Causes Of Glaciation Research Articles

An overview of Rodinia-Gondwana Supercontinents, India - Asia Collision, emergence of Himalaya and Paleobiogeography of the eastern Tethys in Indian Subcontinent, South Asia

The existence of Rodinia Supercontinent during Meso-Neoproterozoic and its subsequent breakup and reassembly as Gondwana Supercontinent is a widely accepted hypothesis in geological history of the Earth. The breakup of the Rodinia resulted in formation of rift basins and passive continental margins around 650 Ma. Major palaeoclimatic events like Neoproterozoic global glaciation (Snowball Earth) followed by global warming have been recorded from different continents including Indian Lesser Himalaya (Blaini -Krol Cryogenian-Ediacaran Period). The emergence of multicellular Ediacaran life in the Upper Krol Formation is consistent with an increase in the atmospheric oxygen. The base of Ediacaran System in the Lesser Himalaya is established in the cap carbonate, the Blaini Formation overlying the glacial diamictites (Blainian). The pink cap carbonate of the Blaini Formation shows negative δ13C value (-3‰ PDB) and invariably correlate with the Marinoan glacial event. Large continents of Gondwanaland Supercontinent South America, Africa, India, Australia and Antarctica were located over the South Polar region and global equatorial to polar oceanic circulation was blocked and may have been the main cause of glaciation. Paleogeographically Carboniferous–Permian diamictite, coal beds and plant fossil bearing Gondwana outcrops are found in South Sikkim and Arunachal Lesser Himalaya of Northeast India. The Late Paleocene – Middle EoceneTethyan foraminiferal – algal carbonate biofacies are well developed after Late Cretaceous – Paleogene mass extinction event in the eastern Tethys, Meghalaya, east India. These Tethyan benthic orthophragmine foraminiferal –algal limestones were deposited in the passive continental margin setting of a shallow marine carbonate shelf in eastern Tethys and Standard Benthic Zones (SBZ) of the Alpine- Adriatic western Tethys are recorded from Meghalaya. The Cretaceous – Tertiary boundary is well marked in these basins by biotic mass extinction. Late Cretaceous mega ammonoid fossils and Sauropod dinosaur bones are abundantly found in the Maastrichtian Mahadeo Formation. The present δ13C and δ18O isotope data is comparable with the marine values of the limestone The Umlatodoh Limestone contains foraminiferal taxa of early Ilerdian and Middle Eocene (early Lutetian) age. The Indo-Myanmar Orogenic Belt (IMOB) represents the eastern suture of Indian plate and it was formed due to the collision of the Indian plate with the Myanmar plate. The Naga-Manipur ophiolites have been assigned to range in age from Upper Cretaceous to Eocene on the basis of faunal assemblages (radiolarian, planktonic foraminefera) in the olistolithic blocks of pelagic limestone and cherts. Pan Indian Pre and Post India–Asia Collision, emergence of Himalaya and Paleogeography of the Indian Subcontinent has been discussed in South Asia.

A Review of the Neoproterozoic Global Glaciations and a Biotic Cause of Them

In the Neoproterozoic Era, the Earth experienced two broad intervals of global glaciation, commonly known as Snowball Earth. There was also a rapid diversification of life, with the evolution of most of the eukaryotic lineages. Here, salient evidence for the Neoproterozoic global glaciations, including the carbon isotope record, is reinterpreted, and an alternative explanation for the causes of glaciation is proposed. The proliferation of life could have led to increases in atmospheric O2 levels and concomitant decreases in CO2 and CH4. Coupled biochemical and geochemical changes would have led to global cooling and glaciation. This so-called biotic hypothesis of the Snowball Earth is consistent with the most salient features of the reported evidence and explains the consecutive episodes of global glaciation.

Revisiting the Causes of the Neoproterozoic Snowball Earth

In the Neoproterozoic Era, the Earth experienced two broad intervals of global glaciation, commonly known as Snowball Earth. There was also a rapid diversification of life, with the evolution of most of the eukaryotic lineages. Here, salient evidence for the Neoproterozoic global glaciations, including the carbon isotope record, is reinterpreted and an alternative explanation for the causes of glaciation is provided. The proliferation of life could have led to increases in atmospheric O2 levels and concomitant decreases in CO2 and CH4. Coupled biochemical and geochemical changes would have led to global cooling and glaciation. This so-called biotic hypothesis of the Snowball Earth is consistent with the most salient features of the reported evidence and explains the consecutive global glaciations.

The Cordilleran Ice Sheet: One Hundred and Fifty Years of Exploration and Discovery

Present concepts about the Cordilleran Ice Sheet are the product of observations and ideas of several generations of earth scientists. The limits of glaciation in the Cordillera were established in the last half of the nineteenth century by explorers and naturalists, notably G. M. Dawson, R. G. McConnell, and T. C. Chamberlin. By the turn of the century, the gross configuration of the Cordilleran Ice Sheet had been determined, but the causes of glaciation and ice-sheet dynamics remained poorly understood. This early period of exploration and discovery was followed by a transitional period, from about 1900 to 1950, during which a variety of glacial landforms and deposits were explained (e.g., Channeled Scablands of Washington; "white silts" of southern British Columbia), and conceptual models of the growth and decay of the ice sheet were proposed. Shortly after World War II, there was a dramatic increase in research into all aspects of glaciation in the Canadian Cordillera which has continued unabated to the present. Part of the research effort during this period has been directed at resolving the Cordilleran Ice Sheet in both time and space. Local and regional fluctuations of the ice sheet have been reconstructed through stratigraphie and sedimentological studies, supported by radiocarbon and other dating techniques. Compilations of late Pleistocene ice-flow directions have shown that the Cordilleran Ice Sheet was a mass of coalescent glaciers flowing in a complex fashion from many montane source areas. During the postwar period, research has also begun or advanced significantly in several other disciplines, notably glaciology, process sedimen-tology, geomorphology, paleoecology, and marine geology. Attempts are now being made to quantitatively model the Cordilleran Ice Sheet using computers and the geological database assembled by past generations of earth scientists.

‘Zipper-rift’: a tectonic model for Neoproterozoic glaciations during the breakup of Rodinia after 750 Ma

The ‘Snowball Earth’ model of Hoffman et al. [Science 281 (1998) 1342] has stimulated renewed interest in the causes of glaciation in Earth history and the sedimentary, stratigraphic and geochemical response. The model invokes catastrophic global Neoproterozoic refrigerations when oceans froze, ice sheets covered the tropics and global temperatures plummeted to −50 °C. Each event is argued to be recorded by tillites and have lasted up to 10 million years. Planetary biological activity was arrested only to resume in the aftermath of abrupt and brutal volcanically generated ‘greenhouse’ deglaciations when global temperatures reached +50 °C. The ‘Cambrian explosion’ is regarded by some as a consequence of post-Snowball glacioeustatic flooding of continental shelves. We shall show by a systematic review of the model that it is based on many long standing assumptions of the character and origin of the Neoproterozoic glacial record, in particular, ‘tillites’, that are no longer valid. This paper focusses on the sedimentological and stratigraphic evidence for glaciation in the light of current knowledge of glacial depositional systems. By integrating this analysis with recent understanding of the tectonic setting of Neoproterozoic sedimentary basins, an alternative ‘Zipper-rift’ hypothesis for Neoproterozoic glaciations is developed. The ‘Zipper-rift’ model emphasises the strong linkage between the first-order reorganisation of the Earth's surface created by diachronous rifting of the supercontinent Rodinia, the climatic effects of uplifted rift flanks and the resulting sedimentary record deposited in newly formed rift basins. Initial fragmentation of Rodinia commenced after about 750 Ma (when the paleo-Pacific Ocean started to form along the western margin of Laurentia) and culminated sometime after 610 Ma (with the opening of the paleo-Atlantic Ocean on the eastern margin of Laurentia). Breakup is recorded by well-defined ‘tectonostratigraphic’ successions that were deposited in marine rift basins. The base of each succession is characterised by coarse-grained synrift strata consisting of mass flow diamictites and conglomerates (many of the ‘tillites’ of the older literature). These facies are interbedded with large olistostromes and contain clastic carbonate debris derived from landsliding of fault scarps along rifted carbonate platforms. Diamictites and conglomerates are dominantly the product of subaqueous mass flow and mixing of coarse and fine sediment populations (the term mixtite has been used in the past). These facies are not uniquely glacial and are produced regardless of climate and latitude. Synrift deposits commonly pass up into thick slope turbidites recording enhanced subsidence and are capped by uppermost shallow marine strata that record a reduction in subsidence rates and overall basin shallowing. Tectonostratigraphic ‘cycles’ can attain thicknesses of several kilometres, but have been commonly misinterpreted as recording globally synchronous ‘glacioeustatic’, falls and rises in sea level. In fact, eustatic sea-level changes in rift basins are suppressed as a result of a strong tectonic control on relative water depths. The great length of newly formed rifted margins around the long perimeter of Laurentia (<20,000 km) ensured that deposition of tectonostratigraphic successions occurred diachronously as in the manner of a zipper between approximately 740 and 610 Ma. Some successions show a definite glacial influence on sedimentation as a consequence of latitude or strong tectonic uplift, but many do not. Regardless, all deposits record a fully functioning hydrological cycle entirely at odds with a supposed fully permafrozen planet. Mapping of those deposits where a definite glacial imprint is apparent indicates that Neoproterozoic glaciation(s) were likely regional or hemispheric in scope and latitudinally constrained. They were perhaps no more severe than other glaciations recorded in Earth history. The regional distribution of ice centres is argued to have been influenced by tectonic topography created by large mantle plumes and by rift shoulder uplift. Paleomagnetic data indicative of tropical glaciation are, in our view, ambiguous because of uncertainty as to when such paleomagnetic characteristics were acquired. A lower solar luminosity may have played a role in lowering snow line elevations and displacing glaciation into latitudes lower than those of Phanerozoic glaciations. Global tectonic and volcanic activity, especially the rapid burial or organic carbon in new rift basins, may explain extreme shifts in C-isotopic values evident in late Neoproterozoic strata.

GCM sensitivity test using increased rotation rate, reduced solar forcing and orography to examine low latitude glaciation in the neoproterozoic

During the Neoproterozoic period, most landmasses were assembled into the super‐continent, Rodinia, and parts experienced glaciation in low paleolatitudes. We examine possible causes of glaciation by increasing rotation rate, reducing the solar constant and carbon dioxide concentrations for an idealized super‐continent that is centered in the Northern Hemisphere tropics‐subtropics. Further, we introduce a 2 km north‐south mountain chain in the western regions of this super‐continent. A mixed layer ocean or prescribed time varying sea surface temperatures are used in these simulations. Our results show that neither an individual factor or a combination of these factors can cool temperatures enough to bring about glaciation on the tropical super‐continent. We conclude that other factors would be needed to initiate glaciation.

Paleoecological Reconstruction of Depositional Environments--Some Techniques of Possible Exploration Interest: ABSTRACT

Abstract Organisms are extremely sensitive to many parameters of the physical environment, and their fossil remains may thus be used in the interpretation of ancient environments. Effective use of paleoecology depends on first determining what environmental parameters are of interest. Second, developing a model based on recent examples which can be tested on the fossil record, and third, testing the model on the record itself. Following this procedure, several methods for determining the depth of water in which deposition took place are considered. A model based on the frequency distribution of three large and easily recognized groups of foraminifera (arenaceous benthonics, calcareous benthonics, and planktonics) appears very promising but has not yet been tested on the fossil record. This model uses a series of departure maps to contour water depth on a 25-foot interval and produces results that compare well with actual fathometer maps. The technique may be applicable to Cenozoic rocks in the Gulf Coast type of environment (Stehli, 1966). The distribution of ocean currents across the continental shelf is considered as a means of locating barriers to circulation (growing positive structures). A model shows that ocean current patterns on the shelf are easily seen in variations in the ratio of planktonic to benthonic foraminifera. This ratio normalizes for the effect of variations and sedimentation rate allowing that parameter to be ignored. A test of the model on Upper Cretaceous rocks of the Gulf Coast region where much independent information is available for comparison shows that this very simple paleoecological technique works rather well (Stehli and Creath, 1964). Climatic conditions strongly affect the distribution of certain stratigraphic traps, particularly such carbonate traps as reefs. Exploration for these traps is fruitless if climatic conditions at a particular time and place were such as to preclude reef development. Determination of past climatic zones is, however, difficult if not impossible, until the positions of the major continental masses in the past can be determined. Paleoecology, with its ability to reconstruct depositional environment, is in a strong position to examine both the question of continental drift and the question of polar wandering. A model which permits such an examination is developed and tested on the fossil record of the Permian. The model utilizes the latitude dependence of organic diversity as a means of determining the position of the equator and of the rotational poles. Smoothing of global diversity data by application of a best-fitting, second-order, spherical harmonic surface allows precise location of both polar and equatorial positions from diversity data relating to living forms. A test of the model on the fossil record of the Permian Period reveals a position for the rotational pole which is the same as that of today. This test casts very considerable doubt on the current interpretation given paleomagnetic measurements because continental configurations determined by paleomagnetic measurements require coincidence of the rotational and magnetic poles as a basic assumption. The test shows that rotational and magnetic poles of the Permian as seen from either North America or Eurasia differed by 45 degrees. Thus it appears on the basis of the paleoecological tests so far completed, that paleomagnetic measurements cannot yield valid data regarding the geographic latitude of continents in the Permian. It also seems that the presently accepted dynamo model for generation of the earth's magnetic field may require revision since it requires coincidence of the magnetic and rotational poles. In a general sense (but without real rigor) the test suggests that neither continental drift across latitude nor polar wandering is likely and that both the rotational poles and the latitudinal position of continents have probably remained unchanged at least since the Permian. If this is true, then the limits of tropical-subtropical conditions have varied videly through time, controlling as they varied the area of the globe suitable for reef development and in fact for extensive carbonate development (Stehli and Helsley, 1963; Stehli, McAlester and Helsley, 1967; Stehli, in press A, B). A modification of the model used to test the hypothesis of continental drift and polar wandering shows promise for reconstructing the pattern of surface-oceanic currents of the deep sea. These currents are closely related to reef development which extends farther both to the north and south on the east side of continents than on the west because of them. The same technique suggests a possible means of learning more of the fundamental causes of glaciation if applied to glacial and interglacial patterns of oceanic circulation as revealed by variations in the diversity of planktonic foraminifera in deep sea cores (Stehli, 1965).

Glaciers and geophysics

To consider the relation of glaciation to other branches of geophysics we must first develop the cause of glaciation; and this will require us to recall some ideas which, though elementary, are fundamental, and it is by keeping fundamental principles in mind that we can build most securely the superstructure.The first requisite for glaciation is the excess of the annual snowfall in a more or less limited region over the melting and dissipation. A mass of snow is thus accumulated which grows in thickness, is gradually converted into ice, and slowly flows away into a region where not only Is the annual snowfall all melted but also the ice which has flowed into it.

Note on Traces of Recent Ice-action in N. China

The question whether N. China was under the grip of Polar severity towards the close of the Tertiary or the beginning of the Pleistocene time, and whether there was sufficient precipitation to allow the existence of large glaciers even if the temperature had become for a time arctic, has, on account of its important bearing on the problem of the cause of glaciation, aroused from time to time forcible but conflicting arguments. As cumulative evidence tends to show the wide prevalence of desert conditions all over N. China throughout recent geological times, geologists seem to have generally agreed, and naturally so, to provide a negative answer to the second part of the question. But as to the first part, it remains so far completely shrouded in doubt. In matter of this kind nobody would expect to wrest out truth by mere theoretical contention. Any relevant fact, therefore, deserves to be placed on record.

Geology: Earth History

THE first volume of this important work, noticed in NATURE of January 19, 1905, and already in its second edition, dealt with geological processes and their results. In the two volumes now before us, which complete the work, geology is treated from the historical side, and we have a comprehensive review of the history of the earth on systematic lines. The treatment of these two formally separable branches of the science is, however, such as to emphasise the essential unity of the whole. As geological processes were discussed with continual reference to the historical application of the principles laid down; so the evolution of the globe, which is the story of these latter volumes, is regarded consistently from the causal point of view. Indeed, some subjects already considered under the head of geological processes, such as the dynamics of deformation, the causes of glaciation, &c., are now more fully discussed in connection with the particular geological periods which most clearly exemplify the phenomena. Geology: Earth History. By Thomas C. Chamberlin Rollin D. Salisbury. Vol. ii., Genesis, Paleozoic, pp. xxvi + 692. Vol. iii., Mesozoic, Cenozoic, pp. xi + 624. (London: John Murray, 1906.) Price 21s. net each.

The Astronomical Theory of the Glacial Period

Two letters have recently appeared in NATURE (October 17, p. 594, and November 29, 1895, p. 29), in which Sir Henry Howorth attacks Sir Robert Ball as the author of a work entitled “The Ice Age,” on the ground that the supposed astronomical cause of glaciation is totally inadequate to produce the alleged effect.

A Glacial Period in Australia

A GREAT many theories have been put forward to explain the extensive glaciation which repeatedly covered Europe and North America with enormous ice-streams. The ingenuity displayed by those who dealt with the subject was well worthy of the importance which attaches to the solution of the problem. However plausible some of the theories propounded may be, still it seems premature to approach such a question until all the available evidence bearing on the subject has been brought together. The southern hemisphere has, up till very recently, revealed only a few, and not very important facts, regarding glaciation, and it is evident that glacier traces in that hemisphere must be of great importance to explain the cause of glaciation; whether we may suppose it to be cosmic or terrestrial. I think, therefore, that my discoveries of glacier traces in Australia may be of sufficient general scientific interest to warrant my giving a short account of them in this journal.