BIOKLASTEN-STRATIGRAFIE OF ...

BIOKLASTEN-STRATIGRAFIE OF ECOZONATIE VOOR HET KRIJT (SANTONIAAN - CAMPANIAAN - MAASTRICHTIAAN) VAN ZUID-LIMBURG EN OOSTELIJK BELGIE

ABSTRACT.
Bioclast-stratigraphy, or ecozonation, of the Cretaceous (Santonian - Campanian -Maastrichtian) in South Limburg (the Netherlands) and eastern Belgium.
A brief overview is presented of lithological subdivisions that have been published over the years for the Upper Cretaceous sediments (Santonian-Campanian-Maastrichtian) in Belgium, the Netherlands and Germany (Fig. 2).
The various Formations and Members with their respective type localities are briefly described, followed by a discussion of bioclasts and bioclasts ecozones. The results of samples from boreholes and outcrops studied for their bioclast content are subdivided into ecozones, such as the ones described previously for the Belgian Campine area (Felder, 1994) (Fig. 3). The bioclast ecozones are compared with the lithological and international subdivi- sions of the Late Cretaceous (Fig. 4 ).
In the outcrop area encompassing the southern part of both Limburg provinces and the northern part of Liège province, samples were taken over considerably shorter intervals (0.15-1.00m ) than in the Belgian Campine and the Brabant Massif where the Cretaceous is only accessible by boreholes (3.00-5.00m). Therefore, more peaks and throughs could be distinguished in the relative number of bioclasts. From a comparison of the data it appears that it is possible to correlate the majority of these peaks. Numbers given here to the peaks have been defined as follows: they are preceded by a capital letter (either followed by a lower cast letter or not) to indicate the bioclast group (e.g. F. Foraminifera, B. Bryozoa, Be. Belemnoidae, Br. Brachiopoda, etc.). The letter (or letters) are followed by the Roman numeral of the bioclast ecozone ( e.g. FII, FV, BIV, BV, BeI, BeIII, BrIII, BrIV) in which the peaks are situated. Finally follows an Arab numeral (e.g. FII3, FV3, BIV3, BV3, BeII3, BeIII3, BrII3, BrIV3) to indicate the order of peaks in the ecozone.
Previous1y subdivided and numbered units within the ecozones are here maintained. For instance, in the Vijlen Member seven units (Vijlen 0- Vijlen 6) were distinguished and the peaks of foraminifera identified with letters (A up to including L) (Felder & Bless, 1994; Felder, 1997a). The Crinoidea units were also numbered within the ecozones IV and V (CR1 up to and CR10), as were the Pelecypoda units previously distinguished in ecozones IVa, IVb and V (Felder, 1997b). To elucidate matters, the letter P is here added to these Pelecypoda units. The peaks within these Pe1ecypoda units were previously distinguished by x and y. Following this numbering, the Pelecypoda in other ecozones (II, III en VI) are subdivided into a similar way. The separate peaks, however, are distinguished in these newly subdivided units, by using successive Arab numerals.
The overviews (Fig. 9, 21, 26, 29 and 30) present an overview of the various ecozones and illustrate the sedimentary variability of the extended Maastricht type area.

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