The interstratified breccias and conglomerates in the Cretaceous flysch of the northern Basque Pyrenees: submarine outflow of diapiric mass

In the Cretaceous flysch of the Northern Pyrenees, polymict conglomerates interbedded in the flysch are described from the vicinity of Orio (near San Sebastián). These contain components derived from rocks of all periods from Paleozoic to Lower Cretaceous. During Late Maastrichtian times a diapir, originated in Keupez evaporites, penetrated the deep-sea Cretaceous flysch which was still undergoing deposition. This resulted in the expulsion of large quantities of diapiric mass. After the solution of the evaporites the pebbles, which had been dragged along with the diapiric masses, slumped into a neighbouring marginal depression where they were redeposited. The reddish strata of Late Maastrichtian and Danian age in this region are interpreted as being out-thrust and transported Keuper shales. It will be shown that the other breccias and conglomerates described by Feuillé and Mathey (1972) from the Late Cretaceous of the Basque Pyrenees probably have the same origin.The comprehensive name “Vascongadian Diapir Zone” is suggested for the diapir field on the northern edge of the Basque sedimentary trough.     

Late Cretaceous – Early Tertiary sedimentation and tectonic inversion in the southern Netherlands

Analysis of the Upper Cretaceous stratigraphy of the Peel Block reveals the basin development of the block to have been influenced by both the inversion of the Roer Valley Graben and Central Netherlands Basin, and the overall Late Cretaceous transgression. Sediments of Santonian to Danian age were deposited on the block. These sediments are compared with the detailed lithostratigraphy of southern Limburg, where Late Cretaceous strata are exposed. Four successions can be recognised in southern Limburg. The two oldest successions, the Santonian Oploo Formation (new name, proposed in the present contribution) and the mainly Early Campanian Vaals Formation, are restricted to the central and northern parts of the block. These siliciclastic formations were deposited under the influence of inversion of the Roer Valley Graben and the Central Netherlands Basin, as well as under the influence of a rising sea level. Towards the north, sands of the Oploo Formation grade into marls and chalks of the Ommelanden Formation. The two youngest successions comprise the largely Late Campanian to Maastrichtian Gulpen and Maastricht Formations and the Danian Houthem Formation. These chalk formations were deposited under the influence of regional subsidence during a sea-level highstand. Subsequent to deposition of the Houthem Formation, a regional regression triggered a change from shallow-marine carbonate to paralic siliciclastic deposition.     

Cretaceous Oceanic Red Beds: Distribution, Lithostratigraphy and Paleoenvironments

Cretaceous oceanic red beds (CORBs) represented by red shales and marls, were deposited during the Cretaceous and early Paleocene, predominantly in the Tethyan realm, in lower slope and abyssal basin environments. Detailed studies of CORBs are rare; therefore, we compiled CORBs data from deep sea ocean drilling cores and outcrops of Cretaceous rocks subaerially exposed in southern Europe, northwestern Germany, Asia and New Zealand. In the Tethyan realm, CORBs mainly consist of reddish or pink shales, limestones and marlstones. By contrast, marlstones and chalks are rare in deep-ocean drilling cores. Upper Cretaceous marine sediments in cores from the Atlantic Ocean are predominantly various shades of brown, reddish brown, yellowish brown and pale brown in color. A few red, pink, yellow and orange Cretaceous sediments are also present. The commonest age of CORBs is early Campanian to Maastrichtian, with the onset mostly of oxic deposition often after Oceanic Anoxic Events (OAEs), during the early Aptian, late Albian-early Turonian and Campanian. This suggests an indicated and previously not recognized relationship between OAEs, black shales deposition and CORBs. CORBs even though globally distributed, are most common in the North Atlantic and Tethyan realms, in low to mid latitudes of the northern hemisphere; in the South Atlantic and Indian Ocean in the mid to high latitudes of the southern hemisphere; and are less frequent in the central Pacific Ocean. Their widespread occurrence during the late Cretaceous might have been the result of establishing a connection for deep oceanic current circulation between the Pacific and the evolving connection between South and North Atlantic and changes in oceanic basins ventilation.     

松辽盆地姚家组-嫩江组地层层序及沉积演化

松辽盆地姚家组-嫩江组是晚白垩世形成的一套完整的水进-水退沉积旋回,分为2个二级层序,6个三级层序,持续时间约4Ma。嫩江组二段最大湖泛期在底部形成了盆地范围内稳定分布的油页岩,其不仅是层序及地层对比的标准界面,而且是重要的烃源岩层和盖层。姚家组与嫩江组一段是水进期大型退积型三角洲沉积,嫩江组三段是水退期大型湖泊与快速进积大型三角洲沉积。嫩江组在水进期长轴物源方向发育大型重力流水道及末端浊积扇,水道延伸距离64km,最大宽度600m;在水退初期短轴方向发育滑塌浊积扇,扇体有复合式和单体式,滑塌最小古坡度为5%～12‰,表面均发育弧状滑塌波纹,波纹密度4～10条/km,最小滑移距离2～10km。     

A new biostratigraphic correlation for Late Cretaceous–Paleocene strata of the Gulf of Guinea: Evidence from dinoflagellate cysts

A new biostratigraphic correlation for Late Cretaceous and Palaeocene strata of the Côte d’Ivoire–Ghana continental margin has been developed from the identification of significant dinoflagellate cyst events in ODP Hole 959D. The Late Cretaceous stage boundaries are mostly consistent with previous studies. However, the Maastrichtian/Danian boundary is placed much lower than previously recognized on the basis of the first occurrences of Carpatella cornuta and Damassadinium californicum. The base of the Selandian is recognized from the last occurrence of Cerodinium diebelii and the first occurrence of Adnatosphaeridium multispinosum. The base of the Thanetian is recognized from the first occurrence of Areoligera gippingensis. The rarity of the age-marker taxa is the main reason for different age determinations among studies of the same section.     

The Cretaceous–Tertiary boundary in southern low-latitude regions: preliminary study in Pernambuco, northeastern Brazil

A preliminary integrated study of a Cretaceous-Tertiary (K/T) boundary section in Pernambuco, northeastern Brazil, provides evidence for an extraterrestrial bolide impact in the earliest Danian. A non-graded, nodular carbonate mudstone/wackestone bed is interpreted as a slump or a mud Flow deposit, induced by a tsunami event or by a gravity mass movement during a sea-level lowstand, the former possibly generated by the K/T boundary Yucatán impact. This bed overlies marlstones deposited in an upper bathyal environment and marks the top of the Cretaceous. Nearly all known latest Maastrichtian planktonic foraminifera are recovered from the Cretaceous strata. Iridium shows a marked peak in a thin hemipelagic claystone layer, about 75 cm above the K/T boundary, deposited in a middle to deep neritic environment. The claystone overlies alternating beds of finegrained limestones and marlstones and a 50 cm-thick graded bioclastic packstone, which rests upon a marly limestone breccia of the lowermost Danian. Abundant reworked Cretaceous and rare lowermost Danian microfossils (e.g. E. edita, E. eobulloides, E. fringa, G. irregularis, P. eugubina, P. cf. pseudobulloides, W. claytonensis and W. hornerstownensis ) have been recovered from these strata. These lowermost Danian beds record the sudden appearance of abundant shock-metamorphosed quartz grains, with several sets of intersecting deformation lamellae and microtektite-like microspherules. This suggests that these deposits were formed by an additional tsunami caused by a second impact event in the earliest Danian, near or at the boundary between the Palaeocene P α and P 1a foraminiferal zones. Impact-derived material has not been found in the uppermost Cretaceous beds.     

The youngest records of mosasaurid reptiles from the Upper Cretaceous of the South-Western Desert in Egypt

Mosasauroid squamates were abundant and had a worldwide distribution during the Late Cretaceous, but records from Sub-Saharan Africa are comparatively scanty and based mainly on fragmentary and isolated material. Here new mosasaur remains from the Maastrichtian (Upper Cretaceous) of Dakhla Oasis in the South-Western Desert of Egypt are recorded, including: a small, fragmentary right dentary of an indeterminate mosasaurine with a single tooth preserved in situ and an isolated tooth crown of the genus Globidens. This material stems from fossiliferous, calcareous sandstones with intercalated shales that form the lower portion of the Dakhla Formation, known to be an intertidal to subtidal deposit. Previously recorded mosasaur remains from the Eastern Desert in Egypt included Globidens phosphaticus, Platecarpus sp., and Igdamanosaurus aegyptiacus. In Africa, mosasaurs of the Maastrichtian age have been recorded from Morocco, Nigeria, Angola, the Democratic Republic of Congo, and Niger. The newly collected material from Dakhla Oasis currently constitutes the youngest record of mosasaurs in Egypt.     

Shallow water agglutinated foraminiferal response to Late Cretaceous–Early Paleocene sea-level changes in the Dakhla Oasis,Western Desert,Egypt

The Late Cretaceous (Maastrichtian) to early Paleocene (Thanetian) shallow water (<100 m) agglutinated foraminifera from a section at Dakhla Oasis (Western Desert, Egypt) were analyzed for their assemblage, species and genera distribution, diversity, depositional environment, community structure and palaeobathymetry with respect to regional tectonics, climate and global eustasy. Data suggest an equitable benthic environment with low species dominance deposited in a brackish littoral and/or marsh setting. Sea level curves using characteristic benthic foraminiferal species, genera and assemblages corroborate quantitatively generated estimate and statistical analysis. Data suggests that in the absence of or of an impoverished benthic foraminiferal fauna, a high resolution agglutinated foraminiferal dataset can be as good a predictor of the benthic community structure and environment, as its calcareous counterpart, at least for shallow settings (<100 m). Present data also provides a good window in better understanding the distribution and interrelationship between the three dominant genera, Haplophragmoides, Trochammina and Ammobaculites. Faunal changes at boundaries (Cretaceous/Paleogene, Danian/Selandian and Selandian/Thanetian) are also evaluated.     

Sedimentological and stratigraphic evolution of northern Lebanon since the Late Cretaceous: implications for the Levant margin and basin

This paper presents an updated review of the Upper Mesozoic and Cenozoic sedimentological and stratigraphic evolution of the Levant margin with a focus on the northern Lebanon. Facies and microfacies analysis of outcrop sections and onshore well cores (i.e., Kousba and Chekka) supported by nannofossil and planktonic foraminifers biostratigraphy, allowed to constrain the depositional environments prevailing in the Turonian to Late Miocene. The “Senonian” (a historical term used to define the Coniacian to Maastrichtian) source rock interval was subdivided into four sub-units with related outer-shelfal facies: (1) Upper Santonian, (2) Lower, (3) Upper Campanian, and (4) Lower Maastrichtian. This Upper Cretaceous rock unit marks the major drowning of the former Turonian rudist platform. This paper confirms the Late Lutetian to Late Burdigalian hiatus, which appears to be a direct consequence of major geodynamic events affecting the Levant region (i.e., the continued collision of Afro-Arabia with Eurasia), potentially enhanced by regressional cycles (e.g., Rupelian lowstand). The distribution of Late Burdigalian–Serravallian rhodalgal banks identified in northern Lebanon was controlled by pre-existing structures inherited from the pulsating onshore deformation. Reef barriers facies occur around the Qalhat anticline, separating an eastern, restricted back-reef setting from a western, coastal to open marine one. The acme of Mount Lebanon’s uplift and exposure is dated back to the Middle–Late Miocene; it led to important erosion of carbonates that were subsequently deposited in paleo-topographic lows. The Late Cretaceous to Cenozoic facies variations and hiatuses show that the northern Lebanon was in a higher structural position compared to the south since at least the Late Cretaceous.     

北羌塘盆地油页岩形成环境及其油气地质意义

最近在北羌塘长蛇山地区新发现了晚侏罗世—早白垩世大套油页岩及巨厚膏盐层,该油页岩与近年来作者在胜利河、长梁山地区发现的多处油页岩连成一片,构成了目前我国规模最大的中生代海相油页岩带—北羌塘油页岩带。沉积岩相、古地理研究表明,晚侏罗世—早白垩世时期,北羌塘盆地总体上为一个向北西开口的相对闭塞的巨大海湾,发育了河流-三角洲、海湾(潮坪-潟湖)和浅海-陆棚等沉积相组合。古气候、古环境研究表明,油页岩(段)沉积期,胜利河地区处于潮湿的热带-亚热带环境,大量淡水的注入以及高的生产力等综合因素,控制了油页岩的形成,其分布主要位于局限海湾-潟湖的边缘带;膏盐层(段)沉积则发育于相对干旱、炎热气候条件下的闭塞环境。北羌塘晚侏罗世—早白垩世油页岩及其上覆膏盐层是重要的烃源岩和区域性封盖层。油页岩及含膏盐层沉积组合的发现,对于重新认识羌塘盆地生烃条件及保存条件,具有十分重要的意义。     

A lithostratigraphic revision and palaeoenvironmental assessment of the Cretaceous System exposed in the onshore Cauvery Basin, southern India

The exposed Cretaceous shelf succession of the Cauvery Basin, southeastern India, has provided a world-class record of mid and Late Cretaceous invertebrates, documented in a substantial literature. However, the lithostratigraphy of the succession has been little studied and previously subject to a range of nomenclature. It is revised here, on the basis of intensive regional mapping, to stabilize the definition and nomenclature of lithostratigraphic units. The Uttattur Group is restricted in outcrop to the Ariyalur district and divided into the Arogypapurum Formation (new; Albian), Dalmiapuram Formation (late Albian), and Karai Formation (late Albian–early Turonian) for which the Odiyam and Kunnam Members are recognized. The Trichinopoly Group follows unconformably and is also restricted in outcrop to the Ariyalur district. It is divided into the Kulakkalnattam Formation (Turonian) and Anaipadi Formation (late Turonian–Coniacian). The Ariyalur Group is more widely distributed. In the Ariyalur district, the Sillikkudi Formation (Santonian–Campanian) and its Kilpaluvari Member, the Kallakurichchi Formation (early Maastrichtian), the Kallamedu Formation (mid and Late Maastrichtian) and the Niniyur Formation (Danian) are recognized. The sequence in the Vriddhachalam area consists of the Parur and Patti formations (Campanian), Mattur Formation (late Campanian–earliest Maastrichtian) and Aladi Formation (Maastrichtian). For the Pondicherry district, the Valudavur and Mettuveli formations (Maastrichtian) and Kasur and Manaveli formations (Paleocene) comprise the succession. The interpreted depositional environments for the succession in the Ariyalur district indicate four eustatic cycles in the mid and Late Cretaceous and earliest Tertiary: late Albian–early Turonian, late Turonian–Santonian, Campanian, Maastrichtian, and Paleocene. Overall the Cauvery Basin sequence is arenaceous and relatively labile in terms of framework grain composition, and contrasts with the pelitic assemblage developed on the west Australian margin from which eastern India separated in the Early Cretaceous (Valanginian). The difference is ascribed to palaeoclimate as controlled by palaeolatitude. For the Late Cretaceous, the Cauvery Basin drifted north on the Indian plate from 40 to 30°S. This zone is inferred to constitute Southern Hemisphere horse latitudes for Late Cretaceous time, characterized by an arid climate, physical weathering and the production of labile sands. By contrast, the west Australian margin of matching tectonic history remained in a high palaeolatitude (>40°S) throughout the Late Cretaceous, experiencing a pluvial climate, the dominance of chemical weathering and the production of clays.     

西藏仲巴地区白垩纪末期—始新世早期海相地层

西藏仲巴县北部地区出露有晚白垩世至古近纪的海相地层 ,本次工作新测制了卓勒剖面 ,并对原错江顶剖面上部地层做了再次研究。地层中化石丰富 ,据有孔虫化石研究结果重新厘定曲下组时代为古新世早期、加拉孜组上段属始新世早期 ,认为该区白垩 /古近纪界线位于曲贝亚组与曲下组之间。在这一界面上 ,古新世磨拉石直接覆于晚白垩世的陆棚碳酸盐台地沉积之上 ,其间存在沉积间断 ,为弧前盆地演化后期的重大沉积转变。古新世早期曲下组为近海相磨拉石沉积 ,古新世晚期至始新世早期加拉孜组为残留海盆沉积。加拉孜组顶部为该区最高海相地层 ,其上为冈底斯群的磨拉石不整合覆盖。冈底斯群的时代应晚于始新世中期。     

准噶尔盆地南缘中-新生界沉积物重矿物分析与盆山格局演化

本文通过分析准噶尔盆地南缘野外剖面、部分钻井岩心和天山内部野外剖面的碎屑重矿物及其组合特征,探讨了准噶尔盆地中-新生代物源体系和盆山格局的演化。准噶尔盆地南缘至少存在3个物源体系,各物源体系的重矿物组合、含量及其反映的物源属性均存在较大差异;其中,南部天山物源还存在东、西两部的差异。不同重矿物组合出现和不稳定重矿物的增加显示中-新生代存在3个构造活动相对活跃期,即晚侏罗世—早白垩世早期、晚白垩世和晚新生代。早-中侏罗世天山内部发育多个分隔的小型盆地,盆地南部边界至少位于后峡附近,不存在地理分隔明显的天山;晚侏罗世—早白垩世早期是天山隆升、盆山格局发生转变的时期,博格达山逐渐构成盆地南缘的又一重要物源;白垩纪—古近纪盆山格局变化不大,新近纪以来的强烈挤压构造背景使得天山山脉快速隆升,盆山格局发生重大改变。准噶尔盆地南缘中-新生代构造相对活跃期和盆山格局演变与欧亚板块南缘发生的构造事件具有良好的对应关系。     

南雄盆地晚白垩世-古新世陆源沉积组份变化的古气候指示

利用陆源沉积中的碎屑组份(泥岩中的碎屑黏土矿物种类和砂岩中砂、粉砂碎屑类型)相对含量变化,对广东北部和江西南部的南雄盆地晚白垩世-古新世古气候进行了分析.结果显示,砂岩碎屑组份含量气候指数(长石/石英比,F/Q)介于0.02~0.14之间;(碎屑)黏土矿物组合主要以伊利石为主,平均79%;伊利石结晶度指数与化学指数分别为0.25~0.39、0.31~0.7.进一步分析表明,研究区这一时期以干旱气候为主,存在暖湿气候间断,古气候演化可分为三个阶段:晚白垩世马斯特里赫特期以干旱-半干旱性气候为主,古新世丹尼期早期转变为相对湿热或与干旱-半干旱气候交替,古新世丹尼期晚期恢复到半干旱性气候,但比第一阶段湿度可能稍有增加.这一总体干旱-半干旱气候格局及其变化总体与同期全球气候变化一致.     

Palynostratigraphy and palaeoenvironmental significance of the Cretaceous palynomorphs in the Qattara Rim-1X well,North Western Desert,Egypt

Palynological and palynofacies analyses were carried out on some Cretaceous samples from the Qattara Rim-1X borehole, north Western Desert, Egypt. The recorded palynoflora enabled the recognition of two informal miospore biozones arranged from oldest to youngest as Elaterosporites klaszii-Afropollis jardinus Assemblage Zone (mid Albian) and Elaterocolpites castelainii–Afropollis kahramanensis Assemblage Zone (late Albian–mid Cenomanian). A poorly fossiliferous but however, datable interval (late Cenomanian–Turonian to ?Campanian–Maastrichtian) representing the uppermost part of the studied section was also recorded. The palynofacies and visual thermal maturation analyses indicate a mature terrestrially derived organic matter (kerogen III) dominates the sediments of the Kharita and Bahariya formations and thus these two formations comprise potential mature gas source rocks. The sediments of the Abu Roash Formation are mostly dominated by mature amorphous organic matter (kerogen II) and the formation is regarded as a potential mature oil source rock in the well. The palynomorphs and palynofacies analyses suggest deposition of the clastics of the Kharita and Bahariya formations (middle Albian and upper Albian–middle Cenomanian) in a marginal marine setting under dysoxic–anoxic conditions. By contrast, the mixed clastic-carbonate sediments of the Abu Roash Formation (upper Cenomanian–Turonian) and the carbonates of the Khoman Formation (?Campanian–Maastrichtian) were mainly deposited in an inner shallow marine setting under prevailing suboxic–anoxic conditions as a result of the late Cenomanian and the Campanian marine transgressions. This environmental change from marginal to open (inner shelf) basins reflects the vertical change in the type of the organic matter and its corresponding hydrocarbon-prone types. A regional warm and semi-arid climate but with a local humid condition developed near/at the site of the well is thought to have prevailed.     

Petrology of a suite of sedimentary rocks associated with some cole-bearing basins in northwestern Thailand

A number of basins in northwestern Thailand contain thick sequences of Cenozoic sedimentary rocks. Oil shales and coals are prominent lithologies within these sequences and occur together in some basins. Most of the sequences are, however, dominated by either oil shales or coals. The major oil shale deposit is in the Mae Sot Basin but oil shales also occur in the Ban Huay Dua, Mae Moh, Ban Pa Ka Li, Mae Teep, Ban Na Hong and Jae Hom Basins.Drilling and detailed mapping, in the Mae Sot Basin indicate thick sequences of oil shales and organic petrological studies show that they contain abundant lamalginite. Trace amounts of telalginite, liptodetrinite, bitumen/resinite and huminite/inertinite are also present in some of the rocks. The parts of the sequences rich in authigenic minerals are, in general, petrographically similar to Green River Formation lamosites. Where clay/silt-sized epiclastics are more abundant, similarities exist to Australian Tertiary lamosites. Vitrinite reflectance date from the oil shales and associated coals indicate a low level of maturity.Oil shales from the other basins are, petrographically similar to the Mae Sot lamosites, however some differences do exist. The Mae Sot and other lamosites were deposited in lacustrine environments that probably had highly variable water depths.     

中非裂谷系前寒武系基岩油气成藏组合

中非裂谷系是在前寒武系结晶基岩基础上发育起来的中新生代裂谷盆地群。通过露头和钻井资料研究发现,基岩主要由前寒武系岩浆岩、正变质岩和少量副变质岩组成。根据暗色矿物含量可以将基岩划分为长英质和铁镁质岩石两大类,前者更有利于风化和裂缝的形成,储层物性较好。寒武纪-侏罗纪长期风化作用形成了广泛分布且厚度较大的球形风化壳(段),早白垩世中非剪切带的走滑拉张应力场与前寒武系刚性基岩的耦合作用在基底产生了大量高角度断层、共轭缝、微裂缝和节理等,风化淋滤、表生和热液作用控制了溶蚀、胶结和次生孔隙发育。风化壳和裂缝储层发育具有“似层状”的特征,垂向上基岩潜山储层序列可进一步划分为风化淋滤带、裂缝发育带、半充填裂缝带和致密带四个区带。中非裂谷系盆地在早白垩世、晚白垩世和古近纪三期裂谷期发育了三期区域性厚层泥页岩,古近系暗色泥岩由于埋藏浅,处于未成熟阶段,不能作为有效烃源岩,上白垩统泥岩以滨浅湖相为主,有机质含量总体不高,以Ⅲ型干酪根为主,下白垩统深湖相泥岩是区域上的优质烃源岩,同时为基岩提供了良好的油源和顶盖层。根据盖层的时代,可以划分出下白垩统、上白垩统和古近系3类成藏组合。乍得Bongor盆地基岩勘探获得极大成功,发现了一批高产稀油油田,打开了中非地区一个新的油气勘探领域。     

Sources of clastic material of Cretaceous–Paleogene deposits in the southwestern part of the Amur–Zeya Basin: results of dating U–Pb detrital zircons

The results of our study indicate that at the Late Cretaceous–Paleogene boundary in the southeastern part of the Amur–Zeya Basin, the sedimentation conditions changed drastically, namely, the change of provenance areas of debris. In the Maastrichtian, the clastic material was mainly transported from the Bureya–Jiamusi Superterrane and the volcanic–plutonic belts of Khingan–Okhotsk and East Sikhote–Alin located to the east: sedimentation occurred simultaneously with magmatic activity. During the Danian Stage, the major source of debris to the southern part of the basin was located to the south of the young mountain system of the Lesser Khingan (the uplifted part of the basement of the Songliao Block).     

Campanian-Maastrichtian chalks of southwestern Arkansas: Petrology,paleoenvironments and comparison with other North American and European chalks

Chalk was deposited in southwestern Arkansas during the Campanian and Maastrichtian. The Saratoga Formation was deposited in a middle-shelf environment during a transgression, with deposition of a condensed facies during the initial transgressive pulse, followed by deposition of sandy chalk and marly chalk. The Annona Formation, which was deposited in a middle- to outer-shelf environment, was also deposited during a transgression, with initial deposition of a condensed facies followed by local accumulation of calcarenitic chalk and then deposition of a substantial thickness of chalk-marly chalk.The Saratoga and Annona, deposited in the western portion of the Late Cretaceous Mississippi embayment, are comparable in lithology to the Campanian-Maastrichtian Demopolis and Prairie Bluff Formations, found on the eastern side of the embayment. The sandy chalk facies is perhaps more conspicuous in the Mississippi embayment than in any other area of Late Cretaceous chalk deposition. In general, North American chalk is characterised by relatively greater input of terrigenous detritus than European chalk. Because of greater dilution by terrigeneous detritus, North American chalk generally was deposited in restricted areas only in periods of transgressive maxima during the worldwide Late Cretaceous transgression.