白垩纪“温室”气候与海洋

白垩纪典型的"温室"气候和海洋一直是地学界关注的焦点之一.与现今地球"冰室"状态相比,温室状态下的气候和海洋遵循着不同的运行模式.本文在近年来取得的大量同位素、古生物以及气候和海洋模拟实验数据的基础上,评述了白垩纪古气候和古海洋研究中取得的重要进展.化石氧同位素数据揭示白垩纪全球平均气温比现今高3～10℃,海洋纬向温度梯度仅0.15～0.3℃/1°,全球海洋结构和大洋环流可能与现今完全不同,大洋环流的驱动很可能是盐度变化而不是温度差异.白垩纪深水沉积显示出从早白垩世碳酸盐台地相、含黑色页岩夹层、黑色页岩和大洋红层大规模出现一直到晚白垩世整体以大洋红层为主的转变.对该沉积转变机制及其与古海洋、古气候关系的研究正是IGCP463/494的主要科学目标.     

Benthic oxygen fluxes and sediment properties on the northeastern New Zealand continental shelf

We examined spatial variations in benthic remineralisation (measured as sediment oxygen consumption (SOC)) and sediment properties on the northeastern New Zealand continental shelf and slope to assess the importance of benthic mineralisation in this ecosystem and to provide data for more complete global carbon budgets. SOC measured in dark incubations conducted in early summer ranged from 128 μmol m⁻² h⁻¹ at the deepest (360 m) to 1222 μmol m⁻² h⁻¹ at the shallowest (4.2 m) site and decreased significantly with water depth (p<0.001, r²=0.78, SOC=1222.8−456.3×log₁₀[water depth], n=14 sites). These rates were in the range found on continental shelves elsewhere (64–1750 μmol m⁻² h⁻¹, n=30 studies) and had a very similar distribution with water depth. SOC was also measured in light incubations at seven sites (4.2–35 m water depth) to examine the effects of microphytobenthos and accounted for 42–106% of rates measured in the dark. Measurements of near-bed light intensities suggested that microphytobenthos production was not solely regulated by light intensity but evidently influenced by other factors. A two-dimensional PCA ordination of surface sediment properties accounted for 83.3% of the total variance in the data and divided the study area into three clusters that corresponded well to its spatial division into the shallow (<30 m) Firth of Thames, the Hauraki Gulf (30–50 m) and the northern shelf-slope region. In the Firth of Thames sediments were very fine-grained with low CaCO₃ and high total organic matter and pigment content, and low C:N ratios. The northern shelf-slope sediments showed the opposite trends to the Firth of Thames and those in the Hauraki Gulf had mostly intermediate values. Dark SOC was significantly correlated with sediment organic matter, carbon, nitrogen, pigments and silt/clay content (p<0.05, r=0.55–0.85) but a multiple linear regression revealed that water depth was the only significant predictor. Calculations suggest that approximately 13%, 10% and 34% of primary production is remineralised in the sediments of the northern shelf-slope region, Hauraki Gulf and Firth of Thames, respectively, indicating a strong benthic–pelagic coupling on the northeastern New Zealand continental shelf that was particularly pronounced in the Firth of Thames due to its shallow depth and significant terrestrial and riverine inputs.     

太平洋中部富REY深海沉积物的地球化学特征及化学分类

赋存于深海沉积物中的稀土资源是一种潜在的稀土资源。对太平洋中部30个重力活塞柱状样中的1 275个深海沉积物样品的常量、稀土化学分析数据进行了系统研究。在涂片鉴定的基础上,采用Ca O和Al2O3含量把太平洋中部深海沉积物划分为钙质软泥类沉积物、硅质软泥类沉积物、深海黏土类沉积物三种成因类型;这三种类型沉积物的稀土分布模式相似,表现为明显的Ce负异常,一定程度的重稀土元素富集和Y正异常,深海黏土类沉积物的ΣREY明显偏高。采用主要元素(包括Ca O/P2O5比值)与REY的关系图可以有效地判别不同成因类型沉积物的混合状况。太平洋中部富P、富含沸石的深海黏土类沉积物是最有利的富REY的深海沉积物类型。太平洋中部深海沉积物REY富集的主要原因是由于深海沉积物中混入了过量的(鱼牙骨碎屑状)磷灰石组分,而钙质生物组分和硅质生物组分的加入对REY含量起了明显的稀释作用。     

Carbon and oxygen isotopes: a tool for Jurassic and early Cretaceous pelagic correlation (southern Spain)

The isotopic evolution of δ¹³C and δ¹⁸O is reported for the Jurassic and early Cretaceous in two pelagic sections of the External Zones in the Betic Cordilleras (SE Spain). Stable isotope curves from pelagic trough and swell sections display similar patterns. Variations in δ¹⁸O and δ¹³C values from strata at equivalent age probably reflect both early diagenetic cementation and later temperature‐related burial diagenesis. Comparison of global isotope curves with those presented in this work allows the differentiation of global from local events. Thus, the anoxic event during the early Toarcian (falciferum Zone) is characterized by elevated δ¹³C and depressed δ¹⁸O values. The isotopic record also allows the detection of the middle Oxfordian transgression. There are other peaks for the late Toarcian, early Bajocian, Callovian and early Berriasian that can also be used as tools for correlation purposes. Copyright © 2002 John Wiley & Sons, Ltd.