The distribution of Pre-Westphalian source rocks in the North German Basin- Evidence from magnetotelluric and geochemical data

For the first time this project attempts to directly correlate magnetotellu ric and geochemical data with the aim of creating a model on the regional d istribution of potential pre-Westphalian source rocks deposited in marine e nvironments in the North German basin. Analysis of the magnetotelluric data shows, that there is a deep good condu ctor at the north-eastern fringe of the North German basin around the islan ds of Rugen and Usedom and on the mainland north east of the Anklam Fault. Through integration with seismic data and the offshore well G14 the conduct or can be correlated with the Cambro-Ordovician Scandinavian Alum shales. T o the south an adjoining area approximately corresponding to the depo-centr e of the Rotliegend basin lacks a deep good conductor. Therefore it can be assumed that a regional distribution of comparable source rocks is unlikely . Another excellent and important conductor starts to the south west of the Lower Elbe Line extending along the Dutch-German border into the North Sea , and into the Munsterland, Its place in the local stratigraphy has not bee n adequately established. It is most likely that this good conductor corres ponds to the black shales of the Early Namurian and the Dinantian, which is the case in the boreholes Munsteriand 1 and Prottlin 1 for example. In thi s paper they are collectively called Rhenohercynian Alum shales. On the Dut ch-German border a transition into the "Bowland Shale" facies or equivalent s is to be expected. It cannot be ruled out that even stratigraphically old er black shales, possibly from the Cambro-Ordovician could contribute to th e high integrated conductivity of the deep good conductor. The evidence of highly conductive layers in the deep subsurface poses the q uestion whether these layers could be potential source rocks for the gases in the north German gas fields. This question can be answered with a clear yes. Gas and isotope geochemical studies on gases from producing Rotliegend deposits have shown that Rhenohercynian Alum shales have been a significan t sourer for these fields. This will be illustrated in detail using the gas fields from the production province "Ems Estuary" as an example.