科学大洋钻探与深部生物圈

从深海钻探计划(DSDP)在20世纪70年代最早提出海洋沉积物中细菌活动性的证据到90年代大洋钻探计划(ODP)获得了令人信服的海底深部生物的存在证据，并成为即将启动的综合大洋钻探计划(IODP)的一个优先研究领域，深部生物圈成为科学大洋钻探近年来最为重大的发现之一，同时它也将有效地促进地球科学和生物学等其他学科的交叉。     

从ODP到IODP

大洋钻探计划（ODP）结束以后实施的整合大洋钻探计划（IODP）与以往钻探计划不同的是将以多个钻探平台为主，其航次将进入过去ODP无法进入的地区，将在古环境、海底资源（包括气体水合物）、地震机制、大洋岩石圈、海平面变化、深部生物圈等研究方面有所突破。从ODP到IODP有一过渡机构－ISAS，于2001年6月开始运作，到IODP开始实施时结束使命。ISAS将负责航次建议书的接受与评估、确保ODP与IODP的平稳过渡及负责与IODP有关的公共活动等工作。     

IODP 311航次底栖有孔虫碳稳定同位素对天然气水合物地质系统的指示

为了探索海洋天然气水合物背景下有孔虫特征的响应,对综合大洋钻探计划(IODP) 311航次岩芯沉积物中底栖有孔虫Uvigerina peregrina和Bulimina mexicana进行了初步研究。通过对冷泉站位U1328和毗邻的非冷泉站位U1327沉积物中底栖有孔虫Uvigerina peregrina和Bulimina mexicana的显微形貌特征和碳、氧稳定同位素测试等,证实有孔虫壳体未受到后期成岩作用的改造和自生碳酸盐岩的交代影响,有孔虫壳体的碳稳定同位素呈现明显的负偏。其中U1327站位中U.peregrina δ¹³C为-0.67‰～-2.75‰（PDB）,B.mexicana δ¹³C为-0.51‰～-1.52‰（PDB）;U1328站位中U.peregrina δ¹³C为 -0.72‰～-2.71‰（PDB）,B.mexicanaδ¹³C为 -0.58‰～-1.45‰（PDB）。底栖有孔虫壳体的碳稳定同位素负偏成因可能与水合物不稳定分解释放的甲烷厌氧氧化作用和食物源有关,因而可较好地指示海底天然气水合物系统地质背景。     

Depositional setting,provenance, and tectonic-volcanic setting of Eocene–Recent deep-sea sediments of the oceanic Izu–Bonin forearc,northwest Pacific (IODP Expedition 352)

New biostratigraphical, geochemical, and magnetic evidence is synthesized with IODP Expedition 352 shipboard results to understand the sedimentary and tectono-magmatic development of the Izu–Bonin outer forearc region. The oceanic basement of the Izu–Bonin forearc was created by supra-subduction zone seafloor spreading during early Eocene (c. 50–51 Ma). Seafloor spreading created an irregular seafloor topography on which talus locally accumulated. Oxide-rich sediments accumulated above the igneous basement by mixing of hydrothermal and pelagic sediment. Basaltic volcanism was followed by a hiatus of up to 15 million years as a result of topographic isolation or sediment bypassing. Variably tuffaceous deep-sea sediments were deposited during Oligocene to early Miocene and from mid-Miocene to Pleistocene. The sediments ponded into extensional fault-controlled basins, whereas condensed sediments accumulated on a local basement high. Oligocene nannofossil ooze accumulated together with felsic tuff that was mainly derived from the nearby Izu–Bonin arc. Accumulation of radiolarian-bearing mud, silty clay, and hydrogenous metal oxides beneath the carbonate compensation depth (CCD) characterized the early Miocene, followed by middle Miocene–Pleistocene increased carbonate preservation, deepened CCD and tephra input from both the oceanic Izu–Bonin arc and the continental margin Honshu arc. The Izu–Bonin forearc basement formed in a near-equatorial setting, with late Mesozoic arc remnants to the west. Subduction-initiation magmatism is likely to have taken place near a pre-existing continent–oceanic crust boundary. The Izu–Bonin arc migrated northward and clockwise to collide with Honshu by early Miocene, strongly influencing regional sedimentation.     

南海大洋钻探及海洋地质与地球物理前沿研究新突破

南海是西太平洋地区规模最大且具有代表性的边缘海盆地之一。经过近几十年的研究积累,尤其是通过实施5个国际大洋钻探航次(1999–2018年)与国家自然科学基金委“南海深海过程演变”重大研究计划(2011–2019年),我国科学家获得了大量宝贵的第一手资料,取得了一系列创新进展与重大突破,标志着南海海洋地质与地球物理研究正走向国际前沿。重要研究成果包括:(1)新提出南海是“板缘张裂”盆地,与经典的大西洋型陆缘模式不同;(2)大洋钻探首次获取了基底玄武岩样品,结合中国在南海首次深拖地磁测量实验,精确测定了南海海盆玄武岩年龄,揭示南海海盆从东向西分段扩张;(3)大洋钻探结果发现南海陆缘岩石圈减薄之初岩浆迅速出现,未发现缓慢破裂造成的蛇纹岩出露;(4)发现南海扩张结束后仍存在大量岩浆活动,可能受控于多种构造与地幔因素;(5)地球化学证据与地球动力学模拟都显示南海岩浆的形成受到周边俯冲带的影响。目前我国的海洋地球科学正在进入崭新的发展阶段,有望以南海为基点,开始拓展到周边大洋,通过主导大型研究计划以及建设我国大洋钻探平台,以提升我国在南海、西太平洋与印度洋海洋地质科学研究的实质性影响力与引领地位。     

Modelling the Shimokita deep coalbed biosphere over deep geological time: Starvation,stimulation, material balance and population models

Basin models can simulate geological, geochemical and geophysical processes and potentially also the deep biosphere, starting from a burial curve, assuming a thermal history and utilizing other experimentally obtained data. Here, we apply basin modelling techniques to model cell abundances within the deep coalbed biosphere off Shimokita Peninsula, Japan, drilled during Integrated Ocean Drilling Program Expedition 337. Two approaches were used to simulate the deep coalbed biosphere: (a) In the first approach, the deep biosphere was modelled using a material balance approach that treats the deep biosphere as a carbon reservoir, in which fluxes are governed by temperature-controlled metabolic processes that retain carbon via cell-growth and cell-repair and pass it back via cell-damaging reactions. (b) In the second approach, the deep biosphere was modelled as a microbial community with a temperature-controlled growth ratio and carrying capacity (a limit on the size of the deep biosphere) modulated by diagenetic-processes. In all cases, the biosphere in the coalbeds and adjacent habitat are best modelled as a carbon-limited community undergoing starvation because labile sedimentary organic matter is no longer present and petroleum generation is yet to occur. This state of starvation was represented by the conversion of organic carbon to authigenic carbonate and the formation of kerogen. The potential for the biosphere to be stimulated by the generation of carbon-dioxide from the coal during its transition from brown to sub-bituminous coal was evaluated and a net thickness of 20 m of lignite was found sufficient to support an order of magnitude greater number of cells within a low-total organic carbon (TOC) horizon. By comparison, the stimulation of microbial populations in a coalbed or high-TOC horizon would be harder to detect because the increase in population size would be proportionally very small.     

21世纪的大洋钻探——IODP

人类在地球科学方面已取得了相当大的成就,但就研究范围而言,却仅仅触及了地球的表层。IODP是一项国际性的大洋钻探计划,预期将于2003年10月正式开始实施。IODP将运用新的科学方法、科技设备,使人类对大洋底乃至整个地球系统得出更深、更广的认识。简单介绍了IODP的由来、组织机构、钻井技术、前期科学目标及中国的深海研究现状,提出中国参与IODP的必要性和可行性。通过了解21世纪的IODP在研究课题及研究技术方面的最新动态,不仅有助于我国根据国际动态调整深海研究的方向,制定符合我国需求的研究计划,而且有助于我国把握参与21世纪IODP的时机和策略,迎接“海洋世纪”的挑战,从而逐步实现“从地学大国走向地学强国”的目标。     

南海IODP 349航次基底玄武岩中碳酸盐岩脉的岩石学特征*

国际大洋发现计划(International Ocean Discovery Program, IODP)349航次在南海东部次海盆和西南次海盆残留扩张脊附近的U1431和U1433站位首次钻取基底玄武岩, 通过对16块基底玄武岩内的碳酸盐岩脉薄片镜下观察以及激光拉曼光谱分析, 揭示碳酸盐矿物为方解石和文石, 为典型的洋壳低温热液蚀变次生矿物。U1431站位碳酸盐岩脉为独立的方解石脉、文石脉交替出现; 而U1433站位则存在方解石脉、文石脉和方解石-文石共生脉三种情况。此外, U1431站位在基底~42.1m处出现了平行的方解石脉和文石脉, 揭示U1431存在不同来源热液的多期活动, 即可能存在多次或多阶段不同的热液注入。U1431和U1433站位的碳酸岩脉中, 文石的矿物集合体形状基本一致, 呈块状、纤维状和放射纤维状; 而方解石存在差异, U1431的方解石以斑块状、块状、粒状和纤维状出现, 而U1433的方解石仅出现块状。U1431站位的碳酸盐岩脉的丰度明显高于U1433站位。这些均揭示U1431站位的低温热液活动强, 而U1433站位则相对弱。两个站位的热液活动不同很可能是由于区域地质环境的差异造成——U1431附近的巨大海山为其提供了热液补给, 而U1433远离热液的补给/渗漏点。     

新生代深海冷水碳酸盐泥丘成因及IODP 307航次初步研究结果

记述了新生代深海冷水碳酸盐泥丘近期的9个重要研究事件;总结了冷水泥丘具有全球海洋(大陆斜坡为主)分布、形态各异、冷水枝状珊瑚构筑泥丘的特点;介绍了冷水泥丘形成的(地质流体渗流和微生物作用)内因及(海底牵引底流作用)外因两种主要观点.对2005年IODP 307航次实施的北大西洋Porcupine Seabight冷水泥丘大洋钻探工作初步成果进行了编译,公布了中国科学家在碳氧同位素方面的初步实验结果.实验结果显示上新世中期以来的2 Ma里冷水碳酸盐泥丘启动和发育过程中存在2次碳氧同位素偏移事件(Ⅰ和Ⅱ),碳氧同位素偏移事件Ⅰ与泥丘的启动相呼应,暗示北大西洋古海洋气候发生巨大变化,可能与北极冰盖极盛有关.     

沉积物粒度对水合物形成的制约：来自IODP 311航次证据

对取自IODP 311航次（东北太平洋Cascadia大陆边缘）所有5个站位、采样间距约为1.5 m的614件沉积物样品，利用Beckman Coulter LS 230激光粒度仪进行了沉积物粒度分析，获得了沉积物粒度随深度变化特征，进而与水合物层位的替代指标进行了位置对比，这些指标包括特殊沉积构造（soupy和mousse like构造）、测井数据（LWD）推算出来的水合物饱和度（Sh）、岩芯红外图像和实际钻取的含水合物沉积物等。发现沉积物粒度分别为31~63 μm和63~125 μm的2组较粗粒径的沉积物数量变化增多的位置与水合物出现层位之间存在较好的位置对应关系。如在U1326站位海底以下5~8 m、21~26 m、50~123 m、132~140 m、167~180 m、195~206 m、220~240 m深度位置出现了沉积物粒度明显偏向粗粒的趋势，而这些位置正好对应于大多数特殊沉积构造出现的深度，也对应于水合物饱和度（Sh）值相对较高的深度，并与一些实际钻取的赋含水合物的浊积沙层观察结果一致。因此，初步研究后认为，沉积物粒度在水合物形成过程中扮演了重要角色，天然气水合物可能偏向形成于粒度大于31 μm的粗粒沉积物中。  