SUMMARIES OF STUDENT XRF/ICP-MS
RESEARCH, 2000 - 2012
(most recent listed at bottom of page)
Kelly Woody (BS Geology, MTSU - 2000) - 'Investigation of the Lithotectonic Sources of Granitic Magmas, Waldoboro Plutonic Complex, Coastal Maine'
This senior thesis project seeks to correlate Acadian age granitic phases within the Waldoboro Plutonic Complex, Maine, to surrounding lithotectonic terranes through major element, trace element, isotopic and U-Pb zircon age studies. Samples of WPC granitic phases were collected during Summer, 1998. Sr, Nd, and O isotopic analyses were completed during Summer, 1999. U-Pb zircon ages were obtained at the UCLA ion probe lab during Summer, 1999. Major and trace element analyses were obtained in the MTSU MDXRF lab during Spring Semester, 2000.
Woody, K., 2000. Zircon Age Dating of the Waldoboro Plutonic Complex, Southeast Maine and Geomorphology of the Surrounding Area. Senior Thesis. Department of Geosciences, Middle Tennessee State University
Beverly Buchanan and Brandy Sue Sanders (MTSU Undergraduate Geology Majors) - 'Investigation of the Effects of Crustal Assimilation and Magma Mixing on Lava Flow and Pyroclastic Deposits of the Cloud Cap Eruptive Series, Mount Hood Volcano, Oregon'
This senior thesis seeks to elucidate effects of pre-eruptive crustal processes (crustal assimilation, magma mixing) on lava and pyroclastic deposits within the Cloud Cap eruptive series at Mount Hood Volcano, Cascade Range, Oregon. Previous field and petrographic studies suggest that magma mixing and/or crustal assimilation played an important role in the chemical evolution of Cloud Cap magmas. This project involves detailed geochemical modeling of the effects of those processes on Cloud Cap lavas using major element, trace element and isotopic data. Samples are to be collected during Summer, 2000. Geochemical data will be obtained during Fall Semester, 2000. All major and trace element data will be obtained by x-ray fluorescence spectrometry in the MTSU MDXRF laboratory.
Cribb, W., Buchanan, B. and Sanders, B.S. 2002. Investigation of crustal and upper mantle source region processes on the geochemical and mineralogical composition of lavas and pyroclastic rocks at Mount Hood volcano, Cascade Range Volcanic Arc, U.S.A. Proceedings and Abstracts, Middle Tennessee State University Student-Faculty Research Symposium.
Lisa Ooten (BS Geography, MTSU - 2001) /Dave Vachon (MTSU Undergraduate Geology Major)- 'McNair Scholars Research: Establishment of Base-Line Geochemical Data for Archeological Sites, Taos Valley, New Mexico'
In conjunction with the McNair Scholars Program at Middle Tennessee State University and the Museum of New Mexico's Office of Archeological Studies, Lisa Ooten will spend Summer, 2000, establishing base-line geochemical data for archeological sites containing basalt quarries, raw materials, and artifacts. These sites are located in north central New Mexico in the Taos Valley of the Rio Grande River. Due to a lack of source analyses in these areas, archeologists, geologists and geographers are currently unable to correlate these artifacts to their source. Major and trace element analyses conducted in the MTSU MDXRF laboratory will provide base-line geochemical data so that future archeological artifacts can be traced to specific quarries in the upper Rio Grande Valley of north central New Mexico.
Boyer, J.L., Moore, J.L and Ooten, L.A. 2001. Volcanic Chipped Stone Quarries: A Preliminary Investigation of Major Material Sources on the Taos Plateau. In, Chipped Stone Material Procurement and Use: Data Recovery Investigations Along NM 522, Taos County, New Mexico. Boyer, J.L. and Moore, J.L. (eds). Museum of New Mexico Office of Archaeological Studies, Archaeology Notes 292. 99-123.
Ooten, L., Cribb, W., and Heffington, J., 2000. Multi-dispersive x-ray fluorescence spectrometry: applications to archeaological provenance studies in the north-central Taos Valley, New Mexico. GSA Abst. with Progs. 32, 7.
Cribb, W., Ooten, L., and Heffington, J., 2000. Application of multi-dispersive x-ray fluorescence spectrometry to archaeological provenance studies, north central Taos Valley, New Mexico. GSA Abst. with Progs 32, 7.
Ooten, L., Heffington, J., Cribb, W. and Boyer, J., 2000. Initial multi-dispersive x-ray fluorescence investigations of basaltic rock quarries in northern New Mexico. McNair Scholars Research Presentations, Middle Tennessee State University
Ooten, L., Cribb, W. and Heffington, J., and Boyer, J., 2001. Multi-dispersive x-ray fluorescence analysis of prehistoric quarries in the upper Taos Valley. SAEOPP/UTK McNair Scholars Conference, The University of Tennessee.
Ooten, L., Cribb, W., Heffington, J. and Boyer, J., 2001. Multi-dispersive x-ray fluorescence analysis of prehistoric quarries in the upper Taos Valley. McNair Scholars Research Presentations, Middle Tennessee State University.
Lange, Nicholas (MS Geology, Vanderbilt University - 2001)
The Secret Pass Canyon area lies on the flank of the Black Mountains accomodation zone and is dominated by east-tilted fault blocks. A thick early to mid-Miocene volcanic sequence suggests that it represents a volcanic crater. This volcanic sequence is beautifully exposed in a relatively coherent block bounded on the west by the east-dipping Arabian Mine fault and on the east by the west-dipping Frisco Mine fault. Exposed strata include (from oldest to youngest) (1) >~500 m of massive trachyandesites and trachydacites, which represent shallow intrusions; (2) a heterogeneous >~150 m sequence of primary and reworked air fall and welded tuffs with possible Peach Springs Tuff; (3) ~600 m of massive rhyolite breccias; (4) ~ 500 m og high-silica rhyolite flows; and (5) trachydacite plugs and sills. All units are characterized by biotite and plagioclase phenocrysts; sanidine is limited to the most evolved rhyolites, and other mafic phenocrysts are extremely sparse. SiO2 ranges from 60-83 wt%, and all of the units are potassic, with K2O >~4 wt% even in andesites. REE patterns are extremely uniform except that high-silica rhyolites are poorer in LREE and have larger negative Eu anomalies. 40Ar/39Ar dates suggest an abrupt transition from the intermediate to silicic to dacitic magmatism between ~18.5-17.4 Ma. Faults cut through all of these units suggesting at least one period of extension that post-dated the main pulse of magmatism.
Lang, N. P., Miller, C.F., Faulds, J.E., Heizler, M.T. and Cribb, W., 2002. Constraining the evolution of the secret pass canyon volcanic center, northern Colorodo River extensional corridor, northwest Arizona: Implications for a source and possible relation to the Peach Springs Tuff.. GSA Cordilleran Section Abstracts with Programs.
Lang, N. P., Miller, C.F., Faulds, J.E., and Cribb, W. 2001. Eruptive history and syn- and post- volcanic tectonism of the Union Pass volcanic center, Arizona. GSA Cordilleran Section Abstracts with Programs.
Lang, N.P., 2001. Evolution of the Secret Pass Volcanic Center, Colorado River Extensional Corridor, Northwest Arizona. MS Thesis. Department of Geology, Vanderbilt University.
Scott Crombie and Jason Powell (MTSU undergraduate geology majors, 2002)
Mt. Hood volcano, Oregon, in the Cascade Range volcanic arc has erupted predominantly basaltic andesite to andesite lava and pyroclastic flow deposits over the past 700,000 years. Most lavas belong to the medium-K calc-alkaline series and show a restricted range of com-position (56 - 63 wt% SiO2). Past studies suggest that Mt. Hood magmas are generated by partial melting of an upper mantle source region, and that the restricted range of erupted compositions is due to repeated cycles of crystal fractionation combined with mixing of evolved and primitive magmas (Cribb and Barton, 1997). A new geochemical study is underway to investigate the possibility that formation of Mt. Hood magmas involves partial melting of subducted oceanic lithosphere (adakites). This study involves geochemical analysis of lavas and pyroclastic deposits extruded during each of Mt. Hood's main eruptive periods: Main Stage (700,000 - 29,000 yrs), Polallie (15,000 - 12,000 yrs), Timberline (1800-1500 yrs), and Old Maid (250-176 yrs).
Results show that Mt. Hood lavas can be classified as high-Mg'
adakites, and exhibit major and trace element signatures similar to adakites
identified in other volcanic arcs and elsewhere in the Cascades (e.g. Mt.
St. Helens): SiO2 > 56 wt%, Al2O3 15 wt%, Na2O 3.5 wt%, Sr 400 ppm, Y
18 ppm, Sr/Y 40 ppm, Zr/Sm 50 ppm. Furthermore, Mt. Hood lavas exhibit
K2O-Na2O-CaO compositions close to those of experimental melts produced by
partial melting of subducted oceanic crust at the amphibolite-eclogite
transition. High Mg concen-trations in Mt. Hood lavas and positive correlation
between compatible (e.g. Nb, Ta) and incompatible (e.g. La, Sr) elements
suggest metosomatic reactions between slab-derived melts and the sub-arc
mantle. Absence of high field-strength element (HFSE)/large-ion litho-phile
element depletions can be attributed to enrichment of HFSE in slab-derived
melts during melt - sub-arc mantle interactions.
Crombie, S., Powell, J. and Cribb, W., 2002. Potential magma formation by partial melting of both mantle and subducted lithosphere at Mt. Hood volcano, Cascade Range volcanic arc. GSA Abst. with Progs. 34, 6.
Jeff Sherard (Undergraduate Anthropology Major, The University of Alabama)
Recent excavations at the Moundville site, located approximately 20
miles south of
recovered include decorated pottery sherds, shell and ceramic beads, mica,
lithic tools, and copper.
Typically, southeastern Native Americans utilized native sheet copper
to fashion body adornments and other ceremonial
objects. Native copper, found
within the Ducktown Formation located in
This artifact category could potentially give archaeologists more information concerning the construction methods and structural elements a prehistoric building. By employing XRF testing technologies, it is hoped that the chemical composition of silica forth can be identified and better understood. By combining the information gained from this analysis with future comparative studies, a better comprehension of this curious artifact category will be generated.
Brian Harper (Undergraduate Geology Major, Vanderbilt University)
Evidence for pluton orientation and possible granite cumulates: Aztec Wash Pluton, Southern Nevada The mid-Miocene Aztec Wash pluton (Eldorado Mts., NV) can be divided into two distinct zones: a homogeneous granitic zone (HG) and a larger heterogeneous zone (HZ) consisting of rocks ranging from basaltic to granitic composition. This project is focused on the HG and attempts to describe contrasting units of granitic composition and answer questions regarding the existence of cumulate granites and pluton orientation. All rocks within this zone are of granitic composition (72-78 wt.% SiO2), but textures and fabrics vary between locations. Toward the southern and western margins of the HG, the granites consist of very large subhedral to euhedral K-spar grains. At the northern and eastern margins, the granite becomes much more fractionated, finer grained, and contains many miarolitic cavities. Felsic enclaves can also be found closer to the HZ, and fine felsic dikes (~0.5m) are found throughout the zone. The HZ also contains granites that resemble those found in the south and western regions of the HG, and geochemistry suggests that these rocks crystallized from a similar magma, although less fractionated. Therefore, we propose that the Aztec Wash pluton was emplaced with its top to the north-northeast. This is consistent with NNE dipping paleohorizontal indicators in the HZ and a NNE fabric found in some of the course granites of the HG. Magma replenishment occurred only in the HZ, where granitic magma began fractional crystallization by crystallizing large feldspars that settled down to the bottom of the chamber. Basaltic magma periodically intruded into the HZ zone also, settling on the floor and squeezing out any remaining melt. Therefore the HZ contains alternating sheets of basaltic material and granitic cumulates, with intermediate composition rocks in between where mixing occurred. In the HG, however, there was no magma replenishment and all rocks crystallized from fractionated melt left behind from fractional crystallization in the HZ. Close examination of granites to the south and west of the HG suggest that they also formed from cumulate processes, although from a more fractionated melt source. The HG, therefore, represents a system of constant fractional crystallization up to the highly fractionated cavity rich rocks at the northeastern margin of the pluton.
Harper, B.E., Miller, C.F., Wiebe, R.A., Cates, N.L. and Cribb, W. 2003. Granite accumulation and fractionation in a dynamic, open-system magma chamber, Aztec Wash pluton, Eldorado Mtns, Nevada. GSA Abst. with Progs. 35, 4.
Scott Crombie, Brian Cosky, Jennifer Baxter, Beverly Buchanan (MTSU Undergraduate Geology Majors, 2003-2004)
The ~ 700,000 year history of Mt. Hood volcano, located in the northern Oregon Cascade Range volcanic arc, is dominated by the eruption of andesitic lava flows and pyroclastic deposits. New geochemical studies of Mt. Hood andesites suggest magma formation by partial melting of subducted oceanic lithosphere (adakites), rather than by partial melting of ultramafic rock within the sub-volcanic arc mantle wedge. Most Mt. Hood andesites exhibit major and trace element characteristics similar to those of slab-derived melts identified along other volcanic arcs: SiO2 > 56.0 wt %, Al2O3 > 15.0 wt %, Na2O > 3.5 wt %, Sr > 400 ppm, Y < 18 ppm, Sr/Y > 40 ppm, Zr/Sm > 50 ppm. MgO concentrations in Mt. Hood andesites (> 2.5 wt % MgO) are characteristic of high-Mg adakites, suggesting chemical interactions between slab-derived melts and Mg-rich peridotite within the sub-arc mantle wedge. Chemical reactions between slab-derived melts and sub-arc mantle rocks also are indicated by positive correlation between compatible (e.g. Nb, Ta) and incompatible trace elements (e.g. La, Sr). The enrichment of high field-strength elements relative to large-ion lithophile elements in Mt. Hood andesites is a possible effect of such reactions within the sub-arc mantle. The melting of subducted oceanic lithosphere may occur beneath Mt. Hood due to a shallow angle of subduction and relative proximity of the volcano to the Cascadia trench, as compared to other volcanoes in the southern Washington to northern Oregon Cascades. A Mt. Hood slab depth of 75-85 km (the range of experimentally determined depths at which partial melting of subducted oceanic lithosphere may occur) suggests a low angle of subduction, a tectonic attribute proposed for the generation of adakite melts elsewhere. Contrastingly, other major Cascade Range volcanic centers in southern Washington to central Oregon do not exhibit strong geochemical evidence for melting of subducted oceanic lithosphere, suggesting deeper slab depths as a function of greater distance from the Cascadia trench. In this region of the Cascades, Mt. Hood appears most similar to Mt. St. Helens where slab depth is ~75-80 km and melting of subducted lithosphere also has been proposed.
Crombie, S., Buchanan, B., Baxter, J. and Cosky, B., 2003. Geochemical and tectonic attributes for melting of subducted oceanic lithosphere, Mt. Hood volcano, Oregon. GSA Abst. with Progs. 35, 6.
Cosky, B., Crombie, S., Baxter, J. and Buchanan, B., 2003. Geochemical investigation of the mechanisms of magma formation beneath the northern Oregon Cascades. Tennessee Academy of Sciences, in press. (Note: Presentation of this paper at the 2003 meeting of the Tennessee Academy of Sciences was awarded second place in the student presentation division.)
Most theories for magma formation within subduction zones center
on partial melting of the sub-arc mantle wedge during chemical interactions
with hydrous fluids released from subducted oceanic lithosphere during the
amphibolite-eclogite transition. However, these theories are augmented by
research showing that magmas also may form by partial melting of young, warm
subducted oceanic lithosphere. The potential for such adakite melts has been
studied previously in the southern Washington Cascade Range at Mt. St.
Helens (Defant and Drummond, 1993). Current research investigates whether
lavas erupted at Quaternary volcanic centers in the northern Oregon Cascades
(Mt. Defiance, Mt. Hood, Pinhead Buttes, Olallie Butte) also exhibit
geochemical signatures characteristic of adakite melts. This region is
appropriate for study because these volcanic centers are located along a
north-south trend with similar distance and depth relationships to the
Cascadia trench and the underlying subducted lithosphere as those of Mt. St.
Helens. Most lavas erupted throughout the study area exhibit major and trace
element concentrations similar to adakites identified elsewhere: SiO2 > 56
wt%, Al2O3 > 15 wt%, Na2O > 3.5 wt%, Sr > 400 ppm, Y < 18 ppm, Sr/Y > 20 -
40 ppm, Zr/Sm > 50 ppm. Furthermore, most lavas fall along a K2O-Na2O-CaO
trend close to that of experimental melts representative of those derived by
partial melting of subducted oceanic crust at the amphibolite-eclogite
transition. However, certain lavas near Mt. Hood and at Pinhead Buttes
exhibit relatively high MgO concentrations (~8 wt%), suggesting significant
sub-arc mantle input. Additionally, positive correlation between compatible
and incompatible trace elements in most lavas suggests metasomatic reactions
between any slab-derived melts and the sub-arc mantle. Lavas from Mt.
Defiance and Pinhead Buttes exhibit Sr/Y similar to typical arc volcanics.
Accordingly, the hypothesis is that although certain northern Oregon
Cascades Quaternary lavas do exhibit geochemical characteristics suggesting
derivation by partial melting of subducted oceanic lithosphere, the region
is largely characterized by the formation of hybrid' adakite magmas
containing melt contributions from both subducted oceanic lithosphere and
the sub-arc mantle.
Cosky, B., Crombie, S., Baxter, J., Gordon, J. and Cribb, W. 2005. Potential Formation of 'Hybrid' Adakite Magmas Within the Northern Oregon Cascadia Subduction Zone. Geol. Soc. Amer. Abst. with Progs. 37, 7.
Josh Gordon (MTSU undergraduate geology major, 2004-2005)
In an effort to gain more understanding of the processes that trigger the onset of volcanic activity, volcanologists are interested in possible influences of external factors such as seasonal changes, the lunar cycle, and weather conditions. To date, most research of this type consists of correlating historical eruptions to seasonal and weather patterns over periods of many years, or gathering similar data during relatively short observation periods at certain volcanoes. In 2004, similar research was conducted at Ol Doinyo Lengai volcano, African Rift Valley, northern Tanzania, by recording eruption data and examining relationships to the corresponding lunar cycle and barometric pressure. Ol Doinyo Lengai was chosen for study because it erupts natrocarbonatite lava, which has the lowest temperature and viscosity of all lavas. The volcano has been in a near-continuous state of eruption since 1983. It is hypothesized that due to the extremely low viscosity of natrocarbonatite magma, tidal and weather influences may be more easily detected at Ol Doinyo Lengai than at volcanoes erupting higher viscosity lavas. From 29 June to 29 July, 2004, a continuous presence was maintained in the summit craters of Ol Doinyo Lengai. Continuous barometric pressure readings were recorded using a NovaLynx Model 230-7020-A barograph. An hourly record of eruption location and intensity was recorded using a numerical scale designed to rate the strength of eruptions. Assessment of eruption strength was based on seven weeks of prior observations in the crater during eight visits between 1997 and 2003. Data are analyzed using theoretical earth tides calculated by TSOFT software, developed by the Royal Observatory of Belgium. Spectral analysis indicates no correlation between eruption frequency and barometric pressure or the diurnal tidal cycle. However, time series analysis of activity data indicates a low frequency component with a period of approximately 8.5 days. The two most intense eruptive episodes occurred within two days of the new and full moon, respectively. The observation period was not long enough to determine if these low frequency components are statistically significant. A second long-term stay during summer 2005 will include observations during new and full moon phases, each of which will nearly coincide with a lunar apogee or perigee.
Gordon, J., Belton, F., Cribb, W. and Henry, J., 2005. Effects of the lunar cycle and changing barometric pressure on the timing and intensity of eruptions at Ol Doinyo Lengai Volcano, Tanzania. GSA Abst. with Progs. 37, 2.
Richard Anderson (MTSU undergraduate geology major, 2005-2008)
The St. Francois Mountains (SFM) complex in Southeast Missouri is comprised of 1.38 to 1.48 billion year-old granites, rhyolites, ash-flow tuffs, basaltic dikes and sills. The precise petro-tectonic setting(s) in which specific SFM lithologies formed remains unclear. An ongoing field, petrographic, major element, and trace element study of SFM felsic rocks investigates this problem. Major element oxide analyses show that most SFM felsic rocks range between 70-80 wt % SiO2, 2-7 wt % K2O, 10-15 wt % Al2O3, 2-6 wt % Na2O, and < 2 wt % CaO. Possible SFM petro-tectonic settings are identified using trace element discrimination diagrams according to Pearce et al., 1984, and by comparison of SFM geochemical signatures to those of similar rocks from known tectonic settings. Notably, a plot of Nb versus Y shows that felsic SFM samples overlap the Within Plate Granite (WPG) and the Volcanic Arc Granite (VAG) + Syn-Tectonic Collision Granite (Syn-COLG) fields, with most samples plotting in the WPG field. A plot of Nb versus SiO2 shows that most samples plot in WPG and Ocean Ridge Granite (ORG) fields, as opposed to VAG, Collision Granite (COLG), and ORG fields. A plot of Rb versus SiO2 shows that all samples plot in the WPG field. Accordingly, trace element data suggest a within plate origin for most SFM rocks under study. Additional investigation of major and trace element data is underway to further correlate specific SFM lithologies to their petro-tectonic setting(s).
Anderson, R, and Cribb, W.
2007. Investigation of petro-tectonic setting(s) of felsic igneous rocks,
St. Francois Mountains, Missouri. Geol. Soc. Amer. Abst. with Progs. 39, 6.
Anderson. R., Beard, J. and Cribb, W., 2007. Geochemical investigation of petro-tectonic setting(s) of felsic igneous rocks, St. Francois Mountains, Maine. Geol. Soc. Amer. Abst. with Progs. 39, 3.
Jennifer Pickering (MTSU Undergraduate geology major, 2007-2008)
Pickering, J., *Tonish, J., *Cares, J. and Cribb, W., 2009. Optimization of x-ray fluorescence spectrometry for environmental analysis of arsenic at low concentrations in sediment and soil materials. Geological Society of America Abstracts with Programs Vol 41, No. 1.
Aaron Mayfield (MTSU Undergraduate geology major, 2007-2008)
Jennifer Pickering, Miller Wyllie (MTSU undergraduate geology majors, 2009), with Matt Jones (Siegel High School Senior) and Scott Crombie (Ravenwood High School Chemistry Teacher)
Distributions, Concentrations, and Transport Processes of Toxic Metals Released from TVA Coal-Ash Surface Impoundments into Public Waterways and River Sediments
On December 22, 2008, approximately 5.4 million
cubic yards of coal ash sludge spilled from a breached
surface impoundment at the Tennessee Valley Authority
Kingston Fossil Plant, about 40 miles west of
The objective of this research
is to investigate the long-term enrichment and/or
attenuation of PDWC metals in river water and riverside
sediments downstream of coal-ash surface impoundments at six
TVA coal-fired power plants: Allen,
Beth Weinman (Vanderbilt Graduate Student, 2007-2008)
The Co-Evolution of Asian Aquifers and
Arsenic: How Understanding Sedimentary History can Help
Predict Patterns of Arsenic Heterogeneity
After a decade of research, there is still no broad-scale understanding of why Asian aquifers support such heterogeneous distributions of groundwater arsenic. In countries like Bangladesh, Nepal, and Vietnam, it is often the case that wells spaced a few meters apart and drilled to the same depth have vastly different concentrations of dissolved arsenic (i.e., <10μg/L to >100μg/L). While there is a general consensus that older Pleistocene sediments are typically depleted in arsenic relative to younger aquifer sediments, little is known about either the geological and geochemical evolution of these aquifers with time or the exact nature of their 3-dimensional stratigraphy. To better, and more broadly, understand why local groundwater arsenic patterns exhibit such heterogeneity, sedimentological investigations were undertaken in three arsenic-contaminated Asian villages, including: (1) a hyper-avulsive floodplain in Nepal's Terai, (2) an abandoned portion of the Brahmaputra River in Bangladesh, and (3) a meander bend along Vietnam's stable, fault-controlled Red River complex. Stratigraphic cross-sections, facies determinations, and luminescence dating of the aquifer sands along transects (~1 km long and ~15 m deep) from each of these villages indicate that the aquifer deposits are not uniform, that they vary in the subsurface, and that their depositional ages correspond to concentrations of arsenic dissolved in the groundwater. Comparisons of arsenic concentrations with aquifer age show that there is an inverse relationship, indicating that the age of the sediment does play a role in arsenic's availability and distribution. While there is still much to be learned about the exact mechanism(s) and rate(s) by which arsenic is being liberated, our investigations overall support a geologic model where much of the arsenic variance is explainable by small variations over small distances (~10 meters) that results from dynamic depositional conditions created by these active fluvial regions.
Weinman, BA., Goodbred, SL., Savage, K., Zheng, Y., Radloff, K., Singhvi, A., Charlet, L., Berg, M., Eiche, E., Cribb, W., and van Geen., A., 2008. The co-evolution of Asian aquifers and arsenic: how understanding sedimentary history can help predict patterns of arsenic heterogeneity. Oral presentation. Session H71. Arsenic and Other Metals as Contaminants in Hydrologic Systems at AGU's Fall 2008 meeting, San Francisco.
Jennifer Pickering and Tommy Hartzog (Vanderbilt Graduate Students, 2010-2012)
The Bengal delta is the gateway for the world’s largest sediment transport system from the Himalaya Mountains to the Bengal Fan. The key to reconstructing the climate, erosion, and transport history of this system is understanding how such processes are recorded in the stratigraphy of the deltaic margin. Here we present the stratigraphic record of a detailed coring transect across two fluvial valleys downstream from a prominent avulsion node of the Brahmaputra River. Sediment samples were acquired from 41 boreholes along a 120 km transect that spans the entire Holocene fluvial valley of the Brahmaputra. Preliminary core data suggests that geomorphic boundaries in the surface morphology are distinctly reflected in the downcore stratigraphy. The transect captures the stratigraphic architecture of these valleys at the transition zone between the Himalayan-sourced mountain streams and the low-lying, flat delta braidbelts. The stratigraphy of the transect is dominantly Holocene sands with gravel beds prevalent below 20 m. We note that the Brahmaputra does not currently transport gravels, which raises the question of how the source input and transport regime have varied throughout the Holocene. Very little mud is preserved below the surface, and those cores that do contain preserved subsurface mud are distal to the active channel locations. This pattern of poorly preserved mud stratigraphy contrasts with widespread mud deposition in the modern delta system. We hypothesize that avulsion and migration of the braidbelt offers little probability of floodplain preservation near the active channels, and those cores with a floodplain cap probably have not been occupied for several hundred years or more. This stratigraphic record of the proximal deltaic sink is an important element in understanding the Brahmaputra dispersal system from source to sink on a post-glacial timescale.