نتایج جستجو برای: acritarchs
تعداد نتایج: 104 فیلتر نتایج به سال:
Compressed organic-walled microfossils attributable to five filamentous taxa, and ten coccoidal eight, (taxa originally spheroidal forms and two originally ellipsoidal, colonial forms), all having long time-ranges in the Proterozoic, have been identified in fine-grained siliciclastic sediments in cores from four bore holes cutting subsurface equivalents of the Mesoproterozoic Conselheiro Mata G...
New data on acritarchs from the Upper Ordovician of the Tungus basin, Siberian Platform; pp. 300–304
An integrated palynological and geochemical approach has been initiated to date precise the events of Pimenteiras Formation, in Late Devonian from Parnaíba Basin, Brazil. Based on good biostratigraphic markers presence index species among miospores, acritarchs chitinozoa, investigated sequences are referred Middle early Frasnian. Among Miospores, Chelinospora concinna Verrucosisporites bullifer...
Sphaeromorphic algal cysts, most probably of the prasinophyte Tasmanites, and acanthomorphic acritarch vesicles, most probably Solisphaeridium, occur in a single 20 cm thick bed of micritic limestone in the lower part of the Middle Devonian (Givetian) Tully Formation near Lock Haven, Pennsylvania. Specimens are composed of authigenic calcite and pyrite crystals about 5–10 μm in length. Some spe...
The Paleoproterozoic Era witnessed crucial steps in the evolution of Earth's surface environments following the first appreciable rise of free atmospheric oxygen concentrations ∼2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca....
Allison, C.W. and Awramik, S.M., 1989. Organic-walled microfossils from earliest Cambrian or latest Proterozoic Tindir Group rocks, northwest Canada. Precambrian Res., 43: 253-294. Uppermost Tindir Group limestones exposed in the headwaters of Tindir Creek, Yukon Territory, Canada, contain a diverse and abundant microbiota of mineralized and organic-walled microfossils. Preserved primarily in c...
Assemblages of clay minerals are routinely used as proxies for paleoclimatic change and paleoenvironmental conditions in Phanerozoic rocks. However, this tool is rarely applied in older sedimentary units. In this paper, the clay mineralogy of the Doushantuo Formation in South China is documented, providing constraints on depositional conditions of the Ediacaran Yangtze platform that host the ea...
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