Lower Cretaceous Deposits Research Articles

Early Cretaceous glacial environment and paleosurface evolution within the Mount Painter Inlier, northern Flinders Ranges, South Australia

Sediments comprising the Radium Ridge Breccia, a stratigraphic unit recognised within the Mesoproterozoic Mount Painter Inlier, are now re-interpreted as Lower Cretaceous (previously interpreted to be Paleozoic) periglacial deposits with associated glacial and pro-glacial facies that extend into adjacent Eromanga Basin sediments. The interpretation is based on distinctive periglacial, glacial and pro-glacial facies, clast lithology, geochronology and consistent stratigraphic position above the Mesoproterozoic basement. Facies recognised are kame deposits, tillites, talus, mass-flow and solifluction lobes. The depositional model presented herein is that the Radium Ridge Breccia unit formed in a glacial/periglacial environment in moderately elevated highlands, in a proximal, mainly terrestrial setting adjacent to the Eromanga Basin, during the Early Cretaceous. LA-ICPMS U–Pb geochronology of the distinctive Sprigg Tillite Member, a lodgement tillite within the Radium Ridge Breccia unit, yielded the youngest zircon ages ca 240–220 Ma and monazite ages ca 365 Ma that are consistent with the interpretation of this subunit, and hence the Radium Ridge Breccia formed during the Early Cretaceous. The Sprigg Tillite Member is correlated with the early Aptian Sheehan Cretaceous glacial event.

Conditions of the formation and filtration-capacitive properties of the lower cretaceous deposits of the Tavdinsk mega outshot in the Iussk oil and gas bearing region

In the presented work, the differences of mechanisms of the formation of the Lower Gotterivian deposits are considered based on the results of lithological-petrophysical studies of core samples on 5 wells of Leushin’s (approx. 150 samples) and Vikulov’s (approx. 150 samples) assises. The area covered by the studies is located on the border of the Khanty-Mansi Autonomous Okrug and Sverdlovsk region. The differences in the mechanisms of the formation of the Vikulov’s and Leushin’s assises with the use of core macrodescription data, biofacies, granulometric, petrographic and X-ray structure analyses are considered and compared. The Lower Cretaceous deposits of the studied area are represented by alternating aleurolites and argillites with rare interbeds of sandstones. The granulometrical factors most commonly used for the interpretation of sedimentation environments, the median grain size (Md), the average grain size (Xcp), the sort factor (S0), the asymmetry factor (As) and the excesses (Ex), reflecting the main characteristics of the grains distribution, are considered. According to the granulometric analysis, bar graphs of the distribution of mass fractions in percent by fractions were built and analysed. For genetic interpretation, the CM Passega diagram, construction of which is based on the mechanism of particle transfer and directly depends on the flow dynamics, was used. Conclusions about the conditions of the deposits formation are made. The reservoir properties of detrital rocks are often influenced by many of the factors discussed above: the median grain size, sorting of the detrital part, composition, amount and type of cement, compaction processes, recrystallisation, bore-hole mining and authigenic mineral formation. Based on the studies carried out, the influence of various factors on reservoir properties was analysed.

Palaeoenvironment, sequence stratigraphy and palaeogeography of the Lower Cretaceous deposits of Mehdi Abad, Yazd Block, Central Iran

Four Lower Cretaceous sections in the southern Yazd Block were measured and studied to interpret the palaeoenvironments, synsedimentary tectonics, and sequence stratigraphy. The Early Cretaceous sedimentary record of this block, consisting of the Sangestan, Taft, Abkuh, and Darreh Zanjir formations, was mainly influenced by synsedimentary tectonic activities in a tectonically unstable basin. Field observations and laboratory studies were used to identify lithofacies and microfacies, based on which six depositional environments were identified: upper coastal plain (alluvial fans), shore, tidal flat, lagoon, shoal, and open marine. A carbonate-siliciclastic shallow platform including an alluvial-coastal plain and an inner platform is suggested for the depositional environment of the Sangestan Formation. The depth of the overall shallow sedimentary basin of Sangestan Formation increases from west to east and deposition was controlled by long- term sea-level changes. A carbonate platform consisting of inner and outer parts, including tidal flat, lagoon, open marine belts, is suggested for the depositional environment of the Taft and Abkuh formations, while the Darreh Zanjir Formation accumulated in a deep basin. The predominant facies demonstrate an overall transgression-regression cycle (the 2rd order cycle) during the depositional time of these formations in the southern Yazd Block.

The Berriasian–Aptian of the Western Gydan Peninsula (West Siberia): Biofacies and Lithofacies Models

Abstract —Well logs and core analyses of Berriasian–Aptian petroliferous sediments from the western Gydan Peninsula are used to model their biofacies and lithofacies and to reconstruct the respective sequence stratigraphy. The sedimentological and palynological data, along with logging results, provide constraints on the history of transgressive and regressive events and make a basis for paleogeographic reconstructions for the Lower Cretaceous deposition of reservoir sand beds.

КОМПЛЕКСНЫЕ РЕШЕНИЯ ПО ПОВЫШЕНИЮ ЭФФЕКТИВНОСТИ РАЗРАБОТКИ МНОГОПЛАСТОВЫХ ГАЗОВЫХ И ГАЗОКОНДЕНСАТНЫХ МЕСТОРОЖДЕНИЙ

Актуальность. С целью снижения капитальных затрат и сокращения времени выработки запасов газа и конденсата многопластового газоконденсатного месторождения актуальной задачей является обоснование технологии одновременной разработки различных по ресурсно-энергетическому потенциалу и/или фильтрационно-емкостным свойствам эксплуатационных объектов с подачей газа в одну газосборную сеть. Решение этой задачи актуально как на стадии проектирования, так и в зрелой стадии разработки месторождения на режиме истощения пластовой энергии. В условиях резкого различия ресурсно-энергетического потенциала и фильтрационно-емкостных свойств разрабатываемых объектов низконапорные скважины при определенном противодавлении в системе сбора газа прекращают фонтанирование и переводятся в бездействующий фонд до снижения линейного давления к необходимому уровню. Цель: обоснование комплексных технологических решений, направленных на повышение эффективности разработки многопластовых газовых и газоконденсатных месторождений с единой газосборной сетью. Объекты: многопластовые газовые и газоконденсатные месторождения, содержащие в геологическом разрезе разобщенные и различные по ресурсно-энергетическому потенциалу и фильтрационно-емкостным свойствам выделенные эксплуатационные объекты. Методы: анализ текущего состояния разработки газовых эксплуатационных объектов Губкинского месторождения, аналитические расчеты технологических режимов работы низконапорных скважин, проведение опытно-промышленных испытаний на газовых скважинах Губкинского месторождения, технико-экономический анализ результатов применения предложенных технологий. Результаты. Произведен анализ текущего состояния Губкинского месторождения, характеризуемого высокой дифференциацией текущих пластовых давлений по продуктивным пластам. Предложены комплексные решения по обеспечению совместной разработки эксплуатационных объектов с подачей газа в общую газосборную сеть, обеспечивающие устойчивые режимы работы скважин и основанные на регулировании устьевого давления различными техническими устройствами. Произведена технико-экономическая оценка влияния представленных комплексных технологических решений на эффективность разработки нижнемеловых пластов Губкинского месторождения.

Supraproduction Volcanism of Chukotka Terrane in the Late Jurassic–Early Cretaceous (Arctic Region, Russia)

The age and geodynamic position of the volcanic source of the Upper Jurassic–Lower Cretaceous deposits of Western Chukotka were determined. Products of synchronous volcanism were revealed by detailed lithological studies. Following sedimentological analysis results we established an admixture of pyroclastic material in the Oxford-Kimmeridgian deposits of the Chukotka microcontinent, indicating the effect of synchronous volcanism on sedimentation. It was shown that the source of pyroclastic material was the intraoceanic Kulpolney island arc, which existed in the northern part of the Proto-Arctic Ocean.The accumulation of the Tithonian‒– Valanginian deposits occurred in the back-arc basin at the edge of Chukotka microcontinent. Characteristics of the Tithonian‒– Berriasian sandstones are given, which contain significant proportion of ash material in the matrix, as well as lithoclasts and monomineral grains of volcanic origin, predominant in the clasts. With the use of geochemical analysis of volcanic pebbles, the presence of the differentiated series from basaltic andesites to rhyolites in the volcanic source is proved. The suprasubduction origin of the volcanic source is established. The cessation of volcanic activity in Valangin era is confirmed by lack of presence of synchronous pyroclastic material and an insignificant amount of volcanic clasts in Valanginian sandstones. The obtained data of U–Pb isotope dating of zircons isolated from the Tithonian-Valanginian sandstones and andesite pebbles of the Tithonian conglomerates made it possible to determine the time for the existence of suprasubduction volcanism on the Chukotka margin in the period of 150–140 Ma.

Bol’shoi Ilek as the ilek formation stratotype of the Lower Cretaceous, and the new dinosaur and mammoth faunae site in the south-east of Western Siberia

The geological section of Bolshoi Ilek (up to 83 m high), southeast of Western Siberia, represented by Cretaceous and Quaternary systems has been reassessed. Its major part is composed with the Lower Cretaceous deposits of deltic genesis that reached 80 m thickness and characterized the Ilek Formation stratotype. During the screen washing of sand fraction the remains of fishes, lizards, turtles, crocodiloformes, dinosaurs, and mammals, typical for the Barremian - Lower Albian, have been revealed. Mesozoic strata are covered by eolian-deluvial and eluvial Quaternary deposits from 3 to 13,5 m. Three layers with mammoth fauna remains were distinguished there. The middle one is dated by 14С as ~ 22500 years ago. The observation have revealed that Bolshoi Ilek is a large landslide more than 1 square kilometre area. All of it allowed to compare it with the coeval section of Shestakovo outcrop that also exposes the part of giant landslide, caused by earthquakes more than 9 points by Richter scale, which indicates a powerful seismic event, occurred in the southeast of region at the very end of Pleistocene.

Комплексное обоснование тектонической природы аномальных разрезов верхнеюрской баженовской свиты и нижнемеловой ачимовской толщи Западной Сибири. Часть 2. Клиноформы нижнемеловых отложений

Комплексное обоснование тектонической природы аномальных разрезов верхнеюрской баженовской свиты и нижнемеловой ачимовской толщи Западной Сибири. Часть 2. Клиноформы нижнемеловых отложений

Triassic lithostratigraphy of the Wandel Sea Basin, North Greenland

The Wandel Sea Basin in eastern North Greenland forms the northern continuation of the offshore Danmarkshavn Basin and the conjugate margin to the western Barents Shelf south of Spitsbergen. The Triassic succession of eastern North Greenland, up to 700 m thick, spans the Induan (Dienerian) – Norian. The Triassic sediments rest unconformably on Upper Carboniferous and Upper Permian sediments, and are unconformably overlain by Upper Jurassic – Lower Cretaceous deposits. Based on recent fieldwork in the Wandel Sea Basin, five new and revised Triassic formations are described and included in the Trolle Land Group (revised). The Lower Triassic (Induan) Parish Bjerg Formation (revised) consists of marine sandstones, fluvial conglomerates and sandstones, and muddy flood-plain deposits. It is conformably overlain by Lower Triassic (Dienerian – lower Spathian) offshore mudstones with minor sand-dominated intervals of the Ugleungernes Dal Formation (new). The upper Spathian to Ladinian Dunken Formation (revised) is represented mainly by marine sandstones. A marked erosional unconformity characterises the base of the overlying Upper Triassic (Carnian – Norian) Storekløft Formation (new) composed of marginal marine to marine, massive sandstones and conglomerates as well as cross-bedded and biomottled marine sandstones and minor mudstone units. The Isrand Formation (mainly Middle Triassic) consists of laminated mudstones with minor thin sandstone units that were deposited in slope and basin floor settings in the eastern deeper part of the Wandel Sea Basin in Kronprins Christian Land. The Triassic succession of the Wandel Sea Basin represents a well-constrained shallow shelf to deep shelf / basin floor transect and thus forms an excellent outcrop analogue to the time-equivalent intervals in the western Barents Sea basins and the Danmarkshavn Basin offshore North-East Greenland.

Trigger mechanisms of gravity flow deposits in the Lower Cretaceous lacustrine rift basin of Lingshan Island, Eastern China

Gravity flows were commonly developed in subaqueous, steep slopes in lacustrine basins, which show distinct sedimentary records due to different flow behaviors and trigger mechanisms. Outcrops of the Lower Cretaceous deposits on the Lingshan Island are well exposed to illustrate flow transformations between turbidity currents and debris flows in shallow water and basin floor in a lacustrine basin. Outcrop sections were carefully measured to characterize sedimentary records of the gravity flows. Facies associations include laminated mudstone (FA1), deformed silty mudstone (FA2), massive very-fine sandstone with rip-up mud clasts (FA3), graded very-fine sandstone with (partial) Bouma sequences (FA4), massive gravelly sandstone with rip-up mud clasts (FA5), gravelly sandstones with partial Bouma sequences (FA6), and cross-stratified pebbly coarse-grained sandstones (FA7). Trigger mechanisms for the gravity flow include mainly plunging of hyperpycnal river discharges and earthquakes, which both induced failure of delta front/slope and the consequent debris flows/turbidity currents. Flow transformations occurred both at the shallow water and basin floor, which produced distinct sedimentary structures, stacking patterns, and architectural units. The high-density hybrid event beds (HEBs) with both gravels and mud clasts overlaid by sandy turbidites were mainly induced by floodwater from the active river mouths of deltas, generating fast-moving debris flows and deceleration of turbidity currents. Damping of turbidity currents and deceleration of muddy debris flows due to high cohesion induced low-density turbidites were overlaid by HEBs, showing thin-bedded, lateral extended sandy beds on the basin floor.

Ontogenetic braincase development in Psittacosaurus lujiatunensis (Dinosauria: Ceratopsia) using micro-computed tomography.

Ontogenetic sequences are relatively rare among dinosaurs, with Ceratopsia being one of the better represented clades, and especially among geologically earlier forms, such as Psittacosaurus. Psittacosaurus is a small, bipedal basal ceratopsian abundant in the Lower Cretaceous deposits of Asia, whose cranial and endocranial morphology has been well studied, but only cursory details have been published on the bones surrounding the brain. Using reconstructions created from micro-computed tomography scans of well-preserved skulls from the Barremian–Aptian Yixian Formation, China, we document morphological changes in the braincase of Psittacosaurus lujiatunensis through three growth stages, hatchling, juvenile, and adult, thus providing the first detailed study of ceratopsian braincase morphology through ontogeny. Notable ontogenetic changes in the braincase of P. lujiatunensis include a dramatic relative reduction in size of the supraoccipital, an increase in the lateral expansion of the paroccipital processes and a decrease in the angle between the lateral semicircular canal and the palatal plane. These ontogenetic morphological changes in the braincase relate to expansion of the cranium and brain through growth, as well as reflecting the switch from quadrupedal juveniles to bipedal adults as documented in the changing orientation of the horizontal semicircular canal through ontogeny. Recognition of these patterns in a basal ceratopsian has implications for understanding key events in later ceratopsian evolution, such as the development of the parieto-squamosal frill in derived neoceratopsians.

Application of the Brooks-Corey model in the conditions of lower cretaceous deposits in terrigenous reservoirs of Western Siberia

The paper deals with the issues of determining Brooks-Corey model parameters in the approximation of capillary curves under the conditions of productive strata of Western Siberia. It was emphasized that in the conditions of reservoirs of Western Siberia, there are close correlations between current water saturation of capillary curves at fixed values of capillary pressure and reservoir properties (absolute permeability, residual water saturation). Using these correlations, the approximation model parameters (initial capillary pressure and capillary curve steepness) were accurately assessed.

Conditions of formation and forecast of natural reservoirs in clinoform complex of the Lower Cretaceous of the Barents-Kara shelf

Unique Leningradsky and Rusanovsky gascondensate fields in the Barrem-Cenomanian layer are discovered in the Kara Sea. Non-industrial accumulations of oil and gas have been discovered in the Lower Cretaceous sediments of the western part of the Barents Sea shelf. However, the structure and oil and gas potential of the Lower Cretaceous sediments of the Barents-Kara shelf remain unexplored. Based on the seismic-stratigraphic and cyclostratigraphic analysis, a regional geological model of the Lower Cretaceous deposits of the Barents-Kara shelf was created, the distribution area and the main stages of the accumulation of clinoforms were identified. As a result of a detailed analysis of the morphology of clinoform bodies, paleogeographic conditions were restored in the Early Cretaceous and a forecast of the distribution of sandy reservoirs was given

Jumping bristletails (Insecta, Archaeognatha) from the Lower Cretaceous amber of Lebanon

AbstractJumping bristletails (order Archaeognatha), the basalmost order of extant insects, include some of the earliest fossil records among hexapods, yet their overall geological occurrence remains sparse and has provided little insight into their evolution. The earliest representatives of crown‐group bristletails are those in Lebanese amber (Cretaceous), hitherto known only from a single species. Here we significantly expand the known fossil record of Archaeognatha, and from the prolific Lower Cretaceous (Barremian) deposits of Lebanon. One new genus and species, Glaesimeinertellus intermedius gen. et sp. nov., and one new species, Macropsontus bachae sp. nov., are described and figured from Hammana amber, whereas one additional Macropsontus species, M. azari sp. nov., and one meinertellid morphotype are described and figured from Al‐Rihan amber. The new taxa are compared with their modern and fossil relatives. Collectively, the new taxa render the Archaeognatha fauna from Lebanese amber the earliest with sufficient preservation to provide character data comparable to modern forms, highlighting the considerable morphological conservatism within the order.

Manifestations of post-sedimentation processes in the Lower Cretaceous sediments of Bolshekhetskaya depression (Western Siberia)

Оbject.The article presents the results of studies of secondary mineral formation in the lower Cretaceous sediments of the Bolshekhetskaya depression, which contain highly promising oil and gas deposits, with established industrial performance at Pyakyakhinskoye, Khalmerpayutinskoye and South-Messoyakhskoye fields. The objects under consideration are located in the most submerged part of the Nadym-Taz syneclise in the zone, where the Taz and Urengoy facies regions meet.Materials and methods.Main types of postsedimentary changes of reservoir rocks selected on the basis of study of core material Pokurskaya, Angelovskaya, Sortymskaya and Megionskaya fms. Petrography and Mineralogy of the rocks under consideration were studied on the basis of stage analysis using optical and electron microscopy, and X-ray diffraction study at the Center of core and reservoir fluids research of “LUKOIL-Engineering’s KogalymNIPIneft branch In Tyumen” (Kogalym). Determination of the mineral type of zeolite was performed by X-ray phase analysis at the Institute of Geology and Geochemistry UrO RAS (Ekaterinburg).Resuts.It was found that for rocks Pokurskaya, Angelovskaya, Sortymskaya and Megionskaya fms characteristic a diverse range of secondary minerals and structures, evidence of the background stage catagenesis and the superimposed processes. The most important among them is the regeneration of quartz, the transformation of feldspar, violation of the crystal structure of biotite, the formation of various clay minerals, crystallization of zeolites and calcite.Conclusions.Studies show that the upper part of the section of the lower Cretaceous deposits of Bolshekhetskaya depression corresponds to the area of the middle catagenesis (gradation MK2), the bottom – changed to the stage of deep catagenesis (gradation MK3). In this case, the epigenetic process proceeded unevenly, pulsation, due to changing tectonic conditions. Particular attention is paid to the origin of zeolites, which is still debatable. It is assumed that their formation is associated with the transformation of “camouflage pyroclastic” in particular, feldspar clastics.

Marine reptiles from the Jurassic/Cretaceous transition at the High Andes, Mendoza, Argentina

Upper Jurassic and Lower Cretaceous deposits of the Vaca Muerta Formation (Neuquén Basin, central-west Argentina) have yielded abundant marine reptile remains. Most of them correspond to faunal assemblages recovered from outcrops in the Neuquén Province (Argentina). Herein we report two new marine reptile-bearing localities documenting the Tithonian–Berriasian transition at the High Andes (Mendoza Province, Argentina). Marine reptiles have been mapped and/or collected in connection with an accurate ammonoid-based biostratigraphic control. All the skeletons have been found preserved in, or associated with, calcareous nodules. At both localities they are frequent in beds assigned to the upper Tithonian Corongoceras alternans ammonite Zone (Microcanthum to “Durangites” Standard Zones), and are rare to common in beds assigned to the upper Tithonian–lower Berriasian Substeueroceras koeneni Zone (“Durangites” to Jacobi Standard Zones). Newly discovered assemblages depict a similar pattern characterized by the lack of plesiosaurs (plesiosauroids and pliosaurids), and by the abundance of mesoconsumers represented by ophthalmosaurids and metriorhynchine metriorhynchids. Macropredator geosaurines, apex metriorhynchids predators, and thalassochelydian turtles are rare components of these assemblages.

How to rely on the unreliable: Examples from Mesozoic bryophytes of Transbaikalia

AbstractThree new fossil bryophytes are described from Jurassic and Lower Cretaceous deposits of the Transbaikalia region of Russia. The complex thalloid hepatic Khasurtythallus monosolenioides gen. et sp. nov. belongs to the Marchantiidae, but its combination of characters precludes unequivocal placement in any of the five orders of this subclass, representing most likely an extinct lineage. Paleaethallus squarrosus gen. et sp. nov. is a thalloid plant with scales similar to those of complex thalloid hepatics, although their arrangement and the overall plant structure has little in common with any extant hepatics. Dispersed moss capsules, three of which have attached calyptrae, are described as a form genus Kulindobryum gen. nov. Despite incomplete preservation, some rare characters indicate possible relationship to the genus Tayloria of the Splachnaceae, an extant family of mosses adapted to grow on animal dung, dead bodies and bones. Notably, Kulindobryum co‐occurs with bones of the small feathered dinosaurs Kulindadromeus, which also supports an affiliation of Kulindobryum with the Splachnaceae. The most common and best known Mesozoic moss for the region, the genus Bryokhutuliinia, is appraised for its systematic position and probable affinities with the Dicranales. A scoring approach is introduced for the comparative method of taxonomic placement of fossils with partial suites of morphological characters at the family or order level.

Mineral composition and gemological characteristics of the petrified wood of the Ulyanovsk region

For the first time, the mineral composition and gemological characteristics of the petrified wood from the Ulyanovsk region, of jewelry and ornamental quality, have been studied. The petrified wood is associated with the Lower Cretaceous deposits and consists mainly of calcite (up to 73 mass. %); pyrite, apatite, gypsum are present; dolomite, anhydrite, hematite, pyrolusite, organic matter and X-ray amorphous substance have been fixed. According to the technological and decorative characteristics, the petrified wood of the Ulyanovsk region is a quality jewelry and ornamental material of the florogenic group.

Advances in the Study of the Non-Marine Ostracods in Luanping Basin, Northern Hebei (North China): A Preliminary Result

The Luanping Basin of northern Hebei, North China, is well known for its continuous nonmarine Lower Cretaceous deposits and the preservation of the Jehol Biota. However, there are still some controversies about the stratigraphic correlation in these regions. Here we report some advances on the study of the nonmarine ostracods of Luanping, focusing on its biostratigraphical utility. Preliminary results indicate that the nonmarine ostracods from Luanping Basin consist of 17 genera and around 44 species. The ostracod assemblages of the Dabeigou, Dadianzi and Xiguayuan formations of this Basin can be assigned to the Luanpingella-Ocrocypris-Eoparacypris (Late Valanginian-Early Hauterivian age), Cypridea-Timiriasevia-Daurina (Late Huaterivian-Barremian age) and Cypridea-Limnocypridea-Lycopterocypris (Aptian stage) zones, respectively. This temporary framework can be served as a stratigraphic correlation tool in northern Hebei, as well as contributed to a better understanding of the evolution of the Jehol Biota.

Geodynamics and Oil and Gas Potential of the Yenisei-Khatanga Basin (Polar Siberia)

The geodynamic development of the north–western (Arctic) margin of the Siberian craton is comprehensively analyzed for the first time based on our database as well as on the analysis of published material, from Precambrian-Paleozoic and Mesozoic folded structures to the formation of the Mesozoic-Cenozoic Yenisei-Khatanga sedimentary basin. We identify the main stages of the region’s tectonic evolution related to collision and accretion processes, mainly subduction and rifting. It is demonstrated that the prototype of the Yenisei-Khatanga basin was a wide late Paleozoic foreland basin that extended from Southern Taimyr to the Tunguska syneclise and deepened towards Taimyr. The formation of the Yenisei-Khatanga basin, as well as of the West-Siberian basin, was due to continental rifting in the Permian-Triassic. The study describes the main oil and gas generating deposits of the basin, which are mainly Jurassic and Lower Cretaceous mudstones. It is shown that the Lower Cretaceous deposits contain 90% of known hydrocarbon reserves. These are mostly stacked reservoirs with gas, gas condensate and condensate with rims. The study also presents data on oil and gas reservoirs, plays and seals in the Triassic, Jurassic and Cretaceous complexes.