12 13We report the material properties of 26 granular analogue materials used in 14 ana-14 logue modelling laboratories. We determined physical characteristics such as bulk 15 density, grain size distribution, and grain shape, and performed ring shear tests to 16 determine friction angles and cohesion, and uniaxial compression tests to evaluate 17 the compaction behaviour. Mean grain size of the materials varied between c. 100 18 and 400 µm. Analysis of grain shape factors show that the four different classes of 19 granular materials (14 quartz sands, 5 dyed quartz sands, 4 heavy mineral sands 20 and 3 size fractions of glass beads) can be broadly divided into two groups consist-21 ing of 12 angular and 14 rounded materials. Grain shape has an influence on friction 22 angles, with most angular materials having higher internal friction angles (between 23 c. 35° and 40°) than rounded materials, whereas well-rounded glass beads have the 24 lowest internal friction angles (between c. 25° and 30°). We interpret this as an ef-25 2 fect of intergranular sliding versus rolling. Most angular materials have also higher 26 basal friction angles (tested for a specific foil) than more rounded materials, sug-27 gesting that angular grains scratch and wear the foil., Most materials have an inter-28 nal cohesion in the order of 20-100 Pa except for well-rounded glass beads, which 29show a trend towards a quasi-cohesionless (C <20 Pa) Coulomb-type material. The 30 uniaxial confined compression tests reveal that rounded grains generally show less 31 compaction than angular grains. We interpret this to be related to the initial packing 32 density after sifting, which is higher for rounded grains than for angular grains. Ring-33 shear test data show that angular grains undergo a longer strain-hardening phase 34 than more rounded materials. This might explain why analogue models consisting of 35 angular grains accommodate deformation in a more distributed manner prior to 36 strain localisation than models consisting of rounded grains.

No abstract

Ferruginous conditions prevailed in the world's deep oceans during the Archean and Protero zoic Eons. Sedimentary iron formations deposited at that time may provide an important record of environmental conditions, yet linking the chemistry and mineralogy of these sedimentary rocks to depositional conditions remains a challenge due to a dearth of information about the processes by which minerals form in analogous modern environments. We identified siderites in ferruginous Lake Towuti, Indonesia, which we characterized using high-resolution microscopic and spectroscopic imaging combined with microchemical and geochemical analyses. We infer early diagenetic growth of siderite crystals as a response to sedimentary organic carbon degradation and the accumulation of dissolved inorganic carbon in pore waters. We suggest that siderite formation proceeds through syntaxial growth on preexisting siderite crystals, or possibly through aging of precursor carbonate green rust. Crystal growth ultimately leads to spar-sized (>50 μm) mosaic single siderite crystals that form twins, bundles, and spheroidal aggregates during burial. Early-formed carbonate was detectable through microchemical zonation and the possible presence of residual phases trapped in siderite interstices. This suggests that such microchemical zonation and mineral inclusions may be used to infer siderite growth histories in ancient sedimentary rocks including sedimentary iron formations.

No abstract

At the northwestern edge of the Hercynian Bohemian Massif (Saxothuringian belt) new U±Pb zircon age data from rift-related magmatic rocks indicate