Plio-Pleistocene glacial history of the Melville Bugt Ice Stream

In this work we use high-resolution seismic reflection surveys collected across the northeast Baffin Bay region to investigate the glacigenic Melville Bugt Trough Mouth Fan (MB-TMF). The MB-TMF stratigraphy is characterised by over 100 km of progradation since ~2.7 Ma and the heterogeneous truncation or subsidence of topset strata. Variation in topset character is thought to relate to the waxing and waning of the northwest sector of the Greenland Ice Sheet across the shelf since ~2.7 Ma. 3D seismic reflection data reveal the preservation of multiple sets of mega-scale glacial lineations, suggesting that grounded ice extended across the shelf a number of times since the onset of the Middle Pleistocene Transition. Seismic geomorphology and facies analysis of the prograding clinoforms show repeated observations of debrites and gully systems. These features, when considered with other evidence of adjacent glacial landforms and strata, are taken to infer gravity-driven processes and the presence of meltwater-related hyperpycnal flows in areas proximal to the ice sheet on the outer shelf. Bottomset contourites at the base of the continental slope also provide insights into the evolution of the West Greenland Current in Baffin Bay through the Pleistocene, with deposition estimated to have started in the latest Calabrian, based on the current age model. Regional stratigraphic mapping shows that the MB-TMF can be summarised into four stages that were primarily controlled by variations in ice sheet erosion patterns, topographic forcing of ice flow, and changes in accommodation that are related to glacigenic deposition and tectonic subsidence.&#160;

Download Full-text

Morphotectonic evidence for widespread active faulting in southern Mongolia

10.5194/egusphere-egu21-13578 ◽

2021 ◽

Author(s):

Jorien L.N. van der Wal ◽

Veit Nottebaum ◽

Georg Stauch ◽

Steven A. Binnie ◽

Ochirbat Batkhishig ◽

...

Keyword(s):

Seismic Reflection ◽

Landscape Evolution ◽

Fault System ◽

Middle Pleistocene ◽

Active Deformation ◽

Seismic Reflection Data ◽

Northern Margin ◽

Exposure Dating ◽

Reflection Data ◽

Quaternary Climate

Four M~8 earthquakes in the 20th century reflect active deformation in western Mongolia as a result of far-field stresses related to the India-Eurasia collision. Historic seismicity indicates that deformation localises around the relatively rigid Hangay dome in central Mongolia, however, tectonic lineaments in the surrounding Valley of Lakes basins suggest more widespread and diffuse deformation. In southern Mongolia, seismicity clusters around the Bogd fault, which ruptured during the 1957 Mw 8.1 Gobi Altai earthquake. To determine whether the kinematics interpreted from this earthquake are regionally representative, especially in consideration of the heterogeneity of intraplate tectonics, we expand the spatial scale of tectonic studies to range between the Gobi Altai and Hangay massifs. We do this by combining observations from regional and local digital elevation models, ground-penetrating radar analyses, geological and geomorphological field data, and seismic reflection data. Additionally, we increase the temporal scale of palaeoseismic studies up until the Middle Pleistocene through OSL and surface exposure dating, to compare the effects of tectonic processes to those of Quaternary climate variations on landscape evolution. We show that reverse and oblique strands of the Bogd fault accommodate <0.3 mm/yr vertical slip rates along the northern margin of the transpressive Gobi Altai massif. Four ~E-W striking faults in the seismically quiescent Valley of Gobi Lakes each have the potential for M~7 earthquakes and they are likely part of a left-lateral strike-slip system rooted at depth. Although cumulatively, the Valley of Gobi Lakes faults are deforming at a regionally representative ~0.3 mm/yr vertical slip rate, recurrence intervals of major earthquakes are much longer than those determined along the Bogd fault (~5-80 ka vs. 3-5 ka). Overall, we interpret the Valley of Gobi Lakes faults to have played a large role in drainage reorganisation and Middle Pleistocene to modern landscape evolution. Sub-surface faults interpreted from seismic reflection data and associated geomorphological irregularities in the Orog Nuur Basin indicate two NW-SE striking lineaments that may connect the Valley of Gobi Lakes fault system to the Bogd fault system. Our observations suggest a more complex and extensive fault system in southern Mongolia than previously expected and the geometry and potential connectivity of faults indicates a continuing northward progression of transpressive deformation from the Gobi Altai towards the Hangay. The obscurity of active deformation in the Valley of Gobi Lakes is likely due to faster erosion and deposition rates and this highlights the importance of understanding the interplay between tectonic, climatic and geomorphological processes and their effects on the landscape system. We suggest that, especially in slowly deforming, intraplate regions, an increase of spatial and temporal scales of active tectonic research is necessary to improve interpretations of tectonically altered landforms, palaeo-environmental reconstructions, and seismic hazard assessments.

Download Full-text