Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Evening Poster

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS20] Evolution of the Pelagic Realm

Wed. May 23, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Atsushi Matsuoka(Department of Geology, Faculty of Science, Niigata University), Toshiyuki Kurihara(Graduate School of Science and Technology, Niigata University), Tetsuji Onoue(熊本大学大学院自然科学研究科, 共同), Katsunori Kimoto(Japan Agency for Marine-Earth Science and Technology)

[MIS20-P06] Sr isotope variations in the Upper Triassic succession at Pizzo Mondello, western Sicily, Italy

*Tetsuji Onoue1, Katsuyuki Yamashita2, Chise Fukuda6, Katsuhito Soda5, Yuki Tomimatsu5, Benedetto Abate3, Manuel Rigo4 (1.Faculty of Advanced Science and Technology, Kumamoto University, 2.Graduate School of Natural Science and Technology, Okayama University, 3.Department of Earth and Sea Sciences, University of Palermo, 4.Department of Geosciences, University of Padova, 5.Graduate School of Science and Technology, Kumamoto University, 6.Faculty of Science, Okayama University)

Keywords:Norman, Tethys, Cimmerian Mountains

The Norian stage in the Late Triassic is exceptionally long (23 Myr) and was subdivided into three substages: the Lacian, Alaunian, and Sevatian. In order to infer the Norian environmental changes in the western Tethys Ocean, the stratigraphic variations of 87Sr/86Sr in the Upper Triassic limestone succession in Sicily were examined. The Pizzo Mondello section studied here mainly consists of a pelagic carbonate sequence of the Scillato Formation, and ranges in age from Tuvalian (late Carnian) to Rhaetian. The Scillato Formation represents a deep-water pelagic facies deposited along the Sicanian Basin in the western Tethys Ocean.

We selected fine-grained limestone samples from both the microfacies of lime-mudstone and wackestone to approximate the primary 87Sr/86Sr signature of the limestone beds. The 87Sr/86Sr values are relatively constant in the Tuvalian and Lacian (early Norian). However, the remarkable rise in 87Sr/86Sr occurred across the Lacian–Alaunian (early–middle Norian) transition. Variations in 87Sr/86Sr values show an increasing trend in 87Sr/86Sr from 0.7077 at the base of Lacian to 0.7080 in the Sevatian (late Norian). In the Sevatian, the 87Sr/86Sr ratios display a sudden negative excursion toward lower values and show a relatively quick recovery to pre-excursion 87Sr/86Sr ratios.

Korte et al. (2003) suggested that the rise in the 87Sr/86Sr values from the middle Carnian to the late Norian coincide with the Cimmerian orogeny. Our new 87Sr/86Sr data from the Pizzo Mondello section reveal a comparable trend, with a sharp increase in 87Sr/86Sr within the Alaunian, suggesting the rapid uplift and erosion in the Cimmerian Mountains at this time. The cause of the 87Sr/86Sr excursion in the Sevatian remains uncertain. However, the biostratigraphic record of conodonts suggests that a morphological evolution towards platform-less elements occurred with the beginning of the Sr-isotope excursion.