Late Ordovician glaciation

This Atlas of Silurian and Middle-Late Ordovician Paleogeographic Maps shows the changing paleogeography from the Middle Ordovician (Darwillian, 464.5 Ma) to the Late Silurian (Ludlow & Prodoli, 419.5 Ma).  The maps are from volume 5 of the PALEOMAP PaleoAtlas for ArcGIS (Scotese, 2014). Absolute age assignments are from Gradstein, Ogg & Smith (2008). 

The following maps are included in the Atlas of Silurian and Middle-Late Ordovician Paleogeographic Maps:

Map 73  Late Silurian (Ludlow & Pridoli, 419.5 Ma) Lochkovian Supersequence Boundary
Map 74  Middle Silurian (Wenlock, 425.6 Ma) Highstand System Tract 
Map 75  Early Silurian (late Llandovery, 432.1 Ma) Maximum Flooding Surface
Map 76  Early Silurian (early Llandovery, 439.8 Ma) Transgressive Systems Tract
Map 77  Late Ordovician (Hirnantian, 444.7 Ma) Llandoverian Supersequence Boundary
Map 78  Late Ordovician (Ashgill, 448.3 Ma) Lowstand Systems Tract & Maximum Flooding Surface
Map 79  Late Ordovician (Caradoc, 456 Ma) Maximum Flooding Surface
Map 80  Middle Ordovician (Darwillian, 464.5 Ma) Llandeilian Supersequence Boundary


This work should be cited as
Scotese,  C.R., 2014.  Atlas of Silurian and Middle-Late Ordovician Paleogeographic Maps (Mollweide Projection), Maps 73 – 80, Volumes 5, The Early Paleozoic, PALEOMAP Atlas for ArcGIS, PALEOMAP Project, Evanston, IL.

The illaenid trilobite Vysocania is widely represented in the Upper Ordovician of the Czech Republic, Portugal and Spain, and is one of the most characteristic taxa in the high-latitude peri-Gondwana palaeobiogeographical region to which it is endemic. Three species of the genus that were formerly assigned to Stenopareia and Zetillaenus, from the Czech Republic and Spain respectively, are herein revised, and a new species is described from the Czech Republic. The genus Octillaenus, of which a new species is described from the Upper Ordovician of Morocco, is considered to have arisen from Vysocania through paedomorphic (neotenic) processes. The relationships between Vysocania, Octillaenus, Stenopareia and Zetillaenus are reviewed and the criteria used in the definition of these taxa discussed. Species assigned to Vysocania are V. vaneki (type-species), V. iberica, V. moraveci sp. nov. and V. panderi; species assigned to Octillaenus are O. hisingeri (type-species) and O. marocanus sp. nov. Vysocania appears for the first time in the lower Berounian (Sandbian) and has its last undoubted record in the upper Berounian (upper Katian); Octillaenus is presently restricted to the Kralodvorian (upper Katian). •

This diagram show the rise and fall of global temperatures during the last 540 million years.  Scotese (2016) describes how this curve was made.  It replaces the curve published in Scotese et al., (1999).

PETM= Paleocene-Eocene Thermal Maximum (55.8 Ma), EEOC = Early Eocene Climatic Optimum (54 Ma – 46 Ma), MECO = Mid-Eocene Climatic Optimum(42 Ma), EOT = Eocene-Oligocene Transition (40 Ma – 33 Ma), MMCO=Mid-Miocene Climatic Optimum (15Ma – 13Ma), LGM = Last Glacial Maximum (21,000 years ago), 2016 = Modern MAT, PAW = Post-Anthropogenic Warming .  White stars indicate rapid cooling episodes (Stoll-Schrag Events26) at 160Ma, 127Ma, 97Ma, 91Ma, 71Ma, and 65 Ma).  Black stars represent rapid warming episodes (Kidder-Worsley Events16) at (Present-day, 15Ma, 43Ma, 56Ma, 65Ma, 93Ma, 120Ma, 183Ma, 200Ma, 251Ma, 300Ma, 359Ma, 374Ma, 444Ma, 499Ma, 520Ma, and 542 Ma).

Please cite as:  Scotese, C.R., 2015.  Phanerozoic Temperature Curve, PALEOMAP Project, Evanston, IL.

To learn more about how this curve was produced see:
Scotese, C.R., 2016.  Some thoughts Global Climate Change: The Transition from Icehouse to Hothouse, in Scotese, C.R., Earth History: The Evolution of the Earth System as Revealed through Plate Tectonics, Paleogeography, Paleoclimate, and the Evolution of Life, PALEOMAP Project, (in preparation), Evanston, IL.

RESUMEN
Se presentan los resultados de un análisis detallado de facies de la sucesión de diamictitas de la Formación Cancañiri en el área de Sella – Negro Muerto al norte de Tarija. La sección estudiada cubre sedimentos del Ordovícico inferior al Silúrico inferior. La Formación Cancañiri yace discordantemente sobre los sedimentos marinos de poca profundidad del Arenigiano medio y está sobrepuesta por areniscas ferruginosas del Llandoveriano basal. La edad de las diamictitas está considerada como ashgilliana superior. La formación está compuesta por tres miembros de diamictitas macizas, poco variables y con abundantes intercalaciones de cuerpos lenticulares de pelitas, areniscas, cuarcitas y conglomerados. Las diamictitas (tilitas) se depositaron en un ambiente glacioterrestre con las tres unidades representando tres avances de un escudo glacial a la región. Los clastos abundantes de rocas cristalinas indican una procedencia del basamento del Masivo Pampeano al sudeste.

ABSTRACT
The results of a detailed facies analysis of the succession of diamictites of the Cancañiri Formation in the region of Sella – Negro Muerto, north of Tarija are presented herein. The studied section is covering sediments of lower Ordovician to lower Silurian age. The Cancañiri Formation rests disconformably upon shallow marine sediments of middle Arenigian age and is overlain by ferriferous sandstones of the basal Llandoverian. The age of the diamictites is considered as upper Ashgillian. The formation is composed of three units of massive diamictites with little variability but with abundant lenticular intercalations of mudstones, sandstones, quartzites and conglomerates. The diamictites (tillites) have been deposited in a glacioterrestrial environment with the three units representing three advances of an ice shield into this region. The abundant crystalline basement clasts indicate a provenance from the basement of the Pampean Massif to the southeast.

The " Taconic Unconformity " is a regional polyphase event that occurred during the Late Ordovician in North Africa. This major unconformity event coincided with regional glaciation episodes that controlled the current configuration of the Lower Paleozoic clastic successions. A case study has been carried out utilizing subsurface data represented by 3D seismic lines and well log data (i.e. geological imaging, element capture spectropscopy, lithology, and facies logs) to understand the impact of the regional unconformity in the Murzuq Basin, southwest Libya. The basin is considered the second largest profitable hydrocarbon potential in Libya, one of the largest in North African, and were developed during Late Precambrian-Early Paleozoic. The main reservoirs in the basin are comprised of clastic sandstones, which were deposited during Middle to Late Ordovician. A series of pre-Ordovician basement faults mapped in the study area trending northwest-southeast have dominantly controlled the trend of the unconformity as well as the post-depositional sedimentation processes. Based on the interpreted data, the unconformity has clearly impacted the geometries of the whole Lower Paleozoic sandstone successions especially the Ordovician deposits (i.e. Hawaz and Mamuniyat Formations). It has been observed the unconformity surface concurred with a severe erosion which have removed the clastic strata from Middle Ordovician deeper into the Cambrian deposits. It is estimated with more than 900 feet (270 meters) have been eroded by the means of glacial incisions along the strike direction of the preexisted basement faults. This mega cycle of erosion has created large scale paleo-lows of more than seven kilometers wide in the study area. These paleo-topographic geometries have controlled the depositional patterns of both Upper Ordovician clastic reservoirs and Silurian source rock in the basin. This study realized the overall clastic successions in the Early Paleozoic have been deposited under multifaceted events of tecto-stratigraphic throughout the tectonic evolution record of the basin. In this poster, an integrated work was accomplished using the subsurface data to illustrate the complexity of reservoir and source rock geometries of the Lower Paleozoic sandstones.

The Upper Ordovician glacial record of southern Jordan (Ammar Fm.) essentially consists of palaeovalley infills and of a subordinate time-transgressive fluvial to shallow-marine succession overstepping both the palaeovalleys and interfluvial areas. Valley size (depth, 60–160 m; width, 1–3 km), steep (20–508) margins, internal organization and depositional facies point to an origin as tunnel valleys. The tunnel valleys are infilled by either fluvioglacial sandstones or fluviodeltaic coarsening-upward successions including fine-grained clayey sediments. Re-occupation of previous valleys is evident in places. At least three generations of tunnel valleys are inferred from cross-cutting relationships, although they most probably only reflect temporary standstills and minor re-advances related to the overall recession following the main glacial advance recorded in Saudi Arabia. Petrophysical measurements indicate that higher permeabilities are located in the glacially related strata (1.5–3 darcy in fluvioglacial infills), with a somewhat reduced porosity (22–28%) relative to the preglacial sandstones owing to a higher clay content, probably of diagenetic origin. Sandstone amalgamation, however, gives the fluvioglacial sandstones a high reservoir quality.

The Late Ordovician was a critical interval in geologic history, during which both the biosphere and marine environments underwent severe perturbations, including one of the 'Big Five' Phanerozoic mass extinctions and the massive but short-term (~0.5-Myr) Hirnantian glaciation. The onset and termination of the Hirnantian glaciation have been widely accepted as the triggers for the two extinction pulses that comprise the Late Ordovician biocrisis, but the mechanisms that caused the Hirnantian glaciation itself remain poorly known. Here, we analyze the nitrogen isotope composition (δ 15 N) of two sections in South China (Wangjiawan and Nanbazi) in order to better understand nitrogen cycle perturbations in the Late Ordovician ocean and their relationship to contempo-raneous climatic and biogeochemical changes. Low δ 15 N (~1‰) in the upper Katian and lower Rhuddanian of both sections suggests intensive (i.e., near-quantitative) denitrification and, thus, nitrogen fixation as the main source of biologically available nitrogen for primary producers. A positive δ 15 N excursion in both sections during the Hirnantian indicates weaker (i.e., non-quantitative) denitrification, possibly as a result of more vigorous ther-mohaline circulation and improved ocean ventilation. Weaker denitrification would have reduced the flux of N 2 O, an intermediate product of denitrification, to the atmosphere. N 2 O is a potent greenhouse gas, and a major decline in its production would have led to cooler climatic conditions and, ultimately, the Hirnantian glaciation. A global survey of published nitrogen isotope records suggests that similar processes operated broadly within the Late Ordovician global ocean.

Detailed mapping and facies analysis of a thick succession of diamictites of the Upper Ordovician Cancañiri Formation in southern Bolivia has revealed a glacioterrestrial origin for these sediments. The Cancañiri diamictites were deposited during three advances of a temperate, grounded ice sheet. They contain subglacial, englacial, and proglacial outwash sediments that increase in abundance from southeast to northwest. Clast fabrics and deformation features indicate SSE to NNW motion of the ice masses. Components of the diamictites usually display abrasion features such as facets and glacial striae. Provenance studies indicate that the pebbles comprise ~35% of siliciclastic sediments, mainly from the underlying shallow marine Ordovician rocks, 27% of slightly metamorphosed sediments that in part can be attributed to the Precambrian–Cambrian Puncoviscana Formation of northwestern Argentina, and a crystalline basement suite of metamorphic rocks (18%) and magmatic (mainly plutonic) rocks (20%). Due to the absence of typical lithologies, the Brazilian Shield, the Paraguay belt, and the southern Arequipa-Antofalla block could be excluded as possible source areas. The crystalline and metasedimentary clasts display strong affinities with the Pampean basement in central Argentina. All data consistently suggest that the Cancañiri tillites of southern Bolivia were deposited by a regional, low-latitude ice sheet that was independent of the main inland ice mass of Gondwana and centered SSE of the study area, in a Neoproterozoic to Cambrian orogenic belt in the area of the present Argentinean Chaco.

Mass extinctions have altered the trajectory of evolution a number of times over the Phanerozoic. During these periods of biotic upheaval a different selective regime appears to operate, although it is still unclear whether consistent survivorship rules apply across different extinction events. We compare variations in diversity and disparity across the evolutionary history of a major Paleozoic arthropod group, the Eurypterida. Using these data, we explore the group's transition from a successful, dynamic clade to a stagnant persistent lineage, pinpointing the Devonian as the period during which this evolutionary regime shift occurred. The late Devonian biotic crisis is potentially unique among the " Big Five " mass extinctions in exhibiting a drop in speciation rates rather than an increase in extinction. Our study reveals eurypterids show depressed speciation rates throughout the Devonian but no abnormal peaks in extinction. Loss of morphospace occupation is random across all Paleozoic extinction events; however, differential origination during the Devonian results in a migration and subsequent stagnation of occupied morphospace. This shift appears linked to an ecological transition from euryhaline taxa to freshwater species with low morphological diversity alongside a decrease in endemism. These results demonstrate the importance of the Devonian biotic crisis in reshaping Paleozoic ecosystems.

In the Valongo Anticline, northern Portugal, the Upper Ordovician-age Sobrido Formation records glacioeustatic sea-level changes and glacially-influenced depositional environments on the north Gondwana platform associated with the Hirnantian glaciation. New stratigraphic data from the Sobrido Formation, taking into account lateral facies variations not exposed in the type section, allow for a better understanding of Hirnantian glacial sedimentary processes, sea-level changes and palaeogeography. The lower member of the Sobrido Formation is composed of quartzites alternating with siltstones and mudstones. The transition to the upper member is most commonly an erosional contact marked by a ferruginous horizon. The lowermost part of the upper member contains a thinly laminated and rhythmically-bedded mudstone that is capped by a thin (mm-scale) shelly bed and overlain by massive diamictites. Laterally, conglomerate beds that have erosion bases are rhythmically interbedded with slates and diamictites that sometimes contain outsized mudstone clasts. The uppermost part of the upper member is very variable in thickness laterally and contains massive to laminated diamictite beds intercalated with quartzites, conglomerates and slates. Massive diamictites commonly exhibit thin horizons with Fe-oxides and occasionally manganese, phosphate and oolitic chamosite. The lower member of the Sobrido Formation is interpreted as ice-proximal outwash that is transitional laterally to subaqueous ice-contact fans formed by debris and mass flows. Erosion followed by chemical weathering of the lower member and variably within the lowermost part of the upper member is interpreted as a response to sea-level fluctuations and development of spatially-variable anoxic conditions and groundwater migration within isolated marine basins. Facies within the upper member of the Sobrido Formation are interpreted as ice-distal (laminated diamictites) and ice-proximal deposits (massive diamictites, quartzites and conglomerates). Groove casts and hummocky cross-stratification within quartzite beds suggest deposition in a shallow shelf setting. The Upper Ordovician-Lower Silurian transition is locally marked by a ferruginous horizon. Black basal quartzites are interpreted to record development of an erosional unconformity during Silurian sea-level rise. In other areas a chloritoid layer indicates proximity to dry land. These palaeoenvironmental interpretations suggest dynamic changes in sedimentary and geochemical processes in response to sea level and related palaeogeographic changes during the Upper Ordovician and transitional to the Lower Silurian on the north Gondwana platform.

Abstract The Late Ordovician was a critical interval in geologic history, during which both the biosphere and marine environments underwent severe perturbations, including one of the ‘Big Five’ Phanerozoic mass extinctions and the massive but short-term (~ 0.5-Myr) Hirnantian glaciation. The onset and termination of the Hirnantian glaciation have been widely accepted as the triggers for the two extinction pulses that comprise the Late Ordovician biocrisis, but the mechanisms that caused the Hirnantian glaciation itself remain poorly known. Here, we analyze the nitrogen isotope composition (δ 15 N) of two sections in South China (Wangjiawan and Nanbazi) in order to better understand nitrogen cycle perturbations in the Late Ordovician ocean and their relationship to contemporaneous climatic and biogeochemical changes. Low δ 15 N (~ 1‰) in the upper Katian and lower Rhuddanian of both sections suggests intensive (i.e., near-quantitative) denitrification and, thus, nitrogen fixation as the main source of biologically available nitrogen for primary producers. A positive δ 15 N excursion in both sections during the Hirnantian indicates weaker (i.e., non-quantitative) denitrification, possibly as a result of more vigorous thermohaline circulation and improved ocean ventilation. Weaker denitrification would have reduced the flux of N 2 O, an intermediate product of denitrification, to the atmosphere. N 2 O is a potent greenhouse gas, and a major decline in its production would have led to cooler climatic conditions and, ultimately, the Hirnantian glaciation. A global survey of published nitrogen isotope records suggests that similar processes operated broadly within the Late Ordovician global ocean.

Although sphinctozoans, multi-chambered
hypercalcified sponges, can be traced from the Cambrian,
their reef-building capacity in the Early Paleozoic
appears limited. The oldest sphinctozoan-coral-microbial
reef is documented here, from the Upper Sanqushan Formation
(Late Katian) of southeast China. This is also the
first report of Ordovician sphinctozoans from South China.
The sponges occur in a >120-m-thick reef that is mainly
constructed by calcimicrobes (Kordephyton, Renalcis, and
Epiphyton) with a low abundance of in situ metazoans, predominantly
sphinctozoan sponges (Corymbospongia) and
rugose corals (mostly Palaeophyllum and Streptelasma).
Tetradium is the only tabulate coral preserved in growth
position. Crinoids and brachiopods are common reef dwellers.
Dasycladacean algae are rare and probably transported
and stromatactis is abundant. Bio- and litho-facies in this
area as well as the characteristics of the microbialite suggest
that the reef developed in a deeper subtidal setting that
was unfavorable for most metazoan reef builders. In contrast
to the high-energy stromatolite-sphinctozoan reefs
from the Late Silurian, this case represents a low-energy community, indicating that the first reef-building sphinctozoans
might have originated in a relatively deep-water
environment on seamounts of a back-arc basin during the
Late Ordovician.

In the Murzuq Basin, the Late Ordovician glaciogenic succession forms a very complex clastic reservoir system. Although the structural setting is simple, the architecture of the stratigraphic succession is particularly intricate, and conventional wireline logs display rather homogeneous signatures. However, when exposed, the glaciogenic sedimentary succession indicates a very large range of depositional environments and clear stratigraphic changes. Based on high-quality processing and interpretation of wireline microresistivity image logs over a single well, our method allows the precise recognition of the internal sedimentary structures and supports the interpretation of the depositional environments within the Late Ordovician succession. During interpretation, it is possible to draw a descriptive sedimentological log, similar to a standard log from cores or outcrops. The image log is interpreted like a regular sedimentary log and compared to an outcrop analog from the nearby outcr...

The Upper Ordovician glacial record of southern Jordan (Ammar Fm.) essentially consists of palaeovalley infills and of a subordinate time-transgressive fluvial to shallow-marine succession overstepping both the palaeovalleys and interfluvial areas. Valley size (depth, 60–160 m; width, 1–3 km), steep (20–508) margins, internal organization and depositional facies point to an origin as tunnel valleys. The tunnel valleys are infilled by either fluvioglacial sandstones or fluviodeltaic coarsening-upward successions including fine-grained clayey sediments. Re-occupation of previous valleys is evident in places. At least three generations of tunnel valleys are inferred from cross-cutting relationships, although they most probably only reflect temporary standstills and minor re-advances related to the overall recession following the main glacial advance recorded in Saudi Arabia. Petrophysical measurements indicate that higher permeabilities are located in the glacially related strata (1.5–3 darcy in fluvioglacial infills), with a somewhat reduced porosity (22–28%) relative to the preglacial sandstones owing to a higher clay content, probably of diagenetic origin. Sandstone amalgamation, however, gives the fluvioglacial sandstones a high reservoir quality.

Study of new conodont collections from the Vaux Limestone exposed at its classical locality at Saint-Hilaire-la-Gérard
in the Sées syncline, the conodont fauna of which was previously described in a preliminary way by Weyant et al. (1977, Un épisode calcaire ashgillien dans l'est du Massif armoricain; incidence sur l'âge des dépôts glacio-marins fini-ordoviciens. Comptes Rendus de l’Académie des Sciences, Paris, 284, Série D, 1147-1149), has provided significant new information about Late Ordovician conodonts from Normandy. A more precise age of this formation has been established based on an unexpectedly abundant conodont fauna of low diversity. Representatives of Amorphognathus, Hamarodus, Sagittodontina, Scabbardella and Eocarniodus are present and the fauna is referable to the middle Katian-lower Hirnantian A. ordovicicus Zone. Our study, the first illustrating Ordovician conodonts from Normandy, shows that the fauna is closely similar to middle Katian faunas from other parts of continental Europe and represents the Sagittodontina robusta-Scabbardella altipes biofacies of the Mediterranean Province.