华南泥盆纪层孔虫生长形态及其环境意义

通过对四川甘溪、贵州独山、广西六景和桂林神湾等泥盆纪剖面中层孔虫"生长形态"的系统研究,识别出层孔虫内部存在2大类7小类年生长条带:密度条带(疏密型、递变型、混杂型、突变型和"生长脊"型)和结构条带(结构差异型、单一结构层式),并发现层孔虫年生长条带广泛发育,在中泥盆世30属203种中均有记录。在层孔虫内部识别出了6类生长间断:含沉积物型、综合型、深色型、突变型、边部型和结构差异型。据此,系统总结了华南泥盆纪层孔虫生长形态及其相带分布规律,发现华南泥盆纪层孔虫主要分布在局限台地、开阔台地和台缘礁等7个相带中,各相带层孔虫生长形态差异明显。同时,发现和总结了与礁单元稳定构建密切相关的5个生长形态参数:总体形态、V/B(高与底宽之比)、基面、生长速率和生长间断。研究表明:层孔虫生长过程多由连续生长和间断二者共同组成,受到周期性环境因素(如冷、暖)和随机环境因素(如沉积速率变化)的共同影响,并以后者为主;提出并验证了层孔虫生长形态是高分辨率沉积环境变化的示踪指标,如利用年生长条带计算沉积速率;同时提出层孔虫生长形态是精细分析珊瑚-层孔虫礁的重要手段,如利用层孔虫生长速率推算礁生长速率等。     

Impact of environmental parameters on coral reef development and drowning: Forward modelling of the last deglacial reefs from Tahiti (French Polynesia; IODP Expedition #310)

The sedimentological and chronological analysis of the last deglacial reef sequences of Tahiti (French Polynesia), drilled during the Integrated Ocean Drilling Program Expedition 310, provide a high‐resolution data set allowing a well‐constrained forward modelling study. This study represents the first attempt to model in three dimensions the coral reef development of Tahiti during the last deglacial sea‐level rise (23 000 to 6000 cal yr bp ) using the software dionisos developed by IFP Energies nouvelles. It allows the testing of the reconstructed last deglacial sea‐level curve and the different environmental parameters (for example, wave energy and sediment fluxes) that could have influenced the reef development. These last deglacial reef sequences form two prominent ridges occurring seaward of the living barrier reef that consist of successive submerged reefs. These reefs have been prone to drowning because the window of maximum carbonate production rate is inhibited by high water turbidity (sediment supply from a nearby river), shallow depth of wave action and substrate availability. These factors, combined with rapid sea‐level rise, have driven the growth of retrograding reef pinnacles. Local factors (substratum nature, sediment supply and wave energy) were the main processes that induced the drowning of the inner ridge, whereas interplay of local and global factors (acceleration of the sea‐level rise) was responsible for the drowning of the outer ridge. This particular acceleration of sea‐level rise of 16 m between 14·6 ka and 14 ka bp corresponds to meltwater pulse 1A.     

Interglacial carbonates of the Cryogenian Umberatana Group,northern Flinders Ranges,South Australia

A detailed sedimentological and chronostratigraphic analysis of the Umberatana Group in the northern Adelaide Geosyncline has uncovered a depositional history involving the rapid progradation (at least 20 km) of a giant reef complex (up to 1.1 km relief) during mid-Cryogenian interglacial times. The reef complex, which occurs in the Balcanoona Formation, displays facies similar to Phanerozoic reefs. These include a basal forereef (slope) facies, overlain by a reef-margin facies (consisting of both stromatolitic and non-stromatolitic frameworks), and an upper backreef (platform) facies consisting of shallow-water peloidal and oolitic carbonate. The thickening of the reef complex in a basinward direction, and the distribution of the key facies are consistent with the progradation of the platform into deep water. Progradation was contemporaneous with deposition of the upper Tapley Hill Formation and had largely ceased after a major margin failure event. Following this event, reef growth continued for a short time before becoming extinct, possibly as a result of global climatic cooling and/or eustatic sea-level fall.     

ADS40相机用于海岛(礁)大比例尺成图的试验

本文利用ADS40相机进行航空摄影,对海岛(礁)区域1∶2000比例尺成图精度进行了分析,比较了差分GPS与精密单点定位技术应用于ADS40航摄的精度。试验结果表明,ADS40相机可满足海岛(礁)大比例尺成图航摄的精度要求,缩短成图周期,精密单点定位技术的平面精度与差分GPS方法相当,高程精度较差,从工程角度考虑,海岛(礁)大比例尺成图时架设地面GPS基站比较稳妥。     

未来海平面上升对涠洲岛珊瑚礁的可能影响

根据涠洲岛珊瑚样品资料和涠洲岛海洋站实测雨量、盐度、pH、潮位、最大波高及珊瑚普查历史资料,分析气候变化、海平面上升对涠洲岛珊瑚礁的可能影响。结果显示:1)涠洲岛的多年平均雨量为1388mm,多年平均盐度为32.1,目前海水pH值为8.0~8.23,均在珊瑚生长合适范围内;2)用P-Ⅲ型算式得出涠洲岛的水文要素百年一遇极值为:年雨量2313mm,最高潮位514cm,最大波高6.1m;3)涠洲岛珊瑚生长率(6~8mm/a)大于海平面上升率(2.2mm/a),涠洲岛最大潮差为450~500cm,夏季白天遇低潮时,会增加珊瑚白化概率;4)若未来海平面上升30cm,遇上512cm高潮位与580cm最大波高,不会对涠洲岛珊瑚礁造成毁灭性破坏。     

塔里木盆地下寒武统微生物礁储集性研究及油气勘探意义

通过塔北西部-柯坪地区大量的野外露头观测及室内薄片观察与物性分析,对塔里木盆地下寒武统肖尔布拉克组上二亚段微生物礁白云岩储集性进行了精细研究。该层微生物礁仅在研究区南部三个剖面有发现,其中在昆盖阔坦剖面发育数量最多、体积最大,呈近东西向带状、串珠状分布;英尔苏和苏盖特布拉克两剖面发育数量和体积皆较小,呈现由南到北逐减趋势。微生物礁白云岩具有粒内孔、晶间孔、溶孔、格架孔、微裂缝和缝合线6种储集空间,但储集性能远低于预期目标,平均孔隙度与渗透率分别仅有1.84%和0.91×10-3 μm2,属于特低孔特低渗储集体。结合前人工作不难发现,塔里木盆地下寒武统甚至更老地层的微生物礁不应再作为台缘带油气勘探的重点对象,而台缘微生物颗粒滩更具有勘探潜力。     

西沙群岛西科1井碳酸盐岩稳定同位素地层学

西科1井由于矿化重结晶作用和白云岩化作用普遍发育, 无法采用传统的氧同位素地层学方法进行地层年代标定.但是该井δ13C变化曲线与南海及全球主要大洋的碳同位素变化曲线完全相同, 可以用来准确标定200 ka以来的地层年龄.该井0~50 m深度对应全球氧同位素1~7期, 5 m处地层时代为14 ka, 为氧同位素1期的底界年龄; 11.70 m处为氧同位素2期的底界, 年龄为29 ka; 13.90 m深度年龄为57 ka; 到35.65 m为氧同位素6期底界, 年龄为191 ka, 同时δ13C值表现出冰期低而间冰期高的特点, 取自25.21 m的珊瑚U-Th定年年龄为131.062±2.320 ka.通过碳同位素定年发现, 石岛缺失近代5 ka以来的沉积物, 在间冰期向冰期转换时因海平面下降造成碳酸盐台地暴露剥蚀.全球气候变化是石岛碳酸盐台地δ13C值发生突变的主要原因.      

西沙石岛西科1井生物礁碳酸盐岩地球化学特征

对西科1井生物礁碳酸盐岩样品进行了地球化学(常量组分、微量及稀土元素含量等)分析, 旨在探讨生物礁的形成演化以及所记录的环境变化信息.结果表明: 西科1井岩心在井深36 m附近存在地球化学参数的显著变化, 暗示该深度是一处重要的地层界面或环境突变界面.岩心中的常量组分可以分为3类组合: 以CaO为主, 辅以K₂O的原生碳酸岩组分, 该组分对应的主要造岩矿物是方解石, 代表了未经白云岩化的生物礁原生碳酸盐沉积; 以MgO为主, 辅以Na₂O和P₂O₅, 代表了白云岩化作用中的富集组分, 反映了相对封闭的泻湖环境; 以SiO₂为主, 加以Al₂O₃、TiO₂、Fe₂O₃和MnO, 代表造礁生物对这些组分的富集作用, 但不能排除火山组分少量混入的可能性.相对于全球第四纪碳酸盐岩、上陆壳及页岩的平均值, 岩心碳酸盐岩中大部分微量元素和稀土元素含量都较低.岩心中氧化还原敏感性微量元素(RSE)含量较低, 指示岛礁发育过程中大部分时期处于氧化环境条件下, 而RSE含量在岩心中的大幅波动体现出氧化/还原环境的交替变化.微量元素含量、ΣREE、ΣLREE、ΣHREE、LREE/HREE、δCe、δEu等地球化学指标在岩心中的分布与岩心样品的矿物组成无明显的相关性, 说明成岩作用和白云岩化作用并没有造成微量和稀土元素含量及特征指标的明显变化.      

西沙地区晚中新世以来碳酸盐岩的沉积演化及储层特征

生物礁滩相碳酸盐岩是南海海域深水区重要的油气储层之一.通过对西科1井(0~576.5 m)岩心的宏观描述及微观分析, 结合古生物、古地磁、高分辨岩心扫描及大量分析测试结果, 对碳酸盐岩-生物礁滩体系展开了精细研究.研究表明: 该井晚中新世以来记录了6次暴露事件、2次淹没事件, 结合古生物、古地磁、Li同位素分析, 可划分为8个三级层序, 其中晚中新世黄流组和第四系乐东组为主要成礁期.通过细致的岩相学研究, 系统刻画了生物礁-碳酸盐岩的岩石类型、成岩作用类型和孔隙类型, 重建了成岩环境.      

Spatial discordance in fish,coral, and sponge assemblages across a Caribbean atoll reef gradient

Certain biodiversity patterns on coral reefs are generally consistent but we still lack fundamental insight into how assemblages vary across spatially heterogeneous reef systems. We compared fish, coral, and sponge assemblages across a symmetrical physiographical gradient (windward forereef, lagoon patch reef, leeward forereef) of the Glover's Reef atoll, Belize. Species richness of fishes and corals was highest in the deep habitat (15 m) on the windward forereef. Sponges were diverse and abundant on both deep windward and leeward forereefs but not on the exposed shallow (5 m) windward forereef. Fish and benthic assemblages were relatively distinct in each reef zone, with the lagoon patch reef communities consisting of a combination of leeward and windward species. Nevertheless, there were no clear patterns in community similarity matrices of fish and benthic assemblages, suggesting that overall coral and sponge assemblages had weak or no direct association with patterns in fish assemblages. A closer examination of fish trophic groups indicated that planktivores and predators were predictably associated with depth, whereas herbivores were associated with shallow protected reefs. None was specifically associated with spatial location along the atoll gradient. These patterns of diversity distribution are important for identifying spatial conservation priorities. A Marine Protected Area (MPA) at Glover's Reef encompasses substantial windward forereef and patch reef habitats. A much lesser extent of protection is afforded the leeward forereef that supports faunal assemblages that are unique and productive, if not as diverse as the windward forereef. Isolated coral atolls can serve as ideal systems to study spatial heterogeneity and biodiversity patterns, but more experimental studies are needed to reveal the mechanistic processes underlying these patterns.