/pdf/global-continental-and-ocean-basin-reconstructions-since-200-huopwd2ldv.pdf

Global continental and ocean basin reconstructions since 200 Ma

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2019GC008515

The Generic Mapping Tools Version 6

Gravity models are powerful tools for mapping tectonic structures, especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment. We combined new radar altimeter measurements from satellites CryoSat-2 and Jason-1 with existing data to construct a global marine gravity model that is two times more accurate than previous models. We found an extinct spreading ridge in the Gulf of Mexico, a major propagating rift in the South Atlantic Ocean, abyssal hill fabric on slow-spreading ridges, and thousands of previously uncharted seamounts. These discoveries allow us to understand regional tectonic processes and highlight the importance of satellite-derived gravity models as one of the primary tools for the investigation of remote ocean basins.

http://science.sciencemag.org/content/sci/346/6205/65.full.pdf

New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure

Late Jurassic–Cenozoic reconstructions of the Indonesian region and the Indian Ocean

We have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self-consistent set of global isochrons and associated plate reconstruction poles. The age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models. We have constructed an age grid with error estimates for each grid cell as a function of (1) the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid, (2) the distance of a given grid cell to the nearest magnetic anomaly identification, and (3) the gradient of the age grid: i.e., larger errors are associated with high age gradients at fracture zones or other age discontinuities. Future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere, the heat loss of the Earth, ridge-push forces through time, asymmetry of spreading, and providing constraints for seismic tomography and mantle convection models.

Digital isochrons of the world's ocean floor

A new stratigraphic model is presented for the evolution of the Cenozoic Victoria Land Basin of the West Antarctic Rift, based on integration of seismic reflection and drilling data. The Early Rift phase (?latest Eocene to Early Oligocene) comprises wedges of strata confined by early extensional faults, and which contain seismic facies consistent with drainage via coarse-grained fans and deltas into discrete, actively subsiding grabens and half-grabens. The Main Rift phase (Early Oligocene to Early Miocene) comprises a lens of strata that thickens symmetrically from the basin margins into a central depocenter, and in which stratal events pass continuously over the top of the Early Rift extensional topography. Internal seismic facies and lithofacies indicate a more organized, cyclical shallow marine succession, influenced increasingly upward by cycles of glacial advance and retreat into the basin. The Passive Thermal Subsidence phase (Early Miocene to ?) comprises an evenly distributed sheet of strata that does not thicken appreciably into the depocentre, with more evidence for clinoform sets and large channels. These patterns are interpreted to record accumulation under similar environmental conditions but in a regime of slower subsidence. The Renewed Rifting phase (? to Recent, largely unsampled by coring thus far) has been further divided into 1, a lower interval, in which the section thickens passively towards a central depocentre, and 2. an upper interval, in which more dramatic thickening patterns are complicated by magmatic activity. The youngest part of the stratigraphy was accumulated under the influence of flexural loading imposed by the construction of large volcanic edifices, and involved minimal sediment supply from the western basin margin, suggesting a change in environmental (glacial) conditions at possibly c. 2 Ma. Citation: Fielding, C.R., J. Whittaker, S.A. Henrys, T.J. Wilson and T.R. Naish (2007), Seismic facies and stratigraphy of the Cenozoic succession in McMurdo Sound, Antarctica: implications for tectonic, climatic and glacial history, in Antarctica: A Keystone in a Changing World – Online Proceedings of the 10 ISAES, edited by A.K. Cooper and C.R. Raymond et al., USGS Open-File Report 2007-1047, Short Research Paper 090, 4 p.; doi:10.3133/of2007-1047.srp09 Introduction In recent years, efforts to resolve the Cenozoic history of Antarctica have increasingly focused on the westernmost part of the West Antarctic Rift System, a north-south-elongate sub-basin named the Victoria Land Basin. Data from fully cored drillholes, together with seismic reflection records, have shown that the Victoria Land Basin preserves a relatively complete archive of Cenozoic environmental change, from the latest Eocene (>34 Ma) onward. To date, however, no study has fully integrated the drilling dataset with information from the extensive array of seismic reflection records from the region. In this paper, we present a stratigraphic framework for the Victoria Land Basin. It draws on seismic reflection records from the McMurdo Sound region and integrates all available drilling data. The internal seismic reflection character of each stratigraphic interval is then described from oldest to youngest, and the insights that these data provide to understanding of Cenozoic basin history and environmental change are summarized. The seismic stratigraphic scheme presented herein is an extension of that published by Fielding et al. (2006), with numerous additions to the younger part of the succession. It recognizes numerous laterally traceable events, many of which correlate to key surfaces of previous workers (Table 1). Stratigraphy Based on integration of regional seismic reflection surveys with available drillcore data, the stratigraphic succession of the western Victoria Land Basin in McMurdo Sound, Antarctica, has been resolved into a series of intervals each reflecting changes in basinforming tectonic processes (Table 1). “Phase 1” of Table 1 refers to formation and exhumation of the Transantarctic Mountains prior to commencement of sediment accumulation in the VLB. The Early Rift phase (34-29 Ma: “Phase 2” of Table 1) is characterized by a thick succession of mainly coarsegrained lithologies that largely lacks evidence of cyclicity. Lithofacies and seismic facies together suggest progradation of coarse-grained fan and delta systems into progressively opening half-graben infra-basins. Available data suggest that sediments were accumulated in shallow water throughout this interval, indicating a ready supply of terrigenous clastic sediment was able to balance the rapid rate of subsidence. The Main Rift phase (29-23 Ma: “Phase 3” of Table 1) is characterized by a more parallel, continuous reflection character, with a gradual eastward expansion of accommodation associated with the transfer of the depocentre to a more basin-central location. This has been interpreted in terms of repeated cycles of shallow marine to coastal facies, with a cyclical motif becoming increasingly recognizable up-section. Cyclicity U.S. Geological Survey and The National Academies; USGS OFR-2007-xxxx, Chp.yyy, doi: 10.3133.zzzzzzzzzz Ver. 7/11/07 2 Table 1. Seismic stratigraphic framework for this study, showing interpretation in terms of rift history and correlation to other seismic stratigraphic schemes for the region (modified after Fielding et al., 2006). Cooper et al., 1987 Brancolini et al., 1995 Bartek et al., 1996 Anderson and Bartek 1992 Horgan et al., 2005 This PAPER RIFT PHASE

/pdf/seismic-facies-and-stratigraphy-of-the-cenozoic-succession-zpv1eq3wr9.pdf

Seismic facies and stratigraphy of the Cenozoic succession in McMurdo Sound, Antarctica: Implications for tectonic, climatic and glacial history

A new method for modeling heat flux shows that the upper crust contributes up to 70% of the Antarctic Peninsula's subglacial heat flux and that heat flux values are more variable at smaller spatial resolutions than geophysical methods can resolve Results indicate a higher heat flux on the east and south of the Peninsula (mean 81 mW m−2) where silicic rocks predominate, than on the west and north (mean 67 mW m−2) where volcanic arc and quartzose sediments are dominant While the data supports the contribution of heat-producing element-enriched granitic rocks to high heat flux values, sedimentary rocks can be of comparative importance dependent on their provenance and petrography Models of subglacial heat flux must utilize a heterogeneous upper crust with variable radioactive heat production if they are to accurately predict basal conditions of the ice sheet Our new methodology and data set facilitate improved numerical model simulations of ice sheet dynamics

/pdf/a-new-heat-flux-model-for-the-antarctic-peninsula-4g7s65quz8.pdf

A new heat flux model for the Antarctic Peninsula incorporating spatially variable upper crustal radiogenic heat production

Discovery of a microcontinent (Gulden Draak Knoll) offshore Western Australia: implications for East Gondwana reconstructions

Sea level fluctuations driven by changes in global ocean basin volume following supercontinent break-up

Whether the seafloor is rough or smooth can have a considerable influence on the circulation and mixing of heat in the ocean and on the dissipation of eddy kinetic energy. The role of seafloor spreading rates in controlling oceanic basement topography is well known. Now a global analysis of seafloor roughness derived from marine gravity data reveals that residual roughness anomalies remain over large swaths of ocean floor: Atlantic ocean floor that formed over mantle previously overlain by the Pangaea supercontinent is anomalously smooth, whereas ocean crust formed above Pacific superswells retains the predicted basement roughness. These results highlight a fundamental difference in the nature of large-scale mantle upwellings below supercontinents and superoceans and provide a framework for reconstructing the seafloor of ancient oceans. This study presents a global analysis of seafloor roughness derived from marine gravity data and finds that residual roughness anomalies remain over large swaths of ocean floor. The Atlantic ocean floor that formed over mantle previously overlain by the Pangaea supercontinent displays anomalously low roughness, and attribute this observation to a sub-Pangaean supercontinental mantle temperature anomaly leading to slightly thicker than normal Atlantic crust. In contrast, ocean crust formed above Pacific superswells is not associated with basement roughness anomalies. Seafloor roughness varies considerably across the world’s ocean basins and is fundamental to controlling the circulation and mixing of heat in the ocean1 and dissipating eddy kinetic energy2. Models derived from analyses of active mid-ocean ridges suggest that ocean floor roughness depends on seafloor spreading rates3, with rougher basement forming below a half-spreading rate threshold of 30–35 mm yr-1 (refs 4, 5), as well as on the local interaction of mid-ocean ridges with mantle plumes or cold-spots6. Here we present a global analysis of marine gravity-derived roughness, sediment thickness, seafloor isochrons and palaeo-spreading rates7 of Cretaceous to Cenozoic ridge flanks. Our analysis reveals that, after eliminating effects related to spreading rate and sediment thickness, residual roughness anomalies of 5–20 mGal remain over large swaths of ocean floor. We found that the roughness as a function of palaeo-spreading directions and isochron orientations7 indicates that most of the observed excess roughness is not related to spreading obliquity, as this effect is restricted to relatively rare occurrences of very high obliquity angles (>45°). Cretaceous Atlantic ocean floor, formed over mantle previously overlain by the Pangaea supercontinent, displays anomalously low roughness away from mantle plumes and is independent of spreading rates. We attribute this observation to a sub-Pangaean supercontinental mantle temperature anomaly8 leading to slightly thicker than normal Late Jurassic and Cretaceous Atlantic crust9, reduced brittle fracturing and smoother basement relief. In contrast, ocean crust formed above Pacific superswells10, probably reflecting metasomatized lithosphere underlain by mantle at only slightly elevated temperatures11, is not associated with basement roughness anomalies. These results highlight a fundamental difference in the nature of large-scale mantle upwellings below supercontinents and superoceans, and their impact on oceanic crustal accretion.

/pdf/how-supercontinents-and-superoceans-affect-seafloor-52wp8bjnug.pdf

Joanne M. Whittaker

Papers

Seismic facies and stratigraphy of the Cenozoic succession in McMurdo Sound, Antarctica: Implications for tectonic, climatic and glacial history

A new heat flux model for the Antarctic Peninsula incorporating spatially variable upper crustal radiogenic heat production

Discovery of a microcontinent (Gulden Draak Knoll) offshore Western Australia: implications for East Gondwana reconstructions

Sea level fluctuations driven by changes in global ocean basin volume following supercontinent break-up

How supercontinents and superoceans affect seafloor roughness