Glacio-eustatic Cycles Research Articles

Sediments and history of the Rottnest Shelf, southwest Australia: a swell-dominated, non-tropical carbonate margin

The Rottnest Shelf is a narrow, wave-dominated open shelf on the passive continental margin of southwest Australia, adjacent to a hinterland of low relief and sluggish drainage. High physical energy, low nutrients in cool subtropical waters, and rapid postglacial transgression have limited carbonate productivity, restricted grain types, and reworked the transgressed surface to form only a thin (< 1 m) blanket of carbonate and relict sediment, with little terrigenous influx. Subaerial weathering of the shelf during Late Pleistocene emergence was followed by postglacial drowning, erosional shoreface retreat, and generation of a transgressive lag deposit. Establishment of the warm temperate biota, dominated by bryozoans and calcareous red algae, resulted in bioerosion of the shelf disconformity surface and generation of hardground veneers and thin skeletal carbonate sheets. Linear topographic ridges of Pleistocene limestone partition the shelf into systems with varying physical energy, biota and sediment supply. The Holocene sediments are a shallowing-upward coastal sequence; wave-ripple cross-stratified grainstone (Inner Shelf); and bioturbated bryozoan grainstone to skeletal wackestone (Outer Shelf to Upper Continental Slope), characterised by seaward fining and increasing percentages of planktic carbonate sediment. Given sufficient time, the Rottnest Shelf could recover from drowning, and form blanket-like skeletal carbonates. Thin (< 1 m) lags overlying disconformities, which underlie shallowing-upward coastal and shelf sediments a few metres thick, will be generated by glacio-eustatic cycles of sedimentation (10 5 y duration). Thick (several tens of metres) sediment bodies, composed of wave-rippled to bioturbated skeletal carbonate sediment with a temperate biota, will be formed during longer term (1–10 My) sedimentation cycles. Such cycles have characterised passive margins during the Cenozoic. The Rottnest Shelf thus provides a facies model for temperate shelf sedimentation along passive continental margins.

Isotope Chronostratigraphy: High-Resolution Stratigraphic Correlations in Deep-Water Exploration Tracts of Northern Gulf of Mexico: ABSTRACT

ABSTRACT On-going stable isotope research with cuttings from over 16 Plio-Pleistocene deep-water wells has established a high-resolution framework for chronostratigraphic tie-lines between Plio-Pleistocene wells. Detailed oxygen isotope (O-18/O-16) records from core material and sixteen exploration wells at 30 intervals provide a large data base by which to establish a chemical stratigraphy record for the Gulf of Mexico. This type section is used to evaluate the stratigraphic integrity of exploration wells and the timing and reliability of important calcareous nannofossil and foraminiferal biostratigraphic datums. Within this framework, freshwater discharge events and local/regional unconformities can be defined with high precision. The record can be used to relate large-scale and fine-scale changes in 1) sediment accumulation rates, 2) the distribution of sand-shale facies, and 3) seismic sequence boundaries of glacio-eustatic cycles. Integration of this information can lead to a more precise definition of the timing and extent of target sand bodies in deep-water exploration tracts.

Glacioeustatic cycles in the Early Jurassic?

Glacioeustatic cycles in the Early Jurassic?

New Zealand Pleistocene and late Pliocene glacio-eustatic cycles

A correlation diagram relates the numbered oxygen isotope stages of Shackleton and Opdyke's oxygen isotope curve for core V28–239, as extended by Gardner, to Nukumaruan, Castlecliffian and younger sedimentary cycles in Hawke's Bay, southern Wairarapa, and Wanganui districts and to the flight of marine terraces (Castlecliffian and younger) recognised by Pillans near Wanganui. Local correlation is principally by biostratigraphy, but also by lithostratigraphy and fission-track dates on tephras. Important calcareous nannofossil datums for both local and international correlation are: (1) FAD of Gephyrocapsa sinuosa in the mid-Nukumaruan of the New Zealand region, both in DSDP site 284, just above the (base Olduvai) LAD of Discoaster brouweri, and in three on-land sequences (within the Olduvai at Mangaopari Stream); (2) LAD of Pseudoemiliania lacunosa, during isotope stage 12, last known in the Castlecliffian Upper Kai-Iwi Siltstone at Wanganui; and (3) FAD of Emiliania huxleyi during isotope stage 8, and recorded tentatively from the Waipuna Delta Conglomerate (Ngarino Terrace cover beds; Hawera Series) near Wanganui. Magnetic polarity is also used for external correlation. Most of the prominent oxygen isotop events in core V28–239 are inferred in New Zealand on-land sequences (about twenty cycles). The Wanganui area demonstrates an apparently unique occurrence of coeval marine terrace deposits and offshore marine rocks representing all major high sea levels between isotope stages 11 and at least 17. Nukumaruan sedimentary cycles recognised in eastern North Island are relatively complete, most inferred glacial periods being represented by shallow marine strata. In contrast, Castlecliffian and younger marine sedimentary cycles in southwestern North Island are less complete, each inferred interglacial deposit being bounded by disconformities. The difference between Nukumaruan and younger sedimentary cycles possibly supports the hypothesis of an increase in the amplitude of sea-level change about a million years ago. The Pliocene/Pleistocene boundary lies above the middle of the New Zealand Nukumaruan Stage.

Glacio-Eustatic Sedimentary Cycles in Trenton Limestone (Middle Ordovician) of Southern Ontario: ABSTRACT

The fully-developed ideal cycle consists of the following, from base to top, always with calcareous clay seams throughout. (a) Coarse, poorly sorted intrabiosparite or biosparite grainstones, in crosscutting (often cross-stratified) lenses, or channelized. In places, grain flow is shown by lobate, steep-sided edges, often smoothed by well-sorted biosparite grainstones. (b) Fine to medium-grained well-sorted biosparite grainstones, parallel or cross-laminated, usually in several thin beds. (c) Very fine-grained, well-sorted, commonly graded biosparite and biomicrosparite packstones and grainstones, with coarser shell fragments concentrated at their bases. (d) Nodular bioturbated biomicrite mudstones and wackestones, alternating with bioturbated calcareous clays. This unit may also contain lenses of poorly sorted biosparite. Units (a) to (c) show abundant evidence of rapid deposition of individual beds, followed by extensive periods of non-deposition, erosion, or both, when the bed surfaces were burrowed by omission-type trace fossil-forming organisms, cemented, and colonized by attached organisms. The abundant and diverse hardgrounds of the Ordovician sequence are concentrated at these horizons. In the more argillaceous sections, subdued cyclicity occurs. The difficulty of explaining these cycles by normal facies changes has led to a glacio-eustatic explanation. Actualistic comparison can be made with the recent Arabian shelf of the Persian Gulf. End_of_Article - Last_Page 1165------------

Modern and Ancient Coastal Sedimentary Facies, Monterey Bay, California: ABSTRACT

Depositional processes and sedimentary structures in both barred and non-barred nearshore environments of the Pacific Coast vary systematically with water depth. These variations allow the construction of idealized progradational sequences of sediments deposited along a wave-dominated coastline. The idealized sequences are very similar to the vertical sequences of sedimentary structures preserved in Pleistocene marine terrace deposits exposed along the margin of Monterey Bay. The central Monterey Bay coastal region has been a subsiding depocenter for marine, fluvial, and eolian sedimentation throughout the Quaternary. It provides an opportunity to study the role of climatic change (including fluctuating sea level) in controlling patterns of Quaternary sedimentation and terrace formation along the non-uplifted portions of the California coastline. Most of the fluvial sediment in these regions was deposited during intervals of rising sea level, hence is out of phase with marine and eolian sediments deposited mainly during intervals of lowering sea level. In combination, however, these deposits form suites of sediments by which glacio-eustatic cycles can be recognized. Evidence of at least 11 such cycles is present within the Quaternary deposits in the north- entral Monterey Bay region. End_of_Article - Last_Page 440------------

Evolution morphologique des basses vallées de l'Atlas atlantique Marocain

During a great part of the Quaternary period (from the Moghrebian = Plio-Pleistocene to the Ouljian = last Inter-glacial), the stages of cutting prevailed over those of accumulation in the low valleys of the Atlantic Atlas. It is rather difficult to join here continental deposits with the raised ancient sea-shore benches that are found, on the contrary, in many points. By means of those marine terraces, it is however possible to show the stages of uplift of that country : neotec-tonics explained the quickness of cutting in the valleys. After the Ouljian transgression, the correlations between alluvial and marine deposits allow to propose a relative chronology, rather precise. Some continental sediments extend more or less : the dunes (chiefly at the late Ouljian and at the early Holocene), the pink silts (at the late Wiirm) or the coarse alluvial deposits. Their succession cannot be explained by a single climatic or glacio-eustatic cycle. The possible causes of these successions of deposits are discussed and some interpretations and correlations presented here are tentative. difficult to join here continental deposits with the raised ancient sea-shore benches that are found, on the contrary, in many points. By means of those marine terraces, it is however possible to show the stages of uplift of that country : neotec-tonics explained the quickness of cutting in the valleys. After the Ouljian transgression, the correlations between alluvial and marine deposits allow to propose a relative chrono¬ logy, rather precise. Some continental sediments extend more or less : the dunes (chiefly at the late Ouljian and at the early Holocene), the pink silts (at the late Wiirm) or the coarse alluvial deposits. Their succession cannot be explained by a single climatic or glacio-eustatic cycle. The possible causes of these successions of deposits are discussed and some interpre¬ tations and correlations presented here are tentative.