Campanian M1 Sandstone is one of the major prospective sandstone units in the Tarapoa field in Oriente Basin, Ecuador. The M1 Sandstone is always markedly sharp based, averages 25 m in thickness, shows upward increasing marine bioturbation and generally fines upward from coarse to very fine grained sandstone. In cores, the sandstones at base are amalgamated coarse to fine grained with prominent cross stratification (dm thick), sometimes clearly bi-directional and contains mud drapes. These suggest strong tidal or fluvial-tidal currents in estuary channels or delta distributary channels. The finer grained intervals in the middle are brackish-water intensely bioturbated and dominated by mud drapes, wavy and flaser bedding suggestive of intertidal flats. Associated overlying coals and coaly shales suggest supratidal conditions. The sandstones at top are cross stratified and contain mud drapes. These again suggest strong tidal or fluvial-tidal currents in estuary channels or delta distributary channels. The stacking pattern of facies in M1 Sandstone reveals the evolution of the M1 depositional system, as well as the sequence stratigraphy of M1 sandstone. The evolution includes four stages of deposition which indicates an initial sea level rise, a subsequent sea level fall, and another sea level rise. Lateral sand-mud heterogeneity exists in the study area, forming “shale barriers”, i.e. elongate shale-rich zones that are lateral barriers to hydrocarbon migration. They are interpreted to be abandoned tidal channels filled with muddy tidal flat deposits during the sea level fall. An alternative hypothesis was established to explain the stacking pattern of facies in M1 Sandstone. A tide-dominated delta with poor fluvial input experienced intense tidal erosion and produced a sharp base at the base of M1 Sandstone. Then subtidal sand bars, intertidal flats, and supratidal sediments were deposited in sequence during a continuous regression. The core and well logs in an extension of the study area in the northwest is interpreted as more distal open shelf deposits, beyond the mouth of the Tarapoa estuary system, where transgressive tidal shelf ridges were coeval with the Tarapoa estuary system. This interpretation allows us to predict the environment between the two areas as a transition zone between tide-dominated estuary and open shelf. / text

The San Andres and Grayburg Formations are important stratigraphic units for constructing correlation frameworks of the Guadalupe Mountains because these strata record the transition between the ramp profiles of the San Andres along the Algerita Escarpment and the reef-rimmed platforms of the Capitan Formation of the southern Guadalupe Mountains (Franseen et al. 1989). Sarg et al. (1999) and Kerans and Tinker (1999) have published significantly different models of shelf-to-basin correlations within this stratigraphic interval. Central to the debate is the correlation of mixed carbonate-siliciclastic strata exposed at Plowman Ridge in the Brokeoff Mountains to the better-constrained strata along the Shattuck Escarpment in the Guadalupe Mountains. This study applies high-resolution cyclostratigraphy, inorganic carbon isotope geochemistry, and sequence stratigraphic concepts to test the hypothesis that the strata exposed at Plowman Ridge are equivalent to Grayburg strata exposed at the Shattuck Escarpment in the southern Guadalupe Mountains (Kerans and Nance 1991, Kerans and Kempter 2002). The shelf-to-basin cyclostratigraphic framework of the Grayburg Formation used in this study was established at the Shattuck Escarpment with data compiled from nine detailed measured sections, high-resolution photopans, and petrographic analysis. Based on one- and two-dimensional cycle stacking analysis, the Grayburg Formation was divided into three high-frequency sequences (HFSs). The high-frequency sequences contain transgressive systems tracts separated by maximum flooding surfaces from the highstand systems tracts. The Grayburg high-frequency sequences are composed of between 6 and 20 high-frequency cycles (HFCs), which were identified and classified into vertical facies successions. The Grayburg succession at Shattuck section 7 (32.09ᵒ, -104.81ᵒ) was selected as the reference section from the Guadalupe Mountains for comparison with Plowman section PR1 (32.03ᵒ, -104.89ᵒ) in the Brokeoff Mountains. Correlation between sections is documented at the 3rd-order composite sequence, high-frequency sequence, and when feasible, high-frequency cycle scale. Three high-frequency sequences recognized at Plowman Ridge section PR1 are equivalent to the G10, G11, and G12 Grayburg sequences described at Shattuck section 7. Correlation of the Grayburg G10-G12 high-frequency sequences with the three sequences at Plowman Ridge is based on comparison of overall thicknesses, facies proportions, cycle number, vertical facies succession, stratigraphic position of diagnostic units, and excursions within the inorganic carbon isotope profiles taken from both sections. Establishing the links between Grayburg strata on the Shattuck wall with strata on Plowman Ridge corroborates the framework/correlation scheme of Kerans and Tinker (1999) in lieu of other published correlation frameworks. / text

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Meren field, located offshore Niger Delta, is one of the most prolific oil-producing fields in the Niger Delta. The upper Miocene D-07, D-08 and E-01 oil sands comprise a series of stacked hydrocarbon reservoirs in Block 2 of Meren field. These reservoir sandstones were deposited in offshore to upper shoreface environments. Seven depositional facies were identified in the studied interval, each with distinct lithology, sedimentary structures, trace fossils, and wire-line log character. The dominant lithofacies are (1) locally calcite-cemented highly-bioturbated, fine-grained sandstones, (middle to lower shoreface facies); (2) cross-bedded, fine- to medium-grained well-sorted sandstones (upper shoreface facies); (3) horizontal to sub-horizontal laminated, very-fine- to fine-grained sandstone (delta front facies); (4) massive very-fine- to fine-grained poorly-sorted sandstone (delta front facies); (5) muddy silt- to fine-grained wavy-bedded sandstone (lower shoreface facies); (6) very-fine- to fine-grained sandy mudstone (lower shoreface facies); and (7) massive, silty shales (offshore marine facies). Lithofacies have distinct mean petrophysical properties, although there is overlap in the range of values. The highest quality reservoir deposits are cross-bedded sands that were deposited in high-energy upper shoreface environments. Calcite cements in lower shoreface facies significantly reduce porosity and permeability. Integration of core and wire-line log data allowed porosity and permeability to be empirically determined from bulk density. The derived equation indicated that bulk density values could predict 80% of the variance in core porosity and permeability values. Three parasequence sets were interpreted, including one lower progradational and two upper retrogradational parasequence sets. The progradational parasequence set consists of upward-coarsening delta front to upper shoreface facies, whereas the upward-fining retrogradational parasequence sets are composed of middle to lower shoreface deposits overlain by offshore marine shales. The limited amount of core data and the relatively small area of investigation place serious constraints on stratigraphic interpretations. Two possible sequence stratigraphic interpretations are presented. The first interpretation suggests the deposits comprise a highstand systems tract overlain by a transgressive systems tract. A lowstand systems tract is restricted to an incised valley fill at the southeastern end of the study area. The alternate interpretation suggests the deposits comprise a falling stage systems tract overlain by transgressive systems tract.

The Upper Devonian-Lower Carboniferous Bakken Formation is present in the subsurface of the Williston Basin in northeastern Montana, North Dakota, southwestern Manitoba and southern Saskatchewan. In the southeastern corner of Saskatchewan, the Bakken Formation either conformably overlies the Upper Devonian Big Valley Formation or unconformably overlies the Torquay Formation, and is conformably overlain by the Lower Carboniferous Souris Valley (Lodgepole) Formation. The Bakken Formation typically includes three members: the lower and upper organic-rich black shale, and the middle calcareous/dolomitic sandstone and siltstone, which makes a “perfect” petroleum system including source rock, reservoir, and seal all within the same formation. According to detailed core analysis in the southeastern corner of Saskatchewan, the Bakken Formation is divided into eight facies, and one of which (Facies 2) is subdivided into two subfacies: Facies 1 (planar cross-stratified fine-grained sandstone); Facies 2A (wavy- to flaser-bedded very fine-grained sandstone); Facies 2B (thinly parallel-laminated very fine-grained sandstone and siltstone); Facies 3 (parallel-laminated very fine-grained sandstone and muddy siltstone); Facies 4 (sandy siltstone); Facies 5 (highly bioturbated interbedded very fine-grained sandstone and siltstone); Facies 6 (interbedded highly bioturbated sandy siltstone and micro-hummocky cross-stratified very fine-grained sandstone); Facies 7 (highly bioturbated siltstone); and Facies 8 (black shale). Our integrated sedimentologic and ichnologic study suggests that deposition of the Bakken occurred in two different paleoenvironmental settings: open marine (Facies 4 to 8) and brackish-water marginal marine (Facies 1 to 3). The open-marine facies association is characterized by the distal Cruziana Ichnofacies, whereas the brackish-water marginal-marine facies association is characterized by the depauperate Cruziana Ichnofacies. Isochore maps shows that both open-marine and marginal-marine deposits are widely distributed in this study area, also suggesting the existence of a N-S trending paleo-shoreline. The Bakken strata in this study area represent either one transgressive systems tract deposits or two transgressive systems tracts separated by a coplanar surface or amalgamated sequence boundary and transgressive surface. This surface has been identified in previous studies west-southwest of our study area, therefore assisting in high-resolution correlation of Bakken strata.

The Devonian Taylor Group (the lower Beacon Supergroup), in the Taylor and Wright Valleys, southern Victoria Land (SVL), Antarctica, is separated from basement by a regional nonconformity, the Kukri Erosion Surface. Thereafter the Taylor Group sediments, observed in this thesis, are affected by two localized unconformities; the Windy Gully Erosion Surface, separating the Terra Cotta Siltstone Formation (TCzst) and older units from the younger overlying New Mountain Sandstone; and the Heimdall Erosion Surface (HES), separating the New Mountain Sandstone Formation (NMSst) and older units from the overlying Altar Mountain Formation. The depositional environments of the Windy Gully Sandstone, New Mountain Sandstone and Altar Mountain Formations have long been under debate. The Kukri Erosion Surface (KES) truncates the crystalline basement and separates the basement rock from the overlying Beacon Supergroup. Interpretation of the erosion surface characteristics and the directly overlying basal conglomerate lithofacies (WG-BCL) suggest a high relief rocky shore platform environment during a sustained and significant relative sea level fall. The environment has been suggested to be similar to what is currently seen on the West Coast, New Zealand today. The Windy Gully Sandstone Formation directly overlies the KES and consists of a basal conglomerate (WG-BCL) followed by moderately to well sorted tabular and trough cross bedded felds- to subfeldsarenites. At one location an interbedded siltstone and cross bedded sandstone lithofacies was observed and interpreted as a tidal flat. Overall interpretation of the WGSst suggests continued progradation from a rocky shore platform (WG-BCL) to a series low angle beach, to shallow marine, and back to low angle beach environments. This occurred during a relative sea level rise. Shallowing of the water column produced a gradational relationship with the Terra Cotta Siltstone Formation (TCzst).. The fine to very fine sandy mottled, well laminated siltstones moving to very fine fissile dark siltstones suggest a progression from sandy estuarine to a mud flat environment. The Terra Cotta Siltsone is truncated by the Windy Gully Erosion Surface The Windy Gully Erosion Surface is observed in the Handsley Valley by the presence of TCzst rip-up clasts in the directly overlying New Mountain Sandstone Formation. Elsewhere the horizon is either very sharp or has desiccation cracks present suggesting a cessation of deposition and subaerial exposure respectively. This suggests a small relative fall in sea level with only localized erosion. The New Mountain Sandstone Formation (NMSst) predominantly consists of a series of low angle tabular and higher angle trough cross beds. It has a subfeldsarenite base that progressively becomes a pure quartz arenites. Interpretation suggests an initial beach environment with rejuvenated sediments moving to quartzose shallow marine and back to beach environments. This represents a relative sea level rise with continued progradation The NMSst is truncated in the north by the HES forming a characteristic saw tooth pattern in the cross bedded sandstones; elsewhere the HES is represented by a feldspathic influx moving into the Altar Mountain Formation. The HES was formed due to a significant relative sea level fall leading to exposure and erosion of lithified NMSst cross beds in the north but continuation of deposition in the south. The Altar Mountain Formation consists of tabular and trough cross bedded subfields- to feldsarenites. The Odin Arkose Member directly overlying the HES is a granule to cobble conglomerate in the north where the HES is erosional and very coarse sand to granule feldsarenite in the south where the HES is conformable. This has been interpreted as a pebbly shore platform to coarse sandy to granular beach environment. The following Altar Mountain Formation is interpreted as a continuation of medium to coarse sandy beach environments with influxes of coarser sediments and possibly moving into shallow marine in places. Sequence stratigraphy identifies three stratigraphic sequences: S1, the Windy Gully Sandstone and Terra Cotta Siltstone Formations; S2, the New Mountain Sandstone Formation; and S3, the Altar Mountain Formation. The first two sequences (S1&S2) show a clear progression through transgression to a high stand systems tract through regression to a low stand systems tract. The Altar Mountain Formation follows a very similar trend but due to the lack of time and data the above measures have been speculated. Zircon age dating suggests the source of the sediments in the area come from the Neoproterozic Skelton Group and the DV2a Granite Harbour Intrusives, both directly underlying the sandstones but are exposed elsewhere in SVL. Laminated sandstone clasts within the New Mountain Basal Conglomerate Lithofacies (NM-BCL) are suggested to be sourced from recycled sediments directly below. Other exotic clasts are also observed in the lithofacies are of unknown origin.

In the mid-Cenozoic, New Zealand underwent slow subsidence interspersed with unconformity development, however significant controversy exists around both the extent of submergence below sea level during this period of maximum drowning, as well as the causes of these unconformities. Detailed field observations, combined with extensive petrographic analyses, stable isotopes, cathodoluminescence, and thin section staining were used to develop lithofacies, depositional, and sequence stratigraphic models of the mid-Cenozoic succession in the Waitaki region, South Island, to address these controversies. Twelve facies types have been described for Late Eocene-Early Miocene sedimentary rocks, leading to the identification of two major (Mid Oligocene & Early Miocene) and one minor (Late Oligocene) sequence boundaries. Surtseyan volcanism in the east produced a palaeohigh, resulting in a submerged rimmed cool-water carbonate platform, with low-lying land to the west. This eastern palaeohigh developed karst during sea-level lowstands, which correlate with silty submarine bored hardgrounds in the west. Glauconitic and phosphatic facies deposited during early marine transgression suggest an authigenic factory supplied by terrigenous clays existed during lowered sea level that was progressively shut down in favour of a carbonate factory as sea level rose and terrigenous supply decreased. The eastern palaeohigh served to nucleate this carbonate factory by raising the sea floor above the influence of siliciclastic sediment supply and providing a shallow substrate for marine colonisation. The higher energy eastern facies display dissolution of aragonitic taxa, while deeper western facies retained an aragonitic assemblage. This early bathymetric high created a barrier to submarine currents, but was gradually reduced by erosion during subsequent lowstands. Calcareous facies were often subjected to minor seafloor cement precipitation to shallow burial diagenesis, while eastern facies developed some meteoric cement during subaerial exposure. Comparisons between sea-level change in the study area and the New Zealand megasequence indicate eustatic changes as the primary driver of water depth in the Waitaki region until the development of the modern plate boundary in the Early Miocene.

No description available.