Depositional Environments

trast the Kunrade Chalk occupies a smaller area The depositional environments of the Maastricht outcrop in the northeast corner of South Limburg between Valken- and Kunrade Chalks (Maastrichtian) from the burg and Heerlen - extending also into West Germany. type area of Limburg, Netherlands Lithofacies: R.E. Pollock by The Maastricht and Kunrade Chalks are essentially calca- of reous, with a varying amount terrigenous clastic con- ABSTRACT: tent which is more evident in the Kunrade Chalk. We Following the deposition of the Gulpen Chalk ICampanian-Maas- the two ‘chalks’ their trichlianl. the Maastricht and Kunrade Chalks exhibit typicalfeate- can split up on, firstly outcrop pat- shallow carbonate There and their res of high energy water deposition. is a tern, on their lithology, finally on depositional progressive shallowing through the depositionof the Maastricht Chalk environments. as typifiedby the changes from calcilutite Ichalk I deposition in the The contemporaneity of these two deposits has in the past lower Maastricht Chalk to medium and coarse grained calcarenities been in but it is fairly well documented that the with occasional calcirudites in the higher levels. This trend is paral- dispute Kunrade Chalk is lateral the leled in the faunal characteristics, exhibiting an increase in abun- a equivalent of Maastricht dance and diversity of the benthos. Chalk In the between (Romein, 1963). area Valkenburg and Kunrade the Maastricht and Kunrade Chalks can be Introduction: seen to interfinger (Kruit, 1949). the Following widespread trangression during the Upper The of these chalks from calcisiltites lithologies range with its in the late and Cretaceous peak Campanian early and calcarenites containing subordinate terrigenous clas- Maastrichtian, there followed over most of Northwest tic horizons in the Kunrade Chalk to medium to coarse with the of the Europe a regional regression deposition calcarenites and calcirudites in the Maastricht Chalk. The late Maastrichtian and Danian ‘chalks’. limestones are generally soft and friable, with irregularly Locally, here in South Limburg, the Maastrichtian Upper comented hard horizons, more prominent in the Kunrade shows the characteristics of re- a transgressive sequence Chalk, characterised by an alternation of well cemented from local the fault sulting downwarping along major and friable horizons of calcisiltite and calcarenite. These block area to the northwest. I wish to describe the fea- well cemented horizons in the Kunrade have an irregular tures of this as seen in the of the sequence deposition aspect and although they extend laterally cannot be fol- Maastricht Chalk and Kunrade Chalk. lowed for great distances and often run into each other. The Maastricht Chalk in the western half of outcrops As stated before, the Kunrade Chalk has a high clastic South Limburg from the vicinity of Valkenburg in the is in the basal of content, this seen best part the section into northwards towards the west, across Belgium, dipping where horizons of prominent quartz and glauconite, with Cretaceous depocentre in the North Sea (Hancock Upper minor amounts of calcarenite, are intercalated with glau- & Scholle, The area around 1975). major outcrop being conite calcisiltites. Higher in the succession, as seen at Maastricht and the type locality at St. Pietersberg. In con- Kunderberg, the calcisiltites and calcarenites have a very Fig. I. Locality Map ofSouth Limburg, Netherlands. 16 NE S W. Fig. 2. Diagrammatic section across South Limburg form to content and often contain clasts of high argillaceous Pietersberg tend to coalesce into larger flint nodules and quartz and quartzite pebbles, clay laths and angular grey often become large sheet-like concretions in the expo- of derived from fragments high rank coal, presumably a the silification of sures in Belgium. In most cases these Carboniferous source (Pollock, 1974). sheet like concretions has not obscured the original bed- The Maastricht in contrast, is a limestone Chalk, very pure ding and burrow systems of the original chalk. Flints do with minimal content. The overall size a terrigenous grain not occur within the Kunrade Chalk at Kunderberg. Ne- of the Maastricht Chalk increases the section from the up vertheless, thin section analysis of these limestones show Mb into Md, apart from irregular shelly calcirudite hori- the of small of presence amounts length-show chalcedony The break between the white calciluti- zons. underlying (lutecite), normally associated with sulphate minerals and tes of the Gulpen Chalk and the yellow calcarenites of evaporate sequences in general (Fok & Pitman, 1972). the Maastricht Chalk is marked by a minor hardground or conglomeratic horizon. Biofacies: The constituents of the calcarenite shell in- These limestones and are debris, yield a very interesting varied fauna, traclasts, rare quartz, pellets and micrite. They have a high contrasting with each other and also with the underlying primary porosity unlike the Kunrade Chalk. Sedimentary Gulpen Chalk. Faunal evidence shows a marked change obcured intense biotur- in the climatic conditions the formations. structures are normally by usually between two bation, but low angle cross stratification can sometimes The fauna of the Gulpen Chalk has affinities with the Bo- be seen in the quartz-glauconite horizons of the Kunrade real zoogeographical region and although the climatic Chalk. Larger scale cross stratification is sometimes pre- conditions prevalent during Gulpen Chalk times were not not- sent within the Md unit of the Maastricht Chalk but truly Boreal, (using the term ‘Boreal’ here in the geogra- the is subhorizontal both mally bedding throughout phic sense), the conditions existing were somewhat sub- chalks. Southwards from St. into the followed sub- Pietersberg Belgium tropical to warm temperate by tropical to size of the Maastricht tends remain grain to constant tropical or Tethyan for the Maastricht Chalk. Faunal affi- with medium calcarenites being the predominant litholo- nities of the Gulpen Chalk are correlated with Northwest gy. The coarse calcirudites are normally absent although Germany and the North Sea area in general, whilst those thin coarse shelly horizons do occur in minor amounts. of the Maastricht can be correlated with the Maastrich- The Maastricht Chalk is generally soft and friable, but tian (Dordonian) fauna’s of the Aquitaine Basin (Voigt, contains, commonly within the Md unit well cemented 1964). formed of non-sedi- differences in the of their fauna ‘hardground’ horizons, during periods Major diversity are appa- mentation.The cementation extends in for 30 between the chalks. The Kunrade Chalk has depth up to rent two an or 40 cms, returning to soft friable calcarenites with depth. essentially bivalve fauna, the main representatives being The hardgrounds extend laterally over considerable dis Nuculana, Limatula, Cucullaea and the ubiquitous ostreiid in the St. minor of small tance as mappable horizons, predominating Pie- Pycnodonte, amounts gastropods also occur tersberg area and becoming less apparent to the east also with rare occurrences of the echinoid, Cardiaster granu- southwards into Belgium. losus (Goldfuss), ammonites and brachiopods. Not only is Flints occur through both the Maastricht and Kunrade the fauna dominantely bivalve, but they are mainly shal- Chalks with a concentration in the Mb unit of the Maas- low burrowing forms which prefer muddy substrates and associated tricht Chalk. At St. Pietersberg, they occur as irregular the turbid bottom conditions. An associated nodules and often follow the shape and form of burrow microfauna of bryozoa, foraminiferaand ostracoda is also also the lower Plant remains systems. They occur sporadically through present. occur commonly, especially the levels the Me These nodules in St. The burrow of Thalas- of unit. irregular seen seagrass Thalassocharis. systems 17 corals and echinoids form unit, where a high percentage of the fauna. The ostreiids Pycnodonte and Agerostrea are very common. Associated with this faunarare ammonites, crinoids, belemnites and rudistids. The bivale fauna shows forms which are normally associated with sediments of sand size grains, but a variety of ecological niches are represented, both infaunal and epifaunal. The Me and Mb units contain an associated fauna of infaunal bivalves, shallow burrowing echinoids, bryozoa and With of occasional oysters. the prepondence hardgrounds within the Md unit, fauna’s preferring a harder substrate predominate - cideroids, corals, thecidean brachiopods, rudistids etc. and free swimming bivalves, e.g. pectinids. With a return of sedimentation, these forms are super- shallow suited ceded by burrowing forms, more to unsta- ble conditions, all the fauna’s represented here are very similar to fauna’s associated with or near to modern reef complexes, although no reefs, as such, have been found within the Maastricht Chalk. An abundance of the corals and also associated algal (Li- thothamnium) remains, show that the water depth was very shallow with high energy conditions prevalent during most of the deposition of the Maastricht Chalk. To the south in Belgium the faunatends to be less diverse although still as abundant, with bivalves predominating. In most cases the faunal remains, show signs of tran- sportation - i.e. fragmentation and the deposition of these chalks are thought to be the flanks of the shoal area at St. Pietersberg. Conclusions: The Maastricht Chalk can be compared to the recent carbonate sheet sands as described

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