Bohrung Metelen 1001—eine Forschungsbohrung zur Erkundung des Campans im nordwestlichen Münsterland (NW-Deutschland)

Zusammenfassung

Die auf dem Schöppinger Berg niedergebrachte Bohrung Metelen 1001 ist eine Forschungsbohrung im Campan des nordwestlichen Münsterlands (NW-Deutschland). Neben einer geologisch-stratigraphischen Bohrungsbearbeitung wurden interdisziplinär Faziesuntersuchungen durchgeführt, deren Ergebnisse in Einzelbeiträgen in dieser Zeitschrift vorgestellt werden. Die Bohrung setzt im oberen Untercampan an und durchteuft zunächst sandigen Mergelstein mit Einschaltungen sandiger Kalksteinbänke. Darunter durchteuft sie das gesamte Untercampan, das weitgehend in Tonmergelsteinausbildung vorliegt. Das Untercampan hat eine unerwartet hohe Gesamtmächtigkeit von 261 m. Obersanton wurde im tiefsten Abschnitt der Bohrung angetroffen. Es untersucheidet sich lithologisch nicht vom Untercampan. Die erbohrte Schichtenfolge läßt sich lithologisch in sechs Abschnitten gliedern. Das Profil (Abb. 2) und das Schichtenverzeichnis der Bohrung werden vorgestellt, die geologische Situation im Umfeld der Bohrung wird beschrieben.

Summary

The borehole Metelen 1001 was sunk on Schöppinger Berg in northwestern Münsterland (NW Germany). This research borehole in Campanian strata served for interdisciplinary facies analysis and geologic-stratigraphical works. The results are represented in contributions in this issue of the journal.

The borehole starts in the upper part of the Lower Campanian with sandy marlstone with intercalated layers of sandy limestone. The rest of the Lower Campanian mainly consists of clayey marlstone. The Lower Campanian has an unexpectedly high total thickness of 261 m. The Upper Santonian was met in the deepest portion of the borehole. It does not differ lithologically from the Lower Campanian. The geological sequence found can be lithologically devided into six units. The profile (Fig. 2), the drill-log and the geological situation of the surrounding are described.

The cross-section A—B (Fig. 3) illustrates the geological situation and the position within the Schöppinger Berg. It crosses the hill in an east-west direction. Two groundwater observation wells exist beside the Metelen 1001 borehole on Schöppinger Berg, each 100 m deep. One of these (borehole Schöppingen 2, R25 85 300, H57 76 180) was used for comparsion in the profile. The boring logs of these observation wells are not suitable für stratigraphic correlation. Cuttings are no longer available. Nevertheless, a connection with the Metelen 1001 borehole is possible based on geophysical logs. In addition, the results of two boreholes (borehole 10047, R. 25 88 740, H 57 77 270 and borehole 10048, R 25 87 900, H 57 76 410), situated east of the hill near Leer have been considered in the profile. Both boreholes with a Cretaceous profile of 14 m and 57.5 m, respectively, were measured by geophysical gammaray-log and classified biostratigraphically.

Arnold (1964 b) andFrieg (1977) demonstrated the flat synclinal bedding of the Schöppinger Berg strata, using tectonical data evaluated from outcrops. The boreholes Metelen 1001, Schöppingen 1 and 2 fit this theory well.Frieg (1977) showed that the biostratigraphical boundary between the Lower and Upper Campanian presumably lies within the layers which he called Schöppinger strata. The boundary lies deeper than the base of the Coesfelder strate (Arnold 1964b and unpublished maps). The Metelen 1001 borehole confirms these results. The Schöppinger Berg consists completely of Upper Campanian sediments. The Lower Campanian starts at its foot.

The boreholes in the eastern foreland of the Schöppinger Berg indicate a fault which subsides the eastern fault-block for about 30 m. Under a Quatarnary cover the borehole 10048 met silty to sandy clayey marlstone with intercalated limestone layers in the upper part of its creataceous profile. This section can be correlated to the lithological unit 1 b (lower Upper Campanian) lithologically and biostratigraphically as well as by log-comparisons. Underneath this section a clayey marlstone going down to the final depth of 66 m corresponds to the lithological units 2 and 3. The short Cretaceous profile of borehole 10047 consists of clayey marlstone and comprises the upper part of the Lower Campanian. Logs allow the boreholes 10048 and Metelen 1001 to be comparwd. The strata dip at about 2° towards the west in the area of the boreholes at the eastern foot of the Schöppinger Berg.

An unexpected result is the great thickness of the Lower Campanian: 176 m in the upper part of the Lower Campanian and 85 m in its lower part. Because of this discrepancyRescher (1991) revised the microfaunal analysis of the Münsterland 1 borehole. Contrary to the published data, the Upper Campanian is thinner in the Münsterland 1 borehole. The thickness for the Lower Campanian corresponds to that of Metelen 1001 (Rescher 1991). The original intention of taking the borehole down to the Middle Santonian has not been fulfilled because of the unexpectedly great thickness of the Lower Campanian.