Journal articles on the topic 'Geology, Stratigraphic Eocene'
To see the other types of publications on this topic, follow the link: Geology, Stratigraphic Eocene.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Geology, Stratigraphic Eocene.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Birgenheier, L. P., M. D. Vanden Berg, P. Plink-Björklund, R. D. Gall, E. Rosencrans, M. J. Rosenberg, L. C. Toms, and J. Morris. "Climate impact on fluvial-lake system evolution, Eocene Green River Formation, Uinta Basin, Utah, USA." GSA Bulletin 132, no. 3-4 (June 19, 2019): 562–87. http://dx.doi.org/10.1130/b31808.1.
Abstract:
Abstract In light of a modern understanding of early Eocene greenhouse climate fluctuations and new highly seasonal fluvial system faces models, the role of climate in the evolution of one classically-cited continental, terminal lake system is re-examined. Detailed stratigraphic description and elemental abundance data from fifteen cores and seven outcrop regions of the Green River Formation were used to construct a ∼150 km cross section across the Uinta Basin, Utah, USA. Lake Uinta in the Uinta Basin is divided into five lake phases: (1) post-Paleocene Eocene Thermal Maximum, (2) peak Eocene hyperthermal, (3) waning hyperthermal, Early Eocene Climatic Optimum (EECO), (4) post-hyperthermal, and (5) post-EECO regimes, based primarily on climatically driven changes in fluvial style in combination with sedimentary indicators of lacustrine carbonate deposition, organic matter preservation, salinity, and lake depth. Basinwide siliciclastic dominated intervals were deposited by highly seasonal fluvial systems and record negative organic carbon isotope excursions associated with early Eocene abrupt, transient global warming (hyperthermal) events. Carbonate dominated or organic rich intervals record stable, less seasonal climate periods between hyperthermals, with lower siliciclastic sediment supply allowing the development of carbonate and organic matter preservation. The stratigraphic progression from alternating organic rich and lean zones to the overlying organic rich Mahogany and R8 zones represents the global transition out of the pulsed early Eocene hyperthermal climate regime to a time of sediment starvation and lake stratification, sequestering sedimentary organic carbon. This study provides a novel approach to terrestrial paleoclimate reconstruction that relies largely on unique sedimentary indicators and secondarily on isotopic proxy records within the context of a large basin-wide sedimentologic and stratigraphic data set, thus setting the stage for future detailed geochemical terrestrial paleoclimate proxy development.
2
Reinhardt, Lutz, Werner von Gosen, Andreas Lückge, Martin Blumenberg, Jennifer M. Galloway, Christopher K. West, Markus Sudermann, and Martina Dolezych. "Geochemical indications for the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM-2) hyperthermals in terrestrial sediments of the Canadian Arctic." Geosphere 18, no. 1 (January 7, 2022): 327–49. http://dx.doi.org/10.1130/ges02398.1.
Abstract:
Abstract During the late Paleocene to early Eocene, clastic fluvial sediments and coals were deposited in northern high latitudes as part of the Margaret Formation at Stenkul Fiord (Ellesmere Island, Nunavut, Canada). Syn-sedimentary tectonic movements of the Eurekan deformation continuously affected these terrestrial sediments. Different volcanic ash layers occur, and unconformities subdivide the deposits into four sedimentary units. Rare vertebrate fossils indicate an early Eocene (Graybullian) age for the upper part of the Stenkul Fiord outcrop. Here, we present carbon isotope data of bulk coal, related organic-rich mud and siltstones, a plant leaf wax-derived alkane, and additional plant remains. These data provide a complete carbon isotope record of one stratigraphic section with defined unconformity positions and in relation to other Eurekan deformation features. A previously dated ash layer MA-1 provided a U-Pb zircon age of 53.7 Ma and is used as a stratigraphic tie point, together with a discrete negative carbon isotope excursion found above MA-1 in a closely sampled coal seam. The excursion is identified as the likely expression of the I-1 hyperthermal event. Based on our isotope data that reflect the early Eocene dynamics of the carbon cycle, this tie point, and previous paleontological constraints from vertebrate fossils, the locations of the Paleocene-Eocene Thermal Maximum (PETM) and Eocene Thermal Maximum 2 (ETM-2) hyperthermals and their extent along the complete section are herein identified. Within the intervals of the PETM and ETM-2 hyperthermal events, increasing amounts of clastic sediments reached the site toward the respective end of the event. This is interpreted as a response of the fluvial depositional system to an intensified hydrological system during the hyperthermal events. Our study establishes an enhanced stratigraphic framework allowing for the calculation of average sedimentation rates of different intervals and considerations on the completeness of the stratigraphic record. As one of the few high-latitude outcrops of early Eocene terrestrial sediments, the Stenkul Fiord location offers further possibilities to study the effects of extreme warming events in the Paleogene.
3
Higgs, Karen E., Stuart Munday, Anne Forbes, Erica M. Crouch, and Matthew W. Sagar. "A geochemical and biostratigraphic approach to investigating regional changes in sandstone composition through time; an example from Paleocene–Eocene strata, Taranaki Basin, New Zealand." Geological Magazine 157, no. 9 (February 17, 2020): 1473–98. http://dx.doi.org/10.1017/s0016756819001596.
Abstract:
AbstractA geochemical and biostratigraphic approach has been applied to investigate the spatial and stratigraphic variability of Palaeogene sandstones from key wells in Taranaki Basin, New Zealand. Chronostratigraphic control is predominantly based on miospore zonation, while differences in the composition of Paleocene and Eocene sandstones are supported by geochemical evidence. Stratigraphic changes are manifested by a significant decrease in Na2O across the New Zealand miospore PM3b/MH1 early Eocene zonal boundary, at approximately 53.5 Ma. The change in Na2O is associated with a decrease in baseline concentrations of many other major (MnO, CaO, TiO2) and trace elements, and is interpreted to reflect a significant change in sandstone maturity. Paleocene sandstones are characterized by abundant plagioclase (albite and locally Na–Ca plagioclase), significant biotite and a range of heavy minerals, while Eocene sandstones are typically quartzose, with K-feldspar dominant over plagioclase, low mica contents and rare heavy minerals comprising a resistant suite. This change could reflect a change in provenance from local plutonic basement during the Paleocene Epoch to relatively quartz- and K-feldspar-rich granitic sources during Eocene time. However, significant quartz enrichment of Eocene sediment was also likely due to transportation reworking/winnowing along the palaeoshoreface and enhanced chemical weathering, driven in part by long-term global warming associated with the Early Eocene Climatic Optimum. The broad-ranging changes in major-element composition overprint local variations in sediment provenance, which are only detectable from the immobile trace-element geochemistry.
4
Siyako, M., and O. Huvaz. "Eocene stratigraphic evolution of the Thrace Basin, Turkey." Sedimentary Geology 198, no. 1-2 (May 2007): 75–91. http://dx.doi.org/10.1016/j.sedgeo.2006.11.008.
5
Galeotti, Simone, Eugenia Angori, Rodolfo Coccioni, Gabriella Ferrari, Bruno Galbrun, Simonetta Monechi, Isabella Premoli Silva, Robert Speijer, and Bruno Turi. "Integrated stratigraphy across the Paleocene/Eocene boundary in the Contessa Road section, Gubbio (central Italy)." Bulletin de la Société Géologique de France 171, no. 3 (May 1, 2000): 355–65. http://dx.doi.org/10.2113/171.3.355.
Abstract:
Abstract An integrated stratigraphic study of the upper Paleocene to lower Eocene Scaglia limestones of the Contessa Road section has allowed us to identify the classical markers of the Paleocene-Eocene transition. The section provides a good magnetostratigraphic record as well as a continuous calcareous nannofossil and foraminiferal biostratigraphy. A negative Carbon Isotopic Excursion (CIE) occurs in the lower part of Chron C24r. The calibration to calcareous plankton zonation indicates that the CIE occurs in the lowermost part of calcareous nannofossil Zone NP10 and the upper part of Zone CP8, that is in the planktonic foraminiferal Zone P5. In the same stratigraphic interval, a distinct turnover in the calcareous benthic foraminifera and a sharp change in the Deep Water Agglutinated Foraminiferal (DWAF) assemblages have been recognised. The record of DWAF, however, indicates a gradual initiation of such a change beginning some 150 k.y. before the CIE and BEE.
6
Riddell, Janet. "Lithostratigraphic and tectonic framework of Jurassic and Cretaceous Intermontane sedimentary basins of south-central British Columbia1This article is one of a series of papers published in this Special Issue on the theme of New insights in Cordilleran Intermontane geoscience: reducing exploration risk in the mountain pine beetle-affected area, British Columbia." Canadian Journal of Earth Sciences 48, no. 6 (June 2011): 870–96. http://dx.doi.org/10.1139/e11-034.
Abstract:
The south-central Intermontane belt of British Columbia has a complex architecture comprising late Paleozoic to Mesozoic volcanic and plutonic arc magmatic suites, marine and nonmarine clastic basins, high-grade metamorphic complexes, and accretionary rocks. Jurassic and Cretaceous clastic basins within this framework contain stratigraphy with hydrocarbon potential. The geology is complicated by Cretaceous to Eocene deformation, dismemberment, and dislocation. The Eocene to Neogene history of the southern Intermontane belt is dominated by non-arc volcanism, followed by Pleistocene to Recent glaciation. The volcanic and glacial cover makes this a difficult region to explore for resources. Much recent work has involved re-evaluating the challenges that the overlying volcanic cover has historically presented to geophysical imaging of the sedimentary rocks in this region in light of technological advances in geophysical data collection and analysis. This paper summarizes the lithological and stratigraphic framework of the region, with emphasis on description of the sedimentary units that have been the targets of hydrocarbon exploration.
7
Nielsen, Jan Kresten. "Commensal association of Corbula gibba (Bivalvia) and a sub-conical boring." Bulletin of the Geological Society of Denmark 45 (January 30, 1999): 135–38. http://dx.doi.org/10.37570/bgsd-1998-45-15.
Abstract:
An examination of fossil and Recent right valves of the infaunal, suspensionfeeding Corbula gibba (Olivi, 1792) revealed the presence of a slender, sub- conical, unbranched boring. The boring is interpreted as the work of a commensal organism, possible a parasite. Stratigraphic range is from Eocene to Recent.
8
Pomerol, Charles. "Limites evenementielles ou limites conventionnelles en stratigraphie?" Bulletin de la Société Géologique de France IV, no. 2 (March 1, 1988): 357–60. http://dx.doi.org/10.2113/gssgfbull.iv.2.357.
Abstract:
Abstract Most events characterising stratigraphic boundaries span an interval of time. The boundaries are often diachronous and they may be affected by environmental conditions. Therefore, the only accurate way to define a boundary is to select a boundary stratotype which records as many paleontological, geophysical and geochemical events as possible. Conventional stratigraphic boundaries are commonly difficult to identify precisely outside the stratotype area. This is why it is necessary to use first and last appearances of diagnostic features which occur below and above the conventional boundary. In this point of view the Eocene-Oligocene boundary is particularly significant.
9
Rasmussen, Dirk M., Brady Z. Foreman, Henry C. Fricke, Kathryn Snell, Lindsey Gipson, and Bernard Housen. "The early Paleogene stratigraphic evolution of the Huerfano Basin, Colorado." Rocky Mountain Geology 55, no. 1 (July 1, 2020): 1–26. http://dx.doi.org/10.24872/rmgjournal.55.1.1.
Abstract:
ABSTRACT Sedimentary basins throughout the North American Western Interior contain a record of Late Cretaceous through Eocene deposition related to the Laramide orogeny. The typical stratigraphic progression includes an uppermost Cretaceous fluvio-deltaic geologic formation that is unconformably overlain by an alluvial or paludal Paleocene geologic formation. The Paleocene unit is usually characterized by drab overbank facies, and overlain by an interval of amalgamated fluvial sand bodies. The overlying Eocene geologic units are characterized by red bed overbank facies. These major stratigraphic changes have been variably linked to long-wavelength dynamic subsidence, local uplift, and climatic shifts. Herein, we evaluate the depositional history of the Huerfano Basin of south-central Colorado in this overarching context. Our study presents a detailed lithofacies analysis of the Poison Canyon, Cuchara, and Huerfano Formations integrated with a new bulk (1) organic carbon isotope record, n = 299 measurements (Data Supplement 1A); and (2) magnetic record, n = 247 measurements (Data Supplement 1B). We interpret that the Paleocene Poison Canyon Formation was deposited by a braided or coarse-grained meandering river system with relatively poorly drained floodplains. The Eocene Huerfano Formation was likely deposited by a coarse-grained meandering river system with a comparatively well-drained floodplain. This pattern mirrors other Laramide basins, and is likely related to a regional drying pattern linked to long-term warming during the early Paleogene. Age of the intervening Cuchara Formation is poorly resolved, but is an anomalously thick and coarse-grained fluvial unit, with evidence for extensive reworking of floodplain deposits and a moderate coarsening-upward pattern. The Cuchara Formation is associated with magnetic trends that suggest greater oxidation and weathering, and greater variability in rainfall patterns, as well as a subtle negative shift in carbon isotope values. This pattern indicates a period of widespread progradation within the basin, potentially related to a major Laramide uplift event that affected Colorado’s Wet Mountains, Front Range, and Sangre de Cristo Mountains.
10
Gearon, James H., Cornel Olariu, and Ronald J. Steel. "The supply-generated sequence: A unified sequence-stratigraphic model for closed lacustrine sedimentary basins with evidence from the Green River Formation, Uinta Basin, Utah, U.S.A." Journal of Sedimentary Research 92, no. 9 (September 20, 2022): 813–35. http://dx.doi.org/10.2110/jsr.2021.096.
Abstract:
Abstract Closed lakes and oceans are stratigraphically distinct systems. However, closed-lake stratigraphy is often interpreted using conventional sequence stratigraphic concepts which were generated for marine settings. As a consequence, lacustrine stratigraphy has long been vexing and applied on an ad-hoc basis. To remedy this, we present a novel, unified sequence stratigraphic model for hydrologically closed (endorheic) basins: the Supply-Generated Sequence (SGS) Model. This model was generated to interpret our outcrop-based correlation—the largest to date at ∼ 30 km—across the Sunnyside Interval member of the middle Green River Formation in Nine Mile Canyon near Price, Utah, USA. The SGS model is based on the fundamental sedimentological and hydrodynamic differences between closed lakes and marine settings wherein the relationship between water discharge and sediment discharge is highly correlated. The SGS model divides packages of genetic lacustrine strata by bounding correlative surfaces, conformable or unconformable, separating facies and surfaces associated with low clastic supply (e.g., carbonates, mudstones, or exposure surfaces) from facies characteristic of relatively higher amounts of clastic supply (subaerial channelized sandstones, subaqueous siltstones, and pedogenic mudstones). We use the SGS model to correlate regional sequences at a higher resolution than previous interpretations and find the greatest amount of clastic deposition occurs during periods of lake-level rise, indicating that the SGSs are characteristically transgressive. Additionally, this model removes the implicit and explicit base-level assumptions of previous sequence stratigraphic models while being agnostic to the source of increased sediment discharge and therefore generalizable to other closed lacustrine settings. We use the high-resolution supply-generated sequences (meters thick) to argue for a climatic origin of the cyclic Sunnyside interval deposits based on sequence durations (40–50 kyr), and aligning sequences with recognized early Eocene transitory hyperthermal event timing and their associated climatic shifts across the region, increasing riverine discharge of sediment and water.
11
Martín-Martín, Manuel, Francesco Guerrera, Alí Maaté, Rachid Hlila, Francisco Serrano, Juan C. Cañaveras, Douglas Paton, et al. "The Cenozoic evolution of the Intrarif (Rif, Morocco)." Geosphere 18, no. 2 (February 8, 2022): 850–84. http://dx.doi.org/10.1130/ges02199.1.
Abstract:
Abstract This paper provides an understanding of the sedimentary-tectonic evolution of the Cenozoic strata of the El Habt and Ouezzane Tectonic Units (Intrarif, External Rif) in Morocco. New data provide information about the depositional architecture and enable a correlation of the evolution of the External Rif in Morocco with that of the Betic Cordillera in Spain and the Tunisian Tell, which provides new insights for hydrocarbon exploration in the region regarding possible source, reservoir, and seal rocks. The reconstructed Cenozoic succession was bio-chronologically defined, and the major unconformities and stratigraphic gaps were identified. The presence of these unconformities allowed three main stratigraphic sequences to be defined by age: Danian p.p., early Ypresian–early Bartonian p.p., and the early Rupelian–early Serravallian p.p. Three secondary stratigraphic sequences in the former upper main sequence were also defined by age: early Rupelian–late Chattian p.p., Burdigalianp.p., and the Langhian–Serravallian p.p. The depositional setting evolved from deep basin during the Late Cretaceous–Paleocene to external platform-slope during the Eocene–Miocene. The Cenozoic sandstones contain metamorphic and sedimentary rock fragments derived from a recycled orogen source area. The clay mineralogy in the Cenozoic strata consists of associations of Ill+(I–S) ± Sme, Ill+(I–S) ± Sme+Kln and Ill+(I–S) ± Sme+Kln+Chl. These associations indicate an initial unroofing in the Paleogene period, then in the Cretaceous period, and finally in the Late Jurassic period during the Eocene–Oligocene. This detritus was followed by variable amounts of a sedimentary mix of Paleogene to Late Jurassic terrains due to several phases of erosion and deposition partly related to syn-sedimentary tectonics during the Miocene. Equivalent features (similar types of sediments, tectofacies, gaps, and unroofing) were also recognized along the Betic Cordillera in Spain and Maghrebian Chain (Morocco and Tunisia) and interpreted as related to a pre-nappe tectonic activity of soft basement folding, which occurred during the Paleogene after the generalized tectonic inversion (from extension to compression) occurred in the Late Cretaceous. The Upper Cretaceous is considered to be the hydrocarbon source rock, while the fractured Eocene and the porous Oligo-Miocene suites are proposed as possible hydrocarbon reservoirs. The Cenozoic stratigraphic architecture and the nappe structure of the region could provide the necessary trap structures.
12
Dechesne, Marieke, Ellen D. Currano, Regan E. Dunn, Pennilyn Higgins, Joseph H. Hartman, Kevin R. Chamberlain, and Christopher S. Holm-Denoma. "A new stratigraphic framework and constraints for the position of the Paleocene–Eocene boundary in the rapidly subsiding Hanna Basin, Wyoming." Geosphere 16, no. 2 (January 16, 2020): 594–618. http://dx.doi.org/10.1130/ges02118.1.
Abstract:
Abstract The Paleocene–Eocene strata of the rapidly subsiding Hanna Basin give insights in sedimentation patterns and regional paleogeography during the Laramide orogeny and across the climatic event at the Paleocene–Eocene Thermal Maximum (PETM). Abundant coalbeds and carbonaceous shales of the fluvial, paludal, and lacustrine strata of the Hanna Formation offer a different depositional setting than PETM sections described in the nearby Piceance and Bighorn Basins, and the uniquely high sediment accumulation rates give an expanded and near-complete record across this interval. Stratigraphic sections were measured for an ∼1250 m interval spanning the Paleocene–Eocene boundary across the northeastern syncline of the basin, documenting depositional changes between axial fluvial sandstones, basin margin, paludal, floodplain, and lacustrine deposits. Leaf macrofossils, palynology, mollusks, δ13C isotopes of bulk organic matter, and zircon sample locations were integrated within the stratigraphic framework and refined the position of the PETM. As observed in other basins of the same age, an interval of coarse, amalgamated sandstones occurs as a response to the PETM. Although this pulse of relatively coarser sediment appears related to climate change at the PETM, it must be noted that several very similar sandstone bodies occur with the Hanna Formation. These sandstones occur in regular intervals and have an apparent cyclic pattern; however, age control is not sufficient yet to address the origin of the cyclicity. Signs of increased ponding and lake expansion upward in the section appear to be a response to basin isolation by emerging Laramide uplifts.
13
Strogen, Dominic P., Karen E. Higgs, Angela G. Griffin, and Hugh E. G. Morgans. "Late Eocene – Early Miocene facies and stratigraphic development, Taranaki Basin, New Zealand: the transition to plate boundary tectonics during regional transgression." Geological Magazine 156, no. 10 (March 11, 2019): 1751–70. http://dx.doi.org/10.1017/s0016756818000997.
Abstract:
AbstractEight latest Eocene to earliest Miocene stratigraphic surfaces have been identified in petroleum well data from the Taranaki Basin, New Zealand. These surfaces define seven regional sedimentary packages, of variable thickness and lithofacies, forming a mixed siliciclastic–carbonate system. The evolving tectonic setting, particularly the initial development of the Australian–Pacific convergent margin, controlled geographic, stratigraphic and facies variability. This tectonic signal overprinted a regional transgressive trend that culminated in latest Oligocene times. The earliest influence of active compressional tectonics is reflected in the preservation of latest Eocene – Early Oligocene deepwater sediments in the northern Taranaki Basin. Thickness patterns for all mid Oligocene units onwards show a shift in sedimentation to the eastern Taranaki Basin, controlled by reverse movement on the Taranaki Fault System. This resulted in the deposition of a thick sedimentary wedge, initially of coarse clastic sediments, later carbonate dominated, in the foredeep close to the fault. In contrast, Oligocene active normal faulting in a small sub-basin in the south may represent the most northerly evidence for rifting in southern Zealandia, related to Emerald Basin formation. The Early Miocene period saw a return to clastic-dominated deposition, the onset of regional regression and the southward propagation of compressional tectonics.
14
Luan, Xiwu, and Peter Lunt. "Eocene to Miocene stratigraphic controls in the far East Java Sea: Implications for stratigraphic studies." Marine Geology 436 (June 2021): 106479. http://dx.doi.org/10.1016/j.margeo.2021.106479.
15
Butler, Robert W. H., Henry W. Lickorish, Jamie Vinnels, and William D. McCaffrey. "Untangling the Annot sand fairway: structure and stratigraphy of the Eastern Champsaur Basin (Eocene–Oligocene), French Alps." Journal of the Geological Society 177, no. 6 (July 7, 2020): 1197–209. http://dx.doi.org/10.1144/jgs2020-015.
Abstract:
Early foredeep successions can yield insight into tectonic processes operating adjacent to and ahead of fledgling orogenic belts but are commonly deformed by the same orogens. We develop a workflow towards stratigraphic understanding of these deformed basins, applied to the Eastern Champsaur Basin of the French Alps. This contains a down-system correlative of the southern-sourced (Eocene–Oligocene) Annot turbidites. These strata are deformed by arrays of west-facing folds that developed beneath the Embrunais–Ubaye tectonic allochthon. The folds vary in geometry through the stratigraphic multilayer. Total shortening in the basin is around 4 km and the restored (un-decompacted) stratal thickness exceeds 980 m. The turbidites are generally sand-rich and bed-sets can be correlated through the entire fold train. The succession shows onlap and differential thickening indicating deposition across palaeobathymetry that evolved during active basement deformation, before being overridden by the allochthon. The sand system originally continued over what is now the Ecrins basement massif that, although contributing to basin floor structure, served only to confine and potentially focus further sediment transport to the north. Deformation ahead of the main Alpine orogen appears to have continued progressively, and the past definition of distinct ‘phases’ (‘pre-’ and ‘post-Nummulitic’) is an artefact of the stratigraphic record.
16
Buffetaut, Eric, and Delphine Angst. "Macrornis tanaupus Seeley, 1866: an enigmatic giant bird from the upper Eocene of England." Geological Magazine 158, no. 6 (February 5, 2021): 1129–34. http://dx.doi.org/10.1017/s0016756820001466.
Abstract:
AbstractA large bone from the upper Eocene Totland Bay Formation of Hordle Cliff (Hampshire), originally described by Seeley (1866) as Macrornis tanaupus and interpreted by him as belonging to a ‘large Struthious bird’, is redescribed and illustrated for the first time. It is not a reptile bone, as previously suggested, but the proximal part of a left avian tibiotarsus. A mass estimate of 43 kg, comparable to that of an emu, suggests that it was flightless. A precise identification is difficult because of the incompleteness of the specimen, and Macrornis tanaupus should probably be considered as a nomen dubium. We exclude Seeley’s interpretation as a ratite, as well as previous attributions to gastornithids. We tentatively suggest that the specimen may belong to a phorusrhacid, which would extend the stratigraphic record of this group in Europe by a few million years. The presence of a large terrestrial bird in the upper Eocene of Europe may have a bearing on the interpretation of enigmatic footprints of very large birds from the upper Eocene Paris gypsum.
17
Lillegraven, Jason A. "Stratigraphic relationships along the monoclinal eastern base of Bald Ridge and northwestern edge of Wyoming’s Bighorn Basin, U.S.A." Rocky Mountain Geology 54, no. 2 (December 1, 2019): 47–95. http://dx.doi.org/10.24872/rmgjournal.54.2.47.
Abstract:
ABSTRACT This geologic study is focused on a less than 5 square-mile (ca. 13 km2) tract of public land in northwestern Wyoming, 8 miles (12.9 km) south-southwest of the small town of Clark in Park County. The study area is south of Clarks Fork of Yellowstone River along the eastern base of the topographic feature called Bald Ridge, also known structurally as Dead Indian monocline. Since the Middle Eocene, the study area has been along the northwestern margin of the Bighorn Basin. Prior to that time, the study area existed near the west–east center of the basin. Bald Ridge became elevated late in the Laramide orogeny (no older than the Early Eocene) through east-directed faulting of basement rocks via the extensive Line Creek–Oregon Basin thrust system. As that active faulting occurred, the overlying Phanerozoic strata (Lower Cambrian through Lower Eocene) responded with numerous west-directed, out-of-the-basin thrusts as a new western-basin margin developed along the eastern realm of the newly born Absaroka volcanic field. Most of that deformation occurred after deposition of uppermost levels of the Lower Eocene Willwood Formation. The key purpose of the present paper was to improve the accuracy of mapping of the Jurassic into Eocene stratigraphy along the newly restricted, northwestern edge of Wyoming’s Bighorn Basin. The stratigraphic column in a north–south band along the eastern flank of the Beartooth Mountains and continuing southward into the present study area was markedly deformed and deeply eroded late during the Laramide orogeny. The present small, more southerly study area is structurally and erosionally simpler than its more northerly equivalent. Thus, its study adds important geological information to the history of the northern Cody Arch, a convex-westward string of related basement-involved uplifts extending southward to southwest of the city of Cody. Progressively steepening eastward dips of strata characterize a west-to-east transect from the summit of Bald Ridge (capped by the shallowly dipping, Mississippian Madison Limestone) to the western edge of strongly overturned outcrops of the Eocene Willwood Formation. The Upper Cretaceous Meeteetse Formation is the stratigraphic horizon at which the dips attain vertical or slightly overturned orientations. All consequential faults within the newly mapped area are thrusts, and they show generally westward (out-of-the-basin) displacements. Despite those west-directed displacements, their primary cause was tectonic shortening at depth below Bald Ridge that was directed to the northeast or east-northeast. During the Laramide orogeny, certain thrust planes within the east-dipping Phanerozoic rock column cut down-section stratigraphically (but uphill relative to Earth’s surface) and thereby placed younger strata upon older. The cumulative result, as recognized at several levels within the present area of study, was marked thinning of the total section. For example, surface exposures of the mostly Paleocene Fort Union Formation, 4,000 feet (1,219 m) thick only 7 miles (11.3 km) to the east, was completely eliminated from the local surface stratigraphy by that means. The northern end of Bald Ridge is formed by the highly asymmetric Canyon Mouth anticline. That structure differs strongly in the attitude of its hinge line from the general east-northeast dip of strata cloaking Bald Ridge. The Canyon Mouth anticline’s hinge line plunges steeply to the southeast, and dips on its northeastern flanks are vertical to partly overturned. Surprisingly, hinge lines and flanks of all other anticlinal/synclinal structures recognized within the present map area share those same orientations with Canyon Mouth anticline. These consistent but unexpected differences in orientation from unfolded strata may represent very late events in the history of Laramide strain vectors across the study area. Working in northern parts of this study area, an independent group determining radiometric ages of detrital-zircon grains reported close agreements in age with their host localities in the Early Cretaceous Mowry Shale and Frontier Formation. However, under the present paper’s interpretation of the local stratigraphy, the other workers misidentified formational hosts for all three samplings. That resulted in age-determination errors of depositional history within the Upper Cretaceous section of as much as 28.8 million years.
18
KARIM, KAMAL H., HEMIN KOYI, MUSHIR M. BAZIANY, and KHALED HESSAMI. "Significance of angular unconformities between Cretaceous and Tertiary strata in the northwestern segment of the Zagros fold–thrust belt, Kurdistan Region, NE Iraq." Geological Magazine 148, no. 5-6 (July 8, 2011): 925–39. http://dx.doi.org/10.1017/s0016756811000471.
Abstract:
AbstractIn this study, two angular unconformities are found and analysed for the first time in the Mesozoic–Cenozoic succession in the northwestern segment of the Zagros fold–thrust belt (ZFTB) in the Kurdistan Region. The first unconformity exists between Lower Cretaceous and Paleocene–Eocene rocks and the second between the Campanian Shiranish Formation and the Maastrichtian Tanjero Formation. Each of these unconformities is found in two different localities in the Zagros Imbricate Zone (i.e. the highly deformed zone immediately SW of the Zagros Suture) of the ZFTB of the Kurdistan Region near the border with Iran. The study uses recent geological mapping, structural and stratigraphic analyses in addition to using previous biozonation of the stratigraphic units that bound the two unconformities. The first unconformity was initiated with obduction of the ophiolite and Lower Cretaceous radiolarite onto the passive margin of the Arabian plate. This unconformity formed during an early phase of the Zagros orogeny, which is associated with the developing of a foreland basin, and resulted in the folding of the radiolarites and their uplift to form high-relief land. The erosion of this high-relief land resulted in the formation of the Paleocene–Eocene Red Bed Series and their deposition on the folded radiolarite. The timing of the deformation that caused this unconformity is hard to determine; however, its stratigraphic position may suggest that it possibly is related to post-Cenomanian movements. The second unconformity is between the tilted Campanian Shiranish Formation (hemipelagite) and Tanjero Formation (500 m of conglomerate in the more proximal area). These unconformities indicate that deformation and uplift of the sedimentary units was variable during ophiolite obduction in this part of the ZFTB. We argue that deformation, ophiolite obduction and collision are likely to have varied in space and time along the c. 2000 km long ZFTB.
19
Stassen, Peter, Christian Dupuis, Etienne Steurbaut, Johan Yans, Jean-Yves Storme, Abdel-Mohsen Morsi, Paola Iacumin, and Robert P. Speijer. "Unraveling the Paleocene-Eocene thermal maximum in shallow marine Tethyan environments: the Tunisian stratigraphic record." Newsletters on Stratigraphy 46, no. 1 (April 1, 2013): 69–91. http://dx.doi.org/10.1127/0078-0421/2013/0028.
20
Passchier, Sandra, Daniel J. Ciarletta, Triantafilo E. Miriagos, Peter K. Bijl, and Steven M. Bohaty. "An Antarctic stratigraphic record of stepwise ice growth through the Eocene-Oligocene transition." Geological Society of America Bulletin 129, no. 3-4 (October 18, 2016): 318–30. http://dx.doi.org/10.1130/b31482.1.
21
Wang, Jianqiao, and Piret Plink-Björklund. "Stratigraphic complexity in fluvial fans: Lower Eocene Green River Formation, Uinta Basin, USA." Basin Research 31, no. 5 (March 13, 2019): 892–919. http://dx.doi.org/10.1111/bre.12350.
22
Maurizot, Pierre. "First sedimentary record of the pre-obduction convergence in New Caledonia: formation of an Early Eocene accretionary complex in the north of Grande Terre and emplacement of the ‘Montagnes Blanches’ nappe." Bulletin de la Société Géologique de France 182, no. 6 (November 1, 2011): 479–91. http://dx.doi.org/10.2113/gssgfbull.182.6.479.
Abstract:
Abstract New Caledonia lies at the northern tip of the Norfolk ridge, a continental fragment separated from the east Gondwana margin during the Late Cretaceous. Stratigraphic data for constraining the convergence that led to ophiolitic nappes being obducted over Grande Terre during the Eocene are both few and inaccurate. To try and fill this gap and determine the onset of the convergence, we investigated the lithology, sedimentology, biostratigraphy and geodynamic context of the Late Cretaceous – Palaeogene sedimentary cover-rock succession of northern New Caledonia. We were able to establish new stratigraphic correlations between the sedimentary units, which display large southwest-verging overfolds detached along a basal argillite series, and reinterpret their interrelationships. The sediments from the Cretaceous-Paleocene interval were deposited in a post-rift pelagic environment and are mainly biogenic with minimal terrigenous input. From the base up, they comprise black organic-rich sulphide-bearing argillite, black chert (silicified equivalent of the argillite), micritic with chert, and micrite rich in planktonic foraminifera. These passive-margin deposits are found regionally on the Norfolk Ridge down to New Zealand, and on the Lord Howe Rise, and were controlled primarily by regional or global environmental factors. The overlying Eocene deposits mark a change to an active-margin regime with distal calciturbidite and proximal breccia representing the earliest Paleogene flysch-type deposits in New Caledonia. The change from an extensional to a compressive regime marks the beginning of the pre-obduction convergence and can be assigned fairly accurately in the Koumac–Gomen area to the end of the Early Eocene (Late Ypresian, Biozone E7) at c 50 Ma. From this period on, the post-Late Cretaceous cover in northern New Caledonia was caught up and recycled in a southwest-verging accretionary complex ahead of which flysch was deposited in a flexural foreland basin. The system prograded southwards until the Late Eocene collisional stage, when the continental Norfolk ridge entered the convergence zone and blocked it. At this point the autochthonous and parautochthonous sedimentary cover and overlying flysch of northern New Caledonia was thrust over the younger flysch to the south to form a newly defined allochthonous unit, the ‘Montagnes Blanches’ nappe, that is systematically intercalated between the flysch and the obducted ophiolite units throughout Grande Terre.
23
Fan, Majie, Ran Feng, John W. Geissman, and Christopher J. Poulsen. "Late Paleogene emergence of a North American loess plateau." Geology 48, no. 3 (January 3, 2020): 273–77. http://dx.doi.org/10.1130/g47102.1.
Abstract:
Abstract The relative roles of tectonics and global climate in forming the hydroclimate for widespread eolian deposition remain controversial. Oligocene loess has been previously documented in the interior of western United States, but its spatiotemporal pattern and causes remain undetermined. Through new stratigraphic record documentation and data compilation, we reveal the time transgressive occurrence of loess beginning in the latest Eocene in the central Rocky Mountains, that expands eastward to the Great Plains across the Eocene-Oligocene transition (EOT). Our climate simulations show that moderate uplift of the southern North America Cordillera initiated drying in the Cordilleran hinterland and immediate foreland, forming a potential dust source and sink, and global cooling at the EOT expanded the drying and eolian deposition eastward by causing retreat of the North American Monsoon. Therefore, the eolian deposition reflects continental aridification induced both by regional tectonism and global climate change during the late Paleogene.
24
Berry, Keith. "Icacinaceae in the early middle Paleocene Raton Formation, Colorado." Mountain Geologist 55, no. 2 (April 2018): 75–86. http://dx.doi.org/10.31582/rmag.mg.55.2.75.
Abstract:
Icacinicaryites corruga is reported from the upper coal zone of the Raton Formation in south-central Colorado. Prior to this report, this endocarp imprint was known from only a single locality near Pagosa Springs in southwestern Colorado (Animas Formation). This demonstrates that Icacinaceae, which characterized the late Paleocene – early Eocene tropical rainforests of western North America, already were present in Colorado’s early middle Paleocene tropical rainforest. This determination agrees with the results of a reevaluation of the stratigraphic distribution of previous records of Icacinaceae from the Paleocene of western North America.
25
Chalouan, Ahmed, Andre Michard, Hugues Feinberg, Raymond Montigny, and Omar Saddiqi. "The Rif mountain building (Morocco); a new tectonic scenario." Bulletin de la Société Géologique de France 172, no. 5 (September 1, 2001): 603–16. http://dx.doi.org/10.2113/172.5.603.
Abstract:
Abstract The building of the Alpine Rif belt (southern limb of the Betic-Rif orocline) is restored, mostly based on the Tertiary stratigraphic and metamorphic data set. The Betic-Rif Internal zones derive from an exotic Alboran Terrane partly involved in a S-dipping Betic subduction during the Late Cretaceous ?-Eocene. Incipient collision of the terrane against Iberia triggered back-thrust tectonics south of the Internal mountain belt during the latest Eocene-Oligocene. A N-dipping Maghrebian subduction developed from that time up to Middle Miocene, responsible for the rifting of the internal Alboran Terrane. Docking of the extending Alboran Terrane onto the North African margin occurred during the Neogene through the closure of the Maghrebian Flysch oceanic trough, with southwestward growth of the external accretionary prism, and foredeep subsidence. Subduction zone westward roll back associated with delamination of the dense lithosphere seem to account for the Betic-Rif late orogenic evolution.
26
Hamon, Youri, Remy Deschamps, Philippe Joseph, Daniel Garcia, and Emmanuelle Chanvry. "New insight of sedimentological and geochemical characterization of siliciclastic-carbonate deposits (Alveolina Limestone Formation, Graus-Tremp basin, Spain)." Bulletin de la Société Géologique de France 187, no. 3 (May 1, 2016): 133–53. http://dx.doi.org/10.2113/gssgfbull.187.3.133.
Abstract:
Abstract This article is a first attempt of combining sedimentological analysis and geochemical systematics of the Alveolina Limestone Formation as a tool to identify the major stratigraphic surfaces, and to improve the sequence stratigraphy interpretation. This formation is Early Eocene in age and crops out in several well-exposed cliffs in the Serraduy – Roda de Isabena area (Graus-Tremp basin, NE Spain). Within this succession, nineteen carbonate and siliciclastic facies have been identified and grouped in environmental facies associations (based on their vertical stacking and lateral relationships): 1) coastal plain; 2) clastic deltaic complex; 3) shallow carbonate inner-ramp; 4) mid-ramp; 5) outer-ramp; 6) reefal facies. The depositional architectures studied in the Serraduy area can be directly assessed on the field, and a 3D reconstruction is proposed. This enables us to build a synthetic depositional model and to identify five small-scale T/R cycles, bounded by different kinds of sedimentary discontinuities : angular unconformity, firmground, erosional surface… In parallel, geochemical analyses (C and O isotopes, major, minor and trace elements) were carried out to help at hierarchizing the cycles and the boundaries previously identified. Four of them may be considered as major stratigraphic surfaces, corresponding either to regional-scale angular unconformities, or to exposure surfaces. The latter are characterized by a selective dissolution, a slight but sharp decrease in δ13CV-PDB and in Mg, Fe and Sr contents below the surface. The absence of typical sedimentary criteria of exposure (with the exception of these geochemical signatures) may be explained by short-term exposure, an arid to semi-arid climate, and a dominant low-magnesian calcite original mineralogy, precluding the development and the preservation of widespread vadose diagenetic products. A new sequence stratigraphy model for the Alveolina Limestone Fm is finally proposed and discussed.
27
Brown, Stewart. "Stratigraphy of the oil and gas reservoirs: UK Continental Shelf." Geological Society, London, Memoirs 14, no. 1 (1991): 9–18. http://dx.doi.org/10.1144/gsl.mem.1991.014.01.02.
Abstract:
The petroliferous sedimentary basins of the UK Continental Shelf are remarkable for the diversity of their reservoir strata. Reservoir rocks in fields currently in production range in age from Devonian to earliest Eocene, but significant hydrocarbon discoveries have also been made in rocks as as young as the mid-Eocene. The reservoirs are predominantly siliciclastic rocks, with facies ranging from continental fluvial and aeolian, to marine gravity flow deposits from sub-wave base environments.In this paper stratigraphic context of the producing horizons in the UK Continental Shelf (UKCS), principally the North Sea, is reviewed, and the sedimentation of the reservoir strata placed in an outline geological history. The main producing horizons are described in summary. Matters of stratigraphic terminology and correlation both between fields and between basins are discussed.A lithostratigraphy for the UK southern North Sea was established by Rhys (1974), and for the central and northern North Sea by Deegan & Scull (1977). Although these schemes have proved to be fairly robust, in the last 13 years the acquisition of new data plus a proliferation of new terms not fully documented in the public domain, argue strongly for a comprehensive revision and rationalization which is beyond the scope of this paper. Attempts in the public domain to standardize nomenclature across international boundaries in the North Sea, pursued by Deegan & Scull (1977) for the UK and Norwegian sectors, have lapsed for the most part in subsequent years.Economic basement in the UK North Sea can be regarded at present
28
Gupta, S., and P. A. Allen. "Implications of foreland paleotopography for stratigraphic development in the Eocene distal Alpine foreland basin." Geological Society of America Bulletin 112, no. 4 (April 1, 2000): 515–30. http://dx.doi.org/10.1130/0016-7606(2000)112<515:iofpfs>2.0.co;2.
29
Hupp, Brittany N., D. Clay Kelly, James C. Zachos, and Timothy J. Bralower. "Effects of size-dependent sediment mixing on deep-sea records of the Paleocene-Eocene Thermal Maximum." Geology 47, no. 8 (May 31, 2019): 749–52. http://dx.doi.org/10.1130/g46042.1.
Abstract:
Abstract Stratigraphic features of the carbon isotope excursion (CIE) marking the Paleocene-Eocene Thermal Maximum (PETM; ca. 55.8 Ma) are used to study ocean-climate change and carbon cycling during this ancient global warming event. Yet discrepancies in its timing and amplitude exist between bulk-carbonate and planktic-foraminifera δ13C records. Here we examine these disparities through the lens of δ13C compositions of size-segregated planktic shells across the pre-CIE to CIE transition in the iconic PETM section of Ocean Drilling Program Site 690 in the Weddell Sea. Our results show that the stratigraphic position of the CIE onset is dependent upon shell size, which we attribute to preferential mixing of smaller shells with pre-CIE δ13C values up into the overlying CIE interval. Hence, the transitory loss of size-dependent δ13C signatures in photosymbiotic planktic foraminifera is a taphonomic artifact, not a geochemical signal of symbiont “bleaching” during the PETM. Our results also indicate that many salient features of the Site 690 bulk-carbonate δ13C record are aberrations caused by size-dependent sediment mixing, and as such, should not be viewed as primary signals of ocean-climate change during what is arguably one of the best ancient analogs for future ocean-climate change.
30
Wang, Bing, Harry Doust, and Jingyan Liu. "Geology and Petroleum Systems of the East China Sea Basin." Energies 12, no. 21 (October 26, 2019): 4088. http://dx.doi.org/10.3390/en12214088.
Abstract:
The back-arc East China Sea Basin lies on extended continental crust at the leading edge of the Eurasian plate. In this study, the basins are described and subdivided according to their tectono-stratigraphic evolution. In order to distinguish between different phases of deformation in basin development, standard basin evolution patterns related to geodynamic drivers are identified as a first step. On the basis of this, standard patterns are recognized in the sedimentary sequences that characterize the area and its tectonic evolution, and linking them to the petroleum systems present is attempted. This is achieved by characterizing and grouping them into basin cycle-related petroleum system types (PSTs). Finally, the development of plays is examined within the petroleum systems in the context of their tectono-stratigraphic evolution, and groups of sub-basins with similar geological history and, therefore, potentially similar petroleum prospectivity are identified. In the East China Sea Basin, four proven and potential PSTs were recognized: (1) Late Cretaceous to Paleocene oil/gas-prone early syn-rift lacustrine–deltaic PST; (2) Eocene gas/oil prone late syn-rift marine PST; (3) Oligocene to Middle Miocene gas/oil-prone early post-rift fluvial–deltaic PST; (4) gas-prone syn-rift turbiditic PST. The geology and petroleum systems of three major sub-basins of the East China Sea Basin, the Xihu Sub-basin, the Lishui Sub-basin, and Okinawa Trough, are discussed in detail, and their petroleum systems and play development are analyzed. Finally, the sub-basins are grouped into “basin families” distinguished by their tectono-stratigraphic development, namely, Northwest to Northeast Shelf Basin (NWSB–NESB), Southwest to Southeast Shelf Basin (SWSB–SESB), and Okinawa Trough basin families, respectively.
31
Ma, Bingshan, Jiafu Qi, and Jiawang Ge. "Development of two-phase transfer zones during multiphase rifting and their influence on sedimentation in the Baxian Sag, Bohai Bay Basin, northern China." Geological Magazine 156, no. 11 (April 3, 2019): 1821–38. http://dx.doi.org/10.1017/s0016756819000190.
Abstract:
AbstractWe investigate the formation and deformation of transfer zones and their impact on sedimentation during multiphase rifting using a three-dimensional seismic dataset in the Baxian Sag, the onshore part of the Bohai Bay Basin, northern China. The fault system in the study area is dominated by two arcuate, opposing boundary faults, that is, the Niudong and Maxi faults, which form an S-type fault system which does not link together. The fault system and structural-stratigraphic features between the Eocene and Oligocene syn-rift sequences were distinctly different during the Palaeogene rifting. These differences allow us to identify the two-phase transfer zones: (1) a NW–SE-trending Eocene transfer zone linking the NW-tilted Baxian Block and the SE-tilted Raoyang Block , and (2) the N–S-trending Oligocene transfer zone forming along the central part of the S-type fault system between the two inward kinks, and linking S-tilted and N-tilted fault blocks. The two-phase transfer zones comprise transverse boundary fault segments and fault styles which are related to strike-slip motion. The strike-slip faults occurred in the sequence where the transfer zone formed. The transfer zones significantly influenced the syn-rift sediments, drainage catchments and reservoir properties during the periods when they formed, and the two-phase transfer zones represent favourable positions for hydrocarbon accumulation in the Eocene and Oligocene sequences, respectively.
32
Aubry, Marie-Pierre. "Where should the Global Stratotype Section and Point (GSSP) for the Paleocene/Eocene boundary be located?" Bulletin de la Société Géologique de France 171, no. 4 (July 1, 2000): 461–76. http://dx.doi.org/10.2113/171.4.461.
Abstract:
Abstract The Working Group (WG) on the Paleocene/Eocene (P/E) boundary will soon have to submit a formal proposal regarding the selection of a GSSP for the boundary. Before it proceeds, a number of critical points must be considered. First, there has been dual definition of the Paleocene/Eocene boundary so that even today the boundary is placed at two different lithostratigraphic horizons by marine and vertebrate paleontologists. The former use the base of the Ypresian Stage = Mont Heribu Member in the Belgium Basin whereas the latter use the Conglomerat de Meudon believed until recently to lie at the base of the Sparnacian Argile plastique of the Paris Basin. A historical review of the definitions of the terms that have become accepted as standard chronostratigraphic units help to explain how this dual definition arose and to show that the definition accepted by most vertebrate paleontologists is spurious. The current placement of the Paleocene/Eocene boundary, i.e., defined by the base of Ypresian Stage (Ieper Clay), conforms to the definition of the Paleocene by Schimper in 1874. Second, the WG must determine whose basic chronostratigraphic procedures to follow. There has been in recent years a profound shift in chronostratigraphic procedures so that the fundamental principles recognized by the International Subcommission on Stratigraphic classification [ISSC, Hedberg, Ed, 1976; Salvador, Ed., 1994] are difficult to reconcile with the rules published by the International Commission on Stratigraphy (ICS) in recent years, based on the precept that "correlation precedes definition". For this reason the WG finds itself in a dilemma, and must weigh the risks associated with the attractive solution that would consist in defining the P/E boundary by a lithostratigraphic level where the late Paleocene carbon isotope excursion (CIE) is recorded. Four possible options that may satisfy Hedberg's principle of chronostratigraphy and/or the need for recognizing globally the Paleocene/Eocene boundary are presented. Whichever option is followed, it is important to remember that chronostratigraphy must remain objective and as arbitrary as possible, and thus independent of any aspect of Earth history, either paleobiologic, tectonic or climatic. In addition, in making a proposal for the definition of the P/E boundary, the WG must ensure that its choice will not contribute to a destabilisation of the current chronostratigraphic framework.
33
Shahid Ghazi, Sadaf Sharif, Tehseen Zafar, Muhammad Riaz, Rashid Haider, and Tanzeela Hanif. "Sedimentology and Stratigraphic Evolution of the Early Eocene Nammal Formation, Salt Range, Pakistan." Stratigraphy and Geological Correlation 28, no. 7 (December 2020): 745–64. http://dx.doi.org/10.1134/s0869593820070047.
34
De Man, E., L. Ivany, and N. Vandenberghe. "Stable oxygen isotope record of the Eocene-Oligocene transition in the southern North Sea Basin: positioning the Oi-1 event." Netherlands Journal of Geosciences - Geologie en Mijnbouw 83, no. 3 (September 2004): 193–97. http://dx.doi.org/10.1017/s0016774600020266.
Abstract:
AbstractPreliminary stable oxygen isotope data are presented from the southern North Sea Basin successions, ranging from the Lutetian to Rupelian. Analyses were performed on fish otoliths, nuculid bivalves and benthic foraminifera and are presented as bulk δ18O values relative to a well established regional sequence stratigraphic framework. The most significant positive shift in δ18O values clearly falls at the top of the regionally recognised Bassevelde 3 sequence, which base corresponds to the Eocene-Oligocene GSSP boundary. The here documented δ18O shift is closely associated with the base of the traditional Rupelian unit-stratotype and is tentatively correlated to the globally recognised Oi-1 event.
35
Zellman, Kristine L., Piret Plink-Björklund, and Henry C. Fricke. "Testing hypotheses on signatures of precipitation variability in the river and floodplain deposits of the Paleogene San Juan Basin, New Mexico, U.S.A." Journal of Sedimentary Research 90, no. 12 (February 18, 2021): 1770–801. http://dx.doi.org/10.2110/jsr.2020.75.
Abstract:
ABSTRACTMuch progress has been made in recent years towards a set of recognition criteria for river discharge variability in river channel deposits, and thus sedimentary proxies for precipitation variability. Despite this progress, there is currently no consensus on how different styles of discharge variability are reflected in river sedimentary records, and whether variable-discharge river records from different climate types can be distinguished. Herein, river discharge and precipitation variability in the Paleogene is investigated using associations between river channel and floodplain deposits across the Paleocene–Eocene boundary from the Paleocene upper Nacimiento Formation and the early Eocene San Jose Formation in the San Juan Basin, New Mexico, USA.The succession is identified as deposits of variable-discharge river systems based on shared channel-deposit characteristics with modern and ancient variable-discharge river systems and the proposed facies models, in addition to alternations of poorly drained and well-drained floodplain deposits and/or slickensides indicating alternating wet–dry cycles. A long-term stratigraphic trend toward increasingly well-drained floodplain deposits is also observed and hypothesized to indicate successively more arid conditions from the Paleocene into the early Eocene. Comparisons with modern rivers from various climate zones suggest a long-term shift from a monsoonal climate in the Paleocene, to a fluctuating subhumid climate, ultimately leading to semiarid to arid conditions in the early Eocene. These observations suggest that floodplain deposits may be a better indicator of ambient climate, whereas channel deposits are records for frequency and magnitude of high-intensity precipitation events. Therefore, the existing facies models for variable-discharge rivers that consider only channel facies may not capture critical information needed to make accurate interpretations of paleoclimatic conditions. This study also adds to a growing body of evidence from geologic records of mid-latitude Paleogene river systems suggesting increases in the magnitude or variability of river discharge coinciding with established climate perturbations.
36
Cai, Fulong, Lin Ding, Qinghai Zhang, Devon A. Orme, Honghong Wei, Jinxiang Li, Ji’en Zhang, Than Zaw, and Kyaing Sein. "Initiation and evolution of forearc basins in the Central Myanmar Depression." GSA Bulletin 132, no. 5-6 (October 14, 2019): 1066–82. http://dx.doi.org/10.1130/b35301.1.
Abstract:
Abstract The forearc basin in Myanmar is significant in understanding the development of continental forearc basins. We present stratigraphic, sandstone petrographic, and U-Pb detrital data from Upper Cretaceous–Eocene strata of Chindwin and Minbu sub-basins in the Central Myanmar Depression. The Upper Cretaceous lower Kabaw Formation consists of turbiditic conglomerate, sandstone, and mudstone in the Minbu sub-basin. The composition of conglomerates are mainly schist and subordinate quartz. Prominent detrital zircon age probability peaks are between 260 and 223 Ma, similar with that of Upper Triassic Pane Chaung turbidites and Kanpetlet schist on the West Burma plate. In the upper Kabaw Formation, turbiditic volcanic-rich sandstones have major age populations ranging from 103 to 70 Ma in both Minbu and Chindwin sub-basins. The Paleocene slope environment Paunggyi Formation, which overlies the Kabaw Formation, mainly consists of conglomerate, sandstone, mudstone, and tuff beds in the Minbu sub-basin. In contrast, the Paunggyi Formation in the Chindwin sub-basin is composed of sandstone and mudstone; major detrital zircon age populations from the Paunggyi Formation are between 100 and 60 Ma. Eocene strata in both basins are composed mainly of shallow marine to delta sandstone and mudstone. Major detrital zircon age populations are 100–36 Ma and 600–500 Ma. The Late Cretaceous–Eocene ages from Upper Cretaceous–Eocene strata overlap with igneous crystallization ages from the Western Myanmar Arc. We propose that the Chindwin and Minbu sub-basins developed as parts of a forearc basin along the west flank of Western Myanmar Arc (present coordinate). The forearc basin initiated in Albian time atop the continental West Burma plate due to the formation of a structural high along the western margin of West Burma plate.
37
Hussein, Mohammad Ali, Mohammad Alqudah, and Olaf G. Podlaha. "Ichnofabrics of Eocene oil shales from central Jordan and their use for paleoenvironmental reconstructions." GeoArabia 19, no. 1 (January 1, 2014): 85–112. http://dx.doi.org/10.2113/geoarabia190185.
Abstract:
ABSTRACT The study of trace fossils is widely used in facies interpretation. It provides a crucial tool for reconstructing depositional paleoenvironments when used in combination with other sedimentological and paleontological proxies. Here we present the first detailed study of Eocene trace fossils from Jordan. Two sections of Early to Middle Eocene age, with a total thickness of 478.7 m, from central Jordan were cored and investigated. The results of individually occurring (isolated) or co-occurring (combined) ichnofabrics and bioturbation levels, in combination with results from biostratigraphic and geochemical studies, were used for stratigraphic and paleoenvironmental reconstructions. The bioturbation index (BI) was used to classify the burrowing density versus the preservation of the original sedimentary structures. The two cores show highly variable grades of bioturbation with BI ranging from 0 to 6. Four ichnogenera were identified: Thalassinoides, Chondrites, Teichichnus and Zoophycos. Both the ichnofabrics and the variations of the BI suggest a shallow, highly dynamic depositional system with rapid changes of water depth and degree of bottom-water oxygenation.
38
Yaseen, Muhammad, Muhammad Shahab, Zeeshan Ahmad, Rehman Khan, Syed Farhan Ali Shah, and Abbas Ali Naseem. "Insights into the structure and surface geology of balanced and retrodeformed geological cross sections from the Nizampur basin, Khyber Pakhtunkhwa, Pakistan." Journal of Petroleum Exploration and Production Technology 11, no. 6 (May 9, 2021): 2561–71. http://dx.doi.org/10.1007/s13202-021-01180-8.
Abstract:
AbstractThe current research work is an attempt to apply the basic geological procedures, methods of geological mapping, surface and subsurface interpretation and restoration of balanced and retrodeformed cross sections from the Nizampur basin, Khyber Pakhtunkhwa, Pakistan. The work also includes the documentation of several surface structural features, i.e., anticlines, synclines and different types of folds and faults exposed in the vicinity of study area. Four central thrust faults were recognized named as Kahi Thrusts along the cross sections. These thrust faults carried the older sequences of rocks over the younger sequences in different portion along the measured cross section. The folded and faulted rocks in the area show that stratigraphic framework comprises of Eocene, Paleocene, Cretaceous and Jurassic succession of rocks. There are Eocene rocks existing in the extreme South of the mapped area with addition of older Cretaceous and Jurassic succession and contains simple and large-scale folds, faults and back thrust. Two structural transect were mapped which encounter different folds and faults, i.e., X-sections AB oriented NS and CD oriented NE-SW. Restoration of the structural transects was calculated and assumed that at the formation of Main Boundary Thrust, the study area was exposed to the tectonic forces which prognosticated 19.5% shortening in rock sequences from Jurassic to Eocene succession along the measured cross section A_B.
39
Hart, Bruce, and Scott Cooper. "Mechanical stratigraphy in Mesozoic rocks of the San Juan Basin: Integration of stratigraphic and structural terms and concepts." Mountain Geologist 58, no. 2 (April 1, 2021): 159–204. http://dx.doi.org/10.31582/rmag.mg.58.2.159.
Abstract:
We characterize relationships between stratigraphy and natural fractures in outcrops of Mesozoic strata that rim the San Juan Basin in New Mexico and Colorado. These outcrops expose fluvial and shallow-marine siliciclastic deposits and calcareous mudstones deposited in a distal marine setting. We focus primarily on a regionally extensive fracture set formed during the Eocene to minimize localized tectonic effects on fracture development. Where possible, we supplement our observations with wireline log- or laboratory-derived measurements of rock properties. Our goals are twofold: 1) to illustrate how direct integration of data and concepts from stratigraphy and structural geology can lead to better fracture characterization, and 2) to develop thought processes that will stimulate new exploration and development strategies. Genetic beds form one scale of stratification in the outcrops we describe. For example, sandstone beds can be arranged into coarsening and thickening upward successions that are the depositional record of shoreline progradation. In fluvial settings, cm- to dm-scale sandstone beds can also be part of m-scale single-storey channel complexes that, themselves, can be arranged into amalgamated channel complexes 10s of m thick. In these and other settings, it is important to distinguish between beds and features that can be defined via wireline logs because it is the former (cm- to dm-scale) that are usually the primary control the distribution of natural fractures. The extension fractures we describe are typically bed-bound, with bedding being defined by lithology contrasts and the associated changes in elastic properties. Fracture spacing distributions are typically lognormal with average spacing being less than bed thickness. Although mechanical bedding and depositional bedding are commonly the same, diagenesis can cut across bed boundaries and complicate this relationship, especially where lithologic contrasts are small. Deposits from similar depositional environments which undergo different diagenetic histories can have substantially different mechanical properties and therefore deform differently in response to similar imposed stresses.
40
Mancini, Ernest A., and T. Markham Puckett. "Paleoenvironmental and stratigraphic changes in Paleocene and lower Eocene strata, eastern Gulf Coastal Plain, USA." GFF 122, no. 1 (March 2000): 99–100. http://dx.doi.org/10.1080/11035890001221099.
41
McPhee, Peter J., Douwe J. J. van Hinsbergen, and Stuart N. Thomson. "Thermal history of the western Central Taurides fold-thrust belt: Implications for Cenozoic vertical motions of southern Central Anatolia." Geosphere 15, no. 6 (November 7, 2019): 1927–42. http://dx.doi.org/10.1130/ges02164.1.
Abstract:
Abstract The modern physiography of central Turkey is dominated by the 1-km-high Central Anatolian Plateau and the Central Tauride mountains that form the southern plateau margin. These correspond to a Cretaceous–Eocene backarc extensional province and forearc fold-thrust belt, respectively. The extent to which the morphology of the Miocene plateau was inherited from the physiography of the Cretaceous–Eocene subduction zone that assembled the Anatolian crust has not been tested but is important if we are to isolate the signal of Miocene and younger subduction dynamics in the formation of the modern plateau margin. There is no known stratigraphic record of the post-Eocene pre-Miocene evolution of the Taurides. We therefore collected rock samples across the Taurides and used zircon (U-Th)/He (ZHe), apatite (U-Th)/He (AHe), and apatite fission-track (AFT) low-temperature thermochronometers to constrain cooling; we interpret these thermochronometers to signal erosional exhumation. We use inverse thermal modeling to aid interpretation of our results and find that: (1) thermochronometers across the Taurides were reset as a result of heating by the emplacement of the Antalya and Bozkır nappes; (2) AFT and ZHe Eocene cooling ages are related to structurally driven uplift and erosional exhumation on major thrust culminations; (3) dispersed AHe ages record low rates of Oligocene–early Miocene cooling and hence low rates of erosional exhumation; and (4) fast rates of cooling were determined for samples along the margin of the Köprüçay Basin. We interpret that early Miocene cooling is a signal of active erosion of the western Central Taurides at a time of marine sedimentation in the Mut Basin on the southern Central Taurides, and these differing histories may reflect evolution above the Antalya and Cyprus slabs. Our thermochronological data, the enigmatic development of the Antalya Basin, and thrusting within the basin may be explained as the surface expression of stepwise delamination of the Antalya slab from the Tauride hinterland to its current position below the Gulf of Antalya since early Miocene time over a distance of ∼150 km.
42
Zakir, Abdelali, Ahmed Chalouan, and Hugues Feinberg. "Tectono-sedimentary evolution of a fore-chain domain : example of the Habt and Sidi Mrayt basins, northwestern external Moroccan Rif ; stratigraphic precisions and tectonic modelling." Bulletin de la Société Géologique de France 175, no. 4 (July 1, 2004): 383–97. http://dx.doi.org/10.2113/175.4.383.
Abstract:
Abstract In this paper, a tecto-sedimentary evolution model of the northwestern external Rif zones (Morocco) is proposed. It is based on the study of structural relationships and the biostratigraphic and sedimentologic analysis of different Tertiary syn-tectonic units. This zone shows alternating foredeep basins and anticlinal ramps with a NNW-SSE structural trend and a vergence toward the WSW. The trend of turbiditic bodies and palaeocurrent directions (from the SSE to the NNW) are parallel to the regional tectonic strike. Sidi Mrayt and El Habt basins are filled with syn-tectonic middle Eocene to middle Miocene sediments; The Habt basin is subdivided in two sub-basins: Asilah-Larache and Rirha-Gzoula. The deposits are distributed in two separated turbiditic complex, each one including a stacking of turbiditic systems. The Rirha-Gzoula and Asilah-Larache sub-basins are located in front of two anticline ridge structures made up of Upper Cretaceous and Lower Eocene material; they are respectively Boujediane and Arbaa Ayacha anticlines. The distribution of turbiditic bodies, unconformities and structural relationships within the thrusts and folds system in the northwestern external Rif indicate the progression toward the external zones of fault-propagation folds and associated basins.
43
Gómez, Manuel, Jaume Vergés, and Carlos Riaza. "Inversion tectonics of the northern margin of the Basque Cantabrian Basin." Bulletin de la Société Géologique de France 173, no. 5 (September 1, 2002): 449–59. http://dx.doi.org/10.2113/173.5.449.
Abstract:
Abstract The northern margin of the Basque-Cantabrian Basin was analysed combining stratigraphic and structural data from both surface and subsurface together with reflectance of vitrinite data from oil wells. The use of cross-section balancing techniques in addition to thermal modelling enabled us to reconstruct the tectonic, burial and thermal evolutions of the basin margin as well as those of the Landes High to the N in two different periods. The section restoration at the end of the Cretaceous shows a northern basin margin structure influenced by evaporites related to south-dipping normal faults. The reconstruction in middle Eocene times yielded up to 1 800 m of Paleocene-middle Eocene deposits on top of the basin margin. Subsequent tectonic inversion related to the Pyrenean compression led to the north-directed thrusting of basement units and to the formation of thrust slices or inverted folds in the cover along the northern margin of the basin. Tectonic subsidence analysis together with maturity data provided evidence that oil was generated in the basin during the late syn-rift and post-rift stages in the Late Cretaceous and became overmature during the period of incipient inversion after 55 Ma. In the autochthonous Landes High, the oil was generated after the tectonic inversion period 37 Ma.
44
Cherchi, Antonietta, Nicoletta Mancin, Lucien Montadert, Marco Murru, Maria Teresa Putzu, Francesco Schiavinotto, and Vladimiro Verrubbi. "The stratigraphic response to the Oligo-Miocene extension in the western Mediterranean from observations on the Sardinia graben system (Italy)." Bulletin de la Société Géologique de France 179, no. 3 (May 1, 2008): 267–87. http://dx.doi.org/10.2113/gssgfbull.179.3.267.
Abstract:
Abstract The Sardinian Cainozoic rifted basin is a useful model for studying the stratigraphic response to the Oligo-Miocene structural extension in the western Mediterranean because it allows precise observations on the relationship between sedimentation and normal faulting based on outcrops and seismic reflection data. The purpose of this paper, essentially of stratigraphic nature is to propose a chronology as precise as possible of the tectonic events and of the sedimentary formations. Indeed the tectono-sedimentary framework is complex, characterized by an extreme facies variability, from continental to marginal transitional and to marine environments (shallow-water, hemipelagic). Rifting, active calc-alkaline volcanism and sea-level changes caused rapid physiographical evolution, which controlled progressive marine ingression. New chronobiostratigraphical data presented in this paper allow correlating the sequences, defining their environment and depth of deposition and specifying precisely the timing of pre-, syn-, and post-rift stages in the Oligo-Miocene graben system. In southwestern Sardinia during the middle-late Eocene, after the Pyrenean phase, a continental graben (Cixerri), W-E oriented, preceded the Oligo-Miocene extension, which reactivated inherited Eocene and Palaeozoic faults. The calc-alkaline volcanic activity ranging from 32 to 13 Ma, provides a good estimate for the time span of the west-dipping Apenninic subduction responsible for the continental extension and the oceanic accretion in the western Mediterranean. In Sardinia the Oligo-Miocene extensional tectonics started in a continental environment, preceding the earliest calc-alkaline volcanic products (32 Ma). The marine ingression is dated to the late Chattian-Aquitanian interval and corresponds to a rapid deepening of the Oligo-Miocene graben system of tectonic origin. The end of the rifting i.e. the end of normal faulting activity is pre-middle Burdigalian in age. When Sardinia was in the post-rift stage, extension continued until late Burdigalian – Langhian in the Algero-Provençal basin with oceanic accretion and rotation of the Corsica-Sardinia block (CSB).
45
Birdwell, Justin, Ronald C. Johnson, and Michael E. Brownfield. "Distribution of mineral phases in the Eocene Green River Formation, Piceance Basin, Colorado—Implications for the evolution of Lake Uinta." Mountain Geologist 56, no. 2 (May 1, 2019): 73–141. http://dx.doi.org/10.31582/rmag.mg.56.2.73.
Abstract:
The mineralogy of the Eocene Green River Formation in the Piceance Basin, Colorado, has been the subject of numerous studies since the 1920s. Most previous work has focused on the resource potential of these lacustrine mudrocks, which in addition to substantial oil shale potential (in-place resources of 353 billion barrels of synthetic crude oil for rocks yielding at least 25 gallons per ton, GPT), includes nahcolite, a currently utilized soda ash resource, and dawsonite, a potential alternative source of aluminum. Another reason to study the mineralogy in this system is that the geographic and stratigraphic distribution of various authigenic minerals may provide insights into the geochemistry and depositional environment of the long-lived Eocene Lake Uinta. In this study, legacy non-quantitative (presence/absence) X-ray diffraction (XRD) data recently published by the U.S. Geological Survey (USGS) for more than 9,000 samples collected from 30 coreholes in the Green River Formation, Piceance Basin were examined. These data were used to better define the stratigraphic and paleogeographic extent of a set of indicator minerals (illite, analcime, albite, dawsonite, and nahcolite) within the Piceance Basin lacustrine strata. This set of minerals was selected based on observations from previous work and variability in their occurrence and co-occurrence within the Piceance Basin. The USGS database has been used to (1) construct maps showing geographic variations in mineral occurrences for 14 stratigraphically defined rich and lean oil shale zones; (2) assess co-occurrences of indicator minerals; and (3) compare occurrence results with quantitative XRD datasets collected on Piceance Basin oil shales. Occurrences of many authigenic minerals (analcime, dawsonite, and nahcolite) varied in the lacustrine strata near and around the depocenter, but others, like quartz, dolomite, and feldspar (potassium + undifferentiated), were widely and consistently present (>90% of samples) across the basin. Shifts in the distribution of indicator mineral occurrences generally coincide with changes identified in previous lake history descriptions and indicate that the water chemistry of Lake Uinta varied significantly going from near-shore to the depocenter and through time.
46
Alvan, Aldo A., Yacory F. Bustamante, Elvis A. Sánchez, and Mirian I. Mamani. "Arquitectura estratigráfica, paleogeografía y proveniencia sedimentaria de las rocas cenozoicas del sur de Perú (Tacna, 18° S)." Andean Geology 47, no. 2 (May 29, 2020): 351. http://dx.doi.org/10.5027/andgeov47n2-3168.
Abstract:
The Cenozoic rocks lying in the Province of Tacna (18° S), southern Perú, represent approximately 600 m of stratigraphic thickness. This stacking groups the Sotillo (Paleocene), Moquegua Inferior (Eocene), Moquegua Superior (Oligocene), Huaylillas (Miocene) and Millo formations (Pliocene), and these are the sedimentary fill of the Moquegua Basin. The sediments of the three latter formations are organized into nine sedimentary facies and five architectural elements. Their facies associations suggest the existence of an ancient highly channelized multi-lateral fluvial braided system, with upward increase of pyroclastic and conglomeratic depositions. The heavy mineral spectra make each lithostratigraphic unit unique and distinguishable, being the sediments of the Moquegua Superior Formation rich in garnets, titanites and zircons; while the sediments of the Huaylillas and Millo formations in clinopyroxenes. This mineral arrangement becomes an excellent tool for stratigraphic correlations between outcrops and subsurface stratigraphy (by means of well cores studies) and allow to sketch out a new stratigraphic framework and a complex of rocky blocks bounded by normal faults, often tilted. The sediment mineralogy also suggests that the rocks conforming the Western Cordillera were the main source of sediments for the Moquegua Basin in Tacna. In this context, the detritus of the Moquegua Superior Formation derives mainly from the erosion of the rocks forming the Coastal Basal Complex (Proterozoic), the Ambo Group (Carboniferous) and the Junerata/Chocolate Formation (Early Jurassic). The Huaylillas Formation is a pyroclastic and sedimentary unit which components derived mainly from the Huaylillas volcanism (Miocene) and partly from the denudation of the Toquepala Group (Late Cretaceous). The Huaylillas Formation widely contrasts to the underlying Moquegua Superior Formation due its mineralogy and facies. Finally, the detritus of the Millo Formation derived mostly from the rocks forming the Barroso Formation (Pliocene), and their facies represent a higher contrast in relation to the underlying units due its notorious conglomerate facies.
47
Podobina, V. M. "NEW DATA ON BIOSTRATIGRAPHY OF THE TAVDA HORIZON (RYUPELIAN STAGE) IN WESTERN SIBERIA (BASED ON THE RESULTS OF THE STUDY OF FORAMINIFERA)." Geology and mineral resources of Siberia, no. 4 (December 2022): 3–13. http://dx.doi.org/10.20403/2078-0575-2022-4-3-13.
Abstract:
The problematic point in the Paleogene biostratigraphy of Western Siberia is the age of the Tavda Horizon as well as the position of Oligocene Stages. In the regional stratigraphic chart for the Paleogene of Western Siberia, unicellular algae and some other data were used as the basis for conclusions on the age of the Tavda Formation (Horizon). As a result, the age of the Tavda Horizon is dated back to the Late Bartonian (Middle Eocene). According to the foraminifera data using geological information, as well as publiсations, the age of the Tavda Horizon is defined as the Ryupelian (Middle Oligocene). The Latdorfian Stage of the Lower Oligocene, as it turned out, falls out of the stratigraphic section of Western Siberia due to manifestation of positive tectonic movements, the rise of this and other northern regions. In the southern regions of Europe, the USA, and the Atlantic, the Latdorfian Stage is present as the Lower Oligocene or as planktonic foraminiferous zones.
48
McInroy, D. B., K. Hitchen, and M. S. Stoker. "Potential Eocene and Oligocene stratigraphic traps of the Rockall Plateau, NE Atlantic Margin." Geological Society, London, Special Publications 254, no. 1 (2006): 247–66. http://dx.doi.org/10.1144/gsl.sp.2006.254.01.13.
49
Cross, Timothy, and Yohan Kusumanegara. "Stratigraphic Controls on Petrophysical Attributes and Fluid-Flow Pathways in an Exhumed Fluvial Reservoir." Mountain Geologist 54, no. 3 (July 2017): 129–45. http://dx.doi.org/10.31582/rmag.mg.54.3.129.
Abstract:
Fluvial, floodplain and lake strata of the Green River Formation (Eocene) occur within an exhumed oil reservoir exposed in a quarry near Sunnyside, Utah. Strata in the quarry highwalls define three, asymmetrical, 15- to 20-m thick, base-level-rise genetic sequences arranged in a long-term base-level-rise (landward stepping) stacking pattern. Variable intensity of oil stain on rock surfaces is a qualitative measure of pore volumes, as all permeable facies are fully saturated with oil. Visual estimates of oil-stain intensity, combined with petrophysical measurements and petrographic analysis of the different facies, were used to define fluid-flow compartments and their boundaries. Strata and facies that functioned as fluid-flow conduits, retardants and barriers were mapped on photomosaics of the quarry highwall. Three separate fluid-flow compartments coincide with the three genetic sequences. Amalgamated fluvial sandstones at the base of each genetic sequence functioned as flow units of varying permeability and degree of interconnectedness. Laterally continuous floodplain and/or lacustrine mudstones, which cap each genetic sequence, entirely lack oil in matrix porosity and functioned as fluid-flow barriers and compartment boundaries. Petrophysical properties of specific sedimentary facies are sensitive to stratigraphic position at three spatial scales, even though the sedimentary facies appear nearly identical. At the long-term scale, porosity and permeability of the same facies (trough cross-stratified sandstone is the most common) in channel sandstones of the three genetic sequences decrease in stratigraphic succession. Within each genetic sequence, porosity and permeability are highest at the base and decrease quasilinearly to the top. Using oil-stain intensity as a proxy, porosity and permeability generally decrease from base to top of each scour-based channel macroform. Petrophysical variations coincide with subtle variations in grain size and trough cross-stratification set thickness within otherwise indistinguishable sedimentary facies. These results demonstrate that conventional crossplots of porosity/permeability versus sedimentary facies are unnecessarily broad and imprecise. When such petrophysical data are plotted in a stratigraphic context, porosity and permeability values have significantly reduced scatter. Porosity and permeability measurements and predictions of each sedimentary facies should be made from a stratigraphic perspective. From our observations of variations in intensity of oil stain, homogeneity of fluid flow may not be equated directly with facies homogeneity. At one extreme of an apparent continuum, fluid-flow pathways are tortuous and extremely variable within homogeneous, high permeability, amalgamated channel sandstones. Sweep efficiencies may be low in these cases. At an intermediate position in the continuum, increased diversity of sedimentary facies and stratigraphic variability usually cause sufficient stratigraphic separation of permeable and impermeable strata such that fluid-flow pathways are more confined and have a reduced tortuosity. Sweep efficiencies may be high in these cases. At the other extreme of the continuum, where diversity of sedimentary facies and stratigraphic variability is very high, stratigraphic units are discontinuous and restricted in area. In such cases, fluid-flow pathways are not laterally connected, and sweep efficiencies would be low.
50
Lillegraven, Jason A. "Alternative viewpoints on the nature and importance of a prominent syncline at the northeastern edge of Wyoming’s Hanna Basin." Rocky Mountain Geology 55, no. 2 (December 1, 2020): 91–129. http://dx.doi.org/10.24872/rmgjournal.55.2.91.
Abstract:
ABSTRACT The geologic history of Wyoming’s Hanna Basin is still being written. Surprisingly, here appeared an opportunity to share insights from previously accomplished work with that conducted anew by other scholars. The area of study was in the southeastern quadrant of Wyoming, which exhibits the state’s most complex history with respect to the Laramide orogeny. Especially important for present purposes were the tectonic conditions of the late Paleocene and earliest Eocene, recorded within the Hanna Formation. Of central focus is the 2020 publication by Dechesne and her six co-authors. Geographically, the landscape they covered was a thin, synclinal slice of the northeastern margin of the Hanna Basin. Key goals for the present publication have been to illustrate positive linkages and to highlight discrepancies between Dechesne et al. (2020) and relevant prior geological work. A concern that permeates all facets of this approach is the ability to verify viability of brand-new geologic descriptions, data, and resulting conclusions. Essential graphical elements were introduced first into this present publication. Once that package of background information was available, more focused analyses were rigorously pursued on diverse issues within the Dechesne et al. (2020) publication. Dechesne’s team presented a significantly modified but adequately defended approximation of the Paleocene–Eocene boundary. Data from fossil plants (macro- and palynofloras), continental mollusks, and bulk organic-carbon isotopes all agree within one measured section (of five sections studied) with an approximated Paleocene–Eocene boundary along with a ‘carbon isotope excursion’ (CIE). Strength of available evidence seems questionable, however, in that the inordinately high variability in bulk organic carbon (characteristic of a CIE) has been demonstrated only in the Hanna Draw Section. Although fluvial, paludal, and lacustrine facies are considered in several contexts, in no sense does the publication’s organizational form provide a ‘detailed stratigraphic framework.’ One zircon-based U–Pb depositional date (54.42 ± 0.27 Ma) came from this study that matched early Wasatchian time. Participants in the Dechesne et al. (2020) project are to be commended in that their resulting paper ranged broadly across the geologic setting, stratigraphy, paleocurrents, paleobotany, continental mollusks, zircon geochronology, associated lithofacies, and paleogeography. Despite that breadth, there exists a plethora of unexpected and wholly avoidable inconsistencies, strong contradictions within what should be homogeneous datasets, and seemingly inexplicable omissions of obviously necessary and sometimes clearly existing but unutilized data, one must question the reliability of much of the information presented in their paper.