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deltas:a new classification expanding Bates's concepts

Journal of Palaeogeography 2021年第3期10卷 341-355页

作者： Carlos Zavala Mariano Arcuri Mariano Di Meglio Agustin Zorzano German Otharan Ainara Irastorza Antonela Torresi Dpto.de Geologia Universidad Nacional del Sur(UNS)Bahia BlancaArgentina GCS Argentina SRL Molina Campos 1508000 Bahia BlancaArgentina Consejo Nacional de Investigaciones Científicas y Tecnicas (CONICET)Buenos AiresArgentina

deltas constitute complex depositional systems formed when a land-derived gravity-flow(carrying water and sediments) discharges into a marine or lacustrine standing body of water. However, the complexity of deltaic sedimentary environments has been oversimplified by geoscientists over the years, considering just littoral deltas as the unique possible type of delta in natural systems. Nevertheless, a rational analysis suggests that deltas can be much more complex. In fact, the characteristics of deltaic deposits will depend on a complex interplay between the bulk density of the incoming flow and the salinity of the receiving water body. This paper explores the natural conditions of deltaic sedimentation according to different density contrasts. The rational analysis of deltaic systems allows to recognize three main fields for deltaic sedimentation, corresponding to(1) hypopycnal(2) homopycnal and(3) hyperpycnal delta settings. The hypopycnal delta field represents the situation when the bulk density of the incoming flow is lower than the density of the water in the basin. According to the salinity of the receiving water body, three different types of hypopycnal littoral deltas are recognized: hypersaline littoral deltas(HSLD), marine littoral deltas(MLD), and brackish littoral deltas(BLD). The basin salinity will determine the capacity of the delta for producing effective buoyant plumes, and consequently the characteristics and extension of prodelta *** littoral deltas(HOLD) form when the density of the incoming flow is roughly similar to the density of the water in the receiving basin. This situation is typical of clean bedload-dominated rivers entering freshwater lakes. Delta front deposits are dominated by sediment avalanches. Typical fallout prodelta deposits are absent or poorly developed since no buoyant plumes are generated. Hyperpycnal deltas form when the bulk density of the incoming flow is higher than the density of the water in the receivi

关键词： deltas Hyperpycnal flows Homopycnal flows Hypopycnal flows Hyperpycnites Turbidites Sediment gravity flows Gravity flows

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Hyperpycnal littoral deltas:A case of study from the Lower Cretaceous Agrio Formation in the Neuquén Basin,Argentina

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Journal of Palaeogeography 2021年第4期10卷 550-570页

作者： Ainara Irastorza Carlos Zavala Debora Mical Campetella Martín Turienzo Daniela Olivera Florencia Peralta Maite Irastorza Paula Martz Dpto.de Geología Universidad Nacional Del Sur(UNS)Bahía Blanca 8000Argentina Instituto Geologico Del Sur(INGEOSUR) Universidad Nacional Del Sur(UNS)-CONICETBahía Blanca 8000Argentina GCS Argentina SRL Molina Campos 150Bahía Blanca 8000Argentina Universidad Nacional Del Sur Bahía Blanca 8000Argentina Universidad Nacional de Río Negro.Instituto de Investigacion de Paleobiología y Geología General Roca 8332Río NegroArgentina Consejo Nacional de Investigaciones Científicas y Tecnicas(CONICET) Instituto de Investigaciones en Paleobiología y GeologíaGeneral Roca 8332Río NegroArgentina

Recent advances in the understanding of deltaic deposits provide new tools for the study and analysis of deltaic deposits in shallow epicontinental *** the introduction of sequence stratigraphic concepts,meter-scale coarsening and thickening upward successions have been considered as“parasequences”originated by high-frequency sea-level ***,recent studies enhanced the importance of wave-aided low-dense hyperpycnal flows in transporting fine-grained sediments in shallow shelfal *** poorly-known(and at the same time very common)types of delta,known as hyperpycnal littoral deltas(HLD),develop very low gradient progradational units,controlled by changes in the sediment supply instead of sea level *** small-scale progradational units are very common in shallow epicontinental seas like the Lower Cretaceous Agrio Formation in the Neuquén *** study provides a first detailed analysis of hyperpycnal littoral deltas from the Agua de la Mula Member(upper Hauterivian-lower Barremian)of the Agrio *** unit has been studied in three locations near Bajada del Agrio locality in the central part of the Neuquén Basin,*** sandy facies,three heterolithic facies,three muddy facies and four calcareous facies were *** facies analysis,three facies associations could be determined,corresponding to offshore/prodelta,distal ramp delta and proximal ramp *** three stratigraphic sections discussed in this study are internally composed of several small-scale sequences showing a coarsening and thickening upward pattern,transitionally going from muddy to sandy wave-dominated facies,and ending with calcareous bioclastics levels on *** small-scale sequences are interpreted as delta front deposits of wave-influenced hyperpycnal littoral deltas,punctuated by calcareous intervals accumulated during periods of low sediment *** is interpreted that the development of hyperpycnal littoral deltas could have been

关键词： deltas Hyperpycnal littoral deltas Prograding sequences Agua de la Mula Member Neuquén Basin

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WORLD deltas AND THEIR EVOLUTION

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地理学报 1999年第1期54卷 32-43页

作者：Ｈ．ＪｅｓｓｅＷａｌｋｅｒＷａｒｅｎＥ．Ｇｒａｂａｕ Louisiana State University 美国 Signal Hill Lane 美国

１ＩｎｔｒｏｄｕｃｔｉｏｎＤｕｒｉｎｇｔｈｅｐｅｒｉｏｄｏｆｔｉｍｅｇｌａｃｉａｔｉｏｎｗａｓａｔｉｔｓｍａｘｉｍｕｍ，ｓｅａｌｅｖｅｌｗａｓ１２０ｍｌｏｗｅｒｔｈａｎａｔｔｈｅｐｒｅｓｅｎｔ．Ｔｈｅｗｏｒｌｄ＇ｓｒ... 详细信息

１ＩｎｔｒｏｄｕｃｔｉｏｎＤｕｒｉｎｇｔｈｅｐｅｒｉｏｄｏｆｔｉｍｅｇｌａｃｉａｔｉｏｎｗａｓａｔｉｔｓｍａｘｉｍｕｍ，ｓｅａｌｅｖｅｌｗａｓ１２０ｍｌｏｗｅｒｔｈａｎａｔｔｈｅｐｒｅｓｅｎｔ．Ｔｈｅｗｏｒｌｄ＇ｓｒｉｖｅｒｓａｔｔｈａｔｔｉｍｅｆｌ...

关键词： deltas Mississippi Nile Ganges Brahmaputra Rhine Meuse Changjiang Po

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When and where rivers meet the sea

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Science China Chemistry 2001年第S1期44卷 10-22页

作者： H.JesseWalker Department

River mouth areas provide one of the most desired locations for human habitation. Although occupying only a small portion of the total length of the world’s shoreline, river mouths are dynamic and complex with highly variable physical and chemical *** size, shape, and position of a river’s mouth are dependent on its geologic and hydrologic history. Further, the processes that operate in a river’s mouth are affected by the sea and its currents, tides, and salinity; the river and its discharge and sediment characteristics; and wind generated waves and storm surges. Present-day locations are, geologically speaking, of recent origin because of the rise in sea level that accompanied deglaciation and the sedimentation that followed drowning.

关键词： rivers estuaries deltas lagoons salinity.

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