1. How do high-frequency, bidirectional flexural adjustments impact the morphology, architecture, and stratigraphic evolution of large delta systems over intermediate time scales?
Our research explores the flexural responses to sediment and water redistribution caused by climate-forced sea-level change over intermediate time scales of 10 6 to 10 7 yrs using the basin and landscape dynamics model BADLANDS. We first develop a continental-scale fluvial-deltaic to deep-water sediment-dispersal system, then perform a series of tests where we impose synthetic and climate-driven sea-level curves of different frequencies to explore the relationships between patterns of sediment accumulation, flexural subsidence, and load partitioning. Our experiments show the cumulative effect of high frequency, bidirectional flexural adjustments caused by climate-forced sea-level changes can significantly impact the morphology, architecture, and stratigraphic evolution of large delta systems. This research provides a more comprehensive method than previous studies, which investigated the role of high-frequency isostatic adjustments in a static manner. The coupling of surface processes with flexural isostasy allows us to investigate feedbacks between sea-level change, erosion, deposition, flexural uplift, and subsidence within a dynamic framework. The findings highlight the importance of considering the cumulative, deep-time vertical movements driven by isostatic responses to sediment and water loads, which can have profound effects on deltaic shorelines over intermediate time scales.
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2. What are the different processes contributing to vertical motions in passive margin deltaic depocenters?
The different processes contributing to vertical motions in passive margin deltaic depocenters include stretching and thinning of the lithosphere during the initial rifting phase, thermal cooling and contraction of upwelled asthenosphere causing post-rift subsidence, flexural isostatic compensation to sediment loading resulting in bending of the lithosphere, hydro-isostatic adjustments due to sea-level changes, growth faults, salt tectonics, long-term compaction, and dewatering and consolidation of Holocene deltaic sediments. These processes operate at different spatio-temporal scales, depths, and rates, with some occurring over annual to millennial time scales and others over longer periods. The rates of subsidence vary, with consolidation and dewatering of Holocene deltaic sediments having higher rates compared to deep-seated subsidence mechanisms. Additionally, motion on growth faults is episodic, with high rates of vertical motion during active fault movement and lower rates when integrated over longer periods.
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3. What is the purpose of using BADLANDS in the study of continental scale deltaic depocenters?
The purpose of using BADLANDS in the study of continental scale deltaic depocenters is to explore how the interplay between climate-forced sea-level change, erosion/deposition, and flexural adjustments in deep time can impact the morphology, architecture, and stratigraphic evolution of these depocenters. BADLANDS links landscape and basin dynamics through simulation of erosion, landscape evolution, and sedimentation. It also calculates the flexural isostatic response of changes in water and sediment load using a two-way coupling with gFlex. The experimental design consists of a series of simulations where sediment is transported by hillslope and channel processes from the continental interior to the continental margin, and where river channels, deltas, shallow-marine shelves, and shelf margins are self-generated. The goal is to better understand first-order relationships between sea-level changes, flexural isostasy, and erosion and deposition.
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4. How do cyclical flexural isostatic adjustments impact delta morphology?
Cyclical flexural isostatic adjustments in response to sea-level change impact delta morphology by altering river-mouth cross-shelf transit distances, river mouth lateral migration, and patterns of accommodation. In non-flexurally-compensated simulations, mean river-mouth transit distances and lateral river-mouth migration distances are significantly greater, leading to reduced accommodation, delta progradation, and lateral river channel migration. Conversely, in simulations with flexural compensation, accommodation increases near the delta front, reducing cross-shelf transit distances and lateral migration. Mean maximum rates of sediment accumulation at the river mouth are also smaller in non-flexurally compensated simulations. These adjustments confirm the role of sea level as the main driver on sediment dispersal in passive margins.
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