Anjar Intertrappean

1. H. Srivastava, A. K. Bhaumik & S. Mohanty
DEPARTMENT OF APPLIED GEOLOGY
IIT(ISM), DHANBAD

2. INTRODUCTION
 The Deccan volcanics erupted at the Cretaceous–Tertiary (K-T) boundary within a short
period of time and covered large areas of western, central and southern India
 Till date intertrappeans and intratrappeans from the K-T boundary have been described
from many parts of India
 late Maastrichtian to early Danian sequence in the Jhilmili area, Chindwara district,
Madhya Pradesh
 The uppermost Maastrichtian sediments around Naskal, Ranga Reddy district, Telengana
 The Danian Rajahmundry beds
 The Maastrichtian Lameta beds of Jabalpur
 The Mamoni intertrappean in Kota district of Rajasthan
 The infra- and inter-trappean beds of Asifabad district, Andhra Pradesh

3.  Several intertrappean beds were studied in Naredi, Kora, Dayapar,
Lakshmipur and Anjar section of Kutch district Gujarat. All represent the
non-marine depositional environment
 Several studies were also carried out on the intertrappean sediment of the
Anjar area using geochemical and biological proxies
 These studies indicate deposition of intertrappean sediments during late
Maastrichtian to early Danian (supported by K-Ar ages of traps) in non-
marine to lacustrine environment

4. OBJECTIVES:
 To infer the palaeodepositional environment of these intra-
and inter-trappean beds using foraminiferal and
sedimentological proxies.
 Thin sections of the intertrappean were also made and
observed microscopically to characterise the constituents
and depositional environment.

5. FORAMINIFERA
 Foraminifera are eukaryotic unicellular organisms with the
general characteristics of protista.
Kingdom:- Protista
Subkingdom:- Protozoa
Phylum:- Sarcomastigophora
Subphylum:- Sarcodina
Superclass:- Rhizopoda
Class:- Granuloreticulosea
Order:- Foraminiferida
Till date approximately 5000 species of benthic
and about 100 species of planktic foraminifera
were identified.
(Armstrong and Brasier, 2004)

6.  The Viri village and its adjacent areas in Bhuj District have outcrops of
seven (VII) phases of lava flows(Ghevariya, 1988; Courtillot et al., 2000)
 Total 26 samples were collected from seven locations (22 were collected
from five locations, L-2 to L-6, positioned within flows II to VII and
remaining 4 samples were collected from the infratrappean, L-1).
Location
numbers
Lithostratigraphic
position
Coordinates No. of
studied
samples
L-1 Below flow II 23̊ 05ˈ47.99″N; 69̊ 59ˈ
26.82″E
04
L-2a
Between flow II and
III
23̊ 05ˈ16.95″N; 69̊ 57ˈ
33.63″E
02
L-2b 23̊ 05ˈ9.8″N; 69̊ 57ˈ 43.82″E 04
L-3 2304.524ʹ N; 6959.939ʹ E 03
L-4 Between flow III
and IV
23̊ 04ˈ4.31″N; 70̊ 00ˈ 9.5″E 06
L-5 Between flow V and
VI
23̊ 02ˈ59.19″N; 69̊ 59ˈ58.32″
E
04
L-6 Above Flow VII 23̊ 02ˈ 16.98″N; 69̊ 59ˈ
37.47″E
03
LOCATIONS

7. Location map of sampling sites near
Viri village, Anjar

8. Materials and Methodology:
Sample soaking
Sample washing
Microscopic observation of washed sample
> 63 µm
>125 µm

9. Schematic representation of sampling
sections at L-3, L-4 and L-5 in which
foraminifera are documented

10. Results and Discussion
Viri Intertrappeans
 Among of these 26 samples, only 13 samples from location numbers L-3, L-
4 and L-5 are productive in terms of foraminiferal abundance
 The most abundant groups are Rotalia spp., Elphidium spp., Nonion spp.,
Quinqueloculina spp. and planktic foraminifera Pseudogloborotalia
ranikotensis
 The other foraminiferal groups (Amphistegina sp., Anomalinoides
pseudodowelleri, Astacolus sp., Bolivina spp., Cibicidoides spp.,
Dobrogelina sp., Ellipsoidella sp., Nodosaria sp.) are rare in abundance. We
also documented single specimen of another planktic foraminifera
Globigerina triloculinoides from L-3b

11. Composite plot of foraminiferal
abundance in L-3 to L-5

12. Thin section of impure polymictic
limestone from L-3
(a) Grainstone with quartz, feldspar and
fragments of basalts. Elliptical micritic
peloids are present.
(b) Wackestone with siliciclast (Quartz,
feldspar) and bioclast grains. Elliptical
micritic peloids are also present.
(c) Enlarged portion of wackestone with
rock fragments of quartz, feldspar and
fragments of basalts. Micrite coating
around the bioclasts and lacking of
internal structure indicates effect of sea
floor diagenesis.
(d) Wackestone with rock fragments and
recrystallised ostracod carapace
boundary
(e) Thin section of Rotalia and Nonion
within the rock
(f) Thin section of Quinqueloculina

13. Conclusion
 The present study on the intertrappeans and intratrappeans of Anjar
documented preservation of foraminifera for the first time within samples L-
3 to L-5 indicating their marine origin.
 The other intratrappeans in L-2 and L-6 are non-marine in nature.
 Foraminiferal association together with detrital sediments, bioclasts and
peloids advocate existence of shallow water inner shelf/open ocean
connected lacustrine environment over the studied site.
 Increased abundance of Nonion spp., Quinqueloculina spp.,
Pseudogloborotalia ranikotensis and Globigerina triloculinoides within L-3
suggest that the intertrappean bed was developed under the influence of
relatively greater water depth within inner shelf/lacustrine condition.
 Sediments of L-1 and L-2 are fluvial, L-3 to L-5 are marine/lacustrine and
L-6 are again fluvial, which suggest event of marine transgression followed
by regression over the studied site.

14. THANK YOU