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Calcite pseudomorphs after ikaite (glendonite) are associated with coldwater depositional systems, including glaciomarine and deepwater settings, as dictated by the limited stability field of ikaite. Ikaite precipitation is favored by elevated alkalinity and dissolved phosphate, conditions encountered commonly in association with organic-rich marine sediments where methane oxidation is occurring. The rapid recrystallization of ikaite to calcite during slight warming or pressure release results in considerable solid volume loss, producing a highly porous crystal mesh. Preservation of the original ikaite crystal form requires precipitation of diagenetic calcite cement during early burial to prevent compaction and collapse of pseudomorph structures. During later burial diagenesis remaining pore space may be filled with deeper burial calcite cement. Glendonites from the Permian of the Sydney Basin occur in subtidal shelf facies containing glacial dropstones and a normal marine fauna. Stable oxygen isotope signatures of modern ikaite suggest carbonate precipitation in equilibrium with ambient seawater; carbon signatures are usually strongly negative relative to normal marine carbonate, consistent with derivation of carbonate from methane oxidation. Review of published data suggests that while Holocene glendonite may provide reliable isotopic records of the conditions of ikaite precipitation, precipitation of later calcite cement within the glendonite structure reduces the significance of the isotopic signature as an indicator of primary depositional conditions. Bulk glendonite samples from the Permian Sydney Basin, Australia, have a broad range of d 18 O and d 13 C (d 18 O PDB = 25 to 215%; d 13 C = 28 to 216%), in contrast to the narrow range for brachiopod carbonate (d 18 O PDB = +1 to 25%; d 13 C = +5 to +7%) from the same strata. Handpicked separates of ''primary'' glendonite and secondary calcite also have a wide range of stable isotope values. The data from Sydney Basin glendonites indicate that diagenetic precipitation of calcite has blurred the isotopic signature of primary ikaite replacement calcite at the scale of micosampling done in this study. Australia) during his visit to the area in 1840 as part of the US Exploring Expedition. During the expedition he also collected specimens from the Astoria area, Oregon, and recognized the similarity between these samples and those from Glendon (Dana 1849). He concluded that the samples were pseudomorphs because of their granular interior, but he was unable to determine the identity of the precursor. These pseudomorphs were subsequently named glendonites by David et al. (1905) after the original locality, but many other names, including barley corns, chrysanthemum stones, fundylite, gennoishi, hedgehogs, jarrowite, opal pineapples, pseudogaylussite, thinolite, and White Sea hornlets, have also

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Sediment records left by coastal hazards (e.g. tsunami and/or storms) may shed light on the sedimentary and hydrodynamic processes happening during such events. Modern onshore and offshore sediment samples were compared with the 2004 Indian Ocean Tsunami, three palaeotsunami and a 2007 storm deposit from Phra Thong Island, Thailand, to determine provenance relationships between these coastal overwash deposits. Sedimentological and stratigraphic characteristics are generally inadequate to discriminate tsunami and storm deposits so a statistical approach (including cluster analysis, principal component analysis and discriminant function analysis) was used based on grain size, mineralogy and trace element geochemistry. The mineral content and trace element geochemistry are statistically inadequate to distinguish the provenance of the modern storm and tsunami deposits at this site, but the mean grain size can potentially discriminate these overwash deposits. The 2007 storm surge deposits were most likely sourced from the onshore