Article

Foraminifera and tidal notches: Dating neotectonic events at Korphos, Greece

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Abstract

Fossil assemblages of foraminifera and thecamoebians from three salt-marsh cores recovered at Korphos, Greece, provided evidence for five transgression events since the mid Holocene. Marsh accretion rates based on radiocarbon-dated peat and geomorphic evidence from a series of discrete, v-shaped, submerged tidal notches indicated that these transgression events were rapid and episodic. Correlation of the tidal notches with the transgression horizons in the salt-marsh stratigraphy revealed a stepwise pattern of relative sea-level change at Korphos, which is best explained by coseismic subsidence related to fault displacement (earthquakes) associated with the Hellenic subduction zone. A comparison between the Korphos data and a model of Holocene sea-level change for the Peloponnesus reinforces this interpretation as sea-level rose in a series of jumps by amounts greater than accounted for by eustatic and glacio-hydro-isostatic factors (up to ~ 2.0 m). This study illustrates that by combining microfossil, sedimentary and geomorphic records of past sea-level change, problems frequently encountered with each record individually (e.g. dating submerged notches and autocompaction of marsh sediments) may be overcome.

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... The distribution of recent benthic foraminifer communities in marginal areas has been related with different environmental parameters , such as salinity (De Rijk, 1995; De Rijk and Troelstra, 1997; Fatela et al., 2007; Sen Gupta, 2002), bathymetry (Sen Gupta, 2002), and sediment grain size (Boltovskoy and Wright, 1976; Murray, 1991 ). Vertical repartition of species in brackish marsh areas is related with topography and tidal regime (Horton et al., 1999 ), so assemblages from vegetated high marsh are differentiated from those of the low marsh with channels and no vegetation (Boomer, 1998; Horton and Murray, 2007; Nixon et al., 2009; Semensatto et al., 2009 ). Sampling of this work has been carefully plannified looking for a good representation of all those environments in the studied estuaries. ...
... Also, the distribution and abundance of several of these species are affected by the tide range (Haslett et al., 2001; Edwards, 2003, 2006; ), allowing the establishment of subenvironments inside the estuary. Thus, J. macrescens and T. inflata dominate the mid and high vegetated marshes (Fatela et al., 2009; Horton and Murray, 2007), which are only flooded during high tides (Boomer, 1998), while M. fusca lives in the low marsh (Nixon et al., 2009; Semensatto et al., 2009). The species A. tepida, C. williamsoni and H. germanica are dominant in zones with variable salinity of the mudflats and channels flooded by the mean high tide, even during the neap tides ( Swallow, 2000). ...
... This species lives in the high marsh and prefers to feed on organic matter derived from algae or vascular plants (Armynot du Châtelet et al., 2009; Scott et al., 2003). It is also abundant in silty–sandy sediments with high organic carbon content (Armynot du Châtelet et al., 2009; Nixon et al., 2009). Subgroups 2B and 2C are characteristic of the silty-sand low marsh where M. fusca dominates. ...
Article
Recent benthic foraminifers from two estuaries in the North Spanish coastal region (Tina Mayor and Tina Menor) were analysed with the aim of characterising the ecology and dynamics of the different estuarine sub-environments. A total of 35 benthic foraminifer species were taxonomically determined in the Tina Mayor estuary, 22 of which contained living individuals during the sampling. For Tina Menor, there were 51 species, 30 of them biocenotic. The most abundant species in these estuaries were Ammonia tepida, Cribroelphidium williamsoni, Jadammina macrescens, Lobatula lobatula, Miliammina fusca, Rosalina globularis and Trochammina inflata. In Tina Menor, Haynesina germanica was also abundant. In the foraminifer assemblages, live (biocenotic) and dead (thanatocenotic) specimens were differentiated and processed statistically by a multivariate cluster-Q type analysis and detrended correspondence ordination analysis (DCA). Groupings of biocenotic assemblages were obtained for both estuaries indicating an ecologic separation of marine mouth, low and high marsh and zones with strong salinity oscillations in these estuaries. Thanatocenotic groupings, nevertheless, showed a different organisation of that of the ecologic groups, which were indicative of a transport of individuals from the mouth to the inner/mid estuary locations, along the main and/or secondary channels of these estuaries. Local differences between Tina Mayor and Tina Menor can be explained by the different physiographies of the estuary as a consequence of the different geological/sedimentological histories of both estuaries. Benthic foraminifer assemblages are distributed in the estuary following three zones: an outer estuary having marine characteristics with L. lobatula and R. globularis, a mid estuary, including a subtidal mudflat with variable salinity (A. tepida, C. williamsoni) and a marsh (J. macrescens, M. fusca and T. inflata), which is different in both estuaries.
... The West Saronic Gulf, between the east coast of the Peloponnese and the islands of Salamis, Aegina and Poros (Fig. 1a, b), is fragmented by active seismic zones that is considered to have caused footwall uplift and hanging wall subsidence during their successive activations throughout the Upper Holocene (Fig. 2). Sea level changes that occurred in specific coastal locations of these areas are mainly attributed to paroxysmal subsidence episodes connected with strong earthquakes (Scranton et al., 1978;Papanastassiou and Gaki-Papanastassiou, 1993;Noller et al., 1997;Nixon et al., 2009;Dao, 2011;Papanikolaou and Roberts, 2011). ...
... Twenty kilometres south, on the Peloponnesian coast of the Saronic Gulf, in the bay of Korphos (Fig. 1b), Nixon et al. (2009) examined and correlated tidal notches with foraminifera/thecamoebians fossil assemblages found in sediment cores drilled in the salt marsh nearby the village of Korphos and so they produced a sea level curve. They argue that much of 4 m rise in relative sea level occurred at Korphos in the last 5500 years during five distinct tectonic phases of subsidence that formed the sea levels of À2.94 m around 5100 BP, À1.74 m~4400 BP, À1.34 m~2650 BP, À0.88 m 1600 BP, and the approximate present level~400 BP. ...
... These conclusions appears to be in flat contradiction to the findings of Nixon et al. (2009), who reported the presence of five tidal notches up to the depth of 2.94 ± 0.16 m along the rocky limestone coast south of the salt-marsh of Korfos, giving a maximum age of 5000 BP to the deepest of them. The systematic underwater survey, however, revealed the existence of a tidal notch clearly formed at a depth of 0.40 m that goes all along the coast and a wave cut platform with relatively rough surface, 5.0 me8.0 m wide, which is formed at a depth of 2.70 me3.50 m. ...
Article
Along the Peloponnesian coast of the Saronic Gulf and on the coast of Aegina and Poros islands, submerged coastal geomorphological features related directly with submerged ancient coastal constructions, indicate three distinct sea levels. Submerged tidal notches incised on the carbonate basement, beachrocks formed in the intertidal zone and archaeological indicators, such as the ancient harbour installations in Kenchreai and Epidaurus and on Aegina island, the extended coastal buildings and constructions in Agios Vlasis, Psifta and Palaiokastro-Methana, and Vagionia on Poros island, are used to determine the age and magnitude of submersion and the extent of the Upper Holocene marine transgression. By the correlation of geomorphological, historical and archaeological indications three distinct sea levels were identified, at −3.30 ± 0.15 m, −0.90 ± 0.15 m and −0.55 ± 0.05 m. Initial change in sea level occurred definitely after AD 400 ± 100. The intermediate change is dated between AD 1586 and 1839, and the most recent change after 1839. Sea transgression followed a long period of sea level stability, which lasted at least 2200 years, from the Middle Bronze Age to the Late Roman period.
... Models incorporating predictions for eustatic and isostatic changes of the sea level change point out that the sea level rose up to 130 m since the last 20K yrs and up to 6 m over the last 6K yrs (Lambeck and Purcell, 2005). However, underwater archaeological data found at sites around the Argolid penisnsula (Methana, Epidauros, Tolo, Flemming et al., 1971;Porto-Heli, Pavlopoulos et al., 2012), data from sediments and beackrock formations from the northern part of Argolid peninsula (Korphos bay, Nixon et al., 2009;Kalamianos bay, Dao, 2011) and data from geomorphological, historical and archaeological indications along the Peloponnesian coast of the Saronic Gulf and on the coast of Aegina and Poros islands (Kolaiti and Mourtzas, 2016) suggest that the total area is under subsidence at least during the Holocene (Fig. 2). Based on previous studies, the estimations of the subsidence rate ranges between 1.0 and 1.5 mm/yr (Flemming, 1978), between 0.6 and 1.3 mm/yr (Lambeck, 1995) and between 0.3 and 0.7 mm/yr (Pavlopoulos et al., 2012). ...
... Based on previous studies, the estimations of the subsidence rate ranges between 1.0 and 1.5 mm/yr (Flemming, 1978), between 0.6 and 1.3 mm/yr (Lambeck, 1995) and between 0.3 and 0.7 mm/yr (Pavlopoulos et al., 2012). Furthermore, the datasets from Korphos bay (Nixon et al., 2009) and along the western coast of the Saronic Gulf (Kolaiti and Mourtzas, 2016) suggest that the sea level rise was not gradual but conducted in jumps related to tectonic activity though the absolute age of the sea level stands is not similar between the studies. ...
... The 210 Pb analyses suggest an average sedimentation rate for the two cores of 0.05 cm/yr (Fig. 8). This finding is comparable with the sedimentation rate estimated for the nearshore zone of the Northern Argolid peninsula from previous studies ranging between 0.06 and 0.05 cm/yr (based on estimations from the Table 2, provided by Nixon et al. (2009)). Low sedimentation rate (0.01 cm/yr) has been also estimated for the Myrtoon basin located south of the surveying area (Geraga et al., 2000). ...
Article
Full-text available
A marine geoarcheological survey was conducted at the southwestern end of the Argosaronic gulf in Greece, an area of archaeological importance. The survey was initiated by the discovery of a Late Bronze Age (LBA) shipwreck off Modi Islet. The survey which employed echo-sounding, sub-bottom profiling, side scan sonar systems and sediment coring extended to the area between Poros Island, Modi Islet and Argolid peninsula, aiming to evaluate the changes of the coastal zone extent in the past. The evolution of the palaeo-shoreline over the last 20 ka is proposed based on the interpretation of the acquired bathymetric and seismic records, the estimation of the thickness of the marine sediments and the examination of existing datasets of the relative sea level changes in the area.
... As a result, detailed mapping of paleo-sea-level markers has been often used as a tool to quantify coastal uplift and RSL changes. Greece has always been a major focus of RSL studies: many authors reported on ancient RSL in the southern Aegean (Kontogianni et al., 2002;Pirazzoli, 2005;Gaki-Papanastassiou et al.;Stiros et al., 2009), in the eastern and western central sectors (Pirazzoli et al., 1999;Stiros et al., 2000;Desruelles et al., 2009;Nixon et al., 2009Evelpidou et al., 20112012) as well as in northwestern Aegean (Pavlopoulos et al., 2007;Ghilardi et al., 2008a,b;Cundy et al., 2010;Pavlopoulos et al., 2010). In contrast, few data are presently available on the northeastern sector of the Aegean Sea, which is a tectonically active area strongly controlled by the North Anatolian Fault (Koral et al., 2009;Erginal et al., 2010). ...
... Issues about the use of beachrocks as precise sea-level indicators were also raised by Knight (2007) and Vött et al. (2010). However, several studies carried out in the Aegean Sea pointed out the importance of beachrocks as sea level indicator (Desruelles et al., 2004;Fouache et al., 2005;Pavlopoulos et al., 2007;Desruelles et al., 2009;Evelpidou et al., 2011) especially if coupled with other morphological and biological proxies (Neumeier et al., 2000;Nixon et al., 2009). For this reason, we followed the robust methodology proposed by Desruelles et al. (2009) to analyze this marker: 10 beachrocks were sampled in their front (seaward) and end (landward) slabs, and thin sections were cut in order to perform petrographic (polarizing and scanning electron microscope) and microstratigraphic analyses. ...
... These estimations in subsidence rates agree with the deductions made in the present study. Furthermore, relative sea level rise up to 3,2-3,8 m over the last 4000 years has been depicted by studies on the most ancient of the submerged harbor installations found in Aegina Island (Saronikos Gulf; Knoblauch, 1972, Mourtzas & Kolaiti, 2013) and a rise of the sea level up to 4 m over the last 5500 years has been suggested for the NE Peloponnesus (Korfos bay; Nixon et al., 2009). The results of all the above studies indicate that the submergence rates in these areas are larger than that predicted by glaciohydro-isostatic factors (LambecK and Purcell, 2005). ...
... The results of all the above studies indicate that the submergence rates in these areas are larger than that predicted by glaciohydro-isostatic factors (LambecK and Purcell, 2005). In addition most of the above studies showed that the subsidence was not gradual but achieved through repetitive subsidence events, potentially of seismic origin (Desruelles et al., 2009, Nixon et al., 2009, Mourtzas & Kolaiti 2013, Evelpidou et al., 2014. At least for the recent submergence in Cyclades Evelpidou et al (2012) provided evidence that this might be an effect of the 1956 Amorgos earthquake. ...
Article
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The present study presents the results of the preliminary marine geophysical survey conducted in 2006 at the gulf of Sounion, southern Attica, Greece. The site is of great archaeological importance since cape Sounion served as a navigational landmark and a naval fortress protecting the sea-lanes towards the metropolis of Athens and the silver mines of Lavreotiki during the Classical and Hellenistic periods. Parts of the coastal ancient installations are now submerged. The results of the collected geophysical data include the examination of the seafloor texture and stratigraphy. Therefore a geomorphological map of the gulf was constructed based on the configuration of the substrate and the seafloor stratigraphy. Archaeological remains lying on the seafloor have been detected on the sonographs and have been correlated with the results of previous studies. The development and the evolution of the gulf during the prehistoric period were evaluated via the sea floor stratigraphy and the prediction of sea level change in the area based on the eustatic and glacio-hydro-isostatic response. The sea level change during the historic period was examined and a relative sea level rise of at least 2,5-3,0 m was suggested for the last 2500 years based on the marine geophysical survey results.
... Ancient harbour basins contain important sediment archives of palaeoenvironmental change and human activities and have become a major focus of geoarchaeological studies in the Mediterranean (Marriner et al., 2007. Multi-disciplinary geoarchaeological studies of harbour sediment have yielded important insights into ancient harbour technology (Reinhardt and Raban, 1999;Boyce et al., 2004Boyce et al., , 2009Marriner et al., 2014;Riddick, 2021), palaeoecology and stratigraphy (Morhange et al., 2003;Reinhardt et al., 2003), sea level change (Morhange et al., 2001;Goodman et al., 2008;Nixon et al., 2009;Riddick, 2021), and longterm records of human modification of natural coastal systems (Marriner at al., 2007(Marriner at al., , 2014Goodman et al., 2009;Riddick, 2021). Harbours can also preserve records of coastal neotectonics, as documented by the uplift or subsidence of harbour structures (Nixon et al., 2009;Stiros and Blackman, 2014;Stiros, 2020), and evidence for earthquake damage and palaeotsunami impacts on coastlines (Reinhardt et al., 1999(Reinhardt et al., , 2006Hadler et al., 2013Hadler et al., , 2015. ...
... Multi-disciplinary geoarchaeological studies of harbour sediment have yielded important insights into ancient harbour technology (Reinhardt and Raban, 1999;Boyce et al., 2004Boyce et al., , 2009Marriner et al., 2014;Riddick, 2021), palaeoecology and stratigraphy (Morhange et al., 2003;Reinhardt et al., 2003), sea level change (Morhange et al., 2001;Goodman et al., 2008;Nixon et al., 2009;Riddick, 2021), and longterm records of human modification of natural coastal systems (Marriner at al., 2007(Marriner at al., , 2014Goodman et al., 2009;Riddick, 2021). Harbours can also preserve records of coastal neotectonics, as documented by the uplift or subsidence of harbour structures (Nixon et al., 2009;Stiros and Blackman, 2014;Stiros, 2020), and evidence for earthquake damage and palaeotsunami impacts on coastlines (Reinhardt et al., 1999(Reinhardt et al., , 2006Hadler et al., 2013Hadler et al., , 2015. Several recent studies have emphasized the importance of earthquakes and tsunamis in the destruction of ancient harbours and coastal settlements in the eastern Mediterranean (Marriner and Morhange, 2007;Hadler et al., 2013Hadler et al., , 2015Goodman-Tchernov and Austin, 2015). ...
Article
Lechaion's inner harbour basin was constructed in the 7th-6th c. BCE and served as Corinth's principal port for over a millennium. The harbour decline and abandonment in the 6th c. CE has been attributed to several causes: natural siltation, co-seismic uplift, coastal subsidence, and damage by tsunami impacts. A multi-proxy palaeoenvironmental study was conducted on seven cores from Lechaion's inner harbour to determine changes in the coastal environments and timing and cause of harbour abandonment. Palaeoenvironments were reconstructed using high-resolution micro-XRF core scanning of sedimentary facies, isotopic (δ¹⁸O, δ¹³C), and micropalaeontological analyses (foraminifera, palynomorphs). The harbour lithostratigraphy consists of an uppermost (∼1 m) sequence of laminated mud and marl overlying interbedded pebbly sand and mud containing abundant marine microfossils and Roman pottery refuse. A thin (<12 cm) calcrete layer at the base of the marl defines a basin-wide paraconformity, marking a transition from a marine-estuarine harbour basin to a restricted, evaporitic lake. Basin restriction is recorded by a sharp decline in terrigenous elements (Si, Ti, K, Fe), increased Sr, δ¹⁸O, a decline in foraminifera and marine dinoflagellate cysts, and an increase in freshwater algae. The event is constrained by AMS ¹⁴C age modelling to the 6th c. CE and interpreted as rapid, co-seismic uplift of the harbour floor, most likely during destructive earthquakes of 524 and 551/552 CE. These seismic events have been linked to a ∼1.1 m uplift of the nearby Perachora Peninsula and sediment liquefaction structures on-site. No evidence was found for 2nd c. BCE or 6th c. CE tsunami events proposed in previous work. This study represents the most comprehensive geoarchaeological study completed to date in Lechaion's inner harbour and confirms its destruction and abandonment in the 6th c. CE as a result of co-seismic uplift and rapid shoaling of the inner basin.
... Local relative sea level (RSL) reconstructions have been performed using a wide range of sea level indicators such as micropaleontology (e.g. salt marsh foraminifera and thecamoebians, Gehrels, 1999;Scott and Medioli, 1978;Scott et al., 2001), abrasion and tidal notches (e.g., Nixon et al., 2009;Evelpidou et al., 2012aEvelpidou et al., , 2012bEvelpidou et al., , 2012cMarriner et al., 2014), beachrocks (Vousdoukas et al., 2007;Desruelles et al., 2009;Mauz et al., 2015), benches and shore platforms (Rovere et al., 2011;Vacchi et al., 2012;Mastronuzzi et al., 2014), archeological features (Sivan et al., 2001;Marriner and Morhange, 2007;Goodman et al., 2009), or marsh and peat deposits (Cronin et al., 2007;Engelhart and Horton, 2012;Engelhart et al., 2015). The smaller the range of vertical error and the more accurately the marker can be dated, the better the sea level marker. ...
... The notch itself is semi-indicative of the tidal regime as its shape and dimensions have some association to the maximum and minimum tidal positions with the central dimensions typically correspond to mean sea level (Evelpidou et al., 2012a, Fig. 1), though recent observations also indicate that the notch can also exceed those limits ; also see response by; Evelpidou and Pirazzoli, 2015). Rapid changes, either due to sea level change or vertical displacement, can lead to the preservation of these features, making them useful earthquake or sea level indicators (Neumann, 1966;Pirazzoli, 1986;Neumann and Hearty, 1996;Rust and Kershaw, 2000;Kershaw and Guo, 2001;Benac et al., 2004;Nixon et al., 2009;Vacchi et al., 2013). ...
Article
The study presented here reports on erosional notches, pits, and potholes observed at present sea level and submerged at a series of sites along the southern Levantine coastline. For such submerged features to be formed and preserved, there must be a period of relative sea level stagnation, followed by drowning. This process can occur in response to sea level change, tectonic or isostatic offsets. The specific coastline hosting these features is not considered tectonically or isostatically affected, and therefore, for much of the Mediterranean, is viewed as a eustatic sea level reference point. While similar features have been observed elsewhere in the eastern Mediterranean, confining their ages has been difficult due to the much older ages of the host rocks, in many cases encompassing multiple glacial cycles. Here, for the first time they are located in relatively young host rock (<65,000 years) confining their production age to the most recent glacial cycle. These features might suggest that a step-like, more punctuated process of sea-level rise occurred along this coastline, providing a window into what might be expected in the future as warming trends continue and the sea level responds.
... Tidal notches can provide valuable information on past sea level positions or they can allow the identification of palaeoseismic events (e.g. Pirazzoli et al., 1994;Nixon et al., 2009;Stiros et al., 2000Stiros et al., , 2009Evelpidou et al., 2012a, b, c). In microtidal areas sheltered from wave action, elevated or submerged (tidal) notches are used to indicate former sea-level positions, with up to decimeter confidence. ...
... Such underwater observations have been devoted most of the time to the measurement and interpretation of a single submerged tidal notch (e.g. Fouache et al., 2000;Benac et al., 2004;Nixon et al., 2009). ...
... While overall the Corinthia has undergone tilting such that the Corinthian Gulf has experienced uplift and the Saronic Gulf has experienced subsidence, there are multiple incidences of these tectonic shifts that can have profound effects at the local level, especially in shallow and low-lying coastal waters as seen in the Kalamianos and Korphos region. Locally significant tectonic activity has been documented for the Korphos and Kalamianos region through the coring of wetlands, examination of beach rock formations and submerged tidal notches, and mapping of tectonic faults (Rothaus et al. 2003: 44-45;Nixon et al. 2009). ...
... Subsequent geological studies, as mentioned above, suggested that Korphos Bay was probably a marsh in the Bronze Age, not suitable as a harbor, and confirmed that indeed Cape Trelli had seen substantial changes since the Bronze Age. Of particular importance was the discovery of three levels of submerged beachrock containing great quantities of ceramics; the ceramics from the lowest level of submerged beachrock (-5.9 m) were clearly of Early Helladic/Early Bronze Age date (Rothaus et al. 2003;Nixon et al. 2009). ...
Article
In the late fourteenth century bc of the Aegean Late Bronze Age (LBA), a large walled settlement was established at Korphos: Kalamianos, on the Saronic Gulf coast of the Corinthia, Greece. Archaeological and geological work by the Saronic harbors Archaeological Research Project has succeeded in reconstructing the LBA coastline and likely harbor basins, as well as documenting the well-preserved plan of an entire Late Helladic town. Kalamianos was a short-lived maritime outpost, purposely founded as a component of state expansion in a climate of intense peer-polity competition in LBA (fifteenth–thirteenth centuries bc) Greece.
... Tidal notches are usually formed in limestone cliffs in the mid-littoral zone, are well known as precise sea-level indicators (Pirazzoli, 1986(Pirazzoli, , 1996(Pirazzoli, , 2005 and they can attest to the modality of sea level change (rapid or slow) allowing to identify palaeoseismic events (e.g. Benac et al., 2004Benac et al., , 2008Nixon et al., 2009;Evelpidou et al., 2011aEvelpidou et al., , 2012aStiros and Blackman, 2014;Trenhaile, 2015;Boulton and Stewart, 2015;Mourtzas et al., 2016). ...
... Information can only derive from assumptions on the rates of intertidal undercutting (Evelpidou et al., 2012b). However, tidal notches may be relatively dated from nearby coastal drillings (Evelpidou and Pirazzoli, 2015); for example Nixon et al. (2009) identified and dated transgression events by correlating saltmarsh cores with tidal notches in the area of Korphos. Marriner et al. (2014) also correlated salt-marsh cores with a tidal notch in the Adriatic Sea. ...
Article
A coastal and submarine geomorphological investigation took place in the coasts of eastern Attica, aiming to identify palaeoshorelines. Former sea-level positions were deduced from emerged and submerged tidal notches. Eight fossil shorelines were deduced in the study area; two emerged ones at about +24 ± 30 and +40 ± 30 cm, and six submerged ones at about −22 ± 30 (modern), −40 ± 30, −60 ± 30, −80 ± 30, −130 ± 30 and −460 ± 30 cm. It is worth mentioning that a rather different tectonic behavior may be distinguished between the south (AT1-AT5) and the north (AT10-AT28) part of the study area.
... The thinning landward, i.e. southeastward, architecture of the coarse-grained unit in the upper part of cores LEF 40, 41 and 42 (Fig. 9), its grain size composition and normally graded sequences (Fig. 8) clearly document water inundation and deposition of beach material into the back-beach area. Moreover, sedimentary findings prove a successive deposition of sediment due to decreasing flow velocities and indicate the event-induced formation of the deposit (Hawkes et al., 2007;Nichols, 2009). Turbulent flow conditions during the event and related erosion of the underlying unit are documented by the increased sand content within the lowermost sedimentary sub-unit of the sequence. ...
... Although no information is available to what extent tectonic controls contributed to the evolution of the barrier system, their influence must be considered. However, co-seismic uplift and/or subsidence may lead to enduring changes of the coastal system (Nixon et al., 2009;Wong, 2009) and are often accompanied by the occurrence of tsunami waves (Altinok et al., 2001;Cisternas et al., 2005;Meltzner et al., 2006). ...
Article
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The Lefkada-Preveza coastal zone, NW Greece, is characterised by an active barrier system and related extensive beachrock sequences. Besides the gradual coastal processes of longshore drift and spit evolution, the presence of active tectonics and the occurrence of tsunamis have been documented in previous studies and are part of the coastal geomorphological system. In this paper, we present the results of detailed multiproxy sedimentological and geomorphological investigations carried out along the northern part of the barrier system and in back-beach positions. Our findings suggest that extreme wave events contributed to coastal and environmental changes and involved temporary breakdown of the barrier system. Sedimentary findings suggest that one generation of event deposits may be related to the 365 AD Crete earthquake and associated tsunami. According to our results, the Lefkada coastal system formed by the interaction of both long-term, gradual and sudden, impulsive littoral geomorphodynamics. Extreme wave events are assumed to have played a significant role in the evolution of the present coastline, acting as recurrent impulsive disturbances of the coastal system. Subsequently, the onset of long-term gradual coastal processes, such as longshore drift, re-established a state of natural coastal balance by re-arranging the coastal sediments. (C) 2011 Elsevier B.V. All rights reserved.
... In tectonically active coastal areas, abrupt relative sea-level changes take place before, during and after earthquake events [35][36][37][38][39][40]. When the origin of vertical displacements is co-seismic, they are generally related to earthquakes with magnitude larger than 6.0, often associated with morphogenic faults, and therefore result in direct surface faulting [41]. ...
... The value of tidal notches for coastal tectonics is often expressed in the literature, especially in the Eastern Mediterranean [15,29,37,[42][43][44][45][46][47][48][49]. In particular, notches, mainly tidal, are often used to deduce relative sea level changes for the late Pleistocene [50] and Holocene [51] and for elucidating vertical tectonic displacements [35,52]. ...
Article
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On 30th October 2020, the eastern Aegean Sea was shaken by a Mw = 7.0 earthquake. The epicenter was located near the northern coasts of Samos island. This tectonic event produced an uplift of the whole island as well as several cases of infrastructure damage, while a small tsunami followed the mainshock. Underwater and coastal geological, geomorphological, biological observations and measurements were performed at the entire coast revealing a complex character for the uplift. At the northwestern part of the island, maximum vertical displacements of +35 ± 5 cm were recorded at the northwestern tip, at Agios Isidoros. Conversely, the southeastern part was known for its subsidence through submerged archaeological remains and former sea level standstills. The 2020 underwater survey unveiled uplifted but still drowned sea level indicators. The vertical displacement at the south and southeastern part ranges between +23 ± 5 and +8 ± 5 cm suggesting a gradual fading of the uplift towards the east. The crucial value of tidal notches, as markers of co-seismic events, was validated from the outcome of this study. The co-seismic response of Samos coastal zone to the 30th October earthquake provides a basis for understanding the complex tectonics of this area.
... In tectonically active coastal areas sudden relative sea-level changes occur before, during and after earthquake events (Hawkes et al., 2005;Shennan and Hamilton, 2006;Nixon et al., 2009). Relicts of former sea-level stands, such as raised or submerged notches, benches, beachrocks, caves, provide valuable data for detecting relative sea-level changes. ...
Article
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Detailed mapping along the coasts of Skyros Island (Aegean Sea) provided new evidence concerning the rates and the modality of subsidence in the area. The results are provided through the study of the shape and the dimensions of the two submerged notches detected around the carbonate coasts of the island.It is apparent that the island has been submerged not only due to the global sea-level rise during the last two centuries (1.8 ± 0.3 mm/year between 1950 and 2000), but also because of tectonic events testified by the type of the submerged notches. Some of these tectonic events seem to be of gradual and some of co-seismic origin. The transition of MSL from the retreat point of the lower notch to the retreat point of the upper notch seems to have been produced by co-seismic subsidence of about 55 cm at slightly less than 850 years BP.
... Evidence of fault motion could be expressed in the geomorphology, surface sediments and shallow stratigraphy of this environment as follows: 1) geomorphologic change that includes formation of open water areas and expansion of water bodies into unique geometries within the marsh interior (White and Morton, 1997;Gagliano et al., 2003;Nichol et al., 2007); 2) quantifiable changes or patterns in fluvial geomorphology, including variations of river and distributary planforms, channel sinuosity, and gradients (Burnett and Schumm, 1983;Maroukian et al., 2008); 3) localized and accelerated wetland loss and rates of subsidence (Morton et al., 2002;Shinkle and Dokka, 2004); 4) quantifiable lateral discontinuities near fault surface traces in sediment accumulation rates over small spatial scales; and 5) subsurface indicators including lateral chronostratigraphic offsets of dated facies, and/or lithostratigraphic or biostratigraphic offsets of facies or fossil assemblages over short distances (400 m), and/or high-resolution seismic reflectors that display deformation in the form of offsets, unique terminations, and abrupt changes of reflector orientations and trends (e.g., Bourgeois and Johnson, 2001;Hayward et al., 2004;Ferranti et al., 2008;Nixon et al., 2009). Other studies focused on the geomorphology and stratigraphy of coastal Louisiana have noted similar physical relationships with fault motion (e.g., Holbrook and Schumm, 1999;Dokka et al., 2006;Morton et al., 2006). ...
Article
Neotectonic processes influence marsh accretion in the lower Pearl River valley. Active growth faults are suggested by groupings of ponded river channel sections, transverse and linear river channel sections, and down- and across-valley contrasts in channel sinuosity. Seismic profiles identified several likely, fault-induced structural anomalies, two of which parallel the axes of surface distributary networks. Lithostratigraphy and biostratigraphy of six cores from across a suspected fault in the West Middle River, combined with 14C-based age control, yielded evidence of vertical offsets, indicating that this river section is on the plane of a growth fault. These data were used to estimate fault slip rates over two time intervals, 1.2 mm/y over the last 1300 yr, and 0.2 mm yr− 1 over the last 3700 yr, and delineated a sinusoidal pattern of deformation moving distally from the fault, which we interpret as resulting from fault-propagation folding. Higher rates of sediment accumulation (of the order of cm yr− 1 from 210Pbxs and 137Cs activity data) on the down-thrown side are consistent with sedimentary response to increased accommodation space, and mass-based sediment accumulation rates (g cm− 2 yr− 1) exhibit a pattern inverse of that shown by fault-driven sinusoidal deformation. We contend that near-surface growth faults are critically important to driving accretion rates and marsh response to sea-level rise.
... Its height (99 cm), much larger than the tidal range, suggests a gradual relative sea level rise at a rate smaller than the local bioerosion rate (Fig. 10 ), which could also be ascribed to recent tectonic movements of the wider area. According to the date AD 1482–1952 obtained from a peat sample at about − 33 cm at the neighboring area of Korphos (Nixon et al., 2009), the upper part of the notch profile was still developing at that time. Part of the submergence of this notch may be ascribed to the recent rapid sea level rise. ...
Article
In this paper, after a short summary on the processes and rates of bioerosion that contribute to the deepening of a tidal-notch profile, some Mediterranean case-studies are presented, where a tidal notch is prevented either from forming or from being preserved. Furthermore, as shown also in a complementary paper, the recent global sea-level rise is preventing the development of new tidal notches in the present mid-littoral zone. This very useful sea-level indicator, of past temporary standstills of the relative sea level in carbonate rock areas, is of great value in assisting interpretations of relative sea-level change in locations where it is preserved. The possibilities of absence of formation or of preservation, however, imply that it should be interpreted carefully before reconstructing local relative sea-level histories. In particular, the lack of fossil tidal notches cannot be relied upon to interpret the absence of past periods of relative sea-level stabilization.
... Our investigation of submerged tidal notches builds on prior studies in the Mediterranean area, especially from the Adriatic and Aegean coasts (e.g. Pirazzoli, 1980; Fouache et al., 2000; Faivre and Fouache, 2003; Antonioli et al., 2004; Benac et al., 2004 Benac et al., , 2008 Nixon et al., 2009; Evelpidou et al., 2011a, b; Furlani et al., 2011). In cases where the absence of the present-day tidal notch has been noted by observers in certain places, it has generally been ascribed to gradual tectonic subsidence. ...
Article
The recent rise in global sea level is causing the disappearance of an important geomorphological sea-level indicator, the tidal notch.Tidal notches have often been used in carbonate coasts for Quaternary and late Holocene sea-level reconstructions and estimation of tectonic movements, especially in uplifting areas. In this paper, we review the rates of tidal notch development, and examine the recent gradual depletion of this feature, during at least the last century, and its relation to the increasing rates of sea-level rise. Some examples of tidal notch development are provided with fossil submerged notches from Greece. Although tidal notches are no longer forming in the present-day mid-littoral zone, underwater marks on carbonate cliffs may still provide evidence of submerged tidal notches corresponding to former sea-level positions, or of recent vertical shoreline displacements of seismic origin.
... Previous recent literature on submerged notches includes several studies (e.g.: Laborel et al., 1999;Fouache et al., 2000;Antonioli et al., 2004;Benac et al., 2004;Faivre et al., 2011;Furlani et al., 2011;Nixon et al., 2009;Evelpidou et al., 2012b), however the case studies considered are generally limited to a single submerged notch, while this new approach consists in extending the investigation to series of superimposed submerged tidal notches, like previous work by Collina-Girard (1999, 2002 was extending it to series of erosion shorelines. ...
... This historic seismicity record provides the notion that beyond any doubt the Kenchreai harbor affected by a series of earthquakes, however, before we correlate the harbor submergence with these earthquakes it is critical to take into account the sea level changes in the Saronikos Gulf. Regarding the Saronikos Gulf there are three different curves of sea level rise represented in Fig. 2. The curves proposed by Lambeck and Purcell (2005) and Nixon et al. (2009), provide evidence for coseismic subsidence in the study area (Table 1). In contrast Kolaiti and Mourtzas, (2016) provided strong arguments for a new curve based on detailed mapping of submerged ancient buildings and ports from a large part of the Saronikos Gulf and showed that the sea level rise in the study area explains the drowning of the south mole of the Kenchreai harbor without any co-seismic subsidence ( Fig. 2 and Table 1). ...
Article
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The Gulf of Corinth in Greece and especially its southeastern part is dominated by a series of step - like north facing normal faults hosting strong earthquake events. The Kenchreai fault zone, located along the Gulf's southeastern coast, is a key fault for analyzing how a north facing fault accommodates N - S extension in the back - arc region. This fault is selected as a well known fault that triggered devastating earthquakes, resulting in the subsidence of its homonymous harbor, operating since antiquity. Despite the spectacular scarp of the Kenchreai fault, which controls the morphological characteristics of the region, our knowledge for fault's earthquake history comes only from historical data. The application of paleoseismological techniques and morphotectonic analysis, offer us the opportunity to investigate the characteristics of past seismic events along this fault trace. Trench excavation in the hanginwall block of the Kenchreai fault sheds light on three past events. The recurrence interval of these events is not systematic and ranges between 5000 and 1000 years, showing shorter intervals in the last 2000 years. Furthermore, the maximum earthquake magnitude, based on empirical relationships, is estimated on the order of 6.3, whereas the slip rate of the fault is on the order of 0.25mm/yr, corresponding to the slip rate of other major fault structures in the area related with similar earthquakes.
... According to Scranton et al. (1978), in the bay of Kenchreai, the Roman port installations were submerged gradually by 2.30 m during three co-seismic subsidence events. Nixon et al. (2009) argue that the sea level has risen by 2.94 m in the last 5000 years southwards along the west coast of the Saronic Gulf in the bay of Korfos. This submersion, which occurred during five distinct tectonic phases of subsidence, produced a sea level of −1.20 m 4000 yr BP, −0.80 m 2350 yr BP, −0.34 m 1350 yr BP, and the approximate present level of 400 yr BP. ...
Article
The extensive ancient harbor installations — today submerged — on the seafront of Kolona in Aegina are associated with the great trading and maritime development of the island from the Middle Bronze Age to the Middle Classical period. Based on geomorphological and archeological indications, three distinct relative sea levels can be defined at depths of 3.17 ± 0.05 m, 0.97 ± 0.05 m and 0.52 ± 0.05 m. The dating of the sea level changes based on archeological evidence and historical sources shows that the initial sea level change in Aegina occurred certainly after AD 170 and most likely after AD 250. The intermediate change is dated between AD 1586 and AD 1839, and the most recent change occurred between 1839 and 1999. A transgression followed a long period of sea level stability that lasted at least 2200 years, from the Middle Bronze Age (ca. 3900 yr BP) to the Late Roman period (ca. 1700 yr BP). According to the paleogeographical reconstruction of the coast, the ancient harbor installations stretch along 1600 m of coastline. The north harbor is bounded by the north breakwater, the riprap on the once wide sandy coast, the detached west breakwater, and the uplift morphology of the west end of Kolona Hill. On the south coast, the harbor installations comprise the fortified “closed harbor” with the shipsheds, the commercial harbor, which is entirely destroyed by the modern port, the anchorage area that is bounded by the west breakwater and built of cone-shaped piles of stones, the tops of which once projected above the sea level, and the south curved breakwater at its southernmost boundary.
... Samples with organic-walled or otherwise delicate individuals were counted wet, and the remainder were dried and floted (for methods, see FISHBEIN and PATTERSON, 1993;SCOTT and MEDIOLI, 1986). Identifications and environmental constraints of particular foraminifera and assemblages were determined based on major regional references (CIMMERMAN and LANGER, 1991;HOTTINGER et al., 1993;MURRAY, 1991) and site-specific references (e.g., AVSAR and ERGIN, 2001;HYAMS, ALMOGI-LABIN, and BENJAMINI, 2002;NIXON, 2001). Species not recognized in those references were described as species A, B, C, and so on. ...
Article
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This study addresses the paleogeographic coastal evolution of the coastal plain in the environs of Iskele, Turkey. Eight sediment cores were collected along a north-south and east-west transect and analyzed to determine whether the coastal environment had changed in the recent past. The results illustrate that the coastal environment consisted of a transgressive systems tract, ending approximately 6000 BP and represented by marine transgression, flooding of incised river channels, and marsh development, followed by a high stand systems tract. Five major environmental facies were identified: terrestrial, wetland, lagoon, foreshore, and upper shoreface. The high stand systems tract was characterized by the development of a beach-barrier consecutive series of longshore transport-derived sandbars. These sandbars contributed to the creation and eventual isolation and terrestrial infilling of nearshore lagoons and wetlands. Sea-level indicators indicate rapid sea-level rise reaching a peak approximately 6000 YBP, followed by deceleration of sea-level rise and resulting shoreline progradation. The construction of a causeway connecting Karantina Island to the mainland approximately 2400 years ago has accelerated the process of progradation east of the causeway by decreasing the wave energy. Sediment that would have previously been transported further east is now deposited in the zone immediately east of the causeway.
... Given that most previous studies on wave-cut notches report findings from micro-tidal, moderate-energy areas like the Mediterranean Sea (Andriani and Walsh, 2007;Benac, Juracic and Bakran-Petricioli, 2004;De Waele, Mucedda and Montanaro, 2009;Kershaw and Guo, 2001;Nixon, Reinhardt and Rothaus, 2009), several existing terms and definitions had to be adapted to the conditions of the meso-tidal, high-energy Algarve coast. For example, Pirazzoli (1986) considered ripple and W notches to be shapes resulting from changes in the relative elevation of the MSL and the cliff. ...
Article
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Marine notches are undercut or groove forms, developing in vertical cliff profiles due to sea corrosion. The present contribution aims to study the spatial distribution and characteristics of notches on the Algarve rocky coast, combining in situ observations, rock sampling, laboratory analyses of chemical resistance and along-shore wave-power flux estimations. A total of 244 tidal notches was identified in 169 cliff profiles, along a 28-km coastal stretch. Tidal notches were more common in sheltered cliffs, while surf notches prevailed in exposed and moderately exposed areas. 58% of the tidal notches were U-shaped, and were linked to energetic wave conditions, which also favoured the formation of single notches. 40% of all tidal notches were V-shaped, mostly found on sheltered sections of the coast. The W combination was found to be dominant, being more common in sheltered cliff sides, while combinations of surf notches appeared in 84% of all cases, linked to increased wave action. The spatial distribution of tidal notches appeared to follow vertical variation of chemical resistance; however, that trend was weaker for the most energetic sections of the coastline, where wave forcing appeared to dominate. Similarly, the effect of chemical resistance was less prominent for abrasion notches; while, for notches forming above abrasion platforms, CaCO3 absorption from fresh water was also an acting mechanism.
... 8. Nixon, Reinhardt, and Rothaus 2009. 9. Rothaus et al. 2003Nixon, Reinhardt, andRothaus 2009. 10. ...
Article
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This article describes the initial phase of investigations at Kalamianos, a recently discovered Mycenaean coastal settlement on the Saronic Gulf in the southeastern Corinthia. To date 50 buildings and 120 rooms of Late Helladic IIIB date have been identified at the site, which is unique for the excellent preservation of aboveground architectural remains. Beyond the site is another large Mycenaean architectural complex, as well as small fortified enclosures and terrace walls also dating to the Bronze Age. The evidence indicates that Kalamianos was a significant center of Mycenaean activity in the 13th century b.c., and possibly served as Mycenae’s principal harbor on the Saronic Gulf.
... In the last decades, foraminiferal studies have been performed in several Holocene Aegean coastal plains and coastal lagoons (Scott et al., 1979;Tassos, 1983;Triantaphyllou et al., 2003Triantaphyllou et al., , 2010Pavlopoulos et al., 2007Pavlopoulos et al., , 2010Nixon et al., 2009;Theodorakopoulou et al., 2009;Evelpidou et al., 2010;Goiran et al., 2011) providing numerous, albeit scattered paleoenvironmental information. This study investigates the foraminiferal composition of Late Holocene sedimentary successions from boreholes drilled in three coastal areas of the Aegean Sea (Alykes Kitros, Lafrouda Thrace and Vravron Attica), which are practically featured by tectonic stability. ...
Article
Benthic foraminiferal composition of sedimentary successions during the last 7500 years, was investigated from boreholes drilled in three rather tectonically stable coastal areas of the Aegean Sea (Alykes Kitros, Lafrouda Thrace and Vravron Attica). The quantitative analysis of foraminiferal fauna enabled separation into two different groups that are supported by the analysis of modern benthic foraminiferal communities in the studied sites. Group A consists of Ammonia tepida and Haynesina germanica (closed lagoon assemblage), whereas the most common species of Group B (open lagoon assemblage) are Aubignyna perlucida, miliolids, Elphidium spp. and Ammonia spp. The foraminiferal composition integrated with radiometric dating provides information on Holocene paleoenvironmental changes in the studied coastal plains, related to seaeland interaction. Alykes Kitros and Lafrouda Thrace boreholes show a similar trend, with an open lagoonal fauna in the lower part, transitional upwards to closed lagoonal conditions. This environmental change has taken place after 6500 cal BP in Alykes Kitros and around 3000 cal BP at Lafrouda Thrace. The benthic communities of Vravron Attica borehole sediments seem to represent continuously an open lagoon/shallow marine environment from 4700 to 400 cal BP.
... With reference to our present study, it is postulated that the rapid sea-level change episode that submerged the Croatian notch will generate a well-defined sedimentary signature in clastic-coast stratigraphy. For the Mediterranean, this approach has been developed in western Istria (Faivre et al., 2011) and in Greece (Nixon et al., 2009;Evelpidou et al., 2011) with a good degree of success. ...
... With reference to our present study, it is postulated that the rapid sea-level change episode that submerged the Croatian notch will generate a well-defined sedimentary signature in clastic-coast stratigraphy. For the Mediterranean, this approach has been developed in western Istria (Faivre et al., 2011) and in Greece (Nixon et al., 2009;Evelpidou et al., 2011) with a good degree of success. ...
Data
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The presence of a regional-wide notch (45 to 115 cm below present biological mean sea level [BMSL]) along the Adriatic coast of Croatia, at a string of sites between Zadar and Rijeka, provides evidence for a rapid but poorly constrained subsidence event(s) after Roman times. For more than a century, this geomorphological tidal level indicator has attracted rich scientific debate but many unresolved questions remain. In this paper, we present new results from Caska Bay (Pag Island) looking at notch morphology and Holocene salt-marsh stratigraphy to constrain the chronology of this crustal deformation on Pag Island. The typical salt-marsh stratigraphy comprises low to high salt-marsh muds interjected by an unconformable marine layer (which lies between − 50 and − 100 cm BMSL) consistent with an abrupt transgression. The palaeoecological record shows an abrupt shift in assemblages across the salt-marsh mud–sand sediment contact translating abrupt coastal changes. Geochronological data constrain this event to around 1000 to 1200 cal. AD. The altitude of the layer is coeval with the submerged notch attested on limestone cliffs around the bay. The U-shape of the notch profile, coupled with the sharp palaecological contacts and submerged Roman pier, implies that sea-level rise was episodic and not gradual as suggested by regional numerical models. Together, our findings shed new light on the chronology of the “enigmatic” Croatian notch on the island of Pag, and highlight the need to couple geomorphological studies of rocky coasts with high-resolution sediment records.
... Respecto al intervalo CI2, desde un punto de vista ecológico, M. fusca es un claro indicador de un ambiente de baja salinidad, mientras que T. inflata y E. macrescens son especies que habitan en marismas vegetadas inter-y supramareales (Nixon et al., 2009). Por tanto, la dominancia de especies salobres, junto con la presencia de taxones marismeños aglutinantes, el incremento de sedimentos de granulometría más fina y la casi total ausencia de caparazones marinos en CI2 indicarían una transición ambiental hacia una zona de marisma baja con, posiblemente, una mayor influencia dulceacuícola (Murray y Hawkins, 1976). ...
Article
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Se ha analizado el registro sedimentario reciente del estuario del Nalón a partir de dos sondeos intermareales que han sido datados mediante 210Pb y 137Cs. Los resultados muestran por primera vez sus asociaciones características de foraminíferos bentónicos, constituidas por un total de 46 especies, así como los importantes cambios experimentados por estas asociaciones, en consonancia con las variaciones en el magnetismo ambiental, com o consecuencia, posiblemente, de las actividades mineras desde 1850 CE que sugieren unas condiciones ambientales deterioradas. Estas malas condiciones persistieron durante décadas, incluso más allá del cese de la minería de mercurio y carbón, hasta el siglo XXI cuando se ha comenzado a observar una leve recuperación ambiental.
... Although Greece has been the focus of many RSL studies (e.g. Desruelles et al., 2009;Evelpidou et al., 2012aEvelpidou et al., , 2012cKershaw and Guo, 2001;Nixon et al., 2009;Vött, 2007), the investigated area has not received particular attention, with a few exceptions (Marinos and Sakellariou-Mane, 1964;Pirazzoli et al., 1994). ...
Article
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New geomorphological investigations along the coasts of Corfu, Othonoi, Paxoi, and Antipaxoi Islands allowed the identification of recent fossil shorelines. Former sea-level positions were deduced from sea-level indicators. A modern' tidal notch, submerged c. -20cm, was observed in all studied islands. This notch is regarded to have been submerged by the global sea-level rise that occurred during the 19th and 20th centuries at a rate exceeding the possibilities of intertidal bioerosion. Its presence provides evidence that no vertical tectonic movements occurred since its formation. On Corfu, impacts of ancient earthquakes have left some marks of emergence at about +130 +/- 11, +110 +/- 11, +65 +/- 11, +40 +/- 11, and +25 +/- 11cm, as well as marks of submergence at about -40 to -50, -85 +/- 11, -120 +/- 11, and -180 +/- 11cm. The emergence of +130 +/- 11cm, previously dated at about 790-400 cal. bc, was detected through erosion notches at various sites in the western part of Corfu and appears to continue even more west, at Othonoi Island. Tidal notches submerged at depths exceeding 0.4 m were observed in the northeastern part of the island and suggest the local occurrence of a sequence of four coseismic subsidences, with average vertical displacements of 40cm, during at least the last few millennia. At Paxoi and Antipaxoi, Holocene vertical movements seem to have been mainly of subsidence. At Paxoi, the modern' notch was found at about -20 to -30cm, while four more submerged tidal notches were distinguished at about -40 +/- 11, -60 +/- 11, -75 +/- 11, and -90 +/- 11cm, while in Antipaxoi, three submerged tidal notches were distinguished at about -60 +/- 11, -75 +/- 11, and -120 +/- 11cm.
... Many palaeoenvironmental studies in the Aegean Sea are based on sedimentary archives extracted from coastal marshes and lagoons (e.g., Evelpidou et al., 2012a;Pavlopoulos et al., 2010;Triantaphyllou et al., 2010;Vouvalidis et al., 2010). Using a multi-proxy approach based on sedimentology, micro-and macrofauna identification and dating, it is possible to reconstruct the coastal evolution and relative sea level changes (e.g., Ghilardi et al., 2014;Marriner et al., 2014;Nixon et al., 2009;Primavera et al., 2011;Vacchi et al., 2017). ...
Article
Although there is rich evidence for human occupation of Paros’ coastline, there is a dearth of data with regards to the evolution of the island's seaboard palaeoenvironments. In this paper, we use sedimentological and palaeontological proxies of late Holocene coastal deposits from lagoonal environment to reconstruct the evolution of coastal landscapes in Paroikia Bay (Paros Island, Greece). A semi-enclosed lagoon existed in the northeastern part of Paroikia from at least 2915–2551 BC, which was gradually infilled after around 780–436 BC. Although it was not possible to chronologically constrain the timing of the infill, it is most likely relatively young, indicating anthropogenic effects. A correlation of our chronostratigraphic data with archaeological remains and tidal notches in the study area suggests that the subsidence observed on Paros Island is linked to long-term subsidence in combination with vertical seismic displacements.
... Cursory studies have been carried out in this context, especially from the subduction zones across the world (e.g., Chagué-Goff et al., 2012;Clague and Bobrowsky, 1994;Costa et al., 2012;Gandhi et al., 2010;Goff et al., 2010;Hawkes et al., 2007;Horton et al., 2013;Horton et al., 2011;Kortekaas and Dawson, 2007;Noda et al., 2007;Pilarczyk and Reinhardt 2012;Shennan et al., 1999;and Smedile et al., 2011). Most of these studies are confined to back-marsh environments because of the high preservation potential of tsunami deposits and least influence from present-day tidal activity (Clague and Bobrowsky, 1994;Guilbault et al., 1996;and Nixon et al., 2009). A recent review emphasizes the importance of foraminifera in a tsunami deposit in terms of their abundance in assemblages, preservation, sorting, adaptation and decolonization (Mamo et al., 2009). ...
Article
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Quantitative and qualitative characteristics of foraminiferal species within the inferred paleotsunami deposits of southwestern Andaman Island were examined using sediment samples from six geoslice sections up to a depth of ∼2.5m. In this study, it is considered that the foraminiferal assemblages of the 2004 tsunami deposit (Unit b) as a modern analogue to trace similar events in the geological past. Paleontological and quantitative data analysis suggests 2 biofacies in the stratigraphy. Biofacies I is indicative of a subtidal sediment provenance and its mixing with intertidal sediments due to the tsunami, whereas, Biofacies II is an intertidal/marshy sediment provenance/environment. Foraminiferal tests >180µm in dimension in the tsunami facies (Biofacies I) show abrasion marks, which otherwise show high preservation potential than the pre-tsunami (Biofacies II) that indicates high dissolution activity and low preservation potential. Based on these inferences, 4 tsunami zones, 4 marsh zones, and 1 basin filling zone was elucidated in the stratigraphical column. In order to refine the chronostratigraphy of this area, the contemporaneous foraminifera recovered from a 15cm thick paleotsunami deposit (Unit g) were dated using 14C accelerator mass spectrometry (AMS). The AMS age suggests that AD 1005–1190 was the predecessor of 2004 Sumatra-Andaman earthquake (Mw 9.3) and associated Indian Ocean tsunami.
... The continuous sedimentation of the lagoon since mid-Holocene and the absence of high energy processes, such as the occurrence of ample riverine inflows, make this coastal feature ideal for the observation of environmental changes and, consequently, ecological changes. During the last decades a great number of studies have been conducted in the Holocene coastal plains and lagoons of Aegean Sea using multiple approaches, such as micropaleontological, malacological, sedimentological and geomorphological analyses (e.g., Avramidis et al. 2013;Evelpidou et al. 2010Evelpidou et al. , 2012Goiran et al. 2011;Koukousioura et al. 2012;Nixon et al. 2009;Pavlopoulos et al. 2007Pavlopoulos et al. , 2010Syrides et al. 2009;Theodorakopoulou et al. 2009;Triantaphyllou et al. 2003Triantaphyllou et al. , 2010bTriantaphyllou et al. , 2016aVouvalidis et al. 2010), providing invaluable paleoenvironmental information. In particular, micro-and macrofaunal analysis is an indispensable tool for recording coastal changes, which occurred in the past, and allows for a detailed reconstruction of paleoclimatic and paleoenvironmental conditions (e.g., Bernasconi et al. 2006;Carboni et al. 2002Carboni et al. , 2010Di Bella et al. 2008;Ghilardi et al. 2010;Morhange et al. 2000;Morigi et al. 2005;Serandrei-Barbero et al. 1997;Scott and Medioli 1980;Scott et al. 2001;Syrides 2008;Syrides et al. 2009;Yanko-Hombach et al. 2006). ...
Article
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The integration of lithology determination, micropaleontological and molluscan analyses, scanning electron microscopy, magnetic susceptibility measurement, and radiocarbon dating contributed to the interpretation of a sedimentary succession recovered from a 870-cm long borehole drilled at the Paliouras coastal lagoon in the eastern Thermaikos gulf (Greece). In this way, the reconstruction of the creation and evolution of the lagoon during the last 8000 years was accomplished. Four main evolutionary phases are identified: (1) initially, the pre-Holocene basement of the study area was inundated during the early Holocene marine transgression; (2) since ~ 8000–7900 cal yr BP an inner lagoon had been formed in the Paliouras coastal plain, within a rather restricted environment characterized by a Haynesina germanica, Cerastoderma glaucum and Hydrobia sp. assemblage, relatively high sediment magnetic susceptibility and an intense presence of abnormal foraminiferal tests and lenticular gypsum crystals; (3) during 7600–6900 cal yr BP, the inner lagoon presented a transition to an open system, clearly connected to the sea and characterized by an Ammonia beccarii, Aubignyna perlucida, and miliolids assemblage, more diversified molluscan fauna, minimum sediment magnetic susceptibility and the occurrence of lenticular gypsum aggregates; and finally (4) since ~ 5900 cal yr BP to the present time, the lagoon water body appears isolated from the marine environment, except of occasional seawater intrusions. The proposed evolutionary scenario for the Paliouras coastal lagoon is in accordance with the existing models of the sea level rise in the Aegean coastal areas concerning the time span before 4000 yr BP and the mid-late Holocene climate events.
... Beachrock outcrops may be one of the few physical records of past climate information on low-lying reef islands but research on their application as an indicator of paleo-environments in the Pacific is underdeveloped (Vousdoukas et al., 2007). As well PROCEEDINGSPEKAN ILMIAH TAHUNAN IAGI 2018 Hotel Pangeran, Pekanbaru, October 28 th -November 1 st ,2018 as providing evidence about the physical depositional environment, beachrock is reported to cement in the intertidal zone (e.g, Rey et al., 2004) within just a few years (Frankel, 1968;Hopley, 1986); it, therefore, has the potential to provide an indication of past sea levels (Hopley, 1986;Nixon et al., 2009). ...
Conference Paper
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The term "beachrock" refers to cemented coastal sediments, which is essentially the lithified paleo-beach that has been rapidly cemented through the precipitation of CaCO3 cement. Beachrock is an important feature of many tropical coastlines as it appears to have an anchoring effect for dynamic islands and provides protection from erosion. All of this identification using petrography analysis with focus on textures and compositions of minerals inside rock samples. In this study, field investigations and laboratory analysis are performed, both of which are aimed at understanding the formation mechanism of fresh beachrock in Okinawa Prefecture, Japan and also Sadranan beach, Yogyakarta, Indonesia. Peloidalmicrite cement, the cement needles aragonite, micritized granules, and the cover of micritic which have been observed in Sumuidebeachrock or Sadranan is a product of diagenesis on phreatic environment of the sea. The exclusive presence of cement aragonitic (needle aragonite and micrite cement peloidal) in Sadrananbeachrock sedimentary diagenesis indicates that coast occurred mainly in the marine environment. The presence of cement on the beachrock is peloidalmicritic. This shows that the micrite has played an important role in the beachrock sedimentary. Origin of cement micriticpeloidal is uncertain. It can be precipitated directly from sea water or it could just be a product of biological activity. In conclusion, it can be generalized in the Sadrananbeachrock occur mainly in the sea conditions and different cement with the Sumuidebeachrock whereas Sadrananbeachrock is more likely where a lot of the existence of the pore and pore filling cement and High-Magnesian calcite is dominant (HMC).
... ii) an area of the eastern Mediterranean where the tectonic influence on relative sea level change can be identified and isolated (e.g. Nixon et al., 2009;Evelpidou et al. 2012aEvelpidou et al. , 2013a. Accurate underwater measurements of appropriate sea-level indicators (i.e. ...
Article
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In this paper the tectonic behavior of Leukas and Meganisi islands (Ionian Sea) is examined through underwater research carried out in both islands. A possible Late Holocene correlation between coseismic subsidences is attempted and evidenced by submerged tidal notches in both islands. These subsidence events probably occurred after the uplift that affected the northernmost part of Leukas around 4 to 5ka BP. In conclusion, although the whole area was affected by a similar tectonic strain, certain coseismic events were only recorded in one of the two islands and in some cases they affected only part of the study area.
... This historic seismicity record provides the notion that beyond any doubt the Kenchreai harbor affected by a series of earthquakes, however, before we correlate the harbor submergence with these earthquakes it is critical to take into account the sea level changes in the Saronikos Gulf. Regarding the Saronikos Gulf there are three different curves of sea level rise represented in Fig. 2. The curves proposed by Lambeck and Purcell (2005) and Nixon et al. (2009), provide evidence for coseismic subsidence in the study area (Table 1). In contrast Kolaiti and Mourtzas, (2016) provided strong arguments for a new curve based on detailed mapping of submerged ancient buildings and ports from a large part of the Saronikos Gulf and showed that the sea level rise in the study area explains the drowning of the south mole of the Kenchreai harbor without any co-seismic subsidence ( Fig. 2 and Table 1). ...
Article
We present the Quaternary slip history of the Kenchreai Fault, Gulf of Corinth, based on geomorphological, palaeoseismological, geo-archaeological data and literally determined events. We also applied a series of geomorphic indices such as the hypsometric curve, asymmetry factor, the stream length-gradient index (SL), the valley floor width to valley height ratio (Vf), the drainage basin shape (Bs) and the mountain-front sinuosity (Smf), in drainage basins flowing perpendicular to the fault. These indices are representative for longer time period and are analyzed as follows. Values of SL are relatively high close to the fault trace. Smf values range from 1.01 to 1.85. Vf mean values range between 0.29 and 1.07. Bs values range from 1.16 to 4.78. Lateral fault growth was likely achieved by propagation primarily towards east while its western end appears to act as persistent barrier. The Holocene palaeoseismic history of the fault investigated by a palaeoseismological trench and ¹⁴C dating of ten samples suggest four linear morphogenic earthquakes in the last 10 ka. The Kenchreai Fault displays a Holocene slip rate in the order of 0.15 mm a⁻¹ and a recurrence interval ranging between 1300 and 4700 years. Thus the fault is classified as a fault of moderate activity with moderate to well-developed geomorphic evidence of activity and an overall slip-predictable earthquake model.
... Sawai et al., 2002), Europe (e.g. Nixon et al., 2009) and New Zealand (e.g. Hayward et al., 2004bHayward et al., , 2006aHayward et al., , 2007. ...
Article
This study documents changes in elevation, plant zones and foraminiferal faunas along a transect through salt marsh taken 14 months prior to, and 12 and 33 months after the Feb 2011 Canterbury Earthquake, which devastated the city of Christchurch, New Zealand. The saltmarsh subsided 0.1 m relative to the adjacent sand spit due to shaking-induced lateral spread. Over the 33-month period the lower 0.3 m elevation of the rush zone died away and a pine tree plantation on the sand spit terrace (~0.3-0.5 m above highest astronomical tide, HAT in 2009) also died and was removed. The foraminiferal faunal composition changed only slowly following the earthquake, except in the highest stations. Here their landward extent had migrated 0.45 m upwards by the end of 2013 and the foraminifera-based elevation estimates (Modern Analogue Technique, MAT) indicated a total subsidence of 0.36-0.62 m, similar to that indicated by LiDAR surveys. Elevation estimates based on the dead foraminiferal faunas in replicate salt-marsh cores 10 m apart indicate a subsidence event of ~0.15-0.2 m at 45 cm downcore. This was probably a result of shaking-induced lateral spread of the marsh into the river channel during a late 19th century earthquake – most probably the 1869 Christchurch Earthquake. A second possible co-seismic subsidence event is indicated at 80 cm downcore but the MAT elevational estimates are less reliable because of the low density foraminiferal faunas. A sudden relative fall in sea-level (or uplift of land) of 0.2-0.25 m is indicated by MAT elevation estimates at 60 cm downcore. As there is no known supporting evidence for a tectonic uplift event, we infer the most likely explanation is that this event spans an erosional time break (>500 yrs). Although we did not recognise its significance at the time, the foraminiferal record in our 2009 salt marsh core indicated that Christchurch had previously experienced significant co-seismic shaking on at least one, and maybe more, occasions within the last 1000 yrs.
... Sawai et al., 2002), Europe (e.g. Nixon et al., 2009) and New Zealand (e.g. Hayward et al., 2004bHayward et al., , 2006aHayward et al., , 2007. ...
Article
This study documents changes in elevation, plant zones and foraminiferal faunas along a transect through salt marsh taken 14 months prior to, and 12 and 33 months after the Feb 2011 Canterbury Earthquake, which devastated the city of Christchurch, New Zealand. The saltmarsh subsided 0.1 m relative to the adjacent sand spit due to shaking-induced lateral spread. Over the 33-month period the lower 0.3 m elevation of the rush zone died away and a pine tree plantation on the sand spit terrace (~ 0.3–0.5 m above highest astronomical tide, HAT in 2009) also died and was removed. The foraminiferal faunal composition changed only slowly following the earthquake, except in the highest stations. Here their landward extent had migrated 0.45 m upwards by the end of 2013 and the foraminifera-based elevation estimates (Modern Analogue Technique, MAT) indicated a total subsidence of 0.36–0.62 m, similar to that indicated by LiDAR surveys.
Article
Underwater geomorphological survey may reveal evidence of submerged tidal notches. In this paper, we present the methodology with the aim to reveal past temporary standstills of relative sea-level. Some examples of tidal notch development and tectonic movements are provided from fossil submerged notches mainly from Greece. A vertical movement causes a displacement of the intertidal bioerosion zone. For this reason the tidal notch profile reflects changes that occurred in the relative sea-level. If the movement is rapid a new tidal notch will be formed. On the contrary, if the movement is slower than the intertidal bioerosion rate, the height of the notch will increase. For this reason underwater marks on carbonate cliffs may provide evidence of recent vertical shoreline displacements of gradual or co-seismic origin.
Book
In a one-stop resource, this book provides a state-of-the-art overview of all aspects of pure and applied forams studies. Building from introductory chapters on the history of foraminiferal research, and research methods, the book then takes the reader through biology, ecology, palaeoecology, biostratigraphy and sequence stratigraphy. This is followed by key chapters detailing practical applications of forams in petroleum geology, mineral geology, engineering geology, environmental science and archaeology. All applications are fully supported by numerous case studies selected from around the world, providing a wealth of real-world data. The book also combines lavish illustrations, including over 70 stunning original picture-diagrams of foraminifera, with comprehensive references for further reading. Accessible and practical, this is a vital resource for graduate students, academic micropalaeontologists, and professionals across all disciplines and industry settings which make use of foram studies.
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Salt marshes and mangrove forests, the intertidal wetlands of the world's coastlines, provide key ecological services to all areas of the globe. This cutting-edge, richly illustrated book introduces the essential elements of coastal wetlands and their applications. The book opens by introducing coastal oceanography, the physical features of wetlands, their ecology, and human impacts upon them, giving all students the necessary background for wetlands studies. It then presents detailed case studies from around the world with extensive illustrations, supplying a wider, global-scale picture of wetlands geomorphology and biodiversity. The final chapters discuss some unique applications of coastal wetlands, including geological monitoring, uses in biotechnology and agriculture, and various experimental mesocosms. This is ideal as supplementary reading to support students on a wide range of earth and life science courses, from environmental science, ecology and palaeoecology to geomorphology and geography. It will also be a valuable interdisciplinary reference for researchers. © David B. Scott, Jennifer Frail-Gauthier and Petra J. Mudie 2014.
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This article reviews and discusses key data, literature, debates and discussions focussed on relative sea-level change since the Last Interglacial (approximately last ~132,000 years) in the Mediterranean Basin. Special reference is given to the geomorphological (physical and environmental) and archaeological (human and cultural) aspects of central and eastern Mediterranean coasts which have changed significantly and repeatedly during at least the last few glacial cycles. This article represents a collaborative synthesis of data, some of which have been collected and analysed by the authors and some of which refers to the existing literature, scholarship that have been reviewed critically or introduced to demonstrate key sites, data, concepts or debates in the various disciplines. We present an interdisciplinary contribution by the MEDFLOOD (MEDiterranean sea-level change and projection for future FLOODing) community in an effort to demonstrate the interwoven, evidence-based and up-to-date scientific and archaeological narrative of sea-level changes and its impacts on past peoples.
Article
The sedimentological and micropaleontological analysis of three mechanical cores in the marshland of Almenara (Valencian Community, Spain) has allowed the reconstruction of the Holocene evolution of this wetland. The cold and dry 8.2-ka event might be represented in Almenara by a massive carbonate precipitation bed, upon which mid- and late-Holocene sediments were subsequently deposited. The direct influence of sea-level changes has been recorded in the two cores (S-4 and S-5) located near the marsh barrier, at 400–450 m from the current coastline. The maximum flood area during MIS 1 (last 11,600 years) is represented in these cores by sediments indicative of different littoral subenvironments (shoreface, foreshore, backshore). These sediments contain typically littoral marine foraminiferal species such as Ammonia beccarii, Rosalina globularis, Asterigerinata mamilla, Adelosina longirostra, Cibicidoides lobatulus, Elphidium macellum, and Bolivina pseudoplicata. The base of these littoral sedimentary materials has been dated as 5480 and 5580 cal. yr BP. At this moment, the inner area (core S-7) was occupied by a restricted oligohaline marsh subject to water-table fluctuations and with scarce individuals of brackish water foraminifera, such as Ammonia tepida, Haynesina germanica, or Cribroelphidium excavatum, that in more recent times (since at least 1700 cal. yr BP) gradually evolved to a palustrine area.
Chapter
The objective of this chapter is to present a broad survey of landforms that are indicators of past sea levels. These landforms are either erosional landforms formed in resistant materials, constructional biologic indicators, or coastal deposits. The chapter initially discusses coralline features as indicators of past sea levels, starting with late Pleistocene coralline terraced landforms and then discussing coral microatolls as relatively precise late Holocene paleogeodetic tools. The chapter then discusses erosional geomorphic indicators of past sea level, beginning with stair-stepped flights of late Pleistocene marine terraces. The chapter then discusses late Holocene shore platform-sea cliff junctions as sea-level indicators. After addressing notches as sea-level indicators, the chapter finally discusses depositional features on the coast as indicators of past sea levels and concentrates discussion on beach ridges.
Chapter
Testate amoebae are single-celled organisms that construct shells that can be found in salt marsh sediments. Surface samples show that different taxa occur at different elevations in relation to sea level and fossil assemblages can therefore be used to reconstruct past sea level. The chapter summarizes the results of existing work on methods and applications of testate amoebae analysis to sea-level research. The approach has only been developed relatively recently, and much more work is needed to make this a routinely and widely applied method.
Article
Recent benthic foraminifers from the Oyambre estuary (north of Spain) have been studied in order to learn their biological response to drastic anthropic environmental changes that this estuary has undergone within the last centuries. Up to 41 species have been identified and 24 of them showed live specimens during the sampling period. The most abundant species are Ammonia tepida, Balticammina pseudomacrescens, Cribroelphidium williamsoni, Entzia macrescens, Haynesina germanica, Cibicidoides lobatulus, Miliammina fusca and Trochammina inflata. The statistical analysis (cluster and correspondence analysis) has allowed the differentiation of four groups of samples that are characterized by three assemblages that define the following environments: sandy outer estuary with marine influence (C. lobatulus), mid and inner estuary that comprises an euryhaline subtidal environment with silty sediment (A. tepida and H. germanica), intertidal channels with the lowest salinity levels (C. williamsoni), and marshes (B. pseudomacrescens, E. macrescens, M. fusca and T. inflata). The great number of species with agglutinated shells reveals the ongoing draining in mud-flat areas, as well as the establishment of the vegetated high marsh, where the invasive exotic plant Baccharis halimifolia is removing the reed bed ecosystem and filling, blocking and reducing main and secondary channels. As a result, there is hardly any sandy low marsh left, which in other nearby estuaries of Cantabria is delimited by the species M. fusca. Thus, areas with tidal levels between MHWNT (Mean High Water Neap Tide) and MHW (Mean High Waters) are scarce. However, foraminifer species that live in the high marsh above MHW are dominant. Entzia macrescens and T. inflata mark the interval between MHW and MHWST (Mean High Water Spring Tide), while B. pseudomacrescens the one from MHSWST to the barren zone (vegetated high marshes, closest to land). A comparison between the biocoenosis and thanatocoenosis assemblages generally shows a good similarity (Sanders’ index > 60%). The few samples with a low similarity reveal the effect of post-mortem processes, specially decantation, and, to a lesser extent, suspended transport, which once again points to the lack of hydrodynamism in the estuary. The percentage of exotic or allochthonous species that are deposited in this estuary is very low (the average ranges from 13.4% in the mouth to 0.7% in the inner area), which reveals that the Oyambre estuary has a mesotidal character in its mouth, while in the mid and inner area it can be considered a microtidal estuary. All these data expose that the works conducted in order to recover the Oyambre estuary between years 2009 and 2010 seem not to have been successful in restoring the marshes to their original hydrodynamic conditions.
Article
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Thorough faunal (benthic foraminifera, ostracods, molluscs) and palynomorph analyses as well as magnetic susceptibility measurements performed on the Piraeus coastal plain sedimentary sequences have shed light on the paleoenvironmental evolution of the area since ca. 9000 cal BP. Benthic and palynomorph assemblages along with magnetic susceptibility suggest a typical lagoonal environment with significant freshwater inputs at the eastern part of the plain after 8700 cal BP. Between 7500 and 5400 cal BP, microfaunal assemblages, mollusc fauna and magnetic susceptibility suggest a shallow marine paleoenvironment, with Piraeus forming a tied island in the center of the bay. Since ca. 4800 cal BP a closed oligohaline lagoon is evidenced in the western part of the Piraeus plain further developed to a marsh after 2800 cal BP, while a coastal environment associated with the fluvio-deltaic system of Kifissos and Korydallos Rivers is continually developing to the west. Signs of cultivation and grazing activities in the area are evidenced since the Early Bronze Age, culminating during the Classical Period. A comparison with a well-dated marine record, recovered from the nearby shallow Elefsis Bay, provides a reasonable estimation of ~5 mm/yr for the absolute sea level rise rate in the inner Saronikos Gulf during the Mid-Holocene.
Article
Underwater geomorphological survey may reveal evidence of submerged tidal notches. In this paper, we present the methodology with the aim to reveal past temporary standstills of relative sea-level. Some examples of tidal notch development and tectonic movements are provided from fossil submerged notches mainly from Greece. A vertical movement causes a displacement of the intertidal bioerosion zone. For this reason the tidal notch profile reflects changes that occurred in the relative sea-level. If the movement is rapid a new tidal notch will be formed. On the contrary, if the movement is slower than the intertidal bioerosion rate, the height of the notch will increase. For this reason underwater marks on carbonate cliffs may provide evidence of recent vertical shoreline displacements of gradual or co-seismic origin.
Article
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Earthquakes in the past few thousand years have left signs of land‐level change, tsunamis, and shaking along the Pacific coast at the Cascadia subduction zone. Sudden lowering of land accounts for many of the buried marsh and forest soils at estuaries between southern British Columbia and northern California. Sand layers on some of these soils imply that tsunamis were triggered by some of the events that lowered the land. Liquefaction features show that inland shaking accompanied sudden coastal subsidence at the Washington‐Oregon border about 300 years ago. The combined evidence for subsidence, tsunamis, and shaking shows that earthquakes of magnitude 8 or larger have occurred on the boundary between the overriding North America plate and the downgoing Juan de Fuca and Gorda plates. Intervals between the earthquakes are poorly known because of uncertainties about the number and ages of the earthquakes. Current estimates for individual intervals at specific coastal sites range from a few centuries to about one thousand years.
Article
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Six foraminiferal biofacies from the marshes and tidal flats of the Fraser Delta, British Columbia vary in faunal makeup according to differences in elevation, salinity and organic content of surficial sediments. Based on the distribution of these biofacies, the marsh may be divided into two major faunal zones: a High Marsh Zone [≈>0.8m above mean sea level (a.m.s.l.)], and a Low Marsh Zone (≈0.0 to 0.8m a.m.s.l.). The fauna from the High Marsh Zone includes the Jadammina macrescens Biofacies, indicative of low salinity, and the Jadammina macrescens/Trochammina inflata Biofacies, indicative of higher salinity. The Low Marsh Zone is characterized by the Ammonia beccarii Biofacies. A Higher Low Marsh Zone (≈+0.5 to +0.8m a.m.s.l.) is characterized by the presence of the Cribroelphidium gunteri Biofacies, whereas a Lower Low Marsh Zone (≈0.0 to +0.5m a.m.s.l.) is delineated by the Miliammina fusca Biofacies. The Trochammina pacifica Biofacies, as well as the Miliammina fusca Biofacies, occur outside the marshes in tidal flats vegetated by Zostera marina (eel grass). The Trochammina pacifica Biofacies may have developed in response to the high organic content of some sediments.
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The advent of readily available computer-based clustering packages has created some controversy in the micropaleontological community concerning the use and interpretation of computer-based biofacies discrimination. This is because dramatically different results can be obtained depending on methodology. The analysis of various clustering techniques reveals that, in most instances, no statistical hypothesis is contained in the clustering model and no basis exists for accepting one biofacies partitioning over another. Furthermore, most techniques do not consider standard error in species abundances and generate results that are not statistically relevant. When many rare species are present, statistically insignificant differences in rare species can accumulate and overshadow the significant differences in the major species, leading to biofacies containing members having little in common. A statistically based “error-weighted maximum likelihood” (EWML) clustering method is described that determines biofacies by assuming that samples from a common biofacies are normally distributed. Species variability is weighted to be inversely proportional to measurement uncertainty. The method has been applied to samples collected from the Fraser River Delta marsh and shows that five distinct biofacies can be resolved in the data. Similar results were obtained from readily available packages when the data set was preprocessed to reduce the number of degrees of freedom. Based on the sample results from the new algorithm, and on tests using a representative micropaleontological data set, a more conventional iterative processing method is recommended. This method, although not statistical in nature, produces similar results to EWML (not commercially available yet) with readily available analysis packages. Finally, some of the more common clustering techniques are discussed and strategies for their proper utilization are recommended.
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Approximately one third (11 species) of the world obligate brackish foraminiferal taxa occur in New Zealand's estuaries and upper reaches of enclosed harbours, inlets and lagoons. The previously confused local taxonomy of New Zealand's obligate (11 species) and common facultative (9 species) brackish foraminifera is integrated with current overseas usage. Nineteen of the 20 brackish species in New Zealand have a world-wide distribution. All 20 species occur in northern New Zealand (lat 35-degrees-S) with a progressive decrease in diversity to 13 species in the south (lat 47-degrees-S). Cluster analysis based on the quantitative faunal counts of 68 samples from 5 study areas results in the recognition of nine brackish foraminiferal associations. Within brackish settings, salinity and secondly tidal exposure, are the two environmental factors having the strongest influence on foraminiferal distribution. With increasing salinity, brackish faunas increase in diversity, decrease in abundance of agglutinated taxa and increase in abundance of calcareous taxa. The associations exhibit the following general trend correlated with increasing salinity: a. Trochamminita (least saline); b. Haplophragmoides wilberti, Miliammina; c. Ammonia - Miliammina; d. Elphidium excavatum, Ammonia - Elphidium, Ammonia; e. Marginal Marine (most saline). Five associations are apparently restricted to the intertidal zone: a. Trochammina inflata (above mean high water); b. Trochamminita, Haplophragmoides wilberti (above mean sea level); c. Elphidium excavatum (predominantly mid-tidal); d. Ammonia - Elphidium (between mean low and mean high water). Tidal current transport of foraminiferal tests produces mixed assemblages in the mouths and lower channels of New Zealand estuaries (diurnal microtidal and low mesotidal ranges).
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Currently some controversy exists in the micropaleontological community concerning the statistically correct number of counts required for quantitative examinations, particularly with respect to the effect of variations in the number ofspedes between samples and the significance of varying fractional abundances on the reliability of results, This analysis of the various statistical methods used to determine the number of required counts has shown that the number of species has no relationship to the number of counts required to measure accurately fractional abundances, As part of the study, logarithmic contours plotting percentage abundance against the total number of specimens, which provide abundance errors at a 95 percent confidence level, have been generated. The plot is displayed logarithmically to emphasize the significance of rare microfossil elements that dominate most assemblages, and which are important in many paleoenvironmental studies. Based on the plot, it is recommended that researchers utilize counts of at least 50 for indicator species having a fractional abundance of approximately 50 percent or greater; 300 counts for species which comprise approximately 10 percent of a sample; 500-1,000 counts for species that make up 5 percent of a sample; and counts of several thousand for defining species that comprise 1 percent ofa sample. It is important to note, however, that where similar biofacies are involved, higher counts are required to accurately distinguish them. It is also recommended that researchers include fractional error abundances with their estimated abundances to provide an indication of their accuracy.
Article
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Non-vital staining, especially with rose Bengal, has been widely used in ecological studies to differentiate between the tests of dead (unstained) foraminifera from those presumed to be living at the time of collection (stained). Doubts have been expressed about staining methods because of the possibility that dead individuals may retain undecayed protoplasm for weeks or months after death; when stained, such individuals would be recorded as living. To assess the importance of such false positives, it is necessary to examine rates of mortality, and the modes of generation of empty tests, i.e., whether due to reproduction, growth stages (leaving empty tests during growth) or death. It can be argued that reproduction, ontogeny, and death through predation lead to tests devoid of protoplasm. Whereas reproduction may affect only a small proportion of the population of each species (due to high pre-reproductive mortality), predation in oxygenated environments may be responsible for the major part of that pre-reproductive mortality. In oxygenated environments, disease or adverse environmental conditions are most likely to lead to dead individuals having tests containing protoplasm. In dysaerobic/anoxic environments, predation by macrofauna may be excluded, so foraminifera die through other causes and thus more tests with dead protoplasm may be potentially available for staining. Therefore, for most other environments, the problem of staining dead individuals is almost certainly overstated. Furthermore, from comparative studies, it seems that the most commonly used technique (staining with rose Bengal) is as reliable as others. Now that new vital staining techniques, especially the use of fluorescent probes, are being introduced, it is timely for further objective comparative studies of all techniques to be made in order to evaluate data already gathered and to develop the best strategies for future ecological studies according to whether they are field-based or experimental.
Article
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Marsh foraminiferal faunas from nine cores in two transects in and around Nanaimo inlet were examined to assess the implications of infaunal habitat and taphonomic processes for biofacies formation. High marsh faunas live slightly deeper infaunally compared to those in the low marsh, reflecting harsher conditions in the high marsh. Most living Jadammina macrescens occur from 0-20 cm in the high marsh and from 0-11 cm in the low marsh; the main depth preference is from 2-8 cm. Most living Trochammina inflata occur between 0-25 cm in the high marsh and from 0-20 cm in the low marsh. Haplophragmoides wilberti is most abundant overall between 3-7 cm, being almost absent at the surface in all cores. H. wilberti is found primarily between 0-15 cm in the high marsh, and from 0-12 cm in the low marsh. Most living Miliammina fusca occur from 0-10 cm, with maximum abundance in the top 3 cm. Five cluster analyses of the foraminiferal data using a sample base of 0-1, 0-3, 0-5, 0-7 and 0-10 cm, respectively, discriminated five biofacies in each case, which were then used to determine which near-surface aliquot is most analogous to deeper subsurface biofacies. Results show near-surface sediment sampling should be done through the 0-10 cm interval. This aliquot allows the main infaunal species characteristics to be observed, yet is thin enough that epifaunal species are also accurately represented. These results indicate that at least in coastal British Columbia traditional sampling strategies that assess modern marsh foraminiferal occurrence based only on examination of the uppermost 0-1 cm will not give an accurate representation of actual marsh species distribution. Modern marsh foraminiferal distribution assessment based on the thicker surface interval that we propose will permit researchers to delineate both subtle and dramatic sea level changes more precisely. This precision is critical not only in studies designed to differentiate the magnitude of seismic events but also to recognize subtle relative sea level change events as well.
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The geographic distribution of Ammonia extends from the Faeroe Islands to South Africa, throughout the Mediterrranenan and the Indian Ocean, around Australia and New Zealand as far as 45°50′S. In the western Atlantic, Ammonia extends from Miramichi Bay, Nova Scotia to Isla de los Estados, Tierra del Fuego, Argentina. The northernmost Pacific occurrences are Samish Bay, Washington on the E and Hokkaido, Japan on the W. These distributions are controlled by the latitudes (and protected waters) where the temperature reaches 17-22°C at least one month during the year. This temperature range is the minimum reproductive temperature of Ammonia. -from Authors
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Rapid and abrupt relative sea-level changes within the last interglacial (substage 5e) are recorded in the island geology of the tectonically stable Bahamas. From 132 to 118 ka, reef growth reached a maximum elevation near +2 m, as indicated by fossil reef elevation across the platform, whereas bioeroded notches are incised in coastal cliffs as high as +6 m. The end of the interval is characterized by voluminous eolianites exhibiting palm tree and frond impressions. It is inferred that sea level for most of the interval remained near +2 m, restraining reef growth, and that the notch at +6 m represents a rapid and brief excursion just before the close of the substage. The subsequent fall must have been rapid in order to leave the notch profile intact and mobilize windward lagoon ooids into dunes before cementation could anchor them. In order to explain the rapid rise to +6 m, glacial surging is invoked. The subsequent fall, also rapid, may be a consequence of the surge flooding high latitudes and providing enough moisture to initiate reglaciation and drawdown.
Article
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This is the first detailed investigation of the distribution and ecology of living (stained) shallow water (0–6 m) foraminifera along the Skagerrak–Kattegat coast, eastern North Sea. A total of 25 species (13 agglutinated; 12 calcareous) are common in the 169 sediment surface samples which were collected from 27 geographic areas. The sediment grain size and total organic carbon (TOC) content are strongly variable and the salinity and temperature ranges were 10–31‰ and 9–30°C, respectively, at the time of sampling (July to October) but temperatures down to freezing occur during the winter. The species are divided into six environmental categories of which the first five comprise euryhaline and the sixth essentially stenohaline taxa: (1) species associated only with marsh plants, (2) species basically, but not entirely, associated with marsh plants, (3) species basically, but not entirely, restricted to non-marsh areas, (4) species solely recorded in non-marsh intertidal to subtidal environments, (5) species restricted to subtidal areas, (6) species basically living in the most open marine areas. In this region, marshes have a patchy distribution and they are small and compressed due to low tidal ranges (80% mud. Ammoscalaria runiana is common only in coarse-grained sediments (
Article
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Non-vital staining, especially with rose Bengal, has been widely used in ecological studies to differentiate between the tests of dead (unstained) foraminifera from those presumed to be living at the time of collection (stained). Doubts have been expressed about staining methods because of the possibility that dead individuals may retain undecayed protoplasm for weeks or months after death; when stained, such individuals would be recorded as living. To assess the importance of such false positives, it is necessary to examine rates of mortality, and the modes of generation of empty tests, i.e., whether due to reproduction, growth stages (leaving empty tests during growth) or death. It can be argued that reproduction, ontogeny, and death through predation lead to tests devoid of protoplasm. Whereas reproduction may affect only a small proportion of the population of each species (due to high pre-reproductive mortality), predation in oxygenated environments may be responsible for the major part of that pre-reproductive mortality. In oxygenated environments, disease or adverse environmental conditions are most likely to lead to dead individuals having tests containing protoplasm. In dysaerobic/anoxic environments, predation by macrofauna may be excluded, so foraminifera die through other causes and thus more tests with dead protoplasm may be potentially available for staining. Therefore, for most other environments, the problem of staining dead individuals is almost certainly overstated. Furthermore, from comparative studies, it seems that the most commonly used technique (staining with rose Bengal) is as reliable as others. Now that new vital staining techniques, especially the use of fluorescent probes, are being introduced, it is timely for further objective comparative studies of all techniques to be made in order to evaluate data already gathered and to develop the best strategies for future ecological studies according to whether they are field-based or experimental.
Article
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Two completely vanished environments in Greece, a shallow coastal bay at Dimini near Volos and a large freshwater lake near Lerna south of Argos, were found and reconstructed with over 200 auger and drill cores. Similarities between the coastal landscapes of modern Volos and Argos with respect to topography and settlement history are attributable to comparable geological settings and Holocene environmental histories; for example, at both places active faulting has played a significant role and shoreline shifts have determined site locations. Near Volos the sea extended 3 km farther inland during the middle Holocene, reaching the base of Dimini Magoula (tell). After the Neolithic the shore gradually receded, resulting in a seaward shift of settlements, thus explaining the presence of several single-component sites in the area. Near Argos, the former presence of a large freshwater lagoon, named Lake Lerna, has been deduced from subsurface deposits. The lake was separated from the open sea by a beach barrier. It originated when the postglacial sea level rise reached its culmination point and extended over a diameter of 4.7 km in the Early Bronze Age. Increased soil erosion then caused a rapid silting, but remnants of Lake Lerna persisted until the last century. Anthropological studies have shown how the inhabitants of this coastal marsh have suffered from malaria in the past. It may be that the story of the legendary fight between Herakles and the Lernaean Hydra reflects the struggle of the Lernaean people as they tried to change the inhospitable environment by draining the lake.
Article
A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0–24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0–26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0–12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4–26.0 cal kyr B P. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14 C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).
Book
Sea-level changes since the last glacial maximum have varied considerably from place-to-place. This book offers a discussion of the main causes of these changes and of the methods employed to recognise former shorelines. Present day sea-level changes are covered along with significant sea-level histories, and examples are used to illustrate these areas. The author concludes by showing how these relative sea-level changes can be used to assess trends of tectonic movements, recognise and date seismic displacements, infer climatic changes, and improve geophysical models of the Earth's interior.
Article
There are over 1000 foraminiferal species presently living in marine environments, but relatively few of these can be used as direct indicators of sea level. We detail here certain assemblages occupying marsh environments that can be used for that purpose. Marsh foraminiferal assemblages have been shown to occur worldwide within narrowly defined vertical zones some of which extend less than 10 cm in total vertical range. These assemblage zones, once known, can be relocated in paleo-marsh deposits and accurately related to paleo-sea level. The key to success of these organisms as sea-level indicators is that their primary controlling factor appears to be elevation above mean sea level. Other foraminiferal assemblages are controlled by a series of parameters (eg. salinity, temperature, dissolved O2, etc.) which often have no direct relationship with actual water depth. Under appropriate circumstances, some information concerning sea level can be derived from other foraminiferal assemblages using indirect means. For instance areas which have undergone substantial emergence often contain small basins which, prior to emergence, were marine. The marine sediments at the bottom can be identified using foraminifera and the sill elevation of the basin can then be related to some prior sea-level stand. Both these methods have imperfections, but in areas where both emergence and submergence have taken place they can be combined to obtain a relatively complete sea-level history.
Article
Elements of the coastal stratigraphy of Washington and Oregon are interpreted as evidence of great Holocene earthquakes caused by the subduction of the Juan de Fuca plate beneath the North American plate. In particular, intercalated sequences of organic and inorganic sediments reflect a repetitive sequence of crustal movements described by the "earthquake deformation cycle'. In its simplest form this cycle consists of interseismic strain accumulation and gradual crustal uplift of the coastal zone of Washington and Oregon, followed by instantaneous coseismic subsidence due to earthquake rupture and strain release. However, superficially similar stratigraphic sequences are common in the coastal lowlands of the U.K., where they are interpreted as a product of coastal processes independent of the "earthquake deformation cycle'. To date, a rigorous test of the complete "earthquake deformation cycle' has not been made. This reflects an emphasis in research on the coseismic element of the stratigrpahic record of Washington and Oregon, combined with a lack of pollen analysis of the organic deposits. Examples from the U.K. show the application of biostratigraphic techniques to the interpretation of coastal stratigraphic sequences. From these is proposed a model of vegetation and sedimentary changes against which the evidence for the "earthquake deformation cycle' in Washington and Oregon may be tested. Such testing is essential for the establishment of an accurate history of great Holocene earthquakes in this region. -Authors
Article
New data on marsh foraminiferal distributions are presented for Hokkaido (Japan), Washington State and northern/ central California (USA). These data, when compared to recently published information from British Columbia, Oregon, Chile and New Zealand, and older data from southern California, allow a comprehensive comparison of biogeographic zonations around the Pacific Rim. Most significant is that high marsh faunas change from brackish to more saline at the California border but all high marsh faunas have the same 2-4 species present. In the southern hemisphere, the species Trochamminita salsa becomes an important high marsh indicator. Their narrow range makes high marsh faunas excellent markers for relocating former sea levels. These data can be used to detect rapid, high amplitude sea-level events associated with earthquakes on the Pacific Rim.
Article
Benthonic Foraminifera were examined from five semi-detailed transects across marsh and mudflat areas of the Acheloos and Evinos River deltas in western Greece. It appears that relationships between marsh Foraminifera and elevation above mean sea level observed in other parts of the world are similar to those in Greece, even though the tidal range is greatly reduced. -from Authors
Article
Although it is generally agreed that beachrock forms within the intertidal zone, the exact upper limit to the cementation processes is uncertain, particularly in areas of high tidal range. Problems occur with dating materials from outcrops: a. maximum age may be obtained from constituent organic materials, a minimum age from the cementing matrix, but difficulties may be encountered in the interpretation of such dates. Where possible beachrock as an indicator of former sea levels should be used in conjunction with other types of evidence. Care needs to be taken not to confuse beachrock sensu stricto with other cemented materials which may outcrop in the intertidal zone.
Article
Two transects were sampled in marshes of eastern Hokkaido for salt marsh foraminifera. Although these marshes were tidal, salinities were very low. Foraminifera present were low in diversity but extremely high in abundance. Miliammina fusca dominated lower areas together with Trochammina macrescens f. macrescens which dominated at all levels in both transects. In the upper elevations of both transects, Haplophragmoides manilaensis became prominent. Vertical zonation was generally poorly developed in both the foraminiferal and vegetation distributions which is typical of very brackish regions with low tidal ranges. -from Authors
Article
Foraminiferal distributions are reported for three marshes bordering the Strait of Juan de Fuca-the Sooke River marsh on Vancouver Island, Canada and the Discovery Bay and Gibson Spit marshes on the north shore of Washington State. Cluster analysis was used to define foraminiferal biofacies with distinct elevation ranges for each marsh. Comparison of these biofacies to foraminiferal zonations on other marshes in the Pacific Northwest suggests some broad similarities in foraminiferal distributions, but also reveals some important contrasts. Variations in marsh zone foraminiferal assemblages and position relative to mean tide level are presumably due to differences in marsh characteristics, including freshwater influence, sedimentation rates and substrate texture, and to differences in the sampling and statistical techniques used to define biofacies. On the marshes included in this study, foraminiferal biofacies analysis has the potential to estimate paleoelevations of subsurface deposits with an accuracy ranging from 0.05-0.45 m. Potential use of biofacies analysis to estimate coseismic subsidence on these marshes is more limited: Gibson Spit marsh lacks a sufficient number of biofacies and at Sooke River marsh, coseismic subsidence would had to have been unrealistically large for this technique to be applicable. Only at Discovery Bay does this approach have possible utility - here coseismic subsidence on the order 0.1-0.56 m could potentially be detected. A review of foraminiferal distributions in marshes of the Pacific Northwest suggests that foraminiferal analysis does have the potential to aid in identifying tsunami layers in high marsh deposits throughout the region.
Article
The exposed reef limestones occur principally on the inner-shelf reefs and can be separated into two groups - organically cemented (reef-rock) and inorganically cemented (beach-rock, rampart-rock, boulder-rock and phosphate-rock). No examples were found of exposed subtidal reef framework; the reef-rock exposed is entirely of intertidal origin resulting from incipient encrustration by intertidal corals and coralline algae. Most of the beach-rock, rampart-rock and boulder-rock exposures are intertidal and many show vadose cement fabrics. The cements, chiefly aragonite needles in beach-rock and cryptocrystalline high Mg calcite in rampart and boulder-rocks, are thought to be derived from seawater, though the environments of precipitation on windward sides of reefs where rampart-rocks form are quite different from those on the leeward sides where beach-rocks form. Phosphate-rock develops supratidally on the surface of some sand cays. Solutions derived from guano precipitate thin layers of phosphatic cement which bring about the centripetal replacement of carbonate grains.
Article
Here is the first comprehensive book to describe specific environmental applications of foraminifera and thecamoebians. These organisms permit the biological characterization of a variety of freshwater and coastal marine environments and react quickly to environmental stress, natural or anthropogenic. Their small size and hard shells lead to preservation in large numbers in core samples, allowing their use as proxies to reconstruct past environmental conditions. The book introduces the topic to nonspecialists and then goes on to give detailed descriptions of the methods and techniques. Resource managers and consultants in the public and private sectors who routinely work on coastal environmental problems will find this book invaluable.
Article
This article is in Free Access Publication and may be downloaded using the “Download Full Text PDF” link at right.
Article
From 1997 to 2003, the Eastern Korinthia Archaeological Survey (EKAS) investigated a 350-km2 region east of the ancient city of Corinth, focusing primarily on the northern Corinthian plain. EKAS developed an interdisciplinary methodology that emphasizes novel applications of geological science, computer-based knowledge systems, and strategies for fieldwork and collaboration among experts. In this article, the research philosophies and methods are presented and their application illustrated with results from the survey. The historical development of one settlement, Kromna in the northern Corinthian plain, is examined in detail to demonstrate the interpretive potential of data collected by these methods.
Article
Discriminant analysis distinguishes foraminiferal assemblages of modern mudflat, low marsh, and high marsh zones. The high marsh is dominated by Trochammina macrescens f. macrescens and T. inflata. The highest part of the high marsh, above mean higher high water, is usually marked by increased in the percentage of T. inflata and Haplophragmoides sp. Miliammina fusca is found throughout the high and low marsh. The low marsh may be divisible into an upper subzone with T. macrescens f. macrescens and T. inflata and a lower subzone with Ammotium salsum and Ammobaculites exiguus. Mudflat assemblages contain Reophax nana, M. fusca, A. salsum, A. exiguus, and low numbers of calcareous species. -from Authors
Article
The sedimentary sequence preserved in the isolation basin at Loch nan Corr (NW Scotland) represents a high resolution record of environmental changes over the last 9.5 ka (virtually the entire Holocene). The final isolation of the basin from the sea is recorded over a 6 m sediment sequence lasting c. 7000 years as the rock sill of the basin passes through the intertidal zone. This isolation is due to relative sea-level fall associated with isostatic rebound from the melting of the Last Glacial Maximum ice sheet. Combining faunal counts of foraminifera and thecamoebians from the same sample preparations allows an accurate reconstruction of sea-level and environmental changes at this site over the Holocene. This study shows the potential for isolation basins in mesotidal areas to provide a series of sea-level index points from a single isolation contact thus improving the ease and accuracy of sea-level reconstructions. Biostratigraphic data improve our understanding of the ecology of foraminifera in these relatively unstudied rock-enclosed lagoonal ecosystems. It seems likely that Miliammina fusca can tolerate the generally low and highly variable salinities in these lagoonal settings more readily than any other foraminiferal species.
Article
Megathrust earthquakes in western North America may be preceded by precursors several years ahead of the main event. For example on March 27, 1964, a 9.2 magnitude (on the Richter scale) earthquake occurred on the coast of Alaska. Changes in foraminifera and diatom biotas provided evidence of a precursor to this earthquake, thereby detailing a previously unknown sequence of events. We describe further evidence from marshes in Turnagain Arm, Alaska, USA and farther south in Netart's Bay, Oregon, USA; this is the first time that two widely spaced locations have been examined for precursors. The Alaska earthquake offers the possibility to compare a modern sequence (1964) of events with the geologic record. The Netart's Bay marsh has experienced no modern earthquake that could be used for comparison, but the nature of mega-thrust earthquakes implies that the modern and ancient events should be physically similar. The new cores examined from Turnagain Arm include both the 1964 earthquake and an event identified and dated at 1800yBP. The foraminifera and thecamoebian biota change from a forest sequence to a mildly brackish sequence just before the 1964 event; this zone was dated as being 15 years or less in length using Pb210 and Cs dating techniques. The event at 1800yBP was also associated with a similar transition indicating a small subsidence just before the major subsidence event. In Netart's Bay a new core was taken from a previously cored site because the chronology had already been determined by carbon-14 dating and also because at least four events were known to have occurred over the last 3000 years. The new core had four visual lithological transitions of which three were from marsh peat to mineralic deposits (possibly deposited by tsunamis) and back to a marsh deposit. Foraminifera indicated that these units represented high marsh transition to lower marsh, the earthquake event, and then rebounding back into marsh deposits. Sand deposits with either no or few foraminifera marked the tsunami/earthquake intervals. These transitions in two widely separated geographical areas indicate that similar mechanisms operate for large megathrust earthquakes from Alaska to Northern California in the Cascadia Subduction Zone thus implying that precursor events also occur and be detected by foraminiferal zonations all along this area as well. In a recent newspaper article scientists from the west coast suggested that "slow" or "silent" earthquakes they had measured with tiltmeters might be indicators of megathrust earthquakes. The transitions we document may be the prehistoric representations of these "silent" quakes. Foraminiferal evidence may help provide more accurate positioning of seismometers along the west coast of North America and therefore lead to more precise and timely earthquake predictions.
Article
Much of the uncertainty in determining the number and magnitude of past great earthquakes in the Cascadia subduction zone of western North America stems from difficulties in using estuarine stratigraphy to infer the size and rate of late Holocene relative sea-level changes. A sequence of interbedded peaty and muddy intertidal sediment beneath a small, protected tidal marsh in a narrow inlet of Coos Bay, Oregon, records ten rapid to instantaneous rises in relative sea level. Each rise is marked by a contact that records an upward transition from peaty to muddy sediment. But only two contacts, dating from about 1700 and 2300 yr ago, show the site-wide extent and abrupt changes in lithology and foraminiferal and diatom assemblages that can be used to infer at least half a meter of sudden coseismic subsidence. Although the characteristics of a third, gradual contact do not differ from those of some contacts produced by nonseismic processes, regional correlation with other similar sequences and high-precision 14C dating suggest that the third contact records a great plate-boundary earthquake about 300 yr ago. A fourth contact formed too slowly to have been caused by coseismic subsidence. Because lithologic and microfossil data are not sufficient to distinguish a coseismic from a nonseismic origin for the other six peatmud contacts, we cannot determine earthquake recurrence intervals at this site. Similar uncertainties in great earthquake recurrence and magnitude prevail at similar sites elsewhere in the Cascadia subduction zone, except those with sequences showing changes in fossils indicative of > 1 m of sudden subsidence, sand sheets deposited by tsunamis, or liquefaction features.
Article
The compression of peat beneath its own weight (autocompaction) is discussed, and it is shown that because of this process radiocarbondated samples of salt-marsh peat or peaty sediment, other than very thin samples cut from the base of the deposit, cannot be correlated with sea level without construction of a sea-level change curve from other types of data. With rising sea level there is a maximum thickness of salt-marsh peat for any given productivity of marsh grass. Because of this limitation, most marshes older than about 5500 years B.P. have been drowned. An important effect of peat autocompaction is the intrusion of wood into older peat horizons and the juxtaposition of wood of different ages. Wood, therefore, should be avoided in the dating of peat profiles. The roots of salt-marsh plants generally descend a foot or more beneath the rhizomes, contaminating older horizons insofar as radiocarbon dating is concerned. This contamination tends to make dates from marsh samples err on the young side. Sixteen radiocarbon dates from the Boston area are used to construct a sea-level curve going back to 14,000 years B.P. Relative sea level was at +60 feet or higher 14,000 years B.P., dropping sharply to approximately -70 feet about 10,000 years B.P. From a low of -70 feet, sea level rose steadily to about -2 feet approximately 3000 years B.P. Since then sea level appears to have kept close to its present level, probably fluctuating about a foot during the course of the stillstand. A crustal movement curve, based on the relative sea-level curve for Boston and the eustatic curve, indicates that about 290 feet of crustal rise occurred between 14,000-6000 years B.P., with a maximum rate of uplift of about 0.2 foot per year at 12,750 years B.P., and that from 6000 to 3000 years B.P., crustal subsidence occurred at Boston.
Article
The position of past sea levels can be reconstructed using a series of sea-level index points that possess information on age, location, altitude, and a quantified vertical relationship with a former tidal frame (the “indicative meaning”). Whilst these points fix the altitude of relative sea-level at one instant in time, they provide no information on its variation between them. Here, a foraminiferal transfer function is used to reconstruct changes in water depth from fossil assemblages preserved within salt-marsh sediments. The transfer function performs reliably in the high marsh zone, where agglutinated foraminiferal species are dominant. In lower marsh environments where calcareous species are prevalent, postmortem test dissolution alters the fossil assemblages and leaves them without modern analogues. To circumvent this problem, a new transfer function based on agglutinated foraminifera and utilising preserved test linings is developed. This new transfer function significantly reduces the number of samples without modern analogues, but at the expense of diminished sensitivity in the low marsh environment. Additionally, the transfer function is used to establish a series of sea-level index points that place observed lateral shifts in depositional environment into a vertical and temporal context. The combination of age-altitude and high-resolution water-level reconstructions offers the potential to obtain more detailed and reliable records of relative sea-level change from salt-marsh sediments.
Article
Grab samples show the effects of combined organic matter pollution and high riverine discharge. Typical estuarine assemblages appear to be displaced offshore as a result of these effects. Benthic foraminiferal assemblages in samples from transects in nearby North Inlet marsh do not appear to be affected by the polluted waters from Winyah Bay. -from Authors
Article
Singleton Swash on the South Carolina coast provides an extended record of storm events for this coast. We used experience gained by looking at storm traces detected as layers of offshore