Japan Geoscience Union Meeting 2016

Presentation information


Symbol B (Biogeosciences) » B-PT Paleontology

[B-PT05] Decoding the history of Earth: From Hadean to Modern

Wed. May 25, 2016 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall HALL6)

Convener:*Tsuyoshi Komiya(Department of Earth Science & Astronomy Graduate School of Arts and Sciences The University of Tokyo), Yasuhiro Kato(Department of Systems Innovation, Graduate School of Engineering, University of Tokyo), Katsuhiko Suzuki(Research and Development Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology)

5:15 PM - 6:30 PM

[BPT05-P12] Stratigraphy of banded iron formation in El Dabbah, Eastern Egypt

*TAISHI SUZUKI1, Shoichi Kiyokawa1, Minoru Ikehara2, Takashi Sano3, Dawood Maher4, Mohamed Abouelhassan4 (1.Kyushu Univ., 2.Kochi Univ., 3.National Museum of Nature and Science, 4.Menoufia Univ.)

Keywords:banded iron formation, Neoproterozoic

In the Eastern Desert of Egypt c. 700 Ma-old, Iron formations are present within greenstone belts (El-Gaby et al., 1990). Since detailed stratigraphy of the iron formation and its sedimentary environment are not well understood, we have conducted detailed geological research at Wadi El Dabbah in the middle of the Eastern Desert greenstone belt. The middle area is characterized by low metamorphic grade compared to the north and south areas that have high metamorphism with upper greenschist to amphibolite facies conditions (Khalil and El-Shazly 2011).
The El Dabbah area has been divided into four geological sections by a left-lateral fault (N-S strike) and reverse fault (E-W strike). In the northeast and northwest areas, volcaniclastic rocks are deposited horizontally, which include thin BIF in the northwest area. In addition, this area is covered unconformably by the Hammamat Group which is a continental sedimentary succession showing a dome-like fold structure. In the southeastern area, the main rock types are gabbro, massive basalt and coarse-grained volcaniclastic rocks. BIF are randomly occurs in several places. In the southwest area, coarse-grained volcaniclastic rocks, pillow lava, black shale and BIF make alternating layers. Strata are mostly dipping to the north at around 40-60 degrees. In the southwest area, gabbro and thick lava mainly comprises the basement. In the central unit of the southwest area, the continuity of stratigraphy is preserved, and BIF and black shale are interbedded with pillow lava and volcaniclastic rocks.
Our study focused on two well-preserved areas. We performed XRF and REE chemical analysis for powdered rock samples from both areas. We also analyzed Corg and δ13Corg of black shales overlying BIF at the other section. Corg is 0.07 ~ 0.12 wt % and δ13Corg is -22.5 ~-23.5 ‰. Trace elements in volcaniclastic rocks around the BIF are indicative of a volcanic arc basalt origin in terms of a Nb−Zr−Y discrimination diagram. The volcanic rocks consist of sparsely vesicular pillow and massive lavas, and sediments of continental origin are not present except for the BIF and black shale. In conclusion, these formations were likely formed near island arc setting. BIF of this area was deposited repeatedly during a resting stage of the volcanic activity.