Record Details

Enhanced methane flux event and sediment dispersal pattern in the Krishna–Godavari offshore basin: Evidences from rock magnetic techniques

DRS at CSIR-National Institute of Oceanography

View Archive Info
 
 
Field Value
 
Title Enhanced methane flux event and sediment dispersal pattern in the Krishna–Godavari offshore basin: Evidences from rock magnetic techniques
 
Creator Usapkar, A.
Dewangan, P.
Kocherla, M.
Ramprasad, T.
Mazumdar, A.
Ramana, M.V.
 
Subject GEOLOGY AND GEOPHYSICS
GEOLOGY AND GEOPHYSICS
GEOLOGY AND GEOPHYSICS
AQUATIC RESOURCES
 
Description Detailed rock magnetic measurements such as susceptibility (X), susceptibility of anhysteric remanent magnetization (XARM), saturation isothermal remanent magnetization (SIRM), soft-isothermal remanent magnetization (soft-IRM) and hard-IRM (HIRM) were carried out on the topmost sediment samples of 73 gravity cores collected in the Krishna–Godavari (KG) offshore basin to understand the distribution of magnetic parameters and the associated diagenetic signatures related to upward methane flux. The variation in magnetic parameters in the KG offshore basin fluctuates around the average value (X = 105 × 10-8 m3 kg-1, XARM = 1.22 × 10-5 m3 kg-1, SIRM = 2040 × 10-5 Am2 kg-1, soft-IRM = 1807 and HIRM = 82) except at the location GC-07 (15.767°N, 81.814°E) where the magnetic parameters X, XARM and SIRM drop to ~1/6th, ~1/14th and ~1/8th of the average near surface value indicating substantial loss in the concentration of primary magnetic iron oxide minerals. Anomalous low value of XARM/X and XARM/SIRM at GC-07 suggests that the magnetic remanence property is governed by coarser pseudo-single domain (PSD) or multi-domain (MD) grains. To understand the nature of the anomalous magnetic parameters at GC-07, complete downcore variation of magnetic parameters was also studied. The magnetic parameters were found to be even more depleted at all depths with susceptibility dropping (at 5.2 mbsf) to ~1/200th of its average near surface value. Interestingly, this core shows a rapid increase in the concentration of dissolved methane from ~0 nM at surface to ~153 nM at around 5.2 mbsf where the sulfate concentration is also reduced to zero. The anaerobic oxidation of methane (AOM) and the sulfate methane transition zone (SMTZ) occur between ~4.2 and 5.2 mbsf based on the present day sulfate concentration profile. The close association between the dissolution of magnetic iron oxide minerals and AOM at GC-07 suggests that the reduced magnetization is primarily due to the release of HS- by AOM. The magnetic iron oxide minerals are dissolved not only at SMTZ but also above the current depth of the SMTZ. It is likely that the methane flux was higher in the past leading to upward shift of the SMTZ, and the HS- released by AOM facilitated the dissolution of magnetic iron oxide minerals at shallower depths. Alternatively, the HS- diffusing upward from the current depth of SMTZ might have lead to dissolution at shallower depth. Therefore, additional geological/geochemical investigations are warranted at GC-07 to establish the dissolution mechanism of magnetic iron oxide minerals. The variability in different magnetic parameters within the slope basin and channels shows systematic decrease in the concentration of magnetic minerals and increase in the abundance of stable single domain (SSD) magnetic grains with water depth. The observed strong correlation between the silt fraction and the magnetic susceptibility for the slope basin and channels suggests that the variation in magnetic parameters is predominantly controlled by the sediment sorting/transport process as finer particles are deposited in deeper water
 
Date 2017-09-27T13:06:45Z
2017-09-27T13:06:45Z
2014
 
Type Journal Article
 
Identifier Marine and Petroleum Geology, vol.58; 2014; 461-475
http://drs.nio.org/drs/handle/2264/5166
 
Language en
 
Rights An edited version of this paper was published by Elsevier. Copyright [2014] Elsevier
 
Publisher Elsevier