30 research outputs found
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Arizona Geology Newsletter v.42 no.2 - Summer 2021
Summer newsletter of the Arizona Geological Survey, 11 pages. Lead article: Updates on the AZGS Geologic Mapping Program by C.A. Richardson and P.A. Pearthree.Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Arizona Geology Newsletter v.42 no.3 - Winter 2021
The winter Arizona Geology newsletter includes the following: Recent Earthquakes Highlight Seismic Hazards in Southeastern Arizona by P.A. Pearthree and J.Y. Ben-Horin; 2001 Monsoon Rains hit Cochise County earth fissures the hardest by J.P. Cook; Arizona Mining Production & Employment 2020: At a Glance; New, Pending, and Revised Publications by AZGS Staff; Happy Holidays 2020 AZGS Staff PictureDocuments in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Geologic Map of Cornville 7.5' Quadrangle, Yavapai County, Arizona
Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Geologic Map of Clarkdale 7.5' Quadrangle, Yavapai County, Arizona
This map depicts the geology of the Clarkdale 7 ½‘ quadrangle in northwestern Verde Valley. The bedrock geology depicted on the map is slightly modified from DeWitt et al. (2008), and surficial and basin deposit mapping is modified from House and Pearthree (1993). Detailed mapping of deposits associated with the Verde River by Cook et al. (2010) is included in the map as well. This new Arizona Geological Survey Digital Geologic Map (DGM) product integrates all of these data sets and makes them available in a variety of digital formats. The map consists of bedrock geology, a moderately detailed depiction of basin deposits (Verde Formation) and the distribution of piedmont alluvial deposits of different ages and their associated geomorphic surfaces, and a strip of Verde River deposits of various ages. Rough age estimates are assigned to each alluvial unit based primarily on relative topographic position and surface and soil characteristics, with limited numerical age constraints that are discussed below. Geologic structures in the bedrock units other than the principal traces of the Verde Fault are not included in these maps. The following is a summary of the geology of the Clarkdale quadrangle, including the Plio-Quaternary evolution of northern Verde Valley derived in part from mapping in adjacent quadrangles. Bedrock units predominate in the western and northernmost parts of the quadrangle. These rocks consist primarily of Mississippian Redwall Limestone, Pennsylvanian Supai Formation, and Pennsylvanian-Permian Hermit Shale, with smaller outcrops of Devonian Martin Formation, Cambrian Tapeats Sandstone, and Proterozoic metasedimentary and metavolcanics basement. Bedrock is overlain, and locally in fault contact with, Miocene volcanic rocks and associated sediments (probably part of the Hickey Formation), and Verde Formation deposits. Exposures of limestone and fine- to coarse-grained siliciclastic deposits of the Verde Formation are widespread in the quadrangle. The Verde Formation was deposited as normal faulting along the base of the Black Hills dropped the valley down. Some of the highest preserved remnants of Verde Formation deposits are found in the Clarkdale quadrangle, up to ~1380 m above sea level on the south flank of Black Mountain near the north edge of the quadrangle. The age of maximum filling of Verde Valley was ~2.5 Ma based on paleomagnetic stratigraphy (Bressler and Butler, 1978); eroded ridges in the Jerome area are capped with thin remnant alluvial fan deposits that are poorly-preserved vestiges of this period. Subsequent river downcutting apparently has been episodic, with river terraces and piedmont alluvial surfaces graded to them representing intervals of stability or minor aggradation. Multiple early to middle Pleistocene river terraces exist in the valley axis (e.g., Qo1r, Qi1r); we map 3 early Pleistocene river terraces and 3 middle to late Pleistocene terraces; the highest terraces are 90-100 m above the modern river channel, and thus are inset far below the maximum level of Verde Formation deposition. Thus roughly 70% of Verde River downcutting had occurred prior to Qo deposition. The extent of Holocene deposits is quite limited except in the Verde River floodplain and low terraces, and tributary alluvial fans graded to the Holocene river. Splays of the Verde fault zone, which separates the bedrock of the Black Hills from the basin deposits of Verde Valley, In some areas there are clearly multiple fault strands, and there are almost certainly more fault strands that are not exposed. There is, however, no clear evidence of displacement of Quaternary surficial deposits along this part of the Verde fault zone. Flood hazards?Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Geologic Map of Cottonwood 7.5' Quadrangle, Yavapai County, Arizona
This map depicts the geology of the Cottonwood 7 ½‘ quadrangle in Verde Valley and the Black Hills of north-central Arizona. This bedrock geology of this area was previously mapped by Anderson and Creasey (1967), and surficial and basin deposits were mapped by House and Pearthree (1993). Deposits associated with the Verde River were mapped in detail by Cook et al. (2010). This new Arizona Geological Survey Digital Geologic Map (DGM) product integrates all of these data sets and makes them available in a variety of digital formats. The map consists of a generalized representation of the bedrock geology, a fairly detailed depiction of basin deposits (Verde Formation), a careful depiction of the distribution of piedmont alluvial deposits of different ages and their associated geomorphic surfaces, and a relatively limited strip of Verde River deposits. Preliminary age estimates are assigned to each alluvial unit based primarily on relative topographic position and surface and soil characteristics, with limited numerical age constraints that are discussed below. Geologic structures in the bedrock units other than the principal traces of the Verde Fault are not included in these maps. This map contains a wealth of geological information concerning the effects of long-term incision of the Verde River on the surrounding landscape and impacts of Quaternary climatic fluctuations on piedmont tributary drainage systems and the Verde River. Evident in these maps is the strong influence of drainage basin and substrate lithology on the evolution of the regional landscape and the persistence of landforms. In addition, the maps contain information relevant to the distribution and character of flood hazards and potential soil problems. The following is a summary of the Quaternary evolution of northern Verde Valley, with substantial evidence drawn from the Cottonwood quadrangle and adjacent Cornville and Clarkdale quadrangles. During the Quaternary the Verde River has downcut at least 300 m into the basin fill deposits of the Verde Formation. The age of maximum filling of Verde Valley was ~2.5 Ma based on paleomagnetic stratigraphy (Bressler and Butler, 1978); a very high remnant alluvial fan surface in the uppermost piedmont near the Black Hills in this map area is the best-preserved vestige of this period. Subsequent river downcutting apparently has been episodic, with river terraces and piedmont alluvial surfaces graded to them representing intervals of stability or minor aggradation. Multiple early to middle Pleistocene alluvial packages (e.g., Qo1, Qi1) can be traced to the valley axis near the modern Verde River in the Cornville quadrangle. The base of Qo1 deposits is about 50 m higher than the modern river near the modern Verde River – Oak Creek confluence. Less than 2 km upstream along the river, the base of Qi1 deposits, which locally contain the 767 ka Bishop Tuff (Crowley et al., 2007), is ~10 m higher than the modern river. Thus, roughly 80% of Verde River downcutting had occurred prior to Qo deposition, and 95% had occurred prior to middle Pleistocene time (780 ka). The middle and late Pleistocene and Holocene have been characterized by periods of substantial aggradation and incision. For example, Qi1 deposition filled several moderately deep tributary paleovalleys cut into Verde Formation deposits, and Qi1 piedmont deposits were graded to and aggrading Qi1r river deposits. Subsequent periods of major tributary and river aggradation almost certainly filled in erosional topography as well. All of this activity has occurred within a landscape framework formed by early and early middle Pleistocene deposits and eroded Verde Formation deposits, however, and net incision has been minor. The extent of Holocene deposits is quite limited except in the Verde River floodplain and low terraces, and tributary alluvial fans graded to the Holocene river. The Verde fault zone, which separates the bedrock of the Black Hills from the basin deposits of Verde Valley, bisects the quadrangle from southeast to northwest. In many areas, the contact between basin deposits and bedrock is quite sharply defined – the approximate location of the fault zone. In some areas there are clearly multiple fault strands, and there are almost certainly more fault strands that are not exposed. There is, however, no clear evidence of displacement of Quaternary surficial deposits along this part of the Verde fault zone. Flood hazards?Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Geologic Map of Page Springs 7.5' Quadrangle, Yavapai County, Arizona
This map depicts the geology of the Page Springs 7 ½‘ quadrangle in northwestern Verde Valley. The bedrock geology depicted on the map is simplified from Holm (2015), and surficial and basin deposit mapping is modified from House and Pearthree (1993). Detailed mapping of deposits associated with the Verde River and Oak Creek by Cook et al. (2010a; 2010b) is included in the map as well. This new Arizona Geological Survey Digital Geologic Map (DGM) product integrates all of these data sets and makes them available in a variety of digital formats. The map consists of bedrock geology, a moderately detailed depiction of basin deposits (Verde Formation) and the distribution of piedmont alluvial deposits of different ages and their associated geomorphic surfaces, and a strip of Oak Creek deposits of various ages. Rough age estimates are assigned to each alluvial unit based primarily on relative topographic position and surface and soil characteristics, with limited numerical age constraints that are discussed below. The following is a summary of the geology of the Page Springs quadrangle, including the Plio-Quaternary evolution of northern Verde Valley derived in part from mapping in adjacent quadrangles. Bedrock units predominate in the northernmost and eastern parts of the quadrangle. These rocks consist of Pennsylvanian Supai Formation, Pennsylvanian-Permian Hermit Shale, and Permian Schnebly Hill Formation. Bedrock is overlain by, and locally in fault contact with, Miocene volcanic rocks and Pliocene Verde Formation deposits. Exposures of limestone and fine- to coarse-grained siliciclastic deposits of the Verde Formation are widespread in the quadrangle. Some of the highest preserved remnants of Verde Formation deposits are found in the Clarkdale quadrangle, up to ~1340 m above sea level near the northwest corner of the quadrangle. The age of maximum filling of Verde Valley was ~2.5 Ma based on paleomagnetic stratigraphy (Bressler and Butler, 1978); eroded ridges in the Jerome area are capped with thin remnant alluvial fan deposits that are poorly-preserved vestiges of this period. Subsequent river downcutting apparently has been episodic, with river terraces and piedmont alluvial surfaces graded to them representing intervals of stability or minor aggradation. Multiple early to middle Pleistocene river terraces exist in the valley axis (e.g., Qo1r, Qi1r); we map 3 early Pleistocene river terraces and 3 middle to late Pleistocene terraces; the highest terraces are 90-100 m above the modern river channel, and thus are inset far below the maximum level of Verde Formation deposition. Thus roughly 70% of Verde River downcutting had occurred prior to Qo deposition. The extent of Holocene deposits is quite limited except in the Verde River floodplain and low terraces, and tributary alluvial fans graded to the Holocene river. Splays of the Verde fault zone, which separates the bedrock of the Black Hills from the basin deposits of Verde Valley, In some areas there are clearly multiple fault strands, and there are almost certainly more fault strands that are not exposed. There is, however, no clear evidence of displacement of Quaternary surficial deposits along this part of the Verde fault zone. Flood hazards?Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Fate of Arizona’s Premier Physical Mining Data Archive
This report documents in-brief the history and fate of the Arizona Mine Data Archive from its earliest days involving collection and curation by the Arizona Department of Mines and Mineral Resources (ADMMR) (1940-2010); to transfer, digitization, and uploading to the Arizona Geological Survey (AZGS) Mine Data website (2011-2016); to a permanent home with the Arizona Historical Society (2021-2022).Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Plio-Quaternary Faulting and Seismic Hazard in the Flagstaff Area, Northern Arizona
Historical seismic activity and the geologic record of young faulting both suggest that there is significant seismic hazard in the Flagstaff area. Geologic investigations of young faults provide information about large prehistoric earthquakes in an area, which can be used with the historical seismic record to evaluate the potential for damÂaging earthquakes. In this report, we provide a perspective on seismic hazard in the Flagstaff area based primarily on geologic assessments of the potentially active faults in the area. Much of our effort was devoted to a detailed paleoseismologic investigation of the Bellemont fault west of FlagÂstaff. We augmented this study with a reconnaisÂsance survey of other faults in the area that have been active during the past 5 million years. This fault data was integrated into several alternative probabilistic assessments of seismic hazard in the Flagstaff area. The Bellemont fault is an active fault capable of producing large earthquakes. The magnitude of the youngest surface-rupturing earthquake on the fault was probably 6.6 to 6.9, which may be characteristic of previous surface ruptures on the fault. The average slip rate during the past 300,000 to 700,000 years is between 0.015 to 0.04 m/ky (ky means thousands of years).Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Detailed Geologic and Geomorphic Mapping and Characterization of the Lake Mary Fault Zone
The Lake Mary Fault System (LMFS) is located in Flagstaff, Arizona. Prior to this study, much was unknown related to its slip rate or whether the fault system was still active. The LMFS is a 30-45km long set of normal faults and multiple splays that displace Pliocene-Quaternary lava flows and sediments. Detailed mapping efforts identified offset lava flows, two of which are Quaternary in age, and resulted in the discovery of less active fault strands in the southern portion of the mapping area. In addition, detailed mapping provided the geologic constraints for locating potential paleoseismic sites. The LMFS has segments that have been active for several million years and have a complex faulting history that has resulted in dense fracturing of bedrock, reactivation of older reverse and normal faults, much of which have little vertical offset. The Lake Mary fault which is considered the active strand of the LMFS appears to be a normal fault with near vertical dip and a strike that varies from N60W to N-S. The main trace of the Lake Mary fault has up to 40m of vertical offset of a colluvial deposit with clasts from a Quaternary basaltic lava flow, dated for this study with 40Ar/39Ar at 1.17Ma old. Geochemical analyses of volcanic clasts found in the Lake Mary fault footwall corroborated the hand identification showing the clasts’ originating from the Qbwc flow. The clasts were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS) for Rare Earth Elements (REEs). ICP-MS data infer 3 different rock types for the 12 samples. Slip rate estimates were calculated using 40Ar/39Ar dates obtained for this study and the vertical offset measurements of Tob (5.9Ma) and Qbwc (< 1.17Ma) for a slip rate range of 0.022mm/yr to 0.035mm/yr.Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]
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Recency and size of young displacements along the Mead Slope fault, Lake Mead Area, Arizona
The Mead Slope fault (MSF) has been considered an active late Quaternary fault for several decades; however, until this study, there have been weak constraints on slip rates, and the age and size of surface-rupturing earthquakes. We used high-resolution DEMs generated from multiple drone flight and ground-control points and aerial imagery to map the fault in detail. We determined that the fault consists of two main strands, both offsetting Quaternary alluvial fan remnants. The northwestern strand offsets late to latest Pleistocene fan deposits, as well as relatively young tributary gravel deposits exposed below a wave-cut bench associated with past high levels of Lake Mead. Examination of this exposure revealed 3 identifiable surface ruptures. Based on Optically-Stimulated Luminescence dating (OSL), the latest two events occurred within the last ~25,000 yrs to 60,000 yrs. In addition, we collected 18 3He cosmogenic surface rock samples to date various Quaternary landforms displaced by the fault. Sampling efforts for the cosmogenic dates were focused on early to middle Pleistocene landforms due to the high age inheritance of the younger fan surfaces. We tentatively estimate the slip rate to range from 0.06mm/yr to 0.13mm/yr based on amount of offset of Qi3-4 channels and the correlation of the soil ages from the wave cut exposure.Documents in the AZGS Documents Repository collection are made available by the Arizona Geological Survey (AZGS) and the University Libraries at the University of Arizona. For more information about items in this collection, please contact [email protected]