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Two sections were sampled near Lootsberg Pass (S31, 51.005; W24, 52.299, and S31, 49.334; W24, 48.565), one section near Wapadsberg Pass (S31, 52.474; W24,. 54.882), one section near Carlton Heights (S30, 35.425; W25, 439.135), one section near Kommandodrift Dam (S31, 76.506; W24, 49.980), and two sections near Bethulie (S30, 24.989; W26, 17.234, and S30, 26.675; W26, 18.006). Four lithostratigraphic fades are present Unit I, dark gray to gray mudstones, siltstones, and sandstones with sedimentary structures typical of meandering river deposits; strata show rubification in the uppermost meters. Unit II, 3- to 5-m-thick, rhythmically bedded laminated mudrock, described as an event bed (37). Unit III, red concretionary mudstone and thin sandstone. Unit IV (Katberg Formation), thick olive-green sandstone with conglomeratic bases interbedded with thinner red siltsone and mudstone; sandstones have sedimentary structures typical of braided river deposits.
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Materials and methods are available as supporting material on Science Online
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Materials and methods are available as supporting material on Science Online.
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13244285653
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All samples passed tests for baked contact, class B reversal, and magnetostratigraphic consistency. The reversal in the upper part of Lootsberg Pass was corroborated at a second parallel section ∼1 km to the east, where a reversal of similar thickness was found at the same stratigraphic horizon. We have used this pattern to correlate and subdivide the Katberg Formation across the Karoo basin.
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18
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13244263731
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The actual P-T boundary is defined by the base of the Triassic system or the first appearance of the conodont H. parvus in marine strata. The base of the Triassic cannot be identified in the Karoo until a terrestrial index fossil is formally chosen. At present, we have placed the P-T boundary at the level of the highest Permian taxon, a practice that runs contrary to accepted stratigraphic procedure. Here, each taxon is treated as a species; we realize that taxonomic study of each is required. Pending the formal systematic treatment of Lystrosaurus (38), we designate the four separate species of Lystrosaurus from our study area as Lystrosaurus sp. A, B, C, and D.
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13244293262
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Preservational biases may also have controlled the observed pattern of extinction. However, because there are more fossils in Units III and IV than in the upper 30 m of Unit I, we would expect to find the Permian taxa if they continued higher in the section. As that is not the case, we conclude that the observed ranges are real samples of the preservable fauna in the depositional basin.
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33
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There has been much recent criticism of the so-called P-T fungal spike as a chronostratigraphic marker, based on the discovery of multiple horizons at some localities and the complete absence of the marker at others, most notably at the important Greenland locality (39), as well as the possibility that the fossils may not have come from fungi at all (40).
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34
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Ward, P.D.1
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13244280936
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We thank the NASA Astrobiology Institute, the NSF, and the National Research Foundation of South Africa for funding. Help in the field and fossil preparation came from the Karoo Paleontology Department, Iziko: South African Museum (P. October, H. Stumer, G. Farrell, preparation by A. Crean, field collection by N. Ward and T. Evans, and lab help by C. Converse and E. Steig). Paleomagnetic software used for data analysis was from C. Jones at the University of Colorado, Boulder. We thank F. Kyte and C. Looy for prereviews.
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