Zuozhen Han

Furongian (late Cambrian) sponge-microbial maze-like reefs in the North China Platform

ABSTRACT During the Furongian (late Cambrian) and Early Ordovician, maze-like (maceriate) microbialites flourished in both Laurentia and Gondwana. The maze-like microbialites are characterized by centimeter- to decimeter-scale branching, complex structures. However, organisms responsible for the formation of maze-like structures are poorly known. In order to understand formational processes of maze-like microbialites, this study focuses on the Furongian microbialites of the North China Platform in which microbial components and siliceous sponges co-occur. The maze-like structures consist of microbial components such as microstromatolites, Girvanella, and Renalcis-like forms, as well as sponge spicule networks, whereas lime mud and bioclasts occupy the space between the structures. The maze-like structures developed on a relatively flat seafloor, forming low synoptic relief (<1 cm) above the sediment surface. Continuous growth of maze-like structures with balanced deposition of sediments led to meter-scale bioherms and biostromes, under the control of both microbes and siliceous sponges. This study suggests that siliceous sponges may have played an important role in the construction of maze-like structures between the end-Cambrian Series 2 extinction and the Great Ordovician Biodiversification Event.

CHAMBERS OF EPIPHYTON THALLI IN MICROBIAL BUILDUPS, ZHANGXIA FORMATION (MIDDLE CAMBRIAN), SHANDONG PROVINCE, CHINA

Abstract Microscopic morphologic variations of Epiphyton thalli in microbial buildups were examined in order to detail controlling factors on morphology and calcification processes, and their implications for identification of calcified microbes. Microbial carbonate of the Zhangxia Formation (Middle Cambrian), Shandong Province, China comprises thrombolites, stromatolites, and Epiphyton buildups, as well as consortia of microbial and metazoan communities. Epiphyton, a rigid framework of the buildups, is subdivided into four types based on characteristics of the branches. Type 1 consists of ∼75-μm-diameter dendritic rods of dense micrite that form bush-shaped and chambered thalli. Type 2 has ∼80-μm-thick branches characterized by transverse segments. Type 3 consists of thin, ∼50-μm diameter micritic branches that form round thalli. Type 4 is characterized by laterally arrayed, branching tubes that form fan-shaped thalli. All morphologic types have bipartite branched filaments as a basic growth pattern. Bush-shaped thalli are dominant in the inner part of the Epiphyton bioherms, while chambered thalli, which are solitary, connected, and tiered, are common in the outer part. Such physical energy conditions as currents or waves control the density, length, and sheath thickness of the branches and propagation pattern of the thalli. Chamber outlines of Epiphyton thalli resemble those of Renalcis, although internal structures of the branching rods and tubes in the chamber walls are distinct. Thalli become similar to that of Renalcis when calcification and diagenesis remove or obliterate the internal fabric of the chamber wall. Morphologic variations of Epiphyton thalli and subsequent textural changes can result in identification as different groups of calcified microbial taxa.

A stem-group cnidarian described from the mid-Cambrian of China and its significance for cnidarian evolution

Palaeontological data of extinct groups often sheds light on the evolutionary sequences leading to extant groups, but has failed to resolve the basal metazoan phylogeny including the origin of the Cnidaria. Here we report the occurrence of a stem-group cnidarian, Cambroctoconus orientalis gen. et sp. nov., from the mid-Cambrian of China, which is a colonial organism with calcareous octagonal conical cup-shaped skeletons. It bears cnidarian features including longitudinal septa arranged in octoradial symmetry and colonial occurrence, but lacks a jelly-like mesenchyme. Such morphological characteristics suggest that the colonial occurrence with polyps of octoradial symmetry is the plesiomorphic condition of the Cnidaria and appeared earlier than the jelly-like mesenchyme during the course of evolution.

Climatic and tectonic controls of lacustrine hyperpycnite origination in the Late Triassic Ordos Basin, central China: Implications for unconventional petroleum development

The Triassic Yanchang Formation contains the main oil-bearing strata in the Ordos Basin, central China. But the sedimentology of the Upper Triassic is still under debate, and flood-generated, hyperpycnal-flow deposits and their implications for unconventional petroleum development have long been overlooked. Our study indicates that hyperpycnites are well developed in the seventh oil member of the Yanchang Formation. They are characterized by couplets of upward-coarsening intervals and upward-fining intervals, separated by microscale erosion surfaces. The origination of hyperpycnal flows was controlled mainly by episodic tectonic movements and the humid climate. The deposits extend from distributary estuaries into the deep lake, have intercalations of dark shales and tuffs, and coexist with debrites and turbidites as a result of the progradation of subaqueous fans. The hyperpycnites have implications for unconventional petroleum reservoirs, because the flows supplied not only large amounts of coarse grains and organic material to the deep-water, fine-grained central lake sediments but also affected the ecosystems, resulting in a higher total organic carbon content in the sediments.

Sequence-stratigraphic comparison of the upper Cambrian Series 3 to Furongian succession between the Shandong region, China and the Taebaek area, Korea: high variability of bounding surfaces in an epeiric platform

This study focuses on the stratigraphic sequences and the bounding surfaces in the upper Cambrian Series 3 to Furongian Gushan and Chaomidian formations in the Shandong region, China. The bounding surfaces are compared with those of the coeval succession in the Taebaek area, Korea. According to the vertical arrangement of the facies associations and the identification of the bounding surfaces, three stratigraphic sequences are recognized, representing dynamic changes in accommodation versus sedimentation. The bounding surfaces can be traced in the Shandong region for about 6,000 km2 in area, but cannot be correlated with those of the Taebaek area (eastern margin of the platform, about 1,000 km apart). Surface 1 is characterized by an abrupt facies change from carbonate to shale, representing a distinct drowning surface. The drowning surface is also diagnosed in the Taebaek area but highly diachronous. Surface 2 is a cryptic subaerial unconformity, reflected by an erosion surface, missing of a trilobite biozone (Prochuangia Zone), and an abrupt increase in carbon isotope value. It is not identified in the Taebaek area where the Prochuangia Zone is present. Surface 3 is a marine flooding surface, indicated by a subtle transition from flat-bedded microbialite to domal microbialite (or grainstone). It may be correlated with that in the Taebaek area, which is, however, represented by an abrupt facies change from sandstone to limestone-shale alternation. The high variability of the sequence-bounding surfaces is indicative of variable regional factors such as topographic relief, carbonate production, siliciclastic input, and hydrodynamic conditions. It suggests that the sequence-bounding surfaces are invalid for a basin-scale correlation, especially in an epeiric carbonate platform.

Depositional and Diagenetic Controls on Sandstone Reservoirs with Low Porosity and Low Permeability in the Eastern Sulige Gas Field, China

In order to determine the genesis and the factors that control the low-porosity and low-permeability sandstone reservoirs in the eastern Sulige Gas Field in the Ordos Basin, systematic studies on the sedimentary facies and diagenesis were conducted by means of analysis of cores, thin sections, fluid inclusions, X-ray diffraction, cathode luminescence and scanning electron microscope. It was found that the sand bodies of the major gas reservoirs in the Shan1 section (P1S1) and the He8 section (P2H8) were formed during the Permian as sedimentary facies such as braided-channel bars, braided-river channels and point bars of a meandering river. Four types of diagenetic facies developed subsequently: in order from the best to the poorest properties these are type A (weak compaction, early calcite cement-chlorite film facies), type B (moderate compaction, quartz overgrowth-feldspar corrosion-kaolinite filling facies), type C (strong compaction, late calcite cement-quartz corrosion facies) and type D (matrix filling and strong compaction facies). This diagenesis is undoubtedly the main reason for the poor reservoir properties of sandstone reservoirs, but the sedimentary facies are the underlying factors that greatly affect the diagenesis and thus the reservoir performance. Favorable diagenetic facies developed mainly in relatively small lithofacies such as braided-river channels, channel bars and point bars. The vertical distribution of the physical properties and the diagenetic facies of the reservoirs are related to the stratigraphic succession. Most of the sandstones between mudstones and thin beds of sandstone are unfavorable diagenetic facies. Analyses indicate that siliceous cementation can hardly be stopped by hydrocarbon filling. Authigenic chlorite could hardly protect the primary porosity. It not only occupies pore space, but also blocks pathways through sandstone reservoirs, so that it has significant influence on the permeability. Authigenic chlorite cannot be used as a marker for a specific sedimentary facies because it can be formed in different sedimentary facies, but it indicates high hydrodynamic conditions and presence of favorable reservoirs.

Geochemistry and geochronology of Upper Permian–Upper Triassic volcanic rocks in eastern Jilin Province, NE China: implications for the tectonic evolution of the Palaeo-Asian Ocean

ABSTRACT We present zircon U–Pb dating, whole-rock geochemistry, and Sr–Nd isotope results for the Upper Permian–Upper Triassic volcanic rocks to constrain the timing of the final closure of the eastern segment of the Palaeo-Asian Ocean. The volcanic rocks were mainly collected from the Yanbian area in eastern Jilin Province, northeastern China. The zircon U–Pb dating results indicate that the samples can be classified as Upper Permian–Lower Triassic basalts (ca. 262–244 Ma) and Upper Triassic dacites (ca. 216 Ma). The whole-rock geochemical results indicate that the rocks predominately belong to the medium-K and high-K calc-alkaline series. The basalts are enriched in large ion lithophile elements (LILEs, e.g. Ba and K) and depleted in high field strength elements (HFSEs, e.g. Nb and Ta), with weak positive Eu anomalies. The dacites are enriched in LILEs (e.g. Rb, Ba, Th, and K) and light rare earth elements (LREEs) and marked depletion in some HFSEs (e.g. Nb, Ta, and Ti), with significant negative Sr, P, and Eu anomalies. Moreover, the Upper Permian–Lower Triassic basalts have low initial 87Sr/86Sr ratios (0.7037–0.7048) and high εNd values (4.4–5.4). In contrast, the Upper Triassic dacites possess relatively high initial 87Sr/86Sr ratios (0.7052) compared with their low εNd values (1.4). The basaltic magma likely originated from the partial melting of a depleted mantle wedge metasomatized by subduction-related fluids, and the felsic magmas likely originated from the partial melting of a dominantly juvenile source with a minor component of ancient crust. Taken together, the Upper Permian–Lower Triassic basalts (ca. 262–244 Ma) are arc basalts that formed in an active continental margin setting, and the Upper Triassic dacites (ca. 216 Ma) are A-type granitic rocks that formed in an extensional setting. Therefore, the final closure of the Palaeo-Asian Ocean occurred during the Middle–Late Triassic.

Two middle Cambrian trilobite genera, Cyclolorenzella Kobayashi, 1960 and Jiulongshania gen. nov., from Korea and China

Cyclolorenzella is an important member of the middle Cambrian trilobite faunas in China and Korea. Morphometric analysis based on well-preserved new material assignable to Cyclolorenzella from China and Korea reveals that most of the species assigned previously to Cyclolorenzella in China are morphologically distinct from the genotype. Accordingly, the new genus Jiulongshania, with J. acalle (Walcott, 1905) as type species, is proposed to accommodate the following species: J. acalle, J. regularis (Walcott, 1906), J. rotundata (Resser & Endo in Endo & Resser, 1937), J. longispina (Wittke & Zhu in Zhu & Wittke, 1989), J. acuta (Duan in Duan et al., 2005) and J. longa sp. nov. Species tentatively transferred to Jiulongshania are J.? subcylindrica (Chu, 1959), J.? yentaiensis (Chu, 1959), J.? humilis (Zhang in Qiu et al., 1983), and J.? latisulcata (Zhang in Qiu et al., 1983). This taxonomic revision results in only two species remaining in Cyclolorenzella, the type species C. quadrata (Kobayashi, 1935) and C. convexa (Resser & Endo in Endo & Resser, 1937). Jiulongshania has a relatively long stratigraphic range from the Damesella–Yabeia Zone to the Blackwelderia Zone of China, whereas Cyclolorenzella is restricted to the stratigraphically younger Drepanura Zone in China and Korea.

A Marine or Continental Nature of the Deltas in the Early Cretaceous Lingshandao Formation—Evidences from Trace Elements

A succession with well-developed soft-sediment deformation structures and well-exposed gravity-flow deposits in the Early Cretaceous Lingshandao Formation has caused considerable controversy on whether the nondisputed deltaic environment was marine or continental. This dispute cannot be solved by mere sedimentological analysis and, moreover, too few fossils are present to be decisive. The main objective of the present contribution is to shed light on this problem on the basis of trace-element analysis.

Ontogeny of the Middle Cambrian Trilobite Shantungia spinifera Walcott, 1905 from North China and Its Taxonomic Significance

The cambrian trilobite Shantungia Walcott, 1905 is a monotypic genus, with S. spinifera Walcott, 1905 as the genotype and is characterized by its long frontal spine extending medially from the anterior cranidial border. The genus has hitherto been known restricted in occurrence to the traditional Drepanura Zone of North China (Walcott, 1913; Endo and Resser, 1937; Qiu et al., 1983; Zhang and Jell, 1987). As Drepanura Bergeron, 1899 is preoccupied by a collembolan insect and Neodrepanura Ozdikmen, 2006 was proposed as a replacement, this zone is referred to as the Neodrepanura Biozone herein. Recently collected trilobites from the Kushan Formation in Shandong Province of North China contain forty specimens of Shantungia spinifera , including protaspid and meraspid forms. Interestingly, the juvenile specimens of S. spinifera are morphologically closely comparable to the specimens recently assigned to Oculishumardia hunania Peng et al., 2003 from the uppermost middle Cambrian Liostracina bella Zone of South China (Peng et al., 2004). Peng et al. (2003) claimed that Oculishumardia is the oldest shumardiid and phylogenetically represents an intermediate stage between ptychoparioids and shumardiids. This note describes the ontogenetic development of Shantungia spinifera from North China and, based on this information, raises the possibility that Oculishumardia may represent meraspid stages of a damesellid trilobite and will explore its taxonomic and phylogenetic significance. All of the specimens examined in this study were collected from the Kushan Formation of the Tangwangzhai section, Shandong Province, China (Fig. 1). The Tangwangzhai section (116°51′42″E and 36°30′33″N) has served as the type section of middle Cambrian to Furongian (upper Cambrian) strata of North China and comprises the Changhia, Kushan, and Chaumitien formations in ascending order (Bureau of Geology and Mineral Resources of Shandong Province, 1996). The Kushan Formation in the section measures ca. 62 m in thickness and is generally …