Allostratigraphic Units Research Articles

Sedimentological and Petrographical Characterization of the Cambrian Abbottabad Formation in Kamsar Section, Muzaffarabad Area: Implications for Proto-Tethys Ocean Evolution

The current sedimentological and petrographical research of the Abbottabad Formation has been carried out in order to understand the formation and evolution of the Proto-Tethys Ocean during the Cambrian on the northern margin of the Indian Plate. The Muzaffarabad region is located east of the Upper Indus Basin and the southern part of the Hazara Kashmir Syntaxis. The geological history of the region varies from the Precambrian to the recent period. The Cambrian Abbottabad Formation is well exposed along the Hazara Kashmir Syntaxis at the core of the 500-m-thick Muzaffarabad anticline. The Abbottabad Formation is an unconformity-bounded allo-stratigraphic unit. It has an unconformable lower contact with the Late Precambrian Dogra Formation and an unconformable upper contact with the Paleocene Hangu Formation. The Abbottabad Formation has been divided into four lithofacies, from bottom to top, namely, thinly interbedded dolomite and shale, cherty-stromatolitic dolomite, oxidized limonitic-brecciated zone, and quartzite, with significant lithological changes. Petrographic studies revealed four types of dolomites: fine crystalline dolomite (Dol. I), dolomitic cryptocrystalline chert (Dol. II), algal mat-stromatolitic dolomite (Dol. III), and intraclastic-dolo-grain stone (Dol. IV). The mineral composition of dolostone was analyzed using X-ray diffraction (XRD) and found to be consistent with previous petrographic studies. The dolomite mineral content decreased from base to top, while chert increased towards the top. Elemental weight percentages through energy dispersive X-ray (EDX) analysis show different elements constitute the minerals found in the dolostone, as confirmed by petrographic and XRD analysis. Using outcrop data, facies information, and geochemical data, a modified depositional model of the Abbottabad Formation was developed. During the Early Cambrian period, the formation was deposited in a shallow subtidal to supratidal setting of the Proto-Tethys Ocean. The top of this deposit marks the Cambrian–Paleocene boundary. Because of the progressively coarsening outcrop sequences, this formation seems to be at the very top of the Proto-Tethys Ocean’s shallow marine system.

Provenance of the Lower Cambrian Khewra Sandstone: Implications for Pan-African Orogeny

This study describes the sedimentological aspects of the Lower Cambrian Khewra Sandstone, along with its lithostratigraphic correlation of globally distributed coeval red sandstones to decipher the imprints of Pan-African Orogeny. Despite the economic significance of Khewra Sandstone, the understanding of its environment of deposition, provenance and lower contact with the suite of igneous body namely Khewrite is poor. The Khewra Sandstone is an allostratigraphic unit bounded by unconformities. The upward coarsening sequence with abundant sedimentary structures and varying sedimentological properties of the topmost bed suggest that the Khewra Sandstone is tempestites deposited under fluvio-deltaic depositional environment. This sandstone is dominated by subarkoses, feldspathic litharenites and sublitharenites which were derived from the craton interior to recycled orogen provenance during the Pan-African orogeny under humid to semi-humid paleoclimatic conditions. The plutonic to metamorphic characteristics of framework grains suggest that the Bundlekhand Craton, Delhi Fold Belt and Aravalli Orogen rocks were the primary provenances. The lower and middle parts of the Khewra Sandstone are significantly affected by diagenesis while the diagenetic action in upper part is negligible and it acts as a potential hydrocarbon reservoir rock. The lithostratigraphic correlation suggests a worldwide series of rifting events before the deposition of Khewra Sandstone and the presence of Khewrite at lower contact marks a similar rifting event on the Indian plate.

Scanning Electron Microscopy (SEM) in the surficial cover analysis of the low fluvial-marine terraces in the southern coast of São Paulo state, Brazil

The Ribeira de Iguape estuarine system in Southeastern Brazil has resulted from the complex interactions betweenallogenic (climate, tectonics, and human interventions) and autogenic geomorphological processes. Early studies have shownthat the relationship between sedimentary balances, fluvial discharge, and Holocene climate pulses resulted in the coastlinedisplacement and low fluvial-marine terraces morphogenesis, which are composed of the marine and fluvial sedimentaryunits. In this perspective, this study aimed to investigate whether the microtextural and morphological records on the quartzgrains associated with the different allostratigraphic units (marine and fluvial) correspond to the paleoenvironmentsidentified in previous studies. In this study we have used a combination of analyses (grain-size, microtextural, and absolutedating) applied to the surficial cover sampled from two fluvial-marine terraces located on the right and left banks of theIguape river channel. The results show correspondences between paleoenvironments and microtextures found on the quartzgrains, confirming the statements addressed in previous studies that indicated the coastline was positioned about 9 kminland around 3.5-2.7 ka.

Sedimentary anatomy and hydrological record of relic fluvial deposits in a karst cave conduit

AbstractThis case study from the renowned Demänová Cave System in the Carpathians of Slovakia demonstrates that the conventional methods of fluvial sedimentology, combined with an allostratigraphic mapping and speleothem U‐series isotopic dating, can give unprecedented insights into the hydrological history of underground karst conduit. The deposits studied are a relic compound sidebar ranging from gravel to mud and encapsulating the conduit’s hydrological history from the middle Pleistocene to the present time. A succession of 10 allostratigraphic units, time‐constrained by speleothems, are recognized in the sidebar deposits, and the corresponding morphodynamics of an evolving cave‐floor sedimentation are reconstructed in considerable detail. The subterranean river water stages recognized from the deposits, time‐constrained by flowstone layers and stalagmites, correlate with and add to the regional record of climate changes. Two distinct episodes of flow ponding (high‐stage slackwater conditions) are recognized and attributed to the independently documented downstream cave‐roof collapses, probably triggered by the Carpathian post‐orogenic earthquakes. This multidisciplinary study may serve as a useful methodological guide for the analysis of fluviokarstic deposits in speleological research and reconstruction of their hosting cave hydrological history.

From cave geomorphology to Palaeolithic human behaviour: speleogenesis, palaeoenvironmental changes and archaeological insight in the Atxurra‐Armiña cave (northern Iberian Peninsula)

ABSTRACTA detailed geomorphological study was performed in the Atxurra‐Armiña cave system (northern Iberian Peninsula) to decode landscape evolution, palaeoenvironmental changes and human use of a cave within an Inner Archaeological Context. The results show an average incision rate of the river of <0.083 mm a–1 for at least the last 419 ka, with interruptions due to sedimentary inputs. Moreover, allostratigraphic units comprising fluviokarstic deposits at the base and flowstone formation at the top have been shown to be climatically controlled, formed either during glacial–interglacial cycles or during interstadial cycles. Finally, when the cave was used by humans in the Late Magdalenian, the lower entrance was closed, and they must therefore have entered the cave through the upper entrance. To reach the sectors selected to decorate the panels, they probably travelled from the upper cave level, as the current crawlway was wider than today, according to our U/Th dating. Once these visitors reached the panels, the floor in the main gallery would have been around 15 cm lower than at present. However, the morphology of the conduit was similar; this has significant implications for understanding and interpreting the human use of the cave during the Palaeolithic.

Holocene sedimentation in the southwestern Black Sea: Interplay between riverine supply, coastal eddies of the Rim Current, surface and internal waves, and saline underflow through the Strait of Bosphorus

An extensive grid of high-resolution Huntec deep-tow seismic reflection profiles (~9150 line-km), complemented by 72 gravity cores and 25 piston cores reveals that the sedimentary architecture of the southwestern Black Sea above a prominent shelf-crossing unconformity α is characterized by three allostratigraphic units (allounits 1b, 1c, 1d), separated by two regional unconformities and their correlative conformities, α1 and α2. A fourth allounit (1a) occurs as patchy remnants between the α unconformity and a deeper Pleistocene erosional unconformity, α0. The chronology is established using 56 radiocarbon dates in five key piston cores. The α unconformity developed as a ravinement surface during the transgression associated with the transition from the Last Glacial Maximum to Holocene, thus defines the base of the Holocene successions. Allounit 1b is bounded at its base and top by the α and α1 unconformities/correlative conformities. It was deposited between ~12.5 and ~7.4 cal ka and shows a notably patchy but widespread distribution across the southwestern shelf. Allounit 1c is bounded at its base and top by the α1 and α2 unconformities/correlative conformities. It was deposited between ~7.4 and ~5.3 cal ka. Allounit 1d accumulated above the α2 unconformity/correlative conformity and was deposited since ~5.3 cal ka.Interpretation of radiometrically-dated cores and several detailed regional maps reveal that the widespread occurrence of ~12.5–7.4 cal ka deposits (allounit 1b) across the middle and outer shelf provides no possibility for a Holocene evaporative drawdown to a lowstand elevation of −120 m at 9.4 cal ka as suggested by Yanchilina et al. (2017). Instead, the volume of detritus in allounit 1b can only be explained if base level was sufficiently high to allow major distant rivers in Bulgaria and Romania (e.g., Kamchiya, Danube) to contribute mud through long-distance marine transport along a submerged shelf. There is no evidence in any cores which sample allounit 1b that the sites were located in limans, rather than on a transgressed shelf which had been flooded by post-glacial meltwater and enhanced river runoff as the climate became more humid in the early Holocene. A prolonged stillstand at the spill depth controlled by the sill in the Strait of Bosphorus is confirmed by the elevation of a drowned recurved spit downdrift from Cape Emine, Bulgaria. The development of the subaqueous unconformities/correlative conformities α1 and α2 was facilitated by storm-induced wave erosion; transport, bypass and erosion under the Rim Current and its anticyclonic eddies, and possibly breaking internal waves. Volumetrics based on isopach maps and pre-industrial sediment discharge rates of various rivers entering the western and southwestern Black Sea suggest that the total sediment yields of Bulgarian and Turkish rivers can only account for ~13–14% of the total Holocene succession (allounits 1b–1d), and that major input from the Danube River via along-shelf long-distance transport must have occurred through the entire Holocene.

Electron spin resonance dating of the culminant allostratigraphic unit of the Mondego and Lower Tejo Cenozoic basins (W Iberia), which predates fluvial incision into the basin-fill sediments

Abstract The Cenozoic basins of western Iberia have a culminant allostratigraphic unit (designated UBS13), which records the beginning of Atlantic drainage and predates the fluvial incision that led to the development of the present drainage networks. However, the available numerical dating is quite limited and mainly restricted to the lower-level terrace deposits. Therefore, this study uses for the first time the electron spin resonance (ESR) method to date this culminant unit in the Mondego and Lower Tejo Cenozoic basins of Portugal. The depositional age of this unit is supposed to lie between ~3.7 Ma (basal deposits) and ~1.8 Ma (uppermost deposits). The Al-centre provided reliable ESR data, but the dates obtained by using the Ti Li centre clearly underestimate the burial ages. With reference to the existing independent dating of the Vale Farpado site (3.7–3.6 Ma) at the lowermost basal level of the UBS13 deposits, the ESR (Al-centre) ages of 3.0 to 2.3 Ma obtained for the UBS13 basal and middle deposits give reliable estimates of the burial age. The ESR ages (Al-centre) obtained for the UBS13 uppermost deposits indicate a probable age of ~1.8 Ma. Thus, these results are of international significance, in that they constitutes the first numerical ages obtained for the uppermost levels of the Cenozoic basin-fills of western Iberia, which predate the fluvial incision that took place in response to lower Quaternary base levels.

Neogene-Quaternary onshore record in the lower Ebro river incised palaeovalley (Ebro margin, Catalan Coastal Range, NE Iberia)

The lower Ebro is a bedrock-alluvial mixed incised valley with a persistent degradational stacking architecture developed from latest Serravallian(?) to Holocene. This degradational pattern was probably controlled by isostatic rebound in NE Iberia and punctuated by major relative sea level changes that temporally accentuated or attenuated the palaeovalley entrenchment and sediment retention. Six allostratigraphic units in the palaeovalley constitute the onshore record of its evolution and the opening and connection of the Ebro Basin with the Mediterranean. This paper deals with the analysis and reinterpretation of these units in order to precise the sequence of events that took place on the onshore part of the Catalan continental margin during the Ebro River drainage entrenchment. Plausible chronology and palaeogeographic evolution of the Neogene-Quaternary drainage incision in the lower Ebro are also proposed. The early evolutionary stages of the incised palaeovalley (Latest Serravallian?-Tortonian-Early Messinian, from 11.63–9? to near 5.6Ma) were dominated by entrenchment and intense sediment transfer from the onshore to the offshore zones (erosion surface S2). These processes were only punctuated by the sedimentation of the alluvial palaeovalley unit M2 (late Messinian). The polygenetic onshore erosion surfaces S2 and S3 are linked here with the onshore erosive processes that fed the sedimentation of the terrigenous shelf-slope system of the offshore Castellon group and considered coeval with the offshore Messinian erosion surfaces (reflectors M and m). During a further evolutionary stage (Pliocene to Early Pleistocene from 5.3 to approximately 2Ma) the Early Pliocene major Mediterranean reflooding caused some sediment retention in the incised palaeovalley (sedimentation of unit P) but sediment transfer into the offshore remained very effective. In the last evolutionary stage (Early Pleistocene-Holocene, from 2Ma to present) the palaeovalley became again mainly degradational (generation of erosion surfaces S4 to S6 and sedimentation of stepped alluvial terraces Q1-2 to Q4). The onshore stratigraphic record, including the allostratigraphic units P and Q1-2 to Q4 and the related bounding surfaces S3 to S6, is correlated with the sedimentation of the terrigenous shelf-slope system of the offshore Ebro group.

Revised Quaternary glacial succession and post-LGM recession, southern Wind River Range, Wyoming, USA

We present here a more complete cosmogenic chronology of Pleistocene glacial deposits for the Wind River Range, Wyoming, USA. Fifty-one new and thirty-nine re-calculated 10Be and 26Al exposure ages from Sinks and North Fork canyons, Stough Basin, Cirque of the Towers and the Temple Lake valley allow us to more tightly constrain the timing and sequence of glacial alloformations in the southern portion of the range.Moraines, diamicts and bedrock exposures here have previously been correlated with as many as five Pleistocene and four Holocene glacial events. Exposure ages from Pleistocene alloformations associated with trunk glaciers in Sinks Canyon and North Fork Canyon generally confirm earlier age estimates. Cosmogenic radionuclide (CRN, 10Be and 26Al) ages from moraines and striated bedrock surfaces previously mapped as Pinedale correspond to MIS2, while boulder exposure ages from moraines mapped as Bull Lake correspond generally to MIS5-MIS6. Geomorphic data from a moraine previously mapped as Younger pre-Sacagawea Ridge appears to correspond most closely to the Sacagawea Ridge glacial episode (MIS-16), but the uncertainty of a single 10Be exposure age suggests the unit could be as young as MIS-10 or as old as MIS-18. Boulders from a diamict on Table Mountain previously reported as Older pre-Sacagawea Ridge yield two 10Be exposure ages that suggest the presence of Early Pleistocene glacial activity here possibly older than 1–2 Ma (>MIS-30).Bedrock exposure ages within Sinks Canyon suggest the Pinedale valley glacier had retreated from the floor of Sinks Canyon to above PopoAgie Falls by ca. 15.3 ka. Cirque glaciers in Stough Basin appear to have retreated behind their riegels by ca. 16 ka, which suggests the cirque glaciers were decoupling across their riegels from the valley glaciers below at this time, prior to their readvance to form Lateglacial moraines.New 10Be boulder exposure ages from moraines previously correlated to the Temple Lake and Alice Lake allostratigraphic units in the cirques of Stough Basin and Cirque of the Towers show general equivalence to the stadial event just prior to the onset of the Bølling interstadial (17.5–14.7 ka) and to the Intra-Allerød Cold Period-Younger Dryas stadial phase (13.9–11.7 ka), respectively. From this evidence, the Temple Lake Alloformation of the Wind River Mountains now should correspond to the INTIMATE GS-2.1a (Oldest Dryas) stadial event while the Alice Lake Alloformation should correspond to the INTIMATE GS-2 stadial (IACP-Younger Dryas). Thus, we consider that evidence no longer exists for early-to mid-Holocene glacial events in the southern Wind River Range.

Sedimentation close to the active Medlicott Wadia Thrust (Western Himalaya): How to estimate climatic base level changes and tectonics

The Medlicott-Wadia Thrust (MWT) is one of the major active out-of-sequence thrusts in the Himalaya. Studies on Quaternary terraces in its vicinity have been performed using sedimentological, geomorphic and geochronological methods. We focus on the Riasi zone, south of the Pir Panjal range, in the Jammu and Kashmir region of India. The sedimentary units of Quaternary landforms have been mapped as a function of their location with respect to the thrust faults, their relative chronology, and their lithology. Three aggrading sedimentary units, five thin units above strath surfaces at the footwall of the fault system, and seven thin units above strath surfaces at its hangingwall are identified. The terraces have been dated by combining Optically Stimulated Luminescence (OSL) on fine-grained deposits and cosmogenic-nuclide dating (10Be) on sandstone pebbles sampled along depth profiles throughout the alluvial units. Three major allostratigraphic units were defined with upper surface ages estimated at ~4, ~15, and 36±3ka; the two older allostratigraphic units are encased terraces at the hangingwall but superposed sedimentary units at the footwall. They are related to phases of elevation of the river level (respectively 30 and 60m) at ~36–38 and 14–15ka and to a phase of extensive lateral incision before ~4ka. These units present vertical offsets induced by the MWT of 50, 190, and 375m, respectively. By taking the aggradation/incision rates at the footwall of the MWT into account, we found that the uplift of the hangingwall remains uniform since 36ka, with a value of ~10mm/yr. Therefore, the aggradation/incision events observed in the Riasi area cannot be ascribed to variations in the tectonic rates and are most likely driven by climatic fluctuations. The high uplift rate is possibly local and related to the Chenab recess, which affects the Himalayan frontal structure. Our results indicate that the MWT is an active growth fault, and one of the main emergences of the active Indian/Asian plate boundary in Western Himalaya.

Late Miocene–early Pliocene planktonic foraminifer event-stratigraphy of the Bajo Segura basin: A complete record of the western Mediterranean

The Bajo Segura basin (eastern Betic Cordillera) has one of the most complete late Miocene–early Pliocene marine records of the western Mediterranean. An updated planktonic foraminifer zonal scheme based on recent astronomically tuned biozones is presented for this interval, documenting a complete succession of biostratigraphic markers, from biozone MMi9 (earliest Tortonian) to MPl3 (latest early Pliocene), of likely significance for regional-scale correlation throughout the Mediterranean. The findings reveal a series of intrazonal events (some unreported until now in the Mediterranean Neogene basin), including the particularly interesting two influxes of the Globorotalia miotumida group during the Tortonian. These biostratigraphic findings are the basis for a framework of the major allostratigraphic units in the basin based on planktonic foraminifer event-stratigraphy: synthems Tortonian I, Tortonian II, Tortonian-Messinian I, Messinian II, and Pliocene. In addition, the timing of the main tectono-sedimentary and palaeogeographic events throughout the basin's evolution has been further constrained. Our results suggest that, at least in the Bajo Segura basin, the late-Messinian barren interval (non-distinctive zone) can be considered an ecobiostratigraphic zone (cenozone) characterized by dwarf fauna of planktonic foraminifera. Consequently, the Bajo Segura composite section can be regarded as a biostratigraphic reference section for Neogene basins in the Betic Cordillera and hence also in the Western Mediterranean.

Depositional architecture and sequence stratigraphy of Pleistocene coarse-grained deltas along the Ligurian coast (Italy)

This study aims to develop a better understanding of the stratigraphy of the southern side of the Maritime Alps and of the Ligurian Sea during the Plio-Pleistocene. Five stratigraphic sections were measured and studied in the Segno River valley (Liguria, Italy). These sections are composed of Lower to Middle Pleistocene marine and continental deposits. Based on detailed mapping and sedimentological analysis, 12 marine and deltaic facies were identified. These facies were grouped into facies associations. Two allostratigraphic units were recognized, namely U1 and U2 from oldest to youngest. The lower unit (U1) represents the evolution of a coarse-grained delta developed in a valley or embayment. Within the deltaic sequence, transgressive and highstand systems tracts were recognized. The coarsening/shallowing upward trend observed within the sections suggests that the delta prograded rapidly in the landward portion of the canyon adjacent to the paleo-river outlet. The upper boundary of U1 is represented by a subaerial unconformity overlain by U2, which is composed of sediments deposited by several alluvial fan systems.

Dating Pleistocene deltaic deposits using in-situ 26Al and 10Be cosmogenic nuclides

The present study aims at testing the possibility of using the in-situ cosmogenic burial dating technique on deltaic deposits. The sequence analyzed is exposed along the Ligurian coast (north-west Italy) and is made of proximal marine and continental deposits previously considered Pliocene or Plio-Quaternary in age. In the study area two allostratigraphic units were recognized. The lower unit represents the evolution of a small coarse-grained delta developed in a fjord or embayment environment. The coarsening/shallowing upward trend observed within the sections, from bottom to top, suggests that the delta prograded rapidly in the landward portion of the canyon placed opposite to the paleo-river outlet. Within the deltaic sequence the transgressive and highstand system tracts were recognized. The unit 2 is composed by several alluvial fan systems deposited in small incised valleys developed within the previously, uplifted deltaic deposits and successively incised by a braided river system. In-situ produced cosmogenic nuclides were used in order to date the age of the deposition of the deltaic deposits. Results suggest that the studied deltaic sediments belonging to the unit 1 were deposited between 1,300,000 and 200,000 year ago thus during the Lower to Middle Pleistocene, whereas the unit 2 was deposited during the Middle Pleistocene as a consequence of a tectonically driven uplift phase. Furthermore samples collected within the prograding part of the delta show the higher denudation rates. The obtained results demonstrate that burial ages and related erosion rates inferred from cosmogenic nuclides concentrations can be considered as a very useful tool to reconstruct the sea level changes over the past 1 million year.

The stratigraphy of the Sima de los Huesos (Atapuerca, Spain) and implications for the origin of the fossil hominin accumulation

The Sima de Los Huesos (SH) is one of the many archaeo-palaeontological sites in the Sierra de Atapuerca. The characteristics of this palaeoanthropological site are unusual, due to the large size of the hominin accumulation and its location far from the karst entrances, at least today. In order to investigate the geological processes involved in the site formation and their relation to the hominin deposit, we have performed a study of the stratigraphical sequence and depositional history of SH. Analysis and correlation of the identified layers has allowed us to redefine the depositional structure of the site based on twelve lithostratigraphic units, which can be further grouped into five allostratigraphic units delimited by erosional boundaries. The results show that there was only one stratigraphic event of hominin accumulation. Cave bears and other carnivores occur with the hominin fossils in the same layer, but carnivores continued accumulating above the hominin deposit in an overlying layer. Our findings also argue against the hypothesis that the hominin or carnivore bones were transported to SH from a locus of primary accumulation remote from their present day location. The present study also reveals that, at the time of the hominin and carnivore fossil accumulations, the only possible access to the SH chamber was a deep vertical conduit, which was impossible to climb.

Architectural–landsystem analysis of a modern glacial landscape, Sólheimajökull, southern Iceland

Glacial terrains are commonly recorded using a landsystem approach, which allows detailed documentation of the geomorphological evolution of the landscape. However, landsystem analysis of Quaternary subsurface stratigraphies in which landforms are not apparent or preserved is problematic, making delineation of the sedimentary architecture of a glaciated basin infill difficult. The purpose of this study is to delineate the sedimentary architecture of the Sólheimajökull (southern Iceland) glacial landsystem and to provide an architectural framework for allostratigraphy and modern analogue purposes. An integrated architectural–landsystem approach is applied here, which utilizes the principles from both architectural element analysis and landsystem analysis. A bounding surface hierarchy (fourth- to seventh-order surfaces) provides a framework within which the architecture is organized. Fieldwork was conducted at Sólheimajökull glacier in 2012 and 2013; and 22 different surface features (bounded by the fourth-order surfaces) were mapped, which were grouped into four different landsystem tracts (glaciofluvial, ice-contact, jökulhlaup, and colluvial slope; bounded by the sixth-order surfaces). Landsystem tracts were deconstructed into smaller architectural units (components; bounded by the fifth-order surfaces), which allowed the delineation of eight allostratigraphic units that record the evolution of the glacial landsystem from ~7000YBP to A.D. 2013. The results of this study can provide insight to interpretation and delineation of the sedimentary architecture of other modern glacial landsystems and subsurface Quaternary deposits in North America and other formerly glaciated areas.

Geological map of the Miocene-Pleistocene successions of the Mejillones Peninsula, Northern Chile

The Mejillones Peninsula (northern Chile) has undergone a complex tectono-sedimentary history from the Miocene onward and is dissected by a network of normal faults that generated three asymmetric half-grabens located in a forearc position with respect to the Chile subduction system. A new 1:50,000-scale geological map of the peninsula, covering an area of ca 800 km2 and based on a detailed facies analysis and field mapping (1:20,000 scale) in conjunction with a comprehensive interpretation of aerial photographs (1:33,000 scale), gives new and updated information about the nature of marine sedimentation and deformation during the Miocene to Pleistocene and permits the geological history of the peninsula during this time period to be reconstructed. An important aspect of organising the Miocene to Pleistocene stratigraphy has been the recognition of three regional allostratigraphic units in the hangingwall basin-fill sediments (the Miocene Caleta Herradura, Pliocene La Portada, and Pleistocene Mejillones alloformations) and two major morphostratigraphic units (PlioMMU and PleiMMU) including extensive flights of Pliocene and Pleistocene marine terraces carved on crestal and flanking areas of adjacent footwall blocks.

Stratigraphic signatures of punctuated rise in relative sea-level in an estuary-dominated heterolithic succession: Incised valley fills of the Toarcian Ostreaelv Formation, Neill Klinter Group (Jameson Land, East Greenland)

The Ostreaelv Formation (latest Pliensbachian–Toarcian) of the Neill Klinter Group is exposed along a >105 km wide, ENE-trending section in Jameson Land, East Greenland. Deposition took place in a large embayment (Jameson Land Basin) that was connected to the proto-Norwegian-Greenland Sea. Lithofacies in the Ostreaelv Formation range from clean sandstone to muddy heterolithic facies typified by strong grain-size contrasts.The Ostreaelv Formation is divided into four distinct and overall retrograding allostratigraphic units each composed of a characteristic set of tide-influenced, tide-dominated and wave-influenced facies associations. The allostratigraphic units are bounded by subaerial unconformities, interpreted as sequence boundaries, and are up to 75 m thick and 16 to >20 km in width. The allostratigraphic units include a sandy heterolithic estuary bay-head delta succession overlain by two sandy tide-dominated estuary fill successions, interbedded with a muddy heterolithic offshore marine succession. Each of the three estuarine allostratigraphic units was accumulated in an incised valley formed during fall in relative sea level and filled during successive transgressions with sediment supplied from marine and reworked fluvial deposits.In the three incised valleys fluvial sediments were deposited on top of an initial subaerial unconformity surface (SU) and were later reworked by succeeding transgressive ravinement along a transgressive surface (TS), thus creating combined SU/TS sequence boundaries. The data from the Ostreaelv Formation also provides knowledge and conceptual understanding of valley infill processes (tidal current, wave and fluvial energy), and both lateral and vertical variations in lithofacies architecture within incised valleys.Moreover, the study provides quantitative input data, such as incised valley dimensions, sand-containing capacity, and geometry to subsurface reservoir characterisation and modelling efforts of estuary fill successions.

Pollen and spore biostratigraphy of the mid-Cretaceous Tupuangi Formation, Chatham Islands, New Zealand

The Tupuangi Formation, a mid-Cretaceous terrestrial stratigraphic succession from the Chatham Islands (New Zealand), provides a unique perspective into high polar latitudinal (75–80°S) conditions that have no modern analogues. Detailed investigations of the biostratigraphy of these sediments have constrained the age of crucial tectonic, climatic and ecologic events of this time. This study examined two sedimentary successions of the Tupuangi Formation on Pitt Island (Chatham Islands), and 41 palynomorph samples were retrieved and processed for biostratigraphic analysis. By comparing the stratigraphy and palynological assemblages of the two examined outcrop successions, this study produced the first island-wide biostratigraphic correlation of the Tupuangi Formation, and four allostratigraphic units (one alloformation subdivided into three allomembers) were identified; the unconformities that define the boundaries of these were verified by pollen and spore index species. Two of these unconformities have correlatives on mainland New Zealand. 18 spore/pollen taxa were used for these correlations, including two new spore taxa (Biretisporites labruplenus sp. nov. and Klukisporites sphaerogoufus sp. nov.), one newly validated spore taxon (Gleicheniidites ancorus sp. nov.), and two new pollen taxa (Liliacidites exquisitus sp. nov. and Trichotomosulcites hemisphaerius sp. nov.). The examined Tupuangi Formation outcrop successions correspond to the Ngaterian to Mangaotanean New Zealand chronostratigraphic stages (Cenomanian to Turonian; 99–89Ma). The timing of deposition for the Tupuangi Formation yields supporting evidence for the notion of a failed-rift basin in eastern Zealandia prior to sea-floor spreading between Zealandia and Marie Byrd Land, Antarctica. Previous studies suggested a negligible time-gap between the Tupuangi Formation, and the overlying Kahuitara Tuff; however, supported by evidence of reworking, this study suggests a temporal hiatus of >4Ma. This time-gap was most likely caused by thermal uplift prior to the onset of sea-floor spreading between Zealandia and Antarctica.

Climatic, geomorphic, and archaeological implications of a late Quaternary alluvial chronology for the lower Salt River, Arizona, USA

Recent archaeological excavations along the lower Salt River, Arizona resulted in the unexpected discovery of buried late Pleistocene soils and cultural features dating 5800–7100cal YBP (Early Archaic), the latter representing the earliest evidence of human activity in the lower Salt River floodplain thus far identified. Because the lower Salt River floodplain has been heavily impacted by recent agriculture and urbanization and contains few stratigraphic exposures, our understanding of the river's geological history is limited. Here we present a late Quaternary alluvial chronology for a segment of the lower Salt River based on 19 accelerator mass spectrometry 14C and four optically stimulated luminescence ages obtained during two previous geoarchaeological investigations. Deposits are organized into allostratigraphic units and reveal a buried late Pleistocene terrace inset into middle-to-late Pleistocene terrace deposits. Holocene terrace fill deposits unconformably cap the late Pleistocene terrace tread in the site area, and the lower portion of this fill contains the Early Archaic archaeological features. Channel entrenchment and widening ~900cal YBP eroded much of the older terrace deposits, leaving only a remnant of fill containing the buried latest Pleistocene and middle-to-late Holocene deposits preserved in the site area. Subsequent overbank deposition and channel filling associated with a braided channel system resulted in the burial of the site by a thin layer of flood sediments. Our study confirms that the lower Salt River is a complex mosaic of late Quaternary alluvium formed through vertical and lateral accretion, with isolated patches of buried soils preserved through channel avulsion. Although channel avulsion is linked to changes in sediment load and discharge and may have climatic linkages, intrinsic geomorphic and local base level controls limit direct correlations of lower Salt River stratigraphy to other large rivers in the North American Southwest.

Rapid and widespread response of the Lower Mississippi River to eustatic forcing during the last glacial-interglacial cycle

The Lower Mississippi Valley provides an exceptional fi eld example for studying the response of a continental-scale alluvial system to upstream and downstream forcing associated with the large, orbitally controlled glacialinter glacial cycles of the late Quaternary. However, the lack of a numerical chronology for the widespread Pleistocene strata assemblage known as the Prairie Complex, which borders the Holocene fl oodplain of the Lower Mississippi River, has so far precluded such an analysis. Here, we apply optically stimulated luminescence (OSL) dating, mainly on silt-sized quartz from Prairie Complex strata. In total, 27 OSL ages indicate that the Prairie Complex consists of multiple allostratigraphic units that formed mainly during marine isotope stages 7, 5e, and 5a. Thus, the aggradation of the Prairie Complex is strongly correlated with the sea-level highstands of the last two glacialinterglacial cycles. Fluvial incision during the sea-level fall associated with the MIS 5a–MIS 4 transition extended as far inland as ~600 km from the present-day shoreline, testifying to the dominant downstream control of fl stratigraphic architecture in the Lower Mississippi Valley. In addition, the short reaction time of the Lower Mississippi River suggests that large fl uvial systems can respond much more rapidly to allogenic forcing than is commonly believed.