1,721,160 research outputs found
High sea surface temperatures were a prerequisite for the development and expansion of the Great Barrier Reef
No full textThe Great Barrier Reef is the largest reef system in the modern ocean. To date, the influence of temperature on the origin and long-term evolution of the Great Barrier Reef remains enigmatic. Here, we present a 900–thousand year TEX86H-derived temperature proxy record from Ocean Drilling Program Site 820 in the Coral Sea. It demonstrates that the onset of reef growth on the outer shelf was preceded by a rise in summer temperature from ~26° to ~28°C at around 700 thousand years ago (marine isotope stage 17). This approximately 2°C rise in summer sea surface temperatures (SSTs) likely resulted in higher carbonate production rates, which were crucial for the formation of the Great Barrier Reef. Subsequently, reconstructed SSTs remained sufficiently warm for the Great Barrier Reef to thrive and evolve continuously. The evolution of the Great Barrier Reef, therefore, appears to be closely linked to SSTs
Lightness measurement from IODP Site 356-U1461
No full textThe North West Shelf of Australia is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the Northwest Shelf. Carbonates occurring within the studied site can be subdivided by color into light and dark sections. These differences are linked to composition and mineralogy, which in turn are related to changes in the sedimentary environment. Based on this relationship, reflectance of visible light (i.e. lightness) can be used as a high-resolution proxy to delineate different facies within the core
Mineral determination from IODP Site 356-U1461
No full textThe Northwest Shelf of Australia (NWS) is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the NWS. X-ray diffraction (XRD) derived mineral data is used to delineate the carbonate mineralogy of the different sedimentary facies occurring in core. It is further utilized to assess the influence of terrigenous influx into the shallow-marine system. Bioclastic sediments, which formed during interglacials, are characterized by comparatively high amounts of siliciclastics and calcitic carbonates. Siliciclastics are thought to reflect the humid climate and associated fluvial influx present during interglacials. Needle mudstones and ooid/peloid packstones, which formed during arid glacials, are characterized by an aragonitic mineralogy with little siliciclastics. These findings indicate that the mineralogy of the Quaternary NWS changes cyclically in response to high-frequency glacioeustatic variations in sea level and climate
XRF measurement from IODP Site 356-U1461
No full textThe North West Shelf of Australia is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the Northwest Shelf. The log ratio of strontium (Sr) to calcium (Ca) is presented as a proxy for relative changes in aragonite content. This relationship is based on the elevated amounts of strontium present in aragonite as compared to calcite and was formerly successfully calibrated against carbonate mineralogy at the studied site (U1461)
P-wave velocity measurement from IODP Site 356-U1461
No full textThe North West Shelf of Australia is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the Northwest Shelf. P-wave velocity of core material was utilized for the creation of an acoustic impedance log as well as to determine its relationship to sedimentary facies. At the studied site, observed p-wave velocities are strongly controlled by grain-size. Mud poor sections display high velocities whereas low velocities characterize sediments rich in carbonate mud. Correspondingly, we observe the occurrence of strong acoustic impedance contrasts and seismic reflections wherever facies changes
Abundance of non-skeletal grains from IODP Site 356-U1461
No full textThe North West Shelf of Australia is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the Northwest Shelf. Throughout the studied core section, several sections rich in ooids and peloids occur. Sediment samples were investigated for their abundance of these non-skeletal grains to better understand the timing and condition of their formation. During arid glacial lowstands, sedimentation is characterized by inorganically precipitated carbonates, including ooids and peloids. Ooids developed under shallow-marine conditions on small-scale flat-topped platforms. Seismic and sedimentological evidence indicates that these platforms grew locally on top of the present-day mid ramp and were typically only active during a single glacial period
Bulk density from IODP Site 356-U1461
No full textThe North West Shelf of Australia is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the Northwest Shelf. Information on bulk density was used for the creation of an acoustic impedance log as well as to determine the influence of sedimentary facies and mineralogy on the creation of seismic reflections. Observed bulk density is strongly correlated to facies related changes in mineralogy and porosity. Low porosity aragonitic sections composed of non-skeletal grains display the largest bulk densities. In comparison, bioclastic sediments, which are largely composed of the less dense calcite, have average bulk densities. Lowest bulk densities can be observed in aragonitic mudstones. This is attributed to the high amounts of microporosity present in this facies. Based on these observations, changes in acoustic impedance are to be expected during facies transitions. Thus, reflections observed in seismic can be linked to changes in the sedimentary system
Porosity analysis from IODP Site 356-U1461
No full textThe North West Shelf of Australia is an extensive tropical carbonate ramp and forms an important template for the interpretation of similar systems in the sedimentary record. Yet, little is known about the development of the distally steepened ramp from the middle to late Quaternary, a period of high frequency glacioeustatic changes in sea level and climate. This research describes core and seismic-reflection data from a mid- to outer ramp transect at the Northwest Shelf. Porosity data is used to assess the effect of facies related porosity changes onto the creation of seismic reflections. Generally, porosity values are high (~60%) where sediments are composed of fine-grained aragonite needle mud whereas bioclastic or non-skeletal grain rich sediments display lower porosities (40-50%). In effect, strong acoustic impedance contrasts are observed wherever facies changes into fine-grained aragonite mud. This agrees with observations in seismic, which reveal the occurrence of strong seismic reflections wherever larger facies changes occur
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
