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The Río Alías Strait developed in the Early Pliocene as a narrow marine corridor at the connection of the microtidal Mediterranean Sea and the north‐eastern margin of the Almería‐Níjar Basin in the eastern Betic Cordillera (South‐East Spain). The orientation and topography of the strait were controlled by the transpressive Carboneras and Polopos/South Cabrera fault systems. Ten sedimentary facies occur in the up to 150 m thick mixed biogenic carbonate‐terrigenous succession distinguished on the basis of their lithology, components, grain size, stratal geometries and sedimentary structures, which were observed in seven sections at well‐exposed outcrops of four sectors. The sedimentary record of the Río Alías Strait reflects the morphological constraints, which conditioned its sedimentary dynamics and facies distribution. Even in this microtidal setting, tidal current amplification through narrow constrictions produced thick accumulations of large cross‐stratified bodies up to 15 m thick formed by the opposite migration of three‐dimensional simple and compound dunes. The Río Alías Strait reconstruction shows: (1) a very narrow constriction in the central sector from which “constriction‐related deltas” (CRDs) formed in the flood downstream (westward) and ebb (upstream) directions and (2) a relatively deep depression (>65 m water depth) separating the eastern and central‐east sectors, where tidal current energy was attenuated and dunes were not generated. The closure of the strait resulted from the tectonic uplift of the antecedent upland of Sierra Cabrera at the northern side, which promoted the southward progradation of deltaic systems over the strait. The Río Alías Strait represents the only clear record of a microtidal strait in the Betic Cordillera since the Miocene. The case study presented here improves existing models on the sedimentary dynamics of ancient tidal‐dominated straits by expanding the knowledge on their spatial environment variability. The Río Alias Strait was a ca 13 km long and 2 km wide, WNW to ESE oriented marine corridor that connected the microtidal open Mediterranean Sea and the north‐eastern margin of the Almería‐Níjar Basin in the eastern Betic Cordillera (South‐East Spain).

Geochemistry of the sediments deposited during the Archaean Era is potentially useful to decipher the Earth’s pristine seawater chemistry and the depositional environment. This study highlights the geochemical evolution, redox conditions, and the sedimentary environment based on carbonate sediments of the Tanwan group rocks, Bhilwara supergroup, Rajasthan, India, deposited during 2.9–2.5 Ga. The petrographic features and variation in major elements of these carbonate sediments indicate extensive dolomitization during this time. The elemental ratios such as Mg/Ca, Fe/Al, Fe/Sr, and Mn/Sr ratios and their mutual relationships suggest anoxic conditions during precipitation of the carbonates. The anoxia is well supported by the redox-sensitive element ratios such as Ni/Co, V/Cr, V/V + Ni, V/V + Cr, and Th/U, which show reducing/anoxic sedimentary environments during 2.9–2.5 Ga. The post-Archaean Australian Shale (PAAS) normalized anomalies, such as Ce anomaly, Gd anomaly, and Eu anomaly, showing average 1–1.48 values, indicate minor positive anomalies in the Archaean seawater. The rare earth elements and yttrium (REY) content in these sediments show no significant contamination, mixing, and alteration because Dissolution II (carbonate leachate) is characterized by Zr from 0.015 ppm to below detection limit (BDL), Th < 1 ppm, Sc < 1.5 ppm, and Al 2 O 3  < 1%. The Y/Ho ratio > 26 represents insignificant detrital input during the precipitation of the carbonates. The Y/Ho ratio versus Nd also supports this contention. The positive anomalies for Y (i.e. Y/Ho > 26), Gd anomaly (Gd/Gd*), and La anomaly (La/La*) confirmed the preservation of anoxic pristine marine seawater signatures in these carbonates of the Bhilwara supergroup that were mainly deposited during the Neoarchaean Era.

Mixed siliciclastic and carbonate sediments are common in the stratigraphic record, but fully homogenised mixes are not. Many occurrences of mixed sediment sequences are dominated by end‐members with stacking of ‘nearly pure’ lithfacies (e.g. cyclothems containing alternating sandstone, limestone and coal units). The Plio‐Pleistocene sediments within south‐west Florida provide insights into the occurrence of fully homogenised siliciclastic/carbonate deposits. In all defined environments from lagoon to supratidal to inner tidal to beach to offshore to coral reef, quartz sand coexists with carbonates. Perhaps the key feature that allowed full homogenisation of the sediments within all facies and subfacies was the relatively shallow water (<10 m), which facilitated mixing during low‐order eustatic sea‐level events and storms. However, four factors contributed to the full homogenisation of the sediment types without termination or inhibition of carbonate organism growth. These factors are (1) the shallow water allowing wave‐driven sediment transport (all environments within the wave orbital depth), (2) close proximity and perhaps irregular nature of the depositional environment boundaries, (3) low influx rate of quartz sand via longshore transport, and (4) the lack of significant terrigenous mud transport into the system. Mixing processes at the large‐scale included movement of sediments from one depositional environment to another during storms, mixing along facies boundaries, and in situ mixing within autochthonous and parautochthonous mollusc death assemblages. At the smaller scale, mixing occurred by bioturbation and diagenetic dissolution of carbonate skeletal grains during minor high sea‐level stands.

The morphology of some lithified wind-blown, carbonate dunes in The Bahamas preserves the signature of erosion from paleo-marine processes: wave-induced swash, scarping, and longshore transport. Digital elevation models were used to distinguish between two dune morphotypes—those disconnected versus connected to beach processes. Dune sinuosity and upwind slope were quantified and used to interpret which dunes remained beach-attached and subject to marine erosion and processes versus dunes that became disconnected from the shoreline via inland migration or shoreline regression. Disconnected dunes possess low slopes over stoss surfaces with sinuous planforms mimicking their crestlines. Beach-connected foredunes preserve steep, kilometers-long linear upwind faces, which are interpreted to be signatures of beach-dune morphodynamics. Foredune morphology serves as a proxy for shoreline position during past sea-level high-stands, while the basal elevations of their stoss dune toes provide an upper limit on the beach and adjacent sea level. A growing library of digital topography will allow for this tool to be used to interpret global paleo-shoreline positions through time and space.

Based on detailed analyses of cores covering the lagoon of Rasdhoo Atoll, Maldives, six carbonate facies, one soil, and one peat facies have been identified. The abundance of carbonate and rare opaque grains was quantified with a point counter. X-ray diffractometry was used to measure mineralogical composition of samples. The statistical delineation of facies using cluster analysis was based on point count, mineralogical, and textural analyses. In decreasing abundance, the six carbonate facies are classified as mollusk–coral–algal floatstone to rudstone (30 %), mollusk–coral–red algae rudstone (23 %), mollusk–coral–algal wackestone to floatstone (23 %), mollusk–coral wackestone (13 %), mollusk–coral mudstone to wackestone (9 %), and mollusk mudstone (2 %). The carbonate facies represent lagoonal background sedimentation, mostly consisting of fine sediments, and event sedimentation depositing transported coarse-grained reefal components. Fifty-seven carbonate samples and one peat sample were dated radiometrically, covering the Holocene transgression from 10 kyrs BP until today. Comparing the sediment accumulation data of the lagoon with two local sea-level curves, three systems tracts can be identified: (1) a lowstand systems tract characterized by karst and soil deposition >10 kyrs BP, (2) a transgressive systems tract with peat and carbonate separated by hiatus 10–6.5 kyrs BP, and (3) a highstand systems tract dominated by carbonate sedimentation 6.5–0 kyrs BP and further divided into three stages (6.5–3, 3–1, and 1–0 kyrs BP). During the Holocene transgression, sedimentation rates increased continuously to a maximum of 1.4 m/kyr during 3–1 kyrs BP. Modern (1–0 kyrs BP) mean sedimentation rates average 0.6 m/kyr. A simple calculation suggests that two processes (background sedimentation and sand apron progradation) will probably fill up the accommodation space of the lagoon during the Holocene highstand, but these processes will not suffice to fill the larger atoll lagoons of the archipelago.

Concealed deep beneath the oceans is a carbon conveyor belt, propelled by plate tectonics. Our understanding of its modern functioning is underpinned by direct observations, but its variability through time has been poorly quantified. Here we reconstruct oceanic plate carbon reservoirs and track the fate of subducted carbon using thermodynamic modelling. In the Mesozoic era, 250 to 66 million years ago, plate tectonic processes had a pivotal role in driving climate change. Triassic–Jurassic period cooling correlates with a reduction in solid Earth outgassing, whereas Cretaceous period greenhouse conditions can be linked to a doubling in outgassing, driven by high-speed plate tectonics. The associated ‘carbon subduction superflux’ into the subcontinental mantle may have sparked North American diamond formation. In the Cenozoic era, continental collisions slowed seafloor spreading, reducing tectonically driven outgassing, while deep-sea carbonate sediments emerged as the Earth’s largest carbon sink. Subduction and devolatilization of this reservoir beneath volcanic arcs led to a Cenozoic increase in carbon outgassing, surpassing mid-ocean ridges as the dominant source of carbon emissions 20 million years ago. An increase in solid Earth carbon emissions during Cenozoic cooling requires an increase in continental silicate weathering flux to draw down atmospheric carbon dioxide, challenging previous views and providing boundary conditions for future carbon cycle models. Oceanic plate carbon reservoirs are reconstructed and the fate of subducted carbon is tracked using thermodynamic modelling, challenging previous views and providing boundary conditions for future carbon cycle models.

The Middle Jurassic rocks of the Kaladongar Formation well exposed in the Kaladongar Hill range of the Patcham Island and Kuar Bet of the Northern Kachchh comprises of ∼450 m thick sequence of mixed siliciclasticcarbonate sediments intercalated with shales. These Mixed siliciclastic-carbonate sediments show wide variation in textural and mineralogical composition and represent genetically related six rock types: micritic sandstone, allochemic sandstone, sandy allochemic limestone, micrtic mudrock, sandy micrite and muddy micrite; which are highly bioturbated and show behaviourally diverse groups of trace fossils. Total 34 ichnogenera are identified, which includes, Arenicolites, Asterosoma, Beaconites, Bergaueria, Chondrites, Cochlichnus, Dactylophycus, Daedalus, Didymaulichnus, Diplocraterion, Gordia, Gyrochorte, Gyrolithes, Ichnocumulus, Laevicyclus, Lockeia, Margaritichnus, Monocraterion, Nereites, Ophiomorpha, Palaeophycus, Phoebichnus, Phycodes, Pilichnus, Planolites, Plug Shaped Form, Protovirgularia , Rhizocorallium, Scolicia, Skolithos, Taenidium, Teichichnus, Thalassinoides and Walcottia . These trace fossils are classified into six morphological groups namely, circular and elliptical structures; simple structures; branched structures; rosette structures; spreiten structures; and winding and meandering structures. These trace fossils are further group into eight assemblages which occurred together into mixed siliciclastic-carbonate sediments, include, Asterosoma assemblage, Gyrochorte assemblage, Rhizocorallium assemblage, Thalassinoides assemblage, Planolites-Palaeophycus assemblage, Phycodes assemblage, Ophiomorpha assemblage and Skolithos assemblage. The recurring pattern of these assemblages through the sequence displays the development of Skolithos and Cruziana ichnofacie s and at places the mixed Skolithos-Cruziana ichnofacies which suggest a low wave and current energy conditions with intervening period of high wave and current energy conditions and an intermediate period of stressful environments, respectively. Sedimentological and ichnological data suggest that the deposition of the mixed siliciclastic-carbonate sediments of the Kaladongar Formation took place in the foreshore to offshore environment under fluctuating wave and current energy condition.

In this study, we investigated the carbonate system in sediments and water columns from five stations in the Sea of Japan (East Sea) (JES) during the R/V Hakuho Maru KH-10-2 research cruise in the summer of 2010. The total alkalinity (TA) and pH were measured. Adopting a saturation degree of 91% and 80% for the lysocline depth and calcite compensation depth (CCD), respectively, we found that those depths corresponded to 1360 and 1980 m. A comparison of the calcite saturation depths, lysocline depths, and CCD depths obtained for 1999 and 2010 suggests that acidification of the interior of the JES occurred. Sediment cores were retrieved using a multi-corer. In the sediment cores, a sharp decrease in the pH by 0.3–0.4 pH units was observed in the subsurface horizons (0–10 cm) compared with the pH of the seawater from the bottom horizons. The TA in the porewaters was significantly higher than that in the overlying seawater. The anaerobic degradation of organic matter is probably the main cause for the increasing TA in the sediments. The porewaters were significantly undersaturated with calcite and aragonite, except in that from the shallowest station, where the sediments below 7.5 cm were saturated, and even supersaturated, with calcite and aragonite. A linear correlation between the dissolved inorganic carbon and the TA for sediments with a slope of 0.9993 was found, despite there being potentially different ways for the diagenesis of the organic matter to occur. The diagenesis of organic matter in the top sediments of the JES forms gradients of TA and CO2* concentrations on the interface of “bottom water–sediments”. Averaged fluxes of TA and dissolved inorganic carbon (DIC) from the sediments to the bottom waters estimated by means of Fickian diffusion were calculated as 44 and 89 mmol/(m2 year) for TA and DIC, respectively.

The Himalaya orogen evolved since the Eocene as the Tethyan‐, Greater‐, Lesser‐ and Sub‐Himalaya thrust sheets were uplifted and exhumed in sequence. Reconstructing the provenance of sediment in Himalayan River systems can inform on stages in the tectonic history of the orogen. Here, we analyze the oxygen, carbon and “clumped” isotope compositions of carbonate minerals from Himalayan bedrock, Ganga River sediments and Bengal Fan turbidite deposits. We demonstrate that river sediments consist of a mixture of Himalayan‐derived and authigenic calcite precipitated in the river system. The relative abundance and clumped isotope apparent temperatures of detrital calcite in turbidite deposits decreased between the Late Miocene and Pliocene, while chemical weathering intensity did not increase during this interval. Considered together, these results reflect the establishment of the Lesser Himalaya as an important carbonate sediment source for Himalayan rivers, driven by the uplift and exhumation of this thrust sheet. Plain Language Summary The Himalaya Range consists of a series of tectonic units that accreted during the last 50 million years as the Indian and Asian continents collided. Sediment provenance analyses are commonly used to reconstruct stages in tectonic evolution of mountain‐belts, but often capture local conditions and/or are altered by various sediment‐transport processes. We overcome these complexities by measuring oxygen, carbon and “clumped” isotope compositions of carbonate minerals in turbidite deposits cored from the Bengal Fan, to constrain sediment provenance at a Himalaya‐wide scale since the Early Miocene. Considered together with records describing weathering intensity, our data suggests that the Lesser Himalaya became the dominant source for detrital carbonate as this tectonic‐unit was uplifted and exhumed between the Late Miocene and Pliocene. Key Points Detrital calcite in Himalayan river systems derives from Himalayan‐bedrock and authigenic sources TΔ47 values of detrital calcite in the Bengal Fan drop between the Late Miocene and Pliocene while weathering intensity remains invariant On a Himalayan‐wide scale, the Lesser Himalaya became an important source of detrital carbonate between the Late Miocene and Pliocene

Carbonate sediments of nonglacial Cryogenian (659 to 649 Ma) and early Ediacaran (635 to 590 Ma) age exhibit large positive and negative δ13Ccarb excursions in a shallow-water marine platform in northern Namibia. The same excursions are recorded in fringing deep-sea fans and in carbonate platforms on other paleocontinents. However, coeval carbonates in the upper foreslope of the Namibian platform, and to a lesser extent in the outermost platform, have relatively uniform δ13Ccarb compositions compatible with dissolved inorganic carbon (DIC) in the modern ocean. We attribute the uniform values to fluid-buffered diagenesis that occurred where seawater invaded the sediment in response to geothermal porewater convection. This attribution, which is testable with paired Ca and Mg isotopes, implies that large δ13Ccarb excursions observed in Neoproterozoic platforms, while sedimentary in origin, do not reflect the composition of ancient open-ocean DIC.