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Dartmouth University: Where the Appalachian Mountains Run
into the Atlantic Ocean
After receiving a BS in Geology at Beloit College, I moved to Dartmouth University,
New Hampshire to undertake a Master’s degree. Dartmouth is located on the
Connecticut River that is incised into the Appalachian Mountains of New Hampshire
and Vermont. Along the ragged and rocky coast of Maine, these ancient Paleozoic
rocks meet the modern Atlantic Ocean. On many field projects we learned how the
formation of the Atlantic Ocean, which began to open about 200 million years ago
(during the Triassic Period) and continues to widen today, tore apart the old supercontinent of Pangaea. The initial rupture ripped the northern portion of the
Appalachian Mountains from Maine, Nova Scotia, and Newfoundland and sent
them on a ~ 3000-mile (~5000 km) journey to what is now western Europe where
they constitute Northern Ireland, Scotland, and northern Scandinavia. The
200- million-year history of opening of our modern Atlantic Ocean, which continues
today, also witnessed development of a major new province on the Atlantic margin
of eastern USA known as the Coastal Plain (subaerial) and Continental Margin
(submarine). This province consists of a massive, seaward thickening wedge of
coastal and marine sediments plastered onto the ancient crystalline rocks of the
Piedmont and Appalachian Provinces.
University of Montana: The Shores of an Interior Seaway
It seemed to me that if a new ocean and landmass could form along the east flank of
the Appalachian Mountains, why shouldn’t there be a similar ocean and deposit of
coastal and marine sediments along the east flank of the Rocky Mountains? Thus, to
study ancient coastal and marine deposits for a PhD degree, I took the seemingly
counter-intuitive step of moving inland to Missoula, Montana! Yes, the ancient
shoreline of another one of the world’s great, former oceans did exist along the
eastern flank of the present Rocky Mountains, but this ocean was much shallower
than the Atlantic and Pacific because it was floored by continental crustal rocks
rather than oceanic crustal rocks. This ocean, known as the Western Interior Seaway,
existed from about 145–65 million years ago (during the Cretaceous Period) when
dinosaurs roamed the Earth. The seaway stretched from the Rockies east to the
Appalachians and northwards from what is now the Gulf of Mexico to the Arctic
Ocean. According to many previous geological studies, Cretaceous-age coastal
marine sediments flanked the eastern side of the main core of the Rocky Mountains.
Consequently, the Rocky Mountains became our classroom with many geology
field trips and laboratory projects to study these ancient deposits. As students we
were taught to question everything. Thus, to investigate the coastal-marine interpretation, we took field trips to modern coastal systems along the US Pacific, Gulf, and
Atlantic coasts. There we observed modern deposits that were identical to those
S. R. Riggs
Dartmouth University: Where the Appalachian Mountains Run
into the Atlantic Ocean
After receiving a BS in Geology at Beloit College, I moved to Dartmouth University,
New Hampshire to undertake a Master’s degree. Dartmouth is located on the
Connecticut River that is incised into the Appalachian Mountains of New Hampshire
and Vermont. Along the ragged and rocky coast of Maine, these ancient Paleozoic
rocks meet the modern Atlantic Ocean. On many field projects we learned how the
formation of the Atlantic Ocean, which began to open about 200 million years ago
(during the Triassic Period) and continues to widen today, tore apart the old supercontinent of Pangaea. The initial rupture ripped the northern portion of the
Appalachian Mountains from Maine, Nova Scotia, and Newfoundland and sent
them on a ~ 3000-mile (~5000 km) journey to what is now western Europe where
they constitute Northern Ireland, Scotland, and northern Scandinavia. The
200- million-year history of opening of our modern Atlantic Ocean, which continues
today, also witnessed development of a major new province on the Atlantic margin
of eastern USA known as the Coastal Plain (subaerial) and Continental Margin
(submarine). This province consists of a massive, seaward thickening wedge of
coastal and marine sediments plastered onto the ancient crystalline rocks of the
Piedmont and Appalachian Provinces.
University of Montana: The Shores of an Interior Seaway
It seemed to me that if a new ocean and landmass could form along the east flank of
the Appalachian Mountains, why shouldn’t there be a similar ocean and deposit of
coastal and marine sediments along the east flank of the Rocky Mountains? Thus, to
study ancient coastal and marine deposits for a PhD degree, I took the seemingly
counter-intuitive step of moving inland to Missoula, Montana! Yes, the ancient
shoreline of another one of the world’s great, former oceans did exist along the
eastern flank of the present Rocky Mountains, but this ocean was much shallower
than the Atlantic and Pacific because it was floored by continental crustal rocks
rather than oceanic crustal rocks. This ocean, known as the Western Interior Seaway,
existed from about 145–65 million years ago (during the Cretaceous Period) when
dinosaurs roamed the Earth. The seaway stretched from the Rockies east to the
Appalachians and northwards from what is now the Gulf of Mexico to the Arctic
Ocean. According to many previous geological studies, Cretaceous-age coastal
marine sediments flanked the eastern side of the main core of the Rocky Mountains.
Consequently, the Rocky Mountains became our classroom with many geology
field trips and laboratory projects to study these ancient deposits. As students we
were taught to question everything. Thus, to investigate the coastal-marine interpretation, we took field trips to modern coastal systems along the US Pacific, Gulf, and
Atlantic coasts. There we observed modern deposits that were identical to those
S. R. Riggs