Miocene Marine Research Articles

Controls on late Miocene marine vertebrate bonebed genesis in northern Chile

The Bahía Inglesa Formation in the Atacama Region of Chile (27°S) hosts one the world's best-preserved Cenozoic marine vertebrate death assemblages attributed to harmful algal bloom (HAB)-mediated mass mortalities. However, the lack of a well-dated depositional model prevents understanding of the timing of fossil accumulation and associated paleoenvironmental conditions. We present a revised chronostratigraphic framework for the Bahía Inglesa Formation at the Cerro Ballena and Mina Fosforita paleontological sites based on detailed field sedimentology, paleontology, and UPb zircon and phosphate geochronology. We integrate maximum depositional ages (MDAs) of intercalated volcanic ash and sandstone beds with published basinal chronostratigraphy to provide the first correlation between both localities. Detrital zircon UPb ages suggest that the highly articulated cetacean carcasses preserved at Cerro Ballena were rapidly deposited in a barrier-protected shoreface environment at ca. 6.1 Ma during periods of voluminous volcanic ash and diatom accumulation on the shelf. Evidence of disarticulated and taxonomically diverse vertebrate fossils within the Mina Fosforita bonebed suggest deposition in an unsheltered offshore transition to inner shelf environment with strong wave action and rapid flooding conditions between ca. 7.4 and 6.8 Ma. We propose that the fossil accumulations at Cerro Ballena and Mina Fosforita were deposited during distinct sedimentation events controlled by local bay paleogeography and rapidly fluctuating relative sea-level conditions. We compare our chronostratigraphic results with 2969 published magmatic ages from the Central Andes and propose a correlation between the mass deaths of marine mammals in northern Chile and intensifications in volcanism, ocean fertilization, phosphogenesis, and HAB blooms during the late Miocene.

Unraveling the palaeoecology of Paralia sulcata-dominated assemblages from Late Miocene marine deposits of Patagonia (South Atlantic, Argentina)

The study of fossil diatom assemblages constitutes an effective tool for inferring past water conditions. Several studies from around the world suggest the Miocene was a key period in the evolutionary history of diatoms. However, Miocene diatom assemblages from the southwestern Atlantic Ocean are nearly unknown. This study aims to provide a palaeoenvironmental interpretation of the analysed succession. Additionally, to highlight temporal and regional changes, the assemblage is compared with known modern and fossil assemblages from Patagonia and other regions of the world. Finally, we provide a detailed description of the extinct diatom taxa recognised throughout the sedimentary succession. A total of 36 diatom taxa were recognised in the 25 analysed samples. Despite the evidence from sedimentology and macro-palaeontology indicating temporal changes from inner shelf to estuarine environments, the diatom assemblages are dominated by the coastal marine Paralia sulcata sensu lato throughout the succession. An important freshwater input into the coastal system is interpreted from our results reflecting more humid climatic conditions when compared with modern diatom assemblages from the same location. In addition, four extinct species were recognised: Thalassiosira cf. yabei, Pseudopodosira westii, Rhaphoneis diamantella, and Lancineis rectilatus. The presence of R. diamantella and L. rectilatus in the analysed deposits would imply an expansion of their geological range.

Eocene contractional deformation in the NW corner of the Arabian plate and its relation to Arabia-Eurasia collision in SE Türkiye

ABSTRACT Field evidence indicates c. 40 Ma (Early-Middle Eocene) contractional deformation in the S Amanos Mountains. Following latest Cretaceous southward ophiolite emplacement, an intra-platform basin infilled with shallow to deeper marine, dominantly carbonate sediments. Localized thrusting, reverse faulting, and folding were followed by subaerial erosion and non-marine clastic deposition, sealed by an Early Miocene marine transgression. Eocene emergence elsewhere in SE Türkiye probably also resulted from regional crustal shortening. Alternative hypotheses for collision in SE Türkiye propose latest Cretaceous, Mid-Late Eocene, Early Miocene, or Late Miocene suturing of S Neotethys. Much geological evidence in SE Türkiye and NW Iran supports Mid-Late Eocene initial continent-continent collision. Plate reconstructions suggest S Neotethys survived in this region until the Mid-Late Eocene. Biogeographical evidence points to minor Eocene mammal migration across S Neotethys, followed by Early Miocene large-scale terrestrial migrations. Seawater isotopic data suggest a major decrease in inter-Indian Ocean-Mediterranean Sea current flow during the Early Miocene. Instrumental geophysics and both numerical and analogue modelling suggest that the northern Arabian platform underthrust Eurasia (>200 km in S central Iran). In SE Türkiye, Eocene initial ‘soft’ collision was followed by Early Miocene ‘hard collision’, with crustal thickening and exhumation continuing until the Late Miocene, followed by westward ‘tectonic escape’.

The first recognition of the enigmatic fossil shark genus Megalolamna (Lamniformes, Otodontidae) from the lower Miocene of Europe and M. serotinus (Probst, 1879) as the newly designated type species for the genus

Megalolamna is an elusive extinct shark genus (Lamniformes: Otodontidae) previously known from the upper Oligocene–Miocene of the USA, Colombia, Ecuador, Peru, and Japan. Here, we document the first occurrence of Megalolamna from Miocene marine deposits in Europe, specifically from Austria, France, Germany, and Italy. Although the taxon is regarded as a monospecific genus, this study reveals that the species name serotinus has the priority over any previously used names for the taxon and thus redescribes it as Megalolamna serotinus (Probst), comb. nov. This study is also significant because it demonstrates the existence of Megalolamna in the Mediterranean and Paratethys seas during the Miocene. Megalolamna inhabited the tropical–mid-latitudinal zones with spotty but wide geographic distribution.

Reconstructing the South American Miocene puzzle: An integrated analysis of the Paraná Formation (Argentina)

In recent decades, Miocene marine transgressions in South America have sparked ongoing debates concerning their boundaries, number of events, regional connectivity, and the existence of an epicontinental sea formed during the Andean orogeny. The bed-by-bed analysis of the Late Miocene Paraná Formation deposits in Entre Ríos Province (Argentina) allow defining six facies associations: (i) beach ridge, (ii) tidal inlet channel and washover fan, (iii) outer estuarine bioherms, (iv) central estuary, (v) tidal bar and sandflat, and (vi) tidal mudflat and creek deposits. Architectural and stacking pattern analyses reveal transgressive-regressive sequences typical of the coastal strip, encompassing shallow marine to estuarine sub-environments. The analysis identified diverse ecological guilds, including bivalve and gastropod assemblages in bioherms, and crustacean traces in tidal flats. Regressive units are characterized by wave-dominated shoreface deposits, while transgressive units comprise fine-grained estuarine deposits interbedded with bioclastic sandstones and storm deposits. The paleoenvironmental and paleoecological data indicate normal salinity marine environments with macroinvertebrates and estuarine components and suggesting tropical brackish conditions. Plant remains point to a range of vegetative communities, including mangroves, palm forests, grasslands, humid riparian forests, and dry upland forests, reflecting tropical to subtropical and humid to semiarid environments. This study concludes that the Paraná Formation correspond to a third-order transgressive system tract influenced by the Miocene Paranaense Sea. The basin-scale implications suggest that the distal Chaco-Paraná basin was affected by eustatic changes due to its low accommodation and topographic relief. The Chaco-Paraná foreland basin's evolution was driven by interactions between tectonic, climatic, and eustatic processes. The comprehensive analysis of sedimentary and fossil records provides a detailed paleogeographic reconstruction of the Miocene marine transgression in southern South America.

The effect of the Tethyan seaway closure on the Oligo−Miocene marine benthic diversity and distribution around Eurasia

The Cenozoic evolution of the Tethyan seaway significantly shaped marine and terrestrial biota around Eurasia. The Tethys Ocean connected the Atlantic and the Pacific during the early Cenozoic, allowing marine faunal exchange. However, during the early Miocene, the ‘ Gomphotherium Landbridge’ developed, restricting the marine connection between the proto-Mediterranean in the west and the provinces of the eastern Tethys Ocean. In contrast to the well-documented phenomena of terrestrial mammalian exchange through the land connection brought about by the closure, little is known about its impact on the marine fauna. To assess the overall effect of this separation on the distribution and diversity of marine organisms, we studied the Oligo−Miocene fossil record of marine benthos including Cnidaria, Echinodermata, Foraminifera and Mollusca. We compiled 15 894 reported occurrences from the early Oligocene to late Miocene comprising 1477 genera, 404 families and 85 orders from four faunal provinces and evaluated their palaeobiogeographic patterns. Our study demonstrates that the proportion of genera shared between the eastern and western provinces decreased after the early Miocene. The majority of the non-shared families developed during or after the early Miocene. High faunal diversity during the early Miocene and increasing endemicity among the eastern provinces are consistent with the development of a shallow seaway that supported speciation and reduced biotic exchange. The considerable variation in the magnitude and timing of the response across taxonomic groups reflects the combined effects of preservation bias and the differential responses of fauna. Our study supports an early Miocene initiation of the Tethyan seaway closure, followed by intermittent connectivity before the complete closure. This closure and its climatic consequences influenced the evolution of the Eurasian biota. Future studies should use a multidisciplinary approach combining the fossil record, genetic divergence and climate proxies to fully understand the effects of environmental changes and the seaway closure on marine benthos diversity dynamics.

Imaging buried anticlines in the Po Plain, northern Italy, based on HVSR frequency and amplitude analyses

The use of the HVSR (Horizontal-to-Vertical Spectral Ratio) method on single-station microtremor measurements is well documented in small alluvial plains for bedrock mapping. In large sedimentary basins, like the Po Plain, its application is still debated. To shed some light on this issue, we investigated two seismogenic structures buried below the Po Plain Quaternary deposits: the Mirandola and Casaglia anticlines. We acquired and analysed a dense distribution of HVSR data covering the two areas and mapped the frequency and amplitude values of the observed resonance peaks. The top of both anticlines is highlighted by high amplitude peaks picturing E-W elongated sectors with high-impedance contrast, where Quaternary deposits are reduced in thickness to about 60–130 m and directly overlay the Pliocene (Mirandola) and Miocene (Casaglia) marine units. In Mirandola, the high-amplitude peaks also correspond to higher resonance frequencies, while in Casaglia, the distribution of resonance frequencies is relatively uniform suggesting a flatter crestal region and the lateral continuity of the resonance surface. The combination of peak frequency and amplitude information on a dense grid of measurement points is thus confirmed to be useful for identifying and mapping buried geological structures such as structural highs. Further modelling is being carried out to estimate the depth of the surface responsible for the observed resonances, through calibration with borehole information.Graphical

Miocene marine successions in the northeast of Kahramanmaraş basin (SE Türkiye)

Miocene marine successions in the northeast of Kahramanmaraş basin (SE Türkiye)

Accumulation and Quantitative Assessment of Terrigenous Organic Matter in Upper Oligocene to Lower Miocene Marine Source Rocks of the Qiongdongnan Basin.

The intense collision between marine and terrestrial agents results in the dual-source (marine and terrigenous) characteristics of marine source rocks. Our research quantitatively assessed terrestrial organic matter and revealed the crucial role of terrestrial organic materials in the organic matter enrichment of lower Miocene to upper Oligocene marine source rocks in the Qiongdognnan Basin. The quantitative assessment was achieved using partial least-squares analysis with eight biomarker parameters associated with n-alkanes, isoprenoids, bicadinanes, taraxerane, tricyclic terpanes, and gammacerane. Differential unloading of terrestrial organic materials based on sedimentary facies of the delta-marginal sea system were observed through oleanane and bicadinane contents. It should be noted that the diagnostic ratio of oleanane was excluded from the quantitative analysis due to the dual influence from differential unloading and contact with seawater of the terrestrial organic materials. Calculation results show that the terrestrial organic matter was highest in the delta front at 70%, followed by prodelta at 59% and inner shallow marine at 57%. From the late Oligocene to the early Miocene, the proportion of terrestrial organic matter in marine source rocks continuously increased, with the highest average value observed in the second member of the Sanya Formation at 69% and the lowest occurring in the third member of the Lingshui Formation at 46%. Increasing terrestrial organic material inputs and preservation driven by the East Asian summer monsoon provided first-order control of the accumulation of organic carbon in the Qiongdongnan Basin during late Oligocene to early Miocene, rather than the bioproductivity of marine algae. The redox conditions of the water column determine the enrichment extent of organic matter.

Mammal-bearing Pleistocene deposits, Vranić, southwestern Pannonian Basin System

Vranić site is a sand quarry that is located on the southern foothills of Papuk Mountain. From bottom to top of the succession, three sedimentary units have been recognized as: Unit 1 containing massive sand with scattered gravel-sized clasts, marl cobbles and boulders, and abundant marine mammal and fish fossils; Unit 2 consisting of sand intercalated with silt, clay and gravel, which may be horizontally bedded; and Unit 3, which is an erosionally-based lenticular matrix to clast-supported structureless gravel. The basal part of Unit 1 shows numerous reworked skeletal remains of Miocene marine mammals. Cosmogenic radionuclides constrain the age of burial of Unit 1 to 895 ± 211 ka, while the source area of Unit 1 had a quick denudation.The massive sands deposited on the slopes of Papuk Mountain were vulnerable to erosion due to the absence of clay. Heavy rainfall or water from snow melting created flash floods that infiltrated the sands, thereby causing slope destabilization and deformation. This process led to slumps that were transformed into a sandy debris flow. This sediment was probably deposited during the interglacial marine isotope age (MIS) 21 period when the scarce vegetation and a warmer climate favored the melting of permafrost ice and consequently triggered slope movements during MIS 22. The reworked skeletal material sampled at the Vranić site comprises fossilized fish along with mammal bones and teeth. Thus, the Vranić site represents an important site for cetacean fossil remains and serves as an important data source for marine life in the Central Paratethys.

New geographic and stratigraphic occurrences of the enigmatic extinct lamniform shark, Megalolamna (Lamniformes: Otodontidae), from the eastern USA

ABSTRACT Megalolamna is an extinct lamniform shark genus that is known from Miocene marine deposits. In this study, three new specimens of Megalolamna collected from the eastern USA are newly described, and the diagnosis of the genus is emended to include a previously undocumented dental characteristic. The new specimens are represented by one tooth from the upper Oligocene Chandler Bridge Formation in South Carolina and two isolated teeth from the lower Miocene Calvert Formation in Maryland. The specimens from the Calvert Formation represent the northern-most occurrence of Megalolamna. Although the taxonomic identification of the specimen from the Chandler Bridge Formation is somewhat tentative, it is considered to represent geologically the oldest record of Megalolamna, suggesting the likelihood that the enigmatic genus has its origin in the Palaeogene no later than 23.5 Ma.

Dating the late Miocene marine sediments around the southern middle Durance valley (Provence, SE France): new evidences for a Tortonian age

The present study aims dating the topmost 50 m of a 115 m-long core retrieved from a valley located in the Cadarache Area (Upper Provence, South East France). Based on burial dating by in situ produced cosmogenic nuclides (10Be, 26Al and 21Ne), and paleomagnetic analyses, a Tortonian age was determined for the sedimentary succession exhibited in the core. In addition, thin sections, grain size analyses and quartz morphoscopy were used to characterize a shallow marine environment and to correlate the sediment core to the surrounding exposed sections. When comparing the studied sedimentary record to global sea level estimates, we establish that the local Tortonian transgression was not synchronous with the global scale sea level high-stand, but happened more likely later, during a global regressive trend. The timing of the Tortonian flooding in Upper Provence was therefore most probably driven by regional tectonic forcing. Finally, the Tortonian shallow marine sediments are topped by lacustrine tight carbonates. These carbonates protect the marine sediments from the following major erosional events resulting from the Messinian sea level drop and from interglacial-glacial fluctuations that both yielded to the present-day valley topography.

Depositional evolution in response to long-term marine transgression in the northern South China Sea

Research on the interaction between depositional evolution process and marine transgression is critical to understanding the transform mechanism of sedimentary systems and guiding hydrocarbon exploration. The early Miocene witnessed the most significant sea-level rise since the Cenomanian, which resulted in extensive marine-influenced deposits worldwide. However, the relationship between the process of depositional evolution and long-term marine transgressions (>1 Ma) remains poorly understood. The Pearl River Mouth Basin in the South China Sea offers a comprehensive deposition record of the early Miocene marine transgression. This study employs high-quality 3D seismic, well-logging, and core data to investigate the impact of the early Miocene transgression on the evolutionary dynamics of the sedimentary system. The regional sea level exhibited a prolonged rise of at least 100 m during the deposition period of the Miocene Zhujiang Formation, corresponding to the long-term marine transgressive in the South China Sea. Throughout this marine transgression, depositional systems developed in the study area include tidal flats, fan deltas, meandering river deltas, and shallow marine shelf sand bodies. The marine transgression process resulted in a significant change in depositional system types, which can be divided into seven units from Unit 1 at the bottom to Unit 7 at the top. The predominant deposition environment transitioned from tidal flats in Units 1-3 to meandering river deltas in Units 4-5, and finally to shallow marine shelf systems in Units 6-7. In the early stage (Units 1-3), the regional uplifts hindered sea level transgression and caused erosion, leading to the development of small-scale proximal fan deltas. In the middle stage (Units 4-5), these regional uplifts submerged, and meandering river deltas dominated with sediments derived from distant extrabasinal sources. During the late stage (Units 6-7), regional sea levels reached their peak, transforming the entire basin into a shallow marine shelf system. Additionally, this marine transgression significantly influenced the distribution of hydrocarbon resources. Notably, the shallow marine shelf sand bodies in Units 6-7 warrant substantial attention for future exploration. This study outlines the complicated transitional processes within depositional systems during long-term marine transgression events, holding relevance for the global evolution of marginal sea basins.

Sedimentology and sequence stratigraphy of shallow and deeper marine Miocene deposits: A case study from the St. Paul and Gebel El‐Zeit blocks, Gulf of Suez, Egypt

AbstractMarginal and deeper marine facies typify the Miocene exposures along the western margin of the Gulf of Suez rift basin. The stratigraphic setting of these facies is a subject of debate and confusing at best. Integrative sedimentological and sequence stratigraphic study of successions exposed in the St. Paul and El‐Zeit blocks provides insight into the lateral relationships between the two facies and their evolution, a topic that is not fully understood. The St. Paul block, located at the basin margin, has thin shallow marine facies, while the succession of El‐Zeit block, situated near the basin axis, consists of basal conglomerates, thin shallow marine carbonates, thick deeper marine shale and marginal evaporites. The facies architecture of these successions is interpreted as belonging to two different depositional models: a fan‐delta/lagoon system followed upwards by an alluvial fans/sabkha‐tidal flat system in the St. Paul hangingwall basin, and carbonate–siliciclastic–evaporite systems on the hangingwall dip‐slope ramp of El‐Zeit block. These models may help understanding the sedimentary history of other similar blocks in the rift basin. The studied facies show many striking features such as deposition during tilting of fault block, abrupt facies and thickness variations, coarse clastic shedding, erosion channel filling, onlapping of high standing blocks and evaporite accumulation. These features are the result of major tectonic events that triggered the formation of unconformities at different hierarchical levels during the late early to middle Miocene. These unconformities subdivide the Miocene facies into five depositional sequences separated by basin‐wide erosional boundaries. This division greatly improves the age control of marginal marine facies. It affords new insight into the evolution of marginal marine facies along the western margin of the basin in relation to deeper facies in the basin centre. Facies and thickness changes in these tectonically induced sequences indicate that basin floor irregularities, subsidence rates, climatic changes, variable sediment influx, sea‐level/brine‐level changes and basin isolation/connection to the Mediterranean Sea are also important factors responsible for their evolution.

Cetacean and hipparion fossils from the upper Miocene near General Marinovo Village, NW Bulgaria

The fossils of cetaceans are common in the Miocene marine deposits of North Bulgaria and along the Black Sea coast, however, they had received little attention until now. We report on abundant whale fossil material from the area near General Marinovo Village, NW Bulgaria. The finding of a hipparion tooth in the same area as the rest of the material implies a late Miocene age for the fossils. Taphonomical, XRD, and palaeohistological analyses reveal details about the pre-burial history and palaeobiology of part of the studied cetacean fossils.

Miocene Stromboid Gastropods (Superfamily Stromboidea Rafinesque, 1815) from the Dwarka Basin, Western India and their Paleobiogeographic Implications

Abstract Stromboid gastropods (Superfamily Stromboidea) are one of the most diverse groups of gastropods present in the Neogene marine successions of western India. In the present endeavor, we report eight stromboid species, of which four are described as new, from the early-middle Miocene marine successions of the Dwarka Basin, western India. The species are Conomurex indica n. sp., Persististrombus deperditus, Persististrombus sp., Dilatilabrum mahalonobisi n. sp., Tibia indica, Terebellum obtusum, Hemithersitea kanerus n. sp. and Hemithersitea nadharus n. sp. Paleobiogeographic distribution of most of the stromboid genera reported here reveals a unidirectional migration from the Tethys Region towards the Indo-Pacific Region during the Paleogene and Neogene. Conomurex originated in the western India and further radiated to the eastern Indian-Western Pacific localities with the onset of the Neogene. Persististrombus and Tibia show widespread distribution in the Mediterranean and gradually radiated towards the eastern Africa-western India localities during the Paleogene. However, from the middle Miocene onwards, these two genera further migrated towards the eastern Indian-Western Pacific localities and became more diverse. The remaining two genera, i.e., Dilatilabrum and Hemithersitea originated in the Mediterranean and later migrated to take refuge in western India during the late Paleogene, and ultimately succumbed to extinction during the middle Miocene.

A new broad-snouted fossil carettochelyid turtle from a previously unknown Caenozoic deposit in Sarawak, Malaysia

Fossils of pan-carettochelyid turtles are known from most continents of the world, except Antarctica. The fossils that have been described indicate a group of estuarine turtles that have little modified their body form since the Cretaceous. The only species for which ecological data exist is the extant Carettochelys insculpta, found in estuarine or fresh waters in Australia and New Guinea. Here we report the discovery of an incomplete skull of a previously unknown carettochelyid Carettochelys niahensis sp. nov. from an undated fossil deposit within or beneath a Miocene marine limestone formation in Niah Great Cave, Sarawak, Malaysia. The skull exhibits many anatomical features characteristic of this turtle group but differs from previously known taxa in that it has a broad, nasal orifice that is proportionately wider than in other carettochelyids and relatively shallow but wider temporal arches. Some aspects of the palaeoecology of this turtle are inferred.Arthur White [arfawhite@gmail.com] Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia;Michael Archer [m.archer@unsw.edu.au] Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia;Suzanne J. Hand [s.hand@unsw.edu.au] Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia;Henk Godthelp [hjgodthelp@gmail.com];Anna K. Gillespie [a.gillespie@unsw.edu.au] Earth and Sustainability Science Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia.

Bridging two oceans: small toothed cetaceans (Odontoceti) from the Late Miocene Chagres Formation, eastern Caribbean (Colon, Panama).

Fossil cetaceans are often found in Miocene marine outcrops across the globe. However, because this record is not homogeneous, the dissimilar increase in occurrences, along with the sampling bias has created regions with extensive records and others with great scarcity. Among these, the Caribbean has remained enigmatic due to the lack of well-preserved cetacean fossils. Here, we report new Caribbean fossil cetaceans from the Upper Miocene Chagres Formation exposed along Piña beach, Eastern Panama, including a scaphokogiine kogiid, an Acrophyseter-like physeteroid and the phocoenid Piscolithax. Along with previous records of the iniid Isthminia panamensis and the kogiine Nanokogia isthmia, the Chagres cetacean fauna shows some similarities with other Late Miocene cetacean communities such as the Californias in the North Pacific, although their closest affinities lie with the eastern South Pacific Pisco Formation, Peru. Such findings indicate that though deep and intermediate Caribbean-Pacific water interchange was reduced by the Middle Miocene due to the shallowing of the Central American Seaway, shallow waters marine connection that persisted until the Pliocene might have facilitated the dispersal of coastal species across both sides of the Isthmus.

Transient response to changes in uplift rates in the northern Atlas-Meseta system (Morocco)

Transient topography represents an opportunity for extracting information on the combined effect of tectonics, mantle-driven processes, lithology and climate across different temporal and spatial scales. The geomorphic signature of transient conditions can be used to unravel landscape evolution, especially in areas devoid of stratigraphic constraints. The topography of the Western Moroccan Meseta domain (WMM) is characterized by elevated non-lithological knickpoints, that delimit an uplifted relict landscape, implying a transient response to a change in uplift rate that occurred during the Cenozoic. Here, we determine denudation rates of selected watersheds and bedrock outcrops from cosmogenic nuclides and perform stream profile, regional and basin-scale geomorphic analysis. Denudation rates of the relict and the rejuvenated landscape range from 15 to 20 m/Myr and from 30 to 40 m/Myr, respectively. Rock uplift rates from river-profile inversions are 10–25 m/Myr from 45 to 22 Ma and 30–55 m/Myr from 22 to 10 Ma. Despite the different time scales, the inverted rates are consistent with 10Be averaged denudation rates (15–20 and 30–40 m/Myr) and river incision values from Pleistocene lava flows (<10 and ~50 m/Myr) for the rejuvenated and relict regions of the WMM. These results agree with geological data and indicate that the observed ~400 m of surface uplift in the WMM started to develop possibly during the early Miocene (first phase). Given the wavelength of the topographic swell forming the topography of the WMM, uplift is here interpreted to reflect localized crustal thickening through magma addition or lithospheric thinning through mantle delamination. More recently, the occurrence of late Miocene marine sediments at ~1200 m of elevation indicates that the adjacent Folded Middle Atlas during the last 5–7 Ma experienced surface uplift at ~170–220 m/Myr. Considering the cumulative amount of surface uplift that varies eastward from 400 to 800 and 1200 m from the Meseta to the Tabular and the Folded Middle Atlas, as well as the spatio-temporal pattern of alkaline volcanism (middle Miocene and Pliocene to Present), we suggest that the most recent episode (second phase) of surface uplift was induced by a larger-scale process that most likely included upwelling of asthenospheric mantle and to a lesser extent crustal shortening in the Folded Middle Atlas.

Geochemistry and Sr, S, and O stable isotopes of Miocene Abu Dhabi evaporites, United Arab Emirates

This study investigates for the first time the subsurface Miocene evaporite facies (Gachsaran Formation) in Abu Dhabi, United Arab Emirates. Forty-five evaporite rock samples were selected for petrographic, mineralogical, and geochemical investigations and stable isotope analyses to decipher their origin and constrain their age. Secondary gypsum with anhydrite relics dominates the investigated evaporitic rocks, with minor amounts of clays, dolomicrite, Fe/Ti oxides, and celestite. These samples are characterized by their excellent purity and low variability in geochemical composition. The distribution of trace element concentrations is significantly influenced by continental detrital intake. The main focus of the study is to determine the strontium, sulfur, and oxygen stable isotope compositions. The measured 87Sr/86Sr values of 0.708411–0.708739 are consistent with Miocene marine sulfates and indicate ∼21.12–15.91 Ma (Late Aquitanian-Burdigalian). The δ34S and δ18O values are 17.10‰–21.59‰ and 11.89‰–19.16‰, respectively. These values are comparable to those of Tertiary marine evaporites. The relatively low values of δ34S suggest that non-marine water possesses little influence on S distribution. The geochemical composition and Sr, S, and O isotope distributions of the Abu Dhabi gypsum facies from the Gachsaran Formation reveals that their source brines were marine (coastal saline/sabkha) with subordinate continental input.