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30-560: The name is derived from Paibi , a village in Hunan , China. The GSSP is defined in the "Paibi section" ( Wuling Mountains , Huayuan County ), an outcrop of the Huaqiao Formation (花桥组). The base is the first occurrence of Glyptagnostus reticulatus which is 396 m above the base of the Huaqiao Formation at the type locality ( 28°23′22″N 109°31′33″E  /  28.3895°N 109.5257°E  / 28.3895; 109.5257 ). At

60-409: A clay platelet has a slight negative charge where the edge has a slight positive charge when two platelets come into close proximity with each other the face of one particle and the edge of the other are electrostatically attracted." Flocs then have a higher combined mass which leads to quicker deposition through a higher fall velocity, and deposition in a more shoreward direction than they would have as

90-550: A cloudy water column which travels under the tidal influence as the wave orbital motion is in equilibrium. The Null-point hypothesis has been quantitatively proven in Akaroa Harbour, New Zealand, The Wash , U.K., Bohai Bay and West Huang Sera, Mainland China, and in numerous other studies; Ippen and Eagleson (1955), Eagleson and Dean (1959, 1961) and Miller and Zeigler (1958, 1964). Large-grain sediments transported by either bedload or suspended load will come to rest when there

120-519: A depth of −13 m relative to mean sea level at the 9 km point down the transect of the central axis. The predominant storm wave energy has unlimited fetch for the outer harbour from a southerly direction, with a calmer environment within the inner harbour, though localised harbour breezes create surface currents and chop influencing the marine sedimentation processes. Deposits of loess from subsequent glacial periods have in filled volcanic fissures over millennia, resulting in volcanic basalt and loess as

150-663: A village in Paibi Township ( 排碧 乡 ), Huayuan County , Xiangxi Tujia and Miao Autonomous Prefecture Hunan , China, is the location of the Global Boundary Stratotype Section and Point (GSSP) which marks the boundary between the third and Furongian epochs of the Cambrian Period on the geologic time scale . Paibi was selected over the Kyrshabakty River section , Malyi Karatau , Kazakhstan , and

180-506: Is because sediment grain size analysis throughout a profile allows inference into the erosion or accretion rates possible if shore dynamics are modified. Planners and managers should also be aware that the coastal environment is dynamic and contextual science should be evaluated before the implementation of any shore profile modification. Thus theoretical studies, laboratory experiments, numerical and hydraulic modelling seek to answer questions pertaining to littoral drift and sediment deposition,

210-597: Is believed to be caused by the expansion of anoxic deep water into shallow regions. SPICE event had a noticeable impact on trilobites. A decrease in their diversity is observed at the beginning and at the termination of its interval, which coincides with the Laurentian End-Marjuman Biomere Extinction (EMBE) and the End-Steptoean Biomere Extinction (ESBE), respectively. The SPICE event was accompanied by cooling, which contributed to

240-404: Is due to the influence of hydraulic energy, resulting in a seaward-fining of sediment particle size, or where fluid forcing equals gravity for each grain size. The concept can also be explained as "sediment of a particular size may move across the profile to a position where it is in equilibrium with the wave and flows acting on that sediment grain". This sorting mechanism combines the influence of

270-468: Is insufficient bed shear stress and fluid turbulence to keep the sediment moving; with the suspended load this can be some distance as the particles need to fall through the water column. This is determined by the grain's downward acting weight force being matched by a combined buoyancy and fluid drag force and can be expressed by: Downward acting weight force = Upward-acting buoyancy force + Upward-acting fluid drag force where: In order to calculate

300-407: Is known as the hypothesis of asymmetrical thresholds under waves; this describes the interaction between the oscillatory flow of waves and tides flowing over the wave ripple bedforms in an asymmetric pattern. "The relatively strong onshore stroke of the waveforms an eddy or vortex on the lee side of the ripple, provided the onshore flow persists, this eddy remains trapped in the lee of the ripple. When

330-448: Is made up partly of the microscopic calcium carbonate skeletons of marine plankton , the deposition of which induced chemical processes ( diagenesis ) to deposit further calcium carbonate. Similarly, the formation of coal begins with the deposition of organic material, mainly from plants, in anaerobic conditions. The null-point hypothesis explains how sediment is deposited throughout a shore profile according to its grain size. This

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360-756: The GSSP was ratified by the International Union of Geological Sciences in late 2003. It established the first formally agreed upon subdivision of the Cambrian. The village gives its name to the Paibian Age in the Cambrian Period. The Paibi section occurs within the Huaqiao Formation , which consists of a thick succession of carbonate beds deposited in the outer part of the Jiangnan Slope Belt , and extends from

390-562: The central axis of the harbour, or if classified into grain class sizes, "the plotted transect for the central axis goes from silty sands in the intertidal zone to sandy silts in the inner nearshore, to silts in the outer reaches of the bays to mud at depths of 6 m or more". See figure 2 for detail. Other studies have shown this process of the winnowing of sediment grain size from the effect of hydrodynamic forcing; Wang, Collins and Zhu (1988) qualitatively correlated increasing intensity of fluid forcing with increasing grain size. "This correlation

420-427: The down-slope gravitational force of the profile and forces due to flow asymmetry; the position where there is zero net transport is known as the null point and was first proposed by Cornaglia in 1889. Figure 1 illustrates this relationship between sediment grain size and the depth of the marine environment. The first principle underlying the null point theory is due to the gravitational force; finer sediments remain in

450-406: The drag coefficient, the grain's Reynolds number needs to be discovered, which is based on the type of fluid through which the sediment particle is flowing, laminar flow, turbulent flow or a hybrid of both. When the fluid becomes more viscous due to smaller grain sizes or larger settling velocities, the prediction is less straightforward and it is applicable to incorporate Stokes Law (also known as

480-559: The fines are suspended and reworked aerially offshore leaving behind lag deposits of the main bivalve and gastropod shells separated out from the finer substrate beneath, waves and currents then heap these deposits to form chenier ridges throughout the tidal zone, which tend to be forced up the foreshore profile but also along the foreshore. Cheniers can be found at any level on the foreshore and predominantly characterise an erosion-dominated regime. The null point theory has been controversial in its acceptance into mainstream coastal science as

510-414: The flow reverses, the eddy is thrown upwards off the bottom and a small cloud of suspended sediment generated by the eddy is ejected into the water column above the ripple, the sediment cloud is then moved seaward by the offshore stroke of the wave." Where there is symmetry in ripple shape the vortex is neutralised, the eddy and its associated sediment cloud develops on both sides of the ripple. This creates

540-531: The frictional force, or drag force) of settling. The cohesion of sediment occurs with the small grain sizes associated with silts and clays, or particles smaller than 4ϕ on the phi scale. If these fine particles remain dispersed in the water column, Stokes law applies to the settling velocity of the individual grains, although due to seawater being a strong electrolyte bonding agent, flocculation occurs where individual particles create an electrical bond adhering each other together to form flocs. "The face of

570-570: The genus Glyptagnostus marks the boundary. Other markers which occur near the boundary include the first appearance of the conodont Westergaardodina proligula and the Steptoean positive carbon isotope excursion , a large positive shift in carbon-13 isotopes . Deposition (sediment) Deposition is the geological process in which sediments , soil and rocks are added to a landform or landmass . Wind, ice, water, and gravity transport previously weathered surface material, which, at

600-451: The individual fine grains of clay or silt. Akaroa Harbour is located on Banks Peninsula , Canterbury, New Zealand , 43°48′S 172°56′E  /  43.800°S 172.933°E  / -43.800; 172.933 . The formation of this harbour has occurred due to active erosional processes on an extinct shield volcano, whereby the sea has flooded the caldera, creating an inlet 16 km in length, with an average width of 2 km and

630-449: The loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment. This occurs when the forces responsible for sediment transportation are no longer sufficient to overcome the forces of gravity and friction , creating a resistance to motion; this is known as the null-point hypothesis. Deposition can also refer to the buildup of sediment from organically derived matter or chemical processes . For example, chalk

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660-469: The main sediment types available for deposition in Akaroa Harbour Hart et al. (2009) discovered through bathymetric survey, sieve and pipette analysis of subtidal sediments, that sediment textures were related to three main factors: depth, distance from shoreline, and distance along the central axis of the harbour. This resulted in the fining of sediment textures with increasing depth and towards

690-492: The middle Cambrian through the Lower Ordovician . It satisfies all the geological and biostratigraphic requirements for a GSSP, is readily accessible, and includes chemostratigraphic , palaeogeographic , facies -relationship, and sequence- stratigraphic information. The section lies at an elevation of 774 metres. The evolution of Glyptagnostus reticulatus (an agnostoid trilobite ) from more basal species of

720-646: The recovery of ecosystems after its onset, but the further warming disrupted the circulation of ocean waters and triggered new redox changes that precipitated the ESBE. Agnostoid genera, including Glyptagnostus , Homagnostus , Pseudagnostus and Acmarhachis , are known from the Paibian deposits. This article related to the Cambrian period is a stub . You can help Misplaced Pages by expanding it . Paibi Paibi ( Chinese : 排碧 ; pinyin : Páibì ),

750-465: The second, with a sharper decline in richness, lasted 1.2 million years, more in the Paibian. After the extinction, species diversity returned to its previous level. Steptoean positive carbon isotope excursion (SPICE) began around the Guzhangian-Paibian boundary. This event is associated with a global carbon-cycle perturbation. The driving mechanism of this change are not fully understood, but it

780-438: The theory operates in dynamic equilibrium or unstable equilibrium, and many fields and laboratory observations have failed to replicate the state of a null point at each grain size throughout the profile. The interaction of variables and processes over time within the environmental context causes issues; "a large number of variables, the complexity of the processes, and the difficulty in observation, all place serious obstacles in

810-560: The turn of the Guzhangian and Paibian ages, an extinction event occurred that reduced the species richness by 45%. This event coincided with Marjuman extinction that can be traced to trilobite and brachiopod assemblages in Laurentia . Two phases of extinction can be traced in the sediments of South China: the first, with a slight decline in species, lasted in Guzhangian, about 1.8 million years;

840-400: The water column for longer durations allowing transportation outside the surf zone to deposit under calmer conditions. The gravitational effect or settling velocity determines the location of deposition for finer sediments, whereas a grain's internal angle of friction determines the deposition of larger grains on a shore profile. The secondary principle to the creation of seaward sediment fining

870-405: The way of systematisation, therefore in certain narrow fields the basic physical theory may be sound and reliable but the gaps are large" Geomorphologists, engineers, governments and planners should be aware of the processes and outcomes involved with the null point hypothesis when performing tasks such as beach nourishment , issuing building consents or building coastal defence structures. This

900-539: Was demonstrated at the low energy clayey tidal flats of Bohai Bay (China), the moderate environment of the Jiangsu coast (China) where the bottom material is silty, and the sandy flats of the high energy coast of The Wash (U.K.)." This research shows conclusive evidence for the null point theory existing on tidal flats with differing hydrodynamic energy levels and also on flats that are both erosional and accretional. Kirby R. (2002) takes this concept further explaining that

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