We have studied the concentrations of 10Be and 26Al in quartz crystals extracted from glacially polished granitic surfaces from the Sierra Nevada range. These surfaces were identified with the glacial advance during the Tioga period ∼11,000 years ago. Our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in SiO2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43.8°–44.6°N and altitudes 2.1–3.6 km. The estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0°–75° with respect to the horizontal. The principal uncertainty arises due to the lack of a precise date for the glacial retreat event, about ±10%. The 26Al/10Be ratio at production (6.0) is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides. Production rates of 10Be and 26Al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling, using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons. Knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies.

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The timing of flood basalt volcanism associated with formation of the Ontong Java Plateau (OJP) is estimated from paleomagnetic and paleontologic data. Much of OJP formed rapidly in less than 3 million years during the early Aptian, at the beginning of the Cretaceous Normal Polarity Superchron. Crustal emplacement rates are inferred to have been several times those of the Deccan Traps. These estimates are consistent with an origin of the OJP by impingement at the base of the oceanic lithosphere by the head of a large mantle plume. Formation of the OJP may have led to a rise in sea level that induced global oceanic anoxia. Carbon dioxide emissions likely contributed to the mid-Cretaceous greenhouse climate but did not provoke major biologic extinctions.

The origin of a series of regionally correlatable seismic horizons in the Neogene sediments of the central equatorial Pacific is examined through seismic modeling and the detailed analyses of stratigraphic and physical property relationships in Deep Sea Drilling Project cores. These regionally traceable reflectors are synchronous; the younger reflectors are the direct result of carbonate dissolution events, the older ones of stratigraphically selective diagenetic processes. The changes in ocean chemistry associated with these events appear to be linked to global reorganizations of surface and bottom-water circulation patterns, the most dramatic of which are associated with reorganizations of North Atlantic bottom waters. These deepwater seismic horizons appear to correlate with the major events on the "relative sea-level" curve of Vail et al. for the Neogene.

The principal findings of drilling on the Galicia margin during ODP Leg 103, supplemented by sampling from the submersible Nautile and calibration of seismic-reflection profiles, are:1. Peridotite, exposed in a ridge at the foot of the margin, is clinopyroxene-bearing spinel harzburgite, more than 90% serpentinized and cut by veins of calcite. During the rifting and lithospheric stretching stage of margin formation, these rocks ascended to the seafloor from a depth of about 30 km, where the temperature was about 1250°C. The rocks record the successive effects of partial melting, stretching, serpentinization, and fracturing.2. The sequence of sedimentary strata in a typical tilted fault block of the margin comprises, in ascending order:a. An unknown thickness (probably > 500 m) of undated sandstone containing volcanic detritus and interbedded with shelly dolomite. (Known only from Nautile samples.) b. A few meters thickness of conglomerate of low-grade clastic metasedimentary clasts, resting on fragments of al tered rhyolite. This rhyolite may not be part of a conglomerate but part of the Hercynian basement.c. About 400 m of Jurassic (Tithonian) shallow-water carbonate rocks, including about 100 m of limestone inter bedded with sandstone and claystone, overlain by about 250 m of intensely fractured dolomite. The strata up to this level are classified as "pre-rift," but may have been deposited during an episode of pre-Cretaceous faulting.d. A syn-rift sequence, more than 1 km thick in the deepest part of the half-graben, consisting of about 40 m of Valanginian calpionellid marlstone overlain by Valanginian-Aptian turbidite sandstone, claystone, and hemipelagic limestone interbedded with debris-flow beds rich in shallow-water bioclasts. At least one angular unconformity inter nally divides the syn-rift sequence.e. Albian-Recent post-rift strata, thickest in the half-grabens and thin to absent over the upper edges of the fault blocks. These strata were not systematically explored during Leg 103.3. The prominent deep seismic reflector, "S," seen on profiles on the western part of the margin, lies within or be neath continential crust.In spite of the significant advances made possible by the drilling during Leg 103, a number of unanswered important questions remain as obstacles to our building a comprehensive geodynamic model for the evolution of the Galicia mar gin:1. The mechanism of emplacement of the ridge of mantle peridotite at the foot of the margin and the respective roles of asthenospheric diapirism and detachment faulting in the uplift and unroofing of the peridotite.2. The extent on the seafloor of peridotite west of the peridotite ridge bounding the margin. 3. The nature of the regional deep seismic reflector termed horizon S, interpreted as the seismic signature of a de tachment fault.4. The stratigraphy of pre-Valanginian ("pre-rift") strata on the margin and a possible episode of Jurassic or older rifting and crustal thinning.5. The possible role of hydrothermal fluids rising along the rift faults in the...