Cannibalism of contourites by gravity flows: explanation of the facies distribution of the Ordovician Pingliang Formation along the southern margin of the Ordos Basin, China

2020 ◽  
Vol 57 (3) ◽  
pp. 331-347
Author(s):  
Hua Li ◽  
A.J. van Loon ◽  
Youbin He
Keyword(s):  
Ordos Basin ◽  
High Energy ◽  
Middle Part ◽  
Turbidity Currents ◽  
Middle Ordovician ◽  
Fine Grained ◽  
Southern Margin ◽  
Gravity Flows ◽  
Facies Associations ◽  
The Ordos Basin

The Late Ordovician Pingliang Formation accumulated along the southern margin of the Ordos Basin in China. The convergence of the Yangtze Plate and Sino-Korean Plate led to a trench–arc–basin system during the Middle Ordovician, with a platform- and slope-dominated setting in the east where a graben complicated the overall simple paleogeographical picture, relatively parallel zones of a platform and a slope setting in the middle, and a change from platform to slope to deep marine to a trench setting in the west. This configuration resulted in various types of gravity flow deposits and contourites with different compositions and pathways. The present study focuses on the typical characteristics of contourites in the geological record and the relationships between contour currents and gravity flows. The Pingliang Formation contains eleven lithofacies grouped into five facies associations. These facies associations represent deep sea autochthonous deposits, several types of debrites, turbidites, and contourites, as well as turbidites within which the fine-grained top portion was reworked by a contour current. The various lithofacies are concentrated in different parts of the study area: micritic contourites and debrites are concentrated in the eastern part; debrites, and sandstone and siltstone turbidites are concentrated in the middle part; and calcarenitic turbidites, contourites, and reworked turbidites occur in the western part. The main contour current ran parallel to the contour lines from east to west. Although most of the contour current continually moved westward in the eastern part of the study area, a minor part split off and followed a semicircular pathway through the Fuping Graben; its velocity became reduced here so that micritic contourites were deposited. The velocity of the contour current was increased locally when it entered a confined trough in the western part of the study area. The relatively high energy of the contour current here resulted in calcarenitic contourites. The velocity of the contour current was low where it ran through an open environment, resulting in fine-grained, thin contourites in the middle part of the study area. Large turbidity currents and debris flows occurred here, and their high energy destroyed almost all earlier deposited contourites. This explains why traces of contour currents in the middle part of the study are very scarce, although the east–west-running contour current must have passed through this area.

scholarly journals Interaction between turbidity currents and a contour current – A rare example from the Ordovician of Shaanxi province, China

Geologos ◽  
2019 ◽  
Vol 25 (1) ◽  
pp. 15-30 ◽  
Author(s):  
Hua Li ◽  
A.J. [lpar]Tom[rpar] van Loon ◽  
Youbin He
Keyword(s):  
Deep Sea ◽  
High Velocity ◽  
Ordos Basin ◽  
Late Ordovician ◽  
Central China ◽  
Shaanxi Province ◽  
Turbidity Currents ◽  
Fine Grained ◽  
Gravity Flows ◽  
The Ordos Basin

Abstract The silty top parts of graded turbidites of the Late Ordovician Pingliang Formation, which accumulated along the southern margin of the Ordos Basin (central China), have been reworked by contour currents. The reworking of the turbidites can be proven on the basis of paleocurrent directions in individual layers: the ripple-cross-bedded sandy divisions of some turbidites show transport directions consistently into the downslope direction (consistent with the direction of other gravity flows), but in the upper, silty fine-grained division they show another direction, viz. alongslope (consistent with the direction that a contour current must have taken at the same time). Both directions are roughly perpendicular to each other. Moreover, the sediment of the reworked turbidites is better sorted and has better rounded grains than the non-reworked turbidites. Although such type of reworking is well known from modern deep-sea environments, this has rarely been found before in ancient deep-sea deposits. The reworking could take place because the upper divisions of the turbidites involved are silty and consequently relatively easily erodible, while the contour current had locally a relatively high velocity – and consequently a relatively large erosional capability – because of confinement within a relatively narrow trough.

Facies and provenance of deep marine sediment gravity flows with fragments of coalified land plants at Lipowica, the Cergowa Beds (Oligocene), Outer Carpathians of Poland

2021 ◽  
Author(s):  
Joanna Pszonka ◽  
Marek Wendorff ◽  
Magdalena Zielińska ◽  
Paweł Godlewski
Keyword(s):  
Organic Matter ◽  
High Density ◽  
Turbidity Currents ◽  
Terrestrial Plants ◽  
Terrestrial Organic Matter ◽  
Fine Grained ◽  
Lower Stage ◽  
Gravity Flows ◽  
Facies Associations ◽  
Outer Carpathians

<p>Facies analysis of the Cergowa Beds of the Polish and Slovak Outer Carpathians shows that this deep-marine siliciclastic unit was deposited by a spectrum of gravity flows ranging from high to low density, which deposited three facies associations (A, B and C). Association A consists of very fine- to medium-grained sandstones with mudstone and coal clasts, granules and rich in coalified organic matter fragments. Sandstones beds reach 8 m in thickness, are massive and subordinately parallel laminated (Ta and Tab). They are interpreted as resulting from incremental, rapid deposition from collapse of a near-bed layer (Ta, Tab) and laterally sheared near-bed layer (Tb) below high-density, turbulent flows and steady turbidity currents or, in case of mud-rich sandstones, en masse deposition by debris flows. Association B comprises very fine- and fine-grained sandstones with mud and coal clasts, granules and coalified plant fragments and detritus. They are massive, parallel- and ripple cross-laminated (Tab, Tabc, Tbc), reach 2 m in thickness and contain mudstone intercalations up to 50 cm. These sandstones seem to have originated from a combination of incremental deposition by high-density turbidity currents (Tab, Tb), low-amplitude bedload waves at the upper stage planar lamination in more dilute turbidity current (Tb) and suspension of fully turbulent and dilute turbidity currents (Tbc, Tc). Association C consists of very fine- to fine-grained sandstones and siltstones with fine organic detritus and minor mud clasts. Parallel- and ripple cross-lamination (Tbc, Tbcd) dominate, bed thickness of sandstones and siltstones amounts to 1-50 cm and mudstones reaches 200 cm. Association C was deposited by transformation of waning, dilute and fully turbulent turbidity currents from ripples into lower stage planar lamination.</p><p>Sandstone and mudstone beds at Lipowica (Poland) contain three types of coalified terrestrial organic matter. Based on their morphology and size these are: (i) coalified plant detritus dispersed in B and C associations, (ii) coalified plant fragments forming elongated lenses in A and B associations and (iii) coalified fragments of tree trunks occurring in A and B facies. Petrographic components of organic matter represented by collotelinite, telinite, gelinite and fusinite with co-occuring framboidal pyrite indicate terrestrial plants affected by fast gelification and burial processes of varying intensity. The size of the plant fragments supplied to the Dukla basin is positively correlated with indicators of hydrodynamic regimes suggested by their hosting sediments. Namely, the larger the fragments, the higher flow energy and steadier and longer lasting sustained sediment delivery.</p><p>Sedimentary features of the Cergowa Beds suggest deposition out of gradually aggrading sustained turbulent sandy gravity flows primarily controlled by hyperpycnal effluents from a delta. Palaeocurrent data and comparison of mineral composition of sandstone infilling a hollow coalified tree trunk at Lipowica quarry with sandstone beds of the hosting succession suggest provenance from shelf fringing the emergent Silesian Ridge, which acted as a source area to the west of the basin. The depositional age NP23 and NP24 during the Oligocene eustatic sea-level fall implies that the delta supplying the Cergowa basin was located at the edge of this shelf.</p>

scholarly journals Halysis Høeg, 1932 — an ancestral tabulate coral from the Ordos Basin, North China

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Li-Jing Zheng ◽  
Hong-Xia Jiang ◽  
Ya-Sheng Wu ◽  
Hong-Ping Bao ◽  
Yue-Yang Zhang ◽  
...  
Keyword(s):  
North China ◽  
Ordos Basin ◽  
Wall Surface ◽  
Reproduction Mode ◽  
Single Tube ◽  
Middle Ordovician ◽  
Tube Type ◽  
The Ordos Basin ◽  
First Time ◽  
Tabulate Corals

Abstract The problematic calcareous microfossil Halysis is abundant in the Middle Ordovician Darriwilian Stage of the western edge of the Ordos Basin, North China. The rich and well-preserved specimens of Halysis in this area facilitate detailed studies for its skeletal construction and tube microstructure. Halysis differs from calcified cyanobacteria and calcareous red and green algae in morphology, skeletal construction and microstructure, as well as reproduction mode. Halysis typically consists of multiple juxtaposed parallel tubes arranged in sheets (‘multiple-tube’ type) or is just composed of one tube (‘single-tube’ type). In ‘multiple-tube’ Halysis, tube fission by bifurcation results from the insertion of a microcrystalline wall at the center of a mother tube. This study demonstrates for the first time that the tube walls of Halysis have a laminofibrous (fibronormal) microstructure, composed of fibrous calcite perpendicular to wall surface, and recognizes the ‘single-tube’ type Halysis composed of one tube; in addition, for the first time, this study finds out that ‘multiple-tube’ Halysis develops buddings from the conjunction of two tubes and ‘single-tube’ Halysis shows wide-angle Y-shaped branchings. Based on these findings, this study further compares Halysis with tabulate corals. Halysis appears stratigraphically earlier than Catenipora and Aulopora, and has a smaller tube size. ‘Multiple-tube’ Halysis resembles Catenipora and ‘single-tube’ Halysis resembles Aulopora in skeletal construction and microstructure, and in their tube walls of laminofibrous microstructure composed of fibrous calcite perpendicular to the tube wall surface. Catenipora and Halysis are both characterized by the absence of septal spines. The similarities suggest that Halysis may be the ancestor of Catenipora-like and Aulopora-like tabulate corals.

scholarly journals Controls of Depositional Environments on Reservoir Quality in Terms of Porosity and Permeability Gabo Field Niger Delta

2019 ◽  
Author(s):  
Richmond Ideozu ◽  
Tochukwu Nduaguibe
Keyword(s):  
Niger Delta ◽  
High Energy ◽  
Depositional Environments ◽  
Grain Size Analysis ◽  
Reservoir Quality ◽  
Fine Grained ◽  
Sedimentary Structures ◽  
Facies Associations ◽  
Porosity And Permeability ◽  
Distributary Channel

The controls of depositional environments on reservoir quality have been evaluated in terms of porosity and permeability of the Gabo Field, Niger Delta, Nigeria. Data used in this research include Well logs, Core data and photos, and grain size analysis for Wells 51 and 52 in the study area. Standard methods as applicable in petrophysical and sedimentological analysis has been adopted. Thirteen reservoir units have been identified in wells 51 and 52 which had 5 reservoirs cored each. The lithofacies units of the identified reservoirs across the study area, comprise pebbly sands, coarse -, medium -, fine- and very fine-grained sands, sandy mud, silty sands and heteroliths. The heteroliths – very fine-grained silty muds are highly bioturbated. Ophiomorpha and skolithos are the major trace fossils with sedimentary structures (ripple lamination, wavy lenticular and planar beds, cross bedded sands, coarsening and fining upward). The facies associations interpreted for the study area are Channel and Coastal barrier systems and the environment of deposition as distributary channel, upper and lower shoreface. The sedimentary processes that deposited facies ranged from high energy regimes, reworking by waves to low energy with periodic influx of silts and muds. The average porosity and permeability for reservoirs in Well 51 is 16.7% and 1317 Md, reservoirs in Well 52 is 28.2% and 2330Md whereas porosity range for the study area is 2% - 32% and permeability is 1.2 – 10600 Md. The reservoir quality reservoir of the sand units in Well 51 (7, 9 and 13) and Well 52 (5, 7, 9, 11 and 13) is excellent - good, this is because of the dynamics environments of deposition (upper shoreface and distributary channel) as well as the mechanisms that play out during deposition such as bioturbation, sorting, sedimentary structures formed. Whereas the poor quality across the reservoirs especially the lower shoreface and prodelta facies is as result of lack bioturbation, connectivity, multiplicity of burrows that may have been plugged by clay and intercalation of shale and sand (heteroliths). This research has shown that environments of deposition have direct influence the reservoir quality in terms of porosity and permeability.

scholarly journals Petrography and facies distribution of Middle Ordovician Ma 51 + 2 tight dolomite reservoirs in the Ordos Basin, Central China

2018 ◽  
Vol 37 (1) ◽  
pp. 473-492 ◽  
Author(s):  
Xinshe Liu ◽  
Daofeng Zhang ◽  
Guodong Dong ◽  
Baobao Wang ◽  
Di Xiao
Keyword(s):  
Ordos Basin ◽  
Central China ◽  
Central Basin ◽  
Hydrocarbon Accumulation ◽  
Facies Distribution ◽  
Middle Ordovician ◽  
Geological Conditions ◽  
Tight Carbonate ◽  
The Ordos Basin ◽  
Lagoon Environment

The Middle Ordovician Majiagou Formation in the eastern Ordos Basin, central China, is an important area in the exploration for tight carbonate gas, especially within weathering crust layers in the first and second submembers of the fifth member of the formation (herein referred to as Ma 51 + 2). However, karstification prevents a clear understanding of the petrological characteristics and facies distribution of these layers, which hinders exploration. Based on cores, thin sections, and cathodoluminescence analysis, we investigate the petrological characteristics of Ma 51 + 2, determine the nature of lateral lithological variations in the eastern and central parts of the Ordos Basin, and constrain facies distribution in the region. In addition to karst breccias with unrecognizable parent rocks, Ma 51 + 2 comprises four lithologies: gypsum/halite mold-bearing micritic dolomite, micritic dolomite, grain dolomite, and microbial dolomite. We recognize three main sedimentary subfacies: restricted lagoon, grain shoal, and mound–shoal complex. Ma 51 + 2 records a complete transgression–regression cycle. The Ma 522 layer was deposited during a transgression associated with enhanced water circulation and abundant mound–shoal complexes, for which their frequency is positively correlated with the thickness of the unit. The Ma 512 layer and overlying deposits correspond to a regression cycle, and the abundance of mound–shoal complexes in these units is negatively correlated with layer thickness. The Ma 513 period represents the timing of maximum regression, when a gypsum-bearing dolomitic lagoon was dominant, associated with a restricted water body. The overall facies distribution is one of a restricted evaporite lagoon environment, similar to the central basin. Therefore, reservoir tightness is unlikely to be related to the sedimentary facies. The next phase of exploration should focus on “sweet spots” resulting from differential diagenesis or hydrocarbon accumulation. Our results provide guidance for research on tight carbonate reservoirs and hydrocarbon accumulation in other regions that experienced similar geological conditions.

scholarly journals Dolomitization of the Ordovician subsalt Majiagou Formation in the central Ordos Basin, China: fluid origins and dolomites evolution

2020 ◽  
Author(s):  
Ying Xiong ◽  
Li-Chao Wang ◽  
Xiu-Cheng Tan ◽  
Yun Liu ◽  
Ming-Jie Liu ◽  
...  
Keyword(s):  
Ordos Basin ◽  
Middle Ordovician ◽  
Deep Burial ◽  
Multi Stage ◽  
S Matrix ◽  
Crystalline Dolomite ◽  
History Of ◽  
The Ordos Basin ◽  
Dolomite Cement ◽  
Microbial Mediation

AbstractThe Middle Ordovician subsalt Majiagou Formation in the Ordos Basin comprises pervasively dolomitized shallow marine limestone and is a major reservoir rich in natural gas resources. Four types of dolomite matrix and cement were identified based on petrographic textures: (very) finely crystalline, non-planar to planar-s matrix dolomite (Md1); finely to medium crystalline, planar-s to planar-e matrix dolomite (Md2); microbialites comprising dolomite microcrystals (Md3); and finely to coarsely crystalline dolomite cement (Cd). The Md1 and Md2 dolomites were controlled by alternating lagoon-shoal facies and have δ13C values (− 1.89 to + 1.45‰ VPDB for Md1, − 1.35 to + 0.42‰ VPDB for Md2) that fall within or are slightly higher than the coeval seawater, suggesting the dolomitizing fluid of evaporated seawater. Md2 dolomite was then subjected to penecontemporaneous karstification by meteoric water and burial recrystallization by sealed brines during diagenesis, as indicated by its relatively lower δ18O values (− 8.89 to − 5.73‰ VPDB) and higher 87Sr/86Sr ratios (0.708920–0.710199). Md3 dolomite comprises thrombolite and stromatolite and is interpreted to form by a combination of initial microbial mediation and later replacive dolomitization related to evaporated seawater. Cd dolomite was associated with early-formed karst system in the Md2 host dolomite. The lowest δ18O values (− 11.78 to − 10.18‰ VPDB) and 87Sr/86Sr ratios (0.708688–0.708725) and fluid inclusion data (Th: 123–175 °C) indicate involvement of hydrothermal fluid from which the Cd dolomite precipitated during deep burial. These results reveal the multi-stage dolomitization history of the Majiagou Formation and provide new constraints on fluid origins and dolomites evolution during deep burial in old superimposed basins, such as the Ordos Basin and elsewhere.

Upper Middle Ordovician submarine fans and associated facies, northeast of Quebec City

1981 ◽  
Vol 18 (6) ◽  
pp. 981-994 ◽  
Author(s):  
Edward S. Belt ◽  
Louise Bussières
Keyword(s):  
Source Region ◽  
Depositional Environments ◽  
Turbidity Currents ◽  
Quebec City ◽  
Submarine Fan ◽  
Bottom Currents ◽  
Middle Ordovician ◽  
Submarine Fans ◽  
Facies Associations ◽  
Carbonate Bank

Autochthonous upper Middle Ordovician strata northwest of Logan's Line and northeast of Quebec City have been subdivided into six facies types. One or more facies type characterizes the revised formations of our previous report (Belt et al.). These facies were deposited in the following depositional environments: moderately shallow carbonate bank; deeper carbonate slope and foot of slope; submarine fan; and basin plain. The submarine fan facies (Beaupré and Saint-Irénée Formations) contain the only facies with appreciable sandstone. The source region of the sandstones (determined by petrography and paleocurrents) lay to the southeast of Logan's Line. This source was uplifted and eroded during the early phases of the Taconic Orogeny. Turbidity currents and debris flows brought sand into a foredeep trough that lay between the mobile Taconic Orogen and the more stable Canadian Shield. During Trenton time, a carbonate bank developed on the margin of the shield, northwest of the trough axis. Olistostromes, produced by bank-edge collapse, slid southeast into the trough and intercalated with the Saint-Irénée sandy fan lobes derived from the other side of the foredeep basin. Bottom currents, reworking the sand, flowed southwest along the axis of the trough. Later, after regional foundering of the carbonate bank, a larger (Beaupré Formation) submarine fan developed in the foredeep basin. Bottom currents continued reworking the sands down the trough to the southwest.The submarine fans found in this region never developed some of the facies associations commonly expected of suprafan lobes. The initial fan facies consists of lenticular coarse and pebbly sandstone and shale that are only rarely organized into coarsening-up successions. No definite feeder channel deposits are found in the Saint-Irénée Formation although three are recognized in the middle Beaupré Formation at the type section. The presence of these channels plus the geometry of all Beaupré facies and the paleocurrent divergence show that these facies are not disorganized base-of-slope or basin-plain deposits, but best fit a submarine fan model.

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