Factors controlling upper Jurassic ammonite assemblages in north central Mexico
Factors controlling upper Jurassic ammonite assemblages in north central Mexico
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墨西哥中北部上侏罗统菊石组合的控制因素
DOI：
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发表时间：
2007
期刊：
影响因子：
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通讯作者：
C. González
中科院分区：
文献类型：
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作者：
F. Olóriz;A. Villaseñor;C. González
在墨西哥帕洛特斯山脉(Durango)和卡托雷斯山脉(San Luis Potosi)研究的下基默里期至下泰山(上侏罗纪)剖面显示，低能量沉积中大型无脊椎动物化石组合的组成，包括大型底栖动物，反映了生物层序控制。单调粉砂岩提供了菊石组合的连续记录，反映了生活区贝壳的主要沉积；同时，贝壳的断续记录是由于贝壳的断续尸解运输，尤其是在风暴的影响下。有节奏的泥灰质-粉砂质石灰岩和泥灰岩说明了一种化石记录，可能是由轻微的海侵-海退脉冲决定的。岩相的主要变化反映在重大洪灾期间沉积的浓缩粉质和磷质泥岩，这些泥岩影响到以陆源沉积为主的地区。这些变化根据化石组合与不断变化的生态条件的关系，或多或少地决定了化石组合的组成发生了重大变化。然而，生态空间的变化与岩相的变化没有直接的关系。身体运输既与海洋洪水有关，也与上游水流格局的变化有关，是影响菊石种群区域分布的主要生物地层因素。壳层输运和沉积速率控制着保存，并最终影响到已记录的菊石组合的多样性。菊石壳体的死后行为(从壳体结构和保存角度解释)以及因此的分布表明，在基默里期-泰山早期，靠近主要碳酸盐和陆源沉积之间不断变化的边界的地区(如东杜兰戈和圣路易斯波托西)，处于浅水环境。在所研究的剖面中没有发现影响菊石生物地层学的改造。
Lower Kimmeridgian to Lower Tithonian (Upper Jurassic) sections studied at Sierra de Palotes (Durango) and Sierra de Catorce (San Luis Potosi), Mexico, show low-energy deposits in which the composition of fossil macroinvertebrate assemblages, including megabenthos, reflects biostratinomic control. Monotonous siltstones provide continuous records of ammonite assemblages and reflect dominant deposition of shells in living areas; meanwhile, discontinues records were forced by episodic post-mortem transportation of shells, which was especially accentuated under storm influence. Rhythmic marly-silty limestones and marls illustrate a fossil record probably determined by minor transgressive-regressive pulses. The major changes in lithofacies are reflected by condensed silty and phosphatic mudstones deposited during significant floodings affecting areas under dominant terrigenous sedimentation. These changes determined more or less significant variations in the composition of fossil assemblages according to their relation to changing ecological conditions. However, shifting ecospaces exhibit no direct relationship to changes in lithofacies. Post-mortem transportation, operating in relation to both marine floodings and changes in the pattern of upper-water currents, was the main biostratinomic factor affecting the areal distribution of ammonite populations. Shell transportation and sedimentation rate controlled preservation and ultimately influenced diversity in recorded ammonite assemblages. The post-mortem behaviour (interpreted from shell structure and preservation), and therefore distribution, of ammonite shells points to shallow-water environments during the Kimmeridgian - Early Tithonian in areas (such as SE Durango and San Luis Potosi) close to the changing boundary between dominant carbonate and terrigenous sedimentation. No reworking affecting ammonite biostratigraphy has been identified in the sections studied.