ABSTRACT About 150 detrital Cr-spinels from the Bovec and Bohinj Cretaceous flysch basins (Southern Alps, Slovenia) have been analyzed via Raman spectroscopy to verify if such technique can be effective in determining their provenance. Because one of the most used diagrams for assigning the provenance of Cr-spinels is the Cr/(Cr+Al) [Cr#] vs. Mg/(Mg+Fe2+) [Mg#] diagram, we relate these parameters to the Raman peaks. The correlation between the Cr# and the A1g peak position is about 0.93, increasing to 0.95 for Cr-spinels with Cr# lower than 0.5. Unfortunately, the Mg# correlation is only about 0.70 for the whole dataset but increases to 0.82 for spinels with Cr# lower than 0.5. Such correlation differentiates Cr-spinels from lherzolite and/or abyssal peridotite and distinguishes them from harzburgite, layered intrusions, and Uralo–Alaskan complexes. Many of the present spinels are characterized by several inclusions. By using spot analyses and 3-D Raman mapping on such inclusions we are to recognize pyroxene-, feldspar-, and amphibole-like inclusions, better constraining the provenance of the spinels.
Hyperpycnal fan deltas (HFDs) represent a distinct deltaic model where subaqueous progradation is governed by sustained, flood-generated hyperpycnal flows, which differ significantly from subaerial deltas, Gilbert-type deltas, or wave-, and tide-dominated deltas. Using the Lower Cretaceous Bantou Formation (SE China) as a rift-lake case study, this paper documents the diagnostic facies architecture and flow evolution of HFDs that seem to be a compound delta. The subaerial clinoform (delta) has deposits of terrestrial debris flows and braided channels, reflecting a conventional fan-delta setting, while sandy-gravelly hyperpycnites dominate the delta-front part of the subaerial clinoform. In contrast, the subaqueous clinoform (delta) is composed of muddy hyperpycnites and fluid-mud deposits. Inferred hyperpycnites form amalgamated composite beds with basal inverse grading and they sometimes develop laminae enriched in plant debris ("lofting rhythmites"). Fluid-mud deposits refer to nonbioturbated mudstones. Inferred muddy to sandy hyperpycnites and fluid-mud deposits are stacked to form coarsening-upwards cycles representing delta progradation. Vertical facies successions reflect downstream evolution of hyperpycnal flows, with a trend from sediment-laden turbulent flow to transitional flow. Clay minerals were transported as clay flocs. In distal settings, hyperpycnal flow and hypopycnal flow may entrain these flocs and promote generation of fluid-mud flow. Clay flocs and plant debris can be deposited because of basinal shear sorting in transitional flow with collapse of a lofting plume or because of suspension settling of fluid-mud flow. Therefore, such flow evolution produces pronounced sedimentary differentiation in the HFD, and its sedimentation rates could be like that of other deltas. HFDs are likely under-recognized in the geological record, particularly in shallow-shelf and lacustrine basins with high suspended-sediment loads. This study emphasizes the critical role of hyperpycnal flows and associated fluid-mud flow in deltaic progradation and provides insights into explaining lacustrine and deltaic facies and its source-to-sink systems.
Despite the importance of equivalent strata in multiple basins as oil, gas, and saltwater disposal reservoirs, and a recent rise in associated seismicity hazards, there remains a lack of modern outcrop studies of the Silurian to Furthermore, dolomitization and silicification, apparent lithologic homogeneity, and severe post depositional erosion prevent identification of Silurian eustatic signals that are evident in other regions. The Fusselman Formation lacks a high-resolution stratigraphic framework, hindering predictive mapping and efforts to relate this unit to coeval strata elsewhere. To address these deficiencies, this study applies a suite of high-resolution outcrop measurements, including spectral gamma ray, Leeb rebound hammer, outcrop image analysis (prevalence of vugs and chert), and reflected-light microscopy (dolomite crystal size), alongside analysis of carbonate-rock facies to six measured sections. These techniques reveal previously obscure stratigraphic relationships. The sections cover both the Fusselman Formation and the underlying Upper Ordovician Montoya Group, which was deposited in a similar setting to the Fusselman Formation but already has an established high-resolution sequence stratigraphic framework. Locations record a loosely distal-to-proximal transect. The Fusselman Formation contains six third-order depositional sequences near its type location in the northern Franklin Mountains. Sequences FT1-FT5 (four complete, one partial) correspond to the four globally established sea-level fluctuations during the Llandovery Epoch of the Silurian. In contrast, FT6 spans the Middle Silurian (Wenlockian) through earliest Devonian but relationships to specific highstand-lowstand episodes are unclear. Post depositional karsting and burial diagenesis may mask higher-frequency cyclicity in FT6. Parts of these sequences thin, become amalgamated, or are truncated by erosion in more proximal locations. The ramp geometries and associated ramp-crest facies change in successive sequences. Shallowing-upwards successions are developed in the lower part of the Fusselman Formation (Sequences FT1-FT3) but become less distinct in the upper sequences (FT4-FT6). This study establishes the first high-resolution chronology and calibration to the global sea-level curve for the Silurian of centralsouthern Laurentia and demonstrates a repeatable method for identifying internal stratigraphy in homogeneous, highly altered Paleozoic carbonate successions in outcrop and subsurface.
ABSTRACT Sequence stratigraphy is a vital tool for interpreting stratal records and paleoenvironmental changes; however, its application to rift basins is often oversimplified using passive-margin models that neglect the complex interplay between eustasy and tectonic controls. In rift basins, the dynamic coupling of axial and transverse sediment systems forms a complex routing network that profoundly influences basin architecture and facies distribution. We present a coupled numerical model that integrates multi-directional sediment sources with tectonic subsidence and eustatic sea-level cycles. By systematically investigating the ratios between the basin-equilibrium timescale (Teq), the tectonic timescale (Tt), and the sea-level-forcing duration (Tz), we evaluate stratigraphic responses across varying forcing scenarios. Our results reveal that key horizons, such as sequence boundaries and maximum flooding surfaces, are inherently fragmented and diachronous, particularly toward the hanging-wall margin where accommodation is rapidly exhausted. Notably, “up-strike” segments (e.g., the Jeju Basin) can maintain a significant marine fraction (approximately 25–30% in our model), even in regions traditionally perceived as terrestrially dominated. This preservation is facilitated by localized depocenters and transgressive bays formed through the interaction of multi-sourced sediment supply and tectonic subsidence. This study provides a rigorous quantitative framework and a stratigraphic model for re-evaluating the depositional history and hydrocarbon potential of underexplored segments in tectonically active extensional basins.
Sedimentary analcime holds dual significance as a proxy for paleoenvironmental reconstruction and a tracer for material transport processes; however, its genesis within fine-grained sedimentary successions remains a subject of considerable debate. The Eocene lower Shahejie Formation in the Huanghua Depression, Bohai Bay Basin of East China, serves as an ideal natural laboratory to address this issue, where analcime occurs in three modes: (1) disseminated matrix constituents; (2) ellipsoidal or patchy aggregates; and (3) pore-filling crystals within microfractures and vugs. The ubiquitous matrix analcime, characterized by a spherical morphology and low Si/Al ratios (mean: 2.17), formed through the interaction of weathering-derived mafic colloids with highly alkaline and saline lake waters resulting from solar evaporation under an arid paleoclimate. Ellipsoidal and patchy aggregates likely reflect the in-situ alteration of basaltic glass shards; however, the absence of thick tuffs and mercury anomalies, coupled with the consistent presence of fine-grained (~2–3 μm) matrix analcime, suggests that volcanic inputs were limited to short-lived, distal events. Pore-filling analcime, distinguished by high homogenization temperatures (140–266 °C), large euhedral crystals (>16 μm), and low 87Sr/86Sr ratios (0.709030–0.710234), probably originated from the circulation of hydrothermal fluids driven by local mafic intrusions. This hydrothermal circulation and alteration was spatially highly restricted, which is supported by the similarity in pyrolysis Tmax values between rocks adjacent to pore-filling analcime (mean: 430 °C) and whole rocks (mean: 434 °C). Additionally, the higher Si/Al ratios of pore-filling analcime (mean: 2.28) relative to matrix analcime (mean: 2.17) and the preservation of the subhedral to anhedral morphology of carbonate minerals confirm the localized extent of this hydrothermal overprint. This study demonstrates the complexity of analcime origin in sedimentary settings and provides an alternative framework for understanding the accumulation of widely distributed analcime in such deposits.
