. Other important inhabitants of the Waulsortian environment were crinoids and - usually small - brachiopods. Lees et al. (1977) suggest that these mudmounds have been formed in water depths of 250 to 300 m, 'perhaps up to many tens of kilometrss from the shoreline'.

Evaporite facies

Evaporites (anhydrite and subordinate gypsum) have been described from several areas within the Belgo-Dutch Platform. The most significant occurrence is in the St.-Ghislain borehole south of the Brabant Massif, where massive and nodular anhydrite is intercalated in the Dinantian succession (total thickness of anhydrite beds more than 500 m; Dejonghe et al., 1976; Groessens et al., 1980). Other important occurrences of anhydrite are known from the Lower Dinantian sequence north of the London-Brabant Massif in central England (George et al., 1976). Nodular anhydrite and/or gypsum crystals have been recognized in several locations along the southern flanks of the Wales-Brabant Massif (George, 1978b; Hance& Hennebert, 1980). Nodular anhydrite and authigenic gypsum may be indicative of sabkha-type sequences. Massive, finely laminated anhydrite may have been deposited under standing water conditions in a lagoonal or sublagoonal environment. Other evaporites, such as rock salt, have not yet been recognized in the Dinantian of northwestern Europe. It is suggested that even rock salt may occur in the deeper parts of the Campine-Brabant and Namur Basins. Schenk, (1969), Hacquebard (1972) and Geldsetzer (1977) have reported Dinantian rock 52 salt deposits from the Fundy Basin of Nova Scotia, Canada. The rock salt posses laterally through anhydrites into solution breccias. It is worthwhile to observe that the stratigraphical position of the most importan~ anhydrite intercalations in the Upper Dinantian of the St.-Ghislain boreho~e is occupied by widespread breccias along both the southern and northern flanks of the Brabant Massif (Fig. 30)~ A tentative model of the lateral passage of these breccias into evaporites north of the Brabant Massif has been proposed by Bless et al, (1980b). This model (Fig. 31) can only be checked by future exploration.

LOEJ@~OUT TURNHOUT RIJSBERGEN-1 ! 1 1

.... :"" "~"...... " N ...... A M ....U ...... R ...... I A N...... s H ...... A ...... L ...... E S ......

....

~ C A M B R O-! S I L U R I A N ~~ '-..EV,;" v v

× x × × × x × × × × × x ~ ~~i~"-..~"'<"r,-~"" ~- x x x x x x x x x x x x; I\'~\ ~ ' ~-.~

i x×xx,,xx

Fig. 31. Tentative cross-section along northern flank of the Brabant Massif at the end of Namurian time (not to scale). The increase of the thickness of the Dinantian carbonates between Loenhout and Turnhout has been proven by boreholes. Also the increase of the thickness of the Namurian between Turnhout and Rijsbergen has been checked by boreholes. It is suggested that the breccia horizon in the Upper Dinantian of Turnhout (and Loenhout?) may pass into evaporitem towards the canter of the basin. (From Bless et al., 1980b.)

Campine-Brabant Basin

The isopach map of the Strunio-Dinantian deposits around the Brabant Massif (Fig. 32) is based on relatively few - partly even incomplete - sections. Three main depositional areas are recognized (Camplne-Brabant, *pp. 29--34. ~' Dinantianin lower sheel:s ~.~ "~""' n,.,,howx'x%'~'X ~ of" Bolland,Soironand ~. ~ \ • "~,X,. • Soumagnemay be @ ~. ~ c A t M PI~,X~ E - ~# allochthonousand _ ~. \ B R~A B A N~X~pT B A S I N ~ have beendisplaced %° ~P "~. \...,.. ~ X~ ~" northwardby the ",, <7 ~/~ \;i~.r:e/\ / XI~ ~,~ ,o ~ .... • ,.....:: Var scan overthrust %. ~.~ .:...'.!:..\ I \\ o ,-.. ' • -~ ,4 "~/~::\::::"-";sow~ho: / "o" Amountof displacementas o' %.\"V#:::.~; , , , \\

~ yet unknown. %%'17 ~ \ \ \ , , N

° -~ . \+. ~ • 2" % "- .. -. v,,,-,O,H

/// ¢" -I //:/ v

4 rs t i "":;;;2"•

"'.. "" ~Den~-~'~:e lZSO-----._~•Ecaussinnes ~ ~ ~ • ...... "...... -.. o~,~00._____~~~ \ ++ ~. o ...... ".+--~,~~---__~~-~\ .~ ,~,,~ ...... +° ...... +~ ~+:.+~:,,+__::~-----m-~,~\\\+.,,.'-..~ .~,++ ...... ~+o...... o,,.. \ \ \ \ ...... _ ...... o------'-- 1150 {~u/ocn) ...... %00u.... m ([NUEMICFAUNAS) / ~+~0-'~ ~ 1 ~ ~ ...... -...... ~,~o-~--~~ ) ) : ~ ...... ~ ~f,o00-~ ~// ...... +..... s i N

Jeumonl• ...... "...... ~- -SO0~ "...... "...... JE~UMONT HIGH ...... "...... c'I- :3" 54

Namur and Diment)which are separated by shoals: Brabant Massif and JeumonL Shoal. It is suggested that sub-basins or troughs may be distinguished within the Campine-Brabant and Nsmur Basins, whereas small shoals occur on the Dinant Shelf. A synthesis of possible basins end highs during the Dinanti~n time is presented in Fig. 33. North of the Brabant Massif, only the Loenhout or Heibaart borahole has yielded a complete sequence of Dinantian strata with overlying Namurian and underlying Famennian rocks. Woensdrecht, Turnhout, Helen and Wijvenheide penetrated the Dinantian strata below overlying Namurian and proved the existence of a sedimentary/erosional gap between the Dinantian and Namur~n which become more important to the west (Bless et al., ~976). These boreheles did not reach the base of the Dinsntian° However, the evidence seems to point to an overall thinning of the deposits from Halenthrough Turnhout and Heibaart to Weensdrecht. This implSes progressive relative subsidence of the basin floor from Woensdrecht to Halen even during the late Dinantian/early Namurian regression (Fig. 31 and 41).

TDOD~, ~ ~) ~ SO~DON-SOUM~

O I N A N T S H E L F "-'~....~N~a?L"b"~.-/ tWAULSORTIAN CARBONATE MUD-MOUNDS) D f N A N T S H E L F (WAULSORTIAN CARBONATE MUD-MOUNDS)

-S H A L E - 0 0 M I N A T E D------K U L M B. A S I N .... -- -K U L M B A $ I N .... A _ _ -- 5 Fig. 33. Tentative palinspestic maps for Strunio-Dinantian deposits on part of the Beige-Dutch Platform (not to scale). Two different interpretations are shown. In Fig. 33A, the Balland, Soiron end Soumagne d~poeits (l~wermost tectonic sheets in boreholgs) are considered as (par-)autochthoneus, in Fig 33B as allochthonous end rgstored to an Original position in the eastern extension of the Jeumont Shoal. (From Bless at el., 1980c.) UPPER V3c ERMALLE-SOUS-ARGFNTEAU RICHELLE "F'L"N"QUARRlES SOUVRi LA FOLIE

E TRANSGRESSION

FAMENNIAN KAASTIFICATION

UPLIFT UPPER FRASNIAN(?) SEA LEVEL

UPLIFT

Fig. 34. Hypothetical. reconstruction of the paleogeographic events in the Vise area during the Frasnian to late Visean period. (From Poty, 1960.) 56

The Devonian-Dinantian boundary was only recognized by the Heibaart en Booischot boreholes. At Booischot, the Upper Dinantien and Namurian strata have been removed by post-Carboniferous denudation. But the existence of pelacsols and terrigenss in the relatively thin Lower Dinantian carbonates (thin in comparison with the VI of Halen anO Turnhout) suggests relatively slow subsidence of the Booischot area with a nearoy erosional higm. The lithology of the nearby,very short ano incomplete Kessel section (reo seas and terrigenes intercalated in the carbonates) suggests similar paleogeographic conditions as for Booischot. Boreholes and outcrops in the Vis~-Villers area have yielded evidence that this region belongs to the Campine-Brabant Basin. A direct communication of this basin with the Pennines and Ireland alonq the northern flanks of the Wales-London-Brabant Massif seems likely because of the ~ersiatent occurrence of Paleotethys (~fro-Asian) faunas in the Visean strata of tne Vis~-Villers area (Kimpe et al., 1978). Such faunas have not been recognized in the more endemic fossil assemblages south of the Brabent Massif. Thick- ness ano facies of the Dinantian in the Vis~-Villers area suggest deposition on a shoal on the northern flank of tne Brebsnt Massif with a karst tooo- graphy that was only completely drowned in late Visean time. ~ reconstruction of this karst landscape has been presented by Poty (1980, Fig. 341. Immediately north of the Vis~ area, a gravity minimum suggests that the basement may occur at increased depth. This might imply an increased thick- neas for the Devono-Dinantian strata (Fig. 35) and possibly the occurrence of evaporite deposits comparable to those of the St.-Ghislain area in South- western Belgium and northern trance (Bless et al., 1977b, "980a). Therefore, the crowdino of the isopachs in the Vis~-Puth area on Fig. 32 and 33 seems justified. The overali ~W-SE trend of the isopachs in the eastern part of the Campine-Brabant Basin is closely matched by the homotexial shorelines of the Namurian transgression (Bouckaert, 1967; Bless et el., 1976), tne isopachs of the Westphalian C strata (Bless et el., 1977a), the southern moroeF of the Lower to Middle Jurassic sediments and by the NW-SE trending faults along the southwestern boroar of the actual Roar Valley Graben (Fig. 36). It is hardly believable that these are mere coincidences. Therefore, it is presumeo that the actual Roer Valley Graben border faults are rejuvenations of much older (Peleozoic) fault systems which orlginally separated fragments of the basin ?loot with differential subsidence. Inverse movements of this part of the Campine-Brebent Basin caused uplift an~ erosion during the late Mesozoic followed by renewed subsidence during the Cenozoic. Practically no information has been published yet on the western part of the Campine-Brabant Basin. It has been suggested that it more or less 57 s _ _~_ ~ ~. ~,~°~.

~":: Tn

//~V~v.//x x x x x x x × I -~ t ~:. ,":?}~'v v

x × ×/× × x x × × × x i × × x × !\ × × /× × × × × × × × × ~× × ×!× ~."< .~.~'~ i × X B A S E M| E N T i X I I ~ ~"~ x x ~ ix x x x x : ix ' x x Ix x x x x x x x x • ~x x'i x x x

Fig. 35. Tentative cross-section (not to scale) across the northern flank of the Brabant Massif in the Vis~ area at the end of Dinantian time. (From Bless et al., 1980b.) coincides with the Westphalian C-D deposits exposed at the Pre-Permian sub- crop. Strong subsidence of that part of the Campine-Brabant Basin during Mesozoic-Cenozoic time is known (Western Netherlands Basin). Although this should not be considered as a proof or even an indication for a western sub- basin, it might be worthwhile to investigate the possibility to distinguish two sub-basins or troughs within the Campine-Brabant Basin during the Dinantian.

Namur Basin

The boundary between the Campine-Brabant and Namur Basins can be located between Moha and Horion (Fig. 32), where a change in facies and fossil assemblages occurs. A progressive increase of the thickness of Dinantian deposits to the west can be observed. This suggests that the distance to the northern border of the Namur Basin increases from Moha to Tournai. Thus, a NW-SE trent for the isopachs seems the most logical one. This trend coincides with the isopachs and facies strikes on the Visean maps of Pirlet (1968). More problematic is the iscpach strike between St.-Ghislain, Jeumont and W@pion where several interpretations are possible. The interpretation proposed 58

DI.$TRIBUTIO["I OF LOWEI~MIDDL[ I ,JenAss~c SEO|~EeTS uPPEe WESTPHALIAMC Z 15opAc,s 3 I'IAMURIAN HOMOTAXlAL SI'IORELINF5 DIrlAPITIAPI I$OPACHS 5 ROER VALLtrY GRABEN 80UItDARY FAULTS

Fig. 36. Comparison of trends in Dinantian, Namurian and Westphalian sediments along northern flank of Brabant Massif with trends of Roer Valley Graben boundary faults and distribution of some Mesozoic deposits. (From Bless et el., 19BOc.)

on Figure 32 is based on accepting a concordant strike for isopachs and facies during the Lower Dinantian ~Bless et el., 1980c). The isopachs strong~ ly suggest the existence of a relatively narrow trough (St.-Ghislain Trough) that reached eastward into the Orneau area and separated the Brabant Massif in the north from a shoal in the south, the Jeumont Shoal. Both the St.- Ghislain Trough and the Jeumont Shoal seem to nave come into existence during the Middle Devonian (see above). The strikes of the Brabant Massif, the Jeumont Shoal and the intermediate St.-Ghislain Trough would be more or leas WNW-ESE. This trend is partly matched by the trenO of actual dome atruetures and solution phenomena in the Heine region of southwestern Belgium. Domes and solution phenomena h~ve meen interprete~ as the result of halokinesis and the aolution of under3ying Devono-Dinantian evaporites (Delmer, 1972). In the ESE prolongation of the St.-Ghislein Trough a aeoono trough or 59

sub-basin is postulated here. Nowadays, this sub-basin is masked by the Midi Overthrust. If we believe that the lower tectonic sheets explored by the boreholes Bolland, Soiron and Saumagne are autochthonous or par- autochthonous, Bolland might be located on the eastern extension of the Brabant Massif, and Soiron and Soumagne on its southern flank adjacent to a hypothetical Soiron-Soumagne Trough. However, if we presume that these tectonic sheets are allochthonous, Bolland (and also the nearby outcrops of Booze and Ls Val-Dieu) might represent as well the eastern (ESE) extension of the Jeumont Shoal. In the latter case, Soiron and Soumagns would be located on the northern flank of the Dinant Shelf, south of the 3sumont- Booze-Le Val Dieu Shoal.

Oinant Shelf

The Strunio-Dinantian deposits of the Dinant Nappe have been thrusted over the Namur Basin and mask the Oeumont Shoal. The thickness of the Dinantian carbonates at Jeumont (some 575 m) is distinctly less than in the Dinant Nappe, where their thickness increases from some 750 m at W6pion to about 900 m near Dinant. Waulsortian carbonate mud-mounds occur in the Dinant area. This increasing thickness might point to a slightly higher rate of subsidence for the southern part of the Dinant Shelf (outer shelf area).

f sr HASTENRATH SANDSTONE

~ VAUGHANITES OOLITE p~.';.~ HASTEN RAT H ®(~ QQ ~ VISEAN LIMESTONE

9 COMMUNICATION 0 5 lOkm TO OPEN I I I MARINE SHELF

Fig. 37. Basal Visean paleogeography of the Aachen region, Federal Republic of Germany. (From Kasig, 1980b.)

Thickness and facies trends of the Dinantian deposits in the Aachen region (mean thickness 200-250 m; Kasig, 1980b) suggest deposition on a shoal with a slope to the north or northwest (Fig. 37). This idea is corroborated by the existence of important breaks in the Dinantian sedimentation. Analysis of fossil assemblages has not yet advanced enough to permit deductions about 60 the original position of the Aachen Shoal. Faunas seem to have strong relationship with those of the Dinmnt Nappe. Thus, it cannot be excluded on forehand that this was a shoal on the Dinant Shelf. Of course, it ±s tempting to consider the Stavelot-Venn Massif as the basement of this shoal. But more work is needed in order to unravel the intricate structural relationships between the Stavelot-Venn Massif, the Aachen region and the Dinant Nappe. Also the Avesnes area in northern France (cf. Fig. 28) shows a reduced thickness of the Tournaisian strata and includes a sedimentary gap of Tn2c-Tn3b (Conil, 1973). The Vieean of the Avesnes area has been truncated by poet-Carboniferous erosion. We suggest that this region was also a shoal on the Dinant Shelf during the Dinantian period.

Namurian

The stratigrmphic subdivision of the Namurian in northwestern Europe (Fig. 38) is based on goniatites which occur in over fifty marine bands. Several of these provide excellent marker horizons which can be traced from Ireland into Czechoslovakia and even beyond that area.

eta[ ~es goniatite zones

old new C YEAOONIAN GI (Goniatit~tes)

MARSDENIAN R2 (Reticuloceras) KINDERSCOUTIAN RI

ALPORTIAN H2 (Homoceras) CHOKIERIAN HI

ARNSBERaIAN E2 (Eumorphoceras) PENDLEIAN El

Fig. 38. Subdivision of the Namurian.

The Namurisn period started with a widespread regression coinciding with the orogenic movements of the Sudetic phase. Only baeinal areas were not directly affected by this regression. The subsequent transgression gradually spread across the shoals but was only completed in Upper Namurian (Kinder- scoutian) times as can be deduced from the example of the Brabant Massif (Figs. 39-41). The depositional environment changes from predominantly merine in the Lower Namurian to paralic in the Upper Namurian. This regressive tendency continued in the Weetphalian when incursions became rare and practically ceased in the late westphalian. 6I

WOENSORECHT \ HEIBAART / \ k_.j

8R4 8A N T BRUSSELS SHOAL 0

~SIPPENAEKEN CHERTAL,

*SOIRON .~.,.~.~THEUX j~ BLATON RONET

/ VIONCEAU \.__, ~ ERTH~ ~ST MIO\ CQUIER ~,

L,-, * DISSOLUTION HOLES IN THE TOP VISEAN ,J R RADIOACTIVITY OCCURRENCE

Fig. 39. Namurian transgression across the Brsbant Massif (shown by homotaxial shorelines), based on age of lowermost marine - goniatite-bearing - horizon overlying the Dinantian deposits (after Bouckaert, 1967).

MASS F

\ ~ ~ E 2c ~._~...... _..~

Fig. 40. Offlap and onlap of late Dinantian and early Namurian deposits along northern flank of Brabant Massif. (After Bless et al., 1980c.) 62

CHERrAL R1: T 7

t I 200m I I i ( i BIOUL MONCEAU MALONNE L OIfE@MEE JAYA . j "--..----1 j,m ~ . . :

E262

E2bl ~ "~ \ c::~ s.,,,e ~~____./ SANOSrOME uMcsroNe COAL SEAM tJ GONIATtTES

Fig. 41. Stratigraphic sections south of the Brabant Massif showing graduai~ transgression of Namurian. (After Bouckaert, 1971.)

Namurian sediments are almost exclusively siliciclastic. Isolated, thin carbonate lenses occur locally in the lower portion of the Namurian succession, whereas economically important coal seams appear usually in the upper part. Sedimentary cycles in the Namurian have been described by many authors. Van Lsckwijck (1964) distinguished an ideal cycle with a mean thickness of 60 m that can be subdivided into four phases (in descending order): Phase d - several rootlet beds which may be overlain by coal seams Phase c - sand-dominated succession Phase b - shale-dominated succession (frequently with non-marine fossils) Phase a - shales with one or mere important marine bands The basal marine shales of several of these cycles contain the diagnostic goniatite faunas which serve for long-distance correlations. Within these 60 m cycles, Van Leckwijck recognized up to eight minor (10 m) cycles, which in turn could be subdivided into so-called 4 m cycles.

French Basin

This term was introduced by Bless et al. (1977a) for the Upper Carbonife- rous (Silesian) deposits bordered in the north by the Brabsnt Massif and in the south by the mobile Variscan belt. To the west, the French Basin was con- nected with the sedimentary area of southwest England and South Wales, to the 68

50km 1 ST.GHISLAIN 0 I I 2 JEUMONT 3 COMBLE-NORB J /., CHERTAL 5 SOUMAGNE (POSSIBLY 0 ALLOCHTHONOUS) 6 INDE AREA (ALLOCHTHONOUS) i '7 TURNHOUT 8 RIJSBERGEN g MUNSTERLAND 10 STENDEN ~!i!iii~THICKNESS IN M ...:h ° \ /

\~3ooo ." , o / ..

IU.:\ \ \% __...... ~,~...... i:ii:::i!ii:~iiiiiiii!!~ili!iiiiiiiii~: v.\ .~.: x<~::ii~., , 290~_---"/k5 --- ~)~ ,

...... k ...... :~u.,::::u:: =:: % ~, !!!iii!Si!i:i :iiai!iiiii~!i~i!5!i! :::::: ~P~80 .6o o ...... ~q!!iiiiii!iiiiiii!~iii~i~iiiiiiiiiiiii~: :6 5,,..170 ~ 660 3-*~n:~iiiiiii!iiiii!iii!i~!iiiililiiii!iii~, 400, /,. iiNiiiiSiHii!i!!iiiiiiiii ,ii..:] ii i ,i..i!..:i 1 / " to" /"'230 H/ i!!!iiii!iiii? :i!!iiiii !!iiiiiii iiiiiiiiiiiiiii!ii!iiiiiiiii1i ;" ii!i!iiiiiiii /// ALLOCHTHONOUSDEPOSITS (FgE@II~l~Ulil)) 1OOO ISOPACHOF NAMURIAN MAIN SEDIMENT TRANSPORT :i!iiii iii i!?! ~i ii~! i! ~! i! ! i! i! POSITIVEAREA

Fig. 42. Namurian - Paleogeography and isopach trends around the Brabant Massif.

east there existed a communication with the Campine-Brabant Basin north of the Brabant Massif. The sedimentary history and the thickness development of Silesian strata within the French Basin arm incompletely known. This is due to post-Variscan erosion of the outcropping Silesian strata in the Dinant Nappe and Namur Basin as well as to the fact that possibly important parts of the autochthonous Silesian deposits in the Namur Basin below the Dinant Nappe have not yet been investigated by boreholes. The thickness of the Namurian deposits in Jeumont, St.-Ghislain and Comble-Nord (Fig. 42) indicates that the St.-Ghislain Trough (cf. Fig. 16 and 32) persisted in Namurien times. The same seems true for the Jeumont Shoal to the south of this trough. Indications for a sub-basin southeast of the Brabant Massif are found in a gradual increase of the thickness of the Namurian beds from Chertal trough Soumagns into the Inde area. Important parts of the Devono-Dinantian Cornwall-Rhenish Basin became incorporated within the northward shifting front of the mobile Variscan belt. These were uplifted by the Sudetic movements and eroded subsequently. 64

This can be deduced from the intercalation of conglomerates in the Namurien strata in the southeastern Dart of the French Basin. These ~onglomerates con tain pebbles reworked from Dinantian ane older deeosits (Klerkx, 19661 Thorez & Bless, 1977). It is curious to observe the (allochthonous) conglomerate fans in the Aachen region (Fig. 43) which occupy the geographic Posi- tion of local sand deoosits at the case of the Vissan on the Aachen shoal (Fig. 37). Presumably, both the Visean sand and the ~amurian conglomerates have been derived from the same source area. me 1 ® ® o o ;" 2 00~0 -o o~o ° o_ --3 --o ~o o_o-- , ",u 00o00__ -- HASTENRATH [~c o " o o ---~o.. oo, o %o o _ . .Oo oO-----o o~ E~]AACHEN [[]AACHEN --Z,,OoO me ,\ °°o 0 O0 ~' wOO 0 ooOo 0 ~./ @O

~.~,0 0 ~

I ,, I

Fig. 43. Extension of Namurian conglomerate fans in the Inde area. (After Hahne & Seidel, 1936.) A: Burgholz or Walhorn Conglomerate; B: Geoau or Ardenne Conglomerate. Compare the position of these fans with that of the basal Visean Hastenrath Sandstone in Fig. 37. ~) Mean diameter of pebbles > 15 mm; 2) mean diameter of pebbles 10-15 mm; 3) mean diameter of pebbles <10 mm.

Campina-Brabant Basin

Our knowledge about the Namurian deposits in the Campine-Brabant Basin is restricted to the southern flank of the same. Shales and siltstones predominate. Thickness varation in the boreholes sub-parallel to the presumed border of the Brabant Massif is relatively small (550-680 m over e distance of moran than 100 km). But the Namurian succession becomes signi- ficantly thicker towards the central parts of the basin as can deduced from the more than 1800 m thick sequence of the Rijsbsrgen-1 borehole. It is likely, that the thickness in the centre of the Campine-Brabant Basin is comparable to that recognized in the Central Province in Great Britain (cf~ Ramsbottom, 1957) or the Ruhr Basin in Germany (cf. Hedemann & TeichmUller, 1971), where a thickness of 3000 m or more has been observed° The northern border of the Campine-Brabent Basin is virtually unknown. However, it is believed that this may match the actual structural highs of Zandvoort, Measbommel and Krefeld. A reduced thickness of the Namurian strata on the 66

Krsfeld High in Stenden (about 800 m) was suggested by Elberskirch & Wolburg (1962). This means that there is good evidence for a shoal at the position of the actual Krefeld High during the Namurian.

Ruhr Basin

The northward shift of the basinal axis of the Cornwall-Rhenish Basin in Germany - that had started during the Vissan - continued in Namurian times. The thickest Namurian deposits are found in the Ruhr Basin that may be considered as the northern part of the Cornwall-Rhenish Basin. It coincides with the area that was predominated by an anoxic starved basin environment during the Dinantian. The quickly growing mobile Variscan belt in the south was the most important source area for the more than 3000 m thick Namurian sediments. This is indicated by conglomerate intercalations in the Namurian succession along the southern flank of the Ruhr Basin (Kulick, 1960). The rapid sedimentation was prohibitive for the growth of important vegetations. However, the occurrence of lenses of allochthonous coal and plant debris (including trunk fragments) suggest the existence of local, short-lived swamps which were practically not preserved in the sedimentary record. Only in Upper Namurian times, the environmental conditions favoured the development of widespread vegetations.

Westphalian

Correlation of the Westphalian deposits in northwestern Europe is based on the occurrence of widespread marine bands, which represent short incursions of the sea in a non-marine to paralic environment. The relative frequency of these marine incursions gradually diminished and finally ceased in Upper Westphalian time. The number of these marine bands in Great Britain seems to exceed that in the Netherlands and Germany, where usually less prolific marine fossil assemblages have been recorded. All these observations suggest that the marine incursions originated from the west or southwest and eventually were restricted to parts of Britain. Only during the most important transgressions, a direct communication with marine environments in the U.S.S.R. seems to have existed (Bless & Winkler Prios, 1972). Sedimentation during the Westphalian was characterized by a cyclothemic development. The cycles are comparable to the 60 m cycles of the Namurian and consist of seat-earth, coal, shale and sandstone. Incomplete cycles are frequent. Van Wijhe & Bless (1974) distinguished three main types in the Wesphalian of South Limburg (southeaeternmost part of the Netherlands). These are represented in Fig. 4~. 66

LOWER UPPER WESTPHALIAN A WESTPHALIAN B

Fig. 44. Schematized cyclothems in the Westphalian A-C of Limburg (the Netherlands) with simplified lithological classification adopted by Bless (1973). Lithologies b, f, l, m, and o are extremely rare and can be ne- glected in practice. Key to symbols: a) coal; b) pseudocannel coal; c) shale with coalstreaks; d) shales and siltetones with rootlets (including seat-earth or underclay); e) slightly sandy sediments with rootlets; f) sandy sediments with rootlets; g) sandy sediments; h) slightly sandy sediments (including striped beds); i) shales and siltstenes; k) shales and siltstones w~th non-marine fauna; l) slightly sandy sediments with non-marine fauna; m) sandy sediments with non-marine fauna; o) conglomerate; p) shales and siltstones with marine fauna. (From Van Wijhe & Bless, 1974.)

Cycles with a marine to brackish phase immediately overlying the (usually thin) coal and with widespread sheet sands practically without erosional channels. These developed in an alluvia-deltaic environment with short- lived coastal marshes. Cycles with a brackish to non-marine phase above the (often well-developed) coal and isolated channel sands in a shale-dominated succession. These represent a back swamp facies at relatively longer distance to the shoreline. - Cycles with a non.marine phase immediately above the coal (often of irre- gular thickness and limited lateral extension) and widespread sheet sands alternating with channel sands. Most likely, these cycles are characteristic of fluvial plains with relatively high rates of sedimentation and local, often short-lived swamps or open moors. Comparable cycles have been described from Westphalian deposits elsewhere in northwestern Europe (e.g. Delmer, 1952; Jessen, Kremp & Michelau, 19S2) and from North America (Weller, 1930; Wanlese, 1969). The Westphalian D deposits north of the Brabant and Rhenish Massife are frequently characterized by fining-upward sequences with a relatively coarse sandstone at the base that passes into siltstones or shales at the top of 6? the rhythm. The base of such rhythms may be an erosion surface. Carbonates are extremely rare or absent in the northwestern European basins. Occasionally, so-called roof-balls occur in the marine horzons, whereas coal- balls typically occur in some coal seams with a marine roof (Evans & Amos, 1961; Moore, 1968). According to Moore, coal-balls have been formed in areas at about sea level. A common feature of the Westphalian deposits is the "wash-outs", which cut down through one or more sedimentary cycles. These are fluviatile channels filled with coarse sand fining-upward to silt or clay. Wash-outs in coal seams appear to be preferably filled with silt or clay. Their thickness, width and length is quite variable. Frequently, several small wash-outs run parallel to each other suggesting a braided river system in a swamp facies. Van Wijhe & Bless (1974) adopted an environmental model for the Westphalian of northwestern Europe (fig. 45) that assumes a vast sedimentary basin with an extremely low relief. In such a situation sea level fluctuations could affect important parts of the depositional area. The progressive withdrawal

DECI~EASING HUMIDITY BECAUSE Of CHAMGIttG CLIMATE

Fig. 45. Environmental model for the Westphalian in northwestern Europe. Idealized relationship between sedimentary facies and vegetational pattern, in time and space. Different vegetation types are indicated by some characteristic miospore genera. Of course, these were not restricted to the indicated areas and time. (From Van W~he & Bless, 1974.) 68 of the marine influence to the west was matched by a gradual change of the climate that became more arid in the younger Westphalian. This more arid climate was prohibitive for the growth of extensive vegetations and is marked by the appearance of red beds. A general migration ~f the arid climate towards the south is illustrated by the fact that the firs~ occurrence of these red beds is much later in the south than in the north (e.g. Lower Westphalian C in Scotland; Upper Westphalian D in Campine-Brabant Basin). Local climatic variations between positive areas and basins are reflected in the slightly earlier appearance of red beds on horst complexes and by the occurrence of so-called "hinterland" floras which presumably pre- ferred a somewhat drier habitat. Examples of such "hinterland" floras have been described from the eastern borders of the Mid Netherlands High (Bless et el., 1977c).

Lower Westphalian

Presumably, the Brabant Massif has been covered by Upper Namurian and Lower Westphalian sediments. But thickness variations of the Westphalien north and south of the Brabant Massif suggest that the downwarp of this ara~ was much slower than that of the French Basin to the south and the Campine- Brabant Basin to the north. Bless (1973) suggested that the Brabant Massif was an island during the Lower Westphalian A Finefrau Nebenbank transgression and may have supplied some sediment into the basin during that peried (Fig. 46). The information about the possible existence of a shoal at the place of the Zandvoort-Krefeld High is inconclusive, although comparison of the thickness of the Westphelian A in the Oostzaan-1 borehole (western Netherlands) with that of e.g. Steenwi]kerwald-1 (some 80-90 km to the northeast) doesn't contradict such a suggestion,

Upper Westphalian

The ~egir Marine Band at the base of the Upper Westahalian C represents the last important marina incursion on the northwestern European continent. This is in contrast to the situation in Great Britain, where several important marine incursions followed during the Lower Wastphalian C. It is believed, that the Brabant massif and the Mid Netherlands High became more or less non-depositional areas that at intervals acted as erosive highs. This idea is supported by the isopach pattern for the Upper Westphalian C (Fig. 47). Presumably, the dlfFerantiation into basins and horst areas was much more pronounced during the Upper Wastphalian. 69

g Gon/eN/es, P/er/o/ds..o/[-shore /auna 0 _--~-_- *" A, -- ¢ p Pleno/i/es neer-5•ore facieJ .,(%7

-_-Z--- Marine days and sz'/t5 ...... ~ ~ \~..~[:' -_~__- ooo Norlhern ~order o/ @tea w/lh coal-~al/5 end roof-hefts .... "%<, -'-= ..... /n/erred boundary Z~elween near-shore and oil-shore £ecles ,,'~"'* V 0

.~" --4-- ¢% ,,/ -:-- i"" ',...: -2~- OFF_ S .--r_ ._ ~ " - - "" _ - -4- H 0 R E -~-~ -- "X,," " " ~t ,** ---:--_4 ...... ~:~ ~.. _~-j/ :/.--" "-..... ;: ',

NEAR - SHORE "-~.-...... '~CI~.s? i,,i "::~....~:.. ,"; A o, --.. J.._. .,.:...-- ,,~ OF S~b~..~.~ : o~ tTA'-J/'.,' ---_~_---#~.~7. Maas~richt . .!'PI~AIN ' -~-~,~--~,~I' ~"~~_- ~

MASSIF ?"'::"" ' /ransg"ress/'°n'l "

~//,,~ ,/ ~o °

De/ta bull/~p durinq oe~ressiye s/age of ffne/rez/ He~in~ank aee ~,o~ ~ S ~ - _--zL.d" ~------

0 ~ ~ " 0 14 8kin t I I

Fig. 46. Westphalian A - Paleogeography of area around eastern spur of Brabant Massif during Finefrau Nebenbank Time. (From Bless, 1973.)

The Mid Netherlands High should not be regarded as one large tectonic block. The term is used here for a complex of several smaller blocks which are distinguished from the surrounding basinal area by a relatively slower subsidence or even uplift. These blocks may have moved independently (at 70

PARALIC DEPOSITS MAIN SEDIMENT TRANSPORT

POSITIVE AREA ~_-Z~" MINORSEDIMENT TRANSPORT

--300-- ISOPACHOF UPPERWESTPHALIAN C ALLOCHTHONOUS DEPOSITS (FRENCH BASIN)

Fig. 47. Upper Westphalian C - Paleogeography and thickness variations around the Brabant Massif and Mid Netherlands High. (After Bless et el., 1977a; Van Staalduinen et al., 1979.)

least at intervals) and with different rates of subsidence and/or uplift (Fig. 48). However, these differences are not expressed in the sedimentary record because of the fragmentary information from bereholes or outcrops. The same holds for the basinal areas which also may consist of several tectonic blocks with different rates of subsidence. A good example of a complex high is the Alston-Askrigg Block in Great Britain, whereas the Plzen Basin in Czechoslovakia illustrates the chess-board structure in a generally subsiding basin. It is suggested that the Mid Netherlands High and the Zandvoort Krefeld High formed a similar complex structure during the Deveno-Carbonife- rous. Future exploration may reveal the existence of narrow troughs in this complex during that time-interval. 71

Fig. 48. Chess-board structure of idealized high (horizontal line screen) and basin (blank). (From Bless at al., 1977a.)

Sources of sediment

The principal source area for the Wastphalian sediments was the mobile Variscan belt. This is illustrated a.o. by the overall increase of rudaceous material from the north towards the south and by the decrease of the thickness of Upper Wsstphalian C deposits from the mobile Variscan belt towards the Fenno-Bcandian Platform in the north. More specific arguments for a southern origin of the Westphalian deposits have been forwarded by M. & R. Taichm~llar (1950) and Mackowsky & K~tter (1962) for the NW German Basin, by Bless & Strael (1976) for the Campine- Brabant Basin, and by Barroie (1910) and Barrois at al.(193B) for the French Basin. M. & R. TeichmOller (1950) recognized reworked coal pebbles in a sandstone overlying the Lower Westphalian C Iduna coal seam (NW German Basin), which according to their coalification rank ("Esskohle") had been derived from Lower Westphalian A rocks along the northern border of the Rhenish Massif, where a similar rank of cealification characterizes rocks of that age (cf. Patteisky & TeichmQller, 1962). Mackowsky & K~tter (1962) described reworked coal pebbles from a sandstone overlying the Lower Wsstphalian Midgart coal seam (NW German Basin), which according to their coalification ("Magerkohla") had been derived from the Upper Namurian rocks along the northern border of the Rhenish Massif, where a similar coalification degree characterizes rocks of that age (cf. Psttaisky & TaichmUller, 1962). 72

Bless & Streel (1976) described rich rsworked miospore assemblages from Upper Wsatphalian sediments in the southeastern part of the Campine-Brabant Basin. These miosporss might have been derived from basal Middle Devonian to Lower Westphalian rocks which presumably covered the Rhenish Massif and northeastern portion of the Dinant Nappe until they became eroded during or immediately after the Malvernlen movements in that area. Barrois (1910) and Barrels et el. (Ig30) analyzed pebbles occurring in Upper Westphalien coal seams and in the Upper Westphalian Roucourt Conglo- merate in the French Basin. They counted some 50% of pebbles and blocks of Lower Westphelian (mainly sandstones and some coaly shales) and Namurian (Ardanne Arkose, phthanitas) age and about 40% of Dinantian limestones (both Tournaisian and Visean) with s.c. brachiopods, against only some 10% of older rocks (notably Frasnian and Famannian). The extreme size of some of the Lower Wastphalian sandstone blocks in the Roucourt Conglomerate (more than 4 tons!) suggests a nearby southern origin for these deposits. A significant aspect of these observations is, that in all cases Devono- Carboniferous sediments were reworked from these southern source areas. Repeated recycling of Devono-Dinantian deposits along the northern border of the mobile Variscan belt has been suggested also by Hasmmann (1975), who noted a difference in maturity between Dinantian, Namurian and Wsstphalian arenites in the NW German Basin. The Dinantian greywackas - deposited in the foredaep north of the Mid German High - are characterized by a high content of rock fragments (more than 25%). The Namurian and Westphalian sediments show an overall change from greywackes through sub-greywackes to relatively well-sorted sandstones in the Westphalien C. These Wmstphalian C sandstones contain only some 5-8% of rock fragments and usually less than 15% of feldspars. Feldspars make up more than 25% in the Dinantian gray- wackes. This repasted recycling process since the Dinantian illustrates the continuous northward shift of the southern border of the sedimentary area of the Cornwall-Rhenish Basin under influence of the Variscan movements (Fig. 49) The coalification rank of reworkad phytoclasts (coal pebbles and miospores) in the Westphalian C deposits of the NW German Basin and Campine-Brabant Basin may be used for calculating the relative uplift of the supply areas during the late Variscan movements. The coalification rank of reworked Upper Namurian and Lower Wastphalian coal pebbles in the NW German Basin appears to be distinctly higher than that of the enclosing Lower Waetphalian C sediments: "Esakohle" to "Magsr- kohla" (Rm: 1.6-2.2) ~or the coal pebbles, and "Flammkohle" (Rm: about 0.7) for the Wsatphalian C sediments. The relatlvaly high coalification rank of the reworkad coal suggests that this was buried at considerable depth (1000- ?3

N _ SedimenI:ary >_ ~,~, Mobile (erosive) Varisean BelE S Basin Z ¢I O0 MATURE SANDS LU ~, M/Jd/e Oeyon/,~n m/ospores .J '" ~p/to~2a/FeldspO,"s ~, o1

UJ % O. O- ~ '~_ Malvernian • Asluric ~ ~. AAAAAAAAAAAAAAA Phases Z U} LW ..J u~ SUBGREYWACKES IX Ill

o ..J 3ude{ic + ErzgebirgianT AAAAAAAAA Phases Z ¢I ~n

-l-

Z n, Cl GREYWACKES Z \ r~ :onnlc AAA Z Phase

Z 0 Ill 0 r¢ LU Katazonal Mesoper~h/te ~J O. J O. NoRthern S e d fm e n t a r ~, [ba sin oF erosive area " lw~ l llll lIE U r O p e

Fig. 49. Strongly idealized and simplified scheme of recycling of deposits within the sedimentary basin of northwestern Europe. The relative amount of detritus involved in the recycling process is indicated by the relative width of the arrows. (From Thorgz & Bless, 1977.) 74

2000 m) before uplift and erosion took place in the Lower Westphalian C. This means that important inverse movements must have affected the northern border of the Rhenish Massif from where the oebbles seem to have been derived (M. & R. TeichmUller, ~950; Mackowsky & K~tter, "962). The reworked Middle Devonian to Lower Westphalian miospores in the Upper Wsstphalian C sediments of the Campine-Brabsnt Basin show the same trans- lucency as the extent Upper Westphalian C miosoores in the studied samples. This suggests that the coalification rank of the rocks from which these had been derived was lower than (or equal to) that of the snvelopping Upper Wsetphalian C sediments ("Gaskohle" to "Gaaflammkohle", Rm: 0.75-1.25)o It is worthwile to note, that the coalification of the Middle Devonian rock~ in the presumable source area of the Rhenish Massif (Paffrath-Eifel area, cf. Fig. 50) is relatively low (Rm: ~). This fact corroOorates the suggestion that the miospores nave seen derived from that area. It also indicates that the Upper Devonian to Lower Westohalian sedimentary cover in that area was relatively reduced (possibly less than 500 m). This means that the central portion of the Rhenish Massif remained a shoal since the Middle Devonian and that its relative uplift during the Westohalian C was considerably less important than that of the northern part.

Stephanian

Btephanian deposits have not been recognized in the French Basin, nor in the Campine-Brabant Basin. These occur in the southern part of the North Sea, where the up to 600 m thick sequence includes thin carbonate beds with echinoderm debris. This suggests that marine incursions may have affected important parts of northwestern Europe during the Stephanian. Stephanian strata are also known from a small area along the northern part of the German-Dutch frontier. There, the about 200-300 m thick succession of red coloured shales and sandstones is separated from the underlying Westphalian rocks by an important sedimentary gap. Coal seams are absent, but the occurrence of rare plant debris suggests the existence of a sparse vegetation in an essentially non-marine environment. It is not impossible that this area was isolated from the more paralic sequence in the southern North Sea. ?5

Mi.JNSTERLAND-1 VERSMOLD-1 o O

X\ .... ~.~7 °/o''"~ ~------~.... "-.. \ \ I \ \\ ~\ ~~, ", ', SOEST-ERWITTE,o\ " \ x k X \ \\ --

I I \

A ( £ It J J

_ J //'~,-- / / 'x'd'~ \\ \ '---. ~"~. f/ / Y 'I f ~).-..,~/ ....-(, .4. :,.... ., ./,...... _ .~.-:::.:: .... ~ :~-..)b':.::: • x,.?. :: ::!:; ~.!.i:-Q.2 ':.: C . : "x4~/ SUGGESTED ISOAPOSTILBES i:!: i~ 7 (=lines of equal reflectance) IN GIVETIAN SEDIMENTS 'o. :'.: .\

.~L¢.~ .~:'~ 0 25KM

Fig. 50. Coalification map for Givetian sediments of the Rhenish Massif and surrounding areas. (Modified after Paproth & Wolf, 1973.)

CONCLUSIONS

The Belgs-Dutch Platform is distinguished from the Caledonian fold belt and the Cornwall-Rhenish Basin by its depositional history during the Devono- Carboniferous. Practically no Old Red sediments seem to have been deposited in this area during the Devonian, this in contrast to the situation in the Caledonian fold belt. During the Eifelian-Frasnian and Dinantian transgressions carbonate facies characterize the platform whereas siliciclastics predominate in the Cornwall- Rhenish Basin. The Variscan deformation was largely restricted to the Cornwall-Rhenish 76

Basin that became incorporated in the mobile Variscan belt during the Car- boniferous period. Linear, fault-bounded basins with an overall ENE-SWS trend separated complex horst areas on this platform since at least the Middle Devonian. Dif- ferential subsidence of basins and horsts is reflected in rapid lateral changes of the thickness of the sediments. Several of the fault systems separating these Peleozoic basins and horsts seem to have been rejuvenated in Mesozoic and Cenozoic times. Climatic conditions favoured reef growth during the Eifelian-Frasnian and Dinantian transgressions, and the formation of extensive peats during the Silesian. The climate favoured also the repeated occurrence of red bed and evaporite facies during the Devono-Carboniferous. The structural-depositional history of the Belgo-Dutch Platform can be compared into detail with that of the North American Crston. Presumably, both areas were located in between the same paleoletitudes. The comparable geology of the Dsvono-Carboniferous rocks in North America and the Belgo-Dutch Platform have often drawn the attention of petroleum geologists. The Devono-Carboniferous rocks of North America include important hydrocarbon resources. These have not yet been recognized in northwestern Europe. However, large portions of the Devono-Carboniferous rocks on the Beige-Dutch Platform are covered by thick sequences of younger deposits and remain to be explored by deep borsholes. Maybe, it is only a Question of time before economically important hydrocarbon occurrences are detected in this area

ACKNOWLEDGEMENTS

We wish to express our sincere gratitude to a team of enthusiastic col- laborators. Without their skilful technical assistance the present paper would never have been possible: Messrs. H.F.J. Bisschoff, G.M.A. Geeraedts, 2.H.L. Jansen, H.J. Kastermans, J.P.M.Th. Meessen, H.M.J. Ruyters, A.J. Schaaf and Mrs. C.A.M. Willems-Oreszen.

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