scholarly journals Depositional environments and bivalve fossil assemblages of the Lower Cretaceous Arida Formation, southwest Japan.

1999 ◽  
Vol 105 (9) ◽  
pp. 643-650 ◽  
Author(s):  
Toshifumi Komatsu
Keyword(s):  
Lower Cretaceous ◽  
Depositional Environments ◽  
Southwest Japan ◽  
Fossil Assemblages

LITHOLOGICAL AND PALEOCOMMUNITY VARIATION ON A MISSISSIPPIAN (TOURNAISIAN) CARBONATE RAMP, MONTANA, USA

Palaios ◽  
2021 ◽  
Vol 36 (3) ◽  
pp. 95-114
Author(s):  
GARETT M. BROWN
Keyword(s):  
Cluster Analysis ◽  
Environmental Gradients ◽  
Depositional Environments ◽  
Third Order ◽  
Depositional Sequence ◽  
Heterogeneous Distribution ◽  
Point Count ◽  
Sediment Types ◽  
Fossil Assemblages ◽  
Replicate Sampling

ABSTRACT The ecological structure of ancient marine communities is impacted by the environmental gradients controlling assemblage compositions and the heterogeneous distribution of sediment types. Closely spaced, replicate sampling of fauna has been suggested to mitigate the effects of such heterogeneity and improve gradient analyses, but this technique has rarely been combined with similar sampling of lithologic data. This study analyses lithological and faunal data to determine the environmental gradients controlling the composition of Mississippian fossil assemblages of the lower Madison Group in Montana. Eighty-one lithological and faunal samples were collected from four stratigraphic columns in Montana, which represent the deep-subtidal, foreshoal, and ooid-shoal depositional environments within one third-order depositional sequence. Cluster analysis identifies three distinct lithological associations across all depositional environments—crinoid-dominated carbonates, peloidal-crinoidal carbonates, and micritic-crinoidal carbonates. Cluster analysis and nonmetric multidimensional scaling (NMS) identifies a highly diverse brachiopod biofacies and a solitary coral-dominated biofacies along an onshore-offshore gradient. Carbonate point count data and orientation of solitary corals indicate that substrate and wave energy are two potential variables that covary with the onshore-offshore gradient. Overlaying lithological information on the NMS indicates a secondary gradient reflecting oxygen that is expressed by increasing bioturbation and gradation from brown to dark gray carbonates to medium-light gray carbonates. Taken together, these findings demonstrates how combining closely spaced, replicate sampling of lithologic and faunal data enhances multivariate analyses by uncovering underlying environmental gradients that control the variation in fossil assemblages.

scholarly journals Stratigraphy and Depositional Environment of Mauddud Formation in Ratawi Oil wells of Southern Iraq

2021 ◽  
Vol 877 (1) ◽  
pp. 012030
Author(s):  
Maha Razaq Manhi ◽  
Hamid Ali Ahmed Alsultani
Keyword(s):  
Deep Sea ◽  
Lower Cretaceous ◽  
Depositional Environment ◽  
Carbonate Platform ◽  
Depositional Environments ◽  
Oil Wells ◽  
Oil Field ◽  
Microfacies Analysis ◽  
Thin Sections ◽  
Southern Iraq

Abstract The Mauddud Formation is Iraq’s most significant and widely distributed Lower Cretaceous formation. This Formation has been investigated at a well-23 and a well-6 within Ratawi oil field southern Iraq. In this work, 75 thin sections were produced and examined. The Mauddud Formation was deposited in a variety of environments within the carbonate platform. According to microfacies analysis studying of the Mauddud Formation contains of twelve microfacies, this microfacies Mudstone to wackestone microfacies, bioclastic mudstone to wackestone microfacies, Miliolids wackestone microfacies,Orbitolina wackestone microfacies, Bioclastic wackestone microfacies, Orbitolina packstone microfacies, Peloidal packstone microfacies, Bioclastic packstone microfacies, Peloidal to Bioclastic packstone microfacies, Bioclastic grainstone microfacies, Peloidal grainstone microfacies, Rudstone microfacies. Deep sea, Shallow open marine, Restricted, Rudist Biostrome, Mid – Ramp, and Shoals are the six depositional environments in the Mauddud Formation based on these microfacies.

scholarly journals Geochemistry of Lower Cretaceous sediments, Inner Zone of Southwest Japan. Constraints on provenance and tectonic environment.

2000 ◽  
Vol 34 (2) ◽  
pp. 155-173 ◽  
Author(s):  
Daniel K. Asiedu ◽  
Shigeyuki Suzuki ◽  
Kenji Nogami ◽  
Tsugio Shibata
Keyword(s):  
Lower Cretaceous ◽  
Southwest Japan ◽  
Tectonic Environment
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