Colgate University hosted this year's meeting of the New York State Geological Association held in Lake George, New York. The event was a co-meeting with the Friends of the Grenville. As usual, the field trips were outstanding. Bruce Selleck from Colgate led Sunday's field trip looking at the Potsdam Formation (Potsdam Sandstone) in the eastern Adirondacks around Lake George and Lake Champlain. The Potsdam (520 Ma) constitutes the basal Cambrian unit overlying Proterozoic gneisses of Ottawan age (1070 Ma) or earlier. The unconformity between the two represents 550 million years of missing geologic record.
Bruce Selleck explaining the outcrop at Stop 1 of the field trip, just north of Lake George village. William Kelly (New York State Geologist) is on the right.
Glacial striae on top of the outcrop at Stop 1.
Bruce pointing out a remarkable example of a dolomitization front in Grenville marble just below the contact with the Potsdam. Mg-rich hydrothermal fluids flowing along and either side of the contact altered the (white) calcitic marble to (dark) dolomite. The fluid pathway in the form of a fracture is visible cutting vertically through the dolomite. This is at Stop 2 along Route 22 north of Whitehall, NY.
Geologists loving life at Stop 3. Bruce Selleck is in the center distance (just to the right of the yellow hard hat). Alan Benimoff (College of Staten Island and NYSGA Executive Secretary) is wearing the yellow hard hat. Dave Franzi (SUNY-Plattsburgh) is on the far left next to the outcrop.
Reddish ferroan dolomite in Potsdam sandstone at Stop 3.
Students looking at typical marine-facies Potsdam (Selleck's 'lower stratified unit') at Stop 3.
The 'Great Unconformity'. Massive Potsdam sandstone overlying vertically banded Proterozoic gneiss. A conglomeritic lens is visible in a trough at the base of the Potsdam. Stop 5.
Ripple marks in Potsdam sandstone used as building stone. A lot of interesting rocks, like this one, were used to build the hydroelectric plant on the Lachute River in Ticonderoga, NY. Stop 6. The Lachute River drains Lake George into Lake Champlain.
Nice fall colors...
Bruce Selleck explaining the outcrop at Stop 1 of the field trip, just north of Lake George village. William Kelly (New York State Geologist) is on the right.
Glacial striae on top of the outcrop at Stop 1.
Bruce pointing out a remarkable example of a dolomitization front in Grenville marble just below the contact with the Potsdam. Mg-rich hydrothermal fluids flowing along and either side of the contact altered the (white) calcitic marble to (dark) dolomite. The fluid pathway in the form of a fracture is visible cutting vertically through the dolomite. This is at Stop 2 along Route 22 north of Whitehall, NY.
Geologists loving life at Stop 3. Bruce Selleck is in the center distance (just to the right of the yellow hard hat). Alan Benimoff (College of Staten Island and NYSGA Executive Secretary) is wearing the yellow hard hat. Dave Franzi (SUNY-Plattsburgh) is on the far left next to the outcrop.
Reddish ferroan dolomite in Potsdam sandstone at Stop 3.
Students looking at typical marine-facies Potsdam (Selleck's 'lower stratified unit') at Stop 3.
The 'Great Unconformity'. Massive Potsdam sandstone overlying vertically banded Proterozoic gneiss. A conglomeritic lens is visible in a trough at the base of the Potsdam. Stop 5.
Ripple marks in Potsdam sandstone used as building stone. A lot of interesting rocks, like this one, were used to build the hydroelectric plant on the Lachute River in Ticonderoga, NY. Stop 6. The Lachute River drains Lake George into Lake Champlain.
Nice fall colors...
