Diagenetische Veränderungen in den Rotliegend Sandsteinen im NW-Deutschen Becken

Abstract

ZusammenfassungMit seinen auf 8000 m bis 6000 m versenkten Schichte11 bildet das Rotliegende in Nordwestdeutschland eine Gasprovinz, deren Lagerst~itten-Inhalte aus dem Karbon im Liegenden abgeleitet werden. Die l:teservoire sind Sandsteine, die mit Tonsteinen wechsellagern. Sie wurden nach einer Phase reger vulkanischer Aktivitgt des untersten Perm als red bed-Sedimente in einem ariden Klima abgelagert.Das Untersuchungsgebiet ist der Raum zwischen Weser und Elbe. Es wurde versucht, eine grunds~itzliche Teufen/Porosit~its-Variation der Sandsteine zu erarbeiten, was wegen der komplexen Gefiigebedingungen sehr schwierig ist. In diesem Zusammenhang ergab sich die Markierung des Endes der mechanischen Kompaktion bei einer Porosit~it um 9.2 % fiir feinkSrnige 'Sandsteine.Die in den Poren (epigenetisch) ausgef~illten allochemischen Zementminerale zeigen Merkmale einer synsediment~iren bis friihdiagenetischen Kristallisation. Nicht zuletzt kommt das in der regionalen pal~iogeographischen Anordnung der Zementminerale Karbonat, Sulfat und Halit zum Ausdruck, in dieser Reihenfolge zunehmend evaporitischen Charakters vom Beckenrand im Siiden zur Beckenachse im Norden hin bevorzugt verteilt.In den Intergranularen der Sandsteine sind authigene Tonminerale welt verbreitet, besonders als Coating-und Overgrowth-Gefiige. Die Reaktion von Feldspat und die gesteigerte Authigenese yon Tonmineralen in einem Gebiet, in dem die gew6hnlich anzutreffenden Effusivgesteine im Liegenden fehlen, werfen ein Licht auf die Herkunft dieser Tonminerale und auf die Migrationsvorg~inge. AbstractWith its sequences attaining depths of 8000 to 6000 m, the Rotliegend in NW Germany forms a gas province whose reservoir contents are derived from underlying Carboniferous. The reservoirs consist of sandstones alternating with shales, which were deposited in an arid climate as red bed sediments after a phase of intensive volcanic activity in the lowermost Permian.The investigated area is situated between the rivers Weser and Elbe. It was tried to obtain a basic depth/porosity variation of the sandstones, a rather difficult attempt because of the very complex fabric conditions. In this connection the end of the mechanical compaction could be marked at a porosity of about 22 ~ for fine-grained sandstones.The alloehemieal cement minerals precipitated (epigenetieally) in the pores show features of a synsedimentary to early-diagenetie erystallisation. This is not least reflected in the regional paleogeographic distribution of the cement minerals carbonate, sulfate and halite which, in the order of their listing, become more evaporitic, with increasing proportions from the basin margin in the south towards the basin axis in the north.In the intergranulars of the sandstones, authigenie clay minerals occur frequently, in particular in the form of coating and overgrowth. Reaction of feldspar and advanced authigenesis of clay minerals in an area where the generally occurring effusive rocks are

Controls on Clay Mineral Distribution and Chemistry in the Early Permian Rotliegend of Germany

“…The distribution and abundance of the different cements vary on a local scale. For example, radial chlorite is found only in the upper parts of Rotliegend sequences showing development of shoreline sandstones, pervasive dickite growth occurs where the Rotliegend lies directly against the Carboniferous Coal Measures (also noted by Drong, 1979), and the abundance of authigenic illite in the Rotliegend increases in the vicinity of the Carboniferous coals and of graben-bounding faults (also seen by Gaida et al, 1989). The presence of underlying volcanics or the abundance of volcanic rock fragments shows no relationship with clay growth, suggesting that volcanic material is not the major source of ions for the clay minerals (as suggested by Hancock, 1978).…”

Contrasting red bed diagenesis: the southern and northern margin of the Central European Basin

“…Southern part of the CEB Rotliegend sandstone diagenesis at the southern margin of the CEB has been described in detail in many articles (Hancock 1978;Drong 1979;Budzinski and Judersleben 1980;Gaupp et al 1993;Platt 1993Platt , 1994Gaupp 1996). A brief review of the most important diagenetic and sedimentological features will highlight the differences to the northern margin of the CEB.…”

“…Diagenesis is mainly controlled by sedimentary facies and by the relative position within the basin during that period (Drong 1979;Platt 1994;Gaupp et al 1993). Eodiagenetic carbonates, sulphates, locally halite, minor quartz and albite, and hematite precipitated from meteoric, partly saline waters which were fed from the Variscan highland areas to the south and the Ringkøbing-Fyn-High to the North, respectively.…”

“…The earliest generation of these sebkha-type cements is indicated by highest IGV (up to 40%) and direct contact to grain surfaces (Budzinski and Judersleben 1980;Gaupp 1996). The distribution of these cements, which have been studied in detail by Drong (1979), Gaupp et al (1993), and Platt (1994), is mainly controlled by sedimentary facies.…”

“…Many attempts aimed at understanding porosity and permeability evolution in these sandstone reservoirs, mostly based upon petrographic studies, and important diagenetic processes and their controls have already been identified (e.g. Glennie et al 1978;Drong 1979;Almon 1981;Seemann 1982;Gaupp et al 1993;Lanson et al 1996;Leveille et al 1997). However, reasons for contrasting diagenetic evolution in different basin compartments are still not well understood and prediction of diagenesis thus remains very limited.…”