USGS Science⌕ Search

SEARCH · USGS Science

Results for “Initial Reports of the D.S.D.P.”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
USGS1981

The geology of Hess Rise, central north Pacific Ocean

The geology of Hess Rise is interpreted from studies of morphology and structure, igneous petrology, sediment lithofacies, seismic stratigraphy, and paleoenvironments. Hess Rise probably formed at a triple junction, between 116 and 95 m.y. ago, in the equatorial zone of the southern hemisphere. A large archipelago, formed by volcanism, subsequently moved northward as part of the Pacific Plate and subsided. A Late Cretaceous-early Tertiary tectonic and(or) volcanic event created oceanic islands and probably influenced the normal subsidence rate. The lithofacies reflect both the northward movement under various surface water masses of differing productivity and the subsidence history, which influenced calcareous-sediment accumulation and dissolution. Hess Rise is informally divided into three physiographic or morphologic provinces: northern Hess Rise, the central platform, and southern Hess Rise. Southern Hess Rise is further subdivided into the northwestern ridge, Mellish Bank, and the eastern ridge. The structure of Hess Rise is dominated by normal faults which bound grabens and horsts. The west and south boundaries of the rise are fault scarps. Most faults trend about 345 ° on northern Hess Rise, 039° to 060° on southern Hess Rise. Igneous rocks are tholeiitic basalt on northern Hess Rise at Site 464, and trachyte at Site 465 on southern Hess Rise. The tholeiite probably is not a mid-ocean-ridge basalt; more likely it is a transitional basalt erupted during off-ridge volcanism. The trachyte at Site 465 was erupted either in shallow water or subaerially; it represents a late-stage differentiate of alkali-basalt magma. Geochemically, the trachyte is similar to late-stage eruptives on many oceanic islands. The alkali basalt clasts in Upper Cretaceous calcareous ooze at Site 466 probably record a Late Cretaceous-early Tertiary tectonic event that brought old crust above sea level, where it was eroded; alternatively, volcanism may have built the islands. Cores recovered from Holes 464, 310, 310A, 465,465A, and 466 (north to south) show three major lithofacies: limestone of mid-Cretaceous (Albian-Cenomanian) age, calcareous ooze and chalk of Late Cretaceous to Quaternary age, and pelagic clay that is Late Cretaceous to Quaternary in age at Site 464 and Eocene in age at Site 310. Minor lithofacies in the carbonates and pelagic clay include siliceous microfossils and chert. The limestone contains as much as 8.6% by weight of organic carbon. The organic-carbon-rich sediments apparently were deposited along the sides of Hess Rise, above the CCD and within a mid-water oxygen minimum, as the rise crossed the highly productive equatorial divergence. Surface sediments are influenced by present-day near-surface water-mass productivity and the depth of deposition. Above about 3000 meters calcareous ooze is deposited, and below about 4000 meters pelagic clay is dominant. Between 3000 meters and 4000 meters, greater clay contents correlate with increased water depth. The seismic stratigraphy interpreted from single-channel seismic-reflection records can be correlated with the lithofacies. Three major acoustic units apparently vary in age, composition, thickness, and geographic distribution. The lowest acoustic unit generally is acoustically opaque; it corresponds to volcanic basement. In places, however, the top parts of this unit may be well-lithified limestone or chert. The middle acoustic unit, in general strongly layered acoustically, is Albian and Cenomanian limestone, chalk, and chert on southern Hess Rise and Albian and Cenomanian chert, chalk, limestone, and clay stone on northern Hess Rise. The middle unit probably is Albian to at least lower Tertiary chalk, chert, and nannofossil ooze on the central platform. The upper acoustic unit is weakly stratified to acoustically transparent and corresponds to Upper Cretaceous to Recent nannofossil ooze on southern Hess Rise and to pelagic clay of the same age on northern Hess Rise. On the central platform, it probably corresponds to Eocene to Recent nannofossil ooze, marl, and pelagic clay

Initial Reports of the D.S.D.P.↗
USGS1981

The geologic history of the Mid-Pacific Mountains in the central North Pacific Ocean; A synthesis of deep-sea drilling studies

The Mid-Pacific Mountains constitute one of the largest aseismic rises in the central North Pacific Ocean. They have been generated by mid-plate volcanic events prior to Barremian time, but their volcanic activity continued through the remainder of the Cretaceous. Evidence of the latest stages of this volcanism are the trachytic ashes included in mid- and Late Cretaceous sediments and the presence of guyots atop the main volcanic pedestal. The thermal and volcanic history of the oldest part of the Pacific Plate and its plate tectonic movements since Cretaceous time have led to considerable horizontal and vertical movements of the Mid-Pacific Mountains. Reconstruction of their subsidence and evidence from the sediments from Site 463 suggest that they once, in Cretaceous time, constituted large, tropical volcanic islands which were covered by vegetation and which shed their erosional debris over the adjacent island slopes. Neritic fossils in Maastrichtian sediments document the presence of shoal areas until the end of the Mesozoic. Since then they have subsided to their present water depth. The horizontal movements of the Pacific Plate have carried the Mid-Pacific Mountains from a position well south of the Cretaceous equator to their present position under the unproductive surface waters of the subtropical central North Pacific Ocean. Site 463, on the western Mid-Pacific Mountains, probably crossed the equator in Maastrichtian time. Shallow-water-derived calcareous fossils are incorporated into the pelagic sediments covering the Mid-Pacific Mountains. They have been displaced from their source areas along the flanks of seamounts over the adjacent regions during times of low sea-level stands. Debris of land plants in Aptian sediments documents the presence of emergent volcanoes during that time. The pelagic sediments penetrated at Site 463 consist largely of a sequence of Cretaceous chalks, limestones, and cherts which accumulated fast and which document the presence of highly productive surface water masses around the former volcanic islands and above the shoals. The development of oxygen-deficient depositional environments and the lack of evidence for intensive reworking suggest at the same time very sluggish water movements in the meso- and bathypelagic environment during Early and mid-Cretaceous times. The Cenozoic calcareous oozes, on the other hand, are very condensed. They are interrupted in several places by hiatuses, and despite their position well above the CCD they show effects of dissolution and poor preservation of the calcareous faunas and floras. The frequency of reworked pelagic material together with the hiatuses indicate episodes of intensive renewal of the meso- and bathypelagic water masses which generated intensive sea-floor erosion and which were probably triggered by the climatic deterioration in the polar regions

Initial Reports of the D.S.D.P.↗
USGS1981

Pacific Coast coccolith stratigraphy between Point Conception and Cabo Corrientes, Deep Sea Drilling Project Leg 63

DSDP Leg 63 recovered Neogene coccoliths from south of Point Conception, California (Site 467), to north of Cabo Corrientes, Mexico (Site 473), as part of a traverse exploring the sedimentary record of the California Current along the Pacific Coast. A combination of temperate and tropical zonations were used to date Leg 63 coccolith assemblages because of intergradations of warm and cool species along the transect. Variations in the abundance and the presence and absence of Discoaster species are useful in recognizing warm-cool intergradations. New taxa described in this report include Discoaster okadai n. sp., D. sanmiguelensis n. sp., Helicosphaera californiana n. sp., H. crouchii n. sp., H. gertae n. sp., and H. vedderi n. sp.

California↗
USGS1981

Silicoflagellate stratigraphy of offshore California and Baja California, Deep Sea Drilling Project, Leg 63.

Quantitative study of middle and upper Miocene silicoflagellate assemblages from Pacific Coast Sites 467 and 469 to 472 has permitted identification of warm- and temperate-water biostratigraphic zones and the formulation of a model for relative paleotemperature values (Ts) on the basis of warm- and temperate-genera abundances. Geographic and temporal trends in Ts for Pacific Coast assemblages are indicated. Three new taxa are described: Dictyocha subclinata Bukry n. sp., Mesocena diodon borderlandensis Bukry n. subsp., and M. hexalitha Bukry, n. sp. The ranges in space and time for several species, such as Dictyocha neonautica var. cocosensis and Distephanus mesophthalmus, are increased. Regionally, barred forms of Distephanus stauracanthus become predominant over ringed forms in the upper part of the middle Miocene Distephanus stauracanthus Subzone.

California↗
USGS1982

Cenozoic silicoflagellates from offshore Guatemala, Deep Sea Drilling Project Site 495

Diverse lower Miocene to Pleistocene silicoflagellate assemblages occur at Deep Sea Drilling Project Site 495, but many samples are dominated by one or two taxa. Low-latitude zonation can be applied throughout. Cool-indicating Distephanus speculum s. ampl. is only abundant in the upper Miocene; however, relative paleotemperature values (Ts) suggest temperature extremes in the lower Miocene similar to those in the upper Miocene. The lower upper Miocene ap pears to be thinned or missing, because no Dictyocha brevispina Zone assemblages are identified. The lower Miocene assemblages of the Naviculopsis ponticula Zone are an important silicoflagellate reference because of several new taxa and associations. New taxa and recombinations described herein include: Corbisema triacantha var. nuda n. var., Dictyocha angulata n. sp., D. delicata n. comb., D. delicata var. bisecta n. var., D. longa n. sp., D. longa var.paxilla n. var., D. ornata ornata n. comb., D. ornata africana n. subsp., D. subaculeata n. comb., Distephanus crux parvus n. comb., D. crux scutulatusn. subsp., D. polyactis var. literatusn. var.,Z speculumpatulus n. subsp., Naviculopsis contraria n. sp., N. lacrima n. sp., N. lata var. obliqua n. var., N. ponticula spinosa n. subsp

Initial Reports of the D.S.D.P.↗
USGS1983

Upper Cenozoic silicoflagellates from offshore Ecuador, Deep Sea Drilling Project Site 504

Diverse and abundant late Miocene to Pleistocene silicoflagellates at DSDP Site 504 can be correlated by tropical biostratigraphic zones and relative paleotemperature values to eastern tropical Pacific reference site DSDP 503A farther to the west. Early Pliocene assemblages, which were poorly known until now, are present and can be correlated locally between DSDP Holes 504, 503A, and 495, using species events associated with the new Dictyocha pulchella Subzone and Dictyocha angulata Subzone. Silicoflagellate relative paleotemperature values show major warming at 4.7 to 5.0 Ma (Cores 45-48), 3.4 to 3.8 Ma (Cores 32-33), 1.5 to 1.7 Ma (Cores 12-16), and 0.5 to 0.8 Ma (Cores 3-6). Major coolings occurred at 5.0 to 5.1 Ma (Core 51), 3.9 to 4.4 Ma (Cores 38-44), and 1.0 to 1.3 Ma (Cores 8-10). The appearance of Dictyocha longa is proposed to replace the asperoid/fibuloid ratio reversal as the bottom of the Dictyocha fibula Zone, because the non-evolutionary ratio reverses several times in the upper Miocene of Hole 5O3A, and at least once in Hole 504. Three new Pliocene silicoflagellates are defined: Dictyocha concinna Bukry, n. sp., D. helix Bukry, n. sp., and D. tamarae Bukry, n. sp.

Initial Reports of the D.S.D.P.↗
USGS1984

Geologic evolution, sedimentation, and paleoenvironments of the Angola Basin and adjacent Walvis Ridge: Synthesis of results of Deep Sea Drilling Project Leg 75

The section recovered at Site 530 (Holes 53OA and 530B) consists of eight sedimentary units and one basalt unit. The composition of the basalt recovered in Hole 53OA is distinct from typical mid-ocean ridge basalts (MORBs) but is similar to that of Hawaiian tholeiites and basalt from the central part of Walvis Ridge. Throughout most of its history, the southern Angola Basin received large volumes of redeposited material in the form of turbidites and, most recently, debris-flow deposits. Most of this material was derived from Walvis Ridge to the south, but thickness trends of acoustic units suggest that some of the sediment was derived from the African continental margin to the east. The basal sedimentary unit (Albian to Santonian) at Site 530 contains 262 beds of black shale that are interbedded with green and red claystone. Black shale makes up less than 10% of the total section, but in two cores of early Turonian age, black shale beds compose about 50% of the section. The black shales contain up to 19% organic carbon (average of about 5%) that is mainly of autochthonous marine origin but with significant contributions from terrigenous organic matter. The origin of these more- and less-reduced interbedded lithologies with varying amounts and types of organic matter, and variable amounts of pelagic, hemipelagic, and turbiditic sediment is complex and cannot be explained by any one simple process. Many factors affecting the concentration of dissolved oxygen in the bottom waters of the Angola Basin varied throughout the middle Cretaceous to produce bottom-water conditions that fluctuated between mildly oxic and oxygen-deficient, but most of the time bottom-waters and sediment-interstitial waters were sufficiently oxic to permit the accumulation of red oxidized sediment. A relatively complete sedimentary record of the Cretaceous/Tertiary boundary was recovered within a sequence of mudstone and marlstone turbidites in Hole 530A. There is a significant increase in the concentration of iridium above background levels at the boundary. High concentrations of many other elements also occur within the same stratigraphic interval as the iridium anomaly. Furthermore, there is a marked decrease in CaCO3 in the Tertiary strata above the iridium anomaly which suggests that the production of shallow-water carbonate also may have been affected by whatever caused elevated concentrations of iridium and other elements. These observations are consistent with the asteroid-impact theory proposed to explain the worldwide occurrence of an iridium anomaly at the Cretaceous/Tertiary boundary. The Cenozoic history of the Angola Basin was controlled mainly by (1) restriction of bottom-water flow from the south by Walvis Ridge; (2) development of glaciation on Antarctica; (3) opening of circulation passages in the southern oceans; (4) rapid turnover of cold, nutrient-rich waters that resulted in high productivity of diatoms; (5) influx of terrigenous sediment mainly by turbidity currents; and (6) production and preservation of carbonate sediment. The most distinctive Cenozoic event recorded in the section at Site 530 is the beginning of extensive glaciation on Anarctica and concomitant initiation of modern thermohaline bottom-water circulation that is manifested as a middle Eocene to middle Oligocene unconformity or compressed section accompanied by a drastic decrease in accumulation of CaCO3. Diatom abundances in HPC cores from Walvis Ridge (Site 532) and Angola Basin (Hole 53OB) indicate that Benguela upwelling in these areas began in the late Miocene, reached a peak in the late Pliocene to early Pleistocene, and declined thereafter. Short-term variations in sediment composition at Site 532 are manifested as cyclic variations in concentrations of clay, CaCO3, and organic carbon with average periodicities of about 30-60 k.y. The main variability that produced the cycles probably was the influx of terrigenous clastic material which diluted the CaCO3. The sediment at Site 532 also contains several percent organic carbon that is dominantly of marine origin, but with significant terrigenous components. Data from multichannel seismic, gravity, and magnetic surveys were used to define the regional stratigraphic and structural evolution of Walvis Ridge and adjacent Cape and Angola basins. Six structural provinces are recognized, four on Walvis Ridge and two additional provinces that correspond to the Cape and Angola basins. The two eastern structural provinces on Walvis Ridge are underlain by continental crust. The two western structural provinces are underlain by oceanic basement. Two main directions of faults are evident in seismic profiles, one trending N 10° and one trending N 60°. The N 60° trend corresponds to the general orientation of the northern and southern flanks of Walvis Ridge as well as to the dominant direction of fracture zones. During the first phase of separation of Africa from South America (ca. 120-130 m.y. ago), a voluminous mass of volcanics was emplaced simultaneous with the emplacement of basalt in the Parana Basin of Brazil and the Kaokoveld Region of South Africa. This period of volcanism also formed the series of seaward-dipping internal basement reflectors that are characteristic of the two structural provinces of Walvis Ridge. A system of fault blocks developed in the brittle upper part of the newly formed crust. During the second phase of rifting, which ended before late Aptian, more tilted fault blocks were created in the upper brittle stratified continental crust. Magnetic lineations in basement rocks in the Angola and Cape basins in the vicinity of Walvis Ridge are not distinct but suggest that oceanic crust began to be emplaced between 120 and 112 m.y. ago (Barremian to early Aptian). At least part of the oceanic crust of the central plateau of eastern Walvis Ridge (structural province 3) may have been emplaced before any oceanic crust formed in the adjacent basins. A ridge jump occurred during the late Aptian to early Albian in the southern part of the Angola Basin which translated the previously formed oceanic crust and its overlying evaporite deposits on the South American side. Several ridge jumps occurred on both sides of Walvis Ridge during the Late Cretaceous and early Tertiary to produce a 500-km-long segment of mid-ocean ridge.

Initial Reports of the D.S.D.P.↗
USGS1984

Middle Cretaceous black shales at Site 530 in the southeastern Angola Basin

The middle Cretaceous black shale interval at Site 530 is 170 m thick and late Albian to Coniacian in age. The organic-carbon-rich sediments occur as 260 separate beds (average 4 cm, maximum 60 cm thick) and make up less than 10% of the recovered section. Associated lithologies are greenish, grayish, and reddish mudstones, marlstones, and rare limestones. Organic-carbon contents of the black shales average about 5% (maximum 16%), and of the interbedded sediments, less than 0.5%. Careful study of the sedimentary and biogenic structures and composition and review of paleoceanographic conditions in the Angola Basin indicate that a complex interplay of processes controlled black shale accumulation. Relatively low oxygen concentrations in sediment and bottom waters occurred periodically, and conditions locally may have been anoxic or near anoxic both in the basin and on the continental margin. Pelagic, hemipelagic, and turbiditic depositional processes all operated to varying degrees at different times.

Initial Reports of the D.S.D.P.↗
USGS1984

Origin and geochemistry of Cretaceous deep-sea black shales and multicolored claystones, with emphasis on Deep Sea Drilling Project Site 530, southern Angola Basin

Deep-water sedimentary sequences of mid-Cretaceous age, rich in organic carbon, have been recovered at many DSDP sites in the Atlantic Ocean. Most of these sequences have a marked cyclicity in amount of organic carbon resulting in interbedded multicolored shale, marlstone, and (or) limestone that have cycle periods of 20,000 to 100,000 years and average 40,000 to 50,000 years. These cycles may be related to some climatic control on influx of terrigenous organic matter and sediment, rates of upwelling and sea-surface production of organic matter, and preservation of organic matter related to deeper-water dissolved oxygen concentration. These variations in supply of organic matter had pronounced effects on the potential of the sediment for subsequent diagenetic changes and geochemical partitioning in adjacent beds. Many trace elements are enriched in organic-carbon-rich lithologies relative to interbedded organic-carbon-poor lithologies. Elements that are most commonly enriched are Cr, Ni, V, Cu, Zn, and Mo. The association of high traceelement concentrations with organic matter may be the result of concentration of these elements by organisms or by chemical sorption and precipitation processes under anoxic conditions. Detailed trace-element profiles from organiccarbon-rich strata at Site 530 suggest that there may be differential mobility of trace elements, with diffusion of some elements over distances of at least tens of meters. The sequence of trace-element mobility, from highest to lowest, is approximately Ba, Mn, Pb, Ni, Co, Cr, Cu, Zn, V, Cd, and Mo. Slowly deposited, oxidized clays directly overlying some black shale sequences are enriched in some metals, particularly Fe, Mn, Zn, and Cu, relative to normal pelagic clays, and this enrichment may be the result of upward migration of metals in pore waters during compaction or diffusion from the underlying black shale. Most depositional models that have been used to explain the accumulation of the organic-carbon-rich strata imply that reducing conditions in the sediments (and therefore the increased degree of preservation of organic matter) were the result of anoxic or near-anoxic conditions in oceanic bottom waters, or in a midwater oxygen-minimum zone. Evidence from several DSDP sites in the Atlantic, however, indicate that some of these middle Cretaceous "black shale" beds may be the result of variations in rate of supply of organic matter that produced anoxia or near-anoxia within midwater oxygen-minimum zones and possibly, under extreme conditions, throughout much of the bottomwater mass. Although bottom-water anoxia may have occurred during periods of organic-carbon-rich strata, it was not necessarily the only cause for accumulation of these strata. The main reason for the accumulation of organic-carbonrich strata was an increase in the relative amount of organic debris being deposited. Some of this organic debris was derived from continental-margin areas of increased production, accumulation, and preservation of organic matter from marine, terrestrial, or mixed sources and transported to slope and basinal sites by turbidity currents.

Initial Reports of the D.S.D.P.↗
USGS1984

Carbonate and organic-carbon cycles and the history of upwelling at Deep Sea Drilling Project Site 532, Walvis Ridge, South Atlantic Ocean

Detailed carbonate and organic-carbon stratigraphies were constructed from samples collected every 20 cm in a 250-m hydraulic piston core recovered at DSDP Site 532 on Walvis Ridge. This sampling interval represents about one sample every 5000 yr., based on sediment accumulation rates calculated from nannofossil biostratigraphic zones. All samples were analyzed for percent CaCO 3 , resulting in a detailed carbonate stratigraphy for the past 5.0 m.y. The samples for the top 110 m of section were also analyzed for organic carbon in order to construct a detailed organiccarbon stratigraphy for the last 2.5 m.y. The recovered section has distinct dark-light color cycles with average periodicities of 55, 58, and 30 k.y. for the Quaternary, upper Pliocene, and lower Pliocene, respectively. Periodicities of carbonate cycles are similar to the color cycles; most carbonate minima correspond to the dark parts of color cycles. The average periodicity for carbonate cycles is about 36 k.y. Darker parts of color cycles usually contain higher concentrations of organic carbon, but the organic-carbon record does not follow the cyclicity of the color cycles in detail, at least for the last 2.5 m.y. Organic-carbon cycles have an average periodicity of about 34 k.y. for the Quaternary and upper Pliocene. The cycles of CaCO 3 and color have periodicities similar to those reported from carbonate stratigraphies from the northeast Atlantic, Caribbean, and eastern equatorial Pacific. The carbonate cycles at Site 532 are the result of external forcing, probably related to global climate, that affected fluctuations in both sediment supply from the African continental margin and productivity of siliceous organisms. The organic-carbon cycles have similar periodicities and similar changes in periodicities to those of the CaCO 3 cycles. Semiquantitative estimates of diatom abundance from smear slides and concentrations of biogenic SiO 2 calculated from chemical analyses suggest that upwelling at Site 532 was minor until about 3 m.y. ago. The Benguela-Current upwelling system either began at that time or, more likely, migrated into the area of Site 532, where it prevailed until some time between about 1.2 and 0.5 m.y. ago. The increase and decline of upwelling in the area of Site 532, however, did not disturb the trend of cyclicities of carbonate and organic carbon. The latest change in conditions at Site 532 was an increase in intensity of bottom currents during the past 0.5 m.y. that winnowed nannofossils, diatoms, and clay and left a lag deposit represented by a foraminifer-rich fades

Initial Reports of the D.S.D.P.↗
USGS1983

Pressure core barrel; application to the study of gas hydrates, Deep Sea Drilling Project Site 533, Leg 76

A pressure core barrel (PCB), developed by the Deep Sea Drilling Project, was used successfully to recover, at in situ pressure, sediments of the Blake Outer Ridge, offshore the southeastern United States. The PCB is a unique, wire-line tool, 10.4 m long, capable of recovering 5.8 m of core (5.8 cm in diameter), maintained at or below in situ pressures of 34.4 million Pascals (MPa), and 1.8 m of unpressurized core (5.8 cm in diameter). All excess internal pressure above the operating pressure of 34.4 MPa is automatically vented off as the barrel is retrieved. The PCB was deployed five times at DSDP Site 533 where geophysical evidence suggests the presence of gas hydrates in the upper 600 m of sediment. Three cores were obtained holding average in situ pressures of 30 MPa. Two other cores did not maintain in situ pressures. Three of the five cores were intermittently degassed at varying intervals of time, and portions of the vented gas were collected for analysis. Pressure decline followed paths indicative of gas hydrates and/or dissolved gas. The released gas was dominantly methane (usually greater than 90%), along with higher molecular-weight hydrocarbon gases and carbon dioxide. During degassing the ratio of methane to ethane did not vary significantly. On the other hand, concentrations of higher molecular-weight hydrocarbon gases increased, as did carbon dioxide concentrations. The results from the PCB experiments provide tentative but equivocal evidence for the presence of .gas hydrates at Site 533. The amount of gas hydrate indicated is small. Nevertheless, this work represents the first successful study of marine gas hydrates utilizing the PCB.

Initial Reports of the D.S.D.P.↗