Test der Gleichaltrigkeit, Abschätzung der Raten und Evaluierung der zeitlichen Muster früh-oberkretazischer Meeresspiegelschwankungen: ein integrierter Ansatz.
Zusammenfassung der Projektergebnisse
The project had its focus on the controversial large and rapid sea-level changes that punctuated the early Late Cretaceous hothouse with its Phanerozoic sea-level highstand. Detailed Cenomanian–Turonian sequence stratigraphic investigations were conducted in several sedimentary basins situated on different tectonic plates (Europe: Münsterland, Saxonian and Danubian Cretaceous basins; northern Africa: Eastern Desert, Egypt; Middle East/Asia: Koppeh Dagh and Yazd Block, Iran). For the comprehensive sequence stratigraphic correlations between costal, shallow marine, hemipelagic and pelagic settings, integrated stratigraphic approaches combining high-resolution macrofossil biostratigraphy with chemo-, cyclo- and event stratigraphy were applied. An extremely careful data interpretation also considered the variable responses of carbonate- and siliciclasticdominated sedimentary systems to sea-level forcing. As a result, altogether ten depositional sequences (DS Ce 1–5, DS Ce–Tu 1, DS Tu 2–5) have been recognized for the investigated time interval (~100–88 Ma) which are defined by ten sequence boundaries, five in the Cenomanian (SB Ce 1–5) and five in the Turonian (SB Tu 1–5). The unconformities occur in identical stratigraphic positions in all investigated basins, meaning that they are in fact strictly time-equivalent, and thus, eustatic in origin. Consequently, the results of the project provide firm evidence that eustatic sea-level changes governed sedimentation patterns and stratigraphic architectures of lower Upper Cretaceous successions across tectonic plates. The quantification of sea-level changes involved in the formation of selected sequence boundaries indicate large-scale variations of up to 50 m within time spans of a hundred thousand years and less. The resulting high rates suggest glacio-eustasy as their driving force. All other so far known geological processes are either too long-term or of too lowamplitude. Therefore, the project provides independent stratigraphic evidence for short-term build-up and decay of significant quantities of continental ice in Antarctica and/or high altitudes during “cold snaps” in a generally very warm Cretaceous super-greenhouse world, supporting recently published results from AGC modeling. Cyclostratigraphic analyses of stratigraphically complete successions deposited in deep intrashelf basins of northern Germany indicate that late Early Cenomanian to Middle Turonian depositional sequences DS Ce 3 to DS Tu 3 all more or less contain an identical number of ca. 60 precession couplets (~20 kyr) bundled into twelve short- (~100 kyr) and three long-eccentricity cycles (~400 kyr). This observation suggests a sequence duration of 1.2 myr with regularly recurring amplified sea-level falls every 2.4 myr (major unconformities SB Ce 3, Ce 5, Tu 2 and Tu 4). This strongly supports long-term amplitude modulation (AM) cycles of the Milankovitch oscillations as triggers for the formation of Cenomanian–Turonian 3rd-order sequences, i.e., the long-period modulation of obliquity (1.2 myr) and eccentricity (2.4 myr). A Cenomanian–Turonian sequence chronological scale based on low-frequency AM cycles is proposed which is in good agreement with the GTS 2012 during the Middle Cenomanian to Middle Turonian (~97–91 Ma). According to astronomical calibrations in the literature, the AM cycles of eccentricity and obliquity are in-phase for the respective time interval. Conflicts exist for the Early Cenomanian and the Late Turonian, maybe related to out-of-phase patterns of AM cycles during these times. The results of the project demonstrate that even during a super-greenhouse such as the early Late Cretaceous (with considerably higher pCO2 than today), the global climate may shift into a cooler mode quite rapidly, and the same must be expected for the recent scenario of global warming. On the other hand, the recent sea-level rise may accelerate significantly when the current temperature-buffering effect of the ocean expires and glacioeustasy unfolds its full capacity. This needs to be considered in any sea-level prognosis.
Projektbezogene Publikationen (Auswahl)
- (2010): Cenomanian – Turonian (Cretaceous) ammonoids from the western Wadi Araba area, Eastern Desert, Egypt. – Cretaceous Research, 31: 473–499
Nagm, E., Wilmsen, M., Aly, M. & Hewaidy, A.
- (2010): Facies pattern and sealevel dynamics of the early Late Cretaceous transgression: a case study from the lower Danubian Cretaceous Group (Bavaria, southern Germany). – Facies, 56: 483–507
Wilmsen, M., Niebuhr, B., Chellouche, P., Pürner, T. & Kling, M.
- (2011): Cenomanian Acanthoceratoidea (Cretaceous Ammonoidea) from the Aitamir Formation (Koppeh Dagh, NE Iran): taxonomy and stratigraphic implications. – Acta Geologica Polonica, 61: 175–192
Mosavinia, A. & Wilmsen, M.
- (2011): Stratigraphy and facies of the Turonian (Upper Cretaceous) Roding Formation at the southwestern margin of the Bohemian Massif (southern Germany, Bavaria). – Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, 162: 295–316
Niebuhr, B., Wilmsen, M., Chellouche, P., Richardt, N. & Pürner, T.
- (2012): Lower Upper Cretaceous standard section of the southern Münsterland (NW Germany): carbon stable-isotopes and sequence stratigraphy. – Newsletters on Stratigraphy, 45: 1–24
Richardt, N. & Wilmsen, M.
(Siehe online unter https://doi.org/10.1127/0078-0421/2012/0012) - (2012): Origin and significance of Upper Cretaceous bioevents: Examples from the Cenomanian. – Acta Palaeontologica Polonica, 57: 759–771
Wilmsen, M.
(Siehe online unter https://doi.org/10.4202/app.2011.0044) - (2013): Late Cenomanian–Early Turonian facies development and sea-level changes in the Bodenwöhrer Senke (Danubian Cretaceous Group, Bavaria, Germany). – Facies, 59: 803–827
Richardt, N., Wilmsen, M. & Niebuhr, B.
(Siehe online unter https://doi.org/10.1007/s10347-012-0337-x) - (2013): Sequence stratigraphy of the lower Upper Cretaceous (Upper Cenomanian–Turonian) of the Eastern Desert, Egypt. – Newsletters on Stratigraphy, 46: 23– 46
Wilmsen, M. & Nagm, E.
(Siehe online unter https://doi.org/10.1127/0078-0421/2013/0030) - Sequence stratigraphy of the lower Upper Cretaceous Elbtal Group (Cenomanian–Turonian of Saxony, Germany). – Zeitschrift der Deutschen Gesellschaft für Geowissenschaften, 165: 29 pp.
Janetschke, N. & Wilmsen, M.
(Siehe online unter https://doi.org/10.1127/1860-1804/2013/0036)
