Timing Of Sea-level Changes Research Articles

COMPARISON OF THE GLOBAL ONLAP CURVE AND SEA-LEVEL CHANGES WITH TIMING OF UNCONFORMABLE SEQUENCE BOUNDARIES FORMATION OF A PALEOCENE SUCCESSION, SIRTE BASIN, LIBYA

The Paleocene sedimentary successions in the NW Sirte Basin in north central Libya have complex stratigraphic architecture and internal configuration. This stratigraphic architecture can provide information on timing of sea-level changes and associated onlaps. Therefore, this study uses the formation timing of the sequence boundaries separating between the stratigraphic sequences and correlate it with the global online curve and global sea-level changes. The number of sequences recognized in the Paleocene succession of the studied platform matches the number of third-order cycles, indicating that each sequence represents a single thirdorder cycle and was created as a consequence of one thirdorder cycle of sea-level fluctuation.

Tectonic Influence on Changes in Neogene Sediment Supply, Western Part of North Serayu Basin

Western part of North Serayu Basin composed of Neogene sequence; Halang, Pemali and Rambatan Formation. The oil seeps discovery in this area is an indication of the presence an active petroleum system. Active tectonic condition occur coincidence with the time of deposition. The tectonic influence on change in sediment supply will be the subject of this research. The combinations of subsidence, eustatic and sediment supply are corresponding to the accommodation space, moreover to the type of sediment which is deposited. The quantity and rate of sediment supply to the basin are closely related to the tectonic activity. In the context of Petroleum Potential, study of sediment supply will provide information about the potential source rock, reservoir and caprock that developed in the research area. During the Neogene at least there have been three times of sea level change in the research area which is related to thickening sedimentary sequence during middle of N18 and thinning in N13 to N17 in some place.

Quantifying rates of change in ocean conditions with implications for timing of sea level change

The importance of southern hemisphere driven climate change is increasingly recognized in paleoclimate research. This is in particular relevant with regard to the rate of climate change initiated in the southern hemisphere and the phasing thereof compared to climate variability elsewhere. Here, we use previously published benthic oxygen isotope data from two deep sea sediment cores from the deep N-Atlantic and the intermediate depth Indian Ocean to quantify rates of oceanic change at the millennial-scale. The oxygen isotope data represent an integrated signal of temperature and global sea level changes. At both locations the sea surface ocean records strongly resemble Greenland climate change. When used to synchronize these surface ocean records with the GISP2 ice core chronology we show that the highest rates of change in the benthic oxygen isotope records, occur during late marine isotope stage 5 (MIS 5), MIS 3 and the last deglaciation, whilst generally modest rates of change prevail during the full glacial conditions of MIS 2. The synchronous variation of oceanic rates of change and Antarctic climate history suggests that the benthic oxygen isotope records from the glacial deep N-Atlantic and the intermediate Indian Ocean reflect variations in southern sourced Antarctic Bottom Water (AABW) and Glacial Antarctic Intermediate Water (GAAIW) respectively. Millennial-scale temperature variations in GAAIW are larger than in AABW. The repeated rapid heat storage in GAAIW during northern hemisphere cold phases points to an important role of GAAIW, potentially acting as an energy buffer, maintaining the pole-to-pole climate imbalance as part of the bi-polar seesaw. Combining the benthic oxygen isotope records with independent sea level records shows a pulsed sea level rise history during the deglaciation with conservative estimates of peak rates change of about ~ 2 m/100 yr. Similar rates of sea level change occurred during most Heinrich Events.

Mid-Turonian to Coniacian changes of sea level around Dallas, Texas

Improved dating by ammonites and inoceramids of the upper part of the Eagle Ford Shales (Middle and Upper Turonian) and the lower part of the Austin Chalk (top Turonian to Coniacian) in the Dallas area has given more accurate timing of sea-level changes. The broad rise in sea level from the Turonian into the Coniacian was a Texan tectonic effect. Individual regressive troughs, in cycles of the order of 100 kyr to 1 myr, seem to be a mainly eustatic effect. The pattern is very different from that over the San Marcos Arch in central Texas.

Direct Determination of the Timing of Sea Level Change During Termination II

An outcrop within the last interglacial terrace on Barbados contains corals that grew during the penultimate deglaciation, or Termination II. We used combined 230Th and 231Pa dating to determine that they grew 135.8 +/- 0.8 thousand years ago, indicating that sea level was 18 +/- 3 meters below present sea level at the time. This suggests that sea level had risen to within 20% of its peak last-interglacial value by 136 thousand years ago, in conflict with Milankovitch theory predictions. Orbital forcing may have played a role in the deglaciation, as may have isostatic adjustments due to large ice sheets. Other corals in the same outcrop grew during oxygen isotope (delta18O) substage 6e, indicating that sea level was 38 +/- 5 meters below present sea level, about 168.0 thousand years ago. When compared to the delta18O signal in the benthic V19-30/V19-28 record at that time, the coral data extend to the previous glacial cycle the conclusion that deep-water temperatures were colder during glacial periods.

A 300 000-yr coral reef record of sea level changes, Mururoa atoll (Tuamotu archipelago, French Polynesia)

The accurate dating of fossil coral reefs is of prime importance in determining the timing of deglaciation events and thus understanding the mechanisms driving glacial–interglacial cycles. So far, the most useful coral reef records of past sea level changes are those related to the last deglaciation and the Last Interglacial period. U/Th ages for older isotopic stages are more limited, due to the scarcity of datable material, reflecting diagenetic alteration. Most data are from emergent parts of reefs and reef terraces in active subduction zones where relative sea level records may be biased by variations in rates of tectonic uplift. New constraints on sea level changes over the past 300 000 yr are based on high-precision U-series age measurements of successive reef units on Mururoa. These have been cored in four continuous 300-m-long drill holes with seaward inclinations of 30 to 45° on the northeastern rim of the atoll. Past sea level positions have been calculated from the radiometric ages of corals by correcting the present depth of subsurface horizons both for thermal subsidence and for depositional palaeodepth. The location of this atoll at a considerable distance from former ice sheets (‘far field’) minimises the influence of glacio–isostatic rebound. Prominent units formed during four periods of relative sea level highstands, including the Holocene and stages 5 (∼125 ka), 7 (∼212 ka) and 9 (∼332 ka). These are primarily composed of coralgal frameworks that grew in very shallow water. Three periods of relative low stand correspond to stages 2 (∼17–23 ka), 4 (∼60 ka) and 8 (∼270 ka) during which small reefs developed in association with large bioclastic accumulations. Good agreement with the timing of sea level changes based on oxygen isotope measurements in deep-sea cores is noted for most of the dated reef units. We report here the first accurate coral record of the Last Glacial Maximum in the Pacific, 135–143 m below the present sea surface, suggesting that sea level may have been lower than expected during this period.

Maps of Pleistocene sea levels in Southeast Asia: shorelines, river systems and time durations

AbstractAimGlaciation and deglaciation and the accompanying lowering and rising of sea levels during the late Pleistocene are known to have greatly affected land mass configurations in Southeast Asia. The objective of this report is to provide a series of maps that estimate the areas of exposed land in the Indo‐Australian region during periods of the Pleistocene when sea levels were below present day levels.LocationThe maps presented here cover tropical Southeast Asia and Austral‐Asia. The east–west coverage extends 8000 km from Australia to Sri Lanka. The north–south coverage extends 5000 km from Taiwan to Australia.MethodsPresent‐day bathymetric depth contours were used to estimate past shore lines and the locations of the major drowned river systems of the Sunda and Sahul shelves. The timing of sea level changes associated with glaciation over the past 250,000 years was taken from multiple sources that, in some cases, account for tectonic uplift and subsidence during the period in question.ResultsThis report provides a series of maps that estimate the areas of exposed land in the Indo‐Australian region during periods of 17,000, 150,000 and 250,000 years before present. The ancient shorelines are based on present day depth contours of 10, 20, 30, 40, 50, 75, 100 and 120 m. On the maps depicting shorelines at 75, 100 and 120 m below present levels the major Pleistocene river systems of the Sunda and Sahul shelves are depicted. Estimates of the number of major sea level fluctuation events and the duration of time that sea levels were at or below the illustrated level are provided.Main conclusionsPrevious reconstructions of sea‐level change during the Pleistocene have emphasized the maximum lows. The perspective provided here emphasizes that sea levels were at their maximum lows for relatively short periods of time but were at or below intermediate levels (e.g. at or below 40 m below present‐day levels) for more than half of each of the time periods considered.

Terrestrial organic carbon accumulation on the Amazon deep sea fan during the last glacial sea level low stand

Sediment cores from the Amazon deep sea fan recovered during R/V Meteor cruise 16-2 show in detail the modern areal distribution of sedimentary organic carbon, stable organic carbon isotopes of the organic matter (OM), as well as variations in the depositional processes. In addition, we studied up to 300 m long drilled sediment records recovered during ODP Leg 155 which allow evaluation of temporal variations on the Amazon fan. Our results reveal new evidence for a very rapid change of fan depositional processes and organic carbon source at times of sea-level change over the middle and lower Amazon fan. To estimate the amount of terrestrial organic carbon stored in sediments from the last glacial in the Amazon fan we used stable organic carbon isotopes of the OM (δ13Corg), organic carbon content (Corg), and age models based on oxygen isotopes, faunal data, and magnetic excursions. Following our results, the organic carbon accumulation on the Amazon deep sea fan is controlled by glacio-eustatic sea-level oscillations. Interglacial sea-level high stand sediments are dominated by marine OM whereas during glacial sea-level low stands terrestrial organic carbon is transported beyond the continental shelf through the Amazon canyon and deposited directly onto the Amazon deep sea fan. Glacial sediments of the Amazon fan stored approximately 73×1015 g terrestrial Corg in 20,000 years or 3.7×1012 g terrestrial Corg yr−1 (equivalent to 7–12% of the riverine organic carbon discharge; assuming constant paleo discharge), which is about the same amount of terrestrial organic carbon as deposited on the Amazon shelf today (3.1×1012 g terrestrial Corg yr−1 or 6–10% of the modern riverine organic carbon discharge).

High-precision chronostratigraphy of a late Pleistocene shelf-edge delta, Louisiana

ABSTRACT The accurate dating of depositional sequences and sea-level changes is essential in the search for hydrocarbons and in the study of global climatic changes. Graphic correlation is a precise and accurate technique that integrates diverse types of time-significant data and compares the events in a new section with the complete range of those events in a reference data base. Graphic correlation is a quantitative method of analyzing complex data to evaluate and test hypotheses of chronostratigraphy. During the Late Pleistocene glacio-eustatic lowstands, sand-prone deltas were deposited at the Louisiana shelf edge. Regional seismic stratigraphic boundaries traced on the seismic data have been tied to important sequence stratigraphic contacts in four coreholes on the outer shelf and upper slope. Fossil abundances and diversities contributed to the interpretation of depositional systems tracts. The ages of these contacts are dated by the graphic correlation integration of fossil tops and oxygen isotope events in two of the cores. Four regional unconformities and five transgressive surfaces were cored in two wells within the uppermost 250 m of section on the shelf margin and upper slope. These contacts were graphically correlated with a composite standard reference section containing oxygen isotope events dated in deep-sea cores (DSDP 502, 552A, 572, ODP 607 and 625). Lowstand events are dated at 332 ka, 254 ka, 168 ka, and 70 ka. Transgressive sea-level-rise events are dated at 475 ka, 313 ka, 209 ka, 125-133 ka, and 14-16 ka. These data define the timing of sea-level changes recorded southeast of the ancestral Mississippi River. The timing of these events compares with sequence boundaries elsewhere in the Gulf of Mexico dated at 400 ka, 200 ka, and 90 ka by Martin et al. (1993). The differences in ages may be a result of the incompleteness of the sediment preserved at each site. Although the sequence boundaries record glacio-eustatic events, their timing is not periodic and does not represent a single Milankovitch frequency. This seeming inconsistency may be a clue to the influence of complex sedimentary processes. Perhaps not all the events have been recorded in this section. Application of continental glacial stages to these events is not recommended.

Protactinium-231 Dating of Carbonates by Thermal Ionization Mass Spectrometry: Implications for Quaternary Climate Change

Measurement of protactinium-231 (231Pa) in carbonates by thermal ionization mass spectroscopy yields 231Pa ages that are more than 10 times more precise than those determined by decay counting. Carbonates between 10 and 250,000 years old can now be dated with 231Pa methods. Barbados corals that have identical 231Pa and thorium-230 (230Th) ages indicate that the timing of sea level change over parts of the last glacial cycle is consistent with the predictions of the Astronomical Theory. Two Devils Hole calcite subsamples record identical 231Pa and 230Th ages, suggesting that the chronology of this climate record is accurate.

Shallow water facies during the Cenomanian-Turonian anoxic event: bio-events, isotopes, and sea level in southern Germany

The sediments, palynofacies, macrofossils, planktic and benthic foraminifera, radiolaria, ostracoda, stable carbon and oxygen isotopes (whole rock and inoceramid prisms) of the hemipelagic Eibrunn Marls at the northern Tethys margin were studied in the Mühlberg section of the Regensburg area, southern Germany. The biotas reveal extinction and origination events that are known elsewhere, although other species may be involved. The palaeontological evidence suggests a control of global changes on the biotas (macroevolutionary impact of the Oceanic Anoxic Event), rather than changes in the local environmental conditions. Carbon isotopes of inoceramid prisms do not reflect the standard isotope stratigraphy; differences in vital effects between Inoceramusand Mytiloidesprobably dominate the isotopic composition. Ridge facies (conglomerates, cliffs, erosional platforms) in Saxony (southeastern Germany) provide evidence of the timing of sea-level changes. The ∂ 1 3C values increase through the section representing a late Cenomanian, long-term sea-level rise, and have a maximum when widespread flooding occurs. Marine erosion (nutrient mobilization) during a long-term sea-level highstand that exceeded previous highstands may have supported higher productivity during the Cenomanian-Turonian Oceanic Anoxic Event, and potentially during other widespread anoxic events in the Mesozoic. Organic matter remineralization may have lead to more acidic bottom waters that reduced carbonate preservation, and amplified the ∂ 1 3C excursion through carbonate dissolution.

Synrift Continental to Marine Depositional Sequences, Tertiary, Gulf of Aden, Yemen

ABSTRACT Tertiary synrift deposits along the northern margin of the Gulf of Aden, Republic of Yemen, provide new information on the controls on deposition and stratigraphic relationships during the transition from continental to marine rift sedimentation. Intracontinental rifting in the region commenced in the Oligocene, developing into a marine extensional margin in the Miocene. The outcropping part of a small subbasin at Wadi Hiru, west of Mukalla, contains carbonate platform, alluvial-fan, fan-delta, and raised-beach deposits that record the development of the rift margin. The spatial relationships between carbonate and clastic units, their location adjacent to rift-border faults, and timing of sea-level changes indicate that tectonics was the overriding control on relative sea-level change . Accommodation space created by fault movement and the morphology of older sediment bodies dictated the three-dimensional architecture of carbonate platforms and clastic fans. Fault movements are documented by changes in clast provenance in fanglomerates. Rift-parallel and rift-perpendicular faults formed a trap-door configuration that controlled long-lived pathways of terrigenous clastic supply throughout rifting. Five local depositional sequences, bounded by erosion surfaces, are recognized. Sequences have a distinct tectonic signature in the form of sequence boundaries overlain by thick fanglomerates followed by transgressive and highstand carbonates. Two of these sequences were dated using 87Sr/86Sr isotope dating. The relative sea-level curve derived from thi study bears little relationship to published eustatic curves.

Does Sequence Stratigraphy Need Biostratigraphy?: ABSTRACT

Abstract The sequence stratigraphy methodology integrates diverse geophysical and geological data sets, which has revitalized both geoscience disciplines. Biostratigraphic data has become essential to the geological interpretation of seismic record sections. Quantitative analyses of fossil abundances, diversities and ranges provide important data for the definition and constraint of hypotheses of sequence stratigraphy. Within carbonate platforms sequence boundaries may separate similar facies and so be difficult to recognize. For example, regional unconformities within skeletal limestones of the Silurian-Devonian Hunton Group in Oklahoma were first clearly defined by means of the biofacies and extinctions. Within mixed siliciclastic and carbonate facies successions the subtle changes in biotic associations define the stacking pattern. Quantitative biotic analyses of the Midcontinent Pennsylvanian cyclothems constrain the depth limits of the cyclothem members. The timing of sea level changes and their correlation within and between basins is essential for distinguishing the relative effects of basinal tectonics and eustasy. Mid-Cretaceous transgressive and regressive depositional cycles in the Denver Basin can be correlated precisely with shoaling-deepening cycles in the East Texas Basin. The consistent delineation of depositional or seismic sequences depends upon the successful integration of biostratigraphic, geochemical and petrographic data with well log and seismic data.

Biostratigraphic Expression of Pleistocene Sequence Boundaries, Gulf of Mexico

The quaternary section west of the Mississippi River delta consists of thousands of meters of terrigenous sediments, but the stratigraphic and paleoclimatic history recorded in these sequences is often distorted as a result of salt and shale diapirism. Quaternary sequences of the western Gulf of Mexico often reflect highly variable sediment accumulation rates within and between isolated salt-withdrawal basins and missing section resulting from unconformities and extensive faulting. The sedimentary record of Ocean Drilling Program's Core 625B (northeast Gulf of Mexico) contains significant unconformaties that represent a record of sea-level change during the Pleistocene. The core may thus serve as a standard for timing of sea-level changes of the Western Gulf. Utilizing primarily relative abundances of the warm-water Globorotalia menardii complex and cool water G. inflata, we have subdivided the pre-zone W Pleistocene of Core 625B into 17 subzones, resulting in an average duration of approximately 100,000 years per unit. Based on graphic correlation, subzonal boundaries are largely coeval between sites and can provide high-resolution biostratigraphic subdivision of the Pleistocene of industrial wells on an operational basis. Also, the subzonation delineates anomalous paleotops that are reworked, erosionally truncated at sequence boundaries or delta-depressed as a result of localized sediment influx.more » Graphic correlation of subzonal boundaries coupled with available biostratigraphic and magnetostrategraphic datums has demonstrated the near synchronomy of subzonal boundaries and their utility in the subdivision of the Pleistocene. Using graphic correlation, the paleontologist can build viable exploration models that can be used to predict the occurrence of hydrocarbon reservoir sands. 87 refs., 13 figs.« less

Sea-level changes and the evolution of benthic marine calcareous algae during the Palaeozoic

Maximum spreads of epicontinental seas in the area now covered by the USSR correlate closely with major periods of diversification of benthic calcareous algae (especially chlorophytes and rhodophytes) during the early-middle Ordovician and the late Devonian-early Carboniferous. This is consistent with the 'species-area' concept of direct relationship between taxonomic diversity and habitat-size. The shape of the Earth's hypsometric curve makes it likely that continental flooding would enlarge the area habitable by benthic algae more than it would for benthos not limited to the photic zone, thus enhancing the species-area effect for algae at times of sea-level change. In contrast, the first occurrence of calcareous algae near the Precambrian-Cambrian boundary does not seem to correlate with a transgressive maximum. Cyanophytes are the main calcified group appearing in the early Cambrian and it is possible that their occurrence at this level reflects a different factor which resulted in the calcification of pre-existing algal groups.