Stratigraphic Relationships Research Articles

Identification, cataloguing and preservation of outcrops of geological interest in monogenetic volcanic fields: the case of La Garrotxa Volcanic Zone Natural Park

Volcanic zones are important geoheritage sites. Active volcanic fields are of special interest because they allow to observe the complex and interesting stratigraphic relationships that often characterise their products and processes, as well as landscapes of unusual beauty. These geological sites enable visitors to appreciate the full complexity of volcanic activity and the importance of the geoheritage values that should be preserved. To ensure a correct preservation of these zones while opening them up to visitors, management plans should establish and consolidate a network of outcrops that allow visitors to get to know the area in question and preserve its geological heritage and the social and economic dynamism. In La Garrotxa Volcanic Field, most of which is protected by a natural park, a new methodology has been created to identify the sites of greatest geological interest and, above all, those that exemplify the diversity of eruptive styles and volcanic products and landforms in the area. Taking into account the most relevant management requirements (conservation and dissemination), in 1994 a total of 60 outcrops were classified as points of geological interest of the area. In this study we further present a specific methodology to select the most suitable sites for the preservation of the main volcanological features of La Garrotxa Volcanic Field. A group of 12 sites were selected from the initially identified outcrops and included in an itinerary as the most representative geological and pedagogical sites while also bearing in mind their ease of access and preservation and the possible impact of visitors (e.g. erosion). The following five criteria were considered when restoring these outcrops: integration into the landscape, consolidation of their geology, regulation of visits, the mitigation of risk, and the participation of the people that live in the area.

A revised stratigraphic and tectonic framework for the Ashele volcanogenic massive sulfide deposit in the southern Chinese Altay: Evidence from stratigraphic relationships and zircon geochronology

The Ashele volcanogenic massive sulfide (VMS) deposit is the largest and most representative VMS deposit in the Chinese Altay Metallogenic Belt, but its stratigraphic sequence, tectonic framework, and morphology are debated. In this paper, on the basis of previous research, field investigations, excavation pits, drill-core sampling, and new LA–ICP–MS U–Pb analyses of zircons from mafic and felsic volcanic rocks, we show that the main structure of the Ashele deposit is an overturned tightly closed syncline, and that the primary orebody is controlled by this structure. Moreover, we show that the Ashele VMS deposit displays a double-layer structure made up of a feeder zone of veinlet-disseminated and stockwork orebodies overlain by massive/stratiform orebodies that are folded. We revise the stratigraphy of the Ashele Formation into five conformable sedimentary subsequences, based on new field investigations and the zircon geochronology of each subsequence. From bottom to top, we divide the formation into a siliceous tuff layer (405.1 ± 1.8 Ma), a dacitic layer (395.9–403 Ma), a rhyolitic layer (390.9 ± 0.83 Ma), an orebody layer (ca. 387 Ma), and a basalt layer (387–377 Ma). The Early to Middle Devonian Ashele Formation unconformably underlies the Late Devonian Qiye Formation.

The past in the past and the present: a study of deep time and the city

Cities have an immortal quality in the minds of their inhabitants, enduring over the span of their lifetimes, ever changing yet familiar as every new stratigraphic relationship in the city's fabric is thrust, hacked or crammed into the centuries and millennia of anthropogenic stratum that shaped the place to that point. What role does this deep time play in the lives of the shoppers, commuters, dwellers, and workers who interact with the largely invisible urban prehistoric landscape? This paper reports on experiential landscape research focused on a possible prehistoric site in Glasgow, the Camphill enclosure, in Queen's Park. An account of the site has been provided detailing the academic histories from antiquarian rediscovery to the present, current interactions, and a phenomenology-based interpretative narrative of past. The paper concludes with a critique of the research undertaken highlighting the limitations of both the methods and practices and some thoughts on deep time in urban places.

Identifying Pyroclastic Density Currents From Partial Outcrop Exposure on Mt. Ruapehu, New Zealand

Mt Ruapehu is one of New Zealand’s most active volcanoes, last erupting in 2007. Few studies have investigated the pyroclastic density current (PDC) occurrence on this volcano, despite PDCs being one of the most hazardous volcanic processes. Poor preservation of PDC deposits, due to past glaciations, erosion, burial, and poor consolidation has left a significant gap in Mt Ruapehu’s eruptive record. By identifying and characterising PDCs on Mt Ruapehu this paper provides an updated account of PDC occurrence on this volcano. Comprehensive field-mapping forms the basis for this study by identifying PDC deposits from partial outcrop exposures. We use field observations of these deposits to describe the lithofacies and infer PDC behaviour. Relative stratigraphy and whole-rock geochemistry are used to correlate deposits with dated units from literature and provide approximate age ranges. This study found 12 PDC deposits representing at least 10 previously unidentified flows. Combined with PDCs identified in previous studies there is a total of 23 PDC deposits found on Mt Ruapehu, including the PDC observed during the 1945 eruption. These PDCs have been emplaced throughout Mt Ruapehu’s 250 ka eruptive history. The PDCs were concentrated and dominated by granular flow or granular fluid-based flow transport regimes. The lithofacies show PDCs forming from column collapse and dome collapse or explosion events. This demonstrates that Mt Ruapehu is capable of producing a spectrum of PDC styles, something that must be considered during future hazard planning on the volcano.

Stratigraphy and its environmental implications of the Late Pleistocene Shuidonggou Formation in the western Ordos Block, North China

The Late Pleistocene sedimentary strata that is widely developed in North China records the signature of prehistoric human settlement. The Late Palaeolithic Shuidonggou Formation that is mainly distributed in the western Ordos Block of North China is best known for containing abundant palaeontological fossils and palaeolithic artefacts with an age span of ~35–20 ka B.P. However, its sequence and chronostratigraphy are poorly understood due to the lack of stratigraphic correlation of a uniform relative stratigraphy, hindering our understanding of the way of human adaptation to the environmental and climatic changes. In this article, analyses of high‐resolution stratigraphy of Shuidonggou Formation complemented with chronostratigraphic framework were performed based on our field investigations, Optically Stimulated Luminescence dating and literature survey, to reconstruct environmental and climatic conditions in western Ordos Block in the Late Pleistocene. Stratigraphic correlations and chronological evidence indicate that the sedimentary units of the Shuidonggou Formation are ~35–10 ka B.P. in age, and three lithologic units of Shuidonggou Formation that is well approximated on a regional basis were identified: gravel layers that were deposited in a fluvial environment at the bottom, rhythm layers consist of sand layers, and clay layers deposited in a lacustrine environment in the lower part, and cycles composed of lacustrine silt and loess in the upper part. These units are defined by sedimentology, matching to lake levels. Continuous and widely developed clay and sandy clay about 3–10 m thick occur at various levels within river terrace II and littoral deposits located 10–20 m above the current lake level provide evidence for the existence of the high lake level/palaeo‐lake in western Ordos Block between ~35 and 22 ka B.P. Palaeo‐lake shrinking occurred after when lakeshore sand and gravel, as well as sandy facies of aeolian origin, started to accumulate in the study area in 22–17 ka B.P. The development of the palaeo‐lake probably had been climate‐controlled since the warmer and humid climate conditions suggested by the lower sequences corresponds to the Marine Isotope Stage 3 while the cool and dry climate were identified in upper sequences corresponds to the Last Glaciation Maximum. Besides, the human occupation in the Shuidonggou site was synchronous with the development of the palaeo‐lake of the same time window. It is suggested that the evolution of the palaeo‐lakes in the Late Pleistocene, together with the environmental effects of climate change, play an important role in the human occupation and survival strategies.

The first upper Silurian land-derived palynological assemblage from South America: Depositional environment and stratigraphic significance

A thick succession of quartz-rich sandstones cropping out in the middle part of the Villacorta Creek, on the western slope of the Sierra del Famatina (Valle Hermoso, La Rioja Province, northwestern Argentina) was recently recognized as the Villacorta Formation. The sandstone package rests disconformably on greenish sandstones of the Ordovician Suri Formation and is overlain along a marked angular unconformity by rocks of the upper Carboniferous Agua Colorada Formation (Paganzo Group). The Villacorta Formation is divided into four intervals, the lower one is formed by quartz-rich sandstones showing large-scale cross-stratification; the second part is similar but includes some levels of intraformational conglomerates and shows a decrease in both grain-size and the scale of the cross-bedding sets. The third section comprises medium- and coarse-grained sandstone with intercalation of fine-grained sandstones. The upper interval corresponds to two thickening and coarsening upwards successions. This last section was deposited in a deltaic environment where the top of mouth bars and lagoon deposits preserved palynological assemblages and phytodebris. A low-diversity palynological assemblage recovered from these mudstone levels includes abundant nematophyte cuticular-like fragments, cryptospores (monads, dyads, tetrads) and trilete spores (e.g., Scylaspora scripta, Emphanisporites protophanus). The stratigraphic relationships of the succession and the palynological assemblage suggest a late Silurian age for the Villacorta Formation. The exclusive presence of land-derived components in the organic residue allows to capture a snapshot of the terrestrial vegetation and constitutes the first record of this type of palynological association and nematophyte remains in this southern region. This assemblage improves previous paleogeographic reconstruction enlarging the extent of Silurian basins in Argentina. The shallowing successions of the Famatina region pass to marine deposits in the Precordillera area, indicating a westward transition to offshore environments.

Architectural evolution of a mixed-influenced deltaic succession: Lower-to-Middle Ordovician Armorican Quartzite in the southwest Central Iberian Zone, Penha Garcia Formation (Portugal)

Facies stacking patterns and stratigraphic relationships resulting from the interaction of fluvial and wave processes, along with the paleoshoreline orientation and key surfaces, are essential to understand the temporal changes in the rate of change of accommodation space (A) versus sediment supply rate (S). High-frequency sea-level fluctuations in deltaic systems are controlled by changing accommodation and accumulation, which are explained mainly by autocyclic or allocyclic mechanisms. In deltaic systems, changes in the A/S ratio can be showed by significant variations of the internal facies architecture and the external morphology of the delta complex. These criteria have been used to investigate the relationship between autocyclic and allocyclic processes on the architectural evolution of a mixed river- and wave-influenced asymmetrical delta during the Lower-to-Middle Ordovician in the southwest Central Iberian Zone, in Portugal. Relying on the sedimentary and ichnological characteristics, the herein defined Penha Garcia Formation is classified into two main groups of facies associations, which are interpreted as deposited in a mixed asymmetrical delta with a trend of along-strike variations between wave-dominated strandplain (updrift) and river-dominated deltaic settings (downdrift). The vertical stacking arrangements of parasequences led to the identification of five depositional phases (I to V). Detailed analysis of geometry and internal architecture of the depositional phases along depositional strike shows a highly variable number of shallowing-upward cycles and facies thicknesses/heterogeneity on the updrift and downdrift side due to changes in rates of accumulation and hydrodynamic processes. The stratigraphic architectural style of the depositional phases I to V, and the trend of the total regressive ascending shoreline trajectory, are evidences that the deposition of the Penha Garcia Formation likely took place under an increasing rate of accommodation due to long-term relative sea-level rise (allocyclic), and high subsidence rates coupled with an increase in sediment supply, which could have been locally amplified by compaction of the prodelta-related muddy beds (autocyclic). This study suggests that in evaluating the autocyclic mechanisms on deltaic processes in short-time scales, there is a remarkable difference in terms of its impact on the internal variability of the depositional phases, both in the updrift and downdrift regions of mixed-influenced asymmetrical deltas. The most important reasons for the different effects of autocyclic mechanisms can be related to facies-dependent differential compaction or local changes in subsidence pattern, differences in the proximity to the distributary channel system, and differences in the influence of intrinsic processes of storm and wave reworking (wave-sweeping mechanisms).

Re‐examination of the Population, Stratigraphy, and Sequence of Mercurian Basins: Implications for Mercury's Early Impact History and Comparison With the Moon

AbstractMercury has one of the best‐preserved impact records in the inner solar system due to the absence of an atmosphere and relatively unmodified ancient surface. However, our knowledge of the early impact record and the nature of the impacting projectiles are far from complete. To get a better understanding of the early impact history, we examined large impact basins (D ≥ 300 km) on Mercury. Here we cataloged 94 basins, 80 of which we classify as certain or probable, 1.7 times more than previously recognized. We re‐evaluate the crater densities of basins using the buffered nonsparseness correction technique, which we successfully applied for the Moon. In contrast with a previous study, we find that basins have a slightly higher N(300) crater density on Mercury than on the Moon, but similar N(500) basin densities. Based on these results and comparison with the Moon, we infer that no more than half of the basin record remains observable and basins older than Borealis have generally been erased from the basin record. Furthermore, we establish the stratigraphic relationships of basins based on N(25) crater frequencies, absolute model ages, and observations of crosscutting relationships. Similarly to our previous study on the Moon, we found no evidence for a change in the size‐frequency distribution of the impacting population; thus, our results are consistent with a single impactor population that bombarded Mercury's surface.

Evolution of the Quaternary silicic volcanic complex of Shiribetsu, Hokkaido, Japan: an example of ignimbrite shield volcanoes in an island arc setting

This paper describes the geology and eruptive history of a Quaternary silicic volcanic complex at Shiribetsu, Hokkaido, Japan, with a focus on volcanic landforms produced by silicic explosive eruptions that were not associated with caldera collapse. The Shiribetsu volcanic complex comprises a dacitic pyroclastic plateau and an overlying dacitic central dome complex. The pyroclastic plateau is 22 × 25 km in size, < 200 m high, and consists of two ignimbrite units (the Km-1 and Km-2 deposits; SiO2 = 67–68 wt%; total volume ~ 10 km3). The central dome complex is 4–5 km wide, rises to 650 m above the pyroclastic plateau, and comprises two adjoining edifices, which are East and West Shiribetsu (SiO2 = 62–64 wt%; total volume = 1.6 km3). East Shiribetsu has a conical morphology, whereas West Shiribetsu comprises lava flows and a dome, and has a large amphitheater. A debris avalanche deposit (volume = 1 km3) extends from the amphitheater to the western foot of West Shiribetsu. A dacitic lava dome (volume = 0.2 km3) occurs within the amphitheater. According to the stratigraphic relationships and new fission-track dating, the Shiribetsu volcanic complex evolved as follows: (1) dacitic explosive eruptions at ca. 130 ka (Km-2) and 70 ka (Km-1) produced the pyroclastic plateau; (2) effusive dacitic eruptions at 70 ka (East Shiribetsu) and 60 ka (West Shiribetsu) produced the central dome complex; (3) sector collapse occurred at West Shiribetsu at 50–60 ka; and (4) lava dome formation within the amphitheater at 50 ka. The evolution of the Shiribetsu volcanic complex resembles that of ignimbrite shield volcanoes in the central Andes. Shiribetsu may be the first identified example of ignimbrite shield volcanoes in an island arc setting. We suggest that these are an independent class of explosive silicic volcanoes, distinct from calderas, and form above small magma chambers.

Stratigraphy, detrital zircon geochronology and provenance of the Morita formation (Bisbee Group) in northeastern Sonora, Mexico

The Morita Formation is a Lower Cretaceous unit of the Bisbee Group that crops out in northern Sonora and southeastern Arizona where it was deposited within the Altar-Cucurpe, and Huachuca sub-basins of the Bisbee basin, respectively. In northern Sonora it either overlies strata of the Upper Jurassic Cucurpe Formation, the Glance Conglomerate, or strata of the Lower Cretaceous Cerro de Oro/Rancho La Colgada formations, and it grades upward into the Mural Limestone. In this contribution we characterize the stratigraphy, petrography and detrital zircon geochronology of the Morita Formation along a ca. 60 km-long northwest-southeast transect that includes the complete columns of the Mule Mountains in southeastern Arizona and the sierras San José, Anibacachi and Rancho Búfalo area in northeastern Sonora. Thickness of these sections varies from a minimum of 555 m in Sierra Anibacachi to a maximum of 855 m in Rancho Búfalo. In most sections, the lower half of the Morita consists of reddish siltstone and mudstone with pedogenic calcareous nodules with interbeds of mostly single-storey sandstone bodies, which changes to isolated multi-storey sandstone bodies in its upper half. In contrast, the lower part of the Rancho Búfalo column consists of reddish mudstone/siltstone with isolated, fining-upward, clast-supported, fine-pebble conglomerate beds that grades into reddish to purple, brown and green mudstone/siltstone with isolated, single-storey to multi-storey sandstone beds of its upper part. Lithofacies association in the Morita Formation suggest it is of fluvial origin but ichnofossils and local herringbone- and flaser-cross bedding in its upper part indicate intermitent marginal marine sedimentation preceding the transgression that deposited the overlying Mural shelf.Sandstone composition of the Mule and San José mountains is dominantly feldspatho-quartzose indicating dominant provenance from basement uplift and transitional continental areas, while composition at Sierra Anibacachi and Rancho Búfalo ranges from feldspatho litho-quartzose to litho-quartzose, indicating provenance from recycled orogen. Detrital zircon grains dated from samples of all the studied sections share very similar populations of Proterozoic to Mesozoic ages, but the Mesoproteozoic and Triassic grains compose ca. 64% of the total grains. Detrital zircon grains of Lower Cretaceous age that are only present in samples from the bottom of the Mule and San José Mountains help to constrain a maximum depositional age of 125.5 ± 0.8 Ma for inception of sedimentation of the Morita Formation in this region. According to this age and to observed stratigraphic relationships, we interpret that the lower contact of the Morita Formation is a disconformity with the underlying Glance Conglomerate, or with the Cerro de Oro Formation in northeastern Sonora. Similarly, according to regional stratigraphic relationships and age data known from the Cucurpe-Tuape region, in north-central Sonora, the age of this unit may be constrained to the Aptian stage, in Sonora, from ca. 125 to 115 Ma. Regional isopach curves confirm merging of the sub-basins in northeastern Sonora, continuous sedimentation of the Morita Formation, and presence of the Cananea high separating them.

A new hydrocarbon exploration play: Upper Cretaceous–Paleocene sand injection complexes in the Austral-Magallanes Basin

Abstract Recent exploration activity in the Austral-Magallanes Basin revealed the presence of sand injection complexes of Upper Cretaceous–Paleocene age. The discovery of these large-scale sandstone intrusions documents the first onshore example of sand injection complexes as hydrocarbon exploration targets and confirms a more widespread phenomenon than previously known. Integration of regional understanding, three-dimensional seismic reflection data, exploration wells, and whole core have allowed the interpretation of large sand injectites associated with a deep-water depositional system in the Austral-Magallanes Basin. These injectites are characterized seismically by circular to elongate amplitude anomalies with cross-cutting and discordant stratigraphic relationships. Additionally, detailed sedimentological analysis from exploration wells and core confirm the presence of facies consistent with injected sand commonly associated with deep-water depositional systems. The presence of giant sand injection complexes in the Austral-Magallanes Basin records a previously undocumented period of pore-fluid overpressure that led to large-scale hydraulic fracturing of the overburden and subsequent fluidization of sand derived from a deep-water depositional system. The discovery of intrusive traps such as sand injection complexes defines a new play with significant exploration potential; however, additional evaluation is required to understand the nature and degree of primary sandbody geometrical modification and the subsequent impact on reservoir distribution, trap geometry, migration pathways and seals.

Seismic stratigraphic framework of the continental shelf offshore Delmarva, U.S.A.: Implications for Mid-Atlantic Bight Evolution since the Pliocene

Understanding how past coastal systems have evolved is critical to predicting future coastal change. Using over 12,000 trackline kilometers of recently collected, co-located multi-channel boomer, sparker and chirp seismic reflection profile data integrated with previously collected borehole and vibracore data, we define the upper (< 115 m below mean lower low water) seismic stratigraphic framework offshore of the Delmarva Peninsula, USA. Twelve seismic units and 11 regionally extensive unconformities (U1-U11) were mapped over 5900 km2 of North America's Mid-Atlantic continental shelf. We interpret U3, U7, U9, U11 as transgressive ravinement surfaces, while U1,2,4,5,6,8,10 are subaerial unconformities illustrating distinct periods of lower sea-level. Based on areal distribution, stratigraphic relationships and dating results (Carbon 14 and amino acid racemization estimates) from earlier vibracore and borehole studies, we interpret the infilled channels as late Neogene and Quaternary courses of the Susquehanna, Potomac, Rappahannock, York, James rivers and tributaries, and a broad flood plain. These findings indicate that the region's geologic framework is more complex than previously thought and that Pleistocene paleochannels are abundant in the Mid-Atlantic. This study synthesizes and correlates the findings of other Atlantic Margin studies and establishes a large-scale Quaternary framework that enables more detailed stratigraphic analysis in the future. Such work has implications for inner continental shelf systems tract evolution, the relationship between antecedent geology and modern coastal systems, assessments of eustacy, glacial isostatic adjustment, and other processes and forcings that play a role in passive margin evolution.

Composition, Stratigraphy, and Geological History of the Noachian Basement Surrounding the Isidis Impact Basin.

The western part of the Isidis basin structure hosts a well-characterized Early Noachian to Amazonian stratigraphy. The Noachian Basement comprises its oldest exposed rocks (Early to Mid-Noachian) and was previously considered a single low-Ca pyroxenes (LCP)- and Fe/Mg-smectite-bearing unit. Here, we divide the Noachian Basement Group into five distinct geological units (Stratified Basement Unit, Blue Fractured Unit, Mixed Lithology Plains Unit, LCP-bearing Plateaus Unit, and Fe/Mg-smectite-bearing Mounds Unit), two geomorphological features (megabreccia and ridges), and a mineral deposit (kaolinite-bearing bright materials), based on geomorphology, spectral characteristics, and stratigraphic relationships. Megabreccia contain four different pre-Isidis lithologies, possibly including deeper crust or mantle materials, formed through mass wasting associated with transient crater collapse during Isidis basin formation. The Fe/Mg-smectite-bearing Stratified Basement Unit and LCP-bearing Blue Fractured Unit likewise represent pre-Isidis units within the Noachian Basement Group. Multiple Fe/Mg-smectite-bearing geological units with different stratigraphic positions and younger kaolinite-bearing bright materials indicate several aqueous alteration episodes of different ages and styles. Units with slight changes in pyroxene spectral properties suggest a transition from low-Ca pyroxene-containing materials to those with higher proportions of pyroxenes higher in Ca and/or glass that could be related to different impact and/or igneous processes, or provenance. This long history of Noachian and potentially Pre-Noachian geological processes, including impact basin formation, aqueous alteration, and multiple igneous and sedimentary petrogeneses, records changing ancient Mars environmental conditions. All units defined by this study are available 20 km outside of Jezero crater for in situ analysis and sampling during a potential extended mission scenario for the Mars 2020 rover.

Geological map and stratigraphic evolution of the central sector of the Carnic Alps (Austria-Italy)

The central sector of the Carnic Alps spans the border between Austria and Italy and consists of a succession ranging from the Upper Ordovician to the lowermost part of the upper Carboniferous that has been recently revised in order to formalize the stratigraphic units. Although this area was mapped both on the Austrian and Italian side, the presence of different units with different stratigraphic boundaries prevented from a complete representation of the stratigraphic relationships and the lateral geometrical variability within the basin. We focused mainly on the Devonian ‘transitional facies’ that indirectly reflect the establishment and the demise of a platform. The basin shows a transition from a ramp-type to a rimmed shelf- type profile that occurred between the upper part of the Pragian to the lower Emsian that is constrained by the increasing abundance of reef-derived gravity-driven rudstone deposits. The platform system reached its maximum expansion around the end of the Eifelian and the beginning of the Givetian when the largest debris deposits have been shown to accumulate. Although less productive, the platform system appears to persist until roughly the lower part of the upper Frasnian when the rudstone deposits become depleted of platform- derived clasts and interbedded with microbial limestone. This evolution might have been caused by a sea-level drop event.

Micromorphology in the archaeological context as a tool for interpretation of prehistoric feature fills: A case study from Tvrdonice, Břeclav district

Micromorphology in the archaeological context is a methodological tool of modern multidisciplinary archeology. It is basically a microscopic characterization of sediments in a direct context of archaeological situations with the aim of detecting formation processes, the knowledge of which is essential for further interpretations. This method was applied to the sediment fill of two features in a stratigraphic relationship from the locality Tvrdonice – “Pole od Týnecka”. Samples were taken from a La Tène recessed structure fill and an earlier Bronze Age pit that is superimposed below the La Tène feature. From a macroscopic and micromorphological point of view, it is evident that the fill of an Early Bronze Age feature consists of wind-blown sands in superposition with in situ or slightly displaced soil material. Micro-layers detected macroscopically are only related to object leveling. The layer of soil beneath the “floor” of the La Tène recessed building displays signs of long-term bioturbated soil, i.e. the La Tène building was founded in an existing depression. The active floor layer of the La Tène building is represented by alternating layers of lighter and darker laminae. While the darker laminae represent the trampled layer, the lighter laminae consist of recrystallized ash, which impregnates the trampled layer. On a social level, this finding can be interpreted as the creators of the La Tène recessed building choosing to minimize labour costs by using the recessed terrain and thus avoiding the excavation of the building floor. The utility area possessed a purposefully modified surface, which is related to ergonomic efficiency, but its function is unknown. The uppermost part of the fill is formed by backfill that does not show any signs of pedogenic influences, which indicates that the object was intentionally filled (leveled).

Local stratigraphic relations at Sandel crater, Venus: Possible evidence for recent volcano-tectonic activity in Imdr Regio

Imdr Regio is a volcano dominated young topographic rise of Venus whose most prominent volcanic structure, Idunn Mons, shows indications of being recently active. Despite its scientific relevance, this region has been poorly studied to date. Idunn Mons is spatially related to a rift system, Olapa Chasma, which dominates the topographic rise. The rift fractures around Idunn Mons form an “hourglass” pattern indicating a close tectonic interaction between the volcano and Olapa Chasma.The principal aim of this work is to understand whether Olapa Chasma has been tectonically active in the recent geologic past. For this purpose, we analyzed Sandel crater (45.7°S/211.7°E), an impact structure 17.9 km in diameter situated NW of Idunn Mons, and we used it as a local stratigraphic marker. Observing the variations in the radar brightness and crosscutting relationships, we produced a local geologic map of impact deposits, volcanic materials and tectonic structures surrounding the crater. Then, we used the map to reconstruct the local stratigraphy and relative ages of the materials for deciphering the temporal relations between the crater and volcano-tectonic activity. Following the existing degradation models for Venusian craters we could also estimate a time range for the formation of Sandel crater. The results show that its formation convincingly occurred during the period between 0.5 T and 0.15 T, where T is the average age of the surface of Venus. We present here a line of evidence that, at least in its last stage, the tectonic activity characterizing Olapa Chasma and Idunn Mons postdate the formation of Sandel crater. Building on the findings from previous studies, we hypothesize that not only volcanism but also the tectonic processes behind the formation of Idunn Mons and Olapa Chasma are geologically recent. For this reason, we refer to Olapa Chasma and Idunn Mons as a recently active volcano-tectonic system of Venus, which deserves to be a potential target site for future missions to Venus, including investigations of surface volcanism and seismicity.

Characteristic foraminifera of the Pre-Cenozoic carbonate formations of Cat Ba island and northern Song Hong Basin, Vietnam

Pre-Cenozoic carbonate formations of the northern Vietnam continental shelf have recently become important petroleum exploration targets, owing to the discovery of hydrocarbon accumulations in the northern Song Hong Basin. However, there is limited stratigraphic information about the carbonate basement in the area; further, the stratigraphic relationship between carbonate formations exposed in adjacent areas, such as outcrops on Cat Ba Island and the subsurface Song Hong Basin, is unclear. This study revealed foraminiferal assemblages that can be used to determine the age of carbonate basement rocks based on samples from outcrops on Cat Ba Island and wells in the northern Song Hong Basin. Foraminifera were identified and divided into eight biozones and one assemblage that are indicative of different ages. Carbonate formations on Cat Ba Island originated from the Famennian to Moscovian, and those in the northern Song Hong Basin originated from the early Tournaisian to early Wuchiapingian. Carbonates in the basement section of well SH1 and the Cat Co, Hung Son, Hien Hao, and Gia Luan sections of Cat Ba Island, originated in the early-mid Tournaisian. In well SH2, basement carbonates are coeval with the upper part of the Gia Luan section, indicating that it originated in the late Serpukhovian to the late Moscovian. This age range is significantly different from the Late Devonian to Early Carboniferous age determined by previous studies. The youngest basement carbonates were identified in well SH3 (early Capitanian to early Wuchiapingian). As these carbonate formations are contemporaneous, they were governed by the same tectonic conditions and may exhibit similar geological characteristics. Therefore, reservoir rock models of the carbonate basement in northern Song Hong Basin could be used to clarify geological carbonate models for Cat Ba Island.

Geology of the Epicentral Area of the November 23, 1980 Earthquake (Irpinia, Italy): New Stratigraphical, Structural and Petrological Constrains

The geology of the epicentral area of the 1980 earthquake (Irpinia-Lucania, Italy) is described with new stratigraphic, petrographic and structural data. Subsurface geological data have been collected during the studies for the excavation works of the Pavoncelli bis hydraulic tunnel, developing between Caposele and Conza della Campania in an area that was highly damaged during 1980 earthquake. Our approach includes geological, stratigraphic, structural studies, and petrological analyses of rock samples collected along the tunnel profile and in outcropping sections. Stratigraphic studies and detailed geological and structural mapping were carried out in about 200 km2 wide area. The main units cropping out have been studied and correlated in order to document the effects of tectonic changes during the orogenic evolution on the foreland basin systems and the sandstone detrital modes in this sector of the southern Apennines. The multi-disciplinary and updated datasets have allowed getting new insights on the tectono-stratigraphic evolution and stratigraphic architecture of the southern Apennines foreland basin system and on the structural and stratigraphic relations of Apennines tectonic units and timing of their kinematic evolution. They also allowed to better understand the relationships between internal and external basin units within the Apennine thrust belt and its tectonic evolution.

LOWER AGE BOUNDARY OF THE FORMATION OF METATERRIGENOUS ROCKS OF THE VYSOKOPILLYA GREENSTONE STRUCTURE, MIDDLE!DNIEPER REGION OF THE UKRAINIAN SHIELD

The stratigraphic relationships of meta-terrigenous rocks of the Kryvyi Rih Series belonging to the Kryvyi Rih-Kremenchuk structure with metasediments of similar composition belonging to the upper part of the greenstone belt section (the Bilozerka Series) in the Middle Dnieper Domain remain unexplored. The adjacent “strip-like” Vysokopillya, Skhidno- Hannivska and Zhovta Richka structures are of particular interest; in these structures, metasediments and ferruginoussiliceous rocks overlie metabasites of the Mesoarchean greenstone belts. The Vysokopillya greenstone belt (GB), which is adjacent to the Likhmanivka syncline of the Kryvyi Rih structure, is a steep-bedding monocline. The northern part of the belt comprises a thick homogeneous meta-tholeiite sequence (the Sura Suite). The Chertomlyk Suite is located higher in the stratigraphic section and includes meta-andesites with subordinate rhyodacites and tholeiitic basalts. They form the southern part of this structure. Subvolcanic rhyolite-dacite bodies (the Solenivka Suite) occur as crosscutting intrusions and dykes. The middle and southern parts of the Vysokopillya GB consist of a heterogeneous mass of orthogneisses and paragneisses, which developed after sedimentary (graywackes, sub-graywackes and melawackes) and volcanic (tuff sandstones, lava breccias, meta-dacites and meta-andesites with a subordinate amount of meta-tholeiites) rocks were deposited. Graywackes host thin beds of quartz-magnetite quartzites and thick (up to 100 m) beds of quartzmagnetite- cummingtonite shales with garnet. We applied LА-ICP-MS for U-Pb dating of 102 detrital zircons from biotite-quartz meta-sandstones and determined their Hf isotope compositions. Among them, four crystals have 207Pb/206Pb age over 3400 (up to 3800) Ma. A single zircon crystal was dated at 2930 Ma. The remaining 97 crystals have ages in the range of 3000-3360 Ma, with distinct peaks at 3065 (15 grains), 3185 (21 grains), 3260 (16 grains), and 3320 Ma (22 grains). Hafnium isotope composition varies over a wide range. The oldest grain dated at 3800 Ma, has eHf = –0,8, whereas the next two younger grains have positive eHf values (+1,2 at 3645 Ma, and +2,2 at 3535 Ma). Crystals dated at ca. 3320 Ma demonstrate wide variations in eHf — from +1,8 to -6,1; those dated at ca. 3260 Ma — from +4,5 to –2,5, those dated at ca. 3185 Ma — from +3,3 to –4,3, and those dated at ca. 3065 Ma — from +6,2 to –3,9. According to the obtained data, metasedimentary rocks of the Vysokopillya GB started to accumulate in the Neoarchean. The same age was established for the metamorphosed sedimentary rocks of the Skhidno-Hannivska and Krasnoyarsk-Alferivka structures, as well as for the Bilozerka Series of the Bilozerka GB. Thus, sedimentary rocks in these structures were formed during the denudation of the Mesoarchaean craton. The source rocks were predominantly represented by the TTG of the Sura complex (3.1-2.96 Ga). For the first time, a significant number (38 grains) of Paleoarchean (3.3 Ga) detrital zircons were discovered in the Middle Dnieper Domain, which indicates the presence of Paleoarchean rocks in the denudation area. Data on Hf isotope systematics indicate the possible presence of Hadean (older than 4.0 Ga) material.

Stratigraphic analysis of Ponta do Mel carbonate platform, Albian-Cenomanian in Potiguar Basin, NE of Brazil

This work intends to understand how the Ponta do Mel carbonate platform was implanted, to characterize its depositional model and its evolution in the light of modern stratigraphy, as well as to understand the stratigraphic relations with beneath, overlapping and contemporary units, from wells and seismic data. The focus area of this study corresponds to a belt in the offshore portion of the Potiguar Basin, which runs parallel to the shoreline, about 40 km from it. The carbonate rocks of the Ponta do Mel Formation date from the Late Albian and, similar to what occurs in the other basins of the Brazilian continental margin, their deposition is related to the separation events of the African and South American continents. In the stratigraphic analysis of the wells (1D analysis), it was possible to characterize carbonate lithofacies, that are the predominant, as well as mixed and siliciclastic lithofacies. It was also possible to individualize shallowing upward cycles and cycle sets, which were associated with the identified systems tracts. In the seismic stratigraphic analysis, in the same way, four seismic facies were visualized, which, in general, are related to the tractive processes involved in the deposition of the carbonate, mixed and siliciclastic lithofacies, defined in the 1D analysis. The integration of the results from the well data analysis to the seismic stratigraphic analysis allowed to understand that the studied interval, which coincides, in lithostratigraphic terms, with the Ponta do Mel Formation, represents a complete depositional sequence, here referred to as the Albian-Cenomanian Sequence, formed by the Lowstand Systems Tract (LST), Transgressive Systems Tract (TST), and Highstand Systems Tract (HST). The sedimentation history of the Ponta do Mel unit started from the deposition of siliciclastic and carbonate facies in a shallow water platform environment. Then, with the increase in the accommodation space, in a transgressive phase, a thick interval of deeper water facies, represented mainly by calcilutites and pelitic rocks, was deposited. At the end of this interval, facies of coarser granulation, represented mainly by thick calcarenites layers, and sometimes calcirrudites, started to dominate the platform scenario, denoting a regressive phase and thus ending the Albian-Cenomanian Sequence.