Diagenetic alteration and burial environment of fossil hard tissues

Research Project

Project/Area Number	07454122
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Research Field	Geology
Research Institution	FUKUOKA UNIVERSITY OF EDUCATION
Principal Investigator	SUZUKI Seiichi Faculty of Education, Professor, 教育学部, 教授 (10154543)
Co-Investigator(Kenkyū-buntansha)	OSANAI Yasuhito Faculty of Education, Associate Professor, 教育学部, 助教授 (80183771) UENO Teiichi Faculty of Education, Associate Professor, 教育学部, 助教授 (10136393)
Project Period (FY)	1995 – 1996
Project Status	Completed (Fiscal Year 1996)
Budget Amount *help	¥6,000,000 (Direct Cost: ¥6,000,000) Fiscal Year 1996: ¥900,000 (Direct Cost: ¥900,000) Fiscal Year 1995: ¥5,100,000 (Direct Cost: ¥5,100,000)
Keywords	fossilization / diagenesis / carbonate cement / mollusca / pore water / silicification / calcite / aragonite
Research Abstract	Carbonate fossil hard tissues were collected from Lower Cretaceous to Quaternary systems in Japan, which are composed of non-carbonate clastic rocks, for the investigation of their diagenetic alteration. In clastic rocks cemented with carbonates (mainly calcite), three types of carbonate tissues (aragonite, low magnesium calcite=calcite and high magnesuim calcite) have the manner different from each other during burial stages, although all of the tissues within the host rocks with non-calcareous cement have usually been dissolved. Calcitic tissues are very stable so that the alteration did not occur in the calcitic specimens from the Upper Cretaceous and more younger strata. High-Mg-calcitic ones are comparatively well remaining in many cases, but they have been converted to low Mg calcite. Aragonitic ones show various patterns of the fossilization, such as preservation without any mineralogical alteration, calcitization (conversion to calcite through a thin solution film), dissolution and replacement with non-carbonate minerals. Original aragonite sometimes remains in the Upper Cretaceous rocks, though the calcitization commonly occurred in the Miocene and more older strata (sometimes in the Piocene and Pleistocene). Silicification of aragonitic tissues was observed in many strata of various ages, and chloritization, glouconitization and pyritization were also recognized in some strata. These are characterized by the preservation of microstructures. The alteration of araginitic tissues seems to have occurred in the mixing zone between marine and meteoric waters located near coastal regions.