Zoogeography of marine Bryozoa around South Africa     

MK Boonzaaier-Davids  WK Florence  MJ Gibbons 《African Journal of Marine Science》2020,42(2):185-198

The zoogeography of marine Bryozoa around South Africa was investigated using published distribution records, museum catalogues, and an examination of previously unworked bryozoan material in (mostly) museum collections. Although a total of 276 valid species are recognised, it was not possible to unambiguously assess geographic patterns of diversity. At all depth zones examined (shore and inner-shelf, 0–30 m; mid- and outer-shelf, 31–350 m; bathyal, >500 m), there was a clear geographic structure to communities that mirrored established regional patterns of biogeography. Too few samples were collected from the shelf edge (351–500 m) and they were consequently excluded from zoogeographic analysis. Communities on the shore and inner-shelf and on the mid- and outer-shelf were more similar to each other than they were to bathyal communities, and the pronounced structure in bathyal communities suggests heterogeneity in the deep sea around South Africa.  相似文献   

High-resolution observations of the near-infrared emission from NGC 6822 Hubble V     

Sungho Lee  Soojong Pak  Sang-Gak Lee  Christopher J. Davis  Michael J. Kaufman  Kenji Mochizuki  Daniel T. Jaffe 《Monthly notices of the Royal Astronomical Society》2005,361(4):1273-1280

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The removal rates of²³⁴Th and²²⁸Th from waters of the New York Bight     

Aaron Kaufman  Yuan-Hui Li  Karl K. Turekian 《Earth and Planetary Science Letters》1981,54(3):385-392

The mean residence time (τ) of thorium with respect to non-radioactive removal from water was determined as a function of location in three traverses of the New York Bight using both²³⁴Th/²³⁸U and²²⁸Th/²²⁸Ra. τ correlates well with salinity increasing from about ten days near shore to 70 days at the shelf break. It shows a much weaker correlation with suspended matter concentrations both because suspended matter varies in its scavenging efficiency and because salinity is a longer-term integrator of scavenging potential.τ's computed from²²⁸Th/²²⁸Ra were often higher than those computed from²³⁴Th/²³⁸U either because of the detrital matter present as reflected in the²³²Th concentrations or because the water parcels had recently arrived from environments of lower scavenging efficiency.Anomalous isotopic concentrations found in three adjacent samples can best be explained as the result of an episodic release of²²⁸Ra from bottom sediments at a rate 200 times the normal one.  相似文献   

Near east paleomagnetic secular variation recorded in sediments from the Sea of Galilee (Lake Kinneret)     

R. Thompson  G.M. Turner  M. Stiller  A. Kaufman 《Quaternary Research》1985,23(2):175-188

Paleomagnetic records of declination and inclination from sediments recovered from the bed of Lake Kinneret (32.4°N, 35.7°E) have been dated by radiocarbon techniques. The sediments span the last 5000 yr. The changes in inclination down the sediment cores are more pronounced than the declination fluctuations and are repeatable between the three coring sites, which are several kilometers apart. Magnetic susceptibility logs display 13 maxima in the 5-m-long sequences, with a pronounced susceptibility minimum about 1000 yr B.P. Many of the susceptibility maxima and minima can be easily correlated between coring sites and are shown to be dominantly related to changes in sediment carbonate content. The natural remanent magnetization intensity follows a similar pattern to that of susceptibility, and the natural remanence of the Kinneret sediments is presumed to reside in detrital magnetite grains carried into the lake by the river Jordan from the basalt-rich bedrock of the rift floor and the Golan Heights. The ¹⁴C chronology is strongly supported by a pollen study in which pronounced changes in the proportion of olive pollen were interpreted as being due to extensive cultivation of olives around Galilee in the Hellenistic and Byzantine periods. The Kinneret paleosecular variation records, if accurately dated, point to a complex spatial pattern of Holocene secular variation with significant variations over distances as small as 1000–2000 km.  相似文献   

Chemostratigraphy of Paleoproterozoic carbonate successions of the Wyoming Craton: tectonic forcing of biogeochemical change?     

A. Bekker  J. A. Karhu  K. A. Eriksson  A. J. Kaufman 《Precambrian Research》2003,120(3-4):279-325

The Archean Wyoming Craton is flanked on the south and east by belts of Paleoproterozoic supracrustal successions whose correlation is complicated by lack of geochronologic constraints and continuous outcrop. However, carbonate units in these successions may be correlated by integrating carbon isotope stratigraphy with lithostratigraphy. The 10 km thick Paleoproterozoic Snowy Pass Supergroup in the Medicine Bow Mountains was deposited on the present-day southern flank of the Wyoming Craton; it contains three discrete levels of glacial diamictite correlative with those in the Huronian Supergroup, on the southern margin of the Superior Craton. The Nash Fork Formation of the upper Snowy Pass Supergroup is significantly younger than the uppermost diamictite and was deposited after the end of the Paleoproterozoic glacial epoch. Carbonates at the base of the Nash Fork Formation record remarkable ¹³C-enrichment, up to +28‰ (V-PDB), whereas those from overlying members of the lower Nash Fork Formation have δ¹³C values between +6 and +8‰. Carbonates from the upper Nash Fork Formation above the carbonaceous shale have carbon isotope values ranging between 0 and +2.5‰. The transition from high carbon isotope values to those near 0‰ in the Nash Fork Formation is similar to that at the end of the ca. 2.2–2.1 Ga carbon isotope excursion in Fennoscandia. This chemostratigraphic trend and deposition of BIFs, Mn-rich lithologies, carbonaceous shales and phosphorites at the end of the global ca. 2.2–2.1 Ga carbon isotope excursion are likely related to ocean overturn associated with the final breakup of the Kenorland supercontinent. Correlative carbonates from the Slaughterhouse Formation in the Sierra Madre, WY, and from the Whalen Group in the Rawhide Creek area in the Hartville Uplift, WY, have highly positive carbon isotope values. In contrast, carbonates from other exposures of the Whalen Group in the Hartville Uplift and all carbonate units in the Black Hills, SD, have carbon isotope values close to 0‰. Combined with existing geochronologic and stratigraphic constraints, these data suggest that the Slaughterhouse Formation and the succession exposed in the Rawhide Creek area of the Hartville Uplift are correlative with the lower and middle Nash Fork Formation and were deposited during the ca. 2.2–2.1 Ga carbon isotope excursion. The Estes and Roberts Draw formations in the Black Hills and carbonates from other exposures in the Hartville Uplift postdate the ca. 2.2–2.1 Ga positive carbon isotope excursion and are most likely correlative with the upper Nash Fork Formation. The passive margin, on which the carbonates with highly positive carbon isotope values were deposited, extended around the southern flank of the Wyoming Craton through the Sierra Madre, Medicine Bow Mountains and Hartville Uplift. The presence of carbonates with carbon isotope values close to 0‰ in the upper Nash Fork Formation and the Whalen Group indicates that the passive margin persisted on the southern flank of the Wyoming Craton after the carbon isotope excursion. Rifting in the Black Hills, likely related to the final breakup of the Kenorland, succeeded the carbon isotope excursion, since the Estes and Roberts Draw formations, deposited during rifting and ocean opening on the eastern flank of the Wyoming Craton, postdate the carbon isotope excursion.  相似文献   

Environmental responses of jellyfish polyps as drivers of medusa populations off the coast of Namibia     

L Ziegler  MJ Gibbons 《African Journal of Marine Science》2018,40(3):323-329

Jellyfish populations in the southeastern Atlantic off the coast of Namibia have increased subsequent to the decline of small pelagic fisheries at the end of the 1960s, although the environment there has also become warmer and the waters off Walvis Bay have become richer in zooplankton in recent years. Laboratory experiments were conducted with the scyphozoan jellyfish Chrysaora fulgida to investigate the effects of food density (0, 30, 70, 100 or 150 Artemia nauplii 200 ml^?1), feeding frequency (once daily or once every third day) and water temperature (12, 16 or 20 °C) on the asexual reproduction, growth and development of polyps. The results of a generalised linear mixed-effects model reveal that all variables impacted asexual reproduction, with greater polyp production attained at higher food concentrations, increased feeding frequencies and increased temperatures. The most common mode of asexual reproduction was by lateral budding. These laboratory results suggest that polyps of C. fulgida may have proliferated off Namibia in recent times, which would contribute to increased numbers of jellyfish there.  相似文献   

The interface between geostatistical modeling of oil and gas discovery and economics     

E. Barouch  G. M. Kaufman 《Mathematical Geology》1978,10(5):611-627

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Erratum     

G. G. Baxter  S. M. Cargill  A. H. Chidester  P. E. Hart  G. M. Kaufman  F. Urquidi-Barrau  D. D. Picklyk 《Mathematical Geology》1979,11(3):343

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Machine learning classifiers for attributing tephra to source volcanoes: an evaluation of methods for Alaska tephras     

Matthew S. M. Bolton  Britta J. L. Jensen  Kristi Wallace  Nore Praet  David Fortin  Darrell Kaufman  Marc De Batist 《第四纪科学杂志》2020,35(1-2):81-92

Glass composition-based correlations of volcanic ash (tephra) traditionally rely on extensive manual plotting. Many previous statistical methods for testing correlations are limited by using geochemical means, masking diagnostic variability. We suggest that machine learning classifiers can expedite correlation, quickly narrowing the list of likely candidates using well-trained models. Eruptives from Alaska's Aleutian Arc-Alaska Peninsula and Wrangell volcanic field were used as a test environment for 11 supervised classification algorithms, trained on nearly 2000 electron probe microanalysis measurements of glass major oxides, representing 10 volcanic sources. Artificial neural networks and random forests were consistently among the top-performing learners (accuracy and kappa > 0.96). Their combination as an average ensemble effectively improves their performance. Using this combined model on tephras from Eklutna Lake, south-central Alaska, showed that predictions match traditional methods and can speed correlation. Although classifiers are useful tools, they should aid expert analysis, not replace it. The Eklutna Lake tephras are mostly from Redoubt Volcano. Besides tephras from known Holocene-active sources, Holocene tephra geochemically consistent with Pleistocene Emmons Lake Volcanic Center (Dawson tephra), but from a yet unknown source, is evident. These tephras are mostly anchored by a highly resolved varved chronology and represent new important regional stratigraphic markers.  相似文献   

COCORP: new perspectives on the deep crust   总被引：7，自引：0，他引：7  

L. Brown  D. Wille  L. Zheng  B. DeVoogd  J. Mayer  T. Hearn  W. Sanford  C. Caruso  T.-F. Zhu  D. Nelson  C. Potter  E. Hauser  S. Klemperer  S. Kaufman  J. Oliver 《Geophysical Journal International》1987,89(1):47-54

Summary. Relict sutures from colliding continents, regions characterized by a "young" Mono, layering and faulting throughout the crust, mid-crustal magma traps, and seismic "bright spots" which suggest deep crustal fluids are among recent COCORP findings. In addition, new studies of signal penetration, noise mitigation, recording geometry, and coherency filtering have yielded better understanding of, and substantial improvements in, data quality. Amplitude anomalies, or "bright spots", in the Basin and Range may be due to magma at mid-crustal levels; in one case, a normal fault appears to link the deep magma with young surface volcanics. Another bright spot. 15 km deep in southeastern Georgia, has a flat geometry that suggests a gas/liquid interface, perhaps within fluids underthrust along an Appalachian suture. The Mono continues to appear relatively undisturbed in many regions of past deformation, suggesting that its formation post-dates these major tectonic episodes. The diversity of reflection patterns from the U.S. Cordillera casts further doubt on the generality of the common model of a reflective, layered lower crust underlying a transparent upper crust.  相似文献