Cenozoic Glacial History Research Articles

Use of Topographic Map Evidence to Locate a New Cenozoic Glacial History Paradigm’s Deep “Hole” Rim in Northeast New Mexico and Southern Colorado, USA

A recently proposed Cenozoic geology and glacial history paradigm requires a thick North American continental ice sheet to have been located within an ice sheet created and occupied deep “hole” and predicts large south-oriented meltwater floods flowed across the deep “hole’s” southern rim before rim uplift progressively diverted floodwaters toward the Mississippi River valley, which in time became the only deep “hole” southern exit (the accepted paradigm does not recognize such an ice sheet created deep “hole”). Possible locations for the new paradigm deep “hole” rim in Great Plains regions east of the Sangre de Cristo Mountains are considered with the one being the Purgatoire-Canadian River drainage divide in the Raton Mesas area along the Colorado-New Mexico border and a second being the Canadian-Pecos River (Arkansas River-Gulf of Mexico) drainage divide in San Miguel County (NM). Detailed topographic maps indicate streams of what could have been south-oriented melt water once crossed the two studied drainage divides with headward erosion of the northeast-oriented Purgatoire River drainage basin diverting south-oriented water toward the east-oriented Arkansas River (and Mississippi River valley) while headward erosion of east-oriented Canadian River tributary valleys beheaded south-oriented flow to the south-southeast oriented Pecos River (flowing to the Rio Grande River–which then flows to the Gulf of Mexico). While the Purgatoire-Canadian River drainage divide has some deep “hole” rim characteristics, those characteristics disappear in an eastward direction and the Canadian River, like the Purgatoire River, is an Arkansas River tributary. East-oriented Canadian River headwaters and tributary valley headward erosion diverted south-oriented flow from the Rio Grande River to the Mississippi River valley (via the Canadian and Arkansas Rivers), which means the new paradigm’s deep “hole” rim southern margin should be located along or near the Arkansas River-Gulf of Mexico drainage divide.

How a New Paradigm Explains Topographic Map Drainage System and Erosional Landform Evidence in the Fremont County Royal Gorge Area, Colorado, USA

A new Cenozoic geologic and glacial history paradigm (new paradigm) describes massive and prolonged continental ice sheet meltwater floods that eroded the Colorado Royal Gorge area and surrounding regions and which were diverted in east, northeast, and even north directions as uplift of a thick ice sheet created deep “hole” rim gradually occurred (the thick ice sheet was located where North American ice sheets are usually recognized to have existed). A deep “hole” rim segment followed what is now the northern and central Colorado east-west continental divide southward to the Arkansas River headwaters area and then continued south along the Sangre de Cristo Mountains crestline to at least the Purgatoire River-Canadian River drainage divide and may have continued east from that point along a less well-defined zone beginning with what is now the Purgatoire River-Canadian River drainage divide. Diverging and converging valley complexes, barbed tributaries, and Arkansas River and other drainage route direction changes (easily seen on United States Geological Survey detailed topographic maps) are interpreted to have developed as the south-oriented floodwaters first flowed across the rising deep “hole” rim to reach the south- and southeast-oriented Rio Grande River drainage basin and were subsequently blocked by deep “hole” rim uplift and diverted to flow in east, northeast, and north directions. The accepted Cenozoic geologic and glacial history paradigm (accepted paradigm) has to date been unable to satisfactorily explain the detailed topographic map drainage system and erosional landform evidence and the new and accepted paradigms are incommensurable and lead to quite different Cenozoic geologic and glacial histories.

How Two Different Cenozoic Geologic and Glacial History Paradigms Explain the Southcentral Montana Musselshell-Yellowstone River Drainage Divide Origin, USA

The accepted Cenozoic geologic and glacial history paradigm (accepted paradigm) considers the southcentral Montana Musselshell-Yellowstone River drainage divide to have originated during Tertiary (or preglacial) time while a new and different Cenozoic geologic and glacial history paradigm (new paradigm) describes how headward erosion of a northeast-oriented Musselshell River valley segment captured huge southeast-oriented meltwater floods to create the drainage divide late during a continental ice sheet’s melt history. Northwest to southeast oriented divide crossings (low points observed on detailed topographic maps where water once flowed across the drainage divide), southeast-oriented Yellowstone and Musselshell River segments immediately upstream from northeast-oriented Yellowstone and Musselshell River segments, and southeast- and northwest-oriented tributaries to northeast-oriented Yellowstone and Musselshell River segments indicate a major southeast-oriented drainage system predated the northeast-oriented Yellowstone and Musselshell River segments. Closeness of the divide crossings, divide crossing floor elevations, large escarpment-surrounded erosional amphitheater-shaped basins, and unusual flat-floored internally drained basin areas (straddling the drainage divide), all suggest the previous southeast-oriented drainage system moved large quantities of water which deeply eroded the region. In the mid-20th century geomorphologists working from the accepted paradigm perspective determined trying to explain such erosional landform evidence from the accepted paradigm perspective was a nonproductive research activity and now rarely investigate erosional landform origins. On the other hand, the new paradigm appears to explain most, if not all observed erosional landform features, although the two paradigms lead to significantly different regional Cenozoic geologic and glacial histories that cannot be easily compared.  

North Platte River-South Platte River Confluence Area Drainage System History as Determined by Topographic Map Interpretation: Western Nebraska, USA

Detailed topographic maps of the western Nebraska North Platte River-South Platte River confluence area show a low relief and gently sloping southeast-oriented upland surface, asymmetrical drainage divides, nearly adjacent and parallel east-oriented North and South Platte River valley segments, barbed tributaries, and shallow divide crossings (low points along drainage divides) in a region south of the Nebraska Sand Hills and at the Nebraska loess region’s western margin. Published interpretations of North and South Platte River confluence area landforms (referred to as the accepted paradigm) do not explain most drainage features and are compared with a new paradigm’s interpretations to determine which of the two paradigms explains the regional drainage history and related surface features in a simple and consistent manner. New paradigm interpretations require large sheets of slowly-moving southeast-oriented water to have flowed toward what was probably an actively eroding Republican River valley and to have shaped the upland surface while the Platte and North and South Platte River valleys eroded headward into and across the region so as to create the asymmetric drainage divides, barbed tributaries, and shallow divide crossings. These new paradigm interpretations are consistent with each other and with recently published new paradigm interpretations of upstream North and South Platte River drainage system history. New paradigm interpretations also suggest the adjacent Nebraska Sand Hills developed on a large flood deposited delta (typical of sand dune areas on former glacial lake deltas further to the north) and the slowly-moving sheets of water may have been responsible for some or all of Nebraska’s loess deposits, although the new paradigm leads to a fundamentally different middle and late Cenozoic regional geologic and glacial history than what workers using the accepted paradigm have described.

Topographic Map Analysis of Mountain Passes Crossing the Continental Divide Between Colorado River Headwaters and North and South Platte River Headwaters to Test a New Geomorphology Paradigm, Colorado, USA

Detailed topographic maps are used to identify and briefly describe named (and a few unnamed) mountain passes crossing high elevation east-west continental divide segments encircling south- and southwest-oriented Colorado River headwaters and linking the Colorado River drainage basin (draining to the Pacific Ocean) with the North and South Platte River drainage basins (draining to the Platte, Missouri, and Mississippi Rivers and Gulf of Mexico). Previous researchers following commonly accepted geomorphology paradigm rules have not explained how most, if any of these mountain passes originated. A recently proposed geomorphology paradigm requires all Missouri River drainage basin valleys to have eroded headward across massive south- and southeast-oriented floods, which implies south- and southeast-oriented floods flowed from what are today north-oriented North Platte River headwaters across the continental divide, the present-day south- and southwest-oriented Colorado River headwaters valley, and then across what is now the continental divide a second time to reach east- and southeast-oriented South Platte River headwaters. Paradigms are rules determining how a scientific discipline governs its research and by themselves are neither correct nor incorrect and are judged on their ability to explain observed evidence. From the new paradigm perspective, a stream eroded each of the passes into a rising mountain range until the uplift rate outpaced the erosion rate and forced a flow reversal in what would have been the upstream valley. The passes and the valleys leading in both directions from the continental divide are best explained if diverging and converging south- and southeast-oriented flood flow channels crossed rising mountain ranges. While explaining observed drainage patterns and erosional landforms such an interpretation requires a fundamentally different regional middle and late Cenozoic glacial and geologic history than what previous investigators using the accepted paradigm perspective have described.

Analyzing Anomalous Topographic MapDrainage System and Landform Evidence as a Glacial History Paradigm Problem: A Literature Review

While not usually stated, detailed topographic maps show well-mapped anomalous drainage system and other erosional landform evidence the accepted North American Cenozoic geologic and glacial history paradigm (accepted paradigm) does not permit geomorphologists to satisfactorily explain. A new and fundamentally different paradigm able to explain the drainage system and other erosional landform evidence has recently emerged, but requires what the accepted paradigm considers to be the preglacial (and probably mid-Cenozoic) Bell River drainage system to have formed on a melting continental ice sheet’s floor. The new paradigm’s melting ice sheet had previously eroded bedrock underneath it and caused crustal warping that raised continental regions and mountain ranges so as to create and occupy a deep “hole” while massive and prolonged meltwater floods flowed across rising continental regions and mountain ranges to the south. The new paradigm leads to a completely different middle Cenozoic geologic and glacial history than the accepted paradigm describes and the two paradigms are analyzed according to good science expectations such as using evidence anyone can see, applying common sense logic during each research step, producing consistent results, and simplicity of paradigm generated explanations. The new paradigm uses topographic map evidence anyone can see, appears to use common sense logic during each research step, and produces remarkably consistent results leading to a simpler Cenozoic northern Missouri River drainage basin region geologic and glacial history than what the accepted paradigm describes. Further work is needed to test the new paradigm’s ability to explain drainage system and erosional landform evidence in other geographic regions such as in the Ohio River drainage basin.

Deep Erosion by Continental Ice Sheets: A Northern Missouri River Drainage Basin Perspective: North America

While accepting some erosion by continental ice sheets most geologists reject a previously proposed deep erosion by continental ice sheets hypothesis, yet common sense logic suggests continental ice sheets should have eroded much more than they are usually given credit for. Such situations arise in scientific communities when an accepted paradigm cannot adequately explain significant observable evidence. A new and fundamentally different paradigm, constructed from detailed topographic map evidence, illustrates how deep erosion (and crustal warping) by at least one continental ice sheet explains previously unexplained northern Missouri River drainage basin erosional landform origins. The new paradigm requires at least one North American continental ice sheet to have created (by deep erosion and by ice sheet related crustal warping) a deep “hole” in which the ice sheet was located. Late during that ice sheet’s melt history north- and northeast-oriented valleys eroded headward from that deep “hole’s” southern end to capture immense southeast-oriented ice-marginal melt-water floods and to create what are today north- and northeast-oriented Missouri River headwaters and tributary drainage routes. While successfully explaining numerous previously unexplained erosional landforms the new paradigm challenges a number of commonly accepted middle and late Cenozoic geologic and glacial history interpretations.

Thresholds for Cenozoic bipolar glaciation

The long-standing view of Earth's Cenozoic glacial history calls for the first continental-scale glaciation of Antarctica in the earliest Oligocene epoch ( approximately 33.6 million years ago), followed by the onset of northern-hemispheric glacial cycles in the late Pliocene epoch, about 31 million years later. The pivotal early Oligocene event is characterized by a rapid shift of 1.5 parts per thousand in deep-sea benthic oxygen-isotope values (Oi-1) within a few hundred thousand years, reflecting a combination of terrestrial ice growth and deep-sea cooling. The apparent absence of contemporaneous cooling in deep-sea Mg/Ca records, however, has been argued to reflect the growth of more ice than can be accommodated on Antarctica; this, combined with new evidence of continental cooling and ice-rafted debris in the Northern Hemisphere during this period, raises the possibility that Oi-1 represents a precursory bipolar glaciation. Here we test this hypothesis using an isotope-capable global climate/ice-sheet model that accommodates both the long-term decline of Cenozoic atmospheric CO(2) levels and the effects of orbital forcing. We show that the CO(2) threshold below which glaciation occurs in the Northern Hemisphere ( approximately 280 p.p.m.v.) is much lower than that for Antarctica ( approximately 750 p.p.m.v.). Therefore, the growth of ice sheets in the Northern Hemisphere immediately following Antarctic glaciation would have required rapid CO(2) drawdown within the Oi-1 timeframe, to levels lower than those estimated by geochemical proxies and carbon-cycle models. Instead of bipolar glaciation, we find that Oi-1 is best explained by Antarctic glaciation alone, combined with deep-sea cooling of up to 4 degrees C and Antarctic ice that is less isotopically depleted (-30 to -35 per thousand) than previously suggested. Proxy CO(2) estimates remain above our model's northern-hemispheric glaciation threshold of approximately 280 p.p.m.v. until approximately 25 Myr ago, but have been near or below that level ever since. This implies that episodic northern-hemispheric ice sheets have been possible some 20 million years earlier than currently assumed (although still much later than Oi-1) and could explain some of the variability in Miocene sea-level records.

New insights into Quaternary glacial dynamic changes on the George V Land continental margin (East Antarctica)

The continental margin of the George V Land represents the seaward termination of one of the largest sub-glacial basins (the Wilkes Basin) of the East Antarctic Ice Sheet (EAIS) and hence is a potentially useful site for the investigation of the Cenozoic glacial history of Antarctica. Because the seafloor morphology relates strictly to recent glacial marine sedimentary processes, we have compiled all available echo-soundings data collected until the year 2001 and integrated the data set with satellite altimetry data. As a result, we have produced a new bathymetric map of the margin, covering an area of more than 80,000 km 2 with a spatial resolution of about 1 km. The bathymetric data have been integrated with sub-bottom profiler data with the purpose of defining sedimentary processes and their variations during the Quaternary. The continental shelf of the Wilkes Land margin is characterised by alternating banks and glacial troughs connected to sub-marine canyons that cut into the continental slope. Our study focussed on the continental rise, where asymmetrical ridges alternate with large deep-sea channels. The ridges have a long gentle eastern side and short steep western side, with axis elongated approximately in north–south direction, perpendicular to the margin. The channels represent the main sediment drainage pattern feeding the ridge depositional system found along the continental rise. The sediment is supplied to the continental shelf edge by ice sheets, and sediment gravity flows are considered the main process for sediment supply to the rise. The modern sedimentary environment of the deep margin is affected by turbiditic down-slope sediment transfer with a minor contribution from along-slope contour currents. The WEGA channel is currently affected by transport and settling of sediment through High-Salinity Shelf Water (HSSW), originating on the continental shelf. We infer that thermohaline circulation has contributed to sediment transport and deposition since the mid-Pleistocene.

A review of the Cenozoic stratigraphy and glacial history of the Lambert Graben—Prydz Bay region, East Antarctica

The Cenozoic glacial history of East Antarctica is recorded in part by the stratigraphy of the Prydz Bay—Lambert Graben region. The glacigene strata and associated erosion surfaces record at least 10 intervals of glacial advance (with accompanying erosion and sediment compaction), and more than 17 intervals of glacial retreat (enabling open marine deposition in Prydz Bay and the Lambert Graben). The number of glacial advances and retreats is considerably less than would be expected from Milankovitch frequencies due to the incomplete stratigraphic record. Large advances of the Lambert Glacier caused progradation of the continental shelf edge. At times of extreme glacial retreat, marine conditions reached > 450 km inland from the modern ice shelf edge. This review presents a partial reconstruction of Cenozoic glacial extent within Prydz Bay and the Lambert Graben that can be compared to eustatic sea-level records from the southern Australian continental margin.

Variability in Cenozoic sedimentation along the continental rise of the Bellingshausen Sea, West Antarctica

Seismic reflection profiles, bathymetric and magnetic data collected along and across the continental margin of the Bellingshausen Sea provide new constraints and interpretations of the oceanic basement structure and Cenozoic glacial history of West Antarctica. Evidence for tectonic boundaries that lie perpendicular to the margin has been identified on the basis of one previously unpublished along-slope multichannel seismic reflection profile. By combining several magnetic data sets, we determined basement ages and verified the positions of possible fracture zones, enabling us to improve previous tectonic and stratigraphic models. We establish three main sediment units on the basis of one seismic along-slope profile and by correlation to the continental shelf via one cross-slope profile. We interpret a lowermost unit, Be3 (older then 9.6 Ma), as representing a long period of slow accumulation of mainly turbiditic sediments. Unit Be2 (from about 9.6 to 5.3 Ma) may represent a period of short-lived ice advances on the continental shelf. The uppermost unit, Be1 (from about 5.3 Ma to present), apparently consists of rapidly deposited terrigenous sediment that we interpret as having been transported to the shelf edge by frequent advances of grounded ice. Listric faults are observed in Be1 and indicate sediment instability due to interactions between different depositional processes. Correlation of the sediment classification scheme with the continental rise of the western Antarctic Peninsula shows obvious differences in sediment depositional patterns. We estimate a very high sedimentation rate for Unit Be1 (up to 295 m/my) which points to an increase in glacial sediment supply due to major glacial outlets that flowed to nearby parts of the shelf edge in Pliocene and Quaternary times. This is in contrast to the situation at the adjacent Antarctic Peninsular margin and many other parts of the continental rise around Antarctica.

Late Cenozoic glacial history and evolution of the Storegga Slide area and adjacent slide flank regions, Norwegian continental margin

Acoustic data and sediment cores collected from the Storegga Slide and its adjacent slide flanks, i.e. the Vøring Plateau to the north and the North Sea Fan to the south, have been used to study the Late Cenozoic glacial history and geological development of this region. Age constrains obtained from the investigated cores show that the Fennoscandian Ice Sheet reached the shelf edge during Marine Isotope Stages (MIS) 12, 10, 8, 6 and 2. Ice sheet fluctuations within each glaciation might have occurred, as is evidenced for the Last Glacial Maximum (MIS 2). The first extensive ice advance is identified in the Early Pleistocene, at c. 1.1 Ma; however, between 2.6 and 0.5 Ma the ice sheets were largely restricted to the fjords and inner shelf. During each glacial maximum, glacigenic debris flows (GDFs) transported basal till, deposited at the shelf edge, into the deep sea along the entire studied margin. The most voluminous GDF sequences are found on the southern Storegga Slide flank (North Sea Fan), where the individual flows are found as far as 500 km from the shelf edge. On the Vøring Plateau glacimarine/hemipelagic sedimentation has dominated the last c. 250,000 yr. During MIS 2 such sediments were rapidly deposited, covering the upper-slope-limited GDF units in this region. Between c. 15,700 and 15,000 14C yr BP, i.e. during the last deglaciation of the Norwegian margin, a presumed meltwater plume, released from the disintegrating Norwegian Channel Ice Stream, transported and rapidly deposited up to 20 m of fine-grained sediments in the region north of the North Sea Fan. The rapid deposition of large volumes of GDFs, glacimarine and meltwater related sediments might have influenced the stability of the slope sediments in the studied region, promoting conditions favorable for failure. Furthermore, these high sedimentation rates also partly account for the high subsidence rates observed on the Norwegian continental margin in the Late Cenozoic.

Strides made in understanding Antarctic stratigraphy and Cenozoic glacial history

It is known that the Antarctic ice sheet greatly affected global climate, sea‐level, ocean circulation, and Southern Hemisphere biota during Cenozoic times, but until recently, how remained largely a mystery. Because few Cenozoic rocks are exposed on the Antarctic continent, the only way to investigate the evolution of the Antarctic ice sheet was through isotopic studies on distant deep‐ocean sediments. The success of these studies was limited—isotopic studies and low‐latitude sea level variation yielded different glacial ice volumes.To take study of Cenozoic Antarctic glaciations and their effects a step further, the Antarctic Offshore Acoustic Stratigraphy project (ANTOSTRAT) assembled a contingent of geoscientists from over 100 institutions in 32 countries. Since 1989, they have compiled and analyzed offshore acoustic and geologic data from the Antarctic continental margin, amassing over 150,000 km of multichannel seismic reflection data, tens of thousands of kilometers of single‐channel, high‐resolution seismic data, and over 1000 cores.

Morphology and late Cenozoic (<5 Ma) glacial history of the area between David and Mawson Glaciers, Victoria Land, Antarctica

Glacio-geological field work and radar ice-thickness sounding were carried out in the area between David and Mawson Glaciers. A subglacial topographic map has been compiled from radio-echo-sounding data. The northern part of this map shows that the trench of David Glacier reaches a depth of more than 1000 m below sea level. The area south of David Glacier comprises a landscape of nunatak clusters dissected by glaciated valleys with ice thicknesses as much as 800 m. Subglacial cirques occur at the outer margins of the nunatak clusters. A model for the regional glacial history is proposed. It starts with a major deglaciation in the Pliocene, which results in marine transgression in basins west of the Transantarctic Mountains. During the late Pliocene, the ice advanced towards the northeast, depositing a thin layer of (Sirius Group) till containing reworked mid-Pliocene marine diatoms. Due to accelerated mountain uplift, the ice cut iIlto the pre-Pliocene peneplain, eroding broad valleys. A period of ice-sheet retreat followed to expose a landscape of large nunataks separated by wide valleys. During this period, local cirque glaciation occurred. When the ice sheet advanced again, another phase of uplift forced the glaciers to cut deeper into the valleys. Probably since the Last Glacial Maximum the ice surface has lowered by about 100 m.

Morphology and late Cenozoic (<5 Ma) glacial history of the area between David and Mawson Glaciers, Victoria Land, Antarctica

Glacio-geological field work and radar ice-thickness sounding were carried out in the area between David and Mawson Glaciers. A subglacial topographic map has been compiled from radio-echo-sounding data. The northern part of this map shows that the trench of David Glacier reaches a depth of more than 1000 m below sea level. The area south of David Glacier comprises a landscape of nunatak clusters dissected by glaciated valleys with ice thicknesses as much as 800 m. Subglacial cirques occur at the outer margins of the nunatak clusters. A model for the regional glacial history is proposed. It starts with a major deglaciation in the Pliocene, which results in marine transgression in basins west of the Transantarctic Mountains. During the late Pliocene, the ice advanced towards the northeast, depositing a thin layer of (Sirius Group) till containing reworked mid-Pliocene marine diatoms. Due to accelerated mountain uplift, the ice cut iIlto the pre-Pliocene peneplain, eroding broad valleys. A period of ice-sheet retreat followed to expose a landscape of large nunataks separated by wide valleys. During this period, local cirque glaciation occurred. When the ice sheet advanced again, another phase of uplift forced the glaciers to cut deeper into the valleys. Probably since the Last Glacial Maximum the ice surface has lowered by about 100 m.

Formation and disintegration of the Antarctic ice sheet

A model of the Antarctic ice sheet has been used to simulate the ice sheet in warmer climates, in order to investigate what kind of ice-sheet geometries one can reasonably expect under what kind of climatic conditions and to discover which physical mechanisms may be involved to explain them. The results of these experiments reveal the considerable stability of; in particular, the East Antarctic ice sheet. It would require a temperature rise of between 17 and 20 K above present levels to remove this ice sheet from the subglacial basins in the interior of the continent and of 25 K to melt down the Antarctic ice sheet completely. For a temperature rise below 5 K, the model actually predicts a larger Antarctic ice sheet than today as a result of increased snowfall, whereas the west Antarctic ice sheet was round not to survive temperatures more than 8–10 K above present values. Furthermore, basal temperature conditions in these experiments point to the problems involved in raising the base of the ice sheet to the pressure-melting point over the large areas necessary to consider the possibility of sliding instability. These results bear on a lively debate regarding the late Cenozoic glacial history of Antarctica. Particularly, based on these findings, it is difficult to reconcile a highly variable East Antarctic ice sheet until the Pliocene with modest warming recorded in, for instance, the deep-sea records for the late Neogene.

Formation and disintegration of the Antarctic ice sheet

A model of the Antarctic ice sheet has been used to simulate the ice sheet in warmer climates, in order to investigate what kind of ice-sheet geometries one can reasonably expect under what kind of climatic conditions and to discover which physical mechanisms may be involved to explain them. The results of these experiments reveal the considerable stability of; in particular, the East Antarctic ice sheet. It would require a temperature rise of between 17 and 20 K above present levels to remove this ice sheet from the subglacial basins in the interior of the continent and of 25 K to melt down the Antarctic ice sheet completely. For a temperature rise below 5 K, the model actually predicts a larger Antarctic ice sheet than today as a result of increased snowfall, whereas the west Antarctic ice sheet was round not to survive temperatures more than 8–10 K above present values. Furthermore, basal temperature conditions in these experiments point to the problems involved in raising the base of the ice sheet to the pressure-melting point over the large areas necessary to consider the possibility of sliding instability. These results bear on a lively debate regarding the late Cenozoic glacial history of Antarctica. Particularly, based on these findings, it is difficult to reconcile a highly variable East Antarctic ice sheet until the Pliocene with modest warming recorded in, for instance, the deep-sea records for the late Neogene.

Formation and disintegration of the Antarctic ice sheet

A model of the Antarctic ice sheet has been used to simulate the ice sheet in warmer climates, in order to investigate what kind of ice-sheet geometries one can reasonably expect under what kind of climatic conditions and to discover which physical mechanisms may be involved to explain them. The results of these experiments reveal the considerable stability of; in particular, the East Antarctic ice sheet. It would require a temperature rise of between 17 and 20 K above present levels to remove this ice sheet from the subglacial basins in the interior of the continent and of 25 K to melt down the Antarctic ice sheet completely. For a temperature rise below 5 K, the model actually predicts a larger Antarctic ice sheet than today as a result of increased snowfall, whereas the west Antarctic ice sheet was round not to survive temperatures more than 8–10 K above present values. Furthermore, basal temperature conditions in these experiments point to the problems involved in raising the base of the ice sheet to the pressure-melting point over the large areas necessary to consider the possibility of sliding instability. These results bear on a lively debate regarding the late Cenozoic glacial history of Antarctica. Particularly, based on these findings, it is difficult to reconcile a highly variable East Antarctic ice sheet until the Pliocene with modest warming recorded in, for instance, the deep-sea records for the late Neogene.

Palaeomagnetism of Ferricrete From Vale of Belvoir, Western Tasmania: Implications For Tasmanian Cenozoic Glacial History

The preliminary results of paleomagnetic studies of ferricretes associated with glacigenic sediments from the Vale of Beivoir, western Tasmania, have important implications for Tasmanian Cenozoic glacial history. The geology of the Vale of Beivoir (Fig. 1) is dominated by glacigenic drift and Tertiary basalt which overlie karstified Ordovician Gordon Group limestones. Ferricrete, up to 2 m in thickness, is developed within and adjacent to the weathered glacigenic sediments and is exposed in road cuttings, as well as in scattered blocky outcrops across the area (Fig. 1). Widely spaced joints in the ferricrete outcrops sometimes give the appearance of crude bedding. The ferricrete blocks appear to have developed in situ, rather than being deposited as erratics. The ferricrete is mainly developed adjacent to basalt in the valley. This suggests derivation of the iron from chemical weathering of the basalt, and its lateral migration and accumulation to produce massive and concretionary horizons controlled by local water-tables.

Further finds of the Derrick Peak meteorite, Transantarctic Mountains, and implications for terrestrial age

Abstract— Nine additional iron meteorite fragments weighing a total of 72 kg were recovered from the Derrick Peak area by a Canterbury Museum geological party in late 1988. One iron was located in the Onnum Valley, 6 km south of the previous finds. Geochemical analysis indicates that all irons belong to a single meteorite shower, greatly increasing the known extent of the fall zone. Kamp and Lowe (1982) have previously estimated the terrestrial age of the meteorite from glacial geological evidence. The location of the 1988 finds supports Kamp and Lowe's interpretation that the meteorites lie in situ, but recent revisions of the chronology of Cenozoic glacial history of the region reduce the interpreted terrestrial age. An age of between Oxygen Isotope stages 6 and 2 is probable (190–125 to 35–12 ka BP). This conflicts with a terrestrial age estimate of 1.0 ± 0.1 Ma BP from cosmogenic radionuclides.