Thermal History of Cambrian Burgess Shale-Type Deposits:New Insights from the Early Cambrian Chengjiang and Qingjiang Fossils of South China

Burgess Shale-type deposits provide a wealth of information on the early evolution of animals.Questions that are central to understanding the exceptional preservation of these biotas and the paleoenvironments they inhabited may be obscured by the post-depositional alteration due to metamorphism at depth and weathering near the Earth’s surface.Among over 50 Cambrian BST biotas,the Chengjiang and Qingjiang deposits are well known for their richness of soft-bodied taxa,fidelity of preservation,and Early Cambrian Age.While alteration via weathering has been well-investigated,the thermal maturity of the units bearing the two biotas has not yet been elucidated.Here we investigate peak metamorphic temperatures of the two deposits using two independent methods.Paleogeotemperature gradient analyses demonstrate that the most fossiliferous sections of the Chengjiang were buried at a maximum depth of∼8500 m in the Early Triassic,corresponding to∼300°C,while the type area of the Qingjiang biota was buried at a maximum depth of∼8700 m in the Early Jurassic,corresponding to∼240°C.Raman geothermometer analyses of fossil carbonaceous material demonstrate that peak temperatures varied across localities with different burial depth.The two productive sections of the Chengjiang biota were thermally altered at a peak temperature of approximately 300°C,and the main locality of the Qingjiang biota experienced a peak temperature of 238±22°C.These results from two independent methods are concordant.Among BST deposits for which thermal maturity has been documented,the Qingjiang biota is the least thermally mature,and therefore holds promise for enriching our understanding of BST deposits.

试论动物非矿化组织的保存

动物非矿物化组织在特异埋葬条件下可保存为化石。缺氧和快速埋葬有利于非矿化组织的保存 ,但不能阻止微生物的破坏作用。无菌环境下可保存软躯体组织 ,但在构造变动和古气候变迁等因素的影响下会彻底破坏 ,不可能在地质历史时期长期存在。最稳定的保存形式是与成岩作用有关的保存类型和以碳化有机质薄膜形式的保存类型。与动物非矿化组织保存有关的常见成岩自生矿物有磷酸盐矿物、碳酸盐矿物和黄铁矿等。其中 ,磷酸盐矿物在成岩作用过程中结晶最早 ,可以保存动物的微细构造。这些矿物可以矿化交代动物的肉质和角质使其成为矿化实体 ;也可以呈假形、铸型或铸模等形式保存。布尔吉斯页岩保存类型中 ,非矿化组织以碳化有机质薄膜或含水的铝硅酸盐矿物两种形式保存。前者可能与粘土矿物吸附有机质、阻止酶的降解作用有关 。

Priapulid worms from the Cambrian of China shed light on reproduction in early animals

In the recent years,exceptional fossil sites have revealed astonishing details on the anatomy,lifestyles and behaviour of Cambrian animals but surprisingly,very little is known about one of their most vital features,reproduction.We describe here in situ eggs(clusters of 3 to 30 oocytes)in the tube-dwelling priapulid worm Paraselkirkia sinica from the Cambrian Stage 3 Xiaoshiba Lagerstätte(ca.514 Ma,South China).These oocytes were accommodated within paired tubular ovaries located in the posterior half of the primary body cavity as in modern meiobenthic priapulid worms,thus indicating that the general organization of female tubular gonads in priapulid worms has remained virtually unchanged for half a billion years.Our findings provide for the first time,key information on the reproductive organs and strategies of early ecdysozoans,a huge animal clade that dominated Cambrian marine ecosystems and accounts for a large part of today’s biodiversity(e.g.arthropods).Moreover,we also emphasize the critical role of ecology on the reproductive strategies and lifestyles of both modern and Cambrian worms.

Kaili Biota: A Taphonomic Window on Diversification of Metazoans from the Basal Middle Cambrian: Guizhou, China

A Burgess Shale-type biota is, in part, characterized by a wide diversity of taxa and soft-part preservation. Each provides unique historical insights into early metazoan evolution. Among the more than 40 globally distributed biotas, the early Cambrian Chengjiang and Middle Cambrian Burgess-type biotas are the largest. The Kaili Biota, from the earliest Middle Cambrian of Guizhou, China, contains representatives of 110 metazoan genera belonging to 10 phyla. It contains many well-persevered soft-bodied specimens. This Chinese biota has become the third most taxonomically diverse Burgess Shale-type fauna. Because the Kaili Biota formed in an outer-shelf environment, its main faunal character is large numbers of eocrinoids and planktoic trilobites. The Kaili is younger than the Chengjiang Biota but older than the Canadian Burgess Shale Biota; it shares 30 genera with the Chengjiang and 38 genera with the Burgess Biota. The Kaili Biota displays a taphonomic window to the diversification and evolution of marine offshore organisms covering 5.13 million years between the Early and Middle Cambrian.

Biodiversity and taphonomy of the Early Cambrian Guanshan biota,eastern Yunnan

The Guanshan biota from eastern Yunnan(Cambrian Series 2,early Stage 4) is a Burgess Shale-type fossil biota with abundant exceptionally preserved soft-bodied fossils after the discovery of the well-known Cambrian Chengjiang fauna and Kaili biota in South China.The geological settings,sedimentology,taphonomy,and the fossil assemblage of the Guanshan biota are briefly summarized here.The Guanshan biota consists of about 60 taxa belonging to more than 10 metazoan groups and algae,among which the lobopods,eldonids,hyolithids with helens,and green algae are reported for the first time.The common occurrence of soft-bodied preservation in many groups,notably the trilobites and brachiopods,makes the Guanshan biota a significant fossil lagersttte for understanding the metazoan evolution during Cambrian explosion and taphonomy of the Burgess Shale-type fossils.