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Current Issue   2021 Vol.  10 No.  1 Published: 2021-01-20 Lithofacies palaeogeography and sedimentology Biopalaeogeography Biopalaeogeography 1 Labechia carbonaria Smith 1932 in the Early Carboniferous of England; affinity, palaeogeographic position and implications for the geological history of stromatoporoid-type sponges Stephen Kershaw, Consuelo Sendino Stromatoporoid sponges were very abundant during the middle Palaeozoic Era and are thought to disappear at the end of the Devonian Period in the Hangenberg Crisis. However, there are records of organisms with stromatoporoid-type structure in Carboniferous strata, the subject of this study. The Viséan fossil Labechia carbonaria Smith 1932 has been discussed previously in literature and its affinity has not been confirmed. In this study, the type material of L. carbonaria collected from the middle part of the Frizington Limestone Formation (previously called Seventh Limestone), Holkerian Substage, stored in the Natural History Museum (London, UK) and British Geological Survey (Keyworth, UK) was re-examined. The Holkerian Substage, in which L. carbonaria was found, lies between ca 335-339 Ma, and the Frizington Limestone Formation ranges from topmost Arundian to upper Holkerian, so middle Frizington Limestone Formation is likely approximately 337 Ma. L. carbonaria comprises thick long pillars connected by thin curved cyst plates consistent with the structure of the stromatoporoid genus Labechia. However, a common opinion is that L. carbonaria fossils may be mistaken for fragments of rugose corals, but there are problems with assigning it to the Rugosa. In vertical section (VS) L. carbonaria could be mistaken for a transverse section (TS) of a Carboniferous rugose coral. However, in TS L. carbonaria shows the rounded cross sections of stromatoporoid pillars. If it was a coral, septal sheets of the VS of a coral should be seen. For a rugose affinity to still apply, a coral structure would have to be composed of free trabeculae, but these are not known after the middle of the Devonian Period; there are no corals of Early Carboniferous age with the structure of L. carbonaria. Another interpretation, that L. carbonaria is a chaetetid, is discounted because it lacks calicles and is very different in structure from chaetetids. We conclude that L. carbonaria is a stromatoporoid. Because the beginning of the Carboniferous Period was ca 359 Ma, stromatoporoids thus occur approximately 22 million years after their purported disappearance at the end-Devonian Hangenberg Crisis. L. carbonaria, together with other rare occurrences in Carboniferous strata of stromatoporoid-form sponges Newellia mira (Newell) in USA, and uncertain taxa Komia Korde and Palaeoaplysina Krottow that have been attributed to stromatoporoids by some authors, supports some published views that end-Devonian stromatoporoid extinction may not have been as final as is traditionally interpreted. Thus Mesozoic stromatoporoids may represent resurgence of sponge lineages that survived the late Palaeozoic, perhaps in uncalcified form. Palaeogeographically, during the Early Carboniferous, the UK was positioned in low latitudes and in a central location of global distribution of reefal buildups during the late Palaeozoic continental assembly towards Pangaea. Thus it is curious that L. carbonaria is found in only one place; future search may determine its true palaeographic distribution, with potential reconsideration of the extinction of stromatoporoids at the end of the Devonian Period. 2021 Vol. 10 (1): 1-18 [Abstract] ( 128 ) [HTML 1KB] PDF (19623 KB)   ( 54 ) 19 Macro- and microfeatures of Early Cambrian dolomitic microbialites from Tarim Basin, China Ying Li, Hong-Xia Jiang, Ya-Sheng Wu, Wen-Qing Pan, Bao-Shou Zhang, Chong-Hao Sun, Guo Yang The fabrics of microbialites preserved in limestones are generally better than in dolostones. What are the fabrics of the microbialites preserved in heavily dolomitized dolostones? This paper presents an example of a strongly dolomitized Cambrian microbialite profile. The Xiaoerblak Formation (Cambrian Series 2 Stage 3 and lower Stage 4) of the Sugaitblak section in Aksu, Xinjiang Uygur Autonomous Region, China is mainly composed of microbial dolostones. Due to strong alteration by diagenesis, their features, formation and environments have not been fully understood. Here, based on detailed observation on outcrops and thin sections, we show that this formation comprises four kinds of microbialites: laminite, thrombolite, thrombolitic laminite, and Renalcis framestone, in five intervals (Interval I to Interval V). We identified three main types of microbialite fabrics, i.e., clotted fabric, laminated fabric and skeletal fabric, and established a high-resolution vertical evolution sequence of the microbialites. The clotted fabric and the laminated fabric were further divided into subtypes. We found that the original fabrics were mainly affected by dolomitization, recrystallization and dissolution, and the alteration degree of the microbialite fabric is stronger in the lower part of this formation. The laminated fabric has the strongest resistance to diagenesis, followed by the clotted fabric. Based on studies of different rock types and sedimentary structures, we concluded that the sedimentary environment of Xiaoerblak Formation consists of three settings: a) Intervals I to III formed in restricted tidal flat environments, b) Interval IV and the lower part of Interval V in restricted deep subtidal environments, and c) upper part of Interval V in shallowing-up open subtidal environments. 2021 Vol. 10 (1): 19-38 [Abstract] ( 117 ) [HTML 1KB] PDF (23065 KB)   ( 52 ) 39 Bioturbation of Thalassinoides from the Lower Cambrian Zhushadong Formation of Dengfeng area, Henan Province, North China Yu-Chao Fan, Yong-An Qi, Ming-Yue Dai, Da Li, Bing-Chen Liu, Guo-Shuai Qing Bioturbation plays a critical role in sediment mixing and biogeochemical cycling between sediment and seawater. An abundance of bioturbation structures, dominated by Thalassinoides, occurs in carbonate rocks of the Cambrian Series 2 Zhushadong Formation in the Dengfeng area of western Henan Province, North China. Determination of elemental geochemistry can help to establish the influence of burrowing activities on sediment biogeochemical cycling, especially on changes in oxygen concentration and nutrient regeneration. Results show that there is a dramatic difference in the bioturbation intensity between the bioturbated limestone and laminated dolostone of the Zhushadong Formation in terms of productivity proxies (Baex, Cu, Ni, Sr/Ca) and redox proxies (V/Cr, V/Sc, Ni/Co). These changes may be related to the presence of Thalassinoides bioturbators, which alter the particle size and permeability of sediments, while also increase the oxygen concentration and capacity for nutrient regeneration. Comparison with modern studies shows that the sediment mixing and reworking induced by Thalassinoides bioturbators significantly changed the primary physical and chemical characteristics of the Cambrian sediment, triggering the substrate revolution and promoting biogeochemical cycling between sediment and seawater. 2021 Vol. 10 (1): 39-54 [Abstract] ( 128 ) [HTML 1KB] PDF (8762 KB)   ( 47 ) 55 Palaeobotanical and biomarker evidence for Early Permian (Artinskian) wildfire in the Rajmahal Basin, India Srikanta Murthy, Vinod Atmaram Mendhe, Dieter Uhl, Runcie Paul Mathews, Vivek Kumar Mishra, Saurabh Gautam This study provides a combined analysis on the palynology, fossil charcoal and biomarkers of the subsurface coal deposits from a borehole RMB #2 drilled at the Dhulia Coal Block, Rajmahal Basin, India, in attempts to establish the chronology of sedimentation and to propose palaeobotanical as well as geochemical evidence for the occurrence of wildfires in these sediments. The palynological investigation suggests a Scheuringipollenites barakarensis palynoassemblage from the lower Barakar Formation, dated as Artinskian (Early Permian) in age. This assemblage reveals the dominance of Glossopteridales and sub-dominance of taxa belonging to Cordaitales and Coniferales. Fossil charcoal in sediments is usually recognized as a direct indicator for the occurrence of palaeo-wildfires. More data involving the anatomical features of fossil charcoal analyzed by Field Emission Scanning Electronic Microscope broaden our knowledge on Early Permian wildfires from the peninsula of India. The studied macroscopic charcoal fragments exhibit anatomical details such as homogenized cell walls, uniseriate simple and biseriate alternate pitting on tracheid walls and rays of varying heights pointing to a gymnospermous wood affinitity. The excellent preservation of charcoal fragments, shown by their large sizes and almost unabraded edges, suggests a parautochthonous origin. The embedded biomarker study performed for charcoal sediments and its characterization demonstrate the presence of n-alkanes, isoprenoids, terpenoids and aromatic compounds. A bimodal distribution pattern of n-alkanes with a Cmax at n-C25 is identified. Diterpenoids and pentacyclic terpenoids are identified, indicating the input of an early conifer vegetation and bacterial activity, respectively. The identified polyaromatic hydrocarbon (PAH) compounds, together with the charcoal fragments, clearly suggest that repeated wildfire events occurred during the deposition of these Artinskian sediments in the Rajmahal Basin. 2021 Vol. 10 (1): 55-75 [Abstract] ( 94 ) [HTML 1KB] PDF (8612 KB)   ( 35 ) Lithofacies palaeogeography and sedimentology 76 Palaeogeographic reconstruction of a fluvio-marine transitional system in Narmada rift basin, India — Implications on Late Cretaceous global sea-level rise Biplab Bhattacharya, Suparna Jha, Prantik Mondal Rising sea-levels in tectonically active epicontinental basins often lead to varied depositional settings and palaeogeography, mostly influenced by the net accommodation resulting from mutual interference of the extent and nature of landward encroachment by the sea and the net sedimentation. The Cenomanian Nimar Sandstone Formation, Bagh Group, Narmada rift basin, uniquely portrays the effect of sea-level rise within an intra-cratonic setting and attributes to the corresponding palaeogeographic changes in west-central India. An integrated sedimentological-sequence-stratigraphic study of the broadly fining-upward Nimar Sandstone Formation (thickness ~20-30 m) depicts the actual nature of changeover from a fluvial to a marine-dominated transitional depositional setting. Detailed sedimentological study reveals total seventeen facies, grouped in five facies associations, viz., the channel-fill facies association (FA-1), the overbank facies association (FA-2), the fluvial-dominated fluvio-tidal facies association (FA-3), the tide-dominated fluvio-tidal facies association (FA-4), and the shoreface facies association (FA-5). Overall facies architecture indicates a west-to-eastward marine encroachment, resulting in stacking of three distinct palaeo-depositional conditions: (i) an initial fluvial system with channel and overbank, changing into a tide-influenced fluvial bay-head delta in the inner estuary, followed by (ii) marine encroachment leading to a tide-dominated central estuary with inter- to sub-tidal settings, and finally, (iii) with further intense marine encroachments, a wave-reworked open shore condition in the outer estuary zone. The overall fining-up succession with a systematic change from fluvial to marine-dominated depositional systems points to a landward shift of the shoreline, signifying a major transgressive event correlated to the Cenomanian global sea-level rise. Characteristic stratal stacking patterns point to four coarsening- and fining-up hemicycles, embedded within the major transgressive succession. These high-frequency cycles attest to the varied interplay of sedimentation, tectonics and sea-level changes, and the resultant net accommodations. A palaeogeographic model is proposed based on the high-frequency transgressive-regressive hemicycles, which envisages the evolution of the depositional environments in relation to the Cenomanian eustatic rise in the intra-cratonic riftogenic fluvio-marine transitional basinal setup. 2021 Vol. 10 (1): 76-97 [Abstract] ( 100 ) [HTML 1KB] PDF (14815 KB)   ( 33 ) 98 A combined geophysical and lithological studies on eruptive history and Quaternary lacustrine stratigraphy of a maar in Leizhou Peninsula, China Cong Chen, Zhuo Zheng, Li-Feng Zeng, Fan Xiao, Li-Ping Tian, Kang-You Huang As the second common type of volcanic vent on Earth, maar-diatreme volcanoes and their post-eruptive lacustrine sediments are a main focus of volcanology, palaeolimnology, palaeoclimatology and palaeontology. A number of maar-type volcanoes have been found in Leizhou Peninsula, South China, but little is known about their eruption processes and detailed stratigraphy of the post-eruptive sediments. We present a combined geophysical and geological analysis to study the eruptive history and post-eruptive sediment stratigraphy of a large maar, the elliptical (1.8×3.0 km2) Jiudouyang (JDY) maar. The stratigraphy revealed by drilling cores shows that the JDY maar has three major stages of evolution: (i) deep-lake sedimentary environment characterized by high autochthonous diatom productivity; (ii) shallow lake to swamp with very low water levels, characterized by a high total organic carbon (TOC) and abundant wood fragments; and, (iii) intermittent shallow lake and alluvial deposits composed of clay minerals and sand. The electrical resistivity tomography (ERT) values and lithological features are highly consistent, which clearly reveal the presence of ca. 50 m thick lacustrine sediments, directly underlain by a ca. 70 m thick basaltic lava rather than diatreme breccia in the crater. This infill sequence implies an alternation of eruption style from phreatomagmatic to Strombolian and/or lava flow, due to high magma flux and ascent rate of the Hainan Plume during the middle Pleistocene. The ERT data also reveal the initial phreatomagmatic crater floor at ca. 120 m depth. The initial crater had a large diameter/depth ratio (ca. 17), with an elongated shape (major axis to minor axis = 0.6), implying possible lateral vent migration during the eruption. A significant erosion under tropical weathering condition during the last few hundred thousand years, accounted for the large size of the maar crater. The study provides insights into the eruptive history and post-eruptive evolution of a large maar, as well as the spatial distribution of the lacustrine sediments. 2021 Vol. 10 (1): 98-111 [Abstract] ( 98 ) [HTML 1KB] PDF (6633 KB)   ( 49 ) 112 Characteristics and origin of a new type of polyhalite potassium ore in the Lower Triassic Jialingjiang Formation, Puguang area, northeastern Sichuan Basin, SW China Wen-Jun Shang, Mian-Ping Zheng, Yong-Sheng Zhang, Jia-Ai Zhong, En-Yuan Xing, Yuan Peng, Bao-Ling Gui, Kong Li A new type of polyhalite potassium ore (NTPPO) was found in the Lower Triassic Jialingjiang Formation, NE Sichuan Basin, SW China. It is water soluble, therefore can be exploited using the water-solution method, and is of great potential of economic value and research significance. Based on cores, thin sections, energy spectrum and SEM analyses, its microfeatures, macrofeatures and origin are discussed, and a genetic model is established to provide a scientific basis for future evaluation, prediction and exploration of potassium ore in the Sichuan Basin. It is proposed that the NTPPO was caused by storm activities: (1) the storm broke the original sedimentary polyhalite-gypsum beds, whose fragments were transported into the salt basin with high content of K+ and Mg2+; (2) in the basin, the polyhalite continued to be formed from gypsum by metasomatism with K- and Mg-rich brine; (3) during diagenesis, under high temperature and high pressure, K-Mg-rich brine from halite continued to replace anhydrite (or gypsum) to form polyhalite. 2021 Vol. 10 (1): 112-124 [Abstract] ( 116 ) [HTML 1KB] PDF (10677 KB)   ( 40 )

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