Global Eustatic Curve Research Articles

Palaeoenvironmental implications of Palaeomicrocodium in Upper Devonian microbial mounds of the Chernyshev Swell, Timan-northern Ural Region

Nine major microfacies and eight transgressive-regressive cycles have been recognized in the middle Frasnian-Famennian microbial mound of the Shar'yu River section in the Chernyshev Swell, Timan-northern Ural region. Rocks including Palaeomicrocodium at the top of each cycle show signs of brecciation, freshwater leaching, and vadose cementation. Palaeomicrocodium, an enigmatic structure, being close in nature to Microcodium, is useful as a palaeoenvironmental indicator and can also be used in regional correlations. Seven levels of subaerial expose surfaces with Palaeomicrocodium correspond to seven breaks in growth of the microbial mound in the Upper Devonian reef-like formation. The high-amplitude sea-level changes recognized are in good correlation with those in the Moscow Syneclise and are also fixed on the global eustatic curve.

Eustatic and palaeogeographic control of the western Aurès Upper Cretaceous sedimentation (Algeria)

Abstract The Upper Cretaceous sedimentation in the Aurès Mountains occurred in a subsident basin delimited to the south by the Saharan platform and by the Preatlasic high zone to the north. In these series 4 transgressive-regressive megasequences are distinguished, the first one (I) in the late Albian-Cenomanian, the second one (II) in the Turonian, the third one (III) in the Coniacian - Santonian and the fourth one (IV) in the Campanian - Maastrichtian. Each megasequence is made up of three or four sequences, which correspond to third order cycles identified in the eustatic chart of Haq et al. [1987]. In late Albian and lower Turonian periods, during the deposition of basal sequences of the megasequences I and II, the reactivation of basement faults in the Aurès basin occurs consecutively to distension phases, resulting in the formation of rotated blocks. At the same time high eustatic levels are reached according to the global eustatic curve. These processes control the drowning of the carbonate platforms pre-existing to these sequences, and deep ramps progressively form on the tilted block tops. This sedimentary setting generates in the late Albian and lower Turonian series anoxic sequences made up of calcareous and shaly transgressive pelagic intervals. The succeeding sequences lack pelagic facies and are composed of alternate marls / carbonate beds deposited on a homoclinal ramp, indicating a gradual development of shallow open marine conditions, which became progressively restricted upwards. Toward the top of these megasequences, lagunal muds and isolated rudists mounds, surrounded by bioclastic and ooid / pellet banks occur. The Coniacian-Santonian and Campanian-Maastrichtian megasequences are characterized by a shallow ramp sedimentation, essentially marly during the Coniacian, Santonian and Campanian periods, interlayered with some bioclastic / ooid carbonate banks and upwards by sequences mostly homogeneous. The Maastrichtian platform carbonates are composed of bioclastic / ooid sands and were deposited in a ramp-barrier-bank system. Some sequences in the Campanian-Maastrichtian megasequence are condensed or absent due to the accommodation reduction related to a weak subsidence rate period.

Neogene marine transgressions, palaeogeography and biogeographic transitions on the Thai–Malay Peninsula

AbstractAim The aim of this review is to contribute to our understanding of the origination of the Sundaic and Indochinese biotas in Southeast Asia. Numerous unsolved problems surround the origination of the differences between these biotas and the determinants of the breadth and current position of the transition between them.Location Literature reviews show that phytogeographical and zoogeographical transitions between the Sundaic and Indochinese subregions lie on the Thai–Malay peninsula just north of the Isthmus of Kra. A second, more widely recognized botanical transition lies 500 km further south at the Kangar–Pattani line near the Thai–Malay border.Results The phytogeographical transition involves 575 genera of plants, and a change from wet seasonal evergreen dipterocarp rain forest to moist mixed deciduous forest. The zoogeographical transition is best characterized for forest birds, and more than half the species present in this region have species boundaries north of the Isthmus of Kra, at 11–13° N latitude. Although the phytogeographical transition is climate‐related today, and the avifaunal transition is viewed as being associated with the vegetation change, there is no obvious present day geological, physiographical or environmental feature to account for the origination of the provincial biotas. Similarly, known Neogene palaeoenvironmental changes on the tectonically stable peninsula, including those associated with periods of lower sea levels and the emergence of Sundaland, fail to account for either the origination of the provincial differences or the current position of the transition.Main conclusions Contrary to earlier palaeogeographical reconstructions, it is suggested that Neogene marine transgressions flooded the peninsula in two areas and created circumstances leading to the biogeographical patterns of the present day. The Vail global eustatic curve, supported by the oxygen isotope record, indicates that sea levels were c. 100 m above the present‐day level during the early/middle Miocene (24–13 Ma) and again during the early Pliocene (5.5–4.5 Ma). Present topography suggests such high sea stands would have created 30–100‐km wide seaways north and south of the Nakhon si Thammarat Range in the central peninsula (southern Thailand). Geological, palaeontological and phylogenetic evidence for such hypothetical seaways is scant (there have been no focussed searches) but does not preclude their occurrence. The role of such Neogene highstands in explaining present day biogeographical patterns in Southeast Asia and elsewhere requires assessment.

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.

ABSTRACT: High-Resolution Magnetostratigraphic Correlation of Triassic Carbonate Platforms, Nanpanjiang Basin, South China, Indicates Differential Platform Subsidence

A high-resolution magnetostratigraphy, extending from the Permo-Triassic boundary into the Late Triassic (Carnian), has been established for carbonate strata from 1) the southwestern margin of the giant Yangtze platform (YP) (a composite section) and 2) the basin margin adjacent to the Great Bank of Guizhou (GBG), an isolated platform 150 km to the south. Positive paleomagnetic “stability” tests, including fold, reversal, consistency and conglomerate tests, and excellent agreement between observed and expected Triassic paleomagnetic directions for the YP and the GBG, indicate the primary origin of the magnetostratigraphic data. Magnetic mineralogic studies argue the presence of geothite, multi- and single-domain titanomagnetite, and hematite. Detailed magnetostratigraphic correlations reveal a prominent deepening event occurred near the Smithian-Spathian boundary (Early Triassic) on the southwestern Yangtze platform but did not effect the Great Bank of Guizhou nor the eastern sector of the Yangtze platform. The global eustatic curve shows a transition to high stand at this time. This apparent differential subsidence is consistent with other evidence that the southwestern sector of the Yangtze platform underwent several episodes of accelerated tectonic subsidence relative to the rest of the platform. This includes 1) slight retreat or vertical accretion of the margin in the early Ladinian whilst the eastern sector prograded at least 1.5 km basinward, 2) drowning of the southwestern sector of the platform at the Ladinian-Carnian transition whilst the eastern sector remained in shallow water, and 3) Middle Triassic strata are appreciably thicker on the southwestern sector.

A Fluvial Record of Long-term Steady-state Uplift and Erosion Across the Cascadia Forearc High, Western Washington State

Six late Quaternary river terraces, preserved along the Clearwater River in northwestern Washington State, provide a ∼140 ka record of long-term incision and uplift across the western side of the Cascadia forearc high. Terrace ages are constrained by weathering rind and radiocarbon dating and by correlation to dated coastal glacio-fluvial deposits and the global eustatic curve. The terraces overlie flat bedrock surfaces, called straths, which represent uplifted segments of the river channel. Bedrock incision is measured by the height of a strath relative to the adjacent modern river channel. The straths along the Clearwater show an upstream increase in bedrock incision, ranging from ∼0 at the coast to a maximum of 110 m in the headwaters. The incision at any point along the profile increases systematically with strath age. The calculated incision rates range from ∼10 ky) the Clearwater River valley has maintained a steady-state profile defined by a long-term balance in the rates of incision and rock uplift. Upstream divergence of terraces is best explained by an increase in the rate of rock uplift from the coast toward the central part of the range. These results are consistent with other evidence indicating a long-term steady-state balance between the accretionary influx and the erosional outflux for this part of the Cascadia subduction wedge since ∼14 Ma. These results help show how terrace deposits form in tectonically active landscapes. The dominantly fluvial Clearwater drainage was forming straths while alpine glaciers were advancing in adjacent drainages. In turn, the straths were buried during the transition to interglacial times because of increased sediment supply due to local deglaciation and because of eustatic highstands that forced aggradation in the lower reach of the drainage and across the continental shelf as well. The fluvial system shows strong forcing by the glacial climate cycle. Even so, the river appears to have returned to the same valley profile during each cycle of strath cutting. Thus, bedrock incision is clearly unsteady at time scales shorter than the glacial climate cycle (∼100 Ky) but appears to be relatively steady when averaged over longer time scales. A simple kinematic model is used to examine how uplift of the Cl. Our analysis indicates that the accretionary flux into the wedge occurs mainly by frontal accretion and not by underplating. If accretion occurred entirely at the front of the wedge, the present west coast should be moving to the northeast at ∼3 m/ky, relative to a fixed Puget Sound. This prediction is in good agreement with offset of a ∼122 ka sea cliff preserved at the southwest side of the Clearwater valley profile. In this case, the long-term margin-perpendicular shortening would account for 20 to 35 percent of the geodetically-measured northeast-southwest shortening across the Olympic Mountains.

Albian-Cenomanian Palynology, Paleoecology and Organic Thermal Maturity of Well DK-B in the Dukhan Oil Field of Western Qatar

ABSTRACT A palynological investigation of the Nahr Umr, Mauddud and Ahmadi formations of the middle Cretaceous Wasia Group in Well DK-B in the Dukhan oil field of Qatar, yielded 30 species of dinoflagellate cysts, 18 of pteridophytic spores, 14 of gymnosperm pollen, and 16 of angiosperm pollen. Based on the investigation, the age of the Nahr Umr Formation is middle to late Albian. The basal part of the Formation was deposited in a marine prodelta or shallow shelf environment, whereas sedimentation of the upper part took place in normal marine conditions of an inner to middle shelf at depths of 10 to 80 meters. The carbonates of the Mauddud Formation are of late Albian (Vraconian) to early Cenomanian age and were deposited in an inner-middle shelf environment (20–100 meters). The shales and limestones of the Ahmadi Formation are of early to middle Cenomanian age and accumulated in open-marine conditions within an outer-shelf environment (100–200 meters). Two regressive pulses or lowstand system tracts can be detected in the lower and middle parts of the Ahmadi Formation that are consistent with published short-term global eustatic curves. Rocks of the Wasia Group studied in Well DK-B are in general enriched in kerogen type II (oil-prone material) except for the lower part of the Nahr Umr Formation that can be attributed to kerogen type III (gas-prone material). The thermal alteration index range of 2, 2+ to 3− suggests that the sediments of the Ahmadi Formation are immature whereas those of the Mauddud and Nahr Umr formations are slightly mature. The Albian-Cenomanian palyno-assemblage of western Qatar is referable to the African-South American Phytogeoprovince as shown by the presence of Crybelosporites pannuceus, ephedroid pollen, elater-bearing pollen, Afropollis, Stellatopollis, Reyrea and Cretacaeiporites species. Arid to semi-arid (tropical to subtropical) climatic conditions prevailed in the African-South American province at this time. Dinoflagellate cysts suggest a Tethyan connection.

Sedimentology and palaeogeography of the regressive-transgressive Kurnub Group (Early Cretaceous) of Jordan

The Early Cretaceous Kurnub Group of Jordan consists of three regressive-transgressive (fluvial-marine) depositional sequences in northern Jordan, recorded here for the first time, whereas continental clastics dominated central and southern Jordan. Deposition of the Kurnub Group started in the late Neocomian above a regional angular unconformity by basal conglomerate and sandstone facies association of an alluvial braidplain origin. During this time the Tethys Seaway was located to the north and northwest of Jordan which afterwards, during the Barremian, advanced in a south- and southeastward direction flooding north Jordan and giving rise to a tidal flat-coastal swamp sequence. Following a subsequent regression of the sea, unconfined braidplain deposits covered the area. The most extensive transgression of the Tethys inundated the region during the late Aptian and early Albian where a mixed siliciclastic-carbonate sequence with interbedded inner shelf carbonates and tidal marsh—coastal swamp black shales and lignites was deposited. The next and last regression took place in the middle Albian where a thin meandering river clastic sequence was deposited. Finally, shallow-marine sedimentation resumed over the region during the remaining time of the Kurnub Group which at the same time prepared for the subsequent regional Cenomanian transgression. Upon comparison with global eustatic curves, these three incursions of the Tethys sea in Jordan are to a great extent in accordance with the global sea-level fluctuations. The various formations of the Kurnub Group and their informal units that are established here for the first time can readily be correlated with equivalent deposits in adjacent countries. The distribution of the shorelines of the Barremian, Aptian and Albian on both sides of the Dead Sea Transform offers new evidence for 100 km northward displacement of the Arabian plate against the Sinai-Palestine plate.

Seismic stratigraphy of McMurdo Sound, Antarctica: implications for glacially influenced early Cenozoic eustatic change?

Analyses by Barrett et al. (1989) of the stratigraphic sequences of the CIROS-1 drill core provided evidence of late Paleogene and early Neogene glacial advances and retreats that appear to correlate with the global eustatic curve of Haq et al. (1987). During Leg 2 of the Polar Duke 90 (PD90) cruise in the Ross Sea approximately 650 km of highresolution seismic data were collected in McMurdo Sound with the main objective of facilitating regional correlation of stratigraphic events observed in the cores of the CIROS-1, DVDP-15, and MSSTS-1 drilling programs, and therefore providing an opportunity to test hypotheses on linkages between Cenozoic eustatic and Antarctic ice volume fluctuations. Twenty unconformity-bound, seismic-stratigraphic sequences (labeled from top A to T) were identified in the McMurdo Sound PD90 data base. However, seismic data from the shallow shelf on which CIROS-1 was drilled show erosional surfaces at many levels, indicating a condensed section in this area. It is difficult to distinguish individual lithological units identified by Barrett et al. (1989) in the seismic data, but seismic units O, P and Q correspond to the upper Oligocene interval where they recognized 3 glacioeustatic events. These three sequences, totaling around 300 m in thickness, can be traced over a distance of almost 100 km. However, they lack the seismic characteristics of glacial facies identified by Anderson and Bartek (1992) and thus the significance of waxing and waning events suggested for upper Oligocene strata in CIROS-1 remains equivocal. The younger sequences in the McMurdo Sound data base are largely Miocene (E-N), the oldest of these forming the upper 70 m in CIROS-1. These sequences can be traced 300 km north into the center of the Victoria Land basin, where they have seismic features characteristic of glacial facies. This suggests that ice sheets of continental scale (and hence large enough to affect eustasy) waxed and waned across the Ross Sea continental shelf at least 10 times during the Miocene. The data presented here for the Oligocene do not preclude similar ice sheet behavior, but are insufficient to test the hypothesis properly.

THE DEVELOPMENT AND REGIONAL SIGNIFICANCE OF RIFT-RELATED DEPOSITIONAL SYSTEMS IN THE DAMPIER SUB-BASIN

The influence of tectonic control is more apparent than eustatic control on the rift-related stratigraphy of the Dampier Sub-basin. The correlation of observed depositional events to causative processes and global events is problematic due to the use of alternative geological time scales, causing ambiguity and uncertainty. The Harland (1989) time scale with a revised palynological allocation, combined with genetic sequence stratigraphy, and Prosser's concept of the tectonic systems tract, has proved useful during evaluation of the stratigraphy of the Dampier Sub-basin.Palaeo-topography was a major factor in sediment distribution and facies architecture of rift-related strata in the Dampier Sub-basin. This must be considered when assessing the stratigraphic trapping potential for hydrocarbons. There is a close association between the styles of depositional systems observed in the Dampier Sub-basin and stage of rifting and basin development. Five tectonic systems tracts, each with unique depositional systems have been identified and described; pre-rift, rift initiation, rift climax, immediate post-rift and late post-rift tectonic systems tracts.The use of a single time scale has enhanced the relationship between tectonic systems tracts (super-cycles) and the timing of depositional events recorded during previous genetic stratigraphic studies in the North West Shelf. The tectonic nature of super-cycle scale events should be temporally and spatially assessed in detail before the effects of eustatic change are evaluated for rift-related successions of the North West Shelf. The problem can be further exacerbated when the absolute error of chronological dating exceed the temporal frequency of eustacy, causing tenuous correlations of depositional events to a global eustatic curve.

Third-order Middle Miocene-Early Pliocene depositional sequences in the prograding delta complex of the Pannonian Basin

Few studies exist in the geologic literature that show the distribution of seismic facies and depositional sequences within a lacustrine basin. The Pannonian Basin of Central Europe offers a unique opportunity to evaluate the influence of the eustatic signal on lacustrine deposition. Seismic stratigraphie and sedimentological studies indicate that the Middle Miocene-Early Pliocene infill of the transtensional Pannonian Basin was formed by large delta systems. Systematic sequence stratigraphie analysis of 6000 km of reflection seismic data and more than 100 hydrocarbon exploration wells in Hungary allowed the identification of twelve third-order sequence boundaries in the late Neogene sedimentary fill. This number of depositional sequences corresponds to that of the published global eustatic curve for this time period. Furthermore, based on magnetostratigraphic and radiometric data, the ages of these depositional sequences can be tentatively correlated with the global eustatic curve. The Pannonian Basin became isolated from the world sea at the Sarmatian/Pannonian (11.5 Ma) boundary and formed a large lake. The stratal patterns and sedimentary facies of individual systems tracts within the lacustrine sequences display the same characteristics as marine depositional sequences. The relatively low rate of thermal subsidence and the high rate of sediment supply resulted in a good sequence resolution. Within the third-order sequences higher-order sequences can be recognized with an average duration of about 0.1–0.5 Ma.

LATE JURASSIC-EARLY CRETACEOUS DEPOSITIONAL SYSTEMS OF THE DAMPIER SUB-BASIN-QUO VADIS?

A diminishing prospect inventory based on traditional structural targets, has placed increasing emphasis upon finding commercially viable stratigraphic traps. This is especially true in the Dampier Sub-basin where recent drilling has identified at least twelve depositional sequences within the Late Jurassic to Early Cretaceous succession. These sequences document a far more complex Late Jurassic to Early Cretaceous sedimentary history than previously acknowledged using traditional litho-stratigraphic mapping techniques. Use of a chronostratigraphic framework to develop Late Jurassic and Early Cretaceous systems tract models, reveals that several repetitive facies suites may be penetrated by the drill, depending on geographic location and frequency of lowstand events. These models have profound implications for prediction of Late Jurassic to Early Cretaceous submarine fan systems, their potential reservoir distribution, and sealing capacity for hydrocarbon entrapment.At least eight lowstand events have been recognised in the Oxfordian to Tithonian sequence alone, associated with both synrift crustal extension and/or related fluctuations in global-eustatic sea level. During these lowstand episodes, huge volumes of coarse clastics were transported by mass-flow into the Lewis Trough with sediment transport of some 5–40 km. The magnitude of shelf-margin tectonic instability, sediment supply, and relative sea level change, controlled the geometry of submarine fan complexes that developed within each lowstand depositional cycle. In general, earlier (Oxfordian) basin-floor sand cycles comprise mixed channel-fill and submarinefan lobe moundforms confined to the Lewis Trough. Following collapse of the Madeleine intra-basinal high in early Kimmeridgian times, these earlier channelised lobes were progressively replaced by more widespread, massive, detached, non-channelised basin floor lobes, which became dominant by end-Tithonian time. The Early Cretaceous succession comprises mainly transgressive-highstand shelf to slope sediments, heralding a change from synrift lowstand to post-rift highstand depositional cycles.Sequence boundaries identified in the Dampier Sub-basin demonstrate a remarkable synchroneity with the worldwide global-eustatic curve, suggesting that a symbiotic relationship may exist between major tectonic events and third-order eustatic cycles, at least within the synrift section of the Dampier Sub-basin.

A Comparison of Tectonic and Eustatic Control on Maastrichtian Depositional Sequences, South-Central Wyoming: ABSTRACT

Timing and geometry of Maastrichtian third-order sequences and systems tracts of south-central Wyoming were mostly controlled by rapid basin subsidence resulting from thrust loading of foreland basin crust. The basement of the Red Desert/Washakie basin was affected by thrusting in the Sevier belt to the west and by thrusting along the edge of the Wind River Mountains and Granite Mountains. A transgressive systems tract consists of the youngest Ericson Formation above a regional unconformity, backstepping Almond Formation nearshore and nonmarine facies, and shelfal mudstones of the lower Lewis Shale. Regionally, the onset of transgression is younger from east to west, beginning at 71.5 Ma in eastern Wyoming and at 70.5-71 Ma in south-central Wyoming. The transgression culminated in a condensed shale section evident on gamma-ray logs that occurs throughout the basin. Above the gamma-ray zone, the highstand systems tract of the middle and upper Lewis Shale, Fox Hills Sandstone, and Lance Formation consists of an aggradational/progradational interval overlain by a dominantly progradational clastic unit. Depositional environments consist of delta, slope, and submarine fan in the Lewis Shale, shoreface and shallow marine in the Fox Hills Sandstone, and nonmarine facies in the Lance Formation. Tectonic control of sequences is indicated bymore » two lines of evidence. (1) The timing of the transgressive, regressive, and condensed section facies does not correlate with the inferred global eustatic curve. The Lewis Shale condensed section occurs at 70.5 Ma and is older than the closest global condensed section at 69.5 Ma. (2) Subsidence, estimated by the amount of delta aggradation of the Lewis, totals 700 m roughly 0.5 Ma and greatly exceeds the 40 m of eustatic rise hypothesized to have occurred at about the same time.« less

Marginal faunal belts and their structural implications, with examples from the Lower Palaeozoic

Fossils provide an independent criterion for testing structural hypotheses generated from field evidence or geochemistry, as well as functioning in their traditional role in the dating of rocks or determining biogeographic realms. On a global scale, the identification of exterior, oceanic biofacies may be of use in discriminating the course of former continental margins. The isograptid graptolite biofacies (Early to Middle Ordovician) can be distinguished from contemporary epicratonic graptolite biofacies; its worldwide occurrence corresponds with continent margins reconstructed from other criteria. Hence a new isograptid record from Irian Jaya (E New Guinea), although based on a small sample, suggests that there may have been an Ordovician oceanic site there. On a continental scale, the tectonic juxtaposition of different biofacies, or of different stratigraphical packages, contributes to an understanding of tectonics and can serve to quantify displacement: the accretionary prism hypothesis for the Southern Uplands of Scotland is supported and contrasted with the rearrangement of biofacies in the Cambro–Ordovician Cow Head Group of western Newfoundland which reveals not only the original shelf-margin–slope topography (now vanished), but also provides an estimate of the movement involved in the emplacement of one Taconic allochthon. On a more local scale, faunal evidence is used in assessing the original position of 'suspect' marginal areas, using the simplest possible model. This shows, for example, that Anglesey was not greatly separated from Gondwana in the early Ordovician—but strike-slip movement cannot be disproved. Local changes in relative sea-level are determinable from sediments and faunas; in marginal belts these may differ from the global eustatic curve, and when this happens it is a measure of local tectonic activity. Particular sea-level curves may serve to define structurally coherent units within mobile belts. New sea-level curves are contrasted for a segment of N Wales (north of the Bala fault) with that for central SW Wales (Arenig–Llandovery); the S Welsh area mostly responded passively to the eustatic curve, which can adequately account for shifts in facies and faunas, while N Wales had a curve often at odds with eustasy and reflecting its structural history.