User:IveGoneAway/sandbox/Abilene conglomerate

The Abilene conglomerate is an informal Pleistocene unit of sand and gravel "cemented by calcarous matter". Here and there are redish sandstone and yellowish chalk cobbles. Outcrops of this mortar bed are found along tributaries of the Smoky Hill River in the vicinity of Abilene and Solomon, Kansas. Pioneering geologists, including F.B. Meek, F.V. Hayden, E. Haworth, C.S. Prosser, and R.C. Moore each reported on the unusual nature of the conglomerate. At that time, each identified or accepted that the unit formed in the Permian, like all of the shale and limestone in the surrounding hills. In particular, Meek and Hayden observed that the unusual conglomerate bed appeared to lie just at the top of the beds of rich Permian marine fossils and repetative massive limestone beds but also just at the base of similar shale that had no fossils or massive limestones (such as they could recognise then). Later geologists would determine that this change in the rock patterns marked the very last of the open marine cycles and the beginning of salt lake sequences.

Moore eventually recognized that the conglomerate was much more recent than the Permian bedrock, inferring that the conglomerate formed only after the Kansas River and Smoky Hill River finished cutting down through all of the Permian layers found in Kansas (between Saline and Riley counties, all of the Kansas Permian is exposed.

Today, this conglomerate bed is thought to be possibly related to the lower, cemented conglomerate found within the McPherson Equus Beds to the southwest.

Some geologist attempted to label the unit as Abilene limestone, in part to reflect the calcareous nature of the outcrop at Abilene, but also to explain how they thought that the conglomerate they could find only in valley side was weathered Permian Hollenberg dolomite.

Permian conjecture
From the middle of the 19th century, geologists recognised that the Kansas River valley, including its upper forks into the Smoky Hills and the High Plains, held excellent exposures of full sequences of the Pennsylvanian, Permian, Late Cretaceous, Neogene, and Quaternary systems. In early exploration of the Permian sequences, a thick bed of calcarous, cemented sand and gravel was encounted in the terraces of the tributaries of the Smoky Hill River near a new stage coach stop then named Mud Creek.

Braving Border ruffians, Bushwhackers, and Jayhawkers as well as battles between the Plains and settler Indian nations, F.B. Meek and F.V. Hayden were the first to scientifically study the valley's geology and the first to describe the conglomerate. Expecting the rock outcrops along that river to continue showing a rising Permian sequence, Meek and Hayden placed the conglomerate they found at Turkey Creek within the Permian Period in their 1859 report.

Meek and Hayden observed that the bold conglomerate outcrop looked to be a marker unit. Even though the shales above and below the conglomerate are similar in color and texture, these early geologist saw other very distinct changes. While marine fossils and limestones are abundant below the conglomerate, none are seen in the shale above the conglomerate. While the shales below the conglomerate feature thousands of feet of famous limestone cyclothems, this pattern abruptly stops at and above the conglomerate. The explorers didn't encounter marine limestone again until they reached the Greenhorn Formation over the Dakota Sandstone high up into the Smoky Hills.

In reality, Meek and Hayden's "No. 10" (the Wellington shale) records a sudden transition from the preceding open marine sequences to the following lacustrine sequences; rather than holding no fossils, the following sequences hold incredible insect fossils. (For further discussion, see Wellington Formation).

Meek and Hayden's incorrect placement of the conglomerate over the shale just above the Herington Limestone caused later geologists to name as a separate unit what in reality was the lowest beds of the Wellington Shale. One such geologist was C. S. Prosser.

In 1895, C. S. Prosser published his classification of the conglomerate, naming it for the famous cow town that had grown on the Mud Creek site. Trying to map the Abilene unit as a limestone, Prosser followed a real Permian dolomite bed that actually runs out from "behind" the Pleistocene terrace at Abilene, tracing that dolomite all the way to Herington and Marion. Prosser then defined a Permian unit he named Marion Formation, and designated the top member of that formation as the Abeline conglomerate, the "underlying" shale he named Pearl Shale and included the known Herington Limestone below that.

The dolomitic Hollenberg Limestone marker bed was then recognized within the Pearl Shale.

These beds of "Abilene" dolomite were of interest to oil drillers as useful markers for drillers playing for the lower known producing beds, but they were also of interest for potential oil production further west. Some argued that the prominent dolomite bed was the true type of the Abilene, and that unit should be reclassified as Abilene Limestone while the conglomerate near Abilene at Solomon were merely reformings of weathered dolomite.


 * {| class="wikitable" border="1"

! rowspan="2" align="center" | Age ! colspan="2" align="center" | Prosser's Classifications ! colspan="2" align="center" | Present Classifications ! Formation ! Member ! Member ! Formation
 * align="left" | Pleistocene
 * Abilene conglomerate
 * McPherson Equus Beds
 * colspan="5" |
 * rowspan="10" align="left" | Permian
 * rowspan="3"| Wellington Shale
 * rowspan="3"|
 * (upper shales)
 * rowspan="5" | Wellington Shale
 * Hutchinson Salt
 * (gypsum beds)
 * rowspan="9" align="left" | Marion limestone
 * align="left" | Abilene conglomerate
 * Hollenberg Limestone
 * Pearl shale
 * (marine shale)
 * Herington limestone
 * Herington Limestone
 * rowspan="3" | Nolans Limestone
 * rowspan="3" | Enterprise shale
 * Paddock Shale
 * Krider Limestone
 * Odell Shale
 * Luta limestone
 * Cresswell Limestone
 * Winfield Limestone
 * }
 * Herington Limestone
 * rowspan="3" | Nolans Limestone
 * rowspan="3" | Enterprise shale
 * Paddock Shale
 * Krider Limestone
 * Odell Shale
 * Luta limestone
 * Cresswell Limestone
 * Winfield Limestone
 * }
 * Luta limestone
 * Cresswell Limestone
 * Winfield Limestone
 * }
 * }
 * }

Effectively, the Marion and Pearl classifications were inventions to accommodate the mistaken interpretation of the Abilene conglomerate as Permian deposits rather than Pleistocene valley infill. Today, the Marion classification is replaced by the Nolans Limestone and the Odell Shale, and the old Pearl Shale is now recognised as the lowest beds of the Wellington Shale.

Pleistocene evidence
Several lines of evidence suggested that the conglomerate bed was later, if not much later, than the Permian Period.
 * No outcrop was found where Wellington Shale was lying in contact over the conglomerate.
 * There was no sign from well logs within the Kansas valley that the conglomerate carried on into the strata buried below the Wellington Formation, demonstrating that the deposits actually came from a partial refilling of the valley some time after the present valley was cut.
 * The inclusion of reddish pebbles and cobbles of Dakota sandstone and mudstone and yellowish Greenhorn chalks made it clear that the sand and gravel were carried from the Creteceous outcrop of the Smoky Hills to the west well after the closure of the Western Interior Seaway and the Neogene uplift of the Colorado plains.
 * The distinctive presence of larger quartz and quarzite pebbles suggests material from the weathering of the Paleogene Rocky Mountains, or later weathering of the Ogallala Formation.
 * Finally, fossils in the conglomerate are relatively recent and the conglomerate is considered similar to the conglomerate bed at the base of the McPherson Equus Beds, so named for the appearance of modern horse fossils.

Developmment
The downcutting of Permian and Pennsylvanian formations to form the Kansas and Smoky Hill river valleys largely did not develop until the deposition of the Ogallala, the lowest bed of the Ogallala only found broad, shallow valleys to fill.

calcite-rich brine

For some time after the sand and gravel were deposited, either a stable and shallow water table was maintained for a time within the Kansas River, such that a deep caliche was formed under the surface, particularly away from the river flow.