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36. Chen, W. P. and Molnar, P., Focal depths of intracontinental and
intraplate earthquakes and their implications for the thermal and
mechanical properties of the lithosphere. J. Geophys. Res., 1983,
88, 4183–4214.
37. Chen, W. P., A brief update on the focal depths of intracontinental
earthquakes and their correlations with heat flow and tectonic age.
Seismol. Res. Lett., 1988, 59, 263–272.
38. Kim, W. Y., Modelling short period crustal phases at regional distances for the seismic source parameter inversion. Phys. Earth
Planet. Int., 1987, 47, 159–178.
39. McCue, K. and Leiba, M. M., Australia’s deepest known earthquake. Seismol. Res. Lett., 1993, 64, 201–206.
40. Arvidsson, R., Wahlstrom, R. and Kulhanek, O., Deep crustal
earthquakes in the southern Baltic shield. Geophys. J. Int., 1992,
108, 767–777.
41. Nyblade, A. A. and Langston, C. A., East African Earthquakes below 20 km and their implications for crustal structure. Geophys. J.
Int., 1995, 121, 49–62.
42. Kiyoshi, I., Regional variations of the cut-off depth of seismicity
in the crust and their relation to heat flow and large inland–
earthquakes. J. Phys. Earth, 1990, 38, 223–250.
43. Maasha, N. and Molnar, P., Earthquakes fault parameters and tectonics in Africa. J. Geophys. Res., 1972, 77, 5731–5743.
44. Simpson, F., Fluid trapping at the brittle–ductile transition reexamined. Geofluids, 2001, 1, 123–136.
45. Manglik, A. and Singh, R. N., Thermomechanical structure of the
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46. Johnston, A. C., Seismotectonic interpretation and conclusions from
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ACKNOWLEDGEMENTS. We thank Dr V. P. Dimri, Director,
NGRI for according permission to publish this work and to Dr H. K.
Gupta (former Director) for his encouragement during this study. We
also thank Dr Heinrich Brasse for his useful comments, which helped
to improve the manuscript. We thank the anonymous reviewer for constructive suggestions.
marks and burrows. The present assemblage could
represent the middle to upper part of the Early Cambrian.
Keywords: Cambrian, Dimorphichnus,
Monomorphichnus, trace fossils.
Diplichnites,
IN the western Lesser Himalaya, the Tal Formation is an
important lithostratigraphic unit of the Neoproterozoic–
Cambrian sequence (Blaini–Krol–Tal succession), which
consists mainly of black shales, chert, siltstone and Quartzite.
Our study area is located on the Mussoorie–Dhanaulti
road section, exactly on the 0 km milestone of Batagad. It
shows exposures of huge Quartzite with sandstone shale
intercalations and represents the lowermost member
(Quartzite member) of Upper Tal Formation (Figure 1).
Trace fossils reported and described here are preserved
within these sand–shale intercalations.
It is well known that trace fossils present in the Neoproterozoic–Cambrian boundary sections in the worldwide
localities are generally well-preserved and well-diversified1–7, and the boundary is defined by the first appearance
of the trace fossil, Treptichnus pedum5. Recent studies in
the Mussoorie hills of Uttaranchal have revealed several
trace fossil-bearing sections, especially in the arenaceous
sandstone–shale beds of the Upper Tal Quartzite member.
The best preserved section is along the Mussoorie–
Dhanaulti road section. The traces are mostly in the form
of burrows and tracks along with scratch marks and are
identified mainly as Monomorphichnus isp, Dimorphichnus
Received 6 October 2005; revised accepted 21 October 2005
Early Cambrian trace fossils from
the Tal Formation of the Mussoorie
Syncline, India
Meera Tiwari* and S. K. Parcha
Wadia Institute of Himalayan Geology, 33 General Mahadeo Singh Road,
Dehradun 248 001, India
A significant assemblage of trace fossils is presently
described from the lowermost Quartzite member of
Upper Tal Formation, in addition to earlier described
trace fossils from Himachal Pradesh. The most common trace fossils described here are Monomorphichnus
isp, Dimorphichnus isp., Dimorphichnus isp A, Diplichnites isp A, Planolites isp, Skolithos isp, Merostomichnites isp, ?Neonereites isp, along with various scratch
*For correspondence. (e-mail: mtiwari@wihg.res.in)
CURRENT SCIENCE, VOL. 90, NO. 1, 10 JANUARY 2006
Figure 1.
Field photograph showing fossiliferous horizon.
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isp., Dimorphichnus isp A, Diplichnites isp A, Planolites
isp, Skolithos isp, Merostomichnites isp, and ?Neonereites isp. The trails occur as grooves and ridges with positive
epirelief. Earlier, after detailed work in the Krol–Tal belt
of the Lesser Himalaya, various researchers have recorded
several trace fossils in addition to mineralized fossils and
organic-walled microfossils (e.g. small shelly fossils, trilobites, acritarchs and cyanobacteria) of the Neoproterozoic–Cambrian boundary interval from the Tal Formation
exposed in Mussoorie, Garhwal, Korgai, Nigalidhar and
Nainital synclines8–26. At the present level, where mineralized fossils and organic-walled microfossils are not reported, this trace fossil assemblage is proved to be significant and
can be used in identifying the Early Cambrian succession.
The youngest litho unit of the Krol Group, the Tal
Formation was described and named by Medlicott27. This
formation was subsequently mapped in four separate areas
of Himachal and Uttaranchal in four major synclines,
namely Nigalidhar, Korgai, Mussoorie and Garhwal, and
classified as Lower and Upper Tal, separated by a disconformity28,29. Bhargava30, however, divided Tal Formation
into Lower, Middle and Upper, where the Middle Tal includes
Lower Tal of Auden29. Shanker31 further divided Lower
Tal Formation into four members, i.e. Chert member, Argillaceous member, Arenaceous member, Calcareous
member, and Upper Tal Formation into Quartzite member
respectively. Singh32 studied the Mussoorie–Jabarkhet toll
barrier succession in detail and divided the lithological
succession into eight lithounits. Units A to D consist of black
shales, chert and phosphorite corresponding to Chert and
Argillaceous members of Shanker31. Unit E consists of
grey-coloured streaky siltstone, and thin sand layers alternating with mud layers corresponding to Arenaceous member.
Unit F consists of purple sandy shale, corresponding to
Calcareous member. Units G and H correspond to
Quartzite member31and Masket member33. Unit G is made
up of purple sandstone and sand/shale intercalations and
unit H is typically white-coloured, coarse-grained Quartzite.
Lithological unit of Tal sediments from Mussoorie to
Jabarkhet Toll barrier31,32:
The trace fossil-bearing horizon, described presently, is
exposed exactly on the 0 km milestone at Batagad near
Jabarkhet toll barrier in the Mussoorie–Dhanaulti road
section (Figure 2 a, b), located at N30°27′17.8″: E78°07′12.9″
and an altitude of 6585 ft asl. The studied section is characterized by the presence of quartz arenite with thinly
layered micaceous shale which is sometimes nodular and
compact. The trace fossil horizon occurs within an outcrop of
~1 m thickness, at the bedding plane of finely laminated
siltstone and nodular, compact sandy shale and falls
within the unit G of Singh32.
Diversified assemblages of trace fossils have been
reported in the Arenaceous member10. It was presumed
that these trace fossils were produced by macrobenthonic
community, and Skolithos dominate over the crawling
traces of arthropod Diplichnites, Merostomichnites, Dimorphichnus, Monomorphichnus, Protichnites and Tasmanadia. Trace fossils Paleophycus and Skolithos along
with arthropod traces, are reported from Quartzite member
of Upper Tal Formation11,34,52, and the Calcareous member which contains a rich assemblage of brachiopods also
shows the presence of trace fossils18,35.
The traces are mostly in the nature of burrows, tracks
and trails along with some scratch marks. The trails occur
as grooves and ridges with positive epirelief on jointed and
fractured micaceous sandstone, but where they occur as
clustered pit-like impressions, it is difficult to interpret
whether these impressions represent negative epirelief or
hyporelief.
Systematic ichnology
Ichnogenus Monomorphichnus Crimes, 1970
Monomorphichnus isp.
(Figure 3 a, c, g (A))
Description: A set of isolated, slightly curved sigmoidal
ridges repeated laterally. The ridges vary in length from 1
to 2 cm and are about 1–2 mm wide and nearly 1.5 mm
apart from one another.
Repository ref.: WIHG/A/1571, 1572, 1573a.
Upper Tal
Lower Tal
114
Quartzite
member
Calcareous
member
Arenaceous
member
Argillaceous
member
Chert
member
H Coarse-grained
Quartzite
*G Purple sandstone with
greenish shaly streaks
F Purple sandy shale
Remarks: The present species differs from Monomorphichnus bilineatus, Crimes 1970 in the pattern, shape
and size of ridges. It differs from Monomorphichnus species
from the Spiti valley and also the species from Kashmir
valley in nature, pattern and size of ridges36,37.
E Streaky siltstone
Locality:
D Grey to black
calcareous shale
C Sandy shales with
black calcareous bands
B Dark coloured shale
with sandy intercalations
A Black shale
Batagad, Mussoorie–Dhanaulti road.
Ichnogenus: Dimorphichnus Seilacher, 1955
Dimorphichnus isp.
(Figure 3 e)
Description: Paired, parallel series of asymmetrical wedge
and rib-shaped markings of varying size. Each individual
CURRENT SCIENCE, VOL. 90, NO. 1, 10 JANUARY 2006
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a
b
Figure 2. a, Geological map of the area modified after Banerjee and Narain8 showing sample location.
b, Lithostratigraphic column showing sample horizon.
wedge is aparted from one another by 5 to 8 mm. The
longest pairs of rib-shaped markings vary from 12 to
18 mm in length and 1 to 2 mm in width. Some markings
are shifted towards the other side, suggesting changes in
the movement of the animal.
Repository ref.: WIHG/A/1574.
Remarks: Specimens apparently show resemblance with
Ichnogenus Dimorphichnus in the curved and sub parallel
ridges. Specimens differ from ichnospecies of Dimorphichnus from Spiti36 in the nature and pattern of markings
of the traces. The present specimen differs from all other
CURRENT SCIENCE, VOL. 90, NO. 1, 10 JANUARY 2006
known ichnospecies of Dimorphichnus. The Ichnogenus
Dimorphichnus is known from the Lower Cambrian successions of Salt Range38.
Locality:
Batagad, Mussoorie–Dhanaulti road.
Ichnogenus: Diplichnites Dawson, 1873
Diplichnites isp. A
(Figure 3 j, p)
Description: Dissimilar paired rows of unequal marks,
individual ridges elongate and oblique. Distances between
two rows about 1 to 4 mm, thickness and length of each
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ridge varies from 2 to 3.5 mm. Distance between the two
ridges varies from 0.5 to 2 mm. The paired marks occur
in a row up to some distance and then shift slightly towards
the left. This disposition of tracks suggests that the animals have moved laterally.
Repository ref.: WIHG/A/1575, 76.
Remarks: The present specimens show close similarity
in pattern and in nature of ridges with Diplichnites recorded widely in Cambrian rocks.
Locality:
Batagad, Mussoorie–Dhanaulti road.
Ichnogenus: Planolites Nicholson, 1873
Planolites isp.
(Figure 3 h)
Description: Straight to slightly curved horizontal trails.
Width of the trail ranges from 1 to 2 cm, individual burrow
is 1 to 2.5 cm long and 5 to 8 mm wide. Burrows are unbranched and irregularly developed.
Repository ref.: WIHG/A/1577.
Remarks: The specimen closely resembles Planolites in
unbranched nature of burrows. The specimen differs with
all the known species of Planolites.
Locality:
Batagad, Mussoorie–Dhanaulti road.
Planolites B
(Figure 3 o)
Description: The burrow is 15 mm long and 5 mm wide,
slightly curved, comparatively wider on one side. Sediments incorporated in the host rock and in the trace are
similar.
Ichnogenus: Merostomichnites Packard, 1960
Merostomichnites isp.
(Figure 3 b)
Description: Two parallel, spindle-shaped rows arranged
obliquely. Individual impression varies in length from 1
to 1.7 cm and in width from 0.5 to 0.9 mm. The trace is
preserved as epirelief.
Repository ref.: WIHG/A/1580.
Remarks: The specimen differs from Dimorphichnus in
behaviour and pattern of ribs.
Locality:
Batagad, Mussoorie–Dhanaulti road.
Ichnogenus: Neonereites Seilacher, 1960
? Neonereites isp.
(Figure 3 l)
Description: Meandering trail with numerous irregular
pellets. Shape of the pustusels and indistinct rows distinguish it from other traces. The trail is generally horizontal.
Repository ref.: WIHG/A/1581.
Remarks: The specimen shows close resemblance
with the Ichnogenus Neonereites in its shape of irregular
pellets.
Locality:
Batagad, Mussoorie–Dhanaulti road.
Ichnogenus A
(Figure 3 d)
Description: It comprises a single row of slightly curved,
2–3 mm wide and 5–6 mm long ridges 1 mm apart from
each other.
Repository ref.: WIHG/A/1584.
Repository ref.: WIHG/A/1583.
Ichnogenus: Skolithos Haldemann, 1840
Skolithos isp.
(Figure 3 m, n)
Description: Unbranched, sub cylindrical burrows; width
of burrows ranges from 2 to 6 mm; space between burrows is wide.
Repository ref.: WIHG/A/1578, 79.
Remarks: In the present material no vertical sections are
available. The form shows some similarity with Skolithos
linearis Haldemann.
Locality:
116
Batagad, Mussoorie–Dhanaulti road.
Locality:
Batagad, Mussoorie–Dhanaulti road.
Ichnogenus B
(Figure 3 k)
Description: The specimen comprises a single U-shaped
horizontal burrow. The trace width is 0.9 to 1.5 mm. The
burrow is infilled by a different material than that of the
host rock.
Repository ref.: WIHG/A/1582.
Remarks: The specimen shows some resemblance with
the Ichnogenus Diplocraterion Torell, 1870 (refs 39, 40)
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a
b
d
c
B
e
g
A
f
i
k
j
h
p
n
m
l
o
Figure 3. a, c, g (A), Monomorphichnus isp.; b, Merostomichnites isp.; d, Ichnogenus A; e, Dimorphichnus isp.;
f, g (B), i, Scratch marks; h, Planolites isp.; j, p, Diplichnites isp. A; k, Ichnogenus B; l, ?Neonereites isp.; m, n,
Skolithos isp.; o, Planolites B; Bar = 1 cm.
but differs in the nature of preservation. The latter possesses a paired circular opening, which is lacking in the
present specimen. Hence the present specimen is grouped
under an open nomenclature as Ichnogenus B.
Scratch marks
(Figure 3 f, g (B), i)
Description: The scratch mark ridges are sigmoidal with
width ranging from 1 to 2 mm and length 7 to 10 mm.
Probably they are produced by trilobites and can be assigned as isolated fragments of Monomorphichnus.
Repository ref.: WIHG/A/1573b; 1585.
Locality:
Batagad, Mussoorie–Dhanaulti road.
CURRENT SCIENCE, VOL. 90, NO. 1, 10 JANUARY 2006
In addition to the above trace fossil genera, various
meandering trails occur, which vary in length from 10 to
30 mm in width with a wider front portion. Other varieties
of trails consist of equal parts with meandering structure
or are slightly straight. These generally cross each other.
In absence of body fossils, trace fossils are found to be
important elements for deciphering Neoproterozoic–Cambrian transition. The Tal Formation is a thick stratigraphic
unit, but most fossils are facies-dependent. The present
assemblage of trace fossils is mostly found in the form of
burrows, tracks and trails along with scratch marks. The
trails occur as grooves and ridges with positive epirelief
on jointed and fractured micaceous sandstone, which makes
it difficult to collect the complete specimen. Sometimes
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these traces are found in a clustered, pit-like form. It is
difficult to assign whether these impressions represent
negative epirelief or hyporelief.
Mostly trace fossils produced by arthropods occur at
the horizon at or shortly below those containing trilobites41.
It has been noticed that the Neoproterozoic trace fossils
are small, simple, unbranched and were made close to the
sediment–water interface, whereas early Cambrian trace
fossils are well-diversified traces of bilaterian animals, showing morphological diversity and complexity2,42–44. Trace
fossils like Monomorphichnus, Planolites, Skolithos,
Diplichnites and Dimorphichnus are known from the other
early Cambrian successions of the Tethyan Himalayan
succession of Kashmir, Spiti. In the Zanskar region, their
occurrence is below the trilobite-bearing horizons45–51.
Monomorphichnus occurs close to the Neoproterozoic–
Cambrian boundary in many sections2. In the Neoproterozoic–Cambrian boundary GSSP in Newfoundland,
Monomorphichnus first appears 2.5 m above the base of
the Treptichnus pedum zone and is used along with Treptichnus pedum in defining the base of the basal Cambrian
Stage5,53. In the Lesser Himalayan sequence, Rai52 assigned
a Lower Cambrian age to the Arenaceous member of the
Lower Tal Formation, on the basis of trace fossil occurrence.
Trace fossils like Skolithos, making pipe rock facies are
abundant in the Arenaceous member of Tal Formation
and is common in Lower Cambrian of Scotland and Sweden10. A diverse assemblage of brachiopods, microgastropods, hyolithids and poriferids of Lower Cambrian
affinity was reported from the Calcareous member9. Further
report of a rich assemblage of brachiopod from shale
member of the Upper Tal Formation suggested Atdabanian (=Qiongzhusian/Chiungchussu) stages of the Early
Cambrian to the Upper Tal Formation18,35. The beds that
overlie and underlie the brachiopod horizon exhibit fairly
well preserved trace fossils, including small vertical burrows
and trilobite fragments. The Lower Quartzite member of
the Upper Tal exposed in Sirmur district, Himachal
Pradesh also shows presence of Palaeophycus isp., Skolithos isp., and arthropod traces of Lower Cambrian affinity11.
It was observed that the trace fossils present in the Tal
Formation shows marked behavioural complexity and diversity and occur at various horizons, but distinct zones
are not evident54,55.
The present finds of trace fossil assemblage can be correlated with other trace fossil assemblages of the Tethyan
and Lesser Himalayan horizons, and hence are of stratigraphic significance. Due to scarcity of body fossils at
this level, the present assemblage can be useful in identifying the complete Early Cambrian succession in the Tal
Formation.
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ACKNOWLEDGEMENTS. We thank the Director, Wadia Institute
of Himalayan Geology, Dehradun for providing the necessary facilities
and for encouragement. We also thank the unknown reviewers for their
constructive suggestions and Sh. Tirath Raj for photographing the samples.
Received 11 July 2005; revised accepted 11 October 2005
Vertebrate steroids and the control of
female reproduction in two decapod
crustaceans, Emerita asiatica and
Macrobrachium rosenbergii
V. Gunamalai1, R. Kirubagaran2 and
T. Subramoniam1,*
1
Unit of Invertebrate Reproduction, Department of Zoology,
University of Madras, Guindy Campus, Chennai 601 025, India
2
National Institute of Ocean Technology, Pallikkaranai,
Chennai 600 302, India
Vertebrate steroids, estradiol-17β
β (E2) and progesterone
(P), have been estimated in the hemolymph, ovary and
hepatopancreas of mole crab Emerita asiatica and
freshwater prawn Macrobrachium rosenbergii during
the reproductive and molt cycle stages by radioimmunoassay. The maximum level of E2 in hemolymph, ovary
and hepatopancreas was detected only during the intermolt stage, whereas the level gradually decreased
during premolt and postmolt stages in E. asiatica. The
*For correspondence. (e-mail: thanusub@yahoo.com)
CURRENT SCIENCE, VOL. 90, NO. 1, 10 JANUARY 2006
E2 level in the hemolymph was high in crabs with mature
ovaries, while those with quiescent ovaries were low or
undetectable. The trend in P level in all tissues during
different molt and reproductive stages was remarkably
similar to that of E2. However, in M. rosenbergii, with
two types of molt cycles, viz. reproductive and common
(non-reproductive) molt, E2 and P levels in hemolymph,
ovary and hepatopancreas showed wide variation between them. During the reproductive molt cycle, the
level of E2 and P in all tissues peaked during intermolt, but declined drastically at premolt and postmolt
stages. On the contrary, the level of E2 in hemolymph was
not detectable in any molt stage during the non-reproductive molt with the ovary containing undeveloped
oocytes. However, the inactive ovary and hepatopancreas
showed basal level of E2 during non-reproductive molt
cycle, whereas P was totally undetectable in the above
tissues. Cumulatively, these studies suggest that the ovary
may synthesize E2 and release them into the hemolymph from where it may reach the hepatopancreas to
stimulate vitellogenin synthesis in the two decapods. P
may have a role in the post-vitellogenic meiotic maturation of the oocytes, as in vertebrates.
Keywords: Crustaceans, estradiol-17β, molting, progesterone, reproduction.
UNLIKE insects, most malacostracan crustaceans continue
growth and molting with reproductive activities. Hormonal
coordination of molting and reproduction in crustaceans
is achieved by the combinatorial effects of eyestalk inhibitory neuropeptides and a variety of trophic hormones.
The control of molting in crustaceans is accomplished by
the common arthropodan molting hormone, ecdysteroid, the
action of which is uniquely inhibited by the molt-inhibiting hormone1. Similarly, the inhibitory role of gonadinhibitory hormone on the reproductive activities, especially
on vitellogenesis, has been well documented2,3. Conversely, there are discordant results concerning the gonad
stimulatory factors among various crustacean species. For
example, earlier studies revealed the occurrence of gonad
stimulatory neuropeptides in the brain and thoracic ganglia
of some crustaceans4. Following this, several hormonal
factors such as methyl farnesoate, a structural homologue
of insect juvenile hormone, ecdysteroids as well as vertebrate steroids like estradiol-17β (E2) and progesterone (P)
have been implicated with inducement of ovarian maturation in different crustacean species (see ref. 5 for review).
Apparently, crustaceans might employ more than one type
of gonad stimulatory principles in the control of vitellogenesis, the central event of oogenesis.
In decapod Crustacea, physiological processes of both
molting and female reproduction are linked and hence the
temporal separation of reproductive and molting activities
becomes a necessity for judicial apportioning of the organic
storage materials for both these energy-demanding processes. Yet another complexity in the female reproduction
of malacostracan crustaceans is that they carry the brood
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