X-ray computed tomography (CT) is a non-destructive technique with wide applications in various geological disciplines. It reveals the internal structure of objects, determined by variations in density and atomic composition. Large numbers of parallel 2D sections can be obtained, which allows 3D imaging of selected features. Important applications are the study of porosity and fluid flow, applied to investigations in the fields of petroleum geology, rock mechanics and soil science. Expected future developments include the combined use of CT systems with different resolutions, the wider use of related X-ray techniques and the integration of CT data with results of compatible non-destructive techniques.X-ray computed tomography (CT) is a nondestructive technique that allows visualization of the internal structure of objects, determined mainly by variations in density and atomic composition. It requires the acquisition of one-or two-dimensional radiographs for different positions during step-wise rotation around a central axis, whereby either the source and detector or the sample are moved. This is followed by the reconstruction of two-dimensional cross-sections perpendicular to the axis of rotation.CT images record differences in the degree of attenuation of the X-rays, which is materialand energy-dependent. The interactions that are responsible for this attenuation are mainly Compton scattering and photoelectric absorption. The contribution of the photoelectric effect depends on the effective atomic number and is especially important at low energies. At high energies, the Compton effect predominates and attenuation is mainly determined by density.X-ray CT was developed as a medical imaging technique in the early 1970s (Hounsfield 1972(Hounsfield , 1973. The possibility of its use in geology and engineering was soon recognised, resulting in large numbers of publications from the early 1980s onwards. Early applications include studies in the fields of soil science (Petrovic et al. In this introductory paper, we present some general information about the technique and a brief overview of its applications in geology, with references to some recent studies. More detailed information can be found in recent review articles by Duliu (1999) and Ketcham & Carlson (2001). Acquisition of transmission dataThe basic components of X-ray CT scanners are an X-ray source, a detector and a rotation system. Various possible configurations exist, whereby the selected configuration is determined by sample size and the desired resolution, besides availability and access restrictions. Ideally, the X-ray beam should be parallel rather than fanor cone-shaped (with a finite size of the origin), in which case the resolution is only determined by detector quality. High resolution (10 ~tm) can also be attained with microfocus X-ray tubes. Another aspect of acquisition is the energy spectrum of the X-ray source. Unless the X-rays are produced by radioactive decay, they are always polychromatic with a wide range in energy. This compli...

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Archaeological excavations at the Biblioteca Magliabechiana, which is part of the Uffizi gallery complex in Florence (Tuscany, central Italy), exposed Dark Earth deposits between alluvial sediments of the nearby Arno River. The term Dark Earth refers to thick, dark colored, and seemingly homogeneous deposits occurring in urban settings throughout Europe, broadly dated to the post- Roman period. The stratigraphic sequence of the Biblioteca Magliabechiana was investigated by integrating geomorphological, chronological, and archaeological information with micromorphological and soil analytical data. This combination of approaches resulted in the identification of an early phase of Dark Earth formation (7th century A.D.) during which the area was characterized by the accumulation of manure or night soil in wet peri-fluvial conditions. After a phase of abandonment, Dark Earth accretion resumed (10th to early 11th century A.D.), at this stage due primarily to the dumping of domestic waste. Subsequent progressive abandonment of the area was followed by the deposition of alluvium, probably during the major flood of November 4, 1177. The present study demonstrates that Dark Earth is the outcome of strong bioturbation and human reworking acting on anthropogenic deposits and possibly on alluvial sediments

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