This work considers the occurrence of the giant trace fossil Megaplanolites ibericus from the Kimmeridgian of the Iberian Chain in Spain with the purpose of interpreting the palaeoenvironmental ...conditions favouring the occurrence and preservation of uncommon giant burrows. The studied section consists of a 32 m-thick succession of silty marlstones with marly-limestone beds and sandstone beds commonly ranging from 5 to 30 cm in thickness. Sandy marlstones present common foraminifera (mainly Lenticulina, Saracenaria and Epistomina) and ostracods. Some samples are composed almost exclusively by Epistomina. The sandstone beds are composed of medium to fine sand (in fining upwards sequences) with parallel lamination at the base as well as groove-casts and flute-casts on the under-surface. Ichnogenera Chondrites, ?Helicodromites, Nereites, Ophiomorpha, Planolites, Phycodes and Thalassinoides are observed in the marly-limestones and sandstones. The giant trace fossils, located in the lower surface of an indurated sandy marlstone bed of 40–50 cm thickness, are horizontal tubular burrows with a mean diameter of 19 cm reaching a maximum of 32 cm. Its maximum length observed in the outcrop is 10.57 m and there is a dominant palaeo-orientation ranging N 140–160° E. Traces are unbranched and unlined, commonly straight but some of them show a variably sinuosity. The record of ammonites and the abundance of Epistomina, which is related to open marine conditions and sea-level rise, indicate an environment relatively deep (>60 m) but with a high input of terrigenous, locally related to high energy deposits, in which Megaplanolites ibericus tracemaker (uncertain tracemaker) developed.
The lower Middle Cambrian of Scandinavia is reviewed and subjected to sequence stratigraphical analysis. Sequences are defined as transgressive–regressive depositional units bounded by maximum ...regressive surfaces and their correlative conformities. The lower Middle Cambrian forms part of a 2nd order sequence, labelled Cambrian Supersequence 3 (CS-3). It is bounded at the base by a regional unconformity ascribed to the so-called Hawke Bay Event, the focus of this paper. CS-3 comprises at least four 3rd order sequences, but the upper part above the Triplagnostus gibbus Zone has not been analysed as yet and the upper supersequence boundary remains undefined for the time being. The oldest sequence of CS-3 is seemingly of Early Cambrian age. There are numerous T/R cycles in the Acadoparadoxides oelandicus Superzone, here ranked as subsequences (4th order sequences), but a classification as 3rd order cycles of some of these is possible, thereby increasing the number of prospective sequences in CS-3. The high frequency sea-level fluctuations are reminiscent of glacioeustasy and the early Mid Cambrian possibly represents a c. 5Ma long glacial interval with overall low global sea-level and frequent sea-level changes.
The Hawke Bay Event, as identified in Scandinavia, primarily reflects an extensive and long-lasting epeirogenic uplift of western Baltica, and using the term event is a misnomer. The uplift is informally referred to as the Hawke Bay uplift. However, the initial rapid uplift in the latest Early Cambrian coincided with ≥100m eustatic lowering of the sea-level, leading to simultaneous regression in the East Baltic area and elsewhere. This forced regression is assumed representing the Hawke Bay Event s.str. In Estonia–Latvia–Lithuania, the unconformity separating the Kibartian and Deimenian regional stages signals the Hawke Bay regression. The Hawke Bay uplift gradually and differentially subsided during the early Mid Cambrian, starting in the Öland–Gotland area, and the collapse then slowly progressed westwards and southwestwards. Subsidence also advanced from western Norway and eastwards whereas the western margin of Baltica apparently remained uplifted throughout the late Mid Cambrian to earliest Ordovician. In central Scandinavia, the last traces of the Hawke Bay uplift eventually disappeared during the Acidusus atavus Chron. As a result the Hawke Bay unconformity represents a greater hiatus in central and southernmost Scandinavia where the uplift persisted for a longer time (locally up to c. 6Ma), causing long-lasting non-deposition associated with minor erosion. The epeirogenic uplift is inferred to have been triggered by stress-induced isostasy linked to major plate-tectonic adjustments, possibly the onset of subduction in the adjacent Iapetus Ocean or cessation of the Timanide collision, or both.
A series of palaeogeographical maps is constructed for the Middle Cambrian of Scandinavia and adjacent countries. Subcrop and onlap maps of the Hawke Bay unconformity, as well as isopach maps for Middle Cambrian formations are also shown. The elongate land area that straddled the axis of the Scandinavian Peninsula during the Early Cambrian disappeared after subsidence of the Hawke Bay uplift and a new basin configuration was established. This had an overall gentle westwardly sloping sea floor delimited by a broad uplift along the western Baltica margin that formed a submarine sill from the medial Mid Cambrian and onwards. The sill, which eventually disappeared in the later part of the Tremadocian, restricted exchange of water masses and the deeper parts of the epicontinental sea became characterized by dysoxic and anoxic conditions. The resulting organic-rich deposit is referred to as Alum Shale.
The sea-level rose eustatically after the terminal Early Cambrian Hawke Bay lowstand (in a strict sense) to reach a temporary highstand during the later part of the A. oelandicus Superchron. It then fell abruptly again at the end of the A. oelandicus Superchron and remained low in the earliest part of the Paradoxides paradoxissimus Superchron. Overall, on a 2nd order scale, the sea-level remained low during the early Mid Cambrian and as a result, the clastic supply was relatively high. The principal sediment supply was from the east; initially minor amounts of clastics were also supplied from the uplifted parts of Scandinavia but overall erosion of the uplifted area was limited, probably due to the extremely flat topography. The high clastic influx from the east resulted in progradation, progressively shifting the coastline westwards. Eventually it reached a position roughly corresponding to the present-day east coast of mainland Sweden.
In addition to the initial Hawke Bay regression (s.str,) in the latest Early Cambrian significant forced regressions occurred at the end of the Acadoparadoxides pinus–Pentagnostus praecurrens Chron (here named the Faludden Lowstand) and in the T. gibbus Chron (the Mid-gibbus Lowstand). Several unnamed sea-level lowerings also occurred in the A. pinus–P. praecurrens Chron. A rapid, major sea-level rise at the beginning of the A. pinus–P. praecurrens Chron, estimated at c. 60–70m, is named the Oelandicus Drowning. Fast sea-level rises at the start and in the middle of the T. gibbus Chron are referred to as the Forsemölla and Exsulans drownings, respectively. From the middle of the T. gibbus Chron onwards into the A. atavus Chron there was a major sea-level rise (Atavus Highstand). This latter rise is estimated at c. 100m and for the first time the sea-level became as high or higher than it was just prior to the Hawke Bay regression. The associated transgression shifted the coastline some 500–700km eastwards and from then onwards, extreme clastic starvation prevailed in the epicontinental sea covering Scandinavia. Simultaneously, the mid-shelf became a net sedimentary bypass zone, either due to regular outboard transport of sediment during storms or due to recurrent erosive events associated with sea-level lowstands.
Two Mid Cambrian depositional phases are recognized, termed Depositional Phases 3 and 4. Depositional Phase 3 encompasses the transient increase in sedimentary supply during the early Mid Cambrian sea-level lowstand, whereas DP4 covers the strongly starved conditions and widespread dysoxia from the A. atavus Chron onwards associated with high sea-level. A gradual expansion of the oxygen minimum zone during the Mid Cambrian developed independently of the rising sea-level and is suggestive of a stratified water column, presumably created by silled basin conditions. It is likely, however, that the general ‘background’ oxygen level in the oceans also was low, perhaps due to sluggish global circulation in a greenhouse world.
Two new regional stages, the Bödan and Almbackenian, are introduced for the Middle Cambrian A. oelandicus and P. paradoxissimus superzones of Scandinavia, respectively. The base of the Middle Cambrian Timofeevia lancare acritarch assemblage zone is located within the upper part of the A. pinus–P. praecurrens trilobite Zone. The T. gibbus trilobite Zone is informally subdivided into a lower Paradoxides jemtlandicus subzone and an upper Bailiaspis dalmani subzone.
Many workers have noted the presence of contorted cross-strata in the Navajo Sandstone and other ancient eolianites, and have recognized their significance as indicators of sediment saturation during ...the accumulation history. Horowitz (1982) proposed a general model for the production of such features in ancient ergs by episodic, seismically induced liquefaction of accumulated sand. A key feature of that popular model is the prevalence of a flat water table, characteristic of a hyper-arid climatic regime, during deformation. Under arid climatic conditions, the water table is established by regional flow and liquefaction is limited to the saturated regions below the level of interdune troughs. However, various paleohydrological indicators from Navajo Sandstone outcrops point toward a broader range of water table configurations during the deformation history of that eolianite.
Some outcrops reveal extensive deformation complexes that do not appear to have extended to the contemporary depositional surface. These km-scale zones of deformation, affecting multiple sets of cross-strata, and grading upward into undeformed crossbeds may represent deep water table conditions, coupled with high intensity triggers, which produced exclusively intrastratal deformation. Such occurrences contrast with smaller-scale complexes formed within the zone of interaction between the products of soft-sediment deformation and surface processes of deposition and erosion. The Horowitz model targets the smaller-scale deformation morphologies produced in this near-surface environment.
This study examines the implications of a wet climatic regime for the Horowitz deformation model. It demonstrates how a contoured water table, characteristic of humid climates, may have facilitated deformation within active bedforms, as well as in the accumulation. Intra-dune deformation would enable deflation of deformation features during the normal course of dune migration, more parsimoniously accounting for: the frequent occurrence of erosionally truncated deformation structures in the Navajo Sandstone; the production of such erosional truncations during bedform climb and aggradation of the accumulation; and the dramatic fluctuations in the water table required to deposit dry eolian sand, deform those deposits under saturated conditions, and then dry the deformed sand to enable deflation.
•Outcrop evidence indicates dune migration under humid conditions in early Jurassic Navajo erg.•Ephemeral water table mounds facilitated intra-dune deformation.•Patterns of highly directional deformation features, truncated by deflation surfaces, indicate intra-dune deformation.•Deep-seated liquefaction produced diverse fold orientations within extensive zones of deformation.
A detailed lithostratigraphic and sedimentologic study was performed in the southern Andes of Ecuador along the Malacatos-Vilcabamba intermontane basin, a thrust-controlled inverted basin developed ...during the middle Miocene. We defined twenty-three sedimentological facies grouped into seven facies associations and three different depositional systems (deltaic, tidal flat and alluvial fan) for the entire basin fill. The 500–1100 m thick Malacatos-Vilcabamba basin fill currently lies at about 1470 m above current sea level. It is unconformably underlain by a metamorphic and volcanic basement and usually exhibits some evidence of synsedimentary deformation and synchronous volcanism. Long-term patterns of basin sedimentation suggest a basal fining-upward sequence of marginal-marine lithofacies that gradually passes upward into a coarsening-upward sequence (conglomeratic) typical of a continental setting. The history of basin-filling was initiated in the middle to late Miocene (15-10 Ma) as a lowland basin. Proximal facies within a deltaic system under tidal influence were preserved as the San José and San Francisco Formations, while a flat tidal system alternating between arid and humid climatic episodes was preserved as the Santo Domingo Formation. During the subsequent continental sedimentation, which occurred in the late Miocene (9-5 Ma), the prior basin-fill was partially deformed and uplifted. This episode of basin inversion is primarily evidenced by the arrival of thick alluvial successions (conglomerates) composing the Cerro Mandango Formation. Compressive tectonics continues throughout the Pliocene with alluvial sedimentation (Suro Unit) and the gradual inversion of the basin-bounding normal faults into thrusting systems that currently predominates at basin borders. An insight into the connection via marine incursions between the Miocene basins and either the Pacific Ocean or the eastern Oriente basin, is provided herein as a discussion based on the data collected and a local paleogeographic model.
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•Lithostratigraphy, Sedimentology and Paleogeography in a marine-intermontane basin.•Basin-fill development in a marine to intermontane setting, Malacatos-Vilcabamba case.•Marine transgressions during middle Miocene in depressed zones of the Northern Andes.
During the middle Permian through the Triassic, Tasmania moved from paleo-latitudes of 78° to 69°S, wedged between Antarctica and Australia, within the paleo-South polar circle. During this time, ...significant global carbon cycle disturbances triggered major environmental and climatic changes and mass extinction events globally. The Bicheno-5 core from Eastern Tasmania, Australia, provides the opportunity to examine middle Permian and Upper Triassic sediments from the paleo-Antarctic, using high-resolution organic carbon isotope (δ
C
) chemostratigraphy, pXRF, and sedimentology, combined with new palynological data integrated with the existing radiometric age model. While there is a significant unconformity in the Upper Permian to the middle Triassic associated with eustatic sea-level fall as a result of regional uplift in eastern Australia, three distinct carbon isotope excursions (CIEs), characterized by negative shifts of up to - 6 ‰ were identified; the middle Permian Guadalupian Carbon Isotope Excursions (G-CIE), the Carnian Pluvial Episode (CPE), and the mid-Norian Event (MNE). These three events highlight a significant climate shift through glacial and interglacial cycles to warmer non-glacial intervals in the Late Triassic, with evidence of the polar record of the Carnian Pluvial Episode and the mid-Norian Event, which are poorly studied in the Southern Hemisphere, specifically within the Paleo-Antarctic circle.
The paper presents the results of a comprehensive interpretation showing the effective way to integrate seismic data into a three-dimensional geological model. Stochastic inversion was used to ...increase the reliability of forecasts of productive thicknesses. A comprehensive interpretation of the geological and geophysical information of the Yu21 formation deposits of the Malyshevskaya formation was carried out, including sedimentological analysis of core data, petroelastic modeling of well logging curves for the purposes of stochastic inversion and stochastic inversion of seismic data. An areal forecast of sedimentation environments (facies) was carried out. The resulting three-dimensional geological model, in more detail, compared to the model without taking into account the spatial seismic forecast, emphasizes the heterogeneity of the distribution of properties in the geological environment, which is especially important when planning production drilling with horizontal wells.
The modern high topography of the eastern Tibetan Plateau is drained by several of the largest rivers on Earth, and exerts a prominent influence on the Asian monsoon pattern. However, when the high ...terrain was formed remains highly debated. Here, we present detrital zircon U‐Pb ages that indicate a south‐flowing drainage system with distal headwaters passed through the Ninglang Basin at ca. 45 Ma. We advocate for early–middle Eocene surface uplift in the Gonjo Basin and areas to the west creating a southeast tilted topography across eastern Tibet. The termination of sedimentation at ca. 40 Ma implies that the river system had deviated from the Ninglang Basin, which we interpret as a result of rise of the Yalong‐Yulong thrust belt. Combined with other lines of evidence from previous studies, we support the establishment of moderate‐high elevation topography of eastern Tibet by late Eocene time.
Plain Language Summary
The eastern Tibetan Plateau has been a hotspot for studying the interactions between tectonic uplift, monsoon evolution, Asian biodiversity, and topographic development during continental collision. However, the timing of high‐elevation topography formation in eastern Tibet is a matter of debate, with age estimates ranging from middle Eocene to late Miocene. This directly leads to contradictory understanding of uplift processes and plateau growth mechanisms. Sedimentary basins are excellent recorders of past drainage pattern and tectonic process, while many Cenozoic basins in eastern Tibet have been understudied. Here we focus on the Ninglang Basin and carry out comprehensive research including stratigraphy, sedimentology, chronology, and provenance analysis. We indicate that the Ninglang Basin was mainly supplied by a south‐flowing exterior drainage system during the middle Eocene, implying the existence of a regional, low‐gradient landscape beveling to the southeast at that time. The extinction of this drainage system in late Eocene time likely means the initiation of the Yalong‐Yulong thrust belt, a major boundary fault system in eastern Tibet. Our study thus support that the topography of eastern Tibet has been elevated in the late Eocene.
Key Points
A large‐scale, south‐flowing fluvial system drained through the Ninglang Basin during the middle Eocene
The demise of the Ninglang Basin in the late Eocene resulted from the uplift of the Yalong‐Yulong thrust belt
The elevated terrain of eastern Tibet was initially formed in the late Eocene
Glacial Lake Outburst Floods (GLOFs) constitute a major threat in glacierized regions. Despite a recent increase in the size and number of glacial lakes worldwide, there is only limited evidence that ...climate change is affecting GLOF frequency. GLOFs are particularly common in the Baker River watershed (Patagonia, 47°S), where 21 GLOFs occurred between 2008 and 2017 due to the drainage of Cachet 2 Lake into the Colonia River, a tributary of the Baker River. During these GLOFs, the increased discharge from the Colonia River blocks the regular flow of the Baker River, resulting in the inundation of the Valle Grande floodplain, which is located approximately 4 km upstream of the confluence. To assess the possible relationship between GLOF frequency and climate variability, four sediment cores collected in the Valle Grande floodplain were analyzed. Their geophysical and sedimentological properties were examined, and radiocarbon-based age-depth models were constructed. All cores consist of dense, fine-grained, organic-poor material alternating with low-density organic-rich deposits. The percentage of lithogenic particles, which were most likely deposited during high-magnitude GLOFs, was used to reconstruct the flood history of the last 2.75 kyr. Results show increased flood activity between 2.57 and 2.17 cal kyr BP, and between 0.75 and 0 cal kyr BP. These two periods coincide with Neoglacial advances that are coeval with periods of lower temperature and increased precipitation. Our results suggest that GLOFs are not a new phenomenon in the region. Although rapid glacier retreat is likely responsible for high GLOF frequency in the 21st century, high-magnitude GLOFs seem to occur more frequently when glaciers are larger and thicker.
•A 2.75 kyr flood record was generated from Valle Grande floodplain sediments.•Flooding most likely represents high-magnitude Glacial Lake Outburst Floods.•First continuous GLOF record that extends beyond instrumental datasets.•High-magnitude GLOFs were more frequent during Neoglaciations III and IV.•High-magnitude GLOF frequency decreases as glaciers thin and retreat.
The electrification of volcanic plumes has been described intermittently since at least the time of Pliny the Younger and the 79 AD eruption of Vesuvius. Although sometimes disregarded in the past as ...secondary effects, recent work suggests that the electrical properties of volcanic plumes reveal intrinsic and otherwise inaccessible parameters of explosive eruptions. An increasing number of volcanic lightning studies across the last decade have shown that electrification is ubiquitous in volcanic plumes. Technological advances in engineering and numerical modelling, paired with close observation of recent eruptions and dedicated laboratory studies (shock-tube and current impulse experiments), show that charge generation and electrical activity are related to the physical, chemical, and dynamic processes underpinning the eruption itself. Refining our understanding of volcanic plume electrification will continue advancing the fundamental understanding of eruptive processes to improve volcano monitoring. Realizing this goal, however, requires an interdisciplinary approach at the intersection of volcanology, atmospheric science, atmospheric electricity, and engineering. Our paper summarizes the rapid and steady progress achieved in recent volcanic lightning research and provides a vision for future developments in this growing field.
