R-3 Repository :: Browsing by Author "Anderson, John B."

Browsing by Author "Anderson, John B."

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4500-year paleohurricane record from the Western Gulf of Mexico, Coastal Central TX, USA
(Elsevier, 2024) Monica, Sarah B.; Wallace, Davin J.; Wallace, Elizabeth J.; Du, Xiaojing; Dee, Sylvia G.; Anderson, John B.
Texas receives the second-highest number of tropical cyclone (TC) landfalls per year in the United States. At present, long-term TC projections from climate models remain uncertain due to the short and biased nature of Atlantic TC observations. Sediment archives of past storms can help extend the observational record of TC strikes over the past few millennia. When a TC makes landfall along the central Texas coast, coastal downwelling channels and storm currents transport and deposit coarse sediment to a zone of rapid accumulation along the shelf, known as the Texas Mud Blanket (TMB). This “backwash” process results in expansive storm deposits along the shelf, making this region ideal for paleotempestological reconstructions. Here, we present two sediment cores, located approximately 6 km southeast of Matagorda Island (TX), that collectively yield a ∼4500-year paleohurricane record. 210Pb and 137Cs are utilized in conjunction with radiocarbon ages to produce high-resolution Bayesian age models. One-centimeter interval grain size analyses are used to identify TC deposits. Two-centimeter interval X-Ray Fluorescence (XRF) is used as an additional measure to verify depositional mechanisms in this shelf environment. We define an intense paleohurricane event threshold through statistical analysis of mean grain size data. The sediment-derived TC record is correlated to Palmer Drought Severity Index (PDSI) data from Paleo Hydrodynamics Data Assimilation (PHYDA) to bolster our interpretation of the TC record, revealing a coupled relationship between PDSI and TCs since ∼300 yr BP. Over the ∼4500-year period, 24 intense TCs were recorded in the sediment record, yielding a long-term annual landfall probability of ∼0.53%. Additionally, comparisons between other TC records within the Atlantic establish a relationship between enhanced TC activity in the Western Gulf of Mexico (GOM) and TCs formed in the Caribbean Sea.
A community-based geological reconstruction of Antarctic Ice Sheet deglaciation since the Last Glacial Maximum
(Elsevier, 2014) The RAISED Consortium; Bentley, Michael J.; Ó Cofaigh, Colm; Anderson, John B.; Conway, Howard; Davies, Bethan; Graham, Alastair G.C.; Hillenbrand, Claus-Dieter; Hodgson, Dominic A.; Jamieson, Stewart S.R.; Larter, Robert D.; Mackintosh, Andrew; Smith, James A.; Verleyen, Elie; Ackert, Robert P.; Bart, Philip J.; Berg, Sonja; Brunstein, Daniel; Canals, Miquel; Colhoun, Eric A.; Crosta, Xavier; Dickens, William A.; Domack, Eugene; Dowdeswell, Julian A.; Dunbar, Robert; Ehrmann, Werner; Evans, Jeffrey; Favier, Vincent; Fink, David; Fogwill, Christopher J.; Glasser, Neil F.; Gohl, Karsten; Golledge, Nicholas R.; Goodwin, Ian; Gore, Damian B.; Greenwood, Sarah L.; Hall, Brenda L.; Hall, Kevin; Hedding, David W.; Hein, Andrew S.; Hocking, Emma P.; Jakobsson, Martin; Johnson, Joanne S.; Jomelli, Vincent; Jones, R. Selwyn; Klages, Johann P.; Kristoffersen, Yngve; Kuhn, Gerhard; Leventer, Amy; Licht, Kathy; Lilly, Katherine; Lindow, Julia; Livingstone, Stephen J.; Massé, Guillaume; McGlone, Matt S.; McKay, Robert M.; Melles, Martin; Miura, Hideki; Mulvaney, Robert; Nel, Werner; Nitsche, Frank O.; O'Brien, Philip E.; Post, Alexandra L.; Roberts, Stephen J.; Saunders, Krystyna M.; Selkirk, Patricia M.; Simms, Alexander R.; Spiegel, Cornelia; Stolldorf, Travis D.; Sugden, David E.; van der Putten, Nathalie; van Ommen, Tas; Verfaillie, Deborah; Vyverman, Wim; Wagner, Bernd; White, Duanne A.; Witus, Alexandra E.; Zwartz, Dan
A robust understanding of Antarctic Ice Sheet deglacial history since the Last Glacial Maximum is important in order to constrain ice sheet and glacial-isostatic adjustment models, and to explore the forcing mechanisms responsible for ice sheet retreat. Such understanding can be derived from a broad range of geological and glaciological datasets and recent decades have seen an upsurge in such data gathering around the continent and Sub-Antarctic islands. Here, we report a new synthesis of those datasets, based on an accompanying series of reviews of the geological data, organised by sector. We present a series of timeslice maps for 20 ka, 15 ka, 10 ka and 5 ka, including grounding line position and ice sheet thickness changes, along with a clear assessment of levels of confidence. The reconstruction shows that the Antarctic Ice sheet did not everywhere reach the continental shelf edge at its maximum, that initial retreat was asynchronous, and that the spatial pattern of deglaciation was highly variable, particularly on the inner shelf. The deglacial reconstruction is consistent with a moderate overall excess ice volume and with a relatively small Antarctic contribution to meltwater pulse 1a. We discuss key areas of uncertainty both around the continent and by time interval, and we highlight potential priorities for future work. The synthesis is intended to be a resource for the modelling and glacial geological community.
A geological and geophysical investigation of sedimentation and recent glacial history in the Gerlache Strait region, Graham Land, Antarctica
(1988) Griffith, Thomas Ward; Anderson, John B.
Piston cores, bottom grabs, and single-channel seismic data acquired during Deep Freeze/USARP cruises have been used to examine sedimentation and recent climatic history in the bays and fjords of the Gerlache Strait region (Antarctic Pensinsula). The local climate and glacial setting exhibit profound influences on sedimentation via the processes associated with subglacial water. Visible sediment plumes are rare, and glacial ice above sea level is pristine white, indicating that debris is entering the water from the glaciers that are grounded below sea level. In the relatively warm and wet Palmer Archipelago, terrigenous muds and sands with a variable IRD component are ponding in every available bathymetric depression, and sediment gravity flow processes are common. Along the colder and drier Danco Coast, diatomaceous sediments drape uniformly across the rugged basement topography, rather than ponding, and resedimentation is rare. In both areas, sedimentation occurs in quiescent water.
A petrologic study of Weddell Sea sediments: implications for provenance and glacial history
(1984) Andrews, Barbara Ann; Anderson, John B.; Baker, Donald R.; Bally, Albert W.
Knowledge of subglacial geology in Antarctica is restricted due to limited outcrop exposure. Investigations of terrestrially derived sediments deposited on the Antarctic continental margin have proved successful for gaining increased understanding of this ice-covered continent. Petrologic analyses conducted on glacial, glacial marine, and sediment gravity flow deposits from the Weddell Sea continental margin provide important evidence concerning subglacial geology and glacial history of land areas contiguous to the Weddell Sea. Petrologic data validates identifications, originally based on sed imen to 1ogic criteria, of basal tills on the Weddell Sea continental shelf. The presence of basal tills indicates a major expansion and coincident grounding of the East or West Antarctic Ice Sheet to the shelf edge. Petrologic evidence suggests that glacial expansion in the area of study was chiefly that of the East Antarctic Ice Sheet. Basal tills and transitional glacial marine sediments form distinct petrologic provinces on the Weddell Sea shelf. Most province boundaries extend inland parallel to ii reconstructed ice paleoflow lines. Till lithologies are dominated by volcanics and quartzose sedimentary rocks, in contrast to metamorphic outcrops of the Weddell Sea region. Comminution does not effectively bias till composition. Till lithologies suggest that mountainous outcrops are not representative of subglacial geology and that sedimentary basins exist beneath the Antarctic Ice Sheet. Four provenance areas for the Weddell Sea basal tills are modeled; correlations between modeled provenance areas and till petrologic provinces are good. Ice-rafted lithologies are limited in number and do not show the expected varied assemblage of Antarctic rock types. Derivation from a limited source area or from lateral moraines is suggested. Sediment gravity flow deposits from the Weddell Sea continental slope and abyssal plain are compositionally very different. Intracanyon slope debris flows and turbidites, composed chiefly of lithic fragments, were generated from basal tills on the adjacent shelf. Abyssal plain turbidites show substantial quartz enrichment and could not have been sourced directly from shelf tills.
A seismic stratigraphic and structural interpretation of the middle Paleozoic Ikpikpuk-Umiat Basin, National Petroleum Reserve in Alaska
(1985) Mauch, Elizabeth A.; Bally, Albert W.; Anderson, John B.; Oldow, John S.
The Ikpikpuk-Umiat Basin is located in the eastern NPRA in northern Alaska. The basin overlies the eroded remnants of a Middle Devonian folded belt and contains up to 18, feet of Late Devonian and Mississippian elastics and up to 8 feet of Mississippian and Pennsylvanian carbonates. These sediments were deposited in two depocenters, an older larger depocenter in the southeast primarily composed of the clastic sequence and a younger, smaller depocenter in the northwest predominantly filled with the carbonate sequence. The sediments in the southeastern depocenter were deposited while the basin was undergoing subsidence and extension whereas sediments in the northwest depocenter were deposited during 8n intra-Mississippian compressional event which affected the entire basin. This compressional event is characterized by north vergent thrust faults trending west-northwest across the basin. A number of these thrust faults are reactivated earlier down-to-the-basin normal faults. The Ikpikpuk-Umiat Basin is tentatively interpreted to be part of an A-subduction related backarc region analogous to the Pannonian Basin in Hungary.
A structural study of the Hukou and Hsinchu areas Northwestern Taiwan
(1985) Liu, Chingju; Bally, Albert W.; Oldow, John S.; Anderson, John B.
Northwestern Taiwan, which includes the Kuanyin, Hukou and Hsinchu areas, was initially a part of the continental shelf of the mainland China coast. The Neogene sediments were deposited m gently east-dipping basement in a stable shelf type environment. The sedimentary sequence shows a regional tilt as well as a thickening of strata towards the southeast, the location of the former ocean. The structures which make up the Hukou and Hsinchu areas are located in the frontal edge of the western foothills range. The structure is dominated by simple-step thrust faults. Frequently, the upthrown blocks of the faults are folded and form the typical asymmetrical folds with steeper north/northwest limbs (e.g. the Hukou and Chingtsaohu Anticlines). A possible solution to the structure of western Taiwan is a progressive change from a simple-step thrust fault in the north to more imbricated faults in the foothills to the southeast. This is similiar to the type of imbrication found in the Canadian Rocky Mountain. Based on the assumption of the oblique plate convergence in the Taiwan area, a model with more westerly substructural involvement of pre-Miocene rocks provides a more conservative estimate of the possible amount of the plate shortening in Taiwan than do previously published studies based on the fault-bend folding model.
A study in the hydrodynamics of sediment transport
(1983) Singer, Jill Karen; Anderson, John B.; Casey, Richard E.; Dunbar, Robert B.
Antarctica is a unique environment where sediments are influenced by the interaction of glaciers and marine currents. This results in little or no sorting of the sediment prior to its introduction into the marine environment. The existing data relating current velocity to grain size were not designed to apply to assess the ability of marine currents to winnow and sort texturally homogeneous glacial and glacial marine sediments. However, estimates from flume studies suggest currents with velocities greater than 4 cm/sec are required to erode consolidated sediments. A puzzling observation made in studying modern Antarctic sediments has been the degree to which compacted and cohesive glacial and glacial marine sediments are being reworked and re-sedimented by bottom currents which move at velocities less than 15 cm/sec. This study has focused on the role of biological mixing in the initiation of sediment erosion and entrainment at low current velocities. This more adequately reflects the conditions which occur today on high latitude seafloors. It was found that with simulated bioturbation of the bed material, particles in the silt and clay-size range were transported at current velocities less than 3 cm/sec, with sand-sized material removed from the bed by 15 cm/sec. Without simulated bioturbation, currents up to 2 cm/sec had a negligable effect on the bed. Important applications of the results from this study include understanding sediment dynamics. It does not appear likely that erosion and sorting of overcompacted and cohesive glacial and glacial marine sediments is possible without the action of bioturbation. The results from this flume study are useful in the indirect determination of the long term normalized current velocity using surface samples and physical oceanographic information. Results can also be applied in the estimation of paleocurrent velocity from downcore variations of textural data.
A subglacial hydrologic drainage hypothesis for silt sorting and deposition during retreat in Pine Island Bay
(Cambridge University Press, 2019) Schroeder, Dustin M.; MacKie, Emma J.; Creyts, Timothy T.; Anderson, John B.
Late Holocene sediment deposits in Pine Island Bay, West Antarctica, are hypothesized to be linked to intensive meltwater drainage during the retreat of the paleo-Pine Island Ice Stream after the Last Glacial Maximum. The uppermost sediment units show an abrupt transition from ice-proximal debris to a draped silt during the late Holocene, which is interpreted to coincide with rapid deglaciation. The small scale and fine sorting of the upper unit could be attributed to origins in subglacial meltwater; however the thickness and deposition rate for this unit imply punctuated- rather than continuous-deposition. This, combined with the deposit's location seaward of large, bedrock basins, has led to the interpretation of this unit as the result of subglacial lake outbursts in these basins. However, the fine-scale sorting of the silt unit is problematic for this energetic interpretation, which should mobilize and deposit a wider range of sediment sizes. To resolve this discrepancy, we present an alternative mechanism in which the silt was sorted by a distributed subglacial water system, stored in bedrock basins far inland of the grounding line, and subsequently eroded at higher flow speeds during retreat. We demonstrate that this mechanism is physically plausible given the subglacial conditions during the late Holocene. We hypothesize that similar silt units observed elsewhere in Antarctica downstream of bedrock basins could be the result of the same mechanism.
Airborne radar sounding evidence for deformable sediments and outcropping bedrock beneath Thwaites Glacier, West Antarctica
(Wiley, 2014) Schroeder, Dustin M.; Blankenship, Donald D.; Young, Duncan A.; Witus, Alexandra E.; Anderson, John B.
The geologic and morphologic records of prior ice sheet configurations show evidence of rapid, back-stepping, meltwater intensive retreats. However, the potential for such a retreat in a contemporary glacier depends on the lithology of the current ice sheet bed, which lies beneath kilometers of ice, making its physical properties difficult to constrain. We use radar sounding and marine bathymetry data to compare the bed configuration of Thwaites Glacier to the bed of paleo-Pine Island Glacier. Using observed and modeled radar scattering, we show that the tributaries and upper trunk of Thwaites Glacier are underlain by ice flow-aligned bedforms consistent with deformable sediment and that the lower trunk is grounded on a region of high bed roughness consistent with outcropping bedrock. This is the same configuration as paleo-Pine Island Glacier during its retreat across the inner continental shelf.
Broadening theories of soils genesis: Insights from Tanzania and simple models
(2007) Little, Mark Gabriel; Lee, Cin-Ty A.; Luttge, Andreas; Tomson, Mason B.; Anderson, John B.; Ewing, Maurice W.; Masiello, Caroline A.
Three basic assumptions of soil formation are challenged herein: the degree of chemical weathering decreases with depth; increased physical weathering due to high topographical gradients causes an increase in chemical weathering; and the mineral soil derives from the transformation of in situ parent material. The first part presents an investigation into the degree and nature of chemical weathering during soil formation on a volcanic substrate on Mt. Kilimanjaro in northern Tanzania. The degree of weathering was found to increase with depth in the soil profile. Observations show that the upper and lower layers of the weathering profile have undergone different weathering histories. The presence of a buried paleosol or enhanced weathering due to lateral subsurface water flow may explain the observations, the latter having novel implications for the transport of dissolved cations to the ocean. The second part presents a model to test the link between chemical weathering associated with soil formation and erosion associated with mass wasting. The predicted ratios suspended/dissolved ratios, however, are all higher than observed in rivers, the discrepancy worsening with increasing topographic relief. This discrepancy arises from the fact that in regions of high relief, mass wasting are so high that soil mantles do not reside on hillslopes long enough to allow for significant chemical weathering. The discrepancy between the model and observations can be explained by: over-estimate of predicted suspended load; absence of chemical weathering of deltaic/alluvial sediments from the model; or chemical weathering associated with groundwater weathering. The third part presents data from a sequential extraction on a basaltic soil from Mt. Meru in Northern Tanzania. The behavior of relatively immobile elements is consistent with soil formation being accompanied by mass loss due to chemical weathering. However, superimposed on this mass loss appears to be enrichment of most elements measured. These data suggest that the surface of the Meru soil columns may have experienced "re-fertilization" by the deposition of volcanic ash.
Carbon cycle and climate fluctuations during the early Paleogene: Sedimentological characteristics and environmental ramifications
(2014-11-13) Slotnick, Benjamin; Dickens, Gerald R.; Lee, Cin-Ty A.; Anderson, John B.; Masiello, Carrie A.; Rudolf, Volker H.W.
The early Paleogene was marked by extensive changes related to Earth surface temperature, carbon cycling, and the hydrological cycle. This included at least two, and probably more, geologically brief (~200-k.yr.) intervals of extreme warming, the Paleocene-Eocene thermal maximum (PETM) and the Eocene thermal maximum-2 (ETM-2) along with a moderately-long (~1.5-2 M.yr.) period of warmth (i.e.; Early Eocene Climatic Optimum [EECO]). This was preceded by a moderately-long (~2 M.yr.) period of cool conditions (i.e. Paleocene Carbon Isotope Maximum [PCIM]) and followed by the initiation of long-term cooling through the Cenozoic. The long-term rise in warmth and numerous short-term “hyperthermal” events, marked by pronounced negative carbon isotope excursions and clay-rich horizons (Zachos et al., 2005; Nicolo et al., 2007), have been linked to massive injections of 13C-depleted carbon into the ocean-atmosphere system and intense global climate change, but the exact character of the hyperthermals is not well-recognized. To better constrain and understand their occurrences, well-resolved and high-resolution records across the entire interval of interest is necessary. Preceding studies demonstrated major fluctuations in carbon cycling and terrestrial weathering (e.g.; Nicolo et al., 2007) during the latest Paleocene and earliest Eocene as well as a significant drop of dissolved oxygen concentrations during the PETM onset (Nicolo et al., 2010). However, causes, environmental impact, and relationships relating carbon release and capture to terrigenous runoff and surface temperatures throughout the exogenic system, particularly in spatial and temporal contexts, remain unclear. The southern Pacific region (Clarence Valley) and Indian Ocean (Ninetyeast Ridge) represent large realms of our planet’s ocean system that have been largely overlooked in part due to limited Paleogene core availability from Integrated Ocean Drilling Program (IODP). There is a need to better improve records related to carbon in the exogenic system throughout the Cenozoic, and in particular, the Paleogene. As of now, records lack in these regions. Clarence Valley in eastern Marlborough, New Zealand trends southwest for ~80 km between the Seaward and Inland Kaikouras. Along the northwest margin is a succession of streams, including Mead and Branch Streams, which have incised and exposed an uplifted and rotated block consisting of Amuri Limestone, a calcareous-rich formation within the Muzzle Group. These outer shelf and upper continental slope strata originally accumulated as terrigenous detrital clay minerals, biogenic silica, and biogenic carbonate. This was situated contiguous to a neritic carbonate platform along a passive margin of proto-New Zealand at ~55-50°S latitude. Ninetyeast Ridge, one of the longest near-linear features on Earth with a length of ~4600 km (from ~10ºN to ~31ºS), is located in the Indian Ocean. Numerous Deep Sea Drilling Program (DSDP) and Ocean Drilling Program (ODP) sites have been drilled adjacent to or along the ridge crest. Three sites in particular drilled during DSDP Leg 22 (i.e.; Sites 213, 214, and 215) include calcareous-rich material from much of the Paleogene. These sediments can provide additional constraints to further our understanding of Indian Ocean paleoceanographic changes during the Paleogene. The lack of data for the Paleogene has been an issue for quite some time now. As such, the Paleogene remains a specific interval of time that has the potential to be much better understood by integrating current views of carbon cycling to new and wellresolved data-sets. Here I analyzed sequences exposed in Clarence Valley and sections from Ninetyeast Ridge DSDP Sites to address these issues. These records were integrated into a global context to relate short-term (<100 k.yr.) and long-term (> 1 m.yr) changes. I generated lithologic and carbon isotopic records to evaluate the entire period of interest, including the PCIM, specific hyperthermals, EECO, and the Middle Eocene Climatic Optimum (MECO). Integration of each section revealed similarities, including long-term trends with similar carbon isotopic baselines and short-term events. Expanded marl-rich units concurrent to lower δ13C, specifically across CIEs, generally characterized marginal sedimentation whereas condensed intervals largely spanned deep-water settings, resulting from carbonate dissolution. Together, these studies indicate carbon addition and removal mechanisms repeatedly spanned much of the Paleogene, causing calcite compensation depth (CCD) fluctuations, related to lithologic, and carbon isotopic changes.
Characteristics of the deforming bed: till properties on the deglaciated Antarctic continental shelf
(Cambridge University Press, 2018) Halberstadt, Anna Ruth W.; Simkins, Lauren M.; Anderson, John B.; Prothro, Lindsay O.; Bart, Philip J.
Contemporary ice stream flow is directly linked to conditions at the ice/bed interface, yet this environment is logistically difficult to access. Instead, we investigate subglacial processes important for ice stream flow by studying tills on the deglaciated Antarctic continental shelf. We test currently-accepted hypotheses surrounding subglacial processes and till properties with a Ross Sea dataset. Till shear strengths indicate a continuum of simultaneous processes acting at the bed, rather than discrete ‘deformation’ and ‘lodgement’ end-members. We identify a threshold water content representing saturated pore spaces, leading to basal sliding and meltwater channelization. Based on observations of till properties relative to glacial landforms, we challenge the assumption that low shear strength is linked to intense deformation. Spatial variability in landform morphology reflects variability in deforming processes at the sub-ice stream scale and suggests a maximum deforming bed thickness of 2 m at the grounding line. Regional till properties generally correlate with seafloor geology and deglacial history; the western Ross Sea is characterized by higher and more variable shear strengths and water contents, while lower-shear strength till was preserved in the Eastern Basin. These observations inform till interpretation and provide context for deforming beds beneath the modern ice sheet and on glaciated continental shelves.
Climate variability and glacial history from the LGM to the present in a southern Patagonia tidewater glacier system
(2007) Boyd, Brandi; Anderson, John B.
The study of tidewater glacier systems from the Last Glacial Maximum to the Present in southern Patagonia provides a relatively continuous high-resolution sedimentary record of climate change. This record enables us to establish the style and rate of sedimentation in the basin, as well as to determine the glacial history of the fjord with respect to the surrounding regions and hemispheric climate forcing. A comprehensive marine geologic study was conducted in Marinelli Fjord (54°S), southern Chile. A major transition is sedimentation at 12.5 ka marks the retreat of Marinelli Glacier with no evidence for glacial re-advance. This is consistent with the climatic trends for southern South America where the final deglaciation of the region ended at ∼12 ka, indicating a Southern Hemisphere climatic forcing. Marinelli Glacier has undergone a modern rapid retreat that is unprecedented in the time interval we recorded and is not related to hemispheric-scale forcing mechanisms.
Coastal lithosome evolution and preservation during an overall rising sea level: East Texas gulf coast and continental shelf
(1993) Siringan, Fernando Pascual; Anderson, John B.
Present coastal systems along the east Texas coast evolved during the past 3.5 ky of relative sea-level stillstand following a rapid sea-level rise 4 ka. Closure of proto-Galveston Bay, caused by spit accretion of Galveston Island and Bolivar Peninsula, formed Bolivar Roads approximately 3.3 ka. Increased tidal prism and entrenchment over the Trinity River incised valley led to inlet stabilization and intensification of tidal influence. The present shoreface and inner shelf package is characterized by a paucity of storm deposits. Strong along-shelf storm currents, low sediment supply, and low effective accommodation space in the region are unfavorable for the preservation of storm beds. Higher sand supply during the early establishment of the present coastal lithosomes resulted in a greater occurrence of storm beds lower in the section. Amalgamated storm deposits on the east Texas shelf are associated with reworked coastal lithosomes. Pods of tidal-inlet, tidal-inlet/spit, and tidal-delta deposits mark previous shoreline positions on the continental shelf. Their distribution mimics the along-strike variation of the present coastal systems, defines six relative sea-level stillstands, including the present, during the past 10.2 ky, and supports the model of a step-like sea-level rise. The seismic architecture of pre-8 ka coastal lithosomes provide evidence for greater tidal influence, greater accommodation space, and higher sedimentation rates compared to the present. The preserved coastal lithosomes indicate that the depth of shoreface ravinement decreases with decreasing shelf gradient, increasing rates of sea-level rise, and increasing sediment supply. Better preservation within incised valleys results from greater accommodation space and the soft valley-fill that allows incision of the inlets beyond the depth of shoreface ravinement. The mechanism of shoreline translation (discontinuous erosional shoreface retreat, transgressive submergence, or in-place drowning), is a function mainly of shelf gradient and rate of sea-level rise. Gentle shelf gradient and rapid sea-level rise favor transgressive submergence. In regions with steep shelf gradient, aggradation may produce stratigraphic signatures consistent with in-place drowning and discontinuous erosional shoreface retreat.
Detailed facies analysis of the Brazos wave-dominated delta, Freeport, Texas
(1995) Hamilton, Michael Darren; Anderson, John B.
In order to better define the facies architecture and controlling processes of a wave-dominated delta, a detailed sedimentary and geomorphologic study was undertaken on the New Brazos River delta. The study indicates a much more complex facies architecture than previously postulated and expands the facies model for wave-dominated deltas. The New Brazos delta is primarily composed of fine-grained sediments. Prodelta clay composes more than half of the sediment volume in the delta. Sands are isolated to the bar and nearshore environments. The facies architecture is distinct from adjacent interfluvial zones and not representative of the strandplain model for wave-dominated deltas. The unique facies architecture is a function of the primary depositional process for the delta--floods. In early 1992, statewide flooding facilitated a major constructional phase of the delta. Significant quantities of fine-grained sediments were deposited in the prodelta. One year after the onset of flooding, a bar emerged offshore of the river mouth, and enabled progradation of the delta.
Diachronous behavior of the Antarctic ice sheets: Weddell Sea, Antarctica
(2012) Stolldorf, Travis; Anderson, John B.
Inaccessibility due to harsh weather conditions and perennial sea ice has left the Weddell Sea embayment (WSE) vastly under-studied in comparison to other regions of Antarctica. Yet understanding its deglacial history since the Last Glacial Maximum (LGM) is vital for understanding the dynamics and stability of the Antarctic ice sheet. Additionally, the debate continues as to the magnitude and timing of West Antarctic Ice Sheet (WAIS), Antarctic Peninsula Ice Sheet (APIS) and East Antarctic Ice Sheet (EAIS) advance during the LGM. Here we present geologic and geophysical evidence from the southern and eastern continental shelves of the WSE that show diachronous retreat by the WAIS and EMS. Detailed analysis of sediment cores display a retreat stratigraphy in the WSE with distal glacimarine sediments overlying proximal glacimarine deposits and till. These results, in combination with AMS radiocarbon ages, demonstrate that the grounding line of the EAIS was very near that of present day as early as 30,476 cal yr BP and indicate little, if any, advance of the EMS during the LGM. In contrast, multibeam swath bathymetry data show mega-scale glacial lineations, indicative of grounded, flowing ice in two troughs on the southern continental shelf, which drain ice from the WAIS. Although there are no radiocarbon ages to absolutely constrain the timing of this grounding event on the southern continental shelf, we interpret the lineations as LGM age based on their pristine nature. Further, there are similar geomorphic features on the western continental margin where the LGM timing of APIS advance has been demonstrated. Thus, during the LGM, the Antarctic ice sheets behaved independently in the WSE.
Diagnosing ice sheet grounding line stability from landform morphology
(Copernicus Publications, 2018) Simkins, Lauren M.; Greenwood, Sarah L.; Anderson, John B.
The resilience of a marine-based ice sheet is strongly governed by the stability of its grounding lines, which are in turn sensitive to ocean-induced melting, calving, and flotation of the ice margin. Since the grounding line is also a sedimentary environment, the constructional landforms that are built here may reflect elements of the processes governing this dynamic and potentially vulnerable environment. Here we analyse a large dataset (n=6275) of grounding line landforms mapped on the western Ross Sea continental shelf from high-resolution geophysical data. The population is divided into two distinct morphotypes by their morphological properties: recessional moraines (consistently narrow, closely spaced, low amplitude, symmetric, and straight) and grounding zone wedges (broad, widely spaced, higher amplitude, asymmetric, sinuous, and highly variable). Landform morphotypes cluster with alike forms that transition abruptly between morphotypes both spatially and within a retreat sequence. Their form and distribution are largely independent of water depth, bed slope, and position relative to glacial troughs. Similarly, we find no conclusive evidence for morphology being determined by the presence or absence of an ice shelf. Instead, grounding zone wedge construction is favoured by a higher sediment flux and a longer-held grounding position. We propose two endmember modes of grounding line retreat: (1) an irregular mode, characterised by grounding zone wedges with longer standstills and accompanied by larger-magnitude retreat events, and (2) a steady mode, characterised by moraine sequences that instead represent more frequent but smaller-magnitude retreat events. We suggest that while sediment accumulation and progradation may prolong the stability of a grounding line position, progressive development of sinuosity in the grounding line due to spatially variable sediment delivery likely destabilises the grounding position by enhanced ablation, triggering large-magnitude retreat events. Here, the concept of “stability” is multifaceted and paradoxical, and neither mode can be characterised as marking fast or slow retreat. Diagnosing grounding line stability based on landform products should be considered for a wider geographic range, yet this large dataset of landforms prompts the need to better understand the sensitivity of marine-based grounding lines to processes and feedbacks governing retreat and what stability means in the context of future grounding line behaviour.
Distribution and ecology of recent benthonic foraminifera of the Dumont D'Urville Sea, Antarctica
(1981) Milam, Robert Wilson; Anderson, John B.; Casey, Richard E.; Schwarzer, Rudy R.
Six distinct benthonic foraminiferal assemblages are recognized in the Dumont D'Urville Sea of Antarctica on the basis of the common occurrence and predominance of taxons. The distribution of calcareous and arenaceous faunal facies on the continental shelf coincides remarkably with the relative distribution of reworked glacial sediments and organic-rich biogenic muds. Surface productivity, seafloor topography, and bottom current velocities are thought to control the distribution of these biogenic muds, which are restricted to shelf depressions, and the surface sediments themselves are thought to control the relative distribution of arenaceous and calcareous populations on the shelf. Depth is a subsidiary factor in controlling faunal distributions on the continental shelf. A mixed calcareous and arenaceous fauna defines the contact of the lysocline with the continental slope, below which lies the oceanic CCD at 19m and a slope arenaceous fauna. Shelf assemblages are generally of low diversity, but high diversity populations underlie upwelling nutrient-rich plumes of modified Upper Circumpolar Deep Water, which have been injected along an isopycnal between underlying dense shelf water and overlying surface water. Benthonic foraminifera are therefore useful as indicators of hydrographic conditions, and models relating the distribution of high diversity standing crops of benthonic foraminifera to such upwelling plumes are discussed.
Early to middle Miocene ice sheet dynamics in the westernmost Ross Sea (Antarctica): Regional correlations
(Elsevier, 2022) Pérez, Lara F.; McKay, Robert M.; De Santis, Laura; Larter, Robert D.; Levy, Richard H.; Naish, Timothy R.; Anderson, John B.; Bart, Philip J.; Busetti, Martina; Dunbar, Gavin; Sauli, Chiara; Sorlien, Christopher C.; Speece, Marvin
The present-day morpho-stratigraphy of the Ross Sea is the result of Cenozoic tectonic and cryospheric events, and constitutes a key record of Antarctica's cryospheric evolution. An enduring problem in interpreting this record in a broader regional context is that the correlation between eastern and western Ross Sea stratigraphy has remained uncertain due to the limited number of drill sites. We correlate the glacial-related features observed on a dense network of seismic reflection profiles in McMurdo Sound with those identified in the Nordenskjöld and Drygalski Basins, as well as the basins farther east in the central Ross Sea. We present an improved correlation of the regional patterns of early to middle Miocene ice-sheet variance across the Ross Sea constrained by new evaluation of seismic facies and age models from one site recovered by the Antarctic Drilling Project (ANDRILL) in the southwestern most part of McMurdo Sound. We also integrate this correlation with the recently published seismic framework in the central Ross Sea. The formation of U-shaped valleys during the early Miocene in McMurdo Sound, together with prograding sedimentary wedges in the western-most basins, and the central Ross Sea, suggest two major phases of overall advance of a marine-terminating ice sheet between ~18 Ma and ~17.4 Ma. Widespread formation of turbiditic channel-levee systems in McMurdo Sound and rapid sediment deposition in Nordernskjöld Basin point to subsequent ice-sheet retreat between ~17.4 Ma and ~15.8 Ma, coinciding with the onset of the Miocene Climate Optimum (MCO; ~17–14.5 Ma). However, the carving of troughs and formation of irregular morphologic features suggest that an extensive ice sheet still remained along the western Ross margin at ~17.4 Ma and a brief episode of ice-sheet advance occurred at ~16.8 Ma in the earliest interval of the MCO. Subsequent marine-based ice sheet advance during the Middle Miocene Climate Transition (MMCT, ~14.0–13.8 Ma) is indicated by widespread erosional features. Our results reconcile the semi-continouous seismic and drill core stratigraphy of the offshore Ross Sea continental shelf with inferences of ice sheet dynamics from continuous far-field deep sea and sea level records, as well as the highly discontinous (and heavily debated) onshore records of pre-MMCT glaciation and aridification of the Transantarctic Mountains at 14 Ma.
Environmental trace element geochemistry of sediments of the Buccaneer offshore oil and gas field: Factors controlling concentrations of trace elements in sediments
(1979) Wheeler, Richard Brian; Anderson, John B.
Sediments are a sensitive record of recent, as well as ancient, physical and chemical paleoenvironmental conditions. In the marine environment, sediments are the ultimate sink for all types of contaminants and, therefore, can be used to indicate the presence of anthropogenic contaminants in the system. Evaluation of contamination levels in sediments, however, is critically contingent upon consideration of sediment physical and mineralogical properties which may profoundly influence chemical composition. This study of trace element contamination in sediments of the Buccaneer offshore oil/gas field attempts to take an objective approach towards this problem. Several trace element-sediment interactive processes are examined in order to evaluate their control over the occurrence of Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr and Zn. Although trace element-sediment interactions could not be quantified, Q-mode cluster analysis was used to classify the sediment samples into similar groups on the basis of the sediment texture, organic carbon and carbonate contents. The Q-mode cluster analysis includes samples collected near the production platforms, as well as control samples collected at some distance from the platforms and supplementary analyses.

Browsing by Author "Anderson, John B."

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