David A. Lindsey

Glacial Sedimentology of the Precambrian Gowganda Formation, Ontario, Canada

The Gowganda Formation is part of the thick Huronian sequence of Precambrian sedimentary rocks that crop out in central Ontario from Lake Superior to Quebec. Although it has long been considered to be glacial, recent work on submarine slump and turbidite deposits has reopened the question of its origin. This study was made to determine its origin and paleogeography. Till-like conglomerates, varved argillites, and abundant dropstones characterize the Gowganda and provide strong evidence for a glacial origin. Pebble fabric parallel to regional paleocurrents, rare striated and grooved pavements, and abundant unweathered detritus are also in harmony with a glacial origin. Local thin-bedded sandstones contain flame structure, graded bedding, contorted bedding, and rippled tops, suggesting deposition by turbidity flows. Association of these sandstones with varved argillites and rafted stones indicates that Gowganda turbidites are glaciolacustrine. Along the southern margin of the Gowganda, at Whitefish Falls, thick, laterally continuous till-like conglomerates contain internal stratification indicative of subaqueous deposition. Argillites that lack varved structure and associated silty limestones suggest a glacial marine environment. In the Cobalt region the apparent long axes of pebbles in conglomerates show a predominant north-south alignment. In the Bruce Mines-Elliot Lake region, the orientation of the long axes of pebbles is more variable. Differences in orientation are related to stratigraphic position. Ripple cross-lamination in sandstones that are interbedded with argillite indicates south-trending paleocurrents. Distribution of varved argillite, silty limestone, and probable marine argillites suggests a northern fresh-water facies and a southern marine facies. Abundant plutonic pebbles and feldspar indicate that the Gowganda ice sheets eroded a northern plutonic terrane and deposited much of their sediment load on the underlying Huronian sediments to the south.

Glacial marine sediments in the precambrian Gowganda formation at Whitefish Falls, Ontario (Canada)

Abstract Study of a well-exposed section of the Gowganda Formation at Whitefish Falls, Ontario, suggests criteria for the recognition of glacial marine sediments. Thickness of hundreds of feet, lateral continuity, faint internal stratification, sorted lenses of sandstone and conglomerate, and dropstones characterize much of the tillite. Thickness of hundreds of feet, lateral continuity, and marked development of irregular and lenticular laminae instead of varve structure characterize much of the argillite. These characteristics, together with evidence for a nearshore, marine-to-deltaic environment for the overlying beds, suggest a glacial marine interpretation even though no fossil evidence is available. Massive tillite, tillite containing faint stratification and lenses of sorted conglomerate and sandstone, and dropstone-bearing argillite, all of which interfinger, suggest a glacial marine environment composed of: (1) a subglacial facies; (2) a periglacial facies; and (3) a facies of marine ice rafting, respectively. Separation of the two tillite-bearing members by as much as 700 ft. of argillite containing no dropstones suggests two distinct ice ages during Gowganda time.

The distribution and mobility of uranium in glassy and zeolitized tuff, Keg Mountain area, Utah, U.S.A.

Abstract The distribution and mobility of uranium in a diagenetically altered, 8 Ma old tuff in the Keg Mountain area, Utah, are modelled in this study. The modelling represents an improvement over similar earlier studies in that it: (1) considers a large number of samples (76) collected with good geologic control and exhibiting a wide range of alteration; (2) includes radiometric data for Th, K and RaeU (radium equivalent uranium) as well as U; (3) considers mineralogic and trace-element data for the same samples; and (4) analyzes the mineral and chemical covariation by multivariate statistical methods. The variation of U in the tuff is controlled mainly by its primary abundance in glass and by the relative abundance of non-uraniferous detritus and uraniferous accessory minerals. Alteration of glass to zeolite, even though extensive, caused no large or systematic change in the bulk concentration of U in the tuff. Some redistribution of U during diagenesis is indicated by association of U with minor alteration products such as opal and hydrous Fe−Mn oxide minerals. Isotopic studies indicate that the zeolitized tuff has been open to migration of U decay products during the last 0.8 Ma. The tuff of Keg Mountain has not lost a statistically detectable fraction of its original U, even though it has a high (≈ 9 ppm) trace U content and has been extensively altered to zeolite. Similar studies in a variety of geological environments are required in order to identify the particular combination of conditions most favorable for liberation and migration of U from tuffs.

Heating, cooling, and uplift during Tertiary time, northern Sangre de Cristo Range, Colorado

Paleozoic sedimentary rocks in a wide area of the northern Sangre de Cristo Range show effects of heating during Tertiary time. Heating is tentatively interpreted as a response to burial during Laramide folding and thrusting and also to high heat flow during Rio Grande rifting. The regional extent of heating is shown by the distribution of low-grade metamorphic minerals, altered conodonts, and reset fission-track ages throughout much of the study area. Alteration of conodonts to a conodont alteration index (CAI) of 4.0 suggests that temperatures reached ∼200 °C in the central part of the area. Temperatures may have reached 300 °C beneath Laramide thrusts on the west side of the range, where conodonts were altered to a CAI of 5.0, and where chloritoid and andalusite are found in sedimentary rocks of Pennsylvanian age. The lowest temperatures that were determined by conodont alteration (CAI = 1.0–2.0, Fission-track ages of apatite across a section of the range show that rocks cooled abruptly below 120 °C, the blocking temperature for apatite, ∼19 Ma ago. Cooling was probably in response to rapid uplift and erosion of the northern Sangre de Cristo Range during early Rio Grande rifting.

Minturn and Sangre de Cristo Formations of Southern Colorado--Prograding Fan-Delta and Alluvial-Fan Sequence Shed from Ancestral Rocky Mountains: ABSTRACT

The Middle Pennsylvanian Minturn Formation and the Pennsylvanian and Permian Sangre de Cristo Formation of the northern Sangre de Cristo Range form a 4,000-m (13,000-ft) thick, progradational sequence of fan-delta and alluvial-fan deposits. This sequence was deposited along the western margin of the central Colorado trough during faulting and uplift of the late Paleozoic Uncompahgre highland of the Ancestral Rocky Mountains. The Minturn Formation is composed mostly of sandstone and shale deposited by fan deltas that prograded into the central Colorado trough. The Minturn of the northern Sangre de Cristo Range is divisible into (1) a turbidite-bearing facies, (2) a limestone-bearing facies, and (3) a red-bed facies. The turbidite-bearing facies is interpreted as deposits of fan deltas that prograded onto the sea bottom below wave base. The limestone-bearing facies is interpreted as deposits of fan deltas that prograded onto a shallow sea bottom above wave base. Turbidites and shallow-marine limestones, although they make up only a minor part of the Minturn Formation, are mutually exclusive deposits that serve to distinguish the two facies. In the limestone-bearing facies, sandstones containing deltaic fore ets overlie thin shallow-marine limestones and are considered diagnostic of that facies. Both facies contain thick intervals of sandstone and shale interpreted as deltaic and alluvial deposits. Where it onlaps the Uncompahgre highland, the lower part of the Minturn Formation contains quartzose and arkosic red beds of probable alluvial origin. The continental Sangre de Cristo Formation conformably overlies the Minturn Formation basinward, but it unconformably overlies Minturn Formation and Precambrian basement near the Uncompahgre highland. The Sangre de Cristo Formation contains (1) a sandstone facies deposited on the distal surfaces of alluvial fans, and (2) a conglomerate facies (Crestone Conglomerate Member) deposited on the proximal surfaces of alluvial fans. The sandstone facies consists of fining-upward cycles of red conglomeratic sandstone and siltstone interpreted as braided-stream deposits. The conglomerate facies consists of poorly sorted conglomerates interpreted as debris-flow and mudflow deposits, and sorted conglomerate and sandstone interpreted as streamflow and sheetflow deposits. End_of_Article - Last_Page 854------------

Geologic Information for Aggregate Resource Planning

Construction and maintenance of the infrastructure is dependent on such raw materials as aggregate (crushed stone, sand, and gravel). Despite this dependence, urban expansion often works to the detriment of the production of those essential raw materials. The failure to plan for the protection and extraction of aggregate resources often results in increased consumer cost, environmental damage, and an adversarial relation between the aggregate industry and the community.

Copper and uranium in Pennsylvanian and Permian sedimentary rocks, northern Sangre de Cristo Range, Colorado

.......................................................................................................................... 1 Introc:luction .................................................................................................................... 1 Ackllowledgments .................................................................................................. 3 Paleoenvironmental Setting............................................................................................ 3 Paleogeography ...................................................................................................... 3 Paleohydrology and Redbed Formation................................................................. 4 Sa.Dlpling and Analytical Methods ................................................................................. 5 Descriptioo of Copper-Urailium Occurrences................................................................ 6 King Midas Claims................................................................................................. 7 Mt. Adams to Mt. Owen......................................................................................... 7 Copper in Veins...................................................................................................... 10 Chemical Compositioo ................................................................................................... 12 Composition and Classification of Mineralized Rocks .......................................... 12 Relationships Among Elements.............................................................................. 16 Proposed Moc:lel for Mineralization................................................................................ 18 Copper .................................................................................................................... 18 Urailium.................................................................................................................. 19 Conclusions .................................................................................. .......... ........................ 20 References Cited............................................................................................................. 21

Laramide and Neogene Structure of Northern Sangre de Cristo Range, South-Central Colorado: ABSTRACT

The Sangre de Cristo Range, from Blanca Peak northward to the Arkansas River in Colorado, is composed mostly of Precambrian crystalline rocks and upper Paleozoic clastic sedimentary rocks. These rocks were folded and faulted by Laramide compressional forces from the Late Cretaceous to Eocene. Laramide structures are large arcuate thrust plates that intersect and overlap one another to form a northwest-trending belt that extends across the range from Huerfano Park to Valley View Hot Springs. All of the thrust plates within the range are bounded by west-dipping faults, some of which extend into the basement of Precambrian crystalline rocks. Along the east side of the range, the Alvarado fault is interpreted tentatively as an east-dipping thrust, bringing Precambrian crystal ine rocks west over Paleozoic rocks. Thrust plates were folded internally before and during thrusting; some plates of Paleozoic rock contain folds that tighten and decrease in amplitude toward the leading edge of the plate. Stacked plates consisting of Precambrian and Paleozoic strata have been folded concordantly after thrusting. Thrust faults are mainly high to medium-angle reverse faults along the leading edge of thrust plates, but they flatten to about 30° at depth. Total shortening within the range is at least 8 km (5 mi) at the latitude of Westcliffe and at least 14 km (9 mi) farther south near the latitude of the Great Sand Dunes. During the Neogene, the Sangre de Cristo Range was uplifted, and the adjoining San Luis and Wet Mountain Valleys were downdropped by extensional rift faulting. Rifting followed late Oligocene intrusion of stocks, sills, and dikes of mafic to felsic igneous rock into the Precambrian and Paleozoic rocks of the range. The horst of the Sangre de Cristo Range probably began to rise in the late Oligocene, rose rapidly in the early Miocene, and rose rapidly again in the late Miocene and Quaternary. Flows of mafic lava were erupted from faults along the southwest side of the Wet Mountain Valley and in the San Luis Valley. Zones of Laramide thrusts along the east and west sides of the range were reactivated to form the Sangre de Cristo and Alvarado normal faults, respectively. The floor of the Neogene sedimentary and volcanic fill of the San Luis Valley has been downdropped 2,000-7,000 m (6,600-23,000 ft) below the top of the range, and the floor of the Wet Mountains Valley has been downdropped about 2,000 m (6,600 ft) below the range. Rifting is still in progress in the San Luis Valley, west of the range, but may have ceased in the Wet Mountain Valley. End_of_Article - Last_Page 941------------