Palaeogeographic Interpretations Research Articles

Sedimentary facies and mineral provenance of Upper Triassic sandstones offshore Kvitøya, Svalbard: implications for palaeogeographic interpretations in the northern Barents Shelf area

Upper Triassic (Carnian) sandstones of the De Geerdalen Formation cored south of the island of Kvitøya (80°N), north-easternmost Svalbard, are described in terms of sedimentary facies and petrography and compared regionally in the northern Barents Shelf. The succession off Kvitøya is characterized by its great thickness and is dominated by deltaic deposits with high sand content of lithic–feldspathic compositions. Comparison of sediment facies and sandstone compositions with adjacent areas suggest that the succession off Kvitøya is part of a larger delta system with its main sediment source from the east. The delta sedimentation was terminated by marine transgression in the earliest Norian. The sandstone compositions off Kvitøya differ from nearby locations by the higher content of cherty rock fragments and reworked volcanic debris in the Kvitøya sandstone, which is most distinct in the lower part of the succession. Provenance signatures are investigated by mineral–chemical analysis of detrital feldspars, rock fragments, garnet and Cr-spinel, characterizing a wide variety of igneous, metamorphic and sedimentary terranes, including palaeo-Urals and areas farther to east. Additional, more proximal sediment source areas may also have existed that could explain the increased sediment thickness and the mineralogical immature sandstone compositions of the Carnian sediments off Kvitøya.

Lower Aeronian (Llandovery, Silurian) graptolites of the genera Rastrites and Stavrites: systematics, biostratigraphy and palaeobiogeography

AbstractThe lower Aeronian graptolite species Rastrites longispinus longispinus Perner, R. approximatus Perner, R. peregrinus Barrande, R.? norilskensis Obut & Sobolevskaya, and Stavrites rossicus Obut & Sobolevskaya have been revised using material from China, the Czech Republic, Siberia, Canada and Spain, together with published data. Rastrites longispinus chenxui subsp. nov. is recognized as a new biogeographical subspecies known only from China and Canada. Rastrites guizhouensis Mu et al., R. confertus Chen & Lin and Stavrites laticellatus Obut & Sobolevskaya, are all considered to be junior synonyms of S. rossicus. Rastrites geinitzii Törnquist is regarded as a junior synonym of R. longispinus longispinus; and R. orbitus Churkin & Carter and R. hemigyratus Chen & Lin are considered to be junior synonyms of R.? norilskensis. We propose that a distinct R.? norilskensis Biozone can be recognized between a lowest Aeronian Demirastrites triangulatus or D. triangulatus – D. pectinatus Biozone in Siberia and northern Canada (possibly in South China, with future work) and the overlying Lituigraptus convolutus Biozone. Cluster analysis of the palaeogeographical distribution of species of Rastrites and Stavrites supports the hypothesis that two graptolite palaeobiographical provinces can be defined in the early Aeronian: a low‐latitude Circumequatorial Province including northern Laurentia, South China, Siberia and peri‐Siberian terranes; and a largely mid‐latitude Rheic – West Gondwana Province comprising Avalonian Britain, the Baltic area, central Europe, western and southern Europe, and cratonic North Africa. None of our studied taxa exhibits a cosmopolitan distribution. Our systematic revision has a significant impact on our palaeogeographical interpretations.

Chronostratigraphic and palaeogeographic interpretation of Nakdong deltaic sequences in the south-eastern Korean Peninsula

We investigated the chronostratigraphy of six boreholes in the Nakdong River delta area in South Korea based on optically stimulated luminescence (OSL) and 14C dating. The standardised growth curves (SGCs) produced from single and multiple boreholes performed well in determining low equivalent dose (De; < 40 Gy). 14C dates from shell and wood fragments were mostly representative of depositional time. Based on 14C and OSL ages, the lowermost fluvial sediments showed relatively low sediment accumulation rates (0.1–0.8 m/kyr−1) prior to 12 ka. A hiatal discontinuity ranging from 12 to a maximum of 50 ka resulted in a break in sedimentation between the Last Glacial Maximum and the Holocene. A thick fluvio-estuarine unit in the lower part indicated relatively high accumulation rates (3.3–9.4 m/kyr−1) from 12 to 9 ka, which corresponded to rapid sea level rise. In the middle part, decreased accumulation rates (1.7–5.5 m/kyr−1) from approximately 9 to 6 ka were interpreted as transgressive deepening. Lower accumulation rates (0.9–3.2 m/kyr−1) during the middle to late Holocene were caused by relative sea level fall and a horizontally extended sedimentation area. In the upper part, the highest sediment accumulation rates (3.5–8.3 m/kyr−1) and rapid delta progradation during the last 2.0 ka might have been caused by widespread human influence and monsoonal climatic change. Isochrons of 1-kyr scale were identified based on the lithologic boundary and age results for each borehole, which represent palaeoshoreline positions during the transgressive cycle and boundaries of considerable delta progradation.

Late Cretaceous palaeogeography of NE Bohemian Massif: diachronous sedimentary successions in the Wleń Graben and Krzeszów Brachysyncline (SW Poland)

This paper provides a new sedimentological and palaeogeographic interpretation of the Late Cretaceous (late Cenomanian to early Coniacian) shallow-marine succession exposed in the Wlen Graben and in the Krzeszow Brachysyncline (NE Bohemian Massif, Sudetic Block). These two tectonic subunits are outliers of the North Sudetic and Intra-Sudetic synclinoriums, respectively, and contain relics of the diachronous sedimentary succession of a seaway linking the Boreal and Tethyan marine provinces during the Late Cretaceous. Results of sedimentological study and facies analysis show that the late Cenomanian sedimentation within this corridor was dominated by strong in situ reworking of the pre-Cretaceous bedrock driven by storm waves and possibly tidal currents. In the latest Cenomanian, siliciclastic sedimentation was followed by the deposition of offshore-transition to offshore muddy calcareous facies in the Krzeszow area, while the deposition of coarse-grained siliciclastic facies continued in the Wlen area. The nearshore clastic belt in the latter area changed into a wider strait dominated by offshore sedimentation in the early Turonian, whereby the interconnected Wlen and Krzeszow passages evolved into a uniform strait of fully-marine sedimentation. In the middle Turonian, the southern part of the strait became progressively filled with coarse-grained siliciclastic material supplied from the east. At the end of the late Turonian and in the early Coniacian, the strait funnelled bi-directional tidal currents along its axis. The youngest Cretaceous strata in the Wlen area comprise erosional relics of the early Coniacian shoreface to offshore-transition deposits. The younger Cretaceous deposits are unpreserved, probably eroded during the post-Santonian(?) tectonic inversion of the Wlen–Krzeszow strait. Despite the relatively small distance between the two relic parts of the strait, the shallow-marine succession reveals distinct diachroneity on a regional scale, reflecting an interplay of eustatic changes, differential tectonic subsidence and clastic sediment supply. This paper presents the first detailed sedimentological logs from the two study areas, with new findings of fossil fauna and flora, proposes a new palaeogeographic interpretation and discusses the influence and development of the source areas for the Cretaceous Sudetic Wlen–Krzeszow marine strait at the NE fringe of the Bohemian Massif.

Salt in the Vulcan sub-basin, NW Australia: observations from high-quality 3D seismic data and implications for palaeogeography

The Vulcan sub-basin is one of the few places in Australia where tectonic features (i.e. diapirs) associated with a mobile substrate can be found. In this presentation one of these features, the Paqualin diapir, and its environs will be described and discussed using the new regional NOVAR MC3D prestack depth migrated seismic dataset. The extent of the NOVAR MC3D seismic dataset makes it possible, for the first time, to integrate the observation of c. 600m of interbedded halite and anhydrite in the Paqualin-1 well, local fault geometries indicative of the movement of a mobile layer and regional tectonic features consistent with the presence of a mobile substrate. In this presentation the observations will be integrated with global analogues, regional palaeogeographic interpretations to refine models for the origin and spatiotemporal distribution of mobile layers in the Vulcan sub-basin.

Evolution of a mixed siliciclastic‐carbonate deep‐marine system on an unstable margin: The Cretaceous of the Eastern Greater Caucasus, Azerbaijan

AbstractMixed siliciclastic‐carbonate deep‐marine systems (mixed systems) are less documented in the geological record than pure siliciclastic systems. The similarities and differences between these systems are, therefore, poorly understood. A well‐exposed Late Cretaceous mixed system on the northern side of the Eastern Greater Caucasus, Azerbaijan, provides an opportunity to study the interaction between contemporaneous siliciclastic and carbonate deep‐marine deposition. Facies analysis reveals a Cenomanian–early Turonian siliciclastic submarine channel complex that abruptly transitions into a Mid Turonian–Maastrichtian mixed lobe‐dominated succession. The channels are entrenched in lows on the palaeo‐seafloor but are absent 10 km towards the west where an Early Cretaceous submarine landslide complex acted as a topographic barrier to deposition. By the Campanian, this topography was largely healed allowing extensive deposition of the mixed lobe‐dominated succession. Evidence for irregular bathymetry is recorded by opposing palaeoflow indicators and frequent submarine landslides. The overall sequence is interpreted to represent the abrupt transition from Cenomanian–early Turonian siliciclastic progradation to c. Mid Turonian retrogradation, followed by a gradual return to progradation in the Santonian–Maastrichtian. The siliciclastic systems periodically punctuate a more widely extensive calcareous system from the Mid Turonian onwards, resulting in a mixed deep‐marine system. Mixed lobes differ from their siliciclastic counterparts in that they contain both siliciclastic and calcareous depositional elements making determining distal and proximal environments challenging using conventional terminology and complicate palaeogeographic interpretations. Modulation and remobilisation also occur between the two contemporaneous systems making stacking patterns difficult to decipher. The results provide insight into the behaviour of multiple contemporaneous deep‐marine fans, an aspect that is challenging to decipher in non‐mixed systems. The study area is comparable in terms of facies, architectures and the presence of widespread instability to offshore The Gambia, NW Africa, and could form a suitable analogue for mixed deep‐marine systems observed elsewhere.

Triassic palaeogeography of NE Bohemian Massif based on sedimentological record in the Wleń Graben and the Krzeszów Brachysyncline (SW Poland)

This paper presents a new sedimentological and palaeogeographic interpretation of the Early to Middle(?) Triassic continental deposits in the Wleń Graben and the Krzeszów Brachysyncline (Sudetes, SW Poland). These two tectonic subunits, located in the peripheral segments of the North Sudetic and Intra-Sudetic synclinoriums, respectively, represent the crucial elements for deciphering the post-Variscan palaeogeographic evolution of the NE termination of the Bohemian Massif. Sedimentological studies and facies analysis show that the Early Triassic siliciclastic deposition in both areas was dominated by fluvial sedimentation of the typical Buntsandstein facies within a gently sloping alluvial plain, locally followed by ephemeral lake environments in the late Early or Middle(?) Triassic. The lithofacies and the measured palaeocurrent directions indicate that the area was drained by braided streams flowing towards the northwest and north. Individual fluvial channels had depths not exceeding 1 m and widths of up to a few metres. Overbank deposits are poorly preserved due to the lateral shifting of channels. Based on available borehole data, an analysis of isopach maps was performed for the first time in the study areas. The study areas are presently separated by crystalline units devoid of sedimentary rocks, but the analysis indicate that they might have been in constant or periodical connection during the Triassic. It is concluded that the present-day extent of Triassic deposits is a result of the primary basin configuration combined with the Middle Triassic to Late Cretaceous erosion and post-Cretaceous tectonic uplift. The paper summarizes the present state of research on the continental Triassic preserved in the terminal parts of the North Sudetic and Intra-Sudetic synclinoriums, presents the first detailed sedimentological logs, and proposes new palaeogeographic interpretation. New findings include bioturbation structures, such as plant-root traces or tunnels formed by invertebrates and possible tetrapod footprints, which shed new light on the sedimentological interpretation of the continental Mesozoic deposits in the NE part of the Bohemian Massif.

Relict slopes and palaeovalleys at Taracena-Guadalajara (central Spain): Geomorphological and palaeogeographical interpretation

Relict talus slopes are of great interest for the reconstruction of Quaternary paleoenvironments. In this study, a special type of talus slope found in the central zone of the Iberian Peninsula is analyzed, which we will refer to as a talus-palaeovalley alignment. These are talus sequences that conserve the intermediate paleovalleys, and are arranged in parallel alignments that are separated by the tributary streams of the Henares River. This special arrangement could explain the accelerated transformation of the Pleistocene talus, with very much higher scarp retreat rates than those recorded in the bibliography. The chronologies obtained using optically stimulated luminescence (OSL) in several of the six differentiated stages (S1-S6) are placed in relation to various climatic reconstructions of the Pleistocene, and especially, with the glacial phases of the Pyrenees (with which they show good temporal correlations). A further two stages of talus flatirons (S7 and S8) which developed during the Holocene at the foot of the older talus are studied. Independent accumulations also formed at the foot of the main scarps (Muela de Alarilla and Valdenoches). The chronology provided by archaeological remains and radiocarbon dating place their formation in the Iron Age Cold Epoch and the Little Ice Age (LIA), respectively.

Interpretation of the Miocene fossils in the Strymon basin in Northern Greece to determine their habitat

Abstract The sedimentary sequences of the upper Miocene in the Strymon basin in Northern Greece are composed of sedimentary rocks and are separated on an entirely new lithostratigraphic shape. Fossil-fauna has been collected from specific parts of the described geological sections, which mainly include mollusks from Bivalvia and Gastropoda. From laboratory research on the micro-fauna and micro-flora a number of taxonomic units of Foraminifera were determined and representatives of Actinozoa, Bryozoa, Crinoidea, Ostracoda, Otolithus, Diatomeae and Charophyta were found, which give a more-complete biostratigraphical image of the sediments. Based on these investigations with the use of the biofacial analysis, through the study of palaeoecology data of the fossils, three basic types of palaeohabitat and development of organisms were identified and a new palaeogeographic interpretation of the depositional environments in the Miocene basin is given.

Reassessing the age of Karpathos ophiolite (Dodecanese, Greece): consequences for Aegean correlations and Neotethys evolution

AbstractWhile the Neogene history of the Eastern Mediterranean region is now fairly well understood, our knowledge of older regional palaeogeographies is less accurate, especially the positions of blocks and nappes constituting the Aegean Islands prior to the Cenozoic. Our study focuses on the ophiolite exposed on the island of Karpathos (Dodecanese), which is located in the Aegean fore-arc at a pivotal position between the ‘western’ and ‘eastern’ ophiolites of the Mediterranean region and where conflicting Late Jurassic and Late Cretaceous ages have led to diverging tectonic and palaeogeographic interpretations. To test these ages, we targeted the radiolarian cherts that depositionally overlie the ophiolite and extracted diagnostic radiolarian assemblages of Aptian (∼125−113 Ma), early–middle Albian (∼113−105 Ma) and Turonian (∼93.9−89.8 Ma) ages. These results suggest that previous Late Cretaceous K–Ar isotopic ages (from 95.3 ± 4.2 Ma to 81.2 ± 1.6 Ma) may have been reset by Late Cretaceous metamorphism or affected by argon loss. Overall, the new Early Cretaceous ages show that the Karpathos ophiolite should not be correlated with the Pindos Nappes of Greece or the ophiolites of Cyprus or Syria but rather with the Lycian Nappes of Turkey and their root located in the Izmir–Ankara–Erzincan Suture Zone. Therefore, the Karpathos ophiolite represents a remnant of the Northern Neotethys, not the Pindos Ocean or the proto-Eastern Mediterranean Basin.

A local clay-varve chronology of Onega Ice Lake, NW Russia

Onega Ice Lake developed in front of the receding Late Weichselian ice margin in Russian Karelia. Glacial varves that formed in Onega Ice Lake have been earlier studied by means of varve counts, palaeomagnetism and 14C AMS dates from small lakes north of modern Lake Onega and from Lake Onega proper. Synchronous changes in magnetic parameters and similar stratigraphy of these varve records together with the existence of basin-wide marker interval of pink-coloured varves have been used for core-to-core correlation and palaeogeographic interpretations. Unfortunately, there are missing varve-to-varve correlations between these cores. We present a 1155 yr long local varve chronology based on 3 parallel overlapping cores from two small lakes in the Zaonezhsky Peninsula at the northern coast of Lake Onega. Varve counts and matching of varve series were made from digital images. Following the textural, structural, colour and thickness changes of varves within Onega Ice Lake varve series, six characteristic varve units are identified. These clay units reflect changing sedimentary conditions at the time of accumulation that in general can be interpreted as a progressively increasing distance to the retreating ice margin. Variations in varve thickness superimposed on that overall trend, namely two episodes of abrupt and consistent decrease in varve thickness, do not correspond to known lake-level changes or shifts in outflow directions. AMS chronology for deglaciation of Lake Onega basin gives some evidences for correlation of above intervals of decreased varve thickness with the GI-1c2 and GI-1B cold events in NGRIP δ 18O event stratigraphy but further age estimations are needed to confirm presented correlations. Interval of reddish-brown varves – earlier described also as the ‘pink horizon’ – was observed in all studied sequences, and according to varve correlation, at the same stratigraphical level, which proves its basin-wide synchronous appearance. Ca 100 km south of our study area, Saarnisto and Saarinen (2001) reported ca 200 more varves compared to our results. Visual correlation of varve thickness graphs places these extra varves to the proximal part of the series and indicate a rapid ice recession from the main lake basin to the northern Lake Onega area with the ice recession rate ca 500 m per year.

Stratigraphic Position of Tills in the Orłowo Cliff Section (Northern Poland): A New Approach

Abstract The site at Orłowo Cliff was used to analyse the stratigraphic position and palaeogeographic interpretations of the properties and depositional conditions of two basal tills from the Late Pleistocene. A multi-proxy approach involved lithofacies, petrographic analysis of the fine gravel fraction, analyses of indicator erratics and till fabric. TL dating of intra-moraine deposits was used to determine depositional time frames of tills. The sediment profile at Orłowo Cliff shows a distinct reduction in number of Pleistocene units. Obtained dating results suggest the presence of Middle and Late Pleistocene fluvial units. The main issue discussed is the stratigraphic position of the older till (Unit O-4). It can be assumed that this till was deposited probably during the Middle Weichselian (MIS4). At Orłowo Horn the till of Unit O-4 reveals incorporation of the erratic material derived from an older till in the surrounded area (according to petrographic composition - probably from MIS 8). The younger till (Unit O-6) was deposited in the Late Weichselian (MIS 2). Moreover, the till of Unit O-6 is characterised by a significant shift towards the south-west in terms of the erratic origin in Unit O-4.

The first occurrence of the earliest species of Acadoparadoxides outside West Gondwana (Cambrian; Holy Cross Mountains, Poland)

AbstractTwo hundred and eighty specimens of paradoxidids from two localities in the Holy Cross Mountains (Poland) have been reanalysed using morphometric techniques. Revision of the dataset provided evidence for the presence of two endemic taxa: Acadoparadoxides kozlowskii (Orłowski, 1959) and Acadoparadoxides samsonowiczi (Orłowski, 1959), both belonging to the earliest group of Acadoparadoxides, initially considered to be present only in Gondwanan successions. Thus, this is the first description of the members of this group outside West Gondwana. The taxonomic revision, and the presence of representatives of the earliest acadoparadoxidines coupled with the absence of taxa typical of Scandinavia that were previously described from this locality have resulted in the modification of the biostratigraphic scheme hitherto used in the Holy Cross Mountains. The newly established A. samsonowiczi – A. kozlowskii Assemblage Zone is correlated with the Morocconus notabilis Zone of Morocco, and thus represents the Cambrian Series 2 and 3 boundary interval. Links with West Gondwana challenge the existing palaeogeographic interpretations for the southern part of the Holy Cross Mountains and point to an urgent need to revise the position of the Małopolska Block during the middle Cambrian.

Tectonically controlled initiation of contemporaneous deep‐water channel systems along a Late Cretaceous continental margin, western British Columbia, Canada

AbstractSubmarine channel‐systems are globally prevalent on continental margins and their deposits record the transfer of significant volumes of sediment from continental catchments to deep‐water environments. These deposits contain signals of past events that can provide critical insight into the geological history of an area, including the long‐term (&gt;1 Ma) controls on sedimentation. Well‐exposed outcrops of the Late Cretaceous Nanaimo Group, British Columbia, Canada, provide an opportunity to investigate long‐term sediment‐routing in a tectonically active setting. This study combines detrital zircon geochronology with stratigraphic analysis to establish a robust, basin‐wide palaeogeographic framework that constrains the timing and distribution of coarse‐grained sediment transport and deposition in the Nanaimo forearc basin. Three south‐west trending submarine conduits are documented along a 135 km long strike‐oriented transect, parallel to the north‐west/south‐east trending basin. Composite conduit deposits are 350 to 700 m thick, 4 to 16 km wide, and record substantial delivery of coarse‐grained detritus (up to boulder‐sized clasts) within submarine channel‐levée systems. Maximum depositional ages derived from detrital zircon datasets constrain contemporaneous sediment transfer and deposition at each conduit location, which spanned between 73·5 ± 1·3 Ma to 69·1 ± 1·1 Ma around the Campanian–Maastrichtian boundary. Submarine conduits are spaced at 40 km and 70 km, and were likely connected to fluvial drainage systems sourced in uplifted catchments. Widespread, coarse‐grained deposits suggest that surface uplift associated with concurrent regional events (such as deformation and/or magma emplacement) along the North American margin may have promoted sediment delivery to the deep‐water basin. Comparisons to modern and ancient analogues support palaeogeographic interpretations, as well as the interpretation that pervasive coarse‐grained deep‐water sediment delivery was linked to tectonic activity. The integrated stratigraphic–geochronological approach used provides unique insight into the influence of regional tectonics on continental margin physiography and the nature of deep‐water sediment dispersal.

The Early to Middle Triassic continental–marine transition of NW Bulgaria: sedimentology, palynology and sequence stratigraphy

AbstractSedimentary facies and cycles of the Triassic continental–marine transition of NW Bulgaria are documented in detail from reference sections along the Iskar river gorge between the villages of Tserovo and Opletnya. The depositional environments evolved from anastomosing and meandering river systems in the Petrohan Terrigenous Group to mixed fluvial and tidal settings in the Svidol Formation, and to peritidal and shallow-marine conditions in the Opletnya Member of the Mogila Formation. For the first time, the palynostratigraphic data presented here allow for dating the transitional interval and for the precise identification of a major sequence boundary between the Petrohan Terrigenous Group and the Svidol Formation (Iskar Carbonate Group). This boundary most probably corresponds to the major sequence boundary Ol4 occurring in the upper Olenekian of the Tethyan realm and thus enables interregional correlation. The identification of regionally traceable sequence boundaries based on biostratigraphic age control is a first step towards a more accurate stratigraphic correlation and palaeogeographic interpretation of the Early to early Middle Triassic in NW Bulgaria.

Understanding coleoid migration patterns between eastern and western Europe – belemnite faunas from the upper lower Maastrichtian of Hrebenne, southeast Poland

The belemnite record of the lower Maastrichtian (as traditionally understood) in Europe is dominated by common and diverse representatives of the genus Belemnella Nowak, 1913. However, our knowledge of species from the middle lower Maastrichtian, in particular from the ‘Bln. sumensis’ belemnite zone, is severely limited, mainly because of a lack of outcrops of strata of this age. In order to understand the diversification and migratory patterns of belemnites from this interval better, I have combined available literature data with newly collected material. The present paper discusses the taxonomy, stratigraphy and palaeobiogeography of the late early Maastrichtian (sumensis Zone) Belemnella lineage, from the eastern part of the Roztocze Hills in southeast Poland. The belemnite material from Hrebenne comprises three species of Belemnella, namely Bln. sumensis Jeletzky, 1949, Bln. praearkhangelskii Naidin, 1964 and Bln. kajnarensis Naidin, 1964, in addition to a single specimen of Belemnitella pulchra Schulz, 1982. The taxonomic composition and diversification of this fauna is compared with contemporary assemblages from the upper Bln. obtusa Zone and the Bln. sumensis Zone of Kronsmoor (northwest Germany) and the Middle Vistula Valley section in central Poland. At a regional scale, the rich and diverse belemnite record of the Roztocze Hills and their simultaneous absence in the Nida Synclinorium is discussed in relation to palaeogeographical interpretations that assume the presence of the so-called Łysogóry-Dobrogea Land (or Krukienic Island) between those areas, which most likely governed the distribution of late early Maastrichtian belemnites in Poland. On a European scale, the taxonomic diversification and migratory pattern (if any) of representatives of the Belemnella stock are discussed and interpreted in comparison with forms known from western Europe and easterly areas as far the peri-Aralian Sea area of Kazakhstan.

Analysis of reworked sediments as a basis of the Palaeogene-Neogene palaeogeography reinterpretation: Case study of the Roztocze region (SE Poland)

Radiometric K/Ar dating of glauconite and nanno- and micropaleontologic analyses of calcareous nannoplankton, foraminifers and dinoflagellates isolated from the Miocene rocks in the Polish part of the Roztocze region, a northeastern part of the fore-bulge of the Carpathian Foreland Basin System - CFBS), SE Poland, reveal that these strata contain numerous microfossils and glauconite grains of the Upper Eocene and Lower Oligocene age. Such occurrences clearly indicate that these materials were redeposited from the Upper Eocene and Lower Oligocene marine rocks that must have originally covered most of the Roztocze and the surrounding area. It is therefore proposed herein that the geographical extent of the boreal, epi-continental basin during the Eocene–Oligocene was much greater than previously considered. Moreover, it appears that this basin was connected with the back-bulge zone of the warm Carpathian Basin (originally a northern part of the Tethys Basin which since Eocene/Oligocene boundary remained isolated as the Paratethys Basin). Hence, it is unlikely that the Roztocze region was uplifted during the Palaeogene as part of the Meta-Carpathian Swell, as it was earlied hypothesized. Instead, the Roztocze Swell formed during the Sarmatian, in the last stage of the development of the fore-bulge structure in the foreland of the up-thrust Carpathian orogenic belt. Multiple redeposition of sediments is the reason that the absolute dating (K/Ar) of glauconite, as well as incomprehensive palaeontological analysis could result in erroneous stratigraphic and palaeogeographic interpretations.

Мікроморфологія і палеогеографічні умови формування горохівського викопного ґрунтового комплексу Подільської височини

The Horokhiv fossil soil complex was formed during the Eemian interglacial and early interstadials of the Upper Pleistocene (MIS 5) within the Podolian Upland. It can be considered as a marking horizon which is quite easy to diagnose. During the Eemian interglacial forest soil was formed and during the early interstadials of the Upper Pleistocene, there were formed three low-thickness and mainly chernozems-like soils which were highly deformed by delluvial-solifluctional processes. These interstadial soils had been called the Kolodiiv soils. All the Kolodiiv soils currently are described only in the Proniatyn section on the Podolian Upland. In the most cases above the Eemian soil, there is the thick humus-accumulative horizon of the second phase Horokhiv soil are developed. It is hard to differentiate this horizon to the distinct soils. Furthermore, it is worth mentioning that on Podillia to the south from Ternopil-Khmelnytskyi latitude during the first (Eemian) stage of soil formation chernozems also were formed. Therefore, it is not always easy to distinguish separate soil horizons of the first and second phases in the profile of Horokhiv pedocomplex. The aim of this work is to investigate the characteristic features of micromorphological structure of the Horokhiv fossil soil complex and on its basis to find out the palaeogeographical conditions of the time when it was formed. A common method of micromorphological studies of fossil soils was used to achieve the goal. General lithological and micromorphological descriptions of the Horokhiv fossil soil complex in a number of key sections of the Podolian Upland are given in the article. The results of micromorphological studies indicate that the soils of the Horokhiv pedocomplex contain a significant amount of carbonate concretions (mainly microcrystalline forms of calcite), often ferruginous, with the numerous evidences of the ferruginous clay movement down the profile in the microstructure. The changing nature of the water-air regime was inherent to them. The nature and content of organic residues, the orientation of the clay material, and the presence of ferruginous manganese concretions make it possible to speak about sufficiently favourable conditions for the development of vegetation. Palaeogeographical interpretation of natural geographical conditions of the Horokhiv fossil soil complex formation based on the analysis of its microstructure allows us to conclude that the pedocomplex could be formed in the conditions of dry steppes and it is similar to modern chernozems. Key words: loess, fossil soil, Horokhiv fossil soil complex, micromorphological analysis, thin sections, Pleistocene, delluvial-solifluctional processes.

Selected Middle Ordovician key conodont species from the Santa Gertrudis Formation (Salta, Argentina): an approach to its biostratigraphical significance

AbstractWe have analysed a newly exposed conodont association from the Santa Gertrudis Formation in the Mojotoro Range, Eastern Cordillera of Salta province, Argentina. The key speciesBaltoniodus triangularis(Lindström),Trapezognathus quadrangulum(Lindström) andErraticodon patuCooper are present. A new species of the genusBaltoniodus(Baltoniodus cooperisp. nov.) and elements ofPeriodonaff.P. flabellumare included in this conodont study. The key conodontB. triangularisindicates an age of lower Dapingian (Middle Ordovician) for the bearing strata. This was also recognized in other localities of the Eastern Cordillera, allowing their correlation. The conodonts from the Santa Gertrudis Formation provide conclusive elements on palaeogeographic interpretation by sharing species with Baltoscandia, South China and Australia, suggesting strong faunal affinities with these provinces.

Physico-chemical tuning of palaeogeographic shifts: Bhuj formation, Kutch, India

The long-standing dilemma between two extremes in palaeogeographic interpretation is resolved for the basal 115 m of the eastern exposures of the Lower Cretaceous Bhuj Formation, at the top of the hydrocarbon prospective Mesozoics of Kutch, India. An explicit record of a mega-scale event of relative sea level rise is found sandwiched between two fluvial stratigraphic intervals that amalgamate only at the eastern extremity of the exposure of the Formation. A localized estuary in the middle had its axis roughly parallel to the pre and post-inundation river channels, although a tributary made a significant detour. Variation in the fine sandstone-mudstone lithology documents decline in depositional energy in the mid-estuary amenable to coal formation. Sediment within the estuary had been routed through both the ends, palaeocurrent turning shore-parallel only at the estuary-mouth. Exception arises in case of some isolated lenses of very poorly sorted and coarse-grained deposits depicting flash floods in the tributary. Burrow characteristics change delicately in response to the inferred changes in the depositional scenario along the estuary.Resting on a coarsening upward ramp the initially fining and then coarsening upward estuarine succession is prograding, though not steadily. It was wave-dominated, but tide left imprint behind the estuary mouth bar gaining in intensity because of valley constriction. Macroscale changes in relative sea level, perhaps eliciting local tectonics, are recorded in the transient hysteresis in the stratigraphic trend with or without palaeocurrent diversions.The fluvial stratigraphic intervals encasing the marine interval have, in terms of architectural elements, many commonalities, but also some significant disparities. The latter indicates channel meandering in the pre-inundation period and braiding after inundation. Unlike the marine sandstones, bar-channel sandstones of the riverine deposits are distinctly less sorted, bimodal, even polymodal in grain-size distribution. Mineralogical composition identifies the sandstones as craton-derived, but their geochemical distinctions point to variation in parent rock composition under the maze of palaeogeographic overprints.