Miocene Sediments Research Articles

Magnetostratigraphy of Early Oligocene-Middle Miocene Deposits in the Xunhua Basin on the Tibet Plateau, China, and Their Paleoclimate Significance

The growth history of the Tibetan Plateau provides a valuable natural laboratory to understand tectonic processes of the India–Asia collision and their impact on and interactions with Asian and global climate change. However, both Tibetan Plateau growth and Asian paleoenvironments are generally poorly documented in pre-Pliocene times and reflect limited temporal coverage for different parts of the plateau. In this paper, the 238 m thick Cenozoic sediments in the Hongzhuang section of the Xunhua Basin were tested and analyzed via paleomagnetic and environmental magnetic methods. The formation age was determined, and the evolution history of the regional climate environment was analyzed. The magnetostratigraphy study shows that the sediments record a continuous sequence of geomagnetic polarity changes from C5ACn to C10r, which spans an interval of approximately 30~14.3 Ma from the early Oligocene to the middle Miocene. The magnetic susceptibility of the Hongzhuang section is basically similar to the deep-sea oxygen isotope fluctuation, indicating that the monsoon climate change indicated by the magnetic susceptibility is affected by global temperature. It is worth noting that at ~27 Ma and ~15 Ma, there is a negative correlation between magnetic susceptibility and deep-sea oxygen isotope, and magnetic susceptibility lags behind the increase in deep-sea oxygen isotope. Combined with the change in the sedimentary rate curve, we explain the asynchrony between the magnetic susceptibility and the deep-sea oxygen isotope around ~27 Ma and ~15 Ma. As the uplift of the plateau leads to the enhancement of the East Asian summer monsoon, the soil formation in the region is strengthened, resulting in an increase in magnetic susceptibility. At the same time, the rapid uplift of the plateau caused the erosion of the surrounding mountains to strengthen, and the input of near-source materials may promote the increase in magnetic susceptibility.

Sedimenty spodního a středního miocénu jihozápadně od Brna ve světle nových poznatků

New knowledge on the occurrence of Lower and Middle Miocene sediments in the southwestern surroundings of Brno has been acquired through geological mapping and documentation work during the recent years. Specific work was focused on: • preparation of the publication on the local national history of the cadastral territory of the village of Bohutice; • salvage study of the former reserved bentonite deposit Ivančice – Réna, which is being gradually remediated and turned into a recreational area; • the area in the foreground of the New Ivančice viaduct, which is susceptible to long-term slope instability; • the western edge of the village of Němčičky near Židlochovice, where extensive construction of family houses is underway; • the area between the municipalities of Moravany, Nebovidy and Ostopovice, where the excavations for new extra-high voltage pylons were documented. The detailed mapping, petrographic and biostratigraphic studies allowed to refine the distribution, lithological characteristics and age of Miocene sediments; specifically, a more extensive occurrence of Lower Miocene sediments compared to previous findings was confirmed (localities Ostopovice, Moravské Bránice – locality 5). These findings support earlier results from the area N of the City of Brno, where the known extent of Ottnangian sediments was expanded at the expense of Badenian sediments. The documentation and sampling of the new excavations (for family houses and extra-high voltage pylons) and old mining pits enabled the description and further study of the sediments. The acquired litho- and biostratigraphic data were correlated with engineering geological findings. In a construction pit in Bohutice, a completely new occurrence of tuffitic sediments of the Ottnangian age was discovered and geochemically verified. Furthermore, the Ottnangian gravels in Němčičky were newly discovered. These contain a large proportion of granitoid pebbles probably derived from the Brno Massif. It was found that the weakly consolidated lithologically variable Lower Miocene sediments are prone to landslides. In the case of the New Ivančice viaduct, extensive suffusion doline were identified, resulting from the ingress of rainwater from the wider area of the railway embankment foreground. Biostratigraphy of the sediments was based on micropaleontological analysis of foraminiferas. Ottnangian sediments were usually fossil- free and/or they contained reworked Cretaceous foraminiferas. Lower Badenian sediments are characterized by occurrence of abundant and diversified fauna represented by foraminifera species such as Martinotiella karreri (Cush.), Globigerinoides bisphericus Todd, Vaginulina legumen (L.), etc.

Palaeomagnetic evidence of the deformation of the Pontides during the closure of the Intra-Pontide Ocean in the early Cretaceous

SUMMARY Several models exist concerning the deformation history of the Pontides in North Anatolia during the Cretaceous period, which vary depending on the positions of the Istanbul and Sakarya zones, the consumption of the northern branches of the Neotethys ocean and the rifting of several sub-basins. Notably, the early Cretaceous tectonic history of the Pontides involved the closure of the northern Neotethys ocean (Intra-Pontide ocean), and the collision between the Istanbul and Sakarya zones, producing thrust structures along the collisional front. The lack of palaeomagnetic data providing evidence for this deformation pattern demonstrates that further investigation is required, particularly focusing on the Lower Cretaceous strata in the Pontides. Thus, this study aimed to examine samples from a total of 78 sites from the Lower–Upper Cretaceous sedimentary rocks, and Middle Eocene to Middle Miocene sedimentary and volcanic rocks. Results of this study indicated large counterclockwise rotations up to R±ΔR = −73.9°±9.1°, and small clockwise rotations of R±ΔR = 14.2°±12.2° in the Istanbul and Sakarya zones, during the Early Cretaceous and Late Cretaceous periods. These rotation patterns are accompanied by the closure of the Intra-Pontide ocean, and the collision between the Istanbul and Sakarya zones during the Early and Late Cretaceous periods. On the other hand, in the Middle Eocene, small counterclockwise rotations of R±ΔR = −6.4°±13.9° and 4.6°±12.9° along the western coastline of the Pontides indicated that the northern margin of the Pontides was stable during this period.

Tectonic and climate forcing of exhumation in the SE Tibetan Plateau over the past 7 Ma: Insights from the deltaic-submarine fan system in the Andaman Sea, northeastern Indian Ocean

The Tibetan Plateau and its adjacent areas are a typical example for studying the relationship between plateau uplift, climate change, and surface erosion. It has been argued that the South Asian monsoon (SAM) strengthened significantly at 10–8 Ma, whereas others suggested that the SAM weakened at that time. Here we report a large deltaic-submarine fan system in the Andaman Sea with a high sediment accumulation rate during the Pliocene. We propose that the formation of the deltaic-submarine fan was a result of climate and tectonics over the past 7 Myr. Our findings are based on multi-method provenance analyses (heavy minerals, bulk-rock geochemistry, detrital zircon UPb ages, and seismic data) of the Late Miocene-Pleistocene deltaic-submarine fan system. The analyses, in combination with those of the modern river sediments and potential source regions, suggest that the Upper Miocene sediments were mainly derived from the eastern Lhasa Terrane and northern West Burma Terrane (Upper Salween and Upper Irrawaddy, respectively), whereas the Pliocene-Pleistocene deposits were primarily derived from the eastern Lhasa Terrane, northern West Burma Terrane, and Tengchong Terrane (Lower Salween River), with small inputs from the Sibumasu and Baoshan terranes. We propose a modified scenario in which the Salween initiated in the early Late Miocene (10 Ma) and the Irrawaddy developed a modern geometrical morphology after the Pliocene. These two large rivers transported eroded materials from the SE Tibetan Plateau into the Andaman Sea and formed the deltaic-submarine fan. The high sediment accumulation rate (>530 m/Myr) in the Pliocene is consistent with the strengthened SAM and heterogeneous crustal deformation of the SE Tibetan Plateau during the same interval. We conclude that both the climate and tectonics have direct effects on exhumation of the SE Tibetan Plateau over the past Late Miocene-Quaternary.

Microfauna complex and bionomy of Sarmatian sediments of Shaigler-Gaibler section (Gobustan oil-gas bearing region)

Biostratigraphic characteristics of Sarmatian sediments in South-eastern Gobustan is presented according to the data of Shaigler-Gaibler section; the systematic composition and characteristic complexes of microfossils – foraminifers, ostracods, otolites and the fish remnants are defined. As a result of the biostratigraphic division of the section carried out, it was revealed that the sediments of Sarmatian stage participate in the geological structure of Shaigler-Gaibler anticline; there are no Upper Sarmatian sediments in the section. The scheme of division of Sarmatian sediments in Shaigler-Gaibler sections which may be applied for the further geological surveys in the other areas of South-eastern Gobustan, has been developed. The results obtained may be used for the biostratigraphic research of deeply buried Miocene sediments of Western edge of South Caspian.

Two Asian cricetodontine-like muroid rodents from the Neogene of western North America

AbstractWe appraise the morphology and potential origin of two Neogene cricetodontine-like muroids, Pliotomodon primitivus from Late Miocene sediments in northern California and an undescribed muroid from the late Oligocene or Early Miocene of central Oregon. Superficial resemblance of the dentition of Pliotomodon with members of the North American galushamyinan neotominins is considered a result of parallel evolution, as shown by the large size and unreduced M3/m3 of the former. Dental features of Pliotomodon are similar to those of Eurasian genera such as Byzantinia, Hispanomys, and Ruscinomys, but the unusual morphology of M3/m3, with continuous enamel connections across their lingual surfaces closing the hypoflexus and posteroflexid, respectively, plus retention of only three roots on M1, suggests Pliotomodon arose from an ancestor distinct from the one that gave rise to the large late Neogene hypsodont cricetodontines of the Old World. In the absence of known ancestral taxa in North America, we postulate Pliotomodon dispersed to North America across Beringia during the Hemphillian (ca. 8.6 Ma, Hh-1). Another archaic cricetodontine-like rodent, from the Warm Springs region of the John Day Formation in Oregon, is named as a new species of Deperetomys, D. dingusi new species. Deperetomys dingusi n. sp. likely descended from a species of Deperetomys intermediate between archaic species such as D. calefactus and D. magnus and more dentally derived species such as D. intermedius and D. hagni, dispersing to North America during the late Oligocene or Early Miocene (Arikareean; ca. 23 Ma, Ar3 or Ar4).UUID: http://zoobank.org/b691db3a-79de-4d3e-8af0-3bda4957b119

Comparison of the Late Miocene Sediments and Early Quaternary Red Paleosols in the Penghu Islands, Taiwan and Zhangpu, Fujian

This study aims to compare the clay mineralogy and whole-soil major chemistry of elements in late Miocene soil sediments and early Quaternary red paleosols in the Penghu Islands, (Pescadores), Taiwan, and Zhangpu Volcanic Park, Fujian. There were the late Miocene Chu Wan (CWI and CWII), Shiao Men Yu (SMY) and two intergrade red soils, Chu Wan (CW(irs)) and Shiao Men Yu (SMY(irs)), with three distinctive zones of different dominating kaolins in the profiles of the Penghu Islands. A Tong Wei (TW) paleosol of early Quaternary basaltic eruptions in the Penghu Islands was collected. The Anzei (AZ), Si Yu (HY) and Chianmei (CM) paleosols were sampled from the Penghu Islands and Yulinshi (YLS) paleosols near the Zhangpu Volcanic Park for this study. The CW and SMY paleosols erupted in the late Miocene, and the other paleosols erupted on the Penghu Islands. These paleosols were fractionated into clay fractions and subjected to soil physical and chemical analyses. Kaolin minerals were dominant in the CW(irs) and SMY(irs) paleosols. The top layer (layer one) in the CW(irs) was 7 Å-halloysite, and order/disordered kaolinites were present in layers two and three. The CW(irs) and SMY(irs) hexagonal-like, platy kaolinites (0.1–0.2 µm in diameter), spheroidal and hollow 7 Å-halloysite (layer 1) was determined with transmission electron microscopic (TEM) investigations. The early Quaternary red soil of TW consisted of kaolinite, illite, vermiculite and smectite clay assemblages. Late Miocene paleosols were classified as fine, kaolinite, hyperthermic and Typic Rhodic Paleudults, and the early Quaternary red paleosols were classified as fine, mixed, hyperthermic and Typic Rodistalf, respectively. Late Miocene paleosols contained more clays, lower SiO2/Al2O3 and higher chemical index of weathering (CIW) than early Quaternary paleosols. The kaolin, illite, smectite and vermiculite mineralogy, physical and chemical properties of paleosols and landscapes in the Zhangpu YLS, Fujian, were similar to those of late Miocene sediments and early Quaternary red paleosols in the Penghu Islands.

A New Specimen of cf. Isanacetus laticephalus (Baleen Whale) from the Oi Formation, Ichishi Group (Late Early Miocene) in Japan

In the history of baleen whales, the early Miocene is one of not a well-known time. Many baleen whales from the Miocene are known as “cetotheres”. The “cetothere” Isanacetus laticephalus was a baleen whale from the early to middle Miocene that is only known from Japan. The holotype and paratype of I. laticephalus are well-preserved, and the age of the species I. laticephalus makes it one of the earlier basal plicogulans; however, its phylogenetic position is unclear. Here, a new cranium including the periotic from an early Miocene deposit (about 18.5 to 17.0 Ma) of the Oi Formation, Ichishi Group in Mie, Japan is reported as cf. I. laticephalus. The specimen displays a combination of four periotic features: (i) a large lateral tuberosity; (ii) a rectangular pars cochlearis; (iii) a robust neck of the posterior process, and (iv) a cerebral aperture of the facial canal that is smaller than that of the dorsal vestibular area. This combination of features could be diagnostic for I. laticephalus, among basal plicogulans from the early and middle Miocene. Adding more referred specimens will expand the diagnoses of I. laticephalus, and firmly support phylogenetic trees with this species.

The geological composition of rifts in Sudan as related to oil and gas content

Gradual increase in hydrocarbon production by the Saudi Arabia, Russia and the USA has led to the fact that today their share in the global production volume is about 42%, according to British Petroleum. At the same time, the market volume for small players, focused primarily on domestic demand and meeting the needs of their nearest neighbors, is falling proportionally. A striking example of this trend is the Republic of Sudan, on whose territory a small number of oil and gas fields are being developed, characterized by a very complex structure associated with rift sedimentary basins, which began to be studied in detail only a few years ago. The first comprehensive regional geological work began only at the end of 1974. As of today, all discovered oil reservoirs are located within rift zones, and the most promising one is the Muglad Basin, which contains eleven discovered oil fields connected with the terrigenous deposits of Upper Cretaceous and Miocene. Based on the study of seismic and core data, sequence stratigraphic and sedimentological models were built of the main depositional structures of the Muglad Basin, the potential was evaluated of the discovery of new hydrocarbon deposits. Keywords: rift valley; fields sedimentary complexes; Muglad Basin; Sudan; sequence stratigraphy.

New evidence for Early Miocene palaeoenvironmental changes in the North Croatian Basin: Insights implicated by microfossil assemblages

An integrated stratigraphic study has been performed of the Lower Miocene deposits of the Poljanska and Mala sections (North Croatian Basin), coupled with 40Ar/39Ar dating, geochemical and mineralogical study of tuffitic and silty sand beds. The sedimentary record evidences deposition influenced by volcaniclastic input. The presence of marine, brackish and non–marine microfossils indicates complex palaeoenvironment, palaeoecology, and palaeobiogeography. Four different units were recognized based on their fossil content and sedimentological data. At the base of the Poljanska section (Unit P1), tuffitic sediments bear common endemic brackish, and rare marine to freshwater and terrestrial microfossils. Radiometric 40Ar/39Ar dating obtained on volcanic glass shards from this layer provided an age of 22.2 ± 1.9 Ma correlating with the earliest Early Miocene and indicating the existence of older volcanic activity in the NCB pro tempore. The succession transitions into the brackish-water lacustrine environments (Unit P2). This unit has two presumed different climatic events: a maximum temperature event in the lower part of the interval and one interruption with lower temperatures recognized in the upper part of the interval. The co-occurrence of limnic and marine species in the uppermost part of the investigated sediments (Unit P3) indicates a marine inflow into the coastal lake. It marks the beginning of a salina-type lake formation in Poljanska. In the Mala section (Unit M1), biostratigraphically dated to the NN4 Zone, a transgressive sequence is documented through the presence of marine calcareous nannoplankton, planktonic and benthic foraminifera, and ostracods.

Ancestors of Ulmus parvifolia from late Miocene sediments in Yunnan, Southwest China and its future distribution

We describe a new elm from Miocene sediments of Southwest China and perform phytogeographical analyses and species distribution modeling. Samaras of U. palaeoparvifolia sp. nov. were collected from late Miocene sediments of the Xiaolongtan Formation in Huaning, Yunnan, Southwest China are obovate-elliptic with surrounding wings. Perianth is persistent and the tepals are lanceolate, and the seed is positioned in the center or upper part of the fruit. The pedicel is shorter than the perianth. The fruits are very similar to those of U. parvifolia (Chinese elm) with respect to size, morphological characters, and seed position. As ancestors of Chinese elm, the appearance of U. palaeoparvifolia in the late Miocene in Huaning indicates that Huaning had a subtropical climate with warmer and more humid summers and its distribution extended more to the west in the late Miocene than at present. However, compared with the current distribution, a bioclimatic model predicts that the optimal distribution of U. parvifolia will shift westward and will be limited to the Qinling area with high altitude in 2100, where the temperature and precipitation will be higher than current values, and will require conservation in the future.

Аlternative local stratigraphical scales of the Upper Miocene of the Rostov Dome

Background. Definition of local stratigraphical units, the main of which are formations, is important for geological mapping and correct understanding of the composition of sedimentary complexes. This task is yet to be solved for some territories. Thus, Upper Miocene deposits extend widely across the Rostov Dome in the southwest of Russia; however, the definition of formations there is still in its nascent phase.Aim. Systematization of ideas about the local stratigraphical units of the Upper Miocene of the Rostov Dome, taking previous assumptions into account.Materials and methods. An analysis of ideas related to the definition of formations in the Upper Miocene of the Rostov Dome was carried out. These ideas were systematized with a focus on the validity of the units based on the current stratigraphical code.Results. An improved local stratigraphical scale of the Upper Miocene of the Rostov Dome is proposed. This scale implies defining the Taganrogskaya (Lower Sarmatian), Rostovskaya (Middle–Upper Sarmatian), Donskaya (lower Upper Maeotian), Merzhanovskaya (upper Upper Maeotian), and Aleksandrovskaya (Lower Pontian) formations. The correspondence of alternative units is shown: the Mokrochaltyrskaya and Berdanosovskaya formations correspond to the Rostovskaya Formation, while and the later proposed Rostovskaya Formation corresponds to the Donskaya and Merzhanovskaya formations. Discussion. The validity of the proposed local stratigraphical units is noted; the priority of defining the Taganrogskaya and Aleksandrovskaya formations is highlighted. The question of creating an automatic system for generalizing information about stratigraphical units is discussed.Conclusion. The need in the parallel existence of alternative local stratigraphical scales of the Upper Miocene of the Rostov Dome is absent. However, subdividing the relevant deposits requires further discussion and refinement.

The Miocene deposits of the Cirò Basin in the evolution of the peri-Ionian region, eastern Calabria

The Cirò Basin is located in the north-eastern partion of Calabria, between the Ionian Sea and the Sila slopes. In this area, basin successions of the Neogene and Quaternary age overlap the Paleozoic metamorphic basement of the Sila Unit. In particular, there are units consisting of continental clastic facies and coastal facies that are the basis of the Tortonian-Messinian transgression. An accurate geological-structural survey, combined with sedimentological and stratigraphic analysis, has allowed to define the limits of the Cirò Basin and the stratigraphic relationships between the various outcropping Miocene deposits. Five distinct litofacies have been recognized, each of which contains both lateral and vertical variations.The main tectonic structures control the architecture and evolution of main Neogene basins of the Calabrian terranes. From the Neogene to the Quaternary, the history of orogenic building was mainly controlled by the activity of NW-SE oriented faults and shear zones characterised by left-trascurrent kinematics. Deformation is well evidenced in the tectono-sedimentary evolution of the wedge-top basins as well as in the retro-arc domain.

Astronomical time scale of the lower Miocene depositional sequences (Aquitanian-Burdigalian) in the Jambour Field, northern Iraq

The Miocene succession is considered one of the major shallow hydrocarbon reservoirs in Iraq. It consists primarily of lagoonal evaporites and carbonate alternations, with many barren intervals and non-diagnostic fauna. An astronomical time scale (ATS) was established in two wells in Jambour Field, Kurdistan, using high-resolution cyclostratigraphic analysis of GR data for the first time in Iraq to determine the absolute age of the Miocene sequences and their boundaries. Sixteen unique carbonate and evaporite facies types were discovered and classified into five facies associations, from the mid-outer ramp to the peritidal carbonate and evaporite ramps. The most significant of these implies that, after astro-climatic frequencies, sea-level change was the dominant regulator of lower Miocene deposition. The difference in GR and facies type is mostly due to third eustatic sequences, which describe a rich series of long and short-period eccentricities in orbitally defined terms. The eustatic sea-level variations of the third-order sequences correlate with the sedimentary noise model applied over the tuned GR. A sharp sediment accumulation rate (SAR) was caused by an abrupt shift in the depositional environment, as demonstrated by the applied eCOCO within the lower Aquitanian part of the Dhiban Formation; consequently, each well was split into two datasets. The SAR ranges from 3.1 to 1.97 cm/kyr in the Ja46 well and 2.3 to 3.3 in the Ja49 well. The MTM spectral analysis of the four datasets revealed the eccentricity cycles' dominance with a high degree of confidence level. The present study employs high-resolution ATS using tuning of the GR with the new merged short and long eccentricity cycle filter output method, which is supported by previous strontium isotope studies and compared to the La 2004 astronomical solution. According to the ATS, the Aquitanian-Burdigalian sequences range from 5.08 myr at Ja46 Well to 4.66 myr at Ja49 Well. The tuning output indicated the presence of two hiatuses, the first in the Dhiban Formation with a time gap of about 0.21 and 0.3 myr in the Ja46 and Ja49 wells, respectively, and the second at the top of the Jeribe Formation with a time gap of about 0.34 myr in the Ja49 well. This pause corresponds to a significant sea-level drop in the Arabian Platform Basin at 21.4–21.0 and 18.5 Ma.

Equatorial Pacific dust fertilization and source weathering influences on Eocene to Miocene global CO2 decline

Stimulation of the biological pump by iron-bearing dust in the eastern equatorial Pacific Ocean plays an important role in long-term carbon sequestration, yet past dust fertilization and its impact on CO2 perturbations over major climate transitions remain debated. Here, we integrate proxies of dust input, source-region weathering, and biological pump activity from late Eocene to early Miocene sediments of Integrated Ocean Discovery Program Hole U1333, which includes the Eocene-Oligocene Transition (~34 million years ago) when a major ice sheet was first established on Antarctica. We find that intensified chemical weathering in the large central Asian dust source region enhanced atmospheric CO2 removal at ~34 Ma. Superimposed dust fertilization and biological pump action amplified this CO2 removal before ~34 Ma, while weakening of this amplification process helped to moderate the CO2 decline after that time. The observed inter-linked, counteracting processes with different timescales illustrate the complexity of carbon cycle feedbacks associated with major climate changes.

The Ostracod Complex of Pontian Sediments of the Sundu Cavern (Gobustan Oil and Gas Basin, Eastern Azerbaijan)

Biostratigraphic characteristics of the Pontian deposits of Gobustan are given based on the materials of the Sundu cavern. The systematic composition and characteristic complexes of ostracods for the lower, middle, and upper sub-tiers are revealed. Biostratigraphic dissection of the section was performed. It is established that sediments of the Pontian regiostage take part in the geological structure of the anticlinal structure of the Sundu. A scheme of dismemberment of the Pontian sediments of Sundu cavern has been developed, which can be applied during further geological exploration in other areas of the SE of Gobustan. The obtained results can also be used for biostratigraphic study of deep-submerged Miocene deposits of the western side of the Southern Caspian.

The genus Acicula W. Hartmann, 1821 in the Caucasus (Gastropoda: Caenogastropoda: Aciculidae)

The Aciculidae is a family of terrestrial operculate snails with a western Palaearctic distribution. Historically three Acicula species were reported from the Caucasus Mountains, which represents the eastern edge of the family's distribution: A. limbata, A. moussoni and A. parcelineata, all from a few localities. We examined extensive material from the entire range of the Caucasus Mountains by means of classic morphology-based taxonomy and geometric morphometries. We arrived at the following conclusions: (1) At least three species inhabit the Caucasus Mountains, two of which are problematic taxonomically and regarding their nomenclature. (2) The two syntypes of A. moussoni have been lost, and both lectotype designations by the former authors were invalid. Therefore, we designate a neotype for A. moussoni. (3) Acicula limbata was described from Lower Miocene deposits of the Czech Republic. Although the fossil Central European and extant Caucasian shells differ only slightly from one another, it is highly unlikely that they would belong to the same species. Therefore, we suggest using A. limbata only for the Czech fossil species and A. moussoni for the Caucasian extant species. (4) In multiple samples, the generally smaller Acicula parcelineata was found syntopic with the generally larger A. moussoni. Therefore, the two are possibly distinct species. However, it is very difficult to distinguish, and the problem of A. moussoni and A. parcelineata needs further attention. (5) A species with a bullet (or torpedo)-shaped shell and an opisthocline apertural profile from the northern Caucasus region has been treated as A. moussoni by previous authors, but it is distinct from the other two Acicula species by consistent conchological characters and was also found with them in syntopy, and is described here as Acicula telum Páll-Gergely, n. sp.

Analysis of a travertine system controlled by the transpressional activity of the Alhama de Murcia fault: The Carraclaca site, eastern Betic Cordillera, Spain

Continental carbonates, such as travertines and tufas, formed from CO2-rich groundwater degassing as it emerges at the Earth’s surface, are often associated with major crustal-scale faults. The Carraclaca site, in the Lorca-Totana section of the Alhama de Murcia Fault, Spain, presents a complex geomorphological landscape controlled by active tectonics. The geology here records the interaction between Quaternary alluvial fans, travertines, and a pop-up structure developed in a transpressional section of the fault. The Alhama de Murcia Fault is an 80 km long left-lateral strike-slip fault that is one of the main seismogenic structures in the Iberian Peninsula. In this work, we examined the relation between travertine precipitation in the Carraclaca site and the tectonic activity of this fault zone through morphological and geochemical studies. The δ13C and δ18O isotopic signals indicate that the carbonate deposits are hydrothermal. In addition, the 87Sr/86Sr ratios in the samples suggest subsurface fluid interaction with the Miocene sediments and the Alpujárride basement, located below the alluvial deposits. Tectonic activity in the Alhama de Murcia Fault might generate the opening of deep water circulation in the crust every time a seismic event occurs, giving rise to hydrothermally derived carbonates precipitation. Deep waters rise and reach the surface interacting with meteoric waters, resulting in travertine formation. Therefore, the Carraclaca carbonate deposits study can inform us about the seismogenic cycle of the fault in the Lorca-Totana section.

Stratigraphic revision of the early Miocene Kiahera Formation from Rusinga Island, Lake Victoria, Kenya

Decades of research in Early Miocene deposits on Rusinga Island, Lake Victoria, Kenya, have made its fossil record pivotal for interpreting floral and faunal evolution in eastern Africa during the early Neogene. Paleontological research has largely focused on Rusinga Island's fossil-rich Hiwegi Formation, and because that work has largely motivated geological research a similar bias can also be found in stratigraphic studies of the island's deposits. Hence, the resolution of paleoclimate, paleohabitat, and floral and faunal community reconstructions from other formations is limited, and discrepancies in stratigraphic placement and correlations among outcrops limit our ability to fully assess the interplay of climate and evolution.New lithostratigraphic and sedimentologic analyses of the Kiahera Formation on Rusinga Island clarify these discrepancies. Our work demonstrates that the Kiahera Formation comprises ten facies and can be divided into three discrete clastic units (from bottom to top): Nyamita Spring Member, Ukowe Member, and Rondo Member. The lithofacies in the formation are composed of conglomerates, sandstones, airfall tuffaceous units, and paleosols. Conglomerates, sandstones, and paleosols are found primarily within fluvially-dominated sediments in the Nyamita Spring and Rondo Members, interpreted to represent little to no volcanic input. Tuffaceous units occur within the middle Ukowe Member and record a series of eruptions of the neighboring Kisingiri Volcano. Importantly, reassessment of the type section of the Wayando Formation, which previous researchers identified as the oldest formation on Rusinga Island, demonstrates that it is stratigraphically and lithologically equivalent with the upper member of the Kiahera Formation. Other deposits historically attributed to the Wayando Formation can likewise be correlated with sections of the Kiahera Formation. Hence, the Kiahera Formation represents the oldest sediments on Rusinga. Finally, our revised descriptions and analysis enabled us to identify the basal member of the Kiahera Formation in outcrops on neighboring Mfangano Island, but stratigraphically well above where previous researchers had positioned them. This provides a new basis for interpreting the relationship between Mfangano Island's important fossil assemblages and the better-known assemblages from Rusinga Island. In total, clarification and consolidation of Rusinga Island's Kiahera Formation significantly impact paleontological and paleoecological characterizations of this unit and of the entire Early Miocene geological sequence on the island, further informing interpretations of how Rusinga's fossil sites formed with respect to the evolving Kisingiri Volcano.

Internal architecture and structural evolution of a horst relay zone from the northern Gulf of Suez rift, Egypt: Implications for syn-rift sedimentation

A remarkable outcrop of an extensional NW-oriented horst block takes place between conjugate normal fault segments at the Akheider-El Ramliya fault block (ARFB), along the northwestern termination of the Gulf of Suez rift. Detailed field geological mapping is accomplished to identify the architecture, linkage style as well as evolution of the encountered normal fault system at the ARFB. The resultant structural model revealed several geometries of normal faults interaction that form soft- and hard-linkage relay zones affecting pre- and syn-rift rock units. Such relay zones are well developed between the boundary faults of the ARFB. Additionally, three E-W oriented fault belts are mapped at the northern, central and southern parts of the ARFB enclosing left-stepping en echelon normal faults, where several relay zones are formed between the overlapped fault segments. Structural analysis and evolution of the mapped area revealed that the overall architecture of the ARFB representing a broad horst relay zone between the conjugate divergent boundary normal faults. Also, two sub-basins have been recognized at the downthrows of the border faults comprising syn-rift Oligocene and Miocene sediments. The results show that these faults are rejuvenated by a continued NE-SW extension through Late Eocene, Oligocene and Miocene times. Additionally, the formed relay zones via growth and propagation of such faults have main controls on syn-sedimentation at the northern Gulf of Suez rift. The results of the present study offer constraints on horst relay zones including, internal structural architecture, geometries and interaction of boundary faults as well as role of inherited structures. Also, it provides an outcrop model for architecture and evolution of similar structural styles (e.g., the Gulf of Suez rift) as well as for subsurface mapping and exploration in extensional relay zones.