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Ocoee series of the southern Appalachians

The Ocoee series is divided into four major units present from northern North Carolina to western Georgia and a fifth, younger, formation present only in southern North Carolina and Georgia. The units recognize dare as follows: The Ocoee series is a broad synclinal belt of resistant Great Smoky quartzite, which forms most of the Great Smoky Mountains and the Bald Mountains, with Nantahala slate and in places the Big Butt quartzite enclosed in synclines; the Hurricane graywacke is on the flanks of the main syncline. In the deeper Murphy syncline the Big Butt quartzite is overlain by the Valleytown formation. The Ocoee series is thrust northwestward on the Great Smoky overthrust over Paleozoic rocks of the Great Valley, and in Tennessee overrides unmetamorphosed sandstone, shale, limestone, and limestone conglomerate which previously were mapped as Wilhite slate and were included in the Ocoee series. These rocks in a few places contain Middle Ordovician fossils and are a newly recognized part of a clastic shore facies equivalent to an expanded Tellico sandstone of undetermined stratigraphic range. This part of the Ordovician shore facies is in the Pulaski block in Tennessee and is exposed also in windows in the Great Smoky overthrust block in Tennessee, North Carolina, and Georgia. The Ocoee series does not resemble the Lower Cambrian Chilhowee group, which it overrides, nor any other Lower Cambrian facies. Lower Cambrian quartzites overlie with erosional unconformity the Catoctin basalt, Swift Run tuff, and Mt. Rogers volcanic series, proving that these volcanic rocks are late pre-Cambrian. The Ocoee series resembles the Lynchburg gneiss, which is equivalent to the late pre-Cambrian Swift Run tuff. The Ocoee series is stratigraphically overlain by the Lower Cambrian Unicoi formation and is late pre-Cambrian. © 1949, The Geological Society of America, Inc.

North Carolina, Georgia↗
USGS1950

Pleistocene history of coastal Alabama

Following its deposition, the late Pliocene or early Pleistocene Citronelle formation was entrenched by consequent streams and then tilted toward the Gulf. Submergence in waters 190 to 210 feet above present sea level then resulted in a compound shore line and marine erosion of the Coharie terrace. Four other marine terraces occur below the Coharie level: the Sunderland at 150 to 160 feet, the Wicomico at 90 to 110 feet, the Penholoway at 60-70 feet, and the Pamlico at 20 to 30 feet. The Coharie, Penholoway, and Pamlico marine terraces are associated with fluvial or estuarine terraces in the Mobile River Valley. After Pamlico submergence, a Mobile River floodplain and delta was formed at 10 to 11 feet below present sea level. © 1950, The Geological Society of America, Inc.

Louisiana↗
USGS1950

Some effects of deformation in the central Appalachians

Deformation in the folded Cambrian to Devonian sedimentary rocks of the central Appalachians has been investigated, mainly in the Potomac River Valley. Interpretations of deforming mechanisms are based on the study of folds, rock cleavages, faults, and lineations. An attempt is made to present a kinematic analysis of deformation. Effects of deforming movements, such as preferred orientations, cleavages, small-scale thrusts, and alterations of primary stratigraphic thicknesses are analyzed and correlated. Changes in deformation are related to (1) differences in location within the folded Appalachian belt; (2) different stratigraphic horizons; (3) different positions in given folds; (4) lithological differences. It has been found that: 1. Deformation decreases westward from the South Mountain-Blue Ridge belt. This corroborates the previous findings of Cloos and Fellows; 2. Less competent limestones are deformed farther toward the west than the more competent sandstones. Each formation of differing relative competency has its own tectonite front, and thus, for the succession as a whole, there is a series of tectonite fronts approximately parallel to the western edge of the Appalachian Valley; 3. Distortion of primary thicknesses are correlated with cleavage-bedding angles in separate beds of a given fold in which transverse cleavage is prominent;4. Changes in thickness corresponding to changes in cleavage-bedding angles occur in the less competent rocks west of the Appalachian Valley; they are inferred for the rocks in the Valley;5. Radical changes in thickness often have been caused by bedding-plane slip, interleafing, and piling-up of shales between more competent layers;6. Bedding-plane thrusts cause repetition of individual layers;7. Bedding-plane slip and thrusting parallel to bedding are the predominant modes of distortion west of the Appalachian Valley. © 1950, The Geological Society of America, Inc.

Geological Society of America Bulletin↗
USGS1951

Geologic history of sea water: An attempt to state the problem

Paleontology and biochemistry together may yield fairly definite information, eventually, about the paleochemistry of sea water and atmosphere. Several less conclusive lines of evidence now available suggest that the composition of both sea water and atmosphere may have varied somewhat during the past; but the geologic record indicates that these variations have probably been within relatively narrow limits. A primary problem is how conditions could have remained so nearly constant for so long. It is clear, even from inadequate data on the quantities and compositions of ancient sediments, that the more volatile materials—H 2 O, CO 2 , Cl, N, and S— are much too abundant in the present atmosphere, hydrosphere, and biosphere and in ancient sediments to be explained, like the commoner rock-forming oxides, as the products of rock weathering alone. If the earth were once entirely gaseous or molten, these “excess” volatiles may be residual from a primitive atmosphere. But if so, certain corollaries should follow about the quantity of water dissolved in the molten earth and the expected chemical effects of a highly acid, primitive ocean. These corollaries appear to be contradicted by the geologic record, and doubt is therefore cast on this hypothesis of a dense primitive atmosphere. It seems more probable that only a small fraction of the total “excess” volatiles was ever present at one time in the early atmosphere and ocean. Carbon plays a significant part in the chemistry of sea water and in the realm of living matter. The amount now buried as carbonates and organic carbon in sedimentary rocks is about 600 times as great as that in today's atmosphere, hydrosphere, and biosphere. If only 1/100 of this buried carbon were suddenly added to the present atmosphere and ocean, many species of marine organisms would probably be exterminated. Furthermore, unless CO 2 is being added continuously to the atmosphere-ocean system from some source other than rock weathering, the present rate of its subtraction by sedimentation would, in only a few million years, cause brucite to take the place of calcite as a common marine sediment. Apparently, the geologic record shows no evidence of such simultaneous extinctions of many species nor such deposits of brucite. Evidently the amount of CO 2 in the atmosphere and ocean has remained relatively constant throughout much of the geologic past. This calls for some source of gradual and continuous supply, over and above that from rock weathering and from the metamorphism of older sedimentary rocks. A clue to this source is afforded by the relative amounts of the different “excess” volatiles. These are similar to the relative amounts of the same materials in gases escaping from volcanoes, fumaroles, and hot springs and in gases occluded in igneous rocks. Conceivably, therefore, the hydrosphere and atmosphere may have come almost entirely from such plutonic gases. During the crystallization of magmas, volatiles such as H 2 O and CO 2 accumulate in the remaining melt and are largely expelled as part of the final fractions. Volcanic eruptions and lava flows have brought volatiles to the earth's surface throughout the geologic past; but intrusive rocks are probably a much more adequate source of the constituents of the atmosphere and hydrosphere. Judged by the thermal springs of the United States, hot springs (carrying only 1 per cent or less of juvenile matter) may be the principal channels by which the “excess” volatiles have escaped from cooling magmas below. This mechanism fails to account for a continuous supply of volatiles unless it also provides for a continuous generation of new, volatile-rich magmas. Possibly such local magmas form by a continuous process of selective fusion of subcrustal rocks, to a depth of several hundred kilometers below the more mobile areas of the crust. This would imply that the volume of the ocean has grown with time. On this point, geologic evidence permits differences of interpretation; the record admittedly does not prove, but it seems consistent with, an increasing growth of the continental masses and a progressive sinking of oceanic basins. Perhaps something like the following mechanism could account for a continuous escape of volatiles to the earth's surface and a relatively uniform composition of sea water through much of geologic time: (1) selective fusion of lower-melting fractions from deep-seated, nearly anhydrous rocks beneath the unstable continental margins and geosynclines; (2) rise of these selected fractions (as granitic and hydrous magmas) and their slow crystallization nearer the surface; (3) essentially continuous isostatic readjustment between the differentiating continental masses and adjacent ocean basins; and (4) renewed erosion and sedimentation, with resulting instability of continental margins and mountainous areas and a new round of selective fusion below.

Geological Society of America Bulletin↗
USGS1951

Older Precambrian structure in Arizona

The older Precambrian rocks of Arizona include the Vishnu, Yavapai, and Pinal schists, all overlain unconformably by nonmetamorphosed younger Precambrian rocks. The older Precambrian schists, unnamed gneisses, and associated granitic masses crop out in many of the mountain ranges southwest of the Colorado plateau. The stratigraphy and structure of the schists can be unraveled to some extent by detailed mapping, and work now in progress by the U. S. Geological Survey in the Bagdad, Prescott-Jerome, and Little Dragoon areas, is revealing folded structures trending generally northwest to northeast. Earlier work by Wilson in the Mazatzal Mountains revealed southeastward-dipping, low-angle thrust faults of older Precambrian age. In the Bagdad and Prescott-Jerome areas, a variety of igneous rocks, including rhyolite, alaskite porphyry, diorite, and gabbro, were intruded into the schists prior to the widespread invasion of granite. Only one period of orogeny followed by the intrusion of granitic rocks can be recognized in each area studied to date. The degree of metamorphism is not uniform and some of the pre-intrusive rocks are nonfoliated, whereas others are highly schistose. Some of the intrusive rocks, including granite, show the effect of dynamic metamorphism. The grade of metamorphism is low to intermediate, except near the large masses of granite where coarse-grained sillimanite-bearing schists are found.

Arizona↗
USGS1951

Iron formation and associated rocks in the Iron River district, Michigan

The iron formation of the Iron River district is part of a Precambrian sequence of strata characterized by a high iron content and varied mineralogy. The iron formation, where unoxidized, consists largely of interlaminated chert and siderite. It is underlain by a graphitic slate containing about 20 per cent iron in the form of very finely disseminated pyrite. Graywacke overlies the iron formation with at least local disconformity; this rock consists of clastic grains in a matrix of siderite or iron-rich chlorite. Above the gray-wacke is a magnetic ironstone, a laminated rock that now consists of iron-rich chlorite, magnetite, chert, and siderite, each layer being an intermixture of two or more of these constituents. The average iron content of the entire sequence, including the iron formation, is approximately 20 per cent. The rocks are only slightly metamorphosed, although the area is one of intense structural deformation. The origin of the rocks is discussed, and it is concluded that the high iron content is primary. The rocks are believed to be the products of an era of iron-rich sedimentation in which the specific iron mineral formed —sulfide, carbonate, or silicate—depended upon the immediate depositional environment. Inasmuch as the formation of iron-rich minerals continued despite extensive changes in both the basin of deposition and the adjacent land areas, the ultimate cause for such an epoch is one that transcended such factors. Evidence is presented to show that the climate of the era, when linked with certain other factors, is entirely adequate to explain the formation of these iron-rich rocks.

Michigan↗
USGS1951

Metamorphic and igneous rocks of the merrimac area, Plumas National Forest, California

The pre-granitic rocks of an area in the northern Sierra Nevada consist of metamorphosed sedimentary and volcanic series ranging in age from Carboniferous to Jurassic. Synkinematic ultrabasic intrusives, now serpentines, cut these rocks concordantly and discordantly. Magmatic series ranging from basalt to dacite and soda-rhyolite occur together with the normal basalt-rhyolite series among the meta-volcanics. The younger intrusives (Sierra Nevada series), ranging from gabbros to granodiorites and granites, show great chemical similarity to the meta-volcanic series. Furthermore, soda-rich members are common among the pre-granitic intrusives and younger dike rocks. The pre-granitic rocks were folded and metamorphosed to green schist and epidote-amphibolite facies prior to emplacement of granodiorite and granite batholiths. The later contact metamorphism affected the areas next to the contacts of the batholitic intrusions, causing crystallization of such minerals as garnet, diopside, epidote, and andalusite. The plutonic rocks obtained the space needed partly by pushing the country rocks aside and partly by stoping and assimilation.

California↗
USGS1951

Geology of the Cedar Hills, Utah

The Cedar Hills, an area of about 320 square miles in central Utah between the northern end of the Wasatch Plateau and the southern end of the Wasatch Mountains, form the boundary zone between the Colorado plateaus and the Great Basin. The oldest exposed rocks are Carboniferous, but most of the area is underlain by Upper Cretaceous and Tertiary continental sediments many thousands of feet thick. The Indianola group, about 15,000 feet thick, consists principally of coarse conglomerates and sandstones indicative of near-by orogeny and contains a tongue of fossiliferous marine sandstones showing that it is of Colorado age. This group is overlain unconformably by thick fluviatile and lacustrine deposits ranging from Montana to Eocene in age (Price River, North Horn, Flagstaff, Colton, and Green River formations), which in turn are overlain unconformably by probably late Tertiary pyroclastics. The area was subjected to come pressive orogenic disturbances in middle Cretaceous, upper Cretaceous (Montana), and probably middle Tertiary time, and to the normal faulting of the Basin-Range disturbance in late Tertiary time. © 1951, The Geological Society of America, Inc.

Utah↗
USGS1952

Method for determining the age of igneous rocks using the accessory minerals

The age of igneous rocks is determinable by a method based on the included accessory minerals . In the common igneous rocks , most of the lead is concentrated in the potassium minerals , and most of the radioactivity is in the zircon and other accessory minerals . The lead in the potassium minerals is believed to be mostly primary lead; that in zircon is probably chiefly radiogenic lead. By separating the zircon of fresh igneous rocks , determining the amount of lead with the spectrograph and the radioactivity by alpha counters, the age of Paleozoic and Precambrian rocks can be determined with an accuracy of approximately 90 per cent. Basalts and gabbros may contain too few accessory minerals for satisfactory age determination by this method . Zircon is the most satisfactory mineral for this kind of determination. Apatite and sphene give high results and therefore must contain primary lead. Sphene gives erratic results.

Geological Society of America Bulletin↗
USGS1952

Glaciation and drainage changes in the fish Lake Plateau, Utah

The Fish Lake Plateau , nearly centrally located among the High Plateaus of Utah , exhibits glacial and other geomorphic features of regional significance. The plateau is divided into two areas by Fish Lake and the wide valley of Sevenmile Creek. The Fish Lake trough is a structural basin; Sevenmile Valley may be largely erosional. Volcanic rocks of Tertiary age underlie most of the plateau ; early Tertiary sedimentary rocks are also present. Glaciated canyons with well-developed cirques are especially prominent along the east-facing sides of the Fish Lake trough and Sevenmile Valley. Ice-eroded features occur over much of the plateau top. Near the mouths of several of the glaciated canyons are two conspicuous sets of moraines. The older set is more extensive and less rugged than the younger and occurs at somewhat lower elevations. Two substages of glaciation thus recognized are correlated with Wisconsin I and II of Ray; probable correlatives of Wisconsin III, IV, and V are represented by moraines which are younger than these two sets. Fish Lake drains north into Fremont River, a tributary of the Colorado River. An abandoned southern outlet and waterfall, the latter at a higher elevation than the present elevation of the original northern bedrock divide, indicate drainage reversal. Evidence is presented which suggests that this reversal was pre-glacial and probably the result of fault-block tilting.

Utah↗
USGS1952

Sedimentary volumes in Gulf Coastal Plain of the United States And Mexico: Part I: Volume of Mesozoic Sediments In Florida and Georgia

Mesozoic sedimentary rocks are present throughout Florida and the Coastal Plain of Georgia, but chiefly in the subsurface in an area of approximately 93,500 square miles. The Mesozoic rocks in this area belong, for the most part, to the Gulf and Comanche series of the Cretaceous system. Rocks tentatively classified as part Jurassic and part Triassic underlie the Comanche series in parts of Florida and Georgia. In the northern part of the Georgia Coastal Plain, an irregular outcrop belt of sandstone and shale belonging to the early Upper Cretaceous Tuscaloosa formation borders on the south the crystalline rocks of the Piedmont. Southward from its outcrop in western Georgia, the Tuscaloosa formation dips under roughly parallel belts of the progressively younger Eutaw formation and formations equivalent to the Selma group of the Gulf series. In central and eastern Georgia, the Eutaw formation and formations equivalent to the Selma group are covered by overlaps of Tertiary formations. Conclusions in regard to the stratigraphy, structure, and thickness of the Mesozoic rocks are based largely on interpretations of the records of approximately 200 oil test wells. The total volume of the Mesozoic rocks in Florida and southern Georgia is estimated at 60,000 to 75,000 cubic miles.

Florida, Georgia↗
USGS1952

Magmatic differentiation in tertiary and quaternary volcanic rocks from Adak and Kanaga Islands, Aleutian Islands, Alaska

Samples of 17 volcanic rocks of Tertiary and Quaternary age from Adak and Kanaga islands have been chemically analyzed and studied microscopically. Spectrograms have been made of 10 of them. The rocks from Adak represent one center of possibly older Tertiary age and two centers of younger Tertiary or Quaternary age. The rocks from Kanaga Island represent both a shield volcano of possibly Tertiary age, partly destroyed by the formation of a caldera, and a young cone of Quaternary age that has grown within the caldera. All the rocks are basalt or andesite. Modally, all are characterized by relatively large crystals of plagioclase more calcic than andesine, and by one or more of the following ferromagnesian minerals: olivine, hypersthene, augite, and hornblende. Apatite and iron ores are common, and late silica minerals and orthoclase occur interstitially in the groundmasses of some rocks . As analyses of no more than four samples are available for each center, the small differences between sets of analyses representing different centers are of doubtful significance. Consequently, the analyses representing all the centers have been plotted on each of the several diagrams used. The several types of variation diagrams show that the province is a calc-alkaline one. The alkali-lime index is in the neighborhood of 63. This very high value is comparable with that for Katmai and is only slightly less than the maximum for the Japanese volcanic rock series. The quantities of minor constituents present are not exceptional for the rock types analyzed; the rocks from Adak are apparently more strontium-rich than those from Kanaga . The chemical analyses of the more basic rock types, as compared with the average analysis of plateau basalt, suggest that the Aleutian parental magma could have been derived from a plateau basalt magma by the addition of plagioclase and the subtraction of pyroxene, iron ore, and some quartz. The distribution of the minor elements can be explained more easily by postulating that, at least on Kanaga Island , some sediments have been assimilated. The derivation of the analyzed rocks from the Aleutian parental magma is most easily explained by the hypothesis that the plagioclase remained in suspension while the ferromagnesian minerals were settling out.

Alaska↗
USGS1952

Pimpled plains of Eastern Oklahoma

Patterns formed by the networks of furrows separating the natural mounds of pimpled plains in eastern Oklahoma are regarded as attributable to shrinkage-polygon systems of coarse texture comparable to those occurring (1) in mound-studded parts of the northwestern United States that are underlain by vertically jointed basalt, (2) in tracts of Alaskan tundra that are occupied by ice-wedge networks, and (3) in beds of playa lakes in the arid southwest that are cut by systems of giant desiccation fissures. While the inter-mound furrow networks characteristic of pimpled plains in the mid-continent region may owe their origin to former frigid climatic conditions, one of a number of alternative possibilities is that the peculiar configuration of these surfaces, as exemplified in eastern Oklahoma , has resulted from erosion of systems of giant soil polygons caused by desiccation. The time of origin of the pimpled plains of eastern Oklahoma is believed to have been not earlier than late Pleistocene.

Oklahoma↗
USGS1952

Late quaternary geology and frost phenomena along Alaska Highway, Northern British Columbia and Southeastern Yukon

Reconnaissance field work along the Alaska Highway in northern British Columbia and southeastern Yukon furnishes preliminary data on the later Quaternary history of the region, and on the processes and results of intensive frost action. Extensive erosion surfaces were developed prior to glaciation, such as the Alberta Plateau of northeastern British Columbia and the Yukon Plateau in southern Yukon . In the region from Dawson Creek to Fort Nelson, British Columbia , the drift is dominantly a slightly weathered bouldery clay till of Wisconsin age, deposited by ice that came from the east. In the northern Rocky Mountains, the last eastward advance of the Wisconsin glaciers to the mountain front preceded the maximum westward advance of the ice sheets. In the foothills belt west of the Highway , the tills of these two advances are separated by lake deposits. Much of the drift is probably pre-Altamont in age and was subjected to vigorous frost action during the Altamont substage. The climate ameliorated perhaps with the advent of the post-glacial optimum and possibly coincident with the development of prairies. A recent change from prairie to forest perhaps indicates a slight cooling in recent time. In the northern Rocky Mountains, four substages of Wisconsin glaciation are recognized tentatively on the basis of morainal deposits and outwash terraces. The upper Liard basin is characterized by extensive pitted outwash plains, probably of late Wisconsin age. From Teslin Lake to Whitehorse, the Highway is bordered by extensive terraces of gravel and sand deposited in ice-marginal streams and lakes. Intensive frost action has modified pre-existing land forms and has produced a wide variety of features, such as talus, blockfields, stone rings, stone stripes, and terraces. Long smooth slopes, chiefly due to mass movements such as solifluction, are characteristic of the landscapes. These slopes and ancient soil structures extend down into forested areas and probably developed prior to the advent of forests, doubtless prior to the post-glacial optimum. Phenomena resulting from intensive frost action at the present time are restricted largely to areas above timber line.

Alaska, Yukon, British Columbia↗