Detailed Stratigraphy Research Articles

The real McCoy: A record of deep‐water basin deposition in southwestern North America during the Cretaceous

AbstractThe McCoy Mountains Formation (McMF) in southern California–Arizona preserves an anomalously thick record of sedimentation during the Mesozoic at a critical time when western North America experienced contrasting tectonic events related to intracontinental rifting along the Mexican Border rift system and consolidation of the North American Cordilleran system. The spaciotemporal interactions among these events and the development of the McCoy basin challenge our understanding of the evolution of the southern extent of North America. At its type locality in the McCoy Mountains, the McMF consists of ~ 7 km of low‐grade metasedimentary rocks, originally interpreted as meandering fluvial to alluvial‐fan deposits. Uncertainty in the initial timing of sedimentation in the McCoy basin has resulted in multiple tectonic models. We measured ~ 7160 m of detailed stratigraphy and present new sedimentological and detrital zircon results showing that the McCoy basin was occupied by deep‐water turbidite systems. These systems deposited an upward‐coarsening succession of fine‐ to coarse‐grained detritus during the Cretaceous (ca. 137–70 Ma). Provenance data indicate that the McCoy basin received sediment from Proterozoic basement rocks and metamorphosed Palaeozoic to early Mesozoic sedimentary units. These source rocks are equivalent to the stratigraphy found in the Grand Canyon and Colorado Plateau regions and were likely shed from the southward‐advancing Maria fold‐thrust belt and possibly the southern Sevier belt in southern Nevada and California. These results, combined with subsidence curves typical of foreland basins, favour deposition within a subaqueous flexural foreland basin system. The presence of a Cretaceous foreland basin this far southwest challenges previously proposed models and suggests that the contractional tectonic regime associated with the North American Cordillera extended into the southwestern most United States during the Early–Late Cretaceous.

Slide Stacking: A new mechanism to repeat stratigraphic sequences during gravity-driven extension

Gravity-driven sliding of sediments down subaqueous slopes results in mass transport deposits (MTDs) recognised both in outcrop studies and from offshore margins where they may extend for 100's km. While seismic sections may reveal the large-scale geometry of such features, they fail to capture some of the structural and stratigraphic detail necessary for a fuller understanding of the processes involved. Using the late Pleistocene Lisan Formation sediments exposed around the Dead Sea Basin as our case study, we show that interplay between bed-parallel translational slides and associated normal faults may result in stratigraphic repetition through a process we term ‘slide stacking’. This mechanism, where retrogressive slope failure results in slides cutting across earlier normal faults, produces repeated sequences with older over younger stratigraphic relationships more usually attributed to compressional (thrust) deformation. Slide stacking results in a ∼25% attenuation of the upper sequence above the basal shear surface (BSS), which is itself associated with liquefaction and fluidised sediment. The displaced stratigraphy above the BSS is also marked by sedimentary rafts that are broken into blocks by normal faults and become increasingly separated from one another during downslope translation. The hangingwalls of synthetic listric faults form roll-overs that are progressively tightened towards the underlying BSS to create overturned anticlines that apparently verge upslope. The paradoxical situation therefore arises of contractional geometries, such as older over younger stratigraphic repetition across slides, and upslope-verging recumbent anticlines with locally overturned limbs being created during downslope-directed gravity-driven extension. The downslope margin of the slide stack displays earlier normal faults that created scarps where much of the sedimentary buttress, that would otherwise support the toe of the slide, was removed. Consequently, this leads to predominantly superficial and unrestrained downslope slipping, resulting in very localised contractional geometries that do not balance the overall extension, as in classical gravity-failure models. Localised deformation of the sedimentary sequence that unconformably overlies the slide stack indicates that downslope translation continued after the initial rapid slope failure, suggesting that the entire MTD remained inherently unstable. Slide stacking operates at km scales with stratigraphic repetition governed by the throw of earlier normal faults and the amount of downslope translation.

LITHOLOGICAL-STRATIGRAPHIC CRITERIA OF KARST ZONING OF THE MIOCENE SULFATE LAYER OF WESTERN UKRAINE

The proposed karst regionalization (zoning) is a novel approach to identifying the unique characteristics of karst processes in specific areas. The sulphate karst of western Ukraine, linked to the Miocene evaporite basin at the junction of the East European Platform and the Pre-Carpathian Foredeep, is a prime example. The previous karst zoning schemes of the East European Plain classified the entire area of sulphate rocks distribution in the west of Ukraine as the Podilsko-Bukovinsky karst Area, with the West Podilsky and Pokutsko-Bukovinsky karst Regions within it. However, with the emergence of numerous detailed stratigraphy works on the evaporite formation of this territory, a new approach to karst zoning in evaporites is necessary. This paper presents a systematic approach to upgrading the mentioned regions to the rank of sub-areas and distinguishing the regions within them based on lithologic-stratigraphic differences. The authors studied six localities as examples. In the first one, the gypsum layer is characterized by the stromatolite, grass-like and sabre-like facies. The last two contain thin carbonate-clay layers, leading to the collapse of large rock blocks inside the Kadubivska Cave. On the second site, the gypsum is composed of stromatolite, coarse-crystalline, and sabre-shaped facies. Only one small Tovtry Cave, which has a hypogene morphology, is known here. The third site has grass-like gypsum facies, and intensive modern karst occurs, with numerous sinkholes, underground rivers, and sinkholes. The influence of facies variability on the development of the mesomorphology of underground galleries is traced here in Pionerka Cave. The fourth area is built of nodular gypsum facies. There are no insoluble layers here, but the facies have many thin mineral films between the grains. Therefore, the entrance parts of the caves are unstable for physical weathering. The fifth section is highlighted as a section of the spread of metasomatic limestone, which replaces sulphate deposits here. They contain a significant cave labyrinth, but whether karstification occurred before or after metasomatization remains unclear. The sixth section is completely composed of stromatolite gypsum facies. It is characterized by stability to collapse due to the monolithic structure of gypsum, which is noticeable in the example of the Cave of Popeliushka (Zolushka) on the border of Ukraine and Moldova. The selected areas are proposed to be considered as examples of karst zoning based on lithologic and stratigraphic features. Key words: karst regionalization; gypsum, limestone; caves, breakdown; relief, landscape.

Stacking pattern transition caused by submarine channel inception and internal levée development

ABSTRACTThe shift from highly amalgamated and laterally offset to aggradational and vertically stacked submarine channels is a pattern that has been widely recognized in seismic reflection datasets as well as in outcropping successions worldwide. However, the sedimentary and stratigraphic details of such an important part of channel evolution and its implications have not been discussed extensively. That gap is addressed here by characterizing a previously undocumented, seismic‐scale outcrop of the Tres Pasos Formation (Magallanes Basin, Chile) that records the transition from a laterally offset/low‐aggradational channel complex to a vertically stacked aggradational complex associated with the development of an internal levée that enhanced channel aggradation. The boundary between the two complexes is defined by a composite erosional surface (up to ca 35 m relief) with two adjacent element‐scale channelized incisions with contrasting sedimentary infills that provide unprecedented insight into this key phase of submarine channel evolution. Observations indicate that, in between these two depositional architecture styles, there is a significant phase of deep incision and bypass. The relief achieved via this deep incision of one or multiple simultaneously active conduits is interpreted to be necessary to set up the conditions for flow stripping and, subsequently, overbank deposition. Finally, the siltstone‐rich intra‐channel lithofacies association observed directly overlying part of the incision is interpreted to represent the stratigraphic expression of the earliest deposits of an active submarine channel preserved due to the abrupt abandonment of this pathway and the development of an adjacent conduit, which resulted in the former being covered with fine‐grained overbank deposits.

The Jurassic-Cretaceous boundary on the northern Tethyan margin: Karpentná and Ropice sections (Outer Western Carpathians, Czech Republic)

Microfacies and high-resolution studies at the Silesian Unit (Outer Western Carpathians, Czech Republic) on calpionellids, calcareous and non-calcareous dinoflagellate cysts, foraminifers and calcareous nannofossils, aligned with paleomagnetism, δ13Ccarb and δ18Ocarb, allow construction of a detailed stratigraphy and palaeoenvironmental interpretations across the Jurassic-Cretaceous (J/K) boundary. Two studied sections consist of allodapic and biomicritic limestones and marlstones. Ropice section spans the stratigraphic range from the upper Tithonian calpionellid Chitinoidella Zone, nannoplankton zone NJT16 to the lower Berriasian calpionellid Alpina Subzone of the Calpionella Zone, nannoplankton NC1 Zone. The J/K boundary is marked by the dominance of small forms of Calpionella alpina, rare occurrence of Nannoconus wintereri, and the first occurrence of organic-walled dinoflagellate cysts Dichadogonyaulax bensonii and Muderongia longicorna. A negative shift in the δ13Ccarb values corresponds to the Tithonian/Berriasian boundary, the base of the Calpionella Zone (Alpina Subzone). Karpentná section is represented by upper Tithonian calpionellid Chitinoidella to Crassicollaria zones. Remagnetization was documented in both sections.

Grain-size and geochemical investigations on the Novyi Tik site (NW Ukraine) and their significance for understanding the local sedimentary environment in the Pleistocene


 
 
 Grain size and geochemical composition of the loess-palaeosol sequences are important evidence of the sedimentary environment in the Pleistocene, which enables to revela- tion of the sedimentation rates, the origin of deposits, and the sources of material that contributed to the loess accumulation and pedogenesis. The Kd index (10-50 μm / <5 μm), and the Ti/Zr, Ti/Nb and Ce/Y ratios considered to be indicators of aeolian silt accumulation, whereas the ratio of physical sand to physical clay have been suggested to reveal the relationship between sedimentation and pedogenesis. The grain size and geochemical analysis were applied at the Novyi Tik section (Volyn’ Upland), which is characterized by detailed stratigraphy and lateral diversity of palaeosols and deposits. Based on grain size and geochemical data from the section, four main units have been distinguished, which represent periods with similar sedimentary environment such as MIS 10-7, MIS 6, MIS 5 and MIS 4-2. During MIS 9 and 7, pedogenesis pre- vailed with a slight sedimentary contribution; during short-term cooling, thin loess beds were formed. High loess accumulation rates occurred during MIS 6, however, the source of aeolian dust material was different from those to other loess units. At the end of MIS 6, a period of dynamic sedimentation began, which resulted in the sandy grain-size composition of soils and non-soil deposits of MIS 5. The highest sedimentation rates presumably occurred during the stadials, therefore the soils could inherit the grain-size composition of the parent material. Moreover, during MIS 5 in the valley of the Styr River, episodes of aeolian sand accumulation could take place, since the sandy grain-size composition of soils of that time is widespread throughout the basin of the modern Khrinnyky reservoir. At the end of MIS 5, abrupt changes occurred in the sedimentary environment: sand sedimentation almost ceased and a period of aeolian silt accumulation began, and proceeded until the Holocene.
 
 

Phosphate δ13Corg chemostratigraphy from the Gantour basin, Morocco: A proof of concept from the K–Pg transition to mid-Thanetian

The Late Cretaceous–early Paleogene interval is globally associated with transient to long-term changes in the stable carbon isotopic composition of marine carbonates (δ13Ccarb). Based on biostratigraphic reconstruction, this critical period of Earth's history is thought to coincide with the deposition of world heritage Paleocene phosphate deposits (phosphorites) in northwestern Morocco. However, the detailed stratigraphy of the Gantour basin, one of the most important Moroccan phosphate deposits, has not yet been constrained. For instance, the former “Montian” Stage has been used to tentatively approximate the Danian, whereas the succeeding Selandian Stage remains to be identified. Here, we develop a detailed organic carbon isotopic (δ13Corg) curve from phosphorus-rich horizons of the western Gantour sedimentary sequence in an attempt to constrain their stratigraphic placement and depositional age model. Upsection, these strata host long-term negative and positive δ13Corg trends that tend to correlate with global δ13Ccarb records of the Cretaceous–Paleogene and mid-Thanetian transitional boundaries. The data support the presence of Danian and Selandian rocks in the Gantour basin, which are succeeded by strata containing characteristic signatures of the well-known Cenozoic δ13C maximum at 58–57.5 Ma (the Paleocene Carbon Isotope Maximum). Our results shift the previously proposed Cretaceous–Paleogene transition in the Gantour basin further down into the older sediment C2M layer without interfering with recorded massive biological turnover in faunal diversity and abundance. Moreover, the refined stratigraphy suggests that the deposition of the Gantour phosphorites spanned ∼8.5 Myr. Our results confirm the utility of δ13Corg chemostratigraphy for dating and correlating phosphate-bearing deposits of the Tethyan province. They have important implications for deciphering Paleocene phosphogenesis, the co-evolution of associated vertebrate groups, and for prospecting phosphorus-rich mineral deposits.

Tonian basins record rifting of Kalahari from Rodinia and no evidence of a pre-Sturtian Kaigas glaciation

Neoproterozoic strata record evidence for two Snowball Earth glaciations during which ice extended to the equator. Geochronological data have confirmed the multi-million year duration, synchroneity, and global extent of the Cryogenian Sturtian and Marinoan glaciations between 717 and 635 Ma. It has been proposed that an earlier ca. 750 Ma glaciation, referred to as the Kaigas glaciation, included glaciomarine deposits that formed at low-latitude. Here we evaluate this hypothesis at the eponymous location with detailed stratigraphy and geochronology through the Kaigas, Rosh Pinah, and Numees formations on the western margin of the Kalahari craton in southern Namibia. We find that glacial deposits previously assigned to the Kaigas Formation are instead ca. 717–661 Ma diamictites of the Sturtian Numees Formation. Pre-Numees strata, including the Kaigas Formation, host facies associations diagnostic of fan delta deposition along an active normal fault. Interbedded volcanic rocks in the Rosh Pinah Formation overlying the Kaigas Formation were dated with U-Pb CA-ID-TIMS on zircon at ca. 752 Ma. These Tonian deposits are interpreted to have been deposited in an active rift basin without evidence for glaciation. Rosh Pinah magmatism could be broadly correlative with the Mount Rogers Complex in Virginia, USA, consistent with a scenario of the Kalahari craton actively rifting from Laurentia and associated terranes within 20° of the equator at the time. We conclude that, at least in marine settings, evidence for low-latitude glaciation is limited to the 717–635 Ma Cryogenian Period.

Aeolian bedrock ridges in Gale crater, Mars

Fields of parallel, regularly-spaced, bedrock ridges observed on Mars and rarely on Earth have been interpreted as aeolian surface features oriented perpendicular to a formative wind. The exact formation process for these ridges, however, including the role of aeolian erosion versus deposition, continues to be debated. We identified forty fields of bedrock ridges on and within the sedimentary strata of Gale crater's central mound, Aeolis Mons. To better constrain the development of these landforms and the winds responsible for their formation, we characterized ridge morphology, orientation, geographic distribution, stratigraphic relationships, and interactions with other aeolian landforms. The study area of Aeolis Mons was chosen to leverage the extensive high-resolution image coverage from orbit, as well as to build upon the detailed stratigraphy compiled from in situ exploration with the Mars Science Laboratory Curiosity rover. Using the orientation of the ridges, we present a wind vector map of Aeolis Mons. The orientation of bedrock ridges in the Mound Skirting Unit, which unconformably drapes Aeolis Mons, suggests the average wind direction in Gale crater may have remained consistent since that unit was emplaced (∼3.8–3.1 Ga). This study explores the implications of these ridges for the history of wind, deposition, and erosion in Gale crater.

Extreme ductile thinning of Cambrian marbles in the Northern Snake Range metamorphic core complex, Nevada, USA: Implications for extension magnitude and structural evolution

The detailed stratigraphy of rocks within the Northern Snake Range metamorphic core complex provides an exceptional opportunity to investigate the geometry and magnitude of ductile strain during high-magnitude continental extension. In the northern part of the range, Middle-Late Cambrian marbles in the footwall of the Northern Snake Range dècollement (NSRD), which have a stratigraphic thickness of 1107 ± 107 m in adjacent ranges, were thinned during Late Eocene-Late Oligocene ductile extension. From west to east across the range, these rocks have been thinned from 869-935-m-thick (15–21% structural thinning) to 54-88-m-thick (92–95% structural thinning) across a 12 km lineation-parallel distance. Ductile extensional strain was accompanied by the development of pervasive linear-planar fabrics and produced megaboudins of calcareous schist units that are 100-500-m-long, 15-25-m-thick, and separated by as much as 1 km. The magnitude of lineation-parallel ductile extension increases eastward across the range from 24 ± 21% to 1226 ± 256%, and total ductile extension across the range is 12.1 ± 2.2 km (167 ± 31%). Quartz recrystallization microstructures and published calcite-dolomite thermometry indicate deformation temperatures of ∼400–550 °C during initial Late Eocene-Late Oligocene ductile extensional shearing. West to east across the range, rocks in the NSRD footwall experienced a progressively longer ductile extensional strain history and a prolonged residence time at higher temperatures, which was aided by the eastward migration of denudation-related cooling and was likely enhanced by strain heating and/or a pre-extensional eastward dip of footwall rocks. These factors promoted the development of the extreme strain gradient.

Sequence stratigraphy and petrographic characteristics of Oligocene sediments in the West trough of the Cuu Long Basin, Vietnam

The Cuu Long Basin is the major source of Vietnam's oil and gas production. In clastic sediments, the Oligocene and Lower Miocene formations are the main objects of oil and gas exploration and exploitation activities. Oligocene sediments are both source and reservoir rocks; therefore, studying the petroleum system of these formations is of great interest. This paper discusses detailed stratigraphy and lithological properties to clarify the Oligocene sedimentary characteristics and their significance in the petroleum system. Study results show that Oligocene sediments are divided into three sequences, including eight parasequences and are dominated by the terrestrial sediments. Sequence E, mainly coarse-grained, contains low palynomorphs and rich organic matter with mainly palynomaceral 1 and is deposited in freshwater fluvial settings under high-energy conditions, showing sediments not so far from the original areas. The high level of detrital matrix materials is the main cause of poor or negligible porosity of the rock. The parasequences of Sequence D contain abundant palynomorph assemblages, characterized by swamp and freshwater alga taxa. They are deposited mainly in the shallow lake with a decreasing energy level pointing upward. The volume of organic matter in sediments is very rich, with sapropel organic matter (SOM) rates reaching up to 80%, indicating that the hydrocarbon generation potential is mainly oil-prone and some oil-gas mixtures. The porosity is poor and reservoir quality is affected by detrital matrix and authigenic minerals. The parasequences of Sequence C are characterized by the extreme abundance of freshwater algae, deposited mainly in the shallow-to-deep lake under moderate energy conditions, and rich sapropel organic matter, suggesting mainly oil-prone in hydrocarbon generation potentials. The porosity ranges from fair to good and the reservoir quality is estimated as the best in Oligocene sediments. A new finding of marker assemblages provides evidence to pinpoint the stratigraphic boundary between the Lower Miocene and Upper Oligocene. This finding helps to complete the stratigraphic framework of the area and to correlate the stratigraphy to adjacent sedimentary basins. This study provides information on depositional environmental conditions, organic matter content, hydrocarbon generation potential, and reservoir quality that relate to source rock, reservoir, and seal; these are the elements of a petroleum system. A complete petroleum system assessment requires a holistic view of all the petroleum system elements.

Trans-Holocene Bayesian chronology for tree and field crop use from El Gigante rockshelter, Honduras.

El Gigante rockshelter in western Honduras provides a deeply stratified archaeological record of human-environment interaction spanning the entirety of the Holocene. Botanical materials are remarkably well preserved and include important tree (e.g., ciruela (Spondias), avocado (Persea americana)) and field (maize (Zea mays), beans (Phaseolus), and squash (Cucurbita)) crops. Here we provide a major update to the chronology of tree and field crop use evident in the sequence. We report 375 radiocarbon dates, a majority of which are for short-lived botanical macrofossils (e.g., maize cobs, avocado seeds, or rinds). Radiocarbon dates were used in combination with stratigraphic details to establish a Bayesian chronology for ~9,800 identified botanical samples spanning the last 11,000 years. We estimate that at least 16 discrete intervals of use occurred during this time, separated by gaps of ~100-2,000 years. The longest hiatus in rockshelter occupation was between ~6,400 and 4,400 years ago and the deposition of botanical remains peaked at ~2,000 calendar years before present (cal BP). Tree fruits and squash appeared early in the occupational sequence (~11,000 cal BP) with most other field crops appearing later in time (e.g., maize at ~4,400 cal BP; beans at ~2,200 cal BP). The early focus on tree fruits and squash is consistent with early coevolutionary partnering with humans as seed dispersers in the wake of megafaunal extinction in Mesoamerica. Tree crops predominated through much of the Holocene, and there was an overall shift to field crops after 4,000 cal BP that was largely driven by increased reliance on maize farming.

Automated multi‐well stratigraphic correlation and model building using relative geologic time

AbstractStratigraphic correlation of geophysical well logs is one of the most important—and most time‐consuming—tasks that applied geoscientists perform on a daily basis. Using the dynamic time warping (DTW) algorithm, automated correlation of two wells is a fairly simple task; DTW can also be used to correlate a large number of wells along a single path. However, errors accumulate along a path and loops cannot be closed. To create a three‐dimensionally consistent correlation framework, we use a Python implementation of the Wheeler and Hale (2014) approach, which is based on the idea of stretching and squeezing all logs into a chronostratigraphic diagram that has relative geologic time (RGT) on its y‐axis. The depth shifts needed for the RGT transformation are computed by translating the outputs of a large number of pairwise DTW correlations into a least‐squares optimization problem that is solved through the conjugate gradient method. The resulting chronostratigraphic diagram provides an overview of the overall stratigraphy and its variability; and the correlation framework is significantly different from what one could get from correlating based on lithologic similarity between two logs. To create geologically intuitive well‐log cross sections, we use a multi‐scale blocking method that relies on the continuous wavelet transform to identify stratigraphic units of a certain scale in one well and then propagate these boundaries to all the other wells. We demonstrate the usefulness of this approach on a data set with close to 700 wells from the Permian Basin, West Texas. Linear channel bodies in the deepwater Spraberry Formation are easily detected and clearly highlighted in maps and cross sections. The methodology is robust enough for mapping subtle stratigraphic details, previously considered feasible only through manual interpretation. More importantly, it can be used to quickly build three‐dimensional stratigraphic models for large segments of sedimentary basins where enough log data are available.

Two-stage emplacement mechanism and symmetrical differentiation process of mafic-ultramafic sills in an arc setting: A case study of the Middle Tonian rock assemblage from the Fanjingshan area

The emplacement and differentiation mechanisms are significant parts of understanding the evolution of a magmatic system. There is debate regarding the emplacement mechanism of long-distance lateral transport of magma. And the differentiation mechanisms mainly target the rock assemblage in mantle plume-related or rift-related settings. As yet, few studies had been followed in the arc setting. In this contribution, the mafic-ultramafic sills formed by long-distance lateral transport of magma in the Fanjingshan area in South China have been selected to decode the magmatic emplacement and differentiation mechanism in an arc system. Voluminous basaltic lava and mafic-ultramafic sills are emplaced, concordant to bedding, within the lower part of the Middle Tonian Fanjingshan Group and laterally extend for tens of kilometers. Some mafic-ultramafic sills display symmetrical lithology and geochemical distribution in vertical sections. We provide a detailed stratigraphy and geochemical analysis of the mafic-ultramafic sills of the Fanjingshan Group. The mafic sills within the underlying strata (the Taojinhe Formation) of the lower part of the Fanjingshan Group were intruded at 832 Ma, which is >8 Ma younger than the basaltic eruptions in the overlying strata (the Huixiangping Formation). Moreover, these mafic sills within the Taojinhe Formation have a positive ɛNd(t) value (+0.9 − +1.6), the lowest Platinum Group Elements (PGE) content and highest Rare Earth Elements (REE) content. Compared with other mafic sills and basalts within different formations (the Huixiangping, Xiaojiahe, and Yujiagou formations), mafic sills within the Taojinhe Formation display a separate field on the principal component analysis diagram, suggesting two stages of mafic magma emplacement with a short interval for the Fanjingshan Middle Tonian volcanic plumbing system. The magma channel of the first stage magma is subsequently used by the second stage magma as suggested by ɛNd(t) values and Nb-Ti anomalies. Although island arc magmas differ greatly from mantle plume magmas in volume, temperature and composition, the calculated dimensionless temperature and dimensionless flux of magma imply that the solidification can affect the formation of mafic-ultramafic sills in the island arc systems. At the same time, the difference in rigidity of the upper and lower strata is not the main reason to control the formation of the mafic-ultramafic sills as suggested by the statistical analysis of the mafic-ultramafic sills occurrence between different wall-rock lithology associations. Through the comparative study of the sills formed by the long-distance lateral transport of magma, it is proposed that the clastic wall-rock provides the first-order control for the sills formed by the long-distance lateral transport of magma. According to the detailed geochemical study of an M-shaped geochemical profile within the Huixiangping Formation, two steps of in situ crystallization model have been suggested. In the first step, minerals crystallizing from the inflowing magma on the floor and roof of mafic-ultramafic sills will become more primitive inwards. In the second step, the magma evolves both downward and upward by uninterrupted in situ crystallization in a closed system that results in the whole-rock becoming more evolved in composition inward.

GC–MS analysis of soil faecal biomarkers uncovers mammalian species and the economic management of the archeological site "Le Colombare di Negrar"

The identification of the mammalian species based on faecal sediments in modern and ancient environments is the aim of the research of archaeologists, forensic scientists and ecologists. Here, we set up and validated an optimized gas chromatography-mass spectrometry (GC–MS) method, characterized by a time-saving sample preparation protocol, for the simultaneous analysis of faecal biomarkers (6 sterols/stanols and 5 bile acids) in 14 soil samples from the archaeological site of “Le Colombare di Negrar” in northern Italy. Although the archaeological sediment samples examined are numerically exiguous, a comparative reading of our faecal biomarkers findings with new studies on faunal materials collected in the same stratigraphic detail during recent excavation campaigns will allow to better clarify the economic interest of the animal species farmed in the Colombare site (such as bovines, goats, sheep and pigs) and to shed light on the management of breeding. Together with archaeozoological and archaeobotanical analyses, the investigation of faecal biomarkers can increase our knowledge of how ancient local communities exploited natural resources and may allow us to deduce what their impact on the landscape was.

The paleoenvironmental implications of pre-Great Oxidation Event manganese deposition in the Mesoarchean Ijzermijn Iron Formation Bed, Mozaan Group, Pongola Supergroup, South Africa

The Ijzermijn Iron Formation Bed occurs in the Vlakhoek Member of the basal Sinqeni Formation of the Mesoarchean Mozaan Group of the Pongola Supergroup of southern Africa. It represents the oldest known supracratonic Superior-type iron formation that has significant manganese enrichments. Lithostratigraphic correlation between the Mozaan Group and the Witwatersrand Supergroup indicates that there was a larger Witwatersrand-Mozaan depositional basin on the Kaapvaal Craton during the Mesoarchean. Detailed stratigraphy, mineralogy, petrography, carbonate mineral chemistry, major and trace element geochemistry and carbonate oxygen and carbon isotopes are presented for two drill cores intersecting the Ijzermijn Iron Formation Bed. Drill core PMH 24, which represents a more coast-distal depositional setting, is characterized by manganese-rich siderite, higher Fe2O3 and lower MnO and Al2O3 contents, more prominent europium anomalies, lower GdSN/YbSN values and less depleted δ13CPDB values. Drill core DDN 1, which represents a more coast-proximal depositional setting, is characterized by iron-rich rhodochrosite, lower Fe2O3 and higher MnO and Al2O3 contents, less prominent europium anomalies, higher GdSN/YbSN values and more depleted δ13CPDB values. The presence of early diagenetic magnetite, hematite and 13C-depleted carbonates indicate the iron and manganese, which were sourced from hydrothermal plumes, were deposited by oxidation, with subsequent diagenetic reduction by organic carbon. The most efficient oxidative mechanism would have been biological oxidation. The increase in manganese contents towards the paleocoastline further supports manganese oxidation as it was redox buffered by Fe2+ in the water column and could only be deposited and preserved once Fe2+ had been removed through oxidation further away from the distal hydrothermal plume source. This is supported by previously published iron isotope data, where δ56/54Fe values are more depleted closer to the paleocoastline. Deposition of iron and manganese was restricted to below the photic zone. This implies that microaerophilic chemolithoautotrophs were responsible for iron and manganese oxidation. This requirement of free oxygen in the Ijzermijn Iron Formation Bed has been supported by earlier molybdenum isotope studies. The presented work therefore further supports the idea of pre-Great Oxidation Event marine oxygen oases that did not lead to any appreciable build-up of oxygen in the atmosphere.

Characteristics of the Stone Age of Crimea in the Creative Heritage of A.S. Moiseev.

The purpose of the article is to characterize the contribution of the Russian scientist Alexander Silovich Moiseev to the archaeological study of the Stone Age of the Mountainous Crimea. To achieve the goal, the following tasks were envisaged: the selection of articles on the primitive archeology of the Crimea from the entire array of scientific publications of the scientist, their subsequent historiographical analysis and generalization. The research methodology was based on the complex application of scientific principles: historicism, objectivity, comparative historical approach, retrospection. The problem field of the research included the following components: establishing continuity in the history of the study of the Stone Age of the Crimean peninsula, formulating priority problems of the primitive archeology of the region in the works of the scientist. The source base for the study was the published articles by A.S. Moiseev on the history of the Stone Age of the Mountainous Crimea. In the course of the conducted research, it was found that during the short-lived but important expeditions of A.S. Moiseev as director of the Natural History Museum in Yalta, the source base was gradually formed in the articles of the scientist and the program of future studies of the ancient history of the peninsula was concretized. A.S. Moiseev put the study of the Stone Age of the Crimea to a qualitatively new level. In particular, he actualized the need to search and excavate primitive monuments with careful fixation of all finds in plan and section, justified the expediency of joint stationary excavations of several well-known archaeological sites with systematic searches in new, not yet explored areas. In addition, the author's innovations are the transition from the simple collection of flints and tools to their systematization and typology, the formation of ordered collections; the creation of a complete archaeological map of primitive sites and locations of the peninsula with their detailed stratigraphy, as well as the strengthening of scientific ties between representatives of regional and academic science in the study of Paleolithic, Mesolithic and Neolithic monuments of the Crimea.

:Metal Finds and Coins: Final Publications from the Danish-German Jerash Northwest Quarter Project II

:<i>Metal Finds and Coins: Final Publications from the Danish-German Jerash Northwest Quarter Project II</i>

Jurassic–Cretaceous intraplatform basins from NW Sicily fold and thrust belt: Implications for oblique rifting of the Southern Tethyan margin

Carbonate intraplatform basins are documented worldwide as peculiar synsedimentary tectonic features forming in rifted margins and especially in those cases where the direction of extension is oblique with respect to the rift axis. A detailed stratigraphy and facies analysis combined with subsidence history of the Upper Triassic-Cretaceous shallow-water carbonates outcropping in the Peninsula of Capo San Vito, representing the NW end of the Sicilian fold and thrust belt, has been performed. Three different sections, separated by faults and characterised by shallow-water and deep-water carbonate sedimentation, were distinguished. Their location and tectonic relationships highlight the occurrence of two structural highs (Monaco and Sparagio sections) separated by a structural low (Acci section).The Acci intraplatform basin, structured since the Pliensbachian, is characterised by mostly pelagic sedimentation with resedimentation of carbonate reef derived-elements from adjacent carbonate platform blocks. On the two structural highs, shallow-water sedimentation, since the Late Triassic, developed with progradational trends shedding out shallow-water elements towards the basin. The evolution of the narrow Acci intraplatform basin appears influenced by a transtensional regime creating a wedge-shaped basin. Backstripping analysis on the three measured sections was able to reconstruct subsidence curves, from which different evolutionary stages, marked by punctual synsedimentary tectonic activity, can be highlighted for the Late Triassic-Eocene time interval.Comparison with the adjacent basin system of Cala Rossa, located 30 km away eastward in the Palermo Mountains, allowed to recognise similar characteristics. The stratigraphic, sedimentologic and tectono-sedimentary common features, trend and kinematic of the paleofaults, and the same chronology of tectonic events, suggest that the two areas represent adjacent basins making part of a unique spindle-shaped basin system. Some variable evolutionary characteristics among the Acci and Cala Rossa basins, including the overall thicknesses, the thickness of the resedimented deposits, the occurrence of Upper Cretaceous shallow-water deposits only in the structural highs of the Acci Basin, are explained as features linked to the different location of the two basins with respect to the master fault. Many of the observed features are described from those rift systems where the direction of extension is not perpendicular to the rift axis, suggesting that this sector of the Southern Tethyan margin could be developed as an oblique rift system.

Stratigraphy and eruption history of maars in the Clear Lake Volcanic Field, California

The Clear Lake Volcanic Field (CLVF) is the northernmost and youngest field in a chain of volcanic fields in the California Coast Range mountains. Effusive and explosive volcanic activity in the field has spanned at least 2.1 million years, with the youngest eruptions comprising a series of maar craters at the edges of, and within, Clear Lake itself. This work documents the first direct ages for many of these maar deposits and builds the stratigraphic basis for interpreting eruptive processes and dynamics of the young eruptions which produced them. Detailed stratigraphy has distinguished maar eruption products from pyroclastic deposits (monolithologic falls and flows, previously mapped together with maars as a single unit) and established a set of six eruption facies from maar deposit lithology, grain size parameters, and depositional structures. Radiocarbon dates from carbon films found on clasts at three outcrops have constrained several of these maar eruptions to ∼8,500–13,500 years BP, coinciding with eruptive periods previously estimated based on lake core tephrachronology. Part of this period also coincides with indigenous inhabitation (&amp;lt;12,000 years BP), which suggests that oral histories of Pomo and other local tribes may contain descriptions of volcanic phenomena experienced by local residents of the CLVF. Collaboration between volcanologists and indigenous historians may add a valuable human dimension to the youngest eruptions of the Clear Lake Volcanic Field, and help inform future volcanic hazard assessment.