Carbonaceous chondrites as analogs for the composition and alteration of Ceres

The mineralogy and geochemistry of Ceres, as constrained by Dawn's instruments, are broadly consistent with a carbonaceous chondrite (CM/CI) bulk composition. Differences explainable by Ceres’s more advanced alteration include the formation of Mg‐rich serpentine and ammoniated clay; a greater proportion of carbonate and lesser organic matter; amounts of magnetite, sulfide, and carbon that could act as spectral darkening agents; and partial fractionation of water ice and silicates in the interior and regolith. Ceres is not spectrally unique, but is similar to a few other C‐class asteroids, which may also have suffered extensive alteration. All these bodies are among the largest carbonaceous chondrite asteroids, and they orbit in the same part of the Main Belt. Thus, the degree of alteration is apparently related to the size of the body. Although the ammonia now incorporated into clay likely condensed in the outer nebula, we cannot presently determine whether Ceres itself formed in the outer solar system and migrated inward or was assembled within the Main Belt, along with other carbonaceous chondrite bodies.     

Ceres's global and localized mineralogical composition determined by Dawn's Visible and Infrared Spectrometer (VIR)

The Visible and Infrared Spectrometer (VIR) instrument on the Dawn mission observed Ceres’s surface at different spatial resolutions, revealing a nearly uniform global distribution of surface mineralogy. Clearly, Ceres experienced extensive water‐related processes and chemical differentiation. The surface is mainly composed of a dark component (carbon, magnetite?), Mg‐phyllosilicates, ammoniated clays, carbonates, and salts. The observed species suggest endogenous, global‐scale aqueous alteration. While mostly uniform at regional scale, Ceres’s surface shows small localized areas with different species and/or variations in abundances. Few local exposures of water ice are seen, especially at higher latitudes. Sodium carbonates have been identified in several areas on the surface, notably in Occator bright faculae. Organic matter has also been discovered in several places, most conspicuously in a large area close to the Ernutet crater. The observed mineralogies, with the presence of ammoniated species and sodium salts, have a strong resemblance to materials found on other bodies of the outer solar system, such as Enceladus. This poses some questions about the original material from which Ceres accreted, suggesting a colder environment for such material with respect to Ceres’s present position.     

Mineralogy and temperature of crater Haulani on Ceres

We investigate the region of crater Haulani on Ceres with an emphasis on mineralogy as inferred from data obtained by Dawn's Visible InfraRed mapping spectrometer (VIR), combined with multispectral image products from the Dawn Framing Camera (FC) so as to enable a clear correlation with specific geologic features. Haulani, which is one of the youngest craters on Ceres, exhibits a peculiar “blue” visible to near‐infrared spectral slope, and has distinct color properties as seen in multispectral composite images. In this paper, we investigate a number of spectral indices: reflectance; spectral slopes; abundance of Mg‐bearing and NH₄‐bearing phyllosilicates; nature and abundance of carbonates, which are diagnostic of the overall crater mineralogy; plus a temperature map that highlights the major thermal anomaly found on Ceres. In addition, for the first time we quantify the abundances of several spectral endmembers by using VIR data obtained at the highest pixel resolution (~0.1 km). The overall picture we get from all these evidences, in particular the abundance of Na‐ and hydrous Na‐carbonates at specific locations, confirms the young age of Haulani from a mineralogical viewpoint, and suggests that the dehydration of Na‐carbonates in the anhydrous form Na₂CO₃ may be still ongoing.     

Coupled finite‐element simulation of injection well testing in unconsolidated oil sands reservoir

This paper presents a finite‐element (FE) model for simulating injection well testing in unconsolidated oil sands reservoir. In injection well testing, the bottom‐hole pressure (BHP) is monitored during the injection and shut‐in period. The flow characteristics of a reservoir can be determined from transient BHP data using conventional reservoir or well‐testing analysis. However, conventional reservoir or well‐testing analysis does not consider geomechanics coupling effects. This simplified assumption has limitations when applied to unconsolidated (uncemented) oil sands reservoirs because oil sands deform and dilate subjected to pressure variation. In addition, hydraulic fracturing may occur in unconsolidated oil sands when high water injection rate is used. This research is motivated in numerical modeling of injection well testing in unconsolidated oil sands reservoir considering the geomechanics coupling effects including hydraulic fracturing. To simulate the strong anisotropy in mechanical and hydraulic behaviour of unconsolidated oil sands induced by fluid injection in injection well testing, a nonlinear stress‐dependent poro‐elasto‐plastic constitutive model together with a strain‐induced anisotropic permeability model are formulated and implemented into a 3D FE simulator. The 3D FE model is used to history match the BHP response measured from an injection well in an oil sands reservoir. Copyright © 2013 John Wiley & Sons, Ltd.     

»Late Jurassic« petroleum geology of the Dutch Central North Sea Graben

The Callovian to Ryazanian (late Middle Jurassic to earliest Cretaceous; here referred to as »Late Jurassic«) sediments of the Dutch Central North Sea Graben, comprising the Central Graben and Scruff Groups, form several potential reservoirs. Source rocks are present within both these groups and the Carboniferous and Late Triassic-Early Jurassic.The structural development of the area is illustrated by a number of cross-sections. A structural subdivision has been made into platform, intermediate platform, outer graben, and inner graben. The complex history of rifting, wrench-faulting, halokinesis, and structural inversion strongly influenced the palaeogeography and ensuing sandstone developments. A few selected burial-history plots are presented as examples of the relationship between the structural subdivision and the hydrocarbon potential of the area.

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Zusammenfassung Die Sedimente des Callov bis zum Ryazan (oberer Mitteljura bis unterste Kreide, hier als »Oberjura« bezeichnet) des zentralen niederländischen Nordsee-Grabens, der den Zentralgraben und die Scruff-Gruppe umfaßt, stellen mehrere potentielle Erdölspeichergesteine dar. In jeder dieser beiden Gruppen sowie im Karbon und von der Obertrias bis zur Unterkreide existieren Speichergesteine.Die strukturelle Entwicklung des Gebietes wird anhand mehrere Profile veranschaulicht. Außerdem schien eine Untergliederuntg in Plattform, Zwischenplattform, äußerer sowie innerer Graben sinnvoll. Die komplexe Entwicklungsgeschichte, die durch Riftingphasen, Wrench-Tektonik, Halokinese und Strukturinversion bestimmt wurde, hat die Paläogeographie und die resultierende Sandsteinbildung intensiv beeinflußt. Eine Anzahl ausgewählter Darstellungen der Geschichte der Sedimentüberlagerung dienen als Beispiele für den Zusammenhang zwischen den strukturell bestimmten Untergruppen und dem Kohlenwasserstoffpotential des Untersuchungsgebietes.

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Résumé Dans le secteur néerlandais du Graben Central de la Mer du Nord, plusieurs réservoirs potentiels sont constitués par les sédiments calloviens à ryazaniens (ensemble allant du sommet du Jurassique moyen au Crétacé inférieur et désigné ici par «Late Jurassic»). Ces sédiments comprennent le groupe du Graben central et le groupe de Scruff. Des rochesmères existent dans chacun de ces deux groupes ainsi que dans le Carbonifère et dans la série Trias terminal-Eojurassique.La constitution structurale de cette région est illustrée par une série de coupes. On distingue, au point de vue structural: une plate-forme, une plate-forme intermédiaire, un graben externe et un graben interne. L'histoire géologique complexe, avec ses processus de rifting, de décrochement, d'halokinèse et d'inversion structurale, s'est répercutèe de manière significative sur la paléogéographie et, par voie de conséquence, sur l'extension des faciès arénacés. Quelques reconstitutions de l'histoire sédimentaire sont présentées à titre d'exemple de manière à illustrer la relation entre les unités structurales et le potentiel en hydrocarbure de la région.

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Observations of mine seismicity in the eastern Wasatch Plateau,Utah, U.S.A.: A possible case of implosional failure

In the summer of 1984, a three-dimensional, high-resolution microearthquake network was operated in the vicinity of two coal mines beneath Gentry Mountain in the eastern Wasatch Plateau, Utah. During a six-week period, approximately 3,000 seismic events were observed of which the majority were impulsive, higher frequency (>10 Hz), short duration (<2–3 sec) events probably associated with the caving of the roof from a longwall operation. In contrast, 234 of the largest located events appeared to occur predominantlybeneath the mines to a depth of 2 to 3 km consistent with previous studies. The magnitudes of these events ranged from less thanM _c 0 to 1.6. In addition to the unusual depths of these latter events, an anomalous aspect displayed by the events was an apparent dilatational focal mechanism suggesting a non-double-couple, possibly implosional source. Implosional events have been observed in other studies of mine seismicity; however, the generally inadequate instrumental coverage of the focal sphere has cast some doubt on the validity of such mechanisms. Previously suggested source mechanisms for such implosional events have included tensional failure through strata collapse, and a shear-implosional displacement mechanism. Shear failure must be involved in the failure process of the Gentry Mountain implosional events as evidenced by well-defined shear waves in the observed seismograms. Simultaneous monitoring in the East Mountain coal mining area to the south by the University of Utah revealed typical shear failure events mixed with implosional events. The observed double-couple, reverse focal mechanisms at East Mountain were similar to mechanisms determined in previous studies and a composite focal mechanism determined in this study for a sequence outside the mining areas. This suggested that the shear events within the mining areas are being influenced by the regional tectonic stress field. Thus in addition to the seismic events associated with caving of the roof from the longwall operation, there appear to be at least two other types of mining-induced seismic events occurring in the eastern Wasatch Plateau, both submine in origin: (1) events characterized by apparent non-double-couple possibly implosional focal mechanisms and well-defined shear waves; and (2) shear events, which are indistinguishable from tectonic earthquakes and may be considered mining triggered earthquakes. The small mining-induced stress changes that occur beyond a few hundred meters from the mine workings suggest both types of seismic events are occurring on critically stressed, pre-existing zones of weakness. Topography, overburden, method of mining, and mine configuration also appear to be significant factors influencing the occurrence of the implosional submine events.     

PHYSICAL GEOGRAPHY IN SOUTHEAST ASIA: PAST THEMES, CURRENT STATUS AND FUTURE TRENDS

Our knowledge regarding the physical geography of Southeast Asia is incomplete to a surprising extent. This paper reviews the past research, describes the ongoing work, and attempts to identify the future trends. Coverage of such a large area, even for the last 25 years, requires study of publications in several languages and coping with literature which is not easily available. Therefore certain topics. which are prominent in current research and likely to remain so in the future were chosen and reviewed in detail. Such topics include studies related to active plate margin features; the Pleistocene in Southeast Asia; erosion and sedimentation rates; rainforest; river systems; karst in Southeast Asia; coastal geomorphology; and the urban environment. Environmental studies are rapidly gaining importance chiefly because of (a) the destruction of the natural vegetation and the associated loss of biodiversity and (b) the growing problems due to accelerated erosion and sedimentation This trend is likely to continue with accelerated destruction of forests, development of coastal areas, and urbanization of the landscape The direction of research in physical geography of Southeast Asia has been determined by a combination of individual research interest, governmental priorities, and international expectations     

FORTY YEARS OF PHYSICAL GEOGRAPHY IN THE JOURNAL

Up to June 1993, 207 articles on physical geography have been published in the Malayan Journal of Tropical Geography (MJTG) (1953–57), Journal of Tropical Geography (JTG) (1958–79) and the Singapore Journal of Tropical Geography (SJTG) (1980–93). These articles are examined initially in terms of their sub-fields (Biogeography, Climatology, Geomorphology, Hydrology, and Soils), area of focus (the tropics, Africa, America, East Asia, South Asia, Southeast Asia excluding Malaysia and Singapore, Malaysia, Singapore, and Southwest Pacific) and the area of origin of the authors. The more significant papers in the sub-fields are indicated. Various factors influencing the contributions to the Journal and some insights on the contributions of local staff (Singapore and Malaysia) are also given. The significance of the Journal as an avenue for local and foreign authors and for papers on physical geography in the tropics is briefly evaluated.     

Genetic structure of bay anchovy (Anchoa mitchilli) populations in Chesapeake Bay

To determine the genetic structure of the bay anchovy (Anchoa mitchilli) within Chesapeake Bay, 16 isozyme systems encoding 21 loci for 20 population were examined using horizontal starch gel electrophoresis. Contingency Chisquare analysis revealed significant allelic frequency differences at nine loci (AAT-1, AAT-2, ALD-1, CPK-2, GAP-1, GLY-1, LDH-1, MDH-1, and MDH-2). Two loci, ALD-1 and MDH-1, were responsible for nine of 14 tests not conforming to Hardy-Weinberg expectations, with some of these deviations attributed to possible scoring and/or sampling error. Estimates for mean average heterozygosity were relatively high, ranging from 0.40 to 0.096, with 33–57% of the loci polymorphic. A low F_st value (0.041) along with high genetic identity estimates (I=0.997) indicated little substructuring of bay anchovy populations within Chesapeake Bay.