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	2020 Vol. 9 No. 3
	Published: 2020-07-20



	Lithofacies palaeogeography and sedimentology Biopalaeogeography

Lithofacies palaeogeography and sedimentology

	267	Hyperpycnal (over density) flows and deposits
		Carlos Zavala
		A hyperpycnal flow forms when a relatively dense land-derived gravity flow enters into a marine or lacustrine water reservoir. As a consequence of its excess of density, the incoming flow plunges in coastal areas, generating a highly dynamic and often long-lived dense underflow. Depending on the characteristics of the parent flow (flow duration and flow rheology) and basin salinity, the resulting deposits (hyperpycnites) can be very variable. According to flow duration, land-derived gravity flows can be classified into short-lived or long-lived flows. Short-lived gravity flows last for minutes or hours, and are mostly related to small mountainous river discharges, alluvial fans, collapse of natural dams, landslides, volcanic eruptions, jökulhlaups, etc. Long-lived gravity flows last for days, weeks or even months, and are mostly associated with medium- to large-size river discharges. Concerning the rheology of the incoming flow, hyperpycnal flows can be initiated by non-Newtonian (cohesive debris flows), Newtonian supercritical (lahars, hyperconcentrated flows, and concentrated flows) or Newtonian subcritical flows (pebbly, sandy or muddy sediment-laden turbulent flows). Once plunged, non-Newtonian and Newtonian supercritical flows require steep slopes to accelerate, allow the incorporation of ambient water and develop flow transformations in order to evolve into a turbidity current and travel further basinward. Their resulting deposits are difficult to differentiate from those related to intrabasinal turbidites. On the contrary, long-lived Newtonian subcritical flows are capable of transferring huge volumes of sediment, freshwater and organic matter far from the coast even along gentle or flat slopes. In marine settings, the buoyant effect of interstitial freshwater in pebbly and sandy hyperpycnal flows can result in lofting due to flow density reversal. Since the excess of density in muddy hyperpycnal flows is provided by silt-clay sediments in turbulent suspension, lofting is not possible even in marine/saline basins. Muddy hyperpycnal flows can also erode the basin bottom during their travel basinward, allowing the incorporation and transfer of intrabasinal sediments and organic matter. Long-lived hyperpycnal flow deposits exhibit typical characteristics that allow a clear differentiation respect to those related to intrabasinal turbidites. Main features include (1) composite beds with gradual and recurrent changes in sediment grain-size and sedimentary structures, (2) mixture of extrabasinal and intrabasinal components, (3) internal and discontinuous erosional surfaces, and (4) lofting rhythmites in marine/saline basins.
		2020 Vol. 9 (3): 267-287 [Abstract] ( 124 ) [HTML 1KB] PDF (16645 KB) ( 35 )

	288	The use of mineral interfaces in sand-sized volcanic rock fragments to infer mechanical durability
		Emilia Le Pera, Consuele Morrone
		The use of mineral interfaces, in sand-sized rock fragments, to infer the influence exerted by mechanical durability on the generation of siliciclastic sediments, has been determined for plutoniclastic sand. Conversely, for volcaniclastic sand, it has received much less attention, and, to our knowledge, this is the first attempt to make use of the volcaniclastic interfacial modal mineralogy of epiclastic sandy fragments, to infer mechanical durability control at modern beach environment. Volcaniclastic sand was collected along five beaches developed on five islands, of the southern Tyrrhenian Sea (Alicudi, Filicudi, Salina, Panarea and Stromboli) from the Aeolian Archipelago, and one sample was collected near the Stromboli island volcanic crater. Each sample was sieved and thin sectioned for petrographic analysis. The modal mineralogy of the very coarse, coarse and medium sand fractions was determined by point-counting of the interfacial boundaries discriminating 36 types of interfaces categories, both no-isomineralic and/or no iso-structural (e.g., phenocrystal/glassy groundmass or phenocrystal/microlitic groundmass boundaries) and iso-mineralic interfaces, inside volcanic lithic grains with lathwork and porphyric textures. A total of 47386 interfacial boundaries have been counted and, the most representative series of interfaces, from the highest to the lowest preservation, can be grouped as: a) ultrastable interfaces, categorized as Pl (Plagioclase)/Glgr (Glassy groundmass) >> Px (Pyroxene)/Glgr >> Ol (Olivine)/Glgr >> Op (Opaque)/Glgr >> Hbl (Hornblende)/Glgr>>Bt (Biotite)/Glgr >> Idd (Iddingsite)/Glgr >> Rt (Rutile) / Glgr; b) stable interfaces, categorized as Pl/Migr (Microlitic groundmass) >> Op/Migr >> Px/Migr >> Ol/Migr; c) moderately stable interfaces, categorized as Op/Px >> Op/Hbl >> Px/P >>Ol/Pl>>Bt/Op; and d) unstable interfaces, categorized as Pl/Pl >> Px/Px >> Ol/Ol >> Op/Op >> Hbl/Hbl >> Bt/Bt. Grains, eroded from the volcanic bedrock, if affected solely by abrasion, developed a rounded and smoothed form, with prevailing no-isostructural interfaces such as Plagioclase/Glassy groundmass, Pyroxene/Glassy groundmass and Olivine/Glassy groundmass interfaces. Grains that during transport suffered fracturing and percussion have a sharp and angular form: these combined transport mechanisms produce mainly volcanic sandy grains with iso-structural interfaces, such as Pl/Pl, Px/Px, Hbl/Hbl, and, to a lesser extent, Bt/Op and Bt/Glgr interfaces.
		2020 Vol. 9 (3): 288-313 [Abstract] ( 82 ) [HTML 1KB] PDF (8959 KB) ( 36 )

	314	Provenance of upper Permian-lowermost Triassic sandstones, Wutonggou low-order cycle, Bogda Mountains, NW China: implications on the unroofing history of the Eastern North Tianshan Suture
		Dong-Yu Zheng, Wan Yang
		This study investigates the provenance of sedimentary rocks in Bogda Mountains, NW China, and reconstructs the lithology and unroofing history of the Eastern North Tianshan Suture. Petrographic point counting data of sandstones and compositions of conglomerates of upper Permian-lowermost Triassic Wutonggou low-order cycle from Zhaobishan, North Tarlong, Taodonggou, and Dalongkou sections in the southern and northern foothills of Bogda Mountains were used to interpret the temporal and spatial variations of lithology of the Eastern North Tianshan Suture, which is the sediment source area. Three compositional trends were identified. A trend of upward-increasing quartz content and granitic pebbles in Zhaobishan section suggests a change from the undissected volcanic arc, accretionary wedge and trench setting to predominantly transitional volcanic arc and subordinate accretionary wedge and trench, in the eastern part of the Eastern North Tianshan Suture. In North Tarlong and Taodonggou sections, however, the lithic content decreases and the contents of quartz and granitic pebbles increase up sections. These trends indicate that the western part of the Eastern North Tianshan Suture changed from an undissected volcanic arc to the transitional volcanic arc, accretionary wedge and trench. No clear trend in the lithic-rich sandstones of the Dalongkou section indicates that sediments were derived from the undissected volcanic arc in the Eastern North Tianshan Suture and local rift shoulders. Compositional variations of studied rocks suggest that the Eastern North Tianshan Suture was an amalgamated complex with great spatial and temporal heterogeneities in lithology and experienced persistent unroofing during late Permian-earliest Triassic. This study reconstructs a key element of the Chinese Tianshan Suture and serves as an example to understand the unroofing processes of ancient sutures.
		2020 Vol. 9 (3): 314-334 [Abstract] ( 99 ) [HTML 1KB] PDF (8224 KB) ( 48 )

	335	Marine transgression(s) to evaporite basin: The case of middle Miocene (Badenian) gypsum in the Central Paratethys, SE Poland
		Danuta Peryt, Przemysław Gedl, Tadeusz Marek Peryt
		The middle Miocene Badenian evaporite basin of the Carpathian Foredeep Basin was a saline lake, separated by a barrier from the sea and supplied with seawater seeping through the barrier or overflowing it occasionally in the form of short-lived marine transgressions. Such transgressions could leave behind marine microfossils in marly clay intercalations. One of them (2.3 m thick) occurs in the uppermost part of the sulphate sequence, in the unit ‘o’, in the Babczyn 2 borehole section. It contains marine palynomorphs (dinoflagellate cysts) and foraminiferal assemblages indicating a marine environment. The low-diversity benthic foraminiferal assemblages are dominated by opportunistic, shallow infaunally living species, preferring muddy or clayey substrate for thriving, brackish to normal marine salinity, and inner shelf environment. Dinoflagellate cyst assemblages, although taxonomically impoverished, consist of marine species; euryhaline forms that tolerate increased salinity are missing. Relatively common microfossils found in clay intercalations within gypsum have important palaeogeographical implications: they strongly suggest that there existed an additional inflow channel supplying the Polish Carpathian Basin from the south during the evaporite deposition and afterwards.
		2020 Vol. 9 (3): 335-352 [Abstract] ( 89 ) [HTML 1KB] PDF (10249 KB) ( 35 )

	353	Paleosols in an outcrop of red beds from the Upper Cretaceous Yaojia Formation, southern Songliao Basin, Jilin Province, NE China
		Li Zhang, Zhi-Dong Bao, Chang-Min Zhang, Lu-Xing Dou, Ping Fu, Jia-Hong Zhao, Wu-Xue Wang, Yu Ji
		Paleosols in an outcrop of fluvial-lacustrine red beds have been recognized in the Upper Cretaceous Yaojia Formation in southern Songliao Basin, Songyuan City, Jilin Province, NE China. They are recognized in the field by pedogenic features, including root traces and burrows, soil horizons and soil structures. Root traces are remnants of small herbaceous plants, elongating and branching downwards in the red paleosols. They are filled by calcite, analcime, and clay minerals in spaces created by the decay of the plant roots. Burrows are found near the root traces with backfilled cells made by soil-dwelling insects. Soil horizons include calcic horizons (Bk horizon) with continuous calcareous layers, argillic horizons (Bt horizon) with clay films and dark brown to black iron-manganese cutans, vertic horizons (Bw horizon) with slickensided claystone, and deformed soil structure and gleyed horizons (Bg horizon) with mottles and reticulate mottles. Soil structures of the paleosols include pseudo-anticlinal structures, subangular blocky structures, and angular blocky structures. The micro-pedogenesis characteristics are also observed, including micrite pedogenic minerals and clay skins. Based on the pedogenic features above, paleosols types including Aridisol, Alfisol, and Vertisol are interpreted in the red beds of the Yaojia Formation. Forming in the Late Cretaceous, the paleosols can provide more details about the seasonal climate conditions and terrestrial sedimentary system in lacustrine basin.
		2020 Vol. 9 (3): 353-362 [Abstract] ( 67 ) [HTML 1KB] PDF (7900 KB) ( 62 )

	363	Demise of the Jabłonna Reef (Zechstein Limestone) and the onset of gypsum deposition (Wuchiapingian, west Poland): carbonate-to-evaporite transition in a saline giant
		Tadeusz Marek Peryt, Marek Jasionowski, Paweł Raczyński, Krzysztof Chłódek
		Microbial deposits commonly occur at the transition between carbonate and sulphate facies, and they also abound in the uppermost part of the middle Wuchiapingian Zechstein Limestone in west Poland. These deposits occur as isolated reefs of the basinal zone and in the condensed sequences in most parts of the study area. The deposits of the latter category reflect evaporative drawdown, and the abrupt boundary between the carbonate and sulphate deposits in the basin suggests the nature of evaporites that start to precipitate as soon as they reach the saturation level. A few-metre-thick unit of mostly brecciated microbial deposits at the top, reefal portion of the Zechstein Limestone records extreme palaeoenvironmental events that occurred at the transition from carbonate to sulphate deposition. These events are related first to subaerial exposure of the reef, which lasted several 10⁵ years and then to the Lower Anhydrite transgression.
		2020 Vol. 9 (3): 363-377 [Abstract] ( 73 ) [HTML 1KB] PDF (10640 KB) ( 33 )

Biopalaeogeography

	378	First record of ostracods from the Upper Ordovician red-coloured marine sandstones of the Tierekeawati Formation in Tarim Basin, NW China: implications on palaeoenvironment and palaeobiogeography
		Jun-Jun Song, Yi-Xin Shen, Peng Tang, Xiao-Le Zhang, Qi-Jian Li, Zheng-Jiang Luo
		Ostracods are described for the first time from the red-coloured marine sandstones of Arisu section (Arisu red beds) of the Upper Ordovician Tierekeawati Formation in Kalpin area of northwestern Tarim Basin, Xinjiang Uygur Autonomous Region (Xinjiang), Northwest China. Twenty-two species belonging to thirteen genera are described and figured. The ostracod fauna suggests a probable Sandbian-Katian age for these beds. The palaeoecological assemblage of ostracod fauna implies the deposition in a nearshore-offshore environment during a regression when the Arisu red beds of the Tierekeawati Formation were laid down in the Tarim Basin. Many cosmopolitan and provincial genera were present in diversified ostracod fauna of the Arisu red beds, suggesting the possible biogeographic relationships among the Tarim, Tibet, and South China plates, as well as Europe and North America continents during the Late Ordovician. Ostracods experienced faunal exchanges between Laurentia and the Tarim Plate during the Late Ordovician Period.
		2020 Vol. 9 (3): 378-387 [Abstract] ( 92 ) [HTML 1KB] PDF (6338 KB) ( 33 )

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