Nicola Walsh

Asymmetrical soft-sediment deformation structures triggered by rapid sedimentation in turbiditic deposits (Late Miocene, Guadix Basin, southern Spain)

SummarySoft-sediment deformation structures in Tortonian turbiditic deposits of the Guadix Basin (southern Spain) have been described. The most common structures are asymmetrical pillow structures and elongated sets of loadcasts. The structures are metric in scale and have been interpreted as the result of liquefaction and/or fluidization processes triggered by the rapid sedimentation of single high concentration turbidites.Final morphology of soft-sediment deformation structures is related to two main driving force systems: unstable density gradient and lateral shear stress. The latter is probably induced by the downslope component of the sediment weight. The asymmetry of deformational structures (in horizontal and vertical cross-section) allows a clarification of the relationship between morphology of deformation and direction of lateral shear stress: this relationship seems ambiguous and confused in the literature. The interpretations both of deformation mechanism and trigger agent have been supported with:-field analyses;-calculations on the liquefaction processes induced by rapid sedimentation;-qualitative models in laboratory.

Physical properties and textural parameters of calcarenitic rocks: qualitative and quantitative evaluations

Abstract Petrophysical and mechanical properties of sedimentary rocks are influenced by size, shape, and packing of grains, porosity, cement and matrix content, all controlled strongly by depositional fabric and postdepositional processes. This paper presents a study on the textural characteristics of soft and porous calcarenites and the main methods to determine petrophysical data. The examined calcarenites, sampled from three quarry districts located in Apulia (southeastern Italy), are fine-grained and coarse-grained grainstones (“A” and “D”) and medium-grained packstones (“B”) belonging to a plio-pleistocenic formation (Calcarenite di Gravina) outcropping in the whole region. The study involved, particularly, textural analysis on thin sections using optical petrographic microscopy and evaluation of total and effective porosity by means of standard geotechnical laboratory tests, mercury intrusion porosimetry and image analysis. Grain size frequency distribution was also carried out by traditional sieve and sedimentation analysis on disaggregated materials and image analysis. Computer analysis of digital images was performed on photomicrographs applying the methods of quantitative stereology to pore size and grain size distributions. A comparison between results showed that each technique used has its limitations linked to the textural characteristics, primarily geometry and topology of the pore network, granulometry, grain shape and packing of calcarenites.

The effects of wetting and drying, and marine salt crystallization on calcarenite rocks used as building material in historic monuments

Abstract The results of a study of the effect of marine salt crystallization on the physical and mechanical properties of Plio-Pleistocene calcarenites cropping out in southern Italy are presented here. Owing to their workability, aesthetic appeal and availability, the calcarenites have been widely used as building stones in many historic monuments. Samples of medium-grained packstones and fine-grained packstones-wackestones were prepared for the salt crystallization test defined by EN 12370, using sea water instead of a 14% solution of Na2SO4 · 10H2O. To determine the effect of imbibition alone on the performance of the calcarenites, the same procedure was followed with distilled water without soluble salts. Microfabric analysis, evaluation of index parameters and grain-size distribution were carried out as well. Particular attention was given to pore-size distribution by mercury intrusion porosimetry (MIP), loss of weight and uniaxial compressive strength determined before and after the tests, and after every five cycles of complete immersion in sea water and distilled water. The results suggest that detailed information on fabric and pore network are indispensable to predicting the weatherability of rocks. Crystallization tests that involve the complete immersion of the samples in a saline solution are not effective for an understanding of the real importance of salt damage on soft and porous calcarenites owing to a significant incidence of imbibition in accelerating deterioration rates and in influencing patterns and intensity of weathering.

Petrophysical and mechanical properties of soft and porous building rocks used in Apulian monuments (south Italy)

Abstract This paper brings a comprehensive review of the main petrophysical and mechanical properties of calcarenite rocks used from time immemorial in Apulia (south Italy), with load-bearing and decorative functions both in constructions of specific historic and architectonic interest and in more common buildings. These soft and porous rocks show a reduced ability to maintain their characteristics of strength, appearance and resistance to decay over a considerable period of time. Even more than other sedimentary rocks, calcarenites belonging to the same formation can change considerably in terms of physical properties and mechanical behaviour due to the complex spatial arrangement of facies strongly conditioned by depositional fabric and diagenetic processes. A number of calcarenite varieties belonging to the Calcarenite di Gravina Fm. and Pietra Leccese Fm. was selected from different parts of Apulia and characterized according to petrographical, physical and mechanical properties. These included porosity, pore size distribution, density, water absorption, degree of saturation, permeability, thermal properties as well as compressive strength and flexural strength. Particular attention was given to the relationships between rock fabric features and physico-mechanical behaviour of the calcarenites. In addition, a comparison of data for the examined varieties was also discussed. A classification of the Apulian calcarenites based on rock fabric features and uniaxial compressive strength was proposed. Critical observations regarding the durability of the Apulian calcarenites were made, taking into account other data from literature.