Testing the preservation potential of early diagenetic dolomites as geochemical archives     

Mathias Mueller  Onyedika A. Igbokwe  Benjamin Walter  Chelsea L. Pederson  Sylvia Riechelmann  Detlev K. Richter  Richard Albert  Axel Gerdes  Dieter Buhl  Rolf D. Neuser  Giovanni Bertotti  Adrian Immenhauser 《Sedimentology》2020,67(2):849-881

Early marine diagenetic dolomite is a rather thermodynamically-stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post-depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ¹³C and δ¹⁸O isotopes, ⁸⁷Sr/⁸⁶Sr ratios, and U-Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike-slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric-preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto-Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high-grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late-stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 10⁸ or more years. Evidence for this preservation includes preserved Late Triassic seawater δ¹³C_DIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically-complex dolomite archives must be considered with caution.  相似文献   

Properties of dust source material and volcanic ash in Iceland     

Mary K. Butwin  Melissa A. Pfeffer  Sibylle von Löwis  Eivind W. N. Støren  Eniko Bali  Throstur Thorsteinsson 《Sedimentology》2020,67(6):3067-3087

The volcanic origin, primarily basaltic, of most of the surface material in Iceland influences its physical properties and appearance. Size distributions, shape analyses and melting experiments were made for surface material collected in high-erosion dust source areas and fresh volcanic ash deposits to determine whether they differ from one another and from dust from other major dust sources. The major differences found between Icelandic dust and dust from other major dust sources in the world, such as the Sahara, are in the particle shapes, lower density and darker colour. Icelandic dust particles greater than 20 μm retain volcanic morphological properties that are also found in fresh volcanic ash. Dust and fresh volcanic ash particles less than 20 μm are crystalline and blocky in nature, similar to the dust from other global source regions. The finer grained (<20 μm) Icelandic particles will have similar suspension and transport behaviours and be similarly hazardous to health and infrastructure as non-Icelandic dust. The coarser particles (>20 μm) will have different suspension and transport behaviours than other dusts due to the volcanic morphology. Icelandic surface material has between 5% and 30% glassy particles compared to fresh volcanic ash which has more than 50% glassy particles. Glassy particles were observed to melt at a lower temperature than the mineral grains; and, as a result, volcanic ash is found to be more threatening to aircraft engines than the typical dust from Iceland. Icelandic dust was observed to be blocky, or plate-like in the respirable size fraction, suggesting similar health hazards as dust from other regions.  相似文献   

Motions about a fixed point by hypergeometric functions: new non-complex analytical solutions and integration of the herpolhode     

Giovanni Mingari Scarpello  Daniele Ritelli 《Celestial Mechanics and Dynamical Astronomy》2018,130(6):42

The present study highlights the dynamics of a body moving about a fixed point and provides analytical closed form solutions. Firstly, for the symmetrical heavy body, that is the Lagrange–Poisson case, we compute the second (precession, \(\psi \)) and third (spin, \(\varphi \)) Euler angles in explicit and real form by means of multiple hypergeometric (Lauricella) functions. Secondly, releasing the weight assumption but adding the complication of the asymmetry, by means of elliptic integrals of third kind, we provide the precession angle \(\psi \) completing the treatment of the Euler–Poinsot case. Thirdly, by integrating the relevant differential equation, we reach the finite polar equation of a special motion trajectory named the herpolhode. Finally, we keep the symmetry of the first problem, but without weight, and take into account a viscous dissipation. The use of motion first integrals—adopted for the first two problems—is no longer practicable in this situation; therefore, the Euler equations, faced directly, are driving to particular occurrences of Bessel functions of order \(-\,1/2\).  相似文献   

Green infrastructure,green space,and sustainable urbanism: geography’s important role     

Lisa Benton-Short  Melissa Keeley  Jennifer Rowland 《Urban geography》2019,40(3):330-351

ABSTRACT

This paper is a broad review of green infrastructure theory and practice relative to urban sustainability and the space for geographers in these discussions. We use examples from various urban sustainability plans to highlight ways in which green infrastructure is being conceptualized and implemented. We explore how geography contributes research on green infrastructure as well as the emerging practices as seen within sustainability plans. We identify four areas in which geographers can influence both green infrastructure theory and practice: 1) scale; 2) mapping distribution; 3) sensitivity to place and locale; and 4) equity and access. We conclude that in these areas geographers have tremendous opportunity contribute more deliberately to sustainable urbanism.  相似文献   

Steeper biomass spectra of demersal fish communities after trawler exclusion in Sicily     

Sweeting  Christopher J.; Badalamenti  Fabio; D'Anna  Giovanni; Pipitone  Carlo; Polunin  N. V. C. 《ICES Journal of Marine Science》2009,66(1):195-202

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Coastal phytoplankton blooms in the Southern California Bight     

Hey-Jin Kim  Arthur J. Miller  John McGowan  Melissa L. Carter 《Progress in Oceanography》2009,82(2):137-147

Surface chlorophyll (CHL) measured at the Scripps Pier in the Southern California Bight (SCB) for 18 years (1983–2000) reveals that the spring bloom occurs with irregular timing and intensity each year, unlike sea-surface temperature (SST), which is dominated by a regular seasonal cycle. In the 1990s, the spring bloom occurred earlier in the year and with larger amplitudes compared to those of the 1980s. Seasonal anomalies of the Pier CHL have no significant correlation with local winds, local SST, or upwelling index, which implies that classical coastal upwelling is not directly responsible for driving chlorophyll variations in nearshore SCB.The annual mean Pier CHL exhibits an increasing trend, whereas the Pier SST has no evident concomitant trend during the CHL observation period. The interannual variation of the Pier CHL is not correlated with tropical El Niño or La Niña conditions over the entire observing period. However, the Pier CHL was significantly influenced by El Nino/Southern Oscillation during the 1997/1998 El Niño and 1998/1999 La Niña transition period. The Pier CHL is highly coherent at long periods (3–7 years) with nearby offshore in situ surface CHL at the CalCOFI (California Cooperative Fisheries Investigations) station 93.27.  相似文献   

Reconstructing pre-colonial oyster demographics in the Chesapeake Bay, USA     

Roger Mann  Juliana M. Harding  Melissa J. Southworth 《Estuarine, Coastal and Shelf Science》2009,85(2):217-222

Recent estimates of growth and mortality rates in extant Chesapeake Bay, USA oyster (Crassostrea virginica) populations are used to quantify changes in both population abundance (dN/dT) and shell accretion (dS/dT) associated with modern population demographics. The demographics of oyster populations that would be required to maintain reef accretion rates commensurate with sea level rise over geological time frames are examined using estimates of oyster longevity in pre-colonial (pre -1600) times combined with parallel estimates of pre-disease endemic mortality. The analysis demonstrates that modern populations, with their disease related, age-truncated demographics, are generally not capable of maintaining and building biogenic reefs through accretion. Estimates of filtration rates associated with Chesapeake Bay oyster populations prior to 1600 considerably underestimate actual benthic-pelagic coupling during that period. Pristine oyster populations would have supported water column turnover rates on the order of minutes to hours. Thus, the spatial footprint of oyster reefs was limited by available productivity in the estuary. Accretion rate calculations for pristine (pre-1600) oyster reefs describe the intimate relationship between benthic-pelagic coupling and the presence or absence of oyster reefs and the associated communities.  相似文献   

Model-based characterization of permeability damage control through inhibitor injection under parametric uncertainty     

Mahmudova  Ayisha  Borsi  Iacopo  Porta  Giovanni Michele 《Computational Geosciences》2022,26(5):1119-1134

Computational Geosciences - Damage in subsurface formations caused by mineral precipitation decreases the porosity and permeability, eventually reducing the production rate of wells in plants...  相似文献