Proceedings Volume: "Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions", New Mexico Geological Society, 2012 Annual Spring Meeting最新文献

{"title":"Trace elements in the Copper Flat porphyry deposit, Hillsoboro mining district, Sierra County, New Mexico","authors":"G. Pruthvidhar, V. McLemore, N. Dunbar","doi":"10.56577/sm-2012.176","DOIUrl":"https://doi.org/10.56577/sm-2012.176","url":null,"abstract":"Copper Flat deposit is a small porphyry copper deposit in the Hillsboro mining district, NM. Copper Flat has proven and probable reserves of 45.5Mt of ore at a reported grade of 0.45% Cu, 0.14g/t Au, 2.3 g/t Ag and 0.0015% Mo. The district consists of Cretaceous andesites surrounded by Paleozoic sedimentary rocks and Quaternary alluvial fan deposits. A quartz monzonite stock (74.93±0.66 Ma) with a breccia pipe is located in the center of the district and a series of latite dikes radiate outwards from the quartz monzonite. The quartz monzonite porphyry and the latite dikes are co-genetic. Replacement deposits, which occur near the porphyry deposit, are also genetically related to porphyry deposit. The Copper Flat porphyry copper deposit consists of Cu, Au, Mo, and Ag disseminations and quartz veins in the breccia pipe. Propagating outward radially from the Copper Flat porphyry are Laramide veins hosted by many of the latite dikes. Chemical analyses range from 8-64,600 ppb Au, 10,000 ppm Pb, and 123->20,000 ppm Zn. As much as130 ppm Te and 3400 ppm Bi also are found. In this study, samples from the Hillsboro district were examined petrographically, and pyrite, chalcopyrite and molybdenite were identified. Samples were then examined by electron microprobe in order to determine the distribution of elements of economic interest. Initial investigation involved qualitative geochemical analysis using wavelength-dispersive scans and chemical maps of 1.5x1.5 cm areas to identify particles with high concentrations of Au, Ag, and Mo. No discrete particles containing Au or Ag were identified, suggesting that either that these elements are present at lower concentrations in other minerals or that particles containing these elements are present at low enough concentrations that they were not present in the scanned area. Following qualitative investigation, quantitative analysis for trace elements was carried out, using long count times in order to obtain detection limits below 100 ppm. The results show detectable Au, Ag, Mo, but Te, Se, Cd, Bi are not detected.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"107 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121876162","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Ar-Ar phlogopite geochronology of the Navajo volcanic field and the Ship Rock diatreme of northwest New Mexico define a 1.4 Ma pulse of potassic magmatism","authors":"J. Nybo, W. Mcintosh, S. Semken","doi":"10.56577/sm-2012.178","DOIUrl":"https://doi.org/10.56577/sm-2012.178","url":null,"abstract":"Newly acquired Ar-Ar phlogopite ages indicate a brief but widespread pulse of magmatism at 25.9 to 24.5 Ma in Navajo Volcanic Field (NVF). Covering approximately 30,000 km2 of the Four Corners region in the southwestern US, the NVF encompasses numerous diatremes, plugs, dikes, and occasional sills and maars including the well-known Ship Rock diatreme. Petrographically the field is dominated by minette and serpentinized ultramafic microbreccia though outcrops of monchiquite, katungite, and olivine melilitite occur as dikes in small numbers. Published K-Ar ages from the NVF range from 33.9 to 19.4 Ma. Phlogopite separates of six dikes from the Shiprock diatreme along with two dikes and two plugs from other locations throughout the NVF were analyzed in this study by the Ar-Ar method using CO 2 laser and resistance furnace incremental heating. The resulting age spectra were generally flat and a selection of the most precise ages range from 25.9 ± 0.1 Ma at Todilto Park, AZ to 24.4 ± 0.1 Ma at Ship Rock, NM. The selected samples spatially represent the full breadth of the NVF and span a range 1.4 Ma. The narrow range of ages found in this study contrasts with the much wider range of published ages implying the bulk of the NVF was emplaced by a short pulse of widespread magmatism rather than series of temporally spaced eruptions. Additional geochronology will assess whether additional eruptive pulses occurred in the NVF.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"10 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126730676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Pennyslvanian strata and Ancestral Rocky Mountain tectonism in Sierra County, New Mexico","authors":"S. Lucas, K. Krainer, W. Nelson, J. Spielmann, F. Cristobal","doi":"10.56577/sm-2012.169","DOIUrl":"https://doi.org/10.56577/sm-2012.169","url":null,"abstract":"Pennsylvanian strata are well exposed in the San Andres, Fra Cristobal, Caballo and Mud Springs Mountains in Sierra County, New Mexico. The oldest of these strata are the Morrowan-Atokan Red House Formation, a mixed siliciclastic-carbonate unit (shale, sandstone and limestone) as much as 50 m thick. The overlying Pennsylvanian lithosome is dominated by cyclically-bedded cherty limestone, nodular limestone and shale, the Atokan-Desmoinesian Gray Mesa Formation (Nakaye Formation and Lead Camp Limestone are unnecessary synonyms) as much as 388 m thick. Member-level subdivisions of the Gray Mesa Formation Elephant Butte, Whiskey Canyon and Garcia members can be recognized in some sections, but not in others, due to substantial lateral facies changes. The youngest Pennsylvanian lithosome is more regionally complex, and is the relatively thin (up to ~63 m at Bar-B Draw) Bar-B (Missourian-Virgilian) and (up to 120 m) Bursum (lower Wolfcampian) formations to the west and the very thick (up to 1000 m) Panther Seep Formation (Missourian-early Wolfcampian) to the east. This lithosome is mixed clastic and carbonate strata within which the Bursum base has a demonstrably disconformable contact on older strata. A comprehensive analysis of lithostratigraphy, facies and biostratigraphy allows us to construct a tectonostratigraphy of the Pennsylvanian strata in Sierra County that identifies three pulses of the ancestral Rocky Mountain (ARM) orogeny: (1) onset of the ARM at about the end of Morrowan time with initial synorogenic Red House clastics deposited unconformably on older Paleozoic strata; (2) a pulse close to the beginning of the Missourian, indicated by basal Missourian conglomerates and/or the relatively thin (locally absent) Missourian section; and (3) a latest Pennsylvanian pulse indicated by the sub-Bursum unconformity. Although eustasy can be invoked to explain some of the stratigraphic architecture of the Pennsylvanian System in Sierra County, much more of it is explicable by ARM tectonism, particularly by a local Caballo uplift (centered near the Derry Hills?) present and tectonically active intermittently during the Pennsylvanian.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"50 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"128171947","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"U-Pb zircon and Sr-isotope constraints on age and contamination of Paleogene volcanic rocks of the Burro Mountains, southwest New Mexico","authors":"T. Jonell, J. Amato, F. Ramos","doi":"10.56577/sm-2012.168","DOIUrl":"https://doi.org/10.56577/sm-2012.168","url":null,"abstract":"","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"365 17","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114087682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vertebrate coprolites from the lower Permian (Lower Wolfcampian) Gallina Well locality, Joyita Hills, Socorro County, New Mexico","authors":"A. Cantrell, T. L. Suazo, J. Spielmann, S. Lucas","doi":"10.56577/sm-2012.159","DOIUrl":"https://doi.org/10.56577/sm-2012.159","url":null,"abstract":"Vertebrate coprolites are the most common trace fossils found at the Lower Permian (middle Wolfcampian) Gallina Well locality in Socorro County, New Mexico (NMMNH locality 4668). Despite the relative abundance of coprolites at the locality, little attention has been paid to the coprolite ichno-assemblage. This ichno-assemblage includes the first occurrence of Dakyronocopros arroyoensis in New Mexico, the earliest appearance of Alococopros triassicus and occurrences of Heteropolacopros texaniensis and amorphous coprolites. The age and faunal associations of Alococopros triassicus from the Gallina Well locality refute earlier assertions that longitudinally-striated coprolite forms were produced by stem archosauromorphs and are restricted to the Mesozoic and Cenozoic Eras.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"48 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"125089818","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Geomorphic Characterization Of The Gilbert River Distributive Fluvial System (Dfs) And Implications For Cretaceous Coastal Fluvial Successions","authors":"K. McNamara, G. Weissmann","doi":"10.56577/sm-2012.222","DOIUrl":"https://doi.org/10.56577/sm-2012.222","url":null,"abstract":"The Gilbert River distributive fluvial system (DFS) of Queensland, Australia, flanks the Gulf of Carpentaria, an epeiric sea that occupies a slowly subsiding intracratonic basin. Approximately 13 km of progradation has occurred over the last 6 ka, largely due to high sedimentation rates, low regional slope, and a slight sea level fall. This system exhibits the same depositional patterns as purely continental DFSs: 1) a radial channel pattern, 2) a down-DFS decrease in both channel and grain size (the latter inferred), 3) a lack of lateral channel confinement, 4) a broad fan shape, and 5) a down-DFS increase in floodplain/channel area. The coastal plain portion (influenced by sea level changes) is characterized by: a) a contact between DFS and marginal-marine deposits, b) channel incision, confinement and lateral movement, c) increased channel width due to tidal influence, d) sediment redistribution (spits, small-scale deltas), and e) evidence of shoreline progradation (wave-cut platforms and beach ridges). Other coastal DFSs are present in passive-margin settings in Australia, India, and Africa. Few modern examples of DFS spanning the terrestrial to marine realm exist, as: 1) modern coastlines are presently flooded due to high-amplitude Quaternary sea level fluctuations, 2) many rivers are incised into large valleys (Mississippi River) or incised into pre-existing coastal DFS deposits (Canterbury Plains of New Zealand, Texas Gulf coastal plain), and 3) anthropogenic modification conceals surface expressions and hinders natural channel behavior (Godhavari River of India). Geomorphic observations on these systems ultimately lead to sedimentologic and stratigraphic predictions regarding coastal DFS deposits that cross the fluvial-marine interface, such as the Cretaceous Williams Fork Formation of Colorado. A purely progradational succession should be characterized by basal shoreface strata cut into by tidally influenced channels, and exhibit an upsection increase in grain size, sand:mud ratios, and channel amalgamation, with a corresponding decrease in tidal influence and coals. The DFS concept may explain common patterns (e.g. upsection changes in sand:mud, sandbody thickness and architecture) observed in Cretaceous rock record examples and is valuable in reservoir modeling at the basin scale.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"75 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130925015","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Investigation of soil pollution sources in the El Paso region using SEM, magnetic susceptibility, and XRF analysis","authors":"J. Tasker, M. Gómez, L. R. Bothern","doi":"10.56577/sm-2012.186","DOIUrl":"https://doi.org/10.56577/sm-2012.186","url":null,"abstract":"In urban area soil pollution is a major concern for the health of residents, development of the land, water usage, and agricultural production. This makes investigation of soils important for maintaining the well-being of people, plants, and animals that reside within the area of study and beyond. In this study, we will investigate soil pollution using three methods: magnetic susceptibility, scanning electron magnification, and x-ray fractionation. Potential sources of pollution in El Paso region include a former artillery range, oil refineries, smelters, power plants, freeways, and other dismantled industry. Magnetic susceptibility is a quick, easy method to detect pollution in soils involving simple sample preparation and provides rapid, repeatable analyses. The iron oxides generated through combustion display high magnetic properties which act as a proxy for heavy metal pollution from the source. The Scanning Electron Microscope (SEM) allows for up to 10,000x magnification of samples and also has an X-ray attachment that allows for elemental analyses of specific sample grains. The X-ray Fractionation instrument available at NMSU will provide us with detailed analyses of trace elements within soil samples. After collection of samples and analysis of data, we hope to better understand processes involved in heavy metal pollution of sample area soils and identify point sources of the pollutants.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"12 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130171181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparison of Miocene tectonism and paleoclimate with rift-basin sedimentation and drainage positions, Espanola Basin, New Mexico","authors":"D. Koning, S. Connell","doi":"10.56577/sm-2012.158","DOIUrl":"https://doi.org/10.56577/sm-2012.158","url":null,"abstract":"We summarize Miocene clastic deposition in the Espanola Basin (EB) and examine how drainage systems may respond to tectonic and paleoclimatic controls. The EB is a half-graben tilted west towards the Embudo–Santa Clara–Pajarito fault system (ESPFS). An arm of the EB, called the Canada Ancha graben (CAG), extends SE away from the ESPFS. A faulted structural platform lies NW of the ESPFS. Syn-rift deposits of the Santa Fe Group are particularly well exposed in the EB, and we could readily map western alluvial slope, central basin floor, and eastern alluvial slope lithofacies assemblages. Abundant tephra and fossils provide exceptional age control. Previous studies documented an increase in ESPFS throw rates at 15-11 Ma and decreased subsidence rates in the CAG after 13.5-13.0 Ma. Paleodrainage changes included: 1) coarsening ca. 13.2 Ma; 2) progressive westward progradation of the eastern alluvial slope during 18-10 Ma and a narrowing of the basin floor, with a particularly rapid advance at 13.5-11 Ma; 3) development of a gravel-bearing ancestral Rio Chama by 12 Ma; and 4) shifting of the axial river onto the northwest structural platform after 11 Ma, at least episodically. The progradation of the eastern alluvial slope is interpreted to be controlled by increased activity along the basin master fault (ESPFS) and slower subsidence in the CAG. Poorly constrained middle Miocene progradation also occurred for eastern alluvial slope deposits in the San Luis Basin to the north, and streams of the western alluvial slope carried coarser bedload at ~14 Ma. These observations imply a paleoclimatic influence for the rapid 13.5-11 Ma progradation, driven by increased discharge and stream competence. Increased precipitation, higher subsidence rates along the ESPFS, and emergence of the nearby Jemez volcanic field perhaps facilitated integration and headward elaboration of streams draining the Colorado Plateau, forming a single river roughly coincident with the location of the modern Rio Chama. High throw rates on a fault west of the ESPFS at 11-8 Ma facilitated the shift of the San Luis Basin-draining, axial river onto the northwest structural platform. But another driver for this westward shift may be larger sediment delivery from streams draining the eastern alluvial slope compared to the western alluvial slope and axial river.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"67 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133415232","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A preliminary geologic map of the Bull Gap quadrangle, Lincoln County, southeastern New Mexico","authors":"K. Zeigler, B. Allen","doi":"10.56577/sm-2012.192","DOIUrl":"https://doi.org/10.56577/sm-2012.192","url":null,"abstract":"The Bull Gap Quadrangle is located in the northern Tularosa Basin, south of Carrizozo and north of Oscura, New Mexico. The topography is primarily low, rolling country with a long hogback of Cretaceous strata trending north-south in the center of the map, and the Carrizozo lava flow trending northeast-southwest across the quadrangle. Exposures of Permian and Cretaceous strata are present in the center of the map area and large tracts of modern alluvium and older fan deposits from the Sacramento Mountains cover bedrock geology to the east. The western one third of the quadrangle lies to the north, south, and east of bedrock uplands and surficial clastic sediments in this area are classified as piedmont deposits with relative age designations based on inset relationships. The Carrizozo lava flow, ~5 ka in age, trends southwest to northeast across the center of the quadrangle. An unnamed Tertiary age (?) conglomerate is locally incised into underlying Cretaceous strata and its base is an angular unconformity with older strata. Tertiary igneous intrusives occur as both sills and dikes and are presumably related to the Oligocene Sierra Blanca volcanic field. Sills observed in the field area are felsic to intermediate in composition and often have porphyritic textures. Dikes in the map area are oriented east-west to southeast-northwest and tend to be short in length (less than 0.75 km). Permian strata in the Bull Gap area include the San Andres Formation and the overlying Grayburg Formation of the Artesia Group, which are overlain by the Lower to Middle Triassic Moenkopi Formation. Cretaceous strata include the Dakota Sandstone that forms the distinctive hogback in the center of the map area, the lower tongue of the Mancos Shale, Tres Hermanos Formation, D-Cross Tongue of the Mancos Shale, Gallup Sandstone and the Crevasse Canyon Formation. The limestones in the lower tongue of the Mancos Shales are the Bridge Creek Beds. Faults in the Bull Gap quadrangle are primarily oblique-slip faults and oriented northwest-southeast to east-west. Both right lateral and left lateral strike slip motion are evident and slickenline lineations observed at a few localities are steeply inclined. A few faults trend north-south to northeast-southwest and appear to be primarily normal faults. These faults are primarily down to the west and are presumably part of the Neogene extensional structural fabric.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"99 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127168128","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"The Distributive Fluvial System (DFS) Paradigm: Re-Evaluating Fluvial Facies Models Based on Observations from Modern Continental Sedimentary Basins","authors":"G. Weissmann, A. Hartley, G. Nichols, L. A. Scuder","doi":"10.56577/sm-2012.224","DOIUrl":"https://doi.org/10.56577/sm-2012.224","url":null,"abstract":"When we think of fluvial systems and associated soils and their preservation in the rock record, we typically draw upon our experiences with tributary rivers which are the most common in the world. Indeed, most facies models that we use to interpret the rock record have been developed on tributary rivers that exist outside active sedimentary basins or, if the river system studied lies within a sedimentary basin, the models developed typically do not place the studied reach into the context of the basin. A review of over 700 modern continental sedimentary basins around the world showed that rivers in active sedimentary basins are generally deposited either (1) as distributive fluvial systems (DFS), variously called megafans, fluvial fans, and even alluvial fans in the literature, or (2) as tributary systems in an axial position that parallel the basin trend or in an interfan area between the large megafans, with the vast majority of sedimentation in the basin occurring on the DFS. In these continental sedimentary basins, we have identified over 400 fluvial megafans (>30km in length), with countless smaller DFS filling the basins. These observations have implications for the interpretation of ancient fluvial deposits and the soils that form on these deposits. Rivers on DFS differ from rivers in degradational settings in many, potentially significant ways, including (1) a radial pattern of channels away from an apex (or intersection point) exists on DFS, (2) channel systems commonly decrease in width and discharge and thus cross-sectional area distally, (3) rivers on DFS do not lie within valleys unless the system is in an incised phase, (4) meanderbelts tend to be more laterally mobile on the open DFS, forming “simple” meanderbelts rather than “amalgamated” meanderbelts during aggradational phases on the DFS, (5) floodplain deposits on DFS are often dominated by avulsion deposits, especially in distal portions of the DFS, (6) greater preservation of floodplain deposits appears to occur on DFS dominated by braided streams than found in braided streams of tributary systems, and (7) axial streams in a basin, if confined laterally, and rivers that are incised into the DFS appear to be similar in character to tributary systems. We also expect soil morphology to vary with position on DFS, with different soil types found in proximal, medial, and distal locations as well as laterally away from the active channel belt. Additionally, cycles of incision and aggradation should develop characteristic soil distributions. We believe that this alternative view to fluvial facies distributions can lead to advances in facies distribution prediction based on paleosol character and channel belt geometries on DFS.","PeriodicalId":240412,"journal":{"name":"Proceedings Volume: \"Evaluating How Continental Sedimentary Basins Fill: Development and Preservation of Sedimentary Successions\", New Mexico Geological Society, 2012 Annual Spring Meeting","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2012-04-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129763186","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}