Outcrop Sections Research Articles

Early Oligocene environment of the Central Paratethys revealed by biomarkers and pyrite framboids from the Tarcău and Vrancea Nappes (Eastern Outer Carpathians, Romania)

The Menilite facies, representing the most prolific hydrocarbon source rocks in the Carpathian fold and thrust belt, has been studied in two outcrop sections of the Vrancea and Tarcău Nappes (Eastern Romania) with the aim of determining the depositional environment during the Early Oligocene in the Vrancea and Tarcău sub-basins of the Central Paratethys. The biomarker composition indicates spatial variability in organic matter sources with mainly algal (particularly diatoms and dinoflagellates) and bacterial contributions in both sub-basins. This is reflected by the occurrence of such biomarkers as triaromatic dinosteroids, C25 highly branched isoprenoid thiophenes, marine n-alkanes, hopanoids and monomethyl alkanes. Solely in the Vrancea domain, the input of terrigenous organic matter of higher plant origin can be anticipated from the presence of abietane-class biomarkers (conifer-derived) and oleanane (angiosperm-derived). Distinct nutrient availability related to different positions of individual sub-basins (i.e. shallower, temporarily eutrophic Vrancea sub-basin vs. open-marine mesotrophic Tarcău domain) is reflected by different paleoproductivity indicators, such as the total organic carbon content, hydrogen index and 17α-hopanes to steranes ratio.Water column stratification with bottom water anoxia enhanced by bacterial sulfate reduction stretching into the chemocline, at least intermittently, is expressed by a characteristic tiny pyrite framboid distribution and the lack of bioturbation. However, molecular indicators (Pr/Ph ratio, C35 homohopane index) imply fluctuations of redox conditions with the dominance of dysoxic conditions, which may suggest the occasional oxidation of bottom waters linked to local upwelling. Early diagenetic organic matter transformations such as photodegradation taking place in the oxidised upper part of the water column could also have affected the biomarker distributions. The presence of aryl isoprenoids and Me,i-Bu-maleimides indicates periods of euxinic conditions within the photic zone only in the Vrancea sub-basin during the deposition of the Lower Menilite Member. This is probably related to freshwater incursions from the adjacent, at least partly emerged forebulge, as suggested by a high MTTC ratio and the occurrence of higher plant-derived organic matter.

Miocene Atlantic transgressive - regressive events in northeastern and offshore Patagonia: A palynological perspective

Key information for regional biostratigraphic, climatic and environmental reconstructions for the Miocene of the southwestern Atlantic margin can be obtained by qualitative and quantitative palynological analysis at the onshore YPF-CH-PV.es-1 borehole (PV borehole) in the Valdés Basin, combined with previously documented organic-walled dinoflagellate cyst data from the Colorado Basin and well-dated outcropping sections on the east coast of Patagonia. A sequence of eleven significant dinocyst bioevents (highest occurrence, HO; highest common occurrence, HCOs) is recognized across the Valdés and Colorado basins. The bioevents occur in the same stratigraphic order and seem to be synchronous across both basins. From the oldest to the youngest, these are: HO of Emmetrocysta urnaformis, HO of Cannosphaeropsis quattrocchiae, HCO and HO of Hystrichokolpoma rigaudiae, HO of Cousteaudinium auybriae, HCO and HO of Dapsilidinium pseudocolligerum, HO of Cleistosphaeridium ancyreum, HO of Labyrinthodinium truncatum, HO of Operculodinium piaseckii and HO of Reticulatosphaera actinocoronata. The presumed climatically-driven extinctions of Dapsilidinum pseudocolligerum and Hystrichokolpoma rigaudiae around the Burdigalian to earliest Langhian, may be linked to global cooling and the re-establishments of the Antarctic ice-sheets since ~14 Ma. Two maximum flooding episodes, characterized by warm, outer (distal) neritic environmental conditions were identified at the PV borehole, presumably related to glacio-eustatic sea level rise. The older occurred in the Burdigalian – earliest Langhian and the younger, in the Tortonian. The latter maximum flooding is followed by environmental and/or climatically-driven change, implying abrupt shifting from neritic to nearshore conditions, the extinction of the warm-water taxa, and dinocysts being largely replaced by acritarchs.

Facies associations and sequence stratigraphy of the Middle-Late Eocene Pila Spi Formation in the High Folded Zone, Kurdistan Region, northeastern Iraq

Facies analysis and sequence stratigraphy of the Pila Spi Formation (Middle-Late Eocene) was studied from two outcrop sections (Bekhma and Gomaspan) within the High Folded Zone, Iraqi Kurdistan Region. The formation consists of light brown dolomitic, crystallized, chalky, limestones, and dolostone, alternating with multicolored marl and marly limestones. Chert nodules are present in the upper part of the formation. The petrographic analysis was based on 65 thin sections, and the results showed that the carbonate rocks are partially dolomitized. The distinguished bioclasts consist of benthic and planktonic foraminifera, micro-gastropods, calcispheres, ostracods, pelecypods, and bryozoans. Non-skeletal grains such as peloids, intraclasts, and extraclasts were also observed. X-ray diffraction analysis revealed that abundant clay minerals are palygorskite with the rare existence of chlorite. Non-clay minerals include dolomite, calcite, and quartz with low pyrite contents. According to field observations, four different lithofacies were recognized. They are dolomitic limestone, chalky limestone, marl-marly limestone, and cherty limestone. Based on detailed microfacies analysis of limestones, four main microfacies and eleven submicrofacies types are observed. These microfacies are subdivided into two groups of facies associations; they are semi-restricted and open lagoon. The results of stable carbon and oxygen isotopes of the studied carbonate samples show negative values of δ18O, and this indicates that the seawater was warm with lower salinity. However the positive δ13C values reflect the deposition of organic-rich sediments with transgression of the sea and deepening of the basin. Two third-order depositional sequences are observed. Each of them is subdivided into a TST and HST, reflecting the transgression and stillstands of the relative sea level during Middle-Late Eocene.

Spatiotemporal evolution of single sandbodies controlled by allocyclicity and autocyclicity in the shallow-water braided river delta front of an open lacustrine basin

Abstract The spatial and temporal evolution of the sandbody architecture of shallow-water deltas in open lacustrine basins is controlled by the classification of allocyclicity and autocyclicity. On the southwestern margin of the Ordos Basin, a braided river system deposited a shallow-water delta in the Late Triassic Period. Based on the principle of sequence stratigraphy and the hierarchical analysis of reservoir architecture, the spatial and temporal evolution of individual sandbodies in the Chang 81 member of the Yanchang Formation in the Zhenbei Oilfield is interpreted by utilizing data from cores, wells and outcrops. The research ideas are as follows: large deposition scale architectural elements (first- to third-order cycles, as defined by Miall) of different sequence levels are affected by allocyclicity associated with changes in tectonic activity, provenance, and sea level, and small deposition scale architectural elements (fourth- to fifth-order cycles, as defined by Miall) of different sedimentary facies mainly consist of individual sandbodies that are affected by autocyclicity associated with lake-level changes caused by various river processes. Based on previous studies, the results are as follows. The sedimentary characteristics of shallow-water deltas have been verified by core and outcrop data. In addition, three ultrashort-term cycles are identified on the basis of boundary sequences and lithofacies’ sequences in the outcrop section of the Rui River, and three sedimentary evolution stages of the delta front are defined. Finally, according to well data, five types of architectural elements at the level of single sandbodies are identified. The vertical superimposition and lateral contact relationships of different architectural elements indicate that during the three sedimentary evolution stages, the hydrodynamics weakened, strengthened slightly, and finally weakened substantially. Among the 20 kinds of architectural element spatial combination patterns formed by single sandbodies, primary and secondary sandbodies have great potential for hosting remaining oil. In the process of architectural spatiotemporal evolution, the geometry and connectivity of the underwater distributary channel gradually weakened, and the spatial relationship between the underwater distributary channel and other architectural elements increased. This article proposes a new method for researching shallow-water deltas and has some guiding significance for exploiting the remaining oil in oil fields.

Underthrusting of the Tarim Lithosphere Beneath the Western Kunlun Range, Insights From Seismic Profiling Evidence

AbstractUplift of the western Kunlun range results from the Indian indentation into Eurasia and induced underthrusting of the Tarim lithosphere. This underthrusting keeps pace with migration of the western Kunlun foreland basin. The basin‐scale sequences provide a decipherable record of the migration. To quantify the underthrusting, we analyzed a ∼323.2‐km‐long seismic profile crossing the middle segment of the western Kunlun foreland. We traced seismic reflectors to investigate the architecture of the foreland sequences and assigned ages of reflectors by correlating them with the dated outcropping sections. The foreland sequences consist of four layers. The lowermost Layer 1 starts to lap on the preforeland unit at ∼40 Ma, indicating that the Cenozoic western Kunlun initiated slightly prior to ∼40 Ma. Layer 2 shows a large sharp step northward to exceed the forebulge at ∼25 Ma, suggesting that the modern geomorphology of the Tarim Basin took shape. The southwestern boundary of Layer 4 migrates northeastwards by a fold row relative to that of Layer 3. The gradual retreat of reflector terminations from ∼40 to ∼30 Ma suggests that the Tarim lithosphere is viscoelastic. The linear fitting of the forelandward envelop of reflector termination sites since ∼30 Ma indicates that the Tarim lithosphere underthrusted at an average rate of ∼8.18 mm/yr. This rate comprises the shortening rate of ∼3.8–5.7 mm/yr and the western Kunlun latitudinal propagation rate of ∼4.4–2.5 mm/yr. The abrupt increase in sedimentation rate since ∼11 Ma suggests that western Kunlun had reached its current elevation.

Pleistocene palaeoenvironments in the Lower Volga region (Russia): Insights from a comprehensive biostratigraphical study of the Seroglazovka locality

There are many Middle-Upper Pleistocene outcrop sections in the Lower Volga region (Caspian Lowland, Russia) in between cities of Volgograd and Astrakhan. The present study focuses on the Seroglazovka locality, which is among the most famous key sites within the Lower Volga region. The Seroglazovka locality is of great regional interest, because of its clear exposure of genetically variable Middle and Upper Pleistocene deposits containing diverse complexes of fauna and flora. Even though the Seroglazovka locality was studied by many researchers, the diversity and along-strike variability of the depositional facies often makes the stratigraphic interpretation challenging. In this study, we performed an extensive and integrated study of the Seroglazovka locality including detailed outcrop mapping with lithological description, as well as diverse biostratigraphy analysis and OSL-dating. In addition to outcrop data, we used recently obtained borehole data near the Seroglazovka locality, which cover almost the entire Quaternary interval. This multidisciplinary approach permitted us to confidently stratify the Quaternary interval of the Seroglazovka locality into a series of regional horizons and subhorizons including the Akchagyl, Apsheron, Tyurkyan, Baku, Khazar and Khvalyn. Furthermore, we correlated the interpreted section to the adjacent parts of the Caspian Lowland and the Regional Stratigraphic Scale. Our results allowed us to determine the main Pleistocene palaeoenvironments and their evolution within the study area. Our findings are important to understand the processes, which led to the modern faunistic composition of the Lower Volga region, and to clarify the role of glacial refugia in the settlement of certain species and further colonization of water basins and land areas with habitable environments. Finally, we suggest the Seroglazovka locality as the key reference Pleistocene section for the Lower Volga region.

Paleoenvironmental inferences based on benthic foraminifera from the Uitpa Formation (Guajira, Colombia)

The Uitpa Formation is a lithostratigraphic unit that crops out in the Guajira peninsula, northeastern Colombia in the Cocinas Basin. This formation consists mainly of marly and argillaceous mudstones of gray to light brown color, intercalated with sandstone and calcarenite beds. The lower contact with de Siamana Formation is unconformable, and at the top the contact with the Jimol Formation is conformable at Uitpa. These units contain an abundant and diverse fauna of planktic and benthic foraminifera that has not been studied in detail yet. In this research, two outcrop sections from the upper Guajira containing the Uitpa Formation were analyzed: the Pisuuluu hill and Jososuwou creek sections. Planktic foraminifera were extracted and taxonomically classified, allowing to assign an age of Chattian (Late Oligocene) (planktic foraminifera biozones O6 - O7). This investigation presents for the first time in Colombia a paleoenvironmental reconstruction integrating various methodologies using quantitative and qualitative analyses in benthic foraminifera. From these analyses an outer neritic to upper bathyal paleodepth was inferred, with environments characterized by high organic matter inputs in eutrophic conditions for both sections. Oxygenation levels were higher in the Pisuuluu hill section, represented by high diversity heterogeneous assemblages, while for the Jososuwou creek section oxygenation was very low producing stressed environments and low diversity homogeneous assemblages.

New insights on the Late Paleocene − Early Eocene dinoflagellate cyst zonation for the Paris and Dieppe basins

The Anglo-Belgo-Paris Basin, historical cradle of the Paleogene stratigraphy since the 19th century, is known by the presence of very specific so-called “Sparnacian” deposits (very diverse and laterally highly variable, predominantly lagoonal to terrestrial facies), which encompass the short stratigraphic interval of the Paleocene-Eocene Thermal Maximum (PETM). Due to the insufficient nature of the paleontological record, the “Sparnacian” succession of the Paris and Dieppe-Hampshire basins still needs to be robustly chronostratigraphically correlated with other Paleogene records worldwide. In order to refine the stratigraphy of the Thanetian-Lower Ypresian succession in northern France a number of cores and outcrop sections have been investigated palynologically. As a result, an updated version of the dinoflagellate cyst zonation for the Paris and Dieppe basins is proposed and contains six new or revised biozones for this stratigraphical interval:Alisocysta margarita,Apectodinium hyperacanthum,Apectodinium-acme,Biconidinium longissimum-acme,Dracodinium astra, andAxiodinium lunare/Stenodinium meckelfeldense. Based on combined bio-, litho- and chemostratigraphic data, it appears that the dinocyst assemblages, corresponding to the PETM event interval (“Sparnacian” deposits, Soissonnais and upper Mortemer formations), are characterized by an acme ofApectodiniumspp. (70–98%) in both basins, sometimes alternating with an acme of a few gonyaulacoid groups in the Dieppe Basin. Dinocyst assemblages from the PETM interval contain a significant number of atypical, longer specimens ofApectodinium parvum, which could represent an ecological onshore substitute forAxiodinium augustumin the Paris and Dieppe-Hampshire basins. The establishment of a newBiconidinium longissimum-acme Zone suggests that the stratigraphic hiatus previously inferred within this sequence in the Paris Basin does not exist.

Large-scale vertical movements in Cenomanian to Santonian carbonate platform in Iberia: indicators of a Coniacian pre-orogenic compressive stress

The Cenomanian to early Santonian interval is usually considered a time of postrifting tectonic quiescence around the northern margins of Iberia that preceded the onset of the Pyrenean convergence by crustal thrusting in the latest Santonian. However, plate kinematic models of the Mesozoic evolution of Iberia poorly constrain the Turonian-Santonian position of Iberia relative to Eurasia. This study reconstructs changes in the sedimentary facies and architecture of the Iberian carbonate platform throughout the Late Cretaceous and sheds new light on the geodynamic evolution of the Iberia-Eurasia relationship at that time. Sixteen outcrop sections were described and 24 sedimentary facies identified that define 5 depositional environments ranging from the deep marine basin to the continental setting. From these and previously published field data we reconstruct the evolution of the Pyrenean carbonate platform, on an east-west transect nearly 400 km long, on the basis of 11 short-term depositional sequences and 5 long-term hemicycles. In our interpretation, the Cenomanian and Turonian correspond to a postrift stage during which the European and Iberian margins, together with the deep basin between them, subside gently, as shown by accommodation rates varying from ∼15 to 30 m/My in the margins and ∼100 to 150 m/My in the basin. The Coniacian and early Santonian are characterized by a large-scale flexural response consisting of (1) uplift of the southern Iberian margin, with negative accommodation rates, karstified surfaces and paleosols, and (2) increasing subsidence rates in the basin and its edges (the northern Iberian margin and eastern Aquitaine platform), with accommodation rates several times greater than during the Turonian. We propose that far-field stress possibly related to the northeastward motion of Africa, and/or onset of shortening at the Iberia-Europe boundary in the central and eastern Pyrenees led to the incipient large-scale flexural deformation in the Pyrenean domain. The late Santonian and Campanian are an early orogenic stage marked by rapid subsidence throughout the Pyrenean domain, except at its western end. We evidence for the first time a pre-orogenic flexure at the Iberia-Europe plate boundary induced by regional plate reorganisation between Africa and Europe during the Coniacian and the early Santonian.

Middle and Late Pleistocene loess of the Western Ciscaucasia: Stratigraphy, lithology and composition

Due to the high preservation of the loess series and the availability of coastal outcrop sections loess cover of Western Ciscaucasia has ample opportunities for spatial paleogeographical reconstructions for the Middle and Late Pleistocene. Currently, the level of knowledge on the structure and composition of the loess-paleosol sequences of Western Ciscaucasia remains unequal. The Azov coast is studied in more detail in comparison with the inner part of the region. The structure and composition of the loess-paleosol sequences of different parts of Western Ciscaucasia (the Sea of Azov coast and western macroslope of the Stavropol Upland) for the Middle and Late Pleistocene are compared. Comparison of the key sections are based on litho- and pedostratigraphy, magnetic susceptibility, grain size, elemental and mineral composition, and luminescence dating. Recent results of luminescence dating allowed correcting the structure of the Mezin pedocomplex (S1). It was found out that this pedocomplex includes three phases of soil formation (S1SS1, S1SS2, S1SS3), which approximately correspond to the warm stages of marine isotope stage 5 (MIS 5) – 5a, 5c, 5e. In all sections, a clear trend towards an increase in the accumulation rates over the last three climatic macrocycles is observed. The last interglacial-glacial macrocycle (MISs 2–5) is characterized by the most significant increase in average accumulation rates, which were ∼1.8 times higher compared to MISs 6–7 and ∼2.3 times higher than during the MISs 8–9. A likely reason for the regional increase in the average dust accumulation rate was the directional increase in climate aridity. The patterns of the spatial distribution of the loess thickness and material composition indicate that the main source of aeolian dust is situated in the east. We suppose that the main sources of dust are sand masses of the alluvial plains of Lover Volga, Terek, Kuma and Kura rivers in the Caspian lowland. The Lower Don sandy province is reconstructed to be a secondary source. Dust is blown from the sandy terraces of the Don, and in the past - from the Don deltas, during the period when the Sea of Azov dried up.

Source rock characterization of the upper Barremian, Albian and Cenomanian–Turonian organic-rich strata outcropping in Oued Bazina area, NE of Thibar diapir: Northern Tunisia

Rock-Eval pyrolysis, total organic carbon (TOC) determination and gas chromatography-mass spectrometry (GC-MS) analysis were performed on samples from outcrop sections of the upper Barremian (M’Cherga Formation), Albian (Fahdene Formation) and Cenomanian–Turonian (Bahloul Formation) in the Oued Bazina area located in the NE of the diapiric structure of Thibar, northern Tunisia. The upper Barremian and Cenomanian–Turonian organic-rich strata display high TOC values with a mean of 3.39% and 2.82%, respectively, while the Albian succession deposits exhibit TOC values lesser than 2%. The half-graben structures developed at these epochs have acted as restricted mini-basins favouring the water stagnation, the accumulation and the preservation of the organic matter and consequently the development of locally euxinic conditions in the bottom waters. The generative petroleum potential (S1 + S2) of the upper Barremian and Cenomanian–Turonian studied organic-rich strata is good to very good and appears to be moderate for the Albian organic-rich deposits. The n-alkane distributions of the Cretaceous source rocks are typical for a marine planktonic origin. The Pristane/Phytane ratio indicates a sub-oxic depositional environment for the upper Barremian and Albian successions and a sub-oxic to anoxic environment for the Cenomanian–Turonian organic-rich strata. Regarding the maturity degree of the three studied organic-rich strata, only the upper Barremian source rock presents a high maturity level with Tmax values ranging from 441 °C to 448 °C, which indicates that the deposits have been deeply buried and consequently have generated hydrocarbons that have been recognized in the studied oil seep. The integration of our results with available data of Tmax values on other outcrops in the salt dome zone allowed drafting a maturity trend of the studied source rocks. A general northeast–southwest trend of maturity increase is observed with Tmax values varying from 436 to 446 °C.

Late Cretaceous Syn-depositional mass transport deposits in the turbidites of Zagros Orogenic belt: examples in the Maastrichtian Tanjero formation, Kurdistan region, NE-Iraq

In the northeast Iraq, the Maastrichtian turbidite deposits, as a Tanjero Formation, consist of very thick succession of sandstones, conglomerates, and calcareous shales. It deposited in a deep and coastal areas of the Early Zagros Foreland basin which is generated after the radiolarites and limestone obductions during Maastrichtian. The foreland basin was bounded from northeast by newly uplifted and highly elevated active terrestrial land from which voluminous amount of the siliciclastic sediments and carbonates transported to the different parts of the foreland basin. In the studied area, two types of lenticular bodies of synsedimentary mass transport deposits (MTDs) are recorded in the turbidite succession and studied in three outcrop sections about 70 km far from each other. The first type is deposits of coarse grain debris flow, characterized by bad sorting, mud supporting, chaotic internal structures, and bearing angular blocks of olistoliths which reveal instable tectonic setting of the basin. The second is Maastrichtian slump debris within sandstone bedsets (succession) which are extremely deformed, wildly fragmented to blocks of olistoliths and boulders. These deformed bedsets are squeezed between intact and unreformed strata of the lower part of the Tanjero Formation. The slump deposits contain folded sandstone beds and their attitudes indicate, on the stereonet, the southwest transport of the slump deposits. This direction is detected from trends of four fold axes included in the slump debris. The fold axes are extending northeast-southeast which indicate the gravitation stress was in the southwest direction. This study includes a first record of the catastrophic submarine coarse grain debris flow, slumping, and olistolith deposition in the Zagros orogenic belt that uncovers important tectonic setting processes and paleogeographic configuration of the Zagros Collisional Belt during Maastrichtian.

Synsedimentary tectonics vs paleoclimatic changes across the Aptian-Albian boundary along the Southern Tethyan margin: The panormide carbonate platform case history (NW Sicily)

The Aptian-Albian boundary is a deeply investigated time interval on the basis of the deep oceanographic, environmental and climatic changes, globally recorded along the sedimentary rock successions.A regional latest Aptian extensional pulse in the Southern Tethyan margin is here envisaged as being responsible for different events of sedimentation and erosion in the Panormide carbonate platform as highlighted by the outcropping sections studied from the NW Sicilian fold and thrust belt.Integrating facies and stratal pattern analysis with backstripping methods has permitted to define the interaction between tectonics and sedimentary factors of the Lower Cretaceous shallow-water carbonates.Based on geometric configuration, lateral facies relationships, and thicknesses variations of the Lower Cretaceous Requienid limestone, is here envisaged a paleophysiography characterised by banks separated by deep channels. The margins of the isolated carbonate platform were oriented towards both the present-day west, where originally the Cala Rossa intraplatform basin developed driven by transtensional movements, and to the present-day east, where the continental slope was spreading.Including subsidence analysis and significance of the top-unconformity of the Requienid limestone a tectonic event at the end of the Aptian was detected as responsible for the fragmentation of the platform in various rotating fault-blocks and reworking of shallow-water carbonates towards the slope. The variable subsidence rates correspond to the different responses, both emersion and drowning, of the various platform-blocks to the extensional tectonics.Paleoceanographic changes, detected around the world during the Aptian-Albian, are well recorded also from the Sicilian sections, where continental clays – as the product of weathering of crystalline rocks – metallic crusts (hardgrounds) and condensed phosphatized pelagic deposits – as the product of sediment starvation, condensation and drowning – cover the Lower Cretaceous shallow-water carbonates respectively in the different faulted blocks of the segmented carbonate platform. Chemical and mineralogical analyses confirm for these deposits an influence in their formation caused by variations in oceanographic and environmental conditions, as increasing of metal ions in the surficial sea-water and high rates of groundwater precipitation. Paleoclimate evaluation reveals changes from the greenhouse arid conditions, developed during the lower Cretaceous and permitting the sedimentation of the shallow-water carbonates, to warm-humid climate condition during the latest Aptian-lower Albian boundary.

Porosity distribution in cyclic dolomites of the Lower Qiulitag Group (Upper Cambrian) in northwestern Tarim Basin, China

ABSTRACT Increasing interests in hydrocarbon resources at depths have drawn greater attentions to the deeply-buried carbonate reservoirs in the Tarim Basin in China. In this study, the cyclic dolomite rocks of Upper Cambrian Lower Qiulitag Group from four outcrop sections in northwestern Tarim Basin were selected to investigate and evaluate the petrophysical properties in relation to depositional facies and cyclicity. The Lower Qiulitag Group includes ten lithofacies, which were deposited in intermediate to shallow subtidal, restricted shallow subtidal, intertidal, and supratidal environments on a carbonate ramp system. These lithofacies are vertically stacked into repeated shallowing-upward, meter-scale cycles which are further grouped into six third-order depositional sequences (Sq1 to Sq6). There are variable types of pore spaces in the Lower Qiulitag Group dolomite rocks, including interparticle, intraparticle, and fenestral pores of primary origin, inter crystal, and vuggy pores of late diagenetic modification. The porosity in the dolomites is generally facies-selective as that the microbially-originated thrombolites and stromatolites generally yield a relatively high porosity. In contrast, the high-energy ooidal grainstones generally have very low porosity. In this case, the microbialite-based peritidal cycles and peritidal cycle-dominated highstand (or regressive) successions have relatively high volumes of pore spaces, although highly fluctuating (or vertical inhomogeneous). Accordingly, the grainstone-based subtidal cycles and subtidal cycle-dominated transgressive successions generally yield extremely low porosity. This scenario indicates that porosity development and preservation in the thick dolomite successions are primarily controlled by depositional facies which were influenced by sea-level fluctuations of different orders and later diagenetic overprinting.

Petrography and stable oxygen and carbon isotopic composition of the Antalo Limestone, Mekelle Basin, Northern Ethiopia: implications for marine environment and deep-burial diagenesis

The depositional environment of the Antalo Limestone was previously interpreted from regional field-based studies and microfacies. However, stable oxygen and carbon isotopes are also invaluable proxies of paleo-environmental conditions, depositional, and diagenetic environments. Hence, the analyses of stable oxygen and carbon isotopic composition of this unit were examined from bulk limestone samples and integrated with a detailed petrographic study to interpret depositional environments and diagenetic evolution. The samples were collected from three outcrop sections, which together represent the full thickness of the unit. The microfacies identified from these samples indicate shallow–deep marine depositional as well as meteoric phreatic, marine phreatic, and deep burial diagenetic environments. The limits of variations of the oxygen isotopic ratios range from − 10.46 to − 3.56‰, with − 6.07‰ mean value. The limits of variations of the carbon isotopic ratios range from − 0.02 to 2.56‰, with 1.4‰ mean value. The calculated z values range from 123.08 to129.7 and the paleo-temperatures are estimated to be 32.4–73.52 °C, with an average temperature of 46.5 °C. The carbon isotope ratios indicate marine-water sources. This was confirmed from z values (> 120), indicating that the samples are marine carbonates. The depleted oxygen isotope ratios and high-temperature values, on the other hand, represent deep-burial diagenesis, which indicates the isotopic composition and the temperature conditions of the cement precipitating diagenetic fluids. The compositional fields of the δ18O–δ13C cross plots, also indicate marine carbonates subjected to mixing zone–deep-burial diagenesis. Therefore, both the petrographic and stable oxygen and carbon isotopic evidences are mutually in agreement, indicating related depositional and diagenetic environments.

Outcrop and thin section scale descriptions of Silurian carbonates within the Hiawatha National Forest, Mackinac County, Upper Peninsula, Michigan, USA

Silurian carbonate outcrops within the southern part of the St. Ignace District of the Hiawatha National Forest (Mackinac County, Michigan) were examined to develop a local description of the exposed geology. The bedrock geology consists of the Manistique Group (dominantly the Cordell Formation) and the Engadine Group (Rockview Formation, Rapson Creek Formation, and Bush Bay Formation). Building on observations and differentiation from previous investigations, outcrops were selected to describe the macroscopic characteristics of these formations in attempt to develop a local description that would be more useful compared to confusing regional descriptions for researchers and forest officials. In Mackinac County, the Cordell Formation is a dark-to-light gray, chert-rich dolostone with abundant corals, stromataporoids, brachiopods, and echinoids. The Rockview Formation is a dark gray-to-white, chert-poor dolostone with microbiolite laminations, and brachiopod molds. The Rapson Creek Formation is a light gray-to-white, chert-free dolostone with abundant stromatoporoids. The Bush Bay Formation is light reddish brown to white in color, chert-poor, crystalline dolostone with abundant echinoids, brachiopods, and corals.

Holocene lake level, vegetation, and climate at the East Asian summer monsoon margin: A record from the Lake Wulanhushao basin, southern Inner Mongolia

Understanding the impact of Holocene climate variations in arid northern China will provide important insights into a better prediction of future water availability in this region. In this study, we present paleoenvironment data from the lacustrine-aeolian deposit sections and a lake sediment core from the Lake Wulanhushao basin, southern Inner Mongolia. Optically Stimulated Luminescence dating and elevation measurements on the outcrop sections provide an estimation of lake-level changes for the past 10.1 kyr. For the sediment core, multi-proxy analyses of pollen, grain size, loss-on-ignition, element, and chroma were undertaken. The pollen result indicates a tendency of moisture increase from 10.6 to 9.1 cal kyr B.P., providing moderate conditions for the gradual expansion of trees in the mountains. The highest moisture availability was reached from 9.1 to 5.6 cal kyr B.P. leading to the maximal arboreal extent. After then, aridification in the region was evidenced by the declined trees and the increase of desert components. Comparing with the pollen result, non-pollen proxies from the lake sediment core and the outcrop sections indicate a slightly different climate pattern. That is, the initiation of Holocene climate optimum in the lake catchment, suggested by a high lake level, increased biological production, and an enhanced chemical weathering occurred about 1.5 kyr earlier than the arboreal expansion in the distal mountains. While the climate patterns were more or less consistent as inferred from the lacustrine pollen records at the East Asian Summer Monsoon margin, catchment-specific responses to regional climate variations might explain this perplexing discrepancy between pollen and non-pollen proxies. Our study emphasizes the importance of multi-proxy analyses from various perspectives when investigating the local and regional responses to Holocene climate variations.

A generalized model for quantitative analysis of sediments loss: A Caputo time fractional model

Sediment loss is an indispensable geological phenomenon that determines the reduction of mass in time interval with the differential influence of controlling factors. In this study, the competence of rocks is considered as a controlling factor while weathering and erosion are termed as the decaying parameter. Attributed to the reduction of the total mass in unit time. A mathematical model is [proposed for the above-mentioned phenomenon and generalized using the Caputo fractional derivatives approach to better understand and predict the sediment loss. The model is solved for exact solutions using the Laplace transform technique. The results obtained for β and -β are in strong agreement with the field images of selected outcrop sections. The memory effect is also shown with different values of αThe results revealed that the mathematical model better explains the geological processes.

Palynostratigraphy and lithostratigraphy of Upper Cretaceous and Paleogene outcrop sections, Mérida Andes (Maracaibo Basin), Western Venezuela

Detailed palynologic and lithostratigraphic studies of outcrop sections on the western flank of the Mérida Andes in Western Venezuela were undertaken to establish a framework for interpreting and correlating regional and local unconformities from the outcrop to subsurface data. The Upper Cretaceous to lower Paleogene section of the Maracaibo Basin consists of laterally continuous rock units attributed to the Mito Juan and Barco/Catatumbo formations, which are characterized by marine sediments deposited relatively close to shore. The continuity of plant and dinoflagellate species across the Cretaceous-Paleogene boundary in this area may have potential significance to K/Pg studies elsewhere. The lower to upper Paleogene Los Cuervos, Mirador, and Carbonera formations were predominantly deposited in non-marine environments, though palynologic and stratigraphic data from each unit show the variable influence of marine and lacustrine conditions. A new chronostratigraphic framework for the study area (the “Venezuelan Composite Standard”) was developed based on first and last appearances of spores, pollen, and dinoflagellates, and three pollen acme events and calibrated to the latest time scale. Graphic correlation plots of the most complete outcrop sections at Río Lobaterita, Río Lora, and Río Chama indicate the presence of significant hiatuses in time, due to erosion and non-deposition (or a combination of the two) reflecting the complex structural and depositional history of the southeastern Maracaibo Basin. A regionally significant upper Paleocene to lower Eocene unconformity, as well as several local and regional intra middle Eocene unconformities appear to have been caused by a drop in base level (sea level plus structural uplift) forming incised valleys over much of the study area. Unconformities are also present in the upper middle Eocene to Oligocene and represent ravinement surfaces caused by transgressive marine reworking of pre-existing units. These surfaces are often marked by the presence of dinoflagellates within the upper Eocene Carbonera Formation. Depositional environments during much of the Upper Cretaceous to Paleogene succession vary from fluvial-floodplain to marginal marine, with newly noted periods of widespread lacustrine deposition in all geologic units. Temporal differences between similar Paleogene lithostratigraphic units in northeastern Colombia and southwestern Venezuela are likely due to the influence and timing of structural events on regional and local depositional environments.

Early Miocene palaeoflora and palaeoecology of the Soma Basin, Western Turkey

In this study comprehensive palaeofloristic data of lower Miocene deposits from the Soma Basin, western Anatolia is presented considering the stratigraphical concept. The sediments of the basin, derived from outcrop sections, were deposited in the terrestrial environment. The basin includes three different successions: lower and middle lignite successions of the Soma Formation and upper lignite succession of the Denis Formation. In this paper, we address the early Miocene palaeoecology via pollen and leaf assemblages from the Soma Basin, dated precisely using radiometric data. High percentages of Cupressaceae in the lower lignite succession of the Soma Formation, and minor quantities of elements such as Carya, Nyssa, Myrica, Ulmus and Salix reflect a local riparian and swamp vegetation. Marls overlying the lower lignite succession represent an environment close to the source area, with a variety of flora. During the deposition of middle lignite succession wet conditions played an essential role in the swamp forest fostering some distance transport of pollen which reflect the mesophytic forest vegetation as well as higher altitudes in the hinterland. The high percentages of lacustrine plankton Botryococcus and presence of Spirogyra in the upper lignite succession of the Denis Formation imply a shallow water environment with less rainfall surrounded by evergreen and deciduous mixed forest.