They are pretty well insulated in the terms of structural geology. I guess technically they represent to top crust of an already deeply buried basin. I would have to dig out some books on LA geology (Lower Alabama) but see the PDF link below. The weight of water and bulk weight of the accumulation of sediments do not lithify for several hundreds of meters in depth, but all weight from above amplifies pressures below. Be it remembered that the top of this batholith is still very close to the surface and maybe 150+ miles of crust and mantle lie between it and the Fallon Slab remnant. I don't know how deep the syncline--it it exists cold run but a total of 20,000-to 40,000 ft of crust was displaced by some segments of the Appalachian Orogeny. It was eroding as it was building but we know from mineralogy of rocks exposed in eroded valleys and from Anthracite that the burial depth had to be 8 miles at least. These were a single "basin terrane" that varied along the length of the chain representing the erosions of first Appalachian Orogeny that were carried westward by the watershed. The over burden of erosion pushed down on them for 200my and were then uplifted by the second episode of collision with the African.
All these Cretaceous and Tertiary/Neogene --semi to non-lithified sediments, dip gently to the west south west and follow a succession of environments which came about as the waters of the great inland waterway withdrew to what is now the Gulf of Mexico. Each occurrence at the surface represents an eroded surface in cross section of the migration of deposition environments as the coast migrated. You will find chalks, sands and marls but no limestones other than coquina which are in reality shell accumulations and not lime deposition. I haven't located a full illustrated stratographic column for the succession of formations that include the Ripley and Eutaw and can't remember at what depth lithified rock formations start to appear.
The Eutaw formation along with about 7-10 others (including your beloved Ripley formation), represent a huge delta of deposition off shore of the dry land erosion to the Northeast. The batholith whose name escapes me, is exposed as Stone Mountain near Atlanta. Take the height of Stone Mountain and triple it to get an idea of just how much erosion was dumped into the Cretaceous waterway off shore of what today is known as the Fall Line of Alabama and Georgia. When you look at a handful of the Ripley Marl you will note tiny mica flakes. This is one of three erosional products and owing to its flexibility and resistance to weathering, survived well in the offshore environment. The other products of granite weathering were quartz which supplied the sands of the region and coast, plus clay derived from felspar. Organic clay is bulk of the Ripley and Eutaw Fms. There is a lot of organic content and calcium carbonate derived from the sea shells that flourished in the marl. Marl is so rich in nutrients especially phosphorous that they were mined for fertilizer in early America and that is where the first dinosaur skeleton was found in a marl pit in Haddley NJ.
IN this PDF are a few illustrations of the geology of Alabama. Not the abrupt disappearance of both the Appalachian and Valley and Ridge Provinces as well as numerous fault lines mapped just short of Eutaw.
From: "Lin Kerns linkerns@gmail.com [geology2]" <geology2@yahoogroups.com>
To: Geology2 <geology2@yahoogroups.com>
Sent: Friday, November 21, 2014 6:03 PM
Subject: Re: [Geology2] Small earthquake rattles west Alabama
Eman,
Another question, if you don't mind...
Since the Eutaw formation is smack down in the middle of the Mississippi Embayment, how would the latter coincide or affect the supposed syncline heading Mexico's way?
Lin
On Fri, Nov 21, 2014 at 4:09 PM, MEM mstreman53@yahoo.com [geology2] <geology2@yahoogroups.com> wrote:
Eutaw, for which the Cretaceous marl formation is named, lies just off on the extended axis of the Appalachian Mountains where buried basins would be. Some researchers believe the Appalachians took a "downwarp" and is an enigma how or why congenital crust would do so. Some researchers using earthquake histories say they have tracked the orogeny all the way into Mexico as a syncline( downwarp).There is a pre-Cambrian formation of granite and gniess( 1.3 billion ybp) which takes a deep down slope to the west from where it surfaces along the Alabama/Georgia border around Columbus/ Phenix City. It is hard to envision the interplay, as most geological research was directed at surface and mid depth oil and gas deposits. Only recently was it announced that a huge batholith of igneous rock under Pennsylvania accounts for the kink in the Appalachians there in the edge of New England.While this doesn't say much about the origin of the Eutaw quake, it is food for thought. BTW many quakes at this depth are attributed to cavern collapse in limestone formations.Eman
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Posted by: MEM <mstreman53@yahoo.com>
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