Early Carboniferous (Mississippian) Neptunian Dykes in Middle Devonian Reef Limestones of the Hahnstätten Quarry, Lahn Syncline, Rheinisches Schiefergebirge

Abstract

Neptunian dykes in Devonian reef limestones are described from the Hahnstatten Quarry in the south-western Lahn Syncline. The echinoderm grainstones of the dykes contain mixed conodont faunas of Late Frasnian to Early Carboniferous age, indicating an Erdbach Limestones I and/or II assignment according to the definition ofKrebs (1966). The almost complete record of all conodont zones of this time interval mentioned above suggests continuous sedimentation at least from the earlyrhenana up to the lateanchoralis Zone on the top of the drowned Devonian Hahnstatten Reef. The preferred orientation, the short time span of development and filling of fissures and crevices, and the coincidence of their formation with the first volcanoclastic sediments as well as the collapse of the northwestern part of the Langenaubach reef (Langenaubach breccia) in the Dill syncline, coincides with the interpretation that the fissures and crevices were caused by crustal stretching and related extensional tectonics.