北半球72 ka BP气候突变事件及其与Toba火山的关系

72 ka BP左右的强降温事件是末次冰期最大的气候突变事件,且同时期发生了第四纪以来最强的火山喷发——Toba火山喷发,后者在此次强降温事件中扮演着什么角色一直是古气候学界研究的热点。对此进行深入的研究,有助于全面评价火山喷发的环境效应,进一步完善末次冰期突变事件的成因机制。系统回顾深海岩芯、极地冰芯、洞穴石笋、黄土、湖泊等古气候载体的研究成果,这些记录对72 ka BP左右的强降温事件和/或Toba火山喷发进行了不同程度的描述,并从不同的角度分析二者的关系。从72 ka BP左右的强降温事件和Toba火山喷发的时间上,以及火山喷发对气候变化影响的机理上看,Toba火山喷发确实对这次强降温事件产生了实质性影响。这个影响在格陵兰冰芯记录中表现得尤为明显,并得到了气候模拟的进一步支持。然而,部分低纬海洋记录研究表明,Toba火山喷发前后气候没有发生显著变化,至少低纬地区的气候不如高纬地区变化明显。古生物研究同时显示出Toba火山喷发并未对其生存环境产生灾难性的影响,由此可见,72 ka BP左右的强降温事件驱动机制及其对Toba火山喷发的响应程度尚存争议。今后的研究应重视提高气候记录分辨率和探测Toba火山喷发证据的研究,从解剖事件的内部结构特征入手,进而建立气候模式与火山效应之间的联系,以此来明确“72 ka事件”驱动机制及其对Toba火山喷发的响应关系。     

Records of Toba eruptions in the South China Sea -Chemical characteristics of the glass shards from ODP 1143A

Three layers of volcanic tephra, sampled from ODP 1143 Site in the South China Sea,were observed at the mcd depth of 5.55 m, 42.66 m, and 48.25 m, and named, in this paper, lay ers of A, B, and C, respectively. All of these tephra layers have an average thickness of ca. 2 cm.They were constrained in age of ca. 0.070 Ma, ca. 0.80 Ma, and ca. 1.00 Ma, respectively, by the microbiostratigraphy data. These tephra layers were predominated by volcanic glass shards with a median grain size of 70-75 μm in diameter. Major chemical compositions analyzed by EMPA and comparison with the previous data from other scatter areas suggest that these three layers of tephra can correspond to the three layers of Toba tephra, YTT, OTT, and HDT, respectively, erupt ing during the Quaternary. The occurrence of these tephra layers in the South China Sea implies that the Toba eruptions often occurred in the summer monsoon seasons of the South China Sea during the Quaternary, and that the strength of eruptions was probably stronger than that previously estimated.     

High-precision 40Ar/39Ar dating of pleistocene tuffs and temporal anchoring of the Matuyama-Brunhes boundary

High-precision ⁴⁰Ar/³⁹Ar ages for a series of proximal tuffs from the Toba super-volcano in Indonesia, and the Bishop Tuff and Lava Creek Tuff B in North America have been obtained. Core from Ocean Drilling Project Site 758 in the eastern equatorial Indian Ocean contains discrete tephra layers that we have geochemically correlated to the Young Toba Tuff (73.7 ± 0.3 ka), Middle Toba Tuff (502 ± 0.7 ka) and two eruptions (OTTA and OTTB) related to the Old Toba Tuff (792.4 ± 0.5 and 785.6 ± 0.7 ka, respectively) (⁴⁰Ar/³⁹Ar data reported as full external precision, 1 sigma). Within ODP 758 Termination IX is coincident with OTTB and hence this age tightly constrains the transition from Marine Isotope Stage 19–20 for the Indian Ocean. The core also preserves the location of the Australasian tektites, and the Matuyama-Brunhes boundary with Bayesian age-depth models used to determine the ages of these events, c. 786 and c. 784 ka, respectively. In North America, the Bishop Tuff (766.6 ± 0.4 ka) and Lava Creek Tuff B (627.0 ± 1.5 ka) have quantifiable stratigraphic relationships to the Matuyama-Brunhes boundary. Linear age-depth extrapolation, allowing for uncertainties associated with potential hiatuses in five different terrestrial sections, defines a geomagnetic reversal age of 789 ± 6 ka. Considering our data with respect to the previously published age data for the Matuyama-Brunhes boundary of Sagnotti et al. (2014), we suggest at the level of temporal resolution currently attainable using radioisotopic dating the last reversal of Earths geomagnetic field was isochronous. An overall Matuyama-Brunhes reversal age of 783.4 ± 0.6 ka is calculated, which allowing for inherent uncertainties in the astronomical dating approach, is indistinguishable from the LR04 stack age (780 ± 5 ka) for the geomagnetic boundary. Our high-precision age is 10 ± 2 ka older than the Matuyama-Brunhes boundary age of 773 ± 1 ka, as reported previously by Channell et al. (2010) for Atlantic Ocean records. As ODP 758 features in the LR04 marine stack, the high-precision ⁴⁰Ar/³⁹Ar ages determined here, as well as the Matuyama-Brunhes boundary age, can be used as temporally accurate and precise anchors for the Pleistocene time scale.     

The Relation between the 72 ka BP Event and the Toba Super-eruption

72 ka BP左右的强降温事件是末次冰期最大的气候突变事件,且同时期发生了第四纪以来最强的火山喷发———Toba火山喷发,后者在此次强降温事件中扮演着什么角色一直是古气候学界研究的热点。对此进行深入的研究,有助于全面评价火山喷发的环境效应,进一步完善末次冰期突变事件的成因机制。系统回顾深海岩芯、极地冰芯、洞穴石笋、黄土、湖泊等古气候载体的研究成果,这些记录对72 ka BP左右的强降温事件和/或Toba火山喷发进行了不同程度的描述,并从不同的角度分析二者的关系。从72 ka BP左右的强降温事件和Toba火山喷发的时间上,以及火山喷发对气候变化影响的机理上看,Toba火山喷发确实对这次强降温事件产生了实质性影响。这个影响在格陵兰冰芯记录中表现得尤为明显,并得到了气候模拟的进一步支持。然而,部分低纬海洋记录研究表明,Toba火山喷发前后气候没有发生显著变化,至少低纬地区的气候不如高纬地区变化明显。古生物研究同时显示出Toba火山喷发并未对其生存环境产生灾难性的影响,由此可见,72 kaBP左右的强降温事件驱动机制及其对Toba火山喷发的响应程度尚存争议。今后的研究应重视提高气候记录分辨率和探测Toba火山喷发证据的研究,从解剖事件的内部结构特征入手,进而建立气候模式与火山效应之间的联系,以此来明确＂72 ka事件＂驱动机制及其对Toba火山喷发的响应关系。     

Multiple interpretive errors? Indeed. Reply to: Climate effects of the 74 ka Toba super-eruption: Multiple interpretive errors in ‘A high-precision 40Ar/39Ar age for the Young Toba Tuff and dating of ultra-distal tephra’ by Michael Haslam

We would like to thank Michael Haslam (Haslam et al., 2013) for his interest in our recent contribution on the dating of the Young Toba Tuff/Tephra (YTT) (Mark et al., 2013). However, we point out errors made by Haslam, using this opportunity to clarify and expand on our discussion while also re-emphasising the important points from our study that have been overlooked.     

西藏昌都妥坝煤田沉积环境与聚煤规律

通过对妥坝煤田内沉积剖面的系统研究分析,对妥坝煤田的沉积相进行总结,判断煤田的沉积环境,恢复了妥坝煤田二叠世构造一岩相古地理格局。在认真研究妥坝煤田控煤因素,特别是控煤沉积环境及控煤构造样式基础上,研究后期地质事件所诱发的主要构造活动对煤层的影响,剖析了该煤田的主要聚煤规律。     

苏门答腊外海13.5万年来的火山灰记录:来自深海沉积物岩心IR-GC1的证据

Three volcanic ash layers were identified in a deep-sea Core IR-GC1 from the north-eastern Indian Ocean, adjacent to western Indonesian arc. They were dominated by glass shards with minor mineral crystals, such as plagioclase, biotite, and hornblende. According to the morphology and major element compositions of the representative glass shards, combined with the δ18O-based age, it is suggested that ash Layer A is correlated to the youngest Toba tuff(YTT), Layer B is supposed to be associated with a new eruption of Toba caldera in an age of 98 to 100 ka. Ash Layer C is different the geochemistry characteristics than those of Layer A and Layer B, suggesting that Layer C was not originated from Toba but registered another volcanic eruption event.     

Records of Toba eruptions in the South China Sea

Three layers of volcanic tephra, sampled from ODP 1143 Site in the South China Sea, were observed at the mcd depth of 5.55 m, 42.66 m, and 48.25 m, and named, in this paper, layers of A, B, and C, respectively. All of these tephra layers have an average thickness of ca. 2 cm. They were constrained in age of ca. 0.070 Ma, ca. 0.80 Ma, and ca. 1.00 Ma, respectively, by the microbiostratigraphy data. These tephra layers were predominated by volcanic glass shards with a median grain size of 70–75 μm in diameter. Major chemical compositions analyzed by EMPA and comparison with the previous data from other scatter areas suggest that these three layers of tephra can correspond to the three layers of Toba tephra, YTT, OTT, and HDT, respectively, erupting during the Quaternary. The occurrence of these tephra layers in the South China Sea implies that the Toba eruptions often occurred in the summer monsoon seasons of the South China Sea during the Quaternary, and that the strength of eruptions was probably stronger than that previously estimated.     

Effect of variations in net basin supply on lake levels and outflows

Starting from a simplified version of the water balance equation, it is shown how the levels and outflows from a open lake can be related to the magnitude and statistical characteristics of the annual net basin supply series, which is defined as the net inflow arising from tributary inflows, rainfall on the lake surface and the lake evaporation. Using the models, estimates are derived for the response time for several large open lakes in Africa and Asia. Also, the observed net basin supply series for three major lakes (Victoria, Malawi and Toba) are investigated in detail. It is suggested that, on an annual basis, the assumption of a random normally distributed series of net basin supply can provide a reasonable first guess for the equilibrium response of a lake and for the likely range of variation of levels. These estimates are likely to be useful in water resources assessments and for investigations of the effects of land use and climate change on lake levels. The effects of departures from this simplified approach are discussed and are illustrated with some practical examples. © 1998 John Wiley & Sons, Ltd.