Facies distribution and retreat of Middle Triassic platform margin, Guizhou province, south China

The southern margin of the vast Yangtze platform in central Guizhou Province, China, retreated during the Anisian (early Middle Triassic) by shedding skeletal debris and boundstone blocks into the margin of the adjacent basin. Anisian platform deposits are shoaling-up cycles that commonly terminated in subaerial exposure. Platform-margin facies are obscured by massive dolomitization and mechanical erosion. Distal basin deposits are terrigenous mudstone and siltstone. At the basin margin a wedge of mixed carbonate and terrigenous rocks consists of (A) thin-bedded dolostone and limestone, (B) lime breccia with thin-bedded mudstone, and (C) lime mudstone with breccia. Blocks within the breccias indicate that the shelf margin contained extensive boundstone formed by ‘Tubiphytes,’encrusting organisms, and early marine cement. Interspersed thin beds of skeletal packstone represent unlithified skeletal debris at the platform margin. The profile of the shelf margin from detailed mapping indicates 1.7–2.7 km of platform-margin retreat during deposition of a basin-margin wedge 250 m thick. Intertonguing of various basin-margin facies reflects alternating minor episodes of advance and retreat of the margin. Near-parallelism of the tongues suggests low relief at the platform margin. An upward stratigraphic progression to more distal, carbonate-free, terrigenous basin facies indicates a cessation of carbonate production on the platform owing to emergence during early Anisian time. Retreat may have occurred entirely by collapse of blocks less than 100 m wide and 30 m thick, the largest observed dimensions. A re-entrant in the margin 7 km wide and 10 km deep could also reflect collapse. Retreat occurred along 175 km of the platform margin. The lack of platform-margin facies along this front suggests 3–7 km of retreat and a total area of 875 km². The Anisian platform-margin retreat in Guizhou is one of relatively few examples of platform-margin retreat in the geological record.     

Short-term morphological change and sediment dynamics in the intertidal zone of a macrotidal beach

This paper describes the morphological and sedimentological evolution of a macrotidal beach over a 20 day period under varying hydrodynamic conditions (significant breaker heights of 0·3–2 m and tidal ranges of 2–5 m). During the field campaign, an intertidal bar developed around the mid‐tide level, migrated onshore, welded to the upper beach and was then flattened under energetic wave conditions. The bar had a wave breakpoint origin and its formation was triggered by a reduction in tidal range, causing more stationary water‐level conditions, rather than an increase in wave height. Most of the onshore bar migration took place while the bar was positioned in the inner to mid‐surf zone position, such that the bar moved away from the breakpoint and exhibited ‘divergent’ behaviour. The depth of disturbance over individual tidal cycles was 10–20% of the breaker height. Such values are more typical of steep reflective beaches, than gently sloping, dissipative beaches, and are considered to reflect the maximum height of wave‐generated ripples. The grain size distribution of surficial sediments did not vary consistently across the beach profile and temporal changes in the sedimentology were mostly unrelated to the morphological response. The lack of clear links between beach morphology and sedimentology may be in part due to shortcomings in the sampling methodology, which ignored the vertical variability in the sediment size characteristics across the active layer.     

Palaeoenvironments associated with caddisfly-dominated microbial-carbonate mounds from the Tipton Shale Member of the Green River Formation: Eocene Lake Gosiute

Caddisfly‐dominated microbial‐carbonate mounds and avian eggshell fragments are common in a nearshore, oolite facies of the Tipton Shale Member of the Eocene Green River Formation. The fossils occur in a 9 m thick carbonate sequence exposed on the south‐west flank of Essex Mountain, Sweetwater County, Wyoming. The eggshell was determined to be of avian origin by examination of the radial eggshell microstructure by scanning electron microscopy and polarized light microscopy. Common allochems in the limestone include: ooids, pisoids, oncoids, ostracods, gastropods, intraclasts, caddisfly larval/pupal cases, fish bones, avian bones and avian eggshell fragments. Carbonate mineralogy varies between 95% calcite and 95% dolomite. Oxygen stable isotopes vary between −10·1 and −1·3‰ (V‐PDB). Carbon and oxygen stable isotopes co‐vary. Co‐variance of oxygen and carbon stable isotopes indicates that Lake Gosiute was hydrologically closed during the formation of this oolite sequence. Positive excursions of oxygen stable isotope values are correlated with dolomite, caddisfly cases and avian eggshell fragments. These factors are probably associated with lake regression and more saline conditions. Negative excursions of oxygen stable isotope values are correlated with calcite, gastropods and intraclasts. These factors are probably associated with lake transgression and lake freshening. In the 9 m oolite sequence studied there are at least two inferred transgressions, three regressions and two storm events. The caddisfly cases and avian eggshell fragments occur in sediments formed only during low‐stands of the lake as determined by other lake level proxies (dolomites and more positive oxygen stable isotope values). As avian eggshell fragments were formed under subaerial conditions, the avian eggshell fragments independently confirm lake regression. In addition, the occurrence of avian eggshell fragments during saline phases of the lake may indicate that the birds which produced the eggshell preferred saline conditions (or that their food preferred saline lake water).     

Palaeoclimatic inferences from upper Palaeozoic siltstone of the Earp Formation and equivalents, Arizona-New Mexico (USA)

The Late Palaeozoic configuration of Pangaea contributed to a palaeoclimatic extreme that was characterized by both icehouse and monsoonal conditions. This study uses sedimentological, geochemical, and provenance data from silty facies of the Earp and equivalent Supai Formations (Arizona, New Mexico) to shed light on atmospheric circulation and glacial–interglacial climate change in westernmost equatorial Pangaea. Five silt‐rich facies comprise both loessite and marine and fluvially reworked loessite. An initial aeolian origin for the silt is indicated by the remarkably invariant grain size and the laterally continuous, sheet‐like geometry of beds. The silt‐rich facies occur in repetitive facies associations (1–20 m scale) that form mixed continental‐marine (loess, marine‐reworked loess), shallow‐marine, and continental (loess, palaeosol) ‘sequences’. Facies repetitions of both mixed continental‐marine and shallow‐marine sequences reflect a linked glacioeustatic–glacioclimatic control, whereas the continental (loess–palaeosol) couplets reflect a primary glacial–interglacial climatic cyclicity linked to glacioeustasy. Stratigraphic interpretations suggest that aeolian silt flux maximized during glacial to incipient interglacial stages (lowstand to early transgression), and decreased significantly or ceased during interglacials (highstand to early falling stage). Detrital‐zircon geochronological data indicate a transition from dominantly north‐easterly winds during the Middle Pennsylvanian to north‐westerly and south‐easterly winds by the Early Permian, which trend is inferred to reflect the onset of monsoonal circulation in western Pangaea. Relative grain‐size data support the detrital‐zircon data, and exhibit a significant decrease from the Sedona arch/Central Arizona shelf (north) to the Pedregosa basin (south) sections. Whole‐rock geochemical data suggest a relatively unweathered source for the silt in the north, and detrital‐zircon data indicate significant silt was derived from the local basement. These large piles of silt(stone) preserve valuable information for reconstructing both long‐term evolution in atmospheric circulation and short‐term fluctuations in glacial–interglacial climate. Many such indicators for long have been applied to ‘recent’ (Plio‐Pleistocene) loess, but are equally applicable to ‘deep‐time’ strata.     

GEOGRAPHICAL REVIEW ESSAY: WHEN THE DOZERS CAME,ONLY MUSIC WAS LEFT: RY COODER ON CHÁVEZ RAVINE*

CHÁVEZ RAVINE: A Record by Ry Cooder. Produced by Ry Cooder , with Little Willie G., Lalo Guerrero , Ersi Arvizu , Don Tosti , Flaco Jimenez , Bla Pahinui CHÁVEZ RAVINE, 1949: A Los Angeles Story. By Don Normark. CHÁVEZ RAVINE: A Los Angeles Story. Directed by Jordan Mechner; produced by Jordan Mechner , Don Normark , Andrew B. Andersen , and Mark Moran ; photographs by Don Normark ; music by Ry Cooder ; narrated by Cheech Marin ; 24 minutes.     

Realistic Sustainability? Urban Transport Planning in Wellington,New Zealand

Urban transport systems have key roles in supporting environmental sustainability. New Zealand's transport planning arrangements are promoted as a model by agencies such as the World Bank. This paper explores the New Zealand transport planning framework using a case study of the Wellington region's strategic balancing of transport modes and projects. The paper argues that despite some positive rhetoric, concerns about the sustainability of transport planning in Wellington remain. The paper concludes by discussing the need to reassess New Zealand's national framework, and identifies some directions for reform.     

Kilauea East Rift Zone Magmatism: an Episode 54 Perspective

On January 29–30, 1997, prolonged steady-state effusionof lava from Pu'u'O'o was briefly disrupted by shallow extensionbeneath Napau Crater, 1–4 km uprift of the active Kilaueavent. A 23-h-long eruption (episode 54) ensued from fissuresthat were overlapping or en echelon with eruptive fissures formedduring episode 1 in 1983 and those of earlier rift zone eruptionsin 1963 and 1968. Combined geophysical and petrologic data forthe 1994–1999 eruptive interval, including episode 54,reveal a variety of shallow magmatic conditions that persistin association with prolonged rift zone eruption. Near-ventlava samples document a significant range in composition, temperatureand crystallinity of pre-eruptive magma. As supported by phenocryst–liquidrelations and Kilauea mineral thermometers established herein,the rift zone extension that led to episode 54 resulted in mixtureof near-cotectic magma with discrete magma bodies cooled to