First report of a Meishucun-type early Cambrian (Stage 2) ichnofauna from the Malyi Karatau area (SE Kazakhstan): Palaeoichnological, palaeoecological and palaeogeographical implications
First report of a Meishucun-type early Cambrian (Stage 2) ichnofauna from the Malyi Karatau area (SE Kazakhstan): Palaeoichnological, palaeoecological and palaeogeographical implications
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DOI：
10.1016/j.palaeo.2013.08.021
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发表时间：
2013-12
期刊：
影响因子：
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通讯作者：
B. Weber;M. Steiner;S. Evseev;G. Yergaliev
中科院分区：
文献类型：
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作者：
B. Weber;M. Steiner;S. Evseev;G. Yergaliev
本文首次报道了哈萨克斯坦东南部小卡拉套地区阿克图盖剖面和科克苏剖面（丘拉克套组）早寒武世磷块岩中的一个遗迹化石组合。根据丰富的小壳化石（SSF）记录，该遗迹动物群可归属于寒武纪基底（Terreneuvian：？沿着罕见的垂直洞穴，遗迹组合产生了丰富的各种遗迹分类群的简单蠕虫状的表皮和下部洞穴，与分支痕迹和（前三叶虫）节肢动物痕迹有关。非节肢动物遗迹动物群由属于Palaeophycussp.的大直到轻微弯曲痕迹的浅浮雕组成，和Psammichnitessp.类型跟踪。这种遗迹动物群伴随着具有Planolites类型的短倾斜U形洞穴的层位。Koksu剖面的Treptichnus Pedum状简单分支（亚）水平痕迹证据已得到证实，但Aktugai剖面仍存在问题，因为它们保存较差，可能与Planolites型痕迹混淆。此外，一个深棕色的磷块岩桑迪白云岩带靠近一个富铁锰叠层石床的基础上的Ushbas成员包含垂直漏斗状洞穴超过一分米的长度，这可能是由于居住洞穴的底栖lingulid腕足动物（？Lingulichnus）。在磷质白云岩周围的几个短而大的（旋钮状）垂直洞穴偶尔显示微弱的保存径向运行和远端分支探头。它们类似于华南梅树村-关山剖面和寒武纪第四期的星状遗迹化石。avalonensis）以及单形亚目（Monomorphichnus）类型和有问题的原始（？）Cruziana型轨道。节肢动物痕迹集中在Aktugai-I和Koksu地区Karatau段（Chulaktau组上部）的块状磷块岩中。其中一些作为正的浅浮雕保存在上覆的绿灰色燧石带的地下块状磷块岩的遗迹分类、岩相、岩性、容矿岩石的沉积体制以及遗迹保存情况与一些较老的磷块岩类似。（Fortunian阶段）云南南部、华南扬子地台的梅树村遗迹动物群，以及在某些方面来自更年轻（第4阶段）的云南乌龙青组的遗迹组合。本文所报道的早寒武世遗迹动物群类型可能是冈瓦纳大陆西北部丰富的以磷块岩为主的寒武纪底陆棚沉积的特征。
A trace fossil assemblage from the early Cambrian phosphorites of the Aktugai and Koksu sections (Chulaktau Formation) of the Lesser Karatau area (= Malyi Karatau in the following text) in SE Kazakhstan is reported for the first time. Based on a rich and biostratigraphically significant Small Shelly Fossil (SSF) record, the ichnofauna can be attributed to the basal Cambrian (Terreneuvian: ?uppermost Fortunian to Stage 2).Along with rare vertical burrows, the ichnoassemblage yielded abundant simple worm-shaped epi- and infaunal burrows of various ichnotaxa being associated with branched traces and (pre-trilobitic) arthropod traces.The non-arthropod ichnofauna consists of hyporeliefs of large straight to slightly meandering traces belonging toPalaeophycusisp., andPsammichnitesisp. type traces. This ichnofauna is accompanied by horizons with short inclined U-shaped burrows of thePlanolites-type. The evidence ofTreptichnus pedum-like simple branching (sub-) horizontal traces is proved for the Koksu section but remains problematic for the Aktugai section as they are poorly preserved and could be mixed up withPlanolites-type traces. Additionally, a dark-brown coloured phosphoritic sandy dolostone band close to an iron- manganese rich stromatolite bed on the base of the Ushbas Member contains vertical funnel-shaped burrows of more than a decimetre in length which could be attributed to dwelling burrows of infaunal lingulid brachiopods (?Lingulichnus). Several short and larger (knob-shaped) vertical burrows in the surrounding phosphoritic dolostones occasionally display faintly preserved radial running and distally branching probes. They resemble star-shaped trace fossils from the Meishucun- and from the younger (Cambrian Stage 4) Guanshan sections of South China.The arthropod traces can be attributed toRusophycus-type traces (probablyR. avalonensis) as well as toMonomorphichnus-type and problematic primitive (?)Cruziana-type trackways. The arthropod traces are concentrated in the massive phosphorites of the Karatau Member (Upper Chulaktau Formation) of the Aktugai-I and the Koksu localities. Some of them are preserved as positive hyporeliefs on the subsurface of an overlaying greenish-grey coloured chert band (panel A of the fourth figure in this article).The ichnotaxonomic inventory, the facies, the lithology and the depositional regime of the hosting rocks as well as the trace preservation in the massive phosphorites resemble the situation in the some older (Fortunian Stage) Meishucun ichnofauna of southern Yunnan, South Chinese Yangtze Platform as well as in some aspects the ichnoassemblage from the much younger (Stage 4) Wulongqing Formation of Yunnan. The here reported type of early Cambrian ichnofauna could be characteristic for the abundant basal Cambrian phosphorite-dominated shelf deposits on the northwestern realm of Gondwana.