Author: Christopher K. Hendrix
Publisher:
ISBN:
Category :
Languages : en
Pages : 127
Book Description
The Upper Cretaceous Cenomanian Buda Formation and Coniacian-Campanian Austin Chalk Group of Texas and northern Mexico are calcareous mudrock (chalk) successions deposited on the drowned lower Cretaceous Comanche platform. Investigations covering depositional systems, lithofacies, and diagenesis have been completed over the years, but no up-to-date chemostratigraphic studies have been conducted on either the Buda or Austin Chalk units. This investigation has supplemented sedimentological analysis with high-resolution X-ray-fluorescence (XRF) geochemical data. Two methods were employed to define chemofacies from an XRF dataset to test whether geochemical data can enhance description of the lithofacies and add insight to the lithostratigraphic analysis. Buda and Austin units are composed of four lithofacies in the subsurface of south-central Texas: (1) calcisphere globigerinid wackestone, (2) calcisphere globigerinid mud-dominated packstone, (3) calcareous mudstone, and (4) argillaceous calcareous mudstone. Observations of elemental curves plotted versus depth identified the alternation of calcite-rich chemofacies with dolomite-, clay-, and pyrite-rich chemofacies. Multiple iterations of hierarchical cluster analysis applied to the XRF dataset revealed seven chemofacies: (1) Ca-enriched, (2) Mg-enriched, (3) Al-enriched, (4) S-enriched, (5) P-enriched, (6) Zn-enriched, and (7) Ni-enriched. Neither chemofacies method is capable of defining lithofacies, but each can be used to substantiate mineralogical variability at the sub-lithofacies scale. The XRF-curve-based chemofacies identified large-scale oscillations in mineralogical composition while the HCA chemofacies identified mineralogical variability at the resolution of XRF sampling. Chemolithofacies are defined as lithofacies that are additionally characterized by chemofacies data. Delineation of the chemolithofacies is achieved by applying geochemical (and in this case mineralogical) descriptors to the lithofacies units based on the geochemical data. Ca-enriched calcisphere globigerinid wackestones and packstones are the dominant chemolithofacies of the Buda Formation and Austin Chalk Group. Calcisphere globigerinid wackestones, calcisphere globigerinid mud-dominated packstones, calcareous mudstones, and argillaceous calcareous mudstones enriched in dolomite, clays, and pyrite make up the other chemolithofacies. Variability in the chemolithofacies is attributed to rock units of more mixed mineralogy as a result of intermittent, sustained periods of increased extrabasinal sediment delivery to the shelf.
Chemolithofacies of the Upper Cretaceous Buda Formation and Austin Chalk Group, South-central Texas
Author: Christopher K. Hendrix
Publisher:
ISBN:
Category :
Languages : en
Pages : 127
Book Description
The Upper Cretaceous Cenomanian Buda Formation and Coniacian-Campanian Austin Chalk Group of Texas and northern Mexico are calcareous mudrock (chalk) successions deposited on the drowned lower Cretaceous Comanche platform. Investigations covering depositional systems, lithofacies, and diagenesis have been completed over the years, but no up-to-date chemostratigraphic studies have been conducted on either the Buda or Austin Chalk units. This investigation has supplemented sedimentological analysis with high-resolution X-ray-fluorescence (XRF) geochemical data. Two methods were employed to define chemofacies from an XRF dataset to test whether geochemical data can enhance description of the lithofacies and add insight to the lithostratigraphic analysis. Buda and Austin units are composed of four lithofacies in the subsurface of south-central Texas: (1) calcisphere globigerinid wackestone, (2) calcisphere globigerinid mud-dominated packstone, (3) calcareous mudstone, and (4) argillaceous calcareous mudstone. Observations of elemental curves plotted versus depth identified the alternation of calcite-rich chemofacies with dolomite-, clay-, and pyrite-rich chemofacies. Multiple iterations of hierarchical cluster analysis applied to the XRF dataset revealed seven chemofacies: (1) Ca-enriched, (2) Mg-enriched, (3) Al-enriched, (4) S-enriched, (5) P-enriched, (6) Zn-enriched, and (7) Ni-enriched. Neither chemofacies method is capable of defining lithofacies, but each can be used to substantiate mineralogical variability at the sub-lithofacies scale. The XRF-curve-based chemofacies identified large-scale oscillations in mineralogical composition while the HCA chemofacies identified mineralogical variability at the resolution of XRF sampling. Chemolithofacies are defined as lithofacies that are additionally characterized by chemofacies data. Delineation of the chemolithofacies is achieved by applying geochemical (and in this case mineralogical) descriptors to the lithofacies units based on the geochemical data. Ca-enriched calcisphere globigerinid wackestones and packstones are the dominant chemolithofacies of the Buda Formation and Austin Chalk Group. Calcisphere globigerinid wackestones, calcisphere globigerinid mud-dominated packstones, calcareous mudstones, and argillaceous calcareous mudstones enriched in dolomite, clays, and pyrite make up the other chemolithofacies. Variability in the chemolithofacies is attributed to rock units of more mixed mineralogy as a result of intermittent, sustained periods of increased extrabasinal sediment delivery to the shelf.
Publisher:
ISBN:
Category :
Languages : en
Pages : 127
Book Description
The Upper Cretaceous Cenomanian Buda Formation and Coniacian-Campanian Austin Chalk Group of Texas and northern Mexico are calcareous mudrock (chalk) successions deposited on the drowned lower Cretaceous Comanche platform. Investigations covering depositional systems, lithofacies, and diagenesis have been completed over the years, but no up-to-date chemostratigraphic studies have been conducted on either the Buda or Austin Chalk units. This investigation has supplemented sedimentological analysis with high-resolution X-ray-fluorescence (XRF) geochemical data. Two methods were employed to define chemofacies from an XRF dataset to test whether geochemical data can enhance description of the lithofacies and add insight to the lithostratigraphic analysis. Buda and Austin units are composed of four lithofacies in the subsurface of south-central Texas: (1) calcisphere globigerinid wackestone, (2) calcisphere globigerinid mud-dominated packstone, (3) calcareous mudstone, and (4) argillaceous calcareous mudstone. Observations of elemental curves plotted versus depth identified the alternation of calcite-rich chemofacies with dolomite-, clay-, and pyrite-rich chemofacies. Multiple iterations of hierarchical cluster analysis applied to the XRF dataset revealed seven chemofacies: (1) Ca-enriched, (2) Mg-enriched, (3) Al-enriched, (4) S-enriched, (5) P-enriched, (6) Zn-enriched, and (7) Ni-enriched. Neither chemofacies method is capable of defining lithofacies, but each can be used to substantiate mineralogical variability at the sub-lithofacies scale. The XRF-curve-based chemofacies identified large-scale oscillations in mineralogical composition while the HCA chemofacies identified mineralogical variability at the resolution of XRF sampling. Chemolithofacies are defined as lithofacies that are additionally characterized by chemofacies data. Delineation of the chemolithofacies is achieved by applying geochemical (and in this case mineralogical) descriptors to the lithofacies units based on the geochemical data. Ca-enriched calcisphere globigerinid wackestones and packstones are the dominant chemolithofacies of the Buda Formation and Austin Chalk Group. Calcisphere globigerinid wackestones, calcisphere globigerinid mud-dominated packstones, calcareous mudstones, and argillaceous calcareous mudstones enriched in dolomite, clays, and pyrite make up the other chemolithofacies. Variability in the chemolithofacies is attributed to rock units of more mixed mineralogy as a result of intermittent, sustained periods of increased extrabasinal sediment delivery to the shelf.
A Facies-scale Chemo-lithostratigraphic Composite Profile of Del Rio Claystone Through Austin Chalk Deposition, Late Cretaceous, Central Texas, USA
Author: Kyle Christopher Gabb
Publisher:
ISBN:
Category :
Languages : en
Pages : 188
Book Description
Late Cretaceous deposition (Comanche/Gulfian Series) across the San Marcos Arch of central Texas is characterized by both aluminosilicate- and carbonate-dominated mudrock successions. Twelve drill cores were recovered from the 2-acre construction site of the AT&T Executive Education and Conference Center on The University of Texas at Austin main campus. Thirteen detailed chemo-lithofacies were defined through a combination of visual description and elemental analysis utilizing energy-dispersive X-ray fluorescence (ED-XRF). Elemental analysis was undertaken at a 0.25-ft sampling interval to provide a record of facies-scale variability. A composite profile from two cores was created by identifying the boundary between the top of the Buda Limestone and bottom of the Eagle Ford Group and then splicing the records together, thus maximizing the length of the composite core to 174 ft and incorporating the Del Rio Claystone, Buda Limestone, Eagle Ford Group, and Austin Chalk formations. Lithofacies within the four formations were defined based on Dunham’s (1962) carbonate and Potter’s (1980) shale classifications. Important sedimentary structures and mineralogical compositions were identified and added as modifiers to the facies description. The shifts between the carbonate formations and the clay-rich formations are caused by changes in sea level, productivity, anoxia, and reworking by bottom currents. The Buda Limestone and Austin Chalk are identified to range in composition from limestone to marl, as the matrixes of the formations are composed of alumo-siliceous mud. Covariance of silicon with aluminum and titanium (proxies for detrital inputs) suggests that the silica is dominantly of terrigenous origin, rather than of biogenic origin. The enrichment of redox elements (molybdenum and vanadium) indicates the occurrence of anoxia during deposition of the Eagle Ford Group. The increased presence of volcanic ash beds within fossil-rich section of the Eagle Ford Group indicates that nutrients supplied by volcanism led to increased primary productivity, triggering depleted oxygen levels and anoxic bottom waters. Whereas sea level was likely the driving force that caused changes within the Del Rio Claystone, Buda Limestone, and Austin Chalk, productivity and anoxia are the drivers of transitions within the Eagle Ford Group.
Publisher:
ISBN:
Category :
Languages : en
Pages : 188
Book Description
Late Cretaceous deposition (Comanche/Gulfian Series) across the San Marcos Arch of central Texas is characterized by both aluminosilicate- and carbonate-dominated mudrock successions. Twelve drill cores were recovered from the 2-acre construction site of the AT&T Executive Education and Conference Center on The University of Texas at Austin main campus. Thirteen detailed chemo-lithofacies were defined through a combination of visual description and elemental analysis utilizing energy-dispersive X-ray fluorescence (ED-XRF). Elemental analysis was undertaken at a 0.25-ft sampling interval to provide a record of facies-scale variability. A composite profile from two cores was created by identifying the boundary between the top of the Buda Limestone and bottom of the Eagle Ford Group and then splicing the records together, thus maximizing the length of the composite core to 174 ft and incorporating the Del Rio Claystone, Buda Limestone, Eagle Ford Group, and Austin Chalk formations. Lithofacies within the four formations were defined based on Dunham’s (1962) carbonate and Potter’s (1980) shale classifications. Important sedimentary structures and mineralogical compositions were identified and added as modifiers to the facies description. The shifts between the carbonate formations and the clay-rich formations are caused by changes in sea level, productivity, anoxia, and reworking by bottom currents. The Buda Limestone and Austin Chalk are identified to range in composition from limestone to marl, as the matrixes of the formations are composed of alumo-siliceous mud. Covariance of silicon with aluminum and titanium (proxies for detrital inputs) suggests that the silica is dominantly of terrigenous origin, rather than of biogenic origin. The enrichment of redox elements (molybdenum and vanadium) indicates the occurrence of anoxia during deposition of the Eagle Ford Group. The increased presence of volcanic ash beds within fossil-rich section of the Eagle Ford Group indicates that nutrients supplied by volcanism led to increased primary productivity, triggering depleted oxygen levels and anoxic bottom waters. Whereas sea level was likely the driving force that caused changes within the Del Rio Claystone, Buda Limestone, and Austin Chalk, productivity and anoxia are the drivers of transitions within the Eagle Ford Group.
Stratigraphic relations of the Austin Chalk (Upper Cretaceous) in central Texas
Author: Mark Allan Miller
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 162
Book Description
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 162
Book Description
Field Conference Guidebook
Author: Baylor Geological Society
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 148
Book Description
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 148
Book Description
Sedimentology and Diagenesis of the Upper Cretaceous Austin Chalk Formation, South Texas and Northern Mexico
Author: Jeffrey James Dravis
Publisher:
ISBN:
Category : Chalk
Languages : en
Pages : 1026
Book Description
Publisher:
ISBN:
Category : Chalk
Languages : en
Pages : 1026
Book Description
Stratigraphy of the Eagle Ford Group (upper Cretaceous) and Its Source-rock Potential in the East Texas Basin
Author: Milton A. Surles
Publisher:
ISBN:
Category : Eagle Ford Group (Tex.)
Languages : en
Pages : 76
Book Description
Publisher:
ISBN:
Category : Eagle Ford Group (Tex.)
Languages : en
Pages : 76
Book Description
Austin Chalk in Its Type Area-- Stratigraphy and Structure
Author: Keith Young
Publisher:
ISBN:
Category : Chalk
Languages : en
Pages : 104
Book Description
Publisher:
ISBN:
Category : Chalk
Languages : en
Pages : 104
Book Description
The Stratigraphy and Depositional Environment of the Austin Chalk (upper Cretaceous) at White Rock Creek, Bellmead, Texas
Author: Kolin Beam
Publisher:
ISBN:
Category : Chalk
Languages : en
Pages : 82
Book Description
Publisher:
ISBN:
Category : Chalk
Languages : en
Pages : 82
Book Description
Supplemental Field and Literature Investigation of the Upper Cretaceous Austin Group (chalk) of Texas with Regard to Its Potential for Radioactive-waste Isolation
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Regional stratigraphy, local stratigraphy, structural geology, mineral resource development, and evaluation of repository potential are discussed. (LK).
Publisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
Regional stratigraphy, local stratigraphy, structural geology, mineral resource development, and evaluation of repository potential are discussed. (LK).
Biostratigraphy of the Upper Cretaceous Austin Group, Travis County, Texas
Author: William Maurice Harris
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 200
Book Description
Publisher:
ISBN:
Category : Geology
Languages : en
Pages : 200
Book Description