Early Transgression Research Articles

Sedimentary evolution since the late Last Deglaciation in the western North Yellow Sea

To decipher the sedimentary evolution and environmental changes since the late Last Deglaciation, two gravity cores were analyzed from the western North Yellow Sea (NYS). The two cores (B-L44 and B-U35) were sampled for grain size, clay minerals, detrital minerals, and 14C dating. They are comparable in lithofaies, and the observed succession was divided into four depositional units based on lithology and mineral assemblages, which recorded the postglacial transgression. Depositional unit 4 (DU 4) (before 11.5 ka) was characterized with enrichment in sand, and was interpreted as nearshore deposits in shallow water during the Younger Dryas Event. DU 3 (11.5–9.6 ka) displayed a fining-upward succession composed of sediments from local rivers, such as the Huanghe (Yellow) River, and from coastal erosion, which clearly were related to the Early Holocene transgression. Stable muddy deposition (DU 2) in NYS began to form at about 9.6 ka, which received direct supply of fine materials from the Shandong subaqueous clinoform. It is believed that the Yellow Sea circulation system played a major role in controlling the formation of fine sediment deposition in DU 1 (after 6.4 ka) after the sea level maximum.

Stable isotope (δ 13C carb and org, δ 15N org) and trace element anomalies during the Late Devonian ‘ punctata Event’ in the Western Canada Sedimentary Basin

Late Devonian marine deposits in the Western Canada Sedimentary Basin were analyzed for (1) accumulations of bioproductivity and paleoredox trace element proxies and for (2) variations of δ 13C (carb and org) and δ 15N org in order to understand and interpret the regional history of the global yet short-term ‘ punctata Event’ geochemical perturbation. Statistical correlations suggest that changes in detrital input and associated micronutrient delivery were the main driver of a eutrophication event noted early and possibly also late in the punctata zone around the isolated Miette platform, manifested by increased TOC, positive δ 13C excursions and concurrent enrichments of all elemental proxies. Evaluation of data within a regional sequence stratigraphic perspective revealed a eustatic sea level influence, with proxy accumulations associated mostly with early transgression (IIc1). Deposition and preservation of organic matter-rich facies occurred during conditions of enhanced primary production and facilitated bottom water suboxia–anoxia. Following eutrophication, lower δ 15N org and δ 13C org values predominated and persisted throughout much of the punctata zone before rebounding toward its close, suggesting a time interval of environmental stagnation and lower overall productivity during which N 2-fixing autotrophs may have had an ecological advantage under nitrate-limited conditions. The punctata Event approximately coincided with the advent of archaeopterid forest expansion beginning around mid-Frasnian time, which fundamentally altered the nature of continental weathering through extensive soil formation and increased nutrient delivery to the oceans. This evolutionary event may have amplified the detrital influx, already elevated by sea level lowstand and early transgression and increased denudation of rising mountain ranges in near-equatorial regions.

'Cape capture': Geologic data and modeling results suggest the Holocene loss of a Carolina Cape

For more than a century, the origin and evolution of the set of cuspate forelands known as the Carolina Capes—Hatteras, Lookout, Fear, and Romain—off the eastern coast of the United States have been discussed and debated. The consensus conceptual model is not only that these capes existed through much or all of the Holocene transgression, but also that their number has not changed. Here we describe bathymetric, lithologic, seismic, and chronologic data that suggest another cape may have existed between Capes Hatteras and Lookout during the early to middle Holocene. This cape likely formed at the distal end of the Neuse-Tar-Pamlico fluvial system during the early Holocene transgression, when this portion of the shelf was flooded ca. 9 cal (calibrated) kyr B.P., and was probably abandoned by ca. 4 cal kyr B.P., when the shoreline attained its present general configuration. Previously proposed mechanisms for cape formation suggest that the large-scale, rhythmic pattern of the Carolina Capes arose from a hydrodynamic template or the preexisting geologic framework. Numerical modeling, however, suggests that the number and spacing of capes can be dynamic, and that a coast can self-organize in response to a high-angle-wave instability in shoreline shape. In shoreline evolution model simulations, smaller cuspate forelands are subsumed by larger neighbors over millennial time scales through a process of ‘cape capture.’ The suggested former cape in Raleigh Bay represents the first interpreted geological evidence of dynamic abandonment suggested by the self-organization hypothesis. Cape capture may be a widespread process in coastal environments with large-scale rhythmic shoreline features; its preservation in the sedimentary record will vary according to geologic setting, physical processes, and sea-level history.

Cross-Basin Variations in Magnetic Susceptibility Influenced by Changing Sea Level, Paleogeography, and Paleoclimate: Upper Devonian, Western Canada Sedimentary Basin

Abstract Upper Devonian rocks in western Canada were deposited as carbonate-platform and surrounding slope and basinal rocks during a second-order sea-level cycle, characterized by long-term climatic warming, that ended with cooling associated with the Frasnian–Famennian mass-extinction event. In this contribution, we assess the hypothesis that high-resolution magnetic susceptibility (MS) data records cross-basin variations that are intimately tied to sea level and associated climatic change, the depositional environment, and the paleogeographic location of siliciclastic sediment sources. Four main trends are apparent in the MS data: (1) the magnitude of the MS signature increases from west to east across western Canada; (2) platform facies generally have low MS signatures compared with off-platform facies; (3) the overall MS signature increases and then decreases throughout the stratigraphic profile, largely in response to changes in depositional setting (i.e., item 2); (4) MS is generally high during third- and fourth-order sea-level lowstand and early transgression and lower during late transgression and highstand. During the late Middle (Givetian) to early Late (Frasnian) Devonian, siliciclastic sediments (silt and fine sand size) sourced from the west Alberta arch and Peace River arch, contributed to relatively high MS signatures in facies deposited proximal to these source areas. Other important detrital sediment sources were the Ellesmerian orogenic belt in northern Canada and the Laurussian continental landmass to the east. These latter sources supplied fine-grained sediments that were dispersed basinwide and resulted in a nearly order-of-magnitude increase in MS values to the east. This trend and fine grain size implies that some detrital sediment was delivered from the east as eolian dust from the “Old Red Continent.” By the early Frasnian, the west Alberta arch was submerged, and by middle to late Frasnian time the Peace River arch was largely covered. During the late middle Frasnian a pronounced rise in MS signatures can be tied directly to deposition of the clay- and locally silt-rich Mount Hawk Formation. During the late middle to late Frasnian, carbonate-ramp facies prograded from east to west, resulting in seaward migration of the shoreline and increased siliciclastic input to the ramp slope that influenced the pronounced increase in MS signatures to the east. By the late Frasnian, cross-basin MS profiles record uniformly low susceptibilities indicating that high MS siliciclastic detritus was either bypassed seaward, was swamped by carbonate input, or was dominated by diamagnetic quartz. Individual MS events can be accurately correlated across much of the basin at a resolution that is higher than single conodont zones despite the local influences on variability of the signature. Variations in the MS signature can thus be explained partly by depositional environment (platforms with low MS, basins with higher MS) and partly by third- and fourth-order sea-level and associated climatic changes. Fourth-order changes in sea level are routinely interpreted to result from variations in paleoclimate in the Milankovitch band and recent work indicates that third-order sea-level changes may be linked to longer-term modulation of Milankovitch-band orbital variations. The increase in MS during prolonged Frasnian warming thus appears to be directly linked to paleoclimatic change, and comparison of the MS signature with more direct measures, like oxygen isotopes, would serve as a test of its utility as a paleoclimate proxy.

Sequence stratigraphy of Cenomanian–Turonian carbonate platform margins (Sarvak Formation) in the High Zagros, SW Iran: an outcrop reference model for the Arabian Plate

Abstract A high resolution sequence stratigraphic model has been constructed for the mid-Cretaceous Sarvak Formation (in the High Zagros region of SW Iran) which was deposited close to the eastern margin of the Arabian Plate. The exceptional outcrop quality, displaying the detailed facies patterns in the transition zone from carbonate platform to intra-shelf basin, offers the rare opportunity to distinguish between the relative control of carbonate sediment supply (S) and accommodation (A) on the depositional geometries of third- and fourth-order depositional sequences. Four third-order sequences have been distinguished in the Sarvak Formation, with a duration varying between 1.5 and 3 Ma, and a thickness of 50–150 m. These are in turn composed of fourth- and fifth-order sequences that form the stratigraphic building blocks of this carbonate system. A significant distinction has been made in the third-order sequences between the early transgression (e-TST) when the system was still flat, and corresponds to a ramp setting, and the late transgression (l-TST) when the carbonate platform to intra-shelf basin topography was created. The rate of accommodation creation is identified as the dominant factor controlling the morphology of the depositional profile, and, as such, the driving motor behind the dynamics of this type of carbonate system. The dip angle of the depositional profile has a major influence on: (1) the hydrodynamics of the system; (2) the type of carbonate sediment; and (3) the volume of carbonate sediment produced. A good correlation with the third-order sequences of the Natih Formation in Oman is demonstrated, which supports a dominant control by eustatic sea-level changes and a similar response of the carbonate system to changes in the rate of sea-level rise on the southern part of the Arabian Plate. This outcrop analogue can be considered as a good reference model for the Cenomanian–Turonian carbonate platform margins of the Arabian Plate, but also as a textbook example of the response of carbonate systems to sea-level fluctuations (relative influence of accommodation and sediment supply).

Factors controlling regional spatial distribution of 53 elements in coastal sea sediments in northern Japan: Comparison of geochemical data derived from stream and marine sediments

Abstract In all, 53 elements were analyzed in 1406 coastal sea sediment samples collected from an area off Hokkaido and the Tohoku region of Japan during a nationwide marine geochemical mapping project. The spatial distribution patterns of the elemental concentrations in coastal seas along with the existing geochemical maps in terrestrial areas were used to define natural geochemical background variation and mass transport processes. The terrestrial area is covered by mafic volcanic rocks and accretionary complexes associated with ophiolite, which has small amounts of felsic volcanic rocks and granite. The spatial distribution patterns of elements enriched in mafic lithologies such as Fe (Total Fe 2 O 3 ) and Sc in marine environments are influenced by adjoining terrestrial materials. The spatial distribution patterns of Cr and Ni concentrations, which are highly abundant in ultramafic rocks on land, are used to evaluate the mass transport from land to the sea and the dispersive processes caused by oceanic currents. The scale of mass transport by oceanic currents occurs up to a distance of 100–200 km from the coast along the coastal areas. The regional differences of elements rich in felsic lithologies such as K (K 2 O), Nb and La in marine sediments are determined mainly by the relative proportion of minerals and lithic fragments enriching felsic materials to those associated with mafic materials. The spatial distribution of elemental concentration is not always continuous between the land areas and coastal sea areas. That difference is interpreted as resulting from (1) transportation of marine sediments by oceanic currents and storm waves, (2) contribution of volcanic materials such as tephra, (3) occurrence of shell fragments and foraminifera tests and (4) distribution of relict sediments of the last glacial age and early transgression age. Contamination with Cu, Zn, Cd, As, Mo, Sn, Sb, Hg, Pb and Bi was not observed in marine environments because the study area has little anthropogenic activity. Terrestrial materials are the dominant source for these metals. The Mo, Cd, Sn, Sb, Hg, Pb and Bi are abundant in silty and clayey sediments locally because of early diagenetic processes, authigenic precipitation and organic substances associated with these elements. The spatial distribution of As concentration shows exceptions: it is concentrated in some coarse and fine sands on the shelf. The enrichment is explained by adsorption of As, sourced from a coal field, to Fe hydroxide.

Tectonic controls on nearshore sediment accumulation and submarine canyon morphology offshore La Jolla, Southern California

CHIRP seismic and swath bathymetry data acquired offshore La Jolla, California provide an unprecedented three-dimensional view of the La Jolla and Scripps submarine canyons. Shore-parallel patterns of tectonic deformation appear to control nearshore sediment thickness and distribution around the canyons. These shore-parallel patterns allow the impact of local tectonic deformation to be separated from the influence of eustatic sea-level fluctuations. Based on stratal geometry and acoustic character, we identify a prominent angular unconformity inferred to be the transgressive surface and three sedimentary sequences: an acoustically laminated estuarine unit deposited during early transgression, an infilling or “healing-phase” unit formed during the transgression, and an upper transparent unit. Beneath the transgressive surface, steeply dipping reflectors with several dip reversals record faulting and folding along the La Jolla margin. Scripps Canyon is located at the crest of an antiform, where the rocks are fractured and more susceptible to erosion. La Jolla Canyon is located along the northern strand of the Rose Canyon Fault Zone, which separates Cretaceous lithified rocks to the south from poorly cemented Eocene sands and gravels to the north. Isopach and structure contour maps of the three sedimentary units reveal how their thicknesses and spatial distributions relate to regional tectonic deformation. For example, the estuarine unit is predominantly deposited along the edges of the canyons in paleotopographic lows that may have been inlets along barrier beaches during the Holocene sea-level rise. The distribution of the infilling unit is controlled by pre-existing relief that records tectonic deformation and erosional processes. The thickness and distribution of the upper transparent unit are controlled by long-wavelength, tectonically induced relief on the transgressive surface and hydrodynamics.

Post-rift marine transgression of the southern Browse Basin margin: controls on hydrocarbon reservoir development and exploration potential

The formation of the Precipice Fold Belt (560 Ma) marked the last significant modification of the basement drainage pattern and catchment area supplying sediment to the southern Browse Basin. Seismic mapping of the Proterozoic basement and the results of exploration drilling confirm the extension of both the geological formations and structural features exposed on the Proterozoic Kimberley Plateau into the offshore study area. As with the present-day shelf, sedimentation during the Late Jurassic to Early Cretaceous marine transgression directly onlapped the basement in the study area and showed the influence of basement topography on stratigraphy. A marked increase in net-to-gross and reservoir sand thickness is observed moving northeast from the Leveque to the Yampi shelves. This broad change in stratigraphy can be related to specific basement-controlled morphologies. A >250 m-high escarpment formed by the Proterozoic Kimberley Plateau basement terrane bounds the Yampi Shelf to the southeast of the Palaeozoic zero-edge line. This escarpment fixed the location of shelf sediment input points forming a barrier to marine transgression, which ensured that the Yampi Shelf was relatively immune from sediment starvation during highstand systems tracts. In contrast, the broad low angle Leveque Shelf experienced large lateral shifts in shelf sediment input points during eustatic changes in sea level with sedimentation dominated by transgressive systems tracts. In addition to shelf morphology, the larger basement-controlled drainage area (80,000 km2) supplying sediment to the Yampi Shelf tended to increase sedimentation rates, leading to shelf delta progradation during highstand systems tracts. The quality and thickness of mass flow deposits seen in the Caswell Sub-basin and along the Prudhoe Terrace are the direct result of the concentration of high net-to-gross sand close to the offlap break on the Yampi Shelf. Given the extreme long term stability of the southern Browse Basin margin, recognition of the influence of basement structure on shelf sedimentation has refined the geological model for the post-rift marine transgression. This model could be used to reduce the risk on reservoir and seal distributions in the Late Jurassic to Early Cretaceous study interval. In a broader context, observations on basement-controlled reservoir and seal distribution from the Browse Basin might be usefully applied to other basins where sediment is supplied from long-lived Proterozoic margins.

Late Quaternary siliciclastic/carbonate sedimentation model for the Capricorn Channel, southern Great Barrier Reef province, Australia

A model is presented for hemipelagic siliciclastic and carbonate sedimentation during the last glacial–interglacial cycle in the Capricorn Channel, southern Great Barrier Reef (GBR). Stable isotope ratios, grainsize, carbonate content and mineralogy were analysed for seven cores in a depth transect from 166 to 2892 m below sea level (mbsl). Results show variations in the flux of terrigenous, neritic and pelagic sediments to the continental slope over the last sea level cycle. During the glacial lowstand terrigenous sediment influenced all the cores down to 2000 mbsl. The percentages of quartz and feldspar in the cores decreased with water depth, while the percentage of clay increased. X-ray diffraction analysis of the glacial lowstand clay mineralogy suggests that the siliciclastic sediment was primarily sourced from the Fitzroy River, which debouched directly into the northwest sector of the Capricorn Channel at this time. The cores also show a decrease in pelagic calcite and an increase in aragonite and high magnesium calcite (HMC) during the glacial. The influx of HMC and aragonite is most likely from reworking of coral reefs exposed on the continental shelf during the glacial, and also from HMC ooids precipitated at the head of the Capricorn Channel at this time. Mass accumulation rates (MARs) are high (13.5 g cm − 3 kyr − 1 ) during the glacial and peak at ~ 20 g cm − 3 kyr − 1 in the early transgression (16–14 ka BP). MARs then decline with further sea level rise as the Fitzroy River mouth retreats from the edge of the continental shelf after 13.5 ka BP. MARs remain low (4 cm − 3 kyr − 1 ) throughout the Holocene highstand. Data for the Holocene highstand indicate there is a reduction in siliciclastic influx to the Capricorn Channel with little quartz and feldspar below 350 mbsl. However, fine-grained fluvial sediments, presumably from the Fitzroy River, were still accumulating on the mid slope down to 2000 mbsl. The proportion of pelagic calcite in the core tops increases with water depth, while HMC decreases, and is present only in trace amounts in cores below 1500 mbsl. The difference in the percentage of HMC in the deeper cores between the glacial and Holocene may reflect differences in supply or deepening of the HMC lysocline during the glacial. Sediment accumulation rates also vary between cores in the Capricorn Channel and do not show the expected exponential decrease with depth. This may be due to intermediate or deep water currents reworking the sediments. It is also possible that present bathymetry data are too sparse to detect the potential role that submarine channels may play in the distribution and accumulation of sediments. Comparison of the Capricorn Channel MARs with those for other mixed carbonate/siliciclastic provinces from the northeast margin of Australia indicates that peak MARs in the early transgression in the Capricorn Channel precede those from the central GBR and south of Fraser Island. The difference in the timing of the carbonate and siliciclastic MAR peaks along the northeast margin is primarily related to differences in the physiography and climate of the provinces. The only common trend in the MARs from the northeast margin of Australia is the near synchronicity of the carbonate and siliciclastic MAR peaks in individual sediment cores, which supports a coeval sedimentation model.

A new view on Bathonian ostracods of Poland

The Bathonian ostracod fauna from Central Poland (Czestochowa region) has been restudied from nearly all ammonite zones. Forty nine well preserved, autochthonous species could be documented; some further, presumably new, taxa were kept in open nomenclature. According to the ostracod fauna, the European palaeobasin was subdivided during the Bathonian into two palaeobiogeographical provinces. According to ammonite data this subdivision existed only in Callovian time. We suggest a sublatitudinal link between the western and eastern bioprovinces that was present during the Bajocian, became restricted during the Bathonian and reopened during the early Callovian transgression.

Benthic Foraminiferal response to sea level change in the mixed siliciclastic‐carbonate system of southern Ashmore Trough (Gulf of Papua)

Ashmore Trough in the western Gulf of Papua (GoP) represents an outstanding modern example of a tropical mixed siliciclastic‐carbonate depositional system where significant masses of both river‐borne silicates and bank‐derived neritic carbonates accumulate. In this study, we examine how benthic foraminiferal populations within Ashmore Trough vary in response to sea level–driven paleoenvironmental changes, particularly organic matter and sediment supply. Two 11.3‐m‐long piston cores and a trigger core were collected from the slope of Ashmore Trough and dated using radiocarbon and oxygen isotope measurements of planktic foraminifera. Relative abundances, principal component analyses, and cluster analyses of benthic foraminiferal assemblages in sediment samples identify three distinct assemblages whose proportions changed over time. Assemblage 1, with high abundances of Uvigerina peregrina and Bolivina robusta, dominated between ∼83 and 70 ka (early regression); assemblage 2, with high abundances of Globocassidulina subglobosa, dominated between ∼70 and 11 ka (late regression through lowstand and early transgression); and assemblage 3, with high abundances of neritic benthic species such as Planorbulina mediterranensis, dominated from ∼11 ka to the present (late transgression through early highstand). Assemblage 1 represents heightened organic carbon flux or lowered bottom water oxygen concentration, and corresponds to a time of maximum siliciclastic fluxes to the slope with falling sea level. Assemblage 2 reflects lowered organic carbon flux or elevated bottom water oxygen concentration, and corresponds to an interval of lowered siliciclastic fluxes to the slope due to sediment bypass during sea level lowstand. Assemblage 3 signals increased off‐shelf delivery of neritic carbonates, likely when carbonate productivity on the outer shelf (Great Barrier Reef) increased significantly when it was reflooded. Benthic foraminiferal assemblages in the sediment sink (slopes of Ashmore Trough) likely respond to the amount and type of sediment supplied from the proximal source (outer GoP shelf).

Late Pleistocene and Holocene sedimentation, organic‐carbon delivery, and paleoclimatic inferences on the continental slope of the northern Pandora Trough, Gulf of Papua

We investigated sediment and organic‐carbon accumulation rates in two jumbo piston cores (MV‐54, MV‐51) retrieved from the midslope of the northeastern Pandora Trough in the Gulf of Papua, Papua New Guinea. Our data provide a first assessment of mass fluxes over the past ∼33,000 14C years B.P. and variations in organic‐carbon sources. Core sediments were analyzed using a suite of physical properties, organic geochemistry, and micropaleontological measurements. MV‐54 and MV‐51 show two periods of rapid sediment accumulation. The first interval is from ∼15,000 to 20,400 Cal. years B.P. (MV‐51: ∼1.09 m ka−1 and ∼81.2 g cm−2 ka−1) and the second occurs at >32,000 14C years B.P. (∼2.70 m ka−1 and ∼244 g cm−2 ka−1). Extremely high accumulation rates (∼3.96 m ka−1; ∼428 g cm−2 ka−1) characterize 15,800−17,700 Cal. years B.P. in MV‐54 and likely correspond to early transgression when rivers delivered sediments much closer to the shelf edge. A benthic foraminiferal assemblage in MV‐51 from ∼18,400 to 20,400 Cal. years B.P. indicates a seasonally variable flux of organic carbon, possibly resulting from enhanced contrast between monsoon seasons. The oldest sediments, >32,000 14C years B.P., contain TOC fluxes >200 g cm2 ka−1, with >50% of it derived from C3 vascular plant matter. Magnetic susceptibility values are 2 to 3 times higher and benthic foraminiferal accumulation rates are 6 times higher during this interval than at any younger time, indicating a greater influence of detrital minerals and labile organic carbon. The MS data suggest more direct dispersal pathways from central and eastern PNG Rivers to the core site.

Numerical Modeling of Tides in the Late Pennsylvanian Midcontinent Seaway of North America with Implications for Hydrography and Sedimentation

Abstract A novel numerical model (the Imperial College Ocean Model, ICOM) is used to simulate tidal circulation in shallow epicontinental seas connected to large, open oceans. ICOM is validated using the present-day North Sea and applied to predict tidal range in the late Pennsylvanian Midcontinent Seaway (LPMS) of North America. The model simulates the effect of the principal tidal constituents (astronomical tides) as well as the tide propagating from the adjacent open ocean (co-oscillating tide). Two base-case Pennsylvanian paleogeographies were tested: (1) a maximum sea-level highstand and (2) the early stages of a transgression. Sensitivity tests determined the importance of paleo-water depth and coastline uncertainty on the prediction of tidal range. During the highstand, tidal ranges in the craton interior (Midcontinent Shelf, Illinois and Appalachian basins) are consistently predicted as microtidal (< 2 m tidal range). Such low tidal ranges would have inhibited water-body mixing in the LPMS, promoting stratification. This, combined with the influx of oxygen-poor water from the Permian Basin to the west and high organic input from tropical rivers, may have contributed to the deposition of core black shales in LPMS cyclothems. Conversely, a mesotidal to macrotidal diurnal (once-daily tide) regime is predicted for the early transgression in a large-scale embayment in eastern Kansas due to resonant amplification of diurnal tidal constituents. Pennsylvanian strata here have been ascribed to a mesotidal to macrotidal setting and include cyclic rhythmites that suggest a strongly diurnal system, as predicted by ICOM.

Age of Khvalynian transgressions in the Caspian Sea region

As follows from a geomorphologic analysis of the Khvalynian sediments in the North Caspian region, radiocarbon dating of their molluskan and plant remains provided more or less reliable age estimates, according to which the Khvalynian transgression occurred approximately 11-20 ka B.P. This value corre- sponds, however, to the terminal transgressive-regressive phase of the latter, i.e., rather to the Late Khalynian transgression than to its Early Khvalynian peak. It is inferred that the high terraces that formed during the max- imal Early Khvalynian transgression are unambiguously older, being 70 to 40 ka in age.

Late Quaternary climatic evolution of the Arno coastal plain (Western Tuscany, Italy) from subsurface data

A multidisciplinary study of a 105-m-long core was carried out on the Tyrrhenian coast of Tuscany, Western Italy. Detailed description of sedimentary facies, foraminifer and ostracod assemblages, pollen, and 14C ages is presented in this paper. Identification in core of two transgressive surfaces (TSs) as the most prominent stratigraphic markers allows subdivision of the Late Quaternary stratigraphic succession into two transgressive–regressive (T–R) sequences, attributed to the last 150 kyr BP. Sequence boundaries have no unequivocal physical expression in the core. Detailed pollen analysis documents a direct relationship between vertical facies evolution and climate fluctuations. Coastal to shallow-marine sediments in the lower part of T–R sequences were deposited during the last two interglacial periods (OIS 1 and 5e), under rising sea-level conditions and during the following sea-level highstands. By contrast, alluvial sedimentation (upper part of T–R sequences) took place during periods of sea-level fall and subsequent sea-level lowstands, and was invariably linked to the onset of glacial periods (OIS 4–2 and 6, respectively). This paper presents the first detailed facies documentation of a Late Quaternary incised-valley fill sequence from Italy. About 51 m of Holocene sediments are recorded beneath the present Arno River valley. Early transgression is documented in the lower part of the incised-valley fill by wave-dominated estuarine facies overlying lowstand fluvial deposits. Late transgression records the rapid landward migration of a beach-barrier system, followed by the establishment of an open-marine environment. Highstand sedimentation is represented by a shallowing-upward succession, which reflects progradation of the modern delta/strandplain.

Palaeoclimatic inferences from upper Palaeozoic siltstone of the Earp Formation and equivalents, Arizona‐New Mexico (USA)

AbstractThe Late Palaeozoic configuration of Pangaea contributed to a palaeoclimatic extreme that was characterized by both icehouse and monsoonal conditions. This study uses sedimentological, geochemical, and provenance data from silty facies of the Earp and equivalent Supai Formations (Arizona, New Mexico) to shed light on atmospheric circulation and glacial–interglacial climate change in westernmost equatorial Pangaea. Five silt‐rich facies comprise both loessite and marine and fluvially reworked loessite. An initial aeolian origin for the silt is indicated by the remarkably invariant grain size and the laterally continuous, sheet‐like geometry of beds. The silt‐rich facies occur in repetitive facies associations (1–20 m scale) that form mixed continental‐marine (loess, marine‐reworked loess), shallow‐marine, and continental (loess, palaeosol) ‘sequences’. Facies repetitions of both mixed continental‐marine and shallow‐marine sequences reflect a linked glacioeustatic–glacioclimatic control, whereas the continental (loess–palaeosol) couplets reflect a primary glacial–interglacial climatic cyclicity linked to glacioeustasy. Stratigraphic interpretations suggest that aeolian silt flux maximized during glacial to incipient interglacial stages (lowstand to early transgression), and decreased significantly or ceased during interglacials (highstand to early falling stage). Detrital‐zircon geochronological data indicate a transition from dominantly north‐easterly winds during the Middle Pennsylvanian to north‐westerly and south‐easterly winds by the Early Permian, which trend is inferred to reflect the onset of monsoonal circulation in western Pangaea. Relative grain‐size data support the detrital‐zircon data, and exhibit a significant decrease from the Sedona arch/Central Arizona shelf (north) to the Pedregosa basin (south) sections. Whole‐rock geochemical data suggest a relatively unweathered source for the silt in the north, and detrital‐zircon data indicate significant silt was derived from the local basement. These large piles of silt(stone) preserve valuable information for reconstructing both long‐term evolution in atmospheric circulation and short‐term fluctuations in glacial–interglacial climate. Many such indicators for long have been applied to ‘recent’ (Plio‐Pleistocene) loess, but are equally applicable to ‘deep‐time’ strata.

Stratigraphy and paleontology of the marine Jurrassic strata in Vietnam

Marine Jurassic strata in Vietnam have yielded characteristic ammonites and occur in: (1) West Quang Binh Province located in the eastern margin of the Nam Theun Basin (the main part of which is located in Middle Laos); (2) the Nong Son Basin situated in the north of the Kon Turn Geoblock; (3) the Da Lat Basin, the largest Jurassic basin in Vietnam, extending from the southern margin of the Kon Turn Geoblock to southeast of Ho Chi Minh City. In the first two, Lower Jurassic marine beds occupy the lower part of the section and grade up into Middle Jurassic red beds. In central Da Lat Basin the section consists completely of marine strata containing many ammonite levels dated from Early Sinemurian to Bajocian, whereas the marginal basin section is like the first two areas. Based particularly on biostratigraphical evidence, a marine transgression is considered to have entered the Indochina Block as early as the Late Hettangian. During the early transgression the fauna was distinctly endemic, showing the separate character of the basins, but since the Late Sinemurian, communication between the Da Lat and other basins was established; the marine regime in Da Lat Basin ended around the Late Bathonian.

The interplay of eustasy, climate and human activity in the late Quaternary depositional evolution and sedimentary architecture of the Po Delta system

The late Pleistocene and Holocene environmental evolution and sequence stratigraphic architecture of the Po Delta region, Northern Italy, are examined. The study units record the depositional evolution from lowstand continental accumulation to marine transgression and highstand progradation. Interpretation of the high-resolution, three-dimension geological mapping of the central Po Delta area was framed within the evolution of the whole of the delta region, stretching from Venice Lagoon to the South of Ravenna. The development of the delta lobes was correlated with the fluvial drainage history. A discussion on the different auto and allocyclic mechanisms controlling the depositional evolution and a quantitative estimation of the changing depositional rates are also provided. Outcrop study was based on field surveying and on the analysis of aerial photography, topographic micro-relief, historical cartography, archaeological and historiographic data. Subsurface analysis was based on stratigraphic coring and cone penetration testing. During the last glacial lowstand, the modern coastal region was the site of middle alluvial plain sedimentation. Deglaciation and early transgression were associated with an erosive disconformity development. In the modern coastal area, transgressive accumulation started between 10 and 9000 yr BP. Back-stepping fluvial and brackish marsh deposits were followed by delta-estuarine sand bodies, influenced by the last important eustatic rise pulses. Transgression climaxed at about 5500 yr BP, during a warm climate phase. Early highstand saw the growth of large sand spits and barrier islands, progressively turning the previous bays into confined lagoons. At about 3500–3000 yr BP, a particularly active meteo-marine regime profoundly affected the depositional dynamics. Etruscan and Roman times were characterised by a warm climate and by riverine stability associated with the development of a large delta lobe. At around 1500 yr BP, transition toward moister and cooler conditions and the abandoning of the Roman Empire hydraulic works coincided with important drainage network instability. The modern delta lobe was induced 400 years ago by an artificial fluvial-mouth cut. The early evolution of the lobe recorded very high accumulation rates. The modern fragile environmental situation is characterised by strong coastal erosion and difficult management.

Glacially-influenced late Pleistocene stratigraphy of a passive margin: New Jersey's Record of the North American ice sheet

Glacial isostasy and the sediment supply changes associated with the waxing and waning of ice sheets have dramatic effects on the stratigraphy of adjacent continental shelves. In ancient stratigraphic records, the glacial influences on such deposits could be difficult to recognize because of the removal of coeval terrestrial glacial deposits by erosion. This study illustrates the effects of the Laurentide Ice Sheet on a basin near its maximum limit, the New Jersey continental shelf. Analysis of 1600 km of Geopulse™, Uniboom™, Minisparker™ and airgun profiles reveals four depositional sequences that have a maximum thickness of ∼75 m near the shelf edge. Sequences I and IV correspond to the major glacial–interglacial sea level changes at Marine Isotope Chron (MIC) 6/5e and 2/1, whereas sequences II and III reflect smaller-scale sea-level fluctuations during chrons 4/3c and 3b/3a, respectively. Sequences I and IV are characterized by relatively thick low stand to early transgressive deposits near the shelf edge formed during times of increased sediment supply, but are thin and discontinuous across much of the shelf. Reflection horizons in these units deepen northward in the northern half of the study area due to collapse of a peripheral bulge that formed at the margin of the Laurentide Ice Sheet. The Hudson River moved from a more southerly drainage pattern to the modern Hudson Shelf Valley position, possibly under the influence of the advancing peripheral bulge. Sequences II and III are largely preserved within a broad mid-shelf swale likely created by the migration of an ancestral Hudson River, and their thickness implies much higher sedimentation rates during chrons 4 and 3 than seen today. If the terrestrial glacial record was eroded, the increased rates of sedimentation during the Pleistocene, dominance of sediments derived from northern New England, and northward tilting of strata could be interpreted as a result of uplift of a northern source area. The unusually high frequency of the relative sea-level oscillations (20 kyr), the concentration of sediment supply during low stands and early transgressions, and the correspondence of sea-level change with climatic change could be used to infer their relationship to a nearby ice sheet. Geologists studying deposits formed during times of widespread continental glaciation should consider possible glacial influences on the stratigraphy of mid-latitude deposits, even in the absence of sediments directly deposited by ice.

Lowstand carbonates, highstand sandstones?

The sedimentary facies, sediment dynamics and sequence architecture of modern high-energy shelves in the mid and high latitudes are largely governed by wave abrasion processes. Cool-water carbonates may form there, if the influx and/or net accretion of siliciclastics is kept at a minimum. Little dilution of the carbonate produced in situ is generally promoted by a wide “epicontinental” shelf, subdued topography of the adjacent mainland, the predominance of limestone outcrops, and an arid climate. The aforementioned requirements are rarely met, and thus will automatically lead to the formation of mixed siliciclastic–cool-water carbonates. Such an example is found in the Early to Mid-Miocene Lagos-Portimão Formation (Algarve, S-Portugal), which formed on a narrow high-energy shelf of the Atlantic Ocean that was bounded by a mountain range. The sediments of the formation consist of fossiliferous sandstone (FS), shell beds, and rhodolith blankets. Along strike, the stratification of the formation is monotonous for tens of kilometres and well exposed in coastal cliffs, whereas no outcrops of dip sections exist. The bulk skeletal composition of the sediments is typical for the warm-temperate climatic zone: various endo- and epibenthic bivalves, bryozoans, coralline algae, echinoderms, gastropods, and large foraminifers ( Heterostegina). In some very rare beds, a few isolated, not framework-forming specimens of zooxanthellate corals ( Porites, Tarbellastrea) indicate temporally elevated surface water temperatures close to the lower threshold of the coral reef ecosystem. In sandstones, the fauna is well preserved and burrowing bivalves are commonly found in life position. In limestone beds, the state of preservation of the grains ranges from intact to disintegrated and abraded specimens. We infer an accumulation of the shell beds through winnowing of fine materials (siliciclastic sand and carbonate mud) at wave abrasion depth and concentration of calcareous skeletons associated with the subsequent attraction of new epibiota in a complex shell bed. The vertical alternation of fossiliferous sandstone and shell beds, and in-phase variations of the “Photo Index” (photic biota vs. bryozoans) and “Bryozoan Index” (bivalves vs. bryozoans) is envisaged to document variations of water depth (and sea level). Sandstone units built up when wave abrasion depth (WAD) rose above the sea floor during TST (and early HST), whereas the shell beds formed during LST when the WAD for sand intersected with the sea floor. Clastic sediments were probably brought on the outer shelf during early transgression, and by longshore currents. Sea-level signatures inferred in the mixed siliciclastic–cool-water carbonate shelf setting of S-Portugal therefore significantly deviate from conventional concepts of carbonate sequence stratigraphy, which were developed for flat-topped platforms. Successful interpretations of ancient mixed sequences must therefore take into consideration the processes of production, concentration and accretion of the carbonate sediments.