Development Of Stratigraphic Sequences Research Articles

A million-year-scale astronomical control on Late Cretaceous sea-level

An evaluation of the global synchronicity and duration of rd sea-level fluctuations during the Cretaceous greenhouse has been hampered by poor constraints on potential climatic and tectonic drivers, and limitations of geochronology and chronostratigraphic correlation. To provide insight into the na- ture of such sea-level fluctuations, here we present a new Late Cretaceous record from the Jordanian Levant Platform, comprising a detailed physical-, bio-, chemo- and sequence stratigraphy. Carbonate content of these strata reflects overall sequence stratigraphic development, and demonstrates a dramatic 3 rd -order-scale cycle that is also apparent in the δ 13 C record. Updated radioisotopic constraints and astrochronologic testing pro- vide support for the inference of an ~ 1 million year long sea-level oscillation associated with this 3 rd -order cycle, which likely reflects a long-period obliquity (1.2 Myr) control on eustasy and stratigraphic sequence development, linked to the global carbon cycle. The observation of cyclic sea-level fluctuations on this time scale suggests sustained global modulation of continental fresh-water-storage. The hypothesized link between astronomical forcing and sea-level forms a baseline approach in the global correlation of sequence bound- aries.

Chemostratigraphy in the Swedish Upper Ordovician: Regional significance of the Hirnantian δ13C excursion (HICE) in the Boda Limestone of the Siljan region

Samples from the Boda Limestone and immediately overlying strata at Osmundsberget in the Siljan region have produced an excellent Hirnantian isotope excursion (HICE) curve, in which the excursion interval is about 22 m thick and the HICE reaches maximum δ13C values of between +5‰ and +6‰. Both the HA and HB stratigraphic unconformities are recognized in the study succession as well as in the coeval stratigraphic interval in the Loka Formation in Västergötland and at Meifod in central Wales. A comparison between these and some other shallow-water successions in North America and northern Europe shows striking similarities in the δ13C curve, the lithology, and the stratigraphic sequence development. This is taken as support for the idea that glacio-eustacy exercised a major control on the depositional pattern in shallow-water successions during Hirnantian time. This applies also to the Osmundsberget succession where the formation of carbonate mounds was stopped by the HA regression that was caused by a major glaciation in Gondwana.

Tectonism: the dominant factor in mid-Cretaceous deposition in the Jeanne d'Arc Basin, Grand Banks

The development of stratigraphic sequences has been demonstrated to be controlled by a set of factors including variations in subsidence, sediment input, eustatic sea level and physiography. Well and seismic data from the Jeanne d'Arc Basin, Grand Banks indicate that mid-Cretaceous tectonism controls at least three of these factors, namely subsidence, sediment input and physiography. North Atlantic rift tectonism was therefore the dominant factor in controlling the migration of coastal to shallow marine environments and the development of sequence stratigraphy in this basin during the mid-Cretaceous. The Avalon Formation respresents a mainly Barremian to Early Aptian regressive phase of clastic, marine to marginal marine sedimentation. This followed the deposition of a thick sequence of mainly marine limestones and shales of the Whiterose Formation above a mid-Valanginian sequence-bounding unconformity. The increased clastic input and northward progradation of coastal environments represented by the Avalon Formation occurred during uplift of a basement arch to the south with subsidence of the basin increasing to the north, accompanied by only relatively minor faulting. These features indicate that a period of epeirogenesis was initiated during the Barremian. Continuing uplift over an expanding area at the southern end of the basin is interpreted to have resulted in the development of an angular unconformity with incised valleys. This mid-Aptian unconformity defines the top of the Whiterose/Avalon sequence. Initiation of brittle fracturing of the sedimentary package and underlying basement (i.e. rifting) in mid-Aptian times resulted in rapid fault-controlled subsidence and fragmentation of the Jeanne d'Arc Basin. This great increase in subsidence rate caused retrogradation of coastal environments across the previously developed sequence-bounding unconformity, despite continuing high rates of sediment input from the uplifted basin margins. The transgressive, siliciclastic Ben Nevis Formation comprises two separate but related facies associations. A locally preserved basal association represents interfingering back-barrier environments and is herein defined as the Gambo Member. An upper, ubiquitous facies association comprises tidal-inlet channel, shoreface and lower shoreface/offshore transition sandstones. This upper facies association onlapped marine ravinement diastems above the laterally equivalent back-barrier facies. The rapid fault-controlled subsidence and high sediment input rate of this mid-Aptian to late Albian rift period resulted in the accumulation and preservation of very thick shoreface sandstones. The transgressive sandstones were buried by laterally equivalent offshore shales of the Nautilus Formation. Flooding of the basin margins induced by the onset of thermal subsidence in latest Albian or early Cenomanian times marks the top of the Ben Nevis/Nautilus syn-rift sequence.

Tectonic and bathymetric controls on stratigraphic sequences within evolving half-graben

Abstract A modification of the domino fault block model is presented, which can be used to evaluate possible tectonic controls on the development of stratigraphic sequences within an evolving half-graben. The model allows average half-graben load to vary with time and allows the rate of faulting to be varied relative to any background component of basin subsidence. The basic domino model predicts only transgressive sequences at the crests of tilted fault blocks. It is found with the modified model that a decreasing average half-graben load (increasing bathymetry) or an increasing strain-rate may induce offlap and regression at the fault block crest. The model is used here successfully to model the syn-rift stratigraphy of a tilted fault block in the Viking Graben (North Sea). It is believed to have general implications for evaluating the syn-rift and early post-rift history of extensional basins. The internal geometry of condensed and unconformable sequences at fault block crests may lie below the limit of seismic resolution. This calls into question the ability of the seismic stratigraphic technique to address successfully the full history of an evolving half-graben.

Hierarchical Stacking Geometries of Genetic Sequences: Implications for Predicting Geometry and Distribution of Reservoir Facies Tracts: ABSTRACT

Stratigraphic successions representing marine shelf to coastal-plain environments are successfully simulated by numerical models. The models are based upon the fundamental controls governing the development of stratigraphic sequences and stratal architecture in sedimentary basins: eustatic fluctuations, tectonic movement, quantity of sediment delivered to a basin, sediment compaction, and isostatic compensation. The models show that the fundamental building block of marine shelf to coastal-plain stratigraphic sequences is the progradational event. Packages of lithologically diverse but temporally equivalent strata deposited during a progradational event are termed genetic sequences. Genetic sequences are arranged systematically in three geometric patterns. Relative to the direction of progradation, these are forward-stepping (seaward), backward-stepping (landward), and vertical stacking. Accompanying these geometric patterns are changes in thickness and lateral extent of similar facies tracts within separate genetic sequences. Shoreface sands are thin and widespread in forward-stepping phases, thick and laterally restricted in vertically stacked phases, and very thin and laterally restricted in vertically stacked phases, and very thin and laterally restricted in backward-stepping phases. By contrast, facies representing fluvial and coastal-plain environments are thickest in backward-stepping phases and thinnest in forward-stepping phases. Different styles of fluvial architecture also are a direct response to the position of a genetic sequencemore » within the hierarchical stacking pattern. Thick, multistoried channel belt sands occur din backward-stepping phases, and thin, multilateral channel belt sands occur in forward-stepping phases.« less