Taphonomy and sedimentology of Arikaree (lower Miocene) fluvial, eolian, and lacustrine paleoenvironments, Nebraska and Wyoming; A paleobiota entombed in fine-grained volcaniclastic rocks

1990 ◽  
pp. 69-112 ◽  
Author(s):  
Robert M. Hunt
Keyword(s):  
Lower Miocene ◽  
Fine Grained ◽  
Volcaniclastic Rocks

scholarly journals Stratigraphy and lithogeochemistry of the Goldenville horizon and associated rocks, Baie Verte Peninsula, Newfoundland

2021 ◽  
Author(s):  
C Mueller ◽  
S J Piercey ◽  
M G Babechuk ◽  
D Copeland
Keyword(s):  
Gold Mineralization ◽  
Iron Formation ◽  
Fine Grained ◽  
Hydrothermal Sediment ◽  
Post Archean Australian Shale ◽  
Oxygenated Water ◽  
Volcaniclastic Rocks ◽  
Laurentian Margin ◽  
Mn Oxides ◽  
Hydrothermal Venting

The Goldenville horizon in the Baie Verte Peninsula is an important stratigraphic horizon that hosts primary (Cambrian to Ordovician) exhalative magnetite and pyrite and was a chemical trap for younger (Silurian to Devonian) orogenic gold mineralization. The horizon is overlain by basaltic flows and volcaniclastic rocks, is intercalated with variably coloured argillites and cherts, and underlain by mafic volcaniclastic rocks; the entire stratigraphy is cut by younger fine-grained mafic dykes and coarser gabbro. Lithogeochemical signatures of the Goldenville horizon allow it to be divided into high-Fe iron formation (HIF; >50% Fe2O3), low-Fe iron formation (LIF; 15-50% Fe2O3), and argillite with iron minerals (AIF; <15% Fe2O3). These variably Fe-rich rocks have Fe-Ti-Mn-Al systematics consistent with element derivation from varying mineral contributions from hydrothermal venting and ambient detrital sedimentation. Post-Archean Australian Shale (PAAS)-normalized rare earth element (REE) signatures for the HIF samples have negative Ce anomalies and patterns similar to modern hydrothermal sediment deposited under oxygenated ocean conditions. The PAAS-normalized REE signatures of LIF samples have positive Ce anomalies, similar to hydrothermal sediment deposited under anoxic to sub-oxic conditions. The paradoxical Ce behaviour is potentially explained by the Mn geochemistry of the LIF samples. The LIF have elevated MnO contents (2.0-7.5 weight %), suggesting that Mn from hydrothermal fluids was oxidized in an oxygenated water column during hydrothermal venting, Mn-oxides then scavenged Ce from seawater, and these Mn-oxides were subsequently deposited in the hydrothermal sediment. The Mn-rich LIF samples with positive Ce anomalies are intercalated with HIF with negative Ce anomalies, both regionally and on a metre scale within drill holes. Thus, the LIF positive Ce anomaly signature may record extended and particle-specific scavenging rather than sub-oxic/redox-stratified marine conditions. Collectively, results suggest that the Cambro-Ordovician Taconic seaway along the Laurentian margin may have been completely or near-completely oxygenated at the time of Goldenville horizon deposition.

Submarine-fan characteristics and dual sediment provenance, Lower Carboniferous Bragdon Formation, eastern Klamath terrane, California

1989 ◽  
Vol 26 (5) ◽  
pp. 927-940 ◽  
Author(s):  
M. Meghan Miller ◽  
Bingquan Cui
Keyword(s):  
Early Carboniferous ◽  
Sediment Provenance ◽  
Dispersal Pattern ◽  
Submarine Fan ◽  
Lower Carboniferous ◽  
Sediment Dispersal ◽  
Fine Grained ◽  
Rock Fragments ◽  
Western Cordillera ◽  
Volcaniclastic Rocks

The Carboniferous Bragdon Formation comprises sandstone, argillite, and conglomerate, which were deposited in a hybrid submarine-fan setting. The Bragdon Formation contains a crudely progradational succession of sand-rich turbidites and intercalated channel fill and debris flows. Apparent paucity of fine-grained rocks and relatively high sedimentation rates may suggest deposition within a small, rapidly subsiding, ponded basin. Three end-member petrologic sandstone types include (i) quartz-rich, chert-rich, and sedimentary-lithic-rich sandstone, (ii) volcanic-lithic- and feldspar-rich sandstone, and (iii) crystal-rich sandstone and tuffaceous argillite. The compositions reflect basement uplift, arc dissection, and the persistence of volcanism, respectively. Interbedded strata of differing provenance, together with little or no provenance mixing within beds, indicate multicomponent source terranes, line-source sediment dispersal pattern, and limited transport distances.Facies associations and provenance together suggest extension or transtension within an arc-related basinal setting during the Late Devonian and Early Carboniferous, resulting in deposition of epiclastic sediments that were rich in sedimentary rock fragments in a Paleozoic succession otherwise dominated by volcaniclastic rocks or fringing carbonates. Mid-Paleozoic chert-rich epiclastic strata are widespread within the western Cordillera in a variety of tectonic regimes that may be broadly related to the same oblique plate margin.

scholarly journals Petrogenesis of the Eudialyte Complex of the Lovozero Alkaline Massif (Kola Peninsula, Russia)

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 581 ◽  
Author(s):  
Julia A. Mikhailova ◽  
Gregory Yu. Ivanyuk ◽  
Andrey O. Kalashnikov ◽  
Yakov A. Pakhomovsky ◽  
Ayya V. Bazai ◽  
...  
Keyword(s):  
Water Solution ◽  
Granite Gneiss ◽  
Gradual Transition ◽  
Eudialyte Group ◽  
Fine Grained ◽  
Phosphorus Mineralization ◽  
Volcaniclastic Rocks ◽  
Layered Complex ◽  
Alkaline Massif ◽  
Fractionation Path

The Lovozero Alkaline Massif intruded through the Archaean granite-gneiss and Devonian volcaniclastic rocks about 360 million years ago, and formed a large (20 × 30 km) laccolith-type body, rhythmically layered in its lower part (the Layered Complex) and indistinctly layered and enriched in eudialyte-group minerals in its upper part (the Eudialyte Complex). The Eudialyte Complex is composed of two groups of rocks. Among the hypersolvus meso-melanocratic alkaline rocks (mainly malignite, as well as shonkinite, melteigite, and ijolite enriched with the eudialyte-group minerals, EGM), there are lenses of subsolvus leucocratic rocks (foyaite, fine-grained nepheline syenite, urtite with phosphorus mineralization, and primary lovozerite-group minerals). Leucocratic rocks were formed in the process of the fractional crystallization of melanocratic melt enriched in Fe, high field strength elements (HFSE), and halogens. The fractionation of the melanocratic melt proceeded in the direction of an enrichment in nepheline and a decrease in the aegirine content. A similar fractionation path occurs in the Na2O-Al2O3-Fe2O3-SiO2 system, where the melt of the “ijolite” type (approximately 50% of aegirine) evolves towards “phonolitic eutectic” (approximately 10% of aegirine). The temperature of the crystallization of subsolvus leucocratic rocks was about 550 °C. Hypersolvus meso-melanocratic rocks were formed at temperatures of 700–350 °C, with a gradual transition from an almost anhydrous HFSE-Fe-Cl/F-rich alkaline melt to a Na(Cl, F)-rich water solution. Devonian volcaniclastic rocks underwent metasomatic treatment of varying intensity and survived in the Eudialyte Complex, some remaining unchanged and some turning into nepheline syenites. In these rocks, there are signs of a gradual increase in the intensity of alkaline metasomatism, including a wide variety of zirconium phases. The relatively high fugacity of fluorine favored an early formation of zircon in apo-basalt metasomatites. The ensuing crystallization of aegirine in the metasomatites led to an increase in alkali content relative to silicon and parakeldyshite formation. After that, EGM was formed, under the influence of Ca-rich solutions produced by basalt fenitization.

Late Albian inoceramid bivalves from the Andes of Tierra del Fuego: Age implications for the closure of the Cretaceous marginal basin

1996 ◽  
Vol 70 (2) ◽  
pp. 272-274 ◽  
Author(s):  
Eduardo B. Olivero ◽  
Daniel R. Martinioni
Keyword(s):  
Indirect Evidence ◽  
Foreland Basin ◽  
Field Work ◽  
First Record ◽  
Tierra Del Fuego ◽  
Fine Grained ◽  
Marginal Basin ◽  
The Andes ◽  
Volcaniclastic Rocks ◽  
Opening And Closing

At the southernmost tip of South America, a thick pile of deep marine volcaniclastic rocks called the Yahgan Formation (Kranck, 1932) was deposited during the Early Cretaceous in a small marginal basin developed between the continent and a Pacific-facing volcanic arc (Katz, 1972; Dalziel et al., 1974). North and northwest of Tierra del Fuego, in the adjacent Austral or Magallanes basin, this unit is laterally replaced by coeval, fine-grained deposits representing basinal, slope, and platform marine settings (Winslow, 1982; Biddle et al., 1986; Wilson, 1991). The geometry of the basins changed markedly with a compressional event that produced the tectonic inversion of the marginal basin and the formation of a retroarc foreland basin in front of the rising cordillera. Closure of the marginal basin and strong deformation of the Yahgan Formation apparently occurred in the mid-Cretaceous (Halpern and Rex, 1972; Dalziel et al., 1974; Wilson, 1991); however, the timing of the opening and closing of the basin is poorly constrained because of the scarcity of fossil evidence. So far, a Late Jurassic-Neocomian age was favored for the Yahgan Formation on the basis of the record of belemnites and ammonites (Aguirre Urreta and Suárez, 1985; Halpern and Rex, 1972; Winn, 1978). Halpern and Rex (1972) mentioned the Hauterivian genus Favrella in Gardiner Island, but this record has been questioned by Thomson et al. (1982) who considered the ammonite imprint to be some kind of heteromorph. Also, the timing of the transition from marginal to foreland basin is not well documented. On the basis of indirect evidence the initiation of the foreland basin stage was assigned to the Albian in the Ultima Esperanza region of Chile (Wilson, 1991) and to the Late Cretaceous in northern Tierra del Fuego (Biddle et al., 1986). Recent field work by the authors in the area of No Top Mountain-Moat River, Tierra del Fuego (Figure 1), has resulted in the first record of diagnostic late Albian inoceramids in the Yahgan Formation. The objective of this note is to document this fauna and to briefly discuss its implications on the control of the timing of the transition from marginal to foreland basin in the area.

Paleoenvironmental and basin analysis of the late Neoproterozoic (Ediacaran) upper Conception and St. John's groups, west Conception Bay, Newfoundland

2007 ◽  
Vol 44 (1) ◽  
pp. 25-41 ◽  
Author(s):  
Aitor A Ichaso ◽  
Robert W Dalrymple ◽  
Guy M Narbonne
Keyword(s):  
Volcanic Ash ◽  
Phase 1 ◽  
Turbidity Currents ◽  
Phase 2 ◽  
Fine Grained ◽  
Volcaniclastic Rocks ◽  
Tectonic Reconstructions ◽  
Late Neoproterozoic ◽  
Conception Bay ◽  
Avalon Peninsula

The Conception and St. John's groups consist of deep-marine, fine-grained siliciclastic–volcaniclastic rocks with abundant impressions of Ediacaran body fossils. Based on previous tectonic reconstructions, these strata are interpreted to have accumulated during the transition from a fore arc (phase 1, ca. 630–560 Ma) to a strike-slip pull-apart basin (phase 2, ca. 560–540 Ma). The Drook and Mistaken Point formations accumulated during phase 1 and are characterized by tabular, thick- to medium-bedded turbidites (east-southeast paleoflow directions), contourites (southwest paleoflow directions), and volcanic ash beds. The high proportion of each bed consisting of TE (Bouma turbidite division) mudstone, and the lack of correlation between bed thickness and basal grain size, suggest ponding of the turbidity currents. The differences in paleoflow directions and texture between Conception Bay and equivalent units at Mistaken Point imply that the two areas may have been geographically isolated from each other; phase 1 deposition in the study area is inferred to have taken place in the basin-plain portion of a transversely supplied, partially confined sub-basin. This "west Conception sub-basin" is bounded to the east by outcrops of the older Harbour Main Group that we speculate may have been a topographic high separating the sub-basin from the main fore-arc basin located to the present-day east. The Trepassey and Fermeuse formations represent phase 2 and are characterized by tabular thin-bedded turbidites, slump deposits, and volumetrically minor amounts of volcanic ash that accumulated on a southwesterly prograding slope. The regional consistency of lithologies and paleoflow directions throughout the Avalon Peninsula suggest that basin differentiation was minimal at this time.

Using iron formations during exploration for c. 1.9 Ga Zn-Pb-Ag sulphide deposits, Jugansbo area, Bergslagen, Sweden

2020 ◽  
Author(s):  
Nils Jansson ◽  
Rodney Allen
Keyword(s):  
Geological Mapping ◽  
Iron Formation ◽  
Sulphide Mineralization ◽  
Fine Grained ◽  
Stratigraphic Analysis ◽  
Mineralization Processes ◽  
Volcaniclastic Rocks ◽  
Thermochemical Reduction ◽  
Stratigraphic Evolution ◽  
Iron Formations

<p>Oxide- and silicate-dominated, stratiform iron formations are abundant in the northern part of the Sala inlier, Bergslagen, Sweden. The iron formations are commonly laminated and are associated with fine-grained siliciclastic and felsic volcaniclastic rocks in a 1.91-1.89 Ga succession dominated by pumiceous and lithic-bearing rhyolitic volcaniclastic rocks. Depositional features are consistent with a volcanically active, submarine environment, in which the iron formations and fine-grained host strata to sulphide mineralization accumulated during pauses in volcanism. At c. 1.87-1.81 Ga, the succession underwent polyphase folding and shearing under lower amphibolite facies conditions, followed by polyphase faulting under more brittle conditions.</p><p>The iron formations are locally directly stratigraphically overlain by  stratiform Zn-Pb-Ag sulphide mineralization. Detailed geological mapping has demonstrated that sulphide-bearing (proximal) iron formation is gradational into sulphide-poor (distal) iron formation along a strike extent of more than 7 km. Proximal iron formation is dominated by magnetite, grunerite, tremolite, quartz, almandine-rich garnet (Alm<sub>54</sub>Sps<sub>35</sub>Grs<sub>8</sub>), muscovite, and chlorite, whereas distal iron formation is characterized by hematite, magnetite, epidote, actinolite, spessartine-rich garnet (Sps<sub>53</sub>Adr<sub>29</sub>Grs<sub>15</sub>) and locally calcite. </p><p>Elevated contents of Mn, Zn and Co are observed in both distal and proximal iron formation, whereby these elements help pinpoint the favorable horizon, but are of less use for vectoring along strike. Whole-rock lithogeochemistry samples of proximal iron formation differ from distal iron formation in: (1) Eu/Eu*>1, (2) Ce/Ce*<1, (3) suprachondritic Y/Ho, (4) elevated Tl, Cs, Cd, Sn, S, Cu, Pb, Sb and Au (5) lower volcaniclastic/siliciclastic content based on lower Al, Ti and Zr. Collectively, these features are indicative of Fe mineralization following interaction of a hot, acid and reduced hydrothermal fluid with oxidized seawater in a vent proximal position which was deprived of clastic or volcaniclastic input.</p><p>Sulphide mineralization, ranging from banded, to disseminated and fracture-hosted, is associated with chlorite-rich, locally graphitic mudstone immediately overlying proximal iron formation. Multi-grain δ<sup>34</sup>S<sub>V-CDT</sub> of sphalerite, pyrite and pyrrhotite are exclusively negative, ranging from -10.6 to -0.25 with no clear mode. The δ<sup>34</sup>S<sub>V-CDT</sub> distribution is unusual for Bergslagen deposits, and is indicative of a significant contribution of sulphur via bacteriogenic or thermochemical reduction of seawater SO<sub>4</sub><sup>2-</sup>.</p><p>Stratigraphic analysis suggest that proximally, the mineralizing event followed a sudden deepening of the basin, and progressed from Fe oxide to polymetallic sulphide mineralization. The temporal zonation probably reflect a decrease in the redox potential of the basin, possibly due to venting and ponding of reduced hydrothermal fluids. Ore textures and host facies are consistent with of an exhalative mode of formation for both deposit types, albeit an importance of subseafloor mineralization processes is implied by lateral variability in both sulphide and chlorite content. In relation to the local stratigraphic evolution in the area, the mineralizing event can be directly linked to an event of basin deepening following a caldera-forming volcanic eruption. The results from stratigraphic analysis along with aforementioned proxies for redox and vent-proximity present first order vectors to stratiform Zn-Pb-Ag mineralization in the Jugansbo area, Bergslagen.</p>

scholarly journals A new deepwater lobster, Metanephrops serendipitus sp. nov. (Crustacea, Decapoda, Nephropidae), from lower Miocene of Meljski hrib (Maribor, Slovenia)

2021 ◽  
Vol 73 (3) ◽  
pp. A240521
Author(s):  
Rok Gašparič ◽  
Dale Tshudy ◽  
Tin-Yam Chan ◽  
Stjepan Ćorić
Keyword(s):  
New Species ◽  
Northern Hemisphere ◽  
Deep Sea ◽  
Brittle Stars ◽  
Central Paratethys ◽  
Lower Miocene ◽  
Fine Grained ◽  
Extant Species ◽  
A New Species

A new species of nephropid lobster, Metanephrops serendipitus sp. nov., is described from the lower Miocene (Ottnangian/Karpatian) in beds of Central Paratethys. Metanephrops serendipitus sp. nov. represents the first fossil representative of the genus from the northern hemisphere and thus extends its known palaeobiogeographical distribution. Additionally, the palaeoecology of the new species is discussed. Similar to extant species of Metanephrops, the fossil nephropid inhabited a fine-grained deep-sea environment, associated with frequent brittle stars.

Ordovician emplacement of the Mount Dingley Diatreme, Western Ranges of the Rocky Mountains, southeastern British Columbia

1994 ◽  
Vol 31 (10) ◽  
pp. 1491-1500 ◽  
Author(s):  
B. S. Norford ◽  
M. P. Cecile
Keyword(s):  
Late Ordovician ◽  
Upper Ordovician ◽  
Lower Paleozoic ◽  
Fine Grained ◽  
The North ◽  
Lower Ordovician ◽  
Intrusive Rocks ◽  
Volcaniclastic Rocks ◽  
Host Rocks ◽  
Early Late

External and internal morphologies are well shown by a newly discovered diatreme that is exceptionally well exposed in a cirque within the north face of Mount Dingley. The diatreme contains abundant brecciated host rocks mixed with highly altered, fine-grained, light-green igneous fragments (minerals include muscovite, chlorite, quartz, carbonate, and some remnant K-feldspar). The diatreme cuts Lower Ordovician rocks of the McKay Group. Olistostromes and other volcaniclastic rocks that are directly associated with the diatreme are bevelled beneath a regional unconformity below the Upper Ordovician Beaverfoot Formation. Lower Ordovician gastropods are present just below the volcaniclastic rocks and within what appears to be a lens of sediment within one of the olistostrome beds. These occurrences indicate a mid-Early Ordovician time of intrusion, but there is the possibility that the pipe was emplaced later within the interval mid-Early to early Late Ordovician. In the Western Ranges, three other episodes of emplacement of diatremes have been documented previously as within the intervals early Middle to early Late Ordovician, latest Early Silurian to early Middle Devonian, and Late Permian. Many of the diatremes are broadly contemporaneous with widespread, but volumetrically small, Ordovician and Lower Paleozoic volcanic and intrusive rocks found throughout the Canadian Cordillera. These volcanic and intrusive rocks have been interpreted as evidence of continued Lower Paleozoic extensional tectonism and some are associated with large base-metal deposits.

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