Sequence Stratigraphic Study Research Articles

シーケンス層序学 その可能性を求めて 石狩平野北部地域新第三系のシーケンス層序

A sequence stratigraphic study in conjunction with a quantitative basin subsidence analysis was undertaken in the northern part of Ishikari plain of Hokkaido to clarify the depositional history, recognize the tectonic influences and predict the sandstone reservoir distribution.An interpretation based on seismic data, well logs and biostratigraphic data indicates that the Miocene strata in the basin are composed of eight 3rd order depositional sequences which can be further subdivided into component systems tracts. In the Miocene depositional history of the basin, three stages of sedimentation are recognized by variations in the development of systems tracts and basin architecture.A quantitative basin subsidence analysis from well data indicates that each sequence boundary was resulted from a relative sea level fall and the stages of sedimentation were strongly influenced by the rate of total basin subsidence.Tectonic activity influenced the development of sequences and their component systems tracts by masking the sea level fall with periods of rapid subsidence, by exaggerating relative sea level fall and by shifts in sediment source direction as well as sediment accumulation rate as a result of regional uplift.This study indicates potentials of new stratigraphic types of plays in the basin by predicting sandstone reservoirs basinward, although the previous exploration activities have been focused on anticline-structural traps.

DEPOSITIONAL MODELLING OF THE GIPPSLAND BASIN AND THE BARROW-EXMOUTH SUB-BASINS

SEDPAK is a forward modelling computer program for depositional processes developed by the University of South Carolina's StratMod Group. It simulates the geometry of generalised lithofacies in a sedimentary sequence or a basin by considering principally four major geological variables: eustatic sea level, tectonic movement, sediment accumulation, and initial and evolving basin surfaces.Based on seismic data, well logs and other information from drill holes, the geometries of sedimentary sequences of the Gippsland Basin and the Barrow-Exmouth Sub-basins have been successfully reproduced on both basin and reservoir scales using SEDPAK 3.12. The simulation results indicate that eustacy, tectonics, sediment input and basin physiography can be equally important in controlling the geometry of strata and basin architecture. However, some differences exist: (1) tectonic movement normally contributes to long-term variations of the first order (megasequence) basin architecture and configuration; (2) the second order (sequence) basin architecture and stratal geometry can be controlled by either sediment supply, eustacy, tectonism or a combination; and (3) high frequency facies variations and stratal geometry within individual sequences are primarily controlled by eustatic sea level variations and basin physiography.This study has demonstrated that SEDPAK is a useful tool for reconstruction of basin evolution histories and for reservoir characterisation. It can also be used to predict sedimentary facies in undrilled exploration frontier areas. In addition, it can be used to address some critical assumptions and problems in the sequence stratigraphy concept. SEDPAK is particularly useful in the study of high frequency sequence stratigraphy and cyclicity, where various sequence or parasequence bounding surfaces and internal geometry can not be easily recognised from seismic data, well logs and outcrops.

A Comparative Sedimentological and Sequence Stratigraphic Study of the Middle Jurassic Beryl Formation within Quad 9, UKCS: ABSTRACT

A Comparative Sedimentological and Sequence Stratigraphic Study of the Middle Jurassic Beryl Formation within Quad 9, UKCS: ABSTRACT

Sequence stratigraphy of the Middle Miocene-Pliocene southern offshore Sandakan Basin, East Sabah

A sequence stratigraphic study was performed in the southern offshore Sandakan Basin with the aim of deriving a workable chronostratigraphic scheme and identifying plays, including stratigraphic traps. The data set includes 1800 km of high quality 1990 seismic and 8 wells. The study area can be divided into a structurally complex landward northern province and a relatively undisturbed basinward southern province. Three chronostratigraphic units were identified, each bounded by Type 1 third-order sequence boundaries. Each unit consists ofthird to fourth-order sequences which can be correlated from landward coastal plain facies to basinward bathyal facies. Unit 1 (Middle Miocene-early Upper Miocene) is characterised by moderate progradation, moderate aggradation; Unit 2 (middle Upper Miocene) by high progradation, low aggradation; and Unit 3 Oate Upper Miocene-Pliocene) by high aggradation, low progradation. . The positions of the prominent shelf edges in Unit 1, Unit 2 and lower Unit 3 indicate a southeastward progradation from Middle to Upper Miocene. Pliocene progradation was probably eastwards as suggested by N-S growth faults in the northeastern part of the study area, and is interpreted to have occurred within a ramp setting, as prominent shelf edges are lacking. The study led to the recognition of two play-types in the southern province, both associated with lowstand systems tract sediments. The fIrst is a slope fan play in Unit 1. The second is a basin floor fan play in Unit 2. Comparison of the locally derived onlap chart and the global onlap chart of Haq et al. (1987) highlighted some differences. The main difference is major Upper Miocene progradation in the study area versus Upper Miocene aggradation in the global chart, testifying to the importance of the interplay of local tectonics and sedimentation in the Sandakan Basin.

Sequence Stratigraphy Analysis of Carapita E Lower Miocene; North of Monagas, Venezuela

The Carapita E sandstone is of lower Miocene age, and occurs in the maturin sub-basin within the active thrust belt of the eastern Venezuela tertiary foreland basin. This basin is a prolific hydrocarbon basin and the Carapita sandstones form an important reservoir system. This study is based on an integration of well logs and cores from 56 wells covering an area of more than 39.000 km[sup 2] the sediments were interpreted in terms of depositional environments and sequence stratigraphic patterns. The sandstone unit overlies a type I sequence boundary (25,5 m.y.) and in the central and western part of the study area it is interpreted as a lowstand systems tract, deposited within an incised valley on the shelf. Further east, the sediments were deposited in a coastal to shelf setting and the unconformable sequence boundary is interpreted to pass into a correlative conformity. These more distal shoreline sands from a shelf-perched lowstand prograding wedge which is coeval with the incised valley fill further landward they comprise coastal and nearshore deposits in the form of prograding coastal/deltaic bars and shoreline sands. This detailed sedimentological and sequence stratigraphic study has resulted in improved productivity and optimization of hydrocarbon recovery from the Carapitamore » E sands.« less

Paleogene sequence stratigraphic framework of the Faeroe Basin

During Paleogene times up to 15 000 ft (4570 m) of clastic sediment was deposited in the Faeroe Basin, north of the Shetland Islands. A sequence stratigraphic study has shown that the Paleogene deposition in the Faeroe Basin was cyclic with prominent basinward and landward shifts in sedimentation. The correlation of major unconformity surfaces allowed the section to be subdivided into genetically related packages. The sequence stratigraphic study utilized approximately 5000 km of seismic data with a line density of approximately 10 × 20 km. Available well control was integrated into the study by means of synthetic seismograms. Limited palaeontological control utilizing largely dinocysts and radiolaria allowed the identification of 11 Paleocene/Eocene bioevents. The section was subdivided into nine Paleocene and six Eocene sequences, each separated by Type 1 unconformities. Four of the Paleocene and one of the Eocene packages had evidence of multiple Type 1 unconformities and these are described as sequence sets. Sequence development has been related to the tectonic subsidence history of the basin. Early in Paleocene times, rapid subsidence resulted in the deposition of thick sequences with distinct shelf, slope and basinal systems. Nine sequences were deposited with a combined maximum thickness of 12000 ft (3660 m). The following period, late Paleocene to early Eocene, was marked by slower subsidence; thin sequences and ramp systems with seven sequences were deposited with a maximum thickness of 2400 ft (730 m). More rapid subsidence during the late Eocene resulted in five sequences with distinct shelf, slope and basinal systems with a thickness of up to 3500 ft (1070 m). The periods of slower subsidence in the Faeroe Basin may have occurred in response to active rifting in other adjacent basins along the Atlantic margin. The distinct basinal systems which developed during times of more rapid subsidence were more likely to develop sand-prone basin floor deposits.

Description and analysis of bioturbation and ichnofabric

A new scheme for the description and analysis of bioturbation and the resultant ichnofabrics is proposed. This system can be used in core and field-based studies and consists of two parts. (1) A bioturbation index in which a descriptive grade is assigned to the degree of bioturbation. This integrates the sedimentology and ichnology, where the higher grades of bioturbation result from increased burrow overlap and the subsequent loss of the primary sedimentary fabric. (2) An ichnofabric constituent diagram which records the detail of the ichnofabric by graphically plotting the dimensional data of the ichnotaxa and their order of emplacement against their coverage. This scheme differs from previous attempts to characterize bioturbation using semi-quantatitive methods and visually portrays the ichnofabric so that comparative studies can be carried out. This is of particular use in facies analysis, the establishment of the ichnocoenoses and tier diagrams, and within sequence stratigraphic studies so that hiatal surfaces can be recognized.

Miller Field: reservoir stratigraphy and its impact on development

The Miller Field lies in UKCS Blocks 16/7b and 16/8b adjacent to the South Brae Field, and its reservoir is a high net-to-gross system of fine- to medium-grained turbiditic sandstones, interbedded with thin mudstones, which was deposited as part of an extensive submarine fan complex of Late Jurassic age, along the margin of the South Viking Graben. Recent studies of sequence stratigraphy in the area have contributed to a better understanding of the elements of the submarine fans, and, coupled with detailed biostratigraphy, have enabled the reservoir units to be correlated across the field with a fair degree of confidence. Pressure data have been incorporated into these studies. While detailed geophysical interpretation continues, a geological reservoir description has been used to map rock properties and reservoir connectivity across the field, and to indicate areas of greatest uncertainty. These uncertainties will be reduced as further data become available during production.

Application of organic geochemistry to sequence stratigraphic analysis: Four corners platform area, New Mexico, U.S.A.

The sequence stratigraphic model of sedimentation postulates the existence of a time-condensed section, deposited at very low sedimentation rates, occurring in the uppermost transgressive systems tract and the lowermost highstand systems tract. This condensed interval has of often been equated with zones of increased hydrocarbon source potential, and invoked as a petroleum source rock, often in the absence of supporting geochemical data. In this study, isotopic, molecular, lithostratographic and paleontological data are presented for 51 outcrop samples from a Cenomanian-Turonian section at Red Wash, New Mexico, U.S.A.; interpretations are made within a sequence stratigraphic framework (ramp model). Sedimentation rates are estimated in order to define the location of the codensed intervalm for comparison with the zone of best source potential. Approximately 80 m of section were sampled. The interval of maximum flooding and westernmost progression of the Cretaceous Seaway shoreline, as defined by paleontological data, is stratigraphically immediately below the occurrence of discontinuities in total organic carbon content, hydrogen index and fluoramorphinite concentration in the kerogen. The overall transgressive event is accompanied by increases in relative concentrations of 24- n-propylcholestane, total steranes, and rearranged steranes. These changes are consistent with a simultaneous decrease in the ratio of terrigenous organic matter to marine algal input as westward flooding proceeded. The simultaneous occurrence of discontinuities in kerogen-related parameters and continuous trends in bitumen-related parameters probably implies mobilization of soluble organic matter across the flooding event boundary. Sedimentation rate estimates for six intervals in the Red Wash section show that the best oil source rock potential occurs immediately above the condensed interval and maximum flooding surface, within the highstand systems tract. Previous studies of Cretaceous sections in other portions of the Western Interior Basin have located the best source rock potential below the condensed zone. We conclude that the equivalence between source rock occurence and condensed sections as applied through the sequence stratigraphic model requires modification before the model may be used to predict the location of oil source rocks in a ramp setting. In this respect, it is critical that the data in sequence stratigraphic studies be used to define the model, and not allow the model to dictate the interpretation of the data.

Stratigraphic and palaeoenvironmental analyses continue to demand the inclusion of high quality palaeontological data

The recent proliferation of sequence stratigraphic studies is giving palaeontology a much needed boost after apparently having been regarded by some geologists for more than a decade as rather a second rate subject. In the face of an onslaught of a variety of new, `more objective' techniques aimed at dating sedimentary successions and analysing the conditions of deposition represented, this was perhaps not surprising. Sedimentologists are, however, now finding that they need palaeontological input if they are to arrive at the best possible age assessments and interpretations of the conditions of deposition of the successions they investigate. Palaeontologists should not let this opportunity pass them by, but it is essential that they do not sacrifice good taxonomic practice in their attempts to provide quick answers. Superficial studies lead to conclusions of a similar kind. No amount of quantitative manipulation using sophisticated, computer-based numerical techniques can provide a correct interpretation if the original data are incomplete and not to be trusted.

Introduction to Trace Fossils and Dedication to Robert W. Frey

Over the years, we've participated in several different workshops and short courses on trace fossils. So why this one? Our intention in bringing together these papers for the Trace Fossil Short Course is to give an overview of how trace fossils can be used in paleontology. Historically, trace fossil research has centered on paleoenvironmental and depositional reconstructions—areas where trace fossils have much to tell. Indeed, the use of trace fossils by sedimentologists has flourished and is experiencing another burst of activity through the use of ichnofabrics in sequence stratigraphic studies. But trace fossils have paleontological stories to tell as well. Their use in uncovering the first occurrences of life in different parts of the stratigraphic column is well documented (e.g., the classic example of trace fossils occurring before body fossils in Precambrian/Cambrian transitional strata) as is their use in detailing different morphological details of unpreserved taxa or body parts.

SEQUENCE STRATIGRAPHY, BASIN-FLOOR FANS AND PETROLEUM PLAYS IN THE DEVONIAN – CARBONIFEROUS OF THE NORTHERN CANNING BASIN

A sequence stratigraphic study of 4 000 kilometres of seismic data and fifty wells from the northern part of the Canning Basin has improved vasdy our knowledge of the evolution of the basin succession and has identified new petroleum play concepts. The Devonian to Lower Carboniferous succession can be subdivided into at least sixteen 'Vail type' sequences. This shows two contrasting phases of development; a reef complex in the Frasnian—Early Famennian, and a ramp in the Late Famennian-Tournaisian. The reef complex was characterised by reciprocal sedimentation with thick clastic lowstand wedges deposited in the Fitzroy Trough and thinner transgressive and highstand carbonate sediments deposited on the Lennard Shelf. The reef complex shows an early phase of backstepping, related to rapid drowning of the platform, and a later phase of marked progradadon when relative subsidence was lower. The ramp, in contrast, has only poorly developed lowstand wedges. Early ramp sequences are lenticular and successively offlap basinward; later sequences are more tabular and progressively onlap landward.Sequence stratigraphy has provided a new perspective on the setting and evolution of the traditional Devonian reef play. It emphasises the attractiveness of the Frasnian cycle of reef growth where source, seal and reservoir potential appear to be better than in the younger, much more extensively drilled Famennian cycle.New and untested stratigraphic targets have been identified in Famennian-Tournaisian highstand ramps and in lowstand fans. These new stradgraphic targets are generally basinward of the more traditional target areas and need to be assessed by either wildcat or stratigraphic drilling. The lowstand fans, especially, are large and extensive and favourably located to trap migrating hydrocarbons. Several prospects, each with the potential to contain in excess of 100 million barrels of recoverable oil, have already been identified on seismic data recorded basinward of the Lennard Shelf.

Wolfcampian Sequence Stratigraphy of the Eastern Central Basin Platform, Texas

Integrated study of well logs, cores, high-resolution seismic data, and biostratigraphy has established the sequence framework of the Atokan (Early Pennsylvanian)-Wolfcampian (Early Permian) stratigraphic section along the eastern margin of the Central Basin platform in the Permian basin. Sequence interpretation of high-resolution, high-fold seismic data through this stratigraphic interval has revealed a complex progradational/retrogradational evolution of the platform margin that has demonstrated overall progradation of at least 12 km during early-middle Wolfcampian. Sequence stratigraphic study of the Wolfcamp interval has revealed details of the internal architecture and morphologic evolution of the contemporaneous platform margin. Two generalized seismic facies assemblages are recognized in the Wolfcampian. Platform interior facies are characterized by high-amplitude, laterally continuous parallel reflections; platform margin facies consist of progradational sigmoidal to oblique clinoforms and are characterized by discontinuous, low-amplitude reflections. Sequence interpretation of carbonate platform-to-basin strata geometries helps in predicting subtle stratigraphic trapping relationships and potential reservoir facies distribution. Moreover, this interpretive method assists in describing complex reservoir heterogeneities that can contribute to significant reserve additions from within existing fields.

DEPOSITIONAL HISTORY AND FACIES ANALYSIS OF THE UPPER JURASSIC SEDIMENTS IN THE EASTERN BARROW SUB-BASIN

Callovian to Tithonian syn-rift sediments in the eastern Barrow Sub-basin can be subdivided into five depositional sequences, each separated by regionally correlatable unconformities. Sequence boundary development can be closely related to periods of major changes in basin configuration associated with the sequential breakup of eastern Gondwanaland. Synchronism of major faulting with sequence boundary development during the early and late Callovian, mid Kimmeridgian, and mid Tithonian times supports tectonism being a dominant control on the development of Type 1 unconformities in the eastern Barrow Sub-basin.Upper Jurassic depositional sequences in the eastern Barrow Sub-basin, whether of tectonic or eustatic origin, consist primarily of lowstand systems tracts comprised, wholly or in part, of detached basin floor fan complexes, channelised and canyon-fed fan systems, slump deposits, outer shelf to slope deposits, and deep marine claystones. Inner shelf to shoreface sediments of the transgressive and highstand systems tracts are absent due to episodic, post-depositional uplift and erosion along the Peedamullah Shelf and Flinders Fault System during the Late Jurassic. The periods of uplift and erosion provided much of the sediment redeposited in basinal areas during lowstand times.Depositional models based on regional sequence stratigraphic studies can be integrated with local seismic stratigraphy to provide a mechanism for estimating likely reservoir quality, once controls on sedimentation (namely tectonics, eustasy, and sediment supply) are understood. This is demonstrated by the recognition of at least seven sandstone facies within the Upper Jurassic sedimentary section. Each sandstone has particular characteristics which can be related to the depositional setting. Reservoir quality is best developed in dominantly medium grained, moderate to well sorted sandstones, deposited as detached, basin floor submarine fan sands or interbedded turbidites. In contrast, reservoir quality is poorly developed in the remaining sand-prone facies deposited as slope fans, slumps, or distal turbidites.

Depositional sequences and correlation of middle(?) to late Miocene carbonate complexes, Las Negras and Nijar areas, southeastern Spain

ABSTRACTDuring Serravallian through Messinian time, marine carbonates flanked topographic highs that rimmed Neogene basins in the Western Mediterranean. Middle to upper Miocene carbonate strata in the Las Negras and Nijar areas (southeastern Spain) are 50‐150 m thick and display 50‐200 m of shelf‐to‐basin relief over 1‐2 km. Detailed studies in those areas document the effects of relative sea‐level change on sedimentation, biotic composition, and reef development. We identify three previously unrecognized, regionally correlatable depositional sequences (DS1, DS2, DS3) that occur between the underlying basement and the overlying Terminal Carbonate Complex. The lower depositional sequences (DS1, DS2) are mostly normal marine shelf (ramp) carbonates deposited on the flanks of basement highs. The basal part of DS2 locally contains some megabreccia reef blocks composed of Tarbellastraea and Porites. These blocks are the first evidence of reef growth in the area and represent a previously unrecognized period of reef development prior to the fringing reef development. The reef blocks probably formed as upslope patch reefs that were eroded and transported to distal slope locations. The upper sequence (DS3) is characterized by clinoform strata of a Porites‐dominated fringing reef complex that prograded basinward in a downstepping style with successively younger reefs forming in a topographically lower and more basinward position as a result of a net sea‐level drop.Regional correlation of Miocene shallow‐marine strata between basins in Spain and elsewhere in the western Mediterranean is complicated because basins were semi‐isolated from adjacent basins making physical correlation impossible. In addition, age‐definitive biostratigraphic markers are poorly preserved in most of the Miocene shallow‐water strata; basinal sediments that are more easily dated by microfossils do not typically interfinger with the shallow‐marine strata in outcrop. Even where datable microfossils are found, resolution of dating is poor.Our studies in the Las Negras and Nijar areas illustrate the usefulness of integrating sedimentological, geometric and biotic data with locally derived relative sea‐level (accommodation space) curves for correlation. The relative sea‐level curves for each area show remarkable similarities in shape and magnitude of sea‐level changes. These curves indicate several relative sea‐level fluctuations during Miocene carbonate deposition prior to the major sea‐level drop at the end of DS3 deposition that culminated in the exposure of the basin margin deposits and the deposition of evaporites in basinal areas during the Messinian.The depositional sequences in the Las Negras and Nijar areas may correlate with depositional sequences of similar age throughout the southern Cabo de Gata area, in Mallorca some 600 km to the northeast, and possibly in other Mediterranean locations. The widespread occurrence and possible correlation of the depositional sequences suggest regional processes such as eustacy or tectonism for their formation.The integration of sedimentological, palaeontological and sequence stratigraphic studies, and the construction of relative sea‐level (accommodation space) curves may help in the interpretation of depositional histories of shallow‐marine carbonate complexes and correlation of these strata between isolated areas. Other dating methods, in addition to microfossil dating, may allow for better age determination of the sequences and aid in identifying the importance of eustacy and tectonism in sequence development.

Geometric modelling of fades migration: theoretical development of f acies successions and local unconformities

ABSTRACTGeometric analysis shows that the angle of migration of coastal sedimentary facies is a function of the relative sea‐level change and the thickness of sediment deposited or eroded. The angle of facies migration compared to the slopes on the sediment surface determines the degree of facies preservation and stratigraphic relationships to the surrounding facies.Vertical facies successions generated by radial migration of environments show a great deal of variety because the sediment surface in both marine and non‐marine areas is concave‐up. Both regressive and transgressive sequences with non‐erosive marine‐nonmarine contacts can be generated. Transgression at a slightly lower angle can form a ravinement surface cut on non‐marine deposits with onlapping barrier sands or shallow marine deposits. Regression with relative sea‐level drop generates a minor erosion surface with baselapping isolated shoreline deposits. Disequilibrium conditions occur when sea level varies at a rate exceeding the ability of the system to supply or redistribute sediment, with resulting changes in surficial slopes.Onlapping and downlapping stratal relationships across erosion surfaces result because of differences in slopes between marine and non‐marine environments. These discontinuities are generally less than one degree, but could possibly be recognized on high quality multichannel seismic lines. Most of these discontinuities are probably not regionally extensive enough to be regarded as sequence boundaries. Tectonic tilting or differential subsidence of strata during depositional hiatuses is necessary to generate true regional unconformities or sequence boundaries.Where facies climb with respect to horizontal, erosion surfaces produced only by this migration may cut across lithostratigraphic units at higher angles, up to 3 or 4 degrees. Low‐angle erosion surfaces relevant to the scales of sequence stratigraphic studies may result only from facies migration, even during a period of relative sea‐level rise.

Ichnology in Sequence Stratigraphic Studies: An Example from the Lower Paleocene of Alabama

Detailed ichno-sedimentological analyses of two Lower Paleocene depositional sequences contained within the Clayton and Porters Creek Formations of western Alabama. The ichnological variations reflect changes in substrate consistency, physical environmental energy, sedimentation rate, and bottom- and/or pore-water chemistry that are consistent with both the phases and magnitudes of the associated sea-level cycles. These results illustrate the potential of extended ichnological studies in the testing and refinement of sequence stratigraphic models and resulting interpretations of sea-level histories

Geological controls on seismic sequence resolution

A seismic sequence analysis of the Canterbury basin, eastern South Island of New Zealand, has illustrated the roles of subsidence, sediment supply, and current activity as controls on sequence resolution and architecture during basin evolution. The rates of sediment supply and subsidence determine the background depositional regime (transgressive or regressive),and effectively determine the frequency response of the continental margin sedimentary section to input signals with a broad range of frequencies, including eustasy. A regressive (progradational) depositional regime and minimal current erosion favor the preservation of high-frequency sequences, particularly at fourth-order level. Under less favorable conditions, the record of sequences is incomplete or ambiguous. Such frequency response characteristics must be considered when inverting sequence records to derive the frequency of the input cyclicity, and when making global comparisons of regional sequence stratigraphic studies. Clastic basins with simple subsidence histories and uniform or increasing rates of sediment supply develop from a transgressive phase, characterized by ramplike major sequence boundaries, to a mature, progradational shelf phase with clinoform sequences and optimum sequence resolution. The mature phase constitutes the preferred setting for sequence stratigraphic analyses.

Submarine Canyon Cut and Fill Morphology and Facies in the Upper Pliocene on the Texas Shelf

ABSTRACT The processes responsible for both the formation and subsequent infill of submarine canyons are significant to the exploration for hydrocarbons in the sediments funneled through them. These processes can be better understood through detailed mapping of both the canyon geometry and the infill sediment facies. TGS Geophysical Company and GECO Geophysical Company have completed a sequence-stratigraphic study of the Plio-Pleistocene and Upper Miocene sediments of the High Island and eastern Galveston south additions of offshore Texas. Approximately 5,000 miles of seismic data in a 2 2 mile grid were interpreted. Sequence boundaries, system tracts and facies within the system tracts were delineated. These seismic interpretations were supported with well logs from nearly 200 wells. Additional control included biostratigraphic data based on detailed analysis of nannofossils and planktonic forminifera from approximately 30 of these wells. We identified and mapped several major submarine canyon features in the upper Pliocene strata in detail using a 1 1 mile seismic data grid. Problems in mapping these canyons come from the difficulty in determining their boundaries. Additionally, partial reactivation of the canyons during subsequent sealevel falls results in downcutting and new episodes of deposition that mask the boundaries. Canyon margins were defined by the lateral limits of chaotic infill. We also recognize a transition one characterized by slump faults in the older shelf sediments. Canyon development is the result of two predominant submarine processes. Initial formation occurs during sealevel fall as a result of slope failure. This initial slumping creates a pathway for the concentration of sediment gravity flows including turbidity currents and grain flows. Continued downcutting by these transport mechanisms destabilizes the canyon margins promoting slumping of the canyon walls. This serves to both enlarge the areal extent as well as infill the canyon. The canyon fill is predominantly sediments of the slope fan system tract with lesser amounts of prograding wedge and highstand system tracts. The sediments of the slope fan system tract are slump block, depositional mounding, channel-levee complexes, overbank deposits and small scale cut and fill features. They are recognized on seismic data by reflection patterns which range from chaotic with imbedded gull wing configurations to subparallel and semi-continuous. Well log patterns show irregular fining upward sequences with occasional thin to blocky sands. The overlying sediments of the prograding wedge and highstand system tracts exhibit prograding clinoforms or laterally continuous subparallel reflections. The distribution of depositional facies within the canyon is to a large extent controlled by the canyon formation mechanisms as well as the canyon geometry. The updip generally narrower portion of the canyon is filled with slump block is associated debris flows. The broader middle and lower canyon fill is composed of gravity flow deposits that exhibit depositional morphologies generally associated with slope fans. End_of_Record - Last_Page 601-------

Utility of Ichnology in Sequence Stratigraphic Studies: Examples from Alabama Paleogene: ABSTRACT

Utility of Ichnology in Sequence Stratigraphic Studies: Examples from Alabama Paleogene: ABSTRACT