jeanflop/post_ocr_correction2 huggingface dataset:
Much of the sand is non to poorly fossiliferous, but from place to place, extraordinary concentrations of microfaunal remains occur. Among these concentrations are found relatively few large mammal bones. In the caverns is a series of younger deposits, comprising extensive speleothems of various ages, and unconsolidated sands and silts. The latter are accumulating at the present day, principally by aeolian transport through the open cave mouths, as well as by infiltration through vertical fissures in the cave roof, aided by water flow during rainy seasons. C. R. Acad. Sci. Paris, t. 307, Série II, p. 1681-1686, 1988 1685 TAPHONOMY. — The Gcwihaba and Nqumtsa caves are occupied by Barn Owls, bats and a varied insect fauna. The former produce large quantities of owl pellets below favoured perches, both within the cave and in trees near the entrance. Bats frequently die within the caverns and fall to the floor where they are consumed by a varied entomological fauna. The gradual consumption of bat carcasses and owl pellets gives rise to concentrations of dental, cranial and postcranial remains within a loose sandy deposit, which closely resembles the Plio-Pleistocene cave fill, save for its unconsolidated nature. The fauna also destroys any bedding within the sediments by constantly rummaging through the top few centimeters of deposit, producing the even floor surface remarked on by Wayland in 1944 [10]. The caves are said to be inhabited by leopards. However, there appear to be few signs that this is a regular feature of the caves, and for most of the time they appear to be unoccupied by these carnivores. There are few large skeletal remains in the cave mouths which could have been transported into the caves by leopards, but in general, large mammal remains are notable by their rarity. In the caves at the southern end of Gcwihaba A Hill, occurs a population of porcupines which are well known for their propensity to collect bones and to transport them to their dens. Porcupines were also present in the area during the Plio-Pleistocene, and may well have played a role in accumulating the large mammals
within the sediments by constantly rummaging through the top few centimeters of deposit, producing the even floor surface remarked on by Wayland in 1944 [10]. The caves are said to be inhabited by leopards. However, there appear to be few signs that this is a regular feature of the caves, and for most of the time they appear to be unoccupied by these carnivores. There are few large skeletal remains in the cave mouths which could have been transported into the caves by leopards, but in general, large mammal remains are notable by their rarity. In the caves at the southern end of Gcwihaba A Hill, occurs a population of porcupines which are well known for their propensity to collect bones and to transport them to their dens. Porcupines were also present in the area during the Plio-Pleistocene, and may well have played a role in accumulating the large mammals found in these deposits. Judging from the close similarity between the subfossil microfaunal concentrations in the unconsolidated cave sediments, and those of Plio-Pleistocene age, the latter very probably represent consumed owl pellet accumulations with a minor contribution from carnivores and porcupines. Only in two places does it appear that live animals became trapped within fissures where they died. One of these at Gcwihaba C Hill is a partial, badly damaged skeleton of a proboscidean which is scattered through a coarse dolomitic breccia. The second is a more complete bovid skeleton found in a circular pothole filling at Gcwihaba A Hill. SIGNIFICANCE OF THE GCWIHABA AND NQUMTSA DEPOSITS. — Apart from their obvious palaeobiogeographic and palaeontological interest, the Ngamiland cave fillings are important for the evidence that they yield regarding the age of the sediments in which they occur and the palaeoecology of the region during the latter part of the Pliocene. The cave fill in which the fossils occur represents the earliest clastic sedimentation following dissolution of the cave systems. The appearance of the sand grains in the sediments resembles that of aeolian sands [5], from which it can be inferred that these deposits accumulated under desertic conditions. Prior to
animals became trapped within fissures where they died. One of these at Gcwihaba C Hill is a partial, badly damaged skeleton of a proboscidean which is scattered through a coarse dolomitic breccia. The second is a more complete bovid skeleton found in a circular pothole filling at Gcwihaba A Hill. SIGNIFICANCE OF THE GCWIHABA AND NQUMTSA DEPOSITS. — Apart from their obvious palaeobiogeographic and palaeontological interest, the Ngamiland cave fillings are important for the evidence that they yield regarding the age of the sediments in which they occur and the palaeoecology of the region during the latter part of the Pliocene. The cave fill in which the fossils occur represents the earliest clastic sedimentation following dissolution of the cave systems. The appearance of the sand grains in the sediments resembles that of aeolian sands [5], from which it can be inferred that these deposits accumulated under desertic conditions. Prior to their accumulation, there occurred a period of cavern formation, presumably under humid climatic conditions ([5], [6]). From a consideration of the available data, it appears that the palaeoclimatic conditions in the region underwent a marked change late in the Pliocene, from humid before to semi-arid or arid after. Since this fundamental change, the climate has fluctuated about a semiarid mean, producing a variety of speleothems and clastic sediments of Pleistocene and Holocene age. Correlation of the oldest cave filling with the oldest local calcrete (Cf of Cooke) at Nqumtsa lends additional support to the inference that conditions became semi-arid to arid, since these limestones represent stage IV calcretes [11], typical of semiarid to arid regions of the world. The establishment of desertic conditions in the Kalahari is thus concluded to have taken place in the Late Pliocene or earliest Pleistocene. 1686 C. R. Acad. Sci. Paris, t. 307, Série II, p. 1681-1686, 1988 PALAEOECOLOGY. — The available faunal evidence yielded by mammals and gastropods provides support for the palaeoclimatic hypothesis outlined above. The dominant fossils in the assemblage from Gcwihaba C Hill (Table), collected by Mr. J. Roger, are dendromurines and gerbils indicating the presence of an arid climate. At
fundamental change, the climate has fluctuated about a semiarid mean, producing a variety of speleothems and clastic sediments of Pleistocene and Holocene age. Correlation of the oldest cave filling with the oldest local calcrete (Cf of Cooke) at Nqumtsa lends additional support to the inference that conditions became semi-arid to arid, since these limestones represent stage IV calcretes [11], typical of semiarid to arid regions of the world. The establishment of desertic conditions in the Kalahari is thus concluded to have taken place in the Late Pliocene or earliest Pleistocene. 1686 C. R. Acad. Sci. Paris, t. 307, Série II, p. 1681-1686, 1988 PALAEOECOLOGY. — The available faunal evidence yielded by mammals and gastropods provides support for the palaeoclimatic hypothesis outlined above. The dominant fossils in the assemblage from Gcwihaba C Hill (Table), collected by Mr. J. Roger, are dendromurines and gerbils indicating the presence of an arid climate. At Nqumtsa South Hill, M. P. discovered shells of Achatina and Xerocerastus identical in morphology and size with species occurring in the region today. According to Van Bruggen [12], these forms are restricted in distribution to the drier parts of the Kalahari Desert. Nevertheless, the presence of several Otomyinae and Graphiurinae indicate the presence, in the region, of swampy areas bordered by trees, a habitat description which accords with the present day environment in the Gcwihaba area, where seasonal pans are common. BIOSTRATIGRAPHY. — The Gcwihaba C Hill small mammal fauna compares most closely with that of Makapansgat [13]. In particular, the two muroids Palaeotomys gracilis and Prototomys campbelli closely resemble those from Makapansgat. Although Makapansgat is not dated directly, it is often considered to be late Pliocene in age on the basis of large mammal faunal correlations with East African sites. Age estimates for Makapansgat range between 3.2 and 2.6 My. CONCLUSIONS. — Five new fossil mammal sites discovered in Northwest Botswana are important for understanding the evolution of climatic conditions in the Kalahari region during the Plio-Pleistocene. Preliminary identifications of the Gcwihaba micromammals indicate an age equivalence with Makapansgat, South Africa, and a semi-arid to arid palaeoenvironment. This discovery
indicate the presence, in the region, of swampy areas bordered by trees, a habitat description which accords with the present day environment in the Gcwihaba area, where seasonal pans are common. BIOSTRATIGRAPHY. — The Gcwihaba C Hill small mammal fauna compares most closely with that of Makapansgat [13]. In particular, the two muroids Palaeotomys gracilis and Prototomys campbelli closely resemble those from Makapansgat. Although Makapansgat is not dated directly, it is often considered to be late Pliocene in age on the basis of large mammal faunal correlations with East African sites. Age estimates for Makapansgat range between 3.2 and 2.6 My. CONCLUSIONS. — Five new fossil mammal sites discovered in Northwest Botswana are important for understanding the evolution of climatic conditions in the Kalahari region during the Plio-Pleistocene. Preliminary identifications of the Gcwihaba micromammals indicate an age equivalence with Makapansgat, South Africa, and a semi-arid to arid palaeoenvironment. This discovery helps to fill what was a huge gap in the known geographical distribution of Plio-Pleistocene African faunas. Note reçue le 5 septembre 1988, acceptée le 26 septembre 1988. RÉFÉRENCES [1] R. KLEIN, The large mammals of Southern Africa: Late Pliocene to Recent, Southern African Prehistory and Palaeoenvironments, A. A. Balkema, Rotterdam/Boston, 1984, pp. 107-146. A. BROOKS and J. E. YELLEN, Archaeological excavations at Ngami: A preliminary report on the first two field seasons, Botswana Notes and Records, 9, 1977, pp. 21-30. L. CAHEN and J. LEPERSOHN, Équivalence entre le système du Kalahari du Congo belge et les Kalahari beds d’Afrique australe, Mem. Soc. géol. Belg. 4, 1952. E. J. WAYLAND, Outlines of Prehistory and Stone Age Climatology in the Bechuanaland Protectorate, Acad. R. Sci. Col. Mem., 25 (4), 1954, pp. 3-47. H. J. COOICE, The paleoclimatic significance of caves and adjacent landforms in Western Ngamiland, Botswana, Geogr. Jl, 141, (3), 1975, pp. 430-444. H. J. COOICE and B. T. VERHAGEN, The dating of cave development: an example from Botswana, Proc. Ith Int. Speleol. Congr., Sheffield, 1984. R. A. DART, A note on the limestone caverns of Leba, near Humpata, Angola, S. Afr. Archaeol. Bull., 5, (20), 1950, pp. 149-151. M.
Rotterdam/Boston, 1984, pp. 107-146. A. BROOKS and J. E. YELLEN, Archaeological excavations at Ngami: A preliminary report on the first two field seasons, Botswana Notes and Records, 9, 1977, pp. 21-30. L. CAHEN and J. LEPERSOHN, Équivalence entre le système du Kalahari du Congo belge et les Kalahari beds d’Afrique australe, Mem. Soc. géol. Belg. 4, 1952. E. J. WAYLAND, Outlines of Prehistory and Stone Age Climatology in the Bechuanaland Protectorate, Acad. R. Sci. Col. Mem., 25 (4), 1954, pp. 3-47. H. J. COOICE, The paleoclimatic significance of caves and adjacent landforms in Western Ngamiland, Botswana, Geogr. Jl, 141, (3), 1975, pp. 430-444. H. J. COOICE and B. T. VERHAGEN, The dating of cave development: an example from Botswana, Proc. Ith Int. Speleol. Congr., Sheffield, 1984. R. A. DART, A note on the limestone caverns of Leba, near Humpata, Angola, S. Afr. Archaeol. Bull., 5, (20), 1950, pp. 149-151. M. TELLES ANTUNES, Sur la faune de Vertébrés du Pléistocène de Leba, Humpata (Angola), Actes du 5th Congr. Panafr. Prehist. et de l’Étude du Quaternaire, Ténérife, 1965, pp. 127-128. E. B. WRIGHT, Geological studies in Northern Kalahari, Geogr. Jl., 144, (2), pp. 235-249. E. J. WAYLAND, Drodsky’s Cave, Geogr. Jl, 103, 1944, pp. 230-233. M. R. LEEDER, Pedogenic carbonates and flood sediment accretion rates; a quantitative model for arid zone lithofacies, Geol. Mag, 112, 1975, pp. 257-270. A. C. VAN BRUGGEN, Notes on non-marine molluscs from Mozambique and Bechuanaland, with a checklist of Bechuanaland species, Ann. Transvaal Mus, 25, (6), 1966, pp. 99-111. E. S. VRBA, Biostratigraphy and chronology, based particularly on Bovidae, of Southern hominid-associated assemblages: Makapansgat, Sterkfontein, Taung, Kromdraai, Swartkrans; also Elandsfontein (Saldanha), Broken Hill (now Kabwe) and Cave of Hearths, Proc. 1st Int. Congr. Human Palaeont., Nice, C.N.R.S., 2, 1982, pp. 707-752. M. P.: Institut de Paléontologie, 8, rue Buffon, 75005 Paris; P. M.: Département des Sciences de la Terre, Université Claude-Bernard-Lyon-I, 27-43, boulevard du 11-Novembre-1918, 69622 Villeurbanne Cedex. C. R. Acad. Sci. Paris, t. 307, Série II, p. 1687-1692, 1988 1687 Mécanique des milieux continus/Computational Mechanics Approche spectrale du calcul tridimensionnel de propriétés équivalentes d’un milieu hétérogène
1944, pp. 230-233. M. R. LEEDER, Pedogenic carbonates and flood sediment accretion rates; a quantitative model for arid zone lithofacies, Geol. Mag, 112, 1975, pp. 257-270. A. C. VAN BRUGGEN, Notes on non-marine molluscs from Mozambique and Bechuanaland, with a checklist of Bechuanaland species, Ann. Transvaal Mus, 25, (6), 1966, pp. 99-111. E. S. VRBA, Biostratigraphy and chronology, based particularly on Bovidae, of Southern hominid-associated assemblages: Makapansgat, Sterkfontein, Taung, Kromdraai, Swartkrans; also Elandsfontein (Saldanha), Broken Hill (now Kabwe) and Cave of Hearths, Proc. 1st Int. Congr. Human Palaeont., Nice, C.N.R.S., 2, 1982, pp. 707-752. M. P.: Institut de Paléontologie, 8, rue Buffon, 75005 Paris; P. M.: Département des Sciences de la Terre, Université Claude-Bernard-Lyon-I, 27-43, boulevard du 11-Novembre-1918, 69622 Villeurbanne Cedex. C. R. Acad. Sci. Paris, t. 307, Série II, p. 1687-1692, 1988 1687 Mécanique des milieux continus/Computational Mechanics Approche spectrale du calcul tridimensionnel de propriétés équivalentes d’un milieu hétérogène Claire GOBBÉ, Jean GOUNOT et Michel QUINTARD Résumé — Un algorithme simple, basé sur une analyse spectrale, est proposé pour étudier les propriétés de transport diffusif dans un milieu hétérogène. À partir de champs de valeurs discrètes 3D du tenseur local de diffusion, on calcule, par une méthode spectrale, le tenseur de diffusion effectif du milieu homogène équivalent. Calculation by a 3D spectral method of effective transport properties of a heterogeneous medium Abstract — A simple numerical technique, based on spectral analysis, is proposed to determine diffusive transport properties in a heterogeneous medium. From 3D discrete point values of the local diffusion tensor, the effective diffusion tensor for the equivalent homogeneous medium is calculated by a spectral method. Abridged English Version — We study a diffusion process for a physical variable [eq. (1)] in a heterogeneous medium. The transport coefficient K is a periodic function of the space variable. The processes we are dealing with can be: (i) molecular diffusion, (ii) thermal conduction, (iii) or one-phase flow through a porous medium (K is the permeability in this last case). We assume that, for a given length scale r0, the medium can be considered as homogeneous with respect to averaged values
tenseur de diffusion effectif du milieu homogène équivalent. Calculation by a 3D spectral method of effective transport properties of a heterogeneous medium Abstract — A simple numerical technique, based on spectral analysis, is proposed to determine diffusive transport properties in a heterogeneous medium. From 3D discrete point values of the local diffusion tensor, the effective diffusion tensor for the equivalent homogeneous medium is calculated by a spectral method. Abridged English Version — We study a diffusion process for a physical variable [eq. (1)] in a heterogeneous medium. The transport coefficient K is a periodic function of the space variable. The processes we are dealing with can be: (i) molecular diffusion, (ii) thermal conduction, (iii) or one-phase flow through a porous medium (K is the permeability in this last case). We assume that, for a given length scale r0, the medium can be considered as homogeneous with respect to averaged values over volumes of dimension r0. It can be shown [1] that the volume average value <f> obeys a new diffusion equation with an effective transport coefficient K* which is given by equation (3). In this equation, a vector b must be calculated by solving a closure problem expressed by equations (4) and (5). Various numerical methods have been used to solve the closure problem. We are interested here in K fields obtained from discrete measurements or image analysis. The grid node values are known and we would like to analyze them in a simple way. In order to solve equations (4) and (5), we use Fourier analysis. The idea is to use Galerkin’s technique to solve equations (4) and (5) with Fourier decomposition for K [eq. (6)] and b [eq. (7)]. K is analyzed by FFT. The components of b over the Fourier basis are solutions of a linear system [eq. (8)]. The domain studied is of dimensions 2HX x 2H2 x 2H3. From the solution of this linear system, it is easy to obtain K* [eq. (9)]. This method deals simply with the periodicity boundary conditions in equation (5) and resembles signal analysis method. The major drawback is the
(4) and (5). Various numerical methods have been used to solve the closure problem. We are interested here in K fields obtained from discrete measurements or image analysis. The grid node values are known and we would like to analyze them in a simple way. In order to solve equations (4) and (5), we use Fourier analysis. The idea is to use Galerkin’s technique to solve equations (4) and (5) with Fourier decomposition for K [eq. (6)] and b [eq. (7)]. K is analyzed by FFT. The components of b over the Fourier basis are solutions of a linear system [eq. (8)]. The domain studied is of dimensions 2HX x 2H2 x 2H3. From the solution of this linear system, it is easy to obtain K* [eq. (9)]. This method deals simply with the periodicity boundary conditions in equation (5) and resembles signal analysis method. The major drawback is the matrix in equation (8), a non-sparse matrix, which makes it impossible to deal with 3D expansions of b with more than 15 x 15 x 15 terms. Among the various test problems we have solved, we present a calculation of K* for a network of spheres. We use as a reference solution, KMa, the Maxwell equation [eq. (10)] (see extensive analysis in [2]). Figure 1 shows the evolution of the relative error between K* and KMa versus the ratio Ks/K2 (K2, continuous phase; K1, discontinuous phase). The agreement is fair between the two values provided that Ks/K2 remains smaller than 100. The technique is then applied to the estimation of the large-scale permeability of a sandstone. An introduction to this problem can be found in [3]. We distinguish two aspects: the calculation of the principal direction and the calculation of the associated principal values. In the principal axis system, methods exist [4] which produce upper and lower bounds for principal components of K*, but principal directions cannot be determined easily. In a simple way, our method solves both these problems. Figure 2 shows the measured permeability field [5] on a Vosges sandstone sample. The calculated K* components are also plotted;
reference solution, KMa, the Maxwell equation [eq. (10)] (see extensive analysis in [2]). Figure 1 shows the evolution of the relative error between K* and KMa versus the ratio Ks/K2 (K2, continuous phase; K1, discontinuous phase). The agreement is fair between the two values provided that Ks/K2 remains smaller than 100. The technique is then applied to the estimation of the large-scale permeability of a sandstone. An introduction to this problem can be found in [3]. We distinguish two aspects: the calculation of the principal direction and the calculation of the associated principal values. In the principal axis system, methods exist [4] which produce upper and lower bounds for principal components of K*, but principal directions cannot be determined easily. In a simple way, our method solves both these problems. Figure 2 shows the measured permeability field [5] on a Vosges sandstone sample. The calculated K* components are also plotted; the principal values are 10. ### CORRECTION ### Balkema, Rotterdam/Boston, 1984, pp. 107-146. A. BROOKS and J. E. YELLEN, Archaeological excavations at Ngami: A preliminary report on the first two field seasons, Botswana Notes and Records, 9, 1977, pp. 21-30. L. CAHEN and J. LEPERSOHN, Équivalence entre le système du Kalahari du Congo belge et les Kalahari beds d’Afrique australe, Mem. Soc. géol. Belg. 4, 1952. E. J. WAYLAND, Outlines of Prehistory and Stone Age Climatology in the Bechuanaland Protectorate, Acad. R. Sci. Col. Mem., 25 (4), 1954, pp. 3-47. H. J. COOICE, The paleoclimatic significance of caves and adjacent landforms in Western Ngamiland, Botswana, Geogr. Jl, 141, (3), 1975, pp. 430-444. H. J. COOICE and B. T. VERHAGEN, The dating of cave development: an example from Botswana, Proc. Ith Int. Speleol. Congr., Sheffield, 1984. R. A. DART, A note on the limestone caverns of Leba, near Humpata, Angola, S. Afr. Archaeol. Bull., 5, (20), 1950, pp. 149-151. M. TELLES ANTUNES, Sur la faune de Vertébrés du Pléistocène de Leba, Humpata (Angola), Actes du 5th Congr. Panafr. Prehist. et de l’Étude du Quaternaire, Ténérife, 1965, pp. 127-128. E. B. WRIGHT, Geological studies in Northern Kalahari, Geogr. Jl., 144, (2), pp.