bathy me try and marine sediments lab

7/30/2019 Bathy Me Try and Marine Sediments Lab

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GOL 106: Historical Geology

Northern Virginia Community College

Dr. Victor P. Zabielski February 2012

Sediment Characteristics and Depositional Environments

Objective:

The objective of this lab is familiarize you with the general types of sedimentscommon to the marine environment and the processes and forces responsible for

distributing and modifying them.

Introduction:

The oceans, unlike most land surfaces, are constantly collecting and accumulatingsediments. In fact, there are very few regions of the ocean that are not accumulating

sediments. What types of sediments are accumulating in the oceans? Are sediments in

the ocean all the same or do they vary from place to place? What controls the type andamount of sediments that will accumulate in any given area? The answers to thesequestions provide the knowledge to understand the distribution of sediments in the

modern (and ancient) oceans and hold the key to unraveling the history of oceancirculation, productivity and even the climate of the Earth over the past hundreds of

millions of years.A geologists job is to read the history of the earth or oceans from the evidence

that is left behind. This is much like a detective who characterizes a persons life andactions by looking through their garbage. In the geologists case, we first need to

familiarize you with what to expect in the garbage (sediments) and how to interpretwhats there, and perhaps more importantly, what is not there.

Marine sediments are an accumulation of particles that were either transported tothe ocean or produced in the oceans. There they are modified by additions or subtraction

of various constituents and by weathering and erosion at the earths surface. Each ofthese actions will leave a noticeable imprint on the sediment. By understanding each of

these processes and identifying their imprints, we can slowly unravel the history of anysediment and propose a potential depositional environment in which these sediments

accumulated. This type of study is widely employed when looking at ancient rocks andsediments produced in depositional environments that are no longer existent.

The first step in understanding this potentially complex mix of effects is to 1)become familiar with the common types of particles encountered in most sediments 2)

learn to identify the physical properties of those sediments and 3) understand the specific

processes that can alter these properties and the affects they have on the sediment.


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There are four primary particle properties used to describe a sediment sample.These are:

1) Particle composition

2) Particle size

3) Particle shape

4) Particle sorting

These properties are controlled largely by the following factors:

Energy of the environment of deposition (high verses low energy) Proximity to original source material (close verses distant) Age of the sediment (degree of exposure to weathering and erosion) Composition of parent material (granite verses basalt, etc.) Mechanism of sediment transport (wind, water, glaciers, etc)

Once you familiarize yourself with how each of the properties is affected by thecontrolling factors, you can make some generalizations about thedepositional

environment in which the sediment must have been deposited. The depositionalenvironment will include the dominant factors of a location affecting the type of sediment

deposited there. This can include local climate (temperature, precipitation), energy level(high or low energy), regional topography, biological factors, geologic setting, etc.

Part I: Particle Types and Properties

1) Particle composition:Oceanic particles can be classified into one of four particle categories based on

there composition and/or origin. These categories are:

1) Lithogenous2) Biogenous3) Hydrogenous4) Cosmogenous

Lithogenous:Lithogenous particles are derived from the weathering and erosion of rocks, either on

land or in the ocean. Thus, their composition can vary depending on the original rockmaterial. The most common types of lithogenous particles encountered in marine

sediments are: Quartz (generally a granitic parent) Clays (weathering product of silicate minerals) Mafics (dark minerals such as olivine [green], amphibole [black], pyroxene

[black], magnetite [black and magnetic] (generally a basaltic/volcanic parentrock)

Rock fragments (indicate incomplete breakdown of parent material, close tosource)


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Biogenous:Biogenous particles are created in the oceans through the action of a living organism,

either a plant or animal. The composition of these particles is usually calcium

carbonate (CaCO3, calcite or aragonite), but can also be silica (SiO2). Thesesediments are either precipitated by microscopic plants or animals living in the upperwater column (planktic) or on the sea-floor (benthic). The most common types of

biogenous sediments encountered in marine sediments are:Foraminifera (animal, CaCO3)

Radiolarians (animal, SiO2)Diatoms (plant, SiO2)

Coccolithophores (plant, CaCO3)Shell fragments

Calcareous algae (halimeda, penicillus, udotea, rhipocephalus)

The saturation state of CaCO3 in ocean waters is directly related to watertemperature and pressure. Warm, shallow waters (tropics, surface) are generally

supersaturated with respect to CaCO3 and cold deep waters (poles, deep ocean) can beundersaturated. Sediments from warm tropical beaches will generally contain

abundant CaCO3, whereas deep ocean contain little to no CaCO3 due to its removalby dissolution.

Unlike CaCO3, SiO2 is undersaturated everywhere in the ocean water and issusceptible to dissolution. Its presence in sediments is generally an indication of high

production rates, and thus high productivity where the inputs of the mineral canoutpace the removal by dissolution.

Forams, radiolarians, diatoms and coccolithophores are found living and growingin most ocean surface waters. Some deep ocean sediments are composed of almost

100% biogenous particles. These sediments are called oozes.

Hydrogenous:Hydrogenous sediments are created by inorganic chemical reactions in the oceans.

Their origin is not linked to any living organism. They can be created in both shallowand deep water and their composition is linked closely with the chemical composition

and physical properties of the seawater in which they were formed. The mostcommon types of hydrogenous sediments encountered in marine sediments are:

Calcite (CaCO3, ooids/ooilites, shallow intertidal tropical shoals)Gypsum (CaSO4, shallow sea water pools prone to evaporation)

Glauconite ((K,Na)(Fe,Al,Mg)2(Si,Al)4O10(OH)2)Phosphates (CaPO4, usually associated with highly productive regions)

Pyrite (FeS2, indicates low oxygen content in the water)Halite (NaCl, shallow sea water pools prone to intense evaporation)

Cosmogenous:

Cosmogenous sediments are derived from extraterrestrial bodies, usually meteors thatenter our atmosphere and break-up. These are the rarest types of sediments to be


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found in the ocean. However, when they are found, the interpretations andrepercussions could be significant. We will not be seeing any of these sediments in

this lab.

You can use Table 2 at the end of this lab to help you estimate the percentage

composition of each particle type.

2) Particle Size:Particle Size is described using the Standard Wentworth Scale.

Wentworth Particle Name Size Range (mm) Screen (m)

Boulder >256 256,000

Cobble 64 - 256 64,000

Pebble 4 - 64 4,000Gravel 2 - 4 2,000

Very coarse sand 1 - 2 1,000

Coarse sand 0.5 - 1 500

Medium sand 0.25 0.5 250

Fine sand 0.125 0.25 125

Very fine sand 0.063 0.125 63

Silt 0.063 0.033 33

Clay


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3) Particle Shape:The shape of a particle can range from angular to rounded. This property is

usually reserved for lithogenous sediments and is controlled by the amount of weathering

and erosion of the particle.

angular sub-angular sub-rounded rounded

Through time, particles will become more rounded as they are exposed to longer

periods of weathering. Thus a very angular particle is likely younger or less mature thana very rounded particle. Since some particles such as calcite (CaCO3) are much softerthan others such as quartz (SiO2), some particles may mature faster than others. By

looking only at the quartz present in a sample, rather than other constituents, you cancompensate for any differences in hardness between particles.

4) Particle Sorting:The sorting of particles refers to the distribution of particle sizes contained in any

sample. Well sorted sediment will be composed of sediment particles of only oneparticle size (for example, coarse sand). Poorly sorted sediment will contain many

different particle sizes, sometimes ranging from clay to cobbles or larger.

well sorted moderately sorted poorly sorted

The sorting of a sediment is controlled primarily by the mechanism of transport whichmoved and redistributed the sediments. The most common means of moving and

redistributing sediments is by water (currents), wind, and glaciers. Wind is by far themost efficient means of sorting sediments and produces sediments that are very well

sorted. This is because wind can generally only carry one size particle. Glaciers are theleast efficient mechanism for sorting, and generally produce very poorly sorted


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sediments. Sediments redistributed by water can produce a range of sorting, butgenerally will always result in a moderate to well sorted sediment.

Part 2: Factors Controlling Sediment Particle Characteristics

The most common factors affecting the composition and characteristics ofsediment particles are the following:

Energy of the environment of deposition (high verses low energy) Proximity to original source material (close verses distant) Composition of parent material (granite verses basalt, etc.) Mechanism of sediment transport (wind, water, glaciers, etc) Age of the sediment (degree of exposure to weathering and erosion)

Energy of the EnvironmentThis refers to the average level of energy to which a sediment sample was

subjected. The energy of the environment has a large effect on the overall size of the

particles in the sample. Fine mud particles are easily washed from a beach and carriedoffshore to be deposited in deeper low energy environments. Thus most beach samples

contain little fine material. A beach that is subjected to very high wave action, on theother hand, will likely not even contain sand and may be composed only of pebbles or

cobbles.

Proximity to Source (lithogenous)The proximity to source refers to how close the sample was to its original parent

material or the site where it was formed. A general rule of thumb states that the closer asediment is to its source, the larger the particle size. This is generally only true for

lithogenous particles (quartz, mafics, etc) since most lithogenous particles will need to betransported to the site where the sediment is accumulating. Biogenous particles can be

formed/precipitated anywhere in the ocean and are often formed in the general vicinity ofwhere they are found. Lithogenous particles on the other hand can be transported

hundreds to thousands of miles.

Composition of Parent Material (lithogenous)The composition of the parent material will have a great affect on the composition

of the subsequent sediment sample. Quartz, one of the most common mineral on earth, is

mostly found in granitic rocks. Granite is mostly found on continents. Thus the presenceof quartz in a rock implies a continental source. Similarly, the absence of quartz in a rockcould imply the lack of a proximal continental source. The presence of mafics implies a

proximal mafic source, usually basalt or another volcanic rock. This would imply aproximal active margin.


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Mechanism of TransportThe mechanism of transport will have a great affect on the sorting of the sediment

particles. As stated previously, transport by wind will produce the most well sortedsediments. Transport by ice (glaciers) generally produces very poorly sorted sediments.

Transport by water generally produces moderate to well sorted particles.

Age of SedimentThe age of the sediment refers to how long the sediment particles have been

removed from their original parent source (in the case of lithogenous particles), or howlong ago they were formed in the case of biogenous or hydrogenous particles. Age can

potentially have an effect on several particle properties including composition, shape, andsorting. Geologist refer to the collective affect of age on a sediment particle as its

maturity. The maturity of a sediment sample refers to the degree to which the sedimentproperties have been modified from their original properties. For instance, an immature

sediment is will have just been formed from its parent material and will have beensubjected to little weathering or erosion (transport). Thus its composition will be very

close to its original parent and contain several types of lithogenous particles, possiblyincluding rock fragments. Since it was not transported very far, it will show poor to

moderate sorting and the lithogenous particles will be angular. A mature sediment, onthe other hand will have been subjected to intense weathering and erosion. The softer

lithogenous particle may have completely weathered away and only the hardest particles(quartz) will remain. The lithogenous sediments will show a high degree of sorting and

will likely be well rounded.

Sources / Sinks / DilutionWhen trying to interpret the depositional setting of a sediment, you will need to

consider factors that explain the presence as well as the absence of the types of particlesthat you find. For instance, given the fact that calcareous sediments are so common in

the ocean, their absence from a sediment sample is highly unusual and could indicate adepositional setting at a high latitude (where many organism cannot thrive), the deep

ocean (which is corrosive to calcite) or a coastal setting with a high input of lithogenousparticles (which will dilute the calcareous material and make it seem less abundant that it

actually is). Similarly, the absence of quartz from a sediment sample may indicate thatthe depositional environment was either distant from a continental source (oceanic island,

oceanic banks, continental edge far from any mountains, etc) or an absence of a means ofdelivering the quartz to the site (no rivers, little wind) Thus, when considering the

presence or absence of specific ocean particles from a sediment sample, you mustconsider each of the following:

Sources (a means of input)

Sinks (mechanisms for removing or dissolving particles)Dilution (a means of masking a particles presence)

As you can clearly see, any one particle characteristic can be affected by several factors.

For instance the sediment composition is both affect by its source, its age and alsopossibly by dilution or dissolution. Thus no one single particle characteristic can be used


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to definitely determine the characteristics of its depositional environment. Instead, youshould attempt to gather as many clues in the form of particle characteristics and come to

a conclusion based on a preponderance of the evidence. Table 1 on the following pageoutlines the affects of many of these factors on sediment particles and can be used as a

rough guide when interpreting depositional environments.


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Table 1Composition Size Shape Sorting

Original composition ofparent material

granite quartz, clayBasalt/volcanics mafics, clay

hot spot mafics,

olivine, clay

Tropical oceans biogenous

Proximity to original

source

near >sand sub-angular

distant


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Lab Exercise

Equipment needed:1 binocular microscope

Samples of various particle compositions (provided)Samples of various sediments

1) Part I:Particle SamplesIn the first part of this lab you will look at a variety of different common sedimentparticles in order to familiarize yourself with the range of composition you can

expect to observe in sediment samples.

2) Part II: Depositional Environments (known locations)Next you will look at sediments from several different known locations anddescribe each sample according to particle a) composition, b) size, c) shape, and

d) sorting and hypothesize on what each particle characteristic can reveal about

the source of the sediment and the depositional environment.3) Part III: Depositional Environments (unknown locations)Finally you will analyze four unknown sediment samples and describe their

sediment characteristics in an attempt to try to identify the depositionalenvironment in which it was formed


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Directions:

Part I: Particle samplesI have placed several examples of someparticle types around the room. Look at each of

these particle types and describe them such that if you were to see them again (such as on

a quiz) you would be able to identify them. A small drawing may help in some instances.If you have any questions, ask me, thats why I am here.

Particles:

Lithogenous particles:

Description Drawing

Quartz (beach): ______________________________________________

______________________________________________

Quartz (desert): _______________________

_______________________

______________________________________________

Mafics: _______________________

______________________________________________

_______________________

Biogenous Particles:

Description Drawing

Foraminifera: _______________________

_______________________

______________________________________________

Radiolarians: _______________________

______________________________________________

_______________________

Diatoms: ______________________________________________

_______________________

_______________________


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Shell fragments: _______________________

______________________________________________

_______________________

Calcareous Algae:

Halimeda: _______________________

______________________________________________

_______________________

Penicillus: _______________________

_______________________

______________________________________________

Udotea: ______________________________________________

_______________________

_______________________

Rhipocephalus: _______________________

_______________________

______________________________________________

Hydrogenous Particles:

Description Drawing

Ooids/ooilites: _______________________

______________________________________________

_______________________

Gypsum: _______________________

_____________________________________________________________________


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Directions:

Part II: Depositional Environments (known locations)I have provided several sediment samples from known locations around the room. Usingthe characteristics discussed previously, describe each of the sediments by approximate

size, composition, particle shape, and sorting. Additionally, make some generalizations

about the environment in which the sediment was created (deposited). Was it a highenergy (beach, river) environment or low energy (lake, pond) environment? Was it anocean beach or desert? Was it moved by water, wind or glaciers? How far has this

sediment traveled from its source? What was the composition of the original source?The answer to each of these questions is contained in the particle properties you

described. Use Table 1 to help you understand what factors can control each of theproperties.

Depositional Environments (Known Samples)

Carolla Beach, North Carolina

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

____________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________

Interpretation: parent material/source :________________________________

proximity to source :___________________________________

energy of environment :________________________________

mechanism of transport :_______________________________

maturity :____________________________________________

comments :_____________________________________________________________________________________________________________________________________________________


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Playa Hermosa, Costa Rica

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

____________________________________________________

________________________________________________________________________________________________________

____________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________





maturity :____________________________________________

comments :________________________________________________________________________________________________

_____________________________________________________

Duck Key, Florida

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

____________________________________________________

________________________________________________________________________________________________________

____________________________________________________

Shape: ________________________________________________________________________________________________________

Sorting: ____________________________________________________

____________________________________________________





maturity :____________________________________________comments :________________________________________________________________________________________________

_____________________________________________________


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White Sands, New Mexico

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

____________________________________________________

________________________________________________________________________________________________________

____________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________





maturity :____________________________________________

comments :________________________________________________________________________________________________

_____________________________________________________

Kanab, Utah

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

____________________________________________________

____________________________________________________________________________________________________________________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________




mechanism of transport :_______________________________maturity :____________________________________________

comments :________________________________________________________________________________________________

_____________________________________________________


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Hawaii (Big Island)

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

____________________________________________________

________________________________________________________________________________________________________

____________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________





maturity :____________________________________________

comments :________________________________________________________________________________________________

_____________________________________________________


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Directions:

Part III: Depositional Environments (unknown locations)I have provided you with four sediment samples from unknown locations. In fact I doknow the exact location that each of these samples came from. Using the same

techniques you used in Part II, analyze each of the unknowns and try to determine some

of the major characteristics of the environment in which this sediment was deposited. Ido not expect you to give me an exact location name (although that would be amazing!).But instead give me generalities of what you think the environment was like.

Depositional Environments (Unknown Samples)

Sample A

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

________________________________________________________________________________________________________

________________________________________________________________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________




mechanism of transport :_______________________________maturity :____________________________________________

comments :_____________________________________________________________________________________________________________________________________________________


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Sample B

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

____________________________________________________

________________________________________________________________________________________________________

____________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________





maturity :____________________________________________

comments :________________________________________________________________________________________________

_____________________________________________________

Sample C

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

____________________________________________________________________________________________________________________________________________________________

____________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________



energy of environment :________________________________mechanism of transport :_______________________________

maturity :____________________________________________

comments :________________________________________________________________________________________________

_____________________________________________________


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Sample D

Size: ____________________________________________________

____________________________________________________

Composition: ____________________________________________________

________________________________________________________________________________________________________

________________________________________________________________________________________________________

Shape: ____________________________________________________

____________________________________________________

Sorting: ____________________________________________________

____________________________________________________





maturity :____________________________________________

comments :________________________________________________________________________________________________

_____________________________________________________


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Table 2

bathy me try and marine sediments lab

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