The late Miocene eolian record at the eastern margin of the Puna Plateau, NW Argentina: Evidence of upper-tropospheric paleocirculation

The Puna–Altiplano Plateau of the Central Andes is the second-highest plateau in the world (after Tibet), with a mean elevation of 4000 m.a.s.l. and an arid to hyperarid climate. Uplift of the Puna–Altiplano Plateau has affected lower-level atmospheric circulation, acting as a barrier to humid easterly winds from the Amazon basin and favoring an across-strike precipitation gradient resulting in a humid climate towards the east of the plateau and an arid to hyperarid climate in the orogen's interior. In the modern climate, the Bolivian High anticyclone regulates upper troposphere circulation, but little is known about the high-altitude tropospheric circulation of the past. This work focuses on the eolian record of the San Antonio de los Cobres basin along the eastern border of the Puna Plateau, NW Argentina, with the aim of analyzing its origin and thus elucidating the late Miocene winds. The eolian deposits are constrained by 7.8 Ma (K/Ar and U/Pb) and 6.4 Ma (U/Pb) ignimbrites at the nearly basal and upper contacts, respectively. Based on stratigraphic, sedimentological, and provenance analysis of the eolian units, we have identified three main facies associations (FAs): FA1) cross-stratified sandstones with large- to small-scale tabular, planar cross-bedding and with trough cross-stratification; FA2) sandstones with planar to low-angle stratification associated with thinly laminated ripple sandstone strata; FA3) medium- to coarse-grained massive sandstones associated with pebbly to bouldery, matrix-supported conglomerates and clast-supported conglomerates. The lateral and vertical facies assemblages indicate a dune field confined to topographic depressions dominated by transverse dunes with straight and sinuous crestlines that laterally grade into sandsheets associated with ephemeral streams. Paleoflows, lithotypes, and grain-size determinations indicate a persistent north-northwest provenance and wind velocities of 24–38 km/h (with maximum velocities of 55–75 km/h). The results of our analysis coupled with data from previous studies indicates that, for at least the last ca. 8 Myr, the winds have been blowing constantly from the north-northwest with an intensity similar to the present. This implies that the paleo-atmospheric circulation had a similar pattern to the present-day one. Therefore, we conclude that the upper-troposphere circulation in the Puna Plateau of NW Argentina was already regulated by the Bolivian High anticyclone during the Miocene, generating constant north-northwesterly winds.

Depositional Model for Turbidite Lobes in Complex Slope Settings Along Transform Margins: The Motta San Giovanni Formation (Miocene—Calabria, Italy)

Intraslope lobes, or perched lobes, are attracting scientific interest because they represent a key archive between the shelf and the deep basin plain when looking at a complete source-to-sink depositional system across a continental margin and can form significant offshore hydrocarbon plays. In this study, we focus on a detailed characterization of intraslope lobes of the Motta San Giovanni Formation (Miocene, Calabria), which were deposited in confined conditions during the Miocene along a transform margin. We determine the typical facies associations and stratigraphic architecture of these intraslope lobes using a 3D digital outcrop model resulting from a combined Uncrewed Aerial Vehicle (UAV) and walking acquisition, together with sedimentological logging and geological mapping. We propose recognition criteria for the identification of intraslope lobes, including facies and geometries, integrated within a depositional model. A comparison with other well-known intraslope and confined lobes, as well as basin floor lobes, is finally discussed, to highlight the peculiarities of intraslope lobes deposited along transform margins. The diagnostic depositional model for these types of intraslope lobes includes four main stages of evolution: 1) Stage 1—isolated detached lobe precursor in response to a flushed hydraulic jump, 2) Stage 2—prograding and aggrading lobe elements associated with a relatively stable and submerged hydraulic jump in the Channel-Lobe Transition Zone (CLTZ), 3) Stage 3—major bypass associated with lateral accretion and local aggradation interpreted as a renewal of a normal hydraulic jump in the CTLZ, and 4) Stage 4—erosion and bypass then abandonment. The development of intraslope lobes along active transform margins is allowed by tectonically induced slope segmentation and local confinement. In such a context, flow stripping and overspill processes occurred. Resulting lobes appear to be particularly small and relatively thin sandy deposits. They could be considered end-member in a lobe classification based on the Net-to-Gross content (high) and taking into account their thickness/width ratio (intermediate between 10:1 and 100:1 lines).

Facies Analysis Of The Late Eocene Deep-Marine Middle- To Outer-Fan Sequence Of The Crocker Formation In Tenom District, Sabah, Malaysia

The Crocker Formation, Late Eocene to Middle Miocene in age, was deposited in a deep-marine environment by a turbidity current. Most of the facies identified in the field are related to the sedimentary bed-form structures belonging to Bouma sequences. These prominently include unit divisions such as Ta referring to grading sand, Tb for parallel laminae, Tc for cross laminae, Td for mud laminae, and Te referring to hemipelagic mud. Five facies have adequately been identified using Bouma sequence implications, namely Facies 1 (F1: Ta-Tb layers), Facies 2 (F2: Ta-Te layers), Facies 3 (F3: Tb-Te layers), Facies 4 (F4: Tb / Tc-Te layers), and Facies 5 (F5: Td-Te layers). Based on the Crocker Formation facies analysis, three distinct groups of facies associations were recognised: Deep-Marine Channel-Lobe Association (Type A1), Deep-Marine Channel-Levee Association (Type A2), and Distal Lobe Association. These facies associations precisely revealed that the Crocker Formation's depositional environments were likely deposited in the middle-fan with associated outer-fan settings.

Basin Analysis of Tertiary Strata in Golden Bay, Nelson

<p>Eocene to Miocene strata comprise the Brunner Coal Measures (Ak-Ld), Takaka Limestone (Ld-Po), Tarakohe Mudstone (P1-S1) and Waitui Sandstone (Sc-Sl), and form a transgressive-regressive sequence on an essentially stable structural platform. Brunner Coal Measures in the Takaka valley (up to 350m thick) consist of cross-bedded sand and gravel, interlaminated sand and silt, bioturbated muddy sandstone, carbonaceous mudstone and coal. Five facies associations are recognized and interpreted as river/floodbasin, estuarine and shallow marine deposits. In the Aorere and Parapara River catchments, two new members are recognized: the Quartz Wash Member, comprising quartzose sand and conglomerate, and the Washbourn Limonite Member, a sedimentary iron-ore deposit. The Takaka Limestone (up to 100m thick), consists of bryozoan, bivalve or sandy grainstone or packstone, deposited on a tidal current-swept shallow-middle shelf with minimal terrigenous influx. Diagenesis was controlled by pressure-solution during deep burial, and resulted in a rightly cemented rock with dolomite and neomorphic features. The Tarakohe Mudstone (up to 900m thick) is dominated in its lower half by massive mudstone of hemipelagic and turbiditic origin, and in its upper half by shallow shelf-estuarine sandstones and mudstones. The Waitui Sandstone (160m thick) comprises shallow marine sandstone. Deposition of the Brunner Coal Measures took place in localized fault-angle depressions. The Takaka Limestone was deposited during a period of regional subsidence and minimal tectonic activity. The Tarakohe Mudstone and Waitui Sandstone were deposited in synclinal basins which were later modified by rising monoclinal boundaries.</p>

The initiation of the Mesoproterozoic Bylot basins (Nunavut, Arctic Canada) as recorded in the Nyeboe Formation, Fury and Hecla Group

ABSTRACT Reconstructing Precambrian sedimentary environments over broad cratonic regions often relies on a combination of facies, structural, and provenance analyses. The Mesoproterozoic (ca. 1270–1090 Ma) Fury and Hecla Group, exposed on the Melville Peninsula and northern Baffin Island (Nunavut, Canada), is considered broadly correlative with strata of the Borden, Hunting–Aston, and Thule basins (together referred to as the Bylot basins). We present the results of updated mapping and the first high-resolution sedimentologic and stratigraphic analysis of the lowermost unit in the Fury and Hecla Group, the Nyeboe Formation. The Nyeboe Formation comprises five distinct facies associations: alluvial to fluvial, eolian-backshore, marine-intertidal, marine foreshore to shoreface, and marine-offshore. Thin mafic units are interbedded within the marine shoreface facies and are interpreted to represent volcanic flows. Lateral relationships between facies associations are complex, but generally, facies associations transition from a terrestrial environment at the base to a nearshore marine environment at the top, indicating a transgression. Considering both the along-strike and -dip thickness trends, the presence of mafic volcanic rock units, and possible syndepositional fault orientations crosscutting the deposits, we infer that the Fury and Hecla Group was deposited in a regime of crustal thinning in a half-graben setting. Our results from the Nyeboe Formation suggest a lithostratigraphic correlation to the Nauyat and Adams Sound formations of the Borden Basin. Therefore, this study establishes a geodynamic link between the opening of the Fury and Hecla Basin to the other Bylot basins and contributes to the understanding of a large late Mesoproterozoic intracontinental-basin system.

Basin Analysis of Tertiary Strata in Golden Bay, Nelson

<p>Eocene to Miocene strata comprise the Brunner Coal Measures (Ak-Ld), Takaka Limestone (Ld-Po), Tarakohe Mudstone (P1-S1) and Waitui Sandstone (Sc-Sl), and form a transgressive-regressive sequence on an essentially stable structural platform. Brunner Coal Measures in the Takaka valley (up to 350m thick) consist of cross-bedded sand and gravel, interlaminated sand and silt, bioturbated muddy sandstone, carbonaceous mudstone and coal. Five facies associations are recognized and interpreted as river/floodbasin, estuarine and shallow marine deposits. In the Aorere and Parapara River catchments, two new members are recognized: the Quartz Wash Member, comprising quartzose sand and conglomerate, and the Washbourn Limonite Member, a sedimentary iron-ore deposit. The Takaka Limestone (up to 100m thick), consists of bryozoan, bivalve or sandy grainstone or packstone, deposited on a tidal current-swept shallow-middle shelf with minimal terrigenous influx. Diagenesis was controlled by pressure-solution during deep burial, and resulted in a rightly cemented rock with dolomite and neomorphic features. The Tarakohe Mudstone (up to 900m thick) is dominated in its lower half by massive mudstone of hemipelagic and turbiditic origin, and in its upper half by shallow shelf-estuarine sandstones and mudstones. The Waitui Sandstone (160m thick) comprises shallow marine sandstone. Deposition of the Brunner Coal Measures took place in localized fault-angle depressions. The Takaka Limestone was deposited during a period of regional subsidence and minimal tectonic activity. The Tarakohe Mudstone and Waitui Sandstone were deposited in synclinal basins which were later modified by rising monoclinal boundaries.</p>

Characterising the late Quaternary facies stratigraphy of floodplains in South Africa

South African river floodplains and their alluvial deposits reflect a diversity of geological and geographical drivers. We use a genetic geomorphic classification system originally developed for dryland wetlands to characterise geomorphic processes and potential successions of sedimentary fill for South African floodplains. Using case studies from the literature, we consider differences between alluvial rivers and mixed bedrock-alluvial rivers in the context of macro-scale geomorphic setting, and evaluate the impact of the setting on floodplain persistence and potential as a palaeo-environmental archive. Sedimentary facies associations represented in South African floodplains, including lateral and oblique accretion, channel, channel infill, levee vertical accretion, floodplain vertical accretion and debris flow deposits, are also evaluated. Floodplains of South Africa’s interior are typically mixed bedrock-alluvial as channel beds are set upon or close to bedrock and sediment thickness is limited. By contrast some floodplains in tectonic basin settings have sediment deposits exceeding 30 m in thickness. The resulting rivers are alluvial, and thus able to adjust their width, depth and slope to accommodate changes in discharge and sediment supply. Similarly, coastal floodplain rivers are alluvial due to downcutting during the last glacial maximum and subsequent sedimentary infilling as sea levels rose. When considering the potential of floodplains as palaeoarchives of environmental change, two considerations emerge. First, floodplain stratigraphy is not a response to a single variable due to complex process-form feedbacks. Rather, floodplain stratigraphy is an outcome of both autogenic and allogenic processes. Second, most South African floodplains are zones of sediment recycling, and as such, preservation potential is typically low. Thus, although floodplain settings of the interior may be a few million years old, the sediment within them may be only thousands to tens of thousands of years old. Our review indicates that research has historically focused on meandering river and mixed bedrock-alluvial anabranching river floodplains, while understanding of other floodplain sub-types remains limited.

Discriminating intra-parasequence stratigraphic units from two-dimensional quantitative parameters

ABSTRACT The intra-parasequence scale is still relatively unexplored territory in high-resolution sequence stratigraphy. The analysis of internal genetic units of parasequences has commonly been simplified to the definition of bedsets. Such simplification is insufficient to cover the complexity involved in the building of individual parasequences. Different types of intra-parasequence units have been previously identified and characterized in successive wave-dominated shoreface–shelf parasequences in the Lower Cretaceous Pilmatué Member of the Agrio Formation in central Neuquén Basin. Sedimentary and stratigraphic attributes such as the number of intra-parasequence units, their thickness, the proportions of facies associations in the regressive interval, the lateral extent of bounding surfaces, the degree of deepening recorded across these boundaries, and the type and lateral extent of associated transgressive deposits are quantitatively analyzed in this paper. Based on the analysis of these quantified attributes, three different scales of genetic units in parasequences are identified. 1) Bedset complexes are 10–40 m thick, basin to upper-shoreface successions, bounded by 5 to 16 km-long surfaces with a degree of deepening of one to three facies belts. These stratigraphic units represent the highest hierarchy of intra-parasequence stratigraphic units, and the vertical stacking of two or three of them typically forms an individual parasequence. 2) Bedsets are 2–20 m thick, offshore to upper-shoreface successions, bounded by up to 10 km long surfaces with a degree of deepening of zero to one facies belt. Two or three bedsets stack vertically build a bedset complex. 3) Sub-bedsets are 0.5–5 m thick, offshore transition to upper-shoreface successions, bounded by 0.5 to 2 km long surfaces with a degree of deepening of zero to one facies belt. Two or three sub-bedsets commonly stack to form bedsets. The proposed methodology indicates that the combination of thickness with the proportion of facies associations in the regressive interval of stratigraphic units can be used to discriminate between bedsets and sub-bedsets, whereas for higher ranks (bedsets and bedset complexes) the degree of deepening, lateral extent of bounding surfaces, and the characteristics of associated shell-bed deposits become more effective. Finally, the results for the Pilmatué Member are compared with other ancient and Holocene examples to improve understanding of the high-frequency evolution of wave-dominated shoreface–shelf systems.

Fluvial-Tidal to Fluvial-Lacustrine Sedimentation of the Middle Miocene to Pleistocene Mapia Formation, Dogiyai, Papua (Indonesia)

A sedimentological and palynological investigation was carried out on outcropping sedimentary rocks at Dogiyai, Papua, proposed to be named as the Mapia Formation. The age range is from Middle Miocene to Pleistocene. The lower Mapia Formation was deposited at Metroxylon type to Nothofagus emarcida Zone, Middle Miocene to Early Pliocene. It is comprised of three facies associations: tidal channel, tidal point bar, and tidal flat deposits. A tidally dominated fluvially influenced depositional environment is suggested for the deposition of sediments of this unit. The upper Mapia Formation was deposited at Malvacipollis diversus Zone, Garcinia cuspidata type Zone, and Proteacidites sp. Zone, Late Pliocene to Pleistocene. It is comprised of five facies associations: delta front, slump, debrite, turbidite, and lacustrine mud deposits. A non-channelized deep-lacustrine slump and debris-flow dominated depositional environment is suggested for the deposition of sediments of this unit. The lower Mapia Formation was deposited as synorogenic clastic sediments at the beginning of Central Range orogeny event while the upper Mapia Formation was deposited in the piggyback basin at the major uplift event.

Sedimentology and stratigraphic architecture of a fluvial to shallow-marine succession: The Jurassic Dhruma Formation, Saudi Arabia

ABSTRACT The interaction of fluvial, tidal, and wave processes in coastal and paralic environments gives rise to sedimentary successions with highly varied styles of facies architecture; these are determined by the morphology and evolutionary behavior of the range of coastal sub-environments, which may be difficult to diagnose in subsurface sedimentary successions with limited well control. This study presents depositional models to account for stratigraphic complexity in a subsurface fluvial to shallow-marine succession, the Middle Jurassic Dhruma Formation, Saudi Arabia. The study achieves the following: i) it examines and demonstrates sedimentary relationships between various fluvial, nearshore, and shallow-marine deposits, ii) it develops depositional models to account for the stratigraphic complexity inherent in fluvial to shallow-marine successions, and iii) it documents the sedimentology and the stratigraphic evolutionary patterns of the lower Dhruma Formation in the studied area of Saudi Arabia. The dataset comprises facies descriptions of 570 m of core from 14 wells, 77 representative core thin sections, 14 gamma-ray logs, and FMI image logs from 4 wells. These data are integrated with quantitative information from &gt; 50 analogous systems from a wide range of modern and ancient settings, stored in a relational database. Stratigraphic correlations reveal the internal anatomy of the succession. Facies associations are representative of fluvial channels, intertidal flats, pedogenically modified supratidal flats or floodplains, river-influenced tidal bars, weakly storm-affected shoreface and offshore-transition zones, storm-dominated delta-front and prodelta settings, and an open-marine carbonate-dominated shelf. These sub-environments interacted in a complex way through space and time. The vertical succession of the studied interval records an overall transition from coastal-plain deposits at the base to marine deposits at the top. As such, the succession records a long-term transgressive, deepening-upward trend. However, this general trend is punctuated by repeated progradational events whereby coastal sand bodies of fluvial, wave, and tidal origin prograded basinward during stillstands to fill bays along a coastline. The nature of juxtaposition of neighboring sub-environments has resulted in a sedimentary record that is highly complex compared to that generated by morphologically simple shoreface systems that accumulate more regularly ordered stratal packages.