The Eastern Cordillera of Colombia is mainly composed of sedimentary rocks deposited since early Mesozoic times. Magmatic rocks are scarce. They are represented only by a few locally restricted occurrences of dykes and sills of mafic composition presumably emplaced in the Cretaceous and of volcanic rocks of Neogene age. This work is focused on the study of the Cretaceous magmatism with the intention to understand the processes causing the genesis of these rocks and their significance in the regional tectonic setting of the Northern Andes. The magmatic rocks cut the Cretaceous sedimentary succession of black shales and marlstones that crop out in both flanks of the Eastern Cordillera. The studied rocks were classified as gabbros (Cáceres, Pacho, Rodrigoque), tonalites (Cáceres, La Corona), diorites and syenodiorites (La Corona), pyroxene-hornblende gabbros (Pacho), and pyroxene-hornblendites (Pajarito). The gabbroic samples are mainly composed of plagioclase, clinopyroxene, and/or green to brown hornblende, whereas the tonalitic rocks are mainly composed of plagioclase and quartz. The samples are highly variable in crystal sizes from fine- to coarse-grained. Accessory minerals such as biotite, titanite and zircon are present. Some samples are characterized by moderate to strong alteration, and show the presence of epidote, actinolite and chlorite. Major and trace element compositions of the rocks as well as the rock-forming minerals show significant differences in the geochemical and petrological characteristics for the different localities, suggesting that this magmatism does not result from a single melting process. The wide compositional spectrum of trace elements in the intrusions is characteristic for different degrees of mantle melting and enrichment of incompatible elements. MORB- and OIB-like compositions suggest at least two different sources of magma with tholeiitic and alkaline affinity, respectively. Evidence of slab-derived fluids can be recognized in the western part of the basin reflected in higher Ba/Nb and Sr/P ratios and also in the Sr radiogenic isotope ratios, which is possible a consequence of metasomatism in the mantle due to processes related to the presence of a previously subducted slab. The trace element patterns evidence an extensional setting in the Cretaceous basin producing a continental rift, with continental crust being stretched until oceanic crust was generated in the last stages of this extension. Electron microprobe analyses (EMPA) of the major elements and synchrotron radiation micro-X-ray fluorescence (μ-SRXRF) analyses of the trace element composition of the early crystallized minerals of the intrusions (clinopyroxenes and amphiboles) reflect the same dual character that has been found in the bulk-rock analyses. Despite the observed alteration of the rocks, the mineral composition shows evidences for an enriched and a relative depleted magma source. Even the normalization of the trace element concentrations of clinopyroxenes and amphiboles to the whole rock nearly follows the pattern predicted by published partition coefficients, suggesting that the alteration did not change the original trace element compositions of the investigated minerals. Sr-Nd-Pb isotope data reveal a large isotopic variation but still suggest an initial origin of the magmas in the mantle. Samples have moderate to highly radiogenic compositions of 143Nd/144Nd and high 87Sr/86Sr ratios and follow a trend towards enriched mantle compositions, like the local South American Paleozoic crust. The melts experienced variable degrees of contamination by sediments, crust, and seawater. The age corrected Pb isotope ratios show two separated groups of samples. This suggests that the chemical composition of the mantle below the Northern Andes has been modified by the interaction with other components resulting in a heterogeneous combination of materials of diverse origins. Although previous K/Ar age dating have shown that the magmatism took place in the Cretaceous, the high error of the analyses and the altered nature of the investigated minerals did preclude reliable interpretations. In the present work 40Ar/39Ar dating was carried out. The results show a prolonged history of magmatism during the Cretaceous over more than 60 Ma, from ~136 to ~74 Ma (Hauterivian to Campanian). Pre-Cretaceous rifting phases occurred in the Triassic-Jurassic for the western part of the basin and in the Paleozoic for the eastern part. Those previous rifting phases are decisive mechanisms controlling the localization and composition of the Cretaceous magmatism. Therefore, it is the structural position and not the age of the intrusions which preconditions the kind of magmatism and the degree of melting. The divergences on ages are the consequence of the segmentation of the basin in several sub-basins which stretching, thermal evolution and subsidence rate evolved independently. The first hypothesis formulated at the beginning of this investigation was that the Cretaceous gabbroic intrusions identified in northern Ecuador could be correlated with the intrusions described in the Eastern Cordillera. The mafic occurrences should mark the location of the most subsiding places of the large Cretaceous basin in northern South America. For this reason, the gabbroic intrusions cutting the Cretaceous succession in the Putumayo Basin, southern Colombia, were investigated. The results of the studies were quite unexpected. The petrologic and geochemical character of the magmatic rocks indicates subduction-related magmatism. K/Ar dating of amphibole yields a Late Miocene to Pliocene age (6.1 ± 0.7 Ma) for the igneous event in the basin. Although there is no correlation between this magmatic event and the Cretaceous magmatic event, the data obtained has significant tectonic and economic implications. The emplacement of the Neogene gabbroic rocks coincides with the late Miocene/Pliocene Andean orogenic uplift as well as with a significant pulse of hydrocarbon generation and expulsion. / Die östliche Kordilliere Kolumbiens besteht hauptsächlich aus sedimentären Gesteinen, die seit dem frühen Mesozoikum angelagert wurden. Magmatische Gesteine sind rar und zeigen sich nur in Form von mafischen Gängen und Lagen die in kreidezeitliches Gestein intrudierten. Diese Arbeit untersucht den kretazischen Magmatismus um die Prozesse zu verstehen, die die Bildung dieser Gesteine ermöglichte. Die magmatischen Gesteine durchschlagen die kretazischen sedimentären Einheiten aus schwarzen Schiefern und Mergeln, die auf beiden Seiten der östlichen Kordilliere aufgeschlossen sind. Die untersuchten Gesteine wurden als Gabbros (Cáceres, Pacho, Rodrigoque), Tonalite (Cáceres, La Corona), Diorite und syenitische Diorite (La Corona), Pyroxen-Hornblende Gabbros (Pacho) und Pyroxen-Hornblendite eingestuft. Die gabbroiden Proben bestehen hauptsächlich aus Plagioklas, Klinopyroxen und/ oder grüner und brauner Hornblende. Die Tonalite sind aus Plagioklas und Quarz zusammengesetzt. Die Proben sind im Bezug auf ihre Kristallgröße sehr variabel. Biotit, Titanit und Zirkon sind in Form von Akzessorien enthalten. Die Proben sind mäßig bis stark überprägt. Diese enthalten zusätzlich Epidot, Aktinolit und Chlorit. Die Haupt- und Nebenelementzusammensetzung der Gesteine wie die Mineralassoziation an sich zeigen deutliche Unterschiede abhängig von der jeweiligen Lokalität. Das deutet auf mehrere Schmelzprozesse die zur Bildung der magmatischen Gesteine führten. Das breite Spektrum an Spurenelementen in den Intrusionen ist charakteristisch für verschiedene Grade der Mantelaufschmelzung und der Anreicherung dieser Schmelzen mit inkompatiblen Elementen. MORB und OIB Zusammensetzungen deuten auf mindestens zwei verschiedene Quellen des tholeiitischen und alkalinen Magmas hin. Im westlichen Teil des Kreidebeckens weisen höhere Ba/Nd und Sr/P Verhältnisse auf subduktionsinduzierte Fluide hin, die eventuell eine Metasomatose des Mantels nach sich zog. Die Verhältnisse der radiogenen Isotope von Sr spiegeln ebenfalls einen Fluideintrag wieder. Aufgrund der Spurenelementmuster kann davon ausgegangen werden, dass im kretazischen Becken extensionale Bewegungen zu einer Ausdünnung der kontinentalen Kruste führte bis im letzten Stadium ozeanische Kruste generiert wurde. Mikrosondenanalysen (EMPA) der Hauptelemente und Röntgenfluoreszenzanalyse mittels Synchrotonstrahlung (μ-SRXRF) der Spurenelemente von früh kristallisierten Mineralen der Intrusionen (Klinopyroxene und Amphibole) reflektieren den selben dualen Charakter wie die Gesamtgesteinsanalysen. Trotz Überprägung mancher Gesteine zeigen die Mineralkompositionen sowohl eine angereicherte als auch eine relativ verarmte Magmaquelle. Durch die Normalisierung der Spurenelemente von Klinopyroxen und Amphibol zum Gesamtgestein konnte gezeigt werden, dass die Überprägung keine Auswirkung auf die originalen Spurenelementkompositionen hatte. Sr-Nd-Pb Daten zeigen eine große Variationsbreite in den Isotopen, trotzdem ist noch der Mantel als initiale Quelle des Magmas sichtbar. Die Proben zeigen mäßige bis hohe radiogene Mengen an 143Nd/144Nd und hohe Verhältnisse von 87Sr/86Sr. Beides spricht für angereicherten Mantel als Ausgangsmaterial der mafischen Intrusiva. Sedimente, Kruste und Meerwasser kontaminieren das Gestein in variablen Anteilen. Korrigierte Pb Isotopenverhältnisse zeigen zwei unterschiedliche Probengruppen. Damit kann vermutet werden, dass die Chemie des Mantels unter den nördlichen Anden durch Interaktionen mit anderen Komponenten modifiziert wurde und so ein heterogenes Material entstand. Frühere K/Ar Datierungen zeigen, dass die Intrusionen der mafischen Gesteine in der Kreide erfolgten. Aufgrund des hohen Fehlers in den Analysen und den Alterationen an den untersuchten Mineralien, sollten derartige Interpretationen mit Vorsicht betrachtet werden. Diese Arbeit zeigt anhand von Ar/Ar Daten, dass sich der Zeitraum der magmatischen Ereignisse über 60Ma hinzieht. Es wurden Alter von 136 Ma bis 74 Ma ermittelt (Hauterivium/Campanium). Extensionsprozesse traten im östlichen Teil des Kreidebeckens bereits im Paleozoikum auf, der westliche Teil wurde an der Trias-Jura-Grenze von der Entwicklung erfasst. Diese frühen Riftprozesse haben maßgeblichen Einfluss auf die Lokalität und Komposition des kretazischen Magmatismus. Daher ist die strukturelle Position und nicht das Alter ausschlaggebend, wenn es um die Art des Magmatismus und den Grad der Aufschmelzung des Mantels geht. Die Spannbreite der ermittelten Alter steht im Zusammenhang mit der Segmentierung des Beckens. Diese Subbecken zeigen eine unterschiedliche thermische Entwicklung sowie eine unabhängige Evolution in Extension und Subsidenz. Eine erste Hypothese die zu Beginn der Arbeit formuliert wurde, ging davon aus, dass die kretazischen gabbroiden Intrusionen im nördlichen Equador mit den Intrusionen in der östlichen Kordilliere korrelierbar sind. Die mafischen Gesteine definieren ein Areal des nördlichen Südamerika, dass wohl die größte Subsidenz erfahren hat. Darum wurden die gabbroiden Gänge in den kretazischen Abfolgen des Putumayo Beckens, Süd-Kolumbien, erforscht. Diese Arbeit zeigt neue Resultate und Ergebnisse, die so nicht erwartet wurden. Der petrologische und geochemische Charakter der Magmatite zeigt subduktionsbezogenen Magmatismus. K/Ar Datierungen von Amphibolen zeigen ein spates Miozänes bis Pliozänes Alter (6.1 ± 0.7 Ma) für das Intrusionsereignis im Kreidebecken. Obwohl es keine Korrelation zwischen diesem magmatischen Ereignis und dem Kretazischen gibt, zeigen die Daten doch tektonische und ökonomische Zusammenhänge auf. Die Intrusion der neogenen Gabbroide überschneidet sich mit der späten miozänen/pliozänen andinen Hebung ebenso wie mit der signifikanten Bildung von Kohlenwasserstoffen und deren Einlagerung.

Graduation date: 1991

Earth is characterized by episodes of glaciations and periods of minimal or no ice through geologic time. Using the linear energy balance model (EBM), nonlinear EBM with empirical ice sheet schemes, the general circulation model coupled with an ice sheet model, this study investigates the occurrence and stability of glaciations in geologic time. The simulations since the last glacial maximum (LGM) suggest that the summertime thawline of ice sheets conforms closely to the equatorward edge of the ice sheets and implies the relative stability toward deglaciation. CO2 levels are indispensable in controlling the initiation of ice sheet in the Cretaceous. At low CO2 levels, ice sheets exist in all periods no matter LGM or the last interglacial (LIG) orbital elements; however, at high CO2 levels ice sheets rarely exist. The simulations agree well with recent geological evidence of the hysteresis of glaciations in the Permo-Carboniferous. Gondwanaland reached its glacial maximum when CO2 level was roughly the same or slightly higher than the preindustrial value. With a further increase of CO2, deglaciation dominates and results in an ice free state. Again, if CO2 decreased to the present level, Gondwanaland would be glaciated once more and start a new cycle of glaciation and deglaciation. Simulations from five paleogeography maps in Gondwanaland with a suite of CO2 levels and different orbital elements reveal that paleogeography, CO2 levels and the Milankovitch cycles all contribute to the glaciations of Gondwanaland. This study shows that orbital elements alone are insufficient to account for the evolution of ice sheets. Net radiative forcing caused by greenhouse gases, such as CO2 and solar constant change are the primary drivers to glacial inception or demise. Continental geography, CO2 levels, solar constant change, and the Milankovitch cycles complicate the glacial history of Earth.

The Haymana basin in Central Anatolia (Turkey) formed on a Late Cretaceous to Middle Eocene fore &amp / #8211 / arc accretionary wedge. The aim of this study is to investigate the sedimentary cyclicity and depositional sequences in the Upper Cretaceous clastic successions of the Haymana basin. To be able to achieve this objective, a 250 m stratigraphic section, which is mainly composed of siliciclastics has been measured in the Haymana Basin. In this study, detailed lithofacies analyses were performed and five different facies were recognized in the studied interval of the Haymana Formation. Sandstones, shales and conglomerates are the most abundant in the succession. In the measured section, two chronozones were identified based on the biostratigraphic data. These are the lower Dicarinella asymetrica chronozone and the upper Globotruncanita elevata - Globotruncana ventricosa chronozone corresponding to the Upper Santonian and Lower to Middle Campanian, respectively. Sedimentological analyses, such as provenance, palaeocurrent and grain-size sphericity were also performed and their relation with depositonal environment and change in depositional conditions were discussed. In order to construct the sequence stratigraphic framework, detailed lithofacies analyses and their vertical association were carried out. The studied interval of the Haymana Formation represents a prograding submarine fan subdivided into three depositional sequences, each with several tens of meters thick successions and two sequence boundaries. Each depositonal sequence consists of system tracts and turbiditic basic sequences with sandstone and conglomeratic beds overlain by mudstones. Turbiditic basic sequences, the sandstone and mudstone alternation allows distinction of smaller subdivisions, namely, basic cyclic units, which are the building blocks of system tracts and turbiditic basic sequences. Depositional sequences of the studied section of the Haymana Formation may correspond to third order relative sea &amp / #8211 / level cycles. Accordingly, fourth &amp / #8211 / and fifth &amp / #8211 / order (Milankovich) cycles might be proposed as basic sequences and basic cyclic units, respectively.

In order to understand the tectonic evolution of the Kalecik region (Ankara, Turkey), a structural field study was performed in a selected area located in the east of Kalecik, where mostly imbricated thrust sheets of the Cretaceous Ophiolitic melange crop out. In the study area, the Cretaceous Ophiolitic melange, Cretaceous radiolaria-bearing sequences and the Paleocene units are all intruded by sub-vertical dykes. The attitudes of planar structures (dykes, beds and faults) and the kinematic data measured on faults were analyzed by using &ldquo / ROCKWORKS 2002&rdquo / and &ldquo / Angelier Direct Inversion Method (version 5.42)&rdquo / softwares, respectively. A major trend of NE-SW (045&deg / N) direction and relatively a post-Paleocene &ndash / pre-Miocene age was determined for the dykes indicating an extension in the NW-SE direction during post-Paleocene. The dykes cut bedded units displaying a dominant set trending in WNW-ESE (297&deg / N) direction and mostly dipping towards NE with moderate dip amounts. But at the same time, the Upper Cretaceous units were observed as intensely folded, faulted and thrusted due to the compressional regime that acted in Central Anatolia during Late Cretaceous. The angular difference between the major trend of dykes and the dominant trend of stratification was found as approximately 108&deg / ., which may also indicate that the dykes and beds were evolved during different deformation periods. The results of the kinematic analyses of different age faults revealed that the post-Paleocene &ndash / pre-Miocene Kalecik basaltic dykes are deformed under a continuous NW-SE-oriented post-Paleocene compressional to strike-slip tectonic regime which was followed by a NNW-SSE oriented post-Miocene extensional-transtensional regime.

The geological range of lamniform sharks stretches from present day species such as Carcharodon carcharias (great white shark) back to the at the moment oldest undoubted fossil finds during the Early Cretaceous. In this paper a geometric morphometric analysis was performed on images of Early Cretaceous lamniform teeth collected from published literature in order to examine the change in disparity (range of morphological variation within a group) throughout the time period. Due to limited availability of published material and time constraints only the Barremian and Albian ages were investigated. The Barremian exhibited tall and narrow tooth morphologies while the Albian showed a wide range of morphological variation including more robust, wide and sometimes triangular shapes but also displayed further specialization of the tall and narrow forms. This change is likely indicative of a dietary and ecological expansion from only eating for example small fish and soft-bodied creatures to a wide range of prey for the group, including larger and more robust animals such as marine turtles and large bony fish. This in combination with the decline of some marine predators as well as the diversification of possible prey is interpreted as that an adaptive radiation of the Lamniformes could have taken place during the latter half of the Early Cretaceous. / Morfologisk disparitet är ett mått på hur stor utsträckningen av morfologisk variation är. Detta mått räknas ut genom att jämföra landmärken utplacerade på bilder av föremål som ska undersökas. I detta projekt undersöktes den morfologiska dispariteten hos tänder från håbrandsartade hajar (Lamniformes) under tidig krita. Att just deras tänder undersöktes beror på att den större delen av hajars skelett är gjort av brosk vilket lätt bryts ned efter djuret avlidit. Deras tänder är dock gjorda av ben vilket har lättare att bli bevarat som fossil. Utöver detta så kan formen på tänder beskriva djurs födoval och levnadssätt. Gruppens tänder undersöktes därför även för att belysa eventuella förändringar i diet och ekologi under tidig krita. Resultatet av denna analys visar på en expansion av tandform under denna period från långa och smala tänder under Barremium till en större variation under Albium där även mer triangelformade och robusta tänder dyker upp. Detta har tolkats som en adaptiv artbildningsperiod för gruppen då både nya byten (t.ex. teleostfiskar och havs-sköldpaddor) diversifierade och uppkom samtidigt som vissa marina predatorer (ichthyosaurer och plesiosaurer) minskade i antal under denna tidsperiod. Detta ändrade troligen de selektiva trycken på håbrandsartade hajars tandmorfologi samt lämnade ekologiska nischer öppna som dessa kunde anpassa sig till vilket i sin tur ledde till expansioner i morfologisk disparitet, diet och ekologi.

The major purpose of this study was to examine in detail the anomalous transgressive "boundary" sandstones which generally are present at formation boundaries throughout the Parras and La Popa basins. These extensive sheet-like sandstone bodies are massive, resistant units up to 20 m thick and up to 25 km wide that form the cap of mountains and hogbacks. These are anomalous units because transgressive deposits thicker than 5-10 m are rare in ancient deposits although they are well-documented for some Holocene deposits. For example there are no known thick transgressive deposits in the well-studied cyclic transgressive-regressive sequences in the Cretaceous rocks of the Rocky Mountains. McBride and others (1975) previously interpreted these boundary sandstone bodies to have been laid down as thick transgressive or regressive blanket deposits as the shoreline moved back and forth across the basins in response to variable basin subsidence and sediment input. In order to clarify this interpretation, we selected deposits formed during the latest part of the first deltaic progradation represented by the Cerro Huerta Formation, and at the beginning of the first marine transgression represented by the Cañon del Tule Formation for detailed study. / text

Recent drilling of deep stratigraphy in subsalt offshore Gulf of Mexico has revealed the presence of thick, amalgamated, Cretaceous siliciclastic reservoirs with the potential to become valid exploration targets. Similar to the Lower Tertiary deepwater play, the significant down-dip distance (> 400 km) from the source deltaics, the data gap across the modern structurally complex salt-tectonics-dominated slope and the difficulties of imaging subsalt stratigraphy pose challenges for the construction of meaningful deepwater system models to aid in exploration and appraisal efforts. A 3D seismic dataset in the Mad Dog field at the basinward end of the modern allochthonous salt canopy and outboard of the Sigsbee Escarpment offers the opportunity to study the nature of the deep stratigraphy at central positions in the basin. The nature of the Cretaceous sedimentary system has been investigated through detailed structural and seismic geomorphologic mapping. An early syndepositional contractional event has been identified and temporally associated with Mesozoic emplacement of a deep salt sheet. These events are masked by the major Neogene-age phase of fold amplification that dominates the present-day subsalt structural framework. Ponded-basin deepwater sedimentation processes control early phases of deposition in the Cretaceous Mad Dog area and sediment-gravity flows are deposited as complexes of low sinuosity amalgamated channelized deposits in roughly-confined sediment pathways. Ponded fills show internal lateral accretion architectures that grow sigmoid in nature as the migrating systems interact with the approaching minibasin margins making evident the structural control on sediment architecture. Later phases of deposition are characterized by slightly sinuous feeder channels with multiple lobe development at their terminus. Variable directions of sediment source pathways indicate a linear-sourced slope apron depositional model for these systems. In addition to the more structured morphologic elements, there were also pervasive mass-transport processes active, presumably triggered by Mesozoic halokinesis. Data in sparse deep wells in the GoM that penetrate the Cretaceous suggest that the Late Cretaceous deepwater depositional system was composed of coarse-grained high density gravity flows. The geometries seen in seismic beneath the Mad Dog area support the existence of such a basinwardly extensive deepwater fan systems developed during the Cretaceous, and the low sinuosity channel geometries and small length:width ratio and amalgamated nature of fan lobes suggest that these systems may have indeed been high-density in nature. / text

The effectiveness of CO₂ injection in the subsurface for storage and EOR are controlled by reservoir quality variation. This study determines the depositional processes and diagenetic alterations affecting reservoir quality of the Lower Tuscaloosa Formation at Cranfield Field. It also determines the origin, time and processes of the grain-coating chlorite and its impacts on reservoir quality. Moreover, by integrating depositional and diagenetic characteristics and by linking them to sequence stratigraphy, the distribution of reservoir quality, could be predicted within a sequence stratigraphic framework. The studied sandstones are composed of medium to coarse-grained, moderately sorted litharenite to sublitharenite with composition of Q76.1F0.4L23.5. Depositional environment of this formation in the Mississippi Interior Salt Basin is interpreted as incised-valley fluvial fill systems. The cross sections and maps at the field show trend of the sandy intervals within channels with a NW-SE paleocurrent direction. During burial of the sandstones, different digenetic alterations including compaction, dissolution, replacement and cementation by chlorite, quartz, carbonate, kaolinite, titanium oxides, pyrite and iron-oxide modified the porosity and permeability. Among these, formation of chlorite coats plays the most important role in reservoir quality. The well-formed, thick and continuous chlorite coatings in the coarser grain sandstones inhibited formation of quartz overgrowth, resulted in high porosity and permeability after deep burial; whereas the finer grain sandstones with the poorly-formed, thin and discontinuous chlorite coatings have been cemented by quartz. The optimum amount of chlorite to prevent formation of quartz overgrowths is 6% of rock volume. The chlorite coats are composed of two layers including the inner chlorite layer formed by transformation of the Fe-rich clay precursors (odinite) through mixed-layer clays (serpentine-chlorite) during early eodiagenesis and the outer layer formed by direct precipitation from pore waters through dissolution of ferromagnesian rock fragments during late eodiagenesis to early mesodiagenesis. In the context of the reservoir quality prediction within sequence stratigraphic framework, the late LST and early TST are suitable for deposition of chlorite precursor clays, which by progressive burial during diagenesis could be transformed to chlorite, and thus results in preserving original porosity and permeability in deep burial. / text

The systematic relationships of basal ornithischian dinosaurs remain contentious, especially the position of basal neornithischians (i.e., ‘hypsilophodontids’). Prior analyses of basal ornithischian relationships have been hampered by the fact that the hypodigm material of many basal neornithischian taxa is fragmentary, denying access to character data crucial to resolving their relationships. The recent discovery of several new basal neornithischian taxa and the referral of more complete specimens to known taxa provide important new data pertinent to resolving these relationships. The results of this study supplement those recent advances by improving our understanding of the anatomy and systematic relationships of basal neornithischian taxa from the Late Cretaceous of North America. These new insights are accomplished through a taxonomic revision of the Maastrichtian taxa Bugenasaura and Thescelosaurus, a detailed anatomical description of the cranial anatomy of Thescelosaurus neglectus based on the referral of a specimen that includes a nearly complete skull (NCSM 15728), and description of a new basal neornithischian taxon from the Kaiparowits Formation (Campanian) of Utah. All of these new data are compiled into a dataset composed of 255 characters for 65 terminal taxa (all species exemplars) focused on assessing basal ornithischian relationships. The recovered strict consensus topology is the most highly resolved, stratigraphically congruent phylogenetic hypothesis of basal ornithischian relationships yet proposed. This analysis places all basal neornithischians except Hypsilophodon foxii outside of Cerapoda, substantially reducing the taxonomic contents of Ornithopoda. A new clade containing fourteen basal neornithischian taxa is recovered as the sister taxon to Cerapoda and includes all North American basal neornithischians from the Cretaceous. The historical biogeography of Ornithischia is also reconstructed using a method that incorporates time calibrated branch lengths that represent the implied missing fossil record of each taxon. The results of this analysis support two dispersals of neornithischian taxa into South America during the Cretaceous: one consisting of basal iguanodontians dispersing from Australia (possibly via Antarctica) and a second consisting of basal neornithischians dispersing from Asia through North America. / text