Lithofacies palaeogeography as a guide to petroleum exploration is a very important topic. By using the following five exploration examples, this paper discusses the guide of lithofacies palaeogeography or of sedimentary facies to petroleum exploration. These examples include the dolostone of the Lower Ordovician Majiagou Formation 5 in the Ordos area, the Donghe Sandstone of the Upper Devonian and Lower Carboniferous in the Tarim Basin, the reef of the Upper Permian Changxing Formation in the Sichuan Basin, the oolitic bank of the Lower Triassic Feixianguan Formation in the Sichuan Basin, and the lacustrine delta sediments and gravity flow sediments of the Middle and Upper Triassic Yanchang Formation in the Ordos Basin.

A clastic dike containing unusually large clasts occurs in the Quaternary deposits that unconformably cover the Mesoproterozoic sediments in the Fangshan District, Beijing area, China. The material into which the dike intruded is also uncommon because it consists mainly of loess-type silts that were deposited by braided rivers. The intrusion of the dike is explained as the result of the expulsion of pore water into the coarse, gravel-containing layers of a braided river system. The large size of the clasts in the dike is explained by an exceptionally strong upwards-directed flow which owed its high energy to a high hydrostatic pressure that had been built up because pore water could not gradually seep through the impermeable silt-sized material during ongoing burial. This uncommon dike is compared with a second example, in similar Quaternary sediments covering the Mesozoic rocks in the Huairou District.

Based on the petrological study, according to single factor analysis and multifactor comprehensive mapping method, the quantitative lithofacies palaeogeography of the Upper Permian Changxing Stage of the Middle and Upper Yangtze Region was studied. The Changxing Stage in the Middle and Upper Yangtze Region is mainly composed of carbonate rocks; in addition, clastic and siliceous rocks occur with rare coals and pyroclastic rocks. Lithofacies can be divided into five types, including clastic rock assemblage, clastic rock-limestone assemblage, limestone assemblage, limestone-siliceous rock assemblage, and siliceous rock-clastic rock assemblage. Four fundamental ecological types and five fossil assemblages were recognized in the Changxing Stage. On the basis of the petrological and palaeoecological study, eight single factors were chosen including thickness, content of marine rocks, content of shallow water carbonate rocks, content of bioclasts with limemud matrix, content of bioclasts with sparry cement, distribution of reefs, content of thin bedded siliceous rocks and content of deep water sedimentary rocks. And eight single factor maps and one lithofacies paleogeographic map of the Changxing Stage were compiled. Paleoenvironments from west to east include an erosional area, fluvial plain, clastic platform, carbonate platform and reefs that developed there, slope and basin, low energy organic banks, and high energy organic banks. Sedimentary environments have an obvious control on the development of the source rocks, and the excellent source rocks are developed in the Dalong Formation. Changxing Stage reservoirs should be dominated by the reef and platform surrounding the Guangyuan-Liangping Basin rim area, and is the most favorable exploration area of the reef petroleum reservoirs of the Changxing Formation.

Palaeozoic stromatoporoids are calcified sponges common between Middle Ordovician and Late Devonian times in reefs and related facies. Taxonomic work is well known, but controversial because of conflict between classification schemes based on the calcareous skeleton versus spicules (which are almost completely lacking in Palaeozoic stromatoporoids); however, lower-level taxonomy (at genus-level) of the calcareous skeleton is considered reliable to be applied in palaeobiological study. Knowledge of stromatoporoid ecology is poorly developed, such that comprehensive information is available for only a few case studies, in some Silurian and Devonian examples. Thus an overall understanding of stromatoporoid responses to environmental conditions has not yet been achieved, although stromatoporoids were likely able to deal with fine-grained sediment where they mostly occur. Many stromatoporoid genera have only certain growth forms, so future focus on the use of low-level taxonomy in ecological studies, by comprehensive sampling in high-resolution studies, may establish the relationships between stromatoporoids and their environments. Intergrown organisms and growth banding in stromatoporoids are aspects that have great potential in such work. Mineralogy of stromatoporoids remains poorly understood. Regardless of their apparent state of preservation (ranging from apparently well-preserved to complete loss of calcareous skeleton features) all stromatoporoids are in fact substantially recrystallized. They underwent a peculiar diagenesis, whereby the calcareous skeleton and gallery cements of all stromatoporoids are overprinted by irregular elongated calcite crystals arranged normal to the growth laminations, most clearly visible in cross-polarized light. Stromatoporoids cooccur with mollusc shells that are always either fully recrystallized or dissolved (present as internal and external moulds); this difference means that while molluscs are likely under-represented in the fossil record, stromatoproids are not, providing confidence for palaeoecological work on their assemblages. Stromatoporoids lack characters which would readily classify them as being originally aragonite or low-Mg calcite; they may have been high-Mg calcite but the evidence is circumstantial. Their peculiar diagenetic fabric also has implications for the debate about the relationship between stromatoporoids and the concept of aragonite/calcite seas, which requires more work.

An interval of limestone, which generally has a dendroid appearance on outcrops, has been found in several Permian-Triassic boundary (PTB) sections in South China, and interpreted to be microbialites. Previous research has examined the paleontology and sedimentology of the unit, however, little attention has been devoted to its diagenesis. This paper discusses the diagenesis of the microbialites in the PTB section at Laolongdong, Chongqing, South China. Examination of multiple outcrops reveals that the structure in this kind of rock is not always dendroid; in many cases it is irregular in shape, and seldom shows the “up-branching” form. In addition, the speckled interval has also been found beneath the dendroid interval. In outcrop, both the speckled and dendroid rocks consist of the darkercolored areas and the lighter-colored areas. Examination of thin sections reveals that the darker-colored areas on outcrops are actually lighter-colored in thin sections, consist of larger crystals, and are more transparent. The lighter-colored areas in thin sections generally consist of large blocky calcite containing scattered small dirty calcite rhombs and irregular residual limestones, which are the same as the lime mudstones between the lighter-colored areas. It is inferred that the dendroid and speckled rocks have experienced the following diagenetic processes: (1) exposure of the carbonate sediments to the subaerial environment because of a sea level drop; (2) dolomitization caused by the downward migration of fluids formed the dendroid and speckled dolomitic patches; (3) dedolomitization of the dolomitic patches formed dendroid and speckled patches of calcite; (4) dissolution occurred in the interstices between relic dolomite crystals formed spongy pores; and (5) filling of the spongy pores by large blocky calcite. Therefore, even though microbes played a critical role in the formation of these microbialites, diagenesis contributed greatly to the formation of the speckled and dendroid pattern of the microbialites.

Integration of sedimentologic and sequence stratigraphic interpretations of the Nkporo Group has provided the basis for a basin-wide framework for prediction of potential source, seal and reservoir rocks in the Anambra Basin, Nigeria. Lithofacies and biostratigraphic data show that the Nkporo Group in the Anambra Basin contains three main facies associations (fluvio-deltaic facies, estuarine central basin/shallow shelf facies and estuarine channel fill facies) that determine the reservoir containers, flow units and seals. The units are arranged to form two stratigraphic sequences represented by the Nkporo Shale-Owelli Sandstone and Owelli Sandstone-Enugu Shale successions, respectively. The transgressive systems tract in each sequence comprises coarse-grained fluvio-deltaic sandstone and an overlying open marine black carbonaceous mud rock. The highstand systems tracts comprise delta front deposits with average porosity, permeability and net-to-gross values estimated in the ranges of 30%, 3000 md and 0.9, respectively. The fluvio-deltaic and delta front facies which are encased in organically rich estuarine central basin/shallow shelf mud rocks are likely the potential reservoirs. Trapping capacity is enhanced by the presence of several N-S trending normal faults, and other microstructures related to the post-Santonian tensional regime in the Benue. The new information presented in this paper on potential seal, source and reservoir lithofacies within the Nkporo Group should serve as a useful contribution to the geological modelling of reservoirs within the Late Cretaceous-Paleocene succession in the Anambra Basin.

The concentrations of redox-sensitive trace elements, such as uranium (U), vanadium (V), molybdenum (Mo), cobalt (Co), chromium (Cr) and rare earth elements (REE+Y) were determined in a given carbonate succession in the Gaoyuzhuang Formation (~1.56 Ga), which spans depths from outer shelf to intertidal, to explore the Early Mesoproterozoic ocean redox conditions. The values of the Zr-normalized redox-sensitive trace element concentrations and some relevant ratios show obvious changes from bottom to top in the succession. Samples from the outer shelf setting (M1 interval) demonstrate significantly enhanced values in Zr-normalized redox-sensitive trace element concentrations and relevant ratios (the peaks of Mo/U, V/Cr and Ni/Co ratios larger than 8, 4.25, and 7, respectively). Authigenic framboidal pyrites were also found within oncolite-like carbonate concretions and surrounding host rocks in this interval. These all indicate a euxinic state in the outer shelf environment. Less enrichment of Zr-normalized redox-sensitive elemental abundances and a mild decrease in the values of geochemical ratios were present in the inner shelf environment (M2 interval) (the V/Cr and Ni/Co ratios fall into a range of 2.5-4.25 and 4-5, respectively), suggesting dysoxic conditions dominant in the inner shelf setting. Samples from the shallower subtidal and intertidal settings (M3 and M4 intervals) are mostly invariable with much lower values of Zr-normalized redox-sensitive elements and relevant ratios, with the V/Cr and Ni/Co ratios typically near or less than 2 and 5 respectively, indicative of oxic conditions in the high-energy subtidal/intertidal zones. A remarkable negative Ce anomaly exhibited in the shale-normalized REE+Y diagram in the M4 interval may provide evidence in support of the hypothesis. Taken together, our results suggest a relatively shallow chemocline in the Early Mesoproterozoic ocean: the transitions between euxinic, dysoxic and oxic may occur in quiet-water outer shelf and highenergy subtidal zone, respectively. The presence of euxinic ocean bottom waters is compatible with low concentrations of seawater sulfate and reduced levels of atmospheric oxygen during this period. The extreme environmental conditions induced by these anoxic oceans could have been responsible for the delayed oxygenation of the biosphere and hindered the evolution of multicellular life.