Characteristics of internal-wave and internal-tide deposits and their hydrocarbon potential

The study of internal-wave and internal-tide deposits is a new research field on sedimentology during the last ten years. Deep-water traction currents induced by internal waves and internal tides are developed on the modern sea floor, which can form not only all kinds of small scale and dispersal deepwater traction currents deposits, but also large-scale sediment wave in km-size scale. In this paper, the concepts and features of internal waves and internal tides in oceanography are introduced, and the characteristics, sedimentary sequences, sedimentary microfacies and sedimentation models of internalwave and internal-tide deposits found and the origin of large scale sediment waves in deep sea bottom are summarized. The relationship between internal-wave and internal-tide deposits and petroleum is discussed, and finally internal-wave and internal-tide deposits are shown to be a new potential field for petroleum exploration.

The characteristics and recognition of internal-tide and internal-wave deposits

Internal-tide and internal-wave deposits are a new and important type of deep-water traction-current deposits. Based on an analysis of documented internal-tide and internal-wave deposits, five facies types can be recognized: ( ⅰ ) bidirectional cross-laminated sandstone facies, ( ⅱ ) unidirectional cross-bedded and cross-laminated sandstone facies, ( ⅲ ) rhythmic alternating sandstone facies and mudstone, ( Ⅳ ) flaser, wavy and lenticular bedded foraminiferal limestone facies, ( Ⅴ ) sandy oolitic limestone facies with flaser, wavy and lenticular bedding and epsilon cross bedding, which formed in submarine channel, unchannelized continental slope and plateau environments respectively. Accoding to the available data and knowledge,three sedimentation models are built; some discriminating characteristics of internal-tide and internal-wave deposits, and the distinction between them and contourites and turbidites are summed up.

Review of research in internal-wave and internal-tide deposits of China

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 charac-teristics, sedimentary successions, types of lithofacies, and depositional models of internal-wave 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.

The first internal-tide deposits found in China

NOT until Gao Zhenzhong and Eriksson studied the Ordovician of Fincastle area, Appalachi-ans, the USA in 1990, did sedimentologist recognize internal-tide deposits in the ancientrecord and begin to use the term of 'internal-tide deposit'. In the Ordovician of Fincastlearea, two facies are recognized: (i) bidirectional cross-laminated very fine grained

Reply to Shanmugam,G.“Review of research in internal-wave and internal-tide deposits of China:Discussion”

We are glad to know that our paper ＂Review of research in internal-wave and internal-tide deposits of China＂ （Gao et al., 2013） published in Journal of Palaeogeography has attracted close attention of international peers, and we noted that Shanmugam has provided a critical assessment of our paper. He claimed that ＂interpretations of ten ancient exam- ples in China and one in the central Appalachians （USA） as deep-water deposits of internal waves and internal tides are unsustainable＂, among many other comments and criticisms, and he concluded that ＂any interpretation of ancient strata as deposits of internal waves and internal tides is premature＂. This article is aimed at responding to his major criticisms. We believe that constructive discussions will benefit the development of the study in internal-wave and internal-tide deposits. Unfortunately, Shanmugam seems not to follow this line of scientific criticism, but is trying to reject all research results in this subject based on his illogical and inconsistent reasoning, and distortion of others＇ points of view. In this article, with facts and evidences, we will refuse the main wrong assertions of Shanmugam＇s, for example, ＂the use of bidirectional cross-bedding as evidence for deposition by baroclinic currents in outcrop studies is sedimentologically erroneous ＂ and ＂any interpretation of ancient strata as deposits of internal waves and internal tides is premature＂. We will also use typical characteristics of the ancient examples to demonstrate that they are certainly not turbidites, or contourites, or tsunami-related deposits, but internal-wave and internal-tide deposits as the most plausible to defend the rationality of our interpretation in our previous papers.