Cyclothemic Succession Research Articles

Current synthesis of the penultimate icehouse and its imprint on the Upper Devonian through Permian stratigraphic record

Abstract Icehouses are the less common climate state on Earth, and thus it is notable that the longest-lived ( c. 370 to 260 Ma) and possibly most extensive and intense of icehouse periods spanned the Carboniferous Period. Mid- to high-latitude glaciogenic deposits reveal a dynamic glaciation–deglaciation history with ice waxing and waning from multiple ice centres and possible transcontinental ice sheets during the apex of glaciation. New high-precision U–Pb ages confirm a hypothesized west-to-east progression of glaciation through the icehouse, but reveal that its demise occurred as a series of synchronous and widespread deglaciations. The dynamic glaciation history, along with repeated perturbations to Earth System components, are archived in the low-latitude stratigraphic record, revealing similarities to the Cenozoic icehouse. Further assessing the phasing between climate, oceanographic, and biotic changes during the icehouse requires additional chronostratigraphic constraints. Astrochronology permits the deciphering of time, at high resolution, in the late Paleozoic record as has been demonstrated in deep- and quiet-water deposits. Rigorous testing for astronomical forcing in low-latitude cyclothemic successions, which have a direct link to higher-latitude glaciogenic records through inferred glacioeustasy, however, will require a comprehensive approach that integrates new techniques with further optimization and additional independent age constraints given challenges associated with shallow-marine to terrestrial records.

Palaeosols in an Upper Pliocene fluvial to shallow marine succession (Valdelsa Basin, Central Italy): A sequence-stratigraphic perspective

The present study provides an example of how palaeopedology and facies analysis may be integrated for the interpretation of a cyclothemic succession in the Upper Pliocene (Piacenzian) of the Valdelsa Basin (central Italy). The stacking of facies and intervening bounding surfaces, including palaeosols, outline a hierarchy of elementary (EDS) and composite (CDS) depositional sequences within the unconformity-bounded stratigraphic units (S4-S6 synthems) which compose the succession. The focus of the study is on synthem S4 and the transition to synthem S5. Synthem S4 records the development of a distal alluvial plain dominated by floodbasin mudstone with subordinated channelized sandstone (S4 1 ), followed by the incision of a fluvial valley aggraded by the cyclical stacking of braided and low sinuosity channelized conglomerate and sandstone (S4 2 ). Synthem S5 includes lower shoreface sandstone and inner shelf mudstone related to a major transgression which affected the study area during the late Piacenzian. Evidence of soil-forming processes is well preserved within sub-unit S4 1 where five palaeosols (PS4a-e) are stacked within the facies architecture of EDS1 c-d , both being defined as transgressive to high stand tracts. Increasing palaeosol development was observed within both EDSs, while palaeosols were generally thicker and more closely stacked within EDS1 d . Palaeosols were interpreted as marking minor cycles of accommodation space creation within EDS1 c , while marking a better defined high stand tract in EDS1 d . Increasing upward soil development was observed within each EDS, with generally better developed soils in EDS S41d. The unconformable transition from S4 to S5 is marked by a thin veneer of slope deposits, bearing pedogenic carbonates reworked from a missing PS4f palaeosol, formed during the shaping of the erosional surface separating sub-units S4 1 and S4 2 . The results of this study indicate that: 1) the sedimentary and pedogenic processes recorded in the channelized facies and palaeosols in the floodbasin facies of sub-unit S4 1 , are coherent with a palaeoenvironmental setting dominated by seasonal climate; 2) the facies-palaeosol architecture of S4 synthem corresponds to those described in sequence-stratigraphic models applied to continental successions. The pedo-sedimentary signature of the major sea-level fluctuation recorded in the transition between S4 and S5 synthem differs from these models. In this case a well-developed and drained palaeosol, expected to record the maximum regressive surface shaped during the falling stage of sea level, is missing. This difference is related to a rapid fall and subsequent rise of relative sea level which marked the transition between S4 and S5 synthems. • Palaeosol and facies analysis coherently restore a Piacenzian fluvial system. • A seasonal climate controlled sediment dispersal and weathering. • Palaeosols are key-surfaces in the cyclical fluvial facies architecture. • Cyclothemic stack of palaeosols partially fits sequence-stratigraphic models. • Major sequence boundary lacks a well developed palaeosol.

Carboniferous Manning Canyon Formation, northern Utah, USA: A carbonate-mud-dominated cyclothem motif recording the main onset of the late Paleozoic Ice Age

A poorly understood Mississippian to basal Pennsylvanian succession is preserved in parts of northern Utah, western USA. The mudrock- and carbonate-dominated Manning Canyon Formation and lateral equivalents have been referred to as “cyclothems” and might therefore be expected to preserve a record of repeated, late Paleozoic sea-level excursions similar to cyclothemic successions elsewhere in the paleotropics. In this paper, we document the sedimentology and stratigraphy of the Serpukhovian to earliest Bashkirian Manning Canyon Formation, focusing on surface exposures in the Oquirrh and Uinta Mountains and a cored subsurface intersection from central Utah. Four facies associations were identified in the Manning Canyon Formation: Mid-Shelf, Muddy Inner Shelf, Deltaic, and Coastal Plain, which are herein interpreted in the context of a muddy, semi-enclosed, epicontinental carbonate shelf fringed by a low-relief coastal plain. These facies associations are broadly comparable to recent and extant environments from a range of equatorial, clay-rich, deltaic, coastal plain, and offshore carbonate-producing environments in the Caribbean Sea, northern Australia, and SE Asia, which can be used as first-order analogues for the Manning Canyon Formation. These modern analogues suggest that several relative sea-level excursions of <40 m are recorded in the unit. The stratigraphically oldest records of substantial relative sea-level oscillations are in the lowermost Manning Canyon Formation. These preceded a more sustained pattern recorded by at least nine 4th-order, high-frequency and high-magnitude (≥40 m) sea-level cycles that characterize the upper two-thirds of the formation. Sea-level highstands are recorded by open marine shelf facies, whereas lowstands are recorded by incised channel and valley fills, and (presumed) laterally equivalent paleosols and thin coals. No record of high frequency/high magnitude relative sea-level oscillations comparable in character to those preserved in the Manning Canyon Formation was documented in the underlying stratigraphy. It is concluded that the Manning Canyon Formation may record the main onset of the eustatic signal associated with the main phase of the late Paleozoic Ice Age at ~330 Ma.

Foraminiferal biostratigraphy of Brigantian-Arnsbergian limestones from eastern Scotland and Northumberland (northeast England)

ABSTRACTForaminifers, calcareous algae and incertae sedis Algospongia of late Asbian to late Brigantian age in limestones from East Fife, East Lothian and Northumberland, enable the base of the late Brigantian to be recognised in all these areas. Preservation of the late Asbian and early Brigantian limestones in cyclothemic successions is generally poor. The St Monans White Limestone (St Monans, Fife), First Abden Limestone (Kirkcaldy, Fife), Middle Longcraig Limestone (East Lothian) and Lower Bath-House Wood/Middle Bath-House Wood (Northumberland) were confidently correlated by their foraminiferal assemblages. These limestones are all assigned to the top of the Assemblage 6 in northern England (Single Post Limestone). The St Monans Brecciated/St Monans Little/Charlestown Main limestones (St Monans, Fife) and the Second Abden/Seafield Tower limestones (Kirkcaldy, Fife), Upper Longcraig/Lower Skateraw limestones (East Lothian), Upper Bath-House Wood/Shotto Wood limestones and Eelwell Limestone (Northumberland) are assigned to the Assemblage 7 in northern England (Scar Limestone and Five Yard Limestone). The paired Middle/Upper Skateraw limestones (East Lothian) and the Acre Limestone (Northumberland) contain representatives of the Assemblage 8 from northern England (Three Yard Limestone). Higher up in the succession, in Northumberland, the foraminiferal assemblage in the Sandbanks Limestone can be compared with Assemblage 9 in northern England (Four Fathom Limestone). Above the Great Limestone and Little Limestone, with their characteristic Pendleian assemblages, the Sugar Sands Limestone and Corbridge Limestone contain Arnsbergian foraminiferal assemblages, typical of the Lower Felltop Limestone in northern England. The Lower Foxton Limestone is correlated with the Upper Felltop Limestone, whereas the Thornbrough Limestone in Northumberland lacks diagnostic Arnsbergian taxa.

Late Mississippian glacio-eustasy recorded in the eastern Paleo-Tethys Ocean (South China)

Long-lived and extensive glaciation during the Carboniferous and early Permian has been the focus of many studies over the past decade revealing systematic changes in sea level and climatic conditions. The nature of the inception of Carboniferous glaciation, however, remains poorly resolved with uncertainty regarding the timing and dynamics of buildup of continental ice sheets. Here we present detailed sedimentary facies and depositional cycles from Upper Mississippian shallow-water platform and contemporaneous carbonate slope successions from the eastern Paleo-Tethys Ocean region (South China) to reveal systematic variations that provide insight into the sedimentary response to the onset of Carboniferous glaciation. Based on detailed sedimentological logging and facies analysis, four upper Visean cycles and four Serpukhovian cycles were identified from the carbonate platform Yashui section, bounded by either subaerial surfaces or zones, or transgressive surfaces. The cycle tops roughly correspond to intervals rich in normally graded bioclastic wacke- to packstones and with distinct rises (~1‰) in conodont δ18OPO4 in the carbonate slope Naqing section. In particular, the four Serpukhovian cycles correlate well to depositional cycles defined in the Lower Yangtze Platform succession of South China and in the cyclothemic successions in the Donets Basin, Ukraine, suggesting a glacio-eustatic control, most likely caused by repeated advance and retreat of Gondwana glaciation during the onset but prior to widespread glaciation across the mid-Carboniferous boundary.

Carboniferous climate teleconnections archived in coupled bioapatite [formula omitted] and 87Sr/86Sr records from the epicontinental Donets Basin, Ukraine

Reconstructions of paleo-seawater chemistry are largely inferred from biogenic records of epicontinental seas. Recent studies provide considerable evidence for large-scale spatial and temporal variability in the environmental dynamics of these semi-restricted seas that leads to the decoupling of epicontinental isotopic records from those of the open ocean. We present conodont apatite δ18OPO4 and 87Sr/86Sr records spanning 24 Myr of the late Mississippian through Pennsylvanian derived from the U–Pb calibrated cyclothemic succession of the Donets Basin, eastern Ukraine. On a 2 to 6 Myr-scale, systematic fluctuations in bioapatite δ18OPO4 and 87Sr/86Sr broadly follow major shifts in the Donets onlap–offlap history and inferred regional climate, but are distinct from contemporaneous more open-water δ18OPO4 and global seawater Sr isotope trends.A −1 to −6‰ offset in Donets δ18OPO4 values from those of more open-water conodonts and greater temporal variability in δ18OPO4 and 87Sr/86Sr records are interpreted to primarily record climatically driven changes in local environmental processes in the Donets sea. Systematic isotopic shifts associated with Myr-scale sea-level fluctuations, however, indicate an extrabasinal driver. We propose a mechanistic link to glacioeustasy through a teleconnection between high-latitude ice changes and atmospheric pCO2 and regional monsoonal circulation in the Donets region. Inferred large-magnitude changes in Donets seawater salinity and temperature, not archived in the more open-water or global contemporaneous records, indicate a modification of the global climate signal in the epicontinental sea through amplification or dampening of the climate signal by local and regional environmental processes. This finding of global climate change filtered through local processes has implications for the use of conodont δ18OPO4 and 87Sr/86Sr values as proxies of paleo-seawater composition, mean temperature, and glacioeustasy.

Problems correlating the late Brigantian–Arnsbergian Western European substages within northern England

AbstractA detailed study of foraminiferal assemblages recorded in limestones from northern England in the Stainmore Trough and Alston Block permits their assignment to different European substages than in previous studies. Comparisons with foraminiferal assemblages, mostly from Russia, allow the biozonations to be correlated with the Viséan, Serpukhovian and Bashkirian international stages, as well as with the Russian (and Ukrainian) substages for the Serpukhovian (Tarussian, Steshevian, Protvian and Zapaltyubian). The Scar Limestone and Five Yard Limestone Members are assigned to the Tarussian and, thus, represent the lowermost part of the formal Serpukhovian Stage. This new correlation coincides closely with the first occurrence of the conodont Lochriea ziegleri from levels equivalent to the Single Post Limestone that could potentially form the revised base for the Serpukhovian. The Three Yard Limestone Member is correlated with the base of the Steshevian substage which also includes the Four Fathom Limestone Member, Great Limestone Member and Little Limestone. The base of the Protvian is considered to lie within the Crag Limestone, whereas the Rookhope Shell Band contains foraminiferal assemblages more typical of the Zapaltyubian in the Ukraine and Chernyshevkian in the Urals. Assemblages of the Upper Fell Top Limestone and Grindstone/Botany Limestones contain foraminiferal species that have been used for the recognition of the Bashkirian elsewhere. There is no other fossil group which allows the calibration of those foraminiferal assemblages, because ammonoids are virtually absent in the shallow‐water cyclothemic successions and conodonts have not been studied in detail in this region. The Mid‐Carboniferous boundary and the Voznessenian substage might be reasonably located below the Upper Fell Top Limestone. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Pennsylvanian–Early Permian cyclothemic succession on the Yangtze Carbonate Platform, South China

Abstract Pennsylvanian (Late Carboniferous)–Early Permian cyclothems are documented for the first time from the shallow-marine carbonate succession on the Yangtze Carbonate Platform, South China. The Zongdi section in southern Guizhou Province comprises bioclast-rich grey limestones with dark-coloured intervals yielding macro- and microfabrics related to emergent events. We recognized 26 depositional sequences (consisting essentially of basal peritidal sediments, middle shallow subtidal sediments and upper peritidal sediments affected by meteoric diagenesis and subaerial exposure) separated by 25 lowstand events. These are interpreted as having been formed by alternating marine transgression and regression resulting from variations in the Gondwanan ice sheets. They are compared with the Midcontinent (Kansas-type) cyclothems in North America. However, the Zongdi cyclothems are relatively thin and consist entirely of very shallow-marine sediments formed above wave base, whereas the Midcontinent cyclothems reflect deposition far below wave base. The Zongdi depositional environment was an upper shelf area, on a platform within the epeiric sea on the South China Craton, where sedimentation occurred in a relatively small (shallow) accommodation space during the highest stands of sea level. They were formed by major (large-scale) transgressions that submerged high-shelf areas, and most of them correspond to the major cyclothems of the North American Midcontinent Basin. The fusuline biostratigraphical framework reveals an uneven stratigraphical pattern of the Zongdi cyclothems, reflecting subtle fluctuations of tectonic subsidence on the epeiric Yangtze Carbonate Platform. Less erosion and karstification on the tops of cyclothems in the Zongdi section, together with the presence of partly calcareous palaeosols, indicates that a dry climate prevailed on the South China Block during the Pennsylvanian–Early Permian when the Zongdi cyclothems were formed.

A paleotropical carbonate-dominated archive of carboniferous icehouse dynamics, Bird Spring Fm., Southern Great Basin, USA

Much of our far-field knowledge of glaciation and climate during the late Paleozoic ice age is built on decades of study of mixed carbonate–siliciclastic cyclothemic successions from paleotropical Euramerica. Far fewer carbonate-dominated successions have been studied despite their high sensitivity to changes in accommodation space and environmental conditions. Here we present a sequence stratigraphic framework for the carbonate-dominated Bird Spring Formation, southern Great Basin, U.S.A. and infer from it a relative sea-level history for the latest Mississippian through latest Pennsylvanian. Correlation of four successions across the paleo-platform documents changes in the lithofacies composition of meter-scale cycles, their cycle stacking patterns, and cycle bounding surfaces that record substantial variation in relative sea-level at several temporal scales during the Pennsylvanian. Ten genetic sequences bounded by intervals of restricted peritidal lithofacies, karst, terra rossa, rooted caliche and/or Protosols are recognized. Within sequences, 126 parasequences stack into parasequence sets that in turn define lowstand, transgressive and highstand systems tracts. The stratigraphic cycle stacking patterns and across-platform architecture of systems tracts suggest a mid-Carboniferous lowstand in relative sea level followed by a middle Morrowan (middle Bashkirian) highstand as previously suggested (Bishop et al., 2010). Subsequent progradation of the platform occurred during a gradual long-term fall through the late Morrowan and Atokan (late Bashkirian–early Moscovian), upon which repeated higher frequency events were superimposed, culminating in widespread exposure across the platform proximal to the Atokan–Desmoinesian boundary. Long-term sea level increased into the mid-Desmoinesian (end-Moscovian) after which progradation (late Desmoinesian) and aggradation (Missourian–Virgilian) of shallow-water and peritidal carbonates occurred across the Bird Spring platform. The progradational-to-aggradational phase involved an abrupt shift from ramp to rimmed shelf geometry in the Missourian (Kasimovian) likely in response to progressively increasing sea level, dampened high-frequency sea level fluctuations and/or to regional faulting along the Bird Spring platform margin. Inferred magnitudes of short-term (105yr) fluctuations superimposed on the longer-term rises and falls range from 20 to >70m during the early to mid-Pennsylvanian and are substantially reduced (≤20m) during the late Pennsylvanian. The early to middle Pennsylvanian sea-level history inferred from the carbonate-dominated Bird Spring platform corresponds well with a recently published Pennsylvanian onlap–offlap history defined from the cyclothemic succession of the Donets Basin and with independent near-field reconstructions of glaciation during the Pennsylvanian.

Sequence stratigraphy and onlap history of the Donets Basin, Ukraine: Insight into Carboniferous icehouse dynamics

The degree to which Permo-Carboniferous cyclothemic successions archive evidence for long-term variations in ice volume during the Late Paleozoic Ice Age is insufficiently resolved. Here we develop the sequence stratigraphy and onlap–offlap history for a 33-my interval of the Carboniferous using the U–Pb calibrated succession of the Donets Basin, Ukraine, in order to assess the relationship between sea-level, high-latitude changes in glacial extent, and climate. Integrated subsurface and outcrop data permit meter-scale correlation of 242 biostratigraphically constrained limestones and coals, and in turn individual cyclothems, across ~ 250 km of the Donets Basin. Rapid uniform subsidence and basinwide continuity of marker beds indicate Pennsylvanian deposition under relatively stable tectonic conditions. Three scales of sequences (avg. durations of ~ 140 ky, ~ 480 ky and 1.6 my) are recognized on the basis of stratigraphic stacking patterns and basinwide architecture of marine to terrestrial facies assemblages. The hierarchy of sequences and the geographic and stratigraphic positions of shifts in base-level sensitive facies across the Donets ramp permit the construction of an onlap–offlap history at a sub-400 ky scale. Major sea-level lowstands occur across the mid-Carboniferous boundary and during the early Moscovian. These lowstands coincide with glacial maxima inferred from high-latitude glacigenic deposits. The middle to late Pennsylvanian is characterized by a stepwise onlap, culminating in an earliest Gzhelian highstand, suggesting contraction of Carboniferous ice sheets prior to the initiation of Early Permian glaciation. The stratigraphic position of climate sensitive facies within individual Donets cyclothems indicates a turnover from seasonal sub-humid or semi-arid climate to everwet conditions during the late lowstand and maximum ice sheet accumulation. Comparison of the stratigraphic and aerial distribution of coals and evaporites in the Donets Basin with the onlap–offlap history further indicates everwet conditions during lowstands and inferred glacial maxima and drier climate during onlap and inferred ice sheet contraction at the intermediate (~ 0.8 to 1.6 my) and long (10 6 yr) time-scales. Taken together, the relationship between inferred climate and glacioeustasy suggests a likely teleconnection between high-latitude ice sheet behavior and low-latitude atmospheric dynamics.

Basin physiography and tectonic influence on sequence architecture and stacking pattern: Pleistocene succession of the Canoa Basin (central Ecuador)

Facies, shell bed features, and sequence stratigraphic framework for the shallow-marine Pleistocene upper Canoa and Tablazo Formations are presented, based on outcrop data from the southern coast of Cabo San Lorenzo, Ecuador. Sediments of this succession exhibit a distinct cyclic pattern, consisting of a stack of eight depositional sequences (cyclothems) likely developed under the main control of orbitally induced sea-level changes. As a rule, within the studied interval an idealized cyclothem is composed of a transgressive systems tract (TST) and a highstand systems tract (HST), whereas deposits attributable to the lowstand and falling-stage systems tracts are not present. Transgressive lithosomes may be defined by estuarine deposits interposed between the sequence boundary and the ravinement surface (back-barrier wedge) and by upward fining shoreface to inner-shelf facies successions above the ravinement (backstepping shelf wedge). Separated by an expanded siliciclastic core, hiatal shell concentrations occur at the base (onlap shell beds) and the top (backlap shell beds) of the transgressive shelf wedges, and some occur at the base of highstand systems tracts (downlap shell beds). On the basis of sedimentary facies, geometry, taphonomy, and paleoecology of shell beds, and the nature of the transition between siliciclastic and mollusk-bearing sediments, cyclothems were classified into two main types that show dependence upon paleoshoreline morphological configuration: sheltered (in the upper Canoa Formation) and exposed (in the Tablazo Formation). Notwithstanding the different synsedimentary tectonic and climatic regimes, the Ecuadorian cyclothems share basic patterns of condensation and facies assemblages with other roughly coeval cyclothemic successions around the world. This suggests that (1) hiatal shell bed development is not just a temperate-latitude phenomenon; (2) a global process, such as glacio-eustatic sea-level change, is the primary mechanism of control for the general architecture of sequences; and (3) specific paleogeographic settings play an important role by determining the taphonomic and paleoecologic characteristics of key shell beds, the nature of their contacts with the encasing sediments, and the type of the component set of facies. At a multicycle time scale, tectonics influenced the long-term trend of the relative sea-level changes and consequently the large-scale stratigraphic organization. Owing to the continued tectonic uplift of the area, successive high-frequency depositional sequences are nested to form a longer-order falling-stage sequence set.

Facies relationships and cyclicity of high-latitude, Late Permian coal measures, Bowen Basin, Australia

The Late Permian Moranbah Coal Measures are developed throughout the northern and central Bowen Basin, eastern Australia, and are subject to large-scale opencut coal mining activity. They were deposited in a rapidly subsiding retroarc foreland basin, during frequent base-level changes. Contemporaneous compressive deformation and volcanism facilitated the supply of abundant volcanoclastic sediments, resulting in rapid, but punctuated, basinal aggradation. To the south and east, transgressive–regressive cycles were marked by the inter-digitation of paralic–shallow marine and alluvial strata. Lonestones (dropstones) are common within the marine deposits and are attributed to ice-rafting indicative of a cold-climate depositional regime. Two basin-wide chronostratigraphic units, the P-tuff bed and the Harrow Creek superseam, have been used to evaluate the facies architecture of the stratigraphic interval they enclose. The lithofacies mosaic of the 25–75 m thick sequence has been examined by means of 26 widely distributed coreholes and two detailed district-scale studies based around the Moranbah–Goonyella and German Creek minesites. Eight alluvial–shallow marine facies associations have been recognised. Their architectural and temporal relationships allow the accurate reconstruction of the coal-bearing depositional system. Two dissimilar, stacked, depositional systems tracts, A (organics) and B (clastics) are recognised. The P-tuff bed is enclosed by facies of tract A, forming a thick, low-ash, coal-bearing interval which was emplaced essentially synchronously across the basin. It represents a time of clastic sediment starvation when basin-wide peat mire accumulation prevailed. Four similar extensive coal-bearing intervals within the Moranbah Coal Measures are also considered to represent basin-wide episodes of peat accumulation. This pattern is in strong contrast to traditional views of coal measure development, which argue that coals formed within a contemporary facies mosaic, in which fluvial channels, levees and crevasse splays were also represented. The second depositional systems tract (B) is characterised by clastic packages, dominated by large-scale (up to 4 km wide and 50 m thick), sandstone bodies deposited by low sinuosity trunk river systems, flanked by substantial crevasse splay deposits (up to 3 km wide and 30 m thick). It represents the product of catastrophic flooding events. The cyclothemic succession of systems tracts A and B is interpreted in terms of eustatic sealevel cycles. The tract A coal-bearing intervals represent relative sealevel lowstands. Systems tract B represents relative sea level highstand with its lower interval at German Creek to the south consisting of paralic and marine facies. The cycles had durations in the order of 400 to 600 ky and are considered to represent 4th order sealevel cycles of the Permian Period.

Exposed coasts vs sheltered bays: contrast between New Zealand and Japan in the molluscan record of temperature change in Plio–Pleistocene cyclothems

Cyclothems in the Omma Formation, on the Japan Sea coast of central Honshu, each contains two ecostratigraphic datums: the appearance and disappearance datums of warm-water molluscs. Cold-water molluscs occur both below (in early TST) and above (in late HST and possibly RST) warm-water ones (which occur in late TST and early HST). In contrast, no New Zealand cyclothems in the main Plio–Pleistocene basins contain both cold- and warm-water faunas in one cycle. Cyclothems in the Petane Group, central Hawke's Bay and in the Castlecliff section, Wanganui Basin, contain entirely eurythermal and warm-water molluscs throughout. Cyclothems in South Wairarapa have entirely eurythermal and cold-water molluscs throughout (the subantarctic Zygochlamys delicatula fauna), even in HSTs of some cycles. This contrast demonstrates the importance of exposure of the deposition site to strong coastal currents for the maximum faunal expression of temperature change. The Omma Formation was deposited in an open site on the Japan Sea coast, where currents transported larvae of a wide variety of molluscs northwards and southwards in response to temperature oscillations. The main New Zealand cyclothemic successions were deposited in large embayments, sheltered from the influence of coastal currents. The maximum faunal expression within one cyclothem of Plio–Pleistocene temperature change can be expected in only those few deposition sites that satisfy the optimum requirements: deposition of reasonably complete sequences (at least TSTs, HSTs and RSTs preserved) in an exposed coastal site influenced by strong currents from both the north and south, on the inner shelf, in the temperate regions (between ca. 30° and 60°, north and south), near the north–south oriented coast of a large continent.

Late Pliocene (2.8 ‐2.4 Ma) cyclothemic shelf deposits, Parikino, Wanganui Basin, New Zealand: Lithostratigraphy and correlation of cycles

The Wanganui River valley in the vicinity of Parikino in western Wanganui Basin, New Zealand, contains a late Pliocene, c. 400 m thick, southward dipping (c. 5°) cyclothemic marine succession. Thirteen sedimentary cycles or cyclothems occur within the succession. The lower two sandstone‐dominated cycles are assigned to the Paparangi Group, which includes a renamed formation (Pitangi Sandstone) and a newly defined formation (Moukuku). The overlying Okiwa Group is emended, its base being relocated to the base of the Wilkies Shellbed. This group contains seven new formations, in ascending order: Whauteihi, Whakaihuwaka, Tirotiro, Parikino, Whariki, Shaw, and Wickham Formations. Most formations contain one or more unconformity‐bounded cyclothems, which comprise a lower thin (0.2–1.5 m thick) coquina (shellbed) member, an overlying siltstone member, and an uppermost sandstone member. The distribution of each formation is presented on a new geological map for the area, and their lithologies are shown on stratigraphic columns. Grainsize analysis on a suite of (200) closely spaced sample sites highlights the sedimentary cyclicity and the gradational change from siltstone into sandstone in most cycles. Combined with the depth paleoecology implied by the macrofauna and benthic foraminifers, regular changes in water depth from mid‐shelf to shoreface paleoenvironments are inferred for each cycle. The cyclothemic succession is correlated with the late Pliocene part of the oxygen isotope stratigraphy for ODP site 846 (eastern equatorial Pacific), based on correlation of the Hautawa Shellbed with Stage 98. The lowermost cycle (1) in the Parikino section accumulated between the peaks of Stages Gil and G10, and the uppermost cycle (13) accumulated during Stages 92 and 93. The one‐to‐one match between cyclothems and the isotope stage couplets means that the cyclothems have the same frequency as the isotope curve, which, for the late Pliocene, corresponds to the dominant 41 000 yr Milankovitch orbital rhythm. It follows that the cyclicity results chiefly from repetitive glacio‐eustatic sea‐level changes. Significantly, the first cyclothem is aged c. 2.8 Ma, which precedes what is commonly regarded as the first major Northern Hemisphere continental glaciation (Stage 100, 2.54 Ma) by 0.26 m.y., but coincides with the first occurrence of significant ice‐rafted debris in core from the Arctic Barents Sea.

Pliocene‐Pleistocene marine cyclothems, Wanganui Basin, New Zealand: A lithostratigraphic framework

Abstract The Rangitikei River valley between Mangaweka and Vinegar Hill and the surrounding Ohingaiti region in eastern Wanganui Basin contains a late Pliocene to early Pleistocene (c. 2.6–1.7 Ma), c. 1100 m thick, southward‐dipping (4–9°), marine cyclothemic succession. Twenty sedimentary cycles occur within the succession, each of which contains coarse‐grained (siliciclastic sandstone and coquina) and fine‐grained (siliciclastic siltstone) units. Nineteen of the cycles are assigned to the Rangitikei Group (new). Six new formations are defined within the Rangitikei Group, and their distribution in the Ohingaiti region is represented in a new geologic map. The new formations are named: Mangarere, Tikapu, Makohine, Orangipongo, Mangaonoho, and Vinegar Hill. Each formation comprises one or more cyclothems and includes a previously described and named d stinctive basal horizon. Discrete sandstones, siltstones, and coquinas within formations are assigned member status and correspond to systems tracts in sequence stratigraphic nomenclature. The members provide the link between the new formational lithostratigraphy and the sequence stratigraphy of the Rangitikei Group. Base of cycle coquina members accumulated during episodes of sediment starvation associated with stratigraphic condensation on an open marine shelf during sea‐level transgressions. Siltstone members accumulated in mid‐shelf environments (50–100 m water depth) during sea‐level highstands, whereas the overlying sandstone members are ascribed to inner shelf and shoreface environments (0–50 m water depth) and accumulated during falling eustatic sea‐level conditions. Repetitive changes in water depth of 50–100 m magnitude are consistent with a giacio‐eustatic origin for the cyclothems, which correspond to an interval of Earth history when successive glaciations in the Northern Hemisphere are known to have occurred. Moreover, the chronology of the Rangitikei River section indicates that Rangitikei Group cyclothems accumulated during short duration, 41 ka cycles in continental ice volume attributed to the dominance of the Milankovitch obliquity orbital parameter. The Ohingaiti region has simple postdepositional structure. The late Pliocene formations dip generally to the SSW between 4° and 9°. Discernible discordances of c. 1° between successively younger formations are attributed to synsedimentary tilting of the shelf concomitant with migration of the tectonic hingeline southward into the basin. The outcrop distribution of the Rangitikei Group is strongly influenced by this regional tilt and also by three major northeast‐southwest oriented, high‐angle reverse faults (Rauoterangi, Pakihikura, and Rangitikei Faults).

Pliocene‐Pleistocene (Nukumaruan) lithostratigraphy of the Tangoio block, and origin of sedimentary cyclicity, central Hawke's Bay, New Zealand

Abstract Eleven formations are defined within the Pliocene‐Pleistocene Petane Group in a 450 km2 uplifted area of central Hawke's Bay (Tangoio block). In ascending order these are: Waipunga Formation (new), Esk Formation, Tutira Formation (new), Aropaoanui Formation (new), Darkys Spur Formation (new), Mairau Formation (new), Tangoio Formation, Te Ngaru Formation, Waipatiki Formation, Devils Elbow Formation, and Kaiwaka Formation. Petane Group strata are cyclothemic and alternate between coarse‐grained lithofacies (greywacke gravel, siliciclastic and carbonate sand/ sandstone and bioclastic limestone) ascribed to nonmarine and inner shelf depositional environments, and sandy/muddy‐silt ("papa") ascribed to mid‐shelf deposition. The Petane Group is characterised by remarkable lateral continuity of formations, contrasting with conspicuous vertical changes. This stratigraphic style is consistent with glacio‐eustatic sea‐level fluctuations as proposed by Vella and Beu & Edwards, whereby coarse‐grained lithofacies were deposited during sea‐level low stands and fine‐grained lithofacies were deposited during sea‐level high stands. Foraminifera extracted from low‐stand lithofacies display opposite ä18O signatures to that predicted for glacio‐eustasy, a result of synsedimentary seawater dilution during sea‐level low stands, and/or isotopic exchange during meteoric diagenesis. Stratigraphic and sedimentary criteria indicate that the Petane Group was deposited under unique circumstances of rapid basinal subsidence and a high rate of sedimentation. This offers an explanation for the general rarity of cyclothemic successions in the Pliocene‐Pleistocene stratigraphic record.