Paleo-ice Flow Research Articles

Mapping Ocean Gateways from 3D Seismic Data Using Color Processing and Analogues from Seismic Data

Mapping sedimentary features to delineate ancient ocean gateways from 3D seismic data has long been a challenge due to their limited vertical resolution. We present the technique of color processing of seismic data which improves the vertical resolution to very few seismic samples corresponding to 5–10 m. The result is a representation of the seismic impedance contrast correlation in Red-Green-Blue (RGB) colors, which creates images similar to satellite images that assist the geological interpretation because the RGB colors can be associated with mud-rich and sand-rich sediments. Using this approach, we have extracted six different sedimentary bedforms from different bottom flow settings and correlated these with the bedform-velocity matrix by Stow et al. (2009). Then we studied bedform assemblies in their regional context for the area covered by the 3D seismic data set. We conclude with comparing a modern and an ancient analogue – both from 3D seismic data – and infer paleo flow direction and velocity using oceanographic measurements available for the modern analogue. The method provides insights into ocean bottom currents and their impact on the formation of contourite depositional systems in modern and ancient ocean gateways which contribute to the reconstruction of the paleoclimate as an input to present day climate change models.

Analysis of current direction in a tropical fluvial system: A study of Ajay river basin within West Bengal, India

The Ajay is an ephemeral, monsoon influenced river, originated from the Chhotanagpur plateau at Batpar of Jamui, Bihar, flowing through heterogeneous lithology and merge with the river Bhagirathi in West Bengal. Here, an attempt has been made to study the directional relationship between paleo-flow and the present flow direction of the Ajay river in West Bengal. Paleocurrent data help to reconstruct the details of paleo-fluvial system, especially the sedimentary environment of the past. The present work was carried out on the basis of detailed field work at different river segments. In this work, paleo-directional data were obtained from the primary sedimentary structure. Present flow direction data were collected using floats, microform developed on active channel bed and also from sediment grain orientation. By using collected directional data, vector mean of paleo and present flow direction were computed. Analytical results reveal that difference is minimum between present and paleo flow direction in studied segments. The directional relationship between the paleo and the present flow direction was divergent in two segments, convergent in four segments and parallel in three segments. The results help us to understand the sedimentary environment and changing flow regimes of the studied segments.

The Miwah high–sulphidation epithermal Au–Ag deposit, Aceh, Indonesia: Geology and spatial relationships of gold with associated metals and structures

Geological, mineralogical, and whole–rock geochemical studies of the Plio–Pleistocene Miwah high–sulphidation Au–Ag deposit in Aceh, Indonesia, revealed evidence of a complex and dynamic interplay between structural development and mineralisation. The mineralisation occurs in a zone of predominantly phreatic breccias measuring 1.1 km long by 400 m wide and 200–350 m deep within a fault-bounded calc–alkaline andesite ridge. Within this zone, low-grade disseminated Au-Ag has superimposed narrow, high-grade Au-Ag zones. Hydrothermal alteration and mineralisation in three mineralised centres, the Miwah Bluff in the west and the West Block M and East Block M in the east, are controlled by steeply dipping (>60°) and northerly trending pre- to syn-mineral feeders. This alteration displays an outward sequence of vuggy silica I, alunite + silica (advanced argillic), and kaolinite + illite (argillic); a distal chlorite + smectite (propylitic) zone may precede or constitute the end product of the above alteration. Late silica flooding converted parts of the vuggy silica I and the alunite + quartz zone into variably sulphide-rich massive silica and vuggy silica II containing pyrophyllite ± alunite, respectively. Penecontemporaneous with the massive silicification, main-stage mineralisation initially deposited intergrowths of pyrite + enargite ± quartz, followed by scattered enargite and pyrite, and finally, rapidly precipitated Ag-bearing native gold dendrites in vugs, with lesser amounts of sulphides. The crack–seal texture of the host rocks, paragenetic variation in precious- and base-metal mineral species, and selective dissolution, fracturing, and shearing of most of the metallic and gangue minerals are interpreted to reflect transient pulses of fluid flows and mineralisation within zones of structural deformation.High–grade Au zones and associated metals formed clusters along the feeders, whereas low–grade disseminations of the same metals were spread across the deposit. These metals are zoned along the feeders from apical Au + Ag to deep Cu + As; Sb, Te, and Sn are variably distributed. Laterally, the zonation is from Au + Ag in the feeders, through Cu, As, Sb, Bi, Te, and Sn and finally to Pb or Zn in the periphery. While these bulk-rock metal abundances indicate the efficacy of certain physico-chemical conditions of the fluids to accumulate the metals, their ratios point to an upward paleo–flow path of the fluids along the northerly striking faults and related fractures. Combining all of the above data, we propose that Miwah developed in fault-fracture networks beneath paleo–solfataras in a volcanic crater where the ascending acidic magmatic gas or gas + fluids (vapours) transformed the phreatic breccia host rocks first into vuggy silica and advanced argillic rocks, which were subsequently resilicified and mineralised into Au- and base-metal-rich massive silica during the depressurisation and condensation of the gas + fluid phases. Mineralisation processes terminated with limited Ag-enrichment by late-stage fluids in the upper segment of the deposit and in deep fractures.

Predict sandstone distribution by integrated study of deformed shale using borehole image and seismic data, a case study from northern Gulf of Mexico

Many Upper Tertiary reservoirs from the Gulf of Mexico (GoM) are sandstones deposited either in channel-levee systems or lobe systems in the intra-slope deepwater environment. One of the major uncertainties about those reservoirs is their distribution, which is likely controlled by salt tectonics. The current salt structure, however, does not represent the salt structure when the sands were deposited. It is difficult, if not impossible, to restore the salt history based on current salt structures. Salt movement resulted in a great amount of deformed shale in GoM. Borehole images on the other hand can be used to characterize the internal structure or texture of deformed shale; and the dips of deformed shale from borehole images may be used to define the paleo slope direction, which controls the movement of deformed shale. The internal structure or texture of deformed shale, therefore, may provide some information about the history of salt movement, which may also control the sand distribution. In this integrated study, all the available data, including borehole images, seismic volumes, and other petrophysical logs, were used to characterize the reservoir sands and shales. The reservoir sands are mainly composed of amalgamated sand, layered sand, and laminated sandstone. Based on dips from borehole images, paleo flow directions of reservoir sands were defined. The shales are categorized as hemipelagic shale and deformed shale. The hemipelagic shale has relatively lower and consistent dips; whereas deformed shale has relatively higher variable in both dip magnitude and dip azimuth. The integrated study suggests the main reservoir of the field is submarine lobe sands deposited above an allochthonous salt in the basin. The evacuation of the salt body below the basin created small geographic lower area for sand lobes to accumulate. The dips from the deformed shale provided information about the center of the small (or mini) basin, thus established a relationship between the dip pattern and sandstone distribution. If this relationship is valid for the other upper Tertiary deformed shale in the GoM area, a new method can be developed, which may enable us to predict the sandstone distribution using borehole images and provide guidance for petroleum evaluation and field development in the future.

Constraining the timing, kinematics and cyclicity of Mississippian-Early Pennsylvanian glaciations in the Paraná Basin, Brazil

Ice-contact deposits emplaced by Late Paleozoic Ice Age (LPIA) glaciers are rarely exposed due to a low degree of preservation and their capping by thick glaciomarine deglaciation sequences. In this paper, we present new data on glacial cyclicity, relative age constraints and paleoice flow interpretations for an ice-contact succession of the lowermost Itararé Group in eastern Paraná Basin (Brazil). The 80 m-thick ice-contact complex rests over the Itararé Group basal unconformity and comprises four stacked informal stratigraphic units regarded as the depositional/deformational record of three ice lobes advance/retreat cycles. Glacial cycle 1 comprises a sheet of massive diamictite resting on striated pavements carved on Devonian sandstones and topped by grooved/fluted surfaces, which indicate subglacial emplacement from a northward flowing ice lobe. The glacial cycle 2 succession was deposited in a proglacial to ice-marginal marine setting and subsequently deformed due to minor ice margin fluctuations of a westward/southwestward flowing grounded ice lobe. Glacial cycle 3 is interpreted as a thick overridden push moraine composed of grounding-line fan deposits capped by a subglacial diamictite emplaced by grounded ice advancing northwestward. A middle Visean-early Serpukhovian palynomorph assemblage was recorded in cycle two deposits, representing the oldest late Paleozoic glacial rocks in the Paraná Basin. The ice-contact complex elucidates multiple waxing and waning phases of the Windhoek Ice Sheet onto the eastern margin of the Paraná Basin during the Mississippian-Early Pennsylvanian, demonstrating that ice sheets of the early stages of the LPIA were also present in the Brazilian-African domain of southwestern Gondwana.

First description of subglacial megalineations from the late Paleozoic ice age in southern Africa.

We identify late Paleozoic ice age (LPIA) subglacial megalineations from field and geospatial imagery of the Twyfelfontein area of northern Namibia, and present the results of a geomorphometric analysis of those data. Asymmetric 0.1–1.5 km-long megawhalebacks indicate a paleo-ice flow to the northwest. We infer that an ice stream draining the LPIA Kaokoveld ice sheet existed within the proto-Huab River valley and that was comparable to ice streams in modern Antarctica. Recognition of a paleo-ice stream in northern Namibia supports interpretations of glaciogenic sedimentary successions (Itararé Group) in southern Brazil that suggest the presence of major, terrestrial glacial outlet systems in southern Africa during the LPIA.

Past ice stream and ice sheet changes on the continental shelf off the Sabrina Coast, East Antarctica

Our understanding of the response of the Antarctic ice sheet to climate and ocean changes requires the improvement of current ice-atmosphere-ocean models and the accurate determination of boundary conditions such as ice thickness and extent at key time intervals, so that satellite gravity observations and isostatic models can be adjusted. However, large portions of the Antarctic margin remain understudied or lack suitable data. One key area where data are lacking, is the Sabrina Coast portion of the East Antarctic Ice Sheet (EAIS) margin where the Totten Glacier, which has the largest ice discharge in East Antarctica, is accelerating, thinning and loosing mass at high rates. In this work, we present the results of the first geological and geophysical marine survey to the continental shelf offshore of the Dalton Ice Tongue and Moscow University ice shelf, east of the Totten Glacier. The data presented include multibeam swath bathymetry and multichannel seismic, focusing on the sea floor morphology and sedimentary section above a regional angular unconformity separating pre- and post-Miocene glacial strata. Sea floor scouring and iceberg keel marks on the outer shelf, associated with gullies on the upper slope indicate that ice expanded in the past and grounded ~5 km from the shelf edge at ~450–500 mbsl, extending ~155 km north of the current Moscow University Ice Shelf. A nearly 1000 m deep area in the inner-middle shelf, oriented NW with paleo-ice flow direction indicated by mega scale glacial lineations (MSGL) and drumlins, is interpreted as a cross shelf glacial trough. A series of geomorphic associations on the north-eastern side of the glacial trough includes glacial lobes, grounding zone wedges (GZW), glacial lineations and transverse ridges, which indicates slower ice, grounding line stabilization and collapse. These geomorphic associations are organized in 4 four sets representing different past ice-flow configurations reflecting changes in ice flow direction, grounding line position, location of fast and slow ice areas, and retreat pattern. Some of the geomorphic features identified are compatible with the presence of an organized subglacial drainage, and others are with rapid grounding line collapse. A well-preserved series of GZWs occurring at different water depths implies they were formed during different glacial stages or cycles. The inferred diminishing ice thickness for consecutives GZWs indicates that the margin of the Antarctic ice sheet evolved to a less extensive coverage of the continental shelf through successive glacial stages or cycles.The identification of different ice flow configurations, evidence of subglacial water and past ice margin collapse indicates a dynamic ice sheet margin with varying glacial conditions and retreat modes. We observe that some of the described morphological associations are similar to those found in the Amundsen sea sector of the West Antarctic Ice Sheet (WAIS) where they are associated with ice sheet and ice stream collapse. Although further studies are needed to assess the precise timing and rates of the glacial processes involved, we conclude that there is enough evidence to support the hypothesis that the EAIS margin can behave as dynamically as the WAIS margin, especially during glacial retreat and icesheet margin collapse.

Exhumed subglacial landscape in Uruguay: Erosional landforms, depositional environments, and paleo-ice flow in the context of the late Paleozoic Gondwanan glaciation

A well-exposed glacial surface sculpted on Precambrian crystalline basement rocks occurs below the glacial succession of the San Gregorio Formation on the eastern border of the Chaco-Parana Basin in Uruguay and was formed in the context of the late Paleozoic Gondwana Ice Age. On the glacial surface are asymmetric parallel streamlined bedrock landforms interpreted as whalebacks. The downglacier (lee-side) faces of the whalebacks have gentle slopes dipping NNW with striated and sometimes polished surfaces on crystalline rocks. These landforms are covered by 10–100-cm-thick layers of tillites and shear-laminated siltstones, suggesting glacial abrasion produced mainly by subglacial till sliding. The subglacial facies are ice-molded, and exhibit meso-scale glacial lineations such as ridges and grooves up to 30 m long and 30 cm deep. The subglacial association is directly overlain by proglacial fine-grained facies (rhythmites) with dropstones indicating a subaqueous depositional environment following ice-margin retreat. The fine-grained facies are erosively cut by a succession of sandstones with wave-generated stratification resting on a basal conglomerate. Intraformational striated surfaces, NNE-oriented, were found on four distinct bedding planes within the sandstone package and interpreted as ice keel scour marks produced by floating ice. The San Gregorio deposits are partially confined in a wide and shallow subglacial trough and the stratigraphic succession is interpreted as the record of a glacial advance-retreat cycle comparable to deglacial sequences from other late Paleozoic localities. The paleo-ice flow to the NNW indicated by subglacial lineations is parallel to that verified in the southernmost Paraná Basin located north of the study area, suggesting a paleogeographic scenario in which glaciers advanced northward into a glaciomarine environment. The proposed palaeogeography does not confirm the previous hypothesis of an ice center on the Sul-Riograndense Shield but, instead, it corroborates a south-derived Uruguayan Ice Lobe advancing to the north, probably with provenance far afield in terranes of the present-day southern African.

The paths and timing of late Paleozoic ice revisited: New stratigraphic and paleo-ice flow interpretations from a glacial succession in the upper Itararé Group (Paraná Basin, Brazil)

This paper examines a glacial diamictite-bearing succession from the upper Itararé Group (Taciba Formation) in eastern Paraná Basin, Brazil. The object of study provides the opportunity to investigate in detail the late stages of glacial sedimentation during the Late Paleozoic Ice Age (LPIA) in this sector of SW Gondwana, with implications for glacial cyclicity and regional paleo-ice flow reconstructions. Sedimentology, geological mapping and palynological analysis allowed the recognition of four facies associations, comprising subaqueous outwash, mass-transport, tide-influenced delta-front, and tide-influenced delta plain deposits. The succession records at least two episodes of ice-margin advance and retreat into a marine-influenced environment and can be placed in the earliest Permian based on the palynomorph assemblage. Cross stratification in outwash facies and deltaic deposits indicate sediment transport to the SW, the same revealed by deformational structures in mass-transport diamictites derived from downslope resedimentation of glaciomarine sediments during deglaciation. A glacial source to NE is therefore indicated and is in agreement with paleo-ice flow directions obtained from previously studied localities to the north. This north-derived early Permian glaciation contrasts with glacial sources to the SE recognized in the lower and middle intervals of the Itararé Group. The scenario suggests a geometric reconfiguration of the Paraná Basin during the LPIA and the migration of ice centers with time during the Late Paleozoic Ice Age in SW Gondwana.

Tracing the source of ancient reworked organic matter delivered to the North Atlantic Ocean during Heinrich Events

A major effort of the geochemical and paleoclimate community has been to identify the specific sources of the ice-rafted debris (IRD) in Heinrich Layers (HLs). Although the general consensus is that the majority of the IRD originated from the Hudson area of northern Canada, the specific sources are not well constrained. Here we compare the diagnostic organic geochemical signature of HLs to that of a number of Paleozoic outcrops across the former margin of the Laurentide ice sheet.We show that the biomarker signature of Upper Ordovician strata from Southampton and Baffin Island is compatible with that found in HLs in the Labrador Sea and North Atlantic, while the biomarker signature of other Paleozoic formations from the former margin of the Laurentide ice sheet is not. In addition to the biomarker signature, key-inorganic characteristics (δ18O, εNd, and 87Sr/86Sr ratios) of these formations from Southampton and Baffin Island are consistent with those reported from HLs. The location of these formations in and around the Hudson Strait is compatible with palaeo-ice flow regimes through the Hudson Strait, allowing for easy entrainment and rapid transport to the ocean. Based on these results we propose that these specific Upper Ordovician formations form a main source of IRD in HLs and hence infer an active role of the Hudson Strait paleo-ice flow in these events.

On the connectivity anisotropy in fluvial Hot Sedimentary Aquifers and its influence on geothermal doublet performance

This study finds that the geothermal doublet layout with respect to the paleo flow direction in fluvial sedimentary reservoirs could significantly affect pump energy losses. These losses can be reduced by up to 10% if a doublet well pair is oriented parallel to the paleo flow trend compared to perpendicular. The chance that flow paths are formed perpendicular to this trend strongly depends on the net sandstone volume in the reservoir. Detailed fluvial facies architecture realisations which are used in this study, are generated with a process-based approach utilizing geological data from the Lower Cretaceous Nieuwerkerk Formation in the West Netherlands Basin. Finally, this study emphasizes the importance of detailed facies architecture modelling for the assessment of both risks and production strategies in Hot Sedimentary Aquifers.

Paleoslope Reconstruction In Sandy Suspended-Load-Dominant Rivers

Constraining the depositional gradient of ancient alluvial river systems can aid in reconstructing landscapes and estimating paleodischarge by establishing boundaries on the climatic and tectonic history of continental sequences. We present three methods for estimating ancient depositional gradients based on the interpreted mode of sediment transport for the range of particle sizes found on the beds of modern rivers or preserved in channel fills. For sandy rivers with suspension as the dominant mode of sediment transport, these methods take advantage of observations that can be directly obtained from preserved strata, including measurements of paleo flow depth and grain size. The first method relates river slope to Shields number at bankfull flow. The second method is similar to the first but allows for variation in Shields number at bankfull flow with grain diameter. The final method relies on criteria required for both suspended- and bed-material load sediment transport in the same system and is the most comprehensive and physically justified method. We present each method and test them with modern river datasets to verify accuracy and help constrain uncertainty—the first step to adapting them to ancient systems. Results indicate that all methods estimate slope within a factor of two. These methods are potentially very powerful for interpreting sandy fluvial deposits because they can provide reasonably accurate quantitative estimates of paleoslope, an elusive yet important environmental variable.

Ice-Keel Scour Marks In the Geological Record: Evidence From Carboniferous Soft-Sediment Striated Surfaces In the Parana Basin, Southern Brazil

Abstract Soft-sediment glacially striated surfaces are common structures in ancient glacial successions, such as the Gondwanic Paleozoic record, and document ice erosion on non lithified beds. In most cases, they have been interpreted as the product of subglacial erosion beneath advancing marine or terrestrial glaciers, although direct evidence for glacial sedimentation in associated strata is infrequent. In this paper we document soft-sediment striated surfaces of Carboniferous age occurring in cross-laminated sandstones of the lower Itarare Group, southern Parana Basin, Brazil, and interpret them as scour marks generated by keels of floating ice. Striated surfaces occur in closely spaced, multiple stratigraphic horizons in the lower half of a deglacial sequence, whose facies characteristics indicate sedimentation in subaqueous outwash and deltaic settings. Surfaces are laterally discontinuous, commonly bordered by marginal berms, and in some cases capped by mudstones with dropstones; they have orientations that deviate from the regional paleo-ice flow indicated by glacial grooves carved on the pre-glacial basement. The characteristics observed are consistent with modern and Pleistocene ice-keel scour marks. In addition, soft-sediment striated surfaces from other Gondwanic localities have similar attributes, suggesting that ice-keel scour marks may be more common in the geological record than previously considered and that vertically repeated striated surfaces do not necessarily indicate multiple ice-sheet advances. Therefore, paleo-ice flow reconstructions based on soft-sediment striated surfaces need to be revaluated considering that the movement of free-floating ice masses is controlled by phenomena other than glacier advance.

Paleo ice flow and subglacial meltwater dynamics in Pine Island Bay, West Antarctica

Abstract. Increasing evidence for an elaborate subglacial drainage network underneath modern Antarctic ice sheets suggests that basal meltwater has an important influence on ice stream flow. Swath bathymetry surveys from previously glaciated continental margins display morphological features indicative of subglacial meltwater flow in inner shelf areas of some paleo ice stream troughs. Over the last few years several expeditions to the eastern Amundsen Sea embayment (West Antarctica) have investigated the paleo ice streams that extended from the Pine Island and Thwaites glaciers. A compilation of high-resolution swath bathymetry data from inner Pine Island Bay reveals details of a rough seabed topography including several deep channels that connect a series of basins. This complex basin and channel network is indicative of meltwater flow beneath the paleo-Pine Island and Thwaites ice streams, along with substantial subglacial water inflow from the east. This meltwater could have enhanced ice flow over the rough bedrock topography. Meltwater features diminish with the onset of linear features north of the basins. Similar features have previously been observed in several other areas, including the Dotson-Getz Trough (western Amundsen Sea embayment) and Marguerite Bay (SW Antarctic Peninsula), suggesting that these features may be widespread around the Antarctic margin and that subglacial meltwater drainage played a major role in past ice-sheet dynamics.

Field test of autogenic control on alluvial stratigraphy (Ferris Formation, Upper Cretaceous-Paleogene, Wyoming)

Internally generated (autogenic) sedimentary processes can obscure signals of tectonic movements, climate conditions, or sea-level fl uctuations in alluvial basins. The stratigraphic effects of autogenic dynamics have been considered negligible on time scales of 10 4 –10 6 yr. However, recent physical and numerical models have shown that over basin-fi lling time scales, self-organization in sedimentary systems can produce stratigraphic patterns similar to those resulting from changing basin boundary conditions. Here, we present the fi rst fi eld-based test for autogenic control on stratigraphy in an ancient alluvial basin. The Ferris Formation (Upper Cretaceous–Paleogene, Hanna Basin, Wyoming) is composed of clusters of closely spaced channel deposits separated by intervals dominated by overbank material—a pattern that has been proposed as an example of a potentially autogenic stratigraphy. In order to evaluate controls on Ferris Formation stratigraphy, spatial patterns of key channel properties were analyzed. These variables (including sand-body dimensions, paleofl ow depth, maximum clast size, paleocurrent direction, and sediment provenance) were chosen because they can change in response to climate, tectonic, or sea-level forcing and are commonly measurable in ancient alluvial successions. No clear statistical trends were detected in the measured variables, which suggests that external forces did not likely control stratigraphic organization in the unit. This study demonstrates that autogenic dynamics in natural, fi eld-scale systems can produce organized stratigraphic patterns over much larger spatial and temporal scales than is typically presumed. This fi nding emphasizes the need for further understanding of autogenic stratigraphy and greater care interpreting climate, tectonic, and eustatic changes from alluvial basins.

Alpine overdeepenings and paleo-ice flow changes: an integrated geophysical-sedimentological case study from Tyrol (Austria)

We present a study of the inneralpine basin of Hopfgarten focused on the analysis of basin fill in order to reveal its formation in relation to paleo-ice flow and tectonics. The study is based on geological mapping as well as seismic (reflection and refraction) and geoelectrical surveys. The oldest sequence in the basin, identified by seismic stratigraphy at 400 m below surface, consists of coarse grained sediments of supposedly Oligocene to Miocene age, which subsided along faults linked to the Inn fault. Three superimposed sequences, each displaying baselaps in contact with a subglacially formed unconformity and sigmoid foresets, show pleniglacial conditions followed by a glaciolacustrine environment. The uppermost of these three sequences lies on top of last glacial maximum till (LGM; Würmian Pleniglacial; MIS 2) and represents Termination I. The middle sequence is classified as Termination II following the Rissian Pleniglacial (MIS 6). The oldest glacial sequence cannot be constrained chronostratigraphically but might correlate with Termination V following the major glaciation of MIS 12. Limited glacial erosion during the LGM occurred only during the ice build-up phase. Further overdeepening was impeded due to topographic barrier and mutual blockades of glaciers within this highly dissected landscape. The occurrence and relative timing of the impediment was controlled by the onset of transfluences and thus by the altitude of coles. The higher amount of overdeepening during older glacial periods is explained by longer phases of free ice advance in the ice build up phase due to higher transfluences routes at that time. Thus, the preservation of older Pleistocene sequences within the basin may be the result of the lowering of watersheds from one glaciation to the next. Our model of an inverse relationship between glacial shaping of the surface and the subsurface may apply to similar Alpine landscapes as well.

The Paleogene California River: Evidence of Mojave-Uinta paleodrainage from U-Pb ages of detrital zircons

U-Pb age spectra of detrital zircons in samples from the Paleogene Colton Formation in the Uinta Basin of northeastern Utah and the Late Cretaceous McCoy Mountains Formation of southwestern Arizona (United States) are statistically indistinguishable. This fi nding refutes previous inferences that arkosic detritus of the Colton was derived from cratonic basement exposed by Laramide tectonism, and instead establishes the Cordilleran magmatic arc (which also provided sediment to the McCoy Mountains Formation) as the primary source. Given the existence of a north-south‐trending drainage divide in eastern Nevada and the north-northeast direction of Laramide paleofl ow throughout Arizona and southern Utah, we infer that a large river system headed in the arc of the Mojave region fl owed northeast ~700 km to the Uinta Basin. Named after its source area, this Paleogene California River would have been equal in scale but opposite in direction to the modern Green River‐Colorado River system, and the timing and causes of the subsequent drainage reversal are important constraints on the tectonic evolution of the Cordillera and the Colorado Plateau.

Using a GIS to Quantify Patterns of Glacial Erosion on Northwest Iceland: Implications for Independent Ice Sheets

Glacial erosion patterns on northwest Iceland are quantified using a Geographic Information System (GIS) in order to interpret subglacial characteristics of part of northwest Iceland affected by ice sheet glaciation. Ice scour lake density is used as a proxy for glacial erosion. Erosion classes are interpreted from variations in the density of lake basins. Lake density was calculated using two different methods: the first is sensitive to the total number of lakes in a specific area, and the second is sensitive to total lake area in a specific area. Both of these methods result in a value for lake density, and the results for lake density calculated using the two methods are similar. Areas with the highest density of lakes are interpreted as areas with the most intense erosion with the exception of alpine regions. The highest density of lakes in the study area exceeds 8% and is located on upland plateaus where mean elevations range from 400 to 800 m a.s.l. Low lake density (0–2%) is observed in steep alpine areas where steep topography does not favor lake development. The GIS analysis is combined with geomorphic mapping to provide ground truth for the GIS interpretations and to locate paleo-ice flow indicators and landforms. The patterns identified in this study illustrate distinct regions of glacial erosion and flow paths that are best explained by two independent ice sheets covering northwest Iceland during the Last Glacial Maximum (LGM). Areas of alpine glacial landforms and the presence of nunataks within the glaciated region support interpretations that ice-free regions or cold-based ice cover existed on parts of northwest Iceland during the LGM. The methods developed in this study are easily transferable to other formerly glaciated regions and provide tools to evaluate subglacial properties of former ice sheets. The data generated yield important subglacial boundary conditions for ice sheet models of Iceland.

Using a GIS to Quantify Patterns of Glacial Erosion on Northwest Iceland: Implications for Independent Ice Sheets

Glacial erosion patterns on northwest Iceland are quantified using a Geographic Information System (GIS) in order to interpret subglacial characteristics of part of northwest Iceland affected by ice sheet glaciation. Ice scour lake density is used as a proxy for glacial erosion. Erosion classes are interpreted from variations in the density of lake basins. Lake density was calculated using two different methods: the first is sensitive to the total number of lakes in a specific area, and the second is sensitive to total lake area in a specific area. Both of these methods result in a value for lake density, and the results for lake density calculated using the two methods are similar. Areas with the highest density of lakes are interpreted as areas with the most intense erosion with the exception of alpine regions. The highest density of lakes in the study area exceeds 8% and is located on upland plateaus where mean elevations range from 400 to 800 m a.s.l. Low lake density (0–2%) is observed in steep alpine areas where steep topography does not favor lake development. The GIS analysis is combined with geomorphic mapping to provide ground truth for the GIS interpretations and to locate paleo-ice flow indicators and landforms. The patterns identified in this study illustrate distinct regions of glacial erosion and flow paths that are best explained by two independent ice sheets covering northwest Iceland during the Last Glacial Maximum (LGM). Areas of alpine glacial landforms and the presence of nunataks within the glaciated region support interpretations that ice-free regions or cold-based ice cover existed on parts of northwest Iceland during the LGM. The methods developed in this study are easily transferable to other formerly glaciated regions and provide tools to evaluate subglacial properties of former ice sheets. The data generated yield important subglacial boundary conditions for ice sheet models of Iceland.

Post-Early Cretaceous Mississippi Valley-type Zn-Pb Mineralization in the Bongara Area, Northern Peru: Fluid Evolution and Paleo Flow from Fluid Inclusion Evidence

Research Article| January 01, 2009 Post-Early Cretaceous Mississippi Valley-type Zn-Pb Mineralization in the Bongara Area, Northern Peru: Fluid Evolution and Paleo Flow from Fluid Inclusion Evidence N.I. Basuki; N.I. Basuki † 1F. Gordon Smith Fluid Inclusion Lab., Department of Geology, University of Toronto, 22 Russell St., Toronto, Ontario M5S 3B1. *Present address: Department of Geology, Institut Teknologi Bandung (ITB), Ganesha 10, Bandung 40132, Jawa Barat, Indonesia. †Corresponding Author: E-mail: basuki@gc.itb.ac.id Search for other works by this author on: GSW Google Scholar E.T.C. Spooner E.T.C. Spooner 1F. Gordon Smith Fluid Inclusion Lab., Department of Geology, University of Toronto, 22 Russell St., Toronto, Ontario M5S 3B1. Search for other works by this author on: GSW Google Scholar Exploration and Mining Geology (2009) 18 (1-4): 25–39. https://doi.org/10.2113/gsemg.18.1-4.25 Article history received: 05 Nov 2007 accepted: 19 Apr 2009 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation N.I. Basuki, E.T.C. Spooner; Post-Early Cretaceous Mississippi Valley-type Zn-Pb Mineralization in the Bongara Area, Northern Peru: Fluid Evolution and Paleo Flow from Fluid Inclusion Evidence. Exploration and Mining Geology 2009;; 18 (1-4): 25–39. doi: https://doi.org/10.2113/gsemg.18.1-4.25 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search nav search search input Search input auto suggest search filter All ContentBy SocietyExploration and Mining Geology Search Advanced Search Abstract The Bongara area, northern Peru, contains Zn-Pb mineralization with characteristics typical of Mississippi Valley-type (MVT) systems. The northwest–southeast-trending late Triassic–Jurassic carbonate host rocks of the Pucará Group were locally replaced by early (D1) and late (D2) dolomite. Fluid inclusion microthermometric data from dolomite and sphalerite are typical of MVT ore fluids (78° to 187°C; ~15–23 wt.% CaCl2 equivalent), and do not show apparent covariation between temperature and salinity.Homogenization temperature data from D1 and D2 dolomite show a decrease from northern (mean Th = 138°C) to central (mean Th = 126°C) to southern areas (mean Th = 102°C), suggesting fluid flow from north to south. Assuming a geothermal gradient of ~30°C/km and an average surface temperature of ~20°C, the lower temperature limits might approximate the ambient host-rock temperatures, whereas the upper temperature limits may represent minimum temperatures of a deeper aquifer, probably at a maximum depth of ~6000 m. The lower temperature limits are also similar to the estimated temperatures if dolomitization and mineralization took place in the Late Cretaceous at ~2000–3000 m depth, probably during the formation of the Peruvian fold and thrust belt near the present day Peru–Ecuador border.Fluid inclusion data show that the fluids in each studied location had relatively uniform temperatures and salinities during dolomitization and mineralization. A significant salinity drop and a slight temperature decrease are observed during late calcite precipitation, suggesting mixing of brines with dilute, cooler fluids. You do not currently have access to this article.