13 NETectonics: New Advances in Structural Geology and Tectonics in the Appalachians (Posters)

Sunday, 19 March 2017
8:00 AM - 12:00 PM
Urban, 17th Floor

IMPLICATIONS OF STRUCTURES IN UNORIENTED CORES OF UTICA BLACK SHALE

Paper number: 13-5
Program: Theme Sessions
Time: 8:00 AM – 12:00 PM

Authors

Abstract

We performed detailed structural analyses on 713.5 m (2341 ft) of Ordovician Utica black shale core from 7 boreholes in the Mohawk Valley region of NYS. We documented 1148 veins and 3 clean fractures, including 58 veins and fractures with slip described in the table below. Sense of slip was deduced from releasing bends (rhombochasms) in calcite-filled fractures, bedding offsets, and slickenside/fiber orientation. That normal, thrust, and oblique slips are observed on fractures are consistent with foreland basin and escape tectonics.

core #

Fault Name

core dist. to fault (km)

throw (m)

Dist. to thrust front (km)

Utica recovered in core (m)

Total Veins⁺

Slip

Normal

Thrust

Oblique/Strike Slip

Bedding Plane Slip

Dip Slip unresolved motion

75NY2

Saratoga-McGregor

0*

137

8

137.4

328

11

16

0

0

0

75NY11

Hoffmans

1.73

381

23

113.7**

46

2

1

1

0

4

74NY12

Hoffmans

0.55

381

23

53.6

412

0

0

1

0

1

74NY11

Fonda

0.87

>40

45

3.7

142

1

1

1

1

1

74NY9

Fonda

2.54

>40

45

101.5

134

1

0

6

1

0

74NY10

E. Stone Arabia

1.46

24

58

83.2

74

4

4

0

0

0

74NY5

Mother Creek

3.97

137

68

220.4

12

0

0

0

0

0

*Core is on a fault splay (Tice, 1993)

**Represents core examined. Total recovered Utica is 163.19 m

⁺No veins are dated

Factors affecting downhole fracture frequency include distance to fault, fault throw, lithology, and the presence of fault splays. Cores in this study are generally too far (>250 m) from major NNE/NE striking Taconic faults for fracture frequency to be affected by the main faults according studies by Agle et al. (2006) and O’Hara et al. (2015), even for faults with large throw. Five cores have % total organic carbon (TOC) and/or % sand data. Of the 17 clusters of high fracture frequency (fracture intensification domains, FIDs), 7 correlate with higher values of brittleness indices. A combination of the factors above and the possible presence of subsurface fault splays could explain the location of FIDs in the cores. Fracture clusters in 74NY10 at the Trenton-Utica contact were omitted because they may represent complications associated with karst collapse and subsequent sediment infilling. In cores with TOC data, possible beef structures correspond to higher TOC intervals, which could indicate overpressure from gas generation was approximately contemporaneous with calcite veining. These relationships provide a check of possible gas/vein ages when coupled with subsidence curves.

Geological Society of America Abstracts with Programs. Vol. 49, No. 2

doi: 10.1130/abs/2017NE-290653

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