Late Eocene Sporopollen and Paleoclimate, Paleoenvironment of the Yuanqu Basin, Shanxi

1.IntroductionTheYuanquBasinisoneoftheearliestst-UdiedCenozoicinlandbasinsinChina.Duetotheabun-dantmammalfossilsexcavatedfromthePaleogenestrataofthebasin,especiallythecompIeteandsuc-cessivestrataaswellasvariousabundantmammalfossilsofLateEocene,whichprovidesasufficientfoundationforthedeterminationofstratigraphicalage,itisregardedasaremarkablecriterionforcor-relationwithotherbasins.TheYuanquBasinIiesatthesouthemmarginoftheNofthChinaplatform,theFigurel.1ndexmapshowingthelocationoftheYuanqu…     

辽宁抚顺盆地始新世古气候定量研究

利用德国科学家 Mosbrugger 和 Utescher 在 1997 年提出的共存分析法对辽宁抚顺盆地始新世古气候进行定量重建。通过共存分析获得的抚顺盆地始新世古气候参数为：年均温度为 14.3～19.8℃（中值为 17.05℃）,最热月均温为 24.1～27.7℃,最冷月均温为 2.5～10.9 ℃,年较差为 17.7～22.7℃,年降雨量为 803.6～1 113.3 mm (中值为 958.45 mm),最大月降雨量为 179.4～268.1 mm,最小月降雨量为 10.2～12.7 mm。与现代气候对比发现：始新世时气温较现在（7.8℃）高9.25℃,年降雨量较现在（734.5 mm）多约224 mm,始新世时属于亚热带季风气候,现今为温带季风气候。     

中国晚始新世—早渐新世地层孢粉组合及其古气候特征

始新世—渐新世是从65Ma恐龙绝灭以来新生代地球历史上最重要的事件, 此时地球从“暖室”过渡到“冰室”, 全球气候突变, 南极冰首次出现, 气候突变引起生物的大绝灭, 而我国的孢粉组合也有明显的变化特征.根据我国各个区始新世晚期—渐新世早期地层中孢粉组合的演化规律来探讨当时我国的古气候变化规律, 研究认为中国从始新世晚期到渐新世早期总体上亚热带、热带植物成分丰度和分异度都降低, 温带植物如桦科和榆科花粉大增, 耐寒山地针叶植物大量发育, 干旱类型植物增加, 草本植物开始繁盛.这些反映了从始新世晚期到渐新世早期植被组成由热带亚热带常绿阔叶树为主的针阔叶林转变为落叶树为主的针阔混交林, 说明晚始新世气候温暖湿润过渡到早渐新世气候变干变冷.孢粉植物群所反映的我国气候变化趋势与全球气候变化趋势一致, 说明我国的陆地也受全球构造的演变和南极大陆冰盖的影响.      

温室背景下陆相抚顺盆地始新世西露天组古气候演化

古近纪古新世—始新世极热事件和始新世后期变冷的古气候事件是目前沉积学和古气候学研究的热点, 但相关研究在陆相地层中较少涉及。前人对抚顺盆地始新世一系列极热事件进行了识别和成因研究, 但针对始新世后期开始变冷的古气候波动状况尚未进行系统分析。本文采用了古气候参数磁化率和色度对抚顺盆地始新世西露天组(晚始新世)古气候的波动和演化特征进行研究。通过对高精度磁化率和色度数据进行聚类分析和垂向演化规律对比发现, 西露天组沉积记录具有高的频率磁化率(12.58%~39.63%)、中高色度a*值(5.6%左右)和中高色度b*值(9.1%左右), 且这些数值均与古气温具有很好的对应性, 鉴于此, 这两种参数可以作为始新世陆相古气候演化研究的有效手段。抚顺盆地西露天组自底部到顶部, 频率磁化率呈由高值到低值缓慢下降的趋势, 色度a*值和b*值总体呈现先增加后减少的趋势, 这些均显示了抚顺盆地始新世整体温室气候背景下的降温过程。本次对晚始新世古气候变化趋势研究的认识, 联合前人在早始新世古气候演化的研究成果, 可以共同为东亚地区完整的始新世古气候演化研究提供可靠素材。     

卢氏盆地中始新世沉积序列自生碳酸盐及其古气候意义

始新世暖期可作为当代全球变暖的历史相似型,研究始新世气候变化及其机制对于理解现代气候变暖的幅度和速率具有重要意义。卢氏盆地位于中国中部秦岭东段,发育了连续的、富含碳酸盐矿物的始新世湖相沉积物,是重建始新世暖期陆地气候的良好材料。本研究在卢氏盆地郑家山-三角沟一带（34°04'N,111°10'E）采集了张家村组中上部和卢氏组的样品,采样层厚约288 m,共采集样品505个。根据岩石薄片镜下鉴定,卢氏盆地中始新世湖相沉积物物质组成以碳酸盐、粘土和粉砂为主,其中碳酸盐沉积为表生条件下封闭或半封闭淡水湖或微咸水湖化学作用自生成因。使用傅里叶红外光谱（FTIR）漫反射法测定沉积物碳酸盐含量,发现其与磁化率具有一定的负相关关系,分别指示了内源化学沉积和外源碎屑输入的贡献量,受控于流域蒸发量与降水量的共同作用,揭示了中始新世卢氏盆地的干湿变化。当流域更加湿润,即降水量增加（蒸发量减少）时,径流量相应增加,不利于碳酸盐沉淀而有利于外源碎屑输入,表现为沉积物碳酸盐含量降低、磁化率数值升高,反之同理。在已有年代框架的基础上,建立了卢氏盆地湖相沉积物碳酸盐含量时间序列,其记录了在中始新世气候适宜期（MECO）卢氏盆地较为湿润的气候环境,并且具有多旋回变化,与地球运动轨道的周期变化相关。

     

Palaeogeographical influence on Late Eocene biosiliceous sponge-rich sedimentation, southern Western Australia

Late Eocene nearshore shallow-marine environments within the Bremer and western Eucla Basins of southern Western Australia were characterized by the thick deposition of spongolite and spiculite deposits. Epibenthic sponge communities dominated estuaries and topographically complex basin margin embayments-archipelagos, while cool-water carbonates with up to 10% sponges accumulated in open-shelf environments. The transition from a biosiliceous to calcareous epibenthos was related to the degree of palaeogeographical 'protection'. Within basement-protected embayments there was an offshore gradation from shoreface spongolite and pure spiculite to a muddy spiculite facies towards central embayment areas. Calcareous fossils are rare throughout embayment facies, but rapidly increase in more open outer archipelago areas. This depositional relationship occurred along 2000 km of the Late Eocene southern Australian coastline. Palaeogeographical protection from strong currents acted in concert with: (1) a planar, low-gradient inland topography with sluggish run-off, supplying fine-grained sediment, nutrients, and abundant dissolved silica; and (2) a microtidal setting, weak to moderate swells and opposing wind and Coriolis surface current forcing, which inhibited water exchange between embayments-estuaries and the open shelf. This situation led to an embayment water chemistry that encouraged prolific sponge growth. Calcareous spiculites record the mixing front between these embayment waters and normal open-shelf waters supporting cool-water carbonates.     

抚顺盆地东露天煤矿早始新世孢粉组合特征及其古气候意义

系统研究了抚顺盆地东露天煤矿主煤层古城子组植物孢粉组合特征,并采用共存分析法(coexistence approach)定量分析了该区早始新世古气候。笔者在古城子组共发现孢粉化石71属159种,其中,被子植物花粉莫米粉(Momipites)、山核桃粉(Caryapollenites)、榆粉(Ulmipollenits)和栎粉(Quercoidites)含量较高;裸子植物花粉含量高,以杉粉(Taxodiaceaepollenites)和无口器粉(Inaperturopollenites)占绝对优势;蕨类植物孢子以水龙骨单缝孢(Polypodiaceaesporites)及紫萁孢(Osmundacidites)为主。亚热带类群丰富且花粉含量较高(56.3%~91.8%)。孢粉组合反映了该盆地分布以杉科(Taxodiaceae)丰富为特征的沼泽湿地林,可能为重要的成煤植物;盆地低山地带分布有常绿和阔叶落叶混交林为主的森林植被。通过共存分析法获得抚顺盆地早始新世年均温为14.9℃~15.8℃,年均降水量为1011.3~1163 mm。孢粉植物群特征及古气候参数综合分析,抚顺盆地早始新世属于温暖湿润的亚热带气候。     

Molecular composition and paleobotanical origin of Eocene resin from northeast India

The molecular composition of fossil resins from early to middle Eocene coal from northeast India, has been analyzed for the first time to infer their paleobotanical source. The soluble component of fossil resin was analyzed using gas chromatography–mass spectrometry (GC–MS). The resin extracts are composed of cadalene-based C₁₅ sesquiterpenoids and diagenetically altered triterpenoids. The macromolecular composition was investigated using pyrolysis gas chromatography-mass spectrometry (Py-GC–MS) and Fourier transform infrared (FTIR) spectroscopy. The major pyrolysis products are C₁₅ bicyclic sesquiterpenoids, alkylated naphthalenes, benzenes and a series of C₁₇–C₃₄ n-alkene-n-alkane pairs. Spectroscopic analysis revealed the dominance of aliphatic components. The presence of cadalene-based sequiterpenoids confirms the resin to be Class II or dammar resin, derived from angiosperms of Dipterocarpaceae family. These sesquiterpenoids are often detected in many SE Asian fluvio-deltaic oils. Dipterocarpaceae are characteristic of warm tropical climate suggesting the prevalence of such climate during early Eocene in northeast India.     

天文驱动下的中始新世东营凹陷气候水文演化与有机质富集机理

中始新世是古近纪温室气候到冰室气候的重要过渡期, 对该时期气候演化的认识主要来自海相沉积记录, 而来自陆相沉积记录的证据相对较少, 因此探索该时期陆相气候特征和演化规律具有重要意义。渤海湾盆地东营凹陷始新统沙河街组的沙四段-沙三段富有机质页岩层系不仅是我国东部陆相页岩油勘探的重点层段, 而且为系统研究中始新世陆相气候演化提供了详实的地质记录。本研究以东营凹陷N1井中始新统(沙四下亚段顶部-沙四上亚段-沙三下亚段下部)厚度约253 m的富有机质页岩层系为分析对象, 利用伽马(GR)测井曲线, 结合沉积速率定量估计的相关系数法(COCO), 开展旋回地层学研究, 建立了天文年代标尺。在此基础上, 进一步综合Ca和Ti含量、Fe/Al比值以及TOC含量数据, 探讨天文驱动力对中始新世东营凹陷气候水文演化和有机质富集的控制作用。结果表明, N1井研究目的层段的沉积年龄为45.06 Ma至40.45 Ma, 记录的沙四上亚段延续时间为2.76 Ma, 与具有良好年代框架的东营凹陷FY1井的分析结果一致。通过建立偏心率周期与高频层序的对应关系, 以GR时间序列的405 ka长偏心率周期作为四级层序的参考曲线, 以约100 ka短偏心率周期作为五级层序的参考曲线, 将研究目的层段划分出11个四级层序和45个五级层序。研究结果显示, 在约41.6 Ma之前, TOC含量、Ca含量和Fe/Al比值时间序列的405 ka周期与Ti含量时间序列和La2010d的405 ka周期呈反相关系; 在约41.6 Ma之后, TOC含量、Ca含量和Fe/Al比值时间序列的405 ka周期与Ti含量时间序列的405 ka周期依然是反相关系, 但与La2010d的405 ka周期转为正相关系。这说明在约41.6 Ma前后, 长偏心率周期影响下的东营凹陷的陆源输入、古生产力、氧化还原条件以及有机质富集机理具有显著差异, 这可能与天文驱动力和该时期区域气候变化(总体由干旱转为潮湿)的叠加效应有关。

     

秦岭东段卢氏盆地始新世沉积序列与气候环境变迁

始新世是新生代重要的暖期,其气候环境的特征与演化备受学界关注。位于秦岭东段的卢氏盆地保存了>1000 m厚的连续的始新世河湖相沉积物,是揭示古气候和环境变化规律的宝贵沉积记录。在前人工作基础上,本研究利用沉积学、古生物学、碎屑年代学等方法对卢氏盆地始新世地层的沉积特征、年代和环境进行了分析。结果表明：1）碎屑磷灰石裂变径迹与碎屑锆石U-Pb年龄指示沉积序列年代晚于约60 Ma,与前人将张家村组-卢氏组化石组合对比到中始新世的结论基本吻合。2）始新统张家村组沉积相演化表现为冲积扇→河流→洪泛平原或滨湖,反映盆地拉张、初期成湖的过程;卢氏组为滨浅湖→深湖/半深湖→滨浅湖或洪泛平原→浅湖/半深湖,反映湖泊开始稳定出现后的扩张、收缩和复活过程;大峪组为河流→洪泛平原→冲积扇,反映湖泊淤满消亡后河流与冲洪积物相继充填的历史。3）沉积相、化石组合、盐类矿物种类揭示中始新世卢氏盆地古气候为半湿润半干旱,地表景观呈现径流活跃、动物种类多样、树木茂盛、发育淡水至微咸水湖的特征,并可能具有一定的季节性。卢氏盆地沉积序列提供了始新世暖期中国中部气候环境变化的重要证据。

     

江汉盆地始新世中、晚期古气候定量重建初探

依据江汉盆地明钾1孔中、晚始新统系统的孢粉资料, 应用化石孢子花粉亲缘植物的生态位估算孢粉组合所反映的古气候特征.气候参数曲线的变化趋势显示江汉盆地始新世中期气候参数与现今北纬2 2°~ 2 6°的数值相接近, 为中-南亚热带湿润半湿润气候.晚期气温较前期低1~ 4℃, 相当于现今北纬2 3°~ 2 8°处的数值, 为北-中亚热带气候.但是, 气候构型与现今截然不同, 具有气温高、年较差小、降水波动大的特点.始新世中期1月均温比今高5~ 9℃, 表明冬季风作用尚不明显, 晚期略显冬季风的影响.气候的降温发生在孔深2 10 0m处, 主要表现为1月均温的下降和年较差增长, 因而孢粉组合中落叶阔叶树种增多.年降水量波动强烈, 一般于30 0~ 170 0mm之间, 这有利于盐类矿物的迁移和堆积.降水量低于10 0 0mm时, 麻黄灌木花粉增多, 且与膏盐堆积深度相一致.高山深盆的干热环境是本区盐类矿物沉积的主要原因, 年降水量波动强烈且偏低, 有利于盐类的持续堆积, 从而有别于现今西北地区的盐类堆积.      

The Paleocene and Eocene in the Russian part of West Eurasia

Biostratigraphic charts of marine Paleocene and Eocene in the European and West Siberian parts of Russia include the unified zonations of nannoplankton, planktonic and benthic foraminifers, dinocysts, radiolarians, diatoms, and palynomorphs of higher plants. These regional zonations summarize comprehensive data on the Lower Paleogene, which have been obtained by paleontologists and biostratigraphers in the last century. In the content and resolution degree, they represent a solid basis for geological and paleogeographic consideration and characterize the time succession of diverse biotic and abiotic events. On the other hand, the depicted biotic events have been controlled by successive tectonic, paleogeographic, and paleoclimatic events, because organisms determining contents of biostratigraphic zones changed not only in the course of evolution, but also in response to transformation of surroundings. As elements of general communication systems, epicontinental seas of the Paleogene have been interconnected via straits and seaways, which promoted interchange of water masses and biotas belonging to the Tethys, Atlantic or Arctic oceans, and inner seas. Size and configuration of the seas and seaways changed under influence of tectonic processes and eustatic events of epeirogenic or regional origin. Widening, narrowing, and cessation of communication ways have been responsible for different-scale changes in sedimentation and biotic environments. New materials on the Paleogene in a vast territory of Russian sector of West Eurasia offer an opportunity to revise somewhat the dynamics of climatic changes in the Northern Hemisphere during the Early Cenozoic, which characterize the terminal phase of transition from the warm to cold biosphere of the Earth.     

Primary Study on Quantitative Reconstruction of Middle-Late Eocene Climate in Jianghan Basin

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｑｕａｎｔｉｔａｔｉｖｅｒｅｃｏｎｓｔｒｕｃｔｉｏｎｏｆｐａｌｅｏｃｌｉｍａｔｅｆａｃｔｏｒｓｉｓｔｈｅｆｏｃｕｓｏｆｓｔｕｄｙｏｎｅｎｖｉｒｏｎｍｅｎｔｉｎｔｈｅｐａｓｔ ,ａｎｄａｎｅｆ ｆｅｃｔｉｖｅｔｏｏｌｆｏｒｔｈｅｑｕａｎｔｉｔａｔｉｖｅｒｅｓｅａｒｃｈｉｎｔｏｔｈｅｐａｌｅｏｃｌｉ ｍａｔｅｉｓｔｈｅｔｒａｎｓｆｏｒｍａｔｉｏｎｏｆｓｐｏｒｅ ｐｏｌｌｅｎｄａｔａ .ＴｈｅｍａｉｎｐｅｒｉｏｄｔｈｕｓｉｎｖｏｌｖｅｄｗａｓｔｈｅＱｕａｔｅｒｎａｒｙｉｎｓｔｅ…     

中-晚始新世渭河盆地古气候变化的红河组磁化率记录

始新世暖期可为理解现代增温过程和机制提供历史相似型。广泛分布于渭河盆地的红河组为中始新世到晚始新世的滨浅湖相-冲积扇堆积,剖面出露厚度超过330 m,盆地沉积中心钻探厚度大于1000 m,为一套红色的碎屑沉积间化学沉积序列。盆地边缘的红河组沉积物含碳酸盐岩、泥岩、砂岩和少量砾岩,沉积中心以泥质灰岩、泥岩和粉砂岩为主。对蓝田支家沟红河组（时代为46~33 Ma）2910个样品的磁化率测试表明,红河组沉积物磁化率值在0~20×10^-8 m³/kg之间,整体偏低,频率磁化率值也相对较低（0~11%）,与中国西北部新生代红层磁化率总体较低相似。高分辨率磁化率测试证实了红河组堆积时期干湿变化的多旋回和阶段性,受到太阳辐射变化影响,并受到下垫面的反馈驱动。红河组泥岩和粉砂岩的磁化率值偏高,而砂岩的磁化率值较低,载磁矿物以赤铁矿为主。盆地周围岩体弱磁性物质的快速输入,降低了红河组粗颗粒沉积物的磁化率值。在中、晚始新世的轨道-构造时间尺度,红河组沉积序列粒度变化受到湖面波动控制。湖面上升时湖滨地区沉积物颗粒偏细,磁化率值高;反之,磁化率值低。因此,磁化率高低变化指示了湖面高低波动,进而指示了气候的干湿变化。分析还表明,中、晚始新世渭河盆地湖面多旋回变化和阶段性变干,与全球温度变化和降温过程可良好对比,指示全球温度降低可能抑制水汽循环,进而驱动始新世东亚内陆干旱的发展。

     

Spatial distribution of climatic conditions from the Middle Eocene to Late Miocene based on palynoflora in Central,Eastern and Western Anatolia

The continental climatic evolution of Anatolia has been reconstructed quantitatively for the last 45 million years using the coexistence approach. Although there were some regional effects, the Anatolian Cenozoic continental climate record correlated with the European climatic condition and the global oxygen isotope record from marine environments. From middle Eocene to late Miocene, continental warming in Anatolia was pronounced for inferred winter temperature and mean annual temperature as in Europe. Generally, the palaeoclimatic property of Anatolia resembles the European climatic changing and marine temperature changing based on the oxygen isotope record; however, climatic values of the terrestrial area in Anatolia are higher from Lutetian to Aquitanian and these values are lower than European values from Aquitanian to Tortonian. Correspondingly, Cenozoic climatic cooling in Anatolia is directly associated with an increase of seasonality, palaeogeographic position and terrestrial condition. Furthermore, mean annual precipitation values of Anatolia remained relatively stable during the Eocene–Oligocene; however, these values indicated changing throughout middle–late Miocene. Moreover, in this study, decline of abundance and variables for the mangrove and back mangrove palaeocommunities during the last 45 million years is recorded because of the decreasing of humidity, temperature and increasing of terrestrial condition.     

东营凹陷中始新统上部-上始新统层序地层模式及其石油地质意义

通过识别沉积基准面旋回产生的层序界面,东营凹陷中始新统上部-上始新统可划分出四个层序。各层序具有相似的成因和体系域构成。其低位域 (LST)发育辫状河、下切水道-浊积扇、扇三角洲、废弃型三角洲和水下扇。湖泊扩张体系域 (EST)发育由深湖泥岩、油页岩、白云岩、滨浅湖组成的湖泊体系、破坏型三角洲及曲流河体系。湖泊萎缩体系域 (RST)发育浅湖、河流三角洲体系及扇三角洲体系。由于同一层序在盆地发育的构造部位不同,可以表现出三种层序样式 :A位于构造坡折带之下的深湖-三角洲环境层序样式,B、位于构造坡折带之上的下切水道-浅湖环境层序样式和C、位于湖域之外的河流-泛滥平原环境层序样式。并在综合研究的基础上建立了东营凹陷中始新统上部-上始新统层序的成因模式。指出在每个三角洲主朵体的前方同生断裂带及其靠近洼陷一侧是低位砂体的主要发育区,也是低位砂体油藏的富集区和寻找隐蔽油藏的主要方向。     

Geochemistry of the Eocene Felsic Porphyric Rocks and High-Mg Potassic Rocks along JARSZ: Implication for the Tectonic Evolution in Eastern Tibet

<正>Eocene felsic porphyric rocks and the high-Mg potassic volcanic rocks(HMPR) occur along the Jinshajiang-Ailao Shan-Red River shear zone(JARSZ) in eastern Tibet.Compared with the HMPR,which are generally believed to be sourced from an enriched mantle,the felsic porphyric rocks show similar K_2O contents,enrichment in LREE and LILE,particularly radiogenic isotope(e.g.Sr and Nd) features much similar to the former,implying generation of the felsic porphyric rocks most likely related to the HMPR,although they both have clearly different major and trace element compositions. The close relationship in spatial-temporal distribution and similar Sr-Nd characteristics between the felsic porphyric rocks and HMPR in eastern Tibet indicate that both of them were possibly formed by a similar tectonic process(event).Combining the basic dikes in southern and eastern Tibet,we suggest that the break-off of north-dipping Neo-Tethyan slab in southern Tibet during 50-40 Ma,triggered formation of high-Mg potassic magma.This led to developing felsic porphyric magma production by partial melting of underplating HMPR in the lower crust,or fractionation crystallization of the high-Mg potassic magmas.The break-off of slab in the Eocene may also have contributed to the abundant ore-forming material related to earlier subduction events,resulting in formation of the porphyric deposits along JARSZ in eastern Tibet.     

青藏高原始新世构造岩相古地理

在前人研究成果的基础上,分析青藏高原始新世残留盆地的构造背景、岩石地层序列和青藏高原始新世期间的构造岩相古地理特征。松潘-甘孜和冈底斯带为大面积构造隆起蚀源区,塔里木东部、柴达木、羌塘、可可西里地区主体表现为大面积的构造压陷湖盆-冲泛平原沉积,高原西部和南部为新特提斯海。从构造岩相古地理演化的角度揭示青藏高原始新世构造隆升与沉积响应的耦合关系,划分出2个强隆升期,分别是强隆升期Ⅰ(55-51Ma)和强隆升期Ⅱ(45-34Ma)。     

Orbital forcing in turbidite accumulation during the Eocene greenhouse interval

The influence of astronomically driven short‐term climate change (Milankovitch cycles) on deep‐marine turbidite systems is not well‐known, particularly in the case of long‐term greenhouse intervals with no significant glacio‐eustatic sea‐level fluctuations. This study, carried out at the Gorrondatxe section (Global Stratotype Section and Point for the base of the Lutetian Stage in the western Pyrenees), demonstrates that the characteristics of lower–middle Eocene fan‐fringe/basin‐plain turbiditic and pelagic deposits varied in line with orbitally forced fluctuations in seasonal rainfall, runoff and terrigenous input to the sea. Reduced turbiditic activity during the formation of pelagic limy precessional hemicouplets indicates subdued seasonality and low terrigenous input. Conversely, turbidity currents were more frequent, had greater energy and were more voluminous during the formation of pelagic marly hemicouplets, suggesting precessional hemicycles with strong seasonality and heavy summer rainfall. These differences at precessional time scales were enhanced at maximum eccentricity because turbiditic activity was most intense when boreal summer occurred at perihelion (i.e. maximum seasonality) but declined when it occurred at aphelion. At minimum eccentricity, with relatively weak seasonality throughout one (or more than one) precessional cycle (>21 kyr), turbiditic activity remained relatively low. The pattern observed at the Gorrondatxe fan‐fringe/basin‐plain succession implies that the orbitally forced environmental changes must also have affected the inner and middle parts of the submarine fan. The astronomical influence on terrigenous sediment input also determined the changing characteristics of the pelagic sedimentation. Thus, terrigenous sediment contribution to pelagic sedimentation fluctuated by a factor of five during opposite precessional situations at maximum eccentricity, whereas there was almost no fluctuation at minimum eccentricity.     

Early Eocene estuary at Strahan,Tasmania

Evidence from sedimentology is combined with that of palynology and macropalaeobotany to arrive at a general reconstruction of the Early Eocene environment in Macquarie Harbour in western Tasmania and its major vegetation types. The environment is interpreted as estuarine with a range of subenvironments including estuarine mouth bar, fully subtidal sands, tidal flat with mangroves, and freshwater swamps. Supratidal freshwater swamp forest (sometimes conifer‐dominated) was fringed with Nypa mangrove swamps in the high tidal regions. Non‐vegetated tidal mud and sand flats occurred in regions with longer tidal submergence. The Macquaríe Harbour beds are given formation status and the Strahan Sand Member is defined.