Anastomosing rivers

Heterogeneity and anisotropy of lithological units influences hydraulic conductivity on several scales. The purpose of this study is to develop a novel method supporting hydrostratigraphic classification by considering horizontal and vertical variations of sand content in relation with the paleo-depositional environment. The workflow was applied for the uppermost ca. 1800 m thick fluvio-deltaic deposits (Great Plain Aquifer) of late Neogene to Quaternary age basin-fill succession in the eastern part of the Pannonian basin in Hungary. Five combined 3D seismic volumes, seven master horizons, and 30 well logs were analyzed. First, RMS amplitude maps were extracted to interpret the seismic geomorphological features and depositional architectures. Their associated lithology was inferred from wireline logs (GR and SP) by calculating the shale volume and the net-togross sand ratio for 30 m thick intervals. These were used to calibrate the seismic facies as a proxy for the horizontal distribution of sand versus shale. This method allowed the identification of sand bodies, i.e.: deltaic lobes, complex channel belts, simple fluvial channels behaving as aquifers, and the dominantly muddy delta plain to flood plain suits as aquitard. The vertical pattern of sand distribution was also evaluated. Three major stratiform and some corridor-like minor hydrostratigraphic units were defined instead of the former regional (basin) scale aquifer unit. 1) Laterally extended interval of stacked deltaic lobes of high sand ratios and high rate of connectedness, at the bottom of the studied interval. 2) General presence of extended muddy floodplains with anastomosing river systems, characterized by 100-200 m wide channels, low sand ratio, and limited connectedness: 3) widespread meandering and/or braided river systems with high sand ratios and high connectedness in the Quaternary. Within unit 2) spatially and temporally variable appearance of major 500-3600 m wide meandering channel belts produce locally high sand-ratio corridors in the NE-SW direction. A workflow adapted from the oil-and-gas industry was successfully applied to distinguish units of varying sand content and hydraulic conductivity. This approach can be used on basin to local scale to build a spatially complex facies-based model of hydrostratigraphy. Thus, a robust heterogeneous geological model serves as a base for investigating fluid flow on the required scale.

The stratigraphy of the Upper Silesian Keuper, a continental, mudstone-dominated succession is poorly known, although the already renowned, newly discovered veterbrate localities highlight the growing demand for a more precise intra-regional correlation and an appropriate stratigraphic reference framework. A major lithostratigraphic unit, preliminarily proposed for the middle Keuper (i.e., above the Schilfsandstein; Stuttgart Formation in "Stratigraphische Tabelle von Deutschland", 2002) by Szulc and Racki (2015; Przegl¹d Geologiczny, 63: 103-113), is described in detail. The redefined Grabowa Variegated Mudstone-Carbonate Formation, the unit previously based on inaccurately presented information, includes the Upper Gypsum Beds and the Steinmergelkeuper in the traditional scheme from Germany (= Weser and Arnstadt formations). Three members are formally defined: the Ozimek (Mudstone-Evaporite) Member, the Patoka (Marly Mudstone-Sandstone) Member and the WoŸniki (Limestone) Member. Two significant bone-bearing horizons (Krasiejów and Lisowice) are placed within the Patoka Mbr. The formation thickness in a composite, regional reference section of the Upper Silesian Keuper, based on the new WoŸniki K1 and Patoka 1 well profiles, is approximately 215 m thick. The Grabowa Fm generally correlates with the Norian stage, with the base located in the undefined upper Carnian, and is topped by a major, erosive disconformity and sedimentary sequence boundary, near the Norian-Rhaetian boundary. However, hiatuses in the Silesian middle Keuper succession are located and paired with a cannibalistic type of sand-mud flat deposition, largely controlled by Early Cimmerian movements of tectonic blocks associated with the Kraków-Lubliniec shear zone.

Gruszka B. and Zieliñski T. (2008)-Ev i dence for a very low-en ergy flu vial sys tem: a case study from the di no saur-bear ing Up per Trias sic rocks of South ern Po land. Geol. Quart., 52 (3): 239-252. Warszawa. The Up per Tri as sic suc ces sion in S Po land in which di no saur bones have been found con sists pre dom i nantly of siltstones and claystones. Three units are dis tin guished. The low er most and the up per most units re flect an al lu vial en vi ron ment, whereas the mid dle one rep re sents lac us trine fa cies. The lower al lu vial unit is in ter preted as a re cord of ephem eral, sin u ous, sus pended-load chan nels with rapid ver ti cal accre tion. Chan nel barforms are lack ing. The en vi ron ment is in ter preted as a low-en ergy anastomosing flu vial sys tem. The clayey mid dle unit is in ter preted as hav ing formed in a wide long-lived lake. The top of the lac us trine de pos its shows signs of vertisol-type pedogenesis, most prob a bly un der sub trop i cal con di tions, with sea son ally-in duced wet and dry in ter vals. The up per unit re flects a low-en ergy me ander ing river sys tem. Silty point bars were abun dant and the chan nels mi grated freely. The en ergy level of this flu vial sys tem was slightly higher than that of the ear lier one, which is in ter preted as an ef fect of base-level low er ing in com bi na tion with an in creas ingly hu mid climate. The al most ex clu sively silty/clayey al lu vial de pos its rep re sent an ex cep tion ally rare fa cies. The drain age ba sin must have been an ex tremely flat low land. The pres ence of ver te brate bones within the anastomosing and me an der ing river de pos its in di cates that low-energy al lu vial plains were ap par ently fa vour able hab i tats for both rep tiles and am phib i ans dur ing the Late Tri as sic: un der the sub trop i cal, sea son ally dry con di tions, the an i mals must have pre ferred moist low ar eas, i.e. the flood bas ins and aban doned chan nels on the flat valley floors.

We re view the three re gional anastomosing flu vial sys tems, both an cient and mod ern. The di no saur-bear ing up per Tri as sic suc ces sion in Krasiejów (S Po land) is com posed of siltstones and claystones that are di vided into three fa cies as so ci a tions. One of the flu vial as so ci a tions is characterized by fea tures typ i cal of a low-en ergy anastomosing river sys tem in a trop i cal semiarid cli mate, in ter preted as the re sult of ac cu mu la tion in deep, wide and low-sin u os ity palaeochannels with pro nounced ver ti cal ac cre tion. De po si tion from sus pen sion pre dom i nated in flows of very low stream power. The up per Neo gene muddy suc ces sion in a tec toni cally ac tive area (Kleczew Graben, cen tral Po land) in cludes a great num ber of flu vial palaeochannels filled with sand and/or mud. These rib bon-shaped flu vial bod ies are deep and wide, and rep re sent chan nels show ing very lim ited lat eral mi gra tion. They were filled mostly un der low-en ergy con di tions, and their mapped course shows an "anabranching" pat tern in plan view. The palaeochannels are tran si tional from sand-to mud-dom i nated. The Ho lo cene up per Narew River (NE Po land) rep re sents a mod ern anastomosing flu vial sys tem. The in ter con nected chan nels form an anabranching pat tern. The chan nels are straight to slightly sin u ous, rel a tively deep and wide. Interchannel, low-ly ing "islands" are cov ered by peat-form ing plants. De spite the low stream power, in-chan nel de po si tion is dom i nated by sand transported as bedload. The chan nel banks are sta bi lised by veg e ta tion, which ef fec tively pre vents their lat eral mi gra tion.

Palaeontologia Polonica is a monograph series published by the Institute of Paleobiology of the Polish Academy of Sciences, associated with the quarterly journal Acta Palaeontologica Polonica. Its format, established in 1929 by Roman Kozłowski, remains virtually unchanged. Although conservative in form, Palaeontologia Polonica promotes new research techniques and methodologies of inference in palaeontology. It is especially devoted to publishing data which emphasise both morphologic and time dimensions of the evolution, that is detailed descriptions of fossils and precise stratigraphic co−ordinates.

The Upper Triassic succession in S Poland in which dinosaur bones have been found consists predominantly of siltstones and claystones. Three units are distinguished. The lowermost and the uppermost units reflect an alluvial environment, whereas the middle one represents lacustrine facies. The lower alluvial unit is interpreted as a record of ephemeral, sinuous, suspended-load channels with rapid vertical accretion. Channel barforms are lacking. The environment is interpreted as a low-energy anastomosing fluvial system. The clayey middle unit is interpreted as having formed in a wide long-lived lake. The top of the lacustrine deposits shows signs of vertisol-type pedogenesis, most probably under subtropical conditions, with seasonally-induced wet and dry intervals. The upper unit reflects a low-energy meandering river system. Silty point bars were abundant and the channels migrated freely. The energy level of this fluvial system was slightly higher than that of the earlier one, which...

Palaeontologia Polonica is a monograph series published by the Institute of Paleobiology of the Polish Academy of Sciences, associated with the quarterly journal Acta Palaeontologica Polonica. Its format, established in 1929 by Roman Kozłowski, remains virtually unchanged. Although conservative in form, Palaeontologia Polonica promotes new research techniques and methodologies of inference in palaeontology. It is especially devoted to publishing data which emphasise both morphologic and time dimensions of the evolution, that is detailed descriptions of fossils and precise stratigraphic co−ordinates.

The stratigraphy of the Upper Silesian Keuper, a continental, mudstone-dominated succession is poorly known, although the already renowned, newly discovered veterbrate localities highlight the growing demand for a more precise intra-regional correlation and an appropriate stratigraphic reference framework. A major lithostrati-graphic unit, preliminarily proposed for the middle Keuper (i.e., above the Schilfsandstein; Stuttgart Formation in "Stratigraphische Tabelle von Deutschland", 2002) by Szulc and Racki (2015; Przegl¹d Geologiczny, 63: 103-113), is described in detail. The redefined Grabowa Variegated Mudstone-Carbonate Formation, the unit previously based on inaccurately presented information, includes the Upper Gypsum Beds and the Steinmergel-keuper in the traditional scheme from Germany (= Weser and Arnstadt formations). Three members are formally defined: the Ozimek (Mudstone-Evaporite) Member, the Patoka (Marly Mudstone-Sandstone) Member and the WoŸniki (Limestone) Member. Two significant bone-bearing horizons (Krasiejów and Lisowice) are placed within the Patoka Mbr. The formation thickness in a composite, regional reference section of the Upper Silesian Keuper, based on the new WoŸniki K1 and Patoka 1 well profiles, is approximately 215 m thick. The Grabowa Fm generally correlates with the Norian stage, with the base located in the undefined upper Carnian, and is topped by a major, erosive disconformity and sedimentary sequence boundary, near the Norian-Rhaetian boundary. However, hiatuses in the Silesian middle Keuper succession are located and paired with a cannibalistic type of sand-mud flat deposition, largely controlled by Early Cimmerian movements of tectonic blocks associated with the Kraków-Lubliniec shear zone.

... Page 2. bone-bear ing sec tion) with the “Lisów Brec cia”. The strati - graphic po si tion of the lat ter is still not clear; it used to be cor re - lated with the Jarkowo Beds or Zb¹szynek Beds, ie with the mid or late Norian (Grodzicka-Szymanko, 1971; Mader, 1997). ...

There are many different alluvial environments which can be studied, described, and classified.  These environments can be found in all climatic regimes, and can include alluvial plains, alluvial valleys, and alluvial fans.  Channel morphology is probably the most important factor in classifying different parts of an alluvial fan system.  Channel classifications however, are not always clear-cut definitions like the classic three type model: meandering, braided, and anastomosing.  Today channels are generally classified on the basis of grain size of bed material, or channel patterns.  In medial to distal alluvial fan settings, the braided river pattern is the division of a single trunk channel into a network of branches, and the growth and stabilization of braid bars.  Today we know braided systems involve the simultaneous interaction of erodible banks, sediment transport and abundant load, and rapid and frequent variations in discharge.  Anastomosing rivers are more permanent distributive channels which flow through an interconnected network.  Because not all rivers flowing through an interconnected network share the same traits, anastomosing rivers are now referred to as a type of anabranching system, which refers to six different types of interconnected rivers.  In the most distal settings of an alluvial fan, gently undulating bodies of sheet sands can be of floodplain, playa, possible aeolian, or even shallow marine origin.  These sands can be deposited by sheet floods, which can transport sediment on a floodplain or playa both in suspension and a bedload, or other factors, such as sediment supply and subsidence, can cause sheet sands to deposit in marine environments.

Creek, in the Red Desert area of the Great Divide Basin, Wyoming, is an arid-region anastomosing stream. The narrow, deep, and sinuous main channel is flanked by anastomosing flood channels, or anabranches. Most anabranches are initiated at meander bends. The primary mechanism of anabranch initiation is avulsion during overbank floods. Anabranch enlargement occurs by headward erosion. Anabranches act as distributary channels during floods, when water and sediment from overbank flows are transported to and deposited on the floodplain via the anabranches. During periods of low discharges, the anabranches act as tributaries to the main channel, transporting runoff from the floodplain and surrounding hillslopes to the main channel of Red Creek.