33. CENOZOIC BIOSTRATIGRAPHY, PHYSICAL … · 33. cenozoic biostratigraphy, physical stratigraphy and paleooceanography in the norwegian-greenland sea, ... süchocorys biconica zone

33. CENOZOIC BIOSTRATIGRAPHY, PHYSICAL STRATIGRAPHYAND PALEOOCEANOGRAPHY IN THE NORWEGIAN-GREENLAND SEA,

DSDP LEG 38 PALEONTOLOGICAL SYNTHESIS

Hans-Joachim Schrader1, Kjell Bj^rklund2, Svein Manum3, Erlend Martini4, and Jan van Hinte5

INTRODUCTION

Leg 38 sites located in the Norwegian-Greenland Seaencompass a span of 13° of latitude from 63°21.06'N(Site 336) to 76°08.98'N (Site 344). They represent arich source of information relating to marine geologicand biologic events in this adjacent sea from the open-ing in early Tertiary to the present. The stratigraphicrecord at each site reflects, in varying degrees, thedynamic evolution of Oceanographic, sedimentary, andtectonic processes characteristic of this area.

BIOSTRATIGRAPHYSixteen sites were cored in the Norwegian-Greenland

Sea and all sites (354 cores) combined resulted in a fair-ly complete Eocene-Recent section. No Paleocene orolder sediments were recovered. The composite se-quence at Site 348 (Recent to Miocene) and Site 338(Recent to Eocene) represents an excellentbiostratigraphic reference section for the Norwegian-Greenland Sea and provides a record of majorbiostratigraphic events spanning a 50 m.y. intervalwithin this cool-temperate to subarctic province.

Microfossils throughout the sequences at Sites 338and 348 confirm that deposition during most of theEocene-Recent interval took place at a bathyal (middleto upper) depth. The uniformity of bathymetric settingis not matched by uniformity of sediment compositionand processes. A perusal of the dominant lithologiespresent within this sequence illustrates that majorvariations have occurred in terms of composition andthus reflect the dominant mode of sediment accumula-tion and transport. About 110 meters of terrigenousmuds were deposited on acoustic basement at Site 338with an abrupt change to 210 meters of biogenicsiliceous ooze, interrupted by a thin calcareous oozesequence in the late Oligocene, and followed by 60meters of a "glacial" sequence. At Site 348 ap-proximately 200 meters of siliceous biogenic sedimentsoverlie 300 meters of terrigenous muds and these areoverlain by approximately 60 meters of "glacial" sedi-

'Geologisch-Palàontologisches Institut und Museum der Uni-versitat, Olshausenstrasse 40/60, D-2300 KIEL, F.R. Germany.

2Universitetet i Bergen, Geologisk Institut Avd.B, Olaf Ryesvei 19,5014 Bergen Universitetet, Norway.

3Universitetet i Oslo, Institut for Geologi, Blindern, Oslo 3,Norway.

Geologisch-Palaontologisches Institut der Johann-Wolfgang-Goethe-Universitat, Senckenberg Anlage 32-34, D-6000 Frankfurt,F.R. Germany.

5Esso Production Research European Laboratories, 213 coursVictor-Hugo, 33321 Beglès, France.

ments. The biogenic siliceous sequence spans an inter-val from Eocene to Pliocene. The pattern of biogenicsedimentation prevailing during the Eocene to Mio-cene abruptly ended within the Pliocene whereterrigenous muds, silts, and fine sands interbedded withthin biogenic calcareous/siliceous sequences appear inabundance representing glacially/interglacially con-trolled sediments.

Figure 1 depicts an encouragingly large number ofbiostratigraphic zones delineated within the variouscored sections of prolifically fossiliferous early Eoceneto late Pleistocene sediments encountered at all sites.These zones are a product of both evolution and eco-logically induced migration of species representingmembers of the planktonic microbiota of the northernhemisphere, along with infrequent incursions of speciesfrom neighboring (Pacific and North-Atlantic) watermasses. The time-scale of Berggren (1972a) and Berg-gren and van Couvering (1974, p. 170) was used as abasis for age determination. However, apart from thecalcareous nannofossils and the silicoflagellates,"standard zonal schemes" could not be applied in thishigh latitude region, and empirical local zonations wereestablished for the different groups of fossils. Ourpreliminary zonal scheme is given in Figure 1 and dis-cussed below.

Silicoflagellate zones, as well as calcareous nan-nofossil zones or assemblages, are based on first andlast occurrences of species and are, aside from diatoms,the only source of micropaleontologic dating outsidethe Norwegian-Greenland Sea at a finer resolutionscale. In all cases, the occurrences of the index speciescan be correlated directly to the standard nan-noplankton zonation or via reference samples or sec-tions containing both fossil groups for thesilicoflagellates (compare Figure 2 in Martini andMuller, this volume).

The diatom zones defined by Schrader (this volume)allow a good scale of biostratigraphic resolution withinthe Pleistocene-Miocene interval in contrast to thelengthy intervals delineated by silicoflagellates andother zones. This may be due to the differences in ratesor evolution of diatoms in cooler provinces as opposedto other groups. Diatom zones are, for the above men-tioned interval, tied via the North Pacific DiatomZonation of Schrader (1973) and Koizumi (1973, 1975)to the Standard Equatorial Pacific Diatom Zonation ofSchrader and Burckle (in press) and can thus be cor-related to the paleomagnetic stratigraphic record andcalibrated to the absolute time scale. All zones belowthe early Miocene are roughly correlated to outsiderelevant reference sections.

1197

H.-J. SCHRADER, ET AL.

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DIATOMS

348 6 5, 15

348-8-1, 70 Rh<zosolen<a barboiZone

Thalassiosira kryophila Zone

348 9 2, 50

348 10CC

Denticula hustedrii Zone348-11 2. 85

34812 3,95 ,

348-13-3.90

348-14-3, 130

348 15 3.90338-8-2, 10 Acr>nocyclus ingens Zone338 8-4, 85 Niuschla so. 8 Zone338-9 1, 135 Scsptromh caducea Zone

338 10-1, 135 Coiαnodhcus plicatm Zone

338 11 2, 85

Rhizosolenia bu/bosa Zone

338 12 3,90

338 13, CC

Nitzschia maleinterpretaria Zone338-15-1,20

Coscinodiscus vigitans Zone338 16 2, 10

338^16 CC338-17 CC Synedra jouseana Zone

338 19 3, 40338 19 5. 135

338 20. CC

338-22 2. 115Pseudodimerogramma filiformis Zone

338-24-2, 86

•ous 1

338-26-2, 30

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338 28-2, 30

base not defined

RADIOLARIA

348-5-5. 147

348 12. CC

338-7. CC

i ichomelissa stigi Zone

338-10-2,60

ActlnommaholmdMllon

338-11-3, 135

Süchocorys biconica Zone

338-12, CC338-13, CC Cynocapsella eldholmi Zone

338-18, CC

338-19 3,80

338 21.CC

338 24 3, 62

337 11.CC

Lophocorys norvegiensis Zone

338 27 3, 76

338-29, CC

339 12, CC

343-5. CC

Figure 1. Bio stratigraphic zones for Leg 38 sediments. The upper andlower boundaries at sites are presented at which zones are estab-lished. To the left are the major geological events in the Norwegian-Greenland Sea.

1198

PALEONTOLOGICAL SYNTHESIS

DINOFLAGELLATE

CYSTS

338-8-2

338-10-2

•

338-13-5

a 338-16-2

338-17-2

338192

3382O2

33824-2

33826-5l v 338272

V

338302

338-305

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338325

3383323 338-4O1

338-41 2

338-422

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NANNOFOSSILS

NN 20

R. pseudoumbilica assemblage

»

NP 25

336 16-2. 11

338 26 1,36

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338 42 1,69

FORAMINIFERA

PLANKTONIC

2) 338-1:348-1

N. pachyderwa

338-6: 348-5

2) 1N. atlantica S

11338 32

338-37

21 partial local caπge lone

BENTHIC

11 338-1:348 1

338 6: 348-6

II 338-7:348-1C

338-11-3. 100:3

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348-19,

— -

338-26 2, 48:

348-33

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338-19-5,51

338-19-5, 141

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33837

EVENTS

- sar1—

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Norw.GreenlandSea(Talwaπi and Eldholm)

(Magnetic Anomaly 24-25)

Figure 1. (Continued).

1199


The standard low latitude radiolarian zonation,applicable for both the Atlantic and Pacific oceans,could not be used for dating Norwegian Sea sediments.All radiolarian zones (Bj^rklund, this volume) arelocal, total range or partial range zones. By compilationof several sites, 15 radiolarian zones are suggested, intime ranging from the early Eocene to the Recent.Correlations to the time scale have been made via thesilicoflagellate/diatom zonation to outside sections.

No applicable standard dinocyst-zonation (Manum,this volume) is available. Based on detailed rangestudies at Site 338 (early Eocene to middle Miocene), aprovisional local zonal scheme was made, which, whenapplied to other sites, gave reasonably good cor-relations compared with results obtained with otherfossil groups. However, it remains to work out rangesat other sites in greater detail to see which members ofthe assemblages are most diagnostic before zones canbe properly defined.

The age of the dinocyst zones is given mainly withreference to local results based on other fossil groups.Since relatively few species from Leg 38 material haveas yet been properly identified, a basis for comparisonwith previously known ranges is limited. The fact thatNeogene ranges are, as yet, poorly known is anotherlimiting factor. However, comparisons which are so farpossible, are consistent with ages based on other fossilgroups.

The standard planktonic foraminiferal zonation usedfor most other DSDP legs cannot be directly applied inthe Norwegian-Greenland Sea. The mainly tropicalspecies on which the standard zonation is based neverlived in this high latitude area. Even zonal schemesrecently established for the North Atlantic (Berggren,1972; Poore and Berggren, 1975) do not apply exceptfor the youngest part of the section. After a more de-tailed (SEM) study of the rare calcareous plankton, itmay be justified to make a high latitude zonation (VanHinte, this volume) which will consist of a few broadzones only.

The impossibility of using planktonic Foraminiferanot only results from poverty of the original pop-ulations, but is also due to the fact that most sectionscored were deposited below or near the carbonate com-pensation surface (CCS, Berger and Winterer, 1974),which, probably throughout the Tertiary, was excep-tionally shallow in the area. Most plankton tests, of alow diversity to start with, were dissolved and have notbeen preserved. Apart from extremely rare Globo-rotalia spp. in the Pleistocene of the V^ring Plateau, notone keeled planktonic test was found

Figure 1 gives a preliminary combined planktonic,calcareous benthonic and arenaceous benthonicforaminiferal zonal scheme. It obviously has a lowresolution. However, the scheme is applicable over theentire area and allows for a broad age determination ofmost of the cores. The age of the zones is based ondirect comparison with northwestern Europe and,where it was possible to check with other fossil groups,it proved to be reliable in time stratigraphic correlation.Detailed work on the Pleistocene is in progress andprobably will result in a finer subdivision. The samemay be true for the calcareous Eocene. The non-

calcareous ooze facies does not have any potential forfurther subdivision unless results of biometric studieson the zonal species allow for some. A more detailedper hole zonation with the arenaceous faunas of theclastic sections ("flysch faunas") will be of interest tointerpret depositional environment, but will not be veryuseful in correlation.

The zones marked with a (1) are local range zonesdefined by the range of their nominal species. The zonesmarked with a (2) are partial range zones defined asfollows. The Neogloboquadrina pachyderma Zone isdefined by the dominant occurrence of left-coiling N.pachyderma. The N. atlantica (S) Zone is defined by thedominance of left-coiling N. atlantica in the planktonicfauna. The (S) and the (D) stand for sinistral and dex-tral, respectively. N. atlantica (D) has a substantialnumber of dextrally coiling specimens, but nosystematic count has been made yet, and the boundaryis not necessarily at 50%. The Spirosigmoilinella sp.Zone is defined by the presence of Spirosigmoilinella sp.without Martinotiella communis and without Spiro-plectammina spectabilis.

The base of N. pachyderma Zone is considered to beabout 2.8 m.y. old. Unlike other participants of Leg 38,van Hinte is of the opinion that this coincides with thePlio-Pleistocene boundary, that is, with the base of theCalabrian stage as defined by Gignoux (1913). The"age of the Plio/Pleistocene boundary" was discussedin a report distributed among Leg 38 participants and isavailable upon request (van Hinte).

PALEOOCEANOGRAPHIC EVENTSIN THE VARIOUS FOSSIL GROUPS

Paleontological events have been observed for thevarious fossil groups and are listed in Figures 2-16 andsummarized in Figure 17.

An abundance peak of the radiolarian Hexalonchesp.A (Bj^rklund, this volume) was observed in Sam-ples 338-7, CC; 341-31-5, 17-19 cm; and 348-15-2, 30-32cm and served to correlate all these horizons under theassumption that this peak occurred time congruent atthe mentioned intervals in early late Miocene. A drasticfloral assemblage change occurred at Site 348 belowSample 16-3, 80 cm, middle Miocene, with a mass oc-currence of Stephanogonia horridus (Schrader, thisvolume), which is followed by a considerable increaseof aberrant silicoflagellates just above (Martini andMuller, this volume).

Mass occurrences of Triceratium barbadense wereobserved in Samples 338-29, CC; 339-6-2, 60 cm to 339-7-2, 70 cm; 340-3, CC; 340-7, CC; and 8, CC, lateEocene. Again this served as a basis for correlation. Anenrichment of large Archaeomonadaceae were found atSite 338, Core 27, late Eocene. High abundances ofPhaeodarians were found in Samples 348-5, CCthrough 348-7, CC.

In the lower Eocene (approximately standardcalcareous nannoplankton zones NP 11/12), the borealnannoplankton species Imperiaster obscurus has been,quite commonly, found at Site 338 (V^ring Plateau)and Site 343 (Lofoten Basin). It is also present in fairnumbers in the central North Sea Basin and to thesouth in Denmark, Northern Germany, Belgium, and

1200


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Figure 2. 5/Ye 336 summary figure with cored and recoveredintervals, major lithologies, occurrence of hiatuses and/orunconformities with upper and lower age boundaries(occurrence of siliceous and calcareous sediments andmicrofossils, paleontological events within the siliceousmicrofossil realm and in the calcareous micro fossil realm).Note: for siliceous and calcareous foraminiferal micro-fossils the total range of occurrences are plotted and notany paleontological event. The change within the marine-dinoflagellate to terrestial spore and pollen ratio from Tto M or from M to T follows. Ages are drawn from Fig-ure 1 as well as numerical ages in m.y. Finally, we have

plotted average sedimentation rates for the indicatedintervals.

England, to the southeast transported by a cold currentvia the Ural-Street down to the northern Caucasus(Martini, 1970, and unpublished data). However, itseems to be rare to the west at Site 117 on the RockallPlateau (Bukry, 1972), and could not be found in theBay of Biscay at Sites 118 and 119. The occurrence ofthis species seems to indicate a rather restricted watermass exchange between the Norwegian-Greenland Seaand the North Atlantic in early Eocene time.

The radiolarian species Arachnocalpis tumulosa wasfrequently found at Site 343. This species has not beenreported from the north Atlantic but from the westSiberian lowland (Kozlova and Gorbovets, 1966).Therefore, the radiolarian assemblage from the Nor-wegian Sea also points to a water exchange between theNorwegian Sea and the west Siberian lowland, mostlikely through the North Sea as suggested by nanno-fossils.

A remarkable abundance of Zygrhablithus bijugatuswas noted (Muller, this volume) in the late Oligocene(nannoplankton zones NP 24 and NP 25) of Site 352(Iceland-Faeroe Ridge), which was also noted at Sites116 and 117 on the Rockall Plateau (Bukry, 1972;Perch-Nielsen, 1972) indicating shallow water or near-

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1201


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shore conditions at that time for both the RockallPlateau and the Iceland-Faeroe Ridge. To the east ofthe Iceland-Faeroe Ridge at Site 336, Zygrhablithus bi-jugatus is rare throughout this interval.

In the early Miocene of Site 348 (Icelandic Plateau)Helicosphaera ampliaperta was noted in Cores 24 to 26(Muller, this volume). This species is characteristic forassemblages in standard nannoplankton zones NN 3and NN 4. It entered the North Sea Basin from the

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North Atlantic through the English Channel in Hem-moorian time (Martini, 1974). Its presence in theIcelandic Plateau area indicates once more a normal ex-change of water masses between the North Sea and theNorwegian-Greenland Sea, and a somewhat restrictedexchange between the Norwegian-Greenland Sea andthe northeastern North Atlantic, as Helicosphaeraampliaperta obviously has not been found at Site 116(Rockall Plateau), although several cores within theranges of Sphenolithus heteromorphus and Helico-sphaera ampliaperta have been recovered (Perch-Nielsen, 1972; Bukry, 1972). Whether this particulardistribution is due to a current system or to a relativelyhigh position of the Icelandic-Faeroe Ridge at that timeis open for discussion.

Neogloboquadrina pachyderma shows an unusuallywide range of morphologic variation in the upper cores(1-3) of the "glacial" section at Site 341. Specimenswith a large hole in the ultimate chamber are common,the interval septa of these individuals are dissolved.Others have bulging, but undamaged, last chambers ora thin-walled bladder on its distal side. Still others havean attached smaller individual from such a bulge orfrom a "normal" last chamber. Abnormal penultimatechambers are less common but also do occur. Similarabnormal forms were found at the other V^ring Plateausites, but are rare. And indeed, the nature of the varia-tion seems to indicate that N. pachyderma in this area

1202


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had peculiar abnormal growth and reproductionproblems; chambers of aberrant form being developedand the offspring remaining attached to the parentaltest or leaving an interiorly dissolved parental testbehind. It will be interesting to determine whether thereare A, A2, or B generation individuals. As to possibleenvironmental causes for the abnormal morphology,we could think of the influence of hydrocarbon leakagefrom nearby diapirs, or the effect of mixing two watermasses: the cool Arctic and the warm Atlantic waters.

SUBSIDENCE OF THE ICELAND-FAEROE RIDGE

Continued submergence to the Oligocene is sug-gested at Site 336 by decrease of grain size in the sedi-ments indicating deposition in deeper waters and by theratio of planktonic/benthonic foraminifera. The latterindicated inner-middle neritic environment at 45 m.y.,neritic at 37 m.y., and outer neritic to upper bathyal at30 m.y.

We have, of course, no sedimentary record from theupper Oligocene to the vicinity of the Pleistocene at thissite. Two alternative possibilities are suggested for theupper Oligocene-Pliocene hiatus at this site: (1) Sedi-ment deposition stopped at the upper Oligocene anddid not resume until the glaciation; or (2) Assume ar-bitrary amounts of sedimentation after Oligocene.

Further study of Site 336 cores is essential to indicatethe climatic changes during the Quaternary. A very

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preliminary study of core-catcher samples shows (seereport on Radiolaria and History of Ice Rafting, thisvolume) that Cores 4, 5, 8, 10, and 11 may representwarm periods, while Cores 1 through 3, 6, 7, 9, 12, and13 may indicate cold periods. Because of the largesampling interval, no precise inferences concerning thenumber of climatic oscillations can be made, but itappears that with careful and detailed study of the

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material, much data might be forthcoming. This alsoapplies for the calcareous nannoplankton.

We will attempt to interpret the information ob-tained from cores at Site 336 in terms of a model for theevolution of the Norwegian Sea via sea-floor spread-ing. In this model, the unusual elevation of the Iceland-Faeroe Ridge may be interpreted as the trail of a "hotspot" in the mantle.

There is controversy about whether the Faeroes lieon continental crust, or whether they belong geneticallyto the oceanic Iceland-Faeroe Ridge. Site 336 lies farenough away from the Faeroes, so that regardless of thecontroversy about the Faeroes, this site can be safelyassumed to be a normal part of the Iceland-FaeroeRidge.

Preliminary shipboard analysis suggests that thebasalt at this site may not be typical of the tholeiiticbasalts formed typically in mid-ocean rifts. However,the range of basalts, in Iceland, for example, which alsohas an origin by sea-floor spreading in association withan underlying hot spot, is so large that it is not possibleto rule out the formation of the basalt at Site 336through extrusion involved in sea-floor spreading. Thisargument is, of course, invalid if Iceland was notcreated by sea-floor spreading.

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At the present time, we have no direct evidence of theage of the basalt. The overlying rubble and sedimentshave been derived from the basalt by subaerial weather-ing, and the contact of these beds with the middleEocene claystones was not observed. However, if weaccept the subsidence history of this site which was dis-cussed earlier, it suggests strongly that there is no majorgap in time between the claystones, which weredeposited in shallow waters, and the basalt. If this isaccepted, the age of the basalt is also middle Eocene.This age does not conflict with that predicted under thesea-floor spreading model, since the Iceland-FaeroeRidge was created during the time between the ini-tiation of sea-floor spreading in the Norwegian Sea inthe Paleocene (about 60 m.y.) and the birth of Icelandin the late Oligocene.

If at the time of its formation, Site 336 was at or nearsea level, the highest point along the active axis of the

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Iceland-Faeroe Ridge (the spreading axis waspresumably transverse to the strike of the ridge) wasmuch higher. At the present time, the differencebetween basement elevation at Site 336 and at the topof the Iceland-Faeroe Ridge is about 950 meters. Ignor-ing erosion and subsidence due to loading, we canroughly postulate that this difference in the twoelevations has been maintained. Thus, the initial eleva-tion of the crest of the ridge at the spreading axis wasabout 950 meters. Inferring from our subsidence

theory, it would take roughly 30 m.y. for the crest of theridge to subside below sea level as it moved away fromthe spreading axis. These calculations use gross ap-proximations and assumptions, and conclusions are,therefore, tentative. However, they seem to support thepicture of a spreading ridge over a hot spot, where thehighest elevation along the spreading axis is severalhundred meters above sea level, and it takes tens ofmillions of years for the highest point to subside belowsea level.

An important shift in the spreading axis occurredabout 30 m.y. from the Norway Basin to the Iceland-Jan Mayen Ridge. It is quite possible that at the sametime a shift occurred from the Iceland-Faeroe Ridge toIceland. If this is so, we can think of the Iceland-FaeroeRidge being formed in the interval 60 m.y. to 30 m.y.By the arguments suggested earlier, this ridge wasemergent during this entire period, and only after theshift of the ridge axis did it begin to be submergedbelow sea level.

During this time the Norway Basin was closed off onthree sides by the Jan Mayen Ridge (then attached toGreenland), Iceland-Faeroe Ridge, and continentalmargin of Norway. Therefore the northern flank of theIceland-Faeroe Ridge had no connection with theNorth Atlantic. The disparity of the Oligoceneforaminiferal fauna at Site 336 with typical NorthAtlantic fauna bears this out. As the Iceland-FaeroeRidge submergence proceeded, the flow of water wouldhave been increasingly responsible for nondepositionand erosion. We are not sure how much sediment wasdeposited in Miocene and Pliocene times at Site 336,but certainly current activity must have played an im-portant role in preventing sediment to be deposited,and in possibly eroding older sediments.

GLACIATION

Major northern hemisphere glaciation was defined(Berggren, 1972c) to have been initiated approximately3 m.y.B.P. Unfortunately, Leg 38 sites did not recover acomplete sedimentary cover for this period of time ex-cept at Sites 341 and 348. How much, and if any, ismissing of the "glacial" history by erosion at the othersites cannot be calculated. Site 336 sediments were usedto calculate past fluctuations of the North Atlantic-Norwegian Current paths and thus indications ofglacial periods (Bj^lrklund, this volume). About 65%and 58% of the total radiolarian fauna were observed toconsist of Cycladophora davisiana in Samples 336-1-4,40 cm and 336-2-1, 92 cm. This species follows, in otherareas, directly the <5Oi8 curve and may be used as adirect ice-cover paleodetector (Hays et al., in press).Intervals being interpreted as representing Interglacialperiods at Site 366 demonstrate calcareous faunas andfloras of even less diversity than these from the Nor-wegian Sea area (Kellogg, 1974).

Sedimentation rates for the "glacial" sequences atthe sites north of Iceland (Site 348) is a maximum of3.7, a minimum of 1.0 cm/1000 yr, and approximately2.0 cm/1000 yr at Site 338 on the V^ring Plateau.Further studies of cores from Site 336 is essential to in-dicate climatic changes during the Quaternary. A totalof 89 samples was studied from the "glacial" sequence

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siliceous and calcareous sediments and micro-fossils, paleontological events within the sili-ceous microfossil realm and in the calcareousmicrofossil realm). See note, Figure 2.

at Site 336 for their radiolarian content (Bj^rklund, thisvolume). Unequally spaced sampling intervals and anoncontinuous sequence did not permit presenting acontinuous glacial history. However, if the presenceand absence of radiolarians and diatoms reflect climaticoscillations, 35 climatic shifts were detected from thesamples. Warmer intervals are found between Samples1-2, 35 cm to 1-4, 40 cm; 2-1, 92 cm to 2-2, 20 cm; 3-1,138 cm to 3-2, 61 cm; 4-2, 84 cm to 4, CC; 5-5, 70 cm to5-5, 125 cm; 5-6, 130 cm to 5, CC; 6-1,40 cm to 6-2, 145cm; 6-4, 145 cm to 6-5, 25 cm; 8-1, 25 cm; 8-2, 35 cm; 8-4, 25 cm to 8-6, 20 cm; 8, CC to 9-1, 125 cm; 9-2, 75 cmto 9-3, 75 cm; 9-4, 120 cm; 10-1, 75 cm; 10-2, 32 cm; 10,CC to 11-3, 110 cm; and 11, CC.

INITIATION OF NORWEGIAN SEAOVERFLOW WATER

The bottom water of the North Atlantic basincurrently forms in the Norwegian Sea as warm salineNorwegian current water cools and becomes moredense by evaporation. This dense water overflows the

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Figure 12. Site 346 summary figure with cored and re-covered intervals, major lithologies, occurrence of hia-tuses and/or unconformities with upper and lower ageboundaries (occurrence of siliceous and calcareous sedi-ments and microfossils, paleontological events within thesiliceous microfossil realm and in the calcareous micro-fossil realm). See note, Figure 2.

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Denmark Strait and the Iceland-Faeroe Ridge to formlower North Atlantic deep water or Norwegian Seaoverflow water (Worthington, 1970). Variations in bot-tom water production could be reflected in the sedi-mentary history, and only could be initiated by the in-fluence of the North Atlantic-Norwegian Sea Current.This mechanism was controlled primarily by the sub-sidence of the Iceland-Faeroe Ridge which was at adepth level to allow a considerable water mass ex-change between the North Atlantic and Norwegian Seaonly at the end of the Miocene (van Hinte, preliminarydata). Unconformities and hiatuses were observed (seeFigure 17) at almost all sites between the overlying"glacial" sediments and the underlying biogenicsiliceous sediments. The base of the Glacial sequenceswas calculated using Berggren's (1972b) data at 3 m.y.Sites on the Iceland Plateau should thus not be as inten-sively disturbed by bottom current than those moreeasterly sites (compare Figure 17). Some data on thefirst connection between the North Atlantic andNorwegian Sea water masses are believed to be gainedfrom the radiolarians.

The species Velicucullus oddgurneri is found to occurfor the first time in Samples 116-18, CC; 336-17, CC,

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and 338-19-3, 80-82 cm, being within the Naviculopsislata Zone, which stratigraphically includes the late

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Oligocene and lowermost early Miocene. V. oddgurneriis never common in North Atlantic sediments, but isquite abundant in certain intervals in Norwegian Seasediments. This is interpreted as a result of betterecological conditions, as V. oddgurneri was trans-ported from the North Atlantic into the NorwegianSea.

Typical low latitude radiolarians are practically ab-sent from Norwegian Sea sediments. However, Cyr-tocapsella tetrapera was first found in Sample 338-17,CC, dated by the silicoflagellates to the upper part ofthe N. lata Zone. C. tetrapera at Site 116, in early Mio-cene sediments, was reported by Benson (1972) to becommon to abundant. This is taken as evidence for adefinite connection of the North Atlantic andNorwegian Sea in lower-middle early Miocene. In other

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words, water exchange between the two oceans waspossible earliest at about 29 m.y. (V. oddgurneri), butdefinite at about 21 m.y. (C. tetrapera) according toradiolarians.

PLATE TECTONIC EVENTS

Talwani and Eldholm (in press) have reported andsummarized the geological history of the Greenland-Norwegian Sea, and have concluded from both seismicand magnetic measurements the following tectonicevents. These, on the other hand, should be reflected inboth sedimentological and paleontological parameters.

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T=Spore-Pollen

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341

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Figure 17. Summary figure with major lithologies, paleontologieal events, accumulation of hiatuses and unconformities,and age of basement-sill (ages within the basement signature areK/Ar dates). Sites are oriented on the basis of ascend-ing age of basement. Sites 344, 339, and 347 are omitted from this figure due to poor recovery and poor micro-paleontological data.

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In Figure 17, we have drawn most of the Leg 38 sites tothe absolute time scale as has been achieved by micro-fossil zonation. Included in this figure are majorlithologies and microfossil events for Radiolaria, cal-careous nannoplankton, silicoflagellates, diatoms,spores/pollen, and dinoflagellates. Events are definedon the basis of mass occurrences, of faunal and floralchanges, of highly variable assemblages, of changeswithin the dinoflagellate to spore and pollen ratio ex-pressed as T to M, change from terrigenous input tomarine input, and vice versa. The ranges offoraminifera represent total occurrences and should notbe considered to represent biological events. We havealso included in the basement-signature the availableK/Ar dates (Kharin et al., this volume).

1) The opening of the Norwegian-Greenland Seastarted at about magnetic anomaly 24 to 25 time, whichon the Heirtzler time scale is dated as 60-63 m.y.; thisage, on the other hand, is and has been subject to revi-sion and we have used a date of about 55 m.y. (Premoli-Silva, personal communication) which, on the otherhand, fits well with our findings. The oldest marinemicrofossil-bearing sediment at Sites 343 and 338belongs to nannoplankton zone NP 12, which isdefinitely of early Eocene age. Anomaly 24 is found inthe Norwegian Sea, but anomaly 25 is not. Sedimentsare mainly terrigenous, but siliceous and calcareousmicrofossils are present. At this time Norway andGreenland broke apart at the Jan Mayen FractureZone. Nannoplankton and diatom assemblages in-dicate a restricted connection between the Norwegian-Greenland Sea and the North Atlantic Ocean (comparediscussion on Imperiaster obscurus) The radiolarianfauna recovered from Site 343 have species in commonwith early Eocene radiolarian faunas described fromwestern Siberian lowland sections, supporting a con-nection between the Norway Basin and the ArcticOcean via the North Sea Basin and further to the East.

2) From the time of early opening to approximatelymagnetic anomaly 20, the connection between the Nor-wegian-Greenland Sea was advanced to form oneocean. Magnetic anomaly 20 is dated on the Sclater etal. (1974) time scale as 46.5 m.y. The manifestation ofthis connection is demonstrated by the hiatus at Sites343 and 338, and in a change from predominantly ter-rigenous sediments to biogenic siliceous sediments atSite 338.

3) From the time of connection between theGreenland-Norwegian Sea to about anomaly 13 time,the Labrador Sea was also opening and the motion ofGreenland was northwest to Eurasia. This is evidencedin a greater opening of the Norwegian Sea, whileGreenland slid past the Barents Shelf and Svalbard.Thus, the Greenland Sea did not open until aftermagnetic anomaly 13 time (38 m.y.). Thus, a limitedconnection between this basin and the Arctic Ocean didnot exist and was blocked by a land connection betweenGreenland and Svalbard. Calcareous and siliceousfaunas and floras do show great similarities with thosefound of the same age along the Caucasus mountains.There was a connection between the Norwegian Seathrough the Viking Graben (Talwani and Eldholm, inpress, fig. 17) to the North Sea Basin and further east.

During the most part of the Oligocene, the diatomassemblages are partly of endemic character and canhardly be correlated to any other floras outside thisarea. The high abundance of marine benthonic speciesaccounts for a rather restricted and partly shallow basinwith abundant littoral and sublittoral diatoms bloom-ing along its margins.

4) Since anomaly 13 time (approximately 38 m.y.),the opening of the Norwegian-Greenland Sea can bedescribed by the separation of the Eurasian and NorthAmerican plates. During this motion Greenland movedin a nearly westerly direction with respect to Norway.The northern part of the Knipovich Ridge axis hasprobably migrated eastward since its inception at aboutanomaly 13 time. Magnetic anomaly 13 time has beendated as being 36 m.y. on the Heirtzler time scale and38 m.y. on the Sclater et al. (1974) time scale. Our datasupport the latter date. This was the time at which thefirst direct connection between the Arctic Ocean andthe Norwegian-Greenland Sea was established alongthe Knipovich Ridge. This inflow of Arctic water causedthe hiatus at Sites 338 and 346, and may be responsi-ble for the pure calcareous ooze at Site 338. The sametype of pure calcareous ooze is also found in the Pacific(Kulm, personal communication) and may mark achange in sea level at early Oligocene time (van Andel,personal communication) associated with a loweredCCS. Again, a drop of sea level can provide a higher in-put of marine benthonic diatom species into pelagicbiogenic siliceous sediments. The event can also be in-dicated by the spore and pollen/dinocyst ratio fromterrigenous to marine at Site 345 and by the absence ofany planktonic foraminifera at Site 345, Core 18.

5) Since anomaly 23 time, the opening has beenalong the Mohns and Reykjanes ridges. After the open-ing there was a probable shift in the axis at anomaly 23time to the "Extinct Axis" in the Norway basin. The"Extinct Axis" was active until about anomaly 7 time.Subsequent to anomaly 7 time, the axis jumped westseparating the Jan Mayen Ridge from Greenland. Thisnew axis of spreading jumped again before anomaly 5time to generate the presently active Iceland-Jan MayenRidge. Magnetic anomaly 7 is dated after Blakeley(1974) to be 25 m.y. and anomaly 5 to be 10 m.y. Thevarious shifts of the spreading axis are also docu-mented in the various sites by changes in the sedimentnature from terrigenous to pelagic and by various bio-logical events (compare Figure 17).

ACKNOWLEDGMENTS

We thank S. White and M. Talwani for providing us withunpublished manuscripts and steady interest for organizing apartly privately funded paleontological meeting in Februaryin Kiel. H. Lacroix helped with drafting and Frau Schmidt-mann with typing.

This paper is partly supported by the DeutscheForschungsgemeinschaft (to E. Martini and H.-J. Schrader),the Norwegian Council for Science and Humanities (Bj^rk-lund Grant D41-31-19), and the National Science Foundationof America.

REFERENCES

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Reports of the Deep Sea Drilling Project, Volume 12:Washington (U.S. Government Printing Office), p. 1085-1113.

Berger, W.H. and Winterer, E.L., 1974. Plate stratigraphyand the fluctuating carbonate line: Spec. Publ. Int. Assoc.Sediment, no. 1, p. 11-48.

Berggren, W.A., 1972a. A Cenozoic time scale—some impli-cations for regional geology and paleobiogeography:Lethaia, v. 5, p. 195-215.

, 1972b. Cenozoic biostratigraphy and paleobio-geography of the North Atlantic: In Laughton, A.S., Berg-gren, W.A., et al., Initial Reports of the Deep Sea DrillingProject, Volume 12: Washington (U.S. Government Print-ing Office), p. 965-1001.

1972c. Late Pliocene-Pleistocene glaciation. InLaughton, A.S., Berggren, W.A., et al., Initial Reports ofthe Deep Sea Drilling Project, Volume 12: Washington(U.S. Government Printing Office), p. 953-963.

Berggren, W.A. and van Couvering, J.A., 1974. The LateNeogene: biostratigraphy, geochronology and paleo-climatology of the last 15-million years in marine and con-tinental-sequences: Pal., Pal., Pla., v. 16, p. 1-216.

Blakeley, R.J., 1974. Geomagnetic reversals and crustalspreading rate during the Miocene: J. Geophys. Res.,v. 79, p. 2979-2986.

Bukry, D., 1972. Further comments on coccolith stratig-raphy, Leg 12, Deep Sea Drilling Project. In Laughton,A.S., Berggren, W.A., et al., Initial Reports of the DeepSea Drilling Project, Volume 12: Washington (U.S.Government Printing Office), p. 1971-2083.

Gigmoux, M., 1913. Les formations marines pliocenes etquaternaires de 1'Italie du Sud et de la Sicile: Ann. Univ.Lyon, N.S., No. 1, fasc. 36, 693 p.

Hays, J.D., Lozano, J., Shackleton, NJ., and Irwing, G., inpress. An 18.000 BP reconstruction of Atlantic andwestern Indian Ocean sectors of the Antarctic Ocean: InCline, R.M. and Jays, J.D. (Eds.), Geol. Soc. Am., Mem145.

Kellogg, T.B., 1974. Late Quaternary climatic changes in theNorwegian and Greenland seas: Climate of the Arctic,p. 3-36.

Koizumi, J., 1973. The late Cenozoic diatoms of Sites 183-193, Leg 19 Deep Sea Drilling Project. In Creager, J.S.,Scholl, D.W., et al., Initial Reports of the Deep Sea Drill-ing Project, Volume 19: Washington (U.S. GovernmentPrinting Office), p. 805-854.

, 1975. Neogene diatoms from the western margin ofthe Pacific Ocean, Leg 31 DSDP. In Karig, D.E., Ingle,J.C., et al., Initial Reports of the Deep Sea Drilling Proj-ect, Volume 31: Washington (U.S. Government PrintingOffice), p. 779-819.

Kozlova, G.E. and Gorbovets, A.N., 1966. Radiolarii verkh-nemelovykh i verkhne-eozenovykh otlozhenii Zapadno-Sibirskoi nizmennosti, nedra. Vses. Neft. Nauchno-issled.Geol.-Razu Inst. No. 248, p. 159.

Martini, E., 1970. Imperiaster n.g. aus dem europaischenUnter-Eozan (Nannoplankton, incertae sedis.): Sencken-berg. Lethaea, v. 51, p. 383-386.

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Poore, R.Z. and Berggren, W.A., 1975. Late Cenozoicplanktonic foraminiferal biostratigraphy and paleo-climatology of Hatton-Rockall Basin: DSDP Site 116: J.Foram. Res., v. 5, p. 270-293.

Schrader, H.-J., 1973. Cenozoic diatoms from the northeastPacific, Leg 18. In Kulm, L.D., von Huene, R., et al. Ini-tial Reports of the Deep Sea Drilling Project, Volume 18:Washington (U.S. Government Printing Office), p. 673-797.

Schrader, H.-J. and Burckle, L.H., in press. Marine diatombiostratigraphy, its correlation to other microfossilzonations and to the paleomagnetic record. In Riedel,W.R. and Saito, T. (Eds.): Symposium "Marine Planktonand Sediments," Kiel.

Sclater, J.G., Jarrard, R.D., McGowran, B., and Gartner, S.,Jr., 1974. Comparison of the magnetic time scales since thelate Cretaceous. In von der Borch, C.C., Sclater, J.G., etal., Initial Reports of the Deep Sea Drilling Project,Volume 22: Washington (U.S. Government Printing Of-fice), p. 381-386.

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33. CENOZOIC BIOSTRATIGRAPHY, PHYSICAL … · 33. cenozoic biostratigraphy, physical stratigraphy and paleooceanography in the norwegian-greenland sea, ... süchocorys biconica zone