Scanning electron microscopic (SEM) examination of the quartz isolated from chert of Transvaal and Swaziland, of 2000 and 3400 million year (MY) ages, respectively, in southern Africa revealed marked differences in quartz morphology. Well-defined individual euhedral quartz crystals, with polyhedral triple-point faces, were clearly evident on freshly fractured Transvaal chert surfaces as well as with the quartz isolates from the chert. The morphology and coarseness suggest crystal growth with little, if any, metamorphism; however, the δ18O values of 23.8–24.1‰ suggest crystallization temperatures of perhaps 40–45°C. In contrast, fracture surfaces of the older, strongly metamorphosed Swaziland cherts revealed a high degree of grain intergrowth which inhibited fracture between quartz grains. Quartz isolates from these showed strongly interlocked quartz crystal clusters and elongated chips of quartz with poorly defined irregular faces. Intercalation of mineral veins in the cherts on a mm scale and the intergrown character of the quartz grain boundaries provide evidence that the latter cherts have been strongly metamorphosed and recrystallized, in keeping with 14.6–15.1‰ δ18O values, corresponding to 80°C fractionation with water. The SEM micrographs of the fine quartz (1–10 µm) isolated from the Otavi dolomite formation of the 700-MY Damara System and from the 2000-MY Transvaal Dolomite Series revealed well-defined subhedral and euhedral quartz crystals of small size which, together with the 26.9–27.8‰ and 23.8‰ δ18O values, respectively, indicate that these dolomites have been affected little, if any, by post-depositional metamorphism; their crystallization temperatures fall in the range of 25–30 and 40–45°C, respectively.

The terrestrialization of life has profoundly affected the biosphere, geosphere and atmosphere, and the Geological Magazine has published key works charting the development of our understanding of this process. Integral to this understanding – and featuring in one of the Geological Magazine publications – is the Devonian Rhynie chert Konservat-Lagerstätte located in Aberdeenshire, Scotland. Here we provide a review of the work on this important early terrestrial deposit to date. We begin by highlighting contributions of note in the Geological Magazine improving understanding of terrestrialization and Palaeozoic terrestrial ecosystems. We then introduce the Rhynie chert. The review highlights its geological setting: the Caledonian context of the Rhynie Basin and its nature at the time of deposition of the cherts which host its famous fossils. There follows an introduction to the development of the half-graben in which the cherts and host sediments were deposited, the palaeoenvironment this represented and the taphonomy of the fossils themselves. We subsequently provide an overview of the mineralization and geochemistry of the deposit, and then the fossils found within the Rhynie chert. These include: six plant genera, which continue to provide significant insights into the evolution of life on land; a range of different fungi, with recent work starting to probe plant–fungus interactions; lichens, amoebae and a range of unicellular eukaryotes and prokaryotes (algae and cyanobacteria); and finally a range of both aquatic and terrestrial arthropods. Through continued study coupled with methodological advances, Rhynie fossils will continue to provide unique insights into early life on land.

A new occurrence of barium silicates has been found in unmetamorphosed sedimentary rocks of central North Greenland. Two different barium minerals have been identified, the Ba-feldspar hyalophane, and an unknown and hitherto undescribed hydrated Ba-silicate with an anhydrous chemical composition identical to cymrite but with about 4 moles of water in the mineral structure. Both silicates are found in a black organic-rich chert sequence in close association with baryte. No replacement textures are observed between the three Ba-minerals.

The hydrated Ba-silicate in the unmetamorphosed rock sequence of the Navarana Fjord area is considered to represent a member in a sequence of Ba-silicates from the unknown Ba-silicate with four H2O in the structure (BaAl2Si2O8·4H2O), through cymrite with one H2O (BaAl2Si2O2O8·H2O) to celsian with none (BaAl2Si2O8). This sequence might reflect the continuous release of water during prograde diagenesis and metamorphism. The association between chert and Ba minerals in the sedimentary rocks of the Navarana Fjord area is believed to reflect an addition of silica and barium by hydrothermal solutions.

A new method for measuring the crystallinity index of quartz is presented. It is based on the measurement of the intensity of the first derivative of the infrared absorption spectrum at the shoulder at c. 1145 cm−1. The results correlate well with X-ray and D.T.A. crystallinity measurements.

A Silurian radiolarian fauna based on 18 species is described from cherts from three sections in two quarries in the Sepon Mine area, central Laos. Each section contains distinctive assemblages but Futobari morishitai, F. solidus, Zadrappolus yoshikiensis and Z. tenuis are found in all three sections and are characteristic of the Ludlow–Pridoli Z. yoshikiensis Assemblage. In addition, the Hoei Yang pit section contains Zadrappolus hitoeganensis, Pseudospongoprunum sagittatum, Futobari sp. and Secuicollacta sp. Section CQ contains Pseudospongoprunum sagittatum, P. tazukawaensis, Praespongocoelia parva, P. sp., Rotasphaera sp. cf. R. quadrata, Secuicollacta sp. cf. cassa. Section QM also contains Pseudospongoprunum parvispina, P. sp., Zadrappolus sp. and Devoniglansus (?) seponensis new species Thassanapak is common. Evidence from Silurian and Devonian strata of the southern Truong Son Terrane indicates deepening towards the southern margin as defined by the Thakhek–Danang Shear Zone and exemplified by deep-marine Ludlow–Pridoli radiolarian cherts in the south, shallowing to fossiliferous, shallow-water sediments to widespread Old Red Sandstone type terrestrial facies 85 km further NE. The radiolarian cherts are in faulted contact with probable Llandovery limestone and Upper Ordovician – Llandovery graptolitic shales. The graptolitic shales are overlain with slight angular unconformity by the submarine fan, volcaniclastic-dominated, Namphuc Formation of Llandovery age. This fan received andesitic materials from the nearby Long Dai Volcanic Arc which extends eastwards to the Tamky Suture in Vietnam. This plutonic–volcanic arc was probably maintained by northwards subduction along the trend of the Permian–Recent Thakhek–Danang Shear Zone.

A reconnaissance survey of part of western Cambodia has found quarries in and near the town of Pailin containing chert, basalt, volcaniclastic rocks, gabbro and serpentinite. Abandoned quarries contain chert and basalt clasts in a volcaniclastic matrix and may constitute a mélange. A new, recently active, quarry contains these rock units in close and coherent contact but they lack the serpentinitic matrix of the Thung Kabin Mélange of eastern Thailand. The rock units are in close contact and may best be described collectively as a dismembered ophiolite. The mélange–ophiolite association constitutes a 3 km wide, 20 km long E–W belt separating a northern 200 km2 block of the mainly amphibolitic Pailin Crystalline Complex from a southern area of Triassic submarine fan siliciclastic rocks. The cherts yield the first documented radiolarian fauna from Cambodia and include a moderately well-preserved Asselian–Sakmarian age fauna consisting of Pseudoalbaillella sakmarensis, Pseudoalbaillella scalprata morphotype scalprata, Pseudoalbaillella sp. cf. P. simplex, Pseudoalbaillella u-forma morphotype II, Pseudoalbaillella sp. cf. P. elegans, Pseudoalbaillella sp. cf. P. lomentaria, Albaillella sp., Pseudoalbaillella spp., Trilonche? sp., Latentifistularia gen. et sp. indet. and Entactinaria gen. et sp. indet. The Pailin ophiolitic rocks, mélange and volcanic rocks occur within a generally E–W-trending belt, which suggests that the Sa Kaeo Suture does not extend southeastwards paralleling the Thai–Cambodian border, nor extend under the Cardamom Mountains but, rather, extends eastwards into Cambodia and possibly then turns southwards along the strike of the Pursat–Kampot Fold Belt.

Over 40 years of archaeological investigations along the south coast of Papua New Guinea has identified a rapid succession of cultural changes during the late Holocene. The so-called ‘Papuan Hiccup’ (c. 1200–800 cal bp) is a poorly understood period of socio-economic upheaval along the coast, identified mainly from changes in archaeological ceramic styles and settlement patterns. During this period, the region-wide Early Papuan Pottery (EPP) tradition diverges into separate, localised ceramic sequences that have generic associations with local ethnographic wares. A correspondence between the timing of the Papuan Hiccup and a period of peak El Niño-Southern Oscillation (ENSO) activity implies a link between cultural and climate change. This paper explores this relationship further by examining changes in interaction networks along the south coast of Papua New Guinea, specifically focusing on chert artefacts. Chemical characterisation (portable X-Ray Fluorescence; pXRF) and technological analysis are used to map changes in lithic technology over time, including access to raw materials and technological organisation, at the site of Taurama, a prehistoric coastal village site that was occupied both prior to and after the Papuan Hiccup. Although the sample sizes are small and the interpretations necessarily circumscribed, it is argued that changes in the number of chert sources being exploited and in the intensity of core reduction at Taurama may be related to climate change in the region.

The 3.46 Ga Marble Bar Chert Member of the East Pilbara Craton, Western Australia, is one of the earliest and best-preserved sedimentary successions on Earth. Here, we interpret the finely laminated thin-bedded cherts, mixed conglomeratic beds, chert breccia beds and chert folded beds of the Marble Bar Chert Member as the product of low-density turbidity currents, high-density turbidity currents, mass transport complexes and slumps, respectively. Integrated into a channel-levee depositional model, the Marble Bar Chert Member constitutes the oldest documented deep-sea fan on Earth, with thin-bedded cherts, breccia beds and slumps composing the outer levee facies tracts, and scours and conglomeratic beds representing the channel systems.

During experiments conducted within the vent pool of Medusa Geyser, Norris Geyser Basin, Yellowstone National Park, USA, amorphous opaline silica (opal-A) was deposited on/within plant tissues within 30 days of immersion. Initially, deposition created inter/intra-cellular films which lined cell walls plus intercellular colloid suspensions (sols) of opal-A nano/microspheres. By 330 days, opal-A deposition created a robust external and internal matrix that stabilised tissues against collapse and replicated plant structure. Opal-A films increased to micron-order thicknesses and intracellular sols were created. Systematic variation of opal-A fabric between tissues comprising living/dead cells at the time of deposition indicate that cell function, architecture and shape influence fabric development. Heterogeneity of opal-A fabric within adjacent cells of similar structure/function indicates spatially/temporally fluctuating physicochemical conditions and the presence of intraorganic microenvironments. Early deposition of opal-A films suggests a period of low silica supersaturation and slow opal-A deposition. In contrast, intracellular sols suggest high levels of supersaturation, and rapid opal-A deposition. Shell-like microsphere growth suggests cyclic variation of silica supersaturation, and alternations between rapid and slower opal-A deposition. Microsphere growth to the upper limit of colloidal stability and colloidal crystal structures indicate prolonged sol stability, whilst floc-like microsphere networks indicate localised sol instabi

Geological and palaeontological research in the Rhynie area, Aberdeenshire, Scotland, has progressed in several stages. Following early surveys in the nineteenth century, Dr William Mackie mapped the western margin of the basin in 1910–1913, and discovered the plant-bearing chert. Following trenching of the chert in 1913, Kidston & Lang described the plant fossils between 1917 and 1921 and Scourfield, Hirst and Maulik the arthropods in the 1920s. Following a ‘dark age’ of some 30 years, Geoffrey Lyon awakened interest in the late 1950s. Trenching in 1963–1971 provided Lyon and his co-workers with new material, and resulted in finds of new plants and reinterpretations of earlier work. The next phase was initiated by Winfried Remy's discovery of gametophytes in material given to him by Lyon. Since 1980, the Münster school has continued to make exciting discoveries. Aberdeen University involvement began in 1987 with geochemical work confirming a hot spring origin for the chert. Drill cores taken in 1988 and 1997, and further trenching have allowed structural, sedimentological and stratigraphic reappraisals, and resulted in the discovery of a new biota in the Windyfield chert. Long-term collaborative international research continues to advance interpretation of this unique Early Devonian hot spring system, and the remarkably diverse freshwater and terrestrial biota of the cherts.

The cyanobacterial fossil record is among the oldest for any group of organisms, possibly reaching back to 3500 Ma ago. The molecular phylogeny of cyanobacteria is complementary to the fossil findings, confirming the antiquity of the group, the role of cyanobacteria in the evolution of planetary primary production, and the symbiotic origins of plastids in algae and plants from cyanobacterial ancestors. The study of fossil cyanobacteria followed the discovery of Precambrian microbial fossils by S.A Tyler and E.S. Barghoorn in 1954, and is still developing. Most fossil cyanobacteria are preserved in permineralized conditions in cherts and phosphorites or as organic compressions in shales. The interpretation of fossil cyanobacteria is aided by the study of modern counterparts, preferably within their natural habitats. These comparisons include the post mortem degradation of cellular remains. The fortuitous preservation and fossilization of ancient cyanobacterial communities in growth position, i.e. in the synsedimentary context, allows one to draw conclusions about their palaeoenvironment, including interactions between cyanobacteria and ancient sediments. These relations are based on cyanobacterial ecological requirements, and they compare well with behavioural responses of modern cyanobacteria in microbial mats and modern stromatolites. The general trend in the evolution of cyanobacteria is one of gradually increasing complexity and diversity, but the group shows a conservative maintenance of morphological adaptations to successful ecological niches. Accordingly, a large proportion of ancient morphological types is still represented among modern cyanobacteria. Fossil to Recent counterparts are identified for several coccoid and filamentous cyanobacteria. Evidence for heterocystous cyanobacteria is indirect, through identification of fossil akinetes.

The Lower Devonian plant- and arthropod-bearing cherts of the Rhynie area of Aberdeenshire, NE Scotland, were deposited from silica-rich waters emanating from the hot-springs of a precious-metal (Au) bearing epithermal system. Cherts were deposited at temperatures up to 100°C. The hot-springs were active in the waning phase of local volcanism and reworked volcanic debris is associated with the hot-spring system. Plant and animal communities inhabited a low energy alluvial plain with small ponds. Hot-springs deposited surficial sinter and silicified standing plants and underlying plant litter in a generally terrestrial setting, but aquatic organisms were present in low temperature pools within areas of sinter deposition. Silicification also affected plants and sediment in the shallow subsurface. The cherts display massive, vuggy, laminated, lenticular, nodular and brecciated textures in laterally impersistent beds. Faunal and floral variation between beds is of local significance, possibly reflecting general water availability. Variations in preservation of plants reflect not only degrees of imperfection in the permineralisation process, but also silicification at different times in the cycle of plant growth and decay.