Large-scale environmental influences on the benthic macroinfauna of the southern Gulf of Mexico

The influence of large-scale natural disturbance from winter storms (‘northers’) and river runoff on the macrobenthic community structure of the southern Gulf of Mexico was investigated in both carbonate and transitional carbonate–terrigenous sedimentary environments. Samples of the infauna were obtained in three seasons from 13 stations from two 250 km transects along 80–170 and 20–50 m water depth. Samples after the northers season had the lowest total number of families and individuals, 114 and 2940, respectively, compared to the dry and rainy seasons with 129 and 132 families and 11580 and 15266 individuals, respectively. Spatial patterns of macroinfauna composition varied across and along the shelf as a response to sedimentary environments and depth. Coarser sediments from the carbonate area harboured the highest mean densities per station with 500–24,000 individuals m⁻² and 108–122 families in total, compared to the transitional sediment with 500–8200 individuals m⁻² and 56–74 families across the three seasons. Univariate and multivariate statistical techniques demonstrated that low densities and number of taxa were associated with winter storms, but storm influence was dependent on depth and sediment type. Multiple linear regression analysis and BIOENV analysis indicated that sediment mean grain size, percentage of clay and organic matter best explained the macroinfauna spatial patterns, although BIOENV indicated that depth has an overriding role. An increase in densities of opportunistic taxa (numerous polychaetes of small sizes) was observed four months after the ‘northers’ and this was more evident in the area of carbonate sediment. Additionally a combined disturbance from northers and river runoff is suspected to be responsible for a naturally impoverished macroinfauna community in the transitional sedimentary environment.     

Sedimentary characteristics of terrigenous debris at site MD05-2905 in the northeastern part of the South China Sea since 36 ka and evolution of the East Asian monsoon

Sediments with high sedimentation rate at site MD05-2905 in the Northeastern slope of the South China Sea provide unique materials for a high-resolution study on the paleoenvironment. Based on precise dating of AMS ¹⁴C, grain size analysis of terrigenous debris at core MD05-2905 was conducted after organic matter, biological carbonate and biogenic opal were removed. The results show that 15.5–63.5 μm coarse grain size ingredients may indicate East Asian winter monsoon changes and that 2–9 μm fine grain size ingredients may be used as a proxy of evolution of the East Asian summer monsoon. The results of grain size analysis, which suggest East Asian monsoon intensity, reveal that a winter monsoon dominated the glacial regime and a summer monsoon dominated the Holocene regime. It was also shown that the summer monsoon increased gradually, experienced several abrupt changes and reached a culmination in the early Holocene (11200–8500 a B.P.) since 36 ka. Controlled by precession periodicity, it may be related with the amount of solar radiation at the highest stage, which needs further study. __________ Translated from Advances in Earth Science, 2007, 22(10): 1012–1018 [译自: 地球科学进展]     

冲绳海槽南部沉积层序的粒度特征

对取自冲绳海槽南部的A2 3孔经前处理后的沉积物样品进行了粒度测试,探讨了陆源沉积层序的粒度特征。沉积物平均粒径、分选系数、偏态、峰态等粒度参数的变化显示出A2 3孔的沉积层序以 4 0 0cm为界可分为上、下两段,下段各参数稳定,代表了比较稳定的水动力条件的沉积环境;上段则波动较大,小规模浊流沉积频繁发育,暗示了不稳定的沉积环境。浊流层内粗粒与细粒组分含量及粒度分布的变化具有明显的规律性。通过分析A2 3孔陆源沉积层序的各沉积参数特征,认为冲绳海槽南部的沉积环境和动力在时间尺度上有较大的变化,东海陆架物质向南部海槽的输运可能是以峡谷为通道的重力作用引起的床底沉积作用为主。另外,对陆源碎屑和全样粒度结果的对比,显示了前处理方法对于海洋沉积物粒度分析的重要性.     

冲绳海槽中段近4万年来沉积物属性和来源

对冲绳海槽中段DGKS9603孔134个样品(孔深0~481cm),测试了18种常、微量元素,对该柱样的29个样品(孔深0~488cm)进行了REE测试。对采自长江三角洲的CYm柱样和黄河三角洲的S3柱样中的晚更新统的5个样品进行了常、微量元素和REE测试。分析表明,冲绳海槽中段在全新世、末次盛冰期和末次间冰期的沉积物均以陆源物质为主,生物沉积为次。末次盛冰期以陆源硅质碎屑沉积的大量增加为特征;全新世生物沉积量有较大的增加;末次间冰期介于上述两者之间,但较全新世更富陆源物质。冲绳海槽的物源演化受末次冰期的影响,具有阶段性。对比冲绳海槽与长江和黄河物源的地球化学参数,包括REE、稀有元素、惰性常、微量元素,判识出末次盛冰期冲绳海槽的陆源物质,具有长江源的物质属性,沉积物可能主要来自古长江。     

陆源碎屑岩中的古土壤在地层分析中的应用

对各种古土壤的分类标准进行比较之后,重点介绍了Mack的古土壤分类及其土壤的演变序列。Mack的古土壤分类主要依据稳定矿物和保存在土壤中的古地貌属性,将古土壤划分为9种。在地层序列中古土壤的识别标志主要包括颜色、粒度、生物成因构造（植物生长痕迹）、原生沉积构造退化特征、层次化和边界特征、宏观结构特征、矿物及地球化学特征等。可以通过野外观察、室内显微镜观察、实验室化验及地震、测井资料来进行鉴别。陆相盆地具有很强的分隔性,盆地相变又非常复杂,寻找区域性较稳定的层序界面比较困难。越来越多的研究证实用古土壤划分陆相成因地层层序、解决地区及全球对比具有重要的实用价值。     

舟山海域陆源溶解有机质变化及其对近岸羽状流的响应

2007年夏季在东海舟山海域河口锋区开展了陆源溶解有机质的调查研究。测定了有色溶解有机质(CDOM)在激发波长370 nm/发射波长460 nm处的荧光强度和在λ=355 nm处的吸收系数,用于代表陆源CDOM浓度,并测定了荧光指数以指示CDOM来源。结果表明,CDOM的荧光值和紫外吸收系数之间呈显著正相关性,陆源CDOM浓度大体有向海方向降低的趋势,但是纵向上存在一些"突跃"现象。在舟山海域东北角不时观测到表层水体含有高浓度的CDOM,但变异性很大,推测可能该海区受到长江口羽状流的影响。在连续观测站发现陆源CDOM浓度在低平潮时往往比高平潮时要高。河海水在混合过程中CDOM浓度与盐度呈显著的线性负相关关系。在低盐度的悬沙锋区(S<24)CDOM浓度明显低于理论稀释值,而在较高盐度的羽状锋区,CDOM浓度接近于理论稀释值。在盐度为24~31范围内,大部分水样的荧光指数在1.50上下波动,表明其中CDOM来源以陆地来源为主;在较低盐度(S<24)的水样中荧光指数在1.70至1.90以上,表明CDOM以海洋来源为主,这与其陆源组分在高浊度的低盐度区存在显著的去除过程有关。研究表明,舟山海域水质存在着显著的变异性,与近岸羽状流密切相关,陆源溶解有机质的分布特征对此有较好的响应。     

南襄盆地泌阳断陷下第三系陆相层序地层

泌阳断陷历经中生代小型拉分盆地、早第三纪断陷盆地和晚第三纪坳陷盆地等３个盆地原型的演化、叠合过程,形成了３个盆地充填序列及其所包含的３个构造层序。泌阳断陷下第三系（即构造层序Ⅱ）为湖盆沉积充填主体,其可划分为７个层序组,各层序组具特定的沉积体系配置关系。作为泌阳断陷油气勘探主要目的层段的下第三系核桃园组可进一步划分为１２个层序。其中,核三上段包括跨时分别为１．０８、１．４０、１．０２Ｍａ的３个陆相层序,由南往北呈现冲积扇—扇三角洲—湖泊—三角洲的沉积体系空间配置。泌阳断陷下第三系层序地层年代框架模式清晰地显示了断陷湖盆成盆演化史、沉积充填史及其陆相层序时空展布特征。     

鄂霍次克海南部晚第四纪的古海洋学记录

鄂霍次克海是太平洋第二大边缘海,在西北太平洋水文环境中扮演重要角色。综合分析了鄂霍次克海南部T00孔沉积物的多种替代性指标,揭示了鄂霍次克海晚第四纪以来的环境变化受季节性海冰变化、大气循环模式、陆源物质通量和表层生产力的共同影响。对比放射虫Cycladophora davisiana的含量曲线与LR04氧同位素记录,该孔沉积物可划分为氧同位素1-7期,底部年龄约为250ka。C.davisiana在间冰期的高含量表明鄂霍次克海中层水是北太平洋中层水的主要源区。蛋白石和有机碳的分析显示鄂霍次克海表层生产力在冰消期突然增大,随后在间冰期逐渐下降,冰期普遍较低。C/N比值曲线的分析说明鄂霍次克海的有机质沉积物主要来源于海洋。沉积物粒度的分析揭示鄂霍次克海冰期时陆源粗颗粒含量较低,至冰消期粗颗粒含量突然增加,而在间冰期陆源粗颗粒含量较高。     

广东省海岸表层沉积物的重矿物特征及其与沉积环境的关系

广东省海岸表层沉积物中的重矿物近40种。含量较高的有钛铁矿、赤矿铁、磁铁矿、话石、电气石、黑云母和普通角闪石等。自生矿物主要为硬石膏、自然铜、黄铁矿及菱铁矿。这些矿物来自附近的母岩。根据物源性质不同,可将不同岸段重矿物区分为陆源矿物组合、近源-自生矿物组合和近源矿物组合三种:除物源控制外,重矿物含量、种类、形态特征及其在平面上的分布主要受沉积环境影响。据此,可将重矿物分布类型划分为河口型、海湾型和海岛型三类,且与上述不同矿物组合性质相对应。     

混合沉积和混积岩的讨论

混合沉积物是指陆源碎屑与碳酸盐(包括异化粒等)在沉积上的混合。混合沉积可分为狭义的和广义的,狭义的是指陆源碎屑与碳酸盐组份的混合(在同一岩层内),而广义的混合则包括了狭义的和陆源碎屑与碳酸盐层构成交替互层或夹层的混合。混合沉积很早就引起了人们的注意,尽管碎屑岩和碳酸盐岩的研究与应用已很成熟,但对混积岩的研究多被忽视了。对狭义的混合沉积物有必要起一成因名称——混积岩。当人们接触到混合沉积时,除了分析研究它们的组分和结构特征外,还必须去思考,它们为什么能经常频繁地交互出观,或是直接混合在一起?倒底是：①陆源碎屑跑到碳酸盐的沉积背景里?②碳酸盐跑到陆源碎屑的沉积背景里?③二分别从各自的源地跑到第三种沉积背景里?还是④二本来就在同一沉积背景里?接下来就要思考是什么动力条件使它(们)能从这个沉积背景(环境)“跑”到另一个沉积背景(环境)里去?是水?是风?是自身?还是别的什么力量?那么,又是怎样的水动力或风动力条件呢?是正常条件,还是突发事件?很明显,要分析研究混合沉积和混积岩。这些问题就不得不细细加以考虑,深入进行研究。