东太平洋地区DSDP573孔始新世末期的微玻璃陨石

通过研究 DSDP5 73孔的岩心样品 ,首次在该孔始新世与渐新世的界线地层含金属粘土层中发现了微玻璃陨石 ,且主要富集在其底部。一个样品 (5 g)中最多可达 12粒。这些微玻璃陨石主要呈球形、椭球形。用电子探针测试了其化学成分 ,Si O2 含量为 2 9.6 4%～ 5 8.93%,Al2 O3 为 3.42 %～ 2 0 .96 %,Fe O为 9.98%～ 2 9.5 5 %,Mg O为 4.32 %～ 16 .0 5 %,Ir为 0 .0 6 %～ 0 .81%。总体来说 ,微玻璃陨石的化学成分变化较大 ,可能与靶岩的成分变化较大有关。始新世末期北美微玻璃陨石场的展布方向约为 2 5 0°,这与太平洋板块运动方向改变所需要的矢量变化(2 45°)仅相差 5°,推测很可能是始新世末期陨星的撞击引起了太平洋板块在该时期的运动方向由 NNW突然变为NWW。     

Lower Eocene carbonate-cemented “chimney” structures (Varna, Bulgaria) — Control of seepage rates on their formation and stable isotopic signature

The genesis of Lower Eocene calcite-cemented columns, “pisoid”-covered structures and horizontal interbeds, clustered in dispersed outcrops in the Pobiti Kamani area (Varna, Bulgaria) is related to fossil processes of hydrocarbon migration. Field observations, petrography and stable isotope geochemistry of the cemented structures and associated early-diagenetic veins, revealed that varying seepage rates of a single, warm hydrocarbon-bearing fluid, probably ascending along active faults, controlled the type of structure formed and its geochemical signature. Slow seepage allowed methane to oxidize within the sediment under ambient seafloor conditions (δ¹⁸O = − 1 ± 0.5‰ V-PDB), explaining columns' depleted δ¹³C ratios of − 43‰. Increasing seepage rates caused methane to emanate into the water column (δ¹³C = − 8‰) and raised precipitation temperatures (δ¹⁸O = − 8‰). Calcite-cemented conduits formed and upward migrating fluids also affected interbed cementation. Even higher-energy fluid flow and temperatures likely controlled the formation of “pisoids”, whereby sediment was whirled up and cemented.     

Reply to comment by Y. Park and J.-H. Ree on 'Chemical remagnetization of the Upper Carboniferous-Lower Triassic Pyeongan Supergroup in the Jeongseon area, Korea: fluid migration through the Ogcheon Fold Belt'

In their comment, Park & Ree have raised several points against the interpretation by Park et al. , and argued that the remagnetization in the Jeongseon area was caused by the thermal effects of a Late Cretaceous pluton and/or associated short-range hydrothermal fluids, rather than by long-range fluids advocated by us.
We disagree with most points raised by Park & Ree and we make a case that these are invalid because of what we believe is incorrect geologic evidence. Hence, our model—that the fluids causing the chemical remagnetization might migrate through the fault system within the Ogcheon Fold Belt—is the most plausible scenario. We recognize that our model needs to be tested in a future study and we welcome new interpretations for or against our model based on reliable geologic or geophysical data.     

四川石渠县沙尔木盆地始新世孢粉的发现

热鲁组因其下部发现孢粉、轮藻等化石，被定为始新世，但其上部地层时代无从定论。笔者等最近在上部地层中发现较多的植物孢粉，并建立了Lycopodiumsporites ooligocenicus-Ephedlripites（Distach yapites）eocenipites-Peltandripites davissii孢粉组合带，确定热鲁组上部地层的形成时代为始新世。     

黄骅坳陷中北区沙河街组四段上亚段地层的确认

以往黄骅坳陷仅在南区的王官屯地区发现过确切的古近系沙河街组四段地层。上世纪 90年代初 ,地层古生物工作者曾根据个别单井孢粉化石资料 ,怀疑黄骅坳陷北区的北塘凹陷局部分布有沙四段。但由于当时的勘探程度较低 ,化石证据不足 ,因而没有得到广泛认可。中区板桥和歧口凹陷过去从未发现沙四段。通过对板桥凹陷地层的系统古生物分析 ,发现中北区沙三段下伏原来部分归属中生界的地层中含大量的藻类、介形虫、腹足类及轮藻化石 ,依据它们的生物群特征 ,这套地层应属于沙河街组四段 ,且为沙四段上亚段。     

Les manifestations tectoniques synsédimentaires associées à la compression éocène en Tunisie : implications paléogéographiques et structurales sur la marge Nord-Africaine

In central Tunisia, a synsedimentary tectonic episode has been pointed out through the tectonic movements affecting the Late Palaeocene–Early Eocene successions. This tectonic episode has controlled, to a large extent, the palaeogeographic setting of the area during that period and confirmed the important effect induced by the Pyrenean shortening phase on the edge of the African plate, which obviously has witnessed a common history with the southern part of the European plate. To cite this article: A. El Ghali et al., C. R. Geoscience 335 (2003).     

青藏高原祖尔肯乌拉山地区火山岩Ar-Ar年代学初步研究

对祖尔肯乌拉山地区 4个火山岩样品进行了Ar -Ar年龄测定 ,其坪年龄分别为 (40 91± 1 18)Ma、(41 0 7± 0 80 )Ma、(42 0 0± 1 31)Ma、(39 0 0± 2 0 6 )Ma。它们代表了这些火山岩的形成时代 ,表明本区在古近纪始新世中期发生过大规模的火山活动     

Did Paleogene North Atlantic rift-related eruptions drive early Eocene climate cooling?

The delivery of volcanogenic sulphur into the upper atmosphere by explosive eruptions is known to cause significant temporary climate cooling. Therefore, phreatomagmatic and phreatoplinian eruptions occurring during the final rifting stages of active flood basalt provinces provide a potent mechanism for triggering climate change.

During the early Eocene, the northeast Atlantic margin was subjected to repeated ashfall for 0.5 m.y. This was the result of extensive phreatomagmatic activity along 3000 km of the opening northeast Atlantic rift. These widespread, predominantly basaltic ashes are now preserved in marine sediments of the Balder Formation and its equivalents, and occur over an area extending from the Faroe Islands to Denmark and southern England. These ash-bearing sediments also contain pollen and spore floras derived from low diversity forests that grew in cooler, drier climates than were experienced either before or after these highly explosive eruptions. In addition, coeval plant macrofossil evidence from the Bighorn Basin, Wyoming, USA, also shows a comparable pattern of vegetation change. The coincidence of the ashes and cooler climate pollen and spore floras in northwest Europe identifies volcanism as the primary cause of climate cooling. Estimates show that whilst relatively few phreatomagmatic eruptive centres along the 3000 km opening rift system could readily generate 0.5–1 °C cooling, on an annual basis, only persistent or repeated volcanic phases would have been able to achieve the long-term cooling effect observed in the floral record. We propose that the cumulative effect of repeated Balder Formation eruptions initiated a biodiversity crisis in the northeast Atlantic margin forests. Only the decline of this persistent volcanic activity, and the subsequent climatic warming at the start of the Eocene Thermal Maximum allowed the growth of subtropical forests to develop across the region.