To see the other types of publications on this topic, follow the link: Stratigraphic Eocene.
Journal articles on the topic '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 '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
Williamson, P. E., C. J. Pigram, J. B. Colwell, A. S. Scherl, K. L. Lockwood, and J. C. Branson. "PRE-EOCENE STRATIGRAPHY, STRUCTURE, AND PETROLEUM POTENTIAL OF THE BASS BASIN." APPEA Journal 25, no. 1 (1985): 362. http://dx.doi.org/10.1071/aj84031.
Full textAbstract:
Exploration in the Bass Basin has mainly concentrated on the Eocene part of the Eastern View Coal Measures with the pre-Eocene stratigraphy hardly being tested. Structural mapping using a good quality Bureau of Mineral Resources regional seismic survey and infill industry seismic data, in conjunction with seismic stratigraphy and well data, has generated an understanding of the structure and stratigraphy of the pre- Eocene basin, which suggests that exploration potential exists in structural and stratigraphic leads of both Paleocene and Cretaceous age.The Paleocene structure is influenced by the reactivation of normal faults developed at the time of the mid Cretaceous rift unconformity and reflects drape over deeper features. Consequently fault dependent structural closures often persist from Paleocene to (?)Jurassic levels. Possible stratigraphic traps are also observed against horst blocks and around the basin margins. The longitudinal fault directions are northwest and west northwest with an oblique northerly direction and a prevailing north northeasterly transverse direction.The Paieocene and Upper Cretaceous part of the Eastern View Coal Measures consists of sands, shales and coals deposited in alluvial fans, on flood plains, and in lakes. These are underlain by Early Cretaceous Otway Groups, sands, shales and volcanics. Both intervals have potential reservoir and source rocks and often occur at mature depths. No pre-Otway Group sediments have been encountered in wells in the Bass Basin. However, the Permo- Carboniferous and possibly Triassic strata that occur in Northern Tasmania exhibit reservoir and source rock potential and may extend offshore beneath the Bass Basin.Pre-Eocene structural and stratigraphic studies of the Bass Basin thus point to reservoir and hydrocarbon source potential for possible multiple hydrocarbon exploration targets.
2
Wade, Bridget S., Mohammed H. Aljahdali, Yahya A. Mufrreh, Abdullah M. Memesh, Salih A. AlSoubhi, and Iyad S. Zalmout. "Upper Eocene planktonic foraminifera from northern Saudi Arabia: implications for stratigraphic ranges." Journal of Micropalaeontology 40, no. 2 (September 28, 2021): 145–61. http://dx.doi.org/10.5194/jm-40-145-2021.
Full textAbstract:
Abstract. The Rashrashiyah Formation of the Sirhan Basin in northern Saudi Arabia contains diverse assemblages of planktonic foraminifera. We examined the biostratigraphy, stratigraphic range and preservation of upper Eocene planktonic foraminifera. Assemblages are well-preserved and diverse, with 40 species and 11 genera. All samples are assigned to the Priabonian Globigerinatheka semiinvoluta Highest Occurrence Zone (E14), consistent with calcareous nannofossil biostratigraphy indicating Zone CNE17. Well-preserved planktonic foraminifera assemblages from the lower part of the upper Eocene are rare worldwide. Our study provides new insights into the stratigraphic ranges of many species. We find older (Zone E14) stratigraphic occurrences of several species of Globoturborotalita previously thought to have evolved in the latest Eocene (Zone E15, E16) or Oligocene; these include G. barbula, G. cancellata, G. gnaucki, G. pseudopraebulloides, and G. paracancellata. Older stratigraphic occurrences for Dentoglobigerina taci and Subbotina projecta are also found, and Globigerinatheka kugleri occurs at a younger stratigraphic level than previously proposed. Our revisions to stratigraphic ranges indicate that the late Eocene had a higher tropical–subtropical diversity of planktonic foraminifera than hitherto reported.
3
Eberle, Jaelyn J., and David A. Eberth. "Additions to the Eocene Perissodactyla of the Margaret Formation, Eureka Sound Group, Ellesmere Island, Arctic Canada." Canadian Journal of Earth Sciences 52, no. 2 (February 2015): 123–33. http://dx.doi.org/10.1139/cjes-2014-0195.
Full textAbstract:
We describe early Eocene (Wasatchian) occurrences of the isectolophid Homogalax, tapiroids Heptodon posticus, Heptodon cf. H. posticus, and Heptodon sp., as well as early middle Eocene (Bridgerian) fossils of the brontothere Palaeosyops from localities in the Margaret Formation of the Eureka Sound Group on Ellesmere Island, Nunavut, Arctic Canada. Their occurrence on Ellesmere Island considerably extends the geographic range of these taxa, previously known from mid-latitude localities in British Columbia (only Heptodon), the Western Interior of the United States, and Asia (Homogalax, Heptodon, and Palaeosyops). We also place the fossil localities near Bay Fiord on central Ellesmere Island into a refined lithostratigraphic framework based upon data from three measured stratigraphic sections. Our stratigraphic data confirm the presence of two, stratigraphically distinct fossil assemblages — a late Wasatchian-aged lower assemblage and a Bridgerian-aged upper assemblage that were previously hypothesized by others based on faunal differences — that are separated by a 478 m thick stratigraphic gap that appears to lack fossil vertebrates. From a paleoenvironmental perspective, occurrence of the tapiroid Heptodon in the Eocene Arctic corroborates an hypothesis put forward by others that tapiroids are proxies for densely forested habitats, although they were adapted to a range of temperatures including near (or at) freezing temperatures of Eocene Arctic winters. Further, Arctic occurrences of tapiroids and brontotheres imply that these typical mid-latitude ungulate mammals were adapted to Arctic environments, thereby increasing the probability of Trans-Beringian dispersal during early and middle Eocene time.
4
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.
Full textAbstract:
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.
5
Mitrovic-Petrovic, Jovanka. "Paleoecological features and stratigraphic significance of the Genus Conoclypus, Echinoidea." Annales g?ologiques de la Peninsule balkanique, no. 64 (2002): 89–105. http://dx.doi.org/10.2298/gabp0264089m.
Full textAbstract:
Five species and a subspecies of the genus Conoclypus from Eocene formations of Croatia and Herzegovina are presented in this paper. Morphology of the genus is analysed. The given paleoecological conclusions are based on morphological data, character of sedimentary rocks containing Conoclypus, associated fauna and mechanical and biotic damages. Stratigraphic significance of this genus is emphasized, because it appeared, flourished, and disappeared in the Eocene period.
6
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.
Full textAbstract:
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.
7
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.
Full text
8
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.
Full textAbstract:
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.
9
Venkatachala, B. S., C. Caratini, C. Tissot, and R. K. Kar. "Palaeocene-Eocene marker pollen from India and tropical Africa." Journal of Palaeosciences 37, no. (1-3) (December 31, 1988): 1–25. http://dx.doi.org/10.54991/jop.1988.1595.
Full textAbstract:
The Palaeocene-Eocene epochs have witnessed a great floral diversification in tropical areas, which is also reflected in the pollen spectra. The important Indian stratigraphical marker taxa have been examined and a comparative study with extant material has provided botanical affinities to some of the taxa. Their comparison with those recorded in Africa leads to reflection on their palaeogeographical distribution. The stratigraphic ranges have been shown in the range chart. Some of the taxa common to India and Africa are: Retistephanocolpites williamsi, Spinizonocolpites spp., Tricolpites reticulatus, Proxapertites spp., Anacolosidites luteoides and Marginipollis spp. A number of Indian, as well as African taxa, are not recorded beyond the terminal Eocene; some of them could have migrated from India to other countries such as Gonystylus (Cryptopolyporites) to Malaysia and Gunnera (Tricolpites reticulatus) to Australia. The relative location and motion of India during these epochs could explain the singularity of the Early Tertiary Indian palynoflora.
10
Carter, Burchard D., and Michael L. McKinney. "Eocene echinoids, the Suwannee Strait, and biogeographic taphonomy." Paleobiology 18, no. 3 (1992): 299–325. http://dx.doi.org/10.1017/s0094837300010861.
Full textAbstract:
Faunal similarity among regions is often used as a means of identifying regions of endemism in fossil faunas. At least two large-scale taphonomic effects can affect apparent faunal similarity: stratigraphic and facies mismatching. In stratigraphic mismatching, an unconformity represents removal of most or all of a complete assemblage zone in one region, and the constituent taxa are mistakenly interpreted as having never inhabited that region. In facies mismatching, environmental differences between two regions (possibly unrecognized) cause the inference of a barrier that never existed. The two types of mismatching can work in concert if a facies was originally represented in a single stratigraphic interval that has been completely removed from one region. Analysis of faunal similarity via multivariate analysis of individual localities, coupled with comparison of the regions as single samples, may indicate mismatching if the results differ significantly.We view these two problems as part of a suite of taphonomic effects that are not evident in paleobiological analyses of smaller geographic scope. First, there is ambiguity in the notion of “barrier,” even when a candidate is obvious. Second, barriers in paleobiogeography are often hidden and must be inferred from their effects rather than observed. Third, stratigraphic and facies mismatching produce effects on regional faunas similar to those produced by barriers. Anyone using barriers to explain faunal disruptions should address these three points.Upper Eocene faunas of central Florida seem taxonomically distinct from those of the remainder of the Gulf Coastal Plain. This has historically been attributed to a known paleogeographic feature, the Suwannee Strait, which acts as a barrier. The amount of dissimilarity of the echinoid faunas is greater than the amount predicted as a result of sampling problems. Comparison of the results of multivariate and whole-region analyses suggests that mismatching of the two faunas, rather than a true barrier, causes the distinction. Principally facies, but also strata are mismatched. Early Late Eocene faunas inhabited terrigenous sands to the north of the strait and carbonate sands to the south and show the highest distinctiveness. Middle Late Eocene faunas inhabited primarily carbonate sands to the south and both carbonate sands and muds to the north. Overall similarity is higher for both local and regional analyses, and the faunas of northern sands are more similar to those of the southern region than to the northern mud faunas. Overall similarity across the strait is highest in the late Late Eocene strata when both regions had carbonate mud and sand facies. The faunas exhibit greater similarity within facies than they do within regions. Upper Late Eocene strata are poorly preserved north of the strait because of post-Eocene erosion.
11
de Santana dos Anjos Zerfass, Geise, Dmitry A. Ruban, Farid Chemale Jr., and Henrique Zerfass. "Cenozoic synthem stratigraphic architecture of the SE Brazilian shelf and its global eustatic context: evidence from the Pelotas Basin (offshore Brazil)." Geologos 19, no. 4 (December 1, 2013): 273–90. http://dx.doi.org/10.2478/logos-2013-0018.
Full textAbstract:
Abstract The Pelotas Basin, located on the SE Brazilian shelf, has evolved since the Aptian. Stratigraphical data from the basin can be used for delineation of the unconformity-bounded units (synthems) on the shelf, which is a first step towards a full understanding of its stratigraphic architecture, evolution, and hydrocarbon potential. Hiatuses in the Cenozoic succession of the Pelotas Basin are established with both biostratigraphic (planktonic foraminifers and calcareous nannofossils) and isotopic (87Sr/86Sr) data. The seven recognised hiatuses are dated respectively as (1) Palaeocene (Danian- Thanetian), (2) Palaeocene/Eocene boundary (Thanetian-Ypresian), (3) Eocene (Ypresian-Lutetian), (4) Eocene-Oligocene (Lutetian-Rupelian), (5) early-late Oligocene (Rupelian-Chattian), (6) early Miocene (Aquitanian-Burdigalian), and (7) middle-late Miocene (Serravallian-Tortonian). These intervals between the hiatuses are correlated with those of the Santos and Campos Basins north from the Pelotas Basin. The breaks in sedimentation that these basins have in common occurred (1) at the Palaeocene-Eocene and (2) Eocene-Oligocene transitions, (3) in the early Miocene, and (4) in the middle-late Miocene. These main unconformities outline five synthems on the SE Brazilian shelf, viz. the SEBS-1 (Palaeocene), SEBS-2 (Eocene), SEBS-3 (Oligocene), SEBS-4 (early-middle Miocene) and SEBS-5 (late Miocene-Holocene). The above unconformities are correlated with those established in the Cenozoic sedimentary successions of different regions such as Western Siberia, Arabia, NW and NE Africa, peninsular India, S Australia, the Gulf of Mexico, NW Europe, and South Africa. The only regional unconformity, near the Oligocene/Miocene boundary, coincides with the nearly-global sedimentation break. The latter was resulted from a climatic event, i.e., the ‘Mi-1 glaciation’. Thus, a eustatic origin is supposed for this regional unconformity. The other regional unconformities also correspond to global sea-level falls (probably with an exception for the Palaeocene/Eocene surface), which suggests that global eustatic movements controlled the development of the regional synthem architecture.
12
Siddiqui, Qadeer A. "The ostracod genus <i>Paijenborchella</i> and some of its species in the Early Tertiary of Pakistan." Journal of Micropalaeontology 25, no. 1 (April 1, 2006): 65–72. http://dx.doi.org/10.1144/jm.25.1.65.
Full textAbstract:
Abstract. Six species of the genus Paijenborchella are described. Five of these species are new, namely Paijenborchella (Eopaijenborchella) angulosa, P. (E.) viriosa, P. (E.) ventricaudata, P. (E.) noar and P. (Paijenborchella) inponticulata. The stratigraphic distribution of these species in the Early Tertiary of Pakistan is given; they range from the Lower Eocene to the Upper Eocene in the Sulaiman Range and one species occurs in the Upper Paleocene of the Sor Range.
13
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.
Full textAbstract:
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.
14
Frieling, Joost, Emiel P. Huurdeman, Charlotte C. M. Rem, Timme H. Donders, Jörg Pross, Steven M. Bohaty, Guy R. Holdgate, Stephen J. Gallagher, Brian McGowran, and Peter K. Bijl. "Identification of the Paleocene–Eocene boundary in coastal strata in the Otway Basin, Victoria, Australia." Journal of Micropalaeontology 37, no. 1 (February 13, 2018): 317–39. http://dx.doi.org/10.5194/jm-37-317-2018.
Full textAbstract:
Abstract. Detailed, stratigraphically well-constrained environmental reconstructions are available for Paleocene and Eocene strata at a range of sites in the southwest Pacific Ocean (New Zealand and East Tasman Plateau; ETP) and Integrated Ocean Discovery Program (IODP) Site U1356 in the south of the Australo-Antarctic Gulf (AAG). These reconstructions have revealed a large discrepancy between temperature proxy data and climate models in this region, suggesting a crucial error in model, proxy data or both. To resolve the origin of this discrepancy, detailed reconstructions are needed from both sides of the Tasmanian Gateway. Paleocene–Eocene sedimentary archives from the west of the Tasmanian Gateway have unfortunately remained scarce (only IODP Site U1356), and no well-dated successions are available for the northern sector of the AAG. Here we present new stratigraphic data for upper Paleocene and lower Eocene strata from the Otway Basin, southeast Australia, on the (north)west side of the Tasmanian Gateway. We analyzed sediments recovered from exploration drilling (Latrobe-1 drill core) and outcrop sampling (Point Margaret) and performed high-resolution carbon isotope geochemistry of bulk organic matter and dinoflagellate cyst (dinocyst) and pollen biostratigraphy on sediments from the regional lithostratigraphic units, including the Pebble Point Formation, Pember Mudstone and Dilwyn Formation. Pollen and dinocyst assemblages are assigned to previously established Australian pollen and dinocyst zonations and tied to available zonations for the SW Pacific. Based on our dinocyst stratigraphy and previously published planktic foraminifer biostratigraphy, the Pebble Point Formation at Point Margaret is dated to the latest Paleocene. The globally synchronous negative carbon isotope excursion that marks the Paleocene–Eocene boundary is identified within the top part of the Pember Mudstone in the Latrobe-1 borehole and at Point Margaret. However, the high abundances of the dinocyst Apectodinium prior to this negative carbon isotope excursion prohibit a direct correlation of this regional bio-event with the quasi-global Apectodinium acme at the Paleocene–Eocene Thermal Maximum (PETM; 56 Ma). Therefore, the first occurrence of the pollen species Spinizonocolpites prominatus and the dinocyst species Florentinia reichartii are here designated as regional markers for the PETM. In the Latrobe-1 drill core, dinocyst biostratigraphy further indicates that the early Eocene (∼ 56–51 Ma) sediments are truncated by a ∼ 10 Myr long hiatus overlain by middle Eocene (∼ 40 Ma) strata. These sedimentary archives from southeast Australia may prove key in resolving the model–data discrepancy in this region, and the new stratigraphic data presented here allow for detailed comparisons between paleoclimate records on both sides of the Tasmanian Gateway.
15
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.
Full text
16
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.
Full textAbstract:
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.
17
Rivandi, Batool, Mohammad Vahidinia, Mehdi Nadjafi, Asadollah Mahboubi, and Abbas Sadeghi. "Biostratigraphy and Sequence Stratigraphy of Paleogene Deposits in Central Kopet-Dagh Basin (NE of Iran)." Journal of Geological Research 2013 (September 15, 2013): 1–12. http://dx.doi.org/10.1155/2013/892198.
Full textAbstract:
In this paper, the biostratigraphy and sequence stratigraphy of marine Paleogene deposits from the Kopet-Dagh basin (NE of Iran) are described. Particularly the absence of Morozovella genus is discussed. In addition, the Paleocene/Eocene boundary has been studied in detail using the record of planktonic and larger benthic foraminifera. This boundary is located probably within a thin red horizon (~10–15 cm) representing a paleosoil. Close to this boundary is located the base of the calcareous test dissolution interval, with the dominance of agglutinated benthic foraminifera and with a sudden decrease in the richness of benthic foraminiferal species. Biostratigraphic studies led to the identification of 33 genera of larger benthic foraminifera and 5 genera of planktonic foraminifera. Petrographical studies indicate that these sediments, consisting of four carbonate lithofacies (15 subfacies), may have been deposited on a shallow carbonate platform (ramp type). These lithofacies have been deposited in open marine, shoal, lagoon, and tidal flat environmental conditions. Sequence stratigraphic analysis led to the identification of four third-order depositional sequences. The interpreted sea-level curve in the Kopet-Dagh basin can be correlated with Paleocene-Eocene global curves, with a sea-level fall in the latest Paleocene, followed by a sea-level rise in the earliest Eocene.
18
Siddiqui, Qadeer A. "Some species of the genus <i>Neocyprideis</i> in the early Tertiary of Pakistan." Journal of Micropalaeontology 19, no. 1 (May 1, 2000): 1–7. http://dx.doi.org/10.1144/jm.19.1.1.
Full textAbstract:
Abstract. Four species of the genus Neocyprideis described in this paper are an addition to the ostracod fauna from the early Tertiary of Pakistan. N. sp. A occurs in the Upper Palaeocene of the Sor Range, and three new species are found in the Eocene of the Sulaiman Range. The new species are Neocyprideis simplex and N. regularis from the upper Lower Eocene, and N. formosa from the uppermost Eocene. The first two species, the associated ostracod fauna and the lithology suggest a shallow marine shelf environment with evaporitic conditions, while N. formosa lived in an open marine shelf environment. The short vertical ranges of these three new species makes them useful stratigraphic markers in this area.
19
Westerhold, T., U. Röhl, H. Pälike, R. Wilkens, P. A. Wilson, and G. Acton. "Orbitally tuned timescale and astronomical forcing in the middle Eocene to early Oligocene." Climate of the Past 10, no. 3 (May 16, 2014): 955–73. http://dx.doi.org/10.5194/cp-10-955-2014.
Full textAbstract:
Abstract. Deciphering the driving mechanisms of Earth system processes, including the climate dynamics expressed as paleoceanographic events, requires a complete, continuous, and high-resolution stratigraphy that is very accurately dated. In this study, a robust astronomically calibrated age model was constructed for the middle Eocene to early Oligocene interval (31–43 Ma) in order to permit more detailed study of the exceptional climatic events that occurred during this time, including the middle Eocene climate optimum and the Eocene–Oligocene transition. A goal of this effort is to accurately date the middle Eocene to early Oligocene composite section cored during the Pacific Equatorial Age Transect (PEAT, IODP Exp. 320/321). The stratigraphic framework for the new timescale is based on the identification of the stable long eccentricity cycle in published and new high-resolution records encompassing bulk and benthic stable isotope, calibrated XRF core scanning, and magnetostratigraphic data from ODP Sites 171B-1052, 189-1172, 199-1218, and 207-1260 as well as IODP Sites 320-U1333, and 320-U1334 spanning magnetic polarity Chrons C12n to C20n. Subsequently orbital tuning of the records to the La2011 orbital solution was conducted. The resulting new timescale revises and refines the existing orbitally tuned age model and the geomagnetic polarity timescale from 31 to 43 Ma. The newly defined absolute age for the Eocene–Oligocene boundary validates the astronomical tuned age of 33.89 Ma identified at the Massignano, Italy, global stratotype section and point. The compilation of geochemical records of climate-controlled variability in sedimentation through the middle-to-late Eocene and early Oligocene demonstrates strong power in the eccentricity band that is readily tuned to the latest astronomical solution. Obliquity driven cyclicity is only apparent during 2.4 myr eccentricity cycle minima around 35.5, 38.3, and 40.1 Ma.
20
Westerhold, T., U. Röhl, H. Pälike, R. Wilkens, P. A. Wilson, and G. Acton. "Orbitally tuned time scale and astronomical forcing in the middle Eocene to early Oligocene." Climate of the Past Discussions 9, no. 6 (December 18, 2013): 6635–82. http://dx.doi.org/10.5194/cpd-9-6635-2013.
Full textAbstract:
Abstract. Deciphering the driving mechanisms of Earth system processes, including the climate dynamics expressed as paleoceanographic events, requires a complete, continuous, and high-resolution stratigraphy that is very accurately dated. In this study, we construct a robust astronomically calibrated age model for the middle Eocene to early Oligocene interval (31–43 Ma) in order to permit more detailed study of the exceptional climatic events that occurred during this time, including the Middle Eocene Climate Optimum and the Eocene/Oligocene transition. A goal of this effort is to accurately date the middle Eocene to early Oligocene composite section cored during the Pacific Equatorial Age Transect (PEAT, IODP Exp. 320/321). The stratigraphic framework for the new time scale is based on the identification of the stable long eccentricity cycle in published and new high-resolution records encompassing bulk and benthic stable isotope, calibrated XRF core scanning, and magnetostratigraphic data from ODP Sites 171B-1052, 189-1172, 199-1218, and 207-1260 as well as IODP Sites 320-U1333, and -U1334 spanning magnetic polarity Chrons C12n to C20n. Subsequently we applied orbital tuning of the records to the La2011 orbital solution. The resulting new time scale revises and refines the existing orbitally tuned age model and the Geomagnetic Polarity Time Scale from 31 to 43 Ma. Our newly defined absolute age for the Eocene/Oligocene boundary validates the astronomical tuned age of 33.89 Ma identified at the Massignano (Italy) global stratotype section and point. Our compilation of geochemical records of climate-controlled variability in sedimentation through the middle-to-late Eocene and early Oligocene demonstrates strong power in the eccentricity band that is readily tuned to the latest astronomical solution. Obliquity driven cyclicity is only apparent during very long eccentricity cycle minima around 35.5, 38.3 and 40.1 Ma.
21
Arditto, P. A. "THE EASTERN OTWAY BASIN WANGERRIP GROUP REVISITED USING AN INTEGRATED SEQUENCE STRATIGRAPHIC METHODOLOGY." APPEA Journal 35, no. 1 (1995): 372. http://dx.doi.org/10.1071/aj94024.
Full textAbstract:
Recent exploration by BHP Petroleum in VIC/ P30 and VIC/P31, within the eastern Otway Basin, has contributed significantly to our understanding of the depositional history of the Paleocene to Eocene siliciclastic Wangerrip Group. The original lithostratigraphic definition of this group was based on outcrop description and subsequently applied to onshore and, more recently, offshore wells significantly basinward of the type sections. This resulted in confusing individual well lithostratigraphies which hampered traditional methods of subsurface correlation.A re-evaluation of the Wangerrip Group stratigraphy is presented based on the integration of outcrop, wireline well log, palynological and reflection seismic data. The Wangerrip Group can be divided into two distinct units based on seismic and well log character. A lower Paleocene succession rests conformably on the underlying Maastrichtian and older Sherbrook Group, and is separated from an overlying Late Paleocene to Eocene succession by a significant regional unconformity. This upper unit displays a highly progradational seismic character and is named here as the Wangerrip Megasequence.Regional seismic and well log correlation diagrams are used to illustrate a subdivision of the Wangerrip Megasequence into eight third-order sequences. This sequence stratigraphic subdivision of the Wangerrip Group is then used to construct a chronostratigraphic chart for the succession within this part of the Otway Basin.
22
Stoykova, Kristalina, and Marin Ivanov. "New data on the age of the Emine Formation (East Balkan, Bulgaria)." Review of the Bulgarian Geological Society 82, no. 3 (December 2021): 126–28. http://dx.doi.org/10.52215/rev.bgs.2021.82.3.126.
Full textAbstract:
The study represents new data about chronostratigraphic range of the Emine flysch Formation in its type section at the Black Sea coast near the “Irakli” touristic resort. In the highest stratigraphic levels, calcareous nannofossils of NP 10 Rhomboaster bramlettei zone have been documented, supporting early Eocene age for the formation. These new finds will shed light on the timing of cessation of the turbiditic sedimentation in East Balkan, as well as on the specific expression of the global event – the Paleocene–Eocene Thermal Maximum (PETM) in deep-water environment.
23
Cotton, Laura J., Wolfgang Eder, and James Floyd. "Larger foraminifera of the Devil's Den and Blue Hole sinkholes, Florida." Journal of Micropalaeontology 37, no. 1 (March 23, 2018): 347–56. http://dx.doi.org/10.5194/jm-37-347-2018.
Full textAbstract:
Abstract. Shallow-water carbonate deposits are well-known from the Eocene of the US Gulf Coast and Caribbean. These deposits frequently contain abundant larger benthic foraminifera (LBF). However, whilst integrated stratigraphic studies have helped to refine the timing of LBF overturning events within the Tethys and Indo-Pacific regions with respect to global bio- and chemo-stratigraphic records, little recent work has been carried out in the Americas. The American LBF assemblages are distinctly different from those of Europe and the Indo-Pacific. It is therefore essential that the American bio-province is included in studies of LBF evolution, biodiversity and climate events to understand these processes on a global scale. Here we present the LBF ranges from two previously unpublished sections spanning 35 and 29 m of the upper Eocene Ocala limestone, as the early stages of a larger project addressing the taxonomy and biostratigraphy of the LBF of Florida. The study indicates that the lower member of the Ocala limestone may be Bartonian rather than Priabonian in age, with implications for the biostratigraphy of the region. In addition, the study highlights the need for multiple sites to assess the LBF assemblages and fully constrain ranges across Florida and the US Gulf and suggests potential LBF events for future integrated stratigraphic study.
24
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.
Full textAbstract:
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.
25
Greenwood, David R., and James F. Basinger. "Stratigraphy and floristics of Eocene swamp forests from Axel Heiberg Island, Canadian Arctic Archipelago." Canadian Journal of Earth Sciences 30, no. 9 (September 1, 1993): 1914–23. http://dx.doi.org/10.1139/e93-169.
Full textAbstract:
A record of polar Eocene forests is preserved as in situ tree-stump fields and leaf-litter mats in Buchanan Lake Formation sediments on Axel Heiberg Island, in the Canadian Arctic Archipelago. Stratigraphic examination at the centimetre to metre scale of peat–coal lithology and macrofossil floristics in two levels of these fossil forests reflects small-scale changes in forest composition and swamp hydrology horizontally and temporal variation vertically. Root system structure and tree base stratigraphy suggest that exposed tree stumps may not include only coeval individuals of a single forest stand, but rather also individuals representing different phases of the forest through one cycle of the hydrological development of this Eocene polar forest community. Earlier calculations of stand density and biomass, based upon the assumption that all stumps represent coeval trees, may therefore be greatly overestimated. A mosaic of Alnus – fern bog, mixed coniferous community, and taxodiaceous (Metasequoia–Glyptostrobus) swamp appears to have produced both the leaf mats and the in situ stumps, with the taxodiaceous swamp the dominant peat-accumulating phase.
26
Arua, I., and V. R. Rao. "New stratigraphic data on the Eocene Ameki formation, southeastern Nigeria." Journal of African Earth Sciences (1983) 6, no. 4 (January 1987): 391–97. http://dx.doi.org/10.1016/0899-5362(87)90082-0.
Full text
27
Chukova, E. I., A. S. Rakhmatullina, and O. V. Sivalneva. "The Lithology of the Eocene-Paleocene Reservoirs of the Central and Eastern Ciscaucasia." E3S Web of Conferences 266 (2021): 07002. http://dx.doi.org/10.1051/e3sconf/202126607002.
Full textAbstract:
The article presents the results of lithological and petrophysical investigations of reservoir rocks of the Eocene-Paleocene Formations, which is one of the main hydrocarbon prolific horizons in the Central and Eastern Ciscaucasia. These results include lithological characteristics and pore space parameters for reservoir rocks of these stratigraphic intervals.
28
Steinthorsdottir, Margret, Amanda S. Porter, Aidan Holohan, Lutz Kunzmann, Margaret Collinson, and Jennifer C. McElwain. "Fossil plant stomata indicate decreasing atmospheric CO<sub>2</sub> prior to the Eocene–Oligocene boundary." Climate of the Past 12, no. 2 (February 25, 2016): 439–54. http://dx.doi.org/10.5194/cp-12-439-2016.
Full textAbstract:
Abstract. A unique stratigraphic sequence of fossil leaves of Eotrigonobalanus furcinervis (extinct trees of the beech family, Fagaceae) from central Germany has been used to derive an atmospheric pCO2 record with multiple data points spanning the late middle to late Eocene, two sampling levels which may be earliest Oligocene, and two samples from later in the Oligocene. Using the inverse relationship between the density of stomata and pCO2, we show that pCO2 decreased continuously from the late middle to late Eocene, reaching a relatively stable low value before the end of the Eocene. Based on the subsequent records, pCO2 in parts of the Oligocene was similar to latest Eocene values. These results suggest that a decrease in pCO2 preceded the large shift in marine oxygen isotope records that characterizes the Eocene–Oligocene transition and that when a certain threshold of pCO2 change was crossed, the cumulative effects of this and other factors resulted in rapid temperature decline, ice build up on Antarctica and hence a change of climate mode.
29
Steinthorsdottir, M., A. S. Porter, A. Holohan, L. Kunzmann, M. Collinson, and J. C. McElwain. "Fossil plant stomata indicate decreasing atmospheric CO<sub>2</sub> prior to the Eocene–Oligocene boundary." Climate of the Past Discussions 11, no. 5 (October 26, 2015): 4985–5019. http://dx.doi.org/10.5194/cpd-11-4985-2015.
Full textAbstract:
Abstract. A unique stratigraphic sequence of fossil leaves of Eotrigonobalanus furcinervis (extinct trees of the beech family, Fagaceae) from central Germany has been used to derive an atmospheric pCO2 record with multiple data points spanning the late middle to late Eocene, two sampling levels which may be earliest Oligocene, and two samples from later in the Oligocene. Using the inverse relationship between the density of stomata and pCO2, we show that pCO2 decreased continuously from the late middle to late Eocene, reaching a relatively stable low value before the end of the Eocene. Based on the subsequent records, pCO2 in parts of the Oligocene was similar to latest Eocene values. These results show that a decrease in pCO2 preceded the large shift in marine oxygen isotope records that characterizes the Eocene–Oliogocene transition. This may be related to the "hysteresis effect" previously proposed – where a certain threshold of pCO2 change was crossed before the cumulative effects of this and other factors resulted in rapid temperature decline, ice build up on Antarctica and hence a change of climate mode.
30
Lichtig, Asher J., Steven E. Jasinski, and Spencer G. Lucas. "Eocene North American Testudinidae and Geoemydidae (Reptilia, Testudines): A Re-Evaluation of Their Alpha Taxonomy, Ecology, and Origin." Proceedings 24, no. 1 (June 4, 2019): 24. http://dx.doi.org/10.3390/iecg2019-06195.
Full textAbstract:
We describe new material, including juvenile specimens, of Hadrianus corsoni, Hadrianus majusculus, Echmatemys haydeni, and Echmatemys naomi. Testudinidae evolved in North America from one of the geoemydid-like forms in the genus Echmatemys, which have their lowest stratigraphic occurrence in the earliest Wasatchian North American land mammal “age” (early Eocene, Ypresian).
31
Yanin, B. T., and V. N. Benyamovsky. "BURROWS OF DECAPOD CRUSTACEANS IN PALEOGENE OF MIDDLE VOLGA AND ITS PALEOGEOGRAPHIC SIGNIFICANCE." Moscow University Bulletin. Series 4. Geology, no. 1 (February 28, 2018): 36–43. http://dx.doi.org/10.33623/0579-9406-2018-1-36-43.
Full textAbstract:
The description of the new finding of the burrows of decapod crustacean from Upper Paleocene and Lower Eocene deposits relating to two ichnotaxons (Thalassinoides suevicus Rieth and Ophiomorpha nodosa Lundgren), clarifies their stratigraphic position and state the paleogeographic significance for determining eustatic phases in the development of semirestricted Early Paleogene Volga-Caspian basin.
32
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.
Full textAbstract:
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.
33
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.
Full textAbstract:
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.
34
Hnylko, Svitlana. "Biostratigraphy of Paleocene-Eocene deposits of the Ukrainian Carpathians based on planktonic foraminifera." Geology and Geochemistry of Combustible Minerals 3-4, no. 185-186 (2021): 56–64. http://dx.doi.org/10.15407/ggcm2021.03-04.056.
Full textAbstract:
Paleogene deposits are the main reservoir of hydrocarbon resources in the Carpathians and creation of the modern stratigraphic scheme of these deposits is the basis for improving the efficiency of geological search works. The reliable stratification is a necessary precondition for the preparation of geological maps. Stratification of the Paleocene–Eocene sediments is provided by foraminifera, nannoplankton, dinocysts, radiolarians, sponge spicules, palynoflora. Planktonic foraminifera is the main stratigraphic group of the Paleogene fauna. In the predominantly non-calcareous flysch of the Paleocene–Eocene of the Carpathians, mainly agglutinated benthic foraminifera of siliceous composition are developed. Planktonic foraminifera are distributed locally – in calcareous facies. The most complete sequence of Paleocene–Eocene planktonic foraminifera is represented in the Metova Formation (the Vezhany nappe of the Inner Carpathians). The results of own researches of natural sections of sediments distributed within the Magursky, Monastyretsky and Vezhany nappes of the Ukrainian Carpathians together with the analysis of literature sources are used. The article presents a generalized biozonal division of the Paleocene–Eocene of the Ukrainian Carpathians by planktonic foraminifera. On the basis of certain correlation levels, a comparison with the Geological Time Scale was made. The Parvularugoglobigerina eugubina Zone (lowermost Danian), Globoconusa daubjergensis Zone (middle Danian), Praemurica inconstans Zone (upper Danian); Morozovella angulata Zone (lower Selandian); Globanomalina pseudomenardii Zone fnd Acarinina acarinata Zone (upper Selandian–Thanetian); Morozovella subbotinae Zone (lower Ypresian), Morozovella aragonensis Zone (upper Ypresian); Acarinina bullbrooki Zone (lower Lutetian), Acarinina rotundimarginata Zone (upper Lutetian); Hantkenina alabamensis Zone (Bartonian); Globigerinatheka tropicalis Zone (lower Priabonian) and Subbotina corpulenta Zone (upper Priabonian) based on planktonic foraminifera are characterized in studied deposits.
35
Grainger, Nancy C., Michael E. Villeneuve, Larry M. Heaman, and Robert G. Anderson. "New UPb and Ar/Ar isotopic age constraints on the timing of Eocene magmatism, Fort Fraser and Nechako River map areas, central British Columbia." Canadian Journal of Earth Sciences 38, no. 4 (April 1, 2001): 679–96. http://dx.doi.org/10.1139/e00-093.
Full textAbstract:
Twenty-three new, precise, Eocene UPb and 40Ar/39Ar age determinations for calc-alkaline volcanic rocks of the Ootsa Lake Group and associated intrusive rocks, widespread in the Nechako Plateau in central British Columbia, constrain the timing of the Eocene magmatism to 53.247.6 Ma, with a local duration of as little as 23 million years. The new dates show that magmatism in the study area is partly coeval with that responsible for the Babine Igneous Suite Newman Volcanic Suite (5350 Ma) to the north, and for the Endako Group (5145 Ma), which overlies the Ootsa Lake Group; however, locally the three magmatic suites are distinct in age and (or) the strata record a magmatic hiatus of as much as 7.5 million years. The ages generally young from north to south (5247 Ma) along the western portion of the study area. The Babine Igneous Suite Newman Volcanic Suite represents the oldest member of this series. However, in the east, the Ootsa Lake Group volcanic rocks are generally older (5351 Ma). The anomalously older ages may be related to the interaction of magmatism and formation of a nearby and coeval core complex, which ongoing studies show was uplifted at about the same time during the Eocene. Felsic plutonism associated with the Ootsa Lake Group occurred between 50.5 and 47.3 Ma. These plutons were emplaced in an extensional setting along north-northeast-trending faults. The new dates, stratigraphic relationships, and suggested correlations of Eocene strata in the study area with that to the west and north require a revision of the stratigraphic nomenclature for the Ootsa Lake and Endako groups.
36
Iakovleva, A. I., E. A. Shcherbinina, N. G. Muzylev, and G. N. Aleksandrova. "Dinocysts from the mid–upper Eocene Aktumsuk section, Ustyurt, Uzbekistan: biostratigraphy and paleoenvironments." Стратиграфия 27, no. 6 (December 12, 2019): 78–102. http://dx.doi.org/10.31857/s0869-592x27678-102.
Full textAbstract:
The results of palynological study of the MidUpper Eocene sediments of the Aktumsuk key-section (Ustyurt Plateau, Uzbekistan), calibrated with nannoplankton data, are presented. Dinocyst stratigraphical distribution permitted to recognize five Dinoflagellate zones from the Peri-Tethys zonation: Costacysta bucina, Enneadocysta pectiniformis, Rhombodinium draco, Rhombodinium perforatum, and Thalassiphora reticulata. First-order calibration with nannoplankton zones permitted to precise the lowermost occurrences of the key dinocyst species. Based on the dinocyst and nannoplankton data, two important stratigraphic hiatuses, corresponding to the upper Ypresian and Upper BartonianLower Priabonian, were recognized. Analysis of quantitative fluctuations of different groups of palynomorphs through the section indicates paleoenvironmental changes in this part of the Peri-Tethys during the LutetianPriabonian: the beginning of significant transgressive phase in the early Lutetian, relative deepening in the Mid Lutetian; after the break in sedimentation at the end of Bartianianbeginning of Priabonian the sedimentation continues again in the open-marine (outer neritic) environment.
37
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.
Full textAbstract:
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.
38
White, M. R. "A new species of <i>Somalina (Somalina hottingeri)</i> with partially vacuolate lateral walls from the Middle Eocene of Oman." Journal of Micropalaeontology 16, no. 2 (October 1, 1997): 131–35. http://dx.doi.org/10.1144/jm.16.2.131.
Full textAbstract:
Abstract. Somalina hottingeri, a new species with partially vacuolate lateral walls is described from the Middle Eocene of Oman. It is distinguished from the only previously recorded species with this wall structure (S. transitorius (Hottinger)) by having equatorial chambers that are relatively low throughout the test. On the basis of this character, it is suggested that S. hottingeri evolved from the Opertorbitolites douvillei Group (redefined here) and that it gave rise to the true somalines. S. transitorius is regarded as arising from O. latimarginalis (ex. O. latimarginalis Group, introduced in this study) but not to have given rise to any other species.Since forms of Somalina with only partially vacuolate walls appear to be confined to the late Early Eocene to early Middle Eocene, it is concluded that the presence of this wall structure provides a useful stratigraphic marker.
39
Kopaevich, L. F., E. M. Bugrova, M. R. Latypova, A. V. Gusev, A. G. Kalmykov, and G. A. Kalmykov. "Foraminifera from the clay pulp of the Shugo mud volcano (Taman Peninsula)." Moscow University Bulletin. Series 4. Geology, no. 3 (December 15, 2022): 3–16. http://dx.doi.org/10.33623/0579-9406-2022-3-3-16.
Full textAbstract:
The foraminiferal assemblages from the mud volcanic breccia of the Shugo mud volcano (Kerch-Taman volcanic region, Taman peninsula) was studied in order to clarify the stratigraphic section of this region. Mud volcanic breccia contain shells of Miocene foraminifera, numerous well preserved Middle Eocene (Lutetian), and Upper Cretaceous (Santonian, Campanian, and Maastrichtian) species. The poorer preservation of the Cretaceous shells may be associated with the composition of the accommodating rocks, probably represented by terrigenous and carbonate-terrigenous turbidites. Finding the remains of the Upper Cretaceous and Middle Eocene foraminifera in the mud volcanic breccia indicates the presence of strata of this age in the section.
40
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.
Full textAbstract:
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.
41
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.
Full textAbstract:
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.
42
Boukhary, Mohamed, Radwan Abul-Nasr, Safia Al Menoufy, Omar Cherif, and Stefan Hontzsch. "Early Eocene Nummulitids from Wadi Dakhl, Egypt: Biometry and stratigraphic implications." Micropaleontology 59, no. 2-3 (2013): 145–66. http://dx.doi.org/10.47894/mpal.59.2.07.
Full textAbstract:
Doncieuxina Boukhary, Al Menoufy and Höntzsch n. gen (type species: Nummulites spirectypa Doncieux 1926), Nummulites partschi De La Harpe 1880, Nummulites roselli Schaub 1981, Nummulitesminervensis Schaub 1981, Aegyptoclypeus dakhlensis Boukhary, Abul-Nasr and Al Menoufy n. gen., n. sp., Discocyclina nudimargo Schwager 1883 and Assilina aff. A. prisca Schaub 1981, collected from two nummulitic banks within the Thebes Formation inWadi Dakhl, Southern Galala, Eastern Desert, Egypt, have been described and photographed. Their age is estimated as Early Eocene (Ypresian) as the assemblage has been assigned to the shallow benthic zone SBZ 6 of Serra-Kiel et al. 1998.
43
Khan, Natasha, Khaista Rehman, Sajjad Ahmad, Jamil Khokher, M. Iqbal Hajana, and M. Hanif. "Sequence stratigraphic analysis of Eocene Rock Strata, Offshore Indus, southwest Pakistan." Marine Geophysical Research 37, no. 3 (August 25, 2016): 207–28. http://dx.doi.org/10.1007/s11001-016-9280-5.
Full text
44
Kessler, Franz L., John Jong, and Mazlan Madon. "Eocene Sediments in the South China Sea, precursor deposits of the Oligocene expansion?" Berita Sedimentologi 47, no. 2 (October 2, 2021): 1–24. http://dx.doi.org/10.51835/bsed.2021.47.2.319.
Full textAbstract:
The stratigraphic record of Eocene in the Malaysian waters of the South China Sea is scarce; the few deep petroleum exploration wells and outcrops are located on the fringes of the SCS. Yet, despite the paucity of data we observe a variety of sediments that cover the range from fluviatile to (at least) neritic marine deposits. Whilst fluvial deposits dominate the Western Rim (Penyu, Malay basins), the Southern Rim (Sarawak) is characterized by deposits of a narrow and rapidly deepening shelf, with fluviatile, shallow marine clastics and carbonates passing seawards to outer shelf and neritic deposits. The proven record of the Eocene to-date is located in relatively small and deep sub-basins. Possibly, the Eocene underlies additional areas of the SCS, but there is to-date no sufficient well data to offer further confirmation. The presence of Eocene strata on the margins of Sundaland is associated with an early phase of extensional and/or transpressional tectonism, probably acting as precursor movements related to the onset of rifting of the crust underlying the SCS.
45
Adrian, Brent, Patricia A. Holroyd, J. Howard Hutchison, and KE Beth Townsend. "Additional records and stratigraphic distribution of the middle Eocene carettochelyid turtle Anosteira pulchra from the Uinta Formation of Utah, North America." PeerJ 8 (August 24, 2020): e9775. http://dx.doi.org/10.7717/peerj.9775.
Full textAbstract:
Background Anosteira pulchra is one of two species of the obligately-aquatic freshwater clade Carettochelyidae (pig-nosed turtles) from the Eocene of North America. Anosteira pulchra is typically rare in collections, and their distribution is poorly documented. The Uinta Formation [Fm.] contains a diverse assemblage of turtles from the Uintan North American Land Mammal Age. Whereas turtles are abundantly preserved in the Uinta Fm., A. pulchra has been reported only from a few specimens in the Uinta C Member. Methods We describe new records of Anosteira pulchra from the Uinta Basin and analyze the distribution of 95 specimens from multiple repositories in the previously published stratigraphic framework of the middle and upper Uinta Fm. Results Here we report the first records of the species from the Uinta B interval, document it from multiple levels within the stratigraphic section and examine its uncommon appearance in only approximately 5% of localities where turtles have been systematically collected. This study details and extends the range of A. pulchra in the Uinta Fm. and demonstrates the presence of the taxon in significantly lower stratigraphic layers. These newly described fossils include previously unknown elements and associated trace fossils, with new anatomical information presented. This study provides insight into the taxonomy of Anosteira spp. in the middle Eocene, and suggests the presence of a single species, though no synonymy is defined here due to limits in Bridger material.
46
Avendaño, Gladys Marcela, Luis Felipe Cruz, Luis Enrique Cruz, and Mario Garcia. "Thermal evolution of Los Cuervos formation in the southern area of the Cesar sub-basin (Colombia), based on geochemical and petrophysical data." Earth Sciences Research Journal 25, no. 2 (July 19, 2021): 179–92. http://dx.doi.org/10.15446/esrj.v25n2.86025.
Full textAbstract:
The tectonic complexity to which the post-Cretaceous Cesar-Ranchería basin has been subjected has generated alterations in the evolution of its oil system, evidence of this is the lack of stratigraphic record in the Cesar sub-basin belonging to ages ranging from the Eocene to the Early Miocene. These units that are no longer present could have been deposited and eroded during this period of time, leaving their mark on the closest overlying units. Previously mentioned hypothesis oriented this research to study how the basin filling was in the time range from the Eocene to the early Miocene based on both organic (24 Tmax and 14 %Ro data) and inorganic (514 data of porosity) paleo-geothermometer data of Paleocene age formations present in two new wells ANH-LA LOMA-2 and ANH-CR-LOS CEREZOS-1X. In addition to the data provided by the wells drilled for this study, 31 published Tmax and 13 %Ro data from Los Cuervos Formation in the Calenturitas and La Jagua Mines were used. The results obtained indicate that the continuous deposition of sedimentary units did occur from the Paleocene to the middle Eocene and it is expected that the Sedimentitas del Eoceno Formation has reached a thickness between 2.5 to 3.5km with characteristics of quartz sandstones (density and compaction). This thickness of rock began to be eroded in the late Eocene to the Miocene according to recent thermo-chronological studies. The evidence obtained allow to improve the thermal evolution models of the oil system, to establish when the greatest advances were made in the transformation ratios and to estimate how the oldest source rocks of the Cesar sub-basin are currently in the studied area.
47
Azevedo Schmidt, Lauren E., Regan E. Dunn, Jason Mercer, Marieke Dechesne, and Ellen D. Currano. "Plant and insect herbivore community variation across the Paleocene–Eocene boundary in the Hanna Basin, southeastern Wyoming." PeerJ 7 (October 15, 2019): e7798. http://dx.doi.org/10.7717/peerj.7798.
Full textAbstract:
Ecosystem function and stability are highly affected by internal and external stressors. Utilizing paleobotanical data gives insight into the evolutionary processes an ecosystem undergoes across long periods of time, allowing for a more complete understanding of how plant and insect herbivore communities are affected by ecosystem imbalance. To study how plant and insect herbivore communities change during times of disturbance, we quantified community turnover across the Paleocene–Eocene boundary in the Hanna Basin, southeastern Wyoming. This particular location is unlike other nearby Laramide basins because it has an abundance of late Paleocene and Eocene coal and carbonaceous shales and paucity of well-developed paleosols, suggesting perpetually high water availability. We sampled approximately 800 semi-intact dicot leaves from five stratigraphic levels, one of which occurs late in the Paleocene–Eocene thermal maximum (PETM). Field collections were supplemented with specimens at the Denver Museum of Nature & Science. Fossil leaves were classified into morphospecies and herbivore damage was documented for each leaf. We tested for changes in plant and insect herbivore damage diversity using rarefaction and community composition using non-metric multidimensional scaling ordinations. We also documented changes in depositional environment at each stratigraphic level to better contextualize the environment of the basin. Plant diversity was highest during the mid-late Paleocene and decreased into the Eocene, whereas damage diversity was highest at the sites with low plant diversity. Plant communities significantly changed during the late PETM and do not return to pre-PETM composition. Insect herbivore communities also changed during the PETM, but, unlike plant communities, rebound to their pre-PETM structure. These results suggest that insect herbivore communities responded more strongly to plant community composition than to the diversity of species present.
48
Vicián, Zoltán, Helmut Krock, and Zoltán Kovács. "New gastropod records from the Cenozoic of Hungary." Földtani Közlöny 147, no. 3 (September 25, 2017): 265. http://dx.doi.org/10.23928/foldt.kozl.2017.147.3.265.
Full textAbstract:
26 newly collected Cenozoic marine gastropod species from Hungary are briefly described. Two Lutetian (Eocene), two Egerian (Oligocene) and 22 Badenian (Miocene) species are represented; most of them are new records, others are illustrated for the first time from the country. Extended stratigraphic and palaeogeographic ranges of species are summarized. A new taxon is introduced: Lautoconus harzhauseri Kovács nov. sp.
49
Alege, T. S. "Sequence Stratigraphic Evaluation of Sediments Domicile in Day Field Located in the Onshore Central Swamp Depobelt of the Niger Delta, Nigeria." Journal of Applied Sciences and Environmental Management 26, no. 6 (June 30, 2022): 1129–35. http://dx.doi.org/10.4314/jasem.v26i6.20.
Full textAbstract:
This study employs the tool of sequence stratigraphy to evaluate Day Field, in the Onshore Niger Delta of Nigeria for hydrocarbon predictions using six (6) well logs displayed at standard scales to enhance log trends for lithologic and stratal package delineation. The identified key stratigraphic bounding surfaces were tied to well-defined palynological (P) zone and foraminiferal (F) zones with the aid of the biostratigraphic data and calibrated using the Niger Delta Chronostratigraphic chart. Five (5) MFSs (34.0, 33.0, 31.3, 28.1, and 26.2 Ma) and six (6) SBs (35.4, 33.3, 32.4, 29.3, 27.3, and 24.9 Ma) were delineated. The stratigraphic surfaces were matched with the palynological (P480– P580) and foraminiferal zones (P20/N1–P22/N3) encountered. The results indicate that the study area is of Late Eocene to Late Oligocene age (26.2–35.9 Ma). The key stratigraphic surfaces also reflect a series of relative sea-level falls (regressive episodes) and sea-level rises (transgressive episodes) that are regionally extensive and correlated across the wells. Five sequences (SEQ1–SEQ5) were recognized, SEQ1 and SEQ5 comprising three system tracts (LST, TST, and HST) revealing four third-order depositional sequences (classified as type 1 sequence), while SEQ2-SEQ4 comprises two system tracts (TST and HST). Two depositional environments were interpreted from the log trends; the Fluvial (shoreface) and Tidal environments. The hydrocarbon exploration prospects identified are the sand units of the LST and HST combining with the shale units of the TST offering good reservoir and seal/source rocks respectively.
50
Albright, L. Barry. "A protocetid cetacean from the Eocene of South Carolina." Journal of Paleontology 70, no. 3 (May 1996): 519–23. http://dx.doi.org/10.1017/s0022336000038440.
Full textAbstract:
Kellogg (1936, p. 242) described “an imperfectly preserved dorsal vertebra” from Texas, which he assigned to the primitive cetacean genus Protocetus. McLeod and Barnes (1990), however, were the first to report unequivocal protocetid remains from the Atlantic Coastal Plain. Since then, Hulbert and Petkewich (1991) and Hulbert (1993) have noted a well-preserved skeleton of a protocetid cetacean from middle Eocene deposits in Georgia. The purpose of this note is to report the recent discovery of additional protocetid remains from the coastal plain of South Carolina and to discuss their stratigraphic and biostratigraphic context.