2004 Senior Independent Study Projects

 

 

 

“Tree-Ring Dated 1000-Year Advance of Columbia

Glacier, Prince William Sound, Alaska”

 

by

 

Matthew Beckwith-Laube

 

A 1000-year advance of Columbia Glacier is documented by over 400 tree-ring calendar dates from subfossil and living tree hemlock trees.  These dates show a continuous advance punctuated by a mid fjord standstill.  Advance beginning before AD 1020 along the northern reaches of the fjord attains advance rates of 40-60 ma-1 and ice thickening rates of 2.5-3.0 ma-1.  Narrow fjord geometry along with the coalescence of two tidewater margins in part forced the moderate advance through this area. Upfojord advance rates decreased as the calving margin enters deep waters and expanded laterally into alleys on the east and west margins.  This period of advance covers about 400 years and covered 8 kilometers averaging rates of approximately 20 ma-1.  This expansion and water depths of 500 meters brought about a standstill that lasted from AD 1450 until AD 1750. 

 

Readvance was underway by AD 1758 after a nearly 300-year standstill. Ice thickened again and expanded into areas along the eastern margin as advance pushes south.  Water depths along the southern portion of the fjord are in excess of 400 meters and expansion continues through the late 1700’s.  Toward the outer portion of the fjord advance greatly increased as water depths shallowed toward the terminal moraine shoal.  Advance in the lower fjord covered about 6 kilometers in 50 years, with an average advance of over 120 ma-1.  Variations in advance rates reflect the surrounding topography of the fjord, especially the water depths at the calving margin.  Comparison with other tidewater glaciers of Prince William Sound display similar patterns of slow advance through deep fjord waters and fast advance in shallow waters approaching a terminal shoal. 

 

 

 

 

“Paleomagnetic and Anisotropy of Magnetic

Susceptibility Tests of Accretion at Fast Spreading

Ridges Using Dikes and Lava Flows in Northern Iceland”

 

by

 

Marc Bryson

 

            Structure at mid-ocean spreading centers and the accretion of oceanic lithosphere are not well understood.  Simple structural models of fast and slow spreading centers have been generated from study of ophiolites, broad superficial surveys, and deep sea drilling data.  Some models depict lavas at fast spreading centers dipping toward the spreading center (Macdonald, 1982) while others describe the exact opposite situation (Karson et al., 2002, Varga et al., in press).  Studies of the Hess Deep Tectonic window (Karson et al., 2002) offer a unique three-dimensional look at subsurface structure along the EPR.  Much of what is found at tectonic windows like the Hess Deep contradicts current models derived from two dimensional observation and superficial surveys.  Iceland’s distinctive position above a mantle plume provides it with a robust magma supply that mimics fast spreading centers.  This makes Iceland an ideal analog to fast spreading ridges that can be studied on land.  Paleomagnetism and AMS were used to analyze the tilting and flow history of dikes and lavas on a fossil copy of the MAR in the Blönduós flexure area of northern Iceland.  The results of these analyses provide support for the model of fast spreading observed at the Troodos ophiolite and the Hess Deep tectonic window (Karson et al., 2002, Varga et al., in press). 

 

 

 

 

“Paleomagnetic Studies of Lava Flows to

Determine if Iceland is an Ideal On-Land Analog of

Mid-Ocean Ridge Tectonic Processes”

 

by

 

Steven M. Burton

 

            The Hess Deep exposure of the East Pacific Rise, offers a tectonic window into fast spreading ridges that can only be viewed in two-dimensions.  On-land analogs of the fast-spreading ridge of the Hess Deep offer a better tectonic window into fast-spreading processes.  Iceland is an ideal model for the Hess Deep as they both have inward dipping lava flows and outward dipping dikes.  We present paleomagnetic remanence data from 15 samples that indicate that the lava flows in Iceland were tectonically tilted after formation, and Iceland can be used as an on-land analog to the tectonic window of Hess Deep allowing a three-dimensional view of fast-spreading ridge processes. 

 

 

 

 

“The Depositional Environment and Ceiling

Integrity of the Vanport Limestone (Pennsylvanian)

in the East Fairfield Coal Company Underground

Mine Located in Petersburg, Ohio”

 

by

 

Jessica Hiznay

 

            Within the East Fairfield Coal Company (EFCC) underground limestone mine in Petersburg, Ohio, the Vanport Limestone demonstrates a varying ceiling integrity.  Sections of the ceiling have fallen creating a serious safety and economic issue for EFCC. 

 

            The comparison of eight samples collected within the mine show a correlation between the amount of phylloid algae preserved in the sample and the integrity of the ceiling.  Each sample was identified to have a micritic matrix with an average slide percentage around 55%.  Every sample in this study is identified as biopelmicrite and wackestone.  Samples collected from the good ceiling, JH-1, JH-3, and JH-4, and transitional ceiling, JH-5, contained less than 25% phylloid algae remains.  While samples from the bad ceiling, JH-2, JH-6, JH-7, and JH-8, all contained 30% or more phylloid algal remains.  The bands of phylloid algae remains weaken the massive bedding of the limestone allowing chunks to fall out onto the mine floor.

 

            The depositional model that represents the Vanport Limestone within the study area appears to be a carbonate mud-mound with a phylloid algal mound or extension accumulating during the same time period.  The depositional environment was identified based upon fossil identification and identified sedimentary features as a low energy system below the fair-weather wave base in a shallow warm environment.  This study identified the changes in ceiling integrity from good to poor ceiling is caused in part by the presence of the remains of a phylloid algal mound.  Understanding the changes of ceiling integrity within the EFCC underground limestone mine will increase the safety of the miners and the productivity of the mine. 

 

 

 

“Paleoecology and Astogeny of Prasopora simulatrix

Colonies of the Decorah Formation of

Northeastern Iowa (Middle Ordovician)”

 

by

 

Aaron M. House

 

            The Tippecanoe epeiric sea that spanned much of the north-central United States during the Ordovician was home to a great many encrusting organisms.  Among these were the domal Prasopora trepostome bryozoans.  These bryozoans are found in the Decorah Formation of northeastern Iowa, occurring most commonly in the Ion Member.  Domicile borings were often made in the Prasopora colonies by filter-feeding organisms attempting to create an appropriate hard-substrate home.  The most widespread boring found on Prasopora was Trypanites.  This boring is characterized by a straight tubular shape, generally normal to the hard substrate that has been bored into.  Organisms making this boring are shown to prefer specific ranges of slopes and theta angles (angle from the center of the base to the boring locus) on their Prasopora hosts.  This indicates that there are specific advantages to the Trypanites-boring organisms to choose these ranges.  This area is where food would settle out of currents flowing over the colonies, and also where any larvae of Trypanites-boring organisms would settle out of the water column.

 

            There is also evidence of ecophenotypic variance in the shape of Prasopora colonies.  Colonies that are more shallow-sloped may have developed in more turbulent waters for stability, whereas the more domal colonies probably formed in less turbulent waters where they would not have been as likely to be toppled over.  Ecological factors triggering degeneration-regeneration cycles in Prasopora colonies are shown in the occurrence of brown bodies in a number of samples. 

 

            Finally, a small number of samples show traces of bioimmuration.  This process involved soft-bodied encrusters establishing themselves on hard substrates, then being overgrown by an episkeletozoan.  After the soft-bodied organism dies and the hard substrate chemically dissolves or is physically removed, its only remains consist of the impression that was made in the episkeletozoan which overgrew it.  The occurrences cited here are the oldest known bioimmurations. 

 

 

 

“Investigating The Possibility Of Using Old-

Growth Trees To Reconstruct A Proxy For Historic

Lake Erie Water Levels”

 

by

 

Carl Kannenberg

 

            Lake Erie fluctuations have a significant impact on both the environment and the economy of the surrounding area.  Lake levels fluctuate in response to a variety of climatic conditions within the basin, which in turn are linked to larger-scale atmospheric teleconnections via the Pacific/North American Oscillation (PNA).

 

            Comparison of NOAA monthly Lake Erie level variations with moisture sensitive tree-ring chronologies from sites within the basin show a positive and negative correlation with March lake levels.  Tree growth in the basin reflects the overall moisture budget of the region, as do lake levels.  Local tree ring chronologies alone are not sufficient to model past lake levels, and I have exploited the PNA seesaw between the upper Midwest and the North Pacific climate, by including a set of coastal Gulf of Alaska ring-width series in the modeling efforts.  These tree-ring chronologies are temperature-sensitive and have a strong negative correlation with March lake levels in Lake Erie.  Warm springs in the Gulf of Alaska are associated with drier conditions, and lower lake levels, in the Lake Erie region. 

 

            A preliminary dendroclimatic model based on North Pacific and Midwestern tree ring series explain over 50% of the variation in March lake levels.  The common period between tree growth and lake level data is 62 years.  The reconstruction model spans from 1790 to 1981 and shows that recent declining lake levels have been experienced in the past as well. 

 

 

 

 

“Volcanic Stratigraphy of Northern Vididalsfjall, Iceland”

 

by

 

Deanne Rider

 

            A detailed stratigraphic study was conducted on a series of Tertiary volcaniclastic rocks exposed within the valley walls in northern Viòidalsfjall, a mountain range in northern Iceland.  The rocks were deposited near the axis of the Snæfellsnes rift which was active 15 to 7 Ma.  To the northeast of the valley, a WNW-striking fault separates the area of predominantly volcaniclastic rocks from a package of thin basaltic lavas.

 

            An 806 m section was described and divided into three units based on lithological differences.  The lower unit represents locally derived volcaniclastic rocks such as lahars.  The middle unit is primarily clast-supported breccia, suggesting some transportation from source in water.  Euhedral crystals within the matrix suggest that the distance traveled is still low.  Within this unit, a 40Ar/39AR age date for a lava is 8.62 +/-0.30 Ma.  The upper unit consists of fine ash and volcanic sandstone to mudstone.  Lithological characteristics suggest greater transportation by either wind or water and some thinly bedded strata may have been deposited in calm water.  Hydrothermal alteration and mineralization are common throughout the sequence.

 

            Major and minor and trace element composition was determined for 13 samples by X-ray spectroscopy.  The majority of these samples plotted as basalts but two are dacitic to rhyolitic.  The basalts are uniformly evolved with MgO of 4.5 to 5% wt.  The lavas within section are not traceable laterally suggesting they were confined by local paleo-topography. 

 

            The section is interpreted to represent the filling of a basin progressing from initial, locally derived rocks to rocks undergoing high levels of transportation before deposition.  The basin originated by normal displacement on the WNW-striking fault.  The geometry of the fault suggests it is part of a transform accommodation zone, accommodating lateral offset of the paleo-rift axis. 

 

 

 

“Behavior and Systematics of Worm-Like Borers

Found in the Arnheim and Bull Fork Formations (Ordovician)”

 

by

 

Andrew M. Shields

 

            Bioerosion is present in almost all Late Ordovician exposures.  Understanding the behaviors, abundances, and evolution of the many types of borings present in the Late Ordovician is dependant upon the collection of copious amounts of size and distribution data.  Trypanites borings are the most prevlavent throughout the entirety of the Ordovician.  They occur in most hard substrates including bryozoans, brachiopods, corals, hardgrounds, etc.

 

            In the Arnheim/Bull Fork Formations the Trypanites borings exhibit several important characteristics.  The selection of less resistant substrates led the Trypanites borers to deviate from their typical vertical boring behavior and travel in a horizontal direction running parallel to the interface between the bryozoan it started in and whatever substrate the bryozoan happened to be encrusting.  Several variations on this ditching pattern can be observed as actual ditches in substrates (brachiopods, rugose corals, and biosparite hardgrounds), and as casts on the underside of bryozoans that were removed from their substrate.  The presence of a ditching pattern is a simple key to indicate a borer’s preference of substrate. 

 

            The diameter of the Trypanites borings in these formations also yields the presence of two size groupings.  The overall average size of 0.5 mm is common amongst all of the different substrates.  In rugose corals and biosparite hardgrounds a second grouping of larger borings can be found, averaging a size of 1.5 mm in diameter.  This separation of size ranges provides the potential for distinguishing different species of Trypanites organisms based on their diameter.