The SACROC unit is an isolated carbonate platform style of reservoir that typifies a peak icehouse system. Icehouse carbonate platforms are one of the least well understood and documented carbonate reservoir styles due to the reservoir heterogeneities they embody. The current study is an attempt to recognize carbonate rock types defined based on rock fabrics by integrating log and core based petrophysical analysis in high-frequency cycle (HFC) scale sequence stratigraphic framework and to improve our ability to understand static and dynamic petrophysical properties of these reservoir rock types, and there by, improve our understanding of heterogeneity in the middle early to late early Canyon (Canyon 2) high frequency sequence (HFS) in the Northern Platform of the SACROC Unit. Based on core descriptions, four different sub-tidal depositional facies were defined in the Canyon 2 HFS. Identified depositional facies were grouped into three different reservoir rock types in respect to their rock fabrics in order for the HFC scale petrophysical reservoir rock type characteristic analysis. Composed of succession of the identified reservoir rocks, twenty different HFCs were determined within the HFC scale sequence stratigraphic framework. The overall trend in the HFCs demonstrate systematic coarsening upward cycles with high reservoir quality at the cycle tops and low reservoir quality at the cycle bottoms. It was observed in terms of systems tracts described within the cycle scale frame work that the overall stacking pattern for high stand systems tracts (HST) and transgressive systems tracts (TST) is aggradational. And, the reservoir rocks representing the HST are more porous and permeable than those of TST. In addition to that, it was detected that the diagenetic overprint on the HST reservoir rocks is more than that of the TST. According to the overall petrophysical observations, the grain-dominated packstone deposited during HST was interpreted as the best reservoir rock. Upon well log analysis on the identified reservoir rocks, some specific log responses were attributed to the identified reservoir rocks as their characteristic log signatures. / text

Not available / text

The mixed carbonate–siliciclastic Abrigo Formation of middle and late Cambrian age, which crops out in southeastern Arizona, was deposited during the Sauk transgression in the craton interior, landward of the passive margin of Laurentia. The Abrigo Formation consists of ten basic rock types: claystone, siltstone, sandstone, lime mudstone, wackestone, bioclastic grainstone, packstone, oolitic packstone, oncolitic packstone, and intraclastic conglomerate. These comprise fifteen lithofacies, which are grouped into eight facies associations. They represent an array of shallow-marine environments that were dominated by wave and storm activity. The interpreted paleoenvironments include lower offshore, upper offshore, offshore transition, and lower, middle and upper shoreface. One hundred eighty-two collections, yielding 940 trilobite remains have been found in the Abrigo Formation. They represent 69 species and 42 genera. Eight of the species are new. The fossil age ranges from early Marjuman to late Steptoean. Eight trilobite biofacies are defined from the generic relative abundance data: Ehmaniella, Olenoides–Bolaspidella, Blairella, Eldoradia, Modocia–Paracedaria, Cedaria, Coosella–Coosina, and Camaraspis. Trilobites collected and identified in this study are assigned to five biostratigraphic zones: Bolaspidella, Cedaria, Crepicephalus, Aphelaspis, and Elvinia zones. In addition, two subzones had been defined. Cedaria eurycheilos Subzone recognized in the upper part of Cedaria Zone and Coosella helena Subzone recognized in the upper part of Crepicephalus Zone. The stratigraphic succession was divided into six distinct phases associated with large-scale relative sea-level fluctuations. An initial flooding over the Bolsa Quartzite forming the transgressive systems tract was terminated by maximum flooding, and a subsequent highstand systems tract developed during Bolaspidella Biozone time. The second sequence starts with another transgressive systems tract, and is overlain by a final highstand systems tract during the Cedaria and Crepicephalus biozones. The uppermost part of the second sequence represents a falling stage systems tract that developed during Aphelaspis Biozone time. The presence of Elvinia Biozone trilobites near the base of the highest sandstone unit suggests that delivery and deposition of these sands took place during the lowstand that followed the protracted and widespread Sauk II–Sauk III hiatus. Sedimentary dynamics were controlled by storm-induced wave action and offshore flows. There are two carbonate factories that operated simultaneously in this Cambrian inner shelf region. Dominance of carbonate versus siliciclastic strata in the offshore transition setting is interpreted to reflect periods when siliciclastic input was depleted, such that increasing accommodation and reduction of clay and possibly nutrients promoted carbonate production. Clay and silt bypassed the nearshore carbonate-depositing zone. Siliciclastic sediment input and dispersal were not only restricted to the falls in sea level, but appear to have dominated the transgressive systems tract and late phase of the highstand. Thus, carbonate sedimentation does not dominate the entire highstand systems tract as is commonly held but, rather, only during the late phase of the transgressive and early highstand phase. The comparison of this Cambrian model with younger mixed carbonate-siliciclastic units will help reveal the subtleties of the carbonate factory and how it operated in response to biotic evolution.

The Middle Jurassic Entrada Sandstone of the Four Corners region, USA, is composed predominantly of very fine-grained, red, silty sandstone with poorly defined sedimentary structures. The origin of this facies is enigmatic, even though it is common both on the Colorado Plateau and globally, and is spatially situated between deposits recording unambiguous marine and aeolian environments. Eleven sections were measured along an 85 km transect from the Blanding Basin in southeastern Utah to the San Juan Basin in northwestern New Mexico. Outcrop and laboratory analyses distinguish eight facies: (1) silty shale, (2) shallow subaqueous reworked, fine- to medium-grained sandstone, (3) brecciated, very fine-grained sandstone, (4) crinkly laminated, very fine-grained sandstone with preserved wind ripples and abundant silty laminae, (5) weakly laminated, fine-grained sandstone with occasional silty laminae, (6) planar-laminated, fine-grained, wind-rippled sandstone, (7) cross-stratified, fine- to medium-grained aeolian cross-stratified sandstone, and (8) micritic limestone. Lateral and vertical relationships of these facies show a proximal to distal transition from cross-bedded wind-lain facies to loess-dominated sabkha facies with increasing abundance of water-lain facies basinward. The well known Todilto Limestone (facies 8) is situated stratigraphically below loess-dominated sabkha facies (facies 4 and 5) within the Entrada Sandstone, reinforcing previous interpretations that the unit represents a catastrophic flooding event and not a local groundwater flux. / text

The study area is situated along the obliquely converging boundary of the Caribbean and South American plates offshore eastern offshore Trinidad. Major structural elements in the shelf break and deep-water slope regions include normal and counter-normal faults to the south and large transpressional fault zones to the north. Well logs and biostratigraphic information were analyzed for twenty-four wells in the study area to refine previous depositional environment interpretations. For purposes of this net sand distribution analysis it was decided to consider the deltaic portion of the shelf transit cycle, against the marine portion of the shelf transit cycle and were named T and R cycles, respectively. T and R cycles were interpreted based on well log patterns and depositional facies shifts. Six T/R cycles were interpreted within the Pliocene to recent stratigraphic succession and shelf edge trajectories were also mapped for each of these cycles based on earlier stratigraphic correlations. Net-to-gross (NTG) ratios were calculated for each component of the T/R cycles and plotted against total thicknesses and net sand values. In addition, NTG trends were mapped for each interval and analyzed based on their proximity to the corresponding shelf edge. Mapping of the shelf edge trajectories (SET) revealed that (1) SET migrate northeasterly across the Columbus Basin through time and (2) shelf edge orientations are parallel to the strike of growth faults in the south but deflect to the northeast near the Darien Ridge indicating a strong underlying structural control. The NTG plots and maps also revealed that (1) For T cycles, NTG values never exceed 60% and are inversely proportional to total thickness, (2) For R cycles, NTG values are highly variably ranging from 35% to 90%, (3) NTG values increase as the shelf break is approached and (4) The distribution of NTG ratios is also controlled by accommodation space created by local structures. The Guiana current is believed to play an important role in the redistribution and reworking of sand in the Columbus Basin. Aggradation and progradation distances were computed for each interval and the results suggest that the younger Sequences C2 (T-R cycle E) and C3 (T-R cycle F) show a stronger progradational trend than the older C4, C5 and C6. This strong progradational trend might indicate delivery of sand basinwards, while for the older intervals; the aggradational trend suggests an increase in sediment storage. In long-term scale (1-2 m.y.) the Orinoco Delta seems to behave as an aggradational delta that increases sediment storage due to growth fault and high subsidence rates. However, in the short-term scale, the Orinoco delta seems to behave as a rapid progradational delta, for the younger sequences C2 and C3, where sediment bypass is more likely to occur; and as a rapid aggradational (slow prograding) margin for the older intervals C4, C5 and C6. / text

The uplift history of the Tibetan Plateau is poorly constrained in part due to its complex and extended tectonic history. This study uses basin analysis, stable isotope analysis, magnetostratigraphy, detrital zircon U-Pb dating, and paleoaltimetry, and frequency analysis to reconstruct the tectonic, spatial, and environmental evolution of the Zhada basin in southwestern Tibet since the late Miocene. The Zhada Formation, which occupies the Zhada basin and consists of ~ 850 m of fluvial, alluvial fan, eolian, and lacustrine sediments, is undeformed and lies in angular unconformity above Tethyan sedimentary sequence strata. The most negative Miocene δ¹⁸Opsw (paleo-surface water) values reconstructed from aquatic gastropods are significantly more negative than the most negative modern δ¹⁸O(sw) (surface water) values. In the absence of any known climate change which would have produced this difference, we interpret it as indicating a decrease in elevation in the catchment between the late Miocene and the present. Basin analysis indicates that the decrease in elevation was accomplished by two low-angle detachment faults which root beneath the Zhada basin and exhume mid-crustal rocks. This exhumation results from ongoing arc-parallel extension and provides accommodation for Zhada basin fill. Sequence stratigraphy shows that the basin evolved from an overfilled to an underfilled basin but that further evolution was truncated by an abrupt return to overfilled, incising conditions. This evolution is linked to progressive damming of the paleo-Sutlej River. During the underfilled portion of basin evolution, depositional environments were strongly influenced by Milancovitch cyclicity: particularly at the precession and eccentricity frequencies.

The whole Mediterranean was a site of carbonate deposition during Miocene. Unlike other Miocene basins in the Mediteranean, the importance of Mut Basin lies in its tectonically undisturbed nature that provides excellent exposures to study sequence stratigraphic architecture and carbonate sedimentology. Opening of Mut Basin began during Oligocene / carbonate deposition started during Early Miocene. The pre-Miocene rocks are characterized by (from bottom to top), 1. ophiolites and Mesozoic limestones, 2. Eocene lacustrine limestones, 3. Burdigalian fluvial sandstones and conglomerates. The carbonate deposition began in Miocene, settling on the preexisting topography. Carbonates have been deposited in a ramp setting, where several sequences formed. The ramp was partly subaerially exposed during Early Miocene due to relative sea level fall / however, no significant lowstand deposits were developed. The subsequent sea level rise caused transgressive deposits to overlie this ramp sequence. The patch reefs on this ramp exhibit a keep-up type depositional setting. As the transgression continued, the basin topography controlled the type of depositional setting. Hence, a transition from ramp to reefal margin type setting occurred. In landward direction the topographically low areas became back reef lagoonal part of this reefal margin. A mature reefal environment formed during highstand times, which is characterized by a rich coral fauna / algal flora in the basinward side. Some of the patch reefs of the ramp transformed into pinnacle reefs. Diagenetic alterations are mostly related to duration and degree of sea level fall, and therefore related to sequence boundaries. The Miocene carbonates in the study area consist of six sequences which may be used for correlation with other Miocene carbonates of the Mediterranean region.

The Oligocene Te Kuiti Group in Waitomo County, North Island, New Zealand, is divided into two subgroups, six formations and seven limestone members; six of the members are new. The stratigraphic definition, distribution, thickness, lithology and contacts of major rock units, and the three dimensional relationships between them, are described and figured in detail. Rapid lateral and vertical lithologic variation in strata is accomodated by recognition of 31 lithofacies. Te Kuiti sediments, which include mainly bioclastic lutites, bioclastic arenites and biocalcarenites, were deposited in sublittoral waters, from a few to about 100 metres depth, as seas transgressed south over a topoqraphically subdued, but locally varied landscape cut in Mesozoic lutites and arenites. Distribution of major paleotectonic elements indicates the gross sedimentary environment was one of a north-facing, partly enclosed basin with a prominent north-trending median basement ridge (Piopio High) in the south. Deposition continued until this ridge was almost completely buried, at which time the Te Kuiti embayment expanded rapidly and linked with more southerly basins. The contact with the overlying Mahoenui Group is generally conformable in Waitomo County. Formations and members are commonly bounded by unconformities, mainly disconformities, some of which preserve features consistent with their interpretation as submarine hardgrounds. The unconformities record periods of erosion or non-deposition during major downward shifts in base level controlled partly by eustatic sea level changes. Comprehensive paleontological charts are prepared for each formation and age relationships established. Macrofossils are generally scarce, and dominated by thick-shelled, epifaunal bivalves. Foraminifera are more abundant and are mainly benthonic forms. Formations may straddle New Zealand stage boundaries and, within Waitomo County, are not strongly diachronous. Primary sedimentary structures in arenites and calcarenites include mainly thinly bedded wavy-, lenticular-, and cross-stratification formed by the spreading and interfering of sand sheets, sand ribbons and sand waves across extensive areas of flat shallow sea floor, possibly under the influence of tidal currents. Lutites and muddy arenites are massive and bioturbated. A new classification for mixed terrigenous-allochemical rocks is proposed and an X-ray technique developed for modal analyses of lutites. The petrography of individual lithofacies is described and illustrated in detail and summarised on pie diagrams. Variations in the kind, quantity, size, sorting and abrasion of bioclasts, in the king and quantity of matrix add/or cement, and in the content of glauconite and terrigenous sand and mud serve to distinguish the various lithofacies. Bioclasts are derived principally from bryozoans, echinoids and benthonic foraminifers and, to a lesser extent, from coralline algae, planktonic foraminifers, molluscs and brachiopods. Siliciclasts include mainly quartz, oligoclase – andesine plagioclase, potash feldspar, montmorillonitic clays and glauconite. Quartz and feldspar were detritally inherited from Mesozoic basement rocks; montmorillonite formed from the marine diagenetic transformation of vermiculite and degraded chlorite and illite derived from Oligocene soils; glauconite developed from mont-morillonitic clays under specific environmental conditions. Complete chemical analyses of seven glauconite concentrates are presented and compared with published analyses. The principal non-opaque heavy minerals in the group are zircon, epidote and apatite. Sediment pores are infilled with granular and rim ortho-sparite cement, or by a variety of matrix materials, including micrite, calcilutite and lutite. Petrologs display the vertical variation in petrographic properties through the group and, in conjunction with grain size analyses of insoluble residues, are used to interpret the energy level of the environment of deposition of individual rock units. Te Kuiti sediments accumulated under a spectrum of environmental energy conditions, ranging from quiet to strongly agitated waters. The primary Te Kuiti sediment was dominated by metastable magnesium calcite and, less abundant, aragonite skeletons. These skeletons underwent syndiagenetic stablisation reactions at, or close below, the sea floor. Large quantities of skeletal aragonite were dissolved from the sediment before lithification. Aragonite was preserved only where anaerobic conditions were maintained in the sediment. Stabilisation of magnesium calcite grains involved the texturally non-destructive process of incongruent dissolution, which yielded a replacement product of calcite. Sources of CaCO3 for cement included (a) solution of aragonite grains, (b) intergranular solution of bioclasts and, most important, (c) pervasive solution of bioclasts, under shallow burial loads, at those levels in the sediment relatively enrichment in siliciclastic, and especially muddy, material. Dissolved CaCO3 was precipitated as calcite cement in adjacent or nearby sediment layers. A paragenetic sequence of diagenetic events is established for the group. Finally, Oligocene paleogeography and paleoclimate are outlined and a synthesis of the environment of formation and depositional history of sediments of the Te Kuiti Group in Waitomo Country is established.

The Oligocene Te Kuiti Group in Waitomo County, North Island, New Zealand, is divided into two subgroups, six formations and seven limestone members; six of the members are new. The stratigraphic definition, distribution, thickness, lithology and contacts of major rock units, and the three dimensional relationships between them, are described and figured in detail. Rapid lateral and vertical lithologic variation in strata is accomodated by recognition of 31 lithofacies. Te Kuiti sediments, which include mainly bioclastic lutites, bioclastic arenites and biocalcarenites, were deposited in sublittoral waters, from a few to about 100 metres depth, as seas transgressed south over a topoqraphically subdued, but locally varied landscape cut in Mesozoic lutites and arenites. Distribution of major paleotectonic elements indicates the gross sedimentary environment was one of a north-facing, partly enclosed basin with a prominent north-trending median basement ridge (Piopio High) in the south. Deposition continued until this ridge was almost completely buried, at which time the Te Kuiti embayment expanded rapidly and linked with more southerly basins. The contact with the overlying Mahoenui Group is generally conformable in Waitomo County. Formations and members are commonly bounded by unconformities, mainly disconformities, some of which preserve features consistent with their interpretation as submarine hardgrounds. The unconformities record periods of erosion or non-deposition during major downward shifts in base level controlled partly by eustatic sea level changes. Comprehensive paleontological charts are prepared for each formation and age relationships established. Macrofossils are generally scarce, and dominated by thick-shelled, epifaunal bivalves. Foraminifera are more abundant and are mainly benthonic forms. Formations may straddle New Zealand stage boundaries and, within Waitomo County, are not strongly diachronous. Primary sedimentary structures in arenites and calcarenites include mainly thinly bedded wavy-, lenticular-, and cross-stratification formed by the spreading and interfering of sand sheets, sand ribbons and sand waves across extensive areas of flat shallow sea floor, possibly under the influence of tidal currents. Lutites and muddy arenites are massive and bioturbated. A new classification for mixed terrigenous-allochemical rocks is proposed and an X-ray technique developed for modal analyses of lutites. The petrography of individual lithofacies is described and illustrated in detail and summarised on pie diagrams. Variations in the kind, quantity, size, sorting and abrasion of bioclasts, in the king and quantity of matrix add/or cement, and in the content of glauconite and terrigenous sand and mud serve to distinguish the various lithofacies. Bioclasts are derived principally from bryozoans, echinoids and benthonic foraminifers and, to a lesser extent, from coralline algae, planktonic foraminifers, molluscs and brachiopods. Siliciclasts include mainly quartz, oligoclase – andesine plagioclase, potash feldspar, montmorillonitic clays and glauconite. Quartz and feldspar were detritally inherited from Mesozoic basement rocks; montmorillonite formed from the marine diagenetic transformation of vermiculite and degraded chlorite and illite derived from Oligocene soils; glauconite developed from mont-morillonitic clays under specific environmental conditions. Complete chemical analyses of seven glauconite concentrates are presented and compared with published analyses. The principal non-opaque heavy minerals in the group are zircon, epidote and apatite. Sediment pores are infilled with granular and rim ortho-sparite cement, or by a variety of matrix materials, including micrite, calcilutite and lutite. Petrologs display the vertical variation in petrographic properties through the group and, in conjunction with grain size analyses of insoluble residues, are used to interpret the energy level of the environment of deposition of individual rock units. Te Kuiti sediments accumulated under a spectrum of environmental energy conditions, ranging from quiet to strongly agitated waters. The primary Te Kuiti sediment was dominated by metastable magnesium calcite and, less abundant, aragonite skeletons. These skeletons underwent syndiagenetic stablisation reactions at, or close below, the sea floor. Large quantities of skeletal aragonite were dissolved from the sediment before lithification. Aragonite was preserved only where anaerobic conditions were maintained in the sediment. Stabilisation of magnesium calcite grains involved the texturally non-destructive process of incongruent dissolution, which yielded a replacement product of calcite. Sources of CaCO3 for cement included (a) solution of aragonite grains, (b) intergranular solution of bioclasts and, most important, (c) pervasive solution of bioclasts, under shallow burial loads, at those levels in the sediment relatively enrichment in siliciclastic, and especially muddy, material. Dissolved CaCO3 was precipitated as calcite cement in adjacent or nearby sediment layers. A paragenetic sequence of diagenetic events is established for the group. Finally, Oligocene paleogeography and paleoclimate are outlined and a synthesis of the environment of formation and depositional history of sediments of the Te Kuiti Group in Waitomo Country is established.

The Oligocene Te Kuiti Group in Waitomo County, North Island, New Zealand, is divided into two subgroups, six formations and seven limestone members; six of the members are new. The stratigraphic definition, distribution, thickness, lithology and contacts of major rock units, and the three dimensional relationships between them, are described and figured in detail. Rapid lateral and vertical lithologic variation in strata is accomodated by recognition of 31 lithofacies. Te Kuiti sediments, which include mainly bioclastic lutites, bioclastic arenites and biocalcarenites, were deposited in sublittoral waters, from a few to about 100 metres depth, as seas transgressed south over a topoqraphically subdued, but locally varied landscape cut in Mesozoic lutites and arenites. Distribution of major paleotectonic elements indicates the gross sedimentary environment was one of a north-facing, partly enclosed basin with a prominent north-trending median basement ridge (Piopio High) in the south. Deposition continued until this ridge was almost completely buried, at which time the Te Kuiti embayment expanded rapidly and linked with more southerly basins. The contact with the overlying Mahoenui Group is generally conformable in Waitomo County. Formations and members are commonly bounded by unconformities, mainly disconformities, some of which preserve features consistent with their interpretation as submarine hardgrounds. The unconformities record periods of erosion or non-deposition during major downward shifts in base level controlled partly by eustatic sea level changes. Comprehensive paleontological charts are prepared for each formation and age relationships established. Macrofossils are generally scarce, and dominated by thick-shelled, epifaunal bivalves. Foraminifera are more abundant and are mainly benthonic forms. Formations may straddle New Zealand stage boundaries and, within Waitomo County, are not strongly diachronous. Primary sedimentary structures in arenites and calcarenites include mainly thinly bedded wavy-, lenticular-, and cross-stratification formed by the spreading and interfering of sand sheets, sand ribbons and sand waves across extensive areas of flat shallow sea floor, possibly under the influence of tidal currents. Lutites and muddy arenites are massive and bioturbated. A new classification for mixed terrigenous-allochemical rocks is proposed and an X-ray technique developed for modal analyses of lutites. The petrography of individual lithofacies is described and illustrated in detail and summarised on pie diagrams. Variations in the kind, quantity, size, sorting and abrasion of bioclasts, in the king and quantity of matrix add/or cement, and in the content of glauconite and terrigenous sand and mud serve to distinguish the various lithofacies. Bioclasts are derived principally from bryozoans, echinoids and benthonic foraminifers and, to a lesser extent, from coralline algae, planktonic foraminifers, molluscs and brachiopods. Siliciclasts include mainly quartz, oligoclase – andesine plagioclase, potash feldspar, montmorillonitic clays and glauconite. Quartz and feldspar were detritally inherited from Mesozoic basement rocks; montmorillonite formed from the marine diagenetic transformation of vermiculite and degraded chlorite and illite derived from Oligocene soils; glauconite developed from mont-morillonitic clays under specific environmental conditions. Complete chemical analyses of seven glauconite concentrates are presented and compared with published analyses. The principal non-opaque heavy minerals in the group are zircon, epidote and apatite. Sediment pores are infilled with granular and rim ortho-sparite cement, or by a variety of matrix materials, including micrite, calcilutite and lutite. Petrologs display the vertical variation in petrographic properties through the group and, in conjunction with grain size analyses of insoluble residues, are used to interpret the energy level of the environment of deposition of individual rock units. Te Kuiti sediments accumulated under a spectrum of environmental energy conditions, ranging from quiet to strongly agitated waters. The primary Te Kuiti sediment was dominated by metastable magnesium calcite and, less abundant, aragonite skeletons. These skeletons underwent syndiagenetic stablisation reactions at, or close below, the sea floor. Large quantities of skeletal aragonite were dissolved from the sediment before lithification. Aragonite was preserved only where anaerobic conditions were maintained in the sediment. Stabilisation of magnesium calcite grains involved the texturally non-destructive process of incongruent dissolution, which yielded a replacement product of calcite. Sources of CaCO3 for cement included (a) solution of aragonite grains, (b) intergranular solution of bioclasts and, most important, (c) pervasive solution of bioclasts, under shallow burial loads, at those levels in the sediment relatively enrichment in siliciclastic, and especially muddy, material. Dissolved CaCO3 was precipitated as calcite cement in adjacent or nearby sediment layers. A paragenetic sequence of diagenetic events is established for the group. Finally, Oligocene paleogeography and paleoclimate are outlined and a synthesis of the environment of formation and depositional history of sediments of the Te Kuiti Group in Waitomo Country is established.