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Mountains to Bay: A travelogue by a sand grain

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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Mountains to Bay: A travelogue by a sand grain

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  1. Mountains to Bay: A travelogue by a sand grain Karen Bemis MARE August 7, 2007

  2. The life of a sand grain Observations and Interpretations

  3. New Jersey Beach Sand What is it? Where is it from? How did it get here?

  4. 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)

  5. 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?

  6. Action Plan Let’s explore … properties of sand and what they tell us • Transport • Source • System

  7. How do these sands differ?

  8. 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

  9. Moving Sediment

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

  11. High energy environments can round grains Round Shell sand from North Shore, Oahu, HI Angular Coral sand from Hauhini, Tahiti Energetic beach Calm beach

  12. 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?

  13. 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)

  14. 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)

  15. 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

  16. Making Sediments: Weathering Physical Weathering: Mechanically breaking rocks down into smaller chunks.

  17. 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?

  18. How do these sands differ?

  19. How do these sands differ?Dominant components Quartz Lava Olivine Coral

  20. 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.

  21. Black and green sands from volcanoes (sometimes even red sands) Lava Olivine

  22. Corals and shells from barrier reefs, oyster bars, etc Coral

  23. Quartz from sandstone or granitic rocks Quartz

  24. 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.

  25. 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?

  26. The life of a sand grain A plate tectonic interlude

  27. Mountains – created by the interactions of tectonic plates

  28. Plate Tectonics: a framework for geologic processes Midwest East coast: New Jersey! West coast: Oregon & Washington

  29. Plate boundaries Defined by earthquakes ( ), volcanoes ( ), and trenches ( )

  30. …distribution of Paleozoic and Mesozoic fossils

  31. …matching of geologic units Fig 3.6 …and mountain ranges

  32. …marine magnetic anomalies Fig 3.24 “stripes”

  33. Divergent Margins Convergent Margins Continental rift Subduction Zone Continental Collisions West Coast East Coast Causes of mountain building…

  34. 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.

  35. 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

  36. 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

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

  38. 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!

  39. The life of a sand grain Putting it into a geologic context

  40. where it all beginsMass movement…

  41. Setting the stage: the creation of relief …leads to fragmentation and weathering

  42. 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

  43. Transporting grains to the sea starts here … Mountain Stream: Big grains, Conglomerate Fig 7.32

  44. A Delta Fig 7.34

  45. Clastic Sedimentary Rocks Weathering Erosion Transportation Deposition

  46. Coastal Landforms:beaches

  47. Beaches move in and out as sea level changes:regressions and transgressions Sea level changes with climate, ice caps and plate tectonics

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

  49. Sandbar = A moving target! Geology and geography of New York Bight beaches at http://www.geo.hunter.cuny.edu/bight/index.html

  50. Coastal Landforms:beach drift and sediment budgets

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