Highstand Sea Research Articles

A complex record of last interglacial sea-level history and paleozoogeography, Santa Rosa Island, Channel Islands National Park, California, USA

Studies of marine terraces and their fossils can yield important information about sea level history, tectonic uplift rates, and paleozoogeography, but some aspects of terrace history, particularly with regard to their fossil record, are not clearly understood. Marine terraces are well preserved on Santa Rosa Island, California, and the island is situated near a major marine faunal boundary. Two prominent low-elevation terraces record the ∼80 ka (marine isotope stage [MIS] 5a) and ∼120 ka (MIS 5e) high-sea stands, based on U-series dating of fossil corals and aminostratigraphic correlation to dated localities elsewhere in California and Baja California. Low uplift rates are implied by an interpretation of these ages, along with their elevations. The fossil assemblage from the ∼120 ka (2nd) terrace contains a number of northern, cool-water species, along with several southern, warm-water species, a classic example of what has been called a thermally anomalous fauna. Low uplift rates in the late Pleistocene, combined with glacial isostatic adjustment (GIA) processes, could have resulted in reoccupation of the ∼120 ka (MIS 5e), 2nd terrace during the ∼100 ka (MIS 5c) high-sea stand, explaining the mix of warm-water (∼120 ka?) and cool-water (∼100 ka?) fossils in the terrace deposits. In addition, however, sea surface temperature (SST) variability during MIS 5e may have been a contributing factor, given that Santa Rosa Island is bathed at times by the cold California Current with its upwelling and at other times is subject to El Niño warm waters, evident in the Holocene SST record. Study of an older, high-elevation marine terrace on the western part of Santa Rosa Island shows more obvious evidence of fossil mixing. Strontium isotope ages span a large range, from ∼2.3 Ma to ∼0.91 Ma. These analyses indicate an age range of ∼500 ka at one locality and ∼ 600 ka at another locality, interpreted to be due to terrace reoccupation and fossil reworking. Consideration of elevations and ages here also yield low, long-term uplift rates, which in part explains the potential for terrace reoccupation in the early Pleistocene. In addition, however, early Pleistocene glacial-interglacial cycles were of much shorter duration, linked to the ∼41 ka obliquity cycle of orbital forcing, a factor that would also enhance terrace reoccupation in regions of low uplift rate. It is likely that other Pacific Coast marine terrace localities of early Pleistocene age, in areas with low uplift rates, also have evidence of fossil mixing from these processes, an hypothesis that can be tested in future studies.

Morphology of fore-reef slopes and terraces, Takapoto Atoll (Tuamotu Archipelago, French Polynesia, central Pacific): The tectonic, sea-level and coral-growth control

A dataset of 41 bathymetric profiles detected by satelline imagery and echo-sounding to a maximum depth of 38 m along the fore-reef slopes of Takapoto Atoll (Tuamotu Plateau, French Polynesia, central Pacific) were qualitatively and quantitatively analyzed in order to identify the main geomorphological features. In addition, scuba-diving investigations from a selected site resulted in defining coral composition and cover rate. Six distinct fore-reef sectors were morphologically differentiated on the basis of seaward extension and slope gradient. Only the north end, and a restricted area of the mid-south-east side extend seawards over an average distance of 150 m, with a relatively low gradient (23°–38°). Most of the outer-slope areas are narrow (<100 m on average) and steep (average slope equals to 45° to up to 70°). Geomorphic features include spur-and-groove systems, sub-horizontal to gently dipping terraces (23–45 m wide) ending seawards in vertical steps (<10 m high) and drop-offs (>10 m high), outer-reef crest-like reliefs (0.5 m–1.5 m high), pinnacles (2 m–17 m high), coral heads (<2 m high), trenchs and concave scars. The recognized seven terrace levels occur at the respective depths of about −5 m, −10 m, −15 m, −20 m, −24 m, −30.5 m and −38 m. Based on comparison with subsurface chronostratigraphy of drilled reef sequences from some other Pacific atolls, the terraces are interpreted as remnants of reef tracts formed during Pleistocene interglacial, high sea-stands, respectively during MIS substage 5e (about −125 ka), MIS substages 7a (about −195 ka), 7c (about −210 ka), 7e (about −240 ka) and 9e (−330 ka). After depth correction of ground lowering during periods of emergence and subsidence effects, terrace elevations were expected to indicate eustatic sea-level positions at each identified high sea-stand, at approximately 7 m (MIS 5e) and 2.2 m (MIS 7a) above present sea level and 9.5 m (MIS 7c), 11 m (MIS 7e) and 8.6 m (MIS 9e) below present sea level. During the post-glacial sea-level rise, from about 9.5 ky, the studied portions of fore-reef slopes were re-flooded. It was assumed that coralgal deposits in the form of thin veneers, coral heads, outer-reef crest-like reliefs and pinnacles have simply overlapped pre-existing structures. Locally, the fore-reef zones are carved by trenchs, i.e. incipient detachment faults, and scars, i.e. imprints of former landslides. Similarly, some drop-offs may be regarded as fault walls. The prevailing direction of faulting–collapsing surfaces is consistent with the SW–NE orientation of the main axis of the atoll and submarine ridges rising up from the north-western floor of the Tuamotu Plateau. Analysis of the composition and distribution of coral communities to −30 m depth revealed high, downslope-increasing coral coverage (24% to 67% on average) and the sharp replacement of robust-encrusting Pocillopora by sub-massive to plate-like Porites from depths greater than −10 m. Significant inter-regional differences were detected with atolls in west Pacific, probably due to local ecological constraints.

Little Islands Recording Global Events: Late Quaternary Sea Level History and Paleozoogeography of Santa Barbara and Anacapa Islands, Channel Islands National Park, California

Marine terraces are common on the Pacific Coast of North America and record interglacial high-sea stands superimposed on either stable or tectonically rising crustal blocks. Despite many years of study of these landforms in southern California, little work on terraces has been conducted on the two smallest of the California Channel Islands, Santa Barbara Island (SBI) and Anacapa Island (ANA). Presented here are new field and laboratory data on the ages, paleontology, and sea level history of marine terraces of these two islands. On both islands, the lowest marine terraces have shoreline angle elevations of ∼11 m above sea level. Amino acid geochronology shows that terrace deposits on both islands host fossils of two ages, one group dating to the ∼120-ka high-sea stand and the other group likely dating to the ∼100-ka high-sea stand. A mix of fossil ages is consistent with the paleontology as well, with SBI in particular showing a faunal assemblage that includes both extralimital southern and southward-ranging species (inferred to be from the ∼120-ka high-sea stand) and extralimital northern and northward-ranging species (inferred to be from the ∼100-ka high-sea stand). Fossil mixing from these two high-sea stands supports the hypothesis that glacial isostatic adjustment (GIA) processes have left a strong imprint on the geologic record of sea level history in southern California. Nevertheless, the elevations of these terraces and that of a low terrace on Santa Cruz Island indicate that modeled GIA estimates of paleo-sea level for the peak of the last interglacial period at ∼120 ka could be too high. Future development of models of GIA effects on the Pacific Coast of North America will need to consider geologic records, such as those from SBI and ANA, in refining reconstructions of sea level history.

Quaternary sea-level history and the origin of the northernmost coastal aeolianites in the Americas: Channel Islands National Park, California, USA

Along most of the Pacific Coast of North America, sand dunes are dominantly silicate-rich. On the California Channel Islands, however, dunes are carbonate-rich, due to high productivity offshore and a lack of dilution by silicate minerals. Older sands on the Channel Islands contain enough carbonate to be cemented into aeolianite. Several generations of carbonate aeolianites are present on the California Channel Islands and represent the northernmost Quaternary coastal aeolianites on the Pacific Coast of North America. The oldest aeolianites on the islands may date to the early Pleistocene and thus far have only been found on Santa Cruz Island. Aeolianites with well-developed soils are found on both San Miguel Island and Santa Rosa Island and likely date to the middle Pleistocene. The youngest and best-dated aeolianites are located on San Miguel Island and Santa Rosa Island. These sediments were deposited during the late Pleistocene following the emergence of marine terraces that date to the last interglacial complex (~120,000yr to ~80,000yr). Based on radiocarbon and luminescence dating, the ages of these units correspond in time with marine isotope stages [MIS] 4, 3, and 2. Sea level was significantly lower than present during all three time periods. Reconstruction of insular paleogeography indicates that large areas to the north and northwest of the islands would have been exposed at these times, providing a ready source of carbonate-rich skeletal sands. These findings differ from a previously held concept that carbonate aeolianites are dominantly an interglacial phenomenon forming during high stands of sea. In contrast, our results are consistent with the findings of other investigators of the past decade who have reported evidence of glacial-age and interstadial-age aeolianites on coastlines of Australia and South Africa. They are also consistent with observations made by Darwin regarding the origin of aeolianites on the island of St. Helena, in the South Atlantic Ocean, more than a century and a half ago.

A contribution to late Middle Paleolithic chronology of the Levant: New luminescence ages for the Atlit Railway Bridge site, Coastal Plain, Israel

The Atlit Railway Bridge (ARB) prehistoric site is located on the northern coastal plain of Israel, within natural caves which formed in calcareous aeolianites (kurkar), perhaps during a high sea-stand. Flint artifacts belonging to the Levantine later Mousterian tradition and faunal remains were found embedded in the kurkar infill of two caves. The aeolianites in which the caves had developed were previously constrained by IRSL50 dating of feldspars to be older than the last interglacial highest sea-stand (Frechen M. et al., 2004; Chronology of Pleistocene sedimentary cycles in the Carmel Coastal Plain of Israel. Quaternary International 121, 1–52), providing a maximum age for the artifacts.Samples for luminescence dating were collected from the infill of the two caves (II and III), from the same deposits as the archaeological finds. Both quartz and alkali feldspars (KF) were extracted and measured using four different luminescence signals: optically stimulated luminescence (blue OSL) and violet stimulated luminescence (VSL) on quartz; and the infrared stimulated luminescence (IRSL) post-IR-IR290 signal and the IR50 signal corrected for anomalous fading on KF.The ages obtained from analyses of the different minerals and signals mostly agree within errors. The new luminescence ages date the sediment infill in Caves III and II to ∼90 ka and ∼70 ka, respectively, indicating that hominin occupation of this locality is coeval with the nearby Skhul Cave and Layer B in Tabun Cave.

Uranium-series ages of fossil corals from Mallorca, Spain: The “Neotyrrhenian” high stand of the Mediterranean Sea revisited

Abstract The emergent marine deposits of the Mediterranean basin have been recognized as an important record of Quaternary sea level history for more than a century. Previous workers identified what have been interpreted to be two separate high stands of sea in the late Quaternary, namely the “Eutyrrhenian” (thought to be ~ 120 ka) and the “Neotyrrhenian” (thought to be either ~ 100 ka or ~ 80 ka). On Mallorca, Spain, both of these named deposits lie close to present sea level, implying paleo-sea levels slightly above present during both marine isotope stages (MIS) 5.5/5e and either 5.3/5c or 5.1/5a. If these interpretations are correct, they conflict, at least in part, with sea level records from far-field localities. We analyzed corals from the Neotyrrhenian beds on Mallorca, which gave U-series ages from ~ 126 ka to ~ 118 ka. These ages are consistent with previously published amino acid data that show that the Neotyrrhenian and Eutyrrhenian deposits are not significantly different in age. A fossil molluscan fauna from the Neotyrrhenian deposits on Mallorca has a warm-water paleozoogeographic aspect, with nine southward-ranging species and four extralimital southern species. When compared with sea surface temperatures obtained from planktonic foraminifera and alkenones from ODP core 977 in the nearby Alboran Sea, the only time period that shows comparable warmth is MIS 5.5/5e, consistent with the U-series ages of corals from the Neotyrrhenian deposits. We propose that the Neotyrrhenian deposits are a beachrock facies of the same age as the Eutyrrhenian deposits. This interpretation is consistent with the differences in physical sedimentology of the two deposits, explains the U-series and amino acid data indicating the same age, is consistent with the very slight elevation difference of the Neotyrrhenian and Eutyrrhenian beds, and explains the similar, though not identical paleozoogeographic aspects of their fossil faunas.

Coastal tectonics on the eastern margin of the Pacific Rim: late Quaternary sea-level history and uplift rates, Channel Islands National Park, California, USA

The Pacific Rim is a region where tectonic processes play a significant role in coastal landscape evolution. Coastal California, on the eastern margin of the Pacific Rim, is very active tectonically and geomorphic expressions of this include uplifted marine terraces. There have been, however, conflicting estimates of the rate of late Quaternary uplift of marine terraces in coastal California, particularly for the northern Channel Islands. In the present study, the terraces on San Miguel Island and Santa Rosa Island were mapped and new age estimates were generated using uranium-series dating of fossil corals and amino acid geochronology of fossil mollusks. Results indicate that the 2nd terrace on both islands is ∼120 ka and the 1st terrace on Santa Rosa Island is ∼80 ka. These ages correspond to two global high-sea stands of the Last Interglacial complex, marine isotope stages (MIS) 5.5 and 5.1, respectively. The age estimates indicate that San Miguel Island and Santa Rosa Island have been tectonically uplifted at rates of 0.12–0.20 m/ka in the late Quaternary, similar to uplift rates inferred from previous studies on neighboring Santa Cruz Island. The newly estimated uplift rates for the northern Channel Islands are, however, an order of magnitude lower than a recent study that generated uplift rates from an offshore terrace dating to the Last Glacial period. The differences between the estimated uplift rates in the present study and the offshore study are explained by the magnitude of glacial isostatic adjustment (GIA) effects that were not known at the time of the earlier study. Set in the larger context of northeastern Pacific Rim tectonics, Channel Islands uplift rates are higher than those coastal localities on the margin of the East Pacific Rise spreading center, but slightly lower than those of most localities adjacent to the Cascadia subduction zone. The uplift rates reported here for the northern Channel Islands are similar to those reported for most other localities where strike-slip tectonics are dominant, but lower than localities where restraining bends (such as the Big Bend of the San Andreas Fault) result in crustal shortening.

Stage 5 high sea stands, climate and human activity on the Cyrenaican coast, NE Libya

Stage 5 high sea stands, climate and human activity on the Cyrenaican coast, NE Libya

Testing cosmic dose rate models for ESR: Dating corals and molluscs on San Salvador, Bahamas

Sealevel curves are best developed on tectonically stable coastlines, like San Salvador, where eolianites preserve transgressive and regressive phases associated with Quaternary high seastands, while reef facies mark the highstands. At 11 locations around San Salvador, terrestrial molluscs ( Cerion ) from the eolianites, lagoonal bivalves ( Codakia ), and corals from the highstand deposits were dated by ESR. Volumetrically averaged sedimentary dose rates were calculated from sedimentary geochemistry and time-averaged cosmic dose rates from each sample’s current and past geologic contexts. Rice Bay Formation corals dated at 3.9 ± 0.3 to 7.1 ± 0.4 ka (OIS 1). Minimum ages for the Cockburn Town Member’s regressive phase ranged from 49 ± 6 to 75 ± 8 ka, correlating with OIS 3–4. Codakia dates showed that an OIS 5a sealevel approached modern levels at 91–78 ka. In situ corals from the Cockburn Town Reef averaged from 127 ± 6 to 138 ± 10 ka, correlating well with OIS 5e. Ages from the Reef’s rubble zones hint that some coral reefs grew as early as OIS 7, but were likely reworked during OIS 5. San Salvador preserves deposits from three mid to late Quaternary highstands above, and as many as three that closely approach, modern sealevel.

OSL dating of marine terrace sediments on the southeastern coast of Korea with implications for Quaternary tectonics

Several flights of marine terraces can be identified along the southeastern coast of Korea. In the Yonghan area, the northern part of this coastline, three sets of marine terraces are usually identifiable; NQt 1 (ca. 4 m), NQt 2 (ca. 15 m) and NQt 3 (ca. 35 m). Aeolian dune sands are well preserved on top of each terrace surface, underlain by palaeo-beach sediments. After various performance tests of the applicability of the single-aliquot regenerative-dose (SAR) protocol (e.g. preheat plateau, dose recovery and thermal transfer tests) we obtained quartz optically stimulated luminescence (OSL) ages ranging between 64±6 and 127±12 ka (NQt 3), 51±2 and 80±4 ka (NQt 2), and 0.09±0.01 and 0.11±0.01 ka (NQt 1) from aeolian dune sands and underlying palaeo-beach sediments on each terrace, all of which appear to be consistent with the established palaeo-sea level record. Of these, the OSL ages of the palaeo-beach sediments from NQt 3 (127 ka) and NQt 2 (73–80 ka) indicate that these terraces were formed during marine isotopic stage (MIS) 5e and MIS 5a, respectively. We obtained quartz SAR OSL ages of 68±4–92±11 ka from sandy gravel layers collected from the Suryum site (MQt 4 terrace, ca. 45 m), where Quaternary faults crosscut the MQt 4 terrace. These data, however, do not show an internal consistency in stratigraphic order, and significantly underestimate the expected timing of emergent interglacial high sea stands. Although the reasons for the inconsistency in OSL ages of the samples from the Suryum site (MQt 4 terrace) are not well known as yet, the OSL ages of other terrace sediments (the NQt 2, NQt 3 and MQt 2 terraces) imply that, unlike the conventional view, the southeastern part of Korean peninsula has not been tectonically very stable during the Late Pleistocene.

Further evidence for a relatively high sea level during the penultimate interglacial: open-system U-series ages from La Marina (Alicante, East Spain)

The elevation and timing of high sea stands during Oxygen Isotope Stage (OIS) 7 are not as well constrained as those of OIS 5e. Conflicting values are reported from Mediterranean coastlines, and fossil dating is inaccurate because of ubiquitous open U-series systems. New morphostratigraphic data from La Marina (eastern Spain) supported by open-system U-series coral ages shed light on the maximum sea level during OIS 7. Fossil corals (Cladocora caespitosa) underlying an OIS 5e marine unit yielded U-series ages from 178 ± 10 to 208 ± 11 ka (±2s; n=7) with an outlier at 240 ± 18 ka. Mean open-system limit ages of 170 ± 10 (minimum age after correction for 234Th -230Th uptake) and 237 ± 20 ka (maximum age after correction for 238U - 234U uptake) were calculated to have a probable age closer to the minimum value, for an assignment of OIS 7a or 7c. The occurrence of a warm-water “Senegalese” fauna (Strombus bubonius) in OIS5e and OIS 7 marine units confirms the arrival of tropical species to the Mediterranean before the last interglacial period. Morpho-sedimentological and neotectonic studies suggest that the maximum paleo-sea level during OIS 7c or 7a was a few meters below that of OIS 5e.

Phylogeographic patterns of HawaiianMegalagriondamselflies (Odonata: Coenagrionidae) correlate with Pleistocene island boundaries

The Pleistocene geological history of the Hawaiian Islands is becoming well understood. Numerous predictions about the influence of this history on the genetic diversity of Hawaiian organisms have been made, including the idea that changing sea levels would lead to the genetic differentiation of populations isolated on individual volcanoes during high sea stands. Here, we analyse DNA sequence data from two closely related, endemic Hawaiian damselfly species in order to test these predictions, and generate novel insights into the effects of Pleistocene glaciation and climate change on island organisms. Megalagrion xanthomelas and Megalagrion pacificum are currently restricted to five islands, including three islands of the Maui Nui super-island complex (Molokai, Lanai, and Maui) that were connected during periods of Pleistocene glaciation, and Hawaii island, which has never been subdivided. Maui Nui and Hawaii are effectively a controlled, natural experiment on the genetic effects of Pleistocene sea level change. We confirm well-defined morphological species boundaries using data from the nuclear EF-1alpha gene and show that the species are reciprocally monophyletic. We perform phylogeographic analyses of 663 base pairs (bp) of cytochrome oxidase subunit II (COII) gene sequence data from 157 individuals representing 25 populations. Our results point to the importance of Pleistocene land bridges and historical island habitat availability in maintaining inter-island gene flow. We also propose that repeated bottlenecks on Maui Nui caused by sea level change and restricted habitat availability are likely responsible for low genetic diversity there. An island analogue to northern genetic purity and southern diversity is proposed, whereby islands with little suitable habitat exhibit genetic purity while islands with more exhibit genetic diversity.

A cool eastern Pacific Ocean at the close of the Last Interglacial complex

New high-precision thermal ionization mass-spectrometric (TIMS) U-series ages of solitary corals ( Balanophyllia elegans) from several marine terrace localities along the California and southern Oregon coasts date to the ∼80,000 yr BP high stand of sea, correlative with marine isotope substage 5a, late in the last interglacial complex. Ages of multiple corals from localities north of Point Año Nuevo (central California) and San Nicolas Island (southern California) suggest that this high sea stand could have lasted at least 8000 yr, from ∼84,000 to ∼76,000 yr BP. These ages overlap with those from marine deposits on tectonically stable Bermuda and tectonically emergent Barbados. Higher-elevation terraces at two California localities, in the Palos Verdes Hills and on San Nicolas Island, have corals with ages that range mostly from ∼121,000 to ∼116,000 yr BP, correlative with marine isotope substage 5e. These ages are similar to those reported for other terraces in southern California but are younger than some ages reported from Hawaii, Barbados and the Bahamas. Marine terrace faunas are excellent proxies for nearshore marine paleotemperatures during past high sea stands. Terraces on the Palos Verdes Hills and San Nicolas Island dated to the ∼120,000 yr BP high sea stand have dominantly zoogeographically “neutral” species in exposed coastal localities, indicating nearshore waters similar to those of today. In contrast, ∼80,000 yr BP, exposed coastal localities typically have molluscan faunas characterized by numerous extralimital northern species and a lack of extralimital southern species. These fossil assemblages are indicative of nearshore water temperatures that were cooler than modern temperatures at ∼80,000 yr BP. Waters at least as warm as today's at ∼120,000 yr BP and cooler than present at ∼80,000 yr BP are in excellent agreement with marine alkenone records and coastal vegetation records derived from pollen data, from both southern and northern California. Decreased insolation or increased upwelling seem inadequate to explain the cool waters off the Pacific Coast from southern Oregon to southern California at ∼80,000 yr BP. We propose that a stronger California Current (or at least one with a greater component of subarctic waters) may explain cooler-than-modern coastal waters during the ∼80,000 yr BP high sea stand.

Foraminifera in Surface Sediments of Mandovi River Estuary: Indicators for Mining Pollution and High Sea Stand in Goa, India

NIGAM, R.; PANCHANG, R., and BANERJEE, P., 2005. Foraminifera in surface sediments of Mandovi River estuary: Indicators for mining pollution and high sea stand in Goa, India. Journal of Coastal Research, 21(4), 853‐859. West Palm Beach (Florida). ISSN 0749-0208. Foraminiferal characteristics of 11 surface sediment samples collected from the Mandovi estuary during 2001 have been compared with similar data based on samples collected during 1994. The study reveals drastic fall in total foraminiferal number in the lower reaches of the Mandovi River estuary, from 138/g dry sediment sample in 1994 to 41/g sediment sample in 2001. The decline is also noted in diversity from 22 in 1994 to only 5 species in 2001. The ever-increasing suspended load in Mandovi estuary, probably due to mining activities in the catchment area of the Mandovi River estuary, is suggested as the plausible reason for the decline of fauna. An intriguing finding of the present study is the presence of substantial amount of reworked/older specimens, at the lower reaches of the estuary, that could be indicators of Holocene high sea stand.

Organic Carbon Inferred Environmental Fluctuations during Late Quaternary, Southwestern Taiwan

terrestrial plant species that inhabit it. In this study, we sampled two cores drilled from the coastal plain of southwestern Taiwan, and conducted concentration and isotopic analyses of organic carbon. Compared with the generally accepted environmental evolution of Taiwan, our study shows the dominant marine organic source have brought on relatively stable carbon abundance and low level isotopic values for total organic carbon (TOC), whilst input from terrestrial sources attributed to arid-climate-induced C 4 plant blooms make TOC content and δ 13 C value vary more widely. The lower parts of the cores indicate the entire study area was inundated by seawater as a result of the high sea-stand of MIS (marine isotope stage) 5. At Machouhou (MCH), the sedimentary environment became terrestrial in MIS 4, but returned to a shallow marine environment in MIS 3. The environment probably remained terrestrial at Tsungyeh (TY) during MIS 2 & 3; a period characterized in the cores as having high fluctuations in TOC with strong C 4 plant signals. Subsequently both of these areas evolved into shallow marine environments after the beginning of the Holocene due to the world-wide postglacial transgression. Although the coastal environment and climate of southwestern Taiwan display characteristics consistent with the major trends in global change oc

Quaternary ichnofacies model for paleoenvironmental and paleosealevel interpretations: a study from the Banas River Basin, western India

Integration of data from ichnological and other interdisciplinary sources from the Quaternary Banas River Basin (India) has permitted the reconstruction of a composite ichnofacies model for the interpretation of paleoenvironments and paleosealevels. A glacioeustatic transgressive–regressive system tract of the ancient Arabian Sea has been recognized from the superposition of ichnofacies. The Pleistocene shallow marine Psilonichnus ichnofacies (ichnogenus Psilonichnus, Skolithos, Arenicolites and Thalassinoides of infaunal polychaete, crab and bivalve origin), developed in the Vadpag–Vend segment of the lower Banas sequence, corresponds to interglacial high sea stands. The overlying late Pleistocene–Holocene continental Coprinisphaera–Scoyenia mixed ichnofacies (paleosol association of delicate surficial traces of terrestrial insects and river floodplain association of aquatic traces of worms and crustaceans), formed in the Radhanpur–Varahi segment of the upper Banas sequence, represents the Last Glacial regressive mode of sealevel. Levee-bound oriented crustacean burrows may be used as new ichnological tools to locate buried paleochannels and aquifers. The juxtaposition of levees with alternate worm burrow and barren zones and floodplains with gastropod and barren zones indicates monsoonal lows and highs in the Holocene. The overprinting of the Coprinisphaera elements on the Scoyenia forms has resulted from the Recent–sub-Recent environmental degradations (rising temperature, spread of desert, shrinking saltmarshes and weakened fluvial forces) probably related to global warming and other Greenhouse processes. The readable ichnological signatures of the Quaternary glacioeustatic sealevel fluctuations and consequent climatic changes qualify the Banas model for wider application.

Topographic History of the Maui Nui Complex, Hawai'i, and Its Implications for Biogeography

The Maui Nui complex of the Hawaiian Islands consists of the islands of Maui, Moloka'i, Lana'i, and Kaho'olawe, which were connected as a single landmass in the past. Aspects of volcanic landform construction, island subsidence, and erosion were modeled to reconstruct the physical history of this complex. This model estimates the timing, duration, and topographic attributes of different island configurations by accounting for volcano growth and subsidence, changes in sea level, and geomorphological processes. The model indicates that Maui Nui was a single landmass that reached its maximum areal extent around 1.2 Ma, when it was larger than the current island of Hawai'i. As subsidence ensued, the island divided during high sea stands of interglacial periods starting around 0.6 Ma; however during lower sea stands of glacial periods, islands reunited. The net effect is that the Maui Nui complex was a single large landmass for more than 75% of its history and included a high proportion of lowland area compared with the contemporary landscape. Because the Hawaiian Archipelago is an isolated system where most of the biota is a result of in situ evolution, landscape history is an important determinant of biogeographic patterns. Maui Nui's historical landscape contrasts sharply with the current landscape but is equally relevant to biogeographical analyses.

Orbital tuning chronology for the Vostok climate record supported by trapped gas composition

We present data on the O 2/N 2 ratios of trapped gas samples for the entire length of the Vostok climate record. As in other cores, O 2/N 2 ratios in these samples are less than the atmospheric ratio, by a small and variable amount, because O 2 is selectively excluded during the gas trapping process, and because O 2 is also preferentially lost in poorly preserved core samples. Samples younger than 150 ka have large and variable O 2 depletions. Samples older than 200 ka have O 2/N 2 ratios that replicate well and vary smoothly with depth. We plot O 2/N 2 ratios of well replicated samples older than 160 ka, using a chronology derived by matching the δ 18O of paleoatmospheric O 2 (δ 18O atm) to northern hemisphere June insolation. On this timescale, O 2/N 2 varies coherently with local (78°S) summertime insolation. Based on time series analysis of the O 2/N 2 record and the dynamics of snow metamorphism at the surface, we conclude that summertime insolation influences physical properties of ice grains that control the degree of O 2 exclusion during bubble closeoff. O 2/N 2 in Vostok is thus arguably a property that records local summertime insolation and can be used to test independent chronologies for the core. We show that the δ 18O atm chronology, supported by the coincidence of O 2/N 2 ratios with insolation, is also compatible with recent radiometric dating of corals from high sea stands. We further successfully test the δ 18O atm tuning chronology by showing that it predicts a chronology for the GISP2 core which is essentially indistinguishable from the standard GISP2 chronology and, therefore, in excellent agreement with the radiometric chronology of Hulu Cave, China. An accurate chronology for the Vostok ice core is now in place.

Timing and warmth of the Last Interglacial period: new U-series evidence from Hawaii and Bermuda and a new fossil compilation for North America

The timing and duration of the Last Interglacial period have been controversial, with some studies suggesting a relatively short duration that is orbitally forced and others suggesting a long duration that is at most only partly related to orbital forcing. New, high-precison thermal ionization mass spectrometric (TIMS) U-series ages of Last Interglacial corals from Hawaii and Bermuda test these competing hypotheses. Waimanalo Formation corals from slowly uplifting Oahu, Hawaii range in age from ∼134 to ∼113 ka, with most ages between ∼125 and ∼115 ka. Combined with published U-series ages from nearby Lanai, the data suggest a long Last Interglacial period that may have occurred from ∼136 to at least 115 ka. The results indicate that orbital forcing may not have been the only control on ice sheet growth and decay, because sea level would have been high at times of relatively low Northern Hemisphere summer insolation. On tectonically stable Bermuda, deposits from the ∼200 ka (penultimate interglacial period), ∼120 ka (peak Last Interglacial period) and ∼80 ka (late Last Interglacial period) high sea stands have been newly dated. Fossil corals on Bermuda are derived from patch reefs that likely were “catch-up” responses to sea level rise. It is expected that U-series ages of Last-Interglacial corals on Bermuda should overlap with, but not be as old as the range of corals on Oahu. Last-Interglacial corals on Bermuda give a range of ∼125–113 ka, which supports this hypothesis. A large number of emergent marine deposits on Hawaii, Bermuda and along coastal North America have now been dated to the Last Interglacial period. Both Oahu and Bermuda have marine invertebrate faunas with a number of extralimital southern species of mollusks, suggesting warmer-than-present waters during the Last Interglacial period. Warmer waters are also suggested for Last-Interglacial localities around most of North America, from Florida to Canada and Greenland and Baja California to Alaska. These observations are consistent with similar warm-water faunas of Last-Interglacial age reported from Japan, the Mediterranean basin and Western Australia. It is likely that significant changes in ocean currents took place during the Last Interglacial period, with a movement of relatively warm waters to higher latitudes than is the case today.

Late Pleistocene Paleoclimates and sea-level change in the Mediterranean as inferred from stable isotope and U-series studies of overgrowths on speleothems, Mallorca, Spain

Phreatic overgrowths on speleothems form at the surface of brackish pools which are present in many coastal caves of Mallorca (Spain). Unlike common vadose speleothems formed in subaerial environments, their occurrence directly identifies the height of the sea level at the time of the carbonate deposition, because such pools are physically connected with the sea. These deposits from the Late Pleistocene have recorded the same global variations in oxygen isotopes as planktonic and benthonic foraminifera, corals and cave deposits. A number of phreatic overgrowths on speleothems have been dated using the Th/U method in order to determine the position of the sea level during Late Quaternary. The same samples, as well as some subaerial speleothems, have been analysed for 18 O/ 16 O and 13 C/ 12 C ratios. The former samples allow the analysis of variations in sea water component in the brackish pools associated with glacio-eustatic Mediterranean fluctuations, and the latter permit inferences concerning past continental climate changes. Some high sea-stands have been recognized in correspondence with Oxygen Isotope Stages (OIS): 9 or older, 7, 5e, 5c and 5a. Phreatic overgrowths on speleothems have also been formed during a colder phase (OIS 4), demonstrating that also in that period there were environmental conditions favourable for this kind of carbonate precipitation. Vadose crystallizations have recorded a cold period at 36 ka, corresponding with the end of OIS 3.