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1.
John F. Wehmiller 《Quaternary Science Reviews》1982,1(2):83-120
Amino acid racemization (AAR) studies of Quaternary mollusks (mostly marine mollusks from coastal deposits) are reviewed. Data obtained in regional studies from the U.S. Atlantic and Pacific coasts, Baffin Island, the United Kingdom, and tropical islands are discussed as they relate to method evaluation, kinetic model development, and aminostratigraphic applications.U.S. Pacific coast studies have been employed for estimating tectonic deformation rates, study of molluscan zonation patterns in the late Pleistocene, and in kinetic model evaluation. U.S. Atlantic coast studies have identified multiple aminostratigraphic zones in areas with complex morphostratigraphic relationships, and have also revealed some important conflicts between aminostratigraphic temperature concepts and radiometric data. Studies in the United Kingdom, involving coastal sites and non-marine interglacial sites, identify some stratigraphic and kinetic conflicts but provide a preliminary chronostratigraphic model for the classical interglacial terminology of the U.K. middle to late Pleistocene. Baffin Island studies, involving AAR data and UTh dating of shells, have resulted in some significant revisions of previous chronologic models. The Arctic environment has also stimulated some novel approaches in the collection and interpretation of AAR results. Tropical island studies, though few in number, aid in calibration of observed racemization and also aid in correlation of coastal deposits with late Pleistocene isotopic ice-volume records. 相似文献
2.
Thomas M. Cronin 《Quaternary Research》1980,13(2):213-229
Marine ostracodes from 50 localities were studied to determine the age and elevation of Pleistocene sea levels in the Atlantic coastal plain from Maryland to northern Florida. Using ostracode taxon and concurrent ranges, published planktic biostratigraphic, paleomagnetic, and radiometric data, ostracode assemblage zones representing early (1.8-1.0 my), middle (0.7-0.4 my), and late (0.3-0.01 my) Pleistocene deposition were recognized and used as a basis for correlation. Ostracode biofacies signifying lagoonal, oyster bank, estuarine, open sound, and inner sublittoral environments provided estimated ranges of paleodepths for each locality. From these data the following minimum and maximum Pleistocene sea-level estimates were determined for the southeastern coastal plain: late Pleistocene, 2–10 m from Maryland to northern Florida; middle Pleistocene, 6–15 m in northern South Carolina; early Pleistocene, 4–22 m in central North Carolina, 13–35 m in southern North Carolina, and 6–27 m in South Carolina. Climatically induced glacio-eustatic sea-level fluctuations adequately account for the late Pleistocene sea-level data, but other factors, possibly differential crustal uplift, may have complicated the early Pleistocene record. 相似文献
3.
D. Q. Bowen 《International Journal of Earth Sciences》1999,88(2):276-284
Early attempts at land–sea correlations between continental glaciations and the marine δ18O record were premature without a high-resolution continental stratigraphy. Existing schemes of continental subdivision and
correlation-based facies floras and facies faunas do not provide the necessary resolution. This paper reports on a new high-resolution
subdivision and correlation of the Pleistocene of the British Isles. Subdivision and correlation is accomplished primarily
by aminostratigraphy based on aminozones which is calibrated by other geochronological means (U-series, TL, OSL, ESR, 14C, palaeomagnetic and 36Cl rock-exposure dating) for correlation with oxygen isotope stratigraphy. These data are then used to test the hypotheses
of Shackleton (1987) and Raymo (1997) that only four major glaciations occurred in the Brunhes Chron: during oxygen isotope
stages 16, 12, 6 and 2. Their hypotheses are confirmed except for stage 2, when at least part of the British ice sheet was
at its maximum somewhat earlier during stages 4 and 3.
Received: 8 June 1998 / Accepted: 27 November 1998 相似文献
4.
Amino acid enantiomeric (D/L) ratios in the mollusk Mercenaria are compared with recently published biostratigraphic and/or U-series solitary coral data from 22 Quaternary localities on the central and southern Atlantic Coastal Plain. In all cases, local relative aminostratigraphic sequences are consistent with relative ages inferred from U-series or biostratigraphic data, although occasionally more depositional events are recognized by aminostratigraphic than biostratigraphic methods. However, if the U-series data are used as age calibrations for the D/L values, latitudinal trends of “isochronous” D/L values are highly variable and conflict with trends expected from the present temperature gradient, which is smooth and nearly linear between 45° and 25° N. Age estimation can be performed independently of the U-series data using a kinetic model that relies on the assumption that Pleistocene temperature gradients have also been smooth functions of latitude, although significantly steeper than the present temperature gradient. Within the uncertainties of this assumption, kinetic model age estimates for localities in the coastal plain fall into the following groups: 70,000–130,000 yr, 200–250,000 yr, 300,000–400,000 yr, 500,000–600,000 yr, 700,000–800,000 yr, and > 1,000,000 yr. Major conflicts between these model age estimates are observed for localities near Charleston, South Carolina and in central Virginia. These conflicts could indicate that the basic temperature assumptions of aminostratigraphy are incorrect, and that apparent local aminostratigraphic sequences (clusters of different D/L values) could be due to factors other than age difference. Alternatively, some of the U-series dates may be only minimum ages for these localities. 相似文献
5.
True 'periglacial' forms and deposits of late (and middle) Pleistocene age can be recognized in the Drakensberg and the adjacent parts of the Cape Province in the latitudinal zone 28° 30'-31°20' S; lower limits in the eastern Cape and Natal appear to lie near 1500–1800 m, rising from southwest to northeast, and at 2600 m in Lesotho. Significant nivation in the Drakensberg is also indicated, but at higher elevations. Alleged 'periglacial' phenomena in Rhodesia, the Transvaal, the Cape Folded Ranges and their coastal margin are not acceptable as such and include no evidence for cryonival or geliflual proceses. Nonetheless, there is bonafide evidence for several phases of accelerated Pleistocene frost-weathering, including sections of the Cape Coast that experience next to no frost today and would require a winter temperature depression of at least 10° C. It cannot be disputed that southern Africa has experienced cold, glacial-age climates, but there is a serious problem about many of the geomorphological observations or their interpretation. 相似文献
6.
Some confusion exists concerning the early life history of ladyfish,Elops saurus, as a result of the use of confusing terms in describing the three morphologically and ecologically distinct growth phases of this species. This has resulted in conflicting data on the occurrence of stage I (leptocephali) and stage II (early metamorphic) larvae in oligohaline and mesohaline estuarine zones. The early life history ofE. saurus is reviewed relative to the collection of 17 stage II larvae at the freshwater transition zone of the James River, Virginia. There are no known spawning populations ofE. saurus north of Cape Hatteras, North Carolina. These collections represent the first recurrent record north of Cape Hatteras and for Chesapeake Bay. 相似文献
7.
《Geochimica et cosmochimica acta》1999,63(3-4):393-403
Potential hydrolysis rates of three different polysaccharides, pullulan, laminarin, and xylan, were measured in intact sediment cores from Cape Lookout Bight, North Carolina, in order to constrain the rates at which a fraction of the high-molecular-weight sedimentary carbon pool may be hydrolyzed to lower molecular weights. Potential hydrolysis rates of pullulan were somewhat higher than those of laminarin and xylan. Highest potential rates were measured in surface sediments; rates at depths of 5–7 and 14–16 cm differed relatively little from one another. Total dissolved carbohydrates, dissolved organic carbon (DOC), sulfate, and sulfate reduction rates were also measured and compared with data previously collected at Cape Lookout Bight in order to investigate carbohydrate dynamics and establish the relative contribution of carbohydrates to the sedimentary carbon budget. Total porewater carbohydrates constitute a disproportionate fraction of DOC, ranging from a maximum of 85% in near-surface intervals to 24% at depths of 14–16 cm. A comparison of potential hydrolysis rates, dissolved carbohydrate concentrations, DOC, and sulfate reduction rates, along with results from a wide range of studies previously conducted at this site suggests that hydrolysis of high-molecular-weight polysaccharides can potentially be very rapid relative to carbon remineralization rates. Dissolved porewater carbohydrates form a dynamic pool that is likely turned over on short timescales in Cape Lookout Bight sediments. 相似文献
8.
牙形石在以碳酸盐岩为主的华北奥陶系划分对比中占有举足轻重的地位。针对华北奥陶纪牙形石的研究已持续近半个世纪,总体上可以分为两个阶段:第一阶段自20世纪70年代到21世纪初,第二阶段为最近10年(2010—2020)。第一阶段以建立牙形石生物地层序列为目标,主要为解决石油勘探过程中地层时代的确定和地层对比的需求;第二阶段的研究以修订化石带为主,目的是与国际地层研究接轨。近年来在华北板块西北缘的工作显示,该区奥陶纪牙形石在纵向上具有显著的生态变化,可分为达瑞威尔期中期、达瑞威尔期晚期—桑比期中期、桑比期晚期—凯迪期中期3个时段。第一时段以介于北美中大陆区和北大西洋区之间的热带台地边缘型牙形石为特征;第二时段以北大西洋型为主混有少量亚澳型牙形石为特征;第三时段以亚澳型和北美中大陆型牙形石混生为特征。在华北西北缘尽可能使用广布性标准牙形石属种进行化石带厘定,共识别牙形石带12个,自下而上分别是达瑞威尔期Histiodella cf. holodentata间隔带、Histiodella kristinae谱系带、Histiodella bellburnensis延限带、Dzikodus tablepointensis间隔带、Eoplacognathus suecicus间隔带、Pygodus serra间隔带和Pygodus anserinus(早期型)间隔亚带,桑比期Pygodus anserinus(晚期型)间隔亚带和Belodina compressa间隔带,凯迪期Belodina confluens间隔带、Yaoxianognathus neimengguensis间隔带和Yaoxianognathus yaoxianensis间隔带。由于部分化石带与国际同名带的对比还存在一些矛盾,尚需今后进一步解决。 相似文献
9.
Stratigraphic, geomorphologic and isoleucine epimerization studies at 15 sites in Mallorca define four aminozones (A, C, E and F-G) of increasing age that are related to transgressive-regressive marine cycles from the Holocene to the mid Pleistocene. Calibration of aminozone E (Glycymeris aIle/Ile mean from all sites = 0.41 ± 0.03 (n=38)) is provided by a 129 ± 7 ka U-series coral age on Cladocora caespitosa from Son Grauet. Of the younger aminozones, A relates to the Holocene transgression and aminozone C to a mid to late isotopic stage 5 event (90 ± 15 ka) revealed only by supralittoral eolianites. Assigning an age to the older, poorly resolved aminozones F and G (called F-G in this case) is uncertain without supporting radiometric data. But an age of > 180 ka can be assigned to these aminozone (s) F-G based on a kinetic model and other examples in the Mediterranean.Several deposits, previously dated (U-series, molluscs) between 75 and > 300 ka appear to belong to the last interglacial complex (Stage 5) and aminozone E. A proposed revision of the positive sea level history of Mallorca shows multiple minor oscillations during the major last interglacial cycle (Stage 5) and two mid Pleistocene sea levels, one lower than present and the other at about 14 m a.s.l. 相似文献
10.
Recently recognized field evidence clearly indicates that both the Nebraskan and Kansan Glaciations are divisible into stades on the basis of a stratigraphic record of ice-margin fluctuations. Two Nebraskan stades and three Kansan stades have been identified; it is suggested that others will be found. Recognition of multiple stades requires a thorough review of all Early Pleistocene stratigraphic and paleontologic age assignments applied in the American Midwest. 相似文献
11.
The Fichtelgebirge and Steinwald areas are situated at the western end of the Cenozoic Eger graben. Repeated Neogene fault activity and polyphase morphogenesis created a complex morphotectonic structure. Based on morphotectonic criteria three stages of tectonic activity can be determined: (a) late Oligocene to early Miocene; (b) middle-late Miocene; and (c) late Pliocene to early Pleistocene. Due to the Neogene tectonic movements, the pre-basaltic (preOligocene to Miocene) landscape has been differentially uplifted/downthrown and intensely modified by post-basaltic surface planation (HF). Broad paleovalleys (AT) of late Miocene to early Pliocene age and a system of Pliocene and Quaternary fluvial terraces and pediments (BT and ET) have been incised into the widespread HF relief elements. Due to repeated faulting and erosion, the stratigraphic record of Neogene sediments within the studied area is fragmentary. 相似文献
12.
J. Tyler Faith 《Quaternary Research》2011,75(1):159-165
The Cape grysbok is endemic to southern Africa's Cape Floral Region where it selectively browses various species of dicotyledonous vegetation. Fossil evidence indicates that the grysbok persisted under glacial and interglacial conditions throughout the late Quaternary and inhabited a range of environments. This study employs mesowear analysis to reconstruct grysbok diets over time and in response to changing environments at Nelson Bay Cave, Die Kelders Cave 1, Klasies River Mouth, and Swartklip 1. Results indicate that the amount of grasses (monocots) versus leafy vegetation (dicots) included in the diet fluctuated over time and largely in agreement with changes in faunal community structure. The case for dietary flexibility is particularly clear at Nelson Bay Cave, where there is a significant trend from mixed feeding towards increased browsing from the late Pleistocene (~ 18,500 14C yr BP) through the Holocene. Dietary shifts at Nelson Bay Cave are consistent with the hypothesis that declining grassland productivity is responsible for the terminal Pleistocene extinction of several large ungulates in southern Africa. Furthermore, the short-term dietary shifts demonstrated here (100s to 1000s of years) provide an important caution against relying on taxonomic uniformitarianism when reconstructing the dietary preferences of fossil ungulates, both extant and extinct. 相似文献
13.
Borings from the barrier island/lagoon system of the Eastern Shore of Virginia penetrated an unconformity which separates Pleistocene barrier island and offshore marine sediments from the overlying Holocene tidal delta and barrier island sediments. Offshore marine sediments and deposits within the flood-tidal delta (marsh, tidal flat-bay, inlet-mouth bar complex) are recognized on the basis of sediment color, composition, grain-size changes in the vertical sequence, presence of organic matter, and faunal suite. Subsurface data, historical records, and morphology of lateral accretion on barrier islands suggest that major inlets in the vicinity of Wachapreague have been relatively stable throughout Holocene time; they appear to be located where Pleistocene stream valleys previously existed. Holocene barrier islands apparently developed on drainage divide areas following post-Wisconsin transgression of the sea.
The initial phase of tidal delta development was characterized by vertically accreting, fan-shaped, inlet-mouth bars; tidal channels stabilized after bar crests had shoaled sufficiently for marsh to form. With landward progradation across the lagoon, sand-rich deposits graded laterally away from the inlets and vertically into clayey sand and silty clay of the tidal flat-bay and marsh environments.
Ebb inlet-mouth bars developed asymmetrically southward in response to littoral drift. Flood tidal deltas also built preferentially toward the south as indicated by: (1) sand distribution of the inlet-mouth bar complex; and (2) greater development of marsh south of the inlets. 相似文献
14.
15.
《Quaternary Science Reviews》2007,26(5-6):773-792
New subsurface data reveal a nearly continuous stratigraphic record of Middle to Late Pleistocene loess sedimentation preserved beneath upland summits in eastern Nebraska, USA. Thickness and grain size trends, as well as pedologic evidence, indicate significant changes in loess sources, accumulation rates, and depositional environments. The newly defined Kennard Formation accumulated in the Middle Pleistocene, and may represent multiple thin increments of distal loess from nonglacial sources on the Great Plains. The overlying Loveland Loess, up to 18 m thick and deposited during Oxygen Isotope Stage 6 (OIS 6) (Illinoian glaciation), probably records the emergence of the Missouri River valley as a major glaciogenic loess source. The prominent Sangamon Geosol formed through long-term pedogenic alteration of the upper Loveland Loess during OIS 5 and 4. Thin loess of the Gilman Canyon Formation records slow loess accumulation and pedogenic alteration in OIS 3. The Peoria Loess (OIS 2) is similar in thickness to Loveland Loess, but may have accumulated more rapidly in an environment less favorable to bioturbation. More importantly, comparison of Peoria and Loveland loess thickness trends indicates much greater influx of nonglaciogenic loess from the Great Plains during OIS 2 than in OIS 6, suggesting colder and/or drier conditions in the Midcontinent during OIS 2 than in earlier glacial stages. 相似文献
16.
Coeval stratigraphic units of similar petrology occur throughout the northern Bahamas islands. The petrographic composition of these limestones provides clues about regional sea level and climate changes during the late Quaternary. At least eight fossil shoreline units, which are linked to transgressive episodes between the middle Pleistocene and the late Holocene, are recognized in the Bahamas. The petrographic composition of these units is either dominated by ooids and peloids or by bioclasts. Sedimentological observations demonstrate that oolitic-peloidal units were formed when sea level was higher than today, whereas skeletal units were deposited at or below modern ordnance datum. Skeletal units may reflect times of partial, or modest platform flooding, when the bulk of sediments brought to islands originates from bank-margin reefs. In contrast, oolitic-peloidal units correspond to major flooding events and active water circulation on the bank top. Cement fabrics further show that the early diagenesis of oolitic units took place during warm and humid climatic conditions, whereas skeletal rock bodies underwent subaerial diagenesis during drier climatic conditions characterized by marked seasonal changes. This example from the Bahamas suggests that compositional analysis of limestone from fossil carbonate platforms could be used for resolving ancient climate and sea-level changes. 相似文献
17.
Seismic-stratigraphic analysis of the coastal zone and inner shelf of Virginia's southern Delmarva Peninsula has revealed three geochronologically significant surfaces of post-Tertiary age that impose a relative chronostratigraphic framework on Quaternary marine transgressive and regressive events. Characteristics of these surfaces indicate that two are sequence boundaries, and one is a ravinement surface.
Lying at depths of 18–70 m (msl datum), the LPb surface (a late Pleistocene basal unconformity) represents the sequence boundary separating the Tertiary Chesapeake Group from the overlying late Pleistocene Nassawadox Formation. High relief (approximately 50 m) on the LPb surface is associated with large fluvial channels. Higher in the stratigraphic section, the LPr, surface is found at depths of 6–28 m, and corresponds to a late Pleistocene transgressive, or ravinement surface. The surface dips southeastward with a regional dip of 0.04° and has local relief of less than 2 m. The LPr surface may represent a ravinement which extended to the west side of the Chesapeake Bay prior to the development of the Nassawadox barrier spit. However, the LPr surface may steepen between the axis of the southern Delmarva Peninsula and the Holocene lagoon to form a shoreface attached to one of several known late Pleistocene shorelines. Lying at depths of 0–20 m, the Hb surface is a basal unconformity that marks the Holocene sequence boundary. It deepens seaward, with maximum local relief of about 15 m, and has a topographic expression very similar to the present-day lagoonal drainage pattern.
Maximum thicknesses of Holocene and Pleistocene sediments (12 and 70 m, respectively) are found above channels on the Hb and LPb surfaces. The Pleistocene channels are large and limited in number and represent high-order channels of a drainage system that drained the Piedmont and Coastal Plain. The greater density of low-order stream channels on the Hb surface suggests a relationship to much smaller drainage basins that were confined to the seaward part of the Coastal Plain east of the Delmarva Peninsula. These late Wisconsinan smaller Hb channels do not re-occupy the former drain paths of the much larger high-order LPb channels. 相似文献
18.
Quaternary coastal lithofacies,sequence development and stratigraphy in a passive margin setting,North Carolina and Virginia,USA 总被引：3，自引：0，他引：3
PETER R. PARHAM STANLEY R. RIGGS STEPHEN J. CULVER DAVID J. MALLINSON W. JACK RINK KEVIN BURDETTE 《Sedimentology》2013,60(2):503-547
Lithofacies analysis is fundamental to unravelling the succession of depositional environments associated with sea‐level fluctuations. These successions and their timing are often poorly understood. This report defines lithofacies encountered within the north‐eastern North Carolina and south‐eastern Virginia Quaternary section, interprets their depositional environments, presents a model for coastal depositional sequence development in a passive margin setting and uses this understanding to develop the stratigraphy and Quaternary evolutionary history of the region. Data were obtained from numerous drill cores and outcrops. Chronology was based on age estimates acquired using optically stimulated luminescence, amino acid racemization, Uranium series and radiocarbon dating techniques. Geomorphic patterns were identified and interpreted using light detection and ranging imagery. Since lithofacies occurrence, distribution and stratigraphic patterns are different on interfluves than in palaeo‐valleys, this study focused on interfluves to obtain a record of highstand sea‐level cycles with minimal alteration by fluvial processes during subsequent lowstands. Nine primary lithofacies and four diagenetic facies were identified in outcrops and cores. The uppermost depositional sequence on interfluves exhibits an upward succession from shelly marine lithofacies to tidal estuarine lithofacies and is bounded below by a marine ravinement surface and above by the modern land surface. Older depositional sequences in the subsurface are typically bounded above and below by marine ravinement surfaces. Portions of seven depositional sequences were recognized and interpreted to represent deposition from late middle Pleistocene to present. Erosional processes associated with each successive depositional sequence removed portions of older depositional sequences. The stratigraphic record of the most recent sea‐level highstands (Marine Isotope Stage 5a and Marine Isotope Stage 3) is best preserved. Glacio‐isostatic adjustment has influenced depositional patterns so that deposits associated with late Quaternary sea‐level highstands (Marine Isotope Stages 5c, 5a and 3), which did not reach as high as present sea‐level according to equatorial eustatic records, are uplifted and emergent within the study area. 相似文献
19.
MARTIN ROSS PATRICK LAJEUNESSE KEVIN G. A. KOSAR 《Boreas: An International Journal of Quaternary Research》2011,40(1):73-91
Ross, M., Lajeunesse, P. & Kosar, K. G. A. 2010: The subglacial record of northern Hudson Bay: insights into the Hudson Strait Ice Stream catchment. Boreas, 10.1111/j.1502‐3885.2010.00176.x. ISSN 0300‐9483. In this paper, we present new insights into the glacial dynamics and potential configuration of the Hudson Strait Ice Stream catchment in the northern Hudson Bay–western Hudson Strait region. Our reconstruction is based on new field observations and till compositional data from Southampton Island, remote sensing imagery and multibeam bathymetric data from the Hudson Bay sea floor, as well as on a re‐examination of previously published data from this vast region. Our findings suggest that, during the late Quaternary, the HSIS catchment consisted of a number of ice‐stream tributaries feeding a curvilinear trunk that potentially extended into western Hudson Bay. In contrast to previous interpretations, the occurrence of fluted bedrock hills, over‐deepened basins, Dubawnt erratics and carbonaceous till on the islands at the head of Hudson Strait is taken to imply that cold‐based conditions did not prevail on these islands. The upland area of Southampton Island and the surrounding channels played an important role in controlling the location of the main tributaries, with the higher central terrain forming a large inter‐ice‐stream zone lacking carbonate detritus. Coats Island contains abundant evidence of vigorous ice flow, such as mega‐scale glacial lineations (MSGLs). MSGLs also occur on the sea floor southwest of Coats Island but the sea‐floor imprint is highly discontinuous. Observations on the western Hudson Bay mainland show evidence of southeastward fast ice flow that is spatially consistent with the Dubawnt dispersal train. Despite the geomorphological discontinuities, this may indicate that the HSIS onset zone extended far inside the Laurentide Ice Sheet and across contrasting geological domains. 相似文献
20.
Regressive and transgressive sequences in a raised Holocene gravelly beach, southwestern Crete 总被引：2，自引：0，他引：2
Both a modern and a raised, late Holocene gravelly beach have been studied along the cliffed coast near the village of Chora Sfakion in southwestern Crete, Greece. The Holocene beach shows the record of regional, well-documented relative sea-level changes, in the form of regressive and transgressive sequences. The texture, fabric and depositional architecture of these sequences are described and compared with those of the modern, microtidal beach there. The depositional history of the raised beach is discussed in terms of the sediment transport processes and relative sea-level changes. The regressive sequences of both the modern and the Holocene beach resemble those of the mesotidal beaches in the Sker district of southwest Wales, described by Bluck (1967). The transgressive sequence of the Holocene beach resembles the mesotidal beach sequence near Newton (southwest Wales), recognized by Bluck as another type of progradational (regressive) beach. Therefore, transgressive beach sequences in the stratigraphic record might easily be overlooked or misinterpreted as regressive. The stratigraphic depositional patterns of gravelly beach systems are, apparently, still poorly understood. 相似文献