Isotopic composition of foraminifera from sediments of DSDP Legs 3, 6-9, 17

Oxygen isotopic compositions of the tests of planktonic foraminifera from several Deep Sea Drilling Project sites provide a general picture of low-latitude marine temperatures from Maastrichtian time to the present. Bottom temperatures determined from the isotopic compositions of benthonic foraminifera are interpreted as being indicative of high-latitude surface temperatures. Prior to the beginning of middle Miocene time, high- and low-latitude temperatures changed in parallel fashion. Following an apparently small and short-lived drop in temperature near the Tertiary-Cretaceous boundary, temperatures remained warm and relatively constant through Paleocene and early and middle Eocene time; bottom temperatures then were on the order of 12°C. A sharp temperature drop in late Eocene time was followed by a more gradual lowering of temperature, culminating in a late Oligocene high-latitude temperature minimum of about 4°C. A temperature rise through early Miocene time was followed in middle Miocene time by a sudden divergence of high- and low-latitude temperatures: high-latitude temperatures dropped dramatically, perhaps corresponding to the onset of major glaciation in Antarctica, but low-latitude temperatures remained constant or perhaps increased. This uncoupling of high-and low-latitude temperatures is postulated to be related to the establishment of a circum-Antarctic circulation similar to that of today. A further drop in high-latitude temperatures in late Pliocene time probably signaled the onset of a major increase in polar glaciation, including extensive sea-ice formation. Early Miocene, small-amplitude (1 per mil) sympathetic fluctuations in isotopic compositions of planktonic and benthonic foraminifera have been identified. These have a period of several hundred thousand years. Superimposed upon these are much more rapid and smaller fluctuations (0.2 to 0.5 per mil) with a period of about 80000 to 90000 yr. This is similar to the period observed for Pleistocene isotopic temperature fluctuations. In low latitudes, much smaller vertical temperature gradients seem to have existed during Maastrichtian and Paleogene time than exist at present. The absence of a sharply defined thermocline during early Tertiary time is also suggested.

Oxygen, hydrogen, and carbon isotopic compositions in deep sea cherts, porcellanites, and coexisting carbonates from DSDP Legs 2, 3, 6, 7, 11, 14, 16, 17, and 20

Seventy four samples of DSDP recovered cherts of Jurassic to Miocene age from varying locations, and 27 samples of on-land exposed cherts were analyzed for the isotopic composition of their oxygen and hydrogen. These studies were accompanied by mineralogical analyses and some isotopic analyses of the coexisting carbonates. d18O of chert ranges between 27 and 39%. relative to SMOW, d18O of porcellanite - between 30 and 42%. The consistent enrichment of opal-CT in porcellanites in 18O with respect to coexisting microcrystalline quartz in chert is probably a reflection of a different temperature (depth) of diagenesis of the two phases. d18O of deep sea cherts generally decrease with increasing age, indicating an overall cpoling of the ocean bottom during the last 150 m.y. A comparison of this trend with that recorded by benthonic foraminifera (Douglas and Savin, 1975; http://www.deepseadrilling.org/32/volume/dsdp32_15.pdf) indicates the possibility of d18O in deep sea cherts not being frozen in until several tens of millions of years after deposition. Cherts of any Age show a spread of d18O values, increasing diagenesis being reflected in a lowering of d18O. Drusy quartz has the lowest d18O values. On-land exposed cherts are consistently depleted in 18O in comparison to their deep sea time equivalent cherts. Water extracted from deep sea cherts ranges between 0.5 and 1.4 wt %. dD of this water ranges between -78 and -95%. and is not a function of d18O of the cherts (or the temperature of their formation).

In vitro study of the Nd : YAG laser effect on human dental enamel: Optical and scanning electron microscope analysis

Objective: the Nd:YAG laser irradiation of dental enamel was evaluated in enamel demineralization experiments in a Streptococcus mutans culture media. Summary Background Data: Previous studies had shown that a continuous wave Nd:YAG laser at an energy of approximately 67 mJ may induce an increased acid resistance in human dental enamel when exposed to severe demineralization conditions. Methods: Enamel windows of 3 x 4 cm in the buccal surface were irradiated with a continuous wave Nd:YAG laser at a wavelength of 1,064 Ecm using energy densities of from 83.75 to 187.50 J/cm(2), Enamel windows of 3 x 4 cm on the lingual surface served as control (without the laser irradiation). The enamel windows were then exposed to a Streptococcus mutans culture media at a temperature of 37 degrees C for 15 and 21 days. The laser effects and demineralization were examined both by optical microscopy and scanning electron microscopy (SEM), Results: A comparison between the lased and the unlased windows of enamel showed fusion and recrystalization of the enamel and increased acid-resistance in all groups irradiated with the Nd:YAG laser, on the other hand, the 3 x 4 delimited enamel surfaces from the control group (not irradiated with the Nd:YAG laser) showed 100% deminerization, Conclusions: These findings are consistent with the finding that laser irradiation of dental results in significant reduction of the effective solubility of enamel mineral.

(Table DR1) Biogenic silica and chert in the Pacific Ocean, DSDP and ODP data

Evidence for the dissolution of biogenic silica at the base of pelagic sections supports the hypothesis that much of the chert formed in the Pacific derives from the dissolution and reprecipitation of this silica by hydrothermal waters. As ocean bottom waters flow into and through the crust, they become warmer. Initially they remain less saturated with respect to dissolved silica than pore water in the overlying sediments. With the diffusion of heat, dissolved ions, and to some extent the advection of water itself, biogenic silica in the basal part of the sedimentary section is dissolved. Upon conductively cooling, these pore waters precipitate chert layers. The most common thickness for the basal silica-free zone (20 m) lies below the most common height of the top of the chert interval above basement (50 m). This mode of chert formation explains the frequent occurrence of chert layers at very shallow subbottom depths in pelagic sections of the Pacific. It is also consistent with the common occurrence of cherts

Paleomagnetic properties of igneous rocks from several DSDP and ODP sites, western Pacific

Oceanic basalts and other related igneous rocks are considered excellent recorders of the Earth's paleomagnetic field. Consequently, basalt core paleomagnetic data are valuable for the constraints they provide on plate tectonic motions, especially for oceanic plates such as the Pacific. Unfortunately, few Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) boreholes have been cored very deeply into the ocean crust. The result is that there are only a few sites at which a large enough number of basalt flows have been cored to properly average secular variation (e.g., Kono, 1980, doi:10.2973/dsdp.proc.55.135.1980; Cox and Gordon, 1984, doi:10.1029/RG022i001p00047). Furthermore, there are a number of sites where basaltic core samples were retrieved but the cores were not measured. Often this occurs because leg scientists had more important sections to work on, or the section was ignored because it was too short to record enough time to average secular variation and obtain a reliable paleolatitude. Even though it may not be possible to determine a precise paleolatitude from such short sections, measurements from a small number of flows are important because they can be combined with other coeval paleomagnetic data from the same plate to calculate a paleomagnetic pole (Gordon and Cox, 1980, doi:10.1111/j.1365-246X.1980.tb02642.x; Cox and Gordon, 1984, doi:10.1029/RG022i001p00047). For this reason, I obtained samples for paleomagnetic measurements from eight Pacific sites (169, 170, 171, 581, 597, 800, 803, and 865), most of which have not been previously measured for paleomagnetism.