Anna van Yperen

• Braathen, Alvar; Midtkandal, Ivar; Mulrooney, Mark; Appleyard, Tyler Ross; Haile, Beyene Girma & van Yperen, Anna Elisabeth (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
• Abels, Hemmo A.; Lauretano, Vittoria; van Yperen, Anna Elisabeth; Hopman, Tarek; Zachos, James C; Lourens, Lucas J; Gingerich, Philip D. & Bowen, Gabriel J. (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

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• Braathen, Alvar; Mulrooney, Mark; Haile, Beyene Girma; Appleyard, Tyler Ross; van Yperen, Anna Elisabeth; Smyrak-Sikora, Aleksandra Anna; Anell, Ingrid Margareta; Ogata, Kei; Midtkandal, Ivar; Osmundsen, Per Terje; Maher, Harmon & Olaussen, Snorre (2017). “Delta collapse” – Edgeøya delta system compared to the Ferron delta (Utah).
• van Yperen, Anna Elisabeth; 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). 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.

• van Yperen, Anna Elisabeth; 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). 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.

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