Tectonic Subsidence of the Cretaceous Western Interior Basin, United States.

The tectonic subsidence history recorded in middle Cenomanian to early Campanian (96 to 80 Ma) strata in the U.S. Cretaceous Western Interior basin was studied by applying two-dimensional flexural backstripping techniques to six regional stratigraphic sections across different segments of the basin. Results indicate that tectonic subsidence over the 16 m.y. study interval consists of two distinct components: a westward-increasing flexural subsidence confined within a few hundred kilometers of the thrust belt, and a spatially uniform residual subsidence that affected the entire basin. The residual subsidence does not represent signals of eustatic sea level changes but instead reflects epeirogenic movements specific to the North American Western Interior. The flexural component exhibits significant spatial and temporal variations along the strike of the Sevier thrust belt. The greatest cumulative subsidence occurred in southwestern Wyoming and northern Utah, whereas concurrent subsidence in northwestern Montana and southern Utah was insignificant. Temporal trends in subsidence also show a distinct regional pattern. From middle Cenomanian to late Turonian (96 to 90 Ma), subsidence rates were high in Utah and much lower in Wyoming and Montana. In contrast, during the Coniacian and Santonian stages (90 to 85 Ma) subsidence accelerated rapidly in Wyoming, increased slightly in Montana, and decreased in Utah. The observed variations in flexural subsidence were probably manifestations of basement structures, particularly those zones of crustal weakness inherited from the Precambrian rifting and early Paleozoic passive margin development

Stratigraphic signatures of convergent orogenesis from the plate interior : studies from Tibet and the southern Rocky Mountains

Fundamental questions remain in geology regarding the growth and development of the continental landscape. The existence of major mountain belts and high plateaus in the plate interior, over a thousand kilometers from a plate boundary, requires a complex combination of tectonic and climatic pre-conditions combined with inherited structures, active tectonics, geodynamic processes, and climatic feedback. Through these studies of the basin records of orogenesis in the Qaidam basin of northern Tibet and the southern Rocky Mountain basins of North America, we provide new constraints on the timing of deformation, the development of proximal basins, and the evolution of continental-scale drainage patterns in two of the most prominent modern mountain belts. Three studies are presented in this dissertation, each investigating a different aspect of continental plate-interior basin development. In Chapter 2, the Cenozoic sedimentary record from the Qaidam basin is investigated through a sedimentological and multi-proxy provenance study. Provenance and stratigraphic analysis reveals syn-collisional exhumation of the Eastern Kunlun Shan and Qilian Shan, marking the early establishment of the borders of the Tibetan plateau. Chapter 3 investigates the record of easternmost Laramide deformation in the southern Rocky Mountains. Detrital zircon U-Pb geochronology of Cretaceous through Eocene sedimentary units in the Raton basin provides new constraints on the uplift and exhumation of the Sangre de Cristo range, revealing initial exhumation of Laramide basement material in the Campanian, the formation of a drainage divide within the Sangre de Cristo range by the Paleocene, and continued exhumation through the Eocene. The final study (Chapter 4) looks at regional patterns of uplift, exhumation, and drainage reorganization during the latest Cretaceous through Eocene in the southern Rocky Mountains. Initial Laramide-style deformation introduced basement material into the basins while maintaining integrated basins, while continued exhumation throughout the Paleogene resulted in partitioning of basins into more localized depocenters. Provenance analysis of strata from the San Juan, Galisteo-El Rito, and Raton basins reveals new depositional ages, as well as patterns of basin filling and drainage integration during Laramide thrusting, pluton emplacement in the San Juan mountains, and the transition to south-directed continental drainage systems that terminate in the Gulf of Mexico. Together, these studies provide a framework for understanding the co-evolution of sedimentary basins and mountain belts in the plate interior based on the recognition of initial deformation, continued exhumation and drainage integration, and partitioning of basins due to the formation of topographic barriers.Geological Science

Detrital Zircon Record of Magmatism and Sediment Dispersal Across the North American Cordilleran Arc System (28–48°N)

As zircon U-Pb geochronology has become a leading method in sediment provenance studies and basin analysis over the past 20 years, the volume of detrital zircon data made available in published literature has enabled researchers to go beyond source-to-sink provenance studies to explore increasingly complex geologic problems. In this review, we utilize the growing body of detrital zircon data acquired from Jurassic-Paleocene forearc and foreland basin strata of the North American Cordillera to investigate the Mesozoic to earliest Cenozoic evolution of the arc and its associated basins between 28°N and 48°N. Our compilation includes 830 detrital zircon samples (101,898 individual ages) from 70 studies published between 2000 and 2020. For comparative purposes, we also compile 1307 igneous zircon U-Pb ages that characterize the magmatic history of the arc. We place primary emphasis on detrital zircon ages between 251 and 56 Ma that we infer to be uniquely derived from magmatic sources in the arc. Informed by existing knowledge of magmatic, structural, and sedimentological processes that acted on the orogen, we investigate spatial and temporal trends in these “arc-derived zircon” to establish a detrital record of arc magmatism, investigate source-to-sink relationships between the arc and adjacent basins, and discuss controls on sediment dispersal across the orogen. Our review shows that compilations of detrital zircon data from the Cordilleran forearc and foreland basin systems are excellent proxies for arc magmatism because the basins are enriched in arc-derived zircon and compilations provide space- and time-integrated records of crystallization ages. The compiled detrital zircon data support a history of continuous arc magmatism throughout Mesozoic and earliest Cenozoic time, characterized by low-volume magmatism from Triassic-Early Jurassic time (~251–174 Ma) and episodic higher-volume magmatism from Middle Jurassic-Late Cretaceous time (~174–66 Ma). These trends elucidate the initiation and timing of magmatic events at the orogen-scale and corroborate our understanding of cyclic arc behavior. Detrital zircon distributions are spatially and temporally variable both within and across basins, which we discuss relative to topographic development of the orogen and attendant responses of sediment dispersal systems. Detrital zircon distributions in the forearc signal rapid transfer of sediment from the arc to basins dominantly via fluvial processes. In contrast, detrital zircon distributions across the foreland reflect the presence of topographic barriers in the hinterland region of the arc that effectively isolated parts of the foreland. The presence of hinterland topography in turn highlights the important role of ash-fall events in delivering arc-derived zircon to the foreland, underscoring the need to consider ash-fall processes in paleodrainage reconstructions. These broad regional trends, and in general the close linkage between orogenic process and sediment dispersal, emerge from our compilation because it averages out much of the local variability observed in studies of more limited geographic or temporal extent

Detrital Zircon U-Pb Geochronology and Paleodrainage Reconstruction of the Blackhawk-Castlegate Succession, Wasatch Plateau and Book Cliffs, Utah

The Blackhawk Formation and Castlegate Sandstone are Campanian fluvial-deltaic and shoreline deposits within the Sevier foreland-basin fill along the Wasatch Plateau and Book Cliffs in Utah. Long-standing age constraints on the Blackhawk and Castlegate are based on correlation to ammonite zones in downdip mudstones, which are themselves constrained by radiometric dating of volcanic ash beds, and are therefore dependent on correlation methods and models. This study examines the Blackhawk-Castlegate succession with the following objectives: (i) test a hypothesis that very fine sands and coarse silts yield a more robust population of maximum depositional ages (MDAs) from volcanogenic detrital zircons (DZs) that approximate true depositional age than medium to fine sands; (ii) develop an independent geochronological framework of MDAs through U-Pb dating of volcanogenic DZs; and (iii) propose a paleodrainage reconstruction for the Blackhawk-Castlegate succession in light of new data. MDAs calculated throughout the succession approximate the time of deposition for the upper Blackhawk (77.7 ± 1.7 Ma in Horse Canyon and 79.6 ± 1.7 Ma in Tusher Canyon), Lower Castlegate (75.8 ± 1.8 Ma in Horse Canyon), and potentially the Bluecastle Tongue (75.9 ± 1.9 Ma in Price Canyon). In the case of the upper Blackhawk and Lower Castlegate, the MDAs are both up to 2 Myrs younger than the age constraints determined by ammonite zone correlations, and raise questions concerning the temporal significance of the classic Castlegate Sequence Boundary and relationships with basin-evolution models. Previous studies indicate that Santonian drainages were dominated by an axial fluvial system with headwaters in the Mogollon Highlands, with lesser contributions from the Sevier fold-and-thrust belt and the various Cordilleran magmatic sources. The DZ U-Pb age data in this study is analyzed using multidimensional scaling, spatial relationships between clusters, and examination of specific peaks in age distributions. Regional sediment routing patterns appear to be quite similar during the Campanian deposition of the Blackhawk-Castlegate succession: there is evidence for an axial drainage flowing north from the Mogollon Highlands that passed by an area that is now Straight Canyon, intersected by transverse fluvial systems in the area that is now Price Canyon that drain the largely recycled strata exposed in the Sevier fold-and-thrust belt. The DZ U-Pb age data collected and used for this thesis are uploaded as three supplementary Excel files: KBH Data, BC Data Unbiased, and BC Data Biased. The first two files have the data used for multidimensional scaling and peak analysis of kernel density estimates, but lack some grains used for MDA calculations. The targeted population of n=50 grains for MDAs is included in the BC Data Biased file

Paleobiogeography of the North American Late Cretaceous Western Interior Seaway: the impact of abiotic vs. biotic factors on macroevolutionary patterns of marine vertebrates and invertebrates

My research investigates the relationship between ecology, evolution, and the environment in the fossil record. I hypothesize that abiotic environmental factors (e.g., climate, sea-level, ocean chemistry, and paleogeography) play a greater role in speciation, extinction, and distribution patterns than biotic factors (e.g., competition, mutualism). The effects of these factors can be observed in the fossil record as changes in species distributions, range sizes, and niche dimensions through time. Using GIS, paleoenvironmental reconstruction, and ecological niche modeling (ENM), I quantitatively investigated hypotheses of the relative influence of abiotic vs. biotic factors on macroevolution in three main studies of marine taxa from the Late Cretaceous Western Interior Seaway (WIS) of North America. The Late Cretaceous was a period of prolonged extreme and equable warmth; thus, this research has potential implications for species biology and biogeography in a projected future warmer world. The first study examined the influence of biotic interactions on patterns of extinction by competitive exclusion in marine vertebrates. Results indicated that competitive replacement was not a mechanism mediating extinctions. Instead other factors, such as environmental changes, likely controlled extinction patterns. The second study investigated the effect of large range size on survivorship and invasion potential in marine mollusks. No relationship between large range size and extinction resistance was recovered, however, endemic species with small range sizes were more likely to become invasive. These results suggest that some biogeographic "rules" (e.g., large range size confers extinction resistance and increased invasion potential) may not prevail under conditions of prolonged and equable global warmth. The last part of my research focused on improving methods for the application of ENM in the fossil record (paleo-ENM). In order to use ENM in the fossil record, detailed environmental layers must be reconstructed from sedimentological and geochemical proxies. Additionally, paleo-ENM requires high-resolution stratigraphic correlations of fossil-bearing formations and collection of large species' occurrence datasets that represent the full temporal and spatial extent of the species modeled. In order to produce high fidelity models, a standardized framework for paleoenvironmental reconstruction is required. Best practices are outlined for paleoenvironmental reconstruction, in addition to the contextual framework and important considerations necessary to appropriately apply paleo-ENM

Depositional Environments and Provenance of Early Paleogene Strata in the Huerfano Basin: Implications for Uplift of the Wet Mountains, Colorado, USA

Sedimentary basins throughout the Western Interior of North America preserve a record of Late Cretaceous through latest Eocene sedimentation derived from flanking Laramide uplifts. In northern and western basins, the strata contain a well-documented proxy history of Laramide-style exhumation and climatic conditions within the region. However, the tectonic and climatic histories of more southerly basins, such as the Huerfano Basin studied herein, are comparatively underdeveloped despite being key in understanding the spatiotemporal evolution of Laramide tectonism and regional climatic gradients. This study addresses this issue and presents the first detailed lithofacies analysis and provenance analysis of the Poison Canyon, Cuchara, and Huerfano formations in the Huerfano Basin (south-central, Colorado, U.S.A.). We interpret a suite of alluvial sub-environments within these formations whose upsection variability and broad depositional patterns are similar to those observed in other early Paleogene successions in Laramide basins. Specifically, these features include deposition of organic-rich strata during the Paleocene; Eocene strata dominated by red-bed formation; and an anomalously coarse-grained intervening fluvial unit. The major difference in the Huerfano Basin compared to other Laramide basins is the exceptionally coarse-grained nature of all the units, which is likely related to its proximal position to Laramide ranges. Overall, the patterns are consistent with the widespread climatic shift between the wet, cooler Paleocene, and the drier, warmer, potentially more seasonal Eocene climate. As part of our provenance analysis, we characterized petrographic compositions of sand-bodies (N = 31 thin sections) and U–Pb detrital zircon age spectra (N = 848 age determinations) from fluvial sandstones within each of the three formations. The results indicate a new unroofing and source history for the sediment within the basin that contradicts previous hypotheses. Diagnostic zircon peaks at 516-517 Ma, 1423-1430 Ma, and 1678-1687 Ma show that sediment delivered to the Huerfano Basin did not originate in the San Luis Highlands or incipient Sangre de Cristo Mountains, but that the Precambrian crystalline core and associated Cambrian plutons of the Wet Mountains were exposed by the time Laramide deposition initiated in the basin. There are no provenance shifts upsection, indicating a largely stable or lithologically uniform sediment source from the Paleocene through at least ~51 Ma. This suggests the major changes in deposition are more likely related to tectonic and climatic conditions rather than lithologic controls on stratigraphic patterns

Chemostratigraphic and Paleoclimatic Studies of Cloverly Formation, Northern Wyoming, U.S.A

The Early – Late Cretaceous transition in Western North America recorded a period of rapid climatic and tectonic change in Earth’s history. Major climate events associated with large igneous province eruptions caused several instances of ocean anoxic events (OAE) and perturbations to the global carbon (C) – cycle. These perturbations to the global C-cycle are observed in the bulk organic C record of both marine and terrestrial deposits and can be used to correlate units across major depositional basins. Major efforts are being made to generate time-constrained palaeontologic and paleoclimate information from the North American Cordilleran foreland basin and C-isotope chemostratigraphy can aid in making these correlations. This study uses the isotopic composition of bulk organic carbon from the Lower Cretaceous Cloverly Formation to constrain the age of the Cloverly Formation within the Bighorn Basin, Wyoming. The study also investigates paleoclimate proxies such as mean annual precipitation and atmospheric CO2 concentrations. C-isotope chemostratigraphy of bulk organic carbon results range between -21‰ and -30.1‰ and average at -23.97 ‰. Two pedogenic carbonates nodules from the Little Sheep Member (CCC-12 and CCC-24) were analyzed for δ13Corg, δ13Ccarb, and δ18Ocarb. The Little Sheep Mudstone Member carbonate nodules have average δ13Ccarb values of -6.72 ‰ at CCC-12 and -7.25 ‰ at CCC-24. The mudstone organic C isotopic values of the carbonate nodules are -26.27 ‰ for CCC-12, and -25.9 ‰ for CCC-24. The S(z) values (soil CO2 concentration) were estimated to be between 1000 – 3000 ppm, typical of micro-high vertic soils. Atmospheric pCO2 concentrations are calculated using the paleosol CO2 paleobarometer of Ekart et al. (1999) and are reported at S(z) = 2000 ± 1000 ppm. Atmospheric C-isotopic composition of pCO2 is estimated using the δ13C of bulk organic C in mudstones and the relationship between plant matter and pCO2 outlined in Arens et al. (2000). Atmospheric pCO2 values at 4 m above the Pryor Conglomerate, 14.5 m above the Cloverly-Morrison lithologic boundary are 352 ± 176 ppm and increase to 931 ± 465 ppm at 18.5 m. Mean annual precipitation (MAP) was calculated from weathering indices of metal oxides in soils using CALMAG and CIA-K equations. MAP increases up section from a minimum of 697- 984 mm/yr in the LSM to a maximum of 1291-1705 mm/yr in the Upper Himes Member. Given the maximum depositional age of the base of the Little Sheep Mudstone Member (129.4 ± 3.4 Ma) from D’Emic et al. (2019), a maximum depositional age for the lower Himes Member at Crooked Creek of 103.6 ± 1.3 Ma (D’Emic et al., 2019), the maximum depositional age of 112.09 ± 0.34 Ma (Carrano et al., 2021) from other Little Sheep Mudstone outcrops, and the high resolution C-isotope chemostratigraphic trend of the Crooked Creek Section (this study) constrains the positive C-isotope trend and decreasing (negative CIE) trend to the C-10 to C-11 C-isotope excursions associated with the CIE of Bralower et al. (1999) that occurs in the Late Aptian to Early Albian

New Insights on the Sequence Stratigraphic Architecture of the Dakota Formation in Kansas–Nebraska–Iowa from a Decade of Sponsored Research Activity

The Cretaceous Dakota Formation in the areas of Kansas, Nebraska, and Iowa contains a rich and well-preserved microflora of fossil palynomorphs. A comprehensive listing of these taxa is presented in this publication as part of a continuing effort to develop a refined biostratigraphic scheme for mid-Cretaceous terrestrial deposits in North America. The Dakota Formation in this region contains four distinctive Albian-Cenomanian palynostratigraphic zones that are used to partition the unit into successive depositional cycles, and each zone records deposition in fluvial-estuarine environments. The late Albian Kiowa-Skull Creek depositional cycle at the base of the Dakota Formation is recognized throughout the study area, and is also recognized in other parts of the Cretaceous North American Western Interior basin. The overlying newly recognized latest Albian "Muddy-Mowry Cycle" is formally defined for the first time in this paper and correlates with depositional cycles recognized by other workers in other parts of the Western Interior basin. The Cenomanian lower Greenhorn Cycle is already widely recognized by many other workers throughout the Western Interior basin. Laterally extensive thin zones of pervasive carbonate mineral cementation are noted in fluvial-estuarine deposits in the Dakota Formation. They are believed to have formed as synsedimentary cements that precipitated below estuarine marine-flooding surfaces in settings related to discharging paleoground waters. The existence of these early diagenetic cementation zones has important implications for the recognition of diagenetic barriers and baffles to modern fluid flow in the Dakota Formation. New stable isotopic data on these authigenic cements are reported in this paper and add to a body of published data on the δ18O of mid-Cretaceous paleoprecipitation in North America