VERTICAL ZONATION OF FORAMINIFERA ASSEMBLAGES IN GALPINS SALT MARSH, SOUTH AFRICA-猫眼课题宝

南非加尔平斯盐沼有孔虫群落的垂直分区

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2015

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作者：

K. Strachan;T. Hill;J. Finch;R. Barnett

摘要盐沼有孔虫是海平面变化的精确指示器，其表面组合随其在潮汐框架中的位置而变化。在南非Galpins盐沼的海拔梯度上采集了表层沉积物样品，以研究有孔虫的垂直分布及其在海平面研究中的潜在用途。沼泽分为三个垂直带（高沼泽，middlemarsh，泥滩）由三个assemblageguides代表，与凝集的物种限制在上游的沼泽和石灰质物种更占主导地位的潮间带通道。高沼泽区以Jadammina macrescens为主，并存在Trochammina inflata。中部沼泽以T. inflata和Miliammina fusca。泥滩中发现的钙质物种包括Haynesina germanica、Battava氨和Quinqueloculina sp.本文描述了如何利用沼泽有孔虫来定义沿着现代沼泽表面的小尺度垂直带以及这些带如何对应于植物区系。我们证明，沼泽有孔虫有可能被用作精确的指标，为海平面重建在南非。引言现代有孔虫组合形式离散的垂直带在盐沼，强烈相关的潮汐水平（斯科特等，2001; Gehrels &纽曼，2004）。现代有孔虫分布与一系列环境变量（包括海拔、植被覆盖、pH值和盐度）之间的关系可以精确量化（例如，使用多变量统计），representinga现代analogue反对比较fossilassemblages。盐沼经历着盐度的每日和季节性变化，以及与潮汐溢流有关的洪水频率。几位作者认为有孔虫的垂直分带与海拔高度密切相关，特别是在温带环境中（Scott & Medioli，1980; Scott & Leckie，1990; Horton & Edwards，2003，2006;Leorri等人，众所周知，各种生态控制对表面有孔虫的分布产生影响（例如，Murray，1971年; Scott等人，一九九八年; Horton，1999年），尽管组合一直显示出根据潮汐框架的垂直分区，无论是直接还是间接（Berkeley等人，2007年）。De Rijk T Horton & Edwards于2006年在马萨诸塞州的大沼泽进行的一项研究）。沼泽有孔虫的现代类似物传统上是在提取沉积物岩心进行古生物学分析的位置采集的（Gehrels，1994;肯普等人，2009年）。如果组合仅在单一地点被确定，则一些化石样本可能缺乏现代类似物，从而影响重建的准确性（Murray，2006年）。现代类似物的缺乏可以通过对更广泛的当代环境进行采样来解决（海沃德等人，2004; Horton & Edwards，2006;肯普等人，2009).研究人员一直在争论最好的组合组成有孔虫种群研究。有些人主张总的组合使用，表明环境条件的季节性和时间波动（斯科特等人，2001;Horton等人，2005年）。根据Murray（1971）的观点，活的种群最能代表现代环境，因为仅仅使用死亡的组合无法解释死后的变化。然而，可以说，生活组合的分布将取决于采样时的条件，而不是平均时间。在温带环境中，一些人认为只使用死亡组合是很重要的，因为它们不受季节变化的影响，因此准确地反映了地下组合（Murray，1979; Horton等人，2005; Horton & Murray，2007）。有时，仍然使用由总组合（活的+死的）组成的训练集，这是基于活的组合在时间上将有助于化石记录的假设（Booth等人，2010年）。对新斯科舍省沼泽表层沉积物中有孔虫组合进行的一项研究得出结论，总有孔虫组合为古环境研究提供了良好的基础（Scott & Medioli，1980）。2010年）。最高的潮间带通常由Jadammina macrescens和Trochamminainflata占主导地位，随着海拔的降低，它们被诸如Haplophrag-moides sp.和Miliammina fusca的物种所取代（Hawkes等人，2010年）。上、中沼泽以凝集种为主，以钙质种为主。这种关系取决于

ABSTRACT Salt-marsh foraminifera are used as precise sea-levelchange indicators as surface assemblages vary in relation totheir position in the tidal frame. Surface-sediment sampleswere collected across an elevation gradient at Galpins saltmarsh, South Africa, to study the vertical distribution offoraminifera and their potential use for sea-level studies. Themarsh is divided into three vertical zones (high marsh, middlemarsh, and mud flats) represented by three assemblagegroups, with agglutinated species restricted to the upperreaches of the marsh and calcareous species more dominanttowards the intertidal channel. The high marsh area isdominated by Jadammina macrescens with a presence ofTrochammina inflata. The middle marsh is characterised byboth T. inflata and Miliammina fusca. Calcareous speciesfound in the mud flats consist of Haynesina germanica,Ammonia batava, and Quinqueloculina sp. This paperdescribes how marsh foraminifera can be used to definesmall-scale vertical zones along modern marsh surfaces andhow these zones correspond to floral zones. We demonstratethat marsh foraminifera have potential to be used as preciseindicators for sea-level reconstructions in South Africa.INTRODUCTIONModern foraminiferal assemblages form discrete verticalzones in salt marshes, strongly correlated with tidal levels(Scott et al., 2001; Gehrels & Newman, 2004). Therelationship between modern foraminiferal distributionand a range of environmental variables, including elevation,vegetation cover, pH, and salinity, can be preciselyquantified (e.g., using multivariate statistics), representinga modern analogue against which to compare fossilassemblages. Salt marshes experience daily and seasonalvariations in salinity and frequency of flooding linked totidal overflow. Several authors suggest that verticalzonation of foraminifera is strongly related to elevation,especially in temperate environments (Scott & Medioli,1980; Scott & Leckie, 1990; Horton & Edwards, 2003, 2006;Leorri et al., 2010).It is well known that a variety of ecological controls exertan influence on the distribution of surface foraminifera(e.g., Murray, 1971; Scott et al., 1998; Horton, 1999),although assemblages are consistently shown to be verti-cally zoned in accordance with tidal frames, either directlyor indirectly (Berkeley et al., 2007). A study conducted inthe Great Marshes of Massachusetts by De Rijk T Horton & Edwards, 2006).Modern analogues of marsh foraminifera are traditionallycollected at the location where a sediment core is extractedfor palaeontological analysis (Gehrels, 1994; Kemp et al.,2009). Where assemblages are identified solely at a singlesite, some fossil samples may lack a modern analogue,thereby compromising the accuracy of the reconstruction(Murray, 2006). This lack of modern analogues could beaddressed by sampling a broader range of contemporaryenvironments (Hayward et al., 2004; Horton & Edwards,2006; Kemp et al., 2009).Researchers have debated the best assemblage make-upfor foraminiferal population studies. Some advocate totalassemblage use, indicating environmental conditions forboth seasonal and temporal fluctuations (Scott et al., 2001;Horton et al., 2005). According to Murray (1971), livingpopulations best represent the modern environment as theuse of dead assemblages alone fails to account for post-mortem changes. However, it can be argued that thedistribution of living assemblages will be dependent on theconditions at time of sampling and not an average overtime. In temperate environments some suggest it isimportant to exclusively use dead assemblages as they arenot susceptible to seasonal variations, thus accuratelyreflecting subsurface assemblages (Murray, 1979; Hortonet al., 2005; Horton & Murray, 2007). On occasion, trainingsets comprised of total assemblages (live + dead) are stillused based on the assumption that live assemblages in timewill contribute to the fossil record (Booth et al., 2010). Astudy conducted on foraminiferal assemblages in surfacesediments from a marsh in Nova Scotia concluded thattotal foraminiferal assemblages provide a good basis forpalaeoenvironmental studies (Scott & Medioli, 1980).Previous studies have described the distribution of salt-marsh foraminifera in temperate environments (e.g. Leorriet al., 2010). The highest intertidal zones are oftendominated by Jadammina macrescens and Trochamminainflata, which are replaced by species such as Haplophrag-moides sp. and Miliammina fusca as elevation decreases(Hawkes et al., 2010). Agglutinated species are prevalent inthe upper and middle marsh while calcareous species arescarce. This relationship depends on the accessibility of

VERTICAL ZONATION OF FORAMINIFERA ASSEMBLAGES IN GALPINS SALT MARSH, SOUTH AFRICA

南非加尔平斯盐沼有孔虫群落的垂直分区

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