Mineralogy,geochemistry, and radiocarbon ages of deep sea sediments from the Gulf of Mexico,Mexico

The mineralogy, geochemistry, and radiocarbon ages of two sediment cores (GMX1 and GMX2) collected from the deep sea area of the Southwestern Gulf of Mexico (∼876–1752 m water depth) were studied to infer the sedimentation rate, provenance, heavy metal contamination, and depositional environment. The sediments are dominated by silt and clay fractions. The mineralogy determined by X-Ray diffractometry for the sediment cores reveals that montmorillonite and muscovite are the dominant clay minerals. The sections between 100 and 210 cm of the sediment cores GMX1 and GMX2, respectively, are characterized by the G. menardii group and G. Inflata planktonic foraminiferal species, which represent the Holocene and Pleistocene, respectively. The radiocarbon-age measurements of mixed planktonic foraminifera varied from ∼268 to 45,738 cal. years B.P and ∼104 to 25,705 cal. years B.P, for the sediment cores GMX1 and GMX2, respectively. The variation in age between the two sediment cores is due to a change in sediment accumulation rate, which was lowest at the location GMX1 (0.006 cm/yr) and highest at the location GMX2 (0.017 cm/yr).The chemical index of alteration (CIA), chemical index of weathering (CIW), and index of chemical maturity (ICV) values indicated a moderate intensity of weathering in the source area. The total rare earth element concentrations (∑REE) in the cores GMX1 and GMX2 vary from ∼94 to 171 and ∼78 to 151, respectively. The North American Shale Composite (NASC) normalized REE patterns showed flat low REE (LREE), heavy REE (HREE) depletion with low negative to positive Eu anomalies, which suggested that the sediments were likely derived from intermediate source rocks.The enrichment factor of heavy metals indicated that the Cd and Zn concentrations in the sediment cores were impacted by an anthropogenic source. The redox-proxy trace element ratios such as V/Cr, Ni/Co, Cu/Zn, (Cu + Mo)/Zn, and Ce/Ce* indicated that the sediments were deposited under an oxic depositional environment. The similarity in major element concentrations, REE content, and the NASC normalised REE patterns between the cores GMX1 and GMX2 revealed that the provenance of sediments remained relatively uniform or constant during deposition for ∼4.5 Ma. The major and trace element based multidimensional discrimination diagrams showed a rift setting for the core sediments, which is consistent with the geology of the Gulf of Mexico.     

Indium mineralisation in SW England: Host parageneses and mineralogical relations

The SW England ore region contains significant amounts of indium (In) in Early Permian granite-related skarn and lode parageneses and, to a lesser extent, Triassic epithermal “crosscourse” veins. Ore parageneses that predate granite emplacement (Devonian and Lower Carboniferous sedimentary exhalative and vein parageneses) are largely devoid of In. Cadmium (Cd) and gallium (Ga) occur widely in all sulphide-bearing parageneses across the region with sphalerite concentrations locally reaching 1.74 wt% Cd and 1750 ppm Ga.Indium displays a strong affinity to sulphide-bearing magmatic-hydrothermal parageneses. It occurs in silicate-sulphide skarns, polymetallic sulphide lodes and sulphide-bearing portions of greisen-bordered sheeted vein systems and quartz-tourmaline lodes across the region. Magnetite-silicate skarns and quartz-tourmaline lodes that are devoid of sulphide, in contrast, were comparatively unfavourable for In precipitation. The highest In concentrations are found in mineral lodes associated with the Carnmenellis and St Agnes granites, which are the districts that had the highest historical production of Sn. Total In concentrations in these areas locally exceed 430 ppm, while concentrations elsewhere are systematically below 200 ppm.The principal In hosts are chalcopyrite, sphalerite and stannite group minerals with local concentrations within cassiterite and tennantite. Surprisingly, chalcopyrite accounts for the majority of the In budget throughout the region, although concentrations are highest in sphalerite and stannite group minerals. Sphalerite locally contains up to 1.42 wt% In, chalcopyrite has up to 2200 ppm and stannite group minerals up to 6800 ppm. No In was detected in löllingite, arsenopyrite, rutile, haematite, magnetite, tourmaline, biotite, chlorite, galena, bornite, chalcocite or pyrrhotite. Scattered concentrations in pyrite relate to impurities rather than incorporation by solid solution. Roquesite and possibly dzhalindite or native In formed locally where In-bearing chalcopyrite or sphalerite has been replaced by bornite and quartz. The In partitioning between sphalerite and chalcopyrite varies broadly between 1:1 and 10:1.Sporadic In was included in Triassic crosscourse veins as a result of interactions between migrating CaCl₂-rich basinal brines and earlier formed granite-related parageneses. The interactions involved at least two distinct components: 1) Incorporation of clasts of magmatic-hydrothermal veins in crosscourse veins during faulting, and 2) Dissolution and re-precipitation of magmatic-hydrothermal vein minerals in crosscourse fluids. Local concentrations reach 140 ppm In.The magmatic-hydrothermal parageneses in SW England are comparable to the South China Tin Belt, Mount Pleasant, as well as Erzgebirge/Krušné Hory. Magmatic-hydrothermal fluids associated with peraluminous granites have developed a variety of skarn, greisen, lode and veins parageneses by interactions with their host rocks and contained fluids. Crosscourse epithermal mineralisation occurred as In was transported by CaCl₂-rich basinal brines in a similar manner as In-bearing veins in the West Shropshire ore field.     

Mineralogy,petrology, and phase relations of glaucophane-lawsonite zone blueschists from the Tavşanli Region,Northwest Turkey

Glaucophane-lawsonite facies blueschists representing a metamorphosed sequence of basic igneous rocks, cherts and shales have been investigated northeast of the district of Tav?anli in Northwest Turkey. Sodic amphiboles are rich in magnesium reflecting the generally high oxidation states of the blueschists. Lawsonite has a very uniform composition with up to 2.5 wt.% Fe₂O₃. Sodic pyroxenes show an extensive range of compositions with all the end-members represented. Chlorites are uniform in their Al/(Al+Fe+Mg) ratio but show variable Fe/ (Fe+Mg) ratios. Garnets from metacherts are rich in spessartine (>50%) whereas those from metabasites are largely almandine. Pistacite rich epidote is found in metacherts coexisting with lawsonite. Phengites are distinctly higher in their Fe, Mg and Si contents than those from greenschist facies. Hematites with low TiO₂ are ubiquitous in metacherts. Fe²⁺/Mg partitioning between chlorite and sodic amphibole is strongly controlled by the calcium content of the sodic amphibole and ranges from 1.1 for low calcium substitution to 0.8 for higher calcium substitution. The Al/Fe³⁺ partition coefficient between sodic amphibole and sodic pyroxene is 2.1. A model system has been constructed involving projections from lawsonite, iron-oxide and quartz onto a tetrahedron with Na, Al, Fe²⁺ and Mg at its apices. Calcite is treated as an indifferent phase. The model system illustrates the incompatibility of the sodic pyroxene with chlorite in the glaucophanelawsonite facies; this assemblage is represented by sodic amphibole. Sodic amphibole compositions are plotted in terms of coexisting ferromagnesian minerals. Five major areas on the sodic amphibole compositional field are delineated, each associated with one of the following minerals: chlorite, stilpnomelane, talc, almandine, deerite.     

广西八渡金矿床含金硫化物矿物学与地球化学研究

广西田林县八渡金矿床主要产于辉绿岩侵入体中,广泛发育乳白色石英网脉,蚀变辉绿岩体即为金矿体,具有硅化、粘土化、碳酸盐化和硫化物化等卡林型金矿热液蚀变特征。本文采用电子探针(EPMA)背散射电子图像(BSE)、波谱(WDS)和能谱(EDS)分析技术,对该矿床原生矿石中含金硫化物显微岩相学结构以及主量和微量元素含量和分布规律进行了系统研究,认为金主要是以不可见化学结合态金(Au+)的形式赋存于含砷黄铁矿和毒砂之中。含金硫化物与热液交代形成的金红石密切共生,并保留含钛铁辉石或钛铁矿等矿物的假象,金红石的形成是辉绿岩中含钛铁辉石或钛铁矿热液蚀变的产物,含金硫化物形成所需要的Fe来自辉绿岩中含钛辉石或钛铁矿等矿物的溶解,Fe的硫化物化过程是导致含金硫化物形成的重要机制。     

Chemical investigations of Atlantis II and discovery brines in the Red Sea

Analytical data for the Atlantis II and Discovery deeps in the Red Sea are given. The data were collected in March and June 1976 during the 22nd cruise of R/V Akademik Kurchatov in the Indian Ocean. On board analyses were performed of density, chlorinity, Mg, Ca, Sr and trace elements. The salinity, calculated from the density, is related to the chlorinity by S = 1.67 Cl + 4.02. The Ca-salinity relation is linear for both deeps showing that intermediate waters are formed by mixing of the brines with Red Sea water (RSDW). The hot brine (62°C) in the Atlantis II deep contains approx. 80 mg/kg of Fe and Mn while the warm brine (45°C) in the Discovery deep has a very low concentration of Fe and approx. 50 mg/kg of Mn. Mixing of RSDW containing 2 ml/l of oxygen with the anoxic deep brines causes precipitation of hydrous Mn(IV) and Fe(III) hydroxides. These two processes occur at different depths in the two deeps due to the formation of the warm (48–49°) intermediate brine in the Atlantis II deep. The oxidation-hydrolysis reactions proposed are supported by alkalinity-depth profiles and measurements of pH. These reactions also explain most of the trace element distributions and the composition of the SiO₂-Fe(III) hydroxide slurry recovered by some water samplers in the Atlantis II deep.     

Mineralogy and geochemistry of reduction spheroids in red beds

Summary The mineralogy and geochemistry of reduction spheroids from continental and marine red beds of Europe, North America and Oman were investigated. Reduction spheroids are spheroidal, isolated reduction sites in hematitic rocks. They consist of a mineralized core (0.1 to 5 cm diameter) and a hematite-dissolution halo (1 to 20 cm diameter). Irrespective of origin and age of host rocks, all reduction spheroid cores show a very similar mineralogy dominated by the vanadian mica roscoelite and a similar pattern of element enrichment relative to their host rocks dominated by V and U. Element enrichments in most reduction spheroids are very similar to those of sandstone-hosted vanadium-uranium deposits except for a lack of a molybdenum enrichment. Isotopically light sulfide of in-situ, low-temperature origin is an indication for the involvement of bacterial sulfate reduction during reduction spheroid formation.

---

Mineralogie und Geochemie von Reduktionshöfen in Rotsedimenten

Zusammenfassung Reduktionshöfe aus kontinentalen und marinen Rotsedimenten von Europa, Nordamerika und aus dem Oman wurden geochemisch und mineralogisch untersucht. Reduktionshöfe sind kugelsymmetrische, isolierte Reduktionszentren in hämatithaltigen Gesteinen. Sie bestehen aus einem mineralisierten Kern von 0.1 bis 5 cm Durchmesser welcher von einem infolge Hämatitlösung gebleichten Hof von 1 bis 20 cm Durchmesser umgeben ist. Reduktionshöfe zeigen unabhängig von ihrer Herkunft und vom Alter des Nebengesteins immer eine sehr ähnliche Mineralogie der mineralisierten Kerne mit dominierendem Roscoelith sowie eine ähnliche Charakteristik der Elementanreicherung relativ zum Muttergestein. Die Elementanreicherung wird von V und U dominiert und gleicht jener von Sandstein-Typ Vanadium-Uran-Lagerstätten mit Ausnahme des Fehlens einer Molybdänanreicherung. In-situ unter Tieftemperaturbedingungen produziertes, isotopisch leichtes Sulfid ist ein Hinweis darauf, dass bakterielle Sulfatreduktion bei der Bildung der Reduktionshöfe eine Rolle spielte.

---

---

With 7 Figures     

Authigenic carbonates in methane seeps from the Norwegian sea: Mineralogy, geochemistry, and genesis

Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active CH₄bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community consists of specific methane-producing bacteria, which act as methanetrophic ones in conditions of excess methane, and sulfate reducers developing on hydrogen, which is an intermediate product of microbial CH₄ oxidation. Isotopically light carbon (δ¹³C_av =−28.9%0) of carbon dioxide produced during CH₄ oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (δ¹⁸O_av = 5%0) in carbonates is inherited from seawater sulfate. A rapid sulfate reduction (up to 12 mg S dm⁻³ day⁻¹) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this, carbonates can only be formed in surface sediments near the water-bottom interface. Authigenic carbonates occurring within sediments occur do notin situ. Salinity, as well as CO ₃ ²⁻ /Ca and Mg/Ca ratios, correspond to the field of nonmagnesian calcium carbonate precipitation. Calcite is the dominant carbonate mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. The radiocarbon age of carbonates is about 10000 yr.     

Low temperature hydrothermal maturation of organic matter in sediments from the Atlantis II Deep,Red Sea

Hydrocarbons and bulk organic matter of two sediment cores (No. 84 and 126, CHAIN 61 cruise) located within the Atlantis II Deep have been analyzed. Although the brines overlying the coring areas were reported to be sterile, microbial inputs and minor terrestrial sources represent the major sedimentary organic material. This input is derived from the upper water column above the brines.Both steroid and triterpenoid hydrocarbons show that extensive acid-catalyzed reactions are occurring in the sediments. In comparison with other hydrothermal (Guaymas Basin) or intrusive systems (Cape Verde Rise), the Atlantis II Deep exhibits a lower degree of thermal maturation. This is easily deduced from the elemental composition of the kerogens and the absence of polynuclear aromatic hydrocarbons of a pyrolytic origin in the bitumen.The lack of carbon number preference among the n-alkanes suggests, especially in the case of the long chain homologs, that the organic matter of Atlantis II Deep sediments has undergone some degree of catagenesis. However, the yields of hydrocarbons are much lower than those observed in other hydrothermal areas. The effect of lower temperature and poor source-rock characteristics appear to be responsible for the differences.     

Mineralogy and chemistry of Cu-Fe-Ni sulfides in orogenic-type spinel peridotite bodies from Ariege (Northeastern Pyrenees,France)

Mantle-derived peridotite bodies of Ariège are composed of spinel lherzolites and harzburgites ranging from remarkably fresh (less than 5% serpentinized) samples with protogranular texture to secondary foliated samples, which are generally 10%–20% serpentinized. The foliated samples have passed through two cycles of deformation and re-crystallization, the earlier ones occurring at temperatures above 950° C for 15 kbar pressure, the later ones at temperatures between 950° and 750° C for 8–15 kbar. Microscopic investigation of 140 samples reveals an accessoy sulfide component which is more abundant in lherzolie than in harzburgite. This component occurs in two differet textural locations, either as inclusions trapped within silicates during the first stage of re-crystallization or as interstitial grains among silicates. Mineralogy and chemistry of both sulfide occurrences are quite similar, at least in samples less than 5% serpentinized. In these fresh samples, sulfides are composed of complex intergrowths between nickel-rich pentlandite and pyrite, coexisting with minor primary pyrrhotite (Fe₇S₈) and chalcopyrite. Pentlandite and pyrite are interpreted as low-temperature breakdown products of upper mantle monosulfide solid solutions. The mineralogy and chemistry of interstitial sulfides in serpentinized rocks vary in parallel with the degree of serpentinization. In samples less than 10% serpentinized, primary pyrrhotite grades into FeS. In samples more than 10% serpentinized, pyrite is replaced by secondary pyrrhotite, and then disappears totally, whereas the coexisting pentlandite is Fe-enriched and replaced by mackinawite. This sequence of alteration indicates a decrease of sulfur fugacity, resulting from serpentinization of olivine at temperatures below 300° C. This is also the case for the inclusions which have been fractured during the tectonic emplacement of the host peridotites within the crust. The presence of non-equilibrium sulfide assemblages in both cases reflects the sluggishness of solid state reactions at near-surface temperatures. It is inferred from these results that sulfides disseminated within orogenic peridotite massifs are so sensitive to serpentinization that most sulfur fugacity estimates based on fractured inclusions and intergranular sulfides are unreliable.     

Greenhouse gas deposits in the deep sea

Gas hydrates are the largest deposits of hydrocarbons in the world. They are distributed throughout marine sediments and their stability depends largely upon temperature and pressure. Typically, ～99 percent of these hydrocarbon deposits are composed of methane, which is a potent greenhouse gas. Methane release from gas hydrates has been implicated in mass extinction events. Present and future changes in ocean temperature have the potential to increase the rate of methane production from gas hydrates and thus to affect Earth's climate. Whilst the deep sea normally serves as a sink for greenhouse gases, the release of methane from gas hydrates could be a hugely significant source in the future and pose a real threat to our efforts to limit greenhouse gas emissions.     

“四深”微生物的地质作用：从气候环境变化到生态灾难

“四深”微生物是指深海、深地、深空和深时环境的微生物,特别是细菌、古菌、真菌、病毒等。人们对“四深”微生物的了解非常有限,是亟待突破的地球生物学前沿领域。“四深”微生物的研究对理解地球生命起源、界定生物圈的边界条件、促进地球科学与生命科学以及行星科学之间的交叉融合具有不可替代性的贡献。随着我国深海、深空、深地等重大工程计划的推进,一系列与“四深”微生物有关的前沿科学问题不断提出,包括地质微生物与气候环境的相互作用、地质微生物的生物安全与生态安全、地质微生物参与的隐匿地质过程等。特别是,“四深”环境活性氧自由基对微生物的影响、地质病毒对生物演化和地质过程的影响等前沿领域都亟待突破。活性氧自由基能对生物分子、细胞、组织和器官,乃至整个生物圈的演化以及微生物地质作用都产生重要影响。病毒引发了现代和近代诸多全球性疫情爆发,地质病毒则可能对生物的背景灭绝和大灭绝以及一些地质过程产生影响。     

“四深”微生物的地质作用——从气候环境变化到生态灾难

“四深”微生物是指深海、深地、深空和深时环境的微生物,特别是细菌、古菌、真菌、病毒等。人们对“四深”微生物的了解非常有限,是亟待突破的地球生物学前沿领域。“四深”微生物的研究对理解地球生命起源、界定生物圈的边界条件、促进地球科学与生命科学以及行星科学之间的交叉融合具有不可替代性的贡献。随着我国深海、深空、深地等重大工程计划的推进,一系列与“四深”微生物有关的前沿科学问题不断提出,包括地质微生物与气候环境的相互作用、地质微生物的生物安全与生态安全、地质微生物参与的隐匿地质过程等。特别是,“四深”环境活性氧自由基对微生物的影响、地质病毒对生物演化和地质过程的影响等前沿领域都亟待突破。活性氧自由基能对生物分子、细胞、组织和器官,乃至整个生物圈的演化以及微生物地质作用都产生重要影响。病毒引发了现代和近代诸多全球性疫情爆发,地质病毒则可能对生物的背景灭绝和大灭绝以及一些地质过程产生影响。     

宁波北仑电厂二期循环水泵房基抗支护与监测

介绍了宁波北仑电厂二期工程地下连续墙支护结构的计算与模型。采用ALGOR有限元分析系统，对基坑开挖引起的应力场、位移场进行了分析计算。对墙体变形、钢筋应力、土压力及沉降进行了观测。通过计算值与实测结果的比较，分析了影响基坑变形的主要因素。     

安徽安庆铜铁矿床钴的赋存状态、分布与富集规律研究

长江中下游成矿带是我国东部最重要的成矿带之一, 广泛发育矽卡岩型铜铁矿床且伴生Co资源, 而成矿带内的矽卡岩型铜铁矿床中关键金属Co元素的赋存状态、分布以及富集规律研究尚未系统开展。本文以矽卡岩型铜铁矿床——安庆铜矿为研究对象, 通过系统采样、显微观察、扫描电子显微镜、全岩化学分析及矿物原位LA-ICP MS微量成分测试手段, 初步估算矿床中伴生Co的资源量约为8769t, 达到中型规模, 查明了伴生Co的平均含量为166×10^-6, 综合利用潜力较大。查明了铜矿石中Co含量(平均含量为166×10^-6)明显高于铁矿石(平均含量为126×10^-6), 尤其是含铜磁黄铁矿型矿石中Co元素富集程度最高, 且计算得出磁黄铁矿、黄铁矿、磁铁矿和黄铜矿分别赋存矿石Co含量的45.1 %、52.8%、0.5%和1.6%。此外, 矿床内不同类型矿化蚀变岩中Co含量与磁黄铁矿和黄铁矿总量具有较强的正相关性, Co主要以类质同像的形式赋存于黄铁矿和磁黄铁矿内, 黄铁矿中Co的含量变化范围较大, 早石英硫化物阶段的黄铁矿(Py1)中Co含量为258×10^-6~25920×10^-6, 晚石英硫化物阶段的黄铁矿(Py2)中Co含量为0.3×10^-6~594×10^-6, 磁黄铁矿中Co含量变化范围较小, 主要集中于311×10^-6~1181×10^-6, Co主要富集于早石英硫化物阶段, 晚石英硫化物阶段不富集。含铜磁黄铁矿型矿石中Co元素变化范围大(85×10^-6~430×10^-6)是由于矿石中黄铁矿和磁黄铁矿的含量以及黄铁矿Co含量极不均匀造成的。综合前人研究, 本次工作认为大气降水混入引起的成矿流体冷却和稀释可能是导致安庆铜矿中Co元素沉淀富集在黄铁矿和磁黄铁矿内的主要因素。

     

Carbon and nitrogen diagenesis in deep sea sediments

The sections penetrated on Leg 58 of the Deep Sea Drilling Project represent periods of geologic time during which depositional conditions apparently remained quite constant, thus offering an unusual opportunity to study the effects of diagenesis on organic material.Organic carbon and nitrogen contents decrease monotonically with increasing depth of burial before levelling off at minimum values of about 0.05-0.10 and 0.01%, respectively. The depths at which minima are reached vary from site to site, but the ages of the sediments at the minima are all about 2–5 Myr.These data indicate that diagenetic transformations are responsible for the gradual depletion of organic carbon and nitrogen. If diagenesis is at least partly the result of microbial activity, then the role of bacterial ecosystems in deep water sediments is much greater than has previously been thought.     

Basic phase relations of polybaric batch, percolative and critical melting

Summary ?Partial melting of the mantle is polybaric which implies that the phase relations change during partial melting. In addition to the pressure the composition of the melt depends on the melting mode. Various melting models have been suggested. Here the basic phase relations of polybaric batch, percolative, and critical melting are considered, using a simple ternary system. The percolative melts are in equilibrium with their residua, but differ somewhat in composition from those of batch melting. Critical melting is a fractional type of melting where the residuum contain interstitial melt. The critical melts differ in composition from batch melts. The linear trends of peridotites from ophiolites show that the extracted melts had nearly constant compositions, and therefore were extracted within a small pressure interval. A comparison between the trends of mantle peridotite and experimental batch melts suggests strongly that the melt extracted from the peridotites are in equilibrium with their residua. This could suggest that either batch or percolative melting are relevant melting modes for the mantle. However, isotopic disequilibria favor instead a critical mode of melting. This inconsistency can be avoided if the ascending melts are accumulated within a source region and equilibrate with the residuum before the melt is extracted from the source region. The evidence for equilibrium suggests that multisaturation of tholeiitic compositions in PT-diagrams is relevant for estimating pressure and temperature of generation of primary tholeiitic magmas. Received September 2, 2001; revised version accepted March 20, 2002     

Rhythms in deep sea, fine-grained turbidite and debris-flow sequences, Middle Ordovician, eastern Tennessee

Rhythms in fine-grained sediments have not previously been studied because of their complex depositional cycles and diagenetic changes. Examination of nearly 9000 layers in outcrops, polished slab samples, and thin sections has led to recognition of rhythms in the Middle Ordovician Whitesburg, Blockhouse, and Sevier formations of east Tennessee. Rhythms have been described in four orders based on relative magnitude. First order cycles (basin-fill sequences, hundreds of metres thick)are composed of thinning upward debris-flow sequences and thickening upward turbiditic shale sequences. Second order cycles (multiple sedimentation units, tens of centimetres thick) consist of: (1) thinning upward cycles; (2) symmetrical cycles; (3) thickening upward cycles; (4) minor multiple cycles; (5) uniform cycles; and (6) dubious cycles. Third order cycles (single sedimentation unit, tens of millimetres thick) have thinning upward and asymmetrical cycles. Fourth order portrays the grain-size variations within a single layer of the third order. First order rhythms were controlled by tectonism and progradation of a deep-sea fan system. Second and third order rhythms were controlled by depositional processes, bottom topography, and sediment source. Depositional processes, sediment source, and bioturbation were the dominant controlling factors in the fourth order. A deep-sea fan model is proposed for the fine-grained turbidites in which channels and lobes coexist in the lower fan. The lower fan/mid fan boundary is marked by the presence of a channel cycle near the top of a lobe sequence. The basin plain/lower fan boundary is suggested by the appearance of minor lobe cycles over the non-cyclic basin plain sequence.     

Alteration of volcanic matter in deep sea sediments: evidence from the chemical composition of interstitial waters from deep sea drilling cores

Six Deep Sea Drilling Project (DSDP) Sites (252, 285, 315, 317, 336, 386) were examined for the chemical composition of the dissolved salts in interstitial waters, the oxygen isotopic composition of the interstitial waters, and the major ion composition of the bulk solid sediments. An examination of the concentration-depth profiles of dissolved calcium, magnesium, potassium, and H₂¹⁸O in conjunction with oxygen isotope mass balance calculations confirms the hypothesis that in DSDP pelagic drill sites concentration gradients in Ca. Mg. K, and H₂¹⁸O are largely due to alteration reactions occurring in the basalts of Layer 2 and to alteration reactions involving volcanic matter dispersed in the sediment column. Oxygen isotope mass balance calculations require substantial alteration of Layer 2 (up to 25% of the upper 1000 m). but only minor exchange of Ca, Mg, and K occurs with the overlying ocean. This implies that alteration reactions in Layer 2 are almost isochemical.