Taphonomy of mammalian fossil remains from Siwalik rocks of Pakistan

Paleobiology ◽  
1986 ◽  
Vol 12 (2) ◽  
pp. 119-142 ◽  
Author(s):  
Catherine Badgley

Siwalik rocks of Pakistan are a virtually continuous, continental sedimentary sequence, extending in age from 18 to 1 ma b.p. This paper describes taphonomic features of late Miocene mammalian assemblages from a highly fossiliferous interval about 400 m thick, based on field documentation of sedimentary environments at 42 fossil localities and systematic fossil collection of 21 localities.Within a broadly fluvial system, I recognize four sedimentary environments of bone accumulation, distinguished by lithology, unit-thickness, unit-geometry, contacts, sedimentary structures, and relationship to adjacent units. Each environment corresponds to an association of lithofacies. Facies Association I is interpreted as the persistent, major channel bodies of a meandering fluvial system; Facies Association II as coarse-grained flood deposits, such as crevasse splays, deposited beyond the main channels; Facies Association III as channel margins, including levees and swales; and Facies Association IV as predominantly subaerial floodplains.Taphonomic features of bone assemblages from each facies association include skeletal-element composition, surface distribution of specimens, degree of articulation, hydraulic equivalence between organic and inorganic sedimentary particles, frequency of juvenile remains, size distribution of fauna, and an estimate of duration of accumulation of individual fossil localities. The distribution of these features among the four facies associations suggests that bone assemblages in Facies Associations I and II accumulated by the action of currents in river channels or floods, whereas bone assemblages in Facies Associations III and IV accumulated through concentration by biological agents and/or attrition at a repeatedly used site of predation.Inclusion in fluvial accumulations depends on initial availability of skeletal remains and hydraulic characteristics of individual skeletal elements, but not taxonomic identity per se. For biological accumulations, however, taxonomic composition reflects the preferences of the individual agents of accumulation. The probability of preservation of taxa in fluvial accumulations is probably mainly a function of body size, as reflected in the sizes of isolated skeletal elements. Thus, in this Siwalik system, bone assemblages that experienced fluvial transport are better representations of original community composition than bone assemblages created by biological agents or passive accumulation.

2019 ◽  
Vol 46 (3) ◽  
pp. 471
Author(s):  
Luis Spalletti ◽  
Ferrán Colombo

The Huarenchenque Formation is a volcano sedimentary unit deposited to the east of the Plio-Quaternary Andean Magmatic Arc. In order to define depositional settings, two lithofacies associations (fluvial and pyroclastic) were defined. The fluvial facies association is composed of polymictic conglomerates with the predominance of basalt- dominated clasts, coarse- medium-grained conglomeratic sandstones and medium- to coarse-grained sandstones. These deposits occur as stacked or single bodies, display both sheet and channelized geometries, and contain a range of internal sedimentary structures, such as planar, low angle stratification and cross-bedding. This facies association is interpreted as the deposit of a multichannel fluvial system characterized by high bed load, steep gradient and non-cohesive bank materials. Facies and architecture of the fluvial deposits are the result of high bank full discharge related to rapid deglaciation of the Andean Last Glacial Maximum. The pyroclastic facies association is characterized by lapilli and ash tuffs deposited from air fall, pyroclastic density current, and density stratified surge mechanisms. In the Huarenchenque Formation the fluvial and the pyroclastic facies associations show a clear physical separation, suggesting that sedimentation occurred in two distinct (intereruptive and syneruptive) phases. During the long-lived intereruptive phases the sedimentary record corresponds mainly to the deposits of the gravelly braided fluvial system, whereas during syneruptive phases the fluvial valley was almost entirely occupied by primary pyroclastic deposits related to high-explosive episodes of the neighbor Andean strato-volcanoes. Although most of the cross-bedded sandstones and conglomerate sandstones are rich in basaltic fragments, some strata are composed almost entirely of pumiceous fragments, while in others there is a marked alternation between “basalt” and “pumiceous” foresets. These attributes reflect the preservation of intrabasinal pyroclastic fragments and allow suggest that: i. explosive volcanic events could be more frequent than reflected by the pyroclastic deposits themselves; ii. syneruptive pyroclastic materials could be eroded (even eliminated) by the fluvial system; iii. contributions of primary pyroclastic material persisted during intereruptive (fluvial-dominated) phases.


2009 ◽  
Vol 60 (5) ◽  
pp. 397-417 ◽  
Author(s):  
Crina Miclăuş ◽  
Francesco Loiacono ◽  
Diego Puglisi ◽  
Dorin Baciu

Eocene-Oligocene sedimentation in the external areas of the Moldavide Basin (Marginal Folds Nappe, Eastern Carpathians, Romania): sedimentological, paleontological and petrographic approachesThe Marginal Folds Nappe is one of the most external tectonic units of the Moldavide Nappe System (Eastern Carpathians), formed by Cretaceous to Tertiary flysch and molasse deposits, piled up during the Miocene closure of the East Carpathian Flysch basin, cropping out in several tectonic half-windows, the Bistriţa half-window being one of them. The deposits of this tectonic unit were accumulated in anoxic-oxic-anoxic conditions, in a forebulge depozone (sensuDeCelles & Giles 1996), and consist of a pelitic background sporadically interrupted by coarse-grained events. During the Late Eocene the sedimentation registered a transition from calcareous (Doamna Limestones) to pelitic (Bisericani Beds) grading to Globigerina Marls at the Eocene-Oligocene boundary, and upward during the Oligocene in deposits rich in organic matter (Lower Menilites, Bituminous Marls, Lower and Upper Dysodilic Shales) with coarsegrained interlayers. Seven facies associations were recognized, and interpreted as depositional systems of shallow to deeper water on a ramp-type margin. Two mixed depositional systems of turbidite-like facies association separated by a thick pelitic interval (Bituminous Marls) have been recognized. They were supplied by a "green schists" source area of Central Dobrogea type. The petrography of the sandstone beds shows an excellent compositional uniformity (quartzarenite-like rocks), probably representing a first cycle detritus derived from low rank metamorphic sources, connected with the forebulge relief developed on such a basement. The sedimentation was controlled mainly by different subsidence of blocks created by extensional tectonic affecting the ramp-type margin of the forebulge depozone.


2021 ◽  
Vol 151 (2) ◽  
pp. 159
Author(s):  
Emese M. Bordy ◽  
Orsolya Sztanó

Two levels of volcaniclastics, comprising conglomerates, sandstones and mudstones, are interbedded with upper middle Miocene (upper Badenian) andesite pyroclastics near the Hungarian-Slovakian border in the distal region of the Central Slovakian Neogene Volcanic Field. Based on the field sedimentological investigations, the facies of the volcaniclastics (e.g., lateral and vertical grain size changes, sedimentary structures, textures, clast composition), their geometry and field relationships are documented herein with the aim of reconstructing the depositional environment. The silica-cemented volcaniclastics are mostly andesite clasts with only ~ 5% being granitoid, quarzitic, and tuff clasts as well as charred fossil wood fragments. The coarse-grained facies association includes crudely stratified, tabular or lenticular, clast-supported pebble-cobble conglomerates with erosive basal surfaces, b-axis imbrication, alternating with sets of cross-bedding. The fine-grained facies association comprises cross-bedded pebbly to medium-grained sandstone and lenses of tuffaceous clayey siltstone with rare horizontal lamination and water-escape structures. Rip-up mudstone clasts, with diametre up to 1 m, are present in both facies associations, revealing the co-existence of abandoned silty palaeo-channel plugs. Facies associations are arranged in several 0.5-4-m-thick, fining-upwards successions that likely formed in shallow channels as downstream- to laterally accreting longitudinal bars, extensive gravel sheets and bars that migrated in peak flow during floods. Palaeocurrent indicators (i.e., clast imbrication, direction of planar cross-bedding, orientation of petrified wood logs) show bedload transport by traction currents, initially towards ~S, and later towards ~W. Intermittently debris flows also occurred. Cross-bedded sandstones formed as in-channel transverse bars during medium/low discharge. Variation of grain size shows frequent discharge fluctuations during permanently wet conditions in the late Badenian. The 4-5-m-deep, low-sinuosity channels were part of a high-energy, gravel-bed braided-river system on the south-eastern foothills of the Lysec palaeo-volcano. Here, pyroclastics were reworked and redeposited as volcaniclastics during inter-eruption, high-discharge episodes.


2001 ◽  
Vol 25 ◽  
Author(s):  
Prakash Das Ulak ◽  
Katsuhiro Nakayama

Along the Tinau Khola section of west central Nepal, the Siwalik Group is a 4 km thick pile of fluvial sedimentary sequence of mudstone, sandstone and conglomerate. It is exposed between the Main Boundary Thrust (MBT) to the north and the Frontal Churia Thrust (FCT), also known as the Main Frontal Thrust (MFT), in the south. The Siwalik Group is lithologically divided into the Arung Khola, Binai Khola and Chitwan formations, in ascending order. Six facies associations (FA1 to FA6) are recognised within the group based on grain size distribution, nature of bedforms, and sandstone-mudstone ratio. The fine-grained sediments of the Lower and Middle members of the Arung Khola Formation belong to the FA1-facies association and were interpreted to have deposited by a low-discharge, low -relief meandering fluvial system. The multiple accumulated thin-layered muddy sandstone sequence in the Upper Member of the Arung Khola and the Lower Member of the Binai Khola formations belong to FA2 and FA3- facies associations and were deposited by a flood flow-dominated meandering fluvial system. The deep sandy braided facies association (FA4) and shallow sandy braided facies association (FA5) are well developed in the Middle and Upper members of the Binai Khola Formation, respectively. The gravelly braided facies association (FA6) is recognised in the Chitwan Formation. The palaeomagnetically well-studied section of the Tinau Khola allows precise dating of the major change of fluvial system during the deposition of the Siwalk Group. The environment of predominantly shallow meandering rivers with low­ relief and low-discharge during the time of deposition of the Arung Khola Formation changed at 9.9 Ma and flooding in the rivers dramatically increased due to the intensification of monsoon precipitation. This hydrographic change also brought the change in facies from the earlier FA1 facies to FA2 and FA3 facies. Change from meandering to braided system occurred at 8.2 Ma because of the obvious regional tectonic upliftment of the Higher Himalaya bringing into FA4 and FA5-facies associations. Finally the FA6-facies association was developed due to the large gravelly braided system development at 2.5 Ma as a result of the Main Boundary Thrust movement along the frontal part of the Himalaya.


1992 ◽  
Vol 11 (1) ◽  
pp. 85-93 ◽  
Author(s):  
Martin R. Langer

Abstract. Two new genera and eight new species of benthic foraminifera are described from the shallow water, tropical lagoon of Madang, Papua New Guinea. The new hauerinid genus Pseudolachlanella is characterized by juvenile cryptoquinqueloculine, adult almost massiline arranged chambers, and a slitlike, curved aperture with parallel sides and a long, slender, curved miliolid tooth. Pitella haigi n. gen., n. sp. is a new foraminifera with cryptoquinqueloculine arranged chambers, an almost entirely pitted shell surface (pseudopores) and a rounded aperture with a short simple tooth. Among the other species described as new are four hauerinids and two agglutinated foraminifera All new species described here occur sporadically in the shallow water back- and forereef environments of the lagoon (0–55m), and live infaunally and epifaunally in well-oxygenated, fine and coarse grained biogenic sediments. They are absent in muddy, organic-rich, low-oxygen sedimentary environments within bay inlets where variations of salinity are considerable.


Author(s):  
O. P. Yermolaev ◽  
V. N. Golosov ◽  
M. V. Kumani ◽  
L. F. Litvin ◽  
I. I. Rysin ◽  
...  

Abstract. Quantitative assessments of soil loss from cultivated land and sediment redistribution along pathways from cultivated fields to river channels have been undertaken using a range of different methods and techniques, including erosion models, detailed studies of sediment redistribution in representative catchments, monitoring of gully head retreat and evaluation of sediment deposition in ponds and small reservoirs. Most of the sediment eroded from arable land is deposited between the lower portions of the cultivated slopes and the river channels. Less than 15% of the eroded sediment is delivered to the river channels. Sediment redistribution rates in the upper parts of the fluvial system have declined during the last 25 years in both the western and eastern parts of the Russian Plain, because of a major reduction of surface runoff during snowmelt and a reduction of the area of arable land in some parts of the study area.


Geology ◽  
2021 ◽  
Author(s):  
Alistair T. Hayden ◽  
Michael P. Lamb ◽  
Alexander J. Carney

The surface of Mars contains abundant sinuous ridges that appear similar to river channels in planform, but they stand as topographic highs. Ridges have similar curvature-to-width ratios as terrestrial meandering rivers, which has been used to support the hypothesis that ridges are inverted channels that directly reflect channel geometry. Anomalously wide ridges, in turn, have been interpreted as evidence for larger rivers on Mars compared to Earth. However, an alternate hypothesis is that ridges are exhumed channel-belt deposits—a larger zone of relatively coarse-grained deposits formed from channel lateral migration and aggradation. Here, we measured landform wavelength, radius of curvature, and width to compare terrestrial channels, terrestrial channel belts, and martian ridges. We found that all three landforms follow similar scaling relations, in which ratios of radius of curvature to width range from 1.7 to 7.3, and wavelength-to-width ratios range from 5.8 to 13. We interpret this similarity to be a geometric consequence of a sinuous curved line of finite width. Combined with observations of ridge-stacking patterns, our results suggest that wide ridges on Mars could indicate fluvial channel belts that formed over significant time rather than anomalously large rivers.


2022 ◽  
Vol 92 (1) ◽  
pp. 32-49
Author(s):  
Jonathan Ledesma ◽  
Cecilia E. Del Papa ◽  
Patricio Payrola

Abstract The Puna–Altiplano Plateau of the Central Andes is the second-highest plateau in the world (after Tibet), with a mean elevation of 4000 m.a.s.l. and an arid to hyperarid climate. Uplift of the Puna–Altiplano Plateau has affected lower-level atmospheric circulation, acting as a barrier to humid easterly winds from the Amazon basin and favoring an across-strike precipitation gradient resulting in a humid climate towards the east of the plateau and an arid to hyperarid climate in the orogen's interior. In the modern climate, the Bolivian High anticyclone regulates upper troposphere circulation, but little is known about the high-altitude tropospheric circulation of the past. This work focuses on the eolian record of the San Antonio de los Cobres basin along the eastern border of the Puna Plateau, NW Argentina, with the aim of analyzing its origin and thus elucidating the late Miocene winds. The eolian deposits are constrained by 7.8 Ma (K/Ar and U/Pb) and 6.4 Ma (U/Pb) ignimbrites at the nearly basal and upper contacts, respectively. Based on stratigraphic, sedimentological, and provenance analysis of the eolian units, we have identified three main facies associations (FAs): FA1) cross-stratified sandstones with large- to small-scale tabular, planar cross-bedding and with trough cross-stratification; FA2) sandstones with planar to low-angle stratification associated with thinly laminated ripple sandstone strata; FA3) medium- to coarse-grained massive sandstones associated with pebbly to bouldery, matrix-supported conglomerates and clast-supported conglomerates. The lateral and vertical facies assemblages indicate a dune field confined to topographic depressions dominated by transverse dunes with straight and sinuous crestlines that laterally grade into sandsheets associated with ephemeral streams. Paleoflows, lithotypes, and grain-size determinations indicate a persistent north-northwest provenance and wind velocities of 24–38 km/h (with maximum velocities of 55–75 km/h). The results of our analysis coupled with data from previous studies indicates that, for at least the last ca. 8 Myr, the winds have been blowing constantly from the north-northwest with an intensity similar to the present. This implies that the paleo-atmospheric circulation had a similar pattern to the present-day one. Therefore, we conclude that the upper-troposphere circulation in the Puna Plateau of NW Argentina was already regulated by the Bolivian High anticyclone during the Miocene, generating constant north-northwesterly winds.


2020 ◽  
Vol 90 (2) ◽  
pp. 250-267 ◽  
Author(s):  
Sergio A. Marenssi ◽  
Carlos O. Limarino ◽  
Laura J. Schencman ◽  
Patricia L. Ciccioli

ABSTRACT Two episodes of lacustrine sedimentation, separated by an erosional surface and fluvial sedimentation, took place in the southern part of the broken foreland Vinchina basin (NW Argentina) between 11 and 5 Ma. The lacustrine deposits, 768 and 740 meters thick, are recorded in the upper part of the Vinchina Formation (“Vinchina lake”) and the lower part of the Toro Formation (“Toro Negro lake”) respectively. According to sedimentological features, four sedimentary facies associations (FAs) are recognized in the lacustrine deposits: 1) thinly laminated mudstones facies association (FA 1), 2) coarsening- and thickening-upward muddy to sandy cycles (FA 2), 3) medium- to coarse-grained sandstones (FA 3), and 4) mudstones, sandstones, and oolitic limestones (FA 4). Altogether, these facies correspond to ephemeral, shallow, lacustrine systems including saline mudflats. The total thickness of each lacustrine interval, the thickness of the individual cycles and their lithology, and the overall aggradational facies arrangement suggest that both lakes developed during underfilled stages of the basin. The coarsening-upward cycles can be regarded as lacustrine parasequences representing cyclic episodes of expansion and contraction of the lake, but unlike marine parasequences these cycles do not correlate to water depth. The development of lacustrine conditions and continuous base-level rise, together with the coeval southward-directed paleoflow indicators, suggest axial drainages and that the basin was externally closed (endorheic) at that time. The large thicknesses of each lacustrine interval also points to high accommodation in the southern part of the Vinchina basin during these times. Lake filling cycles are one order of magnitude thicker than lake depth, so we postulate that subsidence (tectonic) and rise of the spill point (geomorphology) increased accommodation but not water depth. Thus, unlike marine parasequences, the analyzed coarsening-upward cycles do not correlate to water depth, but rather they are controlled by more complex basinal accommodation processes. We hypothesize that the coeval uplift of the Umango and Espinal basement block to the south, coupled with the initial doming of the Sierra de Los Colorados to the east, may have generated the damming of the southward-directed drainage and a zone of maximum accommodation, then controlling the location of the two lakes and the preservation of their thick sedimentary records. Therefore, localized accommodation was enhanced by a combination of tectonic subsidence and topographic growth. The two lacustrine intervals and the intervening fluvial deposits record changing contributions from axial to transverse drainages and different cycles of closed and open conditions in the basin. A low-frequency, closed to open and back to closed (axial to transverse and return to axial drainage) basin evolution, is envisaged by the development of the two lakes (closed stages) and the erosional surface followed by the interval of fluvial sedimentation that separates them (open stage). In addition, several high-frequency lake fluctuations (expansion–contraction) are represented by the coarsening-upward cycles within each lacustrine interval. The thick lacustrine intervals and their intermediate incision surfaces record cyclic filling and re-excavation stages and localized episodes of increased subsidence in the Vinchina basin, which seem to be a common feature of tectonically active broken foreland basins.


2019 ◽  
Vol 56 (10) ◽  
pp. 1027-1040
Author(s):  
Qinghai Xu ◽  
Wanzhong Shi ◽  
Xiangyang Xie ◽  
Changmin Zhang ◽  
Walter L. Manger ◽  
...  

Distributary channels in large deltas can form a channel pattern similar to braided fluvial system or anastomosed fluvial system that have multichannel systems. Although both systems are of generally comparable platforms, their geometry, sedimentology, and facies associations may exhibit unique characteristics. Many ancient multichannel systems have been interpreted as braided patterns, but some are certainly anastomosed patterns. A reevaluation of ancient multichannel architectures and sedimentology patterns is needed to improve discrimination of braided and anastomosed patterns of multichannel systems. This study examines the characteristics of two modern anastomosed pattern channel systems. Those modern systems are compared to ancient examples in the lower Yanchang Formation, southwest Ordos Basin. This comparison indicates that the multichannel systems of the delta, southwest Ordos Basin, exhibit greater similarity to modern anastomosed channel systems of shallow-water deltas. Systems of low-sinuosity distributary channels and interdistributary bays or swamp islands are developed mainly between the channels, and there are no mouth bar deposits. Both modern and ancient multichannel systems suggest that low gradient slope is a significant controlling factor in the formation of anastomosed pattern channels in river-dominated deltas. The identification of anastomosed patterns plays a significant role in reservoir characterization and hydrocarbon exploration and production in delta systems.


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