کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4747601 1359924 2009 12 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Paleosol profiles in the Shiohama Formation of the Lower Cretaceous Kanmon Group, Southwest Japan and implications for sediment supply frequency
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات فسیل شناسی
پیش نمایش صفحه اول مقاله
Paleosol profiles in the Shiohama Formation of the Lower Cretaceous Kanmon Group, Southwest Japan and implications for sediment supply frequency
چکیده انگلیسی

This paper describes the pedogenic features of paleosols in the upper Lower Cretaceous Shiohama Formation, the lowest unit of the Shimonoseki Subgroup, in Yoshimi, Yamaguchi Prefecture, southwest Japan. The paleosol profiles in the Shiohama Formation are compound and complex, characterized by the presence of abundant calcrete horizons. An analysis of these profiles reveals that the floodplain upon which the Shiohama Formation was deposited was part of an unstable aggradation system characterized by the intermittent influx of sediments and occasional erosion. Furthermore, the mean annual range of precipitation was less than about 30 mm, suggesting only minor seasonal change between wet and dry conditions during deposition of the Shiohama Formation. The microstructures of the observed calcretes include dense microfabric, floating detrital grains, micronodules, circum-granular cracks, and complex cracks. These features formed by chemical precipitation under dry conditions, with little bioactivity. The calcrete horizons are classified into seven types (I–VII) based on their modes of occurrence. Two processes of carbonate accumulation can be identified based on the size and abundance of nodules: VI–V–III–(II)–I and VI–(V)–IV–II–I. These processes represent the development of calcrete horizons from the early to late stages of calcretization. Type I represents the most highly developed stage of calcretization. Calcretes within the Lower Member sequence of the Shiohama Formation show repetitions of type I and types II and III. Thus, it is interpreted that the frequency of sediment supply to the floodplain changed repeatedly over time.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Cretaceous Research - Volume 30, Issue 5, October 2009, Pages 1313–1324
نویسندگان
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