Earth and Environmental Sciences Dissertations, Theses, and Plan B Project Papers

Persistent link for this collectionhttps://hdl.handle.net/11299/212256

This collection contains some of the final works (dissertations, theses, and Plan B project papers) produced by master's degree and doctoral students in the Department of Earth and Environmental Sciences (or its predecessors) as part of their requirements to graduate. Specific master's degree programs over the years have included Master of Science in Geology, Master of Science in Geological Sciences, Master of Science in Earth Sciences, and Master of Science in Earth and Environmental Sciences (the current iteration as of spring 2024).

To see final works for specific degrees, click the links below. NOTE: Newer dissertations and theses from roughly 2007 on (including all theses from the Master of Science in Earth Sciences program) will not appear in the lists linked below, though some do appear in this collection. (For the most up-to-date new dissertations and theses, see the University of Minnesota Twin Cities Dissertations and Theses collection.) Newer Plan B project papers will appear in the lists.

Master of Science in Geological Sciences (items date from roughly 2004-2024)
Master of Science in Geology (items date from roughly 1971-2021)
Doctor of Philosophy (PhD) (items date from roughly 1976-2011)

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Now showing 1 - 17 of 17

A 2000 Year Sub-annual Record of Climate Change from Lake Malawi
(2009-08) Petrick, Benjamin Fredericks
Lake Malawi, in East Africa, provides a rare opportunity to look at a sub-annual record of climate change from a region were there is a lack of good climate records. This is possible because the upper most sediments in the north basin Lake Malawi are varved. The varved record extends from back 1200-2000 years depending on dating differences and is well dated back 800 years. In order to construct an overall sub-annual record of climate change, overlapping sections of two cores from the north basin of Lake Malawi taken during the recent Malawi drilling project were examined on a scanning XRF with a step size of .2 mm. This provided an average of 6 measurements per annual varve couplet. Because of the chemical differences between light and dark varves it was possible to count these varves using a high resolution photograph and x-radiography images in conjunction with the chemical data. Four major chemical elements or ratios of chemical element were used to represent the four major components in the sediments of the core: Fe is a proxy for the clay, Si/Ti is a proxy for the Biogenic Silica (BSi, inc/coh scattering ratio is a proxy for %Total Organic Carbon (TOC), and K/Ti is a proxy for volcanic sediments. Comparing Fe to recent records of lake level fall and rise suggests that Fe be when the planktonic community is dominated by diatoms it reflects changes in year to year fluvial input. However at times of change in the planktonic community, the Fefluvial imput relationship breaks down. Comparisons of both the lake level records and to coral records from the Indian Ocean show that both lake level rise and fall are enhanced by increased ocean temperatures over periods of 5-10 years. This suggests that changes in Indian Ocean temperatures have an affect on Lake Malawi. The lake records show no connection to Zimbabwe rainfall but an opposite relationship with Indian rainfall. The inc/coh shows a strong relationship over the last 150 years with IOD and proportion of diatoms in the planktonic community, which tends to change during times with great IOD variability. These relationships suggest that IOD causes changes in the winds that stimulate production of planktonic during the dry season. Looking further back in the record shows that similar shifts to non-diatom dominated planktonic community occurred twice before in the record and there is some evidence in the record that changes in winds might be responsible for these events as well. 11 year and 3-7 year cycles were also found in the record but their meaning is unclear. The times when the 11 year cycle is strong in the lake are not assonated with the record of sunspots and the 3 to 7 year cycle does not seem to be related to changes in ESNO as would be expected. Therefore the meaning of the cycles is still not understood. The longer record suggests dry periods from the bottom of the varved section to around 1250 AD and from 1550 to 1650 AD, with an interceding wetter period from 1250 to 1650 AD. The record from 1650 AD to current day shows some rises and falls and an overall steady record. Comparing this to other records of African lakes and caves shows that this record has similarities to the records of East African lakes but is in opposite of records from Cold Air Cave in Southern Africa. Lastly it also shows similarities to records of Indian monsoon wind strength which is controlled by Indian Ocean temperatures and Cariaco basin records which are a proxy for the ITCZ. Both of these records show that the migration of the ITCZ and changes in Indian Ocean temperatures are important drivers for Lake Malawi and the findings of this paper may be useful in looking at changes both at longer time scales and in the future as well.
Deformation and Metamorphism of Tectonites Exposed in the New York and Clark Mountains, eastern California: A case for Proterozoic mid-crustal shortening in the Mojave Province
(2005-08) Rieser, Michael Edwards
During ~1.76-1.64 Ga crustal growth in southwest Laurentia, an oblique shear zone with components of left-lateral strike-slip and thrust motions juxtaposed two blocks of deep-seated Proterozoic crust presently exposed in the New York and Clark mountains of the Mojave tectonic province, eastern California. Two localities, Mineral Hill and Willow Wash, were subjected to peak metamorphic conditions of ~720°C, 6.5 kbar and ~780°C, 3.5 kbar, respectively, as determined by GASP barometry and Grt-Bt exchange thermometry. Ductile L-S tectonite fabrics consisting of a north-northwest striking, west-dipping tectonic and compositional foliation and a northwest-trending, shallow-plunging mineral stretching lineation characterize the penetrative deformation of both areas. High-temperature quartz c-axis fabrics confirm that peak metamorphic conditions accompanied deformation. Additionally, quartz petrofabric analysis reveals a strong lattice-preferred orientation (LPO) that is geometrically related to the stretching lineation and foliation. Asymmetric S-C foliations, folds, and feldspar "fish" measured in the field and in thin section yield reproducible top-to-the-SE shear sense indicators. Although quartz LPO is well preserved, flat-field extinction in quartz grains is interpreted as evidence of annealing related to post-kinematic regional heating. Synchronous granulitefacies metamorphism, medium metamorphic pressure, and oblique top-to-the-SE, sinistral shear suggest that the deep crust was simultaneously translated and contracted, placing 3.5 kbar crust structurally above 6.5 kbar crust. The kinematic fabrics and contrasting barometry of these two related tectonic blocks may offer a direct example of large-scale Paleoproterozoic strike-slip motions proposed by earlier workers (Bennett and DePaolo, 1987) on the basis of isotopic mapping. The apparent contraction may be related to the 1.705 "Ivanpah Orogeny", which juxtaposed the Yavapai and Mojave tectonic provinces (Wooden and Miller, 1990).
Evidence of Soft-Sediment Post-Depositional Deformation in Lake Superior
(2008-02) Sharpe, Andrew Thomas
In the very fine-grained, gas-poor sediments of Lake Superior, it is possible to collect extremely high resolution images of the subsurface with a 28 kHz echosounder. Penetration depths routinely exceed 20 m. This represents a significant portion of the lake's soft sediment section and makes it possible to image sediments that were deposited during the most recent de-glaciation of the basin. A high-resolution "pseudo-3D" seismic survey recently collected with this system in western Lake Superior provides convincing evidence of buried iceberg scouring in the lakefloor glaciolacustrine sediments. In seismic profiles, the scour appears as localized regions of acoustical blanking that are frequently "U" or "V" -shaped. The scour zones are typically 10s of meters across and up to 6 m deep. In plan-view, they exhibit a curvilinear appearance, frequently running for several kilometers. Features associated with the iceberg scouring include thickening and thinning of beds caused by the building of lateral and terminal berms; and overlying normal faulting due to sediment collapse into the scour marks as the deformed sediment is reconsolidated. Ring-shaped depressions on the modern lake floor are theorized to be the result of sediment dewatering linked to the development of the underlying features.
Fluvial Evolution between the Salt Wash and Brushy Basin Members of the Upper Jurassic Morrison Formation, South-Central Utah
(2007-06) Ali-Adeeb, Riyad Abdulrahim
Abrupt changes in fluvial deposition between the Salt Wash.Member and Brushy Basin Member of the Upper Jurassic Morrison Formation, in western interior North America, have been documented across a seemingly basin-wide depositional unconformity that resulted from poorly understood base level changes. Detailed field observations, paleopedologic analysis, and petrographic analysis of proximal deposits in the Henry Basin in south-central Utah, yield no depositional hiatus in the proximal basin during formation of the unconformity in the distal basin. Rather, the proximal stratal architecture suggest continuous deposition between the two members that likely resulted from a combination ofrelatively high basin subsidence rates and an increase in gravel fraction in the sediment source. Computed subsidence rates in the southern Henry Basin from recent radiometric dates document a time-averaged subsidence rate of 0.121 mm per year, while petrographic evidence suggests an up-section increase in chert-rich sediment source. Collectively these resulted in starving the distal basin of sediment and the formation of a distal depositional hiatus, while the proximal basin accumulated prograding sediments. A south-to-north transect near the western margin of the Morrison Basin documents a rapid pinch out of 150 meters of fluvial gravelly-sandstones of the Salt Wash Member between the southern Henry Basin to the south and the Emery High region 75 miles to the north. Mature paleosols at the base of the Morrison Formation in the north suggest that the lack of Salt Wash Member deposits were due to non-deposition rather than to post depositional erosion or incision. This suggests that syndepositional basin subsidence in the south channeled deposits there, while regions to the north underwent little to subsidence and deposition. The disparity in basin subsidence rates between closely spaced regions in proximal regions, combined with petrographic evidence of increased gravel-fraction in the sediment, suggests that tectonic thrusting to the west may have contributed an important role in producing continuous aggradation of sediment in the proximal basin, while contemporaneously starving the distal basin and forming a depositional unconformity. Incised valley-fill conglomerates at the contact between the two members also suggest that the change in sedimentation was influenced by a drop in base level that followed deposition of the Salt Wash Member.
Fluvial Sedimentation Controlled by Distal Subaqueous Sediment Dynamics
(2006-11) Mohr, Jeré Anthony
In this study, I address a problem that incorporates the themes discussed above. The fundamental question I attempt to answer is: How do non-eustatic processes basinward of the shoreline affect large-scale sedimentation in the fluvial system? The basic idea is that in linked depositional systems, processes seaward of the shoreline can affect the behavior of the fluvial system. To answer this question, I constructed a simple conceptual model of fluviodeltaic dynamics and then conducted a series of physical experiments at Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis. The conceptual model predicts that the sediment dynamics at the base of the delta foreset exert strong control on the dynamics of the fluvial system. The results of the experiments confirm that sediment dynamics at the delta toe play an important role in fluvial sedimentation in a coupled fluviodeltaic system. This thesis presents the theoretical (conceptual) model and the results of experiments designed to test the model.
Glacial History of the Late Wisconsinan Des Moines Lobe in Minnesota: Geomorphic, Lithologic and Stratigraphic Evidence for Two Advances
(2024-05) Arends, Heather E
Continental ice sheets play a significant role in the Earth’s climatic system. Reconstructing the growth and decay of the Laurentide Ice Sheet during the Last Glacial Maximum betters our understanding of how ice sheets respond to climate change and contribute to rising global sea levels. The southwestern margin of the Laurentide Ice Sheet formed discrete terrestrial lobes, influenced by bed topography. The Des Moines lobe (DML), channeled by the Red River and Minnesota River valleys, advanced to a terminal position in central Iowa. Four dated ice margins provide chronological constraints for regional correlations: the Bemis at ~17.0 ka cal BP, the Altamont at ~16.2 ka cal BP, Algona at ~14.8 ka cal BP, and the Big Stone moraine at ~14.0 ka cal BP, which marks the transition to what is known as the Red River lobe. The number and timing of DML phases were reconstructed using multiple lines of evidence derived from geomorphic, lithologic, and stratigraphic analyses. In a study area located in southwestern Minnesota and eastern South Dakota, the delineation of subglacial bedforms was used to identify lateral shear margins positioned at the base of topographic highs. Locations of lateral shear margins also correlate to continuous glacial landforms and the greatest compositional variability within the till sheet, observed from modeling 451 DML till sample sites. Spatial relationships indicate that a single, heterogenous till sheet is surfically exposed throughout the study area and bed topography may have influenced ice-flow dynamics to generate faster flow. Correlations of moraines with the stratigraphy of Late-Wisconsinan sediments indicate there is one continuous basal till unit capped by discontinuous sorted, unsorted, and interbedded sediments that extends from the Bemis margin and continues up-ice of the Altamont moraine. A second till sheet overlies this stratigraphy north of the Algona moraine in Minnesota. Results suggest that the DML experienced two phases. The first, associated with the Bemis advance, is followed by a systematic retreat from the study area and reorganization of the ice mass. A second advance is associated with the Algona margin. The onset of global warming, defined by Greenland Interstade 1 (GI-1), occurred soon after the Algona advance at ~ 14.7 ka cal BP. Rapid climate change caused widespread stagnation and ice retreat to the Big Stone margin at a rate of 250 meters/year. The scale of stagnation and resulting surficial landforms is a unique response to unprecedented global warming associated with the GI-1 and probably not representative of earlier DML ice behavior. The ages of proglacial lakes that bound the Big Stone moraine suggest the margin is a recessional feature and does not represent a third advance.
A High Resolution Study of the Spatial and Temporal Variability of Natural and Anthropogenic Compounds in Offshore Lake Superior Sediments
(2006-05) Van Alstine, Jon D
Nine multi-cores were recovered during the summer of 2005 from an eight square kilometer area that is typical of the deep depositional environments found in the central and western parts of Lake Superior. Core sites were located in the troughs, centers, edges, and ambient regions around ring structures, which are believed to be the surface expression a polygonal fault system generated from the dewatering of underlying glaciolacustrine sediments (Cartwright et al. 2004). One sub-core at each site was extruded at 0.5 cm intervals to 10 or 12 cm depth, and analyzed for 210Pb, biogenic silica (BSi), total organic carbon (TOC), total organic nitrogen (TON), and methyl mercury (MeHg). The accumulation of bulk sediment, BSi, TOC, and MeHg cumulative inventories display large temporal and spatial variation among core sites throughout the study area. The total inventories of all three parameters vary by nearly a factor of two among the core sites. A comparison of BSi and TOC inventories to bulk sediment inventory reveals a direct relationship between the total compound accumulation at a particular core site and its bulk sedimentation rate. MeHg analyses show that spatial and temporal variability in MeHg appears to be due primarily to proximity to ring structures rather than variable bulk sediment accumulation. Our 8 km2 study area exhibits a larger range of MeHg values than shown in previous lake-wide studies of MeHg. Lake Superior is subject to a similar mass balance problem found in the oceans; a previous study determined that up to 80% of the river input of dissolved silica to the lake is not accounted for by either outflow of dissolved silica or by deposition of biogenic silica. However, new estimates based on the mass accumulation of BSi in this study suggests that there is only little imbalance, if any, and that silicate mineral authigenesis is not required to explain the fate of dissolved silica flowing into the lake. Single core analysis is not valid in regions of complex lake-floor terrain found throughout the central and western basins of Lake Superior. To accurately asses the accumulation of natural and anthropogenic compounds future investigations need to recover cores in the regions around complex lake-floor terrain that have exhibited 'normal' sedimentation, or attain duplicate cores to establish the degree of sediment and compound variability.
Late Glacial and Early Holocene History of the Glacial Lakes Aitkin and Upham Basin, North-Central Minnesota: Implications for the Timing of Post Glacial Eolian Activity
(2004-06) Marlow, Lisa Marie
Dune formation throughout Minnesota has been attributed to mid-Holocene aridity, however, the environmental setting of dunes in the Glacial Lake Aitkin and Upham basin suggest a Late Glacial and Early Holocene origin that is closely linked with exposure of source sands rather than aridity. Grigal et al. (1976) dated buried soils within a sequence of eolian sand near Lake Winnibigoshish, Minnesota, and identified several phases of eolian activity. These episodes were related to cycles of aridity and lake level fall during the Middle Holocene. Based on the work of Grigal et al. (1976), subsequent studies of eolian activity in Minnesota (Keen and Shane, 1990; Dean et al, 1996; Dean, 1997) concluded that all dunes in Minnesota are a result of Middle Holocene aridity. Glacial Lakes Aitkin and Upham occupied a basin in north-central Minnesota bounded on the north by the Giants Range and to the east, south, and west by hummocky moraines of the Rainy and Superior Lobes, and the St. Louis sublobe. Dune clusters occur sporadically throughout the Glacial Lakes Aitkin and Upham basin and occur in areas with abundant sources of fine sand. Granulometry indicates a 4q> grain size signature characterizes most dunes in the basin. Maximum dune amplitude is ~5 meters and dune morphologies suggest northwesterly winds. A sediment core collected from Hay Lake (93°W,52°N), located within a dunefield at the edge of Glacial Lake Upham, records three prominent peaks in whole-core magnetic susceptibility between 10, 100 and 6,600 yr BP. All dates referred to this paper are in uncalibrated 14C years B.P.. No elastic input is evident after 6,600 yr B.P., suggesting dune stability. Eolian events recorded in the core are interpreted as eolian activity that resulted from episodic lake drainage and exposure of abundant source sediment during the late Glacial and Early Holocene. The timing of dune formation within the basin has important implications for other dune fields throughout Minnesota. Using a Digital Elevation Model (DEM) the elevation of lake basin was adjusted for isostatic rebound based on the highest lake level, then tilted incrementally through several stages to assess relations among beaches, inlets, and outlets over time. The lake eventually drained, which led to the dune formation on littoral areas of exposed source sand.
Late Holocene Dry Periods Recorded in Speleothems from the Maya Lowlands of the Yucatan Peninsula, Mexico
(2007-05) Endsley, Erin Alison
Evidence for Holocene droughts in Mesoamerica exists from numerous paleolimnological studies. Speleothems from the Yucatan Peninsula can be used to help constrain the timing, intensity, and regional extent of these droughts. Late Holocene wet/dry cycles are inferred from the oxygen isotope record of speleothem calcite and the timing is constrained using U/Th dating. In the lowland neotropics, there is a strong negative correlation between 𝝳18O of precipitation and rainfall amount, i.e. the "amount effect". The 𝝳18O of speleothem calcite can then be used as a proxy for the relative amount of past precipitation in the Maya Lowlands. A speleothem from Cueva Tzabnah, near Tecoh, Yucatan, Mexico, has a basal date of 1240 ±61 yr BP and a top date of 28 ±21 yr BP, indicating growth during most of the Terminal Classic period of Maya prehistory. Oxygen isotopes were measured at 0.5 mm intervals, with an average value of -5.25%. 𝝳18O values increase near the hiatuses in speleothem growth, interpreted as evidence for the presence of drought conditions. The relative increases in 𝝳18O are dated using U/Th methods to constrain the timing of the drought events. In the top 3mm, the mean 18O value is 2.49% greater than the mean speleothem 𝝳18O value, and possibly represents drier conditions beginning in the mid-15th century AD consistent with a nearby lake sediment core record from Aguada X'caamal (Hodell et al., 2005). Another speleothem from Cueva Colurnnas, near Tzucacab, Mexico, has a basal date of 1347 ±63 yr BP and a top date of 520 ±99 yr BP, and a mean 𝝳18O value of -3.80%. Both speleothems contain evidence for past climate fluctuations during the Terminal Classic period, including a relatively drier period from about 850-900 AD recorded in both speleothems.
Lithostratigraphy, Hydrothermal Alteration, and Lithogeochemistry of Neoarchean Rocks in the Lower and Soudan Member of the Ely Greenstone Formation, Vermilion District, Northeastern Minnesota: Implications for Volcanogenic Massive Sulfides
(2007-01) Hoffman, Adam Timothy
Myth as True History: Medicine Wheels and Landmarks as Boundary Markers of the Lakota World
(2016) Burley, Paul D
This investigation examines physical, spatial and temporal characteristics of Native American medicine wheels located on the Northern Great Plains of the Unites States. Direct evidence for date and purpose of construction and use of medicine wheels is limited. As architectural symbols of native science, the structures are understood to be metaphors for native knowledge and creative participation with the natural world in both theory and practice, serving as bridges between the inner and outer realities. However, reasons for the respective location, meaning of architectural design, date of construction, and identification of people who constructed each medicine wheel generally remain unknown. An exception is Cloud Peak medicine wheel located on the west flank of the high point of the Bighorn mountain range in Wyoming, and shown to have been constructed by the Lakota tribe no earlier than about 1700 AD. Documented Lakota migration onto the Great Plains beginning during the early 17th century was reviewed to trace the timeframe and areal extent of the tribe's occupation of the region. Major regional and local physiographic features of the 2 Northern Great Plains were identified as they relate to Lakota traditional ecological knowledge (TEK). The tribe's history and culture, including mythology, cosmology, were reviewed from ethnographic records and documents addressing tribal history and sacred lifeway. Field observations were made of medicine wheel sites and physiographic features on the Northern Great Plains and adjoining regions of known import to the Lakota and other tribes which occupied the region during late prehistory. Observations and measurements of Cloud Peak medicine wheel, the Jennings site in east central South Dakota and additional archaeological sites of significance on the Northern Great Plains, and proximal relationships between those sites and major topographic and hydrogeologic features of the region suggest these features share common spatial, cosmographic and mythological relationships with the spiritual center of the Lakota world at Bear Butte, South Dakota. Based on locations of Cloud Peak medicine wheel and the Jennings site, physiographic and ecological characteristics of those locations and two additional sites of archaeological significance, and ethnographic records of Oceti Sakowin and Lakota TEK it is concluded these features compose primary elements of an Earth-scale sacred hoop delineating the physical boundaries of the traditional Lakota world. This sacred hoop was conceived, designed and built to include most of the Northern Great Plains region and traditional territory of the Lakota in particular. The hoop is interpreted to have been constructed soon after Lakota occupation of the Northern Great Plains by the late 18th century.
Plates for "The petrology, petrogenesis, and metallogeny of the South Kawishiwi intrusion in the Nokomis deposit area, Duluth Complex, northeastern Minnesota"
(2008-12-10) White, Christopher Reed
A Possible Late Pleistocene Impact Crater in Central North America and Its Relation to the Younger Dryas Stadial
(2020-08-04) Tovar Rodriguez, David
The causes that started the Younger Dryas (YD) event remain hotly debated. Studies indicate that the drainage of Lake Agassiz into the North Atlantic Ocean and south through the Mississippi River caused a considerable change in oceanic thermal currents, thus producing a decrease in global temperature. Other studies indicate that perhaps the impact of an extraterrestrial body (asteroid fragment) could have impacted the Earth 12.9 ky BP ago, triggering a series of events that caused global temperature drop. The presence of high concentrations of iridium, charcoal, fullerenes, and molten glass, considered by-products of extraterrestrial impacts, have been reported in sediments of the same age; however, there is no impact structure identified so far. In this work, the Roseau structure's geomorphological features are analyzed in detail to determine if impacted layers with plastic deformation located between hard rocks and a thin layer of water might explain the particular shape of the studied structure. Geophysical data of the study area do not show gravimetric anomalies related to a possible impact structure. One hypothesis developed on this works is related to the structure's shape might be explained by atmospheric explosions dynamics due to the disintegration of material when it comes into contact with the atmosphere. Relationship between structure's diameter (D) and deformed strata thickness (h) as well as the relationship between the diameter of the projectile (d) and the depth of the water column (H ), which is considered in this study due to the geographical considerations of the area 12.9 ky ago and BP, are consistent with an extraterrestrial event. Other hypotheses, such as lake processes and glacial processes, are difficult to reconcile with the reported observations, so the impact hypothesis and its relationship with the formation of the Roseau structure are viable.
Provenance of Glacially Transported Material near Nimrod Glacier, East Antarctica: Evidence of the Ice-Covered East Antarctic Shield
(2007-05) Brecke, Devon Michele
Evaluation by glacial-clast petrography, igneous whole-rock geochemistry, metamorphic mineral composition, and magnetic susceptibility of glacially eroded, transported, and deposited material near Nimrod Glacier, East Antarctica provide information on the composition of the ice-covered East Antarctic shield. Precambrian basement of East Antarctica is only documented in the Transantarctic Mountains near the polar plateau of Nimrod Glacier, providing an ideal location to look for adjacent sub-ice Precambrian terrain. Over 100 igneous and metamorphic rock clasts collected from moraines near the head of Nimrod Glacier show both local and transported material. Physical characteristics of local rock fall show angular edges, whereas distantly transported material exhibits rounded edges, glacial striations, or rock types only seen upstream. Most metamorphic rock types collected show intense deformation fabrics, high-grade mineral assemblages, and high-grade P-T conditions, which are similar to the Archean and Paleoproterozic Nimrod Group. Many igneous rocks may originate from either the Nimrod Group or from the syn-tectonic and post-tectonic Cambrian-Ordovician Granite Harbour Intrusive series, and some come from nearby Ferrar dolerite (Jurassic). These samples are compared to Cambrian-Ordovician rocks in southern Victoria Land, which differ in trace element trends. Although many of the clasts can be explained by local derivation, others appear exotic and may represent more distal origins in the shield interior. Future geochronology will help to refine the relative contributions of local and distal sources to test these conclusions.
Seasonal Delta 18 O and Sr/Ca Records from Submerged Pleistocene Fossil Corals in the Western Equatorial Pacific
(2008-12) Gruhn, Leah Mohr
Five fossil Porites corals from the Huon Gulf have been analyzed for monthly Sr/Ca and ẟ18O variations. Additionally, two nearby modern Porites corals from Sanaroa Island and New Britain, both located within the Solomon Sea (Figure 1-2), have been collected and analyzed for monthly Sr/Ca and ẟ18O variations so that we can better understand how modern Porites corals are recording environmental conditions in the Solomon Sea. The mean ẟ18O and Sr/Ca values, combined with seasonal amplitudes preserved in the geochemical signals in the fossil corals have been compared to those in the modern corals in order to address the following questions: (1) What was the eustatic sea level when the fossil corals were living? Did the fossil corals grow in times of low to intermediate rapidly rising sea level or at high and stable sea level? and (2) What was the climate in terms of SST and SSS in the western equatorial Pacific when the fossil corals were living?
The Sequence Stratigraphy of the Chinle Formation in the Dinosaur National Monument Region, Utah and Colorado, USA
(2007-10) Erickson, Ryan Eric
Deposition of Late Triassic Chinle Formation fluvial and lacustrine sediments in the Dinosaur National Monument (DNM) region of Utah and Colorado is bounded by two major periods of landscape degradation (stratal truncation) and punctuated by a period of non-deposition (well-developed paleosol pedogenesis). Correlation of these unconformable regional features in outcrop and geophysical well-logs enable the identification of two genetically related Chinle depositional sequences. The first depositional sequence includes the Gartra Member and the mottled member. These units are located within regional paleovalley networks that are attributed to Mid-Triassic Tr-3 sequence boundary erosion. The basal Gartra Member conglomeratic sandstone was deposited in topographically-constrained, low-sinuosity fluvial systems. As aggradation continued, the lateral constraint of the paleovalley on the fluvial system decreased and higher sinuosity fluvial deposits and minor floodplain deposits are preserved. Overlapping the paleovalley margins and covering the entire landscape are fine grained mottled member floodplain deposits. Capping the mottled member is a well-developed paleosol that is a non-depositional sequence boundary and the end of the first depositional sequence. The second depositional sequence includes the ocher member and the upper member. Ocher member siltstone deposition occurred in large, shallow, evaporative, nonmarine influenced, lacustrine environments. Initial upper member sandstone and siltstone units were deposited in fluvial-deltaic environments. Later upper member deposits are weak-red lacustrine siltstones with few interbedded fine-grained sandstones. The J-0 erosional unconformity marks the top of preserved Chinle deposition and the bottom of the subsequent Jurassic eolian sandstones. After identification and analysis of Chinle depositional environments and known allogenic influences (a gradually drying climate), an autogenic mechanism is proposed to be the primary influence on the observed facies changes. In a basin with pre-existing erosional topography, the annealing of this landscape could initiate autogenic retreat of the depositional systems leading to distinct facies changes in the distal basin. In the first Chinle depositional sequence (Gartra Member-mottled member), the annealing of the Tr-3 paleovalley network caused a decrease in fluvial energy and the autogenic retreat of deposition into the proximal Eagle Basin. In the distal basin, continued subsidence and a period non-deposition resulted in a well-developed paleosol horizon (mottled member paleosol) and the transgression of lacustrine facies (ocher member). As the sediment-charged fluvial mega-fan prograded out of the Eagle Basin, sedimentation in the distal basin gradually increased until thick fluvial-deltaic deposits (upper member sandstones) developed filling excess basin accommodation. Subsequent allogenic drying climatic conditions may explain a decrease in later distal basin sedimentation and the second observed lacustrine transgression (upper member siltstones).
Stratigraphic Study and Joint-Pattern Analysis in the Biwabik Iron Formation, Virginia Horn Area, Northeast Minnesota
(2003-09) Neilson, Kimberly Jane
The Biwabik Iron Formation of the Mesabi Range in northeastern Minnesota is comprised of chemically precipitated minerals. Cherty (granular) iron-formation formed on a shallow, tidally-influenced shelf, while slaty (fine-grained) iron-formation formed in deeper water. Thirty-nine sections from a 311-foot long drill core taken from north of the EVTAC pit area were studied to determine the mineralogy and paragenesis of the formation. Growth textures and crosscutting relationships indicate the primary minerals are chert (cement), greenalite, hematite and siderite. Very fine-grained carbonaceous material was deposited simultaneously. Secondary minerals include ankerite, magnetite, minnesotaite, and stilpnomelane. There were multiple generations of chert, minnesotaite, and siderite. Minnesotaite and magnetite replaced chert, iron-silicates, and ironcarbonates. Ankerite replaced chert and iron-silicate and grew in close association with magnetite. Magnetite was not replaced by any mineral, and grew abundantly in the cherty iron formation. Stilpnomelane grew abundantly in the slaty iron-formation. A study of joint orientations was undertaken on the premise that the data would be of value in planning the orientations of blasting grids at taconite pits. There are common joint orientations in seven taconite pits near the Virginia Hom area. The joints do not appear to vary with the strike of the iron-formation in the anticline/syncline structure of the Virginia Horn, and dips are generally vertical. A dominant joint direction found in Archean rocks of the Virginia Horn area (280°) is close to the dominant fault strike direction (285°) in the Virginia Horn, suggesting some control of the iron-formation jointing by underlying Archean basement rocks.