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From Crust to Orbits: the Geologic History Recorded on Planetary Surfaces
No full textA first-order question in the studies of the Solar System is how its outer zone, known as the Kuiper Belt, was created and evolved. Among all the Kuiper Belt objects, the Pluto system and Arrokoth are the only targets that have been visited by spacecraft. The airless Charon has been interpreted as being geologically inactive since ∼ 4.0 Ga, which potentially records its orbital and thermal evolution in its geology, serving as a representation of the evolution of mid-sized Kuiper Belt Objects (KBOs) in the early Solar System. However, the flyby style of the New Horizons mission limited data collection primarily to the surface of the targets, including optical images, digital elevation models, and spectra, highlighting the need for further studies to robustly constrain subsurface structures, orbital and thermal evolution, and the potential for past geologic activity.In this thesis, I aim to investigate the geological evolution of planetary bodies based on their surface landforms. By employing a multidisciplinary approach including geomorphologic mapping, topographic analysis, and elastic dislocation model, this research constructs a comprehensive geological evolution history for Charon, relating to its orbital and thermal evolution in the early Solar System. In Chapter 2, I use systematic geomorphological mapping to reconstruct a plausible landscape evolution history for Charon and investigate potential processes that may have modified the crater records on Charon. In Chapter 3, I use surface topography to infer the geometry and kinematics of subsurface structures and explore the dynamic origins of Charon’s thrusting tectonics with the despinning of the body. In Chapter 4, I investigate the dynamic interactions between tectonics and surface processes based on characteristics of related landform systems to better constrain the timing of activity for both. Among all the imaged KBOs, Pluto’s largest icy moon, Charon, appears to preserve the largest size range of seemingly undisturbed craters. Two end-member models involving coagulation vs. streaming instability make different predictions about the cumulative size-frequency distribution (SFD) of Kuiper Belt Objects (KBOs), which are testable by the cratering history of KBOs. Current work shows that Charon’s craters with D < 10 − 20 km are fewer than those expected by the coagulation mechanism, but whether this is an artifact of post-cratering modification of smaller craters is unknown.In Chapter 2, we address this issue by conducting systematic photogeological mapping and performing detailed landform analysis using the highest resolution images obtained by the New Horizons spacecraft that reveal the presence of a range of differentiable terrains on Charon. The most important findings of our work include (1) truncation and omission of large craters (diameters > 30 − 40 km) and their crater rim ridges along the eastern edges of several north-trending, eastward-convex, arcuate ranges in Oz Terra of the northern encountered hemisphere; (2) lobate ridges, lobate knob trains, and lobate aprons resembling glacial moraine landforms on Earth; (3) dendritic channel systems containing hanging valleys; and (4) locally striated surfaces defined by parallel ridges, knob trains, and grooves that are > 40 − 50 km in length. The above observations and the topographic dichotomy of Charon’s encountered hemisphere can be explained by a landscape-evolution model that involves (i) a giant impact that created the Vulcan Planitia basin and the extensional fault zone along its northern rim; (ii) a transient atmosphere capable of driving N2-ice glacial erosion of the water-ice bedrock and transporting water-ice debris to sedimentary basins; (iii) regional glacial erosion and transport of earlier emplaced impact ejecta deposits from the highlands of Oz Terra into the lowland basin of Vulcan Planitia; (iv) syn-glaciation northtrending thrusting interpreted to have been induced by Charon’s despinning; and (v) the development of a water-ice debris cover layer over subsurface N2 ice below Vulcan Planitia during global deglaciation. The infilling of Vulcan Planitia could have been accompanied by cryovolcanism. The extensive modification of impact craters means that the crater size-frequency distributions from Charon should serve only as a lower bound when used to test the formation mechanisms of Kuiper Belt Objects.Records of early geologic and thermal evolution after planetary accretion are rarely preserved on icy moons or small bodies in the solar system. Charon’s ∼ 4.0 Ga surface age suggests the potential preservation of its early orbital evolution-induced tectonics in its surface landforms. In Chapter 3, we show that the despinning-induced stress, estimated from compressive tectonic features, explains latitudinal variations in the observed orientations and types of tectonic features in Oz Terra, Charon. Besides the extensive grabens resulting from global extension, a set of north-trending arcuate ranges in Charon’s northern highlands has been identified and interpreted to have a compressional origin. Using an elastic dislocation model, we infer the geometry and kinematics of two thrust faults by fitting the observed tectonically induced topography. The thrust geometry puts a lower bound for the elastic thickness of Charon’s ice shell at the time, estimated to be 30 ∼ 36 km. The thrusts accommodate a compressive strain of ∼ 1% along the east-west direction in the equatorial area. The corresponding flattening rate change suggests an initial rotation period of ∼ 14.3 h for Charon. The estimated despinning-induced stress patterns, supplemented with global contraction, can explain not only the north-trending arcuate ranges in low latitudes but also the preferred east-west orientation of the extensional features. Our work suggests that Charon’s surface presents the first example that records the early planetary despinning history. The despinning of Charon has reached its tidally locked stage within the first 10 Myr after its formation, which predates the proposed global extension and cryovolcanism. The coevolution of despinning and global contraction favors a cold start for Charon. Constraining the spatiotemporal evolution of the landscape is often complicated due to the interaction between tectonics and surface processes. The lifespan of the proposed transient atmosphere and the timing of the surface processes on Charon remain poorly studied. Chapter 2 provides the first-order evolutionary history of Charon’s landscape, while Chapter 3 relates the timing of thrust tectonics to Charon’s tidal dissipation. In Chapter 4, I take an alternative approach to the common method of buffered crater counting in dating landform features on planetary surfaces. We constrain the timing of tectonics and surface processes by investigating their dynamic interactions to overcome the limitation of buffered crater counting, where lower crater density yielding higher uncertainties. Evidenced by the terrestrial analogue of drainage evolution in the Nepal Himalayas, we found examples of co-evolution between valley networks and tectonics on both Charon and Mars. The combination of geomorphologic mapping and topographic spectrum analyses reveals out-of-sequence development of the thrust system on Charon and syn-tectonic development of the trough networks. This interpretation indicates that the transient atmosphere on Charon lasted at least the first few million years after its accretion, which supports the erosion of the trough networks. We also apply the same techniques to an intersection of valley networks and wrinkle ridges on Mars. The observed valley diversions and anomalies along valley profiles indicate syn to post fluvial tectonic activity. Incorporating the calibrated crater statistic ages of both valley networks and tectonic features, the development of the wrinkle ridge potentially lasted for ∼ 100 Myr
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Millennial-scale erosion and deposition near the San Bernardino Mountains in southern California, United States
No full textSpatial and temporal variations in tectonic uplift and climate are generally known to influence sediment production, erosion, and deposition over millennial timescales. Researchers have quantified the spatial and temporal variations of surface erosion and deposition rates over millennial timescales by utilizing various geochronologic and geomorphologic methods. Located along the restraining bend of the San Andreas fault in southern California, the San Bernardino Mountains consist of diverse landforms, including steep mountains, relict upland surfaces, alluvial fan deposits, and sediment deposits to the nearby Salton Sea. The San Bernardino Mountains have been extensively investigated to better understand the controls of tectonic uplift, climate, and sedimentary processes to produce those landforms. However, how spatial and temporal changes in tectonic uplift rates and channel reorganization can influence erosion rates and landscape evolution of the southern San Bernardino Mountains is still debated. In addition, researchers debate whether alluvial fan formations and sediment deposition in areas like Mission Creek and northern Coachella Valley are influenced more by dry or wet climate. My Ph.D. thesis aims to quantify the rates and variations of sediment erosion from sediment source areas to deposition in sediment sinks and improve our understanding of their controls by applying recently developed, novel geochronologic and geomorphic techniques. Three chapters investigate the controls of erosion and deposition on millennial timescales within and near the San Bernardino Mountains in southern California, extending from the sediment sources, the San Bernardino Mountains, to deposition from the Mission Creek alluvial fans, the Coachella Valley, to the ultimate depocenter of the Salton Sea. In the second chapter, I examine the influence of spatially and temporally varying tectonic uplift and channel reorganization on landscape evolution in the San Bernardino Mountains using 10Be-derived erosion rates. Previous researchers thought that temporal and spatial variations of tectonic rock uplift control long-term erosion rates in the San Bernardino Mountains. However, rivers continuously lengthen and capture drainages in strike-slip fault systems due to ongoing motion across faults, which can induce changes in landscape forms, drainage networks, and local erosion rates. To examine the influence of transient landscape changes, I measured 17 basin-averaged erosion rates using cosmogenic 10Be in river sands (hereafter, 10Be-derived erosion rates) and compiled 31 10Be-derived erosion rates from previous works in the San Bernardino Mountains. I also quantified the degree of topographic disequilibrium using topographic analysis by examining hillslope and channel decoupling, the areal extent of pre-uplift surface, and drainage divide asymmetry across various landscapes. My newly measured and compiled 10Be-derived erosion rates and topographic analysis reveal that transient landscape features such as relict topography and drainage-divide migration may explain local variations in 10Be-derived erosion rates. My work shows that coupled analysis of erosion rates and topographic metrics provide tools for assessing the influence of tectonic uplift and channel reorganization on landscape evolution and 10Be-derived erosion rates in an evolving strike-slip restraining bend in the San Bernardino Mountains.
In the third chapter, I examine the depositional history of multiple sedimentary deposits on alluvial fan deposits of southern California’s well-preserved upper Mission Creek alluvial fan complex using single-grain K-feldspar luminescence age distributions. To do this, I collected 12 samples from 6 alluvial fan subsequences from the upper Mission Creek catchment and analyzed 1,157 single-grain K-feldspar luminescence ages. If similar age clusters are present across the luminescence samples, these could be useful for identifying significant depositional or erosional periods. My work here shows that the old alluvial fan surfaces typically have a single broad age cluster. Interestingly, the multiple age clusters from the younger alluvial fan surfaces include the age clusters from the older surfaces. This correspondence between the single-grain luminescence age clusters may indicate the preservation of past depositional events from recently deposited, reworked sediment. Additionally, the ages researchers believed to be a scatter in previous studies, and therefore not used for interpretations, may be part of an erosional event. Therefore, single-grain luminescence age distributions can be utilized to infer depositional events from the most recent to the distant past and provide insights into extreme erosional events in the sedimentary record.
In the fourth chapter, I constrain the long-term depositional history near the ancient shoreline of ancient Lake Cahuilla in northern Coachella Valley by dating sediment cores using single-grain luminescence techniques. Although Coachella Valley is typically an arid environment, the Colorado River repeatedly filled the basin due to avulsions throughout the Pleistocene and Holocene. The depositional history at the northern shoreline has been constrained within ~2 ka from trenches adjacent to a borehole I examined. Previous studies interpreted that lake fillings are related to major rupture events on the southernmost portion of the San Andreas fault. However, a long-term depositional history is still needed to understand the full extent of lake filling and deposition in Coachella Valley from surrounding mountain ranges. To do this, I collected a borehole from within the structural depression at the Coachella paleoseismic site. I then analyzed 25 p-IR IRSL luminescence samples, 228 grain-size samples, and logged the stratigraphy of the borehole. I show that there have been changes in sedimentation rates and depositional environment within ~6 ka, and a correlation between deposition at the Coachella paleoseismic site and deposition at the Mission Creek catchment provides insights into periods of extreme depositional events.
My thesis projects utilize geomorphology and geochronology to investigate sediment transport from source to sink within and near the San Bernardino Mountains. Recent base-level changes can cause local variations on millennial-scale erosion rates, and understanding how the topography and hillslopes reflect these changes can help researchers understand changes in fault activity. Additionally, using different methods of luminescence dating can help researchers fill in the gaps in depositional history of an area and the influence of regional climate. My findings show that investigating millennial-scale erosion and deposition can provide important information for the processes driving landscape evolution
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Decadal, Millennial, and Million-Year Erosion Rates in the Easternmost Himalaya
Get PDFQuantifying tectonic uplift and erosion rates on various timescales is essential for understanding how tectonic and climate forcings interact to produce the landscape we see today. My dissertation is centered around three topics related to the erosion rates of the easternmost Himalaya in the Indian state of Arunachal Pradesh at decadal, millennial, and million-year timescales to better understand present-day natural hazards to long-term landscape evolution. In my dissertation, I quantify 1) landslide susceptibility, 2) landslide-derived decadal and 10Be-derived millennial erosion rates, and 3) plausible million-year timescale exhumation rates in the easternmost Himalaya to better understand climatic, topographic, and tectonic controls on surface processes and erosion over different timescales. In the second chapter, I mapped landslide occurrences using satellite images, quantified landslide susceptibility using statistical and machine learning methods, and assessed the dominant controls of landslide occurrences in the easternmost Himalaya. Recently, deep neural networks (DNN) have been used in the application of estimating landslide susceptibility alongside physical and statistical models. However, DNNs are uninterpretable, making it difficult to determine mechanistic information about landslide controls in the modeled region. My landslide inventory was ultimately used to train an interpretable superposable neural network (SNN), developed and applied by my colleague, to model landslide susceptibility in the easternmost Himalaya. The SNN performed similarly to a state-of-the-art deep neural network, outperforming commonly used physically and statistically based models while revealing the relative importance of contributing controls. The analyses reveal that both strong slope-climate coupling and microclimates are dominant contributors to landslide occurrences in the region. In the third chapter, I quantified landslide-derived decadal erosion rates over a 20-year interval from satellite images and determined millennial erosion using cosmogenic 10Be. Previous studies generally report a tectonic control on millennial erosion rates across the Himalaya. However, there exist well-understood and well-defined patterns of climate variation, tectonic deformation, and lithologic distribution along-strike of the Himalaya that allows for their disentanglement. In this chapter, I measured cosmogenic 10Be-derived millennial erosion rates of 12 basins from the range front to the hinterland of the Dibang and Lohit valleys. In addition, I compiled 161 10Be-derived erosion rates from the Garhwal, Nepal, and Bhutan Himalaya and grouped basins by dominant metasedimentary or crystalline lithology. I observe a clear correlation between climate metrics and erosion rates for basins dominated by metasedimentary lithology that is absent those dominated by crystalline lithology. Additionally, we find that the response of fluvial and hillslope erosional efficiency to climate differs between lithologies in the Himalaya. Furthermore, the high erosion rates and efficiencies observed in the easternmost Himalayan range front are likely facilitated by rainfall-induced landslides and efficient fluvial erosion and transport in metasedimentary lithology. Future studies may incorporate more extensive datasets including low-temperature thermochronometers, which may further elucidate the links among tectonics, erosion, and climate. In the fourth chapter, I inferred the magnitude and spatial pattern of million-year timescale exhumation rates using five newly measured apatite (U-Th)/He sample ages from the Dibang Valley in the easternmost Himalaya. Fault activity along the active easternmost Himalayan range front is largely unconstrained over recent million-year timescales that are more relevant to our landslide and erosion rate analyses. Additionally, although the persistence of out-of-sequence faulting over recent million-year timescales has been proposed, little is known about the timing and magnitude of exhumation rates over this period. I determine plausible cooling histories using HeFTy inverse thermal modeling for two samples in both the range front and hinterland and infer exhumation rates over the last ~2-1 Ma assuming a simplified geothermal gradient. I observe that exhumation along the range front is highest along the Lalpani thrust and concentrated near the Lohit thrust in the hinterland. My findings potentially support persistent out-of-sequence faulting of the Lohit thrust that continues until the present though at a slower rate than that of the range front. Future studies might include additional thermochronology measurements in the range front to better constrain the spatial extent of high exhumation rates. Additionally, an improved understanding of the geothermal gradient would yield more accurate and reliable exhumation rate estimates
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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