Effects of groundwater flow on mineral diagenesis, with emphasis on carbonate aquifers

 This article provides a critical synopsis of the effects of groundwater flow on mineral diagenesis. Emphasis is placed on those aspects and processes that change porosity and permeability in carbonate aquifers, because they are of particular importance to human societies as sources of supplies of water for human consumption (drinking, irrigation) and of crude oil and natural gas. Diagenetic settings in carbonates as well as clastics are generally ill defined. This paper proposes a new comprehensive classification of diagenetic settings into near-surface, shallow-, intermediate-, and deep-burial diagenetic settings; hydrocarbon-contaminated plumes; and fractures. These settings are defined on the basis of mineralogy, petroleum, hydrogeochemistry, and hydrogeology. This classification is applicable to all sedimentary basins. Diagenesis is governed by various intrinsic and extrinsic factors that include thermodynamic and kinetic constraints, as well as microstructural factors that may override the others. These factors govern diagenetic processes, such as dissolution, compaction, recrystallization, replacement, and sulfate–hydrocarbon redox-reactions. Processes such as cementation, dissolution, and dolomitization require significant flow of groundwater driven by an externally imposed hydraulic gradient. Other processes, such as stylolitization and thermochemical sulfate reduction, commonly take place without significant groundwater flow in hydrologically nearly or completely stagnant systems that are geochemically "closed." Two major effects of groundwater flow on mineral diagenesis are enhancement and reduction of porosity and permeability, although groundwater flow can also leave these rock properties essentially unchanged. In extreme cases, an aquifer or hydrocarbon reservoir rock can have highly enhanced porosity and permeability due to extensive mineral dissolution, or it can be plugged up due to extensive mineral precipitation. Received, April 1998 · Revised, July 1998 · Accepted, September 1998     

Coeval argon‐40/argon‐39 ages of moldavites from the Bohemian and Lusatian strewn fields

Abstract— ⁴⁰Ar/³⁹Ar ages of four tektites (moldavites) from southern Bohemia (near ?eské Budějovice, Czech Republic) and a tektite from Lusatia (near Dresden, Germany) have been determined by 11 step‐degassing experiments. The purpose of the study was to enlarge the ⁴⁰Ar/³⁹Ar data base of moldavites and to check the age relations of the Bohemian and Lusatian samples. The mean plateau‐age of the Bohemian samples, which range from 14.42 to 14.70 Ma, is 14.50 ± 0.16 (0.42) (2σ) Ma (errors in parentheses include age error and uncertainty of standard monitor age). The plateau age of the Lusatian sample of 14.38 ± 0.26 (0.44) (2σ) Ma confirms the previously published ⁴⁰Ar/³⁹Ar age of 14.52 ± 0.08 (0.40) (2σ) Ma, and demonstrates that the fall of Lusatian and Bohemian tektites were contemporaneous. Because of their geochemistry and their ages there is no doubt that the Lusatian tektites are moldavites. Accepting that moldavites are ejecta from the Nördlinger Ries impact, the new ages also date the impact event. This age is slightly younger (about 0.2–0.3 Ma) than the age suggested by earlier K‐Ar determinations.     

Über die DÜnung aus einem Windfeld,welches am Beobachtungsort in einiger Entfernung vorbeizieht

Zusammenfassung Es werden die zum Teil recht verwickelten Bedingungen besprochen, denen eine am festen BeobachtungsortA auftretende DÜnung genÜgt, wenn das wellenerzeugende Windfeld sich dem PunktA wohl nähert, an ihm dann aber in einiger Entfernung vorbeizieht. Es werden getrennt behandelt: 1. wandernde Windfelder, welche seit langer Zeit eine ausgereifte Windsee besitzen, 2. wandernde Windfelder, deren Ausbildung erst kÜrzere Zeit zurÜckliegt.An geeigneter Stelle wird ein Diagramm gegeben, welches die Bestimmung der angular spreading factors (W. J. Pierson jun., G. Neumann und R. W. James [1953]) wesentlich erleichtert.Abschließend wird die Frage erörtert, ob ein Punkt am Rande des Windfeldes den gesamten Windfeld-Leerand ausreichend repräsentieren kann.

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On swell generated by a fetch passing at some distance from the observation point

Summary The paper treats the rather complex conditions that may lead to the occurrence of swell at a fixed observation pointA when the wave generating fetch though approaching pointA passes it at some distance. Two contingencies are separately discussed: 1) moving fetches associated for a long time past with a fully developed wind sea, 2) moving fetches whose generation took place only quite recently.The paper includes a diagram which largely facilitates the determination of the angular spreading factor (W. J. Pierson jun., G. Neumann, and R. W. James [1953]).In the end, the question is discussed whether one point on the border of the fetch may be regarded as being sufficiently representative of the entire lee-side of the fetch.

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Sur une houle soulevée par un »fetch« qui passe le point d'observation à quelque distance

Résumé Ce travail traite les conditions assez complexes qui peuvent conduire à l'apparition de houles à un point fixe d'observationA si le »fetch« qui a soulevé les vagues en question s'approche de ce point mais finit par le passer à quelque distance. On discute deux éventualités: 1) des »fetches« progressifs dont les vagues de vent on depuis longtemps terminé leur developpement, 2) des »fetches« progressifs qui n'ont accompli leur formation que depuis peu.On a introduit dans le travail un diagramme qui rend beaucoup plus facile la détermination des facteurs d'extension angulaire (»angular spreading factors«) (W. J. Pierson, jun., G. Neumann et R. W. James [1953]).Enfin, on discute la question si un seul point sur le bord du »fetch« peut suffisamment représenter les conditions dominant sur tout le bord sous le vent.

     

Paleomagnetism of red beds of Early Devonian age from Central Iran

Paleomagnetic results are reported from 13 sites of red beds of Early Devonian age from Central Iran. Detailed paleomagnetic analyses were carried out. Two types of partial progressive demagnetization were applied, one using alternating magnetic fields, the other heating. These procedures resulted in the detection of the characteristic remanences with a mean direction with D = 24.2°, I = 1.3° (α₉₅ = 10.1°). The paleomagnetic pole is located at 51.3°N, 163.7°W. If one shifts the Iranian landmass to its most likely position in the Gondwana configuration, then the position of the paleomagnetic pole coincides with the alternative polar wander path [14,15] which crossed South America in early Middle Paleozoic times.     

Environmental Factors Contributing to the Development and Demise of a Toxic Dinoflagellate (<Emphasis Type="Italic">Karlodinium veneficum</Emphasis>) Bloom in a Shallow,Eutrophic, Lagoonal Estuary

A dense bloom of the ichthyotoxic dinoflagellate Karlodinium veneficum was discovered in the Neuse River Estuary, North Carolina, on 19 October 2006 and was associated with four subsequent fish kills. Microscopic, photopigment, DNA, and toxicological techniques confirmed bloom identity and toxicity. High-resolution spatio-temporal data from ship-board and fixed automated sampling stations provided a unique opportunity to investigate the environmental conditions that initiated, maintained, and terminated the K. veneficum bloom. Bloom initiation and growth were favored by high nutrient availability and reduced dispersal during the period of declining riverine discharge after Tropical Storm Ernesto. K. veneficum out-competed other co-occurring dinoflagellates, perhaps because of the production of karlotoxins that are known to act as grazing deterrents and to facilitate mixotrophic feeding. Once the bloom was established, small-scale hydrodynamic processes, coupled with vertical migration, concentrated cells along a frontal convergence to high densities (>200,000 cells per milliliter). By 26 October 2006, wind mixing and possible nutrient stress disrupted the bloom. Release of cell-bound toxins during the bloom collapse likely accounted for the associated fish kill events where fish were reported as exhibiting typical symptoms of karlotoxin poisoning. The dynamics of this bloom underscore the tight control of harmful algal blooms by meteorological forcing, hydrology, and sediment nutrient input in this shallow lagoonal estuary.     

The future of the western Baltic Sea: two possible scenarios

Globally coupled climate models are generally capable of reproducing the observed trends in the globally averaged atmospheric temperature. However, the global models do not perform as well on regional scales. Here, we present results from four 100-year, high-resolution ocean model experiments (resolution less than 1 km) for the western Baltic Sea. The forcing is taken from a regional atmospheric model and a regional ocean model, imbedded into two global greenhouse gas emission scenarios, A1B and B1, for the period of 2000 to 2100 with each two realisations. Two control runs from 1960 to 2000 are used for validation. For both scenarios, the results show a warming with an increase of 0.5–2.5 K at the sea surface and 0.7–2.8 K below 40 m. The simulations further indicate a decrease in salinity by 1.5–2 practical salinity units. The increase in water temperature leads to a prolongation of heat waves based on present-day thresholds. This amounts to a doubling or even tripling of the heat wave duration. The simulations show a decrease in inflow events (barotropic/baroclinic), which will affect the deepwater generation and ventilation of the central Baltic Sea. The high spatial resolution allows us to diagnose the inflow events and the mechanism that will cause future changes. The reduction in barotropic inflow events correlates well with the increase in westerly winds. The changes in the baroclinic inflows can be consistently explained by the reduction of calm wind periods and thus a weakening of the necessary stratification in the western Baltic Sea and the Danish Straits.     

Tectonic relation between northeastern China and the Korean peninsula revealed by interpretation of GRACE satellite gravity data

The major continental blocks in northeastern Asia are the North China block and the South China block, which have collided starting from the Korean peninsula. Geologic and geophysical interpretations reveal a well defined suture zone in northeastern China from Qinling through Dabie to Jiaodong. The discovery of high-pressure metamorphic rocks in the Hongseong area of the Korean peninsula, prominent evidence for the collision zone, indicates extension of the collision zone in northeastern China into the Korean peninsula. Interpretation of the GRACE satellite gravity dataset shows two prominent structural boundaries in the Yellow Sea. One extends from the Jiaodong Belt in eastern China to the Imjingang Belt in the Korean peninsula. The other extends from near Nanjing, eastern China, to Hongseong. Tectonic movement in or near the suture zone may be responsible for seismic activity in the western Korean peninsula and the development of the Yellow Sea sedimentary basin.     

Econometric analysis to differentiate effects of various ship safety inspections

This article provides a refined technique to measure and interpret variables associated with the quality of an inspection—be it port state control or vetting inspections towards the probability of a very serious, serious or less serious casualty. It concentrates on filtering out the effect of variables such as detention, the port state control regime that inspected the vessel, time in-between inspections, deficiencies found during an inspection and the effect of vetting inspections. The consensus amongst policy makers in the shipping industry is that data cannot be combined to target vessels. While this article does demonstrate that the decrease in the probability of casualty is stronger for the South American Region, the Indian Ocean Region and Australia versus North Europe, North America or the Caribbean, it also demonstrates that the data can be combined to target vessels for inspections. Since the time in-between inspections and detention is mostly not significant towards decreasing the probability of casualty, these results reflect the lack of coordination amongst port state control regimes and industry inspections. Due to this lack of coordination and trust, a ship might be inspected in several regimes during a relative short time period where the benefit of an inspection can be easily saturated. Our recommendation on direct policy implication is to promote the harmonization of inspection databases across port state control regimes, preferably with the coordination of the development of the Global Integrated Ship Information System (GISIS) of the International Maritime Organization (IMO), to review the policy of a release of a vessel from detention and to increase cooperation amongst regimes with respect to the follow up of the rectification of deficiencies.     

An island arc origin for the Canyon Mountain ophiolite complex,eastern Oregon,U.S.A.

The Canyon Mountain ophiolite, Oregon, is exceptional in lacking sheeted dikes, basaltic pillow lavas, and sediments that are characteristic of many other ophiolites. Instead, the uppermost portion of the complex consists of a significant volume of plagiogranites, which, in addition to minor basalts, intrude a large section of keratophyres believed to be of volcanic origin. The trend of intrusive rocks and of bedding in the keratophyres is mostly parallel to layering in the underlying gabbroic cumulates and to contacts between units in the remainder of the ophiolite. It is suggested that the plagiogranites, basalts, and keratophyres comprise a sill complex. Both the plagiogranites and the keratophyres are similar, respectively, to low-K₂O plutonic and extrusive rocks of island arcs. The mineralogy and penetrative deformation structures of the ultramafic and some of the gabbroic rocks of the ophiolite indicate greater depth of formation, related to magmatism and diapirism above a Benioff zone. Radiometric age dates of plagiogranites confine the minimum age of the complex to the Early Permian. The Canyon Mountain ophiolite may thus be correlative with other fragments of a Lower Permian arc terrane throughout northeastern Oregon which were chaotically mixed during renewed subduction in middle to late Triassic time.