The northern flank of the Tindouf Syncline in southern Morocco exhibits a continuous, well exposed Carboniferous succession with limestones of Late Asbian to Early Bashkirian age containing rich and diverse foraminiferal and rugose coral assemblages. Analysis of these assemblages provides new data on the relatively poorly known Saharan basins. The palaeobiogeographical relationship of the Tindouf Basin with other Palaeotethyan basins is complex. Although there is a predominance of cosmopolitan taxa for the Palaeotethys, it is recognized that there was an influence of basins from NW Europe, such as the UK and Ireland. Some taxa are recorded in both NW Europe and Tindouf without any characteristic contributions from intermediate basins in northern Morocco. The neighbouring Béchar Basin in Algeria presents distinct assemblages. The bulk of the data analyzed suggest that this sector of the western Palaeotethys can be subdivided into four palaeobiogeographical subprovinces: the Atlantic Subprovince (UK, Ireland, N France and Belgium), the Mediterranean Subprovince (Pyrenees, Montagne Noire, Betic Cordillera, Rif (N Morocco) and Balearic Islands), and the Saharan Subprovince (Béchar, Reggan, Ahnet?Mouydir and Tindouf). In between, mobile belts of mixed faunal assemblage characteristics are observed ( e.g. , SW Spain and Central Meseta) forming the West peri-Gondwanan Subprovince. Analysis of the Tindouf Basin faunas shows that, as in other Saharan basins, there is a high diversity and abundance of foraminiferal taxa, with a higher proportion of survivors and longer stratigraphic ranges; these features also are mirrored by rugose corals. This emphasizes the longevity of the carbonate platform in a tropical setting, where periodic transgressions introduced new assemblages, and oceanic currents are interpreted as one of the main controlling factors for the distribution of the taxa in these subprovinces. Moreover, not only were water temperatures on the platform higher, but also tectonic stability greater. It is considered that the effects of the first phases of the Gond?wanan glaciation were minimal on the Tindouf faunas.
Gomphotheriid proboscideans reached South America as Late Cenozoic im?migrants from North America. However, disagreements over alpha taxonomy, age dating and phylogenetic relationships have produced three competing hypotheses about this immigration: (1) a single gomphothere immigration took place soon after the ~ 3 Ma closure of the Panamanian isthmus; (2) two separate gomphothere immigrations took place after closure of the isthmus; or (3) an earlier, Late Miocene (before 9 Ma) immigration brought gomphotheres into South America. A critical re-evaluation of the alpha taxonomy, age dating and phylogenetic relationships of Neotropical gomphotheres identifies two valid genera of South American gomphotheres, Cuvieronius and Notiomastodon (= “ Haplomastodon”, = “Stegomastodon” from South America) and recognizes “ Amahuacatherium” as an invalid genus likely based on a specimen of Notiomastodon . The oldest well?dated South American gomphothere fossil is Marplatan, ~ 2.5 Ma, from Argentina. The case for an age of “ Amahuacatherium” older than 9 Ma is refuted by mammalian biostratigraphy and a re?evaluation of the relevant magne?tostratigraphy. North American Rhynchotherium descended from Gomphotherium during the Late Hemphillian (~ 5-6 Ma) and gave rise to Cuvieronius in North America by the end of the Blancan (~ 2 Ma) time. Notiomastodon evolved from Cuvieronius in South America during the Pleistocene. The case for a close relationship between the Neotropical gomphotheres and Sinomastodon from China is rejected. Central America was not a center of endemic gomphothere evolution and merely acted as a pathway for the immigration of gomphotheres from north to south: Gomphotherium into Central America during the Miocene, Cuvieronius to Central America by Early Pleistocene time and on to South America. After closure of the Panamanian isthmus, Cuvieronius immigrated to South America, where it gave rise to Notiomastodon by Middle Pleistocene time. The South American history of gomphotheres was thus a modest evolutionary diversification from a single Plio-Pleistocene immigration.
Delta systems are ubiquitous around lacustrine rift basins. Its peripheral ge?ometry, progradation structures and sedimentary successions were controlled by both tectonic settings and climatic changes. Peripheral geometry of a delta was strongly influenced by depositional gradients which formed the fan?shape delta on the steep slopes and developed the lobe-shape delta on the gentle slopes. Due to the discharge feed rivers can change rapidly driven by climatic variations, and the nearshore area of deltas display considerable facies variability. The rise of annual rainfall, which suggests the rivers feeding deltas are continuous, and result in distributary mouth bars that are prevalent in the front of deltas since the down-slope flows are greater than the along-slope currents. On the contrary, when the annual rainfall decreases and evaporation increases, the rivers only can feed deltas ephemerally. If the along?slope currents were in a dominant position, the distal bars were deposited. Progra?dation structure and sedimentary successions of deltas were controlled by the gradients of slopes. On gentle depositional slopes, shingle foreset beds predominate with fine sediments and small?scale sedimentary structures or vice versa.
Study of internal?wave and internal?tide deposits is a very young research field in deep-water sedimentology. It has been just twenty years since the first example of internal-wave and internal-tide deposits was identified in the stratigraphic record. Since that time, Chinese scholars have made unremitting efforts and gained some significant research achievements in this field. This paper briefly outlines the history and main achievements of research of internal-wave and internal-tide deposits in China, describes depositional characteristics, sedimentary successions, types of lithofacies, and depositional models of internalwave and internal-tide deposits identified mainly from ancient strata, and summarizes the existing problems in this research field. New advances in marine physics should be applied to research of the subject of internal-wave and internal-tide deposition, whereas the sedimentary characteristics of internal?wave and internal-tide deposits may be used to deduce the physical processes of their creation. Flume experiments on internal-wave and internal-tide deposition should also be put in practice as often as possible, so that the mechanisms of internal?wave and internal-tide deposition can be explored.|
Significant progress has been achieved in the research of tide-dominated envi?ronments in the past two decades. These studies highlight both the importance and diversity of tidal flats in modern coastal environments. Based on their developing settings, tidal flats are subdivided into nine types, which are in turn grouped into sheltered or exposed spectrums according to the magnitude of exposure to waves. The ternary coastal classification model is revised with an embedded triangle to highlight non-open coast tidal flats as major secondorder morphological elements to the first-order coastal environments including deltas, estuaries and lagoons. A new continuous spectrum of open coast depositional settings is proposed from muddy tidal flats of tide dominance with wave influence, through sandy tidal flats of mixed energy (tide-dominated), and tidal beaches of mixed energy (wave-dominated), to beaches of wave-dominance with tide influence. It is worth noting that no open coast setting is absolutely exempt from wave or tide influence. Three diagnostic criteria for the intertidal-flat deposits are proposed. Upon an upward-fining succession, (1) regular changes vertically from flaser bedding, through wavy bedding and to lenticular bedding are diagnostic of most of intertidal flats; (2) cyclical tidal rhythmites point to sheltered intertidal flats typically at the inner part of macrotidal estuaries; (3) rhythmic alternations of storm and tidal deposition are diagnostic of exposed intertidal flats, especially the open coast types. Intertidal-flat deposits are generally topped by saltmarsh deposits, but underlain by different subtidal successions, like thick subtidal channelfills, sand-bar complexes (sheltered coastal settings), and upwards coarsening successions of subtidal flats or thick subtidal sand ridge/bar complexes (exposed coastal environments).|
The North Carnarvon Basin, which lies in the North West Shelf of Australia, is highly rich in gas resources. As a typical passive marginal basin, it experienced the pre-rifting, early rifting, main rifting, late rifting, post-rifting sagging and passive margin stages. The basin was mainly filled with thick Mesozoic-Cenozoic sediments, of which the Mesozoic hosts the principal source, reservoir and seal intervals. Mesozoic palaeogeography has an important control on the oil and gas distribution. Triassic gas-prone source rocks of deltaic origin determine the high endowment of natural gases in the North Carnarvon Basin. The more restricted distribution of oil accumulations is controlled by oil source rocks in the Upper Jurassic Dingo Claystone. The Muderong Shale deposited in the Early Cretaceous marine transgression provides the effective regional seal for the underlying oil and gas reservoirs.
The Caledonian orogeny at the end of the Silurian resulted in great changes in the palaeogeography in the Yunnan-Guizhou-Guangxi area of South China; the continental area of the Early Paleozoic evolved into the extensive Dian-Qian-Gui Sea in the Late Paleozoic. Early in the Devonian, as a result of a major transgression, seawater encroached gradually from the south to the north and clastic facies were deposited. Carbonate deposition was then established in the Yunnan-Guizhou-Guangxi area, with a palaeogeography marked by attached platforms, isolated platforms and narrow basins. As a result of the Ziyun movement towards the end of the Devonian, the Upper Devonian strata are regressive and thin out from the open-sea to the land areas. A study of the nature and distribution of sedimentary facies in space and time recognises 13 third-order sequences in the Devonian strata in Yunnan?Guizhou-Guangxi area, and these form two second-order sequences. The strata of the Lower Devonian comprise 5 third-order sequences (SQ1 to SQ5), which are dominated by transgressive clastics. 4 third-order sequences (SQ6 to SQ9) in the Middle Devonian are characterized by alternations of transgressive clastics and highstand carbonates. In the Upper Devonian, carbonates constitute 4 third-order sequences (SQ10 to SQ13), which are generally marked by the transgressive limestones and highstand dolomites. On the basis of earlier biostratigraphic studies, sea?level changes represented by the third-order sequences with their different facies successions are explored, and the sequence stratigraphic framework is established. Therefore, the Devonian strata in the study area provide an example for further understanding of depositional trends within the sequence-stratigraphic framework.|