Continued Sea-level Rise Research Articles

Water Resources Policy and Practice Issues Exposed by Katrina

Water Resources Policy and Practice Issues Exposed by Katrina

Morphodynamics of Tidal Inlet Systems

In this review we discuss the morphodynamics of tidal inlet systems that are typical of barrier coasts formed during a period of continuous sea-level rise during the Holocene. The morphodynamics concerns feedbacks between three major components: the hydrodynamics of tidal currents and wind waves; the erosion, deposition, and transport of sediment under the action of the former hydrodynamic agencies; and the morphology proper, which results from the divergence of the sediment transport. We discuss the morphodynamics of the different units that characterize a tidal inlet system: the overall system, the ebb-tidal delta, the tidal channels, channel networks, tidal bars and meanders, and finally the intertidal zone of tidal flats and salt marshes. In most of these units, stability analysis is a major guide to the establishment of equilibrium structures.

Elevated CO2enhances biological contributions to elevation change in coastal wetlands by offsetting stressors associated with sea‐level rise

1. Sea-level rise, one indirect consequence of increasing atmospheric CO 2 , poses a major challenge to long-term stability of coastal wetlands. An important question is whether direct effects of elevated CO 2 on the capacity of marsh plants to accrete organic material and to maintain surface elevations outweigh indirect negative effects of stressors associated with sea-level rise (salinity and flooding). 2. In this study, we used a mesocosm approach to examine potential direct and indirect effects of atmospheric CO 2 concentration, salinity and flooding on elevation change in a brackish marsh community dominated by a C 3 species, Schoenoplectus americanus, and a C 4 grass, Spartina patens. This experimental design permitted identification of mechanisms and their role in controlling elevation change, and the development of models that can be tested in the field. 3. To test hypotheses related to CO 2 and sea-level rise, we used conventional ANOVA procedures in conjunction with structural equation modelling (SEM). SEM explained 78% of the variability in elevation change and showed the direct, positive effect of S. americanus production on elevation. The SEM indicated that C 3 plant response was influenced by interactive effects between CO 2 and salinity on plant growth, not a direct CO 2 fertilization effect. Elevated CO 2 ameliorated negative effects of salinity on S. americanus and enhanced biomass contribution to elevation. 4. The positive relationship between S. americanus production and elevation change can be explained by shoot-base expansion under elevated CO 2 conditions, which led to vertical soil displacement. While the response of this species may differ under other environmental conditions, shoot-base expansion and the general contribution of C 3 plant production to elevation change may be an important mechanism contributing to soil expansion and elevation gain in other coastal wetlands. 5. Synthesis. Our results revealed previously unrecognized interactions and mechanisms contributing to marsh elevation change, including amelioration of salt stress by elevated CO 2 and the importance of plant production and shoot-base expansion for elevation gain. Identification of biological processes contributing to elevation change is an important first step in developing comprehensive models that permit more accurate predictions of whether coastal marshes will persist with continued sea-level rise or become submerged.

The impact of sea level rise on developing countries: a comparative analysis

Sea level rise (SLR) due to climate change is a serious global threat. The scientific evidence is now overwhelming. Continued growth of greenhouse gas emissions and associated global warming could well promote SLR of 1m-3m in this century, and unexpectedly rapid breakup of the Greenland and West Antarctic ice sheets might produce a 5m SLR. In this paper, the authors have assessed the consequences of continued SLR for 84 developing countries. Geographic Information System (GIS) software has been used to overlay the best available, spatially-disaggregated global data on critical impact elements (land, population, agriculture, urban extent, wetlands, and GDP) with the inundation zones projected for 1-5m SLR. The results reveal that hundreds of millions of people in the developing world are likely to be displaced by SLR within this century, and accompanying economic and ecological damage will be severe for many. At the country level, results are extremely skewed, with severe impacts limited to a relatively small number of countries. For these countries (such as Vietnam, A. R. of Egypt, and The Bahamas), however, the consequences of SLR are potentially catastrophic. For many others, including some of the largest (such as China), the absolute magnitudes of potential impacts are very large. At the other extreme, many developing countries experience limited impacts. Among regions, East Asia and the Middle East and North Africa exhibit the greatest relative impacts. To date, there is little evidence that the international community has seriously considered the implications of SLR for population location and infrastructure planning in developing countries. The authors hope that the information provided in this paper will encourage immediate planning for adaptation.

Internal structure of a barrier beach as revealed by ground penetrating radar (GPR): Chesil beach, UK

Chesil Beach (Dorset) is one of the most famous coastal landforms on the British coast. The gravel beach is over 18 km long and is separated for much of its length from land by a tidal lagoon known as The Fleet. The beach links the Isle of Portland in the east to the mainland in the west. Despite its iconic status there is little available information on its internal geometry and evolutionary history. Here we present a three-fold model for the evolution of Chesil Beach based on a series of nine ground penetrating radar (GPR) traverses located at three sites along its length at Abbotsbury, Langton Herring and at Ferry Bridge. The GPR traverses reveal a remarkably consistent picture of the internal structure of this barrier beach. The first phase of evolution involves the landward transgression of a small sand and gravel beach which closed upon the coast leading to deposition of freshwater peat between 5 and 7 k yr BP. The second evolutionary phase involves the ‘bulking-out’ of the beach during continued sea level rise, but in the presence of abundant gravel supplied by down-drift erosion of periglacial slope deposits. This episode of growth was associated with a series of washover fans which accumulated on the landward flank of the barrier increasing its breadth and height but without significant landward transgression of the barrier as a whole. The final phase in the evolution of Chesil Beach involves the seaward progradation of the beach crest and upper beach face associated with continued sediment abundance, but during a still-stand or slight fall in relative sea level. This phase may provide further evidence of a slight fall in relative sea level noted elsewhere along the South Coast of Britain and dated to between 1.2 and 2.4 k yr BP. Subsequently the barrier appears to have become largely inactive, except for the reworking of sediment on the beach face during storm events. The case study not only refines the evolutionary picture of Chesil Beach, but illustrates the importance of the subtle interplay between relative sea level and sediment supply in the evolution of a barrier system. In addition, it also illustrates the potential of GPR in resolving the evolutionary history of gravel-rich coastal landforms such as Chesil Beach.

Taphonomy and sequence stratigraphic significance of oyster-dominated concentrations from the San Julián formation, Oligocene of Patagonia, Argentina

Oligocene siliciclastic shallow marine sediments of the San Julián Formation in southeastern Patagonia (Argentina) are interpreted as a deepening–shallowing cycle that represents a depositional sequence in which lowstand system tract deposits are not present. There are no significant compositional differences in the assemblages, all are dominated by the large oyster Crassostrea? hatcheri. However, four types of shell concentrations can be distinguished by differences in stratigraphic, sedimentologic, palaeoecological, and taphonomic features. These four types of shell concentrations are found in distinct positions within the depositional sequence: as a transgressive lag at the early phase of the transgressive system tract (TST), at the top of the TST, at the early phase of the high stand system tract (HST), and at the top of the HST. Oyster-dominated concentration in the early TST has a distinct basal erosional surface (ravinement surface), and the shells are completely disarticulated, fragmented and abraded with a chaotic orientation, suggesting reworking of previous deposited sediments, and deposition in a shoreface environment. Concentration at the end of the TST is a hiatal concentration formed from continued sea-level rise in the context of backlap deposition. It is characterized by high percentages of articulated oysters in life position, with high grades of bioerosion and encrustation. This concentration was accumulated during times of high rates of production of biogenic hard parts and low sedimentation rates, below fair weather wave base in an offshore environment. Concentrations over the maximum flooding surface in the early HST are in situ event concentrations (Census assemblages), characterized by high percentages of individual articulated adult specimens and clusters of juvenile oysters with well-developed endolithic bioerosion and encrustation, formed by rapid sedimentation in an offshore to lower shoreface environment. Concentrations at the top of the HST are multiple-event concentrations formed by densely fossiliferous deposits with completely disarticulated, convex-up oysters with low grades of abrasion and high grades of bioerosion and encrustation, intercalated with repeating beds with benthic colonizers. They were originated below fair weather wave base, in an offshore to lower shoreface environment, by sporadic high-energy events. The basic pattern of condensed deposits formed in the context of onlap, backlap, downlap, and toplap can be applied to the studied deposits. However, some differences are recorded, and these are attributed mostly to differences in the basin characteristics and to the high productivity and high preservation potential of large, thick-shelled oysters.

Inner shelf to shoreface depositional sequence in the Sendai coastal prism, Pacific coast of northeastern Japan: spatial and temporal growth patterns in relation to Holocene relative sea-level change

Temporal and spatial growth patterns of the Holocene wave-dominated inner shelf to shoreface sequence in the Sendai coastal plain, Pacific coast of northeastern Japan are detailed in relation to high resolution AMS 14C data. The sequence, deposited during about 10,000 years of rising to stable relative sea level, is a 22–26 m thick, tripartite inner-shelf to shoreface unit that overlies a transgressive ravinement surface. It is composed successively of laminated fine sand (Facies B), alternating mud and laminated very fine sand (Facies C), and burrowed/laminated fine to coarse sand (Facies D). Facies B consists of transgressive ravinement deposits formed during transgression in a water depth of 12–18 m at the drill sites. Facies C is inner-shelf storm deposits deposited during continued sea-level rise to highstand. Facies D is regressive highstand shoreface deposits. Isochrons show highstand deposits were formed by seaward progradation of the inner shelf to shoreface system. The stacking of deposits during rising sea level was mainly aggradational though there was probably accompanying progradation in the innermost shelf. The significant shelfal aggradation was probably because of an abundant mud supply from coastal rivers during gradual rise of relative sea level.

Late Holocene estuarine–inner shelf interactions; is there evidence of an estuarine retreat path for Tampa Bay, Florida?

The purpose of this study was to determine if and how a large, modern estuarine system, situated in the middle of an ancient carbonate platform, has affected its adjacent inner shelf both in the past during the last, post-glacial sea-level rise and during the present. An additional purpose was to determine if and how this inner shelf seaward of a major estuary differed from the inner shelves located just to the north and south but seaward of barrier-island shorelines. Through side-scan sonar mosaicking, bathymetric studies, and ground-truthing using surface grab samples as well as diver observations, two large submarine sand plains were mapped – one being the modern ebb-tidal delta and the other interpreted to be a relict ebb-tidal delta formed earlier in the Holocene. The most seaward portion of the inner shelf studied consists of a field of lobate, bathymetrically elevated, fine-sand accumulations, which were interpreted to be sediment-starved 3D dunes surrounded by small 2D dunes composed of coarse molluscan shell gravel. Additionally, exposed limestone hardbottoms supporting living benthic communities were found as well. This modern shelf sedimentary environment is situated on a large, buried shelf valley, which extends eastward beneath the modern Tampa Bay estuary. These observations plus the absence of an incised shelf valley having surficial bathymetric expression, and the absence of sand bodies normally associated with back-tracking estuarine systems indicate that there was no cross-shelf estuarine retreat path formed during the last rise in sea level. Instead, the modern Tampa Bay formed within a mid-platform, low-relief depression, which was flooded by rising marine waters late in the Holocene. With continued sea-level rise in the late Holocene, this early embayment was translated eastward or landward to its present position, whereby a larger ebb-tidal delta prograded out onto the inner shelf. Extensive linear sand ridges, common to the inner shelves to the north and south, did not form in this shelf province because it was a low-energy, open embayment lacking the wave climate and nearshore zone necessary to create such sand bodies. The distribution of bedforms on the inner shelf and the absence of seaward-oriented 2D dunes on the modern ebb-tidal delta indicate that the modern estuarine system has had little effect on its adjacent inner shelf.

Paleoenvironment and sea-level change in the early Cretaceous Barents Sea?implications from near-shore marine sapropels

The late Volgian (early Boreal Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottom-water conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by well-preserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.

Evolution of the Coastal Depositional Systems of the Changjiang (Yangtze) River in Response to Late Pleistocene-Holocene Sea-Level Changes

ABSTRACT The paleo-Changjiang (Yangtze) incised-valley fills, approximately 80-90 m thick, provide an opportunity to document the evolution of coastal depositional systems with large sediment supply in response to late Pleistocene-Holocene sea-level fluctuations on time scales of 103 to 104 years. The sedimentary facies of the incised-valley fills record three main depositional systems: fluvial, tide-dominated estuary, and tide-dominated delta. Radiocarbon ages for the incised-valley fills suggest that these depositional systems developed before about 11 ka, between 11 and 8 ka, and after approximately 8 ka, respectively. By applying sequence-stratigraphic concepts, the evolution of the depositional systems can be divided into three systems tracts--a lowstand systems tract (LST), a transgressive systems tract (TST), and a highstand systems tract (HST). Sea-level changes on a 104-year time scale controlled the basic architecture of the sequence of the incised-valley fill. On the other hand, sea-level changes on a millennial time scale affected the stacking pattern of the systems tracts. In particular, the continuous sea-level rise with episodic rapid rises during the last deglaciation affected the stacking pattern of the TST, which is characterized by a combination of aggradation and backstepping. The aggradation of fluvial and estuarine systems was dominant and the shoreline migrated only gradually landward under the relatively slow rise in sea level, and a very rapid sea-level rise around 12 and 10 ka caused the system to migrate abruptly landward. Unlike the transgressive estuarine phase, the stacking pattern of the regressive tide-dominated delta (HST), which developed within the almost filled incised valley and on the surrounding interfluve zones, was characterized by seaward progradation with clinoform architecture. It was initiated with aggradational and progradational stacking about 8 ka during the last phase of decelerated sea-level rise, and was followed by a progradational phase after the highest sea level about 6 ka.

The sedimentary record of the post-glacial transgression on the Gulf of Cadiz continental shelf (Southwest Spain)

Four seismic units (T A to T D) have been identified from the analysis and interpretation of high-resolution seismic profiles in a sector of the Gulf of Cádiz shelf. They constitute a composite seismic unit attributed to the transgressive systems tract (TST) of the last depositional sequence. The earliest transgressive unit was deposited on the outer shelf, and represents the distal facies of a coastal deposit. A process of shelf partitioning seems to have occurred during the formation of the three later transgressive parasequences. The shelf sector offshore from the Guadiana River mouth was a high-energy environment dominated by storm events. By contrast, the shelf sector offshore from the Doñana National Park was a low-gradient shelf, where large barrier island and lagoon systems were formed. The sparse occurrence of marine deposits within the TST is a consequence of the episodic nature of the sea-level rise. The generation and preservation of these transgressive deposits results from the interaction of the following controlling processes: (1) Relative sea-level rise: The formation of coastal transgressive deposits is related to intervals of reduced sea-level rise or stillstands within a period of continuous sea-level rise. Those sea-level changes were probably driven by short-term periods of colder climate during the Late Pleistocene–Holocene deglaciation. The Younger Dryas interval is the most widely recognised climatic event of this type, but probably other events of similar characteristics had the same effect on the glacio-eustatic sea-level rise. (2) Sediment supply changes: Short-lived climatic events probably also involved changes in the sediment supply to the continental shelf due to changes in erosion rates and river regimes of the river basin hinterlands. (3) Effect of the paleophysiography/paleogeography: The sedimentary environments' differentiation processes are associated to the formation of an exposed coastal promontory offshore from the Guadiana River mouth and a semi-protected embayment offshore from Doñana National Park. This coastal configuration was controlled by previous tectonic evolution and influenced the non-uniform landward migration of the coastline.

The holocene transgression into the estuarine central basin of the Odiel River mouth (Cadig gulf, SW, Spain): lithology and faunal assemblages

Six estuarine facies were distinguished recording the Holocene history of sea level rise relating according to the start and development of the Holocene transgression which flooded the coast of Huelva: Facies 2 (gravels), Facies 3 (grey clayey silts), Facies 5 (well sorted sands), Facies 4 (silty sands), Facies 5 (black clayey silts), and Facies 6 (red muds). This group overlies Neogene sediments (Facies 1). Three faunal assemblages (Open bay (OB), Central estuary (CE), and Wave domination (WD)) including remains of macrofauna, foraminifers and ostracods plus depositional features, are identified in a sedimentological log constructed from a borehole with a continuous core, sunk in the central basin of the Odiel River estuary, Huela coast, SW. Spain. The OB assemblage requires shallow and protected zones controlled by low energy tidal currents; the CE assemblage is located within an intertidal zone, where reworked marine forms of foraminifers, ostracods and scattered macrofauna co-exist with small estuarine foraminifers and ostracods; the WD assemblage comprises tests of marine macrofauna with fractured shells plus large marine foraminifers and estuarine ostracods. During the first stage of continuous sea level rise (8720±260 BP to 5390±155 BP), estuarine accretion, high energy tidal currents and wave action took place successively, allowing the development of the OB, CE and WD assemblages. The second stage (5390±155 BP to Present), with a stabilized sea level, comprised a vertical decrease of energy, with tidal currents favouring deposition in shallow tidal channels and marsh zones, leading to less energetic CE assemblages within the estuarine central basin. High sediment supply resulted in deposition during this stage, which shows a regressive nature.

Response of the wadden sea to a rising sea level: a Predictive empirical model

A clue to the stratigraphic evolution in the case of a barrier island migrating up against a landward obstruction has recently been obtained from a detailed analysis of sediment patterns in the mesotidal backbarrier environment of the Wadden Sea (southern North Sea). Here the landward boundary is man-made and comprises a continuous dike line constructed in the wake of extensive land reclamation over the past 1000 years. Sea-level rise currently amounts to 25 cm/century. The system is further characterized by a lack of external sediment supply and a pronounced cross-shore energy gradient resulting in progressive landward fining of the backbarrier sediments. Adjacent to the dike the depositional system today is dominated by mixed flats with mud contents rarely exceeding 30%. Land reclamation has thus truncated the natural succession of sediment facies by eliminating mud flats and salt marshes. Contrary to expectations, the re-establishment of a complete but compressed facies sequence incorporating mud flats and salt marshes has not materialized. This would suggest that energy levels at the foot of the dike today are considerably higher than was previously the case along the undiked shoreline. A quantitative relative measure of backbarrier energy levels is the mean settling velocity of the sediment. In extreme cases the system has reached the stage where the finest sands with settling velocities below 0.3 cm s-1 (mean grain sizes < 0.1 mm) are being eliminated. It is postulated that, in the wake of continued sea-level rise and associated landward migration of the barrier island system, the sediment elimination process adjacent to the dike will continue and involve progressively coarser sediments. In the case of the Wadden Sea, the settling-lag and scour-lag mechanism by which fine-grained sediments are carried shoreward must be modified to incorporate an export loop for those particle sizes which have settling velocities below the local elimination threshold.

Cambrian–Ordovician boundary in the Taconic allochthon, eastern New York, and its interregional correlation

Cambrian–Ordovician boundary interval dendroid graptolites and conodonts occur in continental slope facies in the Taconic allochthon. The upper part of the Hatch Hill Formation has lowest Ordovician (lowest Tremadocian) nematophorous dendroid and lower Fauna B-aspect conodont assemblages with Cordylodus caseyi (emend.) and Iapetognathus preaengensis. Comparable dendroid-conodont faunas occur in Baltoscandia, northeastern China, and western Newfoundland; this suggests that no diachroneity can be demonstrated between the lowest occurrences of Rhabdinopora flabelliformis in a number of faunal provinces.A practical and correlatable Cambrian–Ordovician boundary stratotype horizon defined by the lowest occurrence of a Rhabdinopora flabelliformis assemblage within an interval with lower Fauna B-aspect conodonts is advocated. A biostratigraphic horizon defined by conodonts has far less utility due to strong lithofacies-conodont biofacies linkages, unresolved problems with the species-level taxonomy of cordylodans, and possible diachronous first-appearances of Cordylodus species. Because the areally most extensive Cambrian–Ordovician boundary sequences are siliciclastic-dominated (Avalonian, Baltoscandian, Gondwanan-Hercynian platforms and shale-dominated slope sequences), the lowest local occurrence of R. flabelliformis assemblages provides a practical and traditional definition for the base of the Ordovician System and Tremadocian Series in regions where conodonts are rare or recoverable only with difficulty.Strata correlative with the Cambrian–Tremadocian boundary interval are not represented across most of Laurentia. In this region, the “Sauk III Subsequence” locally has an important unconformity within it, and lower Tremadocian-equivalent rocks can unconformably overlie units as low as the Proterozoic. The earliest Ordovician featured a relatively simple eustatic history characterized by an “early Tremadocian onlap”; no compelling evidence supports a eustatic fall-rise couplet, or “Black Mountain eustatic event,” in this interval. Available stratigraphic information is reinterpreted to demonstrate an initially slow and subsequently higher rate of continued sea level rise in the Cambrian–Ordovician boundary interval.

Coastal response to the Holocene transgression in the Bahamas: episodic sedimentation versus continuous sea-level rise

Sedimentological and petrographic study of Holocene deposits in the Eastern Bahamas shows that sedimentation occurred episodically during this period of continually rising sea-level. The Holocene stratigraphic record exposed on the islands of San Salvador, Lee Stocking and Cat consists of two distinctive units separated by a paleosol: (1) 5000 year-old oolitic eolianites deposited when sea-level was lower than today, and (2) 3000 to 500 year-old bioclastic paleo-beaches and dunes that are congruent with the present stand of sea-level. A five-stage model that reconciles intermittent sedimentation pattern with continuous sea-level rise is presented. Pre-Holocene topography and changes in the rate of the transgression seem to regulate local 4 hydrodynamic conditions, which in turn control onset and offset of sedimentary processes. This Holocene example of episodic sedimentation during an uninterrupted transgression should be considered when studying ancient discontinuities that are systematically interpreted in terms of relative sea-level fall.

Enregistrement de l'eustatisme par les foraminifères dans les séquences de dépôt du Crétacé inférieur du bassin vocontien (SE de la France)

Long and short term variations (at the supercycle level and at the 3rd and lower order sequence levels) are observed within benthic foraminiferal assemblages of lower Cretaceous age from the Vocontian Basin. They are interpreted as a response of these bathyal organisms to eustatic or relative sea-level variations: the absolute or relative high sea-level associations are richer and more diversified, especially calcareous forms. This is true for Valanginian to late Hauterivian times (continuous sea-level rise). However, in upper late Hauterivian and early Barremian time (major sea-level highstand), some anoxic phenomena disturb this process. Nevertheless, foraminifers can be used within some limits for the interpretation of systems tracts in the basin, as is the case on the shelf margin. They also confirm the fact that in basinal setting the base of the sequence, which is mainly calcareous, represents a lowstand systems tract and that the top of the sequence, which is more shaly, represents transgressive and highstand system tracts, according to the sequence stratigraphy concepts sensu Vail.

Model for transgressive black shales?

Many black shales in thick epicontinental basinal successions formed beneath an oxygen-restricted puddle of deep water. Other black shales formed during rapid transgression when basinal deposition expanded to cover basin-margin areas normally characterized by shallow-water deposition. An expanding-puddle model is developed from the Early Jurassic of England wherein rapid sea-level rise leads to marine-sediment starvation due to sediment entrapment in flooded river valleys. Subsidence, sea-level rise, and decreased sediment supply during early transgression are suggested to lead to rapid deepening and therefore the expansion of the are of the puddle such that, in previously shallow-water areas, black shales rest on condensed basal transgressive lags or unconformities that in turn rest on shallow-water facies. Reestablishment of sediment influx and aggradation in excess of any continued sea-level rise cause shallowing throughout the basin and the cessation of black-shale formation.

Holocene evolution of an estuarine coast and tidal wetlands

Research Article| March 01, 1990 Holocene evolution of an estuarine coast and tidal wetlands CHARLES H. FLETCHER, III; CHARLES H. FLETCHER, III 1Department of Geology and Astronomy, West Chester University, West Chester, Pennsylvania 19383 Search for other works by this author on: GSW Google Scholar HARLEY J. KNEBEL; HARLEY J. KNEBEL 2U.S Geological Survey, Woods Hole, Massachusetts 02543 Search for other works by this author on: GSW Google Scholar JOHN C. KRAFT JOHN C. KRAFT 3Geology Department, University of Delaware, Newark, Delaware 19716 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1990) 102 (3): 283–297. https://doi.org/10.1130/0016-7606(1990)102<0283:HEOAEC>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation CHARLES H. FLETCHER, HARLEY J. KNEBEL, JOHN C. KRAFT; Holocene evolution of an estuarine coast and tidal wetlands. GSA Bulletin 1990;; 102 (3): 283–297. doi: https://doi.org/10.1130/0016-7606(1990)102<0283:HEOAEC>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Modern facies-distribution patterns, extensive core data, and chronostratigraphic cross sections provide a detailed history of Holocene inundation within the Delaware Bay estuary and sedimentation in adjacent coastal environments. Flooding of the estuary occurred with rising sea level as the shoreline retreated northwest along a path determined by the pre-transgression topography. Simultaneous migration of an estuarine turbidity maximum depocenter provided the bulk of fine sediments which form the coastal Holocene section of the estuary. Prior to 10 Ka, the ancestral bay was predominantly a tidal river, and the turbidity maximum depocenter was located southeast of the modern bay mouth. By 10 Ka, lowlands adjacent to the ancestral channel of the Delaware River were flooded, forming localized tidal wetlands, and the depocenter had initiated high rates of fine-grained sedimentation near the present bay mouth. At that time, coastal Holocene strata began to onlap the interfluve highlands. By 8 Ka, the fine-grained depocenter had migrated northwest along the main channel of the Delaware River, although the widened mouths of tributary valleys continued to be active sites of sediment accumulation. Following the passage of the fine-grained depocenter, coarse-grained sediments accumulated along the coast in response to increased wind-wave activity. During the middle Holocene, portions of the estuarine coast began to resemble modern geomorphology, and washover barrier sands and headland beach sandy gravels accumulated along the southwest shore. The late Holocene was characterized by erosional truncation and submergence of aggraded coastal lithofacies and by planation of remnant highland areas. Knowledge of the eroded Holocene section is fragmentary. At present, continued sea-level rise is accompanied by deposition of tidally transported muds in coastal environments and deposition of sandy sediments in some offshore regions. An unconformity marks the base of the developing open estuarine sequence of coarse clastic lithofacies and denotes the end of coastal accumulations. Modeling of coastal-lithofacies transitions identifies specific lithofacies complexes in the Holocene stratigraphic section which were influential in the evolution of the coast. Development of the Holocene section of the estuary coast involved both constructive, or aggradational, and destructive, or erosional, phases. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

The early to mid-Jurassic evolution of the northern North Sea

Abstract The early to mid-Jurassic history of the northern North Sea is summarized as a complex transgressive-regressive-transgressive cycle controlled by variations in ‘long-term’ eustatic sea level rise, basin subsidence/margin uplift and sediment supply. The first of the transgressions occurred in the Hettangian when the Boreal Ocean spread southwards during a phase of fluctuating but generally increasing sea level rise. Offshore marine conditions developed in the north of the area during the Hettangian to Pliensbachian, while coastal to non-marine conditions developed around the ocean margins in the Unst Basin, the Beryl Embayment, the central Viking Graben and over parts of the Horda Platform. The coastal systems in the Beryl Embayment and central Viking Graben were drowned in the late Pliensbachian as a result of continued sea level rise. A widespread marine link was established with the Tethys Ocean to the south at this time. Sea level fall and/or basin margin uplift and erosion in the Aalenian led to the shedding of coarse clastic sediment transversely into the East Shetland Basin and the northern end of the Viking Graben. The main reservoir unit of the area, the Middle Jurassic Brent Group, formed in this way. A marine connection was maintained into the central Viking Graben area throughout the transverse progradation further north. Drowning of the progradational clastics and the start of the third major transgression began in the late Bajocian, but offshore conditions did not become fully established throughout the area until the Callovian or early Oxfordian.

Smackover and Haynesville Facies Relationships in North-Central East Texas: ABSTRACT

The Smackover Formation was deposited as a coarsening-upward carbonate unit that developed first with the deposition of transgressive laminated silty limestones in deep anoxic waters. Mudstones and wackestones were deposited during a slow rise in sea level as the carbonate system became established. Packstones and grainstones were deposited at the Smackover shelf margin in thick coarsening-upward sequences. Local lenses of anhydrite and dolomitic mud developed on the shoreward side of the shelf break. Pelleted sands also developed in the low-energy Smackover lagoon. Ultimately, a thin blanket of ooid sands covered the shelf. During Haynesville deposition, a carbonate barrier at the shelf margin created an evaporative lagoon in which Buckner anhydrite and halite precipitated. As sea level rose, limestones and dolomites were deposited along the downdip margin of the Buckner lagoon. Terrigenous clastics began to prograde into the updip areas. Continued sea level rise flooded the shelf, and Gilmer limestones were deposited as far updip as the present Mexia-Talco fault zone. At the end of Haynesville deposition, limestones and shales were deposited on either side of the Gilmer shelf margin as quartzose clastics continued to prograde into updip areas. Evidence in east Texas suggests that the depositional model for the Smackover followed a shelf margin rather than the generally accepted ramp model. The shelf margin is clearly identified as a carbonate barrier during Haynesville deposition, outlining a Buckner lagoon as the depocenter that continued to subside at least through the end of Haynesville deposition. End_of_Article - Last_Page 1220------------