Cretaceous and Tertiary of the Iullemmeden Basin in Nigeria (West Africa)

The Iullemmeden Basin (Mali-Niger-Benin-Nigeria) of tectono-epeirogenic origin was invaded several times by epicontinental transgressions during the Cretaceous and Paleocene.Three major subdivisions are recognized in the Nigerian section of the basin (the “Sokoto Basin”): (1) the lower, continental beds (= Continental Intercalaire) of Late Jurassic to Early Cretaceous age, (2) intermediate marine and brackish water deposits and (3) “Continental T Terminal” of upper Eocene-Miocene age.The geology of the Iullemmeden Basin is reviewed and updated. The relationships between the “Continental Intercalaire” of francophone authors and the Illo and Gundumi Formations are analysed and the type sections of the latter described. It is suggested that the Illo and Gundumi Formations are lateral equivalents.Detailed information on the formations of the Maastrichtian Rima Group is presented. It is concluded that there is no age difference of consequence between the Paleocene Dange, Kalambaina and Gamba Formations.The epicontinental transgressions are interpreted as coming from the north-east, east of the Hoggar massif during the Cenomanian and Turonian and west of the Hoggar during the Maastrichtian and Paleocene. The Sokoto Paleocene molluscan fauna is considered to be terminal Paleocene to Eocene and somewhat younger than the Ewekoro association of coastal Nigeria.A new interpretation of the Continental Terminal is presented. The structural history of the Sokoto Basin is reviewed and partly re-interpreted in the light of new field evidence.     

Stratigraphy of the upper cretaceous and lower tertiary strata in the Tethyan Himalayas of Tibet (Tingri area,China)

The 1500-m-thick marine strata of the Tethys Himalaya of the Zhepure Mountain (Tingri, Tibet) comprise the Upper Albian to Eocene and represent the sedimentary development of the passive northern continental margin of the Indian plate. Investigations of foraminifera have led to a detailed biozonation which is compared with the west Tethyan record. Five stratigraphic units can be distinguished: The Gamba group (Upper Albian - Lower Santonian) represents the development from a basin and slope to an outer-shelf environment. In the following Zhepure Shanbei formation (Lower Santonian - Middle Maastrichtian), outer-shelf deposits continue. Pebbles in the top layers point to beginning redeposition on a continental slope. Intensified redeposition continues within the Zhepure Shanpo formation (Middle Maastrichtian - Lower Paleocene). The series is capped by sandstones of the Jidula formation (Danian) deposited from a seaward prograding delta plain. The overall succession of these units represents a sea-level high at the Cenomanian/Turonian boundary followed, from the Turonian to Danian, by an overall shallowing-upward megasequence. This is followed by a final transgression — regression cycle during the Paleocene and Eocene, documented in the Zhepure Shan formation (?Upper Danian - Lutetian) and by Upper Eocene continental deposits. The section represents the narrowing and closure of the Tethys as a result of the convergence between northward-drifting India and Eurasia. The plate collision started in the Lower Maastrichtian and caused rapid changes in sedimentation patterns affected by tectonic subsidence and uplift. Stronger subsidence and deposition took place from the Middle Maastrichtian to the Lower Paleocene. The final closure of remnant Tethys in the Tingri area took place in the Lutetian.     

Occurrence of Libycoceras ismaeli (Zittel) in the Upper Maastrichtian of Eastern Tademait, Algerian Sahara

No ammonite has ever been reported in the Tademait plateau, Algerian Sahara, above the Turonian. A well-dated Upper Maastrichtian sequence has the first yielded Libycoceras ismaeli (Zittel) in the eastern part of the area. This stratigraphical position is correlative to the occurence of this species in the Tinrhert Hamada (Algeria) and Libya to the east and to the Tanezrouft (Algeria), Niger and eastern Mali (Sphenodiscus Zone) to the south. This find provides a new paleogeographical milestone between the Tinrhert Hamada and the Tanezrouft, along which the trans-Saharan marine channel passed on to the Iullemmeden basin in the Upper Maastrichtian.     

Sedimentationsabläufe im Atlas-Golf (Kreide Küstenbecken Marokko)

The Geological Institute of Bonn University since 1975 investigates in connection with DSDP/IPOD the Cretaceous of the Atlantic coastal basin in south-western Morocco. 30 main stratigraphic sections and numerous auxiliary ones were taken along several traverses, running along distances of 150 to 200 km in west-east direction. The recognized epicontinental facies-pattern along the traverse of the southern High Atlas mountain range depicts clearly, that we cut here the critical region of intertonguing marine, fine-clastic-carbonaceous sediments and continental detritic deposits. The littoral zone successively progrades with three major transgressions (Neocomian, Upper Aptian, Turonian) towards the African Continent. Sedimentation processes, stratigraphy, paleomagnetics, geochemistry, sedimentology and paleogeography are investigated, taking selected horizons on one hand and complete stratigraphic columns on the other. A new sedimentation model reflecting transgression and regression events in the Cretaceous “Atlas Gulf” show some probabilities of eustatic sea-level changes. There are similarities between the Atlas Gulf and other coastal basins on both sides of the Atlantic Ocean. There are certain relations between the sedimentary record of the proand regrading littoral zone on the continent and in the nearby deep sea deposits. There is an exciting coincidence between the stratigraphie succession of the downwarping Atlas Gulf and the sedimentary cover of the interior of Africa, especially the Mesozoic Sahara Basin.     

Late Cenomanian–Early Turonian ammonites of the southern Tethys margin from Morocco to Oman: Biostratigraphy,paleobiogeography and morphology

The Cenomanian–Turonian ammonite biostratigraphical framework for the southern Tethys margin (North Africa, Middle East and the Arabian Peninsula) is becoming better understood. A first attempt at a synthetic range chart is presented, with 85 taxa and precise correlations for ammonites along a west–east transect from Morocco to Oman, inclusive of the Trans-Saharan Seaway as far south as northern Nigeria. On the basis of a critical review of ammonite taxonomy, 13 bioevents can be identified in the interval from the Late Cenomanian to the Early Turonian (c. 3.5 myr) with each bioevent corresponding to a time interval of approximately 270,000 years, on average. They are consistent throughout several regions along the southern Tethys margin, though some gaps remain, at least at the stage boundary. These bioevents are correlated with the zonation defined for the stratotype (GSSP) of the base of the Turonian in the Western Interior (USA). The paleobiogeographic distribution of ammonites reveals some endemism but the predominant picture is that of a homogeneous fauna throughout the area, even though distinct Boreal and Western Tethys (Atlantic domain) marine influences are evident. An interpretation of the evolution of conch morphology and ornamentation through the zones of the Late Cenomanian–Early Turonian is proposed.     

The Cretaceous marine onlap on Palaeozoic deposits (Smara–Lâayoune Basin,South Morocco). Comparison with neighbouring regions

The Cretaceous marine transgression proceeded through successive steps from the Albian to the Turonian (dated with ammonites). The onlapping wedge begins with coastal transgressive–regressive short-term sequences on massive, probably fluvial sandstones to be correlated with the very thick continental Lower Cretaceous succession found in the Puerto Cansado well in the Tarfaya sub-basin to the north. A second step, of probable Cenomanian age, reached the Palaeozoic basement. A third, more pronounced step occurred during the earliest Turonian with platy laminated limestone overlain by marlstone bearing pyritized ammonites. At early Turonian peak transgression, a marine connection was possibly established between the Atlantic and the Tethyan margins, between the Anti-Atlas and the Reguibat Shield. From large-scale correlation integrating what occurred along the southwestern shoulder of the Atlas rift, the South Moroccan Atlantic margin may have undergone a short-lived tectonic uplift around the Cenomanian–Turonian boundary.     

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.     

Controls on clastic sequence geometries in a shallow-marine, transtensional basin: the Bohemian Cretaceous Basin, Czech Republic

The Bohemian Cretaceous Basin combines features of a shallow‐water (mostly < 100 m) epicontinental seaway formed during a global transgression with those of a tectonically active, transtensional setting. The basin formed under a greenhouse climate and was affected by strong axial currents. Dense well‐log coverage, combined with locally high‐quality exposures and biostratigraphic control, make it possible to examine in three dimensions the geometries of genetic sequences and interpret their controlling variables. Sand‐dominated deltas formed sequences at several spatial scales that reflect nested transgressive–regressive cycles with durations ranging from tens of thousands of years to millions of years. Progradation directions and distances, thicknesses and internal geometry of the individual sequences were controlled primarily by intrabasinal faulting, basin‐scale changes in subsidence rate, eustatic fluctuations and localized bathymetric changes due to successive filling of the basin. Along‐strike change in sediment input from different parts of the source area and a short‐lived uplift of a secondary clastic source provided additional controls on the sequence geometry. Efficient hypopycnal transport combined with redeposition of fine clastics in shallow water promoted development of steep slopes of sand‐dominated deltas while preventing downlap of muddy clinoforms; most of the suspended load became deposited downcurrent in subhorizontal or gently dipping bottomsets. Long‐term accommodation rates were low during the Early to Middle Turonian, with minor intrabasinal faulting, but became accelerated in the Late Turonian and Early Coniacian. This acceleration was caused at least partly by increased subsidence rate accompanied by structural partitioning of the depocentre and partly compensated by increased sediment input indicating increased uplift rates in the Western Sudetic Island source area. This event probably reflected an increase in the regional strain rate in Central Europe. The succession of two major flooding events in the Early Turonian and late Early Coniacian, separated by a low‐accommodation interval in the Middle Turonian, shows a close similarity to published estimates of long‐term eustatic curves. However, the eustatic component of accommodation rate in the Bohemian Late Turonian and Coniacian is difficult to separate from accelerated subsidence. In several cases, evidence for short‐term (100 kyr scale) forced regressions, independent of basinal structural activity, suggests small‐scale eustatic falls at rates which, as presently understood, cannot be explained other than by a glacio‐eustatic mechanism.     

对西藏岗巴上白垩统的新认识

在前人研究的基础上对岗巴地区上白垩统的划分做了厘定 ,进一步建立了晚白垩世的 1 2个浮游有孔虫化石带。根据岩性特征及化石带的研究 ,上白垩统被划分为赛诺曼期至土仑早期的冷青热组 ;土仑中期至三冬期的岗巴村口组和康潘期至马斯特里赫特期的宗山组。该区赛诺曼期与土仑期的界线位于冷青热组上部 ,以 H elvetoglobotruncana praehelvetica的初现为标志。     

Orbitally forced sea-level changes in the upper Turonian–lower Coniacian of the Tethyan Himalaya,southern Tibet

Although the mid-Cretaceous is considered to be a typical interval of greenhouse climate and high sea level, cooling events associated with regressions were inferred in recent years. We conducted a biostratigraphic, chemostratigraphic, sequence stratigraphic and cyclostratigraphic investigation of upper Turonian–lower Coniacian marine strata in the Tethyan Himalaya zone, to retrace the sea-level variations and to clarify their global correlations. According to the planktonic foraminiferal zonation, the studied interval is part of the late Turonian–early Coniacian Marginoruncana sigali and D. concavata Zones. The carbon isotope curve shows a good correlation to reference curves in the Boreal and western Tethys realms with all major and minor late Turonian δ¹³C events identified, indicating that the C-isotope curve provides an excellent tool for global stratigraphic correlation in the Turonian. Based on the lithological variations of clastic input and physical and chemical proxies, the succession is divided into two third order and eight fourth order sequences. Spectral analysis indicates that fourth order sea-level changes were linked to the astronomically stable 405-kyr eccentricity cycle. Comparison with classic global sea-level curves, we suggest that late Turonian–early Coniacian sea-level changes along the southeastern Tethyan margin were controlled by eustasy. The significant regressions during ∼90–89.8 Ma and ∼92–91.4 Ma, which are recorded in different continents, may be interpreted as the result of continental ice expansion, giving some support to the notion that ephemeral polar ice sheets existed even in the super-greenhouse world.     

塔里木盆地西部白垩纪—古近纪海相地层框架及对重大地质事件的记录

塔里木盆地西部白垩纪—古近纪发生了大规模的海侵事件,形成一个喇叭状向西开口的海湾,该海湾属于东特提斯洋的一个分支。该地区白垩纪—古近纪海相地层记录了东特提斯洋演化和一系列重大地质事件,具有重要的研究价值,但对其地层的研究仍相对薄弱,对重大地质事件的研究还不够深入。本文拟通过详细的岩石地层、生物地层和其他地层方法,完善地层划分与对比框架,并在此基础上讨论Cenomanian/ Turonian界线大洋缺氧事件(OAE2)、白垩纪/古近纪界线(K/Pg)、古新世—始新世极热事件(PETM)、特提斯海进与海退等一系列重大地质事件。塔里木盆地白垩纪—古近纪海相或海陆过渡相地层自下而上为克孜勒苏群、库克拜组、乌依塔克组、依格孜牙组、吐依洛克组、阿尔塔什组、齐姆根组、盖吉塔格组、卡拉塔尔组、乌拉根组和巴什布拉克组,上述地层中含有丰富的有孔虫、介形虫、钙质超微、沟鞭藻、孢粉、双壳类、腹足类等化石,以及少量菊石、腕足类、海胆和鲨鱼牙齿等化石。综合的生物地层和年代地层研究表明,克孜勒苏群的时代为早白垩世Barremian-Albian期,库克拜组—依格孜牙组的时代为晚白垩世Cenomanian-Maastrichtian期(Cenomanian/Turonian界线可能位于库克拜组三段),吐依洛克组的时代为白垩纪—古近纪过渡期;阿尔塔什组的时代为古新世早中期,齐姆根组为古新世晚期—始新世最早期,盖吉塔格组—乌拉根组的时代为中始新世中晚期,巴什布拉克组的时代为晚始新世,但不排除最上部进入渐新世早期。塔里木盆地的海侵开始于克孜勒苏群中上部沉积期(Albian晚期—Aptian早期),但规模很有限,大规模的海侵始于晚白垩世Cenomanian早期;从晚白垩世—古新世,共经历了5次大规模的海侵—海退事件;大约41 Ma前后,海水退出盆地南部的昆仑山山前,34 Ma前后,海水退出盆地北部的天山山前。上述海侵—海退事件可能受构造和全球海平面变化的双重影响,但构造事件对海侵的启动和结束可能更具决定性的影响。阐述了塔里木盆地西部白垩纪—古近纪海相地层所记录的OAE2、K/Pg界线、PETM和特提斯海侵—海退等事件,其中笔者及团队第一次在塔里木盆地西部齐姆根组中所发现和报道的PETM事件,将有助于揭示全球近岸地区PETM的特征和生物-环境响应。在未来的研究中,需要进一步厘清塔里木盆地西部地层序列,建立更加精细的生物地层和年代地层框架,加强对PETM和特提斯海侵—海退等重大地质事件的研究。     

从有孔虫分析西藏南部白垩纪海平面升降

白垩纪是地质历史中的最大海侵时期。海平面的升降改变了海洋的物理、化学及生物因素,从而影响了有孔虫的演化与发展。根据对有孔虫丰度、分异度及演化类型的研究,认为西藏白垩纪最大海侵时期形成于赛诺曼期与土仑期的界线附近。此后海平面总的处于下降趋势,只是在康尼亚克期至三冬期海平面又有回升。马斯特里赫特末期有孔虫的大量灭绝反映了白垩纪与第三纪界线事件的影响。     

Malargüe Group (Maastrichtian–Danian) deposits in the Neuquén Andes,Argentina: Implications for the onset of the first Atlantic transgression related to Western Gondwana break-up

The discovery of marine to brackish and fresh-water carbonates in the inner Agrio fold-and-thrust belt at Pichaihue, Neuquén, Argentina, located to the west of the Andean orogenic front, imposes important constraints on the paleogeography of the first Atlantic transgression in the Neuquén Basin related to the break-up of Western Gondwana. The constraints on the timing and areal extent of these deposits shed light on the early uplift history of the southern Andes. These limestones are part of the Maastrichtian–Danian Malargüe Group, which was previously only known from its exposures in the extra-Andean area, representing foreland basin deposits. The presence of stromatolites, oncoids, serpulids, bivalves and gastropods as well as silicified stems of macrophytes indicates a shallow marine, partially brackish environment associated with non-marine deposits. These strata are interfingered with and overlie distal tuffs and proximal pyroclastic flows, whose geochemical characteristics point to a magmatic arc source. SHRIMP U–Pb dating of volcanic zircons of these tuffs yielded an age of 64.3 ± 0.9 Ma that confirms the correlation to the Maastrichtian–Paleocene marine transgression from the Atlantic Ocean. The change in the paleoslope of the basin from Pacific Ocean transgressions to this Atlantic transgression is related to the uplift and deformation of the Agrio fold-and-thrust belt. The Pichaihue Limestone is unconformably deposited on volcanic agglomerates which in turn unconformably overlie Early Cretaceous deposits. Based on these data, it is confirmed that the Cretaceous uplift of the Andes was episodic at these latitudes, with a first pulse in the Cenomanian and a second one in pre-Maastrichtian times. The episodic uplift is also related to an eastward migration of the thrust front and the volcanic arc, related to a previously proposed shallowing of the subduction zone. These episodes were controlled by the Western Gondwana break-up and the beginning of absolute motion of South America toward the west.     

塔里木盆地新生代海相沉积问题

基于前人文献,对塔里木盆地新生代海相沉积问题进行梳理,进而探讨该盆地新生代海侵的次数和范围以及海退的时限、原因。研究表明,新生代,塔里木盆地至少经历古近纪的阿尔塔什晚期至齐姆根早期(古新世早期至古新世晚期)、卡拉塔尔期—乌拉根期(始新世中期)、巴什布拉克中期(始新世晚期至早渐新世)等三期海侵;塔里木盆地中新世仍有海相地层这一认识获得广泛认可仍需更多的地质证据来支持。塔里木盆地海侵范围在卡拉塔尔—乌拉根组沉积时期达到最大,向东可达玛扎塔格地区,在盆地北缘和南缘分别可以到达库尔勒以东地区和洛浦县阿其克以东地区。由于受到全球海平面变化和构造运动的共同影响,副特提斯海新生代从塔里木盆地退却的沉积记录包括齐姆根组顶部、乌拉根组顶部、巴什布拉克组第四段和第五段,时间上分别对应于古新世晚期、始新世中晚期和早渐新世。     

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.     

The Relationship between the Distribution of Thick Coal Belts and the Late Carboniferous-Early Early Permian Marine Transgression-Regression in the North China Platform

Four great second-order transgressions occurred during the Late Carboniferous to early Early Permian and they came from both the eastern and western sea areas in the North China Platform. As time went on, depocentres, depositional extent, transgression directions, coastline position and distribution of minable coal seams were changing continuously. The third great second-order transgression occurring at the beginning of the early Early Permian marks the maximum transgression period and before its arrival, i.e. at the close of the late Late Carboniferous, there was the super-regional coal-forming environment. During the second, third and fourth transgressions, the northern North China Platform was all along situated on the transgressive margin of the epicontinental sea and became the major distribution area of thick coal belts because it maintained a coal-forming environment for a long period of time from the close of the late Late Carboniferous to the Early Permian.     

RECENT ADVANCES IN GEOLOGICAL RESEARCH IN PARTS OF LESSER AND TETHYS HIMALAYA OF INDIA, SOUTH OF TIBETAN PLATEAU (KUMAON, GARHWAL AND ARUNACHAL PRADESH)

RECENT ADVANCES IN GEOLOGICAL RESEARCH IN PARTS OF LESSER AND TETHYS HIMALAYA OF INDIA, SOUTH OF TIBETAN PLATEAU (KUMAON, GARHWAL AND ARUNACHAL PRADESH)     

受限陆表海的海侵模式

突发性海侵是受限陆表海的特征之一,受海平面升降引起的峡口启闭控制,多发生在板块的活动边缘。突发性海侵常有相序缺失,常见海陆相交互层;海相层在大范围内分布稳定,无明显相变,具有良好的等时性,可以作为区域对比的标志层。受限陆表海的突发性海浸,有利于油气的生成和聚集。     

Cretaceous sauropod diversity and taxonomic succession in South America

The South American sauropod dinosaurs fossil record is one of the world's most relevant for their abundance (51 taxa) and biogeographical implications. Their historical biogeography was influenced by the continental fragmentation of Gondwana. The scenery of biogeographic and stratigraphic distributions can provide new insight into the causes of the evolution of the sauropods in South America. One of the most important events of the sauropods evolution is the progressive replacement of Diplodocimorpha by the Titanosauriformes during the early Late Cretaceous. The fluctuation of the sea levels is frequently related to the diversity of sauropods, but it is necessary to take into account the geological context in each continent. During the Maastrichthian, a global sea level drop has been described; in contrast, in South America there was a significant rise in sea level (named ‘Atlantic transgression’) which is confirmed by sedimentary sequences and the fossil record of marine vertebrates. This process occurred during the Maastrichtian, when the hadrosaurs arrived from North America. The titanosaurs were amazingly diverse during the Late Cretaceous, both in size and morphology, but they declined prior to their final extinction in the Cretaceous/Paleocene boundary (65.5Yrs).     

Paleocene resurrection of a crocodylomorph taxon: Biotic crises,climatic and sea level fluctuations

Postcranial material of a crocodylomorph from the Danian of Oulad Abdoun Basin (Morocco) is described. Several characters, in particular the shape of its dorsal osteoderms, allows its attribution to Pholidosauridae. Up till now, the latest known pholidosaurid was Terminonaris, from the Early Turonian of North America, so, the Moroccan pholidosaurid extends the stratigraphic range of the group to more than 20 million years younger, and shows that the pholidosaurids survived the K-Pg crisis. The reevaluation and the phylogenetic analysis of Dakotasuchus kingi, Woodbinesuchus byersmauricei, and Sabinosuchus coahuilensis, previously considered as goniopholidids and dyrosaurid, respectively, revealed rather that they are pholidosaurids. This analysis also suggests that at least two independent pholidosaurid lineages reached the Maastrichtian, among which one crossed the K-Pg boundary. This study proposes the first analysis of tethysuchian diversity from the Late Jurassic to the Early Paleogene. Two diversity peaks are observed during the Oxfordian and Cenomanian, two stages of high paleotemperatures evaluated with the δ¹⁸O. The tethysuchian diversity strongly decreases after the Cenomanian, a decline that may be correlated with the “Ocean Anoxic Event” (OAE 2), which caused the strong marine faunal turnover during the Cenomanian-Turonian time interval. The large Turonian-Coniacian oceanic regression could also be a factor in the tethysuchian decline. After that, tethysuchian diversity remains low until the Maastrichtian-lower Paleocene marine tethysuchian dyrosaurid diversification, correlated with the Late Cretaceous-Paleocene transgression. At least one pholidosaurid lineage crossed the K-Pg boundary, confirming the weak impact of this crisis on the crocodylomorphs. Pholidosaurids seem to go extinct at the beginning of the Paleocene, possibly due to the strong radiation of dyrosaurids in marine environments and crocodylians in fresh-water during this time period.