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1.
Coral islands formed of largely unconsolidated sands only a few metres above sea level are thought to be particularly vulnerable to sea-level rise consequent upon global warming. However, scenarios which predict catastrophic flooding and loss of island area need reassessment, particularly in the light of the continued downwards revision of projected rates of future sea-level rise. Revised questions concern the interactions between reef growth and sea-level change, biophysical constraints on coral growth, and the importance to reef systems of potential changes in the magnitude, frequency and location of tropical cyclones and hurricanes. It is clear that most reefs have the growth potential to meet even the highest of future sea-level rise scenarios, but too little is known about physiological and physical constraints to reef growth to adequately evaluate the importance of these two factors in constraining this potential at the present time. Future sea-level rise in the tropical oceans, and coral reef responses, will take place against a backdrop of inter-regional differences in Holocene sea levels, resulting from the varying interaction of eustatic and hydro-isostatic processes. These differences have generated varying constraints on the development of modern reefs and varying inherited topographies upon which future sea-level changes will be superimposed. These controls are particularly important in assessing differences in vulnerability to future sea-level rise for reef islands in the Pacific Ocean and the Caribbean Sea.  相似文献   

2.
The possibility of Holocene subsidence along the northern coast of the Corinth Gulf is often mentioned in the literature; however, systematic detailed evidence that submergence (e.g. of archaeological remains) does not simply depend from eustatic sea-level rise is most often missing. In this paper, a new detailed study of submerged tidal-notch profiles along the limestone coast has shown that periods of sea-level stability are intercalated with periods of rapid subsidence or gradual relative sea-level rise. It appears that most of the sites considered, seem to have been affected by a relatively recent co-seismic subsidence of about half a meter, whereas during the longer period, by stages of relative sea-level stability and/or gradual relative sea-level rise. This evidence of subsidence is confirmed by radiocarbon dating in doline sediments, suggesting that during certain periods, a relative sea-level rise was much faster than the raising suggested by glacio-eustatic or hydro-isostatic estimations. Juxtaposing a list of known earthquakes occurred in the area shows that several earthquakes (e.g. the 1981 one for the easternmost sites considered) are potential candidates for the recent co-seismic displacements and thus supporting the geomorphological interpretations.  相似文献   

3.
In parts of North America and Europe, present and future sedimentary deficits translate into major areal losses of coastal salt marsh. Physically based simulations of medium- to long-term adjustment to accelerated sea-level rise are few, partly due to the difficulty in extrapolating imperfectly understood sedimentation parameters. This paper outlines the implementation and application of a simple one-dimensional mass balance model designed to simulate the vertical adjustment of predominantly minerogenic marsh surfaces to various combinations of sediment supply, tidal levels and regional subsidence. Two aspects of marsh growth are examined, with reference to sites on the macro-tidal north Norfolk coast, U.K.: (i) historical marsh growth under a scenario of effective (long-term) eustatic stability but slow regional subsidence; and (ii) marsh response to various non-linear eustatic rise scenarios for the next century. In contrast to more organogenic North American marshes, sedimentation rates in Norfolk are strongly time-dependent. Where the overall sediment budget is so closely linked to marsh age and relative elevation, some form of numerical simulation offers a preferred means of predicting the impact of accelerated sea-level rise. Simulations performed here show that only the most dramatic eustatic scenarios result in ecological ‘drowning’ and reversion to tidal flat within the conventional 2100 prediction interval. Currently favoured scenarios give rise to accretionary deficits which are clearly sustainable in the short-term, albeit at the expense of increased inundation frequency and consequent changes in the distribution of marsh flora and fauna.  相似文献   

4.
In-Chang Ryu 《Island Arc》2002,11(3):149-169
Abstract Carbonate breccias occur sporadically in the Lower–Middle Ordovician Maggol Limestone exposed in the Taebacksan Basin in the northeastern part of the northeast–southwest‐trending Ogcheon Belt, South Korea. These carbonate breccias have been previously interpreted as intraformational or fault‐related breccias. Thus, little attention has been focused on tectonic and stratigraphic significance of these carbonate breccias. The present study, however, indicates that the majority of these carbonate breccias are solution–collapse breccias, which are causally linked to paleokarstification. Carbonate facies analysis in conjunction with conodont biostratigraphy suggests that an overall regression toward the top of the Maggol Limestone probably culminated in subaerial exposure of platform carbonates during the early Middle Ordovician (earliest Darriwilian). Extensive subaerial exposure of platform carbonates resulted in paleokarst‐related solution–collapse breccias in the upper Maggol Limestone. This subaerial exposure event is manifested as a major paleokarst unconformity at the Sauk–Tippecanoe sequence boundary elsewhere beneath the Middle Ordovician succession and its equivalents, most notably North America and North China. Due to its global extent, this paleokarst unconformity has been viewed as a product of second‐ or third‐order eustatic sealevel drop during the early Middle Ordovician. Although a paleokarst breccia zone is recognized beneath the Middle Ordovician succession in South Korea, the Sauk–Tippecanoe sequence boundary appears to be a conformable transgressive surface on the top of the paleokarst breccia zone in the upper Maggol Limestone. The paleokarst breccia zone beneath the conformable transgressive surface is represented by a thinning‐upward stack of exposure‐capped tidal flat‐dominated cycles that are closely associated with multiple occurrences of paleokarst‐related solution–collapse breccias. This paleokarst breccia zone was a likely consequence of repeated fourth‐ and fifth‐order sealevel fluctuations. It suggests that second‐ and third‐order eustatic sealevel drop may have been significantly tempered by substantial tectonic subsidence near the end of the Maggol deposition. The tectonic subsidence in the basin is also evidenced by the occurrence of coeval off‐platform lowstand siliciclastic quartzite lenses as well as debris flow carbonate breccias (i.e. the Yemi Breccia). With the continued tectonic subsidence, subsequent rise in the eustatic cycle caused drowning and deep flooding of carbonate platform, forming a transgressive surface on the top of the paleokarst breccia zone. This tectonic implication contrasts notably with the slowly subsiding carbonate platform model for the basin as has been previously interpreted. Thus, it is proposed that the Taebacksan Basin in the northeastern part of the Ogcheon Belt evolved from a slowly subsiding carbonate platform to a rapidly subsiding intracontinental rift basin during the early Middle Ordovician. The proposed tectonic model in the basin gives much better insight to unravel the stratigraphic response to tectonic evolution of the Ogcheon Belt, which remains an enigmatic feature in formulating a tectonic framework of the Korean peninsula. The present study also provides a good example that the falling part of the eustatic sealevel cycle may not produce a significant event in a rapidly subsiding basin where the rate of eustatic fall always remained lower than the rate of subsidence.  相似文献   

5.
The legacy of multiple marine transgressions is preserved in a complex morphology of ridges, mounds and reefs on the Carnarvon continental shelf, Western Australia. High-resolution multibeam sonar mapping, underwater photography and sampling across a 280 km2 area seaward of the Ningaloo Coast World Heritage Area shows that these raised features provide hardground habitat for modern coral and sponge communities. Prominent among these features is a 20 m high and 15 km long shore-parallel ridge at 60 m water depth. This ridge preserves the largely unaltered form of a fringing reef and is interpreted as the predecessor to modern Ningaloo Reef. Landward of the drowned reef, the inner shelf is covered by hundreds of mounds (bommies) up to 5 m high and linear ridges up to 1.5 km long and 16 m high. The ridges are uniformly oriented to the north-northeast and several converge at their landward limit. On the basis of their shape and alignment, these ridges are interpreted as relict long-walled parabolic dunes. Their preservation is attributed to cementation of calcareous sands to form aeolianite, prior to the post-glacial marine transgression. Some dune ridges abut areas of reef that rise to sea level and are highly irregular in outline but maintain a broad shore-parallel trend. These are tentatively interpreted as Last Interglacial in age. The mid-shelf and outer shelf are mostly sediment covered with relatively low densities of epibenthic biota and have patches of low-profile ridges that may also be relict reef shorelines. An evolutionary model for the Carnarvon shelf is proposed that relates the formation of drowned fringing reefs and aeolian dunes to Late Quaternary eustatic sea level.  相似文献   

6.
Based on tide gauge observations spanning almost 200 years, homogeneous time series of the mean relative sea level were derived for nine sites at the southern coast of the Baltic Sea. Our regionally concentrated data were complemented by long-term relative sea-level records retrieved from the data base of the Permanent Service for Mean Sea Level (PSMSL). From these records relative sea-level change rates were derived at 51 tide gauge stations for the period between 1908 and 2007. A minimum observation time of 60 years is required for the determination of reliable sea-level rates. At present, no anthropogenic acceleration in sea-level rise is detected in the tide gauge observations in the southern Baltic. The spatial variation of the relative sea-level rates reflects the fingerprint of GIA-induced crustal uplift. Time series of extreme sea levels were also inferred from the tide gauge records. They were complemented by water level information from historic storm surge marks preserved along the German Baltic coast. Based on this combined dataset the incidence and spatial variation of extreme sea levels induced by storm surges were analysed yielding important information for hazard assessments. Permanent GPS observations were used to determine recent crustal deformation rates for 44 stations in the Baltic Sea region. The GPS derived height change rates were applied to reduce the relative sea-level changes observed by tide gauges yielding an estimate for the eustatic sea-level change. For 13 tide gauge-GPS colocation sites a mean eustatic sea-level trend of 1.3 mm/a was derived for the last 100 years.  相似文献   

7.
Peter Flood 《Island Arc》1999,8(1):92-98
Results of the Ocean Drilling Program legs 143 and 144, which investigated the nature and origin of seven guyots in the northwest Pacific Ocean, document a history of prolonged volcanism (128–84 Ma), followed by subsidence, accumulation of shallow-water carbonates, emersion following a sea-level fall, then continued subsidence, and drowning. Generally, the life span of a guyot is of the order of 5–20 million years. The stratigraphic sequence in each guyot consists of 3–10 m-thick, shoaling-upward cycles, which display a 100-Ka periodicity perhaps related to sea-level fluctuations. The drilling results indicate that the demise of the shallow-water carbonate platforms is related to either a temporal (110–100 Ma) event or paleolatitude location (0–10°S) involving nutrient-rich water not conducive to production of calcium carbonate by shallow-water organisms. Following emergence and erosion, re-submergence occurred during a rise of sea-level. However, the rate of sediment accumulation was unable to keep pace with the rate of sea-level rise and the guyots drowned. Subsidence continued as the lithospheric plate cooled. The majority of guyots are now at ~ 1500 m below sea-level. Plate movements over the past 100 million years have carried the guyots from ~ 14°S to their current location in the northwest Pacific. Guyots are flat-topped submerged volcanic islands capped by thick sequences of shallow-water carbonates. The flat-top morphology is constructional, not related to wave planation as originally thought and reported in most textbooks.  相似文献   

8.
Global mean sea level is a potentially sensitive indicator of climate change. Global warming will contribute to worldwide sea-level rise (SLR) from thermal expansion of ocean water, melting of mountain glaciers and polar ice sheets. A number of studies, mostly using tide-gauge data from the Permanent Service for Mean Sea Level, Bidston Observatory, England, have obtained rates of global SLR within the last 100 years that range between 0·3 and 3 mm yr?1, with most values concentrated between 1 and 2 mm yr?1. However, the reliability of these results has been questioned because of problems with data quality and physical processes that introduce a high level of spatial and temporal variability. Sources of uncertainty in the sea-level data include variations in winds, ocean currents, river runoff, vertical earth movements, and geographically uneven distribution of long-term records. Crustal motions introduce a major source of error. To a large extent, these can be filtered by employing palaeo-sea-level proxies, and geophysical modelling to remove glacio-isostatic changes. Ultimately, satellite geodesy will help resolve the inherent ambiguity between the land and ocean level changes recorded by tide gauges. Future sea level is expected to rise by ～ 1 m, with a ‘best-guess’ value of 48 cm by the year 2100. Such rates represent an acceleration of four to seven times over present rates. Local land subsidence could substantially increase the apparent SLR. For example, Louisiana is currently experiencing SLR trends nearly 10 times the global mean rate. These recently reduced SLR estimates are based on climate models that predict a zero to negative contribution to SLR from Antarctica. Most global climate models (GCMs) indicate an ice accumulation over Antarctica, because in a warmer world, precipitation will exceed ablation/snow-melt. However, the impacts of attritional processes, such as thinning of the ice shelves, have been downplayed according to some experts. Furthermore, not all climate models are in agreement. Opposite conclusions may be drawn from the results of other GCMs. In addition, the West Antarctic Ice Sheet is potentially subject to dynamic and volcanic instabilities that are difficult to predict. Because of the great uncertainty in SLR projections, careful monitoring of future sea-level trends by upgraded tide-gauge networks and satellite geodesy will become essential. Finally, because of the high spatial variability in crustal subsidence rates, wave climates and tidal regimes, it will be the set of local conditions (especially the relative sea-level rise), rather than a single global mean sea-level trend, that will determine each locality's vulnerability to future SLR.  相似文献   

9.
Spatial and temporal patterns of recent sea-level rise along the United States coastline have been examined to ascertain rates of rise, and possible causes for high-frequency fluctuations in sea level. Eigenanalysis identified several distinct coastal compartments within each of which sea-level behavior is consistent. The United States east coast has three of these compartments: one north of Cape Cod, where sea-level rise increases with distance to the north; one between Cape Cod and Cape Hatteras where sea-level rise increases to the south; and the third from Cape Hatteras south to Pensacola, where sea-level rise decreases to the south. The western gulf coast represents another compartment (poorly sampled in this study), where subsidence is partly due to compaction. The final compartment is along the United States west coast, where poor spatial sampling produces a highly spatially variable sea-level record that has some temporal uniformity. Spectral analysis shows a dominant time scale of six years for sea-level variability, with different coastal compartments responding relatively in or out of phase. No evidence for increased rates of sea-level rise over the past 10 years was found. This objective statistical technique is a valuable tool for identifying spatial and temporal sea-level trends in the United States. It may later prove useful for identifying elusive world-wide trends of sea level, related to glacial melting, glacial rebound, tectonism, and volcanic activity.  相似文献   

10.
Ningaloo Reef, located along the northwest coast of Australia, is one of the longest fringing coral reefs in the world extending ~300 km. Similar to other fringing reefs, it consists of a barrier reef ~1–6 km offshore with occasional gaps, backed by a shallow lagoon. Wave breaking on the reef generates radiation stress gradients that produces wave setup across the reef and lagoon and mean currents across the reef. A section of Ningaloo Reef at Sandy Bay was chosen as the focus of an intense 6-week field experiment and numerical simulation using the wave model SWAN coupled to the three-dimensional circulation model ROMS. The physics of nearshore processes such as wave breaking, wave setup and mean flow across the reef was investigated in detail by examining the various momentum balances established in the system. The magnitude of the terms and the distance of their peaks from reef edge in the momentum balance were sensitive to the changes in mean sea level, e.g. the wave forces decreased as the mean water depth increased (and hence, wave breaking dissipation was reduced). This led to an increase in the wave power at the shoreline, a slight shift of the surf zone to the lee side of the reef and changes in the intensity of the circulation. The predicted hydrodynamic fields were input into a Lagrangian particle tracking model to estimate the transport time scale of the reef-lagoon system. Flushing time of the lagoon with the open ocean was computed using two definitions in renewal of semi-enclosed water basins and revealed the sensitivity of such a transport time scale to methods. An increase in the lagoon exchange rate at smaller mean sea-level rise and the decrease at higher mean sea-level rise was predicted through flushing time computed using both methods.  相似文献   

11.
The 65 whole-rock REE samples studied come from the classic sections of Early Cambrian to Early Silurian in the Yichang area, Hubei Province. REE concentrations tested on ICP-AES are normalized to the North American Shale Composite (NASC), and Ce anomaly values are calculated based on log[ 3Cen/(2Lan+Ndn)] . With the whole-rock Ce anomaly used as a quantitative index of sea-level changes, 5 prominent eustatic circles are recognized, and a good corresponding relationship is observed between the black shale episodes and the transgressive events. On account of the global distributions of coeval black shales and the specified paleogeographic background of South China, a genetic hypothesis based on the model of O2-minimum zone expansion is suggested for the Early Paleozoic multi-episode black shales in South China.  相似文献   

12.
A marine sampling program, utilizing the PISCES-5 submersible operated by the Hawaii Undersea Research Laboratory (NOAA), has confirmed the presence of a major submerged coral reef offshore from Ka Lae (South Point), Hawaii. The top of the reef is now 150–160 m below sea level. Radiocarbon and Useries dating indicates that it drowned about 13.9 ka by the combined effects of island subsidence (2.5 mm/year) and the rapid rise of sea level at the end of the last glaciation so that the relative submergence rate of more than 10 mm/year exceeded the upward growth rate of the reef. The submerged reef caps the offshore part of the southwest rift-zone ridge of Mauna Loa, which has apparently undergone little volcanic activity offshore since 170 ka, and possibly since 270 ka. This fact suggests that rift zone activity is becoming increasingly restricted toward the upper part of the volcano, a condition possibly heralding the end of the shield-building stage.  相似文献   

13.
We report new mass spectrometric U-series ages for eight Last Interglacial fossil reefs along the continental margin of Western Australia. Corals were selected in growth position from localities that are characterized by apparently low levels of diagenesis and relative tectonic stability so that the fossil reefs provide critical information on Last Interglacial sea-levels without requiring corrections for tectonic movements. In addition, we have improved the constraint on the timing of onset of reef growth by recovering drill core coral from the base of the reefs. Uranium and thorium isotopes were measured with high levels of precision, leading to improvements in age resolution and allowing samples which have undergone diagenetic exchange of uranium and thorium to be more easily identified and discarded. These data supplement our previous results for Rottnest Island and Leander Point, leading to more than seventy mass spectrometric U-series ages from which constraints can be placed on the timing, duration and character of the Last Interglacial sea-level highstand. Reliable ages show that reef growth started contemporaneously at 128 ± 1 ka along the entire Western Australian coastline, while relative sea-levels were at least 3 m above the present level. Because Western Australia is located far from the former Penultimate Glacial Maximum ice sheets and are not significantly effected by glacial unloading, these data constrain the timing of onset of the Last Interglacial period to 128 ± 1 ka, assuming reef growth started soon after sea-level approached interglacial levels. A unique regressive reef sequence at Mangrove Bay constrains the timing of termination of the Last Interglacial period to 116 ± 1 ka. The major episode of reef building, however, both globally and locally along the Western Australian coast, is restricted to a very narrow interval occurring from 128 ka and 121 ka, suggesting that global ocean surface temperatures were warm and/or sea-levels were stable enough to allow prolific reef growth only during the earlier part of the Last Interglacial.  相似文献   

14.
In order to maintain an elevation in the intertidal zone at which marsh vegetation can survive, vertical accretion of the marsh surface must take place at a rate at least equal to the rate of relative sea-level rise. Net vertical accretion of coastal marshes is a result of interactions between tidal imports, vegetation and depositional processes. All of these factors are affected, directly or indirectly, by alterations in marsh hydrology which might occur as a result of sea-level rise. The overall response of coastal marshes to relative sea-level rise depends upon the relative importance of the inorganic and organic components of the marsh soil and the impact of increased hydroperiod on net accumulation. The varied combination of factors contributing to sediment supply, and their complexity at the scale of individual marshes, means that predicting the response of suspended sediment concentration in marsh floodwater to any changes which may occur as a result of sea-level rise, at anything other than the local scale is unlikely to be accurate. The impact of sea-level rise on net below-ground production is also complex. The sensitivity of certain species to waterlogging and soil chemical changes could result in a change in species composition or the migration of vegetation zones. Consequently, predicting the net impact of sea-level rise on organic matter accumulation is fraught with difficulties and requires improved understanding of interactions between vegetation, soil and hydrologic processes.  相似文献   

15.
Abstract

This work presents a method for calculating the contributions of sea-level rise and urban growth to flood risk in coastal flood plains. The method consists of hydraulic/hydrological, urban growth and flood-damage quantification modules. The hydraulic/hydrological module estimates peak annual flows to generate flood stages impacted by sea-level rise within flood plains. A model for urban growth predicts patterns of urbanization within flood plains over the period 2010–2050. The flood-damage quantification module merges flood maps and urbanization predictions to calculate the expected annual flood damage (EAFD) for given scenarios of sea-level rise. The method is illustrated with an application to the Tijuana River of southern California, USA, and northwestern Mexico, where the EAFD is predicted to increase by over US$100 million because of sea-level rise of 0.25–1.0 m and urban growth by the year 2050. It is shown that urbanization plays a principal role in increasing the EAFD in the study area for the range of sea-level rise considered.

Editor Z.W. Kundzewicz

Citation Garcia, E.S. and Loáiciga, H.A., 2013. Sea-level rise and flooding in coastal riverine flood plains. Hydrological Sciences Journal, 59 (1), 204–220.  相似文献   

16.
A one-dimensional wave model was used to investigate the reef top wave dynamics across a large suite of idealized reef-lagoon profiles, representing barrier coral reef systems under different sea-level rise (SLR) scenarios. The modeling shows that the impacts of SLR vary spatially and are strongly influenced by the bathymetry of the reef and coral type. A complex response occurs for the wave orbital velocity and forces on corals, such that the changes in the wave dynamics vary reef by reef. Different wave loading regimes on massive and branching corals also leads to contrasting impacts from SLR. For many reef bathymetries, wave orbital velocities increase with SLR and cyclonic wave forces are reduced for certain coral species. These changes may be beneficial to coral health and colony resilience and imply that predicting SLR impacts on coral reefs requires careful consideration of the reef bathymetry and the mix of coral species.  相似文献   

17.
Vulnerability indicators of sea water intrusion   总被引：5，自引：0，他引：5  
In this paper, simple indicators of the propensity for sea water intrusion (SWI) to occur (referred to as "SWI vulnerability indicators") are devised. The analysis is based on an existing analytical solution for the steady-state position of a sharp fresh water-salt water interface. Interface characteristics, that is, the wedge toe location and sea water volume, are used in quantifying SWI in both confined and unconfined aquifers. Rates-of-change (partial derivatives of the analytical solution) in the wedge toe or sea water volume are used to quantify the aquifer vulnerability to various stress situations, including (1) sea-level rise; (2) change in recharge (e.g., due to climate change); and (3) change in seaward discharge. A selection of coastal aquifer cases is used to apply the SWI vulnerability indicators, and the proposed methodology produces interpretations of SWI vulnerability that are broadly consistent with more comprehensive investigations. Several inferences regarding SWI vulnerability arise from the analysis, including: (1) sea-level rise impacts are more extensive in aquifers with head-controlled rather than flux-controlled inland boundaries, whereas the opposite is true for recharge change impacts; (2) sea-level rise does not induce SWI in constant-discharge confined aquifers; (3) SWI vulnerability varies depending on the causal factor, and therefore vulnerability composites are needed that differentiate vulnerability to such threats as sea-level rise, climate change, and changes in seaward groundwater discharge. We contend that the approach is an improvement over existing methods for characterizing SWI vulnerability, because the method has theoretical underpinnings and yet calculations are simple, although the coastal aquifer conceptualization is highly idealized.  相似文献   

18.
Relationship between subsidence and volcanic load,Hawaii   总被引：1，自引：0，他引：1  
A computer analysis of tide-gage records in the northeast Pacific indicates that the active volcanic islands of eastern Hawaii are subsiding at a rate considerably faster than the eustatic rise of sea level. The rate of absolute subsidence increases progressively toward the center of current activity on the Island of Hawaii. Honolulu, Oahu, appears to be stable; Kahului, Maui, is subsiding at 1.7 mm per year; and Hilo, Hawaii, is subsiding at 4.8 mm per year. This subsidence is apparently related to downbowing of the crust throughout a zone 400 km in diameter by the weight of volcanic material added to the crust by active volcanoes, principally Mauna Loa and Kilauea on the Island of Hawaii. The Hawaiian Arch encircles the subsiding zone and may be uplifted by material moving down and outward from the zone of subsidence. The annual volume of subsidence is about 270×106 m3, whereas the average annual volume of erupted basalt on the Island of Hawaii (based on historic records back to about 1820) is about 50×106 m3. The great excess of subsidence over volcanic addition cannot be reconciled by isostatic models, and is apparently the result of other processes operating in the volcano and its basement thet are poorly understood. Probably the more important of these processes are intrusions and submarine volcanism, both of which are providing additional unseen load on the volcanoes. Furthermore, the rate of eruption may be uplifted by material moving down and outward from the zone of subsidence may be overestimated due to localized downslope movement of the margins of the islands.  相似文献   

19.
Coral-reef terraces on tectonically elevated coasts provide important data on variations of sea level. In this paper a systematic approach is presented for the construction of synthetic reef terraces. Idealized reef terraces are generated assuming a constant rate of tectonic uplift ν and a harmonic variation of sea level with amplitudehwo and period τ. It is further assumed that coral terraces grow only during periods of relative sea-level rise. The behavior is governed by the parameter u = τυ/2π hwo. If u > 1 no reef terraces form. If 0.217 < u < 1 a discontinuous series of terraces form on the uplifting basement. If 0 < u < 0.217 the basement is covered with coral and a series of coral terraces forms on this coral. Uplifted coral-reef terraces on the Huon Peninsula, Papua New Guinea, compare reasonably well with terraces generated by our model with τ = 20,000 years andhwo = 21.4 m. We also compare the observed terraces with model terraces using the paleo sea level inferred from18O/16O data. The observed terraces are qualitatively similar to those predicted using the oxygen isotope data, however, the model terraces require larger relative sea-level variations with a near 20,000 year period than those inferred directly from the18O/16O data.  相似文献   

20.
The Kachchh Basin and the Jaisalmer Basin are two neighboring Mesozoic sedimentary basins at the western margin of the Indian craton. The Jurassic succession of the Kachchh Basin is more complete and more fossiliferous than that of the Jaisalmer Basin. Consequently, intrabasinal correlation of the sedimentary units has been possible in the Kachchh Basin, but not in the Jaisalmer Basin. However, some marker beds existing in the Kachchh Basin can be recognized also in the Jaisalmer Basin. Ammonite evidence shows that they are time-equivalent. The following four units form marker intervals in both basins: (1) the pebbly rudstone unit with Isastrea bernardiana and Leptosphinctes of the Kaladongar Formation (Kachchh Basin) and the Isastrea bernardiana-bearing rudstone of the Jaisalmer Formation (Jaisalmer Basin) both represent transgressive systems tract deposits dated as Late Bajocian; (2) bioturbated micrites with anomalodesmatan bivalves within the Goradongar Yellow Flagstone Member (Kachchh Basin) and bioturbated units in the Fort Member (Jaisalmer Basin) represent maximum flooding zone deposits of the Middle to Late Bathonian; (3) trough-crossbedded, sandy pack- to grainstones of the Raimalro Limestone Member (Kachchh Basin) and the basal limestone-sandstone unit of the Kuldhar section of the Jaisalmer Formation (Jaisalmer Basin) correspond to Late Bathonain transgressive systems tract deposits; and (4) ferruginous ooid-bearing carbonates with hardgrounds of the Dhosa Oolite member (Kachchh Basin) and the middle part of the Jajiya Member (Jaisalmer Basin) are Oxfordian transgressive systems tract deposits. The fact that in both basins similar biofacies prevailed during certain time intervals demonstrates a common control of their depositional history. As the two basins represent different tectonic settings, the most likely controlling factors were the relative sea-level changes produced by eustatic processes, a common subsidence history of the northwestern margin of the Indian craton, and the paleoclimate.  相似文献   

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