Fluvial-lacustrine Environments Research Articles

Dispersal of Late Triassic clam shrimps across Pangea linking northwestern Gondwana and central Pangea rift basins

Clam shrimps are a group of freshwater crustaceans who prospered during the Late Triassic. They were abundant in lacustrine sedimentary records of continental basins distributed throughout Pangea during this time. However, they show significant taxonomic differences between the clamp shrimp faunas from the rift basins of central Pangea and the southern Gondwanan basins. In this contribution, we show new fossil clam shrimp assemblages from the lacustrine sedimentary successions of the Eastern Cordillera of Colombia (the Bocas and Montebel formations), providing information on the Late Triassic species that inhabited the northwestern Gondwana basins. This study demonstrates that the basins of northwestern Gondwana shared Norian clamp shrimp species with rift basins of central Pangea and differed in their faunas with the basins of the southern portion of Gondwana. In addition, the Late Triassic clam shrimps paleobiogeographic distribution reflects the dispersal of this fauna throughout fluvial-lacustrine environments established in the rift valleys along the central Pangea. Therefore, the rift valleys produced during the early fragmentation of central Pangea could have acted as corridors for dispersion. Simultaneously, rift valleys also provided paleobiogeographic barriers that isolated the central Pangea clam shrimp faunas from southern Gondwana.

Investigation of the microscopic properties of natural structured clay

Conducting quantitative research on the microstructure of soft clay can reveal the essence of its soil mechanical behavior, which is of important practical significance for geological disaster risk assessment and prevention. To quantitatively investigate the microscopic properties of natural structured clay, soft clay soils from various sedimentary environments in the Hangzhou Estuarine Bay area were chosen as the research subject in this study. Subsequently, a comprehensive investigation into the microstructure of clay was conducted, involving X-ray phase analysis and SEM imaging analysis. The results revealed the following: (1) In comparison to the deep clay deposited in fluvial-lacustrine environments, the shallow mucky clay in marine sediments had a higher clay mineral content, accounting for 48%. Illite makes up the majority of it, with minor levels of kaolinite and montmorillonite being present. (2) The shallow mucky clay in the Hangzhou Estuarine Bay area had a typical agglomerate-flocculated structure. In contrast, the deeper clay showed a flocculated structure with less uniform particle sizes, strong stacking randomness, poor directional alignment of soil pores, and tends to form arrangements where edges are adjacent to faces or edges are adjacent to other edges. (3) Compared to the deep clay deposited in fluvial-lacustrine environments, the marine-deposited shallow mucky clay displayed orderly pore arrangements, strong directional alignment, significant pore shape variability, and minimal pore size changes between adjacent pores. The microstructure of soil plays a crucial role in determining the physical, mechanical, and other engineering properties of the soil. This study provides insightful information about the relationship between clay microstructure and geotechnical characteristics in Hangzhou and the surrounding areas.

Tectonic movements of the Yanshan-Himalayan period in the northern Longmenshan and their impact on tight gas accumulation of the Shaximiao formation in the Qiulin structure, China

The Jurassic strata constitute a focal area for recent exploration and development of tight gas reservoirs in the western Sichuan Basin. This study investigates the Jurassic Shaximiao Formation in the northern Longmenshan in the Western Sichuan basin, focusing on tight gas reservoirs. The research integrates core and outcrop observations, seismic interpretations, and burial history analyses to understand hydrocarbon source rocks, sedimentation, reservoir characteristics, and structural characteristics. The impact of Yanshan-Himalayan tectonic movements on tight gas reservoir accumulation in the Shaximiao Formation is dissected, primarily around the Qiulin structure. The Western Sichuan Depression basin’s formation is influenced by gravitational gliding tectonics, which can be classified into the ‘Three Zones and One Belt,’ with Longmenshan in the frontal belt. Burial history analysis reveals distinct processes in the foreland belt and the depression basin. In the Qiulin area, gas reservoirs in the Shaximiao Formation are mainly charged by source rocks from the Xujiahe Formation. Tectonic movements play a significant role in creating favorable reservoirs and conditions for hydrocarbon migration and preservation. Natural gas accumulation is primarily controlled by fault connectivity to hydrocarbon sources and effective reservoir thickness. Gravitational sliding tectonics have shaped a fluvial-lacustrine environment for the Shaximiao Formation, with fluvial sand bodies acting as favorable reservoir zones. Small-scale normal faults formed by tectonic movements serve as conduits for natural gas migration. The research findings are of significant guidance for the exploration and development of tight oil and gas resources in western Sichuan basin.

High-northern-latitude forcing modulated fluvial‒aeolian interplay during the Last Glacial Period in the Mu Us Desert, northern central China

Substantial stratigraphic evidence from the Late Quaternary at orbital- and millennial‒scales indicates that the formation and evolution of aeolian‒sand landscapes results from the interaction between regional aeolian and fluvial‒lacustrine activity. In many deserts (sandy lands) across the planet, fluvial‒aeolian interplay at the glacial‒interglacial scale since the Late Quaternary has been responsive to monsoonal precipitation, and linked to atmospheric CO2 and periodic variations in insolation. However, the patterns of fluvial‒aeolian interplay and their relationship with climate change are not always consistent over a given timescale during the Late Pleistocene. The paucity of studies on fluvial‒aeolian interplay in the Mu Us Desert (MUD) during the Last Glacial Period (LGP) hinders our understanding of the relationships between the dynamics of aeolian and fluvial‒lacustrine landscapes and their drivers. Here, based on a comprehensive field survey and stratigraphic dating of a typical fluvial‒aeolian sequence in the MUD, we synthesized the chronology of fluvial‒lacustrine and aeolian strata during the LGP. Our results show that extensive development of a fluvial‒lacustrine environment in the MUD during the LG mainly occurred during the late Last Glacial Maximum (LGMa, 20.1–18.4 ka BP) and Bølling/Allerød interstadial (14.8–12.6 ka BP), while thicker aeolian sands extensively accumulated during the Heinrich Stadial 2, Heinrich Stadial 1, and Younger Dryas periods. However, the development of fluvial‒lacustrine environments showed considerable spatial heterogeneity, mainly occurring on the southern and eastern margins of the desert, while they were extremely rare in the central and western parts of the desert owing to strong wind erosion. Comparisons with other high-resolution geological records from the Asian monsoon region reveal that the fluvial‒aeolian interplay in the MUD during the LGP was highly consistent with the evolution pattern of the East Asian summer monsoon (EASM) on the millennial‒centennial scale, and indicate that the development of fluvial‒lacustrine environments was mainly controlled by an increase in monsoonal precipitation during strengthening of the EASM. Consistency with other broad changes at high latitudes in the Northern Hemisphere suggests that fluvial‒aeolian interplay during the LGP in northern Chinese deserts, as represented by the MUD, was mainly controlled by changes in high-northern-latitude ice volume and the Atlantic Meridional Overturning Circulation.

Late Pleistocene sedimentary environment reconstruction and evolution in the Houtao Plain

Reconstructing the Late Pleistocene sedimentary environment history of the Houtao Plain has great significance not only for revealing the evolution of the Yellow River but also for identifying the formation of paleolake and the northern Ulan Buh Desert. This paper presents the results of the sedimentary facies framework based on a grain-size multi-parameter analysis optically stimulated luminescence and 14C dating for a drilling core DKZ06 with a length of 20.04 m from the Houtao Plain. Grain-size multi-parameter analysis was combined with the grain size of modern environmental sediments to the division of the core sedimentary facies in this area. Sedimentary facies of core DKZ06 indicate that the formation of the Houtao Plain area is dominated by fluvial channel deposition and river changed mainly by frequent fluvial channel since ∼35 ka. The two episodes of shallow lake deposition from a drilling core, suggesting that there will not be a mega-paleolake in the Houtao Plain, and the frequent channel migration of the Yellow River may have caused a series of furiotile lakes during the Late Pleistocene. The appearance of aeolian sand at the top of core DKZ06 combined with previous stratigraphic records from the adjacent areas indicates that the origin of the northern Ulan Buh Desert is relatively late and it formed only 2,000 years ago. We propose that a combination of river migration and large-scale human activity may be responsible for desert formation. The evolution of sedimentary environments has a close correlation with climate change during the Late Pleistocene. During the interglacial stage (MIS3), the sedimentary environment has a particular lacustrine and fluvial–lacustrine environment because of relatively warm–humid conditions. During the glacial stage (MIS2), the Houtao Plain was dominated by a fluvial sedimentary environment because of a relatively cold and dry climate. The sedimentary environment is complex and changeable during the Holocene (MIS1), which was likely due to the frequent climate fluctuation.

C30 and C31 steranes in Permian fossil conifers Protophyllocladoxylon

Steroids with alkyl groups at C-2 and C-3 are not known yet in any living organism, while 4-methylsteranes are previously thought specific to 4-methylsteroids bio-synthesized by limited types of organisms, such as dinoflagellates, microalgae, and certain bacteria. Here we investigate the occurrence of C30 2α-, 3β-, 4α-methyl-24-ethylcholestanes, C31 3β,24-diethylcholestanes, and 3,4-dimethyl-24-ethylcholestane, which are tentatively identified in fourteen fossil conifer Protophyllocladoxylon trunk samples from the upper Permian Wutonggou and Guodikeng formations in northwest China. In contrast to the paucity of alkyl steranes in the background sediments, abundant C30 4α-methyl-24-ethylcholestanes in fossil conifers from diverse fluvial–lacustrine environments suggest that conifers were the most likely biological origin for the 4-methyl steranes in conifer trunk samples, although origins from associated fungi might also be possible. Alternatively, these C-4 methyl steranes might have possible algal or prokaryotic origins. It is noteworthy that diagenetic methylation or bacterial alkylation at early stages of diagenesis during burial may have caused a re-arrangement of classical 24-ethylsterols that were bio-synthesized by plants to generate C-2 and C-3 alkylated steranes. This study reports the presence of 4-methylsteranes in conifer fossils for the first time, pointing toward a likely origin from higher plants. This study also provides the first report of C-2 and C-3 alkylated steranes in plant fossils, a.llowing for the possibility that plants may produce functionalised sterol precursors of orphan alkylsteranes that are abundant in geological sediments but whose functionalised precursors are not known from any living organisms.

Paleoenvironment of the Cerro Negro Formation (Aptian, Early Cretaceous) of Snow Island, Antarctic Peninsula.

A study of macro and microfacies, palynoflora and palynofacies of the non-marine Cerro Negro Formation at President Head Peninsula, Snow Island, northwest of the Antarctic Peninsula, was developed. Two assemblages were recognized: Palynofacies assemblage 1 (P1) at the base of the section with a dominance of fern spores and conifer pollen grains, and facies association consisting of a clastic layer, with the predominance of mudstones; and Palynofacies assemblage 2 (P2) at the top of the section, with remarkable abundance of AOM/Pseudoamorphous particles, associated with facies that includes tuffs. The complete section shows in some levels the presence of freshwater algae and translucent phytoclasts. The integrated data characterizes a fluvial-lacustrine environment, what is reinforced by the occurrence of freshwater algae (Botryococcus) in some levels of P1 and P2. We could verify an increase in volcanic activity towards the top of the section that apparently has played an important role in the collapse of the palynoflora. The occurrence of the spore species Muricingulisporis annulatus, Sotasporites elegans, S. triangularis, Foraminisporis wonthaggiensis, and F. asymmetricus in the Cerro Negro Formation allows the correlation with sections in South America and Australia, suggesting an Aptian age for these deposits.

Palaeovegetation and paleoclimate in the SW Turkey – a study based on the early-middle Miocene coal-bearing sediments from the Büyük Menderes Graben

This study provides the age of coal-bearing sediments of the Büyük Menderes Graben (BMG) and palaeoclimatic and palaeovegetational change from the early to late Miocene. Two palynofloras, the Başçayır and Kızılcayer, are distinguished in the late Burdigalian-early Langhian, and Serravallian-Tortonian boundary. According to the microfloral composition of the Başçayır palynoflora is characterized by subtropical elements, and palaeoclimate is warm subtropical, with the coldest month mean temperature (CMT) 8–13 oC. Based on the palynoflora, the coal-bearing sediments were deposited in the fluvial-lacustrine environments. The abundances of gymnosperm species and the mean annual range of temperature (MART) point out high and middle altitude areas during the deposition of coal-bearing sediments. Based on the Kızılcayer palynofloral composition, palaeoclimate is the warm temperate (CMT: 3.1–13.3 oC), also the abundant presence of herbaceous species indicate open land areas in the Aydın-Kızılcayer area despite the existences of swampy-lowland environments.According to described palynofloral composition, the palaeotopographic conditions of the southern part of the BMG (Aydın-Kuloğulları) are generally higher than the northern parts (Aydın-Başçayır), and deposition areas in this graben are significantly uplifted from the late Burdigalian to early Tortonian. The regional palaeoclimatic condition from the early to late Miocene changed from warm subtropical to temperate in western Anatolia. The palaeotopographic changes related to the tectonic events and/or uplift of the Menderes Massive in western Anatolia could have been effective on regional paleoclimate during the deposition in the BMG, and this uplifting existed in the late Burdigalian and continued until the late Miocene.

The Lower Cretaceous “Continental Intercalaire” around Tidikelt (Central Sahara, Algeria): Sedimentology, palaeontology and ichnology

The Lower Cretaceous strata are exposed over a large surface in the northern part of the Ahnet basin. They consist of transgressive, horizontal formations overlying the folded Palaeozoic formations by angular unconformity across the Tidikelt region. The present study addresses the respective lithostratigraphical units of the “Continental Intercalaire” succession and their subsequent palaeo-environment in the Tidikelt area using a trace fossil analysis combined with sedimentological and palaeontologic data. The lithological and sedimentological features of the study sections recognised eleven sub-units organised within four lithological units: the Lower Clay Unit of Barremian-Neocomian age consisting of three Sub-units (Akablie Sandstone, Sidi Mahmoud Clays and Pebbly Sands); the Quartzite Sandstones Unit referred to a Late Barremian-Early Aptian age; the Middle Clay-Sandstone Unit consisting of a thick deposit of Early Aptian-Albian age, divided into five Sub-units (Tit Sandstones, In Salah Sand-Clay, In Salah Sandstone, Foum El Bouib Sandstone, and Sandstone-Clay); and the Upper Clay Unit comprising the Oued Taleh Sand and the El-Golea Clays Sub-units. Vertebrate remains all evidence a Late Albian-Early Cenomanian age for the top part of the Continental Intercalary. Ichnologic data analysis documents lower diversity of the invertebrate trace fossils: only ten ichnotaxa are recorded so far and grouped in five ichnoassemblages. Fuvial-lacustrine ichnoassemblage represents a continental ichnofacies of a fluvial-lacustrine environment: Mermia, Scoyenia and Skolithos ichnofacies. Fluvial Ichnoassemblage of the Quartzite Sandstone Unit is represented by insect trace fossils typical of the Coprinisphaera ichnofacies. Fluvio-marginal ichnoassemblage corresponds to a tidal-influenced, fluvial deposit transgressive on Unit B, represented by Skolithos and Psilonichnus ichnofacies. Lower shoreface ichnoassemblage shows the upper part of Unit C, documented by horizontal trace fossils such as Thalassinoides and vertical root traces, all supporting a lower shoreface environment in a semi-arid climate interlined by well-oxygenated episode with nutrient-rich conditions and vegetation dominance. Near to shoreface ichnoassemblage coincides with the upper unit D of coastal deposits with fluvial-tidal influence at the base (Oued Taleh Sands) associated with Scoyenia and Skolithos trace fossils and lagoon deposit of the El-Golea Clays Sub-units.

Pleistocene plants from Zarzal Formation, middle valley of the Cauca River Basin, Colombia

We report macro and meso palaeobotanical records from the Zarzal Formation, in the Cauca River Depression, and the Quindío-Risaralda Basin between the Western and the Central Cordilleras of Colombia. The fossils correspond to leaves and seeds obtained from layers of mudstones, diatomites, and tuffaceous sandstones deposited in the inter-Andean valleys of Cauca and La Vieja rivers, separated by the Serranía Santa Bárbara ridge between the Valle del Cauca and Quindío departments. The sediments of the Pleistocene Zarzal Formation were deposited in a fluvial-lacustrine environment, with volcanic influence originated in the Central Cordillera to the east of the depositional area. The study here presented allowed the identification of thirteen morphotypes of leaf impressions grouped in six Angiosperm families: Poaceae?/Cyperaceae? and Araceae of the Monocots group, Melastomataceae, Fabaceae and Lauraceae belonging to the Eudicots group and one family of Lycopsida: Thelypteridaceae. On the other hand, very well-preserved silicified micro-seeds were grouped in eight morphotypes, belonging to the botanical groups Cyperaceae and Asteraceae. The fossils found allowed us to identify two types of plant associations that exhibit paleofloristic richness. In the Cauca River Basin, an autochthonous to parautocthonous plant association could correspond to a sub-Andean gallery forest, whilst in the La Vieja River Basin a parautocthonous plant association indicates a swamped floodplain. Keywords: paleoflora, leaves, seeds, Cauca River, La Vieja River, lacustrine deposit.

Biostratigraphic and petrological characteristics of Cretaceous\u2013Paleogene sediments in the eastern Cuu Long delta

The basic structure of reservoir models is strongly affected by the stratigraphic interpretation and the properties of reservoir rock. The estimation of the volume of hydrocarbon accumulation will depend on the accuracy of predicting and distributing reservoir quality. Biostratigraphic and sedimentary petrologic results provide geological information to clarify the stratigraphy and properties of sedimentary rocks on the eastern margin of the Cuu Long delta plain trough. On the basis of stratigraphic correlation of the wells and studying the structures of the area, the deposition, thickness of sediments and the ability to correlate with prospect rocks on the southeastern Vietnam continental shelf were determined. The results have identified the basement rock of wells TC-1 and TC-2, which are Cretaceous metasandstones and were deposited in freshwater fluvial environments with high-energy conditions. The upper Paleogene sediments were overlaid directly on the Cretaceous basement rock in the TC-2 well but were completely absent in the TC-1 well. The lithologic composition is mainly feldspathic litharenite sandstone, which is formed in freshwater fluvial and freshwater lacustrine environments. This study provides new data on stratigraphic column of the eastern Cuu Long delta plain. The data show that the age of the sedimentary basement rock is Cretaceous which has not been determined in previous studies. The findings of this study can help for better understanding of the geological development history and the completely stratigraphic column of the Cuu Long delta to correlate with objects that are hydrocarbon accumulation in Cuu Long sedimentary basin in order to improve efficiency in petroleum exploration activities.

The Carboniferous-mid Permian successions of the Northern Apennines: new data from the Pisani Mts. inlier (Tuscany, Italy)

This paper updates and partially modifies the knowledge of the geological-palaeoenvironmental and geodynamic framework of the Tuscan segment of the Variscan Chain in Tuscany during Permian times. Particularly, it adds new data on the contact between the upper Carboniferous-lower Permian San Lorenzo schist (SLs) and the mid-Permian Asciano breccia and conglomerate (Abc) clastic formations in the Pisani Mts. metamorphic inlier which represents one of the pinning point outcrops for the study of the upper Paleozoic sequences in the Northern Apennines. Their sharp unconformable contact is well-documented in the literature at map and outcrop scale and was ascribed to the Saalian phase of the Variscan orogeny that would have occurred in correspondence of a climatic change from equatorial to an semi-arid tropical conditions. New geological investigations on the SLs and Abc allowed us to identify the finding of a continuous stratigraphic section in the Pian della Conserva locality (northwestern Pisani Mts.) where the organic matter-rich SLs conformably passes upwards to the reddish immature, mainly coarse-grained deposits of Abc through a decametric transition zone. The section was studied in detail from a lithological-sedimentological point of view and sampled for petrographic, mineralogic and chemical studies. The data show that the passage from SLs to Abc testifies a main change from an equatorial, wet fluvial-lacustrine environment to a well-drained, alluvial fan systems in a monsoon- like climate. This event can be related to the reactivation of the previous late Carboniferous-lower Permian shear zones during the mid-Permian times that produced morpho-tectonic highs subjected to a rapid erosion and the formation of unconformities, whereas the presence of a few residual fluvial plain areas, characterized by dysoxic conditions, is documented by the gradual passage between SLs and Abc in the Pian della Conserva section. In addition, the presence of a metavolcanoclastic or metaepiclastic layer was also recognized in the uppermost part of the SLs and it represents the first evidence of a late Carboniferous-early Permian volcanic event in the Northern Apennines.

Hydrocarbon potential and depositional paleoenvironment of a Middle Jurassic succession in the Falak-21 well, Shushan Basin, Egypt: Integrated palynological, geochemical and organic petrographic approach

The topmost Lower and Middle Jurassic formations of organic-rich clastics with minor carbonate deposits were recognized as very significant source/reservoir rocks in the North Western Desert of Egypt. Although several studies are devoted to their source rock characteristics and petroleum potential, the depositional paleoenvironment and paleoredox conditions are still poorly understood. In the current study, these sediments were assessed in terms of their organic matter richness, hydrocarbon generative potential and thermal maturity, total sulfur (TS) contents and organic petrographic characteristics. Depositional paleoenvironment was investigated using dinoflagellate cysts (dinocysts) and the composition of particulate organic matter along with organic petrographic characteristics. Redox conditions were assessed based on TS- total organic carbon (TOC) relationship and type of kerogen that was derived mainly from palynofacies analysis.TOC contents show fair to excellent generative potential of hydrocarbons mainly of kerogen type III (gas-prone). The thermal maturity, based on Tmax and Rr, indicates mature stage of oil window.Palynological analysis yielded poor to rich intervals of moderately-preserved, biostratigraphically useful dinocysts in the upper part of the Khatatba Formation. An assemblage of 81 species belonging to 54 genera of moderately diverse dinocysts, spores and pollen grains was identified. Freshwater algae, acritarchs and microforaminiferal test linings are sporadically documented within the studied interval. Based on the first downhole appearance (FDA) of the recovered marker dinocyts, the upper part of the Khatatba Formation was palynologically dated as late Bathonian-Callovian.The depositional environment was interpreted and three environments were deduced. The lower interval representing the topmost Ras Qattara and Yakout Red Shale Member was deposited in a fluvial-lacustrine environment, where oxic conditions prevailed as deduced from the color of reddish-brown sandstone and red shale. The middle interval spans Unit IIB, Kabrit and Unit III, which accumulated in a deltaic to shallow marine environment under dysoxic-suboxic settings. The upper interval covers Unit I and Unit IIA that have been deposited in a fluvio-deltaic to shallow marine with high paleoproductivity under suboxic conditions. One sample in the upper interval in Unit IIA reflected anoxic setting.

Volcanogenic fluvial-lacustrine environments in iceland and their utility for identifying past habitability on Mars.

The search for once-habitable locations on Mars is increasingly focused on environments dominated by fluvial and lacustrine processes, such as those investigated by the Mars Science Laboratory Curiosity rover. The availability of liquid water coupled with the potential longevity of such systems renders these localities prime targets for the future exploration of Martian biosignatures. Fluvial-lacustrine environments associated with basaltic volcanism are highly relevant to Mars, but their terrestrial counterparts have been largely overlooked as a field analogue. Such environments are common in Iceland, where basaltic volcanism interacts with glacial ice and surface snow to produce large volumes of meltwater within an otherwise cold and dry environment. This meltwater can be stored to create subglacial, englacial, and proglacial lakes, or be released as catastrophic floods and proglacial fluvial systems. Sedimentary deposits produced by the resulting fluvial-lacustrine activity are extensive, with lithologies dominated by basaltic minerals, low-temperature alteration assemblages (e.g., smectite clays, calcite), and amorphous, poorly crystalline phases (basaltic glass, palagonite, nanophase iron oxides). This paper reviews examples of these environments, including their sedimentary deposits and microbiology, within the context of utilising these localities for future Mars analogue studies and instrument testing.

Cenozoic record of aeolian sediment accumulation and aridification from Lanzhou, China, driven by Tibetan Plateau uplift and global climate

Previous work has shown that aeolian Red Clay first appears at around 8Ma in the main Chinese Loess Plateau and at 25–22Ma in the western Loess Plateau; however, records of aeolian deposition in the North Pacific suggest that aeolian accumulation occurred throughout the Cenozoic, and that changes in aeolian flux occurred in distinct stages. Tracing the Cenozoic aeolian history of the interior of the Asian continent may help us to understand the history of Asian aridification and its driving forces. In the Lanzhou area on the western margin of the Loess Plateau and the northeastern edge of the Tibetan Plateau, the Cenozoic stratigraphic sequence consists of fluvial–lacustrine sediments in the lower part, aeolian Red Clay with intercalated fluvial layers in the middle part, and predominantly aeolian loess in the upper part. We use high resolution paleomagnetic measurements of this sequence to construct a time scale, and measurements of sediment rock magnetic properties, grain-size, and color reflectance and sedimentary facies analysis to reconstruct the paleoenvironment. The results show that prior to 33Ma the area was dominantly a fluvial–lacustrine environment, and that subsequently an aridification trend commenced, as indicated by the appearance of aeolian sediment. This change coincided with, and is thus explained as the environmental response to global cooling. A significant increase in aeolian sediments occurred at ~26Ma, suggesting that a large scale arid environment had formed in the Asian interior since the late Oligocene. Stepwise increases of aeolian sediment, and decreases in sediments of hydraulic origin, occurred at ~22, ~14, ~8 and 2.6Ma and represent important stages in the aridification process. This long-term trend was interrupted by intervals dominated by fluvial sedimentation at 23.6–22Ma and 17.1–14.1Ma and which were probably associated with warming of the global climate and the tectonic uplift of the northeastern Tibetan Plateau. Tectonic events occurring in Lanzhou at ~9–8Ma and ~3.5Ma indicate strong uplift of the northeastern Tibetan Plateau.

A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars

The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

Lithofacies architecture and depositional environment of Late Cretaceous Lameta Formation, central India

Establishment of lithofacies and interpretation of depositional environment of the Lameta Formation have been carried out for a new area having three nearby exposures. Overall, the successions are broadly differentiable into three major units, i.e. arenaceous in the lower part, argillaceous in middle and calcareous at the top, which more or less serve as three lithofacies associations. Each association consists of various lithofacies which are identified and established on the basis of field observations, added with significant petrological details. The arenaceous association includes five lithofacies, viz. massive sandstone lithofacies; green sandstone lithofacies; thinly bedded, yellowish orange and greyish brown sandstone lithofacies; coarse-grained sandstone lithofacies and dark brown bioturbated sandstone lithofacies. The argillaceous lithofacies association consists of yellowish-brownish-greenish clay–siltstone lithofacies and light grey silty–clay with concretions lithofacies, whereas the calcareous lithofacies association is represented by calcrete lithofacies, nodular limestone lithofacies, chertified limestone lithofacies and intraformational breccia lithofacies. The facies analysis reveals that the deposition of Late Cretaceous Lameta sediments took place in fluvial–lacustrine environments in semi arid condition.

From mesic to arid: Leaf epidermal features suggest preadaptation in Miocene dragon trees (Dracaena)

Among the most prominent examples for the disjunct distribution of xeromorphic-sclerophyllous plants in Macaronesia and eastern Africa–Arabia, referred to as the Rand flora biogeographic pattern, is the “dragon tree group” within Dracaena (Asparagaceae). However, little is known about the evolutionary origin of this iconic group of semi-desertic trees. Here, we use exceptionally well-preserved fossils from western Anatolia to demonstrate range and ecological shifts of the lineage probably leading to some of the modern dragon trees. Compression fossils of apical leaf rosettes and detached leaves of Dracaena tayfunii spec. nov. were compared to modern Dracaena using the architecture of leaf-bearing branches, leaf morphology, and highly diagnostic leaf epidermal features observed with light and electron scanning microscopy. The palaeoecology of Dracaena was inferred using the depositional setting and associated plant taxa. The ca. 16million-year-old (Ma) Dracaena from western Anatolia shows a character combination restricted today to the Macaronesian dragon tree, Dracaena draco: (1) Leaves are arranged in terminal rosettes; (2) leaves are ensiform, oblong, with a conspicuously dilated base (pseudo-sheath); and (3) leaf epidermis is strongly papillate with sunken stomata overarched by papillae of four neighbouring epidermal cells. Depositional setting, taphonomy, and the fossil plant association indicate that the Miocene Dracaena either grew in seasonally dry swamps within a complex fluvial–lacustrine environment or on adjacent slopes under a humid, warm climate. Hence, semi-desertic modern dragon trees allied to D. draco displaying distinct xeromorphism may have originated from a western Eurasian mesic lineage that had evolved xeromorphic characteristics by the Miocene. The morphology of this mesic ancestor later enabled the lineage to colonize and survive in the semi-desertic environments where it is found today. The new fossil species of Dracaena represents a classic example of pre-adaptation and niche shift.

An overfilled lacustrine system and progradational delta in Jezero crater, Mars: Implications for Noachian climate

The presence of valley networks and open-basin lakes in the late Noachian is cited as evidence for overland flow of liquid water and thus a climate on early Mars that might have supported precipitation and runoff. Outstanding questions center on the nature of such a climate, its duration and variability, and its cause. Open basin lakes, their interior morphology, and their associated channels provide evidence to address these questions. We synthesize the extensive knowledge of terrestrial open basin lakes, deltaic environments, and fluvial systems to assess these questions with evidence from Jezero crater, a 45km diameter open basin lake and its 15,000km2 catchment area, ∼645-km long drainage network, interior sedimentary facies, and ∼50km long outlet channel system. We document the presence of extensive scroll bars and epsilon cross-bedding, both indicative of meandering distributary channels that are not observed on alluvial fans but are typical of fluvial-deltaic depositional environments. A fluvial-deltaic environment is further supported by the post-formational erosion of the deltaic complex: the present-day “delta front” is actually an erosional escarpment truncating delta plain features with the clay-rich prodelta environment, predicted from facies models to make up the outer third of the complex, having been largely removed by eolian erosion. The extensive development via lateral accretion of scroll bars and epsilon cross-bedding, and the reconstructed sedimentary architecture suggest a stable baselevel, in contrast to an environment of constantly rising and falling baselevel related to variable input and evaporation that would favor incision during lowstands. The development of the outlet channel is interpreted to have provided baselevel control in the Jezero open-basin lake. The maturity of the outlet channel, in contrast to the catastrophically scoured landscapes typical of dam-breach channels, favors a consistent overfilled hydrology for the paleolacustrine environment. Sediment transport modeling studies of other valley network and related deposits on Mars have suggested durations in the decades to centuries range. We review meander migration rates in terrestrial fluvial environments to provide a comparison for considering the temporal stability implied by the evolution of scroll bars; values of 20–40 years are not uncommon for the structures and migration implied by observations in Jezero. Taking sediment accumulation rates from a variety of terrestrial fluvial-lacustrine environments in conjunction with our estimates of the sedimentary basin-fill thickness suggest timescales of the order of 106–107 years, far longer than implied by some sediment transport models, but still a short period of time geologically. The presence of significant residual accommodation space (space available for potential sediment accumulation) in Jezero indicates that sediment transport into the lake terminated before the basin was completely filled. Climate conditions sufficient for sustained overland flow of water in the valley networks are required to fill Jezero crater, to cause its breaching in a non-catastrophic manner, and to form the significant fluvial-deltaic environment of laterally migrating fluvial channels and scroll bars formed with an apparently stable baselevel. The lack of late-stage channel downcutting suggests that the conditions producing overland flow of water into the basin may have ended abruptly. Our estimates of the duration of fluvial activity (of order 106–107 years) suggest longer times than previously suggested (years to centuries) by sediment transport models, but generally relatively short durations from a geologic perspective.

Geohistory analysis and basin development of the Neogene succession, NE Iraq

The Neogene succession in the studied area is represented by seven formations (Serikagni, Euphrates, Dhiban, Jeribe, Fatha, Injana, and Muqdadiya formations). The area of study is located in the Unstable Shelf within the Low Folded Zone and the north part of the Stable Shelf (Mesopotamian Zone). This study included the geohistory analysis of the Neogene succession and interpretation the changes of the accumulation and subsidence rates and compared them with the space available to explanation the basin development. At The Early Miocene (Aquitanian age), the Sirekagni and Euphrates formations was deposited during a major transgression with high rates of subsidence and accumulation in the Himreen, Makhul, and north of Tigris subzones, while the Chemchemal–Arbil and Butmah–Mosul subzones were positive areas. This period ended with a sea withdrawal to the southeast to generate the Dhiban lagoonal basin which was characterized by low accumulation and subsidence rates. During the Early Burdigalian, the Jeribe Formation was deposited during another sea level rise that covered the area except the Chemchemal–Arbil and Butmah–Mosul subzones representing the uplifted positive area. The sea level rise continued to the early Langhian age where the transition beds for the Fatha Formation was deposited to mark the maximum flooding surface covering all the study area. The Fatha Formation was deposited at the Late Langhian to the Early Serravallian during sea level stillstand with high accumulation and subsidence rates in the Himreen subzone and the Chemchemal–Arbil subzone. This period ended without a clear tectonic activity. The period from Late Miocene to Pliocene was characterized by high tectonic activity and sea level fall where fluvial–lacustrine environment prevailed to deposit the Injana and Muqdadiya formations. The Injana Formation was deposited during the Late Serravallian–Tortonian in the Himreen and Chemchemal–Butmah subzones; in addition to the northern part of Tigris subzone. The areas of high rates of accumulation and subsidence were located near Jambour while the southwestern part was affected by an uplift generating the Himreen structure. The Chemchemal–Butmah subzones was characterized by a high uplift in the southeast part where Kirkuk and Chemchemal structures were forming, while The northeastern part (from Bi Hassan to the borehole Kirkuk-117) was with low accumulation and subsidence rates. The linear region between these parts (Khabaz oil field) showed an abnormal values for accumulation and subsidence rates (very high); this region corresponds to the location and direction of Anah–Fatha–Qalat Dizah Fault which suggest that the fault was active during that time. The tectonic activity continued to uplift all the north of the study area as well as the West and the East during the Late Tortonian to the Piacenzian where the Muqdadiya Formation was deposited in the area between Jambour to Khabaz oilfields. Then the succession was deformed and uplifted to approximately 800 m above the sea level as in the present day.