Great Disturbances in the Force

Curtis Formation - (in San Rafael Group)
Age: Deposited from early to late Oxfordian time (161 - 155 Ma) (Wilcox, 2007).

Depositional Environment: Marine and marginal-marine tidal flat. Comprises one unconformably-bound, transgressive-regressive (T-R) sequence (Wilcox, 2007).

Paleogeography: A major transgression of the Late Jurassic seaway drowned the eolian sand sea of the Entrada Formation. Subsequent regressive paleoflow was to the northeast into the Late Jurassic interior seaway (Kocurek & Dott, 1983).

Tectonics: Deposition was in a retroarc to craton-margin basin as the region drifted north (Kocurek & Dott, 1983).

Climate: With paleolatitude range of 5 to 25 degrees north, the paleoclimate was both hot and arid (Kocurek & Dott, 1983).

Features: The Curtis Formation shows a variety of near shore sedimentary structures (e.g. horizontal bedding -> beach, rhythmites and sigmoidal bundles -> tidal). The Jurassic "J3" unconformity, a regional surface of erosion atop the Entrada Formation, marks the basal bounding surface of the Curtis-Summerville T-R sequence. A thin, lower Curtis transgressive systems tract is the finest grained facies of the Curtis Formation topped by a maximum flooding surface. Thick middle and upper Curtis deposits represent a highstand systems tract reflected in upward coarsening cycles from marine shelf to tidal channels to shoreface envirionments. The upper sequence is tidal flat, reddish-brown mudstones and evaporites of the Summerville Formation topped by the "J5" unconformity, the upper sequence bounding surface and the contact with overlying Morrison Formation (Wilcox, 2007).

pubs.geoscienceworld.org/sepm/jsedres/article-abstract/53/1/67/97634/depositional-setting-of-the-salt-wash-member-of?redirectedFrom=fulltext

Noel Tyler, Frank G. Ethridge Journal of Sedimentary Research (1983) 53 (1): 67-82. DOI:
doi.org/10.1306/212F8157-2B24-11D7-8648000102C1865D
Published: March 01, 1983

Abstract

Host to extensive uranium and vanadium mineralization. Sandstones deposited in a complex fluvial system. Facies analysis of the Slick Rock Uranium District documents three major sandstone facies interbedded within a sequence of mudstones, siltstones, and thin sandstones.

Large-scale trough cross-bedded facies is the dominant sandstone. It represents deposition in northeast-flowing, low-sinuosity trunk streams.

The second most abundant sandstone facies is medium- to small-scale trough crossbedded sandstone within lensoid, fining-upward cycles. Vertical decrease in the scale of structures and variable paleocurrent orientations are characteristic of these units. This facies represents the point bars of meandering streams that acted as tributaries to the low-sinuosity trunk channels.

The third sandstone facies, interpreted as crevasse-splay deposits, contains coarsening-upward sandstone packages with variable structures and a distinctive convex geometry. The mudstone, siltstone, and thin sandstone facies averages 50 percent of the member, and represents well-drained floodplain deposits, shallow ephemeral lakes, and abandoned channel fills.

Analysis leads to the conclusion that the Salt Wash Member is a fan apron marginal to an alluvial fan or coalesced fan complex. Sandstones that transect the district represent depositional axes of this fluvial system.--Modified journal abstract.

Kimmeridgian - From Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/Kimmeridgian

In the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 157.3 ± 1.0 Ma and 152.1 ± 0.9 Ma (million years ago). The Kimmeridgian follows the Oxfordian and precedes the Tithonian.[2]

Contents

1 Stratigraphic definition
1.1 Subdivision

2 Palaeontology
2.1 † Ankylosaurs

2.2 Birds

2.3 † Ornithopods
2.4 † Plesiosaurs
2.5 † Sauropods
2.6 † Stegosaurs
2.7 † Thalattosuchians
2.8 † Theropods (non-avian)

2.9 Nautiloids
2.10 † Ammonites
2.11 † Belemnites

2.12 Palaeontological sites

3 References
3.1 Notes
3.2 Literature
4 External links

Stratigraphic definition

The Kimmeridgian stage takes its name from the village of Kimmeridge on the Dorset coast, England. The name was introduced in literature by Swiss geologist Jules Thurmann in 1832.[citation needed] The Kimmeridge Clay Formation has its name from the same type location. It is the source for about 95% of the petroleum in the North Sea.[citation needed]

Historically, the term Kimmeridgian has been used in two different ways.

The base of the interval is the same but the top was defined by British stratigraphers as the base of the Portlandian (sensu anglico)

whereas in France the top was defined as the base of the Tithonian (sensu gallico).

The differences have not yet been fully resolved; As of 2004 Tithonian is the uppermost stage of the Jurassic in the timescale of the ICS.[3]

The base of the Kimmeridgian is at the first appearance of ammonite species Pictonia baylei in the stratigraphic column.[4] A global reference profile for the base (the GSSP of the Kimmeridgian stage) had in 2009 not yet been assigned.[citation needed] The top of the Kimmeridgian (the base of the Tithonian) is at the first appearance of ammonite species Hybonoticeras hybonotum. It also coincides with the top of magnetic anomaly M22An.[4]
Subdivision

The Kimmeridgian is sometimes [weasel words] subdivided into Upper and Lower substages.[citation needed] In the Tethys domain, the Kimmeridgian contains seven ammonite biozones:[citation needed]

zone of Hybonoticeras beckeri
zone of Aulacostephanus eudoxus
zone of Aspidoceras acanthicum
zone of Crussoliceras divisum
zone of Ataxioceras hypselocyclum
zone of Sutneria platynota
zone of Idoceras planula

11. Summary and conclusions
In spite of changes in paleogeography through time, and corresponding shifts in depositional environments, it appears that the climate did not change significantly throughout Morrison deposition. -{? What about the fluvial and radioactive material?}- It remained mostly warm and dry, but with at least seasonal precipitation. Warmth due to the greenhouse effect and the southerly position of the continent, combined with dryness associated with ‘‘rain out’’ of most of the moisture in uplands to the west and southwest of the basin, to create a high rate of net evapotranspiration, a major factor in Morrison climate.

It appears that much of the moisture that reached the depositional basin was from extrabasinal
surface and subsurface water delivered to the basin from uplands to the west and southwest. Surface runoff was delivered to the basin by streams, both perennial and intermittent, depending on the size of the drainage area. Subsurface water reached the basin through shallow, local groundwater flow, and 346 C.E. Turner, F. Peterson / Sedimentary Geology 167 (2004) 309–355
through deeper, regional groundwater flow. The streams that crossed the basin were most likely
‘‘losing’’ streams (water moving underground) in their upstream reaches and contributed to a raised water table in the riparian areas adjacent to them. The scarce perennial streams probably formed green ribbons of vegetation winding through the semi-arid landscape.

During dry seasons, the amount of surface runoff that fed the intermittent streams was not sufficient to maintain flow above the level of the streambed, but may have been sufficient to maintain substream flow, which increased the potential for waterholes in the streambed and the ability to sustain vegetation along the banks. Seasonal precipitation moistened the floodplain
areas not reached by stream flooding, bringing much needed moisture to the groundcover.

Locally, ponds and lakes formed on the floodplain where low-lying areas intersected the water table. A seasonally fluctuating water table appears to have characterized most of Morrison deposition.

Throughout Morrison deposition, upstream to downstream trends can be related to position on an
inferred hydrograph for the basin. Deeper, regional ground-water flow discharged in the low-lying distal parts of the depositional basin, contributing to the wetland and lake environments of east-central Colorado (Dunagan and Turner, this volume). Here, carbonate deposition occurred in wetlands and lakes that maintained hydrologically open and primarily freshwater conditions in the semi-arid climate due to replenishment by groundwater seepage and spring discharge.
Local discharge of shallow groundwater farther upstream occurred during the late Kimmeridgian on the upstream side of the ancestral Uncompahgre uplift.

Here, in the San Juan/Paradox basin, evaporative concentration of pore waters in the dry climate, and the alteration of volcanic ash produced an alkaline, saline lake within a hydrologically closed basin (Turner and Fishman, 1991). For the most part, however, drainages from west to east remained largely interconnected, as suggested by the biogeographic distribution of certain gastropods (Evanoff et al., 1998). Disruptions to shallow groundwater flow were caused by local intrabasinal structures (Peterson, 1986), and remnants of the ancestral Rocky Mountains. The ancestral Rockies were the only known internal source of sediment in the basin.

The hydrograph for the depositional basin also is expressed in the upstream to downstream changes in paleosols. Throughout Morrison deposition, paleosols in the upstream regions reflect drier soil moisture conditions than those of equivalent age farther downstream (Demko et al., this volume). An overall upstream to downstream change from vertic Calcisols to palustrine Protosols and argillic Calcisols (Demko et al., this volume) is consistent with a lower water table upstream than downstream.

Although the climate did not change appreciably during Morrison deposition,{?} paleogeographic reconstructions record differences in the distribution of environments through time. Major eolian environments occurred throughout early and middle Kimmeridgian time, and an alkaline, saline lake environment existed throughout most of the late Kimmeridgian.

Both environments require a dry climate, which constrains climatic interpretations for the Morrison ecosystem. What appear to be slightly wetter conditions in the Tithonian that led to deposition of coal and carbonaceous mudstone may, instead, reflect lower evaporation rates associated with a slight cooling trend and not a significant change in the overall climate (Parrish et al., this volume). A slight cooling trend is consistent with isotopic studies of the ostracodes (Schudack, 1999b). A possible underlying cause for the vertical trend is the inferred slight decrease in the carbon dioxide content of the atmosphere during the Late Jurassic (Ekart et al., 1999).

The major differences in the distribution of environments through time appear to reflect tectonic influences and withdrawal of the Late Jurassic Western Interior Seaway. Marginal marine environments in the early Kimmeridgian were replaced by alluvial plain deposition as the sea retreated to the northwest. {the Uncompahgre uplift}

By middle Kimmeridgian time, large fluvial complexes developed in the upstream reaches
of the depositional basin, while wetlands and lakes developed where the regional water table
discharged in low-lying areas farther downstream in the distal parts of the basin. Terrestrial environments persisted through the late Kimmeridgian, and a large alkaline, saline lake reflects continued high evaporation rates in the basin.
The only strata of known Tithonian age are in Montana and reflect the development of extensive coal swamps and marshes at the edge of the Late Jurassic Western Interior./b] C.E. Turner, F. Peterson / Sedimentary Geology 167 (2004) 309–355 347 Seaway toward the end of Morrison deposition.

Farther south, local fluvial deposits that may be correlative with known Tithonian beds to the north suggest the influx of more detrital sediment from the west and southwest.
Within the overall dry landscape, moisture was available in riparian environments adjacent to the
major stream courses, in wetlands, in lakes and ponds, and more regionally during seasonal precipitationin the basin. Paleosols respond as much to water-table levels as precipitation (Parrish et al., this volume), and, because the climate did not change appreciably, changes in paleosol types through time probably reflect changes in depth to the water table.

Evidence for seasonality is most apparent in unionids from the middle Kimmeridgian (Good, this volume). Lack of seasonal growth bands in early Kimmeridgian unionids (Good, this volume) probably reflects equable conditions caused by a high water table adjacent to the seaway, which reached its farthest extent southward at this time and provided the moderating influence of a coastal environment. Weakly developed growth banding in late Kimmeridgian unionids may be related to a higher regional water table. Changes in paleosols through time parallel the patterns of the unionids. Paleosols show evidence for drier soil moisture conditions in the middle Kimmeridgian than for both the early and late Kimmeridgian. Those in middle Kimmeridgian strata are better drained than those in either lower or upper Kimmeridgian strata, which exhibit weakly developed paleosols (Demko et al., this volume).
The unionids and paleosols probably were influenced mostly by the position of the water table through time, as the climate and evaporation rates apparently remained similar throughout the Kimmeridgian.{?}- The water table is thus inferred to have been lower in the middle Kimmeridgian and higher in the early and late Kimmeridgian.

{And yet the middle is where the “fluvial” appeared!}

The Morrison landscape has been likened to that of a savannah (Parrish et al., this volume). Riparian environments, especially those associated with perennial streams, were among the lushest parts of the ecosystem and probably consistently supported a larger biotic community than elsewhere in the ecosystem.

A gallery of conifer trees provided shade for an understory and groundcover of cycads, ginkgophytes, tree ferns, horsetails, and a variety of ferns.

Life was fairly abundant in this ribbon-like oasis that wended its way across the alluvial plain. Beneath the ‘‘losing’’ streams that characterized the upper part of the alluvial plain, the water table probably was raised to a shallower level than the regional water table.
In addition, flood events and seasonal variations in flow contributed to a fluctuating water table, creating habitats where life forms such as crayfish and termites could flourish (Hasiotis, this volume).
Equable conditions also existed in wetlands and lakes that formed in low-lying areas in the distal
parts of the basin where the water table discharged, and in long-term lakes and ponds elsewhere in the depositional basin where the floodplain also intersected the water table. In the distal wetlands and lakes, food and water probably were available year round, making these distal water bodies excellent refugia.
Elsewhere on the floodplain, resources to sustain life may have been only seasonally available due to seasonally restricted precipitation, but may have had high net productivity during the rainy season, as in modern grasslands (Parrish et al., this volume). Eolian and alkaline, saline wetland/ lake environments were inhospitable to most life forms.

The streams and wetlands, as well as freshwater lakes and ponds, supported an aquatic fauna of
crocodiles, turtles, lungfish, frogs, salamanders, fish, crayfish, bivalves, gastropods, ostracodes, charophytes, sponges, and microbialites (stromatolites).

Conchostracans inhabited more ephemeral aquatic environments. A diverse assortment of insects (Hasiotis, this volume) may have been the dominant small herbivores in the ecosystem and most likely were a primary food resource for the small vertebrates (Engelmann et al., this volume). A cursorial fauna that included lizards, the smaller crocodiles, small dinosaurs, sphenodonts, and mammals probably stayed close to the favorable habitats of the riparian and lacustrine environments, but could extend their range depending on their size and water requirements
(Engelmann et al., this volume).

In the floodplain environments, a herbaceous groundcover that came to life during seasonal rains
may have been a staple in the diet of the giant herbivorous dinosaurs such as Diplodocus and Apatosaurus. They may have supplemented their diets by grazing charophytes in the wetlands and lakes. This 348 C.E. Turner, F. Peterson / Sedimentary Geology 167 (2004) 309–355
left the coarser vegetation along the stream banks to the other herbivores, such as Brachiosaurus and Camarasaurus. As in all semi-arid environments, the Morrison ecosystem was vulnerable to extended periods of drought, which accounts for some of the death assemblages of the large vertebrates in the Morrison Formation.

Although metabolic and migratory advantages associated with size were adaptive assets in the dry climate (Engelmann et al., this volume), the dinosaurs perished along with other inhabitants of the ecosystem during severe droughts.

What is clear, however, is that the giant sauropod herbivores reached their largest body size during Morrison deposition, which suggests that the Morrison ecosystem sustained the most unusual form of life that ever roamed the planet.

pubs.usgs.gov/bul/0988a/report.pdf
- - -
FOSSIL LOGS AND ORE ROLLS
Fossil tree trunks and branches are common in the ore-bearing sandstone. Some are 1 ft or more in diameter and as much as 100 ft long. These logs were rafted into place by streams that deposited the enclosing sands, and when they came to rest in the stream beds, many of them were oriented parallel to the general direction of stream movement, as evidenced by lensing and foreset-bedding of the sandstone. Ore rolls are peculiar concretionary structures in the ore. They are conspicuously elongate in one direction, ranging from 10 to 100 ft or more in length. Locally the long axes of the rolls have a common trend, which is parallel to the dominant orientation of the fossil logs. Ore bodies are also elongate in this same general direction (Fischer, 1942, p. 390).

The common orientation of ore rolls and fossil logs is about normal to the local trend of the Uravan mineral belt (pi. 2). The alinement of ore deposits in a cluster, and the trend of favorable ground enclosing the cluster, likewise are generally normal to the local trend of the mineral belt (see pp. 6-10 and figs. 2,3,4,5). It must be assumed that some geologic conditions having widespread influence controlled the orientation of the fossil logs and the ore rolls in the area of the mineral belt.
- - -

Mi Vida uranium mine (109°15'35.77"W 38°11'25.07"N) near Moab. Note alternating red and white/green sandstone and mudstone. This color variation corresponds to oxidized and reduced conditions in groundwater fluid redox chemistry. The rock forms in oxidizing conditions, and starts with the red coating. It is then "bleached" to the white/green state when a reducing fluid passes through the rock. The reduced fluid can also carry Uranium-bearing minerals