scholarly journals New interpretation of the basal Bambuí Group, Sete Lagoas High (Minas Gerais, E Brazil) by sedimentological studies and regional implications for the aftermath of the Marinoan glaciation: Correlations across Brazil and Central Africa

2020 ◽  
Vol 23 (1-2) ◽  
pp. 1-17 ◽  
Author(s):  
Franck R.A DELPOMDOR ◽  
Archange M. ILAMBWETSI ◽  
Fabricío A. CAXITO ◽  
Antonio C. PEDROSA-SOARES
Keyword(s):  
Central Africa ◽  
Carbonate Ramp ◽  
Gravity Flow ◽  
Intermediate Water ◽  
Anoxic Conditions ◽  
Accommodation Space ◽  
Sediment Gravity Flow ◽  
Wide Range ◽  
Storm Wave ◽  
New Interpretation

Along the preserved southeast border (i.e., the Sete Lagoas High) of the Bambuí basin, the Pedro Leopoldo Member, basal succession of the Sete Lagoas Formation, unconformably overlies the Archean basement, and mostly includes carbonates with thin pelite intercalations and rare ruditic deposits. One of these, the so-called Carrancas conglomerate in its type-section, has been considered one of the lowermost rudite deposits of the Bambuí basin, being frequently ascribed to a Neoproterozoic glaciation. However, our detailed study, based on facies analysis, reveals that the Carrancas conglomerate was deposited by sediment gravity flow currents within the basal Pedro Leopoldo Member. Two outcrop sections in the São José de Lapa and Vespasiano areas, including thirteen abandoned quarry-cut and cliff outcrops, display eight distinct lithofacies (LF1 to LF8) forming a shallowing-upward carbonate ramp succession. It is composed, from the base to the top, by a mixed siliciclastic-carbonate outer ramp distally bounded by a slope-outer ramp system with sediment gravity flow deposits, a deep outer ramp developed below storm-wave base environments, an outer-middle ramp with aragonite pseudomorph crystal fans developed in a CaCO3 oversaturated below storm-wave base environment in suboxic/anoxic conditions. According to published isotope data correlating δ13C trends and values in basal carbonates of the Pedro Leopoldo Member of the Sete Lagoas and Januária highs, the relatively deep outer-slope ramp mixed siliciclastic-carbonate units of the study area appear to be coeval in age with the cap dolostone of shallow-water inner ramp of the Januária High. The absence of a cap dolostone in the Sete Lagoas High could be explained by lack of accommodation space or a regional erosion due to the tectonically driven forebulge uplift of the Sete Lagoas High. The Pedro Leopoldo Member in the Sete Lagoas High was accumulated in a brine-seawater bottom waters under suboxic/anoxic conditions in the relatively deeper portion of the carbonate ramp system, whilst the cap dolostone in the Januária High was developed in oxygenated mixed layer and intermediate water near the surface water in the shallower portion of the carbonate ramp system. Such lateral variations of facies and δ13C fluctuations are similar to those recorded by the cap carbonate sequences of the basal Schisto-Calcaire/Lukala (Sub)Group in the West Congo Belt and the basal Araras Group in the Paraguay Belt, which display a similar wide range of sub-environments like the studied part of the Pedro Leopoldo Member.

Recognizing tide- and wave-dominated compound deltaic clinothems in the rock record

Geology ◽  
2020 ◽  
Vol 48 (12) ◽  
pp. 1149-1153
Author(s):  
Yang Peng ◽  
Cornel Olariu ◽  
Ronald J. Steel
Keyword(s):  
Seismic Data ◽  
Three Dimensional ◽  
Gravity Flow ◽  
Small Scale ◽  
Sedimentary Record ◽  
Sediment Gravity Flow ◽  
Rock Record ◽  
Storm Wave ◽  
Tidal Deposits

Abstract Many modern deltas exhibit a compound geometry that consists of a shoreline clinoform and a larger subaqueous clinoform connected through a subaqueous platform. Despite the ubiquity of compound clinoforms in modern deltas, very few examples have been documented from the ancient sedimentary record. We present recognition criteria for shelf compound-clinoform systems in both tide- and wave-dominated deltas by integration of ancient and modern examples from multiple types of data. The compound clinothem can be identified by using a combination of: (1) the three-dimensional (3-D) configuration identified in bathymetric or seismic data, (2) bipartite stacked regressive units, consisting of a lower muddy coarsening-to-fining-upward (CUFU) or coarsening-upward (CU) unit (30–100 m thick) and an overlying sandier CU unit (5–30 m thick) (together they represent the subaqueous and shoreline clinoform pair), and (3) distinct facies described herein, though both types of delta have highly bioturbated mudstone and siltstone bottomsets. Tide-dominated deltas have muddy foresets with tidal scours containing tidal rhythmites or inclined heterolithic strata in the subaqueous clinothem overlain by river and tidal deposits of the shoreline clinothem. Wave-dominated deltas show mainly wave-enhanced sediment-gravity-flow (WSGF) beds and some thin hummocky/swaley cross-stratified (HCS/SCS) sandstones toward the top in the subaqueous muddy foreset, and upward-thickening HCS/SCS and trough/planar cross-bedded sandstones interbedded with siltstones in the shoreline clinothem. The subaqueous platform, which links the clinoform couplet, shows evidence of frequent tidal or wave reworking and redeposition. The platform in tide-dominated deltas is characterized by tide-generated heterolithic strata (e.g., bidirectional current-rippled and cross-stratified sandstones, spring and neap tidal bundles, tidal rhythmites) with occasional storm-wave–influenced strata. In contrast, the wave-dominated platform comprises small-scale swales with scours and mud clasts and some WSGF deposits. The proposed criteria can aid in the recognition of compound deltaic clinothems in other basins, particularly those with limited amounts and/or types of data.

scholarly journals Rapid gravity flow transformation revealed in a single climbing ripple

Geology ◽  
2020 ◽  
Author(s):  
Jaco H. Baas ◽  
Jim Best ◽  
Jeff Peakall
Keyword(s):  
Plug Flow ◽  
Gravity Flow ◽  
Small Scale ◽  
Geometrical Characteristics ◽  
Gravity Flows ◽  
Sediment Gravity Flow ◽  
Wide Range ◽  
Sediment Deformation ◽  
Rheological Character ◽  
Current Ripples

Sediment gravity flows demonstrate a wide range of rheological behaviors, and past work has shown how transformations between flow types generate spatiotemporal changes in the resultant sedimentary successions. We used the geometrical characteristics of a single climbing ripple to demonstrate how such flows can transform from a turbulent to a quasi-laminar plug flow, with the transitional clay flow sequence being manifested by abnormally large heterolithic sand-clay current ripples with small backflow ripples, and then abundant clay deposition associated with smaller ripples. Analysis of ripple size, angle of climb, grain size, internal erosional surfaces, and soft-sediment deformation suggests that transformation in the rheological character of the sediment gravity flow was rapid, occurring over a period of tens of minutes, and thus probably over a spatial scale of hundreds of meters to several kilometers. Our study indicates how the character of flow transformation can be elucidated from the details of a small-scale sedimentary structure.

Causes of varied sediment gravity flow types on the Alsek Prodelta, northeast Gulf of Alaska

1988 ◽  
Vol 7 (4) ◽  
pp. 317-342 ◽  
Author(s):  
William C. Schwab ◽  
Homa J. Lee ◽  
Bruce F. Molnia
Keyword(s):  
Gulf Of Alaska ◽  
Gravity Flow ◽  
Sediment Gravity Flow

scholarly journals Microtubules soften due to cross-sectional flattening

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Edvin Memet ◽  
Feodor Hilitski ◽  
Margaret A Morris ◽  
Walter J Schwenger ◽  
Zvonimir Dogic ◽  
...  
Keyword(s):  
High Strain ◽  
Three Dimensional ◽  
Elastic Model ◽  
Softening Effect ◽  
Cross Sectional ◽  
Mechanical Compliance ◽  
Wide Range ◽  
Elastic Filament ◽  
New Interpretation ◽  
Effective Mechanical Properties

We use optical trapping to continuously bend an isolated microtubule while simultaneously measuring the applied force and the resulting filament strain, thus allowing us to determine its elastic properties over a wide range of applied strains. We find that, while in the low-strain regime, microtubules may be quantitatively described in terms of the classical Euler-Bernoulli elastic filament, above a critical strain they deviate from this simple elastic model, showing a softening response with increasing deformations. A three-dimensional thin-shell model, in which the increased mechanical compliance is caused by flattening and eventual buckling of the filament cross-section, captures this softening effect in the high strain regime and yields quantitative values of the effective mechanical properties of microtubules. Our results demonstrate that properties of microtubules are highly dependent on the magnitude of the applied strain and offer a new interpretation for the large variety in microtubule mechanical data measured by different methods.

Slumping and a sandbar deposit at the Cretaceous-Tertiary boundary in the El Tecolote section (northeastern Mexico): An impact-induced sediment gravity flow

Geology ◽  
2001 ◽  
Vol 29 (3) ◽  
pp. 231 ◽  
Author(s):  
Ana R. Soria ◽  
Carlos L. Liesa ◽  
Maria Pilar Mata ◽  
José A. Arz ◽  
Laia Alegret ◽  
...  
Keyword(s):  
Gravity Flow ◽  
Sediment Gravity Flow ◽  
Northeastern Mexico

scholarly journals A CARBONATE RAMP EVOLUTION IN THE TRANSITION FROM THE APULIA PLATFORM TO THE IONIAN BASIN DURING EARLY TO LATE CRETACEOUS (NW GREECE)

2018 ◽  
Vol 40 (1) ◽  
pp. 53
Author(s):  
K. Getsos ◽  
F. Pomoni-Papaioannou ◽  
A. Zelilidis
Keyword(s):  
Sea Level ◽  
Late Cretaceous ◽  
Facies Analysis ◽  
Carbonate Ramp ◽  
Time Interval ◽  
Storm Wave ◽  
Lowermost Part ◽  
Storm Deposits ◽  
Homoclinal Ramp ◽  
Apulia Platform

Facies analysis of Cretaceous carbonate sequences from the external and central Ionian zone revealed a homoclinal ramp model of evolution. During Berriasian to Valanginian, the carbonate ramp was differentiated to an inner-mid and outer ramp environment, which corresponded to the external and central Ionian zone, respectively, while the main inner ramp environment is assumed that was located in the Pre-Apulian zone. The external Ionian zone (inner-mid ramp) is characterized by muds tones-wackes tones with fragmented echinoderms, bivalves, radiolarians and rare aptychus considered to be deposited below the fairweather wave base (FWWB). Locally, thin graded storm deposits intervene, indicating deposition above the storm weather wave base (SWB). Minor occurrences of packs tonesgrainstones, with fragmented echinoderms, calcareous algae, tubiphytes, lagenid foraminifera and rare ooids occur, as well, considered to be deposited at the lowermost part of the inner ramp, near the constantly agitated fairweather wave base (FWWB). The central Ionian zone (outer ramp) is mainly characterized by mudstones-wackestones with abundant radiolarians and rare calpionellids and calcispheres, considered to be deposited below the storm wave base (SWB). No talus or breccias deposits were observed, during the mentioned time interval, in any part of the studied area. From Hauterivian to Turonian, continual sea-level rise, led to establishment of outer ramp environment in the external Ionian zone, over the previous inner-mid ramp, and outer ramp-basin environment, over the previous outer ramp, in the central Ionian zone. The transition from shallower to deeper conditions is characterized by an overall deposition of mudstones-wackestones with abundant radiolarians rooted in pure micrite. 

scholarly journals The East and the West

2020 ◽  
pp. 107-134
Author(s):  
Hye K. Pae
Keyword(s):  
East Asian ◽  
Value Systems ◽  
The West ◽  
Philosophical Foundations ◽  
Cultural Aspects ◽  
Everyday Practices ◽  
Wide Range ◽  
New Interpretation ◽  
Attention And Perception ◽  
Analytic Problem

Abstract This chapter reviews the cultural aspects of the East and the West. A wide range of differences between the East and the West is discussed in terms of the extrinsic and intrinsic differences. The extrinsic differences comprise architecture, the mode of clothing, everyday practices, and language and script, while the intrinsic differences consist of culture and value systems, attention and perception (holistic vs. analytic), problem solving (relation vs. categorization), and rhetorical structure (linear vs. roundabout). The locus of these differences is identified with respect to philosophical foundations and the characteristics of Eastern and Western cultures. The prevalent interpretations of the differences between the East and the West center on Diamond’s (1999) guns, germs, and steel, Nisbett’s (2003) geography of thought, and Logan’s (2004) alphabet effects. However, these interpretations cannot explain differences in ideologies, religious practices, and societal values among Chinese, Japanese, and Koreans. Therefore, script relativity becomes a new interpretation of the engine behind the differences among the three East-Asian nations and between the East and the West.

scholarly journals The effect of third-order nonlinearity on statistical properties of random directional waves in finite depth

2009 ◽  
Vol 16 (1) ◽  
pp. 131-139 ◽  
Author(s):  
A. Toffoli ◽  
M. Benoit ◽  
M. Onorato ◽  
E. M. Bitner-Gregersen
Keyword(s):  
Wave Energy ◽  
Finite Depth ◽  
Statistical Properties ◽  
Order Effects ◽  
Intermediate Water ◽  
Third Order ◽  
Wide Range ◽  
Relative Water ◽  
Gaussian Statistics ◽  
Third Order Nonlinearity

Abstract. It is well established that third-order nonlinearity produces a strong deviation from Gaussian statistics in water of infinite depth, provided the wave field is long crested, narrow banded and sufficiently steep. A reduction of third-order effects is however expected when the wave energy is distributed on a wide range of directions. In water of arbitrary depth, on the other hand, third-order effects tend to be suppressed by finite depth effects if waves are long crested. Numerical simulations of the truncated potential Euler equations are here used to address the combined effect of directionality and finite depth on the statistical properties of surface gravity waves; only relative water depth kh greater than 0.8 are here considered. Results show that random directional wave fields in intermediate water depths, kh=O(1), weakly deviate from Gaussian statistics independently of the degree of directional spreading of the wave energy.

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