Linna Zhang

Geobiodiversity Database: a comprehensive section-based integration of stratigraphic and paleontological data

The Geobiodiversity Database (GBDB – www.geobiodiversity.com), an integrated system for the management and analysis of stratigraphic and paleontological information, was started in 2006 and became available online in 2007. Its goal is to facilitate regional and global scientific collaborations focused on regional and global correlation, quantitative stratigraphy, systematics, biodiversity dynamics, paleogeography and paleoecology. It is unique among global, public access databases in that it is a section-based online database system, incorporating data from a wide range of disciplines of stratigraphy and paleontology, with inherent interrelationship between different kinds of data sets. It provides the capability of completely digitizing raw data, as well as integrating of different interpretations to the same paleontological and stratigraphic content. Several Windows-based visualization and analysis applications, either fully integrated with the database or supported by subset-export functions, have been developed to make the database more useful as a scientific and educational tool. The GBDB became the formal database of the International Commission on Stratigraphy (ICS) in August 2012 at the 34th International Geological Congress in Brisbane, and will produce comprehensive and authoritative web-based stratigraphic information service for global geoscientists, educators and the public.

Long-Term Decomposition of Organic Materials with Different Carbon/Nitrogen Ratios

Quantitative information on the decomposition rates and patterns of organic residues is fundamental for a better understanding of organic matter dynamics and nutrient cycling in soils. A laboratory incubation experiment was conducted under constant temperature (30°C) for 3 years to study changes in total carbon (C), total nitrogen (N), and C/N ratio of crop residues (rice, corn, alfalfa) and animal feces (pig, cattle) decomposing with and without soil. On average, rice, corn, and alfalfa residues lost a larger proportion of their original organic C than cattle and pig feces (82 vs. 70%). The presence of soil did not affect the total amount of organic C lost, with the exception of corn residues in which it increased it from 79 to 84%. Alfalfa residues, pig feces, and cattle feces lost a larger proportion of their total N than rice residues (38 vs. 15%). Both rice and corn residues showed an initial increase in total N, which may have been due to N immobilization from the soil and/or N fixation. Rice residues started losing total N after 15 months, whereas corn residues still showed an increase in total N after three years. The presence of soil decreased the loss of total N in alfalfa residue (32 vs. 48%) and pig feces (38 vs. 51%). The C/N ratios of all materials decreased during the decomposition and, with the exception of pig feces were similar to that of the soil by the end of the study (11:1 to 12:1). These results provide quantitative information that could be used to improve the management of residues and feces.

Temporal and spatial distribution of the Wufeng Formation black shales (Upper Ordovician) in South China

The Wufeng Formation black shales (upper Katian to lower Hirnantian) are widely distributed on the Yangtze Platform in South China. Data from 389 sections that span the stratigraphic interval of the Wufeng Formation were captured through the GBDB online database. By using the GBDB online analytical functions and the ArcGIS software, we have visualized the dynamic changes of the geographic distribution of the Wufeng Formation black shales and calculated their sedimentary variables, such as distribution area, rock volume and mean thickness. The distribution area of the Wufeng Formation decreased through the study interval, which likely represents the effect of the global sea-level fall (resulting from the growth of the Gondwana ice sheets) and the gradual uplift of the study area. The extremely low sedimentary rate on the Yangtze Platform reflects a very restricted terrigenous supply during the Late Ordovician. To the south of the Yangtze Platform, there are two areas in which coeval sediments are over 1000 m thick, which probably represent environments with sustained subsidence of the underlying crust and more proximal terrigenous sediment sources.

Geographic dynamics of some major graptolite taxa of the Diplograptina during the Late Ordovician mass extinction in South China

The study of graptolite paleobiogeography is important for understanding the relationship between geography and evolutionary dynamics in graptolites. However, there have been few detailed studies of graptolite paleobiogeography during the Late Ordovician, or the role that geography played in the Hirnantian Mass Extinction (HME). In this study, in order to investigate the geographic dynamics of major graptolite taxa during the HME, a data-set of graptolite occurrences in the late Katian–Hirnantian from 61 localities in South China was compiled using the GBDB online database. The minimum polygon method was used to reconstruct 14 distribution maps of 5 major taxa belonging to the Diplograptina. The geographic dynamics of most diplograptine taxa show a small reduction in their geographic ranges from the Dicellograptus complexus Zone to the Paraorthograptus pacificus Zone, probably because of the contractions in the distribution areas of the coeval marine sediments. A substantial reduction in the distributions of most diplograptine taxa from the P. pacificus Zone to the Metabolograptus extraordinarius Zone mainly represents the effect of the major extinction event. Our study also demonstrates a reduction in the geographic ranges of each taxon to the center of the Yangtze epicontinental sea during the HME. The changes in geographic ranges are mirrored by a similar reduction in species-level total diversity during the study interval.

Geobiodiversity Database (GBDB) in stratigraphic, palaeontological and palaeogeographic research: graptolites as an example

The Geobiodiversity Database (GBDB) Project is dedicated to the construction and maintenance of a web-enabled taxonomic, stratigraphic and geographic database for information gathered from the fossil record. Its goal is to facilitate regional and global scientific collaborations focused on studying the history, diversity, geography and environmental context of life on Earth. After 7 years of development, its abundant data resources and diverse integrated functions make it a useful platform for stratigraphic, palaeontological and palaeogeographic analysis. Graptolites are the first major fossil group that has been the focus of our efforts to compile, standardize, digitize and analyse over the past several years. Here, we use the graptolite group as an example to introduce the major data resources and functionality of the GBDB.

Paleogeographic evolution of the Lower Yangtze region and the break of the “platform-slope-basin” pattern during the Late Ordovician

Wide distribution of the black shales and diversification of the graptolite fauna in South China during the Late Ordovician resulted from its unique paleogeographic pattern, which was significantly affected by the paleogeographic evolution of the Lower Yangtze region. In the study, 120 Upper Ordovician sections from the Lower Yangtze region were collected, and a unified biostratigraphic framework has been applied to these sections to establish a reliable stratigraphic subdivision and correlation. Under the unified time framework, we delineate the distribution area of each lithostratigraphic unit, outline the boundary between the sea and land, and reconstruct the paleogeographic pattern for each graptolite zone. The result indicates that, with the uplift and expansion of the ‘Jiangnan Oldland’ in the beginning of the late Katian, the oldland extended into the Yangtze Sea gradually from south to north, which finally separate the Jiangnan Slope and the Yangtze Platform. Consequently, the longstanding paleogeographic pattern of “platform-slope-basin” in South China was broken. The paleogeographic change led to sedimentary differentiation among the two sides of the ‘Jiangnan Oldland’ during the Late Ordovician. This event also led to the closure of the eastern exit of the Upper Yangtze Sea, and formed a semi-closed, limited and stagnant environment for the development of the organic-rich black shales during the Late Ordovician. The major controlling factors of these paleogeographic changes in the Lower Yangtze region were not consistent from the Katian to the Hirnantian. In the late Katian, the sedimentary differentiation between the east and west sides mostly resulted from regional tectonic movement - the Kwangsian Orogeny. However, during the Hirnantian, the whole Yangtze region became shallower, which was mostly influenced by the concentration of the Gondwana ice sheet and the consequent global sea level drop.

Circumjacent distribution pattern of the Lungmachian graptolitic black shale (early Silurian) on the Yichang Uplift and its peripheral region

Stratigraphic hiatuses of variable time intervals within the Rhuddanian to early Aeronian (Llandovery, Silurian) are identified in the area bordering East Chongqing, West Hubei and Northwest Hunan in central China. Their distribution suggested the existence of a local uplift, traditionally named the Yichang Uplift. The diachronous nature of the basal black shale of the Lungmachi Formation crossing different belts of this Uplift signifies the various developing stages during the uplifting process. The present paper defines the temporal and spatial distribution pattern of the Yichang Uplift, which might be one of the important controlling factors for the preservation and distribution of the shale gas in this region, as it has been demonstrated that the shale gas exploration is generally less promising in the areas where more of the basal part of the Lungmachi Formation is missing. Therefore, better understanding of the circumjacent distribution pattern developed throughout the uplifting process may provide the important guidance for the shale gas exploration. The present work is a sister study to the published paper, “Stage-progressive distribution pattern of the Lungmachian black graplolitic shales from Guizhou to Chongqing, Central China”. These two studies thus provide a complete Ordovician-Silurian black shale distribution pattern in the Middle and Upper Yangtze, a region with the major shale gas fields in China.