High-frequency Sea Level Fluctuations Research Articles

Did eustatic sea-level control deep-water systems at Milankovitch and timescales?: An answer from Quaternary Pearl River margin

As one of the most important forcing factors, sea level fluctuations exert a major influence on deep-water depositional processes, however, it is still not well understood how they control the evolution of the specific deep-water system over different timescales. For relatively longer (1 My) and shorter (100 Ky) timescales, we characterize deep-water sedimentary records on the Pearl River margin using seismic and borehole data, and then compare them with the contemporaneous sea-level curve to exam the varied roles sea levels have played in impacting the development of the deep-marine system. Results indicate that over both the 1 My-scale and the 100 Ky-scale, the studied deep-water system shows systematic variations that are strongly suggested to arise from the modulation of sea levels. Specifically, over the 1 My-scale, facies and depocenters of the deep-water system all show significant changes. Large fan lobes (consisting of both turbidites and mass-transport deposits) with more distal depocenters likely correspond with low-amplitude and high-frequency sea level fluctuations and slightly rising shelf edge trajectories, whereas smaller turbidite fan lobes with more proximal depocenters likely reflect high-amplitude and low-frequency sea level fluctuations and steeply rising shelf-edge trajectories. In contrast, within the 100 Ky-scale of a glacial-interglacial cycle, the composition of deep-water deposits also shows significant variations. Coarser-grained deposits with higher organic carbon (TOC) content and lower calcium carbonate (CaCO3) content are interpreted to reflect periods of glacial sea-level lowstand, whereas finer-grained sediments having lower TOC and higher CaCO3 content reflect interglacial sea-level highstand. Moreover, the spectrum characteristics of these constituent curves are very similar to those of contemporaneous sea levels, reflecting Milankovitch climatic forcings and further validating the tight coupling between sea-level stands and sediment compositions. These correlations between sedimentary records and sea level behaviors suggest that it was mainly a long-term change in the amplitude and frequency of eustatic cycles that controlled the overall architecture of the deep-water system, whereas it was shorter term, changing sea-level stands that played a role and impacted the deep-water sediment composition.

Architectural evolution of a mixed-influenced deltaic succession: Lower-to-Middle Ordovician Armorican Quartzite in the southwest Central Iberian Zone, Penha Garcia Formation (Portugal)

Facies stacking patterns and stratigraphic relationships resulting from the interaction of fluvial and wave processes, along with the paleoshoreline orientation and key surfaces, are essential to understand the temporal changes in the rate of change of accommodation space (A) versus sediment supply rate (S). High-frequency sea-level fluctuations in deltaic systems are controlled by changing accommodation and accumulation, which are explained mainly by autocyclic or allocyclic mechanisms. In deltaic systems, changes in the A/S ratio can be showed by significant variations of the internal facies architecture and the external morphology of the delta complex. These criteria have been used to investigate the relationship between autocyclic and allocyclic processes on the architectural evolution of a mixed river- and wave-influenced asymmetrical delta during the Lower-to-Middle Ordovician in the southwest Central Iberian Zone, in Portugal. Relying on the sedimentary and ichnological characteristics, the herein defined Penha Garcia Formation is classified into two main groups of facies associations, which are interpreted as deposited in a mixed asymmetrical delta with a trend of along-strike variations between wave-dominated strandplain (updrift) and river-dominated deltaic settings (downdrift). The vertical stacking arrangements of parasequences led to the identification of five depositional phases (I to V). Detailed analysis of geometry and internal architecture of the depositional phases along depositional strike shows a highly variable number of shallowing-upward cycles and facies thicknesses/heterogeneity on the updrift and downdrift side due to changes in rates of accumulation and hydrodynamic processes. The stratigraphic architectural style of the depositional phases I to V, and the trend of the total regressive ascending shoreline trajectory, are evidences that the deposition of the Penha Garcia Formation likely took place under an increasing rate of accommodation due to long-term relative sea-level rise (allocyclic), and high subsidence rates coupled with an increase in sediment supply, which could have been locally amplified by compaction of the prodelta-related muddy beds (autocyclic). This study suggests that in evaluating the autocyclic mechanisms on deltaic processes in short-time scales, there is a remarkable difference in terms of its impact on the internal variability of the depositional phases, both in the updrift and downdrift regions of mixed-influenced asymmetrical deltas. The most important reasons for the different effects of autocyclic mechanisms can be related to facies-dependent differential compaction or local changes in subsidence pattern, differences in the proximity to the distributary channel system, and differences in the influence of intrinsic processes of storm and wave reworking (wave-sweeping mechanisms).

Coral reefs and growth dynamics of a low-angle Carboniferous platform: Records from Tianlin, southern China

Metazoan reef building receded globally during the Carboniferous after the Late Devonian extinction events. Shallow-water bioconstructions were generally small and scarce, and corals played a minor role in their construction. However, in southern China, one large (50 m high) and three small (6–16 m high) coral reefs, dating from the Late Viséan–Serpukhovian, have recently been discovered in two localities in Guangxi. To understand the occurrence of these coral reefs and to constrain the factors that controlled their growth, three sections around Langping (Guangxi) were measured, and selected samples were analysed using petrography, biostratigraphy, and chemostratigraphy. The depositional environment of these exceptional Mississippian reefs was interpreted as a low angle platform (1–2.5°), recording oligotrophic conditions and normal salinity. The three small reefs have grown around the fair-weather wave-base, whereas the large coral reef has grown in a deeper environment, between the fair-weather and storm wave-base.During Carboniferous, the global temporal reef distribution can be partly ascribed to paleoclimate changes. However, in southern China, the growth of extended Mississippian coral reefs is restricted to a short time window, the Late Viséan-Serpukhovian, which coincides with high amplitude and high frequency sea-level fluctuations most likely related to glacial pulses. Recent studies revealed that several rugose coral species survived the mid Carboniferous glaciation event thanks to the persistence of warm water ocean currents maintaining tropical conditions on the platform. Due to the scarcity of extended coral reefs elsewhere, it cannot be excluded that Tianlin provided an ecological refuge for corals, related to oceanic currents. Another potential favorable factor could be the mid ramp depositional setting. The deep-water platform areas could potentially provide more stable conditions, less affected by global stress events. However, the ‘deep reef refugia’ hypothesis remains debatable as only very few studies have explored its validity at the community level. Even if the causes of the occurrence of an extended coral reef in southern China cannot be fully constrained, the existence of this large coral framework in the Late Viséan-Serpukhovian provides additional evidence that coral communities did build reefs after the Late Devonian extinction events.

Mut Basin, Turkey: Miocene carbonate depositional styles and mixed systems in an icehouse setting

The Mut Basin in southcentral Turkey contains a rich variety of Cenozoic carbonate deposits that developed on a complex pre-Miocene topography and can be studied in seismic-scale, three-dimensional outcrops. These include open and rimmed carbonate shelves with steep slopes, small isolated platforms, and mixed carbonate–siliciclastic systems showing reciprocal sedimentation. The exceptional preservations of the stratal geometries make it possible to easily link large-scale depositional geometry to depositional facies in a variety of platform types and depositional environments. The Mut Basin provides a better understanding of (1) the control of antecedent topography on carbonate platform development, (2) the influence of icehouse conditions (e.g., high-amplitude, high-frequency sea level fluctuations) on the carbonate system, (3) the link between faunal evolution and the style of carbonate platforms and stratigraphic architecture, (4) lateral and reciprocal carbonate and siliciclastic sedimentation, (5) platform asymmetry and local controls on stratal geometries, and (6) the architecture of steep carbonate margin and associated gravitational collapse deposits. These concepts are directly applicable to time-equivalent Cenozoic carbonate reservoir systems in Southeast Asia, the southern Caribbean, and the eastern Mediterranean.

On the peritidal cycles and their diagenetic evolution in the Lower Jurassic carbonates of the Calcare Massiccio Formation (Central Apennines)

Abstract This paper shows the environmental changes and high-frequency cyclicity recorded by Lower Jurassic shallow-water carbonates known as the Calcare Massiccio Formation which crop out in the central Apennines of Italy. Three types of sedimentary cycle bounded by subaerial erosion have been recognized: Type I consists of a shallowing upward cycle with oncoidal floatstones to rudstones passing gradationally up into peloidal packstone alternating with cryptoalgal laminites and often bounded by desiccation cracks and pisolitic-peloidal wackestones indicating a period of subaerial exposure. Type II shows a symmetrical trend in terms of facies arrangement with peloidal packstones and cryptoalgal laminites present both at the base and in the upper portion of the cycle, separated by oncoidal floatstones to rudstones. Type III displays a shallowing upward trend with an initial erosion surface overlain by oncoidal floatstones to rudstones that, in turn, are capped by pisolitic-peloidal wackestones and desiccation sheet cracks. Sheet cracks at the top of cycles formed during the initial phase of subaerial exposure were successively enlarged by dissolution during prolonged subaerial exposure. The following sea-level fall produced dissolution cavities in subtidal facies, while the successive sea-level rise resulted in the precipitation of marine cements in dissolution cavities. Spectral analysis revealed six peaks, five of which are consistent with orbital cycles. While a tectonic control cannot be disregarded, the main signal recorded by the sedimentary succession points toward a main control related to orbital forcing. High frequency sea-level fluctuations also controlled diagenetic processes.

Sequence stratigraphic modelling and reservoir architecture of the shallow marine successions of Baram field, West Baram Delta, offshore Sarawak, East Malaysia

The Baram Delta Province is located in the northern part of Sarawak (West Baram Delta) and extends north-eastward into Brunei and further into the south-western part of Sabah (East Baram Delta). The delta is a Neogene basin which developed over an accretionary wedge implying Cretaceous to Eocene sediments during the Late Eocene to Late Miocene times (Tongkul, 1991; Hutchison et al., 2000; Morley et al., 2003; Sapin et al., 2011).Facies and well log analyses were carried out on core and well data for the Late Miocene successions of Baram field, a medium-sized oilfield located in the north-eastern flank of the Baram Delta Oil Province, offshore Sarawak. A numerical model of sea-level fluctuations and progradational basin-fill was generated using the Clastic Modeling Program (Hardy and Waltham, 1992a and 1992b; Waltham, 1992) software to evaluate the possible controls of sea-level changes in the development of the siliciclastic successions and their bounding surfaces. This model was based on four lines of evidence, namely core data, fieldwide wireline logs correlation, seismic sections and average thickness variations across the field.Cored intervals of the Upper Cycle V (Late Miocene) display reservoir successions dominated by thick swaley cross-stratified (SCS) sandstones, thin hummocky cross-stratified sandstones and other shallow marine, wave and storm-dominated facies, interbedded with laminated shelfal mudstones. The vertical facies organisation suggests deposition during shoreface progradation associated with a fall of relative sea level.Analysis and correlation of well logs reveal stacking patterns comprising three scales of depositional cyclicity: the parasequences (∼10–∼30 m thick), the parasequence sets (∼45–∼130 m thick) and the major cycles (∼600–800 m thick).Field-wide, dip-oriented seismic sections show very well-developed horizontal to slightly upward convex layers traceable over great distances, which suggests a ramp-type margin, in which the basin floor dipped gradually seaward and lacked a distinct shelf-slope margin.The evidences gathered demonstrate that the deposition and build-up stratigraphy of the Late Miocene sedimentary successions could have been strongly controlled by superimposed short-term, medium-term and long-term sea-level changes.The simulated sea level and sedimentary basin-fill model, generated by the Clastic Modelling Program, match to the well log correlation. This model illustrates that high frequency sea-level fluctuations enable sands to be distributed over large areas within a shallow, low gradient shelf. Our study shows that integrated studies incorporating cores, well logs, seismic sections and simulated models can be employed as important tools for correlation and reservoir modelling.

Facies analysis and depositional architecture of shelf-type deltas in the Crati Basin (Calabrian Arc, south Italy)

This study focuses on facies analysis and depositional architecture of the Arente shelf-type delta, located at the southernmost margin of the Pleistocene Crati Basin (northern Calabria, southern Italy). Tectonically-controlled Gilbert deltas are extensively discussed in the literature, whereas few works document shelf-type deltas and factors controlling sedimentation. This paper contributes to these issues, with a special focus on evaluating eustatic and tectonic control on depositional architecture also by considering the occurrence of coeval Gilbert-delta systems.The Arente delta complex represents part of the coarse-grained sediments presently exposed along the eastern margin of the Crati Basin. It was sourced from the rising Sila Massif to the E and shows an overall westerly progradation.Conventional sedimentological analysis allowed to distinguish seven different facies associations. Well-exposed sections, at the basin margin, generally show an overall upward transition, locally basinward, from mouth-bar conglomerates and sandstones, to deltafront sandstone, to offshore mudstones. Facies distribution and arrangement are interpreted as the record of a shoal-water fan delta.Depositional processes were clearly influenced by the high sediment input, with a dominance of hyperpycnal deposits.Based on the occurrence of a series of bounding surfaces indicating abrupt drowning stages, the Arente deltaic succession can be divided into 5 distinct transgressive-regressive sequences.The fining and the thinning upward trend of the whole succession and the stacked landward-stepping architecture of the transgressiveregressive sequences, i.e. the E-directed retrogradational behavior of the Arente delta complex indicate that.Tectonic subsidence provided the accommodation space for the deposition of the delta complex, for the marked local backstepping of the system, and for the progressive drowning of bedrock. Highfrequency sea level fluctuations led to the repeated arrangement of the facies associations; in particular, the stacking of the individual deltaic sequences separated by transgressive surfaces suggests amplitudes of eustatic sea-level changes of a few tens of metres, thus representative of a higher-order cyclicity. The differing internal architecture, if compared to the steeply-dipping foreset beds of the Gilbert-type delta cropping out to the N of the study area, is interpreted as due to a decrease in displacement toward the southern tip of the Crati system fault.

A paleotropical carbonate-dominated archive of carboniferous icehouse dynamics, Bird Spring Fm., Southern Great Basin, USA

Much of our far-field knowledge of glaciation and climate during the late Paleozoic ice age is built on decades of study of mixed carbonate–siliciclastic cyclothemic successions from paleotropical Euramerica. Far fewer carbonate-dominated successions have been studied despite their high sensitivity to changes in accommodation space and environmental conditions. Here we present a sequence stratigraphic framework for the carbonate-dominated Bird Spring Formation, southern Great Basin, U.S.A. and infer from it a relative sea-level history for the latest Mississippian through latest Pennsylvanian. Correlation of four successions across the paleo-platform documents changes in the lithofacies composition of meter-scale cycles, their cycle stacking patterns, and cycle bounding surfaces that record substantial variation in relative sea-level at several temporal scales during the Pennsylvanian. Ten genetic sequences bounded by intervals of restricted peritidal lithofacies, karst, terra rossa, rooted caliche and/or Protosols are recognized. Within sequences, 126 parasequences stack into parasequence sets that in turn define lowstand, transgressive and highstand systems tracts. The stratigraphic cycle stacking patterns and across-platform architecture of systems tracts suggest a mid-Carboniferous lowstand in relative sea level followed by a middle Morrowan (middle Bashkirian) highstand as previously suggested (Bishop et al., 2010). Subsequent progradation of the platform occurred during a gradual long-term fall through the late Morrowan and Atokan (late Bashkirian–early Moscovian), upon which repeated higher frequency events were superimposed, culminating in widespread exposure across the platform proximal to the Atokan–Desmoinesian boundary. Long-term sea level increased into the mid-Desmoinesian (end-Moscovian) after which progradation (late Desmoinesian) and aggradation (Missourian–Virgilian) of shallow-water and peritidal carbonates occurred across the Bird Spring platform. The progradational-to-aggradational phase involved an abrupt shift from ramp to rimmed shelf geometry in the Missourian (Kasimovian) likely in response to progressively increasing sea level, dampened high-frequency sea level fluctuations and/or to regional faulting along the Bird Spring platform margin. Inferred magnitudes of short-term (105yr) fluctuations superimposed on the longer-term rises and falls range from 20 to >70m during the early to mid-Pennsylvanian and are substantially reduced (≤20m) during the late Pennsylvanian. The early to middle Pennsylvanian sea-level history inferred from the carbonate-dominated Bird Spring platform corresponds well with a recently published Pennsylvanian onlap–offlap history defined from the cyclothemic succession of the Donets Basin and with independent near-field reconstructions of glaciation during the Pennsylvanian.

High frequency sea level fluctuations recorded in the Black Sea since the LGM

This paper presents a 3D geometric interpretation of very high resolution seismic Chirp profiles acquired on the Romanian shelf during ASSEMBLAGE European Project. The results provide a solid record of the Black Sea Last Glacial Maximum (LGM) water level fluctuations. This pseudo-3D seismic interpretation shows that the Black Sea lacustrine shelf deposits form a significant basinward-prograding wedge system. On top of these prograding sequences is a set of sand dunes that delineates a wave cut-terrace like feature around the isobath − 100 m. Landward of this dune field are small depressions containing barkhan-like bodies. The upper part of the last prograding sequence is incised by anastomosed channels which end in the Danube (Viteaz) canyon which are also built on the lacustrine prograding wedge. Ten stratigraphic units were distinguished and correlated with analyses of cores retrieved from this area. The results demonstrate that the first eight sequences represent lacustrine prograding wedges, the ninth sequence is the dune system itself and the tenth is a marine mud drape which covers the entire continental shelf. The lacustrine prograding wedges represent a lowstand deposit characterised by forced regression-like reflectors mapped from the pseudo-3D seismic data. Their hinge point corresponds to the wave erosion surface mapped around − 100 m isobath on the multibeam mosaic. Dated cores give age control on this lowstand period, which lasted from 11 to 8.5 kyr 14C BP as implied by: (1) the continuously dry climatic conditions in the region inferred by high percentages of herbs and steppe elements determined from ASSEMBLAGE cores and, (2) the formation of dunes between 10 and 8.5 kyr 14C BP on the desiccated north-western Black Sea shelf at − 100 m and (3) all of these covered by a marine mud drape confirming that the dune system is no longer active. The buried, anastomosed fluvial channels that suddenly disappear below 90 m depth, and a unique wave-cut terrace between 95 and 100 mbsl on the outer shelf are also consistent with a major lowstand base-level at around − 100 m water depth. Preservation of sand dunes and the occurrence of small, buried incised valleys mark a rapid transgression within less than a century during which ravinement processes related to the water level rise had no time to significantly erode the seafloor.

Reconstruction of outer shelf paleoenvironments in the Turonian–Coniacian of Southeast France (micropaleontology – sedimentology:: local and global controlling factors

Micropaleontological analysis and sedimentological studies were undertaken on the Turonian to the Coniacian strata of the western part of the Vocontian Basin near Nyons, Southeast France, in order to understand the evolution of paleoenvironments. Microfacies examination shows an alternation of two types of deposits: (1) sediments dominated by abundant sponge spicules, echinoderm fragments and quartz packstones–wackestones, suggesting a shallow water environment, and (2) sediments dominated by abundant calcispheres and planktic foraminifera, providing evidence of a deeper water environment. The biostratigraphy is based on a systematic analysis of planktic foraminifera (about 50 taxa). The first appearance of Dicarinella primitiva, associated with Marginotruncana tarfayaensis and Marginotruncana sinuosa, indicates the beginning of the Coniacian. Ostracoda corroborate the Coniacian age given by planktic foraminifera. Amongst the benthic foraminifera, Nodosariidae, Verneuilinidae and Eggerellidae are the most common families represented by the fauna. The qualitative and quantitative changes of benthic and planktic foraminifera population parameters provide precise information about the paleoenvironmental conditions (paleobathymetry, sediment composition, dissolved oxygen). The biological system reflects high-frequency sea level fluctuations. A possible glacially and/or tectonically induced mechanism is discussed in order to explain this kind of variations.

Fossil Shore Platforms and Drowned Gravel Beaches: Evidence for High-Frequency Sea-Level Fluctuations in the Distal Alpine Foreland Basin

Fossil Shore Platforms and Drowned Gravel Beaches: Evidence for High-Frequency Sea-Level Fluctuations in the Distal Alpine Foreland Basin

High-frequency sea-level fluctuations and plant habitats in Cenomanian fluvial to estuarine succession: Pecínov quarry, Bohemia

Abstract The succession of the Peruc and Korycany Members in the Pecinov quarry, Bohemia, reflects the interplay of 4th-order sea-level fluctuations, of approximately 100–120 ka periodicity, and a long-term (3rd-order) sea-level rise of the late middle through early late Cenomanian. The succession studied includes deposits of a shallow, gravelly braided river (unit 1), tide-influenced braided river (unit 2), supratidal marsh (unit 3), tidal flat (unit 4) and ebb-tidal delta to estuary mouth fill (unit 5). Units 1–5 are interpreted as parasequences of a single depositional sequence; units 1–4 together make up a transgressive systems tract and unit 5 is a highstand deposit, capped by a sequence boundary. The presence of deciduous plants attests to a certain degree of seasonality of the climate. The mixing of thermophile and temperate vegetation, together with the presumed palaeolatitudinal position of the Bohemian Massif, suggests a generally slightly semi-arid (i.e., seasonally wet) regional climatic conditions during the deposition of units 1–5; substrates in local habitats in alluvial valleys and estuary margins were damp due to high local water table. The plant habitat of the alluvial valley (units 1 and 2) was characterized by the Myrtophyllum assemblage, which included an angiosperm-dominated gallery forest and shrubs on braid bars and islands. The transition between fluvial and coastal environments was characterized by a taxodioid backswamp forest (the Ceratostrobus assemblage). Coastal vegetation (i.e., the marsh habitats of unit 3 and the upper part of unit 5), changes distinctly between the two units, although both represent similar facies of high intertidal to supratidal origin. The Frenelopsis assemblage of unit 3, representing shrubby marsh vegetation growing seaward of the Ceratostrobus forest, differs strongly from the more xerophytic Sphenolepis assemblage of unit 5, characterized by herbaceous pteridophytes growing in the marsh in front of a coastal taxodioid forest. We explain the differences between units 3 and 5 by the different sequence-stratigraphic position of the two units: a high groundwater table and eutrophic substrate of the transgressive systems tract (unit 3) compared with a lower or falling regional water table and oligotrophic substrate during the late highstand systems tract (unit 5). Thus, temporal changes in coastal plant assemblages of the Pecinov section do not merely reflect lateral shifts of facies belts, but show that similar depositional environments in different systems tracts hosted very different floras.

Depositional Sequences, High-Frequency Sea Level Fluctuations and Active Tectonics in the Middle to Late Ordovician Appalachian Foreland Basin, Kentucky and Virginia: ABSTRACT

Depositional Sequences, High-Frequency Sea Level Fluctuations and Active Tectonics in the Middle to Late Ordovician Appalachian Foreland Basin, Kentucky and Virginia: ABSTRACT

The Itteville Oil Field : An Example of a Stratigraphic Trap in Mid-Jurassic Carbonates of the Paris Basin: ABSTRACT

The Itteville Oil Field is located 30 km south of Paris. The top of the reservoir lies at an average depth of 1450 m below sealevel. The field is situated on a large scale monocline dipping gently toward the present center of the Paris Basin. At reservoir level, no anticline closure is seen to explain the oil accumulation. The reservoir is composed of oolitic, peloidal and bioclastic carbonates of Lower Callovian age, regionally known as {open_quotes}Dalle Nacree{close_quotes}. These carbonate sands were deposited by storm-dominated processes during a phase of major sealevel fall which caused the emersion of the main Burgundy Platform. This shoal is completely isolated from the main platform and surrounded by coeval marine shales. Marls corresponding to the Mid-Callovian major flooding event seal the reservoir. The occurrence of these shoals appears to be tectonically controlled. The Itteville Field is situated on a Liassic faulted block seated on the eastern flank of the so-called {open_quotes}Deep Magnetic Anomaly{close_quotes}. Sedimentological studies and high resolution sequential analysis, carried out on cores from 17 wells of the field, help define three main tabular correlable units within the reservoir. Geochemical studies, including cathodo-luminescence and isotope analysis, help define the diagenetic history. Original poroperm propertiesmore » are strongly enhanced by contemporaneous dissolution events related to high frequency sealevel fluctuations.« less

Pleistocene Shallowing-Upward Sequences in New Providence, Bahamas: Signature of High-Frequency Sea-Level Fluctuations in Shallow Carbonate Platforms

ABSTRACT Examination of several closely spaced cores from western New Providence, Bahamas, shows a classic shoaling-upward progression of facies. Refined age constraints from magnetostratigraphy indicate that since the Brunhes/Matuyama boundary (0.78 Ma), only three sea-level highstands have flooded this part of the platform. The reefal-skeletal-oolitic-peloidal facies sequence, probably representing deposition during fourth-order highstands, show lateral facies changes and perhaps regional climatic influences. This skeletal-to-nonskeletal transition is common in other Bahamian platform records, and appears to be youngest near the edges of the platform. Estimates of sea level during the reversed-polarity Matuyama, without subsidence corrections, show that it reached within about 10 m below pre ent sea level. During the Brunhes chron, at least one highstand came to within 6-7 m of present mean sea level. The uppermost part of a core, containing beach facies, is now about 6 m above sea level and is thought to represent the 0.13 Ma sea-level event.

Ecostratigraphy and sequence stratigraphy in high frequency sea level fluctuations: examples from Jurassic macroinvertebrate assemblages

Sequence stratigraphy is a method for stratigraphic analysis providing interpretative models with the aim of integrating the subsurface and surface information for correlations, and therefore biostratigraphical data has become increasingly valuable in this context. Given the foregoing, unsolved problems still arise out of the difficulty in obtaining local biostratigraphical data, which can certainly be related to the fact that the linkages of contemporaneous depositional systems are facies independent, and also because of the comparatively broad time span accepted for the cycles of high frequency sea level fluctuations (3rd order and lesser ones). Other restrictions have to do with the comparative complexity of ancient (e.g. Mesozoic) platform systems whose extent and subdivision lead to deviations in the stratal patterns as regards those proposed by the existing synthetic models of sequence stratigraphy. Moreover, at present the attempts at correlation of data obtained in ancient platforms with those from distal areas of continental margins, which are normally characterized by low sedimentation rates, are made indirectly (Olóriz et al., 1991) and are still at a comparatively early stage of development. We here propose an ecostratigraphical approach for correlation and characterization of system tracts in the context of high resolution stratigraphy. The interpretation of the geological record must of course be undertaken with regard to recognizable local determining factors. The observable trends in the record of benthic-epibenthic marine macroinvertebrate assemblages are analyzed in this context. Examples of the Upper Jurassic ammonite record, and especially bivalves among benthic faunas are analyzed on the South and West Iberian margins. Using the sequence stratigraphy frame proposed for this margin by Marques et al. (1991), the data obtained are compatible with the contraction-expansion of ecospaces which could presumably be related to the evolution of Highstand, Transgressive and Shelf Margin Wedge System Tracts. We also comment on published data by others authors concerning fluctuations in ammonite assemblages and ammonite phenotypes, chronological aspects related with sequences stratigraphy analyses, and the record of benthic assemblages within the framework of high frequency fluctuations in relative sea level. The approach proposed here proves to be a useful complement in sequence stratigraphy analyses and will also be of use in more profound study of the ecostratigraphic characterization of system tracts and new interpretations of the fossil record.

Reservoir Characterization of a Late Pleistocene Shelf Edge Delta, Northern Gulf of Mexico

Present interest in sequence and seismic stratigraphy necessitates a new appraisal of sedimentologic effect resulting from sea level fluctuations. Deltaic systems are of particular interest because of their reservoir potential and proven hydrocarbon productivity. However, the preservation potential of some deltas built during periods of high sea level may be poor as compared to their low-stand counterparts. Even in a rapidly subsiding basin such as the northern Gulf of Mexico, high-frequency sea level fluctuations caused extensive entrenchment of the inner to middle shelf, evacuating much of the previous high stand deposition. The Gulf of Mexico Shelf/Slope Consortium recently completed a project designed to collect critical data sets necessary for evaluation of the lithologic, biostratigraphic, chronologic, and seismic/sequence stratigraphic characteristics of a Late Pleistocene shelf-edge delta east of the modern Mississippi River delta lobe. Evaluation of a continuous boring from the Main Pass Lease Area and high-resolution seismic profiles across this delta has led to a new understanding about the internal architecture of deltaic deposition and sediment distribution during falling to low sea level periods. This delta appears to have been sourced by the Mobile River. Wide (to approximately 20 km) and deep updip fluvial entrenchment (to over 30 ms ormore » seismic profiles, approximately 25 m) has eliminated much of the coarse sediment from the original delta progradation and the underlying cycle. The broad evacuation created by fluvial scour is filled with coarse sands and gravels commonly exhibiting inclines stratification, interpreted as large migratory bedforms. Cannibalization of its own sand-rich clinoforms and of underlying deposits by fluvial entrenchment during progradation suggests an increased coarse sediment load as progradation proceeded due to the combined effects of falling sea level and accompanying fluvial entrenchment.« less

Depositional Cycles on a Prograding Reef-Rimmed Carbonate Platform During High-Frequency Sea-Level Fluctuations, Upper Miocene Reef Complex of Mallorca, Spain

Depositional Cycles on a Prograding Reef-Rimmed Carbonate Platform During High-Frequency Sea-Level Fluctuations, Upper Miocene Reef Complex of Mallorca, Spain

Quaternary sequence stratigraphy of the Brisbane River delta, Moreton Bay, Australia

The Quaternary geological history of the Brisbane River delta front and prodelta was interpreted using seismic stratigraphic and sequence stratigraphic principles. During the last major glacial sea level episode, the floor of the bay was exposed and eroded by stream channels. In the subsequent postglacial marine transgression, the palaeochannels of the Brisbane and Pine Rivers were backfilled with mud. Sea level continued rising until about 6500 years ago and a highstand has persisted since then. During the Quarternary, sediment deposition in Moreton Bay was controlled by sea-level fluctuations, channel migration, and palaeotopography. There were at least four depositional episodes prior to the last glacial period, plus the presenet postglacial episode. Periods of low sea level occurred between highstands and the sea bed exposed and eroded. Eight major seismic reflectors were recognised and six seismic sequences defined. The seismic sequences represent five highstand systems tracts and one transgressive systems tract. The relationships between eustacy and system tract type were applied to glacio-eustatic sea-level curves to determine relative ages of sequences in Moreton Bay. The application of sequence stratigraphy to high frequency sea-level fluctuations was demonstrated. The stratigraphic system established within the context of sequence stratigraphy will provide a reference for future work within the region.

Sequence Stratigraphy of Eocene Shelf and Slope Deposits, San Diego Embayment, California: ABSTRACT

Analysis of Eocene shelf and canyon deposits of the San Diego embayment illustrates the applicability of sequence stratigraphic principles in tectonically active regions. Formations of the La Jolla Group are separated by widely correlatable sequence boundaries produced by sea level fluctuations. Sequence boundaries chronostratigraphically define, in ascending order, the Delmar, Torrey, Ardath, Scripps, and Friars formations of the La Jolla Group, and the base of the overlying Poway Group. Contemporaneous tectonism produced regional subsidence, resulting in gradual innundation of the shelf, and rapid, fault-related subsidence accompanied by deposition of a localized sedimentary wedge in the Ardath. Consequently, the thickness and paleobathymetry of the Ardath wedge exceed that expected from regional subsidence, erosional accommodation, and eustatic rise alone. Due to shelfal subsidence, the Delmar, Torrey, and Ardath form a transgressive succession of marsh/intertidal, subtidal, and submarine canyon deposits bounded by sequence boundaries, expressed as erosional unconformities. Facies successions across these surfaces generally deepen upward, with basinward facies shifts restricted to the updip limit of these depositional systems. Although falling sea level initiates these sequences, subsidence limits exposure of the shelf and accompanying basinward shift of facies to a narrow band along the shoreline. In contrast, overlying units exhibit a regressive stackingmore » pattern indicative of reduced subsidence and/or increased sedimentation. Facies successions across sequence boundaries between these units exhibit a more widespread basinward shift. The stratigraphy of the La Jolla Group illustrates that high-frequency sea level fluctuations produce depositional sequences that are fundamental chronostratigraphic units of basin fill on both active and stable margins.« less