Geochemistry and Petrology of the Morrison Formation, Dillon, Colorado

Wahlstrom, Ernest E.

doi:10.1130/0016-7606(1966)77[727:gapotm]2.0.co;2

Cited by 7 publications

(14 citation statements)

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“…vironmental change through time expressed in the succession of strata that make up the Morrison Formation. Previous work on clay minerals (e.g Tank 1956;Moberly 1960;Keller 1962;Wahlstrom 1966;Brady 1969;Bilbey et al 1974…”

mentioning

confidence: 99%

Taphonomy and Paleoecology of the Dinosaur Beds of the Jurassic Morrison Formation

et al. 1980

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The Upper Jurassic Morrison Formation has yielded one of the richest dinosaur faunas of the world. Morrison sediments are distributed over more than a million square kilometers in the western United States and represent a mosaic of riverine, lacustrine and floodplain environments developed on a vast alluvial plain nourished by debris from the ancestral Rocky Mountains. Plant productivity must have been reasonably high to support abundant large-bodied herbivores, but the absence of coals, scarcity of small aquatic vertebrates, the abundance of oxidized sediments, and presence of calcretes lead us to believe that water was periodically in short supply. A strongly seasonal climate may have necessitated annual large-scale movements of large herbivores, accounting in part for their remarkably broad and uniform geographic distribution. Dinosaur diversity is lower in the Morrison than in the Late Cretaceous, and taphonomic alteration is higher. Massed accumulations of thousands of bones are characteristic of the Morrison. Morrison dinosaurs were not confined to specific depositional environments but were distributed across the complete spectrum of available habitats, from lakes to dry floodplains; this type of distribution is similar to that of large terrestrial mammals such as elephants and rhinos and is different from that of hippos and crocodiles. Common Morrison taxa were Camarasaurus, Apatosaurus, Diplodocus, Allosaurus and Stegosaurus; these genera probably constituted a true dinosaur community. Stegosaurus may have been partially segregated from the other genera, and Camptosaurus more strongly so. Camarasaurus and Diplodocus were gregarious, with juveniles and subadults of the former particularly common; Apatosaurus was less abundant and more solitary in its habits. Juveniles and subadults are known for a number of dinosaurs.

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confidence: 99%

Taphonomy and Paleoecology of the Dinosaur Beds of the Jurassic Morrison Formation

et al. 1980

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“…A three-fold division also occurs at the reference sec-tion of the Morrison Formation, but with a kaoliniteand illite-dominated lower and middle sections, and a smectitic-dominated (as montmorillonite) upper section (Keller 1953). A three-fold division is also present in the Morrison of the Colorado Plateau (Keller, 1962); it is present, although not as well developed near Dillon, Colorado (Wahlstrom, 1966) where secondary illite has been identified (Bell, 1986). Turner and Fishman (1991) have hypothesized that some illite may form at low syndepositional temperatures, but most illite is believed to be detrital (Keller, 1962).…”

Section: Paleosols In the Unnamed Membermentioning

confidence: 99%

“…The absence of calcium carbonate cement in the upper member of the Morrison supports the possibility that low pH environments did exist and that kaolinite was produced there. Kaolinite is also present low in the Salt Wash Member of the Colorado Plateau, in the lower portions at the type section of the Morrison, near Golden, Colorado, in the lower part of the Morrison at Blue Mesa Reservoir, Colorado, in the upper portions of the Morrison near Dillon, Colorado, and the Black Hills of Wyoming and South Dakota (Keller, 1953(Keller, , 1962Tank, 1956;Wahlstrom, 1966;Fiorillo and McCarty, 1996).…”

Section: Paleosols In the Unnamed Membermentioning

confidence: 99%

Redefining the Upper Jurassic Morrison Formation in Garden Park National Natural Landmark and vicinity, eastern Colorado: Geology of the Intermountain West

Carpenter

Lindsey

2019

GIW

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The Garden Park National Natural Landmark (GPNNL) is north of Cañon City, Colorado, and encompasses all of the major historical dinosaur quarries of the Upper Jurassic Morrison Formation in this area. The formation there can be divided into the lower redefined Ralston Creek Member and an upper unnamed member. The Morrison Formation is bracketed below by the J-5 unconformity and above by the K-1 unconformity. The Ralston Creek Member is composed of up to 55 m of arkosic conglomerate, sandstone, siltstone, and gypsum conformably underlying the unnamed member. Fossil fishes previously used to infer a Middle Jurassic age are non-diagnostic. A diplodocid skeleton 4 m above the J-5 unconformity from the west-adjacent Shaws Park, and a radiometric date of 152.99 + 0.10 Ma from the Purgatoire River area demonstrate that the Ralston Creek rightly belongs in the Morrison Formation and correlates with the Tidwell and Salt Wash Members on the Colorado Plateau. The Ralston Creek was deposited in a broad playa complex analogous to those of central Australia and here called the Ralston Creek boinka. Groundwater flux played an important role in gypsum deposition in gypsisols and playa lakes. The overlying unnamed member in the GPNNL can be subdivided on the west side of Fourmile Creek into a lower part composed largely of mudstone with many thin, discontinuous channel sandstone beds, and a thicker upper part containing more persistent tabular sandstone beds; this subdivision does not occur east of Fourmile Creek. Several thin limestone beds occur in the Ralston Creek Member and in the lower part of the unnamed upper member. The limestone contains fresh water ostracods and aquatic mollusks indicating a lacustrine origin. However, these fauna are apparently stunted and the ostracod valves closed indicating periodic hypersaline conditions. All detrital rocks in the Morrison Formation at Garden Park are composed of varying amounts of quartz, potassic feldspar, and the clay minerals illite, smectite, and kaolinite. Mapping of the clay minerals in the unnamed member reflect various paleosols throughout the mudstone interval, including protosols and argillisols. At the top of the formation, a sandstone previously assigned to the Morrison is reassigned to the overlying Cretaceous Lytle Formation based on similar weathering characteristics, mineral content, and fabric. Thus, the K-1 unconformity between the Morrison and overlying Lytle rests on the uppermost occurrence of the Morrison Formation mudstone-sandstone-limestone complex and beneath the blocky, cliff-forming Lytle Formation.

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“…Granitic material interlayered conformably with the foliation of the gneiss and schist is abundant throughout the unit. Wahlstrom andKim (1959, p. 1228) attributed much of this material to metasomatism and local mobilization.…”

Section: Biotite Gneiss and Schistmentioning

confidence: 99%

General geology of the Harold D. Roberts Tunnel, Colorado

Robinson¹,

Warner²,

Wahlstrom³

1974

Professional Paper

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The Roberts Tunnel transects a geologically complex area in the Front Range of the Colorado Rocky Mountains. The area includes Precambrian igneous and metasedimentary rocks, Paleozoic and Mesozoic sedimentary rocks, and Tertiary igneous rocks. The structural history includes folding and faulting during Precambrian time and the Laramide orogeny.The Precambrian rocks, which constitute about two-thirds of the area penetrated by the tunnel, consist of a sequence of metasedimentary rocks that were invaded by igneous rocks. The age relations among the metasedimentary rocks are still in doubt, owing to the complexity of the structure. These rocks are, from East Portal to West Portal, a sequence of amphibolite and related calc-silicate rocks, a migmatite unit, a microcline gneiss unit, a biotite gneiss and schist unit containing some amphibolite, a sillimanitic biotite gneiss and schist unit, and a hornblende gneiss unit.The Precambrian metasedimentary rocks were intruded by granite of Precambrian age. The older granite, which is similar to the Boulder Creek Granite of other areas in the Front Range, is believed to have been emplaced at about the time of the metamorphism and plastic deformation of the Precambrian sedimentary rocks. The younger granite, which is similar to the Silver Plume Granite of other areas in the Front Range, is believed to have been intruded during a period of cataclastic deformation. Pegmatite and aplite of Precambrian age occur locally throughout the area.Sedimentary rocks are exposed in the western quarter of the tunnel. These are the Entrada(?) Sandstone and Morrison Formation of Late Jurassic age, the Dakota Group of Early Cretaceous age, the Benton Shale of Early and Late Cretaceous age, and the Niobrara Formation and Pierre Shale of Late Cretaceous age. Underlying the sedimentary rocks exposed in the tunnel, and exposed to the west of the tunnel and intersected by drill holes along the tunnel line, are the Maroon Formation of Pennsylvanian and Permian age and the Lykins Formation of Permian and Triassic(?) age. These sedimentary rocks dip eastward toward the axis of the Front Range.Early during the Laramide orogeny the Williams Range thrust fault developed, and Precambrian rocks were superimposed on the Pierre Shale along the fault. After the period of thrusting the Montezuma Quartz Monzonite stock was emplaced. The Williams Range thrust fault, as a result, was folded upward, and the tunnel intersects the fault zone at two places. Between the eastern exposure of the thrust and the Montezuma stock is a sequence of shale and siltstone that becomes more metamorphosed as the stock is approached. This sequence of shale and siltstone is believed to be equivalent, for the most part, to part of the Pierre Shale to the west of the Williams Range thrust.Before and after the intrusion of the Montezuma stock, a series of dikes intruded the Precambrian units around the stock. The oldest dikes are augite and hornblende diorite. Other dikes contemporaneous in age and younger than the stock are latite porph...

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Geochemistry and Petrology of the Morrison Formation, Dillon, Colorado

Cited by 7 publications

References 0 publications

Taphonomy and Paleoecology of the Dinosaur Beds of the Jurassic Morrison Formation

Taphonomy and Paleoecology of the Dinosaur Beds of the Jurassic Morrison Formation

Redefining the Upper Jurassic Morrison Formation in Garden Park National Natural Landmark and vicinity, eastern Colorado: Geology of the Intermountain West

General geology of the Harold D. Roberts Tunnel, Colorado

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