Global Change and plate tectonic history recorded in shallow-water carbonates and deep-water deposits: Turnovers in the Mesozoic of the western Tethys Realm and the lecture of the organisms for the future

The focus of the talk is the Mesozoic history of the Circum-Pannonian realm with several turnovers recorded in the sedimentary successions after the Permian/Triassic Mass Extinction. Some of these turnovers are over-regional (plate-tectonic related) while others are related to global events. The reasons for all turnovers, that are in most cases events resulting in a mass extinction and therefore in a characteristic change in deposition, seems to be clear: discussed are predominantly impacts and large igneous provinces (LIPs) and their effect on the sea-level, the climate, the chemistry of the oceans beside other effects. To compare the exogen evolution preserved in the sedimentary successions around an oceanic domain, which evolution follows normally a Wilson Cycle allow also to distinguish deposits of opposite passive continental margins and to filter over-regional events related to the history of an ocean from global events. Tectonostratigraphy is therefore a powerful tool for palaeogeographic reconstructions: there are still a lot of controversies of the arrangement of oceanic and continental domains in the Circum-Pannonian Realm and palaeogeographic reconstructions contrast significantly.
The classical question “Where and what was the Tethys” and their life cycle is still debated. In fact, in most eastern Mediterranean mountain ranges we see following overall evolution (in fact identical around all proposed small oceanic domains in the area):
1)
A Late Permian to early Middle Triassic graben infilling (rift basin).
2)
A late Middle Triassic to early Middle Jurassic passive margin evolution.
3)
A Middle to early Late Jurassic active margin evolution (ophiolite obduction) followed by mountain uplift and unroofing from the Kimmeridgian/Tithonian boundary onwards.
The final closure of the Neo-Tethys started in the Late Cretaceous.
This evolution describes the history of the Tethys in the sense of Suess since 1888 and contrasts the evolution of the Alpine Atlantic (zentrales Mittelmeer in the sense of Neumayer since 1875) with following history:
1)
An Early Jurassic (?in cases to earliest Middle Jurassic) graben infilling (rift basin).
2)
A Middle Jurassic to Late Cretaceous passive margin evolution.
3)
Late Cretaceous to Palaeogene subduction, Palaeogene collision followed by mountain uplift and unroofing from the Miocene onwards.
The mountain ranges in the eastern Mediterranean, with focus on the area around the Pannonian realm provide in their depositional history deep insights how Global Change is triggered by various parameters, which may work in concert. The Mesozoic-Cenozoic geological history of that area is affected by three mountain building processes, that are 1) the formation of the Neotethyan Belt in Middle-Late Jurassic times in the frame of the ophiolite obduction (closure of the western part of the Neo-Tethys Ocean), 2) the still enigmatic “Mid-Cretaceous” orogenesis which result in a new plate arrangement (various interpretations), and 3) the formation of the Alpine Belt in Palaeogene-Neogene times related to the closure of the Alpine Atlantic Ocean (Ligurian-Piemont-Penninic-Vah) and age-equivalent movements along the Axios-Vardar-Sava-Periadriatic (strike-slip) plate boundary. But the still mysterious and not fully understood “Mid-Cretaceous” orogenesis draw a veil on the older Mesozoic plate configuration and should have an own name. The name “eoalpine” is definitively misleading because this orogenesis is not related to the evolution of the Alpine Atlantic and in fact it also cannot be related to the Neo-Tethys evolution.during almost the entire Mesozoic we can track the evolution of these two oceans in the sedimentological record interrupted by the “Mid-Cretaceous” orogenesis. Especially biogenic sedimentary rocks provide insights in turnovers and Global Change: carbonates and siliceous sedimentary rocks are crucial and indicative for environmental changes, and shallow-water carbonate producers are the most sensitive ones. In the Neo-Tethys cycle we can distinguish several characteristic shallow-water production cycles, intercalated by deep-water sedimentary rocks and expressed by a drowning: 1) the middle Anisian shallow-water cycle (Steinalm/Ravni/Sarl Carbonate Ramp and equivalents) ended abruptly in the late Pelsonian contemporaneously with the opening of the Neo-Tethys. 2) Late Illyrian and early Longobardian shallow-water carbonates appear only locally, whereas the overall latest Ladinian to earliest Carnian Wetterstein Platform evolution experienced a demise around the Julian 1/2 boundary (slightly before the Wrangellian LIP). 3) Late Carnian carbonate production recovery resulted in the complex evolution of the Norian-Rhaetian Dachstein Platform with its extinction at the Triassic/Jurassic boundary (CAMP LIP, Pangea break-up). 4) Earliest Jurassic carbonate production recovery led to the evolution Litiothis platform with its demise in the Toarcian (opening of the Alpine Atlantic and Ferrar-Karoo LIP). 5) The next important shallow-water carbonate cycle (Plassen Platform and equivalents) started in the Kimmeridgian, and its demise started in the Berriasian (?LIP). 6) The Early Cretaceous is characterized by short intervals of shallow-water carbonate production followed by black shale events (e.g. Valanginian, Barremian, Albian/Aptian). In Triassic and Jurassic times the decrease in carbonate production or the demise of ramps/platforms is expressed by deposition of siliceous (radiolaritic) sedimentary rocks on the passive margin in a hemipelagic setting (100-300 m). The demise of shallow-water carbonate production is very often also associated with a sea-level drop, that means a colder climate.
A more detailed look on these Mesozoic examples result in some characteristic differences not fully explained yet. In some cases the carbonate production stopped abruptly after a longer period of recovery following an extinction event. In other cases the demise of shallow-water platforms marks the end of stepwise extinctions. Intense volcanism, often large igneous provinces are associated with the demise of these platform/ramp cycles, but not always intense (over-regional) volcanism decrease carbonate production. It seems that the onset and evolution of LIPs hampered the global recovery of the carbonate system. During these time spans radiolarite deposition occur widespread also on the passive margins = radiolarite events, in cases following short black shale/oceanic red bed events or gaps. However, some differences exist in the demise of the shallow-water cycles which are not fully explained yet. It seems, that a combination of global effects, predominantly LIPs, and plate tectonics affected e.g. the ocean chemistry (“ocean acidification”, anoxia), the sea-level, and the climate (and continental weathering: changes in mode and type of sediment supply, nutrients). Extinction events are the result, a Global Change or turnovers in the depositional record. Global Change describes a situation when the “normal” biological evolution is not able to adapt fast enough to environmental changes, and the effect is expressed in the sedimentary rocks. Rising global temperatures result normally in a rising sea-level, and during periods of a warm (tropical-subtropical) climate shallow-water carbonate systems normally prograde. Climate and sea-level changes have practically no influence on the life cycle of a carbonate platform, as visible in the overall cyclicity in platform evolutions as expressed in their parasequences, but exceptional events interrupt this “normal” life cycle. LIPs, impacts, plate tectonics, and some other reasons can change the overall conditions significantly, especially “ocean acidification” seems to be crucial beside other pollution for a Global Change. The “Anthropocene” – time for a Global Change?