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The geological origin of building stones
Published in John A. Hudson†, John W. Cosgrove, Understanding Building Stones and Stone Buildings, 2019
John A. Hudson†, John W. Cosgrove
Geologists divide rocks into three groups: igneous, sedimentary and metamorphic, Figure 2.2. Igneous rocks crystallise from magma (hot molten rock which forms in the mantle and the lower part of the Earth’s crust, Fig. 2.5).Sedimentary rocks form by weathering and erosion of pre-existing rock to make sediment, which is then lithified (cemented) into rock.Metamorphic rocks form by the deformation and/or recrystallisation of pre-existing rock by changes in temperature, pressure and/or chemistry. All rocks can be placed into one of these three groups.
Minerals, rocks, discontinuities and rock mass
Published in Ömer Aydan, Rock Mechanics and Rock Engineering, 2019
Sedimentary rocks are formed in layers deposited by wind, water or ice. They are the direct products of the weathering process. As sedimentary layers are buried, they are cemented and lithified. Sediments are subdivided into three types (Fig. 2.6): Clastic sedimentary rocksChemical sedimentary rocksOrganic sedimentary rocks
Tectonic subsidence and uplift within Canterbury Basin, South Island, New Zealand
Published in New Zealand Journal of Geology and Geophysics, 2023
Katherine Dvorak, Michelle Kominz, Martin Crundwell
Recent work by Marsaglia et al. (2017) suggests that cements were internally derived from carbonate material, and reprecipitated as authigenic cements. In this situation, the average grain density (including cements) of the sediment does not change as porosity decreases. That is, it is entirely consistent with our backstripping procedure. Some carbonate material loss is observed in the oldest (Eocene and Oligocene) sections of the cores (Marsaglia et al. 2017). While these Eocene and Oligocene processes are consistent with our backstripping protocol, the focus of this study is the Miocene and younger sediments, which show no indication of material loss. Porosity curves based on data from IODP Expedition 317 sites (see below) were applied to progressively decompact each successive sediment unit from its fully lithified thickness to its observed thickness.
A mid-Permian mafic intrusion into wet marine sediments of the lower Shoalhaven Group and its significance in the volcanic history of the southern Sydney Basin
Published in Australian Journal of Earth Sciences, 2022
G. R. Bann, B. G. Jones, I. T. Graham
The small-scale soft-sediment faulting, which occurs beneath the lava sill, indicates that some of the fine-grained sedimentary layers were sufficiently lithified, or perhaps partly frozen, to fracture, while sediments elsewhere were completely unconsolidated and flowed (e.g.Figure 8d; cf. Kokelaar, 1982). Mud, clay and carbonate cement in the finer-grained silt would provide a cohesive component, possibly allowing fracturing to occur (Figure 6a). The squeezing out of the sediment beneath the tube-like structure of the sill (Figure 7e) indicates lithification was minimal. The loading from the magma has displaced incompetent sediments beneath it, as the magma flowed out and laterally away from the dyke. As the magma formed flow tubes with seemingly unmixed sides (i.e. has not bulldozed through and mixed these sediments within the magma), suggests extrusion either onto or just below the sea bed surface. The faulting and squeezing out effects are due to loading from the lava tube being emplaced at a shallow depth (Figure 7d, e). Delaney and Pollard (1982) suggested that conduits that transport lava in the later phases of most basaltic igneous activity are commonly cylindrical (tubular) rather than tabular in form. Augustithus (1978) suggested that tubes form when lava flows onto unconsolidated sediments. Campbell et al. (2001) and Carr and Jones (2001) have documented the existence of lava tubes within the Gerringong Volcanics.
Scientific ocean drilling in the Australasian region: a review
Published in Australian Journal of Earth Sciences, 2022
There were great coring advances through time as the program evolved, although the standard rotary drilling technique, with 9.5 m (30 foot) cores, controlled by the length of standard industry drill pipes, remains as it was (see http://iodp.tamu.edu/tools/index.html). Cores are recovered in plastic liners, core diameter is generally around 6.3 cm (2.5 inches), and split cores (working and archive halves) are stored in 1.5 m lengths. The straightforward DSDP rotary coring of Glomar Challenger gave excellent recovery in consolidated and lithified sediments, and variable recovery in hard basement rocks, but was rather ineffective in the sediment oozes in the top ∼200 m of most sites. The introduction of a hydraulic piston corer for Leg 68 in 1979 revolutionised the recovery of soft sediments, with two virtually continuous sections of upper Neogene and Quaternary sediment recovered in the Caribbean Sea and eastern equatorial Pacific Ocean. The DSDP’s reconnaissance drilling, often aimed at defining unconformities visible in the single-channel seismic profiles of the day, commonly used a spot-coring technique that meant that full geological assessments were not possible.