scholarly journals Sedimentary environments of the Middle Triassic Fukkoshi Formation in the Tsuya area, southern Kitakami Mountains, Japan

1984 ◽  
Vol 90 (12) ◽  
pp. 875-888_3
Author(s):  
Kotaro KAMADA
Keyword(s):  
Middle Triassic ◽  
Sedimentary Environments ◽  
Southern Kitakami Mountains

Calcium carbonate crystal fans: Geologic occurrences and controls on growth

2021 ◽  
Author(s):  
Adam Woods
Keyword(s):  
Calcium Carbonate ◽  
Middle Triassic ◽  
Carbonate Platform ◽  
Lower Triassic ◽  
High Energy ◽  
Seawater Chemistry ◽  
Sedimentary Environments ◽  
Cap Carbonates ◽  
Depositional Systems ◽  
Intertidal Environments

<p>Fans and hemispheres comprised of crystals of calcium carbonate that directly grew on the seafloor are an intriguing feature of ancient carbonate environments. Calcium carbonate fans from across Earth history are typically made up of crystals of neomorphosed calcium carbonate that maintain an acicular morphology that is pseudohexagonal in cross – section with blunt terminations, pointing to an aragonite precursor. Crystal fans may occur as isolated bodies, or may form larger aggregates that are sometimes associated with microbialites, and form larger, reef – like structures. Some of the first occurrences of these features are within Neoarchean carbonates, when the crystals fans grew to impressive sizes, with lengths of over 1 m, formed layers of marine cement that reached thicknesses of up to several meters, are laterally continuous over 10s of km or more, and formed across carbonate platform settings from high energy subtidal settings to lower intertidal environments. Crystalline carbonate fans become less common and smaller (cm – scale) in the Paleoproterozoic, and nearly disappear prior to the Neoproterozoic, when they are associated with cap carbonates, and are primarily found in deeper water or outer shelf settings with low sedimentation rates. Seafloor cements are rare during the Phanerozoic, and are typically limited to small geographic areas with unusual sedimentary conditions, or are found in void spaces, where seawater chemistry was able to undergo modifications that would allow precipitation of cement fans. The exception is during the interval of time that followed the Permian – Triassic mass extinction, when small, cm – scale fans and hemispheres are found in Lower Triassic and lowermost Middle Triassic rocks. These cement fans occur in a variety of settings, although they are typically found in deeper water environments. Calcium carbonate fans that formed following the Permian – Triassic extinction may have microbial remains preserved within the cements, and are frequently found in close lateral or stratigraphic association with microbialites. However, some examples of post – extinction carbonate fans appear to have formed abiotically, without any microbial influence. Overall, crystalline calcium carbonate fans signal high levels of calcium carbonate supersaturation in ancient oceans. The initial decline in seafloor cement growth from the Neoarchean into the Proterozoic may have been the result of accelerated micrite production, while Neoproterozoic calcium carbonate fan growth is associated with glacial decay and retreat. Lower Triassic seafloor cements are likely the result of stratification and stagnation of the deep oceans that led to enhanced alkalinity. Calcium carbonate crystal fans are an intriguing feature of ancient carbonates that signal depositional systems and ocean chemistry that is much different from modern ocean, and provide a fascinating glimpse into non – uniformitarian sedimentary environments.</p>

Redox change in sedimentary environments of Triassic bedded cherts, central Japan: possible reflection of sea-level change

1998 ◽  
Vol 135 (6) ◽  
pp. 735-753 ◽  
Author(s):  
KENICHIRO SUGITANI ◽  
KOICHI MIMURA
Keyword(s):  
Sea Level ◽  
Middle Triassic ◽  
Sedimentary Environment ◽  
Sea Level Change ◽  
Lower Section ◽  
Central Japan ◽  
Sedimentary Environments ◽  
Level Change ◽  
Diagenetic Processes ◽  
Facies Change

Middle Triassic radiolarian bedded cherts in the Mino Belt, central Japan, include a sequence showing an abrupt facies change from the lower to the upper, where grey–black bedded cherts enriched in carbonaceous matter and framboidal pyrite are overlain by brick-red hematitic bedded cherts. Brownish-yellow chert enriched in goethite and purple-red chert occur at the boundary between the grey–black bedded cherts and the brick-red bedded cherts. This facies change is in accordance with stratigraphic variations of geochemical characteristics; the lower section grey–black bedded cherts, compared with the upper section brick-red bedded cherts, are enriched in Ctot and Stot, and are characterized by lower MnO/TiO2, higher FeO/Fe2O3* (total iron as Fe2O3) and more variable Fe2O3*/TiO2 values. Some of the lower section samples, in addition, are characterized by an enrichment in some transition metals (Ni, Cu, and Zn). The covariation of mineralogical and geochemical characteristics indicates that sedimentary environments and diagenetic processes were different between the lower and the upper section bedded cherts. During the deposition of the lower section bedded cherts, the sedimentary environment was anoxic and bacterial sulphate reduction occurred during the early diagenetic stage. In contrast, the upper section bedded cherts were subjected to less reducing diagenetic processes; active sulphate reduction did not occur. The change of sedimentary environment and diagenetic process at the site of deposition is likely to be attributed to the fluctuated concentration of dissolved oxygen in the water mass of a semi-closed marginal ocean basin, which was potentially caused by sea-level change that occurred during Middle Triassic time.

The large superpredators’ teeth from Middle Triassic of Poland

2013 ◽  
Vol 2 (1) ◽  
pp. 91-94 ◽  
Author(s):  
Dawid Surmik ◽  
Tomasz Brachaniec
Keyword(s):  
Marine Sediments ◽  
Middle Triassic ◽  
Morphological Features ◽  
Marine Reptiles

ABSTRACT An unusual large teeth, finding from time to time in marine sediments of Muschelkalk, Silesia, Poland indicate the superpredators occurrence. According to size and morphological features the teeth are similar to archosaurs or giant marine reptiles.

Depositional Sedimentary Environments

1980 ◽  
Author(s):  
Hans-Erich Reineck ◽  
Indra Bir Singh
Keyword(s):  
Sedimentary Environments
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