The Galápagos archipelago is a well‐suited model ecosystem for investigating soil evolution. Here, we study mineral transformations and pedogenesis of the volcanic soils of Galápagos in response to weathering duration (1,500–1,070,000 yr) and climate (humid vs. dry). Our results show that soil pH, electrical conductivity, organic C content, cation exchange capacity (CEC), and water retention decreased whereas clay content and bulk density increased with soil age under humid climate. Andic properties were expressed in soils ≤4,300 yr old, but disappeared relatively early in pedogenesis and were absent in soils ≥26,000 yr old. The clay fraction of the young andic soils (≤4,300 yr old) was dominated by allophane and ferrihydrite. After 26,000 yr of pedogenesis, illitic–vermiculitic phases were predominant, and in the older soils (≥166,000 yr old), kaolinite, hematite, and gibbsite prevailed. The sequence of soil orders from the youngest to the second oldest site was Histosol–Andisol–Alfisol (vermiculitic)–Alfisol (parasesquic)–Ultisol. The oldest soil of the humid chronosequence (1,070,000 yr old) met all diagnostic criteria for an Oxisol except for the required low CEC. The soils at two dry comparison sites were less developed with low clay contents and vitric materials at 26,000 yr of age (Entisol), and dominantly smectitic clay mineralogy and pronounced shrink–swell features at 813,000 yr of age (Vertisol). Our results highlight a rapid transition through the Andisol stage during early pedogenesis as well as strongly divergent pedogenic development in humid vs. dry zones of the Galápagos Islands, both of which have important bearings on soil functioning and ecosystem evolution on this unique archipelago.

Authigenic Mg‐calcite and dolomite are frequently observed in restricted, evaporative environments, such as lagoon or lake systems, but their formation is difficult to capture due to slow growth rates. Lake Neusiedl, an alkaline and subhaline lake with a mean water depth of 0.7 m in Austria, offers a natural system to study the precipitation of Ca‐Mg‐carbonate phases, which occur as fine‐grained, unconsolidated and largely homogenized mud. To elucidate the timing and formation mechanisms of these authigenic carbonate phases, the mineralogical and isotopic composition and radiocarbon age of different sediment grain‐size fractions from 3.0 μm were analysed. X‐ray diffraction analyses show two broad peaks of Mg‐calcite and protodolomite (lacking ordering peaks), suggesting that the carbonates are authigenic rather than detrital in origin. Calibrated carbon‐14 ages range between 200 cal yr bp and 3700 cal yr bp. The linear correlation of age and grain size suggests a very slow growth rate of single crystals of 0.23 to 0.60 μm/ka. These rates suggest an extremely slow sedimentation rate in a shallow lake that existed during most of the Holocene. The higher abundance of protodolomite in older grain fractions, in contrast to the presence of high‐Mg calcite in the youngest fractions, suggests a growth succession where high‐Mg calcite develops first and subsequently transforms into protodolomite. Much higher ages of 6 cal ka bp to 15 cal ka bp are measured in carbonates of lake deposits exposed on land, in a section north‐west of the recent lake, suggesting a growth rate of those carbonate minerals of 0.13 μm/ka. These time constraints further suggest that some carbonate grains could already have nucleated from lake water before or during the last glacial maximum, although under slightly different hydrochemical conditions.