Oxygen isotope stratigraphy and calcareous nannofossil biostratigraphy of the Lower Pleistocene in the Boso Peninsula, central Japan

ABSTRACT: Oxygen isotope stratigraphy and calcareous nannofossil biostratigraphy in the upper part of the Kiwada Formation, which is part of the Kazusa Group in the Boso Peninsula in the central part of the Pacific coast of Japan, were examined to establish a high-resolution age model and estimate the age of the lower part of Pleistocene nannofossil biohorizons in the northwestern Pacific region. The new age model indicates that the upper part of the Kiwada Formation corresponds to Marine Isotope Stage (MIS) 41 through MIS 36. Two nannofossil biohorizons, the last occurrences of large forms of Gephyrocapsa (>5.5 micrometers) and Helicosphaera sellii,were recorded in the examined section. The LO of large Gephyrocapsa spp. coincides with the MIS 37/38 boundary which is 1241.2 plus or minus 0.4 ka. The LO of H. sellii is located in late MIS 40 and has a calculated age of 1291.4 plus or minus 1.4 ka. These biohorizons are traceable even though the LO of H. sellii is a diachronous event. Size variations of Gephyrocapsa from approximately 1250 ka are discussed and fluctuations of small size Gephyrocapsa could represent cyclic changes of the Kuroshio and Oyashio currents.

Environmental significance of benthic foraminifera and microfacies of central Tethyan Upper Triassic strata, central Iran

ABSTRACT: The evolution of the Late TriassicNaybandBasin in central Iranwas influenced by climatic changes and tectonic events. An increase in siliciclastic input and a corresponding carbonate productivity crisis in theQhrogchi area in central Iranwere initiated by the onset of a relatively humid episode in the Carnian, followed by arid to semi-arid conditions in the Norian and Rhaetian. Carbonate sediments of theNayband Formationwere deposited in a range of environments, from outer ramp to marginal marine environments. The rich benthic fauna is predominantly restricted to the limestone bedswithin the upper part of succession. Bivalves, hydrozoans (Heterastridium), calcareous algae, corals and sclerosponges are recorded. The latter two groups form patch reefs on the middle ramp. Benthic foraminifera show strong affinities with assemblages reported from the central Tethys, whereas others are also well-known from the Alpine region and from the eastern Tethys.

Cambrian ooids, their genesis and relationship to sea-level rise and fall: A case study of the Qingshuihe section, Inner Mongolia, China

ABSTRACT: TheCambrian strata at the northwestern margin of the North China Platform in InnerMongolia hold thick oolitic-grain bank deposits.Generally, the strata are dominated by calcareous mudstone of shelf facies in the lower part, micritic limestone consisting of deep to middle ramp facies in the middle part, and oolitic limestone encompassing shallow ramp to grain bank facies in the upper part of each formation. The shelf and deep ramp facies are the result of relative sea-level rise, while oolitic limestones developed in response to relative sea-level fall. Microscopically, the studied ooids are represented by radial crystal structures and concentric laminations with or without cores, single crystal or neomorphosed ooids, and highly bored ooids. The size andmorphology of the ooids indicate a two-fold mechanical influence of microbes; constructive in the Miaolingian and destructive in the Furongian ooids. Based on these observations, it can be inferred that microbes (predominantly composed of filamentous fossils of cyanobacteria) excreted extracellular polymeric substances (EPS) to develop multiple bacterial biofilms microbial mats. The subsequent decay of the EPS through sulfate reducing bacteria most likely caused precipitation around these ooids. The depositional style of ooids occupying the upper parts of the formations, and their possible genesis from microbes provide clue for regional correlation, as well as affirm biological control in the formation of ooids.

Integrated stratigraphy from a transgressive upper Oligocene section in NW Italy

ABSTRACT: The Oligo-Miocene Transition (OMT) is one of the most important climatic transitions of the last 30 million years. This short period of climate warming coincides with a few biotic turnovers, which are well known in deeper marine settings where stratigraphic successions yield a detailed record; in shallowmarine environments they have been proved difficult to recognize as the occurrence and absence of certain taxa due to ecological preferences hamper the study. This study focuses on the Case Cné section in the late Oligocene of the Tertiary Piedmont Basin (TPB) as it represents a gradual transgressive event, which shows the drowning of a locally developed reef complex and development of a deeper marine sedimentary setting influenced by gravity flow mechanics. Larger foraminifera biostratigraphy was used to date the section to the late Oligocene (SBZ23); preliminary strontium isotope data confirms this result. Using sedimentological, semi-quantitative microfacies and geochemical analysis the sedimentary history of the section was reconstructed and divided into four major phases: the drowning of the reef complex, a short prograding phase of the fluvial system, the onset of gravity flow mechanics and a final transgressive phase with an initial turbiditic influence which continues regionally into the Miocene.

Biostratigraphy of planktonic foraminifera in the Abtalkh Formation and determination of the Santonian/Campanian Boundary in the Kopeh-Dagh Sedimentary Basin

ABSTRACT:We studied the Abtalkh Formation from five outcrops (Sheikh, Hajgelichkhan, Qarehso, Muzduran, and Deraz-Ab) in the Kopeh-Dagh sedimentary basin. A total of 30 species of planktonic foraminifera belonging to 21 genera were recorded. These species were used to subdivide the Abtalkh Formation into seven biozones (Dicarinella asymetrica Zone, Globotruncanita elevata Zone, Contusotruncana plummerae Zone, Radotruncana calcarata Zone, Globotruncanella havanensis Zone, Globotruncana aegyptiaca Zone, and Gansserina gansseri Zone). The Abtalkh Formation was deposited during the late Santonian-latest Campanian and the Santonian-Campanian boundary is identified based on the last occurrence of Dicarinella asymetrica. The base of the Campanian stage was delineated by the extinction of the marginotruncanid group, the first occurrences of Pseudotextularia nuttalli and Rugoglobigerina rugosa, and on the last occurrence of Dicarinella asymetrica.

Cretaceous (Aptian-Maastrichtian) stratigraphy of the Shiranish Islam area, northern Iraq

ABSTRACT: The Kurdistan region of northern Iraq contains world-class outcrops that make it possible to examine the Cretaceous deep and shallow marine Tethyan faunal succession. Six separate sections covering the Shiranish, Bekhme, Mergi and Qamchuqa formations have been investigated in this study from the Shiranish Islam area. A number of papers have been published on this area, but no comprehensive biostratigraphic record has been published that fully documents the Cretaceous stratigraphy and the chronostratigraphic interpretation of the succession. As a result, this has led to significant lithostratigraphic and chronostratigraphic uncertainties. The upper part of the Qamchuqa is pervasively dolomitized. Rare occurrences of foraminifera are found in less dolomitized intervals in thin-section indicating an early - middle Albian age for the top of the formation. A thin interval comprising the Gir Bir Formation is Cenomanian in age and is present between the top of the Qamchuqa Formation and the overlying conglomerate. Historical studies indicate that the Turonian Mergi Formation occurs between the Qamchuqa and Bekhme formations, but our field and analytical data does not support it as a discrete lithostratigraphic entity, as Turonian aged faunas were not recognized. The conglomerate separating the top of the Gir Bir and base of the Bekhme is subdivided into three units (A, B & C). Units A and B are late Cenomanian to early Turonian age, whilst Unit C is of Campanian age. A significant hiatus separates the Gir Bir and the Bekhme, which encompasses the intra Turonian to Santonian. The limestone facies of the lower part of the Bekhme Formation contains rich benthic foraminiferal faunas (miliolids, Pseudedomia, Cuneolina) of early - early middle Campanian age. This lower - lower middle Campanian section at Shiranish Islam is considered to be equivalent of the upper part of the Sa'di Formation in central Iraq and is therefore re-assigned on the basis of chronostratigraphic attribution to the Sa'di (equivalent) herein. The top of the early - early middle Campanian biofacies is abruptly truncated by an omission surface, marked by an erosive base, an influx of clastic material and a major up-section biofacies change characterized by an influx of Pseudosiderolites and Orbitoides representing an intra-Campanian hiatus. The bioevent sequence suggests that this hiatus at Shiranish Islam comprises at least the middle Campanian (upper part of the G. elevata Zone) into the late Campanian (intra R. calcarata Zone), from approximately 80.64 Ma to 76.09 Ma with 4.55 my missing. The middle part of the Bekhme Formation comprising the Pseudosiderolites - Orbitoides facies is thin (c. three meters) and is re-assigned to the Lower Bekhme Member. The boundary between the Lower Bekhme Member and the Upper Bekhme Member is conformable and marked by a gradual up-section reduction in the size and presence of larger benthic foraminifera (Orbitoides, Pseudosiderolites) and an increase in the planktic component (small planktics and calcispheres). This trend of gradually increasing water depth continues into the Shiranish Formation, with no apparent major breaks in deposition. The Campanian - Maastrichtian boundary falls within Unit A of the Shiranish Formation. Deposition of the Shiranish continued into the earliest late Maastrichtian and is unconformably overlain by the Danian Kolosh Formation. The hiatus between the top of the Cretaceous and the Paleocene extends from the early late Maastrichtian (c. 68.86 Ma) to the upper part of the Danian (62.2 Ma) with an estimated duration of 6.66 my.

Late Cretaceous (Turonian-Coniacian) sequence stratigraphy, sea level, and deltaic facies, Magothy Formation, U. S. Middle Atlantic Coastal Plain

ABSTRACT: The peak "hothouse" interval of the Turonian-Coniacian (93-87 Ma) is represented on the U.S. middle Atlantic Coastal Plain by sequences of the Raritan/Bass River, Magothy, and Cheesequake Formations deposited on a passive continental margin as mixed wave-, tide-, and river dominated deltas. We apply sequence stratigraphy integrated with biostratigraphy to identify and map two major sequence boundaries separating the Raritan/Bass River, Magothy, and Cheesequake Formations and four to five (Mg1, Mg2, Mg3, ?Mg4, Mg5) Magothy sequences using continuous cores, outcrops, and geophysical logs in New Jersey. We extend correlations into New York and Delaware using well logs. The Magothy sequences disconformably overlie the well-dated (>93 Ma) lower Turonian to Cenomanian marine Raritan/Bass River sequences and are disconformably overlain by the marine Cheesequake Formation, which straddles the Coniacian/Santonian boundary. A "mid-Turonian" hiatus (ca. 93-90 Ma) associated with this major disconformity is a global sequence boundary (K-Tu4) reflecting a ~ 25 m sea-level lowering based on published NJ and Russian Platform backstripping records that indicate this was a major lowering of Global Mean Sea Level (GMSL).Higher-order (~1 Myr scale) sequence boundaries bracketing Mg1-Mg5 apparently correlate with global sequences but are only associated with low-amplitude (<25 m) sea-level falls.Mapping of sequences within the Magothy Formation shows the influence of 2 to 3 moderate-sized river sources, with thickening northeastward toward Long Island, New York, and thinning southwestward toward Delaware. Thick northern depocenters contrast with the preceding Potomac Formation (Barremian-early Cenomanian) with thick southern depocenters. This seesawing of basins on the 100-300 km and 2-10+ Myr scales is due to tectonism likely from changes inmantle dynamic topography. The remarkably widespread distribution of Magothy sequences and facies indicates stability of this deltaic depositional system over ~ 4Myr despite low-amplitude (less than 25m) sea-level variations.Widespread facies correlation provides a predictable distribution of aquifer sands and confining-unit clays tied to sea-level changes on complex deltaic facies.

Benthic foraminiferal assemblages from maximum flooding surface J30, Middle Jurassic Dhruma Formation, Central Saudi Arabia

ABSTRACT: The benthic foraminiferal have been studied from mudstone-wackestones of the D5 Unit of the Dhruma Formation that represent the Middle Jurassic J30 maximum flooding surface of Sharland et al. (2001). The benthic assemblage consists of a mixture of smaller agglutinated species, Haplophragmoides, Kutsevella, Sculptobaculites, Trochammina), and calcareous species (Nautiloculina, nodosariids, ophthalmidiids, polymorphinids, and spirillinids) without any larger foraminifera. The assemblage is indicative of open-marine midshelf conditions, and contains a number of cosmopolitan taxa that are known from the Middle Jurassic in other areas of the Tethys. The recovery of open-marine and cosmopolitan smaller benthic foraminifera in the D5 Unit of the Dhruma Formation provides a new tool for identifying the J30 maximum flooding surface and correlating the interval with other regions of the Tethys.

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.

An Austral radiolarian biozonation for the Paleogene

ABSTRACT: We have integrated southern mid- and high-latitude (Austral) radiolarian biozonations with the well-established low-latitude (Tropical) biozonation using new biostratigraphic and magnetostratigraphic constraints on radiolarian bioevents in the Southwest (SW) Pacific, Southeast (SE) Indian and Northwest (NW) Atlantic Oceans. Our primary study sites include Mead Stream, New Zealand, and DSDP Sites 277 and 207 (SW Pacific; 45-54 degrees South at 50 Ma), ODP Site 752 and IODP Site U1514 (SE Indian; 50 degrees South at 50 Ma), and IODP Site U1403 (NW Atlantic; 30 degrees North at 50 Ma). The Austral and Tropical zonal schemes have been calibrated to GPTS2020. We introduce new zonal codes to rectify current confusion surrounding use of "RP" zones. Austral zones are codified as "RPA" zones and Tropical zones are codified as "RPT". Our study finds that radiolarian datums are generally isochronous within the mid-latitude SW Pacific and SE Indian Oceans from Paleocene to middle Eocene and are also isochronous in the high-latitude Southern Ocean (>60 degrees South paleolatitude) over the late middle Eocene to Oligocene interval of overlap. Older radiolarian assemblages are not known from the Southern Ocean. Early to middle Paleocene radiolarian assemblages in the SE Indian Ocean (zones RPA2-RPA5) differ from coeval SW Pacific assemblages by lacking significant numbers of Cretaceous survivors. The reasons for this difference are uncertain. Although the late Paleocene to Eocene radiolarian assemblages in the SW Pacific and SE Indian Ocean lack many low-latitude index species, the timing of Indian Ocean bioevents agrees better with low-latitude biozonations than the SW Pacific, suggesting a stronger connection with low-latitude watermasses. Assemblages from NW Atlantic IODP Site U1403 include numerous low-latitude index species and can be correlated with zones RPT6-RPT13. Many of the species transitions in biostratigraphically important Eocene lineages, however, occur later than in lower latitudes.