Kevin McCartney

A Model of Correlated Episodicity in Magnetic-Field Reversals, Climate, and Mass Extinctions

Correlated periodicities of mass extinctions, climate, magnetic-field reversals, and other geological phenomena may best be explained by cycles of activity within the mantle and core. We propose that these cycles are due to variations in the thickness of the thermal boundary layer at the base of the mantle as the layer alternates between two phases of activity. In the quiescent phase little flow occurs and the layer thickens with time by thermal diffusion. The active phase begins when the thickening layer becomes dynamically unstable. Hot material erupts from the layer, causing it to become thinner. As the layer thins, the rate of energy supply to the geodynamo, and hence its reversal frequency, increases. The hot material rises to the surface, where it causes widespread basaltic volcanic eruptions. These eruptions release large amounts of

A rare double skeleton of the silicoflagellate Corbisema

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Optimal models of skeletal morphology for the silicoflagellate genus Corbisema

and sulfates which have a pronounced effect on the climate and biota.

Emergence of a Rival Paradigm to Account for the Cretaceous/Tertiary Event

What killed the dinosaurs? This is the most popular question of the “Cretaceous/Tertiary (K/T) controversy,” which is concerned with the extinction some 65 m.y. ago of more than 75% of the worlds existing floral and faunal species [Surlyk, 1980]. A popular hypothesis of their untimely demise is the impact of a meteorite [Alvarez et al., 1980]. However, despite the claim [Alvarez, 1983] that this has been proven, some serious doubts remain [Hallam, 1987; Officer et al., 1987]. A rival claim, that the dinosaurs were done in by a catastrophic volcanic eruption, has attracted some proponents and has some evidence in its favor, but that case is far from proven. However, it does have the advantage of having a definite event to point to the Deccan Traps in India. These are the largest continental flood basalts known from the Phanerozoic. According to recent studies [Courtillot et al., 1986; Feraud et al., 1988], the Deccan Traps were emplaced close to 65 m.y. ago. Is this timing a coincidence or are the two events (the mass extinction and the Deccan volcanism) related?

Two rare silicoflagellate double skeletons of the Star-of-David configuration from the Eocene

Silicoflagellates are usually associated with simple skeletons made of a domal latticework of rod-shaped elements, known as the apical structure, which is attached to a polygonal basal ring. Silicoflagellate reproduction is poorly understood (Moestrup & Thomsen, 1990) but they are known to divide mitotically associated with the construction of a double skeleton. Such double skeletons connected at the abapical face of the basal ring are observed from Recent and fossil material. Double skeletons of Dictyocha and Distephanus noted in Cenozoic sediments (Dumitricǎ, 1973, pl. 4, fig. 8; Boney, 1976) show basal rings positioned with their corners in close proximity. Ling & Takahashi (1985, pl. 1, fig. 5) and Takahashi et al . (2009, pl. 2, figs 3, 5) illustrate Distephanus with the spines of the two skeletons in exact alignment with one another. Recent work in a Campanian sequence of strata near Horton River, District of Mackenzie in the Northwest Territories, Canada …

Using the Internet to Prepare a Term Paper for a Geology Course

Abstract A FORTRAN program is presented for the three-dimensional measurement of silicoflagellate skeletons from the light microscope. The points where skeletal elements intersect are digitized, and x and y coordinates, along with measured height values, are read into the measurement program. The program can calculate three-dimensional distances, the area of skeletal surfaces, and the internal volume for most of the abundantly occurring silicoflagellate skeletal designs.

The Cretaceous/Tertiary Extinction Controversy Reconsidered

The skeletal morphologies of three-sided silicoflagellates can be reproduced by a mathematical model that minimizes the apical surface area. The model allows the basal sides to bow outward; the morphology that best minimizes apical area has a basal ring that approximates a circle. More typical silicoflagellates from the geologic record, however, tend to have a basal ring more triangular in outline; our modeling shows that this can occur where the reduction of skeletal material, and thus weight, is a secondary factor. A model that minimizes the use of skeletal material produces unusual morphologies, indicating that the reduction of skeletal material is not of primary importance.

Indices based on silicoflagellate assemblages offer potential for paleo-reconstructions of the main oceanographic zones of the Southern Ocean

The cause of the Cretaceous/Tertiary transition remains one of the most controversial scientific topics of this decade, with the debate continuing between advocates of an impact or a volcanic cause. The occurrence of a catastrophic event of enormous scale is, however, unquestioned. Rather, the debate concentrates on whether the event was part of an episodic process and whether it might be of extraterrestrial or endogenous origin. The case for an internal cause of the transition has been strengthened recently by the dating of the Deccan basalts to very near 65 Ma and by the development of a model of a volcanic mechanism that produces shocked quartz. The evolving controversy is reviewed here to enliven debate in a college-level seminar.