A spectacular disconformity occurs along both sides of Rt. 61, south of Burkesville, south-central Cumberland County, southern Kentucky, USA.  The roadcut is a little south of a Rt. 61 bridge over the Cumberland River, ~9 miles north of the Kentucky-Tennessee border.


Looking ~SE.


The light gray unit in the lower part of the cut is the Cumberland Formation (Upper Ordovician).  It is overlain by brownish-weathering Chattanooga Shale (Upper Devonian).


The Cumberland Fm. here is a silty dolostone.  The sedimentary structures and fossils present in the Cumberland include mudcracks, horizontal trace fossils, ostracods, small-scale cross laminations, scarce isolated ripples, small scours, rip-up clasts.  These features indicate deposition in marginal marine to intertidal zone facies.


The overlying Chattanooga Sh. here is a black shale unit (equivalent to the Ohio Shale & New Albany Shale - both also Upper Devonian).  It has a fair amount of disseminated microcrystalline pyrite.  With oxidative weathering, the pyrite alters to iron oxides and hydroxy-oxides, which stain the shales brownish to yellowish-brown to whitish.  Bedding planes with compressed, carbonized Foerstia fossil algae (aka Protosalvinia) are not uncommon in the Chattanooga here.


The Cumberland-Chattanooga contact is a bleeding unconformity.  Notice the white streaks & the rusty orange streak on the Cumberland dolostones.  These are the result of staining by downward-seeping rainwater carrying iron oxides and iron hydroxy-oxides.


Note the ages of rocks above & below the unconformity (disconformity).  The entire Silurian is gone, as is the entire Lower and Middle Devonian.  Close to 70 million years of Earth history are unrepresented in this section!





Fossiliferous limestones of the Ft. Payne Formation (Lower Mississippian) are well exposed along a Rt. 61 roadcut south of Burkesville, a little south of the Cumberland River, and about 8 miles north of the Kentucky-Tennessee border, Cumberland County, southern Kentucky, USA.


This is a great place for seeing lateral facies change.  Note the folded rocks in the center of the photo shown below.  It looks like an anticline.  But note that the overyling rocks at the top of the cut are horizontal.  This ain't an anticline.  The structure at bottom-center is a mud mound.  The limestone beds above have draped over the mound, and the flank beds are thicker - this mound is an original, primary feature.


Ft. Payne Formation.  Looking ~NE.


The Ft. Payne Formation is about 270' thick in this section.  Mounds and buildups are relatively common in the Ft. Payne Formation of southern Kentucky.  They are best examined along the shores of nearby Lake Cumberland.  The Ft. Payne is mostly early to middle Osagean in age (late Early Mississippian), but the basal parts of the unit may be Kinderhookian in age (early Early Mississippian).


Crinoids are the most abundant fossils in the Ft. Payne Formation.  Decent crinoid heads can be found relatively easily throughout the Ft. Payne in southern Kentucky.  I found crinoid head material & blastoid head material during visits to this roadcut.



Ft. Payne Formation - articulated camerate crinoid fossils in fossiliferous limestones exposed along the shores of Lake Cumberland, southern Kentucky, USA.



Home page