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1.
T. Sionneau V. Bout-Roumazeilles P.E. Biscaye B. Van Vliet-Lanoe A. Bory 《Quaternary Science Reviews》2008,27(17-18):1740-1751
Maps of the distributions of the four major clay minerals (smectite, illite, kaolinite and chlorite) in and around the Mississippi River drainage basin and in the Northern Gulf of Mexico have been produced using newly acquired data from erodible/alluvial terrestrial sediments and marine surface sediments, as well as from previously published data. East of the Rockies, North America can be divided into four, large, clay-mineral provinces: (1) the north-western Mississippi River watershed (smectite rich), (2) the Great Lakes area and eastern Mississippi River watershed (illite and chlorite rich), (3) the south-eastern United States (kaolinite rich) and (4) the Brazos River and south-western Mississippi River watersheds (illite and kaolinite rich). The clay mineral distributions in surface sediments of the present-day Gulf of Mexico are strongly influenced by three main factors: (1) by relative fluvial contributions: the Mississippi River delivers the bulk of the clay input to the Northern Gulf of Mexico whereas the Apalachicola, Mobile, Brazos and Rio Grande rivers inputs have more local influences; (2) by differential settling of various clay mineral species, which is identified for the first time in Northern Gulf of Mexico sediments; and (3) by oceanic current transport: the Gulf of Mexico surface and subsurface circulation distributes the clay-rich sediments from river mouth sources throughout the Northern Gulf of Mexico. 相似文献
2.
N. N. Rabalais R. E. Turner B. K Sen Gupta D. F. Boesch P. Chapman M. C. Murrell 《Estuaries and Coasts》2007,30(5):753-772
We update and reevaluate the scientific information on the distribution, history, and causes of continental shelf hypoxia
that supports the 2001 Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (Mississippi
River/Gulf of Mexico Watershed Nutrient Task Force 2001), incorporating data, publications, and research results produced
since the 1999 integrated assessment. The metric of mid-summer hypoxic area on the LouisianaTexas shelf is an adequate and
suitable measure for continued efforts to reduce nutrients loads from the Mississippi River and hypoxia in the northern Gulf
of Mexico as outlined in the Action Plan. More frequent measurements of simple metrics (e.g., area and volume) from late spring
through late summer would ensure that the metric is representative of the system in any given year and useful in a public
discourse of conditions and causes. The long-term data on hypoxia, sources of nutrients, associated biological parameters,
and paleoindicators continue to verify and strengthen the relationship between the nitratenitrogen load of the Mississippi
River, the extent of hypoxia, and changes in the coastal ecosystem (eutrophication and worsening hypoxia). Multiple lines
of evidence, some of them representing independent data sources, are consistent with the big picture pattern of increased
eutrophication as a result of long-term nutrient increases that result in excess carbon production and accumulation and, ultimately,
bottom water hypoxia. The additional findings arising since 1999 strengthen the science supporting the Action Plan that focuses
on reducing nutrient loads, primarily nitrogen, through multiple actions to reduce the size of the hypoxic zone in the northern
Gulf of Mexico. 相似文献
3.
R. E. Turner N. N. Rabalais R. B. Alexander G. McIsaac R. W. Howarth 《Estuaries and Coasts》2007,30(5):773-790
We synthesize and update the science supporting the Action Plan for Reducing, Mitigating, and Controlling Hypoxia in the Northern Gulf of Mexico (Mississippi River/Gulf of Mexico Watershed Nutrient Task Force 2001) with a focus on the spatial and temporal discharge and patterns of nutrient and organic carbon delivery to the northern Gulf of Mexico, including data through 2006. The discharge of the Mississippi River watershed over 200 years varies but is not demonstrably increasing or decreasing. About 30% of the Mississippi River was shunted westward to form the Atchafalaya River, which redistributed water and nutrient loads on the shelf. Data on nitrogen concentrations from the early 1900s demonstrate that the seasonal and annual concentrations in the lower river have increased considerably since then, including a higher spring loading, following the increase in fertilizer applications after World WarII. The loading of total nitrogen (TN) fell from 1990 to 2006, but the loading of total phosphorus (TP) has risen slightly, resulting in a decline in the TN:TP ratios. The present TN:TP ratios hover around an average indicative of potential nitrogen limitation on phytoplankton growth, or balanced growth limitation, but not phosphorus limitation. The dissolved nitrogen:dissolved silicate ratios are near the Redfield ratio indicative of growth limitations on diatoms. Although nutrient concentrations are relatively high compared to those in many other large rivers, the water quality in the Mississippi River is not unique in that nutrient loads can be described by a variety of land-use models. There is no net removal of nitrogen from water flowing through the Atchafalaya basin, but the concentrations of TP and suspended sediments are lower at the exit point (Morgan City, Louisiana) than in the water entering the Atchafalaya basin. The removal of nutrients entering offshore waters through diversion of river water into wetlands is presently less than 1% of the total loadings going directly offshore, and would be less than 8% if the 10,093 km2 of coastal wetlands were successfully engineered for that purpose. Wetland loss is an insignificant contribution to the carbon loading offshore, compared to in situ marine production. The science-based conclusions in the Action Plan about nutrient loads and sources to the hypoxic zone off Louisiana are sustained by research and monitoring occurring in the subsequent 10 years. 相似文献
4.
Nutrient changes in the Mississippi River and system responses on the adjacent continental shelf 总被引：1，自引：0，他引：1
Nancy N. Rabalais R. Eugene Turner Dubravko JustiĆ Quay Dortch William J. Wiseman Barun K. Sen Gupta 《Estuaries and Coasts》1996,19(2):386-407
The Mississippi River system ranks among the world's top 10 rivers in freshwater and sediment inputs to the coastal ocean. The river contributes 90% of the freshwater loading to the Gulf of Mexico, and terminates amidst one of the United States' most productive fisheries regions and the location of the largest zone of hypoxia, in the western Atlantic Ocean. Significant increases in riverine nutrient concentrations and loadings of nitrate and phosphorus and decreases in silicate have occurred this century, and have accelerated since 1950. Consequently, major alterations have occurred in the probable nutrient limitation and overall stoichiometric nutrient balance in the adjacent continental shelf system. Changes in the nutrient balances and reduction in riverine silica loading to, the continental shelf appear to have led to phytoplankton species shifts offshore and to an increase in primary production. The phytoplankton community response, as indicated by long-term changes in biological uptake of silicate and accumulation of biologically bound silica in sediments, has shown how the system has responded to changes in riverine nutrient loadings. Indeed, the accumulation of biologically bound silica in sediments beneath the Mississippi River plume increased during the past two decades, presumably in response to, increased nitrogen loading. The duration, size, and severity of hypoxia has probably increased as a consequence of the increased primary production. Management alternatives directed at water pollution issues within the Mississippi River watershed may have unintended and contrasting impacts on the coastal waters of the northern Gulf of Mexico. 相似文献
5.
Previous authors have related the Late Cretaceous/early Tertiary subsidence of the Mississippi embayment to the opening of the Gulf of Mexico, but the Gulf opened earlier in Triassic/Jurassic time. We offer an alternative hypothesis that development of the embayment was coeval with the passage of the Mississippi Valley graben system over the Bermuda hotspot about 90 Ma. Several lines of evidence of significant uplift of the embayment axis accompanying mid-Cretaceous magmatism and prior to Late Cretaceous subsidence support this proposal.
First, reactivation of the Pascola arch in the northern embayment is recorded by flanking deposits of basal Upper Cretaceous gravel. Second, beneath a regional mid-Cretaceous unconformity, subcrops of Jurassic and Early Cretaceous strata define a pronounced southwest-plunging arch in the southern embayment. This arch is collinear with an arch revealed in Paleozoic rocks after restoration to mid-Cretaceous structural geometries. Third, a deep weathering profile on mid-Cretaceous alkalic plutons along the western embayment margin is nonconformably overlain by Paleocene sediments, and rapid mid-Cretaceous cooling of these intrusions has been interpreted from apatite fission tracks. Moreover, exploratory holes along the embayment axis encountered similar weathered alkalic intrusions nonconformably overlain by basal Upper Cretaceous strata. Fourth, there was an anomalous influx of clastic sediment into the northern Gulf of Mexico during mid-Cretaceous time, and subsequent clastic facies patterns suggest the Mississippi River drainage began to enter the Gulf in the Late Cretaceous.
Passage of the Mississippi Valley graben over the Bermuda hotspot during elevated hotspot activity of Cretaceous time may have significantly weakened the previously rifted lithosphere. Rifted continental margin at Charleston, South Carolina, also passed over this hotspot in latest Cretaceous time. Similarly, the St. Lawrence rift system passed over the Great Meteor hotspot during the Cretaceous. It is important to note that these rift systems are the principal loci of strong seismicity in eastern North America, and thus weakening by increased Cretaceous hotspot activity may be an important common factor for these seismic rift zones. 相似文献
6.
During the last deglaciation, the decaying Laurentide Ice Sheet (LIS) delivered huge volumes of meltwater toward the Gulf of Mexico. The present investigation of clay mineralogy and grain-size characteristics of terrigenous sediments deposited in the Orca Basin (Gulf of Mexico) offers a unique opportunity to link the marine record of these meltwater floods with the reconstructed continental glacial history and the modeled drainage patterns. Five peculiar sedimentary levels, characterized by high smectite content and low CaCO3 content, were identified and occurred simultaneously with major meltwater floods. According to recently published clay mineral distribution maps for North America, these results help to pinpoint the southwestern margin of the LIS as a main contributor to most of the meltwater discharges. In addition, the peculiar mineralogical composition (illite and chlorite-rich) of the sediments characterizing the meltwater episode associated with Heinrich event 1 suggests a provenance from the Great Lakes area, supporting the interpretation of destabilization of the LIS southeastern margin during this event. Decreased terrigenous contribution associated with changing provenance of sediments after 12.9 cal ka BP suggests strong modifications of the continental hydrography in relation to Lake Agassiz history and changes in the morphology of Mississippi delta due to rising sea level. 相似文献
7.
Dissolved organic nitrogen (DON) in near-surface (<20 m depth) waters of the Texas-Louisiana continental shelf is the predominant form of total dissolved nitrogen that is advected by the Mississippi-Atchafalaya River plume. Relatively high DON concentrations associated with low-salinity (<33 psu) waters throughout the year can be traced within the plume along the Texas-Louisiana inner shelf. DON concentrations throughout the shelf were significantly higher near the Mississippi-Atchafalaya outflow region relative to downstream inner Gulf shelf locations. Significant intercruise variations were also evident, with the highest concentrations during May 1992 and lower values in October 1992. At a fixed location off the Mississippi River outflow region DON concentration covaried inversely with salinity on time scales of hours to months, confirming that source water is a determining factor for variations of bulk DON concentrations in the region. Similar variations in upper water DON concentrations at different locations and seasons occurred in both plume and nonplume waters, which resembled the seasonal concentration changes of riverine nitrogen, and show that this pool is useful in tracing the influence of riverine-derived nitrogen on the overall nitrogen balance of the NW Gulf of Mexico’s continental shelf. Plume and nonplume DON concentrations deviated from mixing lines between riverine and oceanic endmembers, suggesting that plume waters may be a sink and nonplume waters may be a source of a labile fraction of DON in the region. 相似文献
8.
Sediments from San Antonio Bay, the northwest Gulf of Mexico, and the Mississippi River Delta were acid leached and analyzed
for Fe, Mn, Pb, Zn, Cd, Cu and Ni by atomic absorption spectrophotometry. In order to account for differences in sediment
clay, carbonate, and organic matter content, metal concentrations were normalized to Fe. Significant linear correlations of
metals to Fe were obtained for unpolluted sediments and deviations from these “natural” statistical populations were found
for areas thought to have metal input caused by man.
San Antonio Bay sediments show little evidence of metal pollution despite 70 years of shell dredging in the bay. However,
the San Antonio-Guadalupe River system, the bay's prime sediment source, has 10% to 50% higher than natural levels of Pb,
Cd and Cu.
Sediments from a 1500 km2 area of the Mississippi River Delta have Pb and Cd concentrations 10% to 100% higher than expected levels. The vertical distribution
of Pb and Cd in these sediments suggests that inputs have occurred during the past 30 to 40 years. We find no indication of
metal pollution in other areas of the Delta or along the continental shelf of the northwest Gulf of Mexico. 相似文献
9.
Jean Carlos Montero-Serrano Viviane Bout-Roumazeilles Nicolas Tribovillard Thomas Sionneau Armelle Riboulleau Aloys Bory Benjamin Flower 《Quaternary Science Reviews》2009,28(27-28):3333-3347
Cored sediments from the Pigmy Basin, northern Gulf of Mexico, were analyzed in order to better constrain late deglacial and early Holocene paleoenvironmental and sedimentary changes in response to North American climate evolution. Mineralogical and geochemical proxies indicate the succession of two sedimentary regimes: dominantly detrital during the deglaciation (15–12.9 cal ka BP) whereas biogenic contribution relatively increased later on during the Younger Dryas and early Holocene (12.9 and 10 cal ka BP). Geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the Mississippi River rather than modifications of redox conditions in the basin. Specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode (Meltwater Spike) described or modeled in previous marine or continental studies. During this episode, most parameters display “stair-step-like” – pattern variations highlighting three successive steps within the main meltwater flow. Variations in grain-size and clay mineral assemblage recorded in the Pigmy Basin indicate that the erosional regime was very strong on land during the first part of the Meltwater Spike, and then milder, inducing more subtle modifications in the sedimentary regime in this part of the Gulf. Specific geochemical and mineralogical signatures (notably, clay minerals and trace metal geochemistry) pinpoint a dominant origin from NW North America for detrital particles reflecting meltwater outflow from the south-western Laurentide Ice Sheet (LIS) margin during the most intense freshwater discharge. The observed decrease of the sedimentation rate from about 200 to 25 cm/ka at ca 12.9 ka evidenced a drastic decrease of erosional processes during late phase of discharge, consistently with the hypotheses of major reduction of meltwater flow. The major modification at 12.9 cal ka BP is interpreted to result from both modifications of the main Mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the Younger Dryas, and the increase of sea-surface temperature linked to insolation. Finally, slight grain-size modifications suggest that some freshwater discharges may have episodically reached the Gulf of Mexico after the Younger Dryas reflecting possible small adjustments of the postglacial hydrological regime. 相似文献
10.
世界著名深水油气盆地的构造特征及对我国南海北部深水油气勘探的启示 总被引：6，自引：0，他引：6
介绍世界著名深水油气盆地的主要特征,着重构造特征,并与南海北部深水区进行了对比。世界著名深水油气盆地产出的大地构造条件具多样性,虽然大多数位于开阔大洋被动陆缘（南大西洋裂谷系、北海、澳大利亚西北陆架盆地）,但边缘海的被动陆缘（墨西哥湾盆地）、转换大陆边缘（洛杉矶盆地）、主动陆缘（南沙海槽盆地）也可形成极佳的深水含油气盆地。南海北部深水区具有世界某些重要深水含油气盆地类似的特征,如位于被动陆缘和大河出口下方,以裂陷期的湖相富有机质页岩为主要生油岩,白云凹陷发育上下叠置的6层深水扇等,这都是有利的石油地质条件。但南海北部深水区盐层和盐构造不发育,构造圈闭相对较不发育,使深水油气系统的研究更加困难,也更具开拓意义。
相似文献
11.
12.
《Quaternary Science Reviews》2007,26(7-8):920-940
Sea-level records from the Gulf of Mexico at the Last Glacial Maximum, 20 ka, are up to 35 m higher than time-equivalent sea-level records from equatorial regions. The most popular hypothesis for explaining this disparity has been uplift due to the forebulge created by loading from Mississippi River sediments. Using over 50 new radiocarbon dates as well as existing published data obtained from shallow-marine deposits within the northern Gulf of Mexico and numerical models simulating the impact of loading due to the Mississippi Fan and glacio-hydro-isostasy, we test several possible explanations for this sea-level disparity. We find that neither a large radiocarbon reservoir, sedimentary loading due to the Mississippi Fan, nor large-scale regional uplift can explain this disparity. We do find that with an appropriate model for the Laurentide Ice Sheet, the observations from the Gulf of Mexico can be explained by the process of glacio-hydro-isostasy. Our analysis suggests that in order to explain this disparity one must consider a Laurentide Ice Sheet reconstruction with less ice from 15 ka to its disappearance 6 ka and more ice from the Last Glacial Maximum to 15 ka than some earlier models have suggested. This supports a Laurentide contribution to meltwater pulse 1-A, which could not have come entirely from its southern sector. 相似文献
13.
14.
Most public decisions ultimately have economic content. Decisions that deal with externalities, such as pollution, carry costs as well as benefits for society. Actions that mitigate nutrient over-enrichment in the Gulf of Mexico would require actions throughout the Mississippi River Basin resulting in both direct and indirect economic impacts. This paper describes and explains the economic linkages and trade-offs involved in actions that could be cost effective and meet a public goal of reducing nitrogen over-enrichment within the Mississippi River Basin. The impacts of different approaches that reduce the major source of nitrogen flows to the Gulf, nonpoint pollution from agriculture, are simulated for both source reduction the major source of nitrogen flows to the Gulf, nonpoint pollution from agriculture, are simulated for both source reduction and interception of nitrogen. Lessons learned include the fact that any one approach by itself has increasing marginal cost. The approaches considered have modest direct and indirect costs when only required to mitigate 20% to 25% of the nitrogen losses. Simultaneous multiple approaches appear even more attractive to induce only moderate negative impact. The impacts of mitigation are not just confined to the Mississippi River Basin but spread beyond the basin and are themselves influenced by external factors such as commodity prices and import and export markets for agricultural commodities. Success in reducing excess nitrogen flows will depend on institutional factors as well as technical efficacy. Finally, the nature of soil system sinks and the resulting long lead time likely before results might be apparent present a special obstacle to enlisting cooperation, assessing efficacy, and designing adaptive behavior. 相似文献
15.
16.
Joseph F. Donoghue 《Sedimentary Geology》1992,80(3-4):293-304
Since the beginning of the Tertiary the sedimentology of the Gulf of Mexico Basin has been dominated by the depositional activity of the Mississippi River. The sedimentologic influence of the Mississippi diminishes with distance east or west of the Louisiana shelf, however. The Texas and northwest Florida shelf margins, for example, are characterized by a series of smaller deltas. In the inner and mid-shelf areas of these regions the near-surface sedimentary units include infilled stream channels and small deltas. Such features are commonly observed in sub-bottom seismic records from the middle and inner shelf of the northeastern Gulf, along the Apalachicola River coast of northwest Florida.
The Apalachicola River is the principal source of clastic sediment to the northeastern Gulf of Mexico. During the late Holocene virtually all of the river's sediment load has been deposited in the modern Apalachicola Delta and in the river's estuary, Apalachicola Bay, which has been filling rapidly. During late Quaternary lowstands, prior to the development of the modern estuary, the river traversed the present-day inner and mid-shelf, incising a network of channels. Based on seismic records, many of these buried shelf channels were considerably larger than their modern counterparts.
During lowstands the Apalachicola River also deposited coarse sediment on the shelf as deltaic and associated river-mouth sediments. These deposits comprise the modern near-surface sediments of the inner and middle shelf. An investigation of subsurface sedimentary features observed in seismic profiles provides details on the late Quaternary development of the northeastern Gulf of Mexico shelf. Seismic reflection profiles obtained on the inner and mid-shelf regions of northwest Florida reveal an approximately 50 m thickness of late Quaternary sediments, comprised of two and sometimes three discrete clastic sequences. Two lower fluvial sequences total as much as 40–50 m in thickness. A transgressive marine sand deposit overlies the older features in some places, varying in thickness from 0 to 5 m. Identification of seismic facies, combined with stratigraphic data from a suite of coastal boreholes, enables correlation of offshore seismic stratigraphic units with late Tertiary and Quaternary coastal stratigraphy. 相似文献
17.
A total of 269 tropical storms and hurricanes originated in the North Atlantic basin from 1960–1989. Of these, 76 made landfall on the continental United states. This study divides the 76 tropical storms into their month of formation. Seasonal shifts in the principal areas of tropical cyclone formation over the Atlantic basin have been recognized for many decades. The results of the study suggest that the early and late season tropical cyclones develop in areas which are first affected by the position of the sun, resulting in an increase in water temperatures. These cyclones normally make landfall along the Gulf Coast and usually are of low intensity. Formation areas shift eastward in mid-summer with a slight increase in intensity. By late August and early September, the formation areas have extended to the Cape Verde Islands. These storms tend to strike the east coast of the US and are normally more intense. By the end of the hurricane season, the primary formation area has shifted back to the Gulf of Mexico, with low intensity storms affecting the Gulf Coast. 相似文献
18.
The Persian Gulf Basin: Geological history, sedimentary formations, and petroleum potential 总被引：1，自引：0，他引：1
The Persian Gulf Basin is the richest region of the World in terms of hydrocarbon resources. According to different estimates, the basin contains 55–68% of recoverable oil reserves and more than 40% of gas reserves. The basin is located at the junction of the Arabian Shield and Iranian continental block that belong to two different (Arabian and Eurasian) lithospheric plates. Collision of these plates at the Mesozoic/Cenozoic boundary produced the Zagros Fold Belt and the large Mesopotamian Foredeep, which is a member of the Persian Gulf Basin. During the most part of the Phanerozoic, this basin belonged to an ancient passive margin of Gondwana, which was opened toward the Paleotethys Ocean in the Paleozoic and toward the Neotethys in the Mesozoic. Stable subsidence and the unique landscape-climatic conditions favored the accumulation of a very thick sedimentary lens of carbonate rocks and evaporites (up to 12–13 km and more). Carbonate rocks with excellent reservoir properties are widespread, while the evaporites play the role of regional fluid seals. Organicrich rocks, which can generate liquid and gaseous hydrocarbons (HC), are present at different levels in the rock sequence. 相似文献
19.
侏罗纪时东南亚大陆上形成两个大盆地,西为海相盆地,东为陆相红盆。白垩纪时大盆地闭合或解体。第三纪出现裂谷盆地,其发育受燕山期构造格局控制;拉张应力自南向北变弱,裂谷发育自南向北变晚。第四纪为上叠盆地阶段。滇西与泰国各时期盆地的对比研究有助于更好地认识其演化特征,恢复东南亚大陆侏罗纪以来不断碎裂、局部解体的历史。 相似文献
20.
侏罗纪时东南亚大陆上形成两个大盆地,西为海相盆地,东为陆相红盆。白垩纪时大盆地闭合或解体。第三纪出现裂谷盆地,其发育受燕山期构造格局控制;拉张应力自南向北变弱,裂谷发育自南向北变晚。第四纪为上叠盆地阶段。滇西与泰国各时期盆地的对比研究有助于更好地认识其演化特征,恢复东南亚大陆侏罗纪以来不断碎裂、局部解体的历史。 相似文献