Diagenetic and sedimentary controls on porosity in Lower Carboniferous fine-grained lithologies,Krechba field,Algeria: A petrological study of a caprock to a carbon capture site     

P.J. Armitage  R.H. Worden  D.R. Faulkner  A.C. Aplin  A.R. Butcher  J. Iliffe 《Marine and Petroleum Geology》2010

Fine-grained siliciclastic lithologies commonly act as sealing caprocks to both petroleum fields and host reservoirs for carbon capture (CO₂ sequestration) projects. Fine-grained lithologies are thus of great importance in controlling fluid flow and storage in the subsurface. However, fine-grained rocks are rarely characterised in terms of primary sedimentary characteristics, diagenesis and how these relate to their flow properties (i.e. sealing or caprock quality). Seventeen samples from Lower Carboniferous estuarine caprock to a gas field (also to be used as a carbon capture site), have been analysed using a range of petrological and petrophysical techniques. The rock unit that represents the caprock to this gas field was found to be predominantly silt grade with porosity values as low as 1.8%. In these rocks, caprock quality (porosity) is controlled by intrinsic and extrinsic factors linked to primary mineralogy and diagenetic processes. Depositional mineralogy was dominated by quartz, detrital mica, detrital clay (likely Fe-rich 7Å clay and illite–smectite) with minor feldspar and oxide phases. Diagenetic processes included compaction, minor feldspar dissolution and kaolinite growth and the more important processes of chlorite, siderite and quartz cementation, as well as the likely transformation of smectite into illite. Caprock quality is controlled by the primary quantity of illite-muscovite in the sediment and also by the localised extent of chlorite and quartz cementation. Deposition in an estuarine environment led to highly heterogeneous distribution of primary and diagenetic minerals, and thus caprock quality, between and within the samples.  相似文献   

Salinity management and water resources development     

Dr. W. S. Butcher 《GeoJournal》1979,3(5):457-460

The interrelationship of salinity management and water management is a factor which is sometimes easily overlooked in the water resources planning, even though it can place a limit on the degree of water resource development within a basin. Costs and control measures of salinity management are considered on a case study of the Colorado River basin where salinity damages are found to be higher than previously estimated. After review of the costs of salinity management, the possible control measures, and research on adaptions in agricultural use of more saline water, it can be concluded that, at very least, the management of water quantity and water quality, especially in arid regions, are closely intertwined.  相似文献   

Bar-top hollows: A new element in the architecture of sandy braided rivers     

Jim Best  John Woodward  Phil Ashworth  Greg Sambrook Smith  Chris Simpson 《Sedimentary Geology》2006,190(1-4):241-255

Discrete hollows in the bar tops of the South Saskatchewan River are described that form a newly-recognized morphological element of sandy braided rivers. These bar-top hollows, which are up to 1.7 m deep and may extend for 10–30 m down and across flow, have a circular to ovoid planform and are shown, through use of ground penetrating radar, to be filled by a series of distinct, often angle-of-repose, foresets. The hollows form by both erosion and bar-top deposition and may be generated by bar-tail accretion, cross-bar channel cutoff and subsequent fill or lateral accretion at the bar-head. Bar-top hollows occur in the upper part of the bar depositional sequence and may thus prove useful indicators for braid bar reconstruction in ancient sediments, and should not be confused with channel scour.  相似文献   

High precision slip distribution of the 1944 Tonankai earthquake inferred from tsunami waveforms: Possible slip on a splay fault     

Toshitaka Baba  Phil R. Cummins  Takane Hori  Yoshiyuki Kaneda 《Tectonophysics》2006,426(1-2):119

Inversion of tsunami waveforms is a well-established technique for estimating the slip distributions of subduction zone earthquakes, with some of the most detailed results having been obtained for earthquakes in the Nankai Trough, SW Japan. The present study, although it uses a method and tsunami waveform data set almost identical to previous study, aims to improve on previous work by using a more precise specification of initial conditions for the calculation of tsunami Green's functions. Specifically, we incorporated four improvements in the present study: (1) we used a realistic plate model based only on seismic survey results, and assumed it to be the fault plane of the 1944 Tonankai earthquake; (2) the smallest subfaults consistent with the long wavelength approximation were used in the tsunami inversion analysis; (3) we included the effect of horizontal displacement of the ocean bottom on tsunami generation; and (4) we performed a checkerboard resolution test. As obtained in previous studies, a zone of high slip (> 2.0 m) was resolved off the Shima Peninsula. However, the more precise calculation of tsunami Green's functions has revealed additional detail that was not evident in previous studies, which we demonstrate is resolvable and correlates with the position of known faults in the accretionary prism. While there was little or no slip near the trench axis in the eastern part of the rupture zone, there was up to 1.5 m of slip resolved within 30 km of the trough axis in the western part, along the coast of the Kii Peninsula. This troughward slip zone coincides with the position of a large splay fault mapped in multichannel reflection surveys. Furthermore, it is also clear that the upper edge of the Enshu fault off Shima and Atsumi peninsulas is consistent with the up-dip limit of slip in the eastern part of our model. We tested the possibility that slip occurred on the former splay fault instead of on the plate interface during the 1944 Tonankai earthquake, and find that slip on this splay fault is also consistent with the data, although we cannot distinguish whether slip was dominant on the splay fault or on the plate interface. We further suggest that the position of the Enshu fault may be determined by the subduction of topographic highs, and that such faults may have an important influence on the up-dip rupture limit of the 1944 Tonankai and, potentially, other subduction zone earthquakes.  相似文献   

Development of a Speech-Based Augmented Reality System to Support Exploration of Cityscape     

Phil J. Bartie  William A. Mackaness 《Transactions in GIS》2006,10(1):63-86

When people explore new environments they often use landmarks as reference points to help navigate and orientate themselves. This research paper examines how spatial datasets can be used to build a system for use in an urban environment which functions as a city guide, announcing Features of Interest (FoI) as they become visible to the user (not just proximal), as the user moves freely around the city. Visibility calculations for the FoIs were pre‐calculated based on a digital surface model derived from LIDAR (Light Detection and Ranging) data. The results were stored in a text‐based relational database management system (RDBMS) for rapid retrieval. All interaction between the user and the system was via a speech‐based interface, allowing the user to record and request further information on any of the announced FoI. A prototype system, called Edinburgh Augmented Reality System (EARS), was designed, implemented and field tested in order to assess the effectiveness of these ideas. The application proved to be an innovative, ‘non‐invasive’ approach to augmenting the user's reality.  相似文献   

Correlation of rhyolitic pyroclastic eruptive units from the Taupo volcanic zone by Fe–Ti oxide compositional data     

Phil Shane 《Bulletin of Volcanology》1998,60(3):224-238

Grain-specific analyses of Fe–Ti oxides and estimates of eruption temperature (T) and oxygen fugacity (fO₂) have been used to fingerprint rhyolitic fall and flow deposits that are important for tephrostratigraphic studies in and around the Taupo volcanic zone of North Island, New Zealand. The analysed Fe–Ti oxides commonly occur in the rims of orthopyroxene crystals and appear to reflect equilibrium immediately prior to eruption because of geochemical correlation with the co-existing glass phase. The composition of the spinel phase is particularly diagnostic of eruptive centre for post-65 ka events and can be used to distinguish many tephra beds from the same volcano. The 29 different units examined were erupted over a wide range in T (690–990°C) and Δ log fO₂ (–0.1 to 2.0). These parameters are closely related to the mafic mineral assemblage, with hydrous mineral-bearing units displaying higher fO₂. Such trends are superimposed on larger differences in fO₂ that are related to eruptive centre. At any given temperature, all post-65 ka Okataina centre tephra have higher fO₂ values than post-65 ka Taupo centre tephra. This provides a useful criterion for identifying the volcanic source. There are no temporal T and fO₂ trends in the tephra record; over intervals >20 ka, however, tephra sequences from Taupo centre form characteristic T-fO₂ buffer trends mirroring the glass chemistry. Individual eruptive events display uniform spinel and rhombohedral phase compositions and thus narrow ranges in T (± <20°C) and log fO₂ (± <0.5), allowing these features to identify individual magma batches. These criteria can help distinguish tephra deposits of similar bulk or glass composition that originated from the same volcano. Distal fall deposits record the same T-fO₂ conditions as the proximal ignimbrite and enable distal–proximal correlation. Lateral and vertical compositional and T-fO₂ variability displayed in large volume (>100 km³) ignimbrites, such as the Oruanui, Rotoiti and Ongatiti, is similar to that found in a single pumice clast and thus mainly reflects analytical error; however, thermal gradients of ca. 50°C may occur in some units. Received: 6 April 1998 / Accepted: 16 June 1998  相似文献   

Reply to Comments by S. Mishra and S. N. Rajaguru on “New Geochemical Evidence for the Youngest Toba Tuff in India”     

Phil Shane  John Westgate  Martin Williams  Ravi Korisettar 《Quaternary Research》1996,46(3):342-343

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Interval-valued random functions and the kriging of intervals   总被引：1，自引：0，他引：1  

Phil Diamond 《Mathematical Geology》1988,20(3):145-165

Estimation procedures using data that include some values known to lie within certain intervals are usually regarded as problems of constrained optimization. A different approach is used here. Intervals are treated as elements of a positive cone, obeying the arithmetic of interval analysis, and positive interval-valued random functions are discussed. A kriging formalism for interval-valued data is developed. It provides estimates that are themselves intervals. In this context, the condition that kriging weights be positive is seen to arise in a natural way. A numerical example is given, and the extension to universal kriging is sketched.  相似文献   

Submarine silicic volcanism of the Healy caldera,southern Kermadec arc (SW Pacific): I – volcanology and eruption mechanisms     

Ian C. Wright  John A. Gamble  Phil A. Shane 《Bulletin of Volcanology》2003,65(1):15-29

The submarine Healy volcano (southern Kermadec arc), with a 2-2.5 km wide caldera, is pervasively mantled with highly vesicular silicic pumice within a water depth of 1,150-1,800 m. Pumices comprise type 1 white-light grey pumice with ⢾ mm vesicles and weak-moderate foliation, type 2 grey pumice with millimetre-scale laminae, flow banded foliation, including stretched vesicles ⣗ mm in length, and a minor finely vesicular type 3 pumice. All types are sparsely porphyritic, with undevitrified glassy groundmass (68-70% SiO₂), which is microlite and lithic free. Coexisting pyroxenes yield magma temperatures of ~950 °C. Pumice density is А.5 g cm^-3 and vesicularity is 78-83%. Vesicle size distributions for types 1 and 2 pumice, range from ~20 µm to >20 mm, with a strong power-law relation (with d=-2.5ǂ.4) for vesicles <1-2 mm. Larger vesicles have variable size modes. The vesicle size distribution and packing indicates rapid magma decompression and ascent. Consideration of the pressure dependent, solubility of H₂O at a magma temperature of 𙧶 °C and water content of Ж wt%, with pumice petrography and vesicle granulometry, strongly suggests a pyroclastic eruption. Reconstructions of the submarine edifice between water depths of 1,000 and 550 m constrain the ambient hydrostatic pressure to ~6-9 MPa. Pressures >~9 MPa will limit vesicularity to less than the observed 78-83%, whereas pressure <~6 MPa require a more shallower reconstruction of the edifice and larger-volume syn-eruptive collapse. Uniformly high vesicularity is interpreted as evidence of insulation within an eruption column comprising steam and hot pyroclasts. Most pyroclasts cool, condensing and ingesting water into steam-inflated vesicles, and then sink. Progression into pyroclastic mode would expand the eruption column, displace ambient water, reduce the hydrostatic load, and further promote vesiculation and fragmentation. Pyroclasts within the column would quench at these reduced pressures. We argue that Healy eruptions deeper than ~1,000 m cannot be pyroclastic. Volumes for the lower and upper bounds of edifice size are 2.36 and 3.58 km³, respectively, but do not account for intra-caldera pumice fill. These volumes are considered to be predominantly primary eruption output, as shown by a dearth of accessory lithics in all pumice, yielding (at an average 81% vesicularity) eruptive pumice volumes of between 10 and 15 km³. Some pyroclasts may have risen to the sea surface and be a correlative of the sea-rafted Loisels pumice; the latter occurs in some New Zealand Holocene beach sequences and has a estimated age of 590ᇤ calendar years.  相似文献   

Late Neogene loess deposition in southern Tarim Basin: tectonic and palaeoenvironmental implications   总被引：2，自引：0，他引：2  

Hongbo Zheng  Chris McA Powell  Katherine Butcher  Junji Cao 《Tectonophysics》2003,375(1-4):49

Uplift of the Tibetan Plateau during the late Cainozoic resulted in a thick apron of molassic sediments along the northern piedmonts of the Kunlun and Altyn Mountains in the southern Tarim Basin. Early Neogene sediments are characterised by sandstone, siltstone and red mudstone, representing floodplain to distal alluvial fan environments. The Early Pliocene Artux Formation consists of medium-grained sandstone and sandy mudstone with thin layers of fine pebbly gritstone. The Late Pliocene to Early Pleistocene Xiyu Formation is dominated by pebble to boulder conglomerate typical of alluvial fan debris flow deposits. Sedimentological investigation, together with grain size and chemical analyses of siltstone bands intercalated with sandstone and conglomerate in the Xiyu and Artux Formations, point to an aeolian origin, suggesting desertic conditions in the Tarim Basin by the Early Pliocene. The onset of aeolian sedimentation in the southern Tarim Basin coincided with uplift of the northern Tibetan Plateau inferred from the lithofacies change from fine-grained mudstone and sandstone to coarse clasts. Tibetan Plateau uplift resulted in the shift of sedimentary environments northwards into the southern Tarim Basin, and could well have triggered the onset of full aridity in the Taklimakan region as a whole.  相似文献