[B-PT27_28PO1] Phanerozoic biodiversity change: Extinction and diversification

[BPT27-P01] Spherules layer of the uppermost Triassic (Rhaetian) limestone sequence in the Kardolina section, Slovakia

*Hideko SHIROZU¹, Michalik JOZEF², Soichiro KUSAKA³, Katsuyuki YAMASHITA⁴, Misa YAMASHITA⁴, Tetsuji ONOUE¹ (1.Graduate School of Science and Technology, Kumamoto University, 2.Slovak Academy of Sciences, 3.Research Institute for Humanity and Nature, 4.Graduate School of Science and Technology, Okayama University)

Keywords:Triassic/Jurassic boundary, Rhaetian, limestone, spherule, extinction

Triassic/jurassic (T/J) boundary of approximately 201 million years ago is known as a stratigraphic boundary recorded one of the big five Phanerozoic mass extinctions. Catastrophic processes such as widespread eruption of the Central Atlantic Magmatic Province (CAMP) flood basalts and extraterrestrial impacts have been proposed to account for the mass extinction event. Here we show the results of our analysis of enigmatic spherules in the Upper Rhaetian of the Kardolina section, Slovakia. The Kardolina section is situated on a steep western slope of the Mt Palenica in the Belianske Tatry Mts as the most continuous section of the uppermost Triassic (Rhaetian) Fatra Formation. The Fatra Formation is shallow marine carbonate sequence and is overlain with a sharp contact by marine shale of the lowermost Jurassic (Hettangian) Kopieniec Formation. The Kopieniec Formation consists of a sequence of brown claystone with sandtone and limestone intercalations. The position of the T/J boundary is constrained by foraminiferal assemblages. The limestone sequence containing the spherules exists in the upper part of Fatra Formation. A negative δ¹³C excursion and a positive δ¹⁸O peak have been known from spherules layers. Analysis of the foraminiferal assemblages shoed the diversity of foraminifera have decreased in spherules layers. Spherules are found in at least six sedimentary layers in the Fatra limestone. The size of spherules is approximately 200-300 μm. Spherules are contained ~10 % in the layers and the other component grains consist of lithoclasts, bivalves, and crinoids. These grains were relatively rounded and have reworked fabrics. The results of SEM-EDS analysis indicated that spherules were composed mainly of Si, Al and Mg, and contain small sulfide particles with Fe, Zn, and Cu. Such a geochemical composition was clearly different from ooids and peloids in Fatra Formation, though the origin of spherules in Kardolina section remains uncertain.