R-3 Repository :: Browsing by Author "Rogers, John J. W."

Browsing by Author "Rogers, John J. W."

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A geochemical investigation of the Pre-Cambian Knife Lake Series, northeastern Minnesota
(1969) McKay, Sheila Mahan; Rogers, John J. W.
A geochemical study was made of the Precambrian eugeosynclinal graywackes and slates of the Knife Lake Series in northeastern Minnesota. Unlike some other graywacke sequences, these sedimentary rocks show no systematic secular variations in chemical or mineralogical composition within the stratigraphic sequence. The average composition of the Knife Lake graywackes is similar to the composition of other Precambrian graywackes. A comparison of the composition of the Precambrian graywackes with Paleozoic and Mesozoic graywackes indicates that the Precambrian graywackes are enriched in Fe, Mg and Ca relative to the younger graywackes. The average The/U ratios of the Knife Lake graywackes and slates are 4.5 and 4.8 respectively. Assuming that any variation in the The/U ratio is caused solely by radioactive decay since the time, about 3 by. ago, that the Knife Lake rocks were formed, the original Th/U ratios are calculated to have been 3.1 to 3.6. These values are well within the range 3.0 to 4.0 characteristic of Paleozoic and younger material. Because graywackes represent a comprehensive sample of their crustal source rocks, the Th/U ratio of newly formed crustal material may be presumed to have been relatively constant throughout all of geologic time.
A geochemical investigation of the Valley Spring gneiss and Packsaddle schist, Llano Uplift, Texas
(1962) Billings, Gale K; Rogers, John J. W.
Samples of the Valley Spring gneiss and Packsaddle schist were taken along two profiles in northern and south-eastern Llano County, Texas. These samples were analyzed for the major oxides, thorium, and uranium. A comparison of the Valley Spring gneiss and Packsaddle schist analyses with analyses of other rock types indicated:. 1) the parent rock of the Valley Spring gneiss could have been granitic or arkosic material: 2) banded amphibolites of the Packsaddle schist were originally mafic tuffs mixed with calcareous sediments; and 3) the parent rocks of the non-banded amphibolites of the Packsaddle schist were iron-rich basaltic material, probably tholeiitic.
A lithologic analysis of the Galveston beach sand with special emphasis on heavy minerals
(1958) Adams, Henry Clay; Rogers, John J. W.
In this thesis, mineralogical and textural analyses of the sand-silt beach ,deposits of Galveston. Island, Texas, are presented, with special emphasis on. heavy minerals. It is the intent of the author; 1) to describe the min.eralogical composition. of each of the heavy min.eral suites, an.d to test the significan.ce of variations foun.d among 4 of the more dominant heavy minerals (zircon, tourmaline, hornblende, and garnet); 2) to describe the size-distributions of the zircon and tourmaline present in. each heavy mineral suite; and 3) to postulate means or con.ditions by which any mineralogical or size-distribution. variations may be explained. The present study is concerned with the sand beach which circumscribes Galveston. Isla-nd. The island is composed of recent sandy and silty sediment and occupies a position at the mouth of Galveston. Bay some 50 miles south of Houston. Inasmuch as Galveston Island is essentially an over-sized off-shore bar, which, for the most part, separates the Gulf of Mexico from Galveston Bay, the beaches that rim the island consist of two contrasting sedimentary environments. A frontal beach environment occurs on. the Gulf side of the island, whereas a back-bay environ.ment exists on the bay side. The present thesis is largely concerned with the determination. of any consistent differen.ces, mineralogical or textural, which might exist between. the beach sands formed under these differing conditions. Galveston. Island extends in a NE - SW direction and is approximately 30 miles long. Samples were taken on both sides of the islan.d at roughly 5-mile intervals. This sam.plin.g procedure made possible the grouping of samples in pairs, one from the front-beach and on.e from the back-beach, and. provided opportunity for a continuous check of variations as the laboratory work progressed. The sampling procedure and. sample grouping is explained. more thoroughly in the next section. This thesis is the third in a series concerned with the petrologic and lithologic properties of Gulf Coast sediments, the two previous being written by Powell (1957) and Dawson (1958).
A lithologic investigation of the Manlius and Coeymans limestones
(1958) Fessenden, Franklin W; Rogers, John J. W.
A petrologic study of a portion of the Lower Beaumont clay
(1957) Powell, William Frank; Rogers, John J. W.
Petrologic studies have been made on sixteen samples of the Lower Beaumont clay collected from localities varying both horizontally and vertically on The Rice Institute campus, Houston, Texas. The samples were analyzed to determine the percentage of clay and other minerals, the variety and types of heavy minerals present, the percentage of the heavy mineral suite comprised by each type of mineral, and the size distribution of the zircons. The main concern of this thesis is with the heavy minerals. For many years geologists have been aware that a study of heavy minerals, that is, minerals with a density greater than 2.9* would yield information concerning the source, mode of transportation, depositional environment, and maturity of a sediment. The details of how these characteristics can best be obtained, however, are not obvious. This paper will discuss the possibility of using the character of the heavy mineral suite and the size distribution of the zircons as a guide to the origin and environment of formation of the Lower Beaumont clay. It is the intent of the Department of Geology at The Rice Institute to make a continuing study of the size distribution of heavy minerals of sediments from all types of depositional environments and from the site of deposition upstream to the fresh source rock (Rogers, 1956). The present Investigation is the first in this series.
A study of the non-opaque heavy minerals in the Lissie sandstone
(1958) Dawson, Ross Elmo; Rogers, John J. W.
The work described In the present thesis comprises the second part of a study currently conducted by the Geology Department of The Rice Institute (Rogers, 1956). Powell (1957) wrote the original paper, The project is concerned with the size distribution of non-opaque heavy minerals in sediments formed in various depositional environments, from various source rocks, and at different distances from the source rock. The formation studied for this paper is the Lissie formation of Pleistocene age, which crops out along the Gulf of Mexico in Texas in a band parallel to the present coast and 50 to 100 miles inland (Pig. 1). The writer hopes that the data presented in this study will prove valuable enough to the subsurface stratigrapher that he will use similar methods in the future In the study of the similar sand bodies at depth in the Gulf Coast region. Petrologic studies have been made on samples from 10 localities in and near Harris County, Texas. The samples range from siltstones to conglomeratic sandstones. Most are of Lissie age, but one locality (samples 1-7) may be a Beaumont (upper Pleistocene) levee deposit, while two others (samples 8 - 13) may be of upper Citronelie (Pliocene) age (Doering, 1956). All samples were analyzed as described on pages 8 - 12. For each sample the writer determined the percentages of the non-opaque heavy minerals, the size distribution (by weight) of the entire sample, and the size distributions (by number) of the zircon and tourmaline grains (the most abundant heavy minerals).
A study of the relationships between porosity and certain size parameters of uncemented natural sands
(1959) Head, William Burres; Rogers, John J. W.
A study of the suspended load of the Trinity River, Texas
(1966) Rice, Raymond Howard; Rogers, John J. W.
The Trinity River drains approximately 17,500 square miles of north-central and eastern Texas. Its average annual discharge is 5,166,000 acre-feet and in water year 1965 it carried 5,308,000 acre-feet of water. The river's average annual suspended load contribution to its delta is roughly 3000 acre-feet. During 1965 over 50% of the Trinity River's discharge and over 60% of its suspended load were transported by two major floods. The suspended material delivered to the delta contains about 25% sand, 30% silt, and 45% clay.
A textural study of beach and river sediments along the Texas Gulf Coast
(1959) Strong, Cyrus; Rogers, John J. W.
The object of this study was to compare the textures of samples from beach and river sands of the Texas Gulf Coast. The main problem involved determining what criteria, if any, could be most useful in detecting the origin of lenticular sand bodies for which small samples, such as well cores, are available. Owing to the differences in the nature of the beach and river environments, and to the difficulty of obtaining representative samples from the rivers, samples which appeared similar in grain size and sorting were chosen from each type of deposit. Beach samples were taken along the foreshore of the barrier islands, and the river samples were taken from bars, terraces, flood deposits, and river bottoms within fifty miles of the coast. Much work has been published on the modern sediments of the Texas Gulf Coast, partially under the stimulus of A, P. I. Project 51. Little attention, however, has been directed toward the Texas rivers which are contributing material to the lagoons and barrier islands. The general facies relations of sediments along the Gulf Coast have been described by several writers. Among these, Greenman and LeBlanc (1956) discussed the major facies present on the floor of the northwestern Gulf of Mexico. Shepard and Moore (1955) studied the characteristics of the sediments of the central Texas coast in the Rockport area, and proposed their "coarse-fraction" method of differentiating the various nearshore and continental shelf environments. An investigation into the significance of various grain size parameters was conducted on a sand bar in the Brazos River by Polk and Ward (1957). Using some of these methods, Mason and Polk (1958) found it possible to differentiate beach, dune, and aeolian flat environments on Mustang Island, Texas, by grain size analysis. The value of laminations and internal features in defining depositional environments has been pointed out by Moore and Scruton (1957). McKee (1957) has also described, with the aid of excellent photographs, the types of lamination and stratification common in beach, lagoonal, and nearshore sediments. Several recent papers deal with the transportation of materials on the Texas beaches. Curray (1956) pointed out that sand grains along beaches and streams tend to be oriented with their long axes parallel to the direction of the depositional agent. Thus, if the origin of such a deposit is known, its trend can be predicted. Beal and Shepard (1956) noted a sharp increase in sand grain roundness going from the beaches into the sand dunes, and attributed this to selective wind transportation of the more rounded grains from the beaches. Bradley (1957)> from a study of three profile traverses across the northern end of Mustang Island, found a tenfold volume Increase of the heavy mineral content in the barrier island dune's over the offshore sediments (0.04$ to 0.45$); he attributed this variation to selective wind transportation of the heavy minerals from the beach. The influence of source rocks on the heavy mineral suites of the major Texas rivers and beaches has been discussed by Bullard (1942). Adams (1958) described the competition and size distribution of heavy minerals on the foreshore and backshore of Galveston Island, Texas. Sedimentation rates in some of the Texas estuaries and lagoons were discussed by Shepard (1953); he arrived at an average rate of three feet per century prior to compaction. The potential application of the results of the present study are discussed in this thesis. The determination of the origin of lenticular "shoestring" sand bodies presents a difficult problem to petroleum geologists, especially where detailed sub-surface control is not available. It is believed by the writer that a method of analysis such as outlined in this thesis may provide important clues for the differentiation between sinuous channel deposits and the more linear offshore bar deposits.
An investigation into the failure of neat cement cylinders under independently controlled confining pressure, pore pressure, and axial force
(1961) Victory, Sidney P; Krahl, Nat W.; Sims, James R.; Rogers, John J. W.
The purpose of this investigation was to study the effect of independently controlled confining pressure and pore pressure on the ultimate axial compressive strength of neat cement cylinders. In trying to achieve this purpose the ultimate strength, deformation, and volume change of the material have been studied. The test program consisted of a variation in confining pressure and pore pressure from 0 to 20, 000 psi. For any one test the confining pressure and pore pressure were held constant and the axial load was increased until failure of the specimen occurred. The results indicated that Mohr's Theory by no means begins to explain the complex nature of the failure of the material. An envelope of failure was defined by the circles of stress; however, the failure angles indicated by Mohr's graphical solution did not compare well with those obtained directly from the specimens. An empirical relation of the form: fm= fc + a p 0.81was presented. This relation was found to represent data previously presented as well as the data in this investigation.
Depositional environment and regional significance of the sakaka sandstone, northwestern Saudi Arabia
(1974) Sharief, Farooq A.; Rogers, John J. W.
The Sakaka Sandstone of reported Middle Cretaceous age mostly crops out within Al Jawf area, northwestern Saudi Arabia. The formation is mostly sandstone with some siltstone and clay. The purpose of the investigation was to sub-divide the formation into mappable lithologic units and to determine the age of the formation more precisely on the basis of microfaunal study. A detailed petrographic and structural study was attempted to interpret the depositional environment and the source rocks of the formation. In addition, the regional significance of Al Jawf area will be provided from the results of this study. The principal conclusions drawn from this study were: (1) intensive stratigraphic work has delineated several key beds which afford detailed correlation and divide the sediments into three major members; lower, middle, and upper; (2) no microfossils have been reported from microfaunal study, and no surface evidence for reported Middle Cretaceous age has been found (i.e., the lower contact of the Sakaka Formation is conformable and gradational with the underlying sediments of the Lower Devonian); (3) facies analysis suggests that the depositional environment of the formation changed from fluvial deposits in the lower member to windblown deposits in the middle member and to shoreline sediments in the upper member; (4) measurements of directional features indicate a paleocurrent regime from the southeast to west and southwest directions for the sediments of the lower member; from a southwest direction for the sediments of the middle member; and from various direction for the uppermost part of the upper member; and (5) the Sakaka Sandstone was a positive feature of the Jawf-Rutbah arch, and this arch has acted as a partial barrier to the sea from Mesozoic to Early Tertiary times.
Detailed petrology of the Buchanan massif, Llano and Burnet counties, Texas
(1967) Cook, Beverly Kay Gatlin; Rogers, John J. W.
The Buchanan massif is a Precambrian pluton in the central Texas area, midway between the towns of Llano and Burnet, It shows a roughly concentric zonation over its outcrop area of about; 100 square miles. The general zonation is from fine-grained rocks in the interior of the pluton to coarse-grained and porphyritic rocks near the margin, and the trends of modal composition indicate an increase in acidity toward the margins. This reverse zonation is here explained by an equilibrium (equal fugacity) distribution of water in the intruded magma shortly after emplacement, The higher water content of the cooler, outer zones depresses the crystallization temperature of the magma below the actual temperature in the outer regions, thus allowing the interior to crystallize first. Progressive crystallization outward further increased the water content of the margins, and pegmatitic segregations attest to the saturation of the melt in the outer regions. The high water content maintained crystallization in the two-phase, subsolidus feldspar region throughout most of the pluton. The Enchanted Rock batholith and other less well-known plutons in the central Texas area exhibit the same textural and modal trends as the Buchanan massif, and it is proposed that their crystallization histories are similar. The high water content of the magmas may be indicative of derivation from remelting of crustal rocks.
Differentiation of a lamprophyre sill
(1959) Longshore, John David; Rogers, John J. W.
Differentiation trends in rock bodies of various sizes and types have been studied, from different viewpoints and with contrasting results, by many geologists in this country and abroad* Such studies are of major importance, for magmatic segregation has been proposed by several authors as a means of generating various rock sequences (Bowen, 1956; Wager and Mitchell, 1951; Walker, 1940). Bowen has proposed that most of the rock types occurring at tdie earth's surface today may have been produced chiefly by fractional crystallization of a primary magma, and other authors (among others, Walker, 1953; Edwards, 1942) have demonstrated that rock melts are differentiated into phases of different compositions and textures during crystallization. No detailed work has been published on the differentiation of lamprophyric rocks, which though of minor abundance, are widespread in granitic terranes. It was therefore considered of value to sample and study a well defined lamprophyre intrusion in the hope that definite differentiation trends might be discerned and that, thereby, some information regarding the genesis of this little understood rock type might be gained. The sill chosen for study is located in the La Plata Mountains, southwestern Colorado, in the northeastern part of the La Plata quadrangle (Figure 1). The sill is sufficiently well exposed that it may easily be sampled from upper to lower contact. The contacts are well defined, and there has been little contamination by the wall rock. The sill has evidently been only slightly deformed since the magma was intruded, the only evidence of disturbance being a fault of about thirty feet displacement near the center of the sill. No detailed petrography of the intrusion had been undertaken previously, The choice of this particular body for the present study was made on the basis of its good exposure and on a general field and mineralogical description given by Cross (1899), who indicated an apparent layering within the sill. The field work consisted of sampling the sill vertically from upper contact to lower contact at intervals of one to five feet. A total of thirty-three hand specimens was thus collected, and thin sections of these samples were then examined petrographically, Modal analyses of each section were made by point-counting 1,000 to 1,300 points. Detailed optical properties of the pyroxenes and feldspars were determined with the aid of a Zeiss four-axis universal stage. This thesis is concerned chiefly with the microscopic analysis of the rocks collected in the field and the results derived from this analysis. A detailed petrographic description of the rocks is given* and some conclusions regarding the manner of differentiation of the sill are reached. A possible mode of genesis of the lamprophyre magma, based on results of this investigation, is postulated.
General chemical composition of Precambrian crust in the Llano Uplift, central Texas
(1975) Johnson, Linda Ann; Rogers, John J. W.
Many investigations have been made of the late Proterozoic crystalline rocks in the Llano Uplift, central Texas. No comprehensive chemical treatment of this shield area, however, has as yet been reported. Published chemical and modal analyses and planimetric analysis of geologic maps have been applied in this study to generate estimates of major element chemistry for important contributing lithologies and for the Llano Precambrian crust as a whole. Comparison of average compositions derived for metamorphic rock units in the Llano exposure with published compositions for undeformed rock sequences indicates that: (1) the basal pink gneiss (Valley Spring Gneiss) is similar chemically to rhyolite but slightly higher in Fe, Mg, and Ca; and (2) parts of the overlying, more mafic, metasedimentary and metavolcanic unit (Packsaddle Formation) are chemically similar to typical eugeosynclinal lithologies but that it does contain some abnormally high SiO2 and low AI2O3 metasedimentary rocks. Comparison of the average chemical composition of the one-billion-year-old continental crust exposed in the Llano area with average chemical compositions derived for Archean and Proterozoic rocks exposed in the Canadian shield indicates a continuation of trends of crustal chemical evolution proposed by Fahrig and Eade (1971). Decreases in MgO, Na2O, and CaO, and increases in are observed from the Archean to the youngest Precambrian Llano crustal averages. Higher SiO2 and total alkali , and lower Al2O3 and total mafic oxide components are also evident in the Llano area continental crust relative to the older Canadian shield.
Geochemical and petrological studies of the Lost Creek Gneiss, Mason and McCulloch Counties, Texas
(1960) Ragland, Paul Clyde; Rogers, John J. W.
Geological and geophysical studies of a portion of the Little Llano River Valley, Llano and San Saba counties, Texas
(1960) Almy, Charles Coit; Rogers, John J. W.
A geologic study of the Precambrian Valley Spring gneiss was made in the Babyhead-Wilberns Glen area in northern Llano County, Texas, Magnetic and gravity surveys were made over this and the surrounding areas to determine the relationships of the major rock units: Valley Spring gneiss, Packsaddle schist, associated granite intrusions, and Paleozoic sediments. The area studied lies on the northeast flank of the northwest-trending Babyhead anticline, which forms the major structural control. The Valley Spring gneiss was mapped as four phases: felsic gneiss, mafic gneiss, feldspar-quartz-amphibole-pyroxene gneiss, and biotiteamphibole schist. Two meta-diabase dikes were also mapped. The composition of the Valley Spring gneiss, the constancy of its parallel bands, and its conformity and gradation into the metasedimentary Packsaddle schist indicate a parent rock composed primarily of impure sand stone. Preservation of original structures indicates a lack of mobilized constituents during metamorphism. The Valley Spring gneiss belongs to the quartzo-feldspathic mineral assemblage in the staurolite-quartz subfacies of the almandine-amphibolite facies. After metamorphism the area studied was folded and then intruded by granitic material. From middle Precambrian time to the present, the area studied has under gone only cycles of erosion, deposition, and mild uplift except for faulting at the end of the Paleozoic. The gravity survey indicates a synclinal body of schist trending northwest under the sediments and lying over the Valley Spring gneiss on the northeast flank of the Babyhead anticline. The magnetic survey indicates that the Packsaddle schist does not extend under the sediments to the east, and that mineralization occurred along the llanite dike.
Grain size distributions of various materials in an abrasion mill
(1963) Schubert, Carlos, 1938-; Rogers, John J. W.
Wet abrasion of sand-sized quartz and orthoclase in polyethylene bottles for 912 hours showed that abrasion of fine material is practically negligible, in agreement with Kuenen (1959). The size distributions of the sand. sized quartz and orthoclase remained unchanged. The size distributions of sand-sized quartz, orthoclase, plagioclase, and hornblende abraded off of pebbles appear to be lognormal by number percentage. There is considerable question as to the accuracy of the method of counting grains. The size distributions of quartz and orthoclase crushed or abraded to sized less than 0.5 mm appears to be lognormal, which is in disagreement with Rogers, Krueger and Krog (1963). Several tentative reasons are given. Roundness and sphericity of both crushed sand-sized quartz and orthoclase and sand-sized quartz and orthoclase abraded off of pebbles increase with time in the abrasion mill, the rate of change being greater for the fine sand sizes than for the coarse sand sizes. One result of the experiments described in this report is the indication that the size distributions of natural materials seem to be determined by the size distributions of the source rocks. This result is the basis for criticism of the concept of tectonic control of grain size distribution used by Cadigan (1961). It is concluded that the processes of abrasion, sorting, mixing with other sediments, etc. are at least as important as tectonic environment in the production of particular size distributions in sediments.
Late Cenozoic basalts from the Basin-Range province, western United States
(1969) Leeman, William Prescott; Rogers, John J. W.
Petrographic and chemical analyses demonstrate that late Cenozoic mafic lavas from the Basin-Range province, western United States, are predominantly alkali-olivine basalts. Associated with these lavas are lesser volumes of basaltic andesite which appear to be differentiates from the more primitive alkali basalts. Late Cenozoic basalts from adjacent regions (Columbia River Plateau, Snake River Plain, Yellowstone area, High Cascades and Sierra Nevada) are predominantly tholeiitic. This apparent petrologic provincialism is supported by complementary variations in heat flow, seismic velocities, crustal thickness, magnetic anomalies and geologic setting. Alkali-olivine basalts from Japan and eastern Australia are analogous to those from the Basin-Range province both in composition and tectonic environment. It is suggested that these lavas are the products of a unique environment characterized by high heat flow and a thin crust. Recent melting experiments on peridotites and basalts and measurements of heat flow allow limits to be placed on the depth of origin of Basin-Range alkali-olivine basalt magmas. It is proposed that these lavas are produced by partial melting (less than 20%) of peridotitic mantle material at depths between 40 and 60 km in response to an elevated geothermal gradient. The basaltic andesites may be derived from hydrous alkali basalt magma by fractionation at depths of 30 to 40 km.
Petrochemical study of the Clarno Group: Eocene-Oligocene continental margin volcanism of north-central Oregon
(1975) Novitsky-Evans, Joyce Marie; Rogers, John J. W.
The Clarno Group is a calcalkaline volcanic association developed upon the American plate margin in central Oregon during Eocene-Oligocene time in response to eastward subduction of oceanic terrain beneath western North America.- This volcanic association is characterized by the presence of flows of andesite, basalt, quartz latite and rhyodacite, as well as andesitic and rhyodacitic tuff. Mudflows, agglomerates, lake beds, and volcanogenic sediments are intercalated with the flows and tuffs. Chemical analysis of major and minor elements in addition to Rb and Sr have been carried out on the flow rocks by X-ray fluorescence and, in the case of Na, by neutron activation techniques. The chemical character of the Clarno volcanics fits spatially into the overall chemical continuum of a major east-west calcalkaline province which extends from the Western Cascades of Oregon to western Montana. This province notably displays increasing K2%, K2/Na2 ratios, and the increasing abundance of differentiated rock types in an eastward direction normal to the continental margin. The Clarno volcanics are geographically located near the western margin of the calcalkaline province. Their proximity to the Early Tertiary continental margin is demonstrated by the juxtaposition of the Coast Range tholeiitic province and the calcalkaline province of the Western Cascades. Comparison of the Clarno volcanics with two volcanic provinces (Aleutian Islands and Andes Mountains) that are associated with presently active subducting margins, reveals a close chemical similarity between the Clarno and the Aleutian Island volcanic rocks. The composition of the Clarno volcanics, combined with tectonic and stratigraphic considerations, suggests that the suite formed on poorly developed continental crust; this crust may have been similar to that of the modern western Aleutians, having recently developed from a crust of oceanic character. Considering this, the present 4-kilometer-thick crust in central Oregon is an indication that crustal thickening and processes of continental development have been active on the western margin of the American plate. The Clarno volcanism is a manifestation of compressive plate interactions when the crust underlying the volcanic province was still sub-continental in character.
Petrology of the Cenozoic volcanic rocks of the basal Clarno Formation, central Oregon
(1973) Wilson, Patricia McDowell; Rogers, John J. W.; Baker, Donald R.; Lallemant, Hans G. Avé
The Clarno Formation is a volcanic unit of Eoceneearly Oligocène age in central Oregon. It is unconformably underlain by the Cretaceous clastic rocks of the HudspethGable Creek Formations and succeeded by the tuffs of the John Day Formation. The basal 2-3 feet of the Clarno Formation, consisting of flows, lahars, and pyroclastics, was examined near the town of Mitchell. The flow units were sampled for major element analysis. Analyses were performed for twenty-six basal flows by means of x-ray fluorescence and neutron activation. Several chemical parameters were used to delineate the calcalkaline nature of the basal Clarno Formation: AFM diagrams of Clarno data reveal no iron enrichment; K2O contents range from .4% - 3.56%; KgO/NagO ratios are generally lower than .5* Chemical criteria were also used to classify the Clarno Formation as continental, including: the slope of the potash vs. silica variation diagram, the level of KgO at 55% SiOg, the values of T = [(AlgOg - Na2)/Ti2], and the values of the ratio of total iron to magnesium. An attempt is made to relate the geochemistry of the basal Clarno Formation to the general tectonic regime of the developing continental margin of the Cenozoic Northwestern United States.

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