Paleo-ice Flow Research Articles

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

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 Pucara 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.% CaCl 2 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.

Provenance of the Sirius Group and related Upper Cenozoic glacial deposits from the Transantarctic Mountains, Antarctica: relation to landscape evolution and ice-sheet drainage

Abstract This study uses bulk X-ray diffraction (XRD), heavy mineral analysis and analysis of detrital modes of the Sirius Group and related Upper Cenozoic deposits to evaluate their provenance. The data suggest that deposition of the Sirius Group occurred as a result of long-term glacial denudation of the Transantarctic Mountains. Such a conclusion is in contrast with the traditional view of deposition on a pre-existing high relief glacial topography during one relatively short-term phase of glacial expansion by the East Antarctic Ice Sheet. Two petrofacies are distinguished, which have different geomorphological settings and paleo-ice flow directions. One petrofacies includes much material from the higher elevated sedimentary sequences of the Transantarctic Mountains and represents overriding of the mountains and deposition of part of the Sirius Group during or after the late Oligocene to early Miocene. The second petrofacies is characterized by a large input from crystalline basement sources and represents active erosion and deposition in glacial troughs during the Neogene. The second petrofacies of the Sirius Group shows similarities to the record from Dry Valley Drilling Project core 11 (DVDP-11), which indicates that East Antarctic ice was last flowing through the Dry Valleys in the late Miocene to early Pliocene.

Evidence of glacial abrasion in the Calingasta–Uspallata and western Paganzo basins, mid-Carboniferous of western Argentina

Evidence of glacial abrasion is present in the basal part of the Carboniferous section of the Calingasta–Uspallata and Paganzo (western Argentina), where subglacial and proximal glacial-marine diamictites with pebbly (dropstone) shales constitute the dominant facies association. Intraformational striated pavements are exposed in the Hoyada Verde and Leoncito Formations of the Calingasta–Uspallata basin. Marine invertebrate fossils ( Levispustula zone) in associated shales indicate a mid-Carboniferous age for both units. A single layer striated boulder pavement is superbly exposed in the Hoyada Verde Formation. Local a-axis clast imbrication in the underlying bouldery diamictite and strong parallel striae on the flattened upper surfaces of boulders indicate a subglacial origin for the pavement. Paleo-ice flow directions have an NNE–SSW strike. The Leoncito intraformational pavement is shaped on bioturbated, fine-grained sandstones with plant remains. Glacial striations are straight and parallel with subcircular cross-sections. Dome-like features are present in the surface, which is covered in turn by a sandy bouldery diamictite. Four striated surfaces are present in the western Paganzo basin. Three of them (pavements at the San Juan river valley, Loma de Los Piojos and Agua Hedionda) are developed on basement rocks. They contain parallel to subparallel striations, nailhead striations, crescentic gouges, impact marks and furrows. The pavements are overlain by thin (up to 1.5 m), laterally discontinuous diamictite beds with striated clasts, some of them bullet-shaped. Paleo-ice flow directions are N–NE-directed. An intraformational pavement is also present at the San Juan river valley section; it is carved on the top of the basal diamictite and exhibits furrows, probably caused by subglacial soft-sediment grooving. The dispersion of paleo-ice flow directions in the Calingasta–Uspallata and Paganzo basins indicates: (i) regional slopes toward the north into a brackish water embayment and northwest into the open marine conditions; (ii) glacial erosion by ice grounded below sea level and confined to the margins of the basins.

Basin fill evolution and paleotectonic patterns along the Samfrau geosyncline: the Sauce Grande basin–Ventana foldbelt (Argentina) and Karoo basin–Cape foldbelt (South Africa) revisited

As integral parts of du Toit’s (1927) “Samfrau Geosyncline”, the Sauce Grande basin–Ventana foldbelt (Argentina) and Karoo basin–Cape foldbelt (South Africa) share similar paleoclimatic, paleogeographic, and paleotectonic aspects related to the Late Paleozoic tectono-magmatic activity along the Panthalassan continental margin of Gondwanaland. Late Carboniferou-earliest Permian glacial deposits were deposited in the Sauce Grande (Sauce Grande Formation) and Karoo (Dwyka Formation) basins and Falkland–Malvinas Islands (Lafonia Formation) during an initial (sag) phase of extension. The pre-breakup position of the Falkland (Malvinas) Islands on the easternmost part of the Karoo basin (immediately east of the coast of South Africa) is supported by recent paleomagnetic data, lithofacies associations, paleoice flow directions and age similarities between the Dwyka and the Lafonia glacial sequences. The desintegration of the Gondwanan Ice Sheet (GIS) triggered widespread transgressions, reflected in the stratigraphic record by the presence of inter-basinally correlatable, open marine, fine-grained deposits (Piedra Azul Formation in the Sauce Grande basin, Prince Albert Formation in the Karoo basin and Port Sussex Formation in the Falkland Islands) capping glacial marine sediments. These early postglacial transgressive deposits, characterised by fossils of the Eurydesma fauna and Glossopteris flora, represent the maximum flooding of the basins. Cratonward foreland subsidence was triggered by the San Rafael orogeny (ca. 270 Ma) in Argentina and propogated along the Gondwanan margin. This subsidence phase generated sufficient space to accommodate thick synorogenic sequences derived from the orogenic flanks of the Sauce Grande and Karoo basins. Compositionally, the initial extensional phase of these basins was characterized by quartz-rich, craton-derived detritus and was followed by a compressional (foreland) phase characterized by a paleocurrent reversal and dominance of arc/foldbelt-derived material. In the Sauce Grande basin, tuffs are interbedded in the upper half of the synorogenic, foldbelt-derived Tunas Formation (Early–early Late? Permian). Likewise, the first widespread appearance of tuffs in the Karoo basin is in the Whitehill Formation, of late Early Permian (260 Ma) age. Silicic volcanism along the Andes and Patagonia (Choiyoi magmatic province) peaked between the late Early Permian and Late Permian. A link between these volcanics and the consanguineous airborne tuffs present in the Sauce Grande and Karoo basins is suggested on the basis of their similar compositions and ages.

Depositional Environment of Paleozoic Glacial Rocks in the Central Transantarctic Mountains

Research Article| April 01, 1970 Depositional Environment of Paleozoic Glacial Rocks in the Central Transantarctic Mountains JOHN F LINDSAY JOHN F LINDSAY Institute of Polar Studies, Ohio State University, Columbus, Ohio 43210 AUTHOR'S PRESENT ADDRESS: NASA, MANNED SPACECRAFT CENTER, HOUSTON, TEXAS 77058 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1970) 81 (4): 1149–1172. https://doi.org/10.1130/0016-7606(1970)81[1149:DEOPGR]2.0.CO;2 Article history received: 26 Jun 1969 accepted: 08 Oct 1969 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation JOHN F LINDSAY; Depositional Environment of Paleozoic Glacial Rocks in the Central Transantarctic Mountains. GSA Bulletin 1970;; 81 (4): 1149–1172. doi: https://doi.org/10.1130/0016-7606(1970)81[1149:DEOPGR]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Permian glacial sediments of the Pagoda Formation in the central Transantarctic Mountains range from 126 to 395 m in thickness. Grooved sandstone lenses within the tillite beds indicate that they were deposited during retreat phases from active temperate ice which flowed to the southeast. Several interbeds and sedimentary breaks within the formation suggest possibly as many as 13 minor advances and retreats of the ice front. Grooved surfaces and clast fabrics indicate that the ice moved across the area in a direction of 148° ± 19°. The paleo-ice flow directions vary randomly about the mean from bed to bed, probably in response to local conditions. Between ice advances, streams, some of them quite large, flowed across a subdued topography and were locally diverted or dammed by the retreating ice front.The extent and continuity of the Paleozoic glacial deposits and the consistency in paleo-ice flow direction in Antarctica suggest an ice sheet of continental dimensions centered on southern Victoria Land. Dark shales conformably overlying the tillites over much of their known extent appear to have been deposited as the ice retreated prior to isostatic rebound of the depressed subglacial surface. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Clast Fabric of Till and its Development

ABSTRACT Long-axis clast fabrics from tillites of the Permian Pagoda Formation in Antarctica can be classified into several morphologic types depending on the strength and orientation of the fabric modes. The fabrics result from a large number of processes which take place both englacially, as the clast is being transported in actively deforming ice, and subglacially at the ice-sediment interface at the time of deposition. A few of the clast fabrics from the Pagoda Formation probably developed englacially and a like number were completely reorganized during deposition. However, the largest proportion of the diagrams are intermediate in character between those of fabrics formed englacially and those formed during deposition. This suggests that the subglacial conditions are such during depositio of most till units that the englacial fabrics are generally only partially reorganized. The degree to which subglacial reorganization of the clast fabric takes place depends in large part on the distribution of shear stress at the ice-sediment interface at the time of deposition which in turn depends on bottom roughness and the rate of deposition. Thus clast fabric not only provides information on paleo-ice flow direction but is also valuable in determining the conditions prevailing at the ice-sediment interface during till deposition.