I PREVIOUSLY POSTED on this topic but the author of the article objected, feeling that his copyright had been violated. Unfortunately he has been unforthcoming about his specific objections and how I could correct the post, so I decided to write a second version. It is possible that my first post may have violated copyright by covering too much information. As I was writing my goal was to do the paper justice. It was the culmination of years of research, and is preceded by multiple other articles. It may be that in trying to be correct and thorough I included too much information. In this rewrite I have omitted a good deal of information and brought in a variety of other sources to cover the geography of the region.
During the Triassic much of what is now Germany was undergoing subsidence, and forming the Germanic basin. To the east at this time lay the Tethys Sea. Early in the Triassic the elevation was high enough to block the Germanic Basin from the Tethys Sea, and the strata in the basin at this time show braided rivers draining into a central lake at the lowest area of the basin.1 Over time subsidence continued, and eventually the area had dropped low enough to allow water to flow in from the Tethys Sea.1
Analysis of conodonts reveal continued connection with the Tethys Sea through the Middle Triassic, but a decrease and finally cessation of connection above the Upper Muschelkalk.2 When the Germanic basin initially opened to the Tethys, conodonts migrated west through the East Carpathian (the first route to open) and Silesian-Moravian gates. Further subsidence allowed migration through the Western Carpathian gate, located to the south of the Vindelician-Bohemian Massif (southwest of the Silesian-Moravian gate). By examining the species of conodonts found in the Germanic Basin and in regions of the Tethys, the chronology of flooding of the basin can be determined.
In addition to the record of the various conodont species, we can draw conclusions from the strata laid down in and around the Germanic Basin. The Germanic Basin formed in the late Permian to early Triassic, and we can see a transition in this region from continental strata to marine strata and then back to coastal plains.3 The chief types of rock present during the flooding of the Germanic Basin are limestone, found in marine areas, dolomite associated with sabkha, and laminated carbonate-rich mudstones.
Limestone is characteristic of marine environments and is produced by the precipitation of carbonates by unicellular organisms such as foraminifera. At the coast of the Germanic Basin limestone was often left exposed during times of lowered sea level. The evaporation of groundwater in these areas exposed limestone to magnesium-rich brines, which resulted in the exchange of calcium in the limestone for magnesium, producing dolomite.4 This dolomite would have formed in areas similar to modern-day sabkha, or salt flats.
Laminated mudstones are made of fine-grained carbonates densely colonized by cyanobacteria and algae, and are associated with intertidal zones. In some cases the laminated mudstones show characteristic cracking and “teepees” indicating drying and displacement of surface sediment by upwelling water.4 Laminated mudstones often overlie sabkha, and the microorganisms in biolaminates can be instrumental in precipitating carbonates and in converting sabkha limestone to dolomite by efficiently sequestering magnesium from the water.5
Since the Germanic basin was undergoing subsidence during this time, tectonic activity in the area should be expected. Indeed, the strata show many instances of seismites and tsunamites. These structures are most common in the Lower Muschelkalk but have also been reported for the Middle/Upper Muschelkalk.6 Tsunamites are often characterized by a layer of reworked sediment, a second undisturbed layer, and a third reworked layer, caused by the initial arrival of the tsunami and the backwash as the waters recede. Seismites produce characteristic distortions in sediments that have not yet lithified. Both of these structures are seen repeatedly in Early and Middle Triassic strata in the German Basin.
Most research concentrates on the strata of Triassic Germany, but Diedrich7 has been studying reptile trackways along the coast of the Germanic Basin for many years. The remainder of this post refers to Diedrich’s research.
Diedrich discovered tracks in laminated mudstones matching two characteristic patterns. These sets of tracks were assigned to lithogenus Rhynchosauroides and lithogenus Procolophonichnium. Rhynchosauroides was larger, did not leave tail marks, and had hindfoot prints often overlapping the forefoot prints. Procolophonichnium was smaller and left tail marks, and also had the usual footprint order with forefoot before hindfoot. For both sets of tracks examples have been found of scratches on dry laminated mudstones, clearer marks in wet laminated mudstones, and distorted tracks left in subaerial or subaquatic ooze. Tracks indicate types of motion ranging from resting to walking, running, and swimming.
Rhynochosauroides left prints in carbonate tidal flats, and probably spent most of its time near the water’s edge. A candidate for this track type is Macrocnemus bassani. This prolacertilian was about 1.2 m long, with long hind legs, and probably walked with the hindquarters lifted, explaining the lack of a tail mark.
Procolophonichnium seemed to prefer areas farther from the water’s edge, and left dense tracks in subaerial laminated mudstones near sabkha facies and in dry cracked laminated mudstones. A candidate for the maker of these tracks is Hescherleria ruebeli. The foot anatomy and body size (about 0.5 m) of this reptile are good matches for Procolophonichnium tracks.
Diedrich discovered trackways from both the Lower and Middle Triassic, and these revealed distributions consistent with our previous understanding of geological processes in this area. The Lower Triassic trackways were laid down while the East Carpathian Gate was open, but the Silesian-Moravian gate had not yet opened. Reptiles migrated freely through this area. In the Middle Triassic flooding had peaked and both gates were open, curtailing migration between the Vindelician-Bohemian and Rhenish Massifs.
Since tracks are often dense and have only been recovered from 75 different areas, there are probably millions of tracks remaining to be discovered.
Bourquin, S.; Peron, S.; Durand, M. “Lower Triassic sequence stratigraphy of the western part of the Germanic Basin (west of Black Forest): Fluvial system evolution through time and space.” Sedimentary Geology 2006, 186, 187-211. doi:10.1016/j.sedgeo.2005.11.018
Narkiewicz, K.; Joachim, S. “Controls on migration of conodont fauna in peripheral oceanic areas. An example from the Middle Triassic of the Northern Peri-Tethys.” Geobios 2004, 37, 425-436. doi:10.1016/j.geobios.2003.10.001
Vecsei, A.; Duringer, P. “Sequence stratigraphy of Middle Triassic carbonates and terrigenous deposits (Muschelkalk and Lower Keuper) in the SW Germanic Basin: maximum flooding versus maximum depth in intracratonic basins.” Sedimentary Geology 2003, 160, 81-105. doi:10.1016/S0037-0738(02)00337-8
Schauer, M.; Aigner, T. “Cycle Stacking Pattern, Diagenesis and Reservoir Geology of Peritidal Dolostones, Trigonodus-Dolomite, Upper Muschelkalk (Middle Triassic, SW-Germany).” Facies 1997, 37, 99-114. doi:10.1007/BF02537373
Brehm, U.; Gasiewicz, A.; Gerdes, G.; Krumbein, W. E. “Biolaminoid facies in a peritidal sabkha: Permian Platy Dolomite of northern Poland.” International Journal of Earth Sciences 2002, 91, 260-271. doi:10.1007/s005310100207
Knaust, D. “Pinch-and-swell structures at the Middle/Upper Muschelkalk boundary (Triassic): evidence of earthquake effects (seismites) in the Germanic Basin.” International Journal of Earth Science 2002, 91, 291-303. doi:10.1007/s005310100225
Diedrich, C. “Millions of reptile tracks–Early to Middle Triassic carbonate tidal flat migration bridges of Central Europe–reptile immigration into the Germanic Basin.” Palaeogeography, Palaeoclimatology, Palaeoecology 2008, 259, 410-423. doi:10.1016/j.palaeo.2007.09.019