Geoscience Reports 31:5-6 (Spring 2001).

NOTES FROM THE SCIENTIFIC LITERATURE

Anthropology

Leakey MG, Spoor F, Brown FH, Gathogo PN, Kiarie C, Leakey LN, McDougall I. 2001. New hominin genus from eastern Africa shows diverse middle Pliocene lineages. Nature 410:433-440.

    The term "hominins" is used for species that are considered to be more closely related to humans than to chimpanzees.
    Two skulls thought to be contemporaneous with Australopithecus afarensis have been named Kenyanthropus platyops. The researchers believe the skulls should be placed in a new genus because they have several characters that differentiate them from the australopithecine genus as well as Paranthropus and Homo. The species name comes from the Greek words, platus, which means "flat" and the word for "face," opis.
    Cranial capacity falls within the range for the australopithecines. The right molar, M², was the only molar that was preserved well enough for evaluation and was found to be significantly smaller than stratigraphically equivalent hominins.
    If the small molar size is accepted as a primitive character, Kenyanthropus would replace the australopithecines in the evolutionary tree.

Lieberman D. 2001. Another face in our family tree. Nature 410:419-420.

    The author proposes a new lineage for evolutionary relationships based on the discoveries by Leakey and colleagues and suggests that H. rudolfensis should be reclassified as Kenyanthropus rudolfensis. This proposal places the Kenyanthropus genus off-line from A. anamensis, leaving the australopithecines in the line to humans.
    Comment: Research on hominids has produced at least 9 different proposed lineages for ancestor-descendent relationships. These new skulls will only add to the complexity and confusion that already prevails over the current interpretations for the origin of humans.

Geology

Bourgeois J, Johnson S. 2001. Geologic evidence of earthquakes at the Snohomish delta, Washington, in the past 1200 yr. Geological Society of America Bulletin 113(4):482-494.

    Geologists measured 45 sections along the exposed channels of streams crossing the Snohomish delta in the Puget Lowland. A comparison of the sedimentary structures and relationships of these structures both vertically and laterally suggests three episodes of liquefaction, one abrupt subsidence event and a tsunami deposit. Radiocarbon ages from marsh plant rhizomes suggest that the timing of the tsunami may be related to a large earthquake along the Seattle fault 50 km to the south.
    Comment: Some have claimed that earthquake activity is increasing in frequency and intensity; however, studies such as this remind us that some areas have been impacted by multiple, strong seismic events in the past.

Weinberg R, Sial A, Pessoa R. 2001. Magma flow within the Tavares pluton, northeastern Brazil: compositional and thermal convection. Geological Society of America Bulletin 113(4):508-520.

    Documentation of complex structures in granites has been presented by these researchers in an attempt to describe crystallization, differentiation and convection processes. Granite plumes and diapirs are interpreted from ladder dikes, snail structures and schlieren. Schlieren are regions where it is thought that magma escaped into the postulated mush pores that probably surrounded it. Ladder dikes and snail structures are thought to be cross-sections of granite channels that may be feeding diapirs and plumes. The authors proposed a model of the magma system that explains all of the structures that they described.

McDowell F, Roldán-Quintana J, Connelly J. 2001. Duration of Late Cretaceous–Early Tertiary magmatism in east-central Sonora, Mexico. Geological Society of America Bulletin 113(4):521-531.

    In an effort to understand the magmatic activity in Sonora, Mexico, the authors obtained U-Pb radiometric dates from volcaniclastics associated with the Sonoran batholith. Four samples yielded 13 dates between 73 and 70 Ma; two samples provided 7 dates at 90 and 89 Ma with errors generally < 1 m.y. In five of the six dated samples, zircons gave Proterozoic ages (i.e., greater than 540 Ma). The authors interpreted these dates as representative of material that was incorporated into the magma prior to eruption.
    Comment: The complexity of granites and volcaniclastics as illustrated in these papers is interesting. One cannot help but wonder if this complexity has an impact on radiometric dates from bodies of rock such as this and the conclusions that are drawn from the information.

Burgess P, Wright V, Emery D. 2001. Numerical forward modeling of peritidal carbonate parasequence development: implications for outcrop interpretation. Basin Research 13:1-16.

    Parasequence (a sequence of related sedimentary layers) thicknesses is addressed using a numerical model. The authors produced both uniform and nonuniform thicknesses based on subsidence and sediment transport rates, independent of sea level. Ordered hierarchies were obtained from Fischer plots of their "data." The authors suggest that Fischer plots of outcrop data may not be reliable indicators of sea-level control.
    Comment: For many years Fischer plots have been used to help define stratigraphic sequences that may be controlled by sea-level rise and fall. In addition, much of the work has related these shallowing upward sequences to Milankovitch cycles (orbital forces affecting sea level). This paper is a refreshing change of pace encouraging researchers to reevaluate their assumptions.

Paleontology

Sutton M, Briggs D, Siveter D, Siveter D. 2001. An exceptionally preserved vermiform mollusc from the Silurian of England. Nature 410:461-463.

    The researchers ground a fossiliferous rock at 10µm increments coupled with computer methods to produce a series of 3-dimensional reconstructions. The organism has been named Acaenoplax hayae. The genus name is Greek for "spine or thorn plate." Due to similarities to Aplacophora, the newly discovered organism is thought to be a primitive mollusc.
    Comment: The photographs and description of the structure of this primitive mollusc reveal a very complex organism.

Dorsal view of Acaenoplax hayae, fragment OUM 29529. This photograph is one of the figures in the Nature article cited above and is reproduced with the permission of its authors.