Short-term Sea-level Fluctuations Research Articles

Siliceous deposition in limestone-marl alternations of the Yangtze Carbonate platform during the Permian Chert Event

During the Permian Chert Event (PCE), limestone-marl alternations (LMAs), contemporaneously developing in the Yangtze region with chert-mudstone alternations, differed from typical LMAs by their enrichment in authigenic siliceous components (quartziferous components and Mg-phyllosilicates). However, the factors driving the transition from distal chert deposits to proximal siliceous-rich carbonate deposits remain unclear, and the genesis of authigenic siliceous components is puzzling. Resolving these issues could provide a deeper understanding of the paleoclimate and paleoenvironment during the PCE. Optical and SEM observations and geochemical analyses revealed that Si4+, derived from seawater, silica-secreting organisms, and terrigenous clasts, precipitated as authigenic quartziferous components under relatively acidic conditions, while it precipitated as Mg-phyllosilicates through reverse weathering by combining with the dissolved high-Mg calcites under relatively alkaline conditions. Through the facies division of LMAs, its variations describe relative and short-term sea-level fluctuations in the Yangtze Carbonate Platform (YCP). By integrating tendency comparisons and time series analyses of sea level fluctuations, continental weathering intensity, authigenic siliceous content, and relative proportions of quartz vs. Mg-phyllosilicates, four proxies exhibit covariation and similar astronomical signals, indicating that the high sea level period of the YCP, corresponding to intensified continental weathering, favored the deposition of authigenic siliceous components and reverse weathering. Because the facies variations encompass short eccentricity, obliquity, and precession cycles, sea level fluctuations are considered to have been influenced by Gondwana glaciation P3. The seawater in the continental shelf cooled and became rich in silica and nutrients under the effect of upwelling. Interglacial periods may trigger high sea levels and intensified continental weathering in the YCP, facilitating the influx of Si-rich eutrophic seawater and stimulating biological silica secretion by radiolarians. However, the direct precipitation of activated silica resulted in weakened reverse weathering. Consequently, the lithological transformation from distal to proximal areas during the PCE was attributed to differences in silica-secreting organism abundance, upwelling intensity, biological pump activity, reverse weathering intensity, OM abundance, pH conditions, and seawater temperature between the continental shelf and carbonate platform.

Challenges and new strategies in assessing multidecadal shore platform sandy beach evolution from aerial imagery

The world's coastlines are dominated by rocky coasts, where embayed and shore platform beaches develop. The intrinsic characteristics of these environments make them extremely vulnerable to changes in oceanographic forcing. Assessing long-term beach evolution can be a challenging task because coastline indicators were developed for wide and low-lying sandy beaches. For example, as most shore platforms beaches are limited by a cliff or structure, they have a static landward boundary (coastline), thus inhibiting the use of any coastline indicator as a proxy of beach volume changes. Also, as shoreline position is highly dependent on short-term sea-level fluctuations, the use of shoreline indicators is frequently subject to high uncertainty.This work presents an unconventional way to evaluate shore platform beach evolution by proposing a new indicator - the beach toe (BT) - to assess changes in sand retention for shore platform/perched beaches. BT position, together with a profile model, provide an effective tool to assess beach volume over time.The proposed beach indicator was tested at 12 shore platform beaches located at Cascais coast (Portugal), which can be considered illustrative of this type of beach.Results show that the new approach provides an objective indicator to assess both the beach configuration and changes in volume, being easily implemented using common vertical imagery. The comparison of Beach Toe and High-Water Line indicators with field data show a better performance of the BT indicator, supporting the use of the proposed indicator on shore platform beaches. The proposed analysis can be easily replicated to other similar rocky coasts, thus representing a much-needed advancement in the study of beaches perched on platform shores.

Forecasting sea level fluctuations caused by storm winds at the ports in Odesa Region of the north-western part of the Black Sea

Increasing the draught of ships that may be accepted by ports for loading at their loading berths is one of the main tasks aimed at development and freight turnover enhancement of sea trade ports located in Odesa Region of the north-western part of the Black Sea (cities of Chornomorsk, Odesa and Pivdennyi). An operational forecasting of short-term sea level fluctuations caused by storm winds presents a critical task for ensuring safe navigation across the ports’ water area and approach channels. The article is devoted to analysing and discussing the results of tests of a simplified 2D hydrodynamic model designed for forecasting such phenomena as upsurge and downsurge of the sea level caused by storm winds in the vicinity of sea ports in Odesa Region of the north-western part of the Black Sea. Spatio-temporal variability of wind conditions at the sea-to-atmosphere boundary was set based on the data retrieved from a 10-day synoptic forecast using global atmospheric prediction model GFS (Global Forecast System). The study analyses the results of forecast of significant (the ones exceeding 30 cm) short-term sea level drops and rises at the ports which were observed in 2016, 2017 and 2020.
 It was established that, in case of use of the GFS forecast data, the pattern of sea level denivellations caused by storm winds and their amplitude in the majority of events start approximating to the observed values provided the forecast has a 4-day lead time. Therefore the accuracy of wind conditions variability forecast with application of the GFS model having a longer lead advance time is not sufficient for forecasting the sea level fluctuations caused by storm winds. The study made it possible to get an acceptable equivalence between the values of sea level denivellation amplitudes which were forecast with a 1-to-3-day lead time and the ones observed afterwards. In particular, when the forecast lead time is equal to »2 days, in relation to the expected storm conditions, the average absolute error for the forecast of sea level fluctuations amplitude constituted 7-8 cm, while its permissible value was defined as 15 cm, and the average relative error – 16-18%. It allowed making a conclusion that a hydrodynamic model option, applied alongside with the forecasting information on wind conditions variability retrieved with the help of the GFS weather prediction model, may be used for operational forecasting of short-term sea level fluctuations caused by storm winds with the forecast lead time of up to 4 days.

Beach-Foredune Sediment Budget Response to Sea Level Fluctuation. Curonian Spit, Lithuania

Beach-foredune sediment exchange maintains a coastal system’s stability. Sea level fluctuation is one of the most important factors that modifies the beach and foredune sediment budget. This study aims to assess beach and foredune sand budget changes depending on sea level fluctuations. On the basis of annual measurements of cross-shore profiles on the Curonian Spit in Lithuania, the sediment volumes on the beach and foredune and their changes between 2002 and 2019 were calculated. The sea level fluctuations were examined in parallel. The obtained data revealed that in the case of a sand surplus, a relatively low sea level rise does not have a significant impact on the development of a foredune (and a minimal impact on a beach) on a decadal time-scale. Short-term sea level fluctuations are reflected in year-to-year variability in a beach sediment budget. However, no significant relationship between year-to-year variability in sea level fluctuation and the foredune sediment budget has yet been identified, nor is there a reliable year-to-year variability relationship between the foredune and beach sediment budget. The foredune sediment budget remained positive both through an increase and a reduction in the sediment volume on the beach.

Biological Indicators Reveal Small-Scale Sea-Level Variability During MIS 5e (Sur, Sultanate of Oman)

In this study we aim to document various coastal notches in Sur Lagoon (Oman) and interpret them regarding their use as sea-level indicator. We also unravel any short-term sea-level fluctuations, which are potentially preserved within the trace fossil assemblages of some of the notches. The oldest paleo notches stem from the last interglacial sea-level highstand of MIS 5e. This is concluded from cosmogenic nuclide dating of the fanglomerate bedrock in Sur Lagoon as presented in this study. All outcrops of paleo notches around Sur Lagoon were investigated in regards to the faunal distribution and notch shape. Furthermore, the absolute elevation of the notches and biological markers relative to msl were measured with a differential GPS. The bioerosional notch occurs at the same height around Sur Lagoon indicating that the area remained tectonically stable over the last 125 kyr. According to the elevation of the notch-apex, msl was 3.93 ± 0.12 m higher than today during the last interglacial. The distribution of boring and bioconstructing organisms relative to the notch shape displays at least one phase of short-term sea-level rise subsequent to the notch formation. The beachrocks that are associated with the bioerosion notches in Sur Lagoon show a larger grainsize than any sediment that is deposited in the lagoon nowadays. This, in combination with the occurrence of exceptionally high and deep abrasion notches, indicates that the coastline was more openly exposed and thus experienced a higher wave energy during the notch formation.

Aquifer-eustasy as the main driver of short-term sea-level fluctuations during Cretaceous hothouse climate phases

Abstract A review of short-term (<3 myr: c. 100 kyr to 2.4 myr) Cretaceous sea-level fluctuations of several tens of metres indicates recent fundamental progress in understanding the underlying mechanisms for eustasy, both in timing and in correlation. Cretaceous third- and fourth-order hothouse sea-level changes, the sequence-stratigraphic framework, are linked to Milankovitch-type climate cycles, especially the longer-period sequence-building bands of 405 kyr and 1.2 myr. In the absence of continental ice sheets during Cretaceous hothouse phases (e.g. Cenomanian–Turonian), growing evidence indicates groundwater-related sea-level cycles: (1) the existence of Milankovitch-type humid-arid climate oscillations, proven via intense humid weathering records during times of regression and sea-level lowstands; (2) missing or inverse relationships of sea-level and the marine δ 18 O archives, i.e. the lack of a pronounced positive excursion, cooling signal during sea-level lowstands; and (3) the anti-phase relationship of sea and lake levels, attesting to high groundwater levels and charged continental aquifers during sea-level lowstands. This substantiates the aquifer-eustasy hypothesis. Rates of aquifer-eustatic sea-level change remain hard to decipher; however, reconstructions range from a very conservative minimum estimate of 0.04 mm a −1 (longer time intervals) to 0.7 mm a −1 (shorter, probably asymmetric cycles). Remarkably, aquifer-eustasy is recognized as a significant component for the Anthropocene sea-level budget.

An introduction to causes and consequences of Cretaceous sea-level changes (IGCP 609)

AbstractThe International Geoscience Programme Project IGCP 609 addressed correlation, causes and consequences of short-term sea-level fluctuations during the Cretaceous. Processes causing several ka to several Ma (third- to fourth-order) sea-level oscillations during the Cretaceous are so far poorly understood. IGCP 609 proved the existence of sea-level cycles during potential ice sheet-free greenhouse to hothouse climate phases. These sea-level fluctuations were most probably controlled by aquifer-eustasy that is altering land-water storage owing to groundwater aquifer charge and discharge. The project investigated Cretaceous sea-level cycles in detail in order to differentiate and quantify both short- and long-term records based on orbital cyclicity. High-resolution sea-level records were correlated to the geological timescale resulting in a hierarchy of sea-level cycles in the longer Milankovitch band, especially in the 100 ka, 405 ka, 1.2 Ma and 2.4 Ma range. The relation of sea-level highs and lows to palaeoclimate events, palaeoenvironments and biota was also investigated using multiproxy studies. For a hothouse Earth such as the mid-Cretaceous, humid–arid climate cycles controlling groundwater-related sea-level change were evidenced by stable isotope data, correlation to continental lake-level records and humid–arid weathering cycles.

Multi-proxy reconstruction of Holocene paleoenvironments from a sediment core retrieved from the Wadden Sea near Norderney, East Frisia, Germany

The coastal area of the southern North Sea passed through several stages of development during the Holocene starting with swamps and bogs on Pleistocene sands. These were covered due to the rising sea-level by brackish and intertidal sediments with intercalated peat layers indicating repeated shoreline replacements. Such sedimentary archives are excellent sources for environmental reconstructions and potentially suited to deliver a regional sea-level curve. We analysed a 4.6 m-long sediment core recovered south of the island of Norderney (East Frisia, Germany) using a multiproxy approach. The record comprises a vertical stack of changing sedimentary facies, including a basal peat and a second peat layer intercalated between marine sediments, which provides a sedimentological record of local coastal evolution since 7000 cal. BP. High-resolution stratigraphic, geochemical and paleobiological analyses enables reconstructing environmental variability in response to sea-level changes including a short-lived transgressive-regressive cycle. This took place around 6000 cal. BP and lasted only a few hundred years. Our multiproxy approach demonstrates that the combined analyses of geochemical and biological parameters in concert with statistical evaluation are indispensable for the reconstruction of coastal evolution and short-term sea-level fluctuations.

Sedimentary evolution of a shallow carbonate ramp (Kimmeridgian, NE Spain): Unravelling controlling factors for facies heterogeneities at reservoir scale

Abstract The facies evolution of a Late Jurassic (latest Kimmeridgian) shallow carbonate ramp was reconstructed after the analysis and correlation of 21 logs in a 20 × 30 km outcrop area located south of Zaragoza (northeast Spain). The studied succession belongs to the Higueruelas Formation, which is of potential use as an analogue for understanding facies heterogeneities in certain hydrocarbon carbonate reservoirs (e.g. the Arab Formation, Persian Gulf). The studied succession is arranged in nine sedimentary units bounded by discontinuity surfaces that can be traced over kilometres. Facies analysis permitted the reconstruction of two sedimentary models showing the transition from inner ramp subenvironments (i.e. intertidal, lagoon, backshoal/washover, shoal-sand blanket) to the mid-ramp foreshoal and offshore domains: an oncolitic-peloidal-oolitic and an oolitic-peloidal-dominated ramp. The oncolitic-peloidal-oolitic-dominated ramp is characterized by peloidal-oolitic and oncolitic-dominated shoal-sand blankets that developed in higher-energy inner areas, protecting peloidal-oolitic backshoal and oncolitic lagoon domains including a mosaic of stromatoporoid carpets. Peloidal facies with fenestral porosity accumulated in an intertidal belt or as patches on top of the shoal-sand blankets and washover deposits. Offshore from the shoal-sand blankets, chaetetid/stromatoporoid/coral-rich buildups grew on the more proximal mid-ramp, surrounded by peloidal and peloidal-bioclastic grain- to mud-supported facies. An oolitic-peloidal-dominated ramp developed in a second stage of the evolution of the platform, characterized by the presence of a wide restricted peloidal-bioclastic-oolitic lagoon on the inner ramp grading into a backshoal area dominated by storm-related intraclastic-peloidal deposits. Stromatoporoid carpets disappeared and oncolitic-dominated deposits were constrained to the foreshoal and backshoal domains, and locally to local ponds that developed in the intertidal belt or the restricted lagoon. Internal and external factors controlling facies heterogeneity and the sedimentary evolution of the carbonate ramp include resedimentation, topographic relief, and long- to short-term sea-level fluctuations.

Late Albian calcareous dinocysts and calcitarchs record linked to environmental changes during the final phase of OAE 1d – a case study from the Tatra Mountains, Central Western Carpathians

Calcareous dinocysts and calcitarchs have been investigated for the first time within the Upper Albian limestone and marl succession of the Zabijak Formation from the High-Tatric Unit in the Tatra Mountains (Central Western Carpathians), related to the Oceanic Anoxic Event 1d (OAE 1d). Four groups of morphotaxa of calcareous dinocysts have been distinguished. They totally dominate the assemblages, and belong to the pithonellids. They are represented by Pithonella sphaerica (Kaufmann in Heer) and P. ovalis (Kaufmann in Heer), which dominate, as well as P. trejoi Bonet and P. lamellata Keupp in Keupp and Kienel, which are less abundant. Two other morphotaxa, Colomisphaera gigantea (Borza) and Cadosina oraviensis Borza, occur sporadically in the assemblages. Both forms represent the calcitarch group, which assembled calcispheres of unknown taxonomic affinity. The calcareous dinocyst and calcitarch diversity is low to moderate, compared to the general species richness known from Late Albian assemblages in other Western Tethyan sections. This is interpreted as a result of nutrient input fluctuations due to changes in the circulation pattern of surface and intermediate waters. The changes in the P. sphaerica / P. ovalis ratio along the Upper Albian section are here correlated with short-term (third-order) sea level fluctuations including transgressive and regressive events and a highstand. Pelletization processes might have influenced cyst abundance on the sea floor, especially during periods with oligotrophic surface waters

Wind-Driven Sea-Level Variation Influences Dynamics of Salt Marsh Vegetation

Long-term variation of mean sea level has been considered the primary exogenous factor of vegetation dynamics in salt marshes. In this study, we address the importance of short-term, wind-induced rise of the sea surface in such biogeographic changes. There was an unusual opportunity for examining field data on plant species frequency, sea-level variation, and sedimentation acquired from the Skallingen salt marsh in Denmark since the 1930s. The environmental and floristic history of Skallingen was summarized as (1) continuous sea-level rise with temporal variability (2.3–5.0 mm yr−1), (2) continuous sedimentation with spatial variability (2.0–4.0 mm yr−1), (3) increased frequency of over-marsh flooding events, and (4) contemporary dominance of Halimione portulacoides, indicating little progressive succession toward a later phase. Conventionally, recent eustatic sea-level rise was believed to drive the increased frequency of flooding and such retarded succession. Skallingen, however, has showed more or less equilibrated yearly rates between sea-level rise and surface accretion. This implies that the long-term, gradual sea-level rise alone might not be enough to explain the increased inundation frequency across the marsh. Here, we suggest an alternative chain: Recent trends in the North Atlantic Oscillation index toward its positive phase have led to increased storminess and wind tides on the ocean surface, resulting in increased frequency, duration, and depth of submergence, and hence, waterlogging of marsh soils, which has retarded ecological succession. To conclude, we stress the need for a multitemporal perspective that recognizes the significance of short-term sea-level fluctuations nested within long-term trends.

Punctuated sediment record resulting from channel migration in a shallow sand-dominated micro-tidal lagoon, Northern Wadden Sea, Denmark

Facies analysis of five sediment cores and a detailed absolute chronology, consisting of 35 optically stimulated luminescence (OSL) ages, form the basis for reconstruction of the paleoenvironmental evolution of the coastal lagoon behind the barrier island of Fanø, in the Northern Wadden Sea, SW Denmark. The lagoonal sedimentary succession was deposited within the last 5500yr, and 5 principal depositional environments are identified in the lagoonal fill. These are: 1) tidal channel, 2) sand flat, 3) mouth bar, 4) reed swamp, and 5) mudflat/salt marsh. Sand flats are the dominant present day depositional environment, but tidal channel sediments dominate in the five sediment cores, making up 56% of the 15m of sediment core. Sedimentation in the lagoon alternated between slow vertical aggradation of sand flats (1.5–2mmyr−1) and very fast lateral progradation of point bars in tidal channels, which caused the formation of a punctuated lagoonal fill. Frequent and comprehensive reworking of the sand flat sediments by tidal channel migration entails loss of sedimentary structures and bioturbation related to sand flat deposits, and old sand flat sediments are only very sparsely preserved. We further conclude that long-term (millennial timescale) sediment accumulation in the lagoon was controlled by rising sea-level, whereas short-term (centurial timescale) sediment accumulation was controlled by local erosion and depositional events caused by lateral migration of channels. Records of short-term sea-level fluctuations are not preserved, due to continuous reworking of the lagoonal sediment within the study area. The paper provides significant inputs to a conceptual model describing the Holocene sedimentation in the sand-dominated tidal lagoon. Furthermore, the study successfully demonstrates the role of OSL dating in deciphering complicated sedimentology and stratigraphy of tidal lagoonal environments.

Erosional shelf ridges in the mid-eastern Yellow Sea

In the mid-eastern Yellow Sea, closely spaced high-resolution seismic profiles and a 44-m-long sediment core (YSDP-104) were analyzed to reveal the internal structures and stratigraphy of the shelf ridges currently shaped by tidal currents. Three depositional sequences (sequences I, II and III in descending order) can be recognized. Sequence III, the substratum of the ridges, consists of coarse-grained sediments in the lower part (non-marine deposits) and tide-influenced muddy sediments in the upper part (probable transgressive to highstand systems tract). Sequence II represents internal ridge sediments, similar in character to sequence III, but is demarcated by an undulatory ridge topography. According to radiocarbon dating of marine muds, these sequences range in age from 47,000 to 28,000 years B.P., representing two cycles of short-term sea-level fluctuations during oxygen isotope stage 3. Sequence I consists mostly of late-Holocene transgressive sand veneer on the ridge surface. It also includes minor amounts of early-Holocene muddy sediments occasionally underlying the sand. Most of the ridges are presently undergoing erosion by tidal currents, forming widespread sand dunes on the entire surface.

Late Quaternary depositional architecture of Po and Tevere river deltas (Italy) and worldwide comparison with coeval deltaic successions

Abstract Po and Tevere rivers form two of the most important deltas of the whole Mediterranean area. Detailed investigations have been carried out in the last decade beneath the present delta plains of these two river systems using borehole data correlation. With the aid of radiocarbon dates and other dating methods (pollens, archaeology) a detailed sequence stratigraphic framework has been constructed in both areas, especially for the last glacial-interglacial cycle. Regional subsidence, combined with short-term sea-level fluctuations of relatively high amplitude, played a fundamental role in creating/subtracting accommodation during the long phase of falling sea level, which followed the Tyrrhenian (substage 5e) transgressive event. A discontinuous record of this phase is present in the subsurface of the Po Plain, whereas poor or no preservation has been detected in the Tevere area. Progradational lowstand wedges accumulated during the last glacial maximum mostly in the central part of the basins, far from the present deltas, and are lacking in the study areas, where a hiatal surface is invariably recorded below the transgressive deposits. Glacioeustasy exerted a major control on sedimentation in both areas during the latest Pleistocene–Holocene sea-level rise. Infilling of fluvial valleys and rapid landward migration of barrier-lagoon systems, in the context of wave-dominated estuaries, characterized the transgressive phase in both Po and Tevere systems. In-place drowning and transgressive submergence mechanisms of barrier migration were effective predominantly between 13.5 and 9 ka bp . In contrast, shoreface retreat was dominant in the late transgressive phase. The maximum flooding surface (MFS) can be traced physically from continental to marine deposits, and has similar characteristics in the Po and Tevere river systems, being marked by peat layers or lagoonal deposits at landward locations and by distinctive lithological characteristics and micro- and macrofossils assemblages basinwards. Above the MFS, the early highstand systems tract records initially the filling of the lagoons, followed by the rapid progradation of wave-dominate delta systems and flanking strandplains. Autocyclic processes, such as distributary channel avulsion, delta lobe abandonment, and local subsidence due to sediment compaction were the fundamental controlling factors on sedimentation during deposition of the HST. The stratigraphic architecture of the post-glacial Po and Tevere delta complexes closely resembles the basic facies successions documented from coeval deposits of wave-dominated and wave-influenced clastic coasts, both locally within the Mediterranean area and in other parts of the world. Our study emphasizes, however, some additional features and major differences with previously published depositional models, including (i) the development of backstepping wave-dominated estuaries during transgression; (ii) consistent changes through time in the mechanism of barrier migration; (iii) a later construction of the delta systems, with respect to what traditionally considered.

Late Cretaceous carbon isotope stratigraphy in Europe: Correlation and relations with sea level and sediment stability

Abstract Upper Cretaceous (Upper Cenomanian to Lower Coniacian) stable carbon isotope stratigraphy of German hemipelagic marls (borehole Dresden-Blasewitz), pelagic carbonates (quarries Salzgitter-Salder and Sohlde), and of two Turonian to Santonian pelagic sections in the northern Alpine Helvetic Zone, supplemented by published carbon isotope data (Kent, southern England; Gubbio, Italy), are used for correlations of northern temperate (boreal) and Tethyan sections. General carbon isotopic trends are different in pelagic and hemipelagic carbonates, probably in response to the input of terrestrial organic carbon to the inner shelf carbon reservoir (including sediments). The global component in the carbon isotope stratigraphy is best recorded in pelagic carbonates. Sufficient biostratigraphic control is present to correlate all sections across facies boundaries and between the two biogeographic provinces. Hiatuses produce breaks in the gradual carbon isotopic trends and their duration can be estimated relative to complete sections. A broad δ13C minimum straddles the Turonian-Coniacian boundary at the proposed boundary stratotype Salzgitter-Salder, with its center about 0.5–1 m below the biostratigraphic reference level (first occurrence of C. rotundatus Fiege sensu Troger non Fiege). Increases and maxima of pelagic δ13C values occur during phases of sediment accumulation. Decreasing pelagic °13C values and minima characterise phases of sediment erosion. The amplitudes of these stratigraphic fluctuations may indicate the intensity of sediment reworking. Changes in the sediment accumulation/erosion ratio and accompanied carbon isotopic variation may be related to short-term sea-level fluctuations and their effect on fine-grained sediment stability.

Depositional History of the Smackover Formation, Appleton Field, Escambia County, Alabama: ABSTRACT

Appleton Field is a Smackover field situated above two pre-Mesozoic paleohighs near the updip limit of the Smackover in the Conecuh Embayment of southwestern Alabama, Smackover deposition in Appleton Field was influenced by both pre-Smackover paleotopography and sea level fluctuation. Fourteen lithofacies were identified in the Smackover and the overlying Buckner Anhydrite Member of the Haynesville Formation. These lithofacies were deposited in three depositional stages (early, middle, and late Smackover) that correspond to periods dominated by marine transgression, aggradation, and ultimately progradation. Early Smackover deposition accompanied a rapid sea level rise that inundated the paleohighs. Rapid sedimentation produced a system that was first transgressive and then aggradational in nature. Algal patch reefs developed around the periphery of the paleohighs and onlapped the structures as sea level rose. Middle Smackover deposition was the result of a decrease in the rate of sea level rise. Tidal flat, lagoon, and shoal complexes formed across topographically higher parts of the field, while subwavebase sediments were deposited off structure. Short-term sea level fluctuations produced seven shallowing-upward packages. During Late Smackover deposition long term sea level was relatively stable allowing the Smackover to aggrade and prograde. Upper Smackover deposits are peritidal dominated. Short-term sea level fluctuationsmore » again produced shallowing upward packages capped in crestal locations by exposure surfaces. With continued sedimentation, supratidal sabkhas formed over the crests of the paleohighs and prograded offstructure during early Buckner deposition. Short term fluctuations in sea level produced a series of shallowing upward sabkha cycles. Development of coastal salinas or restriction of the northern Conecuh Embayment led to deposition of subaqueous evaporites in the upper Buckner.« less

Sea Level Control on Platform and Basin Development, Upper Devonian of Western Canada: ABSTRACT

The geometric and sedimentologic relationships between buildup margins and their flanking basin sediments in the Rocky Mountains suggest that superimposed short-term and long-term sea level fluctuations controlled buildup stratigraphy. Preliminary correlation of cycle stacking patterns from one margin to another reveals an ordered hierarchy of possibly three magnitudes of sea level challenge: tentatively fifth, fourth, and third order. The flume platform and overlying upper Cairn biostrome consist of meter-scale shallowing-upward cycles. These cycles are interpreted to have been deposited during short-term high-frequency (fifth-order ) sea level oscillations. Superimposed on this high-frequency cyclicity are larger, broadly shallowing-upward trends in which dominantly subtidal meter-scale cycles gradually pass upward into peritidal cycles of comparable thickness. These intermediate cycles (tens of meters thick) may represent fourth-order eustasy. The Flume, upper Cairn, and overlying Peechee members, together with their time-equivalent basin filling strata represent low-frequency, third-order depositional sequences. The various cycles are best developed in the Main Ranges, where greater subsidence allowed for increased sediment accumulation. Abrupt margins are common to all localities investigated. At lead three major episodes of fourth-order sea level rise (backstepping), punctuated by relative stillstands (prograding tongues of stromatoporoid rudstone into Perdrix basin shales), dominated middle Frasnian Peechee sedimentation. Pervasive dolomitizationmore » prohibits resolution of finer scale cycles. Onlap of the Peechee buildup margins by overlying Mt. Hawk argillaceous limestones and shales indicates an important basin-filling episode during a probable stillstand and/or lowering.« less

Platform/Foreslope Facies and Buildup Geometry Resulting from Short-Term and Long-Term Eustatic Sea Level Fluctuations: Latemar Buildup (Middle Triassic), Dolomites, Northern Italy: ABSTRACT

Superimposed short-term and long-term eustatic sea level fluctuations directly controlled Latemar platform stratigraphy and indirectly influenced the deeper water facies and overall buildup geometry. Deeper water facies, the foreslope and toe of slope, are a function of platform submergence (highstand shedding) and subaerial exposure (lowstand lithification and erosion) and thus only indirectly reflect eustatic fluctuations. The Latemar consists of a platform core (3-4 km wide, 700 m thick) with a narrow margin, flanked by foreslope (30-35/sup 0/ dips), toe of slope, and basin deposits. The shallowing-upward platform sequence records a long-term (about 10 m.y.) eustatic sea level oscillation with an amplitude of about 150 m. The lower 250 m marks an initial catch-up phase (subtidal carbonates); the upper 450 m marks the sequential keep-up phase (meter-scale cyclic carbonates). These cycles record platform submergence and exposure caused by short-term (10/sup 4/-10/sup 5/ years) Milankovitch eustatic oscillations superimposed on the long-term trend. Platform submergence and exposure conditions result in contrasting foreslope deposits. During highstands, platform-derived sands bypass the foreslope, accumulating as toe-of-slope graded beds and basin turbidites. During lowstands, sand supply ceases, producing basin hard-grounds. Foreslope megabreccias contain margin-derived boundstone clasts, with only minor platform-derived sands (highstands) and lithified clasts (lowstands). Asmore » the platform margin/foreslope contact is nearly vertical, a progressively increasing volume of foreslope megabreccia was needed to maintain the depositional geometry. This coincides with the most commonly exposed platform interval, suggesting that platform exposure determines buildup flank geometry by controlling megabreccia clast production.« less