Boulder Beds Research Articles

Further examples of silicate liquid immiscibility and spherical aggregation in the Bushveld Complex

The Boulder Bed and the Merensky Reef occur in the upper portions of the critical zone of the Bushveld Complex. Their origin has been the subject of much debate and so a general review of the more significant literature is presented. An investigation of these occurrences in the Rustenburg area has drawn parallels between their geological settings and geochemistry. Both phenomena display similar features, including aggregates of orthopyroxene, marginal layers of chromitite and coincident bulk chemical and mineralogical trends. The Boulder Bed and the Merensky Reef may be equated on this basis with the spherical orthopyroxenite aggregates previously reported by us from the main zone of the Bushveld Complex in the eastern Transvaal. The formation of these phenomena in the critical zone may be related to the process of spherical agglomeration, whereby orthopyroxene grains were accreted by means of an immiscible bridging liquid which formed in the volatile-rich magma trapped beneath an anorthosite layer.

Palynological evidence of an early Portlandian age for the uppermost Helmsdale Boulder Beds, Sutherland

Synopsis The Helmsdale Boulder Beds have for some years been cited in literature as being entirely of Kimmeridgian age. Recent palynological studies do, however, now indicate that the age of the youngest beds exposed in Navidale Bay is, in part, early Portlandian.

Bedform, facies and basin model of ancient glacial deposit: A study based on Talchir (Upper Carboniferous) rocks of Taratanr, Bihar, India

Study of bedforms, facies and associated sedimentary structures in the Talchir rocks of Taratanr Lower Gondwana basin suggests that the basal Talchir Boulder bed was deposited by both ice (moraines and deltaic moraines) and braided streams of glacier derivation (outwash deposit). The overlying sandstone was deposited by ephemeral streams. Six depositional facies related to the bedforms, ripple, dune, bar, plane bed, transverse rib and current crescent, were identified. Data compared with those from modern environments, show excellent correlation with the features of modern glacial outwash plains and modern braided, high-gradient streams. A comparison of the stratigraphy and sedimentology of Talchir rocks from eight Lower Gondwana basins in eastern India suggests that the tentative basin model for Talchir deposition in the Taratanr basin may serve as a basic model for Talchir sedimentation in all the Lower Gondwana basins in eastern India.

Spheroidal pyroxenite aggregates in the Bushveld Complex — a special case of silicate liquid immiscibility

Spherical aggregates of orthopyroxene are reported from some parts of the Bushveld Complex in a variety of host rocks. Detailed mapping has shown that these spherical aggregates, comprising pyroxenite spheroids in a quartz-norite matrix, are contact phenomena and not stratigraphic markers. Orthopyroxene, biotite and amphibole are enriched in spheroids relative to matrix; their mineral chemistry showing a fairly constant orthopyroxene and plagioclase composition through the spheroids and into the matrix, indicating in-situ formation. Bulk chemistry shows spheroid to matrix tie-lines orthogonal to those generally accepted for silicate liquid immiscibility, but other chemical information is consistent with the occurrence of immiscibility. The formation of the aggregates may be related to the industrial process of spherical agglomeration, by which spheroids are formed by the introduction of an immiscible “bridging liquid” to the melt — probably derived from the floor rocks in this case. The mechanism accounts for the field relationships, petrography and chemistry of the aggregate-matrix system. The petrology of the process equates with a special case of silicate liquid immiscibility induced by local contamination and ageing of the original magma. A similar “bridging liquid” mechanism could also account for the formation of the so-called “boulder bed” beneath the Merensky Reef.

Early Pleistocene Submarine Canyon, Boso Peninsula, Japan: ABSTRACT

The Boso submarine canyon was one of the first fossil canyons to be described. It is also one of the best exposed, because careful quarrying of the economically useful gravel fill has exposed the noneconomic marly rocks into which the canyon was cut. These country rocks (Umegase Formation) are gently dipping, cream-colored siltstones and mudstones. In contrast, the canyon fill (Higashi-higasa Formation) consists of brown to yellow sandstones with marked lenses of polymodal and polymictic conglomerates (with small pebbles of granites, basalts, cherts, and basic tuffs from the Chichibu terrane and much larger clasts of marlstone up to 1 m in diameter). There are also some boulder beds and armored mud balls and many early Pleistocene shelly fossils. End_Page 551------------------------------ Within the canyon-fill sediments, there are some unusual water-escape structures. The southern wall of the canyon is well exposed in a large quarry, where four steps occur in a vertical height of about 60 m. Upcanyon, these pass into fewer but higher steps. Small overhangs caused by protruding bedding surfaces are original features, as gravel fill still adheres to the marly walls. Canyon downcutting toward the east is shown by widening of the present outcrop of the fill in that direction, and eastward-moving paleocurrents are indicated by boulder imbrication. Rapid downcutting and filling is suggested by the well-preserved wall overhangs, and channeling within the fill sediments suggests that the deeply cut canyon was filled by several successive influxes of sediment. End_of_Article - Last_Page 552------------

Structure and stratigraphy of the Dalradian rocks of the Bennabeola area, Connemara, Eire

Summary The geology of an area of 400 sq km of Lower and Middle Dalradian rocks is described. It consists mainly of rocks belonging to the Appin and Argyll Groups which have been strongly deformed during four stages (F 1 –F 4 ) with the major development of tectonic slides occurring before F 3 . Eighteen major F 3 folds, whose geometry is described, are correlated across the Connemara antiform (F 4 ); they refold an earlier nappe-like (? F 2 ) antiform, the Derryclare fold. All of the Appin Group rocks and the Cleggan Boulder Bed Formation are contained within the core of the Derryclare fold, which locally has attenuated limbs. A zone of vertical foliation, the ‘steep belt’, is present in the south of the area. It is superimposed upon the originally steeply inclined, south-facing Derryclare fold and appears to have developed during F 4 .

The detrital zone in the shorty crater cores

The lower part of lunar cores 74002/1 contains pure fine-grained black soil grading upward to orange soil. The section, however, between 10 cm and the lunar surface contains a mixture of orange and dark soil with a clast-in-matrix texture and some agglutinates. Therefore, this upper section is interpreted as a detrital zone. Although Shorty Crater was formed approximately 30 m.y. ago, all indicators of soil age give a much shorter time for residence of the detrital zone. Both absolute agglutinate content and authigenic agglutinate content indicate a surface residence of less than 8 m.y. for the detrital portion of the core. Most calculated ages of the detrital zone cluster are around 3 m.y. Grain size distribution is characteristic of an immature soil and there is little evidence, indicated by lack of upward fining and decrease in coarsest grain sizes, ofin situ maturation of the section. Mixing with adjacent soils is very low, even though such soils lie only 0.5 M from the sampling site. Four of the five sub-strata in the upper 10 cm could have been produced by the impact event that produced the 20 M wide boulder field near the sampling site on the Shorty Crater rim. This event would distribute perched clasts over the sampling site. Thickness of the detrital part of the section is in keeping with its being ejecta from the boulder bed crater. The thickness of the agglutinate-rich zone, 1.5 cm, is reasonable for a less-than 4 m.y. residence time.

The age of the Allt na Cuile Sandstones (Upper Jurassic, Sutherland).

Synopsis New ammonite finds indicate that the Allt na Cuile Sandstones and overlying Loth River Shales range in age from at least basal Cymodoce Zone into the Mutabilis Zone (Kimmeridgian). These sediments differ markedly from the boulder bed facies of those zones to the north and south.

A SERIES OF MONOGRAPHS AND MEMOIRS (ISSN 0300-9491) TO SUPPLEMENT LETHAIA

Acid-resistant organic microfossils are described from outcrops and a boring through the middle and upper units of the VisingsÖ Beds in southern Sweden. 21 previously described acritarch species have been identified, and five new species are erected. The acritarchs include simple, although characteristically ornamented sphaeromorphs, one polygonomorph species and one acanthomorph species. Their mode of occurrence and possible lithofacial relationships are discussed. The acritarchs from the middle unit of the Visingso Beds indicate a Late Riphean age. The upper unit contains acritarchs previously known from Vendian and Lower Cambrian strata in the U.S.S.R., China and elsewhere. A Vendian age is suggested for this unit. A glacial origin is suggested for boulder beds in the middle unit of the VisingsÖ Beds.

The stratigraphy of late Precambrian metasediments between Glen Roy and Lismore

Synopsis The Moinian and Dalradian stratigraphy of the Glen Roy-Lismore area is systematically described and its terminology and definition is revised. The highest formation of the succession, the Lismore Limestone Formation, is of Lower Dalradian age and stratigraphically underlies the Portaskaig Boulder Bed. Succession, Glen Roy-Lismore. Thickness Islay Middle Dalradian Portaskaig B. B. LOWER DALRADIAN Ballachullish Group Lismore Limestone Fmn. ~1200 m Islay Limestone Fmn. (lower part correlated with Lismore Limestone Fmn.) Cuil Bay Slate Fmn. 300 m Appin Phyllite Fmn. 250 m Appin Limestone Fmn. 150 m Appin Quartzite Fmn. 300 m Ballachulish Slate Fmn. 400 m Ballachulish Limestone Fmn. 250 m Lochaber Group Leven Schist Fmn. ~2000 m Glen Coe Quartzite Fmn. 400 m Binnein Schist Fmn. 400 m Binnein Quartzite Fmn. 300 m Eilde Schist Fmn. 400 m Eilde Quartzite Fmn. 600 m Moinian Eilde Flags Fmn. >1000 m At Loch Leven the Lochaber Group is 4 km thick and the entire Lower Dalradian succession 7 km thick. To the north and west the quartzite units wedge out and the succession thins to about 5 km. This regional disparity is attributed to major facies changes and not structural modification as previously maintained (Bailey, 1934). There is a sedimentary contact between the Moinian and Dalradian Assemblages across most of the area. A detailed geological map of Lismore Island is presented together with a stratigraphic table of the Lismore Limestone Formation, which comprises a thick, partly cyclical sequence of alternating limestones and slates. The Eilde Flags Formation, the Lochaber Group and the Ballachulish Group constitute three lithological associations, each diagnostic of particular depositional conditions within a shallow shelf sea environment. The chemical compositions of the limestones and slates are tabulated and briefly discussed.

Short-Headed Stream Delta: Model for Pennsylvania Haymond Formation, West Texas

The most commonly applied deltaic model in lithogenetic analysis of ancient deposits has been that constructed by major river systems. Perhaps an equally important model is the short-headed stream delta model exemplified by the Pennsylvanian Haymond Formation in the Marathon basin. This model consists of clay, silt-sand couplets in the lower part, and bouldery conglomeratic sand in the upper part. The lower fine-grained deposits represent prodelta and delta front, the upper coarse-grained deposits are the delta plain. The difference between short-headed stream-delta deposits and their large river-delta equivalents arises in the nature of the delta front--delta plain deposits. In the Haymond Formation, the flysch-like delta-front interval probably indicates proximity to the source terrane in the southeast and sediment influxes in amounts greater than the organisms can rework. The gravelly sand delta-plain deposits indicate that most of the clay and silt common on other delta plains was flushed farther offshore. The small proportion of current-bedded shale and siltstone suggests a largely subaqueous delta plain; however, some subaerial sedimentation is indicated by bleached, root-marked sandstone. In addition, the delta plain was traversed by braided distributaries as evidenced by multiple-channel sa dstones. That the channels were choked by a vast assortment of large particles probably transported during periods of greatest runoff is indicated by the basal conglomerates and boulder beds. However, some large boulders may have been reworked from nearby coastal scree detritus and steep cliffs during intense storms.

The limits of stratigraphic distribution of Glossopteris in India

The literature reveals that controversy still persists over the lower and upper stratigraphic limits of the distribution of Glossopteris in Indian strata. A fresh approach is therefore made in this paper to evaluate these two limits from a critical reassessment of all published data, supplemented to some extent by field and laboratory investigations made by the author and some unpublished information obtained through personal communication. The lower limit is found to be considerably younger than the end of Talchir glaciation, which is not a sharp stratigraphic datum but seems to be a time-transgressive boundary represented by a succession of more than one boulder bed. The glacial phase was terminated in India, from the evidence of associated marine horizons, in the Early Permian (Sakmarian), although its onset might date back into the Carboniferous. This suggests the lower limit of Glossopteris in India somewhere high in the Sakmarian or at the base of the Artinskian. The upper limit is assessed from a reconsideration of the stratigraphic relations of the macroflora, microflora and vertebrate fauna accompanying the Permo-Triassic transition, particularly the Raniganj-Panchet sequence of Peninsular India. Results of recent research indicate the upper limit of the range of Glossopteris lies some way above the base of the Panchet Formation, i.e. at the summit of its lowermost section. This limit seems to coincide with the lower boundary of the Triassic. From the limits and pattern of the vertical distribution of Glossopteris, a simple scheme of floral zonation for the Indian lower Gondwana sequence is suggested. It is emphasized that the line of division between the lower and upper Gondwanas, which is conventionally placed at the upper boundary of the Panchet Formation from palaeontological and lithological criteria, should be defined on a biostratigraphic (particularly floral) basis, and accordingly lowered to the top of the Glossopteris-Dicroidium (transitional) zone. This zone is believed to be restricted to the lowermost beds of the Panchet Formation with very rare exceptions.

Stratigraphic and structural evolution of the Kumaon Lesser Himalaya

Six years of geological investigations comprising studies of sedimentology, geomorphology, photo-interpretation and field checks carried out by a team of 6–8 geologists have led to a reappraisal of Lesser Himalayan geology. The Algonkian and Early Palaeozoic basin derived its sediments from the south. The Caledonian orogeny had a limited effect, the Himalayan basin was sliced into two parts by a central NW-SE trending arch which became a source of sediments during the later Palaeozoic and Mesozoic evolution. The Damta group of turbidites are of Algonkian-Cambrian age; they serve as a “supra-basement” over the whole region and may have partly been taken up in the later metamorphism of the central zone of the Himalaya. Facies changes between the Deoban-Shali carbonate sequence and the Chandpur-Basantpur black shales and shales are worked out. During the Mesozoic and Tertiary, facies changes are controlled by old arches and fundamental lines of weakness which can be recognized even in the present seismic and geomorphological evolution. The Blaini boulder beds, extensively quoted in literature as tillites and used as “fool-proof” marker beds are shown to be a slumped series at the base of the Krol foredeep sequence. The Krol belt rocks are autochthonous and find an extension across the Tehri-Meenus high in the Kophara black shale series that wedge out towards the north. The occurrence of the Eocene nummulitics is two-fold: 1. (a) in concordance with the Jurassic rocks, this position occurs in quiet synclinal areas; 2. (b) in discordance over all the earlier deposited series, this position occurs over the arches witnessing late Mesozoic erosion. Reversal of metamorphism and production of gravity slides is a logical result in the evolution of the basin.

Quaternary glaciation and Palaeolithic sites in the Liddar Valley (Jammu‐Kashmir)

Abstract For the purpose of fixing the stratigraphical horizon of the Early Palaeolithic tools recently obtained from Pahlgam in the Kashmir basin (India), and to re‐examine the Quaternary glacial sequence in that area, the authors carried out a detailed survey of the Liddar Valley, the report on which is given in this article. The authors found evidence of only one glaciation at the lower altitude of 7,000 ft around Pahlgam. The Early Palaeolithic tools from the boulder bed at Pahlgam seem to be of Middle Pleistocene age.

Coarse Sediment Morphometry: A Comparative Study

ABSTRACT Shape indices of roundness, flatness, dissymetry, oblateness, sphericity, and form-ratio derived for pebbles drawn from ten occurrences of conglomerates and boulder beds formed the basis for environmental interpretations obtained by comparison with standard values. Serious inconsistencies emerged, casting doubt on coarse sediment morphometry as a tool for environmental discrimination. Statistical tests were applied in an effort to resolve the problem, but these led only to further problems. Specifically, roundness, sphericity, and oblateness are found to be unreliable for discriminatory purposes, which, with flatness and dissymetry already questioned, brings to five the number of shape measures whose reliability has been called into question. Positive steps are suggested that may help to resolve the problems surrounding the reliability of coarse sediment morphometry for diagnostic purposes.

Cambrian Fossils from the Hazira Shale, Pakistan

Until recently the Abbottabad Group in the Hazara area, western Pakistan, was thought to be Upper Carboniferous-Permian in age1. But when Latif found Hyolithid shells in the Hazira Shale Formation at the top of the Abbottabad Group, he suggested that a Lower Palaeozoic age was more probable; on lithological grounds he favoured a Cambrian age for the Hazira Shale2. Preparation of Latif's material not only confirmed the presence of Hyolithids (Circotheca? and Linevitus?) but yielded spicules of the Heteractinellid sponge Chancelloria Walcott. Chancelloria is known from the Middle Cambrian of North America3, the Ordian of Australia4, and from the Lower Cambrian in England5. A Cambrian age for the Hazira Shale is therefore fully confirmed. If the Tanakki boulder bed at the base of the Abbottabad Group is of glacial origin1,2 it becomes feasible to correlate it with the widespread late Precambrian glaciation.

Sedimentology of Type Tejon Formation of San Emigdio Mountains, California: ABSTRACT

The type Tejon Formation of the San Emigdio Mountains is a marine clastic sedimentary sequence of middle and late Eocene age that was deposited primarily in a variety of shallow-marine environments during an eastward transgression followed by a westward regression. It lies unconformably on a pre-Tertiary crystalline basement complex and is overlain by the marine San Emigdio Formation and the nonmarine Tecuya Formation. It is more than 4,000 ft thick in the center of the range, but thins and grades laterally eastward into nonmarine conglomerates and sandstones. Paleocurrent data indicate dominant transport of sediments toward the west. Marks defined four members of the Tejon Formation (in ascending order): Uvas Conglomerate, Liveoak Shale, Metralla Sandstone, and Reed Canyon Siltstone. The Uvas contains medium- to large-scale cross-stratification, ripple markings, well-sorted planar-stratified beach-type sandstones, large burrows, boulder beds, locally abundant megafauna, and was deposited adjacent to the transgressive shoreline. The Liveoak shale is primarily an extensively bioturbated silty shale with locally abundant microfauna and abundant sandstone interbeds in its lower and upper parts; it grades laterally eastward from a deep-water shale into shallow-marine sandstones. The Metralla Sandstone Member is typically a bioturbated silty fine-grained sandstone which contains interbedded conglomerates, medium- and la ge-scale cross-stratification, ripple markings, beach-type sandstones, and abundant megafauna in its eastern exposures where it was deposited adjacent to the regressive shoreline; however, on the west it grades laterally into thinly bedded flyschlike sandstones and shales deposited in deeper water. The Reed Canyon Siltstone Member is in an extensively bioturbated thin unit that locally contains some megafauna, microfauna, and thin coal interbeds. End_of_Article - Last_Page 436------------

Boulder Beds in Tesnus and Dimple Formations (Mississippian-Pennsylvanian), Payne Hills, Marathon Region, Texas: ABSTRACT

End_Page 792------------------------------Boulders of sedimentary rock are present in shale units in the Tesnus and Dimple formations near the western margin of the Marathon uplift in the Payne Hills, a terrane underlain by imbricate thrust plates. Although, locally, boulders have been rolled along the thrusts as ball bearings, a sedimentary origin as submarine-slope deposits for the beds is inferred because (1) most boulders are unlike rocks involved in thrusting, (2) boulders are not brecciated, and (3) many boulders do not occur along thrust faults. Boulders range from 1 to 24 ft long and are unevenly distributed along strike. Large boulders lie with their long dimension in the plane of bedding of the host rock. The boulder-bearing unit in the Tesnus is from 5 to 50 ft above the base of the formation; that in the Dimple is about 100 ft above its base. Common boulders are light-colored dolosparite and dolomicrite, mottled, dark-green chert, and chert sharpstone conglomerate; a few boulders are limestone, sandstone, novaculite, and porphyry (Dimple Formation only). The chert resembles, but is not identical with, beds in the Caballos Novaculite, although the other rocks are unlike indigenous Paleozoic strata in the uplift. Early Ordovician, Silurian(?), and Middle Devonian conodonts occur in the carbonate boulders. The boulders were derived from a positive, tectonic element northwest of the basin that was active intermittently throughout Paleozoic time. The lack of fine debris in the boulder beds suggests that the boulders rolled or slid into place and outdistanced finer detritus. End_of_Article - Last_Page 793------------

Stratigraphy and Tectonics of Sedimentary Basins on East Coast of Peninsular India

The stratigraphy and tectonics of the Cauvery, Palar, and Godavari-Krishna basins, on the east coast of India, are considered on the basis of geologic, geophysical, and drilling data. The Cauvery basin was formed during Late Jurassic time by sagging of a part of the Indian shield, mainly along the dominant northeast-southwest basement trends. The basin consists of several depressions separated from each other by subsurface basement ridges aligned parallel or subparallel with the dominant basement trends. The sedimentation in the respective depressions was controlled by movements along these trends from the time of deposition of the Upper Gondwana beds. The depocenters, which were mainly open toward the west during Upper Gondwana deposition, shifted toward the east as a result of general basinal tilt at the beginning of the Tertiary. These movements were responsible for repeated transgressions and regressions, as is evidenced by lithofacies, biofacies, and thickness variations, as well as by sedimentation breaks. Outcrops in the Palar basin include thin Permian boulder beds and shales, a thick paralic Cretaceous sequence, and a thin continental Neogene succession. In the Godavari-Krishna basin the outcropping strata are Middle Jurassic to Lower Cretaceous paralic to shallow-marine sedimentary rocks and thin Trap Volcanics (basalts) overlain by a continental Neogene succession. A synthesis of geologic and geophysical data suggests that the tectonic and sedimentation patterns in the Palar and Godavari-Krishna basins are likely to be analogous to those of the Cauvery basin.

Lower Palaeozoic (? Cambrian) Hyolithids from the Hazara Shale, Pakistan

THE age of rocks forming the Lower Himalayas of Nepal and of the Kumaon, Garhwal, Simla, Kashmir and Hazara areas in the northwestern part of the Indo-Pakistan subcontinent has long been the subject of considerable controversy. The rocks include the Simla Slates, the Chandpur and Nagthat beds, as well as the Hazara Group and Tanol Formation of the Hazara District in northern Pakistan, which are separated from the overlying clastic and carbonate sediments by a disconformity marked by a glacial conglomerate known as the Blaini boulder bed in Nepal and India and the Tanakki boulder bed in Hazara, Pakistan. The post-Blaini or post-Tanakki sequence is known as the Infra-Krol and Krol beds in Nepal, Kumaon and Simla and as the Abbottabad Group in Hazara1,2. In the absence of fossil evidence, both the Blaini and Tanakki boulder beds have been correlated with the fossiliferous Talchir boulder bed and, accordingly, considered to be of Upper Carboniferous-Permian age.