Deep Sea Drilling Project Data Research Articles

Rates of sediment recycling beneath the Acapulco trench: Constraints from (U‐Th)/He thermochronology

The Sierra Madre del Sur mountain range is an uplifted forearc associated with the subduction of the Cocos plate along the Acapulco trench beneath mainland southern Mexico. The shallow subduction angle, the truncation of geologic features along the modern Acapulco trench, and direct seismic and drill hole observations in the trench through deep sea drilling data suggest that subduction erosion is an important process during the evolution of this margin. Turbidites derived from the uplifted forearc are the predominant sedimentary input into this trench, while pelagic sediments are subordinate. Apatite (U‐Th)/He ages were obtained on 23 samples from two transects across the Sierra Madre del Sur (Acapulco and Puerto Escondido) and reveal slow cooling during the Miocene. (U‐Th)/He ages range between ∼25 and 8 Ma and correlate inversely with elevation. Long‐term erosional exhumation rates inferred from these ages range from 0.11 to 0.33 km/m.y., with higher rates in the range core, and suggest that the Sierra Madre del Sur has been a slowly decaying mountain range, since at least the early Miocene. Apparent Miocene‐Pliocene sedimentation (“preservation”) rates in the Acapulco trench derived from Deep Sea Drilling Project data are about an order of magnitude smaller than the Miocene forearc erosion rates estimated from (U‐Th)/He ages, suggesting that the terrigenous input to the trench was almost entirely recycled via subduction erosion, at least during the Miocene. The Miocene subducted flux per unit length of the margin is about 30 km3/(km m.y.), or a subducted volume per unit time of 44 × 103 km3/m.y., when integrated over the length of the trench.

The Cenozoic deep sea microfossil record: Explorations of the DSDP/ODP sample set using the NEPTUNE database

For 30 years the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP) have been drilling the ocean floors and retrieving sediment cores. This study presents a relational micropaleontological and stratigraphic database, Neptune, where a selection of the published studies made on these sediments is available. The selected sites and their stratigraphic extent represent a statistically reproducible subset of the whole DSDP and ODP data set as of 1995 (up to Leg 135). Cenozoic sediments from 165 globally distributed holes were dated with age/depth plots using biochronology of four marine plankton groups (diatoms, nannofossils, foraminifera, and radiolarians). Each hole’s location is available with paleogeographic coordinates. A taxonomic revision of the 8000+ reported species names was also made. The database is searchable and a variety of routines are available. Data can be exported to produce age range charts, geographic distribution maps, and occurrence charts. A rigorous evaluation of the database potentials and limitations is presented together with a summary of the published studies that have been carried on with the data. These include stratigraphic studies (diachrony of Neogene plankton, hiati distribution in Cenozoic sediments) and evolution studies (cladogenesis and evolution of one foraminiferal lineage). Unpublished data on macroevolutionary patterns (species longevity and richness, speciation and extinction rates) are presented as example of Neptune’s potential for paleobiological research. Finally, some suggestions are presented as to how Neptune can be more fully exploited through the addition of sedimentologic and isotopic data. A variety of critical sedimentologic and paleoceanographic questions could be addressed with this extended database.

Reevaluation of Early Oligocene, Eocene, and Paleocene Seawater Strontium Isotope Ratios Using Outcrop Samples from The U.S. Gulf Coast

The Cenozoic strontium isotope (87Sr/86Sr) variation in seawater is largely defined using Deep Sea Drilling Project (DSDP) samples. Examination of non‐DSDP results, particularly for the Paleogene, suggest that the original seawater curve of Burke et al. (1982) may lie above the true seawater ratio during this time. To investigate this possibility, we analyzed the 87Sr/86Sr for 230 Paleogene rock and shell samples from the 83 sites in Alabama, Mississippi, and Louisiana. Many of the samples are from classic sections on which the Gulf Coast Paleogene stratigraphy was originally defined. Multiple analyses of samples from these units show very little scatter, and in most cases, precise agreement is obtained among geographically separated collection sites. We believe that analysis of multiple samples from a unit of established age, collected at more than one site, yields results that most accurately define the actual seawater Sr isotope ratio at any given time. Results from these units define a seawater variation line that tracks well within the range of DSDP data, but is generally below the original seawater line of Burke et al. (1982). It is often assumed that samples from continental settings will exchange with high‐ratio Sr thereby raising 87Sr/86Sr values. Our Gulf Coast samples, which are derived from a continental setting, yield individual 87Sr/86Sr values that are both higher and lower than the estimated contemporaneous seawater ratio. An analysis of our Gulf Coast data and DSDP results show that the direction of isotopic exchange cannot be confidently predicted for individual samples based solely on their derivation from either continental or oceanic settings.

Mesozoic stratigraphy of the Goban Spur, offshore south-west Ireland

A Mesozoic stratigraphic framework for the Goban Spur, offshore Ireland is proposed based on results of the 62/7-1 well. This study integrates the well, Deep Sea Drilling Project data and 3000 km of seismic profiles into a stratigraphic analysis showing vertical and lateral associations of facies in the Mesozoic evolution of the basin. Basin development is believed to have been initiated during the Triassic. The discussed geological section is restricted to the Sinemurian to Maastrichtian interval. Two major hiatuses are recognized with the Late Jurassic and the Turonian absent. They reflect the ‘Middle Cimmerian’ predominantly tectonic event and a mid-Cretaceous predominantly eustatic event, respectively. Significant Middle Jurassic volcanic activity is associated with the Middle Cimmerian tectonism. The breakup unconformity is present between Late Barremian or Early Aptian and Early Albian deposits. Detailed biostratigraphic analyses and palaeoenvironmental interpretations indicate close affinities with adjacent offshore southern Ireland, southern England and eastern offshore Canada. Implications for hydrocarbon exploration are discussed with particular emphasis on the potential source and reservoir characteristics.

Eustatic, Volcanic, and Tectonic Contols on Redeposition of Shallow-Water Carbonate: A Reanalysis of Pacific DSDP Examples: ABSTRACT

On the basis of comparisons between eustatic sea level curves and occurrences of displaced shallow marine carbonate sediment in deep water Pacific DSDP (Deep Sea Drilling Project) cores, several previous workers have proposed that most displaced neritic carbonate is redeposited in the deep sea during eustatic sea level lowstands in a manner similar to siliciclastic sediment. However, reanalysis of these same DSDP data indicates a much more complex set of controls on redeposition including eustatic, volcanic, and tectonic effects. Of the 43 occurrences identified in 20 DSDP sites, eight (including all occurrences of true allodapic calcarenites) were deposited either during eustatic highstands or immediately after cessation of island-building volcanism; establishment of a shallow-water source area probably represents the dominant control on this type of deposition. Twenty-three other occurrences contain volcanic detritus mixed with minor amounts of reworked carbonate. Of these occurrences eight contain volcaniclastic sediment and exhibit no clear correlation with sea level, indicating probable redeposition of shelf carbonate during volcanic events as a result of either gravitational or seismic instability of the shelf. In contrast, the 15 other mixed volcanic/carbonate occurrences represent lowstand deposit and contain epiclastic volcanic detritus, suggesting lowstand erosion of mixed volcanic/carbonate shelf sediments. Five othermore » lowstand occurrences contain only reworked carbonate sediment and probably record either continued outer shelf/slope lowstand carbonate deposition or minor mechanical erosion of shelf carbonate. Six occurrences contain only reworked Inoceramus fragments, which are not necessarily indicative of a shelf source area.« less

Sound velocity as a function of depth in marine sediments

Additional data from sonobuoys and the Deep Sea Drilling Project (DSDP) justify separating sound-velocity-depth functions and velocity gradients (in the first layer of soft marine sediments) into some geographic areas and sediment types. Based on sonobuoy and core measurements (where V is sound velocity in km/s, and h is depth in sediments in km), the following data are obtained: continental shelf basins off Sumatra and Java—V=1.484+0.710h−0.085h2; U. S. Atlantic continental rise—V=1.513+0.828h−0.138h2; deep-sea terrigenous sediments—V=1.519+1.227h−0.473h2; and siliceous sediments of the Bering Sea— V=1.509+0.869h−0.267h2. Selected DSDP data (through leg 74) in similar areas yield: continental terrace silt–clays—V=1.505+0.712h; deep-sea terrigenous sediments—V=1.510+1.019h; and deep-sea siliceous sediments—V=1.533+0.761h. Computed velocity gradients from sonobuoy measurements are generally supported by the DSDP gradients. Only DSDP data give the following: hemipelagic sediments—V=1.501+1.151h; deep-sea calcareous sediments—V=1.541+0.928h; and deep-sea pelagic clay—V=1.526+1.046h. Where fast sediment accumulation occurs, there has not been enough time to reduce sediment pore spaces under overburden pressure; areas of slow accumulation may have relatively high sediment structural strength. Both cases have lower velocity gradients because higher porosities and consequent lower velocities persist to deeper depths.

Geology and geochronology of the line islands

Geological and geophysical studies along the entire length of the Line Islands were undertaken in order to test the hot spot model for the origin of this major linear island chain. Volcanic rocks were recovered in 21 dredge hauls and fossiliferous sedimentary rocks were recovered in 19 dredge hauls. Volcanic rocks from the Line Islands are alkalic basalts and hawaiites. In addition, a tholeiitic basalt and a phonolite have been recovered from the central part of the Line chain. Microprobe analyses of groundmass augite in the alkalic basalts indicate that they contain high TiO2 (1.0–4.0 wt %) and Al2O3 (3.4–9.1 wt %) and are of alkaline to peralkaline affinities. Major element compositions of the Line Islands volcanic rocks are very comparable to Hawaiian volcanic rocks. Trace element and rare earth element analyses also indicate that the rocks are typical of oceanic island alkalic lavas; the Line Islands lavas are very much unlike typical mid‐ocean ridge or fracture zone basalts. Dating of these rocks by 40Ar‐39Ar, K‐Ar, and paleontological methods, combined with Deep Sea Drilling Project data from sites 165, 315, and 316 and previously dated dredged rocks, provide ages of volcanic events at 20 localities along the chain from 18°N to 9°S, a distance of almost 4000 km. All of these dates define mid‐Cretaceous to late Eocene edifice or ridge‐building volcanic events. Eocene volcanic events took place from 15°N to 9°S, and Late Cretaceous events took place from 18°N to 9°S. In the southern Line Islands both Cretaceous and Eocene events took place on the same edifice or ridge, indicating recurrent volcanism at a single locality. The irregular distribution of atolls in the chain, the fact that Late Cretaceous reefs flourished along a distance of approximately 2500 km in the central and southern Line Islands, and the observation that spatially closely related seamounts exhibit different subsidence histories are interpreted as indicating that large segments of the chain have not followed a t1/2 related subsidence path. Magnetic surveys of 11 seamounts show that four of the seamounts, from the central Line chain, give virtual geomagnetic poles which fall well to the north of virtual geomagnetic poles of Cretaceous seamounts. These four poles agree with other paleomagnetic data of middle‐late Eocene‐early Oligocene age from the Pacific. One of these four seamounts yielded a 40Ar‐39Ar total fusion age of 39 Ma. Because the poles of all four seamounts fall into a tight group we infer that they are probably of middle‐late Eocene age to early Oligocene age. The other three seamounts as well as one seamont from the Line Islands analyzed previously all give virtual geomagnetic poles which agree with Late Cretaceous paleomagnetic data from the Pacific. Of these four seamounts, three give Late Cretaceous 40Ar‐39Ar ages ranging from 71 to 85 Ma; another, in the southern Line Islands, is interpreted, on paleontological evidence, to be of Late Cretaceous age. The origin of the Line Islands has been ascribed by previous workers to the effects of a single hot spot and to the action of four hot spots. The single hot spot model cannot account for all of the volcanic edifices in the Line Islands, although it does explain a general age progression of 9.6±0.4 cm/yr from north to south along the chain derived from a number of dated edifices. The four hot spot model accounts for more of the dated volcanic edifices but still does not explain all of the available data. The petrologic data argue against a mid‐ocean ridge or transform fault origin proposed by earlier workers. The complex volcanic province represented by the Line Islands remains a challenge to existing models for the origin of midplate volcanism in the Pacific. An atoll drilling program which could determine edifice building histories, paleolatitudes of seamount formation, and subsidence rates and patterns in the Line Islands is needed.

Marine geology of the Hess Rise: 2. Basement morphology, sediment thickness, and structural geology

The basement morphology and sediment thickness of the Hess Rise, an oceanic plateau in the central North Pacific, have been mapped on the basis of seismic reflection profiles. The acoustic stratigraphy on and around the rise is correlated with the lithostratigraphy at Deep Sea Drilling Project sites 464, 310, 465, and 466. A total sediment isopach chart of the rise reveals small‐scale departures from the expected sedimentary pattern (thick sediment in shallow areas; thin sediment in deep areas). Sediment‐filled basement depressions result from mass transport; thin sediment (<50 m) occurs on steep scarps, basement ridges, and areas affected by bottom currents. A pre‐Senonian sediment isopach chart shows a thickening from less than 50 m to more than 250 m of sediment from the northeast to the southwest. This trend seems explainable only in terms of the time‐transgressive nature of seafloor formed at a mid‐ocean ridge. The axial trend of the rise (N30°W) parallels nearby Mesozoic magnetic lineations and seems to be isochronous as deduced from the Deep Sea Drilling Project data. The Hess Rise began developing in late Aptian time along a segment of the Pacific‐Farallon Ridge. Important events in the history of the rise are late‐stage volcanism on the southern margin of the rise along the Mendocino Fracture Zone, tectonism and volcanism about 85 Ma that resulted in a major regional unconformity (reflector C), and another period of tectonism and volcanism between 65 and 43 Ma that coincided with the formation of the Emperor Seamounts and created structural benches on the western side of the rise. A significant change in the paleoenvironment that apparently occurred around the Paleogene‐Neogene boundary (∼25–20 Ma) caused pronounced changes in the depositional environment and resulted in another major regional unconformity (reflector A).

The Probable Range Concept Applied to the Biostratigraphy of Marine Microfossils

The probable range of a taxon is its most frequently observed range defined for a set of geologic sections. The probable range concept is defined and demonstrated using two applications, both based on Deep Sea Drilling Project data. The first uses a Cenozoic and Mesozoic North Atlantic Ocean data set (calcareous nannoplankton, 228 taxa, 55 sections). The major result is a standardized rangechart at a definable level of minimum confidence for the data set that shows excellent correlation when compared with published range data. The second application uses a Pacific Ocean data set (calcareous nannoplankton, planktonic foraminifera, Radiolaria, 330 taxa, 32 sections). The application results in an estimated maximum attainable resolution of 100,000 years for the Tertiary. The quantitative application of the probable range concept offers the improvement of resolution beyond the 100,000 year level, equally reliable alternatives to standard biostratigraphic zonations, and objective limits of confidence or risk of error in using biostratigraphic sequence trends for age and paleoenvironmental interpretations.

Prediction of velocity-gradients in seafloor sediments

An acoustic model for unconsolidated sediments [R. D. Stoll and G. M. Bryan, J. Acoust. Soc. Am. 47, 1440–1447 (1970)] was used to predict velocity gradients of dilatational and shear waves in two representative seafloor materials (quartz sand and calcareous clay). Sediment porosity and permeability were treated as functions of depth. Porosity profiles were based on Deep Sea Drilling Project data. Permeability was calculated from porosity using empirical formulae. The complex bulk and shear rapdull of the skeletal frame were treated as functions of overburden pressure, using empirical relations obtained from experiments in soil mechanics. Predicted velocity gradients for compressional waves in clays and sands range from 0.3–2.2 s−1; these results agree closely with values published in the geophysical literature. Predicted gradients for shear waves in clays range from 2.4 s−1 near the sediment-water interface to 1.0 s−1 at a depth of 500 m; these results fall within a range of shear-wave gradients predicted from in-situ measurements of saturated terrestrial materials [E. L. Hamilton, Geophysics 41, 985–996 (1976)].

Correlation of Continental-Margin and Deep-Sea Sequences--Neogene Examples from Pacific: ABSTRACT

The Deep Sea Drilling Project (DSDP) has produced fundamental advances in Cenozoic planktonic biostratigraphy and our understanding of the Cenozoic paleo-oceanographic and paleoclimatic history of the world ocean. These new insights and data serve to increase the precision and resolution of provincial biostratigraphies and correlations commonly applied to continental-margin sequences, and thus result in more accurate reconstructions of margin histories. DSDP-IPOD Legs 18, 19, 31, 57, and 63 included drill sites close to tectonically active continental margins surrounding the North Pacific. They provide clear examples of correlation of deep-sea and epicontinental marine deposits in Mexico, California, Japan, and Korea. In particular, DSDP Site 173 off northern California h s yielded an important lower Miocene through Pleistocene (N4-N22) reference section, demonstrating the usefulness of DSDP data for interpretation of margin biostratigraphic, sedimentologic, and tectonic events on a regional scale. Multiple siliceous and calcareous plankton zones within this sequence provide an average biostratigraphic resolution of 0.5 m.y. with paleo-oceanographically induced biofacies trends marking zones of special value for interbasin correlation across latitude. Many of the planktonic datums and biofacies trends clearly defined in the thin (320 m), but nearly complete, Neogene column at DSDP Site 173 can be readily recognized in the thick paleoenvironmentally diverse and structurally disordered, continental-margin deposits now exposed along the Pacific Coast of Nort America. These correlations provide a framework for calibrating provincial biostratigraphic units; estimating rates of sediment accumulation, subsidence, and uplift in margin sequences; and hindcasting periods of increased primary productivity, variations in the oxygen-minimum layer, and deposition of sediments favorable for hydrocarbon generation. End_of_Article - Last_Page 473------------

Volcanogenic effects on the rates of deposition of sediments in the Northwest Pacific Ocean

Seven piston cores, 7–16 m long, taken between the Kuril Islands and Emperor Seamounts, have been dated using radiolarian and diatom extinction levels and correlated using volcanic ash layers. The average rate of deposition in the cores decreases from 6 cm/1000 years near the Kuril Trench to about 3.5 cm/1000 years near the seamounts. Dispersed volcanic ash is the main constituent of the cores and it comprises up to 80% of the sediments. The percentage of the ash in the sediments decreases eastward from the Kuril Islands as the rates of deposition decrease. The total thickness of the sediments in the same latitudinal belt also decreases eastward. The thickness of the sediment inferred from seismic data near the Kuril trench is about 600 m and rates of deposition are approximately 6 cm/1000 years in the Pleistocene cores. Sediment thickness near the seamounts is about 300 m, and rates of deposition are approximately 3 cm/1000 years in the Pleistocene cores. Extrapolated rates of deposition in these cores suggest that the age of the base of the sediment to the east of the Kurils is only about 10 m.y. The anomalously young age for the base of the sediments obtained by extrapolation of an assumed constant rate of deposition can be explained by Deep Sea Drilling Project data from the northwest Pacific. The sediment thickness at DSDP site 192 east of Kamchatka includes sediments from all the Cenozoic epochs except the Paleocene. Rates of deposition of sediment younger than Middle Miocene are an order of magnitude higher than those prior to this time. At DSDP sites east of Japan, either Late Miocene sediments lie directly on the basement, or sediments older than Late Miocene are very thin. Post-Middle Miocene sediments are composed primarily of glass shards. Thus, about 90% of the total thickness of sediments in the northwest Pacific is composed of sediments younger than Middle Miocene with volcanic ash as the main constituent. The volcanic ash results from the present phase of explosive volcanic activity which began in the Late Miocene in the northwest Pacific volcanic arcs.

Geologic History of Pacific Ocean: ABSTRACT

Extrapolations from Deep Sea Drilling Project data suggest that the Pacific plate may be about 200 m.y. old at its west edge, but Cretaceous volcanism has largely buried the older record. Post-Jurassic sedimentary facies patterns reflect the northwestward motion of the plate relative to the equatorial zone of high biological productivity, as well as progressively increasing sea-floor depths as newly formed crust moves away from the East Pacific Rise. The Early Cretaceous volcanism which inundated much of the older western part of the plate was succeeded during the rest of Cretaceous and Cenozoic time by the building and subsidence of long chains of seamounts as the plate moved northwestward, possibly over hot spots beneath the lithosphere. A dearth of calcareous sediments of earliest Tertiary age in the central Pacific and a prominent unconformity beneath widespread middle Eocene cherts suggest a time of erosion and dissolution by especially vigorous deep currents, perhaps associated with the creation of a high-latitude circum-Antarctic Ocean. The Pacific is about a third narrower now than during the Jurassic, owing to the opening of the Atlantic. Crustal consumption has been faster along the east side of the Pacific than on the west, resulting in a progressive eastward shift of the rise crest from its earlier more central position. Additional extra losses of old lithosphere are chargeable to Cenozoic spreading behind the western island arc systems. End_of_Article - Last_Page 663------------