Quaternary Sea-level Changes Research Articles

Fossiliferous sites of the southern coast of Rio Grande do Sul state, Brazil: geoheritage records of Quaternary sea-level, climate and environmental changes

Fossiliferous sites of the southern coast of Rio Grande do Sul state, Brazil: geoheritage records of Quaternary sea-level, climate and environmental changes

Comparative Analysis of the Mineral Associations in the Sediments from Buor-Khaya Bay

According to the results of analysis of 99 samples of bottom sediments and submarine permafrost from wells 1D-14, 3D-14 and 1D-15 drilled in the Buor-Khaya Bay, differences in their mineral composition due to paleogeographic factors, namely Late Quaternary changes in climate and sea level, as well as regional hydrodynamics are shown. The basis of the light fraction of minerals was quartz and feldspar (mainly plagioclases), found in the form of grains of various dimensions and sorting degree, as well as fine grains. To a lesser extent, the presence of chlorites, kaolinite and serpentines is noted, illite and smectite are rare. 42 accessory minerals were identified in the heavy fraction (average yield 0.95%) concentrated in fine-grained sands. It mainly consists of pyroxenes, amphiboles, carbonatite, epidote, zoisite, magnetite, mica, garnet, limonite, sphene, leucoxene, ilmenite. Rutile, kyanite, sillimanite, zircon, tourmaline, apatite, and stavrolite were found in smaller quantities. In the studied strata, plant remnants and carbon-like particles (kerogen) are found, the contribution of which exceeds 5% by weight in a number of samples. The results of the study allowed to conclude that the basis of the petrofund of the studied deposits are most likely sedimentary rocks of the Kharaulakh ridge of the Verkhoyansk mountain system (sandstones, siltstones and mudstones). The presence of characteristic accessory minerals in the sediments marks the unloading of igneous and metamorphic rocks, but their contribution is subordinate. They probably also include rocks of the Verkhoyansk complex, common near the Tiksi.

Climate, not Quaternary biogeography, explains skull morphology of the long-tailed macaque on the Sunda Shelf

Sundaland, comprising the low-lying Sunda Shelf, the major islands of Borneo, Sumatra, and Java, as well as many smaller surrounding islands, formed a contiguous landmass through much of the Pliocene and Pleistocene. Subsequent late-Pleistocene rising sea levels have often been invoked as major zoogeographic barriers to gene flow and associated phenotypic and taxonomic divergence of Sundaic mammals. However, previous examinations of mammalian biogeography have painted a complex picture, suggesting that mammalian diversification in the region cannot easily be explained by a single overarching biogeographical phenomenon. Instead, it may be that the significant climatic changes and their concomitant impacts on local environments were the more significant control. In this context, we study adult skull morphology of a widely distributed primate in insular and continental Southeast Asia, the long-tailed macaque (Macaca fascicularis), using a 3D geometric morphometric (GM) approach. We used principal component analysis and linear discriminant function analysis to analyze the associations between morphological divergence and island biogeography, taxonomy, and phylogeny. Reduced rank regressions (RRR) were employed to investigate associations with climate of the present and last interglacials and the last glacial maximum (LGM). There was very poor morphological divergence and discrimination among specimens from different biogeographical zones. There was also large overlap between M. fascicularis subspecies in skull size and shape, with M. f. fascicularis occupying the largest range of size and shape variation, consistent with its wide geographical distribution. Nonetheless, sundaic M. f. fascicularis and M. f. philippinensis, restricted to the Philippines, were successfully discriminated on size and shape, supporting the latter as a valid subspecies. There was moderate morphological differentiation associated with the deepest split in mitochondrial DNA lineages (M. f. aureus versus the rest) in skull size and shape. Contrary to biogeography, we detected strong associations between skull morphology and climate. Skull form (size and shape combined) was better explained by climate closer to present conditions and correlated most strongly with the current interglacial, even though past climatic conditions do show correlations with cranial morphology. We found no strong evidence that cranial and mandibular variation in M. fascicularis consistently tracks insularity caused by Quaternary sea level change. Instead, the morphological overlap evident in our sample indicates connections between subspecies and is consistent with the history of Sundaland as a single landmass for large portions of the Quaternary.

Increased discharge of Yellow River sediments into the western Bohai Sea since 0.71 Ma

AbstractThe Yellow River originates on the Tibetan Plateau and transports vast amounts of terrestrial sediment to the ocean. However, previous studies have not reached a consensus as to when and how the Yellow River first began to flow into the sea. Here we present Sr-Nd-Pb isotope data and a high-resolution clay mineral record of a 200-m-long sediment core recovered from the modern Yellow River delta. The changes in Sr-Nd-Pb isotopic compositions and clay minerals at 0.71 Ma suggest that a larger proportion of sediment was derived from the Yellow River after this time. We propose that the Yellow River has influenced the Bohai Sea since 1.9 Ma (or even earlier), which provides important evidence for an older Yellow River than 1.2 Ma. A significant increase in discharge of Yellow River sediments since 0.71 Ma is due to continuing subsidence of the eastern China coast, the large amplitude of Quaternary sea-level changes, and increased supply of eroded loess during the last 1.0 Ma. After this time, the contribution of local rivers surrounding the Bohai Sea became negligible due to dilution by the huge amounts of Yellow River sediments. These results provide improved constraints on the evolution of the Yellow River and subsequent land-sea fluxes.

Chronology constraints on the complex sedimentary stratigraphy of the paleo-Yangtze incised valley in China

Numerous studies have documented the sedimentary sequences of the Yangtze Delta in response to relative sea-level changes since the Last Glacial Maximum (LGM). However, the pre-LGM sedimentary history of the paleo-Yangtze Delta remains unknown, especially for the formation timing of the basal fluvial sedimentary succession in the paleo-Yangtze incised valley. Here, based on luminescence dating techniques, the sedimentary stratigraphy of three sediment cores (YD016, YD014 and YD006) were constrained and the sedimentary successions were analyzed. Combining with previously published sedimentary sequences, we infer spatiotemporal variation of the stratigraphic architectures over the Yangtze Delta through the time spanning from the late Pleistocene to the Holocene (∼50–0 ka). Our reconstruction for the paleogeography and environmental evolution of the paleo-Yangtze incised valley showed that the basal fluvial channel belts in the paleovalley associated with coeval laterally extensive paleosol-bearing stratigraphy at the interfluves occurred in the transition between marine isotope stage (MIS) 3 and MIS 2; the overlying sedimentary successions are characterized by the post-glacial floodplain deposits formed between 19 and 12 ka, and estuary to shallow marine deposits during early Holocene (11–8 ka); and then the upper most is the Yangtze Delta depositional systems dated to mid-to-late Holocene (since ∼8 ka). Correlations of the chronostratigraphy of sediment cores over the cross-sections in this region suggest that a superimposed compound fluvial channel complex has probably characterized the paleo-Yangtze incised valley systems since MIS 3. Apart from the post-LGM infilling of the LGM incised valley, the basal MIS 3 fluvial deposits might represent the earlier infilling over another incised valley, which might be formed during MIS 4 although our cores have not reached yet. Such hierarchical incised valley systems in the paleo-Yangtze Delta were likely related to the late Quaternary sea-level changes. In addition, the relict inherited topography since the last glacial period could have played an important role in the stacking patterns of the paleo-Yangtze incised valleys.

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.

The sedimentary succession of the last 2.25 Myr in the Bohai Strait: Implications for the Quaternary paleoenvironmental evolution of the Bohai Sea

The Bohai Strait connects the Bohai Sea with the Yellow Sea, allowing material and energy exchange between the seas. The sedimentary record in this region is important for reconstructing the Quaternary sea-level changes and environmental evolution in the Bohai Sea area; however, long sedimentary sequences with a reliable chronological framework from this area are scarce. We assessed the sedimentary characteristics, grain size, microfossils, accelerator mass spectrometry 14 C ages and optically stimulated luminescence ages of core BHS01 from the Bohai Strait. From these and previous paleomagnetic results, new insights into regional sea-level changes and environmental evolution in the Bohai Strait over the last 2.25 Myr are obtained. The sedimentology and environmental proxies (benthic foraminifera and marine ostracods) indicate that the sedimentary environment of the area around core BHS01 was mainly dominated by fluvial–lacustrine deposits from 2.25 to 0.89 Ma, and subsequently by alternating marine and fluvial deposits. Comparative analyses of the chronological and sedimentary results of core BHS01 with previous drilling records in the eastern marginal seas of China revealed that the Quaternary initial marine transgression of the Bohai Sea occurred no later than 0.89 Ma (latest early Pleistocene) since Quaternary. The initial transgression presumably resulted from the partial subsidence and disintegration of the Miaodao Islands Uplift with sea-level rise during this period or slightly earlier. This result is generally consistent with the timing of the Quaternary regional marine transgressive processes of the Yellow and Bohai seas; thus, we propose a conceptual model in which the first marine transgression of the Yellow Sea and the Bohai Sea during the Quaternary occurred no later than 1.66 Ma and 0.89 Ma, respectively. This study provides new evidence for understanding the Quaternary sea-level changes and regional environmental evolution in the Bohai Sea. • Paleoenvironmental evolution of the Bohai Strait since ~2.25 Ma reconstructed. • Quaternary initial transgression of the Bohai Sea occurred no later than 0.89 Ma. • Conceptual model for Quaternary transgressive processes of the study area proposed.

Marine pollen records provide perspective on coastal wetlands through Quaternary sea-level changes

The response of coastal wetlands to future sea-level rise remains uncertain. Palaeoecological data are essential to constrain the still conflicting ecological models. However, obtaining detailed palaeo-coastal stratigraphic records before Holocene is often difficult due to repeated Quaternary marine transgression-regressions. Here we utilize pollen data from a deep-sea sedimentary archive in northern South China Sea to explore the historical behavior of coastal wetlands at a large river estuary over the last 140-kyr. A recurrent wetland (Cyperaceae)-pioneer species (Selaginella)-zonal forest (Pinus) succession throughout the last glacial-interglacial cycle implies a coastal salt marsh origin of the Cyperaceae pollen. Comparing with global sea-level reconstructions, the increases in Cyperaceae pollen abundance, and hence the expansions of coastal salt marsh, were found to be closely linked with rapid large-scale sea-level rises. This finding indicates a resilience of coastal wetlands to future sea-level rise, and highlights the probable importance of conventionally ignored horizontal adaptability in long-term survival of coastal wetlands. Overall, marine pollen records provide an opportunity to supplement existing palaeoecological observations of coastal wetlands during the Quaternary.

Quaternary Tectono Geomorphic Evolution of the Vaigai Delta as deduced from Geomorphic Mapping

The well preserved landforms of the Vaigai river delta in Tamil Nadu stand testimony to the Quaternary sea level changes, fluvial dynamics of the river and the morphotectonic movements of the region. The geomorphic mapping performed using high resolution satellite images brought out the occurrence of unique set of landforms like beachrocks, abandoned channels, deltaic lobes etc. that indicate the dynamic evolution of the Vaigai delta during the Quaternary period assisted by the palaeo sea level fluctuations, preferential migration of the river and land upliftment due to neotectonic movements. The occurrences of extensive sand dunes further suggest the strong aeolian action in the geomorphic evolution of the delta and also the Quaternary climatic changes of the region.

Late Quaternary subsidence records from the Datça graben and Cnidus ancient city (SW Turkey): sea-level changes versus tectonics

The Datça graben in southwestern Anatolia is a WNW-trending seismically active depression, with tectonic activity since Pliocene time. This tectonic activity is controlled by normal faults, which have effected ancient settlements. The Cnidus city (old and modern) –an ancient mercantile centre during the Hellenistic, Roman and Byzantine periods– is one of the places that has recorded this activity. The ancient harbour walls of Cnidus, lying 2.2-4.0m below sea level, contain important traces about sea-level changes and tectonics over the past 2.6kyr. Palaeostress analysis along boundary faults in the Datça graben yields an almost N–S oriented pure tensional regime, compatible with earthquake focal mechanism solutions located around the Datça Peninsula. Additionally, an almost E−W trending surface rupture related to a historical earthquake in modern Cnidus, which shows normal fault characteristics, gives further support to the ongoing extension along the Kızlan, Karaköy and Cnidus fault zones. Previous studies on late Quaternary sea-level changes around the Datça Peninsula suggest that 2.6kyr ago sea level was 1.0-1.25m lower than today. From the present-day depth of the Old Cnidus harbour remains and regional sea-level records, it can be inferred that tectonics has played a significant role. Our calculations show that the Datça graben is subsiding at rates of 0.36-0.46mm/yr in the central part and 1.05-1.15mm/yr in the southern part. These values match those found in other areas around the Datça Peninsula.

Phylogenetics of mud snakes (Squamata: Serpentes: Homalopsidae): A paradox of both undescribed diversity and taxonomic inflation

Mud snakes (Serpentes: Homalopsidae) are a family of 55 described, mainly aquatic, species primarily distributed throughout mainland Southeast Asia and the Indo-Australian Archipelago. Although they have been the focus of prior research, the basic relationships amongst genera and species remain poorly known. We used a combined mitochondrial and nuclear gene dataset to infer their phylogenetic relationships, using the highest levels of taxon and geographic sampling for any homalopsid phylogeny to date (62% generic and 62% species coverage; 140 individuals). Our results recover two reciprocally monophyletic groups: the fangless Brachyorrhos and its sister clade comprised of all rear-fanged homalopsids. Most genera and interspecific relationships were monophyletic and strongly supported, but intergeneric relationships and intraspecific population structure lack support. We find evidence of both undescribed diversity as well as cases of taxonomic inflation within several species. Tree-based species delimitation approaches (mPTP) support potential new candidate species as distinct from their conspecifics and also suggest that many named taxa may not be distinct species. Divergence date estimation and lineage-through-time analyses indicate lower levels of speciation in the Eocene, with a subsequent burst in diversification in the Miocene. Homalopsids may have diversified most rapidly during the Pliocene and Pleistocene, possibly in relation to tectonic shifts and sea-level fluctuations that took place in Sundaland and the Sahul Shelf. Our analyses provide new insights on homalopsid taxonomy, a baseline phylogeny for the family, and further biogeographic implications demonstrating how dynamic tectonics and Quaternary sea level changes may have shaped a widespread, diverse family of snakes.

The role of late Quaternary tectonic activity and sea-level changes on sedimentary processes interaction in the Gulf of Cadiz upper and middle continental slope (SW Iberia)

A morphological and seismic-stratigraphic analysis of the Gulf of Cadiz area near the Strait of Gibraltar is presented in this work, focused on the sedimentary evolution of the upper and proximal middle-continental slope since the Mid-Pleistocene. Based on the analysis of seismic reflection profiles and swath bathymetry data, this work analyses the close influence of the activity of buried and outcropping diapiric ridges and late Quaternary sea-level changes on the evolution of contouritic features related to the Mediterranean Outflow Water (MOW) and Eastern North Atlantic Central Water (ENACW), gravitational features and fluid-escape structures. The stratigraphic architecture reveals that, under active diapiric deformation, the upper slope plastered drift grew during low sea-level stages, when sediment supply was high and the ENACW swept the upper slope, contrasting with the present-day highstand situation dominated by northwest-trending MOW flow. The south-estward ENACW flow forced asymmetry and lateral migration of gullies incised in the plastered drift. Two evolutionary stages have been established: 1) After the Mid Pleistocene, activity of diapirs with a NE trend determined the location of the deepest depressions which were infilled by plastered contouritic drifts; 2) Between Late Quaternary and present, a drastic change of buried diapirs growth pattern and orientation to a NW trend enhanced slope-derived gravitational processes affecting the bottom current dynamics. Adjustments to tectonic changes led to a phase of plastered drift growth on the upper slope during which depocenters varied their distribution and orientation. In a long-term the structural control on sedimentation shows a northwestward displacement of deformation, resulting in an overall extension of the contourite depositional system to the NW. In a short-term, sea-level changes favored drift deposition, gullies incision and the strengthening of water masses. This work evidences the importance of tectonic deformation in sedimentation at recent time scales, and the two-directional interplay between recent tectonic activity and bottom current dynamics.

Fluvial response to Late Quaternary sea level changes along the Mahanadi delta, east coast of India

This study presents the fluvial response to late Quaternary sea level changes in the Mahanadi delta. Channel morphological adjustments indicative of sea level changes, such asanastomosing-meandering transition, dendritic channels, and river mouth shift, have been used to reconstruct the paleo-coastlines. Major rivers in the Mahanadi delta (e.g., Mahanadi, Devi, Brahmani, and Baitarani) show alteration of anastomosing and meandering fluvial systems at the late Quaternary strandlines. Two generations of dendritic channels, i.e., Early to Mid- (>5 ka) and Mid-to Late (<5 ka) Holocene, have been identified based on OSL ages and affinity to the paleostrandlines. Lateral shift of river mouths in response to sea level changes have been observed in the lower deltaic plain. The delta distributaries such as Bhargavi, Kushabhadra, Brahmani and Baitarani rivers shifted their mouths due to Early to Mid-Holocene (6–7 ka) marine transgression. Different generations of paleochannels in the Mahanadi delta indicate episodes of the delta progradation since Mio-Pliocene. The distributary paleochannels along the Mio-Pliocene strandline indicate the initial stage of Mahanadi delta development. The river morphological response to the changing coastline of the Mahanadi delta is similar to paleo-fluvial morphological adjustments observed along the paleostrandlines of major deltas around the world.

Stratigraphic evolution of the Nakdong River valley in response to late Quaternary sea-level changes

Sequence analysis using borehole samples and high-resolution seismic data in the Nakdong River valley yielded a good example of a river-valley sequence influenced by the complex interplay between the bottom morphology of the steep paleo-valley, varying sediment supply, and Holocene sea-level change associated with coastal currents. The late Quaternary stratigraphic sequence in the Nakdong River Estuary, approximately 60–70 m thick, forms a high-frequency sequence consisting of a set of lowstand, transgressive, and highstand systems tracts that corresponds to a fifth-order (20 ka) sea-level cycle. Four main depositional systems, including ten sedimentary facies, constitute these systems tracts: fluvial, estuarine, coastal/shoreface, and deltaic. The lowstand systems tract (LST), consisting of gravelly sand, forms a fluvial depositional system (Unit I) which fills the thalweg of river valley mainly developed before 12 ka. The transgressive systems tract (TST), showing a succession of retrograding or backstepping depositional arrangements, can be divided into two depositional systems (Unit II and III). The riverine sediments were trapped within the paleo-estuary, forming an estuarine depositional system (Unit II) developed between 12 and 7 ka. As the transgression continued, the coarse sediments were deposited and redistributed by coastal processes, resulting in coastal/shoreface depositional system (Unit III). It is characterized by an isolated sand body and thin sand veneer. The HST is composed of deltaic depositional system including delta plain, delta front, and prodelta (Unit IV). During the delta progradation, most coarse-grained sands derived from the river were deposited in the lower delta plain and delta front, forming sand bars and shoals less than 15 m deep. The remaining fine-grained sediments were transported further offshore in a suspension mode and deposited in the inner shelf off the present river mouth, forming a subaqueous prodelta. Radiocarbon and optically stimulated luminescence (OSL) dating suggest that the Holocene deltaic system was initiated by aggradational and progradational stacking patterns at approximately 8 ka during the last stage of decelerated sea-level rise, and was then followed by a prograding clinoform after the highest sea level at approximately 7 ka.

Deglacial climate and relative sea level changes forced the shift from eolian sandsheets to dunefields in southern Brazilian coast

Quaternary sea level and climate changes can promote spatio-temporal shifts in the morphology of coastal eolian depositional systems. A shift of depositional features such as from sandsheets to dunefields occurs as response to a disequilibrium condition in the system promoted by changes in accumulation space and sediment supply balance. On the other hand, the eolian system migration, with maintenance of morphological patterns, points to an equilibrium conservation under minor variations in the external controlling factors of the system. The Santa Catarina coast in southern Brazil hosts widespread active and stabilized eolian depositional systems with varied morphology. In this study, geomorphologic and stratigraphic changes of eolian deposits of the southern coast of Santa Catarina were constrained by optically stimulated luminescence (OSL) dating. This allowed to assess how coastal eolian systems responded to late Quaternary climate and sea level changes. Eolian sandsheets initiated around 22 ka ago, during the Last Glacial Maximum (LGM), and persisted during most of the deglacial period under conditions characterized by sea level lowstand, wider exposition of shelf sediments, more continental and drier climate and scarcer vegetation cover in the study setting. The shift from eolian sandsheets to dunefields occurred approximately at 6 ka ago and marks the establishment of coastal conditions in the study setting. The development of dunefields since the middle Holocene would result from eolian system disequilibrium in response to a condition characterized by sea level highstand, wetter climate and denser vegetation cover. The maintenance of a dunefield morphology since 6 ka ago, despite its onshore migration, indicates a new equilibrium between accumulation space and sediment supply. Sandsheets evolved to dunefields around 6 ka ago when the coastline stabilized and the accumulation space was limited by onshore vegetation growth, favoring eolian sediment aggradation. The precipitation ridge in the inner margin of the dunefield has been successively stabilized, abandoned and repositioned seaward, accompanying the coastal progradation since 4 ka ago. The decreasing migration rate of dunefields since 4 ka ago is attributed to rainfall reduction, which deplete fluvial sediment supply to coastal systems and, therefore, slow down the coastal progradation rate.

How a river submerges into the sea: a geological record of changing a fluvial to a marine paleoenvironment during early Holocene sea level rise

ABSTRACTCoastal seas, and in particular estuarine systems, were significantly affected by Quaternary sea level changes. Furthermore, the dynamics of shelf and coastal evolution have had a strong impact on coastal landscapes inhabited by humans. The postglacial evolution of the vast North Sea shelf with its huge drainage systems, e.g. the Elbe Paleovalley and its tributary system, is an excellent research target to understand how coastal shelf environments change in response to sea level rise. In this study, we investigate infill sediments of the Paleo‐Ems valley – a drowned extension of the modern Ems River and part of the Elbe Paleovalley drainage system. Radiocarbon‐dated transgression sequences provide several new observations regarding the mode and rate of the river system submerging due to the Holocene transgression. Thus, the Paleo‐Ems valley submerged within a short time span of~200 years since the river was not able to adjust its gradient to the rapid rising sea level. The fate of the Paleo‐Ems is exemplary for the rapid change of a former fluvial landscape into a coastal landscape and finally into a submarine seascape. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley &amp; Sons Ltd.

The impact of Quaternary sea-level changes on the sedimentary organic matter of the Paraíba do Sul Deltaic Complex area, southeastern Brazil

The Paraíba do Sul Deltaic Complex (PSDC) landscapes diversified markedly over the last 123,000 years B.P. The PSDC is characterized by non-marine to marine deposits, and very complex non-marine deposits in its uppermost part. In such a setting, the characterization of the sedimentary organic matter is a useful tool for conduction paleoenvironmental reconstruction. Sea level changes during this interval are reflected in the stratigraphic distribution of sedimentary organic matter recorded in the four sections of the onshore portion of Campos Basin, southeastern Brazil. The succession is dominated by the woody material (phytoclasts), related to a continuous terrigenous input on the area and is characterized by a long-term regressive trend. The stratigraphical distribution of five palynofacies association reveal a wide variety of depositional paleoenvironments. The palynofacies associations attributed to alluvial fan, fluvial, shallow marine and lagoon were recognized. The alluvial fan, in the lowermost part of the succession, is characterized by high contents of opaque and pseudoamorphous particles. The fluvial deposits, in the lower and uppermost parts of the succession, are dominated by wood material (non-opaque) and sporomorphs. The marine deposits (shallow marine and lagoon), in the middle parts of the succession, appear to be related to the dinoflagellate cysts, microforaminifera linings and amorphous organic matter and suggest a notable marine incursion.

Facies Analysis and Sequence Stratigraphy of Al-Kharrar Lagoon Coastal Sediments, Rabigh Area, Saudi Arabia: Impact of Sea-Level and Climate Changes on Coastal Evolution

This study employs the results of facies analyses and sequence stratigraphy of the coastal plain sediments of Al-Kharrar Lagoon, Rabigh, Saudi Arabia, to interpret the impact of Late Quaternary sea-level and climate changes on sedimentation, facies distribution and Red Sea coastal evolution. Facies analysis of the sediments that crop out in a recently excavated quarry section and those recovered from six shallow cores obtained from the tidal flat south Al-Kharrar Lagoon enabled identifying four facies associations characterizing fluvial, intertidal–supratidal, lagoonal and intertidal flat deposits. Facies architecture and sequence stratigraphic interpretations indicate two distinct depositional stages. The first stage included the deposition of marine-influenced gravel-dominated fluvial channel deposits interdigitating with or overlain by grey lagoonal mud and fine sands suggesting deposition during a period of progressive sea-level rise and enhanced precipitation. The second stage records deposition of prograding intertidal–supratidal deposits containing calcareous nodules and mottles and evaporite minerals at quarry section suggesting deposition during a sea-level fall under an arid climate. The results of this study are correlated with the Late Quaternary periods of humidity and aridity. It is found that the first stage corresponds to the postglacial early–middle Holocene sea-level rise and wet climate, whereas the second stage corresponds to the mid- to late Holocene isostatically controlled sea-level fall and arid climate.

Quaternary coastal plains as reservoir analogs: Wave-dominated sand-body heterogeneity from outcrop and ground-penetrating radar, central Santos Basin, southeast Brazil

Sub-seismic sand-body characterization depends largely on understanding the heterogeneities observed in outcrops of equivalent depositional settings to subsurface reservoirs (reservoir analogs). Outcrop information, however, rarely covers the whole depositional system. Ground-penetrating radar (GPR), on the other hand, is a powerful tool for the high-resolution visualization of sand-rich deposits in the shallow subsurface, allowing for the description of their internal architecture, relationships with depositional systems, and its larger scale stratigraphic evolution. The internal character of radar patterns can be interpreted with respect to facies seen in exposures, leading to the prediction of heterogeneities below radar resolution. In this paper we use GPR and outcrops to describe the heterogeneity of Quaternary coastal-plain deposits from central Santos Basin (Paraná state, southern Brazil) where Pleistocene and Holocene, wave-dominated regressive barriers and transgressive lagoons and estuaries were formed under the influence of Quaternary sea level and climatic changes. Sedimentary facies reveal the predominance of sand deposited under the influence of tidal processes, fair-weather and storm wave processes. Radarfacies indicate a tendency of progradation of beach-face reflectors over subtidal radarfacies within two regressive successions separated by a regional unconformity. Interpretation of GPR resulted in the definition of 13 radarfacies arranged in three associations reflecting major depositional systems: (1) strandplains formed by prograding beach/dune-ridge sets over subtidal deposits, (2) spit-inlets, with progradation of beach faces over subtidal deposits and longshore accretion of spits, and (3) paleolagoons/paleoestuaries. Sedimentary facies indicate that strandplains and spit-inlets are predominantly sandy, while a muddy composition is expected in paleolagoons/paleoestuaries. The distribution and evolution of these systems were controlled by base-level oscillations and/or sediment supply that resulted in the formation of two regressive barriers separated by a wave ravinement surface configuring two parasequences with a wide variety of inter- and intra-sand body heterogeneities. This arrangement imprints a relatively high degree of compartmentalization within deposits that are traditionally considered continuous and homogeneous. Therefore, the Quaternary coastal plain of Paraná can be used as an analog for compartmentalized coastal reservoirs.

Influence of Quaternary sea level changes in the littoral of Chubut, Argentina

Geomorphologic and stratigraphic studies accomplished in the littoral area between Cabo Raso and Punta Fabián, eastern Chubut Province, allowed the identification of different features and geomorphologic processes related to the modern dinamic, as well as a set of coastal units related to the different transgressive events occurred from the middle Pleistocene to the Holocene. The distribution and development of the littoral deposits displays a completely different situation from that of the area of Bahía Camarones, Bahía Bustamante, Cabo Raso and Bahía Vera (south and north of the study area), favored by a very hard substrate (Marifil Complex) at higher topographic positions. Abrasion platforms, cliffs, islands, capes and tómbolos form a broken coast in which the most relevant accumulation morphologies are gravel beaches. This situation prevailed as well in each of the high sea level event, forming beach crests in some places that corresponded to bays, wider than the modern ones. According to the altitud of these geoforms, respect to similar ones located to the south which have a significant number of numerical ages, the highest sea levels correspond to 500 k B.P., quite probably the Marine Isotopic Stage 11. This analysis includes a mean elevation of the continent of 0.12 ± 0.04 mm/yr. Although eight beach crests were clearly identified, not necessarily each of them responds to independent transgressive events. In fact, some of them may represent different positions of the same transgression during the regressive phase.