Browsing by Author "Hubbard, Stephen M."

Now showing 1 - 7 of 7
  • Thumbnail Image
    Basin Evolution and Slope System Dynamics of the Cretaceous Magallanes Basin, Chilean Patagonia
    Auchter, Neal C. (Virginia Tech, 2016-12-20)
    Deep-marine basins linked to active continental margins by sloped ocean-floor profiles commonlyhost the final accumulation of sediment that was eroded and transported from the continents. Thedeep-marine sediment archives preserved in these settings commonly offer the most completerecord of sediment transfer from continents to ocean basins over geologic time scales. This isespecially true in basins associated with regions of active tectonism, where loss or alteration ofsediment source terrains leave submarine basin deposits as the only record of the tectonic and cli-matic forcings that govern the transfer of sediment to the deep basin. The overarching goal of thisdissertation is to evaluate controls on submarine slope and basin-floor sedimentation that considersboth large-scale system drivers and the internal complexities and autogenic processes associatedwith sediment routing systems. In pursuit of this goal, the research presented in this dissertationspans a range of spatial and temporal scales. At the largest scale, the influence of sediment recy-cling is addressed to evaluate how changes in intrabasinal sediment sources reflect phases of basinevolution and what influence recycling of previously deposited basin sediments has on the fidelityof the deep-marine sedimentary record at geologic time scales. At the smaller scale, analysis ofsedimentation units and characterization of sedimentary bodies form the foundation for linkingthe stratigraphic preservation of depositional processes to discrete submarine geomorphic condi-tions. Such a linkage can provide insight into changes in slope gradient and the transition fromsediment transport and bypass to sediment deposition along the slope profile. Thirdly, a detailedinvestigation of deformed slope deposits addresses how depositional processes and stratigraphicstacking of submarine fan deposits influences slope stability. Synthesis across these broad spatialand temporal scales required integration of various tools and data types including: (1) detailedoutcrop measurements, (2) cliff-face correlation and characterization of depositional architecture,(3) geologic mapping, (4) basin-scale correlation, (5) detrital geochronology, and (6) carbonategeochemistry.
  • Thumbnail Image
    Flow dynamics as Froude-supercritical turbidity currents encounter metre-scale slope minibasin topography
    Englert, Rebecca G.; Hubbard, Stephen M.; Romans, Brian W.; Kaempfe, Sebastian; Bell, Daniel; Nesbit, Paul R.; Stright, Lisa (Wiley, 2023-12-07)
    Seafloor topography can affect turbidity current dynamics on deep-water slopes, significantly influencing the dispersal of sediment. Despite the common occurrence of topographic complexity, there are few detailed investigations of topographic interactions and their effect on downslope flow evolution in intraslope environments. In this study, the sedimentology and architecture of an Upper Cretaceous intraslope fan succession deposited within an extensional, fault-bound minibasin are described from a rare, well-exposed, near-continuous, oblique depositional-dip outcrop of the Tres Pasos Formation, Chile. The 2 to 8 m thick studied interval transitions downslope from high-energy heterolithic strata, including metre-scale steep-faced scours, to non-amalgamated thick-bedded sandstones. Abrupt increases in sandstone percentage, sandstone bed thickness and grain size occur on the hangingwall blocks of south-east and north-east-dipping normal faults that bound the minibasin. Sandstone beds are dominated by backset or wavy low-angle stratification proximally, contain compositional banding near faults, and are characterised by increased proportions of planar laminated and structureless turbidite divisions downslope along the transect. Experimental observations of turbidity current interactions with topography are synthesised into a qualitative framework, which is used to interpret flow processes and characteristics from deposit trends. The results reconstruct the response of Froude-supercritical, stratified turbidity currents with denser basal layers when encountering metre-scale fault scarps. The analysis shows that metre-scale topographic features can substantially alter the flow properties of stratified turbidity currents, and their downslope flow evolution to include the development of transitional, depositional and flow-stripped sediment gravity currents. However, in comparison to base-of-slope settings, overall flow conditions are interpreted to be more uniform over slope breaks and zones of flow expansion in a partially confined intraslope environment. These findings have considerable implications for understanding flow response to similar scale morphological features on the seafloor and the potential for flow transformations in intraslope settings.
  • Thumbnail Image
    Inherited Depositional Topography Control on Shelf-Margin Oversteepening, Readjustment, and Coarse-Grained Sediment Delivery to Deep Water, Magallanes Basin, Chile
    Bauer, Dustin B.; Hubbard, Stephen M.; Covault, Jacob A.; Romans, Brian W. (2020-01-23)
    A shelf-margin depositional system is the stratigraphic product of terrigenous sediment delivery to the ocean, comprising a flat to low-gradient shelf, or topset, which transitions to a steeper deep-water slope, and, ultimately, a relatively flat basin floor, or bottomset. Erosional and depositional processes across these physiographic domains approximate a clinoform in the stratigraphic record. The shelf margin is a critical environment for terrigenous sediment dispersal because it is a process-regime boundary that links the shelf to deep water and is a marker of basin evolution through time. Additionally, the coarse-grained deposits of strata associated with the shelf-margin zone are important subsurface reservoirs or aquifers. Here, we characterize the shelf-margin and upper slope stratigraphy of the outcropping Upper Cretaceous Tres Pasos and Dorotea formations, Magallanes Basin, southern Chile. The Late Cretaceous Magallanes retroarc foreland basin was an elongate trough oriented parallel to the southern Andean arc and fold-and-thrust belt. The Tres Pasos and Dorotea formations record southward (basin axial) progradation of a high-relief shelf and slope system (>1000 m paleo-water depth) represented by a stratigraphic succession up to 3 km thick that is exposed for tens of kilometers along depositional dip. The character and distribution of deposits that define shelf margins contain evidence for a variety of processes related to deposition, erosion, sediment bypass, and mass wasting. The overall architecture of the Magallanes Basin strata is indicative of a graded shelf-margin system interrupted by periods of slope oversteepening and development of out-of-grade conditions. These punctuated periods are recognized by sedimentological evidence for enhanced bypass of coarse-grained sediment across the upper slope, and thick submarine fan successions in more distal segments. Development of oversteepened depositional topography is particularly significant as it instigated the only two major periods of coarse-grained sediment delivery to deep water over similar to 8 Myr during the Campanian. The controls on sediment dispersal beyond the shelf margin are commonly discussed in terms of allogenic forcings, such as tectonics, climate, eustasy, and receiving-basin geometry, as well as autogenic behavior, such as delta-lobe switching. However, inherited depositional topography does not clearly fit within an allogenic/autogenic dichotomy. Depositional topography inherited from shelf-margin evolution influences the position of subsequent shelf margins, which can promote coarse-grained sediment delivery to deep water.
  • Thumbnail Image
    Intrabasinal sediment recycling from detrital strontium isotope stratigraphy
    Auchter, Neal C.; Romans, Brian W.; Hubbard, Stephen M.; Daniels, Benjamin G.; Scher, Howie D.; Buckley, Wayne (2020-10)
    Temporary storage of sediment between source and sink can hinder reconstruction of climate and/or tectonic signals from stratigraphy by mixing of sediment tracers with diagnostic geochemical or geochronological signatures. Constraining the occurrence and timing of intrabasinal sediment recycling has been challenging because widely used detrital geothermochronology applications do not record shallow burial and subsequent reworking. Here, we apply strontium isotope stratigraphy techniques to recycled marine shell material in slope deposits of the Upper Cretaceous Tres Pasos Formation, Magallanes Basin, Chile. Detrital Sr-87/Sr-86 ages from 94 samples show that the majority (>85%) of the shells are >1-12 m.y. older than independently constrained depositional ages. We interpret the gap between mineralization age (Sr-87/Sr-86 age) and depositional age of host strata to represent the intrabasinal residence time of sediment storage at the million-year time scale. We also use specimen type to infer relative position of intrabasinal source material along the depositional profile, where oysters represent shallow-water (i.e., proximal) sources and inoceramids represent deeper-water (i.e., distal) sources. The combined use of detrital strontium isotope ages and specimen types from linked depositional segments provides an opportunity to identify and quantify sediment storage and recycling in ancient source-to-sink systems.
  • Thumbnail Image
    Multi-scale deep-marine stratigraphic expressions in the Cretaceous Magallanes Basin, Chile: Implications for depositional architecture and basin evolution
    Kaempfe Droguett, Sebastian Andres (Virginia Tech, 2022-06-13)
    Submarine channel-levee systems represent one of the most significant features of sediment transfer on Earth and one of the final segments in source-to-sink routing systems. As such, they serve as conduits as well as intermediate or final storage for large volumes of sediment, paleoenvironmental signals, and pollutants on their way to the deep ocean. Over the years, these systems have been studied through a variety of methods, including: (i) outcropping analogs; (ii) seismic data, occasionally integrated with core analysis; (iii) numerical modeling and physical experiments, and more recently; (iv) repeated multibeam bathymetry and (v) direct measurement of sediment gravity flows. However, as we are able to show in this study, there are still questions about the inherent evolution of these systems that need to be addressed. In this study, we focus on the sedimentary processes and depositional products of submarine channel-levee systems through the characterization, analysis and interpretation at different scales of outcropping analog systems of the Upper Cretaceous Tres Pasos and Cerro Toro Formations in the Magallanes-Austral Basin. In the first research-chapter, Chapter 2, we analyze the transition between laterally offset and vertically stacked channels on a previously undocumented, seismic-scale outcrop of the Tres Pasos Formation. This change in stacking pattern has been widely recognized in submarine channel systems, however, the stratigraphic and sedimentologic details and implications to general conceptual models have not been addressed in the past. Our observations indicate that in between these two depositional architecture styles there is a significant phase of erosion and bypass at a complex-scale (or larger) and that the relief achieved via this deep incision of one or multiple simultaneously active conduits was the necessary condition to promote flow stripping processes and associated overbank deposition. In addition, we discuss the presence of an unusual intra-channel lithofacies association observed directly overlying one of these incisions, which we interpret to represent the along-strike expression of bedforms associated with supercritical flow processes that are found in modern channels and some ancient channel-fill successions. In the next research chapter, Chapter 3, we characterize a 500 m thick fine-grained dominated sedimentary succession interpreted as overbank deposits of the Cerro Toro Formation that have been affected by synsedimentary faulting and crosscut by an extensive injectite network. The scale of this outcrop allows us to resolve the relationship between sedimentary packages and structural features that are commonly overlooked or beyond the resolution of datasets derived from other sources by using high-resolution measurements and quantitative analysis at a cm scale. The orientation of synsedimentary normal faults, paleocurrent directions, and characteristics of 10-36 m thick sandstone-prone intervals suggest a model of overspilling turbidity currents (from the main axial channel belt to the west) on a large levee-slope that might share deformational mechanisms with other depositional slopes. Finally, in Chapter 4, we use detrital zircon U-Pb geochronology to determine maximum depositional ages of seven sandstone samples attributed to the axial channel-belt of the Cerro Toro Formation and shallow-marine deposits of the Dorotea Formation, which extend the chronostratigraphic framework for Ultima Esperanza 55 km southward to help reduce the gap between field sites in the Ultima Esperanza and Magallanes provinces. Based on these new data, we hypothesize that the conglomeratic-rich deposits at this location, which have generally similar lithofacies and large-scale stratigraphic architecture to the Cerro Toro Formation, are unlikely to represent the southward extension of the well-studied axial channel belt deposits to the north, and therefore they potentially represent their own sediment routing system emanating from erosional catchments in the fold-thrust belt to the west. This chapter highlights the value of establishing a chronostratigraphic framework to reconstruct ancient paleogeography in addition to interpretation based purely on observable sedimentary parameters.
  • Thumbnail Image
    The Stratigraphic Evolution of a Submarine Channel: Linking Seafloor Dynamics to Depositional Products
    Hubbard, Stephen M.; Jobe, Zane R.; Romans, Brian W.; Covault, Jacob A.; Sylvester, Zoltan; Fildani, Andrea (2020-07)
    We investigate the relationship between the cross-sectional geomorphic expression of a submarine channel as observed on the seafloor and the stratigraphic product of long-lived erosion, bypass, and sediment deposition. Specifically, by reconstructing the time-space evolution of an individual channel fill (i.e., channel element) exposed in outcrop, we establish a genetic link between thick-bedded channel-element-axis sandstone to thinly interbedded channel-element-margin deposits. Although the bounding surface between axis sandstone and margin thin beds is sharply defined, it is composed of a series of geomorphic surface segments of various ages; as such, the composite stratigraphic surface (similar to 17 m relief) was formed from numerous incision events that repeatedly sculpted the conduit. By demonstrating the origin of the stratigraphic surface, we conclude that geomorphic surfaces with 2-7 m of erosional relief were largely responsible for the observed intra-channel-element architecture (and ultimately, the composite 17-m-thick element). The widely documented channel element axis-to-margin architecture is a product of submarine-channel thalweg dynamics, primarily recording interactions between the seafloor and the basal high-concentration layers of channelized turbidity currents.
  • Thumbnail Image
    Timing of deep-water slope evolution constrained by large-n detrital and volcanic ash zircon geochronology, Cretaceous Magallanes Basin, Chile
    Daniels, Benjamin G.; Auchter, Neal C.; Hubbard, Stephen M.; Romans, Brian W.; Matthews, William A.; Stright, Lisa (2017-09-15)
    Deciphering depositional age from deposits that accumulate in deep-water slope settings can enhance understanding of shelf-margin evolutionary timing, as well as controlling mechanisms in ancient systems worldwide. Basin analysis has long employed biostratigraphy and/or tephrochronology to temporally constrain ancient environments. However, due to poor preservation of index fossils and volcanic ash beds in many deepwater systems, deducing the timing of slope evolution has proven challenging. Here, we present >6600 new U-Pb zircon ages with stratigraphic information from an ~100-kmlong by ~2.5-km-thick outcrop belt to elucidate evolutionary timing for a Campanian– Maastrichtian slope succession in the Magallanes Basin, Chile. Results show that the succession consists of four stratigraphic intervals, which characterize four evolutionary phases of the slope system. Overall, the succession records 9.9 ± 1.4 m.y. (80.5 ± 0.3 Ma to 70.6 ± 1.5 Ma) of graded clinoform development punctuated by out-of-grade periods distinguished by enhanced coarse-grained sediment bypass downslope. Synthesis of our results with geochronologic, structural, and stratigraphic data from the basin suggests that slope evolution was largely controlled by an overall decline in basin subsidence from 82 to 74 Ma. In addition to providing insight into slope evolution, our results show that the reliability of zircon-derived depositional duration estimates for ancient sedimentary systems is controlled by: (1) the proportion of syndepositionally formed zircon in a stratigraphic interval; (2) the magnitude of the uncertainty on interval-bounding depositional ages relative to the length of time evaluated; and (3) the geologic time (i.e., period/era) over which the system was active.