How Episodic Coral Breakage Can Determine Community Structure: A South African Coral Reef Example

Abstract. Africa's southernmost coral reefs are situated in Natal Province, South Africa. The Natal coast is exposed to open Ocean swells and episodic storm swell conditions. Benthic communities on these reefs differentiated into three community types: shallow reefs (8–18 m) were dominated by alcyonacean corals and low-growing, massive Scleractinia; intermediate reefs (18–25 m) were dominated chiefly by branching and tabular Scleractinia of the genus Acropora (A. austera, A. clathrata); deep reefs were not dominated by corals but by sponges. Breakage and recovery experiments indicated that the difference in Acropora dominance between shallow and intermediate sites was caused by breakage in high swell conditions. Survival of experimentally produced A. austera fragments was significantly higher in intermediate than in shallow sites, where higher surge made re-attachment and regeneration unlikely. Also, colony morphology was adapted to differential surge conditions: colonies on the shallow reefs were smaller with shorter branches, while on intermediate reefs they were much bigger with long, widely spreading branches. Episodic breakage and low fragment survival due to high water-motion thus excluded branching corals from shallow reef sites.     

城市空间形态对城市热岛效应的多尺度影响研究进展

随着全球城市化的快速发展和气候变暖及极端高温事件的加剧,城市热岛效应已成为了21世纪影响人类生存发展的重要环境问题。因此,阐明城市热岛强度时空变化特征,揭示多空间尺度下的形成机制是人文地理学和气候学研究的热点和前沿交叉科学问题。从街道峡谷微观尺度、城市街区局部尺度和城市宏观尺度全面总结和系统梳理了城市空间形态对城市热岛效应的多尺度影响和耦合机制,提出了未来通过定量表征城市热岛强度、城市空间形态的空间格局、时间演化特征及规律,构建空间关系分析模型,进而揭示城市空间形态在不同时空尺度对城市热岛强度的作用机制,为城市规划、宜居城市建设以及气候变化的响应与适应研究提供理论指导。     

Predicting air temperature simultaneously for multiple locations in an urban environment: A bottom up approach

Cities are characterized by high heterogeneity that results in varied microclimate effects. The current study introduces a new bottom–up approach linking the urban Canyon Air Temperature (CAT) model with spatially distributed inputs extracted from a GIS data-base and remote sensing products to predict intra-urban temperature variability simultaneously for multiple locations in an urban environment. To provide proof of concept, the model was applied for the city of Bat-Yam, Israel. Simulation shows a maximum nighttime urban heat island (UHI) intensity of 2–2.25 °C, relative to a rural reference point, during both summer and winter, with significant spatial variability related to the height-to-width ratio of urban street canyons and to the surface land cover. The CAT simulation also highlighted the important influence of the local wind regime on the development and persistence of the nocturnal UHI. We conclude that linking CAT to a GIS data-base supports simulations at the city scale that reflect the local intra-urban variability. The model can be used to investigate both macro and micro scale spatio-temporal characteristics of the UHI in various urban development scenarios, which may be applied to generate appropriate geographically-explicit mitigation and adaptation measures.     

Distribution of Chancelloriids in a Middle Cambrian Carbonate Platform Deposit, Taebaek Group, Korea

The onset of the Cambrian witnessed the diversification of “small shelly fossils (SSF)”, which affected carbonate depositional system. One of the problematic SSF, chancelloriids, are common components of the early to middle Cambrian carbonate and shale, and their contributions toward Cambrian carbonates are not yet fully understood. This study assesses distribution patterns of chancelloriid sclerites in the Cambrian Series 3 Daegi Formation based on microfacies analysis and discusses their sedimentologic implications. In the lower part of the formation, partially articulated chancelloriid sclerites occur mainly in bioclastic packstone and grainstone facies, with isolated sclerite rays in nodular packstone to grainstone facies. In the middle part of the formation, chancelloriid fragments occur only sporadically in bioclastic wackestone to packstone, bioclastic grainstone and oolitic packstone to grainstone facies, whereas boundstone facies are nearly devoid of their fragments. There are no chancelloriid fragments in the upper part of the formation, which consists of oolitic packstone to grainstone facies. Chancelloriids are interpreted to have primarily occupied platform margin shoal environments, shedding their sclerites to surrounding areas, and thus contributed as sediment producers. The distribution of Daegi chancelloriid sclerites is similar to other Cambrian examples, with the exception of common chancelloriids in Cambrian Series 2 reefs and their apparent near absence in the Daegi and other Cambrian Series 3 reefs. This disparity resulted from changes in the ecologic niche of chancelloriids after the end-Cambrian Series 2 reef crisis, coupled with an overall decline of chancelloriids in the middle Cambrian.     

川东卧龙河-洋渡溪区带长兴组台内礁滩沉积格局及有利储集体展布

随着川东碳酸盐岩礁滩储层勘探的大力推进,台内礁滩储层成为该区关注的重点之一,但其研究程度较低。本文以岩芯、野外剖面、薄片鉴定资料为基础,确定研究区长兴组早期发育碳酸盐岩缓坡沉积体系;中-晚期发育碳酸盐岩台地沉积体系,开阔台地相构成该区主要沉积类型。层序地层研究表明:长兴组划分为两个三级层序,台内礁滩主要发育于Sq1和Sq2的高位体系域,横向上分布不连续,纵向上发育期次有变化,其中西部构造区带主要发育于Sq2-HST,而在东部Sq1和Sq2高位体系域均有分布,且以Sq1-HST更为发育。物性分析资料表明颗粒白云岩、粉晶白云岩为主要的储集岩类,台内礁滩沉积为主要储集相带,台内礁滩的沉积格局控制着有利储集体的分布,而台内地貌高地对于控制礁滩分布具有关键作用。地质和地震预测结果表明研究区有利台内礁滩储集体的发育主要沿遂宁和广安两个台内高地展布,卧龙河构造带是已经揭示的有利储层发育带,南部高带可能是该区未来台内礁滩储集体勘探的重要方向。     

Platform margins, reef facies, and microbial carbonates; a comparison of Devonian reef complexes in the Canning Basin, Western Australia, and the Guilin region, South China

Devonian reef complexes were well developed in Western Australia and South China, but no detailed direct comparison has been made between reef building in the two regions. The regions differ in several respects, including tectonic, stratigraphic and palaeoceanographic–palaeogeographic settings, and the reef building styles reflect minor differences in reef builders and reef facies. Similarities and differences between the two reef complexes provide insights into the characteristics of platform margins, reef facies and microbial carbonates of both regions. Here we present a comparison of platform margin types from different stratigraphic positions in the Late Devonian reef complex of the Canning Basin, Western Australia and Middle and Late Devonian margin to marginal slope successions in Guilin, South China. Comparisons are integrated into a review of the reefal stratigraphy of both regions. Reef facies, reef complex architecture, temporal reef builder associations, 2nd order stratigraphy and platform cyclicity in the two regions were generally similar where the successions overlap temporally. However, carbonate deposition began earlier in South China. Carbonate complexes were also more widespread in South China and represent a thicker succession overall. Platforms in the Canning Basin grew directly on Precambrian crystalline basement or early Palaeozoic sedimentary rocks, but in South China, carbonate complexes developed conformably on older Devonian siliciclastic strata. Pre-Frasnian reef facies in South China had more abundant skeletal frameworks than in Canning Basin reefs of equivalent age, and Famennian shoaling margins containing various microbial reefs may have been more common and probably more diverse in South China. However, Late Devonian platform margin types have been documented more completely in the Canning Basin. Deep intra-platform troughs (deep depressions containing non-carbonate pelagic sediments — Nandan-type successions) that developed along syndepositional faults characterize Devonian carbonate platforms in South China, but have no equivalent on the Lennard Shelf, Canning Basin where inter-reef areas were more shallow. The South China platform-to-depression pattern was generally continuous from the Lower to Upper Devonian, indicating that many pre-Devonian tectonic features continued to exercise considerable effect through deposition. Localized, fault-controlled subsidence was an important factor in both regions, but similarities in 2nd order aggradation–progradation cycles suggest that eustasy was also an important control on the larger scale stratigraphic development of both regions.     

The contribution of the young Cretaceous Caribbean Oceanic Plateau to the genesis of late Cretaceous arc magmatism in the Cordillera Occidental of Ecuador

The eastern part of the Cordillera Occidental of Ecuador comprises thick buoyant oceanic plateaus associated with island-arc tholeiites and subduction-related calc-alkaline series, accreted to the Ecuadorian Continental Margin from Late Cretaceous to Eocene times. One of these plateau sequences, the Guaranda Oceanic Plateau is considered as remnant of the Caribbean–Colombian Oceanic Province (CCOP) accreted to the Ecuadorian Margin in the Maastrichtien.Samples studied in this paper were taken from four cross-sections through two arc-sequences in the northern part of the Cordillera Occidental of Ecuador, dated as (Río Cala) or ascribed to (Macuchi) the Late Cretaceous and one arc-like sequence in the Chogòn-Colonche Cordillera (Las Orquídeas). These three island-arcs can clearly be identified and rest conformably on the CCOP.In all four localities, basalts with abundant large clinopyroxene phenocrysts can be found, mimicking a picritic or ankaramitic facies. This mineralogical particularity, although not uncommon in island arc lavas, hints at a contribution of the CCOP in the genesis of these island arc rocks.The complete petrological and geochemical study of these rocks reveals that some have a primitive island-arc nature (MgO values range from 6 to 11 wt.%). Studied samples display marked Nb, Ta and Ti negative anomalies relative to the adjacent elements in the spidergrams characteristic of subduction-related magmatism. These rocks are LREE-enriched and their clinopyroxenes show a tholeiitic affinity (FeO_T–TiO₂ enrichment and CaO depletion from core to rim within a single crystal).The four sampled cross-sections through the island-arc sequences display homogeneous initial Nd, and Pb isotope ratios that suggest a unique mantellic source for these rocks resulting from the mixing of three components: an East-Pacific MORB end-member, an enriched pelagic sediment component, and a HIMU component carried by the CCOP. Indeed, the ankaramite and Mg-basalt sequences that form part of the Caribbean-Colombian Oceanic Plateau are radiogenically enriched in ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb and contain a HIMU component similar to that observed in the Gorgona basalts and Galápagos lavas. The subduction zone that generated the Late Cretaceous arcs occurred far from the continental margin, in an oceanic environment. This implies that no terrigenous detrital sediments interacted with the source at this period. Thus, the enriched component can only result from the melting of subducted pelagic sediments.We have thus defined the East-Pacific MORB, enriched (cherts, pelagic sediments) and HIMU components in an attempt to constrain and model the genesis of the studied island-arc magmatism, using a compilation of carefully selected isotopic data from literature according to rock age and paleogeographic location at the time of arc edification.Tripolar mixing models reveal that proportions of 12–15 wt.% of the HIMU component, 7–15 wt.% of the pelagic sediment end-member and 70–75 wt.% of an East-pacific MORB end-member are needed to explain the measured isotope ratios. These surprisingly high proportions of the HIMU/CCOP component could be explained by the young age of the oceanic plateau (5–15 Ma) during the Late Cretaceous arc emplacement. The CCOP, basement of these arc sequences, was probably still hot and easily assimilated at the island-arc lava source.     

Estimating hydraulic conductivity from specific capacity for Hawaii aquifers,USA

Site-specific relationships between specific capacity and hydraulic parameters (transmissivity and hydraulic conductivity) were investigated for volcanic rocks in Maui, Hawaii, USA. Details about well construction were commonly ignored in previous studies. To improve on such efforts, specific-capacity values were normalized by the open interval of the well. Correcting specific capacity for turbulent head losses using step-drawdown tests and including aquifer penetration length improved the correlation between specific capacity and hydraulic conductivity and reduced uncertainty in the prediction of hydraulic parameters. The relationships provide estimates of aquifer parameters with correlation coefficients between 0.81 and 0.99. The relationships for Maui can probably be extended to other Hawaii islands, given the similarity of aquifer formations and a reasonable fit to step-drawdown data from Oahu. Hydraulic conductivity was estimated from 1,257 specific-capacity values in the Hawaii’s well database. Hydraulic-conductivity estimates for dike-free volcanic rocks are consistent on different islands. For all islands, the estimates range from 3 to 8,200 m/d, with a geometric-mean and median value of 272 and 291 m/d, respectively. A geostatistical approach was applied to Maui and Oahu to generate island-wide hydraulic-conductivity maps to facilitate groundwater management efforts.     

西沙海域西琛1井生物礁性质及储层岩石学特征

西沙海域西琛1井生物礁主要是由红藻门壳状珊瑚藻、有节珊瑚藻和绿藻门仙掌藻等钙藻组成的植物礁,其次为珊瑚礁。礁相类型主要有礁核相和礁后泻湖相。岩石矿物成分单一,以碳酸盐矿物为主,包括低镁方解石和铁白云石;结构组分有生物骨架、粒屑、泥晶和亮晶;结构类型有生物格架结构、生物障积结构、生物节片结构、生物捆扎结构和生物粘结结构。岩石类型包括骨架石灰岩/白云岩、粘结石灰岩/白云岩、粒屑石灰岩/白云岩。储集空间类型有粒间孔、生物体腔孔和藻架孔等原生孔隙和铸模孔、裂缝、颗粒内溶蚀孔、藻类溶孔和扩大的粒间溶孔等次生孔隙。孔隙组合类型以粒间孔＋溶孔＋晶间孔最为发育,储集性能较好。     

黔南宾夕法尼亚亚纪生物礁类型及其特征

黔南宾夕法尼亚亚纪海域广大,普遍发育了一套台地相碳酸盐岩.该区碳酸盐台地浅水非常适宜生物生存,特别是底栖生物大量繁盛,生物造岩作用十分强烈.宾夕法尼亚亚纪地层中含有极为丰富的底栖生物化石,其中包括多种造礁生物并建造了不同类型的生物礁,主要礁体有:Fomitchevella 珊瑚骨架礁、叶状藻骨架一障积礁、Ivanovia cf.manchurica珊瑚骨架一覆盖礁、未名造礁生物骨架礁、黏结生物Tubiphytes黏结礁.生物礁不仅种类较多,而且数量可观,反映了该时期生物礁的发展达到了较高的水平,应该是石炭纪生物礁发育的一次高潮期.