Bauer Deep Research Articles

The sedimentary cycle of the boron isotopes

Abstract Marine sediments contain two isotopically distinct components: a non-desorbable fraction with δ11B between −4.3 and +2.8 per mil (n = 10) and a desorbable component with δ11B between 13.9 and 15.8 per mil (n = 6). The adsorption coefficient, K, for the uptake of B from seawater by fluvial suspended material (Mississippi) has an experimentally determined value of 1.54 ± 0.05. The associated isotope fractionation factor, α, is 0.974 ± 0.003. Empirical values for K, determined from the analysis of marine sediments (n = 6), were between 3 and 4. The amount of B adsorbed onto fluvial suspended material during estuarine mixing is about 9 × 109 moles/yr. Based on pore water data, adsorption experiments and comparative size fraction analyses (suspended sediments from the Mississippi River vs. bottom deposits from the Delta) there is no evidence for the incorporation of B into detrital sediments at low temperature. However, the high B content of Bauer Deep metalliferous sediments must be due to incorporation of seawater B during formation of authigenic silicates. The δ11B of these minerals is 2 ± 3 per mil. Hydrothermally altered sediments from DSDP Hole 477, Guaymas Basin, Gulf of California have variable B contents, from 33 ppm, similar to the unaltered detritus, to 1.2 ppm in the recrystallized material. The latter has δ11B as low as −9.0 per mil, substantially lower than the unaltered material. Hydrothermal solutions collected from vents adjacent to the hole have boron contents elevated by about a factor of 4 relative to seawater and δ11B between 16.5 and 23.2 per mil. The B mobilized from the sediments is isotopically fractionated with the fluids being preferentially enriched in the heavy isotope. Analysis of an oxisol profile developed over granite in the Guyana Shield showed that boron is partially mobilized during weathering with an isotopic offset of 2.5 per mil between bedrock and soil. The observed enrichment of B in shales relative to igneous rocks does not occur during weathering or during exposure to seawater at low temperature. Incorporation occurs only during burial diagenesis at temperatures greater than about 60°C. However, the enrichments cannot be attained during a single cycle of primary weathering and burial but must be cumulative over many cycles.

Composition, oxygen isotope geochemistry and origin of smectite in the metalliferous sediments of the Bauer Deep, southeast Pacific

The sediments of the Bauer Deep, an open ocean basin situated on the northwest Nazca Plate in the southeast Pacific, constitute a regional metalliferous deposit dominated by authigenic smectite. Two 2-metre long cores from the Bauer Deep were examined to investigate the nature and origin of the smectite. Infra-red and Mossbauer spectroscopy and wet chemical analysis (LiBO 2 fusion) of isolated smectite, indicate the mineral is a Mg-rich, Al-rich nontronite. Oxygen isotopic compositions for isolated smectite are uniform and translate to a non-hydrothermal temperature of formation of about 3°C. SEM observations show an abundance of well-preserved biogenic opal in surface and near surface sediment but postburial dissolution and transformation of this phase to smectite is evident at depth. Smectite formation is the result of interaction between iron oxyhydroxide, ponded in the Bauer Deep following a hydrothermal origin at the adjacent East Pacific Rise, and biogenic opal. A reaction mechanism is proposed. Regional factors control smectite formation. In particular, formation is inhibited in areas of CaCO 3 accumulation (topographic elevations) but favoured in areas of oxyhydroxide and opal ponding (topographic depressions).

The nature and origin of authigenic smectites in some recent marine sediments

AbstractThree principal modes of formation are apparent for authigenic smectites in Recent marine sediments: alteration of volcanic rocks and glass, low-temperature combination of biogenic silica and Fe-oxyhydroxides, and direct precipitation from hydrothermal fluids. The latter two mechanisms are discussed with reference to new evidence from studies of sediments from the Bauer Deep of the equatorial eastern Pacific and the Atlantis II Deep in the Red Sea. In the Atlantis II Deep sediments, three sub-environments of smectite formation from hydrothermal fluids are recognized. In two of them nontronites are formed, whilst in the third an Fe-poor smectite, intermediate in composition between beidellite and montmorillonite, occurs.

Early to Middle Miocene Planktonic Foraminiferal Datum Levels of the Equatorial and Subtropical Pacific

Early to Middle Miocene Planktonic Foraminiferal Datum Levels of the Equatorial and Subtropical Pacific

Copper-nickel-enriched ferromanganese nodules and associated crusts from the Bauer Basin, northwest Nazca plate

Analysis of a suite of ferromanganese nodules and crusts from the dredge Y73-3-22D in the Bauer Deep (13°40′S, 102°08′W) shows distinct differences between the nodules and crusts. Ultra-slow-scan X-ray diffraction shows that the nodules are more enriched in todorokite while the crusts are more enriched in δ MnO 2. Both have phillipsite and smectite as accessory minerals as well as minor amounts of apatite, barite, and quartz. Chemical analyses show that the nodules also have higher abundances of Mn, Ni, Cu, Zn, and Ba, while crusts are more enriched in Fe, Co, and Ca. We suggest that normal authigenic precipitation of ferromanganese oxyhydroxides from seawater controls the mineralogy and chemistry of the crusts, while nodule mineralogy and chemistry are governed by small-scale diagenetic reactions in the sediment. Todorokite may form because iron in the Fe-Mn oxyhydroxide material dispersed in the sediment reacts with amorphous silica to form iron-rich smectites. The remaining oxyhydroxide material recrystallizes as todorokite.

Phosphorus accumulation rates in metalliferous sediments on the East Pacific Rise

Based on phosphorus, iron and manganese analyses in 16 cores (5 dated) from the crest and flanks of the East Pacific Rise and the Bauer Deep we estimate that phosphorus is being deposited about 20 times faster in metalliferous sediments near the rise crest than in adjacent flank deposits, and about 40 times faster on the crest than in the Bauer Deep. Almost all of the phosphorus on the rise crest is contained in poorly crystallized hydrothermal iron oxyhydroxides, supporting Berner's (1973) proposal of phosphate sorption by these phases. The phosphate is probably derived from seawater, but some hydrothermal contribution cannot be excluded at this time. Flux estimates indicate that metalliferous sedimentation could remove 15–40% of the pre-agricultural river input of dissolved phosphate.

Genesis and transformation of metalliferous sediments from the East Pacific Rise, Bauer Deep, and Central Basin, northwest Nazca plate

Analytical data for northwest Nazca plate sediments can be described in terms of a mixture of hydrothermal, detrital, hydrogenous, and biogenous material. Fe, Mn, Cu, Zn, Ni, Ba, Si, and Al are more than 50 percent hydrothermal in East Pacific Rise samples from lat 10° to 25 °S. The first four elements are dominantly hydrothermal in the Bauer Deep and Central Basin as well. Seventy to 80 percent of the Ni, 60 to 80 percent of the Ba, and 30 to 60 percent of the Cu and Zn in Bauer Deep and Central Basin sediments are hydrogenous. Si, Ba, and Zn are dominantly biogenous on the northern East Pacific Rise crest, where more than one-third of the Cu also is derived from this source. Detrital Al and Si are dominant away from the rise crest, particularly in the Central Basin, where about 40 percent of the Fe and 15 percent of the Zn may also be detrital. Much of the hydrothermal Fe and biogenous Si have been transformed to an iron-rich smectite. The proportion of total Fe bound in this phase varies from less than 20 percent on the southern rise crest to about 40 percent in the Bauer Deep. The distribution of each element is governed by (1) supply from the four basic sources; (2) lateral transport by bottom currents moving east and then south across the northern East Pacific Rise and Bauer Deep to the Central Basin and moving west from the Peru Basin to the Central Basin; and (3) transformation of the unstable metalliferous hydroxides into more stable smectite and ferromanganese oxyhydroxides.

Iron in the metalliferous sediments of the Bauer Deep and East Pacific Rise

This article outlines geomorphological and tectonic elements of the Afar Depression, and discusses its evolution. A combination of far-field stress, due to the convergence of the Eurasian and Arabian plates along the Zagros Orogenic Front, and uplift of the Afar Dome due to a rising mantle plume reinforced each other to break the lithosphere of the Arabian–Nubian Shield. Thermal anomalies beneath the Arabian–Nubian Shield in the range of 150 °C–200 °C, induced by a rising plume that mechanically and thermally eroded the base of the mantle lithosphere and generated pulses of prodigious flood basalt since ∼30 Ma. Subsequent to the stretching and thinning the Afar Dome subsided to form the Afar Depression. The fragmentation of the Arabian–Nubian Shield led to the separation of the Nubian, Arabian and Somalian Plates along the Gulf of Aden, the Red Sea and the Main Ethiopian Rift. The rotation of the intervening Danakil, East-Central, and Ali-Sabieh Blocks defined major structural trends in the Afar Depression. The Danakil Block severed from the Nubian plate at ∼20 Ma, rotated anti-clockwise, translated from lower latitude and successively moved north, left-laterally with respect to Nubia. The westward propagating Gulf of Aden rift breached the Danakil Block from the Ali-Sabieh Block at ∼2 Ma and proceeded along the Gulf of Tajura into the Afar Depression. The propagation and overlap of the Red Sea and the Gulf of Aden along the Manda Hararo–Gobaad and Asal–Manda Inakir rifts caused clockwise rotation of the East-Central Block. Faulting and rifting in the southern Red Sea, western Gulf of Aden and northern Main Ethiopian Rift superimposed on Afar. The Afar Depression initiated as diffused extension due to far-field stress and area increase over a dome elevated by a rising plume. With time, the lithospheric extension intensified, nucleated in weak zones, and developed into incipient spreading centers.

Elemental accumulation rates in the Bauer Deep: A correction

Research Article| October 01, 1976 Elemental accumulation rates in the Bauer Deep: A correction FREDERICK L. SAYLES; FREDERICK L. SAYLES 1Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar T.-L. KU; T.-L. KU 2Department of Geological Sciences, University of Southern California, Los Angeles, California 90007 Search for other works by this author on: GSW Google Scholar PAUL C. BOWKER PAUL C. BOWKER 3Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar Author and Article Information FREDERICK L. SAYLES 1Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 T.-L. KU 2Department of Geological Sciences, University of Southern California, Los Angeles, California 90007 PAUL C. BOWKER 3Department of Chemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1976) 87 (10): 1396. https://doi.org/10.1130/0016-7606(1976)87<1396:EARITB>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation FREDERICK L. SAYLES, T.-L. KU, PAUL C. BOWKER; Elemental accumulation rates in the Bauer Deep: A correction. GSA Bulletin 1976;; 87 (10): 1396. doi: https://doi.org/10.1130/0016-7606(1976)87<1396:EARITB>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract No Abstract Available. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Metal accumulation rates in the Southeast Pacific and the origin of metalliferous sediments

Metal accumulation rates over the East Pacific Rise and Bauer Deep rule out normal authigenic precipitation of iron and manganese as the major mechanism of enrichment to the metalliferous sediments. A hydrothermal source located along the East Pacific Rise is compatible with the transition metal and aluminum accumulation rates. For the Bauer Deep the accumulation rate data suggest either that metal-bearing phases are being transported from the rise to the protected basins of the deep or that a second hydrothermal source exists within the Bauer Deep. A major portion of the minor elements being deposited in the Bauer Deep could result from authigenic precipitation, thus accounting for their distinctive chemical composition.

Hydrothermal metallogenesis in the Bauer Deep of the south-eastern Pacific

SEDIMENTS from the East Pacific Rise that are unusually enriched with iron, manganese, and other metals1,2,3 are correlated with areas of high heat flow on oceanic ridges. With the discovery that sediments rich in iron directly overlie oceanic basaltic basement, it has been suggested that such deposits were formed by circulating hydrothermal fluids generated during mid-oceanic rift volcanism4,5. Other suggested origins are: authigenic precipitation of iron and manganese from seawater6, submarine weathering of basaltic debris, and precipitation during diagenetic remobilisation of manganese in the sediment column7. Our geochemical evidence supports the hydrothermal metallogenesis hypothesis.

Chemistry of ferromanganoan sediment of the Bauer Deep

Sediment from the Bauer Deep in the east Pacific is commonly carbonate free, containing only small amounts of detrital minerals, and is enriched in Fe, Mn, Cu, Co, Ni, Zn, and Ba. An Fe-montmorillonite and ferromanganese compounds, occurring both as colloids and micronodules, are the principal phases present. A large proportion of the Fe occurs in the Fe montmorillonite, which appears to originate from the interaction of hydrothermal solutions with sea water. Adsorption and incorporation of metals from sea water on the micronodules or the Fe and Mn oxide colloids best explain the elemental relationships observed for Fe, Mn, Cu, Zn, and Ni in the oxide fraction of the sediment. These processes are responsible for the enrichment of the sediment in Ni, Co, and possibly Mn. Enrichment in Cu and Zn occurs in both the oxides and the Fe montmorillonite. Sedimentation rates measured in one core provide a minimum value of 2.5 mm/10 3 yr. The rate of accumulation of authigenic material is more than 2 mm/10 3 yr. Elemental accumulation rates of Fe, Mn, Cu, Ni, and Zn are comparable to those found near the crest of the East Pacific Rise.

Implications of heat flow for metallogenesis in the Bauer Deep

The Bauer Deep, in the south-eastern equatorial Pacific, is the only deep ocean basin so far known to be characterised by metalliferous sediments throughout the depositional column. The basin was formed when the eastern Pacific spreading centre jumped from the now fossil Galapagos Rise to the newly formed East Pacific Rise. The distinctly bimodal distribution of heat flow in the Bauer Deep indicates that precipitation from hydrothermal fluids emanating from the oceanic crust may be the mechanism for metallogenesis in the Bauer Deep. The hydrothermal circulation may have been initiated by the emplacement, approximately ~ 6 Myr BP, of a heat source associated with the ridge jump into that vicinity.

Metallogenesis in Southeast Pacific Ocean: Nazca Plate Project: ABSTRACT

The Nazca Plate Project is a detailed and systematic geological, geochemical, and geophysical investigation of a distinct and tectonically active lithospheric plate of the southeast Pacific Ocean basin. Major tectonic boundaries of the Nazca plate are defined by the East Pacific Rise on the west, along which new oceanic crust of basalt is being generated; the Peru-Chile Trench on the east, where older oceanic crust is being consumed by subduction beneath the overriding South American plate; and the Galapagos spreading center and the Chile Rise on the north and south, respectively. The motion of this plate relative to the Pacific plate is estimated to be eastward at more than 16 cm/yr, as documented by stratigraphic, structural, paleontologic, magnetic, and seismic evidenc . Normal sediments of the deep-sea floor cover basaltic basement rocks over much of the plate, but are locally dominated by a metal-rich component on and near the East Pacific Rise and within the Bauer Deep. These metalliferous sediments, which are composed of crystalline ferromanganese hydroxyoxides (goethite, psilomelane, etc) and Fe-montmorillonite, contain anomalously high concentrations of Fe, Mn, Cu, Ni, Zn, and other transition metals. Elemental abundances and ratios, extraordinary high rates of sedimentation, lead-isotope ratios, and statistical analysis of the data suggest that Fe, Mn, Cu, and possibly other metals were deposited by hydrothermal fluids emanating from sources of basaltic magmatism along the East Pacific Rise. However, isotopic abundances of O, Sr, S, and C and di tribution patterns of the rare-earth elements imply that deposition of the metalliferous sediments occurred at normally low temperatures of the ocean floor and that the nonmetallic components were derived from and/or equilibrated with seawater.

Metallogenesis in the southeastern Pacific: A progress report on the IDOE Nazca Plate project

Under the auspices of the International Decade of Ocean Exploration, scientists from Oregon State University and the Hawaii Institute of Geophysics, along with representatives from the several South American countries which border the Nazca Plate, are intensively studying the origin and economic importance of metalliferous sediments which form extensive deposits on and near the East Pacific Rise. The sediments, enriched in iron, manganese, copper, nickel, zinc, silver, molybdenum, and lead are mineralogically and chemically similar to deposits cored by the “Glomar Challenger”, implying a common origin. The metalliferous sediments are especially abundant in an extensive basin, the Bauer Deep, which occurs about 800 km east of the East Pacific Rise. Elemental and isotopic data, supported by geologic information provided by cores and by geophysical instrumentation, suggest that the enriched elements in the sediments originate by the interplay of volcanism and sea water, by precipitation from sea water alone, and perhaps by the influence of deep-ocean physical processes acting on detritus transported from the continents or from the basaltic East Pacific Rise. An additional objective of the project is to define the possible relationship between marine metalliferous sediments of the plate to ore deposits of the Andean Cordillera. As pointed out by several writers, much of the earth's economic mineralization occurs along zones of convergence between subducted oceanic crust, including metalliferous sediments if present, and continental margins. Field and geochemical techniques are being applied to determine if sediments are in fact subducted beneath the Andean margin, and if they are remobilized into the continental ore deposits of the Andes. Isotopic tracers may prove most useful in testing this relation. Before the model can be tested rigorously, one must know not only the important chemical parameters of the ocean sediment that may be subducted, but also those of the pertinent rock and ore bodies of the South American Cordillera.

Origin of Metalliferous Sediments from the Pacific Ocean

Sediments from near the basement of a number of Deep Sea Drilling Project (DSDP) sites, from the Bauer Deep, and from the East Pacific Rise have unusually high transition metal-to-aluminum ratios. Similarities in the chemical, isotopic, and mineralogical compositions of these deposits point to a common origin. All the sediments studied have rare-earth-element (REE) patterns strongly resembling the pattern of sea water, implying either that the REE's were coprecipitated with ferromanganese hydroxyoxides (hydroxyoxides denote a mixture of unspecified hydrated oxides and hydroxides), or that they are incorporated in small concentrations of phosphatic fish debris found in all samples. Oxygen isotopic data indicate that the metalliferous sediments are in isotopic equilibrium with sea water and are composed of varying mixtures of two end-member phases with different oxygen isotopic compositions: an iron-manganese hydroxyoxide and an iron-rich montmorillonite. A low-temperature origin for the sediments is supported by mineralogical analyses by x-ray diffraction which show that goethite, iron-rich montmorillonite, and various manganese hydroxyoxides are the dominant phases present. Sr87/Sr86 ratios for the DSDP sediments are indistinguishable from the Sr87/Sr86 ratio in modern sea water. Since these sediments were formed 30 to 90 m.y. ago, when sea water had a lower Sr87/Sr86 value, the strontium in the poorly crystalline hydroxyoxides must be exchanging with interstitial water in open contact with sea water. In contrast, uranium isotopic data indicate that the metalliferous sediments have formed a closed system for this element. The sulfur isotopic compositions suggest that sea-water sulfur dominates these sediments with little or no contribution of magmatic or bacteriologically reduced sulfur. In contrast, ratios of lead isotopes in the metalliferous deposits resemble values for oceanic tholeiite basalt, but are quite different from ratios found in authigenic marine manganese nodules. Thus, lead in the metalliferous sediments appears to be of magmatic origin. The combined mineralogical, isotopic, and chemical data for these sediments suggest that they formed from hydrothermal solutions generated by the interaction of sea water with newly formed basalt crust at mid-ocean ridges. The crystallization of solid phases took place at low temperatures and was strongly influenced by sea water, which was the source for some of the elements found in the sediments.