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Stratigraphic features of the sedimentary formations of the Clarion-Clipperton province (Eastern equatorial Pacific)
Abstract
The area studied is characterized by a regional stratigraphic gap from the early Miocene up to the Quaternary. Deposits from the late Eocene to the early Miocene were revealed at the bottom surface or under a thin sedimentary cover. Ferromanganese nodules, mostly of the Oligocene age, are deposited over the surface layers of the Tertiary or Quaternary sediments. A detailed micropaleontological study of a block of dense ancient clay coated with a ferromanganese crust was carried out. A study of the composition of the radiolarian and diatomaceous complexes found proved that the crust was formed in the Quaternary over an eroded surface of late Oligocene clay. In the Quaternary, the Neogene sediments were eroded and washed away by the near-bottom currents. It is likely that the erosion began 0.9-0.7 Ma at the beginning of the "Glacial Pleistocene." The erosion could be initiated by the loosening and resuspension of the surface sediments, resulting from the seismic action generated by strong earthquakes in the subduction zone of Central America. The same vibration maintained residual nodules at the seafloor surface. Thus, for the area studied, a common reason and a common Quaternary interval for the formation of the following features is supposed: the regional stratigraphic gap, the formation of the residual nodule fields, and the position of the ancient nodules over the surface of the Quaternary sediments.
... This formulation of the problem was conditioned, first of all, by the impos sibility to explain the existing correlation between the unconsolidated sediments and ferromanganese nodules (erosional cut and "floating" o f the nodules) using the previously considered mechanisms. They include (a) long-term periods when no sediments are accumu lated; (b) regional erosion of the Tertiary sediments and accumulation of ferromanganese nodules as residual elements; (c) the effect of the bottom shaking under the forcing of the seismic waves from the strongest earth quakes; (d) microflux of geogases; (e) bioturbation and extrusion of nodules to the surface of the floor by benthic organisms; (f) rheological properties of the sed iments; and (g) hydrodynamics of the density-stratified bottom water layers [2,4,19]. All these mechanisms cannot explain the facts of erosion of Tertiary sedi ments 34-80 m thick and the location of the denser ancient (mainly Oligocene) ferromanganese nodules (density about 2.0 g/cm3) [11] at the surface of the sed iments of different ages up to recent ones (the density of the consolidated sediments is about 1.2 g/cm3 [12]). ...
In this paper we apply the mechanism of a near-bottom tsunami in the open ocean to explain the
paradoxical location of massive ferromanganese nodules at the surface of sediments of different ages. These tsunamis are generated by the strongest (M > 7.5) earthquakes in the Central American seismic zone and propagate in the near-bottom water layer (3000-5000 m). Their amplitudes are equal to 0.8-3.0 cm, while the velocities reach 180 m/s. Such perturbations of the water layer are able to cause not only the erosion of the sediments
but also the transport (rolling, overturning) of ferromanganese nodules over the ocean bottom. As a result, they
can be located at the surface of sediments of various ages. This confirms our supposition about the mechanism
of “floating” of massive ferromanganese nodules. Previously, in order to solve the problem mentioned above,
we used the mechanism of the Raylpigh waves, which are excited by the strongest (M > 7.5) earthquakes in
Central America. However, an analysis of the amplitudes of the Rayleigh waves showed that, at distances of
3300-5400 km from the seismic zone, these amplitudes are very small (about 0.5 mm). Therefore, they are able to cause erosion at a rate up to 50 m/My by mechanical forcing on the sediments. However, the Rayleigh waves are not able to move ferromanganese nodules because of their small scale (0.5 mm) as compared to the size of the nodules (5-10 cm). Hence, the mechanism of a near-bottom tsunami is preferable for explaining the effect of nodule “floating.”
Micropaleontological investigations in two survey areas show that Tertiary outcrops of different ages are distributed on the bottom surface or under a thin layer of Quaternary sediments. The continuous sediment sequence from the Late Eocene to the Early Miocene (40-17 million years) and the regional hiatus between 17 and 1 million years were revealed. Age intervals of radiolarian complexes in nodules are Tertiary mainly Oligocene. Abundant manganese nodules occur on the bottom mainly on the surface of Quaternary sediments covering the Tertiary deposits of various ages. The statistical probability of the nodule formation age is mainly Oligocene. Consequently, the ages of the manganese nodules and sediments are different, usually older nodules occur on younger deposits.
Most of the micropaleontologically characterized Quaternary sediments are 0.7-0.9 million years old. Micropaleontological investigations were carried out also in a block of the dense ancient miopelagic clay covered by the manganese crust. In contrast to nodules, the crust could be formed only after formation of an erosion surface, on which it accrued. The distribution of microfossil complexes in different samples taken from the block shows that the dense miopelagic clay is of the Late Oligocene age. Early and Middle Quaternary and Recent sediments penetrated it through cracks and burrows. Obviously, the manganese crust was formed in the Quaternary time.
Micropaleontological complexes of Middle and Late Miocene, and Pliocene are present neither in the ancient clay, nor in the manganese crust, nor in Quaternary deposits containing mixed complexes of different ages. During that time the present erosion surface of the Late Oligocene clay was covered by younger deposits of the Late Oligocene, Miocene and Pliocene, which were eroded and washed away in the Quaternary. Probably the erosion begun about 0.9-0.7 million years ago at the beginning of “Glacial Pleistocene” when the ocean circulation, particularly near-bottom currents became more active.
The assumption was stated (Barash, Kruglikova, 1999, 2000), that the erosion of Tertiary deposits by near-bottom currents could be intensified by an effect of strong earthquakes in tectonically active zones which can be affective within several thousands of kilometers. In watersaturated nonconsolidated medium of the ocean bottom the surface seismic Love and Rayleigh waves should be propagated which can cause a vibration effect. The seismic vibration effect on the surface sediment layer must disintegrate and stir up sediments, which are then carried away by the bottom current. Large-size components of the sediment including manganese nodules cannot be carried out by the current and form residual deposits. The same vibration effect causes ancient nodules to float up onto the surface of the Quaternary sediments.
This assumption was considered from the point of view of geophysical mechanisms (Kuzin, Barash, 2001, 2002a, 2002b). We proposed the new approach, which is based on mechanical influence on sediments of Rayleigh waves, generating by strongest (М7.5) earthquakes within the nearest Central American seismic active region. The proposed approach is based on data concerning of oscillations, which were excited by Rayleigh waves of some catastrophic earthquakes (for example, Lisbon, 1775, Assam, 1950, and Alaskan, 1964). These oscillations are observed at epicentral distances from 2000-4000 to 8000 km. The considered mechanism is realistic and allows to use quantitative characteristics of Rayleigh wave amplitudes for the explanation of mechanical influence on sediments. The study of Rayleigh wave amplitudes was carried out with using of 200 records of earthquakes with M=6.0-8.2 at distances 560-9200 km for Petropavlovsk-Kamchatsky and North-Kurilsk seismic stations.
For the analysis there were used data for various seismoactive regions of the Pacific Ocean. The close seismotectonic and seismic analogy between Kurile-Kamchatka and Central American segments of the Pacific belt allows us to apply the data recorded in the first region for study of same phenomena in the second one. Then for distances between investigated areas and the seismoactive Central American region of 3000-5400 km we have amplitudes of Rayleigh wave about 0.5 mm for single earthquake. The earthquakes with M = 7.5 – 8.5 can recure 20 times per 1000 years and capable to cause the “seismological erosion” of sediments up to 10 m/My but they are ineffective for manganese nodules movement, because of large dimensions (3-5 to 10 cm) of the nodules. For the explanation of nodules movement it was necessary to use another mechanism.
For solution of this problem we have used for the first time the mechanism of near-bottom tsunami in open ocean, which are excited by the same way as Rayleigh wave by the strongest (M7.5) earthquakes of the Central American seismic zone. It is known from observations near the California and in the Alaskan Bay, that these tsunami are propagated in the near-bottom water layer (at 3000-5000 m ocean depths) with amplitudes of 0.8-3.0 cm and velocities up to 180 m/s (Filloux, 1982; Milburn, Bernard, 1990) (fig.2).
Minerals of ocean. Int. Conf. 20-23 April. St.Petersburg. VNIIOkeangeologia. 2002. P.55-57.
Mechanism of manganese nodules accumulation and their maintenance at the sediment surface (Clarion-Such perturbations of the near-bottom water layer are capable to cause both the erosion of sediments and the transference (rolling, overturning) of manganese nodules over the ocean bottom. As a result they can occur on the surface of sediment of various ages. That confirms our supposition about the mechanisms of “floating-up” of massive manganese nodules or their maintenance on the bottom surface.
Thus, this assumption suggests one and the same reason for the peculiarities of the Clarion-Clipperton zone, that is, the regional stratigraphic hiatus, the formation of the residual nodule fields, and maintenance of ancient nodules at the surface of the Quaternary deposits.
REFERENCES
Barash, M.S., and S.B. Kruglikova. Age of radiolaria from ferromanganese nodules of the Clarion-Clipperton Province (the Pacific Ocean) and the problem of nodule unsinkability. Oceanology, 1995, V.34, N6, p.815-828.
Barash, M.S., and S.B. Kruglikova. Age of manganese nodules of the Clarion-Clipperton Province and the problem of nodule maintenance at the sediment surface. PACON 99 Proceedings, Symp. on “Humanity and the World Ocean”, 2000, p. 220-230.
Barash, M.S., S.B.Kruglikova, and V.V.Mukhina. Stratigraphic features of sediment formations of the Clarion-Clipperton Province (the east equatorial Pacific). Oceanology, 2000, V.40, N3, p.424-433.
Filloux, J.H. Tsunami recorded on the open ocean floor. Geophys. Res. Lett. 1982. V.9. N.1. P. 25-28.
Kuzin, I.P., and M.S. Barash. On new approach to solution of problem of “floating-up” of manganese nodules in near-equator part of the Pacific Ocean. 14th Int. School on Marine Geology, Abstracts, Moscow, Russian Ac. Sc., 2001, V.2, p. 286-287.
Kuzin, I.P., and M.S. Barash. On influence of Rayleigh waves of strongest (М7.5)
Central American earthquakes at sediment cover within the Clarion-Clipperton Province. Oceanology, 2002 (in press).
Kuzin, I.P., and M.S. Barash. On possible mechanism of manganese nodules “floating-up” in the near-equatorial part of the Pacific Ocean. Oceanology, 2002 (in press).
Milburn H.B., Bernard E.N. Deep ocean tsunami observations. Workshop on scientific uses of undersea cables. Jan.30-Febr.1, 1990. Honolulu. Hawaii.Washington, D.C. 1990. P.69-73.
Benthic current measurements are reported from three locations (A: 8°27′N, 150°49′W; B: 11°42′N, 138°24′W; C: 14°38′N, 125°29′W) in the eastern tropical Pacific. Near-bottom stratification was weak at all sites. The measurements were of 4- to 6- month duration. Mean currents were small and to the northwest; however, low frequency fluctuations dominated the records. These fluctuations had dominant periods for the meridional component of 2 months at all sites; the zonal component had periods varying from 2 months at the easternmost site to about 5 months at the other sites. Low frequency kinetic energy increased from west to east. Vertically, the low frequency motions were coherent over the bottom 200 m. A small speed increase was observed from 200 m to 30 m off the bottom; below this the speed decreased. Interpretation of these data in terms of an Ekman layer showed counterclockwise (looking down) veering between 30- to 6-m levels, which was consistent with the expected layer thickness of 25 m.
High frequency inertial-internal wave oscillations were also investigated. The inertial oscillations were intermittent and showed evidence for downward energy propagation. Mean energy level and lack of correlation between low frequency currents and internal wave energy suggests that the bottom topography is not a strong source of high frequency internal wave energy in our data.
North American stratigraphic principles as developed by geologists mapping on continents can be applied to deep-sea sediments. The ability of the Deep Sea Drilling Project to obtain long cored intervals at many ocean basin sites can provide sufficient data for the definition and recognition of rock-stratigraphic units (e. g. , formations). Deep-sea sediments should be divided and reported in terms of distinctive lithologic units, which may be assigned rock-stratigraphic names if there is reasonably good evidence of their continuity. This practice is preferable to current stratigraphic practices in oceanography of designating sediments in chronostratigraphic terms. The generally accepted North American usage of formation as a mappable lithologic unit devoid of any connotation is recommended over the European usage of formation which commonly is actually a chronostratigraphic unit correlated across major facies changes. Diagrams show data.
Examination of the core records of the first 370 holes of the Deep Sea Drilling Project (DSDP) reveals that manganese nodules are relatively uncommon in the stratigraphic column and that at least 42% of the nodules are from a restricted time period, the Pleistocene. It is suggested that manganese nodules have a more widespread occurrence at present than in the geological past and that the onset of high bottom current velocities approximately 3.5 million years ago as suggested by Kennett and Watkins has been a major influence in favouring nodule growth throughout much of the Pacific. Fossil manganese nodules from Timor formed during the Cretaceous when the present Antarctic circumpolar current was deflected north of Australia.
We report here that a manganese nodule from the Central Pacific manganese nodule province has been dated by fossil diatoms found in mud scraped from near the nodule's centre. The nodule was taken at DOMES Site B from Core B55-56 at 11°50.3'N and 137°28.2'W in a water depth of 4,892 m. It was resting on the sediment surface, with about 1.5 cm of the nodule bottom (of a total nodule height of 4.2 cm) buried in the mud. The top surface of the nodule was covered with a smooth manganese coating, but the bottom had a very rough, crusty texture. It was found that recent mud had leaked in through cracks in the nodule bottom, but that there were no pre-Pleistocene diatoms in this material. The date obtained was compared with the growth rate determined by the 230Th excess method and found to be in reasonable agreement. This study adds to the work of Harada1,2 on the biostratigraphy (mainly coccoliths) of manganese nodules.
Fifty radiolarian events of early Pleistocene and Neogene age were identified in an E-W transect of equatorial DSDP sites, extending from the Gulf of Panama to the western Pacific and eastern Indian Oceans. Our objective was to document the degree of synchroneity or time-transgressiveness of stratigraphically-useful datum levels from this geologic time interval. We restricted our study to low latitudes within which morphological variations of individual taxa are minimal, the total assemblage diversity remains high, and stratigraphic continuity is well-documented by an independent set of criteria. Each of the five sites chosen (503, 573, 289/586, 214) was calibrated to an “absolute” time scale, using a multiple of planktonic foraminiferal, nannofossil, and diatom datum levels which have been independently correlated to the paleomagnetic polarity time scale in piston core material. With these correlations we have assigned “absolute” ages to each radiolarian event, with a precision of 0.1–0.2 m.y. and an accuracy of 0.2–0.4 m.y. On this basis we have classified each of the events as either: (a) synchronous (range of ages <0.4 m.y.); (b) time-transgressive (i.e., range of ages > 1.0 m.y.); and (c) not resolvable (range of ages 0.4–1.0 m.y.).
An attempt is made to outline a satisfactory general theory for the formation of Pacific deep-sea manganese nodules based
on a consideration of the time of initiation of formation of the nodules, a mechanism of maintenance of the nodules at the
sediment surface and the role of biological productivity of the surface waters in influencing nodule characteristics. Using
this model, the principal physical, chemical and distributional features of the nodules and reasons for their differences
on a regional scale in the Pacific can be interpreted.
DOMES Site A, in the equatorial North Pacific, was surveyed in detail in an attempt to relate the distribution of nodules to sedimentation. The sea floor is characterized by a broad east-west-trending valley defined by strongly dissected highlands to the north and south. Sediment recovered from the highlands and from the north margin of the valley is late Quaternary. The associated nodules are small, often polynucleated, have smooth surface textures, and the dominant mineral is δ-MnO2. By contrast, cores along the south margin of the valley contain early Tertiary sediment; the nodules usually are large, discoidal in shape, all have a granular surface texture, and the dominant mineral is todorokite. Cores from the central part of the valley share properties with both of the above environments; the sediment is late Quaternary but the nodules are granular with dominant todorokite. The distribution of sediment and abundance of nodules is interpreted to be controlled primarily by the flow of Antarctic Bottom Water through the valley from west to east. The surface texture and mineralogy of the nodules, and possibly their chemical composition, may, in turn, be controlled by properties of the associated sediment.