Sedimentary Gap Research Articles

Historical vegetation shifts in southeastern Amazonia: Unraveling ecotone dynamics in the Carajás region over the last ∼14000 cal yr BP

This study investigates the Pleistocene–Holocene transition in Serra Leste, a highly endangered southeastern Amazonian ecotone, with a focus on the lake-filling process, climate changes, and potential consequences to forest and savanna dynamics. The lake's development began at approximately 14000 cal yr BP, resulting from the collapse of the fractured lateritic crust. Sedimentation patterns and geochemical, palynological and micro-charcoal proxies reveal shifts in detrital input and redox conditions, forest/savanna areas, and local and regional fire events, indicating a highly dynamic environmental history. The evolution of the lake is characterized by initial deltaic lobe deposition and forest dominance, followed in the Middle Holocene by sedimentary gaps or reduced detrital input; woody vegetation dominance, with a notable shift toward a more open landscape; and savanna and semideciduous dry forest, accompanied by a decrease in ombrophilous forests. A resurgence in arboreal elements recorded in the Late Holocene indicates an expansion of ombrophilous forests under wetter climate conditions and the establishment of a more continuous forest matrix, with the presence of likely “hyperdominant” taxa. Frequent local fire events and the occurrence of temporarily correlated archeological sites in the Serra Leste region suggest the influence of ancient indigenous communities on vegetation changes during the Late Holocene.

A differentiated palynological record of the Eemian interglacial in two palaeolakes Niesadna and Parysów from the Garwolin Plain (Central Poland)

Two neighbouring Eemian (MIS 5e) palaeolakes, discovered during works on reambulation of the Garwolin sheet of the Detailed Geological Map of Poland (scale 1: 50 000), revealed differences in the palynological record of the succession of the Eemian interglacial. In the profile of Parysów WH-125, a very pronounced hiatus in the transition from the mesocratic to the telocreatic period, i.e. from the hornbeam to the spruce-fir zone, is visible. In the pollen diagram of Niesadna, the maximum percentages reached by Quercus, Corylus and Carpinus are very low, although this is undoubtedly an Eemian succession. The reasons for this should be sought in the presence of several sedimentary gaps probably caused by the different geological and geomorphological conditions of the Niesadna palaeolake located on a slope as opposed to the Parysów palaeolake, which was formed by the melting of a block of dead ice in the process of deglaciation of the area during the late Saalian (MIS 6). An additional rationale for the hypothesis of extremely unfavourable conditions for undisturbed sedimentation in Niesadna palaeolake is its geological-geomorphological situation that caused admixtures of mineral material in the organic sediment, including sand intercalations, indicating that erosion was taking place. The two developed pollen successions were presented against other published data on the Eemian interglacial in the Garwolin Plain, with particular emphasis on the continuity of the Eemian succession. The palynological results showed that the Parysów WH-125 profile joins several other profiles lacking representation of the upper part of the hornbeam zone and sometimes also the lower part of the spruce-fir zone (e.g. Żabieniec, Jagodne). On the other hand, the presence of distinct sedimentary gaps in the oak, hazel, and hornbeam zone, as is the case in the Niesadna profile, has not been recorded in any of the profiles in the Garwolin Plain examined to date. The Eemian pollen succession in the studied Niesadna and Parysów palaeolakes is presented against the broader background of the course of this interglacial in the European Lowlands.

Structural analysis of the central Tunisian Atlas: Implications for salt-related structures and conjugate strike-slip faults

This scientific study aims to investigate the geological characteristics and tectonic processes of the central Tunisian Atlas region, focusing on the influence of tectonic events related to the Jurassic-Early Cretaceous Tethyan rifting and the subsequent Cenozoic tectonic inversion and uplift. In particular, this research emphasizes the strong control of tectono-sedimentary events on the geology of the central Tunisian Atlas, with specific attention given to the understudied isolated salt-related structures. To gain insights into the relationship between deep-seated faults, salt tectonism, and the conjugate strikes-slip faults, this study is based on subsurface data, including 2D seismic reflection and gravity data. The analysis investigates, the location of salt extrusions in relation to fault intersections. Results derived from subsurface data indicate that diapiric intrusions primarily occur at the junctions of major fault systems likely inherited from the Triassic-Jurassic Tethyan period. Notably, salt migration was remarkably active during the early Cretaceous, as evidenced by halotectonic sequences and salt-related mini-basins. Furthermore, fault blocks display sedimentary infill above tilted blocks, where salt structures appear to occur at their peripheries. During the subsequent tertiary compressions, the structural configurations of the basin (i.e., Z-shape basin) promote the strike-slip movement along pre-existing faults. This new structural interpretation suggests a closely relationship between fault zones inherited from the Jurassic-Early Cretaceous Tethyan Opening and isolated salt-related structures. The subsequent Cenozoic shortening events, including the Atlassic and Alpine events, have led to uplift of the deep-seated faults, facilitating the ascension and deformation of Triassic evaporitic sediments within subcircular isolated structures. Field observations and seismic sections indicate the presence of sedimentary gaps resulting from these processes. The findings of this study contribute to a comprehensive understanding of the deep tectonic framework and shallow salt-related structures in the central Tunisian Atlas.

Middle to Upper Ordovician stable carbon isotope stratigraphy and sedimentary facies in the Shunbei and Tahe areas, northern-central Tarim, China

The Shunbei area, located in northern-central Tarim (Northwest China), represents a new, important area for petroleum and gas exploration. This study presents high-resolution, conodont biostratigraphically controlled stable carbon isotope data from 540 samples of four deeply buried (∼7000–8000 m) wells in the Shunbei area and its nearby Tahe area spanning the Middle to Upper Ordovician for detailed chemostratigraphic correlations. Additionally, thin sections are obtained from the two studied areas for sedimentary facies analysis. The δ13C data from Shunbei area correlate well with the results from Tahe area and other outcrops in northwestern Tarim. The major global δ13C excursions of the mid-Darriwilian Isotopic Carbon Excursion (MDICE, ∼+1‰) and the Guttenberg Isotopic Carbon Excursion (GICE, ∼+1‰) are recognized from the upper Yijianfang and the Lianglitag formations respectively. Two minor (∼+0.5‰) δ13C positive peaks from the Yingshan Formation of the Shunbei area are comparable to lower Darriwilian strata of platform facies in Tarim, providing a potential tool for correlating lower Darriwilian hydrocarbon reservoirs, such as the Yingshan and Yijianfang formations in the Tarim Basin. A major sedimentary gap is detected in the lower Qiaerbak Formation of the Shunbei area and the upper Yijianfang Formation of the Tahe area, indicating an erosional event occurred in the early Sandbian which could be correlated with the globally tectonic-active interval during the Darriwilian–Sandbian transition. The completely preserved MDICE and GICE in the Shunbei area, as well as its relatively deeper-water sedimentary environment in comparison with the Tahe area, collectively suggest that the Shunbei area is of significance for further geochemical studies on the Middle and Late Ordovician environments and their resources.

The chronology and rotational kinematics in the South-Eastern Jaca Basin (Southern Pyrenees): Las Bellostas section

Despite the large number of magnetostratigraphic studies in the South Pyrenean Basin aiming to calibrate the basin chronostratigraphy and the biostratigraphic scales, the South Eastern Jaca Basin remains unexplored from this perspective, and its relation with the Ainsa Basin is not fully understood. In this work we contribute with new magnetostratigraphic data from the 950m thick Las Bellostas section, located in the northern hinge of the Balzes anticline. Well-proven primary signal (positive fold test and two pseudo-antiparallel polarities) supported by numerous primary data in the surroundings allow us building a reliable local polarity sequence of eight magnetozones (from R1 to N4). Additionally, seven new biostratigraphic samples (Nummulites and Assilina) in the lower part of the section (marine environment) allows tightening the section to the Geomagnetic Polarity Time Scale (GPTS) and proposing a refined age model for the southeastern Jaca Basin. The section starts in the Boltaña Fm., of Cuisian age (Shallow Benthic Zone, SBZ11), is followed by a sedimentary gap from C22n to C20n as witnessed by biostratigraphic data (SBZ11 underneath the hiatus and SBZ16 just atop). The deltaic Sobrarbe Fm. can be tracked until the C19n (Late Lutetian). From this point (200m) until the top of the section (950m), at least, the entire C18n chron can be recognized within the molassic Campodarbe Fm. (C18n.2n-C18n.1r and C18n.1n) (Bartonian) equivalent to the West to the prodeltaic Arguis marls Fm. The Middle Cusian (SBZ11) to Middle Lutetian (SBZ15) stratigraphic hiatus is, in part, enhanced by the structural position at the hinge of the Balzes anticline. These new chronostratigraphic constraints help refining the W-E and N-S stratigraphic relationships in the eastern Jaca Basin and in the Ainsa Basin. This section also allows us to accurately refine the kinematics of the rotational activity in the eastern External Sierras. The important difference in magnetic declination along the section and neighboring paleomagnetic data from the Balzes anticline (from ≈70º clockwise at the base of the stratigraphic section to non-significant at the top) together with the new age model for the Eastern Jaca Basin help characterizing the rotational activity of the Balzes thrust sheet. The rotation took place between chrons C20r (Middle Lutetian; 45Ma) and C17 (Lower Priabonian 37-38Ma) in agreement to nearby structures (Boltaña, Picodel Aguila anticlines) but clearly diachronic to western ones (Santo Domingo anticline). Besides, the rotational activity seems to follow a linear and continuous pattern (velocity 9-11º/Ma, R: 0.83-0.96) in contrast to closer structures that show two distinct rotational velocities (i.e. Boltaña). These new data still let open the debate on the rotational kinematics along the South Pyrenean basal thrust.

Calcareous nannofossil biostratigraphy of the upper Cenozoic in the Okinawa-Miyako Submarine Plateau in the Ryukyu Islands

The upper Miocene to Pleistocene Shimajiri Group, composed mainly of siltstone and sandstone, occurs on some of the Ryukyu Islands in southwestern Japan. This group is thought to have been deposited in a shelf-slope to fore-arc basin setting before the accumulation of Pleistocene coral reef deposits (Ryukyu Group). We investigated the calcareous nannofossil biostratigraphy of the Shimajiri Group in the Offshore Okinawa 1-x well, drilled near the northeastern margin of the Okinawa-Miyako Submarine Plateau, Ryukyu Islands. A sample from 280 m, at the base of Ryukyu Group, contains Gephyrocapsa parralella, which first occurred at 0.987 Ma. Discoaster quinqueramus and D. berggrenii, which define both the top and bottom of the calcareous nannofossil zone NN11, are found throughout the Shimajiri Group, consistent with a late Miocene age between 8.10 Ma and 5.53 Ma. A large sedimentary gap between the Shimajiri and Ryukyu groups suggests that part of the Okinawa-Miyako Submarine Plateau may have been above sea level during the early Pliocene, implying deposition of the Shimajiri Group here was completed earlier than in other regions. This study provides key constraints on the Cenozoic geological history and phylogeography of the Ryukyu Islands.

Challenging the hypothesis of an Arctic Ocean lake during recent glacial episodes

ABSTRACTThe Arctic Ocean is one of the last frontiers on Earth with many unknowns about its geological and climate history and considerable speculation on its role in the Earth's climate and ocean system. It has been proposed recently that it was occupied by a freshwater body of more than 9.5 × 106 km3 underneath a thick ice mass during part of glacial isotopic stages 6 and 4. We argue that such a dramatic scenario, implying replacement of marine waters by freshwater throughout the entire Arctic Ocean and Nordic Seas, is physically implausible. The very low 230Th excesses (230Thxs) observed in sediments from these intervals were used as evidence for the presence of a U‐depleted overlying freshwater column. We show here that they may simply result from short, sporadic sedimentary pulses, below multiyear sea ice or ice shelves, linked to deglacial ice streaming and surging events interrupting long‐duration sedimentary gaps. Due to this sporadic sedimentation regime, interpolating time from 230Thxs data or between benchmark ages in sedimentary sequences would simply be erroneous.

Huge sedimentary hiatus in the southern margin of the North China Craton from mid-Mesoproterozoic to Neoproterozoic

ABSTRACT The Meso- to Neoproterozoic Eras were characterized by environmental, evolutionary, and lithospheric stability in the North China Craton (NCC). It is controversial that huge uplift(s) occurred in the North China Craton during this period. The southern NCC developed early terrestrial deposition in the late-Paleoproterozoic and glacial sequence in the late Neoproterozoic record integrated geological history of the NCC in the intervening interval. Geochemistry compositions of mid-Mesoproterozoic carbonaceous slates (ca. 1330 Ma) show similar provenances to the underlying Mesoproterozoic sedimentary rocks in the southern NCC. Detrital zircons from the mid-Mesoproterozoic strata yield U–Pb ages from ca. 2450 to 1850 Ma with minor ages of 2950 and 2750 Ma. U–Pb ages of detrital zircons from the Neoproterozoic strata yield from ca. 1700 to 1000 Ma besides peak ages of 2600, 2400, and 1950 Ma. The early Paleozoic sedimentary rocks also display peak ages between ca. 1850 and 1000 Ma along with peaks at ca. 2500 and 2300 Ma. These detrital zircon ages are quite different from those of the Mesoproterozoic sedimentary rocks in the NCC. According to paleogeography study, the late-Paleoproterozoic to the early Mesoproterozoic clastic sequences are controlled by Xiong’er volcanic event in the southern NCC and carbonate platform developed later. The Mesoproterozoic sequences are overlain disconformably by the Neoproterozoic strata. In combination with compiled magmatic and detrital zircon ages, a sedimentary gap spanned at least 300 Ma from mid-Mesoproterozoic to Neoproterozoic in the southern NCC. Thus, the disconformity between the Mesoproterozoic and Neoproterozoic sedimentary sequences in the southern NCC should represent a huge sedimentary hiatus. Both the variable provenances and huge sedimentary hiatus between the Mesoproterozoic and Neoproterozoic sedimentary sequences support that the NCC might not split from relict landmass of Columbia Supercontinent before Neoproterozoic. The relict landmass was involved in aggregation of the Rodinia supercontinent.

Late-Holocene forest resilience in the central Pyrenean highlands as deduced from pollen analysis of Lake Sant Maurici sediments

Palynological analysis of the last ca. 4300 cal year BP using a sediment core taken from high mountain (ca. 1900 m elevation) Lake Sant Maurici sediments (southern-central Pyrenees) showed remarkable vegetation constancy during the Bronze Age and the Middle Ages. Records of the Iron Age and the Roman period were missing due to a major sedimentary gap. During the studied periods, the vegetation around the lake was largely dominated by pine ( Pinus) forests with birch ( Betula), oak ( Quercus) and hazel ( Corylus) trees, as is the case today. The composition of these forests and the abundance of their components remained quite stable, despite the occurrence of temperature and moisture shifts. The degree of human disturbance, notably that of pastoralism and cereal cultivation by scattered and temporary settlements, was very low and had little or no effect on the dominant forests. This situation contrasts with most high-elevation (subalpine and alpine) environments of the central Pyrenees that were massively anthropized during the Middle Ages. Further research should be aimed at finding sediments corresponding to the Iron Age and the Roman period to verify whether the vegetation constancy can be extended throughout the Late-Holocene. Past records of this type may allow the estimation of natural and anthropogenic thresholds for irreversible forest changes, which would be useful for conservation purposes.

Early and Middle Jurassic tectonically controlled deposition in the High-Tatric succession (Tatricum), Tatra Mountains, southern Poland: a review

The High-Tatric succession of the Tatra Mountains represents the Tatricum domain of the Central Western Carpathians, which in the Jurassic was located on the southern margin of the incipient and expanding Vahic Ocean – a branch of Western Tethys. This paper describes the various depositional consequences of extensional tectonic activity as it impacted on sedimentation in the High-Tatric succession of the Tatra Mountains during the Early and Middle Jurassic. Evidence of such impacts on depositional style and facies development are present within the Dudziniec, Smolegowa and Krupianka formations, in all the High-Tatric tectonic units. These impacts also include erosional surfaces and sedimentary gaps separating particular formations, commonly associated with minor angular unconformities. The Lower Jurassic, pre-Bajocian, Dudziniec Formation of the Kominy Tylkowe (autochthonous) Unit is developed in mixed carbonate-clastic facies. The occurrence and proportion of sand-dominated and carbonate-dominated facies, as well as their thickness differences, were controlled by syndepositional tilt-block tectonics, taking place both in depositional and in neighbouring source areas. The Smolegowa and Krupianka formations (Bajocian–Bathonian) occur in all High-Tatric tectonic units, but in the Czerwone Wierchy and Giewont units they are represented mainly by laterally discontinuous bodies of crinoidal limestone of very limited thickness. The preservation of these deposits only in some areas, as well as their thickness reductions, are effects of differentiated subsidence and uplift of isolated blocks taking place in an extensional regime. Moreover, the Krupianka Formation abounds in condensed facies with ferruginous crusts and stromatolites – a feature characteristic of rapidly drowning ocean margins. Deposits of the Dudziniec, Smolegowa and Krupianka formations are also preserved as infills of extensive systems of neptunian dykes penetrating mainly the Triassic substrate, which is yet another classic symptom of synsedimentary extension. The dominant influence of tectonics on sedimentary development ceased with the onset of deposition of the Raptawicka Turnia Formation in the Callovian.

Source-to-sink of Late carboniferous Ordos Basin: Constraints on crustal accretion margins converting to orogenic belts bounding the North China Block

The Upper Carboniferous Benxi Formation of the Ordos Basin is the lowest strata overlying Middle Ordovician above the major ca. 150-Myr sedimentary gap that characterizes the entire North China Block (NCB). We apply an integrated analysis of stratigraphy, petrography, and U–Pb dates and Hf isotopes on detrital zircons to investigate its provenance and relationships to the progressive collisions that formed the Xing’an-Mongolia Orogenic Belt to the north and the Qinling Orogenic Belt to the south. The results show that, in addition to regional patterns of siliciclastic influx from these new uplifted sources, the Benxi Formation is composed of two sequences corresponding to long-term glacial-interglacial cycles during the Moscovian to lower Gzhelian stages which drove global changes of eustatic sea level and weathering. The spatio-temporal distribution of sediment isopachs and facies indicate there were two sediment-infilling pulses, during which the southern and the northern Ordos Basin developed tidal-reworked deltas. The age spectra from detrital zircons, trace element patterns and εHf(t) values reveal that the siliciclastics forming the southern delta was sourced in the Qinling Orogenic Belt, whereas the northern delta was derived from the Xing’an-Mongolia Orogenic Belt. The source-to-sink evolution of this Upper Paleozoic system records the progressive development of orogenic belts and uplifts forming on the southern and northern margins of the NCB prior to its collisions with the South China and the Siberian plates, respectively.

Paleocene and Eocene deposits on the eastern margin of the Gulf of Gdańsk (Yantarny P-1 borehole, Kaliningrad region, Russia)

Lithological and palynological studies of Paleogene siliciclastic deposits from the Yantarny P-1 borehole located on the western coast of the Sambian Peninsula (Kaliningrad region, Russia) show that the succession is characterized by numerous sedimentary discontinuities related to lithification horizons and erosional surfaces. Sedimentary gaps are emphasised by hardgrounds. Palynological data suggest the Selandian–Priabonian age of the succession and indicate a number of significant stratigraphic gaps. An important change in heavy mineral composition is recognized between the Paleocene and Eocene deposits in the area studied. A significant number of reworked Cretaceous microfossils is observed in the Selandian part of the succession studied.

The deforestation of Easter Island.

Easter Island deforestation has traditionally been viewed as an abrupt island-wide event caused by the prehistoric Rapanui civilization, which precipitated its own cultural collapse. This view emerges from early palaeoecological analyses of lake sediments, which showed a sudden and total replacement of palm pollen by grass pollen shortly after Polynesian settlement (800-1200CE). However, further palaeoecological research has challenged this view, showing that the apparent abruptness and island-wide synchronicity of forest removal was an artefact due to the occurrence of a sedimentary gap of several millennia that prevented a detailed record of the replacement of palm-dominated forests by grass meadows. During the last decade, several continuous (gap-free) and chronologically coherent sediment cores encompassing the last millennia have been retrieved and analysed, providing a new picture of forest removal on Easter Island. According to these analyses, deforestation was not abrupt but gradual and occurred at different times and rates, depending on the site. Regarding the causes, humans were not the only factors responsible for forest clearing, as climatic droughts as well as climate-human-landscape feedbacks and synergies also played a role. In summary, the deforestation of Easter Island was a complex process that was spatially and temporally heterogeneous and took place under the actions and interactions of both natural and anthropogenic drivers. In addition, archaeological evidence shows that the Rapanui civilization was resilient to deforestation and remained healthy until European contact, which contradicts the occurrence of a cultural collapse. Further research should aim to obtain new continuous cores and make use of recently developed biomarker analyses to advance towards a holistic view of the patterns, causes and consequences of Easter Island deforestation.

New insights on the tectonic evolution of the Miocene gap grabens of Sers–Siliana (Tunisian Atlas) during Neogene to Quaternary: Contribution of chronology of the regional tectonic events

The NW–SE trending grabens of Sers–Siliana, located in the Central Tunisian Atlas, show a peculiarity, compared to adjacent grabens, which comes from the existence of an early Miocene sedimentary gap. This paper discusses the structural evolution of these grabens, during the Neogene–Quaternary episode, which have been poorly studied in previous studies. To better understand the chronology of the two grabens, a set of direct and indirect pieces of evidence are given in order. The results show that the collapse is of Aquitanian–Tortonian age which is synchronous with the regional collapse of the Alpine chain foreland grabens. In addition, our field observations show that the E-trending faults affect the incompetent materials (marls) and assured the mechanical junction between these two grabens. The chronology of tectonic events, during the Neogene–Quaternary time, in the Sers–Siliana area coincides with that described at the regional scale for the Tunisian Atlas domain, allowing a better understanding of the role played by the convergence between African and Eurasian plates.

Late Holocene transformations of lower montane forest in the Beskid Wyspowy Mountains (Western Carpathians, Central Europe): a case study from Mount Mogielica

This article presents a reconstruction of Late Holocene vegetation changes within the lower montane forest zone in the Beskid Wyspowy Mountains (Western Carpathians, Central Europe). Pollen, non-pollen palynomorphs, loss on ignition, and microscopic charcoal analyses were applied to a profile collected from the deposits of the rich fen which developed in the landslide depression. The results reveal that during the period between ca. 4800 ± 70 and 4160 ± 60 cal. BP, Picea abies dominated in the local forests. Between ca. 4800 ± 70 and 4660 ± 60 cal. BP, Acer was an important component in local woodlands, which distinguishes the study site from others in the Western Carpathians. At ca. 4100 ± 60 cal. BP, forests dominated by Abies alba and Fagus sylvatica expanded. Nowadays, this type of vegetation is characteristic of the lower montane zone in the Polish Western Carpathians. This expansion was probably a consequence of environmental disturbances related to the cold and wet ‘4.2 ka BP’ event. The spread of these forests was preceded by a short episode of expansion of Tilia (Tilia cordata and/or Tilia platyphyllos) which was a very local event. The area of the Beskid Wyspowy Mountains provided suitable habitats for the occurrence of T. baccata, which has not been recorded in pollen data spanning the Middle and beginning of the Late Holocene from this mountain range. A significant increase in the percentages of Kretzschmaria deusta, a parasitic fungus, reveals that A. alba–F. sylvatica forests provided an optimal habitat for such species during the period from 4070 ± 60 to 47 cal. BP. Since ca. 2640 ± 110 cal. BP, pollen of pioneer trees, such as Pinus sylvestris and Betula, as well as human activity indicators (Cerealia type and Plantago lanceolata) have become more frequent. Nonetheless, it is highly probable that this section of deposits also includes the presence of one or more sedimentary gaps.

Structural styles, tectonic events, and deformation features along a surface–subsurface structural transect from the South Atlas Front (N–S axis) to the Eastern Sahel foreland basin of Tunisia

2D seismic cross-sections calibrated to exploration wells allow highlighting the structural styles along a structural transect from the N–S axis, west of the Bouthadi–Chorbane anticline to the foreland, with a major regional tectonic anomaly striking roughly E–W along the subsurface Atlas front of the foreland basin. The interpretation of structural data and seismic profiles allow deciphering clearly the occurrence of Late Cretaceous–Paleogene inversion structures, accounting for folds detached along the basal intra-Triassic salt decollement level. These contractional structures in part result from the Middle–Late Eocene compressional events, which induced the first strong positive inversion in both the Atlas domain and adjacent foreland. The growth of these positive structures is outlined by angular unconformities, sedimentary gaps, and differential subsidence within the Paleogene deposits. The foreland area is characterized by a thick-skinned tectonic inversion style, where the Pre-Triassic basement is decoupled from its Jurassic–Quaternary sedimentary cover by a general decollement level located at the Upper Triassic/Lower Jurassic interface. The deformation features imaged by seismic sections are in agreement with such thick-skinned style controlled by deep-seated faults presumably inherited from the Pan-African basement. A regional structural cross-section is presented and discussed, crossing the N–S axis and outcrops of the South Atlas Front in the west and, then, running through the major structural anomaly of Chorbane and the foreland basin to the east. This regional cross-section has been also balanced and restored to its initial and intermediate geometries, i.e., after the Tethyan and Cretaceous extensional events and Paleogene compressional events, thus documenting the major tectonic anomaly of Bouthadi–Chorbane in the foreland as well as the overall structural evolution of the Atlas fold and thrust belt.

A 3700 yr paleoseismic record from the northern San Jacinto fault and implications for joint rupture of the San Jacinto and San Andreas faults

The San Andreas and San Jacinto faults are the primary plate-boundary structures in southern California and present a large earthquake hazard for the region. They approach each other in the Cajon Pass area between the San Gabriel and San Bernardino Mountains, where the northern end of the San Jacinto fault forms a 2-km-wide releasing step with the San Andreas fault. In this study, we used paleoseismic data from sites on the San Jacinto and San Andreas faults near their juncture to evaluate spatial and temporal patterns of surface rupture between these major structures of the North American–Pacific transform plate boundary. We present a new 3700 yr paleoseismic record from the northern San Jacinto fault at Mystic Lake, where trench excavations exposed evidence for at least 16 surface ruptures. A sedimentary gap in our trench exposures separates three ruptures in the oldest part of the record from 13 ruptures during the past 2000 yr. For the past 2000 yr, the mean recurrence times varied from 86 to 312 yr, with a mean recurrence interval of 160 yr. This rate of surface rupture is roughly equal to that of the southern San Andreas fault south of the Cajon Pass juncture, but it is half that of the San Andreas fault north of the juncture, indicating that coseismic strain on the San Andreas fault is split between the southern San Andreas and San Jacinto faults south of Cajon Pass. Comparison of the past 2000 yr of the Mystic Lake record to similar paleoseismic records from nearby sections of the San Andreas fault suggests that: (1) the current open interval on these two faults in the study area is longer than their average recurrence intervals, but that similar intervals of quiescence have occurred in the past 2000 yr; (2) the San Andreas and San Jacinto faults have probably ruptured together multiple times in the past 2000 yr; and (3) a joint rupture of the San Jacinto fault with the Mojave section of the San Andreas fault may be a more likely source of a major earthquake in southern California than a rupture on the San Andreas fault from the Mojave segment to the southern end of the fault.

The epiclastic barrier-island system of the Early‒Middle Jurassic in eastern Spain

During the Early-Middle Jurassic, several mainly volcaniclastic submarine eruptions, which followed well marked lineaments, took place in the Iberian Ranges of eastern Spain. Some of these volcanoes were occasionally emerged during sea-level lowstand periods. In this work we aim to present the signs indicating that a huge volcanic pile, located in the Sierra de Javalambre (Teruel, Spain), could have been subjected to emersion, reworking and colonization by flora. We also intend to date the volcanism and to delimit the most likely period of time when emersion, reworking and colonization were produced. The research work was supported by geological mapping, as well as by preparing stratigraphic sections and their palaeontological sampling. Biostratigraphical dating was achieved though taxonimical determination of ammonites, brachiopods, and data from pre-existing palynological studies. As a result of the shallow marine and subaerial partial erosion of the volcanic edifice, epiclastic bodies, some of which show large scale cross-bedding and bar geometry, were generated. These bedforms are interpreted as sandwaves constituting a barrier-island system protecting a lagoon on which low-energy sediments, rich in plant remains, together with washover fan facies were deposited. An Early Toarcian, Serpentinum Chronozone age for the volcanism is indicated by the brachiopod and ammonite content of infra- and inter-volcanic sediments. However, burial of the volcanic mound by the carbonates of the surrounding platforms ended in the Late Aalenian Bradfordensis Chronozone, about 10 million years after the eruption. This delay was partly due to a significant regional sedimentary gap marked by the hiatus of the Late Toarcian (from the Late Variabilis Chronozone) to the Late Aalenian (Bradfordensis-Concavum chronozones). The emersion of the volcanic pile, the colonization of the emerged islands by continental vegetation and the instauration of the epiclastic barrier-island system occurred between part of the Aalenian Murchisonae and part of the Bradfordensis chronozones. The concurrence of the porous epiclastic lithofacies together with the organic-rich lagoonal sediments could represent an analogue model of an untypical hydrocarbon system located in neritic position, which could probably be applied in other areas of extensive emerged submarine volcanoes present in the geological record.

Stratigraphy and age estimate of Neogene shallow marine fossiliferous deposits in Brunei Darussalam (Ambug Hill, Tutong district)

The Ambug Hill in Brunei is an exceptional geological site where a series of siliciclastic rocks crops out with some layers extremely rich in marine fossils. Such fossiliferous outcrops are extremely rare in the northern part of Borneo and their description is of primary importance as their fossil content can be used to correlate the regional depositional sequences with global biostratigraphic zonations. In this work we present for the first time a detailed sedimentary profile completed with Sr-isotopes and biostratigraphic dating. The succession is divided into four sedimentary units. The first unit comprises bioturbated sandstone followed by a second unit of clay-silt rich levels whose first 9.5 m contain rich marine fossil assemblages. Calcareous nannoplankton data indicate a Late Tortonian – Early Messinian (NN11) age, which is confirmed by Sr-isotope dating derived from bivalves giving a numerical age range from 8.3 to 6.2 My. After a major emersion surface, the third sedimentary unit of sand- and siltstone lacks suitable fossils for bio- and isotope stratigraphy. The age of emersion and the related sedimentary gap can be either correlated with the Me1 (7.25 My) or the Me2 (5.73 My) sequence boundary. A fourth, thin sedimentary unit is recognized on the top of the profile with silt- and claystone beds without age diagnostic remains and calcareous fossils.

Late Holocene wetland transgression and 500\xa0years of vegetation and fire variability in the semi-arid Amboseli landscape, southern Kenya

The semi-arid Amboseli landscape, southern Kenya, is characterised by intermittent groundwater-fed wetlands that form sedimentary geoarchives recording past ecosystem changes. We present a 5000-year environmental history of a radiocarbon dated sediment core from Esambu Swamp adjacent to Amboseli National Park. Although radiocarbon dates suggest an unconformity or sedimentary gap that spans between 3800 and 500 cal year BP, the record provides a unique insight into the long-term ecosystem history and wetland processes, particularly the past 500 years. Climatic shifts, fire activity and recent anthropogenic activity drive changes in ecosystem composition. Prior to 3800 cal year BP the pollen data suggest semi-arid savanna ecosystem persisted near the wetland. The wetland transgressed at some time between 3800 and 500 cal year BP and it is difficult to constrain this timing further, and palustrine peaty sediments have accumulated since 400 cal year BP. Increased abundance of Afromontane forest taxa from adjacent highlands of Kilimanjaro and the Chyulu Hills and local arboreal taxa reflect changes in regional moisture budgets. Particularly transformative changes occurred in the last five centuries, associated with increased local biomass burning coeval with the arrival of Maa-speaking pastoralists and intensification of the ivory trade. Cereal crops occurred consistently from around 300 cal year BP, indicative of further anthropogenic activity. The study provides unique insight in Amboseli ecosystem history and the link between ecosystem drivers of change. Such long-term perspectives are crucial for future climate change and associated livelihood impacts, so that suitable responses to ensure sustainable management practices can be developed in an important conservation landscape.