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The structure of the Earth
Published in John Atkinson, The Mechanics of Soils and Foundations, 2017
Generally soils and rocks become stiffer and stronger with age: London Clay is obviously stronger than the soils found in the English Fens and the slates in North Wales are stronger still. As a very rough guide, materials of Cenozoic age are generally regarded as soils for engineering purposes; materials of Mesozoic age are generally regarded as soft rocks and materials of Palaeozoic age are regarded as hard rocks. The soils and rocks in the stratigraphic column contain fossils which are the most important indicators of their age and provide a record of evolution on Earth. Cambrian and Ordovician rocks contain mollusc shells and corals; land plants occur in the Devonian, reptiles in the Carboniferous, amphibians in the Permian, dinosaurs in the Triassic and birds in the Jurassic; the dinosaurs became extinct in the Cretaceous. Mammals, fishes, insects and birds had evolved by the Eocene, but modern man did not evolve until the middle of the Pleistocene, about 1 million years ago.
Geological Maps
Published in F.G.H. Blyth, M. H. de Freitas, A Geology for Engineers, 2017
F.G.H. Blyth, M. H. de Freitas
The relative ages of strata shown on a map is given by the list of formations or by the stratigraphic column for the area; this information is normally printed in the margin of the map to a uniform vertical scale. An example of each is illustrated in Fig. 12.16. The divisions in a column are normally based on stratigraphy and lithology, and are arranged so that the oldest strata are always at the base of the column. The thicknesses of lithological formations shown in a column are usually the average stratigraphical thicknesses in the area of the map. Marked local variations are recorded by tapering bands in the column, Fig. 12.16a. If there are significant variations in the thickness of formations, over the area of the map, it may be necessary to give more than one stratigraphical column. Stratigraphic columns should not be confused with vertical sections because the latter are obtained from bore-holes, well bores, cliff sections and similar exposures, and the thickness of the strata shown on them is the actual thickness of the strata penetrated at a particular location: the stratigraphic column simply represents the stratigraphical position of all the horizons shown on the map. Vertical sections which reveal gaps in the stratigraphic column indicate the presence of either unconformities or faults. A typical vertical section is illustrated in Fig. 12.16b. In these sections it is customary to write the vertical thickness of the strata on one side of the column and the depth below ground level on the other. The positions of recognizable unconformities (e.g. as shown in Fig. 2.2) are usually emphasized by wavy lines.
Re-visiting the structural and glacial history of the Shackleton Glacier region of the Transantarctic Mountains, Antarctica
Published in New Zealand Journal of Geology and Geophysics, 2022
For the Gondwana succession, stratigraphic sections are available for a number of localities, and extrapolation to adjacent outcrops is possible. Fortunately, the stratigraphic column has a number of well-defined contacts which show up well on photography, specifically the basement/Beacon contact (the Kukri/Maya Erosion Surface), and the abrupt change in lithology at the Mackellar/Fairchild and Buckley/Fremouw formational contacts (both marked by an abrupt change from shale-dominated strata to sandstones). Dolerite sills are widespread, particularly in the Permian part of the section, however, sills may change thickness, change stratigraphic position, and individually are not necessarily extant across the whole region. This makes estimates, for instance, of the sub-ice elevation of the Kukri/Maya Erosion Surface unreliable.
How thermal maturity analysis supports stratigraphic restoration in heavily faulted fluvial outcrops: a case study on Strzelecki Group outcrops, West Gippsland, Victoria, Australia
Published in Australian Journal of Earth Sciences, 2020
H. Aghaei, M. Hall, B. Wagstaff
A recent study by Aghaei et al. (2017) tried to restore the stratigraphic column of about 12 km of highly faulted outcrops in the western part of the basin that exhibits a complex network of extensive multi-generational faulting with a history of significant uplift and erosion after the original syndepositional faulting, fault reactivation and interactions. The focus of that study was on the Lower Cretaceous Strzelecki Group sediments exposed in West Gippsland (see Figure 1) delineated by reactivated normal faults comprising the NE-trending Narracan and Balook blocks (Bernecker, Smith, Hill, & Constantine, 2003; Duddy, 2003). The outcrops are dominantly fine- to medium-grained sandstones with local conglomerate lenses, interbedded with locally organic-rich mudstones and containing coal beds with dips averaging 12° ENE (Aghaei, Valenta, Hall, & Tait, 2016). The major fault surfaces are locally well-exposed and dip more than 80° to the west.
Stratigraphic and igneous relationships west of Yass, eastern Lachlan Orogen, southeastern Australia: subsurface structure related to caldera collapse?
Published in Australian Journal of Earth Sciences, 2019
C. L. Fergusson, B. E. Chenhall, S. Guy, B. G. Jones, M. Solomons, G. P. Colquhoun
The geology of the Talmo area is shown in Figure 4, a cross-section is given in Figure 5 and stratigraphy is shown in the stratigraphic column in Figure 6. Two lineaments are identified in the Talmo area (Figure 7a–c) from magnetic and radiometric data (Geological Survey of New South Wales, 2016a, 2016b, 2016c) with the western lineament adjacent to a northwest-trending fault marking notable changes in stratigraphy and structure across it. An ovoid negative gravity anomaly nearly 9 km long in a northwest–southeast direction underlies the Devonian Mountain Creek Volcanics (Geological Survey of New South Wales, 2016d) (Figure 7d) suggestive of a lower density rock mass at depth.