Silurian to Lower Carboniferous Brachiopods of Central Europe—Palaeogeographic and Palaeobathymetric Constraints
摘要
Brachiopods as one of the major groups of Palaeozoic marine megafossils are present in most Silurian–Mississippian (lower Carboniferous) sedimentary successions of the Central European Variscides; the total number of species for the periods and areas considered probably exceeds 1500. As often stenotopic sessile-benthic marine organisms with a predominantly short-living pelagic larval stage, articulate brachiopods (rhynchonelliforms) are sensitive to (palaeo)bathymetric and (palaeo)geographic changes, but their use as proxies thereof must take into account their strong dependence also on other parameters, such as water turbidity, substrate properties, or bottom-water oxygenation. This chapter summarizes the methodology, obstacles, and present state of respective reconstructions. In comparison with other groups, brachiopod palaeobiogeography is hampered by difficulties in sample standardization. Brachiopod-based palaeobiogeographic patterns are mostly consistent with currently accepted geodynamic reconstructions for the Silurian–Early Devonian that distinguish Laurussia in the north and North Gondwana in the south separated by the Rheic Ocean and possibly additional oceanic belts and terranes in between. Differences between northern and southern faunas, partly caused simply by different facies developments, gradually diminished with the late Emsian–Middle Devonian, possibly corresponding to narrowing and closure of the oceanic barrier(s). The facies analysis with a focus on the brachiopod faunas allows the relatively unproblematic discrimination of successive depth zones and much discussed estimations of absolute water depths. This is exemplified by Lower Devonian successions of the Rhenish Massif. According to previously published data, the shallowest, low-diversity faunas (BA 1) of the successions considered are placed in the intertidal zone or at depths of 0–5 m, the most diverse faunas (BA 2–4) in the shallow to moderately deep subtidal or at about 5–60 m, and those occupying the deepest positions (BA 5–6) in the deeper subtidal at about 60–200 m.