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12.4: Hydrogenous Sediments - Geosciences

12.4: Hydrogenous Sediments - Geosciences


As we saw in section 5.3 seawater contains many different dissolved substances. Occasionally chemical reactions occur that cause these substances to precipitate out as solid particles, which then accumulate as hydrogenous sediment. These reactions are usually triggered by a change in conditions, such as a change in temperature, pressure, or pH, which reduces the amount of a substance that can remain in a dissolved state. There is not a lot of hydrogenous sediment in the ocean compared to lithogenous or biogenous sediments, but there are some interesting forms.

Hydrothermal vents were discussed in section 4.11. Recall that in these systems, seawater percolates into the seafloor, where it becomes superheated by magma before being expelled by the vent. This superheated water contains many dissolved substances, and when it encounters the cold seawater after leaving the vent, these particles precipitate out, mostly as metal sulfides. These particles make up the “smoke” that flows from a vent, and may eventually settle on the bottom as hydrogenous sediment (Figure (PageIndex{1})).

Manganese nodules are rounded lumps of manganese and other metals that form on the seafloor, generally ranging between 3-10 cm in diameter, although they may sometimes reach up to 30 cm (Figure (PageIndex{2})). The nodules form in a manner similar to pearls; there is a central object around which concentric layers are slowly deposited, causing the nodule to grow over time. The composition of the nodules can vary somewhat depending on their location and the conditions of their formation, but they are usually dominated by manganese- and iron oxides. They may also contain smaller amounts of other metals such as copper, nickel and cobalt. The precipitation of manganese nodules is one of the slowest geological processes known; they grow on the order of a few millimeters per million years. For that reason, they only form in areas where there are low rates of lithogenous or biogenous sediment accumulation, because any other sediment deposition would quickly cover the nodules and prevent further nodule growth. Therefore, manganese nodules are usually limited to areas in the central ocean, far from significant lithogenous or biogenous inputs, where they can sometimes accumulate in large numbers on the seafloor (Figure (PageIndex{2}) right). Because the nodules contain a number of commercially valuable metals, there has been significant interest in mining the nodules over the last several decades, although most of the efforts have thus far remained at the exploratory stage. A number of factors have prevented large-scale extraction of nodules, including the high costs of deep sea mining operations, political issues over mining rights, and environmental concerns surrounding the extraction of these non-renewable resources.

Evaporites are hydrogenous sediments that form when seawater evaporates, leaving the dissolved materials to precipitate into solids, particularly halite (salt, NaCl). In fact, the evaporation of seawater is the oldest form of salt production for human use, and is still carried out today. Large deposits of halite evaporites exist in a number of places, including under the Mediterranean Sea. Beginning around 6 million years ago, tectonic processes closed off the Mediterranean Sea from the Atlantic, and the warm climate evaporated so much water that the Mediterranean was almost completely dried out, leaving large deposits of salt in its place (an event known as the Messinian Salinity Crisis). Eventually the Mediterranean re-flooded about 5.3 million years ago, and the halite deposits were covered by other sediments, but they still remain beneath the seafloor.

Oolites are small, rounded grains formed from concentric layers of precipitation of material around a suspended particle. They are usually composed of calcium carbonate, but they may also from from phosphates and other materials. Accumulation of oolites results in oolitic sand, which is found in its greatest abundance in the Bahamas (Figure (PageIndex{4})).

Methane hydrates are another type of hydrogenous deposit with a potential industrial application. All terrestrial erosion products include a small proportion of organic matter derived mostly from terrestrial plants. Tiny fragments of this material plus other organic matter from marine plants and animals accumulate in terrigenous sediments, especially within a few hundred kilometers of shore. As the sediments pile up, the deeper parts start to warm up (from geothermal heat), and bacteria get to work breaking down the contained organic matter. Because this is happening in the absence of oxygen (a.k.a. anaerobic conditions), the by-product of this metabolism is the gas methane (CH4). Methane released by the bacteria slowly bubbles upward through the sediment toward the seafloor. At water depths of 500 m to 1,000 m, and at the low temperatures typical of the seafloor (close to 4°C), water and methane combine to create a substance known as methane hydrate. Within a few meters to hundreds of meters of the seafloor, the temperature is low enough for methane hydrate to be stable and hydrates accumulate within the sediment (Figure (PageIndex{5}) left). Methane hydrate is flammable because when it is heated, the methane is released as a gas (Figure (PageIndex{5}) right). The methane within seafloor sediments represents an enormous reservoir of fossil fuel energy. Although energy corporations and governments are anxious to develop ways to produce and sell this methane, anyone that understands the climate-change implications of its extraction and use can see that this would be folly.


*”Physical Geology” by Steven Earle used under a CC-BY 4.0 international license. Download this book for free at http://open.bccampus.ca


12.4 The Impacts of Earthquakes

Earthquakes can have direct impacts, such as structural damage to buildings from shaking, and secondary impacts, such as triggering landslides, fires, and tsunami. The types and extent of impacts will depend on local conditions where the earthquake strikes. The geological materials in the area matter, as does the type of terrain, and whether the region is near the coast or not. The extent of impact and type of damage will depend on whether the area is predominantly urban or rural, densely or sparsely populated, highly developed or underdeveloped. It will depend on whether the infrastructure has been designed to withstand shaking.


Eb Academia

Biogenous Sediment Map - Marine Geology: The Bottom of the Ocean - Terrigenous sediments, biogenous sediments, and hydrogenous sediments.. Biogenous sediment • the biogenic material in the ocean comes primarily from the exploring sediment distribution in today's activity, we will analyze maps of sediment distribution. Our next flipclass lecture about biogenous sediments. • marine sediments provide clues to past environmental conditions. Biogenous sediments contain the remains of marine organisms. Hydrogenous sediments are formed directly from seawater.

Pteropods (planktonic gastropods molluscs) biogenic sediments (also: • marine sediments provide clues to past environmental conditions. Biogenous sediments sediments that are composed of hard or soft parts, such as shells and tissues that were synthesized by marine organisms. Terrigenous sediments, biogenous sediments, and hydrogenous sediments. Biogenous) continued silica in biogenic sediments diatoms (algae).

Gabi Laske, Digital Sediment Map from igppweb.ucsd.edu Biogenous sediments contain the remains of marine organisms. Relatively low production rates of calcareous plankton. Global map, sediment distribution patterns map natl. 6 hydrogenous map of distribution of sediment recall (from chapter 4) that turbidity biogenous sediments are of biological origin. Organisms that live in sediment. 5.4 video typologies of marine biogenous and hydrogenous sediment13:07. These particles consist primarily of either the microscopic. Type of sediment that comes from the activity of living organisms.

Sediment is one of these.

Biogenous sediment merupakan sedimen yang berasal dari makhluk hidup. • marine sediments provide clues to past environmental conditions. Biogenous sediments are broadly defined as sediments consisting of large amounts of skeletal remains of macroscopic and microscopic organisms or remains of organic production. A map of the world's prevailing winds and atmospheric circulation cells are shown below. Terrigenous sediments, biogenous sediments, and hydrogenous sediments. Biogenous sediments are more abundant in the tropics, especially in coral seas. Biogenous sedimentsediment biogenous sediment coccolithophorids, phytoplankton that carry calcite platelets on the cell wall (coccoliths) is most common in oligotrophic open ocean environments. Come from the remains of living organisms that settle out as sediment when microscopic sediment consists of the hard parts of microscopic organisms, particularly their shells, or. Biogenous sediment is ocean sediment that is derived from biological processes. 6 hydrogenous map of distribution of sediment recall (from chapter 4) that turbidity biogenous sediments are of biological origin. Pteropods (planktonic gastropods molluscs) biogenic sediments (also: Biogenous sediments contain the remains of marine organisms. The genomes represent both completely sequenced organisms and those for which sequencing is in progress.

The genomes represent both completely sequenced organisms and those for which sequencing is in progress. • mostly skeletal material produced by dominant species of plankton. Containing predominantly lithogenous, biogenous, cosmogenous and hydrogenous matter, the sediment is highly complex, with many different materials and sources. Come from the remains of living organisms that settle out as sediment when microscopic sediment consists of the hard parts of microscopic organisms, particularly their shells, or. Learn vocabulary, terms and more with flashcards, games and other study tools.

Ocean sediments from image.slidesharecdn.com These particles consist primarily of either the microscopic. Biogenous sediment • the biogenic material in the ocean comes primarily from the exploring sediment distribution in today's activity, we will analyze maps of sediment distribution. 6 hydrogenous map of distribution of sediment recall (from chapter 4) that turbidity biogenous sediments are of biological origin. Learn vocabulary, terms and more with flashcards, games and other study tools. Hydrogenous sediments are formed directly from seawater. Biogenous sediment merupakan sedimen yang berasal dari makhluk hidup. Sedimentary structures include all kinds of features formed at the time of deposition. The genomes represent both completely sequenced organisms and those for which sequencing is in progress.

Terrigenous sediments form from sediments carried from land to the ocean.

Thank you sediment carolyn almberg oceanography 2b key locations for sediment unique? Terrigenous sediments form from sediments carried from land to the ocean. Come from the remains of living organisms that settle out as sediment when microscopic sediment consists of the hard parts of microscopic organisms, particularly their shells, or. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment. Ada tiga zat penyusun sedimen. The genomes represent both completely sequenced organisms and those for which sequencing is in progress. Biogenous calcium carbonate sediments also require production to exceed dissolution for sediments to accumulate, but the processes involved are a little different than for silica. Containing predominantly lithogenous, biogenous, cosmogenous and hydrogenous matter, the sediment is highly complex, with many different materials and sources. Organisms that live in sediment. • marine sediments provide clues to past environmental conditions. Pteropods (planktonic gastropods molluscs) biogenic sediments (also: • most plankton live near the ocean surface. Biogenous sediment merupakan sedimen yang berasal dari makhluk hidup.

These particles consist primarily of either the microscopic. Biogenous) continued silica in biogenic sediments diatoms (algae). Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment. Biogenous sediment is ocean sediment that is derived from biological processes. Terrigenous sediments form from sediments carried from land to the ocean.

Ocean sediments from image.slidesharecdn.com Relatively low production rates of calcareous plankton. Biogenous sediments sediments that are composed of hard or soft parts, such as shells and tissues that were synthesized by marine organisms. Biogenous sediments contain the remains of marine organisms. Ada tiga zat penyusun sedimen. Containing predominantly lithogenous, biogenous, cosmogenous and hydrogenous matter, the sediment is highly complex, with many different materials and sources. Organisms that live in sediment. 6 hydrogenous map of distribution of sediment recall (from chapter 4) that turbidity biogenous sediments are of biological origin. Come from the remains of living organisms that settle out as sediment when microscopic sediment consists of the hard parts of microscopic organisms, particularly their shells, or.

Global map, sediment distribution patterns map natl.

Biogenous sediments are more abundant in the tropics, especially in coral seas. Biogenous sediments are broadly defined as sediments consisting of large amounts of skeletal remains of macroscopic and microscopic organisms or remains of organic production. Learn vocabulary, terms and more with flashcards, games and other study tools. Sediments and sedimentary rocks are characterized by bedding, which occurs when layers of sediment. Biogenous calcium carbonate sediments also require production to exceed dissolution for sediments to accumulate, but the processes involved are a little different than for silica. Relatively low production rates of calcareous plankton. Biogenous sediment is ocean sediment that is derived from biological processes. These particles consist primarily of either the microscopic. • cores of sediment collected from sea floor. • marine sediments provide clues to past environmental conditions. Global map, sediment distribution patterns map natl. Organisms that live in sediment. • most plankton live near the ocean surface.

Terrigenous sediments form from sediments carried from land to the ocean. Pteropods (planktonic gastropods molluscs) biogenic sediments (also: Biogenous sediments sediments that are composed of hard or soft parts, such as shells and tissues that were synthesized by marine organisms. Type of sediment that comes from the activity of living organisms. Terrigenous sediments, biogenous sediments, and hydrogenous sediments.

• mostly skeletal material produced by dominant species of plankton. Organisms that live in sediment. Thank you sediment carolyn almberg oceanography 2b key locations for sediment unique? Sediment is one of these. The genomes represent both completely sequenced organisms and those for which sequencing is in progress.

Source: www2.ocean.washington.edu

A map of the world's prevailing winds and atmospheric circulation cells are shown below. Sedimentary structures include all kinds of features formed at the time of deposition. Pteropods (planktonic gastropods molluscs) biogenic sediments (also: Biogenous) continued silica in biogenic sediments diatoms (algae). • mostly skeletal material produced by dominant species of plankton.

Thank you sediment carolyn almberg oceanography 2b key locations for sediment unique? Ada tiga zat penyusun sedimen. • mostly skeletal material produced by dominant species of plankton. 6 hydrogenous map of distribution of sediment recall (from chapter 4) that turbidity biogenous sediments are of biological origin. • most plankton live near the ocean surface.

Source: genesisapologetics.com

Biogenous calcium carbonate sediments also require production to exceed dissolution for sediments to accumulate, but the processes involved are a little different than for silica. Biogenous sediment merupakan sedimen yang berasal dari makhluk hidup. A map of the world's prevailing winds and atmospheric circulation cells are shown below. There are four kinds of ocean sediments. Ada tiga zat penyusun sedimen.

Source: image1.slideserve.com

Biogenous sedimentsediment biogenous sediment coccolithophorids, phytoplankton that carry calcite platelets on the cell wall (coccoliths) is most common in oligotrophic open ocean environments. Learn vocabulary, terms and more with flashcards, games and other study tools. Sedimentary structures include all kinds of features formed at the time of deposition. 5.4 video typologies of marine biogenous and hydrogenous sediment13:07. The genomes represent both completely sequenced organisms and those for which sequencing is in progress.

Source: image.slidesharecdn.com

Another factor that affects where biogenous sediments will occur is the depth of the ocean floor. Biogenous sediments are broadly defined as sediments consisting of large amounts of skeletal remains of macroscopic and microscopic organisms or remains of organic production. Also known as cosmic dust. Biogenous sediment merupakan sedimen yang berasal dari makhluk hidup. Biogenous sediments are more abundant in the tropics, especially in coral seas.

Organisms that live in sediment. 6 hydrogenous map of distribution of sediment recall (from chapter 4) that turbidity biogenous sediments are of biological origin. Another factor that affects where biogenous sediments will occur is the depth of the ocean floor. • marine sediments provide clues to past environmental conditions. Our next flipclass lecture about biogenous sediments.

Source: www.researchgate.net

• mostly skeletal material produced by dominant species of plankton. • cores of sediment collected from sea floor. Containing predominantly lithogenous, biogenous, cosmogenous and hydrogenous matter, the sediment is highly complex, with many different materials and sources. Another factor that affects where biogenous sediments will occur is the depth of the ocean floor. Biogenous sediment is ocean sediment that is derived from biological processes.

Source: gsw.silverchair-cdn.com

Learn vocabulary, terms and more with flashcards, games and other study tools.

Source: image2.slideserve.com

Type of sediment that comes from the activity of living organisms.

Biogenous calcium carbonate sediments also require production to exceed dissolution for sediments to accumulate, but the processes involved are a little different than for silica.

Relatively low production rates of calcareous plankton.

Sedimentary structures include all kinds of features formed at the time of deposition.

Source: image.slidesharecdn.com

5.4 video typologies of marine biogenous and hydrogenous sediment13:07.

Another factor that affects where biogenous sediments will occur is the depth of the ocean floor.

Source: image.slidesharecdn.com

Biogenous sediments are broadly defined as sediments consisting of large amounts of skeletal remains of macroscopic and microscopic organisms or remains of organic production.

Organisms that live in sediment.

Relatively low production rates of calcareous plankton.

Source: magnoliafisheries.com

Organisms that live in sediment.

Our next flipclass lecture about biogenous sediments.

Source: image.slidesharecdn.com

Biogenous sediment • the biogenic material in the ocean comes primarily from the exploring sediment distribution in today's activity, we will analyze maps of sediment distribution.

Type of sediment that comes from the activity of living organisms.

Thank you sediment carolyn almberg oceanography 2b key locations for sediment unique?

Source: image1.slideserve.com

Come from the remains of living organisms that settle out as sediment when microscopic sediment consists of the hard parts of microscopic organisms, particularly their shells, or.

Terrigenous sediments, biogenous sediments, and hydrogenous sediments.

Also known as cosmic dust.

• marine sediments provide clues to past environmental conditions.

Biogenous sediment is ocean sediment that is derived from biological processes.

Source: upload.wikimedia.org

• marine sediments provide clues to past environmental conditions.

Learn vocabulary, terms and more with flashcards, games and other study tools.

Source: www.researchgate.net

Our next flipclass lecture about biogenous sediments.

Source: classconnection.s3.amazonaws.com

Biogenous sediments contain the remains of marine organisms.

Source: image.slidesharecdn.com

Biogenous sedimentsediment biogenous sediment coccolithophorids, phytoplankton that carry calcite platelets on the cell wall (coccoliths) is most common in oligotrophic open ocean environments.


12.4: Hydrogenous Sediments - Geosciences

1 U.S. Geological Survey, MS 980 Federal Center, Denver, CO 80225.
2 Department of Geosciences, Pennsylvania State University, University Park, PA 16802.

Leg 1 of the 1988 R/V Knorr expeditions to the Black Sea recovered 90 gravity and box cores. The longest recovery by gravity cores was about 3 meters, with an average of about 2.5 meters, recovering all of the Holocene and upper Pleistocene sections in the Black Sea. During the latest Pleistocene glaciation, sea level dropped below the 35-meters-deep Bosporus outlet sill of the Black Sea. Therefore throughout most of its history the Black Sea was a lake, and most of its sediments are lacustrine.

The oldest sediments recovered (older than 8,000 calendar years) consist of massive to coarsely banded lacustrine calcareous clay designated as lithologic Unit III, generally containing less than 1 percent organic carbon (OC). The base of overlying Unit II marks the first incursion of Mediterranean seawater into the Black Sea, and the onset of bottom-water anoxia about 7,900 calendar years. Unit II contains as much as 15 percent OC in cores from the deepest part of the Black Sea (2,200 meters). The calcium carbonate (CaCO3) remains of the coccolith Emiliania huxleyi form the distinctive white laminae of overlying Unit I.

The composition of Unit III and Unit II sediments are quite different, reflecting different terrigenous clastic sources and increased contributions from hydrogenous and biogenic components in anoxic Unit II sapropel. In Unit II, positive covariance between OC and three trace elements commonly concentrated in OC-rich sediments where sulfate reduction has occurred (molybdenum, nickel, and vanadium) and a nutrient (phosphorus) suggest a large marine source for these elements although nickel and vanadium also have a large terrigenous clastic source. The marine sources may be biogenic or hydrogenous. A large biogenic source is also suggested for copper and cobalt. Because abundant pyrite forms in the water column and sediments of the Black Sea, we expected to find a large hydrogenous iron component, but a strong covariance of iron with aluminum suggests that the dominant source of iron is from terrigenous clastic material. Most elements in lacustrine Unit III sediments have a strong covariance with Al indicating a very dominant terrigenous source. In Unit II, some elements, especially nickel, molybdenum, vanadium, and zinc, do not correlate with aluminum and have concentrations well above terrigenous clastic material, indicating a marine source.

First posted January 10, 2011

For additional information contact:

USGS Geology and Environmental Change Science Center
Box 25046, Mail Stop 980
Denver, CO 80225

This report is presented in Portable Document Format (PDF) the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.

Suggested citation:

Dean, W.E., and Arthur, M.A., 2011, Geochemical characteristics of Holocene laminated sapropel (unit II) and underlying lacustrine unit III in the Black Sea: U.S. Geological Survey Open-File Report 2010&ndash1323, 29 p.

Contents

Introduction and Background

Carbonate and Organic Carbon Stratigraphies—Definition of Lithologic Units

Distribution of Inorganic Elements

Summary—Development of Anoxia in the Black Sea

U.S. Department of the Interior | U.S. Geological Survey
URL: https://pubs.usgs.gov/of/2010/1323/
Page Contact Information: Contact USGS
Page Last Modified: Wednesday, December 07, 2016, 11:01:42 PM


12.4: Hydrogenous Sediments - Geosciences



"It's always best to start at the beginning"
- Glenda, the Good Witch of the North


  • Earth is composed of concentric spherical layers, with the least dense layer on the outside, and the densest as the core. The lithosphere, the outermost solid shell that includes the crust, floats on the hot, deformable asthenosphere. What is density and why is the least dense layer at the surface? How do we know this given that no one has drilled more than 7.5 miles (1/500th of the Earth's radius)?

  • Large regions of Earth’s continents are held above sea level by isostatic equilibrium, a process analogous to a ship floating in water.
Oceanic crust is of higher density because it is made mostly of basalt (high in iron and magnesium) and is thinner. The continental crust is of lower density made mostly of granite (high content of aluminum and magnesium silicate with quartz and feldspar) and tends to be thicker. Why are the more massive parts of the crust higher?


As a result, continents lie higher than oceanic crust
.
  • The ocean basins are characterized by mid-ocean ridges and fringed by shallow continental shelves.


    The age of the ocean floor is much younger (<200 million yrs) than most continental rock and is youngest nearest the ridges (and deposted sediments are the thinnest).

  • Terrigenous sediments: Why do clays make up a greater percentage (38%) of the terrigenous deep sea bed than they do along continental shelves?
  • Biogenous sediments (including deep sea "oozes": calcareous ooze from forams, pteropods and coccolithophores siliceous ooze form radiolarians and diatoms)
  • Hydrogenous sediments

It had long been observed that the continents can be fit together like a jigsaw puzzle.

The idea that continents drift over geologic time was not accepted until (in the 1960's) it was understood that to the mechanism of slow convection (heat-generated) currents flowing in the mantle drove tectonic plate movement.

Plate tectonics theory suggests that Earth's surface is not a static arrangement of continents and ocean, but a dynamic mosaic of jostling segments called lithospheric plates . The plates have collided, moved apart, and slipped past one another since Earth's crust first solidified.

Large-scale features ocean basins may be explained by the interactions of plate tectonics.

  • Mid-ocean ridges form as rising mantle currents create new ocean floor, forcing the ocean floor to spread outward. Because the Earth's suface is spherical, spreading is uneven along the ridge creating transform faults perpendicular to the ridge line.
  • Where plates collide as a result of ocean floor spreading, one plate is subducted underneath the other. For example, the denser oceanic plate edge is pushed downward and melts as the continental plate overrides it (as along the coast of South America).


Where along the plate is one likely to find mountain building, volcanic activity, earthquakes, trenchs, and narrow contentental shelves?

  • Broad continental shelfs were formed a continents separated, thinning the continental lithosphere during initial rifting. On the Atlantic Ocean shelf, incline is

So why is the west coast of the U.S. so geologically different than the east?

The coastal plains from New Jersey to Florida are broad and relatively flat composed mainly unconsolidated marine-derived and eroding Applachain material, whereas the coast to the north tends to be more rugged and rocky.


During the past 2.5 million years, the earth has experienced 20 glacial advances and retreats (times of low global temperatures or "ice ages").

What is this massively heavy sheet of ice likely to do to the landscape as it advances and retreats?

So, why are the coast to the north tends to be more rugged and rocky?


3. Why do barrier islands characterize the southern U.S. east coast?


So, how might we determine from a 'snapshot' which end of an island is growing?


http://faculty.valencia.cc.fl.us/jbeeman/NE_Coast/SandsHistory.htm
How might one determine from bedding of sand layers whether a beach is experiencing erosion or deposition?


    Barrier Islands are dynamic!



    Which end of Wassaw Island is eroding,
    and which end is growing?


    Pelagic clays as archives of marine iron isotope chemistry

    Slowly accumulating pelagic clays are enriched in metals that were formerly in seawater, including iron, an important micronutrient. Because the metals are minimally remobilized in oxygenated porewater, pelagic clays may be a potential archive for records of past marine micronutrient cycling. Here, we present a record of changes in hydrogenous iron (Fe) isotopes since the late Cretaceous derived from pelagic clays that we dated with osmium isotope chronostratigraphy. To optimize the separation of the hydrogenous metal (oxy)hydroxides from bulk sediment, we repeatedly leached an oxic pelagic clay sample under variable conditions (HCl molarity, temperature, time) and measured the element concentrations, Fe isotopes, and Os isotopes. The common behavior of elements amidst the permutations of the leach experiment offers insight into which components were dissolved and we defined a range of successful leaches. We applied our optimal leach for Fe and Os isotopes (1 M HCl, for 24 h at 20 °C) to 45 samples at Site U1366 in the South Pacific Gyre. The resulting record suggests a dynamic Fe cycle in the water column overlying Site U1366 over the past 95 million years. Early in the site's history, trends in the Fe isotopes are interpreted as reflecting changes in hydrothermal Fe with distance from the ridge. Contributions from a background Fe source are identified as well as a transition to dust-like source after 50 Ma until present. Constructing similar records at multiple sites will provide a basin-wide perspective on how the marine Fe cycle has changed over million-year timescales.

    First and second authors contributed equally.


    Microbial processes

    Microbial success in marine sediments is dependent upon their ability to perform anaerobic respiration or fermentation due to the limited availability of oxygen as a terminal electron acceptor. From this step, two different mechanisms can deliver the charge extracellularly via proteins. Type IV pili, found in Geobacter spp. and cytochrome containing outer membrane extensions found in Shewanella spp ( Lovley & Malvankar, 2015) (Pirbadian et al., 2014). Other species are also capable of transferring electrons through cycling between intermembrane spaces and the exterior sedimentary environment (Harris et al., 2010), or discharged onto electron transporters through diffusible transport proteins (Rabaey, et al. 2005).

    Iron Cycling

    Microbial dissimilatory iron reduction (DIR) is an active biogeochemical process in marine sediments (Crosby, Roden, Johnson, & Beard, 2007). Two different forms of iron are generally present in marine sedimentary environments. Fe 3+ is insoluble, and accumulates on sediment granules, while Fe 2+ is a soluble cation, making it more readily available for extracellular uptake. Ferrous Iron (III) can be oxidized or reduced, coupled with negatively charged humic products as electron donors, utilizing the Iron as an electron acceptor. Geobacter are capable of performing complete reduction of Iron (III) to magnetite (Fe3O4) with different electron donors – utilization of monoaromatics, short chain fatty acids, and hydrogen has been observed (Melton, Swanner, Behrens, Schmidt, & Kappler, 2014).

    Carbon Cycling

    Electrogens are able to completely oxidize organic metabolites to carbon dioxide. Increases of dissolved carbon dioxide outside of marine sediments can prove beneficial for marine algal and plant life. The ability of dissimilatory iron-reducing bacteria to break down organic matter trapped in or beneath sediments could result in a trickle-up effect, making use of otherwise hidden organic compounds and making them bioavailable for species at higher water levels (Azam & Fenchel, 1983).


    REE geochemical characteristics and depositional environment of the black shale-hosted Baiguoyuan Ag-V deposit in Xingshan, Hubei Province, China

    By means of techniques such as inductively coupled plasma-mass spectrometry (ICP-MS) and X-ray fluorescence spectrometry (XRF), REE geochemical characteristics and depositional environment of the black shales in Baiguoyuan Ag-V deposit, Xingshan, Hubei Province, were studied in this work. The black shales in a typical TC5 profile of Doushantuo Formation of upper Sinian period were obviously enriched in REE, especially in LREE. The REE patterns of the investigated samples normalized by Post Archean Australian Shale (PAAS) showed a flat or slight rightward inclination. The characteristic elements, their ratio and correlation diagrams showed that it should be hot-water deposit and the black shale in the study area was of a sedimentary origin. Redox sensitive metal elements pattern, trace elements index measurement in anoxic environment, Ce anomaly and δEu negative anomaly showed that the deposit environment of the black shales was a reducing and anoxic one and a slight change of the sea level could be identified. The samples relatively focused on the superimposed area of sedimentary rock and basalt in the diagram of La/Yb-ΣREE and La/Yb-Ce/La. So there might be accession of hot-water sedimentation during the period of the formation of the black rock series, mostly in normal terrigenous sedimentation with the participation of deep hot-water deposit.


    12.4 Measuring Geological Structures

    Geologists take great pains to measure and record geological structures because they are critically important to understanding the geological history of a region. One of the key features to measure is the orientation, or attitude, of bedding. We know that sedimentary beds are deposited in horizontal layers, so if the layers are no longer horizontal, then we can infer that they have been affected by tectonic forces and have become either tilted, or folded. We can express the orientation of a bed (or any other planar feature) with two values: first, the compass orientation of a horizontal line on the surface—the strike—and second, the angle at which the surface dips from the horizontal, (perpendicular to the strike)—the dip (Figure 12.18).

    It may help to imagine a vertical surface, such as a wall in your house. The strike is the compass orientation of the wall and the dip is 90˚ from horizontal. If you could push the wall so it’s leaning over, but still attached to the floor, the strike direction would be the same, but the dip angle would be less than 90˚. If you pushed the wall over completely so it was lying on the floor, it would no longer have a strike direction and its dip would be 0˚. When describing the dip it is important to include the direction. In other words. if the strike is 0˚ (i.e., north) and the dip is 30˚, it would be necessary to say “to the west” or “to the east.” Similarly if the strike is 45˚ (i.e., northeast) and the dip is 60˚, it would be necessary to say “to the northwest” or “to the southeast.”

    Measurement of geological features is done with a special compass that has a built-in clinometer, which is a device for measuring vertical angles. An example of how this is done is shown on Figure 12.19.

    Figure 12.18 A depiction of the strike and dip of some tilted sedimentary beds partially covered with water. The notation for expressing strike and dip on a map is shown. [SE]

    Figure 12.19 Measurement of strike (left) and dip (right) using a geological compass with a clinometer. [SE]

    Strike and dip are also used to describe any other planar features, including joints, faults, dykes, sills, and even the foliation planes in metamorphic rocks. Figure 12.20 shows an example of how we would depict the beds that make up an anticline on a map.

    Figure 12.20 A depiction of an anticline and a dyke in cross-section (looking from the side) and in map view (a.k.a. plan view) with the appropriate strike-dip and anticline symbols. [SE]

    The beds on the west (left) side of the map are dipping at various angles to the west. The beds on the east side are dipping to the east. The middle bed (light grey) is horizontal this is denoted by a cross within a circle. The dyke is dipping at 80˚ to the west. The hinge of the fold is denoted with a dashed line with two arrows point away from it. If it were a syncline, the arrows would point towards the line.

    Exercise 12.3 Putting Strike and Dip on a Map

    This cross-section shows seven tilted sedimentary layers (a to g), a fault, and a steeply dipping dyke. Place strike and dip symbols on the map to indicate the orientations of the beds shown, the fault, and the dyke. Then answer the questions.

    1. What type of fault is this, and is this an extensional or compressional situation?

    2. What are the relative ages of the nine geological features shown here (seven beds, dyke, and fault)?


    Mineralogical and Geochemical Characterization of Gold Bearing Quartz Veins and Soils in Parts of Maru Schist Belt Area, Northwestern Nigeria

    Epigenetic, N-S, NNE-SSW quartz veins crosscut metapelites and metagabbro in Maru area. The objectives of this work were to study field, mineralogy, and geochemical characteristics of gold bearing quartz veins and soils. Euhedral and polygonal magnetite with hematite constituted the major ore minerals. Quartz occurred as main gangue phase with appreciable sericite and chlorite. The mineralogy of soil retrieved from twelve minor gold fields examined with X-ray diffraction is quartz ± albite ± microcline ± muscovite ± hornblende ± magnetite ± illite ± kaolinite ± halloysite ± smectite ± goethite ± vermiculite ± chlorite. The concentration of gold in quartz vein varies from 10.0 to 6280.0 ppb with appreciable Pb (3.5–157.0 ppm) and ΣREE (3.6 to 82.9 ppm). Gold content in soil varies from <

    to 5700.0 ppb. The soil is characterized by As ± Sb gold’s pathfinder geochemical association. Multidata set analysis revealed most favourable areas for gold. Possibility of magmatic fluids as part of ore constituents is feasible due to presence of several intrusions close to quartz veins. Based on field, mineralogical, and geochemical evidences, ore fluids may have been derived from fracturing, metamorphic dewatering, crustal devolatilization of sedimentary, gabbroic protoliths, and emplaced in an orogenic setting.

    1. Introduction

    Precambrian rocks within and around Maru Schist belt host some quartz veins that are gold bearing. The gold deposits were heavily mined during the colonial era approximately before 1960 and after that period by artisanal miners. General descriptive information on gold mineralization in Maru schist belt has been documented [1–3]. Gold occurs primarily in quartz veins and as placers in soil (eluvial) and stream sediments (alluvial). The quartz veins containing gold occur in association with metamorphosed rocks ranging in composition from semipelitic to pelitic and mafic. Primary gold mineralization produced chemical signature in the overburden and surrounding soil probably through weathering processes. Weathering processes provide samples (soils and stream sediments) that yield data on local hidden mineralization or on the potential existence of major or minor mineralization in a wide region. The residual soil is the geochemical sample that is often used to detect the location of hidden mineralization once a zone of economic interest is localized [4]. Migration of groundwater provided chemical response at the surface. This process produces elemental dispersion pattern [5]. Most of these dispersed elements (e.g., Cu, Ag, Zn, Cd, As, Bi, Pb, Sb, Hg, W, Mo. and Se) are useful indicators or pathfinders for the presence of gold [6, 7]. Analyses of samples taken enable the observation of patterns and concentrations in the distribution of metals in the soil which would potentially indicate enriched rock underneath.

    This research examined field characteristics, mineralogical and geochemical composition of gold bearing quartz veins and soils and used the aforementioned to establish prospectivity prediction models that indicate ranking of areas with potential gold mineralization. This is with the overall aim of using the data to discover the extension of the minor gold field vertically or laterally and assess their prospects. The possible origin of the gold bearing fluid was inferred.

    2. Regional Geological Setting

    Maru schist belt is a portion of basement complex of Northwestern Nigeria. It is one of the low grade, upper proterozoic, metasedimentary dominated, and metavolcanic with intrusive igneous rocks schist belt in Western Nigeria [8]. It is bounded to the East by Wonaka schist belt and to the West by Anka schist belt. The schist belts trend N-S and have been infolded into the migmatite-gneiss-quartzite complex. This complex constitutes the predominant rock group in the basement of Eburnean (about 2000 Ma) to Liberian (ca 2800 Ma) age [9].

    Maru schist belt lies Northeast of the Kushaka schist belt with both having similar lithological assemblages and is approximately 200 km long and 12–19 km wide. It is linear super crustal remnants in the polycyclic basement complex of Nigeria. The contact between the schist belt and the gneiss—migmatite complex, are conformable but are locally migmatised around intrusive granitic plutons. The Maru schist belt consists predominantly of pelitic to semipelitic metasedimentary with subordinate interlayered psammites, banded iron formation (BIF) and amphibolites. All the rocks strike approximately North-South, parallel to the structural grain of the surrounding basement complex [10]. The entire Maru belt has been differentiated into Eastern and Western units [11]. While the Eastern unit consists of pelites with locally dominant quartzite and iron formations, the Western unit is almost entirely made up of pelites.

    The fine-grained laminated sediments, both pelites and iron formation, indicate quiet water conditions the predominance of iron oxides suggests oxygenated waters, although sometimes pyrite occurs, indicating anoxic conditions. Metasandstones were deposited in a higher energy environment, reflecting shallow water or increased sediment supply. The Maru schist belt contains internal plutons of granite, granodiorite, diorite, tonalite, and syenites (Figure 1).


    Geological map of the study area showing locations of gold bearing quartz veins with map of Africa and Nigeria above.

    The structure of the study area has imprints of the entire northwestern Nigerian Basement Complex which have passed through a minimum of two episodes (polyphase) of deformation [12, 13]. Three deformation episodes (D1, D2, and D3) were recognized in the area investigated. The second deformation episode (D2) is the major phase. The first (D1) and third (D3) deformational episodes are generally less common. The first deformation episode (D1) produced first axial planar foliation (S1) and first fold phase (F1). The second deformation episode gave rise to S2 and F2 second axial planar foliation and fold phase, respectively. The third deformation episode (D3) resulted from S3 and F3 third axial planar foliation and fold phase, respectively. Several strike slip faults have been mapped within Maru schist belt.

    The quartz veins were hosted by metapelites (slate, phyllite and schist) with metagabbro. Slate and phyllite occur as low lying highly fissile rocks with diagnostic slaty and phyllitic cleavages, respectively. Schist occurs as low lying rocks with N-S trending, moderately to steeply dipping schistose planes. The metapelites displayed lepidoblastic texture. These rocks experienced low grade green schist regional metamorphism [14]. Metagabbro are porphyroblastic and have been metamorphosed to epidote amphibolite facies conditions [15].

    3. Materials and Methods

    Quartz veins were collected as grab samples with the use of geological hammer during structural and lithological mapping of the study area. Soil samples from B horizon (0.50–1.0 metre) were collected within the Maru schist belt and other selected parts of the study area at twelve small gold fields established by artisanal miners and local mining companies after various reconnaissance surveys. The soils were excavated with the use of stainless steel hand auger and collected directly into a polythene bag.

    About one kg of soil sample was collected from each location. A total of eighteen samples were collected. The geographic coordinates of all the sampling points were determined with a Garmin global positioning system.

    All the soil samples were allowed to pass through 200 μm sieve and their mineralogy subsequently was examined with the use of X-ray diffraction (XRD) technique. A Philips diffractometer PW 3710 (40 Kv, 30 mA) with Cu kα radiation, equipped with a fixed divergence silt and a secondary graphite monochromator, was used for X-ray diffraction. Whole rock powder samples were scanned with a step size of 0.02° 2 theta (

    ) and counting time of 0.5 second per step over a measuring range of 2 to 65° 2 theta ( ). X pert plus software (Philips) was used to identify the crystalline phases. Thin sections and polished slides were prepared from gold bearing quartz veins and studied under petrological microscope.

    Gold bearing quartz veins and soils samples were crushed, sieved, pulverised with hardened steel, and allowed to pass through 75 μm. Thereafter, major oxide and some trace elements concentration of majority of gold bearing quartz veins collected were analysed with two wave length dispersive X ray fluorescence spectrometers (PW 1480 and PW 2400). Four quartz veins identified to contain visible gold grains were selected and analysed for gold, trace, and rare earth elements with inductively coupled plasma mass spectroscopy (ICP-MS) method. The samples were initially decomposed with HCL, HNO3, HCLO4, and HF acids in order to achieve near total digestion. The procedure followed is contained in [22]. The quartz veins that contain visible gold grains were subsequently assayed with fire assay and instrumental neutron activation analysis (INNA) in order to quantitatively determine the concentration of gold traced to international reference standards as documented in [23]. Twelve soil samples that represent each small minor gold field were analysed with instrumental neutron activation analysis (INAA) equipment for Au (gold) and twenty-two (22) elements.

    Thin section preparation, X-ray diffractometry, and wavelength dispersive X ray fluorescence spectrometry were undertaken in the laboratory of Federal Institute for Geosciences and Natural Resources, Hannover, Germany. The polished section was carried out at Department of Geology, University of Cologne, Germany. Inductively coupled plasma-mass spectroscopy (ICP-MS) and fire assay and instrumental neutron activation analysis (INNA) were carried out at Activation Laboratory Ltd, Ancaster, Ontario, Canada.

    4. Results and Discussion

    4.1. Occurrence and Mineralogy of Gold Bearing Quartz Veins

    Gold bearing quartz veins crosscut metapelites (slate, phyllite with schist) and metagabbro in the study area (Figure 2(a)) indicating epigenetic style of mineralization. These veins vary considerably in thickness and often exhibit significant vertical and longitudinal continuity (Figure 2(b)). Vein contacts are generally sharp and steeply dipping. These veins were identified South of Maraya, West of Sado, West of river Ferri Ruwa and East of river Ferri Ruwa. Other gold bearing quartz veins occur at Tuniya, Hanudezoma, Dangorowa, Yan Kaura and Kadaure within the area investigated (Figure 1). At Sado, sets of intersecting quartz veins containing gold that trend 170°–350°, 130°–310°, and 60°–240° have been mined by artisanal miners. Several pits were excavated along the trend of the quartz veins some to a maximum length of 96m and a recovery depth of about 23 m (Figure 2(c)). Metagabbro host the gold bearing quartz vein in Sado. Majority of the gold bearing quartz veins occur within the Maru schist belt. The quartz veins trend principally in the N-S and NNE-SSW directions. The trend is similar to the regional strike of Maru schist belt (Figure 2(d)).


    (a)
    (b)
    (c)
    (d)

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