Size variations in foraminifers from the early Permian to the Late Triassic: Implications for the Guadalupian-Lopingian and the Permian-Triassic mass extinctions

The final 10 Myr of the Paleozoic saw two of the biggest biological crises in Earth history: the middlePermian extinction (often termed the Guadalupian–Lopingian extinction [GLE]) that was followed 7–8 Myr later by Earth's most catastrophic loss of diversity, the Permian–Triassic mass extinction (PTME). These crises are not only manifest as sharp decreases in biodiversity and—particularly for the PTME—total ecosystem collapse, but they also drove major changes in biological morphological characteristics such as the Lilliput effect. The evolution of test size among different clades of foraminifera during these two extinction events has been less studied. We analyzed a global database of foraminiferal test size (volume) including 20,226 specimens in 464 genera, 98 families, and 9 suborders from 632 publications. Our analyses reveal significant reductions in foraminiferal mean test size across the Guadalupian/Lopingian boundary (GLB) and the Permian/Triassic boundary (PTB), from 8.89 to 7.60 log10 μm3 (lg μm3) and from 7.25 to 5.82 lg μm3, respectively. The decline in test size across the GLB is a function of preferential extinction of genera exhibiting gigantism such as fusulinoidean fusulinids. Other clades show little change in size across the GLB. In contrast, all Lopingian suborders in our analysis (Fusulinina, Lagenina, Miliolina, and Textulariina) experienced a significant decrease in test size across the PTB, mainly due to size-biased extinction and within-lineage change. The PTME was clearly a major catastrophe that affected many groups simultaneously, and the GLE was more selective, perhaps hinting at a subtler, less extreme driver than the later PTME

ABNBT

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1998.Includes bibliographical references (p. 130-134).The feasibility of a new modality of radiation therapy, Accelerator-Based Neutron Brachytherapy (ABNBT), has been demonstrated through simulations and experimental work. The candidate nuclear reactions investigated are 9Be(d,n)'OB, 9Be(p,n)9B, and 7Li(p,n)7Be, with charged particle beam energies of less than 4.1 MeV. The focus of this work is the treatment of intracranial tumors which limits the diameter of the dose delivery needle tube to 6 mm. A prototype needle tube, a tube-in-tube design with cooling water running in between the inner and outer tubes to cool the beryllium target located at the tip of the inner tube, has been tested to a heat load near 150 Watts. The insertion length is 10 cm. The dosimetric characteristics were simulated using the Monte Carlo code MCNP and the treatment times were then calculated for a given heat load. The simulations and calculations show that the fast neutron dose is the dominant dose component for all the candidate reactions. The 9Be(d,n)oB reaction at Ed=1.5 MeV is capable of delivering a therapeutic dose of 66 RBE.Gy to the boundary of a 4.5 cm diameter tumor in 7.3 minutes at a heat load of 150 Watts. The other two candidate reactions deliver a similar dose rate at the same heat load to the target at a beam energy near 4.0 MeV. However, they show higher potential for dose enhancement with the boron-10 neutron capture reaction due to their soft neutron spectra. For input into dosimetric simulations, the source gammas from a thick beryllium target bombarded by a 1.5 MeV deuteron beam were measured at 600 with a 76 mm x 76 mm NaI(TI) detector. The prominent gammas range from 414 keV to 3.6 MeV. Dose distributions in a water phantom were measured with the prototype needle tube using the dual-ion chamber technique for the 9Be(d,n)10B reaction at Ed=1.5 MeV. The measurements and simulations agree within uncertainties. In conclusion this work has demonstrated the dosimetric desirability and the practical feasibility of ABNBT for the treatment of interstitial or intracavity tumors.by Haijun Song.Ph.D

Early Triassic wrinkle structures on land:stressed environments and oases for life

Wrinkle structures in rocks younger than the Permian-Triassic (P-Tr) extinction have been reported repeatedly in marine strata, but rarely mentioned in rocks recording land. Here, three newly studied terrestrial P-Tr boundary rock succession in North China have yielded diverse wrinkle structures. All of these wrinkles are preserved in barely bioturbated shore-shallow lacustrine siliciclastic deposits of the Liujiagou Formation. Conversely, both the lacustrine siliciclastic deposits of the underlying Sunjiagou Formation and the overlying Heshanggou Formation show rich bioturbation, but no wrinkle structures or other microbial-related structures. The occurrence of terrestrial wrinkle structures in the studied sections reflects abnormal hydrochemical and physical environments, presumably associated with the extinction of terrestrial organisms. Only very rare trace fossils occurred in the aftermath of the P-Tr extinction, but most of them were preserved together with the microbial mats. This suggests that microbial mats acted as potential oases for the surviving aquatic animals, as a source of food and oxygen. The new finds suggests that extreme environmental stresses were prevalent both in the sea and on land through most of the Early Triassic