WHEATLAND - NEW MEXICO, USA
AUG 28TH 2020
THIS LOCATION IS ON PRIVATE PROPERTY AND IS INACCESSIBLE TO THE PUBLIC
Apache Creek is located close to the edge of the Great Plains in the Pecos Valley Section, the Ogallala Formation on the eastern side of the Pecos Valley have not been eroded out and form a sharp escarpment and rimrock on the high plains in the Pecos Valleys eastern boundary. Rivers, specifically the Pecos and Canadian have cut through the Ogallala Formation west of the Sangre de Cristo Mountains up to the Rio Grande. This has resulted in the loss of piedmost cover and has cut deep into the lower rocks forming a broad valley between the two rivers.
Below the Redonda Formation is the Bull Canyon Formation, it is 110 meters thick. The Bull Canyon Formations mudstone is greyish-red, to moderate reddish-brown in colour, it also contains laminar yellowish-grey to greyish-red trough-crossbedded sandstone. The formation is agreed upon to be fluvial in origin and is either unconformable or conformable to the above Redonda Formation depending on location.
The Redonda Formation in east-central New Mexico is the youngest in the Chinle Group, the formation is around 15 to 140 meters in thickness. Its a mix of siltstone, sandstone, variegated shale, and argillaceous limestone. The Redonda Formation is characterized by fine interbedded sandstones and mudstones, above the Redonda is mostly unconformably overlain by younger Jurassic rocks.
The Redonda Formation was most likely deposited within a lacustrine system of small and moderate-sized lakes possibly up to a few kilometres in diameter, the environments surrounding the lakes were most likely forests and small river systems. Layers of organized and localized conglomerates were possibly deposited by debris flows or subaerial alluvial fans, mudstone interbeds are also present in a poorly sorted mud-rich matrix. Debris flows concentrate coarse clastic material in the middle of the beds, this is because the sediment responds to shear stress along the lower and upper flow surfaces.
In some places, very fine thin layers of mudstone represent flood plains and thicker courser layers of small pebbles forming conglomerate represent a river environment. The flood plain environment takes a much longer time to accumulate, this preserves fossils better than the fast-flowing rivers of the time period. Massive sandstone occurs laterally with very fine to medium-grained to moderately sorted sand, the layers are 0.4 to 13 meters thick occurring in single bed units, grain size does vary by location. In the dry wash within the private property fine-grained, well-sorted and calcite-cemented grains contain preserved climbing ripple patterns.
Mudstone visible within the Redonda Formation is red and green in colour, some of the outcrops visible in this location are eroding mudstone while some visible green mudstone has been deposited in-between sandstone layers. The red is formed from oxidising pore water which produces iron 3+ which forms hematite, the green comes from reducing pore water which produces iron 2+ that gives the layer green colours.
Areas within Apache Creek are comprised of different rock types and formations, because of this, the erosion rate is different In areas where the sandstone above and below is a less resilient rock type.
Within the dry wash in the Redonda Formation, a layer of sandstone is visible where the upper and lower mudstone layers have been eroded out, the area then drops down a few feet below the sandstone layer. In areas where the below Redonda Formation and above Entrada Sandstone convene, the sandstone erosion style is very different from the mudstone below.
The wood at Apache Creek most likely fell into an oxbow lake where oxygen was low, this lake was most likely stagnant with no fresh water coming in to replenish the oxygen supply. The condition the lake was able to sustain meant it was very good for the preservation and carbonization of organic materials, this is why carbonized wood is so common in this location. New seasonal river flows have cut into the old lake deposits, this has made the remains of the forest now visible in the long since abandoned stagnant lake deposits.
When petrified wood starts to crystallize silica forms into small spheres one miro meter in diameter, the woods cellulose acts as a outline for crystallization. Silica replaces wood at the same rate that marine sediments are replaced to form opal. The wood in Apache Creek is mostly brown in colour, the colour comes from organic matter and not metals like most other colours visible in petrified wood like in Bisti/De-Na-Zin on the other side of the state.
Fossils found at Apache Creek:
Aetosaur (Revueltosaurus) & Phytosaur (Redondasaurus bermani)
The dig sites located in this private property are famous for abundant east-central New Mexico Phytosaur and Aetosaur fossils in extremely good condition.
The Phytosaur is a crocodile-like Triassic age (230-200 million years old) this specific type of phytosaur was located in the southwest United States mostly in the Redonda Formation, the species was named by Hunt & Lucas in 1993. The Redondasaurus Bermani is one of the more evolutionary advanced species in the genus.
The location also contains Aetosaur fossils, the Aetosaur was heavily armoured, it existed in the southwest United States during the Late Triassic and in the late Carnian to middle Norian stage.
The Phytosuar vertebrate located within course pebbles is visible in a point bar which was deposited by river flows. This one specimen is rather special as its extremely rare to find fossils of that quality in a long since abandoned fast-flowing river environment.
Spencer G. Lucas, Andrew B. Heckert and Adrian P. Hunt, New Mexico Museum of Natural History department of Earth and Planetary Sciences, University of New Mexico, Mesalands Dinosaur Museum, TRIASSIC STRATIGRAPHY, BIOSTRATIGRAPHY AND CORRELATION IN EAST-CENTRAL NEW MEXICO New Mexico Geological Society Guidebook, 52nd Field Conference, Geology of the Llano Estacado, 2001
George E. Mustoe, Mineralogy of Non-Silicified Fossil Wood, Geology Department, Western Washington University, Bellingham, WA, Received: 21 December 2017; Accepted: 27 February 2018; Published: 3 March 2018
Patricia C, & Hester and Spencer G. Lucas. (2001). Lacustrine depositional environments of the Upper Triassic Redonda Formation, east-central New Mexico. New Mexico Geological Society.
Mesalands Community College. (2020). Dinosaur Museum and Natural Science Laboratory. 2019 paleontology trip specific to 'Apache Creek'.
Trimble, D. E. (1980). The geologic story of the Great Plains. United States geological Survey Publications (pp. 45–46). United States geological Survey.
Mindat.org. (n.d.). Redondasaurus bermani.
Mindat.org. (n.d.). Revueltosaurus.
Andrew B. Heckert, Spencer G. Lucas, and Robert M. Sullivan, TRIASSIC DINOSAURS IN NEW MEXICO, Lucas, S.G., and Heckert, A.B., eds., 2000. Dinosaurs of New Mexico. New Mexico Museum of Naturnl History and Science Bulletin No. 17.
C. L. Stein. (1982). Silica recrystallization in petrified wood. Journal of Sedimentary Research. 52 (4): 1277–1282.
Mustoe, G., & Acosta, M. (2016). Origin of Petrified Wood Color. Geosciences, 6(2), 25.