High-resolution Chronostratigraphy Research Articles

The role of tephras in developing a high-resolution chronostratigraphy for palaeoenvironmental reconst-ruction and archaeology in southern Kyushu, Japan, since 30,000 years ago

The role of tephras in developing a high-resolution chronostratigraphy for palaeoenvironmental reconst-ruction and archaeology in southern Kyushu, Japan, since 30,000 years ago

Effects of diagenesis on the astrochronological approach of defining stratigraphic boundaries in calcareous rhythmites: The Tortonian GSSP

Since the establishment of astrochronology, calcareous rhythmites are frequently used as the basis of high-resolution chronostratigraphy. In particular for the Neogene, calcareous rhythmites serve as stratotypes and for absolute dating of stratigraphic boundaries (Global Stratotype Sections and Points – GSSPs). However, the exact mechanisms responsible for the formation of the rhythmic intercalation of lithologies in such successions are complex and not easily reconstructed. To a large extent this is the effect of diagenetic modifications of the original sediment. Here, two examples of Neogene calcareous rhythmites are studied; the Monte dei Corvi section and the Monte Gibliscemi section. The first is the GSSP location of the Serravallian–Tortonian boundary, whereas the second is an auxiliary stratotype for the same boundary. During the past years, astrochronological approaches were applied to these successions to considerably increase time resolution compared to the elaborated biostratigraphic database. The present study focuses on micropetrographic, trace element and clay mineralogical methods in order to gain a better understanding of the genesis of the rhythmites. In the Monte Gibliscemi section, sediment parameters that are robust against diagenetic change clearly reflect primary differences, i.e. cyclical environmental changes. In contrast, no clear primary signal is determined for the Monte dei Corvi section on a couplet scale, leaving the origin of the rhythm ambiguous. This impedes the interpretation of the latter and the comparability between the two successions, and also compromises any bed-by-bed correlation between the two. The unclear origin of the rhythmites of Monte dei Corvi introduces uncertainty into the applicability of astrochronology to this succession.

Integrated Ediacaran (Sinian) chronostratigraphy of South China

The Ediacaran Period was a critical time in the history of life and Earth. Understanding the complex interactions between geological and biological events during this interval requires high-resolution chronostratigraphy. Thanks to its uniquely favorable palaeogeographic setting, South China is an ideal region for constructing a framework for global chronostratigraphic correlation of Ediacaran strata. Here, continuous Ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles. As part of the present study, 62 reference sections distributed throughout the Yangtze Platform were investigated. Analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies. Three major sequence boundaries occur respectively in the middle and upper parts of the Doushantuo Formation and in the middle part of the Dengying Formation. Subdivision and correlation of the Ediacaran successions of the Yangtze Platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections (1075 samples). The sequence boundary (SB2) in the middle part of the Doushantuo Formation is suggested here as the Lower (Xiadongian)/Upper (Yangtzean) series boundary of the Ediacaran which coincides with several globally recognizable events, namely 1) the end of the Neoproterozoic glaciations, 2) the first appearance of animals, 3) the sudden increase in the diversity of acanthomorphic acritarchs, and 4) a negative δ 13C excursion. The Ediacaran System of South China may be subdivided into five stages. Furthermore, the criteria for defining these stages may be applicable throughout the world. Also, the composite carbon isotope profile of the Ediacaran of South China can be used as a global reference for chronostratigraphic subdivision and correlation. In addition to the globally recognizable, negative δ 13C excursion in the cap carbonate at the base of the Ediacaran, the negative δ 13C excursion in the uppermost Doushantuo/Wonoka/Shuram interval represents another, globally correlatable major excursion. The positive δ 13C excursion immediately following the uppermost Doushantuo excursion and ending at 548 Ma is also useful for global correlation. Current Ediacaran chronostratigraphy and global correlations indicate that the upper Doushantuo/Wonoka/Shuram negative δ 13C excursion ranges from ca. 560 Ma to 551 Ma, and therefore coincides with the evolutionary renovation of life. Feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative δ 13C excursion in earth history. Our chronostratigraphic correlations also imply that the earliest known metazoan biotas, namely the Weng'an and characteristic Ediacaran biotas, do not constitute two temporally separate evolutionary lineages, as proposed previously, but represent two parallel evolutionary pathways preceding the Cambrian explosion of animal life.

Astronomical tuning as the basis for high resolution chronostratigraphy: the intricate history of the Messinian Salinity Crisis

The Messinian Salinity Crisis (MSC) in the Mediterranean resulted from a complex interplay between tectonic gateway closure and climate evolution. The climate factor, in turn, can be separated into two components, one associated with dominantly precession controlled regional climate change and the other with dominantly obliquity related glacial cyclicity. The influence of these climate changes occurred superimposed on a long(er)-term tectonic trend. Discrimination into the various forcing factors only recently came within reach due to the development of an integrated high-resolution stratigraphy and astronomically tuned age models, both for the Messinian (pre-)evaporite successions in the Mediterranean and for benthic oxygen isotope records from the open ocean. The application of these time scales in combination with a high-resolution integrated stratigraphic approach showed that 1) the onset of the MSC proper at 5.96 Ma is not related to glacio-eustatic sealevel lowering but its timing can best be attributed to the influence of the 400-kyr eccentricity cycle on regional climate superimposed on a tectonic trend, 2) the main desiccation phase between the Lower and Upper Evaporites coincides with the twin peak glacials TG12-14 suggesting a glacio-eustatic control, 3) the beginning of the Upper Evaporites and Lago Mare phase coincides with the onset of the major deglaciation following peak glacial TG 12, indicating that glacio-eustatic sealevel rise played a role, 4) the Pliocene flooding of the Mediterranean is not related to a glacioeustatic sealevel rise, and 5) the evaporite cycles are controlled by precession induced regional climate changes rather than by obliquity forced glacio-eustatic sealevel change. Our astronomical age model for the Mediterranean Messinian is consistent with 40Ar/39Ar ages of ash layers intercalated in Messinian successions in the Mediterranean. However, the intercalibration between astronomical and 40Ar/39Ar dating has to be taken into account for a direct comparison of these ages.

Limestone–marl alternations as environmental archives and the role of early diagenesis: a critical review

Limestone–marl alternations and other micritic calcareous rhythmites have long appealed to sedimentologists, as they appeared to directly reflect high-frequency environmental change. In particular, when orbital forcing gained popularity amongst sedimentologists and paleoclimatologists in 1980s, such rhythmites seemed to offer an ideal tool for high-resolution chronostratigraphy and environmental reconstruction. However, in spite of the fact that orbital forcing has become a routine interpretation of calcareous rhythmites, and that the processes of formation of calcareous rhythmites are considered well understood, research in the past 10 years again has questioned their primary origin and their direct interpretability. Detailed petrographic, paleontological, and geochemical data from numerous successions through geological time provided the basis for testing whether or not the regular alternation of limestone beds and marl or shale interlayers represents bimodally fluctuating environmental conditions in a direct way. In particular, these data, supplemented by box model simulations, imply that post-depositional alteration (diagenesis) has the potential to not only seriously distort primary environmental signals, but also to mimic primary signals. This questions the use of micritic calcareous rhythmites for high-resolution chronostratigraphy and for environmental interpretations where independent data of diagenetically inert parameters are not available. Diagenetic changes appear to have a yet widely underestimated influence on the appearance of limestone–marl alternations and other calcareous rhythmites. The aim of the present review is to summarize new approaches and give an overview of our research results in this field of the past decade. This review also aims at pointing to still enigmatic aspects that need to be addressed before the interpretation of micritic calcareous rhythmites can be considered a reliable tool for high-resolution chronostratigraphy and paleoenvironmental interpretation.

Empiricism and model-building in stratigraphy: Around the hermeneutic circle in the pursuit of stratigraphic correlation

The discipline of geology has varying theoretical and methodological approaches to the study of the earth and its pro- cesses. By focusing on the ways in which geological theories are constructed and tested through the use of various methodologies, it be- comes evident that research approaches compete with each other to legitimate their own constructions of scientific knowledge. It also becomes clear that uncritical adherence to theoretical and methodological approaches and assumptions may obscure rather than illumi- nate objects under study. The scientific process in geology is exemplified by the hermeneutic circle (Frodeman, after Heidegger), in which empirical obser- vation, generalization and theorizing (induction), are followed by construction of hypotheses (including models) and renewed observa- tions to test and refine or abandon a theory (deduction). Ideally, this is a continuous and circular process, whereby theoretical assumptions are put to the test, but history demonstrates that the inductive and deductive approaches have largely been followed by dif- ferent groups of stratigraphers with different objectives. Further, these stratigraphers have tended to work in isolation from each other. According to Hallam, "geologists tend to be staunchly empirical in their approach", but are also inveterate model builders, at- tempting to explain their universe by developing deductive models. Two contrasting case studies illustrate empirical and model-based approaches to dating and correlation. A synthesis by Callomon (1995) of Jurassic ammonite biostratigraphy, based on a century of data collection, and the inductive building of a biozone scheme, reveals numerous gaps and considerable local stratigraphic variability in the studied sections in southern England. By contrast, a comparison by Gale at al. (2002) of two sections in India and France using a se- quence model for correlations was interpreted by them in terms of global uniformity of sequence-generating processes and eustatic sea-level control. Modern dating methods should be rigorously empirical, including the cross-correlation of multivariate dating techniques and the use of non-events as boundary markers ("golden spike" concept). Extreme caution needs to be employed in introducing such deductive concepts as "global cycles," "event stratigraphy" and "cyclostratigraphy" into methods of high-resolution chronostratigraphy. Cur- rently, cyclostratigraphers have established the Milankovitch model of orbital forcing as the centerpiece of a research program to docu- ment climate change and to provide a basis for a high-resolution time scale. There are at least three problems with this approach: 1) Researchers downplay the probability that orbital frequencies may have differed in the geological past. 2) There is a tendency to make assumptions about stratigraphic completeness and constancy of sedimentation rate that may not be valid. 3) Independent chrono- stratigraphic calibration of cyclostratigraphic data is insufficiently precise, and cannot at present provide adequate constraints on cyclostratigraphic models based on tuning, filtering, and other statistical techniques.

Constraining controls on carbonate sequences with high-resolution chronostratigraphy: Upper Miocene, Cabo de Gata region, SE Spain

A high-resolution chronostratigraphy has been developed for Miocene shallow-water carbonate strata in the Cabo de Gata region of SE Spain for evaluation of local, regional and global factors that controlled platform architecture prior to and during the Messinian salinity crisis. Paleomagnetic data were collected from strata at three localities. Mean natural remanent magnetization (NRM) ranges between 1.53×10−8 and 5.2×10−3 Am2/kg. Incremental thermal and alternating field demagnetization isolated the characteristic remanent magnetization (ChRM). Rock magnetic studies show that the dominant magnetic mineral is magnetite, but mixtures of magnetite and hematite occur. A composite chronostratigraphy was derived from five stratigraphic sections. Regional stratigraphic data, biostratigraphic data, and an 40Ar/39Ar date of 8.5±0.1 Ma, for an interbedded volcanic flow, place the strata in geomagnetic polarity Chrons C4r to C3r. Sequence-stratigraphic and diagenetic evidence indicate a major unconformity at the base of depositional sequence (DS)3 that contains a prograding reef complex, suggesting that approximately 250 000 yr of record (Subchrons C3Br.2r to 3Br.1r) are missing near the Messinian–Tortonian boundary. Correlation to the GPTS shows that the studied strata represent five third- to fourth-order DSs. Basal units are temperate to subtropical ramps (DS1A, DS1B, DS2); these are overlain by subtropical to tropical reefal platforms (DS3), which are capped by subtropical to tropical cyclic carbonates (Terminal Carbonate Complex, TCC). Correlation of the Cabo de Gata record to the Melilla area of Morocco, and the Sorbas basin of Spain indicate that early–Late Tortonian ramp strata from these areas are partially time-equivalent. Similar strata are extensively developed in the Western Mediterranean and likely were influenced by a cool climate or influx of nutrients during an overall rise in global sea-level. After ramp deposition, a sequence boundary (SB3) in Cabo de Gata correlates with a sequence boundary in Morocco and a published third-order eustatic fall suggesting at least a partial eustatic control for the sequence boundary. Coral reefs began to develop earlier in Cabo de Gata than at Melilla or Sorbas, arguing for local factors affecting this major environmental transition. Later Messinian reefs (DS3) from all areas are time-equivalent, suggesting a regional or global control on their formation. Some Halimeda-rich horizons in the Western Mediterranean are not time-equivalent event strata as hypothesized by others. Correlation of the relative sea-level curve for the fringing reef complex (DS3) with a published eustatic curve suggests at least a partial third-order global eustatic control for the highstand part of the sequence. Downstepping DS3 reefs and initial subaerial exposure of earlier DS3 reef strata approximately correlate with initiation of a series of subaerial unconformities in the South Pacific. The longer-term relative fall in sea-level during DS3 downstepping reef progradation does not correlate with a published third-order eustatic fall. Eustatic sea-level fluctuations may have been associated with initiation of the Mediterranean Messinian salinity crisis, but the longer-term fall may have been linked to tectonic uplift in the Mediterranean region. Widespread distribution of ‘TCC-style’ cycles of approximately the same age suggests a regional (Western Mediterranean) or global control on sea-level change responsible for TCC cycles. In addition, four subaerial exposure-capped TCC cycles may correlate with similar subaerial unconformities in the South Pacific, suggesting at least a partial eustatic control on TCC cyclicity. The high rates of relative sea-level change needed to generate a minimum of 25–30 m sea-level changes associated with each cycle are consistent with glacio–eustacy along with rapid evaporitic drawdown in the Mediterranean.

High-resolution chronostratigraphy from downhole susceptibility logging tuned by palaeoclimatic orbital frequencies

High-resolution magnetic records have been obtained by downhole measurement with the Geological High Resolution Magnetic Logging Tool (GHMT) in a well drilled in the North Sea for hydrocarbon exploration. This tool enables a continuous measurement of the polarity of the magnetic remanence and of the magnetic susceptibility throughout the drilled formations. A high-resolution magnetic chronostratigraphy between 2.6 and 1.6 Ma is deduced from the tie points given by the downhole magnetostratigraphy and from a detailed spectral analysis of climatically influenced variations of susceptibility. The orbital frequencies identified by spectral analysis of the magnetic susceptibility in the depth domain allow a refined estimation of the sedimentation rate and determination of a high-resolution chronology of the sequence. Characteristic features of the onset of Northern Hemisphere glaciation and its fluctuations during the Late Pliocene are identified through this analysis of the susceptibility record. Our analysis indicates that massive discharge events of non pelagic deposits — similar, but with a higher amplitude, to Heinrich events that are observed during the last glaciation — occurred between 2.5 and 2.0 Ma and were probably related to instabilities of the Laurentide ice sheet. The relative power of the orbital forcing factors is compared with that documented at other North Atlantic Ocean sites. Comparison with an insolation model does not indicate direct correlation but suggests a strong influence of the Northern Hemisphere ice cover and its local variations.

福島県太平洋岸，塚原海岸における最終間氷期最盛期の海進海退過程とその時期降下したテフラについて

Marine terraces are well preserved in the coastal region facing the Pacific Ocean of northeast Japan. Their geomorphic development has been studied to clarify the history of sea-level changes and crustal movements. The Tsukabara coast located in the southeast part of Haramachi City, Fukushima Prefecture, has a marine terrace named the Kobama surface. Previous studies concluded that this terrace was formed in the last interglacial period. In the basal part of the Tsukabara Formation, which is marine sediment stratigraphically just below the terrace deposit of the Kobama surface, an air fall tephra consists of fine pumice lapilli was discovered. This study clarifies that this tephra contains mainly a well-vesiculated fiber type of glass shard with distinctive low indices (n=1.495-1.499) and small mounts of phenocrysts (orthopyroxene, hornblende, biotite, quartz, plagioclase). These characteristic properties and the chemical composition of the glass shards show that this tephra is correlated to the Tagashira Tephra (TG), which is distributed in the area from southern Fukushima Pref. to north Tochigi Pref., and also to Yokomori Volcanic Ash (YkA) distributed on the easten base of Adatara Volcano.Fission track dating and stratigraphic positions of TG and its related tephra suggest that the Tsukabara Formation and the terrace deposit of Kobama surface were formed during marine isotope stage 5.5. The Tsukabara Formation is most likely to be marine bay sediment, which buried a dissecting valley formed in the low stand of sea-level of MIS 6. Judging from the stratigraphic position of TG in the Tsukabara Formation, TG deposited between the low sea-level period when the Tsukabara coast was dry land and higher sea-level period when this area was submerged in the bottom of the bay with a depth of less than 20m, was associated with the transgression from MIS 6 to MIS 5.5. It is most likely that the present altitude of sea-level at the deposition of TG is about 2 m. This estimate and the elevation of the former strandline of MIS 5.5 indicate that the sea level at the deposition of TG was 28m lower than that at the culmination of MIS 5.5. On the basis of highresolution chronostratigraphy of Martinson et al.(1987), the age of TG is estimated to be135-125ka.After the deposition of TG, the sea invaded landward, resulting in the formation of a bay, with continuous deposition of fine marine silt of the Tsukabara Formation. The regression from MIS 5.5 to MIS 5.4 took place after the culmination of MIS 5.5, associated with the emergence of the Kobama surface. Subsequently, Ad-D tephra estimated to be 125-100ka was deposited. At that time sea-level was at least 17m lower than that of the MIS 5.5 culmination. Paleosealevel of MIS 5.3 is estimated to be less than-8m from the present altitude.

堆積物中に記録された周期性を利用した年代層序の可能性

Cyclic lithologic changes in sediments can be used a chronometer spanning 1/2 day through 100, 000 of years in the geological column. Here we reviews some examples of cyclic sediments, related to tidal currents, seasonal changes, and glacio-eustacy. Particular attention is paid to the oxygen isotope study of turbidites of the Otadai and Umegase Formations drilled through by the study well TR-3, Boso Peninsula. The data clearly demonstrate that the sedimentation of turbidites was closely related to glacio-eustatic changes.All these examples of sediment cyclicity are controlled by constant, cyclic movements of astronomical bodies. Therefore, their signatures in sediments should be very stable through time. For this reason, each astronomically-induced cyclicity in sediments represents a definite time interval, which is useful for high-resolution chronostratigraphy. For example, fluctuations in oxygen isotope data from deep-sea pelagic sediments can be interpreted as an end result of astronomically-induced cyclicity of various origin. Recognition of these cyclicities provides a tool for sequencial dating of the sediments. This article reviews the sequencial dating of the TR-3 by determining the interval sedimentation rates. For this calculation, TR-3 oxygen isotope records were correlated to those of DSDP Site 607 which were well interpreted in terms of the astrochronologic method.

Distinguishing the roles of autogenic versus allogenic processes in cyclic sedimentation, Cisco Group (Virgilian and Wolfcampian), north-central Texas

Meter-scale transgressive-regressive cycles of the subsurface Cisco Group are composed of marine and nonmarine carbonate and siliciclastic rocks deposited on the Eastern shelf of the Midland basin during Late Pennsylvanian and Early Permian time. Five cycle types are characterized by thickness, magnitude, order, and principal lithofacies. Cycle magnitude is defined as the maximum facies shift in a cycle, indicating extent of shoreline migration. Cisco cycles belong to three orders—minor, intermediate, and major—and they are superimposed and form a stratigraphic hierarchy. Each order of cycles has a distinct range of thickness and possibly duration. A cycle is also divided into a lower sand-poor interval, during which coarse siliciclastic supply at the depositional site was diminishing, and an upper sand-rich interval, during which coarse siliciclastic supply was high. Regional thickness and lithofacies variations of sand-rich intervals indicate that progradational infilling at a depositional site lagged marine regression, suggesting a delay in sediment supply from the upland source relative to the time of base-level fall. Regional systematic variations in cycle abundance, continuity, and characteristics along depositional dip and strike record the interplay among regional topography, pattern of siliciclastic supply, and shelf subsidence, which controlled distribution of depocenters and bypass zones and, thus, stratigraphic completeness and resolution. Regional persistence of cycles suggests a eustatic control on regional, ordered transgressive-regressive events. In contrast, local variations of cycle characters suggest controls by local topography and depositional dynamics, which determined depositional loci, differential compaction, and erosion. A predominantly autocyclic Cisco record in the upper platform does not imply the absence of allogenic processes. An allocyclic Cisco record in the lower platform contains abundant autocyclic imprints, because allogenic controls on cyclic sedimentation were accomplished through local autogenic processes. Distinguishing the roles of autogenic versus allogenic processes in cyclic sedimentation is an important step in establishing a high-resolution (meter-scale) chronostratigraphy of any sedimentary record 1 .

Biostratigraphic and Paleoecologic Characterization of Cretaceous Sequences of the Western Interior Basin of North America

Five second-order and numerous third-order sedimentary sequences have been recognized in Cretaceous strata of the Western Interior basin, North America. Regional definition of the predominantly transgressive (TST) and highstand systems tracts (HST), from nearshore coarse clastics to basinal fine-grained facies, depends on a system of detailed biostratigraphy and chronostratigraphic correlation. A predominantly molluscan-based biostratigraphy utilizing composite assemblage zonation provides correlations across the basin at 0.1-0.3 Ma/biozone levels of resolution. High-resolution event chronostratigraphy provides regional correlation at finer (40-100 Ka) intervals, based on integrated bioevent, chemoevent, physical, and composite event units tied through graphic correlation to assemblage biostratigraphy and geochronology. Further, paleoecologic data that reflect changes in relative sea level can be used to better define systems tracts, especially in fine-grained basinal facies where sequence stratigraphic boundaries may be poorly expressed. These data include (1) taphonomic and community data reflecting condensation and offshore starvation during TST and TST-HST boundaries (e.g., shell lags and marine oyster beds); (2) systems tract-specific communities; (3) macrofaunal diversity trends; (4) temporal biofacies patterns where predominantly epifaunal communities characterize most of the basinal TST and early HST, whereas mixed epi- and infaunal communities characterize earliest TST and later HST and lowstand systems tracts; and (5) lateral biofaciesmore » patterns for each systems tract.« less

Sedimentary development of the Louisiana continental shelf related to sea level cycles: Part I—sedimentary sequences

Cyclic sequences occur worldwide in nearly every stratigraphic sequence; they are particularly well developed in marine deposits associated with large river systems. Superimposed on those cycles attributed to shifting sites of deposition are those related to high-frequency sea level changes. The large data base for this study (including 471 deep foundation borings, thousands of line kilometers of high-resolution seismic, and sedimentological and dating analyses) represents the most complete information on high-resolution chronostratigraphy and lithostratigraphy that is available on any modern continental shelf/upper slope. These data are used to document sedimentological characteristics and spatial depositional patterns during three complete sea level cycles over the entire continental shelf/upper slope of offshore Louisiana.

Sedimentary development of the Louisiana continental shelf related to sea level cycles: Part II—seismic response

Cyclic sequences occur worldwide in nearly every stratigraphic sequence; they are particularly well-developed in fluvial and deltaic sediments that have been influenced by high-frequency eustatic sea-level fluctuations. The large data base for this study (including 471 deep foundation borings, thousands of line kilometers of high-resolution seismic, and sedimentological and dating analyses) represents the most complete information on high-resolution chronostratigraphy and lithostratigraphy that is available on any modern continental shelf/upper slope. These data are used to document sedimentological characteristics and high-resolution seismic responses during three complete sea-level cycles over the entire continental shelf/upper slope of offshore Louisiana.

High-Resolution Chronostratigraphy of Offshore Wells Within Pleistocene Through Upper Miocene of Gulf of Mexico: ABSTRACT

High-Resolution Chronostratigraphy of Offshore Wells Within Pleistocene Through Upper Miocene of Gulf of Mexico: ABSTRACT