Anna van Yperen

• Prasojo, Octria Adi; Yperen, Anna van; Hoey, Trevor B.; Owen, Amanda & Williams, Richard (2024). USING DELTA CHANNEL WIDTH TO ESTIMATE PALEODISCHARGE IN THE ROCK RECORD: GEOMETRIC SCALING AND PRACTICAL SAMPLING CRITERIA. Journal of Sedimentary Research. ISSN 1527-1404. 94(1), s. 62–75. doi: 10.2110/jsr.2022.057. Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; More, Miquel Poyatos; Holbrook, John M. & Midtkandal, Ivar (2020). Internal mouth‐bar variability and preservation of subordinate coastal processes in low‐accommodation proximal deltaic settings (Cretaceous Dakota Group, New Mexico, USA). The Depositional Record. 6(2), s. 431–458. doi: 10.1002/dep2.100. Fulltekst i vitenarkiv Vis sammendrag

  Mouth bars are the fundamental architectural elements of proximal deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial, tide and wave‐dominated) is paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low‐accommodation systems, because they are commonly characterized by thin, condensed and top‐truncated sections. This study analyses the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), a fluvio‐deltaic system covering a ca 450 km depositional dip‐parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ca 25 km2 study area at the rim of the Tucumcari Basin. Analysis of facies distributions, depositional architecture and spatial extent of stratigraphic surfaces reveals a 6–10 m thick, sharp‐based and sand‐prone deltaic package, comprising several laterally extensive (>1.4 km width) mouth bars. Composite erosional surfaces infilled with multi‐storey fluvial and marine‐influenced channel deposits (12–20 m thick, 100–250 m wide) scour locally into the deltaic package. Based on differences in sedimentary structures, bed thicknesses, occurrence of interflood beds and bioturbation indexes, four different sub‐environments within single mouth bars were distinguished. These range from mouth‐bar axis, off‐axis, fringe to distal‐fringe deposits, which reflect waning depositional energy with increasing distance from the distributary channel mouth. The interpreted mouth‐bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the fringe and distal fringe components. Mouth‐bar deposits amalgamate to form an extensive sand‐rich sheet body throughout the study area, in which interflood mudstone to very‐fine grained sandstone beds are nearly absent. These features reflect successive coalescence of mouth bars in a low accommodation/supply (A/S) setting. These conditions promoted recurrent channel avulsion/bifurcation and thus the potential reworking of previously deposited mouth‐bar fringe and distal‐fringe sediments, where time and background processes are better recorded. Results of this study evidence internal process‐regime variability within mouth‐bar components. They also caution against the possible loss of preservation of subordinate coastal processes (e.g. tidal indicators), and consequent underestimation of the true mixed influence in low‐accommodation deltaic settings.

• Serck, Christopher Sæbø; Braathen, Alvar; Olaussen, Snorre; Osmundsen, Per Terje; Midtkandal, Ivar & Yperen, Anna Elisabeth van [Vis alle 7 forfattere av denne artikkelen] (2020). Supradetachment to rift basin transition recorded in continental to marine deposition; Paleogene Bandar Jissah Basin, NE Oman. Basin Research. ISSN 0950-091X. doi: 10.1111/bre.12484. Fulltekst i vitenarkiv Vis sammendrag

  A transition from supradetachment to rift basin signature is recorded in the ~1,500 m thick succession of continental to shallow marine conglomerates, mixed carbonate‐siliciclastic shallow marine sediments and carbonate ramp deposits preserved in the Bandar Jissah Basin, located southeast of Muscat in the Sultanate of Oman. During deposition, isostatically‐driven uplift rotated the underlying Banurama Detachment and basin fill ~45° before both were cut by the steep Wadi Kabir Fault as the basin progressed to a rift‐style bathymetry that controlled sedimentary facies belts and growth packages. The upper Paleocene to lower Eocene Jafnayn Formation was deposited in a supradetachment basin controlled by the Banurama Detachment. Alluvial fan conglomerates sourced from the Semail Ophiolite and the Saih Hatat window overlie the ophiolitic substrate and display sedimentary transport directions parallel to tectonic transport in the Banurama Detachment. The continental strata grade into braidplain, mouth bar, shoreface and carbonate ramp deposits. Subsequent detachment‐related folding of the basin during deposition of the Eocene Rusayl and lower Seeb formations marks the early transition towards a rift‐style basin setting. The folding, which caused drainage diversion and is affiliated with sedimentary growth packages, coincided with uplift‐isostasy as the Banurama Detachment was abandoned and the steeper Marina, Yiti Beach and Wadi Kabir faults were activated. The upper Seeb Formation records the late transition to rift‐style basin phase, with fault‐controlled sedimentary growth packages and facies distributions. A predominance of carbonates over siliciclastic sediments resulted from increasing near‐fault accommodation, complemented by reduced sedimentary input from upland catchments. Hence, facies distributions in the Bandar Jissah Basin reflect the progression from detachment to rift‐style tectonics, adding to the understanding of post‐orogenic extensional basin systems.

• Yperen, Anna Elisabeth van; Holbrook, John M.; More, Miquel Poyatos; Myers, Cody & Midtkandal, Ivar (2020). Low‐accommodation and backwater effects on sequence stratigraphic surfaces and depositional architecture of fluvio‐deltaic settings (Cretaceous Mesa Rica Sandstone, Dakota Group, USA). Basin Research. ISSN 0950-091X. 33(1), s. 513–543. doi: 10.1111/bre.12483. Fulltekst i vitenarkiv Vis sammendrag

  The adequate documentation and interpretation of regional‐scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. However, this is often challenged by the amalgamated nature of low‐accommodation settings and control of backwater hydraulics on fluvio‐deltaic stratigraphy. Exhumed examples of full‐transect depositional profiles across river‐to‐delta systems are key to improve our understanding about interacting controlling factors and resultant stratigraphy. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA), which allows mapping of down‐dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio‐deltaic deposition in the Tucumcari sub‐basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down‐dip into single‐story channel sandstones and eventually into contemporaneous distributary channels and delta‐front strata. Down‐dip changes reflect accommodation decrease towards the paleoshoreline at the Tucumcari basin rim, and subsequent expansion into the basin. Additionally, multi‐storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised‐valley fill deposits, based on their regional occurrence, estimated channel tops below the surrounding topographic surface and coeval downstepping delta‐front geometries. This opposes criteria offered to differentiate incised valleys from flood‐induced backwater scours. As the incised valleys evidence relative sea‐level fall and flood‐induced backwater scours do not, the interpretation of incised valleys impacts sequence stratigraphic interpretations. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS). The RCS’ diachronous nature demonstrates that its down‐dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. Formation of a regional composite scour in the fluvial realm throughout a relative sea‐level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low‐accommodation settings to dominantly promote bypass, especially during forced regressions. Source‐to‐sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea‐level cycle.

• Yperen, Anna Elisabeth van; Holbrook, John M.; More, Miquel Poyatos & Midtkandal, Ivar (2019). Coalesced delta-front sheet-like sandstone bodies from highly avulsive distributary channels: the low-accommodation Mesa Rica Sandstone (Dakota Group, New Mexico, USA). Journal of Sedimentary Research. ISSN 1527-1404. 89(7), s. 654–678. doi: 10.2110/jsr.2019.27. Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; Line, Lina Hedvig; Holbrook, John M.; Poyatos-Moré, Miquel & Midtkandal, Ivar (2019). Revised stratigraphic relationships of the Dakota Group in the Tucumcari Basin, San Miguel County, New Mexico, USA. Fall Field Conference Guidebook. ISSN 0077-8567. s. 89–100. Fulltekst i vitenarkiv
• Braathen, Alvar; Midtkandal, Ivar; Mulrooney, Mark; Appleyard, Tyler Ross; Haile, Beyene Girma & Yperen, Anna Elisabeth van (2018). Growth-faults from delta collapse - structural and sedimentological investigation of the Last Chance delta, Ferron Sandstone, Utah. Basin Research. ISSN 0950-091X. 30(4), s. 688–707. doi: 10.1111/bre.12271. Fulltekst i vitenarkiv
• Abels, Hemmo A.; Lauretano, Vittoria; Yperen, Anna Elisabeth van; Hopman, Tarek; Zachos, James C & Lourens, Lucas J [Vis alle 8 forfattere av denne artikkelen] (2016). Environmental impact and magnitude of paleosol carbonate carbon isotope excursions marking five early Eocene hyperthermals in the Bighorn Basin, Wyoming. Climate of the Past. ISSN 1814-9324. 12(5), s. 1151–1163. doi: 10.5194/cp-12-1151-2016. Fulltekst i vitenarkiv
• Yperen, Anna van; Holbrook, John M.; Poyatos-Moré, Miquel & Midtkandal, Ivar (2004). Backwater length estimates in modern and ancient fluvio-deltaic settings: Review and proposal of standardized workflows. Earth-Science Reviews. ISSN 0012-8252. 250. doi: 10.1016/j.earscirev.2024.104692. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Ghinassi, M.; Baccarin, M.; Yperen, Anna van; Finotello, A.; Maitan, R. & Midtkandal, Ivar [Vis alle 7 forfattere av denne artikkelen] (2025). Assessing the reliability of tidal sedimentary structures to detect efficiency of tidal processes: examples from the Venice Lagoon and the Po River Delta, Northern Italy. Fulltekst i vitenarkiv
• Yperen, Anna van; Holbrook, John; Miquel, Poyatos-More & Midtkandal, Ivar (2024). Backwater length estimates in modern and ancient fluvio-deltaic settings: review and proposal of standardized workflows. Fulltekst i vitenarkiv Vis sammendrag

  The backwater effect (i.e. adjustments in open-channel flow as a response to proximity of standing water) is used to predict down-dip changes in fluvial morphodynamics and consequent sediment distribution on delta plains. However, there is currently no standardized method to obtain input parameters to estimate backwater length, nor consensus on where to measure these variables, for both modern and ancient settings. This study reviews existing methods for estimating backwater lengths in ancient and modern settings and proposes workflows to minimize ambiguity in resultant estimates. The proposed workflows are tailored to both modern and ancient settings and are prioritized based on practicality, accuracy, smallest uncertainty ranges and allow different data types as input parameters. For the first time, application of multiple methods, i.e. the proposed workflows, is tested on a single modern and ancient river system. In the modern case study, riverbed intersection with sea level matches previously documented major changes in sedimentary trends. However, backwater lengths based on h/S (h = maximum bankfull channel dept, S = slope) plot downstream of this zone characterized by major changes, when input parameters are derived from discharge and grain size. In the ancient case study, backwater lengths based on maximum bankfull channel depth and slope based on Shields’ empirical relation with grain size, match changes in fluvial architectural style interpreted as a result of backwater effects. The proposed workflows facilitate comparability and applicability of future backwater length estimates and their corresponding influence on the hydrodynamic environment and ultimately quantification of source-2-sink segments.

• Yperen, Anna van; Holbrook, John; Poyatos-Moré, Miquel & Midtkandal, Ivar (2024). Backwater length estimates in modern and ancient fluvio-deltaic settings: review and proposal of standardized workflows. Fulltekst i vitenarkiv Vis sammendrag

  The backwater effect (i.e. adjustments in open-channel flow as a response to proximity of standing water) is used to predict down-dip changes in fluvial morphodynamics and consequent sediment distribution on delta plains. However, there is currently no standardized method to obtain input parameters to estimate backwater length, nor consensus on where to measure these variables, for both modern and ancient settings. This study reviews existing methods for estimating backwater lengths in ancient and modern settings and proposes workflows to minimize ambiguity in resultant estimates. The proposed workflows are tailored to both modern and ancient settings and are prioritized based on practicality, accuracy, smallest uncertainty ranges and allow different data types as input parameters. For the first time, application of multiple methods, i.e. the proposed workflows, is tested on a single modern and ancient river system. In the modern case study, riverbed intersection with sea level matches previously documented major changes in sedimentary trends. However, backwater lengths based on h/S (h = bankfull thalweg channel dept, S = slope) plot downstream of this zone characterized by major changes, when input parameters are derived from discharge and grain size. In the ancient case study, backwater lengths based on bankfull thalweg channel depth and slope based on Shields’ empirical relation with grain size, match changes in fluvial architectural style interpreted as a result of backwater effects. The proposed workflows facilitate comparability and applicability of future backwater length estimates and their corresponding influence on the hydrodynamic environment and ultimately quantification of source-2-sink segments.

• Bello, G.; More, M. Poyatos; Cabello, P.; Yperen, Anna van; Holbrook, J. & Midtkandal, Ivar [Vis alle 7 forfattere av denne artikkelen] (2024). . 3D characterization of sedimentary heterogeneity and its impact on reservoir properties in amalgamated fluvial sheet sandstones: Montllobar Formation (Ypresian, Tremp-Graus Basin, Spain). Fulltekst i vitenarkiv
• Yperen, Anna van; Tognin, Davide; Maitan, Riccardo; Bellizia, E.; Finotello, Alvise & Midtkandal, Ivar [Vis alle 7 forfattere av denne artikkelen] (2024). Finding tidal signatures in river-flood bar deposits in a micro-tidal mixed-energy deltaic setting (Po River, Italy). Fulltekst i vitenarkiv Vis sammendrag

  Recent advances in understanding the morpho-sedimentary dynamics of mixed-energy coastal systems highlight that the interplay of processes (i.e., tides, waves, river) can be cryptic to decipher in ancient sedimentary successions, where common evidence for tidal sedimentary processes can lead to ‘overinterpretation’ of tidal energy. Modern river-and-delta systems offer direct measurements of whether tidal signatures may be present in deltas without clear evidence of tidal control on their overall morphology. To this end, we evaluated the relative importance of tidal and river processes in deposition occurring in the backwater and fluvial marine transition zone (180 km long), of the Po River (Italy). The Po River debouches in the micro-tidal Northern Adriatic Sea and is considered a river-wave, mixed-energy, fluvio-deltaic system based on the absence of macro-morphometric features considered diagnostic of tidal control on morpho-sedimentary processes (e.g., channel funneling). Sediment cores from side-attached bars in the distalmost ~30 river kilometers show heterolithic facies, sparse double mud drapes, sand-mud couplets and sporadic bidirectional current ripples. Trenches reveal meter-scale cycles of alternating intervals with well-defined and poorly-defined laminae in the distal reaches of the delta. In combination with historical water-level data, these cycles are interpreted to result from semi-diurnal tidal modulation during river floods. This contrasts the lack of cyclic patterns in trenches in proximal reaches of the study area, and the rare occurrence of similar cycles in the medial reaches. This study highlights that preservation of tidal rhythmites within intertidal bar deposits is possible, despite the microtidal setting and dominance of river energy at times of deposition. Further, despite no discernible control of tidal forcing on the Po River delta morphodynamics, tide-related structures are widespread. Hence, we support the idea that care should be taken in interpreting dominance of processes based on the occurrence of sedimentary structure, and vice versa.

• Bello, G.; Tejedor, F.; Poyatos-More, M.; Cabello, P.; Yperen, Anna van & Holbrook, J. [Vis alle 8 forfattere av denne artikkelen] (2024). 3D characterization of sedimentary heterogeneity and its impact on reservoir properties in amalgamated fluvial sandstones: Montllobar Formation (Ypresian, Tremp-Graus Basin). Fulltekst i vitenarkiv Vis sammendrag

  In this work we present the study of an amalgamated fluvial sandstone body in the Montllobar Formation (Lower Eocene, Tremp-Graus Basin, Pyrenees), based on facies and paleocurrent analysis, fluvial architecture and stratigraphic correlation, complemented by UAV imagery, together with 3D modelling of facies and reservoir properties. The studied unit shows a multi-storey pattern, with up to three vertically stacked channel fills, mainly composed by coarse- to fine-grained sandstones. These sandstones stack and amalgamate forming mid-channel and lateral bars, interbedded with lenticular mudstone levels, and occasionally conglomerate layers. These features are consistent with the interpretation of a braided fluvial system with a sinuous component, developed under low accommodation conditions and/or high sedimentary input, with a nearby alluvial fan. 3D modelling of the unit characterises the internal facies variability, with porosity, vertical and horizontal permeability values based on subsurface analogs from the North Sea. The presence of thin mudstone lenses results in local baffles and low vertical connectivity; however, the lateral migration of channels and horizontal accumulation of bar deposits would enhance lateral connectivity and fluid expansion in a hypothetical reservoir.

• Toribio, A.; Yperen, Anna van; Poyatos-More, M.; Fuste, J.; Gomez-Gras, D. & Lopez, E. [Vis alle 10 forfattere av denne artikkelen] (2024). The influence of marine processes in fluvial architecture from the Montllobar and Castigaleu formations (Ypresian, Pyrenees). Fulltekst i vitenarkiv Vis sammendrag

  In this study we analise the effect of marine processes in the variability of channel deposits from the Montllobar and Castigaleu formations (Tremp-Graus Basin). Through a stratigraphic, sedimentological, and petrological analysis of different examples of channel deposits (isolated/amalgamated), we have defined their geometry, facies and depositional processes, and established their sedimentary provenance. Our results reveal that channels in the more proximal sections are dominated by sandstones and conglomerates, forming laterally accreting bar complexes (isolated channels) or multistorey complexes (amalgamated channels) with evidence of subaerial exposure and root bioturbation. Basinward, the aspect ratio of channels increases in width (isolated channels) or becomes more variable (amalgamated channels), and a decrease in the root bioturbation is observed, together with a progressive increase in mudstones, bioclasts and invertebrate bioturbation in the channel-fill deposits, all attributed to a higher marine influence. However, the petrological analysis reveals the median grain size of sandstones stays relatively coarse and constant throughout all channels, together with a moderate to poor sorting. This is interpreted to reflect the continuous influence of two transverse alluvial systems: one closer to the proximal part of the system, with a source area dominated by Mesozoic cover rocks, and another closer to the distal part of the system, dominated by igneous rocks. Results of this work suggest that in this case the influence of the marine basin had a stronger effect in the resulting geometry of the channels, than the presence of local coarse-grained supply from transverse alluvial systems.

• Yperen, Anna van; Holbrook, John M.; More, Miquel Poyatos & Midtkandal, Ivar (2022). Assessing predictability in tide-influenced river channel morphology – can we take previous concepts one step further? Fulltekst i vitenarkiv Vis sammendrag

  An increasing number of studies link down-dip changes in channel morphodynamics on rivers and their delta plains to backwater effects, i.e. non-uniform flows causing flow deceleration and subsequent net deposition during low water discharge, or flow acceleration leading to net erosion during high water discharge (e.g. Chatanantavet et al., 2012; Lamb et al., 2012; Nittrouer et al., 2012; Fernandes et al., 2016; Martin et al., 2018; Trower et al., 2018; Ganti et al., 2019; Smith et al., 2020). A potential predictability exists on backwater-mediated trends in changing channel width, depth, sinuosity, and grain size, which in turn controls resulting sedimentary architecture and distribution of heterogeneities. However, backwater concepts originated and are predominantly tested on fluvial-dominated modern river systems. A recent study on large tide-dominated modern river deltas (n=5) shows a consistent area of change in upstream to downstream trends in channel morphology, of which some changes in channel morphodynamics are different from expected backwater-mediated changes (Gugliotta and Saito, 2019). In this study we use satellite data analysis to examine down-dip changes in channel width and sinuosity from 15 modern tide-influenced deltas along their fluvial to marine transition zone. Distances are normalized for comparison across different delta plain sizes. Previously published backwater lengths are sensitive to different acquisition methods which weakens their comparability. We aim to minimize ambiguity by combining digital elevation profiles with channel depth from bathymetric surveys or empirically derived from width-thickness relationships, to detect where the riverbed equals sea level and subsequent backwater length. The results show no significant distance relationship between the backwater length and area of morphological change (i.e. zone recording a change in channel width and sinuosity). Eight out of fifteen deltas show a clear area of morphological change. The other delta plains lack clear areas of morphological change, or changes in channel morphology (i.e. sinuosity or width) occur at different areas along the river system. By comparing the area of morphological change with the apex-to-shoreline distance, the regression line shows a near-one-to-one relationship although the five largest delta plains plot outside the 95% confidence interval. This suggests that factors controlling the area of morphological change and apex location may be different on the largest delta plains than on smaller tide-influenced systems. This presentation will discuss the potential and shortcomings of combining previously established concepts to improve predictability of changes in tide-influenced channel morphology. Preliminary results show that the expected upstream-to-downstream changes (i.e. an increase in channel width and a decrease in channel depth and sinuosity) in large tide-dominated deltas cannot be directly applied to smaller and/or tide-influenced deltas. This cautions against inferring knowledge from large and/or river-dominated delta plains to directly apply to systems with any size and/or process regime system, as the response scale to changes in controlling factors will be different depending on delta plain size and dominant controlling factors. Additionally, it suggests uncertainty in applying these concepts to ancient fluvio-deltaic systems, as the influence of additional variables such as differences in global sea-level conditions is currently not investigated.

• Yperen, Anna van; Holbrook, John M.; More, Miquel Poyatos & Midtkandal, Ivar (2022). Improving predictability of changes in tide-influenced channel morphology – can we take previously established concepts one step further? Fulltekst i vitenarkiv Vis sammendrag

  An increasing number of studies links down-dip changes in riverine morphodynamics on delta plains to backwater effects, i.e. flow deceleration as a river approaches a standing water body and subsequent deposition. A potential predictability exists on backwater-mediated trends in changing river channel width, depth, sinuosity, and grain size, which in turn controls resulting sedimentary architecture and distribution of heterogeneities. However, backwater concepts originated and are predominantly tested on fluvial-dominated modern rivers. A recent study on large tide-dominated modern river deltas (n=5) shows a consistent area of change in upstream to downstream trends in channel morphology, of which some are different than expected backwater-mediated changes. Preliminary results of our study on a larger data set with tide-influenced deltas, show that the expected upstream-to-downstream changes in large tide-dominated deltas cannot be directly applied to smaller and/or tide-influenced deltas. This presentation will discuss the potential and shortcomings of combining previously established concepts to improve predictability of changes in tide-influenced channel morphology. Caution is needed when inferring knowledge from large and/or river-dominated delta plains, as the response scale to changes in controlling factors will be different depending on delta plain size and dominant controlling factors.

• Yperen, Anna van; Holbrook, John M.; Poyatos-Moré, Miquel; Ahokas, Juha & Midtkandal, Ivar (2021). Improving predictability of changes in tide-influenced channel morphology – implications for exploration and reservoir analogue studies. Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; Midtkandal, Ivar; More, Miquel Poyatos & Holbrook, John M. (2021). Diachronous key stratigraphic surfaces in low-accommodation settings fluvio-deltaic settings. Fulltekst i vitenarkiv Vis sammendrag

  The adequate documentation and interpretation of regional-scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. In active depositional systems however, these surfaces are often composite and hence diachronous, which contradicts their original appreciation. This is particularly true in low-accommodation settings due to their amalgamated nature. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA); an example of an exhumed depositional profile across a river-to-delta system. The near-continuous outcrop exposure allows mapping of down-dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio-deltaic deposition in the Tucumcari sub-basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down-dip into single-story channel sandstones and eventually into distributary channel deposits and delta-front strata. Additionally, multi-storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised-valley fill deposits. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS) and can be mapped for >300 km. Basal distributary composite scours, composite surfaces bounding incised valleys, and basal surfaces below dispersed trunk channels incising into deltaic deposits occur at sub-regional scale. The RCS’ diachronous nature demonstrates that its down-dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. Formation of a regional composite scour in the fluvial realm throughout a relative sea-level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low-accommodation settings to dominantly promote bypass, especially during forced regressions. Source-to-sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea-level cycle.

• Yperen, Anna Elisabeth van; Holbrook, John M.; More, Miquel Poyatos & Midtkandal, Ivar (2021). Diachronous key stratigraphic surfaces in low-accommodation fluvio-deltaic settings: from the Dakota Group (USA) to the Cretaceous on Svalbard/Barents Sea. Fulltekst i vitenarkiv Vis sammendrag

  The adequate documentation and interpretation of regional-scale stratigraphic surfaces is paramount to establish correlations between continental and shallow marine strata. In active depositional systems however, these surfaces are often composite and hence diachronous, which contradicts their original appreciation. This is particularly true in low-accommodation settings due to their amalgamated nature. This study utilizes the ~400 km transect of the Cenomanian Mesa Rica Sandstone (Dakota Group, USA), which offers an outstanding example of an exhumed full-transect depositional profile across a river-to-delta system. The near-continuous outcrop exposure allows mapping of down-dip changes in facies, thickness distribution, fluvial architecture and spatial extent of stratigraphic surfaces. The two sandstone units of the Mesa Rica Sandstone represent contemporaneous fluvio-deltaic deposition in the Tucumcari sub-basin (Western Interior Basin) during two regressive phases. Multivalley deposits pass down-dip into single-story channel sandstones and eventually into contemporaneous distributary channel deposits and delta-front strata. Additionally, multi-storey channel deposits bound by erosional composite scours incise into underlying deltaic deposits. These represent incised-valley fill deposits, based on their regional occurrence, estimated channel tops below the surrounding topographic surface and coeval downstepping delta-front geometries. The erosional composite surface below fluvial strata in the continental realm represents a sequence boundary/regional composite scour (RCS) and can be mapped for >300 km. Basal distributary composite scours, composite surfaces bounding incised valleys, and basal surfaces below dispersed trunk channels incising into deltaic deposits occur at sub-regional scale. The RCS’ diachronous nature demonstrates that its down-dip equivalent disperses into several surfaces in the marine part of the depositional system, which challenges the idea of a single, correlatable surface. This work is important to understand other low-accommodation systems elsewhere, such as Lower Cretaceous strata on Svalbard and in the Barents Sea. Here, correlation between onshore and offshore depositional systems has been hampered due to – amongst others – the lack of preserved Lower Cretaceous strata in parts of the northern Barents Sea. Acknowledgment of the diachronous nature of key stratigraphic surfaces holds potential to improve the understanding of fluvio-marine correlations and sandstone distribution. In general, formation of a regional composite scour in the fluvial realm throughout a relative sea-level cycle highlights that erosion and deposition occur virtually contemporaneously at any point along the depositional profile. This contradicts stratigraphic models that interpret low-accommodation settings to dominantly promote bypass, especially during forced regressions. Source-to-sink analyses should account for this in order to adequately resolve timing and volume of sediment storage in the system throughout a complete relative sea-level cycle.

• Yperen, Anna Elisabeth van; More, Miquel Poyatos; Holbrook, John M. & Midtkandal, Ivar (2021). Internal mouth-bar variability and differential preservation of coastal-process indicators in low-accommodation deltaic settings. Fulltekst i vitenarkiv Vis sammendrag

  Mouth bars are fundamental architectural elements of deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial-, tide- and wave-dominated) is therefore paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low-accommodation systems because they are commonly characterized by a thin, condensed and top-truncated expression. In this study we analyze the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), which encompasses a fluvio-deltaic system along a ~450 km depositional dip-parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ~25 km2 study area at the Tucumcari Basin margin. Analysis of facies distribution, depositional architecture and stratigraphic surfaces mapping reveals a 6–10-m-thick, sharp-based and sand-prone deltaic package, comprising several laterally-extensive (>1.4 km width) mouth bars. Within those, we distinguish four different along-strike sub-environments based on differences in grain size, sedimentary structures, bed thicknesses, and bioturbation indices; these are mouth bar axis, off-axis, lateral fringe to distal lateral fringe deposits, and overall reflect waning depositional energy with increasing distality from the distributary channel mouth. The interpreted mouth-bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the lateral fringe and distal fringe environments. However, mouth-bar deposits amalgamate to form an extensive sand-rich sheet body throughout the study area, in which interflood mudstone to very-fine grained sandstone beds are nearly absent. This indicates a low accommodation/supply (A/S) setting, which promoted recurrent channel avulsion/bifurcation and thus reworking of mouth-bar fringe and distal-fringe sediments, where background coastal processes tend to be better recorded. Trends in along-strike changes in sedimentary characteristics from axial to lateral environments are also recognized in other wave- and river-dominated deltaic settings as well, where axial components consist of higher energy facies associations resulting from high-density currents, whereas heterolithics become dominant towards the fringes, where there is an alternation of low- and high-density deposits combined with an increased recording of finer-grained facies associations. Complemented with our study, this suggests that internal hierarchy of mouth bars is evident and observed regardless of dominant coastal processes. Consequently, subdivision of mouth bars into different components can reduce complexity of models deriving from a myriad of facies subdivisions, and guide prediction of facies changes and sand distribution in future studies of proximal deltaic settings. Finally, results of this study evidence internal process-regime variability within mouth-bar components. This cautions against relying solely on the preserved deposits at one given location in a system to infer dominant and subordinate coastal processes (e.g. tidal indicators), with a consequent risk of underestimating the true mixed-influence nature of low-accommodation deltaic settings.

• Yperen, Anna Elisabeth van (2021). Diachronous key stratigraphic surfaces in low-accommodation fluvio-deltaic settings: from the Dakota Group (USA) to the Cretaceous on Svalbard/Barents Sea. Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van (2020). From desert to polar bear in ~400 million years. Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; Holbrook, John M.; More, Miquel Poyatos & Midtkandal, Ivar (2020). From river to delta; diachronous key stratigraphic surfaces in low-accommodation settings (Dakota Group, USA). Fulltekst i vitenarkiv
• Holbrook, John M.; Yperen, Anna Elisabeth van; Bhattacharya, Janok P. & Miall, Andrew D. (2020). The Diachronous Sequence. Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; Poyatos-Moré, Miquel; Holbrook, John M. & Midtkandal, Ivar (2019). From river to delta: down-dip changes in amalgamated sheet sandstones along an exhumed transect. Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; Poyatos-Moré, Miquel; Holbrook, John M. & Midtkandal, Ivar (2019). Internal mouth-bar variability and preservation potential of tide-influence in a low-accommodation setting (Dakota Group, USA). Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; Poyatos-More, Miquel; Holbrook, John; Line, Lina Hedvig & Midtkandal, Ivar (2018). The “filtering” effect and internal delta-lobe variability in low-accommodation fluvial-marine transition zones: the Cretaceous Mesa Rica Sandstone (New Mexico, USA). Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; Midtkandal, Ivar; Holbrook, John M. & Poyatos-More, Miquel (2018). Allogenic and autogenic controls on low-accommodation deltaic systems: the Cretaceous Mesa Rica Sandstone (New Mexico, USA). Fulltekst i vitenarkiv
• Yperen, Anna Elisabeth van; Midtkandal, Ivar; Holbrook, John & Miquel, Poyatos-More (2017). Facies architecture and stratigraphic development of a thin, low-gradient delta along a sandy coast – the Cretaceous Mesa Rica Sandstone in New Mexico (USA). Fulltekst i vitenarkiv Vis sammendrag

  A rare case of thin, low-gradient delta architecture is documented along Albian-Cenomanian cliff sections in New Mexico, where analysis of facies distribution, depositional architecture and the spatial extent of stratigraphic surfaces reveal a characteristic pattern of laterally varying shallowing-upward facies successions. The dominantly fluvial Mesa Rica Sandstone is characterized by a ~350 km NNW-SSE depositional profile from southeast Colorado to northeast New Mexico where it feeds a 15-20 m thick contemporaneous delta. This delta has received limited attention besides micropaleontology, palynology and organic geochemistry, which has been applied to reconstruct sea level fluctuation and coastline migration. Cross-sections were constructed from observations along a 20km+ escarpment. Several facies associations were recognized and form the basis for this reconstruction. The number of vertically stacked parasequences varies locally, but an inverse relationship between thickness and parasequence count results in a generally constant thickness for the whole succession. Within-parasequence variation in dominant processes occurs over short distances. A set of key stratal surfaces shows remarkable similarities with the previously established framework for the updip fluvial part of the system. The presence of sub-regional flooding surfaces and a laterally varying number of paraseqeuences is interpreted to reflect lobe abandonment followed by local subsidence and possible later re-activation. In turn, this suggests that autogenic lobe switching accounts for flooding surfaces of limited lateral reach, whereas allogenic forcing explains widespread flooding and their associated surfaces. Accurate identification and temporal constraints on flooding events may be applied as a framework to improve facies mapping and consideration for compartmentalization in delta successions. Unraveling the interplay of paleo-bathymetry, dominant processes (fluvial, wave, tidal) and slope gradients for the Mesa Rica Sandstone delta will contribute to the understanding of delta development in low-gradient basins in general.

• Yperen, Anna Elisabeth van; Midtkandal, Ivar; Holbrook, John & Miquel, Poyatos-More (2017). Facies architecture and stratigraphic development of a thin, low-gradient delta along a sandy coast – the Cretaceous Mesa Rica Sandstone in New Mexico (USA). Fulltekst i vitenarkiv Vis sammendrag

  A rare case of thin, low-gradient delta architecture is documented along Albian-Cenomanian cliff sections in New Mexico, where analysis of facies distribution, depositional architecture and the spatial extent of stratigraphic surfaces reveal a characteristic pattern of laterally varying shallowing-upward facies successions. The dominantly fluvial Mesa Rica Sandstone is characterized by a ~350 km NNW-SSE depositional profile from southeast Colorado to northeast New Mexico where it feeds a 15-20 m thick contemporaneous delta. The upstream fluvial strata record deposition of an extensive sandstone sheet, as documented by others. Its delta terminus has received limited attention besides micropaleontology, palynology and organic geochemistry, which has been applied to reconstruct sea level fluctuation and coastline migration. Strike-, and dip sections were constructed from observations along a 20km+ escarpment in the Tucumcari Basin, east-central New Mexico, ~60 km down-dip from the first indicators of deltaic development in the hitherto fluvial system. Five facies associations were recognized in the study area, and form the basis for this reconstruction. Moderately bioturbated prodelta mudstones grade into completely bioturbated distal sandstone bars of which the high and uniform bioturbation index suggests slow sedimentation and persistent wave agitation. The presence of thin hyperpycnal deposits in the lower part of the distal bars is evidence for occasional high river-discharge events. The strata grade further into slightly coarser grained indistinctly bedded mouth bar sandstones with a uniform and low bioturbation index. Erosive and channelized cross-stratified channel sandstones (distributary or trunk) with a commonly present pebble-sized lag form the top of the upward shallowing succession. Channel-incision depth varies significantly within the study area, and is ascribed to interplay between sediment supply and base level change. The number of vertically stacked parasequences varies locally, but an inverse relationship between thickness and parasequence count results in a generally constant thickness for the whole succession. Areas with only a few or several stacked parasequences contain thicker or thinner units, respectively. Distal- to mouth bar clinothem geometries are observed in just one locality, typically reaching 120-160 m in down-dip extent. Here, the total interval thickens significantly over a short distance, possibly explained by a local depression in the paleo-basin bathymetry. The presence of sub-regional flooding surfaces and a laterally varying number of paraseqeuences is interpreted to reflect lobe abandonment followed by local subsidence and possible later re-activation. In turn, this suggests that autogenic lobe switching accounts for flooding surfaces of limited lateral reach, whereas allogenic forcing explains widespread flooding and their associated surfaces. Accurate identification and temporal constraints on flooding events may be applied as a framework to improve facies mapping and consideration for compartmentalization in delta successions. The dimensions of the incising channels are comparable with the upstream trunk channels, indicating a further continuation of the delta in the down-dip direction, beyond outcrop exposure to the SSE. Unraveling the interplay of paleo-bathymetry, dominant processes (fluvial, wave, tidal) and slope gradients for the Mesa Rica Sandstone delta will significantly contribute to the understanding of delta development in low-gradient basins in general.

• Braathen, Alvar; Mulrooney, Mark; Haile, Beyene Girma; Appleyard, Tyler Ross; Yperen, Anna Elisabeth van & Smyrak-Sikora, Aleksandra Anna [Vis alle 12 forfattere av denne artikkelen] (2017). “Delta collapse” – Edgeøya delta system compared to the Ferron delta (Utah). Fulltekst i vitenarkiv

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