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85E Ridge Volcanostratigraphic Unit 4 Formation
Click to display on map of the Ancient World at:
85E Ridge Volcanostratigraphic Unit 4 Fm base reconstruction

85E Ridge Volcanostratigraphic Unit 4 Fm


Period: 
Cretaceous

Age Interval: 
Late Santonian - Early Campanian (85-80 Ma)


Province: 
E.India 85º E Ridge

Type Locality and Naming

Reference well: Profile E1290. Informal unit.

[Figure 1: Satellite free-air gravity anomaly color code map of the 85ºE Ridge and adjacent area of the Bay of Bengal (Sandwell et al., 2014)]


Lithology and Thickness

Volcanics. This unit has strong continuous horizontal reflections with a thickness of around 400 m and horizontal spread of about 40-50 km and fills the pre-existing basin/depression before reaching the paleo-offlap break.

[Figure 2a: Coastal parallel deep-water seismic profile E6000 crossing the 85º E Ridge and its interpretation are shown. The profile nearly orthogonally crosses the profile E1290 (after Ismaiel et al., 2017)]

[Figure 2b: Schematic illustration showing the development of the 85°E Ridge through geological age (Ismaiel et al., 2017)]

[Figure 3: The section of the seismic profile E1290 illustrates structure of the 85º E Ridge. The section displays characteristic of volcanic plug, lava-fed delta units, etc. The ridge structure is completely buried under the thick Bengal Fan sediments deposited since the Oligocene-Miocene (~23 Ma). SP shown along the horizontal-axis and BSL marked within the ridge structure indicate the shot-point and Bottomset/Base of the Lava Delta, respectively. (after M.Ismaiel et al., 2017)]


Lithology Pattern: 
Volcanics


Relationships and Distribution

Lower contact

This unit boundary has an unconformable contact with 85E Ridge Volcanostratigraphic Unit 3 Fm.

Upper contact

The upper contact of this unit is 85E Ridge Volcanostratigraphic Unit 5 Fm.

Regional extent


GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[84.9,17.83],[85.7,17.7],[85.22,15.35],[85.7,9.21],[84.7,9.18],[84.28,15.21],[84.9,17.83]]]]}}

Fossils

Biostratigraphic data is given below:

[Figure 4: Superimposition of biostratigraphic data on wire line logs and seismic section (Depth; in-line 1918)]


Age 

Late Santonian - Early Campanian (85-80 Ma)

Age Span: 
s

    Beginning stage: 
Campanian

    Fraction up in beginning stage: 
0.2

    Beginning date (Ma): 
81.35

    Ending stage: 
Campanian

    Fraction up in the ending stage: 
0.35

    Ending date (Ma):  
79.63

Depositional setting


Depositional pattern:  


Additional Information

Foresets beds composed of hyaloclastic breccias due the interaction of lava flows with water.

[Figure 5: Details of seismic facies, geometry and geological interpretation of the 85E Ridge Volcanostratigraphic units of the ridge structure. Classification scheme is followed from Planke et al., 1999,2000. West et al., 2002. Rey et al., 2008. And Elliot and Parson, 2008 (in Ismaiel et al., 2017)]


Compiler:  

Ismaiel, K.S. Krishna.