Rocks in Gabe's head, tassels on his feet....
Spungman,
How prevalent is ironstone in the Cohansey formation? I used to work at the golf course in Waretown (I know, 'tis a shame) where ironstone is virtually everywhere exposed. Was this ironstone formed via bacteria just as it is today in the Pine Barrens?
Good questions, Gabe,
As stated in an earlier Pinelands stone thread (
link below), my discipline concerns only the last couple hundred thousand-years of Pinelands geologic history (
i.e., Late Pleistocene). Still, I’ll try to simplify earlier events, as I understand them. Many people associate the Cohansey Formation with riverine sand from marine, marine marginal, estuarine, deltaic, and fluvial deposits of Miocene age (~23 to 5 million-years ago). But that’s only part of the story.
Throughout the Miocene Epoch sea level fluctuated, especially towards the Middle-to-Late Miocene when oceans progressively lowered as the Earth cooled. Ironstone would have formed during ground exposing lowstands, particularly at water table around swamps and river-bottoms. Ironstone continued to form by during ensuing warm periods, including interglacial intervals. The process continues today. Yes, the bacteria responsible for much of the ironstone formation have been precipitating iron oxide for a very, very long time.
The material that caps northern (
i.e., above the Mullica River) Pine Barrens mounts was derived from the Beacon Hill facies of the Cohansey Formation, and is not a separate geologic entity as earlier supposed. Facies is a somewhat difficult interpretive concept, but basically means that different sedimentary environments can exist at the same time and that the same sedimentary environment can exist at different times. Since sea level was dropping, the ancient river(s) that brought Pine Barrens sediments was no longer near its lower and slower journey’s end where sands and clays deposit. Instead this watercourse was higher upstream so flowed with sufficient power to carry gravels and cobbles. Salients below the Mullica River are composed of younger (
i.e., Late Miocene) Bridgeton Formation gravels and cobbles deposited over-top older Cohansey Formation sediments.
Gabe, you didn't have to wear those funny shoes at the club...
did you?
(
also see earlier thread ? About differences in NJ Stones –
http://forums.njpinebarrens.com/showthread.php?t=6414)