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Callan Bentley's Snapshots

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  1. Pseudomorphs

    Snapshot Title: Pseudomorphs
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Sericite-after-staurolite: retrograde metamorphism.



  2. cm

    Snapshot Title: cm
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    A sense of scale (and distortion!) is provided by this pencil and its 1-centimeter black bars along the side.



  3. Star Trek insignia

    Snapshot Title: Star Trek insignia
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    What is up with this fellow?
    -merely flattened and thus a small hollow has become more exaggeratedly concave?
    -sheared with the left side down, creating a "tail"?
    -is it a dismembered fold hinge?



  4. Stretched clast

    Snapshot Title: Stretched clast
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    May have "fishmouth" structure at far end - perhaps it was boudinaged? (In that case, a mere axial ratio will underestimate the total strain.)



  5. Pseudomorphs

    Snapshot Title: Pseudomorphs
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Sericite-after-staurolite - retrograde metamorphism.



  6. cm

    Snapshot Title: cm
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    A sense of scale is provided by this pencil, which has 1-cm black bars along its side.



  7. Mega-Skolithos

    Snapshot Title: Mega-Skolithos
    Taken by: Callan Bentley

    Image: Tuscarora Sandstone exposed at Hanging Rock Anticline, West Virginia
    Image Owner: Callan Bentley



    Description:

    ((juuuuuuuuuuuuust kidding))



  8. Change in outcrop angle

    Snapshot Title: Change in outcrop angle
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    These clasts have not been folded - they are still pancake-like in their geometry, like (most of) their neighbors.



  9. Offset

    Snapshot Title: Offset
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    A small fault has offset this foliated clast (top to the left) by an inch or so.



  10. Kinked cobbles?

    Snapshot Title: Kinked cobbles?
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    These cobbles appear to have been sheared out and then kinked (top to the left).



  11. Stretched clast

    Snapshot Title: Stretched clast
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    This poor cobble has been all smeared out!



  12. Scale

    Snapshot Title: Scale
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    This pencil provides a sense of scale. It's slightly out of focuse because it's in a hollow in the rock, but you can still tell that the black bars along the side are 1 centimeter in length.



  13. Stretched clast

    Snapshot Title: Stretched clast
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Like a fish in a school



  14. Lichen

    Snapshot Title: Lichen
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Not a stretched clast.



  15. Internal foliation

    Snapshot Title: Internal foliation
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Some of these clasts have an internal layering: could be sedimentary bedding, or volcanic flow banding, or a preceding generation of metamorphic foliation.



  16. Small fault

    Snapshot Title: Small fault
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    This quartzite clast has been offset along a small brittle fracture which must post-date ductile deformation of these clasts.



  17. Stretched clast

    Snapshot Title: Stretched clast
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    This one seems to exhibit a sinistral sense of shear on this loose block of float.



  18. A closer look

    Snapshot Title: A closer look
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    For a view of this face, check out this GigaPan shot on the same day:
    gigapan.com/gigapans/128476



  19. Stray fold hinge

    Snapshot Title: Stray fold hinge
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    To get a better view of this face, try another GigaPan shot the same day, but from a different perspective: gigapan.com/gigapans/128419



  20. Kink
  21. Kink

    Snapshot Title: Kink
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    This kink band is at a conjugate angle relative to the big, prominent one a few inchest to the left.



  22. Stretched

    Snapshot Title: Stretched
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    quartzite clast.



  23. 2 kinks and a stretched clast

    Snapshot Title: 2 kinks and a stretched clast
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    A nice little ensemble.



  24. Intense kinking

    Snapshot Title: Intense kinking
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    About an apparent 90 degree angle here between the kink band foliation and the main foliation that surrounds it.



  25. Kink band

    Snapshot Title: Kink band
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    The foliation has been "kinked" in a band about an inch thick.



  26. Kink band

    Snapshot Title: Kink band
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    The foliation has been "kinked" here.



  27. Scale

    Snapshot Title: Scale
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    This pencil serves as a sense of scale. It's in a hollow, so it's mostly blurry, though thankfully that implies the rock around it should be in focus... Black bars along the side each measure 1 cm.



  28. Clast

    Snapshot Title: Clast
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    With well-defined edges.



  29. Clast with internal layering

    Snapshot Title: Clast with internal layering
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Pre-existing metamorphic foliation? Sedimentary bedding? Volcanic flow banding?



  30. Stretched clast

    Snapshot Title: Stretched clast
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Felsite? Quartzite?



  31. Stretched clast

    Snapshot Title: Stretched clast
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Looks like a dark mica-rich schist cobble?



  32. Pseudomorph

    Snapshot Title: Pseudomorph
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Sericite after staurolite (retrograde metamorphism)



  33. Scale

    Snapshot Title: Scale
    Taken by: Callan Bentley

    Image: Klingle Valley metaconglomerate, Laurel Formation, Rock Creek Shear Zone, Washington, DC
    Image Owner: Callan Bentley



    Description:

    This pencil has one-centimeter black bars along its side.



  34. Stretched clast

    Snapshot Title: Stretched clast
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Maybe with a second clast fused into it at lower left?



  35. Stretched clast

    Snapshot Title: Stretched clast
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    What is the axial ratio of this clast, as expressed on this surface?



  36. 1 inch

    Snapshot Title: 1 inch
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    On a scale card provided by the Virginia DGMR.



  37. Scale pencil

    Snapshot Title: Scale pencil
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Slightly blurry, due to its location in a hollow, but the rock is in focus! 1 cm demarcations on the side of the pencil.



  38. Kinked foliation

    Snapshot Title: Kinked foliation
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Right at the fracture. Right at the transition between brown and gray.



  39. Stretched mafic clasts

    Snapshot Title: Stretched mafic clasts
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Not as obvious to the eye as the milky quartz stretched clasts / boudins, but these dark colored clasts are present, too.



  40. Big clasts

    Snapshot Title: Big clasts
    Taken by: Callan Bentley

    Image: Kink banding in Laurel Formation of Rock Creek Shear Zone, Broad Branch, Washington, DC
    Image Owner: Callan Bentley



    Description:

    Or boudins?



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