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Copyright of Acta Sedimentologica Sinica is the property of Acta Sedimentologica Sinica Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of the Sedimentological Society of Japan / Taisekigaku Kenkyu is the property of Sedimentological Society of Japan and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Ulban terrane composed of a thick sedimentary series of Jurassic clastic deposits is located at the junction of the Mongol-Okhotsk and Sikhote-Alin orogenic belts. The results of studying the deposits assigned to the Middle Jurassic Elgon Formation are presented. The structure of the sedimentary succession and sedimentological features, which indicate sand-rich turbidite sedimentation in a setting of sandy lobe of turbidite fans or ramps, are considered and illustrated. The paleocurrent directions measured in outcrops and calculated using the anisotropy of the initial magnetic susceptibility suggest the transport of clastic material from western or southwestern sources. [ABSTRACT FROM AUTHOR]

The geologic history of Wyoming's Hanna Basin is still being written. Surprisingly, here appeared an opportunity to share insights from previously accomplished work with that conducted anew by other scholars. The area of study was in the southeastern quadrant of Wyoming, which exhibits the state's most complex history with respect to the Laramide orogeny. Especially important for present purposes were the tectonic conditions of the late Paleocene and earliest Eocene, recorded within the Hanna Formation. Of central focus is the 2020 publication by Dechesne and her six co-authors. Geographically, the landscape they covered was a thin, synclinal slice of the northeastern margin of the Hanna Basin. Key goals for the present publication have been to illustrate positive linkages and to highlight discrepancies between Dechesne et al. (2020) and relevant prior geological work. A concern that permeates all facets of this approach is the ability to verify viability of brand-new geologic descriptions, data, and resulting conclusions. Essential graphical elements were introduced first into this present publication. Once that package of background information was available, more focused analyses were rigorously pursued on diverse issues within the Dechesne et al. (2020) publication. Dechesne's team presented a significantly modified but adequately defended approximation of the Paleocene-Eocene boundary. Data from fossil plants (macro-and palynofloras), continental mollusks, and bulk organic-carbon isotopes all agree within one measured section (of five sections studied) with an approximated Paleocene-Eocene boundary along with a 'carbon isotope excursion' (CIE). Strength of available evidence seems questionable, however, in that the inordinately high variability in bulk organic carbon (characteristic of a CIE) has been demonstrated only in the Hanna Draw Section. Although fluvial, paludal, and lacustrine facies are considered in several contexts, in no sense does the publication's organizational form provide a 'detailed stratigraphic framework.' One zircon-based U-Pb depositional date (54.42 ±0.27 Ma) came from this study that matched early Wasatchian time. Participants in the Dechesne et al. (2020) project are to be commended in that their resulting paper ranged broadly across the geologic setting, stratigraphy, paleocurrents, paleobotany, continental mollusks, zircon geochronology, associated lithofacies, and paleogeography. Despite that breadth, there exists a plethora of unexpected and wholly avoidable inconsistencies, strong contradictions within what should be homogeneous datasets, and seemingly inexplicable omissions of obviously necessary and sometimes clearly existing but unutilized data, one must question the reliability of much of the information presented in their paper. [ABSTRACT FROM AUTHOR]

Copyright of Boletin de Geologia is the property of Universidad Industrial de Santander and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rivers with little to no influence of vegetation and their implications for the architecture of Early Paleozoic and Precambrian fluvial deposits are an important topic of investigation for both clastic sedimentology and Earth System evolution perspectives. Despite the long‐held concept of a dominant style of wide, shallow sheet‐braided sandy channels, growing evidence for a great variability of architectural elements in pre‐vegetation settings point to the predictable occurrence of other fluvial styles, which are possibly related to areas of low‐slope alluvial plains. The present work brings sedimentological descriptions and fluvial style interpretations of Silurian fluvial successions of the Serra Grande Group in northeastern Brazil, developed in a glaciated basin margin (therefore with little to no effect of vegetation). The comparison of the resulting channel body architectures integrated to paleocurrent data and a diffusion‐based numerical model enabled the evaluation of the controls on fluvial architecture variability in unvegetated alluvial plains. [ABSTRACT FROM AUTHOR]

Upper Neoproterozoic to lower Paleozoic sedimentary successions in northwestern India are thought to record collision between the continental fragments of Western and Eastern Gondwana, and contain detritus derived from the East African orogen. However, paleocurrent analysis together with U-Pb age distribution and Hf isotopic signatures of detrital zircons from these successions indicate derivation from proximal sources within Eastern Gondwana. Time-equivalent successions from the Qiangtang terrane (Tibetan Plateau) and the northern margin of Neoproterozoic India show a similar provenance record, along with additional input of late Mesoproterozoic and Neoproterozoic detritus from East Antarctica-East India and West Australia. Detritus from the rising East African orogen is abundant in deposits in northern Africa, which constitutes part of Western Gondwana, but absent from equivalent successions in Indian Eastern Gondwana. The consistency in sedimentary provenance of the late Neoproterozoic to early Paleozoic strata in northwestern India, combined with the lack of evidence for deformation or metamorphism since at least ca. 760 Ma, argues against collision between the eastern and western segments of Gondwana in this northern region. These regions remained as passive continental margins separated by a large-scale embayment of the proto-Tethys ocean until late Paleozoic fragmentation of the continental blocks. [ABSTRACT FROM AUTHOR]

Abstract This is the first work focusing on the provenance of Middle Devonian-Early Carboniferous sandstones in the eastern margin of the Parnaíba basin. This sedimentary succession represents the main petroleum system in this basin and is composed, from base to top, of the Itaim, Pimenteiras, Cabeças, Longá and Poti Formations of the Canindé Group. The internal textures and U Pb analyses of detrital zircons allowed defining potential source areas for the sediments of this group. A global tendency of sea level rise in the Middle Devonian, in the evolutionary context of West Gondwana, resulted in the establishment of epicontinental seas and deposition of transgressive sedimentary sequences. Shales and sandstones of the Pimenteiras Formation represent extensive records of these Devonian seas on this paleocontinent. This succession provides zircon ages from 3443 to 438 Ma. Detrital zircons with ages of 538–486 Ma are the most abundant, suggesting derivation mainly from nearby younger sources in the Southern subprovince of the Borborema or Tocantins provinces. The transition between the Middle Devonian and Mississippian Periods is marked by progressive retreat of epicontinental seas with minor marine incursions (represented by the Longá Formation) and resulted in the continental deposits of the Cabeças and Poti Formations. Paleocurrent patterns in both formations suggest direct derivation from the Borborema province. The Cabeças, Longá and Poti Formations contain numerous zircons with ages ranging from 999 to 722 Ma. This detrital population indicates derivation from rocks formed during the Cariris Velhos event in the central portion of the Borborema province. The Cabeças Formation also provided an extensive number of zircons with ages ranging from 2034 to 1830 Ma. Further, the studied geologic units, except for the Pimenteiras formation, show detrital contingents with ages of 1.0–1.2 Ga, also suggesting provenance from distal areas. However, as the spectrum of zircon ages of the Canindé Group is similar to that of the Brasiliano belts surrounding the Parnaíba basin, these belts may also be considered candidates to provide sediments for the Middle Devonian-Early Carboniferous deposits. Highlights • The Brasiliano belts of southern Borborema subprovince, may be considered the mainly candidate to provide sediments for the Middle Devonian-Early Carboniferous deposits. • Pimenteiras Formation display a essentially unimodal pattern, suggesting derivation also from Brasilia belt or reworking of the cratonic basins of the São Francisco craton. • Did the Cariris-Velhos event exclusively contribute to the Stenian-Tonian zircon age spectra found in the Parnaíba basin? [ABSTRACT FROM AUTHOR]

The Lower and Upper Cretaceous turbidites cover large areas in the central Pontides (north‐central Turkey). The Lower Cretaceous turbidites are over 2 km thick and are exposed in an area of 400 × 90 km. The Upper Cretaceous (Campanian‐Maastrichtian) forearc turbidites are up to 1,200 m thick and crop out in NW‐SE trending elongate basins about 40 km wide, extending along the central and eastern Pontides. We present new detrital zircon U–Pb ages, petrography, and paleocurrent measurements from the Campanian‐Maastrichtian turbidites and compare them to those from the Lower Cretaceous turbidites. The Campanian‐Maastrichtian sandstones are dominated by carbonate and magmatic lithic grains. The paleocurrents indicate paleoflow directions parallel to the axis of the basin. The sandstones are dominated by Late Cretaceous zircons indicating derivation mainly from the coeval magmatic arc. In contrast, the Lower Cretaceous sandstones are dominated by quartz and feldspar, and paleocurrents indicate southward transport. The detrital zircons in the Lower Cretaceous sandstones are mainly Archean and Paleoproterozoic, indicating that in the Early Cretaceous, the source of turbidites was from the Archean‐Paleoproterozoic Ukrainian Shield to the north. After the opening of the Black Sea in the Late Cretaceous, the connection between the Pontides and the East European Platform was severed and the Campanian‐Maastrichtian turbidites were sourced principally from the magmatic arc in the Pontides. Our results indicate that the Campanian‐Maastrichtian turbidites represent the first turbiditic sequence deposited after the opening of the Black Sea. Key Points: U–Pb detrital zircon ages and paleocurrent measurements from the Campanian‐Maastrichtian turbidites of the central Pontides, TurkeyA drastic change in the provenance of the Cretaceous turbidites of the central Pontides trigged by the opening of the Black SeaPrerift sandstone were sourced by the Ukrainian Shield; postrift sandstones were mostly sourced by the coeval Pontide magmatic arc [ABSTRACT FROM AUTHOR]

Abstract The Tibetan Plateau offers an example for understanding the processes of continental collision and subsequent intracontinental deformation. The Jiuxi Basin, located at the northeastern margin of the plateau, bears crucial information on the growth processes of the NE Tibetan Plateau. Combined with published magnetostratigraphic constraints, integration of stratigraphic investigation and detrital zircon geochronological analysis on the sediments of the Cenozoic Hongliuxia section in western Jiuxi Basin suggests a major reorganization of the basin infill process at the period between depositions of the Baiyanghe and Shulehe formations at ~17 Ma. This finding is documented by (1) a generally upward-thinning sequence followed by an upward-coarsening sequence with corresponding changes in sedimentary facies, (2) shifting of the paleocurrent from the south to the north, and (3) shifting of the provenance from the Bei Shan-Kuantan Shan-Hei Shan in the north to the North Qilian Shan in the south. These results suggest that tectonic deformation arrived in the North Qilian Shan by ~17 Ma and lend support to the outward-growth model for the Tibetan Plateau. Highlights • Reorganization of basin infill process in the western Jiuxi Basin at ~17 Ma. • Indication that convergence-related deformation arrived in North Qilian Shan. • Support for the outward-growth model of the NE Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Abstract Ten wells (EW-4, EW-5, EW-6, EW-7, EW-8, EW-9, EW-10, EW-12, EW-13 and EW-15) were interpreted using the composite well logs, data of core analysis, gamma-ray logs, formation micro-imager logs (FMI), and 3D seismic data in SEGY format to understand the stratigraphy of the onshore, Nile Delta, Egypt. The amplitude analysis of 3-D seismic horizon slice of Lower Abu Madi rock unit together with the lithostratigraphic correlation through the study area depending on the gamma-ray log "HSGR" (left to right increasing), and the identification of type of bed geometry, nature of bed contacts, type of the sedimentary structures and the dominant formative paleocurrents by using some available borehole micro-resistivity images (FMI) and core photos. All of these techniques are used together to define the different depositional facies and depositional environment of the Messinian clastics (Lower Abu Madi rock unit), which is considered to be the main reservoir in the El-Wastani gas field, onshore Nile Delta, Egypt. The present study of depositional pattern of the Upper Miocene clastics reservoir (Lower Abu Madi rock unit) revealed that it is represented by high sinuous meandering channels or paleo-valley and three types of fluvial facies were defined; channel fill, channel margin, and floodplain basin. [ABSTRACT FROM AUTHOR]

Mesozoic thrusting within the Yanshan fold-and-thrust belt of North China resulted in a series of fault-bounded intramontane basins whose infill and evolution remain poorly understood. In particular, the bounding faults and adjacent sediment accumulations along the western segments of the belt are almost unstudied. A sedimentological and provenance analysis of the Lower Jurassic Xiahuayuan Formation and the Upper Jurassic Jiulongshan Formation have been mapped to show two distinctive clastic wedges: an early Jurassic wedge representing a mass-flow-dominated, Gilbert-type fan delta with a classic tripartite architecture, and an late Jurassic shoal-water fan delta without steeply inclined strata. The basinward migration of the fan-delta wedges, together with the analysis of their conglomerate clast compositions, paleocurrent data and detrital zircon U-Pb age spectra, strongly suggest that the northern-bounding Xuanhuan thrust fault controlled their growth during accumulation of the Jiulongshan Formation. Previous studies have suggested that the fan-delta wedge of the Xiahuayuan Formation was also syntectonic, related to movement on the Xuanhua thrust fault. Two stages of thrusting therefore exerted an influence on the formation and evolution of the Xiahuayuan basin during the early-late Jurassic. [ABSTRACT FROM AUTHOR]

The start of Nile-type trans-Saharan drainage systems in NE Africa during the Cenozoic is disputed. Stratigraphical and sedimentological data in Egypt are partly in conflict with the uplift history of potential source areas of water and sediment in East Africa. Here, we investigate outcrops of the Wadi Awatib Conglomerate in Sudan that provide the first evidence of northerly flowing Neogene rivers in the region. Dimension and relief of basal erosion surfaces, overall geometry of deposits and palaeocurrent indicators demonstrate that the deposits represent the fill of northward-oriented incised valleys. The conglomerates were deposited in deep gravel-bed rivers, by hyperconcentrated flows, tractions carpets and gravel bars, primarily during heavily sediment-laden floods of probably monsoonal origin. Stratigraphical and geomorphological relationships show that the deposits are between Eocene and Pliocene in age. Considering the structural history of the region and periods in the Cenozoic with palaeoclimatic conditions suitable for the production and transport of gravels, we hypothesize that the dramatic base-level fall during the Late Miocene Messinian salinity crisis in combination with a favorable palaeoclimate caused the incision of valleys and their subsequent filling with conglomerates. Sea-level change in the Mediterranean Sea and headward erosion of streams that were connected to the Egyptian Nile might have been the primary cause of valley incision and deposition of conglomerates, despite a location far inland from the coastline. We suggest that the deposits document a relatively young Neogene (Messinian to early Pliocene) trans-Saharan river system unrelated to uplift of the Ethiopian Plateau. [ABSTRACT FROM AUTHOR]

Records from cores 2011031-059 and 2011031-062 (hereafter 59 and 62) have been used to reconstruct changes in the vigor of the Labrador Current in northern Flemish Pass during the last glacial cycle. Grain size proxies for current speed, planktonic foramiferal δ 18 O, X-ray diffraction analysis for dolomite and calcite, and abundance of ice-rafted detritus (IRD) have been determined. An age model back to Marine Isotope Stage (MIS) 5 is based on recognition of seven Heinrich events from total dolomite and calcite, correlated to the IODP U1302/3 record, and confirmed by O-isotope stratigraphy and radiocarbon dates. A straight-line relationship between mean size of sortable silt ( SS ¯ ) and percent of sortable silt (SS%) and the lack of relationship between SS ¯ and IRD (> 500 μm) indicate well-sorted sediments in cores 59 and 62, which can be used to reconstruct the paleocurrent intensity. Intensified current vigor occurred in MIS 5, 3 and 1, so that warmer periods show faster currents, probably through the Irminger Current component of the North Atlantic subpolar gyre. Low values of δ 18 O, SS% and SS ¯ correspond to H events, suggesting a slowdown in the Labrador Current, followed by a rapid return to strong circulation. In some cases current vigor recovery lagged slightly after the H events. Heinrich events with larger amounts of meltwater show higher current vigor. Correlation with deep-water current vigor records in the Iceland Basin show a broad correlation on a multi-millennial scale with Labrador Current variations. As our study is on a shallow sediment drift formed by the Labrador Current, one of the surface currents of the North Atlantic sub-polar gyre, it provides new evidence for a tight connection between surface current vigor fluctuation and the vigor of the deep thermohaline circulation. [ABSTRACT FROM AUTHOR]

Copyright of Mineralia Slovaca is the property of State Geological Institute of Dionyz Stur and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Geologic events related to the opening of the South Atlantic Ocean deeply influenced the sedimentary record of the Araripe Basin. As consequence, upper stratigraphic units of the basin record a marine ingression in northeastern Brazil during the late Aptian. The timing and stratigraphic architecture of these units are crucial to understand the paleogeography of Gondwana and how the proto-Atlantic Ocean reached interior NE Brazil during the early Cretaceous. This marine ingression is recorded in the Araripe Basin as the Romualdo Formation, characterized by a transgressive-regressive cycle bounded by two regional unconformities. In the eastern part of the basin, the Romualdo depositional sequence comprises coastal alluvial and tide-dominated deposits followed by marine transgressive facies characterized by two fossil-rich intervals: a lower interval of black shales with fossil-rich carbonate concretions ( Konservat-Lagerstätten ) and an upper level with mollusk-dominated shell beds and shelly limestones. Following the marine ingression, an incomplete regressive succession of marginal-marine facies records the return of continental environments to the basin. The stratigraphic framework based on the correlation of several sections defines a transgressive-regressive cycle with depositional dip towards southeast, decreasing in thickness towards northwest, and with source areas located at the northern side of the basin. The facies-cycle wedge-geometry, together with paleocurrent data, indicates a coastal onlap towards NNW. Therefore, contrary to several paleogeographic scenarios previously proposed, the marine ingression would have reached the western parts of the Araripe Basin from the SSE. [ABSTRACT FROM AUTHOR]

Up to 12% of the mud-prone, ephemeral distributive fluvial system stratigraphy in the Permo-Triassic lower Beaufort Group, South Africa, comprises tabular fine-grained sandstone to coarse-grained siltstone bodies, which are interpreted as proximal to distal crevasse splay deposits. Crevasse splay sandstones predominantly exhibit ripple to climbing ripple cross-lamination, with some structureless and planar laminated beds. A hierarchical architectural scheme is adopted, in which ~ 1 m thick crevasse splay elements extend for tens to several hundreds of meters laterally, and stack with other splay elements to form crevasse splay sets up to 4 m thick and several kilometers in width and length. Paleosols and nodular horizons developed during periods, or in areas, of reduced overbank flooding are used to subdivide the stratigraphy, separating crevasse splay sets. Deposits from crevasse splays differ from frontal splays as their proximal deposits are much thinner and narrower, with paleocurrents oblique to the main paleochannel. In order for crevasse splay sets to develop, the parent channel belt and the location where crevasse splays form must stay relatively fixed during a period of multiple flood events. Beaufort Group splays have similar geometries to those of contemporary perennial rivers but exhibit more lateral variability in facies, which is interpreted to be the result of more extreme fluctuations in discharge regime. Sharp-based crevasse splay packages are associated with channel avulsion, but most are characterized by a gradual coarsening upward, interpreted to represent progradation. The dominance of progradational splays beneath channel belt deposits may be more characteristic of progradational stratigraphy in a distributive fluvial system rather than dominated by avulsion processes in a trunk river system. This stratigraphic motif may therefore be an additional criterion for recognition of distributive fluvial systems in the ancient record. [ABSTRACT FROM AUTHOR]

The publication of the comments by Vesely & Schemiko (Comment on “From source-to-sink: The Late Permian SW Gondwana paleogeography and sedimentary dispersion unraveled by a multi-proxy analysis” by L. Alessandretti, R. Machado, L.V. Warren, M.L. Assine and C. Lana [Journal of South American Earth Sciences 70 (2016) 368–382], Journal of South American Earth Sciences, this issue) on our paper entitled “From source-to-sink: The Late Permian SW Gondwana paleogeography and sedimentary dispersion unraveled by a multi-proxy analysis” (L. Alessandretti, R. Machado, L.V. Warren, M.L. Assine and C. Lana (Journal of South American Earth Sciences 70 (2016) 368–382) provides a worthy opportunity to further clarify our observations and interpretations regarding the provenance of the Late Permian Rio do Rasto Formation and its implications on SW Gondwana paleogeography and sedimentary dispersion. [ABSTRACT FROM AUTHOR]

Sedimentary structures are very useful in paleocurrent analysis and interpretation of siliciclastic shallow marine environment. These interesting sedimentary structures such as parallel bedding, cross bedding, ripples, and mud cracks as well as synaeresis cracks, are best studied in the field. They are formed by a variety of sedimentary processes, including fluid flow, sediment-gravity flow, soft-sediment deformation and biogenic activity. Gulcheru Formation has evidence of interaction of microbial communities with clastic sedimentation during Palaeoproterozoic time. Because of high porosity-permeability of siliciclastics of Gulcheru Formation, palaeontologists do not expect many fossils preserved in such rocks and thus they have been overlooked. Microbially induced sedimentary structures (MISS) are highlighted in the Gulcheru Formation. They are indicative of shallow marine environment. Gulcheru Formation shows alluvial fan to shallow marine shelf environments within a limited thickness of about ~ 110m, which indicates an alluvial plain coast where alluvial deposits are modified by wave forces. [ABSTRACT FROM AUTHOR]

Planktonic foraminiferal and ice-rafted debris count data, as well as the mean size of mineral particles of the 10-63 μm fraction (sortable silt, $$\overline {SS} $$ ) were used as a proxy for surface and near-bottom paleocurrent intensity variations. The data obtained support our hypothesis about turbiditic origin of the lower (80-370 cm) section of the studied AMK-4515 core. Stratigraphic subdivision of the upper section (0-80 cm) makes it possible to allocate two marine isotope stages (MIS) covering the last 27 ka. The main intervals of the North Atlantic Polar Front (PF) migrations were recorded: south of the modern PF position during early MIS 2 (24-27 ka) with PF presence in the study area during MIS 2 (20-24 ka); south of the study area during the last glacial maximum (18-20 ka). Influence of the near-bottom currents within the investigated interval led to beginning of the channel-related drift formation on the northern slope of the southern channel of the Charlie-Gibbs Fracture Zone. There is a weak relationship between intensity of near-bottom contour currents and long-term climatic cyclicity. However, intervals corresponding to Heinrich events coincide with decrease in bottom currents activity. [ABSTRACT FROM AUTHOR]

The most complete Permian-Triassic Gondwana succession in Antarctica crops out in the central Transantarctic Mountains. The lower Permian strata were deposited in an intracratonic basin that evolved into a foreland basin in late Permian time. Sedimentary petrology and paleocurrent data have been interpreted as indicating a granitic (craton) provenance and a West Antarctic volcanic provenance. To address the West Antarctic provenance and evolution of the detrital input, detrital-zircon grains from nine sandstones (plus three sandstones reported previously) representing the full extent of the Permo-Triassic succession exposed on that flank of the basin, have been analyzed by sensitive high-resolution ion microprobe. Results define three provenances: an early (early to middle Permian) provenance that is dominated by zircons having Ross orogen ages (600-480 Ma); a middle (late Permian) provenance dominated by Permian zircons with subordinate older magmatic arc grains plus lesser Ross orogen-age grains; and a late (Triassic) provenance, which is quite variable and in which the predominant Triassic arc component ranges from very minor to significant and again with a component of Ross orogen-age grains. Detrital zircons imply a more extensive Permo-Triassic arc, in time and space, on the Gondwana margin than is evident from outcrop data. The zircon data are integrated into a model for basin evolution and infilling, providing broad constraints on the timing of tectonic events and the provenance. [ABSTRACT FROM AUTHOR]

Antarctic Intermediate Water (AAIW) is an essential component of the Atlantic meridional overturning circulation (AMOC) contributing to balance the southward flow of North Atlantic Deep Water (NADW). However, the role of AAIW in Holocene abrupt climate changes remains poorly understood. Here we reconstruct changes in the flow strength of AAIW based on a high temporal resolution paleocurrent record from the Southwest Atlantic. Superimposed on a slight increase in AAIW strength at ~ 7 ka BP, a succession of millennial-scale AAIW variations is recognized in our paleocurrent records indicating a highly variable intermediate water circulation throughout the Holocene. Although variations in the strength and position of the Southern Westerlies Winds (SWW) are proposed to greatly influence the formation and circulation of AAIW, we cannot confirm such a potential SWW-AAIW linkage since our records of AAIW flow strength do not correlate to Holocene shifts of the SWW across the Atlantic. However, our data shows a good correspondence with abrupt variations in the AMOC with enhanced (reduced) northward advection of AAIW during periods of reduced (enhanced) NADW circulation. These results provide evidence for a Holocene AAIW-NADW see-saw. Thus, although the exact forcing mechanism remains unresolved, we suggest that Holocene perturbations in AAIW exerted a significant impact on the AMOC. [ABSTRACT FROM AUTHOR]

Facies models for regressive, tide-influenced deltaic systems are under-represented in the literature compared with their fluvial-dominated and wave-dominated counterparts. Here, a facies model is presented of the mixed, tide-influenced and wave-influenced deltaic strata of the Sego Sandstone, which was deposited in the Western Interior Seaway of North America during the Late Cretaceous. Previous work on the Sego Sandstone has focused on the medial to distal parts of the outcrop belt where tides and waves interact. This study focuses on the proximal outcrop belt, in which fluvial and tidal processes interact. Five facies associations are recognized. Bioturbated mudstones (Facies Association 1) were deposited in an offshore environment and are gradationally overlain by hummocky cross-stratified sandstones (Facies Association 2) deposited in a wave-dominated lower shoreface environment. These facies associations are erosionally overlain by tide-dominated cross-bedded sandstones (Facies Association 4) interbedded with ripple cross-laminated heterolithic sandstones (Facies Association 3) and channelized mudstones (Facies Association 5). Palaeocurrent directions derived from cross-bedding indicate bidirectional currents which are flood-dominated in the lower part of the studied interval and become increasingly ebb-directed/fluvial-directed upward. At the top of the succession, ebb-dominated/fluvial-dominated, high relief, narrow channel forms are present, which are interpreted as distributary channels. When distributary channels are abandoned they effectively become estuaries with landward sediment transport and fining trends. These estuaries have sandstones of Facies Association 4 at their mouth and fine landward through heterolithic sandstones of Facies Association 3 to channelized mudstones of Facies Association 5. Therefore, the complex distribution of relatively mud-rich and sand-rich deposits in the tide-dominated part of the lower Sego Sandstone is attributed to the avulsion history of active fluvial distributaries, in response to a subtly expressed allogenic change in sediment supply and relative sea-level controls and autocyclic delta lobe abandonment. [ABSTRACT FROM AUTHOR]

The Late Permian sedimentary succession of the Paraná Basin, southern Brazil, provide a valuable source of information about sediment provenance, tectonic processes and, consequently, the paleogeography of the southwestern Gondwana supercontinent. In order to understand the patterns of sedimentary dispersal and reconstruct the Late Permian source-to-sink dynamic, we report a complete series of U-Pb ages and Hf isotopic compositions of detrital zircons from the Rio do Rasto Formation sandstones allied with detailed paleocurrent and sedimentologic data. Our integrated provenance study reveals a consistent sediment transport from the south to the north and northwest. According to the evaluation of zircon ages and Hf isotopes, it was possible to determine four distinct source areas: (i) a distant Late Paleozoic active magmatic arc located in the southwestern Gondwana margin (i.e. Gondwanides Orogen), corresponding to the North Patagonian Massif; (ii) recycling of orthoquartzites from the uplifted Paleozoic Ventania Fold Belt and immature sandstones from the Claromecó Foreland Basin in central-eastern Argentina and the Silurian-Devonian successions of the southern Paraná Basin (central-northern Uruguay) and North Patagonian Massif; (iii) exhumed areas of the Archean-Paleoproterozoic basement and Neoproterozoic to Early Paleozoic mobile belts of the Damara in southwestern Africa and Ribeira Fold Belt in Uruguay and southern Brazil; and (iv) southeastward provenance of Grenvillian (1.2–1.0 Ga) zircons coming from the mafic to intermediate Mesoproterozoic igneous units of the Namaqua-Natal Belt in South Africa and Namibia. These data allow us to argue that sediments deposited in the Paraná Basin during the Late Permian come from both short- and long-distance source areas. In this context, an important population of Permian detrital zircons comes from the Gondwanides Orogen in the south, probably carried by transcontinental alluvial systems. Close to the source area, antecedent river channels would have eroded older sedimentary rocks of the Ventania Fold Belt, Claromecó and Chaco-Paraná basins and North Patagonian Massif, crosscutting a peripheral bulge and flowing towards the alluvial plain of the intraplate setting to areas further north. Concomitantly, these sediments are reworked by strong winds that even helped carrying the grains to the Paraná Basin depositional site. [ABSTRACT FROM AUTHOR]

Conventional stratigraphic correlations are based on similarity of lithology, order of superposition, marker bed, unconformity, grade of metamorphism, fossil content and geochronology of the rock units. The Gondwana strata have been correlated referring to the above mentioned criteria. In the present work, the Talchir and Karharbari formations of two adjacent Gondwana basins separated by over 200 Km were examined with respect to their palaeocurrent directions. The study suggests that the palaeocurrent populations of different formations in both the basins are statistically dissimilar, this is because, both are stratigraphically distinct in order of superposition and thus are not correlatable. On the other hand, the palaeocurrent populations of the same formation in both the basins are statistically similar and stratigraphically correlatable. It is suggested that the similarity of palaeocurrent can be regarded as a criterion for stratigraphic correlation at least in local and regional scale. [ABSTRACT FROM AUTHOR]

Testate amoebae are common single-celled eukaryotic organisms in aquatic ecosystems. Despite their important role in these ecosystems, and their potential as bioindicators and paleoindicators, they remain poorly studied in Mexico. The major objectives of this study were to: 1) increase knowledge of testate amoebae in Mexico's tropical lakes, and 2) create a catalog of high-quality scanning electron micrographs that can be used for future ecological and paleoenvironmental studies. We collected surface-sediment samples from 29 lakes, located in the Transmexican Volcanic Belt, one at each lake during June and October 2011, and March 2013. Sediments were collected with an Ekman grab and preserved in anhydrous ethanol. Sub-samples were observed under a stereomicroscope and morphometric data for each species were recorded. Total diameter and aperture diameter were measured on circular tests. Irregularly shaped tests were measured for length and width of the aperture and for the size of the whole test. If a specimen possessed spines, the length of one randomly selected spine was measured. The best-preserved specimen of each taxon was photographed with an optical microscope and a scanning electron microscope (SEM). We found 41 taxa of testate amoebae belonging to the genera: Arcella, Argynnia, Centropyxis, Cucurbitella, Cyclopyxis, Cyphoderia, Difflugia, Euglypha, Lesquereusia, Pentagonia, Pseudodifflugia and Scutiglypha. Twelve species not previously reported for Mexico were recorded, along with 13 varieties. The average number of taxa recorded in each lake was eight, and the highest taxonomic richness was 18. The taxon found in the greatest number of lakes was Centropyxis aculeata var. aculeata. Taxonomic richness varied among lakes in the same region. This could reflect lake-specific differences in environmental conditions, underscoring the need for more detailed studies that include collection of data on physical and chemical variables in the lakes. Our results highlighted the need of further studies for the distribution patterns and ecology of lacustrine testate amoebae. [ABSTRACT FROM AUTHOR]

Detrital zircon LA-ICP-MS U–Pb ages of the Paleozoic strata in the southeastern Alxa Block indicate that the primary provenance did not change between the Devonian and the Early Carboniferous. Except for a sample from the Cambrian strata, the Early Paleozoic North Qilian Orogenic Belt may have been a major source of Paleozoic sediments in the study area. The main source of Lower–Middle Devonian sediments was the Early Paleozoic North Qilian Orogenic Belt. The source of the Upper Devonian sediments was the Alxa Block, while the North China Block was a minor contributor. The deformation of the Cambrian and Devonian Systems in the southeastern Alxa Block indicates that a strong east–west compression event occurred in the study area before the Early Carboniferous. The paleocurrents of the Upper Devonian in the southeastern Alxa Block indicate that the source was located to the north and was not the North Qilian Orogenic Belt to the south. Moreover, the deposition of the Upper Devonian in the southeastern Alxa Block was a response to a strong deformation event that occurred along the eastern boundary of the Alxa Block during the Late Devonian and Early Carboniferous. The North China Block became the primary source during the Early Carboniferous, and the Alxa Block was a minor source. A regional stratigraphic comparison also indicates that similar depositional environments were present until the Carboniferous and Permian on the Alxa Block and North China Block. All of these data indicate that amalgamation of the Alxa Block and the North China Block occurred between the Late Devonian and the Early Carboniferous. [ABSTRACT FROM AUTHOR]

The Gan-Hang Belt in Southeast China is characterized by several igneous and siliciclastic basins associated with crustal extension during Late Mesozoic. The sedimentary evolution of the red basins is still poorly understood. In this study, sedimentary facies analysis and pebble counting were performed on outcrop sections of the Late Cretaceous Guifeng Group in the Yongfeng-Chongren Basin in central Jiangxi Province. Thirty-five conglomerate outcrops were chosen to measure pebble lithology, size, roundness, weathering degree and preferred orientation. Results show that gravels are mostly fine to coarse pebbles and comprise dominantly quartzites, metamorphic rocks, granitoids and sandstones. Rose diagrams based on imbricated pebbles indicate variable paleocurrent directions. Combining with typical sedimentary structures and vertical successions, we suggest that the Guifeng Group were deposited in alluvial fan, river and playa lake depositional systems. The proposed depositional model indicates that the Hekou Formation represents the start-up stage of the faulted basin, accompanied by sedimentation in alluvial fan and braided river environments. Then this basin turned into a stable expansion stage during the deposition of the Tangbian Formation. Except for minor coarse sediments at the basin margin, the other area is covered with fine-grained sediments of lake and river environments. The Lianhe Formation, however, is once again featured by conglomerates, suggesting a probable tectonic event. Therefore, the study region possibly suffered two tectonic events represented by the conglomerates of the Hekou and Lianhe formations in the context of the crustal extension in Southeast China. [ABSTRACT FROM AUTHOR]

Over thirty stratigraphic sections of the Himalaya orogen Upper Triassic Langjiexue Group in southern Tibet, China, were studied to interpret the environments and lithofacies. The facies associations channel (A), lobe (B), levee-interchannel (C), and basin plain (D) with nine facies (A1–3, B1–3, and C1–3) were distinguished. They form six architectural elements: channel-interchannel, overbank-levee, crevasse-splay, outer fan-lobe, fan-fringe, and basin plain. Taking into account the facies analysis, (sub-) deposystem correlation, paleocurrent dispersal pattern, and restoration of primary stratal width, the Langjiexue Group displays the architecture of a coalescing submarine fan-dominated deep sea deposystem, measuring about 400–500 km × 600–700 km in size or even more, one of the largest pre-Cenozoic submarine fans ever reported. Subdivisionally, four fans, lacking inner fans, could have coalesced laterally within the submarine fan deposystem, and at least six submarine fan developments were vertically succeeded by mid- to outer-fan deposits with progradational to retrogradational successions. According to the range of 30–70% of sandstone content, the fan deposystem is mud- and sand-rich, suggesting a medium-far (over 400–600 km) transport of sediment from the source area. [ABSTRACT FROM AUTHOR]

The mean size of mineral particles of the 10-63 μm fraction (the so-called 'sortable silt' mean size ( $$\overline {SS} $$)) was used as proxy for the variations in paleocurrent intensity. The modes of grain-size distribution were also examined. Sediments with bimodal grain size distribution (the second mode varies from 10 to 28 μm) correlate with the increased mean size of sortable silt (up to 18-23 μm) at the Hatton and Snorry Drifts. These parameters indicate an increase in bottom-current intensity during MIS 1, 3, and 5e. There is no correlation between grain-size distribution and climatic cyclicity of variations in contour-current intensity at the Gloria Drift. The similarity between AMK-4493 sediments and IRD-containing hemiturbidites of the Labrador Sea render doubtful the contourite nature of the Gloria Drift. [ABSTRACT FROM AUTHOR]

Jura limestone, commercially one of the Federal Republic of Germany's most important rocks, is used extensively as a decorative stone and tile in buildings worldwide. This Jurassic tile is especially common in public buildings in the southeastern United States and often contains abundant fossilized ammonites and belemnites. Azimuthal orientation and dip measurements from seventy-five pairs of belemnite rostra from the Jura tile (Malm Epoch, Upper Bavaria, Germany) used in Southpark Mall, Charlotte, North Carolina, and the Orlando International Airport, Florida, were collected and analyzed to determine relative orientation and possible paleocurrent sorting. Data plots for the fossils from both localities document a unidirectional or bidirectional water currents with the long axis of the belemnite rostra oriented parallel to the direction of flow. Additionally, the minimal average dip of the rostra and ammonite shells relative to the tile quarrying- and cutting-plane suggests the tile was cut parallel to the original bedding plane to maximize the surface area of the fossils for decorative purposes. [ABSTRACT FROM AUTHOR]

To understand the paleocurrent directions and depositional processes in the forearc basin along the active convergent margin of the eastern Nankai Trough, analysis of the anisotropy of magnetic susceptibility (AMS) has been applied to Pleistocene turbidite sediments in a borehole core obtained in the vicinity of the gas hydrate production test site. Sixty-one core specimens mainly sampled from silty and sandy sediments were measured, and the AMS results show generally oblate magnetic fabrics characterized by girdle-distributed weakly-clustered maximum and intermediate susceptibility axes. Diagnostic magnetic fabric parameters show that the sediments generally preserve primary sedimentary structures without significant sediment disturbance due to events such as coring and bioturbation. The characteristic remanent magnetization was also measured to determine the reorientation of each core. Paleocurrent directions estimated from the offset of the minimum susceptibility axes in the stratigraphic coordinates show two predominant directions: one toward the southwest (SW) and the other toward the northwest (NW). On the basis of the interpretations of 3D seismic data, the principal SW direction is generally parallel to the trough-shaped basin axis; this suggests that the sediments were carried by axial turbidity currents within the channel. The subordinate NW direction corresponds to the downslope direction of the Daini–Atsumi Knoll; this may be due to a sediment supply from the southeast associated with a submarine slope failure and landslide evolution or it may be due to flow reflections from the slope toward the basin center. The results of the paleocurrent analysis suggest that the Pleistocene depositional system around the Daini–Atsumi Knoll is affected by the basin configuration. These results are in good agreement with previous studies of the coeval depositional system for the adjacent forearc minibasin around the eastern Nankai Trough. [ABSTRACT FROM AUTHOR]

The Cambrian edrioasteroid Stromatocystites is reported and described from Spain, Sweden and Turkey. All previously known occurrences of the genus are critically reviewed, and S. flexibilis is reinterpreted as a junior synonym of S. pentangularis . Stromatocystites was biogeographically widespread and colonized different areas of Baltica, Gondwana (Arabian, eastern and western margins) and Laurentia (western Newfoundland). Stratigraphically, it ranges from Cambrian Series 2, Stage 4 to Cambrian Series 3, Drumian. Stromatocystites lived in quiet water environments with stabilized substrates. It was attached directly to the substrate by its aboral surface. As these environments were widespread throughout Baltica, Gondwana and Laurentia, availability of suitable substrates for larval settlement and oceanic palaeocurrents led to the successful development of Stromatocystites colonies. [ABSTRACT FROM AUTHOR]

Facies analysis, distinct depositional paleoflow directions and grain size ranges suggest that different fluvial systems fed coeval distinct, independent river-dominated and tide-dominated braid delta systems in the Mesoproterozoic Açuruá Formation. The river-dominated delta system is characterized by: (a) vertical stacking of parasequences up to 30 m which are characterized by coarsening- and thickening-upward trends; (b) gradationally based vertical succession of prodelta, delta front, distributary channels, and floodplain; (c) grain size of sandstone from delta front and distributary channels varies respectively from very fine to medium and medium to coarse; (d) lacking of wave or tide reworking suggests delta development in a relatively low energy marine basin; (e) paleocurrent readings indicate delta front sandstone bodies shifting laterally towards NE to SE directions. The tide-dominated delta system is characterized by: (a) vertical stacking of parasequences up to 25 m which are characterized by coarsening- and thickening-upward trends; (b) gradationally based vertical succession of prodelta, delta front and tide-influenced distributary channels; (c) grain size of sandstone from delta front and tide-influenced distributary channels varies respectively from very fine to coarse and fine to granular; (d) abundance of tide-influenced sedimentary structures suggest tidal dominated delta development; (e) consistent bidirectional paleocurrents with northwards ebb-tide direction and no lobe shifting. The studied braid delta systems belong to a highstand system tract and as such, they exhibit classic parasequence sets with progradational stacking pattern. The facies association variability and overall characteristics of these Mesoproteozoic delta systems are compatible with delta systems of all ages. However, contrary to typically Phanerozoic deltas – which are characterized by progradational clinoforms – the coalescence of the studied braid delta facies associations promoted fairly sheet-like geometry limited by marine flooding surface that more likely resulted from the response of deposition on shallow and wide epeiric sea. [ABSTRACT FROM AUTHOR]

The Talacasto paleovalley is situated in the Central Precordillera of San Juan, Argentina, where upper Carboniferous-Permian rocks (Paganzo Group) rest on Devonian sandstones of the Punta Negra Formation. This outcrop is an excellent example of a glacial valley-fill sequence that records at least two high-frequency cycles of the advance and retreat of a glacier into the valley. The paleocurrent analysis shows transport predominantly to the south, indicating that at this site the ice flow differs from the other nearby paleovalleys. Evidence of the glacial origin of this valley can be seen in the glacial striae on the valley's sides, as well as the U-shape of the valley, indicated by very steep locally overhanging valley walls. Deglaciation is indicated by a set of retransported conglomerates deposited in a shallow-water environment followed by a transgressive succession, which suggests eustatic rise due to meltwater input to the paleofjord. The complete sedimentary succession records distinct stages in the evolution of the valley-fill, represented by seven stratigraphical units. These units are identified based on facies associations and their interpreted depositional setting. Units 1 to 5 show one cycle of deglaciation and unit 6 marks the beginning of a new cycle of glacier advance which is characterized by different types of glacial deposits. All units show evidence of glacial influence such as dropstones and striated clasts, which indicates that the glaciers were always present in the valley or in adjacent areas during sedimentation. The Talacasto paleofjord provides good evidence of the Late Paleozoic Gondwana glaciation in western Argentina and examples of sedimentary successions which have been interpreted as being deposited by a confined wet-based glacier in advance and retreat cycles, with eventual release of icebergs into the basin. The outcrop is also a key for reconstructing the local glacial paleogeography, and it suggests a new interpretation that is not in agreement with previous studies. Finally, the importance of the Talacasto paleovalley for the Paganzo basin lies in its orientation, because it allows the reconstruction of the ice paleoflow and indication, for the first time, that marine ingressions into this area were not taking place along the Jachal trough, as expected, but along a different connection to the sea, which for this work we will call the San Juan Paleotrough. [ABSTRACT FROM AUTHOR]

Para la determinación de las direcciones de paleocorrientes en el Campo Provincia se tomaron 2.664 medidas de los registros de buzamiento (dipmeter), con las cuales se hicieron los análisis estadísticos de las formaciones (fms.) comprendidas entre la Formación (Fm) Umir y el Grupo (Gr) Real (edad Maastrichtiano a Mioceno). Las direcciones de paleocorrientes se definen con base en análisis estadísticos, como son el valor de la media (0, medida en azimuth) y su relación de consistencia (CR). Las direcciones de paleocorrientes son principalmente hacia el noreste para las Fms. Umir, real inferior para las Fms. Lisama, Esmeraldas, Mugrosa, Colorado, y Real Medio y en la dirección sureste para la Fm. Real Superior. En general se observaron cambios importantes en las direcciones de paleocorrientes entre las Fms. Umir-Lisama, Lisama-Esmeraldas, Colorado-Real y entre la parte Media y Superior del Gr. Real. Estos cambios en las direcciones de las paleocorrientes sugieren estar asociados con eventos tectónicos que afectaron esta área.For the determination of the palaeocurrent directions in the Provinica Field, were took 2664 measurements of the dipmeter logs were taken to make the statistical analyses of the Formations that are between Umir and the Real Group (Maastrichtian and Miocene age). The palaeocurrent directions are defined based on statistics analyses, as the average (in azimuth) and its consistency ratio (CR). The paleocurrent directions are principally to the northeast for the Umir and the Lower Real Formations; to the east for the Lisama, Esmeraldas, Mugrosa, Colorado and Middle Real Formations, and in the southeast for the Upper Real Formation. In general, there were observed important changes in the palaeocurrent directions between the Umir-Lisama, Lisama-Emeralds, Colorado-Real and between the medium and the upperpartof the Real Group. These changes in the paleocurrent directions suggest to be associated to tectonic events that involved this area.

Highlights: [•] Ten stratigraphic sections were logged and their facies analyses were carried out. [•] Paleocurrents flow directions from selected localities were measured and analyzed. [•] Paleoenvironments were interpreted from the facies and paleocurrents analyses. [•] Facies distribution shows progradational successions from lacustrine to fluvial systems. [•] Depositional model and stratigraphic framework of Lower Bima Member were constructed. [Copyright &y& Elsevier]

Imbricate structure is a common sedimentary structure and is well developed in sandy sediments. Here, we report a lamina-controlled fine-sand-particle imbricate structure in a set of very fine grained sedimentary rocks (fine sandstone, siltstone, and mudstone) at the Dockyard and Qianceng Cliff areas of Lingshan Island, Qingdao, Shandong, China. Sets of up to 300 laminae are found in stratigraphic profiles in these areas. The laminae are generally less than 1 mm thick, with most being 0.3-0.4 mm thick and the thinnest being <0.1 mm. The dip angle of the imbricate structure varies widely, between 0° and 90°, with an average dip angle of about 40°-50°, which is higher than that of imbricate riverbed gravels (about 34°). The dip angle is a function of the shape and sorting of the particles, as well as the hydrodynamic conditions under which these fine-grained sediments were deposited. Several profiles show well-developed multiscale, soft-sediment deformation structures. Flute casts, load casts, and groove casts are also common. Fragments of carbon remains occur widely and commonly constitute stringers several millimeters thick and up to 10 cm long, together with fine clasts. Vitrain lenticles are also common. Based on the imbricate structure of the Lingshan Island deposits, it is shown that in addition to paleocurrent analysis, the imbricate structure can be used to infer information about fluid properties, transport characteristics, and sedimentary processes of the depositional environment. A near-bottom underflow, either of authigenic origin or derived from cold river water in winter in a delta interdistributary bay or delta-front environment, is inferred to have provided the hydrodynamic setting in which this imbricate structure formed. The imbricate structure, together with other sedimentary structures and features, shows that the sedimentary rocks on Lingshan Island were deposited in an inland, shallow-water environment, such as a delta, and not in a deep-water or submarine continental-slope environment. [ABSTRACT FROM AUTHOR]

The internal orientation of fossil mass occurrences can be exploited as useful source of information about their primary depositional conditions. A series of studies, using different kinds of fossils, especially those with elongated shape (e.g., elongated gastropods), deal with their orientation and the subsequent reconstruction of the depositional conditions (e.g., paleocurrents and transport mechanisms). However, disk-shaped fossils like planispiral cephalopods or gastropods were used, up to now, with caution for interpreting paleocurrents. Moreover, most studies just deal with the topmost surface of such mass occurrences, due to the easier accessibility. Within this study, a new method for three-dimensional reconstruction of the internal structure of a fossil mass occurrence and the subsequent calculation of its spatial shell orientation is established. A 234 million-years-old (Carnian, Triassic) monospecific mass occurrence of the ammonoid Kasimlarceltites krystyni from the Taurus Mountains in Turkey, embedded in limestone, is used for this pilot study. Therefore, a 150×45×140mm3 block of the ammonoid bearing limestone bed has been grinded to 70 slices, with a distance of 2mm between each slice. By using a semi-automatic region growing algorithm of the 3D-visualization software Amira, ammonoids of a part of this mass occurrence were segmented and a 3D-model reconstructed. Landmarks, trigonometric and vector-based calculations were used to compute the diameters and the spatial orientation of each ammonoid. The spatial shell orientation was characterized by dip and dip-direction and aperture direction of the longitudinal axis, as well as by dip and azimuth of an imaginary sagittal-plane through each ammonoid. The exact spatial shell orientation was determined for a sample of 675 ammonoids, and their statistical orientation analyzed (i.e., NW/SE). The study combines classical orientation analysis with modern 3D-visualization techniques, and establishes a novel spatial orientation analyzing method, which can be adapted to any kind of abundant solid matter. [ABSTRACT FROM AUTHOR]

Oriented samples of sediments from Ariyalur Group, Cauvery Basin, south India, were studied for low field anisotropy of magnetic susceptibility (AMS) measurements to unravel the magnetic fabrics and paleocurrent directions. The results of AMS parameters of the sediments indicate primary depositional fabrics for Sillakkudi, Ottakovil and Kallamedu sandstone formations and secondary fabric for Kallankurichchi limestone formation. The obtained low degree of anisotropy ( P), oblate shape AMS ellipsoid and distribution of maximum ( K) and minimum ( K) susceptibility axes on equal area projection confirm the primary sedimentary fabric for Sillakkudi, Ottakovil and Kallamedu Formations. In the case of ferruginous, lower arenaceous, Gryphaea limestone and upper arenaceous limestone beds of Kallankurichchi Formation have recorded more than one fabric. The observed AMS parameters like shape factor ( T) (prolate to oblate), q value and random distribution of minimum ( K) and maximum ( K) susceptibility axes are supported for secondary fabrics in Kallankurichchi Formation as a result of post-depositional processes. Based on petrographic studies, it can be established that K AMS axis of biotite mineral could represent the flow direction. The established paleocurrent direction for Sillakkudi is NW-SE direction while Ottakovil and Kallamedu Formations recorded NE-SW direction. Overall the paleoflow directions observed for Ariyalur Group is NE-SW to NW-SE. [ABSTRACT FROM AUTHOR]

Integrated data on paleocurrents, the morphology of detrital minerals and zircon grains, chemical compositions and U–Pb geochronology, reveal that the flow of the modern Solimões-Amazonas River has changed from west to east since the Plio–Pleistocene. This finding is supported by several lines of evidence, including paleocurrent directions and detrital mineral assemblages in the Içá Formation and in recent sediments. The Içá Formation, which was most likely deposited during the Pliocene, has NE and SE paleocurrents, a high proportion of stable detrital mineral assemblages and U–Pb zircon ages that we interpreted as being derived from the Amazonian craton (e.g., the Rondonian-San Ignácio and Sunsas-Grenvillian geochronologic provinces) and neighboring provinces, including the Neoproterozoic to Cambrian Brazilian Pampean mobile belts. A small proportion is derived from the Cambrian to Silurian Famatinian continental arch. Another source is the Precambrian and Paleozoic basement from the Andes cordillera, which includes several metamorphic inliers in Colombia, Peru and Bolivia. The overlying recent deposits have different provenances and are characterized by a more variable detrital assemblage with zircon grains that are enriched in trace elements and depleted in Si and have Mesoproterozoic ages. In our interpretation, the erosion of the Iquitos Arch after deposition of the Içá Formation allowed the westward expansion of the Solimões-Amazonas system in the Plio-Pleistocene. [ABSTRACT FROM AUTHOR]

Abstract: A comprehensive biostratinomic study was carried out with abundant stems from the Lower Permian Motuca Formation of the intracratonic Parnaíba Basin, central-north Brazil. The fossils represent a rare tropical to subtropical paleofloristic record in north Gondwana. Tree ferns dominate the assemblages (mainly Tietea, secondarily Psaronius), followed by gymnosperms, sphenophytes, other ferns and rare lycophytes. They are silica-permineralized, commonly reach 4 m length (exceptionally more than 10 m), lie loosely on the ground or are embedded in the original sandstone or siltstone matrix, and attract particular attention because of their frequent parallel attitudes. Many tree fern stems present the original straight cylindrical to slightly conical forms, other are somewhat flattened, and the gymnosperm stems are usually more irregular. Measurements of stem orientations and dimensions were made in three sites approximately aligned in a W–E direction in a distance of 27.3 km at the conservation unit “Tocantins Fossil Trees Natural Monument”. In the eastern site, rose diagrams for 54 stems indicate a relatively narrow azimuthal range to SE. These stems commonly present attached basal bulbous root mantles and thin cylindrical sandstone envelopes, which sometimes hold, almost adjacent to the lateral stem surface, permineralized fern pinnae and other small plant fragments. In the more central site, 82 measured stems are preferentially oriented in the SW–NE direction, the proportion of gymnosperms is higher and cross-stratification sets of sandstones indicate paleocurrents mainly to NE and secondarily to SE. In the western site, most of the 42 measured stems lie in E–W positions. The predominantly sandy succession, where the fossil stems are best represented, evidences a braided fluvial system under semiarid conditions. The low plant diversity, some xeromorphic features and the supposedly almost syndepositional silica impregnation of the plants are coherent with marked dry seasons. Thick mudstones and some coquinites below and above the sandy interval may represent lacustrine facies formed in probably more humid conditions. The taphonomic history of the preserved plants began with exceptional storms that caused fast-flowing high water in channels and far into the floodplains. In the eastern site region, many tree ferns only fell, thus sometimes covering and protecting plant litter and leaves from further fragmentation. Assemblages of the central and western sites suggest that the trees were uprooted and transported in suspension (floating) parallel to the flow. Heavier ends of stems (according to their form or because of attached basal bulbous root mantle or large apical fronds) were oriented to upstream because of inertial forces. During falling water stage, the stems were stranded on riverbanks, usually maintaining the previous transport orientation, and were slightly buried. The perpendicular or oblique positions of some stems may have been caused by interference with other stems or shallow bars. Rare observed stems were apparently waterlogged before the final depositional process and transported as bedload. The differences of interpreted channel orientations between the three sites are expected in a braided fluvial system, considering the very low gradients of the basin and the work scale in the order of tens of kilometers. The mean direction of the drainage probably was to east and the flows apparently became weaker downstream. This study seems to provide reliable data for paleocurrent interpretations, especially considering areas with scarce preserved sedimentary structures. [Copyright &y& Elsevier]

Abstract: Sources of ancient volcanic rocks are often unknown if they are either eroded and/or covered by younger deposits. This problem, as well as the provenance of reworked volcaniclastic, fluvial and mass-flow deposits, can be partially solved by the application of anisotropy of the magnetic susceptibility (AMS). For massive and poorly sorted volcaniclastic rocks in particular this may be the only way of finding reliable transport directions and therefore allowing for paleogeographic reconstructions. Here, we present a data set of 428 AMS measurements and 249 measurements of sedimentary paleocurrent indicators from the Miocene Tepoztlán Formation at the southern edge of the Transmexican Volcanic Belt (Central Mexico). The highest degree of reliability of AMS measurements is gained for data from lava samples and the lowest from mass flows. Sedimentary structures in sandstones and conglomerates such as trough cross-stratification, asymmetric ripple marks, and the shape of scours and channels could be used to calibrate the results from AMS data and to prove their reliability. AMS data on fluvial deposits point to a drainage system with a W–E flow direction, indicating an outflow of the river system into the ancient Gulf of Mexico. [Copyright &y& Elsevier]

Abstract: In the Late Neogene (Late Sarmatian s. l. — Dacian; 11 to 4Ma) the Carpathian Mountains to Dacian Basin was an enclosed source-to-sink system. The volume of sediment eroded from the Carpathians (estimated from previous semi-quantitative studies) closely matches the volume of sediment deposited in the Dacian Basin (about 100,000km3). The close values of the eroded and deposited sediment volume indicate the Carpathians as the main sediment source for Dacian Basin, with only limited input from adjacent areas. Based on depocenter thickness, grain size trend and paleocurrent data, two distinct areas in the Carpathian Mountains have been identified as the major sediment sources during this time interval. Each source area most likely delivered sediments to different depocenters within the Dacian Basin creating distinct sediment routing and sinks. Because of the similar sediment volumes sourced in Carpathians and deposited in Dacian Basin connectivity with adjacent basins did not significantly influence the sediment flux and routing of the Dacian Basin unless the sediment was bypassing the Dacian Basin. A probable sea-level drop of 50 to 100m during Pontian (time of the Messinian Salinity Crisis in the Mediterranean Basin) did not inflict important morphological changes to the Carpathians - Dacian Basin source-to-sink system. The system of the semi-enclosed Dacian Basin appears to have been autonomous, efficiently trapping incoming clastic material and apparently preventing significant spillage to the larger and deeper Black Sea Basin until Romanian time when it was filled and depositional environments changed from marine/lacustrine to fluvial. [Copyright &y& Elsevier]

North-trending rifts and associated strike-slip faults in the Tibetan Plateau suggest Cenozoic east-west extension, but the dominant modes of distributed extensional deformation and basin formation are unclear. The Lunggar basin in west-central Tibet is bounded by a <40° low-angle detachment fault, contains active high-angle normal faults, and displays elevated topography toward the central segment of the basin with axial fluvial drainage toward the northern and southern basin terminations. Structural and stratigraphic features are consistent with a high-angle extensional system that evolved into a low-angle fault and supradetachment basin during progressive extension. This study seeks to constrain the depositional and exhumational history of the Lunggar basin and bounding fault system by assessing the sedimentologic, structural, and thermochronologic record of basin fill. Upper Cenozoic facies include alluvial-fan conglomerates and fluviolacustrine sandstones and siltstones. Sandstone petrographic data, conglomerate clast compositions, and detrital zircon U-Pb ages indicate systematic unroofing of the western footwall (including Jurassic-Cretaceous and Miocene granites that intruded Permian-Cretaceous strata). Paleocurrents are orthogonal or opposite to the current dispersal pattern, suggesting that growth of a modern intrabasin high in the central segment of the basin has modified the original basin configuration. As a proxy for footwall cooling histories, four basin-fill sandstones and 11 leucogranite boulders from proximal hanging-wall strata were sampled for low-temperature thermochronometry. Apatite and zircon (U-Th)/He results suggest that extension was underway by 10-8 Ma, with late Miocene-Pliocene exhumation rates of roughly 1 km/Myr. This rapid exhumation generated a conglomeratic unroofing sequence and promoted hanging-wall rebound and erosional recycling of range-front basin fill along the central segment of the detachment fault. The collective results support a model of rift evolution that invokes upper-crustal thinning, supra detachment basin subsidence, and subsequent isostatic rebound along the more-evolved central segments of Tibetan extensional systems. [ABSTRACT FROM AUTHOR]

Abstract: New thermochronological data, facies, paleocurrents and provenance allow us to refine the chronology of deformation in the central segment of the Colombian Eastern Cordillera. Based on a new extensive AFT dataset, we document the spatial evolution of active deformation, from the axial zone of the Eastern Cordillera at about 50 Ma in to active growth of the frontal thin skinned structures in Late Miocene time. Paleocurrents allow us to push backwards into the Middle to Early Late-Miocene the emergence of the easternmost frontal thrust; whereas careful assessment of exposure gates tied to AFT data enable to refine the unroofing history for Eocene to Miocene times. Based on that, we produced a kinematically restored cross section with higher resolution than previous assessments. Using these datasets, we compare the evolution of the central segment of the Eastern Cordillera in this region with the evolution of adjacent areas in the context of climatic forcing of orogenic evolution. We find that in this region and, in the Eastern Cordillera in general, tectonic inheritance and transpression exert an initial dominant control on the initial orogen asymmetry, which is later enhanced due to an orographically-focused erosion. We therefore suggest that it is not climate alone the factor controlling orogenic asymmetry in the Eastern Cordillera of Colombia. [Copyright &y& Elsevier]