The Pemali Formation of Central Java and equivalents: Indicators of sedimentation on an active plate margin

The Pemali Formation is revised from being the oldest known sedimentary unit in north Central Java to being almost the youngest. This, and a new examination of its composition, has implications for regional geological models and petroleum geology. The Pemali Formation was originally interpreted as “early Miocene” but is now shown to be latest Miocene through Pliocene in age, and characterised by both very high rates of sedimentation and a particularly high degree of reworking. The mid-Late Miocene tectonic event that initiated deposition of this formation created a new series of basins that were filled by erosion of new structural highs. Continuing constriction of the basins resulted in the uplift of older Pemali sediments on the basin margins, being reworked into the youngest Pemali strata.Neither the Pemali Formation nor the associated uplift and erosion are seen in the basins in the Java Sea a short distance to the north. Both the severe effects of the mid-Late Miocene tectonism and the Pemali-type sediments are restricted to a particular geologic zone, which is roughly the same as the modern island of Java. This may be above lithosphere of mixed terranes that forms a rim to the sialic Sunda Plate. The onshore Java area has a history of severe tectonism through the Tertiary and consequently a stratigraphy that greatly contrasts with that of the present-day Java Sea.The localised and thick Pemali deposition affected the burial history and the generation of hydrocarbons around the mid-Late Miocene basins, whilst the uplifted areas may include hydrocarbon traps. If basement composition influenced the location and thickness of the Pemali Formation then it is also likely to have fundamentally controlled deposition of older formations, including the unknown source rock for surface oil seeps. Likewise, these controls appear to contrast strongly with the better known rift-sag basins of the Java Sea.     

Crustal contamination and fluid/rock interaction in the carbonatites of Fuerteventura (Canary Islands, Spain): a C, O, H isotope study

Fuerteventura—the second largest of the Canary Islands consists of Mesozoic sediments, submarine volcanic rocks, dike swarms and plutons of the Basal Complex, and younger subaerial basaltic and trachytic series. Carbonatites are found in two Basal Complex exposures: the Betancuria Massif in the central part of the island and the Esquinzo area in the north. values of the carbonatites increase progressively from south to north of the island. This phenomenon is attributed to different degrees of assimilation of sedimentary carbonate. Homogeneous, typically magmatic values for carbonatites which have preserved primary igneous textures and minerals suggest a well-mixed reservoir where changes in values result from the storage of carbonate magmas at different structural levels. The magma storage allowed assimilation of sediment to varying degrees before final emplacement of carbonatites. Shifts in towards more positive and negative values from presumed primary compositions are observed in the carbonatites. On the basis of the oxygen isotope compositions of calcite, mica and K-feldspar, and the hydrogen isotope compositions of micas, the changes in the values of the carbonatites can be related to fluid/rock interactions.     

Age and significance of voluminous mafic–ultramafic magmatic events in the Murchison Domain,Yilgarn Craton

Mafic–ultramafic rocks in structurally dismembered layered intrusions comprise approximately 40% by volume of greenstones in the Murchison Domain of the Youanmi Terrane, Yilgarn Craton. Mafic–ultramafic rocks in the Murchison Domain may be divided into five components: (i) the ～2810 Ma Meeline Suite, which includes the large Windimurra Igneous Complex; (ii) the 2800 ± 6 Ma Boodanoo Suite, which includes the Narndee Igneous Complex; (iii) the 2792 ± 5 Ma Little Gap Suite; (iv) the ～2750 Ma Gnanagooragoo Igneous Complex; and (v) the 2735–2710 Ma Yalgowra Suite of layered gabbroic sills. The intrusions are typically layered, tabular bodies of gabbroic rock with ultramafic basal units which, in places, are more than 6 km thick and up to 2500 km² in areal extent. However, these are minimum dimensions as the intrusions have been dismembered by younger deformation. In the Windimurra and Narndee Igneous Complexes, discordant features and geochemical fractionation trends indicate multiple pulses of magma. These pulses produced several megacyclic units, each ～200 m thick. The suites are anhydrous except for the Boodanoo Suite, which contains a large volume of hornblende gabbro. They also host significant vanadium mineralisation, and at least minor Ni–Cu–PGE mineralisation. Collectively, the areal distribution, thickness and volume of mafic–ultramafic magma in these complexes is similar to that in the 2.06 Ga Bushveld Igneous Complex, and represents a major addition of mantle-derived magma to Murchison Domain crust over a 100 Ma period. All suites are demonstrably contemporaneous with packages of high-Mg tholeiitic lavas and/or felsic volcanic rocks in greenstone belts. The distribution, ages and compositions of the earlier mafic–ultramafic rocks are most consistent with genesis in a mantle plume setting.     

Organic matter in eolian dusts over the Atlantic Ocean

The elemental and mineralogical composition and the microfossil and detritus content of particulate fallout from the lower troposphere over the Atlantic Ocean have been extensively documented in earlier work, and it was possible to ascribe terrigenous source areas to such fallout. A brief review of the organic geochemistry of eolian dust is also presented here. The lipids of eolian dusts sampled from the air mass over the eastern Atlantic from about 35°N to 30°S were analyzed here.These lipids consisted mainly of normal alkanes, carboxylic acids and alcohols. The n-alkanes were found to range from n-C₂₃ to n-C₃₅, with high CPI values and maximizing at n-C₂₇ in the North Atlantic, at n-C₂₉ in the equatorial Atlantic and at n-C₃₁ in the South Atlantic. The n-fatty acids had mostly bimodal distributions, ranging from n-C₁₂ to n-C₃₀ (high CPI), with maxima at n-C₁₆ and in the northern samples at n-C₂₄ and in the southern samples at n-C₂₆. The n-alcohols ranged from n-C₁₂ to n-C₃₂, with high CPI values and maxima mainly at n-C₂₈. The compositions of these lipids indicated that their terrigenous sources were comprised mainly of higher plant vegetation and desiccated lacustrine mud flats on the African continent.     

Nearshore suspended sediment variations,central Surinam coast

Nearshore suspended sediment concentration along the muddy Surinam coast is highly variable; maximum values are many times greater than on other muddy coasts. Water samples taken at four field stations during various stages of the tide range in concentration from 15 to 3,700 mg/l near the surface and from 100 to 30,000 mg/l near the bottom. Highest overall concentrations and greatest variability in concentration occur in water over large banks of fluid mud (thixotropic gel) that extend 2–3 km offshore and 5–10 km along-shore. On both the intertidal and subaqueous portions of these mudbanks highest concentrations are found at low tide. Results provide evidence that an exchange between fluid mud and suspended sediment takes place during each tidal cycle.     

Coastal slope terracing and relative sea-level changes: Deductions based on computer simulations

Although a traditional geological survey of terraced coastal slopes is an essential part of studies aimed to reconstruct relative sea-level changes, the stratigraphic and chronological data so obtained frequently prove inadequate to completely unravel the sometimes very complex history of sea-level fluctuation, especially where erosion has prevailed over deposition and/or deposits are difficult to date. On the basis of our experience we think that much additional information can be gained through geomorphological interpretation of the profiles of those slopes. In order to facilitate such interpretation, a computer simulation model is developed that is able to predict the morphogenic response to a variety of possible relative-sea-level histories. The results can be used to envisage some new interpretation keys for the analysis of real situations and, hopefully, as bases for the conception of general models of coastal slope evolution under the action of a variable sea level. Though preliminary, the results so far obtained permit identification of the geomorphological consequences (in terms of resulting slope profile) of ordered successions of transgressions and regressions of different amplitude, rate, order and style. Moreover they provide interesting insights into the role that different styles of tectonic uplift may play in the phenomenon of multiple terracing of coastal slopes.     

Geochemical Composition of Dolerites as an Indicator of the Distance of a Dike Swarm from the Mantle Plume Center (Case Study of Proterozoic Dike Swarms,Siberian Craton)

Doklady Earth Sciences - Based on investigation of Proterozoic mafic dike swarms of the Siberian Craton, we inferred how the geochemical and isotopic characteristics of dike swarms of dolerites of...     

Gigamasers: the key to the dust-obscured star formation history of the Universe?

A numerical model of the Leonid stream is developed, based on an earlier model which has been applied to the Perseid stream. The results for this model are applied to the 2001 Leonid return. By examining the full three-dimensional dispersion of individual 'streamlets' released from the Leonid parent comet, 55P/Tempel–Tuttle, we have derived an estimate for the temporal change in spatial density of each trail. Using this result along with an estimate for the location of the centres for individual streamlets and fits to previous Leonid storm profiles, we estimate that the activity from the shower will be broad and relatively strong (zenithal hourly rates perhaps in excess of 1000). In particular, streamlets from the 1766 and 1799 ejections contribute to activity peaking near 10 and 12 ut on 2001 November 18, respectively. Additional older material from 1633, 1666 and 1699, as well as more recent ejections from 1866 and 1833, contributes to a much broader secondary maximum near 17.5 ut on November 18. Comparison with other published models of predicted Leonid activity in 2001 shows general agreement in terms of timing, but the models differ significantly in terms of the relative magnitude of the activity (which other models suggest will be larger). Significant anisotropy in the impact hazard exists for satellites in the geostationary belt, with those over western longitudes most likely to be affected. Integrated fluences for the 2001 Leonid return suggest a hazard of order one magnitude greater than occurred for the 1999 Leonid storm.