How Two Different Cenozoic Geologic and Glacial History Paradigms Explain the Southcentral Montana Musselshell-Yellowstone River Drainage Divide Origin, USA

The accepted Cenozoic geologic and glacial history paradigm (accepted paradigm) considers the southcentral Montana Musselshell-Yellowstone River drainage divide to have originated during Tertiary (or preglacial) time while a new and different Cenozoic geologic and glacial history paradigm (new paradigm) describes how headward erosion of a northeast-oriented Musselshell River valley segment captured huge southeast-oriented meltwater floods to create the drainage divide late during a continental ice sheet’s melt history. Northwest to southeast oriented divide crossings (low points observed on detailed topographic maps where water once flowed across the drainage divide), southeast-oriented Yellowstone and Musselshell River segments immediately upstream from northeast-oriented Yellowstone and Musselshell River segments, and southeast- and northwest-oriented tributaries to northeast-oriented Yellowstone and Musselshell River segments indicate a major southeast-oriented drainage system predated the northeast-oriented Yellowstone and Musselshell River segments. Closeness of the divide crossings, divide crossing floor elevations, large escarpment-surrounded erosional amphitheater-shaped basins, and unusual flat-floored internally drained basin areas (straddling the drainage divide), all suggest the previous southeast-oriented drainage system moved large quantities of water which deeply eroded the region. In the mid-20th century geomorphologists working from the accepted paradigm perspective determined trying to explain such erosional landform evidence from the accepted paradigm perspective was a nonproductive research activity and now rarely investigate erosional landform origins. On the other hand, the new paradigm appears to explain most, if not all observed erosional landform features, although the two paradigms lead to significantly different regional Cenozoic geologic and glacial histories that cannot be easily compared.  

Initiation and evolution of knickpoints and their role in cut-and-fill processes in active submarine channels

Submarine channels are the main conduits and intermediate stores for sediment transport into the deep sea, including organics, pollutants, and microplastics. Key drivers of morphological change in channels are upstream-migrating knickpoints whose initiation has typically been linked to episodic processes such as avulsion, bend cutoff, and tectonics. The initiation of knickpoints in submarine channels has never been described, and questions remain about their evolution. Sedimentary and flow processes enabling the maintenance of such features in non-lithified substrates are also poorly documented. Repeated high-resolution multibeam bathymetry between 2012 and 2018 in the Capbreton submarine canyon (southeastern Bay of Biscay, offshore France) demonstrates that knickpoints can initiate autogenically at meander bends over annual to multi-annual time scales. Partial channel clogging at tight bends is shown to predate the development of new knickpoints. We describe this initiation process and show a detailed morphological evolution of knickpoints over time. The gradients of knickpoint headwalls are sustained and can grow over time as they migrate through headward erosion. This morphology, associated plunge pools, and/or development of enhanced downstream erosion are linked herein to the formation and maintenance of hydraulic jumps. These insights of autogenically driven, temporally high-frequency knickpoints reveal that cut-and-fill cycles with depths of multiple meters can be the norm in submarine systems.

Submarine-fan development revealed by integrated high-resolution datasets from La Jolla Fan, offshore California, U.S.A.

ABSTRACT New high-resolution datasets across La Jolla submarine fan, offshore California, illuminate low-relief, down-dip widening conduits emanating from a deep-sea channel that deposited a combination of laterally extensive sand strata seemingly crisscrossed by distributary patterns. Extensive coverage of this sector of the seafloor shows submarine-fan architecture and morphologies essentially different than distributary channelized patterns characteristic of subaerial systems and previous conceptual models of submarine fans. The main La Jolla channel, connected to La Jolla Canyon, loses confinement by widening, decreasing in relief, and developing scoured margins across kilometers-long down-slope and lateral distances. Two scales of distributary patterns are associated with sand-rich deposits down-system from, and outside of, fully formed channels. A larger-scale distributary pattern is identified in backscatter and bathymetry from trains of preferential erosion associated with laterally continuous repetitive steps that extend for kilometers outside channel confinement and may represent net erosional upper-flow-regime transitional bedforms. Smaller-scale distributary backscatter patterns in unconfined sand-rich deposits originate from the wide, low-relief channel. We suggest that the newly imaged La Jolla seascape displays sedimentary features that may be common on deep-sea fans but missed in previous lower resolution studies of submarine fans. Thus, La Jolla provides the basis for integrating previously enigmatic and (or) incomplete images of submarine fans. High-resolution seafloor, subsurface, and sample datasets highlight the importance of channel widening, headward erosion, and unconfined flows in La Jolla submarine-fan development, and may be relevant to other sandy submarine fan systems.

Evaluating the effect of variable lithologies on rates of knickpoint migration in the Wutach catchment, southern Germany

<p>The topographic evolution of landscapes strongly depends on the resistance of bedrock to erosion. Detachment-limited fluvial landscapes are commonly analyzed and modelled with the stream power incision model (SPIM) which parametrizes erosional efficiency by the bulk parameter K whose value is largely determined by bedrock erodibility. Inversion of the SPIM using longitudinal river profiles enables resolving values of K if histories of rock-uplift or base level change are known. Here, we present an approach to estimate K-values for the Wutach catchment, southern Germany. The catchment is a prominent example of river piracy that occurred ~18 ka ago as response to headward erosion of a tributary to the Rhine. Base level fall of up to 170 m triggered a wave of upstream migrating knickpoints that represent markers for the transient response of the landscape. Knickpoint migration along the main trunk stream and its tributaries passed different lithological settings, which allows us to estimate K for crystalline and sedimentary bedrock units of variable erodibility.</p>

Morphological characteristics and lithological conditions of the spring-heads in the Knyszyńska Primeval Forest

The aim of the study was to determine the morphological characteristics of selected spring-heads in the Knyszyńska Primeval Forest and to identify lithological conditions in areas where groundwater flows to the surface. During the study, detailed bed level measurements of the spring-head areas were conducted. Lidar laser data obtained from the Central Department of Geodetic and Cartographic Documentation in Warsaw were also used for the analysis of morphometry. Based on the data, the detailed contour maps were created in the Surfer 12 programme and the basic parameters of the morphometry of the studied springs were determined. To detect lithological conditions, granulometric analyses were conducted and the filtration coefficient of aquifers in the individual spring-heads was calculated using Hazen and USBSC empirical models. Due to the morphological situation, the examined objects were classified as sub-slope and riverbank spring-heads. In terms of shape, spring-head alcoves are classified as basin-shaped, bowl-shaped and spindle-shaped alcoves. Different morphological processes prevail in each of these types. Basin-shaped alcoves are formed mainly by lateral erosion, bowlshaped alcoves by seepage erosion, landsliding and accumulation in the bottom, spindle-shaped alcoves by seepage erosion, headward erosion, breaking and collapsing. In the investigated outflows of groundwater aquifers are sands and glacifluvial sands with gravel of varying grain size. The lithological variation of aquifers in the spring-heads, directly affects the rate of groundwater filtration in different parts of the alcoves, which in turn leads to different morphogenetic processes and results in changes in the morphology of the spring-head alcoves.

Solving a Perplexing Scenic and Sage Creek Basin Drainage History Problem, Pennington County, South Dakota, USA

The escarpment-surrounded Sage Creek and Scenic Basins open in southeast directions toward the northeast and east oriented White River valley while their floors drain in a northwest direction to the northeast oriented Cheyenne River. Located in the South Dakota Badlands region the Sage Creek and Scenic Basins present an intriguing drainage history problem where key puzzle pieces also include the White and Cheyenne River valleys. The puzzle solution requires massive amounts of southeast oriented water to first erode as deep headcuts the east oriented White River valley segment and the two southeast-oriented Sage Creek and Scenic Basins prior to Cheyenne River valley headward erosion. The northeast oriented White River valley segment upstream from the east oriented White River valley segment (and from the Sage Creek and Scenic Basin location) next eroded headward across southeast oriented flow and was initiated by southeast oriented water flowing from the Scenic Basin that turned in a northeast direction to reach the east oriented White River downstream valley segment. Erosion of the Sage Creek and Scenic Basin headcuts abruptly ended when headward erosion of the northeast oriented Cheyenne River valley beheaded southeast oriented flow routes leading to the then actively eroding Sage Creek and Scenic Basin heacuts. Cheyenne River valley headward erosion in a southwest direction next captured massive southeast oriented flow then still moving to the newly eroded northeast oriented White River valley segment. Northwest oriented drainage developed on the Sage Creek and Scenic Basin floors when a flood surge or temporary dam caused water to fill the White River valley and to spill in a northwest direction across low points on the then abandoned Sage Creek and Scenic Basin headcut rims. This spillage eroded narrow northwest oriented valleys and drained water filling the two basins to the Cheyenne River valley while most of the ponded water drained in an east direction down the White River valley. The White River valley, Sage Creek and Scenic Basins, and the Cheyenne River valley were eroded by enormous quantities of southeast oriented water that also deeply eroded the entire South Dakota Badlands region.

Pennypack Creek Drainage Basin Erosion History: Bucks, Montgomery, and Philadelphia Counties, PA, USA

Topographic map evidence is used to interpret Pennypack Creek drainage basin erosion history in and north of the City of Philadelphia, Pennsylvania (USA). Southwest and west-southwest oriented through valleys crossing the south oriented Pennypack Creek drainage basin, barbed Pennypack Creek tributaries, and significant valley direction changes are used to determine that the Pennypack Creek valley eroded headward across massive southwest oriented floods. Initially floodwaters flowed on a low gradient topographic surface at least as high, if not higher, than the highest Pennypack Creek drainage basin elevations today. Shallow low gradient diverging and converging flow channels were eroded into the underlying bedrock surface predominantly along fault lines and other zones of easier to erode materials. Headward erosion of the much deeper Pennypack Creek valley across this anastomosing channel complex captured southwest oriented floodwaters and flow on northeast ends of beheaded channels was reversed so as to move toward the newly eroded and deeper Pennypack Creek valley. These reversed flow channels captured southwest oriented floodwaters still moving north of the actively eroding Pennypack Creek valley head. This captured water then moved in a northeast direction and eroded deep northeast oriented valleys headward from the newly eroded Pennypack Creek valley. These valleys today account for northeast and east oriented Pennypack Creek valley segments and northeast oriented (barbed) tributaries flowing to south oriented Pennypack Creek. The floodwater source cannot be determined from Pennypack Creek drainage basin evidence, but was from the northeast. Melting of a continental ice sheet could produce floods of sufficient volume and duration to overwhelm whatever drainage system previously existed and to erode new drainage basins in a manner similar to how the Pennypack Creek drainage basin was eroded.