Plant and insect remains from the Wisconsinan interstadial/stadial transition at Wedron, north-central Illinois

Organic material exposed within a small swale fill in Pit 6 of the Wedron Silica Sand Co. near Wedron in LaSalle County, Illinois, includes well-preserved pollen, plant macrofossils, and insect remains. This material occurs in slackwater sediment in the lower part of the Peddicord Formation, which was deposited as existing valleys were dammed by fluvial aggradation during the initial late Wisconsinan advance of Laurentide ice into the Wedron area. Wood from the organic horizon has a radiocarbon age of 21,460 ± 470 yr B.P. (ISGS-1486). The pollen spectrum is dominated by Picea, Pinus, and Cyperaceae. Plant macrofossils comprise a mix of boreal-forest taxa, including Picea, Larix laricina, and the moss Campylium stellatum; subarctic species including Betula glandulosa, Empetrum nigrum, and Selaginella selaginoides; along with the predominantly arctic Vaccinium uliginosum var. alpinum, Dryas integrifolia, and Rhododendron lapponicum. The insect fauna contains the western montane ground beetle Opisthius richardsoni; several arctic-subarctic ground beetles including Diacheila polita, Helophorus sibiricus, and Pterostichus (Cryobius) caribou; and a diverse assemblage of insects that today inhabit the boreal forest. We interpret the biotic record to record a phase in the transition from closed boreal forest to open tundra as climatic conditions deteriorated in advance of continental glaciation.     

Volatile organic compounds in Quaternary sediments

The distribution of volatile organic compounds in surface sediments varies widely with the depositional environment. Oxygen and sulfur compounds, alkenes and arenes, are more abundant than alkanes in strongly reducing sediments such as those from around Walvis Bay, West Africa. Among the compounds identified by GC-MS were toluene, benzene, 2-methyl-2-butene, 3,5-dimethylcyclopentene, 3-menthylfuran, 3-methylfuran, 2-methylbutanol, 3-methylbutanol, 3-pentanone, 2-methylthiophene, 3-methylthiophene and dimethylsulfide. Some of these compounds have the isoprene carbon skeleton.In a less reducing environment such as the Arabian Sea-Persian Gulf area, a more diverse alkene assemblage was observed including ethylene, propylene, pentenes, hexenes, cyclohexene, methylpentenes and dimethylcyclopentenes. Also, the sediments contained a few very specific alkane structures. The gem-dimethyl hydrocarbons (neopentane, neohexane, and neoheptane) were dominant among the branched hydrocarbons. The high concentration of volatile alkenes and oxygen and sulfur compounds is not observed in deep sea drilling samples at depths greater than about 100 m.     

The opening of the Woodlark Basin, subduction of the Woodlark spreading system, and the evolution of Northern Melanesia since mid-pliocene time

Magnetic anomaly and seismological data define segments of active seafloor spreading and associated magnetic lineations trending ENE in the Woodlark Basin. The total opening rate has been approximately 6 cm/yr for the last 1 m.y. Spreading rates diminish by over 10% from east to west along the Woodlark spreading system implying a pole of current opening 15°–20° to the west. Commencement of seafloor spreading in the basin has apparently been time-transgressive, beginning prior to 3.5 m.y. in the east, and at successively later times to the west. Earthquake focal mechanisms and geological evidence suggest that the land areas bounding the western end of the Woodlark Basin are undergoing tensional deformation. We believe that eventually the Woodlark Basin plate boundary will propagate westward through the d'Entrecasteaux Islands into the Papuan peninsula. Hitherto unreported shallow seismicity associated with the northern margin of the NE-trending section of the Woodlark Rise probably reflects partial decoupling of the Woodlark and Solomon basins, possibly due to mechanical difficulties in subducting the young Woodlark lithosphere.Analysis of the relative motions between the Solomon, Indo-Australian, and Pacific plates shows that the Woodlark spreading system has been subducted at high rates (> 10 cm/yr) beneath the Solomon Islands during the opening of the Woodlark Basin. Several tectonic and geological features limited to the region of interaction of the Woodlark Basin with the Solomon Trench and arc may be symptomatic of ridge subduction. These features include high heat flow in the Solomon Trench, which shoals to 4 km; low levels of seismicity and only shallow hypocenters; and voluminous eruptions of high olivine basalts and basaltic andesites extremely close to the trench axis. This close association in space and time of an unusual volcanic suite with ridge subduction implies a strong dependence of the petrogenesis on the tectonic regime.A combination of this study of the Woodlark Basin and the previous study of the Bismarck Basin (Taylor, 1979) provides a reconstruction of the positions of the continents, ocean basins, and island chains in northern Melanesia for mid-Pliocene time. In accepting the existence of a Solomon plate, we can explain the trench-like structure off the Trobriand margin of New Guinea, the occurrence of Late Cenozoic calc-alkaline volcanism along the Papuan peninsula, and the presence of intermediate depth seismicity beneath the north Papuan peninsula. The rapid changes in relative motions along or across the New Ireland-Solomons chain over the past 3.5 m.y. may explain the spatial and temporal changes in igneous activity observed on these islands.     

The organic matter of a gulf coast well studied by a thermal analysis-gas chromatography technique

A thermal analysis-gas chromatography technique, previously described by Whelan et al. has been used to analyze cuttings from a Continental Offshore Stratigraphic Test (COST No. 1) drilled in the Gulf Coast of the U.S.A. The data allowed an evaluation of the degree of maturation of the organic matter and provided an accurate determination of the depth of the threshold of intense oil generation at 3048 m (10,000 ft.). Qualitative changes of hydrocarbons in the C₇–C₁₄ range were determined by gas chromatography and confirmed by gas chromatography-mass spectroscopy. These data are discussed in terms of generation and migration processes. The catagenetic evolution results in a strong tendency for a proportional increase in n-alkanes. Mass transfer phenomena may be responsible for updip movement of the lighter hydrocarbons.     

Generation and migration of hydrocarbons in offshore South Texas Gulf Coast sediments

The hydrocarbon content of two thick Tertiary sequences from the offshore Gulf Coast (South Padre Island and Mustang Island) was studied using a headspace technique, thermal distillation, pyrolysis and solvent extraction. The threshold of oil generation was determined to occur in the range of 3050 m (10,000 ft; 120°C) in Miocene sediments.In the South Padre Island well, the distribution of the different classes of hydrocarbons along the sedimentary column suggests some updip migration processes are occurring.     

Evolution of localized folding for a thin elastic layer in a softening visco-elastic medium

Long compressed elastic struts on softening elastic foundations have a tendency to buckle locally. The same tendency is demonstrated here for the instantaneous response of elastic struts supported by visco-elastic media. A governing nonlinear partial differential equation is derived to describe the evolution of the localized form in time. Under the assumed constant end-shortening this is found to be approximated by a coupled set of seven ordinary differential (diffusion) equations. As the load drops to zero, the localized buckle pattern evolves towards the form of the single long wave, but remains aperiodic for all time. Three-dimensional plots show how this localized pattern changes over time.     

Natural Climatic Variability as an Explanation for Historical Climatic Fluctuations

The question as to whether the climatic anomalies associated with the Medieval Warm Period and the Little Ice Age can be attributed to natural climatic variability is explored in this paper. The output from a 500-year run with a global climatic model is used for this purpose. The model exhibits multi-decadal variability in its climatic outputs, which appears to have many of the characteristics of observed climatic data over the last millennium. Global distributions of surface temperature associated with peak warming and cooling phases of the model run highlight the spatial variability which occurs, and the lack of synchroneity in the response from region to region. Considerable year-to-year variability occurs in temperature anomaly patterns during the warming and cooling phases, indicating the complexity of the responses. The model results suggest that such climatic phases should not be considered as lengthy periods of universal warming or cooling. Comparison of observed time series of land surface temperature for the northern hemisphere for the last 500 years with model output indicates that most of the observed features in this climatic record can be reproduced by processes associated with internal mechanisms of the climatic system as reproduced in the model. While the model results do not exclude the possible contribution of external forcing agents as a contributing factor to these climatic episodes, the perception is that such agents would enhance existing naturally-induced climatic features rather than initiate them, at least for this time frame. Given the omnipresent nature of natural climatic variability, it is assumed that such variability rather than external forcing agents has primacy in generating and maintaining the underlying observed climatic variability. An understanding of the mechanisms and behaviour of such climatic features is becoming of increasing importance, in view of their possible role in modulating future climatic trends given the expected influence of the greenhouse effect.