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You searched for +publisher:"Harvard University" +contributor:("Knoll, Andrew Herbert"). Showing records 1 – 2 of 2 total matches.

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Harvard University

1. Creveling, Jessica. Sedimentology, Geochemistry, and Geophysics of the Cambrian Earth System.

Degree: PhD, Earth and Planetary Sciences, 2012, Harvard University

Within this dissertation, I document how—and hypothesize why—the quirks and qualities of the Cambrian Period demarcate this interval as fundamentally different from the preceding Proterozoic Eon and succeeding periods of the Phanerozoic Eon. To begin, I focus on the anomalous marine deposition of the mineral apatite. Sedimentary sequestration of phosphorus modulates the capacity for marine primary productivity and, thus, the redox state of the Earth system. Moreover, sedimentary apatite minerals may entomb and replicate skeletal and soft-tissue organisms, creating key aspects of the fossil record from which paleontologists deduce the trajectory of animal evolution. I ask what geochemical redox regime promoted the delivery of phosphorus to Cambrian seafloors and conclude that, for the case of the Thorntonia Limestone, apatite nucleation occurred under anoxic, ferruginous subsurface water masses. Moreover, I infer that phosphorus bound to iron minerals precipitated from the water column and organic-bound phosphorus were both important sources of phosphorus to the seafloor. Petrographic observations allow me to reconstruct the early diagenetic pathways that decoupled phosphorus from these delivery shuttles and promoted the precipitation of apatite within the skeletons of small animals. Together, mechanistic understandings of phosphorus delivery to, and retention within, seafloor sediment allow us to constrain hypotheses for the fleeting occurrence of widespread apatite deposition and exquisite fossil preservation within Cambrian sedimentary successions. Next, I describe and quantify the nature of carbonate production on a marine platform deposited at the hypothesized peak of Cambrian skeletal carbonate production. I find that fossils represent conspicuous, but volumetrically subordinate components of early Cambrian carbonate reef ecosystems and that despite the evolution of mineralized skeletons, Cambrian carbonate platforms appear similar to their Neoproterozoic counterparts, primarily reflecting abiotic and microbial deposition. Finally, I investigate the geodynamic mechanism responsible for rapid, oscillatory true polar wander (TPW) events proposed for the Neoproterozoic and Phanerozoic Earth on the basis of paleomagnetic data. Using geodynamic models, I demonstrate that elastic strength in the lithosphere and stable excess ellipticity of Earth’s figure provided sufficient stabilization to return the pole to its original state subsequent to convectively-driven TPW.

Earth and Planetary Sciences

Advisors/Committee Members: Knoll, Andrew Herbert (advisor), Johnston, David (committee member), Schrag, Daniel (committee member).

Subjects/Keywords: Cambrian; carbonate; geochemistry; phosphorus; taphonomy; geobiology; biogeochemistry; geophysics; true polar wander

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Creveling, J. (2012). Sedimentology, Geochemistry, and Geophysics of the Cambrian Earth System. (Doctoral Dissertation). Harvard University. Retrieved from http://nrs.harvard.edu/urn-3:HUL.InstRepos:9830350

Chicago Manual of Style (16th Edition):

Creveling, Jessica. “Sedimentology, Geochemistry, and Geophysics of the Cambrian Earth System.” 2012. Doctoral Dissertation, Harvard University. Accessed January 26, 2020. http://nrs.harvard.edu/urn-3:HUL.InstRepos:9830350.

MLA Handbook (7th Edition):

Creveling, Jessica. “Sedimentology, Geochemistry, and Geophysics of the Cambrian Earth System.” 2012. Web. 26 Jan 2020.

Vancouver:

Creveling J. Sedimentology, Geochemistry, and Geophysics of the Cambrian Earth System. [Internet] [Doctoral dissertation]. Harvard University; 2012. [cited 2020 Jan 26]. Available from: http://nrs.harvard.edu/urn-3:HUL.InstRepos:9830350.

Council of Science Editors:

Creveling J. Sedimentology, Geochemistry, and Geophysics of the Cambrian Earth System. [Doctoral Dissertation]. Harvard University; 2012. Available from: http://nrs.harvard.edu/urn-3:HUL.InstRepos:9830350


Harvard University

2. Kotrc, Benjamin. Evolution of Silica Biomineralizing Plankton.

Degree: PhD, Earth and Planetary Sciences, 2013, Harvard University

The post-Paleozoic history of the silica cycle involves just two groups of marine plankton, radiolarians and diatoms. I apply paleobiological methods to better understand the Cenozoic evolution of both groups. The Cenozoic rise in diatom diversity has long been related to a concurrent decline in radiolarian test silicification. I address evolutionary questions on both sides of this coevolutionary coin: Was the taxonomic diversification of diatoms accompanied by morphological diversification? Is our view of morphological diatom diversification affected by sampling biases? What evolutionary mechanisms underlie the macroevolutionary decline in radiolarian silicification? Conventionally, diatom diversification describes a steep, monotonic rise, a view recently questioned due to sampling bias. For a different perspective, I constructed a diatom morphospace based on discrete characters, populated through time using an occurrence-level database. Distances between taxa in morphospace and on a molecular phylogeny are not strongly correlated, suggesting that morphospace was explored early in their evolutionary history, followed by relative stasis. I quantified morphospace occupancy through time using several disparity metrics. Metrics describing average separation of taxa show stasis, while metrics describing occupied volume show an increase with time. Disparity metrics are also subject to sampling biases. Under subsampling, I find that disparity metrics show varied responses: metrics describing separation of taxa into morphospace are unaffected, while those describing occupied volume lose their clear increases. Disparity can have geographic components, analogous to (α) and (β) taxonomic diversity; I find more evidence of stasis in an analysis of (α̅) disparity. Overall, these results suggest stasis in Cenozoic diatom disparity. The radiolarian decline in silicification could result from either macroevolutionary processes operating above the species level (punctuated queilibria) or anagenetic changes within lineages. I measured silicification in three phyletic lineages, Stichocorys, Didymocyrtis, and Centrobotrys, from four tropical Pacific DSDP sites. Likelihood-based model fitting finds no strong support for directional evolution, pointing toward selection among species, rather than within species. Each lineage shows a different trajectory, perhaps due to differences in the ecological role played by the test. Because Stichocorys shows close correspondence to the assemblage-level trend, abundance may be an important factor through which within-lineage changes can influence the macroevolutionary pattern.

Earth and Planetary Sciences

Advisors/Committee Members: Knoll, Andrew Herbert (advisor), Mitrovica, Jerry (committee member), Johnston, David (committee member).

Subjects/Keywords: Paleontology; Geobiology; cenozoic; diatoms; morphospace; radiolarians; silica; subsampling

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Kotrc, B. (2013). Evolution of Silica Biomineralizing Plankton. (Doctoral Dissertation). Harvard University. Retrieved from http://nrs.harvard.edu/urn-3:HUL.InstRepos:11051218

Chicago Manual of Style (16th Edition):

Kotrc, Benjamin. “Evolution of Silica Biomineralizing Plankton.” 2013. Doctoral Dissertation, Harvard University. Accessed January 26, 2020. http://nrs.harvard.edu/urn-3:HUL.InstRepos:11051218.

MLA Handbook (7th Edition):

Kotrc, Benjamin. “Evolution of Silica Biomineralizing Plankton.” 2013. Web. 26 Jan 2020.

Vancouver:

Kotrc B. Evolution of Silica Biomineralizing Plankton. [Internet] [Doctoral dissertation]. Harvard University; 2013. [cited 2020 Jan 26]. Available from: http://nrs.harvard.edu/urn-3:HUL.InstRepos:11051218.

Council of Science Editors:

Kotrc B. Evolution of Silica Biomineralizing Plankton. [Doctoral Dissertation]. Harvard University; 2013. Available from: http://nrs.harvard.edu/urn-3:HUL.InstRepos:11051218

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