Depositional Record

Bedform geometries of volcanogenic sedimentary structures such as dune, low‐ to high‐angle cross‐stratification and planar stratification produced in subaqueous and subaerial environments can be very similar. This has historically created difficulties in unambiguously distinguishing primary from reworked deposits, and gas‐deposited versus water‐deposited ones. The origins of dunes and associated structures within the pyroclastic deposits of basaltic Surtseyan‐style eruptions exposed in seacliffs along the Cape Wanbrow coastline of the Northeast Otago region in the South Island of New Zealand are such an example. Careful analysis of contextual information of these deposits, including granulometry, dune geometry, grading, sorting and particle hydraulic equivalence, has been completed to distinguish between major flow types in different environments. To determine the depositional setting of the Cape Wanbrow dune‐bearing deposits, a number of related sediments have been examined in more detail including well‐described examples of (i) subaerial dry pyroclastic deposits, (ii) subaerial moist pyroclastic deposits, (iii) aeolian deposits, (iv) deposits of unidirectional fluid‐gravity water flows (e.g. rivers) and cyclic tidal flows, and (v) aqueous sediment‐gravity flow deposits encompassing both pyroclastic material and those with non‐pyroclastic material. From this compendium, a framework has been created that allows users to compare the physical controls that shape each example with the factors controlling bedform deposition in that environment. Identifying key characteristics of the Cape Wanbrow dunes and comparing multiple flow types and environments using the designed framework indicates that they were deposited by subaerial dry pyroclastic density currents. This conclusion has wider implications for the entire Surtseyan stack at Cape Wanbrow, because it indicates that at least this volcano (Rua2) became emergent and fully subaerial during its lifespan.

Benjamin L. Moorhouse

James D. L. White

The Depositional Record

Depositional Rec

Interpreting ambiguous bedforms to distinguish subaerial base surge from subaqueous density current deposits

The Miami Oolite of South Florida is representative of a grainstone‐rich carbonate unit that has been surficially karsted, and therefore may be considered as an analogue for subsurface reservoirs/aquifers with ‘high’ permeability extremes. The deposit can potentially serve to improve a conceptual understanding of heterogeneity as imparted by shallow‐marine facies changes and early meteoric diagenetic modification. Reviewed here are recent studies of the Miami Oolite with the intent to emphasize those key aspects of the facies and early diagenesis that most impact permeability and fluid flow. The Miami Oolite displays the preserved morphology of a fossilized ooid sandbody, even though it has been subaerially exposed in a tropical climate since its deposition approximately 120 kyr bp during the last interglacial highstand. The depositional motif is one of a dip‐oriented, tidal bar belt of shoals and shallow channels fronted by a strike‐oriented barrier bar. The barrier bar comprises cross‐stratified grainstones and locally burrowed grain/packstones, while the tidal shoals and channels are more commonly burrowed pack/grainstones. Surficial karst features (dolines and stratiform caves) have been added during the ca 120 kyr of subaerial exposure, but of more significance is the associated solution‐enhancement of the widespread burrowed facies. Since the Miami Oolite is the uppermost portion of the Biscayne Aquifer, there is also an understanding of fluid flow through the deposit that sheds valuable insight on the larger scale, shallow subsurface plumbing. The pore system comprises matrix pores (interparticle and separate vugs) and touching‐vug macropores that are commonly associated with burrowed [Ophiomorpha] intervals. Ground‐penetrating radar, well and flow test data indicate that matrix porosity provides most of the groundwater storage, whereas the touching vug macropores account for the majority of flow. The dolines and shallow caves seem to be sufficiently spaced as to generally not be in direct connection, with the result that they are less important in terms of regional flow than the prevailing pore system.

Paul (Mitch) Harris

Sam Purkis

Impact of facies and diagenetic variability on permeability and fluid flow in an oolitic grainstone—Pleistocene Miami Oolite

Mouth bars are the fundamental architectural elements of proximal deltaic successions. Understanding their internal architecture and complex interaction with coastal processes (fluvial, tide and wave‐dominated) is paramount to the interpretation of ancient deltaic successions. This is particularly challenging in low‐accommodation systems, because they are commonly characterized by thin, condensed and top‐truncated sections. This study analyses the exhumed Cenomanian Mesa Rica Sandstone (Dakota Group, Western Interior Seaway, USA), a fluvio‐deltaic system covering a ca 450 km depositional dip‐parallel profile. The study targets the proximal deltaic expression of the system, using 22 sedimentary logs (total of 390 m) spatially correlated within a ca 25 km2 study area at the rim of the Tucumcari Basin. Analysis of facies distributions, depositional architecture and spatial extent of stratigraphic surfaces reveals a 6–10 m thick, sharp‐based and sand‐prone deltaic package, comprising several laterally extensive (>1.4 km width) mouth bars. Composite erosional surfaces infilled with multi‐storey fluvial and marine‐influenced channel deposits (12–20 m thick, 100–250 m wide) scour locally into the deltaic package. Based on differences in sedimentary structures, bed thicknesses, occurrence of interflood beds and bioturbation indexes, four different sub‐environments within single mouth bars were distinguished. These range from mouth‐bar axis, off‐axis, fringe to distal‐fringe deposits, which reflect waning depositional energy with increasing distance from the distributary channel mouth. The interpreted mouth‐bar components also show internal variability in dominant process regime, with overall river dominance but local preservation of tide influence in the fringe and distal fringe components. Mouth‐bar deposits amalgamate to form an extensive sand‐rich sheet body throughout the study area, in which interflood mudstone to very‐fine grained sandstone beds are nearly absent. These features reflect successive coalescence of mouth bars in a low accommodation/supply (A/S) setting. These conditions promoted recurrent channel avulsion/bifurcation and thus the potential reworking of previously deposited mouth‐bar fringe and distal‐fringe sediments, where time and background processes are better recorded. Results of this study evidence internal process‐regime variability within mouth‐bar components. They also caution against the possible loss of preservation of subordinate coastal processes (e.g. tidal indicators), and consequent underestimation of the true mixed influence in low‐accommodation deltaic settings.

Anna E. Yperen

Miquel Poyatos‐Moré

John M. Holbrook

Ivar Midtkandal

Internal mouth‐bar variability and preservation of subordinate coastal processes in low‐accommodation proximal deltaic settings (Cretaceous Dakota Group, New Mexico, USA)

Living stromatolites have been mostly described within shallow marine and (hyper)saline lacustrine environments. Southernmost South America lacks detailed investigations of these (organo)sedimentary buildups, particularly in regions experiencing extreme and variable environmental conditions. Here, we report and describe living freshwater stromatolites in the Maquinchao region, north‐western Patagonia, Argentina. Fossil stromatolites characterized by globular and cauliflower shapes are also present in a continuous palaeoshoreline of a former lake at an altitude of 830 m, whereas their living counterparts only occur in the calm waters of sheltered or meandering sections of the Maquinchao River. The living stromatolites and their host waters have been sampled and studied using various chemical and microscopic techniques to better constrain the environmental versus biological factors controlling their development. Our results indicate that today stromatolites only proliferate in freshwater when Ca2+ levels are high. A microscopic inspection of the living stromatolite mat indicates stronger photosynthetic activity in the upper green layer associated with crypto/microcrystalline calcite (nanoglobules) compared to the lower beige‐white biofilm. This biofilm contains more low‐Mg calcite (rhombohedra) precipitates, which can form millimetre‐sized aggregates in the underlying anoxic layer. Although sulphate‐reducing bacteria are living in the entire mat, they appear more abundant and widely distributed in the lower beige‐white layer and are always associated with Mg calcite. Low salinity and low‐turbidity water along with microbial (photosynthetic and heterotrophic) activity are the most important factors promoting low‐Mg calcite precipitation in the Maquinchao Basin. These conditions are very different from those proposed for recently described lacustrine stromatolites at high altitude in the subtropical and tropical Andes as well as in Chilean Patagonia. Hence, all these observations in modern freshwater stromatolites show the importance of geomicrobiological studies in identifying proxies of the hydrological conditions prevailing during their formation.

Muriel Pacton

Gabriel Hunger

Vincent Martinuzzi

Gabriela Cusminsky

Beatrice Burdin

Kurt Barmettler

Crisogono Vasconcelos

Daniel Ariztegui

Organomineralization processes in freshwater stromatolites: a living example from eastern
            P
            atagonia

Middle to Upper Ordovician ironstone and associated sedimentary rocks of the West Asturian‐Leonese and Cantabrian tectonostratigraphic zones, Spain, provide new information regarding the Palaeozoic Fe cycle and the palaeoceanography of the Rheic Ocean. Examination of drill cores and outcrops indicates the southeastern margin of this narrow seaway was a dynamic continental shelf where upwelling of ferruginous seawater and storm currents controlled lithofacies character. Parasequence composition and stacking relationships suggest ironstone accumulated during marine transgression as accommodation increased from lowstand conditions. Proximal parasequences record aggradation from deep subtidal to shoreface environments. Hummocky cross‐stratified sandstone and organic‐rich siltstone grade upwards into swaley cross‐stratified sandstone and granular Fe‐silicate‐rich ironstone capped by a flooding surface. Distal parasequences were deposited below storm wave base on the distal shelf and are composed of variably bioturbated organic‐rich siltstone with thin Fe‐chlorite and phosphorite layers. These differences in parasequence character define two different ironstone factories where Fe was concentrated and precipitated in sediment. Lithofacies associations support an emerging model for ironstone deposition where coastal upwelling delivered and stimulated the precipitation of Fe within shelf sediment. This notion provides further evidence for the development of intermittent anoxic water masses in an Ordovician ocean that was near the threshold of becoming fully ventilated. This style of Fe delivery probably represents a tipping point in the oxygenation history of the Phanerozoic oceans and is a throwback to the Precambrian when widespread anoxia allowed hydrothermal Fe to concentrate in the global ocean. New data suggest that minor extinction events punctuating the Great Ordovician Biodiversification Event may be traced to these anoxic waters, which in addition to Fe, were also enriched in biologically toxic, redox sensitive trace elements. Conversely, precipitation of upwelling‐related ironstone may have helped sequester these trace elements, providing a negative feedback response that would aid post‐extinction recovery.

Peir K. Pufahl

Alexandra D. Squires

J. Brendan Murphy

Cecilio Quesada

Stephen W. Lokier

J. Javier Álvaro

Jason Hatch

Depositional Rec.

Ordovician ironstone of the Iberian margin: Coastal upwelling, ocean anoxia and Palaeozoic biodiversity

Although notoriously difficult to delineate from the wider family of carbonate rocks and sediments, nonmarine carbonates represent an important subset, forming in a large variety of depositional settings such as lakes, rivers, hydrothermal vents, caves, soils and sites affected by alkaline pollution (Alonso Zarza & Tanner, 2010; Capezzuoli et al., 2014; Della Porta, 2015; Pentecost, 2005; Figure 1). Due to the erosive and dissolution effect of meteoric waters in terrestrial environments, such carbonates are generally characterised by low preservation potential and their geological record is probably discontinuous and highly altered. Nevertheless, nonmarine carbonates represent a significant component of terrestrial sedimentary basins, providing useful proxies of palaeoenvironmental conditions and can offer a means of passive remediation of sites harmed by human industry, including sequestration and storage of carbon dioxide. Understanding the physicochemical and microbially mediated processes involved in their precipitation helps to constrain biogeochemical cycles, investigate the geological past and plan for the future approaches to global changes. In the last two decades, the study of nonmarine carbonates has progressed from descriptions of local occurrences to frontier research, able to envelope the very latest challenging interests such as the dawn of life on Earth or astrobiological research (including such work as Des Marais & Walter, 2019; Farmer, 2000; Franchi & Frisia, 2020; Rothschild & Mancinelli, 2001), and has become a major target for future geoengineering research. This special issue aims to begin to gather and curate the knowledge necessary to resolve the challenges this frontier research faces. We need better insights into the variety of nonmarine carbonate facies and the physicochemical and biogenic controls on processes of carbonate and associated minerals precipitation to move our studies beyond observation of what has happened, to reconstruct processes in time and space. The collected contributions investigate fossil and modern nonmarine carbonates through multidisciplinary approaches highlighting their variability across different depositional environments and ages and the biological, environmental and chemical factors controlling their formation, fabrics and accumulation rates.

短名	Depositional Rec
Journal Impact	1.86
国际分区	GEOLOGY(Q1)
期刊索引	SCI Q1中科院 3 区

ISSN	2055-4877
h-index	18
国内分区	地球科学(3区)地球科学地质学(2区)

涉及主题	地质学生物古生物学地貌学地球化学构造盆地化学地理计算机科学材料科学有机化学海洋学生态学工程类冶金物理沉积沉积环境历史碳酸盐相考古沉积岩沉积物
出版信息	出版商: John Wiley & Sons Inc.，出版周期: ，期刊类型: journal，开源期刊: 开源
基本数据	创刊年份: 2015，原创研究文献占比: 92.11%，自引率:5.30%， Gold OA占比: 86.55%
期刊费用	$2400详情
平均审稿周期	网友分享经验：16 Weeks

Depositional Record

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Non‐marine carbonate: Wherefore art thou?

Ordovician ironstone of the Iberian margin: Coastal upwelling, ocean anoxia and Palaeozoic biodiversity

Internal mouth‐bar variability and preservation of subordinate coastal processes in low‐accommodation proximal deltaic settings (Cretaceous Dakota Group, New Mexico, USA)

Impact of facies and diagenetic variability on permeability and fluid flow in an oolitic grainstone—Pleistocene Miami Oolite

Interpreting ambiguous bedforms to distinguish subaerial base surge from subaqueous density current deposits

Organomineralization processes in freshwater stromatolites: a living example from eastern P atagonia

Interpreting ambiguous bedforms to distinguish subaerial base surge from subaqueous density current deposits

Impact of facies and diagenetic variability on permeability and fluid flow in an oolitic grainstone—Pleistocene Miami Oolite

Internal mouth‐bar variability and preservation of subordinate coastal processes in low‐accommodation proximal deltaic settings (Cretaceous Dakota Group, New Mexico, USA)

Organomineralization processes in freshwater stromatolites: a living example from eastern P atagonia

Ordovician ironstone of the Iberian margin: Coastal upwelling, ocean anoxia and Palaeozoic biodiversity

Non‐marine carbonate: Wherefore art thou?