The 366 daily episodes in 2014 were chronological snapshots of earth history, beginning with the Precambrian in January and on to the Cenozoic in December. You can find them all in the index in the right sidebar. In 2015, the daily episodes for each month were assembled into monthly packages (link in index at right), and a few new episodes were posted from 2015-18. Beginning in May 2019, I'm adding short entries to the blog (not as podcast episodes, at least not for now, sorry!) mostly taken from the Facebook Page posts. Thanks for your interest!

Monday, May 12, 2014

May 12. Catskill delta

Toward the end of the Ordovician, last March, we talked about the beginning of tectonic collisions in what is now eastern North America – the Taconic Orogeny. The rivers that eroded those mountains shed a vast pile of sediment into what is now Pennsylvania, West Virginia, and Ohio and beyond, creating the Queenston Delta. As collisions continued, mountainous terrains continued to be uplifted and erosion continued. In Middle to Late Devonian time, ongoing collision between parts of the Avalonian extension of Europe with northeastern North America created more uplifts. This is sometimes called the Acadian Orogeny, which we mentioned last month during the Silurian. It pretty much reached its peak during the Devonian. 

The upland was located in southeastern Pennsylvania and northern New Jersey and points further north and south. The sediment that was eroded off the mountains was dumped in especially thick piles in central Pennsylvania and southern New York. River floodplains and deltas lay along a shallow sea. The whole complex is called the Catskill Delta, because the sediments are now exposed as rocks in the present-day Catskill Mountains, as well as the Pocono Mountains of Pennsylvania.

This was a long-lived environment, spanning probably 20 million years about 380 to 360 million years ago. The rocks are similar to those of the Ordovician Queenston Delta – red beds indicating oxidation of iron, river sandstones, flood plain shales, and ephemeral lake deposits. There’s 3,000 feet and more of these rocks. They were deposited on top of the older Marcellus Shale that we talked about yesterday, so that means there was a pretty noteworthy change in the environment, from the oxygen-poor sea waters of the Marcellus to the above-sea-level terrestrial environment of the Catskill Delta.

Catskill delta rocks are to the east (right). Cross-section from USGS.

Because the sea level was fluctuating, there are also some layers of marine rocks interbedded with the deltaic sediments, just as you would find in the Mississippi Delta today.

The sandstones that formed from the distant limits of the Catskill Delta serve as oil reservoirs in western Pennsylvania – the first oil deposits that were exploited in the United States beginning in the 1850s but really taking off in the 1870s.

 Because they are Devonian in age, and many of the rocks are red with oxidized iron, American geologists in the 19th century initially thought the rocks of the Catskill Delta were part of the Old Red Sandstone of Europe. But they’re not, really. The Catskill sediments were eroded off a rising mountain uplift, and deposited in a coastal flood plain. The Old Red Sandstone was deposited within intermontane basins, pretty much entirely terrestrial in origin, except in a few places.

* * *

Maurice Ewing was born today, May 12, 1906, in Lockney, Texas. He was a pioneer in the field of oceanography, especially the use of seismic studies to understand the nature of the ocean basins. Much of his work was fundamental knowledge that led to the comprehensive theory of plate tectonics.

—Richard I. Gibson

Catskills Geology 
Appalachian maps and cross sections
Cross-section from USGS


  1. Richard, I am in a huge scramble trying to prevent a parking lot to be built over the Cheltenham Badlands - a beautiful vivible example of the Queenston shale. Do you have a thumb nail lesson to present to Regional Council of Peel (in Ontario) to relay the importance to preserve this as a biosphere site that should not be trampled on by countless visitors who come now - even before a parking lot is built??? There is no plan to build barriers to prevent foot traffic on the hills and we have watched them erode for the past 14 years.
    Lady Peach

    1. I really doubt if I can add anything about the significance of the biosphere - especially the present-day one.... sorry, I'm no expert on this... but I wish you all the best.