Abstract: The mechanical strength, porosity and permeability of chalk are affected by chemical and mineralogical changes induced by fluids that are chemically out of equilibrium with the host rock. Here, two high-porosity Upper Cretaceous chalk cores from Liège were tested at effective stresses beyond yield at 130°C during flooding with MgCl 2 and NaCl brines. Core L1 (flooded by MgCl 2 brine) deformed more than L2 (flooded with NaCl brine), with volumetric strains of 9.4% and 5.1%, respectively. The porosity losses estimated from strain measurements alone are 5.82% for L1 and 3.01% for L2. However, this approach does not account for dissolution and precipitation reactions. Porosity calculations that are based on strain measurements in combination with (i) the weight difference between saturated and dry cores and (ii) the solid density measurement before and after flooding show an average porosity reduction of 3.69% between the two methods for L1. This discrepancy was not observed for core L2 (with the NaCl brine). The rock and effluent chemistry show that Ca 2+ dissolved and Mg 2+ is retained within the core for the L1 experiment. Therefore, accurate porosity calculations in chalk cores that are flooded by non-equilibrium brines (e.g. MgCl 2 ) require both the volumetric strain and chemical alteration to be considered.

Abstract A unified system of collecting structural data from drill core is proposed. The system encompasses planes and planar fabrics, lineations, fold hinges and hinge surfaces, faults and shear zones, vorticity vectors, shear directions and shear senses. The system is based on standard measurements of angles in the reference frame of the core (α and β angles), which are easily carried out by means of core protractors or templates. The methods for dealing with folds and kinematic analysis of shear zones have not been described previously, but they follow logically from the standard methods for dealing with planes and lines.

Orogenesis within the New England Appalachians has classically been regarded as occurring discontinuously even though the collision of plates driving it was essentially continuous for 200 million years from the Taconic through the Alleghanian orogenies. Structural, metamorphic, and age data obtained from the cores of porphyroblasts reveal a near continuous history of tectonism that is partitioned within and between outcrops as well as regionally. Very prolonged deformation and metamorphic histories predate the foliation parallel to bedding, and the oblique matrix foliations only reflect brief increments of the uplift path of these rocks back to the earth's surface. The matrix shows none of the structural effects of the path down into the crust. This deepening path is revealed by the sequences of foliations that developed about regionally consistent successions of foliation intersection axis trends preserved within porphyroblasts (FIAs). Indirect coupling between plates throughout the period of collision resulted in horizontal shortening accompanied by subvertical foliation development, followed by crustal instability, collapse, and the formation of subhorizontal foliation, repeated over and over until orogenesis ceased. These cycles repeat on time scales as short as 100,000 to 500,000 years, but because of partitioning of the deformation, only the weakest rocks preserve much of this history. Shifting directions of relative plate motion every 5 to 30 million years also results in easily deformed rocks being protected by more competent ones, with none of them seeing the total history. Furthermore, if the bulk composition is not suitable for porphyroblast growth, none of this history will be recorded. The recurring role of gravitational collapse and the variable scale of partitioning of this type of deformation is obscured by repeated reactivation of the bedding parallel foliation in multiply deformed rocks containing porphyroblasts in the New England Appalachians. It is also obscured by the lack of topographic relief relative to total crustal thickness.