Description Of Rocks Research Articles

Plutonic rocks of Western Fiordland, New Zealand: Field relations, geochemistry, correlation, and nomenclature

This paper provides a comprehensive description of the plutonic rocks of western Fiordland between Breaksea and Sutherland Sounds. The area is dominated by the Early Cretaceous Western Fiordland Orthogneiss (WFO), but also includes smaller bodies of Paleozoic and Cretaceous granitoid. Plutonic rocks of western Fiordland intrude metasediments of the Western Province, many of whose age and terrane affinities remain undefined. Paleozoic granitoids in western Fiordland include the Pandora Orthogneiss (c. 500 Ma) and widespread related sills within Paleozoic metasedimentary rocks; the All Round Pluton (c. 340 Ma); the Deas Cove Granite (c. 372 Ma); and possibly the Straight River Granite. The Pandora Orthogneiss is one of the oldest plutons yet found in the Median Batholith. Correlatives include the Jaquiery Granite Gneiss in central Fiordland and orthogneiss in Doubtful Sound. Plutonism of Ross/Delamarian age is therefore widespread in those parts of Fiordland where Cambrian or older Western Province metasedimentary rocks form basement. The All Round Pluton and Deas Cove Granite are correlatives of the S‐type Ridge and A/I‐type Foulwind Suites, respectively. The c. 125–116 Ma WFO includes at least seven major dioritic and monzodioritic plutons in western Fiordland, one in central Fiordland, and one in central Stewart Island. Plutons which compose the WFO are distinguished by differences in their age, petrography, structural and metamorphic histories, and geochemistry. The WFO in northern Fiordland and the correlative Walkers Pluton on Stewart Island were emplaced in the mid crust (4–9 kbar) at depths comparable with some Separation Point Suite plutons of similar age. WFO plutons in southern Fiordland were emplaced at greater depths (10–18 kbar). WFO plutons have been variably recrystallised to eclogite; omphacite‐, garnet‐, two‐pyroxene‐, and hornblende‐granulite; and hornblende‐amphibolite facies assemblages, reflecting different PTX conditions during metamorphism of each body. Some parts of the WFO remain undeformed and unmetamorphosed. Evidence of up to c. 6 kbar loading after emplacement is limited to WFO plutons in northern Fiordland and adjacent country rocks. Extensional ductile shear zones previously shown to locally separate the WFO from adjacent rocks are discontinuous later features, commonly localised along earlier intrusive contacts between WFO plutons and metasedimentary country rocks. They do not form a regionally extensive detachment between the upper and lower plates of a metamorphic core complex. The WFO has previously been included in the Separation Point Suite since both units share a high Sr/Y (HiSY) chemistry and were emplaced at broadly the same time. However, the WFO and Separation Point Suite have distinct chemistries. Separation Point Suite rocks generally contain greater Sr, Na, and Al, and have lower Sr/Rb ratios, rare earth element and Y contents, than WFO rocks with comparable amounts of SiO2. Many aspects of the WFO chemistry (aside from its HiSY character) are similar to that of the older Darran Suite rather than the Separation Point Suite. This may reflect a greater amount of partial melting during generation of the SiO2‐poor WFO than the SiO2‐rich Separation Point Suite. Alternatively it may indicate derivation of the WFO and Separation Point Suite from different sources, albeit at depths greater than those where residual plagioclase is stable. Relatively large variations in the major element chemistry of the Separation Point Suite reflect fractionation and/or accumulation of plagioclase, whereas the more limited variability in the major element chemistry of the WFO reflects minor fractionation and/or accumulation of hornblende and/or clinopyroxene.

Carbonatites in collisional settings and pseudo-carbonatites of the Early Paleozoic Ol’khon collisional system

Carbonatites associated with syenites and subalkalic mafic rocks (lamprophyres) occur in the Himalayan continental collision zone, and this suggests their possible existence in other Phanerozoic collisional settings. The Early Paleozoic Ol’khon collisional system in Western Cisbaikalia is considered one of the possible occurrences. Subalkalic gabbroids as well as peculiar carbonate (brucite marbles) and calc-silicate rocks were found here, within the Tazheran massif of alkalic and nepheline syenites. Alkalic syenites, nepheline syenites, and calciphyres were dated at 471 Ma, 451–464 Ma, and 466 Ma, respectively, and their ages correspond to the main collisional events in the system. A geochemical description of igneous and carbonate rocks in the massif is provided. Close mapping showed unusual syenite and brucite marble combinations and the frequent vein or pipe-like form of carbonates and calciphyres corresponding to their magmatic intrusion. But carbonatite nature of the marble mentioned above does not fit their typical crustal geochemical features. Not ruling out the possibility of total change of geochemical signatures of mantle carbonatite in the collisional medium, we offer two other possible explanations for these facts: (1) melting of carbonate masses by syenite and mafic magmas, followed by carbonate melt intrusion into the upper crust, and (2) protrusion of carbonates into syenites and gabbroids at the late stages of the contact action of a silicate magma. In this case the above-mentioned carbonate structural features result from late recrystallization, whose mechanism is yet to be explained.

An overview of depth imaging in exploration geophysics

Prestack depth migration is the most glamorous step of seismic processing because it transforms mere data into an image, and that image is considered to be an accurate structural description of the earth. Thus, our expectations of its accuracy, robustness, and reliability are high. Amazingly, seismic migration usually delivers. The past few decades have seen migration move from its heuristic roots to mathematically sound techniques that, using relatively few assumptions, render accurate pictures of the interior of the earth. Interestingly, the earth and the subjects we want to image inside it are varied enough that, so far, no single migration technique has dominated practical application. All techniques continually improve and borrow from each other, so one technique may never dominate. Despite the progress in structural imaging, we have not reached the point where seismic images provide quantitatively accurate descriptions of rocks and fluids. Nor have we attained the goal of using migration as part of a purely computational process to determine subsurface velocity. In areas where images have the highest quality, we might be nearing those goals, collectively called inversion. Where data are more challenging, the goals seem elusive. We describe the progress made in depth migration to the present and the most significant barriers to attaining its inversion goals in the future. We also conjecture on progress likely to be made in the years ahead and on challenges that migration might not be able to meet.

Word to the Wise: Felsic & Mafic

In the description of igneous rocks (see the article on pegmatites of Tanakamiyama, Japan, this issue), two commonly used terms are felsic and mafic. These are both used to indicate the chemical co...

Basement interpretations from airborne magnetic and gravity data over the Lambert Rift region of East Antarctica

Geological exposures in the Lambert Rift region of East Antarctica comprise scattered coastal outcrops and inland nunataks sporadically protruding through the Antarctic ice sheet from Prydz Bay to the southernmost end of the Prince Charles Mountains. This study utilized airborne magnetic, gravity, and ice radar data to interpret the distribution and architecture of tectonic terranes that are largely buried beneath the thick ice sheet. Free‐air and Bouguer gravity data are highly influenced by the subice and mantle topography, respectively. Gravity stripping facilitated the removal of the effect of ice and Moho, and the residual gravity data set thus obtained for the intermediate crustal level allowed a direct comparison with magnetic data. Interpretation of geophysical data also provided insight into the distribution and geometry of four tectonic blocks: namely, the Vestfold, Beaver, Mawson, and Gamburtsev domains. These tectonic domains are supported by surface observations such as rock descriptions, isotopic data sets, and structural mapping.

O Monte das Ferraduras (Fentáns, Cotobade): novos achádegos de arte rupestre. Descripción e interpretación

In these lines we present the description and interpretation of a new rock engraving found in O Monte das Ferraduras (Fentans, Galiza). This finding, was the result of an intensive exploration in the area, the most outstanding of this panel is one possible representation of a “rossa camuna” design unknown in the northwest of the Iberian Peninsula. We think therefore, this is singular finding deserve an analisys about parallels found in Western Europe, it will help us to understand the chronological contexts of this panel.

Rocks of Mohave County, Arizona: An Educational Landscape Display

The creation of an educational geologic display at the Lake Havasu City campus of Mohave Community College was accomplished by collecting boulder-sized specimens of representative rock types that occur within the boundaries of Mohave County, Arizona. The intent of the display is to offer students something more comprehensive than hand specimens, to inform residents and visitors of the county's geologic diversity and history as well as to provide curriculum opportunities for K-14 in geology. Forty-nine boulders typifying rock types of the Basin and Range, the Colorado Plateau, and the Colorado River extensional corridor are labeled with a rock description and a map of the collection locality. An informative geologic timeline incorporated with the Colorado Plateau display and more in-depth information on the college's science website provide students and citizens with a good introduction to various concepts in geology. These components, accompanied by biological, environmental, and meteorological campus displays and by similar information on the website, are part of a growing program to promote natural science within the county.

Intrinsic Length Scales in Tool-Rock Interaction

Indentation and cutting experiments in rocks reveal that the action of a tool can induce either ductile and/or brittle failure, with the ductile mode associated with damage of the rock and/or plastic flow, and the brittle mode with the propagation of cracks. In normal indentation, the development of a damaged zone precedes the initiation of tensile cracks; in cutting, the failure mechanism switches from a ductile to a brittle mode as the depth of cut is increased beyond a threshold value. In this paper, we first argue that these observations can be accounted for by introducing an intrinsic length scale lm ∼ ( KIc ∕ σc )2 in the rock description (with KIc denoting the toughness and σc the compressive strength). Next, we report the results of numerical simulation of indentation and cutting tests with the discrete element method. After showing that the internal length scale lm can be modified by the ratio of the shear to normal bond strength, we illustrate by numerical simulations that the selection of the f...

W. Schlager 2005. Carbonate Sedimentology and Sequence Stratigraphy. SEPM Concepts in Sedimentology and Paleontology Series no. 8. viii + 200 pp. Tulsa: SEPM. Price US $55.00 (members); US $77.00 (non-members); hard covers. ISBN 1 56576 116 2.

W. Schlager 2005. Carbonate Sedimentology and Sequence Stratigraphy. SEPM Concepts in Sedimentology and Paleontology Series no. 8. viii + 200 pp. Tulsa: SEPM. Price US 77.00 (non-members); hard covers. ISBN 1 56576 116 2. - Volume 145 Issue 1

A complex investigation of building sandstones from Saxony (Germany)

The present paper provides a methodology for the investigation and characterization of building sandstones. This analytical scheme was designed for distinguishing mature arenites, which in general show very similar properties and are difficult to distinguish. This is shown for Cretaceous sandstones from various occurrences in Saxony (Germany), which have been used for centuries as building materials. The procedure is mainly based on the combination of macroscopic rock description, thin section polarizing microscopy (phase composition, texture, grain-size distribution) and cathodoluminescence (CL) microscopy (quartz types, feldspar and kaolinite content) coupled with image analysis, scanning electron microscopy (accessories, pore cement, diagenetic grain surface features), and analysis of pore space data. Sometimes, additional data from X-ray diffraction or chemical analyses (major and trace elements) can be used. Especially in the case of quartz rich arenites, CL is a powerful tool for provenance analysis. The detailed analysis of sandstone material in most cases allows us to assign historically used building material to a specific sandstone occurrence. These results are important for both interpreting the weathering behaviour of the building material and the conservation, reconstruction and stone replacement of historical monuments.

The Dubrava massif of pyroxenites, alkaline rocks, and carbonatites

The Dubrava massif, composed of pyroxenites, alkaline rocks, and carbonatites, was found in 1961 in northern Kazakhstan and is described for the first time in this paper. A geological map of the deposit was compiled taking into account the results of exploration drilling and magnetic survey on a scale of 1: 10 000. A petrographic description of rocks and their petrochemical characteristics are given. Magmatic carbonatites and metasomatic calcitic rocks are identified on the basis of ICP MS results. The carbonatites are characterized by subeconomic concentrations of Zr, Nb, Ta, and REE and very low U and Th contents. Carbonatites with a high P2O5 grade and metasomatic glimmerites with high contents of rare elements might become of economic interest in the future.

Development of a hydrogeological model description of intrusive rock at different investigation scales: an example from south-eastern Sweden

Site investigations at Oskarshamn, south-eastern Sweden, to determine a suitable repository for spent nuclear fuel, are dependent on hydrogeological modelling, and one part of the modelling rests upon a deformation zone model. One main objective of the investigations, to locate and characterize major and minor deformation zones in the Simpevarp and Laxemar areas, has been largely met with the use of remote sensing and ground geophysics data. Most major deformation zones in the bedrock were initially identified as lineaments using digital elevation models and helicopter-borne geophysics data. Supplementary information was received from a light detection and ranging (LIDAR) survey and dense ground geophysics surveys, providing data also for minor deformation zones. However, surface investigations are needed to explore and confirm the geological and hydrogeological character of the lineaments identified by remote sensing to indicate that a lineament probably represents a deformation zone. The approach, involving two- and three-dimensional planar models to create a site descriptive model of geology and hydrogeology, may be suitable for other parts of the world with a similar geological environment of crystalline bedrock.

Baltazar Hacquet (1739/40-1815), the Pioneer of Karst Geomorphologists

Besides other sciences, B. Hacquet dedicated his research to geology and geomorphology (as we call them now). His most important work “Oryctographia carniolica or Physical (= geological) description of Carniola...” (1778−1789) contains descriptions of rocks, ores, fossils, as well as surface and underground features. In Carniola, karst is prevailing and therefore there is a lengthy description of karst geology and geomorphology included. His classification of mountains specially mentions Montes secundarii formed by grey limestone. Of surface features dolines, glacio-karstic dolines on high plateaus (with temperature and vegetation inversion), and karst poljes are mentioned. Hacquet presumed the evolution from flooded polje (seasonal lake) to a dry one. To explain the weathering and dissolution of limestone Hacquet took into account the differences between the rock, the exposition and its element content. That is the reason why Gams regarded him as a precursor of a climatic geomorphology and the “father” of corrosion theory. Hacquet has also found the difference between limestone and dolomite. His description of dolomite as Lapis suillus preceded the one of D. Dolomieu for 13 years. Hacquet’s statements were not based on observation only, but on the experiment too. When looking upon Hacquet’s explanations and results we must not forget that Hacquet’s time was still time of parapathetic logic, of four elements and of the principle of burning - the flogiston.

Rock/Fluid Characterization and Their Integration—Implications on Reservoir Management

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing recent developments for readers who are not specialists in the topics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and present specific details only to illustrate the technology. Purpose: to inform the general readership of recent advances in various areas of petroleum engineering. Abstract The flow performance of hydrocarbon reservoirs is controlled largely by rock and fluid properties, their variation, and rock/fluid interactions. In this paper, we highlight the rock- and fluid-data needs for various production processes with an emphasis on quality control (QC) and efficient data management. We stress the need for an integrated and a multidisciplinary approach to rock and fluid characterization to minimize measurement uncertainty. Such an approach will ensure reliable rock and fluid data that are required for the determination of accurate volumes in place, reliable recovery factors, and realistic development plans, thus minimizing technical risks and maximizing the economic value of the hydrocarbon assets. Also discussed are the effects of uncertainties in rock and fluid properties on reservoir-performance prediction. The importance of reservoir surveillance through periodic coring, fluid sampling, and testing as well as reservoir simulation for data validation and refinement is further emphasized. Finally, worldwide field examples of sandstone and carbonate reservoirs containing black oil, volatile oil, and gas/condensates are presented to highlight these points. Introduction The performance of hydrocarbon reservoirs is controlled largely by the rock and fluid properties, their spatial and temporal variations, and rock/fluid interactions (Al-Hussainy and Humphreys 1996). High-quality rock and fluid data are critical for reliable geological modeling, reservoir-engineering calculations, and performance predictions by use of reservoir simulators and for subsequent economic analysis. Many pressure-maintenance and secondary- and tertiary-recovery projects have failed because of inadequate geologic description and lack of reliable rock and fluid data. In the absence of good-quality data in adequate quantity, simulation models with multimillion gridblocks, and sophisticated scaleup methodology, do not add any economic value to the resource. In short, the value of rock and fluid data lies in their potential to guide the selection of the most suitable recovery process and its effect on project economics. Rock characterization involves quantification of porosity, permeability, capillary pressure, and relative permeability associated with various recovery processes. Similarly, fluid characterization quantifies the reservoir phase behavior, fluid compositional changes throughout the reservoir, and changes in fluid properties as a result of production and injection processes. The process of data gathering begins with exploration and continues through the life of the reservoir.

Mobile GIS in Geologic Mapping Exercises

We have been developing and teaching the components of mobile GIS in Field Methods courses and will be incorporating them into Structural Geology exercises. Since the bedrock in east central Indiana is topographically invariant, non-inclined, and often not exposed, we have developed a new introductory GIS project that simulates structural features. It utilizes inclined, one-foot square planes that are placed upon a series of pedestals stationed in an open area, each accompanied by a petrographic hand sample and an age label. An introductory one-hour session is held in the field to teach acquiring GIS data. Then the students independently acquire geologic data such as GPS-located “outcrop” locations, rock descriptions, and strike/dip, and enter the geologic data on a base map using Mobile GIS software (ArcPad). In a two-hour follow-up class students learn to add their field data to a map in the PC-based GIS program ArcMap. Strike/dip symbols are computer-generated and displayed at the GPS coordinates taken in the field. This exercise supports spatial organization with data availability of Mobile GIS in the field and prepares students for GIS-based mapping projects in our Field Camp in Wyoming.

Probabilistic integration of geologic scenarios, seismic, and production data—a West Africa turbidite reservoir case study

From reservoir exploration to field abandonment, reservoir modeling plays a central role in understanding and predicting the reservoir key geologic, geophysical, and engineering components. Reservoir models, either as a simple layer cake or as a complex, fully 3D description of structural components, rock and fluid properties, are ideal gateways for aggregating data and expertise from different sources and disciplines. The complexity of such models should be driven by the practical reservoir management question raised, be it the estimation of OOIP (reserve question) or the development and planning of wells/surface facilities and recovery strategies (flow question). At the same time, the limitation of reservoir models should be well understood: reservoir models can only mimic the reservoir's true complexity; they can never fully (nor need they) represent the actual subsurface heterogeneity.

Stereographic Projection Techniques for Geologists and Civil Engineers, Second Edition: (Richard J. Lisle and Peter R. Leyshon)

It is likely that many readers of this journal learned to use stereographic projection in the geometric description of rocks, their structural elements, and their discontinuities from Hoek and Bray's Rock Slope Engineering (1981) or from a textbook on structural geology. More recent texts on rock mechanics (e.g., Goodman's Introduction to Rock Mechanics, 1989; or Brady and Brown's Rock Mechanics for Underground Mining, 1993; or Wyllie's Foundations on Rock , 1999) contain detailed reviews of this aspect of structural geology in the early pages of their textbooks. Therefore, we can conclude that the use of stereonets is of importance in geological engineering practice and, by inference, to the education and training of engineering geologists, as well as those hydrogeologists whose work involves the analysis of fractures in rocks. Lisle and …

Special purpose mapping for waste disposal sites

This report results from work that was first proposed to a meeting of the International Association of Engineering Geology (IAEG), Commission No.1 held in Bratislava (Slovakia) in 1992. Following the publication of the Commission’s report on Engineering Geological Maps (Engineering geological maps (1976) and reports on the description and classification of rock and soil and on recommended symbols for engineering geological mapping (Bull. Int. Assoc. Eng. Geol. 24 (1981) 235; see also 227), a period of consolidation ensued in which the approaches suggested in those reports were implemented. The decision to prepare an additional report reflected the increasing need to apply these approaches to a range of specific activities. The background to the report was provided in a paper by two of the authors presented at the IAEG conference in Athens in 1997 (Proc Int. Symp. Int. Assoc. Eng. Geol. Environ. 2 (1997) 2103).

The challenges of observing geologically: Third graders' descriptions of rock and mineral properties

The understandings of properties that children develop in the context of rock and mineral identification point to the challenges of observing in a manner authentic to the discipline of geology. The notebook entries of 34 third graders written during the enactment of a commercial unit on earth materials were investigated for their descriptions of rocks and minerals, and the extent to which these reflect understandings of properties in both generic and discipline-specific senses. While children were successful in observing minute details of rock and mineral samples, there were few opportunities within the curriculum for students to differentiate between geologically relevant and irrelevant properties, and there were no connections drawn between deeper geological concepts and these observations. In addition, the demands placed on young learners to write their observations in the form of descriptions raise issues of supporting students in their learning of authentic scientific writing. There are challenges faced in representing geological observation authentically, and moving children beyond simple description activities into more complex explanations. Suggestions for improvements that attend to issues of the discipline as well as the elementary context are provided. © 2005 Wiley Periodicals, Inc. Sci Ed 89:276–295, 2005

Maximum flooding or maximum starvation? Exploring the development of the maximum flooding surface in carbonate systems with multi-valued logic

Since the mid 20th century, one of the best horizons for stratigraphic correlations in clastic and carbonate systems has been what is now commonly identified as the “maximum flooding surface". However, various definitions for the term “maximum flooding surface" have appeared over the years, calling on a range of sedimentary processes to form the surface depending on the depositional system. Disagreement over the definition of the maximum flooding surface is largely due to ambiguous characteristics, assorted identification techniques and conflicting genetic interpretations. Multi-valued logic (or fuzzy logic) methods can be used to address some of these problems of uncertainty. This paper discusses how the multi-valued logic methods of “fuzzy classifier design" and “fuzzy inference systems" are used to manage subjectivity in carbonate sequence stratigraphic models. Multi-valued logic methods are used to 1) quantify sedimentary characteristics through fuzzy classifier design to elucidate subjective identification and to facilitate repeated recognition of the maximum flooding surface in rock descriptions and to 2) develop a fuzzy inference system to model the development of the surface. The fuzzy inference system argues that in carbonate systems the time of maximum sediment starvation and maximum water depth are discrete events. The surface of maximum starvation is recorded as a nearly synchronous horizon associated with the maximum rate of sea level rise, whereas the maximum bathymetric event is highly diachronous due to the interplay of rates of sediment accumulation and accommodation space.