Kenneth G. Galli, Ph.D.

RESEARCH

Upcoming Abstract/Poster Presentation: for Baltimore MD GSA Meeting:

Abstract #270354

REANALYSIS OF DEPOSITIONAL MECHANISMS, MICROFACIES SEQUENCES, AND EVENT STRATIGRAPHY OF SQUANTUM DIAMICTITES AND ASSOCIATED STRATA IN THE EDIACARAN BOSTON BAY GROUP

BAILEY, Richard H., Marine and Environmental Sciences, Northeastern University, Boston, MA 02115 and GALLI, Kenneth G., Earth and Environmental Sciences, Boston College, 140 Commonwealth Ave, 213 Devlin Hall, Chestnut Hill, MA 02467, r.bailey@neu.edu


Reanalysis of the Neoproterozoic (Ediacaran) Boston Bay Group on the Squantum Penninsula (Quincy, MA) with a particular focus on the spectacular coastal outcrops of Squantum Head is based on new high resolution mapping combined with detailed measurement and description of stratigraphic sections. Bedding characteristics, sedimentary structures, and microfacies architecture is displayed in digitally rendered stratigraphic panels.

Careful mapping and evaluation of faults that have been omitted or overlooked in most prior published stratigraphic analyses permitted adjustment and proper measurement of stratigraphic sections. Interpretation of sedimentologic data indicates submarine gravity mass transport was the primary mechanism of formation of coarse clastic facies. These processes resulted in a spectrum of interbedded matrix and clast supported conglomerates. Intercalated within the conglomerates are graded pebbly grannulestones and sandstones transported by turbidity currents or as other sorts of cohesionless mass flows.

Most of the fine sediment in the matrix of diamictites was introduced by admixing slope or basinal deposits during transport of proximally derived extrabasinal clast supported gravels and very coarse conglomerates. Evidence of this mixing is well displayed at the basal contacts of diamictites. The two main diamictite horizons are underlain and separated by thick successions of very thinly laminated sand-silt turbidites with slump folded intervals up to 2m thick. One debrite within slope or basinal turbidites contains deformed slope derived intraclasts and olistoliths up to 4m in size. We interpret the main diamictite sequences to represent re-deposited proximal coarse clastics formed during sea level lowstands. Thick sequences of thinly laminated mudstone to sandstone and interbedded slumped strata and intraclast-rich debrites represent deposition during sea level highstands.

 

Abstract Presented:

Basin History, Depositional Mechanics, and Paleoenvironments of Mass-Flow Deposits in the Ediacaran Boston Bay Group, Massachusetts, Bailey, Richard H., and Galli, Kenneth G., 2015,Northeastern Section - 50th Annual Meeting, The Geological Society of America, Monday, March 23, 2015 Poster: Stratigraphy, Sediments, Clastic:

Recent restudy and remapping of portions of the Boston Harbor Islands and surrounding coastal outcrops permits a comparative analysis of the characteristic debrites, such as the well known
Squantum Member, Roxbury Formation of the Boston Bay Group. In addition, there are well exposed outcrops containing a wide variety of coarse mass flow deposits and slumped and
disturbed stratigraphic intervals. All of the conglomeratic facies considered in this analysis are within the Cambridge Argillite or are intimately associated with similar thinly laminated
mudstone/sandstone facies interbedded with diamictite or other conglomeratic facies. These deposits range in bedding scale from centimeters to hundreds of meters and in lateral continuity
from decimeters to possibly kilometers. The thickest matrix-supported debrites contain an assortment of extrabasinal basement clasts up to a meter in diameter and intraclasts or olistoliths
up to several meters in length in a fine-grained mudstone/sandstone matrix. These extrabasinal clast-bearing debrites, representing classic debris flows, vary in thickness, proportion of fine
matrix, and in size and character of intraclasts. It is difficult to determine conclusively from sedimentary evidence alone if these debrites entered the basin from the mountainous, tectonically
and volcanically active source area as terrestrial mass flows or if they were submarine mass flows resedimenting proximal coarse facies deposited on a narrow shelf or ramp. Given the
nature of the matrix and the ubiquity of large basinal intraclasts we favor the latter interpretation. Thinner extrabasinal clast-bearing, clast-supported debrites, typically in the pebble to cobble size
range, probably represent distal edges of shelf or slope derived flows that have outrun the more plastic, matrix-rich portion of the flow. Very common debrites, often overlooked in the Boston
Bay Group, are those containing only or largely mudstone or fine sandstone intraclasts or olistoliths. In some outcrops it is possible to trace laterally an interval with intense soft sediment
deformation and/or slump folding into an intraclastic or intraformational conglomerate. These intraclastic debrites are clearly sourced from a muddy and cohesive slope.

Recent Publications: (The following two articles can also be seen online at:

http://voluminajurassica.org/abstracted.php?level=4&id_issue=876271

Galli, Kenneth G., 2014, Fluvial Architecture Element Analysis of the Brushy Basin Member, Morrison Formation, western Colorado, USA, in Tanner, L.. H., and Lucas, S., eds., Volumina Jurassica, special issue: The Jurassic of North America's Western Interior, Polish Geological Institute, Warsaw, Poland. Volumina Jurassica, 2014, XII (2): 69-106. DOI: 10.5604/17313708.1130130. (get PDF)

Tanner, Lawerence H., Galli, Kenneth G., and Lucas, Spencer, 2014, Pedogenic and lacustrine features of the Brushy Basin Member of the Upper Jurassic Morrison Formation in western Colorado: Reassessing the paleoclimatic interpretation, in: Tanner, L. . H., and Lucas, S., eds., Volumina Jurassica, special issue: The Jurassic of North America's Western Interior, Polish Geological Institute, Warsaw, Poland. Volumina Jurassica, 2014, XII (2): 115-130. DOI: 10.5604/17312708.1130134. (get PDF)

Research Interests:

Boston College
Earth and Environmental Sciences
Sedimentary Petrology Seminars
Spring 2012

 

April 24 (T) 12-1 (Devlin 307) speaker: Dr. Ken Galli (BC E&ES)
“Sedimentary Tectonics of the Morrison Formation, western Colorado”

April 26 (TH) 12-1 (Devlin 307) speaker: Prof. Zhenbing She (Visiting Associate Professor of Sedimentary Petrology, China University of Geoscience, Wuhan)
"Genesis of Neoproterozoic phosphorites in South China"

May 1 (T) 12-1 (Devlin 307) speaker: Dr. Ken Galli (BC E&ES)
“Sedimentary Tectonics of the Sedimentary Sequences of the Boston-Avalon Terrane”