The significance of Upper Cretaceous hardgrounds and other discontinuity surfaces for basin-wide correlations, based on drillcore data from boreholes in northern Poland

Krzysztof LESZCZYŃSKI
2017 Geological Quarterly  
Leszczyñski, K., 2017. The sig nif i cance of Up per Cre ta ceous hardgrounds and other dis con ti nu ity sur faces for ba sin-wide cor re la tions, based on drillcore data from bore holes in north ern Po land. Geo log i cal Quar terly, 61 (4): 825-844, doi: 10.7306/gq.1375 The pa per pres ents the hardgrounds and some other cor re la tive dis con ti nu ity sur faces found in Up per Cre ta ceous (Cenomanian-Maastrichtian) bore hole sec tions of north ern Po land. They were briefly de scribed,
more » ... iefly de scribed, and depositional en vi ronment was iden ti fied for both the un der ly ing de posit (UD) and the over ly ing de posit (OD). The sig nif i cance of these fea tures for both ba sin-wide cor re la tions and broadly un der stood se quence strati graphic tech niques is high lighted. They were cor related with other ma jor dis con ti nu ity sur faces iden ti fied in bore holes of north ern Po land in both drill cores and well logs if such iden ti fi ca tion was re li able based on geo phys i cal bore hole data. All these dis con ti nu ity sur faces were re ferred to the boundaries of the in di vid ual depositional cy cles de ter mined within the Up per Cre ta ceous suc ces sion: K3-II/K3-III, K3-III/K3-IV, K3-IV/K4-I, K3-IV/K4-II, K4-I/K4-II (or II or IV or V), K4-III/K4-IV (or V), K4-IVa/K4-IVb, prob a bly K4-IVb/K4-V, and K4-V/Pc-I. The dis con ti nu ity sur faces can be re lated to both sea level fluc tu a tions and tec tonic ac tiv ity dur ing the Subhercynian phases. Most of them de vel oped in rel a tively calm sed i men tary con di tions, out side the cen tral part of the Mid-Pol ish Trough. The excep tions are three hardgrounds from the Cz³opa-Szamotu³y Zone, which seem to be as so ci ated mainly with the Late Cre taceous tec tonic (in clud ing salt tec ton ics) ac tiv ity of this zone. The most com mon UD/OD con fig u ra tion of sed i men tary en vi ron ments is the open-ma rine car bon ate shelf both be neath and above the dis con ti nu ity sur face. The sec ond most common sit u a tion is the open-ma rine car bon ate shelf be neath and the open-ma rine shelf with car bon ate-si li ceous sed i men ta tion above. The gaps at the sur faces span var i ously long in ter vals, rang ing from short pe ri ods (span ning a frac tion of a depositional cy cle) to long pe ri ods (com pris ing one or more depositional cy cles). The po si tion of the dis con ti nu ity sur faces fa cil i tates search ing for any pos si ble hi a tuses in the sec tions of other bore holes, and pay ing at ten tion to lo cal changes in sed i ment dis tri bu tion pat terns, and lo cal tec tonic ac tiv ity. Key words: Up per Cre ta ceous, dis con ti nu ity sur face, hardground, ba sin-wide cor re la tion, north ern Po land. mark ing cy cle bound aries in depositional se quences (e.g., Han cock, 1989; Witzke and Bunker, 1996; Mortimore et al., 1998) , in di cat ing a cy clic de po si tion of the car bon ate suc ces -*
doi:10.7306/gq.1375 fatcat:dhhliojc2jezvnz6wlkctbouou