ALBERT

Description: The pivotal idea of this study is to unravel the processes that control heterogeneity in the attributes of the pore space in carbonate rocks (i.e. stiffness, connectivity and tortuosity), and, in turn, in the transport and elastic properties. We use starting rocks of variable fabric (i.e. a depositional-dependent microstructure) to induce a specific process (e.g. chemical dissolution under stress) and then observe the development of the microstructure, permeability, porosity and velocity due to the induced chemomechanical processes. We find that the changes in the two end members of the analysed rock types (mudstones and packstones) can lead to two different evolutionary trends of permeability and velocity, depending on the effectiveness of dissolution with respect to compaction. The balance between the two depends on: (a) the fraction of the carbonate phases characterized by large surface area; and (b) the pore stiffness of the rock. Packstones are characterized by low pore stiffness and compact significantly upon dissolution. This behaviour leads to a decrease in velocity because of a reduction in the stiffness at the grain contacts and a slight increase in permeability. The latter is curbed by the ongoing compaction. Mudstones are characterized by higher pore stiffness, experiencing minimal or negligible compaction. This behaviour leads to a slight change in porosity and velocity. However, large permeability changes are observed, related to enhanced connectivity or decreased tortuosity of the pathways.

Description: A study of an International Continental Drilling Program core recovered from the middle of the modern Dead Sea has identified microbial traces within this subsurface hypersaline environment. A comparison with an active microbial mat exhibiting similar evaporative processes characterised iron-sulphur mineralization and exopolymeric substances resulting from microbial activity. Exopolymeric substances were identified in the drilled sediment but unlike other hypersaline environments, it appears that they have a limited effect on the precipitation of calcium carbonate in the sedimentary column. Sulphate reduction, however, plays a role in all types of evaporative facies, leading to the formation of diagenetic iron-sulphides in glacial and interglacial intervals. Their synthesis seems to occur under progressive sulphidation that generally stops at greigite because of incomplete sulphate reduction. The latter may be caused by a lack of suitable organic matter in this hypersaline, hence energy-demanding, environment. Pyrite may be found in periods of high lake productivity, when more labile organic matter is available. The carbon and sulphur cycles are thus influenced by microbial activity in the Dead Sea environment and this influence results in diagenetic transformations in the deep sediment. This article is protected by copyright. All rights reserved.

Description: Reverse faults frequently generate large and destructive earthquakes, yet their seismic hazard remains difficult to assess with traditional paleoseismic tools because their surface expressions are often complex and subtle. This contribution assesses the utility of millennial-scale denudation rates derived from in-situ cosmogenic 10 Be for revealing the spatial patterns and magnitudes of rock uplift produced by slip along reverse faults. We present seventeen basin-averaged denudation rates from rivers draining the Santa Cruz Mountains along the San Andreas fault (California, USA) which closely reproduce known uplift rate patterns associated with a restraining bend along the fault. An additional component of vertical deformation appears to be superposed on the uplift due to the restraining bend; this may result from regional transpression, further irregularities in the fault trace, or interactions with neighboring faults. Our results indicate that 10 Be-derived denudation rates can reveal patterns of rock uplift adjacent to reverse faults over length-scales relevant for characterizing their seismic hazard potential.

Description: Historical events are sometimes expressed in destruction layers. We present here a study in which aspects of construction, destruction, and chronostratigraphy of fired mud bricks were explored using archaeomagnetism, infrared spectroscopy, and micromorphology. We measured 88 oriented samples mostly collected from one stratum, dated ca. 1000 B.C.E., representing a destroyed late Canaanite (late Iron Age I) city in Tel Megiddo, Israel. Firing temperatures, evaluated from infrared spectroscopy, micromorphology, and high‐temperature magnetic susceptibility cycles, range between 300°C and 800°C. Samples studied in one archaeomagnetic site yield a single stable magnetization vector in demagnetization experiments. Archaeomagnetic site means of three standing walls are grouped near the expected direction of the ancient geomagnetic field. We propose that walls in the destruction layer were constructed from sun‐dried mud bricks that later burned during the destruction. Collapsed bricks and tilted walls show variable directions, diagnostic for the relative timing of collapse and cooling of bricks, during and following the destruction event. In addition, we attempt to assign stratigraphic affiliation based on archaeomagnetic considerations to standing walls, which are spatially disconnected from the studied destruction layer. Altogether, this study demonstrates the usefulness of archaeomagnetism to understanding site formation processes related to fire and destruction.

Description: Marine and lacustrine sediments represent an important source of global paleomagnetic data. Although it is usually assumed that detrital iron oxides record most of the magnetic signal in sediments, iron sulfides—which form during bacterial sulfate reduction—can also represent a significant source of sedimentary magnetism. Knowing how sulfate reduction impacts sedimentary magnetism is critical to the interpretation of paleomagnetic records. Here, we show that three distinct types of magnetic particles can be produced by bacterial sulfate reduction, each of which impacts the bulk sediment magnetism in a distinct way. We combined magnetic force microscopy and electron probe microanalysis to image magnetic mineral extracts from Dead Sea sediments from a glacial period and an interglacial period. In sediments from the dry interglacial period, during which bacterial sulfate reduction was suppressed, we found greigite framboids (Fe3S4) with strong intergrain magnetic interactions. Contrastingly, in sediments from the wet glacial period, which experienced extensive sulfate reduction, pyrite (FeS2) is the dominant sulfide phase. High-resolution magnetic imaging of glacial pyrite reveals that greigite is present as single-domain particles within the pyrite. We also found that as titanomagnetite grains undergo bacterially mediated alteration to form pyrite, the original magnetic grains become divided into smaller regions, which potentially facilitates acquisition of secondary magnetization by the reorganization of these magnetic domains. Our results provide a previously undocumented mechanism by which bacterially mediated alteration can overwrite primary detrital magnetic records.

Description: The large and well-studied archaeological record of Israel offers a unique opportunity for collecting high resolution archaeomagnetic data from the past several millennia. Here, we initiate the first catalog of archaeomagnetic directions from Israel, with data covering the past four millennia. The catalog consists of 76 directions, of which 47 fulfill quality selection criteria with Fisher precision parameter (k) ≥ 60, 95% cone of confidence (α95) 〈 6° and number of specimens per site (n) ≥ 8. The new catalog complements our published paleointensity data from the Levant and enables testing the hypothesis of a regional geomagnetic anomaly in the Levant during the Iron Age proposed by Shaar et al. (2016, 2017). Most of the archaeomagnetic directions show 〈 15° angular deviations from an axial dipole field. However, we observe in the tenth and ninth century BCE short intervals with field directions that are 19°-22° different from an axial dipole field and inclinations that are 20°-22° steeper than an axial dipole field. The beginning of the first millennium BCE is also characterized with fast secular variation rates. The new catalog provides additional support to the Levantine Iron Age Anomaly hypothesis.