Age Assignment Research Articles

A LATE MIOCENE – EARLY PLIOCENE PARATETHYAN TYPE OSTRACOD FAUNA FROM THE DENIZLI BASIN (SW ANATOLIA) AND ITS PALAEOGEOGRAPHIC IMPLICATIONS

The upper Miocene – lower Pliocene sedimentary succession of the Denizli Basin (SW Anatolia) displays a unique record of undisturbed stratigraphy and provides an excellent opportunity to study long-term palaeoecological changes. This paper documents the ostracod assemblages of two sections of the Neogene Kolankaya Formation, resulting in the following taxonomic, palaeobiogeographic and ecological interpretations. The ostracod assemblages from the two sections consist of a mixture of oligohaline to mesohaline tolerant taxa but expose fundamental differences in their composition. This is reflected by the fact that out of 32 determined species, both sections only have 3 in common. In the stratigraphic older succession, the diverse ostracod fauna resembles taxa known from the Paratethys. Faunal relations to the brackish lake habitats of the Euxinic and Pannonian basins are apparent and the palaeobiogeographic significance of the fauna is discussed. The ostracod association of the younger section indicates a low brackish water habitat with fluctuating salinities, most likely in the oligohaline range. The ostracod assemblage of the Kolankaya Formation only permits a broad age assignment to the late Miocene – early Pliocene.

A new Upper and Middle Pleistocene stratigraphic and dissolution record from the Carnegie Platform, Eastern Equatorial Pacific

Abstract This study presents new stable isotope and dissolution records for a composite “Carnegie Platform” (CP) sediment record composed of KNR195–5 cores CDH-36 and MC-34A (3° 35.85′ S, 83° 57.79′ W, 3225 m) from the Eastern Equatorial Pacific. Renewed interest in this paleoceanographic site prompted a re-coring in 2009 using the CDH giant piston coring system. Giant piston core CDH-36, with a core length of 42.61 m, nearly triples the length of previous cores at this site. Companion multicore MC-34A (0.36 m length) allowed for recovery of intact surface sediments at 0 ka BP. A new age model utilizing Bayesian analysis of radiocarbon dates in MC-34A and the top 3.4 m of CDH-36, and alignment of the CDH 36C. wuellerstorfi δ18O record with the LR04 benthic stack, demonstrates that the CP record extends from 0 to 720 ka (MIS 18). The age model places Eastern Equatorial Pacific volcanic ash layer “L,” which occurs at 15.80–15.88 m in CDH-36, at 229.6–231.7 ka BP in the CP record, consistent with prior age assignments. Coarse fraction percentage (%CF) is utilized to evaluate the impact of dissolution at the CP site;CP %CF primarily records dissolution cycles of ~100 kyr, with enhanced preservation during glacial episodes, but also exhibits variability consistent with local bathymetric and hydrographic effects. The similarity of the CP %CF record to other tropical Pacific dissolution records supports a basin-wide control on calcium carbonate preservation during the middle and Late Pleistocene.

Crustal extension and salt tectonics of the Danmarkshavn Ridge and adjacent basins, NE Greenland

Abstract Modern 2-D seismic data are used to evaluate the rift architecture, salt tectonics, and structural evolution of the Danmarkshavn Ridge and adjacent basins on the NE Greenland shelf. The Danmarkshavn Ridge is a segmented horst between landward- and basinward-dipping crustal faults. Extension was ongoing from the Devonian through the Cretaceous, with Paleozoic and Mesozoic faults trending mostly N–S and NNE-SSW, respectively. One Paleozoic fault is a low-angle, basinward-dipping detachment interpreted as a reactivated Caledonian thrust/shear zone, with the Moho in its footwall as shallow as 16 km. Salt on the NE Greenland shelf is postulated to be Pennsylvanian to Early Permian in age by analogy to the Gipsdalen Group evaporites of the conjugate Barents Sea margin. There are at least two, and possibly four, distinct mobile levels. The salt layers partly decouple the deformation, with drape folds and truncated drape folds above basement faults. Listric normal faults detached on the upper salt are mostly tectonic but also partly gravity-driven, balanced by salt-cored contractional anticlines. Passive diapirs are present only at the upper salt level. Some were triggered by extension, initiating as reactive diapirs, and others broke out of the contractional folds. Quantitative restorations of eight serial cross sections illustrate the three-dimensional evolution. The results are dependent on the accuracy of the horizon age assignments, which are constrained only for shallow levels in the Danmarkshavn Basin. Given this caveat, the restorations suggest that Permo-Triassic extension was relatively slow but gradually increased from south to north. The main phase of rifting, during the Jurassic and especially Early Cretaceous, was greatest in the southern and central portions of the study area. Upper Cretaceous extension was relatively minor, presumably due to late-stage hyperextension shifting basinward into the Thetis Basin prior to the onset of seafloor spreading at the beginning of the Eocene.

Pleuromeia discovered from the Middle Triassic Linjia Formation of Benxi, Northeast China

A new species Pleuromeia shaolinii Zhang et Wang n. sp. was established under the family Pleuromeiaceae, based on eight specimens of stems and leaves, cones, rhizophores, and adventitious roots that were recently collected from the Middle Triassic Linjia Formation in Benxi, Northeast China. P. shaolinii n. sp. is similar to the type species P. sternbergii, in the morphology of the stem and rhizophore, but differs from it by the transversely rounded sporophylls organized in a heterosporous cone, and the two conspicuous triangular scars present on both sides of the vascular bundle scar. The Linjia flora, an only reliable Middle Triassic flora in Northeast China, was discovered 40 years ago. Although the Linjia Formation can be compared with the Middle Triassic Ermaying Formation from another area of the North China plate, its age was questionable due to the absence of the Early to Middle Triassic index fossil Pleuromeia. Based on the flora similarity, the zircon dating, lithologic characteristics, presence of a disconformity, and the occurrence of the Middle Triassic–Early Cretaceous insect fossil Sogdoblatta, the age of the Linjia Formation can be confirmed as Middle Triassic. The new species not only supplements our knowledge in biology and taxonomy of Pleuromeia, but also supports the Middle Triassic age assignment of the Linjia flora.

Cambrian deposition in northwestern Africa: Relationship of Tamlelt massif (Moroccan‒Algerian border region) succession to the Moroccan Meseta

The Tamlelt massif is physiographically grouped as a continuation of the easternmost High Atlas. However, re-examination of the Tamlelt's Cambrian litho- and biostratigraphy shows a depositional history that differs from that of the Souss Basin to the southwest (i.e., west-central High Atlas and eastern Anti-Atlas of Morocco). Our re-examination leads to recommendations on the local stratigraphic succession and nomenclature. Trilobites from the Al Hamrat Formation in the Tamlelt massif indicate late early Cambrian (upper Epoch 2) siliciclastics overlying shallow marine, carbonate-rich deposits (Jbel Menhouhou Formation) similar to and coeval with those of the distant western Anti-Atlas region but older than and lithologically distinct from fluviatile siliciclastics (Epoch 3) in the nearby eastern Anti-Atlas. The Jbel Menhouhou carbonates unconformably overlie probable terminal Proterozoic volcanics and clastics of the Bou Kaïs Formation (new) and are overlain by shales and arenites of the upper Kheneg El Kahal Group, which features a Cambrian Stage 4 regressive half-cycle. Regional differences in lithofacies disappear in the early Miaolingian with relatively monotonous, mudstone-rich facies in the Tamlelt massif area (Batene El Jdari Formation) comparable to those of the Jbel Wawrmast Formation of the west-central High Atlas and central‒eastern Anti-Atlas. Probable early late Cambrian brachiopods from siliciclastic rocks of the Tamlelt area indicate a later Cambrian depositional history similar to that of the Anti-Atlas and perhaps Moroccan Meseta. The distinctiveness of the upper lower Cambrian deposits of the Souss Basin from those of the Tamlelt massif apparently reflects a depositional framework independent from other regions of the Atlas ranges, and suggests the Tamlelt region was confluent with the Meseta basin to the northwest. Known trilobites permit precise age assignments through the Tamlelt succession and include species (or forms) which contribute to a refined correlation within West Gondwana and improve West Gondwana‒Baltica correlation. The new trilobite species Saukianda? (Saukianda?) dresnayi is proposed.

Strontium stratigraphy of the Oligocene–Early Miocene shellbeds of the Kutch Basin, western India, and its implications

The Kutch Basin is unique among the western Indian sedimentary basins because of its near-complete sequence of post-Palaeozoic rocks. Due to extensive marine influence, the Oligocene–Early Miocene formations of the basin, namely Maniyara Fort, Khari Nadi and Chhasra, contain numerous shellbeds. Although age assignments of these formations exist based on foraminiferal biostratigraphy, detailed numerical age of the lithounits are yet to be established. We have identified a total of eleven distinct shellbeds (oldest SB 01 to youngest SB11) from this interval primarily containing bivalve fossils. Using 87Sr/86Sr of selected oyster and pectinid shells with pristine shell characteristics, we report the age of four shellbeds. The ages of SB 01, SB 04, SB 06 and SB 10 are 24.37, 17.31, 16.85 and 15.38 Ma, respectively. Our dates suggest a Chattian (24.37 Ma) age for SB 01 from the Bermoti Member, validating the previous biostratigraphical estimates from the Maniyara Fort Formation. The Chhasra Formation, however, shows a younger range of ages (17.31–15.38 Ma) characterized by a transition from the Burdigalian (SB 04–SB 06) to the Langhian (SB 10) stages. These dates have important implications in the study of sequence stratigraphy, Palaeobiogeography and tectonic history of the Kutch Basin. A surface with subaerial exposure is found in SB 08 (between 16.85 and 15.38 Ma) that corresponds to a global eustatic sea-level decrease (Mi2). Our new dates will also help evaluate the response of marine fauna to the closure of the Tethyan seaway around 19 Ma due to the formation of ‘Gomphotherium Landbridge’. The dated shellbeds enable us to identify pre- and post-closure fauna and assess the effect of biogeographical separation on these fauna. These dates have important implications in evaluating the regional geological record of western India in the context of various global events.

Lagomorphs (Mammalia) from the early Pliocene of Dorkovo, Bulgaria

The vertebrate locality of Dorkovo yielded a rich mammalian assemblage of which some large mammals have been studied, but not smaller mammals. The previous investigations correlated this fauna to the early Pliocene (early Ruscinian, MN 14). The present paper describes lagomorph remains which consist of one fragment of mandible and 106 isolated teeth. Four species are identified: Ochotona cf. antiqua, Prolagus sorbinii, Alilepus spassovi n. sp. and Trischizolagus crusafonti. The new species is characterised by the derived pattern of its p3 which has trigonid more stretched, enamel infolding stronger than in any other species of Alilepus, and the p3 lacks anteroflexid. The presence of four species of lagomorphs at Dorkovo is in agreement with the diversity dynamics of lagomorphs toward the end of late Miocene and during the early Pliocene in Eurasia, and in particular in Eastern Europe. The time range of the Dorkovo lagomorphs encompasses the Miocene/Pliocene boundary, and this is in agreement with the previous age assignments, i.e., earliest Pliocene, or early part of MN 14 mammalian zone.

Calcareous nannofossil biostratigraphy of the External Dinarides flysch (Vrčić‐Staravasa Pag Island, Croatia): A key to an Eocene tectono‐stratigraphic and paleoenvironmental interpretation

It is largely accepted that in the Dinaric shallow foredeep basin, the onset of Cenozoic synorogenic sedimentation is diachronous along strike and shows orogen‐parallel southward younging, creating a large uncertainty in the age of the Dalmatian flysch. Calcareous nannofossil biostratigraphy was studied to investigate a turbiditic succession exposed in Pag Island (Croatia) with the main purpose of constraining its age, which is still a matter of debate. The age assignment for the turbiditic deposition bears important implications for better understanding of the geodynamic and paleoenvironmental evolution of the External Dinarides. We logged a well‐exposed sedimentary section in the south‐western limb of the Pag anticline and performed calcareous nannofossil quantitative analyses revealing a high species diversity and abundant assemblage. The age diagnostic species indicate CNE14‐CNE15 biozones, suggesting that flysch deposition occurred in the Lutetian–Bartonian. This age can be further restricted to the CNE14 (42.37–40.51 Ma) by means of the lowest occurrence of Reticulofenestra reticulata and the highest occurrence of Sphenolithus furcatolithoides. Vertical facies variation and paleoecological indications suggest an increase in paleobathymetric depth during deposition. Our data support a post‐Lutetian age of folding and thrusting for the Pag Island region and suggest a relatively short time span during the middle‐late Eocene period for the main contractional stage in this sector of the External Dinarides. This result has important implications for the evolution of the Dinaride foreland basin system in Cenozoic times.

The majority of early term elective cesarean sections can be postponed

Introduction To minimize the risk of neonatal respiratory morbidity it is recommended that elective cesarean sections should not be done before 39-week gestation unless medically indicated. However, elective cesarean sections are still being performed at early term (at 370–386 weeks gestation) without sound medical indications. In this study, we evaluated the indications for elective cesarean sections performed at early term to assess the proportion of procedures that could possibly have been postponed until ≥39 weeks to avoid neonatal respiratory morbidity. Material and methods Maternal and neonatal information was collected from medical records on all elective cesarean sections performed in singleton pregnancies at ≥370 weeks gestation over a 20-year period in a population with secure ultrasound gestational age assignment. Indications were grouped and uterine scar, breech, or transverse presentation and maternal request classified as nonurgent. Results There were 3411 elective cesarean sections performed at ≥37-week gestation, of which 790 (23.2%) were at 370–386 weeks. Medical indications were present for 34% (272/790), but 65.6% (518/790) could possibly have been postponed until ≥390 weeks. Of the neonates 5.7% developed respiratory morbidity if delivery was at 370–386 weeks gestation compared to 2.4% at 390–421 weeks gestation (p < .001). Conclusion Of elective cesarean sections before 39-week gestation two-thirds were done without a clear medical indication, thereby exposing the newborn to an increased risk of respiratory morbidity. Scheduling elective cesarean sections at ≥39-week gestation is important to minimize the risk of neonatal respiratory morbidity, unless a clear medical indication dictates earlier delivery.

Jurassic to Cretaceous (upper Kimmeridgian–?lower Berriasian) calcispheres from high palaeolatitudes on the Antarctic Peninsula: Local stratigraphic significance and correlations across Southern Gondwana margin and the Tethyan realm

We report Upper Jurassic–Lower Cretaceous (Kimmeridgian-Berriasian) calcispheres from the Ameghino (Nordenskjöld) Formation at high palaeolatitudes on the northern part of the Antarctic Peninsula. The Ameghino Formation generally contains a relatively poorly preserved association of calcispheres, which are often recrystallized or replaced by silica; however, early-diagenetic calcite concretions are widespread in the mudstone–tuff sequences, and calcisphere in these contexts show very good preservation. Among the seventeen species recognized in this study, thirteen are known from the Upper Jurassic–Lower Cretaceous pelagic sediments of the Tethyan and Andean regions. The remaining three include Stomiosphaera, and two new species, that probably indicate an austral character for the calcisphere association. The following calcisphere zones previously proposed for the Tethyan realm and the Andes are confirmed for the Ameghino Formation: Carpistomiosphaera borzai, Carpistomiosphaera tithonica, Parastomiosphaera malmica, Colomisphaera tenuis, Colomisphaera fortis and Stomiosphaerina proxima. Zones indicate a late Kimmeridgian to early Berriasian age, broadly consistent with previous age assignments based on ammonites and radiolarians. However, calcisphere ages allow partial stratigraphic re-arrangement of the succession cropping out in Sobral Peninsula and support the intercalation of sandy-conglomeratic beds, deposited in submarine fan environment, between the slope-basinal facies typical of the Ameghino Formation. Facies changes suggest basin margins across the Antarctic Peninsula in a complex paleogeography with large emergent landmasses to the southwest of the study area. Possible dispersal routes along the Southern Gondwana margin occurred along the so-called Hispanic and Mozambique corridors. Identified species show a global distribution, being represented in the Andean, the Tethyan and Boreal realms. The cosmopolitan character of Mesozoic calcispheres proves their importance for interregional correlations.

Bartonian to Priabonian dinoflagellate cyst biostratigraphy and paleoenvironments of the M'karcha section in the Southern Tethys margin (Rif Chain, Northern Morocco)

Abstract Palynological analyses were performed on the Eocene sediments of the M'karcha section, which is located in the Taza region, structural Tsoul Unit, eastern External Rif (northeastern Morocco). The palynological content of this section is composed essentially of well-preserved and diverse dinoflagellate cyst assemblages, allowing detailed taxonomic determinations, age assignments, biostratigraphic correlations and paleoenvironmental interpretations. Other palynomorphs, such as spores, pollen grains and foraminiferal linings, are rare and therefore, not taxonomically determined up to the genus level. 131 dinoflagellate cyst species were identified. Age assignments are based on dinocyst bioevents, considered previously as potential biostratigraphic markers of the Bartonian and Priabonian, including the lowest occurrences (LOs) of Glaphyrocysta semitecta, Impagidinium dispertitum, Rhombodinium perforatum, Cooksonidium capricornum, Stoveracysta ornata, Stoveracysta sp. 2 of Brinkhuis and Biffi (1993) and LO and highest occurrence (HO) of Schematophora speciosa. The quantitative palynological analyses, based mainly on dinoflagellate cysts through the M'karcha section revealed an inner neritic, generally lagoon, environment with a low productivity, alternated with short episodes of the open marine influence.

Guideline No. 388-Determination of Gestational Age by Ultrasound.

To assist clinicians in assigning gestational age based on ultrasound biometry. To determine whether ultrasound dating provides more accurate gestational age assessment than menstrual dating with or without the use of ultrasound. To provide maternity health care providers and researchers with evidence-based guidelines for the assignment of gestational age. To determine which ultrasound biometric parameters are superior when gestational age is uncertain. To determine whether ultrasound gestational age assessment is cost effective. Published literature was retrieved through searches of PubMed or MEDLINE and The Cochrane Library in 2013 using appropriate controlled vocabulary and key words (gestational age, ultrasound biometry, ultrasound dating). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies written in English. There were no date restrictions. Searches were updated on a regular basis and incorporated in the guideline to July 31, 2013. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies. The quality of evidence in this document was rated using the criteria described in the Report of the Canadian Task Force on Preventive Health Care (Table 1). Accurate assignment of gestational age may reduce post-dates labour induction and may improve obstetric care through allowing the optimal timing of necessary interventions and the avoidance of unnecessary ones. More accurate dating allows for optimal performance of prenatal screening tests for aneuploidy. A national algorithm for the assignment of gestational age may reduce practice variations across Canada for clinicians and researchers. Potential harms include the possible reassignment of dates when significant fetal pathology (such as fetal growth restriction or macrosomia) result in a discrepancy between ultrasound biometric and clinical gestational age. Such reassignment may lead to the omission of appropriate-or the performance of inappropriate-fetal interventions. RECOMMENDATIONS.

Discussion of “Permian—Triassic vertebrate footprints from South Africa: Ichnotaxonomy, producers and biostratigraphy through two major faunal crises” by Marchetti, L., Klein, H., Buchwitz, M., Ronchi, A., Smith, R.M.H., DeKlerk, W.J., Sciscio, L., and Groenewald, G.H. (2019)

A newly devised tripartite subdivision of the Karoo Basin, South Africa, is based on a number of vertebrate-trackways spanning the Middle Permian (Wordian/Capitanian) to Lower Triassic (reportedly Induan) rocks of the Beaufort Formation. The youngest Footprint Assemblage (FA III) is reported to occur in the lowermost Triassic rocks of the Palingkloof Member. One collection site from which seven trackways are reported, Bethel farm, is a classic South African locality where some authors place the end-Permian extinction event and, coincidentally, the vertebrate-based terrestrial Permian—Triassic Boundary. Published GPS coordinates for the Bethel farm site, though, indicate that these trackways originate from exposures of the Burgersdorp Formation near the town of Aliwal North. Outcrops here are assigned to the Cynognathus Assemblage Zone, and indicate a Middle Triassic age assignment. In addition, we caution the use of any small temporally or spatially restricted dataset, which is of severely limited utility, in making broad generalizations about paleoenvironmental or paleoecological interpretations.

&lt;p&gt;&lt;strong&gt;Remarks on the age of Dominican amber&lt;/strong&gt;&lt;/p&gt;

Amber from the Dominican Republic is famous for the high quality, frequency, and diversity of organic fossils found as inclusions in this mineral (Grimaldi, 1996; Poinar &amp; Poinar, 1999). However, its geological age of origin remains a continuing source of controversy. Over the years a wide variety of age estimates have been made for occurrences of Dominican amber, ranging from Cretaceous (Brouwer &amp; Brouwer, 1982) to Late Eocene (Lambert et al., 1985) to pre-Lower Miocene (Baroni-Urbani &amp; Saunders, 1982). Some authors have also favored a spread of ages that covers much of the Cenozoic (e.g., 40 or 45 Ma to 15 Ma; Poinar &amp; Poinar, 1999). Iturralde-Vinent &amp; MacPhee (1996) attempted to resolve discrepancies in age assignments by taking a multi-pronged analytical approach which yielded a best-fit estimate of mid-Miocene age (20–15 Ma). This estimate has been widely accepted and additionally corroborated by new studies (Iturralde-Vinent, 2001; Ortega-Ariza et al., 2015). However, Braga et al. (2012) have challenged the assessment of Iturralde-Vinent &amp; MacPhee (1996) by arguing for a Pliocene–early Pleistocene date for the amber-bearing Yanigua Formation. Here we address the sources of disagreement and suggest a solution.

Palynology of the Muarádzi sub-basin, Moatize-Minjova Coal Basin, Karoo Supergroup, Mozambique

The detailed palynostratigraphic study of four boreholes in the Muarádzi sub-basin, Moatize-Minjova Coal Basin (MMCB) southeast of Moatize, allowed the assignment of relative ages to the stratigraphic units. Three assemblages were studied in detail and are assigned to the Lopingian. Assemblage L1 is characterized by the rich occurrence of Guttulapollenites and Weylandites. Assemblage L2 is defined on the first occurrence (FO) of abundant Thymospora pseudothiessenii together with Indotriradites niger, Kraeuselisporites spp., Polypodiisporites mutabilis and Polypodiidites sp. Assemblage L3 is characterized by the first occurrence of Osmundacidites senectus together with the taxa described from the previous assemblages. Palynological correlation with other Karoo basins is discussed and three distinct palynostratigraphic events emerge based on the FO and abundance of key taxa (as for instance, FO of G. hannonicus, T. pseudothiensenii and O. senectus). A close palynological correlation between Mozambique (Moatize-Minjova Basin), Tanzania (Selous Basin), Zambia (mid-Zambezi Basin) and Madagascar palynoevents is established. This major region can be assigned to the northern Karoo-aged basins of south-central Africa and the palynoevents can be correlated with Lopingian assemblages of Pakistan, India and some basins of East Antarctica. The southern Karoo-aged basins of south-central Africa, including South Africa and Zimbabwe, show different Lopingian palynoevents and a direct correlation is demanding. These palynological data may open new perspectives for coal exploration in the MMCB as the coal deposits show a wider stratigraphic distribution, reaching until the latest Lopingian.

Upper-plate deformation of Late Pleistocene marine terraces in the Trinidad, California, coastal area, southern Cascadia subduction zone

Abstract Forming at sea level, uplifted shore platforms serve as long-term geodetic markers. The spatial distribution and elevation of marine terrace sequences offer insight into regional tectonics. In the Trinidad coastal area (California, USA), active tectonic processes reflect upper-plate deformation above the southern extent of the Cascadia subduction megathrust. A set of five uplifted and deformed Late Pleistocene marine terraces is preserved in the Trinidad region and provides an opportunity to analyze regional uplift, folding, and faulting. Using lidar imagery embedded within a GIS, we employ a surface classification model (SCM) that identifies uplifted marine terraces on the basis of their micro-topographical characteristics, i.e., low slope and low roughness. The SCM-based identification of marine terraces both supplements and verifies existing field mapping. We demonstrate the utility of the SCM, which can be applied to a variety of surface terrain analysis investigations that seek to identify smooth and/or rough terrain features, e.g., terraces and fault scarps. Age assignments for the five marine terraces, which range from 80 ka to &lt;500 ka, are based on paleo–sea cliff geomorphology and soil development trends. Specifically, the steepest, highest, and most prominent paleo–sea cliff, which is associated with terrace number 3, is correlated to the long-duration sea-level highstand centered at 125 ka (marine isotope stage 5e), exemplifying a novel method in relative age assignment for Pleistocene geomorphic features. Based on these age assignments, the average maximum uplift rates in the Trinidad coastal area are ∼1.0 m/k.y., and the average long-term uplift rate diminishes westward to ∼0.4 – 0.5 m/k.y. on the downthrown side of the Trinidad fault. Based on analysis of deformation using the high-resolution lidar imagery of the marine terraces, the Trinidad hanging-wall anticline represents a fault propagation fold that ceased to be active when the associated reverse fault, the Trinidad fault, daylighted to the surface ca. 80–100 ka. Based on deformation tilts of a marine terrace with an assigned age of 200 ka, the Trinidad anticline has accommodated at least 1 km of shortening in the last 200 k.y., which represents at least 2% of the convergence of the Juan de Fuca plate relative to North America over the same time period. Overall, both the hanging wall and the footwall of the Trinidad fault show long-term positive rock uplift, which implies that the Trinidad anticline and fault are contained within the hanging wall of a deeper structure. Therefore, the Trinidad fault likely splays off of the Cascadia subduction zone megathrust or off of a deeper thrust fault that splays off of the megathrust.

U–Pb zircon dating of Paleozoic volcanic rocks from the Rheno-Hercynian Zone: new age constraints for the Steinkopf formation, Lahn-Dill area, Germany

Small and volumetrically subordinate outcrops of alkali-rhyolitic to trachytic metavolcanic rocks are widespread in the Lahn-Dill area of the Rheinisches Schiefergebirge, Germany. These occurrences are either related to late Early Devonian or to Middle Devonian episodes of volcanic activity. An unambiguous age assignment for the time of eruption could not be established so far. Most volcanic rocks of the study area are not suitable for application of U–Pb geochronology. A notable exception is the Steinkopf rock suite in the SW Lahn-Dill area, but a straightforward interpretation of the LA-ICP-MS U–Pb data is hampered by complex zircon populations recording various processes including crystallization from newly formed melt, inheritance, assimilation of country rocks, variable degrees of Pb-loss and fluid-assisted Zr-mobility. A plausible evaluation of U–Pb zircon data of two metatrachytes and a metavolcaniclastic rock document a coherent age group at ca. 390–384 Ma and a probable eruption age at ca. 385 Ma, suggesting a relationship to Middle Devonian (Givetian) igneous processes. Zircon-bearing veinlets in a metatrachyte indicate post-eruptive infiltration of external hydrothermal fluids and/or internal Zr-redistribution in Late Devonian to Early Carboniferous time (364 ± 10 Ma), but this process is of rather limited importance.

Strontium isotope radiometric dating reveals the late Eocene and Oligocene successions in northern Kuwait

The strata exposed at Jal Az-Zor escarpment in northern Kuwait represent one of the best outcrops in the country, extending over 60 km in length with a cliff-face of around 36 m. The age assignment of these rock units was mostly done during the 1920s to 1960s and was largely based on taxonomy grouping of an oyster-rich bed present at the base of Jal Az-Zor correlated to what appeared to be a similar layer that belongs to the Lower Fars Formation in Iran. In the subsurface, the results of biostratigraphic analysis using different taxonomic groups have suggested ages that position this exposed lithological unit in the range of late Miocene to Pliocene (11.63–2.58 Ma). Due to the lack of radiometric numerical data, the strontium isotope ratio (87Sr/86Sr) age-dating method was applied on carefully selected surface and subsurface samples including an oyster shell, beds with abundant fossils, and calcite cemented specimens. Petrographic, XRD, and SEM-EDX analyses were utilized to determine the rock composition, assist in identifying the biomass, and carbonate content of the samples before performing age dating on selected areas of the sample. Numerical age determination based on (87Sr/86Sr) ratio revealed that an oyster shell taken from the cliff of Jal Az-Zor is 20.53 Ma in age (Aquitanian), the fossiliferous bed exposed at the foot of the escarpment is 24.39 Ma in age (Chattian), and the Sabriyah roadcut beds exhibit an age of 30.32 Ma (Rupelian). The subsurface extracted samples that are dominated by calcite cement uncovered an age range between 36 and 19.41 Ma (Burdigalian to Priabonian). This analysis introduces the late Eocene and Oligocene to Kuwait’s stratigraphy otherwise known to be eroded. The implications of such findings can revamp the Paleogene and Neogene tectonic evolution of Kuwait and potentially lead to the renaming of the undifferentiated Kuwait Group strata to a more representative name, such as the Kuwait Formation that combines the traditional tripartite subdivision of the group.

New Radiocarbon Dates from CA-CCO-138 (Hotchkiss Mound) and CA-CCO-139 (Simone Mound) and Insights into Mounds, Settlement Patterns, and Culture History in the California Delta

ABSTRACTWe report 91 new AMS radiocarbon dates on human bone collagen from two important central California sites: CA-CCO-138 (Hotchkiss Mound; n = 46) and CA-CCO-139 (Simone Mound; n = 45). The sites lie within 500 m of one another in the California Delta and have figured prominently in the formulation of culture historical sequences in central California. The new AMS dates show that the two sites are nearly separate in their occupation sequences, with CA-CCO-139 interments dating between 1,190 and 790 cal BP and CA-CCO-138 between 810 and 150 cal BP (median date ranges). We compare the new dates to previous age assignments based on associated artifacts and depth, and discuss implications for understanding ancient settlement patterns, mound occupation sequences, and culture history in the region.

Les calcaires du Jurassique supérieur-Crétacé inférieur du Massif de Hăghimaș (Carpathes orientales, Roumanie) : Microfaciès, microfossiles et environnements de dépôt.

The Hagimas Massif provides important data for reconstructing the geological evolution of the Transylvanian Carbonate Platform. This unit is present nowadays in the basement of the Transylvanian Depression and as large-scale olistoliths, which crop out in various locations in the Eastern Carpathians and Apuseni Mountains. They contain a large variety of microfacies as well as microfossil assemblages partly encompassing the Jurassic/Cretaceous boundary. This study presents a detailed account of uppermost Jurassic-lowermost Cretaceous limestones from the Lapos Valley (Haghimas Mountains) containing two distinct successions separated by a fault. The first succession contains platform margin and inner platform deposits (subtidal, intertidal) whereas the second one consists of inner platform deposits (shallow-subtidal to peritidal carbonates). The Upper Jurassic Stramberk-type facies is overlain by lower Berriasian regressive peritidal limestones. The upper Berriasian-? lower Valanginian consists mainly of inner platform deposits. They contain alternating, high and low-energy carbonates with rare calpionellids and calcispheres. The age assignment is based on a rich and diverse micropaleontological assemblage containing similar biota reported from other regions of the Tethysian Realm.