Neogene Succession Research Articles

The Pliocene succession of Lyon Metropolis (SE France): an overfill of a Messinian incised-valley

The Pliocene ria, a narrow seaway running up the Rhône Valley, has been mapped for a while by field geologists. Only much later, after the DSDP Leg 13 in 1970, a consensus was reached that this unique geological feature of the Rhône Valley was created by the major Mediterranean sea-level drop associated with the Messinian Salinity Crisis, followed by a sudden sea-level rise caused by the breach of the Strait of Gibraltar and the invasion of the Mediterranean Basin by the Atlantic waters. At the regional level of the Lyon Metropolis in the upper Rhône Valley, main issues were however remaining about the course and depth of the Messinian valley, and about the valley fill, namely where and how do the Pliocene marine strata of the Rhône Valley pass to the continental deposits of the Bresse Basin to the north? These are key-questions in that the Plio-Pleistocene makes up a large fraction of the basement that holds up a large city, not free from potential geological hazards and subject to problems of groundwater management, high-cost tunneling projects, etc. Our survey reviews first the historical researches − descriptions of the outcrops and fossil assemblages. It is followed by an unprecedented analysis and correlation of a thousand boreholes, which makes it possible to physically link and reconcile ancient local observations. Sections across the Messinian valley reveal a proper canyon morphology for the segments that cut the crystalline basement. The magnitude of the incision has been calculated as 335 m to a minimum, three hundred kilometers away from the river mouth. Three major depositional systems are distinguished for the Pliocene − Lower Pleistocene succession. The valley that initially ran much farther north of Lyon was occupied in the Zanclean by a series of pounded lakes, dammed by transverse local alluvial fans, filled by minor Gilbert-type deltas, and repeatedly flooded by marine ingressions. The valley wings were then encroached during the Piacenzian by a major, Alps-rooted alluvial sheet. At the level of Lyon, the fluvial deposits were deflected to the north (Sables de Trévoux) and to the south (Alluvions jaunes) as a dichotomy. The succession was then capped by a gravel-dominated fluvio-glacial fan (Alluvions jaunes sommitales) at the Plio-Pleistocene transition. It spread out from the north-east to the south, and intersected the previous valley overfill due to the shift to the north, i.e., South Jura, of the feeder stream. The depositional and current elevations of the marine-influenced episodes, i.e. marker bands that punctuate the regional Neogene succession, are used to bring out successive uplift and subsidence phases of the region. Finally, we tentatively link the major shifts in the depositional patterns of the Late Neogene succession in the Lyon area to major changes in the thrust belt activity, exhumation story, and outset of glaciers in the western Alps.

Organic facies and hydrocarbon source rock potentiality of the Neogene succession in the Central South Mediterranean, offshore Nile Delta Basin, Egypt

Neogene succession in the offshore Nile Delta region is essential to the hydrocarbon petroleum system. Up to date, little is known about the nature and distribution of organic matter and its potential to generate hydrocarbon. This potential is tested through extensive palynofacies and organic geochemical analyses in a new approach in this region. Based on the palynofacies analysis, the samples from NDOB-1 and Baltim-1wells are discriminated into four types using the statistical application of cluster and principal component analyses. These four types are distal-High Oxic type A, proximal-suboxic type B, proximal-dysoxic type C, and distal-oxic type D. In addition, the analysis leads to identifying the proximal-distal and oxygen depletion trends based on the values of the principal component analysis (axis 1). This palynofacies analysis is used as an environmental framework for hydrocarbon source rock evaluation. This evaluation is integrated with the organic geochemical parameters by pyrolysis (Rock-Eval and gas chromatography) and spectroscopic (Fourier Transform Infrared) methods. This study reveals that the dominant kerogen types are IV (inert) and III (gas-prone) which are remarked by the opaque and brown translucent phytoclasts palynofacies types A and D, respectively. Kerogen type II is presented in a minor abundance in palynofacies types B and C that are distinguished with AOM. However, kerogen type II organic matter is much diluted with kerogen type IV and III, leading to poor to fair organic geochemical quality (S2 and hydrogen index). Both wells' maturity levels are detected within the Kafr El Shiekh Formation. Nevertheless, the poor hydrocarbon source rock quality becomes important if considered with the volume and thickness of the Neogene sediment, as indicated by the source potential index that has a cumulative value of 2.5 t HC/m2 in NDOB-1 well and 2.8 t HC/m2in Baltim-1 well. These values are comparable to some of the prolific hydrocarbon fields in other places.

Facies association and Paleo depositional environment of the exposed Neogene succession in the Sitapahar Anticline of Rangamati Area, Chittagong Tripura Folded Belt (CTFB) region, Bengal Basin, Bangladesh

Neogene sedimentary rocks are exposed in the Chittagong Tripura Folded Belt (CTFB) Region in Bengal Basin. Sitapahar anticline is situated in the middle part of the CTFB Region. In this structure, eleven litho-facies have been identified in fluvial, overbank, shallow marine, deltaic, and deep marine depositional environments. Surma Group is composed of Bhuban and Boka Bil formation during Miocene time and was deposited in shallow marine, deltaic, and deep marine environments and characterized by the identification of interbedded shale facies (ShI), fine sandstone facies (SFs), lenticular laminated silty shale to shale facies (Zw), wavy bedded sandstone siltstone facies (Slsh), flaserbedded sandstone siltstone facies (Sxhs), ripple laminated sandstone facies (Sr), black Shale facies (Shb) and nodular shale facies (Zn). While, Pliocene Tipam group and Plio-Pleistocene Dupi Tila Formations were deposited in fluvial intervention and characterized by crossbedded sandstone facies (Sxbt), mudstone facies (Mf), interbedded mudstone and sandstone facies (MI).

Miocene tropical storms: Carbonate framework approaches and geochemistry proxies in a reservoir model

The Bragantina Platform is an important sedimentary package that occurs in northwestern Brazil, typically around the equatorial western Atlantic coast. Most of the latest Neogene succession of this carbonate-siliciclastic platform consists of the Pirabas Formation of Miocene age (Burdigalian to Serravalian). High-energy coastal storms and hurricanes as a consequence of trade wind anomalies during the Neogene impacted the shallow-water inner marine heterozoan assemblage deposits of the Pirabas Formation. A chaotic overlap of benthic infauna and epifauna, and of demersal and pelagic species in the same section was analyzed using petrography, petrophysics, micro- and macropaleontology, taphonomy, and geochemistry in order to understand sedimentary and paleoenvironmental processes. The equatorial carbonate platform of Brazil reveals high-energy and multiple Miocene tropical storms. This high-energy wave environment caused severe damage to shallow-water heterozoan assemblages at the seafloor, resulting in chaotic faunal arrangements, and removing fine-grained particles thus improving the petrographic properties of the rock (porosity and permeability).

Upper Palaeogene-Lower Neogene Reservoir Characterization in Kirkuk, Bai Hassan and Khabaz Oil Fields, Northern Iraq

The Upper Palaeogene-Lower Neogene succession represent subsurface sections from Kirkuk, Bai Hassan, and Khabaz oilfields were divided to many reservoir units dependent on information derived mainly from petrographical description, well log analysis, and related microfacies. In Khabaz oil Field, the hydrocarbon reservoir includes three reservoir units covered the Jeribe Formation, Anah Formation with its interfingering zone with Azkand Formation and Azkand Formation, the total thickness of this reservoir reaches up to (128 m) with net pay thickness of about (85.7 m) and net average porosity of (0.096) while the net water saturation is (0.185), the volume of shale is (7.130). The hydrocarbon reservoir in Bai Hassan was represented by three reservoir units comprised from the Bajwan and Baba formations, the total thickness of this reservoir is (178 m) with net pay thickness of (154.2m) and net average porosity of (0.121) while the net saturation is (0.156), the volume of shale is (36.837). Four reservoir units comprised the hydrocarbon reservoir in Kirkuk Field where they covered the Bajwan, Baba, Shurau and Sheikh Allas formations. The total thickness of these reservoirs is (136 m) with net pay thickness (124.5m) and net average porosity (0.178) while the net water saturation is (0.159), the volume of shale is (5.82). Many types of porosity were associated with these reservoirs such as the interparticles, intraparticles, intercrystaline, fracture, channel, moldic, vug, and cavern porosities. These porosities are attributed to a combination of dolomitization, fracturing, and dissolution.

Palaeoenvironments and sequence development of the Upper Palaeogene-Lower Neogene Succession in Kirkuk, Bai Hassan and Khabaz oil Fields, Northern Iraq

Microfacies analysis of the Upper Palaeogene-Lower Neogene succession which include Jaddala, Palani, Sheikh Allas, Shurau, Tarjil, Baba, Bajwan, Ibrahim, Azkand, Anah and Jeribe formations within Kirkuk area led to the recognition of many microfacies. They were grouped into nine facies associations ranging from supratidal to basin setting. These facies associations were deposited within a rimmed shelf with a barrier reef during the Palaeogene and a steepened ramp setting with fringing patch reef during the Neogene. The digenetic imprints on the recognized microfacies are prominent and dominated by cementation, neomorphism, dolomitization, precipitation of authigenic minerals, dissolution (leaching), compaction, mechanical degredation, micritization and geopitalstractures.
 The Upper Palaeogene-Lower Neogene succession is represented by a 2nd order cycle, It includes five 3rd order cycles within the shallowing upward upper part (The highstand systems tract) of this cycle. Cycles A and B were deposited during the Oligocene and present in the wells of Kirkuk oil field and bounded below by a transgressive surface and above by Type1 sequence boundary, Cycles C and D were deposited during the Aquitanian Early Miocene and found in Khabaz Field only and bounded below and above by a Type1 sequence boundary. These cycles were formed where the tectonic component was the major controlling factor on their development, This have caused successive episodes of relative sea level rises and stillstands, followed by sea level fall. Another 3rd order cycle within the Jeribe Formation was identified at Bai Hassan and Khabaz fields, this cycle is bounded below and above by a Type1 sequence boundary and also represent a brief episode of relative sea level rise followed by a major fall eroding most of the formation.
 The development of the Upper Palaeogene-Lower Neogene succession went through three main stages. The first stage was represented by the deposition of the basinal Jaddala and Palani formations (Eocene-Early Oligocene) all over the study area. The second stage was characterized by the basin trend being to the south toward the Khabaz Field and the reef buildup was located near Kirkuk Field and an interfingering took place between the Sheikh Allas and Palani formations deposited as a 3rd order cycle (A) therefore the fore reef and reef of Sheikh Allas and the back reef Shurau were deposited as a second 3rd order cycle (B) in Kirkuk Field only whereas the deposition of the basinal facies of the Palani Formation continued in both Bai Hassan and Khabaz areas. The third stage took place during the Aquitanian Early Miocene where a positive area developed as the Baba Dome and the Bai Hassan Field were uplifted with Avanah and Khurmala domes in Kirkuk Field; therefore the Bajwan and Baba formations (Late Oligocene) became subject to erosion, and the Khabaz Field represent the area of reef buildup, and the depositional system was changed from the shelf to ramp setting. During the Langhian new transgression took place where the Bai Hassan and Khabaz areas represent a tidal flat and the Jeribe Formation was deposited, whereas the Kirkuk Field was a positive area.

Exploring Neogene Marine Diatomites in Western Crete: A New Source-Rock Candidate with Hydrocarbon Generation Potential?

Diatomites are sedimentary rocks rich in siliceous algae, mainly diatoms, and are evident in Greece mainly in Neogene successions. Despite their significance and worldwide potential as source rocks for hydrocarbons, little is known about them in the wider area of Greece, limited in their biostratigraphic characteristics and industrial use. This study assesses for the first time the Neogene diatomites in Western Crete and focuses on their source rock quality and hydrocarbon generation potential on top of their stratigraphic characteristics. The studied synthetic outcrop is of the Miocene age and is located in the Apokoronas sedimentary basin, in the Chania province. It is subdivided into four subsections reaching heights of 13 m. It has a total documented, visible extend of 90–100 m and presents adequate thickness in relation to other reported diatomitic occurrences in Crete. A SEM study and bulk sampling of 28 samples has been carried out on this outcrop and geochemical analysis has been conducted by means of a Rock-Eval 6 pyrolysis to facilitate the understanding of hydrocarbon potential. Stratigraphic analysis supports the establishment of system tracts (ST), with transgressive ones (TST) illustrated by fining-upward sequences including highstands (HST). At the top, a final coarsening-upwards sequence suggests a regressive sequence (RST) most probably related to the Messinian Salinity Crisis (MSC) event. Total organic carbon (TOC, %wt.) values are found to reach 3.4% in the diatomites, while siltstone/mudstone interlayers encounter lower TOC (%wt.), yet with exceptions reaching TOC levels as high as the diatomaceous facies. Overall, Rock-Eval pyrolysis shows that organic matter from the studied cross sections is immature with the hydrocarbon generation potential ranging from poor to excellent. The kerogen type is proved to be type III with poor to almost good quality. This suggests the presence of a prolific diatomaceous source rock in Western Crete demonstrating a high significance for the offshore hydrocarbon exploration in the Eastern Mediterranean that could potentially be related to the offshore Western and Southern Crete E&P-awarded blocks.

The Tethyan and Tyrrhenian margin record of the Central Apennines: a guide with insights from stratigraphy, tectonics, and hydrogeology

This guide is a 5-day geotraverse across the Central Apennines, which expose the inherited Meso-Cenozoic sedimentary successions and tectonic architecture of the Apennine Tethyan passive margin. This structure was progressively involved into orogenic and post-orogenic tectonics, related to the Tyrrhenian back-arc dynamics. To show the different margin dynamics, we present: 1) sedimentologic and stratigraphic aspects, 2) relations with Neogene compressive and Quaternary extensional structures and 3) a hydrogeological case-study. The trip starts north of Rome, where Quaternary deposits at the transition from marine to continental deposition, including travertines, record the evolution of the Tyrrhenian passive margin. The excursion then moves to the Mesozoic platform margins of the Latium-Abruzzi and Apulia carbonate platforms, where perfectly preserved Cretaceous to Neogene successions occur. The Maiella mountain and Gran Sasso range testify for carbonate production changes, as recorded in facies associations and isotope geochemistry records, related to global climate shifts and regional tectonics. A focus on the hydrogeologic dynamics of the Gran Sasso aquifer is also offered in relation to the current climate change. This guide is the result of a workshop of GeoSed, the Italian Association for Sedimentary Geology, and it also aims at providing a scientific base for geo-touristic explorers.

Palaeoenvironment of the Miocene Pirabas Formation mixed carbonate–siliciclastic deposits, Northern Brazil: Insights from skeletal assemblages

The Bragantina Platform is an onshore basin of the Brazilian equatorial margin, including the Pirabas Formation, the youngest bioclastic-dominated formation in the area (early–middle Miocene), testifying to the final demise of carbonate factories along this margin area and the transition to a siliciclastic-dominated sedimentation. Although the greatest part of the Pirabas Formation is overlain by the Barreiras Formation and the post-Barreiras deposits, the outcrops provide the opportunity to investigate these Neogene successions that are the onshore equivalent of the large offshore basins (e.g. Amapá Formation: Foz do Amazonas and Ilha de Santana Formation: Pará-Maranhão) of the margin. The latter are deemed to represent an important target for reservoir models. Aiming to thoroughly describe the Pirabas Formation deposits and provide a quantitative and simple approach to analysing the outcropping successions, this study examines seven different successions and a quarry using palaeontological and petrographical methods. Similar to the modern Brazilian equatorial margin, the siliciclastic fraction in the Pirabas Formation rocks decreases as the distance from the coast increases, whereas the bioclastic material is found in greater amounts offshore. However, while the carbonate production close to the Amazon River mouth currently occurs hundreds of kilometres offshore, the carbonate factories in coastal along the Pirabas platform are also located in coastal waters. This indicates that the terrigenous input over the carbonate rocks was still lower than that found at present. The combining analysis of the skeletal and foraminiferal assemblages enabled a separation of protected embayments (characterised by seagrass-related assemblages), exposed areas (characterised by bioclastic shoals) and mangrove forests (characterised by dark fine-grained sediments). This accurate approach serves as an unprecedented reference for the northeastern part of the South American equatorial margin and lays the foundation for future research.

Petrological, Environmental Deposition and Tectonic-Provenance Study of Bhuban Sandstones in Neogene Succession of Aizawl district, Mizoram

Abstract Bhuban sandstones in the Bhuban Formation of Surma Group in Mizoram are well exposed in an N-S trending hill range in the city of Aizawl. The petrological studies reveal that quartz, mica, feldspar and lithic fragments are the main constituents of sandstones. Quartz grains exhibited angular to sub-angular with sub-rounded grains suggesting short transport deposition and immature sediment. The sandstones are poorly sorted and mostly cemented by calcareous materials due to diagenetic effects. The value of Chemical Index Alteration indicate intensive chemical weathering under humid condition during the deposition of the sediments in the source areas. Geochemical classification of sandstones resulted in two classes, namely, arkose and litharenite. The ratio of V/Cr value in the sandstones indicate low ventilation condition in the depositional basin which has resulted in poor to moderate sorting of these sediments and the ratio of Ni/Co indicate oxic depositional condition. The tectonic setting discriminant analysis suggested that the Bhuban sandstones were deposited in an active continental margin. The provenance characteristics suggest the influence of plutonic igneous, metmorphic and subordinate sedimentary rocks source transported mostly from Indo-Myanmar ranges during Oligocene to Miocene time.

On the efficacy and limitations of isolated carbonate platforms as “oceanic dipsticks” to reconstruct subsidence histories, a case study from the Paleogene to Neogene strata on Grand Cayman and Cayman Brac, B.W.I.

Carbonate sedimentary successions that developed on isolated oceanic islands typically comprise a series of unconformity-bounded packages of strata that reflect eustatic sea level changes superimposed on local tectonic movements. Resolving the subsidence and/or uplift of these islands, which are often assumed to have simple tectonic histories, is challenging because the tectonic movements are commonly of similar magnitudes to the eustatic oscillations. The uncertainty associated with each of the components involved in the construction of subsidence diagrams (e.g., age constraints, decompaction, eustatic sea level curves, paleobathymetry), therefore, introduces significant error margins when assessing the tectonic histories of isolated carbonate platforms. By using two end-member subsidence diagrams for the Paleogene to Neogene successions on Grand Cayman and Cayman Brac, it can be shown that their subsidence rates were heterogeneous over time and that the evolution of these islands vary significantly even though they are situated in the same basin. Although these islands, located 150 km apart, were subject to uniform changes in eustatic sea level, they have different stratigraphic architectures owing to their independent tectonic histories. From the Oligocene to the late Pliocene, the tectonic histories of Grand Cayman and Cayman Brac were analogous, and they subsided at a rate of 5.6 to 9.9 m/Myr. From the late Pliocene to ~400 ka, however, northeast Cayman Brac was uplifted by 165 m and tilted with a rotational axis offshore from the southwest end of the island, whereas Grand Cayman was uplifted by ~10 m with no rotational component. The results of this study challenge the assumption that isolated carbonate platforms have simple tectonic histories, while exploring and highlighting the common problems that are encountered with the construction of subsidence diagrams.

Geomorphological characterization of basal flow markers during recurrent mass movement: A case study from the Taranaki Basin, offshore New Zealand

AbstractThis work examines the mode of basal to substrate interaction, and flow dynamics of recurrent mass wasting events from a high‐quality 3D seismic reflection data. The Taranaki Basin, offshore New Zealand offers a unique environment to understand these processes, as the Neogene succession of the area preserves vertical stacks of mass transport deposits (MTDs) from the Miocene to Pliocene. The approach used here combines seismic interpretation of the basal shear zones (BSZs) of the MTD, seismic attribute analyses and colour rendering of both RMS amplitude and energy gradient maps. The five mass transport deposits are characterized into blocky‐MTDs consisting of moderate to high amplitude and variably deformed rafted blocks, and chaotic masses composed of slides and debris flow deposits. Classic examples of kinematic indicators at the BSZ of the MTDs akin to free‐slip flow processes such as liquefaction, hydroplaning and shear wetting are convolute flow fabrics and basal shear zone cut‐offs (fractures). Striations, grooves, mega scours, U‐ and V‐shaped scours, substrate erosion, monkey fingers (peel backs), substrate deformation and shearing are associated with no‐slip flows, suggesting that the mass movements efficiently interacted with the underlying substrate. Importantly, the intersection of different kinematic indicators along the BSZs of all the MTDs suggests an overlap of flow regimes, flow overprinting and transformation during mass movement. Although basal tooling by rafted blocks seems dominant during remobilization of the blocky MTDs, the presence of other kinematic indicators signifies combined mechanisms involving both free‐flow and no‐slip processes during their translation. The classification scheme evaluated here innovatively shows mass movements habitually occur through a combination of flow mechanisms rather than an independent flow regime.

A new stratigraphic framework for the Miocene – Lower Pliocene deposits offshore Scandinavia: A multiscale approach

Here, we present an updated stratigraphic subdivision of the Oligocene to Pleistocene succession (880–610 m) in the newly proposed type well for the Molo Formation, the industrial 6407/9‐5 well, located on the continental shelf in the eastern Norwegian Sea. Furthermore, new data from the Danish North Sea wells Nora‐1, Vagn‐2, and Tove‐1 are presented. The studied succession in the 6407/9‐5 well is composed of five sedimentary units separated by hiati. The dating of these five units is based on correlation to the stratigraphically more complete Neogene succession in the (Danish) central North Sea area. In this study, a robust stratigraphic framework of these five units, based on a combination of dinoflagellate cysts (dinocyst) stratigraphy and seismic data, is established. The Oligocene succession is referred to the NSO zonation of Van Simaeys et al., Review of Palaeobotany and Palynology, 2005, 134, 105–128, while the Miocene–Pliocene succession is referred to the dinocyst zonation of Dybkjær and Piasecki, Review of Palaeobotany and Palynology, 2010, 161, 1–29. In well 6407/9‐5 the two lowermost units, located below the Molo Formation, comprise a Rupelian (Lower Oligocene) succession up to 803 m, and an Aquitanian/Burdigalian (Lower Miocene) succession from 803 to 787 m, respectively. Both of these units are referred to the Brygge Formation. The Molo Formation is separated from the underlying Brygge Formation by an unconformity. Furthermore, and in contrast to previous studies, our study shows that the Molo Formation (787–703 m) has an unconformity within it. The lower part of the formation (787–724 m) is dated to late Tortonian (Late Miocene), and referred to the Hystrichosphaeropsis obscura dinocyst Zone. The upper part (724–703 m) is dated to Zanclean (Early Pliocene), and referred to the Melitasphaeridium choanophorum dinocyst Zone. The uppermost unit studied (703–670 m) in the well is referred to the Gelasian (Lower Pleistocene) and is included in the Naust Formation. The regional correlation of this stratigraphy with the complete succession in the Danish North Sea reveals that the hiati found in the Miocene succession on the Norwegian Sea shelf are controlled by tectonism, while the internal depositional patterns of the Molo Formation were controlled by eustatic sea‐level changes.

Structural style of the NW Zagros Mountains and the role of basement thrusting for its Mountain Front Flexure, Kurdistan Region of Iraq

The NW segment of the Zagros Mountain Front Flexure in the Kurdistan Region of Iraq forms a prominent topographic and structural step separating the High Folded and Foothill zones. Due to scarcity of subsurface data, the geometry of faults underlying this flexure and the degree of basement involvement are poorly constrained. To overcome this, we estimated the structural relief along seven transects across the belt and reconstructed deformed geometries using balanced cross-sections. The average structural relief for six transects is around 2.6 km. Iterative kinematic forward modeling along one of these transects suggests that a multi-stage evolution involving both thin- and thick-skinned deformation can explain the observed structural relief. Our preferred model shows that early detachment folds in the Mesozoic to Neogene succession were overprinted by a NE-dipping basement-rooted thrust system with a cumulative displacement of 6.5 km. Up-dip, the basement thrust bifurcates into two splay thrusts. While the structurally higher splay accommodated 4.2 km of slip and amplified frontal anticlines to form the Mountain Front Flexure, the lower and younger splay took up 2.3 km of slip, which was mainly transferred into the Triassic basal detachment of the Foothill Zone. The shortening across the NW Zagros is calculated at c. 24.8 km. The shortening amount within the topographically low part of the belt implies that the Late Miocene to Quaternary shortening rate was much lower than the geodetically derived convergence rate.

The architecture of the Kattendijk Formation and the implications on the early Pliocene depositional evolution of the southern margin of the North Sea Basin

An east-west correlation profile through the upper Neogene succession north of Antwerp, based on cone penetration tests, reveals the architecture of the lower Pliocene Kattendijk Formation. It shows a basal incision of the Kattendijk Formation down to 20 m in Miocene sands and locally even Lower Oligocene clays. The incision is part of a much larger gully system in the region at the base of the Kattendijk Formation. The strongest gully incision is observed along the western profile, and coincides with increases in the thickness of the Kattendijk Formation from its typical four to six meters thickness in the east towards a maximum of 15 m in the west. Correlations show that this additional thickness represents a separate sequence of the Kattendijk Formation that first filled the deepest part of the gully prior to being transgressed and covered by the second sequence deposited in a larger gully system. Both sequences of the Kattendijk Formation have basal transgressive layers, and are lithologically identical. Initial, deep incision at the base of the Kattendijk Formation might have been the result of the constriction of early Pliocene tidal currents that invaded and expanded fluvial or estuarine gullies that had developed during the latest Miocene sea-level low. A similar mechanism had been proposed for the development of late Miocene gully system at the base of the Diest Formation further southeast in northern Belgium. As the wider area was transgressed and covered by the second sequence of the Kattendijk Formation, flow constriction ended, currents weakened and gully incisions were reduced in size.

Outer forearc high control in an erosional subduction regime: The case of the central Peruvian forearc (6–10°S)

The forearc of the North-Central Peruvian Andes (FNCPA, 6–10°S) provides an exceptional opportunity to study the long-term processes that affect a convergent plate boundary. First, it shows long-term subsidence, depocenter superimposition and individualization. Second, although being mostly extensional and characterized as a typical erosive margin, the FNCPA shows complex uplifted regions. Older deformation is expressed by basement horst and grabens disposed in a complex geometry which onset may have resulted from strike-slip tectonics. A long-lived episode of regional subsidence affected the forearc and led to the relatively thick and regional deposition of the lower Miocene series coeval with a significant increase of the convergence velocity. This period was followed by an episodic uplift of trench-parallel corridors along the so-called Main Deformation Zone. Uplift ceased through the late Miocene and restarted during Pliocene and Quaternary, generating accommodation space by basin flank uplift for a forearc depocenter characterized by landward tilted strata. Significant along-strike differences in the degree of uplift resulted in either uplifting series producing sharp seaward dipping erosional surfaces or less uplifted areas covered by seawards prograding clinoforms. As a consequence of the shallow-water marine setting, the seismic strata geometry, lateral extent and thickness of the deposits for the Neogene successions in the FNCPA have been also tightly controlled by accommodation changes. Uplift is uneven along-strike independently of fault direction and closely followed the increase of the subsidence of the continental slope produced by subduction-erosion. Therefore, sediment underplating seems the most appropriate mechanism at the origin of uplift; as observed in other parts of the Peruvian and Chilean margins. Although the erosive character of the margin, the effects on basin geometry of the raised zone resemble that of typical outer forearc highs in accretionary margins such as in the Kumano basin in Japan.

Neogene palynostratigraphic zonation of the Maranon Basin, Western Amazonia, Peru

The palynology (150 species of pollen grains, 43 species of spores, eight species of dinoflagellate cysts, five genera of algae, two genera of fungal spores, foraminiferal linings, and copepod eggs) of the Neogene succession in the Marañon Basin, north Peru, was thoroughly investigated for the first time from six industrial wells (Arabela-1X, Maynas-1, Tucunare-1X, Tigrillo-30X, Nahuapa-24X, and La Frontera-1). Six palynozones spanning the Early Miocene to the Early Pliocene were defined. The zones in stratigraphically ascending order are as follows: the Mar-A Corsinipollenites oculusnoctis Zone (Aquitanian to early Burdigalian: 23.03–17.71 Ma), delimited by the appearance of Acaciapollenites myriosporites, Retitricolporites wijmstrae and/or Corsinipollenites oculusnoctis and/or the disappearance of Cicatricosisporites dorogensis at the base; the Mar-B Malvacipolloides (Echitricolporites) maristellae Zone (Burdigalian: 17.71–16.1 Ma), from Malvacipolloides maristellae at the base to the disappearance of Retitricolporites wijmstrae at the top; the Mar-C Mauritiidites crassibaculatus Zone (latest Burdigalian to Late Langhian: 16.1–14.2/13.9 Ma), from the appearance of Grimsdalea magnaclavata at the base to the disappearance of Retitriporites dubiosus and/or the appearance of Crassoretitriletes vanraadshooveni and/or Psilastephanoporites tesseroporus; the Mar-D Crassoretitriletes vanraadshooveni Zone (Late Serravallian: 14.2–11.62 Ma), from the appearance of Crassoretitriletes vanraadshooveni and/or Psilastephanoporites tesseroporus to the disappearances of Mauritiidites crassibaculatus, Bombacacidites nacimientoensis, and Cyathidites congoensis; and the Mar-E Psilastephanoporites tesseroporus Zone (Early Tortonian to Late Messinian: 11.62–5.48 Ma) from the disappearance of Corsinipollenites oculusnoctis and/or Cyathidites congoensis to the disappearance of Psilastephanoporites tesseroporus and/or Siltaria santaisabelensis. These zones were corroborated by means of events ordination demonstrated using graphic correlation. The Mar-F Ctenolophonidites suigeneris Zone (latest Messinian to Zanclean) is described only in the Frontera-1 well from the disappearance of Psilastephanoporites tesseroporus to the last record of Ctenolophonidites suigeneris and/or Siltaria hammenii. This study suggests that Pliocene sedimentation is also recorded in the Western Amazonia of Peru, and provides new palynological information compared with the Mio–Pliocene Solimões, Acre, and eastern Amazonas basins.

The Tajik Basin: A composite record of sedimentary basin evolution in response to tectonics in the Pamir

AbstractInvestigation of a >6‐km‐thick succession of Cretaceous to Cenozoic sedimentary rocks in the Tajik Basin reveals that this depocentre consists of three stacked basin systems that are interpreted to reflect different mechanisms of subsidence associated with tectonics in the Pamir Mountains: a Lower to mid‐Cretaceous succession, an Upper Cretaceous–Lower Eocene succession and an Eocene–Neogene succession. The Lower to mid‐Cretaceous succession consists of fluvial deposits that were primarily derived from the Triassic Karakul–Mazar subduction–accretion complex in the northern Pamir. This succession is characterized by a convex‐up (accelerating) subsidence curve, thickens towards the Pamir and is interpreted as a retroarc foreland basin system associated with northward subduction of Tethyan oceanic lithosphere. The Upper Cretaceous to early Eocene succession consists of fine‐grained, marginal marine and sabkha deposits. The succession is characterized by a concave‐up subsidence curve. Regionally extensive limestone beds in the succession are consistent with late stage thermal relaxation and relative sea‐level rise following lithospheric extension, potentially in response to Tethyan slab rollback/foundering. The Upper Cretaceous–early Eocene succession is capped by a middle Eocene to early Oligocene (ca. 50–30 Ma) disconformity, which is interpreted to record the passage of a flexural forebulge. The disconformity is represented by a depositional hiatus, which is 10–30 Myr younger than estimates for the initiation of India–Asia collision and overlaps in age with the start of prograde metamorphism recorded in the Pamir gneiss domes. Overlying the disconformity, a >4‐km‐thick upper Eocene–Neogene succession displays a classic, coarsening upward unroofing sequence characterized by accelerating subsidence, which is interpreted as a retro‐foreland basin associated with crustal thickening of the Pamir during India–Asia collision. Thus, the Tajik Basin provides an example of a long‐lived composite basin in a retrowedge position that displays a sensitivity to plate margin processes. Subsidence, sediment accumulation and basin‐forming mechanisms are influenced by subduction dynamics, including periods of slab‐shallowing and retreat.

Neogene evolution and demise of the Amapá carbonate platform, Amazon continental margin, Brazil

The Amazon continental shelf hosted one of the world's largest mixed carbonate-siliciclastic platforms from the late Paleocene onwards - the Amapá carbonates. The platform architecture, however, remains poorly understood and causes and timing of the cessation of carbonate deposition are still controversial. Here we present a stratigraphic analysis of the Neogene succession of the Amapá carbonates, based on a grid of 2D/3D seismic data correlated to revised micropaleontological data from exploration wells. The results provide improved constraints on the age of the transition from predominantly carbonate to siliciclastic sedimentation, which is shown to have varied through time across three different sectors of the shelf (NW, Central and SE). Four Neogene evolutionary stages of carbonate deposition could be defined and dated with reference to the new age model: (1) between ca. 24 and 8 Ma a predominantly aggrading mixed carbonate-siliciclastic shelf prevailed across the entire region carbonate production gave way to siliciclastic sedimentation across the Central and SE shelves; (2) between 8 and 5.5 Ma carbonate production continued to dominate the NW shelf, as deposition was able to keep up with base level oscillations; (3) between 5.5 and 3.7 Ma (early Pliocene), sediment supply from the paleo-Amazon River promoted the progressive burial of carbonates on the inner NW shelf, while carbonates production continued on the outer shelf (until 3.7 Ma). Longer-lasting carbonate sedimentation on the NW shelf can be explained by a lesser influx of siliciclastic sediments due to the paleo-geography of the Central shelf, characterized by a 150-km-wide embayment, which directed most terrigenous sediments sourced from the paleo-Amazon River to the continental slope and deep ocean; (4) from 3.7 Ma onwards, when the Central shelf embayment became completely filled, continuous sediment supply to the NW shelf resulted in the final transition from carbonate to siliciclastic-dominated environments on the entire Offshore Amazon Basin.

An updated and revised stratigraphic framework for the Miocene and earliest Pliocene strata of the Roer Valley Graben and adjacent blocks

AbstractIn the Netherlands, the bulk of the Miocene to lowest Pliocene sedimentary succession is currently assigned to a single lithostratigraphical unit, the Breda Formation. Although the formation was introduced over 40 years ago, the definition of its lower and upper boundaries is still problematic. Well-log correlations show that the improved lecto-stratotype for the Breda Formation in well Groote Heide partly overlaps with the additional reference section of the older Veldhoven Formation in the nearby well Broekhuizenvorst. The distinction between the Breda and the overlying Oosterhout Formation, which was mainly based on quantitative differences in glauconite and molluscs, gives rise to ongoing discussion, in particular due to the varying concentrations of glauconitic content that occur within both formations. In addition, the Breda Formation lacks a regional-scale stratigraphic framework which relates its various regionally to locally defined shallow marine to continental members.In order to resolve these issues, we performed renewed analyses of material from several archived cores. The results of archived and new dinocyst analyses were combined with lithological descriptions and wire-line log correlations of multiple wells, including the wells Groote Heide and Broekhuizenvorst. In this process, the updated dinocyst zonation of Munsterman & Brinkhuis (2004), recalibrated to the Geological Time Scale of Ogg et al. (2016), was used. To establish regionally consistent lithostratigraphic boundaries, additional data was used along a transect across the Roer Valley Graben running from its central part (well St-Michielsgestel-1) towards the southern rift shoulders (well Goirle-1). Along this transect, chronostratigraphic and lithostratigraphic analyses were integrated with well-log correlation and the analyses of seismic reflection data to constrain geometrical/structural relationships as well.The results led to the differentiation of two distinct seismic sequences distinguished by three recognisable unconformities: the Early Miocene Unconformity (EMU), the Mid-Miocene Unconformity (MMU) and the Late Miocene Unconformity (LMU). The major regional hiatus, referred to as the Mid-Miocene Unconformity, occurs intercalated within the present Breda Formation and compels subdivision of this unit into two formations, viz. the here newly established Groote Heide and the younger Diessen formations. Pending further studies, the former Breda Formation will be temporally raised in rank to the newly established Hilvarenbeek subgroup, which comprises both the Groote Heide and Diessen formations. Whereas these two sequences were already locally defined, a third sequence overlying the LMU represents two newly defined lithostratigraphical units, named the Goirle and the Tilburg members, positioned in this study at the base of the Oosterhout Formation. Besides their unique lithological characteristics, in seismic reflection profiles the Goirle and the Tilburg members stand out because of their distinct seismic facies.Use of an integrated, multidisciplinary and regional approach, an improved southern North Sea framework and more comprehensive lithostratigraphic subdivision of Neogene successions is proposed for the Netherlands, to make (cross-border) correlations more straightforward in the future.