Interglacial Age Research Articles

Phylogeography of Cycas revoluta Thunb. (Cycadaceae) on the Ryukyu Islands: very low genetic diversity and geographical structure

Variations in the chloroplast and mitochondrial DNA of Cycas revoluta Thunb. (Cycadaceae) were examined in 22 populations distributed across the Ryukyu Islands and southern Kyushu. Among the 14,130 bp of sequence examined, only one site mutation and one indel were polymorphic. The identified polymorphisms were located in the spacers between trnS (UGA) and trnfM (CAU) of the chloroplast DNA and between nad1 exon B and exon C of the mitochondrial DNA, respectively. Three haplotypes were identified from the Ryukyu Islands and southern Kyushu. The areas of distribution of the three haplotypes were highly geographically structured. The boundaries of two of the three haplotypes were demarcated by Okinoerabujima Island in the middle Ryukyus. The northern type and southern types lay north and south of the island, respectively. The third haplotype was almost sympatrically distributed with the southern type. The genetic variation within C. revoluta was estimated to be very low (h = 0.641, π = 0.00071) in comparison to its relative in Taiwan, C. taitungensis, which possesses 97 cpDNA haplotypes and 55 mtDNA haplotypes from two relic populations. A reasonable explanation for the low genetic diversity of the cycad on the Ryukyu Islands could be severe bottleneck effects, resulting from the submersion of low islands and the diminished landmass of islands in the interglacial age in the Quaternary period. The geographically restricted nature of the haplotypes could be attributed to vicariance resulting from the land configuration of the Ryukyu Islands, including changes in geography during the interglacial age in the Quaternary.

Bacterial communities in two Antarctic ice cores analyzed by 16S rRNA gene sequencing analysis

Antarctic ice cores could preserve ancient airborne microorganisms. We examined bacteria in two Antarctic ice core samples, an interglacial age sample from Mizuho Base and a glacial age sample from the Yamato Mountains, by 16S rRNA gene sequencing analysis. Bacterial density, the number of bacterial OTUs and Simpson’s diversity index was larger in the Mizuho sample than in the Yamato sample. The 16S rDNA clone library from the Mizuho sample was dominated by the phylum Firmicutes, while the large part of that from the Yamato sample was composed of the Gamma proteobacteria group. Major sources of these identified bacteria estimated from their database records also differed between the samples: in the Mizuho sample bacterial species recorded from animals were higher than that of the Yamato sample, while in the Yamato sample bacteria from aquatic and snow-ice environments were higher than that of the Mizuho sample. The results suggest that these bacteria were past airborne bacteria that would vary in density, diversity and species composition depending on global environmental change. Our results imply that bacteria in Antarctic ice cores could be used as new environmental markers for past environmental studies.

Age and origin of alluvial sediments within and flanking the Mt Lofty Ranges, southern South Australia: a Late Quaternary archive of climate and environmental change

Quaternary alluvial sediments occur within and on the flanks of the Mt Lofty Ranges of southern South Australia. Within the ranges they occupy colluvium-filled bedrock depressions, alluvial-fan sequences at hill/plain junctions and river terraces that flank major streamlines in both locations. Sediments ranging in age throughout the Quaternary have been identified, but this paper focuses on those deposits of Late Quaternary age. Luminescence dating has verified a Last Interglacial age (132–118 ka) for the most widespread of the alluvial units, the Pooraka Formation. A younger, Marine Isotope Stage 3, alluvial unit, in places containing bones of the extinct marsupial Diprotodon, has also been identified. Deposition of the alluvial sediments is associated with relatively warmer and wetter conditions, whereas the valleys that they occupy were eroded under drier climatic conditions. A more widespread occurrence of Stage 3 units is expected to be present but has not yet been verified. Cold, arid environments are inferred from the presence of dunes (∼18 ka) deposited during the Last Glacial Maximum when stream valleys were incised. Grey/black mid-Holocene alluvium (Waldeila Formation), forming present-day floodplains and low river terraces, equates with the Holocene Hypsithermal. The sequence of climatic changes revealed by these sediments is correlated with evidence of Late Quaternary climatic change from other Australian locations. The identification of equivalent units in different tectonic settings reveals that sedimentation is largely climatically driven although active tectonism may accelerate the supply of sediments available for transport.

The last interglacial sea-level high stand on the southern Cape coastline of South Africa

The continental margin of southern South Africa exhibits an array of emergent marginal marine sediments permitting the reconstruction of long-term eustatic sea-level changes. We report a suite of optical luminescence ages and supplementary amino acid racemization data, which provide paleosea-level index points for three sites on this coastline. Deposits in the Swartvlei and Groot Brak estuaries display tidal inlet facies overlain by shoreface or eolian facies. Contemporary facies relations suggest a probable high stand 6.0-8.5 m above modern sea level (amsl). At Cape Agulhas, evidence of a past sea-level high stand comprises a gravel beach (ca. 3.8 m amsl) and an overlying sandy shoreface facies (up to 7.5 m amsl). OSL ages between 138±7 ka and 118±7 ka confirm a last interglacial age for all marginal marine facies. The high stand was followed by a sea-level regression that was associated with the accumulation of eolian dunes dating to between 122±7 ka and 113±6 ka. These data provide the first rigorous numerical age constraints for last interglacial sea-level fluctuations in this region, revealing the timing and elevation of the last interglacial high stand to broadly mirror a number of other far-field locations.

A reappraisal of the diversity of geomorphological and genetic processes of New Caledonian coral reefs: a synthesis from optical remote sensing, coring and acoustic multibeam observations

The diversity of oceanic and continental reef structures of New Caledonia is reviewed, taking into account their geological history and in particular, that since the last interglacial period. To guide this review, a new path is provided by following the diversity of units that have been mapped and characterized using high spatial resolution optical remote sensing data for the main New Caledonian coral reef complexes (banks, atolls, uplifted reefs, drowned reefs, fringing reefs, barrier reefs, patch reefs) and their individual reef-forming units. This interpretation, based on geomorphology, depth, and exposure has provided 161 unit types distributed across 4,537 km2 of reef area and 31,336 km2 of non-reef area. In addition to shallow reefs (0–30 m) described by optical remote sensing, the bathymetry of deep slopes between −20 to −1,000 m were recently mapped using multibeam acoustic data providing additional data to explain the morphological diversity. With the detailed three-dimensional topographic information acquired, hitherto unrecognized marine terraces and faulting became visible, indicating different episodes of formation of the barrier reef and of sea level variations. Finally, dating and coring corals provided a more accurate understanding of the genesis of the present reef structures. In contrast with the synoptic remote sensing data, cores provided only point data, but allowed the addition of a precise temporal dimension to the description of New Caledonian reefs. Cores provided a significant body of the information necessary for the establishment of models of reef settlement and development during the last interglacial ages in the New Caledonian region. The combined examination of the different sources of data, and the exhaustive description of remotely sensed reef units, allow a qualitative synoptic parallel to be drawn between the morphology of modern reefs and the contrasting patterns of reef growth, subsidence, and uplift rates occurring around New Caledonia.

Last Interglacial Age for aeolian and marine deposits and the Nahoon fossil human footprints, Southeast Coast of South Africa

Three hominid footprints preserved as casts were found in 1964 in Pleistocene aeolianites of the Nahoon Formation near East London, South Africa. Dating of the footprint-bearing aeolianite proved a lengthy and problematic task. Previous age estimates included a radiocarbon age of 29,090 − 390 + 410 years BP [Deacon, H.J., 1966. The dating of the Nahoon footprints. South African Journal of Science 62, 111–113], an infrared stimulated luminescence (IRSL) age of 144 ± 4 ka, a thermoluminescence age of 236 ± 8 ka (TL) and a luminescence subtraction age based on the IRSL and TL estimates of 75 ± 9 ka [Vogel, J.C., Wintle, A.G., Woodborne, S.M., 1999. Luminescence dating of coastal sands: overcoming changes in environmental dose rate. Journal of Archaeological Science 26, 729–733]. Thus there was no consistency among the ages derived using different dating methods. Here we describe optically stimulated luminescence (OSL) dating of quartz grains from a new set of samples collected from the footprint-bearing aeolianite and from associated geological formations. We also re-assessed the dose rate parameters for the sample for which TL and IRSL ages were reported and analysed the OSL signal from this sample. The new OSL dating yielded a coherent series of ages consistent with the stratigraphy as well as global and local sea level history. The indicated footprint age of 124 ± 4 ka thus relates to an important period of modern human evolution.

Late Devensian palaeoenvironmental changes in the sea area adjacent to Islay, SW Scotland: implications for the deglacial history of the island

Synopsis From a study of offshore borehole samples collected by the British Geological Survey in 1975, it is suggested that arctic marine or glaciomarine sediments of Dimlington Stadial (DS) age (>13 ka 14 C ka BP) in Loch Indaal, Islay, were laid down following the retreat of a glacier from the head of the loch, possibly only a few hundred radiocarbon years before the opening of the Windermere Interstadial (WI, 13–11 14 C ka bp ). A reworked molluscan fauna in the DS sediments, which is identical to that living in the area today, is believed to be of last interglacial age or earlier. Sediments of WI age and Holocene age (<10 4 C ka bp ) have also been intersected in the boreholes. Deposits of Loch Lomond Stadial age (11–10 14 C ka bp ) are absent from two boreholes investigated from Loch Indaal, but may be present in a borehole east of Islay. The proposal that ice of the Last Glacial Maximum reached only as far west as central Islay is unsupported by both this assessment and the published geomorphological evidence.

The sedimentology of the Late Pleistocene Bannow Till stratotype, County Wexford, southeast Ireland

The sedimentology and structural features of the Bannow Till are presented from two sites in Bannow Bay, County Wexford, southern Ireland, the stratotype for this Irish inland till. Beach deposits of last interglacial age are overlain locally by aeolian sands, providing a maximum age for the deposition of the Bannow Till. Three sedimentary units at Bannow comprise a vertical continuum of sheared bedrock (glacitectonite) grading upwards into a subglacial till of mostly local derivation. Shearing and clast macrofabric data indicate that ice flow was from the north to northeast, indicative of glacier movement from an inland source. At Wood Village, glacier advance from the northeast is recorded by the glacitectonization of bedrock, interglacial marine sands, aeolian sands and periglacial slope deposits. This glacitectonized sequence of sediments is overlain unconformably by an extensive tabular unit of interbedded diamictons and stratified sediments typical of deposition in proximal proglacial outwash fans. The Bannow Till is classified as a glacitectonite-subglacial traction till continuum, having been derived from the shearing and fragmentation of shale bedrock from which blocks and slabs have been displaced along fault planes by brittle deformation and then edge-rounded and pulverized. The stratigraphic nature of the evidence for glaciation at Bannow Bay, and hence the Bannow Till stratotype, is typical of glacier/ice-sheet marginal settings in areas of soft bedrock.

Paleoecology of Organic Deposits of Probable Last Interglacial Age in Northern Ontario

Nonglacial deposits in northern Ontario that may date to the last interglacial interval are well known from the Hudson Bay Lowlands where they have been described in sections along several river valleys. Soil horizons, peat beds and other organic sediment sequences comprise the Missinaibi Formation of the Moose River Basin studied for pollen and macrofossils. Results suggest that the climate was as warm or warmer than present, and spruce woodlands prevailed among broad expanses of bog and fen. The Beaver River peat records conditions similar to the present in the Fort Severn area with open spruce woodlands dispersed in peatlands. South of the Lowlands in the Timmins area, a widespread organic-silt horizon termed the Owl Creek beds is stratigraphically equivalent to the Missinaibi Formation. The waning phase of a warm interval is represented, with early climate possibly similar to the present and the later climate much cooler. Correlation of the Missinaibi Formation with substage 5e of the deep-sea oxygen isotope record is corroborated by amino acid results on marine shells from some associated units. Analysis of shells from beneath the Beaver River peat bed indicate that this interval may be considerably younger, possibly substage 5c or, more likely, 5a. The Owl Creek beds may relate to sub-stage 5e, or to one of the younger intervals, 5c or 5a.

Vertebrates of the Last Interglaciation in Canada: A Review, with New Data

Vertebrate fossils and faunas that are reasonably inferred to be of last (Sangamonian) interglacial age are considered in geographic order from east to west to north in Canada. Data on localities, vertebrate taxa, stratigraphy, geochronology, paleoenvironment and paleoclimate are considered. Information on key faunas from Toronto, Fort Qu'Appelle, Saskatoon. Medicine Hat and Old Crow River is supplemented by data on smaller faunas and, in some cases, individual specimens. New data are included for several localities. Fishes, such as whitefish (Coregonus sp.) and pike (Esox sp.). had broad distributions from eastern to northwestern Canada. Except for a turtle (Emydoidea blandingi) from lnnerkip, Ontario, amphibians and reptiles have not yet been reported from Canada during the Sangamon Interglaciation. Several species of grouse-like birds (Tetraonidae) are known from western Canada. Among the mammals. American mastodons (Mammut americanum), mammoths (Mammuthus sp.), beavers (Castor canadensis), giant beavers (Castoroides ohioensis), muskrats (Ondatra zibethicus), voles (Microtus sp.). white-tailed deer (Odocoileus virginianus), stag moose (Cervalces sp.), bison [perhaps mainly giant bison (Bison latifrons)\ and muskoxen (Ovibovini) were evidently most widespread during the last interglacial interval. The western plains had a characteristic large mammal fauna that included Columbian mammoths (Mammuthus columbi), Scott's horses (Equus scotti), small horses (Equus conversidens), western camels (Camelops hesternus). pronghorns (Antilocapridae), giant bison (Bison latifrons) and helmeted muskoxen (Sy m bos cavifrons).

Amino Acid Evidence Indicating Two or More Ages of Pre-Holocene Nonglacial Deposits In Hudson Bay Lowland, Northern Ontario

Amino acid studies have identified pre-Holocene non-glacial sediments in the Hudson Lowland which are significantly younger than Bell Sea sediments of the Missinaibi Formation. This younger unit is represented by marine sediments on the Severn and Abitibi rivers. Buried organic material on Beaver River is correlated with the younger Severn and Abitibi river marine sediments based on amino acid evidence. Assuming that Bell Sea sediments are of last interglacial (130-120 ka) age, the younger nonglacial sediments may have been deposited late in 18O stage 5 (80-75 ka). Paleoecologic studies of the Beaver River organics indicate climate at least as warm as present.

Global sea-level fluctuations during the Last Interglaciation (MIS 5e)

The geomorphology and morphostratigraphy of numerous worldwide sites reveal the relative movements of sea level during the peak of the Last Interglaciation (Marine Isotope Stage (MIS) 5e, assumed average duration between 130±2 and 119±2 ka). Because sea level was higher than present, deposits are emergent, exposed, and widespread on many stable coastlines. Correlation with MIS 5e is facilitated by similar morphostratigraphic relationships, a low degree of diagenesis, uranium–thorium (U/Th) ages, and a global set of amino-acid racemization (AAR) data. This study integrates information from a large number of sites from tectonically stable areas including Bermuda, Bahamas, and Western Australia, and some that have experienced minor uplift (∼2.5 m/100 ka), including selected sites from the Mediterranean and Hawaii. Significant fluctuations during the highstand are evident at many MIS 5e sites, revealed from morphological, stratigraphic, and sedimentological evidence. Rounded and flat-topped curves derived only from reef tracts are incomplete and not representative of the entire interglacial story. Despite predictions of much different sea-level histories in Bermuda, the Bahamas, and Western Australia due to glacio- and hydro-isostatic effects, the rocks from these sites reveal a nearly identical record during the Last Interglaciation. The Last Interglacial highstand is characterized by several defined sea-level intervals (SLIs) that include: (SLI#1) post-glacial (MIS 6/5e Termination II) rise to above present before 130 ka; (SLI#2) stability at +2 to +3 m for the initial several thousand years (∼130 to ∼125 ka) during which fringing reefs were established and terrace morphology was imprinted along the coastlines; (SLI#3) a brief fall to near or below present around 125 ka; (SLI#4) a secondary rise to and through ∼+3–4 m (∼124 to ∼122 ka); followed by (SLI#5) a brief period of instability (∼120 ka) characterized by a rapid rise to between +6 to +9 m during which multiple notches and benches were developed; and (SLI#6) an apparently rapid descent of sea level into MIS 5d after 119 ka. U/Th ages are used to confirm the Last Interglacial age of the deposits, but unfortunately, in only two cases was it possible to corroborate the highstand subdivisions using radiometric ages. Sea levels above or at present were relatively stable during much of early MIS 5e and the last 6–7 ka of MIS 1, encouraging a comparison between them. The geological evidence suggests that significant oceanographic and climatic changes occurred thereafter, midway through, and continuing through the end of MIS 5e. Fluctuating sea levels and a catastrophic termination of MIS 5e are linked to the instability of grounded and marine-based ice sheets, with the Greenland (GIS) and West Antarctic (WAIS) ice sheets being the most likely contributors. Late MIS 5e ice volume changes were accompanied by oceanographic reorganization and global ecological shifts, and provide one ominous scenario for a greenhouse world.

Age and biostratigraphic significance of the Punung Rainforest Fauna, East Java, Indonesia, and implications for Pongo and Homo

The Punung Fauna is a key component in the biostratigraphic sequence of Java. It represents the most significant faunal turnover on the island in the last 1.5 million years, when Stegodon and other archaic mammal species characteristic of earlier Faunal stages were replaced by a fully modern fauna that included rainforest-dependent species such as Pongo pygmaeus (orangutan). Here, we report the first numerical ages for the Punung Fauna obtained by luminescence and uranium-series dating of the fossil-bearing deposits and associated flowstones. The Punung Fauna contained in the dated breccia is of early Last Interglacial age (between 128 ± 15 and 118 ± 3 ka). This result has implications for the age of the preceding Ngandong Fauna, including Homo erectus remains found in the Ngandong Terrace, and for the timing of Homo sapiens arrival in Southeast Asia, in view of claims for a modern human tooth associated with the Punung breccia.

Reef development at high-latitudes during multiple interglacial cycles: New evidence from Lord Howe Island, southwestern Pacific

Reef development during past Interglacial periods, when sea level and sea surface temperatures were higher than today, provide unique insights into how reef systems may respond to projected human-induced global warming. Lord Howe Island currently represents the southernmost limit of reef development in the Pacific. Reef growth of Pleistocene age has been inferred to have occurred around the island, and this paper provides the first detailed descriptions on the character of this development. Two phases of reef growth are identified, which occurred as isolated fringing reefs along the edge of the basaltic hills of the island. Uranium-series dating indicates that the upper part of the sequence is of Last Interglacial age, however extensive calcite recrystallisation meant the lower part of the sequence does not yield reliable ages. Calcite cements suggest that several phases of recrystallisation have occurred meaning the lower part of the sequence is most likely to represent reef of Penultimate Interglacial age. Component analysis of the sedimentary matrix within the reef indicates coralline algae dominated sands which are very similar to the modern reef environment. This suggests that the environment at Lord Howe Island has remained at or close to the environmental limits for reef growth during the past few interglacials, despite lithospheric plate motion moving this island further north into reef building seas.

Episodes of reef growth at Lord Howe Island, the southernmost reef in the southwest Pacific

Lord Howe Island lies at the present latitudinal limit to reef growth in the Pacific and preserves evidence of episodes of reef development over the Late Quaternary. A modern fringing reef flanks the western shore of Lord Howe Island, enclosing a Holocene lagoon, and Late Quaternary eolianites veneer the island. Coral-bearing beach and shallow-water calcarenites record a sea level around 2–3 m above present during the Last Interglacial. No reefs or subaerial carbonate deposits occur on, or around, Balls Pyramid, 25 km to the south. The results of chronostratigraphic studies of the modern Lord Howe Island reef and lagoon indicate prolific coral production during the mid-Holocene, but less extensive coral cover during the late Holocene. Whereas the prolific mid-Holocene reefs might appear to reflect warmer sea-surface temperatures, the pattern of dates and reef growth history are similar to those throughout the Great Barrier Reef and across much of the Indo-Pacific and are more likely correlated with availability of suitable substrate. Little direct evidence of a Last Interglacial reef is now preserved, and the only evidence for older periods of reef establishment comes from clasts of coral in a well-cemented limestone unit below a coral that has been dated to the Last Interglacial age in a core at the jetty. However, a massive reef structure occurs near the centre of the wide shelf around Lord Howe Island, veneered with Holocene coralline algae. Its base is 40–50 m deep and it rises to water depths of less than 30 m. This fossil reef is several times more extensive than either Holocene or Last Interglacial reefs appear to have been. Holocene give-up reef growth is inferred during the postglacial transgression, but an alternative interpretation is that this is a much older landform, indicating reefs that were much more extensive than modern reefs at this marginal site.

Late Quaternary sea-level highstands in the central and eastern Indian Ocean: A review

The relative sea-level history of several atolls in the central and eastern Indian Ocean, including the Cocos (Keeling) Islands, Chagos Archipelago, and the Maldives–Laccadive Archipelagoes, has been debated for over a century but takes on a particular significance in the face of anticipated climate change. For each of these central and eastern Indian Ocean atolls Pleistocene limestone is encountered at depths of 6–20 m below sea level. On the Cocos (Keeling) Islands this has been dated to Last Interglacial age. Conglomerate platform underlies the reef islands on Cocos within which a sequence of fossil microatolls of massive and branching Porites records a gradual fall of sea level relative to the atoll. In the Maldives, the significance of outcrops of ‘reef rock’ has been vigorously debated without resolving sea-level history. Although in situ Heliopora occurs on the reef flat of Addu Atoll, dated at around 2700 radiocarbon yrs BP, other evidence for higher sea level remains poorly constrained. Conglomerates of a similar age have been described from the Chagos Archipelago, but it has not been unequivocally demonstrated that they formed under conditions of relatively higher sea level. In contrast to reefs further west in the Indian Ocean, each of these atolls has living microatolls of massive Porites that have been constrained in their upward growth by sea level. Interpretation of the upper surface of two such specimens from the Cocos (Keeling) Islands indicates broad fluctuations in the sea surface over the past century; similar microatolls are described from the Maldives implying little change in sea level over recent years. Regardless of minor past fluctuations, most reef islands in the Maldives are particularly low-lying and appear vulnerable to inundation, and extracting a more detailed sea-level history remains an important challenge.

Using cave deposits as geologic tiltmeters: Application to postglacial rebound of the Sierra Nevada, California

Secondary calcite shelfstone deposits in caves can be used to precisely measure tilting over geologic timescales. Calcite deposited along the edges of former pools can be surveyed to within a single millimeter, and can be dated using uranium‐series disequilibrium. Two caves in the southern Sierra Nevada, California, contain tilted calcite deposits of glacial age. A third cave contains a similar but untilted deposit of older interglacial age. The cave deposits record glacio‐isostatic rebound of the Sierra Nevada, following melting of an ice cap ∼15,000 years ago. Models of crustal flexure beneath mapped ice thickness reproduce the observed tilting with an effective elastic thickness (Te) of approximately 5 km.

Overlapping species boundaries and hybridization within the Montastraea “annularis” reef coral complex in the Pleistocene of the Bahama Islands

Recent molecular analyses indicate that many reef coral species belong to hybridizing species complexes or ''syngameons.'' Such complexes consist of numerous genetically distinct spe- cies or lineages, which periodically split and/or fuse as they extend through time. During splitting and fusion, morphologic intermediates form and species overlap. Here we focus on processes as- sociated with lineage fusion, specifically introgressive hybridization, and the recognition of such hybridization in the fossil record. Our approach involves comparing patterns of ecologic and mor- phologic overlap in genetically characterized modern species with fossil representatives of the same or closely related species. We similarly consider the long-term consequences of past hybrid- ization on the structure of modern-day species boundaries. Our study involves the species complex Montastraea annularis s.l. and is based in the Bahamas, where, unlike other Caribbean locations, two of the three members of the complex today are not genetically distinct. We measured and collected colonies along linear transects across Pleistocene reef terraces of last interglacial age (approximately 125 Ka) on the islands of San Salvador, Andros, and Great Inagua. We performed quantitative ecologic and morphologic analyses of the fossil data, and compared patterns of overlap among species with data from modern localities where species are and are not genetically distinct. Ecologic and morphologic analyses reveal ''moderate'' overlap ( .10%, but statistically signifi- cant differences) and sometimes ''high'' overlap (no statistically significant differences) among Pleistocene growth forms (5 ''species''). Ecologic analyses show that three species (massive, col- umn, organ-pipe) co-occurred. Although organ-pipes had higher abundances in patch reef envi- ronments, columnar and massive species exhibited broad, completely overlapping distributions and had abundances that were not related to reef environment. For morphometric analyses, we used multivariate discriminant analysis on landmark data and linear measurements. The results show that columnar species overlap ''moderately'' with organ-pipe and massive species. Compar- isons with genetically characterized colonies from Panama show that the Pleistocene Bahamas spe- cies have intermediate morphologies, and that the observed ''moderate'' overlap differs from the morphologic separation among the three modern species. In contrast, massive and columnar spe- cies from the Pleistocene of the Dominican Republic comprise distinct morphologic clusters, similar to the modern species; organ-pipe species exhibit ''low'' overlap ( ,10%, only at species margins) with columnar and massive species. Assuming that ''moderate'' overlap implies hybridization and ''high'' overlap implies more com- plete lineage fusion, these results support the hypothesis of hybridization among species within the complex in the Bahamas during the Pleistocene. Hybridization involved introgression of three distinct evolutionary lineages, in association with Pleistocene sea level and temperature fluctua- tions, and appears to have been limited geographically primarily to the Bahamas and the northern Caribbean. Thus, not only does the structure of species boundaries within the complex vary geo- graphically, but these geographic differences may have persisted since the Pleistocene.

Uplift rate and landscape development in southwest Fiordland, New Zealand, determined using 10Be and 26Al exposure dating of marine terraces

We demonstrate that cosmogenic nuclide surface exposure dating can be used to provide the first well-constrained age for a Fiordland bedrock surface that was created by coastal erosion and has since been uplifted. Tight clustering of 10Be and 26Al apparent exposure ages between 102–119 kyr on a terrace with strandline at 65 ± 8 m gives a last interglacial age of terrace formation of 130–120 ka, and an uplift rate of 0.52 ± 0.08 mm/yr. Apparent exposure ages from a higher (92–130 m), more incised region of remnant coastal morphology fall in the range 53–111 kyr. The anomalously low ages and large variance demonstrate that weathering and fluvial or rockfall erosion rates are too extreme at the higher sites to determine an age of coastal erosion. Sea level samples have apparent exposure ages in the range 2–11 kyr, with an uncertainty of about 3 kyr. This is consistent with surface exposure during the present sea level high-stand, indicates minimal inheritance of ancient cosmogenic nuclides, and is in accord with geomorphic arguments. Mean 26Al/ 10Be ratios of 6.6 for each sample set is consistent with the actively exhuming late Quaternary tectonic setting. Large boulders and gently convex rocky outcrops formed during coastal erosion preserve surfaces that are least modified during later uplift, and are hence the best sites for determining the age of coastal erosion.

Evolution of marine terraces and sea level in the last interglacial, Cave Hill, Barbados

Research Article| January 01, 2004 Evolution of marine terraces and sea level in the last interglacial, Cave Hill, Barbados R.C. Speed; R.C. Speed 1Department of Earth System Science, University of California, Irvine, California 92697, USA Search for other works by this author on: GSW Google Scholar H. Cheng H. Cheng 2Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA Search for other works by this author on: GSW Google Scholar Author and Article Information R.C. Speed 1Department of Earth System Science, University of California, Irvine, California 92697, USA H. Cheng 2Department of Geology and Geophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA Publisher: Geological Society of America Received: 17 Apr 2002 Revision Received: 01 Jun 2003 Accepted: 05 Jul 2003 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (2004) 116 (1-2): 219–232. https://doi.org/10.1130/B25167.1 Article history Received: 17 Apr 2002 Revision Received: 01 Jun 2003 Accepted: 05 Jul 2003 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation R.C. Speed, H. Cheng; Evolution of marine terraces and sea level in the last interglacial, Cave Hill, Barbados. GSA Bulletin 2004;; 116 (1-2): 219–232. doi: https://doi.org/10.1130/B25167.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The uplifted marine terrace of last interglacial (stage 5e) age at Cave Hill, Barbados, has been investigated with views toward terrace architecture, developmental processes, and sea level history. Methods include stratigraphic analysis of new deep exposures, precise 230Th geochronology, and geomorphic mapping. Cave Hill was central to earlier studies that led to important ideas on reef and terrace evolution but with which we find significant disagreement. We present a new model of terrace evolution that emphasizes the role of marine erosion, deposition of carbonate cover during the full eustatic cycle rather than only at highstand, and principal reef development during transgression rather than at highstand by keep-up rather than catch-up growth. The new model and geochronology contribute to an improved understanding of surficial processes during emergence of uplifting coral coasts and of global sea level changes in the last interglacial.Transgression in stage 5e at Cave Hill was accompanied by progressive marine erosion of a terrace floor and receding seacliff and deposition of a seaward-thickening reefal wedge on the floor and above limestones of stage 6 and 7 ages. The wedge contains a diachronous basal Acropora palmata fringe reef. This is overlain by an in-place A. cervicornis reef that aggraded progressively during sea level rise. The transgressive phase took place between 136 ka (or earlier) and ca. 128 ka. During highstand between ca. 127 and 120 ka, the floor and seacliff continued to recede landward. Re gression began at or after ca. 120 ka, and sea level fell ≥37 m below the highstand level by ca. 115 ka. In stage 5c, the seaward front of the last interglacial terrace was eroded landward an uncertain distance. The sea level record at Cave Hill has implications for timing and constituent events of the penultimate glacial, the last interglacial highstand, and the fall in sea level at the transition from stage 5e to stage 5d.Shoreline angles, which are isochronous linear geomorphic features, are the most accurate markers of sustained highstand levels. Highstand levels and uplift rates interpreted from A. palmata in Barbados are less accurate and lower because the coral grew mainly in transgression. The coral-derived data therefore include uncertainties of depths of growth and collapse. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.