Regional Sea-level Fluctuations Research Articles

Unveiling Regional Climate Patterns Through Global Subsurface Ocean Temperature Data: An AI Multi-Layer Analysis Framework

Regional-scale climate variability has far-reaching implications for both local and global climate systems, impacting factors like temperature, precipitation patterns, oceanic circulation, and the occurrence of extreme weather events. However, despite these influences, there is currently no universal methodology for the automated identification of regional-scale variability modes, including those less dominant globally, and for simultaneously exploring the influence of various ocean depth layers in characterizing these modes and diagnosing regional sea level variations. The presented innovative approach addresses these critical region-specific needs by assisting in the extraction of novel regional depth-layered variability modes and establishing their correlation with regional sea level fluctuations, employing tailored machine-learning techniques. This dual-purpose is achieved through the utilization of an optimized k-means clustering method for the automatic identification of regions with shared variability patterns across all global oceans, revealing previously unexplored regional variability modes. Additionally, guided by an EOF/PC analysis, the approach facilitates an automatic exploration of depth layers that significantly contribute to explaining sea level variability, providing insights into diverse climatic regions. Furthermore, the methodology is specifically designed for a multi-scale analysis, enabling the examination of climate variability spanning from months to several years. The results obtained through this approach have the potential to support informed decision-making regarding local climate-related changes.

Sedimentary evolution of lagoons along the Namibian coast reveals fluctuation in Holocene biogeographic faunal provinces, upwelling intensity and sea level

Within the wave-dominated and high-energy depositional environment of the hyper-arid Namibian coast, lagoons and related saltpans represent one of the few regional settings in which sediments originating from both marine and terrestrial sources can accumulate under sheltered conditions. This allows for an approximately continuous depositional record of mid to late Holocene coastal evolution. For this paleoenvironmental reconstruction, 26 sediment cores from six coastal (paleo-)lagoons were taken and investigated along a 430 km-long latitudinal gradient. Based on 56 age determinations of sediments and shell material, the initial formation of the studied lagoons can be dated back to 6.0–5.3 cal kyr BP. The sediment cores present different types of lithoclastic sediments which can be assigned to five sedimentary facies ranging from sand spit sediments rich in shell material to eolian dune sands and evaporites. From these cores, 221 samples of macrobenthic faunal material have been collected and determined to possess 46 shallow marine species. Biogeographic analyses have resulted in the identification of 10 (sub-)tropical warm water species that are not part of the regional benthic fauna in the present upwelling system. Age determinations of the shell material revealed four phases of biogeographic range expansion/shift into the study area, at 5.3 cal kyr BP, 2.8 cal kyr BP, 1.2–0.9 cal kyr BP, and 0.36–0.12 cal kyr BP from both the northern tropical Angola Current as well as from the southern subtropical Agulhas Current. The combination of datasets from this study with published datasets of regional sea-level fluctuations and upwelling intensities presents an apparent correlation between both processes and presumably an additional linkage to the ENSO and Benguela Niño variability.

Main controlling factors of organic-matter enrichment in the Ordovician-Silurian marine organic-rich mudrock in the Yangtze Block, South China

The Ordovician-Silurian organic-rich black shales located in the Wufeng-Longmaxi Formation in the southeastern part of the Upper Yangtze region are among the most important source rocks for shale gas in China. Given the importance of these sources, this study was initiated to determine the dominant factors controlling organic-matter enrichment in this region through the integration of sedimentology, petrology and geochemistry. Based on the sedimentary fabric features observed in thin section, six major mudrock lithofacies were identified in the Wufeng-Guanyinqiao-Longmaxi Formations black shale: (1) indistinctly laminated siltstone; (2) indistinctly laminated mudrock; (3) parallel-laminated mudrock; (4) nonparallel-laminated mudrock; (5) lenticular mudrock; and (6) normal-graded mudrock. Based on changes in the characteristics of lithofacies, trace-element ratios and the sizes of pyrite framboids, six kinds of mudrock facies were identified in the three formations. First, the indistinctly-laminated mudrock of the Wufeng Formation and the lower part of the Lower Longmaxi Formation that was deposited in a continuous suspension condition with pervasively anoxic and quiet water columns; second, the parallel-laminated mudrock of the upper part of the Lower Longmaxi Formation that was deposited from episodic suspension under an anoxic water column with weak fluctuation; third, the nonparallel-laminated mudrock of the lower part of the Upper Longmaxi Formation that was deposited in debris flow conditions with oxygen-rich and fluctuating water columns (graded mudrock deposited through event sedimentation in a suspension environment with a low-density, oxygen-rich bottom and turbidity currents also occurred in this stage); and finally, the indistinctly-laminated siltstones of the Guanyinqiao Formation and the upper part of the Upper Longmaxi Formation that were deposited in debris flow conditions with oxic and fluctuating water columns. The study then incorporated major- and trace-element analysis, global and regional sea-level fluctuations and regional stratigraphic characteristics to develop the depositional model. The results of the study indicate that the accumulation of organic matter in the middle region of the Sichuan Basin was predominantly controlled by regional tectonic activity.

Sedimentary environment and depositional sequences of the Oligocene Qom Formation in Central Iran based on micro-facies and microtaphofacies analysis

Oligocene deposits of the Qom Formation in central Iran were studied to reconstruct the sedimentary environment and depositional sequences based on microfacies (MF) and micro-taphofacies (MTF) analysis. A total of 310 thin sections (210 and 100 from Vidoje and Neizar respectively) were studied to differentiate eight microfacies (MF) and five microtaphofacies (MTF) types. These MFs are representative of a variety of depositional environments including restricted and semi-restricted lagoons as well as open marine settings. Overall, the distribution of MFs at the two sites suggests an open-shelf setting for the Qom Formation. Three complete third-order depositional sequences together with one incomplete sequence were identified. In the Rupelian stage, sea level changes in the Neizar and Vidoje areas were most likely affected by tectonics controlled by regional faults, whereas regional sea-level fluctuations of the south Tethyan Seaway and the Paratethys Basin controlled sea-level changes in the Chattian stage.

Solar insolation driven periodicities in southwest monsoon and its impact on NE Arabian Sea paleoceanography

In the northeastern (NE) Arabian Sea, the fluctuation in terrestrial and freshwater runoff directly depends on southwest monsoon (SWM) precipitation as well as the meltwater flux provided by Indus River. Therefore, analysis of multi-proxy spectral signatures was carried out to trace the high-resolution SWM periodicities and their influence on the productivity, regional sea level fluctuations and depositional processes in the NE Arabian Sea. The time series data of stable isotopes of oxygen (δ18OG.ruber), carbon (δ13CG.ruber and δ13Corg) and nitrogen (δ15N), Total Organic Carbon (TOC), planktic-benthic foraminiferal ratio (P/B ratio) and >63 μm coarse fraction (CF) were used from two coastal sedimentary cores located offshore Saurashtra, NE Arabian Sea (Core SK-240/485 having 88 m water depth; Core GC/SK-240/496 having 174 m water depth). The REDFIT based spectral analysis recorded significant periodicities (>90% significance) in δ18O time series centered at ∼1609, ∼667, ∼525, ∼296, ∼290 and ∼256 years. Further, the significant periodicities recorded in carbon isotopes time series (δ13CG.ruber and δ13Corg) centered at ∼681, ∼512, ∼471, ∼452, ∼438, ∼360, ∼292, ∼275, ∼269, ∼245 and ∼209 years. The significant periodicities in TOC include ∼471 and ∼322 years whereas δ15N time series recorded significant periodicity centered at ∼360 years. The significant periodicities in P/B ratio time series centered at ∼512, ∼388, ∼304, ∼250, ∼235, ∼217, ∼152, ∼139 and ∼135 years while CF recorded ∼268, ∼216, ∼209, ∼198, ∼188, ∼173 and ∼140 years significant periodicities. The observed periodicities in the multi-proxy record consist of similar cycles (within the radiocarbon dating error) which also match with previously reported solar insolation influenced SWM and other global and regional cycles. Further, the stationarity of the data has been verified using wavelet analysis and shows similar periodicities as observed in REDFIT analysis. Thereafter, the depositional behaviour was studied using correlation analysis of the common periods of δ18O time series of both the cores. The result suggests that the depositional behaviour was different for both the core sites during the early Holocene and became similar during the middle Holocene. The correlation analysis of Total Solar Index (TSI) with δ18O time series reveals a significant correlation with the core SK-240/485 whereas an insignificant correlation with the core GC/SK-240/496. These observations suggest that the solar insolation has been a leading factor responsible for the SWM trends during the Holocene which may have further influenced the productivity, regional sea level fluctuations and depositional conditions in the NE Arabian Sea. However, these trends are better preserved in shallow marine sediments as compared to the deeper marine sediments.

Cephalopod associations and palaeoecology of the Cretaceous (Barremian–Cenomanian) succession of the Alpstein, northeastern Switzerland

The Alpstein (cantons of Appenzell Ausserrhoden, Appenzell Innerrhoden and St. Gallen, northeastern Switzerland) has been of great interest for geologists over the last decades because of its excellent outcrops. However, there was no comprehensive overview over its Cretaceous fossil content. Here, we describe the cephalopod associations, which are moderately to highly diverse in some strata of the Alpstein. Furthermore, we document the regional palaeoecological changes that occurred during the radiation of heteromorph ammonites (ancyloceratids, scaphitids, turrilitids). To examine the palaeoecological changes, we quantitatively determined the macrofossil content of 11 associations of Barremian to early Cenomanian age. Here, we document 6 species (3 genera) of nautilids and 77 species (45 genera) of ammonoids (29 of the species are recorded from Switzerland for the first time). Our palaeoecological analyses revealed the disappearance of nektoplanktonic forms after the late Barremian to the middle early Aptian in the course of the development of a shallow carbonate platform. The upper lower Aptian to middle Albian strata were eroded due to successive emersion phases and condensation processes. In the late Albian, the number of nektoplanktonic species surged again with some benthos, followed by the Cenomanian fauna, which is dominated by nektoplanktonic elements including ammonites, belemnites and nautilids with only very little benthos. These results correlate well with the regional sea level fluctuations.

Depositional environment of Late Cretaceous to Eocene organic-rich marls from Jordan

ABSTRACT Oil-shale beds formed under anoxic conditions that were controlled by various local, regional and global factors. The Jordanian oil shales, which were deposited during the Late Cretaceous to Eocene, are considered as an example for the interplay of these factors. Two cores of organic-rich marls were investigated and analyzed with respect to their lithology, ichnofabrics and carbonate microfacies. The first core (OS-01, 183.3 m; South Jordan) is of Late Cretaceous age, the second one (OS-23, 256.3 m; Central Jordan) is of Eocene age. Our studies revealed that the Upper Cretaceous oil shales were deposited in a shallow-water carbonate shelf. Oyster bioherms acted as physical barriers that reduced the water circulation with the open shelf, thereby causing anoxic conditions. The Eocene oil shales also accumulated on a shallow-water carbonate shelf. In this case, however, synsedimentary tectonics caused subsiding grabens and half grabens, which in turn gave way to anoxic conditions. Both deposition and richness of the Jordanian oil shales were affected by regional sea-level fluctuations and global climatic changes.

Biodiversification of Early to Middle Ordovician conodonts: a case study from the Zitai Formation of Anhui Province, eastern China

The Lower–Middle Ordovician Zitai Formation of the South China palaeoplate consists of a succession of purple red, nodular argillaceous limestones. Palaeogeographically, it is distributed along the southeastern margin of the Yangtze Platform, and is of late Floian to Dapingian age, correlative with the Dawan Formation of the Middle and Lower Yangtze Platform. In Shitai County, Anhui Province, East China, the Zitai Formation is rich in conodonts, enabling the recognition of four biozones based on first appearance data. Detailed palaeontological and biostratigraphical study of these conodonts reveals that the Ordovician conodont radiation in the Lower Yangtze Platform attained its first diversity peak low in the Oepikodus evae Biozone. This diversification is generally consistent with macroevolutionary trends of brachiopods of South China and graptolites of the Upper Yangtze Platform, but was earlier than that of trilobites and acritarchs of the same palaeoplate. Correlation with the sea-level curve for South China suggests that conodont diversity change during the Ordovician radiation was mainly controlled by regional sea-level fluctuations.

Phanerozoic cycles of sea-level change on the Arabian Platform

ABSTRACT The Arabian Plate has experienced a complex tectonic history while also being widely influenced by eustatic sea-level changes. These diastrophic events either affected changes in the rate and/or location of subsidence that in turn led to the creation of significant new sedimentary accommodation, or caused major erosional hiatuses. As a result, both eustasy and tectonics have played important roles in the development of sedimentary sequences and in determining the locus and characteristics of reservoir, source and seal facies on the Arabian Platform. Here, we present a synthesis (Cycle Chart) of the regional sea-level fluctuations affecting the Platform that is based on Phanerozoic epi- and peri-Platform sequence-stratigraphic data. Information used for the synthesis includes sections from Saudi Arabia, Kuwait, the Greater Gulf area, Oman and Yemen. The regional Cycle Chart incorporates interpreted sedimentary onlap patterns on the margins of the Arabian Platform, as well as models of regional sea-level fluctuations that controlled these patterns. These are compared to eustatic data that represents the ‘global-mean’ models of sea-level changes, largely at second-order cycle level for the Paleozoic and third-order cycle level for the Mesozoic and Cenozoic eras. The comparisons reveal that Phanerozoic sediment accumulation patterns on the Platform were broadly controlled by eustasy, with a strong overprint of tectonics for several long intervals. During periods of tectonic quiescence, however, correlations with the eustatic events improve significantly. Thus, for example, during the Cambrian through early Silurian and mid Jurassic through early Paleogene intervals eustasy may have been the significant controlling factor for sedimentary patterns when long-term trends in both regional and global sea-level curves show similarities. The use of the Cycle Chart could facilitate exploration efforts on the Arabian Platform, provide better chronostratigraphic estimates and global correlations, and prove a useful accompaniment for sequence-stratigraphic studies. This integrative effort was greatly facilitated by the recent publication of the sequence stratigraphic synthesis of the Arabian Plate. The ages of Maximum Flooding Surfaces, however, have been recalibrated to the new (GTS 2004) time scale. This synthesis also represents a new recalibration of the Mesozoic and Cenozoic eustatic curves of Haq et al. (1988) to an up-to-date numerical time scale (GTS 2004).

On the minimum amplitude of regional sea-level fluctuations during the Flandrian

The mathematical form of a time–height sea-level curve representing intermediate-frequency fluctuations superimposed on an underlying upward trend yields a simple method for estimating the minimum amplitude of fluctuations from field measurements of the thickness of silt–peat couplets. Drawing on data from the Thames Estuary and the Fenland Basin, fluctuations of relative sea-level with minimum amplitudes between 0.08 m and 0.91 m seem to have occurred in the southeast British region during the mid-Flandrian. © 1997 John Wiley & Sons, Ltd.

Diagenetic and palaeogeographic significance of clay, carbonate and other sedimentary components in the middle Devonian limestones of western Ardenne, France

Abstract Givetian deposits accumulated in a more than 300-m-thick succession on a carbonate platform developed on the passive margin of the so-called Rheic ocean. These rocks crop out in the Ardenne massif at Glageon in a structural context marked by small fault-controlled basins subjected to moderate overburden, tectonic and metamorphic constraints. Data on the clay mineral distribution, associated with detailed information on limestone facies/microfacies, as well as data on the depositional profile and sequence stratigraphic evolution of these rocks indicate strong carbonate diagenesis and moderate clay diagenesis, the latter being favoured by the early occurrence of the former, which prevented further fluid-rock interaction. The clay assemblage distribution, which roughly parallels the palaeomorphologic and palaeobathymetric shape of the Givetian continental margin, is organized in five successive zones indicating large-scale sequence stratigraphic evolution and the control of regional sea-level fluctuations. The clay and other sedimentary components provide additional information on the warm and variably humid climate, northern, relative to southern, terrigenous sources, the open sea relative to restricted depositional environments, the temporary tectonic rejuvenation of the continental hinterland and the chemical conditions allowing early diagenetic modifications.

Quantitative Chemical Stratigraphy of Offshore Exploration Wells, Northern Gulf of Mexico: ABSTRACT

Isotope chronostratigraphy is now a proven form of chemical stratigraphy for high-resolution stratigraphic correlations in late Miocene through Pleistocene sections of exploration wells from the northern Gulf of Mexico (GOM). Detailed oxygen and carbon isotope records from wells spanning the GOM margin from Mississippi Canyon to East Breaks permit the development of a GOM type chemical stratigraphic section. The use of modern techniques of signal-to-noise identification enable us to compare our regional GOM type section to the global isotope record derived from deep-sea sections using coherence, auto-correlation, cross-correlation, and spectral analysis. These quantitative techniques enables us to recognize nearly 200 oxygen and carbon isotope zones or stages in the Piocene-Pleistocene. This chemical stratigraphy zonation offers unparalleled, fine-scaled correlation and depositional modeling of exploration wells. Removal of the global isotope signal from the regional GOM record permit us to determine the effects of meltwater-fluvial discharge episodes and regional sea level fluctuations on sedimentation along the GOM margin.