Regional geomorphology of the continental slope of NW India: Delineation of the signatures of deep‐seated structures

Animal-sediment relationships of two benthic communities (Crustaceans and Polychaetes) were studied around Mandvi coast in the Gulf of Kachchh, Western India. This coast consists of many micro-geomorphic landforms in which benthic communities are inhabited and select their niches and produce endemic biogenic structures. Five intertidal subfacies have been described and four types of grounds are identified, based on substrate consistency. 18 species of crustaceans, 15 species of polychaetes and unsegmented worm nemertea have been identified. Crustacean behavioural activities were observed in dunes, beaches and ridge-runnel in the form of burrowing, pellet making, feeding and crawling traces. Pelleted wall lining burrows of the suspension feeder stomatopodean species of Oratosquilla striata are also abundant in runnels. Motile, deposit feeder polychaetes are abundant on the ridges and are occasionally found on the lower reaches of the beaches, while suspension and filter feeders are found in the runnels. Lagoons consist of mainly grouped funnel branched burrows of Oniphus eremita which is identical to ichnogenus Balanoglossites. Nemertea, which are opportunistic algal grazers, have exploited restricted niches for dwelling-feeding purposes and constructed vertical burrow with pentamerous conical mound. The shore platform consists of cemented, calcareous tubes of filter feeder Serpula along with symbiotic encrusters like Ostrea and barnacles. Ichnocoenoses are discussed and three-dimensional ichno-sedimentologic models are reconstructed for Beach, Ridge, Runnel and Lagoon of the Mandvi intertidal zone.

Section: Geomorphologymentioning

confidence: 99%

Animal-sediment relationship of the crustaceans and polychaetes in the intertidal zone around Mandvi, Gulf of Kachchh, Western India

Patel

Desai

2009

“…The Okha Rann which separates Okhamandal peninsula from the rest of Saurashtra is a manifestation of neotectonism in this part (Merh, 1995). A prominent feature observed offshore Dwarka is the occurrence of Saurashtra arch in NE-SW direction with a plunging nature (Chauhan et al 1993). Major fault zones trending WNW-ESE off the Porbandar coast define the Saurashtra platform and separate it from the deeper zone.…”

Section: Introductionmentioning

confidence: 99%

Joints as fingerprints of stress in the quaternary carbonate deposits along coastal Saurashtra, Western India

Bhonde

Bhatt

2009

Coastal cliffs and shore platforms are important geomorphic features of coastal areas of Saurashtra. These features are composed of medium to coarse grained carbonate sand and are designated as "Miliolitic limestones" that range in age from Middle to Late Pleistocene. Significant jointing has been observed in the Middle Pleistocene Miliolite Formation as well as in the younger shell limestone that comprises Chaya Formation of Late Pleistocene. Along with NE-SW trend which is the direction of maximum horizontal compressive stress [S Hmax ] for Indian sub-continent, other trends recorded are NNE-SSW, N-S, NW-SE and E-W. When compared with other regional studies, neotectonic episode in Saurashtra peninsula appears to be younger than at least 125ky. The present study on joint sets also indicates that they are important to understand stresses associated with anticlockwise rotation of the Indian plate.

“…The Kachchh coastline shows features related to tectonic upliftment (Biswas, 1974(Biswas, , 1982(Biswas, , 1987Kar, 1993;Chauhan et al, 1993) such as raised beaches and dewatered subtidal mud within intertidal zone (Patel and Desai, 1999;Patel, 2008 andPatel, et al 2001). The coast line displays a complex of spits and cuspate along with tidal flats, tidal channels and coastal dunes complexes.…”

Section: Introductionmentioning

confidence: 99%

Burrowing activities of goby fish in the recent intertidal mud flats along the Navinal coast, Kachchh, Western India

Bhatt¹,

Patel

Patel³

et al. 2009

Behavioural activities of the goby fish-Periophthalmodon septemradiatus were observed in the intertidal zone around Navinal coast in the Gulf of Kachchh, western India. Intertidal zone is broad, and comprise of creeks, which are muddy and vegetated by mangrove on eastern side and ridge runnel systems on western side of the study area which are hospitable for the goby fish. Different types of biogenic activities are observed such as crawling, pellet making, grazing and burrowing. The crawling activity is part of movement of the goby fish from one burrow to another burrow and pellet making activity is part of burrow modification. The grazing activity is feeding on the surface mud after receding of tide and exposure of the tidal flat by left and right movement of the front part of the body. The most conspicuous activity is burrowing, they construct unlined, vertical to incline 'I', 'J' and 'Y' shaped branched, circular to oval burrows with varying diameter and depth. In the muddy sediments goby fish produced circular to oval rimmed muddy lumps as surfacial expression around the burrows and further produced funnel shape depression and downward extended cylindrical holes, while in the runnels burrows are usually small and simple. The trail is consisting of fin marking on either side of the tail marks (grooves) which are radiate around the burrows. Occasionally burrows are interconnected in more than one burrow system which is nested within single funnel structure on the surface.The burrow systems of the goby fish in the intertidal sediments serves for protection and dwelling purpose and most importantly these burrows are irrigated by water which supply the oxygen and keep body surface wet. The overall dimensions of the burrow decrease towards the lower intertidal zone. In all, behavioural structure produced by the goby fish marks the combined activity of dwelling, feeding and grazing. The complex behavioural mechanisms have helped the goby fish to survive and flourish in the harsh intertidal environments along the Navinal Coast, in the Gulf of Kachchh.