Open Access

Till Kasielke

• Geologische Entwicklung und Geomorphogenese des Bochumer Raums werden anhand von Aufschlüssen und zahlreichen Abbildungen erläutert. Die präquartäre Entwicklung lässt sich wie folgt umreißen: 1.) Sedimentation der flözführenden Schichten des Oberkarbons in einem großen Delta in einer Randsenke vor dem sich bildenden variskischen Gebrige, 2.) Faltung der Deltasedimente im Zuge der variskischen Orogenese am Ende des Oberkarbons, 3.) flächenhafte Abtragung vom Perm bis in die Unterkreide, 4.) Meerestransgression und Ablagerung mariner Sedimente in der Oberkreide, 5.) flächenhafte Abtragung im Tertiär. Im Quartär führte eine erneute Hebung zur Einschneidung der Täler. In der Saale-Eiszeit erreichte das nordische Inlandeis das Ruhrtal, veränderte den Ruhrlauf im Osten Bochums und hinterließ eine Grundmoräne und Schmelzwasserablagerungen. In der Weichsel-Kaltzeit wurde das Gebiet von Löss bedeckt. Zu den ruhrgebietstypischen Reliefveränderungen der jüngsten Vergangenheit zählen Spuren der Kohlengräberei und Bergsenkungen.
• Bochum is located at the transition between the Rhenish Massif (Rhenish Slate Mountains) in the south and the Münsterland Basin in the north. Sedimentary rocks of the Late Carboniferous (Pennsylvanian) are exposed at the surface in the southern part of Bochum. These sediments were deposited in a deltaic system that developed in a foreland basin at the northern margin of the Variscan orogen. Eustatic sea level changes and the intrinsic morphological dynamic of the delta system caused cyclic deposition of sand, mud and marine clay with numerous intercalated peat beds (coal seams). At the end of the Carboniferous, the sediments were incorporated in the Variscan Orogeny and became folded and thrusted. After a long-lasting period of erosion and the formation of a peneplain, a rising sea-level during the Upper Cretaceous caused flooding of the Bochum area. This was associated with the deposition of horizontally bedded marine sediments, resting with a distinct unconformity on the inclined strata of the Carboniferous. The west-east orientated coastline was situated somewhere south of the Ruhr. Subsequent erosion removed the Cretaceous sediments within the southern part of Bochum, but in the northern part the Carboniferous is still covered by a thick overburden of the Cretaceous. Climate cooling at the transition from the Tertiary to the Quaternary and the contemporaneous beginning of a renewed uplift of the Rhenish Massif caused river incision and the formation of river terraces during the Quaternary. During the Saalian glaciation the Scandinavian ice sheet reached the river Ruhr, and Bochum was covered by ice. The ice sheet dammed the Ruhr and changed its course in the east of Bochum. During the last glacial (Weichselian) Bochum became covered by loess deposits of up to 10 m in thickness. The youngest modifications of the surface are related to soil erosion, primitive coal digging since medieval times, and large scale subsidence resulting from underground mining in the 19th and 20th century.