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1.
《Sedimentary Geology》2006,183(1-2):145-156
Prehistoric depositional signatures for large-scale washover involving marine inundation events such as storms and tsunami have been the subject of considerable research over the last 15 years. Much of this research has focused on the identification of sandsheets in back-barrier environments as depositional records for extreme washover events. All these deposits must have a sediment source and, by their nature, the most likely source of sediment for washover into back-barrier environments is the barrier itself. This study identifies an erosional signature for large-scale washover from a small coastal barrier on the southeast Australian coast. A distinct lens of marine sand, up to 90 cm thick, confined vertically by peat, is found in the upper fill of a closed freshwater back-barrier lagoon sequence. This sand lens is attributed to a large-scale washover event during the last 800 years, and was possibly deposited by a tsunami. The hypothesis for this study was that any event that breached the dune system must have caused considerable geomorphic change to the dunes and hence may have left an erosional signature. Ground penetrating radar transects of the system show an erosional contact between a series of truncated pre-event dunes and several small overlying post-event dunes. This study outlines a relatively simple non-invasive method for the identification of an erosional signature for prehistoric large-scale washovers caused by storm surge, exceptionally large waves, or tsunami. 相似文献
2.
Asbury H. Sallenger Hilary F. Stockdon Laura Fauver Mark Hansen David Thompson C. Wayne Wright Jeff Lillycrop 《Estuaries and Coasts》2006,29(6):880-888
Four hurricanes battered the state of Florida during 2004, the most affecting any state since Texas endured four in 1884.
Each of the storms changed the coast differently. Average shoreline change within the right front quadrant of hurricane force
winds varied from 1 m of shoreline advance to 20 m of retreat, whereas average sand volume change varied from 11 to 66 m3 m−1 of net loss (erosion). These changes did not scale simply with hurricane intensity as described by the Saffir-Simpson Hurricane
Scale. The strongest storm of the season, category 4 Hurricane Charley, had the least shoreline retreat. This was likely because
of other factors like the storm's rapid forward speed and small size that generated a lower storm surge than expected. Two
of the storms, Hurricanes Frances and Jeanne, affected nearly the same area on the Florida east coast just 3 wk apart. The
first storm, Frances, although weaker than the second, caused greater shoreline retreat and sand volume erosion. As a consequence,
Hurricane Frances may have stripped away protective beach and exposed dunes to direct wave attack during Jeanne, although
there was significant dune erosion during both storms. The maximum shoreline change for all four hurricanes occurred during
Ivan on the coasts of eastern Alabama and the Florida Panhandle. The net volume change across a barrier island within the
Ivan impact zone approached zero because of massive overwash that approximately balanced erosion of the beach. These data
from the 2004 hurricane season will prove useful in developing new ways to scale and predict coastal-change effects during
hurricanes. 相似文献
3.
ABSTRACT
The Robbedale and Jydegård Formations (Berriasian-Valanginian) of the Danish island of Bornholm represent a 100 m thick vertical sequence from shoreface, foreshore and beach sands of a high-energy coast through backbarrier flat, bay margin pond and distal washover fan sand and clay, brackish bay clay, to fluvial sands. The longevity of the backbarrier-bay system (c. 10 Myr), thickness (100 m) of the bay deposits and apparently stacked nature of the facies belts suggest a relatively stationary position of the individual subenvironments, with only minor progradation. This reflects strong tectonic control of the depositional system during an important phase of synsedimentary block faulting and wrenching along the Tornquist Zone. The importance of washover fan sands in the backbarrier deposits, and the lack of tidal indications in the whole sequence, suggest a microtidal regime. A system of migrating mud banks formed in shallow water on the landward side of the barrier. The bay waters varied from almost fresh to brackish, and anoxic conditions commonly occurred at the bottom. Adverse living conditions for most organisms in the bay caused seasonal, possibly toxic, dinoflagellate blooms resulting in mass mortality of infaunal bivalves. Bay-margin ponds underwent periodic desiccation, leading to mass mortality of freshwater gastropods. As a general scenario it is envisaged that longshore currents redistributed bedload from a major delta and formed an extensive NW-SE barrier-spit which partly enclosed a major bay to the NE. The barrier was breached during heavy storms and the sand transported along the resulting washover channels was deposited on the backbarrier flat made up of the subaerial parts of coalescent washover fans. Enormous amounts of suspension load from the delta travelled further along the barrier to be deposited in the lee-side bay. 相似文献
The Robbedale and Jydegård Formations (Berriasian-Valanginian) of the Danish island of Bornholm represent a 100 m thick vertical sequence from shoreface, foreshore and beach sands of a high-energy coast through backbarrier flat, bay margin pond and distal washover fan sand and clay, brackish bay clay, to fluvial sands. The longevity of the backbarrier-bay system (c. 10 Myr), thickness (100 m) of the bay deposits and apparently stacked nature of the facies belts suggest a relatively stationary position of the individual subenvironments, with only minor progradation. This reflects strong tectonic control of the depositional system during an important phase of synsedimentary block faulting and wrenching along the Tornquist Zone. The importance of washover fan sands in the backbarrier deposits, and the lack of tidal indications in the whole sequence, suggest a microtidal regime. A system of migrating mud banks formed in shallow water on the landward side of the barrier. The bay waters varied from almost fresh to brackish, and anoxic conditions commonly occurred at the bottom. Adverse living conditions for most organisms in the bay caused seasonal, possibly toxic, dinoflagellate blooms resulting in mass mortality of infaunal bivalves. Bay-margin ponds underwent periodic desiccation, leading to mass mortality of freshwater gastropods. As a general scenario it is envisaged that longshore currents redistributed bedload from a major delta and formed an extensive NW-SE barrier-spit which partly enclosed a major bay to the NE. The barrier was breached during heavy storms and the sand transported along the resulting washover channels was deposited on the backbarrier flat made up of the subaerial parts of coalescent washover fans. Enormous amounts of suspension load from the delta travelled further along the barrier to be deposited in the lee-side bay. 相似文献
4.
John Rivers Max Engel Robert Dalrymple Ruqaiya Yousif Christian J. Strohmenger Ismail Al-Shaikh 《Sedimentology》2020,67(1):534-558
Barrier islands are important landforms in many coastal systems around the globe. Studies of modern barrier island systems are mostly limited to those of siliciclastic realms, where the islands are recognized as mobile features that form on transgressive coastlines and migrate landward as sea-level rises. Barrier islands of the ‘Great Pearl Bank’ along the United Arab Emirates coast are the best-known carbonate examples. These Holocene islands, however, are interpreted to be anchored by older deposits and immobile. The mid-Holocene to late-Holocene depositional system at Al Ruwais, northern Qatar, provides an example of a mobile carbonate barrier island system, perhaps more similar to siliciclastic equivalents. Sedimentological and petrographic analyses, as well as 14C-dating of shells and biogenic remains from vibracored sediments and surface deposits, show that after 7000 years ago a barrier system with a narrow back-barrier lagoon formed along what is now an exposed coastal zone, while, contemporaneously, a laterally-extensive coral reef was forming immediately offshore. After 1400 years ago the barrier system was forced to step ca 3 km seaward in response to a sea-level fall of less than 2 m, where it re-established itself directly on the mid-Holocene reef. Since that time, the barrier has retreated landward as much as 1000 m to its current position, exposing previously-deposited back-barrier lagoonal sediment at the open-coast shoreline. In modern neritic warm-water carbonate settings mobile barrier island systems are rare. Their construction and migration may be inhibited by reef formation, early cementation, and the relative inefficiency of sourcing beach sediments from open carbonate shelves. Carbonate barrier island systems likely formed more commonly during geological periods when ramps and unrimmed shelves predominated and in calcite seas, when meteoric cementation was minimized as a result of initial calcitic allochem mineralogy. As with their siliciclastic analogues, however, recognition of the influence of these transient landforms in the rock record is challenging. 相似文献
5.
Recognition of sequence boundaries and transgressive surfaces (i.e. ravinement surfaces, RS) is now known to be of great importance in stratigraphy. The sedimentary features of deposits immediately above a transgressive surface are well exposed in the Upper Pleistocene Kioroshi Formation of the Kanto Plain in central Japan. The formation comprises mainly coastal and shallow-marine deposits (estuarine, barrier-island and the strand-plain systems) which accumulated along a wavedominated coast in the Late Pleistocene, i.e., the last interglacial to last glacial period. The Kioroshi Formation is bounded above and below by sequence boundaries that formed in the lowstand periods correlative to the glacial periods of oxygen isotope stages 4 and 6, respectively. A significant transgressive surface that was formed by landward migration of barrier islands during the transgressive interval, the ravinement surface (RS), is found within the deposits of the upper shelf environment.
This ravinement surface is characterized by the exotic nature of the overlying sediment veneer (pebbles, shells and scattered mud clasts) which is poorly sorted. The RS shows a very flattened erosional surface in the shore-parallel sense, and the gradient of the surface in shore-normal sense is calculated as 0.0021, where the syndepositional tectonic movement is revised. The RS commonly cuts through the lower sequence boundary. However, in the places where the river or tidal channel valleys incised, the valley-filling sediment shows a deepening-upward sequence recognized as a transgressive systems tract and the RS can be clearly distinguished from the lower sequence boundary. 相似文献
6.
海南岛东南部海岸砂丘风暴冲越沉积记录 总被引：1，自引：0，他引：1
通过海南岛东南部海岸详细的古风暴学考察,在尖岭海岸发现了含有风暴冲越沉积物的海岸沙丘剖面,分别命名为JL-1和JL-2剖面,试图从海岸沙丘沉积记录中提取历史上的风暴事件信息。沉积物粒度、磁化率等参数的指标分析表明,这两个剖面含有典型的风暴冲越沉积物,利用放射性核素AMS14C测年、OSL测年分析,并结合历史文献记载,确定这些风暴沉积层是多次台风作用的产物,其形成机制与风暴浪越过海岸沙丘的堆积有关,风暴流越过沙丘顶部后不能回流,导致风暴流携带的沉积物迅速沉积。此外,依据Stockdon经验公式计算结果,该地点沉积记录所代表的最大风暴事件相当于100到200年一遇的重现期。研究表明,该处海岸沙丘冲越沉积含有南海台风强度与重现期的重要信息。 相似文献
7.
R. Paperno D. M. Tremain D. H. Adams A. P. Sebastian J. T. Sauer J. Dutka-Gianelli 《Estuaries and Coasts》2006,29(6):1004-1010
During the summer of 2004, four hurricanes (Charley, Frances, Ivan, and Jeanne) affected Florida between August 13 and September
27. Two storms (Frances: category 2 and Jeanne: category 3) made landfall in the southern portion of the Indian River Lagoon
(IRL) on the east-central coast of Florida. The presence of Florida Fish and Wildlife Conservation Commission's long-term
fisheries monitoring program in the IRL provided a unique opportunity to examine the effects of large tropical events on estuarine
fish communities. Increased sampling efforts to monitor the effects of tropical disturbances on the fish community within
the IRL and one of its major tributaries (St. Sebastian River) were initiated within days after the passing of the last hurricane
(Jeanne). The objectives of the study were to characterize changes to the composition of the fish community within the lagoon
and river immediately after the passage of two hurricanes, and to examine the recovery of the fish communities. Analyses indicated
that immediately after the last hurricane passed, community diversity within the estuary decreased following these storms
due to the absence of many marine species, whereas the fish community within the St. Sebastian River shifted to one containing
a greater percentage of freshwater species. Recovery of the community structure to pre-hurricane conditions was evident within
several weeks following the last hurricane, and by mid December 2004 (ca. 3 mo after the last storm), there was little difference
between the pre-hurricane and post-hurricane fish communities. 相似文献
8.
Prospects for interregional correlations using Wisconsin and Holocene aridity episodes, northern Gulf of Mexico coastal plain 总被引：1，自引：0，他引：1
Ervin G Otvos 《Quaternary Research》2004,61(1):105-118
Luminescence dating of extensive dune fields and associated eolian sandsheets provided a chronology of recently recognized Pleistocene and early Holocene dry climate episodes in the currently humid warm temperate northern-northeastern Gulf of Mexico region. Scattered parabolic dunes and clusters of intersecting parabolic dunes, along with elongated shore-transverse and shore-parallel dunes, developed. These landforms occur in a 390-km-long and 2- to 3-km-wide, semicontinuous belt in southeast Alabama and northwestern Florida. Dune elevations reach ± 22 m. Sangamon coastal barrier sectors were the primary source of the eolian sand. Deflation was coeval with early Wisconsin to mid-Holocene marine low sea-levels and associated distant shorelines. Early Holocene dune dates were synchronous, with indications of a hypsithermal dry interval in southeast Louisiana, the Yucatan, and the south Atlantic seaboard. Overlapping with dry episodes in Yucatan and the High Plains, Texas dunes and Louisiana and Texas prairie mounds, especially in the southwest Texas coast still dominated by dry climate, suggests intervals of early to late Holocene drought. The dates provide the basis for identifying and correlating Wisconsin, early, and late Holocene climate phases between currently semiarid and humid, coastal and interior areas. They contribute to future studies, including interregional paleoclimate modeling. Although Pleistocene coastal eolian deposition coincided with glaciation in the northern interior and with cooler temperatures of a reduced Gulf of Mexico, Holocene aridity phases may have been related to major variations in the position of high-pressure cells, storm tracks, and branches of the jet stream, and even to prolonged La Niña conditions. 相似文献
9.
The geomorphic and stratigraphic history of six coastal embayments has been studied in the vicinity of Newcastle, New South Wales (N.S.W.), Australia, in order to determine modes of deposition, and the degree to which marine and estuarine deposits can be correlated and dated. Each embayment possesses its own distinctive suite of landforms ranging from those dominated by coastal dunes to those in which beach ridges occur. In four of the bays dual sand barriers, comprising an Inner Barrier and an Outer Barrier, provide the framework for correlation between embayments. Six stages are recognized in the deposition of late Quaternary sediments in this area: (i) Pre-Last Interglacial, involving accumulation of separate composite units consisting of estuarine clays and transgressive dune complexes; (ii) Last Interglacial stage during which Inner Barriers were formed; (iii) Last Glacial reworking of barrier and dune sands by westerly winds; (iv) Postglacial Marine Transgression during which the Outer Barriers were initiated; (v) Mid-Holocene stage following cessation of sea-level rise ca. 6000–6500 yr B.P. on this coast, and involving progradation of Outer Barriers in some embayments; and (vi) Late Holocene episodic eolian reworking of dune complexes and Outer Barriers. The relatively high wave and wind energy as well as the tectonic setting of the central N.S.W. coast results in somewhat different geomorphic histories from barrier-island coasts in North America and Europe. 相似文献
10.
Detailed examination of inter- and supratidal delta and floodplain sediments exposed in eroding bank sections at 52 locations along the Squamish River estuary provides the basis for recognizing seven distinct facies within the 5500 m-long estuary. Estuary sedimentation is initially driven by the development of sand bar complexes along the seaward edge of the intertidal delta. Sedimentation continues within interdistributary bay environments as intertidal sandflats and then tidal marshes develop, Aggradation of the delta within interdistributary bay environments results in a gradual transition from delta to alluvial plain. Of the seven facies identified, only the intertidal sands and tidal marsh deposits provide evidence of their tidal origin. Examination of deposits throughout the riverine estuary reveals a number of gradual yet distinct changes of sediment size, structure, and sequence architecture. These trends record the changing nature of tidal and riverine control on sedimentation along the tidal gradient. Generally, with increasing distance up-estuary, sediment grain-size increases, the thickness of fine-grained overbank deposits decreases, and bedding changes from fine parallel bedding to higher energy bedforms. In addition, fining-upward successions become capped by coarser sands, facies contacts change from gradational to abrupt and occasionally erosional, and facies successions become increasingly complex and less predictable. Squamish River estuary has been divided into four zones based on sedimentological and stratigraphical evidence, each zone reflecting changes in the relative influence of tidal and riverine control on sedimentation. Each zone contains distinctly different facies sequences, although zone boundaries generally are gradational. 相似文献
11.
《Sedimentary Geology》1999,123(3-4):199-218
Gravelly shoreline deposits of the latest Pleistocene highstand of Lake Lahontan occur in pristine depositional morphology, and are exposed in gravel pits along Churchill Butte in west-central Nevada. Four environments differentiated at this site are alluvial fan/colluvium, lakeshore barrier spit, lake lower-shoreface spit platform, and lake bottom. Lakeshore deposits abut, along erosional wave headcuts, either unsorted muddy to bouldery colluvium fringing Churchill Butte bedrock, or matrix-supported, cobbly and pebbly debris-flow deposits of the Silver Springs fan. The lakeshore barrier spit is dominated by granule pebble gravel concentrated by wave erosion of the colluvial and alluvial-fan facies. The lakeward side of the barrier consists of beachface deposits of well-sorted granules or pebbles in broad, planar beds 1–10 cm thick and sloping 10–15°. They interfinger downslope with thicker (10–25 cm) and less steep (5–10°) lakeward-dipping beds of fine to medium pebble gravel of the lake upper shoreface. Interstratified with the latter are 10–40-cm-thick sets of high-angle cross-beds that dip southward, alongshore. Higher-angle (15–20°), landward-dipping foresets of similar texture but poorer sorting comprise the proximal backshore on the landward side of the barrier. They were deposited during storm surges that overtopped the barrier berm. Gastropod-rich sand and mud, also deposited by storm-induced washover, are found landward of the gravel foresets in a 15-m-wide backshore pond. Algal stromatolites, ostracodes, and diatoms accumulated in this pond between storm events. The lake lower shoreface, extending from water depths of 2 to 8 m, consists of a southward-prograding spit platform built by longshore drift. The key component of this platform is large-scale sandy pebble gravel in 16° southward-dipping `Gilbert' foresets that grade at a water depth of about 6–7 m to 4°-dipping sandy toesets. A shift from bioturbated lower-shoreface sand and silt, to flat and laminated lake-bottom silt and mud, occurs between water depths of 10–40 m and over a shore-normal distance of ≥250 m. This lake-bottom mud facies, unlike the others, is areally expansive. 相似文献
12.
Barrier dunes on the northern side of the Tawharanui Peninsula, north of Auckland, New Zealand, appear to have been overtopped by extreme waves that have deposited two large sand washover lobes in a back beach wetland. Present-day storm surges and storm waves are incapable of overtopping the barrier dunes. However, historical data and numerical models indicate tsunamis are amplified by resonance within the adjacent bay and Hauraki Gulf. Further, the location of nearshore reefs in close proximity to the washover lobes suggests that the interaction between tsunamis and the reefs further amplified the waves at those locations. The presence of a distinctive pumice (Loisels Pumice) within the washover deposits suggests that the deposits are associated with a 15th Century eruption from the submarine Mt Healy caldera located northeast of New Zealand. 相似文献
13.
Lawrence M Kiage Daniel Deocampo Terrence A. Mccloskey Thomas A. Bianchette Melissa Hursey 《第四纪科学杂志》2011,26(7):714-722
We present here the first paleotempestology record from Wassaw Island on the Georgia Bight, located in the south Atlantic coast of the United States. In the historical period, the Georgia Bight has experienced less frequent hits by hurricanes than other locations along the US Gulf and Atlantic coasts. The 1900‐year record inferred from the overwash sand layers from a back‐barrier marsh on Wassaw Island suggests that the island was directly struck by major storms on nine occasions during this interval. The Wassaw Island record shows alternating regimes, with periods of increased activity from >2000 a BP until ～1100 a BP, and ～100 a BP until the present, sandwiching a quiet period from ～1100 to 250 a BP. Storm deposits from the most recent active period are perhaps amalgamated, indicating that site‐specific conditions may result in event undercounting and suggests that the relative thickness of sand layers in the sedimentary record is not always indicative of hurricane strength. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
14.
Jonathan Hodgkinson Malcolm E. Cox Stephen McLoughlin Gary J. Huftile 《Sedimentary Geology》2008,203(1-2):64-86
Sediment mineralogy, quartz-grain surface-textures, grain-size analysis, bore-hole logging and ground penetrating radar are combined to develop a three dimensional stratigraphic model of a back-barrier sand island in southeast Queensland, Australia. The island consists of an unconsolidated sedimentary pile above an erosional bounding surface at the top of the underlying bedrock. The stratigraphy is complex, recording the shift in depositional environments from fluvio-deltaic to strandplain, via estuarine stages of evolution. The back-barrier island deposits are correlated with the stratigraphy of the adjacent coastal plain to the west and the barrier island to the east. Extrapolation of optically stimulated luminescence dates obtained from the barrier island combined with direct dating of the back-barrier island sediments is used to constrain the depositional age and chronology of the back-barrier island stratigraphy. The modern depositional environment evolved from a chenier plain into a barrier island system by the flooding of an interdune swale and development of a shore-parallel back-barrier tidal lagoon. The lithological heterogeneity of the back-barrier island succession was controlled by the presence of a bedrock incised palaeovalley and changes in relative sea-level.Sedimentary facies associations constrain the spatial distribution of hydraulic properties controlled by lithological heterogeneity. Post-depositional alteration horizons are integrated with the facies model to account for the effects of weathering and diagenesis on hydraulic behaviour. The derived hydrostratigraphy describes a vertically stacked, dual aquifer, island groundwater system consisting of a semi-confined palaeovalley aquifer overlain by an unconfined strand-plain aquifer.Hydrostratigraphic analysis based on sedimentary facies associations, integrated with post-depositional alteration characteristics reveals great complexity of groundwater systems within small island settings. The facies modelling approach employed in this study more accurately estimates the distribution of lithological heterogeneity and the associated variations in hydraulic properties in the sedimentary pile. 相似文献
15.
We examined interannual differences in fish assemblage structure in Tampa Bay and Charlotte Harbor, Florida, from 1996 to
2005 to reveal the extent of hurricane-induced changes in relation to multiannual variability for five different assemblages
in each estuary: small-bodied fishes (<generally 80-mm standard length) along river shorelines, in river channels, along bay
shorelines, and on the bay shelf (<1.5-m water depth); and large-bodied fishes (>generally 100-mm standard length) along bay
shorelines. Fish assemblages tended to differ, between estuaries, as did interannual variability in assemblage structure.
In the lower portions of tributary rivers to Tampa Bay, the small-bodied shoreline fish assemblage during August 2004 to July
2005, i.e., during and after the multiple hurricanes, was different from assemblages of August to July in previous years.
This may have been a result of physical displacement of fish or suboptimal salinities caused by increased freshwater inflow.
The small-bodied shoreline fish assemblage in Charlotte Harbor also differed between prehurricane and hurricane periods, possibly
because damage to vegetated shorelines affected fish survival through a decrease in feeding and refuge habitats. In the remaining
habitats, fish assemblage structure from August 2004 to July 2005 were within the range of variability exhibited over the
9-yr study period. There were several unusual fish assemblages that appeared to be attributable to drought conditions (1996,
1999–2000), suggesting that other major environmental perturbations may be as important as hurricanes in influencing assemblage
structure. We conclude that although the 2004 hurricane season affected some of the fish assemblages of Tampa Bay and charlotte
Harbor, these assemblages generally appeared quite resilient to natural environmental perturbations from a decadal perspective. 相似文献
16.
A 45 km long barrier island exists west of the town of Guerrero Negro, Mexico, along the western coast of the Baja California peninsula, about 720 km south of San Diego, California. This barrier has developed in a mesotidal, arid-climate regime characterized by steady, strong, onshore winds from the NW. The barrier island W of Guerrero Negro has prograded seaward about 1·6 km in the last 1800 years while an aeolian dunefield fed by sand blown from beaches has advanced inland up to 13 km. Landward progradation of the dune system from the barrier has occurred during relative rise in sea-level; thus, aeolian sediments exist at or below the water table over a wide area. The progradation of dunes across marshes, tidal flats, and tidal channels, as well as the repeated submergence of interdune areas by tidal waters, has created a complex suite of mixed aeolian and subaqueous sediments in the back barrier. The complexity of the suites of aeolian sedimentary structures, together with the inclusion of subaqueously formed structures such as current and oscillation ripples, would make recognition of the aeolian origin of much of the sediments difficult in ancient rocks. In addition to the scientific importance of recognizing the aeolian deposits, the sedimentation model represented by the Guerrero Negro barrier has applications in petroleum exploration and development. Currently, most preservational models for barrier islands attach little volumetric importance to aeolian deposits. This modern example suggests that volumetrically significant aeolian deposits can be preserved behind a barrier, particularly in an arid-climate regime. If preserved and charged with oil, the resulting productive sandstone could have an extremely irregular landward edge comprised in part of onshore-prograded aeolian dune sandstone with excellent reservoir characteristics. As with current barrier models, the reservoir would be sealed landward and above by lagoonal mudstone and silt, evaporites, or evaporitic, sandy sabkha deposits. High organic productivity occurs in lagoons immediately adjacent to the dunefields of Guerrero Negro, suggesting that organic-rich source rock may exist near aeolian sandstone in ancient settings similar to Guerrero Negro. 相似文献
17.
JosMaria Landim Dominguez Abilio Carlos da Silva Pinto Bittencourt Louis Martin 《Sedimentary Geology》1992,80(3-4):213-232
East-northeastern Brazil has a wave-dominated, micro- to meso-tidal coast, lying entirely within the southern Atlantic trade wind belt. Integration of geologic mapping, radiocarbon dating and vibracoring data shows that the Quaternary coastal evolution of this area was controlled by three major factors: (1) sea-level history; (2) trade winds; and (3) climate change.
Sea-level history. Along the east-northeastern coast of Brazil, relative sea level has fallen approximately 5 m during the last 5000 y. Correlation of this sea-level history with the evolution of beach-ridge, lagoonal and coastal plain deposits shows that: (1) sea-level rise favours the formation of barrier island—lagoonal systems and the construction of intralagoonal deltas; (2) sea-level lowering is not conductive to barrier island formation. Rather, lagoons and bays become emergent and beach-ridge plains rapidly prograde.
Trade winds. Sediment dispersal systems along the coastal zone of east-northeastern Brazil have been highly persistent since Pleistocene time, as deduced from beach-ridge orientation. This persistence results from the fact that sediment dispersal in wave-dominated settings is ultimately controlled by atmospheric circulation which, for the east-northeastern coast of Brazil is associated with the South Atlantic high-pressure cell. The remarkable stability of this cell through time, has allowed the accumulation of extensive beach-ridge plains at the longshore drift sinks located along the coast.
Climate change. Effects of Quaternary climate changes on coastal sedimentation are twofold. Climate changes may affect rainfall patterns, thus exerting an important control on coastal dune development. Along the coast of northeastern Brazil, active coastal dunes are only present in those areas in which at least four consecutive dry months occur during the year. Mapping of these areas has shown that dune development during the Holocene has been episodic, these episodes being probably controlled by variations in rainfall patterns associated with climate changes. Secondly, despite its overall stability, the position of the high-pressure cell has experienced small shifts in position during the Holocene in response to climate changes. Changes in wind direction associated with these shifts have induced modifications in the coastal dispersion system, which are recorded in the strandplains as small truncations in the beach-ridge alignments.
These results have important implications in understanding accumulation of ancient sandstone shoreline sequences. 相似文献
18.
M. R. Jones 《Australian Journal of Earth Sciences》2013,60(3):433-444
Central Queensland lies on the passive margin of eastern Australia and owes its landscape to processes that began following rifting and opening of the Tasman Sea. The modern landscape is the result of long-term processes of landform development, and the landforms themselves are the evidence of these processes. Hence, interpreting their significance provides an understanding of long-term landscape evolution. Along the eastern Australian coast, numerous rivers drain into the sea but among these, there are two that stand out: the neighbouring Fitzroy and Burdekin Rivers in central Queensland. These two streams have by far the largest catchments of any rivers along the eastern seaboard of Australia. The Burdekin and Fitzroy catchments contain widespread remnants of Cenozoic deposits, which accumulated predominantly in fluvial and lacustrine environments established during the Palaeogene. Alluvial sediments were supplied by erosion of nearby uplands, and accumulated in depressions and basins on a prior land surface. Volcanic activity also resulted in large lava flows in central western areas. Water was the main agent of sediment transport, distributing unconsolidated deposits along the drainage networks of the time, some of which were directed inland. It is inferred that during the Palaeogene, the divide between coastward and inland draining streams was further to the east than it is at present. Several basins were located west of the former coastal divide, and were characterised by continental environments of deposition in a generally westward drainage system. With continued accumulation of sediments, individual basins overflowed and merged to form a widespread flat-lying Palaeogene landscape that concealed an earlier land surface on which bedrock was more extensive. In the Early Cenozoic, there was a change from the depositional phase that resulted in the continental sequence, to an erosional phase that developed the modern landforms. The change from deposition to erosion probably started during the Palaeogene. Erosion continued through to the present, re-exposing parts of the basal Palaeogene sequence and earlier Mesozoic land surface. The erosional phase that shaped the landforms of the modern Burdekin and Fitzroy catchments can be explained by slowly evolving drainage basins in the interior being captured by small coastal streams—the predecessors of the Burdekin and Fitzroy Rivers. The coastal streams were short and steep in comparison with those in the interior, allowing a more active erosional environment along the coast. As the coastal streams expanded, the drainage divide moved rapidly westwards. Stream capture began a phase of regional erosion, which transported large quantities of sediments to the coast. The sediments contributed to coastal and nearshore features similar to the Holocene high sea-level examples at the mouth of the Burdekin River in the north, and the Fitzroy Delta and the Keppel Coast in the south. Large volumes of sediments were also transported beyond the present coast during low sea-levels of the Cenozoic, forming similar coastal features and contributing to a major eastward bulge on the central Queensland continental shelf. The emptying of continental basins has paralleled the development of the continental shelf bulge from the coast to the Marion Plateau. 相似文献
19.
Tanya C. Forde Mladen R. Nedimović Martin R. Gibling Donald L. Forbes 《Estuaries and Coasts》2016,39(2):363-384
Many coastlines are retreating in response to sea level rise, compounded by glacial–isostatic subsidence in areas marginal to former ice sheets. The resulting barrier and estuarine deposits are dominated by transgressive stratigraphy. Where supplied primarily from relict glacial deposits, this “paraglacial” sediment input may rise and fall, increasing as a new source such as a drumlin headland is exposed to erosion but declining as the source becomes exhausted. Conrads Beach, on the Atlantic coast of Canada, has experienced a succession of barrier growth and reworking as sediment supply from several drumlin sources has varied over the past 3000 years. In the context of long-term regional transgression, there have been intervals of years to centuries characterized by local stability or progradation. Ground-penetrating radar profiles and refraction seismic data were used to image the facies architecture of Conrads Beach to depths of 6–8 and 10–24 m, respectively. Thirteen vibracores provided a record of lithofacies characteristics and geometry. Results show evidence of an estuarine basin at ~2800 years BP. As the outer coast retreated, erosion of drumlins provided multi-century sediment pulses to adjacent beaches and embayments. Locally increased sediment supply fed a prograding beach ridge complex from >600 to ~150 years BP and tidal channels feeding sediment to back-barrier flood delta deposits. This study documents the complexity of coastal adjustment to time- and source-varying sediment supply under long-term rising sea level. It expands and refines previous models, providing guidance required for effective management and hazard mitigation on transgressive paraglacial coasts. 相似文献
20.
各种类型的沉积物床面形态及层理构造大量保存在沉积岩中,成为恢复古沉积环境和古地理的重要标志之一。1981年,作者在山东白沙口海岸,对海岸带不同地貌条件下的床面形态系列及层理构造进行了观测,并对其形成过程进行了探讨。 相似文献