An Early-Middle Guadalupian (Permian) isotopic record from a mid-oceanic carbonate buildup: Akiyoshi Limestone, Japan

作者：Musashi Masaaki^*; Isozaki Yukio; Kawahata Hodaka

来源：Global and Planetary Change, 2010, 73(1-2): 114-122.

DOI：10.1016/j.gloplacha.2010.03.013

• Guadalupian
• carbon isotope
• Panthalassa
• high productivity
• Kamura event
• Akiyoshi
• paleo-atoll

In order to understand the oceanographic changes before the Guadalupian-Lopingian (Permian) boundary mass extinction event, we investigated the isotopic compositions of the inorganic carbon and the oxygen (delta C-13(carb) and delta O-18(carb)) of the Guadalupian (Middle Permian) shallow marine carbonates deposited on a seamount-top in the superocean Panthalassa. The drilled samples were obtained at Kaerimizu in the Akiyoshi area, SW Japan. We focused on the Roadian-Wordian (Middle Guadalupian) interval that spans over 7 fusuline zones; i.e. the Parafusulina kaerimizuensis Zone (Pk Z.), Afghanella ozawai Zone (Ao Z.), Neoschwagerina craticulifera robusta Zone (Ncr Z.), Verbeekina verbeeki-Afghanella schenki Zone (Vv-As Z.), Neoschwageina fusiformis Zone (NfZ.), Verbeekina verbeeki Zone (Vv Z.), and Colania douvillei Zone (Cd Z.), in ascending order. Analytical results showed that the delta C-13(carb) values stayed almost constant around +3.0 parts per thousand. PDB in the Pk Z., Ao Z. and the lower half of the Ncr Z., and those in the upper-section gradually decreased down to -2.0 parts per thousand, of which the lowest was found in the Cd Z. We statistically extracted the samples with presumably better preserved delta C-13(carb) values in the Kaerimizu section ranged between +0.5 and +4.0 parts per thousand with average values of delta C-13(carb) of +2.7 +/- 1.0 parts per thousand, on the basis of delta C-13(carb)-delta O-18(carb) characterization. This interval shows a monotonous decrease in delta C-13(carb) values from ca + 4.0 parts per thousand to + 2.0 parts per thousand. This indicates that the primary productivity might be generally high in the Wordian mid-oceanic domain but slightly declined in the Late Wordian. The studied Early-Middle Guadalupian interval is chemostratigraphically correlated with the other mid-Pansalassan paleo-atoll limestone e.g. Iwato Formation in Japan, suggesting that the relatively high delta C-13(carb) (over + 3.0 parts per thousand) of seawater predominated in shallow mid-superocean during the middle Middle Permian.

• 出版日期2010-8