Global Stratotype Sections and Points (GSSP’s) and their applications in northern Germany. Examples of the Gorleben nuclear waste project
Report of the project:
Symplified palaogeography during the Paleogene and Neogen and locations of the Global Stratotype Sections and Points, the "golden spikes"
Source: BGR
Several most detailed chronostratigraphical and biostratigraphical diagrams of the Paleogene and Neogene stage boundaries were presented in the last years which were derived from Global Stratotype Sections and Points (GSSP’s) and are mainly based on calcareous microfossils (planktonic foraminifera, calcareous nannoplankton).
In 2004, about half of the 18 Paleogene and Neogene GSSP’s were ratified by the International Union of Geological Sciences. The principal correlative events for the GSSP are derived from paleomagnetics and/or biostratigraphy.
All of the Paleogene and Neogene GSSP are located in the former Tethys realm whereas Northern Germany belongs to the boreal Northwest European Tertiary basin.
In the Paleogene and Neogene of Germany, the practical use of the biostratigraphy of the GSSP’s is limited. This is due to the fact that often the index taxa of the different microfossil groups are missing. Furthermore, in the few strata where planktonic foraminifera and calcareous nannoplankton are present, the index-markers of the GSSP’s are also often missing. Therefore, these two groups do not reach the key value as indicated in the international and GSSP schemes and cannot be used for a comprehensive biostratigraphical zonation in Germany.
Examples of the Gorleben nuclear waste project
Around the Gorleben salt dome and its marginal basins, which are filled with thick sequences of Paleocene through Miocene sediments, intensive biostratigraphical investigations had been carried out by planktonic and benthic foraminifers, calcareous nannoplankton and organic walled dinoflagellate cysts (dinocysts). The record on Bolboforma and Uvigerina was very poor. Pollen and spores were investigated in some samples, but turned out to be of limited biostratigraphical value.
The Paleocene-Eocene boundary, which is characterized by a hiatus, could be dated best by means of dinocysts. Calcareous nannoplankton and planktonic foraminifers are not present in the Gorleben area due to facial reasons. The uniform benthic foraminiferal assemblages below and above the Paleocene-Eocene boundary yielded no index taxa useful for defining the boundary. Lithostratigraphically, the Eocene sequence starts with a very fine sandy facies, the Gartow Sand. In seismic sections it was not possible to distinguish the Gartow Sand from the Paleocene clayey facies.
Biostratigraphic markers around the Oligocene/Eocene boundary
Source: BGR
As shown on the right and below, many of the biostratigraphic markers of the Neogene and Palaogene GSSP's are not present in the Gorleben area.
At the Eocene-Oligocene boundary, dinocysts were used likewise as marker species closest to the boundary (last occurrence of Areosphaeridium diktyoplokus). Lithostratigraphically, the Oligocene sequence again starts with a sandy facies (Neuengamme Gassand) that could not be dated precisely neither by benthic foraminifers nor by calcareous nannoplankton. Around the boundary planktonic foraminifers are very rare. In seismic sections the base of the Oligocene is drawn with the Rupelian clay formation.
Biostratigraphic markers around the Miocene/Oligocene boundary
Source: BGR
The Oligocene-Miocene boundary could not be dated properly by any microfossil group. Lithostratigraphically, the Miocene sequence begins with the Lower Browncoal Sands that can be determined in seismic sections. The Lower Browncoal Sands do not contain calcareous microfossils. The dinocysts record is poor and contains the same zone (D15) as in the Upper Oligocene sediments.
Dinocysts are the most useful group in characterizing the main boundaries of the Palaeogene and Neogene in the Gorleben area. Foraminifers and calcareous nannoplankton support occasionally the dinocyst zonation. Due to unfavorable facies conditions with often noncalcareous brackish to marine environments planktonic foraminifera and calcareous nannoplankton are present in a few strata only.
An updated zonation for Northern Germany was recently elaborated (Köthe 2003). But the correlation to the GSSP is more or less vague.
