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Pennsylvania Geological Survey s 73rd Annual Field Conference of Pennsylvania Geologists: Pre-Conference Field Trip to L

LWB Refractories Quarry

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Pennsylvania Geological Survey s 73rd Annual Field Conference of Pennsylvania Geologists: Pre-Conference Field Trip to L

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    1. Pennsylvania Geological Survey’s 73rd Annual Field Conference of Pennsylvania Geologists: Pre-Conference Field Trip to LWB Refractories Quarry in York, County, PA September 25, 2008 All images were captured on a field trip led by Dr. Carol B. de Wet, a geology professor in the Department of Earth & Environment at Franklin and Marshall College in Lancaster, PA; and Dave Hopkins, the Resource/Mining Operations Manager for LWB Refractories in York, PA. All interpretations depicted in the images that follow are based on the work of Dr. de Wet and her colleagues and Dave Hopkins. Field notes, cited as “de Wet, personal communication”, and other referenced information are provided in the notes sections of several of the slides. A comprehensive reference list of the years of research behind the field discussions is included as the last two slides. Special thanks to both presenters and to all of the researchers that have examined these units in the past. All have provided such great insight into the enigma that is carbonate sedimentation at the Laurentian margin during Cambrian times! The work has significant implications in many disciplines and its value cannot be overstated.

    2. LWB Refractories Quarry is a 240 foot deep, 86.5 acre surface mining operation in York County, Pennsylvania extracting high purity dolomite used in the manufacture of refractory brick. The deposit was discovered in 1946 and active mining commenced in 1950. The two major carbonate facies include a massive ooid shoal and neighboring microbial patch reefs. These deposits accumulated under high energy conditions at the shelf margin of the Laurentian continent during the Middle Cambrian (500 to 520 Ma). A modern analog is the well-studied, Late Pleistocene Great Bahama Bank. Exposure of the ancient patch reefs in-situ makes this location remarkably unique. Such Cambrian reef deposits have been noted as off-shelf slump blocks at other locations, but have rarely been observed in place. No other location in Pennsylvania is known to have primary limestone, in-situ exposures of the Ledger reef facies that are of such high quality (de Wet, personal communication). Contrasting permeability characteristics between the facies transformed the ooid shoal into dolomite while leaving the relatively impervious reef facies as limestone. At least three stages of dolomitization have altered the ooid shoal substrate. One initial phase occurred early on and is believed to be related to periods of subaerial exposure resulting from fluctuating sea levels. Evidence of such emergent conditions are not pervasive in the deposit, but have resulted in an intermittently exposed shoreface interpretation for one area flanking the ooid shoals (de Wet, personal communication). Other interesting exposures at the quarry include the Ledger Formation “white marble”, Triassic fanglomerate, and the off-shelf Kinzers Formation. The “white marble” comprises a series of dedolomitized zones believed to be associated with Triassic extensional faulting that marked the beginning of tectonism associated with the break-up of Pangaea. The fault zones were higher permeability and preferentially exposed portions of the Ledger dolomite to circulating calcite-rich fluids (de Wet, personal communication). In some areas, undersaturation of migrating fluids opened up cavities and vugs (paleokarst) that later received an influx of Triassic hematitic sediment (de Wet and Hopkins, 1). A fault contact between the Ledger and the Triassic fanglomerate facies is revealed near the northwestern corner of the quarry (de Wet, personal communication). Such conglomeritic deposits were known to have formed the northern boundary of the Gettysburg basin, a depositional environment constituted of alluvial fan, fluvial, deltaic, and lacustrine environments during most of the Triassic (Smoot, 198-199). The fanglomerate is composed of coarse clastic detritus derived from the Ledger and Triassic sediments and is cemented with mud- to silt-sized hematitic material (de Wet, personal communication). Finally, the Kinzers Formation, which is exposed at the base of the quarry, is well known for its lowermost member, the Emigsville, a deposit of exceptional preservation that captured the “Cambrian Explosion” (Skinner, 167). For a more detailed discussion of the deposits being mined at the LWB Refractories Quarry and their origins along with some excellent figures, please check out Dr. Carol de Wet’s website at: http://www.fandm.edu/x12035.xml .LWB Refractories Quarry is a 240 foot deep, 86.5 acre surface mining operation in York County, Pennsylvania extracting high purity dolomite used in the manufacture of refractory brick. The deposit was discovered in 1946 and active mining commenced in 1950. The two major carbonate facies include a massive ooid shoal and neighboring microbial patch reefs. These deposits accumulated under high energy conditions at the shelf margin of the Laurentian continent during the Middle Cambrian (500 to 520 Ma). A modern analog is the well-studied, Late Pleistocene Great Bahama Bank. Exposure of the ancient patch reefs in-situ makes this location remarkably unique. Such Cambrian reef deposits have been noted as off-shelf slump blocks at other locations, but have rarely been observed in place. No other location in Pennsylvania is known to have primary limestone, in-situ exposures of the Ledger reef facies that are of such high quality (de Wet, personal communication). Contrasting permeability characteristics between the facies transformed the ooid shoal into dolomite while leaving the relatively impervious reef facies as limestone. At least three stages of dolomitization have altered the ooid shoal substrate. One initial phase occurred early on and is believed to be related to periods of subaerial exposure resulting from fluctuating sea levels. Evidence of such emergent conditions are not pervasive in the deposit, but have resulted in an intermittently exposed shoreface interpretation for one area flanking the ooid shoals (de Wet, personal communication). Other interesting exposures at the quarry include the Ledger Formation “white marble”, Triassic fanglomerate, and the off-shelf Kinzers Formation. The “white marble” comprises a series of dedolomitized zones believed to be associated with Triassic extensional faulting that marked the beginning of tectonism associated with the break-up of Pangaea. The fault zones were higher permeability and preferentially exposed portions of the Ledger dolomite to circulating calcite-rich fluids (de Wet, personal communication). In some areas, undersaturation of migrating fluids opened up cavities and vugs (paleokarst) that later received an influx of Triassic hematitic sediment (de Wet and Hopkins, 1). A fault contact between the Ledger and the Triassic fanglomerate facies is revealed near the northwestern corner of the quarry (de Wet, personal communication). Such conglomeritic deposits were known to have formed the northern boundary of the Gettysburg basin, a depositional environment constituted of alluvial fan, fluvial, deltaic, and lacustrine environments during most of the Triassic (Smoot, 198-199). The fanglomerate is composed of coarse clastic detritus derived from the Ledger and Triassic sediments and is cemented with mud- to silt-sized hematitic material (de Wet, personal communication). Finally, the Kinzers Formation, which is exposed at the base of the quarry, is well known for its lowermost member, the Emigsville, a deposit of exceptional preservation that captured the “Cambrian Explosion” (Skinner, 167). For a more detailed discussion of the deposits being mined at the LWB Refractories Quarry and their origins along with some excellent figures, please check out Dr. Carol de Wet’s website at: http://www.fandm.edu/x12035.xml .

    3. LWB Refractories Quarry – Unit Exposures Units exposed at quarry (facing west)Units exposed at quarry (facing west)

    4. LWB Refractories Quarry – York, PA Facing West

    5. LWB Refractories Quarry – “White Marble” and Triassic Fanglomerate

    6. LWB Refractories Quarry – Northern Benches Facing Northwest Northern benchesNorthern benches

    7. LWB Refractories Quarry – Overburden Facing East Overburden (facing east)Overburden (facing east)

    8. LWB Refractories Quarry – Polished Microbialite Reef Facies Polished sample from microbial reef facies: note bands of cavity filling radiaxial fibrous and herringbone calcite cement through center of sample. Surrounding darker material consists of clots, stringers, and stubby shrubs of calcified algae and/or bacteria/cyanobacteria. These are cross-cut by calcite-filled fenestrae (de Wet, personal communication). Sample is property of Dr. Carol de Wet of F&M.Polished sample from microbial reef facies: note bands of cavity filling radiaxial fibrous and herringbone calcite cement through center of sample. Surrounding darker material consists of clots, stringers, and stubby shrubs of calcified algae and/or bacteria/cyanobacteria. These are cross-cut by calcite-filled fenestrae (de Wet, personal communication). Sample is property of Dr. Carol de Wet of F&M.

    9. LWB Refractories Quarry – Polished Microbialite Reef Facies

    10. LWB Refractories Quarry – Microbialite Reef Facies Karst Pinnacles in East Patch Reef

    11. LWB Refractories Quarry – Submarine Cavity Filling Cements and Gas Escape Structure in East Patch Reef Gas escape structures are excellent facing direction indicators in the reef deposit, as they invariably point upward marking the location where fluids and gases associated with decaying biota breached the cavity as they migrated toward the surface (de Wet, personal communication).Gas escape structures are excellent facing direction indicators in the reef deposit, as they invariably point upward marking the location where fluids and gases associated with decaying biota breached the cavity as they migrated toward the surface (de Wet, personal communication).

    12. LWB Refractories Quarry – Submarine Cavity Filling Cements and Gas Escape Structure in East Patch Reef

    13. LWB Refractories Quarry – Submarine Cavity Filling Cements and Gas Escape Structure in East Patch Reef (Comparison with Polished Slab)

    14. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef

    15. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Note Lighter Colored Band of Void Filling Radiaxial and Herringbone Calcite

    16. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Note Lighter Colored Band of Void Filling Radiaxial and Herringbone Calcite

    17. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Note Calcified Algae and/or Bacteria/Cyanobacteria Shrub Above Calcite Filled Void

    18. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Note Calcified Algae and/or Bacteria/Cyanobacteria Shrub Above Calcite Filled Void

    19. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Close-up of Radiaxial and Herringbone Calcite Cement with Grainstone Layer at Base and Enclosure of Microbial Growth Two types of cavities in the microbialite facies, both filled with multiple generations of calcite cement with or without grainstone strata, have been recognized at the LWB Refractories Quarry. The first type formed in response to sediment disruption and occur in strata exhibiting evidence of slumping. They are situated between “jumbled and/or rotated angular blocks of microbialite.” They also are found in areas where erosion or decay processes removed supporting microbialite. The second type are oriented horizontally (see above slide) and are bounded by flat to undulating lower contacts and “irregular, dentate upper surfaces.” Vertical fractures extend through upper cavity boundaries and cross-cut overlying layers. This description of this second type of cavity closely corresponds to stromatacitis described in the literature, although they are generally much larger in scale. It is surmised that the stromatacitis cavities formed via dewatering processes, as enclosing organic matter may consist of up to 99% water (de Wet and Hopkins, 15-18). Two types of cavities in the microbialite facies, both filled with multiple generations of calcite cement with or without grainstone strata, have been recognized at the LWB Refractories Quarry. The first type formed in response to sediment disruption and occur in strata exhibiting evidence of slumping. They are situated between “jumbled and/or rotated angular blocks of microbialite.” They also are found in areas where erosion or decay processes removed supporting microbialite. The second type are oriented horizontally (see above slide) and are bounded by flat to undulating lower contacts and “irregular, dentate upper surfaces.” Vertical fractures extend through upper cavity boundaries and cross-cut overlying layers. This description of this second type of cavity closely corresponds to stromatacitis described in the literature, although they are generally much larger in scale. It is surmised that the stromatacitis cavities formed via dewatering processes, as enclosing organic matter may consist of up to 99% water (de Wet and Hopkins, 15-18).

    20. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Close-up of Radiaxial and Herringbone Calcite Cement (Blue) with Grainstone Layer at Base (Purple) and Enclosure of Microbial Growth (Green)

    21. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Fracture Filled with Secondary Bladed Calcite Crystals

    22. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Grainstone Layer

    23. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Grainstone Layer

    24. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Close-up of Radiaxial and Herringbone Calcite Cement Layer Enclosed by Microbialite

    25. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Cross Bedded Grainstone Strata

    26. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef Cross Bedded Grainstone Strata

    27. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef

    28. LWB Refractories Quarry – In-Situ Pinnacle in East Patch Reef More Calcite Cement and a Gas Escape Structure

    29. LWB Refractories Quarry – Triassic Fanglomerate Exposed Along Quarry Floor Facing South

    30. LWB Refractories Quarry – Triassic Fanglomerate Exposed Along Quarry Floor Facing South

    31. LWB Refractories Quarry – Triassic Fanglomerate

    32. LWB Refractories Quarry – Triassic Fanglomerate Facing North

    33. LWB Refractories Quarry – Fault Contact Between Cambrian Ledger Fm. And Triassic Fanglomerate Facing North

    34. LWB Refractories Quarry – Fault Contact Between Cambrian Ledger Fm. And Triassic Fanglomerate Facing North

    35. LWB Refractories Quarry – Triassic Fanglomerate Note Coarse Dolomite and Limestone Clasts in Fine Hematitic Matrix

    36. LWB Refractories Quarry – Fault Contact Between West Patch Reef and Ooid Shoal Facies Facing South

    37. LWB Refractories Quarry – Fault Contact Between West Patch Reef and Ooid Shoal Facies Facing South

    38. LWB Refractories Quarry – Fault Contact Between Triassic Fanglomerate and Cambrian Ooid Shoal Facies Facing South

    39. LWB Refractories Quarry – Fault Contact Between Triassic Fanglomerate and Cambrian Ooid Shoal Facies Facing South

    40. LWB Refractories Quarry – Void Filling Radiaxial and Herringbone Calcite Cement and Gas Escape Structure Block from West Patch Reef Removed During Blasting; Scale Blocks in Centimeters

    41. LWB Refractories Quarry – Close-Up of Void Filling Radiaxial and Herringbone Calcite Cement and Gas Escape Structure Block from West Patch Reef Removed During Blasting

    42. LWB Refractories Quarry – Close-Up of Void Filling Radiaxial and Herringbone Calcite Cement (Blue-Shaded Area) and Gas Escape Structure (Yellow Circle) Block from West Patch Reef Removed During Blasting

    43. LWB Refractories Quarry – Close-Up Grainstone Layer Block from West Patch Reef Removed During Blasting

    44. LWB Refractories Quarry – View of Ooid Shoal Facies from Quarry Floor Facing South

    45. LWB Refractories Quarry – View of Ooid Shoal Facies from Quarry Floor Facing North; Note Red Hematitic Weathering Products

    46. LWB Refractories Quarry – View of Kinzers Formation Exposure Along North Quarry Wall

    47. LWB Refractories Quarry – View of Kinzers Formation Exposure Along North Quarry Wall

    48. LWB Refractories Quarry – An Amateur Film on High Energy Depositional Systems Double-Click Blue Screen to Play

    49. References and Additional Information

    50. Relevant Abstracts

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