Paleosols of the Southern Cape Coast, South Africa: Implications for Laterite Definition, Genesis, and Age
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_L ~ATERITES and lateritic soils sparked what probably has become the longest and most obfuscating discussion in the history of earth science. Sources'of the confusion surrounding the word laterite can be identified in terms of two general problems with past research.1 The all-important problem has been the general failure to develop a functional definitional framework for laterite. Agronomists, geologists, geomorphologists, and pedologists have applied the term specifically to variably cemented, sesquioxide-rich soil horizons. It has also been widely used to describe any soil profile that contains such a horizon and has even been applied indiscriminately to any reddish colored soil or sediment at or near the earth's surface.2 In addition, assorted mineralogical definitions have been used, particularly by soil scientists. It is unclear whether any or all of these definitions should be considered correct. The definitional problem has been compounded by the different genetic explanations that have been provided for all possible definitions. The second problem with past laterite research has been the general lack of concern for recognition and dating of laterite-like paleosols, which reflect past rather than contemporary weathering conditions. Even when laterites have been identified according to an acceptable definition, they have often been uncritically ascribed contemporary formation in the environment in which they are now found. It is frequently not appreciated that a surficial sediment or weathering profile may be a relict of past environmental settings yet serves in an only slightly modified fashion as the substrate for the modern vegetation cover.3 Furthermore, when laterites have indeed been identified as fossil, dating has generally proved to be difficult. LateritesKeywords:
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Pedological studies contributed to the reconstruction of Quaternary environment of Japan and eastern Asia in 1990s. Study of the material in the Red-Yellow soil, a representative relict paleosol in Japan, improved understandings of the soil's genesis. The origin of Japanese Red-Yellow soils confirmed to be aeolian dust from the Asian continent and can be characterized as a transitional soil between a tropical and a warm regime, which has been developed by weathering during 103kyr. Studies of weathered volcanic ash layers improved the understanding of the formation of tephra-soil sequences widely distributed in Japan. The development of tephra-soil has occurred succestively during intervals between volcanic activity by the addition of weathered tephra and aeolian dust. Interpretations of environmental change in Holocene and late Pleistocene by investigations on tephra-soil and loess-soil sequences were supported by these findings.
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Although the Matuyama–Brunhes boundary (MBB) in the Chinese Loess Plateau (CLP) is very important in reliably correlating Quaternary loess with other sediments in the world, particularly with marine and polar ice cores, its exact stratigraphic position remains controversial. Previous investigations usually placed the MBB between paleosol unit S8 and loess unit L8 in various locations. To better understand the spatial differences in the MBB position, a high-resolution paleomagnetic study was conducted in a loess section of the Lantian Basin at the southern margin of the CLP. The results show that the MBB is situated in the middle of the relatively weak paleosol unit S7, consistent with a recent report on the MBB based on a 10Be study from the Xifeng and Luochuan loess sections of the central CLP. However, the regional anomalously low magnetic susceptibility in paleosols S7 and S8 indicates that it is more reliable to determine the paleoclimate boundaries between loess and paleosol horizons of this segment with median grain size. Then, the MBB in the Yushan section can be correlated with the bottom of paleosol S7, corresponding to the older part of interglacial marine isotope stage 19. This result temporally reconciles the striking discrepancy of the position of the MBB recorded in between loess and other typical sedimentary sequences, and further confirms that the stratigraphic position of the MBB could spatially vary to a certain extent due to regional sedimentary or paleoclimatic conditions in the marginal areas of the CLP. In the Yushan section, the high-frequency variations of paleomagnetic directions during a long period of ∼31 ka before the MBB, however, could not be attributed to a genuine response to the true geomagnetic behaviour. Moreover, the climate offset defined by the magnetic susceptibility and median grain size of the section can be preliminarily attributed to the regional geology and paleoenvironment background. A multiproxy-based stratigraphic division is considered very necessary when paleomagnetic and climatic boundaries are defined exactly in a specific area of the southern CLP.
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Quaternary Huarong uplift is located at the center of Jianghan-Dongting basin.Detailed geological mapping and bore data analysis were conducted to investigate Quaternary tectonic and sedimentary characteristics and geological evolution.EW-trending Huarong uplift is adjacent to north Jianghan basin,south Anxiang sag and Yuanjiang sag of Dongting basin.The framework of the uplift is controlled by several surrounding Quaternary normal faults such as EW-trending Shishou fault,NW-trending Nanxian-Huangshantou fault and NNE-trending Zhuanqiao fault.There generally occurred alluvial or lacustrine deposits in every period of Quaternary in the peripheral sags.Late Early Pleistocene-Holocene deposits are located in the inner lower areas of the uplift and on the edge of the mountainous area,and pre-Quaternary rocks or residual deposits are distributed in the other areas of the uplift.On the basis of studying landforms,boundary faults,distribution of Quaternary deposits and pre-Quaternary rocks,the authors recovered the Quaternary evolution of Huarong uplift and adjacent areas in such aspects as rising and subsidence,sedimentation and denudation.There had occurred original hypsographic differentiation inside Huarong uplift in springtime of Quaternary before denudation.During early Early Pleistocene the normal faults around the uplift moved.At the same time,Jianghan basin,Anxiang sag and Yuanjiang sag subsided and received deposits and Huarong uplift was denuded.During the late Early Pleistocene—middle Middle Pleistocene period the normal faults continued to move,Huarong uplift and peripheral sags subsided,and the uplift rose relative to the sags.At the same time there occurred deposits in low areas of Huarong uplift and its peripheral sags,and there existed tectonic rising and denudation at the end of Early pleistocene.During late Midle Pleistocene Huarong uplift and peripheral sags rose and were denuded,forming vermicular red earth.There was a stable period in late Middle pleistocene when fluvial and lake-frontal deposits were formed on the edge of main Huarong-Zhuanqiao body of the uplift.Alluvial and lacustrine deposits were formed on the edge of the uplift and in the peripheral plain during Late Pleistocene under the relatively stable condition.At the end of Late Pleistoncene regional sea-level was lowered,causing the denudation of Huarong uplift and its peripheral areas.There occurred lacustrine-alluvial deposits in low areas of Huarong uplift and peripheral sags in Holocene due to the rising of regional river and lake level.Controlled by early high topography,the main body of Huarong uplift and parts of south Nanshan sub-uplift and Tanshan sub-uplift were weathered and denuded throughout Quaternary,resulting in the formation of large-sizes residual soil in some areas.Controlled by overall subsidence of Jianghan-Dongting basin,Huarong uplift subsided markedly in Quaternary as a whole.
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ABSTRACT Petrographical and mineralogical studies of the Lower Jurassic sequence exposed at Makhtesh Ramon, have shown the domination of a lateritic suite of epiclastic sediments of pisolite conglomerate and laterite arenite composition. Their subsequent modification by epigenetic processes of chemical weathering has given rise to the formation of flint clay, high alumina flint clay, laterite and mottled and variegated claystone. Within the Nahal Ardon area, both the transported laterite accumulates and the autochthonous lithologies occur interbedded within the same section. In all, a total of ten lithofacies have been defined and mapping of the various units, grouped into allochthonous and autochthonous classes, has established the existence of lateral facies changes between Nahal Ardon, where the sequence rests on a broad undulatory Triassic basement, and the zone to the west where it occurs as infillings of Triassic solution cavities, sink holes and irregular depressions. Vertical profile studies of the lithofacies indicate that the vertical range of ground water movements increased westwards from Nahal Ardon and resulted in the transported laterite accumulates being subjected to varying degrees of chemical weathering. The observed lateral facies changes are a direct consequence of this. Within the ‘karstic’ zone, the laterite accumulates in addition to the overlying younger carbonate lithologies have been converted to flint clay and demonstrate the intraformational genesis of the flint clay, whereby vertical ground water movements are related to recharge of aquifer zones within the underlying Triassic Mohilla Formation.
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Other| July 01, 1986 Late Quaternary foraminifera from raised deposits of the Cape Royds-Cape Barne area, Ross Island, Antarctica Barbara L. Ward; Barbara L. Ward Victoria Univ. Wellington, Antarct. Res. Cent., Wellington, New Zealand Search for other works by this author on: GSW Google Scholar Peter-Noel Webb Peter-Noel Webb Ohio State Univ., United States Search for other works by this author on: GSW Google Scholar Author and Article Information Barbara L. Ward Victoria Univ. Wellington, Antarct. Res. Cent., Wellington, New Zealand Peter-Noel Webb Ohio State Univ., United States Publisher: Cushman Foundation for Foraminiferal Research First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 GeoRef, Copyright 2004, American Geological Institute. Journal of Foraminiferal Research (1986) 16 (3): 176–200. https://doi.org/10.2113/gsjfr.16.3.176 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Barbara L. Ward, Peter-Noel Webb; Late Quaternary foraminifera from raised deposits of the Cape Royds-Cape Barne area, Ross Island, Antarctica. Journal of Foraminiferal Research 1986;; 16 (3): 176–200. doi: https://doi.org/10.2113/gsjfr.16.3.176 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyJournal of Foraminiferal Research Search Advanced Search This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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The Silurian strata of northwest Greenland consist of an intricate assemblage of graptolitic rocks and limestones of varied facies deposited at the seaward edge of a carbonate platform that covered most of northern Greenland during Silurian time. Facies changes are abrupt and the formations are in part facies equivalents of each other. The Offley Island consists of biostromal and biohermal limestones and associated calcarenites and limestone conglomerates. The Schuchert is composed primarily of somewhat argillaceous calcisiltites, but includes minor biostromal and biohermal limestones and related calcarenites. The graptolitic rocks are assigned to the Phillips and consist of calcareous shale and mudstone, chert, argillaceous limesto e, and local strings of small bioherms. The term Cape Tyson Formation is considered obsolete. All the rocks exposed at the studied localities are of about late Llandovery age, but younger and older Silurian rocks may be present elsewhere in northern Greenland. Extensive development of biostromal and biohermal rocks may be characteristic of the seaward edge of the Silurian carbonate platform in Greenland and the Canadian Arctic Islands. The position of the edge can be traced from Greenland to east-central Ellesmere Island and Grinnell Peninsula to Cornwallis Island, from there westward south of Bathurst Island and through southern Melville Island. End_of_Article - Last_Page 2499------------
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_L ~ATERITES and lateritic soils sparked what probably has become the longest and most obfuscating discussion in the history of earth science. Sources'of the confusion surrounding the word laterite can be identified in terms of two general problems with past research.1 The all-important problem has been the general failure to develop a functional definitional framework for laterite. Agronomists, geologists, geomorphologists, and pedologists have applied the term specifically to variably cemented, sesquioxide-rich soil horizons. It has also been widely used to describe any soil profile that contains such a horizon and has even been applied indiscriminately to any reddish colored soil or sediment at or near the earth's surface.2 In addition, assorted mineralogical definitions have been used, particularly by soil scientists. It is unclear whether any or all of these definitions should be considered correct. The definitional problem has been compounded by the different genetic explanations that have been provided for all possible definitions. The second problem with past laterite research has been the general lack of concern for recognition and dating of laterite-like paleosols, which reflect past rather than contemporary weathering conditions. Even when laterites have been identified according to an acceptable definition, they have often been uncritically ascribed contemporary formation in the environment in which they are now found. It is frequently not appreciated that a surficial sediment or weathering profile may be a relict of past environmental settings yet serves in an only slightly modified fashion as the substrate for the modern vegetation cover.3 Furthermore, when laterites have indeed been identified as fossil, dating has generally proved to be difficult. Laterites
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