Search for: All records

Abstract Channel planform patterns arise from internal dynamics of sediment transport and fluid flow in rivers and are affected by external controls such as valley confinement. Understanding whether these channel patterns are preserved in the rock record has critical implications for our ability to constrain past environmental conditions. Rivers are preserved as channel belts, which are one of the most ubiquitous and accessible parts of the sedimentary record, yet the relationship between river and channel-belt planform patterns remains unquantified. We analyzed planform patterns of rivers and channel belts from 30 systems globally. Channel patterns were classified using a graph theory-based metric, the Entropic Braided Index (eBI), which quantifies the number of river channels by considering the partitioning of water and sediment discharge. We find that, after normalizing by river size, channel-belt width and wavelength, amplitude, and curvature of the belt edges decrease with increasing river channel number (eBI). Active flow in single-channel rivers occupies as little as 1% of the channel belt, while in multichannel rivers it can occupy >50% of the channel belt. Moreover, we find that channel patterns lie along a continuum of channel numbers. Our findings have implications for studies on river and floodplain interaction, storage timescales of floodplain sediment, and paleoenvironmental reconstruction. 

Abstract One of the most interesting questions about the climate and hydrology of early Mars is whether oceans existed and, if so, when. Various geologic features have been interpreted as ancient shorelines, but these features do not follow gravitational equipotentials. Prior work has shown that the elevation of the Arabia level, hypothesized to represent a large, early ocean, better conforms to an equipotential when correcting for global topographic change after its formation. Although the shoreline coordinates underlying these studies are debated, exploring the consequences of these topographic corrections allows additional observable consequences to be identified. Here we show that the topographic corrections cause Jezero crater, the landing site of the Perseverance rover, to be submerged under the proposed Arabia ocean. This precludes the ocean’s existence during known fluvio-lacustrine activity at Jezero and suggests the ocean did not exist during the main era of valley network formation in the Noachian/Early Hesperian. We identify a period of ∼10 8 yr years before fluvial activity at Jezero when the ocean could have existed and discuss potential observable consequences.