All undergraduate majors are eligible and encouraged to participate in research. Research opportunities can be a part of an independent study with a faculty member, as a part of a class assignment, or participating in a funded project. All Geology faculty members are involved in undergraduate research because we believe that it significantly enhances the educational experience. Student research enhances observational and interpretative skills, develops oral and written skills, and provides a connection between the classroom and the real world. Some recently completed or ongoing undergraduate research projects are outlined below.
A major threat to water quality in the agricultural Midwest is the amount of nitrate that comes directly from fertilizer used in agricultural fields. In order to better understand how nitrate affects streams and their riparian buffer zones, we have been conducting research at the stream T3, which is located in Hudson, Illinois. This stream flows into Lake Evergreen, one of the drinking water reservoirs for Bloomington-Normal, IL. There is growing concern for the quality of the drinking water as a result of elevated nitrate in the contributing stream. We collected soil samples for 10 nested wells that were installed in various places and depths in the riparian buffer zone to measure nitrate concentrations and percent of organic matter. The soil samples were frozen and then dried at 100°C for at least 24 hours. Samples were mixed with KCl, shook, and then filtered, so they could be analyzed for nitrate concentration in the Ion Chromatograph. Soil percent organic matter was measured by drying a known mass of sample at 540°C for 24 hours. The concentration of nitrate in the soil water ranged from below detection limits to 26.55 mg/L. Nitrate concentrations decrease with depth with an average of 16.26 mg/L at a depth of 1 foot and 7.14 mg/L at a depth of 6 feet. The soil contained a relatively high percent organic matter ranging from 10.94% near the surface to 1.51% at a depth of 6 feet; however, there was no correlation between amount of nitrate and percent of organic matter. The concentrations of organic matter and nitrate suggest that the riparian buffer zone has the capacity to reduce nitrate, and if tile-drained water were diverted into the soil of the riparian buffer zone, denitrification and/or uptake of nitrogen from plants would occur.
This study used soil surveys as well as LIDAR information to convey different Quaternary units located in Tazewell County, Illinois. A 7.5 minute map of the Washington Quadrangle (at a scale of 1:24,000) to display several different units located in that area. There are four major units located in this study: The Peoria Silt, the Tiskilwa Formation, the Henry Formation, and the Cahokia Formation. The majority of this map is covered in the Peoria Silt, a wind blown sediment that is silt-clay in size and was derived from the recent (Wisconsin) glaciation; this silt increases in thickness from west to east. The Tiskilwa formation is another major unit in this area and is a glacial till (diamicton) that has a clay-silt matrix, large boulder clasts, and is often red in color. The Henry Formation is composed of gravel and sand and is valley outwash plains, and is mostly found next to stream cuts along side the Cahokia formation. The Cahokia formation is a clay and silt sediment interbedded with sandy layers and is interpreted to be post-glacial derivation of sediments deposited in stream terraces from the recent glaciation events.
This study was conducted in order to map the surficial geologic units of the Eureka, IL Quadranglet located at 89°15’ to 89°22’30” latitude to 40°45’ to 40°37’30” longitude at the scale of 1:24,000. This Quadrangle includes sediment units deposited during and after the Wisconsin Glacial Episode. The Quadrangle also contains the Eureka Moraine. The methodology used to map this quadrant involved the conversion of soils data, LiDAR data, well water log data and field work. There are five geologic units which are Quaternary age that make up the surficial geology in the Eureka Quadrangle. These units are the Cahokia Alluvium, Peoria Silt, Henry Formation the Tiskilwa Formation, and the Lemont Formation. The Cahokia Alluvium layer is a brown, silt and clay layer which is interbedded with fine sand and rediposited bedrock clasts interpreted to be a post glacial loess and till that has been redeposited on stream beds and valley floors. The Peoria Silt is a light yellow to grey sandy silt which was deposited in an eolian environment and is interpreted to be a pro-glacial loess derived from glacial meltwater channels. The Henry Formation contains stratified layers composed of sand and gravel with cobbles and boulders interpreted to be upland outwash and alluvial fans. The Tiskilwa Formation is a red-gray diamicton associated with gravel, sand, silt and clay interpreted to be derived directly from glacial ice. Lastly, the Lemont Formation is composed of unstratified diamictons, cobbles, boulders and discontinuous layers of sand, gravel, silt and clay which are interpreted to be derived directly from glacial ice and overlain by a thin covering of loess. The distribution of the Cahokia Alluvium is alongside river beds and valleys. The Peoria Silt is just west of the Eureka Moraine and is only mappable if the silt is greater than sixty inches thick. The Henry Formation’s distribution is the smallest amount and is present as outwash alongside river beds. The Tiskilwa Formation is distributed entirely west of the Eureka Moraine. Lastly the Lemont formation is contained in the north-east corner of the map within the Eureka Moraine.
This study involved constructing a surficial geologic map of the Metamora 7.5 Minute Quadrangle in Woodford County, Illinois (Scale 1:24,000). This quadrangle includes the Metamora moraine and part of the Bloomington Moraine, both moraines are of Wisconsin age. Methods used in the development of this geologic map included conversion of soil survey data, as well as LiDAR data and well water data. Four major Quaternary age sediment units are exposed in the Metamora Quadrangle. These formations include the Henry Formation, Wedron Group, the Peoria Silt, and the Cahokia Alluvium. The Henry Formation is gravel and sand interpreted to be valley train outwash. The surface and subsurface is the primary location for outwash gravel. The Wedron Group consists of both the Tiskilwa and Lemont Formations. Tiskilwa is a red-grey to grey calcerous clay loam or loam. This formation lies South and West of the Metamora Moraine. Lemont is a diamicton consisting of grey, blue, brown, black, and green clay interpreted to be a combination of loamy till and silty loess. The Lemont is present in the Metamora Moraine as well as areas to the North and East of it. The Peoria Silt is light yellow tan to grey sandy silt interpreted to be predominantly a pro-glacial loess. This loess is derived from glacial meltwater channels. Lastly, the Cahokia Alluvium is a silty and silty clay interbedded with a fine sand. This Formation is interpreted to be post-glacial loess and till that had been redeposited in fans where streams and ravines emerge from uplands and onto low-slope valley floors.
This study involved constructing a surficial geologic map of the 7.5 minute Bloomington West Quadrangle located in McLean County. The Quadrangle is confined within the area 89°00’ to 89°07’30” latitude and 40°30’ to 40°22’30” at a scale of 1:24,000. The sediments present were deposited during, and after the Wisconsin Glacial Episode. Methods used in the creation of the Quadrangle include the conversion of soilds data, LiDAR data, well water log data and field work. The five formations located in the Blooming West Quadrangle are the Cahokia, Tiskilwa, Lemont, Peroia and Henry. These formations are Quaternary in age. The Cahokia Alluvium is a silty clay interbedded with a fine sand and is located along stream beds and valley floors. The Cahokia Alluvium is interpreted to be post-glacial loess and till that has been redeposited in fans where streams and ravines emerge from uplands and onto low-slope valley floors. The Tiskilwa is a red-grey to grey calcerous clay loam. The Normal Moraine divides the Bloomington West Quadrangle with the Lemont being to the North and Tiskilwa to the South. The Lemont is a diamicton consisting of grey, blue, brown, black, and green clay interpreted to be a combination of silty loess and loamy till. The Peoria Silt is light yellow tan to grey sandy silt interpreted to be mostly a pro-glacial loess. The Peoria Silt is only mapable with a thickness of loess greater than sixty inches and comes from glacial meltwater channels. Lastly, the Henry Formation is gravel and sand interpreted to be valley train outwash.
Mineral ages in sedimentary deposits are used to understand erosion patterns and mountain uplift. In a small catchment we assume all sediments, regardless of size, reveal the same patterns. This research investigates the apatite age distributions of sand and gravel located in stream and moraine deposits in two canyons in the Teton Mountains: Garnet and Cascade. Stream samples from active channels near the mouth of each canyon and moraine samples close to the shores of Bradley and Jenny Lakes were collected and processed at Illinois State University. Gravel samples were crushed, and all samples were washed, sieved, and run through heavy liquids and the Frantz magnetic separator to isolate apatite grains. Samples were then picked to measure He content with mass spectrometry and U-Th with laser ICP-MS. A previous study by Tranel et al. (2011) tested and compared two samples of sand, one found in a Garnet Canyon stream, and the other found in glacial deposits of the Bradley Lake moraine at the mouth of the canyon. This previous study concluded that the sand sediments found in the stream were on average 39ma while the sample from the moraine were on average 42ma. The stream samples ranged from 10ma to 75ma. The moraine sample ranged from 5ma to 80ma. We expect similar apatite ages in the larger and more complex Cascade Canyon. New results from Garnet and Cascade Canyons will determine if the ages in sand and gravel samples are influenced by the size of the sediment collected. Observations of many fractured grains in glacial sediments suggest transport processes may influence the range of ages in our results. The results of this study will help plan effective sampling strategies in future studies investigating erosional patterns in mountain landscapes.
The Benson 7.5 Minute Quadrangle (Scale 1:24,000)
is located in Woodford County, Illinois. Methods used in generating this
surficial geologic map were analysis and conversion of soil data,
analysis of LiDAR data and interpretation of well water logs. Formations
were interpreted and mapped based on lithological and thickness
descriptions of well data from the Woodford County Soil Survey. The
surficial geology of the Quadrangle is comprised of Quaternary glacial
sediment units that were deposited during the Wisconsin episode.
Quaternary units include the Wedron Group, the Henry Formation, the
Peoria Silt, and the Cahokia Alluvium. Units present with less than five
feet in thickness were not considered as mappable. The Wedron Group
makes up the majority of the surficial geology of the Quadrangle. The
Wedron Group contains the Lemont Formation, a grey, silty clay diamicton,
which has been deposited on a ground moraine. The Peoria Silt is a
yellow-brown sandy silt interpreted as loess. The Henry Formation, a
sand and gravel unit of the Mason Group, can be found where outwash
deposits are thick enough to map. The Cahokia Alluvium contains poorly
sorted sand, silt and clay sized grains and can be found in abundance
along the Panther Creek, a modern stream system which flows through the
In the Sacramento Mountains, rainfall and snowmelt from high elevations supply water to ephemeral streams. The mountains are bound on the western flank by a steep escarpment formed by normal faults associated with extension. We are investigating the spatial distribution of erosion in an arid climate stream channel to better understand where erosion is focused and what controls knickpoint evolution. Knickpoints (sharp changes in slope) within longitudinal profiles are formed by resistant bedrock units that are difficult to erode or by slip and offset during faulting. If knickpoints are created by uplift or faulting, they may occur anywhere along the stream channel regardless of the strength of bedrock material. However, if the knickpoint results from the bedrock’s resistance to erosion, there will be a strong correlation between the position of the knickpoint and rock strength. Based on this, we hypothesize that the rock strength of bedrock with knickpoints will be greater than the rock strength of bedrock units without knickpoints. To test this, we used the Schmidt Hammer and Selby rock strength classification to determine the rock mass strength (RMS) of rock units parallel to the channel in Dog Canyon. We then compared RMS results to changes in slope along a longitudinal channel profile created in GIS identifying geologic units and knickpoint features. We also compared RMS values to the average slopes for each bedrock unit. Initial results suggest that the knickpoints occur in the three strongest rock units tested, which were all carbonates. Dolostone had the highest RMS values on average. RMS appears to generally decrease with increasing elevation. Also, RMS and average slopes of bedrock units show a weak positive relationship. Knickpoints were located near formation contacts and between weaker rock units. These results suggest that knickpoints may be controlled by rock strength and their position along the stream profile. Therefore, the height and extent of these knickpoints may be influenced by the thickness of the bedrock units. Future work on this issue will involve analyzing the spatial distribution of erosion with detrital apatite minerals from samples collected in Dog Canyon.
This study involved the construction of a geologic map of the Roanoke 7.5 minute quadrangle in Woodford County at a scale of 1:24,000. This area contained sections of the Eureka Moraine which is included in the Wisconsin glacier event. Methods used to construct this mapping area included using soil data from soil survey, well data, as well as LiDAR data. There were four major sediment formations that were found at the subsurface in the Roanoke quadrangle. The formations include the Cahokia Alluvium, the Wedron Group (Lemont Formation), The Henry Formation, and finally the Peoria formation. The Cahokia Alluvium consisted of interbedded sand, silt, clay, and gravel that were deposited by glacial loess. Alluvium is found along the river systems including West Branch Panther Creek. The Wedron Group consist of the Tiskilwa and Lemont formations but only the Lemont formation is found in the subsurface of the Roanoke quadrangle. The Lemont formation is a diamicton that ranges from blue to brown clay and is interpreted as a of silt loam. The Henry formation consists of an interbedded sand, gravel, and silt. This is interpreted as a glaciofluvial, and was formed when the melting of glaciers carried the deposits downstream. Finally the Peoria formation has been described as a light tan or brown silt to sandy silt eolian deposits.
Miocene basins associated with the oblique rifting of the Inner Continental Borderland offshore Southern California are preserved along the flanks of the transpressional Santa Cruz-Catalina Ridge. Using 184 lines of two-dimensional seismic data including high resolution records from Oregon State University and deep penetration data from Western Geco archived in USGS/NAMSS, we were able to map the configuration of the Miocene basin for 80 kilometers along the northeast flank of the Santa Cruz-Catalina Ridge core complex. Our mapping area is about 1,280 square kilometers. There are distinct middle and late Miocene basins along the flanks of the ridge, which we are using to try to define the initial configuration of the Inner Borderland Rift. Along the hinge, between the uplifted ridge and the sub-horizontal basement in the Santa Monica Basin, and adjacent to the Transverse Ranges lies the thickest parts of the late Miocene sequence, ranging from 750 to 950 meters thick. The middle Miocene basin has distinct sub-basins, with maximum thicknesses of 1400 to 1800 meters, between acoustic basement highs. Pliocene to Recent sediments lap on to the tilted and uplifted Miocene basin sequences and constrain timing of uplift when transpression commenced. Segmentation and other distinctive character of the Miocene basins along the ridge flank may be correlated with similar features in the Miocene basin on the conjugate margin of the rift. Our working model for oblique rifting in the Borderland resembles the Gulf of California, where right-stepping echelon transform faults link left-stepping extensional basins. The objective of our project is to reconstruct the configuration of the middle Miocene rift and to further our quest to understand the rifting process and tectonic evolution of the Pacific-North American plate boundary.
The Danvers Quadrangle is located in McLean and Woodford counties and spans from 40° 30’ to 40° 37’ 30” north latitude and 89° 15’ to 89° 07’ 30” west longitude. This map was prepared using soil maps from the McLean and Woodford County Soil Survey. Parent materials were identified and grouped together, creating formation boundaries. Units had to be at least 2 m in thickness to be mapped. Well data was secured through the Illinois State Geological Survey (125 wells). After boundaries were delineated, a field check was conducted to adjust positions of contact. Quaternary units in excess of 100 m overlie the local bedrock valleys. Major Quaternary units include Cahokia alluvium, the Wedron Group till, the Mason Group glacial outwash, and the Peoria loess. Today, many rivers and streams are still present in the Danvers Quadrangle, and thus Holocene Cahokia alluvium is abundant in less than 5 meters of thickness. The El Paso and Bloomington Moraines are represented by the Wedron Group, which is Tiskilwa till and Lemont formation respectively. These till units consist of pink and grey diamicton units that are interbedded with proglacial river and lake sediments. Henry outwash is a sand/gravel unit of the Mason Group and is found south of the Bloomington Moraine less than 10 meters in thickness. Peoria Silt is fine-grained yellow-orange silt and clay that covers much of the Quadrangle.
We present results of an investigation of the Latest Devonian brachiopod sequence spanning the global Hangenberg Extinction and post-extinction interval in the Illinois Basin based on restudy of type material illustrated in twentieth century studies by Weller, Williams and Carter, and new field-based collections from the type areas of Late-Latest Famennian units in eastern Missouri and Iowa. The fauna from the Hangenberg interval occurs in shale and siltstone shelf facies of the English River Formation in central and southeastern Iowa associated with conodonts spanning the interval of Upper expansa? to costatus-kockeli interregnum (= Lower-Middle praesulcata zones). The English River fauna consists of twenty species of the genera Chonopectus, Mesoplica, Ovatia, Semiproductus Sentosia, Plicohonetes?, Leptagonia, Schuchertella?, Schellwienella, Schizophoria (S.), Paraphorhynhus, Eudoxina, Syringothyris, Kitakamathyris, Hispidaria? Camarorphorella, Iniathyris and Eumetria. Rapid deepening initiated Louisiana Limestone carbonate platform deposition in eastern Missouri, Iowa and western Illinois. The post-Hangenberg survivor and recovery fauna of the Louisiana Limestone occurs with conodonts of the kockeli Zone. Twenty or more brachiopod species known from the Louisiana Limestone are included in the genera Anthocrania, Petrocrania, Rhipidomella, Schuchertella, Plicochonetes, Orbinaria, Cyphotalosia?, Leptolosia, Paraphorhynchus, Cyrtina, Tylothyris, Acanthospirina, Syringothyris, Parallelora, Kitakamathyris, Crurithyriss, Athyris and Camarorphorella. The brachiopod sequence records a near total turnover at the species level of the English River fauna, with only two English River species (Kitakamathyris cooperensis & Camarophorella buckleyi) ranging into the Lousiana (kockeli Zone). Five of eighteen English River genera carryover into the Louisiana fauna. Glacial-eustatic sea level fall terminated Louisiana deposition, and the post glacial sea level rise (sulcata-duplicata zones) re-established subtropical platform deposition in the region with survivor and recovery clades diversifying rapidly in the subtropics during earliest Tournaisian including as many as 37 species described from the western Illinois Basin by Carter.
A surficial geologic map of the Arrowsmith 7.5’
Quadrangle was constructed, spanning from 40° 22’ 30’’ to 40° 30’ north
latitude and 88° 45’ to 88° 37’ 30’’ west longitude. Sediment unit
parent materials were identified using McLean County Soil Survey data,
they were then grouped together to create formation boundaries.
Thickness of major units was determined using water well data, and only
considered present at the surface if greater than 2 meters in thickness.
Quaternary sediment units deposited during the Woodfordian glacial
advance and modern stream alluvium dominate the surficial geology.
Quaternary units reach over 100 meters in thickness where they overlie
buried bedrock valleys. Major Quaternary mapping units include the
Wedron Group, the Henry Formation, the Peoria Formation, and the Cahokia
Alluvium. The Wedron Group includes the Tiskilwa till and Lemont
Formation, which consist of diamicton units that are interbedded with
proglacial river and lake sediments. The Lemont Formation is grey in
color and exists to the north of the Bloomington Moraine, while the
Tiskilwa till is pink in color and lies to the south of the Bloomington
Moraine. The Henry Formation is prominent in the northern half of the
quadrangle (up to 10 meters thick) and consists of sand and gravel that
was deposited in glacial rivers and outwash fans. The Peoria Formation
(up to 3 meters thick) forms the top layer in much of the southern half
of the mapping area and consists of fine-grained yellow silt/clay and is
interpreted as loess deposits. The Cahokia Alluvium (less than 5 meters
thick) is made up of modern river deposits of sand, gravel and silt. A
traditional field check was later conducted to ensure that contacts were
properly placed. Cross sections were also constructed by subsurface
correlation of water well records.
Surficial geologic mapping at the 1:24,000 scale has been completed for the Chenoa 7.5 Minute Quadrangle in the north-central part of McLean County, IL. The longitude of the map ranges between 88°45ˈ to 88°37ˈ30”, and the latitude ranges from 40°45ˈ to 40°37ˈ30”. The map was created as a digital PDF file allowing for quick access to the map and introduces compatibility to other mapping programs for local geology to be completed. The map was mostly ground moraine and it was constructed using soils survey data, water well log, and outcrop descriptions. Using well log data, we were able to obtain the thicknesses of some of the formations; The thickness of the Quaternary units can span over 100m in paleovalleys. The youngest Quaternary units present are within the Mason Group consisting of the Peoria Silt and the Cahokia alluvium. The Cahokia formation contains poorly sorted sand, silt, and clay sized grains that are associated with modern stream systems with thicknesses less than 2m thick. The Peoria Formation contains yellow-brown silt and clay, which is interpreted as loess. The Henry Formation is a sand and gravel unit that forms terraces in valley train outwash systems and alluvial fans varying in thickness between 3-20m. The Wedron Group dominates the north east to the central part of the quadrangle and it contains the Lemont Formation, which is a grey diamicton that is deposited on a ground moraine with thicknesses ranging between 5 and 10m. The Cahokia alluvium occurs in the north-central areas of the Quadrangle and the Peoria silt is found in the southwest portion of the quadrangle. In some regions in the north west area of the Quadrangle the Henry Formation is layered within the Lemont Formation. After the map was drafted a field check was conducted to validate contact placement and water well records.
The Holder Quadrangle is located in McLean County and spans from 40° to 40° 22’ 30” north latitude and 88° 52’ 30” to 88° 45’ west longitude. The majority of the quadrangle consists of the Woodfordian moraine front and the adjacent ground moraine The Quaternary units overlie Pennsylvanian strata of a variety of lithologies. Quaternary units exceed 100 m in thickness where they overlie buried bedrock valleys. Major Quaternary sediment units present in the area are the Wedron Group till units, the Mason Group meltwater deposits, the Peoria Silt, and the Cahokia Alluvium. Carmi Formation lacustrine deposits are also locally present. The Wedron Group consists of the Tiskilwa till (south of the Bloomington Moraine) and the Lemont Formation (north of the Bloomington Moraine). These till units are clay-rich diamicts that are pink and grey in color, respectively. The Peoria Silt is fine-grained yellow-orange silts and clays which covers most of the area in a thin veneer (as much as 2-3 m). The Mason Group is an outwash sand/gravel unit most prominent south of the Bloomington moraine. It is less than 8-10 meters in thickness. The Cahokia Alluvium is less than 5 meters in thickness and is associated with Holocene drainage systems. This map was prepared using soil maps from the McLean County Soil Survey. Parent materials were identified and grouped creating formation boundaries. Units had to be at least 2 m in thickness to be mapped. Water well data was evaluated to indicate thickness of major surficial deposits to indicate their viability as mappable units. After boundaries were delineated, a field check was conducted to adjust contact placement. Cross sections were prepared and subsurface correlations were determined using water well records. More than 100 well records on repository at the Illinois State Geological Survey for the Holder Quadrangle were analyzed as part of this study.
The Paleocene Fort Union Formation was studied at three localities in the western Bighorn Basin of western Wyoming. Detrital zircon U-Pb geochronology was used to determine the provenance of these rocks to better understand the transition between Sevier thin-skinned and Laramide thick-skinned deformation. Uppermost Fort Union strata were sampled near the WY-MT state line near Belfry, MT, just east of Cody, WY and north of Meteetse, WY. A total of 248 zircons were analyzed at the University of Arizona Laserchron Laboratory. Proterozoic zircons dominated each of the samples, ranging from 48-63% of each sample. Numerous Proterozoic orogens supplied these zircons. Mesozoic zircons were the next most abundant component in each sample, ranging in proportion from 20-23%. Archean zircons comprised 8-15% of each of the samples. Paleozoic zircons were the smallest fraction, accounting for only 2-8% of the zircons analyzed. The preponderance of Proterozoic zircons indicates that the principal source area of the Fort Union in the Big Horn Basin is the Sevier Highlands to the west. These zircons were likely recycled from Neoproterozoic metasedimentary rocks that are common throughout that area. The presence of a significant proportion of upper Cretaceous zircons suggests that areas of the Idaho Batholith were exposed as well and supplying sediment. The paucity of Archean zircons indicates that the Beartooth uplift was not as yet unroofed, and thus not a significant source area during Fort Union deposition. Archean zircons present could also have been recycled from distal westerly sources.
|Mary Ann Scroggins|
Quartzite cobble conglomerates occur within the Tertiary strata of the western Big Horn Basin. Our goal in this research is to characterize the age and provenance of these clasts using detrital zircon U/Pb Geochronology. As part of this study, we sampled three different formations (#332 zircon analysis total). The Paleocene Fort Union Formation was sampled along Grass Creek (#83). The lower Eocene Willwood Formation was sampled at two localities: along Gooseberry Creek (#84) and near Meeteetse (#96). The middle Eocene Wapiti Formation was sampled at Jim Mountain (#70). Meso- and Paleoproterozic (1300-2000 Ma) dominated each of the samples, ranging from 79-87%. Each locality also contained smaller amounts of Archean (>2500 Ma 7-17%) and Grenville (950-1200 Ma; 6-10%). The most abundant age for each sample is 1650-1700 Ma. The similarity of detrital zircon signatures indicates that these rocks were most likely derived from the same source area, which is the Sevier highlands to the west. The sandstone protolith of these quartzites were eroded from Yavapai-Mazatzal rocks and then transported north to the Neoproterozoic continental margin of Idaho and Montana. These quartzites were then uplifted during the Sevier orogeny, were weathered, and shed as clasts east into the Western Interior Basin during early Tertiary time. These quartzite clasts have similar deterital zircon spectra to the time equivalent Harebelle and Pinyon Formations to the west.
The Eocene volcanic rocks at Hominy Peak represent a southwestern outlier of the Absaroka Volcanic Supergroup. As part of this study, we used U-Pb dating methods to determine the zircon age spectrum on an ash fall tuff (#32), a polymict agglomerate matrix (#85) and a quartzite cobble conglomerate matrix (#77) from the Hominy Peak Formation. The quartzite cobble conglomerate has a zircon spectrum that is 41% Archean, 30% Proterozoic, 20% Eocene, and 8% Mesozoic. Age of the 10th youngest grain is 50.44 +0.96 -0.68 Ma. The polymict agglomerate had a surprisingly diverse zircon suite that includes 48% Proterozoic, 25% Eocene, 13% Archean, 4% Paleozoic, and 3% Mesozoic ages. The age of the 10th youngest grain for this unit is 49.25 +0.91 -1.20 Ma. The ash fall tuff spectrum consisted of 63% Eocene zircon, with a variety of Paleozoic and Precambrian zircons also present. The weighted mean age of this unit is 50.3 +/- 1 Ma. The zircon provenance of the Hominy Peak Formation is diverse. These rocks contain a surprisingly high proportion of non-Eocene zircons in what has been interpreted to be a primary volcanic unit. During Hominy Peak time, the source areas included the uplifted Laramide Teton Range to the south that produced the Archean ages, the active Absaroka volcanic rocks to the north that yielded the Eocene ages, and the underlying Pinyon and Harbelle Formations that yielded that Proterozoic and and Mesozoic Zircons. The age of 50.3 +/- Ma would make these rocks correlative to other Bridgerian rocks to the east, which would include the Wapiti Formation.
The Cloverly Formation of Wyoming represents the first synorogenic strata shed from the Sevier highlands of ID and MT. Detrital zircon U-Pb geochronology was used to determine the provenance of these rocks to better understand the early stages of unroofing of the Sevier highlands. Lowermost Cloverly Formation Sandstones were sampled at three localities in the Big Horn Basin (#283 zircon total) and two localities in the western Powder River Basin (#185 zircon total). The Big Horn Basin detrital zircon spectra are dominated by Proterozoic ages (78-83%), which are mainly Grenville age zircons. Paleozoic zircons represent 10-15% of the spectra of each sample. Lesser amounts of Mesozoic (1-3%) and Archean (2-6%) also were present. The Powder River zircon spectra also were dominated by Proterozoic zircons, but the proportion was smaller (55-69%) and the age distribution was much more diverse. Mesozoic zircons were more prominent (12-23%), Paleozoic (11-13%), and Archean (9-10%) were more abundant as well. The Proterozoic and Archean zircons were likely recycled from cratonic Mesozoic and Paleozoic strata that was eroded as the Highlands were unroofed. The Mesozoic zircons were derived from the underlying Idaho Batholith and related plutonic rocks in the region. It is curious that the more distal Powder River Basin Cloverly localities are more enriched in younger zircons. This may indicate that distal Cloverly sandstones are comprised of sediment derived from more deeply eroded areas of the Sevier Highlands.
Quartzite conglomerates Late Cretaceous to Eocene in age outcrop in deposits up to 1-4 km thick in areas of Sublette and Teton Counties. Our goal in this research is to characterize the age and provenance of these clasts using detrital zircon U/Pb geochronology. As part of this study, we sampled three different formations (#475; zircon analysis total) at six localities. The Harebell Formation was sampled at along Buffalo Fork (#85) and Pacific Creek (#83). The Pinyon Formation was sampled along Pacific Creek (#=43), in the Gros Ventre Mountains (#=98) and at Hominy Peak (#=82). The Hominy Peak Formation was sampled just south of Hominy Peak (#=84). Meso- and Paleoproteroic zircons dominated these spectra, ranging from 71-91%. Grenville and Archean zircon populations also are present, ranging from 1-15% and 5-18%, respectively. The overlap and similarity indices ranged from 0.62-0.82 and 0.68-0.84, respectively. These data indicate that the protolith sediment of these quartzites were generated in the Yavapai-Mazatzal orogenic belt to the south and east. This sediment was transported to the Neoproterozic continental margin of ID and MT and then metamorphosed. These quartzites were then uplifted during the Sevier Orogeny, were eroded and the clasts were transported eastward into the Western Interior Basin. It is likely that much of this sediment could have been reworked and recycled into younger conglomeratic units. The quartzite clasts studied here have identical detrital zircon spectra to quartzite bearing conglomerates of the Fort Union, Willwood and Wapiti Formations to the east.