Quaternary Sea-level Fluctuations Research Articles

Evolution of sea-surfing plant propagule as revealed by the genomes of Heritiera mangroves.

Coastal forests, such as mangroves, protect much of the tropical and subtropical coasts. Long-distance dispersal via sea-surfing propagules is essential for coastal plants, but the genomic and molecular basis of sea-surfing plant propagule evolution remains unclear. Heritiera fomes and Heritiera littoralis are two coastal plants with typical buoyant fruits. We de novo sequenced and assembled their high-quality genomes. Our phylogenomic analysis indicates H. littoralis and H. fomes originated (at ~6.08 Mya) just before the start of Quaternary sea-level fluctuations. Whole-genome duplication occurred earlier, permitting gene copy gains in the two species. Many of the expanded gene families are involved in lignin and flavonoid biosynthesis, likely contributing to buoyant fruit emergence. It is repeatedly revealed that one duplicated copy to be under positive selection while the other is not. By examining H. littoralis fruits at three different developmental stages, we found that gene expression levels remain stable from young to intermediate. However, ~1000 genes are up-regulated and ~ 3000 genes are down-regulated as moving to mature. Particularly in fruit epicarps, the upregulation of WRKY12 and E2Fc likely constrains the production of p-Coumaroyl-CoA, the key internal substrate for lignin biosynthesis. Hence, to increase fruit impermeability, methylated lignin biosynthesis is shut down by down-regulating the genes CCoAOMT, F5H, COMT, and CSE, while unmethylated lignins are preferentially produced by upregulating CAD and CCR. Similarly, cutin polymers and cuticular waxes accumulate with high levels before maturation in epicarps. Overall, our genome assemblies and analyses uncovered the genomic evolution and temporal transcriptional regulation of sea-surfing propagule.

Holocene Evolution of the Pearl River Delta: Mapping Integral Isobaths and Delta Progradation

The Pearl River Delta (PRD, China) has undergone complex geological development within a multi-island faulted basin, shaped by the interplay of regional tectonic movements, Quaternary sea-level fluctuations, and fluvial-marine interactions. Despite a great number of studies on the Holocene sedimentary sequences and spatial differences of lithofacies and environments, scant attention has been paid to the overarching human influence on deltaic evolution and coastline modifications since the Neolithic epoch. To further elucidate the spatial variation in Holocene sedimentation and its underlying basement topography shaped during the Last Glacial Maximum (LGM), we compiled a comprehensive dataset incorporating borehole data from over 2800 cores (the maximum depth can reach 92.5 m) within the PRD. Subsequently, high-resolution isobath maps of Quaternary deltaic deposits were generated, offering unprecedented insights into sediment distribution. This dataset facilitated a nuanced reconstruction of pre-Holocene topography, revealing a zone characterized by elongated, deep-incised valleys governed by NW-SE fault orientations. Further, we delineated coastline shifts since the period of maximum Holocene transgression (~7000 years BP), contributing to an enhanced understanding of the formation and evolutionary patterns of the delta and river network oscillations. Our findings illuminate an increasing anthropogenic impact on the rate of fluvial sedimentation and land growth, particularly accentuated over the last two millennia, favoring deltaic accretion.

Record of the last interglacial sea level highstand based on new coastal deposits in the Cantabrian margin (Northern Iberian Peninsula)

Quaternary sea level fluctuations have been responsible for significant remodelling of coastal landscapes, generating distinctive sea level indicators at different positions and altitudes that are still visible today. Raised coastal deposits are among the characteristic features of significant value in reconstructing the tectonic and sea-level history of the areas in which they are preserved. To date, few remnants of Quaternary coastal deposits have been described and directly dated along the coast of the Cantabrian margin (on the north of the Iberian Peninsula). In this work, two new deposits located in the towns of Castro-Urdiales and Mendexa were analysed and dated using U/Th geochronology and Optically Stimulated Luminescence. Considering the ages and altitudes of these deposits, it seems most likely that they correlate to the Marine Isotope Stage (MIS) 5e. Furthermore, the data acquired suggest that most of the Cantabrian margin underwent a similar tectonic evolution, with no significant tectonic uplift, since at least MIS 5e.

Deciphering the role of late Quaternary sea level fluctuations in controlling the sedimentation in the Brahmaputra Plains

Continent-continent collision between Eurasian and the Indian plate during the Cenozoic period lead to the formation of the Himalayan Mountain chain and the development of the Indus-Ganga-Brahmaputra foreland basin to the south. Complex climate-tectonic interactions in this orogenic belt are responsible for the rapid erosion and filling of the Indus-Ganga-Brahmaputra foreland basin with the eroded materials. This study based on geomorphic mapping, lithofacies analysis, and geochemical (Strontium-Neodymium i.e., SrNd analysis) provenance characterization, as well as optically stimulated luminescence (OSL) ages, provides a dated sedimentation framework for the western Assam lowland areas. The dated relict fan surface lies ~40 m above mean sea level (msl), is incised and forms a regional valley terrace T1 composed of meandering channel deposits. Modern braided rivers flow on the T0 surface. The findings suggest that the alluvial fan is composed of three distinct lithofacies associations and aggraded during 27 to 3 ka. The bottom-most gravelly-sandy facies indicates progradation of the fan during the last glacial maximum (LGM), owing to the increased gradient of the Himalaya bound rivers. The middle facies is a sheet flood deposit which formed during the Latest Pleostocene-early Holocene period with rising sea level and increasing precipitation. During the Mid-Late Holocene, the uppermost facies is deposited as rivers lost their gradient in response to high sea level stand, resulting in inland sedimentation within muddy meandering channels. Our analysis found that falling sea level during the late Holocene was associated with greater precipitation and allowed the river to incise, to form gullies over the fan surface and form the valley terrace T1. The SrNd isotope fingerprints have been used to identify varying fan sediment sources in the Himalaya's southern front (i.e., Lesser and Higher Himalaya) as a function of changing monsoon conditions.

OSL and radiocarbon dating of a core from the Bohai Sea in China and implication for Late Quaternary transgression pattern

The Bohai Sea is a semi-enclosed continental shelf sea in northern China. Three transgression layers have been identified from the Late Quaternary strata in the western Bohai Sea and the coastal regions, which provide critical information on Late Quaternary sea-level fluctuations and landscape development. The three transgression layers were previously assigned to Marine Isotope Stage (MIS) 1 (transgression 1, T1), MIS 3 (T2) and MIS 5 (T3), respectively, mainly based on 14C dating. However, this chronological framework aroused an enigma that the regional sea level in MIS 3 was even higher than that of MIS 5, conflicting with the context of global sea-level pattern. In order to clarify this issue, here quartz optically stimulated luminescence (OSL) dating (four samples) was used to constrain the T2 chronology of borehole TJC-1 from the western Bohai Sea. Radiocarbon samples (eight) of peaty sediments were also measured for reference and comparison. All the four OSL samples showed saturation ages of >80 ka, suggesting that the T2 layer should have formed at least in MIS 5, instead of in MIS 3. Radiocarbon ages in T2 should have been severely underestimated, with a saturation age range of 22–30 cal ka BP, similar to all the previous published radiocarbon ages. The renewed OSL chronological framework for Late Quaternary transgressions in the western Bohai Sea is in better compliance with the history of global sea-level change.

Modern sedimentation and morphology of the Rocas Atoll shelf, and the role of Quaternary sea-level changes

The Rocas Atoll is in the Fernando de Noronha Fracture Zone South Atlantic Ocean and was developed on top of an ancient oceanic volcano, mainly during the Holocene. Quaternary sea-level fluctuations, especially during the last transgression, left geomorphic marks on the atoll and its surrounding shelf. This study investigated the shelf of Rocas Atoll based on single-beam, sonography, grabbed bottom sediments, and multi-temporal satellite imagery. The Rocas Atoll has a surrounding shelf with general E–W orientation, predominantly flat with a water depth of 25 m. The shelf break occurs between 45 and 50 m water depth, reaching up to 80 m locally on northwestern. Inner and outer shelf zones are marked by step-terrace features. The deepest break in relief (T1) occurs at ∼70 m water depth, a terrace (T2) at 40 m, and another terrace (T3) occurs at 30 m. Most of the hard-bottoms are reefs. Close to the atoll, in shallow depths, reefs occur aggregated, forming a tridimensional structure of low relief mounds and paths. As the water depth increases toward the outer shelf, the reefs occur isolated. The geomorphologic patterns of this shelf are analogous to the northeast Brazilian shelf, reflecting the influence of Pleistocene/Holocene sea-level oscillations. Furthermore, multi-temporal satellite images between 2001 and 2019 reveal that modern processes of reef erosion, as a response to decadal climate phenomena, intensify the shelf sedimentation, and the South Equatorial Currents shape the modern shelf and affect seasonally the sediment transport and sand body dimensions.

Hydrochemical, Isotopic, and Geophysical Studies Applied to the Evaluation of Groundwater Salinization Processes in Quaternary Beach Ridges in a Semiarid Coastal Area of Northern Patagonia, Argentina

Quaternary sea level fluctuations have led to the development of beach ridges on many South Atlantic coasts. The objective of this paper was to asses from lithological, hydrochemical, isotopic, and geophysical studies the salinization processes affecting groundwater stored in Pleistocene and Holocene beach ridges of the northern Patagonian coast. A hydrogeomorphological characterization of the area was performed using digital elevation models, the interpretation of satellite images, and field studies. Vertical electrical soundings were performed on transects running perpendicular to beach ridges in order to define variations in the freshwater-saltwater interface position. The salinity, chemistry, and stable isotopes of the groundwater were analyzed. The results demonstrated that the groundwater salinization of Pleistocene ridges responds to processes associated with the geological-geomorphological evolution of the area. The cementation of these surface sediments limits rainwater infiltration, which consequently prevents the development of freshwater lenses. This suggests that saline water is the result of ancient marine ingressions. Freshwater lenses develop in Holocene beach ridges; however, slight water salinization is detectable in the most populated areas as a result of intensive exploitation. The data provided are useful for freshwater resource prospection along the arid coast of Patagonia, where beach ridge deposits abound and populations experience serious drinking water supply problems.

Late Quaternary deep marine sediment records off southern Africa

Abstract High-resolution mapping, sampling and analysis of upper Quaternary southern African continental margin sediments recovered from beyond the Last Glacial Maximum shoreline (>130 m water depth) have expanded our understanding of how marine and terrestrial records are linked over glacial-interglacial climatic cycles. This paper synthesises data currently available from the deep seafloor around southern Africa and, specifically, core sites that demonstrate terrestrial sedimentological connectivity. Several proxies and case studies reveal the evolution of depositional systems, palaeoceanography and palaeoclimate over the last 191 kyr. Hydroacoustic mapping and investigations of submarine canyons have been carried out primarily on the eastern and southwestern margins, while palaeoceanographic productivity and microfossil assemblages have been applied most extensively on the western marine and southern Agulhas Bank. Studies on the western margin indicate that enhanced productivity, less oxygenated bottom waters and reduced marine faunal diversity in the transition to glacial periods, while glacial terminations are associated with reduced productivity and more oxygenated bottom waters. These changes, linked to palaeoceanography and late Quaternary sea-level fluctuations, influence the sedimentary record and sedimentation rates. On the eastern margin, sediment fluxes applied as proxies for rainfall offshore of the Great Kei, Umzimvubu, Limpopo and Zambezi rivers indicate that the southern African climate responds to changes in orbitally-modulated insolation and in particular, to the ~23 kyr precessional cycle, where the proxy records keep pace with this and then diverge at ~80 to 70 kyr. Since the penultimate glacial (Marine Isotope Stage/MIS 6), more humid conditions observed in southern Africa, as the Northern Hemisphere entered phases of rapid cooling, were potentially driven by a combination of warming in the Agulhas Current and shifts of the subtropical anticyclones. Broadly, the sedimentary records reviewed suggest fluctuations in climate and oceanographic circulation that are strongly correlated with the global benthic δ18O record, suggesting sensitivity to high-latitude forcing, and a strong influence of late Quaternary glacial-interglacial cycles despite these marine sites being far-removed from terrestrial environments.

Late Quaternary uplift and sea level fluctuations along the Tyrrhenian margin of Basilicata - northern Calabria (southern Italy): New constraints from raised paleoshorelines

New analyses of marine terraces in the Tyrrhenian Sea margin of Basilicata - northern Calabria (southern Italy) have been carried out. In the study area, c. 25 km in length, an impressive flight of marine terraces occurs, with the highest terraces reaching ~160 m a.s.l. Detailed geomorphological-stratigraphical analyses on remnants of paleoshorelines located within 60 m a.s.l. have shown that the rocky coast of the investigated coastal stretch has been affected by multiple relative sea-level fluctuations, during which reworking of older shorelines has occurred. Dating of the coral Cladocora caespitosa and speleothems, either predating or postdating single paleoshorelines, has allowed the construction of a chronological framework for the identified relative sea-level markers, and their correlation with MIS 7, MIS 6e and distinct peaks of MIS 5. A mean uplift rate of c. 0.25 mm/y since the Last Interglacial has been quantified, one order of magnitude larger than previous estimates. The uplift rate value has been used to infer the elevations of MIS 5a, 5c and 6e sea level peaks, which are higher than those reported in most sea level curves worldwide, although consistent with several findings from the western Mediterranean. Our results demonstrate that a mere sequential correlation may be misleading in the interpretation of flights of marine terraces and indicates that multiple age controls are crucial to unravelling the complex interaction between uplift and sea-level fluctuations in uplifted coastal areas. The reconstructed MIS 5a, 5c and 6e sea level paleo-elevations, besides contributing to the assessment of late Quaternary sea-level fluctuations in the Mediterranean Sea, may contribute to constrain coeval ice sheets volume variations.

Past connections with the mainland structure patterns of insular species richness in a continental-shelf archipelago (Aegean Sea, Greece).

Recent research in island biogeography has highlighted the important role of late Quaternary sea‐level fluctuations in shaping biogeographic patterns in insular systems but focused on oceanic systems. Through this study, we aim investigate how late Quaternary sea‐level fluctuations shaped species richness patterns in continental‐shelf island systems. Focusing on the Aegean archipelago, we first compiled maps of the area's geography using published data, under three sea‐level stands: (a) current; (b) median sea‐level over the last nine glacial–interglacial cycles (MSL); and (c) Last Glacial Maximum (LGM). We gathered taxon–island occurrences for multiple chorotypes of angiosperms, butterflies, centipedes, and reptiles. We investigated the impact of present‐day and past geographic settings on chorological groups by analyzing island species–area relationships (ISARs) and using generalized linear mixed models (GLMMs) selection based on multiple metrics of goodness of fit. Our results confirm that the Aegean's geography has changed dramatically since the LGM, whereas the MSL only modestly differs from the present configuration. Apart for centipedes, paleogeographic changes affected both native and endemic species diversity through altering connections between land‐bridge islands and the mainland. On land‐bridge islands, we detected over‐representation of native species and under‐representation of endemics. Unlike oceanic islands, sea‐level‐driven increase of isolation and area contraction did not strongly shape patterns of species richness. Furthermore, the LGM configurations rather than the MSL configuration shaped patterns of endemic species richness. This suggests that even short episodes of increased connectivity with continental populations are sufficient to counteract the genetic differentiation of insular populations. On the other hand, the over‐representation of native nonendemic species on land‐bridge islands reflected MSL rather than LGM mainland connections. Our study shows that in terms of processes affecting species richness patterns, continental archipelagos differ fundamentally from oceanic systems because episodic connections with the mainland have profound effects on the biota of land‐bridge islands.

The reptiles of Tinhosa Grande islet (Gulf of Guinea): A taxonomic update and the role of Quaternary sea level fluctuations in their diversification

ABSTRACT The reptile fauna of Tinhosa Grande islet, Gulf of Guinea, comprises an endemic skink, Trachylepis adamastor, and an unidentified species of gecko of the genus Hemidactylus. Until recently, no molecular data were available for either species, impeding their phylogenetic placement. However, due to several synapomorphic characters, it was suggested that the Tinhosa Grande population would be related to the congeners of the neighbouring islands of Príncipe and São Tomé. In a recent survey of Tinhosa Grande islet we collected fresh material of both species, allowing us to examine their phylogenetic relationships to the other members of their respective genera occurring on the neighbouring islands using multigene Bayesian and maximum likelihood analyses. In contrast with the morphological results and previous taxonomic allocations, our molecular results suggest that both T. adamastor and the unidentified Hemidactylus sp. are conspecific with their Príncipe counterparts, Trachylepis principensis and Hemidactylus principensis. While today Tinhosa and Príncipe differ strongly in their environmental conditions, we show that the islands have been repeatedly merged into a single landmass as a result of Quaternary sea level fluctuations. We suggest that the repeated fusion of the islands during low sea levels could have impeded the phylogenetic divergence of both populations, while contrasting habitats might have simultaneously promoted some morphological differences.

Comments on: “Anatomy of a late quaternary carbonate island: Constraints on timing and magnitude of sea-level fluctuations, West Caicos, Turks and Caicos Islands, BWI” by Kerans et al. [Quat Sci. Rev. 205 (2019), 193–223

We comment on interpretations of the evolution of late Pleistocene geology on West Caicos Island, Caicos Platform, B.W.I. by Kerans et al. (2019), which omits our documentation of the interrelationship of carbonate facies in outcrop and in boreholes (Dravis and Wanless, 2017). We further disagree with their geochronological dating assumptions/results that are the basis for interpreting late Quaternary sea-level fluctuations.

Controls on strath terrace formation and evolution: The lower Guadiana River, Pulo do Lobo, Portugal

The lower Guadiana River carves a wide canyon in the Variscan metamorphic rocks of the SW Iberian Peninsula and presents an exceptionally homogeneous and well-preserved case of a strath terrace (ST) some 40 km long and 400 m wide. The rocky surface or strath shows different characteristics and development stages. Upstream, the lateral erosion level forms a flooded riverbed, or submerged strath, that gradually rises above the thalweg and develops into an active floodplain. Downstream, below the 15 m high Pulo do Lobo waterfall, the strath is incised by an inner canyon that forms a terrace on both sides. The inner channel increasingly widens and the ST loses its longitudinal continuity, yet remains prone to flooding during extraordinary magnitude floods. To assess the factors controlling the formation of this ST, we examined the roles of key drivers of ST formation: lithological hardness, tectonic structures and climate change, using cosmogenic data to create a chronologic context. The ST developed favoured by a monotonous succession of phyllites, as shown by Schmidt hammer resistance data, and interbedded more resistant quartz veins do not significantly alter its flat configuration. Variscan structures and measured joints determine the main orientation of the river and control the drainage network pattern. The intersection of the NS and NE-SW fractures promotes a wavy surface due to three-dimensional minor fold trains that act as discontinuities and play an important role in ST erosion through quarrying and plucking. However, we detected no evidence of ST deformation attributable to recent or Late Cenozoic tectonic activity.The upstream active riverbed progressively changes downstream into an ST. This implies that Be radiometric ages obtained at Pulo do Lobo may not represent the ST's genetic age but rather the time of dismantling of its alluvial or sedimentary cover. This means the strath surface formed prior to its cosmogenic age and was therefore controlled by a higher base level, indicating a higher sea level than the current one, given the downstream area studied. The Quaternary sea level fluctuations show records of only a few meters above the current level. Instead, the sea level low stand maintains an average depth of −60 m, reaching −140 m during the last glacial period. This low base level context could justify the strong incision of the inner channel within the ST, but not the age of strath surface genesis and expansion and thus this surface should have evolved previously. The highest possible sea level stand corresponds to the Pliocene transgression, which reached an elevation of 120 m in the region, covering Miocene paleorelief. The mouth of the Guadiana River at that time resembled a fluvio-deltaic embayment between the Algarve domain and the Guadalquivir depression, which was infilled with fluvial deposits at the end of the transgression. Collectively, these data suggest that cosmogenic dating would define the time of exhumation of this Pliocene sedimentary cover.Despite great variation of the ST ages, estimated incision rates at the knickpoint area are consistent with the total entrenchment of the Pulo do Lobo fall, especially if we consider that data correspond to an active erosion site. Highest erosion rates were found for the pothole area compared to those obtained for the higher ST surface. Radiometric ages correspond to the period of lowest Quaternary sea level and during which headward erosion would have been very active in the inner channel. The waterfall area shows more resistant lithology in its concentrated quartz veins, but this effect is inconspicuous at the ST surface. The regular gradient of 0.02 m/m and vast extension of this perched strath, linked upstream to the Guadiana riverbed, indicates a relic exhumed surface beneath its sedimentary cover. Notwithstanding the subsiding activity of the Gulf of Cádiz, the continental margin behaves as a tectonically stable block, which allows for the persistence of former morphologies in these ancient landscapes reshaped by bedrock river dissection.

Sealevel change and tectonic uplift from dated marine terraces along the eastern Mediterranean coast, southeastern Turkey

Tectonic movements among the African, Arabian, Aegean, and Anatolian Plates have deformed the eastern Mediterranean Basin. Since the late Pliocene, these movements caused transtensional opening of the NE-trending Antakya Graben. Tectonic uplift coupled with Quaternary sealevel fluctuations has produced several stacked marine terraces along the Mediterranean coasts on the Antakya Graben. Here, molluscs from terrace deposits that sit on both Graben flanks at elevations between ~ 3 and ~ 175 m were dated using standard electron spin resonance (ESR) dating. For molluscs in situ in the terraces, the ESR ages ranged from ~ 8.3 to ~ 214 ka, but most of the dated terraces contained molluscs reworked from several earlier deposits due to later tectonic movements, sealevel fluctuations, and associated sedimentary processes. By dating in situ fossils, such as Lithophaga, within or just above the basal contacts for the marine terraces, uplift rates were calculated on both sides of the Antakya Graben. North of the Asi River, the regional uplift rate ranges from ~ 0.43 ± 0.11 mm/yr at Samandağ to as high as 2.08 ± 0.70 mm/yr at Mağaracık Dump. South of the Asi River, uplift rates range from 0.81 ± 0.14 mm/yr at the Cliffside terrace to 2.33 ± 0.60 mm/yr at Meydan Dump I. Rather than regional movements, however, local active normal or transtensional faults, such as the Gözene, Altın, and Sinanlı Faults mainly uplifted these deposits.

To adapt or go extinct? The fate of megafaunal palm fruits under past global change.

Past global change may have forced animal-dispersed plants with megafaunal fruits to adapt or go extinct, but these processes have remained unexplored at broad spatio-temporal scales. Here, we combine phylogenetic, distributional and fruit size data for more than 2500 palm (Arecaceae) species in a time-slice diversification analysis to quantify how extinction and adaptation have changed over deep time. Our results indicate that extinction rates of palms with megafaunal fruits have increased in the New World since the onset of the Quaternary (2.6 million years ago). In contrast, Old World palms show a Quaternary increase in transition rates towards evolving small fruits from megafaunal fruits. We suggest that Quaternary climate oscillations and concurrent habitat fragmentation and defaunation of megafaunal frugivores in the New World have reduced seed dispersal distances and geographical ranges of palms with megafaunal fruits, resulting in their extinction. The increasing adaptation to smaller fruits in the Old World could reflect selection for seed dispersal by ocean-crossing frugivores (e.g. medium-sized birds and bats) to colonize Indo-Pacific islands against a background of Quaternary sea-level fluctuations. Our macro-evolutionary results suggest that megafaunal fruits are increasingly being lost from tropical ecosystems, either due to extinctions or by adapting to smaller fruit sizes.

Late Quaternary coastal evolution and aeolian sedimentation in the tectonically-active southern Atacama Desert, Chile

Analyses of aeolianites and associated dune, surficial carbonate and marine terrace sediments from north-central Chile (27° 54′ S) yield a record of environmental change for the coastal southern Atacama Desert spanning at least the last glacial-interglacial cycle. Optically stimulated luminescence dating indicates phases of aeolian dune construction at around 130, 111–98, 77–69 and 41–28ka. Thin-section and stable carbon and oxygen isotope analyses suggest a predominantly marine sediment source for the three oldest dune phases. Aeolianites appear to have accumulated mainly from tectonically-uplifted interglacial marine sediments that were deflated during windier and/or stormier intervals. Bedding orientations indicate that sand-transporting winds varied in direction from S-ESE during MIS 5e and WNW-ESE during MIS 5c-5a. Winds from the southeast quadrant are unusual today in this region of the Atacama, suggesting either major shifts in atmospheric circulation or topographic airflow modification. Thin-section evidence indicates that the aeolianites were cemented by two phases of vadose carbonate, tentatively linked to wetter periods around 70 and 45ka. Tectonic uplift in the area has proceeded at an average rate of 305–542mmkyr−1. The study illustrates the complexity of understanding onshore-offshore sediment fluxes in the context of Late Quaternary sea-level fluctuations for an area undergoing rapid tectonic uplift.

The effects of Quaternary sea-level fluctuations on the evolutionary history of an endemic ground lizard (Tropidurus hygomi)

The Quaternary period is marked by many extensive glaciations and sea level oscillations, mainly during the Pleistocene. Sea level oscillations possibly shaped landscapes in coastal regions, which may have played an important role in the diversification of organisms that live in these areas. In this study, we investigated the population history of the lizard Tropidurus hygomi, which is endemic to a narrow region of the northeastern coast of Brazil, inhabiting areas of white sandy coastal dunes in the Restinga formation. We specifically asked: how did sea level changes in the Quaternary shape population structure and historical demography of T. hygomi? We collected 72 tissue samples throughout the distribution of the species and obtained sequences from the mitochondrial gene cytochrome b. Different tests for population structure identified five distinct mitochondrial DNA clusters (mtDNA clusters) in T. hygomi. Divergence time estimate showed that splits among these mtDNA clusters took place in the Pleistocene, and exhibited temporal agreement with marine transgressive events during these periods. As T. hygomi is a threatened species and our data suggest the presence of five mtDNA clusters, further conservation actions for this species should consider these independent mtDNA clusters in order to preserve the evolutionary history and the diversity within the species.

Postglacial sediment deposition along a mixed carbonate-siliciclastic margin: New constraints from the drowned shelf-edge reefs of the Great Barrier Reef, Australia

A seismic stratigraphy analysis was conducted at two sites, Hydrographers and Noggin passages, separated by about 540km on the shelf-edge of the central Great Barrier Reef (GBR), Australia. We used recently available seismic and bathymetry data and a new synthesis of downhole logs and lithological, petrophysical and radiometric data from cores recovered by the Integrated Ocean Drilling Program Expedition 325 (Great Barrier Reef Environmental Changes). We compared the stratigraphy of both sites, identifying a full depositional sequence with deposits from at least 28ka BP to ~7ka BP, bounded by two marine flooding surfaces. Within this sequence, each systems tract is represented by unique depositional features characteristic of the shelf-edge systems. Despite the broad environmental and geomorphic similarities between the two sites, differences in postglacial reef development were remarkable. These contrasts can be explained as a result of: (1) local antecedent substrate variations and (2) the interplay of shelf physiography with Late Quaternary sea level fluctuations, which favoured changes in biological production and sediment flux as the palaeo-shoreline evolved from linear to complex during intermediate sea levels. During these intermediate sea levels, the northern estuarine coast and its steep substrate at shelf-edge locations contrasted strongly with the protected palaeo-lagoons and the extensive, gentle marginal terraces found at the southern central GBR. This setting enhanced the regional differences in sediment transport and reef development through the last transgression. The conceptual model presented here provides a broader depositional framework and improves the understanding of the main processes controlling the spatial and temporal depositional patterns on the shelf-edge of mixed siliciclastic-carbonate margins.

Pleistocene events and present environmental factors have shaped the phylogeography of the intertidal limpetCellana toreuma(Reeve, 1855) (Gastropoda: Nacellidae) in Southeast Asia and China

High levels of biodiversity and phylogeographic structure in marine species in Southeast Asia are strongly linked to Quaternary sea-level fluctuations and complex oceanographic conditions. Cellana toreuma is a common limpet on intertidal rocky shores and is widely distributed in the Western Pacific. Analyses of partial mitochondrial COI gene sequences from Southeast Asia, combined with previously published sequences from East Asia and Indonesia, revealed the existence of five well-supported clades with high genetic divergences (between 1.4 and 7.6%), namely the East Asia clade, the eastern Southeast Asia clade, the western Southeast Asia clade, the Pelabuan Ratu (Java) clade and the Ogasawara clade. The geographical distribution of the five clades is likely related to the history of glaciations and rapid postglacial population expansions. Analyses of pairwise ΦST and hierarchical analysis of molecular variance shows significant population structure among collections in East and Southeast Asia. These results suggest that historical events have had strong effects on the phylogeographic structure of C. toreuma. In addition, present environmental factors, such as unsuitable habitats and ocean currents, have also affected the genetic footprints of past environments.

Morphology of Salina offshore (Southern Tyrrhenian Sea)

ABSTRACTIn this paper, we present the first complete morphological map of the Salina offshore at a scale of 1:100,000. The submarine flanks of the Salina edifice extend down to −650 to −1300 m, are steep and characterized by an uneven morphology due to the presence of volcanic and erosive-depositional features. The volcanic features cover ∼30% of the submarine portion and include volcanic cones and bedrock outcrops. The remaining ∼70% is affected by a wide series of erosive-depositional features. Among these, features related to Late Quaternary sea level fluctuations comprise the insular shelf surrounding the island and overlying submarine terraced depositional sequences. Mass-wasting features include landslide scars, channels, fan-shaped deposits and waveforms. The presented map provides useful insights for a better understanding of the morphological evolution of the edifice