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Callan Bentley's Snapshots

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  1. Sectioned clast

    Snapshot Title: Sectioned clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Exposed on 2 surfaces



  2. Dark-colored clast

    Snapshot Title: Dark-colored clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Long axis included w/in the plane of foliation (late Ordovician Taconian Orogeny)



  3. Small mica-rich clast

    Snapshot Title: Small mica-rich clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    w/ reaction halo



  4. Large, mica-rich clast

    Snapshot Title: Large, mica-rich clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    bearing a reaction halo around it



  5. Light-colored clast

    Snapshot Title: Light-colored clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Apparently well rounded.



  6. Hammerhead

    Snapshot Title: Hammerhead
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    for scale



  7. Shadow

    Snapshot Title: Shadow
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    of the GigaPan



  8. Fresh vs. weathered surfaces

    Snapshot Title: Fresh vs. weathered surfaces
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    This rock rusts!



  9. Lichen

    Snapshot Title: Lichen
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Not clasts



  10. Foliated clast

    Snapshot Title: Foliated clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Where the (coarser; gneissic) foliation internal to the clast is oblique to the regional foliation in the surrounding matrix.



  11. Quartz clast

    Snapshot Title: Quartz clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Oblique to foliation.



  12. Hammer for scale

    Snapshot Title: Hammer for scale
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Here's the top of the hammer handle.



  13. Weathered out clast

    Snapshot Title: Weathered out clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    You can see a little tail of relatively-unweathered biotite-rich clast to the right of the joint trace.



  14. Bird poop

    Snapshot Title: Bird poop
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Probably a heron.



  15. Recessive weathering

    Snapshot Title: Recessive weathering
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Some clasts are less chemically stable than the surrounding matrix, and weather out to make clast-shaped holes in the rock face.



  16. Another reaction halo

    Snapshot Title: Another reaction halo
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Rimming this mica-rich clast



  17. Felsic clast

    Snapshot Title: Felsic clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Mica poor, relative to matrix



  18. Reaction halo

    Snapshot Title: Reaction halo
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Where the clast reacted w/ surrounding matrix.



  19. Fishlike clast

    Snapshot Title: Fishlike clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Pointy tip and frayed tail



  20. Elongate, flat dark schist clasts

    Snapshot Title: Elongate, flat dark schist clasts
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    And chunkier light-colored clasts.



  21. Contrasting clasts

    Snapshot Title: Contrasting clasts
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Dark-colored, mica-rich clasts tend to be flattened parallel to the plane of foliation. Lighter colored clasts tend to be more chunky and equant.



  22. Sense of scale

    Snapshot Title: Sense of scale
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Tip of hammer (the only part that's in focus!)



  23. Chlorite clast weathering away

    Snapshot Title: Chlorite clast weathering away
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    more rapidly than surrounding rock.



  24. Fresher surface

    Snapshot Title: Fresher surface
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    The rusty, hydrolysed weathering rind has peeled off here, showing fresher (grayer) rock beneath.



  25. Recessive weathering

    Snapshot Title: Recessive weathering
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    of a chlorite-rich clast



  26. Mafic clast

    Snapshot Title: Mafic clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    No reaction rim, though



  27. Slickensides

    Snapshot Title: Slickensides
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Common feature in these rocks.



  28. Two squashed clasts

    Snapshot Title: Two squashed clasts
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Ellipsoidal.



  29. Light-colored clasts

    Snapshot Title: Light-colored clasts
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Some with reaction rims, others (milky quartz) with no obvious reaction rim.



  30. Clast

    Snapshot Title: Clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    of milky quartz



  31. Felsic clast

    Snapshot Title: Felsic clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Must be older than the Sykesville Formation that includes it.



  32. Big tabular clast

    Snapshot Title: Big tabular clast
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    A big slabby chunk of quartzite included in the metagraywacke/schist matrix.



  33. Hammer for scale

    Snapshot Title: Hammer for scale
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Here is the butt end of the hammer.



  34. Reaction rim

    Snapshot Title: Reaction rim
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Another signal of chemical re-equilibration between clast and matrix.



  35. Mafic clast w/ reaction rim

    Snapshot Title: Mafic clast w/ reaction rim
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Amphibolite?



  36. Milky quartz inclusions

    Snapshot Title: Milky quartz inclusions
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    exposed on the plane of foliation.



  37. Hammer for scale

    Snapshot Title: Hammer for scale
    Taken by: Callan Bentley

    Image: Sykesville Formation, Chain Bridge Flats, DC
    Image Owner: Callan Bentley



    Description:

    Top of the handle



  38. Students

    Snapshot Title: Students
    Taken by: Callan Bentley

    Image: Gastropod duplex w/ people for scale
    Image Owner: Callan Bentley



    Description:

    Zack, Matt, and Jake, checking out the structural geology.



  39. Percussion marks

    Snapshot Title: Percussion marks
    Taken by: Callan Bentley

    Image: Second Generation Quartz, Billy Goat Trail
    Image Owner: Marissa Dudek



    Description:

    Great examples.



  40. Percussion marks

    Snapshot Title: Percussion marks
    Taken by: Callan Bentley

    Image: Second Generation Quartz, Billy Goat Trail
    Image Owner: Marissa Dudek



    Description:

    Bouncing cobbles in the ancient Potomac River slammed into this postively-weathering vein to make these features.



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