Ed Thanks for the fascinating analysis. I usually associate layers such as those shown in the image with deposition by water, but don't think about the geological processes involved beyond that. It is very interesting to hear fine-tuned explanations.
Bob Sent from my iPhone On Aug 14, 2009, at 8:57 PM, "Edward Frank" <[email protected]> wrote: > Bob, > > There is a real nice overview of the geology of the Catskills > Wikipedia. http://en.wikipedia.org/wiki/Catskill_Mountains This is > a slight reordering of the information presented there: > The Catskills contain more than thirty peaks above 3,500 feet and > parts of six important rivers. The highest mountain, Slide Mountain > in Ulster County, has an elevation of 4,180 feet (1,274 m). At the > eastern end of the range the mountains begin quite dramatically with > the Catskill Escarpment rising up suddenly from the Hudson Valley. > The western boundary is far less certain, as the mountains gradually > decline in height and grade into the rest of the Allegheny Plateau. > The Poconos, to the immediate southwest in Pennsylvania, are > technically a continuation of the Catskills under a different name. > > The Catskill Mountains are more of a dissected plateau than a series > of mountain ranges. The sediments that make up the rocks in the > Catskills were deposited when the ancient Acadian Mountains in the > east were rising and subsequently eroding. The uplift and erosion of > the Acadian Mountains was occurring during the Devonian and early > Mississippian period (395 to 325 million years ago). The sediments > traveled westward and formed a great delta into the sea that was in > the area at that time. The eastern escarpment of the Catskill > Mountains are near the former (landward) edge of this delta, as the > sediments deposited in the northeastern areas along the escarpment > were deposited above sea level by moving rivers and the Acadian > Mountains were located roughly where the Taconics are located today > (though significantly larger). The further west you travel, the > finer the sediment that was deposited and thus the rocks change from > gravel conglomerates to sandstones and shales. Even further west, > these fresh water deposits intermingle with shallow marine > sandstones and shales until the end in deeper water limestones. Over > time the sediments were buried by more sediments from other areas > until the original Devonian and Mississippian sediments were deeply > buried and slowly became solid rock. Then the entire area > experienced uplift, which caused the sedimentary rocks to begin to > erode. Today, those upper sedimentary rocks have been completely > removed, allowing the Devonian and Mississippian rocks to be exposed. > Bob, as per your specific question, this rock deposit is a sandstone > unit that formed as part of a delta complex. On the image section > below I have marked a boundary with a red line. This is the bottom > of a channel that cut into the layer below and later was refilled by > a later sand deposit, The smaller layers are called crossbeds and > relate to how the individual sand layers were laid down. In a dune > deposit the layers are much steeper than they are here in a river/ > delta deposit. > > <RockSculpturesa.jpg> > > If you look at individual beds you will see that the bottom of the > curved crossbeds turn and horizontally. While the top of the > individual bed curve upward and meet the layer above them at an > angle and are truncated by the overlying bed. > > Ed > > "The most beautiful thing we can experience is the mysterious. > It is the source of all true art and all science." - Albert Einstein > > > --~--~---------~--~----~------------~-------~--~----~ Eastern Native Tree Society http://www.nativetreesociety.org Send email to [email protected] Visit this group at http://groups.google.com/group/entstrees?hl=en To unsubscribe send email to [email protected] -~----------~----~----~----~------~----~------~--~---
