Assista Clicando aqui
Estratificação e Segregação Espontâneas
Aqui vemos Hernán Makse com o aparato experimental utilizado para explorar como certas misturas de dois tipos de grãos estratificam e se segregam espontaneamente. O dispositivo é conhecido como célula de Hele-Shaw quase-bidimensional. Ela consiste de duas folhas de Plexiglas separadas em cerca de 5 mm por espaçadores.
Como ocorre a estratificação espontânea
A mistura de Hernán, derramada lentamente dentro da célula, consiste de grandes grãos de açúcar cúbicos vermelhos, com um diâmetro típico de 0,8, mm e contas de vidro esféricas menores, com um diâmetro aproximado de 0,19 mm. A estratificação é aparente na alternância entre listras vermelhas e brancas. Enquanto a encosta se forma a partir da avalanche simulada de Hernán, ela se alterna entre duas fases:
- Os grãos misturados formam um ressalto no topo da encosta.
- Quando essa pilha fica muito íngreme, subitamente ela cai. À medida que essa mistura se move encosta abaixo, os grãos redondos menores afundam mais na mistura de fluido e se acomodam em uma camada abaixo dos grandes grãos cúbicos.
Enquanto isso, à medida que mais grãos misturados são derramados dentro da célula, uma nova pilha começa a se acumular no topo.
A sequência de imagens a seguir foi extraída de uma simulação desse processo no computador. Ela supõe uma corrente estável de grãos sendo derramados do ponto mais alto da encosta, exatamente como Hernán está fazendo na foto acima. A linha roxa representa os grãos de tamanhos misturados fluindo encosta abaixo. As linhas vermelhas representam os grandes grãos cúbicos em repouso. As linhas verdes representam os pequenos grãos redondos em repouso.
|Sequência da estratificação para grãos grandes facetados e grãos menores esféricos.|
Na maioria dos arenitos, estratificados ou segregados, as áreas de grãos diferentes não se mostram tão claramente como nessas demonstrações. Os grãos foram selecionados para apresentarem cores diferentes, bem como formas e tamanhos diferentes. Na natureza, as cores provavelmente serão muito parecidas.
Como ocorre a segregação espontânea
O que acontece se derramarmos uma mistura de grandes grãos redondos e pequenos grãos facetados dentro da célula? Quando uma mistura de pequenos grãos facetados de areia preta (tamanho típico de 0,3 mm) e grandes contas de vidro esféricas brancas (tamanho típico de 0,8 mm) é derramada dentro uma célula quase-bidimensional de Hele-Shaw, os grãos maiores tenderão a se movimentar encosta abaixo, pois eles são grandes e redondos, ao passo que os grãos pequenos tenderão a se segregar no alto da encosta, pois eles são pequenos e facetados.
Por que isso é importante?
É interessante tentar descobrir como as coisas ocorrem dessa forma. Porém, os cientistas também estão interessados na estratificação e segregação por motivos práticos. A maior parte do petróleo do mundo se encontra nos poros do arenito. O volume de petróleo contido em um arenito particular dependerá de sua porosidade, a qual, por sua vez, depende do tamanho e da forma dos grãos. O entendimento de como ocorrem a estratificação e a segregação nos ajudará a formar uma quadro mais completo das estruturas geológicas subterrâneas.
A Rocha de Petra
Agora sabemos como essa rocha de Petra ganhou suas listras. Ou não sabemos? Na realidade, não temos certeza. As listras poderiam resultar do fenômeno de estratificação que acabamos de examinar ou de algum outro processo. Para se ter certeza, são necessárias investigações adicionais. Porém, existem rochas formadas a partir de dunas de areia antigas, nas quais temos a certeza da ocorrência de estratificação.
online educational seminar on the basic principles of m…
Time Required for Sedimentation Contradicts the Evolutionary Hypothesis
Member of the International Association of Sedimentologists
What I have to say goes to the heart of the subjects discussed at this conference. To contain them in the brief period I have at my disposal I propose addressing the basic question which is developed more fully in my published articles available on my web site: www.sedimentology.fr
Why did I decide to do experiments on the formation of strata?
The answer is simple. Because I was surprised to find how little work had been done on the subject in the past. Of course, sediments had been examined and flume experiments performed in connection with building dams and other construction projects, but none with the object of explaining the mechanics of stratification. I searched the data banks but found little to help with my research. I began to realise that the basic principles of superposition, continuity and initial horizontality laid down in the seventeenth century had been accepted, albeit with elaboration, virtually without question. There seemed to have been little attempt to examine the actual mechanics involved in strata formation. The implications were far-reaching both as concerns the geological time-scale and the fossil record. Indeed, as Prof. Gabriel Gohau of the French Geological Society wrote in his book A History of Geology (1990):
Time is measured by the interval required for sediments to deposit, a fact upon which everybody is more or less agreed, and not by orogenesis or “biological revolutions.”
Prof. Gohau mentioned in his work how Charles Lyell was influenced in the construction of the geological time scale by his belief in "biological revolutions" occurring over 240 millions of years.
It was the geological time-scale, giving the impression that there was a succession and change in fossilised species, which led Darwin to formulate his theory of evolution.
In the 20th century Lyell's figure was replaced by a radiometric date of 542 million years from the Cambrian era.
What Prof.Gohau wrote is perfectly correct, because fossils are buried in sediments. Therefore, it is the time of sedimentation which determines the age of fossils or the time when they were buried, and not a chronology based on "biological revolutions" interpreted now as "biological evolution."
As regards radiometric dating, I refer to Prof. Aubouin, who says in his Précis de Géologie : "Each radioactive element disintegrates in a characteristic and constant manner, which depends neither on the physical state (no variation with pressure or temperature or any other external constraint) nor on the chemical state (identical for an oxide or a phosphate)."
Rocks form when magma crystallizes. Crystallisation depends on pressure and temperature, from which radioactivity is independent. So, there is no relationship between radioactivity and crystallisation.
Consequently, radioactivity doesn't date the formation of rocks. Moreover, daughter elements contained in rocks result mainly from radioactivity in magma where gravity separates the heavier parent element, from the lighter daughter element. Thus radiometric dating has no chronological signification.
It seemed to me, therefore, necessary to study the basis of the Stratigraphic scale which depended upon the stratification of sedimentary rocks.
Stenon was the founder of stratigraphy. It was in 1667 that he introduced in his work Canis Calchariae the postulate: layers of sub-soil are “strata” of ancient successive “sediments” . From this partial interpretation, Stenon drew three initial principles of stratigraphy, formulated in his work Prodromus (1669).
(1) Principle of superposition
At the time when one of the high stratum formed, the stratum underneath it had already acquired a solid consistency. At the time when any stratum formed, the superincumbent material was entirely fluid, and due to this fact at the time when the lowest stratum formed, none of the superior strata existed.
(2) Principle of continuity
Strata owe their existence to sediments in a fluid. At the time when any stratum formed, either it was circumscribed on its sides by another solid body, or else it ran around the globe of the earth.
(3) Principle of original horizontality
At the time when any stratum formed, its lower surface, as also the surfaces of its sides, corresponded with the surfaces of the subjacent body, and lateral bodies, but its upper surface was (then) parallel to the horizon, as far as it was possible.
The sedimentological model corresponding to these three principles is, therefore, the following. In a fluid covering the Earth, except for exposed land, a precipitate deposits strata after strata, covering all of the submerged Earth. After the deposition of each stratum, the sedimentation is interrupted for the time it takes for the stratum to acquire a solid consistency. The stratum being contained between two parallel planes indicates that the sedimentation rate of the precipitate is uniform around the submerged Earth.
DEFICIENCIES OF STENON'S STRATIGRAPHY
The first part of the definition of the principle of superposition is: At the time when one of the highest stratum formed, the stratum underneath it had already acquired a solid consistency . A stratum between 50 cm and 1 m is considered thick. Consequently, submarine drillings should encounter solid strata in the stratified oceanic sediments after a few meters.
The results of sea bottom drilling have shown that the first semi-consolidated sediments appear about 400-800 metres (in depth). Moreover beds of chert have been found under 135 metres of sediment near zones of oceanic transversal faults (Logvinenko, 1980). Stenon's definition, therefore, relative to successive hardening of strata, which would greatly extend the total length of time of deposition, is not supported by these sedimentological observations.
As regards the principle of continuity, I object that no sedimentary layer goes all around the Earth. As concerns the principle of original horizontality, I object that seismic readings and sub-marine coring demonstrate that the strata in ocean deposits are not always horizontal, and that the rate of sedimentation is not uniform on a global scale in the Earth's oceans.
Stenon said that: Strata owe their existence to sediments in a fluid , but he said nothing about the action of the fluid on sediments, so that the relative stratigraphic chronology resulting from his principles did not take it into account (the two later principles of paleontological identity and uniformitarianism changed nothing in this respect). Currents exist in present day oceans, which erode, transport, and deposit sediments, as shown by Strakhov in 1957.
Charles Lyell added a principle of uniformitarianism, giving as an example layers deposited in fresh water in Auvergne. Observing that the layers were less than 1 mm thick, he considered that each one had been laid down annually. At this rate, the 230 m. thick deposit would have taken hundreds of thousands of years to form. As shown in the next section these layers, which are laminae, do not always correspond to annual deposits and may be generated in a time interval much less than that indicated by the modern geological time-scale.
Geologists have now recognized sequences of facies (conglomerate, sandstone, shale, limestone, evaporate) which correspond to marine transgressions and regressions. This is the object of study in sequence stratigraphy today. Diagrams in this discipline, however, give no indication of the current's velocity during these transgressions and regressions. The size of particles of sediment in a sequence corresponds to a minimum current velocity capable of transporting the particles from where they were eroded to their sedimentation site.
MAJOR STAGES OF THE LABORATORY RESEARCH
Two principal stages of the program dwelt upon the following two lines of research: lamination and stratification.
The following abstract of my paper (Berthault, 1986 – Academy of Sciences) provided the basis of my research on the deposit of heterogranular sediments in water, with and without a current: These sedimentation experiments were conducted in still water with a continuous supply of heterogranular material. A deposit is obtained, giving the illusion of successive beds or laminae (Fig. 1). These laminae are the result of a spontaneous periodic and continuous grading process, which takes place immediately, following the deposition of the heterogranular mixture.
The thickness of the laminae appears to be independent of the sedimentation rate but increases with extreme differences in the particle size in the mixture. Where a horizontal current is involved, thin laminated layers developing laterally in the direction of the current are observed.
The second series were performed at the Marseilles Institute of Fluid Mechanics.
The experiments demonstrate that in still water, continuous deposition of heterogranular sediments gives rise to laminae, which disappear progressively as the height of the fall of particles into water (and apparently their size) increases. Laminae follow the slope of the upper part of the deposit. In running water, many closely related superposed types of lamination appear in the deposit (Berthault, 1988 - French Academy of Sciences).
Experiments in stratification were conducted in the Fort Collins hydraulics laboratory of the Colorado State University by the professor of hydraulics and sedimentology Pierre Julien. For these, it was necessary to operate with water in a recirculating flume traversed by a current laden with sediment. As Hjulstrom (1935) and his successors had defined the critical sedimentation rate for each particle size, the current velocity would need to be varied. By modulating the current velocity, a superposition of different sized particles could be obtained.
The flume experiment showed that in the presence of a variable current, stratified superposed beds form simultaneously in the direction of the current. The result, on the scale of strata, also conform, on the scale of facies, to Golovkinskii, Inostrantzev and Walther's law (Walther, 1894; Middleton, 1973; Romanovskii, 1988), according to which the extension of facies of a specific sequence is the same in both a lateral and vertical direction.
Fig. 3 : Experimental results. (a) Schematic formation of graded beds (b) Temporal sequences of deposit formation for t1 < t2 < t3
Laboratory experiments on the desiccation of natural sands also show preferential fracturing (or joints) of crusty deposits at the interface between strata of coarse and fine particles. Rather than successive sedimentary layers, these experiments demonstrate that stratification under a continuous supply of heterogeneous sandy mixtures results from segregation for lamination, non-uniform flow for graded beds ( Fig. 4 ), and desiccation for joints ( Fig. 5 ). Superposed strata are not, therefore, necessarily identical to successive sedimentary layers.
Moreover, the experiments reported in my second paper to the Academy of Sciences and experiments conducted by P. Julien and presented in the video Fundamental Experiments on Stratification at several sedimentological congresses, clearly show that up to the limit of the angle of repose (30o to 40o for the sands), the lamination of the deposit is parallel to the slope ( Fig. 6 ). In this case the principle of horizontality does not apply. It should not, therefore, be concluded that the dip of the strata necessarily implies tectonic movements subsequent to the horizontal deposit of the strata.
The report of the experiment entitled Experiments in Stratification of Heterogeneous Sand Mixtures (Julien et al. , 1993) was published in the Bulletin of the Geological Society of France.
(3) Paleohydraulic conditions
Analysis of the main principles of stratigraphy on the basis of experimental data is necessary to determine the hydraulic conditions that existed when the sediments, which have become rocks, were deposited. In this respect, the relation between hydraulic conditions and configuration of deposits (submarine ripples and dunes and horizontal beds) of contemporary deposits have been the object, especially recently, of well-known observations and experimentation.
Examples are of Rubin (Rubin and McCulloch, 1980) ( Fig. 7 ) in a sea environment (San Francisco Bay) and Southard (Southard and Boguchwal, 1990 – flume experiments)
Fig. 7: Diagram indicating coordinates of: (a) depth of water and the height of underwater dunes (b) depth of water and velocity of current in m/s.
Fig. 7 Graphs of (a) water depth vs. sand-wave height and (b) water depth vs. water velocity, showing bedforms in fine sand expected under different water conditions. The thickness of cross beds observed in fine-grained sandstone is used to estimate sand-wave height. Then, sand-wave height is entered into the graph (a) to estimate the water depth where the sand wave formed. After a water depth is estimated on graph (a), the depth is transferred to graph (b), where the minimum and maximum velocities of water are indicated for the specific water depth.
Meanwhile, Hjulstrom 1930 and his successors Lebedev, 1959; Neill, 1968; Levi, 1981; Maizels, 1983; Van Rijn, 1984; Maza, Flores, 1997 have determined a minimum velocity of erosion and sedimentation for each particle size at a given depth ( table 1 ).
Table 1. Maximum permissible velocities for non-erosive or non-cohesive grounds, in m/s (according to Lischtvan-Lebediev).
These relations can be applied particularly to detrital rocks, such as sandstone, the first stage of a transgressive marine sequence resulting from a process of erosion, transport, sedimentation, driven by an initially erosive powerful current in shallow water. The paleovelocity of current below which particles of a given size deposit, and the corresponding capacity of sedimentary transport of the current can be determined based upon the aforementioned data. These two criteria determine the time for sequences to deposit.
My study Analysis of the Main Principles of Stratigraphy on the Basis of Experimental Data was published by the Russian Academy of Sciences's journal “Lithology and Mineral Resources” in 2002.
I arranged a new series of experiments with the St. Petersburg Institute of Hydrology to study erosion of different types of rocks (sandstone, limestone) at higher velocities of water current up to 27 m/s (results are given in the tables below) to ascertain their rate of erosion in time and to provide the formation of conglomerates, to know the critical velocity of erosion of conglomerates seen in sandstone at the base of transgressive sequences.
Initially, the water current was parallel to the surface plane of the sedimentary sample. The results show that at a velocity of around 25m/s erosion was nil; where the period of the experiment was less than 10h. However, when the period reached 18h the erosion was around 2 grams. Experiment 25 was done with a sample whose surface was at an angle of 2.5° to the direction of the current. In this case erosion reached 6.6g. in 18h.
The experiments are continuing, particularly as regards the last angular sample, to determine the minimum critical velocity of erosion.
A team of Russian sedimentologists directed by Alexander Lalomov (Russian Academy of Sciences' Institute of Ore Deposits) applied paleohydraulic analyses to geological formations in Russia. One example is the publication of a report in 2007 by the Lithology and Mineral Resources journal of the Russian Academy of Sciences. It concerns the Crimean Peninsular. It shows that the time of sedimentation of the sequence studied corresponds to a virtually instantaneous episode whilst according to stratigraphy it took several millions of years. Moreover, a recent report concerning the North-West Russian plateau in the St. Petersburg region shows that the time of sedimentation was much shorter than that attributed to it by the stratigraphic time-scale: 0.05% of the time.
I concluded an agreement with the Institute of Geology of Kazan under which the Moskovite team of sedimentologists would determine the paleohydraulic conditions of the local transgressive sequence studied in 1868 by Golovkinskii, founder of sequence stratigraphy. We presented their report to the 33rd International Congress of Geology, held in Oslo in August 2008 and in Yekaterinburg (Russia) in October at the 5th Conference on Lithology.
Geological chronology has been established on two pillars: stratigraphy and radiometric dating. Our experiments invalidate the principles of stratigraphy. As regards radiometric dating, a fact must be taken into account: radioactivity is independent of the physical or chemical state of the sample. Radioactivity is not, therefore, concerned by the sample having changed from magma into rock. Consequently, as the radiometric dating process is not linked to the solidification of the magma, it cannot date the formation of metamorphic nor volcanic rocks. 1
Paleohydraulic analysis determines the time of sedimentation of a sequence, which is shown to be much shorter than the stratigraphic time. Evidently, this short time period does not support the evolutionary hypothesis that life arose from non-life and that life-forms developed from a common ancestor through innumerable genetic mutations over hundreds of millions of years (see: www.sedimentology.fr ).
As present marine species live in different ecological zones, according to sea depth, latitude and longitude, the superposition in rocks of different fossils may correspond to their paleoecological distribution in depth and to migration patterns.
By calling into question the principles and methods, upon which geological dates are founded, and in proposing the new approach of paleohydrology, I hope to open a dialogue with specialists in the disciplines concerned, who are able to appreciate the implications, and propose a geological chronology in conformity with experimental observation based upon time of sedimentation—time which is insufficient for the evolution of species, as conceived by the proponents of the evolutionary hypothesis.
1 For a critique of radiometric dating of rocks, see JEAN DE PONTCHARRA, “Are Radiodating Methods Reliable?” published in A Scientific Critique of Evolution , Sapienza University, Rome, 2009.
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Berthault, G., Sédimentation d'un mélange hétérogranulaire. Expériences de lamination en eau calme et en eau courante, CR. Acad.Sc. , 1988, vol.306, Série II, pp.717-724.
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Berthault, G., Sedimentological Interpretation of the Tonto Group Stratigraphy (Grand Canyon Colorado River), Lithology and Mineral Resources , Vol. 39. N° 5, 2004, pp.504-508.
Berthault, G., Izotov, VG, Lalomov, AV, Sitdikova, LM, Akhmetshakirov, MM, Analytical Expression of Golovkinsky-Walther's Law with Reference to Research of Permian Strata of Volga-Ural Region , 33rd International Geological Congress, Oslo 2008, August 6-14, SES-01 General Contributions to Sedimentology.
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