(Table DR1) Trace element contents in basalts from ODP Hole 33-317A

Numerous large igneous provinces formed in the Pacific Ocean during Early Cretaceous time, but their origins and relations are poorly understood. We present new geochronological and geochemical data on rocks from the Manihiki Plateau and compare these results to those for other Cretaceous Pacific plateaus. A dredged Manihiki basalt gives an 40Ar-39Ar age of 117.9+/-3.5 Ma (2 sigma), essentially contemporaneous with the Ontong Java Plateau ~2500 km to the west, and the possibly related Hikurangi Plateau ~3000 km to the south. Drilled Manihiki lavas are tholeiitic with incompatible trace element abundances similar to those of Ontong Java basalts. These lavas may result from high degrees of partial melting during the main eruptive phase of plateau formation. There are two categories of dredged lavas from the Danger Islands Troughs, which bisect the plateau. The first is alkalic lavas having strong enrichments in light rare earth and large-ion lithophile elements; these lavas may represent late-stage activity, as one sample yields an 40Ar-39Ar age of 99.5+/-0.7 Ma. The second category consists of tholeiitic basalts with U-shaped incompatible element patterns and unusually low abundances of several elements; these basalts record a mantle component not previously observed in Manihiki, Ontong Java, or Hikurangi lavas. Their trace element characteristics may result from extensive melting of depleted mantle wedge material mixed with small amounts of volcaniclastic sediment. We are unaware of comparable basalts elsewhere.

(Appendix A) Organic facies at DSDP Hole 93-603B

The Palynology of two sections recovered during Leg 93 drilling by the Deep Sea Drilling Project in the continental rise along the western margin of the North Atlantic is reported. In Hole 603B at Site 603, the dinoflagellate stratigraphy indicates that the interval from Cores 603B-82 to 603B-26 ranges in age from late Berriasian to Santonian. The BlakeBahama Formation ranges from late Berriasian to Aptian. The Hatteras Formation ranges from Aptian to Cenomanian, although the uppermost part may be Turonian. Dinoflagellate evidence from the middle part of the Plantagenet Formation indicates an age from late Coniacian or early Santonian to Santonian within the interval of Cores 603B-28 to 603B-26. Magnetic polarity evidence of the stratigraphy of the Early Cretaceous for the western North Atlantic indicates a reliable correlation with the dinoflagellate zonation. The stratigraphic sequence of palynologically defined organic facies in carbonaceous claystone lithologies in Hole 603B shows that organic stratigraphic units consisting predominantly of fecal-pellet-derived, pelagic organic matter (xenomorphic facies) alternate with units consisting predominantly of terrigenous organic matter (tracheal and exinitic facies), corresponding to that described from other sites in the North Atlantic. A terrigenous organic facies is identified for the first time from the Plantagenet Formation. The claystone organic facies and major lithofacies are closely correlated. The tracheal and exinitic facies occur in carbonaceous terrigenous claystones and claystone turbidites associated with sandstone/siltstone terrigenous turbidites. The xenomorphic facies occurs in claystones within pelagic limestones lacking any turbidites, and in blackish, noncalcareous claystones which correlate in age with the marine-carbon-rich sapropels which are widespread in the North Atlantic Cenomanian. This facies also occurs with an admixture of terrigenous organic particles in the Blake-Bahama Formation, but the mixture is consistent with the submarine fan setting of this interval. The concentration of refractory organic matter (carbonized particles) in the micrinitic and carbonized tracheal facies is considered to be the result, at least in part, of the oxidation of sediment buried below a surface slowly accumulating pelagic clays below the carbonate compensation depth. The progressive increase in number of dinoflagellate species per stage through the Early Cretaceous (except for the late Barremian-Aptian) may have resulted indirectly from the generally progressive rise in global sea level during this time. At Site 605, the dinoflagellate stratigraphy across the Cretaceous/Tertiary boundary is remarkably close to that published from the Maestrichtian and Danian of Denmark. The Maestrichtian/Danian boundary is placed precisely within Section 605-66-1 by dinoflagellate evidence, agreeing with that predicted by other microfossils. The new dinoflagellate-cyst-based genus, Pierceites and its new species P. schizocystis, and the new combination P. ( = Trithyrodinium) pentagonum (May) are proposed. Diacanthum hollisteri Habib, type species of Diacanthum, is emended to accommodat e cysts with the archeopyle formulas P3'', 2P2''-3'', 2P3''-4'', and 3P2''-3''-4''.

Geochemistry of black shales from Breitbach Creek

Lower Cretaceous sediments are frequently characterized by a well expressed cyclicity. While the processes influencing environments above the carbonate compensation depth (CCD) are reasonably well understood, almost nothing is known about the deep ocean. Cretaceous sub-CCD sediments from the Tethys and Atlantic Oceans typically show rhythmic black/green shale successions. To gain insight into the nature of these black/green shale cycles, we performed detailed geochemical analyses (X-ray fluorescence, Rock-Eval and reactive iron analysis) on a 3 m long section of latest Aptian age. The major-element distribution of the analyzed shale sequence indicates a periodic change from a high-productivity and well-oxygenated green shale mode to a low-productivity oxygen-deficient black shale mode. It is proposed here that the preservation of organic matter was dependent on the strength of salinity-driven deepwater generation. Furthermore, the data show that the Corg content covaries with changes in the detrital composition. Therefore we hypothesize that Tethyan deepwater circulation was sensitive to changes in the monsoonal system. Time series analysis suggests that these changes are periodic in nature, although we are currently unable to prove that the dominant periodicity is related to the precession component of the Milankovitch frequencies.

Paleomagnetic of DSDP Leg 91 basalts and sediments

Paleomagnetic studies were carried out on 23 basalt and 74 sediment samples from Leg 91 of the Deep Sea Drilling Project, recovered from a portion of the southwestern Pacific plate (24°S, 166°W) dating back to the Early Cretaceous to perhaps Late Jurassic. The expected geocentric axial dipole inclination at this latitude is -41°. The corrected mean stable inclination of -75° for the basalts indicates a paleolatitude of 63°S for their formation and thus 39° of northward motion during the last 100 m.y. Sediment inclinations steepen rapidly below 13-m depth in the core, suggesting little northward motion of this part of the Pacific plate until about 25 m.y. ago. Examination of the opaque minerals in polished section, as well as the Curie temperatures determined for six basalt samples, reveals no evidence of high- or intermediate-temperature oxidation and thus no reheating of the basement rock since its formation.

Paleomagnetic of igneous rocks of ODP Leg 114

A paleomagnetic study was made of 12 samples of trachytic basalt from the base of ODP Hole 698A on the Northeast Georgia Rise (southwest Atlantic) and four samples of andesitic basalt and nine samples of volcanic breccia from the base of ODP Hole 703A on the Meteor Rise (southeast Atlantic). The magnetic intensities of the Hole 703A samples are anomalously low, possibly reflecting alteration effects. The mean magnetic intensity of the Hole 698A samples is high, and compatible with the model of Bleil and Petersen (1983) for the variation of magnetic intensity with age in oceanic basalts, involving progressive low-temperature oxidation of titanomagnetite to titanomaghemite for some 20 m.y. followed by inversion to intergrowths of magnetite and other Fe-Ti oxides during the subsequent 100 m.y. These results support the interpretation of the Hole 698A basalts as true oceanic basement of Late Cretaceous age rather than a younger intrusion. Well-defined stable components of magnetization were identified from AF and thermal demagnetization of the Hole 698A basalts, and less well-defined components were identified for the Hole 703A samples. Studies of the magnetic homogeneity of the Hole 698A basalts, involving harmonic analysis of the spinner magnetometer output, indicate the presence of an unevenly distributed low-coercivity component superimposed on the more homogeneous high-coercivity characteristic magnetization. The former component is believed to reside in irregularly distributed multidomain magnetite grains formed along cracks within the basalt, whilst the latter resides in more uniformly distributed finer magnetic grains. The inclination values for the high-coercivity magnetization of five Hole 698A basalt samples form an internally consistent set with a mean value of 59° ± 5°. The corresponding Late Cretaceous paleolatitude of 40° ± 5° is shallower than expected for this site but is broadly compatible with models for the opening of the South Atlantic involving pivoting of South America away from Africa since the Early Cretaceous. The polarity of the stable characteristic magnetization of the Site 698 basalts is normal. This is consistent with their emplacement during the long Campanian to Maestrichtian normal polarity Chron C33N.

Isotopic record across the Aptian/Albian boundary of ODP Hole 171-1049C

Geochemical analyses of extraordinarily well preserved late Aptian-early Albian foraminifera from Blake Nose (Ocean Drilling Program Site 1049) reveal rapid shifts of d18O, d13C, and 87Sr/88Sr in the subtropical North Atlantic that may be linked to a major planktic foraminifer extinction event across the Aptian/Albian boundary. The abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0.8-1.4 million years at the boundary contact, but the values before and after the hiatus indicate that major oceanographic changes occurred at this time. 87Sr/88Sr increase by ~0.000200, d13C values decrease by 1.5 per mil to 2.2 per mil, and d18O values decrease by ~1.0 per mil (planktics) to 0.5 per mil (benthics) across the hiatus. Further, both 87Sr/88Sr ratios and d18O values during the Albian are anomalously high. The 87Sr/88Sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter-basin differences in seawater 87Sr/88Sr during the Albian or revision of the seawater curve. For d18O, planktic values in some Aptian samples likely reflect a diagenetic overprint, but preservation is excellent in the rest of the section. In well preserved material, benthic foraminiferal values are largely between 0.5 and 0.0 per mil and planktic samples are largely between 0.0 per mil to -1.0 per mil, with a brief excursion to -2.0 per mil during OAE 1b. Using standard assumptions for Cretaceous isotopic paleotemperature calculations, the d18O values suggest bottom water temperatures (at ~1000 -1500 m) of 8-10°C and surface temperatures of 10-14°C, which are 4-6°C and 10-16°C cooler, respectively, than present-day conditions at the same latitude. The cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid-Cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present. Because of their exquisite preservation, whole scale alteration of the analyzed foraminifera is an untenable explanation. Our proposed solution is a high evaporative fractionation factor in the early Albian North Atlantic that resulted in surface waters with higher d18O values at elevated salinities than commonly cited in Cretaceous studies. A high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and, like the Sr isotopes, implies limited connectivity among the individual basins of the Early Cretaceous proto-Atlantic ocean.

Calcareous nannofossil stratigraphy and datums of sediments from ODP Leg 198 sites

During Ocean Drilling Program Leg 198, Sites 1207, 1208, 1212, 1213, and 1214 were drilled on Shatsky Rise, coring Lower to mid-Cretaceous successions of nannofossil chalk, porcellanite, and chert. Although recovery was poor, these sites yielded an outstanding record of calcareous nannoplankton, providing valuable data concerning the evolutionary succession and paleobiogeography of the largest Cretaceous marine habitat. Mid-Cretaceous sections (Aptian-Cenomanian) were recovered at all sites, and Site 1213 includes an apparently complete Berriasian-Hauterivian section. Biostratigraphic dating is problematic in places because of the absence or rarity of zonal fossils of both Boreal and Tethyan affinity. The majority of nannofossil assemblages are relatively typical of this age, but there are clear differences that set them apart from coeval epicontinental assemblages: for example, Lithraphidites carniolensis is common to abundant throughout and was most likely an oceanic-adapted taxon; the cold- to temperate-water species Crucibiscutum salebrosum, Repagulum parvidentatum, and Seribiscutum primitivum are entirely absent, indicating the persistence of tropical, warm surface water temperatures; and the warm-water species Hayesites irregularis is common. Most striking, however, is the virtual absence of Nannoconus and Micrantholithus, both taxa that were conspicuous and often common components of many Tethyan and Atlantic nannofloras. These forms were almost certainly neritic adapted and usually absent in deep open-ocean settings away from guyots and platforms. Other Tethyan taxa are also absent or rare and sporadically distributed (e.g., Calcicalathina oblongata, Conusphaera spp., Tubodiscus verenae, and Lithraphidites bollii), and factors related to neritic environments presumably controlled their distribution. Site 1213 also records extended Early Cretaceous ranges for species previously thought to have become extinct during the Late Jurassic (e.g., Axopodorhabdus cylindratus, Hexapodorhabdus cuvillieri, and Biscutum dorsetensis), suggesting these species became Pacific-restricted prior to their extinction. Watznaueria britannica may also have been a species with Pacific affinities before reexpansion of its biogeography in the early Aptian. One new genus (Mattiolia) and thirteen new species (Zeugrhabdotus clarus, Zeugrhabdotus petrizzoae, Helicolithus leckiei, Rhagodiscus amplus, Rhagodiscus robustus, Rhagodiscus sageri, Rhagodiscus adinfinitus, Tubodiscus bellii, Tubodiscus frankiae, Gartnerago ponticula, Haqius peltatus, Mattiolia furva, and Kokia stellata) are described from the Shatsky Rise Lower Cretaceous section.

Organic geochemistry of sediment samples from Prydz Bay

High molecular weight aliphatic hydrocarbons were extracted from sediments at two sites (741 and 742) drilled during Ocean Drilling Program Leg 119 in Prydz Bay, a major embayment on the continental shelf of East Antarctica. The distributions of n-alkanes and triterpenoid and steroid hydrocarbons suggest that the n-alkanes and steranes are mainly of terrestrial origin and that the hydrocarbons are immature to slightly mature in the Lower Cretaceous sediments and immature to mature in the Tertiary sediments. At Site 741, the Lower Cretaceous depositional sequence, which is generally characterized by immature hydrocarbons, is interrupted by sediment having more mature components, suggesting a change of source during part of Early Cretaceous time. At Site 742, the mature geochemical parameters of a Pliocene sample correlate with results reported elsewhere for Site 739. In all but one of the other Tertiary samples, the geochemical parameters indicate intermediate maturity. The Lower Cretaceous and Pliocene sediments average about 1.9% organic carbon, a value of interest from the point of view of potential sources of petroleum offshore from Antarctica.

(Table 1) Chemical composition of volcanic rocks from the Mariisky sequence and extrusive vent rocks of the Mary Cape, Schmidt Peninsula (North Sakhalin)

Early Cretaceous volcanic rocks of the Mariisky sequence and Early Cenozoic extrusive-vent rocks of the Mary Cape are exposed at the most northwest of the Schmidt Peninsula, North Sakhalin. In chemical composition, all the rocks are subdivided into four groups. Three groups include volcanic rocks of the Mariisky sequence, which consists, from bottom to top, of calc-alkaline rocks, transitional calc-alkaline-tholeiite rocks, and incompatible element-depleted tholeiites. These rocks show subduction geochemical signatures and are considered as a fragment of the Moneron-Samarga island arc system. Trace-element modeling indicates their derivation through successive melting of a garnet-bearing mantle and garnet-free shallower mantle sources containing amphibole; pyroxene; and, possibly, spinel. The mixed subduction and intra-plate characteristics of the extrusive vent rocks of the Mary Cape attest to their formation in a transform continental margin setting.

Chemical composition of rocks from the Marcus-Necker Rise

The Marcus Necker Rise has two geologically distinct parts: the western one is composed of the Marcus Wake seamounts and the eastern one of the Wake-Necker seamounts. The first contain differentiated alkali basaltoids, while the second show a distinctive prolonged and complicated history. The latter contain Early Cretaceous olivine basalts and Late Cretaceous alkali and hornblende basaltoids.

Mineral and chemical compositions of sedimentary and volcano-sedimentary rocks drilled in DSDP Legs 43 and 44

Sedimentary cover on the bottom of the Northwest Atlantic Ocean is underlain by Late Jurassic - Cretaceous tholeiite-basalt formation. It consists of come sedimentary formations with different lithologic features and age. Their composition, stratigraphic position and, distribution are described on materials of deep-sea drilling. Mineralogical and geochemical studies of DSDP Leg 43 and Leg 44 holes lead to new ideas about composition and genesis of some sediment types of and their associations. High metal contents in the chalk formation of black clays on the Bermuda Rise probably result from exhalations. Connection of red-colored and speckled deposits with hiatuses in sedimentation is shown. Main stages of geological history of the North American Basin are reflected in accumulation of the followed formations: ancient carbonate formation (Late Jurassic - Early Cretaceous), formation of black clays rich in organic matter (Cretaceous), formation of speckled clays (Late Cretaceous), siliceous-clayey turbidite formation (Eocene), hemipelagic and pelagic clayey formation (Neogene), and terrigenous turbidite formation (Pleistocene).

Composition of rocks and minerals from the Bolshoy Lyakhovsky Island (New Siberian Islands)

In the southeast of the Bolshoi Lyakhovsky Island there are outcrops of tectonic outliers composed of low-K medium-Ti tholeiitic basic rocks represented by low altered pillow basalts, as well as by their metamorphosed analogs: amphibolites and blueschists. The rocks are depleted in light rare-earth elements and were melted out of a depleted mantle source enriched in Th, Nb, and Zr also contributed to the rock formation. The magma sources were not affected by subduction-related fluids or melts. The rocks were part of the Jurassic South Anyui ocean basin crust. The blueschists are the crust of the same basin submerged beneath the more southern Anyui-Svyatoi Nos arc to depth of 30-40 km. Pressure and temperature of metamorphism suggest a setting of "warm" subduction. Mineral assemblages of the blueschists record time of a collision of the Anyui-Svyatoi Nos island arc and the New Siberian continental block expressed as a counter-clockwise PT trend. The pressure jump during the collision corresponds to heaping of tectonic covers above the zone of convergence 12 km in total thickness. Ocean rocks were thrust upon the margin of the New Siberian continental block in late Late Jurassic - early Early Cretaceous and mark the NW continuation of the South Anyui suture, one of the main tectonic sutures of the Northeastern Asia.

Geochemistry of marin ash layers and epiclastic rocks from the Kerguelen Plateau

Epiclastic volcanogenic rocks recovered from the Kerguelen Plateau during Ocean Drilling Program Legs 119 and 120 comprise (pre-)Cenomanian(?) claystones (52 m thick, Site 750); a Turonian(?) basaltic pebble conglomerate (1.2 m thick, Site 748; Danian mass flows (45 m thick, Site 747); and volcanogenic debris flows of Quaternary age at Site 736 (clastic apron of Kerguelen Island). Pyroclastic rocks comprise numerous Oligocene to Quaternary marine ash layers. The epiclastic sediments with transitional mid-ocean-ridge basalt (T-MORB) origin indicate weathering (Site 750) and erosion (Site 747) of Early Cretaceous T-MORB from a then-emergent Kerguelen Plateau, connected to Late Cretaceous tectonic events. The basal pebble conglomerate of Site 748 has an oceanic-island basalt (OIB) composition and denotes erosion and reworking of seamount to oceanic-island-type volcanic sources. The vitric- to crystal-rich marine ash layers are a few centimeters thick, have rather uniform grain sizes around 60 ± 40 µm, and are a result of Plinian eruptions. Crystal-poor silicic vitric ashes may also represent co-ignimbrite ashes. The ash layers have bimodal, basaltic, and silicic compositions with a few intermediate shards. The basaltic ashes are evolved high-titanium T-MORB; a few grains in a silicic pumice lapilli layer have a low-titanium basaltic composition. The silicic ashes comprise trachytic and rhyolitic glass shards belonging to a high-K series, except for a few low-K glasses admixed to a basaltic ash layer. Feldspar and clinopyroxene compositions fit the glass chemistry: high-Ti tholeiite-basaltic glasses have Plagioclase of An40-80 and pigeonite to augite clinopyroxene compositions. Silicic ashes have K-rich anorthoclase and minor Plagioclase around An20 and ferriaugitic to hedenbergitic clinopyroxene compositions. The line of magmatic evolution for the glass shards is not compatible with simple two-end member (high-Ti T-MORB and high-K rhyolite) mixing, but favors successive Ca-Mg-Fe pyroxene, Ti magnetite, and apatite fractionation, and K-rich alkali feldspar fractionation in trachytic magmas to yield rhyolitic compositions. Plagioclase fractionation occurs throughout. This qualitative model is in basic accordance with the observed mineral assemblage. However, as the time span for explosive volcanism spans >30 m.y., this basic model cannot comply with fractional crystallization in a single magma reservoir. The ash layers resulted from highly explosive eruptions on Kerguelen and, with less probability, Heard islands since the Oligocene. The explosive history starts with widespread Oligocene basaltic ash layers that indicate sea-level or subaerial volcanism on the Northern Kerguelen Plateau. After a hiatus of 24 m.y.(?), explosive magmatic activity was vigorously renewed in the late Miocene with more silicic eruptions. A peak in explosive activity is inferred for the Pliocene-Pleistocene. The composition and evolution of Kerguelen Plateau ash layers resemble those from other hotspot-induced, oceanic-island realms such as Iceland and Jan Mayen in the North Atlantic, and the Canary Islands archipelago in the Central Atlantic.