Johann Peter Groetzner im Ruhestand

Biographie und Danksagung an Johann Peter Groetzner

Frühdiagenetische Karbonatzementation in glazigenen und fluviatilen Sedimenten des Wesertales NW Hameln

In the Weser valley NW Hameln early diagenetic carbonate cementation is present in the upper Elsterian to Drenthe sediments. Examination of the calcite cement indicated a multiphase formation. Cementation occured mainly in vadose environment above ground-water table. This process generated predominantly brown calcite cement with a crystal size of <5 to 20pm. Next to meniscus-cement this fine-crystalline calcite forms further cements typical for vadose zone. In one layer of the „Mittelterrasse'-sediments, deposited in the late Elsterian age, a calcite cement is present, which may already have formed in the Holstein Interglacial. Cementation started in the upper-most layers of the „Mittelterrasse'-sediments in a late phase of „Mittelterrasse“-accumulation in this area. The so formed consolidated layers were deformed by the Drentheglacier. After ice melting cementation continued in at least 3 phases, creating nonluminiscent phreatic, orange to red luminiscent vadose and nonluminiscent vadose calcite cement.

Oberjurassische Korallen-Geschiebe (Thamnasteria concinna) aus einer Kies-/Sandgrube bei Freden/Leine (Leinebergland)

Upper-Jurassic geschiebe-corals (Thamnasteria concinna) from a gravel-/sandpit at Freden/Leine are described. They are slightly bored by bivalves (Gastrochaenolites) and worms (Trypanites). Some oysters (Nanogyra Inana) encrusted the surface. The corals growed as massiv head-like (bulbous) colonies with "multicolumnar growth form" and ragged outlines. Similar shaped colonies are reported from Easteuropean Upper Jurassic (Pommerania), but are never reported for NW-Germany. Beds in which the coral-geschiebe were found - Drenthe stage in age - contain a high content of local geschiebe-material. The low degree of abrasion of the coral-geschiebe indicates short glacial transportation. It is possible, that the geschiebe originate from the Heersumer Schichten from Selter to Thüster Berg.

Elfas und Ahlsburg - die Struktur der Schollengrenze zwischen Hils und Solling

The Elfas, Ahlsburg, and Salzderhelden overthrusts have been considered for a long time to be halotectonic structures caused by diapiric rise of Zechstein salt into thrust planes and other zones of weakness in the overlying rocks. Much of the Markoldendorf syncline between the overthrusts is covered by Quaternary deposits. The structure of the syncline and its western and southern boundaries were mapped with the help of many boreholes and micropalaeontological dating during remapping of the 1 : 25 000 geological sheet 4124 (Dassel). The Ahlsburg overthrust has now been shown to continue to the NW and to lead into the Lüthorst graben, which truncates the syncline in the west and passes into the crestal fault of the Elfas anticline. Figure 6 shows the NW-SE trending faults bounding three blocks which, according to seismic interpretation (Geotectonic Atlas 1996), have moved several times, in some areas in opposite senses. The NNE-SSW-trending grabens act as hinges, separating the NW-SE faults into sections that have undergone different movement.

Geschiebekundlich-stratigraphische Untersuchungen in der südlichen Lüneburger Heide

An outline of the Pleistocene history of the southern Lüneburg Heide is given based on the interpretation of exposed sections and indicator-stone analysis. Locally, Elsterian sediments crop out at the surface, mainly near the Holsteinian kieselgur (diatomite), thus indicating the existence of a pre-Saalian relief. Most of the Pleistocene deposits were formed during the three Saali- an ice advances. The ground moraine (basal till) of the first advance (the main Drenthe moraine) and its outwash sands are only locally exposed and only at the margin of the Aller valley do they form a relatively extensive plain. To the north, they are overlain by outwash sands of the late Drenthe advance. Also the Uelzen end moraine consists mainly of these outwash sands. The Uelzen moraine was overridden by the same ice advance. The Warthe ice sheet left only minor traces ridge; its advance came to a final stop at the already dumped morainic material.

Oberjura-Riffe in NW-Deutschland : ein Überblick

For the first time, in this study NW-German coral and reef localities are comprised. Three well exposed and developed reefal units, which have been analyzed by a working group located at the Institut für Geologie und Paläontologie in Hannover, are extensively described and classified orientated with pre-existing reef classifications. The paleoecologic interpretation of these reefs is compared with several similar reefal units from throughout W and SW Europe.

Kies- / Sandkörper im Wesertal zwischen Rinteln und Porta Westfalica

In this article the sand-/gravelbodies from Hausberge-Veltheim and Krankenhagen- Möllenbeck in the Wesertal are described and compared considering their depositional and architectural regime. A scenario is developed to explain the genetic sequence of the deposits. The sand-/gravel-body exposed at Krankenhagen-Möllenbeck was deposited first in form of a marginal käme. Subsequently during the Drenthe-stade of the Saale ice age, the sedimentation of the sand- /gravelbody at Hausberge-Veltheim took place under the depositional environment of an end- moraine.

Der Schwermineral-Gehalt von Saale-zeitlichen Moränen- und Schmelzwasser-Ablagerungen des Münsterlandes

This article is a first summary of the heavy-mineral content of moraine and meltwater deposits of the Saalian glaciation in the Münsterland and its northeastern extension (NW Germany). In the beginning the appearance and distribution of both types of sediments are described (E. Speetzen), then the heavy mineral composition of selected outcrops is reported and the results are compared (D. Henningsen). Generally the predominant heavy minerals are garnet, minerals of the epidote group, zircon, and ordinary hornblende. The heavy mineral contents of moraine sediments sometimes are similar to that of meltwater deposits, in other cases they are different. Obviously there exists no relation between the heavy mineral composition and various advances of the Scandinavian ice sheet and their sediments, the content of heavy minerals rather depends on local influences.

Aufbau und Nutzung des Fachinformationssystems Geologie im Niedersächsischen Bodeninformationssystem NIBIS

Digital data from various scientific fields is stored in separate information systems („FIS geology“, „FIS pedology“, etc.) in the Lower Saxony Geo-Information System NIBIS so that it can be processed and interpreted; this is necessary to meet increasing demand for soil-relevant information for decision-making and planning purposes. The necessary work will be considerably accelerated and its quality improved by setting up and actually using such a tool. A detailed account is given of the Lower Saxony Geo-Information System NIBIS, in particular how the data base is set up and how the NIBIS is used in cases where concrete problems occured.

Verteilungsmuster der Mesofauna im hohen Ober-Hauterive Nordwestdeutschlands

The vertical distribution pattem of mesofaunal elements is described from clay-marl bedding rhythms from the Frielingen section (Hannover, NW Germany), which exposes latest Hau- terivian sediments (early Cretaceous). Some mesofaunal groups show a correlation with the pale- dark bedding rhythms. The pale, marly beds are chracterised by bryozoans. In addition remnants of crinoids, echinoids, asteroids, ophiuroids and holothuroids are more common in pale layers than in dark ones. Converseley, the relative abundance of serpulids, fish remains, bivalves and gastropods shows no relationship to the bedding rhythms.

Quantifizierung postholsteinzeitlicher Subrosionen am Salzstock Gorleben durch statistische Auswertung von Bohrergebnissen

The Gorleben salt dome is actually investigated for its suitability as a repository for radioactive waste. It is crossed by a subglacial drainage channel, formed during the Elsterian glaciation (Gorleben channel). Some units of its filling vary strongly in niveau and thickness. Lowest positions and/or largest thickness are found above the salt dome. This is interpreted as a result of subrosion during the Saalean glaciation. The rate can be calculated from niveau differences of sediments formed during the Holsteinian interglacial. However, their position might have been influenced by other factors also (relief of the channel bottom, glacial tectonics, settlement of underlying clay-rich sediments). Their relevance was estimated applying statistical techniques to niveau and thickness data from 79 drillings in the Gorleben channel. Two classes of drillings with features caused by either Saalean subrosion or sedimentary processes during the filling of the Gorleben channel can be distinguished by means of factor and discriminant analysis. This interpretation is supported by the results of classwise correlation and regression analysis. Effects of glacial tectonics on the position of Holsteinian sediments cannot be misunderstood as subrosional. The influence of the settlement of underlying clay sediments can be estimated quantitatively. Saalean subrosion rates calculated from niveau differences of Holsteinian sediments between both classes differ with respect to the method applied: maximum values are 0,83 or 0,96 mm/a, average values are 0,31 or 0,41 mm/a.

Fluviatile und äolische Prozesse im Gebiet der unteren Elbe bei Neuhaus (Niedersachsen) seit dem Weichselspätglazial

The Late Glacial and Holocene landscape development in the vicinity of the River Elbe near Neuhaus, Lower Saxony, was studied during geological mapping of the area. The geological and geobotanical methods used in these investigations were chosen to cope with the difficulties which arise during research on Quaternary flood plains in low country. Paleochannel fill and areas of flood-plain sediments were drilled, the lithology examined, and the sediments dated on the basis of their pollen content. No evidence was found for the existence before the Middle Ages of paleo- channels the size of the present River Elbe. Before the first measures were made to regulate the Elbe River, it was an anastomosing river system with numerous small branches. The lower parts of the flood-plain profiles are predominantly sand and the upper parts silty-clayey loam. With the construction of effective levees over the last several centuries, the flow velocity of the Elbe has increased considerably during high water periods and instead of the deposition of meadow loam, sand was deposited as natural levees. The main belt of sand dunes on the east bank of the Elbe overlies Preboreal to Boreal lake mud and is, therefore, of Holocene age.

Neue Erkenntnisse zum geologischen Bau des “Kleinen Berges” zwischen Bad Laer und Bad Rothenfelde (südwestliches Niedersachsen) aufgrund der Ergebnisse der Tiefbohrung ‘Bad Laer Z 1’

The 2108,0 m deep exploration well "Bad Laer Z 1" (1993) has been carried down in order to investigate the deeper ground lying beneath the "Kleiner Berg" anticline, concerning the existence of reservoir beds which was postulated according to preceeding seismic investigations. This aim of the borehole was not attained, because no formations have been drilled suitable for the construction of an artificial gas reservoir. On the other hand the bore hole revealed a great amount of new regional geologic, stratigraphic, mining, coalification and coal bed gas data. Therefore, from a scientific point of view the exploration well must be considered successful. After the drilling of a stratigraphic succession, mainly consisting of cretaceous "Pläner" limestones (from Albian to Turonian), surprisingly in a depth of only 439 m productive Upper Carboniferous rocks formed by the Lembeck beds of uppermost Westfalian C have been found. In addition to this discovery, nearly the whole Westfalian C and B reaching down to the coal bed "Katharina" at the Westfalian A boundary were drilled through revealing over 66 partly minable coal beds. Investigations of the coalification pattern showed a more or less continuous increase of the rank gradient with depth reaching from the step of gas flame coal down to 700 m over that of gas coal down to 1600 m to that of fat coal down to the bottom of the borehole. An additional surprising result of the exploration well was the observation, that immediately below the base of the Cretaceous the coal beds revealed a high gas content without the presence of a desorption zone. This result must also be considered as success of the drilling with respect to the strong interest in a potential utilization of coal bed methane nowadays.