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Mountains to Bay: A travelogue by a sand grain. Karen Bemis MARE August 7, 2007. The life of a sand grain. Observations and Interpretations. New Jersey Beach Sand. What is it? Where is it from? How did it get here?. Sand from other beaches.

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the life of a sand grain

The life of a sand grain

Observations and Interpretations

new jersey beach sand
New Jersey Beach Sand

What is it?

Where is it from?

How did it get here?

sand from other beaches
Sand from other beaches

Close-up of sand from a beach in Vancouver, showing a surface area of ~1-2 cm2. (Wikipedia)

Close up of black volcanic sand from Perissa, in Santorini, Greece. (Stan Zurek, Wikipedia)

Sand from Guam. (http://www.microscope-microscope.org/applications/sand/microscopic-sand.htm)

Coral sand. (Wikipedia)

some questions to ask at a beach
Some questions to ask at a beach
  • Overall composition
    • Minerals? Shells? Other material?
  • Color
    • White? Yellow? Red? Black? Green?
  • Shape
    • Rounded? Angular?
    • Long & skinny? Round?
  • Size
    • Mud? Normal sand size? Pebbles? Boulders?
action plan
Action Plan

Let’s explore … properties of sand and what they tell us

  • Transport
  • Source
  • System
how do these sands differ shape
How do these sands differ?Shape

Angular

Coral sand from Hauhini, Tahiti

Intermediate

Shell sand from St Maartin, Caribbean

Angular

Shell sand from Lake Powell, Utah

Round

Shell sand from North Shore, Oahu, HI

rounding
Rounding

Sediment grains get rounder and smoother as they bang together -- just like agates or stones put in a tumbler to polish!

high energy environments can round grains
High energy environments can round grains

Round

Shell sand from North Shore, Oahu, HI

Angular

Coral sand from Hauhini, Tahiti

Energetic beach

Calm beach

what can you infer about nj sands

What can you infer about NJ sands?

Are they in a high energy environment? Today? In the past?

Do they come from far away? Or nearby?

what s different about these beaches
What’s different about these beaches?

Pebbles at the beach, Bay of Fundy, Nova Scotia (T. Mcculloch)

Red sand beach, Santorini, Greece (kgb)

Mudflats in Brewster, Massachusetts. (Wikipedia)

Pebbles at the beach, Budleigh Salterton, England (I. West & D. Harvey)

what s different about these beaches not sand
What’s different about these beaches?Not sand!

Big angular grains

Big round grains

Red sand beach, Santorini, Greece (kgb)

Tiny grains

Mudflats in Brewster, Massachusetts. (Wikipedia)

Pebbles at the beach, Budleigh Salterton, England (I. West & D. Harvey)

grain size related to the combination of creation erosion and transport
Grain size related to the combination of creation (erosion) and transport

Smallest grains at final resting place

Median grains en route

Big grains still being broken down

slide16

Making Sediments: Weathering

Physical Weathering: Mechanically breaking rocks down into smaller chunks.

what can you infer about nj sands17

What can you infer about NJ sands?

Are they in a high energy environment? Today? In the past?

Do they come from far away? Or nearby?

slide20
Sand grains are parts of rocks or individual minerals.Two factors control exactly what rocks or minerals …
  • Type of rock at source of sediment
    • All grains of sand started with bigger pieces of rock somewhere else.
  • Time
    • Chemical weathering takes time.
chemical weathering the effects of time
Chemical Weathering: The effects of time

Relative Mineral Stability:

Olivine + Pyroxene: Least stable

Feldspar: Somewhat stable

Quartz: Stable

Chemical Weathering: The chemical reactions that destroy or alter rock at the Earth’s surface.

what can you infer about nj sands25

What can you infer about NJ sands?

What kind of source rocks do you expect based on the minerals or rock bits you see?

Are there locally derived materials like shells or shell bits?

the life of a sand grain26

The life of a sand grain

A plate tectonic interlude

plate tectonics a framework for geologic processes
Plate Tectonics: a framework for geologic processes

Midwest

East coast:

New Jersey!

West coast:

Oregon & Washington

plate boundaries
Plate boundaries

Defined by earthquakes ( ), volcanoes ( ), and trenches ( )

slide31

…matching of geologic units

Fig 3.6

…and mountain ranges

slide32

…marine magnetic anomalies

Fig 3.24

“stripes”

causes of mountain building

Divergent Margins

Convergent Margins

Continental rift

Subduction Zone

Continental Collisions

West Coast

East Coast

Causes of mountain building…
continental rifting
Continental Rifting
  • Crust thins
  • Asthenosphere rises
  • Melting, volcanism.
  • New ocean floor?

This happened on the East coast in early Mesozoic time as the dinosaurs started to populate the landscape.

differences
Differences

Active Margin

e.g., subduction zone

Passive Margin

Former continental rift

  • Wide shallow shelf (continental crust thins and transforms to oceanic)
  • Subsidence
  • Sediment deposition
  • Narrow steeply dipping shelf
  • Earthquakes, tsunamis, volcanoes!
  • Erosion of new mountains
new jersey s newark basin is a failed rift system related to the opening of the atlantic ocean
New Jersey’s Newark Basin is a failed rift system related to the opening of the Atlantic ocean

Geology and geography of New York Bight beaches at http://www.geo.hunter.cuny.edu/bight/index.html

slide37

Geology and geography of New York Bight beaches at http://www.geo.hunter.cuny.edu/bight/index.html

slide38

Paleozoic (old) interbedded sandstones and limestones

Valley and Ridge:

Highlands:

Precambrian (even older) marbles, gneisses and granites

Peidmont (rifting):

Mesozoic (dinosaurs) conglomerate, sandstone and siltsones (lots of red rocks)

Coastal Plain:

Late Mesozoic to Cenozoic (recent) Sand and clay deposits – not quite rocks yet!

Some of the material on NJ beaches may have been used several times!

the life of a sand grain39

The life of a sand grain

Putting it into a geologic context

slide41

Setting the stage: the creation of relief

…leads to

fragmentation and

weathering

slide42

Pulling the trigger…factors causing slope failure…

• Shocks and vibrations

• Changes in slope angles, slope load, and slope strength

The importance of tectonic setting…

• Earthquakes and vibrations

• Faulting and uplift

• Volcanic eruptions

slide43

Transporting grains to the sea starts here …

Mountain Stream:

Big grains,

Conglomerate

Fig 7.32

slide44

A Delta

Fig 7.34

slide45

Clastic Sedimentary Rocks

Weathering

Erosion

Transportation

Deposition

beaches move in and out as sea level changes regressions and transgressions
Beaches move in and out as sea level changes:regressions and transgressions

Sea level changes with climate, ice caps and plate tectonics

longshore currents
Longshore Currents

Geology and geography of New York Bight beaches at http://www.geo.hunter.cuny.edu/bight/index.html

sandbar a moving target
Sandbar = A moving target!

Geology and geography of New York Bight beaches at http://www.geo.hunter.cuny.edu/bight/index.html

barrier island offshore sandbar that grew and grew and grew
Barrier Island: offshore sandbar that grew and grew and grew

Geology and geography of New York Bight beaches at http://www.geo.hunter.cuny.edu/bight/index.html

slide52

Diagram showing the environments of a barrier island system

(from Blatt, et al, 1980, Petrology of Sedimentary Rocks).

summary
Summary
  • Interactions of “rigid” lithospheric plates results in mountains
  • Mountains erode to create sediment, which gets progressively smaller, rounder and mature as it travels towards the ocean
  • The final resting place of sediment depends on its size and density
    • Sand ends up at the coast – beaches!
    • Mud in the deep ocean
  • The composition of a beach depends on
    • The sediment source in the nearest mountains
    • Local production of shells and other biologically related material
    • The distance to mountains
    • The energy of the average waves that reach the beach
  • Barrier islands
    • Form on shallow gently dipping continental shelves (usually associated with passive margins, that is, former continental rifts)
    • Move along the coast as controlled by wave directions
    • Are really neat! (I hope you agree. )
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