SE Coast Research Articles

Using detrital zircon U[sbnd]Pb geochronology to track the provenance of Miocene sediments in the northern Pearl River Mouth Basin, South China Sea

The Late Cenozoic provenance study of the Pearl River Mouth Basin (PRMB) holds significant implications for understanding the tectonic-climatic interactions, drainage evolution, and oceanic circulation in the northern South China Sea. However, the Miocene sediment routing system remains poorly understood due to the paucity of zircon geochronological data and the effects of sediment mixing and homogenization. This study reconstructs the ancient source-to-sink system by means of detrital zircon analyses from the northern PRMB and zircon age-based mixture modeling of well-defined provenance end-members. The results disclose varied and complex source-to-sink scenarios since the Early Miocene, involving three primary contributors: the Pearl River drainage system, coastal SE China, and Taiwan Island. In combination with seismic facies and climatic proxies, the intensive addition of Precambrian zircons suggests that, during the Middle and Late Miocene, progressive drainage expansion within the Yangtze Block likely contributed to the increasing sediment supply from the western Pearl River drainage system. Furthermore, the provenance shift in the northern PRMB, as indicated by the Mesozoic ages, may reflect a response to the activation of oceanic circulation and intensification of the East Asian monsoon. Additionally, though less significant, contributions from the Hainan and Luzon Island are also observed, indicating the input of the branch of the Kuroshio Current during the Late Miocene.

Fishery, Biology, and Dynamics of Parapenaeopsis maxillipedo (Alcock, 1905) off the SE Coast of Tamil Nadu (India)

Fishery, Biology, and Dynamics of Parapenaeopsis maxillipedo (Alcock, 1905) off the SE Coast of Tamil Nadu (India)

Paleoenvironmental significance of Holocene foraminiferal taphocoenoses in Guayaguayare Bay, Trinidad, West Indies: A coral reef near the Orinoco Delta

A small suite of seafloor sediment samples (water depth less than 20 m) was collected in 2005 from the sheltered, logarithmic-spiral Guayaguayare Bay along the SE coast of Trinidad, West Indies. The easternmost shielded part of the bay was then occupied by a meadow of the seagrass Halodule wrightii, the closest seagrass bed to the Boca Grande, the main distributary of the Orinoco Delta. Four foraminiferal taphofacies were distinguished, ascribable to a relict coral reef system: (1) A shallow-water (approx. 5 m) taphofacies dominated by Pararotalia sarmientoi. (2) A back-reef taphofacies (approx. 5 m) with abundant Discorbis rosea, apparently associated with the H. wrightii. (3) A fore-reef taphofacies (water depth approx. 20 m) co-dominated by Amphistegina gibbosa and Quinqueloculina bicostata. (4) A reef-flat (approx. 5 m) taphofacies dominated by Q. bicostata. A ternary plot of specimen wall types (agglutinated, porcellaneous, calcareous hyaline) clearly distinguished Taphofacies 1 from Taphofacies 4, porcellaneous specimens being rare in the former. A similar plot of staining + test abrasion for A. gibbosa indicated that those on Taphofacies 3, assumed to be in situ, were more heavily stained than those elsewhere and were larger. Tiny but pristine, presumably allochthonous A. gibbosa were recovered from Taphofacies 1. Two formae of Asterigerina carinata, both widely illustrated in the literature, are distinguished for the first time and named A. carinata forma conica and A. carinata forma discoida. The bay is currently filled with turbid water. The coral reef system, postdating the early Holocene transgression, would have required clear water, perhaps when the Orinoco Delta had not prograded sufficiently to impact the bay greatly. The known best depth range for the growth of amphisteginids, which are symbiotic with algae, coupled with known Holocene sea level curves for the SE Caribbean, suggest an age of approx. 4000 YBP. Sedimentation in the protected bay has since the development of the reef been limited.

The Central Indian Tectonic Zone: A Rodinia supercontinent-forming collisional zone and analogy with the Grenville and Sveconorwegian orogens

Abstract In the paleogeographic reconstructions of the Rodinia supercontinent, the circum-global 1.1–0.9 Ga collisional belt is speculated to skirt the SE coast of India, incorporating the Rodinian-age Eastern Ghats Province. But the Eastern Ghats Province may not have welded with the Indian landmass until 550–500 Ma. Instead, the ~1500-km-long, E-striking Central Indian Tectonic Zone provides an alternate option for linking the 1.1–0.9 Ga circum-global collisional belt through India. The highly tectonized Central Indian Tectonic Zone formed due to the early Neoproterozoic collision of the North India and the South India blocks. Based on a summary of the recent findings in the different crustal domains within the Central Indian Tectonic Zone, we demonstrate that the 1.03–0.93 Ga collision involved thrusting that resulted in the emplacement of low-grade metamorphosed allochthonous units above the high-grade basement rocks; the development of crustal-scale, steeply dipping, orogen-parallel transpressional shear zones; syn-collisional felsic magmatism; and the degeneration of orogenesis by extensional exhumation. The features are analogous to those reported in the broadly coeval Grenville and Sveconorwegian orogens. We suggest that the 1.1–0.9 Ga circum-global collisional belt in Rodinia swings westward from the Australo-Antarctic landmass and passes centrally through the Greater India landmass, which for the most part welded at 1.0–0.9 Ga. It follows that the paleogeographic positions of India obtained from paleomagnetic data older than 1.1–0.9 Ga are likely to correspond to the positions of the North and South India blocks, respectively, and not to the Greater India landmass in its entirety.

The role of magma chamber depth on porphyry mineralization: Insights from the late Jurassic Gutian porphyry Cu-Mo deposit in coastal SE China

Porphyry deposits (less than5 km) contain the world’s major Cu and Mo reserves, as well as a significant amount of Au, and are genetically linked to porphyries originated from deep (8–15 km depth) upper crust magma chambers. The role of magma chamber depth in the porphyry ore formation remains an unresolved key issue. Here, we analyzed various rock-forming minerals to constrain the magmatic physicochemical conditions of three coeval and cogenetic intrusions which are difference in fertility for porphyry Cu-Mo formation from the Gutian porphyry Cu-Mo deposit. Our results show that the barren granodiorite, barren granodiorite porphyry (P1), and fertile granodiorite porphyry (P2) have similar crystallization temperatures, oxygen fugacities, and water and sulfur contents, and are water saturated. However, only the P2 intrusion that sourced from a deep magma chamber (8.6–11.4 km) generated porphyry Cu-Mo mineralization. It indicates that magma chamber depth exerted a major control on porphyry Cu-Mo formation. Moreover, the emplacement depth of the fertile P2 intrusion is similar to that of the barren granodiorite and P1 intrusion (i.e., 3.7 ± 0.5 km), indicating significant decompression during the emplacement of P2 magma. This dramatic pressure drop is recorded by the plagioclase XAn (mole fraction of anorthite [An]) value, triggering fluid exsolution and rapid mineral crystallization, as supported by the micro-/crypto-crystalline groundmass of the P2 intrusion. Our results highlight that deep magma chambers can accumulate a larger volume of magma (and thus metals) to provide sufficient ore-forming materials and can promote fluid exsolution that extracts metals from the magma.

The Discovery and Geochemical Characteristics of an Eocene Peridotite Xenolith-Bearing Mafic Volcanic Neck in Coastal Southeast China

The mantle beneath coastal SE China evolved from enriched to depleted between the Cretaceous and the Neogene, although the precise timing of this change remains unclear. Here, we focus on a newly discovered Eocene mafic volcanic neck that contains peridotite xenoliths in the Fuding area of Fujian Province, and present new whole-rock Ar–Ar data which indicate that flood basalts formed during the Eocene (ages of 38.5 ± 1.2 and 42.3 ± 2 Ma). The basalt, gabbro, and diabase in the Fuding area are geochemically similar to ocean island basalt (OIB) and have SrI values that range from 0.703794 to 0.703911 (average of 0.703865) and εNd(t) values from 3.05 to 4.56 (average of 3.90). These samples yield two-stage Nd model (TDM2) ages of 0.61–0.73 Ga (average of 0.67 Ga). These data indicate that all of these units formed from magmas derived from an OIB-type mantle source, with both the gabbro and diabase units recording minor amounts of crustal contamination. Its OIB type geochemical characteristics may be inherited from crustal materials with similar characteristics. Peridotite xenoliths within the Fuding basalts provide evidence of the nature of the Eocene mantle in this area, especially the post late-Mesozoic evolution of the mantle beneath coastal SE China. The mantle beneath coastal SE China evolved from enriched in the Cretaceous to depleted in the Neogene, with this change occurring during the Eocene.

Volcanological evolution and paleoenvironment of the Late Cretaceous Changyu volcano in the coastal SE China

火山是唯一能够直接反映地球深部存在岩浆的地球动力学现象，对于地球气候演变和宜居性具有重要影响。相比年轻火山，古老火山因其活动过程完整、且可能剥蚀出露多阶段火山喷发产物及岩浆通道、岩浆房等，从而为揭示火山岩浆系统演化和火山活动过程提供重要的研究窗口。本文选择中国东南沿海晚白垩世长屿破火山为研究对象，对其开展火山地质、岩石学、年代学及地球化学研究，以期揭示其火山活动历史及其对中国东南沿海白垩纪古环境的启示意义。长屿火山出露面积约100km²，呈近圆形分布，具有较厚的火山地层厚度(总厚度约570m)，类似于破火山内的火山堆积特点。由早至晚三个喷发阶段形成的流纹质角砾凝灰岩都显示了典型的火山碎屑流相的特点，发育典型的条纹斑状结构，但表现出不同的晶屑、玻屑及岩屑含量以及熔结程度等岩相学特征，反映火山喷发从初始到高峰、再到减弱的过程，最后岩浆沿火山通道侵出形成流纹斑岩穹隆，标志着火山活动的结束。长屿火山的火山碎屑流式喷发伴随着快速的岩浆房塌陷，以及缺少普林尼式空落堆积，反映了火山活动发生在伸展的构造背景。系统的LA-ICP-MS锆石U-Pb年代学研究获得了不同阶段火山岩一致的形成年龄(97~96Ma)，暗示它们具有较短的形成时限，是由同期火山岩浆活动先后喷发形成的。长屿火山岩高的SiO₂含量(67%~76%)以及分异的锆石微量元素地球化学特征，表明喷发岩浆来自晶粥提取的熔体，并有晶粥来源晶体的混入。此外，我们在长屿火山岩中发现了南洋杉型丝炭化木(贝壳杉型木属)，暗示晚白垩世中国东南沿海地区可能为温暖湿润的亚热带山地气候环境，表明中国东南沿海白垩纪大规模火山活动，在古武夷山脉以东地区形成了地形高耸的海岸山脉。

Litho-climatic characteristics and its control over mangrove soil geochemistry: A macro-scale approach

Brazil hosts an extensive coastal area, marked by a great diversity of geoenvironments. The present study evaluated the role of geoclimatic factors in the geochemistry of mangrove soils by using wet extractions and several physical and chemical parameters. Soil samples were collected in 11 mangrove forests from NE (n = 94) and SE Brazil (n = 230). Our results show an important effect of the surrounding geology and climate on the geochemistry of the mangrove soils. NE mangroves are dominated by suboxic soils (mean: Eh of +150 ± 174 mV and pH 7.1 ± 0.5, respectively) while anoxic conditions prevail in the SE mangrove soils (mean: Eh −46 ± 251 mV and pH 6.5 ± 0.5). In the NE region, a period of several months without rainfall and high temperatures leads to soil suboxic conditions. Conversely, at the SE coast, the surrounding mountain range contributes to well-distributed rain favoring anoxic conditions. The contrasting geochemical environment caused differences in the geochemistry of elements such as C, Fe, and S. Significantly higher Fe (193 ± 24 μmol g−1) and organic carbon contents (6.9 ± 7.1%) were recorded in the SE coast. The higher organic carbon contents are possibly related to Fe organo-mineral associations. These differences are ultimately associated with the contrasting geological surroundings (crystalline massifs at the SE and the iron poor sedimentary formations at the NE). The higher contents of reactive Fe and organic carbon also triggered more intense pyritization in the SE mangroves (pyritic Fe: 93 ± 63 μmol g−1). Our results demonstrate that climate and geological surroundings create identifiable patterns at a regional level and, thus, studies should take these factors into account on future global modelling approaches.

Non-Indigenous Species on Artificial Coastal Environments: Experimental Comparison between Aquaculture Farms and Recreational Marinas

Globally, there is growing concern regarding the effects of the increasing anthropogenic pressures in marine communities. Artificial structures such as marinas and aquaculture facilities serve as invasion hotspots; hence, monitoring fouling communities on these structures can be valuable for detecting new invasions. In the current study, 24 settlement PVC plates were deployed for three months to compare the recruitment ability of these two artificial environments along the south coast of the offshore island of Madeira (NE Atlantic). The results showed higher variations in the species richness between regions (SW vs. SE) than between artificial habitats (sea-cages vs. marinas), although the community composition differed. Cnidaria and Bryozoa were the most representative groups in the aquaculture systems, while Bryozoa and Chordata were in the marinas. A sum of 18 NIS was recorded for the study, accounting for between 21.88% and 54.84% of the total number of species in the aquaculture facilities and marinas, respectively. The higher NIS percentage from the marinas was even more explicit in the SE coast, where Cradoscrupocellaria bertholletii, Parasmittina alba, and Botrylloides niger distinctly dominated fouling populations. The results suggest that at least some particular NIS previously reported in the studied marinas successfully colonized sea-cages. Future assessments need to address the potential role of aquaculture facilities as drivers for the secondary spread of NIS. Additionally, two new records are considered for Madeira: Eudendrium capillare and Ericthonius punctatus.

Early Cretaceous subduction in NW Kalimantan: Geochronological and geochemical constraints from the Raya and Mensibau igneous rocks

The Kuching zone in NW Kalimantan and Malaysia Sarawak might be the southerly-extending segment of the paleo-Pacific subduction that is developed along the Coastal South China and SE Vietnam, and separated the Sundaland “old-land” from the Cenozoic Sibu zone. However, establishing this link is hindered by the lack of data on the Mesozoic orogenic history in NW Kalimantan. This paper presents zircon U-Pb geochronological and Hf-O isotopic data as well as whole-rock elemental and Sr-Nd-Pb isotopic results for the Raya Volcanics and their equivalents, as well as the Mensibau batholith in NW Kalimantan. The Raya Volcanics and Mensibau granitoids formed at 130–144 Ma, synchronous with the Menunuk Volcanics, but significantly older than the Pakong-Serabang mafic rocks and Serian Volcanics (~77–98 Ma) in the Sarawak Kuching zone. The Raya Volcanics and their equivalents belong compositionally to tholeiitic to low-K calc-alkaline series, and exhibit “spiky” PM-normalized patterns with Nb/La = 0.16–0.32, (87Sr/86Sr)i = 0.70187–0.70671 and εNd(t) = +0.9 to +3.6. Their (206Pb/204Pb)i, (208Pb/204Pb)i and (207Pb/204Pb)i range from 18.49 to 18.83, 38.39 to 39.19 and 15.57 to 15.70, and zircon εHf(t)-δ18O values from +4.1 to +16.1, and 5.21‰ to 6.05‰, respectively. They are derived from mantle wedge modified by recycled sediments. The Mensibau batholith is dominated by I-type granodiorite and granite. They share similar elemental ratios and Sr-Nd-Pb-Hf-O isotopic compositions with the Raya Volcanics, and originated from wedge-derived juvenile mafic crust. The temporal-spatial and geochemical accordance for the Raya Volcanics and Mensibau batholith document the extensive development of the early Cretaceous igneous rocks in NW Kalimantan. The Kuching zone is a northeasterly-propagated Cretaceous accretionary system that developed in response to the subduction of the paleo-Pacific plate.

Analysis of the Makran Coastline of Iran’s Vulnerability to Global Sea-Level Rise

The SE coast of Iran is of great economic and environmental importance. Global climate change affects this coastline through sea level rise (SLR), compounded by a decrease in sediment budgets in coastal areas. This study developed a Coastal Vulnerability Index (CVI) for the SE coast of Iran using satellite, instrumental and field data. Eight risk variables were defined: coastal slope, regional coastal elevation, mean tidal range, mean significant wave height, rate of relative sea-level change, rate of shoreline change, environmental sensitivity and socio-economic sensitivity. The coast was divided into 27 segments based on geomorphic, environmental and socioeconomic traits. Coastal segments were categorized based on their vulnerability to each risk factor using a CVI. The resulting maps highlighted the vulnerability of each coastal segment to SLR. Approximately 50% of the coast is comprised of mostly rocky shores, which are less vulnerable to SLR. Approximately 33% of the coastal length, including sandy beaches, tidal flats and mangrove forests, were determined to be highly vulnerable to SLR. Approximately 12% of the coastline was determined to be moderately vulnerable. Population centers and infrastructure were ranked as highly-to-moderately vulnerable to SLR. This study highlighted the high vulnerability of low-lying areas, such as lagoons and mangroves, in the western part of the Iranian coast of Makran. Proper coastal management and mitigation plans are essential in the future to protect coastal societies and environments.

Effect of a tropical cyclone on the distribution of heavy metals in the marine sediments off Kameswaram, Southeast coast of India

Cyclones and heavy rainfalls are the main reasons for incessant environmental aggravation in the coastal regions and the distribution of pollutants from the contaminated terrestrial areas to the offshore regions. Twenty-five surface sediment samples were collected off Kameswaram, SE coast of India, and assessed for their geochemical and sedimentological characteristics post Cyclone Gaja. Sediment texture and various geochemical analyses were carried out to assess the metal distribution in the study area. Environmental impacts caused by heavy metal contamination in the marine sediments were assessed using different sediment pollution indices and it was found that metals such as Cu, Zn, Ni, and Co were moderately contaminated. Fe and Cr were uncontaminated to moderately contaminated, and Mn fall under the uncontaminated category. Multivariate statistical analyses revealed that the enrichment of organic-rich mud helps in entrapping the heavy metals, thus polluting the environment. Moreover, these metals were mainly derived from anthropogenic activities.

Coastal Ecosystem Vulnerability and Sea Level Rise (SLR) in South Florida: A Mangrove Transition Projection

We used static, elevation and land cover data to estimate sea level rise impacts (SLR) to urban, developed lands and coastal wetland systems in Everglades National Park and the East and West coastal regions in South Florida. Maps and data tables estimating potential state change to open water were compiled through overlay analysis of elevation, land cover, and SLR masks with future land cover projected using a land cover transition threshold model. Analysis was based on a 2–5-km-wide longitudinal band along the SW and SE coasts of Florida where sea-level rise has no surface impediments to inundation and will likely cause coastline transgression and wetland migration. Analysis used three different projections; 0.27 m (0.9 ft), 0.76 m (2.5 ft) and 1.13 m (3.7 ft) greater than current sea level by 2070 estimated by NOAA and IPCC. Under a 0.27 m SLR projection 51% of the coastal land cover may be impacted. Under 0.76 and 1.13 m projected SLR, coastal land cover areas were impacted by 56.5 and 59.1%, respectively. Migration of coastal wetlands from their current location into more inland areas in response to increased water depths and as a function of empirically derived marsh and mangrove accretion rates were also evaluated. With a SLR of 0.76 m by 2070, without accretion, 1,160 sq km of wetland became open estuarine water. However, with accretion values of 0.211 m (4.1 mm yr–1) and 0.55 m (11 mm yr–1) by 2070, there was a transition of wetland cover to open estuarine water of only 349 and 41 sq km, respectively. Under a low SLR of 0.27 m by 2070 scenario with accretion, the coastal mangroves were able to migrate inland while maintaining the current coastline. It was only under the more extreme scenario of 1.13 m SLR by 2070 that accretion was not able to compensate for inundation and there was a loss of wetland coastline everywhere.

How to turn off a lava lake? A petrological investigation of the 2018 intra-caldera and submarine eruptions of Ambrym volcano

In December 2018, an unusually large intra- and extra-caldera eruption took place at Ambrym volcano (Vanuatu). The eruption drained the volcano’s five active lava lakes and terminated, at least momentarily, the surface activity that had been ongoing for decades to hundreds of years, sustaining the largest recorded persistent degassing on the planet. Here, we investigate the mechanisms and dynamics of this major eruption. We use major elements and volatiles in olivine and clinopyroxene-hosted melt inclusions, embayments, crystals and matrix glasses together with clinopyroxene geobarometry as well as olivine and clinopyroxene geothermometry and diffusion modelling in crystals and embayments to reconstruct the chronology and timing of the subsurface processes that accompanied the eruption. We find that the eruption began with the meeting, mingling and limited chemical mixing of mostly two magma bodies occupying similar vertical but different horizontal locations in the crust, one corresponding to the main plumbing system at Ambrym that fed the lava lakes and the other corresponding to an older, previously cutoff and more chemically evolved branch of the plumbing system. Within the primitive magma, two texturally distinct components—one microlite rich and one microlite poor—can further be identified. The 2018 eruption hence provides a detailed image of Ambrym’s complex plumbing system. Our diffusion timescales and geobarometric estimates coincide closely with geophysical observations. They point to a reconnection of the evolved magmatic branch with the main system occurring less than 10 h prior to the intra-caldera eruption and a period of 2 days for the subsequent > 30-km lateral magma transport along a deeper dike prior to submarine eruption just off the SE coast of the island with the more primitive magma reaching first followed by mingled magma containing both compositions. Magma ascent rates are estimated at 95 ± 24 m/s in the last ~ 2.5 km of ascent during the intra-caldera eruption and at 80 ± 6 m/s in the last ~ 4 km of ascent during the submarine eruption. Comparison with other lava lake draining eruptions reveals striking similarities both in terms of precursory activity, with lake level rising prior to the eruption in all cases, and in terms of plumbing system organization with the presence of peripheral magma pockets, isolated from the main magmatic system but that can be mobilized and erupted when met by dikes propagating laterally from the main system.

Provenance of Neogene sandstones in western Taiwan traced with garnet geochemistry and zircon geochronology

AbstractIn this study, we use provenance analysis to shed light on the Neogene evolution of river drainage and sediment dispersal in eastern Asia as a consequence of the Himalayan orogeny and topographic rise of the Tibetan Plateau. As an attempt to envisage how sediment‐routing systems operated in the past, and to identify the ultimate source of siliciclastic detritus originally generated in mainland China and now incorporated in, and recycled from, the western Taiwan accretionary prism, we have used Raman spectroscopy of detrital garnet in modern river sands and upper Neogene sandstones, complemented by detrital‐zircon geochronology and by petrographic and heavy‐mineral analysis. Garnet grains are relatively abundant and largely represented by almandine with various percentages of pyrope molecules in Yangtze sand as in western Taiwan sandstones and modern river sand derived from them. Instead, they are rare and largely represented by grossular or andradite in the sand of the Pearl River and of coastal rivers of SE China facing the Taiwan Strait. This finding supports the result of detrital geochronology, which documents a sharp difference between U‐Pb age spectra of Pearl River and coastal SE China zircons (characterised by a Paleozoic‐Mesozoic triple peak) and Yangtze and western Taiwan zircons (characterised by prominent Neoproterozoic, Paleoproterozoic, and latest Archean clusters). The Pearl River and minor rivers facing the Taiwan Strait are thus ruled out as ultimate sources of upper Neogene sandstones exposed today along the western front of the Taiwan fold‐thrust belt. In the envisaged scenario, sand mostly supplied by the paleo‐Yangtze River was entrained for ~ca.1,000 km southward by longshore currents and deposited on the Chinese passive margin before being accreted along the front of the Taiwan orogen since ~6 Ma. Littoral sand drift represents a major factor of long‐distance sediment transport in modern shelves and needs to be taken into full account in source‐to‐sink studies and paleogeographic reconstructions.

Petrographic and geochemical analyses of dune sands from southeastern Mexico, Oaxaca, Mexico

Dune sands in southeastern Mexico are compositionally and geomorphologically controlled by fluvial input, eastward longshore currents, and the intense winds traveling through the Isthmus of Tehuantepec. Tehuano winds are mainly responsible for the remarkable dune sand entrapment circumscribed to the exposure of volcano‐sedimentary outcrops. Compositionally, the dunes are potentially influenced by granite denudation, volcano‐sedimentary rocks, metamorphic units, and Quaternary sediments besides alluvium. Mono‐ to polycrystalline subangular to angular quartz, K‐feldspar, and schists suggest that granitic‐metamorphic rocks control the river and dune sands composition. Subordinate fractions of mica, Fe–Ti oxide minerals, and reduced amphibole (actinolite) indicate metamorphic‐volcano sedimentary‐granite as the potential parent rock of sand sources. The dune sands compositional framework shows slight flat‐type rare earth elements (REE) trends with a low light rare earth elements (LREE)/heavy rare earth elements (HREE) ratio (e.g., 6.13 ± 6.00), suggesting a significant control of granite rocks. Geochemical signals, CIA and CIW chemical indices support moderate weathering. The petrographic and geochemical analyses indicate little dune sand recycling by aeolian transport despite strong wind systems along the SE coast of Mexico. This provenance study evidences the exhumation of granite, metamorphic, and volcano‐sedimentary materials in the Oaxaca dune sands, confined by the regional geomorphology.

Stable carbon and nitrogen isotopes in Panulirus argus phyllosomas in the Mexican Caribbean

The spiny lobster Panulirus argus (Latreille, 1804) is a commercially important fishery resource in the Caribbean Sea. The complex life cycle of P. argus, particularly during its pelagic life (phyllosoma larvae) is influenced by various oceanographic factors and makes it difficult to develop basic studies about its trophic ecology. The δ13C and δ15N values of the phyllosoma larvae sampled off the SE coast of Quintana Roo, Mexico contributes to assess the migration, feeding and trophic level of the early and intermediate stages of the P. argus life cycle. The δ13C values of the phyllosomas (−18‰ to −22‰) are characteristic of pelagic food resources in oligotrophic oceanic regions, also rich in lipids (ratio C:N 5 to 6). From stage I to IV, the observed δ15N value was enriched by 2.8‰ and remain without change between stages IV and VI, this isotopic equilibrium with the diet was reached between 60 and 70 days of life. The observed enrichment of 15N in P. argus phyllosoma larvae of the Mexican Caribbean suggests a change in trophic level from the early (I–III) to the intermediate stages (IV–VI), during which P. argus larvae remain feeding at the same trophic level.

Chapter 5 Tectonic evolution of the Oman Mountains

Abstract The tectonic evolution of the Oman Mountains as of the Neoproterozoic begins with a major extensional event, the Neoproterozoic Abu Mahara rifting. It was followed by the compressional Nabitah event, still during the Neoproterozoic, in Oman but possibly not in the study area. During the earliest Cambrian, the Jabal Akhdar area was affected by the Cadomian Orogeny, marked by NE--SW shortening. It is unclear, whether the Saih Hatat area was exposed to the Cadomian deformation, too. Still during the lower Cambrian, the Angudan Orogeny followed, characterized by NW--SE shortening. An episode of rifting affected the Saih Hatat area during the mid-Ordovician. During the mid-Carboniferous, both dome areas were deformed by tilting and large-scale open folding in the course of the ‘Hercynian’ event. As a consequence, a major unconformity formed. As another Late Paleozoic event, the Permian break-up of Pangaea and subsequent formation of the Hawasina ocean basin, are recorded in the Southeastern Oman Mountains. As a result, a passive margin formed which existed until the mid-Cretaceous, characterized by deposition of mostly shelfal carbonates. This interval of general tectonic quiescence was interrupted during the early Jurassic by uplift and tilting of the Arabian Platform. The platform collapsed during the late Cretaceous, related to the arrival of the obducted allochthonous nappes including the Semail Ophiolite, transforming the passive margin to an active margin. The Semail Ophiolite formed most likely above a subduction zone within the Neo-Tethys Ocean during the Cenomanian while parts of the Arabian Plate were subducted to the NE. Formation of oceanic lithosphere and SW-thrusting was broadly coeval, resulting in ophiolite obduction onto the Hawasina Basin. The Semail Ophiolite and the Hawasina rocks combined were thrust further onto the Arabian Plate. Their load created a foreland basin and forebulge within the Arabian Platform. Once the continental lithosphere of the Arabian Platform was forced into the subduction zone, a tear between the dense oceanic lithosphere and the buoyant continental lithosphere developed. This led to rapid uplift and exhumation of subducted continental lithosphere of the Saih Hatat area, while obduction was still going on, causing in multiple and intense folding/thrusting within the eastern Saih Hatat Dome. Exhumation of the Saih Hatat Dome was massive. The emplacement of the ophiolite was completed during the Campanian/Maastrichtian. For completeness, we also present alternative models for the developmental history of the Semail Ophiolite. Immediately after emplacement, the Arabian lithosphere underwent intense top-to-the-NE extensional shearing. Most of the Saih Hatat Dome was exhumed during the latest Cretaceous to Early Eocene, associated with major extensional shearing at its flanks. Further convergence during the late Eocene to Miocene resulted in exhumation of the Jabal Akhdar Dome and some gentle exhumation of the Saih Hatat Dome, shaping the present-day Southeastern Oman Mountains. In the coastal area, east and SE of the Saih Hatat Dome, some late Cretaceous to present-day uplift is evident by, e.g., uplifted marine terraces. The entire Oman Mountains are uplifting today, which is evident by the massive wadi incision into various rock units, including wadi deposits which may form overhangs.

Provenance versus weathering control on sediment composition in tropical monsoonal climate (South China) - 2. Sand petrology and heavy minerals

Together with the companion article dedicated to sedimentary geochemistry and clay mineralogy, this study investigates the interplaying controls on the generation and composition of river sediments across South China. In the Pearl River and southern Yangtze catchments, dominantly sedimentary and basaltic rocks of the Yangtze block shed quartzo-lithic sedimentaclastic sand, whereas mostly granitic and sedimentary rocks of the Cathaysia block generate feldspatho-quartzose sand. Rivers of the Fujian and Zhejiang Provinces draining the SE Coast Magmatic Belt carry feldspatho-litho-quartzose volcaniclastic sand containing epidote with minor clinopyroxene and olivine locally. Within the Pearl River catchment, 35–40% of the sand is derived from the Yangtze block, and 60–65% from the Cathaysia block. Erosion rates are fairly evenly distributed across the basin, reaching higher values in the Hongshui headwaters where topographic relief is greater. South China hosts one of the largest and most spectacular karst areas on Earth, where two landscape types are characterized by different intensity of chemical dissolution. In fengcong (cone) karst, carbonate detritus attacked by carbonic and sulfuric acids is partly preserved, whereas carbonate grains are completely dissolved in fenglin (tower) karst developed in wetter regions to the east. The strong climatic gradient from the dry Tibetan plateau in the west to monsoon-drenched coastal areas is faithfully reflected in illite-rich vs. kaolinite-rich clay-mineral assemblages, but in sand the weathering effect is much harder to isolate from the dominant effects of source-rock lithology and recycling. The different durability of tectosilicates (quartz > microcline > orthoclase > plagioclase) and the degree of corrosion displayed by detrital minerals offer essential qualitative information but cannot represent robust proxies to quantify weathering intensity. The sand generation index SGI reveals whether lithologies are under- or over-represented in detrital assemblages and proved to be most useful to trace different weathering regimes across South China.

Coastal Boulders on the SE Coasts of Cyprus as Evidence of Palaeo-Tsunami Events

Cyprus has a long history of tsunami events, as noted by archaeological and geological records. At Cape Greco (southeastern Cyprus) large boulders have been noted, however, no detailed geomorphological research has taken place so far and the related high energy event was undated until now. Our research aims to record in detail and interpret these large boulders deposits. The boulders, located between ≈3 and 4.5 m a.m.s.l., are fragments of an upper Pleistocene aeolianite, which is overlaying unconformly a lower Pleistocene calcarenite. Dimensions and spatial distribution of 272 small, medium, and large boulders were documented, while their precise distance from the coastline was recorded by field mapping and remote sensing, using Differential GPS (DGPS), drone, and Geographic Information Systems (GIS) technics. Field data were subsequently combined with hydrodynamic equations, in order to determine the extreme event(s) that caused their transport inland, and radiocarbon dating was accomplished on three samples of Vermetus sp. to determine the chronological context. Our findings appear to broadly correlate with the 1303 AD tsunami, which has displaced at least part of the studied boulders, and one other undocumented event at AD 1512-1824. The large number of boulders and sizes in our study area further indicate that their dislocation is most likely owed to multiple events from various sources.