NEW MEXICO U.S.A
The study area is located within the west-central San Juan Basin, the rocks within the basin contain mostly sedimentary rocks which were deposited during the Cambrian and the Holocene age, the basin is around 14,000 feet thick. The Cretaceous aged formations contain the most abundant coal, oil and natural gas which are also present in the area but are located deeper below the surface.
The rocks in Bisti/De-Na-Zin were formed from the retreat of the Western Interior Seaway. The Lewis Shale and Pictured Cliffs Sandstone layers are not visible in the study area but lie below the Fruitland Formation and represent the Western Interior Seaway during its last succession.
The other rock formations were formed by the retreat of the inland sea, it did advance and regress on occasion which is why the area has many layers of shale and coal. The younger layers lack of marine sediment is visible through more Sandstone layers and less shale.
The top layer in Bisti/De-Na-Zin is the Ojo Sandstone which represents the 4th and final regression of the Inland Seaway where the lower shale changes to Sandstone.
The sedimentary Bisti/De-Na-Zin badlands are located in what was once a part of the Western Interior Seaway. The last advancement of the inland sea includes the pictured cliffs Sandstone (once an ancient shoreline) and the Lewis Shale which are not visible in the area as they are older layers and remain buried. The Fruitland Formation was the final regression of the Marine Environment as the inland sea retreated further.
The oldest layer visible in the Bisti/De-Na-Zin region is the Fruitland Formation which was deposited in the Late Cretaceous period (100 to 66 million years ago). The formation is comprised of coal, shale, claystone and siltstone, the formation lacks sandstone which is only visible on rare occasions.
The Fruitland Formation was most likely formed by open standing water like lakes or ponds. The colours in the Formation are represented by the environment it was deposited by, the rare occurrence of sandstone indicates old stream channels and swamp-like environments are represented by lignite coal and shale.
The contact between the Fruitland and the above Kirtland Formation is gradational and is 0 to 152 meters (0 to 500 feet) in thickness.
The Fruitland Formation is comprised of 2 Members:
. Ne-Nah-Ne-Zad Member
The member is 51 meters (167 feet) in thickness and it contains carbonized plant debris. The coal beds are brown to black in colour and are hard and brittle, they are lignitic to bituminous. Tonsein layers and very fine to fine-grained yellowish-grey crossbedded sandstone are also present and laterally grade into sandy mudstones.
. Fossil Forest Member (Not Visible In this Area)
The Fossil Forest Member is reserved for the Fossil Forest Research Natural Area, it lacks any economic coal beds and contains a much higher percentage of sandstone and non-carbonaceous mudrocks. Mudstone and silty mudstone is grey yellow and greenish in colour along with the crossbeded sandstone.
The layer above the Fruitland Formation is called the Kirtland Formation it represents the receding Western Interior Seaway. The formation is comprised of shale and bands of Brown-capped sandstone which are apart of the Bisti Bed Member, the formation is void of any coal beds.
Controversy over the names like the Hunter Wash Member and the De-Na-Zin member of the Kirtland Formation still continue to be an issue, this is because of the North American Stratigraphic Code. The code states that a new unit must serve a clear purpose and that names should not be modified without explaining the need. Because of issues with the name and the Ojo Alamo Sandstone above the Naashoibito Member is considered to be apart of the Kirtland Formation and is no longer apart of the Ojo Alamo Sandstone.
The Kirtland Formation is comprised of 7 Members:
. lower shale member
The Lower Shale Member contains shale, claystone and siltstone, the only difference between the Fruitland Formation and the Lower Shale Member is the lack of coal as they have almost identical lithologies.
. Farmington Sandstone Member
The Farmington Sandstone Member is comprised of closely spaced discontinuous channel-sandstone beds. The lower bed of sandstone is at different stratigraphic levels at different locations, the differences are at most tens of meters and shift either up or down.
. Upper Shale Member
. Hunter Wash Member
Contains Ash in the lower section of the member.
. Bisti Bed (Inside the Hunter Wash Member)
The Bisti Bed is comprised of light brownish-grey sandstone, and very fine-grained trough crossbedded (curved lower surfaces represents past sand movement) hematitic litharenite where sandstone contains more rock fragments then feldspar grains and 25% detrital rock.
. De-Na-Zin Member
. Naashoibito Member
The Naashoibito Member contains the lower medial shale unit, conglomerate, and soft white sandstone above. The conglomeratic sandstone is only 2-4 feet thick while the overlying soft sandstone and shale unit is 22 feet thick. The member was deposited within a varied and widespread fluvial deposition environment. The difference in erosional channels at the top of the shale unit and the soft sandstone unit sharply separates it from the upper Ojo Alamo Sandstone.
OJO ALAMO SANDSTONE
The Ojo Alamo Sandstone was deposited in the Paleocene Age. A Discomformity overlies the Kirtland Shale, in some locations in the north of the San Juan Basin, where the Kirtland Shale was entirely eroded prior to the deposition of the Ojo Alamo Sandstone.
The Geologic Unit represents overlapping stream-channel systems
but also contains flood-plain deposits. The sandstone was deposited in sheetlike sequences with a mix of conglomerate and interbedded sequences of shale. The Sandstone is Arkosic and is light brown to a rust-like colour, medium to coarse grain size and the abundance of pebbles decrease from east to west.
Visible at the top of the Ojo Alamo Formation in some places is a darker variant of sandstone, this is still considered apart of the Ojo Alamo Sandstone but is a harder iron-cemented cap-rock. The cap-rock has been protecting the weaker sandstone below from weathering and erosion in the windswept environment of the badlands.
The name Ojo Alamo Sandstone is restricted only for the Conglomerate and Sandstone layers, while the Ojo Alamo Formation was everything below. In 1973 Powell divided the Ojo Alamo into a lower member named the Naashoibito Member. That member was then defined as a part of the Kirtland Shale. Some still do refer to the Naashoibito Member as a part of the Ojo Alamo Sandstone although in 2006 there was a decision to abandon the name within the Ojo Alamo Sandstone.
Coal visible in the Bisti/De-Na-Zin is located in several formations, the Fruitland Formation and the Kirtland formation.
The coal in the area is formed from a wetland or swamp type of environment when the Western Interior Seaway was receding during the late cretaceous period from 70-75 million years ago.
In some areas, red layers are visible in the badlands, they are called "clinkers" which are formed from underground Coal Fires. When the coal beds caught fire, it created a reaction that oxidised the coal seams; Iron Oxide also alters the colour from the surrounding shale and siltstone.
The Ojo Alamo Sandstone contains the majority of the petrified wood, most is mineralized with silica. The cellular features are mostly preserved in detail but the colour of the original wood is lost completely.
Colour is formed from trace metals, chemicals, and physical factors which can affect the hue and form complex patterns within mineralized wood. The dark red colours visible in Bisti/De-Na-Zin were formed from high iron levels, the white colours are formed from a lack of heavy metals altogether. The variety of brown colours come from organic materials rather than trace metals but this still needs more research to conclude.
Weathering and Erosion takes place rather fast within the badlands, as there is no vegetation to tie down the sediment. The wind carves out interesting formations like hoodoos and spires, this is mostly formed by differential erosion.
Differential erosion occurs when softer rock formations erode away and leave the harder materials behind, its visible in Bisti/De-Na-Zin where petrified wood is exposed on softer shale or coal along with hoodoo formations.
Erosion by seasonal river flow also creates interesting landscapes, as the water cuts through the rocks it forms distinct crevasses that are deep and thin. The crevasses will continue to widen into a slot canyon and eventually wider canyons as erosion continues.
This cave is located within the Fruitland Formation and is undocumented and unnamed, others are most likely visible in the study area but no maps show documented locations of these caves.
Caves in the badlands are formed from sediment erosion, when the monsoon rains move through the area they take out and move clastic sediment. Over time more materials are transported and the hole made by erosion widens. once the gap gets large enough layers of rock collapse from the ceiling and the cave expands.
As all of the sediment is sedimentary it erodes faster then igneous and metamorphic rocks, especially since most of the formations contain coal and shale which are relatively weak.
There is a range of different types of hoodoos in the Bisti/De-Na-Zin badlands. The most prominent in the area are capped with the Ojo Alamo Sandstone most have iron-cemented cap-rocks which protect the lower layers of sandstone or even shale within the Naashoibito Member of the Kirtland Formation from erosion and weathering.
One of the more interesting hoodoo formations within the badlands are clay, mudstone, or sandstone spherical concretions, these form rapidly in a shallow marine environment a few tens of meters deep. They form from decaying organic matter which produces carbonate material, that material defuses starting from the inside and extends outward from the concretion, the carbonate material then precipitates out as calcite which cements it together.
Spencer G. Lucas, Adrian P. Hunt, Justin A. Spielmann, & Patricia M. Hester. (2006). Field Guide to Upper Cretaceous Stratigraphy and Paleontology, Bisti and De-Na-Zin Wilderness areas, San Juan Basin, New Mexico. Fossils from Federal Lands, New Mexico Natural History and Science Bulletin 34, 179–182.
James E. Fassett. (2009, January). New geochronologic and stratigraphic evidence confirms the paleocene age of the dinosaur-bearing Ojo Alamo Sandstone and Animas Formation in the San Juan Basin, New Mexico and Colorado. Palaeontologia Electronica.
James E. Fassett. (1973). The Saga of the Ojo Alamo Sandstone; or The Rock-Stratigrapher and the Paleontologist Should be Friends. Four Corners Geological Society, Cretaceous and Tertiary Rocks of the Southern Colorado Plateau, 123–130.
Neykar Kotyk. (2014). The San Juan Basin and Geology of the Bisti/De-Na-Zin Wilderness. San Juan College, Geology 110 paper spring semester.
Ridgley, J.L., Condon, S.M., and Hatch, J.R. (2013). Geology and oil and gas assessment of the Fruitland Total Petroleum System, San Juan Basin, New Mexico and Colorado, chap. 6 of U.S. Geological Survey San Juan Basin Assessment Team, Total petroleum systems and geologic assessment of undiscovered oil and gas resources in the San Juan Basin Province, exclusive of Paleozoic rocks, New Mexico and Colorado: U.S. Geological Survey Digital Data Series 69–F, p. 1–100
Palaeo Electronica. (2009). NW to SE Thinning of Cretaceous strata in SW San Juan Basin.
Alan M. Bielski, United States Department of the Interior, United States Geological Survey, Janet L. Brown, & Jerry R. Hassemer. (1983). Mineral resource potential of the Bisti (NM-010-057), De-Na-Zin (NM-010-004), and Ah-Shi-Sle-Pah (NM-010-009) Wilderness Study Areas, San Juan County, New Mexico. United States Geological Survey.
James E. Fassett & New Mexico Geological Society. (2010). Stratigraphic nomenclature of rock strata adjacent to the Cretaceous-Tertiary interface in the San Juan Basin. Geology of the Four Corners Region, 113–124.
Steven D. Craigg. (2001). Geologic Framework of the San Juan Structural Basin of New Mexico, Colorado, Arizona, and Utah with Emphasis on Triassic through Tertiary Rocks. Regional Aquifer-system analysis San Juan Basin, New Mexico. United States Geological Survey.
Lucas, Spencer & Hunt, Adrian & Sullivan, Robert. (2006). Stratigraphy and age of the Upper Cretaceous Fruitland Formation, west-central San Juan Basin, New Mexico. New Mexico Museum of Natural History and Science Bulletin. 35.
Mustoe, G., & Acosta, M. (2016). Origin of Petrified Wood Color. Geosciences, 6(2), 25.
Yoshida, H., Yamamoto, K., Minami, M. et al. (2018). Generalized conditions of spherical carbonate concretion formation around decaying organic matter in early diagenesis. Sci Rep 8, 6308.
Lehman, T. M. (1985). Depositional environments of the Naashoibito Member of the Kirtland Shale, Upper Cretaceous, San Juan Basin, New Mexico. New Mexico Bureau of Mines and Mineral Resources Circular, 195, 55-79.