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11.
Poul Schiøler Karyne Rogers Richard Sykes Chris J. Hollis Brad Ilg Dylan Meadows Lucia Roncaglia Chris Uruski 《Marine and Petroleum Geology》2010
Detailed palynofacies analysis of sidewall core samples taken from below, within and above the Tartan Formation (Thanetian, Late Paleocene, 58.7–55.8 Ma), a potential source rock in the epeiric Great South Basin, shows that the formation is characterised by very high percentages of degraded brown phytoclasts, rare marine algae and amorphous organic matter and thereby represents a mix of terrestrial and marine kerogen. The results indicate that the formation was deposited in a marginally marine (hyposaline), proximal environment under bottom conditions that varied from anoxic to oxic along a nearshore–offshore transect. Samples from the upper part of the underlying Wickliffe Formation indicate deposition in a marginal to normal marine, proximal environment under anoxic to oxic bottom environments. The lower part of the overlying Laing Formation was deposited in an open marine, relatively distal setting under anoxic to oxic bottom environments. 相似文献
12.
I. D. Marsden 《新西兰海洋与淡水研究杂志》2013,47(2):359-370
Paphies donacina (Spengler, 1793) populations were surveyed at 11 low tide sites on surf beaches along Pegasus Bay, Canterbury, New Zealand, during summer 1998. Random sampling was not feasible. At the non‐random sites chosen the average number of tuatua per 5 m of shoreline ranged between 0.1 and 62. Total wet weight biomass m‐2 was highest at the southern sites in the Bay. There were site‐related differences in length frequency distributions of tuatua populations. Northern populations included a wide length range and southern populations were dominated by larger bivalves. Average shell length increased significantly with distance south, being close to 40 mm at Waikuku and 80 mm at Taylors Mistake. The shell length: width and weight relationships were similar for tuatua collected over the whole geographic range. Average dry weight condition index varied significantly between sites (ANOVA F= 23.3, d.f. = 10, 329) depending on the length distribution of the contributing population. Where populations included a wide length range the condition index was positively correlated with shell length but in populations dominated by larger bivalves there was either no relationship or a negative relationship with shell length. Juvenile tuatua were found at average densities between 81 and 1200 m‐2 at all sites except Taylors Mistake. The mean length of recruits ranged from 2.2 to 3.1 mm and shell length was independent of both juvenile and adult density. These results are discussed in relation to the environmental and other factors thought to influence population structure and recruitment of tuatua in Pegasus Bay. 相似文献
13.
This paper examines the observed directionality of ground motions in the Christchurch urban area during the 2010–2011 Canterbury, New Zealand earthquakes. A dataset of ground motions recorded at 20 strong motion stations over 10 different earthquake events is utilized to examine the ratios of various response spectral directionality definitions and the orientation of the maximum direction. Because the majority of previous related studies have utilized overlapping ground motion datasets from the NGA database, the results of this study provide a largely independent assessment of these ground motion aspects. It is found that the directionality ratio between the maximum (100th percentile) and 50th percentile orientation‐independent spectral acceleration is similar to that obtained from recent studies. Ground motions from the 4 September 2010 Darfield earthquake are shown to exhibit strong directionality for source‐to‐site distances up to Rrup = 30 km, notably further than results from a previous study, which suggests that such effects are generally limited to Rrup < 5 km. The adopted dataset also offers the unique potential to consider site‐specific effects on directionality ratios and maximum direction orientations; however, in both cases, site‐specific effects are found not to be significant in the observed empirical results. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
14.
Economic concentrations of detrital gold are rare in young foreland basins due to paucity of significant gold sources, and a paucity of sediment recycling processes during filling of the foreland basin. Gold shed into the foreland basins is typically widely dispersed in an overwhelming volume of immature basin-fill detritus of no economic significance. In the actively forming Canterbury Basin of New Zealand, minor gold concentration occurs at the mountain front in the bed of the Rakaia River, and 60 km downstream on beaches and the crest of foredunes at the river mouth. The Cretaceous–Tertiary Denver and Western Canada Basins in North America also have minor gold concentrations at the mountain front, and minor gold dispersal into the basin. Tectonic quiescence in the middle Tertiary in the Denver Basin kept gold within 20 km of the mountain front, where renewed uplift in late Tertiary caused minor economic concentrations to form in modern streams. Gold has been transported ca. 200 km across the Western Canada basin by progressive recycling of gravel during slow (ca. 10 to 50 m/Ma) middle Tertiary–Recent regional uplift and tilting, but little concentration has occurred. Development of significant placers in a foreland basin, the generally accepted setting for the Witwatersrand Au-U palaeoplacers, appears to require specific tectonic conditions during and/or after basin evolution to drive the sedimentary recycling necessary for significant placer development. Such tectonic conditions have not occurred in an any of the three young foreland basins examined in this study. 相似文献