The use of magnetic measurements to investigate the mineralogy of Icelandic lake sediments and to study catchment processes

Magnetic measurements made on sediment and catchment samples from two contrasting Icelandic lakes show how susceptibility and saturation isothermal remanent magnetisation alter as magnetic minerals pass from rock to soil to stream and into the lakes. There is no detectable growth of secondary magnetic minerals in Icelandic soil profiles and susceptibility peaks in the 62.5–1000 μm size range of mineral particles in the lake sediments. Changes in sediment source can be detected using combinations of magnetic measurements.     

南海ODP1144站深海沉积牵引体的岩石物理模型研究

ODP1144站是南海唯一钻揭深海沉积牵引体的站位,其完整的岩芯和测井资料为开展该沉积牵引体的岩石物理模型研究提供了良好的基础。此项研究对于理解南海深海沉积物中岩性参数与弹性参数间的关系具有重要意义,并可为根据反射地震资料开展定量岩性参数预测提供依据。对现有的深海沉积物岩石物理模型包括Wood悬浮模型、等球体颗粒接触模型、Sun速度一孔隙度关系模型进行了综述。根据岩芯分析资料将1144站深海沉积物的矿物组分简化为粘土矿物、碳酸盐、陆源碎屑和硅质生物4类;其中后3种组分的弹性模量及密度值分别由其代表矿物——方解石、石英及蛋白石的理论值代替,粘土矿物组分的等效弹性模量和等效密度则分别由Voigt-Reuss-Hill平均和体积平均计算得出。将3种岩石物理模型应用于1144站,计算得出深海沉积物的纵波速度并将其与声波测井纵波速度进行比较。结果表明,Sun模型计算结果与实测结果的吻合最好,误差最小;Wood模型所得结果在浅层与实测结果较吻合,在深层与实测结果出现偏差,误差较小;而等球体颗粒接触模型计算结果整体偏高,误差较大。     

http://www.sciencedirect.com/science/article/pii/S1674987115000407

The western continental margin of India is one of the highly productive regions in the global ocean.Primary productivity is induced by upwelling and convective mixing during the southwest and northeast monsoons respectively.Realizing the importance of high primary productivity,a sediment core was collected below the current oxygen minimum zone(OMZ) from the southwestern continental margin of India.This was dated by AMS radiocarbon and as many as 60 paleoclimate/paceoceanographic proxies,such as particle size,biogenic components,major,trace and rare earth elements(REEs) which were measured for the first time to determine sources of sediment,biogeochemical processes operating in the water column and their variations since the last glacial cycle.R-mode factor analysis of comprehensive data indicates that the dominant regulator of paleoproductivity is the southwest monsoon wind induced upwelling.Other paleoproductivity related factors identified are the marine biogenic component and biogenic detritus(as an exported component from the water column added to the bottom sediment).All paleoproductivity components increased significantly during the marine isotope stage-1(MIS-1)compared to those accumulated from MIS-4 to MIS-2.The second group of factors identified are the terrigenous sediments with heavy minerals like zircon and ilmenite.The terrigenous sediment,in particular,increased during MIS-2 when the sea-level was lower;however,the heavy mineral component fluctuated over time implying pulsed inputs of sediment.The diagenetic fraction and reducing component are the third group of factors identified which varied with time with increased accumulation during the MIS transitions.The primary productivity along the southwestern continental margin of India seems to have been controlled principally by the upwelling during the southwest monsoon season that was weaker from MIS-4 to MIS-2,as relative to that during the MIS-1.In contrast,increased glacial productivity noticed in sediments deposited below the current oxygen minimum zone(OMZ) along the north of the study area that can be linked to entrainment of nutrients through the intensified convective mixing of surface water during the northeast monsoon.The sequestration of greenhouse gases by the western continental margin of India was higher during glacial than interglacial cycles.     

Magnetic parameters,trace elements,and multivariate statistical studies of river sediments from southeastern India: a case study from the Vellar River

This contribution constitutes a new study using magnetic parameters and trace element determinations of pollutants in river sediments from the Tamil Nadu state. The Vellar River covers a total length of about 200 km and flows into the Bay of Bengal. Sediment samples were collected at different sediment depths (up to 90 cm) from 12 sites to investigate their magnetic properties (27 samples) and the contents of trace elements (21 out of 27 samples) along the river; as well as to perform magnetic studies for various grain size fractions (16 sub samples). The magnetic results of magnetic susceptibility and remanent magnetizations suggest that the magnetic signal of these sediments is controlled by ferrimagnetic minerals magnetite-like minerals and a minor contribution of antiferromagnetic carriers (such as hematite minerals). Detailed studies of selected samples showed a higher magnetic concentration in finer grain-sized fractions and a slightly different magnetic mineralogy. Magnetic concentration-dependent parameters evidenced high values, which, together with the background values, allowed us to identify magnetic enhancement at some sites. The Pearson correlation and multivariate statistical studies (Principal Component Analysis, Canonical Correlation Analysis) supported the relationship between the magnetic and chemical variables; in particular, magnetic susceptibility, anhysteretic and isothermal remanent magnetization are closely correlated to Co, Cr, Cu, Fe, V, Zn, and the pollution load index. In addition, Principal Coordinate Analysis and fuzzy C-means cluster analysis allowed us to make a classification and to perform a magnetic-chemical characterization of the data into four groups, thereby identifying critical (possibly polluted) sites from the Vellar River.     

The magnetic properties of Quaternary and Tertiary sediments in the southern North Sea

Cores from boreholes penetrating late Quaternary, glacial, interglacial and postglacial sediments and the underlying late Cenozoic delta complex of the southern North Sea have been examined for their magnetic properties. A magnetic polarity stratigraphy has been established as an aid to biostratigraphic dating of the sediments; the Kaena-Gauss and Gauss—Matuyama transitions and the base and top of the Olduvai subchron have been identified. The strength and stability of laboratory-induced isothermal remanent magnetisation display clear magneto-petrological variations, which match lithostratigraphic changes in the cores. Principal component analysis has picked out a basin-wide and palaeoenvironmental consistency in the magnetic data. Large, multi-domain magnetite grains predominate in the post-deltaic and fluvio-deltaic sediments, whereas smaller greigite or titanomagnetite grains are concentrated in the intertidal and marine deltaic facies. Since heavy mineral analysis indicates that most of the deltaic detritus derived from common source areas, the differences in magnetic mineralogy have probably been caused by the sediment transport processes operating within the delta complex.     

Sources and distribution of terrigenous organic matter delivered by the Atchafalaya River to sediments in the northern Gulf of Mexico

Suspended sediments (SS) from the Atchafalaya River (AR) and the Mississippi River and surficial sediment samples from seven shallow cross-shelf transects west of the AR in the northern Gulf of Mexico were examined using elemental (%OC, C/N), isotopic (δ¹³C, Δ¹⁴C), and terrigenous biomarker analyses. The organic matter (OM) delivered by the AR is isotopically enriched (∼−24.5‰) and relatively degraded, suggesting that soil-derived OM with a C4 signature is the predominant OM source for these SS. The shelf sediments display OC values that generally decrease seaward within each transect and westward, parallel to the coastline. A strong terrigenous C/N (29) signal is observed in sediments deposited close to the mouth of the river, but values along the remainder of the shelf fall within a narrow range (8-13), with no apparent offshore trends. Depleted stable carbon isotope (δ¹³C) values typical of C3 plant debris (−27‰) are found near the river mouth and become more enriched (−22 to −21‰) offshore. The spatial distribution of lignin in shelf sediments mirrors that of OC, with high lignin yields found inshore relative to that found offshore (water depth > 10 m).The isotopic and biomarker data indicate that at least two types of terrigenous OM are deposited within the study area. Relatively undegraded, C3 plant debris is deposited close to the mouth of the AR, whereas more degraded, isotopically enriched, soil-derived OM appears to be deposited along the remainder of the shelf. An important input from marine carbon is found at the stations offshore from the 10-m isobath. Quantification of the terrigenous component of sedimentary OM is complicated by the heterogeneous composition of the terrigenous end-member. A three-end-member mixing model is therefore required to more accurately evaluate the sources of OM deposited in the study area. The results of the mixing calculation indicate that terrigenous OM (soil-derived OM and vascular plant debris) accounts for ∼79% of the OM deposited as inshore sediments and 66% of OM deposited as offshore sediments. Importantly, the abundance of terrigenous OM is 40% higher in inshore sediments and nearly 85% higher in offshore sediments than indicated by a two-end-member mixing model. Such a result highlights the need to reevaluate the inputs and cycling of soil-derived OM in the coastal ocean.     

Assessment of suspended particulate pollution in the Bhadra River catchment,Southern India: an environmental magnetic approach

Open-cast mining generates sediment in river systems at globally significant scales. One of the challenges in attributing measured sediment loads to upstream mining activities is establishing the source of sediments that are a mixture of natural and mining-based materials. The environmental magnetic data (mass-specific magnetic susceptibility, anhysteretic remanent magnetisation, isothermal remanent magnetisation and inter-parametric ratios) on 57 samples of suspended sediment from the Bhadra River in the Sahyadri (the Western Ghat) of India have been used in this study. Samples were collected upstream, adjacent to and downstream of Kudremukh, a mountainous and high rainfall site where the largest mechanised open-cast mine in south Asia was located. Graphical and multivariate analyses and modelling of the data show that on average ~29% of the river suspended load downstream of the mine is derived from mining and allied activities at Kudremukh although the mine occupies less than 5% of the catchment. The contribution of primary ore is the maximum (18%), followed by transitional hard weathered ore (7%) and weathered ore (4%). The model has done a fairly good job of unmixing; the sum of errors is <1 for 40 samples, 1–4,254 for five samples and >71,000 for four samples. Modelling of samples with small mass seems to produce large errors. This investigation demonstrates the utility of environmental magnetic data, which can be obtained in a simple and rapid manner, and the unmixing of such data in identifying the contribution of mining activities to the total suspended sediment load.     

环境磁学反映的藏南沉错地区1300年来冷暖变化

塔里木西缘帕米尔-西昆仑山北麓和西南天山南麓前陆盆地中巨厚的晚新生代磨拉石建造在岩石地层上包括阿图什组、西域组、乌苏组和戈壁组.通过对这套磨拉石建造及其中生长地层和生长不整合的野外观测,结合磁性地层年代学,初步研究了西域砾岩(即西域组)和西域运动的起始年代以及西域运动可能的演化阶段,得到如下初步认识:1)研究区西域砾岩开始沉积于3.5～4 6 Ma B.P.之前,其底界具有穿时性,其年代从山体向前陆盆地一般逐渐变新;2)在上述前陆盆地分布着4～6排由晚新生代磨拉石建造组成的逆断层-褶皱带.各排褶皱带均发育有生长地层及生长不整合,生长地层的开始沉积指示了该排褶皱和相应生长不整合的开始形成.从最靠山体一排褶皱带生长地层开始沉积的年代,初步判定西域运动的起始年代在西昆仑山叶城附近约为3.6 Ma B.P.,在西南天山喀什附近显然早于2.4 Ma B P.此后该运动可能经历了4～6个活动阶段,每一阶段又由若干个相对活跃期和相对稳定期组成.它们可通过各排褶皱带内生长地层的产状、组成和年代测定来确定.本文还探讨了生长地层和生长不整合形成过程中构造变形与侵蚀-剥蚀和沉积作用间的相互关系.     

Sediment Organic Carbon in Todos Santos Bay, Baja California, Mexico

Sediment grain size and organic carbon (OC) data collected over the past 50 years, together with δ¹³C values of OC in recently collected samples, were analyzed to improve understanding of sediment OC distribution and abundance in Todos Santos Bay. Sediments in the submarine canyon at the mouth of the bay and in quiet-water locations along the shore are fine grained, high in OC, and have generally low δ¹³C values; sediments in high-energy environments are low in OC and have high δ¹³C values. A bivariate isotopic mixing model indicates that none of the sediments contain >50% terrigenous OC (average ~30%), and that the terrigenous OC content of the sediments is a small proportion of the OC content of local soils. Sediment OC composition is apparently controlled by energy-related sorting and deposition, oxidation of much of the original terrigenous OC, and replacement of some terrigenous OC by marine OC.     

Palaeoenvironmental application of magnetic measurements from inter-drumlin hollow lake sediments near Dungannon, Co. Tyrone, Northern Ireland

Measurements of palaeomagnetic horizontal remanent intensity, saturation isothermal remanence, coercivity of remanence, high field remanence and magnetic susceptibility, have been made on lateglacial and postglacial sediments from two small, inter-drumlin hollow lakes from central Northern Ireland. These magnetic measurements have been compared with pollen and chemical analyses from the same profiles and with complementary mineral magnetic data from local soils. Representative sediment samples have also been divided into a range of particle size fractions and each fraction has been subjected to magnetic investigation. Five distinctive stratigraphic horizons have been identified on the basis of the magnetic mineralogy. Two horizons relate to phases of pronounced erosion. One of these is connected with solifluction processes in the lateglacial and the other to an intensive period of farming activity which started in Medieval times. Two horizons are associated with periods of very high iron and manganese deposition and are possibly related to the precipitation of magnetic minerals within the lake. Hydrological changes during periods of local anthropogenic activity appear to produce magnetic mineral assemblages indicative of stream bed/bank substrate sources. The particle size data also support the suggestion that downcore changes in the mineral magnetic record are mainly caused by changes in the sediment source rather than particle size or sedimentological effects.     

Shift in detrital sedimentation in the eastern Bay of Bengal during the late Quaternary

Down-core variations of granulometric, geochemical and mineral magnetism of a 70-cm long sediment core retrieved from the eastern Bay of Bengal abyssal region were studied to understand sedimentation pattern and sediment provenance during the last ～12 kyr BP. Based on down-core physical and elemental variations, three units were identified: unit 3 (70–43 cm) is a ～30 cm thick clayey silt organic carbon-rich (0.5–0.92%) turbidite probably delivered by the Brahmaputra River during the late Quaternary period. Units 2 (43–24 cm) and 1 (24–0 cm) represent enhanced and reduced supply of coarse-grained detrital sediments from the Ganges River during early and late Holocene period, respectively. Increased terrigenous supply dilutes calcium carbonate (CaCO₃) and biogenic elements (P, Ba and Cu) in units 3 and 2. On the contrary, a reduction in detrital input enhances CaCO₃ and biogenic elements in unit 1. Lithogenic elements (Ti, Al, K and Rb) and shale-normalized REE patterns in all three units suggest terrigenous source. The shift in provenance from the Brahmaputra to the Ganges derived sediments is evident by a sharp increase in sediment grain size, increased concentration and grain size assemblages of magnetic minerals, lithogenic elements concentration and La_n/Yb_n ratio. This study highlights terrigenous dilution on biogenic sedimentation in the eastern Bay of Bengal sediments.     

Diagenetic Dissolution of Biogenic Magnetite in Surface Sediments of the Benguela Upwelling System

Intense primary biologic productivity in the surface waters of the Benguela upwelling system provides a high supply of organic matter to the sea floor at the continental slope off Namibia and sustains extreme concentrations of magnetite producing bacteria in the top sediment layers. Biogenic magnetite is thus by far the dominant carrier of the magnetic signal in these deposits also because of a very minor input of terrigenous ferrimagnetic minerals. Reducing conditions in the sediment column cause a selective dissolution of the bacterial magnetite fraction just a few centimeters below the main mineralization horizon. This diagenetic process is documented in detail by high-resolution rock magnetic analyses and transmission electron microscopy. Concentration dependent and grain-size sensitive magnetic parameters, such as susceptibility, laboratory imparted remanences, and hysteresis data, reveal a significant drop in ferrimagnetic mineral content within the upper 10 cm of the sediments accompanied by a gradual downward coarsening of the ferrimagnetic mineral assemblage from primarily magnetic single-domain particles in the top centimeters to multi-domain grains in deeper strata. Electron microscope observations enable both an unequivocal identification of bacterial magnetite on the basis of shape and grain-size and to trace dissolution effects on the biogenic magnetic mineral component to depth. Received: 9 November 1998 / Accepted: 10 October 1999     

Spatial trends in the geochemical composition of sediments in the Panuco River discharge area, Gulf of Mexico.

Major and trace elements, organic matter, carbonates, loss of ignition, grain size, gravel, sand, silt, clay, and qualitative mineralogical composition were determined on surficial marine sediments sampled during the stormy (February), dry (May), and rainy (September) seasons in the coastal area adjacent to Panuco River discharges into the Gulf of Mexico. The sediments supplied by the river move in a north-east direction, and are deposited in the north-east extreme of the studied area. Terrigenous sediments show a strong association of Al₂O₃ with Fe₂O₃, Na₂O, K₂O, P₂O₅, Rb, Cu, Zn, organic matter, clay, and grain size (Mz). Mineralogical analysis shows that they are formed by quartz, kaolinite, montmorillonite, illite-montmorillonite and biotite. The highest metal concentration of Cu (25 mg/kg), Zn (155 mg/kg), Pb (50 mg/kg) and organic matter (1.26%) was observed in the sampling points located very close to the river mouth. A statistical analysis was done with the information contained in the variables. Five significant factors explain 77% of the total variance: factor 1 is due to sediments from a terrigenous source, factor 2 corresponds to sediments from a biogenous source, factor 3 is associated to sediments with heavy minerals, factor 4 is due to Co concentration, and factor 5 is due to Ni concentration. The sediments supplied from the river had a short-term local impact on the sediment distribution, as observed by the carbonate and heavy mineral concentration of the sediments.     

Geochemical and mineral magnetic characterisation of urban sediment particulates,Manchester, UK

Urban sediments are part of a complex system in which particulates accumulate potentially toxic pollutants, ultimately posing a threat to urban water-bodies and public health. It is therefore important to recognise sources, signatures and pathways of urban particulates. Urban sediment samples were analysed from both inner and outer city road surfaces of Manchester, UK. High metal concentrations, coupled with the largely ferrimagnetic multi-domain (MD) mineral magnetic composition of the particulates, indicate inputs of anthropogenic origin, primarily particulates derived from automobiles, as being the dominant source to the urban sediment system. Iron and Pb concentrations show a clear spatial trend, whereby concentrations are enhanced in the inner city samples. Lead concentrations for inner and outer city samples average 354 and 185 μg g⁻¹, respectively. Iron concentrations for inner and outer city samples average 11302 and 6486 μg g⁻¹, respectively. Sequential extraction analysis shows the metals Mn, Fe, Zn and Pb are largely associated with the reducible fraction, whereas Cu is largely associated with the oxidisable fraction. Zinc is the only metal showing significant association with the exchangeable fraction (up to 33%), suggesting that it may be the most susceptible metal to mobilisation during runoff. Metal fractions identified as showing larger associations with the reducible and oxidisable fractions will continue to be vulnerable to mobilisation as a result of changes in ambient pH and/or redox conditions. Mineral magnetic concentration parameters, such as the saturation isothermal remanent magnetisation (SIRM), together with hysteresis parameters such as the coercive force and interparametric ratios (such as (B_o)_cr/H_c and IRM_-100mT/SIRM) show that ferrimagnetic MD minerals dominate the Manchester urban sediments. Average results for frequency-dependent susceptibility as a percentage (2%) suggest that the composition of these Manchester sediments is not dominated by soil-derived material, and therefore magnetically coarser, anthropogenically-derived material is dominant. Unlike Pb and Fe concentrations, mineral magnetic characteristics of the Manchester urban sediment samples exhibit no significant spatial variation.     

Magnetic properties of Pleistocene sediments from the Mediterranean sea: a correlation with the palaeoclimatic record

The magnetic properties of the late Quaternary hemipelagic sediment from piston core BS77-15 taken in the Tyrrhenian Sea were investigated and the results compared with palaeoclimatic records. The magnetic mineralogy of the sediment was studied and the magnetic carriers were identified by their spectra of coercivity and unblocking temperature. Investigations of rock magnetic parameters such as the Natural Remanent Magnetization (NRM), the low-field magnetic susceptibility χ, the frequency-dependent susceptibility χ fd , the acquisition of Anhysteretic Magnetization (ARM) and Isothermal Magnetization (IRM) and the Median Destructive Field (MDF) have established the downcore variations in terms of magnetic mineralogy, grain size and coercivity in the sediments. The rock magnetic parameters were compared with an alternative climatic record from the same core based on the faunal association of planktonic foraminifera. A significant correlation was found between faunal climatic record and χ fd . Together with the magnetic properties of the sediment this suggests that a palaeoclimatic signal is recorded by a fine-grained low-coercivity fraction of the magnetic minerals.     

甘肃环县剖面记录的末次间冰期地磁场

环县剖面的古地磁研究结果表明，在第一层古土壤S1的上部和下部分别存在两个地磁场异常。通过剖面磁化率曲线与深海沉积物氧同位素曲线的对比，建立了地磁场变化的时间序列。S1上部记录的地磁场异常，年龄与挪威-格陵兰海及大西洋中发现的地磁异常年龄相当。S1下部的地磁异常，以磁偏角方向强烈摆动，偶极磁场强度明显下降为特征，其年龄与报道的布莱克事件的年龄相当，也与索马里海和地中海所记录的大幅度偶极磁场减弱相吻合，但与西宁剖面的记录不同的是，环县剖面记录的地磁场从没有达到完全的倒转，VGP曲线表现为围绕采样点旋转的经过南半球低纬地区的大环。这些特征表明，在偶极磁场减弱期，具有强烈区域性的非偶极磁场的变化可能对地磁场起着重要的作用。     

Diterpenoid compounds and other lipids in deep-sea sediments and their geochemical significance

Cyclic diterpenoid compounds have been found by various investigators in the geosphere (e.g. fossil resins, coals, soil, shale and deep-sea sediments). These compounds occur in significant amounts only in higher plants and are therefore potential markers of terrigenous plant lipids.Diterpenoids with the abietane skeleton (mainly dehydroabietic acid) have been identified in the lipids of sediment samples from the northeast Pacific Ocean, Black Sea and North Atlantic Ocean. The presence of these resin-derived compounds correlated with the terrigenous clay components and with the presence of pollen. The presence of polycyclic diterpenoids was also correlated with the distribution patterns and inferred sources of other sediment lipid constituents (e.g. n-alkanes, n-fatty acids, etc.).Potamic transport, followed by turbidite redistribution are the probable input mechanisms of these resin-derived compounds to the deep-sea sediments. These diterpenoids appear to be excellent biological markers of resinous higher plants.     

The influence of rivers on the geochemistry of shelf sediments, southwestern coast of India

Geochemical and magnetic susceptibility studies of shelf sediments off Mangalore were carried out to understand the influence of rivers on sediment geochemistry, to study the elemental distribution patterns, and to evaluate the importance of the shelf as a source/sink for base metals. The contents of Cu, Pb, Mn, Fe and Al in the surficial sediments are lower by factors of 1.6–5.6, except Ca which is higher by a factor of 3.4 in relation to riverine suspended particulate matter (SPM). This is due to the seaward decrease of terrigenous influx which is reflected in the offshore protrusion of contours of Al, Fe, Cu, Zn, Ni and magnetic susceptibility values, particularly off Netravati and Gurpur rivers. Lower Mn content is also due to its remobilization from the anoxic-sulphidic shelf sediments. In contrast to the elements mentioned above, Ca increases seaward, suggesting that it is biogenic. The enrichment factor (EF) indicates that the surficial sediments are depleted in Cu, Zn and Mn compared to average shale and other anoxic sediments, and marginally enriched with Ni, Co, and Pb in relation to the average shale. However, a comparison between the EF of SPM of Netravati-Gurpur rivers in the hinterland and surficial sediments indicates that the latter are depleted in Mn and Co, but enriched with Ni, Pb, and Fe, thereby suggesting a source and a sink for the former and latter elements, respectively, to the Arabian Sea.     

Preliminary magnetic studies of lagoon and stream sediments from Chascomús Area (Argentina)—magnetic parameters as indicators of heavy metal pollution and some results of using an experimental method to separate magnetic phases

Magnetic properties of lagoon and stream sediments from Chascomús area (Buenos Aires Province) and the relevance of various magnetic parameters as giving pollution status are studied in the present work. This work is focussed on magnetic parameters, such as concentration-dependent (magnetic susceptibility, saturation anhysteric and isothermal remanent magnetisation) and feature-dependent parameters (S-ratio, coercivity of remanence, anhysteric susceptibility/magnetic susceptibility-ratio), as pollution indicators. Firstly and most importantly, different magnetic parameters and chemical measurements were correlated in order to investigate their goodness, obtaining the best results for feature-dependent magnetic parameters. Coercivity of remanence correlate very well with chemical variables, showing correlations at high level of significance up to 0.9094, and the anhysteric susceptibility/magnetic susceptibility-ratio also shows very good correlations (up to 0.8376). Some results and advantages of using a new experimental method in order to discriminate hard and soft magnetic phases are also shown. This method uses alternately backfield isothermal remanent magnetisation and alternating field demagnetisation. From the experimental separation, the presence of hard magnetic phases in some samples was confirmed.     

Early carbonate diagenesis in slope sequences and at their boundaries, Cenozoic, offshore New Jersey (ODP Leg 150)

This paper reports the genetic links among the depth distribution, mineralogy, and stable isotopic composition of diagenetic carbonates with sedimentation rates and types and preservation of organic matter in the terrigenous and biogenic sediments of Oligocene and Miocene age on the New Jersey slope. Calcites formed close to the sediment surface at sequence boundaries and maximum flooding surfaces, when the profile of early-diagenetic reactions was stabilized in the sediment column for extended periods. Dolomites precipitated in the sulfate reduction zone when diagenetic profiles stabilized during truncation, sequence boundary formation, and the deposition of lowstand sediments that overlie the sequence boundaries. Most dolomites occur in distal slope sediments that were deposited before the shelf had prograded into the study area. Siderites formed during a later stage of burial in the methanogenic zone; they are not directly genetically related to the sequence stratigraphy of the New Jersey slope. The diagene-tic dolomites and siderites occur in widely separated depth intervals below the present sea floor. The distribution of the diagenetic carbonates and their preferential occurrence in separated depth intervals resulted from different combinations of sedimentation rates and organic matter types and preservation.