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	2021 Vol. 10 No. 2
	Published: 2021-04-20



	Palaeoclimatology Lithofacies palaeogeography and sedimentology Biopalaeogeography

	125	The turbidite-contourite-tidalite-baroclinite-hybridite problem: Orthodoxy vs. empirical evidence behind the "Bouma Sequence"
		G. Shanmugam
		The underpinning problems of deep-water facies still remain unresolved. (1) The Tb, Tc, and Td divisions of the turbidite facies model, with traction structures, are an integral part of the "Bouma Sequence" (Ta, Tb, Tc, Td, Te). However, deposits of thermohaline contour currents, wind-driven bottom currents, deep-marine tidal currents, and baroclinic currents (internal waves and tides) also develop discrete rippled units, mimicking Tc. (2) The application of "cut-out" logic of sequences, which was originally introduced for the "Bouma Sequence", with sharp basal contacts and sandy divisions containing well-developed traction structures, to muddy contorts with gradational basal contacts and an absence of well-developed traction structures is incongruent. (3) The presence of five internal divisions and hiatus in the muddy contoured facies model is in dispute. (4) Intersection of along slope contour currents with down slope sediment-gravity flows, triggering hybrid flows, also develops traction structures. (5) The comparison of genuine hybrid flows with down slope flow transformation of gravity flows is inconsistent with etymology of the term "hybrid". (6) A reexamination of the Annot Sandstone at the Peira Cava type locality in SE France fails to validate either the orthodoxy of five internal divisions of the "Bouma Sequence" or their origin by turbidity currents. For example, the "Ta" division is composed of amalgamated units with inverse grading and floating mudstone clasts, suggesting a mass-transport deposit (MTD). The "Tb" and "Tc" divisions are composed of double mud layers and sigmoidal ===cross bedding, respectively, which suggest a tidalite origin. (7) Although it was reasonable to introduce a simplistic "Bouma Sequence" in 1962, at a time of limited knowledge on deep-water processes, it is obsolete now in 2021 to apply this model to the rock record amid a wealth of new knowledge. (8) The disconnect between 12 observed, but questionable, modern turbidity currents and over 10,000 interpreted ancient turbidites defies the doctrine of uniformitarianism. This disconnect is attributed to routine application of genetic facies models, without a pragmatic interpretation of empirical data. (9) A suggested solution to these problems is to interpret traction structures in the sedimentary record pragmatically on the basis of empirical field and experimental evidence, without any built-in bias using facies models, such as the "Bouma Sequence". (10) Until reliable criteria are developed to distinguish traction structures of each type of bottom currents based on uniformitarianism, a general term "BCRS" (i.e., bottom-current reworked sands) is appropriate for deposits of all four kinds of bottom currents.
		2021 Vol. 10 (2): 125-156 [Abstract] ( 165 ) [HTML 1KB] PDF (16872 KB) ( 327 )

Biopalaeogeography

	157	Diversified calcimicrobes in dendrolites of the Zhangxia Formation, Miaolingian Series (Middle Cambrian) of the North China craton
		Ming-Xiang Mei, Muhammad Riaz, Zhen-Wu Zhang, Qing-Fen Meng, Yuan Hu
		As a type of non-laminated microbial carbonates, dendrolites are dominated by isolated dendritic clusters of calcimicrobes and are distinct from stromatolites and thrombolites. The dendrolites in the upper part of the Miaolingian Zhangxia Formation at Anjiazhuang section in Feicheng city of Shandong Province, China, provide an excellent example for further understanding of both growth pattern and forming mechanism of dendrolites. These dendrolites are featured by sedimentary fabrics and composition of calcified microbes as follows. (1) The strata of massive limestones, composed of dendrolites with thickness of more than one hundred meters, intergrade with thick-bedded to massive leiolites, formimg the upper part of a third-order depositional sequence that constitutes a forced regressive systems tract. (2) A centimeter-sized bush-like fabric (shrub) typically produced by calcified microbes is similar to the mesoclot in thrombolites but distinctive from clotted fabrics of thrombolites. This bush-like fabric is actually constituted by diversified calcified microbes like the modern shrub as a result of gliding mobility of filamentous cyanobacteria. Such forms traditionally include: the Epiphyton group (which actually has uncertain biological affinity), the Hedstroemia group which closely resembles modern rivulariacean cyanobacteria, and the possible calcified cyanobacteria of the Lithocodium-Bacinella group. (3) Significantly, dense micrite of leiolite is associated with sponge fossils and burrows, and is covered by microstromatolite. The Lithocodium-Bacinella group is a controversial group of interpreted calcified cyanobacteria in the Cambrian that has also been widely observed and described in the Mesozoic. Therefore, dendrolites with symbiosis of leiolites in the studied section provide an extraordinary example for further understanding of growing style of bush-like fabrics (shrubs) of the dendrolites dominated by cyanobacterial mats. Furthermore, the present research provides some useful thinking approaches for better understanding of the history of the Early Paleozoic skeletal reefs and the microbe-metazoan transitions of the Cambrian.
		2021 Vol. 10 (2): 157-181 [Abstract] ( 155 ) [HTML 1KB] PDF (19798 KB) ( 52 )

	182	Late Tremadocian (Early Ordovician) reefs on the Yangtze Platform, South China, and their geobiological implications: a synthesis
		Jian-Po Wang, Qi-Jian Li, Stephen Kershaw, Yuan-Yuan Zhang, Shen-Yang Yu, Yue Li
		This study provides an overview and discussion of controls on the distribution of organic reefs during the Early Ordovican Period, in the Yangtze Platform, a region of epicontinental sedimentary rocks in South China. The Yangtze Platform was located in low latitudes during the Early Ordovician and recorded rich and diverse reefs through that time. During the late Tremadocian Epoch, dolomitic and stratiform stromatolites were common in supratidal to intertidal zones of the western Yangtze Platform, while columnar stromatolites formed in deeper waters of the eastern Yangtze Platform. Skeletal-dominated reefs occurred in upper subtidal settings of the central Yangtze Platform. A transition from microbial-dominated to metazoan-dominated reefs with shallowing-upward cycles was evident, indicating that the composition of the main reef-builders was driven mainly by water depth. Increasing metazoan competition during the Great Ordovician Biodiversification Event reduced the abundance of microbial reefs. Sufficient nutrient supply is interpreted to have promoted development of skeletal-dominated reefs locally in shallow settings in the central Yangtze Platform, especially represented by the expansion of abundant solitary fossils of lithistid sponges and Calathium. High salinity environmental settings facilitated the bloom of stromatolites in near-shore locations. Low oxygen content in deep subtidal settings may have led to the absence of skeletal reefs in these habitats, so the mass occurrences of stromatolites was located in the shallower-water central and eastern platform. No keratose sponge-bearing stromatolite can be confirmed across the platform during this interval.
		2021 Vol. 10 (2): 182-196 [Abstract] ( 127 ) [HTML 1KB] PDF (7713 KB) ( 37 )

	197	Different accretion and diagenetic patterns within the fabrics of the Permian-Triassic boundary microbialites on the Leye isolated carbonate platform, South China Block
		Xi-Yang Zhang, Yue Li, Guan Wang, Hong-Qiang Yang
		A comprehensive study on the accretion and diagenesis of the Permian-Triassic boundary microbialites is conducive to a better understanding of the ecological community after the end-Permian mass extinction. Here we studied the special microbialite sequences at the Tianba section of Leye isolated carbonate platform, South China Block. The microbialites are shown as small columnar stromatolites, stromatolitic thrombolites, spotted thrombolites, and domical digitate thrombolites in an ascending order. Thin section analyses, coupled with cathodoluminescence photos and oxygen isotopic data, reveal that all types of microbially-mediated laminae/clots are partly recrystallized. Layers of the Polybessurus-like fossils commonly occur in the recrystallized fabrics of stromatolitic laminae. However, the Polybessurus-like fossils are rare in quantity and generally fragmentary and structureless in stromatolitic clots and spotted clots. Such taphonomic features are likely interpreted as the early decomposition by heterotrophic bacteria in an oxygen-depleted microenvironment caused by rapid accumulations of organic matter in the calm water. More enrichments of ¹³C in the laminae of stromatolite and in the clots of stromatolitic thrombolite and spotted thrombolite than in adjacent interstitial matrixes signify the photosynthesis-dominated isotopic fractionation during the growth of microbial communities. Rare calcimicrobial structures but many calcite crystal fans were found in the ¹³C-depleted digitate clots. These phenomena indicate that seawater on the carbonate platform was ¹²C-enriched and supersaturated, accelerating carbonate precipitations and decompositions of organic matter within the microbial community. Different preservations of the Polybessurus-like fossil revealed the complicated microbially-dominated sedimentation and post-depositional diagenesis in the abnormal seawater after the catastrophe.
		2021 Vol. 10 (2): 197-208 [Abstract] ( 133 ) [HTML 1KB] PDF (10841 KB) ( 29 )

	209	Eocene to Oligocene nannofossils stratigraphy and environmental conditions in Izeh Province, Zagros Basin, East Tethys
		Saeedeh Senemari, Farah Jalili
		Data obtained from the calcareous nannofossils, distributed in the upper part of the Pabdeh Formation (Priabonian-Rupelian) and the lower part of the Asmari Formation (Chattian) in the Bid-Zard section, were used to investigate the Eocene to Oligocene palaeoenvironmental conditions in the southwest of Izeh, southwestern Iran (eastern Tethys). The upper part of the Pabdeh Formation was composed of shale, thin-bedded pelagic limestone and dolostone, which is disconformably overlain by the Asmari Formation. For the first time, 29 species of calcareous nannofossils belonging to 13 genera were identified in the studied section. The calcareous nannofossils in the upper part of the Pabdeh Formation indicate the Isthmolithus recurvus Zone/Sphenolithus pseudoradians Zone (combined zone), Ericsonia subdisticha Zone, Helicosphaera reticulata Zone and Sphenolithus praedistentus Zone, from the Priabonian to the Rupelian. The Sphenolithus ciperoensis Zone of the Chattian was identified in the lower part of the Asmari Formation. Calcareous nannofossil stratigraphy across the upper Eocene-Oligocene interval also reveals a disconformity at the Rupelian/Chattian transition due to a bio-event. Shallowing of the basin and environmental changes in this part of the Tethyan domain could have led to the lithostratigraphic and biostratigraphic changes . In fact, during the late Eocene to late Oligocene, marine phytoplankton was sensitive to climate changes such as decreasing temperature, as well as possibly to a nutrient increase and changes in basin depth.
		2021 Vol. 10 (2): 209-221 [Abstract] ( 131 ) [HTML 1KB] PDF (5228 KB) ( 35 )

Lithofacies palaeogeography and sedimentology

	222	Shoreline evolution and modern beach sand composition along a coastal stretch of the Tyrrhenian Sea, southern Italy
		Consuele Morrone, Fabio Ietto
		This contribution focuses on a multidisciplinary research showing the geomorphological evolution and the beach sand composition of the Tyrrhenian shoreline between Capo Suvero promontory and Gizzeria Lido village (Calabria, southern Italy). The aim of the geomorphological analysis was to reconstruct the evolutionary shoreline stages and the present-day sedimentary dynamics along approximately 6 km of coastline. The results show a general trend of beach nourishment during the period 1870-2019. In this period, the maximum shoreline accretion value was estimated equal to +900 m with an average rate of +6.5 m/yr. Moreover, although the general evolutionary trend is characterized by a remarkable accretion, the geomorphological analysis highlighted continuous modifications of the beaches including erosion processes. The continuous beach modifications occurred mainly between 1953 and 1983 and were caused mainly by human activity in the coastal areas and inside the hydrographic basins. The beach sand composition allowed an assessment of the mainland petrological sedimentary province and its dispersal pattern of the present coastal dynamics. Petrographic analysis of beach sands identified a lithic metamorphi-clastic petrofacies, characterized by abundant fine-grained schists and phyllites sourced from the crystalline terrains of the Coastal Range front and carried by the Savuto River. The sand is also composed of a mineral assemblage comparable to that of the Amato River provenance. In terms of framework detrital constituents of QFL (quartz:feldspars:aphanitic lithic fragments) and of essential extraclasts, such as granitoid:sedimentary:metamorphic phaneritic rock fragments (Rg:Rs:Rm), sand maturity changes moderately from backshore to shoreface, suggesting that transport processes had a little effect on sand maturity. Moreover, the modal composition suggests that the Capo Suvero promontory does not obstruct longshore sand transport from the north. Indeed, sands displaced by currents driven by storm-wave activity bypass this rocky headland.
		2021 Vol. 10 (2): 222-243 [Abstract] ( 105 ) [HTML 1KB] PDF (8468 KB) ( 38 )

	244	A record of deglaciation-related shifting of the proximal zone of a sandur - A case study from the Gwda sandur, NW Poland (MIS 2)
		Mateusz Mleczak, Małgorzata Pisarska-Jamroży
		The study analyses a 7.5-m-thick sedimentary succession deposited in the largest sandur (the Gwda sandur, a glacial outwash plain) in NW Poland, during the late Weichselian (MIS 2). Although the study site is located in the distal zone of the sandur, its sedimentological features and palaeohydrological parameters reflect the presence of an energetic, powerful environment typical of the proximal zone. Three sedimentary units were recognized in the studied sedimentary succession: (1) lower unit - fine-grained sands with ripple cross-lamination and horizontal lamination; (2) middle unit - gravelly coarse-grained sands and sandy gravels with planar cross-stratification; and, (3) upper unit - sands and gravelly sands with trough cross-stratification. Although the age of deposition of the sandur is accepted to be convergent with that of end-moraines of the same phase, the sediments in the distal zone of the Gwda sandur correlate with an earlier glaciation phase/subphase. Our findings hint at a complex problem: large sandurs such as the Gwda sandur were probably deposited over a long time, and their successions might record the textural and structural features of the proximal subenvironment, even in their distal parts due to deglaciation-related shifting of the proximal zone of a sandur. This paper presents a new approach to analysing the depositional processes in large sandurs, shows a new light on glaciofluvial water supply dynamics of distal parts of sandurs, and may solve several fundamental problems related to the sandur deposition.
		2021 Vol. 10 (2): 244-258 [Abstract] ( 106 ) [HTML 1KB] PDF (7711 KB) ( 35 )

Palaeoclimatology

	259	Characteristics and evolution of inertinite abundance and atmospheric pO₂ during China’s coal-forming periods
		Dong-Dong Wang, Lu-Sheng Yin, Long-Yi Shao, Da-Wei Lyu, Hai-Yan Liu, Shuai Wang, Guo-Qi Dong
		Coal, especially the inertinite in it, is highly sensitive to climate changes, showing an obvious response to paleoclimate conditions, in particular, to paleo-oxygen concentration (pO₂). In this study, the inertinite abundance data of typical coal-forming periods in China were systematically collected and analyzed. Its characteristics and control factors were studied, and its evolution was established. Based on inertinite abundance data, pO₂ evolution curves of various coal-forming periods in China were established, which fluctuated between 15% and 30% during the entire Phanerozoic. The inertinite abundance in coal deposits during Paleozoic in China was basically consistent with that of other areas of the world, while it was quite different globally from the Mesozoic to the Cenozoic. The results show that the inertinite abundance in coal deposits is controlled by pO₂ and other factors including climatic zones, plant differentiation, sedimentary environments, and tectonic activities. The inertinite abundance in coal deposits in China during the Jurassic was high, suggesting dry paleoclimate of inland China.
		2021 Vol. 10 (2): 259-283 [Abstract] ( 131 ) [HTML 1KB] PDF (5588 KB) ( 49 )

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