Wide Range Of Lithologies Research Articles

Compressional and shear‐wave logging in open and cased holes using a multipole tool

We have found in field observations that the multipole sonic logging tool can effectively measure formation P‐wave and S‐wave data in a cased hole. The multipole tool, containing both monopole and quadrupole source‐receiver systems, was originally designed to log P‐ and S‐waves directly, in all lithologies, for an open borehole. The monopole source‐receiver system (P‐wave) operates at 7–10 kHz, as compared with 15–25 kHz for a conventional sonic tool, while the quadrupole source‐receiver system (S‐wave) operates at 3–7 kHz. These lower operating frequencies enable the signals to penetrate the well casing and cement more effectively than signals from a conventional sonic tool. As a result, the formation P‐ and S‐waves recorded by the multipole tool are generally much stronger than the unwanted waves which travel along the well casing and cement. Formation arrivals can be easily identified and separated from the casing arrivals for a wide range of lithologies. Logs run before and after the wells were cased show remarkable agreement even in severely washed out zones.

Groundwater in the Quaternary deposits of Scotland: a valuable resource and a potential engineering hazard

Abstract The Scottish Quaternary strata contain a wide range of lithologies with an equally wide spectrum of hydrogeological properties. The more permeable material contains valuable groundwater resources which increasingly are being exploited for rural and island communities. However, the common juxtaposition of high and low permeability strata, the occurrence of confined groundwater in clay-capped gravels, and the risk of ground subsidence due to dewatering, together provide a range of potential Engineering problems and hazards.

Granulite fades Nd-isotopic homogenization in the Lewisian complex of northwest Scotland

A published Sm–Nd whole-rock isochron of 2,920 ± 50 Myr, obtained from a wide range of lithologies in the Lewisian complex of north-west Scotland, was interpreted1 as the time of protolith formation. This date is ∼260 Myr older than estimates for the timing of high-grade metamorphism in the complex at ∼ 2,660 Myr2'3, and this period is considered to represent the duration of the Lewisian crustal accretion-differentiation superevent (CADS)4. Here we give new Sm-Nd data, obtained specifically from granulite facies tonalitic gneisses, that yield a date of 2,600 ±155 Myr. Although depleted-mantle model ages (tDM suggest >200 Myr of premetamorphic crustal residence, the regression date and its associated initial Nd-isotopic parameters demonstrate Nd-isotopic homogenization during the high-grade event, as well as the probability of general rare-earth-element (REE) mobility. Models for selective element depletion in the complex have previously assumed REE immobility since 2,920 Myr, but the data presented here suggest that a reappraisal of the depletion mechanism is required.

Fossils and tectonics along the Highland Boundary Fault in Scotland

The tectonic significance of fossil discoveries from the Highland Border Complex of Scotland is described. These sparse but diverse macro- and microfossils have been recovered from a wide range of lithologies across Scotland, and range in age from early to late Ordovician, thereby refuting any attempt to incorporate the HBC within the Dalradian Supergroup. The Lower Cambrian trilobite fauna from the Leny Limestone could represent an isolated remnant of an early development of the Ordovician HBC basin(s), or alternatively may provide an upper age limit for Dalradian sedimentation. Further palaeontological prospecting in the zone, especially in relatively undeformed late Dalradian sediments, could resolve this and other problems which complicate the regional tectonic interpretations.