Retrogradational Parasequence Sets Research Articles

The Upper Jurassic sediments, Marib-Shabwa Basin, Yemen: Lithofacies aspects and sequence stratigraphic analysis

The present study is devoted to understanding the evolution of the Upper Jurassic Sab'atayn Formation in the Marib-Shabwa Basin, Yemen, through a sequence stratigraphic analysis based on integrating datasets of sedimentology, seismic sections, and well logs. The Sab'atayn Formation (Tithonian age) is represented by a series of clastic and evaporites that were deposited under fluvio-deltaic to prodeltaic settings. It is divided into four members including Yah (at the base), upwards to Seen, Alif, and Safir at the top. Two third-order depositional sequences were determined for the Tithonian succession which were separated by three sequence boundaries. These sequences were classified into their systems tracts signifying several sedimentation patterns of progradational, aggradational, and retrogradational parasequence sets. The first depositional sequence corresponds to the early-middle Tithonian Yah and Seen units that can be classified into lowstand, transgressive, and highstand systems tracts. The second sequence comprises the late Tithonian Alif unit that can be subdivided into transgressive and highstand systems tracts. The sandy deposits of the Alif Member (highstand deposits) represent the most productive hydrocarbon reservoir in the basin. The Upper Jurassic sediments in the study area were resulted from a combination of eustatic and tectonic effects.

Facies analysis and depositional framework of Late Permian-Jurassic sedimentary successions, Western Salt Range, Pakistan: implications for sequence stratigraphic trends and paleogeography of the Neo-Tethys Sea

Facies analysis and T-R sequence stratigraphic approach of Late Permian to Jurassic sedimentary units in Western Salt Range, Pakistan were accomplished to construe the depositional environments and basin evolution. The analysis affirms the rendition of sequence stratigraphic trends and paleogeography of first megasequence phase of Neo-Tethys Sea. Sedimentological contingents, T-R sequence stratigraphic framework and sea level curve of the strata argue active tectonic’s effects on sedimentation. During Late Permian, the rift related magmatic activities deceased, which imparted to the onset of transgression and deposition of shelf carbonates with retrogradational (transgressive) parasequence sets in Wargal Formation. Respective rifting and tectonic uplift events induced the sea level fall ascertaining the onset of terrigenous shelves and deltaic successions in terminal Permian and Early-Mid Triassic with an enlighten switch from agradational to progradational parasequence sets (regressive parasequences) in Chhidru, Mianwali and Tredian formations. The closure of Paleo-Tethys and emergence of semi-arid hot tropical climate throughout Late-Triassic, led the onset of tidal-lagoonal environments and deposition of retrogradational (transgressive) parasequence sets in Kingriali Formation. During Early Jurassic, a well-known northward drift of Pangaea ensued in global cooling and increased humidity, which consequently stimulated clastic-carbonate sedimentation of Datta and Samana Suk formations with progradational and retrogradational parasequence sets respectively.

Mississippian Meramec lithologies and petrophysical property variability, stack trend, Anadarko Basin, Oklahoma

Mississippian Meramec reservoirs of the Sooner Trend in the Anadarko (Basin) in Canadian and Kingfisher Counties (STACK) play are comprised of silty limestones, calcareous siltstones, argillaceous calcareous siltstones, argillaceous siltstones, and mudstones. We found that core-defined reservoir lithologies are related to petrophysics-based rock types derived from porosity-permeability relationships using a flow-zone indicator approach. We classified lithologies and rock types in noncored wells using an artificial neural network (ANN) with overall accuracies of 93% and 70%, respectively. We observed that mudstone-rich rock type 1 exhibits high clay and relatively low calcite, whereas calcareous-rich rock type 3 has high calcite and low clay content with rock type 2 falling in between as a balance between rock types 1 and 3. Results of the ANN were applied to a suite of well logs in noncored wells in which we generated lithology and rock-type logs for the Meramec. We identified that the Meramec consists of seven stratigraphic units characterized as strike-elongate, shoaling-upward parasequences; each parasequence is capped by a marine-flooding surface. The lower three parasequences (lower Meramec) form a retrogradational parasequence set that back steps to the northwest and is capped by a maximum flooding surface. The upper Meramec is characterized by parasequences that form an aggradational to progradational stacking pattern followed again by a retrogradational trend. We predict that the parasequence stacking, associated lithology distribution, and diagenetic cements appear to control the spatial distribution of petrophysical properties (porosity, permeability, and water saturation), pore volume, and hydrocarbon pore volume (HCPV). Calcareous-rich lithologies exhibit lower porosity, permeability, HCPV, and higher water saturation. We deduced that argillaceous-rich lithologies that occur near the maximum flooding surface are the most favorable reservoir intervals because they exhibit relatively higher porosity, permeability, HCPV, and lower water saturation. Productivity could not be directly correlated to rock types as operational and completion factors as well as overpressure and oil phase play important roles on production.

Rift activity and sequence stratigraphy of the Oligocene Dongying Formation in the Nanpu Sag, eastern China: Implications for rift sequence stratigraphy in lacustrine basins

Rifting plays an important role in accommodation variations in rift basins. However, fluvial discharge as another important factor affecting lacustrine rift sequence stratigraphy is not well explored. In this work, seismic and well data are used to investigate the stratigraphic features, rift activity, and effect of fluvial discharge in the Nanpu Sag, Bohai Bay Basin. The syn‐rift deposition of the Dongying Formation (28.5–23.8 Ma) is divided into four sequences (SQ1, SQ2, SQ3, and SQ4), and the rift‐related subsidence rate along two parallel boundary faults is calculated. The results indicate that the rift activity weakens from SQ1 to SQ4 and that the two parallel boundary faults consist of a total of four fault segments. As the fault segmented, three propagation folds formed intrabasin highs on which the Beipu, Laoyemiao, and Gaoliu outlets developed. Well logs and 3D seismic data show that from SQ1 to SQ3, retrogradational stacking patterns occur in Beipu, Laoyemiao, and the hanging‐wall ramp, while progradational stacking patterns occur in the Gaoliu outlet. In SQ4, the sequence stacking patterns are progradation‐dominated. By evaluating channel erosion and sediment supply, the fluvial discharge can be estimated, and the result indicates that the Gaoliu outlet has the strongest fluvial discharge from SQ1 to SQ3 with strong channel erosion, and in SQ4, the fluvial discharge of each outlet is comparable and relatively low. The high fluvial discharge of the Gaoliu outlet from SQ1 to SQ3 is considered to be the primary reason for the lake level rise in the intervals between the pulses of rift activities. Sequence stacking patterns and depositional trends in our study intervals are not in line with the rift subsidence rate; this indicates that rifting is not the only factor controlling the rift sequence stratigraphy and variations in the accommodation of lacustrine rift basins. While the Gaoliu outlet has predominant fluvial discharge from SQ1 to SQ3, progradational parasequence sets deposit in the Gaoliu outlet. In contrast, the retrogradational parasequence sets occurred in the Beipu outlet, Laoyemiao outlet, and the hanging‐wall ramp. As the fluvial discharge of the Gaoliu outlet decreased in SQ4, the fluvial discharge in each outlet became low, and the stacking patterns were dominated by progradation. Consequently, this research suggests that fluvial discharge is a significant factor controlling the accommodation creation in lacustrine rift basins, and a sequence model which gives a full consideration of fluvial discharge is constructed for lacustrine rift basins.

Architecture of tectonic sequences, depositional systems, and tectonic controls of the sedimentary fills of the rift‐related Wenchang Formation in the Lufeng Depression, Pearl River Mouth Basin, China

Different sequence types were formed in various stages associated with tectonic variations and changes of the sediment supply in the rift‐related Wenchang Formation. Based on cores, wire logging, and seismic data, the sequence stratigraphy, depositional systems, and controls on the depositional systems of the Wenchang Formation in the Lufeng Depression were studied. The Wenchang Formation developed braided‐delta, lacustrine, fan‐delta, and nearshore subaqueous fan deposits and represents one first‐order sequence and three second‐order sequences, indicating three stages of tectonostratigraphic evolution. (a) The early syn‐rift sequence (SSQ1) developed fan‐delta and shallow lacustrine deposits. (b) The rift climax sequence (SSQ2) contains the early rift climax systems tract and the middle‐late rift climax systems tract. The early rift climax systems tract formed primarily braided‐delta and shallow lacustrine deposits, whereas the middle‐late rift climax systems tract developed mostly semi‐deep to deep lacustrine deposits. (c) The late syn‐rift sequence (SSQ3) developed braided‐delta and shallow lacustrine deposits. In the SSQ3 transgressive systems tract, retrogradational parasequence sets developed along the southern dip slope because of the weak sediment supply from the Huilu low uplift, whereas westward aggradational–progradational parasequence sets developed along the long axis because of the stronger sediment supply from the Lufeng eastern low uplift. Tectonic activity primarily controlled the early syn‐rift and rift climax deposition; syn‐depositional faults formed the transfer zones and slope break zones. Three types of transfer zones for sedimentary transport into the basin were distinguished, including synthetic approaching transfer zones, strike ramps, and collateral transfer zones. Three types of slope break zones were also recognised, including fault scarp zones controlling fan deltas and nearshore subaqueous fans, fault terrace zones controlling low‐stand fan deltas, and antithetic fault terrace dip‐slope zones controlling braided deltas.

Sequence Stratigraphy and Rudist Facies Development of the Upper Barremian‐Lower Cenomanian Platform, Northern Sinai, Egypt

AbstractThe Lower Cretaceous sections in northern Sinai are composed of the Risan Aneiza (upper Barremian‐middle Albian) and the Halal (middle Albian‐lower Cenomanian) formations. The facies reflect subtle paleobathymetry from inner to outer ramp facies. The inner ramp facies are peritidal, protected to open marine lagoons, shoals and rudist biostrome facies. The inner ramp facies grade northward into outer ramp deposits. The upper Barremian‐lower Cenomanian succession is subdivided into nine depositional sequences correlated with those recognized in the neighbouring Tethyan areas. These sequences are subdivided into 19 medium‐scale sequences based on the facies evolution, the recorded hardgrounds and flooding surfaces, interpreted as the result of eustatic sea level changes and local tectonic activities of the early Syrian Arc rifting stage. Each sequence contains a lower retrogradational parasequence set that constituted the transgressive systems tracts and an upper progradational parasequence set that formed the highstand systems tracts. Nine rudist levels are recorded in the upper Barremian through lower Cenomanian succession at Gabal Raghawi. At Gabal Yelleg two rudist levels are found in the Albian. The rudist levels are associated with the highstand systems tract deposits because of the suitability of the trophic conditions in the rudist‐dominated ramp.

Lombardi reservoir, San Ardo field, California: Sequence stratigraphy in a deltaic environment associated with local tectoni

The Lombardi reservoir at San Ardo oil field in California is extremely sand rich (>90%) and appears to be a relatively simple reservoir several hundred feet thick. The purpose of this study is to characterize stratigraphic complexities in the Lombardi reservoir that may affect later production and interpret how changes in stratigraphic architecture are tied to local syndepositional tectonism. Two parasequence sets are present in the Lombardi: the reservoir exhibits clinoform geometries along the western edge of the field and stacking patterns within the reservoir change across the field. Based on stacking pattern, core, and correlation studies, two possible sequence boundaries are recognized in the Lombardi sand. A lower sequence boundary is proposed approximately in the middle of the Lombardi sand, and an upper sequence boundary is proposed at the top of the Lombardi sand. In the southern part of the field, the Lombardi sand consists of two progradational parasequence sets, separated by the mid-Lombardi sequence boundary. The upper sequence boundary clearly truncates underlying folded Lombardi sand. Just a few miles (∼5 km) away, in the northwest part of the field, the Lombardi sand consists of a lower progradational parasequence set and an upper retrogradational parasequence set, separated by the mid-Lombardi sequence boundary. The upper sequence boundary at the top of the Lombardi sand shows little evidence of truncation of underlying units and is recognized by onlapping of younger strata. The difference in reservoir architecture between the south and northwest part of the field, a distance of only a few miles (∼5 km), is interpreted to be related to syndepositional uplift accompanying tectonism in the south. In core, the Lombardi sand consists mostly of homogeneous sand and bioturbated sand, arranged in upward-coarsening successions. The Lombardi sand is interpreted to be the product of deltaic deposition based on (1) the presence of homogeneous and laminated sandstones interpreted to represent mass flow deposits and (2) its restricted geographic distribution within the Salinas basin. No evidence of deposition in a wave-dominated or tidal-dominated shoreline is indicated. The interpretation presented here is that the sediments were deposited on the front of a delta emptying into a wave-protected estuary or bay, with minimal tidal effects. Complexities in stratigraphic architecture along the western edge of the field do not currently affect production but will likely become important during later stages of field development. That is, in the developed part of the field, reservoir continuity is not an issue, because of high sand content and sheet-like geometries. However, at the margins of the field, which will be produced in the future, clinoform geometries and sandstone tongues clearly affect reservoir continuity and will create vertical compartments during draining.

Lithostratigraphic and sequence stratigraphic architecture of the Winduck Interval, central Darling Basin, Australia, based on integration of wireline logs, cores and cuttings data

An integration of lithostratigraphy and general sedimentary facies character for non-marine rocks can be a powerful tool in understanding the sequence stratigraphic architecture of the subsurface latest Silurian to Early Devonian Winduck Interval in the Blantyre and western Neckarboo sub-basins, central Darling Basin. This study integrates wireline logs (gamma ray and resistivity), cores and cuttings data to determine the sequence stratigraphic subdivision of the study area. The lithostratigraphy of the Winduck Interval could be subdivided into three units (A, B and C, in ascending order) in the four available wells (Mount Emu 1, Kewell East 1, Booligal Creek 1 and Booligal Creek 2). Closer study of the sequence stratigraphy in the approximately 850-m-thick Winduck Interval revealed ten parasequences (A–J) in progradational to retrogradational parasequence sets and three main Winduck sequences, WKS1, WKS2 and WKS3. Use of the suggested sequence stratigraphic model of the Winduck Interval has the potential to refine existing lithostratigraphic schemes and, given the higher resolution and more detailed correlation, may significantly improve subsurface stratigraphic reconstructions and aid in prediction of hydrocarbon-bearing reservoirs.

The Cretaceous/Paleogene boundary in Jordan

The Cretaceous/Paleogene (K/Pg) boundary in Jordan is marked by a major depositional hiatus that differs in magnitude from place to place due to variable structural movements of the Syrian Arc Fold Belt that resulted in irregularity of Jordan/Levant depositional basin after the deposition of Maastrichtian succession. To elucidate the nature of this hiatus, fieldwork was carried out at a number of locations including lithofacies and stratigraphic analysis, and a multi-proxy study of microplanktonic biostratigraphy (calcareous nannofossilis and planktonic formaminifera). However, the duration of this hiatus extended over latest Maastrichtian and early Danian stages. This is based on the absence of the planktonic foraminifera; Pseudoguembelina hariaensis (CF3), Pseudoguembelina palpebra (CF2), Plummerita hantkeninoides (CF1), Guembelitria cretacea (P0), Parvularugoglobigerina eugubina (P&) zones and Parasubbotina pseudobulloides (P1a) subzones and the coeval calcareous nannofossils Nephrolithus frequens and Markalius inversus zones. We estimate that in the paleo-lows areas an unexpected 3.96Ma hiatus is present. Conversely, in swell areas, the duration of the hiatus represents the entire Danian–Selandian interval and revealed an unexpected 10.33Ma hiatus, especially in the central part of Jordan. Subsequently, a marked transgression took place over the whole of Jordan which resulted in the prevalence of deep water conditions (Zones P4 or equivalent NP7/8); this caused the deposition of a retrogradational parasequence set of middle shelf pelagic marl and chalk during a rapid relative rise of sea-level.A correlative hiatus and time gap have also been reported in different parts of the Arabian and African plates, indicating that Jordan was influenced by regional tectonics that combined with the latest Maastrichtian sea-level fall resulted in a long-term sub-marine hiatus and/or non-deposition of sediments. A combination of sea level changes and tectonic uplift are the likely cause for such a long gap in the sediment record in the region.

Anatomy And Sequence Architecture of the Early Post-Rift In the Neuquen Basin (Argentina): A Response To Physiography and Relative Sea-Level Changes

Abstract A detailed architectural and sequence stratigraphic analysis was carried out in the early-post-rift succession of central Neuquen Basin (Middle Jurassic Cuyo Group), integrating outcrop and subsurface information from a 3,000 km2 area. Sedimentary facies analysis allowed the definition of six marine facies associations, which are grouped in two main depositional systems. During the late Toarcian to early Bathonian a storm- and wave-dominated shoreface to offshore system was developed. This is overlain by a late Bathonian–early Callovian fluvio-deltaic depositional system. The sequence stratigraphic analysis of this succession identified parasequences limited by marine flooding surfaces with little evidence of erosion. Parasequences could be grouped into four parasequence sets that show the evolution of the depositional systems and can be interpreted in terms of shoreline trajectories. In this sense, a log-term transgressive event defined by a complicated retrogradational stacking pattern and spanning for almost 10 My is identified for the older deposits. This succession is eventually replaced by a progradational unit that represents highstand conditions. The Cuyo succession identified in this part of the basin is completed by the development of a regressive surface and the onset of a deltaic depositional system with no parasequence development but indicating an abrupt basinward facies shift. The long-term transgression that dominates the early post-rift succession in this part of the basin is interpreted to represent a period of sustained accommodation creation produced by the combination of thermal subsidence, differential compaction of syn-rift deposits, and eustatic rise under a relatively low sediment supply. Changes in the stacking pattern of retrogradational parasequence sets are thought to be produced by changes in the bathymetry of the topography being flooded, which is a relic of a complex array of footwalls and shoulders generated during the syn-rift stage. Regional changes in thickness and timing for the early post-rift succession could be therefore the result of the relatively passive infill of an inherited topography of the syn-rift, suggesting that most of the accommodation was already created before the onset of the long-term transgressive trend that characterizes the post-rift succession in this part of the basin. The Cuyo Group succession reported here reflects the complexity in terms of depositional styles, sequence stratigraphic patterns, and controls that can be expected during the early-post rift infill of syn-rift structural depressions. Therefore, the results of this study can provide useful lessons for post-rift systems having prolific hydrocarbon production worldwide (e.g., in the Northern North Sea, Norwegian Sea, Thailand, and Argentina and Chile).

Sequence characteristics of foreland basin and its difference from those of other types of basin

Based on the case history study of sequence stratigraphic framework, sequence model, and the controlling factors on sequence formation in the southern Junggar foreland basin, a contrasting comparison of the characteristics among the foreland basin, the faulted basin, and the sag basin is made in the aspects of sequence architecture, filling style, the controlling factors on sequence development, the migrations of basin center and depocenter, etc.. The current study results show that there are major differences and these are documented as follows. (1) The accommodation space in foreland basin is mainly created by the subsidence caused by thrusting and napping in the foothill belt, resulting in progradational-dominated parasequence sets in the foothill area and retrogradational parasequence sets in the ramp region. (2) The accommodation space in an open-lake system in faulted basin is mainly created by the activities of the basin margin faults; thus, tectonic sequences are formed. However, in the closed-lake system, the subaqueous accommodation is mainly controlled by climatic-influenced lake-level fluctuations, and climatic sequence is formed. (3) In sag basin, a closed-lake system is easily formed due to its generation often within the cratons and isolation from the sea, and its accommodation space creation is mainly controlled by climatic lake-level fluctuations; thus, the sequence architecture in sag basin is similar to that formed on the passive continental margin.

High‐resolution sequence stratigraphy of the Maastrichtian‐Ypresian succession along the eastern scarp face of Kharga Oasis, southern Western Desert, Egypt

AbstractA thick Maastrichtian‐Ypresian succession, dominated by marine siliciclastic and carbonate deposits of the regionally recognized Nile Valley and Garra El‐Arbain facies associations, is exposed along the eastern escarpment face of Kharga Oasis, located in the Western Desert of Egypt. The main objectives of the present study are: (i) to establish a detailed biostratigraphic framework; (ii) to interpret the depositional environments; and (iii) to propose a sequence stratigraphic framework in order to constrain the palaeogeographic evolution of the Kharga sub‐basin during the Maastrichtian‐Ypresian time interval. The biostratigraphic analysis suggests the occurrence of 10 planktonic zones; two in the Early Maastrichtian (CF8b and CF7), four in the Palaeocene (P2, P3, P4c and P5) and four in the Early Eocene (E1, E2, E3 and E4). Recorded zonal boundaries and biostratigraphic zones generally match with those proposed elsewhere in the region. The stratigraphic succession comprises seven third‐order depositional sequences which are bounded by unconformities and their correlative conformities which can be correlated within and outside Egypt. These depositional sequences are interpreted as the result of eustatic sea‐level changes coupled with local tectonic activities. Each sequence contains a lower retrogradational parasequence set bounded above by a marine‐flooding surface and an upper progradational parasequence set bounded above by a sequence boundary. Parasequences within parasequence sets are stacked in landward‐stepping and seaward‐stepping patterns indicative of transgressive and highstand systems tracts, respectively. Lowstand systems tracts were not developed in the studied sections, presumably due to the low‐relief ramp setting. The irregular palaeotopography of the Dakhla Basin, which was caused by north‐east to south‐west trending submerged palaeo‐highs and lows, together with the eustatic sea‐level fluctuations, controlled the development and location of the two facies associations in the Kharga Oasis, the Nile Valley (open marine) and Garra El‐Arbain (marginal marine).

Towards the standardization of sequence stratigraphy: Is the parasequence concept to be redefined or abandoned?

After more than thirty years from the introduction of the sequence-stratigraphic concepts (Payton, 1977), and their refinement in the classic SEPM special publication 42 (Wilgus et al., 1988), sequence stratigraphy has becomemoremature and now represents a widely used tool to study sedimentary successions. More recently, review publications (e.g. Miall, 1997; Posamentier and Allen, 1999; Catuneanu, 2006; Catuneanu et al., 2009) have put order among the various sequence-stratigraphic models and attempted to standardize the terminology. Among the historical issues raised by sequence-stratigraphic concepts and terminology, one deals with the high-frequency cycles that compose sequences, which have been named parasequences. A parasequence was defined as ‘a relatively conformable succession of genetically related beds or bedsets bounded by marine flooding surfaces and their correlative surfaces... Parasequences are progradational and therefore the beds within parasequences shoal upward’ (Van Wagoner et al., 1987, 1988, 1990). The flooding surface was defined as ‘a surface across which there is an abrupt shift of facies that may indicate an increase in water depth or a decrease in sediment supply’ (Van Wagoner et al., 1988, 1990). Parasequences may be stacked to form progradational, aggradational and retrogradational parasequence sets, which typify systems tracts composing a sequence (VanWagoner et al., 1990), the latter being defined as ‘a stratigraphic unit composed of a relatively conformable succession of genetically related strata and bounded at its top and base by unconformities or their correlative conformities’ (Mitchum, 1977).

Sequence stratigraphic framework and distribution of depositional systems for the Paleogene in Liaodong Bay area

With a comprehensive geological and geophysical data base, the Paleogene in the Liaodong Bay area, which consists of the Kongdian, Shahejie and Donghying Formations from the base to top, was divided into 4 second-order sequences and 8 third-order sequences based on the characteristics of the sequence boundaries. Each third-order sequence is subdivided into the lowstand, lake transgressive and highstand systems tracts. The Lowstand systems tract (LST) is mainly composed of progradational parasequence sets, while the lake transgressive systems tract (TST) largely consists of the retrogradational parasequence sets and the highstand systems tract (HST) is dominated by the progradational parasequence sets. The main types of depositional systems include the shallow lake, semi-deep lake, deep lake, delta, fan delta, braided fluvial delta and nearshore subaqueous fan. The braided fluvial delta and fan delta depositional systems are mainly confined to the sequences of the lower SEs4-Ek, SEs3 and SEs1+2, while the sequences of SEd3, SEd2 and SEd1 are dominated by the delta and nearshore subaqueous fan depositional systems with the latter being developed at the downthrown side of the basin-bounding fault in each sequence. The evolution of the depositional systems is always controlled by the paleo-tectonic setting and the ancient landform in the space and geological time. It is concluded that the most favorable reservoirs are distributed in the Liaoxi low uplift and the central Liaozhong sag.

Sequence stratigraphy of the siliciclastic East Puolanka Group, the Palaeoproterozoic Kainuu Belt, Finland

The 2300–2600 m thick Palaeoproterozoic East Puolanka Group within the central Fennoscandian Shield records four major transgressions on the cratonic margin within the approximate time period 2.25–2.10 Ga. Stacking of siliciclastic facies in parasequences and parasequence sets provides data to evaluate oscillation of relative sea-level and subsidence on different temporal scales. The lowermost part of the passive margin prism is characterized by alluvial plain to shallow marine sediments deposited in incised valleys. The succeeding highstand period is recorded by ca. 250 m of progradational parasequence sets of predominantly rippled and horizontally laminated sandstones, representing stacked wave-dominated shoreline units in sequence 1, capped by a hiatus or, in some places, by a subaerial lava. As relative sea-level rose again, sand-rich barrier-beach complexes developed with microtidal lagoons and inlets, corresponding to a retrogradational parasequence set. This was followed by a highstand period, with aggradation and progradation of alluvial plain and coastal sediments grading up into wave-tide influenced shoreline deposits in sequence 2. In sequence 3, the succeeding mudstones represent tidal flat deposits in a back-barrier region. With continued transgression, the parasequences stacked retrogradationally, each flooding episode being recorded by increasingly deeper water deposits above low-angle cross-bedded sandstones of the swash zones. The succeeding highstand progradation is represented by alluvial plain deposits. The next transgressive systems tract, overlying an inferred erosional ravinement surface, is recorded by a retrogradational parasequence set dominated by low-angle cross-stratified swash zone deposits in sequence 4. The large-scale trough cross-bed sets in these parasequences represent sand shoals and sheets of the inner shelf system. The overall major transgression recorded in the lowermost part of the Palaeoproterozoic cratonic margin succession was related to first- to second-order sea-level changes, probably due to increasing regional thermal subsidence of the lithosphere following partial continental breakup. The stratigraphic evolution can be related to changes of relative sea-level with a frequency of ca. 25 million years, probably propagated by episodic thermal subsidence. The parasequences identified here are related to high-frequency cycles of relative sea-level change due to low-magnitude eustatic oscillations.

Sedimentary facies and palynofacies assemblages in an Eocene perennial lake, Lumbrera formation, northwest Argentina

The combined application of sedimentary facies and palynofacies analyses constitutes a valuable method for paleoenvironmental and paleoclimatic reconstructions, especially in continental strata in which fossil information is scarce or absent. In this paper, we present an integrated model based on this methodology for the Eocene lacustrine rocks of the Lumbrera Formation in northwest Argentina. The new data contribute to the understanding of the evolution of the final post-rift stage of the Salta Group in northwest Argentina. The lacustrine deposits of the Lumbrera Formation are named Faja Verde I and Faja Verde II. In the Alemanı́a area, the Faja Verde II consists of green claystones and mudstones interbedded with sandstones and deposited in a perennial lake and fluvio-dominated delta complex. In addition, there are two major cycles that are separated by a flooding surface. The basal cycle is a retrogradational parasequence set, and the upper cycle is a progradational parasequence set. The palynofacies analysis and organic matter analytical data (TOC and Pyrolysis Rock-Eval) of each sedimentary facies are closely related to the dynamics of the depositional environment. Proximal prodelta (Palynofacies association I), distal prodelta (Palynofacies association II), lacustrine (Palynofacies association III), and interdistributary bay fill (Palynofacies association IV) subenvironments are differentiated. Each is characterized by a definitive relationship of phytoclasts, amorphous, palynomorphs, fluorescence index, quality, and quantity of the organic matter. The variation of occurrence of the Pediastrum– Botryococcus algae reflects fluctuations in the level of water related to identified cycles of shallowing.

The relationship between glacio-eustatic parasequences and a third-order sequence in the Kakegawa Group, central Japan

The Plio–Pleistocene Kakegawa Group, central Japan, consists of a third-order depositional sequence (2.6–1.0 Ma). The northwestern part of the Kakegawa sequence consists of up to 500 m of alluvial, shoreface, shelf, slope and submarine-channel facies. It contains at least sixteen upward-shallowing cycles (parasequences), the deposition of which was affected by high-frequency eustatic sea-level cycles. The lower part of the sequence is characterized by a retrogradational parasequence set, which formed a transgressive systems tract (2.2–1.75 Ma) followed by a progradational parasequence set comprising a highstand systems tract (1.75–1.4 Ma). Subsidence analysis and evaluation of changes in the shelf sedimentation rate estimated from cross-sections, suggest that formation of the third-order sequence was controlled by tectonic subsidence and variation in the sedimentation rate. Rapid subsidence and a high rate of sedimentation during 2.2–2.0 Ma resulted in deposition of the lower part of the transgressive systems tract, characterized by thick backstepping successions. The rate of subsidence decreased in the period 2.0–1.75 Ma. The sedimentation rate also decreased due to a high rate of sediment bypassing. However, subsidence was still the dominant factor, leading to the formation of thin backstepping successions. The 1.75–1.4 Ma progradational succession resulted from a combination of a low rate of subsidence and moderate sedimentation. The progradational units become thicker basinward owing to faster subsidence in the basin center. The maximum flooding surface was formed around 1.75 Ma even though subsidence was slow at this time.

A Liassic isolated platform controlled by tectonics: South Iberian Margin, southeast Spain

The middle and upper members of the Gavilán Formation near Vélez-Rubio (Almería Province, southeast Spain) are interpreted as carbonate platform deposits. The studied outcrops form geologically part of the External Zones of the Betic Cordillera (South Iberian Palaeomargin). A genetic unit limited by intra-Sinemurian and intra-Upper-Carixian sedimentary breaks is defined. The evolution of the parasequence sets in the area, and the development of deeper sedimentation in its northern outcrops, suggest that this platform was isolated with regard to the South Iberian Margin. Three distinct parasequence sets are proposed: progradational parasequence set (only locally present), retrogradational parasequence set (middle member of the Gavilán Formation) and aggradational parasequence set (basically composed of the upper member of the Gavilán Formation). Sedimentary features (such as neptunian dykes, sharp lithological changes, thickness variations), the presence of palaeofaults and the subsidence history all lead to the conclusion of a significant regional tectonic influence in the genetic unit evolution. Normal extensional faulting has been proposed as a major control on sedimentation on this isolated platform. This regional factor has completely distorted the effect of the eustatic fluctuations for this period of time.

Sequence Stratigraphic and Synsedimentary Tectonic Controls on Reservoir Compartmentalization in a Transgressive Sequence Set: Almond Formation, Southwest Wyoming: ABSTRACT

The Campanian upper Almond Formation in Southwestern Wyoming contains at least 15 aggradational to backstepping microtidal to low mesotidal barrier/shoreline complexes laid down during a period of net transgression from 72 to 70.5 million years ago. Reservoir compartmentalization in the upper Almond occurs at several scales, including an aggradational to retrogradations sequence set composed of 3 retrogradational parasequence sets; numerous parasequences, and diverse barrier sub-facies units. The lowstand shorelines of these sequence sets stack aggradationally prior to transgression by a really extensive, marine mudstone horizons which separate the sequences. Highstand systems tracts are poorly preserved, often completely removed below fourth of fifth order sequence boundaries which cause seaward jumps of facies in excess of 30 Km and place fluvial sediment, coal and lagoonal deposits abruptly over marine mudstone. Each sequence in the upper Almond is composed of several parasequences (sanding-upward, storm-dominated barrier shorefaces) which intercalate with marine mudstone to the east and grade into oyster-bearing, organic-rich lagoonal mudstone to the west. Compartmentalization in the barrier complexes occurs at most parasequence boundaries and in association with major sub-facies; boundaries (barrier margins, tidal inlets, flood-tidal deltas, washover fans). Further reservoir compartmentalization is induced by synsedimentary faulting and subsidence which locally preserve isolatedmore » reservoir-quality barrier/shoreline sandstone bodies by dropping them below the depth of ravinement (5-30 m). The recognition of synsedimentary faulting and subsequent ravinement is critical to accurate sequence stratigraphic analysis and for prediction of reservoir compartments.« less

Sequence Stratigraphy and Depositional Setting of the Tiber Delta: Integration of High-resolution Seismics, Well Logs, and Archeological Data

ABSTRACT Using archeological evidence, radiocarbon data, well logs, and high-resolution seismic profiles, we applied sequence-stratigraphic analysis to sediments deposited during the last glacio-eustatic cycle on the Tyrrhenian continental margin embracing the Tiber River months. These sediments form a high-frequency sequence of fifth order that has developed over the last 20,000 yr since the last lowstand, hereafter referred to as the Tiber Depositional Sequence (TDS). The TDS is still evolving and lies on a Type 1 sequence boundary that has been identified both on the shelf and below the present delta plain. This sequence consists of lowstand, transgressive, and highstand systems tracts. The lowstand deposits are not present on the shelf but are found on the continental slope, where they constitute the last progradation set of the continental margin. A network of gullies, active when the river mouth was at the shelf break, is present within the lowstand deposits. The transgressive-systems-tract (TST) deposits lie directly on the basal unconformity. Landwards the TST is represented by a retrogradational parasequence set of fluvial, coastal barrier-lagoon, and lagoonal delta facies. Seaward, on the shelf, these parasequences merge into a seismically transparent deposit that forms a condensed section. The flooding surfaces that bound the parasequences are marked by peat layers that were dated by 14C. The radiometric ages were used to draw a carve of sea-level rise for the last 11,000 yr. The top of the transgressive systems tract (maximum flooding surface) is represented by the last peat layer, which was formed about 4700-5000 yr BP and buried 4-5 m below the present upper delta plain. The highstand systems tract is made up of deposits of the present Tiber wave-dominated delta, i.e., upper and lower delta plain, delta front, and prodelta slope. The aligned beach ridges mark the position of the prograding coastline, which for the last 2500 yr can be dated by archeological and historical data. The recent very fast progradation of the Tiber delta, during the last 500 years, is consistent with historical data on floods of the city of Rome and the suspended load of the Tiber River.