PACON 99Proceedings

Symposium on

HUMANITY AND THE WORLD OCEAN:Interdependence at the Dawn

of the New Millennium

PACON International 2000

Published by PACON International

P.O. Box 11568 Honolulu, Hawaii 96828-0568

U.S.A.

Printed in the United States of America

AGE OF MANGANESE NODULES OF THE CLARION-CLIPPERTON PROVINCE AND THE PROBLEM OF NODULE MAINTENANCE AT

THE SEDIMENT SURFACE

Max S. Barash and Svetlana B. Kruglikova

P. P. Shirshov Institute of Oceanology, Russian Academy of SciencesMoscow, RUSSIA

barash@geo.sio.rssi.ru

ABSTRACT

The radiolarian complexes were investigated in sediments, in manganese nodules located on the bottom surface mainly on a thin layer of the Quaternary sediments, and in sediment covered by manganese crust. A continuous sequence of radiolarian biostratigraphic zones from the Late Eocene to the Early Miocene (40-17 million years) and a regional hiatus between 17 and 1 million years were revealed. Age intervals of radiolarian complexes in nodules are Tertiary mainly Oligocene. The age of the crust is Quaternary, it accrued on eroded surface of the Late Oligocene clay. Deposits of the end of the Late Oligocene as well as of Miocene and Pliocene were eroded and washed away in the Quaternary by near-bottom currents. Probably the erosion began about 0.9-0.7 million years ago at the beginning of «Glacial Pleistocene» when the ocean circulation became more active. The erosion of Tertiary deposits by near-bottom currents could be intensified by an effect of strong earthquakes in tectonically active zones of transform faults and subduction. 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 form residual deposits. The same vibration effect causes ancient nodules to float up onto the surface of the Quaternary sediments. Thus, this hypothesis 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 floating up of ancient nodules to the surface of the Quaternary deposits.

INTRODUCTION

Sedimentary formations in the region between the Clarion-Clipperton transform faults in the eastern equatorial Pacific attract attention because of the need to study sedimentary processes related to the formation of manganese nodules which are widely distributed and abundant there. These nodules are of great commercial interest.

Features of sedimentary layer structure of the area were investigated by means of deep-sea drilling, seismostratigraphy, and by traditional methods (Hays, 1970; Buckry et al., 1973; Dinkelman, 1973; Van Andel and Heath, 1973; Van Andel et al., 1979; Kruglikova, 1974, 1978; Cook, 1975; Quintemo and Theyer, 1979; Piper and Fowler, 1980; Piper and Blueford, 1982; Von Stackelberg et al., 1987; Theyer et al., 1989; Dorn, 1989; Barash et al., 1993; and others). The sedimentary layer in the equatorial Pacific forms a lens with a maximum thickness of up to

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500 m. The total section cover ages range from the Upper Eocene to the Quaternary. The sedimentary strata display a folded structure. The Tertiary deposits in the wide area have undergone regional erosion. The combination of folds with the erosion relief brings sediments of different age to the seafloor surface. Often they are covered by thin Quaternary deposits. The depth of the erosion increases generally to the north of the equator so that in general earlier stratigraphic levels are exposed on the bottom surface (Van Andel and Heath, 1973). According to direct observations (Hayes, 1979; Demidova et al., 1990) recent bottom currents have small velocities insufficient for the erosion of deposits.

Quaternary sediments contain mixed complexes of Tertiary radiolarians, often with a quantitative dominance over Quaternary ones (Dinkelman, 1973; Quintemo and Theyer, 1979). In the central Pacific redeposited Eocene radiolarians are abundant in Quaternary deposits but usually absent in Miocene layers (Johnson and Johnson, 1970; Johnson, 1972). These authors concluded that erosion and redeposition of Middle Eocene up to Lower Miocene sediments mainly occurred during the Quaternary and were caused by enhanced activity of bottom currents during glacial stages.

Under a thin Quaternary layer Piper and Blueford (1982) found Early Tertiary and Early Miocene deposits. They assumed that the flow of Antarctic bottom water (AABW) prevented or temporary stopped the sedimentation. Data of the 25 cruise of R/V»Sonne» confirmed the existence of the stratigraphic hiatus between the Early Miocene and the Late Pliocene (Von Stackelberg et a l, 1987). The coincidence of the beginning of the stratigraphic hiatus in numerous sedimentary cores with the time of the activation of the AABW about 15 million years ago has resulted in the assumption that this current has become a reason of the erosion and redeposition of deposits (Dorn, 1989). Thus there are different assumptions of the beginning and duration of erosion of Tertiary sediments.

The manganese nodules are abundant on the sea-floor surface. But the deep-sea drilling has shown that they are found also in Quaternary and Tertiary sediments (Glasby, 1978). What is the age of nodules which are in Quaternary sediments or on their surface? By different methods the nodule growth rates in the eastern equatorial Pacific are estimated to be several millimeters per million years (Baturin, 1988) ajust like in the Southwestern Pacific Basin (Mangini et al., 1990). The Quaternary sedimentation rates are 0.5-1 mm per thousand years, which is higher by three orders of magnitude. These data show discrepancy of sedimentation rates and nodule growth rates. Consequently, the ages of the manganese nodules and sediments are different.

Direct micropaleontological studies of nodules are scanty (Kadko and Burckle, 1980; Janin, 1987; Skomyakova et al., 1992; Alekseyeva, 1993; Barash and Kruglikova, 1995). Interpretation of results is complicated by the fact that usually nodules have radial cracks by which the surrounding sediments with microfossils penetrate them. Some micropaleontological investigations of nodules from the Clarion-Clipperton area have shown the presence of Eocene, Oligocene and Miocene microfossils, mainly radiolarians. Sometimes Pliocene and Quaternary microfossils can be found. Therefore some authors believe that the age of nodules corresponds to this age. In a number of cases the penetration of young microfossils into cracks is proved. There are some data that in the inner parts of nodules microfossils are older than in the outer parts. Thus, there are evidences of ancient age of nodules in this area.

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This paradox of the occurrence of older nodules on younger deposits was found by many investigators. Several hypotheses for the mechanisms of floating up of the nodules were proposed: extended periods of nondeposition of sediments; removal of sediment from nodules by bottom currents and their accumulation as residual elements during regional reworking of Tertiary sediments of various ages, shaking of the bottom by seismic shocks and the effect of screen sizing (surfacing of large-sized elements in granulometrically nonuniform mixtures); microflow of «geogas»; bioturbation and uplift of nodules by bottom organisms; rheological properties of sediments; hydrodynamic features of density-stratified oceanic bottom water (Glasby, 1977, 1982; Glasby et al., 1982; Krishnaswami and Cochran, 1978; Piper and Fowler, 1980; Baturin, 1986, 1988; Barenblatt and Baturin, 1989).

Thus this area is characterized by the following features: by the regional stratigraphic hiatus; by the formation of fields of high nodules concentration on the bottom surface; by the occurrence of older nodules on younger deposits. Are these features connected? When did washing away and redeposition of deposits begin? What is the duration of erosion? We have obtained new data in addition to the available information necessary to answer these questions.

DATA

Detailed studies of sediment stratigraphy and microfossils in manganese nodules were carried out on the samples collected during the 41st cruise of the R/V»Dmitriy Mendeleev» (1988) in two survey areas. The center of the survey area M-l (8x15 miles) was situated at 10°N, 140°W, the center of the area M-2 (12x12 miles) was located at 13.5°N, 133,5°W. Samples of bottom deposits and nodules were obtained by means of gravity tubes and bottomgrabs. Some results of detailed biostratigraphic investigations of the samples obtained during the expedition were published (Barash et al., 1993; Barash and Kruglikova, 1995). In our study radiolarian, diatom and foraminifera analyses were used. The radiolarian fauna was most representative, so it was used as the basis for establishing ages.

Stratigraphy of sediments

In both survey areas Paleogene and Neogene sediments have been identified. They are mostly represented by alternating layers of low-carbonate or carbonate-free miopelagic clays and nannooozes. They are exposed on the bottom or covered by a thin layer of Quaternary deposits. In the area M-l Tertiary sediments were found at 20 of 40 stations. Their ages range from the Late Eocene to the Early Miocene. The Lower Miocene sediments (four radiolarian zones) prevail (50% of Tertiary samples). In the area M-2 Tertiary sediments were found on 22 of 68 stations. Seventy percent of Tertiary samples belong to the Oligocene, mainly to the Early Oligocene. Seafloor erosion in this region has thus affected the deeper stratigraphic horizons. Samples of Tertiary sediments in both areas make up a continuous series of biostratigraphic radiolarian and nannoplankton zones ranging from the Late Eocene to the Early Miocene and covering an age interval from approximately 40 to 17.5 million years ago.

Quaternary sediments in both areas are not thicker than tens of centimeters. Diatom analysis shows that most of the micropaleontologically characterized sediments are 0.7-0.9 million years

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old. Quaternary sediments contain large quantities of redeposited Tertiary (mainly Oligocene) radiolarians.

Thus, deposits accumulated between 40 and 17 million years B.P. were partially washed out. And deposits which could be accumulated between 17 and 1 million years are absent at all.At an average rate of sedimentation of 2 mm/kyr (Von Stackelberg et al., 1987), from 80 to 34 m of Tertiary deposits were eroded. Small-grain components of the deposits were removed by bottom currents. Coarse-grain components formed residual sediments or were included in Quaternary deposits as residual components. Microfossils of various ages, in particular skeletons of radiolaria and ichtyolites, are assigned to them (Barash et al., 1993). Naturally, massive iron manganese nodules contained in the washed out Tertiary deposits could not be removed by the bottom currents, and remained on the surface of the eroded bottom on deposits of various ages.

Thus, in our areas the only large regional stratigraphic hiatus occurs between Tertiary deposits of various ages (Eocene to Early Miocene), the Quaternary sediments overlapping them. As Tertiary deposits sometimes outcrop, it can be concluded that erosion and/or conditions of no sedimentation occur up to the present day.

Nodules

In the survey areas manganese nodules located predominately on the surface of the bottom: on the surface layer of Quaternary sediments or on outcropped Tertiary deposits. Nineteen nodules were used to determine the age of radiolaria embedded in ore matter. In total, 85 species of radiolaria were identified in the nodules (Barash and Kruglikova, 1995). Radiolaria assemblages identified in the nodules are distributed in age intervals in the following way: Late Eocene to Early Oligocene, Early Oligocene, Oligocene, Oligocene to Early Miocene, and Pliocene/Pleistocene. The last sample was taken from the outer layer of a nodule where influx of radiolaria through cracks was most probable. The age of radiolaria assemblages from various parts of the nodules has proved to be identical within determination accuracy. The statistical probability of the nodule formation age is mainly Oligocene.

Manganese crust

The question on the time of erosion and the formations of the erosion surface on which nodules from the washed out sediments have been collected, can be cleared up by new data of the microfossil study in the 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 block was obtained by a bottomgrab in the area M-2 (station 3833-13, 13°33.0' N, 133°02.0'W, water depth 4920 m). Its size is about 30x25x20 cm. It is penetrated by numerous cracks and burrows of digging organisms, contains lenses of other deposits. The samples for micropaleontological analyses were taken from the manganese crust, basic sediment, cracks, lenses, and burrows.

35 radiolarian and 2 diatom species were identified. Comparison of the known age intervals of the species (Petrushevskaya and Kozlova, 1972; Kruglikova, 1974; Johnson and Knoll, 1975; Johnson and Nigrini, 1985; Sanfilippo et al., 1985; Morley and Nigrini, 1995; Sanfilippo and Nigrini, 1998) has made it possible to determine some complexes. The Middle-Upper Eocene

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complex includes radiolarian species Dictyoprora (= Theocampe) mongolfieri and possible Lithomitra aff. elizabethae, Triceraspyris triceros, Theocyrtis tuberosa, and Arthophormis barbadensis. The Late Oligocene complex consists of two diatom species Coscinodiscus craspedodiscus and Cestodiscus pulchelus as well, as radiolarian species Arthophormis gracilis, Dendrospyris anthocyrtoides, Didymocyrtis (=Cannartus) prismatica, Orosphaerida spines, Dorcadospyris ateuchus, Theocyrtis annosa, Lychnocanoma elongata, Theocorys spongoconum, Cyclampterium pegetrum, Stichocorys subigata and possible Lithomitra aff. elizabethae, Triceraspyris triceros, Theocyrtis tuberosa, and Arthophormis barbadensis. The life intervals of the most part of these species are Early Oligocene to Early Miocene or Late Oligocene to Early Miocene.

The Quaternary complexes include radiolarian species Acrosphaera murrayana, Anthocyrtidium ophirense, Arachnocorallium calvata, Botryocyrtis scutum, Buccinosphaera invaginata, Carpocanium nigriniae, Collosphaera cribrosa, Collosphaera ortoconus, Collosphaera tuberosa, Comutella verrucosa, Euchitonia sp., Hymeniastrum euclydis, Larcospira quadrangula, Lophophena hispida, Ommatartus tetrathalamus, Pterocanium praetextum, Pterocorys minytorax, Solenosphaera zanguebarica, Spongaster tetras, Theocorythium trachelium, and a diatom species Pseudoeunotia doliolus.

The distribution of these 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. Its basis could be made by small residual nodules washed out from the Late Oligocene - Early Miocene deposits. More ancient microfossils were involved in it during the erosion of the surrounding outcrops.

DISCUSSION

It is important to note complete absence of complexes of Middle and Late Miocene and Pliocene. They are not present in the ancient clay, where they could get through cracks and burrows. They are not present in the manganese crust, where they could be involved at its increase or through cracks. They are not present in Quaternary deposits containing mixed complexes of different ages, where they could get from washed out outcrops. It is obvious that during this interval of time the present erosion surface of the Late Oligocene clay was covered by younger deposits of the Late Oligocene, Miocene and Pliocene. If this surface was exposed at the ocean bottom from a moment in Late Oligocene or in the Neogene till now, radiolarians of these ages would get in cracks, in burrows and in the increasing manganese crust, as it is now with Quaternary microfossils. It is possible to assume that the erosion and washing away of sediments by near­bottom currents from this area began in the Quaternary time.

From of diatom analysis data the age of the most part of micropaleontologically characterized Quaternary deposits is 0.7-0.9 million years. It shows a comparatively large thickness of this horizon and high activity of erosion-accumulation processes at that time. In the Quaternary sediments there are redeposited radiolarians of different age intervals from Eocene up to Pliocene got there at erosion of the appropriate deposits. The overwhelming majority of

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redeposited microfossils are of Oligocene age, that corresponds to the greatest distribution in this area of just Oligocene outcrops. However, rare Pliocene microfossils are also met. This implies that erosion removing of fine sediment fractions and redeposition of larger particles of Tertiary deposits began approximately in the Middle Quaternary time, 0.9-0.7 million years ago. This time corresponds to the beginning of the so-called «Glacial Pleistocene», to the time of the activation of continental glaciations of the Northern hemisphere. At the same time, 0.7 million years ago, the marked build-up of the eastern Antarctic ice cap began (Frakes, 1978). The increase of zonal climatic contrasts should have caused strengthening of convection processes in the atmosphere and the ocean, including strengthening of bottom currents.

However, it is doubtful whether near-bottom current, even stronger than really measured in this area, could wash away some tens of meters of densed Tertiary deposits. This could be intensified by an effect of earthquakes in tectonically active zones of the transform faults and subduction. Such zones are more than in 1000 km distant to the east from the described area, however it is known, that the effects of strong earthquakes were observed at distances of thousands of kilometers, in particular, in ground reservoirs, where seismic waves penetrate through hard rocks of their bottoms. So, the Lisbon earthquake of 1775 (the magnitude was no less than 8.5) caused appreciable waves in lakes on European territory, Holland, Switzerland, Scotland and Sweden inclusive, and the earthquake of July 9, 1958 on Alaska (the magnitude was 8.6) stirred up water in wells up to the coast of the Mexican Gulf, i.e. at a distance of four thousand km from the epicenter (Bolt et al., 1977). Certainly, such strong earthquakes are rather rare. So, in the Kuril- Kamchatka zone the periodicity of recurrence of strong earthquakes (magnitude no less than 7.75) is once per 140 years (Fedotov, 1968). However, during millions of years such periodicity can exert great influence on geological processes.

In water saturated dense medium of the ocean bottom the superficial seismic Love and Rayleigh waves should be distributed which can cause a vibration effect. The Love waves move faster and cause horizontal displacement of the medium, the Rayleigh waves move slightly slower and cause vertical moving. The interference of these waves strengthens their vibration influence on deposits.

Action of seismic vibration effect on surface sediment layer must disintegrate and stir up sediments which are then carried away by the bottom current. Large-size components of the sediment 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 Quaternary sediments (a known effect of screen sizing or surfacing of large-sized particles of a granulometrically nonuniform mixture). Thus, this hypothesis 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 floating up of ancient nodules to the surface of the Quaternary deposits.

SUMMARY

Micropaleontological investigations in two survey areas show that Tertiary outcrops are distributed on the bottom surface or under a thin layer of Quaternary sediments. The continuous sequence of radiolarian biostratigraphic zones from the Late Eocene to the Early Miocene (40-

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17 million years) and the regional hiatus between 17 and 1 million years were revealed. Quaternary sediments in both areas are not thicker than tens of centimeters. Diatom analysis shows that most of the micropaleontologically characterized sediments are 0.7-0.9 million years old. Quaternary sediments contain large quantities of redeposited Tertiary (mainly Oligocene) radiolarians.

Abundant manganese nodules occur on the bottom mainly on the surface of Quaternary sediments covering the Tertiary deposits of various ages. In nineteen nodules 85 species of radiolaria were identified. The radiolaria assemblages are distributed in age intervals from Late Eocene to Early Miocene, mainly in Oligocene. The age of radiolaria assemblages from various parts of the nodules proved to be identical within determination accuracy. 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.

Micropaleontological investigations were carried out 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 these 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.

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 erosion of Tertiaiy deposits by near-bottom currents could be intensified by an effect of strong earthquakes in tectonically active zones of the transform faults and subduction which can be affective within several thousands of kilometers. In watersaturated nonconsolidated medium of the ocean bottom the superficial seismic Love and Rayleigh waves should be distributed 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. Thus, this hypothesis suggest one and the same reason for the peculiarities of the Clarion-CIipperton zone, that is, the regional stratigraphic hiatus, the formation of the residual nodule fields, and floating up of ancient nodules to the surface of the Quaternary deposits.

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ACKNOWLEDGMENTS

The authors thank Prof. G. P. Glasby for the useful critical remarks and Prof. I. P. Kuzin for constructive discussion of a seismological hypothesis and valuable advises, and Dr. V. 'V. Mukhina for diatom analysis.

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