Depositional processes and stratigraphic evolution of the Campanian deltaic system of La Anita Formation, Austral-Magallanes Basin, Patagonia, Argentina

Coastal depositional systems are commonly classified in terms of the relative interaction of wave, tide and fluvial processes. The La Anita Formation represents the opportunity to study and better understand coastal sedimentary systems. It is a poorly studied prograding siliciclastic deltaic-coastal wedge accumulated in the Campanian during the foreland stage of the Austral-Magallanes Basin. A detailed depositional process-based facies analysis have allowed the definition of 13 sedimentary facies and 9 facies associations for the La Anita Formation, ranging from prodelta to interdistributary delta-channel deposits. According to the spatial distribution of these facies associations, the La Anita Formation was divided into two informal units bounded by a regional erosion surface. The lower unit shows abundant hummocky cross-bedded and bioturbated sandstones, coarseningupward trends and mainly aggradational to progradational vertical stacking pattern, and it was interpreted as a wave-dominated fluvial-influenced delta. The upper unit is characterized by unidirectional dune cross-bedding, coarseningupward trend and a progradational vertical stacking pattern, and was interpreted as a fluvio-dominated delta with no evidence of tide or wave influence. These two units represent two genetically unrelated depositional sequences bounded by a regional erosion surface, which is interpreted as a sequence boundary triggered by a relative sea-level fall. The lower unit is part of a progradational highstand systems tract which involves the underlying deep-marine Alta Vista Formation. The upper unit deposits reflect a complete relative sea-level cycle which includes an undifferentiated lowstand and transgressive systems tracts and, toward the top, highstand systems tract.Fil: Moyano Paz, Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Tettamanti, Camila. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Varela, Augusto Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Cereceda, Abril. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; ArgentinaFil: Poire, Daniel Gustavo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentin

Tellurium, selenium and cobalt enrichment in Neoproterozoic black shales, Gwna Group, UK : Deep marine trace element enrichment during the Second Great Oxygenation Event

We are grateful to John Still for his skilled technical support and the ACEMAC facility at the University of Aberdeen. Research funded by NERC grant NE/M010953/1 and NERC facility grant IP-1631-0516. AJB is funded by NERC support of the Isotope Community Support Facility SUERC. The authors thank Eva Stüeken, Ross Large and one anonymous reviewer for their constructive feedback on the original manuscript.Peer reviewedPublisher PD

A new model for the formation of microbial polygons in a coastal sabkha setting

The stratigraphic record of microbially induced sedimentary structures spans most of the depositional record. Today, microbes continue to generate, bind and modify sediments in a vast range of depositional environments. One of the most cited of these settings is the coastal microbial mat system of the Persian/Arabian Gulf. In this setting, an extensive zone of microbial mat polygons has previously been interpreted as resulting from desiccation‐related contraction during episodic drying. This study employs 15 years of field‐based monitoring of the interaction between environmental factors and the development and evolution of polygon morphologies to test the desiccation model in this setting. On the basis of these observations, a new model is proposed that accounts for the genesis and development of microbial polygons without the need for desiccation‐induced shrinkage. Conversely, the formation, development and erosion of microbial polygons is a direct result of the production of large amounts of organic matter in a healthy, yet spatially limited, microbial community. The recognition of microbial polygons has previously been applied as a diagnostic tool for the reconstruction of ancient depositional environments. The present study calls these interpretations into doubt. It is inferred that preservation of the microbial polygons as a recognizable form would be rare. Biological degradation and compaction will reduce polygons to produce the ‘wispy’ laminae that are a common feature of ancient sabkha lithofacies

The Carboniferous Southern Pennine Basin, UK

Many of the Carboniferous outcrops located in the Derbyshire region of the Peak District National Park, UK, have provided sites for both significant and pioneering research relating to the clastic sedimentology of marine palaeoenvironments, particularly so during the 1960s and 1970s when early models describing the sedimentary architecture of fluvio-deltaic, submarine slope and deep-marine submarine-fan sedimentation were first developed. The area was subject to hydrocarbon exploration from the 1920s to 1950s, which although unsuccessful in economic terms left a legacy of sub-surface data. Despite a long-history of sedimentological research, the deposits exposed at several classic localities in the Pennine Basin continue to broaden and challenge our current understanding of sedimentary processes to this day

Eastern Taranaki Basin field guide.

Linking the onshore and offshore parts of Eastern Taranaki Basin: Insights to stratigraphic architecture, sedimentary facies, sequence stratigraphy, paleogeography and hydrocarbon exploration from the on land record

Submarine depositional terraces at Salina Island (Southern Tyrrhenian Sea) and implications on the Late-Quaternary evolution of the insular shelf

The integrated analysis of high-resolution multibeam bathymetry and single-channel seismic profiles around Salina Island allowed us to characterize the stratigraphic architecture of the insular shelf. The shelf is formed by a gently-sloping erosive surface carved on the volcanic bedrock, mostly covered by sediments organized in a suite of terraced bodies, i.e. submarine depositional terraces. Based on their position on the shelf, depth range of their edge and inner geometry, different orders of terraces can be distinguished. The shallowest terrace (near-shore terrace) is a sedimentary prograding wedge, whose formation can be associated to the downward transport of sediments from the surf zone and shoreface during stormy conditions. According to the range depth of the terrace edge (i.e., 10–25 m, compatible with the estimated present-day, local storm-wave base level in the central and western Mediterranean), the formation of this wedge can be attributed to the present-day highstand. By assuming a similar genesis for the deeper terraces, mid-shelf terraces having the edge at depths of 40–50 m and 70–80 m can be attributed to the late and early stages of the Post-LGM transgression, respectively. Finally, the deepest terrace (shelf-edge terrace) has the edge at depths of 130–160 m, being thus referable to the lowstand occurred at ca. 20 ka. Based on the variability of edge depth in the different sectors, we also show how lowstand terraces can be used to provide insights on the recent vertical movements that affected Salina edifice in the last 20 ka, highlighting more generally their possible use for neo-tectonic studies elsewhere. Moreover, being these terraces associated to different paleo-sea levels, they can be used to constrain the relative age of the different erosive stages affecting shallow-water sectors

Timing of initiation of reverse displacement on the Taranaki Fault, northern Taranaki Basin: Constraints from the on land record (Oligocene Te Kuiti Group)

Structures associated with the wedge of basement overthrust into Taranaki Basin along the Taranaki Fault, are regarded as hydrocarbon plays and have been tested by drilling through the tip of the overthrust. The timing of initiation of reverse displace ment on Taranaki Fault is difficult to interpret from available seismic reflection data across it because the evidence has been masked by later movements. The record from the basin, as summarised in King & Thrasher (1996), suggests that the fault evolved from normal to reverse character during the mid-Oligocene. This was inferred from formation of a foredeep parallel to, and west of, Taranaki Fault and a marked increase in its paleo-water depth, as indicated by foraminiferal assemblages of Late Oligocene age. A comprehensive re-assessment of the lithostratigraphy and sequence stratigraphy of the Late Eocene-Oligocene Te Kuiti Group exposed on land east of Taranaki Fault in central-western North Island, between Port Waikato and Awakino, provides new constraints on the early history of Taranaki Fault displacement. New age control has been achieved by a review of existing foraminiferal biostratigraphy combined with determination of Sr isotope ages from macrofossil samples. Six unconformity-bound sequences have been identified and mapped within the Te Kuiti Group. A major subaerial unconformity between sequences TK3 and TK4 combined with a basinward shift in the position of onlap for sequence TK4 indicate a dramatic change in stratigraphic development and basin dynamics during the mid-upper Whaingaroan at c. 29 Ma, corresponding to the change from mild extension (sag basin) to shortening across the Taranaki Fault Zone. We consider sequences TK4 – TK6 to each represent tectonic cycles of subsidence and basin inversion and we attribute the origin of these cycles to periodic locking of the Taranaki Fault décollement in underlying Murihiku basement, the accumulating strain causing uplift in the basin east of the fault zone, followed by free displacement, relaxation in the upper crust and subsidence. A 1st order model is presented of the Late Oligocene to earliest Miocene vertical and horizontal displacement of basement on the Taranaki Fault Zone for a west –east transect through Awakino. It implies that the mid- to Late Oligocene displace¬ment on the fault zone in the vicinity of Awakino was episodic, and that the thrust belt was narrow (c. 15 km). North of Kawhia Harbour there will have been a different displacement history with most of the total displacement occurring during the devel opment of the c. 29 Ma unconformity at the base of Sequence TK4, whereas to the south between Awakino and Kawhia Harbour the majority of the total displacement occurred during the Otaian and at the end of it. The model also shows that the start of reverse/thrust displacement on Taranaki Fault must have involved the development of a completely new fault trace(s), rather than involving a change of sense of movement on the pre-existing normal fault. The Manganui Fault is part of the Taranaki Fault Zone and probably became active at c. 27 Ma during development of the unconformity between sequences TK4 & TK5. The model presented here has been validated against the subsurface Oligocene stratigraphy in Taranaki Basin