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L&C Allom Stone Clift

A cache by catsnfish Send Message to Owner Message this owner
Hidden : 06/23/2008
Difficulty:
1.5 out of 5
Terrain:
1.5 out of 5

Size: Size:   not chosen (not chosen)

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Geocache Description:

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ThisEarthcache is located in a Nebraska State Park,

Park permit required for all vehicles.


Presently the limestone exposure observed by L&C is mostly obscured by cottonwoods. The EarthCache location has been changed to give a better view of the exposure that is still visible and the cliff swallows’ nests.

New logging tasks: In an email to the EC developer answer the following questions:

Which type sediments are visible from this location? Estimate the depth of each sediment layer you see.


Locate a fossil at the foot of the cliff; describe the color and texture of both it and the surrounding rock. Do you think these fossils are from what was, at the time, an inland sea or from a river? Why?


What evidence do you find that these sediments were deposited layer by layer?


What material do you think the swallows use to build their nests? What is the most likely source for that material?

 

The Journal Entries

(Clark) August 22, 1804

Seven miles above is a Clift of Allom Stone of a Dark Brown Colr. Containing also in crusted in the Crevices & Shelves of the rock great qts. of Cabalt, Semented Shels & a red earth.

(Ordway) August 22, 1804

passed a Red ceeder Bluff on the South Side & little above on the Same Side we passed an Alum Stone clift about 50 feet high & a great nomber of birds nests, near the top of the clift.

    Long before the voyage of  the Corps of Discovery, long before the river's meanders, long before the glaciers' cold grip upon the land, this area was covered by the inland seas of the late Cretaceous Period roughly 100 to 65 million years ago. At times they were deep, cold seas, with soft, sandy or muddy bottoms creating shale or siltstones, at other times, the seas were shallow, and warm, teeming with so much life that it's bottoms were layered in skeletal remains rich in calcium, giving us limestone. Ever changing, always depositing sediments and building layers unique to the climactic conditions and living organisms present.

    The passage of great amounts of time, compaction and pressure, hardened these layers into rock, leaving a record of the conditions and animal life present at those times. When these seas receded,  deposits of sand, and windblown silts from later climatic conditions covered the layers of limestone and shale. Shifts in the earth's crust raised some areas and lowered others while winds and waters eroded earlier deposits to finally expose, in places, the rocks, formations and fossils from those long ago sea beds.

      Discovered by men who sought to explore and understand the new territory, these outcroppings are now studied by those who seek to understand our Earth and the processes of its formation.

 

            Stratigraphy of the Principal Rock Exposure at Ponca State Park:      Stratigraphy is the study of the layers of rock ,what they are made of and their relation to other rock. The strata is identified by system which represents a time period and by groups of rock in sequence with some common characteristics. The groups are made up of formations (greenhorn/graneros) of similar type rock such as sandstones or limestones. Units within formations are layers with  noticeable differences in color, texture or grain structure in the same basic  type of rock. For example a siltstone, which was originally a mud deposit could have a fine grain structure and  may break up into thin sheets.  Each unit is a record of some change in the environment that affected the deposits,the clay units in the Graneros shale formation suggest that volcanic ash was deposited in this area at 3 separate times. 

 Starting from the top of the cliff (latest layers) and working down to the base (oldest layers.)

Quaternary System: 1.8 million years ago to present

Ø       Peoria Loess  windblown deposits of  rock that has been finely ground by glacial action

Upper Cretaceous System: 100-65 million years ago

Colorado Group

Ø       Greenhorn Limestone consisting of 8 units of varying density, color and grain. Fossils are mostly clam-like bivalves.

Ø       Graneros Shale consisting of 1 unit of limestone, 6 units of siltstones, 3 units bentonitic clay (a chemical alteration of volcanic ash.) Fossils are sparse, mostly fish scales or bivalves.

Dakota Group  Not exposed at this site, there are Dakota Group exposures further downstream, along the river trail.

Ø       Omadi Sandstone mostly dark orange brown and medium grained, no fossils found in this group within the park area.

Logging Requirements:

Which type sediments are visible from this location? Estimate the depth of each sediment layer you see.


Locate a fossil at the foot of the cliff; describe the color and texture of both it and the surrounding rock. Do you think these fossils are from what was, at the time, an inland sea or from a river? Why?


What evidence do you find that these sediments were deposited layer by layer?


What material do you think the swallows use to build their nests? What is the most likely source for that material?

 You will not need to wait for a response to log the cache online, however, logs not meeting all of the requirements within a reasonable time frame will be deleted.

This Earthcache was developed by a Platinum Earthcache Master 

For more information regarding the Earthcache Masters Program click on the Earthcache logo. Photobucket

 

References:

University of Nebraska Press / University of Nebraska-Lincoln Libraries-Electronic Text Center.

The Journals of the Lewis and Clark Expedition. http://lewisandclarkjournals.unl.edu/

 Geological Society of America Centennial Field Guide-North-Central Section, 1987

Late Cretaceous strata exposed at Ponca State Park, Dixon County, Nebraska

Roger K. Pabian and Dennis R. Lawton, Conservation and Survey Division, IANR, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0517

Lewis and Clark and the Geology of Nebraska and Parts of Adjacent States

R. F. Diffendal Jr. and Anne P. Diffendal, Educational Circular No.18 Dec. 2003. Conservation and Survey Division/School of Natural Resources Institute of Agriculture and Natural Resources/College of Arts and Sciences, University of Nebraska-Lincoln

 

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