LITHOSTRATIGRAPHY OF THE NEWLY PROPOSED MIDDLE CRETACEOUS “BIBAI GROUP”, WESTERN SULAIMAN FOLD-THRUST BELT, PAKISTAN

The newly proposed Middle Cretaceous “Bibai Group”, named after the Bibai peak, is exposed in Kach-Ziarat, Spera Ragha-Chingun areas of the Western Sulaiman Fold-Thrust Belt, Pakistan. It comprises thick succession of the mafic volcanic rocks, volcanic conglomerate, mudstone and sandstone. The stratigraphic nomenclature proposed by previous workers was not clear enough, as they used different names for the succession, such as “Kahan Conglomerate Member” of the Mughal Kot Formation, “Parh-related volcanics” by considering it as part of the “Parh Group, “Bibai Formation” and “Bela Volcanic Group”, which were confusing and misleading. Also previous workers did not realize that the succession may be further classified into distinct mappable lithostratigraphic units and deserved the status of a “Group”. Therefore, we carefully examined and mapped the area and hereby propose the name “Bibai Group” for the overall volcanic and volcaniclastic succession of the Middle Cretaceous age. Based on distinct lithostratigraphic characters we further subdivided the “Group” into two lithostratigraphic units of formation rank, for which we propose the names “Chinjun Volcanics” and “Bibai Formation”. Also based on distinct lithostratigraphic characters we further propose to subdivide our “Babai Formation” into three lithostratigraphic units of member rank, which we named as the “Kahan Conglomerate Member”, “Ahmadun Member” and “Kach Mudstone Member”. In this paper we have defined and briefly described the Bibai Group, its constituent formations and their members. Also we examined and discussed the validity and status of the proposed subdivisions; e.g. formations and members, of the Bibai Group, and are fully satisfied that the proposed subdivisions are appropriate and comply with the Article 24 and 25 of the North American Stratigraphic Codes (2005) and that the previous nomenclatures are inconsistent, confusing and do not comply with the International Stratigraphic Codes.

Sedimentological And Stratigraphical Analysis Of Kaki Bukit Formation (Lower Setul Member) At Teluk Ewa, Pulau Langkawi

The identification of new units on the carbonate sequence of Teluk Ewa (from Tg. Mendidih to Teluk Ewa) has given an idea for the review of stratigraphic succession of Kaki Bukit Formation (Lower Setul Member). The analysis is related to a sedimentology study, where the sedimentary sequences formed as a mixed siliciclastic–carbonate shallow marine system that combines the carbonate and silisiclastic deposits. Eight facies have been recognised such as (1) argillite facies, (2) interlayer of mudstone and limestone facies, (3) wavy stromatolites limestone facies, (4) linear stromatolites limestone facies, (5) heterolithic of mudstone-limestone facies, (6) shale facies, (7) massive limestone facies and (8) thrombolites limestone facies. Each facies are divided into four litostratigraphic units based on the evaluation from Malaysian Stratigraphic Nomenclature Committee (1997) and North American Stratigraphic Code 2005. (1) The clastic unit referring to the uppertmost part of Machinchang Formation maintains it's name. Meanwhile, the suggested nomenclature for the new units such as (2) The Sabung Member is referring to the basal carbonate unit comprising microbial facies and mixed silisiclastic-carbonate sediment. (3) The Pesak Seluar Member in the middle is a silisiclastic unit that consists of shale facies and (4) The Ewa Member at the top representing the upper limestone unit. All units show a similar litostratigraphic characteristics that are found in Tarutao Group, Pante Malaka Formation, Rung Nok Formation and Lae Tong Formation in Thailand as described by Wongwanich et al. (1990; 2002) and Imsamut & Abdul Rahman (2017).

Indonesian Stratigraphic Nomenclature revision: The first progress report

A team was formed by the Indonesian Association of Geologist (IAGI) in early 2021 to revisit the Indonesian Stratigraphic Nomenclature which was issued in 1996. After 25 years many experts find that the document needs to be updated. The team is a mix of geologists with both academic and industry background. Several representatives from the Geological Agency who are involved in the Stratigraphic Lexicon document were also invited in the discussion. The team meeting was set on a regular basis to evaluate the existing nomenclature and look on areas for improvement. In each meeting the team will discuss a certain section of the nomenclature document. A three years work programme was set and reported on this article. In the first year the team will investigate areas for improvement, followed by revising necessary content in the second year. Implementation and promoting the nomenclature are planned for the third year.This short communication aims to engage a wider community on the process in revisiting the Indonesian Stratigraphic Nomenclature. Several examples of discussion topics in the meetings were included in this article. Readers will see potential areas for improvement and the team are open for suggestions.

An age-depth model and revised stratigraphy of vertebrate-bearing units in Natural Trap Cave, Wyoming

Almost a half-century ago excavations at Natural Trap Cave (NTC) began to yield evidence of the steppe paleoecology along the western slope of the Bighorn Mountains in north central Wyoming. The first decade of fieldwork led to the discovery of a diverse fauna that existed at the end of the Last Glacial Maximum. Stratigraphic deposits below the entrance of the cave were studied soon after excavations began, but never formally published. Although stratigraphy, taphonomy, and depositional circumstances were briefly discussed over the following years, little has been done to correlate the numerous stratigraphic schemes used by various authors. In this study, four stratigraphic sections were measured and analysed to establish an easily modifiable lithostratigraphic system of nomenclature. We provide the first correlations of all stratigraphic nomenclature used throughout excavations at NTC to facilitate comparisons with current and previous collections and publications. By leveraging more than 100 radioisotopic dates we developed an age-depth model and chronostratigraphic framework to further interrogate spatiotemporal relationships between strata, paleoenvironmental proxies, and fossil assemblages. Deposition is shown to be discontinuous; sediment accumulation in the study area is restricted to the buildup through peak penultimate and Last Glacial maxima. More recent (<10 ka) Holocene deposits unconformably cover the eroded surface of underlying Pleistocene strata. There is active reworking of sediments with transport and deposition of reactivated sediments within the Lower Chamber. We note that the two hiatuses coincide with interglacial periods and may reflect changing depositional circumstances within the cave such as extended periods of non-deposition, erosion, or bypass (possibly leading to deposition in the Lower Chamber). Contrary to previous reports, we demonstrate that it is unlikely a prominent snow cone existed or contributed to the pattern of sediment and fossil distribution within the study area, furthermore, we do not observe a continuous Pleistocene-Holocene transition in the study area. Further stratigraphic work will be needed to better understand the interrelationship between Main and Lower chamber deposits and the evolution of sediment accumulation in NTC.

Cambrian–Lower Ordovician of SW Quebec–NE New York

ABSTRACT The Ottawa aulacogen/graben on the NE US—Canadian (SW Quebec and eastern Ontario) border is a long ENE-trending structure formed with initial late Neo proterozoic rifting of the Rodinia supercontinent. This rifting formed the active spreading arms (New York Promontory and Quebec Reentrant) along the (presently) NE margin of the new Laurentia paleocontinent, with the Ottawa aulacogen commonly regarded as a failed arm of the rifting. However, no sediment accumulation in the aulacogen is recorded until the late early Cambrian subsidence of a SE- trending belt that includes the aulacogen and its extension, the Franklin Basin, in NW Vermont. Late early Cambrian marine onlap (Altona Formation) followed by more rapid late middle Cambrian subsidence and deposition of fluviatile arkoses (Covey Hill Formation of SW Quebec and Ausable Formation/Member of eastern New York) record rapid foundering of this “failed arm.” Subsequent deposition (latest middle Cambrian–Early Ordovician) in the Ottawa aulacogen produced a vertical succession of lithofacies that are fully comparable with those of the shelf of the New York Promontory. One of the greatest challenges in summarizing the geological history of the Ottawa aulacogen is the presence of a duplicate stratigraphic nomenclature with lithostratigraphic names changing as state and provincial borders are crossed.

Overview of Cordilleran oceanic terranes and their significance for the tectonic evolution of the northern Cordillera

Ophiolite complexes are an important component of oceanic terranes in the northern Cordillera and constitute a significant amount of juvenile crust added to the Mesozoic Laurentian continental margin during Cordilleran orogenesis. Despite their tectonic importance, few systematic studies of these complexes have been conducted. Detailed studies of the pseudostratigraphy, age, geochemistry, and structural setting of ophiolitic rocks in the northern Cordillera indicate that ophiolites formed in Permian to Middle Triassic suprasubduction zone settings and were obducted onto passive margin sequences. Re-evaluation of ophiolite complexes highlights fundamental gaps in the understanding of the tectonic framework of the northern Cordillera. The previous inclusion of ophiolite complexes into generic 'oceanic' terranes resulted in significant challenges for stratigraphic nomenclature, led to incorrect terrane definitions, and resulted in flawed tectonic reconstructions.

Lithogeochemical, isotopic, and U–Pb (zircon) age constraints on arc to rift magmatism, northwestern and central Avalon Terrane, Newfoundland, Canada: implications for local lithostratigraphy

The northwestern Avalon Terrane, Newfoundland, is underlain by Neoproterozoic rocks traditionally divided into older Love Cove Group, medial Connecting Point Group, and the unconformably overlying Musgravetown Group. New lithogeochemical, isotopic, and updated U–Pb (zircon) age data demand changes to stratigraphic nomenclature and maps and help constrain the tectonomagmatic evolution. U–Pb age constraints include 620 ± 2 Ma for the calc-alkaline Broad Island Group (former Love Cove Group); 605 ± 1.2 Ma for rhyolite from near Bull Arm (type area, Bull Arm Formation, lower Musgravetown Group); 589 ± 2.0 Ma for a schist from the Love Cove type locality; 568.7 ± 1.4 Ma for rhyolite of the Rocky Harbour Formation, upper Musgravetown Group; and 572 ± 2 Ma for Louil Hills granite. In light of these results, remnants of the main Avalonian arc are re-designated “Broad Island Group”, for the site of the dated 620 Ma tuff. The ca. 589 Ma schist from Love Cove is included in the Musgravetown Group and may be a tectonized equivalent of Bull Arm Formation. Our data outline a tectonomagmatic change from arc-dominated magmatism at ca. 620 Ma, to an extensional regime ca. 605–589 Ma, culminating in alkaline magmatism by ca. 572 Ma. εNdt values (t = 620–569 Ma) for felsic rocks range from 3.7 to 5.6 and yield TDM ages consistent with derivation from a juvenile Neoproterozoic (878–730 Ma) basement. Mafic rocks exhibit a time-progressive increase in εNdt, indicating more juvenile mantle sources through time. Further delimitation of map units of the area await integrated lithostratigraphy, precise modern U–Pb geochronology, and lithogeochemistry.

NORTH AMERICAN COMMISSION ON STRATIGRAPHIC NOMENCLATURE Report 14 - Revision of Articles 73, 81, 82 and Table 2 of the North American Stratigraphic Code to Formalize Subseries and Subepochs

At the 75th Annual Meeting of the North American Commission on Stratigraphic Nomenclature, 22 October, 2020, in connection with GSA 2020 Connects Online, the Commission voted unanimously to accept the revision of Articles 73, 81 and 82 of the North American Stratigraphic Code (North American Commission on Stratigraphic Nomenclature, 2005 with subsequent updates), and concomitant changes to Table 2; specific revisions of the Code are indicated in red color. These replace all older versions of the specified Articles. An application for this revision (Aubry et al. 2019) was published in Stratigraphy more than one year prior to the meeting; thus, the vote on this application for revision follows Article 21 of the Code.

Dating of Guperas Formation rhyolites changes the stratigraphy of the Mesoproterozoic Sinclair Supergroup of Namibia

The volcanosedimentary Guperas Formation contains the youngest volcanic rocks of the Sinclair Supergroup in the Konkiep Terrane of southern Namibia. Precise U-Pb zircon microbeam dating shows that the Guperas Formation as mapped includes felsic volcanic rocks which belong to both the first (1.37 to 1.33 Ga) and the third (1.11 to 1.07 Ga) magmatic cycle of the Sinclair Supergroup. Volcanic rocks of the ‘true’ Guperas Formation are dated by three samples, with a combined age of 1108 ± 10 Ma. The sedimentary rocks mapped as Guperas Formation are also distinguished by two different detrital age spectra into the ~1 100 Ma true Guperas Formation and the Aruab Member of the ~1 217 Ma Barby Formation. Geochronology now resolves the previous stratigraphic separation of the very similar Nubib and Rooiberg (Sonntag) Granites. The two small outcrops of 1 334 ± 5 Ma Rooiberg Granite are now shown to be part of the regional 1 334 ± 8 Ma Nubib Granite batholith. The Konkiep Terrane was affected by faulting and shear zones, but was only gently folded and not involved in regional metamorphism, despite its proximity to the Namaqua-Natal Province to the southwest. This is due to the Konkiep Terrane having a thick and strong continental basement which may have formed as part of the mainly Palaeoproterozoic Rehoboth Province. However no Palaeoproterozoic rocks are exposed in the Konkiep Terrane, which is now interpreted as an unaffiliated terrane. The three cycles of extrusive and plutonic magmatism in the Sinclair Supergroup formed in chronologically distinct periods and different tectonic settings, which requires revision of the stratigraphic nomenclature. The Konkiep Group is replaced by three new groups which are separated by &gt;100 million-year unconformities. The Betta Group, represented by the mainly volcanic Kumbis, Nagatis and Welverdiend formations in the first magmatic cycle, probably formed in a passive continental rift setting due to breakup of the Rehoboth Province between 1 374 and 1 334 Ma. The Vergenoeg Group, represented by the sedimentary Kunjas and volcanic Barby and Haiber Flats formations, formed in a subduction setting at the margin of the Konkiep Terrane. This ~1 217 to 1204 Ma magmatic cycle ended with the accretion of Namaqua-Natal terranes to the Kalahari Craton. The ~1 100 Ma Ganaams Group, represented by the volcanic Guperas Formation and sedimentary Aubures Formation, was the result of interplay between the continental-scale Umkondo mantle heating event and movements between crustal blocks following the Namaqua-Natal collisional orogeny.

Triassic mudstones of the Central North Sea: cross-border characterization, correlation and their palaeoclimatic significance

The Triassic of the Central North Sea is a continental succession that contains prolific hydrocarbon-bearing fluvial sandstone reservoirs stratigraphically partitioned by mudstones. Within the Skagerrak Formation of the UK sector, hydrocarbon accumulations in the Judy, Joanne and Josephine Sandstone members are top sealed by the Julius, Jonathan and Joshua Mudstone members, respectively. However, UK and Norwegian stratigraphic correlations have been problematical for decades, largely due to biostratigraphic challenges but also due to the non-uniqueness of the lithotypes and because the cross-border stratigraphic nomenclature differs and has yet to be rationalized. This study focuses on mudstones rather than sandstones to unify cross-border correlation efforts at a regional scale. The mudstone members have been characterized by integrating sedimentological, petrophysical and geophysical data. The facies are indicative of playa lakes that frequently desiccated and preserved minor anhydrite. These conditions alternated with periods of marshy, palustrine conditions favourable for the formation of dolostones. Regional correlations have detected lateral facies changes in the mudstones which are important for their seismically mappable extents, resulting palaeogeographies and, ultimately, their competency as intraformational top seals. Significant diachroneity is associated with the lithological transitions at sandstone–mudstone member boundaries and although lithostratigraphic surfaces can be used as timelines over short distances (e.g. within a field), they should not be assumed to represent timelines over longer correlation lengths. Palaeoclimatic trends are interpreted and compared to those of adjacent regions to test the extent and impact of climate change as a predictive allogenic forcing factor on sedimentation. Mudstone member deposition occurred as a result of the retreat of large-scale terminal fluvial systems during a return to more arid ‘background’ climatic conditions. The cause of the member-scale climatic cyclicity observed within the Skagerrak Formation may be related to volcanic activity in large igneous provinces which triggered the episodic progradation of fluvial systems.