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Current Issue   2019 Vol.  8 No.  3 Published: 2019-07-20 Biopalaeography and palaeoecology 209 Eocene foraminiferal biofacies in Kutch Basin (India) in context of palaeoclimate and palaeoecology Sonal Khanolkar, Pratul Kumar Saraswati The Eocene Epoch passed through multiple hyperthermal events and recorded highest temperatures in the Cenozoic. Very few studies from Eocene palaeotropical sites have recorded changes in shallow marine foraminiferal assemblages. The present study investigates the foraminiferal biofacies of shallow marine successions from a palaeotropical site in western India (Kutch Basin) to understand the palaeoclimate and its impact on the ecology of foraminifera. The sections were biostratigraphically constrained using planktic and larger benthic foraminifera. Four biofacies are recognized by detrended correspondence analysis of the sample-wise distribution of foraminifera. Low diversity and dwarfed foraminifera characterize Bulimina-Chiloguembelina biofacies (SBZ5/6-SBZ10), corresponding to the interval of Paleocene-Eocene Thermal Maxima (PETM) and Eocene Thermal Maxima 2 (ETM 2). Rectilinear benthic foraminifera and biserial and triserial planktic foraminifera, typical of high runoff, upwelling or eutrophic conditions, are dominant taxa in this biofacies. The specialist taxa increased significantly in Asterigerina-Cibicides biofacies, corresponding to SBZ11 (Early Eocene Climatic Optimum, EECO), and the environment became oligotrophic. The Jenkinsina-Brizalina biofacies (E12) is distinguished by foraminiferal assemblage ecologically like that of Bulimina-Chiloguembelina biofacies. It is characterized by high abundance of rectilinear benthic foraminifera and bloom of triserial planktic foraminifera, suggesting eutrophy and high runoff at the initiation of Middle Eocene Climatic Optimum (MECO). The foraminifera were more diverse and abundant in Cibicides-Nonion biofacies. The highly diverse larger benthic foraminiferal assemblage in this biofacies, signify warm and clear-water oligotrophic sea that promoted the development of platform carbonate in Kutch Basin and other basins in western India. The EECO and MECO did not have an adverse impact on shallow marine foraminifera, and particularly the larger benthic foraminifera attained high diversity, high abundance, larger size and wider latitudinal distribution in the middle Eocene. 2019 Vol. 8 (3): 209-224 [Abstract] ( 255 ) [HTML 1KB] PDF (16726 KB)   ( 59 ) 225 Early Triassic microbialites from the Changxing Region of Zhejiang Province, South China Ya-Fei Huang, David P.G. Bond, Yong-Biao Wang, Tan Wang, Zhi-Xing Yi, Ai-Hua Yuan, Jia-Yuan Jia, Yu-Qi Su Microbialites, often considered as a signal of extreme marine environment, are common in the Lower Triassic strata of South China where they flourished in the aftermath of the end-Permian mass extinction. Early Triassic microbialite facies are known to vary palaeogeographically, perhaps due to differing climates, ocean chemistry, and water depths. This paper provides the first record of a brief, but spectacular development of microbialites in the aftermath of the end-Permian mass extinction at Panjiazhuang section, Changxing Region of Zhejiang Province (eastern South China). Here, the Upper Permian Changxing Formation comprises typical shallow platform facies rich in calcareous algae and foraminifera, the development of which was terminated by the major end-Permian regression. A 3.4-m-thick microbialite began to form at the onset of the transgression in the earliest Triassic. The microbialite at Panjiazhuang section is composed of thrombolite that contains abundant calcified cyanobacteria, small gastropods, microconchid tubes and ostracods, representing a low-diversity shallow marine community in the aftermath of the end-Permian crisis. The microbialites are succeeded by thin-bedded micrites bearing thin-shelled bivalves, which record a rapid sea-level rise in the Early Triassic. Abundant populations of small pyrite framboids are observed in the upper part of the microbialites and the overlying thin-bedded micrites, suggesting that dysoxic water conditions developed at that time. The appearance of microbialites near the Permian-Triassic boundary (PTB) at Panjiazhuang section was the result of peculiar marine conditions following the end-Permian regression, whilst their disappearance was due to the increasing water depth and the development of dysoxia. 2019 Vol. 8 (3): 225-237 [Abstract] ( 186 ) [HTML 1KB] PDF (11824 KB)   ( 57 ) 238 Characteristics of Early Cretaceous wildfires in peat-forming environment, NE China Shuai Wang, Long-Yi Shao, Zhi-Ming Yan, Ming-Jian Shi, Yun-He Zhang Inertinite maceral compositions in coals from the Early Cretaceous Erlian, Hailar, and Sanjiang Basins in NE China are analyzed in order to reveal palaeowildfire events and palaeoclimate variations. Although huminite is the dominant maceral group in the studied basins, the inertinite group, as a byproduct of palaeowildfires, makes up a considerable proportion. Occurrence of inertinite macerals indicates that wildfires were widespread and frequent, and supports the opinion that the Early Cretaceous was a “high-fire” interval. Inertinite contents vary from 0.2% to 85.0%, mostly within the range of 10%-45%, and a model-based calculation suggests that the atmospheric oxygen levels during the Aptian and Albian (Early Cretaceous) were around 24.7% and 25.3% respectively. Frequent fire activity during Early Cretaceous has been previously related to higher atmospheric oxygen concentrations. The inertinite reflectance, ranging from 0.58%Ro to 2.00%Ro, indicates that the palaeowildfire in the Early Cretaceous was dominated by ground fires, partially reaching-surface fires. These results further support that the Cretaceous earliest angiosperms from NE China were growing in elevated O2 conditions compared to the present day. 2019 Vol. 8 (3): 238-250 [Abstract] ( 217 ) [HTML 1KB] PDF (4508 KB)   ( 61 ) Lithifacies palaeography and sedimentology 251 Development characteristics and controlling factor analysis of the Neogene Minghuazhen Formation shallow water delta in Huanghekou area, Bohai offshore basin Li-Xin Tian, Hao Liu, Cheng-Min Niu, Xiao-Feng Du, Bo Yang, Xiao-Dong Lan, Dan-Lei Chen Based on a combination of high resolution 3-D seismic, drilling and well logging and core data, this study focuses on describing the depositional features of the Neogene Minghuazhen Formation shallow water delta in Huanghekou area (HHKA), Bohai offshore basin and discussing the evolution and control factors of shallow water delta sandbody. An obvious meandering fluvial delta system developed in the sequence 1 (SQ1) of the Neogene in HHKA with thinner sandbody of distributary channels and poor development of mouth bar. The sequence texture obviously influences the vertical development and stacking pattern of sandbodies and controls the distribution of sandbodies in plain view as well. In shallow water lacustrine basins, relative topographic height difference leads to change of distribution of accommodation space, and sandbodies of distributary channels usually develop well in local low-lying areas where accommodation space increases.. The delta is dominated by distributary channel sandbodies during the early period of base level rising and sandbodies contacted with each other in a lateral stacking pattern and characterized by a fan shape in plain view. Distributary channels gradually narrow and tend to shift and change during the mid- late-period of base level rising, while the sandbodies are characterized by a mesh shape in plain view. During the period of base level slow falling, the multistory/multilateral channel sandbodies dominated the inner delta front of shallow-water delta and the delta sand dispersal in the plain distributes as a lobe shape. 2019 Vol. 8 (3): 251-269 [Abstract] ( 254 ) [HTML 1KB] PDF (14469 KB)   ( 45 ) 270 Palaeoenvironmental setting of lacustrine stromatolites in the Miocene Wudaoliang Group, northern Tibetan Plateau Ling-Qi Zeng, Hai-Sheng Yi, Guo-Qing Xia, Klaus Simon, Christine Heim, Gernot Arp Lacustrine stromatolites were widespread in the Miocene Wudaoliang Group (stromatolites of the Wudaoliang Group), northern Tibetan Plateau; but only at one location nearby the Wudaoliang Town, they occurred intensively in thick, laterally traceable beds (Wudaoliang stromatolites). Although deposited in lacustrine environment, the lack of fossils in these rocks hampers determining whether the stromatolites formed in freshwater or saline conditions. To address this problem, and in an attempt to identify criteria to distinguish differences of freshwater and saline conditions, we studied the laminae microfabrics, stable carbon and oxygen isotope ratios, rare earth element patterns and biomarkers of the stromatolites. These stromatolites can be divided into fenestral stromatolites and agglutinated stromatolites. The fabric of fenestral stromatolites is formed by microcrystalline carbonate enclosing spar-cemented, angular crystal traces. Essentially, this fabric is interpreted as pseudomorph after former formed evaporite crystals. Faecal pellets identical to that of the present-day brine shrimp Artemia, lack of other eukaryotic fossils, and stable isotopic signals point to a shallow, evaporation-dominated hypersaline lake setting. Covariation of carbon and oxygen isotopes indicates hydrologically closed conditions of the Miocene lake on northern Tibetan Plateau. However, if compared to other lacustrine carbonates of the Wudaoliang Group, the high δ13C values of the investigated Wudaoliang stromatolites reveal an additional photosynthetic effect during the deposition of the stromatolites. Furthermore, although no direct evidence is available from field observations and microfabrics, a positive europium anomaly of Wudaoliang stromatolites indicates that a palaeo-hydrothermal inflow system had existed in the outcrop area. These new results favour a hypersaline lake setting subject to hot spring inflow for the Wudaoliang stromatolites, in contrast to earlier interpretations suggesting a freshwater lake setting (e.g. Yi et al. 2008; Zeng et al. 2011). This approach may be appropriate for other lacustrine, unfossiliferous microbialites in settings where the environmental conditions are difficult to determine. 2019 Vol. 8 (3): 270-284 [Abstract] ( 183 ) [HTML 1KB] PDF (5124 KB)   ( 47 ) Geochemistry and sedimentry environments 285 Growth mechanisms and environmental implications of carbonate concretions from the ~1.4 Ga Xiamaling Formation, North China An-Qi Liu, Dong-Jie Tang, Xiao-Ying Shi, Li-Min Zhou, Xi-Qiang Zhou, Mo-Han Shang, Yang Li, Hu-Yue Song Carbonate concretions provide unique records of ancient biogeochemical processes in marine sediments, and have the potential to reflect seawater chemistry indirectly. In fine-siliciclastic settings, they preferentially form in organic-rich mudstones, owing to a significant fraction of the bicarbonate required for carbonate precipitation resulted from the decomposition of organic matter in sediments. In the Member IV of the Xiamaling Formation (ca. 1.40-1.35 Ga), North China, however, carbonate concretions occur in organic-poor green silty shales (avg. TOC = ~0.1 wt%). In order to elucidate the mechanism of the concretion formation and their environmental implications, a thorough study on the petrographic and geochemical compositions of the concretions and their host rocks was conducted. Macro- to microscopic fabrics, including deformed shale laminae surrounding the concretions, “cardhouse” structures of clay minerals and calcite geodes in the concretions, indicate that these concretions are of early diagenetic origin prior to the significant compaction of clay minerals. The carbon isotope compositions of the concretions (-1.7‰ to +1.5‰) are stable and close to or slightly lower than that of the contemporaneous seawater, indicating that the bicarbonates required for the concretion formation were mainly sourced from seawater by diffusion rather than produced by methanogenesis or anoxic oxidation of methane (AOM); the rare occurrence of authigenic pyrite grains in the concretions likely indicates that bacterial sulfate reduction (BSR) did not play a significant role in their formation either. Almost all the calcite in the concretions has low Mn-Fe in nuclei but high Mn-Fe in rims with average Mn/Fe ratio close to 3.3. The calcite shows positive Ce anomalies (avg. 1.43) and low Y/Ho ratios (avg. 31). This evidence suggests that Mn reduction is the dominant process responsible for the formation of calcite rims while nitrate reduction probably triggered the precipitation of calcite nuclei. Prominence of Mn reduction in the porewater likely indicates that there was sufficient oxygen to support active Mn-redox cycling in the overlying seawater. 2019 Vol. 8 (3): 285-300 [Abstract] ( 133 ) [HTML 1KB] PDF (10294 KB)   ( 41 ) Academic discussiob 301 Words of the Editor-in-Chief —— Some ideas about the comments and discussions of hyperpycnal flows and hyperpycnites Zeng-Zhao Feng* I basically agree with the viewpoints of Shanmugam (2018) and Zavala (2019) who cited, refined and interpreted the definitions of hypopycnal flow, homopycnal flow and hyperpycnal flow. I appreciate two typical case studies of hyperpycnal flows induced by the Yellow River and Yangtze River, and the Gaoping River. The former is a normal type while the latter is catastrophic. They make up a complete knowledge about hyperpycnal flows and hyperpycnites. According to the interpretation of the word “hyperpycnal” from Greek to English, the “hypopycnal flow” should be “less density flow” or “lower density flow” (“低密度流”), the “homopycnal flow” should be “equal density flow” (“等密度流”), and the “hyperpycnal flow” should be “higher density flow” or “over density flow” (“高密度流” or “超密度流”). Some geologists called the “hypopycnal flow” as “异轻流” (“abnormally light flow”) and called the “hyperpycnal flow” as “异重流” (“abnormally heavy flow”). There are at least more than 10 names or terms about the “density flows” and the “deposits of density flows”. It is a problem indeed. In addition, the density could be changed by salinity, temperature and pressure of water. Therefore, the term “density flow” may be problematic either. Another problem is that reliable and irrefutable identification markers of ancient hyperpycnites are lacking. We should observe the policy of “A hundred flowers blossom and a hundred schools of thought contend” to discuss these problems and to promote progress and development of hyperpycnal flows and hyperpycnites. 2019 Vol. 8 (3): 301-305 [Abstract] ( 151 ) [HTML 1KB] PDF (3690 KB)   ( 40 ) 306 The new knowledge is written on sedimentary rocks - A comment on Shanmugam’s paper “The hyperpycnite problem” Carlos Zavala In a recent contribution G. Shanmugam (2018) discusses and neglects the importance of hyperpycnal flows and hyperpycnites for the understanding of some sediment gravity flow deposits. For him, the hyperpycnal flow paradigm is strictly based on experimental and theoretical concepts, without the supporting empirical data from modern depositional systems. In this discussion I will demonstrate that G. Shanmugam overlooks growing evidences that support the importance of hyperpycnal flows in the accumulation of a huge volume of fossil clastic sediments. Sustained hyperpycnal flows also provide a rational explanation for the origin of well sorted fine-grained massive sandstones with floating clasts, a deposit often wrongly related to sandy debris flows. 2019 Vol. 8 (3): 306-313 [Abstract] ( 194 ) [HTML 1KB] PDF (1571 KB)   ( 48 ) 314 The hyperpycnite problem: comment A. J.van Loon, Heiko Hüneke, Thierry Mulder A recent review article (“The hyperpycnite problem”) by Shanmugam (2018) in this journal has some shortcomings, comes to scientifically incorrect conclusions, and calls for student education in a way that would significantly diminish the students’ changes for a geological career. Having studied - and still studying - hyperpycnites in the field, it seems only appropriate to inform the readers of this journal about our concerns regarding the review article mentioned above. Actually, the article by Shanmugam (Journal of Palaeogeography 7(3):197–238, 2018) is not a review paper but rather a comment, criticizing all researchers who have come to the conclusion, on the basis of both field research and theory, that hyperpycnal flows result in sediments (hyperpycnites) with characteristics that make it possible to distinguish them from deposits formed in another way. This is also the essence of Shanmugam’s comment: as he states himself, he is “an ardent critic of all genetic facies models”. 2019 Vol. 8 (3): 314-320 [Abstract] ( 177 ) [HTML 1KB] PDF (1269 KB)   ( 46 )

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