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Terrestrial evidence for the Lilliput effect across the Cretaceous-Paleogene (K-Pg) boundary

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Abstract

Recent research has demonstrated that the Lilliput effect (reduction of body size in response to a mass extinction) affected all trophic levels in the marine realm following the Cretaceous-Paleogene (K-Pg) event. However, it is unclear if this size change was strictly a marine signal, or a global phenomenon that also affected continental ecosystems. Herein we present the results of an ichnological proxy for body size of soil-dwelling insects across the K-Pg boundary in Big Bend National Park, Texas, U.S.A. Quantitative efforts focused on Naktodemasis isp., which are characterized as unbranching burrows composed of ellipsoidal packets of backfill menisci. These traces were likely produced by beetle larvae or cicada nymphs based on previous comparison with structures generated in modern soils and laboratory experiments. As an approximation for the body size of the subterranean insects, this dataset indicates that a smaller Naktodemasis diameter (DN) is statistically correlated (α < 0.05) with several edaphic factors including poor drainage and weak development (Entisols). Additionally, the DN in strata immediately superjacent to the highest Cretaceous-specific taxa is smaller by 23% (5.6 ± 1.8 mm) in comparison to DN within the subjacent Cretaceous interval (7.3 ± 2.7 mm). This abrupt shift occurs in a well-drained Inceptisol, and cannot be attributed to facies changes, drainage, or paleosol maturity. Furthermore, a reduced DN (6.6 ± 2.3 mm) persists above this anomalous shift for at least 20 stratigraphic meters within chron 29r. The cause for this negative response in body size within soil-dwelling biota may be attributed to plant-community shifts in taxonomic composition and ecological strategies, which would have caused fundamental alterations to the diet of the herbivorous, subterranean insects. This study provides empirical evidence that the Lilliput effect was not restricted to marine environments during the aftermath of the K-Pg event.

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We analyzed samples for paleomagnetism, ⁴⁰Ar/³⁹Ar detrital sanidine ages, and mammalian fauna to produce a precise chronostratigraphic framework for the Upper Cretaceous to Lower Paleocene Dawson Creek section of Big Bend National Park, west Texas. Prior to this work, the absolute ages and durations of the Upper Cretaceous Aguja and Javelina Formations and Paleocene Black Peaks Formation were relatively poorly constrained. The documented polarity zones can be correlated to C32n-C31n, C29r, and C27r of the geomagnetic polarity time scale, with three hiatuses spanning more than 1.5 m.y. each. Rock magnetic analyses indicate that the dominant magnetic carrier in the Aguja and Black Peaks Formations is titanomagnetite, while the Javelina Formation has varying magnetic carriers, including hematite, magnetite, and maghemite. An overprint interval surrounding the Cretaceous-Paleogene boundary suggests the primary magnetic carrier, titanohematite, was likely reset by burial and/or overlying basaltic flows. These are the first independent age constraints for the Cretaceous-Paleocene strata at the Dawson Creek section that determine the age and duration of deposition of each formation in the section, as well as the age and duration of multiple unconformities through the succession. As a result, these age constraints can be used to reassess biostratigraphic and isotopic correlations between the Big Bend area and other Cretaceous-Paleogene basins across North America. Based on this new data set, we reassign the age of the mammalian fauna found in the Black Peaks Formation from the Puercan to the Torrejonian North American Land Mammal age. Our age constraints show that the dinosaur fauna in the Javelina Formation in the Dawson Creek area is latest Maastrichtian and restricted to chron C29r. Thus, the Javelina dinosaur fauna is correlative to the Hell Creek Formation dinosaur fauna from the Northern Great Plains, indicating differences between the faunas are not due to differences in age, and providing support for the hypothesis of provinciality and endemism in dinosaur communities in the late Maastrichtian. Further, the age constraints indicate that the previously documented mid-Maastrichtian and late Maastrichtian greenhouse events were rapid ( < 200 k.y.) and correlate closely with climate events documented in the marine record.
Article
Climate simulations that consider injection into the atmosphere of 15,000 Tg of soot, the amount estimated to be present at the Cretaceous-Paleogene boundary, produce what might have been one of the largest episodes of transient climate change in Earth history. The observed soot is believed to originate from global wildfires ignited after the impact of a 10-km-diameter asteroid on the Yucatán Peninsula 66 million y ago. Following injection into the atmosphere, the soot is heated by sunlight and lofted to great heights, resulting in a worldwide soot aerosol layer that lasts several years. As a result, little or no sunlight reaches the surface for over a year, such that photosynthesis is impossible and continents and oceans cool by as much as 28 °C and 11 °C, respectively. The absorption of light by the soot heats the upper atmosphere by hundreds of degrees. These high temperatures, together with a massive injection of water, which is a source of odd-hydrogen radicals, destroy the stratospheric ozone layer, such that Earth's surface receives high doses of UV radiation for about a year once the soot clears, five years after the impact. Temperatures remain above freezing in the oceans, coastal areas, and parts of the Tropics, but photosynthesis is severely inhibited for the first 1 y to 2 y, and freezing temperatures persist at middle latitudes for 3 y to 4 y. Refugia from these effects would have been very limited. The transient climate perturbation ends abruptly as the stratosphere cools and becomes supersaturated, causing rapid dehydration that removes all remaining soot via wet deposition.
Article
The Early Toarcian (Early Jurassic) global marine mass extinction is associated with one of the most important environmental perturbations of the Mesozoic, the Toarcian Oceanic Anoxic Event (T-OAE), usually interpreted as a global oceanic anoxic event. In the Lusitanian Basin (LB) — one of the reference areas for the study of the T-OAE — despite an elevated extinction rate among marine invertebrates, the anoxia hypothesis has been discarded based on geochemical and isotopic data. In the Fonte Coberta section the T-OAE is characterised by the extinction of the previously well-represented brachiopod taxa, a decreased abundance of ammonoids, and the establishment of a well-developed endobenthic community mainly composed by Thalassinoides tracemaker, which indicates favourable environmental parameters at least for this community. Thus, the palaeoenvironmental changes associated with the T-OAE event bear a minor incidence on the macrobenthic tracemaker community at the level of extinctions and changes in diversity or abundance; yet they exert a major effect on the behaviour and palaeobiology of tracemakers. The Thalassinoides specimens show an exclusively horizontal development and unusual architectural features during the extinction interval, tied to behavioural adaptations to nutrient availability and/or substrate firmness. Smaller burrow diameters are registered at the base of the T-OAE, and then an increase is observed during the T-OAE. This could be associated with a palaeobiological response (Lilliput effect) to palaeoecological changes at the beginning of the T-OAE, followed by a progressive change to pre-event environmental parameters. This study therefore sheds light on how environmental alterations can determine specific behavioural and palaeobiology changes of the producer, as reflected by variations in significant features of Thalassinoides architecture.
Book
In Plants and the K-T Boundary, two of the world's leading experts in palynology and paleobotany provide a comprehensive account of the fate of land plants during the ‘great extinction’ about 65 million years ago. They describe how the time boundary between the Cretaceous and Paleogene Periods (the K-T boundary) is recognized in the geological record, and how fossil plants can be used to understand global events of that time. There are case studies from over 100 localities around the world, including North America, China, Russia and New Zealand. The book concludes with an evaluation of possible causes of the K-T boundary event and its effects on floras of the past and present. This book is written for researchers and students in paleontology, botany, geology and Earth history, and everyone who has been following the course of the extinction debate and the K-T boundary paradigm shift.
Article
The Agost section (Betic Cordillera, Alicante Province, south-eastern Spain) is one of only a few places in the world where complete sedimentary successions across the Cretaceous–Palaeogene (K–Pg) boundary are available. Agost enables a high-resolution ichnological analysis illustrating the influence of environmental perturbations on burrowing organisms before, during and after the K–Pg boundary event. The uppermost Maastrichtian calcareous marlstones and marly limestones of the Raspay Formation (Plummerita hantkeninoides Biozone), beside the light-filled Maastrichtian trace fossils, contain dark-coloured early Danian trace fossils including Chondrites targionii, Chondrites ?affinis, Chondrites isp., Pilichnus isp., Planolites isp., ?Teichichnus isp., Thalassinoides isp., Trichichnus linearis, Trichichnus isp., and Zoophycos isp. The ichnotaxonomic composition of the late Maastrichtian and early Danian trace fossil association does not reveal major differences, indicating no significant influence on composition of their trace makers immediately after the K–Pg event. The main factors that most likely promoted survivorship of the trace makers were their feeding strategy (deposit feeders, microbe gardeners) and an increased delivery of organic matter to the seafloor due to the high mortality during the K–Pg boundary event. However, the differences in the size of trace fossils are noted: They are distinctly smaller in the dark boundary layer (Guembelitria cretacea Biozone) than in the underlying uppermost Maastrichtian calcareous marlstones. This is an example of the Lilliput Effect. The dwarfed ichnoassociation was produced during and shortly after sedimentation of the dark boundary layer pointing to a delayed reaction of the burrowing organisms to the K–Pg boundary event compared to other groups of organisms. The dwarfing might be caused by environmental stress resulting from lower food supply due to collapse of primary production in the later phases of the K–Pg boundary event.
Article
The New Jersey Inner Coastal Plain is underlain by a Campanian (Upper Cretaceous) to Thanetian (Paleocene) stratigraphic sequence containing fossil assemblages from before, during and after the K/T boundary mass extinction event. The lithostratigraphic framework and the microfossil zonation of these faunal changes is reviewed. Microstratigraphic analysis of the sequence reveals that dominant marine organisms of the Upper Cretaceous such as ammonites and oysters are selectively extirpated at the K/T boundary, while those organisms with a non-planktotrophic reproductive strategy were the surviving marine invertebrates. Comparative taphonomy is applied to two fossil assemblages in the sequence to demonstrate the differences between reworked taphocoenoses of nearshore and estuarine environments and those of deeper-water taphocoenoses. A complete synonymy for all New Jersey K/T vertebrate taxa is presented, and all valid taxa are plotted on a stratigraphic range chart with guild/niche information about each group. Two geochemical investigations are evaluated for their bearing on the question of catastrophic extinction processes caused by asteroid impact. It is concluded that the methodology of comparative taphonomy can be a useful tool in determining the difference between transported, reworked fossil assemblages produced by physical events like storms, and those assemblages which accumulated in deeper-water settings where modification was primarily biological. The mass extinction event as recorded in this sequence was gradual, but exacerbated by a sharper mass mortality at the end of the Cretaceous; diversity rebound to pre-K/T levels did not occur until the Thanetian. Plankton crash most drastically affected those organisms with a planktotrophic larval stage. The drop in plankton biomass was mediated upward in the food chain to duraphagous predators (and to those who ate them) by way of the die-off in previously abundant Cretaceous mollusks. The iridiuim data are ambiguous, and toxic metal data lend no support to the Strangelove Ocean hypothesis. Finally, it would appear that a combination of gradual climatic changes coupled with a sudden event like a bolide impact caused a protracted period of mass extinctions with suppression of full biomass productivity lasting well into the Paleocene.
Article
Trace fossil analysis of the Cretaceous-Paleogene (K/Pg) boundary interval at El Kef (Tunisia) has provided new information on the response of the macrobenthic tracemaker community to the K/Pg boundary event. Ichnological data from the Global Stratotype Section and Point (GSSP) for the Cretaceous-Paleogene (K/Pg) boundary were completed with those from a new, well-exposed section nearby. The trace fossil assemblage consists of dominant Trichichnus, frequent Chondrites, and rare Thalassinoides and Zoophycos in the uppermost Maastrichtian, and only Trichichnus in the lowest Danian, the diversity being comparatively lower than in other K/Pg boundary sections worldwide. Bioturbational structures are observed continuously across the K/Pg boundary interval, without primary lamination; this discards anoxic conditions. However, the upward-decreasing diversity in the sections may be related to a transition from a moderately dysoxic or slightly dysoxic macrobenthic habitat in the sediment during the latest Maastrichtian to a strong or very strong dysoxia during early Danian. Comparison with micropaleontological data reveals a minor influence of the K/Pg boundary event on the macrobenthic tracemaker community, while the change in oxygenation of pore waters at the El Kef sections can be attributed to local or regional phenomenon, marked by increasing clay content in the Danian sediments.
Article
Lower Permian (Asselian) deposits of the Washington Formation (Dunkard Group) in West Virginia (U.S.A.) represent proximal to distal expressions of a migrating, anastomosing river and associated floodplain environments. These deposits are part of the upper fluvial plain province of the Dunkard Basin characterized by thick-to-thin sandstone bodies, shales, and paleosols. The paleosols and associated ichnofossils record a wealth of paleoenvironmental, paleoecological, and paleoclimatic data which improve our understanding of the autogenic and allogenic processes that result in the spatial and temporal variability of ancient fluvial systems. This study integrates field and laboratory analysis of paleosols and ichnofossils including macro- to micromorphology, bulk geochemistry, and clay mineralogy to better understand variations in soil-forming processes across this Early Permian floodplain. Nine different pedotypes were identified including proximal, poorly developed Entisols and Inceptisols, poorly drained Histosols, and thick, moderately to well-drained Inceptisols and Vertisols. Lateral differences in paleosol properties were minor compared to the diversity of paleosols present in the vertical exposure and were largely a result of localized variations in drainage and topography. Differences in the properties of the paleosols in the vertical succession could not be explained by variable drainage due to position on the floodplain. Cyclicity was largely controlled by avulsion, but was overprinted by changes in climate. While climatic drying during the Early Permian as a general trend is well established, smaller scale fluctuations between wet and dry intervals contributed significantly to observed paleosol properties. Dominance by calcareous Vertisols in the upper fluvial plain facies province and their representation of strongly seasonal conditions are consistent with previous research; however, thorough investigation of the paleosols suggests that more humid conditions existed than the arid to semiarid climate that has been suggested.
Article
The influence of substrate firmness as shear strength on the nesting behavior of the wasp Bembix oculata is analyzed in "natural" conditions. The experimental area (a landing pit at the athletics stadium in Granada, southern Spain), is characterized by the existence of a non-random distribution of nesting holes made by Bembix oculata. The analysis of sediment features shows homogeneity in some substrate properties such as grain size and mineralogy. However, the quantitative analysis of substrate firmness leads to recognition of a close relationship between shear-strength values and burrow distribution. Experiments performed by Torvane testing in 13 sampling sites reveal changes in shear strength related to variations in water content of the substrate. These changes in shear strength are closely associated with distribution of nests. Thus, a gradual increase in substrate shear strength, over 1000-1500 Pa, is recorded toward the area where nesting holes appear, whereas burrows are most abundant where shear strength is higher (above 2500 Pa). Substrate firmness is revealed to be of prime importance in the nesting behavior of Bembix oculata. The relationship between the obtained shear-strength values and the soil water content could be interpreted as the influence of water content in substrate firmness. However, we do not discard the influence of water content as an independent factor (soil moisture).
Article
Analysis of molluscan collections from a 3+my interval around the Cretaceous-Tertiary (K-T) interval in east Texas suggests that molluscs suffered an extinction at or near the K-T boundary, followed by a prolonged period of stress which lasted through the P0 and P1a planktic foraminiferal zones. Species richness and the relative abundance of deposit feeders generally track the 13C depletion curve suggesting that the stress was caused by a lack of primary production. A stable, relatively diverse, suspension feeding molluscan community was reestablished less than two million years after the K-T boundary. -from Authors
Article
Geochemical and isotopic analyses of the Cretaceous–Paleogene (K/Pg) boundary deposits were conducted at the Caravaca section (External Subbetic, southeast of Spain) in order to evaluate the recovery of the macrobenthic tracemaker community and the bioturbational disturbance. Samples from the infilling material of several lower Danian dark-colored trace fossils (Chondrites, Planolites, Thalassinoides and Zoophycos) located in the uppermost 8-cm of the light upper Maastrichtian strata, as well as samples from the host sedimentary rock of these trace fossils, were analyzed and compared with data from the lower Danian deposits. The values of element ratios indicative of extraterrestrial contamination (Cr/Al, Co/Al and Ni/Al) are higher in the infilling trace fossil material than in the upper Maastrichtian and lower Danian deposits, which suggests a contribution of the ejecta layer. Regarding the isotope composition, the δ13C values are lower in the infilling material than in the Maastrichtian host sedimentary rocks surrounding the traces, while the δ18O are higher in the infilling material. The geochemical and isotopic compositions of the infilling material evidence the unconsolidated character of the sediment, including the red boundary layer. Softground conditions confirm a relatively rapid recovery by the macrobenthic tracemaker community, starting a few millimeters above the K/Pg boundary layer. The mixture of the infilling material of the trace fossils moreover reveals a significant macrobenthic tracemaker activity affecting K–Pg boundary transition sediments that may have significantly altered original signatures.
Article
Two types of root casts attached to in situ stump casts of early trees from the Catskill Delta Complex are described and contrasted. The first type is attached to bulbous sand-stone tree-stump casts (Eospermatoperis sp. ?) occurring in a low-chroma (gray-green), pyritic, gley siltstone paleosol of Middle Devonian (Givetian) age that is interpreted as waterlogged; this paleosol formed in a coastal-margin setting characterized by a shallow water-table. Root casts in the Middle Devonian paleosol are horizontal to subhorizontal, strap-like (measuring 0.5-2 cm in width and up to meters long), and radiate outward from stump casts with distinctly flared bases. Root casts with a similar morphology also occur attached to the upper portions of stump casts, and comprised an aerial root mantle. The second type of root cast is attached to weakly flared to corm-like sandstone tree-stump casts of probable progymnosperms (Archaeopteris sp. ?) occurring in a moderate-chroma (red), oxidized sandy paleosol of Late Devonian (Famennian) age that is interpreted as well-drained; this paleosol formed proximal to active alluvial channels. Root casts are dominantly vertical, taproot-like (measuring up to 10-15 cm in diameter and up to 1.5m long), and descend downward from the bases of stump casts with approximately a 60° angle of attachment. The two types of tree-root casts differ due to development under different soil-drainage conditions. Preservation of in situ Devonian tree-stump casts and attached root casts involved degradation of interior tissues, followed by sediment infilling; outer tissue (periderm) persisted longer before decay and infilling. Preservation is favored by conditions of rapid sediment accumulation, generally associated with sandstone deposition, as is the case for Carboniferous lycopod tree stumps documented by other workers. Lack of preservation in fine-grained claystone paleosols associated with either coastal-margin mudflat or alluvial floodplain deposition reflects either (1) no colonization of these soil environments by mature trees, (2) selective destruction of the root traces by intensive physical mixing associated with vertic (shrink-swell) soil processes in clay paleosols, or (3) average sediment accumulation rates that were too low to bury and preserve in situ stump casts.
Article
The purpose of this chapter is to evoke new concepts, provide guidelines and new frontiers for future research, and demonstrate that invertebrate traces actually comprise the “backbone” of continental (as well as marine) ichnology. Invertebrate organisms that inhabit the continental, nonmarine realm include some of the most diverse and populous classes in the animal kingdom. For example, both the Insecta and Crustacea exhibit burrowing behaviors unique to subaqueous freshwater and subaerial systems. Because of the sheer biomass of burrowing pupae, larvae, juvenile, and adult stages of these organisms, invertebrates dependent on the position of the water table form the basis for ecological niche-partitioning of depositional systems within all of the continental realm. A distinction must be made here between continental and marine ichnocoenoses because they represent distinctly different styles of living. These in turn dictate different behavioral and genetic responses of the organisms that inhabit them. Burrow architectures that occur in both continental and marine ichnocoenoses can be differentiated by subtle differences in morphology that are due to convergence of the burrowing mechanisms of the respective organisms.
Article
The first Cicadomorpha, Gallodunstania grauvogeli gen. et sp. nov., is described from the Triassic of the Vosges (France) and is provisionally attributed to the Palaeontinoidea family Dunstaniidae.
Paleosol properties are routinely characterized by whole-rock geochemistry, compromising the interpretation of important biogeochemicalinformation in deep time. As a consequence, we employ a new pedotransfer function approach to the characterization of paleosols and apply this methodology to Late Cretaceous (Campanian and Maastrichtian) and early Paleocene (Danian) landscapes from the Dawson Creek study area of the western interior to: (1) reconstruct collodially based physical and chemical soil properties, and (2) assess climate and soil biogeochemical controls on evolving terrestrial ecosystems. Nine paleoseries (i.e., pedotypes) characterize the range of soil properties within the fluvial stratigraphic succession, which includes Entisols, Inceptisols, and Vertisols. All soils had optimal water-holding potential as inferred from low bulk densities, whereas poorly drained and colonizing landscapes likely suffered from poor aeration during seasonal water logging. Even with high water-holding capacity, Maastrichtian soils experienced seasonal moisture stress because of lower rainfall than Campanian and Danian soils. Fertility levels were sufficient for the growth of most plants judging from high cation exchange capacity and base saturation, negligible aluminum toxicities because of nonacid pH, and limited salinity and sodicity from relatively low exchangeable sodium and soluble salts in solution. Unlike warm-temperate and forested paleosols with neutral pH from the Campanian and Danian, subtropical and alkaline paleosols from the Maastrichtian apparently supported a woodland plant formation adapted to low availability of iron and manganese, which were fixed with calcium in carbonate, and low availability of phosphorous because it formed insoluble compounds with iron and manganese. Carbon, nitrogen, phosphorous, and sulfur cycling through microbially mediated mineralization of soil organic matter was limited from low litter inputs in both early and midsuccessional ecosystems, particularly in woodland soils. Results do not revealdemonstrable changes in soil characteristics through the K-T transition.
Article
The Clayton sands, thin discontinuous sand bodies found at or near the Cretaceous-Tertiary (K-T) boundary at various sites in Alabama, previously have been attributed to (1) catastrophic tsunami deposition associated with a K-T boundary impact or, alternatively, (2) noncatastrophic transgressive infilling of incised valleys cut during a preceding sea-level low-stand. New observations on the geometry and ichnosedimentologic character of a Clayton sand body, enveloping strata, and associated bounding surfaces exposed along Mussel Creek (central Alabama) refute the tsunami origin and support the latter mechanism. Studies of other boundary deposits in the gulf region, which may similarly benefit from ichnofossil investigations, should consider more rigorously the evidence for sea-level change near the K-T transition.
Article
The marine to terrestrial transition in the Big Bend area falls within the Late Cretaceous Aguja Formation, and the Cretaceous-Tertiary boundary falls within the Javelina Formation. No record of a catastrophic event is apparent in the Javelina Formation. The Javelina, Black Peaks, and Hannold Hill Formations and the Big Yellow Sandstone Member of the Canoe Formation record increasing uplift in the region. Volcanism in the Chisos Mountains is the source of upper Canoe Formation sediments. The sequence of changes produced by this trend is gradual and the Javelina through Black Peaks units are not lithostratigraphically distinct at the formation level. The Aguja Formation and the Tornillo Formation are united in the Chilicotal Group (new), which spans the deposits from the first significant influxes of terrestrial sediments, formed as the Cretaceous sea retreated, up to the beginning of local volcanism in the Chisos. The volcanic strata of the upper Canoe Formation are reassigned to the Chisos Formation.-from Authors
Article
A marked change in paleosols coincides with the Cretaceous/Tertiary transition in fluvial sediments of the Big Bend region in Texas. Early Paleocene paleosols exhibit thick, black epipedons and a greater depth to the argillic and petrocalcic horizons compared to Late Cretaceous paleosols. These features and comparison with modern soils suggest that early Paleocene soils developed under conditions of higher rainfall and cooler temperatures than did Late Cretaceous soils. The change in paleosols occurs abruptly at the highest occurrence of dinosaur bones in the section.
Article
Paleosol-bearing alluvial strata of latest Cretaceous and earliest Tertiary age are continuously exposed along Dawson Creek, in Big Bend National Park, west Texas, U.S.A., and exhibit a three-tier hierarchy of depositional cyclicity. Meter-scale, fluvial aggradational cycles (FACs) occur as fining-upward successions that are gradation-ally overlain by paleosols or are sharply overlain by the coarser-grained base of the succeeding FAC without an intervening paleosol. FACs stack into decameter-scale, fluvial aggradational cycle sets (FAC sets) that also fine upward, and from base to top contain either a grad-ual upsection increase in soil maturity and soil drainage or a somewhat symmetrical pattern of increasing and decreasing paleosol maturity. Longer-period trends of FAC thickness, lithologic proportions, paleosol maturity, and paleosol drainage indicate that two complete, and two partial, hectometer-scale fluvial sequences occur within the study in-terval. From base to top, each sequence is characterized by an asym-metric increase and decrease in FAC thickness, a decrease in the pro-portion of sand-prone fluvial facies, an increase in paleosol maturity, and better paleosol drainage. Whereas FACs and FAC sets are interpreted to record cyclic epi-sodes of channel avulsion and stability, and longer-term avulsive chan-nel drift within the alluvial valley, respectively, fluvial sequences may coincide with third-order sea-level changes within the North American Western Interior Seaway. As such, the Cretaceous–Tertiary (K–T) transition within the Tornillo Basin may provide an example of me-gascale stratigraphic cyclicity that is controlled by eustatic sea level within a fully fluvial succession. Thickening and thinning successions of FACs record a third-order period of accelerating (transgressive-equivalent) and decelerating (highstand-equivalent) base-level rise, and subsequent base-level fall (falling stage-to lowstand-equivalent). Se-quence boundaries are placed at the sharp inflection between thinning and thickening FACs. Sand-prone facies and immature, more poorly-drained paleosols are associated with the transgressive-equivalent por-tion of each sequence, and mudrock-dominated overbank facies and their associated mature, well-drained paleosols are associated with the highstand-and falling stage-equivalent.