ABSTRACT
Sedimentological, textural, and microscale analyses of the Mount McRae Shale revealed a complex postdepositional history, previously unrecognized in bulk geochemical studies. We found that metal enrichments in the shale do not reside with depositional organic carbon, as previously proposed by Anbar et al., but with late-stage pyrite, compromising claims for a "whiff" of oxygen ~50 million years before the Great Oxygenation Event.
ABSTRACT
Transient appearances of oxygen have been inferred before the Great Oxygenation Event (GOE) [â¼2.3 billion years (Ga) ago] based on redox-sensitive elements such as Mo and Smost prominently from the â¼2.5-Ga Mount McRae Shale in Western Australia. We present new spatially resolved data including synchrotron-based x-ray spectroscopy and secondary ion mass spectrometry to characterize the petrogenesis of the Mount McRae Shale. Sediments were primarily composed of organic matter and volcanic ash (a potential source of Mo), with U-Pb ages revealing extremely low sedimentation rates. Catagenesis created bedding-parallel microfractures, which subsequently acted as fluid pathways for metasomatic alteration and recent oxidative weathering. Our collective observations suggest that the bulk chemical datasets pointing toward a "whiff" of oxygen developed during postdepositional events. Nonzero Δ33S in trace-metalpoor, early diagenetic pyrite and the unusually enriched organic carbon at low sedimentation rates instead suggest that environmental oxygen levels were negligible â¼150 million years before the GOE.
ABSTRACT
The Paleoproterozoic (1.7 Ga [billion years ago]) metasedimentary rocks of the Mount Barren Group in southwestern Australia contain burrows indistinguishable from ichnogenera Thalassinoides, Ophiomorpha, Teichichnus, and Taenidium, known from firmgrounds and softgrounds. The metamorphic fabric in the host rock is largely retained, and because the most resilient rocks in the sequence, the metaquartzites, are too hard for animal burrowing, the trace fossils have been interpreted as predating the last metamorphic event in the region. Since this event is dated at 1.2 Ga, this would bestow advanced animals an anomalously early age. We have studied the field relationships, petrographic fabric, and geochronology of the rocks and demonstrate that the burrowing took place during an Eocene transgression over a weathered regolith. At this time, the metaquartzites of the inundated surface had been weathered to friable sandstones or loose sands (arenized), allowing for animal burrowing. Subsequent to this event, there was a resilicification of the quartzites, filling the pore space with syntaxial quartz cement forming silcretes. Where the sand grains had not been dislocated during weathering, the metamorphic fabric was seemingly restored, and the rocks again assumed the appearance of hard metaquartzites impenetrable to animal burrowing.
Subject(s)
Geologic Sediments/analysis , Geologic Sediments/chemistry , Animals , Australia , FossilsABSTRACT
Objective To observe the changing rules of the voltage-current characteristics and blood flow perfusion of Sanyinjiao (SP6) at different time points of a menstrual cycle in healthy female subjects, and provide evidence for acupoint specificity.Method Fifty-one healthy college students were observed for the voltage-current characteristics and blood flow of Sanyinjiao and its control point before, during and after menstruation.Result The increasing volt-ampere area, decreasing volt-ampere area and inertial area of left Sanyinjiao were significantly smaller than those of the control point during and at the end of menstruation (P<0.05), and the inertial area of right Sanyinjiao was significantly smaller than that of the control point during menstruation (P<0.05); during non-menstruation period and at the end of menstruation, the blood flow perfusion of bilateral Sanyinjiao was significantly larger than that of the control point (P<0.05), and the blood flow of left Sanyinjiao was significantly larger than that of the control point (P<0.05) during menstruation period; the blood flow perfusion of right Sanyinjiao showed a significant negative correlation with the increasing volt-ampere area and inertial area (P<0.05).Conclusion Acupoint can sensitively reflect the qi-blood change of human body, and the rich blood flow in acupoint area should be a crucial reason causing the low resistance.
ABSTRACT
Objective To observe the changing rules of the voltage-current characteristics and blood flow perfusion of Sanyinjiao (SP6) at different time points of a menstrual cycle in healthy female subjects, and provide evidence for acupoint specificity.Method Fifty-one healthy college students were observed for the voltage-current characteristics and blood flow of Sanyinjiao and its control point before, during and after menstruation.Result The increasing volt-ampere area, decreasing volt-ampere area and inertial area of left Sanyinjiao were significantly smaller than those of the control point during and at the end of menstruation (P<0.05), and the inertial area of right Sanyinjiao was significantly smaller than that of the control point during menstruation (P<0.05); during non-menstruation period and at the end of menstruation, the blood flow perfusion of bilateral Sanyinjiao was significantly larger than that of the control point (P<0.05), and the blood flow of left Sanyinjiao was significantly larger than that of the control point (P<0.05) during menstruation period; the blood flow perfusion of right Sanyinjiao showed a significant negative correlation with the increasing volt-ampere area and inertial area (P<0.05).Conclusion Acupoint can sensitively reflect the qi-blood change of human body, and the rich blood flow in acupoint area should be a crucial reason causing the low resistance.
