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At least 631 records · Page 35Linked to original sources
USGS2010

Devonian and carboniferous arcs of the oyu tolgoi porphyry Cu-Au district, South Gobi region, Mongolia

The Central Asian orogenic belt consists of microcontinental blocks and mobile belts positioned between the Siberian craton and the Tarim and North China cratons. Extending across Asia for 5000 km, the belt consists of terranes that decrease in age southward away from the Siberian craton. A time-stratigraphic-structural sequence for the rocks is critical to defining the tectonic evolution of the belt. In the Oyu Tolgoi area of the South Gobi Desert (Mongolia), Devonian and Carboniferous rocks record the construction of multiple arcs, formation of a giant porphyry Cu-Au system, exhumation, and polyphase deformation. The oldest rocks are basaltic volcanic and subvolcanic rocks of the Devonian Alagbayan Group intruded by Late Devonian quartz monzodiorite stocks and dikes, which host giant porphyry Cu-Au deposits. The rocks were exhumed, overlain by pyroclastic rocks, and then tectonically buried by marine mafic supracrustal rocks prior to the youngest Devonian granodiorite intrusions. The postmineral Carboniferous Gurvankharaat Group unconformably overlying the deformed terrane consists of effusive, pyroclastic, subvolcanic and volcaniclastic rocks, as well as sedimentary units. The supracrustal rocks underwent polyphase shortening after 330 Ma and prior to 290 Ma. Variations in stratigraphic sequences suggest that the region is underlain by a submarine arc that became emergent during the Upper Devonian and remained subaerial to shallow subaqueous through much of the Carboniferous. Xenocrystic zircons in igneous rocks suggest that the offshore arcs were sufficiently close to ancient crust to have interacted with detritus shed into marine basins, most likely from the Siberian craton and fringing early Paleozoic terranes. ?? 2011 Geological Society of America.

Geological Society of America Bulletin↗
USGS2003

Stratigraphic inferences derived from borehole data of Tertiary basin-filling rocks of the Pahrump Valley basin, Nevada and California

This report summarizes the results from the compilation and interpretation of lithologic information from 266 driller?s logs from the Pahrump Valley, NV-CA. Borehole records for the Pahrump Valley were selected from a total of several thousand available well logs as those having lithologic data and high confidence in the well locations. Driller?s descriptions were reduced into one of 14 lithologic categories to produce a set of subsurface data that were internally consistent and amenable to contouring. Using the lithologic descriptors, the aggregate thickness of general lithologic types (coarse grained material, fine grained material, limestone, and volcanic material) were computed for each borehole. These data were used to compute ratios such as percent coarse-grained component of sedimentary rocks penetrated in each borehole that could be contoured.

Open-File Report↗
USGS1999

Integrated use of continuous seismic-reflection profiling and ground-penetrating radar methods at John's Pond, Cape Cod, Massachusetts

Continuous seismic-reflection profiling (CSP) and ground-penetrating radar (GPR) surveys were conducted by the U.S. Geological Survey in April 1998 over the northern part of John’s Pond, a glacial kettle pond southeast of Otis Air National Guard Base, Cape Cod, Massachusetts. The surveys were conducted to delineate the types and thickness of sedimentary units that may control the infiltration of contaminated groundwater into John’s Pond. Sand-and-gravel deposits, collapse features and recent organic sediments were imaged with the CSP and GPR methods. Hummocky to chaotic reflections were interpreted as sand- and-gravel deposits. Slightly wavy, parallel reflections located in depressions in the sand-and- gravel deposits were interpreted as filled collapse features. Lower amplitude, horizontal, laminar reflections were interpreted as organic sediments. Entrapped methane gas within some of the organic sediments created a reflection zone that obscured deeper reflections in the CSP records. The CSP and GPR methods provide complementary information over most of the surveyed part of the pond. The methods detect similar interfaces, but a particular interface may produce a stronger reflection in one record than in the other. For example, regions of the pond containing organic sediments with entrapped methane gas, which prevent penetration of the acoustic signal, were penetrated and imaged by GPR. Conversely, regions of the pond containing electrically conductive sediments or deep water, which attenuate the GPR signal, were imaged using CSP. The CSP and GPR data were interpreted to generate a bathymetric map and a map of sediment type and thickness beneath John’s Pond.

Massachusetts↗
USGS2026

The Great Salt Lake (Utah, USA) acoustic and sedimentary archive of Wasatch Front earthquakes

As the largest low-relief basin in the western United States, the Great Salt Lake offers an opportunity to explore acoustic and sedimentary archives of earthquake ruptures in a shallow terminal basin. Here, we use subbottom compressed high intensity radiated pulse (Chirp) profiles and sedimentary cores to address questions related to how Great Salt Lake sediments respond to surface rupture and earthquake shaking and whether the lake is sensitive to both Great Salt Lake fault (GSLF) and Wasatch fault zone (WFZ) earthquakes. Chirp profiles reveal laterally continuous seismic stratigraphy with vertically displaced strata, onlap surfaces, and growth stratigraphy produced by GSLF surface ruptures. We identify and date two ruptures on the Fremont Island section and three on the Antelope Island section; temporal overlap of these ruptures supports synchronous rupture of both sections. Combined with previous data, our results yield a record of four Holocene surface-rupturing (M W 6.9−7.3) earthquakes on the GSLF with a mean recurrence of ∼3.2 k.y. Sediment cores include ≤41-cm-thick, massive, homogeneous to normally graded disturbance beds that interrupt laminated bioclastic sediment. Disturbance bed correlations yield four lacustrine earthquake deposits since ca. 1.7 ka; the youngest possibly records the most recent GSLF surface rupture whereas older deposits were likely produced by WFZ earthquakes. Modeled historical earthquakes yield a Great Salt Lake sediment disturbance shaking threshold of MMI ∼VI, controlled in part by the lake-bottom expression of the GSLF scarp. Our integration of primary (fault-related) and secondary (shaking-related) earthquake evidence improves our understanding of sediment disturbance processes and the archival potential of low-relief lake basins.

Utah↗
USGS2009

Photomosaics and logs of trenches on the San Andreas Fault near Coachella, California

The Coachella paleoseismic site is located on the San Andreas Fault along the northeast edge of the Coachella Valley in southern California east of Dillon Road and south of Avenue 44. Three benched trenches, a total of more than 950 m, were excavated across the fault zone as part of an Alquist-Priolo fault investigation study. These trenches exposed a thick section of latest Holocene lacustrine, fluvial, and shoreline deposits. Only the central and eastern trenches exposed faulting so we confined our investigations to those two trenches. In the central trench, we photographed and logged in detail both walls of about 70 m of the trench where it spanned several zones of complex faulting which form a 15-m-wide depression. After carefully cleaning the trench walls, we put up a 1- by 0.5-m string- and nail-grid. We photographed each 1- by 0.5-m panel individually and then photologged features directly on these unrectified photos. The photos were digitally rectified later to remove distortion caused by irregularities in the trench walls and to correct the slight distortion introduced by the camera lens. The rectified photos were spliced together to make photomosaics of the trench walls. Most of the field linework and descriptions were then transferred to the rectified photomosaics. For the eastern trench, we took a set of overview photographs of the full length (about 200 m) of each wall. These photographs were taken from the top of the trench towards the opposite wall. Because the photographs were taken at a downward angle, there is significant distortion. We logged directly on these photos in the field, recording significant contacts, primarily between lacustrine and subaerial deposits, along with descriptions. For this report, we spliced together these unrectified overview photos and transfered field linework and some descriptions. For both trenches, contacts and lithologhic descriptions of stratigraphic units, faults and carbon sample locations are indicated on the photomosaics. Lacustrine deposits are tinted to better show deformation across the fault zones. Evidence for six paleoearthquakes rated as “probable” is indicated with red stars that contain the sequential event number (1 is most recent event). Evidence for two additional “possible” paleoearthquakes is indicated with blue stars. The sedimentary deposits contain abundant dateable material which includes detrital charcoal, lenses of organic material formed in-situ, and shells. Two organic fractions, humic acids and acid-alkali-acid-pretreated (AAA), were dated for 13 of 15 samples taken from organic layers and both dates are shown for these samples on the photomosaics and tables 1 and 2. All radiocarbon dates are in 14 C years B.P. (considered to be A.D. 1950). Horizontal distance is measured along the trenches from the southwest ends of the logged exposures (marked as 0 m), and depth is measured from the highest points on the ground surface within the logged exposures. Bench locations are indicated by white lines and gaps in the photomosaics. Note that faults and contacts that are somewhat oblique to the trench walls occasionally appear disconnected owing to the approximately 1 m width of the benches.

California↗
USGS2019

Holocene sedimentary architecture and paleoclimate variability at Mono Lake, California

Mono Lake occupies an internally drained basin on the eastern flank of the Sierra Nevada, and it is sensitive to climatic changes affecting precipitation in the mountains (largely delivered in the form of snowpack). Efforts to recover cores from the lake have been impeded by coarse tephra erupted from the Mono Craters, and by disruption of the lake floor due to the uplift of Paoha Island ~300 yr ago. In this study, we describe the stratigraphy of cores from three recent campaigns, in 2007, 2009, and 2010, and the extents and depths of the tephras and disturbed sediments. In the most successful of these cores, BINGO-MONO10-4A-1N (BINGO/10-4A, 2.8 m water depth), we used core stratigraphy, geochemistry, radiocarbon dates, and tephrostratigraphy to show that the core records nearly all of the Holocene in varying proportions of detrital, volcanic, and authigenic sediment. Both the South Mono tephra of ca. 1350 cal yr B.P. (calibrated years before A.D. 1950) and the 600-yr-old North Mono–Inyo tephra are present in the BINGO/10-4A core, as are several older, as-yet-unidentified tephras. Laminated muds are inferred to indicate a relatively deep lake (³10 m over the core site) during the Early Holocene, similar to many records across the region during that period. The Middle and Late Holocene units are more coarsely bedded, and coarser grain size and greater and more variable amounts of authigenic carbonate detritus in this interval are taken to suggest lower lake levels, possibly due to lower effective wetness. A very low lake level, likely related to extreme drought, is inferred to have occurred sometime between 3500 and 2100 cal yr B.P. This interval likely corresponds to the previously documented Marina Low Stand and the regional Late Holocene Dry Period. The BINGO/10-4A core does not preserve a complete record of the period encompassing the Medieval Climate Anomaly, the Little Ice Age, and the historical period, probably due to erosion because of its nearshore position.

Califiornia↗
USGS1985

Quaternary sedimentation of the Alaskan Beaufort shelf: Influence of regional tectonics, fluctuating sea levels, and glacial sediment sources

The offshore stratigraphy of the Quaternary Gubik Formation of Arctic Alaska has been studied on high-resolution seismic profiles with a maximum sub-seafloor penetration of about 100 m. In general, marine transgressive subunits of the Gubik Formation are wedge-shaped on the shelf, thickening slightly seaward to the shelf break, beyond which they are offset by landslides and slumps. Beneath the eastern third of the Alaskan Beaufort shelf, active folding has created two persistent structural depressions, the Eastern and Western Wedge Terranes, in which the wedge morphology is especially well developed. The youngest transgressive marine wedge, which was deposited in such a way as to fill these depressions, leaving a generally flat present-day shelf surface, is inferred to be late Wisconsin or younger in age because it overlies a prominent disconformity interpreted to have been formed during the late Wisconsin glacial sea-level minimum. The thickness of this youngest wedge, Unit A, locally exceeds 40 m on the outer shelf, yet apparently relict gravel deposits collected from its seabed surface indicate that the depositional rate is presently quite low on the middle and outer shelf. Lithologies of the gravels are exotic to Alaska, but similar to suites exposed in the Canadian Arctic Islands. These observations suggest a depositional scenario in which the retreating Laurentide Ice Sheet shed sediment-laden icebergs from the Canadian Arctic Islands into the Arctic Ocean following the late Wisconsin glacial maximum. These bergs were then rafted westward by the Beaufort Gyre and grounded on the Alaskan shelf by northeasterly prevailing winds. Especially large numbers of bergs accumulated in the wedge terrane embayments-created as sea level rose-and melted there, filling the embayments with their sedimentary cargo. As glacial retreat slowed, depositional rates on the shelf dwindled. This mode of deposition in the Alaskan Beaufort wedge terranes may be typical of early post-glacial transgressive phases throughout Quaternary time. It has resulted in the preservation of disconformities that apparently formed during glacioeustatic lowstands, and whose seaward termination depths, appropriately corrected, may yield estimates of lowstand magnitudes. Knowledge of global sea-level fluctuations back through the Sangamon Interglacial (oxygen isotope stage 5e) and possible correlations with dated onshore deposits have facilitated a tentative correlation of major disconformities in the Beaufort Sea record with major 18O enrichment maxima in the oxygen isotope curve back through stage 8. In this tentative scheme, close similarities between the two data sets occur both in magnitudes and in numbers of fluctuations intervening between major correlation points. Further testing of the Quaternary depositional model suggested here and of the resulting sea level curve awaits the collection and dating of core samples from the Beaufort wedge terranes.

Alaska↗
USGS1988

Seismic stratigraphy and late Quaternary shelf history, south-central Monterey Bay, California

The south-central Monterey Bay shelf is a high-energy, wave-dominated, tectonically active coastal region on the central California continental margin. A prominent feature of this shelf is a sediment lobe off the mouth of the Salinas River that has surface expression. High-resolution seismic-reflection profiles reveal that an angular unconformity (Quaternary?) underlies the entire shelf and separates undeformed strata above it from deformed strata below it. The Salinas River lobe is a convex bulge on the shelf covering an area of approximately 72 km 2 in water depths from 10 to 90 m. It reaches a maximum thickness of 35 m about 2.5 km seaward of the river mouth and thins in all directions away from this point. Adjacent shelf areas are characterized by only a thin (2 to 5 m thick) and uniform veneer of sediment. Acoustic stratigraphy of the lobe is complex and is characterized by at least three unconformity-bounded depositional sequences. Acoustically, these sequences are relatively well bedded. Acoustic foresets occur within the intermediate sequence and dip seaward at 0.7° to 2.0°. Comparison with sedimentary sequences in uplifted onshore Pleistocene marine-terrace deposits of the Monterey Bay area, which were presumably formed in a similar setting under similar processes, suggests that a general interpretation can be formulated for seismic stratigraphic patterns. Depositional sequences are interpreted to represent shallowing-upwards progradational sequences of marine to nonmarine coastal deposits formed during interglacial highstands and/or during early stages of falling sea level. Acoustic foresets within the intermediate sequence are evidence of seaward progradation. Acoustic unconformities that separate depositional sequences are interpreted as having formed largely by shoreface planation and may be the only record of the intervening transgressions.

Marine Geology↗
USGS1989

Geologic map of the Latir Volcanic Field and adjacent areas, northern New Mexico

This map was first published as a printed edition in 1989. The geologic data have now been captured digitally and are presented here along with images of the printed map sheet and component parts as PDF files. This map encompasses all or parts of ten 7.5 minute quadrangles in the Taos Range of the Sangre de Cristo Mountains in northern New Mexico. Geologic mapping was initiated in this area by the U.S. Geological Survey in response to its mandate under the Wilderness Act of 1964 to evaluate the mineral resource potential of the Latir and Wheeler Peak Wildernesses and the Columbine-Hondo Wilderness Study Area in the Carson National Forest. The mapping was later extended to adjacent areas in order to better understand the regional geology and geologic history of the range. The present map focuses on the early Tertiary (largely Oligocene) Latir Volcanic Field and plutonic rocks associated with it. The basement rocks in the map area are Paleoproterozic amphibolite-facies metasedimentary and metavolcanic rocks intruded by large bodies of quartz monzonite, granodiorite and gabbro dated at between 1,750 and 1,690 Ma. The basement rocks are locally overlain by Mississippian limestone or by Pennsylvanian and Permian redbeds. The basement rocks were thrust eastward across a thick section of similar late Paleozoic rocks along low-angle faults during the Laramide Orogeny. Post-Laramide erosion largely removed the sedimentary cover from the basement rocks and reduced the topography to a low-relief surface locally overlain by scattered lenses of Eocene to Oligocene shale, sandstone, and conglomerate. It was on this surface that the earliest rocks of the Latir Volcanic Field were deposited, beginning in the Oligocene, about 30 Ma. The early volcanic rocks comprise a thick sequence of andesite, dacite, and minor rhyolite, deposited as flows, breccia, and volcaniclastic sediments from numerous local volcanic centers; thin layers of rhyolite tuff are from distant eruptions, some probably in the San Juan Mountains. These volcanic rocks probably record early growth of an upper-crustal batholith. At 25 Ma enormous eruptions of peralkaline rhyolite ash-flow tuff were accompanied by collapse of the roof of the growing batholith to form the Questa Caldera, a volcanic depression at least 14 km across. The ash flows traveled for tens of kilometers from the caldera rims to form a widespread sheet of densely welded tuff; ash also fell back to fill the subsiding caldera depression. Concurrent extension along northwest-trending faults segmented the volcanic edifice and rotated the originally sub-horizontal layers, so that some are nearly vertical. Formation of the caldera was accompanied by further batholith growth, involving intrusion of large plutons of granite, granodiorite, and related rocks into both caldera fill and the adjacent rocks, including both the earlier volcanic rocks and the basement rocks. The large molybdenum deposit along the Red River east of Questa is related to the emplacement of one of these late granitic plutons. Intrusive activity continued into the Miocene. Development of the Rio Grande Rift beginning at about 15 Ma was accompanied by development of the north-south trending normal faults along the western foot of the Taos Range. The rift is filled with thousands of meters of clastic sediments interleaved with basalt flows, some as young as 3.6 Ma. The bounding faults of the rift cut the Questa Caldera so that the western part of the original structure is now deeply buried beneath the rift fill.

New Mexico↗
USGS1980

Modern sedimentary facies of the open Pacific coast and Pleistocene analogs from Montery Bay, California

Depositional processes and sedimentary structures of wave-dominated Pacific coastal environments vary systematically with water depth. The depth-limited open-coast facies identifiable by their sedimentary structures are the inner shelf, barred or nonbarred nearshore, beach, and coastal dune facies. These facies are most commonly preserved in shallowing-upward progradational sequences. The vertical sequence of sedimentary structures preserved in marine terrace deposits in the northern Monterey Bay region is very similar to that predicted on the basis of the modern facies. Few marine sediments deposited during the marine transgression that accompanied rising sea level were preserved. Most of the the marine and eolian sediments form a progradational sequence deposited mainly during intervals of falling sea level. In contrast, the sediments that form the adjacent fluvial terraces were deposited mainly during periods of rising sea level and became entrenched during the subsequent lowering of sea level. In combination, these fluvial, marine, and eolian deposits provide a record of a complete eustatic cycle. The recognition of the role of changing sea level in controlling patterns of coastal sedimentation and landform development during the Quaternary allows the development of a generalized model for Quaternary sedimentation along a wave-dominated coastline. The application of this model has aided in the interpretation of older Pleistocene sediments in the region (e.g. the Aromas Sand). It also has resulted in the recognition of at least eleven glacio-eustatic cycles preserved in the stratigraphic record of the Monterey Bay area during the Quaternary.

California↗
USGS1999

Laramide to Holocene structural development of the northern Colorado Front Range

The Rocky Mountain province of the United States is a classic basement-involved foreland orogen. Deformation during the Late Cretaceous to Eocene Laramide orogeny created an anastomosing system of basement-cored arches that bound the northern and eastern margins of the Colorado Plateau and the elliptical sedimentary basins of the Rockies. The tectonic mechanism for Laramide deformation remains controversial, with proposed mechanisms ranging from subcrustal shear during low-angle subduction (Bird, 1988, 1998; Hamilton, 1988) to detachment of the upper crust during plate collision to the west (Oldow and others, 1990; Erslev, 1993). The Rocky Mountains south of Wyoming have the additional complication of a period of mid-Tertiary igneous activity and sedimentation that coincides with Neogene extension along the Rio Grande rift. This field trip (Fig. 1) will explore the Laramide to Holocene structural development of the southern Rocky Mountains by examining the geologic record exposed in the northern Front Range of Colorado. The Front Range starts north of Canon City, Colorado, and trends north-northwest to Golden, Colorado. North of Golden, the range takes a more northerly trend toward the Wyoming border where it bifurcates into the north-trending Laramie Range (Brewer and others, 1982) and the north-northwest-trending Medicine Bow Range.

Colorado↗
USGS1988

Ferromanganese deposits from the Gulf of Alaska Seamount Province: Mineralogy, chemistry, and origin

Ferromanganese-oxide deposits dredged from four seamounts (Welker, Miller, Murray, and Patton) in the Gulf of Alaska Seamount Province include poorly crystallized microlaminated crusts on basalt substrate, well-crystallized Mn-oxide veins in epiclastic sedimentary rocks, and crystalline Mn-oxide layers and micronodules in phosphorite. The principal rock types dredged are alkali-basalt pillow fragments and tuffaceous conglomerate and sandstone. The glassy rims of pillow fragments, the glassy goundmass of large volcanic clasts, and the tuffaceous component of the sediment are altered to palagonite. Other low-temperature alteration products include phillipsite, smectite, and carbonate-apatite.Thick (10–50 mm) Fe–Mn crusts consist mainly of δ-MnO 2 ; straight and cuspate growth laminae indicate variable growth rates and periods of nondeposition. A larger number of detrital particles toward the top of thick crusts record the increasing influence of active volcanoes of the Aleutian arc during northwestward movement of the Pacific plate. Thick crusts on basalt substrate have higher Mn/Fe ratios and lower Co content than Fe–Mn crusts from low-latitude seamounts of the central Pacific region. Thin (< 10 mm) crusts on volcaniclastic substrate contain todorokite and birnessite and have higher Mn/Fe ratios, Ni, and Cu and lower Fe and Co than thick Gulf of Alaska crusts.Veins of todorokite and cryptomelane with complex internal structure occur in altered tuffaceous sandstone and conglomerate from Miller Seamount. Fibrous todorokite has a composition similar to those of other marine examples but may contain up to 7% Mn 2+ in M2 sites. Microprobe analysis of the marine cryptomelane indicates a composition that is approximately (K,Ba) 1–2 (Mn 4+ ,Co) 7–8 O 16 ∙ x (H 2 O).A third type of Fe–Mn deposit in phosphorite is an intimate mixture of todorokite (and minor δ-MnO 2 )-bearing layers and micronodules, carbonate-apatite, and phillipsite that encloses grains of altered volcanic glass and lithic fragments.The microlaminated structure, mineralogy (predominantly δ-MnO 2 ), and composition (Mn/Fe ratio and transition metal, rare earth element, U, and Th contents) of the thick crusts are characteristic of hydrogenetic Fe–Mn crusts elsewhere in the Pacific. Conversely, the crystallinity and chemical composition of the Mn-oxide veins and thin crusts indicate formation during diagenesis of the volcanogenic sediment substrate. Mn and other transition metals are mobilized during low-temperature oxidative alteration (palagonitization) of basaltic volcanic glass; the oxidation of Fe 2+ to Fe 3+ during palagonitization and the dissolution of the dilute biogenic fraction of the sediment combine to lower the Eh of ambient pore fluid and enhance the mobility of Mn 2+ . Diagenesis in the phosphatic sandstone from Patton Seamount involves organic-rich sediment and pore waters elevated in phosphorus owing to upwelling above a large volcanic edifice.

Alaska↗
USGS2026

Growth and erosion of volcanic islands since 1963 analyzed by multi-sensor satellite data and historical records

Most volcanic activity is taking place in the oceans. Depending on water depth, eruption recurrence times and volumes, a new island can form. The power of erosional forces, the type of erupted material and the efficiency of secondary processes determine the island’s lifetime. Since the famous eruption of Surtsey (Iceland) in 1963, at least another 23 volcanic islands have appeared. Some islands remained intact for years or decades, whereas others disappeared within just weeks or months. In this study, we analyzed satellite data to determine growth and erosion rates of the volcanic edifices related to these 24 islands. We combined multi-sensor (optical, thermal, radar) satellite data time series with information from literature and the Global Volcanism Program database. We developed a comprehensive dataset, including 19 parameters, on the islands’ lifetime, shape, area, volume, eruption style and duration, environmental conditions, development of sedimentary deposits, and the geomorphic evolution of the island over time. Our dataset is available in a database format. This database allows us to test eight hypotheses about factors influencing the islands’ lifetime. Our results show that instead of one single critical factor, a combination of different factors influences the life history of volcanic islands. For instance, we show that larger islands do not necessarily live longer. The mechanical properties of the eruption products affect the island’s structural integrity. Irrespective of the material, a minimum initial area of around 50,000 m 2 seems to be a reasonable threshold to give the island a chance to exist longer.

Bulletin of Volcanology↗
USGS2022

Assessing reproducibility in sedimentary macroscopic charcoal count data

Current understanding of global late Quaternary fire history is largely drawn from sedimentary charcoal data. Since publication, CharAnalysis increasingly has been relied upon as a robust method for analyzing these data. However, several underlying assumptions of the algorithm have not been tested. This study uses replicated charcoal count data to examine the assumption of Poisson distribution and reproducibility of peak detection. Results show <10% of the replicate counts are Poisson distributed, a maximum peak replication rate of 60%, and, for >90% of the data, intra-level count differences were larger than the threshold used to identify significance in inter-level differences. A pronounced “edge effect” was observed at the beginning and end of the records, cautioning against validation of results based on sections corresponding to the historical period. The proximal cause for low reproducibility is likely a lack of spatial randomness of charcoal particles at the scale of a core diameter. Until and unless decomposition methods can be developed that accommodate the observed limitations inherent in particle count data, best practices for interpreting charcoal records may be to rely on qualitative interpretations based on smoothed influx values and minimum particle count values in the hundreds.

Quaternary Research↗
USGS2010

Database of recent tsunami deposits

This report describes a database of sedimentary characteristics of tsunami deposits derived from published accounts of tsunami deposit investigations conducted shortly after the occurrence of a tsunami. The database contains 228 entries, each entry containing data from up to 71 categories. It includes data from 51 publications covering 15 tsunamis distributed between 16 countries. The database encompasses a wide range of depositional settings including tropical islands, beaches, coastal plains, river banks, agricultural fields, and urban environments. It includes data from both local tsunamis and teletsunamis. The data are valuable for interpreting prehistorical, historical, and modern tsunami deposits, and for the development of criteria to identify tsunami deposits in the geologic record.

Open-File Report↗
USGS2000

Late Albian Kiowa-Skull Creek marine transgression, lower Dakota Formation, eastern margin of Western Interior Seaway, U.S.A

An integrated geochemical-sedimentological project is studying the paleoclimatic and paleogeographic characteristics of the mid-Cretaceous greenhouse world of western North America. A critical part of this project, required to establish a temporal framework, is a stratigraphic study of depositional relationships between the Albian-Cenomanian Dakota and the Upper Albian Kiowa formations of the eastern margin of the Western Interior Seaway (WIS). Palynostratigraphic and sedimentologic analyses provide criteria for the Dakota Formation to be divided into three sedimentary sequences bounded by unconformities (D 0 , D 1 , and D 2 ) that are recognized from western Iowa to westernmost Kansas. The lowest of these sequences, defined by unconformities D 0 and D 1 , is entirely Upper Albian, and includes the largely nonmarine basal Dakota (lower part of the Nishnabotna Member) strata in western Iowa and eastern Nebraska and the marine Kiowa Formation to the southwest in Kansas. The gravel-rich fluvial deposits of the basal part of the Nishnabotna Member of the Dakota Formation correlate with transgressive marine shales of the Kiowa Formation. This is a critical relationship to establish because of the need to correlate between marine and nonmarine strata that contain both geochronologic and paleoclimatic proxy data. The basal gravel facies (up to 40 m thick in western Iowa) aggraded in incised valleys during the Late Albian Kiowa-Skull Creek marine transgression. In southeastern Nebraska, basal gravels intertongue with carbonaceous mudrocks that contain diverse assemblages of Late Albian palynomorphs, including marine dinoflagellates and acritarchs. This palynomorph assemblage is characterized by occurrences of palynomorph taxa not known to range above the Albian Kiowa-Skull Creek depositional cycle elsewhere in the Western Interior, and correlates to the lowest of four generalized palynostratographic units that are comparable to other palynological sequences elsewhere in North America. Tidal rhythmites in mudrocks at the Ash Grove Cement Quarry in Louisville (Cass County), Nebraska record well-developed diurnal and semimonthly tidal cycles, and moderately well developed semiannual cycles. These tidal rhythmites are interpreted to have accumulated during rising sea level at the head of a paleoestuary that experienced at least occasional mesotidal conditions. This scenario places the gravel-bearing lower part of the Nishnabotna Member of the Dakota Formation in the mouth of an incised valley of an Upper Albian transgressive systems tract deposited along a tidally influenced coast. Furthermore, it provides a depositional setting consistent with the biostratigraphic correlation of the lower part of the Nishnabotna Member of the Dakota Formation to the marine Kiowa Formation of Kansas.

Iowa↗
USGS2014

Sequence stratigraphy of the Upper Cambrian (Furongian; Jiangshanian and Sunwaptan) Tunnel City Group, Upper Mississippi Valley: Transgressing assumptions of cratonic flooding

New data from detailed measured sections permit comprehensive analysis of the sequence framework of the Furongian (Upper Cambrian; Jiangshanian and Sunwaptan stages) Tunnel City Group (Lone Rock Formation and Mazomanie Formation) of Wisconsin and Minnesota. The sequence-stratigraphic architecture of the lower part of the Sunwaptan Stage at the base of the Tunnel City Group, at the contact between the Wonewoc Formation and Lone Rock Formation, records the first part of complex polyphase flooding (Sauk III) of the Laurentian craton, at a scale smaller than most events recorded by global sea-level curves. Flat-pebble conglomerate and glauconite document transgressive ravinement and development of a condensed section when creation of accommodation exceeded its consumption by sedimentation. Thinly-bedded, fossiliferous sandstone represents the most distal setting during earliest highstand. Subsequent deposition of sandstone characterized by hummocky or trough cross-stratification records progradational pulses of shallower, storm- and wave-dominated environments across the craton before final flooding of Sauk III commenced with carbonate deposition during the middle part of the Sunwaptan Stage. Comparison of early Sunwaptan flooding of the inner Laurentian craton to published interpretations from other parts of North America suggests that Sauk III was not a single, long-term accommodation event as previously proposed.

Minnesota;Wisconsin↗
USGS1994

Sedimentary patterns across the Paleocene-Eocene boundary in the Atlantic and Gulf Coastal Plains of the United States

Fossiliferous clay and sand belonging to calcareous nannofossil Zones NP 9 (latest Paleocene) and NP 10 (earliest Eocene) are widespread in the US Gulf and Atlantic Coastal Plains. Although the thickness of Zone NP 9-NP 10 strata is several times greater in the eastern Gulf Coastal Plain than in the Atlantic Coastal Plain, the hiatus that usually is present between these two zones in inner neritic strata is of longer duration in the Gulf Coast. Although 6 sequences are found in Zones NP 10-NP 11 in both the Atlantic and Gulf Coastal Plains, the number of sequences in each NP zone differs in the 2 areas. There is continuous deposition across the Zone NP 9-NP 10 boundary only in the northern Atlantic Coastal Plain, where middle to outer neritic deposits record the presence of several latest Paleocene (upper Zone NP 9) events that occurred at approximately 55.2 Ma.

Atlantic Coastal Plain, Gulf Coastal Plain↗