Exploring the aftermath of the Cambrian explosion: The evolutionary significance of marginal- to shallow-marine ichnofaunas of Jordan
Exploring the aftermath of the Cambrian explosion: The evolutionary significance of marginal- to shallow-marine ichnofaunas of Jordan
复制标题
DOI：
10.1016/j.palaeo.2012.05.029
复制
发表时间：
2013-03
期刊：
影响因子：
--
通讯作者：
M. Mángano;L. Buatois;R. Hofmann;Olaf Elicki;R. Shinaq
中科院分区：
文献类型：
--
作者：
M. Mángano;L. Buatois;R. Hofmann;Olaf Elicki;R. Shinaq
约旦死海地区中寒武统Burj组的Hannh段和中、上寒武统的Umm Ishin组均含有保存完好和丰富的遗迹动物。遗迹化石存在于各种各样的沉积环境中，从潮汐控制的陆架到前三角洲、三角洲前缘和分流-海湾间潮滩。在不同的层序地层背景下，发现了12个遗迹化石组合，即早期海侵潮下沙丘和沙坝杂岩、晚期海侵孤立沙丘斑块和沙地遗弃、高位三角洲进积和强迫海退三角洲进积。这些动物群提供的信息有助于我们了解寒武纪辐射后寒武纪生态系统的性质。约旦海底动物群显示了海底或海底附近坚固的地面条件。这些措施包括(1)在大多数Cruziana和Rusophycus ichnoos物种中保存完好的划痕，(2)附着在Gyroliths polonicus洞穴上，以及(3)无衬线被动填充的Diplcraterion isp。渗透到下面的泥岩中。而Diplcraterion互联网服务提供商。产状是与侵蚀折返有关的Glossigerites遗迹相的典型例子，而坚固的G.polonicus与最大洪泛面有关，不涉及侵蚀。以三叶虫结构为主的遗迹化石套装是Cruziana遗迹相的确凿例子，提出了关于该遗迹相的底物亲和力的问题，这通常被认为是软土地的指示。我们的研究强调了对这一遗迹相的演化控制，表明以三叶虫踪迹和轨道为主的下古生界产出反映了坚固的底质，年轻的底质代表了典型的软地面实例。在乌姆伊什林组辫状河三角洲杂岩中的分流-海湾间潮坪中发现了丰富的双叶类遗迹化石、划痕和轨迹，这为节肢动物在寒武纪能够侵入边缘-海相微咸水环境提供了证据。对分层结构的分析表明，社区相对简单，对基础生态空间的利用有限。低能全海相和边缘海相遗迹组构以浅层沉积和碎屑补给遗迹化石为主。在全海洋低能量环境的遗迹组构中，存在碎屑捕食者的深层结构，而在高能量潮下带，悬浮捕食者的深层遗迹化石占主导地位。
The middle Cambrian Hanneh Member of the Burj Formation and the middle to upper Cambrian Umm Ishrin Formation of the Dead Sea area, Jordan, contain well-preserved and abundant ichnofaunas. Trace fossils are present in a wide variety of depositional environments, from tide-dominated shelf to prodelta, delta front and interdistributary-bay tidal flats. Twelve trace fossil assemblages have been identified within a number of sequence-stratigraphic settings, namely early transgressive subtidal dune and bar complex, late transgressive isolated dune patches and dune-field abandonment, highstand deltaic progradation, and forced-regressive deltaic progradation. These ichnofaunas provide information that helps us to understand the nature of Cambrian ecosystems in the aftermath of the Cambrian radiation. The Jordan ichnofaunas display evidence of firm ground conditions at or near the sea bottom. These include (1) well-preserved scratch marks in most Cruziana and Rusophycus ichnospecies, (2) adhering Gyrolithes polonicus burrows, and (3) unlined passively filled Diplocraterion isp. penetrating into underlying mudstone. Whereas the Diplocraterion isp. occurrences are a classic example of the Glossifungites ichnofacies linked to erosional exhumation, the firmground G. polonicus is associated to a maximum flooding surface with no erosion involved. The trace fossil suites dominated by trilobite structures are firmground examples of the Cruziana ichnofacies, raising issues with respect to the substrate affinities of this ichnofacies, which is typically considered indicative of softgrounds. Our study underscores evolutionary controls on this ichnofacies, suggesting that lower Paleozoic occurrences, which are dominated by trilobite trails and trackways, reflect firm substrates and younger ones represent the typical softground examples. The occurrence of abundant bilobate trace fossils, scratch marks and trackways in interdistributary-bay tidal flats within a braidplain delta complex in the Umm Ishrin Formation provides evidence that arthropods were able to foray into marginal-marine brackish-water settings during the Cambrian. Analysis of the tiering structure indicates relatively simple communities and limited use of the infaunal ecospace. Low-energy fully marine and marginal-marine ichnofabrics are dominated by shallow-tier deposit- and detritus-feeding trace fossils. Deep-tier structures of detritus feeders are present in ichnofabrics from fully marine low-energy settings, whereas deep-tier trace fossils of suspension feeders are dominant in high-energy subtidal zones.