Dakota Sandstone Research Articles

Rinded iron‐oxide concretions: hallmarks of altered siderite masses of both early and late diagenetic origin

AbstractIron‐bearing concretions are valuable records of oxidation states of subsurface waters, but the first concretions to form can be altered drastically during later diagenetic events. Distinctive concretions composed of heavy rinds of iron oxide that surround iron‐poor, mud‐rich cores are common along bases of fluvial cross‐bed sets of the Cretaceous Dakota Formation, Nebraska, USA. Concretion rinds thicken inward and cores contain 46 to 89% void space. Millimetre‐scale spherosiderites are abundant in palaeosols that developed in floodplain facies. Evolution of rinded concretions began when intraformational clasts were eroded from sideritic soils, transported, abraded and deposited in river channels. Alteration of siderite and formation of rinds occurred much later, perhaps in the Quaternary when sandstone pore waters became oxic. Dakota concretions are analogous to ‘rattlestones’ in Pleistocene fluvial channels of The Netherlands, and their rinded structure is analogous to that of iron‐rich concretions in the aeolian Navajo Sandstone of Utah. In all three deposits, rinded concretions formed when pre‐existing, siderite‐cemented concretions were oxidized within a sand matrix. Unlike fluvial examples, siderite in the Navajo Sandstone was autochthonous and of late diagenetic origin, having precipitated from carbon dioxide and methane‐enriched waters moving through folded and jointed strata. Iron‐rich rinds formed in all these strata because concretion interiors remained anaerobic, even as oxygen accumulated in the pore waters of their surrounding, permeable matrix. Iron oxide first precipitated at redox boundaries at concretion perimeters and formed an inward‐thickening rind. Acid generated by the oxidation reaction drove siderite dissolution to completion, creating the iron‐poor core. Iron‐oxide rinds are indicators of the former presence of siderite, a mineral that forms only under reducing conditions, during either early or late diagenesis. Siderite is vulnerable to complete oxidation upon exposure, so the distinctive rinded concretions are valuable clues that aid in deciphering diagenetic histories and for recognizing methanic floodplain palaeoenvironments and wet palaeoclimate.

Outcrop versus core and geophysical log interpretation of mid-Cretaceous paleosols from the Dakota Formation of Kansas

Paleosols of the mid-Cretaceous (late Albian to early Cenomanian) Dakota Formation in Kansas and Nebraska are well exposed in road, river and clay pit exposures, but show systematic overprinting by modern weathering. Examination of deep drill cores reveals that modern weathering effects include (1) oxidation of pyrite to jarosite, (2) reaction of jarosite and calcite to clear selenite, and (3) oxidation of sphaerosiderite and siderite nodules to hematite. Surface oxidation in this region extends no deeper than 2m from the surface. Hematite nodules and coatings of leaves are found in core only at one stratigraphic horizon, which was not as appears in outcrop, a laterite. Transformed matrix density and photoelectric absorption logs of cores reveal that kaolinite clays are most abundant within deeply weathered paleosols (Sayela pedotype) at this stratigraphic level, near the Albian–Cenomanian boundary, when angiosperm forests were especially diverse and lived in a subtropical humid climate. Other paleosols of the early Cenomanian were less deeply weathered, and fossil plants of this age included temperate humid angiosperm mangal and swamp woodland, but conifer-dominated floodplain forests. This short-lived mid-Cretaceous warm–wet spike has also been recognized in other paleosols of Minnesota, Utah, Nevada, and New Mexico, and coincides with marine black shale of the Breitstroffer event, midcontinental marine transgression, a sequence-stratigraphic boundary, and a marked increase in early angiosperm diversity.

Fossil footprints from the Dakota Group (Cretaceous) John Martin Reservoir, Bent County, Colorado: New insights into the paleoecology of the Dinosaur Freeway

The John Martin Reservoir tracksites from the Dakota Group of Bent County, in southeastern Colorado form part of the mid Cretaceous Dinosaur Freeway characterized by abundant ornithopod footprints ( Caririchnium). Over 350 tracks (331 Caririchnium, 1 Magnoavipes, 22 crocodiles, and a few pterosaurs) were discovered at 10 new tracksites. All tracks were found as natural casts, including Caririchnium trackways that were still in-situ, parallel and regularly spaced, suggesting gregarious behavior. Most crocodile tracks are swimming tracks that consist of three or four scratch marks also with parallel orientations in many cases. A few pterosaur tracks consist of pes footprints and scratch marks suggesting swimming or floating activity in shallow water. This is the first pterosaur evidence from the Dakota Group. The Caririchnium size structure from John Martin Reservoir is consistent with the size structure tendency of the whole Dinosaur Freeway, which shows larger track size in the north. This tendency could be interpreted as evidence for more than one ornithopod species spread out across the Dinosaur Freeway. The alternative, that there was one ornithopod species that migrated north and south seasonally is less likely. The John Martin paleoecosystem is interpreted from the track evidence as a well-vegetated coastal plain environment with many ornithopods and a few theropods on land, crocodiles in the water, and pterosaurs in the skies and on the water.

Jared R. Morrow (October 8, 1959-October 7, 2010)

Jared R. Morrow (October 8, 1959-October 7, 2010)

Mineralogical, chemical, organic and microbial properties of subsurface soil cores from Mars Desert Research Station (Utah, USA): Phyllosilicate and sulfate analogues to Mars mission landing sites

AbstractWe collected and analysed soil cores from four geologic units surrounding Mars Desert Research Station (MDRS) Utah, USA, including Mancos Shale, Dakota Sandstone, Morrison formation (Brushy Basin member) and Summerville formation. The area is an important geochemical and morphological analogue to terrains on Mars. Soils were analysed for mineralogy by a Terra X-ray diffractometer (XRD), a field version of the CheMin instrument on the Mars Science Laboratory (MSL) mission (2012 landing). Soluble ion chemistry, total organic content and identity and distribution of microbial populations were also determined. The Terra data reveal that Mancos and Morrison soils are rich in phyllosilicates similar to those observed on Mars from orbital measurements (montmorillonite, nontronite and illite). Evaporite minerals observed include gypsum, thenardite, polyhalite and calcite. Soil chemical analysis shows sulfate the dominant anion in all soils and SO4>>CO3, as on Mars. The cation pattern Na>Ca>Mg is seen in all soils except for the Summerville where Ca>Na. In all soils, SO4correlates with Na, suggesting sodium sulfates are the dominant phase. Oxidizable organics are low in all soils and range from a high of 0.7% in the Mancos samples to undetectable at a detection limit of 0.1% in the Morrison soils. Minerals rich in chromium and vanadium were identified in Morrison soils that result from diagenetic replacement of organic compounds. Depositional environment, geologic history and mineralogy all affect the ability to preserve and detect organic compounds. Subsurface biosphere populations were revealed to contain organisms from all three domains (Archaea, Bacteria and Eukarya) with cell density between 3.0×106and 1.8×107cells ml−1at the deepest depth. These measurements are analogous to data that could be obtained on future robotic or human Mars missions and results are relevant to the MSL mission that will investigate phyllosilicates on Mars.

Analysis of mineral matrices of planetary soil analogues from the Utah Desert

AbstractPhyllosilicate minerals and hydrated sulphate minerals have been positively identified on the surface of Mars. Studies conducted on Earth indicate that micro-organisms influence various geochemical and mineralogical transitions for the sulphate and phyllosilicate minerals. These minerals in turn provide key nutrients to micro-organisms and influence microbial ecology. Therefore, the presence of these minerals in astrobiology studies of Earth–Mars analogue environments could help scientists better understand the types and potential abundance of micro-organisms and/or biosignatures that may be encountered on Mars. Bulk X-ray diffraction of samples collected during the EuroGeoMars 2009 campaign from the Mancos Shale, the Morrison and the Dakota formations near the Mars Desert Research Station in Utah show variable but common sedimentary mineralogy with all samples containing quantities of hydrated sulphate minerals and/or phyllosilicates. Analysis of the clay fractions indicate that the phyllosilicates are interstratified illite–smectites with all samples showing marked changes in the diffraction pattern after ethylene glycol treatment and the characteristic appearance of a solvated peak at ∼17 Å. The smectite phases were identified as montmorillonite and nontronite using a combination of the X-ray diffraction data and Fourier–Transform Infrared Spectroscopy. The most common sulphate mineral in the samples is hydrated calcium sulphate (gypsum), although one sample contained detectable amounts of strontium sulphate (celestine). Carbonates detected in the samples are variable in composition and include pure calcium carbonate (calcite), magnesium-bearing calcium carbonate (dolomite), magnesium, iron and manganese-bearing calcium carbonate (ankerite) and iron carbonate (siderite). The results of these analyses when combined with organic extractions and biological analysis should help astrobiologists and planetary geologists better understand the potential relationships between mineralogy and microbiology for planetary missions.

Sequence stratigraphy of a condensed low-accommodation succession: Lower Upper Cretaceous Dakota Sandstone, Henry Mountains, southeastern Utah

Cretaceous low-accommodation deposits have been extensively studied in the subsurface of the Western Interior of North America because of their prolific hydrocarbon production and remaining potential. Understanding the stratigraphic complexities of these deposits in the subsurface relies strongly on detailed outcrop analogs. In this study, the Dakota Sandstone was examined along 100 km (62 mi) of semicontinuous outcrop between the towns of Hanksville and Ticaboo in the Henry Mountains of southeastern Utah. This region represented a low-accommodation setting located over the forebulge of the Cretaceous Western Interior Basin during accumulation of the unit. The Dakota Sandstone is 0 to 38 m (125 ft) thick, of Cenomanian age, and records multiple cycles of sediment accumulation. The Dakota Sandstone is subdivided into two condensed top-truncated stratigraphic sequences, the upper of which contains two parasequences. The basal parts of both sequences are composed of braided fluvial conglomerates and sandstone overlain by tidally influenced fluvial sandstone, inclined heterolithically stratified estuarine mudstone, carbonaceous shale, and coal. The overlying parasequences consist of coarsening-upward lower to upper shoreface mudstone, sandstone, tidal inlet deposits, and oyster shell concentrations. These facies define tripartite subdivisions of depositional environments typical of wave-dominated estuaries. The fluvial deposits may represent lowstand deposits, but overall sediments accumulated during transgressive systems tracts (TST). The parasequences recorded in the Henry Mountains are similar to the Dakota Sandstone of northwestern New Mexico and to high-frequency sequences identified in the Kaiparowits Plateau, approximately 80 km (~50 mi) to the southwest, which suggests eustatic driving mechanisms. The best potential for hydrocarbon reservoirs occurs in fluvial sandstones and conglomerates.

Early cretaceous bird-dominated and dinosaur footprint assemblages from the northwestern margin of the Junggar Basin, Xinjiang, China

Here we describe a number of mostly isolated bird and non-avian dinosaur footprints from the Huangyangquan track site in the Lower Cretaceous Lower Layer of the Tugulu Group near Huangyangquan Reservoir in the Wuerhe District, Karamay, Xinjiang Uyghur Autonomous Region, China. Bird footprints at the site pertain to Koreanaornis dodsoni n. ichnosp., Goseongornipes isp., Aquatilavipes isp., and Moguiornipes robusta n. ichnogen. n. ichnosp. Moguiornipes tracks may be the products of a bird with lobed feet. These shorebird-morph tracks are the first solid evidence of birds in the Tugulu Group, and greatly enrich the known faunal diversity of the Lower Layer of the Tugulu Group. The Huangyangquan avian ichnofauna is comparable to those of the Jindong Formation, Korea and the Dakota Formation, USA. Non-avian dinosaur footprints at the site pertain to cf. Jialingpus isp., Asianopodus isp., and Kayentapus isp. This is the first report of Jialingpus from Lower Cretaceous strata. The discoveries of Asianopodus isp. and Kayentapus isp. increase the known ranges of these two ichnogenera.

Experimental Investigations of the Mitigation of Paraffin Wax Deposition in Crude Oil Using Chemical Additives

Wax deposition from crude oil is a very expensive problem for oil producers around the world. The objective of this study is to understand the characteristics of paraffin wax deposition and to test the effectiveness of solvents in the inhibition of the crystallization and subsequent precipitation of the paraffin wax and to test the most effective concentration of the solvent used. The oil used here is from the Dakota formation from the Fourteen Mile Field in the Big Horn Basin of Wyoming. Two paraffin inhibitors were tested for this crude oil on a horizontal flow system. The inhibitors are mixtures of solvents, pour point depressants, and wax crystal modifiers. These inhibitors were tested at different concentrations and temperatures and the deposition rates were obtained for each. One inhibitor especially designed for this crude oil was relatively successful, reducing the deposition by up to 59% depending on the temperature.

Occurrence of the Extinct Carpet Shark,Orectoloboides, in the Dakota Formation (Late Cretaceous; Middle Cenomanian) of Kansas

Re-examination of previously reported micro-vertebrate specimens collected from the upper portion of the Dakota Formation (Middle Cenomanian) in Russell County, Kansas, has identified two teeth of the extinct Carpet Shark, Orectoloboides sp. While the teeth of Orectoloboides have been described from Africa and Europe, the only previous report of the genus in North America is from the Cenomanian of Saskatchewan in Canada. The presence of Orectoloboides in Kansas represents a more than 2000 km southward extension of the range of this group into the central portion of the Western Interior Seaway.

New Insights on the Sequence Stratigraphic Architecture of the Dakota Formation in Kansas–Nebraska–Iowa from a Decade of Sponsored Research Activity

The Cretaceous Dakota Formation in the areas of Kansas, Nebraska, and Iowa contains a rich and well-preserved microflora of fossil palynomorphs. A comprehensive listing of these taxa is presented in this publication as part of a continuing effort to develop a refined biostratigraphic scheme for mid-Cretaceous terrestrial deposits in North America. The Dakota Formation in this region contains four distinctive Albian-Cenomanian palynostratigraphic zones that are used to partition the unit into successive depositional cycles, and each zone records deposition in fluvial-estuarine environments. The late Albian Kiowa-Skull Creek depositional cycle at the base of the Dakota Formation is recognized throughout the study area, and is also recognized in other parts of the Cretaceous North American Western Interior basin. The overlying newly recognized latest Albian "Muddy-Mowry Cycle" is formally defined for the first time in this paper and correlates with depositional cycles recognized by other workers in other parts of the Western Interior basin. The Cenomanian lower Greenhorn Cycle is already widely recognized by many other workers throughout the Western Interior basin. Laterally extensive thin zones of pervasive carbonate mineral cementation are noted in fluvial-estuarine deposits in the Dakota Formation. They are believed to have formed as synsedimentary cements that precipitated below estuarine marine-flooding surfaces in settings related to discharging paleoground waters. The existence of these early diagenetic cementation zones has important implications for the recognition of diagenetic barriers and baffles to modern fluid flow in the Dakota Formation. New stable isotopic data on these authigenic cements are reported in this paper and add to a body of published data on the δ18O of mid-Cretaceous paleoprecipitation in North America.

An Early Cretaceous fruit with affinities to Ceratophyllaceae

A new genus and species with affinities to Ceratophyllaceae from the Lower Cretaceous of Kansas, USA is reported. The fruits of Donlesia dakotensis gen. et sp. nov. are smooth achenes with two winged lateral spines, two winged facial spines, one stylar spine, and a long peduncle with a distinctive groove. The facial spines are arranged perpendicular to the lateral spines. The seed contains two cotyledons and a central plumule. Dichotomous leaves associated with Donlesia dakotensis fruits are whorled, petiolate, and lack denticles. The fruit morphology of D. dakotensis differs from extant and fossil members of Ceratophyllaceae in its tetra-radial symmetry, the presence of two winged facial spines, a long peduncle, and the lack of other appendages on the fruit surface. It seems to be more closely related to section Ceratophyllum of extant Ceratophyllum. This relationship suggests that section Ceratophyllum of extant Ceratophyllum may represent the ancestral members of the ancient Ceratophyllum lineage. The presence of this species in the Dakota Formation further confirms that there were diverse aquatic plants living in freshwater lakes along the eastern margin of the Western Interior Seaway during the Early Cretaceous.

New interpretations of Ignotornis, the first-reported Mesozoic avian footprints: implications for the paleoecology and behavior of an enigmatic Cretaceous bird

The type material of Ignotornis mcconnelli, the first reported Mesozoic bird track, consists of a large, monospecific sample of ∼70 footprints comprising at least 15 recognizable trackways. However, the exact type horizon and locality, discovered in 1930 in the Cretaceous Dakota Group near Golden, Colorado, was not indicated in the original 1931 description by Maurice Mehl, and only the single holotype trackway was illustrated. In 1988, the known sample was doubled by the discovery of ∼70 additional tracks representing at least seven trackways, but again the exact type horizon and locality remained uncertain. In 2007, we discovered what we infer to be the original type locality, and identified approximately 150 additional footprints comprising at least 17 additional trackways. During the study we also located three more specimens, in other collections, comprising at least 60 tracks and 10 trackways. Thus, the type (holotype, paratype, and topotype) sample now consists of ∼360 footprints comprising about 50 trackways, of which 41 have been measured. Although most footprints from the 1930, 1988, and 2007 finds all appear to originate from the same “type” horizon associated with a volcanic ash, a few tracks were found in 2007 at two additional levels. The relatively long, reversed hallux and the incipient semi-palmate webbing in the hypex between digits III and IV make Ignotornis distinct from any other Cretaceous bird tracks known from North America. These features, used to infer the extant forms with which Ignotornis is most convergent, are reminiscent of small herons, and unlike the typical tracks of most Cretaceous shorebird-like species which resemble those of plovers and sandpipers. Clearly defined parallel and sub parallel trackways indicate gregarious behavior, while some trackways indicate unusual “shuffling” and “stop-start” progression, probably related to some type of “foot-stirring” foraging activity. The concentration of abundant Ignotornis tracks at a single locality within the ichnologically-famous “Dinosaur Freeway” (represented by more than 60 dinosaur and crocodile dominated track assemblages) suggests that the Ignotornis track maker was a “rare-bird” in the region during the Cretaceous.

An Electrical Resistivity Survey of a Small Private Cemetery, Lincoln County, Kansas

An electrical resistivity (ER) survey was conducted in a cemetery located on private ground in Lincoln County, Kansas. The purpose was to ascertain ER signatures of known, side-by-side graves as well as that of one suspect grave in the cemetery. No modern grave stone markers are present in the cemetery; only rectangular ‘Outlines’ made of local, cobble-size Dakota Sandstone lying on the surface of the ground express the graves. No historical records or documented grave maps exist; only word-of-mouth information is available. The ER measurements ranged from 10-ohm-meters to 200 ohm-meters. The ER anomaly map and selected 2D-depth ER cross sections show higher ER anomaly values and similar grave shape-anomaly patterns over the two closely-spaced known graves. Lower ER values with no anomalous patterns are observed over the suspect grave position. Electrical resistivity is useful for targeting the location of the known graves at the Lincoln County site but was not as exact for the suspect grave. Physical exc...

First report of the small bird track Koreanaornis from the Cretaceous of North America: implications for avian ichnotaxonomy and paleoecology

Although body fossils of shorebirds and shorebird-like species are extremely rare from the Cretaceous, rapid increase in the discovery of bird footprint sites provides valuable alternate evidence to help fill gaps in the story of the early evolution of shorebird-like species. Newly discovered bird tracks from the Albian-Cenomanian Dakota Formation in northeastern Utah represent the first report of the ichnogenus Koreanaornis from North America and only the second report of bird tracks from this formation. These tracks are not attributable to Aquatilavipes as previously claimed. Three well-preserved trackways are described and provisionally referred to Koreanaornis cf. hamanensis (Kim). However, a review of the ichnotaxonomy of shorebird ichnites reveals that this ichnotaxon also closely resembles the Miocene ichnospecies Avipeda sirin (Vyalov). This latter comparison points to the need for a thorough evaluation of the similarity between Mesozoic and Cenozoic avian ichnotaxa, which may be over-split in some cases and under-differentiated in others. The new material helps distinguish ichnogenus Koreanaornis from the larger bird track Aquatilavipes, which is more abundant and widespread in North America. In some cases Aquatilavipes has been incorrectly used as a catch-all ichnogenus both in North America and Asia. The Dakota Formation stratigraphy at the tracksite indicates that the track makers lived in a marginal marine paleoenvironment. However, despite the widespread distribution of such facies, often replete with dinosaur tracks, the bird track record of the Dakota Formation, and the Cretaceous of the western USA remains relatively sparse in comparison with other areas such as east Asia.

Cenomanian invertebrate assemblage from the Dakota Sandstone near Ghost Ranch, Rio Arriba County, New Mexico

Cenomanian invertebrate assemblage from the Dakota Sandstone near Ghost Ranch, Rio Arriba County, New Mexico

Numerical age calibration of the Albian/Cenomanian boundary

New biostratigraphic and sequence stratigraphic correlations of the U.S. Western Interior Albian/Cenomanian sections with North Texas and European sections calibrate the Albian/Cenomanian boundary at 97.2 Ma, which supports previous correlations in the Western Interior. This age, however, is 2.4 myr younger than the recent calibration at 99.6 Ma derived from radiometric ages of volcanic beds with diagnostic marine fossils in northern Japan. This discrepancy suggests that additional analyses are required to test the age calibration of the geologic time scale. New data of cosmopolitan dinoflagellates enable direct correlation with the European reference sections of the Albian and Cenomanian. Previous correlations in the Western Interior were based on endemic or Boreal ammonites. The first and last occurrences of dinoflagellate species bracket the Albian/Cenomanian boundary in Europe and many of these species also bracket the Clay Spur Bentonite bed previously dated 97.17±0.69 Ma. The high number of radiometrically dated bentonites in the Western Interior provides a numeric age control for the ranges of many dinoflagellates. Sequence stratigraphic correlation of the North Texas section with the U.S. Western Interior sections also demonstrates that the Clay Spur Bentonite bed correlates with the Ablian/Cenomanian boundary in Texas defined by the ammonite succession. The flooding contact SB WA6 in Texas at the Albian/Cenomanian zonal boundary of Stoliczkaia dispar and Mantelliceras mantelli correlates into the Western Interior with an erosional sequence boundary SB4 at the base of the Romeroville Sandstone in New Mexico and the Dakota Sandstone in Colorado. This contact correlates with the base of the Belle Fourche Shale that overlies the Clay Spur and the Mowry Shale in Montana. The revised correlation of the Western Interior poses two questions. 1) What is the accurate age of the boundary? Both cannot be correct. 2) What were the durations of the Albian and Cenomanian stages? Cyclostratigraphic analyses estimate that the Albian was 11.9 to 11.6 myr in duration but the Western Interior data project the duration at about 15 myr.

New species of angiosperm pollen from the Dakota Formation (Cenomanian, upper Cretaceous) of Minnesota, U.S.A.

Five new species of angiosperm pollen described from three localities in south‐central Minnesota support a Cenomanian age for the Dakota Formation in this area. The new taxa,Cupliferoidaepollenites microscabratus, Dryadopollis minnesotensis, Nyssapollenites microfoveolata, Phimopollenites striolata, and Tricolpites labeonis, are described using both light and scanning electron microscopy, are easily recognizable, and are useful age indicator species. Because of the extent and transgressive nature of the Dakota Formation, age determination has been difficult. The new angiosperm pollen species described here may help to support age determination for the Dakota Formation over a broader geographic area.

Mesofossils with platanaceous affinity from the Dakota Formation (Cretaceous) in Kansas, USA

The Platanaceae holds a basal position in the phylogeny of eudicots and therefore is of great interest to angiosperm systematists. The fossil record of the family is found in strata ranging from the Cretaceous to Recent in America, Europe and Asia. The research on the Platanaceae in the Dakota Formation can be traced back to 19th century; however, mesofossils of reproductive organs of the Platanaceae were never reported in the Midwest of North America before. This paper reports several specimens of Friisicarpus (Platanaceae) from the Dakota Formation in Kansas, USA. It complements the existing fossil records, and provides more information on reproductive biology of the family. The comparison with similar fossils from eastern North America and Europe provides some hints on biostratigraphy of the Cretaceous.

Evidence for glacioeustatic control of large, rapid sea-level fluctuations during the Albian-Cenomanian: Dakota formation, eastern margin of western interior seaway, USA

Sequence stratigraphic analysis of the Albian-Cenomanian marginal marine succession (Dakota Formation) along the eastern margin of the Western Interior Seaway in eastern Nebraska reveals large-scale fluvial incision (13–28 m) that coincides with sequence boundaries. Construction of a relative sea-level curve constrained by high-resolution palynological correlations indicates rapid incision rates (>10 m/m.y.). Lithologic and palynologic analyses of the strata above and below the D 2 sequence boundary show that this hiatus includes the Albian-Cenomanian biostratigraphic boundary. Comparison with the eustatic sea-level curves published by Haq and Al-Qahtani (2005) and Sahagian et al. (1996) places the D 2 sequence boundary in eastern Nebraska at a global sea-level minimum at 99.5 m.y.a. The interpreted sea-level changes from this succession are comparable to other Albian-Cenomanian successions from around the world indicating a eustatic mechanism. We attribute these large-scale and rapid sea-level falls during the mid-Cretaceous greenhouse world to glacioeustasy. The implication that a glacioeustatic mechanism operated during the mid-Cretaceous suggests that the definition of a “greenhouse world” as being ice-free needs to be reevaluated. Perhaps many, if not all, of the “greenhouse” climatic settings included some ice, either in the form of alpine glaciers, small “continental” ice sheets, or both. Understanding past climate changes and their ramifications may be the key to predicting future climatic changes.