Paleo-water Depth Research Articles

Sequence stratigraphy and biozonation of the Upper Eocene Anqabiya Formation, Gebel Anqabiya, Egypt

Few studies on bio-sequence stratigraphy of the late Eocene succession in the study area have published so far. Accordingly, an exposed section of the Anqabiya Formation at Gebel Anqabiya along Cairo–Suez district of Egypt, was examined in detail to determine its foraminiferal and nannoplankton assemblages and to produce a sequence stratigraphic classification. We reveal that in this section, foraminifera and calcareous nannoplankton are generally rare, with relatively poor to moderate preservation, and restricted to certain horizons. Nineteen species of planktonic foraminifera and 24 species of calcareous nannoplankton were identified, leading to the classification of two planktonic foraminiferal zones (Globigerinatheka semiinvoluta Zone E14 and Globigerinatheka index Zone E15) and one calcareous nannoplankton zone (NP19–20). Forty-seven species of benthic foraminifera were identified and quantitatively analyzed to determine changes in paleo-water depth. Three local benthic biofacies, the Elphidium biofacies, the Cibicides biofacies and the Uvigerina biofacies, were recognized, and six microfacies types were distinguished. These analyses indicate that the studied succession was deposited under shallow marine environmental conditions representing a single 3rd-order depositional sequence. The interpreted sea-level curve can be correlated with the global curves during the late Eocene, and the correlation suggests a sea-level rise during E14 Zone, followed by a sea-level fall in E15 zone.

Depositional environments beneath the shelf-edge slopes of the Great Barrier Reef, inferred from foraminiferal assemblages: IODP Expedition 325

To understand sea-level changes since the Last Glacial Maximum (LGM) and their effects on coral reef systems, the shelf-edge slopes of the Great Barrier Reef (GBR) were cored during the Integrated Ocean Drilling Program (IODP) Expedition 325. Recovered unconsolidated sediments beneath the submerged shelf edge reefs contain abundant foraminiferal tests, which record changes in depositional environments and paleo-water depths. A total of 177 sediment samples were collected from 17 holes along three transects located within two geographical areas (Noggins Pass and Hydrographers Passage), and were analyzed to determine stratigraphic changes in foraminiferal assemblages (2–0.5 mm size fraction). Results show that four foraminiferal assemblages (A, B, C and D) are delineated by multivariate analyses (Q-mode cluster analysis and non-metric multidimensional scaling: NMDS), and these assemblages correspond to a back-reef to reef margin zone (0–10 m deep; Assemblage A), an upper photic zone (10–30 m deep) associated with hard substrates (Assemblage B), an intermediate to lower photic zone (30–90 m deep) characterized by soft substrates (Assemblage C), and a lower photic zone (90–130 m deep) only found in modern shelf slopes (Assemblage D). Gradual shifts in these four foraminiferal assemblages superimposed on a two-dimensional NMDS ordination mainly reflect water-depth gradients and the relative dominance of two substrate types (hard and soft substrates). Pre-LGM (older than Marine Isotope Stage 3: ≥MIS3) sediments along transects at Hydrographers Passage were deposited at intermediate to lower photic zones. In contrast, relatively shallow-water sequences found in ≥MIS3 deposits at Noggins Pass likely owe their origin to either turbidite and/or land slide processes. The lack of Assemblage D in ≥MIS3 deposits from all transects could be related to lowering temperature and/or increasing terrestrial influences (i.e. more light attenuation). Shallowing upward sequences found in LGM (MIS 2) deposits at Hydrographers Passage are likely related to stepwise sea-level falls to the full extent of the LGM. These foraminifer-based paleoenvironmental interpretations suggest that the GBR shelf edge slopes have changed their depositional environments continuously in response to sea-level fluctuations during the last glacial cycle.

Relative sea-level change during the Last Interglacial as recorded in Bahamian fossil reefs

Despite an abundance of UTh age data for Last Interglacial fossil corals in the Bahamas, the accuracy and precision of corresponding elevation data are poor, casting uncertainty on existing estimates of peak relative sea level and rates of sea-level change inferred from these deposits. We revisited two key sites at Great Inagua (GI) and San Salvador (SS) Island to test existing hypotheses about (1) the rate of sea level changes during the Last Interglacial period and (2) a possible gradient in peak sea level between these sites. Here, we provide precise elevation survey results for discrete stratigraphic horizons preserved at both locations, where two stages of reef growth are separated by a discontinuity that truncates corals in the lower reef. The discontinuity at Great Inagua manifests as a sharp wave-cut bench, with a maximum elevation of +1.14 m above mean sea level (MSL), that is sub-horizontal on the promontories and gradually slopes seaward in the embayments. At San Salvador, we observed a discontinuity that undulates between +0.85 and + 1.52 m. The uppermost surface of corals in growth position was measured at +1.94 m (GI) and +2.76 m (SS), although in situ collapse and truncation of large Acropora palmata colonies at the latter site implies that primary coral elevations were somewhat higher. Ultimately, assumptions regarding the amount of material truncated and paleowater depth of the observed reef facies at both sites dominate the uncertainty in calculating past sea level position and hence rates of sea-level change. Full consideration of errors associated with age and elevation data implies an ephemeral sea level drop of at least 1 m over a time frame of approximately one thousand years between two peaks in sea level.

The influence of paleo-bathymetry on total organic carbon distribution tested in the Cretaceous Hammerfest Basin, Barents Sea

Abstract In basin modelling and petroleum system analysis geometries during deposition of sediments (paleo-water depth) and distribution of organic matter are initial parameters used for further interpretation or modelling. This paper presents an approach, combining backstripping with a probabilistic forward sedimentary model to calibrate paleo-water depth (PWD). The stochastic PWD results serve as an input for organic facies models and the study demonstrates how PWD will influence models for total organic carbon distribution in a sedimentary basin. For the Early Cretaceous Hammerfest Basin, mainly shelfal to upper bathyal bathymetries (average PWD values vary between 118 and 318 m) result in average total organic carbon (TOC) varying between 0.47 and 5.24 wt% across the basin. For the different models basin averaged TOC values are similar but vertical and lateral distribution pattern change significantly, especially towards the shallow end-member PWD. The results indicate that PWD uncertainties propagate non-linearly into source rock distributions.

Petroleum systems modeling on gas hydrate of the first experimental exploitation region in the Shenhu area, northern South China sea

Two-dimensional gas hydrate petroleum system modeling was conducted to understand gas hydrate accumulation mechanisms and spatial distribution related to geologic and geochemical processes in the first experimental gas hydrate exploitation region in the Shenhu area of the South China Sea. Based on the gas production in core samples, a new biogenic methane generation model was created and incorporated into a kinetic model. With the results of a rock pyrolysis experiment, a thermogenic gas kinetic model for deep formations in the study area was also developed. The entire dynamic evolution process from gas generation to migration and gas hydrate formation and accumulation in the perspective area was simulated with the petroleum system modeling method. The results showed that the gas hydrate stability zone (GHSZ) began to form after 3.88 Ma, and its thickness was greatest when the paleowater depth peaked at 3.66 Ma. The mass of thermogenic gas generation in deep formations is large, and that of biogenic gas in shallow formations is relatively small. Formations that overlap the gas hydrate bearing layers act as cap rocks that prevent the gas from migrating vertically to shallow layers. There was a geological time gap between thermogenic gas generation, migration and GHSZ formation. However, the timing of biogenic gas generation, which is typically of recent generation in the shallow layer, matched well with the formation of the GHSZ. Finally, coupling of the age and space of gas migration and GHSZ formation has allowed gas hydrate accumulation at structural highs in the Shenhu area. The evaluation technique of petroleum system modeling is of great significance for the improvement of gas hydrate exploration in frontier areas in the future, particularly where survey data are limited.

A quantitative model of paleowind reconstruction using subsurface lacustrine longshore bar deposits – An attempt

The paleo-atmospheric flow field is an important component of climate. However, the difficulty of constraining paleowind fields using geological information hinders quantification of paleo-atmospheric conditions. In this paper, it is proposed that the geometric characteristics of lacustrine longshore bars, widespread in both modern and ancient shallow lakes, can be used as proxies for paleowind fields. The self-organizational model of longshore bar formation indicates that bar geometry and dimensions are determined by breaking waves. Accordingly, a simple geometric model is proposed that incorporates empirical constraints, including: 1) the ratio of paleowater depths between bar crest and adjacent landward trough is constant, and 2) the bar landward slope reaches the angle of repose. The model suggests that the parameters longshore bar thickness (t), topographic slope of the bar-basement (α) and paleo-fetch of the basin (F) are sufficient to constrain paleowave conditions, and hence, based on wave statistics and wind-wave relationships, paleowind conditions. The method is then applied to an ancient example, the Dongying Depression in East China, to determine wind direction and strength during part of the Eocene (~45.0–44.2 Ma). The results show that contemporaneous northerly and southeasterly winds existed, with highest wind speeds of 6.9–13.5 m s−1 and 7.5–18.2 m s−1, respectively. These findings provide a new perspective on delineating paleowind conditions. Error analyses reveal that for a sufficiently large lake (fetch exceeding 30 km), calculation errors will be small to negligible, if longshore bar thickness is determined as precisely as possible. The method is applicable only for bars whose formation conforms to the self-organizational model.

High-resolution seismic reflection data acquisition and interpretation, Lake Neusiedl, Austria, northwest Pannonian Basin

A combined 400+ km of single- and multichannel seismic reflection data were acquired on Lake Neusiedl in northeast Austria in May 2013. This geophysical campaign was a multinational academic effort among the Universities of Vienna, Budapest, Bremen, and Southampton. Lake Neusiedl is an exceptionally shallow lake, with an average water depth of only approximately 1.4 m. Although high-resolution single-channel seismic reflection data have been collected before on this lake, the multichannel seismic acquisition, towing a 60 m cable and an air gun behind a retrofitted ferry boat, was a completely new approach in this area. The quality of the multichannel data turned out to be exceptionally good; i.e., the high-frequency data illuminated the subsurface of the lake for the first time, down to the pre-Cenozoic basement at approximately 600 m depth. The most prominent findings of the new data include (1) a consistent southeasterly dip of erosionally truncated Late Miocene (Pannonian) sediments beneath a very thin Holocene mud layer, (2) the presence of major throughgoing fault systems (including a positive flower structure), (3) at least one Pannonian progradational sequence defined by seismic clinoforms indicating a paleowater depth of approximately 40–80 m, (4) flat spots in several locations of the study area corresponding to possibly biogenic gas in a few hundred meters depth beneath the lake, (5) vertical data wipeouts, which are interpreted as gas chimneys reaching the lake bottom, and (6) definition of the pre-Cenozoic basement. Interestingly, the gas chimneys are interpreted to correspond to the well-known gas seeps (“Kochbrunnen”) in Lake Neusiedl, which were originally described as subaqueous water springs on the lake floor responsible for ice-free areas in the lake ice cover during winter.

Sedimentary characteristics and formation mechanisms of lacustrine beach-bars in the fourth member of the Shahejie Formation in the Shubei area, western depression of the Liaohe Oilfield, China

Beach-bars are well developed in the fourth member of the Shahejie Formation in the Shubei area, western depression of the Liaohe oilfield. The fourth member is composed of two three-order sequences, including a lower Sequence 1 (SQ1) and an upper Sequence 2 (SQ2). SQ2, which is the focus of this study, comprises a lowstand systems tract (LST) and a transgressive system tract (TST). Three types of beach-bars have been recognized: shallow-littoral lacustrine sandy beach-bars, semi-deep lacustrine storm-related sandy beach-bars and shallow-littoral lacustrine carbonate beach-bars. Paleo-environments during the deposition of SQ2, including the paleo-geomorphology, paleo-water depth and paleo-source have been reconstructed to determine the formation mechanisms of the different types of beach-bars. The shallow-littoral lacustrine sandy beach-bars formed mainly by waves and currents and were mostly deposited in the LST, where water depths ranged from 3 to 9 m and the terrestrial clast supply is sufficient. The storm-related sandy beach-bars developed in the TST in the southern part of the study area near previously massively deposited sand bodies where there was sufficient water depth to preserve them. The carbonate beach-bars formed primarily in the TST in the Shubei low buried hill belt where there was a lack of terrestrial clast supply and complex, uneven geomorphology that easily gave rise to a lagoonal environment.

Testing the applicability of a benthic foraminiferal-based transfer function for the reconstruction of paleowater depth changes in Rhodes (Greece) during the early Pleistocene.

We present paleo-water depth reconstructions for the Pefka E section deposited on the island of Rhodes (Greece) during the early Pleistocene. For these reconstructions, a transfer function (TF) using modern benthic foraminifera surface samples from the Adriatic and Western Mediterranean Seas has been developed. The TF model gives an overall predictive accuracy of ~50 m over a water depth range of ~1200 m. Two separate TF models for shallower and deeper water depth ranges indicate a good predictive accuracy of 9 m for shallower water depths (0–200 m) but far less accuracy of 130 m for deeper water depths (200–1200 m) due to uneven sampling along the water depth gradient. To test the robustness of the TF, we randomly selected modern samples to develop random TFs, showing that the model is robust for water depths between 20 and 850 m while greater water depths are underestimated. We applied the TF to the Pefka E fossil data set. The goodness-of-fit statistics showed that most fossil samples have a poor to extremely poor fit to water depth. We interpret this as a consequence of a lack of modern analogues for the fossil samples and removed all samples with extremely poor fit. To test the robustness and significance of the reconstructions, we compared them to reconstructions from an alternative TF model based on the modern analogue technique and applied the randomization TF test. We found our estimates to be robust and significant at the 95% confidence level, but we also observed that our estimates are strongly overprinted by orbital, precession-driven changes in paleo-productivity and corrected our estimates by filtering out the precession-related component. We compared our corrected record to reconstructions based on a modified plankton/benthos (P/B) ratio, excluding infaunal species, and to stable oxygen isotope data from the same section, as well as to paleo-water depth estimates for the Lindos Bay Formation of other sediment sections of Rhodes. These comparisons indicate that our orbital-corrected reconstructions are reasonable and reflect major tectonic movements of Rhodes during the early Pleistocene.

The early Quaternary North Sea Basin

The onset of the Quaternary (2.58 Ma) corresponds to significant paleo-environmental events, such as the intensification and southward extension of Northern Hemisphere glaciation. In the North Sea Basin a significant late Cenozoic succession has been identified as a high-resolution archive of paleo-environmental changes during the Pliocene and Pleistocene. However, the identification of the base of the Quaternary has been a long-standing issue owing to lack of stratigraphic calibration. This study incorporates continuous, regional 3D seismic data with high-quality chronostratigraphic markers to map the base-Quaternary surface at high resolution across the entire North Sea. Depth conversion, backstripping, seismic geomorphology and sedimentation rate calculations are integrated to analyse the paleogeographical evolution of the North Sea Basin and its infill of c . 83 × 10 3 km 3 of northward prograding marine to deltaic sediments. The basin is 600 km long from SSE to NNW and largely localized above residual topography of the Mesozoic graben system. During the earliest Quaternary (2.58 – 2.35 Ma) paleo-water depths were c. 300 ± 50 m and solid sedimentation rates (calculated from 0% porosity) c. 32 km 3 ka −1 . The base-Quaternary provides an important marker for further studies of the changing environment of the Quaternary of NW Europe as well as resource and shallow geohazard analysis. Supplementary material: A base Quaternary two-way travel time structure map is available at https://doi.org/10.6084/m9.figshare.c.3900343

Cool eastern rim of the North Pacific during Late Cretaceous time: A seep-carbonate paleothermometry from the Nanaimo Group, British Columbia, Canada

A crater-shaped carbonate body newly recognized in the uppermost Northumberland Formation (Nanaimo Group) of the Canadian Pacific coast, is identified as a remnant of methane seepage during latest Campanian time in the northeastern Pacific region. A two meter-long elliptical mound with central concavity is found on a Cretaceous bedding plane observed at Hornby Island, British Columbia, exposed on an expansive intertidal platform. Microstructures characteristic of carbonate associated with methane seepage are readily observed within the rock body and indicate it was formed near the sediment-water interface. Carbon isotope values of the carbonate range between −45.5 and +4.9‰, where the lowermost values characterize anaerobic oxidation of biogenic methane as the primary process that controlled the carbonate precipitation. Oxygen isotope values also exhibit a wide range of values, from −9.8 to +0.6‰. Areas preserving features of earliest precipitation (i.e., radiaxial bladed calcite and micrite with clotted fabric) on cross-sections exhibit the highest δ18O values and indicate a paleotemperature 8.0±0.7°C for seawater at the seafloor. Development of cool water on uppermost bathyal or outer shelf depths in the northeastern North Pacific is thus implied during the Campanian-Maastrichtian transition. This paleotemperature determination shows a significant variance with those obtained from similar paleo-water depths of the northwestern North Pacific.

Differences in radiocarbon ages among molluscan shells, plant materials, and total organic carbon: An example from the paleo-Changjiang incised-valley fill, China

Radiocarbon dating of samples from the CM97 cores of Late Pleistocene to Holocene sediments in the paleo-Changjiang incised valley, China, was performed, and age differences among molluscan shells, wood and other plant materials, and bulk total organic carbon (TOC) were evaluated. The incised-valley fill consists of fluvial, estuarine, and deltaic deposits in ascending order. In the dating results, samples of wood and other plant materials yielded similar ages to molluscan shell samples. In contrast, in samples from estuarine and deltaic sediments, radiocarbon ages of TOC were systematically older, by up to 6500 calibrated years, than those of molluscan shells. This result suggests that the paleo-Changjiang River transported aged terrigenous organic matter to its mouth. The magnitude of the age offset increased upward within the transgressive estuarine sediments, and the largest offset, ∼4500 calibrated years on average, was observed in the prodelta sediments deposited after the maximum transgression. Grain size, the C/N ratio, δ13C values, and the sediment accumulation rate of the incised-valley-fill sediments and the paleo-water depth indicated a weak terrestrial influence and a strong marine influence in the prodelta sediments. Therefore, the large age offsets in the prodelta sediments likely reflect reworking and resuspension in a strongly tide-dominated setting of sediments deposited earlier on the inner shelf, resulting in the supply of both fine-grained resuspended sediments and old organic carbon to the prodelta in addition to the supply of terrigenous organic carbon from the paleo-Changjiang River. The upward (deepening) increase of the age offset in the estuarine sediments supports this interpretation. The magnitude of the age offset in the past prodelta sediments was comparable to the old radiocarbon ages of the surface sediments in the present prodelta to inner shelf area. This result suggests that the supply, dispersal, recycling, and burial of terrestrial organic carbon on the inner shelf has been mostly stable during the past 8000 years.

Antarctic climate, Southern Ocean circulation patterns, and deep water formation during the Eocene

AbstractWe assess early‐to‐middle Eocene seawater neodymium (Nd) isotope records from seven Southern Ocean deep‐sea drill sites to evaluate the role of Southern Ocean circulation in long‐term Cenozoic climate change. Our study sites are strategically located on either side of the Tasman Gateway and are positioned at a range of shallow (<500 m) to intermediate/deep (~1000–2500 m) paleowater depths. Unradiogenic seawater Nd isotopic compositions, reconstructed from fish teeth at intermediate/deep Indian Ocean pelagic sites (Ocean Drilling Program (ODP) Sites 738 and 757 and Deep Sea Drilling Project (DSDP) Site 264), indicate a dominant Southern Ocean‐sourced contribution to regional deep waters (εNd(t) = −9.3 ± 1.5). IODP Site U1356 off the coast of Adélie Land, a locus of modern‐day Antarctic Bottom Water production, is identified as a site of persistent deep water formation from the early Eocene to the Oligocene. East of the Tasman Gateway an additional local source of intermediate/deep water formation is inferred at ODP Site 277 in the SW Pacific Ocean (εNd(t) = −8.7 ± 1.5). Antarctic‐proximal shelf sites (ODP Site 1171 and Site U1356) reveal a pronounced erosional event between 49 and 48 Ma, manifested by ~2 εNd unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites. This erosional event coincides with the termination of peak global warmth following the Early Eocene Climatic Optimum and is associated with documented cooling across the study region and increased export of Antarctic deep waters, highlighting the complexity and importance of Southern Ocean circulation in the greenhouse climate of the Eocene.

The Sierra del Cuera (Pennsylvanian microbial platform margin) in Asturias, north Spain

ABSTRACT Stratal geometry and lithofacies architecture from carbonate outcrops provide critical information for subsurface prediction of rock types, their spatial distribution, and reservoir quality. Such observations guide and support exploration, appraisal, development, and production strategies. The Pennsylvanian Sierra del Cuera (SDC) carbonate platform outcrop of the Cantabrian Mountains in north Spain offers such information through a seismic-scale cross section of a microbial, unrimmed, and high-relief platform to basin transect, deposited during an icehouse period. The SDC outcrops provide alternative platform margin models to those developed from coral–algal-dominated Neogene carbonate systems and serve as direct analogs for supergiant fields such as Tengiz, Kashagan, and Karachaganak in the Pricaspian Basin of Kazakhstan and potentially for other high-relief platforms with microbial margins. Key features of the SDC platform are (1) a flat-topped platform with a rollover into a steep (30°–40°) and high-relief (600–850 m [1960–2790 ft]) depositional slope and (2) the presence of a microbial boundstone factory from the platform break to nearly 300 m (984 ft) paleowater depth on the slope, stabilized by pervasive marine cementation. The SDC represents a nonactualistic type of carbonate platform margin where the microbial carbonate factory on the upper slope controlled the rate of progradation instead of the platform top–sourced sediment input. These features have significant implications for the interpretation of the evolution and controlling factors of carbonate depositional systems in outcrops and in the subsurface.

Cenozoic North Atlantic deep circulation history recorded in contourite drifts, offshore Newfoundland, Canada

In the North Atlantic Ocean, contour-following deep currents have created regional erosional unconformities and deposited contourite drifts that exceed 2km in thickness and extend for 100s of km. The stratigraphic records in the drifts have been used to reconstruct variations in North Atlantic deep-water circulation throughout the Cenozoic; however, uncertainties remain about certain aspects of the timing, intensity, depth distribution, and regional impact of these currents. Here, we use an integrated dataset of seismic-reflection profiles and IODP core data (lithology, biostratigraphy, and magnetostratigraphy) to document sedimentation history and the development of current effects in the Cretaceous to present sedimentary record on the J-Anomaly Ridge and Southeast Newfoundland Ridge, offshore Newfoundland, Canada. The Newfoundland ridges are in a key location, lying between well-studied areas in the northern and western North Atlantic and under the path of both the modern Deep Western Boundary Current and the Gulf Stream. Late Cretaceous through Early Eocene sedimentation on the ridges was dominated by biogenic pelagic sedimentation, but at ~47Ma, near the Early-Middle Eocene boundary, well developed contourite drifts began to accrete in paleo-water depths of ~4000–4500m, accompanied by an order-of-magnitude increase in terrigenous sediment mass accumulation rates. From this time forward, drift deposition, interrupted by brief episodes of erosion, continued unabated. This timing for the onset of persistent deep currents is coincident with reorganization of Atlantic circulation inferred from a change from biosiliceous to non-biosiliceous sedimentation in the western North Atlantic (Horizon AC) and with the current-eroded Intra-Eocene Unconformity (IEU) in the northern North Atlantic. A change in sedimentation style occurred within the Middle Eocene to upper Oligocene drift sequence, and it likely was related to a shift to deeper, more intense currents that eroded the widespread Horizon AU along the margin of eastern North America about Early Oligocene time. Beginning in the Late Oligocene (~25Ma) a thick drift exhibiting seismically laminated mudwaves was deposited in a distinct belt at ~3500–4500m paleodepth on the Southeast Newfoundland Ridge. This development correlates with widespread Late Oligocene through Miocene-Pliocene drift accumulation throughout the North Atlantic. The most recent phase of drift deposition, since Late Pliocene time (~3Ma), occurred after a shift to the ‘modern’ circulation system of deeper, swifter currents, and it includes mixed pelagic-hemipelagic sediments and ice-rafted debris that reflect glacial-interglacial influences on sedimentation.

Channel-belt scaling relationship and application to early Miocene source-to-sink systems in the Gulf of Mexico basin

In past decades, numerous studies have focused on the alluvial sedimentary record of basin fill. Paleo–drainage basin characteristics, such as drainage area or axial river length, have received little attention, mostly because the paleo–drainage system underwent erosion or bypass, and its record is commonly modified and overprinted by subsequent tectonism or erosional processes. In this work, we estimate the drainage areas of early Miocene systems in the Gulf of Mexico basin by using scaling relationships between drainage area and river channel dimensions (e.g., depth) developed in source-to-sink studies. Channel-belt thickness was used to estimate channel depth and was measured from numerous geophysical well logs. Both lower channel-belt thickness and bankfull thickness were measured to estimate the paleo–water depth at low and bankfull stages. Previous paleogeographic reconstruction using detrital zircon and petrographic provenance analysis and continental geomorphic synthesis constrains independent estimates of drainage basin extent. Comparison of results generated by the two independent approaches indicates that drainage basin areas predicted from channel-belt thickness are reasonable and suggests that bankfull thickness correlates best with drainage basin area. The channel bankfull thickness also correlates with reconstructed submarine fan dimension. This work demonstrates application to the deep-time stratigraphic archive, where records of drainage basin characteristics are commonly modified or lost.

The development of volcanic sequences at rifted margins: New insights from the structure and morphology of the Vøring Escarpment, mid‐Norwegian Margin

AbstractOn the Vøring Margin offshore mid‐Norway, Paleogene continental breakup was characterized by the extrusion of large volumes of flood basalts erupted in different depositional environments. The transition from subaerial to submarine emplacement environment is marked by the formation of the Vøring Escarpment which records the early encroachment of flood basalt into the basin and the buildup of a lava delta system. The increased availability of new and reprocessed high‐quality seismic data allows a more detailed characterization of the along‐strike and across‐strike continuity and variability of the different volcanic seismic facies units. Detailed seismic interpretation shows that the ~350 km long NE‐SW trending Vøring Escarpment is a prominent feature along the Vøring Margin with a height ranging between 200 and 1600 m. Structurally, the Vøring Escarpment is segmented along strike into five segments (E1–E5) with different controlling factors leading to variation in accommodation space. Relative sea level change and magma supply are the major controlling factors for segments E2 and E4 which are characterized by a well‐developed lava delta system and significant escarpment height. Tectonic movements along the Jan Mayen Fracture Zone resulted in second‐order segmentation of the E1 segment into pseudoescarpments with a very thin lava delta system and limited escarpment height. Segments E3 and E5, situated along the flanks of Cretaceous/Paleocene highs, are controlled by the structural highs, which were possibly reactivated during breakup time. Our mapping results provide crucial information about the paleogeography and yield important information regarding the paleo–water depth and depocenter locations prior to and during the breakup of the Vøring Margin.

Impact of eustatic and tectonic processes on the southeastern Mediterranean shelf during the last one million years: Quantitative reconstructions using a foraminiferal transfer function

Benthic foraminifera-based transfer function models provide accurate sea-level reconstructions for shelf and coastal environments around the world. This study presents for the first time results of a foraminiferal transfer function aiming at the reconstruction of relative sea-level in the southeastern Mediterranean shelf during the past one million years. A Weighted Averaging-Partial Least Squares (WA-PLS) regression method was used for the development of the transfer function based on an extensive set of surface samples (modern training data set) from the study area. The transfer function was applied to three shelf sediment successions retrieved from Haifa Bay, Israel. The Modern Analog Technique (MAT) and the random TF test were used to investigate similarity between modern and fossil foraminiferal faunas, testing the reliability and significance of our model for paleowater depth reconstruction. The performance of the WA-PLS transfer functions suggests a strong relationship between the observed and estimated water depths in the modern data set with relatively precise reconstructions of 7.0m (Root Mean Squared error of Prediction) over a water depth range of 3 to 80m. The deepest paleo water depths were reconstructed for the earliest sea-level highstands recorded in the sediment records (MIS 27? and MIS 29?) in the down-faulted boreholes due to tectonic movements, whereas the younger interglacial sedimentary units (MIS 25?, 13, 11, 7, 5.5 and 1) were mostly deposited at <15m water depths or slightly deeper during MIS 7. The relative sea-level history of the southeastern Mediterranean shelf reveals deviations from the global sea-level trend during MIS 5.5, which may have resulted from minor tectonic movements in the study area and/or un-representation of the phase of maximum sea-level in the sediment succession. Our paleowater depth estimates demonstrate a shallowing trend during the Holocene, generally matching other regional Mediterranean sea-level records.

Orbital obliquity cycles recorded in Kuroshio Current region, eastern Asia, around Plio–Pleistocene boundary

Global climate underwent a period of significant cooling at the Plio–Pleistocene Transition (∼2.6 Ma). The influence of this change on the Kuroshio Current region in the Pacific Ocean, off eastern Asia, is not well known. In this study, we clarify temporal changes in the paleoenvironment under the influence of the Kuroshio Current during the late Pliocene and early Pleistocene using high-resolution faunal proxy records of fossil Ostracoda (Crustacea). The study unit is the Ananai Formation in the southeastern region of Shikoku, southwest Japan. The modern analog technique (MAT) is employed for the quantitative estimation of paleo-bottom water temperatures (PBWTs) and paleo-water depth (PWD) during the deposition of the formation. Ostracode MAT results show PBWT fluctuations during warmest and coldest months, with values of 16°C–20 °C and 12°C–16 °C, respectively, and a PWD of 70–140 m, reflecting sea-level oscillations. Moreover, the PBWT in the coldest month is 3 °C–4 °C lower than present-day water temperatures at the same shallow water depths. Temporal changes in these paleoenvironmental variables based on MAT are in good agreement with global oxygen isotope records. Orbital obliquity cycles with 41-kyr periodicity are recorded for the first time in an onshore section in the Kuroshio Current region at the Plio–Pleistocene boundary interval.

Modeling gas hydrate petroleum systems of the Pleistocene turbiditic sedimentary sequences of the Daini-Atsumi area, eastern Nankai Trough, Japan

We have performed 2D and 3D gas hydrate (GH) petroleum systems modeling for the Pleistocene turbiditic sedimentary sequences distributed in the Daini-Atsumi area in the eastern Nankai Trough to understand the accumulation mechanisms and their spatial distribution related to geologic and geochemical processes. High-resolution seismic facies analysis and interpretations were used to define facies distributions in the models. We have created a new biogenic methane generation model based on the biomarker analysis using core samples and incorporated it into our model. Our 2D models were built and simulated to confirm the parameters to be used for 3D modeling. Global sea level changes and paleogeometry estimated from 3D structural restoration results were taken into account to determine the paleowater depth of the deposited sedimentary sequences. Pressure and temperature distributions were modeled because they are the basic factors that control the GH stability zone. Our 2D modeling results suggested that the setting of biogenic methane generation depth is one of the most important controlling factors for GH accumulation in the Nankai Trough, which may be related to the timing of methane upward migration (expulsion) and methane solution process in pore water. Our 3D modeling results suggested that the distribution of sandy sediments and the formation dip direction are important controlling factors in the accumulation of GHs. We also found that the simulated amount of GH accumulation from the petroleum systems modeling compares well with independent estimations using 3D seismic and well data. This suggests that the model constructed in this study is valid for this GH system evaluation and that this type of evaluation can be useful as a supplemental approach to resource assessment.