TY - JOUR
T1 - Origin of atoll dolomites distinguished by geochemistry and crystal chemistry
T2 - Kita-daito-jima, northern Philippine Sea
AU - Suzuki, Yuka
AU - Iryu, Yasufumi
AU - Inagaki, Shizue
AU - Yamada, Tsutomu
AU - Aizawa, Shoichi
AU - Budd, David A.
N1 - Funding Information:
We are grateful to Dr. H. Matsuda of the Department of Earth Sciences, Faculty of Science, Kumamoto University for his valuable suggestions. We thank Dr. Art Saller of UNOCAL Corporation, Texas, USA and an anonymous reviewer for their helpful comments and suggestions concerning the manuscript. Deep appreciation is expressed to Mr. M. Shishido and Mr. H. Sasaki for making thin sections. Our special thanks are due to Mr. N. Okiyama, for helpful assistance in the field. Funding for this study was provided, in part, by Grants-in-Aid for Scientific Research, Japan Society for the Promotion of Science (to Y. I.; 07740408) and grants from the Saito Gratitude Foundation (Sendai, Japan), the Fukada Geological Institute (Tokyo, Japan), and the Kuribayashi Gakujutu Zaidan (Sapporo, Japan).
PY - 2006/1/15
Y1 - 2006/1/15
N2 - Kita-daito-jima is a carbonate island located at the northwestern region of the Philippine Sea (25°55.6′-57.6′N, 131°16.9′-19.8′E). Dolomites extend from the island surface to a depth of 100 m below the ground surface (mbgs). Strontium isotope stratigraphy indicates that subsurface Units C1 (0-49.7 mbgs) and C2 (49.7-103.4 mbgs) were dolomitized at 5.5 Ma and 2.0 Ma, respectively, and that island-surface dolomites are products of dolomitization at 1.6-2.0 Ma. X-ray diffraction analysis indicates that the island-surface and borehole dolomites comprise variable mixtures of four and three dolomite crystal phases, respectively. Each of these phases is distinguished by a different Ca and Mg content. Three textural types can be recognized in the Kita-daito-jima dolomites, fabric-preserving crystalline nonmimetic (CNM), crystalline mimetic (CM), and fabric-preserving microsucrosic (MS). CNM dolomites contain more calcian phases, whereas MS dolomites commonly are richer in more stoichiometric phases. Backscattered electron images indicate that calcian dolomite phases were precipitated earlier than the more stoichiometric dolomite phases and that there is no significant hiatus between the phases, although they are diachronous. Both the island surface and borehole cores dolomites show linear relationships between whole-rock δ18O composition and Mg contents and between whole-rock trace element concentrations (Sr and Na) and Mg contents. These covariances result from phase mixing, not stoichiometric effects. Deconvolution of whole-rock isotopic and elemental compositions based on the relative abundance of phases reveals that each phase has a distinct chemical and isotopic composition. Oxygen isotopic compositions of the island surface and borehole dolomites suggest that all dolomite phases formed in seawater and that dolomitization primarily occurred during glacio-eustatic sea-level lowstands and cooler ocean temperatures.
AB - Kita-daito-jima is a carbonate island located at the northwestern region of the Philippine Sea (25°55.6′-57.6′N, 131°16.9′-19.8′E). Dolomites extend from the island surface to a depth of 100 m below the ground surface (mbgs). Strontium isotope stratigraphy indicates that subsurface Units C1 (0-49.7 mbgs) and C2 (49.7-103.4 mbgs) were dolomitized at 5.5 Ma and 2.0 Ma, respectively, and that island-surface dolomites are products of dolomitization at 1.6-2.0 Ma. X-ray diffraction analysis indicates that the island-surface and borehole dolomites comprise variable mixtures of four and three dolomite crystal phases, respectively. Each of these phases is distinguished by a different Ca and Mg content. Three textural types can be recognized in the Kita-daito-jima dolomites, fabric-preserving crystalline nonmimetic (CNM), crystalline mimetic (CM), and fabric-preserving microsucrosic (MS). CNM dolomites contain more calcian phases, whereas MS dolomites commonly are richer in more stoichiometric phases. Backscattered electron images indicate that calcian dolomite phases were precipitated earlier than the more stoichiometric dolomite phases and that there is no significant hiatus between the phases, although they are diachronous. Both the island surface and borehole cores dolomites show linear relationships between whole-rock δ18O composition and Mg contents and between whole-rock trace element concentrations (Sr and Na) and Mg contents. These covariances result from phase mixing, not stoichiometric effects. Deconvolution of whole-rock isotopic and elemental compositions based on the relative abundance of phases reveals that each phase has a distinct chemical and isotopic composition. Oxygen isotopic compositions of the island surface and borehole dolomites suggest that all dolomite phases formed in seawater and that dolomitization primarily occurred during glacio-eustatic sea-level lowstands and cooler ocean temperatures.
KW - Dolomite
KW - Kita-daito-jima
KW - Marine dolomitization
KW - Multigenerational dolomite
KW - Oxygen isotope
KW - Sea-level change
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U2 - 10.1016/j.sedgeo.2005.09.016
DO - 10.1016/j.sedgeo.2005.09.016
M3 - Article
AN - SCOPUS:30444457739
SN - 0037-0738
VL - 183
SP - 181
EP - 202
JO - Sedimentary Geology
JF - Sedimentary Geology
IS - 3-4
ER -
