Abstract Devonian limestone and dolostone formations are superbly exposed in numerous mountain ranges of southeastern Nevada. The Devonian is as thick as 1500 m there and reveals continuous exposures of a classic, long-lived, shallow-water carbonate platform. This field guide provides excursions to Devonian outcrops easily reached from the settlement of Alamo, Nevada, ~100 mi (~160 km) north of Las Vegas. Emphasis is on carbonate-platform lithostratigraphy, but includes overviews of the conodont biochronology that is crucial for regional and global correlations. Field stops include traverses in several local ranges to study these formations and some of their equivalents, in ascending order: Lower Devonian Sevy Dolostone and cherty argillaceous unit, Lower and Middle Devonian Oxyoke Canyon Sandstone, Middle Devonian Simonson Dolostone and Fox Mountain Formation, Middle and Upper Devonian Guilmette Formation, and Upper Devonian West Range Limestone. Together, these formations are mainly composed of hundreds of partial to complete shallowing-upward Milankovitch-scale cycles and are grouped into sequences bounded by regionally significant surfaces. Dolomitization in the Sevy and Simonson appears to be linked to exposure surfaces and related underlying karst intervals. The less-altered Guilmette exhibits characteristic shallowing-upward limestone-to-dolostone cycles that contain typical carbonate-platform fossil- and ichnofossil-assemblages, displays stacked biostromes and bioherms of flourishing stromatoporoids and sparse corals, and is punctuated by channeled quartzose sandstones. The Guilmette also contains a completely exposed ~50-m-thick buildup that is constructed mainly of stromatoporoids, with an exposed and karstified crest. This buildup exemplifies such Devonian structures known from surface and hydrocarbon-bearing subsurface locations worldwide. Of special interest is the stratigraphically anomalous Alamo Breccia that represents the middle member of the Guilmette. This spectacular cataclysmic megabreccia, produced by the Alamo Impact Event, is as thick as 100 m and may be the best exposed proven bolide impact breccia on Earth. It contains widespread intervals generated by the seismic shock, ejecta curtain, tsunami surge, and runoff generated by a major marine impact. Newly interpreted crater-rim impact stratigraphy at Tempiute Mountain contains an even thicker stack of impact breccias that are interpreted as parautochthonous, injected, fallback, partial melt, resurge, and possibly post-Event crater fill.

Abstract Beach cliffs north of San Diego, California, provide superb three-dimensional exposures of an exhumed Eocene submarine-canyon complex. This interpretation is based on large-scale erosional and depositional geometries, channel architecture, lithofacies relationships, sedimentology, and micropaleontology. The canyon fill is composed of multiple, cross-cutting channels on a multitude of scales and with widely diverse lithologies. Individual channels range from subtly scoured and only a few meters (feet) deep to more than 1 km (0.6 mi) wide and up to 100 m (328 ft) deep. Photomosaics aid in analyzing bounding surfaces and lithologic patterns. An irregular sequence boundary defines the canyon base. Two stratigraphic sequences are truncated by the canyon floor; two sequences compose the canyon fill. Lagoonal and tidal deposits of the underlying Delmar andTorrey sequences are unconformably separated from bathyal units of the Ardath Sequence, which comprises the lowermost canyon interval. A second submarine-sequence boundary occurs within the canyon succession, eroding into the top of the Ardath Sequence and dividing it from the overlying Scripps Sequence. A fifth (shallow-marine) sequence, which is not described here, truncates the Scripps Sequence to the north and inland. Pleistocene wave-cut terraces plane off the Eocene interval at the top of the cliffs. The lowermost canyon section (Ardath Sequence) comprises amalgamated, pebbly, and diffusely laminated sandstones. These fine upward to convolute-bedded, fine-grained sandstones, which then grade into laminated to bioturbated silty mudstones. The mudstones fill channels that exhibit a sinuous morphology. Multiple erosional episodes scoured each channel; channel fill predominantly occurred during abandonment. Subsequent flows evacuated a multitude of cross-cutting conduits.

Based on evaluation of past results and new research, we have partitioned the distribution of the Alamo Breccia in southeastern Nevada and western Utah into six genetic Realms that provide a working model for the marine Late Devonian Alamo Impact Event. Each Realm exhibits discrete impact processes and stratigraphic products that are enumerated here. The first five form roughly concentric semicircular bands across the Devonian shallow-water carbonate platform. These are: (1) Rim Realm, where a newly defined impact stratigraphy includes both autogenic and allogenic breccias associated with the crater rim; (2) Ring Realm, where breccias are now interpreted to have formed sequentially by seismic shock, passage of the ejecta curtain, tsunami waves or surge, and runoff that accumulated over tilted terrace(s) bounded by syn-Event, ring-forming, listric faults; (3) Runup Realm, where graded breccias were stranded by tsunami surge or waves; (4) Runoff Realm, where sheet-floods carried traces of impact debris across the distal platform beds and channels filled with impact debris; (5) Seismite Realm, where near-surface beds far across the platform were uniquely deformed; and (6) Runout/Resurge Realm, where offshore channels of thick off-platform Alamo Breccia, together with large-scale olistolith(s), signal contemporaneous massive collapse of the platform margin, possibly into the central crater. Five breccia Units characterize the newly interpreted Rim Realm, in ascending order: (1) deformed target rocks, (2) injected dikes and sills, (3) chaotic fallback, (4) smeared fallback, and (5) resurge. This succession is covered by deepwater limestones deposited inside the crater rim, or across a new slope created after platform margin collapse. Unit 1 exhibits shatter-cone-like structures interpreted as impact products. Newly discovered Ordovician and probable older meter-scale clasts in Unit 3 confirm a minimum excavation depth of 1.5 km. Microscopic components in Units 3 and 4 indicate high pressures (>10 GPa), probable quenched carbonate melt, and accreted particles that may be new kinds of impact products. Postimpact tectonics and other factors obscure the full panorama, including the location and character of the missing central crater, but the assemblage of Realms offers a working model to compare with expected impact paradigms.

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Abstract The east-trending Piaui Basin off the northern Brazilian continental margin is an Atlantic-type rifted basin. The stratigraphic and structural framework of the basin is interpreted as recording wrenching during separation of South America and Africa along the equatorial Romanche Fracture Zone. Superposition of rifting and wrenching resulted in a diverse set of structures that are uncommon in Atlantic-type basins. The basin was initiated during Aptian time. The structural grain of the adjacent Precambrian Parnaiba Platform probably influenced the orientations of normal faults which strike between northeast and east-northeast. Dominantly non-marine siliciclastic sediments were deposited during the rift stage, prior to the development of a mid-Aptian (112 Ma) regional unconformity. Oblique, northeast-southwest separation of South America and Africa between mid-Aptian and early Cenomanian time, was accompanied by the deposition of thick transitional marine and marine clastic sediments. During the middle Cenomanian, the direction of sea-floor spreading between South America and Africa changed to east-west, leading to convergent wrenching between asperities of the two continents along the Romanche Fracture Zone. Rift faults are thought to have been reactivated as oblique- and strike-slip faults; other faults are interpreted as synthetic (N70° to N75°W) and antithetic (north to N20°E) strike-slip faults. Associated structures include flower structures, en echelon folds, and shale ridges (N20°E). Wrenching created a 200 km by 50 km uplifted transpressive belt (Atlantic High) in the Piaui Basin, where erosion occurred from the Late Cretaceous to the Eocene. Oligocene-Miocene shallow-marine sediments cover the Cretaceous rocks unconformably over most of the basin.

ABSTRACT Heads of submarine canyons may occur anywhere on continental margins, from river mouths to continental slopes, producing a distinctive interface between shallow- and deep-marine environments. Inception of most canyons is subaerial, fluvially cut during lowered sealevel. Submarine mass flow also commences canyon formation. Submarine erosion shapes all canyons, and is especially effective in the headward region. Sliding and slumping are volumetrically most important as erosive agents, but sand spillover, bioerosion, sand flow, sand creep, and debris flow all play a part. Fluctuating channelized currents and low-velocity turbidity currents also erode and transport sediments. Canyons alter shelfbreak circulation and sedimentation. They remove detritus from fluvial outflow, longshore transport, and cross-shelf drift, and may influence the position of rip currents. On narrow shelves, surface waves diverge over canyon heads, providing a transport corridor for the return of turbid water. Suspensates downwell along canyons as high-density nepheloid layers. Channelized currents winnow fines in upper canyon heads; focused internal tides and waves may actually break, producing more extensive erosion. Although research on modern canyon systems has rapidly increased, detailed studies of ancient canyons remain sparse. An Eocene example from Southern California contains a tripartite fill representing progressive detachment from a nearshore source during a eustatic sealevel rise. Suspensate fallout, tractional flow, and mass-flow processes formed a basal amalgamated pebbly sandstone overlain by planar- to convolute-laminated sandstone, topped by variegated cut-and-fill mudstone channels. This tributary system fed the main canyon, filled with fining- and thinning- upward complexes. The Pigeon Point and Carmelo Formations of coastal California and Tethyan submarine canyons of Czechoslovakia display similar fining-upward canyon fills. Contrasting Fill sequences include coarse-grained units that dominate French Maritime Alps and New Zealand canyon complexes, and shales that plug canyons in the Gulf Coast, Sacramento Valley, and Israel. Shelf size and gradient, rates of eustacy, tectonism, and subsidence, and sedimentary-source input and migration interact to create this diversity of fills in ancient submarine canyons. Quantified analyses of canyon formation, maintenance, and Fill, and application of sedimentary hydrodynamics to observed mass transport processes and their resultant ancient counterparts, are still needed.

Abstract I am talking to you tonight mainly because I am a survivor. Of the small group who formed the informal association of oceanographic laboratories for ocean drilling, and thought up the name JOIDES, Maurice Ewing, Fritz Koczy, and Columbus Iselin are no longer with us, nor is Harry Hess, who inspired us all. One of the values of being a survivor is that I canremember the ideas about the earth we had when we were young. This can give some perspective to the revolution in understanding that has come about during the last 15 years.

Abstract The Deep Sea Drilling Project drilled a substantial number of sites that bear on the origin of linear island and seamount chains, aseismic ridges and other more regional expressions of intraplate volcanism. Drilling in the Emperor Seamounts during Leg 55 was particularly successful. Results from this leg include: 1) the volcanoes of the Hawaiian- Emperor chain continue to increase in age away from Kilauea as predicted. 2) Suiko Seamount formed at a paleolatitide of 26.9 ± 3.5°N, 7° north of present-day Hawaii, but far south of its present latitude of 44.8°N. 3) the volcanic rock types recovered include hawaiite, mugearite, alkalic basalt and tholeiitic basalt in the sequence and relative volume expected for Hawaiian volcanoes. 4) the tholeiitic and alkalic basalts recovered are geochemically similar to those in the Hawaiian Islands, only the ratio of 87Sr/86Sr appears to change through time. All the lavas appear to be derived from a source that has small-scale heterogeneities, but is homogeneous on a large scale. 4) The Emperor Seamounts were once volcanic islands that underwent subaerial and shallow marine erosion, and deposition of shallow-water biogenic carbonate sediments that capped all or most of each volcano Drilling in other regions has yielded less conclusive results. For example, it is uncertain if the Line Islands are an age progressive chain (hot-spot trace) or result from some other type of intraplate volcanism. The mid-Pacific Mountains also show evidence of originating from a regional episode of volcanism in the mid-Cretaceous. Drilling in the Nauru Basin encountered a voluminous mid-Cretaceous volcanic flow-sill complex that overlies Jurassic .magnetic anomalies, yet is composed of depleted tholeiite. In the Indian Ocean, drilling on the Ninety-East Ridge established that it 1) is volcanic in origin; 2) is older to the north; 3) formed in shallow water, and 4) formed further south and has moved northward. It appears that the Ninety-East Ridge, like the Hawaiian-Emperor chain, is a hot spot trace. In the Atlantic Ocean, drilling on the Iceland-Faeroe Ridge and the Rio Grande Rise-Walvis Ridge suggests that all the se aseismic ridges are hot spot traces generated by the Iceland and Tristan de Cunha hot-spots.

Abstract Several major seismic horizons in the deep basin of the western North Atlantic Ocean have been calibrated according to age and physical and lithologic character by JOIDES drilling. Three horizons are discussed that are representative of the spectrum of stratigraphic relations in the basin. Horizon which ranges from Hauterivian to Barremian in age, correlates with a sharp upward transition from limestones to black clays coincident with a rise in the calcite compensation depth. In Eocene time, sediments enriched in biogenic silica were widely deposited, and subsequent diagenesis formed chert beds; the upper Lower to lower Middle Eocene surface of these cherts correlates with Horizon A c which is one of the strongest and most widespread reflectors in the basin. Widely distributed borehole data indicate that both Horizon β and Horizon A c normally occur within continuously deposited sedimentary sections. Beneath the continental rise, Horizon A u correlates with a major unconformity eroded between Late Eocene and Early Miocene time by southward-flowing abyssal currents. The reflector may have limited chronostratigraphic significance because of lateral migration of the abyssal current system with time. Several simple models are used to assess potential age significance of the seismic and lithologic boundaries and are compared to borehole data.

Abstract Recently available multichannel-seismic data have provided a detailed look at many Atlantic passive margins. DSDP holes and COST (Continental Offshore Stratigraphic Test) wells have provided geologic calibration. Reefal-carbonate bank underpinnings were involved in continental slope migration seaward of the original continental edge, especially in the Jurassic-Early Cretaceous. Tertiary erosion has caused a large landward retreat of the continental slope. These erosional events are nearly coeval on both sides of the Atlantic Ocean, indicating that they were caused by some basin- wide oceanographic change Deeper crustal layers are identified on the modern reflection and refraction data. Intermediate seismic velocity layers, 7.1 km/sec, near the continental edge on both sides of the Atlantic might be characteristic of transitional-type crusts, or merely continuations of Layer 3 under the slope and shelf. Deep, listric normal faults are observed where the soles of the faults merge into a lower crustal layer (6.3 km/sec velocity). Thinning with listric faulting of apparent continental crust has brought the mantle (8.2 km/sec) to within 14 km depths of the surface. Viscous creep in the lower continental crust appears necessary to account for the measured crustal thinning. Detailed analysis of the multichannel reflection data permits sequence identification within the thick margin sediments. Sealevel cycles can be identified, and correlations reveal the configuration of genetically related stratigraphic units. Such analyses define the subsidence history and paleobathymetry of the margins. Some passive margins start with an uplift and rifting phase, whereas others are rifted through previous deepbasins without uplift or volcanism. Other margins are dominated by volcanism in the early stages, and outer ridge structures have formed. Others have been involved in ridge-jump early in the seafloor spreading history which isolated transitional crusts of dispersed volcanism and continental slivers.

Abstract IPOD transects across convergent margins have provided time stratigraphic and environmental information to support the general concepts of spreading during the opening of backarc basins and tectonic accretion at the front of the underthrust plate. Three convergent margins are without large accretionary complexes, and other less frequently applied concepts are necessary to interpret them. Much sediment is subducted beneath the four margins investigated; along all of the margins there are periods when the continental framework was truncated and somehow removed by tectonic erosion. Vertical motions have been recorded during active arc magmatism (and, by implication, subduction) including not only uplift but also equally rapid subsidence. Off Japan the seaward part of the margin subsided from above sea level to 6 km depth. The scope of tectonic processes along convergent margins is much greater than was anticipated when the program was first planned.

Abstract Ten years of deep-ocean drilling have helped to assemble an enormous and largely untapped body of new data about the evolution of the Mesozoic and Cenozoic oceans. The rapid physiographic-tectonic evolution of the ocean basins and the fluctuations of the earth's climate during the Late Mesozoic and Cenozoic, including the climatic deterioration of the past 30 m.y., led to very important changes in the depositional regimes in the deep oceans. These changes are related to the initiation of a vigorous polar bottom-water formation and the generation of steep zonal hydrographic gradients in the surface water-masses. The effects of these changes on pelagic sedimentation cannot be separated easily from each other, but sedimentation rates of pelagic deposits have been used here to quantify the sediment flux into the Late Mesozoic and Cenozoic North Atlantic Ocean. Phases of high (>10- >50 m/10 -6 y) sediment input at 140-110 m.y.BP, 55-45 m.y.BP and during the past 25 m.y. alternated with intervals of much lower sediment input. Hiatuses which interrupted the sediment record are most frequent at 2-3 km and 4-5 km paleodepth. Processes such as dissolution or downslope displacement generated these hiatuses. They produced a distinctive depth-related accumulation pattern of the North Atlantic deep-sea deposits during the past 140 m.y. Concentrations of pelagic sediment components (calcareous, siliceous, organic and terrigenous detrital material) have been used to describe the temporal and spatial distribution of North Atlantic deep-sea deposits. Biogenic components outweighed by far the terrigenous detrital flux throughout the past 140 m.y. Carbonate- secreting organisms made quantitatively the most important contribution to the Late Mesozoic and Cenozoic North Atlantic deep-sea sediments. Two phases of sedimentation of carbonate-rich deposits were separated by an interval between 100 and 80 m.y.BP when CaCO 3 particles were deluted by chiefly terrigenous detrital material. Before 110 m.y.BP ago the highest concentrations of calcareous matter were confined to the deepest part of the then 4.0-4.5 km- deep North Atlantic Ocean. Since 80 m.y.BP sediments with high concentrations of calcareous matter were deposited above 3 km paleodepth and also between 4 and 5.5 km paleodepth during the past 25 m.y.BP. The deeper occurrence is associated with indications of downslope displacement of calcareous material into the deep abyssal plains in the North Atlantic. Siliceous particles are the second most important biogenic components (> 20%), but they were preserved only during two relatively brief intervals, 120-100 and 50-40 m.y.BP. Organic carbon concentrations were high (> 1%) 130-100 m.y.BP, coincident with the older maximum of opaline material, and during the past 5 m.y. when they were confined to the part of the basin deeper than 5 km. The North Atlantic did not receive a very high input of terrigenous material during its early history, but about 100-90 m.y.BP sediments with high concentrations of terrigenous material were shed into the basin. During the past 80 m.y. terrigenous material was essentially confined to the deepest part of the basins.

Abstract Deep-sea drilling has provided data on the distribution and changes in composition of redeposited sediment in deep- sea settings through time. The collection of such data by drilling, however, has not been very systematic or purposeful, and has contributed relatively little to the direct understanding of mechanisms of sediment redeposition. A review of reported occurrences of redeposited sediment in DSDP initial reports through Leg 54 shows some temporal patterns: Pleistocene continental margin sequences are thick and dominated by redeposited, relatively coarse-grained terrigenous material, whereas Middle to Upper Eocene and Albian-Cenomanian sequences are characterized by radiolarian turbidites. Moreover, DSDP has recovered an inordinate number of redeposited volcanogenic sequences in the Upper Cretaceous (centered on the Campanian) of all ocean basins and to a lesser extent in the Eocene. These commonly drape the flanks of aseismic rises, ridges, and plateaus and imply episodic volcanism along these features. Deep Sea Drilling Project cores have also contributed greatly to increasing recognition of the importance of redeposition of large volumes of mud both in fan and non-fan turbidite settings along active and passive margins. Pelagic environments are not devoid of redeposited material; so-called “pelagic turbidites” are common and comprise redeposited pelagic calcareous and siliceous biogenic components derived from the flanks of submarine highs. Redeposited sediments found in DSDP cores have also been extremely important in reconstruction of the tectonic history of numerous features, such as the drowning and demise of Jurassic-Lower Cretaceous carbonate platforms on young passive margins bordering the Atlantic, the destruction and upbuilding of the continental rise along Atlantic margins in the mid-Cenozoic, the history of uplift and volcanism on linear island chains in the Pacific, and the formation and destruction of slope basins along active margins. With the advent of the Hydraulic Piston Coring system, the future holds promise for more complete documentation of deep-sea fans, a closer examination of controls on timing and frequency of turbidite events, and detailed studies of turbidite physical properties and early diagenesis.

Abstract A synthesis of deep sea drilling results through Leg 70 indicates that siliceous rocks have been recovered in a variety of lithofacies from almost all major ocean basins. Reconstructed distributions of these rocks delineate original sites of deposition. During the Neogene, these areas included the equatorial Pacific, the Southern Ocean, the southern Bering Sea, the Red Sea, and local centers off Japan, California and northwest Africa. Paleogene occurrences describe a wide equatorial belt in the Pacific, Caribbean, Atlantic, and Indian Oceans, and several smaller regions in the North Atlantic, South Atlantic, and southern Indian Ocean. Cretaceous areas of deposition also included the equatorial Pacific and Atlantic with a few sites off western Australia. By analogy with present circulation patterns and areas of opal accumulation, reconstructed distributions of DSDP siliceous rocks delineate areas of past oceanic divergence. The rate of accumulation of silica, when compared with better known accumulation rates of opal, is a crude index to past productivity in these areas. Opal-CT and quartz are the principal authigenic silica minerals in siliceous rocks recovered from the deep sea; both are derived predominantly from biogenic silica comprising sponge spicules and the tests of radiolarians and diatoms. Time and temperature are important, though not the only, controls of the transformation rates of silica. Plots of age versus present subsurface temperature of opal-CT and quartz in DSDP siliceous rocks generally match the time and temperature stability fields of these two minerals determined from experiments. Using the experimental results, the transformation history of silica can be estimated. High thermal gradients and rates of burial apparently favor rapid transformations. Oxygen isotopic compositions of opal-CT and quartz depend upon the temperature of formation and the isotopic composition of the equilibrating fluid. Comparisons of present subsurface temperatures with temperatures computed from isotopic values, in conjunction with isotopic data on interstitial water squeezed from deep sea sediments, suggest the 5,80 values of opal-CT and quartz in deep sea siliceous rocks reflect a restricted range of formation temperatures, generally less than 50°C, and equilibration with interstitial water having a 6,80 range of 0%0 to -3%0. Siliceous rocks are important seismic reflectors in the western North Atlantic (Horizon A°), in the southern Bering Sea (Bottom Simulating Reflector), and in the northwest Pacific. The strength and continuity of these reflectors are complex functions of degree of silicification and bedding characteristics. Any seismic analysis must treat siliceous rocks as both sedimentary and diagenetic facies because stratigraphic and diagenetic boundaries do not always coincide.

Abstract This paper represents a review of observations made on the composition of interstitial waters of sediments recovered during the Deep Sea Drilling Project. In pelagic sediments with relatively slow rates of deposition (< 50 m/10 6 yr) increases commonly are measured in dissolved calcium and decreases in dissolved magnesium and potassium as well as H 2 18 O. These changes, to a large extent, can be understood in terms of alteration reactions occurring in the basalts of Layer II of the oceanic crust, and, to a lesser extent, in terms of alteration of volcanic matter dispersed in the sediment column (Layer I). Dissolved silica concentrations are generally enhanced in sediments containing opaline biogenic silica. Such enhanced silica activities in turn provide an environment in which reactions involving the alteration of volcanic matter in the sediments may occur. These reactions are particularly evident in zones of silicification, in which opal-A is transformed to opaJ-CT and quartz. Dissolved strontium concentrations in carbonate sediments are affected by carbonate recrystallization processes, which release strontium to the interstitial waters. These increases imply that Sr/Ca distribution coefficients in calcites must be smaller than generally accepted. In carbonate-free sediments increased strontium is often the result of reactions involving volcanic matter in the sediments and/or the underlying basalts. This relationship is particularly evident from observations on the 87 Sr/ 86 Sr ratio of dissolved strontium. Dissolved manganese and lithium appear to be released by biogenic silica. For Mn such sediments contain relatively more reactive organic carbon, which appears to act as the reducing agent in marine sediments. In rapidly-deposited hemipelagic sediments complex concentration-depth gradients result, particularly as a result of processes involving sulfate reduction and methane gas generation. High alkalinities (bicarbonate) result, as well as high dissolved ammonia values. Carbonate precipitation (calcite, ankerite, dolomite) can be important in such sediments. Freshwater acquifers near salt deposits can result in saline brines being advected into the sediment column in areas on the continental shelves and slopes.

Abstract Global land-sea carbonate flux for the past 60 m.y. averages 10.3-12.5 × 10 14 g/y, surprisingly close to 12.2 × 10 14 g/y calculated using data from today's rivers. However, oceanic carbonate accumulation rates vary between 7.8 × 10 14 g/y and 28.6 × 10 14 g/y, a factor of four. Furthermore carbonate accumulation oscillates between periods of high (0-6, 22-30, 45-53 m.y.) and low deposition. Prior to 30 m.y.BP all oceans behaved in concert, but since then significant partitioning between the Pacific and Atlantic-Indian oceans has complicated the picture. Prior to 15 m.y.BP the Pacific consumed two-thirds of the total pelagic carbonate, but since that time has never consumed more than 50 percent of the total, and for the past 3 m.y. only 38 percent. This trend is related to hypsometry and changes in carbonate dissolution rates as well as to changes in relative size of the oceans resulting from seafloor spreading. Global carbonate flux through time appears to be simply related to changing land-sea ratios as calculated from sea level curves. In this system, maximum exposed continental area correlates with high pelagic carbonate flux. Deviations from this simple relationship are attributable to changes in carbonate production-dissolution ratios, latitudinal hypsometric differences, global climatic changes, and biases introduced by the simple averaging techniques used in the calculations.

Abstract DSDP cores at selected sites provide a continuous carbonate sediment record characterized by comparative compositional simplicity, vertical homogeneity, and uniformity of diagenetic environment. These circumstances have allowed detailed reconstruction of diagenetic events, most notably those during burial. Burial diagenesis converts carbonate oozes to chalks which in turn may become transformed into dense limestones. The most important variables affecting these first-order changes are burial depth and pore water chemistry, but burial lithification is not related to burial depth in a simple way. Instead, differences in original sediment composition appear to predetermine the depths at which the transformations occur. Such differences in composition, caused by major and minor ocean events, may also be important in developing acoustic reflectors in the sediment pile. Some cementation occurs early during diagenesis; but this is comparatively rare in DSDP cores and apparently took place in chemically reactive sediments, such as those with abundant braarudosphaerid pentaliths. Carbonate sediments have a “diagenetic potential” which results from their preburial history and which in part determines subsequent diagenetic events during burial. Gravitational compaction is significant in the upper 50 to 200 meters of sediment; the dominant processes below these depths are pressure solution and reprecipitation of calcite cement, both of which are highly taxa- and site- specific. This lithification proceeds without external sources of calcium carbonate, thus cementation is calcite conservative. Sr ++ and 18 O in the carbonate tend to decrease with increasing burial depth, a consequence of solution-reprecipitation. But variations in the composition of the original sediment can cause deviations from these trends. Lithification of carbonate sediments associated with oceanic basalts appears to be a consequence of the submarine weathering of basalt. Shallow-water carbonate sediments have been infrequently encountered in the DSDP; but recognition of diagenetic features in them has allowed reconstruction of important geologic events such as intervals of subaerial exposure and of extremely rapid subsidence. Dolomite and other authigenic carbonate minerals in oceanic carbonate sediments apparently have formed in quite diverse ways. Some pelagic oozes were dolomitized by saline fluids emanating from underlying evaporites, some by Mg-rich pore waters derived from subaqueously weathered basalt; other dolomites formed as a by-product of the diagenesis of organic matter in sediments. The origin of other dolomite as well as siderite, ankerite, and other authigenic minerals in pelagic carbonates has not been systematically investigated.

Abstract Limestones whose constituents were deposited in shallow water are useful indicators of post-depositional uplift, subsidence and latitudinal changes through time. A review of such limestones, drilled at several dozen DSDP sites in all of the major ocean basins, demonstrates their utility in deciphering the geologic history of major structural features and in contributing to our knowledge of paleoceanographic conditions. Drilling in the northeast Providence Channel of the Bahamas, on the Blake Nose and off the Grand Banks of Newfoundland has extended our knowledge of the Cretaceous reef trends and carbonate shelf margins in the Atlantic passive margin province and has demonstrated subsidence of several kilometers there since Cretaceous time. The Rio Grande Rise and the Walvis Ridge both had Late Cretaceous and Eocene shallow-water histories related to their subsidence as paired aseismic ridges. On Orphan Knoll and Rockall Bank, Jurassic to Paleogene shallow-water sediments containing rich Paleocene bryozoan faunas confirm plate reconstructions for the early opening of the Atlantic. On the aseismic Ninetyeast Ridge in the Indian Ocean shallow-water sediments, including lignite deposits, directly above the basalt basement indicate a progressive subsidence history for the ridge similar to that of an island-seamount chain. In the Pacific Ocean the widespread occurrence of Campanian-Maestrichtian reef faunas from the Line Islands to the Nauru Basin-Marshall Islands leads to an interpretation of central Pacific bathymetric history reminiscent of the Darwin Rise of Menard in that mid-plate volcanism resulted in regional uplift in the central Pacific between ~ 115-110 and 70 m.y.BP. This uplift contributed to the major Cretaceous transgression during that period. Invocation of a spreading rate increase along mid-ocean ridges as the sole explanation for this transgression may not be necessary. The large benthic foraminifers of Late Cretaceous age recovered along the Line Islands and in the Nauru Basin have affinities to those of the Caribbean, indicating that the mid-Pacific atoll scene was not dominated by an Indo-Pacific fauna until Cenozoic time. Further, the Caribbean affinities of the central Pacific Late Cretaceous reef faunas lends credence to earlier suggestions that the Caribbean plate is a relic of the Farallon plate. Analysis of vertical tectonics in the Pacific shows that estimates of paleo-CCD levels should take into account periods of uplift which interrupted normal plate subsidence. Cenozoic reef debris found in turbidite units in deep-water fan deposits adjacent to the Line and Marshall islands chains record global sealevel changes. Drilling on the Emperor Seamounts has revealed Paleogene bryozoan- algal limestones whose latitude of deposition confirms paleomagnetic data from Suiko Seamount which indicate that this seamount did not form at the latitude of the present Hawaiian hot spot.