Susan Halgedahl

Last updated
Susan L. Halgedahl
Scientific career
InstitutionsUniversity of Utah
Thesis The Dependence of Magnetic Domain Structure upon Magnetization State in Naturally-Occurring Pyrrhotite and Titanomagnetite  (1981)
Doctoral advisor Michael Fuller

Susan Halgedahl is a geologist known for her research into the physics that govern magnetic rocks and for her work on fossils from Utah's Wheeler Formation.

Contents

Education and career

Halgedahl has a B.A.in applied physics from the University of California, San Diego (1975). She earned her Ph.D. in geological sciences from the University of California, Santa Barbara in 1981. [1] [2] She subsequently worked at ARCO Oil and Gas Company and Lamont-Doherty Geological Observatory before moving to the University of Utah in 1993. [1] As of 2021, Halgedahl is an Associate Professor Emerita in the Geology and Geophysics Department at the University of Utah. [1]

Research

For her Ph.D. research, Halgedahl investigated rocks that retain their magnetic orientation, such titanomagnetite, [3] in samples from the Ocean Drilling Program. Her Ph.D. research investigated how specific rocks retain a magnetic signal [4] [5] which has implications for the ability of these rocks to track changes in Earth's magnetic field over time. Her research also examined the impact of temperature on the ability of rocks to maintain their magnetic signature [6] and how changes in the volume and chemical composition of pyrrhotite do not alter its retention of a magnetic signal. [7] The magnetic signal in rocks can be used to reconstruct the development of the Arctic Basin over geologic time. [8]

Halgedahl's research into fossils in the Wheeler Formation in Utah used geophysical measurements to define changes in sea level that led to the high abundance of fossils found in the region. [9] She subsequently discovered multiple jellyfish fossils [10] [11] in Utah and this research extended the age of jellyfish to 505 million years ago, within the middle Cambrian era. [12] [13] [14]

Selected publications

Awards and honors

Related Research Articles

<span class="mw-page-title-main">Geochronology</span> Science of determining the age of rocks, sediments and fossils

Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is provided by tools such as paleomagnetism and stable isotope ratios. By combining multiple geochronological indicators the precision of the recovered age can be improved.

A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged. The Earth's field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons.

<i>Canadaspis</i> Extinct genus of arthropods

Canadaspis is an extinct genus of bivalved Cambrian arthropod, known from North America and China. They are thought to have been benthic feeders that moved mainly by walking and possibly used its biramous appendages to stir mud in search of food. They have been placed within the Hymenocarina, which includes other bivalved Cambrian arthropods.

<span class="mw-page-title-main">Chirodropidae</span> Family of jellyfishes

Chirodropidae is a family of venomous box jellyfish within the class Cubozoa. Like other members of the order Chirodropida, they have branched pedalia, in contrast to the unbranched pedalia of box jellyfish in the order Carybdeida. Each branch houses its own individual tentacle. Nematocyst composition and type can vary among individuals within this family based on body size and life stage. Like other box jellyfish, chirodropids can be found in coastal and shallow marine areas, but they have also been found to occur at benthic depths.

<i>Peytoia</i> Genus of anomalocarids

Peytoia is a genus of hurdiid radiodont, an early diverging order of stem-group arthropods, that lived in the Cambrian period, containing two species, Peytoia nathorsti from the Miaolingian of Canada and Peytoia infercambriensis from Poland, dating to Cambrian Stage 3. Its two frontal appendages had long bristle-like spines, it had no fan tail, and its short stalked eyes were behind its large head.

The Gauss–Matuyama Reversal was a geologic event approximately 2.58 Ma when the Earth's magnetic field underwent a geomagnetic reversal from normal polarity to reverse polarity. The reversal is named after German physicist Johann Carl Friedrich Gauss and Japanese geophysicist Motonori Matuyama.

<i>Waptia</i> Cambrian arthropod

Waptia is an extinct genus of arthropod from the Middle Cambrian of North America. It grew to a length of 6.65 cm (3 in), and had a large bivalved carapace and a segmented body terminating into a pair of tail flaps. It was an active swimmer and likely a predator of soft-bodied prey. It is also one of the oldest animals with direct evidence of brood care. Waptia fieldensis is the only species classified under the genus Waptia, and is known from the Burgess Shale Lagerstätte of British Columbia, Canada. Specimens of Waptia are also known from the Spence Shale of Utah, United States.

<span class="mw-page-title-main">Wheeler Shale</span> Geologic formation in Utah notable for trilobite fossils

The Wheeler Shale is a Cambrian (c. 507 Ma) fossil locality world-famous for prolific agnostid and Elrathia kingii trilobite remains and represents a Konzentrat-Lagerstätte. Varied soft bodied organisms are locally preserved, a fauna and preservation style normally associated with the more famous Burgess Shale. As such, the Wheeler Shale also represents a Konservat-Lagerstätten.

Plate reconstruction is the process of reconstructing the positions of tectonic plates relative to each other or to other reference frames, such as the Earth's magnetic field or groups of hotspots, in the geological past. This helps determine the shape and make-up of ancient supercontinents and provides a basis for paleogeographic reconstructions.

Cambrorhytium is an enigmatic fossil genus known from the Latham Shale (California), and the Chengjiang (China) and Burgess Shale lagerstätte. 350 specimens of Cambrorhytium are known from the Greater Phyllopod bed, where they comprise 0.7% of the community.

<span class="mw-page-title-main">Marjum Formation</span>

The Marjum Formation is a Cambrian geological formation that overlies the Wheeler Shale in the House Range, Utah. It is named after its type locality, Marjum Pass, and was defined in 1908. The formation is known for its occasional preservation of soft-bodied tissue, and is slightly younger than the Burgess Shale, falling in the Ptychagnostus praecurrens trilobite zone.

Iron(II,III) sulfide is a blue-black (sometimes pinkish) chemical compound of iron and sulfur with formula Fe3S4 or FeS·Fe2S3, which is much similar to iron(II,III) oxide. It occurs naturally as the sulfide mineral greigite and is magnetic. It is a bio-mineral produced by and found in magnetotactic bacteria. It is a mixed valence compound, featuring both Fe2+ and Fe3+ centers, in 1:2 ratio.

The Steptoean Positive Carbon Isotope Excursion (SPICE) was a geological event which occurred about 495 million years ago near the beginning of the International Furongian Epoch of the Cambrian Period. The SPICE represents an increase in the atmospheric 13C to 12C ratio, known as the δ13C, and lasted for around 2 to 4 million years.

<i>Ooedigera</i> Ovoid Cambrian animal with a bulbous tail

Ooedigera peeli is an extinct vetulicolian from the Early Cambrian of North Greenland. The front body was flattened horizontally, oval-shaped, likely bearing a reticulated or anastomosing pattern, and had 5 evenly-spaced gill pouches along the midline. The tail was also bulbous and flattened horizontally, but was divided into 7 plates connected by flexible membranes, allowing movement. Ooedigera likely swam by moving side-to-side like a fish. It may have lived in an oxygen minimum zone alongside several predators in an ecosystem based on chemosynthetic microbial mats, and was possibly a deposit or filter feeder living near the seafloor.

<i>Skeemella</i>

Skeemella clavula is an elongate animal from what is now the Middle Cambrian Wheeler Shale and Marjum lagerstätte of Utah. It has been classified with the vetulicolians.

<span class="mw-page-title-main">Paleontology in Oklahoma</span>

Paleontology in Oklahoma refers to paleontological research occurring within or conducted by people from the U.S. state of Oklahoma. Oklahoma has a rich fossil record spanning all three eras of the Phanerozoic Eon. Oklahoma is the best source of Pennsylvanian fossils in the United States due to having an exceptionally complete geologic record of the epoch. From the Cambrian to the Devonian, all of Oklahoma was covered by a sea that would come to be home to creatures like brachiopods, bryozoans, graptolites and trilobites. During the Carboniferous, an expanse of coastal deltaic swamps formed in areas of the state where early tetrapods would leave behind footprints that would later fossilize. The sea withdrew altogether during the Permian period. Oklahoma was home a variety of insects as well as early amphibians and reptiles. Oklahoma stayed dry for most of the Mesozoic. During the Late Triassic, carnivorous dinosaurs left behind footprints that would later fossilize. During the Cretaceous, however, the state was mostly covered by the Western Interior Seaway, which was home to huge ammonites and other marine invertebrates. During the Cenozoic, Oklahoma became home to creatures like bison, camels, creodonts, and horses. During the Ice Age, the state was home to mammoths and mastodons. Local Native Americans are known to have used fossils for medicinal purposes. The Jurassic dinosaur Saurophaganax maximus is the Oklahoma state fossil.

The Shady Dolomite is a geologic formation composed of marine sedimentary rocks of early Cambrian age. It outcrops along the eastern margin of the Blue Ridge province in the southeastern United States and can be found in outcrops in the states of Alabama, Georgia, Tennessee, North Carolina, and Virginia. It can also be found in the subsurface of Kentucky, Ohio, and West Virginia. The Shady is predominantly composed of dolomite and limestone with lesser amounts of mudrock. It contains fossils of trilobites, archaeocyathids, algae, brachiopods, and echinoderms, along with the enigmatic fossil Salterella. The Shady Dolomite was first described by Arthur Keith in 1903 and was named for exposures in the Shady Valley of Johnson County in the state of Tennessee. Near Austinville, Virginia, the Shady hosts ore deposits that have been mined extensively for lead and zinc ore.

Magellan Rise is an oceanic plateau in the Pacific Ocean, which covers a surface area of 500,000 square kilometres (190,000 sq mi). There is another geological structure with the same name west from the Marshall Islands.

<span class="mw-page-title-main">Magnetic field of Mars</span>

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Subir Kumar Banerjee is an Indian-American geophysicist, known for research on rock magnetism, palaeomagnetism, and environmental magnetism.

References

  1. 1 2 3 "SUSAN L HALGEDAHL - Research - Faculty Profile - The University of Utah". faculty.utah.edu. Retrieved 2021-06-24.
  2. ↑ https://www.worldcat.org/oclc/{{{8940652}}} [ bare URL ]
  3. ↑ Halgedahl, S.; Fuller, M. (1980). "Magnetic domain observations of nucleation processes in fine particles of intermediate titanomagnetite". Nature. 288 (5786): 70–72. Bibcode:1980Natur.288...70H. doi:10.1038/288070a0. ISSN   1476-4687. S2CID   4306966.
  4. ↑ Halgedahl, S.L.; Fuller, M. (1981-07-01). "The dependence of magnetic domain structure upon magnetization state in polycrystalline pyrrhotite". Physics of the Earth and Planetary Interiors. 26 (1–2): 93–97. Bibcode:1981PEPI...26...93H. doi:10.1016/0031-9201(81)90101-1. ISSN   0031-9201.
  5. ↑ Halgedah, S.; Fuller, M. (1983). "The dependence of magnetic domain structure upon magnetization state with emphasis upon nucleation as a mechanism for pseudo-single-domain behavior". Journal of Geophysical Research: Solid Earth. 88 (B8): 6505–6522. Bibcode:1983JGR....88.6505H. doi:10.1029/JB088iB08p06505. ISSN   2156-2202.
  6. ↑ Halgedahl, Susan L.; Jarrard, Richard D. (1995-02-01). "Low-temperature behavior of single-domain through multidomain magnetite". Earth and Planetary Science Letters. 130 (1–4): 127–139. Bibcode:1995E&PSL.130..127H. doi:10.1016/0012-821X(94)00260-6. ISSN   0012-821X.
  7. ↑ Halgedahl, S. (2000-03-30). "Observed effects of mechanical grain-size reduction on the domain structure of pyrrhotite". Earth and Planetary Science Letters. 176 (3–4): 457–467. Bibcode:2000E&PSL.176..457H. doi:10.1016/S0012-821X(00)00022-4. ISSN   0012-821X.
  8. ↑ Harbert, William; Frei, Leah; Jarrard, Richard; Halgedahl, Susan; Engebretson, David (1990-01-01). "Paleomagnetic and plate-tectonic constraints on the evolution of the Alaskan-eastern Siberian Arctic". The Arctic Ocean Region. pp. 567–592. doi:10.1130/DNAG-GNA-L.567. ISBN   0813752116.
  9. ↑ Halgedahl, S.L.; Jarrard, R.D.; Brett, C.E.; Allison, P.A. (2009-06-01). "Geophysical and geological signatures of relative sea level change in the upper Wheeler Formation, Drum Mountains, West-Central Utah: A perspective into exceptional preservation of fossils". Palaeogeography, Palaeoclimatology, Palaeoecology. 277 (1–2): 34–56. Bibcode:2009PPP...277...34H. doi:10.1016/j.palaeo.2009.02.011. ISSN   0031-0182.
  10. ↑ Briggs, Derek E. G.; Lieberman, Bruce S.; Hendricks, Jonathan R.; Halgedahl, Susan L.; Jarrard, Richard D. (2008). "Middle Cambrian arthropods from Utah". Journal of Paleontology. 82 (2): 238–254. Bibcode:2008JPal...82..238B. doi:10.1666/06-086.1. ISSN   0022-3360. S2CID   31568651.
  11. ↑ Morris, Simon Conway; Halgedahl, Susan L.; Selden, Paul; Jarrard, Richard D. (2015). "Rare primitive deuterostomes from the Cambrian (Series 3) of Utah". Journal of Paleontology. 89 (4): 631–636. Bibcode:2015JPal...89..631C. doi:10.1017/jpa.2015.40. ISSN   0022-3360. S2CID   3962956.
  12. ↑ Cartwright, Paulyn; Halgedahl, Susan L.; Hendricks, Jonathan R.; Jarrard, Richard D.; Marques, Antonio C.; Collins, Allen G.; Lieberman, Bruce S. (2007-10-31). "Exceptionally Preserved Jellyfishes from the Middle Cambrian". PLOS ONE. 2 (10): e1121. Bibcode:2007PLoSO...2.1121C. doi: 10.1371/journal.pone.0001121 . ISSN   1932-6203. PMC   2040521 . PMID   17971881.
  13. ↑ "Fossil Record Reveals Elusive Jellyfish More Than 500 Million Years Old". ScienceDaily. Retrieved 2021-06-24.
  14. ↑ Briggs, Derek E. G.; Lieberman, Bruce S.; Hendricks, Jonathan R.; Halgedahl, Susan L.; Jarrard, Richard D. (2008). "Middle Cambrian arthropods from Utah". Journal of Paleontology. 82 (2): 238–254. Bibcode:2008JPal...82..238B. doi:10.1666/06-086.1. ISSN   0022-3360. S2CID   31568651.
  15. ↑ "Union Fellows | AGU". www.agu.org. Retrieved 2021-06-24.
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