A Geoscience Digital Image Library
A Geoscience Digital Image Library
| Title | Strained graptolites from Mount Merino Formation (Carodocian) |
|---|---|
| Description | This shows strained graptolites from Mount Merino Formation (Carodocian) in Taconic slate belt near Granville, New York. Two individuals of the genus Orthograptus illustrate the use of fossil distortion in determining finite strain. Spacing of the thecae (sawtooth-like structures at edge of strips) is a constant in undeformed individuals, allowing a measure of the extension from the deformed spacing. Further, undeformed individuals have thecal apertures (straight edge of thecae) perpendicular to the axis of the stipe. A measure of the departure of this angle from 90 degrees yields angular shear strain. in this sample (a view of the cleavage plain), the grain elongation which marks the X direction of the strain ellipsoid is clear. Theoretically, one could determine the XY state of strain using Mohr circle analysis (see Ramsay and Huber). |
| Chronostratigraphy | Carodocian |
| Lithostratigraphy | Mount Merino Formation |
| Location | USA ▹ New York. Near Granville. |
| Photographer | Arthur Goldstein. 1995. |
| Collection | Keck Structural Geology Slide Set #AG4. |
| Key words | graptolites, New York, distortion, thecae |
| Tech details | 520 KB. Hand specimen. |
| GeoDIL number | 3004 |
| Copyright | Arthur Goldstein |