Contributions to Geology 2.1

Columnar jointing in sandstone

D. L. BLACKSTONE, JR. Department of Geology, University of Wyoming, Laramie

Pages
7-12

Keywords
columnar jointing, sandstone, Miocene, Browns Park Formation

Abstract
Columnar joints in cross-bedded sandstone of the Miocene Browns Park formation adjacent to sills and dikes are similar in most aspects to columnar jointing described in igneous rocks. The occurrence is located in secs. 20 and 21, T. 12 N., R. 89 W., Moffat County, Colorado, in the northern part of the Elkhead Mountains volcanic field. The columnar joints (figured) are oriented normal to the igneous contacts, but at random to the bedding and cross-lamination. The columns vary from three-fourths inch to five inches in diameter and are up to three feet long. Some columns are curved but no "ball and socket" joints were observed. The sandstone was cemented by introduction of opaline silica prior to cooling. Jointing is due to the same processes as those reported to cause columnar joints in the igneous rock masses.

Correlation of volcanic rock units in the southern Absaroka Mountains, northwest Wyoming

WILLIAM H. WILSON Geological Survey of Wyoming, Laramie

Pages
13-20

Keywords
volcanic rocks, Absaroka Mountains, Wyoming

Abstract
The Southern Absaroka Mountains are composed of layered rocks ranging in age from middle Eocene to Oligocene. Most of the rocks, which reach a maximum thickness of approximately 5,000 feet, are volcanic sediments of andesitic composition. Locally, they interfinger with andesite flows and flow breccias.

Hague's (1899) nomenclature, Early and Late Basic Breccias, is considered inappropriate for these volcanic sedimentary units. Later nomenclature, such as Aycross and Tepee Trail, etc., suggested as correlative with Hague's nomenclature is not considered completely compatible from a mapping standpoint. It is suggested that the terms Pitchfork and Wiggins formations respectively replace the Early and Late Basic Breccia terminology. The two formations, then, are completely correlative on a mappable basis with those of Hague's that have been in use for more than 60 years.

Compositions of silicate surfaces and surface phenomena

GEORGE W. DEVORE Department of Geology, Florida State University, Tallahassee, Florida

Pages
21-38

Keywords
silicate surfaces, chemistry, composition

Abstract
A general discussion of the problems of silicate surface chemistry is offered in order to describe the surface phenomena and to make significant surface contributions in petrologic relationships. The application of the principles of crystal and physical chemistry to surface phenomena make possible interpretations, generalizations, and predictions with a minimum of assumptions.

Surface compositions for various silicates differ markedly from the mineral compositions and differ for different surfaces of the minerals. Surface phenomena are interpreted in terms of a proposed atomistic ion exchange -- crystal growth model that makes significant the roles of water, atomic order, and interfacial energy.

Several degrees of atomic order are proposed for muscovite. It is suggested that several ordered states might occur in disordering process.

Crystal growth, crystal habit, preferred mineral associations, oriented exsolutions, and overgrowths and the formation of rocks instead of loose assemblages of grains and the texture, structure and fabric of the rock are in large part the result of the system's response to solve the problems and minimize the energy created by the mineral surfaces.

Environmental significance of sharks in the Shotgun fauna, Paleocene of Wyoming

PAUL O. MCGREW Department of Geology, University of Wyoming, Laramie

Pages
39-42

Keywords
sharks, selachians, Shotgun, Fort Union, Cannonball Sea, Wyoming, Paleocene

Abstract
The selachians found in the Shotgun member of the Fort Union formation indicate that the waters in which the deposits were formed were saline. The suggestion is made that during middle and possibly late Paleocene a remnant of the Cannonball Sea prevailed in the western Plains region. It is postulated that periodic flooding from the Cannonball Sea of parts of the Wind River basin took place to produce sufficient salinity to support a selachian fauna in Waltman Lake.

Ice expansion ramparts on south arm of Yellowstone Lake, Wyoming

JOHN DE LA MONTAGNE Department of Earth Sciences, Montana State College, Bozeman

Pages
43-46

Keywords
ice expansion, Yellowstone Lake, Wyoming

Abstract
Ice expansion ramparts two miles south of Plover Point on South Arm of Yellowstone Lake were formed by expansive force of lake ice during intense thaws. Width of the Arm (one and one half miles) is within limits necessary for ice to maintain competence for shoreward thrusting (Scott, 1927). Wind-induced ice thrust forces are unlikely here, but were observed May 20, 1960, forming ramparts on windward northern shores of the lake which were exposed to optium fetch.

The South Arm ramparts are sinuous in plan and located both above normal summer strand lines and in drowned positions as much as 60 feet out from them. The latter stand six feet above rock-veneered bottoms and formed during winter low water stage. Simplicity and singularity of the ramparts suggests that conditions for their formation have not often occurred. Following Hobbs (1911) an expectable genetic sequence is:

(1) Freezing of lake ice; continued chilling with concomitant formation of tension cracks; widely fluctuating temperatures.

(2) Water freezes in cracks increasing potential ice volume.

(3) Sudden marked warming is communicated to bare ice expanding it to new and greater volume; ice thrusts onto shore if competent.

Laramide vertical movements in central Wyoming

W. R. KEEFER and J. D. LOVE: U. S. Geological Survey, Laramie, Wyoming

Pages
47-54

Keywords
subsidence, uplift, Wyoming, Cretaceous, Paleocene, Eocene

Abstract
New data, chiefly from drilling and palynology, refine age determinations of thick sequences of uppermost Cretaceous, Paleocene, and lower Eocene sedimentary rocks, and indicate types of Laramide crustal movements that occurred in and around the margins of structural basins in central Wyoming. The movements began with extensive downfolding of the basins, which continued to be tectonically active through early Eocene time. Subsidence of large segments of some basins equalled, or exceeded, the uplift of bordering mountains.

Pedestal rocks in the Laramie Range, Albany County, Wyoming

LOUIS W. CRAMER Department of Geology, University of Wyoming, Laramie

Pages
55-58

Keywords
pedestal rocks, differential weathering, Wyoming

Abstract
Pedestal rocks are mushroom-shaped masses of bedrock possessing structural and lithologic homogeneity and which are produced by differential weathering or erosion. They are thus differentiated from balanced rocks. The separate components of the pedestal rocks are the cap, pedestal or shaf, and base. Pedestal formation begins with exfoliation rounding the corners of a cubical joint block. Wind action undercuts the western face, shifts the crest eastward, and subsequently deflates the entire block. The eastern side of the block is undercut more than the western side due to the effects of hydration and frost action. The final stage is reached when the block is reduced to a relatively flat base.

Rubidium in alkali feldspar perthites

RONALD B. PARKER, JOHN S. KING, and RONALD G. WORL Department of Geology, University of Wyoming, Laramie

Pages
59-62

Keywords
rubidium, alkali feldspar perthites, x-ray emission

Abstract
Twenty-eight alkali feldspar perthites were analyzed for rubidium content by x-ray emission spectrography, and the microcline/plagioclase ratios determined by x-ray diffraction. Pink perthites range from 78-82 weight per cent microcline and contain up to 0.31 weight per cent Rb. White perthites range from 73-94 weight per cent microcline and contain up to 0.18 weight per cent Rb. Green perthites show the greatest range in microcline content, from 70-100 weight per cent, and show a systematic relationship among color intensity, microcline percentage, and Rb content. Rubidium content of green microcline ranges from 0.06-1.00 weight per cent and is highest in dark green, microcline-rich samples.

A Wyoming specimen of Dendrophycus

DONALD W. BOYD and H. THOMAS ORE: Department of Geology, University of Wyoming, Laramie

Pages
63-68

Keywords
dendrophycus, Wyoming

Abstract
A patterned surface on the underside of a siltstone slab from Wyoming Triassic redbeds bears a striking resemblance to Dendrophycus triassicus described by Newberry in 1888 from Triassic redbeds of the Connecticut Valley. D. triassicus has been considered a rill mark by some and a plant imprint by others.

The Wyoming specimen was found in the Red Peak member of the Chugwater formation. The pattern represents a system of branching ridges which filled grooves on a continuous underlying surface, rather than a series of tubes or imprints of independent branches.

Distinctive features shared by the Chugwater pattern and D. triassicus specimens from Connecticut include development of the pattern on a broad surface with significant relief, straightness of major ridges, close spacing and sharp definition of long, narrow, straight-sided ridges, dichotomous aspect of branching of these ridges, lack of anastomosis of closely spaced ridges, and lack of undissected areas between adjacent minor branches.

Laboratory experiments have failed to duplicate the pattern in full detail, but suggest that it is inorganic and formed at the edge of a body of water which repeatedly transgressed and regressed over a sloping surface of unconsolidated silt.

The chemistry of fossil bones from Wyoming and adjacent states

HEINRICH TOOTS Department of Geology, University of Wyoming, Laramie

Pages
69-80

Keywords
fossil, Wyoming, Oligocene, elements, Tertiary, Cretaceous, Pleistocene

Abstract
Bone fragments ranging in age from Late Cretaceous to Pleistocene have been analyzed for heavy elements by x-ray emission spectrography. Common elements in bone are Fe, Sr, Y, Mn, Ba, and As, while U, Pb, Sb, Sn(?), La, and In are occasionally present. Of these Fe, Sr, Mn, As, and possibly Y show systematic variation in distribution by age. Fe shows a general trend of increased concentration with increase in age. Mn is generally restricted to the stratigraphic levels below the Middle Oligocene while As is restricted to certain parts of the Late Tertiary. Sr and Y, though generally present show maxima at certain stratigraphic intervals. These data seem useful for approximate determinations of stratigraphic level within the area studied.

Non-paleontological methods of correlation of rocks of Tertiary age in Wyoming: Part II - glass shards

R. S. HOUSTON Department of Geology, University of Wyoming, Laramie

Pages
81-86

Keywords
glass shards, Tertiary, Wyoming, correlation, Miocene

Abstract
Various properties of glass shards that can be determined in thin sections of volcanic sedimentary rocks of Tertiary age have been tabulated to learn their value in stratigraphic studies and also in stratigraphic correlation. Certain characteristics such as index with respect to balsam, alteration, abrasion, and color do not appear to be useful in stratigraphic correlation. Variation in the shape of shards may be valuable in distinguishing certain ash falls. An ash fall of Late Miocene (Barstovian) age of considerable extent was noted to have shards with a distinctive needle-like shape.

Rhythmic alternation in the Triassic Chugwater and Brunswick Formations, Wyoming and New Jersey

M. DANE PICARD and LEE R. HIGH: Princeton University, Princeton, New Jersey

Pages
87-100

Keywords
Brunswick Formation, Chugwater Formation, alternation, sandstone, siltstone, Triassic, Wyoming, New Jersey

Abstract
Alternations in the Red Peak member of the Chugwater (Triassic) formation of western Wyoming consist of: (1) a massive siltstone; and (2) a less massive, fissile and non-fissile, poorly sorted siltstone, commonly with interbeds of well sorted siltstone, silty claystone, sandstone, and mudstone. Commonly, the massive siltstone can be divided into three parts on the basis of bedding characteristics; the alternations are then asymmetrically cyclical. From base to top, these cycles contain: (1) a platy to flaggy siltstone (about 1 foot); (2) a massive siltstone; (1) a platy to flaggy siltstone (about 1 foot); and (3) a less massive, fissile and non-fissile, poorly sorted siltstone, with interbeds of well sorted siltstone. The 1, 2, 1 part of the cycle corresponds to the massive siltstone of the alternations.

Forty-nine alternations average 10.1 feet in thickness, ranging from 4.3 to 17.1 feet. The massive siltstone parts average 8.1 feet. The less massive, fissile and non-fissile, poorly sorted siltstone and mudstone parts average 2.0 feet.

The alternations begin 20 to 75 feet below the base of the Alcova limestone member, and extend downward 200 to 425 feet in the sequence. This is 35 to 55 per cent of the total thickness of the Red Peak member.

Seventy-five to 85 per cent of the Red Peak member in western Wyoming is silt-sized sediment, with almost 45 per cent of the total volume of silt in the alternations.

Alternations in the Brunswick (Triassic) formation of New Jersey consist of: (1) a resistant ledge of predominantly poorly sorted siltstone, with sandstone interbeds; and (2) less resistant mudstone and poorly sorted siltstone, with minor silty claystone and sandstone interbeds.

Twenty-five measured alternations average 8.4 feet in thickness, ranging from 3.5 to 15.8 feet. The massive, ledge-forming part of the alternations averages 3.6 feet; the less massive part averages 4.8 feet.

Karst-like features in badlands of the Arizona Petrified Forest

BRAINERD MEARS, JR. Department of Geology, University of Wyoming, Laramie

Pages
101-104

Keywords
karst, badlands, Arizona, Petrified Forest, channel

Abstract
Sinks, disappearing streams, hanging valleys, and natural bridges add a karst-like element to the miniature mountain topography represented in badlands. The Chinle formation of the Petrified Forest in Arizona largely consists of compact, montmorillonitic and illitic claystones. Sinks in it result from disaggregation of swelling clay minerals rather than solution which affects limestone in true karsts.

Ravines whose bottoms are pierced by sinks may develop into hanging valleys because their channels, robbed of surface flow downstream from these swallow holes, cannot keep pace with downcutting in the master drainage to which they are tributary. Growth of the sinks soon creates a disappearing stream that continues to deepen the upstream segment of a ravine. Thus the abandoned downstream segment beyond the sinks, no longer eroded by the stream, develops into a transverse barrier. Where the abandoned channel was initially short, the barrier may be eventually narrowed by weathering and slope erosion to form a natural bridge. Other bridges consist of jumbled material that has collapsed from steep valley walls, undercut by small stream meanders.