China
Africa
Explore chapters and articles related to this topic
Knowledge-Based Module for Site Characterisation
Published in Nebojša Kukurić, Development of a Decision Support System for Groundwater Pollution Assessment, 2020
Rock types are described, especially with respect to their hydrogeological characteristics. This topic is also meant to be a reminder on basic classification and characteristics of rocks. Although at a first glimpse superfluous, the Topic is important, especially for the users with a nongeological background. Knowledge on rocks origin, genesis and composition is crucial for understanding aquifer evolution and nature. The nature and distribution of groundwater systems are controlled by lithology, stratigraphy (sedimentary rocks) and structure of the geological deposits. For the sedimentary unconsolidated rocks and soil, texture is an important parameter for lithological characterisation. Colour can be used as indicator of similarities or differences among the lithological units. Deposits of the sedimentary rocks of different age and lithology form so-called lithostratigraphic units. If the GWS contains lithostratigraphic units, their spatialdistribution has to be determined.6 Finally, various structures that occur in soil and rocks could substantially influence the spatial distribution of GWS units, as well as groundwater flow and contaminant transport within the system.
Stratigraphy
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Geologists investigate rock lithologies and stratigraphy using several approaches. The main kinds of stratigraphy fall into three areas: lithostratigraphy, biostratigraphy, and chronostratigraphy. Lithostratigraphy involves identification and classification of strata based on their lithologic (physical) characteristics. Biostratigraphy involves identifying and correlating rocks of similar ages based on the fossils they contain. Chronostratigraphy— closely related to biostratigraphy—involves rock age too, but the goal is to assign absolute ages to lithographic units. Thus, biostratigraphers may determine that one formation is older than another, and chronostratigraphers may be more concerned with how many million years ago a particular formation formed. Other kinds of stratigraphy, all closely related to the three main kinds, include chemostratigraphy (study of the variation in rock chemistry), cyclostratigraphy (study of variations in sedimentary rocks due to long-term climate cycles), magnetostratigraphy (study of variations in the magnetic fields recorded by rocks), and archaeological stratigraphy (study of the stratigraphy associated with archaeological studies).
Stratigraphy and Sedimentation
Published in Supriya Sengupta, Introduction to Sedimentology, 2017
The ‘material units’ and the ‘temporal and chronostratigraphic units’ of Table 8.2 correspond respectively to the observable and inferential units of the conventional scheme. Of the material units, again the lithostratigraphic units are used for categorising and ranking of deposits of sediments in the field. The fundamental lithostratigraphic unit, called a formation, is defined as ‘a body of rock identified by lithic characteristics and stratigraphic position; it is prevailingly, but not necessarily tabular and is mappable at the earth’s surface or traceable in the subsurface.’
Sequence stratigraphy of the ca 1640 Ma Barney Creek Formation, McArthur Basin, Australia
Published in Australian Journal of Earth Sciences, 2022
M. Kunzmann, V. Crombez, T. N. Blaikie, O. Catuneanu, R. King, G. P. Halverson, S. Schmid, S. C. Spinks
The significant thickness and facies changes that are recorded by sequences B1, B2 and L1 can be reconciled with the onset of structural re-organisation of the southern McArthur Basin during deposition of sequence B1 of the lower Barney Creek Formation (Blaikie & Kunzmann, 2020; McGoldrick et al., 2010). This structural event caused significant temporal and spatial variations in the available accommodation. Our sequence stratigraphic and facies analyses demonstrate that shallow subtidal to intertidal environments existed in every studied drill core during maximum regression of sequence B1 (Figure 16a). Together with general homogeneity in facies and thickness of lithostratigraphic units underlying the Barney Creek Formation (Ahmad et al., 2013), this result indicates that the southern McArthur Basin underwent broad thermal subsidence during deposition of the lower McArthur Group.
Origin and diagenetic priming of a potential slow-slip trigger zone in volcaniclastic deposits flanking a seamount on the subducting plate, Hikurangi margin, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2022
Sydney M. Allen, Kathleen M. Marsaglia, Julia Morgan, Alison Franco
At Site U1520, located 16 km seaward of the deformation front (Figure 1), a representative stratigraphic section was drilled along the western flank of Tūranganui Knoll. Two holes were cored (Holes U1520C and U1520D), sampling much of the stratigraphy to a depth of ∼1050 m below seafloor (mbsf). The composite stratigraphy was subdivided into six lithostratigraphic units (Barnes et al. 2019), ranging from Pleistocene to Cretaceous in age based on shipboard biostratigraphy (Figure 2A). Units I and III consist of Quaternary age clay-rich hemipelagic sediments with silt and sand interlayers. Unit II is compositionally similar but is interpreted to be a mass transport deposit. Unit IV consists of Paleocene to Pleistocene pelagic facies dominated by marl and chalk, with several debris-flow deposits containing dispersed volcaniclastic debris. Unit V is a 168m-thick (848.45–1016.24 mbsf) succession of Late Cretaceous volcaniclastic conglomerate and sandstone with an intervening marl interval. The underlying Unit VI is also Late Cretaceous in age and contains a mixture of lithologies including volcaniclastic conglomerate, sandstone, and siliceous mudstone, along with minor siltstone, organic-rich mudstone, basalt, and limestone (Barnes et al. 2019). The base of the hole sampled amygdular basalt of uncertain origin, possibly an in situ flow or a clast.
First-Order Seismic Loss Assessment at Urban Scale: A Case Study of Skopje, North Macedonia
Published in Journal of Earthquake Engineering, 2022
Violeta Mircevska, Ahmad Abo-El-Ezz, Irena Gjorgjeska, Alex Smirnoff, Miroslav Nastev
The ongoing geophysical and geotechnical measurements in the Skopje plain indicate VS30 values mainly in the range of 360< VS30 < 760 m/s for the deposits of very dense sand and gravel or very stiff clays. Near the ground surface, the interval shear wave velocities are about 200 m/s to rapidly attain 400 m/s in average at 10 m depth (Gjeorgjievska 2018). To better reflect the variation in local geology and potential site amplification, a regular mesh was set with spacing of 350 m in the EW direction and 420 m in the NS direction. In this way, the study area of approximately 60 km2 is covered with 402 cells for which the site geology was interpreted by the observed lithostratigraphic formations and depths. Figure 4 shows the proposed site classification with stiff soil conditions covering the entire alluvial plane, whereas rock site conditions are characteristic to the foothill areas where older Neogene units crop out. It is, however, acknowledged that despite the strong correlation found between the spatial distribution of the surficial units and the VS30, Fig. 4 needs further refinements principally due to the lack of exhaustive field measurements.