China
Africa
Explore chapters and articles related to this topic
Recognising the different types of building stone
Published in John A. Hudson†, John W. Cosgrove, Understanding Building Stones and Stone Buildings, 2019
John A. Hudson†, John W. Cosgrove
A conglomerate is a coarse-grained sedimentary rock composed of large, sub-angular to rounded clasts (fragments) cemented in a matrix. The example in Figure 3.83 is of a Brno conglomerate (Czech Republic). The individual pebbles (the clasts) although slightly rounded by transportation in rivers, are still relatively angular. They are made of quartzite, a metamorphosed sandstone. In such rocks, the original sand (quartz) grains have been recrystallised and the original texture of the sandstone, which was made up of sand grains between which were pores, has been lost. The individual grains now form an interlocking mosaic of irregularly sized quartz crystals with very low porosity. Note that the matrix that surrounds the large-scale clasts is itself a smaller scale quartzite conglomerate.
Diagenesis and Properties of Sedimentary Rocks
Published in Aurèle Parriaux, Geology, 2018
Conglomerates are the product of the cementation of boulders, cobbles, and gravels. If the grains are rounded, the conglomerate is called a puddingstone. Angular grains form a rock called a sedimentary breccia, which generally forms as a result of the collapse of a cliff (Fig. 10.7).
Diagenesis and Properties of Sedimentary Rocks
Published in Aurèle Parriaux, Geology, 2018
Conglomerates are the product of the cementation of boulders, cobbles, and gravels. If the grains are rounded, the conglomerate is called a puddingstone. Angular grains form a rock called a sedimentary breccia, which generally forms as a result of the collapse of a cliff (Fig. 10.7).
Observational method as risk management tool: the Hvalfjörður tunnel project, Iceland
Published in Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards, 2023
Mats Tidlund, Johan Spross, Stefan Larsson
The geology in the area is characterised by the Mid Atlantic Ridge with previous volcanic activities. The bedrock consists of layers of solidified magma of Piacenzian age (approx. 2.6–3.6 million years old) with thin interbeds of sediments of ash and sand, as detailed in Figures 2 and 3. The solidified magma layers often had an impermeable central layer of good-quality basalt (high Q-value), but with vertical fractures due to the solidification process. The outer layers of the solidified magma, called “scoria”, usually had less strength and higher permeability than the central layers. The rock was faulted along the fjord with a general spacing of 50–200 m and a filling of scaly or silty material, with thicknesses ranging from a few millimetres to 300 mm. The larger faults were brecciated with a thickness of up to 2 m. Due to earlier magma flows, there were basalt dikes cutting through the sequence of horizontal layers. The contacts were often slightly brecciated or filled with clay or silty material. In some places, there were layers of conglomerate of silt, sand, gravel, stones and boulders between the scoria and basalt. Clays found in dike contacts and faults were tested for swelling properties, the existence of which were detected at four places along the tunnel.
Scientific ocean drilling in the Australasian region: a review
Published in Australian Journal of Earth Sciences, 2022
An intact record of a nascent (ca 47 Ma) arc is preserved in Unit IV comprising mudstones and overlying interlayered tuffaceous sandstones and silts plus sparse basaltic andesite lavas (Waldman et al., 2020). A local volcanic edifice preceding the development of the Kyushu–Palau Ridge is inferred. This is overlain by Unit III, consisting of 1046 m of Eocene–Oligocene tuffaceous mudstone, tuffaceous sandstone, sandstone with gravel, and breccia-conglomerate with pebble/cobble-sized volcanic and sedimentary rock clasts. Above that is 139 m of Oligocene tuffaceous mudstone, siltstone, and fine sandstone with localised slumping. The sequence is completed with 160 m of uppermost Oligocene to Recent mud and ooze of terrigenous and biogenic origin, with interspersed, predominantly Ryukyu Arc-derived tephra layers.
Genesis of heterogeneity in conglomerate reservoirs: insights from the Baikouquan formation of Mahu sag, in the Junggar Basin, China
Published in Petroleum Science and Technology, 2021
Jiang He, Haoxuan Tang, Linsheng Wang, Zuoming Yang, Yong Wang, Xuyang Zhang, Qingxiong Hu, Bingqian Wan
Sedimentation affects the physical properties of the reservoir. This is mainly observed as follows: (1) the physical properties of fan delta front displayed more favorable values than those of fan delta plain. The overall hydrodynamic forces in a fan delta plain were too strong. The sand, gravel, and mud in the sediment are mixed and accumulated, diminishing the capacity of the water body for draining; (2) the hydrodynamic force of the fan delta front was moderate. When it interacts with the elutriation of the water body, the argillaceous can be reduced. This process improves the physical properties of the reservoir. A high-energy environment with relatively stable hydrodynamic forces is dominated cross bedding conglomerate facies and traction currents with granular supporting conglomerate facies. These facies contain spherical particles with a small particle size, a well-preserved primary pore structure and good pore throat connectivity. These characteristics favor the infiltration of organic acids and the formation of secondary pores; (3) the physical properties of different reservoirs sharing the same lithology are affected by the content of the complex base. The reservoir porosity and permeability decrease with increasing heterogeneity of the base content. Clay minerals have intergranular pores in the form of pore filling, which significantly reduces the porosity and permeability of the reservoir.