One occurrence of sedimentary OM greets me frequently while I am walking the dog. I live in an old neighborhood of lawns, large trees, and pachysandra (my personal trace plant for old neighborhoods); most of the homes were built around 1900. Although numerous sidewalks are now cement, many remain the original large slabs of Pennsylvania Bluestone, some with fossil wood fragments exposed on cut or slabbed surfaces. Pennsylvania Bluestone is a Middle to Upper Devonian feldspathic sandstone of the Catskill delta or Catskill/Pocono clastic wedge, outcropping now in southern New York, northeastern Pennsylvania, and northern New Jersey. It is the "molasse" of the Acadian orogeny, whose thermal and deformational peak in the northern Appalachians to the east (Maine, New Hampshire, Massachusetts, Connecticut) occurred in the Lower Devonian.
|Bluestone in disrepair but shows typical sidewalk slab size and thickness. Twenty-pound (9 kg) puppy for scale.|
|Ripple marks (interference ripples?) on bluestone sidewalk slabs.|
|Ripple marks, in different location than above, on wet sidewalk in street lights at night.|
|Patio bluestone showing range of color, some ripple marks, and, in slab in foreground, dispersed fossil wood fragments.|
|Old bluestone sidewalk slab; fossil wood weathered out leaving casts.|
|Three more examples of oriented fossil wood in Pennsylvania Bluestone. Blue color in bottom two photos due primarily due to time of day, just prior to sunset.|
|(from Potter and others, 1979, Devonian Paleocurrents in the Appalachian Basin)|
BTW, at the time this post was written, the blog background was an extreme close-up of wood fragments in bluestone (below).
*Catskill delta field guides:
Facies and Sedimentary Environments of the Catskill System Tract in Central Pennsylvania, Pittsburgh Association of Petroleum Geologists, 2009 http://www.papgrocks.org/PAPGGuidebook_Spring09.pdf
From Tunkhannock to Starrucca: Bluestone, Glacial Lakes, and Great Bridges in the “Endless Mountains” of Northeastern Pennsylvania, Field Conference of Pennsylvania Geologists, 2009.