Marine Incursion Research Articles

Middle Wisconsinan marine shells near Repulse Bay, Nunavut, Canada: implications for Marine Isotope Stage 3 ice‐free conditions and Laurentide Ice Sheet dynamics in north‐west Hudson Bay

ABSTRACTEvidence suggesting a reduction of the Laurentide Ice Sheet (LIS) during Marine Isotope Stage 3 (MIS 3) is widespread but the boundaries of the ice sheet and the timing of minimum ice extent are still poorly constrained. Radiocarbon dating of glacially transported marine mollusks in Rae Isthmus ice stream till south of Repulse Bay, Nunavut, Canada, provides new evidence for MIS 3 deglaciation in the north‐west part of Hudson Bay. Middle Wisconsinan finite 14C ages varying between 31.7 and 39.2k 14C a BP (∼35.0 and 43.7k cal a) indicate a marine event(s) for a minimum of ∼8.7k cal years. Our findings suggest ice‐free conditions in the ice stream source area in proto‐Roes Welcome Sound, and therefore significant glacial recession of the LIS margin during the Middle Wisconsinan, much farther in the interior of the ice sheet than previously known. The marine incursion possibly occurred because of a calving bay developed from the north in the Gulf of Boothia − Committee Bay area following the recession and collapse of the ice stream. After the MIS 3 marine episode(s), the topographically controlled ice stream stemming from the eastern end of the Keewatin Ice Divide was re‐activated, and maintained until deglaciation.

Evolution of the depositional environments of the Jurassic Walloon Coal Measures, Surat Basin, Queensland, Australia

AbstractThe Jurassic Walloon Coal Measures of the Surat Basin in eastern Australia host the continent's most significant coal bed methane resources. Previous studies have interpreted the Walloon Coal Measures within a single depositional facies model encompassing a wholly terrestrial setting. Using a multidisciplinary approach (facies analysis, palynology and wireline logs), the evolution of the Walloon Coal Measures is described within a new chronostratigraphic framework defined by accurate and precise U–Pb tuff dates. Analysis of sedimentary facies indicates that the majority of the Walloon Coal Measures was deposited by relatively small (<300 m wide), low gradient rivers on a poorly‐drained floodplain with numerous small lakes and mires. However, this study also identified some marine‐influenced facies with brackish palynomorphs (notably dinoflagellate cysts) and tidal sedimentary structures. These facies appear to have been deposited in estuaries during times of transgression. The evidence for base level shifts suggests that the coals may not have coevally accumulated with at least some of the thicker sandstones. Palaeogeographic maps for eleven time intervals suggest that rivers drained towards to the south/south‐west and south‐east, as indicated by sandstone percentage and gross unit isopach maps, presumably into proximal estuarine complexes. Marine incursions into the continent probably came from the north and east during times of high eustatic sea level and as precursors to those of the more persistent and extensive transgressions of the Early Cretaceous. A similar multidisciplinary approach should help to elucidate the evolution of other fluviolacustrine systems in other basins and aid in resource prediction.

Pyrite sulfur isotopes constrained by sedimentation rates: Evidence from sediments on the East China Sea inner shelf since the late Pleistocene

Isotopic compositions of coeval sulfide and sulfate have been widely employed to reconstruct the seawater chemistry evolution over geologic time; however, these signals can be modulated by other factors, such as the sedimentation rate. Here, we present a data set of pyrite sulfur isotopes (δ34Spy) derived from 60-m drilled core sediments deposited on the inner shelf of the East China Sea since 16.5 ka. The resulting δ34Spy values range from −38.2 to 15.0‰ (Vienna Canyon Diablo Troilite; V-CDT), representing a range of 53.2‰. Freshwater deposition before 12.3 ka produced a limited pyrite abundance and δ34Spy values that fall within the typical range of freshwater environments. After the marine incursion in the study area at 12.3 ka, variations in the δ34Spy values become significantly correlated with sedimentation rates (SRs; r = 0.78, p < 0.01), which were controlled by the intensity of coastal currents in response to the East Asian winter monsoon. Specifically, pyrite sulfur is markedly depleted in 34S during the intervals with low SRs (δ34Spy < −30‰) relative to that observed during the intervals with high SRs (δ34Spy > 0‰), suggesting that SRs exert controls on δ34Spy values. We propose that these sedimentary controls are expressed by modulating the connectivity between porewaters and the overlying seawater. Low SRs tend to form an open diagenetic system, in which the pyrites are able to preserve the large biological fractionations associated with microbial sulfate reduction (and disproportionation). In contrast, high SRs favour a restricted diagenetic system, in which the distillation of porewater sulfate produces pyrites enriched in 34S, masking the magnitude of biological fractionation during microbial sulfur cycling. These findings highlight the critical effect of the local sedimentation regime on pyrite sulfur isotopic compositions, especially within shallow depositional environments, over geologic time.

Provenance of detrital zircons of the canindé group (Parnaíba basin), northeastern Brazil

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 UPb 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.

Organic geochemistry, petrology, and conventional and unconventional hydrocarbon resource potential of Paleogene saline source rocks in eastern China: The Biyang Sag of the Nanxiang Basin

Abstract Basins containing Paleogene organic-rich shales formed in a saline lacustrine environment are widespread in eastern China, and they provide sources of hydrocarbons in numerous petroleum fields. However, research on these basins has been patchy, which limits our understanding of the hydrocarbon source rocks. To address this problem, we selected the relatively understudied Nanxiang Basin as the study area and, more specifically, the third member of the Paleogene Hetaoyuan Formation (Eh3), which is the main hydrocarbon-generating layer in the Biyang Sag of this basin. In this paper, we report on the organic petrology and geochemistry of Eh3, and further analyze both its conventional and unconventional hydrocarbon potential. Our results show that the organic matter (OM) within the shales of Eh3 had bioprecursors that were mainly phytoplankton, bacteria, and benthic algae, with relatively small contributions from animal and higher plant materials. The shales have an average OM abundance (total organic carbon, or TOC) of 2.96 wt%, thus meeting the criterion of a good-quality source rock. Their organic-matter is mainly type I to type II, and in terms of thermal maturity they range from low maturity to mature, thus displaying the characteristics required to generate oil. The results of our molecular geochemical analyses show that the sediments of Eh3 in the Biyang Sag belong predominantly to deep or semi-deep lake facies, and they were deposited in a reducing environment and may have been affected by a marine incursion. The evidence for this includes Pr/Ph values of

The shutdown of an anoxic giant: Magnetostratigraphic dating of the end of the Maikop Sea

Paratethys, the lost sea of central Eurasia, was an anoxic giant during Oligocene – early Miocene (Maikop Series) times. With a size matching the modern-day Mediterranean Sea and a history of anoxic conditions that lasted for over 20 Myrs, the eastern part of this realm (Black Sea-Caspian Sea domain) holds key records for understanding the build-up, maintenance and collapse of anoxia in marginal seas. Here, we show that the collapse of anoxic Maikop conditions was caused by middle Miocene paleogeographic changes in the Paratethys gateway configuration, when a mid-Langhian (Badenian-Tarkhanian) transgression flooded and oxygenated the Eastern Paratethys. We present an integrated magneto-biostratigraphic framework for the early Middle Miocene (Tarkhanian-Chokrakian-Karaganian regional stages) of the Eastern Paratethys and date the lithological transition from anoxic black shales of the Maikop Series to fossiliferous marine marls and limestones of the regional Tarkhanian stage. For this purpose, we selected two long and time-equivalent sedimentary successions, exposed along the Belaya and the Pshekha rivers, in the Maikop type area in Ciscaucasia (southern Russia). We show that a significant but short marine incursion took place during the Tarkhanian, ending the long-lasting Maikop anoxia of the basin. Our magnetostratigraphic results reveal coherent polarity patterns, which allow a straightforward correlation with the time interval 15–12 Ma of the Geomagnetic Polarity Time Scale. The Tarkhanian flooding occurred during a relatively short normal polarity interval that correlates with C5Bn, resulting in an age of 14.85 Ma. The regional Tarkhanian/Chokrakian stage boundary is located within C5ADn at an age of 14.75 Ma and the Chokrakian/Karaganian boundary is tentatively correlated with C5ACn and an age of 13.9–13.8 Ma. Our new Tarkhanian flooding age reveals a paleogeographic scenario that is different from many previous reconstructions. Instead of envisaging marine connections to the Indian Ocean, we show that major changes in connectivity between the Eastern and Central Paratethys seas have caused the influx of marine waters during the Tarkhanian. An increase in marine connectivity with the Mediterranean during a short episode of rapid sea-level rise triggered mixing and ended the widespread anoxia in the Eastern Paratethys. The mixing episode was short-lived (~100 kyr) as the sea-level rise slowed down and connectivity degraded because of tectonic uplift in the gateway area.

Jurassic break-up of the Peri-Gondwanan margin in northern Colombia: Basin formation and implications for terrane transfer

Jurassic extensional basins developed along the northwestern margin of South America during the break-up of Pangea. Presently, these basins are dispersed in several tectonic blocks of the northern Andes and Mexico, hindering reconstruction of western equatorial Pangea before break-up. This is the case of the Cosinas Basin (Guajira block) and the Machiques Basin (Perijá Range), in northern Colombia, which are filled by Jurassic sedimentary and volcano-sedimentary successions. Autochthonous and para-autochthonous hypotheses on the origin of this basins have been proposed. The purpose of this research is to document the sedimentological evolution, depositional age (Sr-isotope + U-Pb geochronology), sediment provenance and paleogeography of the Cosinas and Machiques basins in order to constrain whether these basins formed within a single extensional margin or they formed as extensional basins in different tectonic blocks. Volcanic detrital zircon U-Pb ages documented in La Quinta Formation in the Machiques Basin and at the base of Rancho Grande Formation in the Cosinas Basin suggest that extensional basins were active in Early Jurassic time. However, a significant difference exists in their subsequent history. Whereas in the Machiques Basin dominates the accumulation of Lower and Middle Jurassic volcanoclastic deposits with abrupt lateral thickness changes, accumulation in the Cosinas Basin is dominantly of siliciclastic strata, with the record of two major marine incursions in Late Jurassic time. Integration of provenance results indicates that the Santander Massif supplied sediments to the Machiques Basin. In contrast, Middle to Upper Jurassic sandstones of the Cosinas Basin document unroofing of basement blocks that include metamorphic, sedimentary and plutonic rocks from the Guajira and Maya blocks. The similarity in age and composition of pre-Jurassic rocks in northwestern South America and the so-called peri-Gondwana blocks in the Mexican subcontinent (i.e., Maya and Oaxaquia blocks) challenge the use of detrital zircon population as an indicator of the autochthonous or para-autochthonous origin of the Guajira block. Large uncertainty of paleomagnetic results, and the lack of constraints for the time magnetization acquisition preclude estimating paleolatitudes for the Guajira block in Jurassic time but support previous interpretation of ca. 70°-90° clockwise rotation of the Guajira block relative to stable South America craton.Our preferred paleogeography considers that the Cosinas and Machiques basins were close to each other along the western continental margin of Pangea during the onset of extension in Early Jurassic time. The change from continental to marine depositional environments in Middle to Late Jurassic time along the Cosinas Basin, which have not been identified in the Machiques Basin or other autochthonous Jurassic basins in northwestern South America, allow us to propose that these blocks were separated during the Callovian - Tithonian interval, with the Cosinas Basin remaining closer to a conjugate Mexican margin, that we interpret as the Maya block. Collision of the Guajira block with the South American margin occurred near the Jurassic-Cretaceous boundary, as documented by deformation of Jurassic units previous to deposition of Berriasian strata in the Guajira block.

A Barremian-?Aptian Tethyan precursor of the Cretaceous marine flooding of Morocco: Evidence from the red-bed series within the “Marginal Folds” of the eastern High Atlas

Stratigraphic, sedimentologic, and micropaleontologic studies have been undertaken on the “Infra-Cenomanian” continental red beds (= Dekkar Group) located on the northern side of the Moroccan eastern High Atlas. Rich charophyte assemblages containing Sphaerochara magna, Ascidiella stellata, Hemiclavator sp. A, Globator trochiliscoides, Atopochara trivolvis, At. triquetra, and Flabellochara harrisii indicate a late Barremian age for the lower part of the series. Within the continental deposits we have discovered in the Middle Member of the Dekkar 2 Formation limestones and marls containing echinoderms, dasycladacean algae and foraminifera (miliolids, Ammobaculites sp., Choffatella decipiens). The existence of two littoral to lagoonal-marine intercalations within the continental sedimentation reveals marine transgressive events during the late Barremian–?early Aptian. The lateral extension of these marine sediments allows the erection of paleogeographic boundaries that define a « Marginal Folds Gulf » characterized mainly by restricted marine paleoenvironments. This E-W directed gulf is a relatively long depression, a few tens of kilometers wide and one hundred kilometers long, developed in an area which is now at the foot of the eastern High Atlas. The infilling deposits is dominantly controlled by the distance from the North High Atlas Fault. The gulf terminated westward and probably opened northeastward into the Tethyan domain. This narrow gulf was separated from both the Tethyan Gulf known in the Central Middle Atlas during the Aptian and the coeval Atlantic Gulf located on the northern side of the Marrakech and Central High Atlas. Thus, the « Marginal Folds Gulf » is a new paleogeographic feature that documents marine incursions within the Jurassic–Early Cretaceous continental areas of the NW Africa.

Fossil glochidia (Bivalvia: Unionida: Hyriidae) from the middle Miocene of western Amazonia (Peru)

Unionid bivalves are a common and widely distributed group of freshwater mussels, presumably known since the Triassic. One peculiar trait is their life cycle, with brooding of eggs in portions of the gills and release of usually fish-parasitizing larvae. The morphology of these larvae (glochidia or lasidia) is an important character for unionid classification and hence for phylogenetic reconstructions. Dispersal capacity and success of unionids through geological times is assumed to be largely affected by the evolution of temporary parasitism. Nevertheless, pre-Quaternary fossil proof of unionid larvae has been lacking until now, which renders some palaeobiological, phylogenetic and palaeobiogeographical scenarios arguable. Here we document late middle Miocene glochidia from the Pebas Formation (Porvenir, north-eastern Peru). Based on morphological comparisons with Recent glochidia and the accompanying fossil record, these larvae are related to the Hyriidae genus Diplodon Spix, 1827. Due to the lack of ‘hooks’ (inward-directed projections on the ventral edge of the glochidium) the larvae probably did not parasitize (fish) hosts, which restricted their dispersal ability. In this case, ‘unhooked’ is presumably a derived feature related to direct larval development. The strata containing these glochidia have been interpreted as marginal marine deposits with high-frequency salinity fluctuations. The associated mollusc and ostracod fauna is strongly dominated by euryhaline, endemic species. Only subordinately ‘freshwater’ and ‘marginal marine’ taxa co-occur, as well as euryhaline foraminifers. Stable isotope analyses (δ18O, δ13C) performed on ostracods and foraminifers furnished very light ratios, indicative of freshwater conditions. It remains unresolved if some marine-derived ostracods and also foraminifers were able to adapt to freshwater settings or if marine incursions affected western Amazonia in late middle Miocene times. Possibly the combination of, for example, fluctuating oxygenation and/or salinity and the complex reproductive strategy diminished the competitiveness of unionids within the Pebas wetlands.

Identifying marine incursions into the Paleogene Bohai Bay Basin lake system in northeastern China

The extent of marine influence on the Paleogene Bohai Bay Basin in northeastern China, which accumulated mainly continental (e.g., fluvial and lacustrine) facies, remains under debate. Evidence from geochemical, paleontological, and lithological data have documented several marine incursions, but no systematic study has been conducted to investigate their timing and frequency and their significance for understanding the Paleogene tectonic evolution of northeastern China. In order to address the marine influence on sediment accumulation and to identify variations in paleosalinity during deposition of the mid-Eocene lower Es3 (Es3L) Member of the Shahejie Formation, this study analyzed multiple paleosalinity proxies (B/Ga, Sr/Ba, and S/TOC) in fine-grained siliciclastic (argillaceous) sediments of the Luo-69 drillcore from the Dongying Depression. All three proxies yielded similar paleosalinity interpretations, with peak salinity and marine influence (i.e., maximum B/Ga, Sr/Ba, and S/TOC values) occurring at the base of the Es3L Member, and progressively declining salinities, representing a shift toward brackish conditions, upsection over an interval of 185.5 m representing ~2.2 Myr of sedimentation. This paleosalinity record suggests gradual long-term variations that were probably due to changes in tectonically controlled gateways linking the Bohai Bay Basin to the Yellow Sea. In addition to analysis of the mid-Eocene Es3L Member, published data on the stratigraphic distribution of marine fossils, glauconite, and elemental paleosalinity proxies are applied to evaluate the history of marine incursions into the Bohai Bay lake system throughout the mid to late Paleogene (~50–24 Ma). This analysis revealed four intervals of probable major marine incursions dating to the early Eocene, the middle Eocene, the early Oligocene, and the late Oligocene.

Sedimentary and microfossil imprint from historical earthquakes and tsunamis, Jalisco coast, Mexican subduction

Tsunamis are high energy events capable of leaving their imprint in the geological record. The western Mexican Pacific coast, located in the Mexican Subduction Zone, is prone to large earthquakes (M ≥ 8.0) where tsunami hazard has been underrated. The geologic archive obtained in a sheltered coastal lagoon was analyzed applying a multi-proxy approach to reveal the occurrence of historical earthquakes in the Jalisco coast. Foraminifera and Ostracoda aid identifying earthquake and tsunami geologic evidence in this section of the Mexican Pacific coast, where tropical conditions prevail. We present the evidence of changes in stratigraphy, grain size, biostratigraphy supported by archaeomagnetic dating. They were complemented with published 210Pb dating, magnetic properties, and historical data. We identified three events: the tsunami deposit left by the June 3rd, 1932 tsunami, produced by the largest earthquake (M = 8.2) recorded in instrumental history in México and the coseismic deformation resulting from the 1932 event, also a probable tsunami deposit likely produced by an historical earthquake in 1900, and the coseismic deformation associated to this event, and the coseismic deformation resulting produced by the 1563 earthquake. The site geomorphology, with a marginal lagoon closed by a little barrier 7 m ± 1 m above sea level, precludes tropical storms as responsible for marine incursions. This work contributes to strengthening the earthquake and associated tsunamis chronology, aiming to improve coastal hazard assessment for the area.

Benthic foraminiferal paleoecology of the Maastrichtian succession at the Kharga Oasis, Western Desert, Egypt

The present work deals with the benthic foraminiferal investigations and analyses of the Maastrichtian succession from two sections in the Kharga Oasis (Naqb El-Rufuf and Gabal Teir), to evaluate the prevailing paleobathymetric and paleoenvironmental conditions. Three benthic foraminiferal assemblages have been distinguished by the R-mode cluster analysis. The first two clusters are dominated by simple-walled and complex-walled non-calcareous agglutinated foraminifera, respectively; while the third assemblage is characterized by calcareous agglutinated and calcareous benthic foraminiferal species. The Q-mode Detrended Correspondence Analysis (DCA) of the studied samples indicates five main groups designated as five biofacies (IV), each with a characteristic faunal structure. The overall dominance of the non-calcareous agglutinated foraminifera and the sporadic occurrence of the calcareous benthic foraminifera suggest deposition in a shallow water environment of restricted brackish, lagoonal, and littoral setting with occasional marine incursions. The distribution of the identified benthic foraminiferal species suggests deposition under oxygen-depleted conditions with high organic matter flux. Surficial epifaunal taxa dominate the benthic assemblages at certain intervals suggesting episodes of stagnation and elevated position of the redox boundary relative to the water/sediment interface.

Coastal wetlands as markers of transgression in proximal extensional systems (Berriasian, W Cameros Basin, Spain)

The early stages of intraplate extensional systems commonly are recorded by deposition of continental sediments. In this context, given appropriate tectonics and eustasy, transgressions can be well recorded in the areas of the basins located close to the sea, but they may be difficult to recognize in the innermost landwards areas of the system. This situation occurs in the innermost Upper Jurassic-Early Cretaceous Cameros Basin, part of the Iberian Extensional System (N. Spain), where a Berriasian transgression is recorded. The Berriasian succession in this area consists of siliciclastic deposits (sandstone and mudstone) of the Salcedal Formation and of carbonate and mixed carbonate-fine siliciclastic deposits (limestone and marl) of the San Marcos Formation. The sedimentological analysis of this depositional succession indicates that a Berriasian carbonate coastal wetland system occupied that sector of the Cameros Basin during deposition of the San Marcos Formation. This carbonate coastal wetland system consisted of shallow and quiet water bodies including some with marine influence others with no to very little marine influence, and palustrine areas. A semiarid climate characterized by the seasonal alternation of short wet and long dry periods caused water bodies of the system to undergo episodic desiccation and subaerial exposure. Moreover, this complex mosaic of sub-environments was connected laterally with a distal zone of a distributive fluvial system that was rimmed by siliciclastic tidal flats during phases of greater marine influence. The paleogeographic arrangement of this coastal wetland depositional system indicates that the marine influence came from the Basque-Cantabrian Basin to the north. During the period of Berriasian maximum marine influence, accommodation linked to the eustatic rise added to accommodation generated by tectonic subsidence from the extensional reactivation of late Variscan strike-slip faults. All these factors favored marine incursion into the west Cameros Basin from the Basque-Cantabrian Basin to the north. The example of the Berriasian transgression recorded in the W Cameros Basin by establishment of coastal wetland systems matches the interpretations of previous studies in neighboring areas. In those areas, complex coastal systems record transgressions in the innermost parts of the intraplate extensional basins of the Iberian Plate. This observation suggests that this paleogeographic and sedimentological arrangement may be common in the innermost parts of intraplate extensional basins during transgressive episodes throughout the geological record.

Low‐Temperature Thermochronology of the Chatkal‐Kurama Terrane (Uzbekistan‐Tajikistan): Insights Into the Meso‐Cenozoic Thermal History of the Western Tian Shan

AbstractThe Chatkal‐Kurama terrane represents a key region in understanding the tectonic evolution of the western Tian Shan. In this contribution, we present new thermochronological data (zircon [U‐Th‐Sm]/He, apatite fission track, and apatite [U‐Th‐Sm]/He) and the associated thermal history models for 30 igneous samples from the Chatkal‐Kurama terrane within Uzbekistan and Tajikistan (west of the Talas‐Fergana Fault) and integrate our data with published data from the central Tian Shan (east of the Talas‐Fergana Fault). The Chatkal‐Kurama terrane experienced a phase of rapid cooling during the Triassic‐Jurassic at ca. 225–190 Ma, which we interpret as a far‐field response to the closure of the Palaeo‐Asian Ocean or the accretion of the Qiangtang terrane on to the Eurasian margin. In the Late Jurassic to the Early Cretaceous, the Chatkal‐Kurama terrane experienced a period of tectonic stability and denudation, before transitioning into a period of marine incursions of the Paratethys Sea. In contrast, fast cooling is recorded for the Kyrgyz central Tian Shan to the east of the Talas‐Fergana Fault. The differing thermal histories at either side of the Talas‐Fergana Fault suggest that the fault induced a topographic divide during the Late Jurassic‐Early Cretaceous, with high relief in the east (Kyrgyz Tian Shan) and low relief to the west (Uzbek‐Tajik Tian Shan). Finally, the Chatkal‐Kurama terrane experienced renewed tectonic activity since ca. 30 Ma, related with the distant India‐Eurasia collision and Pamir indentation. The Cenozoic reactivation induced crustal tilting of the Chatkal‐Kurama terrane, progressively exposing deeper rocks to the southwest.

Deposition in a changing paleogulf: evidence from the Pliocene–Quaternary sedimentary succession of the Nile Delta, Egypt

Sedimentary complexes of ancient gulfs provide valuable information about paleoenvironmental dynamics. The study of several Pliocene–Pleistocene sections allowed reconstruction of the regional stratigraphical framework in the southwestern fringes of the Nile Delta. The Kafr El-Shiekh, the Gar El-Muluk, and the Kom El-Shelul formations of the Zanclean Age and the Wastani Formation of the Piacenzian Age constitute the Pliocene sedimentary succession in the study area. The establishment of 11 facies types related to 5 facies associations coupled with the results of the stratigraphical study indicate the existence of a paleogulf corresponding to the modern delta and lower valley of the Nile. This Nile Paleogulf appeared and reached its maximum spatial extent in the beginning of the Pliocene. Then, it retreated gradually and disappeared before the end of this epoch when alluvial sedimentation reestablished. There was significant flux of siliciclastic material to the study area. The Zanclean Flood in the Mediterranean Sea allowed marine incursion in the study area where the river valley incised during the precedent Messinian Salinity Crisis. Regional tectonic uplift and filling of the accommodation space with siliciclastic material from the eroded land were the main controls on the paleogulf evolution. Strengthened glaciation triggered global sea level fall, and alluvial deposition dominated the study area in the late Pliocene–Pleistocene.

Syn-tectonic sedimentary evolution of the continental late Palaeozoic-early Mesozoic Erill Castell-Estac Basin and its significance in the development of the central Pyrenees Basin

The break-up of Pangea remains one of the most interesting moments in the Earth's history. In the Pyrenees this geological moment is represented by continental successions, giving rise to a magnificent example of the creation of new basins and their sedimentary fill. In this work we present a study based on stratigraphy, sedimentology and synsedimentary tectonics data; on this basis, we define for the first time the different tectono-stratigraphic phases that occurred in the evolution of the incipient continental basin of the Erill Castell-Estac Basin (Southern Pyrenees, NE Spain). Traditionally, four lithostratigraphic units have been defined in the area and grouped into tectono-stratigraphic units, but we propose three sedimentary cycles characterized by fining upward trends and separated by angular unconformities. The first sedimentary cycle (late Carboniferous-early Permian) is strongly related to intense volcanic activity and is characterized by isolated sub-basins. In the upper part of this cycle, fluvial and lacustrine deposits were deposited in a volcanic and transtensive tectonic context. In the second sedimentary cycle (early-middle Permian), the connection between the sub-basins started in a transtensive tectonic context. The main deposits in this cycle are lacustrine and fluvial, relative to playa-lake environments with a minor volcanic influence. Finally, the third sedimentary cycle (Early-Middle Triassic) is represented by meandering fluvial deposits with scarce lacustrine environments and no volcanic influence. The syn-depositional tectonic context is extensional, at the top of this last cycle the first Mesozoic marine incursions are preserved. Detailed description of the evolution of the Erill Castell-Estac Basin provides a new example of the sedimentary filling of strike-slip basins and is a key point to further considerations of the still unknown role of the Carboniferous to Triassic Pyrenean basins in Pangea break-up.

Palynology and micropalaeontology of the Pliocene - Pleistocene transition in outcrop from the western Caspian Sea, Azerbaijan: Potential links with the Mediterranean, Black Sea and the Arctic Ocean?

New palynological, ostracod and foraminiferal data are presented from a long outcrop section in the Jeirankechmez river valley, Azerbaijan, near the western coast of the Caspian Sea. The interval studied includes the upper part of the Pliocene Productive Series and overlying Plio-Pleistocene Akchagylian (Akchagyl) and Apsheronian (Apsheron) regional stages. Productive Series sediments were deposited in a closed fluvio-lacustrine basin, isolated from any marine influence. The onset of Akchagyl deposition is marked by a lithological change associated with a significant flooding event that, at its maximum extent, reached the Sea of Azov and into present-day Iran, Kazakhstan, Turkmenistan and Russia. At the Jeirankechmez locality, the lowermost beds of the Akchagyl contain predominantly freshwater assemblages with very minimal marine or brackish content showing that the onset of Akchagyl deposition was not a marine induced event. Reworked Mesozoic palynomorphs occur frequently in this lowermost interval, including the reworked pollen taxa Aquilapollenites-Triprojectus that were eroded from the north or north-east.Significant marine influence is evident ca. 30 m above the base of the Akchagyl in the studied outcrop, marked by the ‘Cassidulina Beds’ which contain a distinct but low diversity assemblage of foraminifera that occurs widely and can be correlated in many parts of the greater Caspian region. Dinoflagellate cysts (dinocysts) in the marine interval include frequent specimens very similar to Algidasphaeridium capillatum (Matsuoka and Bujak), a species only previously recorded from the northern Bering Sea. The combined evidence from these dinocysts and foraminifera suggests that a marine (i.e. seaway) connection existed briefly between the Arctic Ocean and the Caspian Sea at the very end of the Pliocene.Re-examination of core material from the Adriatic Sea shows that Cassidulina reniforme (Nørvang) was present in the Mediterranean during and shortly after the Last Glacial Maximum. The possibility that the end Pliocene marine incursion came from the Mediterranean via the Black Sea region to the Caspian Sea cannot be entirely ruled out but is considered unlikely. Biometric analyses are applied to obtain a better understanding of the palaeoenvironmental significance of the assemblages dominated by cassidulinids.An interval >300 m thick is assigned to the Apsheron regional stage on the basis of predominantly brackish ostracod and dinocyst associations. The dinocysts are of ‘Peri-Paratethyan’ affinity and closely resemble species first described from Miocene and Pliocene sediments in the Pannonian and Dacic basins of Eastern Europe. Many similarities exist in the microplankton records (dinocysts and acritarchs) between the Caspian Sea, the Black Sea and Central Paratethys.

Isolation by marine barriers and climate explain areas of endemism in an island rodent

AbstractAimThe Indonesian island of Sulawesi is home to thousands of endemic terrestrial animal species. Phylogeographical studies of some of these taxa revealed concordant distribution patterns (areas of endemism; AoEs), suggestive of a shared evolutionary or ecological mechanism driving divergence among various terrestrial taxa. Generally, AoEs have been attributed to Pleistocene marine incursions, geological fault zones and Sulawesi's history as an archipelago. We test, for the first time, the hypothesis that population divergences are associated with unsuitable climate spaces at the boundaries between these areas.LocationSulawesi, Indonesia.TaxonMaxomys musschenbroekii, a common murid rodent endemic to Sulawesi.MethodsWe sequenced a mitochondrial gene, four nuclear protein‐coding genes and hundreds of ultraconserved elements from individuals sampled across the island, which we used to build intraspecific phylogenies and identify population structure. To test climate‐related hypotheses, we used multiple regression to assess the extent to which genetic distances, over‐land geographical distances, environmental distances (derived from ecological niche model resistance surfaces) and areas of endemism are correlated.ResultsIn all three genetic datasets, we inferred phylogeographical structure that is geographically concordant with previously defined AoEs. Ecological niche models showed a similar geography of suitability across the island since the Last Glacial Maximum, with varying levels of unsuitable climate space between AoEs. Genetic distances were more strongly correlated with environmental distances than geographical distances and interspecific divergences arose just in the past 1.5 Myr.Main ConclusionsPopulation divergences within M. musschenbroekii are consistent with AoE definitions from other taxa. Stable areas of unsuitable habitat near AoE boundaries probably supplemented marine incursions in generating population structure within M. musschenbroekii and other co‐distributed species.

Sky, sea, and forest islands: Diversification in the African leaf‐folding frog Afrixalus paradorsalis (Anura: Hyperoliidae) of the Lower Guineo‐Congolian rain forest

AbstractAimTo investigate how putative barriers, forest refugia, and ecological gradients across the lower Guineo‐Congolian rain forest shape genetic and phenotypic divergence in the leaf‐folding frog Afrixalus paradorsalis, and examine the role of adjacent land bridge and sky‐islands in diversification.LocationThe Lower Guineo‐Congolian Forest, the Cameroonian Volcanic Line (CVL), and Bioko Island, Central Africa.TaxonAfrixalus paradorsalis (Family: Hyperoliidae), an African leaf‐folding frog.MethodsWe used molecular and phenotypic data to investigate diversity and divergence among the A. paradorsalis species complex distributed across lowland rain forests, a land bridge island, and mountains in Central Africa. We examined the coincidence of population boundaries, landscape features, divergence times, and spatial patterns of connectivity and diversity, and subsequently performed demographic modelling using genome‐wide SNP variation to distinguish among divergence mechanisms in mainland (riverine barriers, forest refugia, ecological gradients) and land bridge island populations (vicariance, overwater dispersal).ResultsWe detected four genetically distinct allopatric populations corresponding to Bioko Island, the CVL, and two lowland rain forest populations split by the Sanaga River. Although lowland populations are phenotypically indistinguishable, pronounced body size evolution occurs at high elevation, and the timing of the formation of the high elevation population coincides with mountain uplift in the CVL. Spatial analyses and demographic modelling revealed population divergence across mainland Lower Guinea is best explained by forest refugia rather than riverine barriers or ecological gradients, and that the Bioko Island population divergence is best explained by vicariance (marine incursion) rather than overseas dispersal.Main conclusionsWe provide growing support for the important role of forest refugia in driving intraspecific divergences in the Guineo‐Congolian rain forest. In A. paradorsalis, sky‐islands in the CVL have resulted in greater genetic and phenotypic divergences than marine incursions of the land bridge Bioko Island, highlighting important differences in patterns of island‐driven diversification in Lower Guinea.

Middle-Late Eocene marine record of the Biga Peninsula, NW Anatolia, Turkey

The Eocene shallow marine deposits marking the first marine incursion in the Biga Peninsula (NW Turkey) after the collision of the Sakarya and Anatolide-Tauride plates were investigated based on paleontological, litho- and chrono-stratigraphic data. Larger Benthic Foraminifera (LBF) from patchily distributed outcrops were studied in order to i) revise the stratigraphy of Eocene shallow marine units, and ii) establish a modern biostratigraphic setting and a correlation scheme. The Sevketiye Formation (Fm.) is herein defined as a predominantly shallow marine clastic deposit with subordinate carbonates overlying the Camlica metamorphic rocks, and passing laterally to the Sogucak Fm., a carbonate unit that is widely represented in the Thrace Basin. The record of alveolinids, primitive developmental stages of heterosteginids, and orthophragminids in the Sevketiye Fm. suggests that this formation is part of the Shallow Benthic Zones (SBZ) 16?/17 (Late Lutetian?/Early Bartonian), SBZ17?/18 and SBZ19A (Early Bartonian/earliest Priabonian). The Sogucak Fm., which overlies the Eocene volcanics, on the other hand, yielded advanced developmental stages of heterosteginids, Spiroclypeus sp. and Nummulites fabianii lineages, implying a younger marine incursion during the Late Eocene (earliest Priabonian; SBZ19A). A drastic shift in the depositional regime is marked amid Priabonian by the deposition of deep-marine clastics and volcanoclastics of the Ceylan Fm. In conclusion, the Eocene Sea transgressed first Gokceada (in the Aegean Sea) during the Late Lutetian, then reached the Biga and Gelibolu peninsulas in the Bartonian, and finally led to the widespread deposition of carbonate and siliciclastic rocks in the Biga Peninsula and the Thrace Basin during the Late Bartonian and Priabonian.