In recent years, the Journal of Palaeogeography (Chinese Edition and English Edition) continually received manuscripts in which some authors are from China and some are from Pakistan, Lithuania, Morocco, South Africa, etc. The authors of these manuscripts, according to the viewpoint and method of Miall’s paper (1985), selected rocks from each bed in the clastic section of their study areas and induced some rock types, such as conglomerates, sandstones and fine-grained stones, and considered them as lithofacies. It does not conform to the definition of lithofacies. I wrote some papers, i.e., Feng (2018, 2019, 2020), to point out the problems and hope that the authors worldwide, especially Chinese authors, will not continually cite, spread and follow Miall’s paper (1985) viewpoint and method blindly.Prof. Miall is the first person who considered rocks (in fact, the sediments) as lithofacies and proposed a facies analysis method. His viewpoint and facies analysis method confused the definition of facies and facies analysis method. My current paper is a special article to discuss the principal problems of Miall’s paper (1985), i.e., he considered the sediments as lithofacies and utilized lithofacies to analyze facies, but not to discuss the contributions and less strictness of architectural elements of his paper.Here, I have to declare that the facies in my current paper is the facies of sedimentary petrology, but not of other geological disciplines, such as igneous petrology, metamorphic petrology, palaeontology, stratigraphy, geophysics, geochemistry.Certainly, the definitions of facies and lithofacies are controversial. My current paper will adhere to the policy of “A hundred flowers blossom and a hundred schools of thought contend”. I hope that through academic discussions, contends and geological practice, these problems will be solved gradually.

Sedimentary successions in the northwestern Gulf of Suez provide important clues to the understanding of the geological evolution of NE Africa during the middle and late Eocene. This study focuses on detailed facies analyses in order to characterize the depositional environments and system tracts of the Bartonian-Priabonian succession cropping out in this area. Bartonian-Priabonian carbonate deposits in five stratigraphic sections constitute, from base to top, the Gebel Hof, Observatory, Sannur, Qurn, and Wadi Hof Formations. These formations contain four local assemblage zones of larger benthic foraminifers. Analyses of litho-, bio-, and microfacies in the succession resulted in the recognition of 12 lithofacies types. These lithofacies are represented by packages of lime-mudstones, wackestones, packstones, pack- to grainstones, grainstones, rudstones, boundstones and dolomites. These lithofacies have been grouped into four genetically-related facies associations that represent, respectively, tidal flats/shallow subtidal, restricted-shelf/lagoonal, shoal bar, and outer-shelf lagoon/reefal depositional environments in a downslope shallow-marine inner-ramp setting. The vertical transitions of these facies associations, representing facies changes through time, imply fluctuations of the regional sea level. The two peaks in the Bartonian correspond to well-known global eustatic sea-level rises; the pronounced Priabonian regression must be ascribed to the known global eustatic sea-level fall in combination with regional tectonic activity. The facies distribution suggests that the study area was located in the direct vicinity of some islands during the Bartonian-Priabonian.

Bioturbation plays an important role in enhancing the reservoir capacity of tight reservoirs. This study aims to understand the alteration mechanism and effects of bioturbation on oil and gas reservoirs, to clarify the key control factors and constraints influencing the production of bioturbation. The petrophysical characteristics of bioturbation and host sediments in carbonate rocks, such as mineral composition, pore spaces, porosity and permeability, were studied based on the detailed observation and description of the Ordovician cores from the Tahe oilfield. The effect of bioturbation on petrophysical properties of carbonate rocks were carefully analyzed. The results show: (1) Two types of bioturbation, Thalassinoides-like burrows and Planolites-like burrows, mainly occur in the Ordovician cores of the Tahe oilfield, ranging from the Lower-Middle Ordovician Yingshan Formation to the Middle Ordovician Yijianfang Formation. The burrow-fills are mainly composed of dolomite with subhedral and euhedral crystals. The host sediments mainly consist of micrite. (2) The pores in the host sediments are poorly developed and are incapable of forming effective reservoir spaces. However, well-developed intercrystalline pores among dolomites and microfractures in bioturbated sediments with better connectivity can form effective pore spaces. The results of porosity and permeability show that the host sediments without bioturbation are characterized by poor porosity and permeability. However, with the increase of bioturbation intensity, the porosity of the bioturbated sediments firstly increases and then decreases, whereas the permeability increases all the time. (3) Multiple burrows overprinted in the Ordovician carbonate rocks, forming a large-scale bioturbated carbonate rocks with lateral continuity and vertical connectivity, due to the suitable sedimentary setting, ecological conditions, favorable spatiotemporal sediment matching, and abundant organism-substrate interaction. Subsequently, diagenesis (particularly dolomitization and dissolution) has played a positive role in altering the rock fabric and improving the petrophysical properties of bioturbated carbonates.

The role of microorganisms in the formation of giant ooids is one of the areas of long-term controversy in ooidal research, but it has not been confirmed conclusively. Abundant giant ooids developed in the Zhangxia Formation of the Cambrian Miaolingian Series in North China. Giant ooids in the study area were examined by using Polarized Light Microscopy and Field Emission Environmental Scanning Electron Microscopy. The nuclei of the ooids consist of micritic pellets or radial ooids with diameters less than 2 mm and are formed in a weak-agitating seawater environment. Their cortices are concentric, and are characterized by the alternations of the dark laminae of micritic calcite or Girvanella filaments and light laminae of microsparry calcite. In the environments of inter-bank sea with the alternating development of medium and low energy and chiefly weak-agitating conditions, giant ooids were formed under the joint action of Girvanella filamentous growth, biologically-induced calcification and/or biologically-influenced calcification and inorganic calcium carbonate precipitation. The microfossils of Girvanella are distributed in inner and outer cortices of giant ooids, especially dense in the latter. This distinctly indicates that microbes play a significant role in the formation of giant ooids, and also provides a vital example for discussing the microbial origin of giant ooids.

Conophyton (Maslov) is a cylindroidal stromatolite form-genus characterized by nested conical laminae. Well-preserved Conophyton, up to 4 m tall and with basal diameters of up to 50 cm , are exposed in the Proterozoic Atar Formation of Mauritania, where many occur together, in growth position, as fields of individual columns spaced between 5 to 70 cm apart. The uniformity of these forms and their regular distribution suggest that they grew in quiet-water environments below wave base. Evidence for their penecontemporaneous organomineralization is indicated by nearby toppled examples of undeformed Conophyton forms alongside eroded lithified Conophyton fragments in carbonate breccias. Two characteristics of Conophyton have been used to classify the structures - the form of the lamination and the nature of its axial structure. A mathematical/physical model provides an explanation for the growth pattern of Conophyton. It predicts that coniform structures with thickened axial zones form when upward organic growth of a biofilm moderately exceeds the rate of its mineralization. The varying characteristics of these features between different forms of Conophyton are thought to reflect biomineralization of the decaying biofilm rather than differences in the composition of microbial communities. A modern example of a syngenetic mineralization process capable of producing similar structures has been observed in the contemporary sediments of Lake Preston, Western Australia, where benthic microbial mats are being transformed into coniform lithified crusts. The initial biomineralization of the coniform mat forms magnesium silicate that first coats and permineralizes web-like microbial extracellular polymeric substances (EPS) and then coalesces into a uniform mass that provides mechanical strength to the cones. At a later stage, massive carbonate crystal growth occurs that over-prints much of this texture, leaving only small, remnant areas of the magnesium silicate phase. Many fossil Conophyton are composed of dolomite, and the remains of the microbial communities responsible for their construction are rarely found, except in areas of chert within the Conophyton. It is suggested that Proterozoic Conophyton were constructed in a tranquil environment through the accretion of microbial mats that were syngenetically permineralized by a magnesium silicate such as a smectite. Later, much of the unstable smectite would be susceptible to diagenetic replacement by either dolomite, or chert in which remnants of microbes that had been coated or permineralized could, potentially, be preserved.

The overall occurrence, stratigraphical distribution, palaeoenvironmental and palaeobiogeographical significances of the ostracod faunas from the Silurian Pulu Formation in the Yalai West II section, Nyalam region, southern Tibet, China, are documented for the first time. Thirty-two species belonging to 19 genera are identified and figured herein. The ostracod fauna in the Pulu Formation indicates an age of the late Llandovery-Pridoli. The ostracods belong to a podocope-rich association, which suggests an offshore environment for the Yalai West II section. The ostracods of the Pulu Formation have strong affinities with the South China taxa and also share some similarities with those from Baltica. This implies that ostracods could probably benefit from sea-level changes to facilitate faunal exchanges between peri-Gondwana and Baltica. Geographical isolation and global sea-level changes are proposed as the primary factors controlling the palaeobiogeographical distribution of ostracods during the Silurian.

The Middle Jurassic is characterized by major plate tectonic changes, variable atmospheric CO₂ concentrations (pCO₂), and climate oscillations in both marine and terrestrial realms. However, the limited evidence from the terrestrial sedimentary records hampers a comprehensive understanding of global climate state in this period. Well-exposed strata of the Shaximiao Formation in the Sichuan Basin, Southwest China, preserve successions of paleosols that offer the possibility of evaluating the terrestrial paleoclimatic changes during the Middle Jurassic (Bajocian to Callovian). A total of 151 paleosol profiles belonging to four paleosol types (Entisol-like, Inceptisol-like, Aridisol-like and argillic Inceptisol-like paleosols) were identified and characterized. The quantitative paleoclimate reconstructions based on the bulk geochemistry of paleosol horizons and depths of carbonate nodules indicate a generally semiarid-subhumid climate alternating with arid-humid and cool/warm-temperate climates during this time interval. This dynamic climate terminated in a dry, subhumid, humid/perhumid and superhumid moisture regime characterized by steppe/wet or rain forest floral provinces. We suggest that these climatic fluctuations may have been related to global geodynamic (e.g., the fragmentation of Pangea, “megamonsoonal” circulation, and bolide impacts) and regional tectonic uplift (e.g., the uplift of the Longmenshan Mountains in the South China Block) during the Middle Jurassic. The pCO₂ estimates suggest relatively low pCO₂ levels within the range of ~100 ppm to ~890 ppm during the Bajocian to Callovian. Our results coincide with the threshold for the initiation of glaciation and may help to explain the occurrence of cool intervals in the generally warm Jurassic. These pCO₂ fluctuations, which coincide with paleotemperature variations in the low paleolatitudes of the Northern Hemisphere, are possibly attributable to global geological events (e.g., wildfire events, eustatic sea-level oscillations, and the transient development of glaciations) in the Middle Jurassic.

The study presents integrated palynofacies, organic carbon isotope, and biomarker data to reconstruct palaeoenviromental setting for the Permian sediments (borehole MGK-6) of the Kachinapalli block of the Godavari Valley Coalfield, southern India. The palynofacies data reveal three distinct palynofacies (A-C) as follows. Palynofacies A is dominated by abundant arborescent vegetation (glossopterids and conifers) along with structured organic matter, suggesting freshwater forest swamps in proximal settings. Palynofacies B is dominated by abundant degraded organic matter and amorphous organic matter, suggesting lakeshore/flooded palaeomires in slightly dismal settings. It has a high water level in the hinterland, which enables bacterial degradation of organic matter and establishes low-oxygenation conditions within the water column. These conditions would have provided grounds for the accumulation of either degraded or amorphous organic matter. Palynofacies C is dominated by the abundance of charcoal/opaque phytoclasts, indicating prolonged transportation or post-depositional alteration, suggesting a highly-oxidizing condition in distal settings. The bulk organic δ¹³C range (-25.1‰ to -20.9‰) in the borehole MGK-6 is in close agreement with the global Permian records. This study also shows a weak but statistically significant correlation with the major forms of palynofacies A and C. The interlinked behaviour of bulk organic δ¹³C and palynofacies suggests that the changes in palaeobiogeography/palaeodepositional settings were most likely driven by the change in mean annual precipitation. The biomarker study shows the presence of n-alkane from C₁₅ to C₃₁ with unimodal and bimodal distribution patterns, revealing the source materials as vascular plants and microbially-altered organic matter. The combined palynofacies, organic carbon isotope, and biomarker data provide vital clue to salient findings for the development of environmental conditions of Godavari Valley Coalfield during lower Gondwana sedimentation.