@phdthesis{Li2023,
  author    = {Li, Zhen},
  title     = {Formation of Sub-Permafrost Methane Hydrate Reproduced by Numerical Modeling},
  doi       = {10.25932/publishup-60330},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-603302},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XII, 109},
  year      = {2023},
  abstract  = {Natural gas hydrates are ice-like crystalline compounds containing water cavities that trap natural gas molecules like methane (CH4), which is a potent greenhouse gas with high energy density. The Mallik site at the Mackenzie Delta in the Canadian Arctic contains a large volume of technically recoverable CH4 hydrate beneath the base of the permafrost. Understanding how the sub-permafrost hydrate is distributed can aid in searching for the ideal locations for deploying CH4 production wells to develop the hydrate as a cleaner alternative to crude oil or coal. Globally, atmospheric warming driving permafrost thaw results in sub-permafrost hydrate dissociation, releasing CH4 into the atmosphere to intensify global warming. It is therefore crucial to evaluate the potential risk of hydrate dissociation due to permafrost degradation. To quantitatively predict hydrate distribution and volume in complex sub-permafrost environments, a numerical framework was developed to simulate sub-permafrost hydrate formation by coupling the equilibrium CH4-hydrate formation approach with a fluid flow and transport simulator (TRANSPORTSE). In addition, integrating the equations of state describing ice melting and forming with TRANSPORTSE enabled this framework to simulate the permafrost evolution during the sub-permafrost hydrate formation. A modified sub-permafrost hydrate formation mechanism for the Mallik site is presented in this study. According to this mechanism, the CH4-rich fluids have been vertically transported since the Late Pleistocene from deep overpressurized zones via geologic fault networks to form the observed hydrate deposits in the Kugmallit-Mackenzie Bay Sequences. The established numerical framework was verified by a benchmark of hydrate formation via dissolved methane. Model calibration was performed based on laboratory data measured during a multi-stage hydrate formation experiment undertaken in the LArge scale Reservoir Simulator (LARS). As the temporal and spatial evolution of simulated and observed hydrate saturation matched well, the LARS model was therefore validated. This laboratory-scale model was then upscaled to a field-scale 2D model generated from a seismic transect across the Mallik site. The simulation confirmed the feasibility of the introduced sub-permafrost hydrate formation mechanism by demonstrating consistency with field observations. The 2D model was extended to the first 3D model of the Mallik site by using well-logs and seismic profiles, to investigate the geologic controls on the spatial hydrate distribution. An assessment of this simulation revealed the hydraulic contribution of each geological element, including relevant fault networks and sedimentary sequences. Based on the simulation results, the observed heterogeneous distribution of sub-permafrost hydrate resulted from the combined factors of the source-gas generation rate, subsurface temperature, and the permeability of geologic elements. Analysis of the results revealed that the Mallik permafrost was heated by 0.8-1.3 °C, induced by the global temperature increase of 0.44 °C and accelerated by Arctic amplification from the early 1970s to the mid-2000s. This study presents a numerical framework that can be applied to study the formation of the permafrost-hydrate system from laboratory to field scales, across timescales ranging from hours to millions of years. Overall, these simulations deepen the knowledge about the dominant factors controlling the spatial hydrate distribution in sub-permafrost environments with heterogeneous geologic elements. The framework can support improving the design of hydrate formation experiments and provide valuable contributions to future industrial hydrate exploration and exploitation activities.},
  language  = {en}
}
@phdthesis{Stoltnow2023,
  author    = {Stoltnow, Malte},
  title     = {Magmatic-hydrothermal processes along the porphyry to epithermal transition},
  doi       = {10.25932/publishup-61140},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-611402},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxviii, 132},
  year      = {2023},
  abstract  = {Magmatic-hydrothermal systems form a variety of ore deposits at different proximities to upper-crustal hydrous magma chambers, ranging from greisenization in the roof zone of the intrusion, porphyry mineralization at intermediate depths to epithermal vein deposits near the surface. The physical transport processes and chemical precipitation mechanisms vary between deposit types and are often still debated. The majority of magmatic-hydrothermal ore deposits are located along the Pacific Ring of Fire, whose eastern part is characterized by the Mesozoic to Cenozoic orogenic belts of the western North and South Americas, namely the American Cordillera. Major magmatic-hydrothermal ore deposits along the American Cordillera include (i) porphyry Cu(-Mo-Au) deposits (along the western cordilleras of Mexico, the western U.S., Canada, Chile, Peru, and Argentina); (ii) Climax- (and sub-) type Mo deposits (Colorado Mineral Belt and northern New Mexico); and (iii) porphyry and IS-type epithermal Sn(-W-Ag) deposits of the Central Andean Tin Belt (Bolivia, Peru and northern Argentina). The individual studies presented in this thesis primarily focus on the formation of different styles of mineralization located at different proximities to the intrusion in magmatic-hydrothermal systems along the American Cordillera. This includes (i) two individual geochemical studies on the Sweet Home Mine in the Colorado Mineral Belt (potential endmember of peripheral Climax-type mineralization); (ii) one numerical modeling study setup in a generic porphyry Cu-environment; and (iii) a numerical modeling study on the Central Andean Tin Belt-type Pirquitas Mine in NW Argentina. Microthermometric data of fluid inclusions trapped in greisen quartz and fluorite from the Sweet Home Mine (Detroit City Portal) suggest that the early-stage mineralization precipitated from low- to medium-salinity (1.5-11.5 wt.\% equiv. NaCl), CO2-bearing fluids at temperatures between 360 and 415°C and at depths of at least 3.5 km. Stable isotope and noble gas isotope data indicate that greisen formation and base metal mineralization at the Sweet Home Mine was related to fluids of different origins. Early magmatic fluids were the principal source for mantle-derived volatiles (CO2, H2S/SO2, noble gases), which subsequently mixed with significant amounts of heated meteoric water. Mixing of magmatic fluids with meteoric water is constrained by δ2Hw-δ18Ow relationships of fluid inclusions. The deep hydrothermal mineralization at the Sweet Home Mine shows features similar to deep hydrothermal vein mineralization at Climax-type Mo deposits or on their periphery. This suggests that fluid migration and the deposition of ore and gangue minerals in the Sweet Home Mine was triggered by a deep-seated magmatic intrusion. The second study on the Sweet Home Mine presents Re-Os molybdenite ages of 65.86±0.30 Ma from a Mo-mineralized major normal fault, namely the Contact Structure, and multimineral Rb-Sr isochron ages of 26.26±0.38 Ma and 25.3±3.0 Ma from gangue minerals in greisen assemblages. The age data imply that mineralization at the Sweet Home Mine formed in two separate events: Late Cretaceous (Laramide-related) and Oligocene (Rio Grande Rift-related). Thus, the age of Mo mineralization at the Sweet Home Mine clearly predates that of the Oligocene Climax-type deposits elsewhere in the Colorado Mineral Belt. The Re-Os and Rb-Sr ages also constrain the age of the latest deformation along the Contact Structure to between 62.77±0.50 Ma and 26.26±0.38 Ma, which was employed and/or crosscut by Late Cretaceous and Oligocene fluids. Along the Contact Structure Late Cretaceous molybdenite is spatially associated with Oligocene minerals in the same vein system, a feature that precludes molybdenite recrystallization or reprecipitation by Oligocene ore fluids. Ore precipitation in porphyry copper systems is generally characterized by metal zoning (Cu-Mo to Zn-Pb-Ag), which is suggested to be variably related to solubility decreases during fluid cooling, fluid-rock interactions, partitioning during fluid phase separation and mixing with external fluids. The numerical modeling study setup in a generic porphyry Cu-environment presents new advances of a numerical process model by considering published constraints on the temperature- and salinity-dependent solubility of Cu, Pb and Zn in the ore fluid. This study investigates the roles of vapor-brine separation, halite saturation, initial metal contents, fluid mixing, and remobilization as first-order controls of the physical hydrology on ore formation. The results show that the magmatic vapor and brine phases ascend with different residence times but as miscible fluid mixtures, with salinity increases generating metal-undersaturated bulk fluids. The release rates of magmatic fluids affect the location of the thermohaline fronts, leading to contrasting mechanisms for ore precipitation: higher rates result in halite saturation without significant metal zoning, lower rates produce zoned ore shells due to mixing with meteoric water. Varying metal contents can affect the order of the final metal precipitation sequence. Redissolution of precipitated metals results in zoned ore shell patterns in more peripheral locations and also decouples halite saturation from ore precipitation. The epithermal Pirquitas Sn-Ag-Pb-Zn mine in NW Argentina is hosted in a domain of metamorphosed sediments without geological evidence for volcanic activity within a distance of about 10 km from the deposit. However, recent geochemical studies of ore-stage fluid inclusions indicate a significant contribution of magmatic volatiles. This study tested different formation models by applying an existing numerical process model for porphyry-epithermal systems with a magmatic intrusion located either at a distance of about 10 km underneath the nearest active volcano or hidden underneath the deposit. The results show that the migration of the ore fluid over a 10-km distance results in metal precipitation by cooling before the deposit site is reached. In contrast, simulations with a hidden magmatic intrusion beneath the Pirquitas deposit are in line with field observations, which include mineralized hydrothermal breccias in the deposit area.},
  language  = {en}
}
@phdthesis{Khawaja2023,
  author    = {Khawaja, Muhammad Asim},
  title     = {Improving earthquake forecast modeling and testing using the multi-resolution grids},
  school      = {Universit{\"a}t Potsdam},
  pages     = {107},
  year      = {2023},
  language  = {en}
}
@phdthesis{Kudriavtseva2023,
  author    = {Kudriavtseva, Anna},
  title     = {Interactions between tectonics, climate, and surface processes in the Kyrgyz Tian Shan},
  doi       = {10.25932/publishup-60372},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-603728},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XV, 164},
  year      = {2023},
  abstract  = {During the Cenozoic, global cooling and uplift of the Tian Shan, Pamir, and Tibetan plateau modified atmospheric circulation and reduced moisture supply to Central Asia. These changes led to aridification in the region during the Neogene. Afterwards, Quaternary glaciations led to modification of the landscape and runoff. In the Issyk-Kul basin of the Kyrgyz Tian Shan, the sedimentary sequences reflect the development of the adjacent ranges and local climatic conditions. In this work, I reconstruct the late Miocene - early Pleistocene depositional environment, climate, and lake development in the Issyk-Kul basin using facies analyses and stable δ18O and δ13C isotopic records from sedimentary sections dated by magnetostratigraphy and 26Al/10Be isochron burial dating. Also, I present 10Be-derived millennial-scale modern and paleo-denudation rates from across the Kyrgyz Tian Shan and long-term exhumation rates calculated from published thermochronology data. This allows me to examine spatial and temporal changes in surface processes in the Kyrgyz Tian Shan. In the Issyk-Kul basin, the style of fluvial deposition changed at ca. 7 Ma, and aridification in the basin commenced concurrently, as shown by magnetostratigraphy and the δ18O and δ13C data. Lake formation commenced on the southern side of the basin at ca. 5 Ma, followed by a ca. 2 Ma local depositional hiatus. 26Al/10Be isochron burial dating and paleocurrent analysis show that the Kungey range to the north of the basin grew eastward, leading to a change from fluvial-alluvial deposits to proximal alluvial fan conglomerates at 5-4 Ma in the easternmost part of the basin. This transition occurred at 2.6-2.8 Ma on the southern side of the basin, synchronously with the intensification of the Northern Hemisphere glaciation. The paleo-denudation rates from 2.7-2.0 Ma are as low as long-term exhumation rates, and only the millennial-scale denudation rates record an acceleration of denudation. This work concludes that the growth of the ranges to the north of the basin led to creation of the topographic barrier at ca. 7 Ma and a subsequent aridification in the Issyk-Kul basin. Increased subsidence and local tectonically-induced river system reorganization on the southern side of the basin enabled lake formation at ca. 5 Ma, while growth of the Kungey range blocked westward-draining rivers and led to sediment starvation and lake expansion. Denudational response of the Kyrgyz Tian Shan landscape is delayed due to aridity and only substantial cooling during the late Quaternary glacial cycles led to notable acceleration of denudation. Currently, increased glacier reduction and runoff controls a more rapid denudation of the northern slope of the Terskey range compared to other ranges of the Kyrgyz Tian Shan.},
  language  = {en}
}
@phdthesis{Rembe2023,
  author    = {Rembe, Johannes},
  title     = {Hercynian to Eocimmerian evolution of the North Pamir in Central Asia},
  doi       = {10.25932/publishup-59751},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-597510},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxvi, 154, CX},
  year      = {2023},
  abstract  = {The North Pamir, part of the India-Asia collision zone, essentially formed during the late Paleozoic to late Triassic-early Jurassic. Coeval to the subduction of the Turkestan ocean—during the Carboniferous Hercynian orogeny in the Tien Shan—a portion of the Paleo-Tethys ocean subducted northward and lead to the formation and obduction of a volcanic arc. This Carboniferous North Pamir arc is of Andean style in the western Darvaz segment and trends towards an intraoceanic arc in the eastern, Oytag segment. A suite of arc-volcanic rocks and intercalated, marine sediments together with intruded voluminous plagiogranites (trondhjemite and tonalite) and granodiorites was uplifted and eroded during the Permian, as demonstrated by widespread sedimentary unconformities. Today it constitutes a major portion of the North Pamir. In this work, the first comprehensive Uranium-Lead (U-Pb) laser-ablation inductively-coupled-plasma mass-spectrometry (LA-ICP-MS) radiometric age data are presented along with geochemical data from the volcanic and plutonic rocks of the North Pamir volcanic arc. Zircon U-Pb data indicate a major intrusive phase between 340 and 320 Ma. The magmatic rocks show an arc-signature, with more primitive signatures in the Oytag segment compared to the Darvaz segment. Volcanic rocks in the Chinese North Pamir were indirectly dated by determining the age of ocean floor alteration. We investigate calcite filled vesicles and show that oxidative sea water and the basaltic host rock are major trace element sources. The age of ocean floor alteration, within a range of 25 Ma, constrains the extrusion age of the volcanic rocks. In the Chinese Pamir, arc-volcanic basalts have been dated to the Visean-Serpukhovian boundary. This relates the North Pamir volcanic arc to coeval units in the Tien Shan. Our findings further question the idea of a continuous Tarim-Tajik continent in the Paleozoic. From the Permian (Guadalupian) on, a progressive sea-retreat led to continental conditions in the northeastern Pamir. Large parts of Central Asia were affected by transcurrent tectonics, while subduction of the Paleo-Tethys went on south of the accreted North Pamir arc, likely forming an accretionary wedge, representing an early stage of the later Karakul-Mazar tectonic unit. Graben systems dissected the Permian carbonate platforms, that formed on top of the uplifted Carboniferous arc in the central and western North Pamir. A continental graben formed in the eastern North Pamir. Zircon U-Pb dating suggest initiation of volcanic activity at ~260 Ma. Extensional tectonics prevailed throughout the Triassic, forming the Hindukush-North Pamir rift system. New geochemistry and zircon U-Pb data tie volcanic rocks, found in the Chinese Pamir, to coeval arc-related plutonic rocks found within the Karakul-Mazar arc-accretionary complex. The sedimentary environment in the continental North Pamir rift evolved from an alluvial plain, lake dominated environment in the Guadalupian to a coarser-clastic, alluvial, braided river dominated in the Triassic. Volcanic activity terminated in the early Jurassic. We conducted Potassium-Argon (K-Ar) fine-fraction dating on the Shala Tala thrust fault, a major structure juxtaposing Paleozoic marine units of lower greenschist to amphibolite facies conditions against continental Permian deposits. Fault slip under epizonal conditions is dated to 204.8 ± 3.7 Ma (2σ), implying Rhaetian nappe emplacement. This pinpoints the Central-North Pamir collision, since the Shala Tala thrust was a back-thrust at that time.},
  language  = {en}
}
@phdthesis{Pons2023,
  author    = {Pons, Micha{\"e}l},
  title     = {The Nature of the tectonic shortening in Central Andes},
  doi       = {10.25932/publishup-60089},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-600892},
  school      = {Universit{\"a}t Potsdam},
  pages     = {160},
  year      = {2023},
  abstract  = {The Andean Cordillera is a mountain range located at the western South American margin and is part of the Eastern- Circum-Pacific orogenic Belt. The ~7000 km long mountain range is one of the longest on Earth and hosts the second largest orogenic plateau in the world, the Altiplano-Puna plateau. The Andes are known as a non-collisional subduction-type orogen which developed as a result of the interaction between the subducted oceanic Nazca plate and the South American continental plate. The different Andean segments exhibit along-strike variations of morphotectonic provinces characterized by different elevations, volcanic activity, deformation styles, crustal thickness, shortening magnitude and oceanic plate geometry. Most of the present-day elevation can be explained by crustal shortening in the last ~50 Ma, with the shortening magnitude decreasing from ~300 km in the central (15°S-30°S) segment to less than half that in the southern part (30°S-40°S). Several factors were proposed that might control the magnitude and acceleration of shortening of the Central Andes in the last 15 Ma. One important factor is likely the slab geometry. At 27-33°S, the slab dips horizontally at ~100 km depth due to the subduction of the buoyant Juan Fernandez Ridge, forming the Pampean flat-slab. This horizontal subduction is thought to influence the thermo-mechanical state of the Sierras Pampeanas foreland, for instance, by strengthening the lithosphere and promoting the thick-skinned propagation of deformation to the east, resulting in the uplift of the Sierras Pampeanas basement blocks. The flat-slab has migrated southwards from the Altiplano latitude at ~30 Ma to its present-day position and the processes and consequences associated to its passage on the contemporaneous acceleration of the shortening rate in Central Andes remain unclear. Although the passage of the flat-slab could offer an explanation to the acceleration of the shortening, the timing does not explain the two pulses of shortening at about 15 Ma and 4 Ma that are suggested from geological observations. I hypothesize that deformation in the Central Andes is controlled by a complex interaction between the subduction dynamics of the Nazca plate and the dynamic strengthening and weakening of the South American plate due to several upper plate processes. To test this hypothesis, a detailed investigation into the role of the flat-slab, the structural inheritance of the continental plate, and the subduction dynamics in the Andes is needed. Therefore, I have built two classes of numerical thermo-mechanical models: (i) The first class of models are a series of generic E-W-oriented high-resolution 2D subduction models thatinclude flat subduction in order to investigate the role of the subduction dynamics on the temporal variability of the shortening rate in the Central Andes at Altiplano latitudes (~21°S). The shortening rate from the models was then validated with the observed tectonic shortening rate in the Central Andes. (ii) The second class of models are a series of 3D data-driven models of the present-day Pampean flat-slab configuration and the Sierras Pampeanas (26-42°S). The models aim to investigate the relative contribution of the present-day flat subduction and inherited structures in the continental lithosphere on the strain localization. Both model classes were built using the advanced finite element geodynamic code ASPECT. The first main finding of this work is to suggest that the temporal variability of shortening in the Central Andes is primarily controlled by the subduction dynamics of the Nazca plate while it penetrates into the mantle transition zone. These dynamics depends on the westward velocity of the South American plate that provides the main crustal shortening force to the Andes and forces the trench to retreat. When the subducting plate reaches the lower mantle, it buckles on it-self until the forced trench retreat causes the slab to steepen in the upper mantle in contrast with the classical slab-anchoring model. The steepening of the slab hinders the trench causing it to resist the advancing South American plate, resulting in the pulsatile shortening. This buckling and steepening subduction regime could have been initiated because of the overall decrease in the westwards velocity of the South American plate. In addition, the passage of the flat-slab is required to promote the shortening of the continental plate because flat subduction scrapes the mantle lithosphere, thus weakening the continental plate. This process contributes to the efficient shortening when the trench is hindered, followed by mantle lithosphere delamination at ~20 Ma. Finally, the underthrusting of the Brazilian cratonic shield beneath the orogen occurs at ~11 Ma due to the mechanical weakening of the thick sediments covered the shield margin, and due to the decreasing resistance of the weakened lithosphere of the orogen. The second main finding of this work is to suggest that the cold flat-slab strengthens the overriding continental lithosphere and prevents strain localization. Therefore, the deformation is transmitted to the eastern front of the flat-slab segment by the shear stress operating at the subduction interface, thus the flat-slab acts like an indenter that "bulldozes" the mantle-keel of the continental lithosphere. The offset in the propagation of deformation to the east between the flat and steeper slab segments in the south causes the formation of a transpressive dextral shear zone. Here, inherited faults of past tectonic events are reactivated and further localize the deformation in an en-echelon strike-slip shear zone, through a mechanism that I refer to as "flat-slab conveyor". Specifically, the shallowing of the flat-slab causes the lateral deformation, which explains the timing of multiple geological events preceding the arrival of the flat-slab at 33°S. These include the onset of the compression and of the transition between thin to thick-skinned deformation styles resulting from the crustal contraction of the crust in the Sierras Pampeanas some 10 and 6 Myr before the Juan Fernandez Ridge collision at that latitude, respectively.},
  language  = {en}
}
@phdthesis{Ribacki2023,
  author    = {Ribacki, Enrico},
  title     = {Intra-granitic pegmatites of the Las Chacras-Potrerillos batholith, Argentina},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XVIII, 183},
  year      = {2023},
  language  = {en}
}
@phdthesis{Kooten2023,
  author    = {Kooten, Willemijn Sarah Maria Theresia van},
  title     = {Structural inheritance of the Salta Rift basin and its control on exhumation patterns of the Eastern Cordillera between 23 and 24°S},
  doi       = {10.25932/publishup-61798},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-617983},
  school      = {Universit{\"a}t Potsdam},
  pages     = {XIX, 188},
  year      = {2023},
  abstract  = {The deformation style of mountain belts is greatly influenced by the upper plate architecture created during preceding deformation phases. The Mesozoic Salta Rift extensional phase has created a dominant structural and lithological framework that controls Cenozoic deformation and exhumation patterns in the Central Andes. Studying the nature of these pre-existing anisotropies is a key to understanding the spatiotemporal distribution of exhumation and its controlling factors. The Eastern Cordillera in particular, has a structural grain that is in part controlled by Salta Rift structures and their orientation relative to Andean shortening. As a result, there are areas in which Andean deformation prevails and areas where the influence of the Salta Rift is the main control on deformation patterns. Between 23 and 24°S, lithological and structural heterogeneities imposed by the Lomas de Olmedo sub-basin (Salta Rift basin) affect the development of the Eastern Cordillera fold-and-thrust belt. The inverted northern margin of the sub-basin now forms the southern boundary of the intermontane Cianzo basin. The former western margin of the sub-basin is located at the confluence of the Subandean Zone, the Santa Barbara System and the Eastern Cordillera. Here, the Salta Rift basin architecture is responsible for the distribution of these morphotectonic provinces. In this study we use a multi-method approach consisting of low-temperature (U-Th-Sm)/He and apatite fission track thermochronology, detrital geochronology, structural and sedimentological analyses to investigate the Mesozoic structural inheritance of the Lomas de Olmedo sub-basin and Cenozoic exhumation patterns. Characterization of the extension-related Tacur{\´u} Group as an intermediate succession between Paleozoic basement and the syn-rift infill of the Lomas de Olmedo sub-basin reveals a Jurassic maximum depositional age. Zircon (U-Th-Sm)/He cooling ages record a pre-Cretaceous onset of exhumation for the rift shoulders in the northern part of the sub-basin, whereas the western shoulder shows a more recent onset (140-115 Ma). Variations in the sedimentary thickness of syn- and post-rift strata document the evolution of accommodation space in the sub-basin. While the thickness of syn-rift strata increases rapidly toward the northern basin margin, the post-rift strata thickness decreases toward the margin and forms a condensed section on the rift shoulder. Inversion of Salta Rift structures commenced between the late Oligocene and Miocene (24-15 Ma) in the ranges surrounding the Cianzo basin. The eastern and western limbs of the Cianzo syncline, located in the hanging wall of the basin-bounding Hornocal fault, show diachronous exhumation. At the same time, western fault blocks of Tilcara Range, south of the Cianzo basin, began exhuming in the late Oligocene to early Miocene (26-16 Ma). Eastward propagation to the frontal thrust and to the Paleozoic strata east of the Tilcara Range occurred in the middle Miocene (22-10 Ma) and the late Miocene-early Pliocene (10-4 Ma), respectively.},
  language  = {en}
}
@phdthesis{LauerDuenkelberg2023,
  author    = {Lauer-D{\"u}nkelberg, Gregor},
  title     = {Extensional deformation and landscape evolution of the Central Andean Plateau},
  doi       = {10.25932/publishup-61759},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-617593},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xviii, 195},
  year      = {2023},
  abstract  = {Mountain ranges can fundamentally influence the physical and and chemical processes that shape Earths' surface. With elevations of up to several kilometers they create climatic enclaves by interacting with atmospheric circulation and hydrologic systems, thus leading to a specific distribution of flora and fauna. As a result, the interiors of many Cenozoic mountain ranges are characterized by an arid climate, internally drained and sediment-filled basins, as well as unique ecosystems that are isolated from the adjacent humid, low-elevation regions along their flanks and forelands. These high-altitude interiors of orogens are often characterized by low relief and coalesced sedimentary basins, commonly referred to as plateaus, tectono-geomorphic entities that result from the complex interactions between mantle-driven geological and tectonic conditions and superposed atmospheric and hydrological processes. The efficiency of these processes and the fate of orogenic plateaus is therefore closely tied to the balance of constructive and destructive processes - tectonic uplift and erosion, respectively. In numerous geological studies it has been shown that mountain ranges are delicate systems that can be obliterated by an imbalance of these underlying forces. As such, Cenozoic mountain ranges might not persist on long geological timescales and will be destroyed by erosion or tectonic collapse. Advancing headward erosion of river systems that drain the flanks of the orogen may ultimately sever the internal drainage conditions and the maintenance of storage of sediments within the plateau, leading to destruction of plateau morphology and connectivity with the foreland. Orogenic collapse may be associated with the changeover from a compressional stress field with regional shortening and topographic growth, to a tensional stress field with regional extensional deformation and ensuing incision of the plateau. While the latter case is well-expressed by active extensional faults in the interior parts of the Tibetan Plateau and the Himalaya, for example, the former has been attributed to have breached the internally drained areas of the high-elevation sectors of the Iranian Plateau. In the case of the Andes of South America and their internally drained Altiplano-Puna Plateau, signs of both processes have been previously described. However, in the orogenic collapse scenario the nature of the extensional structures had been primarily investigated in the northern and southern terminations of the plateau; in some cases, the extensional faults were even regarded to be inactive. After a shallow earthquake in 2020 within the Eastern Cordillera of Argentina that was associated with extensional deformation, the state of active deformation and the character of the stress field in the central parts of the plateau received renewed interest to explain a series of extensional structures in the northernmost sectors of the plateau in north-western Argentina. This study addresses (1) the issue of tectonic orogenic collapse of the Andes and the destruction of plateau morphology by studying the fill and erosion history of the central eastern Andean Plateau using sedimentological and geochronological data and (2) the kinematics, timing and magnitude of extensional structures that form well-expressed fault scarps in sediments of the regional San Juan del Oro surface, which is an integral part of the Andean Plateau and adjacent morphotectonic provinces to the east. Importantly, sediment properties and depositional ages document that the San Juan del Oro Surface was not part of the internally-drained Andean Plateau, but rather associated with a foreland-directed drainage system, which was modified by the Andean orogeny and that became successively incorporated into the orogen by the eastward-migration of the Andean deformation front during late Miocene - Pliocene time. Structural and geomorphic observations within the plateau indicate that extensional processes must have been repeatedly active between the late Miocene and Holocene supporting the notion of plateau-wide extensional processes, potentially associated with Mw ~ 7 earthquakes. The close relationship between extensional joints and fault orientations underscores that 3 was oriented horizontally in NW-SE direction and 1 was vertical. This unambiguously documents that the observed deformation is related to gravitational forces that drive the orogenic collapse of the plateau. Applied geochronological analyses suggest that normal faulting in the northern Puna was active at about 3 Ma, based on paired cosmogenic nuclide dating of sediment fill units. Possibly due to regional normal faulting the drainage system within the plateau was modified, promoting fluvial incision.},
  language  = {en}
}
@phdthesis{Zuhr2023,
  author    = {Zuhr, Alexandra},
  title     = {Proxy signal formation in palaeoclimate archives},
  doi       = {10.25932/publishup-58286},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-582864},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xx, 167},
  year      = {2023},
  abstract  = {Throughout the last ~3 million years, the Earth's climate system was characterised by cycles of glacial and interglacial periods. The current warm period, the Holocene, is comparably stable and stands out from this long-term cyclicality. However, since the industrial revolution, the climate has been increasingly affected by a human-induced increase in greenhouse gas concentrations. While instrumental observations are used to describe changes over the past ~200 years, indirect observations via proxy data are the main source of information beyond this instrumental era. These data are indicators of past climatic conditions, stored in palaeoclimate archives around the Earth. The proxy signal is affected by processes independent of the prevailing climatic conditions. In particular, for sedimentary archives such as marine sediments and polar ice sheets, material may be redistributed during or after the initial deposition and subsequent formation of the archive. This leads to noise in the records challenging reliable reconstructions on local or short time scales. This dissertation characterises the initial deposition of the climatic signal and quantifies the resulting archive-internal heterogeneity and its influence on the observed proxy signal to improve the representativity and interpretation of climate reconstructions from marine sediments and ice cores. To this end, the horizontal and vertical variation in radiocarbon content of a box-core from the South China Sea is investigated. The three-dimensional resolution is used to quantify the true uncertainty in radiocarbon age estimates from planktonic foraminifera with an extensive sampling scheme, including different sample volumes and replicated measurements of batches of small and large numbers of specimen. An assessment on the variability stemming from sediment mixing by benthic organisms reveals strong internal heterogeneity. Hence, sediment mixing leads to substantial time uncertainty of proxy-based reconstructions with error terms two to five times larger than previously assumed. A second three-dimensional analysis of the upper snowpack provides insights into the heterogeneous signal deposition and imprint in snow and firn. A new study design which combines a structure-from-motion photogrammetry approach with two-dimensional isotopic data is performed at a study site in the accumulation zone of the Greenland Ice Sheet. The photogrammetry method reveals an intermittent character of snowfall, a layer-wise snow deposition with substantial contributions by wind-driven erosion and redistribution to the final spatially variable accumulation and illustrated the evolution of stratigraphic noise at the surface. The isotopic data show the preservation of stratigraphic noise within the upper firn column, leading to a spatially variable climate signal imprint and heterogeneous layer thicknesses. Additional post-depositional modifications due to snow-air exchange are also investigated, but without a conclusive quantification of the contribution to the final isotopic signature. Finally, this characterisation and quantification of the complex signal formation in marine sediments and polar ice contributes to a better understanding of the signal content in proxy data which is needed to assess the natural climate variability during the Holocene.},
  language  = {en}
}