Peter R. Vail

Mesozoic-Cenozoic sequence stratigraphy of European basins

The preliminary results of the project, [open quotes]Mesozoic-Cenozoic Sequence Stratigraphy of European Basins[close quotes] (introduced at a seminar in Dijon, France, on May 18-20, 1992), show that the Mesozoic-Cenozoic stratigraphic succession of western Europe can be subdivided into a series of transgressive-regressive facies cycles (second order, 3-50 m.y.) and related to tectonic events by subsidence analysis and regional geology. The distribution of the second-order cycles are shown on a series of transects that extend from the Mediterranean to the North Sea. Where possible, each transgressive-regressive phase has been subdivided into a series of higher frequency sequence cycles (third order, 0.5-3 m.y.). These sequence cycles are identified in regions with good outcrops and biostratigraphic control. The sequence stratigraphy interpretation of these outcrop sections provides documentation for the age and distribution of the second- and third-order stratigraphic cycles of western Europe. Subsurface seismic and well data from the North Sea Basin, Paris basin, and the Mediterranean area are interpreted in terms of sequence stratigraphy and correlated to the outcrop reference sections. Chronobiostratigraphy and numerical ages are based on a series of new charts made especially for this project that show the latest correlation of the biostratigraphic zones for both microfossils and macrofossilsmorexa0» across Europe. The charts also include a numerical time scale that reconciles the differences between existing time scales.«xa0less

Sequence stratigraphy of the Jurassic: New data from the Paris-London basin compiled on well logs

A sequence stratigraphic analysis of the Jurassic sedimentary succession in Paris basin is derived from an integration of subsurface log correlations, field observations, and reinterpretations of field descriptions. The analysis is presented on two log sections, one crossing the basin from northeast to southwest and the other from northwest to southeast (approximately 80 logs). A vast quantity of field data, collected all around the Parsi basin (English Dorset, French Normandy, Manche, Ardennes, Lorraine, Bourgogne) allowed the sequences and system tracts boundaries to be traced and dated at the same time or prior to being recognized on well log data. In comparison with the Haq et al. 1987 cycle chart, 16 new sequences have been added: three for the Lias, seven for the Dogger, and six for the Malm. Occasionally, ages of some of the already recognized sequences boundaries have been slightly modified to fit new biostratal data. These biostratal data were usually at the scale of the ammonite sub-zone and the actual give ages all tie with the 1987 Haq et al. chart time scale.

Time Stratigraphy from Seismic Data: ABSTRACT

The seismic reflection process expresses the interbedding of sediments as a pattern of seismic cycles which End_Page 367------------------------------ parallel time-stratigraphic bedding surfaces. Changes in rock stratigraphy, that is, lithology and facies, are expressed as changes in seismic parameters such as amplitude and interval velocity; these changes may occur within time-stratigraphic units, or may transgress the pattern of time-stratigraphic zones. Seismic stratigraphy is limited by the resolution of the seismic system and is somewhat complicated by the need to exclude unwanted signals, such as coherent noise patterns. Nevertheless, high-resolution seismic sections are the most powerful tool available to modern stratigraphers. Two studies document the relation of bedding surfaces to seismic reflections. Well log correlations, seismic sections, a seismic model study, and a synthetic seismogram study document time-stratigraphic and rock-stratigraphic relations in Oligocene-Miocene strata in a South American basin. The second study involves a seismic line shot in the western United States across a series of wells spaced about 1 mi apart. Lateral facies changes within interfingering Cretaceous marine and nonmarine sediments demonstrate the continuity of time-stratigraphic surfaces and of reflections across major facies changes. End_of_Article - Last_Page 368------------

Punctuated equilibria plate tectonics and exploration strategies: Examples from Australia and South America

Understanding the interplay between plate tectonic events, subsidence, flexure, and depositional systems is critical to successful exploration, play concept development, and maturation modelling in frontier exploration. Conventional exploration techniques (seismic/well log mapping, geohistory, geophysical, and forward modelling) are used to quantitatively describe the stratigraphic packages observed in basins, but the driving force creating and destroying the packages has typically been qualitatively described as subsidence/uplift events. In order to predict depositional systems patterns, the driving force of these events must be more quantitatively understood. We observe that the tectonic history of plates is characterized by long periods of fairly constant motion interrupted by short events of re- organization ({open_quotes}punctuated equilibria{close_quotes}). We also observe that these events are usually regional in nature and cause changes in regional subsidence patterns. Furthermore, these changes cause changes in major depositional system locations and characteristics. Analysis of-the plate tectonic history of motion predicts times of quiescence and times of rapid change in basin stratigraphy and therefore produce more effective exploration strategies. We have performed integrated sequence stratigraphic analysis in three basins (Barrow/Dampier, Otway, Santos-Pelotas), on two widely displaced continents (Australia and South America), spanning the Cretaceous Period. Although the tectonic histories are different, each basin respondsmorexa0» to its tectonic history in a similar fashion: slow (or negative) subsidence diminishes volume and recognizability of transgressive and highstand systems tract and increases the volume and recognizability of lowstand systems tracts. The alternate case (rapid subsidence) produces the alternate result.«xa0less

Sequence stratigraphic model of the Rio Grande Delta, south west Texas: Potential analog for the Niger Delta

A sequence stratigraphic model developed from the ancient Rio Grande Delta in South West Texas is suggested as an analog for the Niger Delta. The two delta systems are characterized by high sand bedloads, shale diapirism with associated listric normal faulting, and large amounts of tidal and wave influence forming lower coastal plains characterized by swamps and estuaries. The sequence stratigraphic model of the ancient Rio Grande delta is based on approximately 1200 kilometers of single channel, 15 cubic inch water gun data, lithologic descriptions from approximately 25 long cores (28-30 m) located in 17-94 meters water depth, three gamma ray logs, paleontologic data from two cores, and oxygen isotopic data from one core (152 meters in length and located in 94 meters water depth). The combined data indicate that considerable quantities of sand are sequestered on the continental shelf and point sourcing the slope. The Rio Grande sequence stratigraphic model provides an improved understanding of sand deposits on the shelf, of the role of sediment bypass during lowstands, and of the base of slope deposits formed by headward eroding canyons ( ) or channels ( ) located at the shelf break. This information regarding the distribution of sand inmorexa0» the Rio Grande system can provide valuable insight into the reservoir distribution in the Niger system, improving existing reservoir predictions.«xa0less

Tectonic and eustatic controls on facies distribution in the middle of upper Jurassic, Viking Graben, Norwegian North Sea

The Middle of Upper Jurassic in the Viking Graben area was deposited during an overall transgression. From the lower Toarcian to the base of the cretaceous, there are seven 2nd-order (3-5 m.y.) transgressive-regressive (T/R) facies cycles that are related to regional tectonic events. These cycles dominate facies distribution, appear synchronous, and can be correlated throughout the study area. Local tectonics and sediment supply can modify these cycles. Local tectonics, sediment supply, and position in the T/R facies cycles control development of 3rd-order (0.5-3 m.y.) cycles. Where sediment supply is low, 3rd-order sequences are poorly developed. During a 2nd-order regression, shelfal areas and local highs are often eroded. Third-order sequences have well developed lowstands system-Y tracts (LST) and poorly developed transgressive systems tracts (TST). During 2nd-order transgressions, 3rd-order sequences have enhanced TST, starved HST, and poorly developed LST. Thick, stacked, shoreface sandstones may develop in the TST on terraces or on gently dipping slopes if sediment supply is high. The base of these sequences often shows an abrupt basinward shift in facies followed by backstepping facies. turbidites develop during 3rd-order lowstands when there is a steeply dipping slope and high sediment supply, but their distribution is more limited.

Tectonic and stratigraphic evolution of Neuquen Basin, Argentina

Neuquen Basin is a mature basin with a long history of hydrocarbon production. It is the most productive subandean basin of Argentina. It was a Mesozoic backarc basin which evolved into a foredeep basin when a fold and thrust belt was formed to the west in the upper Cretaceous. The sedimentary infill is Permo-Triassic to recent. It is continental and marine in origin and was deposited in a generally shallow, slowly subsiding basin. The main factors that help subdivide the stratigraphy of the basin were relative changes of sea level. Detailed sequence stratigraphic analysis of upper Jurassic to lower Cretaceous marine and continent clastics, carbonates and evaporites allowed to explain the mechanisms by which subtle stratigraphic traps may have been created. The Neuquen Dorsal, a positive east-west structure in the relatively undeformed basin, has been tentatively interpreted as an inversion. This hypothesis must be further analyzed using additional data. Deformation in the fold and thrust belt took place from the Companion to Pliocene, and shows three distinct zones. From east to west a broad arch is followed by an intricate series of tight anticlines formed by both east and west verging thrusts which use four different decollement surfaces. To themorexa0» west of these, a east verging ramp anticlinal structure is identified, which involves a deeper decollement surface.«xa0less

Integrated well-log, seismic, and biostratigraphic approach to sequence stratigraphy in Late Cenozoic expanded sections, Gulf of Mexico

Increased emphasis on well-log signatures and recognition criteria for stratigraphic sequence boundaries, systems tracts, and condensed sections in a sequence-stratigraphic context has enhanced facies interpretation and reservoir prediction capabilities. Integration of well logs with high-resolution biostratigraphy and paleobathymetry, high-quality seismic configuration data, and the latest eustatic cycle chart provides the best data base for sequence-stratigraphic analysis. This approach is particularly effective for thick, rapidly deposited slope and basin sediments, such as in the Plio-Pleistocene of the Gulf of Mexico basin. The general sequence-stratigraphic model consists of a depositional sequence with lowstand basin floor fan, slope fan, and prograding complex, transgressive systems tract, and highstand systems tract. Each systems tract is deposited at a predictable position in an interpreted eustatic cycle and has recognizable signatures in well logs and seismic data. Any given basin to which this model is applied is strongly controlled by its own tectonic subsidence and accommodation history, and by the type and rate of sediment supply, but the higher frequency eustatic cyclicity is superposed on the other basinal controls. A typical depositional model for the Plio-Pleistocene of the Gulf of Mexico basin is a diapir-controlled subbasin associated with a large contemporaneous expansion fault. The environment of depositionmorexa0» is closely related to the history of fault development. Reservoir sand distribution is characteristic and predictable for each systems tract. Carefully planned evaluation and completion techniques are based on these characteristics.«xa0less

High-frequency progradational sequences in Leonardian Bone Springs and Victorio Peak formations, Delaware Basin, Texas and New Mexico

Leonardian shelf-edge carbonates exposed along the western fault scarp of the Guadalupe Mountains are composed of numerous high-frequency (fourth order) progadational sequences. Individual sequences occupy channels up to 1,000 m wide and 100 m deep. Lowstand sequences onlap the updip parts and downlap the downdip parts of channels. Highstand sequences downlap the entire length of the channels and onlap or toplap against the previous shelf. In both lowstand and highstand sequences, shelf deposits are massive, thickbedded fossil grainstones that dip gently toward the basin. Slope deposits are wavy to horizontal-laminated, thin-bedded packstones and wackestones that dip toward the basin at angles between 15/sup 0/ and 28/sup 0/; soft-sediment deformation features are common. Basinal facies are thin-laminated wackestones and packstones that dip gently toward the basin. The direction of Leonardian progradation in the western Guadalupe Mountains varied from N50/sup 0/E to S70/sup 0/E and apparently did not shift systematically through time. On seismic lines farther to the east, the Bone Springs-Victorio Peak Interval is a third-order sequence that can be divided into lowstand transgressive and highstand systems tracts. These same third-order systems tracts are exposed along the western scarp of the Guadalupe Mountains, but they are more subtle than the fourth-ordermorexa0» sequences because of the scale of observation.«xa0less

Episodic and Cyclic Sedimentation: ABSTRACT

At the 1982 meeting of the SEPM in Calgary, Robert H. Dott, Jr., of the University of Wisconsin gave a very thought-provoking presidential address on episodic sedimentation. He defined episodic sedimentation as punctuated or discontinuous deposition. He concluded that sediments are deposited episodically and are controlled by such factors as the local storms, floods, and tides. Considered by itself, the concept implies that one basin has no predictable relation to another. Thus, when applying the End_Page 536------------------------------ episodic concept it follows that the best way to determine the distribution of sedimentary rocks within a basin is to understand facies relationships and the tectonic setting of the basin. This concept makes good sense and obviously applies to the vast majority of sediments. The weakness of the concept is its inability to explain the rare event. For these rare events, the episodic-oriented geologist commonly calls on the 1,000 yr storm, the 500-ft (150-m) waves from meteorites, the blanket of dust that extinguishes life. Our experience, based on seismic stratigraphic studies tied to well and outcrop sections, indicates that yes, sediments are deposited episodically, but they are packaged in genetically related depositional packages or sequences that are shifted back and forth in a predictable global cyclic pattern. We believe this global cyclic pattern is caused by rapidly fluctuating eustatic changes of sea level superimposed on more slowly changing tectonics. Each sequence is composed of all the rocks deposited during a complete cycle of sea level starting with the fall and progressing through the succeeding low, rise, and high before the next fall. We believe orderly cyclic sedimentation caused by eustatic sea level changes is a better explanation for many of the rare events. Deep-marine massive sa d fans and debris flows commonly ascribed to 1,000 yr storms or 500-ft (150-m) tidal waves may be explained better by rapidly falling sea level or sea level lows. Rapid rises of sea level and their associated condensed stratigraphic sections offer an alternative explanation for the massive faunal extinction and rare deposits associated with the Cretaceous-Tertiary or Eocene-Oligocene boundaries. End_of_Article - Last_Page 537------------