Eustatic Sea-level Curve Research Articles

Eustatic sea-level change at the Mid-Pleistocene climate transition: new evidence from the shallow-marine sediment record of Japan

Abstract Based on the excellent sedimentary record, we have identified five depositional sequences in the upper part of the Omma Formation, exposed along the Japan Sea coast of central Japan. The base of this stratigraphic section is placed just below the top of the Jaramillo Subchron, and the top is located below the Brunhes-Matuyama boundary. Biostratigraphy supports the interpretation that the lower three sequences correlate with marine oxygen isotope stages (MIS) 28–26, 26–24 and 24–22, respectively. We have reconstructed a eustatic sea-level curve from analyses of sedimentary facies, fossil molluscs, basin subsidence and sediment accumulation. The resulting sea-level curve shows that mean eustatic sea-level dropped between 1.0 and 0.9 Ma, and that sea-level was lowest at MIS 22, which has the heaviest δ 18O value between MIS 28 and 22. The total fall in mean sea-level is inferred to be 20–30 m. This independent sea-level record demonstrates that ice-sheet volume rapidly increased at the Mid-Pleistocene Climate Transition (MPT) and culminated in MIS 22, as inferred from the δ 18O record. The upper two depositional sequences imply the contribution of precession to changes in ice sheet volume would have arisen in MIS 21, just after the MPT.

The upper Shemshak Formation (Toarcian–Aalenian) of the Eastern Alborz (Iran): Biota and palaeoenvironments during a transgressive–regressive cycle

The siliciclastic, up to 4,000 m thick Upper Triassic–Bajocian Shemshak Formation is widespread across the Iran Plate, especially in the Alborz Mountains of northern Iran. In contrast to its lower, generally non-marine part, the upper part is marine. Based on the Tazareh section of the eastern Alborz, an integrated analysis of this marine interval is presented. The 1,700 m thick marine sedimentary succession records a gradual deepening from inner to mid and outer shelf environments from the Middle Toarcian to early Late Aalenian. During the Late Aalenian–Early Bajocian, the trend was reversed and infilling of the basin by a large delta system occurred. This general facies development reflects a nearly symmetrical transgressive–regressive (T–R) megacycle, terminated by the inter-regional mid-Cimmerian tectonic event. A renewed transgression in the early Late Bajocian initiated a subsequent sedimentary megacycle. The bioturbated mid and outer shelf sediments contain a low to moderately diverse benthic fauna dominated by deep burrowing bivalves, often preserved in the growth position. A hierarchy of four orders of sedimentary cycles can be recognized (parasequences, parasequence sets, unconformity-bounded third-order depositional sequences, and the 13 ma long second-order T–R megacycle). A regional correlation with the Jajarm area (200 km to the east) shows a very similar temporal facies pattern of the upper Shemshak Formation. The eastern Alborz T–R cycle is completely out-of-phase with other (eustatic) sea-level curves, suggesting regional tectonic control. Rough estimates of subsidence rates give an average value of 126 m/ma. However, much higher values for the Aalenian (230 m/ma), particularly the Late Aalenian (700 m/ma), indicate a distinct increase in subsidence rate towards the Early Bajocian mid-Cimmerian tectonic event. These high subsidence rates suggest that the sediments of the Shemshak Formation of the eastern Alborz formed in a (young) rift basin.

Paleoenvironmental interpretations of rare earth element signatures in mosasaurs (reptilia) from the upper Cretaceous Pierre Shale, central South Dakota, USA

Rare earth elements were analyzed from fossil marine reptile (Mosasauridae) bones collected from five superposed members (Sharon Springs, Gregory, Crow Creek, DeGrey, and Verendrye) of the upper Cretaceous Pierre Shale at localities along the Missouri River in Brule, Buffalo, Hughes, and Hyde counties in central South Dakota. Fossil bones from each member of the Pierre Shale have different rare earth element (REE) signatures that may be distinctive over wide geographic areas. Fossils from the Sharon Springs Member have distinctive REE signatures that may be further subdivided into three superposed groups that correspond with the upper, middle, and lower Sharon Springs Member. REE signatures are distinctive from each stratigraphic unit; therefore, fossils eroded from their stratigraphic context may be assigned to their proper depositional unit based on REE signature comparisons. Differences in REE compositions of bones among members appear to result from differential mixing of oxygenated and anoxic seawaters. If differences in mixing are interpreted as depth differences, the lower Sharon Springs Member was deposited in deep, anoxic water; water depths decrease in the middle and upper Sharon Springs, and the overlying Gregory and Crow Creek Members were deposited in even more shallow water. Finally, according to this interpretation, the overlying DeGrey and Verendrye members were deposited in progressively deeper marine waters, but not as deep as the lower Sharon Springs. These interpretations are generally consistent with those based on faunal diversity and eustatic sea level curves.

Paleoenvironmental interpretations of rare earth element signatures in mosasaurs (reptilia) from the upper Cretaceous Pierre Shale, central South Dakota, USA

Abstract Rare earth elements were analyzed from fossil marine reptile (Mosasauridae) bones collected from five superposed members (Sharon Springs, Gregory, Crow Creek, DeGrey, and Verendrye) of the upper Cretaceous Pierre Shale at localities along the Missouri River in Brule, Buffalo, Hughes, and Hyde counties in central South Dakota. Fossil bones from each member of the Pierre Shale have different rare earth element (REE) signatures that may be distinctive over wide geographic areas. Fossils from the Sharon Springs Member have distinctive REE signatures that may be further subdivided into three superposed groups that correspond with the upper, middle, and lower Sharon Springs Member. REE signatures are distinctive from each stratigraphic unit; therefore, fossils eroded from their stratigraphic context may be assigned to their proper depositional unit based on REE signature comparisons. Differences in REE compositions of bones among members appear to result from differential mixing of oxygenated and anoxic seawaters. If differences in mixing are interpreted as depth differences, the lower Sharon Springs Member was deposited in deep, anoxic water; water depths decrease in the middle and upper Sharon Springs, and the overlying Gregory and Crow Creek Members were deposited in even more shallow water. Finally, according to this interpretation, the overlying DeGrey and Verendrye members were deposited in progressively deeper marine waters, but not as deep as the lower Sharon Springs. These interpretations are generally consistent with those based on faunal diversity and eustatic sea level curves.

A semi-quantitative method for the reconstruction of eustatic sea level history from seismic profiles and its application to the southern South China Sea

A quantitative model is proposed to estimate the magnitude of eustatic sea level fluctuations on the basis of definitions of relative and eustatic sea level. In this model, factors such as erosion, sedimentation, compaction, basement tectonic and loading subsidence, and paleo-bathymetry are considered. To estimate incremental changes in eustatic sea level, we developed methods to solve for the variables involved in the model on the basis of interpretation of seismic profiles. We reconstructed the onlap/offlap points removed by erosion by fitting the effective thickness in areas without erosion with a piecewise-defined function and extrapolating this function to zero thickness. We used decompaction and backstripping algorithms to remove the effect of compaction and to calculate loading subsidence of the basement. Regional data, however, are needed to estimate the paleo-water depths and the tectonic subsidence. For this reason, our methodology is considered semi-qualitative. As an application of this model, an eustatic sea level curve since the Pliocene (5.33 my) was deduced from interpretation of our high-resolution seismic data from the northern Sunda Shelf, South China Sea (SCS). On this curve, 36 fourth order sea level cycles were recognized with periods ranging from 0.08 to 0.29 my. The curve matches well with the smoothed deep-sea stable oxygen isotope curves from benthic foraminifera.

Dinocyst stratigraphy and palynofacies studies used for refining a sequence stratigraphic model—uppermost Oligocene to lower Miocene, Jylland, Denmark

The uppermost Oligocene– Miocene deposits in the central and southern parts of Jylland, Denmark, comprise a complex succession of siliciclastic, paralic deposits. The coarse-grained parts of the succession comprise important groundwater reservoirs. A sequence stratigraphic model has gradually been developed during the last 7 years and the succession is now subdivided into six sequences (sequence A–F). The model is based on a combination of seismic data, geophysical logs and lithological data from boreholes and sedimentological measurements of outcrops. The present study documents the composition of assemblages of organic-walled dinoflagellates (dinocysts) in the lower part of the succession (sequences A–C). The data come from seven water supply boreholes and one outcrop section. The dinocyst data are an important tool for pointing out the sequence stratigraphic surfaces in the individual boreholes, showing distinct changes at the sequence boundaries and increased relative abundance and diversity of dinocysts at marine flooding surfaces. The dinocysts are also used for correlating between the studied boreholes and outcrops, for interpreting changes in the depositional environment and for dating the sequences in more detail than earlier datings based on molluscs and foraminifers. The datings allow correlation to eustatic sea-level curves. The good match between the sequence development and climatic changes suggests that eustatic sea-level changes were the main factor in sequence formation and changes in the depositional environment.

Slip rates of the Aigion and Eliki Faults from uplifted marine terraces, Corinth Gulf, Greece

Along the southern coast of the Gulf of Corinth, important coastal uplift is illustrated by raised Late-Pleistocene marine platforms. Terrace remnants preserved on the footwall of the Aigion and Eliki Faults were mapped in detail. To derive cumulative uplift rates, the individual terraces were tentatively correlated with the eustatic sea-level curve, constrained by some direct dating of the deposits blanketing the terraces. We obtain uplift rates of 1.05–1.2 mm yr−1 for the Aigion Fault footwall and of 1.0 and 1.25 mm yr−1 for the East and West Eliki Fault footwalls respectively. A forward modelling procedure was adopted to fit the best-preserved terrace transects, using a code based on standard dislocation theory and assuming reasonable scenarios of regional uplift. We obtained maximum slip rates consistently in the range of 7–11 mm yr−1 for the West and East Eliki Faults and of 9–11 mm yr−1 for the Aigion Fault. To cite this article: P.M. De Martini et al., C. R. Geoscience 336 (2004).

Upper Triassic–Lower Cretaceous seismic sequence stratigraphy and basin tectonics at Bornholm, Denmark, Tornquist Zone, NW Europe

An integrated analysis of seismic sequence stratigraphy and structural evolution of a dynamic intraplate fault basin was conducted along a segment of the Tornquist Zone at the boundary between the Northwest European Craton and the Baltic Shield-East European Platform. High-quality regional seismic-reflection lines document the Late Triassic through early Late Cretaceous tectonic history and depositional sequence architecture. The stratigraphic package was divided into three major transgressive/regressive cycles (1st-order sub-cycles). The upper Upper Triassic through Lower Cretaceous siliciclastic cycles I and II are divided into 2nd-order transgressive/regressive facies cycles composed of higher frequency 3rd-order sequences. The lowstand basin fill comprises stacked successions of lowstand systems tracts produced by relative sea-level rises and falls. During the 3rd-order regressive intervals highstand-dominated depositional conditions prevailed to the northwest while lowstand-dominated conditions occurred to the southeast. Cycle III records an Upper Cretaceous major siliciclastic–chalk cycle. The magnitude of the relative sea-level highs and lows increased up through the studied interval. A two-dimensional structural-evolution analysis is based on the variation of the sediment thickness across the fault blocks up through the sedimentary column. Basin subsidence can be divided into successive structural/tectonic regimes. Fault block rotation and structural inversion characterized the early subsidence of the basin floor. During the second interval, inversion ceased while fault-block rotation continued. In the third interval, the rotation also stopped and no deformation of the basin is recognized. The three major transgressive/regressive facies cycles and associated relative sea-level cycles are linked with the structural regimes. Contemporaneous deposition of 3rd-order highstand- and lowstand-dominated complexes related to differential subsidence and uplift is also evidence of basin tectonics as the controlling factor on relative sea-level changes. Comparison of the relative sea-level curve developed for the study area with eustatic sea-level curves shows that they follow different trends. The deviations between these curves, and the correlation of sequence boundaries with changes of the tectonic regime, support the conclusion that tectonics was a major control on relative sea-level fluctuations in the study area. The 2nd-order cycles linked with deformation episodes along the Tornqist Zone correlate with Lower-Middle Jurassic 2nd-order cycles in England. Deformation along the Tornquist Zone may thus have influenced the sequence stratigraphy across the entire Northwest European Craton.

Late Quaternary deglaciation and sea-level history of eastern Juan de Fuca Strait, Cascadia

Eastern Juan de Fuca Strait of southwestern British Columbia/northwestern Washington State is near the western and southern terminus of Late Wisconsinan glaciation in North America. Seismic-reflection profiles, bathymetric data, sediment core data and 41 new radiocarbon dates provide insight into the history of ice retreat and sea-level change in the eastern portion of the strait. The retreating ice margin appears to have passed through the area between 14,460±200 and 13,595±145 14C yr. Glacial marine sediments date between 12,889±50 and 11,110±50 14C yr BP. Wave-eroded unconformities, drowned prograded deposits and a partially isolated low-stand basin are evidence attributed to low-stand sea levels following deglaciation and five new control points on the local eustatic sea level curve are assigned based on radiocarbon dating of these features. Sea-level change was rapid: from +75 m immediately after deglaciation to possibly −60.4 m at 9920±60 14C yr BP. After this time, gradual sea level transgression took place. Relative sea level reached its approximate present position by 5470±115 14C yr BP. Since then, relative sea level has remained constant suggesting eustatic rise is balanced by crustal uplift.

Deciphering Holocene sea-level history on the U.S. Gulf Coast: A high-resolution record from the Mississippi Delta

Published Holocene relative sea-level (RSL) curves for the U.S. Gulf Coast are in mutual conflict, with some characterized by a smooth RSL rise akin to widely accepted eustatic sea-level curves versus others, including several recent ones, that are characterized by a conspicuous “stair-step” pattern with prolonged (millennium-scale) RSL stillstands alternating with rapid (meter-scale) rises. In addition, recent work in Texas and Alabama has revitalized the notion of a middle Holocene RSL highstand, estimated at 2 m above present mean sea level. An extensive sampling program in the Mississippi Delta (Louisiana) focused on the collection of basal peats that accumulated during the initial transgression of the pre-existing, consolidated Pleistocene basement. We used stable carbon isotope ratios to demonstrate that many of these samples accumulated in environments affected by frequent saltwater intrusion in the <30 cm zone between mean spring high water and mean sea level, and we selected plant macrofossils that were subjected to AMS 14C dating. Nearly 30 sea-level index points from a ∼20 km2 study area on the eastern margin of the delta suggest that RSL rise followed a relatively smooth trend for the time interval 8000–3000 cal yr B.P., thus questioning the occurrence of major RSL stillstands alternating with abrupt rises. Given the narrow error envelope defined by our data set, any sea-level fluctuations, if present, would have amplitudes of <1 m. Although a true middle Holocene highstand never occurred in the Mississippi Delta, the high level of detail of our time series enables a rigorous test of this hypothesis. Correction of our data set for a hypothetical tectonic subsidence rate of 1.1 mm yr−1 (assuming a constant subsidence rate compared to the tectonically relatively stable adjacent coast of Texas) leads to sea levels near 2 m above present during the time interval 6000–4000 cal yr B.P. However, this model also implies a RSL position near −2 m around 8000 cal yr B.P., which is inconsistent both with data of this age from Texas, as well as with widely accepted sea-level data from elsewhere. We therefore conclude that a middle Holocene highstand for the U.S. Gulf Coast is highly unlikely, and that the entire area is still responding glacio-isostatically, by means of forebulge collapse, to the melting of the Laurentide Ice Sheet.

Sequence stratigraphy of the Jurassic of the Danish Central Graben

A sequence stratigraphic framework is established for the Jurassic of the Danish Central Graben based primarily on petrophysical log data, core sedimentology and biostratigraphic data from about 50 wells. Regional seismic lines are used to assist in the correlation of some wells and in the construction of isochore maps. In the Lower Jurassic (Hettangian–Pliensbachian) succession, five sequences have been identified. The Middle Jurassic is subdivided into four sequences that together span the uppermost Aalenian/lowermost Bajocian to the Callovian. In the Upper Jurassic, better well coverage permits greater stratigraphic resolution, and 11 sequences are identified and mapped. On the basis of the sequence stratigraphic correlation and the construction of isochore maps for individual sequences, the Jurassic basin history of the Danish Central Graben can be subdivided into seven discrete phases: (1) Shallow marine and offshore sediments deposited in a prerift basin extending from the North Sea to the Fennoscandian Border Zone (Hettangian–Pliensbachian). (2) Uplift and erosion in association with a Toarcian–Aalenian North Sea doming event. A major hiatus represents this phase in the study area. (3) Terrestrial and marginal marine sedimentation during initial rifting (latest Aalenian/earliest Bajocian – Late Callovian). (4) Early Oxfordian – Early Kimmeridgian transgression during and after a rift pulse. The sedimentary environment changed from coastal plain and marginal marine to fully marine. (5) Regression associated with a cessation or slowing of subsidence during a structural rearrangement that took place in the Late Kimmeridgian during a break in the main rift climax. Shallow to marginal marine sandstones were deposited above an erosion surface of regional extent. (6) Deep-water mudstones deposited in a composite graben with high subsidence rates related to rift pulses (latest Late Kimmeridgian – middle Middle Volgian). (7) Deposition of organic-rich mudstones and turbidite sandstones during the late Middle Volgian – Early Ryazanian. The main basin shallowed, became more symmetrical and experienced a decreasing rate of subsidence, recording the onset of the post-rift stage. A relative sea-level curve is constructed for the Middle–Late Jurassic. It shows close similarity to published eustatic (global) and relative (North Atlantic area) sea-level curves in the latest Bathonian – late Early Kimmeridgian, but differs in the Late Kimmeridgian – Middle Volgian interval, probably due to the high rate of subsidence in the study area.

The impacts of sea-level changes during latest Pleistocene and Holocene times on the morphology of the Ionian and Aegean seas (SE Alpine Europe)

The tentative coastline configuration in the Ionian and Aegean seas in three Late Pleistocene–Holocene time slices is given, based on the global eustatic sea-level curve in combination with local geological and geoarcheological data. At lowstand stage 2 (21 500 cal yr BP (years before present), sea level −120 m), extensive shelves existed in the northern Aegean Sea and, to a second degree, in the eastern Aegean Sea and in the northern and central parts of the Ionian Sea. Many islands were connected with each other and with the mainland. A great part of the periphery of gulfs that have an entrance less than 120 m deep was subaerially exposed, while in their central parts lakes were formed. At 11 500 cal yr BP (sea level −60 m) the exposed shelf was much restricted, most of the gulfs were overflowed by the advancing sea and only a few islands were still connected with the mainland. Finally, at 8000 cal yr BP and onward, the sea initially intruded the lowlands and the gulfs, but the subsequent sediment input by the rivers regressed the sea to its present position. Thus many human settlements and old cities that were maritime during Hellenistic or older times are now a few to tens of kilometers inland.

Jurassic foraminifera from the Queen Charlotte Islands, British Columbia, Canada: biostratigraphy, paleoenvironments and paleogeographic implications

Lower and Middle Jurassic (Sinemurian to Callovian) foraminifera were examined from 66 localities of the Queen Charlotte Islands, British Columbia, Canada. Over 200 species of well preserved benthic calcareous and agglutinated taxa belonging to 50 genera were identified. Foraminifera from the Lower Jurassic are represented by an abundant and diverse, Tethyan-derived calcareous assemblage, with Boreally derived agglutinated taxa becoming gradually more dominant in the upper Lower Jurassic to lower Middle Jurassic. Sedimentary strata and their faunal components and position of hiatuses correlate approximately with the Jurassic eustatic sea-level curve. Sea-level changes have resulted in a variety of depositional environments ranging from deep-water euxinic shales with abundant tuff beds, characterized by small pyritized foraminifera, to a well oxygenated outer shelf setting, characterized by a major faunal increase, to shoreface sandstones and conglomerates with absent to rare benthic foraminifera. A gradual shallowing from a slope- to a shelf-dominated deposition, with a magmatic arc provenance, is suggested for the Lower Jurassic, changing in the Middle Jurassic to an inner shelf to upper shoreface setting dominated by sedimentary strata of volcaniclastic origin. A marked faunal turnover is observed in the Lower Jurassic Whiteaves Formation (middle Toarcian) with the extinction of several earlier species and the appearance of a new diverse assemblage of 225 taxa. This turnover is also observed in the ammonite and radiolarian assemblages of the Queen Charlotte Islands. In comparison to the dominantly Tethyan-derived taxa of pre-middle Toarcian age, many of the species from the middle Toarcian are found in northern latitudes such as on the northern slope of Alaska, Arctic Islands and the Northwest Territories. Hence, foraminifera, in conjunction with existing radiolarian and ammonite data, suggest a northward displacement of the Queen Charlotte Islands from low to mid-paleolatitudes by late Early Jurassic (Toarcian) to early Middle Jurassic (Bajocian) time.

Late Ordovician–Early Silurian (Ashgillian–Llandovery) sea level curve derived from conodont community analysis, Anticosti Island, Québec

Earlier workers have established sea level curves for the Ashgillian–Llandovery sequence on Anticosti Island, Québec, Canada, based on sedimentology and on brachiopod and reef communities. The complete Anticosti sequence has been collected for conodonts to provide a database of over 77 600 conodonts derived from 272 samples through the 800–1100 m sequence. This paper uses a statistical analysis of the database to establish the pattern of conodont communities and their interpreted water depths. This allows the establishment of a eustatic sea level curve for the sequence. This curve is in general agreement with those of the earlier workers, but is more detailed and better constrained stratigraphically given the large sampling program. The curve reflects more oscillating sea level changes for the whole sequence than those constructed earlier, and different water depths for certain intervals from those established earlier. The curve is valuable given that the Anticosti sequence is one of the most complete in the world for this interval, and its divergence from global eustatic curves for this interval is noted.

The impact of Milankovitch-scale climatic forcing on sediment supply

Abstract Stratigraphy is the main technique to predict the occurrence of potential reservoirs and seals in the oil industry. Stratigraphic tools used are stratigraphic observations from drilled wells (rock samples and wireline logs) and seismic interpretation. Nowadays, computer modelling allows scenario forecasting of the sequence to be expected. Application of these tools indicates that the key input parameters are initial basin topography, subsidence, eustasy and sediment supply. The first three parameters are usually well constrained or can readily be deduced from well and seismic data. However, the fourth, sediment supply, is loosely defined, and because of that, it is used to calibrate the model. In the present article, the controls on sediment supply are reviewed and the impact of, in particular, Milankovitch-scale climatic forcing on sediment supply is tested on the Neogene of the Niger Drainage and Delta system. Sediment supply is controlled by a complex interplay of geographic and climatic factors, such as: (1) relief or mountain height; (2) the size and temporal storage capacity of the drainage area; (3) overall climate; (4) amount and seasonality of precipitation; and (5) vegetation cover. Studies in geomorphology have indicated that although complex, computer models can be made to predict erosional product for the present. A large-scale sediment supply prediction should be based on the combination of palaeogeographical, palaeoclimatological and erosion potential maps. More detailed sediment supply predictions should include Milankovitch scale variations. The climatic impact of these variations is mainly felt when we are in a transition between two climates, then the area will experience regular climatic changes, from e.g., wet (rainforest) to dry monsoonal climate, or low to high sediment supply, respectively. This concept was tested in the forward modelling package STRATAGEM on the Neogene of the Niger Delta. Four scenarios were evaluated, using various combinations of large and Milankovitch-scale sediment supply curves combined with global or Milankovitch-scale eustatic sea-level curves. The results confirm the impact of both large-scale and Milankovitch-scale climatic forcing on sediment supply. However, in an icehouse world, the various scenarios also suggest that the effect of eustatic sea-level fluctuations overshadows the impact of Milankovitch-scale sediment supply. By contrast, in a greenhouse world, the impact of Milankovitch-scale sediment supply is expected to be more significant in the absence of significant sea-level fluctuations.

Sedimentation and basin evolution of the Oligocene-Miocene Mesohellenic basin, Greece

The Oligocene-Miocene Mesohellenic basin of northern Greece and southern Albania is filled with up to 4 km of marine turbidites and basin margin strata. Surface outcrops include fan deltas, prodeltaic facies, and sandy and shaly submarine fan facies. All these facies in outcrop can be directly correlated with seismic facies in the subsurface, which in turn are compared with seismic facies in modern sandy submarine fans. Twelve seismic markers provide a stratigraphic framework that has been dated by new nannofossil biostratigraphy. Lowstand facies include erosional channels on the basin slope that aggrade basinward with sandy overbank levees to give composite sand bodies with an overall lobelike character. Distally, these pass into sandy channel-termination depositional lobes. Highstand facies are characterized by shaly basin slopes and shaly turbidites in the basin, with irregular reflections interpreted to represent shallow channels and slumps. The stratigraphic occurrence of lowstand facies compares closely with published eustatic sea level curves. The basin has the potential for significant gas, principally in stratigraphic traps. The Mesohellenic basin developed as a strike-slip half graben, synchronous with the Ionian foreland basin to the west of a mountain belt formed by the Pindos nappes.

On eustatic sea level history: Last Glacial Maximum to Holocene

This paper addresses the question of the magnitude and time dependence of the globally averaged (eustatic) rise of sea level that occurred subsequent to the time of Last Glacial Maximum (LGM) at approximately 21,000 calendar years before present. Through the analysis of relative sea level (RSL) histories predicted by a realistic mass conserving and gravitationally self-consistent theory of postglacial sea level change, it is demonstrated that there are preferred oceanic locations at which this eustatic function is well approximated by local sea level history. One such location is the Island of Barbados in the Caribbean Sea, a site from which a coral based record exists that extends from mid-Holocene to LGM. Because of the sea level ambiguity that is inherent to coral based records, however, it is important that the global ice-equivalent eustatic sea level curve inferred on the basis of the Barbados data be tested against observations at other locations from which similarly extensive records are also available but which are derived on the basis of sea level indicators which are not subject to the ambiguities inherent to corals. It is shown that, when the eustatic function employed in the global theoretical model is tuned so as to enable the model to fit the Barbados observations, where the maximum relative sea level (RSL) depression is assumed to be near 120 m, then the theory misfits the record from the Sunda Shelf in the Indonesian Archipelago as well as the record from J. Bonaparte Gulf in northern Australia. Both of these recently published records appear to constrain the LGM low stand of RSL to a value above 120 m. The implications of these results for interpretation of the long coral derived records from the Huon Peninsula of Papua, New Guinea and the island of Tahiti are also discussed.

Use of Sedimentary Structures in the Recognition of Sequence Boundaries in Upper Jurassic–Upper Cretaceous Peritidal Carbonates of the Western Taurides, Turkey

Subtidal, intertidal, and supratidal carbonate facies are recognized in the Upper Jurassic (Kimmeridgian)-Upper Cretaceous (Cenomanian) peritidal carbonates of the Fele area (Western Taurides, Turkey). Vertical stacking patterns of these facies are of a cyclical character; shallowing upward is the trend of the cyclicity in these carbonate facies. In-situ karstic breccias, collapse breccias, caliche (laminar calcrete), “Microcodium” accretion, and root casts are structures commonly indicative of third-order sequence boundaries. However, mud cracks, solution pores or vugs, sheet cracks, loferites, and birds-eye structures are commonly delineated by parasequence boundaries. In-situ or collapse breccias can be genetically derived from sheet cracks, mud cracks, solution pores or vugs, and birds-eye structures with increasing exposure time. The use of such sedimentary structures in the recognition of sequence boundaries is highly practical in the ancient carbonate platforms of the world, inasmuch as the sequence boundaries, as demonstrated in this study, correlate with the eustatic sea level curves.

ABSTRACT: A Comparison of Two Lower Miocene Carbonate Margins: The Zhujiang Carbonate Platform (Subsurface, South China Sea) and The Pirin&amp;ccedil; Platform (Outcrop, Southern Turkey)

Early Miocene carbonate platform complexes have been the subject of extensive exploration efforts in Southeast Asia (for example, the Gunung Putih carbonate complex, East Java Sea, and the Zhujiang and Liuhua platforms, Pearl River Mouth Basin). However, few outcrop equivalents of these early Miocene platforms have been published to date. In this study, we present an outcrop that is an excellent analog for this petroleum province. The Pirin outcrop is an early Miocene carbonate platform-to-basin transition exposed on the northern flank of the Mut Basin in southern Turkey. The carbonates were deposited during a time of relative tectonic quiescence in the early Miocene (Burdigalian) over a relict paleotopography inherited from Oligocene tectonic activity. The interval described here is interpreted to be influenced by three large, relative sea level cycles with 100–150-m amplitude. These generated a steep-edged platform with prograding slope and margin geometries during the highstands, whereas during the lowstands, thin carbonate platforms developed with onlapping geometries against the older underlying slump deposits. Stratigraphic relationships indicate that collapse of the platform margin occurred during late highstand to early lowstand times and was coincident with major sea level falls. During transgression, an isolated platform complex developed. Carbonate production on these platforms shut down around the maximum flooding, leading to terminal drowning. This may have been the result of eutrophication caused by the arrival of nutrients from an encroaching deltaic system, combined with a period of rapid relative sea level rise. The subsurface Zhujiang Platform (Pearl River Mouth Basin, China) is an early Miocene carbonate platform that developed along the flank of a basement high in the basin. A steep, prograding, carbonate-shelf margin developed with large-scale slumping and collapse features in places. Pinnacles and small isolated platforms grow across a zone seaward of the margin. A strikingly similar stratigraphic organization (steep shelf margin, slumps, and isolated platforms) is observed in the Pirin outcrop. These similarities are attributed to a common tectonostratigraphic setting (the rapid marine flooding of a complex relict topography during a time of relative tectonic inactivity) and a Burdigalian eustatic sea level curve with cycles of sufficiently large amplitude to have a significant impact on the platform morphology. At the exploration scale, the outcrop allows us to test three play concepts. From outcrop observations, the slump packets (play concept 1) do not seem to be sufficiently interconnected to make a viable prospect. The development of an enhanced porosity wedge (play concept 2) at the shelf margin will be testable with future outcrop studies. In addition, with future outcrop work, a predictive model for the development of porosity in the isolated platforms can be developed (play concept 3) to more successfully predict porosity prior to drilling. At the reservoir scale, observations of subseismic bedding patterns from the outcrop will help us construct more accurate reservoir models. Additionally, outcrop observations of the dimensions of facies belts and their lateral and vertical variability will improve the way in which we populate a reservoir model with facies and reproduce variability on a scale finer than the interwell spacing.

Cenomanian–Coniacian transition from siliciclastic to carbonate marine deposition, Giralia Anticline, Southern Carnarvon Platform, Western Australia

Three formations exposed in the Giralia Anticline record the transition from siliciclastic to carbonate-dominated sedimentation on the Southern Carnarvon Platform, a stable shelf on the passive western Australian continental margin. The succession consists of condensed and partly eroded sequences that record maximum marine flooding events and the unconformities between them. The stratigraphic record of the depositional change is evident in four <2-m-thick sections analysed here by outcrop logging and micropalaeontological analysis. The oldest sequence, at 96–94Ma, includes transgressive-phase deposits truncated by an unconformity, but reflecting a maximum water depth of less than 50m in the preserved record. This sequence is represented in the uppermost 0.5m of the Gearle Siltstone in its type area as a dark grey mudstone that belongs to nannofossil Zone CC10a (Middle Cenomanian). The second sequence, dated at 92–91Ma, is evidenced by a very thin (<0.25m thick) unit of yellowish brown to pale yellow marl that belongs to the upper Lower Turonian (based on the overlap of the upper part of nannofossil Zone CC11 and the planktic foraminiferal Helvetoglobotruncana helvetica Zone). A middle neritic (water depth about 100m) depositional setting is suggested by the foraminiferal assemblage. The transgressive base of the third sequence (dated at 88–87Ma) includes the lowest 20cm of the Toolonga Calcilutite that contains abundant nannofossils indicative of zone CC14 (mid Coniacian). The basal marls and calcilutites of this sequence were deposited on a marine erosion surface at water depths of about 50m. There is broad correspondence between the local record of bathymetric change and the eustatic sea-level curve for the mid Cenomanian to mid Coniacian interval. In shallow waters (50–100m deep) relatively close to the shoreline, influx of siliciclastic mud decreased allowing accumulation of nannofossiliferous muds during the Turonian and Coniacian interval. A decrease in the amount of precipitation, erosion and river transport of sediment onto the continental shelf (indicative of climatic change, perhaps to more arid conditions in the hinterland) was probably the main factor that led to the change from marine siliciclastic to carbonate sedimentation that occurred between 96–94Ma and 92–91Ma in the Giralia region.